Interaction between abrasive particles and films during chemical-mechanical polishing of copper and tantalum

Abstract

Chemical-Mechanical Polishing (CMP) of copper is a critical step for the formation of interconnect on wafer during the manufacturing of advanced microelectronic devices. One of the key performance metrics of a copper CMP slurry is the removal rate selectivity between copper and its corresponding adhesion/barrier layer such as Ta or TaN. In order to create a slurry that has the desirable and/or tunable removal rate selectivity, it is critical to understand the influential factors that control the removal rates. In this study, such influential factors are elucidated based on the relative importance of interaction between abrasive particle and the film to be polished. More specifically, particles with varying bulk and surface properties are used to obtain the removal rate selectivity for copper and Ta. It is found that the Ta material removal rate has a direct correlation with the effective hydroxyl content on the surface of abrasive particles. The material removal rate and surface quality of copper, on other hand, is heavily influenced by the hardness of the abrasive particles and the presence of oxidizer/complexing agent. The reliance on the interaction with abrasive surface hydroxyl groups for Ta removal is further confirmed with a set of experiments in which the silica surface hydroxyl content are significantly reduced via alkylation of the hydroxyl groups. As expected, the surface treatment that remove some of the surface hydroxyl groups also reduce the Ta material removal rate. The difference in removal mechanism for copper and tantalum is also explained with the distribution of the abraded materials between spent slurry and pad.