Al-Cu interconnect corrosion prevention in post metal etch and wet polymer clean wafers

Aluminium-copper (Al-Cu) interconnect corrosion can be observed in some integrated circuit technologies processed through dry metal etch using chlorine (Cl) gas followed by wet polymer clean and wet particle removal steps. Corrosion onset after metal etch, wet polymer clean and wet particle removal were investigated respectively. For each steps, 3 major tests were used to induce corrosion: (a) environment exposure test; (b) time idling test and (c) cassettes box moisture test. Corrosion only happened in these 3 tests after wet polymer clean. Anion extraction test for Cl− and F− indicated that both ions increased under moisturized environment. This proved that Cl− and F− that were detected from corrosion spot were not originated from metal etch gas or wet polymer clean chemistry, but from moisture. Moisture residues after wet polymer clean was identified as main root cause of corrosion. Increasing isopropyl-alcohol (IPA) purge time by 10 secs and wafers lift up time by 18 secs in Marangoni drying step for this process proved to be efficient in preventing corrosion.