ECE 4813 Dr. Alan Doolittle
ECE 4813
Semiconductor Device and Material Characterization
Dr. Alan Doolittle School of Electrical and Computer Engineering
Georgia Institute of Technology
As with all of these lecture slides, I am indebted to Dr. Dieter Schroder from Arizona State University for his generous contributions and freely given resources. Most of (>80%) the figures/slides in this lecture came from Dieter. Some of these figures are copyrighted and can be found within the class text, Semiconductor Device and Materials Characterization. Every serious microelectronics student should have a copy of this book!
ECE 4813 Dr. Alan Doolittle
Ion Beam Characterization
Secondary Ion Mass Spectrometry Rutherford Backscattering
ECE 4813 Dr. Alan Doolittle
Ion Beam Characterization
Reflection Sputtering Secondary Ion Mass Spectrometry Rutherford Backscattering
Emission Photon Spectroscopy Particle Induced X-Ray Emission Electron Emission
Absorption Ion Implantation
Ei
ECE 4813 Dr. Alan Doolittle
Secondary Ion Mass Spectrometry Ion Beam
Sample
Spectrum
Ion Counter
CRT Image
Profile
Mass filter
Primary Ions Secondary Ions
Screen
Microchannel Plate
1 2 3 4 5
Mass Spectrometer
ECE 4813 Dr. Alan Doolittle
Secondary Ion Mass Spectrometry Secondary ion mass spectrometry (SIMS) is the most common doping
profile method Principle: Atoms sputtered from the sample; mass of the ejected ions
analyzed Ion mass ⇒ element identification; ion intensity ⇒ element density
Advantages: Gives depth profiles. Can analyze all elements; most sensitive of all analytical techniques. Can measure several impurities simultaneously
Limitations: Destructive method. Subject to matrix effect: ion yields influenced by a change in surface composition. Need standards for concentration determination, independent depth measurement
Sensitivity: Depends on impurity. Highest sensitivity is boron in Si at ~ 1014 cm-3; all other elements less sensitive. Sensitivity limited by interference from ions of similar mass/charge
ECE 4813 Dr. Alan Doolittle
SIMS Ion count ⇒ density: use calibrated standard Time ⇒ depth: measure depth of crater
0 200 400 600 Time (s)
0 0.2 0.4 0.6 0.8 1 Depth (µm)
1020
1019
1018
1017
1016
1015
1014
Den
sity
(cm
-3)
Ion
Cou
nts
106
105
104
103
102
101
100
ECE 4813 Dr. Alan Doolittle
Time-of-Flight SIMS (TOF-SIMS) Pulsed ion beam sputters the
sample Ion time of flight is measured Measure transit time
⇒ charge/mass ratio Low beam current ⇒ low
sputtering rate Suitable for organic surface
contamination Sensitive for low metallic
contamination (~ 108 cm-2)
M.A. Douglas and P.J. Chen, “Quantitative Trace Metal Analysis of Si Surfaces by TOF-SIMS,” Surf. Interface Anal. 26, 984-994, Dec. 1998.
qm
VLt
toft 2=
Sample
ExtractorPrimary
Ions
Detector
Reflector(For EnergyFocusing)
SampleL
Detector
Sputtering Ion
Sputtered IonsM1
M2M3
ECE 4813 Dr. Alan Doolittle
TOF-SIMS Example 70 Line Cu grid on Si wafer
Blue/green: SiO2 features Red/orange: tungsten features Purple: chlorine and carbon
contamination
www.llnl.gov/str/Hamza.html
360 µm
TOF Image
ECE 4813 Dr. Alan Doolittle
TOF-SIMS Example Bond pad failure; covered with siloxane Siloxane mapped distinctly from elemental Si
Bonding pad with poor wire bond
www.materialinterface.com/surface5.html
ECE 4813 Dr. Alan Doolittle
Rutherford Backscattering (RBS) The incoming ping pong ball loses the most energy
when it is scattered from which of the four balls?
