JP6935872B2 - Adhesive sheet for semiconductor processing - Google Patents

Description

The present invention relates to an adhesive sheet for semiconductor processing, and more particularly to an adhesive sheet for protecting the surface of a semiconductor wafer used for protecting the surface of a semiconductor wafer with bumps.

As information terminal devices are rapidly becoming thinner, smaller, and more multifunctional, the semiconductor devices mounted on them are also required to be thinner and denser, and semiconductor wafers are also required to be thinner. ing. Conventionally, in order to meet the demand, the back surface of the semiconductor wafer has been ground to reduce the thickness. Further, in recent years, in semiconductor wafers, bumps made of solder or the like having a height of about several tens to several hundreds of μm may be formed on the wafer surface. When such a bumped semiconductor wafer is back-ground, a surface protection sheet is attached to the surface of the wafer on which the bumps are formed in order to protect the bump portion.

As the surface protective sheet, as disclosed in Patent Documents 1 and 2, for example, an adhesive sheet in which an intermediate layer and an adhesive layer are provided in this order on a base material is used. In Patent Documents 1 and 2, the elastic modulus and gel content of the intermediate layer are adjusted in order to suppress wafer contamination and to improve the followability to the unevenness of the wafer surface as an adherend.
Further, in Patent Documents 1 and 2, even if the pressure-sensitive adhesive layer is blended with an energy ray-curable oligomer or a carbon-carbon double bond is introduced into the polymer constituting the pressure-sensitive adhesive to make it energy ray-curable. Good things are disclosed. Since the surface protective sheet uses an energy ray-curable pressure-sensitive adhesive, the adhesive strength of the pressure-sensitive adhesive layer is reduced by irradiation with energy rays, so that the surface protective sheet can be easily peeled off from the semiconductor wafer after use.

Japanese Patent No. 4367769 Japanese Patent No. 4369584

However, the pressure-sensitive adhesive layer cured by energy rays may have insufficient adhesion strength with the intermediate layer. As a result, when the surface protective sheet is peeled from the semiconductor wafer after the energy ray curing, delamination may occur between the intermediate layer and the pressure-sensitive adhesive layer. When delamination occurs, for example, when the surface protective sheet is peeled off, the adhesive may remain on the semiconductor wafer and cause wafer contamination.
The present invention has been made in view of the above circumstances, and prevents delamination that occurs between the intermediate layer and the pressure-sensitive adhesive layer when the pressure-sensitive adhesive sheet for semiconductor processing is cured and peeled from the work. Make it an issue.

As a result of diligent studies, the present inventors have made both the intermediate layer and the pressure-sensitive adhesive layer into a predetermined composition having energy ray curability, and set the elastic modulus difference after these energy ray curing to a certain value or less. It was found that the above problems could be solved, and the following invention was completed. The present invention provides the following (1) to (8).
(1) A pressure-sensitive adhesive sheet for semiconductor processing, which comprises a base material, an intermediate layer, and a pressure-sensitive adhesive layer in this order.
For forming an intermediate layer, the intermediate layer containing a non-energy ray-curable acrylic polymer (A) and an energy ray-curable acrylic polymer (B) having a weight average molecular weight of 50,000 to 250,000. Along with being a layer formed from the composition, the pressure-sensitive adhesive layer is energy ray-curable.
A pressure-sensitive adhesive sheet for semiconductor processing in which the elastic modulus difference between the intermediate layer and the pressure-sensitive adhesive layer after energy ray curing at 23 ° C. is 20 MPa or less.
(2) The semiconductor processing according to (1) above, wherein in the composition for forming an intermediate layer, the amount of the acrylic polymer (B) is less than 25 parts by mass with respect to 100 parts by mass of the acrylic polymer (A). Adhesive sheet for.
(3) The pressure-sensitive adhesive sheet for semiconductor processing according to (1) or (2) above, wherein the acrylic polymer (A) has a weight average molecular weight of 300,000 to 1,500,000.
(4) The semiconductor processing according to any one of (1) to (3) above, wherein the pressure-sensitive adhesive layer is formed from a pressure-sensitive adhesive composition containing an energy ray-curable acrylic polymer (C). Adhesive sheet for.
(5) The acrylic polymer (C) has a structural unit derived from an alkyl (meth) acrylate (c1) having an alkyl group having 1 to 18 carbon atoms and a structural unit derived from a functional group-containing monomer (c2). The semiconductor according to (4) above, which is an acrylic copolymer (C1) which is a reaction product obtained by reacting an acrylic copolymer (C0) having an acrylic copolymer with a polymerizable compound (Xc) having an energy ray-polymerizable group. Adhesive sheet for processing.
(6) The pressure-sensitive adhesive sheet for semiconductor processing according to (4) or (5) above, wherein the acrylic polymer (C) has a weight average molecular weight of 100,000 to 1.5 million.
(7) The composition for forming an intermediate layer contains 0.3 to 15 parts by mass of a photopolymerization initiator with respect to 100 parts by mass of the acrylic polymer (A), and the pressure-sensitive adhesive composition comprises. The pressure-sensitive adhesive sheet for semiconductor processing according to any one of (4) to (6) above, which contains 0.5 to 15 parts by mass of a photopolymerization initiator with respect to 100 parts by mass of the acrylic polymer (C). ..
(8) The acrylic polymer (B) contains a structural unit derived from an alkyl (meth) acrylate (b1) having an alkyl group having 1 to 18 carbon atoms and a structural unit derived from a functional group-containing monomer (b2). Acrylic copolymer (B1) which is a reaction product of a polymerizable compound (Xb) having an energy ray-polymerizable group with an acrylic copolymer (B0) having the above (1) to (7). The adhesive sheet for semiconductor processing according to any one of the above items.

According to the present invention, when the pressure-sensitive adhesive sheet for semiconductor processing is cured by energy rays and peeled from the work, it is possible to prevent delamination that occurs between the intermediate layer and the pressure-sensitive adhesive layer.

In the following description, "weight average molecular weight (Mw)" is a polystyrene-equivalent value measured by a gel permeation chromatography (GPC) method, and specifically, it was measured based on the method described in Examples. The value.
Further, in the description in the present specification, for example, "(meth) acrylate" is used as a term indicating both "acrylate" and "methacrylate", and the same applies to other similar terms.

Hereinafter, the present invention will be described in more detail using embodiments.
The adhesive sheet for semiconductor processing of the present invention (hereinafter, also simply referred to as “adhesive sheet”) includes a base material, an intermediate layer provided on one surface of the base material, and an adhesive layer further provided on the intermediate layer. And have. Further, the pressure-sensitive adhesive sheet may be further provided with a release material on the pressure-sensitive adhesive layer. The release material protects the pressure-sensitive adhesive layer and is removed from the pressure-sensitive adhesive layer when the pressure-sensitive adhesive sheet is attached to the work.
The adhesive sheet may have a layer other than the above. For example, in order to improve the adhesion between the intermediate layer and the base material, an easy-adhesion layer formed of various curable resins or the like may be provided on one surface of the base material. Further, in order to prevent the pressure-sensitive adhesive sheet from being charged, an antistatic layer containing a known antistatic agent may be provided on one surface of the base material.

The intermediate layer is a composition for forming an intermediate layer containing a non-energy ray-curable acrylic polymer (A) and an energy ray-curable acrylic polymer (B) having a weight average molecular weight of 50,000 to 250,000. It is a layer formed from an object. The pressure-sensitive adhesive layer is a layer formed of an energy ray-curable pressure-sensitive adhesive composition. The difference in elastic modulus between the intermediate layer after energy ray curing and the pressure-sensitive adhesive layer after energy ray curing at 23 ° C. is 20 MPa or less. The elastic modulus at 23 ° C. is the value of the storage elastic modulus at 23 ° C. when the storage elastic modulus at -30 to 200 ° C. is measured (frequency: 1 Hz) at a heating rate of 3 ° C./min with a viscoelasticity measuring device. Specifically, it is a value measured based on the method described in the examples.
In the present invention, both the intermediate layer and the pressure-sensitive adhesive layer are energy ray-curable. Therefore, when the adhesive sheet attached to the adherend is irradiated with energy rays, the intermediate layer and the adhesive layer are hardened to reduce the adhesive force to the adherend, and the adhesive sheet is easily peeled off from the adherend. Will be. Further, since the difference in elastic modulus between the intermediate layer and the pressure-sensitive adhesive layer after energy ray curing is small, delamination between the intermediate layer and the pressure-sensitive adhesive layer is prevented when the pressure-sensitive adhesive sheet is peeled off.

On the other hand, if the elastic modulus difference exceeds 20 MPa, the interlayer strength between the intermediate layer and the pressure-sensitive adhesive layer becomes low when cured by energy rays. Therefore, when the pressure-sensitive adhesive sheet is peeled off from the adherend after the energy ray curing, delamination is likely to occur between the intermediate layer and the pressure-sensitive adhesive layer. From the viewpoint of improving the interlayer strength between the intermediate layer and the pressure-sensitive adhesive layer and more effectively suppressing delamination, the elastic modulus difference is preferably 15 MPa or less, and more preferably 8 MPa or less.
Further, from the viewpoint of suppressing delamination, the elastic modulus difference should be low, but in order for the intermediate layer and the pressure-sensitive adhesive layer to have desired functions, the elastic modulus difference must be 0.1 MPa or more. It is preferably 0.5 MPa or more, and more preferably 0.5 MPa or more.

