Via-Shape-Control for Copper Dual-Damascene Interconnects With Low-k Organic Film

Copper dual-damascene (DD) interconnects are fabricated with low-k organic film (SiLKtrade) without any etch-stop layers by use of dual hard mask (dHM) process combined with sidewall-hardening etching step. It is a key point to reduce shoulder loss during trench etching at connecting regions of vias and trenches, so that hardening of the via-sidewall by fluorocarbon plasma during via etching is implemented. Careful designs of dual hard mask structures and their patterning sequence are carried out for the process without etch-stop layer under the trench. The two-layered interconnect with low-k structure has achieved low via-resistance of 0.65 Omega at 0.28 mumOslash with keeping large tolerance of misalignment up to 0.1 mum.