Study On Failure Mechanism Of Super-Junction Mosfet Under Electrical Stress,Thermal Stress And Humidity Stress

Super-junction MOSFETs are popular in the field of power devices because of the unique PN column region instead of the single doped drift region,break the"Silicon Limit"of traditional silicon-based devices,and have lower specific on-resistance under the same voltage level.The advantage of super-junction structure is based on the premise of charge balance,but the charge balance itself is very fragile.In the service life of several years or even decades,the device will continue to age under the influence of the environment and its own,which will affect the charge balance of the device,making the performance of the super-junction device degenerate and the reliability decline.Therefore,it is of great significance to carry out reliability research on aging test of super-junction MOSFETs.This thesis focuses on one of the aging tests:high temperature,high voltage and high humidity reverse bias(H~3TRB)test,which affects the reliability of super-junction MOSFETs.It is found that super-junction MOSFETs are more likely to fail than traditional MOSFETs under this test condition;In addition,it is also found that the failure hotspots of the super-junction MOSEFT during the test are mainly concentrated at the edge of the gate bus in the transition region,and it is inferred that the failure is related to the termination of the super-junction MOSFET;The results of 80%drain voltage and 100%drain voltage H~3TRB tests are also compared.It is found that the effect of drain voltage in the failure process cannot be ignored.At the same time,an HTRB test was designd without the influence of moisture,and it was found that all devices passed the test.Based on this,it was inferred that moisture had a significant impact on the degradation of device performance.The electrochemical migration phenomenon was not observed in the above tests,and it is difficult to explain with the existing theory.Therefore,this thesis proposes the H~3TRB failure model,which is highly consistent with the experimental and simulation results.It describes the failure process from the perspectives of moisture,electrical stress,thermal stress,mechanical stress,and points out that the joint effect of moisture and electrical stress is the key factor leading to device performance degradation.Based on the H~3TRB failure model,this thesis also improves the super-junction MOSFET from the three aspects of packaging materials,the terminal structure of the super-junction MOSFET and the passivation layer.Reasonably adds field limiting rings and field plates,selects packaging materials with lower diffusion coefficient,and reduces the mechanical stress between the materials of the passivation layer.The improved chips have all passed the H~3TRB test without failure.