JP7765381B2 - Double-sided adhesive sheet and method for manufacturing semiconductor device - Google Patents

Description

The present invention relates to a double-sided adhesive sheet and a method for manufacturing a semiconductor device using the double-sided adhesive sheet.

In addition to being used to semi-permanently secure components, adhesive sheets are also used as temporary fixing sheets to temporarily secure components (hereinafter also referred to as "adherends") that are to be processed or inspected when processing or inspecting building materials, interior materials, electronic components, etc. For example, temporary fixing sheets are used when processing semiconductor wafers in the manufacturing process of semiconductor devices.

In the manufacturing process of semiconductor devices, semiconductor wafers are processed into semiconductor chips through processes such as a grinding process in which the wafer is ground to reduce its thickness and a singulation process in which the wafer is cut and separated into individual pieces. During this process, the semiconductor wafer undergoes the required processing while temporarily fixed to a temporary fixing sheet. The semiconductor chips obtained after the required processing are then separated from the temporary fixing sheet and, as necessary, undergo an expanding process to increase the spacing between the semiconductor chips, a rearrangement process to arrange multiple semiconductor chips with increased spacing, and an inversion process to flip the semiconductor chips over, before being mounted on a substrate. In each of the above processes, a temporary fixing sheet suitable for the respective application can be used.

Patent Document 1 discloses a heat-peelable adhesive sheet for temporary fixing electronic components when cutting them, which has a heat-expandable adhesive layer containing heat-expandable microspheres provided on at least one side of a substrate. The document also states that the heat-peelable adhesive sheet ensures a predetermined contact area with the adherend when cutting electronic components, thereby providing adhesion that can prevent adhesion problems such as chipping. However, after use, the sheet can be heated to expand the heat-expandable microspheres, reducing the contact area with the adherend and allowing for easy removal.

Patent No. 3594853

When using a temporary fixing sheet for processing an object to be processed, the object to be processed may be attached to one side of the sheet and the other side may be attached to a support, and then the sheet may be subjected to a predetermined processing in this state. In this case, a double-sided pressure-sensitive adhesive sheet having pressure-sensitive adhesive layers on both sides is used as the temporary fixing sheet.
When a double-sided pressure-sensitive adhesive sheet is used as a temporary fixing sheet, by making the adhesive layer on one side and the adhesive layer on the other side have different mechanisms for reducing the adhesive strength, it is possible to avoid unintentionally reducing the adhesive strength of one of the pressure-sensitive adhesive layers when performing a process to reduce the adhesive strength of the other pressure-sensitive adhesive layer.
The inventors focused on the above advantages and discovered that a double-sided pressure-sensitive adhesive sheet in which the pressure-sensitive adhesive layer on one side is one whose adhesive strength decreases due to the effect of thermal expansion, and the pressure-sensitive adhesive layer on the other side is an energy ray-curable pressure-sensitive adhesive layer whose adhesive strength decreases when irradiated with energy rays is hardened, is suitable for semiconductor device manufacturing processes, etc.

When an adherend with no or low light transmittance is attached to an energy ray-curable adhesive layer, the energy rays for curing the energy ray-curable adhesive layer must be irradiated from the side opposite the energy ray-curable adhesive layer (i.e., the heat-expandable layer side). Depending on the process used, it may be necessary to separate the energy ray-curable adhesive layer from the adherend after thermally expanding the heat-expandable layer. However, after thermally expanding the heat-expandable layer, the double-sided PSA sheet has a reduced total light transmittance due to the expansion of the heat-expandable particles, making it difficult for energy rays irradiated from the heat-expandable layer side to reach the energy ray-curable adhesive layer. This results in insufficient curing of the energy ray-curable adhesive layer, resulting in an insufficient reduction in adhesive strength.

The present invention has been made in consideration of the above-mentioned problems, and aims to provide a double-sided pressure-sensitive adhesive sheet having a heat-expandable layer and an energy ray-curable pressure-sensitive adhesive layer, in which the adhesive strength of the energy ray-curable pressure-sensitive adhesive layer can be sufficiently reduced by irradiating the heat-expandable layer with energy rays from the heat-expandable layer side, even after the heat-expandable layer has been thermally expanded, and a method for manufacturing a semiconductor device using the double-sided pressure-sensitive adhesive sheet.

The inventors focused on the total light transmittance of double-sided pressure-sensitive adhesive sheets after thermal expansion and discovered that the above problem could be solved by adjusting the total light transmittance measured under specific conditions to fall within a specific range, thereby completing the present invention.

That is, the present invention relates to the following [1] to [15].
[1] A double-sided PSA sheet having a PSA layer (X1), a base layer (Y), and a PSA layer (X2) in this order,
at least one of the pressure-sensitive adhesive layer (X1) and the base layer (Y) is a heat-expandable layer containing heat-expandable particles,
the pressure-sensitive adhesive layer (X2) is an energy ray-curable pressure-sensitive adhesive layer,
A laminate (LA) for total light transmittance measurement obtained by laminating a 1.1 mm thick glass plate made of soda lime glass to the pressure-sensitive adhesive layer ( _X2 ) of the double-sided pressure-sensitive adhesive sheet and heating the laminate for 1 minute at a temperature of the expansion starting temperature (t) of the heat-expandable particles + 22°C has a total light transmittance ( _TA ) in the thickness direction at a wavelength of 380 nm of 20% or more.
[2] The double-sided pressure-sensitive adhesive sheet according to [1] above, wherein the thickness of the heat-expandable layer before thermal expansion is 10 to 200 μm.
[3] The double-sided pressure-sensitive adhesive sheet according to [1] or [2] above, wherein the content of the heat-expandable particles in the heat-expandable layer is 1 to 25 mass % relative to the total mass (100 mass %) of the heat-expandable layer.
[4] The double-sided pressure-sensitive adhesive sheet according to any one of [1] to [3] above, wherein the expansion starting temperature (t) of the thermally expandable particles is 50°C or higher but lower than 125°C.
[5] The double-sided pressure-sensitive adhesive sheet according to any one of the above [1] to [4], wherein the thickness of the entire double-sided pressure-sensitive adhesive sheet before thermal expansion is 90 to 300 μm.
[6] The double-sided pressure-sensitive adhesive sheet according to any one of the above [1] to [5], wherein a laminate ( _LB ) for total light transmittance measurement, obtained by laminating a 1.1 mm thick glass plate made of soda lime glass to the pressure-sensitive adhesive layer (X2) of the double-sided pressure-sensitive adhesive sheet before thermal expansion, has a total light transmittance ( _TB ) in the thickness direction at a wavelength of 380 nm of 50% or more.
[7] The double-sided pressure-sensitive adhesive sheet according to any one of the above [1] to [6], wherein the energy ray-curable pressure-sensitive adhesive layer is a pressure-sensitive adhesive layer that is cured by irradiation with ultraviolet light, thereby reducing its adhesive strength.
[8] The double-sided pressure-sensitive adhesive sheet according to any one of the above [1] to [7], wherein the base layer (Y) is a base laminate in which a heat-expandable base layer (Y1) containing heat-expandable particles and a non-heat-expandable base layer (Y2) are laminated together, and the double-sided pressure-sensitive adhesive sheet has the pressure-sensitive adhesive layer (X1), the heat-expandable base layer (Y1), the non-heat-expandable base layer (Y2), and the pressure-sensitive adhesive layer (X2) in this order.
[9] The thermally expandable base layer (Y1) contains the thermally expandable particles in a resin material,
The double-sided pressure-sensitive adhesive sheet according to [8] above, wherein the resin material has a total light transmittance ( _TR ) of 60% or more at a wavelength of 380 nm when the resin material has a thickness of 100 µm.
[10] The double-sided pressure-sensitive adhesive sheet according to the above [8] or [9], wherein the total thickness of the pressure-sensitive adhesive layer (X1), the heat-expandable base layer (Y1), the non-heat-expandable base layer (Y2), and the pressure-sensitive adhesive layer (X2) is 90 to 300 μm.
[11] A method for manufacturing a semiconductor device using the double-sided pressure-sensitive adhesive sheet according to any one of [1] to [10] above, comprising the following steps 1A, 2A, a first separation step, and a second separation step:
Step 1A: a step of attaching an object to be processed to the pressure-sensitive adhesive layer (X2) of the double-sided pressure-sensitive adhesive sheet, and attaching a support to the pressure-sensitive adhesive layer (X1) of the double-sided pressure-sensitive adhesive sheet; Step 2A: a step of subjecting the object to one or more treatments selected from a grinding treatment and a singulation treatment; First separation step: a step of heating the double-sided pressure-sensitive adhesive sheet to the expansion initiation temperature (t) or higher, and separating the pressure-sensitive adhesive layer (X1) from the support; Second separation step: a step of irradiating the pressure-sensitive adhesive layer (X2) with energy rays, thereby curing the pressure-sensitive adhesive layer (X2), and separating the pressure-sensitive adhesive layer (X2) from the object to be processed. [12] The expansion initiation temperature (t) of the thermally expandable particles is 50°C or higher and lower than 125°C,
After the step 2A, a step 3A is included in which a thermosetting film having thermosetting properties is attached to a surface of the object to be processed that has been subjected to the treatment, the surface being opposite to the pressure-sensitive adhesive layer (X2),
the first separation step is a step of heating the double-sided PSA sheet to an expansion initiation temperature (t) or higher and lower than 125°C to separate the PSA layer (X1) from the support;
The method for manufacturing a semiconductor device according to [11] above.
[13] A method for manufacturing a semiconductor device using the double-sided pressure-sensitive adhesive sheet according to any one of [1] to [10] above, comprising the following steps 1B, 2B, a first separation step, and a second separation step:
Step 1B: a step of attaching an object to be processed to the pressure-sensitive adhesive layer (X1) of the double-sided pressure-sensitive adhesive sheet, and attaching a support to the pressure-sensitive adhesive layer (X2) of the double-sided pressure-sensitive adhesive sheet; Step 2B: a step of subjecting the object to one or more treatments selected from a grinding treatment and a singulation treatment; First separation step: a step of heating the double-sided pressure-sensitive adhesive sheet to the expansion initiation temperature (t) or higher, and separating the pressure-sensitive adhesive layer (X1) from the object to be processed; Second separation step: a step of irradiating the pressure-sensitive adhesive layer (X2) with energy rays, thereby curing the pressure-sensitive adhesive layer (X2), and separating the pressure-sensitive adhesive layer (X2) from the support; [14] The expansion initiation temperature (t) of the thermally expandable particles is 50°C or higher and lower than 125°C,
After the step 2B, a step 3B is included in which a thermosetting film having thermosetting properties is attached to a surface of the object to be processed that has been subjected to the treatment, the surface being opposite to the pressure-sensitive adhesive layer (X1),
the first separation step is a step of heating the double-sided PSA sheet to an expansion initiation temperature (t) or higher and lower than 125°C to separate the PSA layer (X1) from the object to be processed;
The method for manufacturing a semiconductor device according to [13] above.
[15] A double-sided pressure-sensitive adhesive sheet with a release material, comprising a release material on one or both surfaces of the double-sided pressure-sensitive adhesive sheet according to any one of [1] to [10] above.

The present invention provides a double-sided pressure-sensitive adhesive sheet having a heat-expandable layer and an energy ray-curable pressure-sensitive adhesive layer, in which the adhesive strength of the energy ray-curable pressure-sensitive adhesive layer can be sufficiently reduced by irradiating the heat-expandable layer with energy rays, even after the heat-expandable layer has been thermally expanded, and a method for manufacturing a semiconductor device using the double-sided pressure-sensitive adhesive sheet.

1 is a cross-sectional view showing an example of the configuration of a double-sided pressure-sensitive adhesive sheet of the present invention. FIG. 2 is a cross-sectional view showing another example of the configuration of the double-sided pressure-sensitive adhesive sheet of the present invention. 1A to 1C are cross-sectional views illustrating an example of a process for manufacturing a semiconductor device according to the present invention. 1A to 1C are cross-sectional views illustrating an example of a process for manufacturing a semiconductor device according to the present invention. 1A to 1C are cross-sectional views illustrating an example of a process for manufacturing a semiconductor device according to the present invention. 1A to 1C are cross-sectional views illustrating an example of a process for manufacturing a semiconductor device according to the present invention. 1A to 1C are cross-sectional views illustrating an example of a process for manufacturing a semiconductor device according to the present invention. 1A to 1C are cross-sectional views illustrating an example of a process for manufacturing a semiconductor device according to the present invention. 1A to 1C are cross-sectional views illustrating an example of a process for manufacturing a semiconductor device according to the present invention.

In this specification, the term "active ingredient" refers to the components contained in the target composition excluding the diluent solvent.
In this specification, the mass average molecular weight (Mw) is a value measured by gel permeation chromatography (GPC) in terms of standard polystyrene, and specifically, is a value measured based on the method described in the examples.

In this specification, for example, "(meth)acrylic acid" refers to both "acrylic acid" and "methacrylic acid," and the same applies to other similar terms.
Furthermore, in this specification, for preferred numerical ranges (e.g., ranges of content, etc.), the lower limit and upper limit values described in stages can be independently combined. For example, the description "preferably 10 to 90, more preferably 30 to 60" can be combined with the "preferable lower limit (10)" and the "more preferable upper limit (60)" to form "10 to 60."

In this specification, the term "energy rays" refers to electromagnetic waves or charged particle beams that have an energy quantum, and examples thereof include ultraviolet rays, radioactive rays, and electron beams. Ultraviolet rays can be irradiated using, for example, an electrodeless lamp, a high-pressure mercury lamp, a metal halide lamp, a UV-LED, or the like as an ultraviolet light source. Electron beams can be irradiated using those generated by an electron beam accelerator, or the like.
In this specification, "energy ray polymerizable" means a property of being polymerized by irradiation with energy rays, and "energy ray curable" means a property of being cured by irradiation with energy rays.

In this specification, whether a "layer" is a "non-thermally expandable layer" or a "thermally expandable layer" is determined as follows.
When the layer to be judged contains thermally expandable particles, the layer is heat-treated for 3 minutes at the expansion starting temperature (t) of the thermally expandable particles. If the volume change rate calculated using the following formula is less than 5%, the layer is judged to be a "non-thermally expandable layer," and if it is 5% or more, the layer is judged to be a "thermally expandable layer."
Volume change rate (%)={(volume of the layer after heat treatment−volume of the layer before heat treatment)/volume of the layer before heat treatment}×100
A layer that does not contain thermally expandable particles is referred to as a "non-thermally expandable layer."

In this specification, the "front surface" of a semiconductor wafer or semiconductor chip refers to the surface on which circuits are formed (hereinafter also referred to as the "circuit surface"), and the "back surface" of a semiconductor wafer or semiconductor chip refers to the surface on which circuits are not formed.

In this specification, the thickness of each layer is the thickness at 23°C and means the value measured using the method described in the examples.

In this specification, the adhesive strength of each layer refers to the adhesive strength to the mirror surface of a silicon mirror wafer, measured at a pulling speed of 300 mm/min using the 180° peel method in accordance with JIS Z0237:2000 under an environment of 23°C and 50% RH (relative humidity).

In this specification, total light transmittance refers to the value obtained by measuring the transmission spectrum using ultraviolet-visible spectroscopy, and specifically refers to the value measured using the method shown in the examples below.

[Double-sided adhesive sheet]
The double-sided pressure-sensitive adhesive sheet of one embodiment of the present invention comprises:
A double-sided PSA sheet having a PSA layer (X1), a base layer (Y), and a PSA layer (X2) in this order,
at least one of the pressure-sensitive adhesive layer (X1) and the base layer (Y) is a heat-expandable layer containing heat-expandable particles,
the pressure-sensitive adhesive layer (X2) is an energy ray-curable pressure-sensitive adhesive layer,
A laminate obtained by laminating a 1.1 mm thick glass plate made of soda lime glass on the pressure-sensitive adhesive layer (X2 ₎ of the double-sided pressure-sensitive adhesive sheet and heating the laminate for total light transmittance measurement at a temperature (t) of the expansion starting temperature of the heat-expandable particles + 22°C for 1 minute has a total light transmittance ( _TA ) in the thickness direction at a wavelength of 380 nm of 20% or more.

The double-sided pressure-sensitive adhesive sheet of one embodiment of the present invention has a laminated structure of a double-sided pressure-sensitive adhesive sheet having a pressure-sensitive adhesive layer (X1), a substrate layer (Y), and a pressure-sensitive adhesive layer (X2) in this order.
With this configuration, an adherend can be attached to either the pressure-sensitive adhesive layer (X1) or the pressure-sensitive adhesive layer (X2), and a support can be attached to the other pressure-sensitive adhesive layer. By fixing the adherend to the support via the double-sided pressure-sensitive adhesive sheet, vibration, displacement, and breakage of the adherend if the adherend is fragile can be suppressed when the adherend is subjected to one or more of processing and inspection, and processing accuracy, processing speed, and inspection accuracy, and inspection speed can be improved.

In one embodiment of the double-sided pressure-sensitive adhesive sheet of the present invention, the heat-expandable particles contained in the heat-expandable layer, which is at least one of the pressure-sensitive adhesive layer (X1) and the base layer (Y), are heated to a temperature equal to or higher than the expansion onset temperature (t) to expand, thereby forming irregularities on the adhesive surface of the pressure-sensitive adhesive layer (X1) and significantly reducing the contact area between the adhesive surface and an adherend attached to the adhesive surface of the pressure-sensitive adhesive layer (X1). This significantly reduces the adhesion between the adhesive surface of the pressure-sensitive adhesive layer (X1) and the adherend, allowing the double-sided pressure-sensitive adhesive sheet to be easily separated from the adherend.
Furthermore, in the double-sided pressure-sensitive adhesive sheet of one embodiment of the present invention, even after the heat-expandable layer has been thermally expanded, the adhesive strength of the energy ray-curable pressure-sensitive adhesive layer (X2) can be sufficiently reduced by irradiation with energy rays from the heat-expandable layer side. Therefore, even if an adherend that has no light transmittance or extremely low light transmittance is attached to the energy ray-curable pressure-sensitive adhesive layer after the heat-expandable layer has been thermally expanded, the adherend can be easily separated by irradiation with energy rays.

<Configuration of double-sided adhesive sheet>
The double-sided pressure-sensitive adhesive sheet of one embodiment of the present invention may have only the pressure-sensitive adhesive layer (X1), the base layer (Y), and the pressure-sensitive adhesive layer (X2) in this order, or may have other layers as necessary, provided that one surface of the double-sided pressure-sensitive adhesive sheet of one embodiment of the present invention is the adhesive surface of the pressure-sensitive adhesive layer (X1), and the other surface of the double-sided pressure-sensitive adhesive sheet of one embodiment of the present invention is the adhesive surface of the pressure-sensitive adhesive layer (X2).
The double-sided pressure-sensitive adhesive sheet of one embodiment of the present invention may have a release material on the adhesive surface of at least one of the pressure-sensitive adhesive layer (X1) and the pressure-sensitive adhesive layer (X2), and those having a release material are classified as "double-sided pressure-sensitive adhesive sheets with release material" described below.

In the double-sided pressure-sensitive adhesive sheet of one embodiment of the present invention, at least one of the pressure-sensitive adhesive layer (X1) and the base layer (Y) may be a heat-expandable layer containing heat-expandable particles.
An example of a double-sided PSA sheet in which the base layer (Y) is a heat-expandable layer containing heat-expandable particles is a double-sided PSA sheet in which the base layer (Y) is a base laminate in which a heat-expandable base layer (Y1) containing heat-expandable particles and a non-heat-expandable base layer (Y2) are laminated together, and which has, in this order, a pressure-sensitive adhesive layer (X1), a heat-expandable base layer (Y1), a non-heat-expandable base layer (Y2), and a pressure-sensitive adhesive layer (X2). Hereinafter, a double-sided PSA sheet having this configuration may be referred to as a "double-sided PSA sheet of the first aspect."
Furthermore, in the double-sided pressure-sensitive adhesive sheet of one embodiment of the present invention, when the pressure-sensitive adhesive layer (X1) is a heat-expandable layer containing heat-expandable particles, the double-sided pressure-sensitive adhesive sheet may have, in this order, the pressure-sensitive adhesive layer (X1), a base layer (Y), and a pressure-sensitive adhesive layer (X2). Hereinafter, a double-sided pressure-sensitive adhesive sheet having this configuration may be referred to as a "double-sided pressure-sensitive adhesive sheet of a second embodiment."

Next, the configuration of one embodiment of the double-sided adhesive sheet of the present invention will be explained in more detail with reference to the drawings.

An example of the double-sided pressure-sensitive adhesive sheet according to the first aspect of the present invention is a double-sided pressure-sensitive adhesive sheet 1a shown in FIG. 1( a), which has a pressure-sensitive adhesive layer (X1), a heat-expandable base layer (Y1), a non-heat-expandable base layer (Y2), and a pressure-sensitive adhesive layer (X2) in this order.
The double-sided pressure-sensitive adhesive sheet of the first embodiment may or may not have another layer between at least any of the layers between the pressure-sensitive adhesive layer (X1) and the heat-expandable base layer (Y1), between the heat-expandable base layer (Y1) and the non-heat-expandable base layer (Y2), and between the non-heat-expandable base layer (Y2) and the pressure-sensitive adhesive layer (X2).
However, in the double-sided pressure-sensitive adhesive sheet of the first embodiment, from the viewpoint of effectively transmitting the deformation of the heat-expandable base layer (Y1) due to the expansion of the heat-expandable particles to the pressure-sensitive adhesive layer (X1), it is preferable that the pressure-sensitive adhesive layer (X1) and the heat-expandable base layer (Y1) are directly laminated together.

