Retaining ring for cmp

A retaining ring, comprising:

• a generally annular body having an inner surface to constrain a substrate, an outer surface, and a bottom surface, the bottom surface having a plurality of channels extending from the 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 has the same shape and each island has the same shape, wherein each channel of the plurality of channels comprises a leading edge and a trailing edge that are asymmetric across a centerline of the channel, and the trailing edge of the channel includes a substantially azimuthally extending portion.