Process optimization for the 4H-SiC/SiO2 interface.

This thesis aims to optimize the process for the 4H-SiC/SiO2 interface formations. The experiments are made on metal-oxide-semiconductor (MOS) structures, where the semiconductor is an n-type epitaxially grown 4H-SiC thin film. The oxide is fabricated either with thermal oxidation, or by using plasma-enhanced chemical vapour deposition (PeCVD), utilising two different tools, Precision 5000 Mark II (P5000) and Plasmalab 80Plus system (Pekka). The deposition temperature is varied for the thermally grown oxide, while power, pressure and gas ratio of N2O/SiH4 is investigated for the PeCVD method. Also the post deposition annealing (PDA) temperature is studied for both techniques. The oxide formation and PDA is done in N2O ambient in order to study the effect of nitrogen passivation of the traps that exist at the interface of 4H-SiC/SiO2. After the dielectric formation the structures are electrically and structurally characterized. The electrical characterization is done by capacitance-voltage (CV) and current-voltage (IV) measurements while the structural characterization is done with atomic force microscopy (AFM). The density of interface traps (Dits) is extracted using the Terman method from CV data. It is observed that the flatband voltage drops almost to zero when the samples are annealed in nitrogen rich ambient, resulting in a more electrically uniform oxide. Also, Dits can also be reduced by nitrogen treatment when the oxide is deposited by the PeCVD technique. However, it appears that the Terman method cannot determine the amount of traps along the entire bandgap and it is clear that a large amount of Dits are still present closer to the conduction band. Finally, it is found that there is a larger spread in the data extracted from the samples deposited by P5000 in comparison to Pekka, indicating that Pekka is a more reliable tool for oxide deposition in SiC substrate