The Study On Body Termination For High-Voltage SiC PiN Power Diode

Traditional Si power devices,limited by material characteristics,no longer meet the requirements of high voltage,high temperature,and radiation resistance in high-speed rail transportation,new energy vehicles,aerospace and other fields.Due to the wide band gap,high critical electric field,and high thermal conductivity of SiC materials,SiC power devices have been widely studied and accelerated commercialization.The high-voltage 4H-SiC PiN power diode is one of the main research directions of power devices.It has the characteristics of large breakdown voltage,small on-state voltage drop,and low reverse leakage.At present,the compound junction termination extension(JTE)termination is used to obtain the high voltage in PiN diodes,but the interfacial charge and strong surface electric field degrade the breakdown characteristics.At last the breakdown voltage stability of the device is poor.In this paper,a new type of body termination technology for high voltage SiC PiN power diode is studied to realize the wide JTE doping concentration window and improve the breakdown characteristics of devices.The study is detailed as follows:First,the physical process of the reverse breakdown design of the high-voltage SiC PiN power diode is briefly introduced.The relationship between the key parameters(drift region thickness,doping concentration)and breakdown voltage of the ideal device is analyzed by theoretical calculations.For the punch-through PiN diode with a design target of 3k V,the optimal parameters of drift region are doping concentration of 3×10¹⁵cm^-3 and thickness of30?m.By solving the Poisson equation,the field crowding effect at the edge of device is proved,and the commenly termination technologies which are used to suppress the field crowding are introduced.Due to high breakdown efficiency,simple process and low cost,JTE is chosen in this work.The device models in sentaurus TCAD for calculating the breakdown characteristics of devices are briefly introduced.Second,the effects of humidity,temperature and electrical stress on the JTE stability of SiC PiN diodes are analyzed in wet-heat cycle experiments and high-temperature reverse bias experiments.The result of the wet-heat cycle experiments shows that under high humidity and low-temperature cyclic impact stress,the breakdown characteristics of the device remain unchanged.The reason is that JTE keep stable by the protection of the passivation layer and the incompletely sealed characteristics of the plastic packaging material.The result of high temperature reverse bias experiments shows that the reverse characteristics of the device are degraded under the combined effect of high temperature and electrical stress.Through simulation analysis proves that the interface state of the device slowly captures electrons under the action of high-temperature and electrical stress,so it increases the effective doping concentration of JTE.The too high effective doping concentration of JTE exacerbates the electric field crowding at the outer edge of JTE,and eventually causes the premature breakdown in device.For high-voltage devices working under electrical and high-temperature stress,the termination should have a wide optimal JTE doping concentration window.In this way,the stability of the device's reverse withstand voltage will be improved.Furthermore,based on simulation of the body single zone JTE(B-SZ-JTE)termination,the mechanism of the modulated middle layer is analyzed and parameters of the modulated middle layer are optimized.A physical model of compensation between the interfacial fixed charge and the modulated middle layer is established,and the migration mechanism of the optimal JTE doping concentration of the B-SZ-JTE termination under the action of the interfacial fixed charge is revealed.Different from the surface single zone JTE(S-SZ-JTE)termination,the optimal JTE doping concentration of the B-SZ-JTE termination can be controlled by adjusting parameters of the modulated middle layer under the compensation mechanism.The potential breakdown risk of the device was also reduced by optimizing parameters for regulating the coverage area of the modulated middle layer.At last,based on the mechanism of modulated middle layer in the B-SZ-JTE termination,the breakdown characteristics of the body multiple floating zones JTE(B-MFZ-JTE)termination with easier control in preparation process are studied.The modulated middle layer assists the MFZ-JTE to fully deplete,which makes the macroscopic electric field distribution more balanced in device,and ultimately effectively improves the breakdown characteristics of the B-MFZ-JTE termination.Compared with the traditional S-MFZ-JTE termination,the B-MFZ-JTE termination has the following advantages:1)wider 3k V JTE doping concentration window W_{3k V-JTE}=1.4×10¹⁷cm^-3,an increase by 27.3%;2)an optimal JTE doping concentration window that the breakdown voltage is unchanged in this JTE window and maintains the maximum breakdown efficiency;and 3)lower peak electric field at the oxide interface,a decrease of the maximum interfacial electric field by 45%.Therefore,it is easier to achieve high breakdown efficiency and stable breakdown voltage under the process for the device with the B-MFZ-JTE termination.