Pressure-sensitive adhesive

Abstract

To provide a pressure-sensitive adhesive sheet capable of suppressing heavy peeling even when using an aqueous pressure-sensitive adhesive composition.SOLUTION: A pressure-sensitive adhesive sheet according to an embodiment of the present invention includes: a base material; and a pressure-sensitive adhesive layer formed of a water-dispersible pressure-sensitive adhesive composition containing a water-dispersible polymer, wherein a surface concentration of a carboxyl group on a surface of the pressure-sensitive adhesive layer obtained by an X-ray photoelectron spectroscopy (ESCA) gas phase chemical modification method is a detection limit value or less.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a pressure-sensitive adhesive sheet. [Background technology]

[0002] Pressure-sensitive adhesive sheets are widely used for the purposes of protecting the surface of and fixing adherends. For example, in the processing of semiconductor wafers, they are used to properly hold the semiconductor wafers as adherends during the back-grinding and dicing processes. Pressure-sensitive adhesive sheets used in the processing of semiconductor wafers are peeled off from the semiconductor wafers after use, so pressure-sensitive adhesive sheets with removability are preferably used. Solvent-based pressure-sensitive adhesives are widely used as removably adhesives (e.g., Patent Document 1). In recent years, there has been a demand for reducing environmental impact, and attempts have been made to use water-based pressure-sensitive adhesives (e.g., Patent Document 2). [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Publication No. 2019-31620 [Patent Document 2] Japanese Patent Application Laid-Open No. 2009-73920 Summary of the Invention [Problem to be solved by the invention]

[0004] The wafer surface after the back-grinding process is highly active, and when a pressure-sensitive adhesive sheet is attached to the activated wafer surface after the back-grinding process, problems with releasability may occur due to the interaction between the pressure-sensitive adhesive layer surface and the wafer surface. When a water-based pressure-sensitive adhesive is used, peeling from the adherend becomes difficult, and the releasability problem tends to become more pronounced. [Means for solving the problem]

[0005] 1. An adhesive sheet according to an embodiment of the present invention comprises a substrate and an adhesive layer formed from a water-dispersible adhesive composition containing a water-dispersible polymer, and the surface concentration of carboxyl groups on the surface of the adhesive layer, as determined by X-ray photoelectron spectroscopy (ESCA) vapor phase chemical modification, is below the detection limit. 2. In the pressure-sensitive adhesive sheet described in 1 above, the water-dispersible pressure-sensitive adhesive composition may further contain an active energy ray-curable resin and a photopolymerization initiator. 3. In the pressure-sensitive adhesive sheet according to the above 1 or 2, the monomer composition used for polymerization of the water-dispersible polymer may contain a carboxyl group-containing monomer. 4. In the pressure-sensitive adhesive sheet described in 3 above, the monomer composition used for polymerization of the water-dispersible polymer may contain less than 3 parts by weight of the carboxyl group-containing monomer in terms of acrylic acid equivalent, per 100 parts by weight of the total of all monomer components. 5. In the pressure-sensitive adhesive sheet according to any one of 2 to 4 above, the active energy ray-curable resin may be a self-emulsifying water-based active energy ray-curable resin. 6. In the pressure-sensitive adhesive sheet according to any one of 1 to 5 above, the detection limit may be 0.034 atomic %. 7. The pressure-sensitive adhesive sheet according to any one of 1 to 6 above may be used for semiconductor wafer processing. 8. The pressure-sensitive adhesive sheet according to any one of 1 to 6 above may be a dicing tape. [Effects of the Invention]

[0006] According to an embodiment of the present invention, it is possible to provide a pressure-sensitive adhesive sheet that is suppressed from becoming too peelable even when it is attached to an activated wafer. Furthermore, since the pressure-sensitive adhesive layer is formed using a water-based pressure-sensitive adhesive, the environmental impact can also be reduced. [Brief explanation of the drawings]

[0007] [Figure 1] 1 is a schematic cross-sectional view of a pressure-sensitive adhesive sheet according to one embodiment of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0008] A. Overall structure of adhesive sheet A pressure-sensitive adhesive sheet according to an embodiment of the present invention comprises a substrate and a pressure-sensitive adhesive layer formed from a water-dispersed pressure-sensitive adhesive composition containing a water-dispersed polymer. The surface concentration of carboxyl groups on the surface of the pressure-sensitive adhesive layer is below the detection limit as determined by X-ray photoelectron spectroscopy (ESCA) gas-phase chemical modification. If the surface concentration of carboxyl groups as determined by ESCA gas-phase chemical modification is below the detection limit, heavy release properties can be suppressed even when the sheet is attached to an activated semiconductor wafer surface. In aqueous pressure-sensitive adhesives such as water-dispersed pressure-sensitive adhesive compositions, a monomer component having a carboxyl group can be used in the polymerization of the base polymer to impart mechanical stability. Polar groups such as carboxyl groups are likely to interact with the activated semiconductor wafer surface, making the heavy release properties more pronounced. The use of an active energy ray-curable pressure-sensitive adhesive is known as a method for improving the release properties of pressure-sensitive adhesive sheets. When a water-dispersed pressure-sensitive adhesive composition is used, it can be difficult to achieve sufficiently light release properties, even when an active energy ray-curable pressure-sensitive adhesive is used. In the pressure-sensitive adhesive sheet according to an embodiment of the present invention, the surface concentration of carboxyl groups on the pressure-sensitive adhesive layer surface obtained by the ESCA vapor-phase chemical modification method is below the detection limit. If the surface concentration of carboxyl groups is below the detection limit, heavy peeling due to the interaction between the pressure-sensitive adhesive layer surface and the activated semiconductor wafer surface can be suppressed. Therefore, damage to thinned and miniaturized semiconductor wafers can be suppressed when the pressure-sensitive adhesive sheet is peeled. Furthermore, since a water-based pressure-sensitive adhesive is used as the pressure-sensitive adhesive, the environmental impact can also be reduced.

[0009] FIG. 1 is a schematic cross-sectional view of a pressure-sensitive adhesive sheet according to an embodiment of the present invention. The pressure-sensitive adhesive sheet 100 comprises, in this order, a substrate 20 and a pressure-sensitive adhesive layer 10. The pressure-sensitive adhesive layer 10 is formed using a water-dispersible pressure-sensitive adhesive composition. As described above, the surface concentration of carboxyl groups on the pressure-sensitive adhesive layer surface of the pressure-sensitive adhesive sheet according to an embodiment of the present invention, as determined by X-ray photoelectron spectroscopy (ESCA) gas-phase chemical modification, is below the detection limit. Such a pressure-sensitive adhesive layer 10 can suppress heavy peeling even when attached to an activated wafer surface. The pressure-sensitive adhesive sheet 100 may further include any appropriate layer. For example, an intermediate layer (not shown) may be formed between the substrate 20 and the pressure-sensitive adhesive layer 10. When an intermediate layer is included, adhesion to an adherend having an uneven surface can be improved.

[0010] As described above, the surface concentration of carboxyl groups obtained by X-ray photoelectron spectroscopy (ESCA) gas-phase chemical modification of the pressure-sensitive adhesive layer surface is below the detection limit. Even when the pressure-sensitive adhesive uses, for example, a carboxyl group-containing monomer for polymerization of the base polymer, if the carboxyl group concentration on the pressure-sensitive adhesive layer surface is below the detection limit, the interaction between the pressure-sensitive adhesive layer surface and the activated wafer surface of the adherend can be suppressed, and the pressure-sensitive adhesive sheet can be prevented from exhibiting heavy release properties. Furthermore, when the pressure-sensitive adhesive sheet and semiconductor wafer are stored in a laminated state for a long period of time, heavy release properties are more likely to progress. With the pressure-sensitive adhesive sheet of an embodiment of the present invention, heavy release properties can be suppressed even when the pressure-sensitive adhesive sheet and semiconductor wafer are left in a laminated state at high temperatures. In this specification, the surface concentration of carboxyl groups obtained by ESCA gas-phase chemical modification refers to the carboxyl group concentration measured by the following method. The detection limit when measured using this method is 0.034 atomic%. Therefore, the pressure-sensitive adhesive sheet of one embodiment of the present invention may have a surface concentration of carboxyl groups of 0.034 atomic % or less on the pressure-sensitive adhesive layer surface, as determined by X-ray photoelectron spectroscopy (ESCA) vapor phase chemical modification. <Gas-phase chemical modification ESCA measurement> If a release liner is attached to the adhesive layer, the release liner is peeled off from the adhesive sheet. The surface of the adhesive layer of the adhesive sheet is chemically modified using trifluoroethanol. Next, ESCA measurement is performed under the conditions in Table 1 below. The detection limit for this measurement method was 0.034 atomic %. [Table 1]