Hereinafter, each layer constituting the adhesive sheet will be described in more detail.
<Middle class>
In the pressure-sensitive adhesive sheet, the intermediate layer is a layer provided between the pressure-sensitive adhesive layer and the base material. The intermediate layer may be formed directly on the base material, but as described above, when another layer such as an easy-adhesion layer or an antistatic layer is provided on the base material, the intermediate layer may be formed of the other layer. Formed on top.
As described above, the intermediate layer contains a non-energy ray-curable acrylic polymer (A) and an energy ray-curable acrylic polymer (B) having a weight average molecular weight of 50,000 to 250,000. It is a layer formed from a composition for forming an intermediate layer. The acrylic polymer (A) may be abbreviated as "component (A)" below. The same applies to other ingredients.
In the intermediate layer, the component (A) exerts a cohesive force, and the component (B) having a low molecular weight exhibits stress relaxation. The pressure-sensitive adhesive sheet having such an intermediate layer has high holding performance for the adherend, for example, the followability to the adherend having unevenness is improved. Therefore, when grinding a wafer or the like to which an adhesive sheet is attached, it is possible to prevent the wafer from being damaged and the grinding debris or grinding water from entering the surface of the wafer.

The elastic modulus of the intermediate layer at 23 ° C. after energy ray curing is preferably 0.5 to 40 MPa, more preferably 1.0 to 30 MPa, still more preferably 1.5 to 20 MPa. When the intermediate layer has such an elastic modulus, it is easy to reduce the above-mentioned elastic modulus difference while sufficiently exerting the function as the intermediate layer before the energy ray irradiation. Further, by setting the elastic modulus within these ranges, it becomes easy to increase the interlayer strength.

Further, the elastic modulus of the intermediate layer after energy ray curing at 23 ° C. may be lower or higher than the elastic modulus of the pressure-sensitive adhesive layer after energy ray curing at 23 ° C.
The elastic modulus of the intermediate layer at 23 ° C. after energy ray curing is, for example, the blending amount of the acrylic polymer (B) or the amount of the energy ray-polymerizable group introduced into the acrylic polymer (B) ( It can be adjusted by the value of α, which will be described later). For example, when the blending amount of the acrylic polymer (B) or the amount of the energy ray-polymerizable group is increased, the elastic modulus tends to increase. Further, it can be appropriately adjusted depending on the type and amount of the monomer constituting the acrylic polymer (A), the amount of the cross-linking agent blended in the intermediate layer, the amount of the photopolymerization initiator, and the like.

[Acrylic polymer (A)]
The acrylic polymer (A) is a non-energy ray-curable polymer having a structural unit derived from (meth) acrylate. The acrylic polymer (A) preferably contains an acrylic copolymer (A1) having a structural unit derived from an alkyl (meth) acrylate (a1) and a structural unit derived from a functional group-containing monomer (a2). , It is more preferable to be composed of this acrylic copolymer (A1).
The form of copolymerization of the acrylic copolymer (A1) is not particularly limited, and may be a block copolymer or a random copolymer. The content of the acrylic copolymer (A1) is preferably 70 to 100% by mass, more preferably 70% by mass, based on the total amount (100% by mass) of the component (A) contained in the composition for forming the intermediate layer. Is 80 to 100% by mass, more preferably 90 to 100% by mass, and even more preferably 100% by mass.

As the alkyl (meth) acrylate (a1), an alkyl (meth) acrylate having an alkyl group having 1 to 18 carbon atoms is used. Specifically, methyl (meth) acrylate, ethyl (meth) acrylate, propyl (meth) acrylate, n-butyl (meth) acrylate, n-pentyl (meth) acrylate, n-hexyl (meth) acrylate, 2-ethylhexyl. (Meta) acrylate, isooctyl (meth) acrylate, n-decyl (meth) acrylate, n-dodecyl (meth) acrylate, n-tridecyl (meth) acrylate, myristyl (meth) acrylate, palmityl (meth) acrylate, stearyl (meth) ) Acrylate and the like can be mentioned. The alkyl (meth) acrylate (a1) may be used alone or in combination of two or more.

The content of the structural unit derived from the alkyl (meth) acrylate (a1) in the acrylic copolymer (A1) is preferably relative to the total structural unit (100% by mass) of the acrylic copolymer (A1). It is 50 to 99.5% by mass, more preferably 60 to 99% by mass, still more preferably 70 to 97% by mass, and even more preferably 80 to 95% by mass.
When this content is 50% by mass or more, the holding performance of the pressure-sensitive adhesive sheet is enhanced, and it becomes easy to improve the followability to an adherend having a large unevenness difference. Further, if it is 99.5% by mass or less, a certain amount or more of the constituent units derived from the component (a2) can be secured.

Among the above, the alkyl (meth) acrylate (a1) is preferably an alkyl (meth) acrylate having an alkyl group having 1 to 8 carbon atoms in order to make the elastic coefficient of the intermediate layer an appropriate value. It is more preferable to contain an alkyl (meth) acrylate having 4 to 8 carbon atoms in the group (hereinafter, may be referred to as a monomer (Y)). Specifically, as the monomer (Y), 2-ethylhexyl (meth) acrylate and n-butyl (meth) acrylate are preferable, and n-butyl (meth) acrylate is particularly preferable.
Here, all of the alkyl (meth) acrylates (a1) constituting the acrylic copolymer (A1) may be the monomer (Y), or some of them may be the monomer (Y). Specifically, the monomer (Y) is preferably 75 to 100% by mass, more preferably 80 to 100% by mass, still more preferably 90 to 100% by mass, based on the total amount of the alkyl (meth) acrylate (a1).

The functional group-containing monomer (a2) is a monomer having a functional group such as a hydroxy group, a carboxy group, an epoxy group, an amino group, a cyano group, a nitrogen atom-containing ring group, and an alkoxysilyl group. Among the above, the functional group-containing monomer (a2) is preferably one or more selected from a hydroxy group-containing monomer, a carboxy group-containing monomer, and an epoxy group-containing monomer.

Examples of the hydroxy group-containing monomer include 2-hydroxyethyl (meth) acrylate, 2-hydroxypropyl (meth) acrylate, 3-hydroxypropyl (meth) acrylate, 2-hydroxybutyl (meth) acrylate, and 3-hydroxybutyl ( Hydroxyalkyl (meth) acrylates such as meta) acrylate and 4-hydroxybutyl (meth) acrylate; unsaturated alcohols such as vinyl alcohol and allyl alcohol can be mentioned.
Examples of the carboxy group-containing monomer include (meth) acrylic acid, maleic acid, fumaric acid, and itaconic acid.

Examples of the epoxy-containing monomer include an epoxy group-containing (meth) acrylic acid ester and a non-acrylic epoxy group-containing monomer. Examples of the epoxy group-containing (meth) acrylic acid ester include glycidyl (meth) acrylate, β-methylglycidyl (meth) acrylate, (3,4-epoxycyclohexyl) methyl (meth) acrylate, and 3-epoxycyclo-2-. Examples thereof include hydroxypropyl (meth) acrylate. Examples of the non-acrylic epoxy group-containing monomer include glycidyl crotonate and allyl glycidyl ether.
The functional group-containing monomer (a2) may be used alone or in combination of two or more.
Among the functional group-containing monomers (a2), the carboxy group-containing monomer is more preferable, and (meth) acrylic acid is more preferable, and acrylic acid is most preferable. When a carboxy group-containing monomer is used as the functional group-containing monomer (a2), the cohesive force of the intermediate layer is enhanced, and the holding performance of the intermediate layer and the like can be further improved.

The content of the structural unit derived from the functional group-containing monomer (a2) in the acrylic copolymer (A1) is preferably 0 with respect to the total structural unit (100% by mass) of the acrylic copolymer (A1). .5 to 40% by mass, more preferably 1 to 30% by mass, still more preferably 3 to 20% by mass, still more preferably 5 to 15% by mass.
When the content of the constituent unit derived from the component (a2) is 0.5% by mass or more, the cohesive force of the intermediate layer is high, and the compatibility with the component (B) is easily improved. On the other hand, when the content is 40% by mass or less, the constituent unit derived from the component (a1) can be secured in a certain amount or more.

The acrylic copolymer (A1) may be a copolymer of an alkyl (meth) acrylate (a1) and a functional group-containing monomer (a2), but the component (a1), the component (a2), and these It may be a polymer with other monomers (a3) other than the components (a1) and (a2).
Examples of the other monomer (a3) include cyclohexyl (meth) acrylate, benzyl (meth) acrylate, isobornyl (meth) acrylate, dicyclopentanyl (meth) acrylate, dicyclopentenyl (meth) acrylate, and dicyclopentenyloxy. Examples thereof include (meth) acrylate having a cyclic structure such as ethyl (meth) acrylate, vinyl acetate, styrene and the like. The other monomer (a3) may be used alone or in combination of two or more.
The content of the structural unit derived from the other monomer (a3) in the acrylic copolymer (A1) is preferably 0 to 0 with respect to the total structural unit (100% by mass) of the acrylic copolymer (A1). It is 30% by mass, more preferably 0 to 20% by mass, still more preferably 0 to 10% by mass, and even more preferably 0 to 5% by mass.

