JP7632304B2 - Semiconductor processing tape - Google Patents

Description

The present invention relates to a tape for semiconductor processing.

In response to the demand for thinner semiconductor devices, a backgrinding process is carried out in the manufacturing process of semiconductor devices. In the backgrinding process, the front surface of the semiconductor wafer is protected with a backgrinding tape, and then the back surface of the semiconductor wafer is ground to thin the semiconductor wafer.
This application claims priority based on Japanese Patent Application No. 2019-227280, filed on December 17, 2019, the contents of which are incorporated herein by reference.

Conventionally, various backgrind tapes have been proposed for use in protecting the surface of semiconductor wafers. In recent years, there has been a demand for backgrind tapes that have sufficient unevenness absorption properties for semiconductor wafers with uneven surfaces, such as semiconductor wafers with bumps (electrodes) made of solder or the like formed on their surfaces.

Conventionally, when peeling backgrind tape from a semiconductor wafer, static electricity known as peeling electrification can occur, which can destroy the circuits on the semiconductor wafer or cause foreign matter to adhere to the semiconductor wafer. For this reason, backgrind tape is required to have sufficient antistatic properties.

It is believed that treatment to prevent peeling static electricity is effective when applied to the adhesive side. However, adding antistatic materials such as surfactants, conductive fillers, and carbon black to the adhesive itself changes the physical properties of the adhesive. In addition, it becomes difficult to adjust or suppress the adhesive properties and their changes over time. Furthermore, when peeling off the adhesive tape, the adhesive or the added antistatic material itself may migrate to the adherend and contaminate the adherend. In this case, visible glue residue, adhesion of microscopic particles, or adhesion of liquid matter that cannot be observed optically may occur on the surface of the adherend, which may have adverse effects such as poor adhesion of parts in subsequent processes.

Against this background, for example, Patent Document 1 discloses an adhesive film for semiconductor wafer processing that is a backgrind tape that combines both irregularity absorption and antistatic properties, and that comprises, in that order, a base layer, an irregularity-absorbing resin layer, an antistatic layer, and an adhesive resin layer.

JP 2018-6540 A

However, the adhesive film for semiconductor wafer processing described in Patent Document 1 requires each layer to be formed into a sheet and then laminated together, making the manufacturing procedure complicated. Also, the backgrind tape is required to have adhesive strength sufficient to fix an adherend such as a semiconductor wafer to the backgrind tape. However, if a backgrind tape with high adhesive strength is applied to an adherend, the adherend is processed, and then the backgrind tape is peeled off, there is a possibility that the adhesive layer of the backgrind tape will be transferred to the adherend, leaving a residue of adhesive.

The present invention has been made in consideration of the above circumstances, and aims to provide a semiconductor processing tape that has sufficient unevenness absorption properties, appropriate adhesive strength, and antistatic properties, is less likely to leave adhesive residue after being peeled off, and can be manufactured with fewer manufacturing steps.

The present invention includes the following aspects.
[1] A semiconductor processing tape comprising a sheet-like substrate having a substrate body and an antistatic layer provided on at least one surface of the substrate body, and a pressure-sensitive adhesive layer formed on the antistatic layer,
the antistatic layer contains a polypyrrole compound,
The pressure-sensitive adhesive layer is a cured product of a pressure-sensitive adhesive composition,
The thickness of the pressure-sensitive adhesive layer is 50 to 500 μm,
The pressure-sensitive adhesive composition includes a polyurethane (A), a (meth)acrylate monomer (B), a chain transfer agent (C), and a photopolymerization initiator (D),
The polyurethane (A) contains polyurethane (a1),
the polyurethane (a1) has a skeleton containing a structure derived from a polyoxyalkylene polyol and a structure derived from a polyisocyanate, and has (meth)acryloyl groups at a plurality of terminals;
A tape for semiconductor processing, characterized in that the (meth)acrylate monomer (B) contains a monofunctional (meth)acrylate and a polyfunctional (meth)acrylate.
[2] The semiconductor processing tape according to [1], wherein the pressure-sensitive adhesive layer has a single layer structure.
[3] The tape for semiconductor processing according to [1] or [2], wherein the chain transfer agent (C) is a polyfunctional thiol.
[4] The semiconductor processing tape according to any one of [1] to [3], wherein the pressure-sensitive adhesive layer has a gel fraction of 50 to 65 mass %.
[5] The tape for semiconductor processing according to any one of [1] to [4], wherein the pressure-sensitive adhesive layer has a surface resistivity of less than 1×10 ¹² Ω/□.
[6] The (meth)acrylate monomer (B) contains 85 to 99 mol % of the monofunctional (meth)acrylate and 1 to 15 mol % of the polyfunctional (meth)acrylate. The semiconductor processing tape according to any one of [1] to [5].
[7] The pressure-sensitive adhesive composition,
20 to 50% by mass of the polyurethane (A),
35 to 79% by mass of the (meth)acrylate monomer (B),
0.5 to 8% by mass of the chain transfer agent (C),
The semiconductor processing tape according to any one of [1] to [6], comprising 0.01 to 5 mass% of the photopolymerization initiator (D).
[8] The semiconductor processing tape according to any one of [1] to [7], wherein the pressure-sensitive adhesive composition further contains a fatty acid ester (E).

According to the present invention, it is possible to provide a semiconductor processing tape that has sufficient unevenness absorption, appropriate adhesive strength, and antistatic properties, and is less likely to leave adhesive residue after being peeled off.

Moreover, the semiconductor processing tape of the present invention has an adhesive layer which is a cured product of an adhesive composition and has sufficient unevenness absorbency and adhesive strength, so that it is not necessary to separately provide a layer having unevenness absorbency and a layer having adhesive strength, and it can be manufactured with fewer manufacturing steps. Furthermore, by forming the adhesive layer on a substrate having an antistatic layer, it is possible to obtain sufficient antistatic performance.
Therefore, the semiconductor processing tape of the present invention is suitable as a backgrinding tape used to protect the surface during the backgrinding process of an adherend having an uneven surface, such as a semiconductor wafer having bumps formed on its surface.

The following describes in detail the embodiments of the present invention. However, the present invention is not limited to the embodiments described below.

<Tape for semiconductor processing>
The semiconductor processing tape in this embodiment has a sheet-like substrate and a pressure-sensitive adhesive layer formed on one side of the substrate. The substrate has a substrate body and an antistatic layer provided on at least one side of the substrate body. The antistatic layer contains a polypyrrole compound. The pressure-sensitive adhesive layer is a cured product of a pressure-sensitive adhesive composition described below. The pressure-sensitive adhesive layer has a thickness of 50 to 500 μm. The pressure-sensitive adhesive composition contains polyurethane (A), a (meth)acrylate monomer (B), a chain transfer agent (C), and a photopolymerization initiator (D). The polyurethane (A) contains polyurethane (a1). The polyurethane (a1) has a skeleton containing a structure derived from a polyoxyalkylene polyol and a structure derived from a polyisocyanate, and has (meth)acryloyl groups at a plurality of ends. The (meth)acrylate monomer (B) contains a monofunctional (meth)acrylate and a polyfunctional (meth)acrylate.
It should be noted that the "tape" referred to here is not limited to strip-shaped tapes, but also includes rectangular or circular sheets.

(Substrate body)
The material of the substrate body can be appropriately selected, and examples thereof include resin materials. Examples of resin materials include polyolefins such as polyethylene (PE) and polypropylene (PP); polyester sheets such as polyethylene terephthalate (PET), polybutylene terephthalate (PBT), and polyethylene naphthalate; polyvinyl chloride (PVC); polyimide (PI); polyphenylene sulfide (PPS); ethylene vinyl acetate (EVA); and polytetrafluoroethylene (PTFE). Among these resin materials, PE, PP, and PET are preferably used because they provide a sheet with appropriate flexibility. The resin materials may be used alone or in combination of two or more types.

When a resin sheet made of a resin material is used as the substrate body, the resin sheet may be a single layer or a multi-layer structure of two or more layers (e.g., a three-layer structure). In a resin sheet having a multi-layer structure, the resin material constituting each layer may be a resin material containing only one type alone or a resin material containing two or more types.

Furthermore, the surface of the substrate body on which the antistatic layer is formed may be subjected to an adhesion enhancing treatment such as acid treatment, alkali treatment, primer treatment, corona treatment, plasma treatment, ultraviolet treatment, or ozone treatment, if necessary.

The thickness of the substrate body can be appropriately selected depending on the material of the substrate body. When the semiconductor processing tape is applied to a semiconductor wafer having an uneven surface and then peeled off, or when the semiconductor processing tape uses a resin sheet as the substrate body, the thickness of the substrate body is preferably 10 to 1000 μm, and more preferably 50 to 300 μm. When the thickness of the substrate body is 10 μm or more, the rigidity (stiffness) of the semiconductor processing tape is high. Therefore, when the semiconductor processing tape is applied to or peeled off from the semiconductor wafer, which is the adherend, the semiconductor processing tape tends to be less likely to wrinkle or float. In addition, when the thickness of the substrate body is 1000 μm or less, the semiconductor processing tape applied to the semiconductor wafer is easily peeled off from the semiconductor wafer, and the workability (handling ability, handling) is improved.

(Antistatic Layer)
At least one surface of the substrate body has an antistatic layer. The antistatic layer contains a polypyrrole compound. The polypyrrole compound is not particularly limited as long as it is a polymer of pyrrole and/or a pyrrole derivative, and may contain a small amount of other monomers as polymerization components other than pyrrole and pyrrole derivatives. Examples of pyrrole derivatives include N-alkylpyrrole, 3-alkylpyrrole, 3,4-dialkylpyrrole, 3-alkoxypyrrole, 3,4-dialkoxypyrrole, 3-chloropyrrole, and 3,4-dichloropyrrole. By having an antistatic layer containing a polypyrrole compound, the antistatic effect of the semiconductor processing tape becomes stable over time and has good non-contamination properties.

