Design And Reliability Research Of 100V Shield Gate Trench Power MOSFET

Power semiconductor devices are the core component of various electrical equipments.With the rise of fast-charging mobile phones,electric vehicles,brushless motors and lithium batteries,there is an increasing demand for medium-voltage metal-oxide-semiconductor field-effect transistor（MOSFET）.The shield gate trench metal-oxide-semiconductor field-effect transistor（SGT-MOSFET）,as a representative of medium-voltage power devices,uses the charge balance principle to break the silicon limit between the breakdown voltage and the specific on-resistance of conventional MOSFET.In the SGT-MOSFET,the electric field distribution in the drift region is optimized by using a shield gate as the field plate within the trench to assist the depletion of drift region.At the same time,the shield gate structure reduces the overlapping area between the gate electrode and the drain electrode,thereby greatly reducing the gate-drain capacitance.Therefore,the SGT-MOSFET possesses advantages of low conduction loss and fast switching speed,and occupies a large market share in the field of medium-and low-voltage MOSFETs.With rapidly increasing applications of SGT-MOSFET,its efficiency conversion and reliability have become an attractive research hotspot.In this thesis,the SGT-MOSFET devices with low conduction loss and high reliability are investigated in detail.The main research contents of this thesis can be summarized as follows.1.An SGT-MOSFET with a p-ring structure is proposed.In this structure,a p-type arc-shaped region is formed at the bottom of the trench by implanting boron ions after etching the trench.By adding the p-ring structure to the conventional SGT device,the vertical electric field distribution of the device is optimized,so that the electric field distribution at the bottom of the trench becomes more uniform.As a result,the reverse withstand voltage of the device is increased.Using the process simulation software TSUPREM4,the structural parameters of the device are optimized and simulated.It is determined that the device performance is optimal when the boron ion implantation dose of the p-ring structure is 4×10¹² cm^-2 at an implantation energy of 120 ke V.The tape-out test results show that,compared with the conventional SGT-MOSFET,C_ISS,C_OSS and C_RSS of the SGT-MOSFET with a p-ring structure are reduced by 29.5%,25.6%and 27.0%at a V_DS of 50 V,respectively,and Q_g is reduced by 26.0%.2.Based on the repeated unclamped inductive switching（UIS）avalanche test method,the reliability of SGT-MOSFET with a p-ring structure is studied in detail.At the same time,the UIS test is also carried out on the SGT device with the conventional structure for comparison.The static and dynamic parameters of the two devices are tested after applying repeated UIS avalanche stress for a fixed number of times,and the degradation mechanism of the devices is further studied by combining Technology Computer Aided Design（TCAD）simulation and high temperature recovery experiments.It is proposed that the device parameters degrade due to the hole injection into Si/Si O₂ interface at the avalanche state.Finally,two failure modes,thermally induced failure and gate oxide breakdown,are used to explain the failure mechanism of the device.3.An SGT-MOSFET with a sub-trench structure（ST-SGT）is proposed,which modulates the charge balance of the epitaxial layer by inserting a sub-trench between the deep trenches of conventional structure,so that the vertical electric field distribution becomes more uniform.Meanwhile,a double-layer epitaxial structure is adopted to further reduce the characteristic on-resistance of the device.The structural parameters of the novel ST-SGT device are optimized by TACD simulations,and the optimal parameters are determined as follows:the upper layer epitaxial resistivity is 0.23Ω·cm,the lower layer epitaxial resistance is 0.5Ω·cm,and the depth and width of the sub-trenches are 2.5μm and 0.5μm,respectively.Compared with the conventional SGT device,the figure of merit（FOM）value of the optimized ST-SGT device is improved by 19.6%.