Structural Design And Characteristic Research Of Trench Gate Superjunction SiC IGBT

The SiC material has the advantages of wide band-gap,high critical breakdown electric field,high thermal conductivity,high electron saturation drift speed,etc.It is ideal for processing power semiconductor devices.Silicon carbide insulated gate bipolar transistor(SiC IGBT)not only has the excellent characteristics of IGBT high input impedance,high current density,saturation voltage reduction,low driving power,etc.,but also possesses high voltage resistance,high temperature resistance and corrosion resistance,anti-radiation and high working frequency.These properties make this material an ideal choice for application in high-voltage and high-current areas and very bright development prospects.During the design of SiC IGBT,improving the contradiction between the breakdown voltage and the on-state voltage drop has always been the focus of research.With regards to this background,this thesis designs trench-gate superjunction SiC IGBT and trench-gate semi-superjunction SiC IGBT,analyzes the working characteristics of these two structures simultaneously and optimize the structural parameters.The main efforts and contributions are summarized as follows:1.A trench gate SiC IGBT is designed in this thesis,and the influence on the blocking characteristics,conduction characteristics and turn off characteristics from the structural parameters,like drift region doping concentration,drift region thickness,P-body doping concentration,buffer layer doping concentration,and buffer layer thickness is studied.The two pairs of compromise relationships,between breakdown voltage and on-state resistance and on-state voltage drop and turn-off loss of the device,are analyzed,and a device structure with a good compromise relationship is selected subsequently.Eventually,a trench gate SiC IGBT with a threshold voltage of 14.1V,a breakdown voltage of 14.97kV,a on-state voltage drop is 4.16V when output current density is 100A·cm2,and a turn-off time of 30ns is obtained.2.For the purpose of improving the contradiction between the on-state voltage drop and the breakdown voltage,this thesis proposes a trench gate superjunction SiC IGBT structure.The addition of the superjunction structure makes the electric field distribution of the IGBT at the withstand voltage uniform,and has a small effect on the conduction characteristics of the device in the meantime.Therefore the compromise relationship between the on-state voltage drop and the breakdown voltage of the device is optimized.The simulation results show that the cell width and the doping concentration of the P-body have a significant effect on the conduction characteristics of the device.After analyzing the carrier concentration distribution of the device,it was found that this was caused by the reduction of the carrier concentration due to the lateral depletion layer of the P/N column squeezing toward the N column region.As a result of optimizing the structural parameters of the device,a trench gate superjunction SiC IGBT with a threshold voltage of 5.8V,a breakdown voltage of 16.25kV,a on-state voltage drop is 3.14V when output current density is 100A·cm-2,and a turn-off time of 27ns is obtained.Compared with the trench gate SiC IGBT,the breakdown voltage of the superjunction SiC IGBT is 128V higher,and its saturation voltage is reduced by 24.5%.3.It is difficult to manufacture deep P-pillar regions with SiC materials.In order to reduce the processing difficulty and improve the feasibility of actual production,this thesis proposes a trench gate semi-superjunction SiC IGBT structure.Designing the structural parameters,this thesis focuses on the influence of device characteristics from pillar doping concentration,pillar thickness and drift region doping concentration.In addition,the factor of charge imbalance in the pillar area is discussed,and its influence on the breakdown voltage and conduction characteristics of the device is analyzed.As a consequence of the optimization design,the threshold voltage of the trench gate semi-superjunction SiC IGBT is 4.57V,the breakdown voltage is 13.83kV,the on-state voltage drop is 3.03V when output current density is 100A·cm-2,and the turn-off time is 31ns.Compared with the trench gate SiC IGBT,the trench gate semi-superjunction SiC IGBT has a better compromise between the breakdown voltage and the on-state voltage drop,and its semi-superjunction structure can significantly reduce the difficulty of device processing.