The Variation of Physical Properties of Plasma‐Deposited Silicon Nitride and Oxynitride with Their Compositions

Abstract

Silicon nitride and silicon oxynitride films with refractive indices varying from 1.60 to 1.95 were deposited on siliconsubstrates using plasma-enhanced chemical vapor deposition (PECVD) processing. Variation of the film's physicalproperties with composition is examined. Refractive indices, infrared, Auger analysis, and plasma etching of plasma-depositedfilms are studied before and after an annealing cycle. A direct correlation between etch rates and etchprofiles of the deposited films with their composition was observed. Plasma etching, using a 92% CF4 + 8% O2 gas mixture,showed that the etch rate of oxynitride film increases with hydrogen concentration and decreases as the oxygencontent increases. The length of the undercut, i.e., etch profile, depends on the amount of oxygen and hydrogen contentin the films. Infrared data suggests that silicon oxynitride film with a refractive index of 1.75 is more stable underthermal annealing cycles, as compared to other silicon oxynitride films. Ellipsometric measurements showed that filmthickness and refractive index uniformity are comparable with those of CVD processing. However, Auger depth profileanalysis revealed poor compositional uniformity in all deposited films, especially at the silicon or silicon dioxide substrateinterfaces.©1984 The Electrochemical Society, Inc.