Investigating slurry transport beneath a wafer during chemical mechanical polishing processes

In order to better understand the role of thr fluid behavior in chemical me chanical planarization, we measured slurry transport beneath a glass wafer. We quantified the slurry transport using residence time distribution techn iques and two measures of slurry transport efficiency, defined as the perce ntage of new slurry beneath a wafer. Slurry transport efficiency depended o n platen speed, flow rate, and the conditioning method. We found that the a verage fluid residence rimes under the wafer decreased roughly linearly wit h platen speed, A threefold increase in platen speed decreased slurry mean residence time by a factor of 3.5. Changing the flow rate from 20 to 50 mL/ min decreased the slurry mean residence times by 80%. In situ conditioning generally increased the slurry mean residence times and the amount of slurr y mixing. In situ conditioning also decreased gradients in the slurry compo sition across the wafer. Pad topography had a large effect on the slurry gr adients that developed across the wafer. Finally, we found that the slurry mixing history can he accurately modeled using a simple continuous function . (C) 2000 The Electrochemical Society. S0013-4651(99)05-005-3. All rights reserved.