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Degradation of Electrical Parameters of Power Semiconductor Devices – Process Influences and Modeling

7.3 Comparison and conclusions

Fig. 7.8 directly compares the increase of the density of interface traps after PBTS and HCS.


Fig. 7.8: Increase of the density of interface traps for HCS and PBTS [Pob+14]. The characteristic labeled “PBTS 170 °C” was performed at 30 °C chuck temperature using the poly-heater only during the stress phase. All other measurements are performed at the chuck temperature indicated in the legend.

The difference in the virgin (math image) is either due to device-to-device variations or because the temperature dependence of the material parameters of (math image) and (math image) is neglected. However, it is evident that only HCS increases the density of interface traps measurable with CP. This indicates that HCS creates interface traps while PBTS creates only oxide traps. This is further supported by the voltage dependent shift in the transfer characteristics evident only after HCS, as compared directly in Fig. 7.9.


Fig. 7.9: Gate voltage dependent shift of the transfer characteristics after PBTS (top) or HCS (bottom).

The results are explained in the following way: Interface traps at the SiC-SiO2 interface have been reported to be passivated by nitrogen (N) atoms [McD+03]. Other work states that N bonds strongly to Si or carbon (C) atoms [Dar70; Nau+93]. It is therefore speculated that only the high energetic carriers during HCS are capable of dissociating an Si-N or Si-C bond. BTS, in contrast, causes a field and temperature dependent dissociation of precursor defects within the SiO2 which could be very similar to the mechanism in Si-MOSFETs.