Optical emission spectroscopy characterization of a hydrogen diluted silane plasma for microcrystalline silicon thin film deposition

Abstract

Plasma deposition of intrinsic microcrystalline silicon films is a key process for the fabrication of high efficient silicon thin-film solar cells. The process results are extremely determined by the plasma properties. Recent studies have shown that the concentration of the radical species in hydrogen diluted silane plasma is time-dependent during the deposition process and results in inhomogeneous film growth. 1-2 The major reason of process drift is believed to be as a result of the change of chamber wall surface condition. In this study, trace rare gases-optical emission spectroscopy (TRG-OES) 3 was used to determine the absolute species concentrations (e.q. Si, SiH x , H) by deriving from their optical emissions signals, as well as the temporal variation of electron temperature during the deposition process. The experimental results show that the OES intensities have obvious spikes after plasma is ignited and then decreases to a lower level at the first stage in about 10 seconds. This is because of the pressure unbalance between the throttle valve control and the expanded number density of gas induced by plasma heating and dissociation reaction in the chamber. After the transient of pressure unbalance, the intensity of H α increases close to 20 % and the SiH * decreases 10 % during the deposition in 10 minutes. The growth structure and crystallinity of deposited microcrystalline silicon films will also be presented.