The influence of pulsed plasma on the properties of a-Si:H films

• Main Authors: Hung-Shih chan, 洪士展
• Other Authors: 江雨龍
• Format: Others
• Language: zh-TW
• Published: 2016
• Online Access: http://ndltd.ncl.edu.tw/handle/55308922014844799567

碩士 === 國立中興大學 === 光電工程研究所 === 104 === In this thesis, a 13.56 MHz plasma-enhanced chemical vapor deposition (PECVD) with a pulse modulation RF Power has been used to fabricate hydrogenated amorphous (a-Si:H) silicon thin films. The a-Si:H films are fabricated with fixed chamber pressure, RF power, gas flow rate and temperature, and varying plasma turn-on time (ton) and turn-off time (toff). The effect of plasma turn-on time and turn-off time on the optical and structural properties of a-Si:H films are investigated. The composition of silicon monohydride (SiH) bonds and silicon dihydride (SiH2) bonds of a-Si:H films are measured by Fourier-transform infrared spectrophotometer (FTIR). The refractive index (n), extinction coefficient (k), dielectric function (ε), absorption coefficient (α), optical band gap and thickness of a-Si:H films are measured by spectroscopic ellipsometry (SE). The plasma turn-on time and turn-off time, the periods of pulsed-wave plasma, and base vacuum pressure were 10, 15 and 20 ms, 1, 5 and 10 ms, 240,000 cycle, and 2.2 × 10-6 torr, respectively. For toff increase from 1 ms to 5 ms, the SiH bonds are increased and SiH2 bonds are decreased. The micro-structure parameter (Rs) of a-Si:H films is reduced, which indicates that the a-Si:H film became more compact. For toff increase from 5 ms to 10 ms, Rs has no significant change. Further increase in plasma turn-off time would create no change in much of the structural properties of a-Si:H films. For increasing toff from 1 ms to 5 ms, the band gap, deposition rate, and thickness of a-Si:H films are reduced, and the refractive index (n), extinction coefficient (k), and dielectric constant (ε) of a-Si:H films are increased, which indicate these a-Si:H films have more compact structure. For toff increase from 5 ms to 10 ms, the optical properties of a-Si:H films are maintained without much difference. The results demonstrate that a toff time larger than 5 ms can effectively neutralize plasma. Further increase in plasma turn-off time could not significantly alter the optical properties of a-Si:H films.