Effect of Particle Size During Tungsten Chemical Mechanical Polishing

Abrasive particle size plays a critical role in controlling the polishing rate and the surface roughness during chemical mechanical polishing (CMP) of interconnect materials during semiconductor processing. Earlier reports on the effect of particle size on polishing of silica show contradictory conclusions. We have conducted controlled measurements 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 μm to 10 μm diameter have been used in these experiments. The polishing experiments showed that the local roughness of the polished tungsten surfaces was insensitive to alumina particle size. The tungsten 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. The concept developed in our work showing that the removal rate is controlled by the contact surface area between particles and polished surface is in agreement with the different explanations for tungsten removal.