The beneficial effects of citric acid in inhibiting alumina particle deposition onto silica areas during tungsten chemical mechanical planarization were investigated. The electrokinetics of alumina in the presence of citric acid and the uptake of citric acid by alumina were studied experimentally. At a pH of 4, as the citric acid concentration was increased, the zeta potential of alumina became less positive and reversed sign. Slurry dip tests and small-scale polishing experiments were carried out and the surface cleanliness of contaminated oxide surfaces was characterized with a field emission scanning electron microscope and image analysis. It has been demonstrated that citric acid is very effective in controlling alumina contamination on oxide surfaces when added into the slurry. Electrochemical tests showed that citric acid does not significantly attack tungsten films. A mechanism for the interaction between citric acid and alumina particles has been proposed.
ASJC Scopus subject areas
- Electronic, Optical and Magnetic Materials
- Renewable Energy, Sustainability and the Environment
- Surfaces, Coatings and Films
- Materials Chemistry