The means for providing the antistatic layer is not particularly limited, and various known methods can be used, for example, the following methods (i) to (vi).
(i) A method in which pyrrole and/or a pyrrole derivative is dissolved in an organic solvent such as diethyl ether, methanol, or tetrahydrofuran (THF), applied to a substrate body, and then the organic solvent is dried and removed (e.g., JP-A-3-122115);
(ii) A method in which pyrrole and/or a pyrrole derivative is applied to a substrate body, the substrate is immersed in an organic solvent of a salt or an acid, water or a mixture thereof for doping, and then the solvent is dried and removed (e.g., JP-A-4-285626);
(iii) A method in which a substrate body is placed in a treatment solution and a pyrrole monomer is polymerized in the presence of a chemical oxidation polymerization catalyst and a dopant according to a chemical oxidation polymerization method, thereby coating the surface of the substrate body with polypyrrole (e.g., JP-A-2000-280335);
(iv) A method in which an aqueous solution containing fine particles surface-coated with pyrrole and/or a pyrrole derivative is applied to the surface of a substrate body, and the applied solution is stretched after drying (e.g., JP-A-8-58044);
(v) A method of laminating a layer containing polypyrrole and/or a polypyrrole derivative, an organic electron acceptor, and a thermoplastic resin on the surface of a substrate body (for example, JP-A-10-278188);
(vi) A method in which fine particles of polypyrrole and/or a polypyrrole derivative are dispersed in a hydrophilic solvent using a polymer dispersant and/or a dopant, and then mixed with a hydrophilic binder resin to prepare a resin composition; the resin composition is applied onto a substrate body such as a polymer film, and the solvent is then dried and removed to form a film (e.g., JP-A 2001-334598).

Among these, from the viewpoint of adhesion to the substrate body and adhesion to the adhesive layer, the method of "(vi) dispersing fine particles of polypyrrole and/or polypyrrole derivative in a hydrophilic solvent using a polymer dispersant and/or dopant, and further mixing with a water-soluble or water-dispersible binder resin to prepare a resin composition; applying the resin composition onto the substrate body, and then drying and removing the solvent to form a film" is preferred. For example, a known coating method such as a bar coater, air knife coater, blade coater, rod coater, gravure coater, size press coater, or gate roll coater may be used.

The thickness of the antistatic layer is preferably 0.1 to 20 μm, and more preferably 0.5 to 10 μm. If the thickness of the antistatic layer is within this range, sufficient antistatic performance is exhibited. The content of the polypyrrole compound in the antistatic layer is preferably 5 to 80% by mass, and more preferably 10 to 70% by mass. If it is 5% by mass or more, sufficient antistatic performance is obtained, and if it is 80% by mass or less, it is also economical.

Specific examples of the polymer dispersant include polymer acids, salts of these polymer acids, and esters of these polymer acids, and these may be used alone or in combination of two or more.Specific examples of the polymer acids include polymer acids such as polystyrene sulfonic acid, polyacrylic acid, polyallyl sulfonic acid, and alginic acid.Specific examples of the salts of the polymer acids include neutralized salts such as sodium salts, potassium salts, and ammonium salts.
The dopant is not particularly limited, but it is preferable to use molecular iodine and/or iodine ions. When iodine ions are used, the iodine ion valence is not particularly specified. By using iodine and/or iodine ions, the electrical conductivity and adhesion to the substrate body are further improved.

Examples of water-soluble or water-dispersible binder resins include polyester, polyurethane, acrylic resin, vinyl resin, epoxy resin, amide resin, etc. The skeletal structure of each of these may have a substantially composite structure due to copolymerization or the like. Examples of binder resins having a composite structure include acrylic resin grafted polyester, acrylic resin grafted polyurethane, vinyl resin grafted polyester, vinyl resin grafted polyurethane, etc. By containing these resins, the strength of the antistatic layer and the adhesion to the substrate body can be improved. The water-soluble or water-dispersible binder resin may be used alone or in combination of two or more types.

The resin composition may also contain a crosslinking reactive compound as necessary. The crosslinking reactive compound can improve the cohesiveness, surface hardness, scratch resistance, solvent resistance, and water resistance of the coating layer mainly by crosslinking with functional groups contained in other resins or compounds, or by self-crosslinking. Examples of crosslinking reactive compounds that can be used include amino resins such as melamine-based, benzoguanamine-based, and urea-based, as well as oxazoline-based, epoxy-based, and glyoxal-based compounds. Polymer-type crosslinking reactive compounds that have reactive groups on other polymer skeletons are also included.

The resin composition may contain additives such as surfactants, defoamers, coatability improvers, thickeners, organic lubricants, organic particles, inorganic particles, antioxidants, UV absorbers, dyes, pigments, etc. These additives may be used alone or in combination of two or more types as necessary.

(Adhesive Layer)
The pressure-sensitive adhesive layer is formed on the antistatic layer of the substrate.
When antistatic layers are formed on both sides of the substrate body, an adhesive layer is formed on one of the surfaces.

The adhesive layer is a cured product of the adhesive composition described later. The adhesive layer is particularly a photocured product of the adhesive composition described later. The semiconductor processing tape may be used in applications where it is attached to an adherend such as a semiconductor wafer having an uneven surface and then peeled off. In that case, the adhesive layer has a role of protecting the surface of the adherend during the back grinding process by fixing the semiconductor processing tape to the surface of the adherend with sufficient adhesive strength. In addition, the adhesive layer has a role of improving the accuracy of the back grinding process by absorbing and smoothing the unevenness of the adherend surface. Furthermore, the adhesive layer reduces the peeling charge generated when the semiconductor processing tape is peeled off from the adherend. In addition, the adhesive layer of the semiconductor processing tape of this embodiment does not leave any adhesive residue when the semiconductor processing tape is peeled off.

The thickness of the adhesive layer in this embodiment is 50 to 500 μm, preferably 60 to 400 μm, and more preferably 70 to 300 μm. When the thickness of the adhesive layer is 50 μm or more, the semiconductor processing tape has good unevenness absorption and adhesive strength. Furthermore, when the thickness of the adhesive layer is 500 μm or less, it is easy to control the thickness of the adhesive layer.

When the semiconductor processing tape of this embodiment is applied to an adherend having an uneven surface, the thickness of the adhesive layer is largely dependent on the height of the uneven surface of the adherend. The thickness of the adhesive layer is preferably equal to or greater than the height of the uneven surface so that sufficient unevenness absorption can be obtained. Therefore, for example, when the uneven surface is a bump formed on a semiconductor wafer, the thickness of the adhesive layer is preferably at least twice the height of the bump. The height of the bump is usually 30 to 200 μm. For example, when the bump height is 100 μm, the thickness of the adhesive layer is preferably 200 μm or more, and when the bump height is 200 μm, the thickness of the adhesive layer is preferably 400 μm or more.

The adhesive layer may be a single layer structure, or a multilayer structure in which the adhesive layer of this embodiment and one or more other adhesive layers different from the adhesive layer of this embodiment are laminated. As the other adhesive layer, a conventionally known adhesive layer can be used. In this embodiment, when the adhesive layer has a multilayer structure, the adhesive layer of this embodiment must be present on the outermost surface. In addition, in the semiconductor processing tape of this embodiment, a layer other than the adhesive layer may be present between the adhesive layer and the substrate, as long as the layer does not inhibit the curing of the adhesive layer. In terms of shortening the process, it is preferable that the adhesive layer has a single layer structure.

The gel fraction of the adhesive layer is preferably 50 to 65% by mass. When the gel fraction is 50% by mass or more, the occurrence of adhesive residue caused by peeling off the semiconductor processing tape attached to the adherend can be more effectively suppressed. Furthermore, when the gel fraction is 65% by mass or less, the adhesive layer has sufficient fluidity, and the unevenness absorbency of the semiconductor processing tape becomes even better. The gel fraction of the adhesive layer is more preferably 52% by mass or more. Furthermore, the gel fraction of the adhesive layer is more preferably 63% by mass or less.
The gel fraction of the pressure-sensitive adhesive layer can be achieved in a preferred range, for example, by adjusting the composition of the pressure-sensitive adhesive composition described below to fall within a preferred range.

(Measurement of Gel Fraction of Pressure-Sensitive Adhesive Layer)
The gel fraction of the adhesive layer is measured by the following method. First, a sheet of about 1 g size is cut out from the semiconductor processing tape, the adhesive layer is peeled off from the substrate to obtain a measurement sample, and its mass is measured. Next, the measurement sample is immersed in 50 ml of toluene and left at room temperature for 72 hours. After that, the measurement sample is taken out of the toluene, dried at 80° C. for 5 hours, and the mass is measured again. Then, the gel fraction is calculated based on the following formula.
Gel fraction (%) = [A/B] x 100
A: Mass of the measurement sample after immersion in toluene (excluding the mass of toluene)
B: Mass of the measurement sample before immersion in toluene

The surface resistivity of the pressure-sensitive adhesive layer is preferably less than 1× ¹⁰ Ω/□, and more preferably less than 1× ¹⁰ Ω/□. If the surface resistivity is less than 1× ¹⁰ Ω/□, peeling static electricity generated when the semiconductor processing tape attached to the adherend is peeled off is reduced, resulting in a semiconductor processing tape with even better antistatic performance.

The semiconductor processing tape may have a transparent separator on the surface of the adhesive layer for the purpose of protecting the adhesive layer. The separator is preferably laminated on the surface of the adhesive layer. For example, paper, plastic film, etc. can be used as the material of the separator, and it is preferable to use a plastic film because of its excellent surface smoothness. The plastic film used as the separator is not particularly limited as long as it can protect the above-mentioned adhesive layer, and examples thereof include polyethylene, polypropylene, polyethylene terephthalate, polybutene, etc.

