Research Of Breakdown Stability For SGT MOSFET

Power MOSFET has the advantages of fast switching speed,high input impedance,good thermal stability and high working frequency.It is widely used in consumer and industrial fields,mainly for power conversion.As a typical representative,the SGT MOSFET(Shield Gate Trench Metal Oxide Semiconductor Field-effect Transistor)device enhances the two-dimensional depletion of the drift region of the device through the shielded gate electrode in the body,and optimizes the position of the peak electric field in the drift region of the device.Under the condition of pressure,the resistivity of the grown epitaxial layer can be reduced and the on-resistance can be reduced.At the same time,the overlap area of the gate electrode and the drain electrode is reduced due to the introduction of the shielded gate electrode,so that the gate-drain capacitance is significantly reduced.SGT MOSFET combines the advantages of low power loss,high switching speed,and good high frequency characteristics,and has become the mainstream switching device in the current medium and low voltage field.Due to the introduction of shielding gate,time-dependent avalanche breakdown instability exists in SGT,which has seriously affected the reliability of SGT devices.So far,the research on the breakdown stability of SGT is still incomplete,and there is no effective design scheme that can guide how to improve the breakdown stability of such devices.Based on this,this topic studies the breakdown stability mechanism of SGT MOSFET,analyzes the influence of design and process factors on its breakdown stability,and proposes an optimization scheme.The main work of this paper is as follows:1.Study on the breakdown instability mechanism of SGT MOSFET.The electrical characteristics of SGT MOSFET devices are analyzed.Based on the existing research,the breakdown instability mechanism of SGT MOSFET is analyzed,including the depassivation reaction of cell region and the effect of the width of transition region on the breakdown stability.Secondly,the related models of the depassivation mechanism and the shortcomings of the existing theories are analyzed,and the experimental data of the breakdown and instability of two SGT MOSFET device samples of 40 V and 150 V are obtained through testing.2.Based on the design parameters,process flow,breakdown instability experimental data and depassivation reaction model of the device sample,the breakdown instability phenomenon of SGT MOSFET was reproduced through TCAD simulation and the machine was analyzed and improved.The effects of design and process factors,such as doping concentration in drift zone,injection dose of Pwell,depth of groove,width of cell,thickness of gate oxide layer and thickness of shielded gate oxide layer,on breakdown stability were analyzed.Then the influence of the width of the transition zone on the breakdown voltage was analyzed by 3D simulation,and the design window was obtained.Based on the above,the design scheme of optimized breakdown stability was proposed,and the layout of the device was studied and designed.The 40 V SGT MOSFET device was actually made.Compared with the original structure,the breakdown stability was optimized to a certain extent under the condition that the basic parameters of the device met the design requirements.