A method of using a polishing system includes securing a wafer in a carrier head, the carrier head including a housing enclosing the wafer, in which the housing includes a retainer ring recess and a retainer ring positioned in the retainer ring recess, the retainer ring surrounding the wafer, in which the retainer ring includes a main body portion and a bottom portion connected to the main body portion, and a bottom surface of the bottom portion includes at least one first engraved region and a first non-engraved region adjacent to the first engraved region; pressing the wafer against a polishing pad; and moving the carrier head or the polishing pad relative to the other.