A method and apparatus for planarizing a substrate are provided. A substrate carrier head with an improved cover for holding the substrate securely is provided. The cover may have a bead that is larger than the recess into which it fits, such that the compression forms a conformal seal inside the recess. The bead may also be left uncoated to enhance adhesion of the bead to the surface of the groove. The surface of the cover may be roughened to reduce adhesion of the substrate to the cover without using a non-stick coating.
