Investigation of the kinetics of tungsten chemical mechanical polishing in potassium iodate-based slurries II. Roles of colloid species and slurry chemistry

We investigated the role of colloid species and slurry chemistry in tungsten chemical mechanical polishing. Specifically, we measured polish rate and process temperature in potassium iodate-based slurries as a function of colloid species and concentration, slurry pH, and potassium iodate concentration, as well as polish pressure and polish rotation rate. We investigated slurries containing yttrium-, zirconium-, cerium, and aluminum-based oxide and hydroxide colloids. We found that the colloid species had a large effect on polish rate and process temperature. The colloids showed two orders of magnitude in the polish rate range from similar to 15 to similar to 1975 Angstrom min(-1) under otherwise identical experimental conditions (same polisher, pad, slurry chemistry, pressure, and rotation rates). Colloids of the same metal species from different sources also showed a large range in polish rates. Process temperature was a function of colloid species, however, the trend in polish rate did not always follow that of process temperature. Both polish rate and process temperature were dependent on potassium iodate concentration and slurry pH (controlled with a buffer). We also introduce a heuristic polish mechanism to investigate the role of the colloid surface chemistry and its interaction with the tungsten surface. The data indicate that the surface characteristics of the colloid and how this surface interacts with the tungsten surface play a significant role in the mechanism of tungsten removal during polish. (C) 1999 The Electrochemical Society. S0013-4651(98)09-034-X. All rights reserved.