An example of the double-sided pressure-sensitive adhesive sheet according to the second aspect of the present invention is a double-sided pressure-sensitive adhesive sheet 2a shown in FIG. 1( b), which has a pressure-sensitive adhesive layer (X1) that is a heat-expandable layer, a base layer (Y), and a pressure-sensitive adhesive layer (X2) in this order.
The double-sided pressure-sensitive adhesive sheet of the second embodiment may or may not have another layer between at least one of the layers between the pressure-sensitive adhesive layer (X1) and the base material layer (Y) and between the base material layer (Y) and the pressure-sensitive adhesive layer (X2).

<Total light transmittance>
A laminate (LA) for total light transmittance measurement obtained by laminating a 1.1 mm thick glass plate made of soda lime glass to the pressure-sensitive adhesive layer ( _X2 ) of a double-sided pressure-sensitive adhesive sheet according to one embodiment of the present invention and heating the laminate for 1 minute at a temperature of the expansion starting temperature (t) of the heat-expandable particles + 22°C has a total light transmittance ( _TA ) in the thickness direction at a wavelength of 380 nm of 20% or more.
In the following description, when simply referring to "total light transmittance ( _TA )", this refers to the total light transmittance ( _TA ) of the laminate ( _LA ) for total light transmittance measurement measured under the above conditions.
By having a total light transmittance ( _TA ) of 20% or more, the adhesive strength of the energy ray-curable pressure-sensitive adhesive layer can be sufficiently reduced by irradiation of energy rays from the heat-expandable layer side, even after the heat-expandable layer has been thermally expanded. Furthermore, the amount of energy ray irradiation required to cure the energy ray-curable pressure-sensitive adhesive layer can be kept low, and heat generation caused by energy rays can be suppressed, thereby suppressing thermal changes in the adherend.
On the other hand, if the total light transmittance ( _TA ) is less than 20%, when the heat-expandable layer is thermally expanded and then irradiated with energy rays from the heat-expandable layer side, the energy rays have difficulty reaching the energy ray-curable pressure-sensitive adhesive layer, and the adhesive strength of the energy ray-curable pressure-sensitive adhesive layer may not be sufficiently reduced. Furthermore, the amount of energy rays required to sufficiently reduce the adhesive strength increases, which may result in a decrease in productivity and thermal changes to the adherend due to heat generated by the energy rays.
In this specification, the total light transmittance (T _A ) is measured by the method described in the examples below.

The total light transmittance (T _A ) is 20% or more, preferably 21% or more, and more preferably 22% or more, from the viewpoint of sufficiently reducing the adhesive strength of the energy ray-curable pressure-sensitive adhesive layer even after thermal expansion. There is no particular upper limit for the total light transmittance (T _A ), and it may be 100% or less. However, from the viewpoint of maintaining a good balance with other performance properties such as the peelability of the pressure-sensitive adhesive layer (X1) and the strength of the double-sided pressure-sensitive adhesive sheet, it is preferably 80% or less, more preferably 70% or less, and even more preferably 60% or less. From the same viewpoint as above, the total light transmittance (T _A ) may be 45% or less, 35% or less, or 30% or less.

Furthermore, the total light transmittance (T B ) in the thickness direction of a laminate (L _{B ) for total light transmittance measurement, which is obtained by laminating a 1.1 mm thick glass plate made of soda lime glass on the pressure-sensitive adhesive layer (X2 )} of the double-sided pressure-sensitive adhesive sheet before thermal expansion, is preferably 50% or more.
In the following description, when simply referring to "total light transmittance (T _B )", this refers to the total light transmittance (T _B ) of the laminate (L _B ) for total light transmittance measurement measured under the above conditions.
The double-sided pressure-sensitive adhesive sheet of one embodiment of the present invention has a total light transmittance (T _B ) of 50% or more, which makes it easy to adjust the total light transmittance (T _A ) to fall within the above range.
From the same viewpoint, the total light transmittance (T _B ) is more preferably 52% or more, and even more preferably 54% or more. There is no particular restriction on the upper limit of the total light transmittance (T _B ), and it may be 100% or less, but from the viewpoint of maintaining a good balance with other performance properties such as the easy peelability of the pressure-sensitive adhesive layer (X1) and the strength of the double-sided pressure-sensitive adhesive sheet, it is preferably 90% or less, more preferably 80% or less, and even more preferably 75% or less. Furthermore, from the same viewpoint as above, the total light transmittance (T _B ) may be 70% or less, 65% or less, or 60% or less.
In this specification, the total light transmittance (T _B ) is measured by the method described in the examples below.

The total light transmittance (T _A ) and the total light transmittance (T _B ) can be adjusted to fall within the above ranges by, for example, appropriately adjusting the materials used to form the pressure-sensitive adhesive layer (X1), the base layer (Y), the pressure-sensitive adhesive layer (X2), etc., the thickness of each layer, the content of the thermally expandable particles, etc.

<Thermal Expanding Particles>
The thermally expandable particles used in the double-sided pressure-sensitive adhesive sheet of one embodiment of the present invention may be particles that expand when heated, and the expansion initiation temperature (t) is selected appropriately depending on the application of the double-sided pressure-sensitive adhesive sheet.

In recent years, when mounting a semiconductor chip on a substrate, a process has been adopted in which the semiconductor chip is attached to the substrate via a thermosetting film-like adhesive called a die attach film (hereinafter also referred to as "DAF").
The DAF is attached to one side of a semiconductor wafer or a plurality of singulated semiconductor chips, and is divided into pieces having the same shape as the semiconductor chips either simultaneously with singulation of the semiconductor wafer or after being attached to the semiconductor chips. The singulated semiconductor chips with DAFs are attached to a substrate from the DAF side (die-attached), and then the DAF is thermally cured to bond the semiconductor chip to the substrate. At this time, the DAF must retain its pressure-sensitive or heat-adhesive properties until it is attached to the substrate. However, when the semiconductor chips with DAFs are used as the adherend of a heat-peelable adhesive sheet, the heating required to expand the thermally expandable particles can cause the DAF to harden before die-attachment, reducing the adhesive strength of the DAF to the substrate. Since a reduction in the adhesive strength of the DAF reduces the reliability of the bond between the semiconductor chip and the substrate, it is desirable to suppress it. In other words, it is desirable to suppress thermal changes in the adherend during heat-peel.
From this perspective, in the double-sided pressure-sensitive adhesive sheet of one embodiment of the present invention, the expansion initiation temperature (t) of the thermally expandable particles is preferably less than 125°C, more preferably 120°C or less, even more preferably 115°C or less, still more preferably 110°C or less, and even more preferably 105°C or less.

Furthermore, if heat-expandable particles with a low expansion initiation temperature are used in a heat-peelable pressure-sensitive adhesive sheet, the heat-expandable particles may expand due to a temperature rise when the adherend is ground, etc. Such unintended expansion of the heat-expandable particles may lead to unintended separation or displacement of the adherend, and therefore should be suppressed.
From this perspective, in the double-sided pressure-sensitive adhesive sheet of one embodiment of the present invention, the expansion initiation temperature (t) of the thermally expandable particles is preferably 50°C or higher, more preferably 55°C or higher, even more preferably 60°C or higher, and even more preferably 70°C or higher.
In this specification, the expansion starting temperature (t) of the thermally expandable particles means a value measured based on the following method.

(Method for measuring the expansion initiation temperature (t) of thermally expandable particles)
A sample is prepared by adding 0.5 mg of the thermally expandable particles to be measured to an aluminum cup having a diameter of 6.0 mm (inner diameter 5.65 mm) and a depth of 4.8 mm, and placing an aluminum lid (diameter 5.6 mm, thickness 0.1 mm) on top.
Using a dynamic viscoelasticity measuring device, the height of the sample is measured while a force of 0.01 N is applied to the sample from above the aluminum lid using a pressure pin. Then, while a force of 0.01 N is applied using the pressure pin, the sample is heated from 20°C to 300°C at a temperature increase rate of 10°C/min, the amount of displacement of the pressure pin in the vertical direction is measured, and the temperature at which displacement in the forward direction begins is defined as the expansion initiation temperature (t).

The thermally expandable particles are preferably microencapsulated foaming agents that are composed of an outer shell made of a thermoplastic resin and an encapsulated component that is encapsulated in the outer shell and vaporizes when heated to a predetermined temperature.
Examples of the thermoplastic resin that constitutes the outer shell of the microencapsulated foaming agent include polyvinyl alcohol, polyvinyl butyral, polymethyl methacrylate, polyacrylonitrile, polyvinylidene chloride, polysulfone, and copolymers obtained by polymerizing two or more types of monomers that form the structural units contained in these thermoplastic resins.

Examples of the encapsulated component, which is the component encapsulated in the outer shell of the microencapsulated blowing agent, include low-boiling point liquids such as propane, propylene, butene, n-butane, isobutane, isopentane, neopentane, n-pentane, n-hexane, isohexane, n-heptane, n-octane, cyclopropane, cyclobutane, and petroleum ether.
Among these, from the viewpoints of suppressing thermal changes in the adherend during heat peeling and suppressing unintended expansion of the heat-expanding particles due to temperature increases when the adherend is ground, when the expansion starting temperature (t) of the heat-expanding particles is set to 50°C or higher but lower than 125°C, the encapsulated components are preferably propane, isobutane, n-pentane, and cyclopropane.
These encapsulated components may be used alone or in combination of two or more.
The expansion starting temperature (t) of the thermally expandable particles can be adjusted by appropriately selecting the type of encapsulated component.

The average particle size of the thermally expandable particles used in one embodiment of the present invention before expansion at 23° C. is preferably 3 to 100 μm, more preferably 4 to 70 μm, even more preferably 6 to 60 μm, and still more preferably 10 to 50 μm.
The average particle size of the thermally expandable particles before expansion is the volume median particle size (D50), and refers to the particle size corresponding to a cumulative volume frequency of _50% , calculated from the smaller particle size of the thermally expandable particles before expansion, in the particle distribution of the thermally expandable particles before expansion measured using a laser diffraction particle size distribution measuring device (for example, Malvern, product name "Mastersizer 3000").

The 90% particle size (D ₉₀ ) of the thermally expandable particles used in one embodiment of the present invention before expansion at 23° C. is preferably 10 to 150 μm, more preferably 15 to 100 μm, even more preferably 20 to 90 μm, and still more preferably 25 to 80 μm.
The 90% particle size ( _D90 ) of the thermally expandable particles before expansion refers to the particle size corresponding to a cumulative volume frequency of 90%, calculated from the smaller particle size of the thermally expandable particles before expansion, in the particle distribution of the thermally expandable particles before expansion measured using a laser diffraction particle size distribution analyzer (for example, Malvern, product name "Mastersizer 3000").

The maximum volume expansion rate of the thermally expandable particles used in one embodiment of the present invention when heated to a temperature equal to or higher than the expansion initiation temperature (t) is preferably 1.5 to 200 times, more preferably 2 to 150 times, even more preferably 2.5 to 120 times, and even more preferably 3 to 100 times.

The content of the thermally expandable particles in the thermally expandable layer is preferably 1% by mass or more, more preferably 3% by mass or more, even more preferably 7% by mass or more, and even more preferably 10% by mass or more, based on the total mass (100% by mass) of the thermally expandable layer. The content of the thermally expandable particles in the thermally expandable layer is preferably 25% by mass or less, more preferably 20% by mass or less, even more preferably 16% by mass or less, and even more preferably 14% by mass or less, based on the total mass (100% by mass) of the thermally expandable layer.
When the content of the heat-expandable particles is 1% by mass or more, the peelability during heat peeling tends to be improved. Furthermore, when the content of the heat-expandable particles is 25% by mass or less, the adhesive strength of the energy ray-curable pressure-sensitive adhesive layer can be further sufficiently reduced by energy ray irradiation from the heat-expandable layer side, even after the heat-expandable layer has been thermally expanded.

<Thickness of the thermally expandable layer>
In one embodiment of the present invention, the thickness of the thermally expandable layer before thermal expansion is preferably 10 to 200 μm, more preferably 20 to 150 μm, and even more preferably 25 to 120 μm.
When the thickness of the heat-expandable layer before thermal expansion is 10 μm or more, the formation of irregularities due to the heat-expandable particles before thermal expansion can be suppressed. Also, when the thickness of the heat-expandable layer before thermal expansion is 200 μm or less, it becomes easy to adjust the total light transmittance ( _TA ) within the above range.

<Overall thickness of double-sided adhesive sheet>
The double-sided pressure-sensitive adhesive sheet according to one embodiment of the present invention preferably has an overall thickness of 90 to 300 μm, more preferably 100 to 250 μm, and even more preferably 130 to 200 μm before being thermally expanded.
When the double-sided PSA sheet has an overall thickness of 90 μm or more, the double-sided PSA sheet has good mechanical strength and is easy to handle. When the double-sided PSA sheet has an overall thickness of 300 μm or less, it is easy to adjust the total light transmittance ( _TA ) to within the above range.

Next, preferred embodiments of each layer of the double-sided pressure-sensitive adhesive sheet of one embodiment of the present invention will be described.
Preferred embodiments of the double-sided PSA sheet of the first embodiment and the double-sided PSA sheet of the second embodiment will be described below, but the present invention is not limited to these embodiments.

[Double-sided pressure-sensitive adhesive sheet of first embodiment]
The double-sided pressure-sensitive adhesive sheet of the first embodiment is a double-sided pressure-sensitive adhesive sheet having, in this order, a pressure-sensitive adhesive layer (X1), a heat-expandable base layer (Y1), a non-heat-expandable base layer (Y2), and a pressure-sensitive adhesive layer (X2).

<Pressure-sensitive adhesive layer (X1)>
The pressure-sensitive adhesive layer (X1) of the double-sided pressure-sensitive adhesive sheet of the first embodiment may be a heat-expandable layer or a non-heat-expandable layer, but is preferably a non-heat-expandable layer.
When the pressure-sensitive adhesive layer (X1) is a non-thermally expandable layer, the volume change rate (%) of the pressure-sensitive adhesive layer (X1) calculated from the above formula is less than 5%, preferably less than 2%, more preferably less than 1%, even more preferably less than 0.1%, and still more preferably less than 0.01%.
The pressure-sensitive adhesive layer (X1) preferably does not contain thermally expandable particles, but may contain thermally expandable particles within a range that does not contradict the object of the present invention. When the pressure-sensitive adhesive layer (X1) contains thermally expandable particles, the lower the content, the better, and is preferably less than 3 mass%, more preferably less than 1 mass%, even more preferably less than 0.1 mass%, still more preferably less than 0.01 mass%, and still more preferably less than 0.001 mass%, relative to the total mass (100 mass%) of the pressure-sensitive adhesive layer (X1).

The pressure-sensitive adhesive layer (X1) of the double-sided pressure-sensitive adhesive sheet of the first embodiment can be formed from a pressure-sensitive adhesive composition (x-1) containing a pressure-sensitive adhesive resin.
Each component contained in the pressure-sensitive adhesive composition (x-1) will be described below.

(Adhesive resin)
The adhesive resin may be a polymer that has adhesiveness by itself and has a mass average molecular weight (Mw) of 10,000 or more.
The mass average molecular weight (Mw) of the adhesive resin is preferably 10,000 to 2,000,000, more preferably 20,000 to 1,500,000, and even more preferably 30,000 to 1,000,000, from the viewpoint of improving the adhesive strength of the adhesive layer (X1).

Specific examples of adhesive resins include rubber-based resins such as acrylic resins, urethane resins, and polyisobutylene resins, polyester resins, olefin resins, silicone resins, and polyvinyl ether resins.
These adhesive resins may be used alone or in combination of two or more.
Furthermore, when these adhesive resins are copolymers having two or more types of structural units, the form of the copolymer is not particularly limited, and may be any of a block copolymer, a random copolymer, and a graft copolymer.

Here, in one aspect of the present invention, from the viewpoint of imparting excellent adhesive strength to the adhesive layer (X1), it is preferable that the adhesive resin contains an acrylic resin.

The content of the acrylic resin in the adhesive resin is preferably 30 to 100% by mass, more preferably 50 to 100% by mass, even more preferably 70 to 100% by mass, and even more preferably 85 to 100% by mass, relative to the total amount (100% by mass) of adhesive resin contained in the adhesive composition (x-1) or the adhesive layer (X1).

In one aspect of the present invention, examples of acrylic resins that can be used as adhesive resins include polymers containing structural units derived from alkyl (meth)acrylates having linear or branched alkyl groups, and polymers containing structural units derived from (meth)acrylates having a cyclic structure.

The mass average molecular weight (Mw) of the acrylic resin is preferably 100,000 to 1.5 million, more preferably 200,000 to 1.3 million, even more preferably 350,000 to 1.2 million, and even more preferably 500,000 to 1.1 million.

The acrylic resin used in one embodiment of the present invention is preferably an acrylic copolymer (A1) having a structural unit (a1) derived from alkyl (meth)acrylate (a1') (hereinafter also referred to as "monomer (a1')") and a structural unit (a2) derived from a functional group-containing monomer (a2') (hereinafter also referred to as "monomer (a2')").

The number of carbon atoms in the alkyl group of the monomer (a1') is preferably 1 to 24, more preferably 1 to 12, even more preferably 2 to 10, and still more preferably 4 to 8, from the viewpoint of imparting excellent adhesive strength to the pressure-sensitive adhesive layer (X1).
The alkyl group contained in the monomer (a1') may be a linear alkyl group or a branched alkyl group.

Examples of the monomer (a1') include methyl (meth)acrylate, ethyl (meth)acrylate, propyl (meth)acrylate, n-butyl (meth)acrylate, sec-butyl (meth)acrylate, iso-butyl (meth)acrylate, tert-butyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, lauryl (meth)acrylate, tridecyl (meth)acrylate, and stearyl (meth)acrylate.
These monomers (a1') may be used alone or in combination of two or more.
As the monomer (a1'), n-butyl acrylate and 2-ethylhexyl acrylate are preferred.

The content of the structural unit (a1) is preferably 50 to 99.9% by mass, more preferably 60 to 99.0% by mass, even more preferably 70 to 97.0% by mass, and even more preferably 80 to 95.0% by mass, based on the total structural units (100% by mass) of the acrylic copolymer (A1).

Examples of the functional group contained in the monomer (a2') include a hydroxyl group, a carboxyl group, an amino group, and an epoxy group.
That is, examples of the monomer (a2') include hydroxyl group-containing monomers, carboxyl group-containing monomers, amino group-containing monomers, and epoxy group-containing monomers.
These monomers (a2') may be used alone or in combination of two or more.
Among these, as the monomer (a2'), hydroxyl group-containing monomers and carboxyl group-containing monomers are preferred, and hydroxyl group-containing monomers are more preferred.

Examples of hydroxyl group-containing monomers include hydroxyalkyl (meth)acrylates such as 2-hydroxyethyl (meth)acrylate, 2-hydroxypropyl (meth)acrylate, 3-hydroxypropyl (meth)acrylate, 2-hydroxybutyl (meth)acrylate, 3-hydroxybutyl (meth)acrylate, and 4-hydroxybutyl (meth)acrylate; and hydroxyl group-containing compounds such as unsaturated alcohols such as vinyl alcohol and allyl alcohol.

Examples of carboxyl group-containing monomers include ethylenically unsaturated monocarboxylic acids such as (meth)acrylic acid and crotonic acid; ethylenically unsaturated dicarboxylic acids and their anhydrides such as fumaric acid, itaconic acid, maleic acid and citraconic acid; 2-(acryloyloxy)ethyl succinate; and 2-carboxyethyl (meth)acrylate.

The content of the structural unit (a2) is preferably 0.1 to 30% by mass, more preferably 0.5 to 20% by mass, even more preferably 1.0 to 15% by mass, and even more preferably 3.0 to 10% by mass, relative to the total structural units (100% by mass) of the acrylic copolymer (A1).

The acrylic copolymer (A1) may further include a structural unit (a3) derived from a monomer (a3') other than the monomers (a1') and (a2').
In the acrylic copolymer (A1), the total content of the structural units (a1) and (a2) is preferably 70 to 100% by mass, more preferably 80 to 100% by mass, even more preferably 90 to 100% by mass, and still more preferably 95 to 100% by mass, based on all structural units (100% by mass) of the acrylic copolymer (A1).

Examples of monomer (a3') include olefins such as ethylene, propylene, and isobutylene; halogenated olefins such as vinyl chloride and vinylidene chloride; diene monomers such as butadiene, isoprene, and chloroprene; (meth)acrylates having a cyclic structure such as cyclohexyl (meth)acrylate, benzyl (meth)acrylate, isobornyl (meth)acrylate, dicyclopentanyl (meth)acrylate, dicyclopentenyl (meth)acrylate, dicyclopentenyloxyethyl (meth)acrylate, and imide (meth)acrylate; styrene, α-methylstyrene, vinyltoluene, vinyl formate, vinyl acetate, acrylonitrile, (meth)acrylamide, (meth)acrylonitrile, (meth)acryloylmorpholine, and N-vinylpyrrolidone.

The content of the adhesive resin in the adhesive composition (x-1) is preferably 35 to 100% by mass, more preferably 50 to 100% by mass, even more preferably 60 to 100% by mass, and even more preferably 70 to 99.5% by mass, relative to the total amount (100% by mass) of the active ingredients of the adhesive composition (x-1).

(Crosslinking agent)
In one embodiment of the present invention, when the pressure-sensitive adhesive composition (x-1) contains a pressure-sensitive adhesive resin having a functional group, such as the above-mentioned acrylic copolymer (A1), it is preferable that the pressure-sensitive adhesive composition (x-1) further contains a crosslinking agent.
The crosslinking agent reacts with the adhesive resin having a functional group, and crosslinks the adhesive resins together using the functional group as the crosslinking starting point.