[0011] The adhesive strength of the adhesive sheet to an activated Si wafer before irradiation with active energy rays is preferably 2 N / 20 mm or more, more preferably 3 N / 20 mm or more. If the adhesive strength of the adhesive sheet to an activated Si wafer before irradiation with active energy rays is within the above range, the adhesive sheet has sufficient adhesion to the adherend. Furthermore, the adhesive strength to an activated Si wafer is, for example, 15 N / 20 mm or less. In this specification, the adhesive strength to an activated Si wafer refers to the adhesive strength measured by the following method. The adhesive sheet is cut to a width of 20 mm and a length of 80 mm. The semiconductor wafer is back-ground under the following conditions. Within 5 minutes after the back-grinding process, the adhesive sheet is pressed against the back-ground surface of the silicon mirror wafer by moving a hand roller back and forth once in an atmosphere at 23°C. The force required to peel the adhesive sheet is then measured by a 90° peel test at 23°C, 50% RH, and a pulling speed of 300 mm / min. <Back grinding conditions> Grinder: DISCO, product name "DFG-840" 1st axis: #600 grinding wheel (rotation speed: 4800 rpm, down speed: P1: 3.0 μm / sec, P2: 2.0 μm / sec) 2-axis: #4000 grinding wheel (rotation speed: 5500 rpm, down speed: P1: 0.8 μm / sec, P2: 0.6 μm / sec)

[0012] The adhesive sheet has an integrated light intensity of 460mJ / cm 2The adhesive strength of the pressure-sensitive adhesive sheet to the activated Si wafer after irradiation with ultraviolet rays is preferably less than 0.4 N / 20 mm, more preferably 0.35 N / 20 mm or less, and even more preferably 0.3 N / 20 mm or less. If the adhesive strength to the activated Si wafer after irradiation with ultraviolet rays, which are active energy rays, is within the above range, easy peelability can be achieved. The smaller the adhesive strength after irradiation with active energy rays (ultraviolet rays), the more preferable. In this specification, when the integrated light dose is 460 mJ / cm 2 The adhesive strength of the adhesive sheet to the activated Si wafer after irradiating with ultraviolet light is a value measured using the following method. The adhesive sheet is cut into a width of 20 mm and a length of 80 mm. The semiconductor wafer is back-ground under the following conditions. Within 5 minutes after the back-grinding process, the adhesive sheet is pressed onto the back-grind-treated surface of the silicon mirror wafer by moving a hand roller back and forth once in an atmosphere of 23°C. The wafer is then left to stand for 30 minutes. After that, ultraviolet light (UV) is applied to the wafer until the cumulative light intensity reaches 460 mJ / cm. 2 The adhesive layer is irradiated with light at a wavelength of 365 nm (equivalent to 365 nm). The force required to peel the adhesive sheet is then measured by a 180° peel test under conditions of 23°C, 50% RH, and a pulling speed of 300 mm / min. <Back grinding conditions> Grinder: DISCO, product name "DFG-840" 1st axis: #600 grinding wheel (rotation speed: 4800 rpm, down speed: P1: 3.0 μm / sec, P2: 2.0 μm / sec) 2-axis: #4000 grinding wheel (rotation speed: 5500 rpm, down speed: P1: 0.8 μm / sec, P2: 0.6 μm / sec)

[0013] The adhesive sheet was stored at 50°C for one week, and then the cumulative light intensity was 460 mJ / cm 2The adhesive strength to an activated Si wafer measured after irradiation with ultraviolet light so as to satisfy the above condition is preferably less than 0.4 N / 20 mm, more preferably 0.35 N / 20 mm or less, and even more preferably 0.3 N / 20 mm or less. If the adhesive strength to an activated Si wafer after irradiation with ultraviolet light, which is an active energy ray, after storage at 50°C for one week is within the above range, the film can have easy peelability. The smaller the adhesive strength after irradiation with active energy ray (ultraviolet light), the more preferable. In this specification, when the integrated light dose is 460 mJ / cm 2 The adhesive strength of the adhesive sheet to the activated Si wafer after irradiating with ultraviolet light is a value measured using the following method. The adhesive sheet is cut into a width of 20 mm and a length of 80 mm. The semiconductor wafer is back-ground under the following conditions. After the back-grinding process, the adhesive sheet is pressed onto the back-ground surface of the silicon mirror wafer within 5 minutes by moving a hand roller back and forth once in an atmosphere of 23°C. Then, the wafer is left to stand at 50°C for one week. After that, ultraviolet light (UV) is applied until the cumulative light intensity reaches 460 mJ / cm. 2 The adhesive layer is irradiated with light at a wavelength of 365 nm (equivalent to 365 nm). The force required to peel the adhesive sheet is then measured by a 180° peel test under conditions of 23°C, 50% RH, and a pulling speed of 300 mm / min. <Back grinding conditions> Grinder: DISCO, product name "DFG-840" 1st axis: #600 grinding wheel (rotation speed: 4800 rpm, down speed: P1: 3.0 μm / sec, P2: 2.0 μm / sec) 2-axis: #4000 grinding wheel (rotation speed: 5500 rpm, down speed: P1: 0.8 μm / sec, P2: 0.6 μm / sec)

[0014] The thickness of the pressure-sensitive adhesive sheet according to the embodiment of the present invention can be set to any appropriate thickness, and is preferably 30 μm to 400 μm, more preferably 40 μm to 300 μm, and even more preferably 50 μm to 200 μm.

[0015] A-1. Base material The substrate may be made of any suitable resin. Specific examples of resins constituting the substrate include polyester-based resins such as polyethylene naphthalate (PEN), polybutylene terephthalate (PBT), and polybutylene naphthalate (PBN); polyolefin-based resins such as ethylene-vinyl acetate copolymer, ethylene-methyl methacrylate copolymer, polyethylene, polypropylene, and ethylene-propylene copolymer; polyvinyl alcohol, polyvinylidene chloride, polyvinyl chloride, vinyl chloride-vinyl acetate copolymer, polyvinyl acetate, polyamide, polyimide, cellulose, fluorine-based resins, polystyrene-based resins such as polyether and polystyrene; polycarbonate, polyethersulfone, and polyetheretherketone. Polyolefin-based resins or polyester-based resins are preferred. Because these resins transmit ultraviolet light, a pressure-sensitive adhesive layer can be formed using an active energy ray-curable pressure-sensitive adhesive, such as an ultraviolet-curable pressure-sensitive adhesive, to provide a pressure-sensitive adhesive sheet with easy peelability.

[0016] The substrate may further contain other components within the range that does not impair the effects of the present invention. Examples of other components include antioxidants, ultraviolet absorbers, light stabilizers, heat stabilizers, antistatic agents, etc. The types and amounts of other components can be any appropriate amount depending on the purpose.

[0017] The thickness of the substrate is preferably 30 μm to 200 μm, more preferably 40 μm to 180 μm, and even more preferably 45 μm to 180 μm.

