Abrading – Machine – Rotary tool
Utility Patent
1998-01-21
2001-01-02
Eley, Timothy V. (Department: 3723)
Abrading
Machine
Rotary tool
C451S262000, C451S269000, C451S342000, C451S343000
Utility Patent
active
06168506
ABSTRACT:
TECHNICAL FIELD
The present invention relates, generally, to techniques for polishing workpieces and, more particularly, to the use of improved plate support structures to increase pressure uniformity at the workpiece surface.
BACKGROUND ART AND TECHNICAL PROBLEMS
Polishing technology has been largely driven by the need for exceptionally smooth and planarized surfaces on high-tech materials and components such as magnetic disks, semiconductors, and the like. In the case of semiconductor wafers, for example, polishing techniques are employed not just for polishing and planarizing the bulk wafer, but also for planarization of those layers which comprise the active circuitry; e.g., conductor metals, passivation, and inter-layer dielectrics.
In a paradigmatic polishing operation, a platen/polishing-pad assembly is employed in conjunction with a slurry, for example a water-based slurry comprising colloidal silica particles. When pressure is applied between the polishing pad (e.g., a polyurethane pad) and the workpiece being polished, mechanical stresses are imparted to the workpiece surface. Abrasive particles within the slurry act to create zones of localized stress, which in turn creates mechanical strain on the chemical bonds comprising the surface being polished. Consequently, microscopic regions are removed from the surface being polished, enhancing planarity of the polished surface.
Furthermore, in a chemical-mechanical planarization context (CMP), the slurry is used to effect chemical as well as mechanical polishing and planarization. More particularly, the slurry suitably comprises a chemically and mechanically active solution, for example, abrasive particles coupled with chemically reactive agents. Suitable chemically reactive agents include hydroxides, but may also include highly basic or highly acidic ions.
See, for example, Arai, et al. U.S. Pat. No. 5,099,614, issued March, 1992; Karlsrud, U.S. Pat. No. 5,498,196, issued March, 1996; Arai, et al., U.S. Pat. No. 4,805,348, issued February, 1989; Karlsrud et al., U.S. Pat. No. 5,329,732, issued July, 1994; and Karlsrud et al., U.S. Pat. No. 5,498,199, issued March, 1996, for further discussion of presently known lapping and planarization techniques. By this reference, the entire disclosures of the foregoing patents are hereby incorporated herein.
A key variable used to characterize a particular polishing or grinding process is the material removal rate. The material removal rate of a process is simply the rate at which material is removed from the workpiece surface, and is typically expressed as a length per unit time (e.g., microns per minute).
Many factors can and do affect material removal rate. For example, the material properties of the polishing surface, the mechanical and chemical properties of the slurry, and the properties of the workpiece surface itself are all important factors. In addition, and more important for the purposes of the present invention, removal rate is a strong function of applied pressure. That is, removal rate increases as the local normal compressive force applied to the workpiece surface increases.
Presently known polishing/grinding techniques are unsatisfactory in several regards. In many polishing configurations, for example, particularly those where processing of multiple or large workpieces is performed, material removal rate can vary significantly from workpiece-to-workpiece and across individual workpieces themselves due to uneven force distribution at the workpieces. More particularly, polishing, of multiple workpieces is often performed using a large ring-shaped top plate. When such a plate is supported at points substantially close to the inner or outer diameters, or otherwise supported non-optimally, the compressive force varies radially; that is, the ring in the vicinity of the support points is rigidly supported and hence will necessarily exhibit less deflection and impart a greater downward force than will those regions of the ring which lack a rigid support.
Presently known techniques are also unsatisfactory in that, due to manufacturing limitations, polishing plates often exhibit minor non-planarities. It is common for such plates to be either concave or convex in shape (for example, 10 micron profile variation over a span of 24 inches is not uncommon), and even minor variations in plate planarity can have a significant impact on applied stress at the workpiece surface. These non-planarities are exacerbated by the support techniques mentioned earlier. When a non-planar ring is supported, for example, by a series of posts near the inner diameter, it is possible that deflection of the ring during processing will work to increase the overall non-planarity of the polishing surface.
Chemical mechanical planarization techniques are thus needed which reduce variation in material removal rates resulting from force variations across the polishing surface introduced as a result of non-optimum plate supports.
SUMMARY OF THE INVENTION
In accordance with the present invention, a set of plate supports are advantageously disposed between a backing plate and a top plate having a polishing surface useful for polishing workpieces, thereby producing a substantially uniform material removal rate. In a preferred exemplary embodiment, a structure useful in the context of the present invention suitably comprises a non-isosceles triangular element. In a particularly preferred embodiment, a set of eight such structures are distributed evenly at 45 degree increments around a ring-shaped top plate.
In accordance with one aspect of the present invention, a preferred support reduces radial stress variations arising from non-optimum positioning of support points with respect to the inner and outer diameters of the polishing surface.
In accordance with another aspect of the present invention, a preferred support reduces radial stress variations arising from the effects of increasing applied pressure; that is, the stress distribution at the workpiece surface remains substantially constant as applied pressure is increased.
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Eley Timothy V.
Snell & Wilmer L.L.P.
SpeedFam-IPEC Corporation
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