<Adhesive composition>
The adhesive layer of the semiconductor processing tape of this embodiment is a cured product of an adhesive composition. The adhesive composition used as the material of the adhesive layer in the semiconductor processing tape of this embodiment will be described in detail below.
The pressure-sensitive adhesive composition of the present embodiment contains a polyurethane (A), a (meth)acrylate monomer (B), a chain transfer agent (C), and a photopolymerization initiator (D).

(Polyurethane (A))
The polyurethane (A) contains the polyurethane (a1) described below. The polyurethane (A) may contain not only the polyurethane (a1) but also the polyurethane (a2) described below for the purpose of adjusting the cohesive strength in the cured product of the pressure-sensitive adhesive composition. It is preferable that the polyurethane (A) does not contain any components other than the polyurethane (a1) and the polyurethane (a2) contained as necessary.

[Polyurethane (a1)]
The polyurethane (a1) has a skeleton including a structure derived from a polyoxyalkylene polyol and a structure derived from a polyisocyanate. The polyurethane (a1) also has (meth)acryloyl groups at a plurality of terminals. The (meth)acryloyl groups at the terminals of the polyurethane (a1) are preferably part of a (meth)acryloyloxy group.

In the present invention, the "multiple ends" of a polyurethane refer to two ends when the polyurethane is a linear polymer, and refer to two or more ends out of the same number of ends as the number of branched chains when the polyurethane is a branched polymer.
In the present invention, the (meth)acryloyl group means one or more groups selected from the functional group represented by the chemical formula CH ₂ ═CH—CO— and the functional group represented by the chemical formula CH ₂ ═C(CH ₃ )—CO—.

[Polyurethane (a2)]
The polyurethane (a2) has a skeleton containing a structure derived from a polyoxyalkylene polyol and a structure derived from a polyisocyanate, similar to the polyurethane (a1). Unlike the polyurethane (a1), the polyurethane (a2) has a (meth)acryloyl group at only one end. The (meth)acryloyl group at the end of the polyurethane (a2) is preferably a part of a (meth)acryloyloxy group. In the polyurethane (a2), the end not having a (meth)acryloyl group preferably has one selected from the group consisting of an isocyanato group, a structure derived from an alkyl alcohol, and a structure derived from an alkyl isocyanate, and more preferably has a structure derived from an alkyl alcohol.

"Polyoxyalkylene polyol-derived structure"
The polyoxyalkylene polyol having a structure derived from the polyoxyalkylene polyol contained in the skeleton of the polyurethane (a1) and the polyurethane (a2) preferably has an alkylene chain having 2 to 4 carbon atoms. Specific examples include polyoxyethylene polyol, polyoxypropylene polyol, polyoxybutylene polyol, etc.

The polyoxyalkylene polyol having a structure derived from the polyoxyalkylene polyol may contain one type of alkylene chain, or may contain two or more types of alkylene chains.
The polyoxyalkylene polyol having a structure derived from polyoxyalkylene polyol is preferably one having two or three hydroxyl groups at the terminals (diol-type or triol-type polyoxyalkylene polyol), more preferably a polyoxyalkylene glycol (diol-type), and particularly preferably a polypropylene glycol having an alkylene chain with three carbon atoms.

For example, when the polyoxyalkylene polyol is polypropylene glycol, the hydroxyl value is preferably 20 to 120 mgKOH/g, more preferably 30 to 100 mgKOH/g, and even more preferably 40 to 80 mgKOH/g. A specific example of polypropylene glycol is polypropylene glycol having a hydroxyl group (hydroxy group) at the end and a hydroxyl value of 56 mgKOH/g (Actocol D-2000; manufactured by Mitsui Chemicals, number average molecular weight 2000, diol type).

Here, the hydroxyl value of polyoxyalkylene polyol is the hydroxyl value of polyoxyalkylene polyol measured according to JIS K0070. In other words, it means the number of milligrams of potassium hydroxide required to neutralize the free acetic acid when 1 g of polyoxyalkylene polyol is acetylated. Specifically, it can be determined by acetylating the hydroxyl groups in the sample (polyoxyalkylene polyol) using acetic anhydride and titrating the free acetic acid generated at that time with a potassium hydroxide solution.

The number average molecular weight of the polyoxyalkylene polyol is preferably 500 to 5,000, more preferably 800 to 4,000, and even more preferably 1,000 to 3,000. When the number average molecular weight of the polyoxyalkylene polyol is 500 or more, the semiconductor processing tape having an adhesive layer which is a cured product of the adhesive composition containing polyurethane (A) synthesized using the polyoxyalkylene polyol has high peel strength. In addition, when the number average molecular weight of the polyoxyalkylene polyol is 5,000 or less, the polyurethane (A) synthesized using the polyoxyalkylene polyol contains a sufficient amount of urethane bonds. Therefore, the cured product obtained by curing the adhesive composition containing polyurethane (A) has good cohesion.

The structure derived from the polyoxyalkylene polyol contained in the skeleton of each of the polyurethanes (a1) and (a2) may be of only one type, or may be of two or more types.
The polyurethane (a1) and the polyurethane (a2) may have a structure in which structures derived from two or more different polyoxyalkylene polyols are bonded via a structure derived from a polyisocyanate.
The structure derived from a polyoxyalkylene polyol contained in the skeleton of the polyurethane (a1) and the structure derived from a polyoxyalkylene polyol contained in the skeleton of the polyurethane (a2) may be the same as or different from each other.

"Polyisocyanate-derived structure"
As the polyisocyanate having the polyisocyanate-derived structure contained in the skeleton of the polyurethane (a1) and polyurethane (a2), a compound having a plurality of isocyanate groups is used, and it is preferable to use a diisocyanate.
Examples of diisocyanates include tolylene diisocyanate and hydrogenated products thereof, xylylene diisocyanate and hydrogenated products thereof, diphenylmethane diisocyanate and hydrogenated products thereof, 1,5-naphthylene diisocyanate and hydrogenated products thereof, hexamethylene diisocyanate, trimethylhexamethylene diisocyanate, tetramethylxylylene diisocyanate, isophorone diisocyanate, 4,4'-dicyclohexyl diisocyanate, 1,3-bis(isocyanatemethyl)cyclohexane, and norbornane diisocyanate.

Among these polyisocyanates, it is preferable to use a hydrogenated product of isophorone diisocyanate or diphenylmethane diisocyanate from the viewpoint of controlling the light resistance of the polyurethane (A) synthesized using the polyisocyanate and the reactivity with polyoxyalkylene polyol. It is more preferable to use a hydrogenated product of diphenylmethane diisocyanate from the viewpoint of reactivity with polyoxyalkylene polyol.

Specific examples of polyisocyanates with a polyisocyanate-derived structure include hydrogenated diphenylmethane diisocyanate (Desmodur W, manufactured by Sumika Covestro Urethanes) and isophorone diisocyanate (Desmodur I, manufactured by Sumika Covestro Urethanes).

The polyisocyanate-derived structure contained in the skeleton of each of the polyurethanes (a1) and (a2) may be of only one type, or may be of two or more types.
Furthermore, the structure derived from a polyisocyanate contained in the skeleton of the polyurethane (a1) and the structure derived from a polyisocyanate contained in the skeleton of the polyurethane (a2) may be the same as or different from each other.

It is preferable that the polyisocyanate-derived structure and the polyoxyalkylene polyol-derived structure contained in the skeletons of polyurethane (a1) and polyurethane (a2) are the same. In this case, polyurethane (a1) and polyurethane (a2) can be synthesized simultaneously, and polyurethane (A) can be produced efficiently.

The proportion of polyurethane (a1) contained in polyurethane (A) is preferably 80 to 100%, more preferably 90 to 100%, and even more preferably 100%, of polyurethane (A) in terms of the number of molecules.
The proportion of polyurethane (a2) contained in polyurethane (A) is preferably 0 to 20%, more preferably 0 to 10%, and even more preferably 0%, of polyurethane (A) in terms of the number of molecules.
When the proportion of polyurethane (a1) contained in polyurethane (A) is 80% or more, the cured product of the pressure-sensitive adhesive composition containing polyurethane (A) has sufficiently high cohesive strength, which is preferable.

Of the total number of terminals contained in polyurethane (A) (the total number of terminals of polyurethane (a1) and polyurethane (a2) contained as necessary), it is preferable that 90 to 100% (on a molecular number basis) have (meth)acryloyl groups introduced, more preferably 95 to 100%, and even more preferably 100%. If the amount of (meth)acryloyl groups introduced is 90% or more (on a molecular number basis) of the total number of terminals contained in polyurethane (A), the cohesive strength of the cured product obtained by curing the pressure-sensitive adhesive composition containing polyurethane (A) is sufficiently high.

The ratio of the number of terminals to which a (meth)acryloyl group has been introduced, based on the number of molecules, to the total number of terminals contained in polyurethane (A) can be calculated using the results of analyzing polyurethane (A). Examples of the analysis method include infrared absorption spectroscopy (IR) and nuclear magnetic resonance spectroscopy (NMR).

The ratio of the contents of polyurethane (a1) and polyurethane (a2) contained in polyurethane (A), i.e., the ratio of the number of terminals into which a (meth)acryloyl group has been introduced on a molecular number basis out of the total number of terminals contained in polyurethane (A), can be adjusted by the manufacturing method of polyurethane (A) described below.

The mass average molecular weight of polyurethane (A) is preferably 30,000 to 200,000, more preferably 50,000 to 150,000, and even more preferably 60,000 to 100,000. When the mass average molecular weight of polyurethane (A) is 30,000 or more, the cured product obtained by curing the adhesive composition containing polyurethane (A) has good flexibility. Furthermore, when the mass average molecular weight of polyurethane (A) is 200,000 or less, the adhesive composition containing polyurethane (A) is easy to handle and has good workability.