The weight average molecular weight (Mw) of the acrylic polymer (A) is preferably 300,000 to 1.5 million, more preferably 400,000 to 1.2 million, still more preferably 400,000 to 1.1 million, and even more preferably 450,000 to 90. It is ten thousand. By setting Mw to these upper limit values or less, the acrylic polymer (A) has good compatibility with the acrylic polymer (B). Further, by setting Mw within the above range, it becomes easy to improve the holding performance of the adhesive sheet.
The content of the acrylic polymer (A) in the intermediate layer forming composition is preferably 60 to 99% by mass, more preferably 70 to 70% by mass, based on the total amount (100% by mass) of the intermediate layer forming composition. It is 97% by mass, more preferably 75 to 92% by mass or more.
When the composition for forming an intermediate layer is diluted with a diluted solution such as an organic solvent as described later, the total amount of the composition for forming an intermediate layer means the total amount of solid content excluding the diluted solution. .. The same applies to the pressure-sensitive adhesive composition described later.

[Acrylic polymer (B)]
The acrylic polymer (B) is an acrylic polymer having energy ray curability by introducing an energy ray-polymerizable group. The acrylic polymer (B) has a weight average molecular weight (Mw) of 50,000 to 250,000. In the present invention, it is considered that by using the component (B) in the intermediate layer, when the energy ray is irradiated, the component (B) reacts with the energy ray curing component in the pressure-sensitive adhesive layer and is bonded. Therefore, in combination with the small difference in elastic modulus, the interlayer strength between the intermediate layer and the pressure-sensitive adhesive layer after energy ray curing is improved.

When the Mw of the acrylic polymer (B) is less than 50,000, when the pressure-sensitive adhesive sheet is stored for a long period of time, a part of the component (B) moves into the pressure-sensitive adhesive layer, and the adhesive strength of the pressure-sensitive adhesive sheet becomes unstable. At the same time, the adhesive layer may be excessively hardened after irradiation with energy rays. As a result, the pressure-sensitive adhesive sheet has a strength between the intermediate layer and the pressure-sensitive adhesive layer after energy ray irradiation, for example, when it is used after long-term storage or when it is left for a long time in a state of being attached to an adherend. May be inadequate. Further, even when the Mw of the component (B) exceeds 250,000, the interlayer strength between the intermediate layer and the pressure-sensitive adhesive layer after the energy ray irradiation tends to decrease.
From the above viewpoint, the weight average molecular weight (Mw) of the acrylic polymer (B) is preferably 60,000 to 220,000, more preferably 70,000 to 200,000, still more preferably 80,000 to 180,000, and even more preferably. Is 85,000 to 150,000.

The acrylic polymer (B) is an acrylic polymer having an energy ray-polymerizable group introduced therein and having a structural unit derived from (meth) acrylate. The energy ray-polymerizable group of the acrylic polymer (B) is preferably introduced into the side chain of the acrylic polymer. The energy ray-polymerizable group may be a group containing an energy ray-polymerizable carbon-carbon double bond, and examples thereof include a (meth) acryloyl group and a vinyl group. Among them, a (meth) acryloyl group is preferable. ..

The acrylic polymer (B) is energy ray-polymerized on an acrylic copolymer (B0) having a structural unit derived from an alkyl (meth) acrylate (b1) and a structural unit derived from a functional group-containing monomer (b2). It is preferable to contain an acrylic copolymer (B1) which is a reaction product obtained by reacting a polymerizable compound (Xb) having a sex group, and more preferably it is composed of this acrylic copolymer (B1).
The form of copolymerization of the acrylic copolymer (B0) is not particularly limited, and may be any of a block copolymer, a random copolymer, and the like. The content of the acrylic copolymer (B1) is preferably 70 to 100% by mass, more preferably 80, based on the total amount (100% by mass) of the component (B) contained in the composition for forming the intermediate layer. It is ~ 100% by mass, more preferably 90 to 100% by mass, and even more preferably 100% by mass.

As the alkyl (meth) acrylate (b1), an alkyl (meth) acrylate having an alkyl group having 1 to 18 carbon atoms is used, and specific examples thereof include those exemplified as the component (a1). They may be used alone or in combination of two or more.
The content of the structural unit derived from the alkyl (meth) acrylate (b1) in the acrylic copolymer (B0) is preferably relative to the total structural unit (100% by mass) of the acrylic copolymer (B0). It is 50 to 95% by mass, more preferably 55 to 90% by mass, still more preferably 60 to 85% by mass, and even more preferably 65 to 80% by mass. When this content is 50% by mass or more, the shape of the formed intermediate layer can be sufficiently maintained. Further, if it is 95% by mass or less, a certain amount of the structural unit derived from the component (b2) which is the reaction point with the polymerizable compound (Xb) can be secured.

Further, the alkyl (meth) acrylate (b1) is preferably an alkyl (meth) acrylate having an alkyl group having 1 to 8 carbon atoms, like the component (a1), and further, a monomer (Y) (that is, that is, , Alkyl (meth) acrylate having 4 to 8 carbon atoms in the alkyl group) is more preferable. The suitable compound as the monomer (Y) is the same as the above (a1), and n-butyl (meth) acrylate is particularly preferable.
Here, all of the alkyl (meth) acrylates (b1) contained in the acrylic copolymer (B0) may be the monomer (Y), but it is preferable that some of them are the monomers (Y). .. The monomer (Y) is preferably 65 to 100% by mass, more preferably 70 to 100% by mass, still more preferably 80 to 95% by mass, based on the total amount of the alkyl (meth) acrylate (b1).

The functional group-containing monomer (b2) includes a monomer having a functional group exemplified in the above-mentioned functional group-containing monomer (a2), and is selected from a hydroxy group-containing monomer, a carboxy group-containing monomer, and an epoxy group-containing monomer 1. Seeds or more are preferred. Examples of these specific compounds include the same compounds as those exemplified as the component (a2).
Further, as the functional group-containing monomer (b2), a hydroxy group-containing monomer is preferable, and among them, various hydroxyalkyl (meth) acrylates such as 2-hydroxyethyl (meth) acrylate are more preferable. By using the hydroxyalkyl (meth) acrylate, it becomes possible to relatively easily react the polymerizable compound (Xb) with the acrylic copolymer (B0).

Further, the functional groups in the functional group-containing monomer (a2) used in the acrylic polymer (A) and the functional group-containing monomer (b2) used in the acrylic polymer (B) are the same as each other. It may be different, but it is preferable that it is different. That is, for example, if the functional group-containing monomer (a2) is a carboxy group-containing monomer, the functional group-containing monomer (b2) is preferably a hydroxyl group-containing monomer. As described above, when the functional groups are different from each other, for example, the acrylic polymer (B) can be preferentially crosslinked by a crosslinking agent described later, and the above-mentioned adhesive sheet holding performance and the like can be improved. It will be easier to make it better.

The content of the structural unit derived from the functional group-containing monomer (b2) in the acrylic copolymer (B0) is preferably 5 with respect to the total structural unit (100% by mass) of the acrylic copolymer (B0). It is ~ 50% by mass, more preferably 10 to 45% by mass, still more preferably 15 to 40% by mass, still more preferably 20 to 35% by mass. When it is 5% by mass or more, a relatively large number of reaction points with the polymerizable compound (Xb) can be secured, and energetic polymerizable property can be easily introduced into the side chain. Further, if it is 50% by mass or less, the shape of the formed intermediate layer can be sufficiently maintained.

The acrylic copolymer (B0) may be a copolymer of an alkyl (meth) acrylate (b1) and a functional group-containing monomer (b2), but the component (b1), the component (b2), and these It may be a copolymer with other monomers (b3) other than the components (b1) and (b2).
Examples of the other monomer (b3) include those exemplified as the above-mentioned monomer (a3).
The content of the structural unit derived from the other monomer (b3) in the acrylic copolymer (B0) is preferably 0 to 0 with respect to the total structural unit (100% by mass) of the acrylic copolymer (B0). It is 30% by mass, more preferably 0 to 20% by mass, still more preferably 0 to 10% by mass, and even more preferably 0 to 5% by mass.

The polymerizable compound (Xb) is a substituent capable of reacting with an energy ray-polymerizable group and a functional group in a structural unit derived from the component (b2) of the acrylic copolymer (B0) (hereinafter, simply "reactive substitution"). It is a compound having a "group").
Examples of the energy ray-polymerizable group include (meth) acryloyl group and vinyl group as described above, and (meth) acryloyl group is preferable. The polymerizable compound (Xb) is preferably a compound having 1 to 5 energy ray-polymerizable groups per molecule.
The reactive substituent in the polymerizable compound (Xb) may be appropriately changed according to the functional group of the functional group-containing monomer (b2), and examples thereof include an isocyanate group, a carboxyl group, and an epoxy group. An isocyanate group is preferable from the viewpoint of reactivity and the like. When the polymerizable compound (Xb) has an isocyanate group, it can easily react with the acrylic copolymer (B0), for example, when the functional group of the functional group-containing monomer (b2) is a hydroxy group. become.

