Microscopic and Spectroscopic Characterization of Chemo-Mechanically Polished, Furnace-Annealed, Nitrogen-Doped 4H:SiC

The effect of chemical–mechanical polishing and high-temperature furnace annealing at temperatures ranging from 1000 °C to 1600 °C on nitrogen-doped crystalline 4H:SiC was investigated. Techniques used to characterize the samples included environmental scanning electron microscopy (ESEM), energy-dispersive X-ray spectroscopy (EDS), X-ray photoelectron spectroscopy (XPS) and micro-Raman spectroscopy. The ESEM micrographs and EDS data indicated that there were structural defects on the unannealed sample that did not propagate into the sample or vary in composition from the bulk. The sample annealed at 1000 °C showed oxygen-rich and carbon-depleted surface defects. Annealing at temperatures above 1200 °C introduced defects that grew out of the sample surface. These were carbon and oxygen rich, but depleted in silicon. This supported the XPS data, which showed an increase in the surface C bonding with annealing temperatures above 1200 °C. The XPS data also suggested that the oxycarbide content may be increasing on annealing above 1200 °C. Raman micro-probe data from the defects on the sample annealed at 1200 °C showed the maximum shift in the transverse optical phonon mode at 776 cm-1, indicating that the beginning of carbon out-diffusion may be accompanied with structural changes. Optimal annealing temperatures are thus below 1200 °C