Examples of the crosslinking agent include an isocyanate-based crosslinking agent, an epoxy-based crosslinking agent, an aziridine-based crosslinking agent, and a metal chelate-based crosslinking agent.
These crosslinking agents may be used alone or in combination of two or more.
Among these crosslinking agents, isocyanate-based crosslinking agents are preferred from the viewpoints of increasing cohesive strength and improving adhesive strength, and of ease of availability.
Examples of the isocyanate crosslinking agent include aromatic polyisocyanates such as tolylene diisocyanate, diphenylmethane diisocyanate, and xylylene diisocyanate; alicyclic polyisocyanates such as dicyclohexylmethane-4,4'-diisocyanate, bicycloheptane triisocyanate, cyclopentylene diisocyanate, cyclohexylene diisocyanate, methylcyclohexylene diisocyanate, methylenebis(cyclohexyl isocyanate), 3-isocyanatomethyl-3,5,5-trimethylcyclohexyl isocyanate, and hydrogenated xylylene diisocyanate; and polyvalent isocyanate compounds such as acyclic aliphatic polyisocyanates such as hexamethylene diisocyanate, trimethylhexamethylene diisocyanate, and lysine diisocyanate.
Further, examples of the isocyanate crosslinking agent include a trimethylolpropane adduct modified product of the polyvalent isocyanate compound, a biuret modified product obtained by reacting the polyvalent isocyanate compound with water, and an isocyanurate modified product containing an isocyanurate ring.
Among these, from the viewpoint of suppressing a decrease in the elastic modulus of the pressure-sensitive adhesive layer (X1) during heating and suppressing adhesion of residue derived from the pressure-sensitive adhesive layer (X1) to the adherend, it is preferable to use an isocyanurate-type modified product containing an isocyanurate ring, it is more preferable to use an isocyanurate-type modified product of an acyclic aliphatic polyisocyanate, and it is even more preferable to use an isocyanurate-type modified product of hexamethylene diisocyanate.

The content of the crosslinking agent is adjusted appropriately depending on the number of functional groups possessed by the adhesive resin, but is preferably 0.01 to 10 parts by mass, more preferably 0.03 to 7 parts by mass, and even more preferably 0.05 to 5 parts by mass per 100 parts by mass of the adhesive resin having functional groups.

(Tackifier)
In one embodiment of the present invention, the pressure-sensitive adhesive composition (x-1) may further contain a tackifier from the viewpoint of further improving adhesive strength.
In this specification, the term "tackifier" refers to a component that auxiliary improves the adhesive strength of an adhesive resin, and has a mass average molecular weight (Mw) of less than 10,000, and is distinguished from the adhesive resin described above.
The mass average molecular weight (Mw) of the tackifier is less than 10,000, preferably 400 to 9,000, more preferably 500 to 8,000, and even more preferably 800 to 5,000.

Examples of tackifiers include rosin-based resins, terpene-based resins, styrene-based resins, C5-based petroleum resins obtained by copolymerizing C5 fractions such as pentene, isoprene, piperine, and 1,3-pentadiene produced by the thermal decomposition of petroleum naphtha, C9-based petroleum resins obtained by copolymerizing C9 fractions such as indene and vinyltoluene produced by the thermal decomposition of petroleum naphtha, and hydrogenated resins obtained by hydrogenating these.

The softening point of the tackifier is preferably 60 to 170°C, more preferably 65 to 160°C, and even more preferably 70 to 150°C.
In this specification, the "softening point" of a tackifier means a value measured in accordance with JIS K 2531.
The tackifier may be used alone or in combination with two or more types differing in softening point, structure, etc. When two or more types of tackifiers are used, it is preferable that the weighted average of the softening points of the multiple tackifiers falls within the above range.

The content of the tackifier is preferably 0.01 to 65% by mass, more preferably 0.1 to 50% by mass, even more preferably 1 to 40% by mass, and even more preferably 2 to 30% by mass, relative to the total amount (100% by mass) of the active ingredients of the adhesive composition (x-1).

(Adhesive additives)
In one embodiment of the present invention, the PSA composition (x-1) may contain, in addition to the additives described above, PSA additives used in general PSAs, as long as the effects of the present invention are not impaired.
Examples of such adhesive additives include antioxidants, softeners (plasticizers), rust inhibitors, pigments, dyes, retarders, reaction accelerators (catalysts), ultraviolet absorbers, energy ray-curable compounds and photopolymerization initiators, which will be described later.
These adhesive additives may be used alone or in combination of two or more.

When these adhesive additives are contained, the content of each adhesive additive is, independently, preferably 0.0001 to 20 parts by mass, more preferably 0.001 to 10 parts by mass, per 100 parts by mass of the adhesive resin.

(Adhesive Strength of Pressure-Sensitive Adhesive Layer (X1) Before Thermally Expanding Heat-Expandable Base Layer (Y1))
The adhesive strength of the pressure-sensitive adhesive layer (X1) before thermally expanding the heat-expandable base layer (Y1) is preferably 0.1 to 12.0 N/25 mm, more preferably 0.5 to 9.0 N/25 mm, even more preferably 1.0 to 8.0 N/25 mm, and still more preferably 1.2 to 7.5 N/25 mm.
If the adhesive strength of the pressure-sensitive adhesive layer (X1) before thermally expanding the heat-expandable base layer (Y1) is 0.1 N/25 mm or more, unintended peeling from the adherend during temporary fixing, positional displacement of the adherend, etc. can be more effectively suppressed. On the other hand, if the adhesive strength is 12.0 N/25 mm or less, releasability during heat peeling can be further improved.

(Adhesive strength of pressure-sensitive adhesive layer (X1) after thermal expansion of heat-expandable base layer (Y1))
The adhesive strength of the pressure-sensitive adhesive layer (X1) after thermally expanding the heat-expandable base layer (Y1) is preferably 1.5 N/25 mm or less, more preferably 0.05 N/25 mm or less, even more preferably 0.01 N/25 mm or less, and even more preferably 0 N/25 mm. Note that an adhesive strength of 0 N/25 mm means an adhesive strength below the measurement limit in the method for measuring adhesive strength after thermal expansion described below, and also includes cases where the adhesive strength is too small when fixing the double-sided pressure-sensitive adhesive sheet for measurement, resulting in unintentional peeling.
In this specification, the adhesive strength of the pressure-sensitive adhesive layer (X1) after thermally expanding the heat-expandable base layer (Y1) can be measured by the method described in "Measurement of adhesive strength of pressure-sensitive adhesive layer (X2)" in the Examples described later, except that the pressure-sensitive adhesive layer (X2) is replaced with the pressure-sensitive adhesive layer (X1).

(Thickness of Pressure-Sensitive Adhesive Layer (X1))
The thickness of the pressure-sensitive adhesive layer (X1) in the double-sided pressure-sensitive adhesive sheet of the first aspect is preferably 3 to 10 μm, more preferably 3 to 8 μm, and even more preferably 3 to 7 μm, from the viewpoints of exhibiting good adhesive strength and favorably forming unevenness on the adhesive surface of the pressure-sensitive adhesive layer (X1) when the thermo-expandable particles are expanded by heating.
By adjusting the thickness of the pressure-sensitive adhesive layer (X1) to fall within the above range, the pressure-sensitive adhesive layer (X1) can be easily formed, and good unevenness can be easily formed on the adhesive surface of the pressure-sensitive adhesive layer (X1).

<Thermal Expandable Base Layer (Y1)>
The heat-expandable base layer (Y1) of the double-sided pressure-sensitive adhesive sheet of the first embodiment is a heat-expandable layer containing heat-expandable particles in a resin material, and is a layer provided between the pressure-sensitive adhesive layer (X1) and the non-heat-expandable base layer (Y2).

When the resin material contained in the thermally expandable base layer (Y1) has a thickness of 100 μm, the total light transmittance ( _TR ) at a wavelength of 380 nm is preferably 60% or more, more preferably 70% or more, and even more preferably 75% or more. There is no particular upper limit to the total light transmittance ( _TR ), and it may be 100% or less.
The double-sided pressure-sensitive adhesive sheet of the first embodiment has a total light transmittance (T _R ) of 60% or more, which makes it easy to adjust the total light transmittance (T _A ) to fall within the above range.
The total light transmittance (T _R ) can be measured using a resin material molded into a sheet having a thickness of 100 μm as a measurement sample, using an apparatus and measurement conditions used for measuring the total light transmittance (T _A ).

The thermally expandable substrate layer (Y1) is preferably a non-adhesive substrate.
The probe tack value on the surface of the thermally expandable substrate layer (Y1) is usually less than 50 mN/5 mmφ, preferably less than 30 mN/5 mmφ, more preferably less than 10 mN/5 mmφ, and even more preferably less than 5 mN/5 mmφ.
In this specification, the probe tack value on the surface of a substrate means a value measured by the following method.
<Probe tack value>
The substrate to be measured was cut into a square with a side length of 10 mm, and then left to stand for 24 hours in an environment of 23 ° C. and 50% RH (relative humidity). The test sample was then placed in an environment of 23 ° C. and 50% RH (relative humidity). Using a tack tester (manufactured by Nippon Tokushu Sokki Co., Ltd., product name "NTS-4800"), the probe tack value on the surface of the test sample was measured in accordance with JIS Z0237:1991. Specifically, a stainless steel probe with a diameter of 5 mm was brought into contact with the surface of the test sample for 1 second with a contact load of 0.98 N / cm ² , and then the force required to separate the probe from the surface of the test sample at a speed of 10 mm / sec was measured, and the obtained value can be used as the probe tack value of the test sample.

From the viewpoint of improving the interlayer adhesion between the thermally expandable base layer (Y1) and another layer to be laminated therewith, the surface of the thermally expandable base layer (Y1) may be subjected to a surface treatment such as an oxidation method or a roughening method, an easy-adhesion treatment, or a primer treatment.
Examples of the oxidation method include corona discharge treatment, plasma discharge treatment, chromic acid treatment (wet), hot air treatment, ozone treatment, and ultraviolet irradiation treatment, and examples of the roughening method include sandblasting and solvent treatment.

The thermally expandable substrate layer (Y1) is preferably formed from a resin composition (y-1) containing a resin and thermally expandable particles.
A preferred embodiment of the resin composition (y-1) will be described below. The preferred embodiment of the thermally expandable particles is as described above.

(resin)
The resin contained in the resin composition (y-1) may be a non-sticky resin or a sticky resin.
In other words, even if the resin contained in the resin composition (y-1) is a sticky resin, in the process of forming the thermally expandable base layer (Y1) from the resin composition (y-1), the sticky resin undergoes a polymerization reaction with a polymerizable compound, the resulting resin becomes a non-sticky resin, and the thermally expandable base layer (Y1) containing the resin becomes non-sticky.

The mass average molecular weight (Mw) of the resin contained in the resin composition (y-1) is preferably 1,000 to 1,000,000, more preferably 1,000 to 700,000, and even more preferably 1,000 to 500,000.
Furthermore, when the resin is a copolymer having two or more types of structural units, the form of the copolymer is not particularly limited, and may be any of a block copolymer, a random copolymer, and a graft copolymer.

The resin content is preferably 50 to 99% by mass, more preferably 60 to 95% by mass, even more preferably 65 to 90% by mass, and even more preferably 70 to 85% by mass, relative to the total amount (100% by mass) of active ingredients in resin composition (y-1).

The resin contained in the resin composition (y-1) preferably contains one or more resins selected from the group consisting of acrylic urethane resins and olefin resins, from the viewpoint of facilitating the formation of irregularities on the adhesive surface of the pressure-sensitive adhesive layer (X1) and improving the sheet shape retention after thermal expansion. That is, the thermally expandable base layer (Y1) preferably contains one or more resins selected from the group consisting of acrylic urethane resins and olefin resins.
As the acrylic urethane resin, the following resin (U1) is preferred.
An acrylic urethane resin (U1) obtained by polymerizing a urethane prepolymer (UP) and a vinyl compound containing a (meth)acrylic acid ester.
In this specification, a prepolymer refers to a compound obtained by polymerizing a monomer, which can be further polymerized to form a polymer.

[Acrylic urethane resin (U1)]
The urethane prepolymer (UP) that forms the main chain of the acrylic urethane resin (U1) may be a reaction product of a polyol and a polyisocyanate.
The urethane prepolymer (UP) is preferably obtained by further subjecting it to a chain extension reaction using a chain extender.

Examples of polyols that can be used as raw materials for the urethane prepolymer (UP) include alkylene polyols, ether polyols, ester polyols, ester amide polyols, ester-ether polyols, and carbonate polyols.
These polyols may be used alone or in combination of two or more.
The polyol used in one embodiment of the present invention is preferably a diol, more preferably an ester-type diol, an alkylene-type diol, or a carbonate-type diol, and even more preferably an ester-type diol or a carbonate-type diol.

Examples of ester-type diols include condensation polymers of one or more diols selected from alkanediols such as 1,3-propanediol, 1,4-butanediol, 1,5-pentanediol, neopentyl glycol, and 1,6-hexanediol; and alkylene glycols such as ethylene glycol, propylene glycol, diethylene glycol, and dipropylene glycol; and one or more dicarboxylic acids such as phthalic acid, isophthalic acid, terephthalic acid, naphthalenedicarboxylic acid, 4,4-diphenyldicarboxylic acid, diphenylmethane-4,4'-dicarboxylic acid, succinic acid, adipic acid, azelaic acid, sebacic acid, HET acid, maleic acid, fumaric acid, itaconic acid, cyclohexane-1,3-dicarboxylic acid, cyclohexane-1,4-dicarboxylic acid, hexahydrophthalic acid, hexahydroisophthalic acid, hexahydroterephthalic acid, and methylhexahydrophthalic acid, and anhydrides thereof.
Specific examples include polyethylene adipate diol, polybutylene adipate diol, polyhexamethylene adipate diol, polyhexamethylene isophthalate diol, polyneopentyl adipate diol, polyethylene propylene adipate diol, polyethylene butylene adipate diol, polybutylene hexamethylene adipate diol, polydiethylene adipate diol, poly(polytetramethylene ether) adipate diol, poly(3-methylpentylene adipate) diol, polyethylene azelate diol, polyethylene sebacate diol, polybutylene azelate diol, polybutylene sebacate diol, and polyneopentyl terephthalate diol.

Examples of alkylene diols include alkane diols such as 1,3-propanediol, 1,4-butanediol, 1,5-pentanediol, neopentyl glycol, and 1,6-hexanediol; alkylene glycols such as ethylene glycol, propylene glycol, diethylene glycol, and dipropylene glycol; polyalkylene glycols such as polyethylene glycol, polypropylene glycol, and polybutylene glycol; and polyoxyalkylene glycols such as polytetramethylene glycol.

Examples of carbonate-type diols include 1,4-tetramethylene carbonate diol, 1,5-pentamethylene carbonate diol, 1,6-hexamethylene carbonate diol, 1,2-propylene carbonate diol, 1,3-propylene carbonate diol, 2,2-dimethylpropylene carbonate diol, 1,7-heptamethylene carbonate diol, 1,8-octamethylene carbonate diol, and 1,4-cyclohexane carbonate diol.

Examples of polyisocyanates that can be used as raw materials for the urethane prepolymer (UP) include aromatic polyisocyanates, aliphatic polyisocyanates, and alicyclic polyisocyanates.
These polyisocyanates may be used alone or in combination of two or more.
Furthermore, these polyvalent isocyanates may be trimethylolpropane adduct-type modified products, biuret-type modified products reacted with water, or isocyanurate-type modified products containing an isocyanurate ring.

Among these, diisocyanates are preferred as the polyisocyanate used in one embodiment of the present invention, and one or more selected from 4,4'-diphenylmethane diisocyanate (MDI), 2,4-tolylene diisocyanate (2,4-TDI), 2,6-tolylene diisocyanate (2,6-TDI), hexamethylene diisocyanate (HMDI), and alicyclic diisocyanates are more preferred.

Examples of alicyclic diisocyanates include 3-isocyanatomethyl-3,5,5-trimethylcyclohexyl isocyanate (isophorone diisocyanate, IPDI), 1,3-cyclopentane diisocyanate, 1,3-cyclohexane diisocyanate, 1,4-cyclohexane diisocyanate, methyl-2,4-cyclohexane diisocyanate, and methyl-2,6-cyclohexane diisocyanate, with isophorone diisocyanate (IPDI) being preferred.

In one embodiment of the present invention, the urethane prepolymer (UP) that forms the main chain of the acrylic urethane resin (U1) is preferably a linear urethane prepolymer that is a reaction product of a diol and a diisocyanate and has ethylenically unsaturated groups at both ends.
As a method for introducing ethylenically unsaturated groups into both ends of the linear urethane prepolymer, a method of reacting the NCO groups at the ends of the linear urethane prepolymer obtained by reacting a diol with a diisocyanate compound with a hydroxyalkyl (meth)acrylate can be mentioned.

Examples of hydroxyalkyl (meth)acrylates include 2-hydroxyethyl (meth)acrylate, 2-hydroxypropyl (meth)acrylate, 3-hydroxypropyl (meth)acrylate, 2-hydroxybutyl (meth)acrylate, 3-hydroxybutyl (meth)acrylate, and 4-hydroxybutyl (meth)acrylate.

The vinyl compound that forms the side chain of the acrylic urethane resin (U1) contains at least a (meth)acrylic acid ester.
The (meth)acrylic acid ester is preferably at least one selected from alkyl (meth)acrylates and hydroxyalkyl (meth)acrylates, and more preferably an alkyl (meth)acrylate and a hydroxyalkyl (meth)acrylate are used in combination.

When alkyl (meth)acrylate and hydroxyalkyl (meth)acrylate are used in combination, the blending ratio of hydroxyalkyl (meth)acrylate per 100 parts by mass of alkyl (meth)acrylate is preferably 0.1 to 100 parts by mass, more preferably 0.5 to 30 parts by mass, even more preferably 1.0 to 20 parts by mass, and even more preferably 1.5 to 10 parts by mass.

The number of carbon atoms in the alkyl group of the alkyl (meth)acrylate is preferably 1 to 24, more preferably 1 to 12, even more preferably 1 to 8, and even more preferably 1 to 3.

Furthermore, examples of hydroxyalkyl (meth)acrylates include the same hydroxyalkyl (meth)acrylates used to introduce ethylenically unsaturated groups to both ends of the above-mentioned linear urethane prepolymer.

Examples of vinyl compounds other than (meth)acrylic acid esters include aromatic hydrocarbon vinyl compounds such as styrene, α-methylstyrene, and vinyltoluene; vinyl ethers such as methyl vinyl ether and ethyl vinyl ether; and polar group-containing monomers such as vinyl acetate, vinyl propionate, (meth)acrylonitrile, N-vinylpyrrolidone, (meth)acrylic acid, maleic acid, fumaric acid, itaconic acid, and metha(acrylamide).
These may be used alone or in combination of two or more.

The content of (meth)acrylic acid ester in the vinyl compound is preferably 40 to 100% by mass, more preferably 65 to 100% by mass, even more preferably 80 to 100% by mass, and even more preferably 90 to 100% by mass, relative to the total amount (100% by mass) of the vinyl compound.

The total content of alkyl (meth)acrylate and hydroxyalkyl (meth)acrylate in the vinyl compound is preferably 40 to 100% by mass, more preferably 65 to 100% by mass, even more preferably 80 to 100% by mass, and even more preferably 90 to 100% by mass, based on the total amount (100% by mass) of the vinyl compound.

The acrylic urethane resin (U1) used in one embodiment of the present invention can be obtained by mixing a urethane prepolymer (UP) with a vinyl compound containing a (meth)acrylic acid ester and polymerizing the mixture.
The polymerization is preferably carried out in the presence of a radical initiator.

In the acrylic urethane resin (U1) used in one embodiment of the present invention, the content ratio [(u11)/(u12)] of the structural unit (u11) derived from the urethane prepolymer (UP) to the structural unit (u12) derived from the vinyl compound is preferably 10/90 to 80/20, more preferably 20/80 to 70/30, even more preferably 30/70 to 60/40, and even more preferably 35/65 to 55/45 by mass.

[Olefin Resin]
The olefin resin suitable for use as the resin contained in the resin composition (y-1) is a polymer having at least a structural unit derived from an olefin monomer.
The olefin monomer is preferably an α-olefin having 2 to 8 carbon atoms, and specific examples thereof include ethylene, propylene, butylene, isobutylene, and 1-hexene.
Of these, ethylene and propylene are preferred.

Specific examples of olefin-based resins include polyethylene resins such as very low-density polyethylene (VLDPE, density: 880 kg/m ^{or more and} less than 910 kg/m), low-density polyethylene (LDPE, density: 910 kg/m ^{or more} and less than 915 kg/m), medium-density polyethylene (MDPE, density: 915 kg/m or ^{more and} less than 942 kg/m), high-density polyethylene (HDPE, density: 942 kg/m or ^more ), and linear low-density polyethylene; polypropylene resin (PP); polybutene resin (PB); ethylene-propylene copolymer; olefin-based elastomer (TPO); poly(4-methyl-1-pentene) (PMP); ethylene-vinyl acetate copolymer (EVA); ethylene-vinyl alcohol copolymer (EVOH); and olefin-based terpolymers such as ethylene-propylene-(5-ethylidene-2-norbornene).

In one embodiment of the present invention, the olefin-based resin may be a modified olefin-based resin that has been further modified by one or more methods selected from acid modification, hydroxyl group modification, and acrylic modification.

For example, examples of acid-modified olefin resins obtained by subjecting olefin resins to acid modification include modified polymers obtained by graft polymerizing unsaturated carboxylic acids or anhydrides thereof onto the above-mentioned unmodified olefin resins.
Examples of the unsaturated carboxylic acid or anhydride thereof include maleic acid, fumaric acid, itaconic acid, citraconic acid, glutaconic acid, tetrahydrophthalic acid, aconitic acid, (meth)acrylic acid, maleic anhydride, itaconic anhydride, glutaconic anhydride, citraconic anhydride, aconitic anhydride, norbornene dicarboxylic acid anhydride, and tetrahydrophthalic anhydride.
The unsaturated carboxylic acids or anhydrides thereof may be used alone or in combination of two or more.

