SELECTIVITY FAILURE IN THE CHEMICAL VAPOR DEPOSITION …/67531/metadc... · Cheek, Roger,...
Transcript of SELECTIVITY FAILURE IN THE CHEMICAL VAPOR DEPOSITION …/67531/metadc... · Cheek, Roger,...
Yt\A t t .
SELECTIVITY FAILURE IN THE CHEMICAL VAPOR DEPOSITION OF
TUNGSTEN
DISSERTATION
Presented to the Graduate Council of the
University of North Texas in Partial
Fulfillment of the Requirements
For the Degree of
DOCTOR OF PHILOSOPHY
By
Roger W. Cheek, B.S.
Denton, Texas
August, 1994
Yt\A t t .
SELECTIVITY FAILURE IN THE CHEMICAL VAPOR DEPOSITION OF
TUNGSTEN
DISSERTATION
Presented to the Graduate Council of the
University of North Texas in Partial
Fulfillment of the Requirements
For the Degree of
DOCTOR OF PHILOSOPHY
By
Roger W. Cheek, B.S.
Denton, Texas
August, 1994
Cheek, Roger, Selectivity Failure in the Chemical Vapor Deposition of Tungsten.
Doctor of Philosophy (Analytical Chemistry), August, 1994, 114 pp., 1 table, 25 figures,
bibliography, 115 titles.
Tungsten metal is used as an electrical conductor in many modern microelectronic
devices. One of the primary motivations for its use is that it can be deposited in thin films
by chemical vapor deposition (CVD). CVD is a process whereby a thin film is deposited
on a solid substrate by the reaction of a gas-phase molecular precursor. In the case of
tungsten chemical vapor deposition (W-CVD) this precursor is commonly tungsten
hexafluoride (WFg) which reacts with an appropriate reductant to yield metallic tungsten.
A useful characteristic of the W-CVD chemical reactions is that while they proceed rapidly
on silicon or metal substrates, they are inhibited on insulating substrates, such as silicon
dioxide (Si02). This selectivity may be exploited in the manufacture of microelectronic
devices, resulting in the formation of horizontal contacts and vertical vias by a self-aligning
process. However, reaction parameters must be rigorously controlled, and even then
tungsten nuclei may form on neighboring oxide surfaces after a short incubation time.
Such nuclei can easily cause a short circuit or other defect and thereby render the device
inoperable. If this loss of selectivity could be controlled in the practical applications of
W-CVD, thereby allowing the incorporation of this technique into production, the cost of
manufacturing microchips could be lowered.
This research was designed to investigate the loss of selectivity for W-CVD in an
attempt to understand the processes which lead to its occurrence. The effects of
passivating the oxide surface with methanol against the formation of tungsten nuclei were
studied. It was found that the methanol dissociates at oxide surface defect sites and blocks
such sites from becoming tungsten nucleation sites. The effect of reactant partial pressure
ratio on selectivity was also studied. It was found that as the reactant partial pressures are
varied there are significant changes in the product partial pressure ratios, which are
associated with gas phase reactions which contribute to the loss of selectivity.
TABLE OF CONTENTS
Page
LIST OF FIGURES v
Chapter
I. INTRODUCTION 1
Microelectronics Applications of Tungsten 1
Tungsten CVD Chemistry 5
Reduction of WF6 by Si 7
Reduction of WF6 by H2 8 Reduction of WF6 by SiEfy 10 Other Reductants 11
Selective Deposition of Tungsten 11
Loss of Selectivity Mechanism 12
Foreign Material 12
Volatile Reaction Products 13
Gas Phase Nucleation 14
Ultra-High Vacuum Techniques 15
Auger Electron Spectroscopy 16
Mass Spectrometry 18
Temperature Programmed Desorption 20
Micro-Volume Mass Spectrometry 20
Chapter References 23
111
II. METHANOL INTERACTIONS WITH SI02 SURFACES 34
Introduction 34
Experimental 35
Results 40
Summary and Conclusions 44
Chapter References 47
III. IN SITU MASS SPECTROMETRY OF A COMMERCIAL TUNGSTEN
CHEMICAL VAPOR DEPOSITION REACTOR 48
Introduction 48
Experimental 49
A model of the sampling capillary 51
Results and Discussion 55
Conclusions 65
Chapter References 67
APPENDIX 69
BIBLIOGRAPHY 105
IV
LIST OF FIGURES
Figure 1. Schematic for using blanket and selective tungsten CVD for metallizing trenches
and vias in a silicon based microelectronic device 2
Figure 2. Schematic of 'step coverage' for a CVD thin film over a high aspect ratio structure 3
Figure 3. Schematic of the Auger process. K, L, and M are the core electron energy levels
for the atom 17
Figure 4. Quadrupole mass filter 18
Figure 5. Schematic of a differentially pumped mass spectrometer attached to a
high pressure chamber 22
Figure 6. Ultra high vacuum chamber for TPD studies 36
Figure 7. Apparatus for dosing a sample in UHV with a controlled amount of gas 37
Figure 8. Auger spectrograph of SiC>2 sample after Ar+ ion sputtering to remove
foriegn material 38
Figure 9. Auger spectrograph of the same SiC>2 sample as in figure 8 after an oxygen anneal 39
Figure 10. TPD spectra (normalized) of methanol from a lightly sputtered SiC>2 surface 41
Figure 11. Mass spectrum of methanol in the UHV chamber at 1 x 1(H* torr 42
Figure 12. TPD spectra of CH4 desorption from an Ar+ sputtered and methanol dosed Si02 surface 43
Figure 13. TPD spectrum of CH4 desorption from a methanol dosed unsputtered
SiC>2 surface 44
Figure 14. Auger spectrograph showing W on SiC>2 after the TPD experiments 45
Figure 15. TPD spectra of WF5+ (characteristic of WFg) from a WFg dosed SiC>2 surface 46
Figure 16. Schematic diagram of the experimental setup used to investigate the reactions in a commercial tungsten CVD reactor 50
Figure 17. Schematic diagram of the capillary sampling system and the differentially pumped mass spectrometer 51
Figure 18. Pressure at the mass spectrometer as a function of the pressure in the CVD chamber for argon 54
Figure 19. Plot of the mass spectrometer response for the CVD reactants, WFg and S1H4,
versus the SiFfy/WFg inlet flow ratio 56
Figure 20. Plot of the mass spectrometer response for four of the mass fractions of SiF4 57
Figure 21. Plot of the mass spectrometer response for four of the mass fractions of SiHF3 59
Figure 22. Mass spectrometer signals as the Siffy/WFg inlet flow ratio is stepped from a selective regime (0.25) to a non-selective regime (3.0) 60
Figure 23. Adding a large amount of Ar to the reaction mixture of Figure 22 decreases the magnitude and location of the maximum signal divergence for the mass 85 and 67 signals 62
Figure 24. SiHF2+/SiF3+ ratios from Figure 22 (low Ar partial pressure) and Figure 23 (high Ar partial pressure) 64
Figure 25. Thermodiffusion results in the depletion of WF6 relative to Ar near a heated surface in the CVD chamber 66
VI
CHAPTER I
INTRODUCTION
Tungsten metal is used as an electrical conductor in many modern microelectronic
devices. One of the primary motivations for its use is that it can be deposited in thin films
by chemical vapor deposition (CVD). This deposition may occur selectively when the
reaction parameters are such that tungsten is deposited only on certain types of surfaces,
usually conducting or semiconducting, to the exclusion of other surfaces, usually
insulating. For selective deposition to be successful then, tungsten must deposit rapidly on
one surface and not at all on a nearby different surface, even though both surfaces are
located in the same reaction environment. This study focused on the chemical reactions
and processes which lead to selectivity failure in tungsten chemical vapor deposition (W-
CVD).
Microelectronics Applications of Tungsten
CVD tungsten (blanket or selective) has many applications in the construction of
silicon based microelectronic devices. There are two main reasons for this usefulness.
First, it is a good electrical conductor, having a bulk resistivity of 5.39 |iQ-cm (7). The
resistivity of thin film CVD tungsten is not generally as low as bulk tungsten since the
CVD process can cause the incorporation of impurities (e.g., silicon or fluorine) and other
defects into the growing tungsten (2-4). This results in electrical resistivities which are at
best approximately 9 n£2-cm (5). This resistivity makes tungsten adequate for many
metallization applications in microelectronics, such as diffusion barriers, via fills, and some
interconnects.
The second reason for CVD tungsten's usefulness is that since deposition is by
heterogeneous reaction of a gas-phase precursor (usually WFg) at a surface, the resulting
thin film can be conformal with any physical structures present in the substrate (6,7). In
microelectronic devices these structures take the form of trenches or vias which may have
lateral dimensions much less than one micron. This deposition may proceed in either a
I -
Dielectric layer with etched grooves and vias
Blanket tungsten CVD
Selective tungsten CVD
Etchback of tungsten
Si or Metal
Figure 1. Schematic for using blanket and selective tungsten CVD for metallizing trenches and vias in a silicon based microelectronic device.
'blanket' mode, with all surfaces receiving a tungsten film, or a 'selective' mode, with
tungsten deposition occurring only on regions of metal or semiconductor, but not on
adjacent insulating surfaces. When blanket deposition is used, it must be followed by a
lithographic etchback step which patterns the metal into useful structures (Figure 1) (8-
10). Selective deposition obviates this lithographic etchback step. The microelectronic
applications of metal CVD in general and tungsten CVD in particular (both selective and
blanket) have been discussed by many authors (11-25).
There are several reasons that tungsten is of interest relative to more conductive
metals such as copper or aluminum (Table 1). First of all, copper and aluminum suffer
from the lack of a reliable CVD technique. These materials can be physically deposited
(sputtered or evaporated) very effectively on low aspect ratio surfaces (where vertical
dimensions are much smaller than horizontal dimensions) (26-28). Unfortunately, ever
shrinking device geometries require that the metal be deposited in trenches or vias with
high aspect ratios. It is difficult to physically deposit films on such structures and maintain
good conformality, or 'step coverage', which for blanket deposition may be defined as the
ratio of the deposited film thickness on the structure sidewall to the film thickness on the
top surface (Figure 2) (29). CVD techniques are far superior to physical deposition
a. b.
Figure 2. Schematic of 'step coverage' for a CVD thin film over a high aspect ratio structure. Step coverage is defined as the ratio of the deposit thickness on the feature sidewall to the thickness on the top surface, a. Step coverage = 1, b. step coverage < 1.
Metal
Property Cu A1 W Si
Coefficient of linear expansion at 25°C
x lO^nCC) - 1 (37)
16.5 23.1 4.5 4.68
Melting Point (°C) (37) 1085 660 3422 1412
Resistivity at 25°C (|iQ-cm) (38) 1.71 2.71 5.39
Table 1. Properties of some metals important to silicon based microelectronics compared to silicon.
techniques for obtaining good step coverages (21). Recent advances have been made in
the CVD of both A1 (30-34) and Cu (35,36), but CVD-W remains a more mature
technology.
The refractory nature of tungsten is another of its advantages over aluminum or
copper (Table 1). Its high melting point means that once a tungsten film or structure is
deposited, it is not likely to be affected by later processing steps which may occur at high
temperatures. The melting point of aluminum and copper are 660°C and 1085°C,
respectively (Table 1) (37), and the temperature at which device structure and
performance are adversely affected is much lower than the melting point. For instance,
once an aluminum layer is added to a device, subsequent process steps which occur at
temperatures greater than approximately 350°C may adversely affect the structure of the
aluminum layer. Tungsten, on the other hand, has a melting point of 3422°C (37), far
above the temperature range required for any potential subsequent process step.
The thermal expansion coefficient of tungsten is very near that of silicon (Table 1)
(37). This is an advantage for reducing film stress where tungsten is deposited on silicon.
The thermal expansion coefficients of copper and aluminum are less closely matched to
silicon (Table 1) (37). This may cause deposited films of these metals to peel away from
the substrate, or may cause stress induced void formation in metal lines {39,40).
Tungsten's electromigration resistance is superior to both aluminum and copper
(41). Electromigration is electronic-current induced atomic diffusion, which results from
the transfer of momentum from electrons to the atoms of the conductor. The result is
movement of the conductive material in the direction of the electron transport, which can
cause a break in the metal line at the cathode end and an accumulation of metal at the
anode end (40). This is important in microelectronic devices where the current density can
be as high as 4 x 10^ A/cnP-, which compares to 100 A/cm^ as the maximum allowed for
house wiring (42). Aluminum suffers from very poor resistance to electromigration
(31,32), while copper has a four orders of magnitude better resistance to electromigration
(41,43), and tungsten suffers virtually no electromigration for the currents ordinarily
encountered in microelectronic devices (41).
Tungsten is also highly inert toward SiC>2, and forms a stable interface with silicon.
Aluminum is known to react chemically with silicon, causing what is commonly referred to
as "spiking" (18,31), that is, long slender "spikes" of aluminum protruding into the
substrate. Copper has a high diffusion coefficient in both silicon and SiC>2 (36). Both of
these effects can sometimes be overcome by using diffusion barriers such as titanium
nitride, tungsten silicide, or Ti-W intermetallic (36,44). Tungsten does not diffuse through
or chemically react with silicon or SiC>2 enough to have a significantly adverse affect on
semiconductor device performance, as long as deposition is carried out under proper
processing conditions.
Tungsten CVD Chemistry
Tungsten deposition for microelectronics is normally carried out by the reduction
of tungsten hexafluoride (WFg) by silicon (Si), hydrogen (H2), or silane (Silfy). These
reductants may be used either individually or in some combination. Many other reductants
have also been investigated by various workers {45-47). However, largely for historical
and process integration reasons, these three remain the most widely used and researched
reactions. For the silicon reduction of WFg two reactions have been identified, producing
SiF4 and SiF2 (J1,14,48-50):
2WF6(g) + 3Si(s) -» 2W(s) + 3SiF4 (g) (1)
WF6(g) + 3Si(s) —> W(s) + 3SiF2(g) (2)
The hydrogen reduction is given by (51-54):
WF6(g) + 3H2(g) -> W(s) + 6HF(g) ^
The principal reactions for the silane reduction are (50,55-58):
4WFfi(g) + 3SiH4(g) -> 4W(s) + 3SiF4(g) + 12HF (4)
2WF6(g) + 3SiH4(g) -> 2W(s) + 3SiF4(g) +3H2 (5)
WF6(g) + 2SiH4(g) -> W(s) + 2SiHF3(g) + 3H2 (6)
All of these reactions have WFg as a gas-phase molecular precursor (source of tungsten)
which reacts heterogeneously at an appropriate surface to yield metallic tungsten. The fact
that these reactions are surface catalyzed is the primary reason for their ability to deposit
tungsten films selectively. That is, they proceed rapidly on some surfaces and slowly or
not at all on other surfaces. In order for the deposition to proceed, the substrate must be
capable of either reducing WFg to metallic W, or dissociatively adsorbing WFg and H2
and/or S1H4, Most oxides, including SiC>2, do not readily support these processes (59).
Silicon, however, can reduce WFg directly, and tungsten (and many other conducting and
semiconducting surfaces) supports the necessary dissociation (60). Therefore, the
deposition which results from the above stated chemical reactions are selective for
surfaces of silicon and tungsten versus surfaces of Si02 or other insulators.
Reduction of WFg bv Si
The elementary surface chemical reactions involved in the Si reduction of WF5
have been investigated by Jackman and Foord (61), and others (49,62-64). They found
that when WFg is adsorbed on silicon below 120 K the molecule remains intact (non-
dissociative adsorption). However, at room temperature and above the WF5 adsorbs
dissociatively on surfaces of both Si(100) (55) and Si( l l l ) (62). High-resolution
photoemission experiments (62) demonstrated that WFg adsorption on Si(l 11) at room
temperature results in complete dissociation of the WFg into metallic tungsten and a range
of fluorosilyl compounds SiFx (x=l,2,3). The behavior of WFg on Si(100) is reported to
be quantitatively similar (49). At room temperature, the reaction proceeds no further. The
surface is saturated with tungsten and fluorine species which prevent further dissociative
adsorption of WFg. If the temperature is elevated, however, the deposition of tungsten
may continue by the removal of the SiFx species as volatile reaction products. Yu et al.
(49) used mass spectrometry to identify the reaction products from the silicon reduction
reaction. They found that SLF4 is the principal product (reaction 1) when the reaction
temperature is below approximately 450°C. S1F2 was found to be the principal product
(reaction 2) when the reaction temperature was between approximately 450°C and 700°C.
By removal of these volatile fluorinated species from the surface, the deposition of
tungsten may continue, at least until a monolayer of tungsten is deposited. The silicon
reduction reaction would be expected to become "self-limited" at this point, as the
reductant (silicon) has been physically isolated from the oxidant (WFg). This is not what is
observed. This reaction has been found to become self-limited only after at least 100A to
200A of tungsten has been deposited (25). YarmofF and McFeely (62), and Yu et al. (49)
have identified silicon from the substrate at the surface of the growing tungsten film. This
indicates that silicon from the substrate is diffusing to the surface of the tungsten film
where it can react by the mechanism just described. This diffusion is attenuated as the
tungsten film grows thicker, thus stopping the reaction at the characteristic self-limited
thickness.
The silicon reduction is useful for microelectronics only for tungsten films less than
about 200A thick. One reason is the self-limiting nature just described, but more
importantly, the reaction consumes the silicon substrate. The stoichiometry of reaction 1
indicates that 1.9A of silicon should be consumed for each lA of tungsten deposited (65).
This correlates well to the observation that the ratio of silicon depth consumed to tungsten
thickness deposited is approximately 2:1 (65). This means that tungsten deposition of
more than approximately 200A results in silicon consumption that is near the dimensions
of the active regions in a modern semiconducting device (66). This results in damage to
the device by consuming the silicon substrate which contains the active regions. For
tungsten deposition of greater than a few tens of angstroms thick, another reductant must
be introduced. This is the topic of the next two sections.