[0018] A-2.Adhesive layer The pressure-sensitive adhesive layer of the pressure-sensitive adhesive sheet according to an embodiment of the present invention is formed from a water-dispersible pressure-sensitive adhesive composition containing a water-dispersible polymer. To ensure dispersibility, the base polymer of the water-dispersible pressure-sensitive adhesive composition may be designed to have polar groups, such as carboxyl groups. However, when the pressure-sensitive adhesive sheet is attached to the surface of a wafer activated by a back-grinding process or the like, the polar groups of the components contained in the pressure-sensitive adhesive layer may interact with the activated wafer surface, resulting in hard peeling. The pressure-sensitive adhesive sheet may be stored in a state attached to the semiconductor wafer. When the pressure-sensitive adhesive sheet and the semiconductor wafer are stored in a bonded state for a long period of time, hard peeling tends to progress more easily. As described above, the surface concentration of carboxyl groups on the pressure-sensitive adhesive layer surface, as determined by X-ray photoelectron spectroscopy (ESCA) vapor-phase chemical modification, is below the detection limit. When the surface concentration of carboxyl groups on the pressure-sensitive adhesive layer surface is below the detection limit, even when the pressure-sensitive adhesive layer is attached to an activated wafer surface, an excessive increase in adhesive strength and hard peeling can be suppressed. Furthermore, even after long-term storage, the strong interaction between the pressure-sensitive adhesive layer surface and the activated wafer surface can be suppressed, resulting in hard peeling. As a result, when used as a dicing tape, for example, a pressure-sensitive adhesive sheet with excellent pick-up properties and which is less likely to damage wafers or the like can be obtained.

[0019] A-2-1. Water-dispersible polymer Any appropriate polymer can be used as the water-dispersed polymer. The water-dispersed polymer can be obtained by emulsion polymerization of any appropriate monomer component in water. That is, the water-dispersed polymer is an emulsion of any polymer. Preferably, the water-dispersed polymer is a water-dispersed acrylic polymer (hereinafter also referred to as an acrylic polymer). The average particle size of the acrylic polymer emulsion is preferably 80 nm to 400 nm, more preferably 100 nm to 300 nm, and even more preferably 100 nm to 200 nm. In this specification, the average particle size of the water-dispersed acrylic polymer refers to the volume-based median diameter (D50) measured by laser diffraction / scattering method.

[0020] The glass transition temperature (Tg) of the water-dispersible acrylic polymer is preferably −40°C to 0°C, more preferably −40°C to −5°C, and even more preferably −40°C to −10°C. When the glass transition temperature is within the above range, a pressure-sensitive adhesive composition having excellent adhesion to an adherend before UV irradiation can be obtained when used as an active energy ray-curable pressure-sensitive adhesive. Furthermore, the resulting pressure-sensitive adhesive composition has improved coatability, allowing a pressure-sensitive adhesive layer with excellent appearance to be formed. As a result, for example, when the pressure-sensitive adhesive sheet is used in the processing of semiconductor wafers, water penetration between the pressure-sensitive adhesive layer and the adherend, which can lead to wafer chipping and chipping, can be suppressed. In this specification, the glass transition temperature of the water-dispersible acrylic polymer refers to a theoretical value calculated using Fox's equation from the monomer units constituting each polymer and their proportions. The theoretical glass transition temperature calculated using Fox's equation can be consistent with the measured glass transition temperature determined by methods such as differential scanning calorimetry (DSC) or dynamic viscoelasticity measurement. As described below, when a theoretical value cannot be calculated, the measured glass transition temperature can be used.

[0021] The Fox equation, as shown below, is a relational expression between the Tg of an acrylic polymer and the glass transition temperature Tgi of a homopolymer obtained by homopolymerizing each of the monomers that make up the acrylic polymer. 1 / Tg=Σ(Wi / Tgi) (In the formula, Tg is the glass transition temperature (unit: K) of the acrylic polymer, Wi is the weight fraction of monomer i in the acrylic polymer (copolymerization ratio by weight), and Tgi is the glass transition temperature (unit: K) of the homopolymer of monomer i.)

[0022] The glass transition temperature of the homopolymer used to calculate Tg can be any value described in any appropriate document. For example, for the monomers listed below, the following values ​​are used as the glass transition temperatures of the homopolymers of the monomers: 2-Ethylhexyl acrylate -70℃ Methyl methacrylate 8℃ Acrylic acid 106℃ Hydroxyethyl methacrylate 55℃

[0023] For the glass transition temperatures of homopolymers of monomers other than those exemplified above, the values ​​described in, for example, "Polymer Handbook" (3rd Edition, John Wiley & Sons, Inc., 1989) can be used. When multiple values ​​are listed, the highest value is used.

[0024] For monomers for which the glass transition temperature of the homopolymer is not listed in the Polymer Handbook, the value obtained by the measurement method described in JP 2007-51271 A can be used. Specifically, 100 parts by weight of the monomer, 0.2 parts by weight of azobisisobutyronitrile, and 200 parts by weight of ethyl acetate as the polymerization solvent were charged into a reactor equipped with a thermometer, a stirrer, a nitrogen inlet tube, and a reflux condenser, and the mixture was stirred for 1 hour while passing nitrogen gas through. After removing oxygen from the polymerization system in this manner, the temperature was raised to 63°C and the reaction was continued for 10 hours. The mixture was then cooled to room temperature to obtain a homopolymer solution with a solids concentration of 33% by weight. This homopolymer solution was then cast onto a release liner and dried to prepare a test sample (sheet-like homopolymer) approximately 2 mm thick. This test sample was punched out into a disk with a diameter of 7.9 mm, sandwiched between parallel plates, and subjected to a shear strain of 1 Hz using a viscoelasticity tester (ARES, manufactured by Rheometrics). Viscoelasticity was measured in shear mode at a temperature range of -70°C to 150°C and a heating rate of 5°C / min. The peak top temperature of tan δ was taken as the Tg of the homopolymer.

[0025] In one embodiment, the water-dispersible acrylic polymer may be a polymer having a core-shell structure (hereinafter also referred to as a core-shell polymer). When the water-dispersible acrylic polymer is a core-shell polymer, a polymer having a glass transition temperature of 2 or more can be easily obtained. When the water-dispersible acrylic polymer is such a core-shell polymer, it is possible to provide a water-dispersible PSA composition that has excellent adhesive strength and can achieve both adhesion to an adherend and easy releasability.

[0026] The water-dispersible acrylic polymer that is a core-shell polymer can be obtained by emulsion polymerization of any appropriate monomer components in a stepwise manner, for example, by emulsion polymerization of a monomer composition that forms a core portion by any appropriate method, and then emulsion polymerization of a monomer composition that forms a shell portion in the presence of the polymer particles that become the core portion.

[0027] The water-dispersible acrylic polymer, which is a core-shell polymer, preferably has a core ratio of 5% by weight or more, more preferably 10% by weight or more. When the weight ratio of the core part to the shell part is within the above range, it is possible to provide a water-dispersible PSA composition that has excellent adhesive strength and can achieve both adhesion to an adherend and easy releasability.

[0028] A-2-2. Monomer component The monomer composition used for polymerization of the water-dispersible acrylic polymer (for forming the core or shell in the case of a core-shell polymer) contains any appropriate monomer component. The monomer component may be used alone or in combination of two or more.

[0029] Any suitable acrylic monomer can be used as the monomer component. A typical monomer component is a (meth)acrylic acid alkyl ester. Specific examples of the (meth)acrylic acid alkyl ester include methyl (meth)acrylate, ethyl (meth)acrylate, propyl (meth)acrylate, isopropyl (meth)acrylate, butyl (meth)acrylate, isobutyl (meth)acrylate, s-butyl (meth)acrylate, t-butyl (meth)acrylate, pentyl (meth)acrylate, hexyl (meth)acrylate, heptyl (meth)acrylate, octyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, isooctyl (meth)acrylate, and (meth) Examples of (meth)acrylic acid C1-20 alkyl esters include nonyl acrylate, isononyl (meth)acrylate, decyl (meth)acrylate, isodecyl (meth)acrylate, undecyl (meth)acrylate, dodecyl (meth)acrylate, tridecyl (meth)acrylate, tetradecyl (meth)acrylate, pentadecyl (meth)acrylate, hexadecyl (meth)acrylate, heptadecyl (meth)acrylate, octadecyl (meth)acrylate, nonadecyl (meth)acrylate, and eicosyl (meth)acrylate. These (meth)acrylic acid alkyl esters may be used alone or in combination of two or more. In this specification, (meth)acrylic refers to acrylic and / or methacrylic.

