The effect of pad wear on the chemical mechanical polishing of silicon wafers

The Chemical Mechanical Polishing process planarises wafers with a high degree of success, however wear on the polishing pad causes the planarisation rate and the post-process planarity to deteriorate. To date, there has been no method of predicting the effect of this wear on the wafer planarity. Using finite element models of the process for new and worn pads the wafer stress distribution on the wafer surface can be predicted. Equating high stresses to high material removal rates these models predict that the process should become 'centre slow' as the pad wears. This correlates well with experimental data.