Materials processing and spectroscopic characterization of 4H-SiC

Abstract

The effect of chemical-mechanical polishing and high temperature furnace annealing on nitrogen-doped crystalline 4H-SiC was investigated using spectroscopic and microscopic techniques. SiC wafers were processed by Chemical-Mechanical Polishing (CMP) and high temperature furnace annealing up to 1600C. The X-ray Photon Spectroscopy (XPS) results indicate that annealing at the higher temperatures varies the surface chemical composition of the samples. The non-bridging oxygen content increases with annealing temperature. This suggests that the oxycarbide content may be increasing with temperature, a fact that could affect the free carrier concentration. Preliminary experiments suggest that the forbidden Raman mode is visible at temperatures around 1200C and indicating more out of plane stress. Preliminary experiments also suggest that the transverse optic phonon mode shows a slight shift indicating in plane stress at the same temperature. The environmental scanning electron microscope (ESEM) was used to image the defects on the sample surfaces. The chemical composition of the bulk and specifically that of the defects were also determined using Energy Dispersive x-ray Spectroscopy (EDS). The defects on the unannealed CMP samples were mostly confined to the surface. SEM micrographs obtained by backscattered electrons did not indicate defects propagating into the sample. The samples annealed at 1000C and 1200C showed an increase in oxygen content in the bulk. Higher temperatures of annealing introduced defects that were carbon rich. However, for 1400C only a single silicon rich defect was observed. The carbon rich defects were found to increase with annealing temperature and grow out of the surface of the samples. Lines were found to appear on the samples at 1200 C although the chemical composition did not appear to vary. These lines increased in length for samples annealed at 1400 C. The Raman results correlate with surface structural variations at this temperature. This investigation concludes that the optimal furnace annealing temperature for an argon atmosphere could be below 1200oC