Robust Cu Dual Damascene Interconnects With Porous SiOCH Films Fabricated by Low-Damage Multi-Hard-Mask Etching Technology

Low-damage hard-mask (HM) plasma-etching technology for porous SiOCH film (k=2.6) has been developed for robust 65-nm-node Cu dual damascene interconnects (DDIs). No damage is introduced by fluorocarbon plasma etching irrespective of whether rigid (k=2.9) or porous (k=2.6) SiOCH films are used, due to the protective CF-polymer layer deposited on the etched sidewall. The etching selectivity of the SiOCH films to the inorganic HMs is kept high by controlling the radical ratio of carbon relative to oxygen in the etching plasma gas. However, oxidation damage penetrates the films from the sidewalls due to the O₂ plasma used for photoresist ashing. This damage is increased by the porous structure. As a result, we developed a via-first multi-hard-mask process for the DD structure in porous SiOCH film with no exposure to O ₂-ashing plasma, and we controlled the via-taper angle by RF bias during etching. We fabricated robust Cu DDIs with tapered vias in porous SiOCH film that can be applied to 65-nm-node ULSIs and beyond