The Design Of Power VDMOS Termination Structure

Power MOS field effect transistors have developed rapidly in the field of power devices.As one of the main components of power MOS,high-voltage VDMOS has attracted widespread attention from scholars at home and abroad.In the peripheral terminal protection structure,the concentration of the electric field lines caused by the junction curvature effect at the edge of the main junction is prone to cause early breakdown of the device,thus limiting the development of VDMOS in the high-voltage field.This paper proposes three different 700V VDMOS termination new structures around the problem of breakdown voltage,and simulates and analyzes them with the 2D semiconductor device simulation software Silvaco TCAD.(1)According to the design index of 700V VDMOS termination structure,design a suitable cell structure,and analyze the influence of each parameter on the cell performance through theory and computer simulation,respectively,Finally,the cell structure and main related parameters that meet the requirements are determined.(2)A new VDMOS termination structure with uniform shallow trenches is proposed.In this structure,the source field plate reduces the high electric field near the main junction and expands the depletion region.In addition,many electric field peaks are introduced in the shallow trenches under the field plate,which increases the average electric field strength on the surface,both increase the breakdown voltage of the device.Simulation results show that the breakdown voltage of this structure is 706 V at the termination length L_d=132μm.Compared with the conventional field plate termination structure,the breakdown voltage is increased by 119%,reaching 97%of the parallel plane junction(cell),which almost eliminate the effect of the edge curvature effect completely.(3)In order to further reduce the use area of the termination area and reduce costs,based on the uniform shallow trenches VDMOS termination structure,a non-uniform shallow trenches VDMOS termination structure was designed by changing the width,distance and height of the surface dielectric trenches.The simulation results show that the breakdown voltage of this structure is 702 V when the termination length L_d is105μm.Compared with the uniform shallow trenches termination structure with almost the same breakdown voltage,the termination length is reduced by 27μm,which is a decrease of 20.5%.(4)A surface variable doping terminal structure with SIPOS material is proposed.Two different concentrations of P-Top regions were injected on the surface of the terminal area,and a layer of SIPOS with high resistance characteristics was overlaid on the surface field oxygen layer to adjust the surface electric field distribution in the drift region.Simulation results show that the structure achieves a high voltage of 697.5V at a terminal length of 109μm,which is an increase of 18%compared with the conventional structure.