Comparative Study of TID Irradiation Effect on SiC Planar and Trench MOSFET

In this work, the mechanisms of total ionizing dose irradiation (TID) induced charge collections are analyzed and compared between SiC planar and trench gate metal-oxidesemiconductor field effect transistor (DMOSFET and UMOSFET). The threshold shift and the blocking capability of the post-irradiated devices are strongly associated with degradation of the MOS channel regions. Furthermore, SiC UMOSFET with low dose irradiation of <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$100 \text{Krad}(\text{Si})$</tex> exhibits a higher degree of degradation of electrical characteristics than that of the DMOSFET with irradiation of <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$300 \operatorname{Krad}(\text{Si})$</tex>. For comparison, the fabricated DMOSFET shows negligible change in gate leakage current and stable blocking capability after <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$100 \text{Krad}(\text{Si})$</tex> irradiation. Also, the edge-corner topography of gate poly-Si in both of SiC MOSFETs is found to have influence on the formation of latent gate damage induced by TID irradiation. For purpose of deep understanding of these results, the charge interaction on both sides of the gate oxide is clarified by dynamic capacitance comparisons obtained by experimental and numerical methods. SiC UMOSFET with a large portion of the trench surrounded by p-type regions shows greater capacitance shift than the DMOSFET. It is indicated that the ratio of gate/p-type-regions overlap in one cell may have effects on the charge collection of post-irradiated devices. These results will provide meaningful guidance for the design and fabrication of a radiation tolerant SiC MOSFETs.