Semiconductor device manufacturing: process – Bonding of plural semiconductor substrates – Thinning of semiconductor substrate
Reexamination Certificate
2002-05-17
2004-04-20
Robertson, Jeffrey B. (Department: 1712)
Semiconductor device manufacturing: process
Bonding of plural semiconductor substrates
Thinning of semiconductor substrate
C438S026000, C438S118000, C438S706000, C438S976000, C438S977000
Reexamination Certificate
active
06723619
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a pressure sensitive adhesive sheet for semiconductor wafer processing. More particularly, the present invention relates to a pressure sensitive adhesive sheet which is suitable to the processing of semiconductor wafers in vacuum.
BACKGROUND OF THE INVENTION
It is common practice to subject a semiconductor wafer having circuits formed on its surface to grinding of a back side thereof so as to remove an oxide layer on the back side or so as to reduce and uniformalize the thickness of the semiconductor wafer. In particular, in recent years, the semiconductor wafer is occasionally ground to a thickness of 100 &mgr;m or less in accordance with the demand for reduction of chip thickness. At the grinding of the back side of semiconductor wafer, a pressure sensitive adhesive sheet is stuck to the circuit surface of semiconductor wafer so as to protect the circuits or so as to fix the semiconductor wafer.
The above reduction of semiconductor wafer thickness deteriorates antifolding strength of the wafer due to grinding marks on the back side of semiconductor wafer which has resulted from mechanical grinding with the use of a grindstone, a grinder or the like. Therefore, it is proposed to remove the grinding marks on the back side of semiconductor wafer by dry etching.
This dry etching is generally performed in a vacuum of 10
−3
to 10
−4
torr. However, in such a vacuum, when fixing semiconductor wafer with the use of conventional ultraviolet curable pressure sensitive adhesive sheets, such a problem has occasionally invited that volatile components come out from the layer of ultraviolet curable pressure sensitive adhesive of the ultraviolet curable pressure sensitive adhesive sheet with the result that generated gases from volatile components contained in the layer of ultraviolet curable pressure sensitive adhesive are trapped between the semiconductor wafer of extremely reduced thickness and the ultraviolet curable pressure sensitive adhesive sheet, thereby causing the semiconductor wafer to deform due to a pressure difference between outside and inside the semiconductor wafer to stick pressure sensitive adhesive sheet. This deformation of semiconductor wafer has occasionally caused the pressure sensitive adhesive to remain stuck to deformed portions (dented portions) of the semiconductor wafer, even after the stripping of the pressure sensitive adhesive sheet, to thereby foul the semiconductor wafer.
The present invention has been made in view of the above state of the prior art. It is an object of the present invention to provide a pressure sensitive adhesive sheet for semiconductor wafer processing which, even in the processing of a semiconductor wafer in vacuum, is free from generating gases from the pressure sensitive adhesive sheet to thereby enable avoiding wafer deformation and adhesive transfer.
SUMMARY OF THE INVENTION
The pressure sensitive adhesive sheet for semiconductor wafer processing according to the present invention is a pressure sensitive adhesive sheet used to fix a semiconductor wafer in semiconductor wafer processing in vacuum, which comprises:
a substrate and, superimposed on one side or both sides thereof, a layer of ultraviolet curable pressure sensitive adhesive composition comprising an ultraviolet curable copolymer having ultraviolet polymerizable groups as side chains and a phosphorous photopolymerization initiator.
In the present invention, it is preferred that the phosphorous photopolymerization initiator be an acylphosphine oxide compound, preferably a compound having a CO—PO bond in its molecule, and still preferably a compound represented by the formula:
wherein R
1
represents an aromatic group which may have substituent, and each of R and R
3
independently represents phenyl group, alkyl group, alkoxy group or aromatic acyl group which may have substituent.