Specific examples of the polymerizable compound (Xb) include (meth) acryloyloxyethyl isocyanate, meta-isopropenyl-α, α-dimethylbenzyl isocyanate, (meth) acryloyl isocyanate, allyl isocyanate, and glycidyl (meth) acrylate. Examples include (meth) acrylic acid. These polymerizable compounds (Xb) may be used alone or in combination of two or more.
Among these, (meth) acryloyloxyethyl is a compound having an isocyanate group suitable as the reactive substituent and having an appropriate distance between the main chain and the energy ray-polymerizable group. Isocyanates are preferred.
The polymerizable compound (Xb) is preferably 40 to 98 equivalents, more preferably 50 to 95 equivalents, out of the total functional groups (100 equivalents) derived from the functional group-containing monomer (b2) in the acrylic copolymer (B1). , More preferably 60-90 equivalents, even more preferably 70-85 equivalents, are reacted with the functional group.

The value of α calculated from the following formula (1) is an index representing the number of energy ray-polymerizable groups possessed by the acrylic copolymer (B1). In the acrylic polymer (B1), the value of α is preferably 5 to 40, more preferably 10 to 35, and even more preferably 15 to 30.
By using the acrylic copolymer (B1) having such an α value in a blending amount described later, it becomes easy to adjust the elastic modulus of the intermediate layer to a desired range.
Equation (1): α = [P _b ] × [Q _b ] × [R _b ] / 100
(In the formula (1), [P _b ] indicates the content of the structural unit derived from the functional group-containing monomer (b2) with respect to 100 parts by mass of all the structural units of the acrylic copolymer (B0) [Q _b ]. Indicates the equivalent of the polymerizable compound (Xb) with respect to 100 equivalents of the functional group derived from the functional group-containing monomer (b2) contained in the acrylic copolymer (B0). [R _b ] is the polymerizable compound (Xb). Indicates the number of energy ray-polymerizable groups possessed by.)

In the composition for forming the intermediate layer, the content of the acrylic polymer (B) is preferably less than 25 parts by mass, preferably 1 to 24 parts by mass, based on 100 parts by mass of the acrylic polymer (A). It is more preferably 8 to 23 parts by mass, and more preferably 8 to 23 parts by mass. By reducing the content of the component (B) in this way, the stress relaxation property of the intermediate layer is improved, and the intermediate layer has a high unevenness-following property.
Further, when the content of the acrylic polymer (B) is reduced, the elastic modulus of the intermediate layer after energy ray curing does not become so high, so that the above-mentioned elastic modulus difference can be reduced and delamination is prevented. It becomes easy to be done.

[Crosslinking agent]
The composition for forming an intermediate layer preferably further contains a cross-linking agent. Examples of the cross-linking agent include an isocyanate-based cross-linking agent, an epoxy-based cross-linking agent, an aziridine-based cross-linking agent, and a metal chelate-based cross-linking agent. Among these, an isocyanate-based cross-linking agent is preferable. When an isocyanate-based cross-linking agent is used, for example, when the component (B) has a hydroxy group, the cross-linking agent preferentially cross-links the acrylic polymer (B).
The composition for forming an intermediate layer is crosslinked by a cross-linking agent, for example, by heating after coating. The intermediate layer is crosslinked with an acrylic polymer, particularly a low molecular weight acrylic polymer (B), so that a coating film is appropriately formed and the intermediate layer easily exhibits a function as an intermediate layer.
The content of the cross-linking agent is preferably 0.1 to 10 parts by mass, more preferably 0.5 to 7 parts by mass, and further preferably 1 to 5 parts by mass with respect to 100 parts by mass of the acrylic polymer (A). Is.

Examples of the isocyanate-based cross-linking agent include polyisocyanate compounds. Specific examples of the polyisocyanate compound include aromatic polyisocyanates such as tolylene diisocyanate, diphenylmethane diisocyanate, and xylylene diisocyanate, aliphatic polyisocyanates such as hexamethylene diisocyanate, isophorone diisocyanate, and alicyclic polyisocyanates such as hydrogenated diphenylmethane diisocyanate. And so on. Moreover, these biuret form, isocyanurate form, and adduct form which is a reaction product with low molecular weight active hydrogen-containing compound such as ethylene glycol, propylene glycol, neopentyl glycol, trimethylolpropane, and castor oil can also be mentioned.
These may be used individually by 1 type, or may be used in combination of 2 or more type. Further, among the above, a polyhydric alcohol (for example, trimethylolpropane or the like) adduct of an aromatic polyisocyanate such as tolylene diisocyanate is preferable.

Examples of the epoxy-based cross-linking agent include 1,3-bis (N, N'-diglycidyl aminomethyl) cyclohexane, N, N, N', N'-tetraglycidyl-m-xylylene diamine, and ethylene glycol. Examples thereof include diglycidyl ether, 1,6-hexanediol diglycidyl ether, trimethylpropan diglycidyl ether, diglycidyl aniline, and diglycidyl amine. These may be used individually by 1 type, or may be used in combination of 2 or more type.
Examples of the metal chelate-based cross-linking agent include polyvalent metals such as aluminum, iron, copper, zinc, tin, titanium, nickel, antimony, magnesium, vanadium, chromium and zirconium, as well as acetylacetone, ethyl acetoacetate and tris (2,4). -A compound or the like coordinated with (pentangionate) or the like can be mentioned. These may be used individually by 1 type, or may be used in combination of 2 or more type.
Examples of the aziridine-based cross-linking agent include diphenylmethane-4,4'-bis (1-aziridine carboxamide), trimethylolpropane tri-β-aziridinyl propionate, and tetramethylolmethanetri-β-aziridinyl. Propionate, toluene-2,4-bis (1-aziridine carboxamide), triethylene melamine, bisisophthaloyl-1- (2-methylaziridine), tris-1- (2-methylaziridine) phosphine, Examples thereof include trimethylolpropane tri-β- (2-methylaziridine) propionate and hexa [1- (2-methyl) -aziridinyl] triphosphatriazine.

[Photopolymerization initiator]
The composition for forming an intermediate layer preferably further contains a photopolymerization initiator. Since the intermediate layer forming composition contains a photopolymerization initiator, it becomes easy to proceed with energy ray curing of the intermediate layer forming composition by ultraviolet rays or the like.
Examples of the photopolymerization initiator include acetophenone, 2,2-diethoxybenzophenone, 4-methylbenzophenone, 2,4,6-trimethylbenzophenone, Michler ketone, benzoin, benzoin methyl ether, benzoin ethyl ether, benzoin isopropyl ether and benzoin. Isobutyl ether, benzyl diphenisulfide, tetramethylthium monosulfide, benzyl dimethyl ketal, dibenzyl, diacetyl, 1-chloroanthraquinone, 2-chloroanthraquinone, 2-ethylanthraquinone, 2,2-dimethoxy-1,2-diphenylethane- 1-one, 1-hydroxycyclohexylphenyl ketone, 2-methyl-1- [4- (methylthio) phenyl] -2-morpholinopropanone-1,2-benzyl-2-dimethylamino-1- (4-morpholinophenyl) ) -Butanone-1,2-Hydroxy-2-methyl-1-phenyl-propan-1-one, diethylthioxanthone, isopropylthioxanthone, 2,4,6-trimethylbenzoyldiphenyl-phosphine oxide and other low molecular weight polymerization initiators , Oligo {2-hydroxy-2-methyl-1- [4- (1-methylvinyl) phenyl] propanone} and other oligomerized polymerization initiators. These may be used alone or in combination of two or more. Among these, 1-hydroxycyclohexylphenyl ketone is preferable.
The content of the photopolymerization initiator is usually 0.3 to 15 parts by mass with respect to 100 parts by mass of the acrylic polymer (A), but a small content of the acrylic polymer (B) is sufficient. As the curing progresses, in order to facilitate increasing the elastic modulus of the intermediate layer after curing, it is preferable to increase the content relatively, preferably 1 to 10 parts by mass, and more preferably 3 to 8 parts by mass.

The composition for forming an intermediate layer may contain other additives as long as the effects of the present invention are not impaired. Examples of other additives include antioxidants, softeners (plasticizers), fillers, rust inhibitors, pigments, dyes, tackifiers and the like. When these additives are contained, the content of each additive is preferably 0.01 to 6 parts by mass, more preferably 0.01 to 2 parts by mass with respect to 100 parts by mass of the acrylic polymer (A). It is a mass part.
The thickness of the intermediate layer may be appropriately selected depending on, for example, the height of the bumps formed on the semiconductor wafer as the adherend, but is preferably 10 to 800 μm, more preferably 15 to 600 μm. , More preferably 20 to 500 μm.