[0030] The monomer composition may further include any other suitable monomer copolymerizable with the (meth)acrylic acid alkyl ester. For example, carboxyl group-containing monomers such as acrylic acid, methacrylic acid, and carboxyl group-containing monomers represented by the formula (1) described below; acid anhydride monomers such as maleic anhydride and itaconic anhydride; hydroxyl group-containing monomers such as hydroxyalkyl (meth)acrylates such as 2-hydroxyethyl (meth)acrylate, 2-hydroxypropyl (meth)acrylate, 2-hydroxybutyl (meth)acrylate, 3-hydroxypropyl (meth)acrylate, 4-hydroxybutyl (meth)acrylate, 6-hydroxyhexyl (meth)acrylate, 8-hydroxyoctyl (meth)acrylate, 10-hydroxydecyl (meth)acrylate, 12-hydroxylauryl (meth)acrylate, and (4-hydroxymethylcyclohexyl)methyl (meth)acrylate; sulfonic acid group-containing monomers such as styrenesulfonic acid and allylsulfonic acid; (N-substituted) amide monomers such as diacetone acrylamide, (meth)acrylamide, and N,N-dimethyl(meth)acrylamide; and aminoalkyl (meth)acrylates such as aminoethyl (meth)acrylate. vinyl monomers such as vinyl acetate, vinyl propionate, N-vinylpyrrolidone, and methylvinylpyrrolidone; cyanoacrylate monomers such as acrylonitrile and methacrylonitrile; epoxy group-containing acrylic monomers such as glycidyl (meth)acrylate; glycol-based acrylic ester monomers such as polyethylene glycol (meth)acrylate and polypropylene glycol (meth)acrylate; acrylic ester monomers having a heterocycle, halogen atom, silicon atom, or the like, such as tetrahydrofurfuryl (meth)acrylate, fluorine (meth)acrylate, and silicone (meth)acrylate; olefin-based monomers such as isoprene, butadiene, and isobutylene; and vinyl ether-based monomers such as vinyl ether.By including these monomer components, cohesive strength, heat resistance, crosslinkability, etc. can be improved. These monomer components may be used alone or in combination of two or more. Each monomer component is used in any appropriate ratio.

[0031] The monomer composition preferably contains a carboxyl group-containing monomer. If a carboxyl group-containing monomer is used as a monomer component used in the polymerization of the water-dispersible acrylic polymer, which is the base polymer, a base polymer having a carboxyl group can be obtained. If a base polymer having a carboxyl group is used, a water-dispersible PSA composition having a stable dispersion state can be obtained. Any appropriate carboxyl group-containing monomer can be used. Specific examples thereof include, as described above, acrylic acid, methacrylic acid, and carboxyl group-containing monomers represented by formula (1). These monomers may be used alone or in combination of two or more. [ka] (In the formula, R 1 represents a hydrogen atom or a methyl group, and R 2 represents a divalent hydrocarbon group, x represents an integer of 1 to 20, and y represents 0 or 1).

[0032] R 1 represents a hydrogen atom or a methyl group. x is an integer of 1 to 20, preferably an integer of 1 to 10, and more preferably an integer of 1 to 8. y is 0 or 1. R 2 represents a divalent hydrocarbon group. Examples of the divalent hydrocarbon group include saturated aliphatic hydrocarbon groups such as alkylene groups, saturated alicyclic hydrocarbon groups such as cycloalkylene groups, aromatic hydrocarbon groups such as phenylene groups, unsaturated aliphatic hydrocarbon groups, and unsaturated alicyclic hydrocarbon groups. Preferably, R 2is a linear or branched alkylene group or cycloalkylene group, more preferably a linear or branched alkylene group or cycloalkylene group having 1 to 20 carbon atoms, and even more preferably a linear or branched alkylene group or cycloalkylene group having 1 to 10 carbon atoms. 2 When is a divalent hydrocarbon group as described above, a pressure-sensitive adhesive having excellent dispersion stability and coatability can be obtained.

[0033] Specific examples of the carboxyl group-containing monomer represented by formula (1) include 2-acryloyloxyethyl succinic acid, 2-methacryloyloxyethyl succinic acid, 2-acryloyloxyethyl hexahydrophthalic acid, ω-carboxy-polycaprolactone (n≒2) monoacrylate, and 2-methacryloyloxyethyl hexahydrophthalic acid.

[0034] The carboxyl group-containing monomer represented by formula (1) may be a commercially available product, such as "HOA-MS," "Light Ester HO-MS(N)," or "Light Acrylate HOA-HH(N)" manufactured by Kyoeisha Chemical Co., Ltd., or "Aronix M-5300" manufactured by Toagosei Co., Ltd.

[0035] The monomer composition used in the polymerization of the water-dispersible polymer preferably contains less than 3 parts by weight of the carboxyl group-containing monomer in terms of acrylic acid equivalent, more preferably 2.5 parts by weight or less, and even more preferably 2 parts by weight or less, per 100 parts by weight of the total of all monomer components. If the content of the carboxyl group-containing monomer in the monomer composition is less than 3 parts by weight in terms of acrylic acid equivalent, a PSA sheet with better suppressed heavy release can be obtained. From the viewpoint of obtaining a water-dispersible PSA composition with better dispersion stability, the carboxyl group-containing monomer is preferably 1 part by weight or more in terms of acrylic acid equivalent. In this specification, the acrylic acid equivalent of the carboxyl group-containing monomer can be calculated from the molar mass of the carboxyl group-containing monomer and the molar mass of acrylic acid. Specifically, it refers to the value calculated using the following formula. When the monomer composition contains two or more types of carboxyl group-containing monomers, the acrylic acid equivalent of the carboxyl group-containing monomer contained in the monomer composition is the sum of the acrylic acid equivalents of the individual carboxyl group-containing monomers. When the water-dispersible acrylic polymer is a core-shell acrylic polymer, the acrylic acid equivalent of the carboxyl group-containing monomer in each of the monomer compositions used to form the core portion and the shell portion is referred to as the acrylic acid equivalent of the carboxyl group-containing monomer in each of the monomer compositions used to form the core portion and the shell portion. Acrylic acid equivalent = molar mass of carboxyl group-containing monomer (g / mol) / molar mass of acrylic acid (72.06 g / mol)

[0036] A-2-3.Surfactants Any appropriate surfactant can be used as the surfactant used in the polymerization of the water-dispersible acrylic polymer. Preferably, a reactive surfactant can be used. The reactive surfactant not only functions as a surfactant but also has a radically polymerizable functional group in the molecule (e.g., a radically reactive group such as an ethenyl group, a propenyl group, an allyl group, or an allyl ether group). The use of a reactive surfactant can reduce contamination of the adherend caused by the pressure-sensitive adhesive using the water-dispersible acrylic polymer and can improve the adhesive strength of the pressure-sensitive adhesive composition before radiation irradiation treatment. In addition, the water resistance of a pressure-sensitive adhesive sheet (e.g., a pressure-sensitive adhesive layer) using the pressure-sensitive adhesive composition can be improved, and peeling of the pressure-sensitive adhesive sheet can be suppressed even when water is splashed on it during processing.

[0037] Examples of reactive surfactants include surfactants in which a radically polymerizable functional group (radical reactive group) such as a propenyl group or an allyl ether group has been introduced into any suitable surfactant (e.g., anionic surfactants, nonionic surfactants, etc.). Reactive surfactants have a radically polymerizable functional group associated with an ethylenically unsaturated double bond, and can reduce the saturated water absorption of the pressure-sensitive adhesive layer formed compared to non-reactive surfactants. Furthermore, from the viewpoints of the stability of the aqueous dispersion and the durability of the pressure-sensitive adhesive layer, the reactive surfactants preferably used may be used alone or in combination of two or more.

[0038] Specific examples of anionic surfactants include higher fatty acid salts such as sodium oleate; alkylarylsulfonates such as sodium dodecylbenzenesulfonate; alkylsulfate salts such as sodium lauryl sulfate and ammonium lauryl sulfate; polyoxyethylene alkyl ether sulfate salts such as sodium polyoxyethylene lauryl ether sulfate; polyoxyethylene alkylaryl ether sulfate salts such as sodium polyoxyethylene nonylphenyl ether sulfate; alkylsulfosuccinate salts and derivatives thereof such as sodium monooctyl sulfosuccinate, sodium dioctyl sulfosuccinate, and sodium polyoxyethylene lauryl sulfosuccinate; and polyoxyethylene distyrenated phenyl ether sulfate salts. Specific examples of nonionic surfactants include polyoxyethylene alkyl ethers such as polyoxyethylene lauryl ether and polyoxyethylene stearyl ether; polyoxyethylene alkyl phenyl ethers such as polyoxyethylene octylphenyl ether and polyoxyethylene nonylphenyl ether; sorbitan higher fatty acid esters such as sorbitan monolaurate, sorbitan monostearate, and sorbitan trioleate; polyoxyethylene sorbitan higher fatty acid esters such as polyoxyethylene sorbitan monolaurate; polyoxyethylene higher fatty acid esters such as polyoxyethylene monolaurate and polyoxyethylene monostearate; glycerin higher fatty acid esters such as oleic acid monoglyceride and stearic acid monoglyceride; polyoxyethylene-polyoxypropylene block copolymers, and polyoxyethylene distyrenated phenyl ether.

