Flexible polishing surface (FPS) vs rigid polishing surface (RPS) in CMP: pros and cons

Two major conceptual CMP approaches, namely flexible polishing surface (utilized in linear belt CMP) and rigid polishing surface (hard platen rotary and orbital CMP) concepts are compared with regard to process stability, uniformity, planarization efficiency and other performance features. A new CMP characteristic, Normalized Removal Work, the amount of wafer layer material removed by a unit of active pad area (NRW=(Thickness removed)/(Active pad area), [A/sq. inch]), is used to analyze and compare the concepts. The NRW shows how much of the removed material is transferred and redeposited over a unit of pad area. It influences all aspects of the CMP process. Low NRW is good for CMP, high NRW is bad for CMP.