11:45 〜 12:00
▼ [20a-D103-11] XPS study of nitrogen profiles at SiO2/4H-SiC(0001) interfaces with NO annealing
キーワード：Interface nitridation, SiO2/SiC(0001) interface, NO post oxidation annealing (POA)
Recently, Hatakeyama et al. reported that the field effect mobility of n-channel 4H-SiC(0001) MOSFETs increased by NO-POA as the annealing duration was increased from 10 to 60 min and then it slightly degraded for a longer annealing duration of 120 min [1]. In this study, to evaluate the physical features near the SiO2/SiC interface for different NO-POA durations, we carefully investigated the nitrogen depth profiles in SiO2/SiC structures through scanning x-ray photoelectron spectroscopy (XPS) analysis. For that purpose, slope-shaped SiO2/4H-SiC(0001) samples with three different NO-POA durations of 10 min (NO10), 60 min (NO60) and 120 min (NO120) were prepared. We found that the N 1s peak intensity (normalized by Si 2p intensity) of NO10 was much lower than those of NO60 and NO120 and almost constant regardless of the SiO2 thickness. This means that most of nitrogen atoms were localized at the SiC side of SiO2/SiC interface for NO10. On the other hand, the N 1s peak intensities of NO60 and NO120 were almost identical when the oxide thickness is below 0.5 nm. Furthermore, the N 1s intensity for NO120 increases with increasing SiO2 thickness above 1 nm and its slope is larger than that of NO60. These results suggest that nitrogen atoms are incorporated at only a small part of the interface in NO10 and by increasing the annealing duration to 60 min, the interface was mostly occupied by nitrogen (NO60). Hence, when the annealing duration was further increased to 120 min (NO120), the excess nitrogen atoms diffused into the SiO2 layer within a few nanometers from the interface since nitrogen atoms at the interface have already reached to a saturation point. Therefore, the slightly lower channel mobility of NO120-MOSFETs [1] can be explained by interface degradation owing to the diffusion of nitrogen atoms towards the SiO2 side.
[1] T. Hatakeyama et al., Appl. Phys. Exp. 10, 046601 (2017).
[1] T. Hatakeyama et al., Appl. Phys. Exp. 10, 046601 (2017).