Examples of acrylic-modified olefin resins obtained by acrylic modification of olefin resins include modified polymers obtained by graft polymerizing alkyl (meth)acrylate as a side chain onto the above-mentioned unmodified olefin resin as a main chain.
The alkyl group of the alkyl (meth)acrylate preferably has 1 to 20 carbon atoms, more preferably 1 to 16 carbon atoms, and even more preferably 1 to 12 carbon atoms.
Examples of the alkyl(meth)acrylate include the same compounds as those selectable as the monomer (a1') described above.

Examples of hydroxyl group-modified olefin resins obtained by subjecting olefin resins to hydroxyl group modification include modified polymers obtained by graft polymerizing a hydroxyl group-containing compound onto the above-mentioned unmodified olefin resin main chain.
Examples of the hydroxyl group-containing compound include the same compounds as those mentioned above.

[Resins other than acrylic urethane resins and olefin resins]
In one embodiment of the present invention, the resin composition (y-1) may contain a resin other than the acrylic urethane resin and the olefin resin, as long as the effects of the present invention are not impaired.
Examples of such resins include vinyl resins such as polyvinyl chloride, polyvinylidene chloride, and polyvinyl alcohol; polyester resins such as polyethylene terephthalate, polybutylene terephthalate, and polyethylene naphthalate; polystyrene; acrylonitrile-butadiene-styrene copolymer; cellulose triacetate; polycarbonate; polyurethanes that do not fall under the category of acrylic urethane resins; polysulfone; polyether ether ketone; polyether sulfone; polyphenylene sulfide; polyimide resins such as polyetherimide and polyimide; polyamide resins; acrylic resins; and fluorine-based resins.

However, from the viewpoint of facilitating the formation of irregularities on the adhesive surface of the pressure-sensitive adhesive layer (X1) and improving the sheet shape retention after thermal expansion, the content of resins other than the acrylic urethane resin and the olefin resin in the resin composition (y-1) is preferably small.
The content of resins other than acrylic urethane resins and olefin resins is preferably less than 30 parts by mass, more preferably less than 20 parts by mass, even more preferably less than 10 parts by mass, still more preferably less than 5 parts by mass, and even more preferably less than 1 part by mass, relative to 100 parts by mass of the total amount of resins contained in resin composition (y-1).

(Additives for substrates)
The resin composition (y-1) may contain an additive for the substrate, if necessary, within a range that does not impair the effects of the present invention.
Examples of the additives for the substrate include ultraviolet absorbers, light stabilizers, antioxidants, antistatic agents, slip agents, antiblocking agents, and colorants.
These additives for substrates may be used alone or in combination of two or more.
When these base material additives are contained, the content of each base material additive is independently preferably 0.0001 to 20 parts by mass, more preferably 0.001 to 10 parts by mass, per 100 parts by mass of the resin.

(Solvent-free resin composition (y-1a))
One embodiment of the resin composition (y-1) used in one aspect of the present invention is a solventless resin composition (y-1a) that contains an ethylenically unsaturated group-containing oligomer having a mass average molecular weight (Mw) of 50,000 or less, an energy ray-polymerizable monomer, and the above-mentioned thermally expandable particles, and does not contain a solvent.
In the solventless resin composition (y-1a), no solvent is blended, but the energy ray polymerizable monomer contributes to improving the plasticity of the oligomer.
By irradiating the solventless resin composition (y-1a) with energy rays, the oligomer having an ethylenically unsaturated group, the energy ray polymerizable monomer, etc. are polymerized to form a thermally expandable substrate layer (Y1).

The mass average molecular weight (Mw) of the oligomer contained in the solventless resin composition (y-1a) is 50,000 or less, preferably 1,000 to 50,000, more preferably 2,000 to 40,000, even more preferably 3,000 to 35,000, and even more preferably 4,000 to 30,000.

The oligomer may be any resin contained in the resin composition (y-1) described above, as long as it has an ethylenically unsaturated group and has a mass average molecular weight of 50,000 or less. The urethane prepolymer (UP) described above is preferred, and a linear urethane prepolymer having ethylenically unsaturated groups at both ends is more preferred.
As the oligomer, a modified olefin resin having an ethylenically unsaturated group can also be used.

The total content of the oligomer and energy ray-polymerizable monomer in the solventless resin composition (y-1a) is preferably 50 to 99% by mass, more preferably 60 to 95% by mass, even more preferably 65 to 90% by mass, and even more preferably 70 to 85% by mass, relative to the total amount (100% by mass) of the solventless resin composition (y-1a).

Examples of energy ray-polymerizable monomers include alicyclic polymerizable compounds such as isobornyl (meth)acrylate, dicyclopentenyl (meth)acrylate, dicyclopentanyl (meth)acrylate, dicyclopentenyloxy (meth)acrylate, cyclohexyl (meth)acrylate, adamantane (meth)acrylate, and tricyclodecane acrylate; aromatic polymerizable compounds such as phenylhydroxypropyl acrylate, benzyl acrylate, and phenolethylene oxide-modified acrylate; and heterocyclic polymerizable compounds such as tetrahydrofurfuryl (meth)acrylate, morpholine acrylate, N-vinylpyrrolidone, and N-vinylcaprolactam. Among these, isobornyl (meth)acrylate and phenylhydroxypropyl acrylate are preferred.
These energy ray polymerizable monomers may be used alone or in combination of two or more.

The content ratio of the oligomer to the energy ray-polymerizable monomer in the solventless resin composition (y-1a) [oligomer/energy ray-polymerizable monomer] is preferably 20/80 to 90/10, more preferably 30/70 to 85/15, and even more preferably 35/65 to 80/20, by mass.

In one embodiment of the present invention, the solventless resin composition (y-1a) preferably further contains a photopolymerization initiator.
By including a photopolymerization initiator, the curing reaction can be sufficiently promoted even by irradiation with energy rays having a relatively low energy.
Examples of the photopolymerization initiator include 1-hydroxycyclohexyl phenyl ketone, benzoin, benzoin methyl ether, benzoin ethyl ether, benzoin propyl ether, benzyl phenyl sulfide, tetramethylthiuram monosulfide, azobisisobutyronitrile, dibenzyl, diacetyl, β-chloroanthraquinone, and bis(2,4,6-trimethylbenzoyl)phenylphosphine oxide.
These photopolymerization initiators may be used alone or in combination of two or more.
The amount of the photopolymerization initiator to be blended is preferably 0.01 to 5 parts by mass, more preferably 0.01 to 4 parts by mass, and even more preferably 0.02 to 3 parts by mass, based on the total amount (100 parts by mass) of the oligomer and the energy ray-polymerizable monomer.

(Thickness of the thermally expandable substrate layer (Y1))
In one embodiment of the present invention, the thickness of the thermally expandable base layer (Y1) before thermal expansion is preferably 10 to 200 μm, more preferably 20 to 150 μm, and even more preferably 25 to 120 μm.
When the thickness of the heat-expandable base layer (Y1) before thermal expansion is 10 μm or more, the formation of unevenness due to the heat-expandable particles before thermal expansion can be suppressed, and the adhesive strength of the pressure-sensitive adhesive layer (X1) can be improved. When the thickness of the heat-expandable base layer (Y1) before thermal expansion is 200 μm or less, it becomes easy to adjust the total light transmittance ( _TA ) within the above range.

<Non-thermally expandable base layer (Y2)>
The non-thermally expandable base layer (Y2) of the double-sided pressure-sensitive adhesive sheet of the first embodiment is provided on the surface of the heat-expandable base layer (Y1) opposite to the surface on which the pressure-sensitive adhesive layer (X1) is laminated.

The non-thermally expandable substrate layer (Y2) is preferably a non-adhesive substrate. The probe tack value on the surface of the non-thermally expandable substrate layer (Y2) is typically less than 50 mN/5 mmφ, preferably less than 30 mN/5 mmφ, more preferably less than 10 mN/5 mmφ, and even more preferably less than 5 mN/5 mmφ.

The total light transmittance (T _Y2 ) of the non-thermally expandable base layer (Y2) at a wavelength of 380 nm is preferably 70% or more, more preferably 80% or more, and even more preferably 85% or more. There is no particular upper limit to the total light transmittance (T _Y2 ), and it may be 100% or less.
When the total light transmittance (T _Y2 ) of the non-thermally expandable base layer (Y2) is 70% or more, it becomes easy to adjust the total light transmittance (T _A ) to the above range.
The total light transmittance (T _Y2 ) can be measured using the non-thermally expandable base layer (Y2) as a measurement sample using the same device and measurement conditions as those used to measure the total light transmittance (T _A ).

Materials for forming the non-thermally expandable substrate layer (Y2) include, for example, resin, metal, paper, etc., and can be selected appropriately depending on the application of the double-sided adhesive sheet.

Examples of resins include polyolefin resins such as polyethylene and polypropylene; vinyl resins such as polyvinyl chloride, polyvinylidene chloride, polyvinyl alcohol, ethylene-vinyl acetate copolymer, and ethylene-vinyl alcohol copolymer; polyester resins such as polyethylene terephthalate, polybutylene terephthalate, and polyethylene naphthalate; polystyrene; acrylonitrile-butadiene-styrene copolymer; cellulose triacetate; polycarbonate; urethane resins such as polyurethane and acrylic-modified polyurethane; polymethylpentene; polysulfone; polyether ether ketone; polyether sulfone; polyphenylene sulfide; polyimide resins such as polyetherimide and polyimide; polyamide resins; acrylic resins; and fluorine-based resins.
Examples of metals include aluminum, tin, chromium, and titanium.
Examples of paper materials include thin paper, medium-quality paper, fine paper, impregnated paper, coated paper, art paper, parchment paper, and glassine paper.
Among these, polyester resins such as polyethylene terephthalate, polybutylene terephthalate, and polyethylene naphthalate are preferred.

These materials may be composed of one kind or two or more kinds in combination.
Examples of the non-thermally expandable base layer (Y2) using two or more forming materials in combination include a paper material laminated with a thermoplastic resin such as polyethylene, and a resin film or sheet containing a resin and having a metal film formed on the surface thereof.
Examples of methods for forming the metal layer include a method of depositing the above metal by a PVD method such as vacuum deposition, sputtering, or ion plating, or a method of attaching a metal foil made of the above metal using a general adhesive.

In addition, in order to improve the interlayer adhesion between the non-thermally expandable base layer (Y2) and other layers to be laminated thereto, if the non-thermally expandable base layer (Y2) contains a resin, the surface of the non-thermally expandable base layer (Y2) may also be subjected to surface treatment such as oxidation or roughening, easy-adhesion treatment, or primer treatment, as with the above-mentioned thermally expandable base layer (Y1).

Furthermore, when the non-thermally expandable substrate layer (Y2) contains a resin, it may contain, together with the resin, the above-mentioned substrate additives that may also be contained in the resin composition (y-1).

The non-thermally expandable base layer (Y2) is a non-thermally expandable layer determined based on the above-mentioned method.
Therefore, the volume change rate (%) of the non-thermally expandable base layer (Y2) calculated from the above formula is less than 5%, preferably less than 2%, more preferably less than 1%, even more preferably less than 0.1%, and still more preferably less than 0.01%.

The non-thermally expandable base layer (Y2) may contain thermally expandable particles as long as the volume change rate is within the above range. For example, by selecting the resin contained in the non-thermally expandable base layer (Y2), it is possible to adjust the volume change rate to the above range even if thermally expandable particles are contained.
However, the content of the thermally expandable particles in the non-thermally expandable base layer (Y2) is preferably as small as possible.
The specific content of the thermally expandable particles is usually less than 3 mass%, preferably less than 1 mass%, more preferably less than 0.1 mass%, even more preferably less than 0.01 mass%, and still more preferably less than 0.001 mass%, relative to the total mass (100 mass%) of the non-thermally expandable base layer (Y2).It is even more preferable that the layer does not contain any thermally expandable particles.

(Storage modulus E'(23) of non-thermally expandable base layer (Y2) at 23°C)
The storage modulus E'(23) of the non-thermally expandable base layer (Y2) at 23°C is preferably 5.0 x 10 ⁷ to 5.0 x 10 ⁹ Pa, more preferably 5.0 x 10 ⁸ to 4.5 x 10 ⁹ Pa, and even more preferably 1.0 x 10 ⁹ to 4.0 x 10 ⁹ Pa.
If the storage modulus E'(23) of the non-thermally expandable base layer (Y2) is 5.0 × 10 ⁷ Pa or more, the deformation resistance of the double-sided PSA sheet is likely to be improved. On the other hand, if the storage modulus E'(23) of the non-thermally expandable base layer (Y2) is 5.0 × 10 ⁹ Pa or less, the handleability of the double-sided PSA sheet is likely to be improved.
In this specification, the storage modulus E'(23) of the non-thermally expandable base layer (Y2) means a value measured by the method described in the examples.

(Thickness of Non-Thermal Expandable Base Layer (Y2))
The thickness of the non-thermally expandable base layer (Y2) is preferably 5 to 500 μm, more preferably 15 to 300 μm, and even more preferably 20 to 200 μm. If the thickness of the non-thermally expandable base layer (Y2) is 5 μm or more, the deformation resistance of the double-sided PSA sheet is easily improved. On the other hand, if the thickness of the non-thermally expandable base layer (Y2) is 500 μm or less, the handleability of the double-sided PSA sheet is easily improved and the total light transmittance (T _A ) can be easily adjusted to the above range.

<Adhesive layer (X2)>
The pressure-sensitive adhesive layer (X2) of the double-sided pressure-sensitive adhesive sheet of the first embodiment is an energy ray-curable pressure-sensitive adhesive layer, and is a layer provided on the surface of the non-thermally expandable base layer (Y2) opposite to the surface on which the heat-expandable base layer (Y1) is laminated.
The pressure-sensitive adhesive layer (X2) is a pressure-sensitive adhesive layer that is cured and loses its adhesive strength when irradiated with energy rays, and is preferably a pressure-sensitive adhesive layer that is cured and loses its adhesive strength when irradiated with ultraviolet rays.

The pressure-sensitive adhesive layer (X2) is preferably a non-thermally expandable layer.
When the pressure-sensitive adhesive layer (X2) is a non-thermally expandable layer, the volume change rate (%) of the pressure-sensitive adhesive layer (X2) calculated from the above formula is less than 5%, preferably less than 2%, more preferably less than 1%, even more preferably less than 0.1%, and still more preferably less than 0.01%.
The pressure-sensitive adhesive layer (X2) preferably does not contain any heat-expanding particles, but may contain heat-expanding particles as long as this does not contradict the object of the present invention.
When the pressure-sensitive adhesive layer (X2) contains thermally expandable particles, the smaller the content is, the better. The content is preferably less than 3 mass%, more preferably less than 1 mass%, even more preferably less than 0.1 mass%, still more preferably less than 0.01 mass%, and even more preferably less than 0.001 mass%, relative to the total mass (100 mass%) of the pressure-sensitive adhesive layer (X2).

The pressure-sensitive adhesive layer (X2) is preferably formed from a pressure-sensitive adhesive composition (x-2) containing a pressure-sensitive adhesive resin. Below, each component contained in the pressure-sensitive adhesive composition (x-2) is described.

The adhesive composition (x-2) contains an adhesive resin and, if necessary, may contain a crosslinking agent, a tackifier, a polymerizable compound, a polymerization initiator, and adhesive additives other than those listed above that are commonly used in adhesives.

(Adhesive resin)
The adhesive resin may be a polymer that has adhesiveness by itself and has a mass average molecular weight (Mw) of 10,000 or more.
The mass average molecular weight (Mw) of the adhesive resin is preferably 10,000 to 2,000,000, more preferably 20,000 to 1,500,000, and even more preferably 30,000 to 1,000,000, from the viewpoint of further improving the adhesive strength of the adhesive layer (X2).

The adhesive resin may be the same as that contained in the adhesive composition (x-1).
These adhesive resins may be used alone or in combination of two or more.
Furthermore, when these adhesive resins are copolymers having two or more types of structural units, the copolymer may be in the form of a block copolymer, a random copolymer, or a graft copolymer.

The adhesive resin contained in the adhesive composition (x-2) is preferably an adhesive resin having an energy ray-polymerizable functional group in a side chain, from the viewpoint of making the resulting adhesive layer (X2) into an adhesive layer whose adhesive strength decreases upon curing by energy ray irradiation.
Examples of the energy ray polymerizable functional group include those having a carbon-carbon double bond, such as a (meth)acryloyl group, a vinyl group, and an allyl group.

The adhesive resin preferably contains an acrylic resin from the viewpoint of exhibiting excellent adhesive strength.
The content of the acrylic resin in the pressure-sensitive adhesive composition (x-2) is preferably 30 to 100 mass%, more preferably 50 to 100 mass%, even more preferably 70 to 100 mass%, and still more preferably 85 to 100 mass%, relative to the total amount (100 mass%) of the pressure-sensitive adhesive resin contained in the pressure-sensitive adhesive composition (x-2).

The content of the adhesive resin in the adhesive composition (x-2) is preferably 35 to 100% by mass, more preferably 50 to 100% by mass, even more preferably 60 to 98% by mass, and even more preferably 70 to 95% by mass, relative to the total amount (100% by mass) of the active ingredients of the adhesive composition (x-2).

(Energy ray curable compound)
The pressure-sensitive adhesive composition (x-2) may contain, together with the pressure-sensitive adhesive resin, a monomer or oligomer that can be polymerized and cured by energy ray irradiation as an energy ray-curable compound.
Examples of such energy ray-curable compounds include polyvalent (meth)acrylate monomers such as trimethylolpropane tri(meth)acrylate, pentaerythritol (meth)acrylate, pentaerythritol tetra(meth)acrylate, dipentaerythritol hexa(meth)acrylate, 1,4-butylene glycol di(meth)acrylate, and 1,6-hexanediol (meth)acrylate; and oligomers such as polyfunctional urethane (meth)acrylate, polyfunctional polyester (meth)acrylate, polyfunctional polyether (meth)acrylate, and polyfunctional epoxy (meth)acrylate.
Among these, polyfunctional urethane (meth)acrylate oligomers are preferred from the viewpoint that they have a relatively high molecular weight and are less likely to reduce the elastic modulus of the pressure-sensitive adhesive layer (X2).
The molecular weight of the energy ray-curable compound (in the case of an oligomer, the mass average molecular weight (Mw)) is preferably 100 to 12,000, more preferably 200 to 10,000, even more preferably 400 to 8,000, and still more preferably 600 to 6,000.

(Photopolymerization initiator)
The pressure-sensitive adhesive composition (x-2) preferably further contains a photopolymerization initiator.
By including a photopolymerization initiator, the polymerization of the energy ray-polymerizable component can be more efficiently promoted.
Examples of the photopolymerization initiator include the same ones as those exemplified in the description of the solvent-free resin composition (y-1a), and among these, 1-hydroxycyclohexyl phenyl ketone is preferred.
The content of the photopolymerization initiator is preferably 0.01 to 10 parts by mass, more preferably 0.03 to 5 parts by mass, and even more preferably 0.05 to 2 parts by mass, relative to 100 parts by mass of the total amount of the adhesive resin having an energy ray-polymerizable functional group.

(Crosslinking agent)
In one embodiment of the present invention, when the pressure-sensitive adhesive composition (x-2) contains a pressure-sensitive adhesive resin having a functional group, it is preferable that the pressure-sensitive adhesive composition (x-2) further contains a crosslinking agent.
The crosslinking agent reacts with the adhesive resin having a functional group, and crosslinks the adhesive resins together using the functional group as the crosslinking starting point.

Examples of crosslinking agents that may be contained in the pressure-sensitive adhesive composition (x-2) include those that are the same as or equivalent to the crosslinking agents that may be contained in the pressure-sensitive adhesive composition (x-1). However, from the viewpoints of increasing cohesive strength and improving adhesive strength, and ease of availability, isocyanate-based crosslinking agents are preferred.

The content of the crosslinking agent is adjusted appropriately depending on the number of functional groups possessed by the adhesive resin, but is preferably 0.01 to 10 parts by mass, more preferably 0.03 to 7 parts by mass, and even more preferably 0.05 to 5 parts by mass per 100 parts by mass of the adhesive resin having functional groups.

(Tackifier)
In one embodiment of the present invention, the pressure-sensitive adhesive composition (x-2) may further contain a tackifier from the viewpoint of further improving adhesive strength.
As the tackifier that may be contained in the pressure-sensitive adhesive composition (x-2), the same tackifier as the tackifier that may be contained in the pressure-sensitive adhesive composition (x-1) can be used.

(Adhesive additives)
Examples of the additives for pressure-sensitive adhesives include the same additives for pressure-sensitive adhesives that may be contained in the pressure-sensitive adhesive composition (x-1).

The adhesive composition (x-2) can be produced by mixing an adhesive resin, a crosslinking agent, a tackifier, adhesive additives, etc., which are used as needed.

(Adhesive strength of pressure-sensitive adhesive layer (X2) before energy ray irradiation)
The adhesive strength of the pressure-sensitive adhesive layer (X2) before irradiation with energy rays is preferably 1.1 to 30.0 N/25 mm, more preferably 3.0 to 25.0 N/25 mm, and even more preferably 5.0 to 20.0 N/25 mm.
When the adhesive strength of the pressure-sensitive adhesive layer (X2) before energy ray irradiation is 1.1 N/25 mm or more, unintended peeling from the adherend, misalignment of the adherend, etc. can be more effectively suppressed. On the other hand, when the adhesive strength is 30.0 N/25 mm or less, the releasability after energy ray irradiation can be further improved.
The adhesive strength of the pressure-sensitive adhesive layer (X2) before irradiation with energy rays can be measured by the method described in the Examples.

