SILICON AND BORON CARBONITRIDE FIMLS OBTAINED BY CVD METHODS

N.I.Fainera), M.L.Kosinovaa), V.S. Sulyaevaa), Yu.M.Rumyantseva), E.A.Maximovskiia), B.M.Ayupova), B.A.Kolesova), F.A.Kuznetsova),

V.G.Kesler b), M.Terauchi c), K.Shibatac), F.Satoh c), Z.X.Caod)

a)Nikolaev Institute of Inorganic Chemistry SB RAS, Novosibirsk, Russia, 630090, b)Institute of Semiconductor Physics SB RAS, Novosibirsk,

Russia, 630090, c)IMRAM, Tohoku University, Sendai, Japand)Institute of Physics CAS, P.O. Box 603, Beijing 100080, P.R. China

Nanocrystalline hard silicon carbonitride films were synthesized by RPECVD using the gas mixture of hexamethyldisilazane with ammonia and helium within temperature range of 723-1073 K. IR and Raman spectroscopy, AES, XPS, ellipsometry, XRD using the synchrotron radiation, SEM, HREM, SAED, AFM, measurements of hardness by nanoindenter and spectrophotometry measurements were applied to study their physicochemical properties. The SiCxNy films exhibit high optical transmittance in the spectra range of 1200-2200 nm. Microhardness of these films increases from 18 to 28 GPa, while Young's modulus changes from 135.5 to 185.5 GPa with Si-C bonds content. Boron carbonitride films were deposited on silicon wafers by low pressure chemical vapor deposition from gaseous mixture of trimethylamino borane (TMAB) or triethylamino borane (TEAB) complexes and ammonia, nitrogen or helium. BCxNy films with different composition were obtained by varying composition of initial gas mixture and deposition temperature. BCxNy films with microhardness up to 40 GPa was synthesized.

P art I. N anocrystalline films of silicon carbonitride: chemical composition and bonding and functional properties

IntroductionSi–C–N nanocomposite materials are of great scientific and

technological interest because of wide spectra of their remarkable properties from high hardness, superplasticity to a high strength and

47

toughness depending on the composition as well as their excellent high temperature properties, enhanced oxidation and corrosion resistance. The enhancement of these properties has been attributed to complex-covalent chemical bonding and a low oxygen diffusion coefficient in the structure of the silicon carbonitride. The nanocrystalline SiCxNy

materials are chemically and thermally stable, and they possess wide bandgap and high hardness of 27-42 GPa. Currently, silicon carbonitride films have been produced with ion sputtering deposition of carbon and silicon in nitrogen atmosphere, N+ implantation into SiC surface, laser vapor phase reaction of hexamethyldisilazane (HMDS) with ammonia, chemical vapor deposition (CVD) and plasma enhanced CVD using Si(CH3)4-NH3-H2, SiH4-NH3(N2)-CH4 (or N2H4)-H2(Ar), SiCl4+NH3+C3H8+H2, as initial atmospheres (1-4). The use of siliconorganic compounds has attracted interest due to these compounds containing the silicon, nitrogen and carbon, can serve as precursors for Si3N4, SiC or Si–C–N ceramics, powders and films. The nature of the organic groups bound to silicium influences the physical and chemical properties of polysilazanes as well as the Si–C–N compounds after conversion. The molecules of HMDS contain the -C-Si-N-Si-C- bridges ready for preparation of the final nanocomposite material. The SiCxNy

obtained via the plasma enhanced chemical vapour deposition of organometallic compounds exhibit improved thermo-mechanical properties in comparison with conventionally processed.

The goal of our research is the study of physical and chemical, functional properties of nanocrystalline SiCxNy films and determination of correlation between functional properties and chemical composition and bonding.

ЕxperimentalNanocrystalline SiCxNy films were synthesized in wide interval of

chemical composition: from composition close to SiC up to one close to Si3N4. The synthesis was carried out by remote plasma enhanced decomposition of hexamethyldisilazane (HMDS) as single-source precursor using two gas mixtures: (HMDS+He) and (HMDS+ NH3+He) in temperature range of 723-1073 K and total pressure in reactor of (4-6) 10-2 Torr (5). Initial PNH3/PHMDS ratios were equal to 0.3, 0.73, 1.0, 1.7, and 2.1. The effect of the growth temperature, chemical composition of the initial

48

gas phase, r.f. plasma power, total pressure in the reactor on the formation of certain microstructure, chemical and phase composition of the growing films were studied. The influence of chemical composition on physical and chemical properties of the obtaining silicon carbonitride films was investigated using a complex of modern methods: IR and Raman spectroscopy, high-resolution electron micrography (HREM), selected area electron diffraction (SAED), scanning electron microscopy (SEM), atomic force microscopy (AFM), X-ray photoelectron spectroscopy (XPS), Auger electron spectroscopy (AES), optical measurements, and XRD - SR. The hardness of films was measured by the Vickers indentation method. The indentation tests were carried out using a CSZM Nano Hardness tester under a load of 5 and 10 mN.

