Chemical mechanical planarization (CMP) is used during the semiconductor manufacturing process at each layer of the wafer to remove excess materials and create a smooth surface. This is done through the interaction of a pad and slurry on a polishing tool.
The main functions of the retainer ring are :
- To hold the wafer in place during polishing.
- To ensure that each die on the outer edge of the wafer can be effectively planarized. The ring applies a larger force on the pad than the wafer and is able to push out the undulations present in the PU-pad conformation. This allows a uniform polishing all across the wafer.
- To permit the flow of the polishing slurry into/out from underneath the wafer through millimeter-sized channels carved into the ring.
