US 3504457 A
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Description (OCR text may contain errors)
April 7, 1970 H, R, JACOBSEN ET AL 3,504,457
POLISHING APPARATUS Filed July 5, 1966 40W iy//5/ BEAR/NG CON 754C 7' (IRG/N6 MF4/V5 INVENTORS HANS REM/#0107' .fS/V B52/.MER M JENSEN 2@ @Mge ys.
United States Patent O York Filed July 5, 1966, Ser. No. 562,757 Int. Cl. B24b 5/00, 29/00, 11/00 U.S. Cl. 51-131 4 Claims ABSTRACT OF THE DISCLOSURE A device for polishing semiconductor wafers wherein the polishing tool comprises a poromeric material of polyurethane reinforced with a polyester and with a polishing slurry thereon is urged into contact with the workpiece.
This invention relates to an apparatus for processing workpieces and, more specifically for imparting a polished finish to elements subjected thereto.
Many applications of present day interest require thin, fragile semiconductor wafers having a highly polished critical surface. To produce such a finish, prior art organizations have rotated such semiconductor elements against a lapping substrate in the presence of a polishing slurry.
The surface of the lapping plate in contact with the semiconductor elements has typically included thereon -as the active polishing member a pitch composition, papers, pseudo papers or other nonwovens, or felt substances. However, the above and other prior art operative polishing surfaces are characterized by at least several of the following deficiencies: (1) temperature sensitivity, and therefore instability at high polishing rates; (2) unhomogeneous consistency; (3) a propensity to pick up and retain foreign elements; (4) poor wear characteristics requiring frequent replacement; (5) variations from sample to sample; (6) the characteristics of being impermeable, and thereby preventing a polishing slurry from reaching all surface areas of a product being operated upon; (7) relatively little tensile strength, thereby being subject to distortion; and (8) a resistance to bonding, thereby being difiicult to affix to cooperating compositions and/or a lapping plate.
It is therefore an object of the present invention to provide an improved apparatus for polishing workpieces.
More specifically, an object of the present invention is the provision of a resilient, homogeneous polishing organization which is porous, relatively insensitive to temperature, and which may be fabricated with little variation from sample to sample.
These and other objects of the present invention are realized in a specific illustrative polishing organization which comprises a layer of Corfam (a trademark of the Du Pont Corporation for a poromeric material) afiixed to a lapping substrate via layers of an adhesive, chemically inert nitrile rubber, and a pressure sensitive, clean release adhesive. A pororneric material, such as Du Ponts Corfam, comprises polyurethane reinforced with polyester. In this regard see, for example, Chemistry of Organic Compounds by C. R. Noller, published by W. B. Saunders Company in 1965, at chapter 36.
The active, or free Corfam surface is adapted to be fiat such that the surface of the work elements brought into rotational bearing contact therewith will be polished, i.e., will be rendered flat. In an alternative embodiment of the present invention a porous film e.g., of foam polyurethane, is attached to the Corfam to function as the active polishing surface.
A complete understanding of the present invention and of the above and other objects thereof may be gained 3,504,457 Patented Apr. 7, 1970 from a consideration of an illustrative embodiment thereof depicted in the accompanying drawing.
Referring now to the drawing, there is shown in crosssectional form an illustrative polishing organization which embodies the principles of the present invention. The arrangement includes a layer of Corfam 20 which has a layer 35 of a, chemically inert material, eg., nitrile rubber, afiixed thereto by an adhesive 30. A layer 40` of a pressure sensitive, clean release adhesive 40 is bonded to the bottom of the nitrile rubber layer 35 for purposes of facilitating the attachment and removal of the composite polishing laminated structure with respect to a metal lapping substrate 45. It is noted that other poromeric materials, as well as other compositions embodying the attributes of Corfam described herein, may be employed in place of the Corfam layer 20.
The Corfam layer 20 is fabricated such that the upper surface thereof exhibits the requisite flatness required for a particular polishing operation (assuming that a fiat surface is desired for the workpiece), Employing such a layer 20,the lapping substrate 45 is urged into a bearing pressure contact with elements 15 to be polished. Such elements 15 may comprise, for example, semiconductor wafers, with these elements being shown in the drawing as mounted on a rotating mounting block 10. Further, the polishing operation may advantageously take place in a polishing liquid slurry environment, with the slurry being supplied by a slurry source 50 via a nozzle 51.
