Effect of particle size during tungsten chemical mechanical polishing

The size of the abrasive particles plays a critical role in controlling the polishing rate and the surface roughness during chemical mechanical polishing of interconnect materials during semiconductor processing. Earlier reports on the effect of particle size on polishing in silica show contradictory conclusions. To the best of our knowledge, a systematic study of the effect of particle size on tungsten (W) polishing has not been published. This paper describes the controlled measurements that were conducted to determine the effect of alumina particle size during polishing of tungsten. Alumina particles of similar phase and shape with size varying from 0.1 to 10 mu m diam were used in these experiments. The polishing experiments showed that the local roughness of the polished W surfaces was insensitive to alumina particle size. The W removal rate was found to increase with decreasing particle size and increased solids loading. These results suggest that the removal rate mechanism is not a scratching type process, but may be related to the contact surface area between particles and polished surface controlling the reaction rate. (C) 1999 The Electrochemical Society. S1099-0062(98)10-101-3. All rights reserved.