<Adhesive layer>
In the pressure-sensitive adhesive sheet, the pressure-sensitive adhesive layer is a layer formed on the intermediate layer, and the pressure-sensitive adhesive sheet is attached to the adherend by the pressure-sensitive adhesive layer. The pressure-sensitive adhesive layer is usually formed directly on top of the intermediate layer. The pressure-sensitive adhesive layer is an energy ray-curable layer as described above. The adhesive sheet has a high adhesive force capable of sufficiently holding the work before the energy ray irradiation, but after the energy ray irradiation, the adhesive layer is cured to reduce the adhesive force, and the adhesive sheet is an adherend. It can be easily peeled off from a wafer or the like.

The elastic modulus of the pressure-sensitive adhesive layer at 23 ° C. after energy ray curing is preferably 1 to 60 MPa, more preferably 1.5 to 30 MPa, still more preferably 1.8 to 12 MPa. By setting the elastic modulus of the pressure-sensitive adhesive layer after energy ray curing in such a range, it becomes easy to reduce the above-mentioned elastic modulus difference. In addition, before irradiation with energy rays, it becomes easy to develop appropriate adhesiveness as an adhesive layer. Further, by setting the elastic modulus within these ranges, it becomes easy to increase the interlayer strength.

The pressure-sensitive adhesive composition forming the pressure-sensitive adhesive layer contains, for example, an acrylic polymer, a polyurethane, a rubber-based polymer, a polyolefin, a silicone, or the like as a pressure-sensitive adhesive component (sticky resin) capable of exhibiting stickiness in the pressure-sensitive adhesive layer. contains. Among these, an acrylic polymer is preferable.
The pressure-sensitive adhesive composition forming the pressure-sensitive adhesive layer may have energy ray-curable properties by blending an energy ray-curable compound separately from the pressure-sensitive adhesive resin, but the above-mentioned pressure-sensitive adhesive resin itself is an energy ray. It is preferably curable. When the adhesive resin itself has energy ray curability, an energy ray-polymerizable group is introduced into the adhesive resin, but it is preferable that the energy ray-polymerizable group is introduced into the main chain or side chain of the adhesive resin. ..

When an energy ray-curable compound is blended separately from the adhesive resin, a monomer or an oligomer having an energy ray-polymerizable group is used as the energy ray-curable compound. The oligomer is an oligomer having a weight average molecular weight (Mw) of less than 10,000, and examples thereof include urethane (meth) acrylate. Even when the adhesive resin itself has energy ray curability, the pressure-sensitive adhesive composition may contain an energy ray curable compound in addition to the adhesive resin.

Hereinafter, the case where the energy ray-curable pressure-sensitive adhesive resin contained in the pressure-sensitive adhesive composition is an acrylic polymer (hereinafter, also referred to as “acrylic polymer (C)”) will be described in more detail.
[Acrylic polymer (C)]
The acrylic polymer (C) is an acrylic polymer having an energy ray-polymerizable group introduced therein and having a structural unit derived from (meth) acrylate. The energy ray-polymerizable group is preferably introduced into the side chain of the acrylic polymer.
The acrylic polymer (C) is energy ray-polymerized on an acrylic copolymer (C0) having a structural unit derived from an alkyl (meth) acrylate (c1) and a structural unit derived from a functional group-containing monomer (c2). It is preferable to contain an acrylic copolymer (C1) which is a reaction product obtained by reacting a polymerizable compound (Xc) having a sex group, and more preferably it is composed of this acrylic copolymer (C1).
The form of copolymerization of the acrylic copolymer (C0) is not particularly limited, and may be any of a block copolymer, a random copolymer, and the like. The content of the acrylic copolymer (C1) is preferably 70 to 100% by mass, more preferably 80 to 100% with respect to the total amount (100% by mass) of the component (C) contained in the pressure-sensitive adhesive composition. It is by mass, more preferably 90 to 100% by mass, and even more preferably 100% by mass.

As the alkyl (meth) acrylate (c1), an alkyl (meth) acrylate having an alkyl group having 1 to 18 carbon atoms is used, and specific examples thereof include those exemplified as the component (a1). May be used alone or in combination of two or more.
The content of the structural unit derived from alkyl (meth) acrylate (c1) in the acrylic copolymer (C0) is the acrylic copolymer (C0) from the viewpoint of improving the adhesive strength of the formed pressure-sensitive adhesive layer. It is preferably 50 to 99% by mass, more preferably 60 to 98% by mass, still more preferably 70 to 97% by mass, still more preferably 80 to 96% by mass, based on the total constituent units (100% by mass) of the above. ..

Further, the alkyl (meth) acrylate (c1) is preferably an alkyl (meth) acrylate having an alkyl group having 1 to 8 carbon atoms, like the components (a1) and (b1), and further, an alkyl group. More preferably, it contains an alkyl (meth) acrylate having 4 to 8 carbon atoms (ie, monomer (Y)). The suitable compound used as the monomer (Y) is the same as the above (a1) and (b1), and among them, n-butyl (meth) acrylate is particularly preferable.
Here, the alkyl (meth) acrylate (c1) may be entirely a monomer (Y), but a part of the alkyl (meth) acrylate (c1) may be a monomer (Y) in order to preferably adjust the adhesive performance and elastic modulus of the pressure-sensitive adhesive layer. Is preferable. Specifically, the monomer (Y) is preferably 65 to 98% by mass, more preferably 70 to 95% by mass, still more preferably 75 to 90% by mass, based on the total amount of the alkyl (meth) acrylate (c1).

For example, the alkyl (meth) acrylate (c1) may contain an ethyl (meth) acrylate in addition to the above-mentioned monomer (Y). When ethyl (meth) acrylate is used, it is easy to reduce the elastic modulus of the pressure-sensitive adhesive layer even after energy ray curing, and it is easy to reduce the difference in elastic modulus from the intermediate layer. In addition, it becomes easy to adjust the adhesive performance of the adhesive layer to a desired one.
Further, the alkyl (meth) acrylate (c1) may contain a methyl (meth) acrylate in addition to the above-mentioned monomer (Y) or the monomer (Y) and the ethyl (meth) acrylate. By containing methyl (meth) acrylate, it becomes easy to adjust the adhesive performance of the adhesive layer to a desired one.

The total amount of ethyl (meth) acrylate and methyl (meth) acrylate is preferably 2 to 35% by mass, more preferably 5 to 30% by mass, based on the total amount of alkyl (meth) acrylate (c1). ~ 25% by mass is more preferable.
The ethyl (meth) acrylate is preferably 2 to 30% by mass, more preferably 5 to 25% by mass, still more preferably 10 to 20% by mass, based on the total amount of the alkyl (meth) acrylate (c1).

Examples of the functional group-containing monomer (c2) include monomers having a functional group exemplified as the above-mentioned functional group-containing monomer (a2), and specifically, a hydroxy group-containing monomer, a carboxy group-containing monomer, and an epoxy group-containing monomer. One or more selected from the monomers is preferable. Examples of these specific compounds include the same compounds as those exemplified as the component (a2).

As the functional group-containing monomer (c2), the hydroxy group-containing monomer is more preferable, and the hydroxyalkyl (meth) acrylate is more preferable, and 2-hydroxyethyl (meth) acrylate and 4-hydroxybutyl (meth) are more preferable. Acrylate is more preferred, and 4-hydroxybutyl (meth) acrylate is particularly preferred.
By using hydroxyalkyl (meth) acrylate as the component (c2), it becomes possible to relatively easily react the polymerizable compound (Xc) with the acrylic copolymer (C0). Further, when 4-hydroxybutyl (meth) acrylate is used, the tensile strength of the intermediate layer is increased, and it becomes easy to prevent adhesive residue.

The content of the structural unit derived from the functional group-containing monomer (c2) in the acrylic copolymer (C0) is preferably 1 with respect to the total structural unit (100% by mass) of the acrylic copolymer (C0). It is ~ 40% by mass, more preferably 2 to 30% by mass, still more preferably 3 to 25% by mass, still more preferably 4 to 15% by mass.
When the content is 1% by mass or more, a certain amount of functional groups serving as reaction points with the polymerizable compound (Xc) can be secured. Therefore, since the pressure-sensitive adhesive layer can be appropriately cured by irradiation with energy rays, it is possible to reduce the adhesive strength after irradiation with energy rays. Further, it becomes easy to improve the interlayer strength between the pressure-sensitive adhesive layer and the intermediate layer after irradiation with energy rays. Further, when the content is 40% by mass or less, a sufficient pot life can be ensured when the solution of the pressure-sensitive adhesive composition is applied to form the pressure-sensitive adhesive layer.

The acrylic copolymer (C0) may be a copolymer of an alkyl (meth) acrylate (c1) and a functional group-containing monomer (c2), but the component (c1), the component (c2), and these It may be a copolymer with other monomers (c3) other than the components (c1) and (c2).
Examples of the other monomer (c3) include those exemplified as the above-mentioned monomer (a3).
The content of the structural unit derived from the other monomer (c3) in the acrylic copolymer (C0) is preferably 0 to 0 with respect to the total structural unit (100% by mass) of the acrylic copolymer (C0). It is 30% by mass, more preferably 0 to 20% by mass, still more preferably 0 to 10% by mass, and even more preferably 0 to 5% by mass.

