| Super junction MOSFET is especially suitable for full bridge and half bridge circuit because of its low on-resistance and fast switching speed.It is widely used in DC charging station and high power supply.Compared with traditional power VDMOS devices,super junction MOSFET has a better trade-off between breakdown voltage and specific on-resistance,but its structure inevitably increases the junction area of parasitic body diode,which makes its reverse recovery characteristics worse.The softness factor of super junction MOSFET is smaller,which is easy to cause circuit oscillation or voltage overshoot and cause failure,which limits the application of super junction MOSFET in higher frequency system.Therefore,the optimization of the body diode of the super junction devices has become a common concern in the industry.This paper first introduces the development of super junction MOSFET.From the perspective of application and market demand,it expounds the research significance of optimizing the body diode of super junction MOSFET,and introduces the research status of the body diode optimized super junction MOSFET.Then,the working principle of super junction MOSFET is introduced,and its main dynamic and static parameters are analyzed.The reverse recovery principle of the parasitic body diode is analyzed from the point of view of the change of carrier concentration distribution with time,and the external and internal factors affecting the reverse recovery characteristics are deduced.Then the method of optimizing the reverse recovery characteristics of the body diode of the super junction device is summarized from the theoretical analysis.Then,based on the theoretical analysis results,the super junction MOSFET cell is optimized by using the simulation software.The simulation design of the super junction termination is carried out to get the super junction termination which meets the design requirements.And the influence of implant dose of p-pillar,carrier lifetime and N-buffer on the reverse recovery characteristics of the body diode is studied,and the optimization direction of this design is determined.Further,based on the simulation results and the mature process platform of the company,the process flow design of the super junction MOSFET devices is carried out.After determining the process flow,the key process parameters were optimized through experiments with the radiation dose,annealing temperature and time after irradiation taken as independent variables.The influence of radiation related processes on reverse recovery characteristics was studied,the simulation results were verified,the process tolerance was determined,and the optimized process flow and related process parameters were obtained.Finally,according to the optimized process flow,the wafer is manufactured,sliced and packaged.After packaging,the static parameters and reverse recovery parameters of the product are tested and compared with the original super junction MOSFET devices,which without optimized body diode.Parameters of the tape finished product meet the design index.Compared with the original super junction MOSFET devices,the static parameters are equivalent but the reverse recovery time is reduced by 34% and softness factor is increased by 91%. |
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