Design Of Low-Voltage Split-Gate Trench MOSFET(Master Thesis)

Power semiconductor device is the core for electrical energy conversion and circuit control of electronic power devices.With the development of new energy vehicles and smart homes,the market's demand for power semiconductor devices continues to grow.In the current,domestic industry is upgrading and the country is giving strong support to local power device companies from multiple dimensions such as capital,policy,and industrial chain.With the continuation of the Sino-US trade dispute,the wave of domestic devices replacing imported devices has emerged.As a Trench MOSFET,the structure of a split gate is creatively adopted by SGT MOSFET(Split-Gate MOSFET).Through this structure,the capacitance of gate and drain is converted into the capacitance of gate and source,which greatly reduces the capacitance of gate and drain and brings a large ratio of input capacitance/Miller capacitance.So that SGT MOSFET has excellent performance in the field of medium and low voltage power MOSFET.But at present,there is still a certain gap between domestic products and foreign products of the same type,so it is of great practical significance to develop a low-voltage SGT MOSFET with excellent electrical parameters and excellent performance.Firstly,the structural characteristics and working principle of SGT MOSFET are analyzed from a theoretical perspective,and suitable theoretical models are builded for the static and dynamic characteristics of the device,especially the equivalent plate capacitance parallel model is established for the gate capacitance of the device.Through the establishment of models and formula derivation,the main influencing factors of various electrical parameters are studied.And then the cell structure optimization scheme is determined based on the on-resistance,breakdown voltage and capacitance characteristics of the device.Secondly,the process simulation software Tsuprem4 is used to simulate cell size,epitaxial layer thickness,and split gate length of the device,and by means of control variables the simulation results under various bias conditions are compared and analyzed to determine the optimized cell structure of the device.Subsequently,the SGT MOSFET is compared with the Trench MOSFET under the same withstand voltage and the results show that the Miller capacitance of SGT MOSFET is 84%lower than that of Trench MOSFET,the input capacitance is 98%higher than that of Trench MOSFET when V_ds is 10 volt,so that the SGT MOSFET has a high ratio of input capacitance/Miller capacitance.Then,based on the determination of the cell structure of the device,combined with the actual process flow of SGT MOSFET,simulation comparisons are made on the process parameters such as polysilicon gate deposition,control of gate oxide thickness,P body implantation concentration and annealing time.After considering the on-resistance,breakdown voltage and gate capacitance,the overall process flow of the device is optimized,and the final optimized SGT MOSFET is obtained.Comparison with similar products on the market shows that the technological design of the low-voltage SGT MOSFET designed in the thesis is reasonable,and the electrical parameters of the device meet the design requirements.Finally,a multi-step sidewall oxide structure is applied to the optimized SGT MOSFET with reference to the relevant design and the simulation results show that the on-resistance of the multi-step SGT MOSFET is further reduced.