Crystallographic texture change during abnormal grain growth in Cu-Co thin films

Abstract

The addition of 0.4-8.6 at. % Co to Cu thin films strongly influences the temperature evolution of microstructure, stress, and resistivity. For concentrations near 1 at. % Co in coevaporated Cu-Co on oxidized Si, normal grain growth begins at about 75°C, about 50°C lower than in pure Cu. There is an abrupt decrease in resistivity and stress at a temperature which increases with Co content from 120°C (0% Co) to 250°C (8.6 at. % Co), and coincides with precipitation of Co within Cu grains. A dramatic change in texture is observed in both coevaporated and electroplated Cu-Co films upon annealing above 250°C. As-deposited films have a three-component texture of (111) fiber, (200) fiber, and random but annealed films have a dominant (200) fiber texture. This "cube" texture differs from the dominant (111) texture of annealed pure Cu, and appears to be coupled to an abnormal grain growth process since many grains are observed to be larger than ten times the film thickness. It is proposed that segregation of Co to external surfaces or to Cu grain boundaries may favor this (200) texture by selectively affecting grain-boundary mobility or the surface energy driven grain growth.