Bahram Roughani

Chemical-Mechanical Polishing and Rapid Thermal Annealing of SiC: Raman Spectroscopy and ESCA (XPS) Studies

The effects of Chem-Mechanical Polishing (CMP) and Rapid Thermal Annealing (RTA) on n-type 4H:SiC samples doped with nitrogen were investigated using Raman scattering and X-ray Phtoelectron Spectroscopy (XPS a.k.a. ESCA) measurements. A comparison of the Raman spectra from Mechanically Polished (MP) SiC annealed at 600°C and 800°C displays a frequency shift in the coupled plasmon LO-phonon mode. Since the coupled mode frequency is a direct measure of the free carrier concentration, this observation may suggest the removal of polishing induced carrier traps with increasing annealing temperature. The CMP samples did not show this frequency shift, thereby indicating that such polishing traps were not created in that process. The Si-peak observed in the XPS spectra of the unannealed CMP sample indicates primarily a Si-C bonding, while that for the MP sample is more complex, indicating other bonds beside Si-C. Drastic changes in O, C, Si surface content were observed for annealing between 1000°C and 1100°C. The peaks in the XPS spectra associated with the chemical environment for C, O, and N are complex and may be explained as silicon oxycarbide type structures near the surface or possibly around the interface of the SiC substrate with a thin surface oxide layer.