Low Temperature Growth of Silicon Carbide Thin Film for High Temperature MEMS based Sensor Applications The document summarizes research on growing silicon carbide thin films using plasma enhanced chemical vapor deposition for applications in high temperature MEMS sensors. Key findings include: 1) Amorphous silicon carbide thin films up to 3 micrometers thick were grown at low temperatures of 300-400°C using silane and methane gases. 2) The films withstood temperatures of 500°C without cracking or peeling and had smooth surfaces with roughness under 5nm. 3) Analysis showed the films were amorphous hydrogenated silicon carbide with properties dependent on deposition parameters like gas flow ratios and RF power. 4

1. Low Temperature Growth of Silicon
Carbide Thin Film for High Temperature
MEMS based Sensor Applications
Presented by: Ms. Bhavana Peri
Supervisor: Dr. Raj Kishora Dash
School of Engineering Sciences and Technology
University of Hyderabad
17th Dec 2013
BhavanaPeri, BikashBorah, and Raj Kishora Dash

2. Outline
 Introduction
 PECVD Growth method
 Thickness using FESEM
 Structure Analysis
 Microstructure- XRD, Raman,
 Bonding- FTIR
 Roughness and morphology – AFM
 Mechanical properties - Nanoindentation
 Other properties: Residual stress, resistivity, high temperature effects
 Summary
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A.A. Yasseen, et. al., J Microelectromechanical Systems (1999).

3. Introduction
 MEMS devices are used for
 aerospace applications (turbine engines, combustion chambers, etc ),
 nuclear power instrumentation, satellites, space exploration,
 geothermal wells etc.
 MEMS devices which can be operated in high temperature regime (typically
beyond 500˚C) are required.
 Existing clean room technologies are limited to 250˚C
 Materials for such applications are silicon carbide (SiC), aluminum nitride (AlN),
gallium nitride (GaN), boron nitride (BN), diamond and zinc selenium (ZnSe) *.
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*J.Huran , I.Hotovy, A.P.Kobzev, N.I.Balalykin. Thin Solid Films 459 (2004) 149–151.
 MEMS – Micro Electro Mechanical
Systems
 Devices that are capable of combining
electronic abilities with control abilities such
as Sensing and Actuation

4. Why SiC ?
Properties of SiC
High mechanical properties:
Young’s modulus ~ 450GPa, Hardness
~30GPa
High thermal conductivity
(~ 3.6 Wcm-1K-1)
Good thermal stability
High melting point (~2800˚C)
Good adhesion to underlying thin films
Good electrical stability over 300 ˚C
High Fracture toughness > 2.2 M Pa m0.5
Chemical inertness
Can withstand HF & KOH etching
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V Cimalla, et. al.,Phys. D: Appl. Phys. 40 (2007) 6386–6434

5. SiC Growth
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PECVD
 Lower temperatures that are compatible with the existing clean room process technology.
 The deposited a-SiC has a coefficient of thermal expansion (CTE) relatively similar with
that of Si
 The parameters that can be varied to control the nature of the structure
1. Gasses and their flow rate 3. Temperature
2. Pressure 4. Power
Growth Methods
 CVD (Chemical Vapor Deposition)
LPCVD – Most preferred method; gives crystalline SiC layers but high temperatures (800-
1200 °C) are required
PECVD – Low temperature method (200 - 400 °C) ; gives amorphous layers but can be used
for deposition on various kinds of substrates and underlying thin films
 Sputtering – Amorphous layers but have some “hollow voids” which inhibit material properties

6.  PECVD system: Oxford Instruments
Plasmalab System 100 (CeNSE, IISc)
 The Si (n-type, 100) wafers were initially
cleaned in Piranha solution followed by a
HF Dip
 Chamber cleaning was done using CF4
gas and prior to deposition the chamber
was conditioned for SiC deposition
 Deposition of SiC using the gases silane
(SiH4) and methane (CH4) using Argon as
a carrier gas
 Deposition time was varied from 22mins
to 45mins
Experimental Process
SiH4 + CH4 SiC + 4H2
Source: Oxford
Instruments
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7.  The table shows the variation range
in the process parameters
 The samples presented here are those
samples which have sustained the
heating at high temperatures (500
˚C) without any cracking or peeling.
 Different materials SiO2 and Si3N4
were also used as substrates for the
deposition process. But these
substrates were also deposited on a
Si substrate using PECVD. Upon
heating the SiC on SiO2 showed no
change while those deposited on
Si3N4 were peeled off.
PECVD Process Parameters
Parameters Range
Pressure 800-1200 mTorr
RF Power 300-400 W (HF)
Temperature 300-400˚C
Gas flow ratio - SiH4 : CH4 1:2 – 1:7
Carrier gas flow rate (Ar) 700sccm (constant)
Sample
No.
Temperature
(˚C)
RF Power Flow
Ratio
1 380 400W 1:5
2 380 300W 1:5
3 380 300W for 10s;
200W for 20s
1:5
4 400 350W 1:4
5 400 350W 1:7
Growth of SiC thin film
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Pressure was
kept constant
at 1200mTorr
for all
samples