(Method for measuring weight average molecular weight of polyurethane (A))
The weight average molecular weight of the polyurethane (A) is a value calculated in terms of polystyrene measured by gel permeation chromatography (GPC-101; Shodex (registered trademark) manufactured by Showa Denko K.K.) (hereinafter referred to as GPC). The measurement conditions for GPC are as follows.
Column: LF-804 (Showa Denko K.K.)
Column temperature: 40°C
Sample: 0.2% by mass solution of polyurethane (A) in tetrahydrofuran Flow rate: 1 ml/min Eluent: tetrahydrofuran Detector: RI detector (differential refractive index detector)

The content of polyurethane (A) in the adhesive composition of this embodiment is preferably 20 to 50% by mass, more preferably 25 to 45% by mass, and even more preferably 30 to 40% by mass. When the content of polyurethane (A) is 20% by mass or more, the cured product obtained by curing the adhesive composition has sufficient cohesive strength and excellent adhesive strength. In addition, in a semiconductor processing tape using this cured product as an adhesive layer, the softness of the adhesive layer is in an appropriate range, and air bubbles are less likely to be trapped between the adhesive layer and the adherend. In addition, when the content of polyurethane (A) is 50% by mass or less, the cured product obtained by curing the adhesive composition has sufficient flexibility. Therefore, a semiconductor processing tape using this cured product as an adhesive layer has good wettability to the adherend.

((Meth)acrylate Monomer (B))
The (meth)acrylate monomer (B) is other than the polyurethane (A) and contains a monofunctional (meth)acrylate and a polyfunctional (meth)acrylate.

In the present invention, the term "monofunctional" in the monofunctional (meth)acrylate means a (meth)acrylate having only one (meth)acryloyloxy group.
In the present invention, the term "polyfunctional" in the polyfunctional (meth)acrylate means a (meth)acrylate having two or more (meth)acryloyloxy groups.

As the (meth)acrylate monomer (B), it is preferable to use a combination of a monofunctional (meth)acrylate and a polyfunctional (meth)acrylate from the viewpoint of the cohesive strength of the cured product obtained by curing the adhesive composition and the curability of the adhesive composition. It is more preferable to contain a monofunctional (meth)acrylate and a trifunctional or higher (meth)acrylate. In particular, it is most preferable to contain a monofunctional (meth)acrylate and a trifunctional (meth)acrylate having three (meth)acryloyloxy groups.

Examples of monofunctional (meth)acrylates include alkyl (meth)acrylates, cyclic alkyl (meth)acrylates such as isobornyl (meth)acrylate, alkoxyalkyl (meth)acrylates, alkoxy(poly)alkylene glycol (meth)acrylates, hydroxyl group-containing (meth)acrylates, carboxyl group-containing (meth)acrylates, fluorinated alkyl (meth)acrylates, dialkylaminoalkyl (meth)acrylates, (meth)acrylamides, epoxy group-containing (meth)acrylates, and (meth)acryloylmorpholine. These may be used alone or in combination of two or more.

Among these monofunctional (meth)acrylates, it is preferable to contain an alkyl (meth)acrylate. This is because the adhesive strength (peeling strength) and gel fraction of the cured product obtained by curing the adhesive composition tend to be in a more appropriate range when the cured product is used as an adhesive layer of a semiconductor processing tape. It is more preferable to use an alkyl (meth)acrylate having an alkyl group having 4 to 10 carbon atoms as the alkyl (meth)acrylate. Specifically, examples of the alkyl (meth)acrylate include methyl (meth)acrylate, ethyl (meth)acrylate, n-butyl (meth)acrylate, and 2-ethylhexyl (meth)acrylate. Among these, it is particularly preferable to use 2-ethylhexyl (meth)acrylate and/or n-butyl (meth)acrylate.

The polyfunctional (meth)acrylate is a compound having a plurality of (meth)acryloyloxy groups other than the polyurethane (A). As the polyfunctional (meth)acrylate, it is preferable to use a poly(meth)acrylate of a polyol compound.
Specific examples of the polyfunctional (meth)acrylate include polyethylene glycol di(meth)acrylate, diethylene glycol di(meth)acrylate, neopentyl glycol di(meth)acrylate, triethylene glycol di(meth)acrylate, tripropylene glycol di(meth)acrylate, hydroxypivalic acid ester neopentyl glycol di(meth)acrylate, 1,3-bis(hydroxyethyl)-5,5-dimethylhydantoin di(meth)acrylate, α,ω-di(meth)acryl bisdiethylene glycol phthalate, trimethylolpropane tri(meth)acrylate, ethylene glycol di(meth)acrylate, tetraethylene glycol di(meth)acrylate, 1,4-butanediol di(meth)acrylate, 1,6-hexanediol di(meth)acrylate, diacryloxyethyl phosphate, and pentaerythritol tetra(meth)acrylate. Among these, it is preferable to use trimethylolpropane tri(meth)acrylate as the polyfunctional (meth)acrylate from the viewpoint of curability of the pressure-sensitive adhesive composition. These polyfunctional (meth)acrylates may be used alone or in combination of two or more.

The ratio of monofunctional (meth)acrylate and polyfunctional (meth)acrylate is preferably 85 to 99 mol% monofunctional (meth)acrylate and 1 to 15 mol% polyfunctional (meth)acrylate when the total of (meth)acrylate monomer (B) is 100 mol%. In this case, the content of monofunctional (meth)acrylate is more preferably 90 to 99 mol%, and even more preferably 95 to 98 mol%. The content of polyfunctional (meth)acrylate is more preferably 1 to 10 mol%, and even more preferably 2 to 5 mol%.

When the content of monofunctional (meth)acrylate is 85 mol% or more, the fluidity of the cured product obtained by curing the adhesive composition is in a preferred range when the cured product is used as an adhesive layer of a semiconductor processing tape. Therefore, a semiconductor processing tape using this cured product as an adhesive layer has sufficient unevenness absorption properties, and when applied to an adherend having uneven parts on the surface, it is less likely to generate gaps between the uneven parts of the adherend, which is preferable. In addition, when the content of monofunctional (meth)acrylate is 99 mol% or less, a semiconductor processing tape using a cured product of the adhesive composition as an adhesive layer is less likely to leave adhesive residue when peeled off from the adherend, which is preferable.

When the content of the polyfunctional (meth)acrylate is 1 mol% or more, the fluidity of the cured product obtained by curing the adhesive composition is not too high, which is preferable. Also, when the content of the polyfunctional (meth)acrylate is 15 mol% or less, the fluidity of the cured product obtained by curing the adhesive composition is in a preferable range when the cured product is used as an adhesive layer of a semiconductor processing tape. Therefore, a semiconductor processing tape using the cured product as an adhesive layer has sufficient unevenness absorption properties, and when applied to an adherend having uneven parts on the surface, it is difficult for gaps to occur between the uneven parts of the adherend, which is preferable.

The content of (meth)acrylate monomer (B) in the adhesive composition of this embodiment is preferably 35 to 79% by mass, more preferably 40 to 73% by mass, and even more preferably 45 to 66% by mass. When the content of (meth)acrylate monomer (B) is 35% by mass or more, the viscosity of the adhesive composition does not become too high, and excellent coatability is obtained, which is preferable. Furthermore, when the content of (meth)acrylate monomer (B) is 79% by mass or less, the viscosity of the adhesive composition does not become too low, and it is easy to control the thickness of the coating film made of the adhesive composition, which is preferable.

(Chain Transfer Agent (C))
The chain transfer agent (C) is contained in the pressure-sensitive adhesive composition for the purpose of controlling the unevenness absorbency and gel fraction of a cured product obtained by curing the pressure-sensitive adhesive composition.
As the chain transfer agent (C), it is preferable to use a thiol compound. In particular, it is preferable to use a polyfunctional thiol. The polyfunctional thiol is a compound having two or more mercapto groups in the molecule.

The polyfunctional thiol is not particularly limited, but examples thereof include 1,2-ethanedithiol, 1,4-bis(3-mercaptobutyryloxy)butane, tetraethylene glycol bis(3-mercaptopropionate), trimethylolethane tris(3-mercaptobutyrate), trimethylolpropane tris(3-mercaptobutyrate), trimethylolpropane tris(3-mercaptopropionate), pentaerythritol, Examples of the chain transfer agent (C) include pentaerythritol tetrakis(3-mercaptobutyrate), pentaerythritol tetrakis(3-mercaptopropionate), 1,3,5-tris(3-mercaptobutyloxyethyl)-1,3,5-triazine-2,4,6(1H,3H,5H)-trione, tris-[(3-mercaptopropionyloxy)-ethyl]-isocyanurate, and dipentaerythritol hexakis(3-mercaptopropionate). Among the above, it is preferable to use pentaerythritol tetrakis(3-mercaptobutyrate) as the chain transfer agent (C) from the viewpoint of the reactivity of the pressure-sensitive adhesive composition.

The content of the chain transfer agent (C) in the adhesive composition of this embodiment is preferably 0.5 to 8 mass%, more preferably 1 to 5 mass%, and even more preferably 3 to 4.5 mass%. When the content of the chain transfer agent (C) is 0.5 mass% or more, the fluidity of the cured product obtained by curing the adhesive composition is in a preferred range when the cured product is used as an adhesive layer of a semiconductor processing tape. Therefore, a semiconductor processing tape using the cured product as an adhesive layer has sufficient unevenness absorption properties and is less likely to generate gaps between the uneven parts of the adherend, which is preferable. When the content is 8 mass% or less, a semiconductor processing tape using the cured product of the adhesive composition as an adhesive layer is less likely to leave adhesive residue when peeled off from the adherend, which is preferable.

