The Study And Application Of 4H-SiC Ohmic Contact

4H-SiC has been a promising material for the application of high temperature, high frequency and high power devices due to its superior properties, such as wide bandgap, high breakdown voltage and high thermal conductivity. However, in the process of device fabrication, some difficulties still exist. One of the important processes is good ohmic contact formation. This thesis focuses on systematical study on ohmic contacts of 4H-SiC and relevant application on devices.Based on investigation on p- and n-type SiC ohmic contact, including the choice of metal system and the mechanism of ohmic contact formation, the Ni/Ti/Al ternary system is confirmed as contact metal scheme to form p-and n-type 4H-SiC ohmic contact simultaneously. Through numerous systematic experiments, the effect of different Ni layer thickness and annealing condition on p- and n-type ohmic behavior are studied. Ohmic contact formation is achieved with the specific contact resistance of 4.2×10-5 Ω·cm2 and 7.8×10-5Ω·cm2 for p- and n-type 4H-SiC, respectively. In addition, we use XRD, AES and AFM to analyze the mechanism of ohmic contact formation. The optimized p-type ohmic contact is applied to fabricate 3300V 4H-SiC PiN and the forward Ⅰ-Ⅴ characteristics is good.Based on the key processes of 4H-SiC MOSFET, ion implantation is studied. The simulation of ion implantation is completed by TRIM, and the implanatation condition of p+, p well and n+ region are obtained. By combination with ion implantation experiments, activation annealing experiments and optimized ohmic contact results, we developed the three key processes of 4H-SiC MOSFET successfully. In addition, the main preparation flow of 4H-SiC MOSFET is illustrated, which would be used to realize device fabrication.