Optimization of 1700-V 4H-SiC Superjunction Schottky Rectifiers With Implanted P-Pillars for Practical Realization

A class of vertical 1700-V 4H-SiC superjunction (SJ) Schottky diodes have been simulated and optimized, producing results that are below the unipolar limit, while also ensuring practical and costeffective realization. A conventional vertical SJ is obtained in T-CAD software, using an n-type drift region of 9-μm and etching trenches through this region to the substrate to leave isolated mesa structures. P-columns are then created through implantation into the trench sidewalls. The charge-balanced SJ diode maximizes the breakdown voltage ( VBD) and minimizes the specific ON-resistance ( RON,SP). However, a narrow implantation window would make the vertical structure hard to fabricate. Therefore, by introducing an angled trench sidewall ( α), 10° off vertical, a graded charge profile is introduced reducing VBDby 2.5% and increasing RON,SPby 9%. However, the implantation window is widened by 20% compared with the vertical device, making the successful production of the devices more likely. To rebalance the 10° structure, a 1- μm region of increased n-type doping is introduced at the top of the n-pillar. This partially recovers the lost VBDand RON, SPwhile maintaining an implantation window wider than the vertical SJ. The balance between RON,SPand implantation window can be tuned depending on the doping of the 1- μm top region. The 10° structure can also be rebalanced by introducing a second 4- μm region of intermediate n-type doping, underneath the 1- μm surface region. This recovers RON,SP, while maintaining an implantation window that is 7% wider.