The CESL 1 - Etch step is a critical phase in the contact module of the 40nm BSI CMOS Image Sensor flow, executed immediately after the PMD and CESL 2 etches P1.During the preceding main contact etch, the thick pre-metal dielectric (PMD) is removed, and the etch process is designed to selectively terminate on the Contact Etch Stop Layer (CESL) to prevent damage to the underlying active regions and gate structures A1.In advanced technologies, the CESL is often deposited via PECVD as a highly stre