Adhesive bonding and miscellaneous chemical manufacture – Methods – Surface bonding and/or assembly therefor
Reexamination Certificate
2001-01-18
2002-11-12
Mayes, Curtis (Department: 1734)
Adhesive bonding and miscellaneous chemical manufacture
Methods
Surface bonding and/or assembly therefor
C156S247000, C156S273300, C156S275500, C428S345000, C438S464000
Reexamination Certificate
active
06478918
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates generally to adhesive tapes useful for processing semiconductor wafers and, more specifically, to tapes having nonpressure sensitive adhesive compositions that include a copolymer of acrylic-functional monomers. These tapes are useful in the grinding and/or dicing of semiconductor wafers.
2. Description of the Related Art
Semiconductor integrated circuit (IC) chips are commonly used in electronic components, whether for sophisticated industrial machinery, automobiles or everyday household appliances. The production of semiconductor IC chips begins with the manufacture of semiconductor wafers containing many semiconductor elements. Ultimately, the wafer is sawn or diced into individual semiconductor elements (called die), each element becoming a semiconductor IC chip.
Typically, a semiconductor wafer is prepared by slicing or sawing a single, high purity silicon ingot into thin circular wafers about 500 microns (&mgr;m) to about 1000 &mgr;m thick. A wafer may be doped to alter its electrical properties. Electronic circuitry is then applied to the front side of the wafer, usually by photolithography. Separation lines are also photolithographed onto the wafer to provide saw marks for eventual dicing of the wafer into individual semiconductor IC chips.
Wafer diameters were traditionally about 3 inches (7.6 cm) to about 4 inches (10.2 cm). However, as individual IC chips have become larger, the typical wafer diameter has increased to about 5 inches (12.7 cm) to about 8 inches (20.3 cm) so as to permit more die to be formed from a single wafer. It is expected that wafer diameters will eventually expand to about 12 inches (30.5 cm) to about 16 inches (40.6 cm), and perhaps to even larger sizes.
To protect the delicate electronic circuitry from atmospheric contamination by dust, moisture, airborne corrosive acids and the like, the front side of the wafer is provided with a passivation or protective layer which may be an inorganic material such as silicon oxynitride or an organic material such as polyimide.
To facilitate the manufacture of electronic components, it is desirable to reduce the thickness of the wafers (and hence the thickness of the semiconductor IC chips formed therefrom). A common process involves holding the front side of the wafer against a vacuum table while grinding the backside of the wafer to a thickness of about 200 &mgr;m to about 500 &mgr;m in the presence of a water spray to remove the grinding debris. However, the wafers are inherently fragile and are susceptible to breaking during the grinding process, a problem which is enhanced as the wafer diameter becomes larger. Moreover, the front side of the wafer is held against the vacuum table, which could abrade the passivation/protective layer and the underlying circuitry. Consequently, there is a need to protect the wafer (especially the front side) from breakage, contamination, and abrasion.
Early approaches to this problem used a layer of paraffin wax over the front side of the wafer, with the wax being eventually removed by a solvent wash. The deficiencies of this approach are described in U.S. Pat. No. 4,853,286 (Narimatsu et al.). In other approaches, a photoresist coating was spin-coated onto the front side of the wafer, but this did not always eliminate wafer breakage.
Historically, adhesive products have been employed to protect the front side of the wafer. Sometimes the tapes are used alone and sometimes they are used in conjunction with a photoresist coating to provide a surface to which the tape can stick and to protect the passivation/protective layer from staining and/or delamination by the tape. However, according to the technical literature, adhesive tapes have not provided a complete solution to the wafer protection problem. The previously mentioned U.S. Pat. No. 4,853,286 indicates that wafer breakage still occurs and that the adhesive surface accumulates dust that can contaminate the wafer. Also, there can be difficulty in subsequently removing the tape if it has high initial adhesion to the wafer or if the adhesion increases from the time that the tape is applied to the wafer until it is removed.
Various adhesive tapes that are reportedly useful in semiconductor wafer backside grinding operations (sometimes referred to herein as “wafer grinding”) have been described. For example, the aforementioned U.S. Pat. No. 4,853,286 discloses a wafer processing film that is used in the grinding of wafers to prevent breakage. The film includes a base film, a layer of a commercially available, common adhesive (such as an acrylic ester, urethane, or synthetic rubber adhesive) that can preferably include a nonionic surface active agent and an ethylene glycol derivative, and an optional supporting film laminated to the nonadhesive side of the base film. U.S. Pat. No. 5,126,178 (Takemura et al.) describes a wafer processing film that includes a base film with a pressure sensitive adhesive on one side (which is protected by a removable release film), and a phosphoric acid-based surfactant on the backside. The pressure sensitive adhesive can be acrylic-based, vinyl-based, or rubber-based, although an aqueous emulsion type pressure sensitive adhesive is preferred.
European Patent Publication No. 0 530 729 discloses a pressure sensitive adhesive tape used in grinding the backside of a semiconductor wafer. The pressure sensitive adhesive, which reportedly has a small initial adhesion and shows no adhesion strength increase with time, comprises an aqueous acrylic resin emulsion adhesive, a nonionic surfactant, an epoxy type and/or an aziridine type crosslinking agent, and a water soluble organic compound.
However, there still remains a need for an adhesive tape that has even greater utility in semiconductor wafer grinding processes. Preferably, such tapes will possess several desirable properties. For example, the tape should preferably quickly provide sufficient initial adhesion to surfaces such as silicon, polyimide, silicon oxynitride, and other integrated circuit coatings such that the semiconductor wafers will readily survive post-processing steps yet be easily removed when required. Preferably, a single tape will provide acceptable initial adhesion to each of these surfaces so as to eliminate the need for storing different tapes for different surfaces. However, the final adhesion should not be so high that removing the tape breaks or fractures a larger number of wafers than is permitted under conventional industry standards (typically about one wafer or less per one thousand), or leaves adhesive residue that could impair subsequent processing of the wafer. Many tapes used in the semiconductor industry require the application of heat to the wafer at the time of removal of the tape to prevent the wafer from being broken. It would be desirable if no such heating step were required.
It would also be desirable if the initial and final adhesion properties of the tape were preferably maintained over several days and, more preferably, over several weeks of storage. That is, preferably, there should be no process or material-limiting increase in adhesion over time (sometimes referred to as adhesion build), a problem associated with certain adhesives. Similarly and preferably, there should be no other significant change in adhesion over time, as could occur if fugitive or migratory surfactants and other mobile components in the adhesive migrate to the adhesive bond line so as to form a weak boundary layer. An adhesive that generally maintains its initial and final adhesion properties during storage would not only provide tapes having long shelf lives, but would also eliminate the need to carry out the grinding process shortly after taping the semiconductor wafers.
Another desirable attribute would be the ability to remove the adhesive tape without substantial staining, which refers to a change in the optical density of the semiconductor wafer that is detected when the semiconductor wafer is viewed under a microscope. This typically results fro
Alahapperuma Karunasena A.
Bennett Greggory S.
Bennett Richard E.
Moore Cheryl L.
Winslow Louis E.
3M Innovative Properties Company
Mayes Curtis
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