During the fabrication process of certain semiconductor wafers, it is necessary to polish the wafer to selectively remove excess material, e.g., oxides, polysilicon, and aluminum, from a surface of the wafer. Such polishing is frequently referred to as "planarization", wherein an appropriate chemical is applied to the wafer to selectively remove an outer layer of material from the surface, while leaving embedded material to provide appropriate patterning for the wafer.
To polish the wafer, the wafer is supported on a carrier and is in contact with a generally circular polishing pad. The polishing pad has an outer surface of polyethylene terephthalate (i.e., MYLAR), and elongated fibers extending upwardly from the surface. The elongated fibers are coated with the appropriate chemical and brought into contact with a surface of the semiconductor wafer. As the pad is rotated and the fibers move across the surface of the wafer, the unwanted material is removed from the wafer.
During the polishing process, spent polishing materials and by-products become imbedded in the fibers of the polishing pad. Moreover, the fibers tend to become flattened against the polishing pad which results in a "glazed" effect on the surface of the pad. The flattened fibers and imbedded spent polishing materials and by-products reduce the efficiency of the polishing process by extending the time required to polish the wafer. In fact the pads finally became so filled with by-products or become so glazed no further polishing action will occur.
It is known that processes have been developed for reconditioning polishing pads. For example, direct pad contacting means such as nylon brushes, sandpaper, or diamond-coated blades are used. However, these processes generally require interruption of the wafer polishing process and in certain instances require removal of the polishing pad from the polishing assembly. Moreover, since these processes abrade the surface of the pads, the polishing pads must still be replaced frequently, and in some cases after only a few (e.g., ten) semiconductor wafers have been polished.
One technique which has been developed for removing particles from a planar surface is described in U.S. Pat. No. 3,031,195, to Lunsford. This patent shows an apparatus for removing particles from the surface of a phonograph record wherein air is directed downwardly through a tone arm against the surface of the record to remove the particles.
Other techniques have been developed for removing residue on polishing pads. Some of these techniques are shown in Drzewiecki, U.S. Pat. No. 3,907,257; and Scandaletos, U.S. Pat. No. 3,754,359. The Drzewiecki patent shows a tubular housing designed to have a polishing pad wrapped around the circumference of the housing. A plurality of openings are formed in the housing which allow air to pass through the pad and remove residue. Similarly, the Scandaletos patent shows a perforated, flexible disc designed to provide an airflow through the perforations when the disc is rotated. The airflow removes residue on the surface of the disc.
The foregoing references that disclose techniques for removing residue or particles from a polishing pad generally require the fluid to pass through the pad and none were capable of working with pads having imperious backing and were not designed to: 1) raise flattened fibers of a polishing pad, and 2) to simultaneously remove by-products and spent polishing materials from the surface of the pad during the polishing process and 3) to do so without interruption of the polishing process. The present invention accomplishes all this while allowing not only proper polishing of each semiconductor wafer, in the same amount of time but does so without frequent replacement of the polishing pads and without interruption of the polishing process.