First-principle-based Investigation Of SiO₂/SiC Dangling Bonds

Silicon Carbide is the third generation semiconductor material that with high application potential.Compared with traditional Silicon semiconductor, SiC has the properties of wide band-gap, high critical breakdown electric field, high thermal conductivity, high saturated carrier drift velocity. Besides of that, SiC is the unique compound semiconductor material that can be thermal oxidized to form SiO2 insulating film in a similar way to silicon. For the reasons above, it is predicted that SiC will play an important role in the application of high temperature, radiation resistant, high frequency and high power devices.Presently, the development of lateral SiC MOSFETs is hindered by excessively small field-effect mobilities.Mobility degradation is believed to be directly related to the very large density of traps measured at the SiC/SiO2 interface.To solve the problem, large amounts of investigation have been done to improve the SiC/SiO2 interface quality. Though many new fabrication technologies were introduced, the density of traps at the SiC/SiO2 interface is still much higher than that of Si/SiO2 interface.It is generally considered that the Dit at the SiC/SiO2 interface is due to the incomplete oxidation of Silicon atoms located at the interface. Annealing the gate oxide in the presence of nitrogen or hydrogen has been found to improve the interface, resulting in a net reduction of Dit, and an increase in MOSFET mobility. Although annealing treatment is an important processing step leading to device quality SiC MOSFETs, there is still no clear consensus regarding the physical mechanisms involved.In this paper, we first introduced the possible origins of the SiO2/SiC interface trap density, including the carbon cluster, transition layer and Dangling bands. Here we used the density function theory to perform the theory investigation. We introduced the basic theory of DFT-GGA method, including the theory framework, total energy calculation and the application of CASTEP code.In order to perform the first principle calculation, the slab mode was introduced to construct the interface model.We investigated the passivation of the (0001) Si face of 4H-SiC by H, N and P atoms respectively. Although an oxygen environment is not considered, these findings concur with some experimental studies that indicted the presence of H, N and P would reduce the density of states in the SiC/SiO2 interface.Compared with H passivation, N and P atoms were more effective in reducing the interface states induced by the Si dangling band. In addition, from the energy point of view, P atoms passivation would be more excellent than N, and we gave the possible explanation of the passivation mechanism. In summary, the results of this paper showed that N and P could effectively reduce the interface states introduced by Si incomplete oxidation. These results play an important role in studying and improving the SiC MOSFET process, especially for the annealing of the interface.