Following the ILD 1-2 Oxide Etch, the MET2 trenches are structurally defined but their surfaces remain heavily contaminated with unreacted photoresist (PR), bottom anti-reflective coating (BARC), and highly crosslinked fluorocarbon (CFx) polymers P1.This Ashing & Strip/Clean step is critically positioned to eradicate these residues entirely before the downstream deposition of the Ta-based liner and copper seed (Engineering Practice).Unlike general front-end sacrificial cleans, this specific step