Following dopant activation and the initial CESL 1 deposition, the CESL 2 deposition completes the Contact Etch Stop Layer stack before the thick Pre-Metal Dielectric (PMD) deposition A1.In a 40nm CMOS image sensor flow, integrating a secondary CESL layer serves two primary functions: providing highly selective etch-stop capabilities during the subsequent high-aspect-ratio contact hole formation, and modulating intrinsic channel stress A1, P4.Unlike CESL 1, which typically acts as a direct, thin