Studies of thermal oxidation of single crystal 4 hydrogen- and 6 hydrogen-silicon carbide

This thesis presents the results of studies of the thermal oxidation of single crystal 4H- and 6H-silicon carbide. In particular, the phase diagram for the oxidation of SiC is obtained both theoretically and experimentally.; The theoretical analysis involves calculating the change of Gibbs free energy for all possible reactions for the SiC+O₂ system. In this way, the dominant reaction for a given oxygen pressure and temperature has been found. Thus different products can be obtained as the temperature and oxygen pressure are varied. From our thermodynamic model, not only has the active-passive transition been predicted, as by other thermodynamic models, but also two additional boundaries involving the formation of solid carbon have been predicted. It is now found that the quality of the SiO₂/SiC interface is worse than that of the SiO₂/Si interface, and this is a barrier for the development of SiC MOS devices. The solid carbon predicted by our model can play an important role in degrading the quality of the SiO ₂/SiC interface.; We have also studied the thermal oxidation behavior of single crystal 4H- and 6H-SiC for temperatures in the range 1200∼1500°C and oxygen pressures from 10−3 to 0.6 torr. The boundary of the active-passive transition and also the boundary for the formation of solid carbon on the C face at high temperatures are determined experimentally. The different oxidation behaviors of the C- and Si-terminated faces of SiC are observed in situ for the same oxygen pressure. For example, the temperature of the active-passive transition for the Si-terminated face is observed to be higher than that for the C face. Both the etching velocity and the SiO₂ film growth rate of the Si face are lower than those of the C face, etc. For the boundary for the formation of carbon, the critical temperature for the Si face is lower than that for the C face.; Comparing the phase diagram obtained experimentally to the predictions of our model, we find that kinetic factors must be considered as playing important roles during the oxidation. The results presented in this thesis help to clarify the complicated behavior that can occur on the surface of SiC when it reacts with oxygen at high temperature. In addition, they will also be important in helping to guide the development of improved processing methods used for future SiC electronic and ceramic applications.