The PMD 3 CMP step serves as the definitive global planarization process within the Middle-of-Line (MOL) module for the 40nm BSI CMOS Image Sensor A1.Following the sequential deposition of PMD layers, the wafer surface exhibits substantial layout-dependent topography that must be eliminated before contact formation P3.The primary objective of this step is to create an optically flat surface to satisfy the stringent Depth of Focus requirements of the subsequent Metal 0 and Contact photo step P1.W