This Nitride Etch step is a critical pattern-transfer operation within the Shallow Trench Isolation (STI) module, serving to transfer the photoresist and intermediate hard mask patterns directly into the primary silicon nitride layer P1.Unlike later wet etch removal steps that simply strip sacrificial layers, or anisotropic spacer back-etches that form sidewall structures, this highly directional dry etch step strictly defines the active area critical dimensions (CD) A1.Following the preceding o