TW201542753A - Adhesive thin sheet - Google Patents

Abstract

The present invention provides an adhesive thin sheet, which is the adhesive thin sheet having a rigid substrate with Young's modulus of 1000 MPa, a buffer layer disposed on one side of the rigid substrate, and an adhesive layer disposed on the other side of the rigid substrate. It is characterized in that the aforementioned buffer layer is the layer formed with the buffer layer composition containing energy ray polymerizable compound, and a triangular pyramid-shaped indenter with tip radius of curvature of 100 nm and an edges-included angle of 115 DEG is used to squeeze into the buffer layer at the tip velocity of indenter of 10 [mu]m/min. When the compressive load reaches 2 mN, the squeezed depth (X) must be larger than 2.5[mu]m. The adhesive thin sheet has excellent foreign object absorbing property, and can prevent the semiconductor wafer from facture when it is used as the background thin sheet for the grinding processing of semiconductor wafer.

Description

Adhesive sheet

The present invention relates to adhesive sheets, and more particularly, for example, It is an adhesive sheet which can prevent a crack of a semiconductor wafer when it is used as a back-grinding sheet of the grinding process of a semiconductor wafer.

In the rapid development of the miniaturization, the miniaturization, and the multi-functionalization of the information terminal device, the semiconductor wafers are mounted in the same manner, and the thickness and density are being sought. Conventionally, it has been necessary to produce a semiconductor wafer having a thickness of about 350 μm, which is as thin as 50 to 100 μm or less. In order to meet the demand for thinning of such a semiconductor wafer, the inner surface of the semiconductor wafer is being ground to be thinned.

In recent years, bumps (electrodes) made of solder or the like having a height of about 30 μm to 100 μm are formed on the surface, and the inner surface of the semiconductor wafer having the uneven portions is ground. When the inner surface of the semiconductor wafer with such a bump is ground, in order to protect the surface of the bump portion, a dedicated adhesive sheet (back-polished sheet (BG sheet)) is attached to the surface on which the bump portion is formed.

For example, Patent Document 1 discloses that a groove having a specific depth is formed from the surface side of the wafer, and then the cutting is performed from the inner surface side of the wafer. In the cutting method, in order to protect the adhesive sheet used on the surface side of the wafer. The adhesive sheet disclosed in Patent Document 1 has a structure in which a vibration relaxation layer is provided on a surface on one side of a rigid base material, and an adhesive layer is provided on the other surface.

In the adhesive sheet disclosed in Patent Document 1, since the thickness of the rigid substrate and the Young's modulus, and the thickness of the vibration relaxation layer and the maximum value of the dynamic viscility tan δ are adjusted to a specific range, the first cutting method is used as the BG. When the sheet is used, a semiconductor wafer which is extremely thin and free from cracks or discoloration can be produced.

[Previous Technical Literature] [Patent Literature]

[Patent Document 1] Japanese Patent Laid-Open Publication No. 2005-343997

However, in the cutting process of the inner surface of the semiconductor wafer, when the BG sheet of the semiconductor wafer to which the BG sheet is attached is placed on the chuck holder of the wafer inner surface cutting machine, it is attached to the chuck holder. For the foreign matter, there is a case where the semiconductor wafer is broken due to the cutting process of the semiconductor wafer.

In other words, when a BG sheet of a semiconductor wafer with a BG sheet is provided on the chuck holder to which the foreign matter is attached, the BG sheet is only the thickness of the foreign matter, and swells on the opposite side of the foreign matter to form a convex portion on the inner surface of the semiconductor wafer. . In this state, when the inner surface of the semiconductor wafer is cut, the vicinity of the convex portion formed on the inner surface of the semiconductor wafer is thinner than the other portions, and cracking is likely to occur.

Further, in Patent Document 1, there has been no research on wafer cracking due to foreign matter on such a chuck holder.

Therefore, in the adhesive sheet for the cutting process of such a semiconductor wafer, it is sought to suppress the foreign matter adsorption property of the degree of swelling on the side opposite to the foreign matter even if the adhesive sheet is provided on the seat to which the foreign matter is attached.

The present invention provides an adhesive sheet having excellent foreign matter adsorption properties, for example, when used as a BG sheet for grinding a semiconductor wafer, an adhesive sheet which can prevent cracking of a semiconductor wafer.

