This step forms the Metal 5 trench in the inter-layer dielectric (ILD) as part of a copper dual-damascene integration scheme P2. Following the Metal 5 photolithography, this fluorocarbon-based plasma etch transfers the trench pattern into the oxide or low-k dielectric P1. Unlike front-end pad oxide etches that primarily clear thin conformal layers over silicon, this BEOL step must precisely define high-aspect-ratio interconnect trenches to ensure reliable subsequent Ta-based liner and Cu seed de