Retaining ring structure for edge control during chemical-mechanical polishing

A retaining ring for a rotatable chemical mechanical polishing head comprising:

• (a) an inner peripheral surface;
• (b) an outer peripheral surface;
• (c) a lower surface adapted to contact and depress an upper surface of a polishing pad during chemical mechanical polishing of the lower surface of a substrate contained within said inner peripheral surface during chemical mechanical polishing;
• and
• (d) said lower surface having a even numbered plurality of evenly spaced slurry channels, originating at said outer peripheral surface and angled toward said inner peripheral surface, each of said plurality of evenly spaced slurry channels being radially angled in the direction of rotation of said polishing head, and wherein said plurality of evenly spaced straight slurry channels are further arranged in an alternating sequence of long and short channels, proceeding around the perimeter of said retainer ring, wherein each one of said long channels extends from said inner peripheral surface to said outer peripheral surface and each one of said short channels extends from said outer peripheral surface to a corresponding cavity of a plurality of cavities formed in the lower surface, each one of said plurality of cavities extending from said inner peripheral surface towards said outer peripheral surface for a radial depth and a height above said lower surface sufficient, to prevent depression of a subjacent polishing pad under the edge of a retained wafer adjacent to said cavity, each of said plurality of cavities being further bounded laterally by non-recessed regions which form segmented tabs through which adjacent long channels pass, there being as many segmented tabs as there are long channels, each of said segmented tabs having a rounded edge, tangent to the inner circumference of said retaining ring, meeting said inner circumference at an end of and symmetrical with a non-recessed long channel and whereby each said segmented tab has an effective contact width at said inner peripheral surface against a wafer enclosed therein.