Process design methodology for via-shape-controlled, copper dual-damascene interconnects in low-k organic film

By dual hard mask (dHM) process combined with sidewall-hardening etching step, copper dual-damascene (DD) interconnects are fabricated in low-k organic film without any etch-stop layers under the trench. Careful designs of dHM structures and their patterning sequence enable us to harden the via-sidewall by fluorocarbon plasma, which is a key to reduce final via-shoulder loss at the via/trench connecting region. The low-k structure has low via resistance such as 0.65 /spl Omega//0.28 /spl mu/m/sup /spl phi//-via while keeping the large tolerance of misalignment in via/trench, appreciable for 0.1 /spl mu/m-generation CMOS ULSIs.