A Study on Pre-Oxidation Nitrogen Implantation for the Improvement of Channel Mobility in 4H-SiC MOSFETs

Detailed investigations on the pre-oxidation nitrogen implantation process for the improvement of channel mobility in 4H-SiC MOSFETs are reported. Comparisons with conventional thermally nitrided gate oxides are highlighted. The results of a nitrogen dose dependence study indicate that higher N implantation doses lead to higher peak field-effect mobilities but lower threshold voltages. This apparently correlates with the interface trap density near the conduction band of 4H-SiC, as previous work suggests, but an alternate mechanism associated with counter doping of the MOSFET p-well via N implantation is proposed here. Analysis of the experimental results suggests that the counter-doping mechanism is more likely to be the dominant effect.