The Influence of Additive-Free Process on the Microstructure of Very Narrow Cu Wires in the Lower Region of a Trench

Abstract

Microstructure distribution along the trench depth direction of nano-scale copper interconnects was studied as a function of plating material purity. It was shown that, after annealing in the lower region of the trench, the Cu wire fabricated by the additive-free process has 13% larger grains and 80% lower ratio of small grains (less than 45 nm) than the wire fabricated by the high-purity process, and 25% larger grains and 92% lower ratio of small grains than the wire fabricated by the low-purity process. The grain size distribution in the trench depth direction for the Cu wire plated without additives was much more uniform than that plated with additives.