Adhesive composition, protective sheet, and method for producing semiconductor device

Abstract

An adhesive composition containing an ethylenically unsaturated group-containing (meth)acrylic resin (A2), a crosslinking agent (B2), and a photopolymerization initiator (C), and containing 1,000-100,000 mass ppm of silicon atoms, wherein the ethylenically unsaturated group-containing (meth)acrylic resin (A2) has a plurality of functional groups that react with functional groups of the crosslinking agent (B2), and the ethylenically unsaturated group-containing (meth)acrylic resin (A2) is an adduct of an epoxy group-containing ethylenically unsaturated compound (a2-3) to a (meth)acrylic resin (A2-0) having as raw material monomers at least an alkyl (meth)acrylate (a2-1) and a carboxy group-containing ethylenically unsaturated compound (a2-2).

Description

Pressure-sensitive adhesive composition, protective sheet, and method for manufacturing semiconductor device

[0001] The present disclosure relates to a pressure-sensitive adhesive composition, a protective sheet, and a method for producing a semiconductor device.

[0002] Various protective sheets are used in the manufacturing process of semiconductor devices. Specific examples include backgrinding tape and dicing tape. Backgrinding tape is a sheet used to protect semiconductor wafers during the backgrinding process, while dicing tape is a fixing sheet used in the dicing process, in which the semiconductor wafer is cut into small element pieces. These protective sheets are removable protective sheets that are attached to the semiconductor wafer as an adherend and are peeled off from the adherend after the specified processing steps are completed.

[0003] In recent years, with the miniaturization and increasing density of electronic devices, flip-chip mounting has become mainstream as a method for mounting semiconductor elements in the smallest possible area. In flip-chip mounting, semiconductor chips (e.g., Through Silicon Via (TSV) chips) with solder-tipped bump electrodes are used to bond chips together. These bumped semiconductor chips are electrically bonded to other semiconductor chips or substrates through a reflow process, in which the chips are heated to a temperature above the melting point of the solder, typically 200°C or higher, for mounting. However, when mounting semiconductor chips in communication electronic devices, electromagnetic waves generated inside the chip can cause communication problems. To prevent this, a sputtering process is sometimes performed to deposit a metal film around the periphery of the semiconductor chip as an electromagnetic wave shield. The sputtering process is typically performed at 150°C or higher. A removable protective sheet is used to protect the bump surface during the reflow and sputtering processes.

[0004] For example, Patent Document 1 describes a method for manufacturing an electronic device using an electronic component having a circuit formation surface and an adhesive laminated film having, in this order, a base layer, an irregularity-absorbing resin layer, and an adhesive resin layer.

[0005] Japanese Patent Application Laid-Open No. 2021-163785

[0006] High heat resistance is required for removable protective sheets. Insufficient heat resistance can lead to problems such as outgassing from the protective sheet during high-temperature treatments such as the reflow process and sputtering process, causing the sheet to lift off the adherend, or leaving adhesive residue on the adherend when peeled off. The sputtering process is a process for coating the periphery of a semiconductor device with a metal film. Therefore, gaps exist between the semiconductor devices, and the metal film is also vapor-deposited onto the protective sheet during sputtering. From the perspective of preventing contamination in the semiconductor manufacturing process, it is desirable for the metal film attached to the protective sheet to remain on the protective sheet even after the semiconductor device is peeled off from the protective sheet.

[0007] However, conventional protective sheets have not satisfied all of the above requirements. For example, in Patent Document 1, adhesive residue may remain on the semiconductor device when the protective sheet is peeled off due to insufficient heat resistance. Furthermore, when the semiconductor device is picked up and peeled off from the protective sheet after the sputtering process is completed, the adhesion between the protective sheet and the metal film is insufficient, and the metal film may detach from the protective sheet, contaminating the semiconductor device or becoming a source of contamination in the semiconductor manufacturing process.

[0008] The present disclosure provides a pressure-sensitive adhesive composition that can be used through various processing steps to form a photocurable pressure-sensitive adhesive layer that adheres to the surface of a semiconductor device, such as a bumped semiconductor chip or bumped PCB, and can be peeled from the semiconductor device after UV irradiation without leaving any adhesive residue, while maintaining excellent adhesion to coated metal films even after UV irradiation. In particular, the present disclosure provides a pressure-sensitive adhesive composition that can be used through a high-temperature treatment process, such as 200°C, to form a photocurable pressure-sensitive adhesive layer that can be peeled from the semiconductor device after UV irradiation without leaving any adhesive residue, while maintaining excellent adhesion to coated metal films even after UV irradiation. The present disclosure also provides a protective sheet that can be used through various processing steps to adhere to the surface of a semiconductor device, such as a bumped semiconductor chip or bumped PCB, and can be peeled from the semiconductor device after UV irradiation without leaving any adhesive residue, while maintaining excellent adhesion to coated metal films even after UV irradiation. Furthermore, the present disclosure provides a method for manufacturing a semiconductor device using the protective sheet.

[0009] The present disclosure includes the following aspects: [1] A pressure-sensitive adhesive composition containing an ethylenically unsaturated group-containing (meth)acrylic resin (A2), a crosslinking agent (B2), and a photopolymerization initiator (C), and containing 1,000 to 100,000 mass ppm of silicon atoms, wherein the ethylenically unsaturated group-containing (meth)acrylic resin (A2) has a plurality of functional groups that react with functional groups contained in the crosslinking agent (B2), and the ethylenically unsaturated group-containing (meth)acrylic resin (A2) is an adduct of an epoxy group-containing ethylenically unsaturated compound (a2-3) to a (meth)acrylic resin (A2-0) containing at least an alkyl (meth)acrylate (a2-1) and a carboxy group-containing ethylenically unsaturated compound (a2-2) as raw material monomers. [2] The pressure-sensitive adhesive composition according to [1], wherein the ethylenically unsaturated group-containing (meth)acrylic resin (A2) is an adduct of an epoxy group-containing ethylenically unsaturated compound (a2-3) with a (meth)acrylic resin (A2-0) containing, as raw material monomers, at least an alkyl(meth)acrylate (a2-1), a carboxy group-containing ethylenically unsaturated compound (a2-2), and a silicon-containing ethylenically unsaturated compound (a2-4). [3] The pressure-sensitive adhesive composition according to [1] or [2], further comprising a silicon-containing photocurable compound (D). [4] The pressure-sensitive adhesive composition according to any one of [1] to [3], wherein the ethylenically unsaturated group-containing (meth)acrylic resin (A2) has an acid value of 1 to 100 mgKOH / g. [5] The pressure-sensitive adhesive composition according to any one of [1] to [4], wherein the ethylenically unsaturated group-containing (meth)acrylic resin (A2) has an ethylenically unsaturated group equivalent of 500 to 5,000 g / mol. [6] The pressure-sensitive adhesive composition according to any one of [1] to [5], wherein the glass transition temperature (Tg) of the ethylenically unsaturated group-containing (meth)acrylic resin (A2) is −80 to 0° C. [7] The pressure-sensitive adhesive composition according to any one of [1] to [6], wherein the crosslinking agent (B2) is at least one selected from the group consisting of epoxy crosslinking agents and aziridine crosslinking agents. [8] The pressure-sensitive adhesive composition according to any one of [1] to [7], wherein the content of the carboxy group-containing ethylenically unsaturated compound (a2-2) is 1 to 60 mol % based on the total raw material monomers of the (meth)acrylic resin (A2-0).[9] The pressure-sensitive adhesive composition according to any one of [2] to [8], wherein the content of the silicon-containing ethylenically unsaturated compound (a2-4) is 0.01 to 10 mol % relative to the total raw material monomers of the (meth)acrylic resin (A2-0).

[10] The pressure-sensitive adhesive composition according to any one of [1] to [9], wherein the content of the alkyl (meth)acrylate (a2-1) is 30 to 99 mol % relative to the total raw material monomers of the (meth)acrylic resin (A2-0).

[11] The pressure-sensitive adhesive composition according to any one of [1] to

[10] , wherein the amount of the epoxy group-containing ethylenically unsaturated compound (a2-3) is 0.5 to 55 mol relative to 100 mol of the total raw material monomers of the (meth)acrylic resin (A2-0), and wherein the addition rate of the epoxy group-containing ethylenically unsaturated compound (a2-3) to the carboxy groups derived from the carboxy group-containing ethylenically unsaturated compound (a2-2) is 10 to 99%.

[12] A protective sheet comprising a substrate and a photocurable pressure-sensitive adhesive layer that is a thermally cured product of the pressure-sensitive adhesive composition according to any one of [1] to

[11] .

[13] The protective sheet according to

[12] , comprising the substrate and, on one main surface of the substrate, an intermediate layer and the photocurable pressure-sensitive adhesive layer, in this order.

[14] The protective sheet according to

[13] , wherein the intermediate layer has a thickness of 30 to 600 μm, the photocurable pressure-sensitive adhesive layer has a thickness of 1 to 100 μm, and the thickness ratio of the intermediate layer to the photocurable pressure-sensitive adhesive layer (intermediate layer / photocurable pressure-sensitive adhesive layer) is 1 to 50.

[15] The protective sheet according to

[13] or

[14] , wherein the intermediate layer is a thermosetting product of a resin composition containing an ethylenically unsaturated group-free (meth)acrylic resin (A1) and a crosslinking agent (B1), and the ethylenically unsaturated group-free (meth)acrylic resin (A1) has a plurality of functional groups that react with functional groups contained in the crosslinking agent (B1).

[16] A method for manufacturing a semiconductor device having bump electrodes, comprising: a protecting step of attaching the photo-curable adhesive layer surface of the protective sheet according to any one of

[12] to

[15] to a surface of a semiconductor device having bump electrodes, an active energy ray irradiation step of irradiating the protective sheet with active energy rays to photo-cure the photo-curable adhesive layer, a heating step of the semiconductor device having the protective sheet attached thereto, and a peeling step of peeling the protective sheet from the surface of the semiconductor device having bump electrodes.

[17] The method for manufacturing a semiconductor device according to

[16] , wherein d / H is 1.00 to 100, where H [μm] is the height of the bump electrode and d [μm] is the total thickness of the intermediate layer and the photo-curable adhesive layer.

[18] The method for manufacturing a semiconductor device according to

[16] or

[17] , wherein the maximum temperature reached in the heating step is 80 to 300°C.

[0010] According to the present disclosure, it is possible to provide a pressure-sensitive adhesive composition that can be used through various processing steps to form a photocurable pressure-sensitive adhesive layer that can be peeled from the semiconductor device without leaving any adhesive residue after UV irradiation, while maintaining excellent adhesion to coated metal films even after UV irradiation. In particular, it is possible to provide a pressure-sensitive adhesive composition that can be used through a high-temperature treatment process, such as 200°C, to form a photocurable pressure-sensitive adhesive layer that can be peeled from the semiconductor device without leaving any adhesive residue after UV irradiation, while maintaining excellent adhesion to coated metal films even after UV irradiation. According to the present disclosure, it is possible to provide a protective sheet that can be used through various processing steps to form a photocurable pressure-sensitive adhesive layer that can be peeled from the semiconductor device without leaving any adhesive residue after UV irradiation, while maintaining excellent adhesion to coated metal films even after UV irradiation. Furthermore, it is possible to provide a method for manufacturing a semiconductor device using the protective sheet.

[0011] The adhesive strength of the photocurable pressure-sensitive adhesive layer of the protective sheet is reduced by irradiation with active energy rays. Specifically, the photocurable pressure-sensitive adhesive layer exhibits sufficient adhesive strength to the adherend before irradiation with active energy rays, and after irradiation with active energy rays, the unsaturated bonds in the resin form a three-dimensional crosslinked structure and harden, thereby reducing the adhesive strength and exhibiting excellent releasability, and sufficient prevention of adhesive residue on the adherend after peeling. On the other hand, even when the adhesive strength of the photocurable pressure-sensitive adhesive layer of the protective sheet is reduced by irradiation with active energy rays, the pressure-sensitive adhesive layer still maintains a certain degree of adhesion to the metal film. Therefore, the amount of metal film coated on the photocurable pressure-sensitive adhesive layer that detaches after irradiation with active energy rays can be reduced, thereby reducing metal contamination in semiconductor processes.

[0012] FIG. 1 is a schematic cross-sectional view of a protective sheet in one embodiment.

[0013] Hereinafter, embodiments of the present invention will be described in detail, but the present invention is not limited to the embodiments described below.

[0014] In this specification, when "to" is used to describe a numerical range, the numerical values ​​at both ends are the upper and lower limits, respectively, and are included in the numerical range. When multiple upper or lower limits are listed, numerical ranges can be created using all combinations of the upper and lower limits. Similarly, when multiple numerical ranges are listed, separate numerical ranges can be created by individually selecting and combining the upper and lower limits from those numerical ranges.

[0015] In the present disclosure, (meth)acrylic means "acrylic" or "methacrylic", (meth)acrylate means "acrylate" or "methacrylate", and (meth)acryloyloxy means "acryloyloxy" or "methacryloyloxy".

[0016] In the present disclosure, the term "ethylenically unsaturated bond" refers to a double bond formed between carbon atoms excluding carbon atoms forming an aromatic ring, the term "ethylenically unsaturated group" refers to a group having an ethylenically unsaturated bond, and the term "ethylenically unsaturated compound" refers to a compound having an ethylenically unsaturated bond.

[0017] In the present disclosure, the "weight average molecular weight (Mw)" and "number average molecular weight (Mn)" are values ​​measured using gel permeation chromatography (GPC) under the following conditions at room temperature (23°C) and determined using a standard polystyrene calibration curve. Apparatus: Shodex™ GPC-101 (Resonac Inc.) Column: Shodex™ LF-804 (Resonac Inc.) Column temperature: 40°C Sample: 0.2% by mass solution of sample in tetrahydrofuran Flow rate: 1 mL / min Eluent: tetrahydrofuran Detector: RI detector

[0018] In the present disclosure, the glass transition temperature (Tg) of a (meth)acrylic resin refers to a value obtained by converting the glass transition temperature Tga in absolute temperature, which is obtained using the FOX equation (Fox, T. G., Bull. Am. Phys. Soc., 1 (1956), p. 123) of the following formula (1), into Celsius temperature: 1 / Tga=Σi(Wi / Tgi) (1) (In formula (1), Tga is the glass transition temperature (unit: absolute temperature) of the (meth)acrylic resin. Wi is the mass proportion of each monomer i in the (meth)acrylic resin. Tgi is the glass transition temperature (unit: absolute temperature) of a homopolymer formed only from each monomer i.)

[0019] In the present disclosure, the "acid value (mg KOH / g)" is a value measured in accordance with JIS K 0070:1992.

[0020] In the present disclosure, the "hydroxyl value (mg KOH / g)" is a value measured in accordance with JIS K 0070:1992.

[0021] In the present disclosure, the "ethylenically unsaturated group equivalent (g / mol)" is a value calculated from the iodine value measured in accordance with JIS K 0070:1992.

[0022] [Adhesive Composition] The adhesive composition contains an ethylenically unsaturated group-containing (meth)acrylic resin (A2), a crosslinking agent (B2), and a photopolymerization initiator (C). The ethylenically unsaturated group-containing (meth)acrylic resin (A2) has multiple functional groups that react with functional groups contained in the crosslinking agent (B2). The ethylenically unsaturated group-containing (meth)acrylic resin (A2) is an adduct of an epoxy group-containing ethylenically unsaturated compound (a2-3) to a (meth)acrylic resin (A2-0) having as raw material monomers at least an alkyl (meth)acrylate (a2-1) and a carboxy group-containing ethylenically unsaturated compound (a2-2). The adhesive composition contains 1,000 to 100,000 ppm by mass of silicon atoms. The adhesive composition forms a photocurable adhesive layer, described below, by thermal curing. In the photocurable pressure-sensitive adhesive layer, irradiation with active energy rays such as ultraviolet rays decomposes the photopolymerization initiator (C), causing the ethylenically unsaturated groups in the ethylenically unsaturated group-containing (meth)acrylic resin (A2) to initiate radical polymerization, thereby forming a further crosslinked structure, i.e., photocuring. By having a photocurable pressure-sensitive adhesive layer, the protective sheet exhibits good adhesion to the adherend without causing lifting, even when subjected to various processing steps while attached to the adherend. Furthermore, after the processing steps are completed, irradiation with active energy rays reduces the peel strength of the photocurable pressure-sensitive adhesive layer, allowing the pressure-sensitive adhesive layer to be peeled off from the adherend without leaving any adhesive residue. Furthermore, by incorporating silicon atoms into the photocurable pressure-sensitive adhesive layer, the adhesion between the pressure-sensitive adhesive layer and metal can be improved. As a result, even after forming a metal film by a coating process such as sputtering and then irradiating it with active energy rays, the metal film can be prevented from detaching from the protective sheet and contaminating the adherend or becoming a source of contamination in the semiconductor manufacturing process.

[0023] The silicon atom content of the pressure-sensitive adhesive composition is 1,000 ppm by mass or more, preferably 2,000 ppm by mass or more, and more preferably 3,000 ppm by mass or more. The silicon atom content of the pressure-sensitive adhesive composition is 100,000 ppm by mass or less, preferably 80,000 ppm by mass or less, and more preferably 50,000 ppm by mass or less. A silicon atom content of 1,000 ppm by mass or more improves adhesion between the photocurable pressure-sensitive adhesive layer and the metal film coated thereon, reducing contamination sources derived from the metal film in the semiconductor manufacturing process and reducing metal contamination of electronic components. A silicon atom content of 100,000 ppm by mass or less ensures sufficient adhesive strength of the protective sheet. The silicon atom content of the pressure-sensitive adhesive composition is preferably 2,000 to 80,000 ppm by mass, more preferably 3,000 to 50,000 ppm by mass.

