"Gas Cluster Ge Infusion for Si(1-x)Ge(x) Strained-Layer Applications"

1. Abstract
Materials processing with a gas cluster ion beam (GCIB) is an
emerging technology that produces novel material properties in
the near-surface (<40nm) regime. Results are presented from a
series of GCIB infusions of GeH4 into Si(100) substrates for
the purpose of producing a strained Si(1-x)Gex layer relative to
the Si substrate. A broad range of post-GCIB anneal schedules
over a range of 400 ºC to 1200 ºC was investigated. Selected
samples were analyzed by RBS/channeling, cross-sectional
TEM, and SIMS to assess composition and crystal quality.
High-resolution axial scans about the <110> channeled
direction were surveyed for evidence of lattice strain
(tetragonal distortion). Comparison is made to a commercial
epitaxial Si75Ge25 film.
1

2. Gas Cluster Ion Beam (GCIB)
Atmospheric
Front End
High Voltage
Electronics
Facilities
User
Interface
Low Voltage
Electronics
Beam-Line
Process
Chamber
Atmospheric
Front End
High Voltage
Electronics
Facilities
User
Interface
Low Voltage
Electronics
Beam-Line
Process
Chamber
Gas clusters are
formed by adiabatic
expansion of a jet of
gas introduced into
high vacuum through
a nozzle. Ionization
and acceleration
produce a directed,
energetic chemical
beam for unique
materials processing.
2

3. GCIB “Infusion”
~30 Å~30 Å
Si(100)
typical
GeH4/Ar cluster impact
“infused” Ge
amorphized region [2]
2 – 40nm scales to (keV)1/3
At impact, the cluster
immediately dissociates
and a transient (<10psec)
thermal and pressure
spike [1] defines the
amorphized infusion
region.
High energy (keV) cluster
effects a low energy/atom
(<10eV/atom) processing
of the surface.
Result is extreme chemical and
physical reactions in the near-
surface region independent of
dopant mass.
dopant
3

4. Experiment
Substrate: 200mm Si(100) oxide stripped
Process: GeH4/Ar infused at 30keV
Infusion dose: 3.6E16 Ge/cm2
Cleaved for tube-furnace anneals in overpressure of UHP N2
Various anneal schedules included VLTA (very low
temperature anneal) steps and HTA (high temp. anneal) steps.
VLTA HTA
Single Step
Two Step 375 º - 550 ºC 700 º - 1200 ºC
550 ºC – 900 ºC
4

5. Ge Profile vs. Anneal
1E+19
1E+20
1E+21
1E+22
1E+23
0 200 400 600 800 1000 1200
Depth (Å)
Concentration(Geatoms/cm3
)
700C_1 Hr
900C_10min
400C_ 1Hr + 900C_1 Hr
400C_1Hr + 1000C_10min
400C_1Hr + 1200C_5min
SIMS Profiles
Selected post-anneal samples showing anneal schedules.
5

6. Cross-sectional TEM
(on-axis imaging)
6
Surface
As-infused 400 ºC+900 ºC 400 ºC+1200 ºC
• As-infused has 240Å deep amorphous region
• Higher temperature (>900 ºC) necessary to reduce defects
• 1200 ºC has lower contrast and indicates Ge diffusion

7. Cross-sectional TEM
(on-axis imaging)
7
Surface
400 ºC+900 ºC 400 ºC+1200 ºC
All high temperature anneals resulted in regrowth
epitaxial to Si(100) substrate.

8. 8
RBS/channeling
2.0 MeV @ 169.7º scattering
400 ºC - 1 Hr. + 1000 ºC - 10 Min.
0
100
200
300
400
500
600
700
100 200 300 400 500 600 700
Channel
Counts
Random
<100>
Si
Ge
58%
aligned
to
Si<100>
700 ºC - 1 Hr.
0
50
100
150
200
250
300
350
400
450
500
100 300 500 700 900
Channel
Counts
Random
<100> Si
d
Ge
8%
aligned to
Si<100>
900 ºC - 10 Min.
0
50
100
150
200
250
300
350
400
450
500
100 300 500 700 900
Channel
Counts
Random
<100>
Si
Ge
19%
aligned
to
Si<100>
400 ºC - 1 Hr. + 900 ºC - 1 Hr.
0
50
100
150
200
250
300
350
400
450
500
100 300 500 700 900
Channel
Counts
Random
<100> Si
Ge
44%
aligned
to
Si<100>

9. 9
RBS/channeling
Comparison of Ge infusion (400º/1200 ºC) with 340Å Epi Si75Ge25
Comparison of Ge Infusion to 340Å EPI
0
10
20
30
40
50
60
70
400 500 600 700 800 900
Channel
Counts
Si
Ge
signal
3X
to show
detailEPI control
Infusion
<100> χmin
Si Ge
Infused: 17% 18%
EPI: 11% 12%

10. Determination of Lattice Strain
SiGe
Si(100)
(a) (b)
10
Origin of “kink angle”
Presence of a “kink angle” θκ denotes tetragonal elongation εT along the <100> axis
due to the Poisson effect from constraint in the {100} plane. (a) from [3] and
(b) from [4]
εT

11. 11
Channeling scan about <110>
Axial scan about <110> for the 400º/1200ºC anneal. A kink angle of 0.05º indicates
tetragonal distortion (strain) relative to the Si(100) lattice.
Normalized Angular Scan about <110>
6th order Polynomial Fit
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1
-0.50 -0.30 -0.10 0.10 0.30 0.50
Tilt axis theta (degree)
NormalizedYield
0.075º
Si
θκ = 0.05º
Ge
0.025º
3.8 MeV He+

12. 12
Summary
GCIB Ge infusion of silicon with appropriate annealing can
produce recrystallization of a graded SiGe layer of comparable
crystal quality to commercial epitaxial growth methods. High
temperature anneals above 900 ºC are required to reduce
defects such as stacking faults. Highly localized lattice strain in
the form of tetragonal distortion is demonstrated. Quantitative
assignment of strain is not straightforward due to Ge gradient.
Modeling of this is underway.
Acknowledgments
The authors gratefully acknowledge the efforts of Jie Zhu at SUNY-Albany for
countless late-night hours of data collection at the accelerator and Allysa Vanderpot
for tireless sample preparation and annealing. We extend our sincere thanks to
Kevin Jones, University of Florida, for our XTEM micrographs.

13. References
13
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