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- $\mu \text{m}$ 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 ( ${V}_{\text {BD}}$ ) and minimizes the specific ON-resistance ( ${R}_{{\mathrm{\scriptstyle{ON}}},\text {SP}}$ ). However, a narrow implantation window would make the vertical structure hard to fabricate. Therefore, by introducing an angled trench sidewall ( $\alpha $ ), 10° off vertical, a graded charge profile is introduced reducing ${V}_{\text {BD}}$ by 2.5% and increasing ${R}_{{\mathrm{\scriptstyle{ON}}},\text {SP}}$ 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- $\mu \text{m}$ region of increased n-type doping is introduced at the top of the n-pillar. This partially recovers the lost ${V}_{\text {BD}}$ and ${R}_{{\mathrm{\scriptstyle{ON}}},\text {SP}}$ while maintaining an implantation window wider than the vertical SJ. The balance between ${R}_{{\mathrm{\scriptstyle{ON}}},\text {SP}}$ and implantation window can be tuned depending on the doping of the 1- $\mu \text{m}$ top region. The 10° structure can also be rebalanced by introducing a second 4- $\mu \text{m}$ region of intermediate n-type doping, underneath the 1- $\mu \text{m}$ surface region. This recovers $R_{{\mathrm{\scriptstyle{ON}}},\text {SP}}$ , while maintaining an implantation window that is 7% wider.