The elastic properties of thin-film silicon nitride

The elastic properties of thin-film silicon nitride (Si/sub 3/N/sub 4/) were investigated using surface-acoustic-wave (SAW) propagation data for plasma-enhanced chemical-vapor-deposition (PECVD) grown Si/sub 3/N/sub 4/ on gallium arsenide. For three films with thicknesses of 102 nm, 250 nm, and 497 nm, elastic constants were calculated from least-squares fits of theoretical dispersion curves to phase velocity data at different film thickness-to-wavelength ratios. The measured film density decreased from 2800 to 2500 kg/m/sup 3/ with increasing film thickness. Within this density range the longitudinal elastic modulus averaged near 1.83*10/sup 11/ N/m/sup 2/ and the shear elastic modulus decreased from 0.918*10/sup 11/ N/m/sup 2/ to 0.561*10/sup 11/ N/m/sup 2/ as the film density decreased. The elastic moduli of thin-film silicon nitride are comparable to those of Si/sub 3/N/sub 4/ ceramics at similar densities. >