Monitoring of Film Qualities of Amorphous SiO 2 films/Si(100) Substrates by Measuring Bulk and Surface Acoustic Waves in Terms of Brillouin Spectroscopy

Acoustic properties of amorphous SiO2 thin films deposited on the Si(100) substrate were investigated by using Brillouin spectroscopy. The Brillouin spectrum was obtained by tilting the sample to investigate both the longitudinal acoustic (LA) mode and the surface acoustic wave (SAW) modes. Sound velocities of both modes, the two elastic moduli (longitudinal and shear moduli), and the Poisson ratio of the film could be obtained by combining the Brillouin data and the measured refractive index. The longitudinal sound velocity and the longitudinal elastic modulus increased with increasing Ar ratio in the Ar:O2 gas mixture, which was attributed to the better stoichiometry of the film grown at higher Ar ratio.