Design And Fabrication Of 4H-SiC MOSFET

Because of its excellent electrical and physical properties, i.e., wide band-gap, high electron saturation velocity, high critical electric field, and high thermal conductivity, 4H-Silicon carbide (SiC) becomes one of the materials for advanced next-generation power electronics for high frequency, high temperature and high voltage applications, which has made 4H-SiC metal-oxide-semiconductor field-effect transistors (MOSFET) a promising candidate for higher breakdown voltage, higher switching speed, lower on-resistance, better high-temperature and radiation environment capability devices. Recently, SiC device technology is rapidly maturing to a point where it can significantly impact the future of industrial electronics. This work focuses on the design and fabrication of 4H-SiC MOSFET, and the main contributions are shown as follows:Based on the survey of the research and fabrication of 4H-SiC MOSFET, the design and fabrication scheme of 1200V 4H-SiC MOSFET is realized. Through the Physics and Math calculation, the basic devices characteristics are gained. Furthermore, the parameters of the drift layer thickness and doping, the P well depth and doping, the JFET region width etc. are calculated.In consideration of the specific material features of 4H-SiC, a series of developed simulation models are introduced, especially for the mobility models, incomplete ionization model, anisotropic models, bandgap narrowing model etc. Caughey-Thomas mobility models, SIC4H0001 models and influence of interface states are introduced. Based on the platform of Silvaco TCAD, a great deal of simulation work are finished. Finally, the 15 and 20 FLRs structures gained with satisfied breakdown characteristics are reached. The working mechanism of FLRs structure is analyzed with electrical field distribution. The forward biased characteristics are also simulated and the basic turn-on, Ⅰ-Ⅴ and transfer characteristics curves are gained. A new design of non-uniform P Well is introduced, and improved turn-on characteristics are reached with a comparable breakdown voltage, which is analyzed with the energy band theory.A great deal of work is made on the fabrication process of 4H-SiC MOSFET. The simulation of ion implantation is performed with SRIM and the N+, P+ and P Well implantation schemes are reached. A good ion implantation result is gained through the ion implantation, activation annealing and SIMS experiments. Based on the Ohmic contact experiments, the method of forming the P and N Ohmic contact is reached simultaneously with the Ni/Ti/Al(30/80/30nm) metal system and 950℃/5min Ohmic annealing condtion.Finally, the fabrication flow is realiezed. Based on the results of simulation and survey, large devices layout of 1200V 4H-SiC MOSFET is achieved by L-Edit.