Chemical mechanical polishing with selective slurries

The first chemical mechanical polishing of silicon dioxide did not use selective slurries. These slurries are now widely used, such as in metal polishing. In practice, they polish quickly through high polish rate material and slow down greatly when lower polish rate material is exposed. However, though the final thickness of the lower polish rate material can be well controlled, the post-polish surface, with both high rate and low rate materials are exposed, is not planar. The dishing, recess and erosion near features of the higher rate material can be greatly influenced by the structures and properties of the polishing pad. The standard two layer pad, with a stiff urethane layer over a compressible layer, can lead to long range dishing. The asperities created by conditioning on the top of the urethane pad can lead to recess and erosion. The properties of the asperities can be altered by modifying the bulk properties of the top pad as well as varying the conditioning of the surface of the top pad.