Workpiece processing sheet and method of use

Abstract

To provide a sheet for workpiece processing which exhibits excellent anti-static property while exhibiting sufficient adhesive strength.SOLUTION: A sheet for workpiece processing comprises a substrate and an adhesive layer laminated on one side of the substrate, and is constituted of an active energy ray-curable adhesive formed of an adhesive composition containing a phosphonium salt of the following formula (1), (In the formula (1), at least three of R1-R4 are alkyl chains having 3 or more carbon atoms, and the rest are hydrocarbon groups other than the alkyl chains, and X- is an anion not including a halogen, or an anion including a halogen in such an amount that the halogen content in the adhesive layer is 1,000 ppm or less).SELECTED DRAWING: None

Description

[Technical Field]

[0001] This invention relates to a workpiece processing sheet used for processing workpieces such as semiconductor wafers, and to a method for using the same. [Background technology]

[0002] Semiconductor wafers such as silicon and gallium arsenide, as well as various packages, are manufactured in a large diameter state, then cut into chips (dicing), peeled off (picked up), and then moved to the next process, the mounting process. At this time, the workpieces, such as semiconductor wafers, are stacked on an adhesive sheet (hereinafter sometimes referred to as a "workpiece processing sheet") which has a base material and an adhesive layer, and then processed with processes such as backgrinding, dicing, washing, drying, expanding, picking up, and mounting.

[0003] In the above-mentioned workpiece processing sheet, a release sheet may be laminated on the side of the adhesive layer opposite to the substrate (hereinafter sometimes referred to as the "adhesive surface") for the purpose of protecting that surface. When the workpiece processing sheet is used, the release sheet is peeled off from the adhesive surface, and at this time, static electricity called peeling charge may be generated. Furthermore, after processing a workpiece on the workpiece processing sheet, peeling charge may also occur when separating the processed workpiece from the workpiece processing sheet.

[0004] Such delamination charging can cause problems, such as the destruction of circuits formed on a semiconductor chip when the processed workpiece is one such chip. Therefore, from the viewpoint of preventing delamination charging, workpiece processing sheets have been developed in which a predetermined ionic liquid (also called an ionic liquid, etc.) is contained in the adhesive layer (for example, Patent Documents 1 and 2). [Prior art documents] [Patent Documents]

[0005] [Patent Document 1] Japanese Patent Publication No. 2015-003988 [Patent Document 2] Japanese Patent Publication No. 2009-260332 [Overview of the project] [Problems that the invention aims to solve]

[0006] Incidentally, in the workpiece processing sheet described above, it is required that the workpiece be sufficiently held on the adhesive surface before processing is complete, while at the same time that the processed workpiece can be easily separated after processing is complete. From this viewpoint, an adhesive that exhibits active energy ray curing properties is sometimes used as the adhesive that constitutes the adhesive layer. In a workpiece processing sheet equipped with such an adhesive layer, the adhesive layer can be cured by irradiating it with active energy rays after processing is complete, thereby sufficiently reducing the adhesive force to the processed workpiece and enabling easy separation of the workpiece.

[0007] However, with conventional workpiece processing sheets, it has been difficult to achieve a good balance between controlling the adhesive strength and the antistatic properties that prevent the aforementioned peeling charge. In particular, increasing the content of ionic liquid in the adhesive layer provides sufficient antistatic properties but insufficient adhesive strength, while decreasing the content provides sufficient adhesive strength but insufficient antistatic properties.

[0008] This invention has been made in view of the above circumstances, and aims to provide a workpiece processing sheet that exhibits excellent antistatic properties while also providing sufficient adhesive strength. [Means for solving the problem]

[0009] To achieve the above objective, firstly, the present invention provides a workpiece processing sheet comprising a base material and an adhesive layer laminated on one side of the base material, wherein the adhesive layer is a phosphonium salt of the following formula (1). [ka] (In formula (1), at least three R1 to R4 are alkyl chains having 3 or more carbon atoms, and the remainder are hydrocarbon groups other than the alkyl chains, X - The present invention provides a workpiece processing sheet characterized by being composed of an active energy ray curable adhesive formed from an adhesive composition containing either a halogen-free anion or an anion containing a halogen in an amount such that the halogen content in the adhesive layer is 1000 ppm or less (Invention 1).

[0010] In the workpiece processing sheet according to the above invention (Invention 1), the adhesive layer is composed of an active energy ray curable adhesive formed from the above-mentioned adhesive composition containing a phosphonium salt, thereby exhibiting excellent antistatic properties while providing sufficient adhesive strength. Furthermore, in the workpiece processing sheet according to the above invention (Invention 1), the adhesive strength to the processed workpiece can be effectively reduced by irradiation with active energy rays. As a result, the workpiece processing sheet according to the above invention (Invention 1) suppresses peeling charge and enables good workpiece processing.

[0011] In the above invention (Invention 1), the content of the phosphonium salt in the adhesive composition is preferably 0.2% by mass or more and 30% by mass or less (Invention 2).

[0012] In the above inventions (Inventions 1 and 2), it is preferable that all of R1 to R4 in the phosphonium salt are alkyl chains having 3 or more carbon atoms (Invention 3).

[0013] In the above inventions (inventions 1 to 3), X in the phosphonium salt - Preferably, it is at least one of tosylate, dicyanamide, and methyl sulfate (Invention 4).

[0014] In the above inventions (Inventions 1 to 4), it is preferable that the adhesive composition contains a (meth)acrylic acid ester polymer in which an active energy ray curable group is introduced into the side chain (Invention 5).

[0015] In the above inventions (Inventions 1 to 5), it is preferable that the ratio (after irradiation / before irradiation) of the adhesion of the work processing sheet to the mirror surface of the silicon wafer with respect to the work processing sheet before and after irradiating the work processing sheet with active energy rays is 0.001 or more and 0.3 or less (Invention 6).

[0016] In the above inventions (Inventions 1 to 6), it is preferable that the work processing sheet is used as at least one of a dicing sheet and a pickup sheet (Invention 7).

[0017] Second, the present invention provides a method of using the work processing sheet (Inventions 1 to 7), which includes a step of attaching a surface of the adhesive layer opposite to the base material to a work, and a step of processing the work on the work processing sheet (Invention 8).

Effects of the Invention

[0018] The work processing sheet according to the present invention exhibits excellent antistatic properties while exerting sufficient adhesion.

Modes for Carrying Out the Invention

[0019] Hereinafter, embodiments of the present invention will be described. The work processing sheet according to the present embodiment includes a base material and an adhesive layer laminated on one side of the base material.

[0020] 1. Components of the Work Processing Sheet (1) Base Material The substrate in this embodiment is not particularly limited as long as it exhibits the desired function when used as a workpiece processing sheet. In particular, the substrate is preferably a resin film mainly composed of resin-based materials. Specific examples include polyolefin films such as polyethylene film, polypropylene film, polybutene film, polybutadiene film, polymethylpentene film, ethylene-norbornene copolymer film, and norbornene resin film; polyester films such as polyethylene terephthalate film, polybutylene terephthalate film, and polyethylene naphthalate; ethylene-vinyl acetate copolymer film; ethylene copolymer films such as ethylene-(meth)acrylic acid copolymer film, ethylene-(meth)acrylate copolymer film, and other ethylene-(meth)acrylic acid ester copolymer films; polyvinyl chloride films such as polyvinyl chloride film and vinyl chloride copolymer film; (meth)acrylic acid ester copolymer film; polyurethane film; polyimide film; polystyrene film; polycarbonate film; and fluororesin film. Modified films such as crosslinked films and ionomer films can also be used. Furthermore, the substrate may be a laminated film formed by laminating multiple of the above-mentioned films. In this laminated film, the materials constituting each layer may be of the same type or different types.

