The present invention relates generally to apparatuses and methods for cleaning thin discs, such as semiconductor wafers, compact disks, and the like. More particularly, the invention relates to removing material (such as processing residue or deposited material) from the edge of a thin disk.
To manufacture a thin disk such as a semiconductor wafer, an elongated billet of semiconductor material is cut into very thin slices, about xc2xd mm in thickness. The slices or wafers of semiconductor material are then lapped and polished by a process that applies an abrasive slurry to the wafer""s surfaces. Likewise, polishing processes are employed to planarize layers deposited on the wafer during device formation. After polishing, slurry residue is generally cleaned or scrubbed from the wafer surfaces via mechanical scrubbing devices, such as polyvinyl acetate (PVA) brushes, brushes made from other porous or sponge-like material, or brushes made with nylon bristles. Although these conventional cleaning devices remove a substantial portion of the slurry residue which adheres to the wafer edges, slurry particles nonetheless remain and may produce defects during subsequent processing.
In addition to slurry particles, other sources of edge residue/particles also exist. For example, during metal film deposition, a clamp ring typically is employed to secure a wafer to a heated pedestal within the deposition chamber and to shield wafer edges from film disposition (e.g., to prevent metal from depositing along wafer edges and shorting subsequently formed devices). Because the wafer and the clamp ring possess different coefficients of thermal expansion, each expands at a different rate during metal film deposition, the shear force between the clamp ring and the wafer""s edge also may generate edge particles that serve as a defect source. Additionally, if the clamp ring surface does not make intimate contact with the wafer surface along the entire circumference of the wafer, or if the ring and wafer are not concentrically aligned, a portion of the wafer""s edge may be exposed erroneously and coated with metal. Thereafter, processing steps are undertaken to pattern the wafer with semiconductor circuitry. Patterning, including selective doping through photoresist masks, deposition of blanket or selective thin film layers, and selective etching of materials, may deposit further residue particles on wafer edges, including ashed photo-resist, metals such as Cu, Ta, W, TaN, Ti, etc., material from non-metallic depositions, etc. Yet another source of potential contamination is the cassettes into which wafers are loaded for transport from one processing station to another. While the aforementioned mechanical means do remove some edge residue/particles, it is often difficult to remove all edge residue/particles, and subsequent processing has been shown to redistribute edge residue/particles to the front of the wafer, causing defects.
Co-pending U.S. patent application Ser. No. 09/113,447, having a filing date of Jul. 10, 1998 and assigned to the present assignee, entitled xe2x80x9cWafer Edge Scrubberxe2x80x9d, provides an improved scrubbing apparatus having a profiled surface to more effectively mechanically remove residue/particles from the wafer""s edge. While highly effective for removal of residue, an additional edge cleaning apparatus for use in conjunction with the disclosed scrubbing apparatus would further reduce edge residue/particle levels. Moreover, the scrubbing aparatus of U.S. patent application Ser. No. 09/113,447 is not able to remove layers erroneously deposited on a wafer""s edge.
Accordingly, the field of disk cleaning requires a method and apparatus which effectively removes both residue and deposited material from a disk""s edge without adversely impacting the disk""s major surfaces.
The present invention addresses the need for more effectively removing material from the edge of a disk by providing a method and apparatus for etching material layers and/or for cleaning residue from the edge of a disk. In a first aspect, an etchant is applied to the disk""s edge via an absorbent swab into which a fluid supply line extends. The swab is placed in contact with the disk""s edge and the etchant is supplied via the fluid supply line as the disk is rotated. Given the potential for the etchant to drip and thereby come into contact with patterned areas of the disk as the disk rotates away from the etchant supply (e.g., away from the swab), a rinsing fluid source (e.g., a trough or a nozzle) is positioned to remove the etchant from the disk""s edge.
In a second aspect an etchant is supplied to the disk""s edge via an etchant filled trough in which the edge of a vertically oriented disk is submerged. The trough may include a transducer which enhances material removal by imparting megasonic energy to the etchant. Thus, in the first and second embodiments, the invention uniformly etches material from the edge of the disk without the particle generation often experienced by the edge rings conventionally employed to prevent edge deposition.
In a third aspect, cleaning fluid is applied to the disk""s edge via a cleaning fluid filled trough in which the edge of a vertically oriented disk is submerged. The trough includes transducers which enhance cleaning by imparting megasonic energy to the cleaning fluid. An optional swab may be positioned such that the disk""s edge is contacted by the swab prior to reaching the trough or after leaving the trough. The swab loosens and/or removes particles which may be continuously flushed from the surface of the swab via a fluid supply line which extends into the swab.
Each aspect of the invention may be used alone, or with any other cleaning apparatus that rotates a vertically oriented disk. Particularly, to provide the combined cleaning of both scrubbing and megasonics in a single step, the inventive cleaning trough may be used with a vertically oriented scrubber such as that disclosed in commonly assigned U.S. patent application Ser. No. 09/113,447, filed Jul. 10, 1998, the entire disclosure of which is incorporated herein by this reference. Thus, the invention may be used to remove deposited material layers from disk edges and/or may provide superior edge cleaning by combining both scrubbing via the swab or via a vertical scrubber, and megasonic cleaning via the inventive trough. The invention is particularly well suited for removing material from semiconductor substrates (silicon or a processed substrate having layers thereon) and for removing material from electroplated disks. For instance, during copper electroplating, it is difficult to ensure that no copper is deposited on the edge of the wafer. Because the barrier layer deposited prior to copper electroplating often is of insufficient thickness or continuity at the wafer""s edge, any copper deposited thereon can diffuse into the wafer via the edge, degrading the electrical performance of devices being fabricated on the wafer. The present invention allows for the complete removal of copper from the wafer""s edge. Similarly, tungsten can be inadvertently deposited on the wafer""s edge. Because the adhesion layer at the wafer""s edge is often of insufficient thickness or continuity, tungsten deposited on the wafer""s edge will often have poor adhesion. Due to poor adhesion, and also due to tungsten""s high internal stress, the wafer""s edge can be a source of tungsten particles which may fall upon the wafer surface during subsequent processing. The present invention allows for the complete removal of tungsten from the wafer edge.
Other objects, features and advantages of the present invention will become more fully apparent from the following detailed description of the preferred embodiments, the appended claims, and the accompanying drawings.
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