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

Abstract 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 SiH 3 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°C have performance (on/off ratio, mobility, and stability under applied stress) approaching that of typical higher temperature devices.