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This study examines the impact of supercritical fluid treatment on 1200V 4H-SiC vertical double diffusion MOSFETs (VD-MOSFETs). When exposed to pure carbon dioxide or carbon dioxide mixed with nitrous oxide, there is a significant increase in the improvement ratio of drain current, which is contingent upon channel mobility but has no effect on threshold voltage. Conversely, the degradation of drain current caused by ammonia gas treatment is attributed to a reduction in channel mobility. Furthermore, the treatment with pure carbon dioxide or carbon dioxide mixed with nitrous oxide effectively passivates shallow defects, while the presence of hydrogen atoms in ammonia gas leads to an increase in shallow defects.

In this study, the new method featuring low-temperature and high-pressure hydrogenation (LTHP-H) which is applied to 0.13- $\mu \text{m}$ bipolar-CMOS-DMOS technology is compared with the conventional 400 $^{\circ }\text{C} \text{H}_{{2}}$ annealing, and the technology without H2 treatment is used as a control group. It is found that the LDMOS processed by the LTHP-H has such following improvements as 11% increase of the on-state performance, which is 3% higher than that of H2 annealing, 61% increase of the interface quality and about 5 to 10 % improvement of the hot carrier degradation (HCD). The method not only lowers the process temperature, but also helps H2 enter the supercritical fluid state to form a large number of free radicals. Therefore, the interface quality is well passivated and Si-H bonds with stable strength are formed, which inhibits the generation of HCD accordingly. With the results of this research, this technology can improve the performance and reliability of LDMOS.