(Photopolymerization Initiator (D))
The photopolymerization initiator (D) is not particularly limited, but a photoradical polymerization initiator is preferred. As the photopolymerization initiator (D), for example, a carbonyl-based photopolymerization initiator, a sulfide-based photopolymerization initiator, an acylphosphine oxide-based photopolymerization initiator, a quinone-based photopolymerization initiator, a sulfochloride-based photopolymerization initiator, a thioxanthone-based photopolymerization initiator, etc. can be used. Among these photopolymerization initiators (D), it is preferable to use a carbonyl-based photopolymerization initiator and/or an acylphosphine oxide-based photopolymerization initiator from the viewpoint of the transparency of the cured product obtained by photocuring the pressure-sensitive adhesive composition. Specifically, it is more preferable to use a 2,4,6-trimethylbenzoyldiphenylphosphine oxide agent and/or a 1-hydroxycyclohexyl-phenyl ketone.

The content of the photopolymerization initiator (D) in the adhesive composition of this embodiment is preferably 0.01 to 5 mass%, more preferably 0.05 to 3 mass%, and even more preferably 0.1 to 2 mass%. When the content of the photopolymerization initiator (D) is 0.01 mass% or more, the photocuring of the adhesive composition proceeds sufficiently. Furthermore, when the content of the photopolymerization initiator (D) is 5 mass% or less, the amount of low molecular weight components does not become too large during photocuring of the adhesive composition. For this reason, when a semiconductor processing tape using a cured product of the adhesive composition as an adhesive layer is peeled off from an adherend, it is less likely to leave adhesive residue, which is preferable.

(Fatty Acid Ester (E))
The pressure-sensitive adhesive composition of the present embodiment contains a polyurethane (A), a (meth)acrylate monomer (B), a chain transfer agent (C), and a photopolymerization initiator (D), and may further contain a fatty acid ester (E) as necessary.
The fatty acid ester (E) is contained in the adhesive composition for the purposes of controlling the adhesive strength in a semiconductor processing tape that uses a cured product of the adhesive composition as an adhesive layer, and improving the lamination properties (wettability) and bubble removal properties (ease of removal of air bubbles trapped when the semiconductor processing tape is bonded to the adherend) of the adhesive layer.

As the fatty acid ester (E), an ester of a fatty acid and an alkyl alcohol can be used. From the viewpoint of compatibility with other components, it is preferable to use a fatty acid ester selected from the group consisting of an ester of a fatty acid having 8 to 18 carbon atoms and a monofunctional alcohol having a branched hydrocarbon group having 3 to 18 carbon atoms, and an ester of an unsaturated fatty acid having 14 to 18 carbon atoms and a di- to tetra-functional alcohol.

Examples of esters of fatty acids having 8 to 18 carbon atoms and monofunctional alcohols having a branched hydrocarbon group having 3 to 18 carbon atoms include isostearyl laurate, isopropyl myristate, isocetyl myristate, octyldodecyl myristate, isopropyl palmitate, isostearyl palmitate, isocetyl stearate, 2-ethylhexyl stearate, octyldodecyl oleate, diisostearyl adipate, diisocetyl sebacate, trioleyl trimellitate, and triisocetyl trimellitate. Among these, it is preferable to use isopropyl myristate, isopropyl palmitate, and 2-ethylhexyl stearate, and it is particularly preferable to use isopropyl myristate and/or 2-ethylhexyl stearate.

Examples of esters of unsaturated fatty acids having 14 to 18 carbon atoms with difunctional to tetrafunctional alcohols include esters of unsaturated fatty acids such as myristoleic acid, oleic acid, linoleic acid, linolenic acid, isopalmitic acid, and isostearic acid with alcohols such as ethylene glycol, propylene glycol, glycerin, trimethylolpropane, pentaerythritol, and sorbitan.

The content of the fatty acid ester (E) in the pressure-sensitive adhesive composition of the present embodiment is preferably from 3 to 18 mass %, and more preferably from 5 to 15 mass %.
When the content of fatty acid ester (E) is 3% by mass or more, the adhesive strength of the semiconductor processing tape using the cured product of the adhesive composition as the adhesive layer falls within a preferred range, and the lamination property and bubble releasing property of the adhesive layer become good. When the content of fatty acid ester (E) is 18% by mass or less, adhesive residue containing fatty acid ester (E) is unlikely to occur when the semiconductor processing tape using the cured product of the adhesive composition as the adhesive layer is peeled off from the adherend, which is preferable.

(solvent)
The pressure-sensitive adhesive composition of the present embodiment may contain a solvent, but is more preferably a solvent-free composition that is substantially free of solvent.
When the pressure-sensitive adhesive composition of the present embodiment contains a solvent, the solvent can be used, for example, as a leveling agent and/or a softening agent.

When the adhesive composition of this embodiment is solvent-free, the step of heating and drying the solvent can be omitted when using the adhesive composition to form an adhesive layer of a semiconductor processing tape, resulting in excellent productivity. In particular, when using the adhesive composition of this embodiment to manufacture a semiconductor processing tape having an adhesive layer with a thickness of more than 50 μm, the productivity improvement effect of omitting the step of heating and drying the solvent is significant, so it is preferable that the adhesive composition be solvent-free.

In the present invention, the adhesive composition being "substantially free of solvent" means that the solvent content in the adhesive composition is 0 to 1 mass %, preferably 0 to 0.5 mass %, and more preferably 0 to 0.1 mass %.

(others)
The pressure-sensitive adhesive composition of the present embodiment may contain other additives as necessary within the range that does not impair the effects of the present invention. Examples of the additives include plasticizers, surface lubricants, antioxidants, antiaging agents, light stabilizers, ultraviolet absorbers, polymerization inhibitors, benzotriazole-based light stabilizers, phosphate ester-based and other flame retardants, dyes, etc.

<Method of producing pressure-sensitive adhesive composition>
Next, the manufacturing method of the adhesive composition of this embodiment will be described in detail with examples. Hereinafter, among the components contained in the adhesive composition of this embodiment, a preferred synthesis method for polyurethane (A) will be described with examples. Among the components contained in the adhesive composition of this embodiment, each component other than polyurethane (A), such as (meth)acrylate monomer (B), chain transfer agent (C), photopolymerization initiator (D), and fatty acid ester (E), can be easily purchased as a commercially available product. In addition, the synthesis method differs depending on the type of compound used as each component. Therefore, the description of the synthesis method will be omitted.

<Method for synthesizing polyurethane (A)>
Hereinafter, an example of a preferred synthesis method for the polyurethane (A) contained in the pressure-sensitive adhesive composition of the present embodiment will be described. Note that the synthesis method for the polyurethane (A) is not limited to the synthesis method shown below, and can be appropriately changed depending on conditions such as raw materials and equipment used in the synthesis.

In the synthesis method of polyurethane (A) shown below, the reaction between hydroxyl groups and isocyanato groups is carried out in the presence of an organic solvent inactive to isocyanato groups in each step using a urethanization catalyst. Examples of this urethanization catalyst include dibutyltin dilaurate, dibutyltin diethylhexoate, and dioctyltin dilaurate. In addition, the reaction between hydroxyl groups and isocyanato groups is preferably carried out continuously for 1 to 5 hours at 30 to 100°C in each step. The amount of the urethanization catalyst used is preferably 50 to 500 ppm by mass based on the total mass of the reactants (raw materials).

To synthesize polyurethane (A), first, polyoxyalkylene polyol and polyisocyanate are charged in a ratio such that the amount of isocyanato groups (based on the number of molecules, the same applies below) is greater than the amount of hydroxyl groups (based on the number of molecules, the same applies below). The polyoxyalkylene polyol and polyisocyanate are then reacted to synthesize polyurethane having isocyanato groups at the ends as a precursor of polyurethane (A). Specific examples of polyoxyalkylene polyols and polyisocyanates used as raw materials are as exemplified in the section on polyurethane (A).

At this time, the molecular weight (degree of polymerization) of the polyurethane having isocyanato groups at its terminals can be adjusted by adjusting the ratio of the amount of isocyanato groups to the amount of hydroxyl groups contained in the raw material. Specifically, the smaller the excess amount of isocyanato groups relative to the amount of hydroxyl groups, the higher the molecular weight of the polyurethane having isocyanato groups at its terminals. Also, the greater the excess amount of isocyanato groups relative to the amount of hydroxyl groups, the lower the molecular weight of the polyurethane having isocyanato groups at its terminals. In this embodiment, the weight average molecular weight of the target polyurethane (A) is adjusted by adjusting the molecular weight of the polyurethane having isocyanato groups at its terminals.

Next, a polyurethane having an isocyanato group at a terminal is reacted with a compound having a hydroxy group and a (meth)acryloyl group to produce a polyurethane (A) containing a polyurethane (a1). The polyurethane (a1) has a skeleton containing a structure derived from a polyoxyalkylene polyol and a structure derived from a polyisocyanate, and has (meth)acryloyl groups at multiple terminals. The (meth)acryloyl groups at the terminals of the produced polyurethane (A) are preferably part of a (meth)acryloyloxy group.

The compounds having a hydroxy group and a (meth)acryloyl group include, but are not limited to, hydroxyalkyl (meth)acrylates such as 2-hydroxyethyl (meth)acrylate, 2-hydroxypropyl (meth)acrylate, and 4-hydroxybutyl (meth)acrylate; monools having a (meth)acryloyl group derived from various polyols such as 1,3-butanediol mono(meth)acrylate, 1,4-butanediol mono(meth)acrylate, 1,6-hexanediol mono(meth)acrylate, and 3-methylpentanediol mono(meth)acrylate. These compounds having a hydroxy group and a (meth)acryloyl group may be used alone or in combination of two or more types. Among these compounds having a hydroxy group and a (meth)acryloyl group, it is preferable to use 2-hydroxyethyl (meth)acrylate in terms of reactivity with the isocyanato group of polyurethane having an isocyanato group at the end and photocurability of the adhesive composition.

Alternatively, the polyurethane (A) may be produced by reacting a compound having a hydroxy group and a (meth)acryloyl group with an alkyl alcohol having no (meth)acryloyl group and one hydroxy group, together with a polyurethane having an isocyanato group at its terminal.
The alkyl alcohol is not particularly limited as long as it does not have a (meth)acryloyl group and has one hydroxyl group, and may be a linear, branched, or alicyclic alkyl alcohol, etc. The alkyl alcohol may be used alone or in combination of two or more kinds.