(Adhesive strength of pressure-sensitive adhesive layer (X2) after energy ray irradiation)
The adhesive strength of the pressure-sensitive adhesive layer (X2) after energy ray irradiation is preferably 1.0 N/25 mm or less, more preferably 0.9 N/25 mm or less, even more preferably 0.8 N/25 mm or less, and still more preferably 0.7 N/25 mm or less. There is no particular restriction on the lower limit of the adhesive strength of the pressure-sensitive adhesive layer (X2) after energy ray irradiation, and it may be 0 N/25 mm or more.
When the adhesive strength of the pressure-sensitive adhesive layer (X2) after irradiation with energy rays is 1.0 N/25 mm or less, the releasability from the adherend is more excellent.
The adhesive strength of the pressure-sensitive adhesive layer (X2) after irradiation with energy rays can be measured by the method described in the Examples.

(Thickness of Pressure-Sensitive Adhesive Layer (X2))
The thickness of the pressure-sensitive adhesive layer (X2) in the double-sided pressure-sensitive adhesive sheet of the first embodiment is preferably 5 to 150 μm, more preferably 8 to 100 μm, even more preferably 12 to 70 μm, and still more preferably 15 to 50 μm.
If the thickness of the pressure-sensitive adhesive layer (X2) is 5 μm or more, sufficient adhesive strength is likely to be obtained, and unintended peeling from the adherend during temporary fixing, displacement of the adherend, etc. will tend to be suppressed. On the other hand, if the thickness of the pressure-sensitive adhesive layer (X2) is 150 μm or less, handling of the double-sided pressure-sensitive adhesive sheet will tend to be easier.

In the double-sided pressure-sensitive adhesive sheet of the first aspect, the total thickness of the pressure-sensitive adhesive layer (X1), the heat-expandable base layer (Y1), the non-heat-expandable base layer (Y2), and the pressure-sensitive adhesive layer (X2) before thermal expansion is preferably 90 to 300 μm, more preferably 100 to 250 μm, and even more preferably 130 to 200 μm.
When the total thickness is 90 μm or more, the double-sided PSA sheet has good mechanical strength and is easy to handle. When the total thickness is 300 μm or less, it is easy to adjust the total light transmittance (T _A ) to the above range.

<Method for producing double-sided pressure-sensitive adhesive sheet of first embodiment>
The method for producing the double-sided pressure-sensitive adhesive sheet of the first embodiment is not particularly limited, and examples thereof include a method for producing a double-sided pressure-sensitive adhesive sheet comprising the following steps (1a) to (5a).
Step (1a): A step of applying a pressure-sensitive adhesive composition (x-1) onto the release-treated surface of a release liner to form a pressure-sensitive adhesive layer (X1).
Step (2a): A step of applying the resin composition (y-1) to one surface of the non-thermally expandable base layer (Y2) to form a base laminate in which the non-thermally expandable base layer (Y2) and the thermally expandable base layer (Y1) are laminated.
Step (3a): A step of bonding the adhesive surface of the pressure-sensitive adhesive layer (X1) formed in step (1a) to the surface of the thermally expandable base layer (Y1) of the base laminate formed in step (2a) to obtain a single-sided pressure-sensitive adhesive sheet.
Step (4a): A step of applying a pressure-sensitive adhesive composition (x-2) onto the release-treated surface of a release liner to form a pressure-sensitive adhesive layer (X2).
Step (5a): A step of bonding the adhesive surface of the pressure-sensitive adhesive layer (X2) formed in step (4a) to the surface of the non-thermally expandable base layer (Y2) of the single-sided pressure-sensitive adhesive sheet formed in step (3a).

In the method for producing the double-sided pressure-sensitive adhesive sheet, the resin composition (y-1), the pressure-sensitive adhesive composition (x-1), and the pressure-sensitive adhesive composition (x-2) may be further blended with a dilution solvent to form a solution.
Examples of the coating method include spin coating, spray coating, bar coating, knife coating, roll coating, blade coating, die coating, and gravure coating.

In addition, in the process of drying the coating film formed from resin composition (y-1), adhesive composition (x-1), and adhesive composition (x-2), it is preferable to carry out the drying temperature at a temperature lower than the expansion initiation temperature (t) of the thermally expandable particles, in order to suppress the expansion of the thermally expandable particles.

[Double-sided pressure-sensitive adhesive sheet of second embodiment]
The double-sided pressure-sensitive adhesive sheet of the second embodiment is a double-sided pressure-sensitive adhesive sheet having a pressure-sensitive adhesive layer (X1) that is a heat-expandable layer, a substrate layer (Y), and a pressure-sensitive adhesive layer (X2) in this order.

The description of the base layer (Y) of the double-sided pressure-sensitive adhesive sheet of the second embodiment is the same as the description of the non-thermally expandable base layer (Y2) in the double-sided pressure-sensitive adhesive sheet of the first embodiment, and the description of the adhesive layer (X2) of the double-sided pressure-sensitive adhesive sheet of the second embodiment is the same as the description of the adhesive layer (X2) in the double-sided pressure-sensitive adhesive sheet of the first embodiment.

<Pressure-sensitive adhesive layer (X1)>
The pressure-sensitive adhesive layer (X1) of the second embodiment is a heat-expandable layer containing heat-expandable particles, and preferably contains a polymer of an energy ray-polymerizable component and heat-expandable particles.
The polymer is obtained by irradiating a polymerizable composition (hereinafter also referred to as "polymerizable composition (x-1')") containing, as the energy ray-polymerizable components, a monomer (b1) (hereinafter also referred to as "component (b1)") having an energy ray-polymerizable functional group and a prepolymer (b2) (hereinafter also referred to as "component (b2)") having an energy ray-polymerizable functional group.
In this specification, a prepolymer refers to a compound obtained by polymerizing a monomer, which can be further polymerized to form a polymer.

The energy ray-polymerizable component contained in the polymerizable composition (x-1') is a component that polymerizes upon irradiation with energy rays and has an energy ray-polymerizable functional group.
Examples of the energy ray-polymerizable functional group include those having a carbon-carbon double bond, such as a (meth)acryloyl group, a vinyl group, an allyl group, etc. In the following description, functional groups that partially contain a vinyl group or a substituted vinyl group, such as a (meth)acryloyl group or an allyl group, and the vinyl group or substituted vinyl group itself may be collectively referred to as a "vinyl group-containing group."
Each component contained in the polymerizable composition (x-1') will be described below.

(Monomer (b1) having an energy ray-polymerizable functional group)
The monomer (b1) having an energy ray-polymerizable functional group may be any monomer having an energy ray-polymerizable functional group, and may have, in addition to the energy ray-polymerizable functional group, a hydrocarbon group, a functional group other than the energy ray-polymerizable functional group, etc.

Examples of the hydrocarbon group contained in component (b1) include aliphatic hydrocarbon groups, aromatic hydrocarbon groups, and groups that combine these groups.
The aliphatic hydrocarbon group may be a straight-chain or branched-chain aliphatic hydrocarbon group, or may be an alicyclic hydrocarbon group.
Examples of the linear or branched aliphatic hydrocarbon group include aliphatic hydrocarbon groups having 1 to 20 carbon atoms, such as a methyl group, an ethyl group, an n-propyl group, an isopropyl group, an n-butyl group, a tert-butyl group, a sec-butyl group, an n-pentyl group, an n-hexyl group, a 2-ethylhexyl group, an n-octyl group, an isooctyl group, an n-decyl group, an n-dodecyl group, an n-myristyl group, an n-palmityl group, and an n-stearyl group.
Examples of the alicyclic hydrocarbon group include alicyclic hydrocarbon groups having 3 to 20 carbon atoms, such as a cyclopentyl group, a cyclohexyl group, and an isobornyl group.
An example of the aromatic hydrocarbon group is a phenyl group.
Examples of the group combining an aliphatic hydrocarbon group and an aromatic hydrocarbon group include a phenoxyethyl group and a benzyl group.
Among these, from the viewpoint of further improving the adhesive strength of the pressure-sensitive adhesive layer (X1), it is preferable that the component (b1) contains a monomer (b1-1) having an energy ray-polymerizable functional group and a linear or branched aliphatic hydrocarbon group (hereinafter also referred to as "component (b1-1)"), a monomer (b1-2) having an energy ray-polymerizable functional group and an alicyclic hydrocarbon group (hereinafter also referred to as "component (b1-2)"), or the like.

When the component (b1) contains the component (b1-1), the content thereof is preferably 20 to 80 mass%, more preferably 40 to 70 mass%, and even more preferably 50 to 60 mass%, relative to the total amount of the component (b1) (100 mass%).
When the component (b1) contains the component (b1-2), the content thereof is preferably 5 to 60 mass%, more preferably 10 to 40 mass%, and even more preferably 20 to 30 mass%, relative to the total amount of the component (b1) (100 mass%).

Examples of the monomer having an energy ray-polymerizable functional group and a functional group other than the energy ray-polymerizable functional group include monomers having, as the functional group other than the energy ray-polymerizable functional group, for example, a hydroxy group, a carboxy group, a thiol group, a primary or secondary amino group, etc. Among these, from the viewpoint of further improving the formability of the pressure-sensitive adhesive layer (X1), it is preferable that the component (b1) contains a monomer (b1-3) having an energy ray-polymerizable functional group and a hydroxy group (hereinafter also referred to as "component (b1-3)").
When the component (b1) contains the component (b1-3), the content thereof is preferably 1 to 60 mass%, more preferably 5 to 30 mass%, and even more preferably 10 to 20 mass%, relative to the total amount of the component (b1) (100 mass%).

The number of energy ray-polymerizable functional groups in the component (b1) may be 1 or 2 or more. From the viewpoint of further improving the releasability of the pressure-sensitive adhesive layer (X1), the component (b1) preferably contains a monomer (b1-4) having 3 or more energy ray-polymerizable functional groups (hereinafter also referred to as "component (b1-4)").
When the component (b1) contains the component (b1-4), the content thereof is preferably 1 to 20 mass%, more preferably 2 to 15 mass%, and even more preferably 3 to 10 mass%, relative to the total amount of the component (b1) (100 mass%).

As the monomer having one energy ray-polymerizable functional group, a monomer having one vinyl group-containing group (hereinafter also referred to as a "polymerizable vinyl monomer") is preferred.
As the monomer having two or more energy ray-polymerizable functional groups, a monomer having two or more (meth)acryloyl groups (hereinafter also referred to as a "polyfunctional (meth)acrylate monomer") is preferred. When the component (b1) contains the above-mentioned compound, the cohesive strength of the pressure-sensitive adhesive obtained by polymerizing these is improved, and a pressure-sensitive adhesive layer (X1) can be formed that causes little contamination of the adherend after peeling.

[Polymerizable vinyl monomer]
The polymerizable vinyl monomer is not particularly limited as long as it has a vinyl group-containing group, and any conventionally known polymerizable vinyl monomer can be used as appropriate.
The polymerizable vinyl monomers may be used alone or in combination of two or more.

Examples of polymerizable vinyl monomers include compounds corresponding to the above-mentioned component (b1-1), such as methyl (meth)acrylate, ethyl (meth)acrylate, propyl (meth)acrylate, butyl (meth)acrylate, pentyl (meth)acrylate, hexyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, isooctyl (meth)acrylate, decyl (meth)acrylate, dodecyl (meth)acrylate, myristyl (meth)acrylate, palmityl (meth)acrylate, and stearyl (meth)acrylate; compounds corresponding to the above-mentioned component (b1-2), such as cyclohexyl (meth)acrylate and isobornyl (meth)acrylate; and (meth)acrylates that do not have functional groups other than vinyl group-containing groups in the molecule, such as phenoxyethyl (meth)acrylate, benzyl (meth)acrylate, and polyoxyalkylene-modified (meth)acrylates. Of these, 2-ethylhexyl acrylate and isobornyl acrylate are preferred.

The polymerizable vinyl monomer may further contain a functional group other than the vinyl group-containing group in the molecule. Examples of such functional groups include a hydroxy group, a carboxy group, a thiol group, and a primary or secondary amino group. Among these, a polymerizable vinyl monomer having a hydroxy group corresponding to the above component (b1-3) is preferred.
Examples of polymerizable vinyl monomers having a hydroxy group include hydroxyalkyl (meth)acrylates such as 2-hydroxyethyl (meth)acrylate, 2-hydroxypropyl (meth)acrylate, 3-hydroxypropyl (meth)acrylate, 2-hydroxybutyl (meth)acrylate, 3-hydroxybutyl (meth)acrylate, and 4-hydroxybutyl (meth)acrylate; and hydroxy group-containing acrylamides such as N-methylol acrylamide and N-methylol methacrylamide. Examples of polymerizable vinyl monomers having a carboxy group include ethylenically unsaturated carboxylic acids such as acrylic acid, methacrylic acid, crotonic acid, maleic acid, itaconic acid, and citraconic acid. Of these, 2-hydroxyethyl acrylate and 4-hydroxybutyl acrylate are preferred.

Other polymerizable vinyl monomers include, for example, vinyl esters such as vinyl acetate and vinyl propionate; olefins such as ethylene, propylene, and isobutylene; halogenated olefins such as vinyl chloride and vinylidene chloride; styrene-based monomers such as styrene and α-methylstyrene; diene-based monomers such as butadiene, isoprene, and chloroprene; nitrile-based monomers such as acrylonitrile and methacrylonitrile; amide-based monomers such as acrylamide, methacrylamide, N-methylacrylamide, N-methylmethacrylamide, N,N-dimethyl(meth)acrylamide, N,N-diethyl(meth)acrylamide, and N-vinylpyrrolidone; and tertiary amino group-containing monomers such as N,N-diethylaminoethyl (meth)acrylate and N-(meth)acryloylmorpholine.

[Polyfunctional (meth)acrylate monomer]
The polyfunctional (meth)acrylate monomer is not particularly limited as long as it is a monomer having two or more (meth)acryloyl groups in one molecule, and any conventionally known monomer can be used as appropriate.
The polyfunctional (meth)acrylate monomers may be used alone or in combination of two or more.

Examples of polyfunctional (meth)acrylate monomers include bifunctional (meth)acrylate monomers such as 1,4-butanediol di(meth)acrylate, 1,6-hexanediol di(meth)acrylate, neopentyl glycol di(meth)acrylate, polyethylene glycol di(meth)acrylate, neopentyl glycol adipate di(meth)acrylate, hydroxypivalic acid neopentyl glycol di(meth)acrylate, dicyclopentanyl di(meth)acrylate, caprolactone-modified dicyclopentenyl di(meth)acrylate, ethylene oxide-modified phosphate di(meth)acrylate, di(acryloxyethyl)isocyanurate, allylated cyclohexyl di(meth)acrylate, and isocyanuric acid ethylene oxide-modified diacrylate; trimethylolpropane tri(meth)acrylate, dipentaerythritol tri(meth)acrylate, and the like. Examples of polyfunctional (meth)acrylate monomers that fall under the category of component (b1-4) include acrylate, propionic acid-modified dipentaerythritol tri(meth)acrylate, pentaerythritol tri(meth)acrylate, propylene oxide-modified trimethylolpropane tri(meth)acrylate, tris(acryloxyethyl)isocyanurate, bis(acryloxyethyl)hydroxyethyl isocyanurate, ethylene oxide isocyanurate-modified triacrylate, ε-caprolactone-modified tris(acryloxyethyl)isocyanurate, diglycerol tetra(meth)acrylate, pentaerythritol tetra(meth)acrylate, propionic acid-modified dipentaerythritol penta(meth)acrylate, dipentaerythritol hexa(meth)acrylate, and caprolactone-modified dipentaerythritol hexa(meth)acrylate.

<<Content of component (b1)>>
The total content of the polymerizable vinyl monomers in the polymerizable composition (x-1') is preferably 10 to 80 mass%, more preferably 30 to 75 mass%, and even more preferably 50 to 70 mass%, based on the total amount (100 mass%) of the active ingredients of the polymerizable composition (x-1').
The total content of the polyfunctional (meth)acrylate monomers in the polymerizable composition (x-1') is preferably 0.5 to 15 mass%, more preferably 1 to 10 mass%, and even more preferably 2 to 5 mass%, relative to the total amount (100 mass%) of the active ingredients of the polymerizable composition (x-1').
The total content of the component (b1) in the polymerizable composition (x-1') is preferably 15 to 90 mass%, more preferably 35 to 80 mass%, and even more preferably 55 to 75 mass%, relative to the total amount (100 mass%) of the active ingredients of the polymerizable composition (x-1').

(Prepolymer (b2) having an energy ray-polymerizable functional group)
Examples of the prepolymer (b2) having an energy ray-polymerizable functional group include a prepolymer having one energy ray-polymerizable functional group, a prepolymer having two or more energy ray-polymerizable functional groups, etc. Among these, from the viewpoint of forming a pressure-sensitive adhesive layer that is excellent in releasability and causes little contamination of the adherend after peeling, the component (b2) preferably contains a prepolymer having two or more energy ray-polymerizable functional groups, more preferably contains a prepolymer having two energy ray-polymerizable functional groups, and even more preferably contains a prepolymer having two energy ray-polymerizable functional groups and having the energy ray-polymerizable functional groups at both ends.

The component (b2) preferably contains a prepolymer having two or more (meth)acryloyl groups as energy ray-polymerizable functional groups (hereinafter also referred to as a "polyfunctional (meth)acrylate prepolymer"). By including such a compound in the component (b2), the cohesive strength of the PSA obtained by polymerizing it is improved, allowing for the formation of a PSA layer (X1) that has excellent releasability and reduces contamination of the adherend after peeling.

[Polyfunctional (meth)acrylate prepolymer]
The polyfunctional (meth)acrylate prepolymer is not particularly limited as long as it is a prepolymer having two or more (meth)acryloyl groups in one molecule, and any conventionally known prepolymer can be used as appropriate.
The polyfunctional (meth)acrylate prepolymers may be used alone or in combination of two or more.

Examples of polyfunctional (meth)acrylate prepolymers include urethane acrylate prepolymers, polyester acrylate prepolymers, epoxy acrylate prepolymers, polyether acrylate prepolymers, polybutadiene acrylate prepolymers, silicone acrylate prepolymers, and polyacrylic acrylate prepolymers.

Urethane acrylate prepolymers can be obtained by esterifying a polyurethane prepolymer obtained by reacting a compound such as polyalkylene polyol, polyether polyol, polyester polyol, hydrogenated isoprene having hydroxyl groups at the ends, or hydrogenated butadiene having hydroxyl groups at the ends with polyisocyanate, with (meth)acrylic acid or a (meth)acrylic acid derivative.

Examples of polyalkylene polyols used in the production of urethane acrylate prepolymers include polypropylene glycol, polyethylene glycol, polybutylene glycol, and polyhexylene glycol, with polypropylene glycol being preferred. To obtain a urethane acrylate prepolymer with three or more functional groups, suitable combinations of glycerin, trimethylolpropane, triethanolamine, pentaerythritol, ethylenediamine, diethylenetriamine, sorbitol, sucrose, and the like may be used.

Examples of polyisocyanates used in the production of urethane acrylate prepolymers include aliphatic diisocyanates such as hexamethylene diisocyanate and trimethylene diisocyanate; aromatic diisocyanates such as tolylene diisocyanate, xylylene diisocyanate and diphenyl diisocyanate; and alicyclic diisocyanates such as dicyclohexylmethane diisocyanate and isophorone diisocyanate. Among these, aliphatic diisocyanates are preferred, with hexamethylene diisocyanate being more preferred. Polyisocyanates are not limited to those with two functionalities; trifunctional or higher functional ones can also be used.

(Meth)acrylic acid derivatives used in the production of urethane acrylate prepolymers include, for example, hydroxyalkyl (meth)acrylates such as 2-hydroxyethyl acrylate and 4-hydroxybutyl acrylate; 2-isocyanate ethyl acrylate, 2-isocyanate ethyl methacrylate, and 1,1-bis(acryloxymethyl)ethyl isocyanate; of these, 2-isocyanate ethyl acrylate is preferred.

Another method for producing urethane acrylate prepolymers involves reacting the hydroxyl groups of compounds such as polyalkylene polyols, polyether polyols, polyester polyols, hydroxy-terminated hydrogenated isoprene, and hydroxy-terminated hydrogenated butadiene with the -N=C=O moiety of an isocyanate alkyl (meth)acrylate. In this case, examples of the isocyanate alkyl (meth)acrylate that can be used include the above-mentioned 2-isocyanate ethyl acrylate, 2-isocyanate ethyl methacrylate, and 1,1-bis(acryloxymethyl)ethyl isocyanate.

Polyester acrylate prepolymers can be obtained, for example, by esterifying with (meth)acrylic acid the hydroxy groups of a polyester prepolymer having hydroxy groups at both ends, which is obtained by condensing a polycarboxylic acid with a polyhydric alcohol. They can also be obtained by adding an alkylene oxide to a polycarboxylic acid to obtain a prepolymer, and esterifying with (meth)acrylic acid the hydroxy groups at the ends of the prepolymer.

Epoxy acrylate prepolymers can be obtained, for example, by esterifying the oxirane ring of relatively low-molecular-weight bisphenol epoxy resins, novolac epoxy resins, etc. with (meth)acrylic acid. It is also possible to use carboxy-modified epoxy acrylate prepolymers, which are epoxy acrylate prepolymers partially modified with dibasic carboxylic acid anhydrides.

Polyether acrylate prepolymers can be obtained, for example, by esterifying the hydroxy groups of polyether polyol with (meth)acrylic acid.

