| Blocking high voltages is the most important characteristic of power semiconduc-tor devices.The reverse blocking performance of power semiconductor devices can be drastically degraded by various non-ideal factors in the chip edge region of the actual fabrication process.Junction termination techniques are designed to weaken the effects of these non-ideal factors.Variation of Lateral Doping(VLD)termination is one of the most common termination design methods for medium and high voltage power devices,which can effectively extend the depletion region and relieve the electric field concen-tration by injecting a region of gradual impurity concentration at the edge of the device,so that the device can exhibit better blocking performance.The VLD termination has a smaller termination area compared to the field-limited ring and field plate termination,and has better blocking performance compared to the JTE termination,and is less sensi-tive to the dose shift of the termination impurity injection.Industry and academia have been working to improve VLD terminations to achieve better blocking performance and reliability.The most reported optimization approach is the use of composite structure of VLD terminations.This optimization method is not only difficult to achieve in terms of manufacture process,but also brings higher fabrication cost.Modifying the impurity concentration distribution inside the VLD termination to achieve better blocking perfor-mance is a simple,low-cost optimization solution with high application value,but few related studies have been reported.In this paper,we propose a square root distributed impurity concentration distribution design for VLD terminations,which can not only be widely used in power devices with different breakdown voltage levels,but also simple to implement without adding extra steps in the process.In TCAD simulation and tape out experiments,the square root distributed VLD termination has obvious advantages over the traditional linear impurity concentration distribution design.In addition,the square root distributed VLD termination has the best resistance to the reliability problems caused by the degradation of the field oxide layer performance.The main contents of this paper are as follows:First,through theoretical analysis and mathematical modeling,improved linear dis-tribution and square root distribution VLD termination design methods are proposed,and they are compared and analyzed with the most commonly used linear distribution VLD terminations in the industry today.And specific mask designs are given.Next,TCAD simulations of the above three VLD terminations are verified on a1500(1 VDMOS cell.This paper also proposes a method for TCAD simulation to as-sess the reliability of VLD terminations.The simulation results show that the square root distributed VLD termination achieves the best blocking performance and reliability per-formance,and can save the termination area to a great extent.Finally,three VLD termination designs based on 1500(1 VDMOS devices were tested in the tape out and HTRB reliability tests.The square root distributed VLD termination group obtained the highest blocking voltage of 1689(1,and it was the only group that passed the 1200(1,168?,and 100-110-120-125~°HTRB tests among the three schemes.The experiment not only confirms the TCAD simulation results,but also proves once again the superiority of the square root distribution design. |
