Retaining ring for cmp

A retaining ring, comprising:

• a generally annular body having an inner surface to constrain a substrate and a bottom surface, the bottom surface having a plurality of channels extending from an outer surface to the inner surface, and a plurality of islands separated by the channels and providing a contact area to contact a polishing pad, wherein each channel of the plurality of channels comprises a leading edge and a trailing edge, wherein the leading edge comprises a first linear segment at a first angle relative to a radial direction from the first linear segment, and wherein the trailing edge comprises a second linear segment at a second angle from a radial direction from the second linear segment, wherein the second angle is less than the first angle, and wherein the trailing edge comprises a third linear segment that is farther from the inner surface than the second linear segment and that extends substantially perpendicular to the second linear segment.