The polymerizable compound (Xc) reacts with the energy ray-polymerizable group and the functional group in the structural unit derived from the component (c2) of the acrylic copolymer (C0), similarly to the above-mentioned polymerizable compound (Xb). It is a compound having a possible substituent (reactive substituent), and preferably a compound having 1 to 5 energy ray-polymerizable groups per molecule.
Specific examples of the reactive substituent and the energy ray-polymerizable group are the same as those of the polymerizable compound (Xb). Therefore, the reactive substituent is preferably an isocyanate group, and the energy ray-polymerizable group is a (meth) acryloyl group. preferable.
In addition, examples of the specific polymerizable compound (Xc) include those similar to those exemplified as the above-mentioned polymerizable compound (Xb), and (meth) acryloyloxyethyl isocyanate is preferable. The polymerizable compound (Xc) may be used alone or in combination of two or more.
The polymerizable compound (Xc) is preferably 30 to 98 equivalents, more preferably 40 to 95 equivalents, out of the total functional groups (100 equivalents) derived from the functional group-containing monomer (c2) in the acrylic copolymer (C0). , More preferably 50-92 equivalents, even more preferably 80-92 equivalents, are reacted with the functional group.

The weight average molecular weight (Mw) of the acrylic polymer (C) is preferably 100,000 to 1,500,000, more preferably 250,000 to 1,000,000, still more preferably 300,000 to 900,000, and even more preferably 350,000 to 80. It is ten thousand. Having such Mw makes it possible to impart appropriate adhesiveness to the pressure-sensitive adhesive layer.
The content of the acrylic polymer (C) in the pressure-sensitive adhesive composition is preferably 70 to 99% by mass, more preferably 75 to 98% by mass, based on the total amount (100% by mass) of the pressure-sensitive adhesive composition. More preferably, it is 80 to 96% by mass or more.

The value of β calculated from the following formula (2) is an index representing the number of energy ray-polymerizable groups possessed by the acrylic copolymer (C1). In the acrylic copolymer (C1), the value of β calculated from the following formula (2) is preferably 0.5 to 30, more preferably 1.0 to 20, and even more preferably 1.2 to 15. Even more preferably, it is 2 to 12.
By containing the acrylic copolymer (C1) having such a β value in the pressure-sensitive adhesive layer, the elastic modulus of the pressure-sensitive adhesive layer can be easily adjusted to a desired range.
Equation (2): β = [P _c ] × [Q _c ] × [R _c ] / 100
(In the formula (2), [P _c ] indicates the content of the structural unit derived from the functional group-containing monomer (c2) with respect to 100 parts by mass of all the structural units of the acrylic copolymer (C0) [Q _c ]. Indicates the equivalent of the polymerizable compound (Xc) with respect to 100 equivalents of the functional group derived from the functional group-containing monomer (c2) contained in the acrylic copolymer (C0). [R _c ] is the polymerizable compound (Xc). Indicates the number of energy ray-polymerizable groups possessed by.)

[Crosslinking agent]
The pressure-sensitive adhesive composition preferably further contains a cross-linking agent. The pressure-sensitive adhesive composition is cross-linked by a cross-linking agent, for example, by heating after coating. In the pressure-sensitive adhesive layer, the acrylic polymer (C) is crosslinked by a cross-linking agent, so that a coating film is appropriately formed and the pressure-sensitive adhesive layer easily exhibits a function as a pressure-sensitive adhesive layer.
Examples of the cross-linking agent include an isocyanate-based cross-linking agent, an epoxy-based cross-linking agent, an aziridine-based cross-linking agent, and a chelate-based cross-linking agent. Among these, an isocyanate-based cross-linking agent is preferable. The cross-linking agent may be used alone or in combination of two or more. Specific examples of the isocyanate-based cross-linking agent include those exemplified as a cross-linking agent that can be used in the composition for forming an intermediate layer, and the same applies to preferred compounds thereof.
The content of the cross-linking agent is preferably 0.01 to 10 parts by mass, more preferably 0.1 to 7 parts by mass, and further preferably 0.3 to 4 parts by mass with respect to 100 parts by mass of the acrylic polymer (C). It is a mass part.

[Photopolymerization initiator]
The pressure-sensitive adhesive composition preferably further contains a photopolymerization initiator. Examples of the photopolymerization initiator include those exemplified as the photopolymerization initiator used in the above-mentioned composition for forming an intermediate layer. The photopolymerization initiator may be used alone or in combination of two or more. Among the above, 2,2-dimethoxy-1,2-diphenylethane-1-one and 1-hydroxycyclohexylphenyl ketone are preferable.
The content of the photopolymerization initiator is usually 0.5 to 15 parts by mass with respect to 100 parts by mass of the acrylic polymer (C), but more preferably 1 to 12 parts by mass, still more preferably 4. 5 to 10 parts by mass. When the content of the photopolymerization initiator is relatively high in this way, the elastic modulus of the pressure-sensitive adhesive layer after curing tends to be high.

The pressure-sensitive adhesive composition may contain other additives as long as the effects of the present invention are not impaired. Examples of other additives include tackifiers, antioxidants, softeners (plasticizers), fillers, rust inhibitors, pigments, dyes and the like. When these additives are contained, the content of each additive is preferably 0.01 to 6 parts by mass, more preferably 0.01 to 2 parts by mass with respect to 100 parts by mass of the acrylic polymer (C). It is a mass part.
The thickness of the pressure-sensitive adhesive layer is preferably 1 to 100 μm, more preferably 1 to 75 μm, and even more preferably 3 to 50 μm.

When the acrylic polymer (C) is used, the elasticity of the pressure-sensitive adhesive layer is determined by, for example, the type and amount of the monomers constituting the acrylic polymer (C), and the acrylic polymer (C). It can be adjusted by the amount of energy ray-polymerizable group introduced into (β value) and the like. For example, increasing the amount of energy ray-polymerizable groups (value of β) tends to increase the elastic modulus. Further, it can be appropriately adjusted by the amount of the cross-linking agent blended in the pressure-sensitive adhesive layer, the amount of the photopolymerization initiator, and the like.

Each of the intermediate layer forming composition and the pressure-sensitive adhesive composition is further diluted with an organic solvent from the viewpoint of improving the coatability when forming the intermediate layer and the pressure-sensitive adhesive layer on the surface of the base material, the release material and the like. , It may be in the form of a solution of the composition for forming an intermediate layer or the pressure-sensitive adhesive composition.
Examples of the organic solvent include methyl ethyl ketone, acetone, ethyl acetate, tetrahydrofuran, dioxane, cyclohexane, n-hexane, toluene, xylene, n-propanol, isopropanol and the like. As the organic solvent used, the organic solvent used at the time of synthesizing the components (A) to (C) may be used as it is, or one or more kinds of organic solvents other than the organic solvent used at the time of synthesis may be added. good.
In the form of the solution as described above, the solid content concentration of the solution is preferably 5 to 70% by mass, more preferably 10 to 60% by mass, and further preferably 15 to 50% by mass.

<Base material>
The base material used for the pressure-sensitive adhesive sheet is preferably a resin film from the viewpoint of improving the holding performance for the work. Examples of the resin film include polyethylene film, polypropylene film, polybutene film, polybutadiene film, polymethylpentene film, polyvinyl chloride film, vinyl chloride copolymer film, ethylene-vinyl acetate copolymer (EVA) film, and polyethylene terephthalate. Film, polyethylene naphthalate film, polybutylene terephthalate film, ethylene- (meth) acrylic acid copolymer film, ethylene- (meth) acrylic acid ester copolymer film, polycarbonate film, polystyrene film, polyphenylene sulfide film, Cycloolefin polymer-based film, polyurethane-based film, ionomer resin film, polyimide-based film, fluororesin film and the like can be mentioned.

The base material may be a resin film having only one kind of the above-mentioned resin, or may have two or more kinds of the above-mentioned resins. For example, it may be a single-layer film made of one resin film, or a multi-layer film in which a plurality of resin films are laminated. Further, the resin film may be these crosslinked films.
Among the above resin films, a polyethylene film, a polypropylene film, an ethylene-vinyl acetate copolymer (EVA) film, and a polyethylene terephthalate film are preferable in order to improve the holding performance of the work.
Further, the resin film may contain a known filler, colorant, antistatic agent, antioxidant, organic lubricant, catalyst and the like. Further, the resin film may be transparent or may be colored if desired.
The thickness of the base material is preferably 10 to 500 μm, more preferably 15 to 300 μm, and even more preferably 20 to 200 μm.

<Release material>
The wafer protective pressure-sensitive adhesive sheet of the present invention may further have a release material on the pressure-sensitive adhesive layer.
Examples of the release material include a release sheet subjected to double-sided release treatment, a release sheet subjected to single-sided release treatment, and the like. Examples of these release sheets include those in which a release agent is applied on a base material for a release material.
Examples of the base material for the release material include the resin film used as the above-mentioned base material, and polyester-based films such as polyethylene terephthalate, polybutylene terephthalate, and polyethylene naphthalate, and polyolefin-based films such as polypropylene and polyethylene are preferable. ..
Examples of the release agent include rubber-based elastomers such as silicone-based resins, olefin-based resins, isoprene-based resins, and butadiene-based resins, long-chain alkyl-based resins, alkyd-based resins, and fluorine-based resins.
The thickness of the release material is not particularly limited, but is preferably 10 to 200 μm, more preferably 20 to 150 μm.