In the present invention, it is preferred that the layer of ultraviolet curable pressure sensitive adhesive composition contain 0.005 to 20 parts by weight of phosphorous photopolymerization initiator per 100 parts by weight of the ultraviolet curable copolymer.
DETAILED DESCRIPTION OF THE INVENTION
The present invention will be described in greater detail below. The pressure sensitive adhesive sheet for semiconductor wafer processing according to the present invention is a pressure sensitive adhesive sheet used to fix a semiconductor wafer in semiconductor wafer processing in vacuum, which comprises:
a substrate and, superimposed on one side or both sides thereof, a layer of ultraviolet curable pressure sensitive adhesive composition comprising an ultraviolet curable copolymer (A) having ultraviolet polymerizable groups as side chains and a phosphorous photopolymerization initiator (B).
The ultraviolet curable copolymer (A) exhibits not only stickiness but also ultraviolet curability. Details of the ultraviolet curable copolymer having ultraviolet polymerizable groups as side chains are described in, for example, Japanese Patent Laid-open Publication Nos. 5(1993)-32946 and 8(1996)-27239.
For example, the ultraviolet curable copolymer (A) is obtained by reacting an acrylic copolymer (a1) comprising units of a monomer containing a functional group with a compound (a2) containing an unsaturated group which has a substituent reactive with the above functional group.
The monomer containing a functional group refers to a monomer having in its molecule not only a polymerizable double bond but also a functional group such as a hydroxyl group, a carboxyl group, an amino group, a substituted amino group or an epoxy group. Preferably, an unsaturated compound containing a hydroxyl group or an unsaturated compound containing a carboxyl group is employed.
Specific examples of these functional group containing monomers include an acrylate containing a hydroxyl group, such as 2-hydroxyethyl acrylate, 2-hydroxyethyl methacrylate, 2-hydroxypropyl acrylate or 2-hydroxypropyl methacrylate; and a compound containing a carboxyl group, such as acrylic acid, methacrylic acid or itaconic acid.
The above functional group containing monomers may be used individually or in combination. The acrylic copolymer (a1) is composed of structural units derived from the above monomer containing a functional group and structural units derived from a (meth)acrylic ester monomer or a derivative thereof. As the (meth)acrylic ester monomer, there can be used a cycloalkyl (meth)acrylate, benzyl (meth)acrylate or an alkyl (meth)acrylate in which the alkyl group has 1 to 18 carbon atoms. Of these, an alkyl (meth)acrylate in which the alkyl group has 1 to 18 carbon atoms is especially preferred which is, for example, methyl acrylate, methyl methacrylate, ethyl acrylate, ethyl methacrylate, propyl acrylate, propyl methacrylate, butyl acrylate or butyl methacrylate.
The acrylic copolymer (a1) generally contains the above structural units derived from the monomer containing a functional group in an amount of 3 to 100% by weight, preferably 5 to 40% by weight, and still preferably 10 to 30% by weight. Further, the acrylic copolymer (a1) generally contains the above structural units derived from the (meth)acrylic ester monomer or derivative thereof in an amount of 0 to 97% by weight, preferably 60 to 95% by weight, and still preferably 70 to 90% by weight.
The acrylic copolymer (a1) is obtained by copolymerizing the above monomer containing a functional group with the above (meth)acrylic ester monomer or derivative thereof according to the customary procedure. In this copolymerization, a small amount (for example, 10% by weight or less, preferably 5% by weight or less) of another monomer such as vinyl formate, vinyl acetate or styrene may be used in addition to the above monomers.
The ultraviolet curable copolymer (A) can be obtained by reacting the above acrylic copolymer (a1) comprising units of a monomer containing a functional group with a compound (a2) containing an unsaturated group which has a substituent reactive with the above functional group.
The compound (a2) con
Ebe Kazuyoshi
Nagamoto Koichi
Lintec Corporation
Robertson Jeffrey B.
Webb Ziesenheim & Logsdon Orkin & Hanson, P.C.
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