By reacting a compound having a hydroxy group and a (meth)acryloyl group with an alkyl alcohol having one hydroxy group but no (meth)acryloyl groups, and a polyurethane having an isocyanato group at its terminal to produce polyurethane (A), it is possible to adjust the amount of (meth)acryloyl groups introduced into the polyurethane having an isocyanato group at its terminal.

More specifically, according to the above reaction, polyurethane (A) is produced that contains multiple types of polyurethanes with different amounts of (meth)acryloyl groups introduced at the ends. The multiple types of polyurethanes include polyurethane (a1) having multiple (meth)acryloyl groups at their ends. Furthermore, the multiple types of polyurethanes include not only polyurethane (a1) but also polyurethanes in which at least some of the multiple ends have a structure derived from the above alkyl alcohol. Therefore, the multiple types of polyurethanes produced include polyurethanes in which at least some of the multiple ends do not have (meth)acryloyl groups. Furthermore, the multiple types of polyurethanes produced may also include polyurethane (a2) having a (meth)acryloyl group at only one end.

<Another Example of the Method for Synthesizing Polyurethane (A)>
Next, another preferred example of the synthesis method for the polyurethane (A) will be described.
In the synthesis method of polyurethane (A) shown below, as in the above synthesis method example, the reaction between the hydroxyl group and the isocyanato group is carried out in the presence of an organic solvent inactive to the isocyanato group using a urethanization catalyst in each step. Examples of the urethanization catalyst include dibutyltin dilaurate, dibutyltin diethylhexoate, and dioctyltin dilaurate. In addition, the reaction between the hydroxyl group and the isocyanato group is preferably carried out continuously for 1 to 5 hours at 30 to 100° C. in each step. The amount of the urethanization catalyst used is preferably 50 to 500 ppm by mass based on the total mass of the reactants (raw materials).

When polyurethane (A) is synthesized using this synthesis method, unlike the above-mentioned example synthesis method, a polyurethane having a hydroxyl group at its terminal is synthesized as a precursor of polyurethane (A).
Specifically, first, a polyoxyalkylene polyol and a polyisocyanate are charged in a ratio such that the amount of hydroxyl groups (based on the number of molecules, the same applies below) is greater than the amount of isocyanato groups (based on the number of molecules, the same applies below).Then, the polyoxyalkylene polyol and the polyisocyanate are reacted to synthesize a polyurethane having a hydroxyl group at its terminal as a precursor of polyurethane (A).

At this time, the molecular weight (degree of polymerization) of the polyurethane having hydroxyl groups at its terminals can be adjusted by adjusting the ratio of the amount of hydroxyl groups to the amount of isocyanato groups contained in the raw material. Specifically, the smaller the excess amount of hydroxyl groups relative to the amount of isocyanato groups, the higher the molecular weight of the polyurethane having hydroxyl groups at its terminals. Also, the greater the excess amount of hydroxyl groups relative to the amount of isocyanato groups, the lower the molecular weight of the polyurethane having hydroxyl groups at its terminals. In this embodiment, the mass average molecular weight of the target polyurethane (A) is adjusted by adjusting the molecular weight of the polyurethane having hydroxyl groups at its terminals.

Next, the polyurethane having a hydroxyl group at the end is reacted with a compound having an isocyanato group and a (meth)acryloyl group to produce polyurethane (A) having a skeleton including a polyoxyalkylene polyol-derived structure and a polyisocyanate-derived structure, and including polyurethane (a1) having (meth)acryloyl groups at multiple ends. The (meth)acryloyl groups at the ends of the produced polyurethane (A) are preferably part of (meth)acryloyloxy groups.

Compounds having an isocyanato group and a (meth)acryloyl group include, but are not limited to, 2-(meth)acryloyloxyethyl isocyanate, 2-(meth)acryloyloxypropyl isocyanate, 1,1-bis(acryloyloxymethyl)ethyl isocyanate, etc. Examples of commercially available compounds having an isocyanato group and a (meth)acryloyl group include Karenz MOI (registered trademark) and Karenz AOI (registered trademark) manufactured by Showa Denko K.K. These compounds having an isocyanato group and a (meth)acryloyl group may be used alone or in combination of two or more types. Among these compounds having an isocyanato group and a (meth)acryloyl group, it is preferable to use 2-(meth)acryloyloxyethyl isocyanate in terms of reactivity with the hydroxyl group of polyurethane having a hydroxyl group at the end and the photocurability of the adhesive composition.

Alternatively, the polyurethane (A) may be produced by reacting a compound having an isocyanato group and a (meth)acryloyl group with an alkyl isocyanate having no (meth)acryloyl group and one isocyanato group, together with a polyurethane having a hydroxyl group at its terminal.
The alkyl isocyanate is not particularly limited as long as it does not have a (meth)acryloyl group and has one isocyanato group, and may be a linear, branched, or alicyclic alkyl isocyanate, etc. The alkyl isocyanate may be used alone or in combination of two or more kinds.

By reacting a compound having an isocyanato group and a (meth)acryloyl group with an alkyl isocyanate having one isocyanato group but no (meth)acryloyl group, and a polyurethane having a hydroxyl group at its terminal to produce polyurethane (A), the amount of (meth)acryloyl groups introduced into the polyurethane having a hydroxyl group at its terminal can be adjusted.

More specifically, according to the above reaction, polyurethane (A) is produced that contains multiple types of polyurethanes with different amounts of (meth)acryloyl groups introduced at the ends. The multiple types of polyurethanes include polyurethane (a1) having multiple (meth)acryloyl groups at their ends. Furthermore, the multiple types of polyurethanes include not only polyurethane (a1) but also polyurethanes in which at least some of the multiple ends have a structure derived from the above alkyl isocyanate. Therefore, the multiple types of polyurethanes produced include polyurethanes in which at least some of the multiple ends do not have a (meth)acryloyl group. Furthermore, the multiple types of polyurethanes produced may also include polyurethane (a2) having a (meth)acryloyl group at only one end.

<Method of mixing components contained in pressure-sensitive adhesive composition>
The pressure-sensitive adhesive composition of the present embodiment can be produced by a method of mixing the polyurethane (A) obtained by the above-mentioned synthesis method, a (meth)acrylate monomer (B), a chain transfer agent (C), a photopolymerization initiator (D), and, if necessary, a fatty acid ester (E) and other additives.
The method for mixing the components contained in the pressure-sensitive adhesive composition of the present embodiment is not particularly limited, and can be carried out using, for example, a stirring device equipped with stirring blades such as a homodisper or a paddle blade.

<Method of manufacturing tape for semiconductor processing>
Next, a method for producing the semiconductor processing tape of this embodiment will be described.
The method for producing the semiconductor processing tape of this embodiment is not particularly limited, and the tape can be produced using a known method.
For example, fine particles of polypyrrole and/or polypyrrole derivative are dispersed in a hydrophilic solvent using a polymer dispersant and/or a dopant, and further mixed with a water-soluble or water-dispersible binder resin to prepare a resin composition; this resin composition is applied onto a substrate body such as a polymer film, and the solvent is then dried and removed to obtain a substrate having an antistatic layer. Next, a pressure-sensitive adhesive composition is applied onto the antistatic layer of the substrate, and a transparent separator film is laminated to form a laminate. Thereafter, the pressure-sensitive adhesive composition is irradiated with ultraviolet light through the separator to photocure the pressure-sensitive adhesive composition. This results in a semiconductor processing tape having a pressure-sensitive adhesive layer, which is a cured product of the pressure-sensitive adhesive composition, formed on a substrate having an antistatic layer.

The method of applying the adhesive composition to the substrate is not particularly limited and can be selected appropriately. For example, methods of applying the adhesive composition to the substrate include methods using various coaters such as a gravure roll coater, reverse roll coater, kiss roll coater, dip roll coater, bar coater, knife coater, spray coater, comma coater, and direct coater, and screen printing methods.

Examples of light sources for photocuring the pressure-sensitive adhesive composition include black lights, low-pressure mercury lamps, high-pressure mercury lamps, extra-high-pressure mercury lamps, metal halide lamps, and xenon lamps.
The light irradiation intensity is preferably set to a condition that allows the pressure-sensitive adhesive composition to be sufficiently cured and the gel fraction of the cured product to be within a range of 50 to 65% by mass, for example, 50 to 3000 mW/cm ^2. If the light irradiation intensity is too weak, curing takes a long time, resulting in reduced productivity.

In this embodiment, the adhesive composition is irradiated with ultraviolet light through a transparent separator, but if the substrate is transparent, ultraviolet light may be irradiated from the substrate side, or an opaque separator may be used.

<Uses and required performance of tape for semiconductor processing>
The semiconductor processing tape of this embodiment can be used, for example, in applications where it is attached to an adherend having an uneven surface and then peeled off. Specifically, it can be used suitably as a backgrind tape for semiconductor wafer processing, which is attached to the surface of a semiconductor wafer on which bumps are formed to protect the surface of the semiconductor wafer and is peeled off after a predetermined wafer processing step.

When the semiconductor processing tape of this embodiment is used to protect the surface of a semiconductor wafer having bumps formed on its surface, the peel strength (adhesive strength) of the semiconductor processing tape must be such that the semiconductor processing tape is firmly fixed to the semiconductor wafer, for example, in the backgrinding step in the semiconductor device processing process. On the other hand, the peel strength of the semiconductor processing tape must be strong enough not to damage the components of the semiconductor device when the semiconductor processing tape is peeled off from the semiconductor wafer after a specified processing step.

