Research On Surge Failure Mechanism Of 4H-SiC PiN Diode

Compared with traditional Si PiN power diodes,4H-SiC PiN power diodes have advantages in breakdown voltage,switching speed,current density,and junction temperature tolerance.However,in the actual application process of 4H-SiC power PiN diodes,it is inevitable that they will experience high current,overshoot voltage and other working environments,resulting in micro or macro damage in the device,which will affect the reliability of the device.In recent years,the relevant research results of the SiC PiN diode surge capability indicate that the self-heating effect is closely related to the surge resistance of the device.However,the influence of the changes in the internal defects of the device on the static electrical parameters and the surge current resistance has not been considered.This article focuses on the above problems,and the main work is as follows:In this paper,the reliability of the surge current of the 4H-SiC PiN diode developed by our research group is studied.The device performs a single pulse surge current experiment at room temperature.The results show that the surge current is 17A(about 6800A/cm²)When the electrical performance of the device is degraded.When the surge current increases to20A,the turn-on voltage increases from 3.45V to 4.1V,and the breakdown voltage decreases from 2400V to 1820V.During the surge current stress test,the device is in a high-temperature and large-current working environment for a short period of time,so it is easy to produce new defects.This paper first studies the effect of Z_1/2 and EH_6/7two kinds of body defects on the conduction characteristics of the device.Simulation results show that these defects will act as traps and recombination centers for electrons and holes,will reduce the density of free carriers,and introduce recombination current into the device,resulting in degradation of conduction characteristics.Subsequently,interface traps and interface fixed charges were added to the SiC/SiO₂ interface in the JTE terminal area.The simulation results showed that there were hole trapping traps or positively charged fixed charges at the interface.When there is an electron trap type trap or a negatively charged fixed charge,the electric field concentrates and shifts to the outside of the JTE terminal area.This shows that when the effective charge density at the interface changes,the blocking characteristic degrades because the effective JTE concentration deviates from the optimal concentration.Through the C-V test before and after the surge and the simulation results,it can be seen that the positive charge introduced by the surge stress at the Si O₂/SiC interface of the termination area is the cause of the degradation of the reverse breakdown voltage.To further explain the surge degradation mechanism of 4H-SiC PiN diodes,the defects were characterized qualitatively by deep level transient spectroscopy(DLTS).The DLTS test results show that there is a defect level inside the device before the experiment,which is located at E_C-0.171ev,which is caused by Al impurities implanted on the surface of the anode region.After the experiment,a new defect energy level was generated,located at E_C-0.515ev,and related research showed that the energy level at this position in the SiC material was due to the Z_1/2 defect caused by the C vacancy.Therefore,it can be concluded that the surge current stress induces additional Z_1/2 defects.The existence of Z_1/2 defects reduces the minority carrier lifetime in 4H-SiC PiN diodes,which leads to an increase in recombination current,on-resistance,and ideal factors,and the forward conduction characteristics of the device deteriorate.The section processing after the surge test found that the damage of the metal in the active area is the main limitation of the surge reliability of the SiC PiN diode.Therefore,in order to improve the ability of the device to resist surge current,this paper proposes to replace the original electrode material of the device from aluminum to silver with better thermal conductivity and higher melting point.The simulation results show that using silver as the electrode material can theoretically improve the surge current resistance by 16.7%.The second solution is to do impurity compensation implantation in the anode region of the4H-SiC PiN diode.After the implantation,it is found that the device's conduction characteristics are improved,the surge IV curve hysteresis is reduced,and the thermal power consumption is reduced to the original 89%.This method can improve the anti-surge current capability of the device to a certain extent.