Bowling Ball
Baseball
Tennis Ball
Golf Ball
Ping Pong Ball
ECE 4813 Dr. Alan Doolittle
Rutherford Backscattering He ions with several MeV energy are scattered by the
sample atoms The mass of the sample atom is determined from the energy
of the scattered ions
Helium Ion
Detector
ScatterEvent
Sample
Incident He Ion
Scattered He Ion
Sample Detector
ECE 4813 Dr. Alan Doolittle
Ion Scattering
Conservation of energy
2/2/2/ 222
21121
2010 vMvMEEvME +=+==
Conservation of momentum φθ coscos: 221101 vMvMvMParallel +=
φθ sinsin0: 2211 vMvMlarPerpendicu −=
Eliminating φ and v2
21
122
122
0
1 cossinMM
MMMvv
++−±
=θθ
For M1 < M2, use “+” 2
21
122
122
0
1 cossin
++−
=MM
MMMEE θθ
ECE 4813 Dr. Alan Doolittle
Rutherford Backscattering He ions of 2-3 MeV are
scattered; energy loss gives information
Nondestructive Good for heavy elements on
light substrate, e.g., silicides Sensitivity ∼ 1018 - 1019 cm-3
K: kinematic factor R = M1/M2
[ ]2
22
0
1
)1()cos())sin((1
RRR
EEK
++−
==θθ
E. Rutherford
ECE 4813 Dr. Alan Doolittle
Rutherford Backscattering
He, 1-3 MeV
N Si Ag AuEnergy ~Mass
Yiel
d
0.5 1 1.5 2
Energy (MeV)
Yiel
d
Si Substrate
N
Ti
100 nm TiN on Si
RBS works best for heavy elements on light substrates
ECE 4813 Dr. Alan Doolittle
Rutherford Backscattering RBS works best for heavy elements on light substrates
Energy ~ Mass
Yiel
d
He, 1-3 MeV
Si (x=t)Si (x=0)
Au (x=t)Au (x=0)
x t 0
QNtYield Ω= σ
( )2
22
421
2
)sin(1cos)sin(1
sin4
4 θθθ
θσ
RR
EZZq
−+−
=
σ: scattering cross section Ω: solid detector angle Q: no. of incident ions N: target atom density t: thickness
ECE 4813 Dr. Alan Doolittle
Rutherford Backscattering
Ag TiN
Energy
Channel
C
N O Si Ti
Ag
Yield Pa-n
Si 3.7 MeV He
100 600
3 1
ECE 4813 Dr. Alan Doolittle
Channeling He ions are scattered more when they are not channeled
Channeling
Scient. Am. 218, 90 (March 1968)
ECE 4813 Dr. Alan Doolittle
Thickness Measurements Thickness determined by measuring the various energies
E3=K1E0
d
M1M2E0
E0
E0-∆Ein
K1(E0-∆Ein)E2=K1(E0-∆Ein)-∆Eout E1 E2 E3 E0 E
∆E
Yield
outin EEEKEEKE ∆−∆−== )(; 012013
[ ]dSEEKEEE outin 0123 =∆+∆=−=∆
[S0]: backscattering energy loss factor (eV/Å)
outin EEEKE ∆−∆−= )( 021
ECE 4813 Dr. Alan Doolittle
Silicide Formation RBS is ideal for measuring
the formation of silicides
E22E11
d
PtSi
E
Yiel
d
PtSi
E1 E2 E3
E3=K1E0
d
PtSi E0
E1 E2 E3 E
Yiel
d
M.A. Nicolet et al. Science, 177, 841 (1972)
ECE 4813 Dr. Alan Doolittle
RBS Examples
M.A. Nicolet et al. Science, 177, 841 (1972)
O Na ClK
Fe
Sr I
Pb
Energy
Yiel
d2 MeVHe
Blood
Carbon
EnergyYi
eld
O
SrPb
Ca
2 MeVHe
AbaloneShell
ECE 4813 Dr. Alan Doolittle
Review Questions What is the main application for SIMS? What is the principle for RBS? What is TOF-SIMS? What is channeling? How are the SIMS vertical and horizontal data
converted?
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