In the 40nm BSI CMOS Image Sensor flow, the Optical Pad 1 Etch step is executed after the Lower Vertical Grid Trench Photo to selectively open access to specific contact or alignment pads within the Light Shield Grid (LS_GRID) module A1.This step is distinct from the subsequent Optical Pad 2 and 3 etches because it targets the outermost optical dielectric layers, establishing the primary via or pad exposure before deeper or secondary pad structures are defined A1.By removing the targeted dielect