Impact of UV irradiation on thermally grown 4H-SiC MOS devices

摘要

The impact of ultraviolet (UV) light irradiation on thermally grown SiO_2/4H-SiC structures was investigated by characterizing the 4H-SiC metal-oxide-semiconductor (MOS) capacitors fabricated with and without UV irradiation onto the oxide layers. The UV irradiation was found to significantly increase a hysteresis in capacitance-voltage (C-V) characteristics and cause a positive flatband voltage (V_(FB)) shift, suggesting the generation of oxide charges and traps. Since the values of C-V hysteresis and V_(FB) shift depend on the UV irradiation time, the electrical defects were considered to be induced during UV irradiation. In contrast, UV irradiation caused no marked change for the reference Si-MOS capacitors, indicating that the generation of UV-induced electrical defects was an intrinsic property of thermally grown SiO_2/SiC structures. A detailed characterization of SiC-MOS capacitors with terraced SiO_2 layers revealed that the UV-induced defects were located near the SiO_2/SiC interface. The interfacial fixed charge density (Qox) was estimated to be 1.7×10~(12) cm~(-2) for the sample with UV irradiation, while that of the sample without UV irradiation was 1.0 × 10~(12) cm~(-2). Also, a slight increase was found in interface state density (D_(it)) due to UV irradiation. These results imply that the UV-induced defect generation correlates with residual carbon impurities at the SiO_2/SiC interface.