Recent development of device fabrication of SiC is awaiting detailed study of the machining of the surfaces. We scratched 4H-SiC surfaces with a sliding microindenter made of a SiC chip, and characterized machining affected layers by micro-Raman spectroscopy. The results of the Raman measurement of the scratching grooves revealed that there were residual stress, defects, and stacking faults. Furthermore, with heavy scratching load, we found clusters of amorphous SiC, Si, amorphous carbon, and graphite in the scratching grooves. Analysis of the Raman spectra showed that SiC amorphization occurs first and surface graphitization (carbonization) is subsequently generated through the phase transformation of SiC. We expect that the Raman characterization of machined surfaces provides information on the machining mechanism for compound semiconductors.

We have investigated Raman spectra of p-type 4H-SiC crystals with hole concentration ranging from 3×1016to 1×1021cm-3. For folded transverse acoustic (FTA) doublet modes, Fano interference profiles were analyzed, and the frequency shift due to Fano interference was obtained as a function of hole concentration. We demonstrated that the shift of the FTA doublet modes is a quantitative measure for evaluating of hole concentration of p-type 4H-SiC. Spectral features of transverse optical (TO) and longitudinal optical phonon-plasmon coupled (LOPC) modes were also studied for various carrier concentrations. The results show that the full width at half maximum of the LOPC and relative intensity of TO and the LOPC can be used as other calibration measures for hole concentration.

Raman intensity profiles are measured for 10H-SiC crystals, for which various zone-folded phonon modes are observed. Raman intensity profiles are calculated based on a bond polarizability model assuming several stacking sequences for the 10H polytype using a linear chain model. Among several candidates for the stacking sequences, the 3322 stacking structure provides the best-fit profile for experimental spectral profiles. The hexagonality value of 0.4 predicted from the stacking sequence of this polytype is consistent with that derived from the frequency splitting between the experimental A1 and E-type transverse optical modes. This fact is consistent with an empirical rule that the value of the reduced wavevector for the strongest folded transverse acoustic and optical modes are equal to the hexagonality of the polytype. In the present analysis of the Raman intensity profiles, the calculated intensity profiles for specified folded transverse optical modes are found to be relatively strong and strikingly dependent on force-field parameters in α-SiC that consists of the mixture of the cubic and hexagonal stacking structures. These force-field parameters can reproduce well the experimental Raman intensity profiles of various SiC polytypes including 10H-SiC.