Method and apparatus for polishing metal surfaces

Abstract

A technique for chemically planarizing an exposed surface of metal on a substrate to a pre-determined thickness is provided. The substrate has an exposed metal surface such as copper circuitry on a dielectric substrate which is to be planarized. Typically, this will be circuitization extending above a photoresist layer. A planarizing head is rotated against the substrate, with the planarizing head in contact with the metal surface on the substrate. A chemical etchant, essentially free of abrasive material, is continuously supplied to the interface between the metal surface and the planarizing head. The planarizing continues until a predetermined thickness of the metal has been reached. In circuit board manufacturing, this will form a surface co-planar with the photoresist. In some instances where significant height reduction is required, thus requiring significant metal removal, several passes of the substrate may be required or a device with multiple heads may be used. On all but the last pass or last head, the planarizing head may include a film of polyester impregnated with very fine grit, such as 15.mu. or less silicon carbide (SiC). However, on the final pass or head, a relatively hard surface roll, e.g., rubber, free of added grit, is used to ensure a planar surface free of gouges.