Impact of UV Irradiation on Thermally Grown 4H-SiC MOS Devices

Abstract

The impact of ultraviolet (UV) light irradiation on thermally grown SiO2/4H-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 (VFB) shift, suggesting the generation of oxide charges and traps. Since the values of C-V hysteresis and VFB 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 SiO2/SiC structures. A detailed characterization of SiC-MOS capacitors with terraced SiO2 layers revealed that the UV-induced defects were located near the SiO2/SiC interface. The interfacial fixed charge density (QOX) was estimated to be 1.7×1012 cm-2 for the sample with UV irradiation, while that of the sample without UV irradiation was 1.0×1012 cm-2. Also, a slight increase was found in interface state density (Dit) due to UV irradiation. These results imply that the UV-induced defect generation correlates with residual carbon impurities at the SiO2/SiC interface.