Reduction of WF5 by Fb
For tungsten films thicker than approximately 200A, a reductant other than the
silicon substrate must be employed. Hydrogen can act as the reductant on tungsten
surfaces (67). The role of hydrogen on the tungsten surface is qualitatively similar to that
of silicon which has segregated at the surface from the substrate. Whereas in the silicon
reduction, silicon atoms on the tungsten surface react with fluorine from dissociated WFg
to produce SiFx species, in the hydrogen reduction, dissociated hydrogen atoms react with
the fluorine to produce HF (reaction 3) (25):
H2 (g) + 2* <-» 2H(a) (7)
WF6(g) + 6* O W(s) + 6F(a) (8)
F(a) + H(a) —> HF(g) + 2* (9)
where * indicates an empty surface site.
While the hydrogen reduction reaction allows tungsten films on the order of 1 |im
in thickness to be deposited, the effect on the silicon substrate is still problematic. Stacy et
al. (65) and others (69-7J) used scanning electron microscopy to observe the tungsten
films formed from the hydrogen reduction reaction on patterned Si/SiC>2 wafers. They
found that there is significant consumption of the silicon substrate, as well as lateral
encroachment of the tungsten into silicon which is under SiC>2 regions adjacent to growing
tungsten films. Tunnels or "wormholes" with diameters ranging from 20 to 40 nm were
also observed which, in extreme cases, penetrated 1 jum into the silicon substrate. At the
end of each of these tunnels they found a tungsten particle with a diameter approximately
equal to the tunnel diameter. Clearly, such destruction of the structure of the silicon
substrate severely limits the usefulness of this reaction for use in microelectronics.
Apparently, the silicon reduction reaction proceeds quickly relative to the hydrogen
reduction reaction, resulting in the same level of silicon substrate consumption whether
silicon or hydrogen is used as the reductant. Therefore, even though hydrogen reduction
overcomes the self-limiting thickness nature of the silicon reduction reaction, consumption
of the substrate remains a problem.
Despite the problem of substrate damage, much work has been done on the
hydrogen reduction reaction as regards its selectivity. The surface mediated reactions 7
and 8 are not readily supported on oxide surfaces (25) which is presumably the reason that
selective deposition is possible. The mechanism by which selectivity is lost will be
discussed in detail below.
10
Reduction of WFg bv SifiLf
An important and widely researched alternative to hydrogen as a reductant for
tungsten deposition from WFg is silane (SiFfy). Silane is known to undergo complete
dissociative adsorption on clean tungsten surfaces (72,73). The hydrogen atoms on the
surface which result from this dissociative adsorption are readily displaced by silicon
atoms during large silane exposures (72). In this way silane provides a continuous source
of silicon atoms on the tungsten surface. The fluorine which is on the surface as a result of
WFg dissociation (reaction 8) can then react with the silicon to form volatile silicon
fluorides (SiFx), as in the silicon reduction discussed above. The hydrogen atom from the
dissociative adsorption of silane may leave the surface as either H2 or HF, with fluorine
coming from WFg dissociation (reaction 8). Clearly the situation on the tungsten surface is
very complex, and which particular reaction pathways are important is a result of a
dynamic equilibrium which is reached between the adsorption of precursor molecules,
their competitive dissociation, the reaction and interactions of the dissociation products on
the surface, and the subsequent evolution of volatile reaction products. Empirical studies
of the reaction products by mass spectrometry (4,50,55,56,74,75) and Fourier transform
infrared spectroscopy (2,57,58,76-78) have identified H2, SiF4, and SiHF3 as the principal
reaction products. HF was observed to be present in the reaction product mixture only in
small amounts, if at all. This indicates that reactions 5 and 6 above are the likely reaction
pathways for the silane reduction process on tungsten surfaces.
The silane reduction process does not cause damage to the silicon substrate such
as is observed by the hydrogen reduction (74). The silane process does exhibit the
selectivity which is observed for the hydrogen reduction, and it yields a much higher rate
of deposition (79-81). For these reasons the silane reduction of WFg has become the most
widely used process for the chemical vapor deposition of tungsten for microelectronics
11
manufacture. The mechanism by which this process losses selectivity is a central focus of
the present work and will be discussed in detail below.
Other Reductants
Several other reductants have been investigated for CVD of tungsten from WFg.
Germane (Geffy) (46), digermane (Ge2Hg) (82), polysilane (Si2Hg and Si3Hg), diborane
(BiHg), and phosphine (PH3) (45), and dichlorosilane (83) have been studied and
compared to silane as a reductant for WFg. While some of these reductants are reported
to slightly improve on one or more of the characteristics of the silane reduction process,
there has been no impetus to abandon this well characterized and widely employed
process.
Selective Deposition of Tungsten
The selective nature of the CVD-W process has received much interest because of
the potential benefits that selectivity holds for microelectronics (Figure 1) (25). The vast
majority of process steps used in making a microelectronic device are intended to result in
the formation of some form of patterned structure, either within or on top of the silicon
substrate. In broad terms, these structures may be in the form of regions in the silicon with
an excess electron donor (e.g. phosphorus or arsenic) or acceptor (e.g. boron or
aluminum) concentration, or regions which are electrically insulating or conducting. It is
the ability to make these structures in an extremely controlled way for patterns which have
minimum dimensions of much less that one micrometer that has resulted in the so called
'computer revolution' of recent decades (84,85). However, most processes which produce
these regions of varying electrical characteristics do not do so in an area selective manner,
and so do not inherently result in the required patterns. For instance, common
metallization techniques, whether chemical or physical in nature, deposit the metal in a
blanket, or non-selective, fashion. This means that additional process steps are required to
12
produce the required patterns. These additional steps may take the form of etchback as in
Figure 1, or photolithography (86-87). These techniques, while quite reliable, introduce
several process steps to the procedure. Since each added process step has the potential to
introduce errors or defects, and add to the cost of the device, it is desirable to eliminate as
many such steps as possible. Processes which are 'self-aligning' (i.e. area selective) do not
require the etchback or photolithographic steps, and as such are desirable.
Despite the advantages that selective tungsten deposition holds over non-selective
techniques, it has not been widely used in the industrial manufacture of microelectronic
devices. The reason for this is that selectivity is not easily maintained under production
conditions. Selectivity is said to be lost when tungsten is deposited not only on the desired
metal or semiconductor, but on a nearby dielectric material (usually Si(>2). This loss of
selectivity can result in an electrical short circuit or other defect in a microelectronic
device, rendering the device useless. The cause of this loss of selectivity is the subject of
the present work.
Loss of Selectivity Mechanism
Loss of selectivity (i.e., tungsten deposition on SiC>2) can proceed via three routes.
The first is a result of foreign material on the oxide acting as a nucleation site for tungsten
film growth by direct reduction of WFg. The second is the adsorption and
d ispropor t iona te of volatile tungsten containing reaction products on the oxide. The
third is gas phase nucleation of particulates, during the silane reduction process, which fall
on the oxide.
Foreign Material
The physical cleanliness of the oxide surface has a profound effect on selectivity.
The presence of organic residues such as photoresist and bacteria have been shown to act
as nucleation sites for tungsten deposition from WFg (88,89). However, since the surfaces
13
(wafers) that are used in the selective W-CVD are generally handled in clean room
environments, this physical contamination does not pose a serious problem for loss of
selectivity under production conditions.
Volatile Reaction Products
When tungsten is observed to deposit on SiC>2 during the hydrogen reduction
process, the source of tungsten is apparently not WFg but a volatile product of the
reaction of WFg with nearby tungsten or other metal. (WF6 itself is apparently inert on
high quality Si(>2 surfaces at temperatures up to 400 °C (90,91)). The most important
observation which leads to this conclusion is the existence of a proximity effect for loss of
selectivity nucleation. It has been observed by many workers (91-95) that the number of
tungsten nuclei (loss of selectivity nuclei) on an oxide surface decreases exponentially with
distance from a tungsten surface. This phenomenon has been observed even for regions of
tungsten and oxide which are not contiguous, that is, on separate but nearby wafers.
Creighton (96-100) has identified tungsten subfluorides ~ probably WF5 ~ as a volatile
reaction product of the hydrogen reduction reaction which can diffuse through the gas
phase to SiC>2 surfaces and dissociate there, yielding metallic tungsten.
The tungsten subfluoride mechanism for loss of selectivity is intrinsic to the
tungsten CVD process, and as such, can be expected to eventually cause loss of selectivity
whenever WFg is used as the source of tungsten. That selectivity is attainable at all is
apparently due to the differing initial tungsten nucleation rates on silicon or tungsten
relative to SiC>2. There is an initial incubation period on the oxide before loss of selectivity
begins, during which time the deposition proceeds rapidly on the metal surface. This
incubation time before loss of selectivity sets in varies with the condition and genesis of
the oxide surface. It is a function of processing parameters (2,79) and the nature of the
oxide surface (101,102). Some workers have attempted to achieve high degrees of
14
selectivity by repeatedly alternating between tungsten deposition and tungsten etch steps
(103,104), which act to etch the loss of selectivity nuclei and remove them before they
become too large or numerous.
The mechanism for the loss of selectivity for the silane reduction process has not
been investigated to the extent that the hydrogen reduction process has. The silane process
may be affected by the presence of volatile tungsten subfluorides, as in the hydrogen
reduction process. This assumes, however that the surface chemistry is substantially the
same for the two processes. At this time, there is no empirical evidence to support this
assumption. Indeed, silicon subfluorides are products of the silane reduction (50,58,75)
and may be more detrimental for selectivity than tungsten subfluorides (102). The silane
process also can result in gas phase nucleation under some conditions, as will be discussed
in the next section.
Gas Phase Nucleation
A few workers have reported results which indicate that gas phase reactions occur
for the silane reduction process for certain reactant ratios (75,76,105,106). Nakamura et
al. (76), observed that for inlet flow ratios (SiFfy/WFg) in the range of 1.3 to 2.5 visible
luminescence was observed around the gas inlet to the reaction chamber. They further
observed the presence of tungsten powders on the walls of the chamber following the
deposition experiments. These powders were analyzed by x-ray diffraction and scanning
electron microscopy and were found to be polycrystalline (3-phase tungsten. No such
luminescence or particles were observed when the inlet flow ratio was less that 1.3 SCCM
(standard cubic centimeters per second). Mclnerney et al. (106), performed a similar
experiment but used a particle counter on the exhaust port of their chamber as a detector.
They observed the production of particles as the inlet flow ratio became greater than one.
Cheek et al. (75), used mass spectrometry to observe significant changes in the volatile
15
product distribution when the inlet flow ratio was less than one, compared to inlet flow
ratios between 1.2 and 3.0. Many other workers have observed a correlation between the
inlet flow ratio and the selectivity of the process (80,107), with selectivity being lost as the
inlet flow ration becomes greater than approximately 1.0. Kobayashi et al. (58), have
proposed the following homogeneous (gas-phase) reaction:
WF6(g) + 6SiHF3(g) -> W(s) + 6SiF4(g) + 3H2(g) (10)
which can account for the observed phenomena.
The gas-phase production of tungsten particles during the silane reduction process
is a major factor for the loss of selectivity when the inlet flow ratio is greater than
approximately one. The particles are able to land on any surface and, if the temperature is
appropriately high, act as a nucleation site for loss of selectivity.
Ultra-High Vacuum Techniques
Several analytical techniques were used in this study to investigate the phenomena
which lead to loss of selectivity for the tungsten CVD process. As in many surface science
investigations, the techniques are used alone or in various combinations to yield
information about the process in question. Several of the techniques are carried out in
ultra-high vacuum. This is done to prevent contamination of the surface under
investigation by contact with atmospheric gasses or other impurities. The ultra-high
vacuum environment is somewhat analogous to an ultra clean and inert solvent that might
be used in standard "wet" chemistry. UHV is roughly defined as the pressure region from
1q-9 Torr to 10"12 Torr (10"^ Pa to 10"^ Pa) (108). Surface science experiments are
frequently carried out in this pressure range because the rate of collision of gas phase
molecules with surface sites is low enough to allow a surface which has been cleaned in
UHV to remain clean long enough to complete most experiments. Assuming a pressure of
16
7.5 x 10~10 Torr of air at room temperature, it takes approximately 43 minutes for each
surface site to be impacted at least once by a gas phase species. If each impacting
molecule sticks, this is how long it would take to form one monolayer on the surface of
the solid—the so-called "monolayer formation time" (J 09). In practice, it is rare that each
impact results in a new surface species, and pressures are commonly near 2 x 1 0 " ^ Torr.
This means that actual monolayer formation times may be many times longer than the 43
minutes stated above.
Auger Electron Spectroscopy
Auger electron spectroscopy provides elemental analysis of the surface region of a
solid. This is accomplished by directing an electron beam of appropriate energy onto the
surface and analyzing the kinetic energy spectrum of the secondary electrons which are
emitted. This spectrum contains peaks whose position and intensity identify the elements
present in the near surface region of the sample. The Auger process begins when an atom
is ionized by an incident electron, resulting in a core level vacancy. The atom then relaxes
by an electron transition from an outer (lower energy) level. The energy of this transition
may then be released by either photon emission or by ejection of another electron. This
latter electron is called an Auger electron (Figure 3). The kinetic energy of the Auger
electron shown in Figure 3 is given by (110)
E = F - F - F*
Where E*^ is the binding energy for the s level in the presence of a core hole. Each
element has a few characteristic Auger transitions, resulting in electron energy spectra
with peaks at locations and intensities that uniquely identify the element from which the
Auger electron originated. Since Auger peaks are small peaks on a rapidly varying
secondary electron background, it is common to record spectra in a differential mode,
17
dN(E)/dE vs. E. This can be accomplished by analog or digital methods(7/7). Auger
spectra have been carefully studied and examples compiled in reference volumes which are
used to qualitatively determine the elemental composition of a sample {111).
The Auger process is surface sensitive because only electrons which originate near
the surface are likely to escape the solid matrix without losing some kinetic energy to
interactions with the matrix. Loss of energy in this way results in the loss of the
information which leads to elemental identification. Depending on the material, this
"escape depth" is in the range 2-10 atomic layers (112). Auger spectroscopy was used in
this study to verify the elemental composition and cleanliness of the Si and Si02 surfaces
under study.
VAC
E f
M
1-2,3
Li
K
Auger Electron
Initial State Core vacancy resulting from
incident electron
-•—o-
- • — • -
Emission of an Auger electron
Final State
Figure 3. Schematic of the Auger process. K, L, and M are the core electron energy levels for the atom. Ef is the fermi level for the solid, and VAC is the vacuum level where the electrons are removed from the influence of the solid.
18
Mass Spectrometry
Mass spectrometry is an analytical technique which measures the mass to charge
ratio (m/Z) for gas phase analyte species {113). In general, these devices work by ionizing
incoming gas phase species and then electrostatically accelerating them into an area that
performs mass separation, usually by magnetic or electrostatic means. The analyte species,
which may become fragmented by the ionization process, are then detected, usually by
either a Faraday cup or an electron multiplier. There are several design options for each
step of this process—ionization, filtering, and detection. Each option has characteristics
which may be used to optimize the process for a specific application. The mass
spectrometer used in some of the experiments for this study is commonly referred to as a
quadrupole type. The term "quadrupole" actually refers to the mass separation part of the
device. However, since it is nearly always combined with an electron impact ionizer and a
Faraday cup—electron multiplier detector, the single term is usually used to describe the
whole apparatus. In the semiconductor industry this type of mass spectrometer
arrangement is frequently referred to as a "residual gas analyzer" or RGA.
The mass spectrometric process used in the current study begins with electron
impact ionization of the analyte species. This is accomplished using a tungsten filament as
a source of electrons. These electrons are electrostatically accelerated and directed into a
region containing the gas phase analyte species. Some of the electrons impact some of the
analyte species and strip off one or more of their electrons, creating positive ions. These
0 - ) ->
Species in —. from ionizer E x i t t o D e t e c t o r
Figure 4. Quadrupole mass filter.
19
positive ions are electrostatically accelerated and focused into the quadrupole region
which performs the mass separation. The quadrupole mass filter consists of four
cylindrical rods, arranged with their long axes parallel, as shown in Figure 4. Two
opposite rods have a positive direct current potential (dc) applied to them while the other
two rods have a negative dc current applied. Superposed on these dc potentials is a radio
frequency (RF) signal which sets up an electric field in-between the quadrupoles which
varies in time. This field causes ionic species moving along between the quadrupoles to be
jostled back and forth. For a given dc potential and RF value, only particles with a small
range of masses has a stable trajectory from the inlet to the exit of the quadrupole.
Particles with other masses are collected by one of the poles. By changing the dc potential
and RF values, the mass for which a stable trajectory is possible can be changed as a linear
function of time. The species surviving to the exit of the quadrupole are detected by a
combination Faraday cup—electron multiplier detector. A computer controls the
potentials on the quadrupoles and receives the signal from the detector. The computer can
then integrate the signal from the detector over the time that the quadrupoles are set for a
particular mass and thus determine how much of that particular mass is present in the
analyte gas.
The interpretation of the mass spectral data is complicated by several factors. Most
important is the fact that the ionization process results not only in ionizing analyte
molecules, but also can cause the molecules to fragment. This fragmentation results in
mass spectra which contain several peaks of characteristic intensities, the so-called
"cracking pattern", not simply one peak with a mass value of the parent molecule.
Additionally, some fragments may become doubly ionized which may result in the
misinterpretation of the mass as being half of the actual value (the mass spectrometer
measures the mass to charge ratio, m/Z). The presence of various isotopes of some
20
elements adds to the number of peaks in a mass spectrum. For example, tungsten has
isotopes with mass values of 182, 183, 184, and 186 which have natural abundances of
from 14% to 30% {114). Mass spectrometry is a very useful analytical tool if the data are
interpreted carefully.
Temperature Programmed Desorption
Temperature programmed desorption (TPD), also called thermal desorption, is the
process of exposing a solid substrate at low temperature in a vacuum to a gas phase
species, and then heating the substrate in a controlled fashion while observing the volatile
species being evolved with a mass spectrometer. If the pumping speed for the vacuum
chamber is high enough, then the mass spectrometer signal for a given species is
proportional to the rate of desorption of that species at each temperature. It is common
that a species has more than one desorption maxima. This indicates the existence of more
than one adsorption environment on the surface. TPD is a very usefUl technique for
gaining some understanding of the molecular interactions which take place on the surface
of a solid. Since the pioneering work of Redhead (115) many authors have provided useful
applications for TPD (116-119), including detailed analysis of spectra to extract
parameters for desorption kinetics and elucidation of surface structures. This study made
use of TPD to identify chemical species present on an SiC>2 surface.