[0039] As the reactive surfactant, commercially available products may be used. Specific examples of anionic reactive surfactants include alkyl ether reactive surfactants such as "Aqualon KH-05," "Aqualon KH-10," and "Aqualon KH-20" manufactured by Dai-ichi Kogyo Seiyaku Co., Ltd., "ADEKA REASOAP SR-10N" and "ADEKA REASOAP SR-20N" manufactured by Asahi Denka Kogyo Co., Ltd., and "Latemul PD-104" manufactured by Kao Corporation; sulfosuccinate ester reactive surfactants such as "Latemul S-120," "Latemul S-120A," "Latemul S-180P," and "Latemul S-180A" manufactured by Kao Corporation, and "Eleminol JS-20" manufactured by Sanyo Chemical Industry Co., Ltd.; and "Aqualon H-2855A," "Aqualon H-3855B," "Aqualon H-3855C," "Aqualon H-3856," "Aqualon HS-05," "Aqualon HS-10," "Aqualon HS-20," and "Aqualon H" manufactured by Dai-ichi Kogyo Seiyaku Co., Ltd. alkylphenyl ether or alkylphenyl ester reactive surfactants such as "ADEKA REASOAP SDX-30," "AQUALON BC-05," "AQUALON BC-10," "AQUALON BC-20," and "ADEKA REASOAP SDX-222," "ADEKA REASOAP SDX-223," "ADEKA REASOAP SDX-232," "ADEKA REASOAP SDX-233," "ADEKA REASOAP SDX-259," "ADEKA REASOAP SE-10N," and "ADEKA REASOAP SE-20N," manufactured by Asahi Denka Kogyo Co., Ltd.; (meth)acrylate sulfate ester reactive surfactants such as "ANTOX MS-60" and "ANTOX MS-2N," manufactured by Nippon Nyukazai Co., Ltd., and "ELEMINOL RS-30," manufactured by Sanyo Chemical Industries, Ltd.; and phosphate ester reactive surfactants such as "H-3330PL," manufactured by Dai-ichi Kogyo Seiyaku Co., Ltd., and "ADEKA REASOAP PP-70," manufactured by Asahi Denka Kogyo Co., Ltd.Specific examples of nonionic reactive surfactants include alkyl ether reactive surfactants such as those manufactured by Asahi Denka Kogyo Co., Ltd. under the trade names "ADEKA REASOAP ER-10," "ADEKA REASOAP ER-20," "ADEKA REASOAP ER-30," and "ADEKA REASOAP ER-40," and those manufactured by Kao Corporation under the trade names "LATEMUL PD-420," "LATEMUL PD-430," and "LATEMUL PD-450"; alkyl phenyl ether or alkyl phenyl ester reactive surfactants such as those manufactured by Dai-ichi Kogyo Seiyaku Co., Ltd. under the trade names "AQUALON RN-10," "AQUALON RN-20," "AQUALON RN-30," and "AQUALON RN-50," and those manufactured by Asahi Denka Kogyo Co., Ltd. under the trade names "ADEKA REASOAP NE-10," "ADEKA REASOAP NE-20," "ADEKA REASOAP NE-30," and "ADEKA REASOAP NE-40"; and (meth)acrylate sulfate ester reactive surfactants such as those manufactured by Nippon Nyukazai Co., Ltd. under the trade names "RMA-564," "RMA-568," and "RMA-1114."

[0040] As the reactive surfactant, an anionic reactive surfactant is preferably used. Anionic reactive surfactants often have excellent polymerization stability and are preferred from the viewpoints of particle stability and appearance. Anionic reactive surfactants and nonionic reactive surfactants may be used in combination.

[0041] In one embodiment, the reactive surfactant is preferably SO4 2- The concentration of ions is 100 μg / g or less. The reactive surfactant is preferably an ammonium salt type surfactant. In an embodiment of the present invention, the adhesive sheet may be an adhesive sheet used in the processing of semiconductor wafers. Therefore, impurity ions contained in the adhesive may be a problem. Therefore, it is preferable that the adhesive contains as few impurity ions as possible. SO4 2- If the ion concentration is within the above range and an ammonium salt surfactant is used, the adverse effects of impurity ions can be suppressed. Note that any appropriate method can be used to reduce or remove impurity ions, such as an ion exchange resin method, a membrane separation method, or a method of precipitating and filtering impurities using alcohol.

[0042] The reactive surfactant is used in any appropriate amount. The reactive surfactant is preferably 0.1 to 5 parts by weight, more preferably 0.5 to 3 parts by weight, per 100 parts by weight of the monomer composition. If the reactive surfactant content exceeds 5 parts by weight per 100 parts by weight of the monomer composition, when the pressure-sensitive adhesive composition is used as a pressure-sensitive adhesive sheet for processing semiconductor wafers, small pieces of the device may peel off from the pressure-sensitive adhesive sheet during the dicing process or a subsequent process. Furthermore, if the reactive surfactant content is less than 0.1 part by weight per 100 parts by weight of the monomer composition, a stable emulsified state may not be maintained.

[0043] In addition, a reactive surfactant and a surfactant not having a radical polymerizable functional group may be used in combination. Examples of surfactants not having a radical polymerizable functional group include anionic surfactants and nonionic anionic surfactants such as sodium lauryl sulfate, ammonium lauryl sulfate, sodium dodecylbenzenesulfonate, sodium polyoxyethylene alkyl ether sulfate, ammonium polyoxyethylene alkylphenyl ether sulfate, sodium polyoxyethylene alkylphenyl ether sulfate, and sodium polyoxyethylene alkyl sulfosuccinate; and nonionic surfactants such as polyoxyethylene alkyl ether, polyoxyethylene alkylphenyl ether, polyoxyethylene fatty acid ester, and polyoxyethylene polyoxypropylene block polymer. These surfactants may be used alone or in combination of two or more.

[0044] A-2-4. Polymerization method for water-dispersible acrylic polymer The water-dispersible acrylic polymer can be polymerized by any suitable method. For example, water such as ion-exchanged water, a monomer composition, a surfactant, a polymerization initiator, and optional additives can be added to a reaction vessel and mixed, followed by emulsion polymerization to obtain a water-dispersible acrylic polymer. When the water-dispersible acrylic polymer is a core-shell polymer, for example, a monomer composition containing a monomer that forms the core portion, water, a surfactant, a polymerization initiator, and optional additives can be added to a reaction vessel and mixed, followed by emulsion polymerization to form polymer particles that will become the core portion. Next, a monomer composition containing a monomer that forms the shell portion, water, a surfactant, a polymerization initiator, and optional additives can be added to a reaction vessel and mixed, followed by emulsion polymerization to form the shell portion, thereby obtaining a water-dispersible acrylic polymer that is a core-shell polymer. Examples of optional additives include chain transfer agents and silane coupling agents.

[0045] Any suitable polymerization initiator can be used as the polymerization initiator. For example, azo-based polymerization initiators such as 2,2'-azobisisobutyronitrile, 2,2'-azobis(2-amidinopropane) dihydrochloride, 2,2'-azobis[2-(5-methyl-2-imidazolin-2-yl)propane] dihydrochloride, 2,2'-azobis(2-methylpropionamidine) disulfate, and 2,2'-azobis(N,N'-dimethyleneisobutylamidine) are used; persulfates such as potassium persulfate and ammonium persulfate are used; benzoyl persulfate is used; and peroxide-based polymerization initiators such as peroxide, t-butyl hydroperoxide, and hydrogen peroxide; and redox-based initiators formed by combining a peroxide with a reducing agent (for example, a combination of a peroxide and ascorbic acid (e.g., a combination of aqueous hydrogen peroxide and ascorbic acid), a combination of a peroxide and an iron (II) salt (e.g., a combination of aqueous hydrogen peroxide and an iron (II) salt), a combination of a persulfate and sodium hydrogen sulfite, etc.). Only one type of polymerization initiator may be used, or two or more types may be used in combination.

