Stock material or miscellaneous articles – Web or sheet containing structurally defined element or... – Adhesive outermost layer
Reexamination Certificate
1999-05-21
2002-06-11
Zirker, Daniel (Department: 1771)
Stock material or miscellaneous articles
Web or sheet containing structurally defined element or...
Adhesive outermost layer
C428S525000, C523S111000
Reexamination Certificate
active
06403215
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to an energy beam curable hydrophilic pressure sensitive adhesive composition and a use thereof. More particularly, the present invention relates to a pressure sensitive adhesive composition suitable for use in a wafer surface protective pressure sensitive adhesive sheet which is used for protecting a circuit pattern formed on a wafer surface from grinding dust, etc. during grinding of the back of the wafer.
BACKGROUND OF THE INVENTION
Pattern is formed on a surface of a wafer of semiconductor such as silicon or gallium arsenide by, for example, the etching or liftoff method. The wafer having pattern formed on the surface generally has its patterned surface covered with a pressure sensitive adhesive sheet and, in that form, the back of the wafer is polished by means of, for example, a grinder. The first object of grinding the back of the patterned wafer is to remove any oxide layer which may occur on the back of the wafer at the etching step. The second object of grinding the wafer back is to regulate the thickness of the wafer having pattern formed thereon.
The grinding of the back of the wafer having pattern formed on its surface is conducted while washing the wafer back with purified water in order to remove dust raised by grinding and heat generated during the grinding. Before the grinding of the wafer back is conducted, the pressure sensitive adhesive sheet (surface protective sheet) is stuck to the wafer surface so that the pattern formed on the wafer surface is protected from grinding dust and washing water for grinding.
This type of pressure sensitive adhesive sheet is, for example,
a hydrophilic one such as pressure sensitive adhesive sheet of Japanese Patent Laid-open Publication No. 62(1987)-101678 using a pressure sensitive adhesive containing a nonionic surfactant or pressure sensitive adhesive sheet of Japanese Patent Publication No. 5(1993)-77284 using a water swellable pressure sensitive adhesive, which, after the completion of the grinding, is directly peeled so that the stain on wafer surface caused by pressure sensitive adhesive components can easily be removed by washing with purified water; and
an energy beam curable one such as pressure sensitive adhesive sheet disclosed in Japanese Patent Laid-open Publication No. 8(1996)-27239, which, after the completion of back grinding, is irradiated with energy beams to thereby extremely reduce the adhesive strength to the wafer so that traces of pressure sensitive adhesive would not remain even upon peeling of the pressure sensitive adhesive sheet.
Although the above two types of pressure sensitive adhesive sheets for wafer back grinding have appropriately been employed in view of the respective characteristics and in conformity with encountered conditions, an energy beam curable pressure sensitive adhesive sheet which exhibits low peeling resistance at the time of peeling of pressure sensitive adhesive sheet and is free from breaking the wafer would increasingly be demanded in the future in accordance with the increase of the diameter of the wafer and the reduction of the thickness of the wafer.
However, this energy beam curable pressure sensitive adhesive has not water washability. Thus, the problem would be encountered such that, when a residual pressure sensitive adhesive remains on a wafer surface for some reason (e.g., shortage in quantity of energy beams applied at the time of irradiation therewith; abnormally high temperature caused by excess irradiation; energy beam irradiation deficiency attributed to the clinging of grinding dust raised at the time of wafer back grinding onto the surface of the sheet; poor cohesive strength of the pressure sensitive adhesive; nonuniformity of the composition of the pressure sensitive adhesive; etc.), the residual pressure sensitive adhesive cannot be removed by water washing. Therefore, when conventional energy beam curable pressure sensitive adhesive remains on a wafer surface, it is common practice to conduct washing with an organic solvent. This, however, requires improvement from the viewpoint of, for example, environmental protection.
OBJECT OF THE INVENTION
It is an object of the present invention to provide a pressure sensitive adhesive composition suitable for use in a wafer surface protective sheet which, at the time of grinding of a wafer back, is used to protect the circuit pattern formed on the wafer surface from grinding dust, etc.
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, even if remaining on a wafer surface after the peeling of the pressure sensitive adhesive sheet, can easily be removed by washing with water.
SUMMARY OF THE INVENTION
The energy beam curable hydrophilic pressure sensitive adhesive composition of the present invention comprises a polymer (A) having an energy beam polymerizable group and an acid group and a neutralizer (B).
In this energy beam curable hydrophlic pressure sensitive adhesive composition, it is preferred that the polymer (A) be a polymer having a side chain of an energy beam polymerizable group, obtained by reacting an acrylic copolymer (A1) having monomer units containing functional groups with a compound (A2) containing energy beam polymerizable group and a substituent reactive with the functional groups, all or some of the functional groups being acid groups, wherein at least some of the acid groups remain in the polymer (A) even after the reaction of the acrylic copolymer (A1) with the compound (A2).
In particular, the acrylic copolymer (A1) having the monomer units containing functional groups is preferably a polymer obtained by polymerizing a polymerizable monomer (a1) containing an acid group and another monomer (a2) that is copolymerizable with the polymerizable monomer containing acid group.
It is especially preferred that the copolymerizable other monomer (a2) be a compound represented by the formula:
wherein each of X
1
, X
2
and X
3
independently represents hydrogen 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 an integer of 1 to 10.
The energy beam curable hydrophilic pressure sensitive adhesive composition of the present invention preferably comprises a photopolymerization initiator (C) in addition to the above components.
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. The pressure sensitive adhesive sheet is preferably used in wafer processing.
This pressure sensitive adhesive sheet is preferably used in the grinding of the back of a wafer, which comprises the steps of:
sticking the pressure sensitive adhesive sheet to a patterned wafer surface, and
grinding the back of the wafer while feeding water thereonto.
The pressure sensitive adhesive composition of the present invention possesses both energy bean curability and hydrophilicity. Therefore, the adhesive strength is sharply reduced by the irradiation with energy beams to thereby enable easily peeling the pressure sensitive adhesive sheet from an adherend. Further, the composition of the pressure sensitive adhesive is homogeneous and the pressure sensitive adhesive is excellent in terms of cohesive strength, so that the pressure sensitive adhesive does not remain on the adherend surface at the time of peeling of the pressure sensitive adhesive sheet. Still further, even when the pressure sensitive adhesive remains on an adherend surface for some reason, the residual pressure sensitive adhesive can easily be removed by washing with water.
DETAILED DESCRIPTION OF THE INVENTION
The energy beam curable hydrophilic pressure sensitive adhesive composition and use thereof according to the present invention will be described in detail below.
The energy beam curable hydrophilic pressure sensitive adhesive composition
Kato Kiichiro
Kondo Takeshi
Minerua Yoshihisa
Takahashi Kazuhiro
Lintec Corporation
Webb Ziesenheim & Logsdon Orkin & Hanson, P.C.
Zirker Daniel
LandOfFree
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