Among other things, a method comprises polishing a surface of a substrate by applying a pressure between the surface of a substrate and a surface of a polishing pad. The surface of the polishing pad defines one or more grooves separated by one or more partition regions. The one or more grooves have an initial depth before the polishing starts and extend from an initial outer surface of the one or more partition regions to an initial bottom of the one or more grooves. The method also comprises removing material below an initial bottom of the one or more grooves such that a distance between an outer surface of the one or more partition regions and a bottom of the one or more grooves remain substantially the same as the initial depth.