Stress control in trench field-plate power MOSFETs and its impact on on-resistance reduction

The limitations regarding lateral cell pitch narrowing and on-resistance reduction were investigated. Trench field plate MOSFETs feature deep trenches with thick oxide films. This disrupts the stress balance, leading to significant wafer warpage, which poses a critical challenge in device integration. Stress control has become essential for enabling cell pitch narrowing, achieving high breakdown voltage device designs, and implementing innovative device pattern layouts such as dot pattern cell structures. In this study, stress and wafer warpage associated with lateral cell pitch narrowing were estimated using 3D simulations. Based on these results, the on-resistance reduction limit was also estimated through analytical models. For stripe pattern cell structures, pitch narrowing was constrained by both increased wafer warpage and on-resistance saturation. Notably, the X-direction wafer warpage was identified as the limiting factor for pitch narrowing in high breakdown voltage device designs. In contrast, the dot pattern cell structure significantly reduced wafer warpage and allowed narrower pitches compared to the stripe pattern, despite a weakened mobility enhancement effect.