Analysis of high-rate a-Si:H deposition in a VHF plasma

Abstract

VHF glow discharges are employed for high-rate a-Si:H deposition, maintaining good optoelectronic properties. A more efficient radical generation, either due to higher electron densities or an enhanced high-energy electron tail, is generally assumed as the mechanism. A VHF a-Si:H depositing plasma was investigated between 40 and 250 MHz by optical emission spectroscopy, mass spectroscopy, ion energy measurements and electrical impedance analysis. The present study shows that the increase of deposition rate with frequency is essentially due to enhanced ion flux to the growth surface, such that models of deposition kinetics taking into account only neutral species and neglecting the role of ions impinging on the substrate can therefore not be applied to VHF plasma deposition.