8. Cross-Sectional FESEM
Power- 350 W, Temp-400 ˚C, Pressure: 1200mTorr,
SiH4/CH4/Ar-25/100/70 sccm
Power- 350 W, Temp-400 ˚C, Pressure: 1200mTorr,
SiH4/CH4/Ar-15/100/700 sccm
Power- 300 W (10s) and 200W (20s), Temp-400 ˚C,
Pressure: 1200mTorr, SiH4/CH4/Ar-20/100/700 sccm
Power- 300 W , Temp-400 ˚C, Pressure: 1200mTorr,
SiH4/CH4/Ar-20/100/700 sccm
Power- 400 W , Temp-400 ˚C, Pressure: 1200mTorr,
SiH4/CH4/Ar-20/100/700 sccm
Element Wt% At%
C K 35.00 55.73
Si K 65.00 44.27
(PECVD Growth of SiC thin film)
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Element Wt% At%
C K 32.86 53.36
Si K 67.14 46.64
Element Wt% At%
C K 39.07 59.99
Si K 60.93 40.01
Element Wt% At%
C K 34.13 54.79
Si K 65.87 45.21
Element Wt% At%
C K 35.18 55.93
Si K 64.82 44.07
2.8µm 3.04µm 1.35µm
0.74µm
1.8µm
Growth rate of
82nm/min

9. Structure Analysis: XRD and Raman
 The XRD plots shows that the thin films are all amorphous in nature
 The peaks appearing in the low frequency range around 285 cm-1 and 491 cm-1 are
due to Si-Si vibrations while the peaks at 910 cm-1 are due to the second order
modes of Si-Si vibrations.
 760-790 cm-1 can be assigned to amorphous Si-C vibration
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20 30 40 50 60 70 80
SiC/Si-Sample 4
SiC/Si-Sample 1
SiC/Si-Sample 2
SiC/Si-Sample 3
SiC/Si-Sample 5
Intensity
(a.u.)
2(Degree) 250 500 750 1000 1250 1500
Raman
Intensity
(a.u.)
Relative Wavenumber (cm
-1
)
SiC/Si-Sample 5
SiC/Si-Sample 4
SiC/Si-Sample 3
SiC/Si-Sample 2
SiC/Si-Sample 1
SiC
SiC is amorphous in nature
(PECVD Growth of SiC thin film)
Z. Hua,b, et. al., Journal of Crystal Growth 264 (2004) 7–12.

10. Bonding Analysis: FTIR
 Peaks of significant importance
 740-800 cm-1 : Si-C bonds
 2050-2100 : Si-H bonds
 ~1000 cm-1: Si-CHn bonds
 Peaks shift from 760cm-1 for 1:4
SiH4/CH4 flow ratio to 775cm-1 for
1:7 SiH4/CH4 flow ratio (indicating a
higher carbon content*)
 Hydrogen content decreased as the
CH4 flow rate was increased
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*M. V. Pelegrini, et. al., Phys. Status Solidi C, 2010, 7, No 3-4, 786– 789
All samples are amorphous hydrogenated SiC
SiHn
SiCHn
SiC
(PECVD Growth of SiC thin film)
3500 3000 2500 2000 1500 1000 500
SiC/Si-Sample 5
SiC/Si-Sample 3
SiC/Si-Sample 4
SiC/Si-Sample 2
SiC/Si-Sample 1
Absorbance
(a.u.)
Wave number (cm
-1
)

11. Roughness - AFM
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 For variations of
flow ratio or the
RF Power the
average
roughness of the
thin films did not
vary much.
The Roughness values were
less than ~5nm for all the
samples of a-SiC
Rrms = 4.1nm Rrms = 3.3nm Rrms = 3.1nm
Rrms = 2.4nm Rrms = 0.8nm
Sample 1 Sample 2 Sample 3
Sample 4 Sample 5
(PECVD Growth of SiC thin film)