Results and discussionThe thickness of synthesized silicon carbonitride films were

2003000 nm. Chemical composition of these films was examined using spectroscopic methods: IR and Raman spectroscopy, AES and XPS.

IR-Spectroscopy. According to the data of IR spectroscopy, a wide band of 450-1200 cm -1 is observed in the spectra of films synthesized within the whole of investigated temperature range. Hydrogen-related bonds were not detected. Mathematical analysis of the IR spectra of SiCxNy films was carried out. For this purpose, the main IR spectrum was approximated by a sum of three Gaussian curves and their integral intensities were calculated. This analysis showed that the main IR adsorption band mostly corresponds to the superposition of asymmetric stretching vibration of Si-N-Si bonds at 450 cm-1, symmetric stretching vibration of Si-N bonds at 950 cm-1, and stretching vibration of Si-C bonds at 800 cm-1. Apparently, the above-mentioned positions of vibration modes slightly differ in ternary films. The incorporation of C into Si-N network damages the symmetric vibration modes of Si-N bonds of binary compound, thus shifting their absorption bands. Realized analysis of IR spectra revealed that the integral intensity ratios as I(Si-C)/I(Si-N) depend on the growth temperature and the PNH3/PHMDS ratios. The rise of the temperature up to 1073 K leads to the monotonic increasing of these rations in IR-spectra of films grown in (HMDS+He) gas mixture. Opposite the rise of ammonia concentration

49

in (HMDS+NH3+He) system and the growth temperature leads to increase of concentration of Si-N bonds in films.

Raman Spectroscopy. Raman spectroscopy is a sensitive tool that provides valuable structural information on the translation symmetry of materials, and so is useful for the study of disorder and crystalline formation. The Raman spectra of the SiCxNy films were analyzed in a similar manner as that used for carbon films. The G mode is due to the stretching vibration of any pair of sp2 atoms in both chains and rings, whereas the D mode is related to the breathing vibration of sp2 sites only in rings. Thus, an increase in I(D)/I(G) is ascribed to an increase in the number and/or in the size of sp2 clusters. Fig. 1a illustrates the typical Raman spectrum of SiCxNy film. The band of 1200-1600 cm-1 was deconvoluted, using Gaussian line shapes, into D and G bands. The dependence of the integral intensity ratios of the D and the G bands on the growth temperature and the PNH3/PHMDS ratios are given in Fig.1b and Fig.1c, respectively. As appears from these data, the rise of temperature leads to the decrease of the intensity of the D band, but the increase of ammonia concentration promotes to an increase of the D band intensity. These regularities seemingly connect with increase of nanocrystal size with the growth temperature rise and decrease of nanocrystal size due to the increase concentration of nitrogen in films.

Fig. 1. Typical Raman spectra of SiCxNy film–(a); the I(D)/I(G) ratio as function of the growth temperatures at PNH3/PHMDS=1.6 – (b) and ammonia concentration in gas mixture– (c).

AES and XPS study. Characterization of the atomic bonding was performed using XPS and AES. Before the measurements the SiCxNy

50

800 1000 1200 1400 1600 1800

Si(100)G

D

Raman shift (cm-1)

Inte

nsity

2LO

a

)c

))

b

700 800 900 1000 1100 1200 13000,0

0,5

1,0

1,5

2,0

2,5

3,0

3,5

4,0

4,5

5,0

Tsynthesis, K

I(D

)/I(G

)

- HMDS+NH3+He

- HMDS+He

0,0 0,5 1,0 1,5 2,0 2,53,2

3,4

3,6

3,8

4,0

4,2

PNH3/PHMDS

Tsynthesis= 873 K(HMDS+NH3+He)

