The ILD 3-2 Oxide Etch step defines the Metal 4 interconnect trench within the Back-End-Of-Line (BEOL) dual-damascene integration scheme A2.After the trench photo-lithography step, this process transfers the M4 trench pattern deeply into the interlayer dielectric (ILD) P2.This operation creates the precise physical cavity that will subsequently be metallized with a Ta-based liner and copper seed (Engineering Practice).Unlike early-flow pad oxide etches that merely serve as sacrificial layers for