Investigating the Impact of Pad Groove Depth Reduction on Process Variation in Oxide Chemical Mechanical Polishing

The groove depth of a polishing pad diminishes due to continuous wear from the diamond conditioner. Over the course of approximately 20 h of use, this reduction in groove depth enhances slurry flow across both the pad grooves and surface. A fluid simulation analysis indicates that the new slurry mass fraction at 0.51 s increases from 72.34% for an 850 μm groove depth to 100.00% for a 250 μm depth. Consequently, polishing performance metrics including removal rate, within-wafer nonuniformity (WIWNU), and added defects exhibit variations commensurate with groove depth alterations. To explore the influence of process parameters on these polishing performance metrics, oxide film polishing experiments were conducted using pads with initial groove depths of 250, 500, 750, and 850 μm. The effects of process parameters, including pad cut rate, retainer ring pressure, and slurry flow rate on polishing were separately examined across different groove depth pads. Generally, shallow groove pads display improved removal rates but worse WIWNU. Additionally, the maximum surface temperature of the pads was recorded, serving as an indirect indicator of individual parameter effects. The findings have implications for advanced process control, guiding the optimization of polishing protocol in consideration of pad lifetime.