SiC epitaxial wafer is available for fabricating MOSFET devices, wafer specifications can be found in https://www.powerwaywafer.com/sic-mosfet-structure.html

1.  Epitaxial Pits

Epitaxial pits, as one of the most common surface morphology defects, have a typical surface morphology and structural profile as shown in Fig.1. The position of thread dislocation (TD) corrosion pits observed after KOH corrosion on the back of the device corresponds significantly to the position of epitaxial pits before device preparation, indicating that the formation of epitaxial pit defects is related to thread dislocations.

Fig. 1 Cross section diagram of epitaxial pit defects in the SiC epitaxial layer

2. Effects of Epitaxial Pit Defects on SiC MOSFET

The influence of epitaxial pit defects on the characteristics of MOSFET devices is analyzed as follows:

Fig.2 shows the statistical distribution histograms of five characteristics of devices with epitaxial pit defects. The blue dashed line represents the segmentation line of device degradation, and the red dashed line represents the segmentation line of device failure. It can be seen from this that the number of devices with epitaxial pit defects in SiC MOSFET samples is equivalent to the number of devices with triangular defects. The impact of epitaxial pit defects on device characteristics is different from that of triangular defects.

Fig. 2 Histograms of various characteristic distributions of SiC MOSFET devices with epitaxial pit defects

In terms of device failure, the failure rate of devices containing epitaxial pit defects is only 47%. Compared with triangular defects, the influence of epitaxial pit defects on the reverse leakage characteristics and gate leakage characteristics of the device is significantly reduced, with degradation rates of 53% and 38%, respectively, as shown in following table. On the other hand, the influence of epitaxial pit defects on threshold voltage characteristics, bulk diode conduction characteristics, and conduction resistance is greater than that of triangular defects, with degradation rates reaching 38%.

Overall, the morphology defects of epitaxial pits have a significant impact on the failure and characteristic degradation of SiC MOSFET devices. Devices with epitaxial pit defects have a lower failure rate of 47%. However, the influence of epitaxial pit defects on the threshold voltage, bulk diode conduction characteristics, and conduction resistance of the device is greater than that of triangular defects.

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