[Manufacturing method of adhesive sheet]
The method for producing the adhesive sheet for protecting the wafer of the present invention is not particularly limited, and it can be produced by a known method.
For example, it can be manufactured by preparing a base material with an intermediate layer provided with an intermediate layer on one surface of the base material, and further laminating an adhesive layer on the intermediate layer of the base material with the intermediate layer. ..
A base material with an intermediate layer can be produced, for example, by applying a composition for forming an intermediate layer or a solution thereof on one surface of the base material, and then heating and drying to form an intermediate layer. Alternatively, the composition for forming an intermediate layer or a solution thereof is applied to the peeling-treated surface of the release material, and then heated and dried to form an intermediate layer on the release material, and the intermediate layer is attached to a base material. , A base material with an intermediate layer may be obtained. The release material may be peeled off before the pressure-sensitive adhesive layer is laminated on the intermediate layer.

The pressure-sensitive adhesive layer forms a pressure-sensitive adhesive layer by applying the pressure-sensitive adhesive composition or a solution thereof on the peeling-treated surface of a release material different from the release material used at the time of producing the intermediate layer, heating and drying. , The pressure-sensitive adhesive layer with the release material may be laminated on the intermediate layer. The release material may be peeled from the pressure-sensitive adhesive layer, or may be used as it is as a release material provided on the pressure-sensitive adhesive layer.
Further, the pressure-sensitive adhesive layer may be formed by directly applying the pressure-sensitive adhesive composition on the intermediate layer of the base material with the intermediate layer, and then heating and drying. In this case, a release material may be further attached on the pressure-sensitive adhesive layer.

Examples of the method of applying the composition for forming an intermediate layer, the adhesive composition, or a solution thereof onto a substrate or a release material include a spin coating method, a spray coating method, a bar coating method, a knife coating method, and a roll. Examples include a coating method, a blade coating method, a die coating method, and a gravure coating method.
Further, when forming a relatively thick intermediate layer, a solution of the composition for forming an intermediate layer is applied on the peeling surface of the release material and dried to form two or more intermediate layers, and the intermediate layer is formed. The intermediate layer may be formed by laminating each other or sequentially laminating a plurality of intermediate layers on the base material. The same applies to the pressure-sensitive adhesive layer.

[How to use the adhesive sheet]
The adhesive sheet of the present invention is attached to various workpieces such as semiconductor wafers and used when processing the workpiece, and is preferably attached to a workpiece surface having irregularities or protrusions.
Further, it is more preferable to attach it to the surface of the semiconductor wafer, particularly the surface of the wafer on which bumps are formed, and use it as an adhesive sheet for protecting the surface of the semiconductor wafer. Further, it is more preferable that the adhesive sheet is attached to the surface of the semiconductor wafer and used as a bag grind tape that protects the circuit formed on the wafer surface at the time of subsequent grinding of the back surface of the wafer. When the pressure-sensitive adhesive sheet of the present invention has an intermediate layer, the embedding property is good even if there is a height difference due to bumps or the like on the wafer surface, so that the protective performance of the wafer surface is good.

In the present invention, the pressure-sensitive adhesive layer and the intermediate layer are energy ray-curable. Therefore, the adhesive sheet attached to the surface of the work such as a semiconductor wafer is irradiated with energy rays and cured by the energy rays, and then peeled off from the surface of the work. As a result, the adhesive sheet is peeled off after the adhesive strength is reduced, so that the peelability is improved. Further, when the pressure-sensitive adhesive sheet is peeled off, the delamination that occurs between the pressure-sensitive adhesive layer and the intermediate layer is prevented as described above, and adhesive residue is less likely to occur on the wafer surface.
The use of the adhesive sheet is not limited to the back grind sheet, and it can be used for other purposes. For example, the adhesive sheet may be attached to the back surface of the wafer and used as a dicing sheet for holding the wafer when dicing the wafer. In this case, the wafer may have protrusions or irregularities such as bumps formed on the back surface of the wafer, such as those on which through electrodes are formed.

Hereinafter, the present invention will be described in more detail based on examples, but the present invention is not limited to these examples.

The measurement method and evaluation method in the present invention are as follows.
[Weight average molecular weight (Mw)]
It was measured under the following conditions using a gel permeation chromatograph device (product name "HLC-8220", manufactured by Tosoh Corporation), and the value measured in terms of standard polystyrene was used.
(Measurement condition)
Columns: "TSK guard colon HXL-H""TSK gel GMHXL (x2)""TSK gel G2000HXL" (all manufactured by Tosoh Corporation)
Column temperature: 40 ° C. Developing solvent: Tetrahydrofuran Flow rate: 1.0 mL / min

[Measurement of elastic modulus]
Using the intermediate layer forming composition and adhesive composition used in each Example and Comparative Example, polyethylene terephthalate (PET) -based release film (manufactured by Lintec Corporation, product name "SP-PET38131", thickness) on both sides. : 38 μm) was attached to a 200 μm-thick intermediate layer and an adhesive layer. The intermediate layer having a thickness of 200 μm was obtained by preparing a plurality of intermediate layers having a thickness of 50 μm formed on the release film by the same method as in Examples and Comparative Examples and sequentially laminating them. The same applies to the pressure-sensitive adhesive layer.
Then, the intermediate layer and the adhesive layer were irradiated with ultraviolet rays with an ^{illuminance of 230 mW / cm 2} and an integrated light intensity of 500 mJ / cm ² with an ultraviolet irradiation device (manufactured by Lintec Corporation, product name "RAD-2000 m / 12"). Next, the intermediate layer and the pressure-sensitive adhesive layer cured by ultraviolet rays were cut into a size of 4 mm × 50 mm to prepare a sample for measuring viscoelasticity. Using the sample, a viscoelasticity measuring device (manufactured by Orientec, product name "Leovibron") was used to measure the storage elastic modulus of -30 to 200 ° C at a heating rate of 3 ° C / min (frequency: 1 Hz). The value of the storage elastic modulus at 23 ° C. was taken as the elastic modulus after the energy ray curing of each layer.

[Interlayer strength measurement]
Double-sided tape (Lintec Corporation, product name "Tackliner") is attached to the SUS board, and the base material surface of the dicing tape (Lintec Corporation, product name "ADWILL D-510T") is attached on top of it. On the adhesive surface of the tape, an adhesive sheet (length 200 mm, width 25 mm) produced in Examples and Comparative Examples and from which the release film was peeled off was placed, and the surface of the adhesive sheet on the adhesive layer side was the adhesive surface of the dicing tape. It was attached so that it would be adhered to. After that, the prepared sample was irradiated with UV (illuminance: 230 mW / cm ² , light intensity: 500 mJ / cm ² ) using RAD-2000 m / 12 manufactured by Lintec Corporation, and "Autograph AG-IS 1 kN" manufactured by Shimadzu Corporation. , The peeling speed was 600 mm / min and the peeling angle was 180 ° under a 50% RH environment at 23 ° C., and the interlayer strength between the intermediate layer and the pressure-sensitive adhesive layer was measured.

[Example 1]
(Preparation of base material A with intermediate layer)
An acrylic copolymer (weight average molecular weight: 600,000) obtained by copolymerizing 91 parts by mass of n-butyl acrylate (BA) and 9 parts by mass of acrylic acid (AA) is used as the acrylic polymer (A). I prepared it. Further, a methacryloyloxyethyl isocyanate is added to an acrylic copolymer obtained by copolymerizing 62 parts by mass of n-butyl acrylate (BA), 10 parts by mass of methyl methacrylate (MMA), and 28 parts by mass of 2-hydroxyethyl acrylate (2HEA). An acrylic copolymer (weight average molecular weight:: 100,000) was prepared as an acrylic polymer (B).
2. 100 parts by mass of the acrylic polymer (A), 13 parts by mass of the acrylic polymer (B), and trimethylpropane adduct tolylene diisocyanate (manufactured by Toso Co., Ltd., product name "Coronate L") as a cross-linking agent. Add 2 parts by mass and 3.71 parts by mass of 1-hydroxycyclohexylphenyl ketone (manufactured by BASF, product name "Irgacure 184") as a photopolymerization initiator, and adjust the solid content concentration to 37% by mass using toluene. Then, the mixture was stirred for 30 minutes to obtain a solution of the composition for forming an intermediate layer.

Next, the solution of the composition for forming the intermediate layer is applied to a PET-based release film (manufactured by Lintec Corporation, product name "SP-PET38131", thickness 38 μm), heated at 100 ° C. for 2 minutes, dried, and peeled. An intermediate layer with a film was formed. The thickness of the intermediate layer was 50 μm. Two intermediate layers with this release film were prepared. Next, the intermediate layer side of one of the intermediate layers with a release film is bonded to an ethylene-vinyl acetate film (manufactured by Gunze Co., Ltd., product name "Funkrea LEB", thickness 120 μm) as a base material, and is placed on the intermediate layer. The release film was peeled off. Then, the other intermediate layer with a release film is further bonded onto the intermediate layer laminated on the base material, the thickness of the intermediate layer is 100 μm, and the middle layer is made of a release material / intermediate layer / base material. Base material A was obtained.