[0046] The polymerization initiator can be used in any appropriate amount depending on the type of polymerization initiator used, the composition of the monomer composition, etc. The content of the polymerization initiator is, for example, 0.01 to 1 part by weight, and preferably 0.02 to 0.5 parts by weight, per 100 parts by weight of the monomer composition.

[0047] The chain transfer agent can be used, for example, to adjust the molecular weight of the water-dispersible acrylic polymer. Any appropriate chain transfer agent can be used. Specific examples include lauryl mercaptan, glycidyl mercaptan, mercaptoacetic acid, 2-mercaptoethanol, thioglycolic acid, 2-ethylhexyl thioglycolate, and 2,3-dimethylcapto-1-propanol. The chain transfer agent may be used alone or in combination of two or more. The content of the chain transfer agent is usually 0.001 to 0.5 parts by weight per 100 parts by weight of the monomer composition.

[0048] The water-dispersible acrylic polymer can be obtained by emulsion polymerization of a monomer composition, a reactive surfactant, a polymerization initiator, and optional additives such as a chain transfer agent. Therefore, the water-dispersible acrylic polymer can be prepared in the form of an emulsion. Any appropriate method can be used for emulsion polymerization. Specific examples include emulsion polymerization methods using a general batch charging method (bulk polymerization method), a monomer dropping method, and a monomer emulsion dropping method. When adding monomers or the like by dropping, the addition can be continuous or divided into portions. The polymerization temperature can be set to any appropriate value depending on the type of polymerization initiator, for example, in the range of 5°C to 100°C. It is also preferable to add aqueous ammonia, various water-soluble amines, or an aqueous alkali solution such as an aqueous sodium hydroxide solution or an aqueous potassium hydroxide solution to the solution of the water-dispersible acrylic polymer obtained by emulsion polymerization to adjust the pH to, for example, 6 to 11, preferably 7 to 10.

[0049] The gel fraction of the water-dispersible acrylic polymer is preferably 50% by weight or more, more preferably 70% by weight or more. If the gel fraction of the water-dispersible acrylic polymer is less than 50% by weight, the adhesive strength after irradiation with active energy rays is less likely to decrease, and the adherend is more likely to be contaminated by the sol component. The gel fraction of the water-dispersible acrylic polymer is, for example, 99% by weight or less. The gel fraction of the water-dispersible acrylic polymer can be determined by any appropriate method. For example, the gel fraction can be determined as the content insoluble in a solvent such as ethyl acetate. Specifically, the gel fraction is determined as the weight fraction (unit: wt%) of the insoluble component after immersing the water-dispersible acrylic polymer in ethyl acetate at 23°C for 7 days relative to the sample before immersion.

[0050] A-3. Active energy ray curing resin The aqueous dispersion pressure-sensitive adhesive composition used in the present invention may further contain an active energy ray-curable resin and a photopolymerization initiator. If the aqueous dispersion pressure-sensitive adhesive composition contains an active energy ray-curable resin and a photopolymerization initiator, an aqueous dispersion pressure-sensitive adhesive composition that is an active energy ray-curable pressure-sensitive adhesive composition can be obtained. Even when the aqueous dispersion pressure-sensitive adhesive composition is used as an active energy ray-curable pressure-sensitive adhesive, it may not be possible to achieve sufficiently easy releasability. If the pressure-sensitive adhesive sheet according to an embodiment of the present invention further contains an active energy ray-curable resin and a photopolymerization initiator, an adhesive sheet that can achieve even easier releasability can be obtained, even when attached to an activated wafer surface.

[0051] As the active energy ray-curable resin, any appropriate resin that can be cured by active energy rays such as ultraviolet rays can be used. Preferably, an ultraviolet-curable resin is used. As the ultraviolet-curable resin, for example, an ultraviolet-curable monomer and / or oligomer can be used. Examples of ultraviolet-curable monomers include urethane (meth)acrylate, trimethylolpropane tri(meth)acrylate, tetramethylolmethane tetra(meth)acrylate, pentaerythritol tri(meth)acrylate, pentaerythritol tetra(meth)acrylate, dipentaerythritol monohydroxypenta(meth)acrylate, dipentaerythritol hexa(meth)acrylate, and 1,4-butanediol di(meth)acrylate. Examples of ultraviolet-curable oligomers include urethane-based oligomers, polyether-based oligomers, polyester-based oligomers, polycarbonate-based oligomers, and polybutadiene-based oligomers. Oligomers having a molecular weight of approximately 100 to 50,000 are preferably used. The monomers and oligomers may be used alone or in combination of two or more. The active energy ray curable resin may be emulsified using any suitable surfactant or self-emulsifying urethane (meth)acrylate, as needed. By emulsifying, the water-dispersible adhesive can be easily prepared.

[0052] Commercially available active energy ray curable resins may be used. Examples include UBE's trade name "ETERNACOLL UW-9102," DIC's trade name "HYDRAN Exp UV-100S," Arakawa Chemical Industries' trade name "BEAMSET EM-90" and "BEAMSET EM-94," Kyoei Chemical's trade name "UAW-1000W30," Daicel-Allnex's trade names "UCECOAT7655," "UCECOAT7200," and "UCECOAT7773," and Fujifilm Wako Pure Chemical Industries' trade names "FOM-03006" and "FOM-03009." From the viewpoint of compatibility with water-dispersible acrylic polymers, water-based resins (water dispersions of resins) may be appropriately selected and used.

[0053] The active energy ray-curable resin is preferably a self-emulsifying water-based active energy ray-curable resin. Use of a self-emulsifying water-based active energy ray-curable resin can provide a PSA sheet in which the PSA layer is further prevented from peeling easily.

[0054] The self-emulsifying water-based active energy ray curable resin may be a commercially available product, such as "ETERNACOLL UW-9102" manufactured by UBE Corporation.

[0055] The active energy ray curable resin can be used in any appropriate amount depending on the type of water-dispersible acrylic polymer, etc. For example, the amount is preferably 5 to 200 parts by weight, more preferably 20 to 150 parts by weight, and even more preferably 50 to 150 parts by weight, relative to 100 parts by weight of the water-dispersible acrylic polymer.

[0056] A-4. Photopolymerization initiator Any suitable initiator can be used as the photopolymerization initiator. Examples of the photopolymerization initiator include acylphosphine oxide photopolymerization initiators such as ethyl 2,4,6-trimethylbenzylphenylphosphinate and (2,4,6-trimethylbenzoyl)phenylphosphine oxide; α-ketol compounds such as 4-(2-hydroxyethoxy)phenyl(2-hydroxy-2-propyl)ketone, α-hydroxy-α,α'-dimethylacetophenone, 2-methyl-2-hydroxypropiophenone, and 1-hydroxycyclohexylphenylketone; acetophenone compounds such as methoxyacetophenone, 2,2-dimethoxy-2-phenylacetophenone, 2,2-diethoxyacetophenone, and 2-methyl-1-[4-(methylthio)-phenyl]-2-morpholinopropane-1; benzoin ether compounds such as benzoin ethyl ether, benzoin isopropyl ether, and anisoin methyl ether; and benzyl dimethyl ketal. aromatic sulfonyl chloride compounds such as 2-naphthalenesulfonyl chloride; photoactive oxime compounds such as 1-phenone-1,1-propanedione-2-(o-ethoxycarbonyl)oxime; benzophenone compounds such as benzophenone, benzoylbenzoic acid, and 3,3'-dimethyl-4-methoxybenzophenone; thioxanthone compounds such as thioxanthone, 2-chlorothioxanthone, 2-methylthioxanthone, 2,4-dimethylthioxanthone, isopropylthioxanthone, 2,4-dichlorothioxanthone, 2,4-diethylthioxanthone, and 2,4-diisopropylthioxanthone; camphorquinone; halogenated ketones; acylphosphonates; and α-hydroxyacetophenones such as 2-hydroxy-1-(4-(4-(2-hydroxy-2-methylpropionyl)benzyl)phenyl)-2-methylpropane-1. The photopolymerization initiator may be used alone or in combination of two or more. Preferably, a photopolymerization initiator that is liquid at room temperature (e.g., 23°C) is used because it can be dissolved (compatible) in the water-dispersed acrylic polymer solution.