[0021] Among the above, it is preferable to use at least one of polyolefin films and ethylene copolymer films, and in particular, it is preferable to use an ethylene-(meth)acrylic acid copolymer film. In this specification, "(meth)acrylic acid" means both acrylic acid and methacrylic acid. The same applies to other similar terms. In this specification, "polymer" also includes the concept of "polymer".

[0022] The base material may contain various additives such as flame retardants, plasticizers, antistatic agents, lubricants, antioxidants, colorants, infrared absorbers, ultraviolet absorbers, and ion scavengers. While there are no particular limitations on the content of these additives, it is preferable to keep it within a range that allows the base material to exhibit the desired function.

[0023] The surface of the substrate to which the adhesive layer is laminated may be subjected to surface treatments such as primer treatment, corona treatment, or plasma treatment in order to improve adhesion with the adhesive layer.

[0024] The thickness of the base material can be appropriately set depending on the method in which the workpiece processing sheet is used, but it is preferably 200 μm or less, and particularly preferably 150 μm or less. Furthermore, the thickness of the base material is preferably 10 μm or more, and particularly preferably 25 μm or more.

[0025] (2) Adhesive layer The adhesive layer in this embodiment is a phosphonium salt of the following formula (1). [ka] It is composed of an active energy ray curable adhesive formed from an adhesive composition containing [a specific substance].

[0026] Here, in formula (1) above, at least three R1 to R4 are alkyl chains having 3 or more carbon atoms, and the remaining ones are hydrocarbon groups other than the alkyl chains (e.g., methyl group, ethyl group, etc.). Also, in formula (1) above, X - X is either a halogen-free anion or an anion containing halogen in an amount such that the halogen content in the adhesive layer is 1000 ppm or less. - It is an anion that is essentially halogen-free.

[0027] In this embodiment, the workpiece processing sheet has an adhesive layer composed of an active energy ray-curable adhesive, which allows for good control of the adhesive strength. That is, while exhibiting good adhesive strength before irradiation with active energy rays, the adhesive layer can be cured by irradiation with active energy rays, thereby sufficiently reducing the adhesive strength. As a result, the processed workpiece can be easily separated from the workpiece processing sheet by irradiation with active energy rays.

[0028] In particular, the phosphonium salt of formula (1) above has at least three alkyl chains with 3 or more carbon atoms (R1 to R4), which makes it less prone to a decrease in adhesive strength compared to when conventional phosphonium salts or other ionic liquids are used. Furthermore, the presence of the alkyl chains improves the compatibility between the phosphonium salt of formula (1) and other components in the adhesive layer composition. As a result, even when the formed adhesive layer comes into contact with water (especially the washing water used during dicing), the outflow of the phosphonium salt is suppressed, and consequently, the decrease in adhesive strength is also suppressed. Consequently, the workpiece processing sheet according to this embodiment exhibits good adhesive strength to the workpiece (before irradiation with active energy rays), and problems such as chip flying during dicing can be effectively suppressed.

[0029] Furthermore, the workpiece processing sheet according to this embodiment, by using the phosphonium salt described above, exhibits the excellent adhesive performance described above while also having a sufficiently reduced surface resistivity, thereby effectively suppressing the occurrence of peeling charge. As a result, the workpiece processing sheet according to this embodiment effectively suppresses problems such as electrostatic discharge damage to the workpiece after processing.

[0030] Furthermore, generally speaking, if a workpiece processing sheet contains halogens, the halogens may migrate from the workpiece processing sheet to the processed workpiece, and depending on the application of the workpiece, these halogens may cause defects. However, in the workpiece processing sheet according to this embodiment, the phosphonium salt X -As the anions are substantially halogen-free as described above, the workpiece processing sheet according to this embodiment can be suitably used even in applications where halogens may cause problems. Furthermore, the cations of the phosphonium salt described above are halogen-free, as is clear from the definitions of R1 to R4 described above.

[0031] Regarding the cations constituting the above phosphonium salt, it is preferable that all of R1 to R4 are alkyl chains having 3 or more carbon atoms. This makes it easier to achieve a good balance between controlling adhesion by active energy ray irradiation and excellent antistatic properties.

[0032] Furthermore, with respect to the cation constituting the phosphonium salt, the number of carbon atoms in the alkyl chain is preferably 4 or more, and particularly preferably 6 or more. The upper limit of the number of carbon atoms is not particularly limited, but for example, it is 20 or less. Preferred examples of the alkyl chain include isobutyl group, sec-butyl group, tert-butyl group, n-butyl group, n-pentyl group, n-hexyl group, n-heptyl group, n-octyl group, n-nonyl group, n-decyl group, n-dodecyl group, n-tetradecyl group, etc. Note that the alkyl chains R1 to R4 may be the same, or some or all of them may be different. When the cation satisfies these conditions, it becomes easier to achieve a good balance between controlling the adhesive force by active energy ray irradiation and excellent antistatic properties.

[0033] Regarding the anion constituting the above phosphonium salt, X - Preferably, the material is at least one of tosylate, dicyanamide, and methyl sulfate. This makes it easier to achieve a good balance between controlling the adhesive strength by active energy ray irradiation and excellent antistatic properties.

[0034] Also, X -However, if the halogen content in the adhesive layer is 1000 ppm or less and the anion contains halogen, the halogen content is preferably 500 ppm or less, particularly preferably 100 ppm or less, and even more preferably 10 ppm or less.

[0035] Preferred specific examples of the above phosphonium salts include tributylmethylphosphonium tosylate, triisobutylmethylphosphonium tosylate, tetrabutylphosphonium methylsulfonate, trihexylmethylphosphonium tosylate, trihexylethylphosphonium tosylate, trihexyltetradecylphosphonium dicyanamide, tributylmethylphosphonium tosylate, tributylmethylphosphonium methylsulfate, tetrabutylphosphonium tridecylsulfosuccinate, (trihexyl)tetradecylphosphonium diisobutyldithiophosphate, ethyltri(butyl)phosphonium diethylphosphate, tetradecyl(tributyl)phosphonium dodecylsulfonate, tetrabutylphosphonium glycolate, (trihexyl)tetradecyl Examples include diphosphonium diisobutyl monothiophosphate, tri(isobutyl)methylphosphonium dimethyl phosphate, tetrabutylphosphonium benzoate, (trihexyl)tetradecylphosphonium bis(2-ethylhexyl) phosphate, tributylmethylphosphonium dibutyl phosphate, tributylmethylphosphonium dibutyl phosphate, triethylmethylphosphonium dibutyl phosphate, trihexyltetradecylphosphonium bis(2,4,4-trimethylpentyl) phosphinate, tetradecyl(trihexyl)phosphonium bis(2,4,4-trimethylpentyl) phosphinate, trihexyl(tetradecyl)phosphonium bis{(oxalate(2-)) borate, and tetradecyl(trihexyl)phosphonium decanoate.

