Design and fabrication of high-voltage n-channel DMOS IGBTs in 4H silicon carbide

Xiaokun Wang, Purdue University

Abstract

The IGBT is a bipolar device. Structurally, it is very similar to the vertical MOSFET, except that the substrate of the MOSFET is replaced by a layer with opposite polarity. In the on-state, the drift region of the IGBT is conductivity modulated, resulting in a linear dependence of the power dissipation on the on-current, in contrast to the quadratic dependence of the MOSFET. This property makes the IGBT superior to the MOSFET at high blocking voltage, low frequency ratings. The high-voltage n-channel DMOS IGBT was fabricated in 4H-SiC, due to the preferred properties of the material. DMOS design is adopted because it is easier to fabricate and has demonstrated good performance. The physics of operation of the IGBT was studied. Design issues were addressed. A novel inverted growth process was employed, resulting in the fabrication taking place on the C-face. Studies show that thermal oxides on the C-face annealed in NO have a lower breakdown field than those on the Si-face. The finished devices were characterized using an HP4156 Semiconductor Parameter Analyzer. The best device could carry 27.3 amps per centimeter squared current density at a power dissipation of 300 watts per centimeter squared. Simulation shows that with better contacts, this current density could be increased to around 50 amps per centimeter squared. Future studies on C-face thermal oxides are proposed to improve the oxide quality.

Degree

Ph.D.

Advisors

Cooper, Purdue University.

Subject Area

Electrical engineering

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