A novel seed layer scheme to protect catalytic surfaces for electroless deposition

This paper describes a new technique to protect catalytic surfaces for electroless copper deposition. The barrier and seed (each ̃10 nm) are first evaporation deposited or sputter deposited onto the substrate. A thin protective aluminum film (̃10 to 20 nm) is deposited on top of the seed layer without breaking the vacuum. When the substrate is immersed into the electroless bath, the protective aluminum film is quickly etched away in basic electroless copper baths. The unoxidized seed surface is hence exposed in situ to the electroless bath and acts as an excellent catalytic seed layer for electroless copper deposition. Using this technique, copper can be used as a seed layer for electroless copper deposition. The use of higher resistivity (and contaminating) gold, platinum, or palladium seed layers are avoided. Experimental results pertaining to the fundamental aspects of this technique are presented. The practical application of this technique for ultralarge scale integration (ULSI) interconnects is also demonstrated with submicron electroless copper deposited conformally into vias and trenches with aspect ratios of 2:1, and into horizontal submicron tunnels with aspect ratios of 500:1.