Instantaneous, high resolution, in-situ imaging of slurry film thickness during CMP

Dual Emission Laser Induced Fluorescence (DELIF) is used to attain measurements of slurry film thickness during Chemical Mechanical Polishing (CMP). A Nd/Yag UV laser is used in tandem with two 12 bit CCD cameras with a zoom lens to obtain an instantaneous, high spatial and temporal resolution images in-situ. We are able to image individual pad asperities bending under the wafer during polishing. Once the intensities in the images are correlated to slurry layer thickness values, slurry layer roughness is observed. DELIF shows the slurry layer roughness beneath a flat wafer is 4.5±0.5 urn. This value compares well to profilometer measurements of pad surface roughness, 4.3+0.3 urn. Slurry layer roughness under 27 urn deep etched wells in the wafer features is greater than the roughness outside the wells suggesting asperity expansion under features. Slurry layer roughness under air pockets that have accumulated under the wells in the wafer is less than the slurry filled regions under the wafer suggesting incomplete immersion of asperities under the air pockets.