I(D

)/I(G

)

films were etching in weak dilution of HF acid to eliminate any surface impurities adsorbed during air handling and no destruct any chemical bonds in the films. AES study showed that the synthesized films are characterized by good homogeneity of chemical composition over thickness, as it follows from Fig. 2a. Because of the inherent uncertainties in the energy referencing due to sample charging it was impossible to determine the exact XPS and AES peak positions. Instead, in order to circumvent this limitation for the Si component the Auger parameter ( which is determined by measuring the energy difference between the Si 2p (XPS) and Si KLL (bremsstrahlung-excited AES) peaks was obtained. As the Auger parameter is an energy difference value, it is charge independent and uniquely defines the bonding configuration of the elements under analysis. The Auger parameters for Si, SiO2, Si3N4, SiC are equal to 1716.1, 1712.2, 1714.45, 1716.05 eV, respectively (6). It was found that linear dependence of the Si Auger parameter values on the growth temperature is closely related monotonic change of character of surrounding of Si atoms in SiCxNy films (Fig. 2b). The Si Auger parameter of SiCxNy films grown from (HMDS+He) mixture in the temperature region of 523 – 973 K change from 1714.2 up to 1715.0 eV which lie midway between that of Si3N4 (1714.45 eV) and SiC (1716.05 eV). The temperature rise leads to such Si electron configuration which has a bonding scheme involving both mainly C and negligibly N.

Fig. 2. Typical AES depth profile of distribution of chemical elements in the SiCxNy film grown from (HMDS+He) – (a). Dependence of the Si Auger parameter on the growth conditions – (b).

51

0 50 100 150 200 250 300

0,0

0,1

0,2

0,3

0,4

0,5

0,6

0,7

0,8

0,9

1,0

C

Si

NO

Con

cent

ratio

n

Sputtering time (min)

a b

400 500 600 700 800 900 1000 1100 1200

1713,6

1713,8

1714,0

1714,2

1714,4

1714,6

1714,8

1715,0

1715,2

PNH3

/ PHMDS

=1.6

Tsynthesis, K

(HMDS+NH3+He)

(HMDS+He)

The

Aug

er p

aram

eter

, eV

At addition of ammonia to initial gas mixture the Si Auger parameter of SiCxNy films grown in the temperature region of 673 – 973 K changes from 1713.7 up to 1714.3 eV. Last fact was explained that Si - N bonds predominate in network with the temperature increase. XPS analysis gives direct information about the composition and the bonding type of atoms in solid phases. Chemical shift in bonding energy of photoelectron peak occurs when there is a change in valence state of the bonding atoms. Fig. 3 shows the evolution of N 1s, Si2p and C 1s XPS spectra of SiCxNy films as a function of growth temperature in the region of 673-973 K and chemical composition of initial gaseous mixtures.

Fig. 3. N 1s, Si2p and C 1s XPS spectra of SiCxNy films as a function of growth temperatures and chemical composition of initial gaseous mixtures.

In case of films grown using (HMDS+He) mixture the N 1s spectra could be deconvoluted into main peak with binding energy of ~ 397.5 eV, corresponding to N-Si bonding, and negligible peak with binding energy of ~ 398.8 eV, corresponding to N-C(sp2) bonding. The Si 2p spectra could be deconvoluted into 3 subpeaks with binding energies of

52

N-C

(sp2 ) Si-NN 1s

Si-CN

-Si

Si 2p

C(s

p2 )-NC

-CC

-Si

C 1s

402 400 398 396 394 104 102 100 98 288 286 284 282 280

Inte

nsity

, arb

.uni

ts

Binding energy, eV

873 K

773 K

673 K

873 K

773 K

673 K

673 K

773 K

873 K

973 K

673 K

773 K

873 K

973 K

673 K

773 K

873 K

673 K

773 K873 K

973 K

(HMDS+He)

(HMDS+NH3+He)

