Thermal expansion and elastic properties of plasma-deposited amorphous silicon and silicon oxide films

Abstract

The thermomechanical properties of amorphous glow-discharge deposited silicon and silicon oxide films were measured as a function of film composition. Hydrogenated amorphous silicon films, deposited at 250 °C with a density of 2.0 g/cm3 and 20 at. % of hydrogen, exhibit a linear thermal expansion coefficient of about 4.4×10−6/°C and a biaxial elastic modulus of 150 GPa. The expansion coefficient of plasma-deposited silicon oxide films shows a systematic dependence on the fabrication conditions and ranges from about 10−5/°C to negative values. Strong correlations between the hydrogen concentration of the films, the film density, and thermal expansion coefficient were observed and are discussed. The biaxial elastic modulus of the oxide films is not strongly dependent on the gas ratio and is about 40 GPa, substantially smaller than the values obtained for thermally grown oxides. These differences are attributed to the effect of network terminations by hydrogen and −OH groups.