The effect of polymer hardness, pore size, and porosity on the performance of thermoplastic polyurethane-based chemical mechanical polishing pads

Solid-state microcellular foaming (SSMF) process was used to produce porous chemical mechanical polishing (CMP) pads in a variety of pore size and porosity range, using a variety of thermoplastic polyurethane (TPU) resin hardness. By controlling the pore size, porosity, and pad hardness, one is able to manufacture CMP pads that offer tunable pad properties. A brief introduction to the SSMF manufacturing process and thereby, unique microstructures created is first addressed followed by inner layer dielectric (ILD) CMP results, describing the effects of top TPU foam sheet properties, such as hardness, pore size, and porosity on ILD removal rate (RR) and wafer defects. Softer TPU-based porous pads showed significantly lower wafer scratch counts, while only a moderate increase in the ILD RR was seen with increasing resin hardness for similar pore size and porosity pads. Pore size has insignificant influence on wafer defect count but has significant influence on the ILD RR profile. CMP pads made from small pore size foams cause a nonflat RR profile.