[0024] The silicon atom content (mass) of the pressure-sensitive adhesive composition is a calculated value calculated from the amounts of raw materials charged. In the present disclosure, the silicon atom content of the pressure-sensitive adhesive composition means the silicon atom content relative to the total amount of components excluding the solvent.

[0025] Silicon can be introduced into the pressure-sensitive adhesive composition by, for example, using the silicon-containing ethylenically unsaturated compound (a2-4) as a raw material monomer for the (meth)acrylic resin (A2-0), adding the silicon-containing photocurable compound (D) to the pressure-sensitive adhesive composition, or both.

[0026] (Ethylenically Unsaturated Group-Containing (Meth)acrylic Resin (A2)) The ethylenically unsaturated group-containing (meth)acrylic resin (A2) is not particularly limited, as long as it is an adduct of an epoxy group-containing ethylenically unsaturated compound (a2-3) with a (meth)acrylic resin (A2-0) containing at least an alkyl (meth)acrylate (a2-1) and a carboxy group-containing ethylenically unsaturated compound (a2-2) as raw material monomers. The present inventors have found that the ethylenically unsaturated group-containing (meth)acrylic resin (A2) is less likely to leave adhesive residue on an adherend than a resin in which an ethylenically unsaturated group is introduced into the side chain of the (meth)acrylic resin using a compound having an isocyanato group. This is thought to be because, when an ethylenically unsaturated group is introduced into the side chain of the (meth)acrylic resin using a compound having an isocyanato group, the urethane bond formed during the reaction between the compound having an isocyanato group and the (meth)acrylic resin is cleaved during the heating process, resulting in the compound separating from the (meth)acrylic resin and leaving adhesive residue. On the other hand, by forming a photocurable pressure-sensitive adhesive layer using an ethylenically unsaturated group-containing (meth)acrylic resin (A2), which is an adduct of an epoxy group-containing ethylenically unsaturated compound (a2-3) to a (meth)acrylic copolymer having a carboxy group, the protective sheet has high heat resistance and maintains high adhesion to the adherend even when exposed to high temperature conditions from the step of attaching to the adherend, to the processing step, and the peeling step. In addition, when peeling the protective sheet from the adherend after the processing step, good peelability can be obtained by irradiating with active energy rays.

[0027] The raw material monomers for the (meth)acrylic resin (A2-0) include at least an alkyl (meth)acrylate (a2-1) and a carboxy group-containing ethylenically unsaturated compound (a2-2). The alkyl (meth)acrylate (a2-1) is preferably at least one selected from 2-ethylhexyl (meth)acrylate and n-butyl (meth)acrylate. The total content of 2-ethylhexyl (meth)acrylate and n-butyl (meth)acrylate relative to the total raw material monomers for the (meth)acrylic resin (A2-0) is preferably 30 mol % or more, more preferably 40 mol % or more, and even more preferably 55 mol % or more. The upper limit of the total content of 2-ethylhexyl (meth)acrylate and n-butyl (meth)acrylate relative to the total raw material monomers of the (meth)acrylic resin (A2-0) is not particularly limited, and may be, for example, 99 mol %, 90 mol %, or 80 mol %.

[0028] Examples of the functional group contained in the ethylenically unsaturated group-containing (meth)acrylic resin (A2) that can react with the functional group contained in the crosslinking agent (B2) include a carboxy group when the functional group contained in the crosslinking agent (B2) is at least one selected from the group consisting of an epoxy group, an aziridinyl group, and a hydroxy group. For example, when the functional group contained in the crosslinking agent (B2) is a hydroxy group, examples of the functional group that can react with the functional group contained in the crosslinking agent (B2) include an isocyanato group, a carboxy group, etc.

[0029] In one embodiment, a silicon-containing ethylenically unsaturated compound (a2-4) may also be used as a raw material monomer for the (meth)acrylic resin (A2-0). By adjusting the content of the silicon-containing ethylenically unsaturated compound (a2-4), the silicon atom content of the photocurable pressure-sensitive adhesive layer can be adjusted, thereby achieving a balance between adhesive strength to the adherend and adhesion to the metal film, and obtaining a protective sheet with a reduced amount of metal film detachment.

[0030] The ethylenically unsaturated group-containing (meth)acrylic resin (A2) may be used alone or in combination of two or more kinds.

[0031] The glass transition temperature (Tg) of the ethylenically unsaturated group-containing (meth)acrylic resin (A2) is preferably −80° C. or higher, more preferably −70° C. or higher, and even more preferably −60° C. or higher. The glass transition temperature (Tg) of the ethylenically unsaturated group-containing (meth)acrylic resin (A2) is preferably 0° C. or lower, more preferably −10° C. or lower, and even more preferably −20° C. or lower. When the glass transition temperature is −80° C. or higher, a photocurable pressure-sensitive adhesive layer with high cohesive strength is obtained, thereby preventing elution of the resin during sheet molding. When the glass transition temperature is 0° C. or lower, the adhesion between the substrate or intermediate layer and the photocurable pressure-sensitive adhesive layer is further improved.

[0032] The weight-average molecular weight of the ethylenically unsaturated group-containing (meth)acrylic resin (A2) is preferably 100,000 to 2,000,000, more preferably 150,000 to 1,500,000, and even more preferably 200,000 to 1,000,000. When the weight-average molecular weight is 100,000 or more, a photocurable pressure-sensitive adhesive layer with high cohesive strength can be obtained, and resin elution during sheet formation can be prevented. When the weight-average molecular weight is 2,000,000 or less, forming and processing are easy.

[0033] The ethylenically unsaturated group equivalent of the ethylenically unsaturated group-containing (meth)acrylic resin (A2) is preferably 500 g / mol or more, more preferably 550 g / mol or more, and even more preferably 600 g / mol or more. The ethylenically unsaturated group equivalent of the ethylenically unsaturated group-containing (meth)acrylic resin (A2) is preferably 5000 g / mol or less, more preferably 4000 g / mol or less, and even more preferably 2000 g / mol or less. The ethylenically unsaturated group equivalent of the ethylenically unsaturated group-containing (meth)acrylic resin (A2) may be 1500 g / mol or less, or may be 1000 g / mol or less. When the ethylenically unsaturated group equivalent is within the above range, sufficient curability can be imparted.

[0034] The acid value of the ethylenically unsaturated group-containing (meth)acrylic resin (A2) is preferably 1 mgKOH / g or more, more preferably 5 mgKOH / g or more, and even more preferably 10 mgKOH / g or more. The acid value of the ethylenically unsaturated group-containing (meth)acrylic resin (A2) is preferably 100 mgKOH / g or less, more preferably 50 mgKOH / g or less, and even more preferably 35 mgKOH / g or less. When the acid value is 1 mgKOH / g or more, the resin can sufficiently react with a crosslinking agent having a functional group reactive with an acid group, resulting in a photocurable pressure-sensitive adhesive layer with high cohesive strength. When the acid value is 100 mgKOH / g or less, the cohesive strength of the resulting resin is not too high, resulting in good handleability.

[0035] The content of the alkyl (meth)acrylate (a2-1) relative to the total raw material monomers of the (meth)acrylic resin (A2-0) is preferably 30 mol% or more, more preferably 40 mol% or more, and even more preferably 55 mol% or more. The content of the alkyl (meth)acrylate (a2-1) relative to the total raw material monomers of the (meth)acrylic resin (A2-0) is preferably 99 mol% or less, more preferably 90 mol% or less, and even more preferably 85 mol% or less. When the content of the alkyl (meth)acrylate (a2-1) is 30 mol% or more, adhesion between the substrate or intermediate layer and the photocurable pressure-sensitive adhesive layer is good. When the content of the alkyl (meth)acrylate (a2-1) is 99 mol% or less, the content of the carboxy group-containing ethylenically unsaturated compound (a2-2) can be sufficiently ensured, thereby ensuring a sufficient amount of crosslinking with the crosslinking agent (B2), and improving the cohesive strength of the photocurable pressure-sensitive adhesive layer. Additionally, because a sufficient amount of ethylenically unsaturated groups can be introduced, the peel strength of the protective sheet can be sufficiently reduced when irradiated with active energy rays.

[0036] The content of the carboxyl group-containing ethylenically unsaturated compound (a2-2) relative to the total raw material monomers of the (meth)acrylic resin (A2-0) is preferably 1 mol% or more, more preferably 5 mol% or more, and even more preferably 10 mol% or more. The content of the carboxyl group-containing ethylenically unsaturated compound (a2-2) relative to the total raw material monomers of the (meth)acrylic resin (A2-0) is preferably 60 mol% or less, more preferably 50 mol% or less, and even more preferably 40 mol% or less. When the content of the carboxyl group-containing ethylenically unsaturated compound (a2-2) is 1 mol% or more, a sufficient amount of crosslinking with the crosslinking agent (B2) is ensured, improving the cohesive strength of the photocurable pressure-sensitive adhesive layer. In addition, a sufficient amount of ethylenically unsaturated groups can be introduced by the addition reaction of the epoxy group-containing ethylenically unsaturated compound (a2-3), thereby sufficiently reducing the peel strength of the protective sheet when irradiated with active energy rays.

[0037] The amount of the epoxy group-containing ethylenically unsaturated compound (a2-3) is preferably 0.5 mol or more, more preferably 3 mol or more, and even more preferably 5 mol or more, relative to a total of 100 mol of the raw material monomers of the (meth)acrylic resin (A2-0). The amount of the epoxy group-containing ethylenically unsaturated compound (a2-3) is preferably 55 mol or less, more preferably 45 mol or less, and even more preferably 35 mol or less, relative to a total of 100 mol of the raw material monomers of the (meth)acrylic resin (A2-0). The addition rate of the epoxy group-containing ethylenically unsaturated compound (a2-3) relative to the carboxy groups derived from the carboxy group-containing ethylenically unsaturated compound (a2-2) is preferably 10% or more, more preferably 20% or more, and even more preferably 40% or more. The addition rate of the epoxy group-containing ethylenically unsaturated compound (a2-3) to the carboxy groups derived from the carboxy group-containing ethylenically unsaturated compound (a2-2) is preferably 99% or less, more preferably 95% or less, and even more preferably 90% or less. By setting it within the above range, it is possible to ensure a sufficient amount of ethylenically unsaturated groups introduced while ensuring the amount of crosslinking with the crosslinking agent (B2).

[0038] As a raw material monomer for the (meth)acrylic resin (A2-0), at least one selected from the group consisting of silicon-containing ethylenically unsaturated compounds (a2-4) and other monomers (a2-5) may be used, if necessary.

[0039] When a silicon-containing ethylenically unsaturated compound (a2-4) is used as a raw material monomer for the (meth)acrylic resin (A2-0), its content is preferably 0.01 mol% or more, more preferably 0.02 mol% or more, and even more preferably 0.1 mol% or more, based on the total amount of raw material monomers. When a silicon-containing ethylenically unsaturated compound (a2-4) is used as a raw material monomer for the (meth)acrylic resin (A2-0), its content is preferably 10 mol% or less, more preferably 5 mol% or less, and even more preferably 1 mol% or less, based on the total amount of raw material monomers. When the content of the silicon-containing ethylenically unsaturated compound (a2-4) is 0.01 mol% or more, the adhesion between the photocurable pressure-sensitive adhesive layer and a metal film formed by a coating treatment such as sputtering is improved. When the content of the silicon-containing ethylenically unsaturated compound (a2-4) is 10 mol % or less, sufficient adhesion can be ensured between the photocurable pressure-sensitive adhesive layer and the substrate, or between the photocurable pressure-sensitive adhesive layer and the intermediate layer.

[0040] When the other monomer (a2-5) is used as a raw material monomer for the (meth)acrylic resin (A2-0), the content thereof is preferably 0.1 to 30 mol %, more preferably 0.1 to 20 mol %, and even more preferably 0.1 to 10 mol %, based on the total amount of the raw material monomers.

[0041] The alkyl(meth)acrylate (a2-1) is not particularly limited as long as it is a compound that does not have a functional group such as a hydroxy group or a carboxy group and a silicon atom, but has an alkyl group and a (meth)acryloyloxy group. Specific examples include linear or branched alkyl(meth)acrylates such as methyl(meth)acrylate, ethyl(meth)acrylate, n-propyl(meth)acrylate, n-butyl(meth)acrylate, tert-butyl(meth)acrylate, isobutyl(meth)acrylate, 2-ethylhexyl(meth)acrylate, isodecyl(meth)acrylate, n-hexyl(meth)acrylate, isooctyl(meth)acrylate, and lauryl(meth)acrylate; and cyclic alkyl group-containing (meth)acrylates such as cyclohexyl(meth)acrylate, isobornyl(meth)acrylate, dicyclopentanyl(meth)acrylate, and dicyclopentanyloxyethyl(meth)acrylate. Among these, at least one selected from methyl (meth)acrylate, ethyl (meth)acrylate, n-butyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, and isooctyl (meth)acrylate is preferred, and at least one selected from n-butyl (meth)acrylate and 2-ethylhexyl (meth)acrylate is more preferred. From the viewpoint of step-conforming ability, it is preferred to use a linear or branched alkyl (meth)acrylate in which the alkyl group has 4 to 20 carbon atoms, more preferred to use a linear or branched alkyl (meth)acrylate in which the alkyl group has 4 to 12 carbon atoms, and even more preferred to use at least one selected from n-butyl (meth)acrylate, tert-butyl (meth)acrylate, isobutyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, and lauryl (meth)acrylate. The alkyl (meth)acrylate (a2-1) may be used alone or in combination of two or more kinds.

[0042] The carboxy group-containing ethylenically unsaturated compound (a2-2) is not particularly limited as long as it is a compound having a carboxy group and an ethylenically unsaturated group. The ethylenically unsaturated group is preferably a (meth)acryloyloxy group. Specific examples include (meth)acrylic acid, carboxymethyl (meth)acrylate, and β-carboxyethyl (meth)acrylate. From the viewpoint of ease of polymerization, (meth)acrylic acid is preferred. The carboxy group-containing ethylenically unsaturated compound (a2-2) may be used alone or in combination of two or more.

[0043] The epoxy group-containing ethylenically unsaturated compound (a2-3) is not particularly limited as long as it does not have a carboxy group and has an epoxy group and an ethylenically unsaturated group. In the present disclosure, the term "epoxy group-containing ethylenically unsaturated compound" also encompasses ethylenically unsaturated compounds containing an oxetane ring instead of an epoxy group. Specific examples include glycidyl (meth)acrylate, 4-hydroxybutyl (meth)acrylate glycidyl ether, 3,4-epoxycyclohexylmethyl (meth)acrylate, 3,4-epoxycyclohexane-1-allyl carboxylate, 3,4-epoxytricyclo[5.2.1.0]propanol ... ２，６ ]decaneoxyethyl acrylate, (3-ethyloxetan-3-yl)methyl (meth)acrylate, etc. Among these, glycidyl (meth)acrylate is preferred from the viewpoint of ease of synthesis, and 3,4-epoxycyclohexylmethyl (meth)acrylate is preferred from the viewpoint of heat resistance. The epoxy group-containing ethylenically unsaturated compound (a2-3) may be used alone or in combination of two or more types.

[0044] The silicon-containing ethylenically unsaturated compound (a2-4) is not particularly limited as long as it does not have a carboxy group and has a silicon atom and an ethylenically unsaturated group. The ethylenically unsaturated group is preferably a (meth)acryloyloxy group. The silicon-containing ethylenically unsaturated compound (a2-4) is preferably at least one selected from the group consisting of [(meth)acryloyloxy]alkyltrialkoxysilane, [[(meth)acryloyloxy]alkyl]alkyldialkoxysilane, and a silicone compound having a polydimethylsiloxane skeleton in its molecular structure and a methacryloyloxy group at one end, and more preferably a silicone compound having a polydimethylsiloxane skeleton in its molecular structure and a methacryloyloxy group at one end. Specific examples of the silicon-containing ethylenically unsaturated compound (a2-4) include [(meth)acryloyloxy]alkyltrialkoxysilanes and [(meth)acryloyloxy]propylsilanes such as [(meth)acryloyloxy]methyltriethoxysilane, [(meth)acryloyloxy]ethyltriethoxysilane, [(meth)acryloyloxy]propyltrimethoxysilane, [(meth)acryloyloxy]propyltriethoxysilane, [(meth)acryloyloxy]octyltrimethoxysilane, and [(meth)acryloyloxy]octyltriethoxysilane. [(meth)acryloyloxy]alkyl]alkyldialkoxysilanes such as [(meth)acryloyloxy]propylmethyldimethoxysilane, [(meth)acryloyloxy]propylmethyldiethoxysilane, [(meth)acryloyloxy]ethylmethyldiethoxysilane, and [(meth)acryloyloxy]nonylmethyldiethoxysilane; p-styryltrimethoxysilane; methacryloyloxypropyltris(trimethylsilyloxy)silane; and silicone compounds having a polydimethylsiloxane skeleton in the molecular structure and one terminal end being a methacryloyloxy group.