[0036] The content of the phosphonium salt in the above adhesive composition is preferably 0.2% by mass or more, particularly preferably 1% by mass or more, and more preferably 5% by mass or more. A content of 0.2% by mass or more makes it easier to exhibit excellent antistatic properties. Furthermore, the content is preferably 30% by mass or less, particularly preferably 25% by mass or less, and more preferably 20% by mass or less. A content of 30% by mass or less makes it easier to exhibit good adhesive strength (before irradiation with active energy rays).

[0037] The active energy ray curable adhesive constituting the adhesive layer in this embodiment is not particularly limited, and examples include acrylic adhesives, rubber adhesives, silicone adhesives, urethane adhesives, polyester adhesives, polyvinyl ether adhesives, and the like. Among these, it is preferable to use an acrylic adhesive from the viewpoint of easily exhibiting the desired adhesive strength.

[0038] When using an acrylic adhesive, preferred embodiments of the adhesive composition in this embodiment include an adhesive composition containing at least an acrylic polymer (A) with an active energy ray curable group introduced into the side chain and the phosphonium salt, an acrylic polymer (B) without an active energy ray curable group introduced into the side chain, and an adhesive composition containing at least an active energy ray curable component and the phosphonium salt. Among these adhesive compositions, it is preferable to use an adhesive composition containing at least an acrylic polymer (A) with an active energy ray curable group introduced into the side chain and the phosphonium salt, from the viewpoint of making it easier to separate the processed workpiece from the adhesive surface after irradiation with active energy rays.

[0039] (2-1) Acrylic polymer (A) in which an active energy ray curable group is introduced into the side chain. The acrylic polymer (A) in which an active energy ray curable group is introduced into the side chain in this embodiment (hereinafter sometimes referred to as "active energy ray curable polymer (A)") is not particularly limited, but is preferably obtained by reacting, for example, an acrylic copolymer (a1) having a functional group-containing monomer unit with an unsaturated group-containing compound (a2) having a functional group bonded to that functional group.

[0040] The above acrylic copolymer (a1) preferably contains structural units derived from functional group-containing monomers and structural units derived from (meth)acrylic acid ester monomers or their derivatives.

[0041] The functional group-containing monomer used as a constituent unit of the acrylic copolymer (a1) is preferably a monomer having a polymerizable double bond and a functional group such as a hydroxyl group, carboxyl group, amino group, substituted amino group, or epoxy group within its molecule.

[0042] Examples of hydroxyl group-containing monomers include 2-hydroxyethyl (meth)acrylate, 2-hydroxypropyl (meth)acrylate, 3-hydroxypropyl (meth)acrylate, 2-hydroxybutyl (meth)acrylate, 3-hydroxybutyl (meth)acrylate, and 4-hydroxybutyl (meth)acrylate, which can be used individually or in combination of two or more.

[0043] Examples of carboxyl group-containing monomers include ethylenically unsaturated carboxylic acids such as acrylic acid, methacrylic acid, crotonic acid, maleic acid, itaconic acid, and citraconic acid. These may be used individually or in combination of two or more.

[0044] Examples of amino group-containing monomers or substituted amino group-containing monomers include aminoethyl (meth)acrylate and n-butylaminoethyl (meth)acrylate. These may be used individually or in combination of two or more.

[0045] When the acrylic copolymer (a1) contains the above-mentioned functional group-containing monomer, the mass percentage of the structural portion derived from the functional group-containing monomer in the acrylic copolymer (a1) is preferably 5% by mass or more, more preferably 10% by mass or more, and even more preferably 15% by mass or more. Furthermore, the above percentage is preferably 45% by mass or less, more preferably 40% by mass or less, and even more preferably 35% by mass or less. By having the proportion of the structural portion derived from the functional group-containing monomer within the above range, it becomes easier to adjust the amount of unsaturated group-containing compound (a2) introduced to a suitable range.

[0046] As the (meth)acrylic acid ester monomer constituting the acrylic copolymer (a1), alkyl (meth)acrylates having 1 to 20 carbon atoms in the alkyl group are preferably used.

[0047] As alkyl (meth)acrylates, alkyl (meth)acrylates in which the alkyl group has 1 to 18 carbon atoms are particularly preferred, such as methyl (meth)acrylate, ethyl (meth)acrylate, propyl (meth)acrylate, n-butyl (meth)acrylate, and 2-ethylhexyl (meth)acrylate. These may be used individually or in combination of two or more.

[0048] When the acrylic copolymer (a1) contains the above-mentioned (meth)acrylic acid ester monomer, the mass percentage of the structural portion derived from the above-mentioned (meth)acrylic acid ester monomer in the acrylic copolymer (a1) is preferably 50% by mass or more, particularly preferably 55% by mass or more, and even more preferably 60% by mass or more. Furthermore, the above percentage is preferably 95% by mass or less, particularly preferably 90% by mass or less, and even more preferably 85% by mass or less. Having the proportion of the structural portion derived from the (meth)acrylic acid ester monomer within the above range makes it easier to exhibit the desired adhesive strength.

[0049] The above-mentioned acrylic copolymer (a1) may contain components other than the monomers described above as constituent monomers, for example, dimethylacrylamide, vinyl formate, vinyl acetate, styrene, monomers having an alicyclic structure, etc.

[0050] An active energy ray curable polymer (A) is obtained by reacting an acrylic copolymer (a1) having the above-mentioned functional group-containing monomer units with an unsaturated group-containing compound (a2) having a functional group bonded to the functional group.

[0051] The functional group of the unsaturated group-containing compound (a2) can be appropriately selected according to the type of functional group of the functional group-containing monomer unit of the acrylic copolymer (a1). For example, if the functional group of the acrylic copolymer (a1) is a hydroxyl group, an amino group, or a substituted amino group, the functional group of the unsaturated group-containing compound (a2) is preferably an isocyanate group or an epoxy group. If the functional group of the acrylic copolymer (a1) is an epoxy group, the functional group of the unsaturated group-containing compound (a2) is preferably an amino group, a carboxyl group, or an aziridinyl group.

[0052] Furthermore, the above-mentioned unsaturated group-containing compound (a2) contains at least one, preferably 1 to 6, and more preferably 1 to 4, active energy ray polymerizable carbon-carbon double bonds per molecule. Specific examples of such unsaturated group-containing compounds (a2) include, for example, 2-(meth)acryloyloxyethyl isocyanate, meta-isopropenyl-α,α-dimethylbenzyl isocyanate, (meth)acryloyl isocyanate, allyl isocyanate, 1,1-(bisacryloyloxymethyl)ethyl isocyanate; acryloyl monoisocyanate compounds obtained by the reaction of a diisocyanate compound or polyisocyanate compound with hydroxyethyl (meth)acrylate; acryloyl monoisocyanate compounds obtained by the reaction of a diisocyanate compound or polyisocyanate compound with a polyol compound with hydroxyethyl (meth)acrylate; glycidyl (meth)acrylate; (meth)acrylic acid, 2-(1-aziridinyl)ethyl (meth)acrylate, 2-vinyl-2-oxazoline, 2-isopropenyl-2-oxazoline, etc.

