Interest of surface treatment at gate oxide level for power MOSFETs quality and reliability

In this paper, the impact of pre-gate and post-gate oxide surface treatments on the reliability and the robustness of low power vertical MOSFET dedicated to automotive applications are investigated. In these applications, components quality is linked with gate oxide robustness and tests like Qbd, TDDB and HTGB exist to evaluate its reliability. The study concludes that post-gate oxide cleaning has a significant impact on oxide quality as shown with Qbd on final product and GOI measurements. Moreover, an AFM characterization has demonstrated that a mechanical ultrasonic cleaning step can damage irreversibly gate oxide surface roughness in opposition to chemical surface treatment. Nevertheless, the TEM analysis of oxide-polysilicon interface does not highlight any difference. The root cause of power MOSFET failure mechanism is linked with gate oxide quality which depends to surface treatment performed. The cavitation erosion phenomenon has been highlighted to be responsible for Qbd degradation.