[0045] As the silicon-containing ethylenically unsaturated compound (a2-4), commercially available products can be used. For example, "X-22-174ASX", "X-22-174BX", "X-22-2404", "KF-2012" (all of which are single-terminated methacrylic-modified silicone oils, Shin-Etsu Chemical Co., Ltd.), "FM-0711", "FM-0721", "FM-0725" (all of which are Silaplane, JNC Corporation), and the like, have a polydimethylsiloxane skeleton in their molecular structure, Examples of suitable silane coupling agents include silicone compounds having a methacryloyloxy group at one end; "TM-0701T" (Silaplane, JNC Corporation); silane coupling agents having a trialkoxysilyl group in the molecular structure, such as "KBE-503," "KBM-503," "KBM-5103," "KBM-5803," and "KBM-1403"; and silane coupling agents having an alkyldialkoxysilyl group in the molecular structure, such as "KBE-502" and "KBM-502." Among these, from the perspective of reactivity, it is preferable to use at least one selected from "X-22-174ASX," "KF-2012," "FM-0711," "FM-0721," and "FM-0725." In the present disclosure, a silane coupling agent is a compound having a hydrolyzable silyl group and a reactive organic functional group. The silicon-containing ethylenically unsaturated compound (a2-4) may be used alone or in combination of two or more.

[0046] The other monomer (a2-5) other than (a2-1), (a2-2), and (a2-4) is not particularly limited as long as it is a compound other than (a2-1), (a2-2), and (a2-4) and has an ethylenically unsaturated group copolymerizable therewith. Examples include hydroxy group-containing (meth)acrylates, alkoxyalkyl (meth)acrylates, alkoxy(poly)alkylene glycol (meth)acrylates, aromatic group-containing (meth)acrylates, fluorinated alkyl (meth)acrylates, dialkylaminoalkyl (meth)acrylates, and (meth)acrylamide compounds. The other monomer (a2-5) may be used alone or in combination of two or more.

[0047] The hydroxy group-containing (meth)acrylate is not particularly limited as long as it is a compound having a hydroxy group and a (meth)acryloyloxy group. Specific examples include 2-hydroxyethyl (meth)acrylate, 2-hydroxypropyl (meth)acrylate, 3-hydroxypropyl (meth)acrylate, 4-hydroxybutyl (meth)acrylate, 1,3-butanediol (meth)acrylate, 1,4-butanediol (meth)acrylate, 1,6-hexanediol (meth)acrylate, and 3-methylpentanediol (meth)acrylate. From the viewpoint of conformability to uneven surfaces, hydroxyalkyl (meth)acrylates having a hydroxy group at the terminal of a linear alkyl group are preferred, and at least one selected from 2-hydroxyethyl (meth)acrylate, 3-hydroxypropyl (meth)acrylate, and 4-hydroxybutyl (meth)acrylate are more preferred.

[0048] Examples of alkoxyalkyl (meth)acrylates include ethoxyethyl (meth)acrylate, methoxyethyl (meth)acrylate, and butoxyethyl (meth)acrylate.

[0049] Examples of alkoxy(poly)alkylene glycol (meth)acrylates include methoxydiethylene glycol (meth)acrylate, ethoxydiethylene glycol (meth)acrylate, 2-methoxyethoxyethyl (meth)acrylate, and methoxydipropylene glycol (meth)acrylate. (Poly)alkylene means "alkylene" or "polyalkylene."

[0050] Examples of aromatic group-containing (meth)acrylates include benzyl (meth)acrylate, phenoxyethyl (meth)acrylate, phenoxydiethylene glycol (meth)acrylate, 3-phenoxyphenyl acrylate, 4-phenoxyphenyl acrylate, 2-biphenyl acrylate, 4-biphenyl acrylate, phenoxypolyethylene glycol (meth)acrylate, phenoxypropyl (meth)acrylate, and phenoxypolypropylene glycol (meth)acrylate.

[0051] An example of the fluorinated alkyl(meth)acrylate is octafluoropentyl(meth)acrylate.

[0052] Examples of dialkylaminoalkyl(meth)acrylates include N,N-dimethylaminoethyl(meth)acrylate and N,N-diethylaminoethyl(meth)acrylate.

[0053] Examples of the (meth)acrylamide compound include (meth)acrylamide; N-alkyl(meth)acrylamides such as N-methyl(meth)acrylamide, N-ethyl(meth)acrylamide, N-propyl(meth)acrylamide, N-isopropylacrylamide, and N-hexyl(meth)acrylamide; N,N-dialkyl(meth)acrylamides such as N,N-dimethyl(meth)acrylamide and N,N-diethyl(meth)acrylamide; (meth)acryloylmorpholine; and diacetone acrylamide.

[0054] Other specific examples of the other monomer (a2-5) include acrylonitrile, methacrylonitrile, styrene, α-methylstyrene, vinyl acetate, vinyl propionate, vinyl stearate, vinyl chloride, vinylidene chloride, alkyl vinyl ethers, vinyl toluene, N-vinylpyridine, N-vinylpyrrolidone, itaconic acid dialkyl esters, fumaric acid dialkyl esters, allyl alcohol, hydroxybutyl vinyl ether, hydroxyethyl vinyl ether, 4-hydroxymethylcyclohexylmethyl vinyl ether, triethylene glycol monovinyl ether, diethylene glycol monovinyl ether, methyl vinyl ketone, allyltrimethylammonium chloride, and dimethylallyl vinyl ketone.

[0055] (Crosslinking Agent (B2)) The crosslinking agent (B2) is not particularly limited as long as it is a compound that does not contain silicon atoms and has multiple functional groups capable of reacting with any of the multiple functional groups contained in the ethylenically unsaturated group-containing (meth)acrylic resin (A2). Since the ethylenically unsaturated group-containing (meth)acrylic resin (A2) has a carboxy group, examples of crosslinking agents that can be used for the crosslinking agent (B2) include epoxy crosslinking agents and aziridine crosslinking agents. When the photocurable pressure-sensitive adhesive layer contains the crosslinking agent (B2), the cohesive strength of the photocurable pressure-sensitive adhesive layer is improved, and adhesive residue when the protective sheet is peeled from the adherend can be reduced. The crosslinking agent (B2) may be used alone or in combination of two or more types.

[0056] The epoxy crosslinking agent is a compound having two or more epoxy groups. Examples include 1,3-bis(N,N'-diglycidylaminomethyl)cyclohexane, bisphenol A-type epoxy resin, N,N'-[1,3-phenylenebis(methylene)]bis[bis(oxiran-2-ylmethyl)amine], ethylene glycol diglycidyl ether, polyethylene glycol diglycidyl ether, glycerin diglycidyl ether, glycerin triglycidyl ether, 1,6-hexanediol diglycidyl ether, trimethylolpropane triglycidyl ether, sorbitol polyglycidyl ether, polyglycerol polyglycidyl ether, pentaerythritol polyglycidyl ether, and diglycerol polyglycidyl ether. The epoxy crosslinking agents may be used alone or in combination of two or more.

[0057] The aziridine crosslinking agent is a compound having two or more aziridinyl groups. Examples thereof include ethylene glycol-bis-[3-(2-aziridinyl)propionate], trimethylolpropane-tris[3-(2-aziridinyl)propionate], trimethylolpropane-tris[3-(1-aziridinyl)propionate], trimethylolpropane-tris[3-(2-methyl-1-aziridinyl)propionate], tetramethylolmethane-tris[3-(2-aziridinyl)propionate], pentaerythritol-tris[ 3-(1-aziridinyl)propionate], N,N'-diphenylmethane-4,4'-bis(1-aziridinecarboxamide), N,N'-hexamethylene-1,6-bis(1-aziridinecarboxamide), tris-2,4,6-(1-aziridinyl)-1,3,5-triazine, tris(1-aziridinyl)phosphine oxide, 2,2-bis(hydroxymethyl)butanol-tris[3-(1-aziridinyl)propionate], etc. The aziridine crosslinking agent may be used alone or in combination of two or more thereof.

[0058] The content of the crosslinking agent (B2) is preferably 0.05 to 30 parts by mass, more preferably 0.1 to 20 parts by mass, and even more preferably 0.1 to 10 parts by mass, relative to 100 parts by mass of the ethylenically unsaturated group-containing (meth)acrylic resin (A2). When the content of the crosslinking agent (B2) is 0.05 parts by mass or more, a three-dimensional crosslinked structure is sufficiently formed in the photocurable pressure-sensitive adhesive layer, resulting in a photocurable pressure-sensitive adhesive layer with sufficiently high cohesive strength. When the content of the crosslinking agent (B2) is 30 parts by mass or less, an appropriate gelation time can be ensured during sheet molding.

[0059] (Photopolymerization initiator (C)) Examples of the photopolymerization initiator (C) include benzophenone, benzil, benzoin, ω-bromoacetophenone, chloroacetone, acetophenone, 2,2-diethoxyacetophenone, 2,2-dimethoxy-2-phenylacetophenone, p-dimethylaminoacetophenone, p-dimethylaminopropiophenone, 2-chlorobenzophenone, 4,4'-dichlorobenzophenone, 4,4'-bisdiethylaminobenzophenone, Michler's ketone, benzoin methyl ether, benzoin isobutyl ether, benzoin-n-butyl ether, benzyl methyl ketal, 1-hydroxycyclohexyl phenyl ketone, 2-hydroxy-2-methyl-1-phenyl-propan-1-one, 1-(4-isopropylphenyl)-2-hydroxy-2-methylpropan-1-one, Examples of the photopolymerization initiator include carbonyl-based photopolymerization initiators such as methyl benzoyl formate, 4'-dimethylaminoacetophenone, and 2-methyl-1-[4-(methylthio)phenyl]-2-morpholinopropan-1-one; sulfide-based photopolymerization initiators such as diphenyl disulfide, dibenzyl disulfide, tetraethyl thiuram disulfide, and tetramethylammonium monosulfide; acyl phosphine oxide-based photopolymerization initiators such as 2,4,6-trimethylbenzoyldiphenylphosphine oxide and 2,4,6-trimethylbenzoylphenylethoxyphosphine oxide; quinone-based photopolymerization initiators such as benzoquinone and anthraquinone; sulfochloride-based photopolymerization initiators; and thioxanthone-based photopolymerization initiators such as thioxanthone, 2-chlorothioxanthone, and 2-methylthioxanthone.

[0060] Among these, it is preferable to use at least one selected from the group consisting of carbonyl-based photopolymerization initiators and acylphosphine oxide-based photopolymerization initiators, from the viewpoint of high sensitivity to ultraviolet light and heat resistance.

[0061] The photopolymerization initiator (C) may be used alone or in combination of two or more kinds.

[0062] The content of the photopolymerization initiator (C) is preferably 0.1 to 10.0 parts by mass, more preferably 0.5 to 5.0 parts by mass, per 100 parts by mass of the ethylenically unsaturated group-containing (meth)acrylic resin (A2). When the content of the photopolymerization initiator (C) is 0.1 parts by mass or more, the photocurable pressure-sensitive adhesive layer can be cured at a sufficiently fast curing rate by irradiation with active energy rays, thereby sufficiently reducing the peel strength of the pressure-sensitive adhesive layer after irradiation with active energy rays. When the content of the photopolymerization initiator (C) is 10.0 parts by mass or less, the pressure-sensitive adhesive layer is less likely to remain on the adherend when the protective sheet is peeled from the adherend. Even if the content of the photopolymerization initiator (C) exceeds 10.0 parts by mass, the effect commensurate with the content of the photopolymerization initiator (C) is not observed, so by setting the content to 10.0 parts by mass or less, the pressure-sensitive adhesive composition can be produced economically.

[0063] (Silicon-Containing Photocurable Compound (D)) The pressure-sensitive adhesive composition or photocurable pressure-sensitive adhesive layer may contain a silicon-containing photocurable compound (D) as needed. The silicon-containing photocurable compound (D) is not particularly limited as long as it is a compound containing a silicon atom and two or more ethylenically unsaturated groups in the molecule. The ethylenically unsaturated group is preferably a (meth)acryloyloxy group. Examples of the silicon-containing photocurable compound (D) include silicone compounds having a polydimethylsiloxane skeleton in the molecular structure and methacryloyloxy groups at both ends; silicone compounds having a polydimethylsiloxane skeleton in the molecular structure and vinyl groups at both ends; bis(divinyl)-terminated polydimethylsiloxane; silicone compounds having two or more acryloyloxy groups such as silicone diacrylate, silicone hexaacrylate, and silicone hexaurethaneacrylate; and silane coupling agents in which the reactive organic functional group has an allyl isocyanurate structure. Among these, from the viewpoint of solubility in the ethylenically unsaturated group-containing (meth)acrylic resin (A2), at least one selected from the group consisting of a silicone compound having a polydimethylsiloxane skeleton in its molecular structure and methacryloyloxy groups at both ends, a silicone diacrylate, and a silicone hexaacrylate is preferred.

[0064] As the silicon-containing photocurable compound (D), commercially available products can also be used, for example, "X-22-164", "X-22-164AS", "X-22-164A", "X-22-164B", "X-22-164C", "X-22-164E", "X-12-1290" (all Shin-Etsu Chemical Co., Ltd.), "FM-7711", "FM-7721", "FM-7725" (all Silaplane, JNC Corporation), "EBECRYL 350", "EBECRYL 1360", "EBECRYL 1365", "KRM8479" (all Daicel Allnex Co., Ltd.), "DMS-V34", "DMS-R11", "DMS-VD11" (all Azumax Corporation), and the like. Among these, from the viewpoint of solubility in the ethylenically unsaturated group-containing (meth)acrylic resin (A2), at least one selected from "X-22-164A," "X-22-164B," "X-22-164C," "X-22-164E," "FM-7721," "FM-7725," "EBECRYL 350," and "EBECRYL 1360" is preferred. The silicon-containing photocurable compound (D) may be used alone or in combination of two or more.

[0065] By adjusting the content of the silicon-containing photocurable compound (D), the content of silicon atoms in the photocurable pressure-sensitive adhesive layer can be adjusted, thereby achieving a balance between adhesion to the adherend and adhesion to the metal film, thereby obtaining a protective sheet with a reduced amount of metal film detachment. The content of the silicon-containing photocurable compound (D) is preferably 0.1 to 20.0 parts by mass, more preferably 0.5 to 10.0 parts by mass, and even more preferably 1.0 to 5.0 parts by mass, per 100 parts by mass of the ethylenically unsaturated group-containing (meth)acrylic resin (A2). When the content of the silicon-containing photocurable compound (D) is 0.1 parts by mass or more, the adhesion between the photocurable pressure-sensitive adhesive layer and the metal film coated thereon is improved. When the content of the silicon-containing photocurable compound (D) is 20.0 parts by mass or less, sufficient adhesive strength of the protective sheet can be obtained.

[0066] (Other Components) The pressure-sensitive adhesive composition may optionally contain other components in addition to the above-described ethylenically unsaturated group-containing (meth)acrylic resin (A2), crosslinking agent (B2), photopolymerization initiator (C), and optional silicon-containing photocurable compound (D). Examples of other components include a tackifier, a solvent, and various additives.

[0067] <<Tackifier>> Conventionally known tackifiers can be used without any particular limitation. Examples of tackifiers include terpene-based tackifier resins, phenol-based tackifier resins, rosin-based tackifier resins, aliphatic petroleum resins, aromatic petroleum resins, copolymer-based petroleum resins, alicyclic petroleum resins, xylene resins, epoxy-based tackifier resins, polyamide-based tackifier resins, ketone-based tackifier resins, and elastomer-based tackifier resins. The tackifiers may be used alone or in combination of two or more.

[0068] When the PSA composition contains a tackifier, the content thereof is preferably 30 parts by mass or less, and more preferably 5 to 20 parts by mass, per 100 parts by mass of the ethylenically unsaturated group-containing (meth)acrylic resin (A2).

[0069] <<Solvent>> A solvent can be used to dilute the pressure-sensitive adhesive composition in order to adjust the viscosity of the pressure-sensitive adhesive composition. For example, when the pressure-sensitive adhesive composition is applied, the viscosity of the pressure-sensitive adhesive composition can be adjusted to an appropriate value using a solvent. The solvent is removed when the photocurable pressure-sensitive adhesive layer is formed.

[0070] Examples of the solvent that can be used include organic solvents such as methyl ethyl ketone, methyl isobutyl ketone, acetone, ethyl acetate, propyl acetate, tetrahydrofuran, dioxane, cyclohexanone, hexane, toluene, xylene, n-propanol, isopropyl alcohol, etc. The solvents may be used alone or in combination of two or more.

[0071] <<Additives>> Examples of additives include plasticizers, surface lubricants, leveling agents, softeners, antioxidants, antiaging agents, ultraviolet absorbers, polymerization inhibitors, benzotriazole-based and other light stabilizers, phosphate ester-based and other flame retardants, surfactants, and antistatic agents.

[0072] [Method for producing ethylenically unsaturated group-containing (meth)acrylic resin (A2)] The method for producing the ethylenically unsaturated group-containing (meth)acrylic resin (A2) is not particularly limited. The ethylenically unsaturated group-containing (meth)acrylic resin (A2) can be obtained, for example, by copolymerizing the raw material monomers of the (meth)acrylic resin (A2-0) by a known polymerization method, and then adding an epoxy group-containing ethylenically unsaturated compound (a2-3) to at least a portion of the carboxy groups of the (meth)acrylic resin (A2-0). Examples of the polymerization method include solution polymerization, emulsion polymerization, bulk polymerization, suspension polymerization, and alternating copolymerization. Among these polymerization methods, solution polymerization is preferred in terms of ease of reaction.

[0073] When the (meth)acrylic resin (A2-0) is produced by solution polymerization, a radical polymerization initiator is used as needed.

[0074] The radical polymerization initiator is not particularly limited, and can be appropriately selected from known initiators. Examples of the radical polymerization initiator include azo-based polymerization initiators such as 2,2'-azobis(isobutyronitrile), 2,2'-azobis(4-methoxy-2,4-dimethylvaleronitrile), 2,2'-azobis(2,4-dimethylvaleronitrile), 2,2'-azobis(2-methylbutyronitrile), 1,1'-azobis(cyclohexane-1-carbonitrile), 2,2'-azobis(2,4,4-trimethylpentane), and dimethyl-2,2'-azobis(2-methylpropionate); and oil-soluble polymerization initiators such as peroxide-based polymerization initiators such as benzoyl peroxide, t-butyl hydroperoxide, di-t-butyl peroxide, t-butyl peroxybenzoate, dicumyl peroxide, 1,1-bis(t-butylperoxy)-3,3,5-trimethylcyclohexane, and 1,1-bis(t-butylperoxy)cyclododecane.

