Investigating Slurry Transport beneath a Wafer during Chemical Mechanical Polishing Processes

In order to better understand the role of the uid behavior in CMP, we measured slurry transport beneath a glass wafer. We quanti ed the slurry transport using Residence Time Distribution techniques and two measures of slurry transport e ciency de ned as the percentage of new slurry beneath a wafer. Slurry transport e ciency depended on platen speed, ow rate, and the conditioning method. We found that the average uid residence times under the wafer decreased roughly linearly with platen speed. A threefold increase in platen speed decreased slurry mean residence times by three and a half times. Changing the ow rate from 20 cc/min to 50 cc/min decreased the slurry mean residences by 80%. In situ conditioning generally increased the slurry mean residence times and the amount of slurry mixing. In situ conditioning also decreased gradients in the slurry composition across the wafer. Pad topography had a large e ect on the slurry gradients that developed across the wafer. Finally, we found that the slurry mixing history can be accurately modeled using a simple continuous function.