Angstrom surface on copper induced by novel green chemical mechanical polishing using ceria and silica composite abrasives

Abstract

Toxic and corrosive slurries are widely employed in traditional chemical mechanical polishing (CMP), leading to the pollution to the environment. Consequently, it is a challenge to acquire angstrom surface using green CMP. To solve this challenge, a novel green CMP was developed for copper (Cu), including only four ingredients. Ceria and silica are used as composite abrasives. Tartaric acid was applied to adjust the pH value of the developed green slurry to 6.5. After CMP, surface roughness Ra is 0.1 nm measured by atomic force microscopy and surface profilometer respectively, with measurement areas of 5 × 5 μm2 and 50 × 50 μm2, correspondingly. So far, this is the lowest surface roughness reported in such a large measurement area. Transmission electron microscopy confirms that the thickness of damaged layer after CMP varies from 0.4 to 2 nm. CMP mechanism is elucidated by X-ray photoelectron spectroscopy and Fourier transform infrared spectroscopy. Firstly, the Cu surface was oxidized by hydrogen peroxide, then solved via hydrogen ions, and finally chelated with hydroxyl groups of tartaric acid. These findings provide a novel approach and new insights to achieve angstrom level surface, for the potential use in high-performance devices of Cu.