The Wet Etch Removal of Excess Nitride step is critical in the 40nm BSI CMOS Image Sensor Deep Trench Isolation (DTI) module to completely clear residual silicon nitride (SiN) following the bulk planarization by CMP A1.Upstream CMP processes inherently struggle with global uniformity across varying pattern densities, often leaving localized SiN residues or micro-scale overburden to avoid severe dishing into the high-aspect-ratio DTI structures P2.Therefore, this wet etch step functions as a high