Deposition of silicon nitride by glow-discharge decomposition of silane–nitrogen mixtures in a saddle-field plasma

Abstract

High-quality silicon nitride films have been deposited onto a variety of substrates including c-Si, GaAs, and InP at temperatures in the range 50–350 °C by the dc glow-discharge decomposition of silane–nitrogen mixtures in a saddle-field cavity. The effect of the N2–SiH4 flow ratio [Formula: see text] and the effect of a dc bias Vb applied to the substrate holder on the properties of the resulting films were systematically investigated. The N/Si ratio in the resulting films, as determined by Auger analysis, could be varied from 0 to 1.8 by adjusting [Formula: see text], with [Formula: see text] yielding stoichiometric silicon nitride. The total hydrogen content, as determined by 15N profiling, decreased linearly with [Formula: see text]. Far infrared absorption measurements indicated that hydrogen was incorporated mainly into Si–H sites at lower N2–SiH4 flow ratios in the range 1–2; higher N2–SiH4 flow ratios of 5–15 resulted in approximately equal concentrations of Si–H and N–H sites with a total bonded hydrogen content of about 12 at.% for films deposited at 250 °C. Ellipsometry measurements indicated that a refractive index as low as 1.82 at 632.8 nm was achieved. Refractive index and thickness variations of less than 5% were observed in films deposited on 4 in (1 in = 2.54 cm) diameter c-Si wafers. Scanning electron microscopy and photoluminescence studies of the thermal stability of SiNH films deposited onto semiinsulating GaAs indicated improved annealing behaviour with positive substrate bias.