Polyacrylacrylate prepolymers may have acryloyl groups in their side chains, or at both or one end. Polyacrylacrylate prepolymers with acryloyl groups in their side chains can be obtained, for example, by adding glycidyl methacrylate to the carboxyl groups of polyacrylic acid. Polyacrylacrylate prepolymers with acryloyl groups at both ends can be obtained, for example, by introducing acryloyl groups to both ends of a polyacrylate prepolymer synthesized by the ATRP (Atom Transfer Radical Polymerization) method, utilizing the polymer growth terminal structure.

The mass average molecular weight (Mw) of component (b2) is preferably 10,000 to 350,000, more preferably 15,000 to 200,000, and even more preferably 20,000 to 50,000.

<<Content of component (b2)>>
The total content of the polyfunctional (meth)acrylate prepolymers in the polymerizable composition (x-1') is preferably 10 to 60 mass%, more preferably 15 to 55 mass%, and even more preferably 20 to 30 mass%, relative to the total amount (100 mass%) of the active ingredients of the polymerizable composition (x-1').
The total content of the component (b2) in the polymerizable composition (x-1′) is preferably 10 to 60 mass%, more preferably 15 to 55 mass%, and even more preferably 20 to 30 mass%, relative to the total amount (100 mass%) of the active ingredients of the polymerizable composition (x-1′).

The content ratio of the (b2) component to the (b1) component in the polymerizable composition (x-1') [(b2)/(b1)] is, by mass, preferably 10/90 to 70/30, more preferably 20/80 to 50/50, and even more preferably 25/75 to 40/60.

Among the above energy ray-polymerizable components, the polymerizable composition (x-1') preferably contains a polymerizable vinyl monomer, a polyfunctional (meth)acrylate monomer, and a polyfunctional (meth)acrylate prepolymer.
The total content of the polymerizable vinyl monomer, the polyfunctional (meth)acrylate monomer, and the polyfunctional (meth)acrylate prepolymer in the energy ray-polymerizable component contained in the polymerizable composition (x-1') is preferably 80% by mass or more, more preferably 90% by mass or more, even more preferably 95% by mass or more, still more preferably 99% by mass or more, relative to the total amount (100% by mass) of the energy ray-polymerizable component, and may be 100% by mass.

The total content of energy ray-polymerizable components in polymerizable composition (x-1') is preferably 70 to 98% by mass, more preferably 75 to 97% by mass, even more preferably 80 to 96% by mass, and even more preferably 82 to 95% by mass, relative to the total amount (100% by mass) of active components in polymerizable composition (x-1').

(Other ingredients)
The polymerizable composition (x-1') may contain other components in addition to the energy ray polymerizable component and the thermally expandable particles.
Examples of the other components include a photopolymerization initiator, a tackifier, and adhesive additives other than the above components that are used in general adhesives.
These components include the same components as those described for the double-sided PSA sheet of the first embodiment.

The polymerizable composition (x-1′) may contain a solvent such as a diluent within the scope of the present invention, but preferably does not contain a solvent. That is, the polymerizable composition (x-1′) is preferably a solvent-free polymerizable composition.
Since the polymerizable composition (x-1') is a solventless polymerizable composition, the step of drying the solvent by heating can be omitted when forming the pressure-sensitive adhesive layer (X1), and therefore the expansion of the heat-expandable particles during heating and drying can be suppressed.
When the polymerizable composition (x-1′) contains a solvent, the smaller the content of the solvent, the better. The content is preferably 10% by mass or less, more preferably 1% by mass or less, even more preferably 0.1% by mass or less, and still more preferably 0.01% by mass or less, relative to the total amount (100% by mass) of the active ingredients of the polymerizable composition (x-1′).

The polymerizable composition (x-1') can be produced by mixing an energy ray-polymerizable component, thermally expandable particles, and other components that may be contained as needed. The resulting polymerizable composition (x-1') is subsequently polymerized by energy ray polymerization, and therefore, when forming a layer, the viscosity can be adjusted to an appropriate level using a low-molecular-weight energy ray-polymerizable component. Therefore, the polymerizable composition (x-1') can be used as is as a coating solution to form the pressure-sensitive adhesive layer (X1) without adding a solvent such as a diluent.
The pressure-sensitive adhesive layer (X1) formed by irradiating the polymerizable composition (x-1') with energy rays contains a wide variety of polymers formed by polymerization of energy ray-polymerizable components and thermally expandable particles dispersed in the polymers, but there are circumstances in which it is impossible or almost impractical to directly identify these by their structure and physical properties.

(Adhesive strength of pressure-sensitive adhesive layer (X1))
The explanation of the adhesive strength of the pressure-sensitive adhesive layer (X1) before and after thermal expansion in the double-sided pressure-sensitive adhesive sheet of the second embodiment is the same as the explanation of the adhesive strength of the pressure-sensitive adhesive layer (X1) before and after thermal expansion of the heat-expandable base layer (Y1) in the explanation of the double-sided pressure-sensitive adhesive sheet of the first embodiment.

(Thickness of Pressure-Sensitive Adhesive Layer (X1))
The thickness of the pressure-sensitive adhesive layer (X1) of the double-sided pressure-sensitive adhesive sheet of the second embodiment before thermal expansion is preferably 10 to 200 μm, more preferably 20 to 150 μm, and even more preferably 25 to 120 μm.
If the thickness of the pressure-sensitive adhesive layer (X1) before thermal expansion is 10 μm or more, sufficient adhesive strength is easily obtained, and unintended peeling from the adherend during temporary fixation, positional displacement of the adherend, etc. tend to be suppressed. On the other hand, if the thickness of the pressure-sensitive adhesive layer (X1) before thermal expansion is 200 μm or less, releasability during heat peeling is improved, and curling of the double-sided pressure-sensitive adhesive sheet during heat peeling tends to be suppressed, and handleability tends to be improved. In addition, it becomes easier to adjust the total light transmittance ( _TA ) within the above range.

<Method for producing the double-sided pressure-sensitive adhesive sheet of the second embodiment>
The method for producing a double-sided pressure-sensitive adhesive sheet of the second aspect is preferably a method for producing a double-sided pressure-sensitive adhesive sheet in which the method for forming the pressure-sensitive adhesive layer (X1) includes a step of irradiating a polymerizable composition (x-1') containing the energy ray-polymerizable component and the thermally expandable particles with energy rays to form a polymer of the energy ray-polymerizable component, and more preferably a production method including the following steps (1b) to (3b):
Step (1b): A step of forming a polymerizable composition layer made of a polymerizable composition (x-1') on one side of a substrate (Y). Step (2b): A step of forming a polymer of the energy ray-polymerizable component by irradiating the polymerizable composition layer with energy rays, and forming a pressure-sensitive adhesive layer (X1) containing the polymer and the thermally expandable particles. Step (3b): A step of forming a pressure-sensitive adhesive layer (X2) on the other side of a substrate (Y).

An example of step (1b) is a method in which a polymerizable composition (x-1′) is applied to a release-treated surface of a release material to form a polymerizable composition layer, the polymerizable composition layer is irradiated with a first energy ray to prepolymerize the energy ray-polymerizable component in the polymerizable composition layer, and then a substrate (Y) is attached to the prepolymerized polymerizable composition layer.
As described above, the polymerizable composition (x-1') is preferably a solventless polymerizable composition. When the polymerizable composition (x-1') is a solventless polymerizable composition, the step of heating and drying the solvent in this step is not necessary, and the expansion of the thermally expandable particles can be suppressed.

Step (2b) is a step of irradiating the polymerizable composition layer formed in step (1b) with energy rays to form a polymer of the energy ray-polymerizable component, and forming a pressure-sensitive adhesive layer (X1) containing the polymer and thermally expandable particles.
Here, when the first energy ray irradiation is performed in the step (1b), the energy ray irradiation in the step (2b) is the second energy ray irradiation performed on the polymerizable composition layer after the prepolymerization.
Unlike the first energy ray irradiation, the energy ray irradiation in step (2b) is preferably carried out to an extent that further irradiation with energy rays does not substantially cause polymerization of the energy ray-polymerizable component to proceed. The energy ray irradiation in step (2b) causes polymerization of the energy ray-polymerizable component to proceed, and a polymer of the energy ray-polymerizable component that constitutes the pressure-sensitive adhesive layer (X1) is formed.

Examples of step (3b) include a method in which a pressure-sensitive adhesive composition (x-2) is applied to one side of a release material to form a pressure-sensitive adhesive layer (X2), and the pressure-sensitive adhesive layer (X2) is then attached to the other side of the substrate (Y).

In either of the steps included in the above steps (1b) and (2b), it is preferable that the step of heating the polymerizable composition is not included, from the viewpoint of suppressing expansion of the thermally expandable particles.
Here, "heating" means intentional heating, for example, during drying, lamination, etc., and does not include a temperature increase due to heat imparted to the polymerizable composition by energy ray irradiation, polymerization heat generated by polymerization of the energy ray-polymerizable composition, etc.

[Uses and methods of use of double-sided pressure-sensitive adhesive sheets]
The double-sided pressure-sensitive adhesive sheet of one embodiment of the present invention can easily peel off a temporarily fixed adherend by heating, and is therefore applicable to a variety of uses. Specifically, the sheet is suitable for, for example, a dicing sheet used when dicing an adherend such as a semiconductor wafer, a backgrinding sheet used in the process of grinding an adherend, an expandable tape used to increase the distance between adherends such as semiconductor chips that have been individualized by dicing, a transfer tape used to turn over an adherend such as a semiconductor chip, and a temporary fixing sheet for temporarily fixing an object to be inspected for inspection.

The adherend to which the double-sided pressure-sensitive adhesive sheet of one embodiment of the present invention is applied is not particularly limited, but examples thereof include semiconductor chips, semiconductor wafers, compound semiconductors, semiconductor packages, electronic components, sapphire substrates, displays, and panel substrates.
In one embodiment of the double-sided pressure-sensitive adhesive sheet of the present invention, when the expansion initiation temperature (t) of the heat-expandable particles is set to less than 125°C, thermal peeling is possible at low temperatures, making the sheet suitable for temporarily fixing adherends that are susceptible to thermal changes, such as semiconductor chips with DAFs.
Furthermore, in one embodiment of the double-sided pressure-sensitive adhesive sheet of the present invention, if the expansion initiation temperature (t) of the heat-expandable particles is set to 50°C or higher, unintended expansion of the heat-expandable particles due to temperature rise when grinding the adherend, for example, can be suppressed, making the sheet suitable for use as a backgrinding sheet in the process of grinding the adherend.

The heating temperature when the double-sided pressure-sensitive adhesive sheet of one embodiment of the present invention is heat-peeled from an adherend is equal to or higher than the expansion start temperature (t) of the heat-expandable particles, preferably "a temperature higher than the expansion start temperature (t)," more preferably "expansion start temperature (t) + 2°C" or higher, even more preferably "expansion start temperature (t) + 4°C" or higher, and even more preferably "expansion start temperature (t) + 5°C." Furthermore, from the viewpoint of energy conservation and suppressing thermal changes in the adherend during heat-peeling, the heating temperature is preferably "expansion start temperature (t) + 50°C" or lower, more preferably "expansion start temperature (t) + 40°C" or lower, and even more preferably "expansion start temperature (t) + 20°C" or lower.
Furthermore, from the viewpoint of suppressing thermal changes in the adherend, the heating temperature during thermal peeling is preferably less than 125°C, more preferably 120°C or less, even more preferably 115°C or less, still more preferably 110°C or less, and even more preferably 105°C or less, within a range equal to or higher than the expansion starting temperature (t).

The heating method is not particularly limited as long as it can heat the material to a temperature above the expansion temperature of the thermally expandable particles. For example, electric heaters; dielectric heating; magnetic heating; and heating using electromagnetic waves such as near-infrared, mid-infrared, and far-infrared rays can be used as appropriate. The heating method may be a contact heating method such as a heating roller or a heating press, or a non-contact heating method such as an atmospheric heating device or infrared irradiation.

[Double-sided adhesive sheet with release liner]
A release-lined double-sided pressure-sensitive adhesive sheet according to one embodiment of the present invention is a release-lined double-sided pressure-sensitive adhesive sheet having a release material on one or both surfaces of the above-described double-sided pressure-sensitive adhesive sheet according to one embodiment of the present invention.
An example of a double-sided adhesive sheet with a release material according to one embodiment of the present invention is the double-sided adhesive sheet with a release material 1b shown in Figure 2(a), in which release materials 10a and 10b are arranged on both sides of the above-mentioned double-sided adhesive sheet 1a.
Another embodiment of the double-sided adhesive sheet with a release material of the present invention is, for example, the double-sided adhesive sheet with a release material 2b shown in Figure 2(b), in which release materials 10a, 10b are arranged on both sides of the above-mentioned double-sided adhesive sheet 2a.

2(a) and (b), if the peel force required to peel release material 10a from adhesive layer (X1) and the peel force required to peel release material 10b from adhesive layer (X2) are similar, attempting to peel both release materials outward can result in the adhesive layer being torn apart and peeled away along with the two release materials. To prevent this phenomenon, it is preferable to use two types of release materials for the two release materials 10a and 10b, each designed to have different peel forces from the adhesive layer to which it is attached.

Another embodiment of the double-sided pressure-sensitive adhesive sheet with a release material of the present invention may be a double-sided pressure-sensitive adhesive sheet with a release material configured such that a release material having a release treatment applied to both sides is laminated on one adhesive surface of the pressure-sensitive adhesive layer (X1) and the pressure-sensitive adhesive layer (X2) described above in double-sided pressure-sensitive adhesive sheet 1a (Figure 1(a)) or 2a (Figure 1(b)), and the sheet is then wound into a roll.

As the release material, a release sheet with double-sided release treatment, a release sheet with one-sided release treatment, etc., is used, and examples thereof include a release material substrate coated with a release agent.
Examples of substrates for release materials include plastic films, papers, etc. Examples of plastic films include polyester resin films such as polyethylene terephthalate resin, polybutylene terephthalate resin, and polyethylene naphthalate resin; and olefin resin films such as polypropylene resin and polyethylene resin. Examples of papers include fine paper, glassine paper, and kraft paper.

Examples of release agents include rubber-based elastomers such as silicone resins, olefin resins, isoprene resins, and butadiene resins; long-chain alkyl resins, alkyd resins, and fluorine-based resins. One type of release agent may be used alone, or two or more types may be used in combination.

The thickness of the release material is preferably 10 to 200 μm, more preferably 20 to 150 μm, and even more preferably 35 to 80 μm.

[Method of manufacturing a semiconductor device]
The present invention also provides a method for manufacturing a semiconductor device using the double-sided pressure-sensitive adhesive sheet of one aspect of the present invention.
One aspect of the method for manufacturing a semiconductor device of the present invention is to use a double-sided pressure-sensitive adhesive sheet of one aspect of the present invention as a temporary fixing sheet for processing and/or inspecting an adherend (hereinafter also referred to as the "first aspect of the method for manufacturing a semiconductor device").
In this specification, the term "semiconductor device" refers to any device that can function by utilizing semiconductor properties, such as a wafer having an integrated circuit, a thinned wafer having an integrated circuit, a chip having an integrated circuit, a thinned chip having an integrated circuit, an electronic component including such a chip, and electronic equipment including such an electronic component.

<Method for manufacturing semiconductor device according to first embodiment>
A more specific embodiment of the first aspect of the method for manufacturing a semiconductor device includes a step of attaching an object to be processed and inspected to a double-sided pressure-sensitive adhesive sheet of one aspect of the present invention, subjecting the object to one or more processes and inspections, and then heating the double-sided pressure-sensitive adhesive sheet to the expansion starting temperature (t) or higher.
Examples of the processed and inspected objects include semiconductor chips, semiconductor wafers, compound semiconductors, semiconductor packages, electronic components, LED elements, sapphire substrates, displays, and panel substrates.
The processing performed on the inspection object is not particularly limited, but examples thereof include grinding and singulation.
The inspections performed on the processed inspection object are not particularly limited, but examples include defect inspection using an optical microscope or laser (e.g., dust inspection, surface scratch inspection, wiring pattern inspection, etc.), and visual surface inspection.

In the first embodiment of the semiconductor device manufacturing method, the adhesive layer of the double-sided adhesive sheet to which the processing and inspection object is attached may be adhesive layer (X1) or adhesive layer (X2). However, it is preferable to attach the processing and inspection object to one of the adhesive layers and attach a support to the other adhesive layer. Fixing the processing and inspection object to the support via the double-sided adhesive sheet reduces vibration, misalignment, and damage to fragile processing and inspection objects during at least one of processing and inspection, thereby improving processing accuracy and processing speed, as well as inspection accuracy and inspection speed. In this case, the support may be attached to adhesive layer (X1) and the processing and inspection object may be attached to adhesive layer (X2), or the processing and inspection object may be attached to adhesive layer (X1) and the support may be attached to adhesive layer (X2). In addition, the double-sided pressure-sensitive adhesive sheet of one embodiment of the present invention has a higher degree of freedom in usage than conventional methods, because the adhesive strength of the pressure-sensitive adhesive layer (X2), which is an energy ray-curable pressure-sensitive adhesive layer, can be sufficiently reduced by irradiating the heat-expandable layer with energy rays from the heat-expandable layer side, even after the heat-expandable layer has been thermally expanded.

In an embodiment in which a support is affixed to the adhesive layer (X1) and an object to be processed and inspected is affixed to the adhesive layer (X2), the support is affixed to an adhesive layer (X1) that exhibits excellent peelability after heat treatment, allowing the double-sided adhesive sheet and support to be heat peeled without bending, even if the support is made of a hard material. Furthermore, the adhesive strength of the adhesive layer (X2) can be reduced by irradiation with energy rays, allowing the object to be peeled without contaminating it with residues derived from the heat-expandable particles. Furthermore, because the adhesive strength of the adhesive layer (X2) is sufficiently reduced by irradiation with energy rays from the heat-expandable layer side, it is possible to select an object to be processed and inspected on the adhesive layer (X2) side even if it does not have light transmittance.

On the other hand, in the case where the processing test object is attached to the adhesive layer (X1) and the support is attached to the adhesive layer (X2), by attaching the processing test object to the adhesive layer (X1) which has excellent releasability after heat treatment, when heat peeling is performed after processing, the processing test object does not need to be picked up individually, and can be easily peeled all at once, thereby improving productivity of the semiconductor device. Furthermore, since the adhesive strength of the adhesive layer (X2) is sufficiently reduced by irradiation of energy rays from the heat expandable layer side, the support on the adhesive layer (X2) side can be selected even if it does not have light transparency.
Furthermore, when the double-sided pressure-sensitive adhesive sheet of one embodiment of the present invention is used as a temporary fixing sheet for inspecting processing inspection objects as part of a manufacturing process, the inspection can be carried out with multiple processing inspection objects attached to the pressure-sensitive adhesive layer (X1) of the double-sided pressure-sensitive adhesive sheet. After the inspection, for example, a portion of the double-sided pressure-sensitive adhesive sheet to which the multiple processing inspection objects are attached can be locally heated to selectively heat and peel off specific processing inspection objects attached to that portion.

<Second embodiment of semiconductor device manufacturing method>
A second embodiment of the method for manufacturing a semiconductor device includes a manufacturing method (hereinafter also referred to as "manufacturing method A") that uses a double-sided pressure-sensitive adhesive sheet according to one embodiment of the present invention and includes the following steps 1A, 2A, a first separation step, and a second separation step.
Step 1A: a step of attaching an object to be processed to the pressure-sensitive adhesive layer (X2) and attaching a support to the pressure-sensitive adhesive layer (X1); Step 2A: a step of subjecting the object to one or more treatments selected from a grinding treatment and a singulation treatment; First separation step: a step of heating the double-sided pressure-sensitive adhesive sheet to the expansion starting temperature (t) or higher to separate the pressure-sensitive adhesive layer (X1) from the support; Second separation step: a step of irradiating the pressure-sensitive adhesive layer (X2) with energy rays to cure the pressure-sensitive adhesive layer (X2) and separate the pressure-sensitive adhesive layer (X2) from the object to be processed.

Manufacturing method A will be explained below with reference to the drawings. Note that the following explanation will mainly focus on an example in which a semiconductor wafer is used as the workpiece, but the same applies to other workpieces. Examples of other workpieces include those similar to those listed above as workpieces to be processed and inspected.

(Step 1A)
Step 1A is a step of attaching an object to be processed to the pressure-sensitive adhesive layer (X2) of the double-sided pressure-sensitive adhesive sheet, and attaching a support to the pressure-sensitive adhesive layer (X1).
FIG. 3 shows a cross-sectional view illustrating the process of attaching a semiconductor wafer W to the adhesive layer (X2) of the double-sided adhesive sheet 1a and attaching a support 3 to the adhesive layer (X1).
The semiconductor wafer W is attached so that the front surface W1, which is the circuit surface, faces the adhesive layer (X2).
The semiconductor wafer W may be a silicon wafer, or may be a wafer made of gallium arsenide, silicon carbide, sapphire, lithium tantalate, lithium niobate, gallium nitride, indium phosphide, or the like, or a glass wafer.
The thickness of the semiconductor wafer W before grinding is usually 500 to 1000 μm.
The circuit on the surface W1 of the semiconductor wafer W can be formed by a conventional method such as etching or lift-off.

The material of the support 3 may be appropriately selected in consideration of the required properties such as mechanical strength and heat resistance depending on the type of workpiece and the processing content.
Examples of materials for the support 3 include metal materials such as SUS; non-metallic inorganic materials such as glass and silicon wafer; resin materials such as epoxy resin, ABS resin, acrylic resin, engineering plastic, super engineering plastic, polyimide resin, and polyamide-imide resin; and composite materials such as glass epoxy resin. Of these, SUS, glass, and silicon wafer are preferred.
Examples of the engineering plastic include nylon, polycarbonate (PC), and polyethylene terephthalate (PET).
Examples of the super engineering plastics include polyphenylene sulfide (PPS), polyethersulfone (PES), and polyetheretherketone (PEEK).