Micro-Volume Mass Spectrometry
Micro-Volume Mass Spectrometry is the name we have given to the technique of
using a small diameter capillary as a sampling conduit into a vacuum pumped mass
spectrometer. The sampling capillary provides two functions—pressure reduction and
localization of sampling. The pressure reduction is a result of the limited capacitance of
the capillary, and the localized sampling is a result of the fact that the open end of the
sampling capillary is chosen to be on the order of, or larger than, the mean free path of the
21
gaseous species being sampled. The pressure reduction is essential if it is desired to
analyze the gas mixture in a region where the pressure is above approximately 1 * 10~5
Torr, which is the normal maximum operating pressure for a common quadrupole mass
spectrometer.
The pressure reduction that the capillary affords can be approximated by treating it
as a long round tube in molecular flow. Molecular flow is defined as the pressure region
where the mean free path of the gas is long compared to the diameter of the capillary
(J20). In this region the flow of the gas is determined entirely by gas-wall collisions. The
conductance of a gas through a circular tube under molecular flow has been given as {121)
n K d 3
( — y capillary ^ £
where v is the mean velocity of the gas particles, d is the diameter of the capillary, and t is
the length of the capillary, and (122)
8 RT V~inM
whereR is the ideal gas constant, T is the temperature in Kelvin, and M i s the molar mass
of the gas. Combining these two equations leads to
r i - H . capillary " | | ^
where a is a constant.
O'Hanlon (123) analyzed the situation of a differentially pumped mass
spectrometer attached to a chamber with a relatively high pressure by means of a capillary
22
High Pressure Chamber
Mass Spectrometer Vacuum
pump
^Connecting Capillary
Figure 5. Schematic of a differentially pumped mass spectrometer attached to a high pressure chamber.
(Figure 5) and found that the pressure in the spectrometer could be related to the pressure
in the chamber by
P = chamber
spectrometer J + (Sp/C)
where SP is the pumping speed of the pump on the mass spectrometer, and C is the
conductance of the connecting capillary. Inspection of this equation reveals that the
pressure in the spectrometer can be reduced by increasing the pumping speed of the pump
on the spectrometer, or by reducing the conductance of the connecting capillary. In this
study a mass spectrometer was connected to a CVD reaction chamber operating at 300
mTorr via a capillary of 0.53 mm inside diameter and a length of 0.6 m.
23
Chapter References
(1) Briggs, D.; Seah, M. P., Eds. Practical Surface Analysis by Auger and X-ray Photoelectron Spectroscopy, John Wiley & Sons: Chichester, 1983; p. 186.
(2) Suzuki, M.; Kobayashi, N.; Mukai, K. In Tungsten and Other Advanced Metals for VLSI/ULSIApplications V; Wong, S. S.; Furukawa, S., Eds.; Materials Research Society: Pittsburgh, 1990; pp. 259-265.
(3) van der Jeugd, C. A.; Verbruggen, A. H.; Leusink, G. J.; Janssen, G. C. A. M.; Radelaar, S. In Tungsten and Other Advanced Metals for VLSI/ULSI Applications V; Wong, S. S.; Furukawa, S., Eds.; Materials Research Society: Pittsburgh, 1990; pp. 267-272.
(4) Sivaram, S.; Dass, L.; Davies, P.; Frost, T.; Murray, J.; Tracy, B. In Tungsten and Other Advanced Metals for VLSI/ULSI Applications V; Wong, S. S.; Furukawa, S., Eds.; Materials Research Society: Pittsburgh, 1990; pp. 301-309.
(5) Green, M. L.; Levy, R. A. J. Electrochem. Soc. 1985, J 32(5, May), 1243.
(6) Brors, D. L.; Monnig, K. A.; Fair, J. A.; Coney, W.; Saraswat, K. C. Solid State Technol. 19S4(April), 313.
(7) Saraswat, K. C.; Wulu, H. C.; Rey, J. C.; Cheng, L. Y.; IslamRaja, M. M.; McVittie, J. P. In Tungsten and Other Advanced Metals for ULSI Applications in 1990; Smith, G. C.; Blumenthal, R., Eds.; Materials Research Society: Pittsburgh, 1991; pp. 239-247.
(8) Broadbent, E. K.; Flanner, J. M.; ven den Hoek, W. G. M.; Connick, I.-W. H. In Tungsten and Other Refractory Metals for VLSI Applications III; Wells, V. A., Ed.; Materials Research Society: Pittsburgh, 1988; pp. 191-199.
(9) Schmitz, J. E. J.; Van Dijk, A. J. M.; Suijker, J. L. G.; Buiting, M. J.; Ellwanger, R. C. Appl. Surf. Sci. 1989, 38, 350.
24
(10) Lee, P.-L.; Cronin, J.; Kaanta, C. J. Electrochem. Soc. 1989,136, 2108.
(11) Shaw, J. M.; Amick, J. A. RCA Rev. 1970, 31, 306.
(12) Amick, J. A.; Kern, W. In Chemical Vapor Deposition, Blocker, J. M., Sr.; Withers, J. C., Eds.; Electrochemical Society: New York, 1971; p. 551.
(13) Cuomo, J. J. In Proceedings of the 3rd International Conference on Chemical Vapor Deposition, Glaski, F. A., Ed.; American Nuclear Society: Illinois, 1972; p. 270.
(14) Melliar-Smith, C. M.; Adams, A. C.; Kaiser, R. H.; Kushner, R. A. J. Electrochem. Soc. 1974,121, 298.
(15) Kern, W.; Ban, V. S. In Thin Film Processes-, Vossen, J. L.; Kern, W., Eds.; Academic Press: New York, 1978; p. 257.
(16) Miller, N. E.; Beinglass, I. Solid State Technol. 1980, 23, 79.
(17) Miller, N. E.; Beinglass, I. Solid State Technol. 1982, 25, 85.
(18) Green, M. L.; Levy, R. A. J. Metals 1985, 37(6), 63.
(19) Cooke, M. J. Vacuum 1985, 35, 67.
(20) Sherman, A. Chemical Vapor Deposition for Microelectronics: Principles, Technology, and Applications, Noyes Publications: Park Ridge, NJ, 1987; pp. 92-118.
(21) Green, M. L. In Deposition and Growth: Limits for Microelectronics-, Rubloff, G. W., Ed.; American Institute of Physics: New York, 1988; p. 173.
(22) Rossi, R. C. In Handbook of Thin-Film Deposition Processes and Techniques; Schuegraf, K. K., Ed.; Noyes Publications: Park Ridge, 1988; p. Chap. 3.
25
(23) Hieber, K.; Korner, H.; Treichel, H. Thin Solid Films 1989,181, 75.
(24) Jensen, K. F.; Kern, W. In Thin Film Processes II; Vossen, J. L.; Kern, W., Eds.; Academic Press: San Diego, 1991; p. 283.
(25) Creighton, J. R.; Parmeter, J. E. Crit. Rev. Solid State Mater. Sci. 1993,18(2), 175-238.
(26) Murarka, S. P. In VLSI Technology, 2nd ed.; Sze, sm, Ed.; McGraw-Hill: New York, 1988; p. chap. 9.
(27) Deshpandey, C. V.; Bunshah, R. F. In Thin Film Processes IT, Vossen, J. L.; Kern, W., Eds.; Academic Press: San Diego, 1991; p. 79.
(28) Parsons, R. In Thin Film Processes II; Vossen, J. L.; Kern, W., Eds.; Academic Press: San Diego, 1991; p. 177.
(29) Schmitz, J. E. J.; Ellwanger, R. C.; van Dijk, A. J. M. In Tungsten and Other Refractory Metals for VLSI Applications III; Wells, V. A., Ed.; Materials Research Society: Pittsburgh, 1988; pp. 55-61.
(30) Cooke, M. J.; Heinecke, R. A.; Stern, R. C.; Maes, J. W. C. Solid State Technol. 1982, 25, 62.
(31) Levy, R. A.; Green, M. L.; Gallagher, P. K. J. Electrochem. Soc. 1984,131, 2175.
(32) Levy, R. A.; Green, M. L. J. Electrochem. Soc. 1987, 134, 37C.
(33) Greene, M. L.; Levy, R. A ; Nuzzo, R. G.; Coleman, E. Thin Solid Films 1984, 114, 367.
26
(34) Kwakman, L. F. T.; Sluijk, B. G.; Piekaar, H.; Granneman, E. H. A. In Tungsten and Other Refractory Metals for VLSI Applications IV; Blewer, R. S.; McConica, C. M., Eds.; Materials Research Society: Pittsburgh, 1989; pp. 315-321.
(35) Jain, A.; Chi, K.-M.; Farkas, J.; Kodas, T. T.; Hampden-Smith, M. J. Semicond. Int. in press.
(36) Murarka, S. P. In Tungsten and Other Advanced Metals for ULSI Applications in 1990; Smith, G. C.; Blumenthal, R. O. C., Eds.; Materials Research Society: Pittsburgh, 1991; p. 179.
(37) Lide, D. R., Ed. CRC Handbook of Chemistry and Physics, 74th ed.; The Chemical Rubber Company: Dayton, 1993; pp. 12-134.
(38) Lide, D. R., Ed. CRC Handbook of Chemistry and Physics, 74th ed.; The Chemical Rubber Company: Dayton, 1993; pp. 12-32.
(39) Flinn, P. A.; Mack, A. S.; Besser, P. R.; Marieb, T. N. MRS Bulletin 1993, 18( 12, Dec), 26-35.
(40) Ho, P. S.; Moske, M. A.; Hu, C. K. In Advanced Metallization for ULSI Applications 1992; Cale, T. S.; Pintchovski, F. S., Eds.; Materials Research Society: Pitssburgh, 1993; pp. 3-15.
(41) d'Heurle, F. M.; Ho, P. S. In Thin Films—Interdiffusion and Reactions; John Wiley: New York, 1978; p. 243.
(42) Thompson, C. V.; Lloyd, J. R. MRS Bulletin 1993, 75(12, Dec), 19-25.
(43) Shingubara, S.; Nakasaki, Y.; Keneko, H. Appl. Phys. Lett. 1991, 58, 42.
(44) Schulte, J.; Brodsky, S. B.; Lin, T.; Joshi, R. V. In Tungsten and Other Refractory Metals for VLSI Applications III; Wells, V. A., Ed.; Materials Research Society: Pittsburgh, 1988; pp. 367-373.
27
(45) Ohba, T.; Furumura, Y. J. Instn. Electronics & Telecom. Engrs. 1991, 57(2), 212-219.
(46) van der Jeugd, C. A.; Leusink, G. J.; Oosterlaken, T. G. M.; Alkemade, P. F. A.; Nanver, L. K.; Goudena, E. J. G.; Janssen, G. C. A. M.; Radelaar, S. J. Electrochem. Soc. 1992,139(12), 3615-3623.
(47) Kaplan, L. H.; d'Heurle, F. M. J. Electrochem. Soc. 1970,117, 693.
(48) Crowell, C.; Savace, J.; Sze, S. Trans. Metal. Soc. AIME 1965, 233, 478.
(49) Yu, M. L.; Eldridge, B. N.; Joshi, R. V. In Tungsten and Other Refractory Metals for VLSI Applications IIP, Wells, V. A., Ed.; Materials Research Society: Pittsburgh, 1988; pp. 75-81.
(50) Yu, M. L.; Ahn, K. Y.; Joshi, R. V. IBM J. Res. Develop. 1990, 34(6), 875-883.
(51) Miller, A.; Barnett, G. D. J. Electrochem. Soc. 1962,109, 973.
(52) Berkeley, J. F.; Brenner, A.; Reid, W. E., Jr. J. Electrochem. Soc. 1967,114, 561.
(53) Bryant, W. A.; Meier, G. H. J. Electrochem. Soc. 1973,120, 559.
(54) Miller, N.; Beinglass, I. Solid State Technol. 1965, 23, 79.
(55) Yu, M. L.; Eldridge, B. N.; Joshi, R. V. In Tungsten and Other Refractory Metals for VLSI Applications IV; Blewer, R. S.; McConica, C. M., Eds.; Materials Research Society: Pittsburgh, 1989; pp. 221-230.
(56) Yu, M. L.; Eldridge, B. N. J. Vac. Sci. Technol. A 1989, 7(3, May/June) 625-629.
28
(57) Kobayashi, N.; Goto, H.; Suzuki, M. In Tungsten and Other Advanced Metals for ULSI Applications in 1990; Smith, G. C.; Blumenthal, R., Eds.; Materials Research Society: Pittsburgh, 1991.
(58) Kobayashi, N.; Goto, H. J. Appl. Phys. 1991, <59(2), 1013-1019.
(59) Somorjai, G. A. Introduction to Surface Chemistry and Catalysis', John Wiley & Sons, Inc.: New York, 1994.
(60) Somorjai, G. A. Introduction to Surface Chemistry and Catalysis', John Wiley & Sons, Inc.: New York, 1994; p. 452.
(61) Jackman, R. B.; Foord, J. S. Surf Sci. 1988, 201, 47-58.
(62) Yarmoff, J. A.; McFeely, F. R. J. Appl Phys. 1988, 63, 5213.
(63) Raupp, G. B.; Hindman, G. T. In Tungsten and Other Refractory Metals for VLSI Applications IV', Blewer, R. S.; McConica, C. M., Eds.; Materials Research Society: Pittsburgh, 1989; pp. 231-237.
(64) Groenen, P. A. C.; Holscher, J. G. A.; Brongersma, H. H. Appl. Surf Sci. 1991, 53, 30-34.
(65) Broadbent, E. K.; Ramiller, C. L. J. Electrochem. Soc. 1984,131(6, Jun), 1427-1433.
(66) Mayer, J. W.; Lau, S. S. Electronic Materials Science: For Integrated Circuits in Si and GaAs; Macmillan Publishing Company: New York, 1990; p. 5.
(67) Bryant, W. A. J. Electrochem. Soc. 1978,125, 1534.
(68) Stacy, W. T.; Broadbent, E. K.; Norcott, M. H. J. Electrochem. Soc. 1985,132, 444.
29
(69) Colgan, E. G.; Gambino, J. P.; Kastl, R. H. J. Electrochem. Soc. 1993,140(1), 159-166.
(70) Broadbent, E. K.; Sadana, D. K.; Morgan, A. E.; Flanner, J. M.; Ellwanger, R. C. In Tungsten and Other Refractory Metals for VLSI Applications III; Wells, V. A., Ed.; Materials Research Society: Pittsburgh, 1988; pp. 111-113.
(71) Blewer, R. S.; Headley, T. J.; Tracy, M. E. In Tungsten and Other Refractory Metals for VLSI Applications III; Wells, V. A., Ed.; Materials Research Society: Pittsburgh, 1988; pp. 115-122.
(72) Sault, A. G.; Goodman, D. W. Surf Sci. 1990, 28-46.
(73) Brors, D. L.; Fair, J. A.; Monnig, K. A.; Saraswat, K. C. Solid State Technol. 1983, 26, 186.
(74) Kusumoto, Y.; Takakuwa, K.; Hashinokuchi, H.; Ikuta, T.; Nakayana, I. In Tungsten and Other Refractory Metals for VLSI Applications III; Wells, V. A., Ed.; Materials Research Society: Pittsburgh, 1988; pp. 103-109.
(75) Cheek, R. W.; Kelber, J. A.; Fleming, J. G.; Blewer, R. S.; Lujan, R. D. J. Electrochem. Soc. 1993,140(12, Dec), 3588-3590.
(76) Nakamura, Y.; Kobayashi, N.; Goto, H.; Homma, Y. Extended Abstracts of the 1991 International Conference on Solid State Devices and Materials 1991, 216-218.
(77) Kobayashi, N.; Goto, H.; Suzuki, M. Extended Abstracts of the Fall Meeting of the Electrochemical Society 1990,840-841
(78) Kobayashi, N.; Goto, H.; Suzuki, M. Extended Abstracts of the 22nd Conference on Solid State Devices and Materials, Sendai 1990, 865-868.
(79) Ohba, T.; Suzuki, T.; Hara, T.; Furumura, Y.; Wada, K. In Tungsten and Other Refractory Metals for VLSI Applications IV; Blewer, R. S.; McConica, C. M., Eds.; Materials Research Society: Pittsburgh, 1989; pp. 17-25.
30
(80) Schmitz, J. E. J.; Buiting, M. J.; Ellwanger, R. C. In Tungsten and Other Refractory Metals for VLSI Applications IV\ Blewer, R. S.; McConica, C. M., Eds.; Materials Research Society: Pittsburgh, 1989; pp. 27-33.
(81) Colgan, E. G.; Chapplesokol, J. D. J. Vac. Sci. Technol. B 1992,10(3), 1156-1166.
(82) Wintterlin, J.; Avouris, P. Surf Sci. Lett. 1993, 286, 529-534.
(83) Hillman, J. T.; Triggs, W. M.; Aruga, M. J. Electrochem. Soc. 1992, 739(12), 3574-3578.
(84) Mayer, J. W.; Lau, S. S. Electronic Materials Science: For Integrated Circuits in Si and GaAs; Macmillan Publishing Company: New York, 1990.
(85) Sotola, J.; Savkin, V.; Knor, Z. Collection of Czechoslovak Chemical Communications 1992, 57(12), 2481-2493.
(86) Runyan, W. R.; Bean, K. E. Semiconductor Integrated Circuit Processing Technology, Addison-Wesley: Reading, MA, 1990.
(87) Holleman, J.; Hasper, A.; Kleijn, C. R. J. Electrochem. Soc. 1993,140(3), 818-825.
(88) Hirase, I.; Sumiya, T.; Schack, M.; Ukishima, S.; Rufin, D.; Shishikura, M.; Matsuura, M.; Ito, A. In Tungsten and Other Refractory Metals for VLSI ApplicationsIH\ Wells, V. A., Ed.; Materials Research Society: Pittsburgh, 1988; pp. 133-140.
(89) Sellers, J. A.; Kottke, M.; Wilson, S. R.; Mattox, R. J. In Tungsten and Other Advanced Metals for VLSI/ULSI Applications V\ Wong, S. S.; Furukawa, S., Eds.; Materials Research Society: Pittsburgh, 1990; pp. 227-232.
