The Oxide Hard Mask Removal step is strategically positioned after the planarization and wet etch clearance of the excess Deep Trench Isolation (DTI) SiN fill P1.At this stage in the flow, the oxide hard mask—which previously served as the robust template for high-aspect-ratio Deep Reactive Ion Etching (DRIE) of the silicon trenches—has fulfilled its structural purpose P2.Leaving this thick oxide layer in place would disrupt the topographical baseline required for the subsequent shallow trench i