[0075] The radical polymerization initiators may be used alone or in combination of two or more.

[0076] The amount of the radical polymerization initiator used is preferably 0.01 to 5 parts by mass, more preferably 0.02 to 4 parts by mass, and even more preferably 0.03 to 3 parts by mass, per 100 parts by mass of the total of the raw material monomers of the (meth)acrylic resin (A2-0).

[0077] A common solvent can be used as the solvent when producing the (meth)acrylic resin (A2-0) by solution polymerization. Examples of the solvent include esters such as ethyl acetate, propyl acetate, and butyl acetate; aromatic hydrocarbons such as toluene, xylene, and benzene; aliphatic hydrocarbons such as hexane and heptane; alicyclic hydrocarbons such as cyclohexane and methylcyclohexane; ketones such as methyl ethyl ketone and methyl isobutyl ketone; glycols such as ethylene glycol, propylene glycol, and dipropylene glycol; glycol ethers such as methyl cellosolve, propylene glycol monomethyl ether, and dipropylene glycol monomethyl ether; and glycol esters such as ethylene glycol diacetate and propylene glycol monomethyl ether acetate.

[0078] The solvents may be used alone or in combination of two or more.

[0079] When the epoxy group-containing ethylenically unsaturated compound (a2-3) is added to at least a portion of the carboxy groups of the (meth)acrylic resin (A2-0), the temperature of the addition reaction is preferably 80 to 150°C, and particularly preferably 90 to 130°C. When the temperature of the addition reaction is 80°C or higher, a sufficient reaction rate can be obtained. When the temperature of the addition reaction is 150°C or lower, crosslinking of the double bonds due to thermal radical polymerization and the formation of a gel can be prevented. The solvent used in the addition reaction is the same as that described for the solution polymerization method.

[0080] In the addition reaction, a known catalyst can be used as necessary. Examples of the catalyst include primary amines such as n-butylamine, n-hexylamine, benzylamine, diethylenetriamine, triethylenetetramine, and diethylaminopropylamine; tertiary amines such as triethylamine, tributylamine, dimethylbenzylamine, 1,8-diazabicyclo[5.4.0]undec-7-ene, 1,5-diazabicyclo[4.3.0]non-5-ene, and 1,4-diazabicyclo[2.2.2]octane; aromatic amines such as aniline, toluidine, phenylenediamine, diaminodiphenylmethane, and 1,8-diaminonaphthalene; pyridine compounds such as pyridine, 2,6-lutidine, and 4-dimethylaminopyridine; imidazole compounds such as imidazole, 2-methylimidazole, 2-ethylimidazole, and 2-ethyl-4-methylimidazole; tetramethylamine, ... Ammonium salts such as tetramethylammonium chloride, tetramethylammonium bromide, tetrabutylammonium chloride, tetrabutylammonium bromide, tetrabutylammonium iodide, and tetrabutylammonium hydroxide; alkyl ureas such as tetramethylurea; alkyl guanidines such as tetramethylguanidine; phosphine compounds such as triphenylphosphine, dimethylphenylphosphine, tricyclohexylphosphine, tributylphosphine, tris(4-methylphenyl)phosphine, tris(4-methoxyphenyl)phosphine, tris(2,6-dimethylphenyl)phosphine, tris(2,6-dimethoxyphenyl)phosphine, tris(2,4,6-trimethylphenyl)phosphine, and tris(2,4,6-trimethoxyphenyl)phosphine;and phosphonium salts such as tetraphenylphosphonium chloride, tetraphenylphosphonium bromide, tetraphenylphosphonium iodide, tetraphenylphosphonium tetraphenylborate, tetraphenylphosphonium tetrakispentafluorophenylborate, 4-hydroxyphenyl-2-(triphenylphosphonium)phenolate, 4-hydroxyphenyl-2-{tris-(4-methylphenyl)phosphonium}phenolate, benzyltriphenylphosphonium chloride, methyltriphenylphosphonium bromide, ethyltriphenylphosphonium bromide, and butyltriphenylphosphonium bromide. Among these, from the viewpoint of reactivity, it is preferable to use a pyridine compound, an imidazole compound, an ammonium salt, a phosphine compound, or a phosphonium salt.

[0081] The amount of the catalyst used in the addition reaction is preferably 0.01 to 20 parts by mass, more preferably 0.05 to 10 parts by mass, and even more preferably 0.1 to 5 parts by mass, per 100 parts by mass of the total of the (meth)acrylic resin (A2-0) and the epoxy group-containing ethylenically unsaturated compound (a2-3).

[0082] Furthermore, during the addition reaction, a gas having a polymerization-inhibiting effect may be introduced into the reaction system, or a polymerization inhibitor may be added. By introducing a gas having a polymerization-inhibiting effect into the reaction system, or by adding a polymerization inhibitor, gelation during the addition reaction can be prevented.

[0083] Examples of gases that have a polymerization-inhibiting effect include gases that contain oxygen to an extent that does not fall within the explosive range of the substances in the system, such as air.

[0084] The polymerization inhibitor may be any known one and is not particularly limited, but examples thereof include 4-methoxyphenol, hydroquinone, methoquinone, 2,6-di-t-butylphenol, 2,2'-methylenebis(4-methyl-6-t-butylphenol), and phenothiazine. The polymerization inhibitor may be used alone or in combination of two or more.

[0085] The amount of the polymerization inhibitor used is preferably 0.005 to 5 parts by mass, more preferably 0.03 to 3 parts by mass, and even more preferably 0.05 to 1.5 parts by mass, relative to 100 parts by mass of the total of the (meth)acrylic resin (A2-0) and the epoxy group-containing ethylenically unsaturated compound (a2-3). When the amount of the polymerization inhibitor used is 0.005 parts by mass or more, gelation during the addition reaction can be prevented. On the other hand, when the amount of the polymerization inhibitor used is 5 parts by mass or less, sufficient exposure sensitivity of the photocurable pressure-sensitive adhesive layer can be obtained when irradiated with active energy rays.

[0086] It is more preferable to use a gas having a polymerization inhibitor effect in combination with a polymerization inhibitor, since this allows the amount of polymerization inhibitor used to be reduced and the polymerization inhibitor effect to be enhanced.

[0087] [Method for producing pressure-sensitive adhesive composition] The pressure-sensitive adhesive composition can be produced by a conventionally known method, for example, by mixing and stirring the ethylenically unsaturated group-containing (meth)acrylic resin (A2), the crosslinking agent (B2), the photopolymerization initiator (C), and optionally the silicon-containing photocurable compound (D), and other components such as a tackifier, a solvent, and various additives, using a conventionally known method.

[0088] The method for mixing and stirring the components contained in the PSA composition is not particularly limited. Mixing and stirring can be performed using, for example, a stirring device equipped with stirring blades such as a homodisper or paddle blade.

[0089] <Protective Sheet> The protective sheet of one embodiment includes a substrate and a photocurable pressure-sensitive adhesive layer that is a thermosetting product of a pressure-sensitive adhesive composition. Because the protective sheet includes a photocurable pressure-sensitive adhesive layer, it can be peeled off without leaving any adhesive residue after irradiation with active energy rays, even when subjected to a high-temperature treatment process such as 200°C. Furthermore, by incorporating silicon atoms into the pressure-sensitive adhesive layer, the adhesion between the pressure-sensitive adhesive layer and metal can be improved. As a result, even after forming a metal film by a coating process such as sputtering and then irradiating it with active energy rays, the metal film coated on the exposed surface of the protective sheet can be prevented from detaching from the protective sheet and contaminating the adherend or becoming a source of contamination in the semiconductor manufacturing process. The protective sheet may include an intermediate layer between the substrate and the photocurable pressure-sensitive adhesive layer. The protective sheet of one embodiment includes a substrate and, on one main surface of the substrate, an intermediate layer and a photocurable pressure-sensitive adhesive layer, in this order. When the protective sheet has an intermediate layer, even after a high-temperature treatment at, for example, 200°C, the protective sheet adheres to the irregularities on the adherend, suppressing lifting. FIG. 1 is a schematic cross-sectional view of a protective sheet according to one embodiment. The protective sheet 10 includes a substrate 12, an intermediate layer 14 disposed on one main surface of the substrate 12, and a photocurable pressure-sensitive adhesive layer 16 disposed on the intermediate layer 14. In FIG. 1, the intermediate layer 14 is disposed on the upper main surface of the substrate 12. The protective sheet 10 may further include a release sheet 18 disposed on the photocurable pressure-sensitive adhesive layer 16, as needed. The release sheet 18 is attached to the outside of the photocurable pressure-sensitive adhesive layer to protect the surface of the photocurable pressure-sensitive adhesive layer, i.e., the surface that is attached to the adherend, until the protective sheet is used. The protective sheet can be suitably used, for example, as a backgrinding tape or a dicing tape.

[0090] The protective sheet may be used as a protective sheet formed into a shape corresponding to the shape of the adherend by a method such as punching, or as a roll formed by winding and cutting the protective sheet.

[0091] The thickness of the protective sheet depends on the unevenness of the adherend surface, for example, the bump height, but is preferably 36 μm to 1000 μm, more preferably 50 μm to 800 μm, and even more preferably 75 μm to 600 μm. From the viewpoint of more reliably following the unevenness of the adherend surface and ensuring the processing accuracy of the adherend during the processing step, it is preferable that the thickness of the protective sheet be about 1.00 to 100 times the unevenness of the adherend surface.

[0092] The peel strength of the protective sheet depends on the thickness of the protective sheet, the type of adherend, and the type and order of processing steps, but for example, the peel strength before active energy ray irradiation is preferably 2.0 to 25 N / 25 mm, more preferably 3.0 to 20 N / 25 mm, and even more preferably 5.0 to 15 N / 25 mm. If the peel strength before active energy ray irradiation is 2.0 N / 25 mm or more, the adhesive strength to the adherend before active energy ray irradiation is good. If the peel strength before active energy ray irradiation is 25 N / 25 mm or less, it is possible to sufficiently reduce the peel strength during peeling, thereby reducing adhesive residue on the adherend.

[0093] The peel strength of the protective sheet decreases upon irradiation with active energy rays, enabling it to be easily peeled from the adherend in the peeling step without leaving any adhesive residue. The peel strength of the protective sheet after irradiation with active energy rays varies depending on the thickness of the protective sheet, the type of adherend, and the type and order of processing steps, but is preferably, for example, 0.001 to 1.0 N / 25 mm, more preferably 0.005 to 0.75 N / 25 mm, and even more preferably 0.01 to 0.5 N / 25 mm.

[0094] In the present disclosure, peel strength refers to the value measured by a tensile test in the 180° direction at a peel rate of 300 mm / min in an environment of 23°C and 50% humidity in accordance with JIS Z 0237:2009, to measure the peel strength (N / 25 mm) of the protective sheet against the adherend.

[0095] [Substrate] As the substrate, any known sheet-shaped material can be appropriately selected and used. As the substrate, a resin sheet manufactured using a transparent resin material is preferably used.

[0096] Examples of resin materials include polyesters such as polyethylene terephthalate (PET), polybutylene terephthalate (PBT), and polyethylene naphthalate (PEN); polyether ether ketone (PEEK); polyamide (PA); polyimide (PI); polyphenylene sulfide (PPS); and polytetrafluoroethylene (PTFE). Among these resin materials, at least one selected from the group consisting of PET, PEN, PEEK, PA, and PI is preferably used as the resin material, as this provides a sheet with appropriate flexibility and heat resistance. The resin materials may be used alone or in combination of two or more.

[0097] When a resin sheet is used as the substrate, the resin sheet may be a single layer or a multilayer structure of two or more layers, for example, a three-layer structure. In a resin sheet having a multilayer structure, the resin material constituting each layer may be one type or two or more types.

[0098] The thickness of the substrate can be appropriately selected depending on the type of semiconductor processing, the material of the substrate, etc., but may be, for example, 5 μm or more, 10 μm or more, or 20 μm or more, and 300 μm or less, 100 μm or less, or 60 μm or less. When the protective sheet protects a bumped semiconductor chip or bumped flexible printed circuit board (FPC) during a reflow process or a sputtering process and the substrate is a resin sheet, the thickness of the substrate is preferably 5 to 300 μm, more preferably 10 to 300 μm. When the substrate thickness is 5 μm or more, the rigidity of the protective sheet is high. Therefore, when the protective sheet is attached to an adherend such as a semiconductor chip or peeled from the adherend, the protective sheet tends to be less likely to wrinkle or lift. In addition, the protective sheet attached to the adherend can be easily peeled from the adherend, providing good workability. When the substrate thickness is 5 μm or more, the protective sheet is less likely to wrinkle, thereby reducing the detachment of the coated metal film during a sputtering process or the like. When the thickness of the substrate is 300 μm or less, the rigidity of the protective sheet is appropriate and workability is good.

[0099] When a resin sheet is used as the substrate, the substrate can be produced using the above-mentioned resin material by appropriately employing a conventional sheet molding method, such as extrusion molding, T-die molding, inflation molding, uniaxial or biaxial stretching molding, etc.

[0100] The surface of the substrate that comes into contact with the photocurable pressure-sensitive adhesive layer or intermediate layer may be subjected to a surface treatment to improve adhesion between the substrate and the photocurable pressure-sensitive adhesive layer or intermediate layer, such as corona discharge treatment, acid treatment, ultraviolet irradiation treatment, plasma treatment, and primer coating.

[0101] [Photocurable Pressure-Sensitive Adhesive Layer] The photocurable pressure-sensitive adhesive layer is a thermosetting adhesive composition containing an ethylenically unsaturated group-containing (meth)acrylic resin (A2), a crosslinking agent (B2), and a photopolymerization initiator (C), and contains 1,000 to 100,000 ppm by mass of silicon atoms. The thermosetting adhesive is a reaction product between a functional group contained in the ethylenically unsaturated group-containing (meth)acrylic resin (A2) that is reactive with a functional group contained in the crosslinking agent (B2) and a functional group contained in the crosslinking agent (B2), i.e., a crosslinked product, and is not a photocured product formed by the photopolymerization initiator (C). In the photocurable pressure-sensitive adhesive layer, irradiation with active energy rays such as ultraviolet rays decomposes the photopolymerization initiator (C), causing the ethylenically unsaturated groups contained in the ethylenically unsaturated group-containing (meth)acrylic resin (A2) to initiate radical polymerization, forming a further crosslinked structure, i.e., photocuring. By having a photocurable pressure-sensitive adhesive layer, the protective sheet does not lift off and has good adhesion to the adherend even when it undergoes various processing steps while attached to the adherend. Furthermore, after the processing steps are completed, the peel strength of the photocurable pressure-sensitive adhesive layer can be reduced by irradiation with active energy rays, allowing the pressure-sensitive adhesive layer to be peeled off from the adherend without leaving any adhesive residue. Furthermore, by incorporating silicon atoms into the photocurable pressure-sensitive adhesive layer, the adhesion between the pressure-sensitive adhesive layer and metal can be improved. As a result, even after forming a metal film by a coating process such as sputtering and then irradiating it with active energy rays, the coated metal film can be prevented from detaching from the protective sheet and contaminating the adherend or becoming a source of contamination in the semiconductor manufacturing process.

[0102] The silicon atom content of the photocurable pressure-sensitive adhesive layer is 1000 ppm by mass or more, preferably 2000 ppm by mass or more, and more preferably 3000 ppm by mass or more. The silicon atom content of the photocurable pressure-sensitive adhesive layer is 100,000 ppm by mass or less, preferably 80,000 ppm by mass or less, and more preferably 50,000 ppm by mass or less. When the silicon atom content is 1000 ppm by mass or more, the adhesion between the photocurable pressure-sensitive adhesive layer and the metal film coated thereon is improved, reducing contamination sources derived from the metal film in the semiconductor manufacturing process and reducing metal contamination of electronic components. When the silicon atom content is 100,000 ppm by mass or less, sufficient adhesive strength of the protective sheet can be obtained. The silicon atom content of the photocurable pressure-sensitive adhesive layer is preferably 2,000 to 80,000 ppm by mass, and more preferably 3,000 to 50,000 ppm by mass.

[0103] The silicon atom content (mass) of the photocurable pressure-sensitive adhesive layer is a calculated value calculated from the amounts of raw materials charged.

[0104] Silicon can be introduced into the photocurable pressure-sensitive adhesive layer by, for example, using a silicon-containing ethylenically unsaturated compound (a2-4) as a raw material monomer for the (meth)acrylic resin (A2-0), adding a silicon-containing photocurable compound (D) to the pressure-sensitive adhesive composition, or both.

[0105] The thickness of the photocurable pressure-sensitive adhesive layer is preferably 1 μm or more, more preferably 5 μm or more, and even more preferably 10 μm or more. The thickness of the photocurable pressure-sensitive adhesive layer is preferably 100 μm or less, more preferably 50 μm or less, and even more preferably 30 μm or less. When the thickness of the photocurable pressure-sensitive adhesive layer is 1 μm or more, the adhesion to the adherend is good. When the thickness of the photocurable pressure-sensitive adhesive layer is 100 μm or less, the occurrence of adhesive residue can be further suppressed.