(90) Kepten, A.; Reisman, A.; Ray, M.; Smith, P. L.; Temple, D.; Tapp, F. J. Electrochem. Soc. 1992, 759(8), 2331-2337.
31
(91) McConica, C. M.; Cooper, K. J. Electrochem. Soc. 1988, 755(4, April), 1003-1008.
(92) Broadbent, E. K.; Stacy, W. T. Solid State Technol. 1985, 28(12, December), 51.
(93) Moriya, T.; Itoh, H. In Tungsten and Other Refractory Metals for VLSI Applications-, Blewer, R. S., Ed.; Materials Research Society: Pittsburgh, 1986; p. 21.
(94) Kwakman, L. F. T.; Vermeulen, W. J. C.; Granneman, E. H. A.; Hitchman, M. L. In Tungsten and Other Refractory Metals for VLSI Applications III\ Wells, V. A., Ed.; Materials Research Society: Pittsburgh, 1988; pp. 141-147.
(95) McConica, C. M. In Tungsten and Other Refractory Metals for VLSI Applications, Broadbent, E. K., Ed.; Materials Research Society: Pittsburgh, 1987; pp. 51-57.
(96) Creighton, J. R. In Tungsten and Other Refractory Metals for VLSI Applications //; Broadbent, Ed., Materials Research Society: Pittsburgh, 1987: pp. 43-50.
(97) Creighton, J. R. J. Vac. Sci. Technol. A 1989, 7(3), 621-624.
(98) Creighton, J. R. J. Electrochem. Soc. 1989, 136(1), 271-276.
(99) Creighton, J. R. J. Vac. Sci. Technol. A 1987, 5(4, Jul/Aug), 1739-1740.
(100) Creighton, J. R.; Rogers, J. W. J. In Tungsten and Other Refractory Metals for VLSI Applications III; Wells, V. A., Ed.; Materials Research Society: Pittsburgh, 1988; pp. 63-68.
(101) Bradbury, D. R.; Kaminis, T. I. J. Electrochem. Soc. 1986,133(6, Jun), 1214-1217.
32
(102) Chow, R. L.; Schmitz, J. E. J.; Arnold, P. W. In Tungsten and Other Advanced Metals for ULSI Applications in 1990; Smith, G. C.; Blumenthal, R., Eds.; Materials Research Society: Pittsburgh, 1991; pp. 89-97.
(103) Reisman, A.; Shin, D. R.; Jones, G. W. J. Electrochem. Soc. 1990,137, 722.
(104) Fleming, J. G.; Omstead, T. R.; Dominguez, F. In Advanced Metallization for ULSI Applications; Rana, F. F. S.; Joshi, R. V.; Ohdomari, I., Eds.; Materials Research Society: Pittsburgh, 1992; pp. 233-239.
(105) Park, H. L.; Yoon, S. S.; Park, C. O.; Chun, J. S. Thin Solid Films 1989,181, 85-93.
(106) Mclnerney, E. J.; Mountsier, T. W.; Chin, B. L.; Broadbent, E. K. In Advanced Metallization for ULSI Applications; Rana, V. V. S.; Joshi, R. V.; Ohdomari, I., Eds.; Materials Research Society: Pittsburgh, 1992; p. 69.
(107) Suzuki, M.; Kobayashi, N.; Mukai, K.; Kondo, S. J. Electrochem. Soc. 1990, 737(10, October), 3213-3218.
(108) O'Hanlon, J. F. A User's Guide to Vacuum Technology, 2nd ed.; John Wiley & Sons: New York, 1989; p. 4.
(109) O'Hanlon, J. F. A User's Guide to Vacuum Technology, 2nd ed.; John Wiley & Sons: New York, 1989; p. 13.
(110) Briggs, D.; Seah, M. P., Eds. Practical Surface Analysis by Auger and X-ray Photoelectron Spectroscopy; John Wiley & Sons: Chichester, 1983; pp. 94-95.
(111) Davis, L. E.; MacDonald, N. C.; Palmberg, P. W.; Riach, G. E.; Weber, R. E. Handbook of Auger Electron Spectroscopy, 2nd ed.; Physical Electronics Industries, Inc.: Eden Prairie, MN, 1976.
(112) Briggs, D.; Seah, M. P., Eds. Practical Surface Analysis by Auger and X-ray Photoelectron Spectroscopy; John Wiley & Sons: Chichester, 1983; p. 186.
33
(113) O'Hanlon, J. F. A User's Guide to Vacuum Technology, 2nd ed.; John Wiley & Sons: New York, 1989; chapter 8.
(114) Lide, D. R., Ed. CRC Handbook of Chemistry and Physics, 74th ed.; The Chemical Rubber Company: Dayton, 1993; pp. 1-10.
(115 ) Redhead, P. A. Vacuum 1962,12, 203-211.
(116) Miller, J. B.; Siddiqui, H. R.; Gates, S. M.; Russell, J. N.; Yates, J. T. J.; Tully, J. C.; Cardillo, M. J. J. Chem. Phys. 1987, 57(11), 6725.
(117) King, D. A. Surf Sci. 1975, 47, 384-402.
(118) Madey, T. E.; Yates, J. T. J. Surf Sci. 1977, 63, 203-231.
(119) Yates, J. T. J. In Solid State Physics: Surfaces; Park, R. L.; Lagally, M. G., Eds.; Academic Press, Inc: Orlando, 1985; Vol. 22, pp. 425-464.
(120) O'Hanlon, J. F. A User's Guide to Vacuum Technology, 2nd ed.; John Wiley & Sons: New York, 1989; p. 25.
(121) O'Hanlon, J. F. A User's Guide to Vacuum Technology, 2nd ed.; John Wiley & Sons: New York, 1989; p. 33.
(122) O'Hanlon, J. F. A User's Guide to Vacuum Technology, 2nd ed.; John Wiley & Sons: New York, 1989; p. 9.
(123) O'Hanlon, J. F. A User's Guide to Vacuum Technology, 2nd ed.; John Wiley & Sons: New York, 1989; pp. 142-143.
CHAPTER II
METHANOL INTERACTIONS WITH S I 0 2 SURFACES
Introduction
The interaction of methanol with an Si02 surface was investigated by temperature
programmed desorption (TPD). Methanol was observed to dissociate at oxygen vacancy
sites yielding adsorbed methyl groups. Interactions of WFg with the Si02 surface were
blocked by exposure of the surface to methanol vapor prior to WFg treatment.
Implications of this site blocking for maintaining selectivity for selective CVD tungsten are
discussed.
A demonstrated mechanism for loss of selectivity for tungsten CVD, as stated in
chapter one, is the reaction of volatile reaction products (e.g., tungsten subfluorides, page
13) on Si02- Izumi, et. al. (7), report that pretreatment of Si/Si02 patterned wafers with
methanol prior to tungsten CVD prevents the loss of selectivity. We carried out a series of
TPD and Auger spectrometry experiments directed at gaining an understanding of the
mechanism by which methanol inhibits loss of selectivity on Si02 surfaces. Our TPD
studies showed that methanol dissociates at active sites on the Si0 2 surface to yield
adsorbed methyl groups. These methyl groups were observed to recombine with H and
desorb as methane at approximately 475 K and above. The methane yield at this
temperature was increased by Ar+ sputtering of the surface prior to methanol dosing. Ar+
sputtering is known to produce oxygen deficiencies and partially reduced silicon on Si02
surfaces (2,3). These data indicate that the methanol reacts at surface defect sites which
contain Si in a reduced oxidation state. Our studies also showed that such pre-adsorbed
34
35
methyl groups inhibit the reaction of WF6 with the surface. This suggests that oxygen
vacancy sites are active sites for tungsten nucleation, and are passivated by chemisorbed
methyl groups resulting from exposure to methanol. We note that selective tungsten
deposition begins with the reduction of WFg by Si®, as outlined in chapter one.
Experimental
Six inch diameter single crystal silicon wafers which had been thermally oxidized to
yield a surface oxide film approximately 180 A thick were obtained from Sandia National
Laboratories. These relatively thin oxides were used to avoid charging during Auger
electron spectroscopy (AES). The wafers were cut into one square centimeter samples for
use in these experiments. The samples were lightly etched with dilute (50:1) HF for - 1 0
seconds immediately prior to UHV studies. This procedure parallels typical industry
practice, and thus gives an approximation of surfaces encountered under industrial W-
CVD conditions.
Temperature programmed desorption (TPD) experiments were conducted in a
turbomolecularly pumped multi-port UHV chamber (Figure 6). This chamber is equipped
with a CMA Auger spectrometer (PHI model 10-150), a quadrupole mass analyzer (UTI
model 100C), an argon ion sputter gun (PHI model 04-161), and a leak valve and doser
tube system for controlled exposure of the sample to methanol or WFg vapor. The sample
may be cooled to liquid nitrogen temperatures and heated to > 900 K by resistively heating
the sample holder with a programmable power supply. The thermocouple junction was in
contact with the front surface of the sample near the edge. The power supply and mass
analyzer are simultaneously controlled by a computer which records the analytical signal
from 10 channels of the mass analyzer as a function of sample temperature.
AES was used to determine the elemental composition at the surface of the SiC>2
samples. The Si LMM peak at 76 eV is characteristic of SiC>2 (4). The incident electron
36
beam from the AES was observed to reduce the Si(>2 surface to Si^ unless the beam
energy was kept appropriately high (4 keV in the present experiments) (5). As a further
precaution against disrupting the Si(>2 surface the sample was not subjected to the Auger
e"-beam until after the TPD data were collected.
Initial Auger analysis always revealed the presence of carbon contamination on the
SiC>2 sample. This type of contamination is commonly found on samples before cleaning in
UHV, and is presumably from hydrocarbons on the sample from the laboratory
environment. In this study the samples were cleaned, in situ, first by Ar+ ion sputtering
followed by an O2 anneal. The sputtering was kept as gentle as possible to avoid excessive
disruption of the oxide surface. Typical sputtering parameters were a 15 mA sample
Mass Spectrometer
Doser Tube
Ar+ ion sputter gun Auger
Spectrometer
Sample
Vacuum Pump
AES/TPD Chamber
Turbo Pumped 2x10-10 Torr
Sample: 180A thermally oxidized silicon
Sample Temp. 120K - 900K
Figure 6. Ultra high vacuum chamber for TPD studies.
37
current (as measured by an external picoammeter placed between the sample and ground)
of 0.5 kV Ar+ ions for 5 minutes. This sputtering procedure was sometimes repeated if
subsequent AES analysis revealed continued presence of excessive carbon contamination.
The sputtering causes the volatilization of oxygen from the SiC>2, resulting in the
formation of small amounts of elemental silicon (Si®) at the surface (2) (Figure 8). The
S1O2 surface was recovered by annealing the sample, in situ, at 700 K and lx 10"^ torr
O2 for 15 minutes, followed by 850 K for 1 minute at the system base pressure (typically
3x 10"10 torr). This resulted in a surface of SiC>2 with very little carbon contamination
(approximately 3% C, using the method of ref. 4) (Figure 9).
S1O2 samples thus cleaned were exposed to methanol and tungsten hexafluoride
vapors by means of a UHV dosing system (Figure 7). This consisted of a network of
stainless steel vacuum lines with on/off valves and UHV leak valves arranged so that a
/ UHV
/ Controlled
V Leak Valve
UHV Chamber 10"10 torr
Methanol
On/Off valve
Vacuum Pump UP torr
Figure 7. Apparatus for dosing a sample in UHV with a controlled amount of gas.
38
I
I s
i IW
1 6, £ I x •a
1 e
I s 0>
I e s aa
I oo B 3p
39
I
,1
i | S
1
a
I
00
1
.a <3 p*
C*
9 00
I *r fi ea> £
i <D &£
3
ON
I OA •i—i
40
controlled amount of the desired gas could be directed onto the Si(>2 surface in the UHV
analytical chamber. The TPD experiments began by cooling the cleaned SiC>2 sample by
liquid nitrogen cooling of the sample holder (sample temperature approximately 100 K to
130 K). The sample was then dosed by opening the appropriate leak valve (methanol or
WFg) for a controlled length of time, while monitoring the UHV chamber pressure. After
the sample was dosed, it was moved in front of the mass spectrometer and the sample
holder was resistively heated at a rate of approximately 5 K to 10 K per second. The
resulting plot of mass spectrometer signal versus sample temperature yields information on
the interaction of the dosed gas with the SiC>2 surface.
Results
Figure 10 shows results of TPD studies with methanol on lightly sputtered (one
minute with A r + ions at 0.5 kV) SiC>2. The mass 32 (methanol) desorption spectra
indicated no significant desorption peaks other than a low temperature ( -250 K) peak.
The mass 15 and 16 spectra show a corresponding low temperature peak, but also a
second peak at approximately 475 K. We attribute the low temperature peak in each
spectrum to the mass spectrometer cracking pattern of methanol (See Figure 11) because
there is a correlation in the TPD spectra between the parent ion (CH30H + ) and the
daughters. The high temperature peaks in the mass 15 and 16 spectra are not from
methanol cracking since there is no corresponding parent ion correlation. The high
temperature peak is also not from OH (yielding 0 + , mass 16, as a mass fraction) since the
mass 15 peak correlates to the mass 16 peak in the TPD, and the mass 15 peak can not
come from OH. We attribute the high temperature peak in the mass 15 and 16 spectra to
CH4 (CH3 + and CH4"1" respectively). This TPD peak at 475 K indicates that CH3OH has
dissociated at active sites on the Si02, yielding adsorbed CH3. The CH3 recombines with
H and desorbs to yield the observed peak at 475 K. The two spectra in Figure 12 show the
41
mass 32 TPD
200 — ,
300 — , —
400 500 600 700 —I
800
1 I m
6
I CO CO in
mass 16 TPD
200 — i —
300 — , —
400 500 600 700 800
mass 15 TPD
200 300 400 500 600 700 I
800
Temperature (K)
Figure 10. TPD spectra (normalized) of methanol from a lightly sputtered Si(>2 surface. Comparing these spectra reveal that the high temperature ( - 475 K) mass 16 peak is due to CH4, not oxygen.
42
*<
CO CM
E 5 4-* o V a
-O C 3 o u <50
cS 03
\
:
N
0
1 <D
Sf x: o
V)
1
(sjiun ^jy) 3su0ds3>[ jQpuiojpQds ssbjv
e p W) IE
43
effect of Ar + sputtering on the population of adsorbed methyl groups. The dotted curve
(labeled "light sputtering") was sputtered for one minute with Ar + ions at 0.5 kV. The
solid curve (labeled "heavy sputtering") was the same sample sputtered an additional 10
minutes at 1 kV. It is clear from these data that sputtering creates active sites on the SiC>2
for methanol dissociation. This is corroborated by the fact that TPD spectra of SiC>2 which
has not been subjected to AES or ion sputtering showed no desorption above 400 K for
either CH4 or CH3OH (Figure 13).
Figure 15 shows the results of TPD studies with WFg on SiC>2. WFg desorption
was monitored by observing WF54" (281 amu) which is the most abundant mass
spectrometer fragment of WFg. A WFg desorption maximum at approximately 475 K is
fl.B
1 ** 2 p > • A-* a: o
0.2
<1.0
CH^ D e H o r p t i o n :
M e O H o n S10 a
Haavy Sputtflrrng
- - - Lfght SputtBrfnfl
100 200 300 400 500 7am para turn (K)
&00 700 000
Figure 12. TPD spectra of CH4 desorption from an Ar+ sputtered and methanol dosed Si02 surface.
44
1.0 r
"> 0.8
CH4 desorption
800
Temperature (K)
Figure 13. TPD spectrum of CH4 desorption from a methanol dosed unsputtered SiC>2 surface.
observed when no methanol pretreatment is used. AES revealed the presence of tungsten
on the SiC>2 following the TPD cycle (Figure 14). This strongly suggests
disproportionation of tungsten fluoride or subfluorides (WFX), leading to deposition of
tungsten and WF6 desorption (6). The high temperature WFg desorption peak is not
observed when the SiC>2 is lightly dosed with methanol prior to WF5 dosing. The
methanol was dosed at 110 K to give a multilayer, then flashed to 200 K to remove the
multilayer, leaving only actively adsorbed methanol on the surface. The WFg was dosed at
110 K to give a multilayer. These data indicate that WFg, the precursor to CVD tungsten,
adsorbs at active sites on SiC>2 which are deactivated by methanol for WFg adsorption.
45
>» £f
A IW e
1 Iuj
T CO
§ S
1 <o Q
I & £ 6 CO §
00 cs £ 1 X5 Cl, 2
<D 60 5
$ 3 £ a
&) • r—4
46
oo
CO
Temperature (K)
Figure 15. TPD spectra ofWF5+ (characteristic ofWFg) from a WF5 dosed Si02 surface. The multilayer peak has been omitted for clarity. A) after Ar+ ion sputtering as described in the text. B) no Ar+ sputtering.
Summary and Conclusions
It is clear that loss of selectivity must be preceded by, among other things,
adsorption of tungsten hexafluoride or subfluoride. Our data indicate that this adsorption
step may be stopped by deactivating the surface with methanol. The methanol dissociates
and leaves a methyl group at the active site rendering it inactive for WFX adsorption,
thereby blocking any loss of selectivity. The nature of these active sites may be inferred
from the observed increase in adsorbed CH3 with sputtering and the fact that Ar+
sputtering is known to produce oxygen deficiencies and partially reduced silicon on Si02
surfaces (2).
47
Chapter References
(1) Izumi, A.; Touei, K.; Yamano, A.; Chong, Y.; Watanabe, N. In Proceedings of the Eleventh International Conference on Chemical Vapor Deposition; Spear, K. E.; Cullen, G. W., Eds.; The Electrochemical Society, Inc: Pennington, NJ, 1990; pp. 425-433.
(2) Thomas, J. H., Ill; Hofmann, S. J. Vac. Sci. Technol. A 1985, 3(5, Sep\Oct), 1921-1928.
(3) McGuire, G. Surf. Sci. 1978, 76, 130.
(4) Davis, L. E.; MacDonald, N. C.; Palmberg, P. W.; Riach, G. E.; Weber, R. E. Handbook of Auger Electron Spectroscopy, 2nd ed.; Physical Electronics Industries, Inc.: Eden Prairie, MN, 1976; p 53
(5) Johannessen, J. S.; Spicer, W. E.; Strausser, Y. E. J. Appl. Phys. 1976, ¥7(7), 3028-3037.
