SILICON THIN FILMS PREPARED BY PECVD USING VHF POWER IN A CIRCULAR-PARALLEL-PLATE PLASMA REACTOR

Abstract

The deposition rate of μc-Si films was investigated for four excitation frequencies 30, 40, 60, 70 and 80 MHz with other deposition parameters fixed. Deposition rate increases with the increasing of excitation frequency, while Raman crystallinity behaves more complicated. With the optimization of deposition parameters, p-i-n solar cells at an initial efficiency of 5.41% were fabricated. With the increasing of plasma excitation frequency, the non-uniformity of these thin films increases. To better understand the cause of the non-uniformity of these films, a numerical simulation was carried out. The numerical results generally followed the experimental data. It turned out that the standing waves and the evanescent wave guide modes on the electrode surface played an important role. In order to achieve highly uniform thin films, a triode-electrode was employed together with a pulsed power source. We found that with a proper choice of pulse frequency and DC voltage applied to the mesh, non-uniformity is less than 8% for films deposited on 10×10 cm 2 substrates. Simulations were also applied to analyze the results.