Surface reactions in very low temperature (<150°C) hydrogenated amorphous silicon deposition, and applications to thin film transistors

This article discusses surface processes to control bonded hydrogen content in hydrogenated amorphous silicon (a-SI:H) deposited by plasma enhanced chemical vapor deposition. Experiments with helium diluted silane under typical plasma deposition conditions show that ion bombardment can be used to control Si-H bond concentrations at very low temperature through ion-enhanced silicon-hydrogen disproportionation reactions. Hydrogen dilution can also be used to control Si-H concentrations, where important reactions include H abstraction by H and by SiH3 radicals, and H insertion into strained Si-Si bonds leading to silicon etching. Experimental results are supported by calculations of reaction energetics, including overall reaction enthalpies and kinetic barrier heights. Amorphous silicon thin film transistors fabricated at a maximum processing temperature of 110 degrees C have performance (on/off ratio, mobility, and stability under applied stress) approaching that of typical higher temperature devices. (C) 2000 Published by Elsevier Science B.V. All rights reserved.