(6) Creighton, J. R. J. Electrochem. Soc. 1989, 136(1), 271-276.
CHAPTER III
IN SITU MASS SPECTROMETRY OF A COMMERCIAL TUNGSTEN
CHEMICAL VAPOR DEPOSITION REACTOR
Introduction
This chapter describes micro-volume mass spectrometry studies which were
carried out in a commercial tungsten chemical vapor deposition reactor. A capillary with
an inside diameter of 0.53 mm was incorporated between the mass spectrometer (which
had its own vacuum pump) and the interior of the CVD reaction chamber (Figure 16). The
capillary created the required pressure difference between the CVD chamber and the mass
spectrometer. It also enabled localized sampling inside the CVD chamber. This novel
application of in situ high pressure mass spectrometry was used to investigate the
observed correlation between the reactant inlet flow ratio (SiH^/WFg) and the loss of
selectivity for tungsten CVD (See "Gas Phase Nucleation", page 14).
The identity of the products of the reaction between SiH4 and WFg on surfaces
has been the subject of some debate (See page 6). H2 and S1F4 have been previously
observed using mass spectrometry (1,2). However, other workers have used FT-IR to
observe that SLHF3 is produced in greater amounts than SiF4 (3). In this study, the
production of both SiF4 and SiHF3 were observed with partial pressure ratios that vary
with the Sffl^/WFg inlet flow ratio.
In this study, the SiF4 and SiHF3 partial pressures were monitored over a tungsten
coated wafer at 320°C as the S i ^ / W F g inlet flow ratio was varied from a selective (0.25)
to a non-selective (3.0) regime (See page 14). We observed the SiHF3/SiF4 product ratio
48
49
to decrease dramatically at reactant ratios associated with the onset of loss of selectivity
(1-1.5). Previous experiments using the same CVD tungsten reactor used in this work
confirm that a transition from selective to blanket tungsten deposition occurs at an inlet
flow ratio between 1 and 1.5. These data provide insight concerning loss of selectivity
mechanisms, and illustrate the potential of this mass spectrometric technique for real-time
in situ process control.
Experimental
In these experiments, we employed an in situ sampling technique in a configuration
novel to CVD studies to investigate the observed relationship between inlet flow ratio and
loss of selectivity. A differentially pumped mass spectrometer was fitted with a fused silica
capillary at its vacuum inlet. A commercial tungsten CVD reactor was modified so that,
with appropriate fittings, the capillary could be fed through the wall of the reactor. This
configuration allowed the mass spectrometer to sample the environment inside the reactor
at discrete locations. CVD processes were then carried out with the mass spectrometer
continuously sampling the environment just above a tungsten coated wafer. The inlet flow
of S1H4 was stepped from 50 to 600 seem with the WFg flow held constant in order to
observe the transition from selective to blanket tungsten deposition.
The experimental apparatus used consisted of a Leybold Inficon quadrupole mass
spectrometer, and a Genus 8720 CVD reactor (a six site deposition system). The mass
spectrometer had an integral 50-L/s turbomolecular pump. The inlet to this mass spectro-
meter was fitted with 1/16 inch Swagelok fittings that could accept a graphite ferrule for a
fused silica capillary (commonly used in gas chromatography). Similar fittings were added
to the chamber wall of the CVD reactor. Two additional small holes (1/32 inch) were
drilled in parts internal to the reactor to provide a direct line-of-site path from the fitting in
50
the reactor wall to the wafer chuck face. This configuration allowed the capillary to be
placed so as to communicate the volatile species near a reacting wafer surface directly to
the mass spectrometer without dilution. The minimum length of capillary required was
approximately 60 cm. The capillary itself did not have an internal stationary phase coating,
such as is commonly used in gas chromatography. Instead, the inner wall of fused silica
had been deactivated by a silanization process performed by the vendor. The capillary is
made sturdy by an external polyimide coating. The internal diameter was 0.53 mm. It was
possible to position the open end of the capillary from less than 1 mm to several
centimeters from the reacting tungsten coated wafer surface.
The total pressure in the chamber was maintained at 300 mTorr by means of a
computer controlled butterfly valve on the chamber pump exhaust. The WFg inlet flow
was kept constant at 200 seem. The wafer temperature was 320°C. The SM4 inlet flow
was varied from 50 to 600 seem in steps, with three minutes at each step to allow
equilibration. Argon was used as a carrier gas and was maintained at 100 seem inlet flow
Sampling Capillary
Mass Spectrometer
0.001 nit
Genus 8720 W-CVD Reactor ( s ix position )
Figure 16. Schematic diagram of the experimental setup used to investigate the reactions in a commercial tungsten CVD reactor.
51
for one set of experiments, and at 2000 seem for another. Complete mass scans in the
range 15 amu to 285 amu were acquired throughout the experiments. The mass
spectrometer was not designed to observe masses below 10 amu.
A model of the sampling capillary
Figure 17 shows a somewhat simplified model (J) of the capillary sampling system.
This treatment allows the estimation of the geometry of the capillary which is required to
achieve the desired pressure differential between the CVD chamber and the mass
spectrometer. The operational pressures in the chamber and the spectrometer vary widely.
CVD pressures range from several 10's of millitorr up to atmospheric pressure. The mass
spectrometer had an upper pressure limit of approximately 1 * 10"4 torr. Here it is assumed
that the CVD chamber has infinite volume, so that the its pressure is not affected by the
removal of gas by the spectrometer's vacuum pump.
The quantity of gas Q (the volume of gas at a known pressure) that flows into the
spectrometer through the capillary is given by (6) :
Qin = C(pc ~ps)
wherePc and Ps are the CVD chamber pressure and the spectrometer pressure,
CVD Chamber
Spectrometer Chamber
Vacuum Pump
Sn
Figure 17. Schematic diagram of the capillary sampling system and the differentially pumped mass spectrometer (4).
52
respectively, and C is the conductance of the capillary, with units of m-Vs or L/s. The
quantity of gas that flows out of the spectrometer through the vacuum pump is given by:
Qou, = S P P S
where Sp is the pumping speed of the vacuum pump on the spectrometer, with the same
units as the conductance, namely m^/s or L/s.
Since at equilibrium the flow into the spectrometer Qin must equal the flow
out Qout, these last two equations may be combined to yield:
P . ' • 1 S
1 + ( s , / c )
The conductance C through long round tubes under molecular flow (where the
mean free path of the gas particles is long compared to the diameter of the tube) has been
derived (7) and is given by:
n (f C = — v —
12 £
where d is the diameter of the capillary, £ is its length, and v is the average velocity of a
gas particle and is given by (<§):
8 RT V~inM
whereR is the ideal gas constant, T is temperature in kelvin, and Mis the molar mass of
the gas. Combining these last two equations and collecting the constants yields:
53
C 3 A m f ^ l = const. I sec. J
and
const. = 3.809 x 10"
when d is in millimeters, t is in meters, T is in kelvins, and M is in grams per mole. By
combining this equation for the conductance of the capillary C with the previous equation
for the pressure in the spectrometer/^, one may estimate the pressure of a particular gas
in the spectrometer by knowing its pressure in the CVD chamber, the geometry of the
sampling capillary, and the speed of the vacuum pump on the spectrometer. These
parameters are easily obtained in most cases.
The conductance C has a mass dependence that varies as M ' ^ 2 . The pumping speed
also has a mass dependence, with the lighter elements, having higher average velocity
being pumped more slowly by the turbomolecular pump than the more massive elements
(P). This means that the mass spectrometer signal is a function of not only the partial
pressure of the analyte gas in the CVD chamber, but also its molecular weight. It is
important to note, however, that the mass spectrometer signal is directly proportional to
the partial pressure of any particular analyte gas in the process chamber (where M does
not vary). The mass dependence of the spectrometer signal may be eliminated by
controlling the conductance between the spectrometer and the vacuum pump ( J O ) , but this
was not attempted in the present study. Experiments with pure argon were conducted to
verify the linear relationship between partial pressure in the process chamber and the
pressure at the spectrometer for a given gas (Figure 18).
54
Experiments were also conducted to verify that the observed species were not an
artifact of the sampling capillary. In the geometry described above, the open end of the
capillary was within a few millimeters of the wafer surface, which was at 320°C. Tungsten
deposition was observed on the polyimide coating of the capillary over approximately the
last four centimeters near the hot wafer. The amount of deposition decreased with distance
from the wafer, apparently as a function of the temperature of the capillary. By
1 2 - i
fc o
3 lifl t U
e £ <U a
R* =0.998
200 400 600 800 1000 Aigon Pressure in CVD Chamber (intoIT)
Figure 18. Pressure at the mass spectrometer as a function of the pressure in the CVD chamber for argon. These data show that there is a linear relationship between the pressure of a gas in the CVD chamber and the pressure of that gas in the mass spectrometer.
55
withdrawing the capillary so that it extended less than one centimeter from the water
cooled wall of the reaction chamber, we were able to repeat the experiment with the end
of the capillary approximately 290°C cooler. The results were essentially unchanged. The
same products were observed to vary in the same way relative to the reactant inlet flow
ratio. This result clearly indicates that the species observed were not artifacts of the
capillary. There were differences in the absolute partial pressures due to the less than
optimum placement of the sampling capillary relative to the wafer surface.
Results and Discussion
The mass spectrum of the gas mixture present in the CVD chamber during process
is very complex. There are several chemical species present, some with complex cracking
patterns. By acquiring complete spectral scans in the range 15 to 285 amu, important
identifications could be made by careful comparison of the data from several mass
channels as the inlet flow of reactants was varied.
Figure 19 shows the mass spectrometer response for the two gas phase reactants,
WFg and Silfy, from the same experiment. This figure clearly indicates that when the
Silfy/WFg inlet flow ratio is low—the selective deposition regime—there is an excess of
unreacted WFg present in the CVD chamber. Conversely, when the Silfy/WFg inlet flow
ratio is high—the non-selective deposition regime—there is excess SiHLj in the CVD
chamber. The WFg signal is only just detectable due to the high molecular weight of WFg
and the mass dependence of the conductance of the capillary (See page 53).
Figure 20 shows the mass spectrometer response for four of the mass fragments of
SiF4 as the inlet flow of S1H4AVF5 was varied from 0.25 (selective) to 3.0 (non-
selective). The signal for the parent ion SiF4+ (top) is especially important in the
identification of SiF4 as the analyte molecule present in the CVD reactor. The other
I
i <D 00 e o ex
£
£ S o <D CU DO 00 00
56
SiH,
WF,
//a^A/V
1*1
0.25 3.0
SiH4 /WF6 inlet flow ratio
Figure 19. Plot of the mass spectrometer response for the CVD reactants, WFg and Siffy, versus the Silfy/WF^ inlet flow ratio.
57
V)
c <D E o> CO
C O I
£ o
£ o
3
i i i i i i
CO
CD
I 1 1 1 1
( s j m n q j e ) e s u o d s e j o a d s s s e i u
fa w o m a 0
1 Xft
£
<+-<
O U D <2
«2 0> </) C o CX V3
CJ s s 0 <D OH
CO
1 J5 +-*
Cm O O S
o CN
£ . § >
E
58
fragments are identified as daughters of S1F4 because they show the same variations in
intensity as a function of inlet flow ratio.
Figure 21 shows the mass spectrometer response for four mass fragments of
SiHF3 during the same experiment. The identification of SiHF3 as the species giving rise
to these spectra is not as straightforward as the identification of SiF4. The intense mass 67
signal could be from Sff ly^ (m/Z=68) losing a hydrogen, or from SiHF3 (m/Z=86) losing
a fluorine. The situation is not resolved by analysis of the parent ion spectrum, as was
done for SiF4, since there are interfering species with masses of 68 amu (^SiHF2) and 86
amu (29siF3) Therefore, the existence of the 29s; isotope which has the same mass as
2&Si plus H obviates the unambiguous identification of the parent molecule for the spectra
of Figure 21 by considering the mass spectral data alone. There is, however, other
evidence that the m/Z=67 signal is from SiHF3 losing a fluorine. First is by analogy with
the cracking pattern of other fluorinated molecules, which readily lose fluorine (77), as in
SiF4 and WF5 in this study. Second is the data of Kobayashi et al. (3), which identifies
SiHF3 as a product of the silane reduction reaction by in-situ infrared spectroscopy. Other
fluorosilanes, such as SiH2F2 and SiF^F, were not detected in their experiments.
In this study, then, the m/Z=85 channel is used to monitor the SiF4 partial
pressure, and the m/Z=67 is used to monitor the S1HF3 partial pressure. These data
indicate that both SiF4 and SiHF3 are present as products of the SM4 + WFg CVD
reaction (See reactions4, 5, and 6 on page 6), but their relative partial pressures vary as a
function of the SiFfy/WFg inlet flow ratio.
Figure 22 combines the SiF4 most abundant ion (MAI) data from Figure 20 with
the SiHF3 MAI data from Figure 21 and includes the mass spectrometer signal for the
HF+ (m/Z =20) channel. This figure then compares the mass spectrometer response for
5 9
( 0
c 0 )
E o> 2
L J -
c o
L L .
X CO
I
£ o L l _
<
*
o *-» CD L. §
o «+-
0
C
CO L L
X CO
I I I I I I I I I I I T~\ I I I I I I T ' I I I
( s ; j u n q j e ) e s u o d s o j o e d s s s e u u
CO
O
G 0
1
c o CA O S
1
o S 3
c 2
u <2
( U CA c o &
2
Ix 2 0 >
I < D
a , CO CO CO c d
4
Cm O
o 5
< N
£
I * g
60
$
( s n . u n q j e )
0 S U O d S 9 J 0 8 d s SSBLU
© <3 C-
1 I 2 "Bb
8 CA .£ *2 ts
S 8 cs cs <u I U3
61
the three principal reaction products from the SH4 + WFg CVD reaction (See reactions
4, 5, and 6 on page 6 ff.) as the Siffy/WFg inlet flow ratio is varied. The qualitatively low
HF signal is consistent with the findings of other workers using mass spectrometry and
in-situ Fourier transform infrared spectroscopy, and HF is not considered further here.
The signals from the two fluorinated silane products in Figure 22 show interesting
dependencies on the Silfy/WFg inlet flow ratio. For low inlet flow ratios in the range 0.25
to 1.0 the two signals rise in concert, which corresponds to an increased surface reaction
rate. Between inlet flow ratios of 1.1 and 1.2 there is a substantial divergence of the
signals, with the m/Z=85 (SiF3+) signal rising sharply while the m/Z=67 (SiHF2+) signal
drops sharply. This signal divergence goes through a maximum and then decreases until
the m/Z=67 signal becomes slightly higher than the m/Z=85 signal. It is important to note
that for the ratio steps (1.2 to 1.8) the two signals have an inversely related component.
That is, when the m/Z=85 signal increases slightly (as in the 1.5 and 1.8 steps) the increase
is anti-correlated in the m/Z=67 signal. This suggests that the same reaction or reactions
that produce the abrupt rise in the m/Z=85 signal also produce the drop in the m/Z=67
signal.
There are two possible explanations for the divergence observed in Figure 22. One
is that there is a gas phase reaction occurring that has SiHF3 as a reactant and SiF4 as a
product. A second possibility is that there is an abrupt change in the surface chemistry;
from one set of reactions producing both SiF4 and SiHF3 without preference, to a second
set that produces SiF4 in preference to SLHF3. To distinguish between the surface and gas
phase reactions, the experiment was repeated with a substantially increased Ar partial
pressure in order to attenuate any gas phase reactions(/2).
Figure 23 shows the effect of increasing the amount of Ar in the reaction mixture
(from 100 seem to 2000 seem, total pressure maintained at 300 mt). This changes the
62
(s\\un - q j e )
0 s u o d s 9 j ' o e d s s s e u i
$ Cm O C5 o o 0
1 d>
1 a
+3 (/> <L>
3 o 0> *T3
CS
<0
I xn
1 O . 1 (U fa B vo • § 1 C i n O 00 t j cfl
I I
• § - I 2 < 2
O o £P I
c
i . a> § gp § ) e3 'S3
B i s
**0 H * 0 CO c s
m cs 2
. 1 p i
63
profile of the graphs in two ways. First, the maximum divergence between the mass 85
and 67 signals occurs at the inlet flow ratio of 1.0; a downward shift from 1.3. Second, the
extent of the divergence is diminished. This is clearly seen by comparing the mass 67
signal in Figure 22 and Figure 23. Figure 24 compares the data from the low argon flow
experiment with the data from the high argon flow experiment.
That the magnitude of the divergence is reduced when the Ar partial pressure is
increased indicates that it is caused by a gas phase reaction. With the introduction of high
argon flow, the residence times of the reaction products decrease, thereby reducing the
probability of gas phase interactions. The observed reduction in divergence indicates that
the effect is due to a gas phase reaction that has been attenuated by dilution with argon.
Such a gas phase reaction has been proposed by Kobayashi, et al. (3), and is discussed
above (equation 10 on page 15). Apart from this gas phase reaction, the data show trends
in product ratios from the surface reaction as well. These trends are especially evident
when the argon partial pressure is high (Figure 23). The partial pressure of the more silane
like SiHF3 is observed to rise as the amount of SH4 in the reaction mixture rises. The
more fluorinated SiF4 is the more abundant product when WFg is the dominant reactant
(at low inlet flow ratios) and the surface is presumably highly fluorinated.
The other significant effect that is apparent in Figure 24 is the shift in the maximum
divergence. This can be explained as a result of thermodifiusion (J3). Thermodiffusion is
caused by differences in the diffusion coefficients of the different gases. The result is the
existence of partial pressure gradients resulting from the temperature gradient inside the
CVD reactor (the wall of the reactor is water cooled to 25°C, and the wafer is at 320°C).
