The ILD 1-1 SiCN Etch step serves as the critical etch-stop layer (ESL) opening process in the Via 1 (V1) integration module of the 40nm BEOL flow A2.Following the ILD 1-2 Oxide Etch, which clears the bulk via dielectric, the etch front lands on the underlying SiCN layer, which previously protected the Metal 1 (M1) copper from process damage and over-etching P4.This distinct SiCN breakthrough step removes the barrier to physically expose the M1 conductive routing for the subsequent via metalliza