PNH3/PHMDS=1.6

~ 102.8, 101.7 and 101.0 eV. The first component has less intensity and corresponds to Si-O bonding (oxygen is impurity in SiCxNy films). The component with binding energy of ~ 101.7 eV closes to peak of stoichiometric silicon nitride. The third component with binding energy of ~ 101.0 eV is intermediate position between Si-N and Si-C bonding. Thus, in these films SiC compound was not disclosed but component with binding energy of ~ 101.0 eV indicates to the existence of polysubstituted tetrahedrons (CnSiN4-n) due to partial replacement of N atoms in Si-N bonding by C atoms. The C 1s XPS spectra could be deconvoluted mainly into 3 subpeaks with binding energies of ~ 283.2, 284.6, 286 eV, corresponding to C-Si, C-C and C(sp2)-N bonding, respectively. With rise of the growth temperature, the total C concentration in films increases up to 60 % exceeding initial concentration in HMDS molecules (44.7%), and the total N and Si concentrations monotonically decrease and become low then their concentrations in HMDS. Addition of ammonia to initial gas mixture promotes the formation of SiCxNy films of high concentration of nitrogen from 30% up to 50% (more higher then in HMDS) with the temperature rise. Contrarily, C concentration decreases from 28% up to 5% and becomes in these films more less then in HMDS at analogous change of the growth conditions. The components of Si2p and C1s spectra with binding energies of ~ 101.0 and 283.2 eV, respectively, monotonically decrease with the temperature rise. This fact is evidence of the primary tendency to the formation of SiCxNy films close to stoichiometric silicon nitride at high temperatures.

Microstructural features. Investigation of the micromorphology of surface by SEM and AFM showed that the films synthesized from gas mixtures (HMDS+He) and (HMDS+NH3+He) exhibit uniform distribution of tightly packed nanocrystals. Their size increases from 10 up to 20 nm with temperature rise. Besides, more large scale conglomerate formations (50-100 nm) consist of tens of fine nanocrystals were observed. Fig. 4 gives AFM images of SiCxNy films, which show a very smooth surface with a root mean square roughness of 0.5-0.7 nm. The temperature rise leads to increase of average size of grains a in the films prepared from (HMDS+He) gas mixture: at temperatures of 773 and 973 K grain sizes are 20 and 80 nm, respectively (Fig. 4a-b). Addition of ammonia to (HMDS+He) promotes decrease size of grains until 40 nm in film synthesized at same

53

temperature of 973 K (Fig. 4, c). Transmission Electron Microscopy was employed to investigate the microstructure of the SiCxNy films. In the vicinity of the interface between the substrate and film the HREM images and SAED pattern of these films were shown in Fig. 5a. It was clearly seen that SiCxNy films are composed of nanocrystals embedded in the amorphous phase. The SAED pattern consists of a halo and weak diffraction rings indicating the presence of the amorphous and crystalline constituents in this film. Their size depends on the growth temperatures and initial gas composition: more large scale grains (~ 2 nm at 773 K) form in case of using (HMDS+He) gas mixture (Fig. 5a); addition of ammonia leads to decreasing of particles size (less 1.5 nm) at the same growth conditions (Fig. 5c). The temperature rise until 823 K promotes increase of their size to ~ 5 nm. Fig. 5b shows the augmented HREM image of several nanocrystals indicated in Fig. 5a. The d spacings appearing in the HREM image of nanoparticles were measured to be 0.24 nm and 0.21 nm. These values are consistent with the d-values calculated for the 1st and 2nd rings in the SAED pattern. The d-spacing of the 3rd ring in SAED pattern is not observed in this HREM image.

Fig. 4. AFM images of SiCxNy films obtained using (HMDS+He) system at 773 K – (a) and 973 K (b) temperatures and using (HMDS+ NH3+He) gas mixture at 973 K – (c).

It may be that the d-value of 0.15 nm is critical to resolve by the performance of the TEM used. Obtained SAED d spacings are close to -Si3N4 (7).

54

ba)

c

a = 40 nmRrms= 0.6 nm

10 nm nmнм

c)

4 nm

a)

0,21 nm

0,24 nm

b)

a = 20 nmRrms= 0.5 nm

a = 80 nmRrms= 0.7 nm

Fig.5. Cross-sectional HREM images of SiCxNy films grown at 773 K using (HMDS+He)-(a, b) and (HMDS+ NH3+He)-(c) gas mixtures.

The structure and phase composition of SiCxNy films were investigated at the station «Anomalous scattering» of the Siberian Center of Synchrotron Radiation (INP SB RAS) by XRD-SR technique specially developed by us for thin films containing of lightweighed elements (8). Shown in Fig.6 the diffraction patterns of SiCxNy samples are typical ones for all silicon carbonitrides films grown in all interval of growth conditions. The comparison of the interplanar distances suggests that the lattice parameters of hexagonal unit cells of SiCxNy and -Si3N4

(7) are close within the experimental errors (8). Inasmuch as, both IR-spectroscopy and XPS analysis indicates on presence of complex bonding between Si, N and C elements in the films we can imply that carbon atoms substitute only for the silicon sites without changes in valency in the -Si3N4 structure so that C and Si are always “bridged” by nitrogen in the SiCxNy films. On the broadening of diffraction peak, we estimated the size of nanocrystals. Their size varied from 5 to 50 nm, depending on the growth conditions. There is good coincidence in microstructural data obtained by SEM, AFM, TEM and XRD-SR techniques.

