Silver metallization by damascene method

Abstract

Silver interconnects are formed by etching deep grooves into an insulating layer over the contact regions, exposing portions of the contact regions and defining the interconnects. The grooves are etched with a truncated V- or U-shape, wider at the top than at any other vertical location, and have a minimum width of 0.25 .mu.m or less. An optional adhesion layer and a barrier layer are sputtered onto surfaces of the groove, including the sidewalls, followed by sputter deposition of a seed layer. Where aluminum is employed as the seed layer, a zincating process may then be optionally employed to promote adhesion of silver to the seed layer. The groove is then filled with silver by plating in a silver solution, or with silver and copper by plating in a copper solution followed by plating in a silver solution. The filled groove which results does not exhibit voids ordinarily resulting from sputter deposition of metal into such narrow, deep grooves, although seams may be intermittently present in portions of the filled groove where metal plated from the opposing sidewalls did not fuse flawlessly at the point of convergence. Portions of the silver and other layers above the insulating material are then removed by chemical-mechanical polishing, leaving a silver interconnect connected to the exposed portion of the contact region; and extending over adjacent insulating regions to another contact region or a bond pad. Silver interconnects thus formed may have smaller cross-sections, and thus a greater density in a given area, than conventional metallic interconnects.