Microstructural and chemical study of silicon dioxide/silicon carbide interfaces and correlations with electrical properties of silicon carbide MOS diodes and silicon carbide MOSFETs

Our goals of this study are to understand the possible origins of the low channel mobilities in SiC MOSFETs and the high D_it values at the SiO₂/SiC interfaces from a materials science point of view. We use AFM, SEM, TEM (EFTEM and STEM-based EELS) and electrical measurements to characterize the microstructure, chemistry, and electrical properties of the SiO₂/SiC interface.; Our observations are briefly summarized as follows. Firstly, we report the observation of carbon clusters at the SiO₂/6H-SiC(0001) interfaces as identified by TEM/EELS analyses. The carbon clusters were shown to be products of the thermal oxidation process. Secondly, we report the presence of excess carbon at the interface as a function of oxidation temperatures and re-oxidation conditions. Re-oxidation at 950 C for 3 h significantly reduced, but did not eliminate, the amount of excess interfacial carbon. This observation explain the re-oxidation process lower the Dit values. Thirdly, structural, chemical and electrical analyses were performed on SiC MOSFETs from Purdue University. Wavy SiO₂/4H-SiC interfaces are the result of high temperature (1400°C) post ion-implantation annealing. Excess carbons were observed on the MOSFET samples with nitric oxide (NO) annealing. Nitric oxide annealing at 1175°C for 2 h removed excess carbon from the interface.