Microhardness measurements. CSZM Nano Hardness tester was used to determine the mechanical properties of SiCxNy/Si(100) samples of 1-2 m thick. A Berkovich diamond pyramidal tip and a single loading – unloading cycle in the coordinates: load – depth of the indenter penetration were applied.

Fig.6. XRD-SR patterns of SiCxNy films grown at 1073 K using (HMDS+He) – (a) and (HMDS+NH3+He) - (b) gas mixtures; l=1.5405 A. (c) – the enlarged image of (101) peak of XRD pattern (b).

55

10 20 30 40 50 60 70 80

10

100

1000

10000

Inten

sity Si

(400

)(5

00)

(322

)

(320

)(3

12)

(222

)(3

02)

(220

)(2

12)

(101

)

?

20 30 40 50 60 70 80 90 100

10

100

1000

10000

(303

)

(421

)

Si(4

00)

(103

) (504

)

(512

)

(114

)

(312

)(2

03)

(210

)

?

(200

)

Inte

nsity

20,5 21,0

-1000

0

1000

2000

3000

4000

5000

6000

7000

8000

Inten

sity

(101

)

b ca

650 700 750 800 850 900

1,7

1,8

1,9

2,0

2,1

2,2

2,3

2,4

2,5

T growth, K

(HMDS+He)

Si2p

(Si-N

(C)/S

i2p(

Si-N

)

760 780 800 820 840 860 880

20

21

22

23

24

25

26

27

28

Tsynthesis, K

H, G

Pa

HMDS+NH3+He

HV of Si3N4 - 20 GPa SiC - 32 GPa

750 800 850 900 950 1000

18

20

22

24

26

28HV of Si3N4 - 20 GPa SiC - 32 GPa

(HMDS+He)

Tsynthesis

, K

H, G

Pa

650 700 750 800 850 900 950 1000

0,0

0,5

1,0

1,5

2,0

Si2p

(Si-N

(C)/S

i2p(

Si-N

)

T growth, K

(HMDS+NH3+He)

Measurements were carried out with the maximal load of 5 and 10 mN and with indenter penetration depth restricted up to 140 nm. The analysis of these curves according to Oliver and Pharr’s procedure allows determining microhardness and elastic modulus of these thin films. Measurements showed that the microhardness of silicon carbonitride films is from 18 to 28 GPa, while Young's modulus changes from 135.5 to 185.5 GPa. The increase of concentration of Si-C bonds in films grown in (HMDS+He) gas mixture is accompanied by the increase of hardness values from 18 up to 28 GPa (Fig. 7). In case of films grown in gas mixture with ammonia the increase of growth temperature leads to the decrease of hardness values from 28 to 20 GPa that may be connected with high concentration of Si-N bonds. Obtained results are in good agreement with references for commercial silicon carbide (32 GPa) and silicon nitride (20 GPa).

The optical properties. The SiCxNy films grown on fused silica substrates from (HMDS+He) mixture exhibited high optical transmittance (~ 80-90 % for l=1200-2200 nm). The SiCxNy films grown from (HMDS+NH3+He) gas mixture have very high optical transmittance (~ 85-95 % for l=600-2200 nm). Adsorption of the SiCxNy films occurred in the below 370 nm range of wavelength, beyond which these films demonstrated excellent transparency, characteristic for wide band gap materials. A progressive blue shift of the steepest part in the absorption band was observed with adding of ammonia to initial gas mixture but growth temperatures rise leaded to red shift. Tauc’s formula was used to estimate bandgap of our films. The bandgap of the films change from ~ 4.2 eV for SiCxNy films having high concentration of nitrogen to ~ 2 eV for samples having low content of N. The bandgap of Si3N4 is 5.0 eV which indicates that the SiCxNy films with high content of N close to silicon nitride.

56

Fig.7. Dependence of Si2p(Si-C)/Si2p(Si-N) ratio and hardness of SiCxNy films on the growth conditions.

PART II. Synthesis, nanoindentation and AFM studies of CVD boron carbonitride films

IntroductionCompounds of the B-C-N ternary system are of considerable

interest as promising materials for electrical, optical and mechanical applications. During the recent years, much attention is paid to the synthesis of thin films of boron carbon nitride (BCxNy) and to the investigation of their physicochemical properties. However, the optical, electrical, mechanical, and tribological characteristics, as well as their dependence on chemical and phase composition of films are still insufficiently investigated.