[0053] The amount of the unsaturated group-containing compound (a2) is preferably 40 mol% or more, and more preferably 50 mol% or more, in terms of the amount of functional groups in the acrylic copolymer (a1). Furthermore, the amount of the unsaturated group-containing compound (a2) is preferably 99 mol% or less, more preferably 95% or less, and even more preferably 90 mol% or less, in terms of the amount of functional groups in the acrylic copolymer (a1).

[0054] In the reaction between the acrylic copolymer (a1) and the unsaturated group-containing compound (a2), the reaction temperature, pressure, solvent, time, presence or absence of a catalyst, and type of catalyst can be appropriately selected depending on the combination of functional groups present in the acrylic copolymer (a1) and the functional groups present in the unsaturated group-containing compound (a2). As a result, the functional groups present in the acrylic copolymer (a1) react with the functional groups in the unsaturated group-containing compound (a2), introducing unsaturated groups into the side chains of the acrylic copolymer (a1), and yielding an active energy ray-curable polymer (A).

[0055] In particular, the reaction between the acrylic copolymer (a1) and the unsaturated group-containing compound (a2) is preferably carried out in the presence of at least one organometallic catalyst selected from organotin compounds, zirconium complexes, zinc complexes, and zirconium-containing metal soaps. The use of such an organometallic catalyst makes it easier for the adhesive layer and the substrate to exhibit excellent adhesion, and makes it easier to suppress separation of the substrate and the adhesive layer during use.

[0056] Examples of the above organotin compounds include dibutyltin dilaurate (DBTDL), dioctyltin dilaurate (DOTDL), dibutyltin diacetate (DBTDA), dioctyltin diacetate (DOTDA), dioctyltin malate (DOTM), and dibutyltin malate (DBTM). Among these, dibutyltin dilaurate (DBTDL) is preferred.

[0057] When an organotin compound is used as the organometallic catalyst, the content of the organotin compound in the adhesive composition is preferably 0.001 parts by mass or more, particularly preferably 0.01 parts by mass or more, and even more preferably 0.02 parts by mass or more, based on 100 parts by mass of the total amount of monomers constituting the acrylic copolymer (a1). Furthermore, the content is preferably less than 0.3 parts by mass, particularly preferably 0.1 parts by mass or less, and even more preferably 0.07 parts by mass or less.

[0058] The weight-average molecular weight (Mw) of the activated energy ray-curable polymer (A) obtained in this manner is preferably 100,000 or more, particularly preferably 200,000 or more, and even more preferably 300,000 or more. Furthermore, the weight-average molecular weight (Mw) is preferably 1,200,000 or less, particularly preferably 1,000,000 or less, and even more preferably 800,000 or less. In this specification, the weight-average molecular weight (Mw) is a value on a standard polystyrene basis measured by gel permeation chromatography (GPC).

[0059] (2-2) Acrylic polymers in which active energy ray curable groups are not introduced into the side chains (B) As an acrylic polymer (B) in which active energy ray curable groups are not introduced into the side chains, for example, the same components as those of the acrylic copolymer (a1) described above can be used.

[0060] Furthermore, when the acrylic copolymer (a1) used as the acrylic polymer (B) contains the functional group-containing monomer described above, the mass percentage of the structural portion derived from the functional group-containing monomer in the acrylic copolymer (a1) is preferably 0.1% by mass or more, particularly preferably 1% by mass or more, and even more preferably 3% by mass or more. In addition, the above percentage is preferably 30% by mass or less, particularly preferably 25% by mass or less, and even more preferably 20% by mass or less. When the proportion of the structural portion derived from the functional group-containing monomer is within the above range, it becomes easier to exhibit the desired adhesive strength.

[0061] Furthermore, when the acrylic copolymer (a1) used as the acrylic polymer (B) contains the aforementioned (meth)acrylic acid ester monomer, the mass percentage of the structural portion derived from the (meth)acrylic acid ester monomer in the acrylic copolymer (a1) is preferably 70% by mass or more, particularly preferably 75% by mass or more, and even more preferably 80% by mass or more. The above percentage is also preferably 99.9% by mass or less, particularly preferably 99% by mass or less, and even more preferably 97% by mass or less. Having the proportion of the structural portion derived from the (meth)acrylic acid ester monomer within the above range makes it easier to exhibit the desired adhesive strength.

[0062] (2-3) Active energy ray curing components The active energy ray curable component in this embodiment is not particularly limited as long as it is a component that is curable by active energy rays. In this specification, the active energy ray curable component is defined as being different from an acrylic polymer (A) in which an active energy ray curable group is introduced into the side chain.

[0063] In this embodiment, if the adhesive composition contains an acrylic polymer (B) in which active energy ray-curable groups are not introduced into the side chains, the adhesive layer in this embodiment will exhibit good active energy ray curability if the adhesive composition further contains an active energy ray-curable component. However, even if the adhesive composition in this embodiment contains an acrylic polymer (A) in which active energy ray-curable groups are introduced into the side chains, the adhesive composition may still contain an active energy ray-curable component.

[0064] Preferred examples of active energy ray curable components include active energy ray curable monomers and / or oligomers. Specific examples include monofunctional acrylic acid esters such as cyclohexyl (meth)acrylate and isobornyl (meth)acrylate; polyfunctional acrylic acid esters such as trimethylolpropane tri(meth)acrylate, pentaerythritol tri(meth)acrylate, pentaerythritol tetra(meth)acrylate, dipentaerythritol hexa(meth)acrylate, 1,4-butanediol di(meth)acrylate, 1,6-hexanediol di(meth)acrylate, polyethylene glycol di(meth)acrylate, and dimethylol tricyclodecane di(meth)acrylate; polyester oligo(meth)acrylate; polyurethane oligo(meth)acrylate; and others. These may be used individually or in combination of two or more.

[0065] In this embodiment, when the adhesive composition contains an active energy ray-curable component together with an acrylic polymer (B) in which active energy ray-curable groups are not introduced into the side chains, the content of the active energy ray-curable component in the adhesive composition is preferably more than 30 parts by mass, and particularly preferably 60 parts by mass or more, per 100 parts by mass of the acrylic polymer (B). Furthermore, the content is preferably 250 parts by mass or less, and particularly preferably 200 parts by mass or less, per 100 parts by mass of the acrylic polymer (B).

[0066] (2-4) Crosslinking agents The adhesive composition in this embodiment may also preferably contain a crosslinking agent. The inclusion of a crosslinking agent in the adhesive composition allows the acrylic polymer (A) or acrylic polymer (B) to crosslink in the adhesive layer, forming a good three-dimensional network structure. This further improves the cohesive strength of the resulting adhesive, effectively suppressing the generation of adhesive residue in the workpiece separated from the workpiece processing sheet after irradiation with active energy rays. When the adhesive composition contains a crosslinking agent, the acrylic copolymer (a1) preferably contains the above-mentioned functional group-containing monomer as the monomer units constituting the polymer, and in particular, it is preferable to contain a functional group-containing monomer having a functional group that is highly reactive with the crosslinking agent used.

