MICRO: green mfg

Ara Philipossian and Farhang Shadman, Patrick Levy, Saied Tousi, and Barry Gotlinsky, W. Scott Rader, Paul Lefevre, and Isamu Koshiyama, Chemical-mechanical polishing (CMP) technology has played an enabling role in attaining near-perfect planarity of interconnection and metal layers, an essential step for realizing and miniaturizing high-performance devices. To ensure stable and high-performance CMP characteristics, optimization of the slurry, the pad, and other consumables is critical. Additionally, the relatively high cost of ownership associated with CMP consumables warrants novel approaches to reduce these expenses. Previous studies have demonstrated the feasibility of regenerating slurry. One study in particular showed that high-purity colloidal silica could be reclaimed because of its higher dispersion and lower tendency to clog than fumed silica. For these reasons, fumed silica slurry used in interlayer dielectric (ILD) CMP applications was chosen for the study discussed in this article. The goals of the study were to characterize the slurry, which was regenerated using filtration techniques, and to determine whether it could be rendered analytically and functionally equiv- alent to fresh slurries. All polishing experiments were performed on 100-mm thermally grown SiO wafers using a scaled version of a 472 polisher from SpeedFam-IPEC (now Novellus Systems, San Jose). Details of the experimental apparatus are described elsewhere. To measure the shear force between the pad and the wafer during polishing, a sliding table was placed beneath the polisher. The sliding table consisted of a bottom and a top plate on which the polisher rested. As the wafer and pad were engaged, the top plate slid with respect to the bottom plate in only one direction because of friction between the pad and wafer. The degree of sliding was quantified by coupling the two plates to a load cell. The load cell was attached to a strain gauge amplifier that sent a voltage signal