Abstract: A technique for controlling a polishing rate across a substrate surface when performing CMP, in order to obtain uniform polishing of the substrate surface. A support housing which underlies a polishing pad includes a plurality of openings for dispensing a pressurized fluid. The openings are arranged into a pre-configured pattern for dispensing the fluid to the underside of the pad opposite the substrate surface being polished. The openings are configured into a number of groupings, in which a separate channel is used for each grouping so that fluid pressure for each group of openings can be separately and independently controlled.