Presentation

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!