[0106] When the protective sheet has an intermediate layer, the thickness ratio of the intermediate layer to the photocurable pressure-sensitive adhesive layer (intermediate layer / photocurable pressure-sensitive adhesive layer) is preferably 1 to 50, more preferably 1 to 40, and even more preferably 1 to 30. When the thickness ratio is within the above range, both the ability to conform to irregularities and heat resistance can be achieved. The thickness ratio of the intermediate layer to the photocurable pressure-sensitive adhesive layer (intermediate layer / photocurable pressure-sensitive adhesive layer) may be 3 to 20, or may be 5 to 15.

[0107] [Method for producing photocurable pressure-sensitive adhesive layer] The photocurable pressure-sensitive adhesive layer can be produced, for example, by the method shown below. First, a pressure-sensitive adhesive composition is applied onto a release sheet, and if a solvent is contained, the composition is heated and dried to remove the solvent, thereby forming a pre-thermally cured photocurable pressure-sensitive adhesive layer. Thereafter, if necessary, a release sheet may be attached to the surface of the pre-thermally cured photocurable pressure-sensitive adhesive layer to be attached to the substrate, intermediate layer, or pre-cured intermediate layer until immediately before lamination onto the substrate, intermediate layer, or pre-cured intermediate layer. The pre-thermally cured photocurable pressure-sensitive adhesive layer may undergo a curing reaction by heat curing the obtained sheet in an oven or the like for a certain period of time, thereby forming a crosslinked structure. The curing reaction may be carried out after laminating the pre-thermally cured photocurable pressure-sensitive adhesive layer to the substrate, intermediate layer, or pre-cured intermediate layer.

[0108] The photocurable pressure-sensitive adhesive layer can also be produced by the following method. The pressure-sensitive adhesive composition is applied directly to a substrate or to an intermediate layer of a sheet having an intermediate layer on one main surface of the substrate. If a solvent is contained, the composition is heated and dried to remove the solvent, thereby forming a pre-thermally cured photocurable pressure-sensitive adhesive layer. Thereafter, if necessary, a release sheet is laminated onto the pre-thermally cured photocurable pressure-sensitive adhesive layer. The resulting sheet is then processed as described above to form a crosslinked structure. When a thermosetting intermediate layer is used, the pressure-sensitive adhesive composition may be applied directly onto the pre-cured intermediate layer of a sheet having a pre-cured intermediate layer on one main surface of the substrate. If a solvent is contained, the composition is heated and dried to remove the solvent, thereby forming a pre-thermally cured photocurable pressure-sensitive adhesive layer. Thereafter, if necessary, a release sheet is laminated onto the pre-thermally cured photocurable pressure-sensitive adhesive layer. Then, the pre-cured intermediate layer and the pre-thermally cured photocurable pressure-sensitive adhesive layer are simultaneously cured. These methods can omit the step of laminating an intermediate layer and a photocurable pressure-sensitive adhesive layer to obtain a protective sheet.

[0109] The pressure-sensitive adhesive composition can be applied to the substrate, release sheet, intermediate layer, or pre-cured intermediate layer by any known method, including, for example, a method using a conventional coater such as a gravure roll coater, reverse roll coater, kiss roll coater, dip roll coater, bar coater, knife coater, spray coater, comma coater, or direct coater.

[0110] The conditions for heat-drying the applied pressure-sensitive adhesive composition are not particularly limited, but are typically 25 to 180°C, preferably 60 to 150°C, for typically 1 to 20 minutes, preferably 1 to 10 minutes. Heat-drying under these conditions allows the solvent contained in the pressure-sensitive adhesive composition to be removed. The reaction conditions for curing the photocurable pressure-sensitive adhesive layer after heat-drying are not particularly limited, but are typically 25 to 100°C, preferably 30 to 80°C, for typically 1 to 14 days, preferably 1 to 7 days. By carrying out the curing reaction under these conditions, the ethylenically unsaturated group-containing (meth)acrylic resin (A2) and the crosslinking agent (B2) are crosslinked, allowing the gelation rate of the photocurable pressure-sensitive adhesive layer to be adjusted to the desired range.

[0111] (Release sheet) As the release sheet, a known sheet-shaped material can be appropriately selected and used. The release sheet is sometimes called a separator. As the release sheet, the same material as the above-mentioned resin sheet used as the substrate can be used.

[0112] The thickness of the release sheet can be appropriately selected depending on the application of the protective sheet, the material of the release sheet, etc. When a resin sheet is used as the release sheet, the thickness of the release sheet is preferably 5 to 300 μm, more preferably 10 to 200 μm, and even more preferably 25 to 100 μm.

[0113] The release surface of the release sheet, i.e., the surface that is placed in contact with the photocurable pressure-sensitive adhesive layer, may be subjected to a release treatment using a conventionally known release agent such as a silicone-based, long-chain alkyl-based, or fluorine-based release agent, if necessary.

[0114] [Intermediate Layer] The protective sheet may have an intermediate layer to improve its conformability to uneven surfaces. The material constituting the intermediate layer is not particularly limited, and materials commonly used for protective sheets can be used. Examples of materials constituting the intermediate layer include (meth)acrylic resins, polyurethane resins, polyester resins, silicone resins, and rubber-based resins. Among these, (meth)acrylic resins are preferred. From the perspective of improving conformability to uneven surfaces and ensuring the heat resistance of the protective sheet, the intermediate layer is preferably a thermoset product of a resin composition containing an ethylenically unsaturated group-free (meth)acrylic resin (A1) and a crosslinking agent (B1). This thermoset product is a reaction product, i.e., a crosslinked product, between a functional group in the ethylenically unsaturated group-free (meth)acrylic resin (A1) that is reactive with a functional group in the crosslinking agent (B1) and a functional group in the crosslinking agent (B1). By including an intermediate layer, the protective sheet exhibits good conformability to uneven surfaces, even when the surface of the adherend has large bump heights, for example.

[0115] The thickness of the intermediate layer is preferably 30 μm or more, more preferably 50 μm or more, and even more preferably 80 μm or more. The thickness of the intermediate layer is preferably 600 μm or less, more preferably 300 μm or less, and even more preferably 200 μm or less. When the thickness of the intermediate layer is 30 μm or more, the protective sheet has good conformability to steps on the adherend surface. When the thickness of the intermediate layer is 600 μm or less, the processing precision of the adherend in the processing step is good.

[0116] (Ethylenically Unsaturated Group-Free (Meth)acrylic Resin (A1)) The ethylenically unsaturated group-free (meth)acrylic resin (A1) is not particularly limited as long as it contains a (meth)acrylic acid ester as an essential raw material monomer, has an ethylenically unsaturated group equivalent of more than 5000 g / mol, does not contain an ethylenically unsaturated group, and has a plurality of functional groups reactive with the functional group contained in the crosslinking agent (B1). In one embodiment, the ethylenically unsaturated group-free (meth)acrylic resin (A1) does not contain an ethylenically unsaturated group. Examples of functional groups reactive with the functional group contained in the crosslinking agent (B1) include a hydroxy group, a carboxy group, an isocyanato group, a glycidyl group, an amino group, and an amide group. The ethylenically unsaturated group-free (meth)acrylic resin (A1) may be used alone or in combination of two or more. By forming the intermediate layer using the (meth)acrylic resin (A1) that does not contain an ethylenically unsaturated group, the protective sheet has high heat resistance and exhibits high conformability to the irregularities of the adherend even when exposed to high temperature conditions from the step of attaching the sheet to the adherend to the processing step and the peeling step. In addition, it exhibits good conformability to the irregularities even when the irregularities on the adherend surface become large.

[0117] Specific examples of raw material monomers for the ethylenically unsaturated group-free (meth)acrylic resin (A1) include alkyl(meth)acrylate (a1-1), hydroxy group-containing (meth)acrylate (a1-2), carboxy group-containing ethylenically unsaturated compound (a1-3), (meth)acrylamide compound (a1-4), and other monomers (a1-5), which will be described later. The ethylenically unsaturated group-free (meth)acrylic resin (A1) is preferably a copolymer containing alkyl(meth)acrylate (a1-1) and hydroxy group-containing (meth)acrylate (a1-2) as essential raw material monomers, and more preferably a copolymer containing alkyl(meth)acrylate (a1-1), hydroxy group-containing (meth)acrylate (a1-2), and carboxy group-containing ethylenically unsaturated compound (a1-3) as essential raw material monomers. As the alkyl (meth)acrylate (a1-1) which is a raw material monomer of the ethylenically unsaturated group-free (meth)acrylic resin (A1), it is preferable to use at least one selected from 2-ethylhexyl (meth)acrylate and n-butyl (meth)acrylate. The total content of 2-ethylhexyl (meth)acrylate and n-butyl (meth)acrylate relative to the total raw material monomers of the ethylenically unsaturated group-free (meth)acrylic resin (A1) is preferably 50 mol% or more, more preferably 60 mol% or more. The upper limit of the total content of 2-ethylhexyl (meth)acrylate and n-butyl (meth)acrylate relative to the total raw material monomers of the ethylenically unsaturated group-free (meth)acrylic resin (A1) is not particularly limited, and may be, for example, 99 mol%, 95 mol%, or 80 mol%.

[0118] The glass transition temperature (Tg) of the ethylenically unsaturated group-free (meth)acrylic resin (A1) is preferably −80° C. to 0° C., more preferably −70° C. to −10° C., and even more preferably −60° C. to −20° C. If the glass transition temperature is −80° C. or higher, an intermediate layer with high cohesive strength can be obtained, thereby preventing resin elution during sheet molding. If the glass transition temperature is 0° C. or lower, the adhesion between the intermediate layer and the photocurable pressure-sensitive adhesive layer can be further improved.

[0119] The weight-average molecular weight of the ethylenically unsaturated group-free (meth)acrylic resin (A1) is preferably 100,000 to 2,000,000, more preferably 150,000 to 1,500,000, and even more preferably 200,000 to 1,000,000. When the weight-average molecular weight is 100,000 or more, an intermediate layer with high cohesive strength can be obtained, and resin elution during sheet formation can be prevented. When the weight-average molecular weight is 2,000,000 or less, molding and processing are easy.

[0120] As described below, examples of the crosslinking agent (B1) that can be used include an isocyanate crosslinking agent and an epoxy crosslinking agent. The isocyanate crosslinking agent is a compound having a plurality of isocyanato groups, and the epoxy crosslinking agent is a compound having a plurality of epoxy groups.

[0121] In an embodiment in which the crosslinking agent (B1) is an isocyanate crosslinking agent, the ethylenically unsaturated group-free (meth)acrylic resin (A1) is preferably a copolymer having, as raw material monomers, at least an alkyl (meth)acrylate (a1-1) and a hydroxy group-containing (meth)acrylate (a1-2). If necessary, at least one raw material monomer selected from the group consisting of a carboxy group-containing ethylenically unsaturated compound (a1-3), a (meth)acrylamide compound (a1-4), and other monomers (a1-5) may also be used for the ethylenically unsaturated group-free (meth)acrylic resin (A1).

[0122] In this embodiment, the hydroxyl value of the ethylenically unsaturated group-free (meth)acrylic resin (A1) is preferably 0.5 to 100 mgKOH / g, more preferably 1 to 50 mgKOH / g, and even more preferably 5 to 30 mgKOH / g. When the hydroxyl value is 0.5 mgKOH / g or more, the resin can react sufficiently with the isocyanate crosslinking agent, resulting in an intermediate layer with high cohesive strength. When the hydroxyl value is 100 mgKOH / g or less, the resulting resin is soluble in commonly used organic solvents such as ethyl acetate and toluene, resulting in excellent handleability.

[0123] In this embodiment, the content of the alkyl (meth)acrylate (a1-1) relative to the total raw material monomers of the ethylenically unsaturated group-free (meth)acrylic resin (A1) is preferably 50 to 99.5 mol%, more preferably 60 to 95 mol%, and even more preferably 70 to 90 mol%. When the content of the alkyl (meth)acrylate (a1-1) is 50 mol% or more, the intermediate layer has good adhesion to the substrate and the photocurable pressure-sensitive adhesive layer. When the content of the alkyl (meth)acrylate (a1-1) is 99.5 mol% or less, the content of the hydroxy group-containing (meth)acrylate (a1-2) can be sufficiently ensured, thereby ensuring a sufficient amount of crosslinking with the crosslinking agent (B1), and improving the cohesive strength of the intermediate layer.

[0124] In this embodiment, the content of the hydroxy group-containing (meth)acrylate (a1-2) relative to the total raw material monomers of the ethylenically unsaturated group-free (meth)acrylic resin (A1) is preferably 0.5 to 30 mol%, more preferably 1 to 20 mol%, and even more preferably 1.5 to 10 mol%. When the content of the hydroxy group-containing (meth)acrylate (a1-2) is 0.5 mol% or more, a sufficient amount of crosslinking with the crosslinking agent (B1) is ensured, improving the cohesive strength of the intermediate layer. When the content of the hydroxy group-containing (meth)acrylate (a1-2) is 30 mol% or less, the resulting resin is soluble in commonly used organic solvents such as ethyl acetate and toluene, resulting in excellent handleability.

[0125] In this embodiment, when a carboxyl group-containing ethylenically unsaturated compound (a1-3) is used as a raw material monomer for the ethylenically unsaturated group-free (meth)acrylic resin (A1), the content thereof is preferably 0.01 to 10 mol %, more preferably 0.05 to 5 mol %, and even more preferably 0.1 to 3 mol %, based on the total amount of raw material monomers. When the content of the carboxyl group-containing ethylenically unsaturated compound (a1-3) is 0.01 mol % or more, the cohesive strength of the intermediate layer is good. When the content of the carboxyl group-containing ethylenically unsaturated compound (a1-3) is 10 mol % or less, the cohesive strength of the resulting resin is not too high, and the handleability is good.

[0126] In this embodiment, when the (meth)acrylamide compound (a1-4) is used as a raw material monomer for the ethylenically unsaturated group-free (meth)acrylic resin (A1), the content thereof is preferably 0.5 to 30 mol %, more preferably 1 to 25 mol %, and even more preferably 5 to 20 mol %, based on the total amount of the raw material monomers.

[0127] In this embodiment, when the other monomer (a1-5) is used as a raw material monomer for the ethylenically unsaturated group-free (meth)acrylic resin (A1), the content thereof is preferably 0.5 to 30 mol %, more preferably 1 to 25 mol %, and even more preferably 5 to 20 mol %, based on the total amount of the raw material monomers.

[0128] The alkyl (meth)acrylate (a1-1) is not particularly limited as long as it is a compound that does not have a functional group such as a hydroxy group or a carboxy group and has an alkyl group and a (meth)acryloyloxy group. Specific examples and suitable examples of the alkyl (meth)acrylate (a1-1) are the same as those of the alkyl (meth)acrylate (a2-1). The alkyl (meth)acrylate (a1-1) may be used alone or in combination of two or more.

[0129] The hydroxy group-containing (meth)acrylate (a1-2) is not particularly limited as long as it is a compound having a hydroxy group and a (meth)acryloyloxy group. Specific examples include 2-hydroxyethyl (meth)acrylate, 2-hydroxypropyl (meth)acrylate, 3-hydroxypropyl (meth)acrylate, 4-hydroxybutyl (meth)acrylate, 1,3-butanediol (meth)acrylate, 1,4-butanediol (meth)acrylate, 1,6-hexanediol (meth)acrylate, and 3-methylpentanediol (meth)acrylate. From the viewpoint of conformability to uneven surfaces, hydroxyalkyl (meth)acrylates having a hydroxy group at the terminal of a linear alkyl group are preferred, and at least one selected from 2-hydroxyethyl (meth)acrylate, 3-hydroxypropyl (meth)acrylate, and 4-hydroxybutyl (meth)acrylate are more preferred. The hydroxy group-containing (meth)acrylate (a1-2) may be used alone or in combination of two or more kinds.

[0130] The carboxy group-containing ethylenically unsaturated compound (a1-3) is not particularly limited as long as it does not have a hydroxy group and has a carboxy group and an ethylenically unsaturated group. The ethylenically unsaturated group is preferably a (meth)acryloyloxy group. By using the carboxy group-containing ethylenically unsaturated compound (a1-3) as a raw material monomer for the ethylenically unsaturated group-free (meth)acrylic resin (A1), the carboxy group derived from the carboxy group-containing ethylenically unsaturated compound (a1-3) crosslinks with the hydroxy group derived from the hydroxy group-containing (meth)acrylate (a1-2) during the formation of the intermediate layer, thereby improving the cohesive strength. When the photocurable pressure-sensitive adhesive layer contains a carboxy group, the interlayer adhesion between the photocurable pressure-sensitive adhesive layer and the intermediate layer is improved. Furthermore, if the crosslinking agent (B2) of the photocurable pressure-sensitive adhesive layer is an epoxy crosslinking agent, crosslinking of the carboxy groups derived from the carboxy group-containing ethylenically unsaturated compound (a1-3) by the epoxy crosslinking agent of the photocurable pressure-sensitive adhesive layer proceeds at the interface between the photocurable pressure-sensitive adhesive layer and the intermediate layer, thereby obtaining stronger interlayer adhesion, which is preferable.

[0131] Specific examples and suitable examples of the carboxyl group-containing ethylenically unsaturated compound (a1-3) are the same as those of the carboxyl group-containing ethylenically unsaturated compound (a2-2). The carboxyl group-containing ethylenically unsaturated compound (a1-3) may be used alone or in combination of two or more.

[0132] Examples of the (meth)acrylamide compound (a1-4) include (meth)acrylamide; N-alkyl(meth)acrylamides such as N-methyl(meth)acrylamide, N-ethyl(meth)acrylamide, N-propyl(meth)acrylamide, N-isopropylacrylamide, and N-hexyl(meth)acrylamide; N,N-dialkyl(meth)acrylamides such as N,N-dimethyl(meth)acrylamide and N,N-diethyl(meth)acrylamide; (meth)acryloylmorpholine; and diacetone acrylamide.

