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

Abstract

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 ( V <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">BD</sub> ) and minimizes the specific ON-resistance ( R <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">ON,SP</sub> ). 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 V <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">BD</sub> by 2.5% and increasing R <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">ON,SP</sub> by 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 V <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">BD</sub> and R <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">ON, SP</sub> while maintaining an implantation window wider than the vertical SJ. The balance between R <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">ON,SP</sub> and 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 R <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">ON,SP</sub> , while maintaining an implantation window that is 7% wider.