The Corfam material 20 is very porous, and hence the slurry is translated by the layer 20 to all portions of the surface of the elements 15 thereby effecting uniform polishing. Also, the Corfam material 20 is essentially insensitive to temperature, at least in the temperature range of interest for polishing operations. Accordingly, polishing may be accomplished at high rates of speed. Further, the layer 20 is homogeneous, and may be fabricated in relatively large quantities to produce many uniform polishing layers without material variation from element to element.
Moreover, Corfam is resilient and prevents damage to elements 15 being polished by absorbing mechanical vibrations and any compaction caused by overshoot of the mounting members 10 or 45. In addition, the layer 20 is durable which is beneficial from maintenance and batch processing rate standpoints.
Still further, the active, upper surface of the Corfam layer 20 can be treated or impregnated when required for special polishing operations. Such treatment may comprise, for example, brushing, napping, skiving or texturing the polishing Corfam surface to increase the number for active polishing fibers, or calendering the surface to increase its atness.
The composite laminated polishing organization 20-30- 35-40 is easily attached to, and removed from the lapping substrate 45 by reason of the properties of the pressure sensitive, clean release adhesive layer 40. The inert layer 35 is employed to insulate the adhesive 40 from the layers thereabove, and also from the slurry which would otherwise reach the adhesive I40 through the porous Corfam layer 20. Such lforeign substances would tend to change the physical state of the adhesive 40, e.g., harden it thereby making attachment to and removal from the plate 45 more difficult.
By way of -functional operation, when rotational bearing contact is established between the Corfam upper surface and the lwork pieces 15, the desired polishing surface is imparted to the lower, critical surface of these elements. Hence, the desired polishing is accomplished.
In an alternative embodiment of the invention a porous film 23, e.g., of foam polyurethane, is afiixed to the upper surface of the Corfam layer 20 by a porous adhesive 25. In such an arrangement, the upper face of the film 23 is the effective polishing surface, with the Corfam backing layer 20 providing resiliency and strength, while maintaining a composite porous organization which is desirable in a polishing organization for the reasons given hereinabove. Thus it is noted that compositions 4which are porous only in film thicknesses, but which otherwise have desirable polishing properties, may be used as a polishing surface when mounted on a Corfam backing layer 20.
Thus, the organization shown in the drawing, both with and without the film 23 and the adhesive 25, has been shown by the above to function as a very desirable polishing structure.
1t is to be understood that the above described method and organizations are only illustrative of the application of the principles of the present inventions. Numerous other arrangements and modes of operation may be devised by those skilled in the art without departing from the spirit and scope of this invention. For example, the active polishing surface, i.e., the upper surface of the Corfam 20 or the lm 23 if such a lm is employed, may exhibit a geometry other than a at plane -when a nonat work piece of a corresponding geometry is to be polished. In addition, other known bonding mechanisms, such as mechanical interlocking or distortion, may be used to fabricate the composite laminated polishing structure shown in the drawing vwithout the use of the adhesives 25 and 30.
1. In combination in a polishing organization, a poromeric material comprising polyurethane reinforced with polyester, a porous film axed to said poromeric material, wherein said poromeric material has rst and second surfaces, said rst surface engaging said porous hlm, and further comprising an inert layer of nitrile rubber I affixed to said second surface of said Corfam.
plate, and means for selectively urging work pieces to be polished into a bearing relationship with said lapping plate.
3. In combination in a polishing organization, a poromeric material comprising polyurethane reinforced with polyester, a porous hlm aixed to said poromeric material, Iwherein said porous lm is polyurethane, and means for selectively urging work pieces to be polished into bearing contact with said porous film.
4. In combination in a polishing organization, a lapping substrate, a poromeric layer comprising polyurethane reinforced with polyester mounted on said substrate, said poromeric layer including a polishing surface thereon, and means for urging work pieces to be polished into bearing contact with said poromeric polishing surface.
References Cited UNITED STATES PATENTS 2,644,280 7 l 95 3 ONeil 51-406 3,050,909 8/ 1962 Rawstron 51-124 3,082,582 3/1963 Jeske 51-407 X 3,123,953 3/1964 Merkl 51-283 3,360,889 1/1968 Borish 51-131 X 671,130 4/1901 Darden 51-401 804,853 11/1905 Ireson. 1,923,719 8/1933 Fuller 51-301 X 2,650,158 8/1953 Eastman 51-407 X FOREIGN PATENTS 681,832 3/1964 Canada.
OTHER REFERENCES Boot and 'Shoe Recorder, Oct. l, 1963, article titled The Story of Corfam pages 1-2 thereof.
HAROLD D. WHITEHEAD, Primary Examiner U.'S. C1. XR.