[0067] Examples of the above crosslinking agents include isocyanate-based crosslinking agents, epoxy-based crosslinking agents, amine-based crosslinking agents, melamine-based crosslinking agents, aziridine-based crosslinking agents, hydrazine-based crosslinking agents, aldehyde-based crosslinking agents, oxazoline-based crosslinking agents, metal alkoxide-based crosslinking agents, metal chelate-based crosslinking agents, metal salt-based crosslinking agents, and ammonium salt-based crosslinking agents. These crosslinking agents can be selected according to the functional groups derived from the functional group-containing monomers present in the acrylic copolymer. These crosslinking agents can be used individually or in combination of two or more.

[0068] The isocyanate-based crosslinking agent contains at least a polyisocyanate compound. Examples of polyisocyanate compounds include aromatic polyisocyanates such as tolylene diisocyanate, diphenylmethane diisocyanate, and xylylene diisocyanate; aliphatic polyisocyanates such as hexamethylene diisocyanate; alicyclic polyisocyanates such as isophorone diisocyanate and hydrogenated diphenylmethane diisocyanate; and their biuret and isocyanurate forms, as well as adducts which are reaction products with low molecular weight active hydrogen-containing compounds such as ethylene glycol, propylene glycol, neopentyl glycol, trimethylolpropane, and castor oil. Among these, trimethylolpropane-modified aromatic polyisocyanates, particularly trimethylolpropane-modified tolylene diisocyanate, are preferred.

[0069] In this embodiment, if the adhesive composition contains a crosslinking agent, the amount of crosslinking agent in the adhesive composition is preferably 0.1 parts by mass or more, more preferably 0.5 parts by mass or more, and more preferably 3 parts by mass or more, per 100 parts by mass of the total amount of acrylic polymer (A) and acrylic polymer (B) (or, if only one of acrylic polymer (A) and acrylic polymer (B) is contained, the amount of the component contained). Furthermore, the amount is preferably 20 parts by mass or less, and more preferably 5 parts by mass or less. A crosslinking agent content of 0.1 parts by mass or more makes it easier to improve the cohesive force of the adhesive layer after irradiation with active energy rays, thereby effectively suppressing adhesive residue. Furthermore, a crosslinking agent content of 20 parts by mass or less results in an appropriate degree of crosslinking, making it easier for the adhesive layer to exhibit the desired adhesive strength.

[0070] (2-5) Photopolymerization initiator The adhesive composition in this embodiment may also preferably contain a photopolymerization initiator. By containing a photopolymerization initiator in the adhesive composition, the polymerization curing time and the amount of light irradiation when curing the adhesive layer by irradiation with active energy rays can be reduced.

[0071] Examples of photopolymerization initiators include benzophenone, acetophenone, benzoin, benzoin methyl ether, benzoin ethyl ether, benzoin isopropyl ether, benzoin isobutyl ether, benzoin benzoic acid, benzoin methyl benzoate, benzoin dimethyl ketal, 2,4-diethylthioxanthone, 1-hydroxycyclohexylphenyl ketone, 2-hydroxy-1-{4-[4-(2-hydroxy-2-methylpropionyl)-benzyl]phenyl}-2-methyl-propane- Examples include 1-one, benzyl diphenyl sulfide, tetramethylthiuram monosulfide, azobisisobutyronitrile, benzyl, dibenzyl, diacetyl, β-chloranthraquinone, (2,4,6-trimethylbenzyldiphenyl)phosphine oxide, 2-benzothiazole-N,N-diethyldithiocarbamate, oligo{2-hydroxy-2-methyl-1-[4-(1-propenyl)phenyl]propanone}, and 2,2-dimethoxy-1,2-diphenylethane-1-one. Among these, 2-hydroxy-1-{4-[4-(2-hydroxy-2-methyl-propionyl)-benzyl]phenyl}-2-methyl-propan-1-one is preferred. The above-mentioned photopolymerization initiators may be used alone or in combination of two or more.

[0072] In this embodiment, if the adhesive composition contains a photopolymerization initiator, the content of the photopolymerization initiator in the adhesive composition is preferably 0.1 parts by mass or more, and particularly preferably 1 part by mass or more, per 100 parts by mass of the total amount of acrylic polymer (A) and acrylic polymer (B) (or, if only one of acrylic polymer (A) and acrylic polymer (B) is contained, the content of the component contained). Furthermore, the content is preferably 10 parts by mass or less, and particularly preferably 5 parts by mass or less. By having the photopolymerization initiator content within the above range, the adhesive layer can be efficiently cured by irradiation with active energy rays, thereby making it easier to effectively reduce the adhesive strength of the workpiece processing sheet to the adherend.

[0073] (2-6) Other ingredients The adhesive composition in this embodiment can contain desired additives, such as silane coupling agents, antistatic agents, tackifiers, antioxidants, light stabilizers, softeners, fillers, refractive index adjusters, etc., as long as they do not impair the effects of the workpiece processing sheet according to this embodiment.

[0074] (2-7) Method for preparing adhesive composition The adhesive composition in this embodiment can be produced by manufacturing an acrylic polymer (A) or an acrylic polymer (B), and then mixing the obtained acrylic polymer (A) or acrylic polymer (B) with the phosphonium salt described above, and optionally an active energy ray curable component, a crosslinking agent, a photopolymerization initiator, and an additive. At this time, a diluent solvent may be added optionally to obtain a coating solution of the adhesive composition.

[0075] Examples of the diluent solvents used include aliphatic hydrocarbons such as hexane, heptane, and cyclohexane; aromatic hydrocarbons such as toluene and xylene; halogenated hydrocarbons such as methylene chloride and ethylene chloride; alcohols such as methanol, ethanol, propanol, butanol, and 1-methoxy-2-propanol; ketones such as acetone, methyl ethyl ketone, 2-pentanone, isophorone, and cyclohexanone; esters such as ethyl acetate and butyl acetate; and cellosolve solvents such as ethyl cellosolve.

[0076] The concentration and viscosity of the coating solution prepared in this manner are not particularly limited as long as they are within the range of coating, and can be appropriately selected depending on the situation. For example, the adhesive composition is diluted to a concentration of 10% by mass or more and 60% by mass or less. Note that the addition of a diluent is not a necessary condition when obtaining the coating solution; if the adhesive composition has a viscosity suitable for coating, a diluent may not be added. In this case, the adhesive composition becomes a coating solution in which the polymerization solvent of the acrylic copolymer (a1) is used directly as the diluent.

[0077] (2-8) Thickness of the adhesive layer In this embodiment, the thickness of the adhesive layer is preferably 1 μm or more, particularly preferably 3 μm or more, and even more preferably 5 μm or more. A thickness of 1 μm or more in the adhesive layer makes it easier for the workpiece processing sheet to exhibit good adhesive strength, and effectively suppresses chip flying and peeling charge. Furthermore, the thickness is preferably 50 μm or less, particularly preferably 30 μm or less, and even more preferably 20 μm or less. A thickness of 50 μm or less in the adhesive layer makes it easier to pick up the workpiece more effectively.

[0078] (3) Release sheet In the workpiece processing sheet according to this embodiment, a release sheet may be laminated on the side of the adhesive layer opposite to the substrate (the adhesive side) for the purpose of protecting that side until it is attached to the workpiece.

