Double-sided and single-sided polished 6H-SiC wafers with subsurface damage layer studied by Mueller matrix ellipsometry

Abstract

The complex optical constants and the subsurface damage layer of uniaxial doped 6H-SiC wafers are measured using Mueller matrix spectroscopic ellipsometry. A comparison is made between measurements on a single-sided polished wafer that can be treated as a semi-infinite substrate and on a double-sided polished wafer that is studied with the partial-wave theory. The refractive indices and extinction coefficients for ordinary and extraordinary directions are determined below the bandgap after point-by-point fitting of experimental Mueller matrices. The thickness of the subsurface damage layer caused by mechanical polishing and chemical mechanical polishing determined by ellipsometry is consistent with the result of transmission electron microscope. The ellipsometry results show that the analysis based on a double-sided polished wafer is more informative about the optical properties of 6H-SiC than that of the single-sided polished wafer as it renders information properties about the bulk properties of the material, for example, allowing the determination of the very weak absorption coefficient (k≈10−4) due to doping.