The gradients in partial pressures result in the more massive gas (WFg in this case)
becoming rarefied near the heated surface. This means that when the SiFLi/WFg inlet flow
64
Ifl
. 2
P4 £
o PU|
a
vo
r - , Tt a CO
SOI1BH p s u & s / £ J H ! S
£ 3 CO £ Q< 73 • »•*
*W) £ <N s S) w "5
2 2 CO £ Cu
" r t
O.
|
O' CN CS CO £ 3> ts S o «h w O • «—4 H +
<T) fe C/3 + (N
^r <s £ . 1 Ph
65
ratio is set at, for instance, one, the actual SiJfy/WFg r a t ' ° a t the hot wafer surface is
something greater than one. If the thermodiffusion effect is increased (e.g., by the
introduction of more of the lighter gas argon) the actual SiHLj/WFg ratio at the surface
increases even more. This means that when the thermodiffusion effects are greater (in the
high Ar partial pressure case), the same surface ratio is reached when the inlet flow ratio is
lower. Hence, the location of the observed divergence in Figure 23 is at a lower
Siffy/WFg inlet flow ratio than in Figure 22 (See also Figure 24).
Conclusions
This study has revealed the presence of a previously unreported relationship in the
SiF4 and SiHF3 product partial pressures as a function of the SiFty/WFg inlet flow ratio.
The ratio of the products changes abruptly when the inlet flow ratio changes from a
regime associated with selective deposition to one associated with non-selective
deposition (Figure 24). For Silfy/WFg inlet flow ratios less than one, both SiF4 and
SiHF3 partial pressure increase with increasing SiPfy partial pressure. As the inlet flow
ratio increases beyond one, the S1HF3 partial pressure is anti-correlated with the SiF4
partial pressure. Dilution with argon demonstrates that this anti-correlation is probably due
to a gas phase reaction between WF5 and SiHF3 which yields solid W and S1F4 as
products (equation 10 on page 15).
Apart from this gas phase reaction, the data from these experiments show trends in
product ratios from the surface reaction as well. These trends are especially evident when
the argon partial pressure is high (Figure 23 and Figure 24). The more silane like SiHF3
partial pressure is observed to rise as the amount of SH4 in the reaction mixture rises.
The more fluorinated SiF4 is the more abundant product when WFg is the dominant
reactant (at low inlet flow ratios) and the surface is highly fluorinated. The SiF4 signal
decreases as Silfy becomes more dominant.
66
Thermodiffusion effects were investigated by introducing a mixture of 10% WF6
in AT into the CVD chamber and recording the mass spectrometer signal for the two
gasses at varying distances from the heated wafer chuck (no Si wafer was used in this
experiment). This was possible because the sampling capillary could be positioned at any
distance above the chuck up to the wall of the CVD chamber. Figure 25 shows the results
of this experiment.
a
0mm 10mm 20mm 30mm 40mm 50mm 60mm 70mm
Distance from hot chuck (420°C)
Figure 25. Thermodiffusion results in the depletion of WF6 relative to Ar near a heated surface in the CVD chamber.
This study also indicates that micro-volume mass spectrometry has significant
potential for real-time process control in commercial CVD reactors. These data
demonstrate that appropriate mass spectrometer monitoring of reaction products permits
the real-time determination of whether the process is operating in the selective or blanket
deposition regimes.
67
Chapter References
(1) Yu, M. L.; Eldridge, B. N.; Joshi, R. V. In Tungsten and Other Refractory Metals for VLSI Applications IV; Blewer, R. S.; McConica, C. M., Eds.; Materials Research Society: Pittsburgh, 1989; pp. 221-230.
(2) Yu, M. L.; Eldridge, B. N. J. Vac. Sci. Technol. A 1989, 7(3, May/June), 625-629.
(3) Kobayashi, N.; Goto, H. J. Appl. Phys. 1991, 69(2), 1013-1019.
(4) O'Hanlon, J. F. A User's Guide to Vacuum Technology, 2nd ed.; John Wiley & Sons: New York, 1989; p. 142.
(5) O'Hanlon, J. F. A User's Guide to Vacuum Technology, 2nd ed.; John Wiley & Sons: New York, 1989; pp. 142-143.
(6) O'Hanlon, J. F. A User's Guide to Vacuum Technology, 2nd ed.; John Wiley & Sons: New York, 1989; p. 27.
(7) O'Hanlon, J. F. A User's Guide to Vacuum Technology, 2nd ed.; John Wiley & Sons: New York, 1989; p. 33.
(8) O'Hanlon, J. F. A User's Guide to Vacuum Technology, 2nd ed.; John Wiley & Sons: New York, 1989; p. 10.
(9) O'Hanlon, J. F. A User's Guide to Vacuum Technology, 2nd ed.; John Wiley & Sons: New York, 1989; chapter 8.
(10) O'Hanlon, J. F. A User's Guide to Vactmm Technology, 2nd ed.; John Wiley & Sons: New York, 1989; p. 143.
68
(11) Bell, D. A.; Zhiming L.; Falconer, J. L.; McConica, C. M. In Tungsten and Other Advanced Metals for ULSI Applications in 1990; Smith, G. C.; Blumenthal, R., Eds.; Materials Research Society: Pittsburgh, 1991; pp. 31-37.
(11) Nakamura, Y.; Kobayashi, N.; Goto, H.; Homma, Y. Extended Abstracts of the 1991 International Conference on Solid State Devices and Materials 1991, 216-218.
(12) Jost, W. Diffusion in Solids, Liquids and Gases; Academic: New York, 1960; pp. 492-501.
APPENDIX
COMPUTER PROGRAM
69
70
The following computer program was written to control, and acquire data from, a
UTI100C quadrupole mass spectrometer () present in an ultra-high vacuum chamber. The
program was written using Asyst (), a commercial version of the computer language
Forth. The data acquisition and control functions are carried out by interface with a
Labmaster DMA computer board (). The analog signal out of the Labmaster board's
DAC(O) channel is used as an input to the UTI lOOC's "external in" connector. A
potential applied to this "external in" connector in the range 0-10 Volts controls the mass
spectrometer's mass selection over the range 1 to 300 amu. The computer program thus
controls the desired mass setting on the mass spectrometer by sending an appropriate
number to DAC(0), which then converts this number to a potential at the "external in"
connector, which causes the mass spectrometer to select the corresponding mass value to
monitor. The Labmaster board's ADC(0) channel then recieves the signal from the "signal
out" connector on the mass spectrometer, which is proportional to the signal from the
mass spectrometer's detector. The program then correlates the mass selection information
with the signal coming from the mass spectrometer to produce a plot of intensity versus
m/Z. The program is menu driven and easy to use.
71
ECHO.OFF
\ MSPEC.ast
\
\ Description: Mass Spectrometer Acqusition and Control
LMDMA LINE.EDIT FORGET.ALL
15 SET.FILE.PARSE
\ ***** Declatation of Menus *****
MENU TOP.MENU
MENU SCAN.MENU
MENU ACQUISITION.MENU
MENU SAVE.FILE.MENU
MENU RETRIEVE.MENU
\ ***** Declaration of Windows *****
{[]DATA} 3 10 18 69 SET.WINDOW {DEF}
{[]PROMPT} 24 0 24 79 SET.WINDOW {DEF}
{[]INSERT} 1 5 1 60 SET.WINDOW {DEF}
{[]STATUS} 1 64 1 79 SET.WINDOW {DEF}
2 10 2 79 WINDOW {[]LABELS}
2 10 5 73 WINDOW {FILE.ERROR.WINDOW}
\ ***** Declaration of Vuports *****
VUPORT SCAN.VUPORT \ Where the M/S scan is displayed
72
NORMAL.COORDS
AXIS.DEFAULTS
0 0 VUPORT.ORIG
1 .81 VUPORT.SIZE
.03 .10 AXIS.ORIG
0 .03 DATA. ORIG
.03 .10 AXIS.POINT
.94 .86 AXIS.SIZE
1 1 DATA. SIZE
15 COLOR
1 VUPORT.COLOR
3 AXIS.COLOR
3 LABEL.COLOR
4 CURSOR.COLOR
HORIZONTAL AXIS.FIT.OFF GRID.OFF LABEL.SCALE.OFF
VERTICAL AXIS.FIT.OFF AXIS.OFF GRID.OFF LABEL.SCALE.OFF
NO.LABELS
\ ***** Declaration of Strings *****
30 STRING HORIZONTAL.LABEL \ Label for horizontal axis
30 STRING SETUP,FILENAME \ Filename of TPD setup file
64 STRING FILE.COMMENTS1
\ ***** Declaration of Tokens *****
73
TOKEN SCAN.IN EXP.MEM> SCAN.IN \ Each element is the ave. for
a channel
\ changed here 9/17
TOKEN CHANNEL.IN exp.mem> channel.in
TOKEN MASS,POINTS EXP.MEM> MASS.POINTS
TOKEN D/A.LOOKUP.ARRAY EXP.MEM> D/A.LOOKUP.ARRAY
TOKEN HIGHMASS.LOCATIONS EXP.MEM> HIGHMASS.LOCATIONS
TOKEN LOWMASS.LOCATIONS EXP.MEM> LOWMASS.LOCATIONS
TOKEN TPD. PARAMETERS. ARRAY EXP.MEM> TPD. PARAMETERS .ARRAY
TOKEN RUN. TIME. ARRAY EXP.MEM> RUN. TIME .ARRAY
TOKEN RUN.TEMP.ARRAY EXP.MEM> RUN.TEMP.ARRAY
\ ***** Declaration of Arrays *****
INTEGER DIM [ 300 ] ARRAY. BECOMES> D/A. LOOKUP .ARPAY
DIM[ 2 , 50 ] ARRAY.BECOMES> HIGHMASS.LOCATIONS
DIM[ 2 , 10 ] ARRAY.BECOMES> LOWMASS.LOCATIONS
DIM[ 16 , 5 ] ARRAY. BECOMES> TPD. PARAMETERS .ARRAY
REAL DIM[ 7500 ] ARRAY PIXBUF \ Used for fast erasure of lines
DIM[ 80 ] ARRAY MASS.LOCATIONS \ Used in calibration
routines
\ ***** Declaration of Scalars *****
INTEGER SCALAR FIRST.MASS
SCALAR FIRST.D/A
74
SCALAR LAST.MASS
SCALAR TOTAL. CHANNELS
SCALAR SAMPLES . PER. CHANNEL
SCALAR MAX. SIGNAL
SCALAR MASS. PEAK. ELEMENT
SCALAR LOWMASS.COUNT
SCALAR HIGHMASS.COUNT
SCALAR #MASSES
SCALAR MASS#
SCALAR SCAN#
SCALAR TEMPORARY
SCALAR MAX.TEMP
SCALAR ICE. PEAK.TEMP
SCALAR CHANNEL.TIME
REAL SCALAR FIRST
SCALAR SECOND
DP. REAL SCALAR TIME. ZERO
\ ***** Declaration of Templates *****
0 0 A/D. TEMPLATE M/S . SIGNAL. IN
0 0 D/A.TEMPLATE M/S.CONTROL.OUT
1 1 A/D.TEMPLATE TEMPERATURE.IN
1 1 D/A.TEMPLATE HEATER.CONTROL.OUT
75
\ ********** Generic Colon Defs *********** ^ *****************************************
\ Makes the foreground text red.
\ [ - ] < - )
: RED.LETTERS
RED MIX FOREGROUND INTEN.ON
\ Makes the foreground text yellow. \ [ - ] ( - )
: YELLOW.LETTERS
RED GREEN MIX FOREGROUND INTEN.ON
\ Makes the foreground text white.
\ [ - ] ( - )
: WHITE.LETTERS
WHITE MIX FOREGROUND
\ Waits for "Y" or "N" to be entered and repeats if invalid
character
\ Returns a true if "Y" was entered, false if "N".
\ [ - ] ( - T/F)
76
: GET.Y/N
BEGIN
7REL.C0L ?REL.ROW
of error
\ Save col and row in case
repeat
PCKEY NOT
IF
DUP 90 > IF 32 - THEN
DUP 89 = NOT
DUP 78 = NOT AND
ELSE
TRUE
THEN
\ Make lowercase
\ If not "Y" and not "N",
\ If a function key, repeat
WHILE
BELL
DROP
Y or N"
1000 MSEC.DELAY
7REL.COL 3 PICK - 1 +
3 PICK 3 PICK GOTO.XY
SPACES
GOTO.XY
REPEAT
\ Oops! Not a number
\ Drop the key value
\ Print error message
\ and wait a bit
\ Get current col
\ Back up to orig pos
\ Erase entry
\ Return to orig position
77
UNROT 2 *DROP
pos info
89 =
\ Got a good key, so drop
\ Place true on stack, if =
\ Waits for number to be entered and repeats if an invalid entry. \ [ - # ] ( - )
: #INPUT&CHECK
BEGIN
7REL.C0L ?REL.ROW
of error
#INPUT
NOT
WHILE
BELL
7REL.COL 3 PICK - 1 +
3 PICK 3 PICK GOTO.XY
SPACES
GOTO.XY
REPEAT
\ Save col and row in case
\ Get number
\ Valid?
\ Oops! Not a number
\ Get current col
\ Back up to orig pos
\ Erase entry
\ Return to orig position
UNROT 2 *DROP
78
\ Got a good number, so drop
pos info
\ Waits for string to be entered and repeats if a null string.
\ [ ~ ] ( - string )
: "INPUTSCHECK
BEGIN
"INPUT
"LEN 0 =
WHILE
BELL "DROP
start over
REPEAT
\ Get a string
\ Is string length 0 ?
\ Not a good string, so
SEPARATE. ARRAY
DUP XSECT[ 2 , ! ]
SWAP XSECT[ 1 , ! ]
\ ****************************************
\ ***** Show Calibration Definitions ***** \ ****************************************
79
PEAK. AD JUST
SCAN.IN
SUB[ 1 , 2 ; MASS.PEAK.ELEMENT 2 - , 5 ]
XSECT |[ 1 , ! ]
SORT&INDEX
SWAP DROP
[ 5 ] 3 -
PEAK.MAX
XSECT[ ! , MASS.PEAK.ELEMENT PEAK.ADJUST + ]
DUP [ 1 ] MASS.POINTS [ 1 , 1 FIRST.MASS - 1 + ]
[ 2 ] MASS. POINTS [ 2 , 1 FIRST.MASS - 1 + j| : =
SHOW.MASS.POINTS
LAST.MASS 1 + FIRST.MASS
DO
SCAN.IN X.ARRAY
D/A. LOOKUP.ARRAY [ I ]
INDEX.INTERPOLATE DROP
MASS.PEAK.ELEMENT :=
PEAK.MAX
LOOP
MASS. POINTS SEPARATE.ARRAY
80
" +" SYMBOL
XY. DATA. PLOT
CURSOR.OFF
SOLID
\ ******* * *****************************
\ ***** Scan Plotting Definitions ***** ^ *************************************
: ADD. LABELS
NORMAL.COORDS
0 LABEL.DIR 0 CHAR.DIR 0.55 0.05 POSITION
HORIZONTAL.LABEL CENTERED.LABEL
WORLD.COORDS
GET.MAX.SIGNAL
XSECT[ 1 , ! ] []MAX
MAX.SIGNAL :=
SETUP.HORIZONTAL.WORLD
FIRST.D/A DUP TOTAL.CHANNELS +
HORIZONTAL WORLD.SET
81
SETUP. VERTICAL. WORLD
DUP
WORLD.COORDS
GET.MAX.SIGNAL
MAX.SIGNAL DUP .0 100 A/D.SCALE 72 4 GOTO.XY FIX .