[0133] Among these, from the viewpoint of improving adhesion to the adherend, N,N-dialkyl(meth)acrylamide is more preferred, and N,N-dimethyl(meth)acrylamide is even more preferred.

[0134] The other monomer (a1-5) is not particularly limited as long as it is a compound other than (a1-1) to (a1-4) and has an ethylenically unsaturated group copolymerizable therewith. Examples include alkoxyalkyl (meth)acrylate, alkoxy(poly)alkylene glycol (meth)acrylate, aromatic group-containing (meth)acrylate, fluorinated alkyl (meth)acrylate, and dialkylaminoalkyl (meth)acrylate. These compounds can be the same as those listed for the other monomer (a2-5). The other monomer (a1-5) can be used alone or in combination of two or more.

[0135] Other specific examples of the other monomer (a1-5) include acrylonitrile, methacrylonitrile, styrene, α-methylstyrene, vinyl acetate, vinyl propionate, vinyl stearate, vinyl chloride, vinylidene chloride, alkyl vinyl ethers, vinyl toluene, N-vinylpyridine, N-vinylpyrrolidone, itaconic acid dialkyl esters, fumaric acid dialkyl esters, allyl alcohol, hydroxybutyl vinyl ether, hydroxyethyl vinyl ether, 4-hydroxymethylcyclohexylmethyl vinyl ether, triethylene glycol monovinyl ether, diethylene glycol monovinyl ether, methyl vinyl ketone, allyltrimethylammonium chloride, and dimethylallyl vinyl ketone.

[0136] In an embodiment in which the crosslinking agent (B1) is an epoxy crosslinking agent, the ethylenically unsaturated group-free (meth)acrylic resin (A1) is preferably a copolymer having, as raw material monomers, at least an alkyl (meth)acrylate (a1-1) and a carboxy group-containing ethylenically unsaturated compound (a1-3). If necessary, at least one monomer selected from the group consisting of a hydroxy group-containing (meth)acrylate (a1-2), a (meth)acrylamide compound (a1-4), and other monomers (a1-5) may also be used as a raw material monomer for the ethylenically unsaturated group-free (meth)acrylic resin (A1).

[0137] In this embodiment, (a1-1) to (a1-5) can be the same as those described above.

[0138] In this embodiment, the content of the alkyl (meth)acrylate (a1-1) relative to the total raw material monomers of the ethylenically unsaturated group-free (meth)acrylic resin (A1) is preferably 50 to 99.5 mol%, more preferably 60 to 99 mol%, and even more preferably 70 to 98 mol%. When the content of the alkyl (meth)acrylate (a1-1) is 50 mol% or more, the intermediate layer has good adhesion to the substrate and the photocurable pressure-sensitive adhesive layer. When the content of the alkyl (meth)acrylate (a1-1) is 99.5 mol% or less, the content of the carboxyl group-containing ethylenically unsaturated compound (a1-3) can be sufficiently ensured, thereby ensuring a sufficient amount of crosslinking with the crosslinking agent (B1), and improving the cohesive strength of the intermediate layer.

[0139] In this embodiment, the content of the carboxyl group-containing ethylenically unsaturated compound (a1-3) relative to the total raw material monomers of the ethylenically unsaturated group-free (meth)acrylic resin (A1) is preferably 0.01 to 30 mol%, more preferably 0.1 to 20 mol%, and even more preferably 1 to 10 mol%. When the content of the carboxyl group-containing ethylenically unsaturated compound (a1-3) is 0.01 mol% or more, an intermediate layer with high cohesion strength can be obtained. When the content of the carboxyl group-containing ethylenically unsaturated compound (a1-3) is 30 mol% or less, the cohesion strength of the obtained intermediate layer is not too high, and the handleability is good.

[0140] In this embodiment, the acid value of the ethylenically unsaturated group-containing (meth)acrylic resin (A1) is preferably 1 mgKOH / g or more, more preferably 3 mgKOH / g or more, and even more preferably 5 mgKOH / g or more. The acid value of the ethylenically unsaturated group-containing (meth)acrylic resin (A1) is preferably 30 mgKOH / g or less, more preferably 20 mgKOH / g or less, and even more preferably 10 mgKOH / g or less. When the acid value is 1 mgKOH / g or more, it can react sufficiently with the crosslinking agent (B1), resulting in an intermediate layer with high cohesive strength. When the acid value is 30 mgKOH / g or less, the cohesive strength of the resulting intermediate layer is not too high, and handling is good.

[0141] In this embodiment, when a hydroxy group-containing (meth)acrylate (a1-2) is used as a raw material monomer for the ethylenically unsaturated group-free (meth)acrylic resin (A1), its content is preferably 0.01 to 30 mol %, more preferably 0.1 to 20 mol %, and even more preferably 0.1 to 10 mol %, based on the total amount of raw material monomers. When the content of the hydroxy group-containing (meth)acrylate (a1-2) is 0.01 mol % or more, a sufficient amount of crosslinking with the crosslinking agent (B1) can be ensured. When the content of the hydroxy group-containing (meth)acrylate (a1-2) is 30 mol % or less, the resulting resin is soluble in commonly used organic solvents such as ethyl acetate and toluene, and therefore has excellent handleability.

[0142] In this embodiment, when the (meth)acrylamide compound (a1-4) is used as a raw material monomer for the ethylenically unsaturated group-free (meth)acrylic resin (A1), the content thereof is preferably 0.5 to 30 mol %, more preferably 1 to 25 mol %, and even more preferably 5 to 20 mol %, based on the total amount of the raw material monomers.

[0143] In this embodiment, when the other monomer (a1-5) is used as a raw material monomer for the ethylenically unsaturated group-free (meth)acrylic resin (A1), the content thereof is preferably 0.1 to 45 mol %, more preferably 0.1 to 35 mol %, and even more preferably 0.1 to 25 mol %, based on the total amount of the raw material monomers.

[0144] (Crosslinking Agent (B1)) The crosslinking agent (B1) is not particularly limited as long as it is a compound having a plurality of functional groups capable of reacting with any of the functional groups possessed by the ethylenically unsaturated group-free (meth)acrylic resin (A1), and can be selected in accordance with the functional groups possessed by the ethylenically unsaturated group-free (meth)acrylic resin (A1). For example, when the ethylenically unsaturated group-free (meth)acrylic resin (A1) has a hydroxy group, it is preferable to use at least one selected from the group consisting of an isocyanate crosslinking agent and an epoxy crosslinking agent as the crosslinking agent (B1), and it is more preferable to use an isocyanate crosslinking agent. When the ethylenically unsaturated group-free (meth)acrylic resin (A1) has a carboxy group, it is preferable to use at least one selected from the group consisting of an isocyanate crosslinking agent, an epoxy crosslinking agent, and an aziridine crosslinking agent as the crosslinking agent (B1), and it is more preferable to use an epoxy crosslinking agent. By including the crosslinking agent (B1) in the intermediate layer, the cohesive strength of the intermediate layer is improved, and cohesive failure of the intermediate layer can be prevented when the protective sheet is peeled off from the adherend. The crosslinking agent (B1) may be used alone or in combination of two or more types.

[0145] Preferred combinations of the ethylenically unsaturated group-free (meth)acrylic resin (A1) and the crosslinking agent (B1) include a combination of the ethylenically unsaturated group-free (meth)acrylic resin (A1) having a hydroxy group and an isocyanate crosslinking agent, a combination of the ethylenically unsaturated group-free (meth)acrylic resin (A1) having a carboxy group and an epoxy crosslinking agent, and a combination of the ethylenically unsaturated group-free (meth)acrylic resin (A1) having a carboxy group and an aziridine crosslinking agent, and more preferred is a combination of the ethylenically unsaturated group-free (meth)acrylic resin (A1) having a hydroxy group and an isocyanate crosslinking agent.

[0146] An isocyanate crosslinking agent is a compound having two or more isocyanato groups. Here, the term "isocyanato group" includes compounds that generate an isocyanato group upon deblocking. Specific examples of the isocyanate crosslinking agent include 2,4-tolylene diisocyanate, 2,6-tolylene diisocyanate, hydrogenated tolylene diisocyanate, 1,3-xylylene diisocyanate, 1,4-xylylene diisocyanate, diphenylmethane-4,4'-diisocyanate, isophorone diisocyanate, 1,3-bis(isocyanatomethyl)cyclohexane, an isocyanurate of hexamethylene diisocyanate, tetramethylxylylene diisocyanate, 1,5-naphthalene diisocyanate, a tolylene diisocyanate adduct of trimethylolpropane, a xylylene diisocyanate adduct of trimethylolpropane, triphenylmethane triisocyanate, and methylenebis(4-phenylmethane)triisocyanate. Of these, an isocyanurate of hexamethylene diisocyanate and a tolylene diisocyanate adduct of trimethylolpropane are preferred. The isocyanate crosslinking agents may be used alone or in combination of two or more.

[0147] The epoxy crosslinking agent and aziridine crosslinking agent may be the same as those used as the crosslinking agent (B1). The epoxy crosslinking agent may be used alone or in combination of two or more. The aziridine crosslinking agent may be used alone or in combination of two or more.

[0148] The content of the crosslinking agent (B1) is preferably 0.05 to 30 parts by mass, more preferably 0.1 to 20 parts by mass, and even more preferably 0.1 to 10 parts by mass, relative to 100 parts by mass of the ethylenically unsaturated group-free (meth)acrylic resin (A1). When the content of the crosslinking agent (B1) is 0.05 parts by mass or more, a three-dimensional crosslinked structure is sufficiently formed in the intermediate layer, resulting in an intermediate layer with high heat resistance. When the content of the crosslinking agent (B1) is 30 parts by mass or less, an appropriate gelation time can be ensured during sheet molding.

[0149] (Other Components) The resin composition may contain other components other than the ethylenically unsaturated group-free (meth)acrylic resin (A1) and the crosslinking agent (B1) as necessary. Examples of other components include a tackifier, a solvent, and various additives. The tackifier, the solvent, and the various additives may be the same as those described for the pressure-sensitive adhesive composition.

[0150] [Method for producing ethylenically unsaturated group-free (meth)acrylic resin (A1)] The method for producing the ethylenically unsaturated group-free (meth)acrylic resin (A1) is not particularly limited. For example, the ethylenically unsaturated group-free (meth)acrylic resin (A1) can be obtained by copolymerizing raw material monomers of the ethylenically unsaturated group-free (meth)acrylic resin (A1) by a known polymerization method.

[0151] The ethylenically unsaturated group-free (meth)acrylic resin (A1) can be obtained by the same method as the method for producing the (meth)acrylic resin (A2-0). Among these, solution polymerization is preferred, and the types and amounts of the radical polymerization initiator and solvent used are also the same as those described for the method for producing the (meth)acrylic resin (A2-0).

[0152] [Method for Producing Resin Composition] The resin composition can be produced by a conventionally known method, for example, by mixing and stirring the ethylenically unsaturated group-free (meth)acrylic resin (A1), the crosslinking agent (B1), and other components, such as a tackifier, a solvent, and various additives, which may be contained as needed, by a conventionally known method.

[0153] The method for mixing and stirring the components contained in the resin composition is not particularly limited. Mixing and stirring can be performed using a stirring device equipped with stirring blades such as a homodisper or paddle blade.

[0154] [Method for Producing Intermediate Layer] The method for producing an intermediate layer will be described below, taking as an example a case where an intermediate layer is produced using a resin composition containing an ethylenically unsaturated group-free (meth)acrylic resin (A1) and a crosslinking agent (B1). When using the above resin composition, the intermediate layer can be produced, for example, by the following method. First, the resin composition is applied to a substrate, and if a solvent is contained, the composition is heated and dried to remove the solvent, thereby forming a pre-cured intermediate layer. Thereafter, a release sheet is attached to the pre-cured intermediate layer as needed until just before laminating the photocurable pressure-sensitive adhesive layer or the pre-thermocurable photocurable pressure-sensitive adhesive layer. The pre-cured intermediate layer may be cured by heating and curing the obtained sheet for a certain period of time in an oven or the like to form a crosslinked structure. The curing reaction may be carried out after laminating the pre-cured intermediate layer and the photocurable pressure-sensitive adhesive layer or the pre-thermocurable photocurable pressure-sensitive adhesive layer.

[0155] The intermediate layer can also be produced by the following method. A resin composition is applied to a release sheet, and if a solvent is contained, the resin composition is heated and dried to remove the solvent, forming a pre-cured intermediate layer. The release sheet having the pre-cured intermediate layer is then placed on a substrate with the surface of the pre-cured intermediate layer facing the substrate, and the intermediate layer is transferred onto the substrate. The resulting sheet may be subjected to the above-described process to form a crosslinked structure.

[0156] The method for applying the resin composition to a substrate or a release sheet, the conditions and preferred ranges for heating and drying the applied resin composition, and the conditions and preferred ranges for curing the uncured intermediate layer in an oven for a certain period of time after heating and drying are the same as those described for the method for producing a photocurable pressure-sensitive adhesive layer.

[0157] (Release Sheet) As the release sheet, any known sheet-shaped material can be appropriately selected and used. As the release sheet, the same material as the resin sheet used as the substrate described above can be used.

[0158] The thickness of the release sheet can be appropriately selected depending on the material of the release sheet, etc. When a resin sheet is used as the release sheet, the thickness of the release sheet is preferably 5 to 300 μm, more preferably 10 to 200 μm, and even more preferably 25 to 100 μm.

[0159] The release surface of the release sheet, i.e., the surface that is placed in contact with the intermediate layer, may be subjected to a release treatment using a conventionally known release agent such as a silicone-based, long-chain alkyl-based, or fluorine-based release agent, if necessary.

[0160] [Method for producing protective sheet] The protective sheet can be produced, for example, by laminating a substrate or intermediate layer and a photocurable pressure-sensitive adhesive layer. When a thermosetting intermediate layer is used, the protective sheet may be produced by first curing either the pre-cured intermediate layer or the pre-thermosetting photocurable pressure-sensitive adhesive layer, laminating the other pre-cured layer, and curing the pre-cured layer. Alternatively, the protective sheet may be produced by laminating the pre-cured intermediate layer and the pre-thermosetting photocurable pressure-sensitive adhesive layer and curing both layers simultaneously. The protective sheet may also be produced by laminating a thermosetting intermediate layer and a thermosetting photocurable pressure-sensitive adhesive layer.

[0161] A specific example of a method for producing a protective sheet when a thermosetting intermediate layer is used is shown below. A sheet having a pre-cured intermediate layer on one main surface of a substrate, and a sheet having a pre-thermosetting light-curable pressure-sensitive adhesive layer on a release sheet are prepared. If a release sheet is laminated on the bonding surfaces of the two sheets, this is peeled off, and the sheets are bonded together so that the bonding surface of the pre-cured intermediate layer, i.e., the surface opposite the substrate, faces the bonding surface of the pre-thermosetting light-curable pressure-sensitive adhesive layer, i.e., the surface opposite the release sheet.

[0162] The pre-cured intermediate layer and the pre-thermosetting photocurable pressure-sensitive adhesive layer are then subjected to a curing step in which the laminated layer is heated in an oven for a certain period of time to thermally cure the pre-cured intermediate layer and the pre-thermosetting photocurable pressure-sensitive adhesive layer, yielding a cured product of both layers. The conditions for the curing step are not particularly limited, but curing is typically performed at 30 to 100°C, preferably 40 to 80°C, for 1 to 14 days, preferably 1 to 7 days. Curing under these conditions can adjust the gel fraction of each layer to a desired range. Depending on the combination of components, crosslinking at the interface between the intermediate layer and the photocurable pressure-sensitive adhesive layer, i.e., crosslinking between the resin in the intermediate layer and the crosslinking agent (B2) in the photocurable pressure-sensitive adhesive layer, and crosslinking between the ethylenically unsaturated group-containing (meth)acrylic resin (A2) in the photocurable pressure-sensitive adhesive layer and the crosslinking agent in the intermediate layer, can also be expected. Therefore, the curing step is expected to improve the interlayer adhesion between the intermediate layer and the photocurable pressure-sensitive adhesive layer.

[0163] [Method for manufacturing a semiconductor device having bump electrodes] In one embodiment, a method for manufacturing a semiconductor device having bump electrodes includes: a protection step of attaching the photocurable adhesive layer surface of a protective sheet to the bump electrode-bearing surface of an unprocessed semiconductor device; an active energy ray irradiation step of irradiating the protective sheet with active energy rays to photocure the photocurable adhesive layer; a heating step of the unprocessed semiconductor device with the protective sheet attached; and a peeling step of peeling the protective sheet from the bump electrode-bearing surface. Note that a processing step of the unprocessed semiconductor device may be performed between the protection step and the peeling step, and the order of the other steps may be reversed as long as the protection step is performed first and the peeling step is performed last.

[0164] (Protection Process) In the protection process, the photocurable adhesive layer surface of the protective sheet is attached to the bump electrode-bearing surface of the pre-processed semiconductor device having bump electrodes. This protects the bump electrode-bearing surface of the pre-processed semiconductor device. Specific examples of pre-processed semiconductor devices include semiconductor devices with uneven surfaces, such as bumped semiconductor chips, bumped printed wiring boards (PCBs), and bumped flexible printed circuit boards (FPCs). These semiconductor devices are subjected to various processing steps in the manufacturing process up to the mounting step in which the bump electrodes are connected to other electronic devices. Protecting the bump electrode-bearing surface during the processing steps can prevent scratches, damage, contamination, etc. on the bump electrode-bearing surface. The protective sheet can also serve as a temporary fixation function for the pre-processed semiconductor device for subsequent processing steps.

