Research On Characteristics Of SiC LDMOS Devices Based On BCD Process

With the continuous development of the power electronics industry,the demand for power semiconductor devices is increasing day by day,which not only requires better characteristics of the device itself,but also requires higher level of integration.While ordinary Si-based power devices have been continuously researched and developed,they are almost close to the physical limit of Si materials,and the advent of the third-generation semiconductor materials represented by Si C has immediately become a research hotspot in various semiconductor laboratories.At the same time,the development of integrated processes that can simultaneously fabricate bipolar devices,CMOS devices,and DMOS devices(BCDs)has also made it possible to achieve smaller device areas.Si C-based laterally diffused metal-oxide-semiconductor(LDMOS)devices have gradually gained attention due to their ability to achieve superior characteristics than Si-based devices and to achieve better integration through the BCD process.The purpose of this thesis is to study the reverse withstand voltage characteristics,forward transfer characteristics and forward amplification characteristics of 4H-Si C LDMOS devices.Si C LDMOS has stronger reverse blocking capability than ordinary Si-based devices,and because the structure of the device itself is more suitable for the BCD process,it can achieve higher integration.In this thesis,through the numerical simulation of LDMOS device,the influence of different process structure parameters on device characteristics is obtained.The main contents are as follows:(1)Theoretical analysis.Based on theory,the working principle of LDMOS device is analyzed,and the design basis is expounded.(2)Structural parameter design.Based on the theoretical analysis of LDMOS devices,the drift region,channel and gate oxide layer are designed,including specific parameters such as doping concentration,length and thickness in the region.(3)Device simulation.Based on the simulation software,the characteristics of the designed Si C LDMOS device are simulated and verified.Using the control-variable method,simulations are performed to analyze the effects of different covariates on device characteristics,such as drift zone doping concentration,drift zone length,channel doping concentration,channel length,gate oxide thickness,number of field-limited rings and field-limited ring doping concentration.The simulation results are analyzed,and the conclusions are as follows:(1)When the channel doping concentration increases,the threshold voltage increases,and the specific on-resistance increases,but has little effect on the breakdown voltage.The doping concentration of the channel should be minimized during design.(2)The channel length is reduced,and the specific on-resistance is reduced,but the smaller channel length will cause the device to have punch-through breakdown at low voltage.Therefore,when the reverse characteristics of the device are guaranteed to be normal,the channel length should be reduced as much as possible.(3)The thinner the gate oxide thickness is,the smaller the threshold voltage is,but the breakdown voltage of the device decreases accordingly.Therefore,after ensuring that the breakdown voltage meets the requirements,the thickness of the gate oxide should be thinner.(4)The lower the doping concentration in the drift region,the higher the breakdown voltage of the device and the higher the specific on-resistance.As the length of the drift region increases,the breakdown voltage rises,but a constant value exists and the specific on-resistance increases.(5)The number of floating field limiting rings increases,and the breakdown voltage of the device increases,but when the floating field limiting ring is too close to the drain,the breakdown voltage will drop.Therefore,the ring closer to the drain should be discarded in the design.(6)The doping concentration of the floating field limiting ring increases,and the breakdown voltage first increases and then decreases.Both larger and smaller doping concentrations reduce the electric field strength,thereby reducing the breakdown voltage.In this thesis,the reverse breakdown characteristics,forward transfer characteristics and forward amplification characteristics of LDMOS devices with different drift region doping concentration,drift region length,channel doping concentration,channel length,gate oxide thickness,number of floating field limiting rings and floating field limiting ring doping concentrations are studied.It has certain significance for the design and application of Si C-based LDMOS devices,especially to obtain the influence of the doping concentration of the drift region and the floating field limiting ring structure on the breakdown voltage of the device,which has reference value for improving the reverse withstand voltage characteristics of the device.