The support 3 is preferably attached to the entire adhesive surface of the pressure-sensitive adhesive layer (X1). Therefore, the surface area of the support 3 on the side attached to the adhesive surface of the pressure-sensitive adhesive layer (X1) is preferably equal to or larger than the area of the adhesive surface of the pressure-sensitive adhesive layer (X1). In addition, the surface of the support 3 on the side attached to the adhesive surface of the pressure-sensitive adhesive layer (X1) is preferably flat.
The shape of the support 3 is not particularly limited, but is preferably a plate shape.
The thickness of the support 3 may be appropriately selected in consideration of the required properties, but is preferably 20 μm or more and 50 mm or less, and more preferably 60 μm or more and 20 mm or less.

(Step 2A)
Step 2A is a step of subjecting the object to one or more treatments selected from a grinding treatment and a singulation treatment.
Examples of one or more processes selected from grinding processes and dicing processes include grinding processes using a grinder or the like; dicing processes using a blade dicing method, a laser dicing method, or a stealth dicing (registered trademark) method; grinding processes and dicing processes using a blade tip dicing method or a stealth tip dicing method; and the like.
Among these, the dicing process using the stealth dicing method, the grinding process and dicing process using the blade tip dicing method, and the grinding process and dicing process using the stealth tip dicing method are preferred, and the grinding process and dicing process using the blade tip dicing method and the grinding process and dicing process using the stealth tip dicing method are more preferred.

The stealth dicing method forms a modified region inside a semiconductor wafer by irradiating it with laser light, and then separates the semiconductor wafer using the modified region as the starting point for division. The modified region formed in the semiconductor wafer is a portion embrittled by multiphoton absorption, and when the semiconductor wafer is expanded, stress is applied parallel to the wafer surface and in the direction of the wafer expansion, causing cracks to propagate from the modified region toward the front and back surfaces of the semiconductor wafer, resulting in the semiconductor wafer being separated into individual semiconductor chips. In other words, the modified region is formed along the dividing line during division.
The modified region is formed inside the semiconductor wafer by irradiating the semiconductor wafer with laser light focused on the inside of the semiconductor wafer. The incident surface of the laser light may be the front or back surface of the semiconductor wafer. The incident surface of the laser light may also be the surface to which a double-sided adhesive sheet is attached. In this case, the laser light is irradiated onto the semiconductor wafer through the double-sided adhesive sheet.

The blade-tip dicing method is also known as the DBG method (Dicing Before Grinding). This method involves first forming grooves in a semiconductor wafer along the intended dividing lines, shallower than the wafer's thickness, and then thinning and singulating the wafer by back-grinding the wafer until the grinding surface reaches at least the grooves. The grooves reached by the grinding surface become cuts that penetrate the semiconductor wafer, and the semiconductor wafer is divided along these cuts into individual semiconductor chips. The pre-formed grooves are typically provided on the front surface (circuit surface) of the semiconductor wafer and can be formed, for example, by dicing using a conventional wafer dicing device equipped with a dicing blade.

The stealth dicing method is also called the SDBG (Stealth Dicing Before Grinding) method. Like the stealth dicing method, the stealth dicing method is a method of forming a modified region inside a semiconductor wafer by irradiating it with laser light and dividing the semiconductor wafer using the modified region as the starting point for division. However, the stealth dicing method differs from the stealth dicing method in that the semiconductor wafer is thinned by a grinding process while being divided into semiconductor chips. Specifically, a semiconductor wafer having a modified region is thinned by back-grinding, and the pressure applied to the semiconductor wafer during this process causes cracks to extend from the modified region toward the adhesive surface of the semiconductor wafer, thereby dividing the semiconductor wafer into semiconductor chips.
The grinding thickness after forming the modified region may be a thickness that reaches the modified region, but even if it does not reach the modified region strictly, it may be ground to a position close to the modified region and then fractured using the processing pressure of a grinding wheel or the like.

When the semiconductor wafer W is diced into individual pieces by a blade tip dicing method, it is preferable to form grooves in advance on the surface W1 of the semiconductor wafer W to be attached to the adhesive layer (X2) in step 1A.
On the other hand, when the semiconductor wafer W is diced into individual pieces by a stealth first dicing method, the semiconductor wafer W to be attached to the adhesive layer (X2) in step 1A may be irradiated with laser light to form a modified region in advance, or the semiconductor wafer W attached to the adhesive layer (X2) may be irradiated with laser light to form a modified region.

FIG. 4 shows a cross-sectional view illustrating a process of forming a plurality of modified regions 5 using a laser beam irradiation device 4 on a semiconductor wafer W attached to an adhesive layer (X2).
The laser light is irradiated onto the back surface W2 side of the semiconductor wafer W, and a plurality of modified regions 5 are formed inside the semiconductor wafer W at approximately equal intervals.

5A and 5B are cross-sectional views illustrating the process of thinning the semiconductor wafer W and singulating it into a plurality of semiconductor chips CP.
5(a), the back surface W2 of the semiconductor wafer W on which the modified region 5 is formed is ground by a grinder 6, and at that time, the pressure applied to the semiconductor wafer W causes a fracture starting from the modified region 5. As a result, as shown in FIG. 5(b), the semiconductor wafer W is thinned and divided into a plurality of semiconductor chips CP.
The semiconductor wafer W on which the modified region 5 has been formed has its back surface W2 ground, for example, while the support 3 supporting the semiconductor wafer W is fixed on a fixed table such as a chuck table.

The thickness of the semiconductor chip CP after grinding is preferably 5 to 100 μm, more preferably 10 to 45 μm. When the grinding process and the singulation process are performed by the stealth tip dicing method, the thickness of the semiconductor chip CP obtained by grinding can be easily set to 50 μm or less, more preferably 10 to 45 μm.
The size of the semiconductor chip CP after grinding in a plan view is preferably less than 600 mm ² , more preferably less than 400 mm ² , and even more preferably less than 300 mm ² . Note that the plan view refers to a view in the thickness direction.
The shape of the semiconductor chips CP after separation in a plan view may be square or an elongated shape such as a rectangle.
In addition, the double-sided pressure-sensitive adhesive sheet used in the semiconductor device manufacturing method of the second aspect has a thermally expandable particle expansion starting temperature (t) of 50°C or higher, which makes it possible to avoid situations where the thermally expandable particle expands unintentionally due to temperature rises during grinding, etc. Therefore, unintentional separation, misalignment, etc. of the workpiece can be suppressed.

(Step 3A)
It is preferable that the production method A further includes the following step 3A.
Step 3A: a step of attaching a thermosetting film to the surface of the object to be processed that has been subjected to the treatment, opposite to the pressure-sensitive adhesive layer (X2). However, in production method A, step 3A is an optional step, and an embodiment may not include step 3A.
When step 3A is performed, the expansion initiation temperature (t) of the thermally expandable particles contained in the double-sided PSA sheet used in production method A is preferably 50° C. or higher and lower than 125° C. This makes it possible to prevent the thermosetting film from unintentionally curing when the first separation step described below is performed.

Figure 6 shows a cross-sectional view illustrating the process of attaching a thermosetting film 7 having a support sheet 8 to the side opposite the adhesive layer (X2) of multiple semiconductor chips CP obtained by the above-mentioned process.

The thermosetting film 7 is a thermosetting film obtained by forming a film from a resin composition containing at least a thermosetting resin, and is used as an adhesive when mounting a semiconductor chip CP on a substrate. The thermosetting film 7 may contain a curing agent for the thermosetting resin, a thermoplastic resin, an inorganic filler, a curing accelerator, etc., as necessary.
As the thermosetting film 7, for example, a thermosetting film that is generally used as a die bonding film, a die attach film, or the like can be used.
The thickness of the thermosetting film 7 is not particularly limited, but is usually 1 to 200 μm, preferably 3 to 100 μm, and more preferably 5 to 50 μm.
The support sheet 8 may be any material capable of supporting the thermosetting film 7, and examples thereof include the resins, metals, paper materials, etc. listed as examples of the non-thermally expandable base layer (Y2) of the double-sided pressure-sensitive adhesive sheet of one embodiment of the present invention.

The thermosetting film 7 can be attached to the semiconductor chips CP by lamination, for example.
The lamination may be performed with or without heating. When the lamination is performed with heating, the heating temperature is preferably "a temperature lower than the expansion start temperature (t)", more preferably "expansion start temperature (t) - 5°C" or less, even more preferably "expansion start temperature (t) - 10°C" or less, and still more preferably "expansion start temperature (t) - 15°C" or less, from the viewpoint of suppressing the expansion of the thermally expandable particles and suppressing thermal changes in the adherend.

(First separation step)
The first separation step is a step of heating the double-sided pressure-sensitive adhesive sheet to the expansion starting temperature (t) or higher to separate the pressure-sensitive adhesive layer (X1) from the support.
FIG. 7 shows a cross-sectional view illustrating the step of heating the double-sided pressure-sensitive adhesive sheet 1a to separate the pressure-sensitive adhesive layer (X1) from the support 3.

The heating temperature in the first separation step is equal to or higher than the expansion start temperature (t) of the thermally expandable particles, preferably "a temperature higher than the expansion start temperature (t)," more preferably "expansion start temperature (t) + 2°C" or higher, even more preferably "expansion start temperature (t) + 4°C" or higher, and even more preferably "expansion start temperature (t) + 5°C" or higher. From the viewpoints of energy conservation and suppressing thermal changes in the adherend during thermal peeling, the heating temperature in the first separation step is preferably "expansion start temperature (t) + 50°C" or lower, more preferably "expansion start temperature (t) + 40°C" or lower, and even more preferably "expansion start temperature (t) + 20°C" or lower, within a range of less than 125°C.
From the viewpoint of suppressing thermal changes in the adherend, the heating temperature in the first separation step is within a range equal to or higher than the expansion initiation temperature (t), and is preferably less than 125° C., more preferably 120° C. or less, even more preferably 115° C. or less, still more preferably 110° C. or less, and even more preferably 105° C. or less. In particular, if the heating temperature in the first separation step is less than 125° C., unintended curing of the thermosetting film can be suppressed when the above-mentioned step 3A is performed.

(Second separation step)
The second separation step is a step of curing the pressure-sensitive adhesive layer (X2) by irradiating the pressure-sensitive adhesive layer (X2) with energy rays, thereby separating the pressure-sensitive adhesive layer (X2) from the object to be processed.
Here, since the adhesive strength of the pressure-sensitive adhesive layer (X2) is sufficiently reduced by irradiation with energy rays from the heat-expandable layer side, the energy rays can be irradiated onto the pressure-sensitive adhesive layer (X2) in the second separation step from the heat-expandable layer side.
Figure 8 shows a cross-sectional view illustrating the process of curing the adhesive layer (X2) by irradiating energy rays 9 in the thickness direction of the double-sided adhesive sheet 1a from the side of the thermally expandable base layer (Y1), which is a thermally expandable layer, and separating the adhesive layer (X2) from multiple semiconductor chips CP.
The conditions for energy ray irradiation are not particularly limited, and may be appropriately selected so that the formed pressure-sensitive adhesive layer (X2) is cured and its adhesive strength is sufficiently reduced. According to the method for producing a semiconductor device of one embodiment of the present invention, the total light transmittance of the double-sided pressure-sensitive adhesive sheet is high even after thermal expansion, so that the amount of energy ray irradiation required to cure the energy ray-curable pressure-sensitive adhesive layer can be kept low. This makes it possible to suppress deterioration, such as thermal changes, of the adherend.

Through the above steps, a plurality of semiconductor chips CP attached to the thermosetting film 7 are obtained.
Next, it is preferable to divide the thermosetting film 7 to which the plurality of semiconductor chips CP are attached into pieces of the same shape as the semiconductor chips CP to obtain semiconductor chips CP with the thermosetting film 7. As a method for dividing the thermosetting film 7, for example, methods such as laser dicing using a laser beam, expanding, and fusing can be applied.
FIG. 9 shows the semiconductor chip CP with the thermosetting film 7, which has been divided into the same shape as the semiconductor chip CP.

The semiconductor chips CP with thermosetting film 7 are then subjected to various processes, such as an expanding process to increase the spacing between the semiconductor chips CP, a rearrangement process to arrange the increased spacing between the semiconductor chips CP, and an inversion process to invert the semiconductor chips CP, as needed, before being attached (die-attached) to a substrate from the thermosetting film 7 side. The thermosetting film can then be thermally cured to bond the semiconductor chips to the substrate.

The method for manufacturing a semiconductor device according to the second embodiment may be a manufacturing method (hereinafter also referred to as "manufacturing method B") including the following steps 1B to 2B, the following first separation step, and the following second separation step.
Step 1B: a step of attaching an object to be processed to the pressure-sensitive adhesive layer (X1) of a double-sided pressure-sensitive adhesive sheet, and attaching a support to the pressure-sensitive adhesive layer (X2) of the double-sided pressure-sensitive adhesive sheet; Step 2B: a step of subjecting the object to one or more treatments selected from a grinding treatment and a singulation treatment; First separation step: a step of heating the double-sided pressure-sensitive adhesive sheet to a temperature equal to or higher than the expansion starting temperature (t) and lower than 125°C, thereby separating the pressure-sensitive adhesive layer (X1) from the object to be processed; Second separation step: a step of irradiating the pressure-sensitive adhesive layer (X2) with energy rays to cure the pressure-sensitive adhesive layer (X2), thereby separating the pressure-sensitive adhesive layer (X2) from the support.

It is preferable that the production method B further includes the following step 3B.
Step 3B: a step of attaching a thermosetting film to the surface of the object to be processed that has been subjected to the treatment, opposite to the pressure-sensitive adhesive layer (X1). However, in production method B, step 3B is an optional step, and an embodiment may not include step 3B.
When step 3B is performed, the expansion initiation temperature (t) of the thermally expandable particles contained in the double-sided PSA sheet used in production method B is preferably 50° C. or higher and lower than 125° C. This makes it possible to prevent the thermosetting film from unintentionally curing when the first separation step described below is performed.

Steps 1B to 3B are explained by replacing the adhesive layer (X1) in the explanation of steps 1A to 3A with the adhesive layer (X2) and the adhesive layer (X2) with the adhesive layer (X1).

The first separation step is a step of heating the double-sided pressure-sensitive adhesive sheet to the expansion starting temperature (t) or higher to separate the pressure-sensitive adhesive layer (X1) from the object to be processed.
The heating conditions, such as the heating temperature of the double-sided PSA sheet, in the first separation step are the same as those explained in production method A. In particular, when step 3B is performed, the first separation step is preferably a step of heating the double-sided PSA sheet to a temperature equal to or higher than the expansion initiation temperature (t) and lower than 125°C, to separate the PSA layer (X1) from the object to be processed.
The first separation step provides a plurality of semiconductor chips attached to the thermosetting film. Thereafter, the thermosetting film is divided in the same manner as in the manufacturing method A described above, to provide semiconductor chips with the thermosetting film.

The second separation step is a step of curing the pressure-sensitive adhesive layer (X2) by irradiating the pressure-sensitive adhesive layer (X2) with energy rays, and separating the pressure-sensitive adhesive layer (X2) from the support.
Here, since the adhesive strength of the pressure-sensitive adhesive layer (X2) is sufficiently reduced by irradiation with energy rays from the heat-expandable layer side, the energy rays can be irradiated onto the pressure-sensitive adhesive layer (X2) in the second separation step from the heat-expandable layer side.
The conditions for the energy ray irradiation may be appropriately selected so that the pressure-sensitive adhesive layer (X2) is cured and the adhesive strength is reduced.

Note that Figures 3 to 9 show an example using the double-sided adhesive sheet 1a of the first embodiment, but manufacturing method A and manufacturing method B can be explained in the same way when the double-sided adhesive sheet 2a of the second embodiment is used.

<Another embodiment of the method for manufacturing a semiconductor device>
The method for manufacturing a semiconductor device of the present invention is not limited to the method for manufacturing a semiconductor device of the first and second aspects described above, and may be a method for manufacturing a semiconductor device of an aspect other than the first and second aspects.

Another example of a method for manufacturing a semiconductor device of another embodiment is a method in which an object to be processed that is attached to another sheet is separated from the other sheet using a double-sided pressure-sensitive adhesive sheet of one embodiment of the present invention.
For example, multiple semiconductor chips spaced apart on the expanding tape are attached to the adhesive surface of the expanding tape, but picking up these chips one by one is cumbersome. According to one aspect of the method for manufacturing a semiconductor device of the present invention, the adhesive layer (X1) of the double-sided adhesive sheet of one aspect of the present invention is attached to the exposed surfaces of multiple semiconductor chips attached to the expanding tape, and then the expanding tape is peeled off from the multiple semiconductor chips, thereby allowing the multiple semiconductor chips to be separated from the expanding tape all at once. At this time, if a support is attached to the adhesive layer (X2), the adhesive layer (X2) can be cured by irradiating the adhesive layer (X2) from the thermally expandable layer side, thereby making it possible to easily separate the adhesive layer (X2) from the support.
The separated semiconductor chips may be transferred to another double-sided adhesive sheet, or may be subjected to a rearrangement step in which the semiconductor chips are aligned after being separated.

The present invention will be described in more detail with reference to the following examples, but the present invention is not limited to these examples. Note that the physical properties in each production example and example were measured using the following methods.

[Mass average molecular weight (Mw)]
Measurement was carried out using a gel permeation chromatograph (manufactured by Tosoh Corporation, product name "HLC-8020") under the following conditions, and the values measured were converted into standard polystyrene values.
(Measurement conditions)
Column: "TSK guard column HXL-L", "TSK gel G2500HXL", "TSK gel G2000HXL", and "TSK gel G1000HXL" (all manufactured by Tosoh Corporation) connected in series. Column temperature: 40°C
Developing solvent: tetrahydrofuran Flow rate: 1.0 mL/min

[Thickness of each layer]
The thickness was measured at 23° C. using a constant pressure thickness measuring instrument manufactured by Teclock Corporation (model number: PG-02J, standard specifications: compliant with JIS K6783, Z1702, Z1709).

[Average particle size (D ₅₀ ) and 90% particle size (D ₉₀ ) of thermally expandable particles]
The particle size distribution of the thermally expandable particles before expansion at 23° C. was measured using a laser diffraction particle size distribution measuring device (for example, Malvern, product name "Mastersizer 3000").
The particle sizes corresponding to 50% and 90% cumulative volume frequencies calculated from the smaller particle sizes in the particle distribution were defined as the "average particle size ( _D50 ) of the thermally expandable particles" and the "90% particle size ( _D90 ) of the thermally expandable particles," respectively.

[Storage modulus E'(23) of non-thermally expandable substrate layer (Y2) at 23°C]
The storage modulus E' at 23°C of the non-thermally expandable base layer (Y2) cut into a size of 30 mm length x 5 mm width was measured using a dynamic viscoelasticity measuring device (manufactured by TA Instruments, product name "DMAQ800") under the conditions of a test start temperature of 0°C, a test end temperature of 200°C, a heating rate of 3°C/min, a vibration frequency of 1 Hz, and an amplitude of 20 µm. As a result, the storage modulus E'(23) at 23°C of the PET film serving as the non-thermally expandable base layer (Y2) described below was 2.27 x ¹⁰⁹ Pa.

[Method for measuring total light transmittance in the thickness direction at a wavelength of 380 nm]
The transmission spectrum of each measurement sample was measured under the following conditions, and the total light transmittance at a wavelength of 380 nm in the thickness direction was obtained.
<Measurement conditions>
Measurement wavelength range: 200 to 800 nm
Measurement temperature: 23℃
Measurement atmosphere: Air Measurement device: Ultraviolet-visible-near-infrared spectrophotometer (Shimadzu Corporation, product name "UV-3600") equipped with an integrating sphere accessory (Shimadzu Corporation, product name "ISR-3100")

In the following manufacturing examples and working examples, the details of the materials used to form each layer are as follows:

<Adhesive resin>
Acrylic copolymer (A1): A solution containing an acrylic copolymer having a Mw of 600,000 and having structural units derived from raw material monomers consisting of n-butyl acrylate (BA) / methyl methacrylate (MMA) / acrylic acid (AA) / 2-hydroxyethyl acrylate (HEA) = 86/8/1/5 (mass ratio), dilution solvent: ethyl acetate, solid content concentration: 40 mass%
Acrylic copolymer (A2): A solution containing an energy beam-curable acrylic copolymer having a molecular weight of 500,000, obtained by reacting an acrylic copolymer having structural units derived from raw material monomers consisting of n-butyl acrylate (BA) / methyl methacrylate (MMA) / 2-hydroxyethyl acrylate (HEA) = 52/20/28 (mass ratio) with 2-methacryloyloxyethyl isocyanate (MOI) such that the addition rate relative to the total hydroxyl groups in the acrylic copolymer was 90% on a molar basis; dilution solvent: ethyl acetate; solid content concentration: 35% by mass.

