Optimization Design Of 650V Power MOSFET

Power MOSFETs are one of the most widely used semiconductor devices.Vertical double-diffused field effect transistors（VD-MOSFETs）are mainly used in high voltage and low current applications.The breakdown voltage is one of the most important parameters of power semiconductor devices.It is often determined that the magnitude of the reverse breakdown voltage is the termination of the device.When size of chip is determined,length of termination will affect the variation in the on-resistance,and the variation of on-resistance directly affects the breakdown voltage.In order to improve the contradiction between the on-resistance and the reverse breakdown voltage,it is proposed to optimize the on-resistance which to change the structure of traditional termination and to shorten the length of termination.Combined with the basic principle of pn junction,the optimal value of the epitaxial parameter is calculated by the optimal formula of on-resistance and breakdown voltage.The breakdown voltage is decided the epitaxial parameters in the cell region,and the lateral withstand voltage of the device is determined by the termination.The variable lateral doping technology,the implantation dose is changed by the different mask size.Finally,a gradient p-type region with junction depth and doping concentration is formed at the main junction.The p-type region is fully depleted when operating in the reverse breakdown region to maximize the radius of curvature at the edges of the depletion layer.According to principle of the cylindrical junction and spherical junction,the larger curvature radius of the cylindrical junction,the closer it gets to the breakdown voltage of parallel planer junction.The device of 650V floating field ring（FFR）and variable lateral doping（VLD）structure termination was designed by the computer process simulation software Sentaurus TCAD.The simulation results show that length of variable lateral doping termination is 118μm and length of floating field ring termination is 132μm.Compared to the floating field ring termination,the length of variable lateral doping termination is shortened by 10.6%,and the on-resistance is reduced by 13.1%.The breakdown voltage of floating field ring termination is 679.5V,the breakdown voltage of variable lateral doping termination is increased by 3.0%to 700V.The maximum electric field of the FFR structure termination is 2.76×10⁵V?cm^-1,and the maximum electric field of the VLD structure termination is 2.68×10⁵V?cm^-1.Therefore,the decrease of electric field improves the stability and reliability of the device.Finally,layout design software L-edit was used to complete the mask design of650V VDMOS,and we had completed the tape-out work.At the same time,the threshold voltage,on-resistance and breakdown voltage test board was completed by the circuit PCB design software Altium Designer 10.The test results for one sample showed that the breakdown voltage was 693.9V,the on-resistance was 3.37Ω,and the threshold voltage was 3.05V,between of which met the design specifications.In addition,the process of VLD structure termination is relatively complicated,requires an additional layer of mask,and is difficult to design.