Kenta Chokawa

Intrinsic origin of negative fixed charge in wet oxidation for silicon carbide

We demonstrate on the basis of first-principles calculations that the formation of carbonate-like moiety in SiO2 could be the intrinsic origin of negative fixed charge in SiC thermal oxidation. We find that two possible origins for the negative fixed charges are O-lone-pair state and a negatively charged CO3 ion in SiO2. Such CO3 ion is able to be formed as a result of the existence of residual C atoms in SiO2, which are expected to be emitted from the interface between SiC and SiO2, and the incorporation of H atoms during wet oxidation.

A New-Type of Defect Generation at a 4H-SiC/SiO2 Interface by Oxidation Induced Compressive Strain

Our message is oxidation process must be minimized as possible. Many carbon-related defect structures are reported in SiC/SiO2 interface. In this paper, we investigated the effect of oxidation to the defect forming by density functional theory (DFT). In the result, we found carbon defect structure that completely different from in the present report. This defect structure has carbon-carbon single bond with no dangling bond. To see the forming process, compressive strain from inserted oxygen atoms induce the rearrangement of structure and cause C-C defect structure. We can know that this structure is formed with energy gain about 3.8eV. And this C-C defect induces trap state under the conduction bottoms.

First principles study of SiC/SiO 2 interfaces towards future power devices

We clarify the intrinsic problems of SiC/SiO2 interfaces by the first principles calculations. The unique nearly free electron like characteristics of SiC conduction band bottom causes unexpected formation of interface states near the conduction band bottoms by process induced strain. These results indicate that strain free process is necessary for fabricating high quality NMOSFET. Another proposal is developing PMOSFET instead of presently popular NMOSFET. Moreover, we also discuss the Vth instability caused by proton diffusion.

Origins of Negative Fixed Charge in Wet Oxidation for SiC

We demonstrate that the formation of carbonate-like moiety in SiO2 could be the origin of negative fixed charge in SiC thermal wet oxidation, based on first-principles calculations. We find that negative CO3 ion appears in SiO2 due to not only the existence of residual C atoms that are expected to be emitted from the SiC/SiO2 interface, but also a large enough number of incorporated H atoms during wet oxidation.

Theoretical Study of N Incorporation Effect during SiC Oxidation

We investigated the atomistic mechanism of N incorporation during SiC oxidation by the first principles calculation. We found that N atoms play two characteristic roles in NO oxidation of SiC surface. One is that N atoms tend to form three-fold coordinated covalent bonds on a SiC(0001) surface, which assist the termination of surface dangling bonds, leading to improve the interface properties. The other is that N atoms form N-N bond like a double bond. The N2 molecule is desorbed from SiC surface, which do not disturb the oxidation process of SiC surfaces. These results indicate that N incorporation is effective to suppress defect state generation at SiO2/SiC interfaces during SiC oxidation.