[0079] The composition of the release sheet described above is arbitrary, and examples include plastic films that have been treated with a release agent. Specific examples of such plastic films include polyester films such as polyethylene terephthalate, polybutylene terephthalate, and polyethylene naphthalate, and polyolefin films such as polypropylene and polyethylene. As the release agent, silicone-based, fluorine-based, long-chain alkyl, and rubber-based agents can be used, and among these, silicone-based agents are preferred because they are inexpensive and provide stable performance.

[0080] There are no particular restrictions on the thickness of the release sheet mentioned above; for example, it may be between 16 μm and 250 μm.

[0081] (4) Others In the workpiece processing sheet according to this embodiment, the adhesive layer may be laminated on the side of the adhesive layer opposite to the substrate. In this case, the workpiece processing sheet according to this embodiment can be used as a dicing / die bonding sheet. With this sheet, a workpiece can be attached to the side of the adhesive layer opposite to the adhesive layer, and by dicing the adhesive layer together with the workpiece, a chip can be obtained in which individual pieces of the adhesive layer are laminated. The chip can be easily fixed to the object on which it is mounted by these individual pieces of adhesive layer. As the material constituting the adhesive layer described above, it is preferable to use one that contains a thermoplastic resin and a low molecular weight thermosetting adhesive component, or one that contains a B-stage (semi-cured) thermosetting adhesive component.

[0082] Furthermore, in the workpiece processing sheet according to this embodiment, a protective film forming layer may be laminated on the adhesive surface of the adhesive layer. In this case, the workpiece processing sheet according to this embodiment can be used as a protective film forming and dicing sheet. With such a sheet, a workpiece is attached to the side of the protective film forming layer opposite to the adhesive layer, and the protective film forming layer is diced together with the workpiece to obtain a chip with individual pieces of the protective film forming layer laminated on it. Preferably, a workpiece with a circuit formed on one side is used, and in this case, the protective film forming layer is usually laminated on the side opposite to the side with the circuit formed. By curing the individual pieces of the protective film forming layer at a predetermined timing, a protective film with sufficient durability can be formed on the chip. Preferably, the protective film forming layer is made of an uncured curable adhesive.

[0083] 2. Physical properties of workpiece processing sheets In the workpiece processing sheet according to this embodiment, the adhesive force to the silicon wafer (the mirror surface of a silicon wafer that has been mirror-finished, hereinafter the same) before irradiation with active energy rays is preferably 2000 mN / 25 mm or more, particularly preferably 2500 mN / 25 mm or more, and even more preferably 3000 mN / 25 mm or more. In the workpiece processing sheet according to this embodiment, the adhesive layer is composed of an active energy ray curable adhesive formed from the above-mentioned adhesive composition containing the phosphonium salt, making it easier to achieve the high adhesive force described above. Furthermore, an adhesive force of 2000 mN / 25 mm or more to the silicon wafer before irradiation with active energy rays makes it easier to fix the workpiece well onto the workpiece processing sheet, and makes it easier to prevent unintended detachment of the workpiece (especially after it has been pieced) (especially chip flying). While there are no particular limitations on the upper limit of the adhesive strength, it is preferably 20,000 mN / 25 mm or less, particularly preferably 10,000 mN / 25 mm or less, and even more preferably 7,000 mN / 25 mm or less. Details of the method for measuring the adhesive strength are described in the test examples below.

[0084] Furthermore, in the workpiece processing sheet according to this embodiment, the adhesive force to the silicon wafer after irradiation with active energy rays is preferably 500 mN / 25 mm or less, particularly preferably 300 mN / 25 mm or less, and even more preferably 100 mN / 25 mm or less. In the workpiece processing sheet according to this embodiment, since the adhesive layer is composed of an active energy ray curable adhesive, it is possible to sufficiently reduce the adhesive force after irradiation with active energy rays as described above. And, by having an adhesive force to the workpiece of 500 mN / 25 mm or less after irradiation with active energy rays, the processed workpiece becomes easier to peel off from the workpiece processing sheet. Furthermore, the adhesive force to the silicon wafer after irradiation with active energy rays is preferably 10 mN / 25 mm or more, particularly preferably 15 mN / 25 mm or more, and even more preferably 20 mN / 25 mm or more. This makes it easier to suppress unintended separation and detachment of the workpiece at a stage after irradiation with active energy rays. Details of the method for measuring the above adhesive force are described in the test examples below.

[0085] In the workpiece processing sheet according to this embodiment, the ratio of the adhesive strength to the mirror surface of the silicon wafer before and after irradiation with active energy rays (after irradiation / before irradiation) is preferably 0.3 or less, more preferably 0.1 or less, particularly preferably 0.05 or less, and even more preferably 0.02 or less. In the workpiece processing sheet according to this embodiment, the adhesive layer is composed of an active energy ray curable adhesive formed from the above-mentioned adhesive composition containing a phosphonium salt, which makes it possible to achieve such a low ratio. With a ratio of 0.3 or less, the workpiece and the processed workpiece can be well fixed to the adhesive surface before irradiation with active energy rays, and the processed workpiece can be easily separated from the adhesive surface after irradiation with active energy rays. The lower limit of the above ratio is not particularly limited and may be, for example, 0.001 or more, particularly 0.005 or more, and even more preferably 0.01 or more.

[0086] In the sheet for workpiece processing according to this embodiment, the surface resistivity of the adhesive layer is preferably 1×10 13 Ω / □ or less, particularly preferably 1×10 12 Ω / □ or less, and even more preferably 1×10 11 Ω / □ or less. Since the adhesive layer of the sheet for workpiece processing according to this embodiment is composed of an active energy ray-curable adhesive formed from the above-described adhesive composition containing the phosphonium salt, the surface resistivity within the above-described range can be favorably achieved, thereby favorably suppressing the occurrence of peeling charge. The lower limit value of the surface resistivity is not particularly limited and may be, for example, 1×10 6 Ω / □ or more. Details of the method for measuring the surface resistivity are as described in the test examples described later.

[0087] 3. Method for manufacturing a sheet for workpiece processing The method for manufacturing the sheet for workpiece processing according to this embodiment is not particularly limited, and is preferably manufactured by laminating an adhesive layer on one side of a base material.

[0088] The lamination of the adhesive layer on one side of the base material can be performed by a known method. For example, it is preferable to transfer the adhesive layer formed on a release sheet to one side of the base material. In this case, an adhesive composition constituting the adhesive layer and, if desired, a coating liquid further containing a solvent or a dispersion medium are prepared, and the coating liquid is applied onto the release-treated surface of the release sheet (hereinafter sometimes referred to as the "release surface") by a die coater, a curtain coater, a spray coater, a slit coater, a knife coater, an applicator, or the like to form a coating film, and the coating film is dried to form the adhesive layer. The properties of the coating liquid are not particularly limited as long as it can be applied, and it may contain components for forming the adhesive layer as a solute or as a disperse phase. The release sheet in this laminate may be peeled off as a process material or may be used to protect the adhesive surface of the adhesive layer until the sheet for workpiece processing is attached to an adherend.

