SiC MOSFET Device Design And Research On Threshold Voltage Stability

With the development of semiconductor industry and the increasing requirement of power semiconductor,Silicon Carbide on behalf of wide bandgap semiconductor is widely concerned because it can be used in high temperature,high pressure,high frequency and irradiation environment.Different from Si devices,SiC devices have less energy loss and smaller volume,which can improve the energy conversion efficiency.At present,SiC MOSFET devices have been commercially produced in foreign countries.However,the domestic research is still insufficient.For planar SiC MOSFET devices,the high interface state density of SiC/Si O₂ leads to the threshold voltage drift,and the threshold voltage of devices is usually about 2-3V,which easily leads to spurious triggering.Apart from that,the differences of threshold voltage drift can reduce the efficiency of parallelization.Therefore,it is important to study the design and stability of high threshold voltage SiC MOSFET devices,which is of great significance to improve the reliability of SiC MOSFET devices.In view of the problem that the threshold voltage of planner SiC MOSFET is lower than expected,this paper designs a 1200V short channel SiC MOSFET device whose threshold voltage is higher than 3.5V and channel length is 0.2?m.Also,through the tests of hysteresis effect and BTI,the threshold voltage stability of the 1200V/80A SiC MOSFET device is studied.Firstly,based on the Silvaco TCAD simulation platform,the cell and terminal structure of 1200V short channel SiC MOSFET device is designed.The epitaxial parameters of short channel SiC MOSFET device are determined.The drift concentration is 8×10¹⁵cm^-3 and the thickness is 12?m.In order to solve the channel breakdown problem of short channel devices and the JFET pinch-off problem,the doping distribution of Pbase region is optimized by Silvaco simulator Athena and Atlas.Gaussian distribution is used for the Pbase doping with the surface impurity concentration is 2.6×10¹⁷cm^-3,the peak impurity concentration is 5×10¹⁸cm^-3,and the junction depth is about 710nm.Also,the N_csl is 8×10¹⁶cm^-3,the depth of CSL is 1.2?m,the T_ox is 30nm.As a result,a short channel 4H-SiC MOSFET device is designed,whose threshold voltage is 3.7V and specific On-resistance is 8.3m?cm²,and the saturation current of this device is reduced at the same time.Also,a variety of field-limited loop terminal structures are designed,and the blocking voltage of P+field-limited Ring is 1800V.Secondly,in view of the stability of SiC MOSFET threshold voltage,this paper completes the evaluation of 1200V/80A SiC MOSFET threshold voltage stability and respectively studies the hysteresis effect and BTI of SiC MOSFET threshold voltage for fast shift and permanent shift.In the test of hysteresis effect,the influences of some facts such as the starting gate voltage,the stopping gate voltage,the gate voltage scanning speed and the temperature are studied and the mechanism hysteresis effect is analyzed.Because of the device is shifting between open state(inversion)and close state(accumulation),the non-steady state of the semiconductor leads to the hole capture and emission at the moment the gate stress changes,which is the main cause of the hysteresis effect.In the test of BTI,the experimental and analytical study on NBTI and PBTI of SiC MOSFET devices is also carried out.It is found that the device degrades accumulatively as the time goes by under the stress of BTI and the degradation failure caused by NBTI is not negligibleAbove all,this paper designs a 1200V short-channel SiC MOSFET device and studies its threshold voltage stability,which has a certain reference significance for the design of SiC MOSFET devices.