(Invited) Study on Impact of MOS Interface Passivation Processes on Band Alignment and Flat-Band Voltage of 4H-SiC Gate Stacks

Abstract

Change of band alignment at SiO2/4H-SiC was observed by extending the duration of interface nitridation process to passivate the interface defects. The conduction-band offset on (0001) stack increases but that on (000-1) and (1-100) stacks decrease, which does not result only in a difference of flatband voltage (Vfb) but also in a difference of gate leakage characteristics among those stacks on different crystal faces. An introduction of an additional dipole layer in the gate stack was demonstrated by depositing a few-nm-thick Al2O3 on SiO2 to cause a positive shift of Vfb without degrading the quality of SiO2/SiC MOS interface. Control of those factors to cause Vfb shift is crucially important to reduce the mobility degradation in SiC MOSFET inversion channel by increasing the channel doping concentration to tune the threshold voltage.