[0089] If the coating liquid for forming the adhesive layer contains a crosslinking agent, the crosslinking reaction between the acrylic copolymer and the crosslinking agent in the coating film can be advanced by changing the drying conditions (temperature, time, etc.) or by providing a separate heat treatment, thereby forming a crosslinked structure with a desired density in the adhesive layer. To ensure this crosslinking reaction progresses sufficiently, after laminating the adhesive layer onto the substrate by the method described above, the resulting workpiece processing sheet may be cured by, for example, leaving it undisturbed in an environment of 23°C and 50% relative humidity for several days.

[0090] Instead of transferring the adhesive layer formed on the release sheet to one side of the substrate as described above, the adhesive layer may be formed directly on the substrate. In this case, the coating liquid for forming the adhesive layer is applied to one side of the substrate to form a coating film, and the adhesive layer is formed by drying the coating film.

[0091] 4. How to use the workpiece processing sheet The workpiece processing sheet according to this embodiment can be used for processing workpieces such as semiconductor wafers. That is, after attaching the adhesive surface of the workpiece processing sheet according to this embodiment to a workpiece, processing of the workpiece can be performed on the workpiece processing sheet. Depending on the processing, the workpiece processing sheet according to this embodiment can be used as a backgrinding sheet, dicing sheet, expandable sheet, pickup sheet, etc. Examples of workpieces include semiconductor wafers, semiconductor components such as semiconductor packages, and glass components such as glass plates.

[0092] As described above, the workpiece processing sheet according to this embodiment exhibits excellent adhesive strength and effectively suppresses the occurrence of peeling charge. In particular, it can effectively separate workpieces such as semiconductor wafers into individual pieces while suppressing chip breakage, and furthermore, the obtained chips can be easily separated while suppressing peeling charge. For this reason, the workpiece processing sheet according to this embodiment is particularly suitable for use as at least one of a dicing sheet and a pickup sheet.

[0093] If the workpiece processing sheet according to this embodiment includes the aforementioned adhesive layer, the workpiece processing sheet can be used as a dicing and die bonding sheet. Furthermore, if the workpiece processing sheet according to this embodiment includes the aforementioned protective film forming layer, the workpiece processing sheet can be used as a protective film forming and dicing sheet.

[0094] The embodiments described above are provided to facilitate understanding of the present invention and are not intended to limit it. Accordingly, each element disclosed in the above embodiments is intended to include all design modifications and equivalents that fall within the technical scope of the present invention.

[0095] For example, other layers may be provided between the substrate and the adhesive layer, or on the surface of the substrate opposite to the adhesive layer. [Examples]

[0096] The present invention will be described in more detail below with reference to examples, but the scope of the present invention is not limited to these examples.

[0097] [Example 1] (1) Preparation of the base material An 80 μm thick EMAA film was obtained by extruding an ethylene-methacrylic acid copolymer (EMAA) (manufactured by Mitsui DuPont Polychemicals, product name "Nucrel N0903HC") using a small T-die extruder (manufactured by Toyo Seiki Seisakusho Co., Ltd., product name "Laboplastmill"). This EMAA film was used as a substrate.

[0098] (2) Preparation of adhesive composition 62 parts by mass of n-butyl acrylate, 10 parts by mass of methyl methacrylate, and 28 parts by mass of 2-hydroxyethyl acrylate were polymerized by solution polymerization to obtain a (meth)acrylic acid ester polymer. Subsequently, 2-methacryloyloxyethyl isocyanate (MOI) in an amount equivalent to 80 mol% of the 2-hydroxyethyl acrylate constituting the (meth)acrylic acid ester polymer was added, and dibutyltin dilaurate (DBTDL) as a tin-containing catalyst was added in an amount of 0.13 parts by mass per 100 parts by mass of the (meth)acrylic acid ester polymer. After that, the reaction was carried out at 50°C for 24 hours to obtain a (meth)acrylic acid ester polymer in which active energy ray curable groups were introduced into the side chains. The weight-average molecular weight of the active energy ray curable polymer was measured by the method described later and was found to be 500,000.

[0099] 100 parts by mass (on a solid content basis, the same applies hereafter) of the (meth)acrylic acid ester polymer obtained above, in which an active energy ray curable group is introduced into the side chain, 11.4 parts by mass of triisobutylmethylphosphonium tosylate (manufactured by Iolitec), 2 parts by mass of 2-hydroxy-1-{4-[4-(2-hydroxy-2-methyl-propionyl)-benzyl]phenyl}-2-methyl-propan-1-one (manufactured by IGM Resins, product name "Omnirad 127") as a photopolymerization initiator, and 0.71 parts by mass of trimethylolpropane-modified tolylene diisocyanate (manufactured by Mitsui Chemicals, product name "Takenate D-101E") as a crosslinking agent were mixed in a solvent to obtain a coating solution for the adhesive composition.

[0100] (3) Formation of the adhesive layer A release sheet (Lintec Corporation, product name "SP-PET381031"), which has a silicone-based release agent layer formed on one side of a polyethylene terephthalate film with a thickness of 38 μm, was coated with the adhesive composition solution obtained in step (2) above, and dried at 90°C for 1 minute. This process formed a laminate on the release sheet with a 5 μm thick adhesive layer using a comma coater.

[0101] (4) Preparation of workpiece processing sheets After applying corona treatment to the surface layer side of the substrate obtained in step (1) above, the corona-treated surface and the adhesive layer side of the laminate obtained in step (3) above were bonded together to obtain a sheet for workpiece processing.

[0102] (5) Measurement of weight-average molecular weight The weight-average molecular weight (Mw) mentioned above is the weight-average molecular weight on a standard polystyrene basis, measured using gel permeation chromatography (GPC) under the following conditions (GPC measurement). <Measurement conditions> • Measuring device: Tosoh Corporation, HLC-8320 • GPC column (passes through in the following order): Manufactured by Tosoh Corporation TSK Gel Super H-H TSK gel superHM-H TSK Gel Super H2000 • Measurement solvent: tetrahydrofuran ·Measurement temperature: 40℃

[0103] [Example 2] A workpiece processing sheet was obtained in the same manner as in Example 1, except that the amount of triisobutylmethylphosphonium tosylate was changed as shown in Table 1.

[0104] [Examples 3-6 and Comparative Examples 2-3] A workpiece processing sheet was obtained in the same manner as in Example 1, except that the additives listed in Table 1 were used in the amounts listed in Table 1 instead of triisobutylmethylphosphonium tosylate.

[0105] Furthermore, trihexyltetradecylphosphonium dicyanamide and tributylmethylphosphonium methyl sulfate were manufactured by Iolitec, while 1-ethyl-3-methylimidazolium tosylate was manufactured by TCI.

[0106] [Comparative Example 1] A sheet for workpiece processing was obtained in the same manner as in Example 1, except that triisobutylmethylphosphonium tosylate was not used.

[0107] [Test Example 1] (Measurement of Adhesion) The workpiece processing sheets produced in the examples and comparative examples were cut into strips 25 mm wide. The release sheet was peeled off the obtained strip-shaped workpiece processing sheets, and the adhesive side of the exposed adhesive layer was attached to the mirror-finished surface of a silicon wafer using a 2 kg rubber roller at a temperature of 23°C and a relative humidity of 50%, and left to stand for 20 minutes to be used as a measurement sample. The mirror-finished surface of the silicon wafer was a surface that had been ground for more than one month and had lost its activity (normal surface).