<Crosslinking agent>
Isocyanate-based crosslinking agent (i): manufactured by Tosoh Corporation, product name "Coronate HX", isocyanurate-type modified hexamethylene diisocyanate, solid content: 100% by mass
Isocyanate-based crosslinking agent (ii): manufactured by Tosoh Corporation, product name "Coronate L", solution containing trimethylolpropane-modified tolylene diisocyanate, solid content: 75% by mass

<Energy ray curable compound>
Energy ray curable compound (i): manufactured by Nippon Synthetic Chemical Industry Co., Ltd., product name "Shiko UT-4332", multifunctional urethane acrylate

<Photopolymerization initiator>
Photopolymerization initiator (i): bis(2,4,6-trimethylbenzoyl)phenylphosphine oxide Photopolymerization initiator (ii): 1-hydroxycyclohexyl phenyl ketone

<Additives>
・Phthalocyanine pigments

<Thermal Expanding Particles>
- Thermal expandable particles: manufactured by Nouryon, product name "Expancel (registered trademark) 031-40" (DU type), expansion start temperature (t) = 88 ° C., average particle diameter (D ₅₀ ) = 12.6 μm, 90% particle diameter (D ₉₀ ) = 26.2 μm

<Release material>
Heavy-duty release film: manufactured by Lintec Corporation, product name "SP-PET382150", a polyethylene terephthalate (PET) film with a release agent layer formed from a silicone-based release agent on one side, thickness: 38 μm
Light release film: manufactured by Lintec Corporation, product name "SP-PET381031", a PET film with a release agent layer formed from a silicone-based release agent on one side, thickness: 38 μm

Production Example 1: Formation of pressure-sensitive adhesive layer (X1) 0.74 parts by mass (solid content ratio) of an isocyanate-based crosslinking agent (i) was blended with 100 parts by mass of the solid content of the acrylic copolymer (A1), diluted with toluene, and stirred uniformly to prepare a pressure-sensitive adhesive composition (x-1) with a solid content concentration (active ingredient concentration) of 25% by mass.
The prepared pressure-sensitive adhesive composition (x-1) was then applied to the release surface of the heavy release film to form a coating film, and the coating film was dried at 100°C for 60 seconds to form a pressure-sensitive adhesive layer (X1) having a thickness of 5 µm.

Production Example 2: Formation of pressure-sensitive adhesive layer (X2) To 100 parts by mass of the solid content of the acrylic copolymer (A2), 12 parts by mass (solid content ratio) of the energy ray-curable compound (i), 1.1 parts by mass (solid content ratio) of the isocyanate-based crosslinking agent (ii), and 1 part by mass (solid content ratio) of the photopolymerization initiator (i) were blended, diluted with toluene, and stirred uniformly to prepare a pressure-sensitive adhesive composition (x-2) having a solid content concentration (active ingredient concentration) of 30% by mass.
The prepared pressure-sensitive adhesive composition (x-2) was then applied to the release surface of the light release film to form a coating film, and the coating film was dried at 100°C for 60 seconds to form a pressure-sensitive adhesive layer (X2) having a thickness of 20 µm.

Examples 1 to 4, Comparative Examples 1 and 2: Formation of Double-Sided PSA Sheet (1) Preparation of Solventless Resin Composition (y-1a) A linear urethane prepolymer having ethylenically unsaturated groups at both ends, which is an oligomer having a mass average molecular weight (Mw) of 5,000, was obtained by reacting an isocyanate-terminated urethane prepolymer obtained by reacting an ester-type diol with isophorone diisocyanate (IPDI), with 2-hydroxyethyl acrylate.
Then, 40 parts by mass (solid content ratio) of the urethane prepolymer synthesized above was blended with 40 parts by mass (solid content ratio) of isobornyl acrylate (IBXA) and 20 parts by mass (solid content ratio) of phenylhydroxypropyl acrylate (HPPA) as energy ray-polymerizable monomers, and 2.0 parts by mass (solid content ratio) of photopolymerization initiator (ii) and 0.2 part by mass (solid content ratio) of a phthalocyanine pigment and 20 parts by mass of cyclohexyl acrylate (CHA) as additives were further blended relative to the total amount (100 parts by mass) of the urethane prepolymer and energy ray-polymerizable monomers to prepare an energy ray-curable composition.
Then, thermally expandable particles were blended into the energy ray-curable composition so that the content of the thermally expandable particles relative to the total mass (100 mass%) of the resulting thermally expandable base layer (Y1) would be the content shown in Table 1, thereby preparing a solventless resin composition (y-1a) that did not contain a solvent.

(2) Formation of a substrate laminate obtained by laminating a thermally expandable substrate layer (Y1) and a non-thermally expandable substrate layer (Y2) As the non-thermally expandable substrate layer (Y2), a PET film (manufactured by Toyobo Co., Ltd., product name "Cosmoshine A4300", thickness: 50 μm) was prepared. The PET film was used as a measurement sample, and the total light transmittance (T _Y2 ) at a wavelength of 380 nm in the thickness direction measured by the above method was 90.9%.
Next, the solventless resin composition (y-1a) was applied to one surface of the PET film so that the thickness of the thermally expandable substrate layer (Y1) to be formed was the thickness shown in Table 1, to form a coating film.
Then, using an ultraviolet irradiation device (manufactured by iGraphics Co., Ltd., product name "ECS-401GX") and a high-pressure mercury lamp (manufactured by iGraphics Co., Ltd., product name "H04-L41"), ultraviolet rays were irradiated under conditions of an illuminance of 160 mW/ ^cm2 and a light quantity of 500 mJ/ ^cm2 to cure the coating film, thereby obtaining a substrate laminate in which a thermally expandable substrate layer (Y1) having a thickness shown in Table 1 was formed on a PET film as a non-thermally expandable substrate layer (Y2). The illuminance and light quantity during ultraviolet irradiation were values measured using an illuminance/actinometer (manufactured by EIT Co., Ltd., product name "UV Power Puck II").
Furthermore, to measure the total light transmittance (T _R ) at a wavelength of 380 nm when the resin material constituting the thermally expandable substrate layer (Y1) was set to a thickness of 100 μm, a solventless resin composition was prepared that contained only thermally expandable particles and all other materials were the same as the solventless resin composition (y-1a). This solventless resin composition was applied to the release agent layer side of a light release film so that the thickness after curing was 100 μm, and cured by irradiation with ultraviolet light under the same conditions as above. The release agent layer side of a heavy release film was then attached to protect the surface, yielding a resin material laminate. Thereafter, the light release film and heavy release film were removed, yielding a resin material molded into a sheet with a thickness of 100 μm. Using this sheet as a measurement sample, the total light transmittance (T _R ) at a wavelength of 380 nm in the thickness direction measured by the above method was 78.2%.

(3) Formation of double-sided pressure-sensitive adhesive sheet with release liner The adhesive surface of the pressure-sensitive adhesive layer (X1) formed in Production Example 1 was bonded to the surface of the thermally expandable base layer (Y1) of the base laminate formed in (2) above. Next, the adhesive surface of the pressure-sensitive adhesive layer (X2) formed in Production Example 2 was bonded to the surface of the PET film of the base laminate.
As a result, a double-sided PSA sheet with a release liner having the following configuration was produced.
<Heavy Release Film> / <Adhesive Layer (X1), Thickness: 5 μm> / <Thermal Expandable Base Layer (Y1), Thickness: Thickness Listed in Table 1> / <Non-Thermal Expandable Base Layer (Y2), Thickness: 50 μm> / <Adhesive Layer (X2), Thickness: 20 μm> / <Light Release Film>

[Measurement of total light transmittance ( _TA ) and ( _TB )]
The light release film was removed from the pressure-sensitive adhesive layer (X2) of the double-sided pressure-sensitive adhesive sheet with release material obtained above, and a glass plate (soda-lime glass, thickness 1.1 mm) was pressed onto the exposed adhesive surface of the pressure-sensitive adhesive layer (X2) using a vacuum laminator (manufactured by Nikko Materials Co., Ltd., product name "V-130") at 60°C and 0.2 MPa for 30 seconds to be attached, and the heavy release film was removed from the pressure-sensitive adhesive layer (X1) to produce a laminate ( _LB ) for total light transmittance measurement in which the double-sided pressure-sensitive adhesive sheet before thermal expansion and the glass plate were laminated.
Furthermore, a laminate ( _LB ) for measuring total light transmittance prepared in the same manner as above was placed on a hot plate with the glass plate in contact with the hot plate and the double-sided PSA sheet not in contact with the hot plate, and heated for 1 minute at 110°C (i.e., a temperature of 88°C + 22°C, which is the expansion initiation temperature (t) of the heat-expandable particles). This produced a laminate ( _LA ) for measuring total light transmittance, in which the thermally expanded double-sided PSA sheet and the glass plate were laminated together.
The total light transmittance (TA) and (TB) at a wavelength of 380 nm in the thickness direction of the double-sided PSA sheet were measured under the conditions described above using the laminates ( _{LA )} and ( _LB ) for total light transmittance measurement prepared above as measurement samples. The light incident surface was the surface on the PSA layer ( _X1 ) side.

[Measurement of adhesive strength of pressure-sensitive adhesive layer (X2)]
(1) Preparation of adhesive strength measurement sample before energy ray irradiation The light release film was removed from the adhesive layer (X2) of a double-sided adhesive sheet cut to 25 mm × 250 mm, and the adhesive surface of the exposed adhesive layer (X2) was attached to the mirror surface of the adherend, a silicon mirror wafer, by rolling a 2 kg roller back and forth once according to JIS Z0237: 2000, and then left to stand for 20 minutes in an environment of 23 ° C. and 50% RH (relative humidity). Thereafter, the heavy release film was removed from the adhesive layer (X1), and the silicon mirror wafer was placed on the hot plate so that it was in contact with the hot plate and the exposed adhesive layer (X1) was on the side not in contact with the hot plate, and heated at 110 ° C. for 1 minute, and then left to stand for 30 minutes in an environment of 23 ° C. and 50% RH (relative humidity) to obtain an adhesive strength measurement sample before energy ray irradiation.
(2) Preparation of adhesive strength measurement sample after energy ray irradiation An adhesive strength measurement sample prepared by the same method as in (1) above was irradiated with ultraviolet light from the adhesive layer (X1) side toward the thickness direction of the double-sided adhesive sheet (i.e., the adhesive layer (X2) direction) using an ultraviolet irradiation device (manufactured by iGraphics Co., Ltd., product name "ECS-401GX") and a high-pressure mercury lamp (manufactured by iGraphics Co., Ltd., product name "H04-L41") under conditions of an illuminance of 230 mW/cm ² and a light quantity of 90 mJ/cm ² to cure the adhesive layer (X2), and this was used as an adhesive strength measurement sample after energy ray irradiation. Note that the illuminance and light quantity during ultraviolet irradiation are values measured using an illuminance/actinometer (manufactured by EIT Co., Ltd., product name "UV Power Puck II").
(3) Measurement of adhesive strength and calculation of adhesive strength reduction rate The adhesive strength of the adhesive strength measurement sample before energy ray irradiation prepared in (1) above and the adhesive strength measurement sample after energy ray irradiation prepared in (2) above was measured at an environment of 23°C and 50% RH (relative humidity) using a tensile tester (manufactured by A&D Co., Ltd., product name "Tensilon (registered trademark)") by the 180° peel method based on JIS Z0237:2000 at a pulling speed of 300 mm/min.
The adhesive strength reduction rate (%) was calculated using the following formula.
Adhesive strength reduction rate (%) = {(adhesive strength before energy ray irradiation - adhesive strength after energy ray irradiation) / adhesive strength before energy ray irradiation} × 100
The evaluation results are shown in Table 1.

It can be seen from Table 1 that the double-sided PSA sheets of Examples 1 to 4 have a total light transmittance (T _A ) of 20% or more, and therefore the adhesive strength of the PSA layer (X2) in the thermally expanded double-sided PSA sheets is significantly reduced by irradiation with energy rays from the heat-expandable layer side. In contrast, the double-sided PSA sheets of Comparative Examples 1 and 2 have a total light transmittance (T _A ) of less than 20%, and therefore the adhesive strength of the PSA layer (X2) in the thermally expanded double-sided PSA sheets is not sufficiently reduced by irradiation with energy rays.

1a, 2a Double-sided adhesive sheet 1b, 2b Double-sided adhesive sheet with release material 10a, 10b Release material 3 Support 4 Laser light irradiation device 5 Modified region 6 Grinder 7 Thermosetting film 8 Support sheet 9 Energy beam W Semiconductor wafer W1 Circuit surface of semiconductor wafer W2 Back surface of semiconductor wafer CP Semiconductor chip (X1) Pressure-sensitive adhesive layer (X1)
(X2) Adhesive layer (X2)
(Y) Base material layer (Y)
(Y1) Thermally expandable base layer (Y1)
(Y2) Non-thermally expandable base layer (Y2)

Claims (15)

A double-sided PSA sheet having a PSA layer (X1), a base layer (Y), and a PSA layer (X2) in this order,
at least one of the pressure-sensitive adhesive layer (X1) and the base layer (Y) is a heat-expandable layer containing heat-expandable particles,
the pressure-sensitive adhesive layer (X2) is an energy ray-curable pressure-sensitive adhesive layer,
a laminate (LA) for total light transmittance measurement obtained by laminating a 1.1 mm thick glass plate made of soda lime glass on the pressure-sensitive adhesive layer ( _X2 ) of the double-sided pressure-sensitive adhesive sheet and heating the laminate for 1 minute at a temperature of the expansion starting temperature (t) of the heat-expandable particles + 22°C has a total light transmittance ( _TA ) in the thickness direction at a wavelength of 380 nm of 20% or more ;
A double-sided pressure-sensitive adhesive sheet, wherein the content of the heat-expandable particles in the heat-expandable layer is 1 to 25 mass % relative to the total mass (100 mass %) of the heat-expandable layer . A double-sided PSA sheet having a PSA layer (X1), a base layer (Y), and a PSA layer (X2) in this order,
at least one of the pressure-sensitive adhesive layer (X1) and the base layer (Y) is a heat-expandable layer containing heat-expandable particles,
the pressure-sensitive adhesive layer (X2) is an energy ray-curable pressure-sensitive adhesive layer,
A laminate obtained by laminating a 1.1 mm thick glass plate made of soda lime glass on the pressure-sensitive adhesive layer (X2) of the double-sided pressure-sensitive adhesive sheet was heated for 1 minute at a temperature of the expansion starting temperature (t) of the heat-expanding particles + 22°C to obtain a laminate (L) for measuring total light transmittance. _A ) the total light transmittance (T _A ) is 20% or more,
The double-sided pressure-sensitive adhesive sheet, wherein the expansion initiation temperature (t) of the thermally expandable particles is 50°C or higher and lower than 125°C. A double-sided PSA sheet having a PSA layer (X1), a base layer (Y), and a PSA layer (X2) in this order,
at least one of the pressure-sensitive adhesive layer (X1) and the base layer (Y) is a heat-expandable layer containing heat-expandable particles,
the pressure-sensitive adhesive layer (X2) is an energy ray-curable pressure-sensitive adhesive layer,
A laminate obtained by laminating a 1.1 mm thick glass plate made of soda lime glass on the pressure-sensitive adhesive layer (X2) of the double-sided pressure-sensitive adhesive sheet was heated for 1 minute at a temperature of the expansion starting temperature (t) of the heat-expanding particles + 22°C to obtain a laminate (L) for measuring total light transmittance. _A ) the total light transmittance (T _A ) is 20% or more,
the base layer (Y) is a base laminate in which a heat-expandable base layer (Y1) containing heat-expandable particles and a non-heat-expandable base layer (Y2) are laminated together, and the double-sided PSA sheet has the pressure-sensitive adhesive layer (X1), the heat-expandable base layer (Y1), the non-heat-expandable base layer (Y2), and the pressure-sensitive adhesive layer (X2) in this order. The double-sided pressure-sensitive adhesive sheet according to any one of claims 1 to 3 , wherein the thickness of the heat-expandable layer before thermal expansion is 10 to 200 µm. The double-sided pressure-sensitive adhesive sheet according to any one of claims 1 to 4, wherein the overall thickness of the double-sided pressure-sensitive adhesive sheet before thermal expansion is 90 to 300 μm. The double-sided pressure-sensitive adhesive sheet according to any one of claims 1 to 5, wherein a laminate (L _B ) for total light transmittance measurement, which is obtained by laminating a 1.1 mm thick glass plate made of soda lime glass on the pressure-sensitive adhesive layer (X2) of the double-sided pressure-sensitive adhesive sheet before thermal expansion, has a total light transmittance (T _B ) in the thickness direction at a wavelength of 380 nm of 50% or more. The double-sided pressure-sensitive adhesive sheet according to any one of claims 1 to 6, wherein the energy ray-curable pressure-sensitive adhesive layer is a pressure-sensitive adhesive layer that hardens and loses adhesive strength upon exposure to ultraviolet light. the thermally expandable base layer (Y1) comprises a resin material containing the thermally expandable particles,
The double-sided pressure-sensitive adhesive sheet according to claim 3 , wherein the resin material has a total light transmittance ( _TR ) of 60% or more at a wavelength of 380 nm when the resin material has a thickness of 100 μm. 9. The double-sided pressure-sensitive adhesive sheet according to claim 3 or 8, wherein the total thickness of the pressure-sensitive adhesive layer (X1), the heat-expandable base layer (Y1), the non-heat-expandable base layer ( Y2 ), and the pressure-sensitive adhesive layer ( X2 ) is 90 to 300 μm. A method for manufacturing a semiconductor device using the double-sided pressure-sensitive adhesive sheet according to any one of claims 1 to 9 , comprising the following steps 1A, 2A, a first separation step, and a second separation step:
Step 1A: a step of attaching an object to be processed to the pressure-sensitive adhesive layer (X2) of the double-sided pressure-sensitive adhesive sheet, and attaching a support to the pressure-sensitive adhesive layer (X1) of the double-sided pressure-sensitive adhesive sheet; Step 2A: a step of subjecting the object to one or more treatments selected from a grinding treatment and a singulation treatment; First separation step: a step of heating the double-sided pressure-sensitive adhesive sheet to the expansion starting temperature (t) or higher to separate the pressure-sensitive adhesive layer (X1) from the support; Second separation step: a step of irradiating the pressure-sensitive adhesive layer (X2) with energy rays to cure the pressure-sensitive adhesive layer (X2), and separating the pressure-sensitive adhesive layer (X2) from the object to be processed. The expansion starting temperature (t) of the thermally expandable particles is 50°C or higher and lower than 125°C,
After the step 2A, a step 3A is included in which a thermosetting film having thermosetting properties is attached to a surface of the object to be processed that has been subjected to the treatment, the surface being opposite to the pressure-sensitive adhesive layer (X2),
the first separation step is a step of heating the double-sided PSA sheet to an expansion initiation temperature (t) or higher and lower than 125°C to separate the PSA layer (X1) from the support;
The method for manufacturing a semiconductor device according to claim 10 . A method for manufacturing a semiconductor device using the double-sided pressure-sensitive adhesive sheet according to any one of claims 1 to 9 , comprising the following steps 1B, 2B, a first separation step, and a second separation step:
Step 1B: a step of attaching an object to be processed to the pressure-sensitive adhesive layer (X1) of the double-sided pressure-sensitive adhesive sheet, and attaching a support to the pressure-sensitive adhesive layer (X2) of the double-sided pressure-sensitive adhesive sheet; Step 2B: a step of subjecting the object to one or more treatments selected from a grinding treatment and a singulation treatment; First separation step: a step of heating the double-sided pressure-sensitive adhesive sheet to the expansion starting temperature (t) or higher, thereby separating the pressure-sensitive adhesive layer (X1) from the object to be processed; Second separation step: a step of irradiating the pressure-sensitive adhesive layer (X2) with energy rays to cure the pressure-sensitive adhesive layer (X2), thereby separating the pressure-sensitive adhesive layer (X2) from the support. The expansion starting temperature (t) of the thermally expandable particles is 50°C or higher and lower than 125°C,
After the step 2B, a step 3B is included in which a thermosetting film having thermosetting properties is attached to a surface of the object to be processed that has been subjected to the treatment, the surface being opposite to the pressure-sensitive adhesive layer (X1),
the first separation step is a step of heating the double-sided PSA sheet to an expansion initiation temperature (t) or higher and lower than 125°C to separate the PSA layer (X1) from the object to be processed;
The method for manufacturing a semiconductor device according to claim 12 . A double-sided pressure-sensitive adhesive sheet with a release material, comprising the double-sided pressure-sensitive adhesive sheet according to any one of claims 1 to 9 , having a release material on one or both surfaces thereof. A method for manufacturing a semiconductor device using a double-sided pressure-sensitive adhesive sheet having a pressure-sensitive adhesive layer (X1), a base layer (Y), and a pressure-sensitive adhesive layer (X2) in this order, the method comprising the following steps 1B, 2B, a first separation step, and a second separation step:
at least one of the pressure-sensitive adhesive layer (X1) and the base layer (Y) is a heat-expandable layer containing heat-expandable particles,
the pressure-sensitive adhesive layer (X2) is an energy ray-curable pressure-sensitive adhesive layer,
A laminate obtained by laminating a 1.1 mm thick glass plate made of soda lime glass on the pressure-sensitive adhesive layer (X2) of the double-sided pressure-sensitive adhesive sheet was heated for 1 minute at a temperature of the expansion starting temperature (t) of the heat-expanding particles + 22°C to obtain a laminate (L) for measuring total light transmittance. _A ) the total light transmittance (T _A ) is 20% or more.
Step 1B: A step of attaching an object to be processed to the pressure-sensitive adhesive layer (X1) of the double-sided pressure-sensitive adhesive sheet and attaching a support to the pressure-sensitive adhesive layer (X2) of the double-sided pressure-sensitive adhesive sheet
Step 2B: A step of subjecting the object to one or more treatments selected from a grinding treatment and a singulation treatment.
First separation step: a step of heating the double-sided pressure-sensitive adhesive sheet to the expansion starting temperature (t) or higher to separate the pressure-sensitive adhesive layer (X1) from the object to be processed.
Second separation step: a step of curing the pressure-sensitive adhesive layer (X2) by irradiating the pressure-sensitive adhesive layer (X2) with energy rays, and separating the pressure-sensitive adhesive layer (X2) from the support.