A Simulation Study Of Interfacial Properties Of SiO₂/4H-SiC MOS

SiC MOSFET plays an important role in high-power,high temperature and other applications due to the unique and excellent structure and properties of SiC materials.However,the existence of high trap concentration severely limits the device of its mobility and affects the device threshold voltage stability,which affected the device operating frequency,reliability and other properties.What's more,the understanding of influence mechanism of traps on capacitance and electrical properties of devices is incomplete at home and abroad.Therefore,it is very important to explore the influence mechanism of trap charge on MOS capacitors and the electrical characteristics of devices to explain the common experimental phenomena and promote the devices SiC MOSFET development.In this paper,research work carried out from the following several aspects:Based on the Sentaurus software,a simulation model of channel electron mobility in 4H-SiC n-MOSFET anisotropic inversion layer was established.The model includes impurity ionization,lattice,surface phonon,interface roughness and interface Coulomb scattering mechanism on the channel electron mobility.The simulation results are in good agreement with the experimental results.Then,the influence of each scattering mechanism on the mobility and its relationship with temperature were analyzed by this model.The results show that bulk scattering,interface rough scattering and interface Coulomb scattering are the main scattering mechanisms to limit the mobility.In the low field,the interface Coulomb scattering plays a major role,but in the high field,the interface rough scattering is the decisive factor.The effect of the bulk scattering on the mobility is small but not negligible.The effect of the surface phonon on the mobility is smaller and negligible and will not affect the simulation results.The bulk scattering mobility has a negative temperature coefficient and plays a major role at high temperatures.The surface phonon scattering mobility has a negative temperature coefficient,and the contribution to the channel electron mobility is small and negligible.In the low field,the interface rough scattering mobility can be regarded as temperature independent,but with a more obvious negative temperature coefficient in high field.The interface Coulomb scattering mobility has a positive temperature coefficient and plays a major role at low temperatures.The influence mechanism of three kinds of traps charge on the MOS capacitor is analyzed from trap energy level position and trap concentration.It is found that the interfacial traps mainly affect the accumulation and depletion regions of the C-V curve.The shallow-level interface traps mainly affect the MOS capacitance and the deep-level interface traps to drift the C-V curve.In addition,the existence of near interfaceial traps leads to the phenomenon of hysteresis in the forward and backward scanning C-V.As the trap energy level distance increases from the bottom of the SiO₂ conduction band,the hysteresis voltage increases first and then decreases.This is because the trap is far from the bottom of the SiO₂ conduction band,the closer to the SiC conduction band,the more electrons tunneled into trap energy level and be captured,the greater the hysteresis voltage,but as the trap farther from the bottom of the SiO₂ conduction band,the trap's electron capture rate is getting smaller,the electron trapped charge density decreases,the smaller the hysteresis voltage.High density interface traps will not only affect the size of the MOS capacitor,but also the C-V curve drastic drift.When the interface edge density is equal to 1×10¹³?88?^-20)(1^-1,the CV curve drift is about 0.1 V,the interface trap density is greater than 1×10¹³?88?^-20)(1^-1,the CV drift increases rapidly and the slope of the curve becomes slower.When the near interfaceial trap concentration is less than 5×10¹⁸?88?^-3,the hysteresis voltage is relatively small,which has little effect on the flat voltage of the C-V curve and the threshold voltage of the device.When the near interfaceial trap concentration is equal to 5×10¹⁸?88?^-3,the hysteresis voltage is about 0.3 V,but when near interfaceial trap concentration is larger than5×10¹⁸?88?^-3,the hysteresis voltage rapidly increases,the flat voltage of the CV curve and the threshold voltage of the device will increase rapidly to affect the performance of the device.The fixed charge of the oxide layer only affects the flat voltage of the C-V curve.When the oxide density of the oxide layer is less than 1×10¹²?88?^-2,the curve drift is small,the density is equal to 1×10¹²?88?^-2,the curve drifts about 0.1 V,but when the density is greater than 1×10¹²?88?^-2 drift increases linearly,which can be critical to the reliability of the device.The way of the three traps to linit mobility are discussed by comparing the mobility of the shielded Coulomb scattering model or not with ideal mobility.The reasults show that interfacial traps limits the mobility by capturing electrons and Coulomb scattering,and the effect of electron trapping increases with the increase of trap concentration,and finally the together with Coulomb scattering used to limit the electron mobility.Both the near interfaceial traps and the oxide fixed charges are mainly limited by mobility through the Coulomb scattering,but compared with interface traps the degree of restriction on the mobility is negligible.The effect of the trap on the device with the temperature change is simulated.Firstly,the introduction of the interface trap will lead to n 4H-SiC MOSFET field-effect peak mobility with the temperature rise first and then decline,this is because the Coulomb scattering mobility has a positive temperature coefficient and dominates at lower temperatures,the field-effect electron mobility varies with the temperature according to the Coulomb scattering mobility,that is,with a positive temperature coefficient,and then with the temperature increasing the bulk scattering mobility is increasing and dominates finally,and the field effect mobility decreases with the increase of temperature.For near interfaceial trap charges,the introduction of traps at low temperatures?less than 300??has little effect on the threshold voltage,but at high temperatures?greater than 300??it can lead to severe temperature dependence of the device threshold voltage and then affect the reliability of the device.The effect of the fixed charge on the threshold voltage of the device does not vary with temperature.