Amorphous Si:B films: Microstructure and electrical properties

Abstract

A theoretical study of the electronic structure and spectroscopic properties of the low-lying electronic states of the molecule SiBThe properties of and potential uses for thin films of amorphous Si:B alloys are summarized. The films were deposited by low-pressure chemical vapor deposition of silane and dihorane. The boron content of the samples was controlled by regulating the reaction of diborane and silane gases during the deposition. The alloy and its oxides possess many desirable properties for microelectronic applications, including high microhardness, resistance to chemical etching, high and tailorable conductivity, ease of oxidation, and (for the oxide) high resistivity and dielectric strength. The microstructural stability of the films is excellent. The volume fraction of crystallinity of the as-deposited films was reduced dramatically by increasing the boron content, as was crystallization upon annealing. Transport at low temperatures is seen to be dominated by hopping. The linear oxidation rate was observed to be radically enhanced by the presence of large amounts of boron. The electrical properties of the oxides were seen to be comparable to Si0 2 . Using a simple model relating the physical mode of boron incorporation in the amorphous network, mechanisms for the crystallization inhibition, the oxidation enhancement, and the electrical properties are discussed. These are consistent with stoichiometric and spectroscopic properties of the alloy and its oxides.