From these viewpoints, the peel strength of the semiconductor processing tape used for the above-mentioned applications is preferably 10 to 300 gf/25 mm, more preferably 15 to 200 gf/25 mm, and even more preferably 20 to 150 gf/25 mm, when the peel speed is 0.3 m/min. and the thickness of the adhesive layer is 50 to 200 μm. When the thickness of the adhesive layer is 200 to 500 μm, it is preferably 50 to 500 gf/25 mm, more preferably 60 to 400 gf/25 mm, and even more preferably 70 to 300 gf/25 mm. A specific method for measuring the peel strength of the semiconductor processing tape will be described later in the examples.

The semiconductor processing tape of this embodiment has an adhesive layer, which is a cured product of the adhesive composition of this embodiment, on one side of a substrate on which an antistatic layer is formed. Therefore, the semiconductor processing tape of this embodiment has sufficient adhesive strength, is unlikely to leave adhesive residue on the adherend where the adhesive layer is transferred to the adherend after the semiconductor processing tape is peeled off, and has excellent unevenness absorption and antistatic performance. Therefore, the semiconductor processing tape of this embodiment is suitable for applications in which it is attached to an adherend having uneven portions on its surface and then peeled off.

The semiconductor processing tape of this embodiment can be suitably used as a semiconductor processing tape that is applied during the backgrinding process of a semiconductor wafer having uneven portions made of bumps on its surface, and is peeled off after the backgrinding process. In this case, the semiconductor processing tape of this embodiment fixes the semiconductor wafer with sufficient adhesive strength. Moreover, since the semiconductor processing tape has sufficient unevenness absorption properties, gaps are unlikely to occur between the semiconductor processing tape applied to the semiconductor wafer and the periphery of the bumps. Therefore, it is possible to prevent the water used in the backgrinding process from penetrating the gap between the semiconductor processing tape and the periphery of the bumps, thereby preventing the semiconductor wafer from being contaminated. In addition, since the semiconductor processing tape of this embodiment has sufficient antistatic properties, peeling electrification can be suppressed when the semiconductor processing tape applied to the semiconductor wafer is peeled off after the backgrinding process. Furthermore, it is preferable that glue residue is unlikely to occur around the bumps of the semiconductor wafer from which the semiconductor processing tape has been peeled off after the backgrinding process.

The semiconductor processing tape of this embodiment can have a single-layer structure in which the adhesive layer is a cured product of the adhesive composition. In this case, the adhesive layer can be formed by simply performing the process of forming one layer. Therefore, the semiconductor processing tape of this embodiment can be easily manufactured with fewer manufacturing steps compared to, for example, forming a semiconductor processing tape provided with a layer having irregularity absorbency and a layer having adhesive strength.

The present invention will be explained in more detail below with reference to examples and comparative examples, but the present invention is not limited to the following examples.

(Production Example 1)
<Production of sheet-like substrate 1 having antistatic layer>
Polypyrrole dispersion (PPY-12, solid content 8%, manufactured by Marubishi Petrochemical Co., Ltd.) 9.4 parts by mass, polyester binder (BI-12, solid content 30%, manufactured by Marubishi Petrochemical Co., Ltd.) 5.0 parts by mass, melamine crosslinking agent (CL-12, solid content 25%, manufactured by Marubishi Petrochemical Co., Ltd.) 2.6 parts by mass, polyoxyethylene lauryl ether 0.05 parts by mass, water 830.0 parts by mass were mixed to prepare an aqueous dispersion. Next, the resin composition was applied to one side of a 50 μm thick PET film (manufactured by Toyobo Co., Ltd., product name: Ester (trademark) film E5100) as the substrate body using a gravure coater so that the film thickness after heat curing was 1.0 μm. Next, the sheet-like substrate 1 was obtained by curing at 130 ° C. for 1 minute. The electrical resistance of the substrate 1 measured with a low resistivity meter (Loresta-AX, manufactured by Mitsubishi Chemical Analytech Co., Ltd.) was 8 × 10 ⁵ Ω · cm.

(Comparative Production Example 1)
<Production of sheet-like substrate 2 having antistatic layer>
Polythiophene (HC Starck Clevios (trademark) P solid content 1%) 93.0 parts by weight, polyester resin (Toyobo Vylonal (trademark) MD-1930, solid content 31%) 6.8 parts by weight, melamine-based crosslinking agent (Marubishi Yuka Kogyo Co., Ltd. CL-12, solid content 25%) 2.4 parts by weight, polyoxyethylene lauryl ether 0.05 parts by weight, water 900.0 parts by weight were mixed to prepare an aqueous dispersion. Next, the resin composition was applied to one side of a 50 μm thick PET film (Toyobo Co., Ltd., product name: Ester (trademark) film E5100) as the substrate body using a gravure coater so that the film thickness after heat curing was 1.0 μm. Next, the sheet-like substrate 2 was obtained by curing at 130 ° C. for 1 minute. The electrical resistance of the substrate 2 measured with a low resistivity meter (Loresta-AX manufactured by Mitsubishi Chemical Analytech Co., Ltd.) was 4×10 ⁵ Ω·cm.

(Synthesis Example 1)
<Synthesis of Polyurethane (A-1)>
A reactor equipped with a thermometer, a stirrer, a dropping funnel, and a cooling tube with a drying tube was charged with 0.55 kg (2.1 mol) of a hydrogenated product of diphenylmethane diisocyanate (Desmodur W, manufactured by Sumika Covestro Urethane Co., Ltd.), 4.01 kg (2.0 mol) of polypropylene glycol having a hydroxyl group at its end and a hydroxyl value of 56 mg KOH/g (Actocol D-2000, manufactured by Mitsui Chemicals, number average molecular weight 2000), and 0.8 g of a urethanization catalyst dioctyltin (Neostan U-810, manufactured by Nitto Kasei Co., Ltd.).

The reactor was then heated to 60°C and reacted for 4 hours to obtain a polyurethane having isocyanato groups at both ends as a precursor of polyurethane (A). 23.22 g (0.2 mol) of 2-hydroxyethyl acrylate was then added to the reactor, and the temperature was raised to 70°C to react for 2 hours to obtain 4.58 kg of polyurethane (A-1) with a mass average molecular weight of 67,000.

The resulting polyurethane (A-1) was analyzed using infrared absorption spectroscopy (IR). As a result, no peaks derived from isocyanato groups were observed. Therefore, it was confirmed that polyurethane (A-1) was polyurethane (a1) in which acryloyloxy groups had been introduced at all ends.

(Synthesis Example 2)
<Synthesis of Polyurethane (A-2)>
A polyurethane (A-2) having a mass average molecular weight of 66,000 was obtained in the same manner as in the synthesis of polyurethane (A-1), except that 2.1 mol of isophorone diisocyanate (Desmodur I, manufactured by Sumika Covestro Urethane Co., Ltd.) was used instead of the hydrogenated product of diphenylmethane diisocyanate.

The resulting polyurethane (A-2) was analyzed using infrared absorption spectroscopy (IR). As a result, no peaks derived from isocyanato groups were observed. Therefore, it was confirmed that polyurethane (A-2) was polyurethane (a1) in which acryloyloxy groups had been introduced at all ends.

(Formulation Examples 1 to 3, Comparative Formulation Examples 1 to 4)
<Preparation of Pressure-Sensitive Adhesive Composition>
The polyurethane (A) obtained by the above synthesis method, the (meth)acrylate monomer (B), the chain transfer agent (C), the photopolymerization initiator (D) and the fatty acid ester (E) shown in Table 1 were blended in the ratios shown in Table 1 and mixed at 25°C using a disper to obtain pressure-sensitive adhesive compositions c1 to c7 of Blending Examples 1 to 3 and Comparative Blending Examples 1 to 4.

The following symbols shown in Table 1 represent the compounds shown below.
2EHA: 2-ethylhexyl acrylate (manufactured by Toagosei Co., Ltd.)
BUA: n-butyl acrylate (manufactured by Toagosei Co., Ltd.)
ACMO: Acryloylmorpholine (manufactured by Shin-Nakamura Chemical Co., Ltd.)
TMPTA: Trimethylolpropane triacrylate (manufactured by Toagosei Co., Ltd.)

PE1: Pentaerythritol tetrakis(3-mercaptobutyrate) (manufactured by Showa Denko K.K.)
NR1: 1,3,5-tris(3-mercaptobutyloxyethyl)-1,3,5-triazine-2,4,6(1H,3H,5H)-trione (manufactured by Showa Denko K.K.)
TPO (Omnirad TPO H): 2,4,6-trimethylbenzoyldiphenylphosphine oxide (manufactured by IGM Resins B.V.)
184 (Omnirad 184): 1-hydroxycyclohexyl-phenyl ketone (manufactured by IGM Resins B.V.)
Exepar IPM: Isopropyl myristate (Kao Corporation)
Exepar EH-S: 2-ethylhexyl stearate (manufactured by Kao Corporation)

Example 1
The pressure-sensitive adhesive composition c1 of Formulation Example 1 in Table 1 was applied to the antistatic layer side of the substrate 1 using an applicator so as to give a thickness of 150 μm after curing.
Next, a 75 μm-thick silicone-based ultra-light release PET film (product name: E7006, manufactured by Toyobo Co., Ltd.) was attached as a separator to the surface coated with the pressure-sensitive adhesive composition using a rubber roller.
Thereafter, the adhesive composition was irradiated with ultraviolet light through the separator using an ultraviolet irradiation device (manufactured by iGraphics Co., Ltd., UV irradiation device 3 kW, high pressure mercury lamp) under conditions of an irradiation distance of 25 cm, a lamp moving speed of 1.0 m/min, and an irradiation amount of 1000 mJ/ ^cm2 , to photocure the adhesive composition. This resulted in the semiconductor processing tape of Example 1 in which the adhesive layer, which was the cured product of the adhesive composition, and the separator were laminated on the substrate.

(Examples 2 to 3 and Comparative Examples 1 to 6)
Semiconductor processing tapes were produced in the same manner as in Example 1, except that the substrate and adhesive compositions c2 to c7 shown in Table 2 were used and the adhesive layer had a thickness shown in Table 2. As a result, the semiconductor processing tapes of Examples 2 to 3 and Comparative Examples 1 to 6 were obtained.

