The Triangular Voltage Sweep Measurement And Improvement Of Mobile Charges In SiO₂ Layer Of SiC

The third-generation wide band gap compound semiconductor silicon carbide?SiC?has developed rapidly in the fields of materials and devices due to its high breakdown electric field,high saturation drift rate,and high thermal conductivity.Moreover,SiC is also the only compound semiconductor material capable of growing a silicon dioxide?SiO₂?layer through a thermal oxidation process,which further determines its uniqueness.However,the SiC MOS devices actually fabricated by SiC have serious high-temperature instability,which is manifested in the decrease of the breakdown field strength and the drift of the threshold voltage.These problems have always hindered the further development of SiC devices.After research,it was found that the threshold voltage drift is mainly caused by the mobile charge existing in the MOS oxide layer.Therefore,how to accurately measure the mobile charge concentration becomes a hot issue in the research of SiC devices.This paper considers that TVS method is an excellent method to measure the mobile charge concentration of Si system accurately,so referring to the testing theory of TVS method in Si system,by controlling the influencing factors of TVS measurement,the feasibility of the TVS method to determine the SiC MOS mobile charge concentration is verified,and the quasi-static equilibrium of the best test conditions for TVS method in SiC system is cleared.According to the influence of metal interface traps of SiC MOS capacitance on measurement accuracy,TVS method is improved and optimized in this paper.The sodium ions move differently in different directions between the two interfaces.After comparative analysis,sodium ions are more likely to leave the silicon carbide interface and require a larger electric field to leave the metal interface.The quasi-static conditions were found by controlling the scanning rate and the test temperature.The experimental results show that both the reduction of scanning rate and the increase of temperature can promote quasi-static equilibrium,and the two are mutually restrictive.Under the experimental conditions of this paper,when the temperature is 190°C,200°C and 210°C,the scanning rate is less than or equal to 20mv/s,34mv/s and 66mv/s respectively,and the movement of sodium ions from the semiconductor interface to the metal interface reaches quasi-static conditions,while the reverse movement has not yet reached quasi-static conditions.By comparing the TVS measurement results before and after optimization,the optimized calculation results and measurement results all achieved the expected results,and the measurement accuracy of the TVS method was significantly improved?My work provides ideas for obtaining the exact value of the mobile charge concentration of the SiC system,and lays the foundation for further development of the device threshold voltage.