[0057] As the photopolymerization initiator, commercially available products may be used, for example, trade names of Omnirad 500, Omnirad TPO-L, Omnirad MBF, Omnirad 1173, etc., manufactured by IGM Resins, may be mentioned.

[0058] The photopolymerization initiator can be used in any appropriate amount. The content of the photopolymerization initiator is preferably 0.5 to 20 parts by weight, more preferably 1 to 10 parts by weight, relative to 100 parts by weight of the water-dispersible acrylic polymer. If the content of the photopolymerization initiator is less than 0.5 parts by weight, the composition may not be sufficiently cured when irradiated with ultraviolet light. If the content of the photopolymerization initiator exceeds 20 parts by weight, the storage stability of the water-dispersible pressure-sensitive adhesive composition may be reduced.

[0059] A-5. Crosslinking agent In one embodiment, the pressure-sensitive adhesive composition may further contain a crosslinking agent. The gel fraction of the pressure-sensitive adhesive composition can be adjusted by using a crosslinking agent. Any appropriate crosslinking agent can be used. Examples of the crosslinking agent include bifunctional or higher epoxy crosslinking agents, isocyanate crosslinking agents, carbodiimide crosslinking agents, oxazoline crosslinking agents, aziridine crosslinking agents, melamine resin crosslinking agents, metal chelate crosslinking agents, peroxide crosslinking agents, and hydrazine crosslinking agents. Only one crosslinking agent may be used, or two or more crosslinking agents may be used in combination.

[0060] Specifically, examples of the crosslinking agent include epoxy-based crosslinking agents such as N,N,N',N'-tetraglycidyl-m-xylylenediamine, 1,3-bis(N,N-glycidylaminomethyl)cyclohexane, and 1,6-hexanediol diglycidyl ether; isocyanate-based crosslinking agents (blocked isocyanate-based crosslinking agents, etc.) such as tolylene diisocyanate (blocked); carbodiimide-based crosslinking agents such as "Carbodilite V-01 (manufactured by Nisseibo Co., Ltd.)"; epoxy-based crosslinking agents such as polyethylene glycol diglycidyl ether and polyglycerol polyglycidyl ether; and water-dispersible isocyanate-based crosslinking agents such as "Elastron BN-69 (manufactured by Daiichi Kogyo Seiyaku Co., Ltd.)." oxazoline-based crosslinking agents such as trade name "Epocross WS-500 (manufactured by Nippon Shokubai Co., Ltd.)"; aziridine-based crosslinking agents such as trade name "ChemiTite PZ-33 (manufactured by Nippon Shokubai Co., Ltd.)"; hydrophilic-treated carbodiimide-based crosslinking agents such as trade names "Carbodilite V-02" and "Carbodilite V-04 (manufactured by Nisshinbo Co., Ltd.)"; crosslinking agents containing an active methylol group or an active alkoxymethyl group, such as an active methylol group such as hexamethylol melamine, or an active alkoxymethyl group such as hexamethoxymethyl melamine; metal chelate-based crosslinking agents such as trade name "Orgatix AI135 (manufactured by Matsumoto Pharmaceutical Industries Co., Ltd.)"; and hydrazine-based crosslinking agents such as adipic acid dihydrazide and phthalic acid dihydrazide.

[0061] The content of the crosslinking agent is, for example, 0.01 to 10 parts by weight, preferably 0.05 to 5 parts by weight, and more preferably 0.1 to 3 parts by weight, relative to 100 parts by weight of the water-dispersible acrylic polymer. As described above, the water-dispersible PSA composition may not contain a crosslinking agent (i.e., the content of the crosslinking agent may be 0 part by weight).

[0062] A-6. Additives The PSA may contain any suitable additives as needed. Examples of the additives include catalysts (e.g., platinum catalysts), tackifiers, plasticizers, pigments, dyes, fillers, antioxidants, conductive materials, UV absorbers, light stabilizers, release modifiers, softeners, flame retardants, solvents, etc. The additives are used in any suitable amount depending on the purpose.

[0063] The thickness of the pressure-sensitive adhesive layer can be set to any appropriate value. The thickness of the pressure-sensitive adhesive layer is preferably 2 μm to 200 μm, more preferably 3 μm to 150 μm, and even more preferably 5 μm to 100 μm. When the thickness of the pressure-sensitive adhesive layer is within the above range, it can exert sufficient adhesive strength to the adherend.

[0064] B. Manufacturing method of adhesive sheet The PSA sheet of the embodiment of the present invention can be produced by any appropriate method. For example, it can be obtained by applying a PSA to a release liner, drying it, forming a PSA layer on the release liner, and then transferring the PSA layer to a substrate. Alternatively, the PSA sheet can be obtained by applying a PSA to a substrate and drying it. As a method for applying the PSA, various methods can be used, such as bar coater coating, air knife coating, gravure coating, gravure reverse coating, reverse roll coating, lip coating, die coating, dip coating, offset printing, flexographic printing, and screen printing. As a drying method, any appropriate method can be used.

[0065] C. Applications of adhesive sheets The pressure-sensitive adhesive sheet of the embodiment of the present invention can be suitably used in the manufacturing process of semiconductor wafers.As mentioned above, the pressure-sensitive adhesive sheet of the embodiment of the present invention can suppress the heavy peeling of the pressure-sensitive adhesive layer even when it is attached to the surface of an activated wafer.Therefore, it can be suitably used as a pressure-sensitive adhesive sheet to be attached to a semiconductor wafer after a back-grinding process, for example, as a dicing tape. [Example]

[0066] The present invention will be described in more detail below with reference to examples, but the present invention is not limited to these examples. In the examples, "parts" and "%" are by weight unless otherwise specified.

[0067] [Example 1] 1. Synthesis of acrylic polymer A A reaction vessel equipped with a condenser, nitrogen inlet, thermometer, and stirrer was mixed with 325 parts by weight of water, 73 parts by weight of 2-ethylhexyl acrylate (2EHA), 26 parts by weight of methyl methacrylate (MMA), 1 part by weight of acrylic acid (AA), and 4.4 parts by weight of a reactive surfactant (Sanyo Chemical Industries, Ltd., product name "Eleminol JS-20"), emulsified by stirring with a homomixer, and then purged with nitrogen for 1 hour while stirring. The internal bath temperature during polymerization was then controlled at 60°C. 0.02 parts by weight of a water-soluble azo initiator (Fujifilm Wako Pure Chemical Industries, Ltd., product name "VA-057") was added to initiate polymerization, and the mixture was heated for 2 hours to produce the core. Next, 75 parts by weight of water, 46 parts by weight of 2EHA, 53 parts by weight of MMA, 1 part by weight of AA, and 1.6 parts by weight of a reactive surfactant (manufactured by Sanyo Chemical Industries, Ltd., product name "Eleminol JS-20") were mixed and stirred with a homomixer to prepare a shell monomer emulsion. 0.04 parts by weight of a water-soluble azo initiator (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd., product name "VA-057") was added to the aqueous dispersion solution containing the core particles. After a 10-minute induction period, the emulsified shell monomer emulsion solution was added over 2 hours, and the mixture was allowed to age for another 2 hours to produce an emulsion containing acrylic polymer A.

