Asperity size distribution near wafer features during CMP

Dual Emission Laser Induced Fluorescence (DELIF) is used to attain in-situ images of the slurry layer between the polishing pad and wafer during chemical mechanical planarization (CMP). The slurry layer under a flat wafer takes the shape of the polishing pad. As a wafer feature passes over the pad, the pad adapts to the wafer shape and expands into the well. Here, we present a comparison of the shape of the polishing pad inside and outside 14 urn deep wafer wells. By comparing asperity size distribution histograms we see no asperity compression inside the wells. However, in the region outside the wells where the pad and the wafer are in contact, asperities are compressed approximately 2.5um with an applied pressure to the wafer of 6.0 psi. In addition to asperity compression we observe an increase in pad-wafer contact from the 0.5 psi to the 6.0 psi case.