Some authors studied mechanical characteristics of boron carbonitride films (9 – 15). BCxNy films were obtained by chemical vapor deposition (CVD) from a mixture of diborane with methane and nitrogen (9, 10). It was established that microhardness (Н) of the samples of the composition B0,106-0,554C0,751-0,252N0,117-0,145 is changed from 5 to 29 GPa, while that of compositions BC1.1N1.4, BC1.5N1.2, BC1.6N2.5, BC3.7N0.8 is changed from 7 to 13 GPa. The films obtained by reactive pulsed laser ablation from graphite and h-BN were characterized by microhardness 2,9 GPa (for the composition of BC2N) (11). Nanocrystalline B0,42C0,33N0,25 films prepared using the electron-cyclotron-wave-resonance plasma assisted deposition had Vicker’s microhardness over 28 GPa, and Young’s modulus was 240 GPa (12).

57

BCxNy films synthesized by dual cesium ion sputtering had the hardness 30,6 GPa and stoichiometry BC0,9N0,7 (13). All the authors note regular increase in microhardness of the samples with an increase in carbon content in the boron carbonitride films. Influence of composition and structure on the mechanical properties of BCxNy coatings was studied in (14), where it was shown that microhardness of maximum 20 GPa was achieved in the range of approximately 20-45 at.% carbon, affected by the way of its incorporation into the hexagonal turbostratic lattice as well as by the crystallite size and texture. The films of both c- BCxNy and h- BCxNy were studied in (15). It was defined that with an increase in the C content, the content of a cubic phase in films was reduced, and the structure of films changed from cubic phase to hexagonal phase at more than 13,1 at.% content of the carbon., while the hardness value of 60 GPa was reduced to 10 GPa, respectively. For comparison, according to literature data, Vicker’s hardness of the h-BN is 20, of the c-BN – 53, of the diamond – 88 GPa (16).

Experimental methodsIn this work, synthesis of BCxNy layers was carried out by low

pressure chemical vapor deposition (LPCVD). The scheme of the experimental set-up was described previously (17). The precursor was a volatile elementorganic compound containing all the elements necessary for the synthesis (B, C, N): trimethylamine borane complex (CH3)3NBH3 or triethylamine borane complex (C2H5)3NBH3. These compounds are uninflammable and stable to the action of the atmosphere; their use in technology is preferable in comparison boron trichloride or diborane. In addition, these compounds have rather high vapor pressure, which allows using them as a single-source precursors in gas-phase processes. The temperature of the TMAB and TEAB sources was constant and equal to 0 oC and 20 oC, correspondingly. Polished single crystal silicon plates Si(100) were used as substrates. Various chemical composition of BCxNy films were realized by changing precursor type, the composition of initial gaseous mixture and deposition temperature. The films were deposited from the gas phase containing a mixture of TMAB or TEAB with ammonia, nitrogen or helium within temperature range of 400 - 700 oC. The process was carried out at low pressure, P = (2 4)·10-2 Torr and with different TMAB:NH3 (He) and TEAB: NH3 (N2 or He) ratios. Physicochemical and functional

58

characteristics of boron carbonitride films were studied with use of wide variety of above-mentioned methods.

Results and discussionThe thickness values of the BCxNy films were in the range of 200 1000 nm. Refractive index had values from 1,9 to 2,8; growth rate was 50 130 A/min within the investigated range of synthesis conditions. All films had a good adhesion to the Si(100) substrate. Morphology of the film surface was studied by means of SEM and AFM techniques. Electron microscopic images of the film surface (Fig. 9a-9c) indicate that the surface is smooth, uniform, has no pores and is tightly packed crystallites. During CVD process from both TMAB and TEAB nanocrystalline films BCxNy are formed. The size of crystallites increases with increase of deposition temperature. AFM images of the surface of these films (Fig. 10) show similar results. The size of the particles increases with growth temperature from 10 nm (Tdep. = 400oC) to 60 nm (Tdep. = 700oC). At the temperature above 500 oC it is observed self-organization of grains to large-scale crystallites of pseudo-hexagonal form, size, which obtains 350 – 460 nm. Surface morphology of the films is characterized by root-mean-square roughness, which is within the range 1 - 4 nm. More information on microstructure of the BCxNy films can be found with use of cross-sectional high resolution transmittance electron microscopy. HREM image of a part of film near interface shows the nanometer crystals with size of 2-3 nm embedded in an amorphous matrix (Fig. 9d).

