Interface quality and reliability of n- and p-type 6H-SiC MOS capacitors with dielectric prepared by wet N2O nitridation (bubbling N2O gas through de-ionized water at 95degreesC) or dry N2O nitridation plus wet reoxidation were investigated. When compared with the conventional dry N2O nitridation, the two nitridation processes greatly reduce interface-state density and enhance reliability of both n- and p-SiC MOS devices. The involved physical mechanisms could be attributed to steam-enhanced out-diffusion of CO and removal of interstitial carbon as well as carbon clusters, steam-enhanced nitrogen passivation and steam-induced hydrogen passivation of dangling bonds and carbon-related traps at the interface. As a result, N2O nitridation with slight modification could still be a superior process for preparing high-quality gate dielectric of both n- and p-SiC MOS devices in the industry-preferred N2O environment. (C) 2003 Elsevier Science Ltd. All rights reserved.