I have seen higher ox rates dependent on doping level if the N doping is high enough, i.e. substrate doping level. 5E18-E19. Was the C Face the back side of a 4H substrate?
Thx
Article Differences in SiC thermal oxidation process between crystal...
The doping concentration of the C-face substrate used is 7E15, which is homo-epitaxially grown on a bulk SiC wafer by National Institute of Advanced Industrial Science and Technology (AIST), Japan.