Investigation of lattice mismatch stress in SoS thin film systems by Raman scattering and XRD techniques

This paper investigates the residual stress of epitaxial silicon film deposited on Sapphire (SoS). The emphasis is to examine the effect of lattice mismatch on the total stress. To this end, we examined the stress at different depth. For the 5μm to 1.3μm thick films, similar equi-biaxial residual stresses around 580 MPa were detected by Raman scattering, which implies the uniformity of residual stress from the surface of 5 μm film to the depth of 1.3μm close to interface. In a thinner film, however, a larger stress of 724MPa was found, manifesting the effects of lattice mismatch. In order to prove this, high temperature XRD experiment was conducted. It was found that at room temperature, the stress detected by XRD and Raman shift was consistent. When the sample was heated up to the film deposition temperature, where the sample is free from the thermal stress, a compressive stress of 82MPa was detected, which is merely due to lattice mismatch from the film growth process.