Research On The Mechanism And Reinforcement Of Total Ionizing Dose Effect Of Shielded Gate MOSFET

Shielded Gate Trench Metal-Oxide-Semiconductor Field Effect Transistor(SGT MOSFET),as a representative of medium and low voltage power devices,has the advantages of low power loss and fast switching speed.However,the research on the Total Ionizing Dose(TID)effect of SGT MOSFETs at home and abroad is still very rare.Therefore,this thesis explores the mechanism of total ionizing dose effect of SGT MOSFET by means of experiments and simulations,establishes a failure model,and puts forward anti-radiation reinforcement measures accordingly.The main contents and achievements of this thesis are as follows:Firstly,through the systematic experimental research on the total ionizing dose effect of SGT MOSFET,the variation law of its threshold voltage,on-resistance and breakdown voltage after being subjected to radiation is clarified.Next,the total ionizing dose degradation of SGT MOSFET is simulated and analyzed by Sentaurus.The results show that the most severe degradation behavior of SGT MOSFETs affected by total ionizing dose is the large reduction in threshold voltage and breakdown voltage.Among them,the threshold voltage decreases linearly under the influence of the total dose of radiation,and the breakdown voltage shows a"slow-fast-slow"degradation trend with the increase of radiation dose.According to the simulation results and theoretical analysis,the reasons why the electrical parameters of the device are degraded by radiation are explained.Based on the two-dimensional Poisson equation,an analytical model of the TID-induced electric field redistribution is established,which provides theoretical guidance for the breakdown voltage anti-radiation hardening.Then,based on the conclusions obtained from experiments and simulations,some anti-radiation reinforcement measures of SGT MOSFETs are proposed.From the perspective of structural parameter improvement,three reinforcement measures,namely,reducing the thickness of the gate oxide layer,reducing the thickness of the shielded gate oxide layer and reducing the doping concentration of the drift region,are proposed respectively.Among them,reducing the thickness of the gate oxide layer can suppress the threshold voltage drop after radiation,and the latter two methods based on the TID-induced electric field redistribution model can improve the breakdown voltage degradation phenomenon.Besides,a new structure named BLD(Buffer above Linear Drift)-SGT MOSFET with uniform lightly doped buffer layer and linearly doped drift region is proposed according to theoretical derivation.Compared with simply reducing the doping concentration of the drift region,the BLD-SGT MOSFET structure not only can better suppress the breakdown voltage degradation after total ionizing dose,but also has obvious advantages in on-resistance.Compared to conventional SGT MOSFET with the same on-resistance,BLD-SGT MOSFET achieves twice the breakdown voltage anti-radiation ability.In order to explore the stability of the reinforcement method of the BLD-SGT MOSFET structure,the effects of the doping concentration gradient k in the drift region,the Buffer layer thickness L_d1 and the Buffer layer doping concentration N_d1 on the basic performance and radiation resistance of the structure were studied respectively.Finally,from the perspective of process optimization,the GOX-last process and the sacrificial oxidation method are given,which are beneficial to obtain an oxide layer with fewer defects.