Hillock morphology and density in AlTa and AlCu alloy films encapsulated with aluminum oxide layers

Abstract

The effect of surface oxide layers on annealed hillock formation was examined in 1 μm thick films of AlTa and AlCu with artificial aluminum oxide caps. An anodic oxide layer or a sputter-deposited oxide layer was formed on the top of the Al alloy films, and the test samples were annealed at 573 K for 3.6 ks in a vacuum of less than 1×10−4 Pa. How hillocks formed on the films and the dependence of hillocking density on oxide thickness were investigated. It was observed that hillocks formed under the oxides or broke through them. Scanning electron micrographs and cross-sectional transmission electron micrographs provided a clear view of the flexibility of the surface oxides. AlTa films exhibited a much lower hillock density than AlCu films. There was no significant dependence of hillock density on oxide thickness or type of surface oxide. It was determined that the hillock density was independent of defects or of the properties of the thin surface oxide layers.