[0165] When the protective sheet has an intermediate layer, where H [μm] is the height of the bump electrode and d [μm] is the total thickness of the intermediate layer and the photocurable pressure-sensitive adhesive layer, d / H is preferably 1.00 or more, more preferably 1.05 or more, and even more preferably 1.10 or more. d / H is preferably 100 or less, more preferably 20 or less, and even more preferably 10 or less.

[0166] When a release sheet is provided on the photocurable pressure-sensitive adhesive layer, the release sheet can protect the photocurable pressure-sensitive adhesive layer until use. When a release sheet is provided on the photocurable pressure-sensitive adhesive layer, the release sheet can be peeled off to expose the photocurable pressure-sensitive adhesive layer, and the application surface of the photocurable pressure-sensitive adhesive layer can be efficiently pressure-bonded to the surface of the semiconductor device with bump electrodes before processing.

[0167] When a semiconductor device has a plurality of surfaces with bump electrodes, a protective sheet is attached to some or all of the surfaces with bump electrodes in the protection step. For example, when stacking semiconductor chips as disclosed in JP 2014-225546 A, a protective sheet can be attached to the non-mounting surfaces excluding the mounting surfaces of the surfaces with bump electrodes.

[0168] (Processing Step) The method for manufacturing a semiconductor device may include a processing step between the protection step and the peeling step described below.

[0169] As the processing step, any processing step used in the manufacture of conventionally known semiconductor devices can be applied without any particular restrictions. For example, when the protective sheet is used as a wafer dicing tape, in the protection step, the protective sheet is attached to a wafer on which multiple components are formed, and then in the processing step, a dicing step is performed in which the wafer is cut into individual components to obtain small element pieces (also called chips). When a semiconductor chip stacking step is performed as the processing step, only the non-mounting surface of the surface with bump electrodes is protected in the protection step, and the mounting surfaces not attached with the protective sheet are brought into contact with each other and electrically connected while being stacked.

[0170] (Heating Step) The method for manufacturing a semiconductor device includes a heating step between the protection step and the peeling step described below. When the method for manufacturing a semiconductor device includes a processing step after the protection step, the order of the processing step and the heating step is not limited. From the viewpoint of maximizing the protective function and temporary fixing function of the protective sheet, i.e., the adhesion performance, it is preferable that the processing step and the heating step be performed simultaneously, or that the processing step be performed before the heating step.

[0171] The heating step can be any heating step known in the art and used in the manufacture of semiconductor devices, including, for example, an after-cure step for a PCB with bumps, a sputtering step for a semiconductor chip, and a reflow step for connecting a semiconductor chip.

[0172] The conditions for the heating step are not particularly limited. By performing the protection step before the heating step, the surface with the bump electrodes can be well protected even when high-temperature treatment is performed at, for example, 150°C or higher, 180°C or higher, or 200°C or higher. The maximum temperature reached in the heating step is not particularly limited, but may be, for example, 80°C or higher or 100°C or higher, and 260°C or lower, or 230°C or lower. The maximum temperature reached in the heating step is not particularly limited, but from the viewpoint of the heat resistance of the protective sheet, it is preferably 300°C or lower, more preferably 270°C or lower. The heating time is not particularly limited, but is, for example, 1 minute to 180 minutes, preferably 1 minute to 120 minutes, and more preferably 1 minute to 60 minutes.

[0173] The conditions for the sputtering process are not particularly limited. For example, metals such as Cr, Cu, Ti, Ag, Pt, and Au, alloys such as Ni—Cr, SUS, and Cu—Zn, or ITO, SiO ２ , TiO ２ , Nb ２ O ５ The film may be formed using a metal oxide such as ZnO as a target and an inert gas such as Ar. Examples of sputtering methods include magnetron sputtering, bipolar sputtering, DC (direct current) sputtering, RF (radio frequency) sputtering, reactive sputtering, and ion beam sputtering. The film formation temperature in the sputtering step is not particularly limited, but even when the film is formed at a high temperature of, for example, 100° C. or higher, 130° C. or higher, or 150° C. or higher, the surface with the bump electrode can be well protected.

[0174] If gaps exist between semiconductor chips before the sputtering process, for example, if a semiconductor device is diced into small pieces and gaps exist between the semiconductor chips, the photocurable adhesive layer of the protective sheet is exposed in the gaps between the semiconductor chips. Therefore, a metal film is formed not only on the surface of the semiconductor chip but also on the exposed portions of the photocurable adhesive layer during the sputtering process. Even after the active energy ray irradiation process, the protective sheet maintains adhesion to the metal film until the peeling process, thereby reducing detachment of the metal film. Therefore, metal contamination of the equipment and semiconductor chips used in each process can be reduced.

[0175] (Active energy ray irradiation step) In the active energy ray irradiation step, active energy rays are usually irradiated from the substrate side of the protective sheet. If the adherend is light-transmitting, active energy rays may be irradiated from the adherend side toward the protective sheet. Irradiation with active energy rays can crosslink and cure the photocurable pressure-sensitive adhesive layer, thereby increasing the heat resistance of the protective sheet or improving the releasability of the protective sheet. The active energy ray irradiation step may be performed between the protection step and the peeling step described below, and the order of the processing step and the heating step is not limited.

[0176] The active energy ray irradiation step may be performed in two separate steps. For example, the active energy ray irradiation step may be performed between the protection step and the processing step, and a portion of the ethylenically unsaturated groups contained in the photocurable pressure-sensitive adhesive layer may be crosslinked and cured, thereby improving the heat resistance of the protective sheet. Furthermore, the second active energy ray irradiation step may be performed immediately before the peeling step described below, and the remaining ethylenically unsaturated groups may be crosslinked, thereby reducing the peel strength of the protective sheet and improving its releasability from the adherend.

[0177] Examples of active energy rays include gamma rays, ultraviolet rays (UV), visible light, infrared rays, radio waves, alpha rays, beta rays, electron beams, plasma flows, ionizing rays, and particle beams, with ultraviolet rays (UV) being preferred. Examples of light sources used to irradiate the protective sheet attached to the adherend with UV before peeling include LED lamps, high-pressure mercury lamps, ultra-high-pressure mercury lamps, carbon arc lamps, xenon lamps, metal halide lamps, chemical lamps, and black lights. It is preferable to use an LED lamp, high-pressure mercury lamp, or metal halide lamp for active energy ray irradiation.

[0178] The active energy ray irradiation dose applied to the protective sheet is 50 to 3000 mJ / cm ２ is preferably 100 to 1500 mJ / cm ２ It is more preferable that the active energy ray irradiation dose applied to the protective sheet is 50 mJ / cm. ２ When the exposure dose of active energy rays to the protective sheet is 3000 mJ / cm or more, the photocurable pressure-sensitive adhesive layer can be cured at a sufficiently high curing rate by exposure to active energy rays, and the adhesive strength of the photocurable pressure-sensitive adhesive layer after exposure to active energy rays can be sufficiently reduced. ２ Even if the active energy ray irradiation dose is set to 3000 mJ / cm or more, no corresponding effect can be obtained. ２ By setting the following, it is possible to economically crosslink the ethylenically unsaturated groups contained in the photocurable pressure-sensitive adhesive layer while reducing the influence of active energy ray irradiation on the adherend.

[0179] (Peeling Step) In the peeling step, the protective sheet is peeled and removed from the surface with the bump electrodes. The peeling step is performed after the photocurable pressure-sensitive adhesive layer is cured by irradiating it with active energy rays. By irradiating it with active energy rays, the ethylenically unsaturated bonds contained in the photocurable pressure-sensitive adhesive layer form a three-dimensional crosslinked structure and are cured. As a result, the peel strength of the photocurable pressure-sensitive adhesive layer is reduced. Thereafter, the protective sheet is peeled from the semiconductor device.

[0180] According to one embodiment of the method for manufacturing a semiconductor device having bump electrodes, even when a heating step is performed, a semiconductor device can be obtained without outgassing and without adhesive residue on the surface of the bumped substrate, allowing the resulting semiconductor device to be subjected to the subsequent mounting step without any problems. Furthermore, even when a metal film coated by a sputtering step or the like is formed on a partially exposed photocurable adhesive layer, the photocurable adhesive layer maintains adhesion to the metal film until the peeling step, reducing the amount of metal film detachment. This reduces metal contamination of the equipment used in each step and the semiconductor device.

[0181] 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.

[0182] The raw materials used are as follows. Alkyl (meth)acrylate (a1-1) or (a2-1): Methyl methacrylate, Nippon Shokubai Co., Ltd., n-butyl acrylate, Osaka Organic Chemical Industry Ltd., 2-ethylhexyl acrylate, Osaka Organic Chemical Industry Ltd. Hydroxy group-containing (meth)acrylate (a1-2) or other monomer (a2-5): 2-hydroxyethyl acrylate, Nippon Shokubai Co., Ltd. Carboxy group-containing ethylenically unsaturated compound (a1-3) or (a2-2): Acrylic acid, Nippon Shokubai Co., Ltd. (meth)acrylamide compound (a1-4): N,N-dimethylacrylamide Radical polymerization initiator: 2,2'-azobis(isobutyronitrile), Fujifilm Wako Pure Chemical Industries, Ltd. Epoxy group-containing ethylenically unsaturated compound (a2-3): Glycidyl methacrylate, NOF Corporation, 3,4-epoxycyclohexylmethyl methacrylate, Daicel Corporation. 4HBAGE (4-hydroxybutyl acrylate glycidyl ether), Mitsubishi Chemical Corporation. Silicon-containing ethylenically unsaturated compound (a2-4): FM-0711 (compound represented by the following formula, number average molecular weight (Mn): 1000), JNC Corporation. FM-0721 (compound represented by the following formula, number average molecular weight (Mn): 5000), JNC Corporation. (wherein m represents the number of repetitions) KF-2012 (a silicone compound having a polydimethylsiloxane skeleton in its molecular structure and one end terminated in a methacryloyloxy group), Shin-Etsu Chemical Co., Ltd. Isocyanato group-containing ethylenically unsaturated compound: Karenz (trademark) MOI (2-isocyanatoethyl methacrylate), Resonaq Co., Ltd. Crosslinking agent (B1): L-45E (a tolylene diisocyanate adduct of trimethylolpropane), Tosoh Corporation, trade name: Coronate L-45E Crosslinking agent (B2): L-45E (a tolylene diisocyanate adduct of trimethylolpropane), Tosoh Corporation, trade name: Coronate L-45E Tetrad X (N,N'-[1,3-phenylenebis(methylene)]bis[bis(oxiran-2-ylmethyl)amine]), Mitsubishi Gas Chemical Company, Inc., trade name: TETRAD-X Photopolymerization initiator (C): TPO (2,4,6-trimethylbenzoyldiphenylphosphine oxide), BASF, trade name: L-TPO. Silicon-containing photocurable compound (D): EBECRYL 1360 (silicone hexaacrylate), Daicel Allnex Corporation. FM-7725 (compound represented by the following formula, number average molecular weight (Mn): 10,000), JNC Corporation. (In the formula, n represents the number of repeats.)

[0183] Synthesis Example 1: Production of Ethylenically Unsaturated Group-Free (Meth)acrylic Resin (A1-1) A mixed solution containing 6.7 parts by mass of methyl methacrylate, 48.1 parts by mass of n-butyl acrylate, 33.7 parts by mass of 2-ethylhexyl acrylate, 9.6 parts by mass of N,N-dimethylacrylamide, 1.4 parts by mass of 2-hydroxyethyl acrylate, and 0.5 parts by mass of acrylic acid as raw material monomers, and 0.10 parts by mass of 2,2′-azobis(isobutyronitrile) as a polymerization initiator per 100 parts by mass of the raw material monomers, was prepared.

[0184] A four-necked flask equipped with a stirrer, a dropping funnel, a condenser, and a nitrogen inlet tube was charged with 122.2 parts by mass of ethyl acetate per 100 parts by mass of the raw material monomers as a solvent, and the temperature was raised to 80°C under a nitrogen gas atmosphere. While maintaining the reaction temperature at 80°C ± 2°C, the above mixed solution was added dropwise to the four-necked flask at a uniform rate over 4 hours. After completion of the dropwise addition, stirring was continued for an additional 6 hours at a temperature of 80°C ± 2°C to carry out polymerization, and the mixture was diluted with 27.8 parts by mass of ethyl acetate to obtain a reaction solution (solids content: 40% by mass) containing an ethylenically unsaturated group-free (meth)acrylic resin (A1-1) (weight average molecular weight (Mw): 300,000, glass transition temperature (Tg): -42°C, acid value: 3.74 mgKOH / g, hydroxyl value: 6.97 mgKOH / g).

[0185] Synthesis Example 2: Production of ethylenically unsaturated group-containing (meth)acrylic resin (A2-1) A first mixed solution was prepared containing raw material monomers, namely, 81.0 parts by mass of 2-ethylhexyl acrylate, 1.5 parts by mass of FM-0711, and 17.5 parts by mass of acrylic acid, and 0.10 parts by mass of 2,2′-azobis(isobutyronitrile) as a radical polymerization initiator per 100 parts by mass of the raw material monomers.

[0186] Next, a second mixed solution was prepared, which contained 31.0 parts by mass of glycidyl methacrylate as the epoxy group-containing ethylenically unsaturated compound (a2-3), 1.5 parts by mass of tris(4-methylphenyl)phosphine (TPTP) as a catalyst, and 98.8 parts by mass of butyl acetate as a solvent, relative to a total of 100 parts by mass of the raw material monomers and the epoxy group-containing ethylenically unsaturated compound (a2-3) used in the first mixed solution.

[0187] A four-neck flask equipped with a stirrer, dropping funnel, condenser, and nitrogen inlet tube was charged with 100 parts by mass of butyl acetate as a solvent per 100 parts by mass of the raw material monomers, and the temperature was raised to 80°C under a nitrogen gas atmosphere. While maintaining the reaction temperature at 80°C ± 2°C, the first mixed solution described above was added dropwise to the four-neck flask at a uniform rate over a period of 4 hours. After completion of the dropwise addition, the mixture was stirred at 80°C ± 2°C for an additional 6 hours to carry out polymerization, yielding a carboxy group-containing copolymer ((meth)acrylic resin (A2-0)). Thereafter, 0.15 parts by mass of 4-methoxyphenol as a polymerization inhibitor was added to the reaction system per 100 parts by mass of the raw material monomers and the epoxy group-containing ethylenically unsaturated compound (a2-3) combined.

[0188] The reaction system to which 4-methoxyphenol had been added was heated to 100°C, and the second mixed solution was added dropwise over 0.5 hours. After that, stirring was continued at a temperature of 100°C for 8 hours, and the mixture was cooled to room temperature (23°C) to obtain a reaction solution (solid content: 40% by mass) containing an ethylenically unsaturated group-containing (meth)acrylic resin (A2-1) (weight average molecular weight (Mw): 510,000, glass transition temperature (Tg): −41°C, acid value: 10.6 mgKOH / g, hydroxyl value: 93.3 mgKOH / g, ethylenically unsaturated group equivalent: 602 g / mol).

[0189] Synthesis Examples 3 to 5: Production of ethylenically unsaturated group-containing (meth)acrylic resins (A2-2) to (A2-4) Reaction solutions containing ethylenically unsaturated group-containing (meth)acrylic resins (A2-2) to (A2-4) were obtained in the same manner as in Synthesis Example 2, except that the raw material monomers and the epoxy group-containing ethylenically unsaturated compound (a2-3) shown in Table 2 were used in the blending amounts shown in Table 2 and the amount of butyl acetate was adjusted so that the solid content was 40 mass%.

[0190] Comparative Synthesis Example 1: Production of ethylenically unsaturated group-containing (meth)acrylic resin (cA2-1) A mixed solution containing 50 parts by mass of ethyl acetate, 86.5 parts by mass of 2-ethylhexyl acrylate, 13.4 parts by mass of 2-hydroxyethyl acrylate, and 0.1 part by mass of acrylic acid as raw material monomers, and 0.10 parts by mass of 2,2′-azobis(isobutyronitrile) as a radical polymerization initiator per 100 parts by mass of the raw material monomers was prepared.

[0191] A four-neck flask equipped with a stirrer, dropping funnel, condenser, and nitrogen inlet tube was charged with 50.0 parts by mass of ethyl acetate as a solvent per 100 parts by mass of raw material monomer, and the temperature was raised to 80°C under a nitrogen gas atmosphere. While maintaining the reaction temperature at 80°C ± 2°C, the above mixed solution was added dropwise to the four-neck flask at a uniform rate over 4 hours. After completion of the dropwise addition, polymerization was carried out by continuing stirring at a temperature of 80°C ± 2°C for an additional 6 hours. Next, the temperature of the reactant was lowered to 60°C, and a mixed solution of 16.0 parts by mass of 2-isocyanatoethyl methacrylate, 0.05 parts by mass of dibutyltin dilaurate as a urethanization catalyst, and 74 parts by mass of ethyl acetate was added dropwise through the dropping funnel. After completion of the dropwise addition, the reaction system was maintained at 70°C for 4 hours to eliminate the isocyanato groups, thereby obtaining a reaction solution (solid content: 40% by mass) containing an ethylenically unsaturated group-containing (meth)acrylic resin (cA2-1) (weight average molecular weight (Mw): 600,000, glass transition temperature (Tg): -44°C, acid value: 0.8 mgKOH / g, hydroxyl value: 5.9 mgKOH / g, ethylenically unsaturated group equivalent: 1125 g / mol).

