Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Polymers from only ethylenic monomers or processes of...
Reexamination Certificate
1998-02-12
2001-01-30
Pezzuto, Helen L. (Department: 1713)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Polymers from only ethylenic monomers or processes of...
C526S210000, C526S211000, C526S217000, C526S220000, C526S329200, C526S329300
Reexamination Certificate
active
06180742
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a pressure sensitive adhesive composition and a use thereof. More particularly, the present invention is concerned with a pressure sensitive adhesive composition which is suitable for use in a wafer surface protective pressure sensitive adhesive sheet employed for protecting a circuit pattern formed on a wafer surface from cutting debris, etc. at the time of polishing the back of the wafer and is concerned with such a use of the pressure sensitive adhesive composition.
BACKGROUND OF THE INVENTION
A circuit pattern is formed on a surface of a semiconductor wafer of, for example, silicon or gallium arsenide by the etching or lift off method. The wafer having patterned surface generally has its back polished by, for example, a grinder while having the patterned surface protected by a pressure sensitive adhesive sheet applied thereto. The objective of polishing the back of the patterned wafer is first to remove any oxide layer which may be formed on the wafer back in the etching conducted during the patterning and second to regulate the thickness of the patterned wafer.
The polishing of the back of the wafer having patterned surface is conducted while washing the wafer back with purified water in order to remove any generated polishing debris and in order to remove heat generated during the polishing. In the polishing of the wafer back, a pressure sensitive adhesive sheet (surface protective sheet) is stuck to the wafer surface for the purpose of protecting the pattern formed on the wafer surface from the polishing debris. After the completion of the polishing of the wafer back, the pressure sensitive adhesive sheet is stripped from the wafer surface. At the time of the stripping, it has been inevitable for part of the pressure sensitive adhesive to remain on the patterned wafer surface. Thus, it has been necessary to wash away the remaining pressure sensitive adhesive from the wafer surface. Although washing with the use of an organic solvent has been carried out for removing pressure sensitive adhesive which remains adhering to the wafer surface, it is now the mainstream practice to conduct the washing with the use of purified water in view of the consideration of environmental protection and other problems. Accordingly, the pressure sensitive adhesive which can be washed away by water is increasingly used in the above surface protective sheet.
Examples of pressure sensitive adhesive compositions for use in the above pressure sensitive adhesive sheet include those based on nonionic surfactants described in Japanese Patent Laid-open Publication Nos. 62(1987)-101678 and 63(1988)-153814 and water swellable pressure sensitive adhesive compositions described in Japanese Patent Publication No. 5(1993)-77284.
In the use of the former pressure sensitive adhesive compositions, use is made of nonionic surfactants whose molecular weight is relatively low, so that they would become the cause of residue on the wafer surface after the stripping of the pressure sensitive adhesive sheet thereby inviting the possibility of adversely affecting the circuit surface of the wafer. Such a low molecular weight component would not always be entirely removed even if the washing away operation is conducted. The surfactants employed in the above use are not those intended for antistatic performance, so that a peel electrification occurs at the time of stripping of the pressure sensitive adhesive sheet after completion of the polishing. Thus, the antistatic characteristics of the pressure sensitive adhesive compositions based on nonionic surfactants are not satisfactory.
On the other hand, the latter pressure sensitive adhesive compositions do not use surfactants and are water swellable, which include, for example, a blend of a water soluble polymer and a (meth)acrylic polymer. The molecular weights of the water soluble polymers generally used in these compositions are smaller than those of the (meth)acrylic polymers. Thus, an adhesive residue would occur on the wafer surface after the stripping of the pressure sensitive adhesive sheet. Further, the washing away of (meth)acrylic polymers is not easy although the water soluble polymers can easily be removed by washing with water.
OBJECT OF THE INVENTION
It is an object of the present invention to provide a pressure sensitive adhesive composition which is suitable for use in a wafer surface protective sheet employed for protecting a circuit pattern formed on a wafer surface from cutting debris, etc. at the time of polishing the back of the wafer.
It is another object of the present invention to provide a pressure sensitive adhesive composition suitable for use in a wafer surface protective sheet, which exhibits an extremely low peel electrification voltage at the time of stripping of the pressure sensitive adhesive sheet and which, even if it remains on the wafer surface, can easily be removed by washing with water.
SUMMARY OF THE INVENTION
The pressure sensitive adhesive composition of the present invention comprises:
(A) a carboxyl group containing copolymer obtained by solution polymerization of (a) a carboxyl group containing polymerizable monomer and (b) another monomer copolymerizable with the monomer (a);
(B) a neutralizer; and
(C) a crosslinking agent.
In this pressure sensitive adhesive composition, it is preferred that the other monomer (b) be a compound represented by the formula:
wherein each of X
1
, X
2
and X
3
independently represents a hydrogen atom or a methyl group, R
1
represents a divalent hydrocarbon group having 2 to 12 carbon atoms, R
2
represents a hydrocarbon group having 1 to 10 carbon atoms, and n is a number of 1 to 10.
The pressure sensitive adhesive sheet of the present invention comprises a substrate and, superimposed thereon, a pressure sensitive adhesive layer composed of the above pressure sensitive adhesive composition. This pressure sensitive adhesive sheet is preferably used in wafer processing.
The above pressure sensitive adhesive sheet is preferably used in a method of polishing a back of a wafer, which comprises the steps of:
sticking the pressure sensitive adhesive sheet to a wafer surface having a pattern formed thereon; and
polishing the back of the wafer while feeding water thereto.
The pressure sensitive adhesive composition of the present invention is a solvent type and is a water soluble (water swellable) composition containing no surfactant. Hydrophilicity is imparted to the pressure sensitive adhesive polymer per se, so that the pressure sensitive adhesive composition is excellent in water washability and exhibits an extremely low peel electrification voltage at the time of stripping of the pressure sensitive adhesive sheet. Moreover, water solubility (water swellability) is imparted to the pressure sensitive adhesive composition of the present invention without executing a blending of a water soluble polymer and a (meth)acrylic polymer, so that an adhesive residue is extremely little at the time of stripping of the pressure sensitive adhesive sheet.
REFERENCES:
patent: 5508107 (1996-04-01), Gutman et al.
patent: 0252739 (1993-06-01), None
patent: 0530729 (1993-10-01), None
Japanese Patent Publication No. 62-101678 Abstract, May 12, 1987, 1 p., English language.
Japanese Patent Publication No. 06184508, Abstract, Jul. 5, 1994, 1 p., English language.
Japanese Patent Publication No. 07173445, Abstract, Jul. 11, 1995, 1 p., English language.
Kato Kiichiro
Kondoh Takeshi
Takahashi Kazuhiro
Lintec Corporation
Pezzuto Helen L.
Webb Ziesenheim & Logsdon Orkin & Hanson, P.C.
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