Process Improvement for Stabilizing the VLD Effective Dose of 4500V Trench-Gated IGBT Platform

A ultra-high temperature diffusion process with thin oxide layer capped with polysilicon film to get a deep VLD (Variable Lateral Doping) junction edge termination of 4500V trench-gated IGBT platform is presented in this paper. Conventionally, the VLD high temperature drive-in process is performed with oxide cap layer only, during which severe segregation of boron occurs at Si/Oxide interface, resulting in most of the implanted boron ions loss from silicon to oxide. Subsequently, the effective dose of VLD is decreased significantly with a poor controllability. As the consequence, it is difficult to get a uniform distribution of breakdown characteristics of the edge termination. Thru the proposed process disclosed in this paper, the segregation of boron at Polysilicon/Oxide interface acts as an effective barrier for the boron diffusion in underlying layers and the boron loss from silicon is considerably reduced. Both simulated and experimental results confirm that the improved process is highly manufacturable and can achieve excellent breakdown characteristics with a high production yield.