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Preparation and property investigation of silicon carbide thin films synthesized by RF plasmas
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Type
Thesis
Author
Cheng, Qijin
Supervisor
Xu, Shuyan
Abstract
During the last decade, nano-structured semiconductor materials have been extensively studied due to their unique physical and optical properties that pave the way for promising applications in microelectronic and optoelectronic devices. With its wide band gap, excellent thermal conductivity, high breakdown electric field, high saturated electron drift velocity and large bonding energy, silicon carbide (SiC) offers attractive applications in microelectronics and optoelectronics operating at high temperature, high frequency, high power, and chemically hostile environment.
In this thesis, two types of plasma enhanced chemical vapor deposition (PECVD) systems, namely, an inductively coupled PECVD system and an inductively coupled plasma (ICP) assisted rf magnetron sputtering system, have been used to fabricate SiC films on two different types of substrates (single-crystal silicon and quartz substrates) simultaneously. The ICP plasma source features highly-uniform, large-area, high-density plasmas with low sheath potentials near the substrate surface, independent control of the plasma density and the ion energy, etc. The deposited SiC films were investigated using various analytical tools such as scanning electron microscopy, high-resolution transmission electron microscopy, x-ray diffraction, Fourier transform infrared spectroscopy, ultraviolet-visible spectroscopy, x-ray photoelectron spectroscopy, energy dispersive x-ray spectroscopy, and Raman spectroscopy in detail. The main achievements of this work are:
Firstly, hydrogenated amorphous silicon carbide (a-Si1-xCx:H) films with different carbon contents x from 0.09 to 0.71 have been successfully synthesized from feedstock gases SiH4 and CH4 by inductively coupled PECVD. All fabricated a-Si1-xCx:H samples exhibit low-temperature (77 K) photoluminescence, whereas only the carbon-rich a-Si1-xCx:H samples (x ≥ 0.5) exhibit room-temperature (300 K) photoluminescence. This behavior is explained by the static disorder model. Moreover, the effects of substrate temperature and inductive rf power on the photoluminescence of carbon-rich a-Si1-xCx:H films have been studied.
Secondly, stoichiometric nanocrystalline cubic silicon carbide films have been synthesized from feedstock gases SiH4 and CH4 (the CH4/SiH4 gas flow ratio was approximately equal to 2) heavily diluted with hydrogen ([hydrogen flow (SCCM)]/[silane + methane flow (SCCM)] was approximately equal to 4) at a low substrate temperature of 250 0C by inductively coupled PECVD. The nanocrystalline silicon carbide films are made up of silicon carbide nanocrystallites (the mean grain size of the SiC nanocrystals is around 5 nm) embedded into an amorphous matrix, with a clear, uniform, and defect-free Si-SiC interface. Moreover, the effects of substrate temperature, CH4/SiH4 gas flow rate ratio, and different hydrogen dilution ratios on the
growth of nanocrystalline silicon carbide films have been studied.
Finally, high-quality nanoislanded nanocrystalline cubic silicon carbide films have been successfully synthesized by an inductively coupled plasma assisted rf magnetron sputtering deposition system from a sintered SiC target ([Si]/[C]=1) in a reactive argon and hydrogen gas mixture ([hydrogen flow (SCCM)]/ argon flow (SCCM)] was approximately equal to 2). The SiC nanoisands are chemically pure, highly stoichiometric, have a typical size of 10-35 nm, and contain small (~6 nm) nanocrystalline inclusions. Moreover, the properties of nanocrystalline SiC films can be effectively controlled by the plasma parameters such as deposition time, SiC target power, substrate temperature, inductive rf power, and working gas pressure.
In this thesis, two types of plasma enhanced chemical vapor deposition (PECVD) systems, namely, an inductively coupled PECVD system and an inductively coupled plasma (ICP) assisted rf magnetron sputtering system, have been used to fabricate SiC films on two different types of substrates (single-crystal silicon and quartz substrates) simultaneously. The ICP plasma source features highly-uniform, large-area, high-density plasmas with low sheath potentials near the substrate surface, independent control of the plasma density and the ion energy, etc. The deposited SiC films were investigated using various analytical tools such as scanning electron microscopy, high-resolution transmission electron microscopy, x-ray diffraction, Fourier transform infrared spectroscopy, ultraviolet-visible spectroscopy, x-ray photoelectron spectroscopy, energy dispersive x-ray spectroscopy, and Raman spectroscopy in detail. The main achievements of this work are:
Firstly, hydrogenated amorphous silicon carbide (a-Si1-xCx:H) films with different carbon contents x from 0.09 to 0.71 have been successfully synthesized from feedstock gases SiH4 and CH4 by inductively coupled PECVD. All fabricated a-Si1-xCx:H samples exhibit low-temperature (77 K) photoluminescence, whereas only the carbon-rich a-Si1-xCx:H samples (x ≥ 0.5) exhibit room-temperature (300 K) photoluminescence. This behavior is explained by the static disorder model. Moreover, the effects of substrate temperature and inductive rf power on the photoluminescence of carbon-rich a-Si1-xCx:H films have been studied.
Secondly, stoichiometric nanocrystalline cubic silicon carbide films have been synthesized from feedstock gases SiH4 and CH4 (the CH4/SiH4 gas flow ratio was approximately equal to 2) heavily diluted with hydrogen ([hydrogen flow (SCCM)]/[silane + methane flow (SCCM)] was approximately equal to 4) at a low substrate temperature of 250 0C by inductively coupled PECVD. The nanocrystalline silicon carbide films are made up of silicon carbide nanocrystallites (the mean grain size of the SiC nanocrystals is around 5 nm) embedded into an amorphous matrix, with a clear, uniform, and defect-free Si-SiC interface. Moreover, the effects of substrate temperature, CH4/SiH4 gas flow rate ratio, and different hydrogen dilution ratios on the
growth of nanocrystalline silicon carbide films have been studied.
Finally, high-quality nanoislanded nanocrystalline cubic silicon carbide films have been successfully synthesized by an inductively coupled plasma assisted rf magnetron sputtering deposition system from a sintered SiC target ([Si]/[C]=1) in a reactive argon and hydrogen gas mixture ([hydrogen flow (SCCM)]/ argon flow (SCCM)] was approximately equal to 2). The SiC nanoisands are chemically pure, highly stoichiometric, have a typical size of 10-35 nm, and contain small (~6 nm) nanocrystalline inclusions. Moreover, the properties of nanocrystalline SiC films can be effectively controlled by the plasma parameters such as deposition time, SiC target power, substrate temperature, inductive rf power, and working gas pressure.
Date Issued
2008
Call Number
QC611.8.S5 Che
Date Submitted
2008