The STI Final Densification Anneal follows the chemical-mechanical planarization (CMP) and post-CMP cleaning steps, serving as a critical thermal treatment before the removal of the protective silicon nitride (SiN) pad P1.At this stage in the 40nm BSI CMOS Image Sensor flow, the shallow trenches are filled and planarized, but the deposited oxide retains non-ideal structural characteristics and residual mechanical stress P4.This final anneal is required to fully densify the remaining isolation ox