59

a b

c d

Fig. 9. SEM images of surface of BCxNy films (a, b, c), synthesized from TMAB+He mixture at Tdep.=700 oC (a) and 600 oC (b), and from TMAB+NH3 mixture at Tdep.=700 oC. HREM image of BCxNy film deposited from TMAB+He mixture at Tdep.=600 oC (d).

Chemical composition of films was studied by Auger electron spectroscopy. Main components: boron, carbon, nitrogen as well as oxygen (impurity at the level up to 3 at. %) are determined by this method (Fig. 11a). AES studies revealed that films have a good uniformity of chemical composition (Fig. 11b). BCxNy films synthesized from a mixture of TMAB with helium at the temperature of 450 and 500 oC had chemical composition B0,72C0,23N0,04O0,01 and B0,68C0,27N0,04O0,01, respectively. Addition of ammonia leads to increasing of nitrogen content in the films. Increase of deposition temperature promotes growth of carbon content in the BCxNy films.

Fig. 10. AFM images of surface of BCxNy films deposited from TEAB+NH3 mixture (PNH3 = 4 x 10-3 Torr) at Tdep.=700 oC(a) and 500 oC (b).

60

a b

a b

Fig. 11. Typical AES spectrum of surface and profile of distribution of elements in the BCxNy film, deposited from TMAB+NH3 at Tdep. = 400 oC.

Depending on conditions of synthesis, boron carbon nitride films can have different composition and structure: from boron nitride to a ternary compound BCxNy. The IR spectra of the obtained films revealed the presence of bonds characteristic for h-BN and BCxNy. The bands at 1380 and 800 cm-1 are characteristic to the hexagonal boron nitride and relate to the in-plane B-N stretching and out-of-plane B-N-B bending vibrations. Boron carbide has only one absorption band at 1100 cm-1. The absorption band in the region of 1250 – 1450 cm-1 is assigned to C=C and/or C – N stretching vibrations (18). The IR spectra of the films synthesized at T = 700 oC with different partial pressure of ammonia in the initial gas mixture were obtained (Fig. 12a). The spectrum is close to the one of the hexagonal boron nitride. An increase in ammonia concentration causes changes in the IR spectrum of the films; we observe an increase in the intensity of the peak at 780 cm-1 which is attributed to the interplanar vibrations of B – N – B. For the films

61

synthesized from a mixture of TMAB with helium, there is one broad peak between 600 and 1600 cm-1 in the IR spectrum (Fig. 12b); the fitting of this peak gives a superposition of two Gaussian curves corresponding to the stretching vibrations of B-C and B-N bonds. This gives us reason to assume that a ternary compound (boron carbon nitride) is formed in this case. The same IR spectra were obtained for films grown from mixture of TEAB+NH3.

We carried out X-ray phase analysis of the films using the synchrotron radiation. The diffraction pattern obtained with -2 scanning procedure is shown in Fig. 13. The diffraction patterns contain peaks which correspond to the phases of boron carbide and hexagonal boron nitride and also unknown peaks. At higher concentration of ammonia in initial gas mixture the films of hexagonal boron nitride were obtained.

Micro-hardness of the samples was measured by nanoindenter. The typical loading/unloading curves of 0.94 m thick BCxNy film is shown in Fig. 14.

Maximal micro-hardness of boron carbonitride films synthesized from a mixture of TMAB with helium at T = 500 and 700 oC is equal to 34 GPa, and from a mixture of TEAB with nitrogen at 700 oC - H=40 GPa.

а

62

b

c d

e f

Fig. 12. The IR spectra of BCxNy films synthesized from a mixtures of TMAB+NH3 (a), TMAB+He (b). Dependence of relative content of B-C bonds in films (c, d) and hardness (e, f) on growth conditions.

63

Fig. 13. The X-ray diffraction pattern of the BCxNy film synthesized from TMAB + NH3 mixture (PNH3 = 4·10-3 Torr)

Fig. 14. The typical loading/unloading curves of 0.94 m thick BCxNy

film.

These values exceed data given in the literature data (9-14) for hexagonal phase BCxNy. Lower hardness is exhibited by the films obtained from a mixture of TMAB (or TEAB) with ammonia, H = 10-15 GPa. The values of Young’s modulus, which characterizes the elasticity of the films are 226 and 115 GPa for the films synthesized from TMAB + He and TMAB + NH3, respectively. There is correlation between relative content of B-C bonds (IB-C/IB-C+IB-N) and hardness values. Rise of

??