[0192]

[0193]

[0194] (Production of Intermediate Layer (X1-1) Before Curing) A resin (A1-1) solution containing 30 mass % of resin (A1-1) was obtained by adding ethyl acetate as a dilution solvent to a reaction solution containing the ethylenically unsaturated group-free (meth)acrylic resin (A1-1) (also simply referred to as resin (A1-1)) obtained in Synthesis Example 1. Using the resin (A1-1) solution, a resin composition (X1) for an intermediate layer was obtained by the method shown below.

[0195] In a room shielded from active energy rays, the resin (A1-1) solution and L-45E as the crosslinking agent (B1) were added to a plastic container in the amounts (parts by mass) shown in Table 3 and stirred to obtain a resin composition (X1) for an intermediate layer. The numerical values ​​for the resin (A1) solution in Table 3, i.e., the ethylenically unsaturated group-free (meth)acrylic resin (A1) solution, are the amounts (parts by mass) used of the resin (A1) solution containing 30% by mass of resin (A1). The numerical values ​​for the crosslinking agent (B1) are the amounts (parts by mass) added per 100 parts by mass of the resin (A1) solution.

[0196] The resin composition (X1) was applied directly to a substrate so that the film thickness after heat curing would be 125 μm, and the resulting film was dried by heating at 100°C for 5 minutes to form a pre-cured intermediate layer (X1-1). A release sheet was then attached to the pre-cured intermediate layer (X1-1). A 25 μm-thick polyethylene terephthalate (PET) film (E5100, Toyobo Co., Ltd.) was used as the substrate. A 25 μm-thick polyethylene terephthalate (PET) film (E7006, Toyobo Co., Ltd.) was used as the release sheet. The film thickness after heat curing was measured on the intermediate layer (X1-1) obtained by curing the pre-cured intermediate layer (X1-1) in an oven at 40°C for 3 days.

[0197] (Production of Pre-Cure Intermediate Layer (X1-2)) A pre-cured intermediate layer (X1-2) with a release sheet attached was obtained in the same manner as in the production of the pre-cured intermediate layer (X1-1), except that a 25 μm thick polyamide (PA) film (EX-25, Unitika Ltd.) was used as the substrate, and the film thickness after thermal curing was measured.

[0198] (Production of Pre-Cure Intermediate Layer (X1-3)) A pre-cured intermediate layer (X1-3) with a release sheet attached was obtained in the same manner as the production of the pre-cured intermediate layer (X1-1), except that a 50 μm thick polyethylene naphthalate (PEN) film (Q83, Toyobo Co., Ltd.) was used as the substrate, and the film thickness after thermal curing was measured.

[0199]

[0200] (Production of Pre-thermally Cured Photocurable Pressure-Sensitive Adhesive Layer (Y1-1)) A resin (A2-1) solution containing 30 mass % of resin (A2-1) was obtained by adding ethyl acetate as a dilution solvent to a reaction solution containing the ethylenically unsaturated group-containing (meth)acrylic resin (A2-1) (also simply referred to as resin (A2-1)) obtained in Synthesis Example 2. Using the resin (A2-1) solution, a pressure-sensitive adhesive composition (Y1) for a photocurable pressure-sensitive adhesive layer was obtained by the method described below.

[0201] In a room shielded from active energy rays, the resin (A2-1) solution, Tetrad X as the crosslinking agent (B2), and TPO as the photopolymerization initiator (C) were added to a plastic container in the blending amounts (parts by mass) shown in Table 4, and the mixture was stirred to obtain a pressure-sensitive adhesive composition (Y1) for a photocurable pressure-sensitive adhesive layer.

[0202] The numerical values ​​for the resin (A2) solution in Table 4, i.e., the ethylenically unsaturated group-containing (meth)acrylic resin (A2) solution, are the amount (parts by mass) of the resin (A2) solution used, where the resin (A2) content is 30% by mass. The numerical values ​​for the resin (cA2) solution in Table 4, i.e., the ethylenically unsaturated group-containing (meth)acrylic resin (cA2) solution, are the amount (parts by mass) of the resin (cA2) solution used, where the resin (cA2) content is 30% by mass. The numerical values ​​for the crosslinker (B2) and the photopolymerization initiator (C) are the amounts (parts by mass) blended per 100 parts by mass of the resin (A2) solution or the resin (cA2) solution. However, the numerical value for the silicon-containing photocurable compound (D) is the amount (parts by mass) blended per 100 parts by mass of the resin (A2).

[0203] The pressure-sensitive adhesive composition (Y1) was applied directly onto a release sheet so that the film thickness after thermal curing would be 25 μm, and the applied layer was dried by heating at 100°C for 2 minutes to form a pre-thermally cured photocurable pressure-sensitive adhesive layer (Y1-1). A release sheet was then attached to the pre-thermally cured photocurable pressure-sensitive adhesive layer (Y1-1). A 25 μm-thick polyethylene terephthalate (PET) film (E7006, Toyobo Co., Ltd.) was used as the release sheet. The film thickness after thermal curing was measured on the photocurable pressure-sensitive adhesive layer (Y1-1) obtained by curing the pre-thermally cured photocurable pressure-sensitive adhesive layer (Y1-1) in an oven at 40°C for 3 days.

[0204] (Production of Pre-thermally Cured Photocurable Pressure-Sensitive Adhesive Layers (Y2-1) to (Y7-1)) Pressure-sensitive adhesive compositions (Y2) to (Y7) were obtained in the same manner as in the production of pressure-sensitive adhesive composition (Y1), except for using the raw materials and blending amounts shown in Table 4. Pre-thermally cured photocurable pressure-sensitive adhesive layers (Y2-1) to (Y7-1) with release sheets attached were obtained in the same manner as in the production of pre-thermally cured photocurable pressure-sensitive adhesive layer (Y1-1), except for using pressure-sensitive adhesive composition (Y2) instead of pressure-sensitive adhesive composition (Y1), and the film thicknesses after thermal curing were measured.

[0205]

[0206] [Example 1] (Production of protective sheet) The release sheet was peeled from the pre-curing intermediate layer (X1-1) to which it had been attached, and the release sheet was peeled from one side of the pre-thermo-cure light-curable pressure-sensitive adhesive layer (Y1-1) to which the release sheet had been attached, and the two were attached with the exposed surfaces facing each other. Thereafter, the sheets were cured in an oven at 40°C for 3 days to crosslink and cure the pre-curing intermediate layer (X1-1) and the pre-thermo-cure light-curable pressure-sensitive adhesive layer (Y1-1), thereby obtaining the protective sheet of Example 1.

[0207] Examples 2 to 4, Comparative Examples 1 to 3 Protective sheets were obtained in the same manner as in Example 1, except that the pre-cured intermediate layer (X) and pre-thermo-cured photocurable pressure-sensitive adhesive layer (Y) shown in Table 5 were used.

[0208] The resulting protective sheets were evaluated for the following items using the methods described below. The results are shown in Table 5.

[0209] [Peel strength before UV irradiation] The protective sheet was cut into a size of 25 mm length and 100 mm width, and the release sheet on the photocurable pressure-sensitive adhesive layer side was peeled off to expose the photocurable pressure-sensitive adhesive layer. Next, the protective sheet was attached to a glass plate so that the exposed photocurable pressure-sensitive adhesive layer, i.e., the measurement surface, was in contact with the glass plate, and a 2 kg rubber roller (width: approximately 50 mm) was rolled back and forth once to obtain a sample for measuring peel strength before UV irradiation.

[0210] The obtained measurement sample was left for 24 hours in an environment of 23°C and 50% humidity. Thereafter, a tensile test was carried out in the 180° direction at a peel rate of 300 mm / min in an environment of 23°C and 50% humidity using a tensile tester (Texture Analyzer, Eiko Seiki Co., Ltd.) in accordance with JIS Z 0237:2009, to measure the peel strength (N / 25 mm) of the pressure-sensitive adhesive sheet to the glass plate.

[0211] [Peel strength after UV irradiation] A sample identical to that used for measuring peel strength before UV irradiation was prepared, and the surface on the protective sheet side was irradiated with an irradiation dose of 1000 mJ / cm ２ The sample was irradiated with ultraviolet (UV) rays under the conditions of (a) to (c) to obtain a sample for measuring peel strength after UV irradiation. For UV irradiation, a conveyor-type ultraviolet irradiation device (Eye Graphics Co., Ltd., 2 kW lamp, 80 W / cm) was used.

[0212] The peel strength (N / 25 mm) of the pressure-sensitive adhesive sheet to the glass plate of the obtained measurement sample was measured in the same manner as in "Peel strength before UV irradiation."

[0213] [Adhesive Residue] After heating the sample for measuring peel strength before UV irradiation at 200°C for 2 hours, the protective sheet side was irradiated with an amount of 1000 mJ / cm ２ The protective sheet was then peeled off from the glass plate under the conditions of 1. The adhesive residue was evaluated as "good" if no adhesive residue remained on the glass surface, and "poor" if any adhesive residue remained.

[0214] [Gap Filling Ability: Protection Step] The release sheet of the protective sheet was peeled off to expose the photocurable adhesive layer. Next, the exposed photocurable adhesive layer and a PCB with bumps (bump diameter φ=20 μm, bump spacing 30 μm, bump height 45, 80, or 100 μm) were attached to each other using a mounter (Hugle Electronics, HS7800) at 40° C. for 5 minutes to obtain a sample for process testing. This sample was observed under an optical microscope from the protective sheet side, and the gap filling ability in the protection step was evaluated as "excellent" when the area containing air bubbles was 1% or less of the entire PCB with bumps, "good" when it was greater than 1% and less than 10%, and "poor" when it was 10% or more.

[0215] [Step filling ability: dicing process] The process test sample obtained in the protection process was diced with a blade (SDC200 R100NMR, kerf width: 0.3 mm, blade rotation speed: 28000 rpm, cutting speed: 30 mm / sec, cutting depth: 100 μm, Tokyo Seimitsu Co., Ltd.) to obtain small pieces of process test samples. A 50 mJ / cm 2 beam was applied to the surface of the protective sheet side. ２ The photocurable adhesive layer was partially cured by irradiating with UV under the conditions of (a) and (b). A conveyor-type ultraviolet irradiation device (Eye Graphics Co., Ltd., 2 kW lamp, 80 W / cm) was used for UV irradiation. The sample after UV irradiation was observed with an optical microscope from the protective sheet side, and the step filling ability in the dicing process was evaluated as "excellent" when the area where air bubbles were mixed was 1% or less of the entire PCB with bumps, "good" when the area where air bubbles were mixed was greater than 1% and less than 10%, and "poor" when the area where air bubbles were mixed was 10% or more.

[0216] [Step-filling ability: heating process] The small process test samples obtained in the dicing process were subjected to a heat treatment for 2 hours at 200° C. After cooling, the samples were observed with an optical microscope from the protective sheet side, and the step-filling ability in the heating process was evaluated as "excellent" when the area where air bubbles were mixed in was 1% or less of the entire PCB with bumps, "good" when the area where air bubbles were mixed in was greater than 1% but less than 10%, and "poor" when the area where air bubbles were mixed in was 10% or more.

[0217] [Metal Film Adhesion] The small process test samples obtained in the dicing process were subjected to sputtering at temperatures of 60 to 150° C. and pressure of 7×10 using a sputtering device SDH series (product name, ULVAC, Inc.). －１ A copper film with a thickness of about 1.8 μm was formed under the condition of 500 mJ / cm 2 Pa to form an electromagnetic shield. ２The photocurable adhesive layer was cured by irradiating with UV under the conditions of 9 mm collet size, 13 pins, and a push-up speed of 20 mm / sec using a die bonder BESTEM-02 (product name, Canon Machinery Inc.). The bumped PCB was then picked up using a die bonder BESTEM-02 (product name, Canon Machinery Inc.) under conditions of a collet size of 9 mm, a pin count of 13, and a push-up speed of 20 mm / sec to obtain a protective sheet having a copper film on a portion of its surface. When the protective sheet was oriented so that the surface having the copper film was facing downward, the metal film adhesion was evaluated as follows: if the area ratio of the copper powder peeled off from the protective sheet was 1% or less, it was "excellent"; if it was greater than 1% and less than 10%, it was "good"; and if it was 10% or more, it was "poor." The area evaluation was performed using an optical microscope.

[0218]

[0219] In Examples 1 to 4, all adhesive residue was "good" and all metal film adhesion was "excellent." In Comparative Examples 2 and 3, in which the ethylenically unsaturated group was introduced by a compound having an isocyanato group, adhesive residue was "poor." In Comparative Examples 1 and 3, which did not contain silicon atoms, metal adhesion was "poor."

[0220] 12 Substrate 14 Intermediate layer 16 Photocurable adhesive layer 18 Release sheet 10 Protective sheet

Claims

1. A pressure-sensitive adhesive composition comprising an ethylenically unsaturated group-containing (meth)acrylic resin (A2), a crosslinking agent (B2), and a photopolymerization initiator (C), and containing 1,000 to 100,000 mass ppm of silicon atoms, wherein the ethylenically unsaturated group-containing (meth)acrylic resin (A2) has a plurality of functional groups that react with functional groups possessed by the crosslinking agent (B2), and the ethylenically unsaturated group-containing (meth)acrylic resin (A2) is an adduct of an epoxy group-containing ethylenically unsaturated compound (a2-3) to a (meth)acrylic resin (A2-0) having as raw material monomers at least an alkyl (meth)acrylate (a2-1) and a carboxy group-containing ethylenically unsaturated compound (a2-2).

2. The pressure-sensitive adhesive composition according to claim 1, wherein the ethylenically unsaturated group-containing (meth)acrylic resin (A2) is an adduct of an epoxy group-containing ethylenically unsaturated compound (a2-3) to a (meth)acrylic resin (A2-0) having as raw material monomers at least an alkyl (meth)acrylate (a2-1), a carboxy group-containing ethylenically unsaturated compound (a2-2), and a silicon-containing ethylenically unsaturated compound (a2-4).

3. The pressure-sensitive adhesive composition according to claim 1, further comprising a silicon-containing photocurable compound (D).

4. The pressure-sensitive adhesive composition according to claim 1 or 2, wherein the ethylenically unsaturated group-containing (meth)acrylic resin (A2) has an acid value of 1 to 100 mgKOH / g.

5. The pressure-sensitive adhesive composition according to claim 1 or 2, wherein the ethylenically unsaturated group-containing (meth)acrylic resin (A2) has an ethylenically unsaturated group equivalent of 500 to 5,000 g / mol.

6. The pressure-sensitive adhesive composition according to claim 1 or 2, wherein the ethylenically unsaturated group-containing (meth)acrylic resin (A2) has a glass transition temperature (Tg) of -80 to 0°C.

7. The pressure-sensitive adhesive composition according to claim 1 or 2, wherein the crosslinking agent (B2) is at least one selected from the group consisting of epoxy crosslinking agents and aziridine crosslinking agents.

8. The pressure-sensitive adhesive composition according to claim 1 or 2, wherein the content of the carboxyl group-containing ethylenically unsaturated compound (a2-2) is 1 to 60 mol % based on the total amount of raw material monomers of the (meth)acrylic resin (A2-0).

9. The pressure-sensitive adhesive composition according to claim 2, wherein the content of the silicon-containing ethylenically unsaturated compound (a2-4) is 0.01 to 10 mol % based on the total amount of raw material monomers of the (meth)acrylic resin (A2-0).

10. The pressure-sensitive adhesive composition according to claim 1 or 2, wherein the content of the alkyl (meth)acrylate (a2-1) is 30 to 99 mol % based on the total amount of raw material monomers of the (meth)acrylic resin (A2-0).

11. The pressure-sensitive adhesive composition according to claim 1 or 2, wherein the amount of the epoxy group-containing ethylenically unsaturated compound (a2-3) is 0.5 to 55 moles per 100 moles of the total of the raw material monomers of the (meth)acrylic resin (A2-0), and the addition rate of the epoxy group-containing ethylenically unsaturated compound (a2-3) to the carboxy groups derived from the carboxy group-containing ethylenically unsaturated compound (a2-2) is 10 to 99%.

12. A protective sheet comprising: a substrate; and a photocurable adhesive layer that is a thermoset product of the adhesive composition according to any one of claims 1 to 3 and 9.

13. The protective sheet according to claim 12, comprising the substrate, and an intermediate layer and the photocurable adhesive layer, in this order, on one main surface of the substrate.

14. The protective sheet according to claim 13, wherein the intermediate layer has a thickness of 30 to 600 μm, the photocurable pressure-sensitive adhesive layer has a thickness of 1 to 100 μm, and the thickness ratio of the intermediate layer to the photocurable pressure-sensitive adhesive layer (intermediate layer / photocurable pressure-sensitive adhesive layer) is 1 to 50.

15. The protective sheet according to claim 13, wherein the intermediate layer is a thermoset product of a resin composition containing an ethylenically unsaturated group-free (meth)acrylic resin (A1) and a crosslinking agent (B1), and the ethylenically unsaturated group-free (meth)acrylic resin (A1) has a plurality of functional groups that react with functional groups contained in the crosslinking agent (B1).

16. A method for manufacturing a semiconductor device having bump electrodes, comprising: a protection step of attaching the photocurable adhesive layer surface of the protective sheet described in claim 13 to the bump electrode-bearing surface of the semiconductor device before processing; an active energy ray irradiation step of irradiating the protective sheet with active energy rays to photocure the photocurable adhesive layer; a heating step of the semiconductor device before processing to which the protective sheet has been attached; and a peeling step of peeling the protective sheet from the bump electrode-bearing surface.

17. The method for manufacturing a semiconductor device according to claim 16, wherein, when the height of the bump electrode is H [μm] and the total thickness of the intermediate layer and the photocurable adhesive layer is d [μm], d / H is 1.00 to 100.

18. The method for manufacturing a semiconductor device according to claim 16, wherein the maximum temperature reached in the heating step is 80 to 300°C.

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