Electric heating – Metal heating – By arc
Reexamination Certificate
2000-02-10
2001-09-11
Paschall, Mark (Department: 3742)
Electric heating
Metal heating
By arc
C219S121420, C219S121430, C219S121350, C204S192340, C204S298360, C156S345420, C156S922000, C250S492210, C438S712000, C438S697000, C216S067000, C216S066000
Reexamination Certificate
active
06288357
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of Invention
The present invention relates generally to a method and apparatus for smoothing surfaces having fine irregularities, of the order of a few microns and up to about 200 microns in size. In particular, the method and apparatus of the invention is useful in planarizing or polishing the surfaces of semiconductor wafers, precision optical lenses and the like using an ion beam in the presence of a radio frequency generated plasma.
2. Description of The Related Art
With advances in technology, there is increasingly a demand, in certain technologies, for precision planarization or polishing of surfaces for a variety of purposes. For example, highly polished precision surfaces are needed in optics and in the fabrication of semiconductors, using silicon wafers. Indeed, as explained below, requirements in the two technical fields are frequently interrelated, in that optical instruments are used in the manufacture of semiconductors.
The fabrication of very large scale integrated circuits on silicon wafers is a process requiring extreme precision because of the very fine details of the circuits. Indeed, the width of circuit lines are continually decreasing as the technology advances, and is now in the range of 0.18-100 microns. Since the circuits are produced using photolithographic techniques, extremely accurately ground lenses are required to provide fine detail. As a necessary consequence of providing such precise focusing, the lenses lack depth of field, i.e., an image is accurately produced only at a specific distance from the lens, and any deviation in this distance produces an increasingly unfocused or fuzzy image. Therefore, the surface onto which the image is projected must be as perfectly planar as possible to eliminate out-of-focus image fuzziness. A failure to maintain planarity exacerbates the problem as additional layers are formed on the nonplanar surface resulting in an increased proportion of defective semiconductors that must be rejected.
At present, the standard technique for restoring surface planarity, after certain processes that lay down component layers on the wafer, is chemical mechanical planarization (CMP). During this process, the surface of the wafer is polished with a polishing pad, and in certain instances with a chemical slurry, to remove excess material and also to replanarize the surface. When a slurry is used, it contains an abrasive, such as silica or alumina, and chemical additives that are designed to selectively react with and soften the composition of those components that must be planarized or removed from the wafer surface. Chemical slurries are not always used, and certain planarization and polishing steps may be carried out using a “fixed abrasive” in which an abrasive substance or composition is fixed in a polishing pad or other substrate that is used to polish the wafer surface.
SUMMARY OF THE INVENTION
This summary of invention section is intended to introduce the reader to aspects of the invention and is not a complete description of the invention. Particular aspects of the invention are pointed out in other sections hereinbelow, and the invention is set forth in the appended claims which alone demarcate its scope.
The invention provides a method of planarizing a surface of a substrate that has micro irregularities using an ion beam of suitable energy, while the surface of the substrate is energized with radio frequency generated plasma. The technique of the invention may be applied to a wide range of substrates, including semiconductor wafers (as a substitute for chemical mechanical polishing), hard disk fabrication (for computers), optical lenses, and other devices that require exceptionally accurately planarized or smoothed surfaces.
In accordance with one aspect of the method of the invention, a substrate is placed in a holder in a vacuum chamber equipped with a radio frequency inductive plasma generator. The surface to be polished or planarized is exposed to a source of energetic ions, such as an ion gun. The chamber is filled with a gas, and the gas is ionized with radio frequency energy to form inductive plasma that surround the substrate. An ion beam is mounted above the substrate and directed to scan the surface of the substrate that must be polished or planarized. The ion beam is selected to have sufficient energy to remove surface micro irregularities from the surface of the substrate. Preferably, the ion beam milled surface is scanned and inspected for surface smoothness characteristics. When a predetermined surface smoothness characteristic has been achieved, the ion beam milling is discontinued.
The method of the invention eliminates the need for chemical mechanical planarization, and provides a method of achieving surface smoothness and planarization, without generation of hazardous waste for disposal. Moreover, the method is exceptionally well suited to automation, and may be carried out at high speed resulting in a high throughput of polished substrates. Further, the technique is flexible in that an appropriate selection of ion beam energy and plasma may be custom tailored for a particular substrate. Accordingly, the invention provides many advantages over prior art techniques, such as chemical mechanical polishing.
REFERENCES:
patent: 4806829 (1989-02-01), Nakao
patent: 4874459 (1989-10-01), Coldren et al.
patent: 5744400 (1998-04-01), Dyer
patent: 6013191 (2000-01-01), Nasser-Faili et al.
patent: 6042738 (2000-03-01), Casey, Jr. et al.
Paschall Mark
Snell & Wilmer L.L.P.
SpeedFam-IPEC Corporation
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