12. Microstructure - AFM
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 Comparison of RF Power Variation
400W 300W Mixed
 Comparison of Flow ratio Variation
SiH4/CH4 - 1:4 SiH4/CH4 - 1:7
 The mixed frequency samples showed higher density than the other sample
 Higher RF Power also reduced the density of the samples
 Flow ratio: higher the CH4 flow, the more denser the samples were
(PECVD Growth of SiC thin film)

13. Properties of PECVD SiC Thin Films
 Resistivity
 In-situ doping using Ammonia was tried but the resistivity was still very high
 Investigation into various processes to reduce the resistivity is being studied
 High Temperature testing
 The samples discussed in the previous slides were all heated to 500˚C
 The samples withstood this temperature and there was no change in the structure of the
samples. Also there were no cracks or peeling.
 All samples were treated with Piranah (H2SO4:H2O2 – 3:1) solution and SiC
layer showed good adhesion to the substrate.
 Residual stress
 Mechanical properties
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14. 300 W 350W 400W Mixed
-400
-300
-200
-100
0
100
-400.9
-224.6
-112.2
35.9
Residual
Stress
(MPa)
RF Power
Variation of Residual Stress with RF Power
Influence of RF Power on Residual Stress
 The residual stress is lower for
lower RF Power.
 In the case of mixed frequency and
higher power the dissociation of
the precursors is much higher
 Leading to a higher concentration
of reactive ions in the plasma with
a direct impact on the deposition
rate.
 The residual stress tends towards
being more and more compressive
as the RF power is increased*
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*Avram M., Semiconductor Conference (CAS), 2010 International (Volume:01 ), 11-13 Oct, 2010
The lower the RF Power the
more tensile the residual stress
of the a-SiC thin film
(PECVD Growth of SiC thin film)

15. Nanoindentation
Sample
ID
Hardness
(Gpa)
Elastic
modulus
(Gpa)
1 13.25 104.52
2 9.32 90.83
3 13.1 129
4 10.82 109
5 13.68 138.3
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(PECVD Growth of SiC thin film)
 The maximum load applied was 8kN at a loading
rate of 500µN/s
 The increase in CH4 flow rate showed an increase
in the hardness and young’s modulus values. But
the trade-off lies between the mechanical
properties and the rate of deposition.

16. Summary
 A low temperature PECVD process for deposition of SiC was presented
 XRD, Raman and FTIR studies confirm that the samples deposited using PECVD were
amorphous hydrogenated SiC samples.
 The residual stress becomes more tensile as the RF Power is reduced.
 All samples were very uniform and smooth and the roughness of the samples are less
than ~5nm from AFM studies.
 A maximum thickness of ~3µm of SiC was achieved in a deposition time of 45mins
 High growth rate of ~82nm/min was also achieved.
 The samples withstood temperatures of 500˚C without any cracking or peeling.
 The resistivity changes were not observed in the samples that were doped with N2
 Although the residual stress and thickness of the a-SiC layer was very good, its
mechanical properties were very low. Further research is going on to optimise the
mechanical properties.
17th Dec 2013

17. References
 J.Huran , I.Hotovy, A.P.Kobzev, N.I.Balalykin. Thin Solid Films 459 (2004) 149–151.
 M. V. Pelegrini, et. al., Phys. Status Solidi C, 2010, 7, No 3-4, 786– 789
 M. Kunle, S. Janz, K. Gerog Nickel and O. Eibl, Phys. Status Solidi A, 2011, 208, No. 8, 1885–1895
 H. Guo, et. al., Proc. of the 1st IEEE International Conference on Nano/Micro Engineered and Molecular
Systems, Jan 18-21, 2006, Zhuhai, China
 Avram M., Semiconductor Conference (CAS), 2010 International (Volume:01 ), 11-13 Oct, 2010
 V Cimalla, J Pezoldt and O Ambacher. J. Phys. D: Appl. Phys. 40 (2007) 6386–6434
 C. Iliescu and D. P. Poenar, 978-953-51-0917-4, 2012
 Y.M. Sun, T. Wigmore, J. K. Sonoda, N. W.Yoshihiko, Journal of Applied Physics, Vol.82, Issue.5, pp.2334-
2341, 1997.
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Acknowledgements
 Funding was provided by NPMASS, Aeronautical Development Authority, India (Project code:
ADA: NP-MASS: Proj Sanc:1.27).
 Fabrications were done in CeNSE, Indian Institute of Science, Bangalore, India.

18. 17th Dec 2013
Thank you!