Phase Diagrams for the Optimization of rf Plasma Enhanced Chemical Vapor Deposition of a-Si:H: Variations in Plasma Power and Substrate Temperature

Abstract

ABSTRACTReal time spectroscopic ellipsometry (RTSE) has been applied to characterize surface roughening transitions during the growth of undoped hydrogenated silicon (Si:H) thin films by rf plasma-enhanced chemical vapor deposition (PECVD). In particular, the amorphous–to–amorphous surface roughening transition [→] and the amorphous–to–(mixed-phase-microcrystalline) roughening transition [a→(a+µc)] observed during Si:H growth have been studied under different PECVD conditions of hydrogen dilution ratio R=[H2]/[SiH4], rf plasma power P, and substrate temperature T. For Si:H growth on crystalline Si substrates under the different conditions, phase diagrams have been constructed by plotting the bulk film thicknesses at which these transitions occur as a function of R. The effects of the substrate (c-Si wafers versus amorphous Si:H films) on the a→(a+µc) transition of the phase diagram are also explored. The results provide deeper insights into recent attempts to improve the material properties and solar cell performance for a-Si:H i-layers prepared by rf PECVD at higher rates.