-2045 <=
IF
-2049 -2046 VERTICAL WORLD.SET
ELSE
-2049 MAX.SIGNAL DUP 204 8 + 0.05 * + VERTICAL WORLD.SET
THEN
VUPORT.CLEAR
XY.AXIS.PLOT
ADD.LABELS
PIXBUF LINE.BUFFER.ON
: PLOT.THE.SCAN
IF \ First time through scan
INTEGER DIM[ 2 , LAST.MASS FIRST.MASS - 1 + ] ARRAY.BECOMES>
MASS.POINTS
" % Full Scale" 60 4 GOTO.XY "TYPE
SETUP.HORIZONTAL.WORLD
SETUP. VERTICAL. WORLD
82
SEPARATE. ARRAY
XY. DATA. PLOT
SHOW.MASS.POINTS
ELSE
DUP
GET.MAX. SIGNAL
MAX. SIGNAL AYMAX >
IF
SETUP. VERTICAL. WORLD
ELSE
MAX. SIGNAL 2048 + AYMAX 2048 4- 0.70 *
IF
AYMAX -2025 >
IF
SETUP . VERTICAL. WORLD
THEN
THEN
THEN
ERASE.LINES
SEPARATE. ARRAY
XY. DATA. PLOT
SHOW.MASS.POINTS
THEN
83
\ ***** Scanning Definitions *****
: SCANNING.MESSAGE
12 FOREGROUND
26 0 GOTO.XY " Scanning - any key stops" "TYPE
2 FOREGROUND
SCAN.DESCRIPTION \ Finds first, last, and # of channels
D/A.LOOKUP.ARRAY [ LAST.MASS ]
D/A.LOOKUP.ARRAY [ FIRST.MASS ] DUP 7 - FIRST.D/A :=
- 14 + TOTAL.CHANNELS :=
CHANNEL.IN.SIZE
CHANNEL.TIME 0.025 /
SETUP.FOR.SCANNING
RELEASE.OVERLAY
M/S.SIGNAL.IN
CLEAR.TEMPLATE.BUFFERS
INTEGER DIM[ 2 , TOTAL.CHANNELS ] ARRAY.BECOMES> SCAN.IN
DIMf CHANNEL.IN.SIZE ] ARRAY.BECOMES> CHANNEL.IN
84
CHANNEL.IN TEMPLATE.BUFFER CYCLIC
0.025 CONVERSION.DELAY
A/D.INIT
SCAN \ Word for scanning and displaying mass spec
SCANNING.MESSAGE
SCAN.DESCRIPTION
SETUP.FOR.SCANNING
M/S.CONTROL.OUT
D/A. INIT
M/S.SIGNAL.IN
A/D.IN>ARRAY
CHANNEL.TIME 1 + SYNC.PERIOD
ERASE.LINES
TRUE
BEGIN
FIRST.D/A D/A.OUT
5 MSEC.DELAY
TOTAL.CHANNELS 1 + 1
DO
I FIRST.D/A + DUP
D/A. OUT
SYNCHRONIZE
SCAN.IN [ 2 , 1 ] :=
85
CHANNEL.IN MEAN
SCAN.IN [ 1 , 1 ]
LOOP
SCAN.IN
PLOT.THE.SCAN
FALSE
?KEY
UNTIL
PCKEY 7DROP 7DROP DROP
\ CLEAR.TEMPLATE.BUFFERS
\ ***** M/S Calibration Definitions *****
^ -k'k'k-k-k'kiir'k'k-k-Jc'k-k-k-k-k-k'k-Jir-k-k'k-iir'k'k'k-k-k-k'k'k-k^k-k-k'fc-k-k-k
: SAVE. CAL. FILE
LOAD. OVERLAY DATAFILE. SOV
FILE.OPEN CALIB.DAT
D/A. LOOKUP.ARRAY ARRAY>F1LE
FILE.CLOSE
: CALIBRATION
LOAD.OVERLAY MATFIT.SOV
HIGHMASS.LOCATIONS SUB[ 1 , 2 ; 1 , HIGHMASS.COUNT ]
86
SEPARATE. ARRAY
1 \ degree of polynomial fit
LEASTSQ.POLY.FIT
DUP [ 1 ] FIRST :=
DUP [ 2 ] SECOND :=
DROP
301 1
DO
I FIRST * SECOND -t-
D/A. LOOKUP. ARRAY [ I ] : =
LOOP
LOWMASS. COUNT 1 + 1
DO
LOWMASS.LOCATIONS [ 1 , 1 ]
D/A.LOOKUP.ARRAY [ LOWMASS.LOCATIONS [ 2 , 1
LOOP
SAVE. CAL. FILE
0 HIGHMASS.COUNT :=
0 LOWMASS.COUNT :=
ASSIGN.MASSES
#INPUT
IF
DUP 10 >
87
IF HIGHMASS.COUNT 1 + HIGHMASS.COUNT :=
HIGHMASS.LOCATIONS [ 2 , HIGHMASS.COUNT ]
MASS.LOCATIONS [ #READOUTS 2 * 1 - ]
HIGHMASS.LOCATIONS [ 1 , HIGHMASS.COUNT ]
ELSE LOWMASS.COUNT 1 + LOWMASS.COUNT :=
LOWMASS.LOCATIONS [ 2 , LOWMASS.COUNT ] :=
MASS.LOCATIONS [ #READOUTS 2 * 1 - ]
LOWMASS.LOCATIONS [ 1 , LOWMASS.COUNT ] :=
THEN
ELSE NOP
THEN
WAIT.FOR.DEL
BEGIN
PCKEY
IF INTERPRET.KEY FALSE
ELSE DUP 43 = \ + sign is hit
IF 71 INTERPRET.KEY
ASSIGN.MASSES BELL BELL BELL DROP FALSE
ELSE 27 =
THEN
THEN
UNTIL
83 INTERPRET.KEY
88
GET.SCAN.VALUES
0 CURSOR.INCREMENT
12 FOREGROUND
2 2 GOTO.XY " ESC to return to menu " "TYPE
2 FOREGROUND
SCAN.IN SEPARATE.ARRAY
VUPORT.CLEAR
XY. DATA. PLOT
MASS.LOCATIONS READOUT>ARRAY
NORMAL.COORDS
0.5 0.975 READOUT>POSITION
WORLD.COORDS
ARRAY.READOUT
WAIT.FOR.DEL
\ ***** TPD Setup Definitions *****
: SETUP.TPD
LOAD.OVERLAY AR-EDIT.SOV
16 ROWS 5 COLUMNS
89
TPD.PARAMETERS.ARRAY ARRAY.EDIT(MANUAL)
{[]LABELS}
" Mass Pre-ice Post-ice Display? Color"
7 1 GOTO.XY "TYPE {DEF}
INSERT
TPD.PARAMETERS.ARRAY TRANS[ 1 , 2 ] DUP
XSECT[ 1 , ! ] 300 [<=] TRUE.INDICES LOOKUP DUP
XSECT[ 1 , ! ] 1 [>=] TRUE.INDICES LOOKUP DUP
XSECT[ 1 , ! ] SORT&INDEX SWAP DROP LOOKUP
TRANS[ 1 , 2 ]
BECOMES> TPD.PARAMETERS.ARRAY
[]SHAPE DROP #MASSES := DROP DROP
\ ***** TPD Setup File Definitions ***** \ **************************************
: FILE.ERROR.MESSAGE
{FILE.ERROR.WINDOW) 4 BACKGROUND HOME
." Wrong filename or drive is not ready." CR
." Hit any key to try again."
PCKEY
1 BACKGROUND
STACK. CLEAR
90
FILE. EXISTS.MESSAGE
{FILE.ERROR.WINDOW} 4 BACKGROUND HOME
RED.LETTERS
." File already exists. Overwrite? (Y/N)
GET.Y/N
WHITE.LETTERS
1 BACKGROUND
FILE.EXISTS?
DEFER> FILE.SIZES SWAP DROP
0 <>
CREATE.SETUP.FILE
LOAD.OVERLAY DATAFILE.SOV
REGULAR.DATAFILE
FILE.TEMPLATE
1 COMMENTS
INTEGER DIM[ #MASSES , 5 ] SUBFILE
END
SETUP.FILENAME -TRAILING DEFER> FILE.CREATE
SETUP.FILENAME FILE.OPEN
91
FILE.COMMENTS1 1 >COMMENT
TPD. PARAMETERS .ARRAY ARRAY>FILE
FILE.CLOSE
\ Main word for retrieveing files. Executes the menu
RETRIEVE.MENU. Upon
\ leaving RETRIEVE.MENU the number of files tagged for deletion are
on the
\ number stack and the corresponding strings are on the symbol
stack.
\ [ - ] ( - )
: RETRIEVE.SETUP.TPD
STACK. CLEAR
RETRIEVE.MENU MENU.EXECUTE
LOAD. OVERLAY DATAFILE. SOV
DUP 0 =
IF \ If no items tagged drop and do
nothing
DROP
ELSE
DROP
12 "LEFT
-TRAILING DEFER> FILE.OPEN \ Open the tagged file
92
FILE>UNNAMED.ARRAY DUP
FILE.CLOSE
BECOMES> TPD.PARAMETERS.ARRAY
[]SHAPE DROP #MASSES := DROP DROP
THEN VUPORT.CLEAR
SAVE.SETUP.TPD
SAVE.FILE.MENU MENU.EXECUTE
SETUP.FILENAME FILE.EXISTS?
IF
FILE.EXISTS.MESSAGE
IF CREATE.SETUP.FILE
ELSE NOP
THEN
ELSE
CREATE.SETUP.FILE
THEN
ONERR:
?ERROR#
CASE
480 OF FILE.ERROR.MESSAGE ENDOF \ Invalid path or
filename
93
27 OF FILE.ERROR.MESSAGE ENDOF \ Duplicate file or not
found
11 OF FILE.ERROR.MESSAGE ENDOF \ file not found
30 OF FILE.ERROR.MESSAGE ENDOF \ file can't be copied
onto itself
237 OF FILE.ERROR.MESSAGE ENDOF \ drive not ready
58 OF FILE.ERROR.MESSAGE ENDOF \ require unambiguous
filename
25 OF FILE.ERROR.MESSAGE ENDOF
ENDCASE
\ ***** TPD Plotting words *****
^ -k-k "k-k-k-k-k-k-k-k *k-k-k ~k-k ~k-k-k-k k k-k ~k-k-k ~k k-k ~k-k
\ plots the data from the tpd run to the screen in real time
: PLOT.TPD,DATA
NOP
^ •k'k-k'k-k-k-k-k-k-k'k-k-k-k-k-k-k-k-k-kk-k-k-k-k-k-k-k-k-k-kiir-k-k-k'k-k
\ ***** Temperature Control Words *****
^ •k-k-k-k-k-k-k-k-k-k-k-k-k-k-k-k-k-k-k-k-k^c-k'k-k-k-k-k-kk-k-k-k-k-kkr-k
\ Holds sample at a user defined temperature
94
\ run in background so temp can stabalize while
\ other things are set up.
: CONSTANT.TEMP
NOP
\ Ramps sample temperature at user defined rate
: RAMP.TEMP
NOP
\ Displays set point and current sample temperature on screen
: RUN.TEMP
100
^ •k-k'k'k'k-k'k-k'k-k'k'k'k'kic'k'k-k'k-k-k-kic-k'k'k-k'k-k-jc-kic-k
\ ***** TPD Acquisition Words *****
^ •k-ie-k-k-k-k'k-k-k-k'k-k-k-k-k-k-k-k-k-k-k-k-kjc-k-k-kik-k-k-k-k-k
: NEED.SETUP.FILE.MESSAGE
{FILE.ERROR.WINDOW} 4 BACKGROUND HOME
RED.LETTERS
." Please specify a setup file first." CR
. " Hit any key to continue."
95
PCKEY
WHITE.LETTERS
1 BACKGROUND
\ Opens data file for storing TPD run
: CREATE. DATA. FILE
LOAD. OVERLAY DATAFILE. SOV
REGULAR. DATAFILE
FILE.TEMPLATE
3 COMMENTS
\ Puts value of REL.TIME in variable TIME.ZERO
: START.RUN.CLOCK
REL.TIME TIME.ZERO :=
\ Returns the current run time in seconds,
: RUN.TIME
REL.TIME TIME.ZERO - 1000 /
\ Sets mass spec, sensitivity to 10e-6 for moving
\ between masses. This avoids saturating the detector
96
\ if a huge peak is passed.
: SET.SENS.LOW
NOP
\ Sets mass spec, sensitivity to value specified in
\ TPD. PARAMETERS.ARRAY
: SET.SENS.PEAK
DROP
\ calculates the max number of scans possible for 32,768 elements
\ in SCAN.IN
: MAX.#.SCANS
32768 #MASSES /
\ saves the arrays scan.in, run.time.array, and run.temp.array
\ to a disk file.
: SAVE.TPD.RUN
NOP
\ appends the data from the most recent scan to the three arrays
\ scan.in, run.time.array, and run.temp.array
97
: APPEND. SCAN
BELL
NOP
\ Finds the maximum value in the five element array scan.in
\ obtained around the mass of interest
: FIND.MAX
3 MASS.PEAK.ELEMENT :=
SCAN.IN
PEAK.MAX
\ Main word for acquiring the TPD Spectrum
: DO.TPD
TPD.PARAMETERS.ARRAY [ 1 , 1 1 0 =
IF
NEED.SETUP.FILE.MESSAGE
EXIT
THEN
INTEGER DIM [ MAX.#. SCANS ] ARRAY. BE COMES > RUN. TIME .ARRAY
DIM [ MAX.#. SCANS ] ARRAY. BECOMES > RUN. TEMP .ARRAY
DIM[ 2 , #MASSES ] ARRAY.BECOMES> MASS.POINTS
1 SCAN# :=
98
1 FIRST.MASS :=
M/S.CONTROL.OUT
M/S.SIGNAL.IN
A/D.IN>ARRAY{DMA)
CHANNEL.TIME 1 + SYNC.PERIOD
D/A.INIT
SCANNING.MESSAGE
START.RUN.CLOCK
BEGIN \ this loop executes until temp gets to end point
RUN.TIME RUN.TIME.ARRAY [ SCAN# ] :=
RUN.TEMP RUN.TEMP.ARRAY [ SCAN# ] :=
RAMP.TEMP
M/S.CONTROL.OUT
M/S.SIGNAL.IN
#MASSES 1 + 1 \ loops through masses as set by user in
DO \ tpd.parameters.array
SET.SENS.LOW
5 MSEC.DELAY
D/A.LOOKUP.ARRAY [ TPD.PARAMETERS.ARRAY [ 1 , 1 ] ] 2
DUP
FIRST.D/A :=
D/A.OUT
5 MSEC.DELAY
RUN.TEMP ICE.PEAK.TEMP <
IF TPD.PARAMETERS.ARRAY [ 1 , 2 ] SET.SENS.PEAK
99
ELSE TPD. PARAMETERS.ARRAY [ 1 , 3 ] SET.SENS.PEAK
THEN
5 MSEC.DELAY
\ below is loop for acquiring data finding peak max
5 TOTAL.CHANNELS :=
SETUP.FOR.SCANNING
D/A.INIT
6 1 \ five times through the loop
DO
I FIRST.D/A + 1 - DUP
D/A.OUT
SYNCHRONIZE
SCAN.IN [ 2 , 1 ] :=
CHANNEL.IN MEAN
SCAN.IN [ 1 , 1 ] :=
LOOP
FIND.MAX
LOOP
SET.SENS.LOW
PLOT.TPD.DATA
APPEND.SCAN
SCAN# MAX.#.SCANS <
IF SCAN# 1 + SCAN# ;=
ELSE ?KEY.ON
THEN
100
MAX.TEMP RUN.TEMP >= ?KEY OR \ end of loop and experiment
UNTIL
PCKEY 7DROP DROP
SAVE.TPD. RUN
\ ***** Menu Definitions *****
^ -k -k -k-k-k -k -k -k -k -k-k-k-k k -k
\ -k-k-k-k-k TOP.MENU *****
TOP.MENU
" Main Menu" MENU.TITLE
MENU.NO.STORE
1 1 4 79 MENU.SHAPE
1 2 MENU.COLOR
15 MENU.PROMPT.COLOR
1 15 " Scan and Calibrate" MENU.ITEM{ SCAN.MENU )
1 45 " Data Acquisition" MENU.ITEM{ ACQUISITION.MENU
MENU.END
\ ***** SCAN.MENU *****
SCAN.MENU
" Scan and Calibrate"
MENU.STORE.MEMORY
MENU.TITLE
101
1 1 4 79 MENU.SHAPE
1 2 MENU.COLOR
15 MENU.PROMPT.COLOR
0 30 " Begin Scanning" MENU.ITEM{ SCAN }
1 2 " First Mass : " MENU.ITEM{ FIRST.MASS }
1 28 " Last Mass : " MENU.ITEM{ LAST.MASS }
1 50 " Channel Time (ms) : " MENU.ITEM{ CHANNEL.TIME }
2 28 " Calibrate " MENU.ITEM{ GET.SCAN.VALUES }
3 28 " Save New Calibration" MENU.ITEM{ CALIBRATION }
MENU.END
\ ***** ACQUISITION.MENU *****
ACQUISITION.MENU
" Data Acquisition" MENU.TITLE
MENU.STORE.MEMORY
1 1 4 79 MENU.SHAPE
1 2 MENU.COLOR
15 MENU.PROMPT.COLOR
0 1 " Set Sample Temp" MENU.ITEM{ CONSTANT.TEMP }
0 30 " Begin TPD" MENU.ITEMf DO.TPD }
1 1 " Setup Acquisition" MENU.ITEMf SETUP.TPD }
2 1 " Retrieve A Previous Setup" MENU.ITEM{
RETRIEVE.SETUP.TPD }
3 1 " Save The Current Setup" MENU.ITEM{ SAVE.SETUP.TPD }
MENU.END
102
\ ***** SAVE.FILE.MENU *****
SAVE.FILE.MENU
" Save setup file" MENU.TITLE
MENU.NO.STORE
MENU.NO.PROTECT
2 10 5 73 MENU.SHAPE
0 15 MENU.COLOR
1 1 " File name to save to" MENU.ITEM{ SETUP.FILENAME )
2 1 " Comments: " MENU.ITEM{ FILE.COMMENTS1 }
MENU.END
\ ***** RETRIEVE.MENU *****
RETRIEVE.MENU
" Retrieve File - Arrows to Scroll, Enter to choose" MENU.TITLE
MENU.BLOW.UP
MENU.STORE.DISK
3 3 25 55 MENU.SHAPE
4 15 MENU.COLOR
9 MENU.PROMPT.COLOR
1 50 MENU.DISPLAY DIR \ Max taggable Items = 1
MENU.END
Initialize and start the program *****
103
INIT.VALUES
12 FIRST.MASS :=
19 LAST.MASS :=
200 ICE.PEAK.TEMP :=
17 CHANNEL.TIME :=
667 SAMPLES.PER.CHANNEL :=
-2048 MAX.SIGNAL :=
13.826 FIRST :=
-2063.56 SECOND :=
0 HIGHMASS.COUNT :=
0 LOWMASS.COUNT :=
" D/A Channel #" HORIZONTAL.LABEL
" DEFAULT.SET" SETUP.FILENAME ":=
Load.Overlay Datafile.Sov
file.open calib.dat
D/A.LOOKUP.ARRAY FILE>ARRAY
FILE.CLOSE
SYNC.ERROR.OFF
INIT.DISPLAY
GRAPHICS.DISPLAY
{STACK}
15 FOREGROUND
104
SCAN. VUPORT
3 ARRAY. READOUT. TYPE
SCREEN.CLEAR
VUPORT.CLEAR
NEWCAL
STACK. CLEAR
MENU.STACK.CLEAR
INIT.VALUES
INIT.DISPLAY
VUPORT.CLEAR
TOP.MENU MENU.EXECUTE
BIBLIOGRAPHY
Amick, J. A.; Kern, W. In Chemical Vapor Deposition', Blocker, J. M., Sr.; Withers, J. C., Eds.; Electrochemical Society: New York, 1971; p. 551.
Berkeley, J. F.; Brenner, A.; Reid, W. E., Jr. J. Electrochem. Soc. 1967,114, 561.
Blewer, R. S.; Headley, T. J.; Tracy, M. E. In Tungsten and Other Refractory Metals for VLSI Applications III; Wells, V. A., Ed.; Materials Research Society: Pittsburgh, 1988; pp.115-122.
Bradbury, D. R.; Kaminis, T. I. J. Electrochem. Soc. 1986,133(6, Jun), 1214-1217.
O'Hanlon, J. F. A User's Guide to Vacuum Technology, 2nd ed.; John Wiley & Sons: New York, 1989a; p. 25.
Briggs, D.; Seah, M. P., Eds. Practical Surface Analysis by Auger and X-ray Photoelectron Spectroscopy; John Wiley & Sons: Chichester, 1983b; pp. 94-95.
Broadbent, E. K.; Ramiller, C. L. J. Electrochem. Soc. 1984,131(6, Jun), 1427-1433.
Broadbent, E. K.; Stacy, W. T. Solid State Technol. 1985, 25(12, Dec), 51.