(Making an adhesive sheet)
An acrylic system obtained by copolymerizing 70 parts by mass of n-butyl acrylate (BA), 15 parts by mass of ethyl acrylate (EA), 5 parts by mass of methyl methacrylate (MMA), and 10 parts by mass of 4-hydroxybutyl acrylate (4HBA). Acrylate obtained by adding methacryloyloxyethyl isocyanate (manufactured by Showa Denko Co., Ltd., product name "Karen's MOI") to a copolymer so that the addition rate is 90 equivalents with respect to the hydroxyl group (100 equivalents) of 4HBA. A system copolymer (weight average molecular weight: 600,000) was prepared as an acrylic polymer (C).
To 100 parts by mass of the acrylic polymer (C), 1.5 parts by mass of trimethylolpropane adduct tolylene diisocyanate (manufactured by Toso Co., Ltd., product name "Coronate L") as a cross-linking agent, 2 as a photopolymerization initiator , 2-Dimethoxy-1,2-diphenylethane-1-one (Irgacure 651, manufactured by BASF) was added in an amount of 7.3 parts by mass, adjusted to a solid content concentration of 20% by mass using toluene, and stirred for 30 minutes. To obtain a solution of the pressure-sensitive adhesive composition.
Next, a solution of the pressure-sensitive adhesive composition was applied to a PET-based release film (manufactured by Lintec Corporation, product name "SP-PET381031", thickness: 38 μm), heated at 90 ° C. for 1 minute, dried, and adhered to a thickness of 10 μm. A drug layer was prepared. The release film on the base material A with an intermediate layer prepared earlier is removed, and the exposed intermediate layer is bonded onto the pressure-sensitive adhesive layer to form an adhesive sheet composed of a release material / pressure-sensitive adhesive layer / intermediate layer / base material. Was produced.

[Example 2]
(Preparation of base material B with intermediate layer)
A base material B with an intermediate layer was prepared in the same manner as in Example 1 except that the amount of the acrylic polymer (B) added was changed to 23 parts by mass.
(Making an adhesive sheet)
Methacryloyloxyethyl isocyanate (Showa) is added to an acrylic copolymer obtained by copolymerizing 74 parts by mass of n-butyl acrylate (BA), 20 parts by mass of methyl methacrylate (MMA), and 6 parts by mass of 2-hydroxyethyl acrylate (2HEA). An acrylic copolymer (weight average molecular weight: 600,) obtained by adding (product name "Karens MOI") manufactured by Denko Co., Ltd. so that the addition rate is 50 equivalents with respect to the hydroxyl group (100 equivalents) of 2HEA. 000) was prepared as an acrylic polymer (C).
To 100 parts by mass of the acrylic polymer (C), 0.5 parts by mass of trimethylolpropane adduct tolylene diisocyanate (manufactured by Toso Co., Ltd., product name "Coronate L") as a cross-linking agent, 1- as a photopolymerization initiator 6.0 parts by mass of hydroxycyclohexylphenyl ketone (Irgacure 184 manufactured by BASF) was added to adjust the solid content concentration to 20% by mass using toluene, and the mixture was stirred for 30 minutes to obtain a solution of the pressure-sensitive adhesive composition. ..
Next, a pressure-sensitive adhesive sheet was prepared in the same manner as in Example 1 except that the solution of this pressure-sensitive adhesive composition was used and the base material B with an intermediate layer was used instead of the base material A with an intermediate layer.

[Comparative Example 1]
(Making an adhesive sheet)
Methacryloyloxyethyl isocyanate (Showa) is added to an acrylic copolymer obtained by copolymerizing 52 parts by mass of n-butyl acrylate (BA), 20 parts by mass of methyl methacrylate (MMA), and 28 parts by mass of 2-hydroxyethyl acrylate (2HEA). An acrylic copolymer (weight average molecular weight: 600,) obtained by adding (product name "Karens MOI") manufactured by Denko Co., Ltd. so that the addition rate is 90 equivalents with respect to the hydroxyl group (100 equivalents) of 2HEA. 000) was prepared as an acrylic polymer (C).
To 100 parts by mass of the acrylic polymer (C), 0.5 parts by mass of trimethylolpropane adduct tolylene diisocyanate (manufactured by Toso Co., Ltd., product name "Coronate L") as a cross-linking agent, 1 as a photopolymerization initiator -Hydroxycyclohexylphenylketone ("Irgacure184" manufactured by BASF) was added in an amount of 1.4 parts by mass, adjusted to a solid content of 20% by mass using toluene, and stirred for 30 minutes to obtain a pressure-sensitive adhesive composition. Using the obtained pressure-sensitive adhesive composition, a pressure-sensitive adhesive sheet was prepared in the same manner as in Example 1.

[Comparative Example 2]
A base material C with an intermediate layer was obtained in the same manner as the base material A with an intermediate layer (Example) except that the amount of the acrylic polymer (B) added was changed to 67 parts by mass. A surface protective sheet was prepared in the same manner as in Example 2 except that the base material C with an intermediate layer was used.

[Comparative Example 3]
A base material D with an intermediate layer was obtained in the same manner as in the base material A with an intermediate layer (Example 1) except that the amount of the acrylic polymer (B) added was changed to 107 parts by mass. A surface protective sheet was prepared in the same manner as in Example 2 except that the base material D with an intermediate layer was used.

As is clear from Examples 1 and 2 above, by reducing the elastic modulus difference to 20 MPa or less, the interlayer strength is increased. Therefore, when the adhesive sheet for semiconductor processing is cured and peeled from the work, the intermediate layer is formed. It is possible to prevent delamination that occurs between the and the pressure-sensitive adhesive layer.
On the other hand, in Comparative Examples 1 to 3, the interlayer strength was lowered due to the large difference in elastic modulus. Therefore, when the pressure-sensitive adhesive sheet for semiconductor processing was cured and peeled from the work, the intermediate layer and the pressure-sensitive adhesive layer were separated from each other. Delamination that occurs between them cannot be sufficiently prevented.

Claims (8)

A pressure-sensitive adhesive sheet for semiconductor processing, which comprises a base material, an intermediate layer, and a pressure-sensitive adhesive layer in this order.
For forming an intermediate layer, the intermediate layer containing a non-energy ray-curable acrylic polymer (A) and an energy ray-curable acrylic polymer (B) having a weight average molecular weight of 50,000 to 250,000. Along with being a layer formed from the composition, the pressure-sensitive adhesive layer is energy ray-curable.
A pressure-sensitive adhesive sheet for semiconductor processing in which the elastic modulus difference between the intermediate layer and the pressure-sensitive adhesive layer after energy ray curing at 23 ° C. is 20 MPa or less. The pressure-sensitive adhesive sheet for semiconductor processing according to claim 1, wherein in the composition for forming an intermediate layer, the amount of the acrylic polymer (B) is less than 25 parts by mass with respect to 100 parts by mass of the acrylic polymer (A). The pressure-sensitive adhesive sheet for semiconductor processing according to claim 1 or 2, wherein the acrylic polymer (A) has a weight average molecular weight of 300,000 to 1,500,000. The pressure-sensitive adhesive sheet for semiconductor processing according to any one of claims 1 to 3, wherein the pressure-sensitive adhesive layer is formed of a pressure-sensitive adhesive composition containing an energy ray-curable acrylic polymer (C). The acrylic polymer (C) is an acrylic polymer having a structural unit derived from an alkyl (meth) acrylate (c1) having an alkyl group having 1 to 18 carbon atoms and a structural unit derived from a functional group-containing monomer (c2). The pressure-sensitive adhesive sheet for semiconductor processing according to claim 4, which is an acrylic copolymer (C1) which is a reaction product of a copolymer (C0) reacted with a polymerizable compound (Xc) having an energy ray-polymerizable group. .. The pressure-sensitive adhesive sheet for semiconductor processing according to claim 4 or 5, wherein the acrylic polymer (C) has a weight average molecular weight of 100,000 to 1,500,000. The composition for forming an intermediate layer contains 0.3 to 15 parts by mass of a photopolymerization initiator with respect to 100 parts by mass of the acrylic polymer (A), and also contains
The semiconductor according to any one of claims 4 to 6, wherein the pressure-sensitive adhesive composition contains 0.5 to 15 parts by mass of a photopolymerization initiator with respect to 100 parts by mass of the acrylic polymer (C). Adhesive sheet for processing. The acrylic polymer (B) is an acrylic polymer having a structural unit derived from an alkyl (meth) acrylate (b1) having an alkyl group having 1 to 18 carbon atoms and a structural unit derived from a functional group-containing monomer (b2). The claim 1 to any one of claims 1 to 7, which is an acrylic copolymer (B1) which is a reaction product obtained by reacting a copolymer (B0) with a polymerizable compound (Xb) having an energy ray-polymerizable group. The described adhesive sheet for semiconductor processing.