Next, the following items were evaluated for the semiconductor processing tapes of Examples 1 to 3 and Comparative Examples 1 to 4. The results are shown in Table 2.
<Measurement of surface resistivity>
The semiconductor processing tape was cut into a size of 120 mm long and 120 mm wide, and left for 3 hours in an environment of 23°C temperature and 50% RH relative humidity to condition the humidity. Thereafter, the release PET film was peeled off to expose the adhesive layer, and the surface resistivity of the adhesive layer side was measured using a high resistivity meter (HIRESTER-UX, manufactured by Mitsubishi Chemical Analytech Co., Ltd.) under the condition of an applied voltage of 100V x 60 seconds. Then, it was evaluated according to the following criteria. The smaller the surface resistivity, the less likely peeling static electricity occurs when the semiconductor processing tape attached to the semiconductor wafer is peeled off, and it can be said that the semiconductor processing tape has excellent antistatic performance.

Evaluation criteria: ⊚: surface resistivity is less than 1×10 ¹¹ Ω/□; ◯: surface resistivity is 1×10 ¹¹ Ω/□ or more and less than 1×10 ¹² Ω/□; △: surface resistivity is 1×10 ¹² Ω/□ or more and less than 1×10 ¹³ Ω/□; ×: surface resistivity is 1×10 ¹³ Ω/□ or more

<Peeling force (peeling strength)>
The semiconductor processing tape was cut into a size of 25 mm long and 150 mm wide, and the separator was peeled off to expose the adhesive layer. The entire surface of the exposed adhesive layer was then laminated onto a glass plate, and a rubber roller (diameter: 85 mm, width: 50 mm) with a mass of 2 kg (load 19.6 N) was rolled once to obtain a measurement sample. The obtained measurement sample was left for 30 minutes in an environment of a temperature of 23°C and a relative humidity of 50% RH. Then, a tensile test was performed in the 180° direction at a peel speed of 0.3 m/min in accordance with JIS K 6854-2 to measure the peel strength (gf/25 mm) against the glass plate.

<Irregularity absorption>
The semiconductor processing tape was cut into a size of 25 mm long and 50 mm wide, and the separator was peeled off to expose the adhesive layer. Then, the surface of the exposed adhesive layer was placed facing the bumps of a bumped wafer (WALTS-TEG FC150SCJY LF (PI), bump height: 75 μm, bump size: diameter 90 μm, manufactured by Waltz Corporation). Then, a rubber roller (diameter: 85 mm, width: 50 mm) with a mass of 2 kg (load 19.6 N) was reciprocated three times at a speed of 10 mm/sec on the substrate of the semiconductor processing tape to bond the semiconductor processing tape and the bumped wafer.

The bumped wafer laminated with the semiconductor processing tape was observed from the substrate side of the semiconductor processing tape with a digital optical microscope (RH-2000, manufactured by Keihin Hirox Co., Ltd.), and the unevenness absorbency of the bumps was evaluated according to the following criteria.
"standard"
◯: No gap is present between the adhesive layer of the semiconductor processing tape and the periphery of the bumps of the bumped wafer.
×: There is a gap between the adhesive layer of the semiconductor processing tape and the periphery of the bumps of the bumped wafer.

<Contamination caused by glue residue>
The semiconductor processing tape was cut into a size of 25 mm long and 50 mm wide, and the separator was peeled off to expose the adhesive layer. The exposed surface of the adhesive layer was then placed facing the bumps of a bumped wafer (WALTS-TEG FC150SCJY LF (PI), bump height: 75 μm, bump size: diameter 90 μm, manufactured by Waltz Corporation). A rubber roller (diameter: 85 mm, width: 50 mm) with a mass of 2 kg (load 19.6 N) was then reciprocated three times at a speed of 10 mm/sec on the substrate of the semiconductor processing tape to bond the semiconductor processing tape and the bumped wafer together.

The bumped wafer attached to the semiconductor processing tape was left at 23° C. for 24 hours, and then the semiconductor processing tape was peeled off by hand at a speed of about 2 m/min. The surface of the bumped wafer was then observed with a digital optical microscope (RH-2000, manufactured by Hirox Co., Ltd.) and the presence or absence of contamination due to adhesive residue was evaluated according to the following criteria. Note that "adhesive residue" means that the adhesive layer itself remains attached to the wafer surface, causing the wafer surface to be sticky.
"standard"
◯: No contamination due to adhesive residue around the bumps.
x: Contamination due to adhesive residue around the bumps.

<Measurement of Gel Fraction>
The adhesive composition was applied using an applicator onto a 75 μm-thick release PET film (manufactured by Higashiyama Film Co., Ltd., product name: Clean Sepa (trademark) HY-S10-2) so that the thickness after curing would be 150 μm. Note that for Comparative Example 4, the thickness after curing was adjusted to 30 μm. Next, the surface to which the adhesive composition was applied was covered with a 75 μm-thick silicone-based ultra-light release PET film (manufactured by Toyobo Co., Ltd., product name: E7006).

Next, using an ultraviolet irradiation device (manufactured by iGraphics Co., Ltd., UV irradiation device 3 kW, high-pressure mercury lamp), ultraviolet rays were irradiated through the ultra-light peeling PET film under conditions of an irradiation distance of 25 cm, a lamp movement speed of 1.0 m/min, and an irradiation amount of 1000 mJ/ ^cm2 , thereby curing the pressure-sensitive adhesive composition to obtain a cured product (pressure-sensitive adhesive layer).

Next, the cured product (adhesive layer) was cut into a size of about 1 g, and the PET films on both sides were peeled off to prepare a measurement sample, and its mass was measured. Next, the measurement sample was immersed in 50 ml of toluene and left at room temperature for 72 hours. After that, the measurement sample was taken out of the toluene, dried at 80° C. for 5 hours, and its mass was measured again. Then, the gel fraction was measured based on the following formula.
Gel fraction (%) = [A/B] x 100
A: Mass of the measurement sample after immersion in toluene (excluding the mass of toluene)
B: Mass of the measurement sample before immersion in toluene

As shown in Table 2, the semiconductor processing tapes of Examples 1 to 3 were shown to have low surface resistivity and excellent antistatic performance. In addition, they had high peeling strength (adhesive strength), excellent irregularity absorption, and did not cause contamination due to adhesive residue when peeled off from a wafer with bumps.
In contrast, Comparative Example 1, in which the substrate 2 not containing a polypyrrole compound was used in the antistatic layer, showed high surface resistivity and poor antistatic performance. Comparative Examples 2, 3, and 6, in which the chain transfer agent (C) was not used as the adhesive composition, could not control the gel fraction of the adhesive layer within an appropriate range, resulting in poor peeling force, unevenness absorbency, and adhesive residue. Comparative Example 4, in which the adhesive layer was thin, did not provide sufficient unevenness absorbency. Comparative Example 5 used adhesive composition c6, which did not use chain transfer agent (C) and had an increased amount of photopolymerization initiator (D) compared to adhesive composition c1. As a result, the gel fraction was equivalent to that of Example 1, but the unevenness absorbency was insufficient, and contamination due to adhesive residue also occurred.

According to the present invention, a semiconductor processing tape is provided that has sufficient unevenness absorption, antistatic properties, and adhesive strength, is unlikely to leave adhesive residue, and can be manufactured with fewer manufacturing steps. The semiconductor processing tape can be preferably used in the semiconductor wafer processing step to protect the surface of the semiconductor wafer and to peel off after the processing step. In particular, it is suitable as a backgrind tape used to protect the surface during the backgrinding step of an adherend having uneven surfaces, such as a semiconductor wafer with bumps formed on the surface.

Claims (8)

A sheet-like substrate having a substrate body and an antistatic layer provided on at least one surface of the substrate body;
A semiconductor processing tape having an adhesive layer formed on the antistatic layer,
the antistatic layer contains a polypyrrole compound,
The pressure-sensitive adhesive layer is a cured product of a pressure-sensitive adhesive composition,
The thickness of the pressure-sensitive adhesive layer is 50 to 500 μm,
The pressure-sensitive adhesive composition includes a polyurethane (A), a (meth)acrylate monomer (B), a chain transfer agent (C), and a photopolymerization initiator (D),
The polyurethane (A) contains polyurethane (a1),
the polyurethane (a1) has a skeleton containing a structure derived from a polyoxyalkylene polyol and a structure derived from a polyisocyanate, and has (meth)acryloyl groups at a plurality of terminals;
A tape for semiconductor processing, characterized in that the (meth)acrylate monomer (B) contains a monofunctional (meth)acrylate and a polyfunctional (meth)acrylate. The semiconductor processing tape according to claim 1, wherein the adhesive layer has a single layer structure. The semiconductor processing tape according to claim 1 or 2, wherein the chain transfer agent (C) is a multifunctional thiol. A semiconductor processing tape according to any one of claims 1 to 3, wherein the gel fraction of the adhesive layer is 50 to 65 mass %. The tape for semiconductor processing according to any one of claims 1 to 4, wherein the pressure-sensitive adhesive layer has a surface resistivity of less than 1 x 10 ¹² Ω/□. A semiconductor processing tape according to any one of claims 1 to 5, wherein the (meth)acrylate monomer (B) contains 85 to 99 mol% of the monofunctional (meth)acrylate and 1 to 15 mol% of the polyfunctional (meth)acrylate. The pressure-sensitive adhesive composition,
20 to 50% by mass of the polyurethane (A),
35 to 79% by mass of the (meth)acrylate monomer (B),
0.5 to 8% by mass of the chain transfer agent (C),
The semiconductor processing tape according to any one of claims 1 to 6, comprising 0.01 to 5 mass % of the photopolymerization initiator (D). A semiconductor processing tape according to any one of claims 1 to 7, wherein the adhesive composition further contains a fatty acid ester (E).