The CESL 2 - Etch step occurs immediately after the bulk Pre-Metal Dielectric (PMD) oxide has been anisotropically etched to open the contact holes P1.In the 40nm BSI CMOS Image Sensor flow, the contact module utilizes a multi-layer Contact Etch Stop Layer (CESL) scheme to provide both robust etch stopping capabilities and highly localized channel strain P1.Because the preceding PMD etching processes use high-selectivity fluorocarbon plasmas designed to stop efficiently on the uppermost nitride