The role of hydrogen in hydrogenated microcrystalline silicon film and in deposition process with VHF-PECVD technique
Yang Hui-Dong (杨恢东)ab, Su Zhong-Yi (苏中义)b
a Department of Electronic Engineering, Jinan University, Guangzhou 510632, China; b Department of Electric Engineering, Shanhai Dianji University, Shanghai 200240, China
Abstract The role of hydrogen in hydrogenated microcrystalline silicon ($\mu $c-Si:H) thin films in deposition processes with very high frequency plasma-enhanced chemical vapour deposition (VHF-PECVD) technique have been investigated in this paper. With in situ optical emission spectroscopy (OES) diagnosis during the fabrication of $\mu $c-Si:H thin films under different plasma excitation frequency $\nu _{\rm e }$ (60MHz--90MHz), the characteristic peak intensities ($I_{{\rm SiH}^*}$, $I_{{\rm H}\alpha^*}$ and $I_{{\rm H}\beta ^*}$) in SiH$_{4}$+H$_{2}$ plasma and the ratio of ($I_{{\rm H}\alpha^* }$ + $I_{{\rm H}\beta^*}$) to $I_{{\rm SiH}^*}$ were measured; all the characteristic peak intensities and the ratio ($I_{{\rm H}\alpha^* }$ + $I_{{\rm H}\beta^* }$)/$I_{{\rm SiH}^*}$ are increased with plasma excitation frequency. It is identified that high plasma excitation frequency is favourable to promote the decomposition of SiH$_{4}$+H$_{2 }$ to produce atomic hydrogen and SiH$_x$ radicals. The influences of atomic hydrogen on structural properties and that of SiH$_x$ radicals on deposition rate of $\mu $c-Si:H thin films have been studied through Raman spectra and thickness measurements, respectively. It can be concluded that both the crystalline volume fraction and deposition rate are enhanced with the increase of plasma excitation frequency, which is in good accord with the OES results. By means of FTIR measurements, hydrogen contents of $\mu $c-Si:H thin films deposited at different plasma excitation frequency have been evaluated from the integrated intensity of wagging mode near 640 cm$^{ - 1}$. The hydrogen contents vary from 4{\%} to 5{\%}, which are much lower than those of $\mu $c-Si:H films deposited with RF-PECVD technique. This implies that $\mu $c-Si:H thin films deposited with VHF-PECVD technique usually have good stability under light-soaking.
Fund: Project supported by the Natural Science Foundation of Guangdong
Province, China (Grant No 05300378), the State Key Development Program for Basic Research
of China (Grant Nos G2000028202 and G2000028203) and the Program on Natural
Science of Jinan University, Guangzhou, China (Grant No 51204056).
Cite this article:
Yang Hui-Dong (杨恢东), Su Zhong-Yi (苏中义) The role of hydrogen in hydrogenated microcrystalline silicon film and in deposition process with VHF-PECVD technique 2006 Chinese Physics 15 1374
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