Performance analysis of 4H-SiC super-junction devices: impact of trench angle and improvement with multi-epi structure

Abstract

This paper studies the impact of the trench angle on SiC super-junction device performance through the numerical simulation. Devices with different structure parameter sets (mesa width, epi doping) targeting different voltage ratings have been considered. It is found that with the optimum epi doping, the highest Baliga’s figure of merit (BFOM) is always achieved at the trench angle of 90°. The advantage of 90° trench angle can be further increased by reducing the mesa width (MW). However, the 90° trench is hard to be achieved through the current fabrication technology. Once the trench angle is reduced slightly, the device BFOM will decrease evidently especially for high voltage devices. At this condition, the reduction of mesa width does not necessarily produce higher BFOM. For example, at the trench angle of 89° and trench depth of 25 μm, the BFOM of the device with MW = 3 μm is substantially higher than that of the device with MW = 1 μm. Such a phenomenon is contrary to conventional theory, which is crucial for device design. Finally, in order to improve the performance of devices with non-90° trenches, the multi-epi structure is proposed. With such a novel structure, significant improvements have been observed in the simulation. The BFOM increments for 2 kV, 3.5 kV and 5 kV voltage rating devices are 27.4%, 60.8% and 102.6% respectively, demonstrating the superiority of the proposed multi-epi structure for SiC super-junction devices.