Diffusion isolation layer for maskless cladding process

Abstract

Disclosed is a maskless metal cladding process for plating an existing metallurgical pattern by utilizing a protective layer to isolate those areas of underlying metallurgy on which additional metal plating is not desired. The layer acts as an isolation barrier to protect the underlying metallurgy from deposition and subsequent diffusion of the heavy metal (e.g., gold) overlay. The composition of the protective layer is selected as one having sufficient mechanical integrity to withstand process handling and support the gold overlay and having the thermal integrity to withstand the high temperatures reached during metal sputtering and diffusion processes. The isolation barrier layer has an organic component as a binder which thermally decomposes, either in a heating step before metal deposition or during the diffusion cycle, leaving no carbonaceous residue but leaving an inert, inorganic standoff to support the metal. After diffusion of the metal, the remaining inorganic standoff layer, overlying metal and any undiffused metal remaining on the non-patterned substrate is easily removed by a standard technique, such as ultrasonics.