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  Apparatus and method for chemical mechanical polishing with improved uniformityUSPTO Application #: 20080051008Title: Apparatus and method for chemical mechanical polishing with improved uniformity Abstract: A chemical mechanical polishing (CMP) apparatus includes a workpiece carrier configured for retaining a workpiece thereupon, a polishing platen configured for retaining a polishing pad thereupon, and an electromagnetic coil surrounding a periphery of the workpiece carrier. The electromagnetic coil is configured to provide a magnetic field of alternating polarity to cause the rotation of ferromagnetic slurry particles disposed on the workpiece to facilitate polishing of the workpiece. (end of abstract) Agent: Cantor Colburn LLP - IBM Fishkill - Hartford, CT, US Inventors: Laertis Economikos, Deok-Kee Kim, Byeongju Park USPTO Applicaton #: 20080051008 - Class: 451 8 (USPTO) The Patent Description & Claims data below is from USPTO Patent Application 20080051008. Brief Patent Description - Full Patent Description - Patent Application Claims
BACKGROUND [0001]The present invention relates generally to semiconductor device processing techniques and, more particularly, to an apparatus and method for chemical mechanical polishing with improved uniformity. [0002]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, it is patterned by lithographic processes and subsequently 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; that is, the topography of the exposed surface contains significant variations in the height of the surface. This non-planar surface presents problems in the photolithographic steps of the integrated circuit fabrication process because the lithographic processes can handle only limited variations in the height of the surface. Therefore, there is a need to periodically planarize the substrate surface. [0003]Chemical mechanical polishing (CMP) is the most commonly used process in semiconductor processing for reducing the aforementioned non-planar topography of the semiconductor surfaces. In a typical implementation of chemical mechanical polishing, the substrate is mounted on a carrier head or polishing head. A polishing pad and retaining ring, typically of a greater diameter than the wafer, are provided on the opposite side of the carrier. The polishing pad and wafer are pressed together while both the carrier head and the polishing pad are rotated. This is achieved by providing the carrier head with a controllable load (i.e., pressure) on the substrate to push it against the polishing pad. The carrier head and polishing pad may be rotated at different rates, and with different axes of rotation to help remove the material uniformly (that is, the average amount of removed material does not depend on the location within the substrate). The polishing pad may be either a "standard" pad or a fixed-abrasive pad. A standard polishing pad has durable roughened surface, whereas a fixed-abrasive pad has abrasive, submicron particles (e.g., ceria (CeO.sub.2)) embedded in a containment media. A polishing slurry, including at least one chemically reactive agent, and abrasive particles (where a standard pad is used) is supplied to the surface of the polishing pad. [0004]With standard pad polishing, the passive motion of the slurry is caused by mechanical movement of the moving parts (e.g., wafer, carrier head, polishing pad, platen, etc.). However, the mechanical rotation of the moving parts is characterized by a non-uniform rate of movement of slurry particles in the radial direction. As such, controlling the rate of polishing becomes a challenge since the linear velocity of the slurry necessitates a compensation of the polishing rate with respect to other variables such as the down force of the polishing pad, and the angular velocity of the polishing pad and/or chuck. Any polishing mechanism that provides a higher polishing rate for higher linear velocity of the polishing slurry faces the challenge of converting uniform angular velocity of the carrier head and polishing pad into uniform linear velocity of the polishing slurries across the substrate. Accordingly, it would be desirable to be able to provide a CMP mechanism that provides a more uniform polishing rate across a semiconductor wafer. SUMMARY [0005]The foregoing discussed drawbacks and deficiencies of the prior art are overcome or alleviated by a chemical mechanical polishing (CMP) apparatus including a workpiece carrier configured for retaining a polishing pad thereupon, a polishing platen configured for retaining a workpiece thereupon, an electromagnetic coil configured to generate a magnetic filed on the workpiece, and an alternating current supply to provide alternating current through the electromagnetic coil. [0006]In one embodiment, the electromagnetic coil surrounds the periphery of the workpiece carrier. The magnetic field is substantially perpendicular to the plane of the substrate. [0007]In another embodiment, the electromagnetic coil is enclosed within the frame that also contains the polishing pad. The magnetic field is substantially perpendicular to the plane of the substrate. [0008]In still another embodiment, the electromagnetic coil is embedded in an enclosure in which the polishing pad and polishing head are contained and either the enclosure or the assembly containing the polishing pad and polishing head slide in or out to facilitate the loading and unloading of the substrate. The magnetic field is substantially within the plane of the substrate. TECHNICAL EFFECTS [0009]As a result of the summarized invention, a solution is technically achieved in which a magnetic slurry is used in combination with an electromagnetic coil that provides a magnetic field of alternating polarity. The alternating magnetic field imparts a spin on the magnetic slurry particles, which in turn creates additional and more uniform pressure on a workpiece, thereby enhancing erosion of material during CMP. BRIEF DESCRIPTION OF THE DRAWINGS [0010]Referring to the exemplary drawings wherein like elements are numbered alike in the several Figures: [0011]FIG. 1(a) is a top view of a conventional CMP apparatus wherein the polishing pad and polishing head are depicted off-axis to illustrate a typical implementation; [0012]FIG. 1(b) is a side view of the CMP apparatus of FIG. 1(a); [0013]FIG. 2(a) is a schematic diagram of a CMP apparatus with magnetically spinning slurry particles responsive to an alternating magnetic field, in accordance with a first embodiment of the invention; [0014]FIG. 2(b) is a side sectional view of the apparatus shown in FIG. 2(a); [0015]FIG. 3(a) is a schematic diagram of a CMP apparatus with magnetically spinning slurry particles responsive to an alternating magnetic field, in accordance with a second embodiment of the invention; [0016]FIG. 3(b) is a side sectional view of the apparatus shown in FIG. 3(a); [0017]FIG. 4(a) is a schematic diagram of a CMP apparatus with magnetically spinning slurry particles responsive to an alternating magnetic field, in accordance with a third embodiment of the invention; and [0018]FIG. 4(b) is a side sectional view of the apparatus shown in FIG. 4(a). DETAILED DESCRIPTION [0019]Disclosed herein is an apparatus and method for implementing chemical mechanical polishing with improved uniformity. Briefly stated, a magnetic slurry is used in combination with an electromagnetic coil that provides a magnetic field of alternating polarity. The alternating magnetic field imparts a spin on the magnetic slurry particles, which in turn creates additional (and more uniform) pressure on the wafer, thereby enhancing erosion of material. Consequently, large wafers (e.g., 300 mm or more) may be polished with a high degree of uniformity, with the polishing rate less dependent upon the radial distance from the center of the chuck/pad. Furthermore, the need for radial adjustment of down force is minimized, and polishing can be carried out at reduced rotational speeds of the polishing head and/or pad. Continue reading... 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