Broadbent, E. K.; Flanner, J. M.; ven den Hoek, W. G. M.; Connick, I.-W. H. In Tungsten and Other Refractory Metals for VLSI Applications III, Wells, V. A., Ed.; Materials Research Society: Pittsburgh, 1988; pp. 191-199.
Broadbent, E. K.; Sadana, D. K.; Morgan, A. E.; Flanner, J. M.; Ellwanger, R. C. In Tungsten and Other Refractory Metals for VLSI Applications III, Wells, V. A., Ed.; Materials Research Society: Pittsburgh, 1988; pp. 111-113.
105
106
Brors, D. L.; Fair, J. A.; Monnig, K. A.; Saraswat, K. C. Solid State Technol. 1983, 26, 186.
Brors, D. L.; Monnig, K. A.; Fair, J. A.; Coney, W.; Saraswat, K. C. Solid State Technol. 1984(April), 313.
Bryant, W. A. J. Electrochem. Soc. 1978, 125, 1534.
Bryant, W. A.; Meier, G. H. J. Electrochem. Soc. 1973,120, 559.
Cheek, R. W.; Kelber, J. A.; Fleming, J. G.; Blewer, R. S.; Lujan, R. D. J. Electrochem. Soc. 1993,140(12, Dec), 3588-3590.
Chow, R. L.; Schmitz, J. E. J.; Arnold, P. W. In Tungsten and Other Advanced Metals for ULSIApplications in 1990\ Smith, G. C.; Blumenthal, R., Eds.; Materials Research Society: Pittsburgh, 1991; pp. 89-97.
Colgan, E. G.; Chapplesokol, J. D. J. Vac. Sci. Technol B 1992,10, 1156-1166.
Colgan, E. G.; Gambino, J. P.; Kastl, R. H. J. Electrochem. Soc. 1993,140(1), 159-166.
Cooke, M. J. Vacuum 1985, 35, 67.
Cooke, M. J.; Heinecke, R. A.; Stern, R. C.; Maes, J. W. C. Solid State Technol. 1982, 25, 62.
Creighton, J. R. In Tungsten and Other Refractory Metals for VLSI Applications III; Broadbent, E. K., Ed.; Materials Research Society: Pittsburgh, 1987, pp. 43-50.
Creighton, J. R. J. Vac. Sci. Technol. A 1987, 5(4, Jul/Aug), 1739-1740.
Creighton, J. R. J. Electrochem. Soc. 1989, 736(1), 271-276.
107
Creighton, J. R. J. Vac. Sci. Technol. A 1989, 7(3), 621-624.
Creighton, J. R.; Parmeter, J. E. Crit. Rev. Solid State Mater. Sci. 1993, 18, 175-238.
Creighton, J. R.; Rogers, J. W. J. In Tungsten and Other Refractory Metals for VLSI Applications III, Wells, V. A., Ed.; Materials Research Society: Pittsburgh, 1988; pp. 63-68.
Crowell, C.; Savace, J.; Sze, S. Trans. Metal. Soc. AIME1965, 233, 478.
Cuomo, J. J. In Proceedings of the 3rd International Conference on Chemical Vapor Deposition-, Glaski, F. A., Ed.; American Nuclear Society: Illinois, 1972; p. 270.
Davis, L. E.; MacDonald, N. C.; Palmberg, P. W.; Riach, G. E.; Weber, R. E. Handbook of Auger Electron Spectroscopy, 2nd ed.; Physical Electronics Industries, Inc.: Eden Prairie, MN, 1976.
Deshpandey, C. V.; Bunshah, R. F. In Thin Film Processes //; Vossen, J. L.; Kern, W., Eds.; Academic Press: San Diego, 1991; p. 79.
d'Heurle, F. M.; Ho, P. S. In Thin Films—Interdiffasion and Reactions', John Wiley: New York, 1978; p. 243.
Fleming, J. G.; Omstead, T. R.; Dominguez, F. In Advanced Metallization for ULSI Applications', Rana, F. F. S.; Joshi, R. V.; Ohdomari, I., Eds.; Materials Research Society: Pittsburgh, 1992; pp. 233-239.
Flinn, P. A.; Mack, A. S.; Besser, P. R.; Marieb, T. N. MRS Bulletin 1993,18( 12, Dec), 26-35.
Green, M. L. In Deposition and Growth: Limits for Microelectronics', Rubloff, G. W., Ed.; American Institute of Physics: New York, 1988; p. 173.
Green, M. L.; Levy, R. A. J. Metals 1985, 57(6), 63.
108
Green, M. L.; Levy, R. A. J. Electrochem. Soc. 1985, J32(5, May), 1243.
Green, M. L.; Levy, R. A.; Nuzzo, R. G.; Coleman, E. Thin Solid Films 1984,114, 367.
Groenen, P. A. C.; Holscher, J. G. A.; Brongersma, H. H. Appl. Surf. Sci. 1991, 53, 30-34.
Hieber, K.; Korner, H.; Treichel, H. Thin Solid Films 1989,181, 75.
Hillman, J. T.; Triggs, W. M.; Aruga, M. J. Electrochem. Soc. 1992, 139(12), 3574-3578.
Hirase, I.; Sumiya, T.; Schack, M.; Ukishima, S.; Rufin, D.; Shishikura, M.; Matsuura, M.; Ito, A. In Tungsten and Other Refractory Metals for VLSI Applications III, Wells, V. A., Ed.; Materials Research Society: Pittsburgh, 1988; pp. 133-140.
Ho, P. S.; Moske, M. A.; Hu, C. K. In Advanced Metallization for ULSI Applications 1992\ Cale, T. S.; Pintchovski, F. S., Eds.; Materials Research Society: Pitssburgh, 1993; pp. 3-15.
Holleman, J.; Hasper, A.; Kleijn, C. R. J. Electrochem. Soc. 1993,140(3), 818-825.
Izumi, A.; Touei, K.; Yamano, A.; Chong, Y.; Watanabe, N. In Proceedings of the Eleventh International Conference on Chemical Vapor Deposition', Spear, K. E.; Cullen, G. W., Eds.; The Electrochemical Society, Inc: Pennington, NJ, 1990; pp. 425-433.
Jackman, R. B.; Foord, J. S. Surf. Sci. 1988, 201, 47-58.
Jain, A.; Chi, K.-M.; Farkas, J.; Kodas, T. T.; Hampden-Smith, M. J. Semicond. Int. in press.
Jensen, K. F.; Kern, W. In Thin Film Processes IT, Vossen, J. L.; Kern, W., Eds.; Academic Press: San Diego, 1991; p. 283.
109
van der Jeugd, C. A.; Verbruggen, A. H.; Leusink, G. J.; Janssen, G. C. A. M.; Radelaar, S. In Tungsten and Other Advanced Metals for VLSI/ULSI Applications V; Wong, S. S.; Furukawa, S., Eds.; Materials Research Society: Pittsburgh, 1990; pp. 267-272.
van der Jeugd, C. A.; Leusink, G. J.; Oosterlaken, T. G. M.; Alkemade, P. F. A.; Nanver, L. K.; Goudena, E. J. G.; Janssen, G. C. A. M.; Radelaar, S. J. Electrochem. Soc. 1992, J39(12), 3615-3623.
Johannessen, J. S.; Spicer, W. E.; Strausser, Y. E. J. Appl. Phys. 1976, 47, 3028-3037.
Jost, W. Diffusion in Solids, Liquids and Gases; Academic: New York, 1960; pp. 492-501.
Kaplan, L. H.; d'Heurle, F. M. J. Electrochem. Soc. 1970,117, 693.
Kepten, A.; Reisman, A.; Ray, M.; Smith, P. L.; Temple, D.; Tapp, F. J. Electrochem. Soc. 1992, 739(8), 2331-2337.
Kern, W.; Ban, V. S. In Thin Film Processes; Vossen, J. L.; Kern, W., Eds.; Academic Press: New York, 1978; p. 257.
King, D. A. Surf Sci. 1975, 47, 384-402.
Kobayashi, N.; Goto, H. J. Appl. Phys. 1991,69, 1013-1019.
Kobayashi, N.; Goto, H.; Suzuki, M. Extended Abstracts of the 22nd Conference on Solid State Devices and Materials, Sendai 1990, 865-868.
Kobayashi, N.; Goto, H.; Suzuki, M. In Tungsten and Other Advanced Metals for ULSI Applications in 1990; Smith, G. C.; Blumenthal, R., Eds.; Materials Research Society: Pittsburgh, 1991.
110
Kusumoto, Y.; Takakuwa, K.; Hashinokuchi, H.; Ikuta, T.; Nakayana, I. In Tungsten and Other Refractory Metals for VLSI Applications III; Wells, V. A., Ed.; Materials Research Society: Pittsburgh, 1988; pp. 103-109.
Kwakman, L. F. T.; Vermeulen, W. J. C.; Granneman, E. H. A.; Hitchman, M. L. In Tungsten and Other Refractory Metals for VLSI Applications III; Wells, V. A., Ed.; Materials Research Society: Pittsburgh, 1988; pp. 141-147.
Kwakman, L. F. T.; Sluijk, B. G.; Piekaar, H.; Granneman, E. H. A. In Tungsten and Other Refractory Metals for VLSI Applications IV; Blewer, R. S.; McConica, C. M., Eds.; Materials Research Society: Pittsburgh, 1989; pp. 315-321.
Lee, P.-L.; Cronin, J.; Kaanta, C. J. Electrochem. Soc. 1989,136, 2108.
Levy, R. A.; Green, M. L. J. Electrochem. Soc. 1987, 134, 37C.
Levy, R. A.; Green, M. L.; Gallagher, P. K. J. Electrochem. Soc. 1984, 131, 2175.
Lide, D. R., Ed. CRC Handbook of Chemistry and Physics, 74th ed.; The Chemical Rubber Company: Dayton, 1993.
Madey, T. E.; Yates, J. T. J. Surf Sci. 1977, 63, 203-231.
Mayer, J. W.; Lau, S. S. Electronic Materials Science: For Integrated Circuits in Si and GaAs; Macmillan Publishing Company: New York, 1990.
McConica, C. M. In Tungsten and Other Refractory Metals for VLSI Applications; Broadbent, E. K., Ed.; Materials Research Society: Pittsburgh, 1987; pp. 51-57.
McConica, C. M.; Cooper, K. J. Electrochem. Soc. 1988, 135(4, April), 1003-1008.
McGuire, G. Surf Sci. 1978, 76, 130.
I l l
Mclnerney, E. J.; Mountsier, T. W.; Chin, B. L.; Broadbent, E. K. In Advanced Metallization for ULSI Applications; Rana, V. V. S.; Joshi, R. V.; Ohdomari, I., Eds.; Materials Research Society: Pittsburgh, 1992; p. 69.
Melliar-Smith, C. M.; Adams, A. C.; Kaiser, R. H.; Kushner, R. A. J. Electrochem. Soc. 1974,121, 298.
Miller, A.; Barnett, G. D. J. Electrochem. Soc. 1962, 109, 973.
Miller, J. B.; Siddiqui, H. R.; Gates, S. M.; Russell, J. N.; Yates, J. T. J.; Tully, J. C.; Cardillo, M. J. J. Chem. Phys. 1987, 87, 6725.
Miller, N. E.; Beinglass, I. Solid State Technol. 1980, 23, 79.
Miller, N. E.; Beinglass, I. Solid State Technol. 1982, 25, 85.
Moriya, T.; Itoh, H. In Tungsten and Other Refractory Metals for VLSI Applications-, Blewer, R. S., Ed.; Materials Research Society: Pittsburgh, 1986; p. 21.
Murarka, S. P. In VLSI technology, 2nd ed.; Sze, sm, Ed.; McGraw-Hill: New York, 1988; p. chap. 9.
Murarka, S. P. In Tungsten and Other Advanced Metals for ULSI Applications in 1990; Smith, G. C.; Blumenthal, R. O. C., Eds.; Materials Research Society: Pittsburgh, 1991; p. 179.
Nakamura, Y.; Kobayashi, N.; Goto, H.; Homma, Y. Extended Abstracts of the 1991 International Conference on Solid State Devices and Materials 1991, 216-218.
O'Hanlon, J. F. A User's Guide to Vacuum Technology, 2nd ed.; John Wiley & Sons: New York, 1989
Ohba, T.; Furumura, Y. J. Instn. Electronics & Telecom. Engrs. 1991, 37(2), 212-219.
112
Ohba, T.; Suzuki, T.; Hara, T.; Furumura, Y.; Wada, K. In Tungsten and Other Refractory Metals for VLSI Applications IV; Blewer, R. S.; McConica, C. M., Eds.; Materials Research Society: Pittsburgh, 1989; pp. 17-25.
Park, H. L.; Yoon, S. S.; Park, C. O.; Chun, J. S. Thin Solid Films 1989,181, 85-93.
Parsons, R. In Thin Film Processes IT, Vossen, J. L.; Kern, W., Eds.; Academic Press: San Diego, 1991; p. 177.
Raupp, G. B.; Hindman, G. T. In Tungsten and Other Refractory Metals for VLSI Applications IV, Blewer, R. S.; McConica, C. M., Eds.; Materials Research Society: Pittsburgh, 1989; pp. 231-237.
Redhead, P. A. Vacuum 1962,12, 203-211.
Reisman, A.; Shin, D. R.; Jones, G. W. J. Electrochem. Soc. 1990,137, 722.
Rossi, R. C. In Handbook of Thin-Film Deposition Processes and Techniques', Schuegraf, K. K., Ed.; Noyes Publications: Park Ridge, 1988; p. Chap. 3.
Runyan, W. R.; Bean, K. E. Semiconductor Integrated Circuit Processing Technology, Addison-Wesley: Reading, MA, 1990.
Saraswat, K. C.; Wulu, H. C.; Rey, J. C.; Cheng, L. Y.; IslamRaja, M. M.; McVittie, J. P. In Tungsten and Other Advanced Metals for ULSI Applications in 1990; Smith, G. C.; Blumenthal, R., Eds.; Materials Research Society: Pittsburgh, 1991; pp. 239-247.
Sault, A. G.; Goodman, D. W. Surf Sci. 1990, 28-46.
Schmitz, J. E. J.; Ellwanger, R. C.; van Dijk, A. J. M. In Tungsten and Other Refractory Metals for VLSI Applications III; Wells, V. A., Ed.; Materials Research Society: Pittsburgh, 1988; pp. 55-61.
113
Schmitz, J. E. J.; Buiting, M. J.; Ellwanger, R. C. In Tungsten and Other Refractory Metals for VLSI Applications IV; Blewer, R. S.; McConica, C. M., Eds.; Materials Research Society: Pittsburgh, 1989; pp. 27-33.
Schmitz, J. E. J.; Van Dijk, A. J. M.; Suijker, J. L. G.; Buiting, M. J.; Ellwanger, R. C. Appl Surf Sci. 1989b, 38, 350.
Schulte, J.; Brodsky, S. B.; Lin, T.; Joshi, R. V. In Tungsten and Other Refractory Metals for VLSI Applications III, Wells, V. A, Ed.; Materials Research Society: Pittsburgh, 1988; pp. 367-373.
Sellers, J. A.; Kottke, M.; Wilson, S. R.; Mattox, R. J. In Tungsten and Other Advanced Metals for VLSI/ULSI Applications V; Wong, S. S.; Furukawa, S., Eds.; Materials Research Society: Pittsburgh, 1990; pp. 227-232.
Shaw, J. M.; Amick, J. A. RCA Rev. 1970, SI, 306.
Sherman, A. Chemical Vapor Deposition for Microelectronics: Principles, Technology, and Applications; Noyes Publications: Park Ridge, NJ, 1987; pp. 92-118.
Shingubara, S.; Nakasaki, Y.; Keneko, H. Appl. Phys. Lett. 1991, 58, 42.
Sivaram, S.; Dass, L.; Davies, P.; Frost, T.; Murray, J.; Tracy, B. In Tungsten and Other Advanced Metals for VLSI/ULSI Applications V; Wong, S. S.; Furukawa, S., Eds.; Materials Research Society: Pittsburgh, 1990; pp. 301-309.
Somorjai, G. A. Introduction to Surface Chemistry and Catalysis; John Wiley & Sons, Inc.: New York, 1994a.
Sotola, J.; Savkin, V.; Knor, Z. Collection of Czechoslovak Chemical Communications 1992, 57, 2481-2493.
Stacy, W. T.; Broadbent, E. K.; Norcott, M. H. J. Electrochem. Soc. 1985, 132, 444.
114
Suzuki, M.; Kobayashi, N.; Mukai, K. In Tungsten and Other Advanced Metals for VLSI/ULSIApplications V; Wong, S. S.; Furukawa, S., Eds.; Materials Research Society: Pittsburgh, 1990; pp. 259-265.
Suzuki, M.; Kobayashi, N.; Mukai, K.; Kondo, S. J. Electrochem. Soc. 1990, 737(10, October), 3213-3218.
Thomas, J. H„ III; Hofmann, S. J. Vac. Sci. Technol. A 1985, 3(5, Sep\Oct), 1921-1928.
Thompson, C. V.; Lloyd, J. R. MRS Bulletin 1993, J8( 12, Dec), 19-25.
Wintterlin, J.; Avouris, P. Surf. Sci. Lett. 1993, 286, 529-534.
Yarmoff, J. A.; McFeely, F. R. J. Appl. Phys. 1988, 63, 5213.
Yates, J. T. J. In Solid State Physics: Surfaces', Park, R. L.; Lagally, M. G., Eds.; Academic Press, Inc: Orlando, 1985; Vol. 22, pp. 425-464.
Yu, M. L.; Eldridge, B. N. J. Vac. Sci. Technol. A 1989, 7(3, May/June), 625-629.
Yu, M. L.; Eldridge, B. N.; Joshi, R. V. In Tungsten and Other Refractory Metals for VLSI Applications III, Wells, V. A., Ed.; Materials Research Society: Pittsburgh, 1988; pp. 75-81.
Yu, M. L.; Eldridge, B. N.; Joshi, R. V. In Tungsten and Other Refractory Metals for VLSI Applications IV; Blewer, R. S.; McConica, C. M., Eds.; Materials Research Society: Pittsburgh, 1989; pp. 221-230.
Yu, M. L.; Ahn, K. Y.; Joshi, R. V. IBM J. Res. Develop. 1990, 34(6), 875-883.