PMD 2 Etch is a critical intermediate process step in the multi-step contact opening sequence within the 40nm BSI CMOS image sensor flow P1.Following photolithography and the initial PMD 4 and PMD 3 etch steps, this step continues the high-aspect-ratio anisotropic removal of the thick pre-metal dielectric (PMD) stack to form vertical pathways to the active device regions P2.The incremental multi-step approach is utilized to tightly control the evolving etch profile and minimize cumulative micro-