Polyhydride Bonding Groups in PECVD Amorphous Si Thin Films.

Abstract

AbstractIn glow discharge deposition (GD) of a-Si:H alloys, the concentration of electronically-active defects increases as the incorporation of bonded hydrogen in polymerized dihydride groups, (SiH2)n increases. Since the fraction of dihydride groups increases strongly with decreasing substrate temperature (Ts), the incorporation of these bonding groups can only effectively be reduced by restricting Ts to about 230°C or higher. We have found that a-Si:H films produced by remote Plasma Enhanced Chemical Vapor Deposition (remote PECVD) are qualitatively different than the GD films in the following ways: 1) the amount of bonded hydrogen for Ts > 100°C is less by about a factor of two; and 2) the fraction of polyhydride bonding is also significantly less than the monohydride fraction for Ts > 100°C. We develop a statistical model that provides a basis for translating any process-dependent representation of data for the polyhydride fraction into a universally-obeyed scaling relationship in which the independent variable is [H]. The agreement between the statistical model and the experimental data, replotted as a function of [H], supports our observation that the fraction of polyhydride bonding is not determined simply by Ts, but is a function of the particular reaction pathways in the deposition process chemistry.