Following dopant activation, the integration flow transitions into the middle-of-line (MOL) phase with the deposition of the Contact Etch Stop Layer (CESL) A1.The CESL serves a dual purpose: it acts as a highly selective barrier to protect underlying active areas during the aggressive contact hole etch, and it introduces mechanical strain into the transistor channel to enhance carrier mobility P1.In the context of a 40nm CMOS image sensor flow, CESL 1 is typically deposited to cover a specific d