[0068] 2. Creating adhesive sheets 100 parts by weight of the obtained emulsion containing acrylic polymer A was neutralized with 10% aqueous ammonia to a pH of 8. The emulsion was then mixed with 100 parts by weight of a UV-curable resin (manufactured by UBE, trade name "ETERNACOLL UW-9102"), 1 part by weight of a crosslinking agent (manufactured by Nisshinbo Chemical Inc., trade name "Carbodilite V-04"), 3 parts by weight of a photopolymerization initiator (manufactured by IGM Resins BV, trade name "Omnirad TPO L"), and a leveling agent (manufactured by Daiichi Kogyo Seiyaku Co., Ltd., trade name "Neocoll") A water-dispersed adhesive solution was prepared by mixing 1 part by weight of an adhesive (manufactured by San Nopco: trade name "SN Thickener 612") and 1 part by weight of a thickener (manufactured by San Nopco: trade name "SN Thickener 612"). The obtained adhesive solution was applied to the silicone release treated surface of a polyester film (thickness 38μm) that had been subjected to a silicone release treatment so that the thickness after drying would be 5μm, and dried at 125°C for 3 minutes to form an adhesive layer. A polyolefin (PO) (thickness 80μm) that had been subjected to a surface oxidation treatment using a corona discharge method was bonded to the adhesive surface of the adhesive layer, and the adhesive layer was transferred to prepare an adhesive sheet.

[0069] [Example 2] A core-shell water-dispersible acrylic polymer B was obtained in the same manner as in Example 1, except that the content of AA used in the polymerization of the core and shell portions was changed to 2 parts by weight. A pressure-sensitive adhesive sheet was obtained in the same manner as in Example 1, except that the obtained acrylic polymer was used.

[0070] [Example 3] A core-shell water-dispersible acrylic polymer C was obtained in the same manner as in Example 1, except that the content of AA used in polymerization of the core and shell portions was changed to 2 parts by weight and 3 parts by weight of hydroxyethyl methacrylate (HEMA) was further added as a monomer used in the core and shell portions. A pressure-sensitive adhesive sheet was obtained in the same manner as in Example 1, except that the obtained acrylic polymer was used.

[0071] [Example 4] Except for not adding a crosslinking agent, a pressure-sensitive adhesive solution was prepared in the same manner as in Example 2. Except for using the prepared pressure-sensitive adhesive solution, a pressure-sensitive adhesive sheet was obtained in the same manner as in Example 2.

[0072] (Comparative Example 1) A core-shell water-dispersible acrylic polymer D was obtained in the same manner as in Example 1, except that the content of AA used in the polymerization of the core and shell portions was changed to 3 parts by weight. A pressure-sensitive adhesive sheet was obtained in the same manner as in Example 1, except that the obtained acrylic polymer was used.

[0073] (Comparative Example 2) An adhesive sheet was obtained in the same manner as in Example 2, except that UAW-1000W30 (manufactured by Kyoei Chemical Co., Ltd., product name "UAW-1000W30") was used instead of UW-9102 as the UV-curable resin.

[0074] (Comparative Example 3) An adhesive sheet was obtained in the same manner as in Example 2, except that UV-100S (manufactured by DIC Corporation, trade name "HYDRAN Exp UV-100S") was used as the UV-curable resin instead of UW-9102.

[0075] <Evaluation> The pressure-sensitive adhesive sheets used in the examples and comparative examples were evaluated as follows, and the results are shown in Table 3. 1. Pickup (PU) performance evaluation The adhesive sheet was mounted on the ground surface of a 6-inch silicon wafer (thickness 100 μm) that had been background under the following background grinding conditions in an environment of 23° C. immediately after grinding (within 5 minutes after grinding was completed). <Back grinding conditions> Grinder: DISCO, product name "DFG-840" 1st axis: #600 grinding wheel (rotation speed: 4800 rpm, down speed: P1: 3.0 μm / sec, P2: 2.0 μm / sec) 2-axis: #4000 grinding wheel (rotation speed: 5500 rpm, down speed: P1: 0.8 μm / sec, P2: 0.6 μm / sec) Next, the silicon wafer was diced under the following dicing conditions to form semiconductor chips. <Dicing conditions> Dicer: DISCO, product name "DFD-651" Blade: DISCO, product name "27HECC" Blade rotation speed: 40,000 rpm Dicing speed: 120mm / sec Dicing depth: 25 μm Cutting mode: Down cutting Dicing size: 5.0mm x 5.0mm After dicing, the wafer was heated and stored at 50°C for one week, and then irradiated with ultraviolet light from the back side of the adhesive sheet (integrated light intensity 460 mJ / cm 2 After that, a random chip was picked up from the adhesive sheet under the following pick-up conditions, and if the pick-up was successful, it was marked as ◯ (good), otherwise it was marked as × (room for improvement). <Pickup conditions> Die Ponder: NEC, product name "Machinery CPS-100" Number of pins: 4 Pin spacing: 3.5mm x 3.5mm Bottle tip curvature: 0.250mm Pin thrust amount: 0.50mm Adsorption retention time: 0.2 seconds Expanded amount: 3mm

[0076] 2. Adhesive strength An adhesive sheet cut into a length of 80 mm and a width of 20 mm was attached to a 6-inch silicon wafer (thickness 500 μm) that had been back-ground under the following back-grinding conditions. Immediately after grinding (within 5 minutes after grinding was completed), the wafer was laminated to the ground surface with a 2 kg roller in an environment of 23°C. The adhesive strength measured 30 minutes after lamination was "before UV (initial)" and 30 minutes after lamination, UV irradiation was performed (integrated light intensity 460 mJ / cm). 2 The adhesive strength measured on the adhesive sheet was "after UV." The adhesive sheet was heated and stored at 50°C for one week after lamination, and then irradiated with UV (460 mJ / cm 2 The measured value was recorded as "after UV heating." Each adhesive strength was measured by a 90° peel test under conditions of 23°C, 50% RH, and a pulling speed of 300 mm / min. <Back grinding conditions> Grinder: DISCO, product name "DFG-840" 1st axis: #600 grinding wheel (rotation speed: 4800 rpm, down speed: P1: 3.0 μm / sec, P2: 2.0 μm / sec) 2-axis: #4000 grinding wheel (rotation speed: 5500 rpm, down speed: P1: 0.8 μm / sec, P2: 0.6 μm / sec)

[0077] 3. Gas-phase chemical modification ESCA measurement The release liner was peeled off from the pressure-sensitive adhesive sheet, and the surface of the pressure-sensitive adhesive layer was chemically modified with trifluoroethanol. ESCA measurement was then carried out under the conditions shown in Table 2 below. The detection limit of this measurement method was 0.034 atomic %. [Table 2]

[0078] [Table 3]

[0079] The adhesive sheets of the examples of the present invention had a carboxyl group (COOH group) on the surface of the adhesive layer below the detection limit (0.034 atomic%). The adhesive sheets of the examples of the present invention prevented excessive increases in adhesive strength even when irradiated with UV light after heating, and exhibited excellent pick-up properties for semiconductor wafers after dicing. [Industrial Applicability]

[0080] The pressure-sensitive adhesive sheet according to the embodiment of the present invention can be suitably used for processing semiconductor wafers. [Explanation of symbols]

[0081] 10 adhesive layer 20 Base material 100 adhesive sheets

Claims

1. a substrate; and a PSA layer formed from a water-dispersible PSA composition containing a water-dispersible polymer, The pressure-sensitive adhesive sheet has a surface concentration of carboxyl groups on the surface of the pressure-sensitive adhesive layer, which is determined by X-ray photoelectron spectroscopy (ESCA) vapor phase chemical modification method, below the detection limit.

2. The pressure-sensitive adhesive sheet according to claim 1 , wherein the water-dispersible pressure-sensitive adhesive composition further comprises an active energy ray-curable resin and a photopolymerization initiator.

3. The pressure-sensitive adhesive sheet according to claim 1 , wherein the monomer composition used in the polymerization of the water-dispersible polymer contains a carboxyl group-containing monomer.

4. The pressure-sensitive adhesive sheet according to claim 3 , wherein the monomer composition used for polymerization of the water-dispersible polymer contains less than 3 parts by weight of the carboxyl group-containing monomer in terms of acrylic acid equivalent, per 100 parts by weight of all monomer components.

5. The pressure-sensitive adhesive sheet according to claim 2 , wherein the active energy ray-curable resin is a self-emulsifying water-based active energy ray-curable resin.

6. The pressure-sensitive adhesive sheet according to claim 1 , wherein the detection limit is 0.034 atomic %.

7. The pressure-sensitive adhesive sheet according to claim 1 , which is used for semiconductor wafer processing.

8. The pressure-sensitive adhesive sheet according to claim 1 , which is a dicing tape.

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