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4.5 Summary

The impact of various high-temperature processing steps on the charge state of the SiC/SiO2 interface was investigated using 4H-SiC n-MOSCAPs and CV measurements. By comparing the measured CV curves to an ideal, simulated CV curve, it was shown that during the processing of SiC/SiO2 based semiconductor structures a significant accumulation of positive charges occurs at the semiconductor-insulator interface. The build-up of positive charges starts after the deposition of the polycrystalline gate contact and continues in all additional processing steps, in which the sample is exposed to a high thermal budget with temperatures above 500 °C. The positive charge accumulation leads to a significant shift of the flatband voltage (math image). The observed flatband voltage shift (math image) ranges from \( \ac {dVfb} \approx \SI {0.3}{\V } \) after the deposition of the poly-Si gate contact at \( T \approx \SI {500}{\celsius } \), to approximately \( \ac {dVfb} \approx \SI {2.3}{\V } \) after the formation of the metal contact at a temperature of approximately \( T \approx \SI {1100}{\celsius } \).

The origin of these charges is still unknown. However, two possible candidates have been discussed:

To summarize, a significant amount of positive charge accumulates at the SiC/SiO2 interface during high-(math image) processing steps. The atomic origin of the charge build-up is still unknown but likely linked to hydrogen, which is incorporated during the poly-Si deposition. However, to enable a better understanding, further studies on the observed behavior are mandatory. Here, especially a combination with measurement techniques like secondary ion mass spectrometry (SIMS), which enable the analysis of the exact composition of the specimen, should be advantageous.

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