Inhibition of alumina deposition during tungsten chemical mechanical planarization through the use of citric acid

The beneficial effects of citric acid in inhibiting alumina particle deposi tion onto silica areas during tungsten chemical planarization ware investig ated. 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 alu mina became less positive and reversed sign. Slurry dip tests and small-sca le polishing experiments carried out and the surface cleanliness of contami nated oxide surfaces was characterized with a field emission scanning elect ron microscope and image analysis. It has been demonstrated that citric aci d is very effective in controlling alumina contamination on oxide surfaces when added into the slurry. Electrochemical tests showed that citric acid d oes not significantly attack tungsten films. A mechanism for the interactio n between citric acid and alumina particles has been proposed. (C) 1999 The Electrochemical Society. S0013-4651(98)07-070-0. All rights reserved.