Si

64

deposition temperature leads to increase of both carbon content and hardness values of the films (Fig. 12c, e). Addition of ammonia to initial gas mixture leads to a decrease of carbon concentration and hardness of BCxNy material (Fig. 12d, f).

ConclusionsSo, hard nanocrystaline films of SiCxNy (H ~ 28 GPa) prepared by

RPECVD using HMDS with mixture of ammonia and helium possesed a very complex bonding structure. Analysis of results obtaned by spectroscopic methods such as IR spectroscopy, AES and XPS showed the presence of chemical bonding among Si, N, and C elements. Thus, in these films SiC compound was not disclosed but component with binding energy of ~ 101.0 eV indicates to the existence of polysubstituted tetrahedrons (CnSiN4-n) due to partial replacement of N atoms in Si-N network by C atoms. According to data of XRD-SR, HREM, and SAED the formation of the solid substitution solution SiCxNy occurs, having lattice parameters close to those of the standard phase -Si3N4 in which a part of silicon atoms is substituted by carbon atoms. The analysis of structural, optical and mechanical properties of these films indicates possibility for applications as wide band gap materials, hard protective coatings, and transparent layers in wide region of visible and far infrared region spectra.

The superhard nanocrystalline films of boron carbon nitride were synthesized by low pressure chemical vapor deposition. Trimethylamine borane and triethylamine borane complexes were used as the single-source precursors. It was determined that chemical and phase composition of films depends on growth conditions: deposition temperature and content of initial gas mixture. Hardness of the films correlates with content of B-C bonds in material. BCxNy films with the maximal microhardness of 40 GPa was synthesized.

AcknowledgmentsThe present work was supported by RFBR grant N 06-03-32713,

Interdisciplinary Project of SB RAS N 67, Grant from the Presidium of RAS N 8.14 and President of RF N NSh-4419.2006.3.

65

References1. S.Boughaba, G.I.Sproule, J.P.McCaffrey et al, Thin Solid Films, 402,

99 (2002)2. I.V.Afanasyev-Charkin, M.Nastasi, NIM, B, 206, 736 (2003)3. A.Bendeddouche, J.Appl.Phys. 81, 6147, (1997)4. A.Badzian, J. Am. Ceram. Soc., 85, 16, (2002) 5. N.I.Fainer, Yu.M.Rumyantsev, A.N.Golubenko, M.L.Kosinova,

F.A.Kuznetsov, J.Crys. Growth., 248C, 175, (2003)6. X.M He, T.N.Taylor, R.S.Lillard, et al, J.Phys.:Condens.Matter, 12,

L591 (2000)7. JCPDS Int. Center for Diffraction Data, 1988, USA, 41, card N 360 8. N.I.Fainer, E.A.Maximovskii, Yu.M.Rumyantsev, M.L.Kosinova,

F.A.Kuznetsov, NIMA, 470, 193, (2001)9. M.C. Polo, E. Martinez, J. Esteve, and J.L. Andujar. Diamond Relat.

Mater. 7, 376 (1998)10. T. Nasegava, K. Yamomoto, and Y. Kakudate. Diamond Relat.

Mater. 11, 1290 (2002)11. M Dinescu, A. Perrone, et.al. Appl. Surf. Sci. 127-129, 692 (1998)12. Z.X. Cao, and H. Oechsner. J. Appl. Phys. 93, 1186 (2003)13. E.Byon, J.-R.Kim et al. Surf. Coat. Tech. 169-170, 340 (2003)14. S.Stockel, K.Weise, D.Dietrich, T.Thamm, et al., Thin Solid Films.

420-421, 465 (2002)15. S.Kurooka, T.Ikeda, M.Suzuki, and A.Tanaka. Diamond Relat.

Mater. 12, 1122 (2003)16. X. Jiang, J. Philip, W.J. Zhang, P. Hess, and S. Matsumoto. J. Appl.

Phys. 93, 1515 (2003)17. M.L. Kosinova, N.I. Fainer, et al. in Chemical Vapor Deposition/

2003, M.Allendorf and, Editors, 2003-08, p. 709, Electrochemical Society Proceedings Series, Pennington, NJ (2003)

18. M.Kawaguchi. Advan. Mater. 9, 615 (1997)

66