Chemical mechanical polishing with multiple polishing pads

#The present invention relates generally to chemical mechanical polishing of substrates, and more particularly to polishing with fixed-abrasive polishing pads.

#Integrated circuits are typically formed on substrates, particularly silicon wafers, by the sequential deposition of conductive, semiconductive or insulative layers. After each layer is deposited, the layer is etched to create circuitry features. As a series of layers are sequentially deposited and etched, the outer or uppermost surface of the substrate, i.e., the exposed surface of the substrate, becomes increasingly non-planar. This non-planar outer surface presents a problem for the integrated circuit manufacturer. Therefore, there is a need to periodically planarize the substrate surface to provide a relatively flat surface. However, in some fabrication processes, planarization of the outer layer should not expose underlying layers.

#Chemical mechanical polishing (CMP) is one accepted method of planarization. This planarization method typically requires that the substrate be mounted on a carrier or polishing head. The exposed surface of the substrate is placed against a rotating polishing pad. The polishing pad may be either a “standard” pad or a fixed-abrasive pad. A fixed-abrasive pad has abrasive particles held in a containment media, whereas a standard pad has a durable surface, without embedded abrasive particles. The carrier head provides a controllable load, i.e., pressure, on the substrate to push it against the polishing pad. A polishing slurry, including at least one chemically-reactive agent, and abrasive particles if a standard pad is used, is supplied to the surface of the polishing pad.

#FIG. 1 is a schematic exploded perspective view of a chemical mechanical polishing apparatus.

#FIG. 2A is a schematic cross-sectional view of the first polishing station of the CMP apparatus of FIG. 1.

#FIG. 2B is a schematic cross-sectional view of the final polishing station of the CMP apparatus of FIG. 1.

#Referring to FIG. 1, one or more substrates 10 will be polished by a chemical mechanical polishing apparatus 20. A description of polishing apparatus 20 may be found in U.S. Pat. No. 5,738,574, the entire disclosure of which is incorporated herein by reference. Polishing apparatus 20 includes a lower machine base 22 with a table top 23 mounted thereon and a removable outer cover (not shown). Table top 23 supports a series of polishing stations, including a first polishing station 25a, a second polishing station 25b, and a final polishing station 25c, and a transfer station 27. Transfer station 27 forms a generally square arrangement with the three polishing stations 25a, 25b and 25c. Transfer station 27 serves multiple functions, including receiving individual substrates 10 from a loading apparatus (not shown), washing the substrates, loading the substrates into carrier heads, receiving the substrates from the carrier heads, washing the substrates again, and finally, transferring the substrates back to the loading apparatus.

#Each polishing station includes a rotatable platen 30 on which is placed a polishing pad. The first and second stations 25a and 25b may include a fixed-abrasive pad 100, whereas the final polishing station may include a standard pad 110. If substrate 10 is an “eight-inch” (200 millimeter) or “twelve-inch” (300 millimeter) diameter disk, then the platens and polishing pads will be about twenty inches or thirty inches in diameter, respectively. Each platen 30 may be a rotatable aluminum or stainless steel plate connected to a platen drive motor (not shown). For most polishing processes, the platen drive motor rotates platen 30 at thirty to two hundred revolutions per minute, although lower or higher rotational speeds may be used.

#Polishing station 25c may include a pad conditioner apparatus 40. Pad conditioner apparatus 40 has a rotatable arm 42 holding an independently-rotating conditioner head 44 and an associated washing basin 46. The pad conditioner apparatus 40 maintains the condition of the polishing pad so that it will effectively polish substrates. Polishing stations 25a and 25b do not require a pad conditioner apparatus because fixed-abrasive pads generally do not require conditioning. However, as illustrated, each polishing station may include a conditioning station in the event that the CMP apparatus is used with other pad configurations.