Consideration on SiO2/4H-SiC Band Alignment Modulation by NO Annealing

Abstract

NO post-oxidation annealing (NO-POA), introducing nitrogen at the SiO2/4H-SiC interface, is an excellent method not only for the reduction of the interface trap density, but also for the improvement of the MOSFET performance. However, a significant negative shift of the threshold voltage of MOSFET is frequently observed after NO-POA, which can be a critical issue for the industrial application. Therefore, it is important to understand the SiO2/4H-SiC interface after nitridation from various perspectives. Here, we experimentally demonstrated that the shift of the flat-band voltage is directly related to the change of the SiO2/4H-SiC band alignment. We estimated the flat-band voltage without a fixed charge effect and observed the negative shift of flat-band voltage on (0001) & (11-20) 4H-SiC. Moreover, we observed the shift of the band alignment of various samples by F-N tunneling current measurement and XPS analyses. There was a relationship between the conduction band offset and NO-POA duration for both crystal orientations and we suggested a model with dipole layer formation as an origin. On (0001) & (11-20) 4H-SiC, due to the increase of the conduction band offset, flat-band voltage showed a negative shift but the leakage current level also decreased, which can be an advantage for the reliability property. These findings show new opportunities to modulate the band alignment between SiC and SiO2 just by substituting a foreign element for the atoms at the interface.