Hydrogenated silicon nitride thin films deposited between 50 and 250 °C using nitrogen/silane mixtures with helium dilution

Silicon nitride thin films, deposited by plasma enhanced chemical vapor deposition at temperatures between 250 and 50 degrees C from SiH4, N-2 and He, were characterized using transmission infrared spectroscopy, ellipsometry, wet etch rate, and current-voltage analysis. At 250 degrees C using SiH4/N-2 /He flow ratios of 1/150/75, films with refractive index = 1.80 and H concentrations < 20%, distributed equally in Si-H and N-H units were obtained. The concentration of hydrogen and its distribution in N-H and Si-H bonds are sensitive to process temperature, suggesting that thermally driven N incorporation reactions are important during growth. Inert gas dilution allows films to be formed at <100 degrees C, with bonded hydrogen configurations similar to films deposited at higher temperatures. Current versus voltage traces of as-deposited films show charge trapping, which can be reduced by extended low temperature anneals. These results show that chemical composition can be controlled in low temperature silicon nitride deposition. This processing approach may be useful for encapsulation or for barrier layer formation on low temperature organic electronic devices or flexible transparent plastic substrates. (C) 1999 American Vacuum Society. [S0734-2101(99)02101-6].