[0108] For the obtained measurement samples, a universal tensile testing machine (Orientec Co., Ltd., product name "Tensilon UTM-4-100") was used to peel the workpiece processing sheet from the silicon wafer at a peeling speed of 300 mm / min and a peeling angle of 180°. The adhesive force (mN / 25mm) to the silicon wafer was measured using the 180° peeling method in accordance with JIS Z0237:2009. The adhesive force obtained is listed in Table 1 as the adhesive force "before" irradiation with active energy rays.

[0109] Furthermore, the measurement samples obtained in the same manner as described above were subjected to ultraviolet (UV) irradiation (illuminance: 230 mW / cm²) using a UV irradiation device (Lintec Corporation, product name "RAD-2000m / 12") 20 minutes after being attached to the silicon wafer, under conditions of 23°C and 50% relative humidity. 2 , Light amount: 190mJ / cm 2 The following procedure was performed. For the measurement samples after the UV irradiation, the workpiece processing sheet was separated from the package and the adhesive strength (mN / 25mm) was measured in the same manner as described above. The adhesive strength obtained is listed in Table 1 as the adhesive strength "after" irradiation with active energy rays.

[0110] Furthermore, based on the adhesive strength measured as described above, the ratio of the adhesive strength after irradiation to the adhesive strength before irradiation (after irradiation / before irradiation) was calculated. The results are shown in Table 1.

[0111] [Test Example 2] (Evaluation of substrate adhesion) The workpiece processing sheets manufactured in the examples and comparative examples were irradiated with ultraviolet light (illuminance: 230 mW / cm²) from the substrate side using an ultraviolet irradiation device (Lintec Corporation, product name "RAD-2000m / 12"). 2 , Light amount: 190mJ / cm 2 ) was performed.

[0112] Next, the release film was peeled off, and the exposed adhesive layer was cross-cut in a grid pattern with 5 mm intervals and 10 x 10 cut lines, creating a cross-cut area with 100 squares. Then, adhesive tape (manufactured by Nichiban Co., Ltd., product name "Sellotape (registered trademark)") was applied to the adhesive surface to cover the cross-cut area, and a peel test was performed in accordance with the grid tape method of JIS K5600-5-6:1999 (cross-cut method).

[0113] Out of 100 squares, the number of squares that had peeled (including those where only the edges of the cut peeled) was counted. The results are shown in Table 1.

[0114] [Test Example 3] (Evaluation of tip drop) The release sheet was peeled off from the workpiece processing sheets manufactured in the examples and comparative examples, exposing the adhesive layer. Then, the exposed adhesive layer of the workpiece processing sheet was attached to the ground surface of a 6-inch silicon wafer (350 μm thick), which had been pre-ground on one side using a grinder (Disco Corporation, product name "DFG8540"), using a laminator.

[0115] One hour after application, the silicon wafer was divided into individual chips by dicing on a workpiece processing sheet using a dicing device (DISCO Corporation, product name "DFD6362") under the following dicing conditions. Dicing conditions Tip size: 3mm x 3mm Cutting height: 60 μm Blade: Product name "ZH05-SD2000-Z1-90 CC" Blade rotation speed: 35,000 rpm Cutting speed: 40 mm / sec Cutting water amount: 1.0L / min Cutting water temperature: 20℃

[0116] Then, the number of chips that were lost during the dicing process was counted. The results are shown in Table 1.

[0117] [Test Example 4] (Measurement of surface resistivity) The workpiece processing sheets manufactured in the examples and comparative examples were cut into 100 mm x 100 mm pieces, and these were used as samples for surface resistivity measurement. After conditioning these surface resistivity measurement samples at 23°C and 50% relative humidity for 24 hours, the release sheet was peeled off, and the surface resistivity (Ω / □) of the adhesive surface was measured using a digital electrometer (manufactured by ADVANTEST) with an applied voltage of 100 V. The results are shown in Table 1.

[0118] [Table 1]

[0119] As can be seen from Table 1, the workpiece processing sheets obtained in the examples showed good adhesive strength before irradiation with active energy rays. Furthermore, the adhesive strength was sufficiently reduced by irradiation with active energy rays. In other words, the adhesive strength of the workpiece processing sheets obtained in the examples could be well controlled by irradiation with active energy rays. In addition, the surface resistivity of the workpiece processing sheets obtained in the examples was sufficiently reduced. Therefore, it is expected that the workpiece processing sheets obtained in the examples can effectively suppress peeling charge.

[0120] On the other hand, the workpiece processing sheets according to Comparative Examples 1 and 2 have high surface resistivity, and therefore, it is expected that peeling charge cannot be sufficiently suppressed. Furthermore, the workpiece processing sheet according to Comparative Example 3 has low adhesive strength before irradiation with active energy rays, and as shown in the substrate adhesion evaluation, peeling is likely to occur at the interface between the substrate and the adhesive layer, and as shown in the chip flying evaluation, the processed workpiece cannot be sufficiently held to the adhesive surface. [Industrial applicability]

[0121] The workpiece processing sheet of the present invention can be suitably used for processing workpieces such as semiconductor wafers.

Claims

1. A workpiece processing sheet comprising a base material and an adhesive layer laminated on one side of the base material, The adhesive layer is a phosphonium salt of the following formula (1). 【Chemistry 1】 (In formula (1), R １ ~R ４ At least three of them are alkyl chains having 3 or more carbon atoms, and the rest are hydrocarbon groups other than the alkyl chains, X － (This refers to an anion that does not contain halogen, or an anion that contains halogen in an amount such that the halogen content in the adhesive layer is 1000 ppm or less.) A workpiece processing sheet characterized by being composed of an active energy ray curable adhesive formed from an adhesive composition containing [a specific substance].

2. The workpiece processing sheet according to claim 1, characterized in that the content of the phosphonium salt in the adhesive composition is 0.2% by mass or more and 30% by mass or less.

3. In the phosphonium salt, R １ ~R ４ The workpiece processing sheet according to claim 1, characterized in that all of them are alkyl chains having 3 or more carbon atoms.

4. X in the phosphonium salt － The workpiece processing sheet according to claim 1, characterized in that it is at least one of tosylate, dicyanamide, and methyl sulfate.

5. The workpiece processing sheet according to claim 1, characterized in that the adhesive composition contains a (meth)acrylic acid ester polymer in which an active energy ray curable group is introduced into the side chain.

6. The workpiece processing sheet according to claim 1, characterized in that the ratio of the adhesive force of the workpiece processing sheet to the mirror surface of the silicon wafer before and after irradiation with active energy rays (after irradiation / before irradiation) is 0.001 or more and 0.3 or less.

7. The workpiece processing sheet according to claim 1, characterized in that the workpiece processing sheet is used as at least one of a dicing sheet and a pickup sheet.

8. A method for using the workpiece processing sheet described in claim 1, A step of attaching the side of the adhesive layer opposite to the substrate to the workpiece, A step of processing the workpiece on the workpiece processing sheet. A method of use characterized by including the following.

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