The present inventors have found that a rigid substrate having a Young's modulus of a specific value or more has a buffer layer on one surface side and an adhesive layer on the other surface side, and the buffer layer presses a specific shape of the indenter into the buffer layer. The adhesive sheet having a compression depth of 2 mN and having a specific depth of more than a specific value can solve the above problems, and the present invention has been completed.

That is, the present invention provides the following [1] to [9].

[1] An adhesive sheet comprising a rigid substrate having a Young's modulus of 1000 MPa or more, a buffer layer provided on one side of the rigid substrate, and an adhesive provided on the other side of the rigid substrate The adhesive sheet of the layer is characterized in that the buffer layer is a layer formed of a buffer layer forming composition containing an energy ray polymerizable compound, and a triangular hammer shape indenter having a tip end radius of curvature of 100 nm and an interangle angle of 115°. The apex of the apex at a speed of 10 μm/min, and the compression depth (X) necessary for the compression load to reach 2 mN when being squeezed into the buffer layer is 2.5 μm or more.

[2] The adhesive sheet according to the above [1], wherein the buffer layer-forming composition contains the urethane (meth) acrylate (a1) and has a ring-forming atom as the energy ray-polymerizable compound. A polymerizable compound (a2) having 6 to 20 alicyclic groups or a heterocyclic group, and a polymerizable compound (a3) having a functional group.

[3] The adhesive sheet according to the above [2], wherein the content ratio (a2)/(a3) of the component (a2) to the component (a3) in the buffer layer-forming composition is 0.5 to 3.0.

[4] The adhesive sheet according to the above [2] or [3] wherein the component (a2) is an alicyclic group-containing (meth) acrylate.

[5] The adhesive sheet according to any one of the above [2] to [4] wherein the component (a3) is a hydroxyl group-containing (meth) acrylate.

[6] The adhesive sheet according to any one of the above [1], wherein the buffer layer has a thickness of 5 to 100 μm.

[7] The adhesive sheet according to any one of the above [1] to [6] wherein a maximum value of tan δ of dynamic viscoelasticity at -5 to 120 ° C of the buffer layer is 0.5 or more.

[8] The adhesive sheet according to any one of the above [1], wherein at least one of the rigid substrate and the buffer layer and the rigid substrate and the adhesive layer are at least one of Has an easy layer.

[9] The adhesive sheet according to any one of the above [1] to [8], which is used for cutting a semiconductor wafer, and is used as a backside polishing sheet for protecting a surface side of the semiconductor wafer.

The adhesive sheet of the present invention is excellent in foreign matter adsorption property. Therefore, when the adhesive sheet of the present invention is used as, for example, a BG sheet for grinding a semiconductor wafer, cracking of the semiconductor wafer can be prevented.

1a, 1b, 1c, 1d‧‧‧ adhesive sheets

11‧‧‧Rigid substrate

12‧‧‧ Buffer layer

13‧‧‧Adhesive layer

14a, 14b‧‧‧ peeling sheets

15a, 15b‧‧‧Easy layer

Fig. 1 is a cross-sectional view showing an adhesive sheet of an example of an adhesive sheet of the present invention.

In the description of the present specification, the "energy line" means, for example, an ultraviolet ray or an electron beam, and is preferably an ultraviolet ray or an electron beam.

In the description of the present specification, the "mass average molecular weight (Mw)" means a value in terms of standard polystyrene measured by a gel permeation chromatography (GPC) method, and specifically, the method according to the examples. The value of the measurement.

In addition, in the description of this specification, for example, "(meth) acrylate" means the words "acrylic ester" and "methacrylate", and other similar terms are the same.

[Composition of adhesive sheets]

The adhesive sheet of the present invention is not particularly limited as long as it has a rigid base material, a cushion layer provided on one surface side of the rigid base material, and an adhesive layer provided on the other surface side of the rigid base material.

BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 is a cross-sectional view showing an adhesive sheet of an example of an adhesive sheet of the present invention.

As an example of the adhesive sheet structure of the present invention, as shown in Fig. 1(a), the buffer layer 12 is provided on the surface side of the rigid substrate 11 side, and the surface side of the other side of the rigid substrate 11 is adhered. The adhesive layer 13 has an adhesive sheet 1a.

Moreover, the adhesive sheet of the present invention is adhered as shown in Fig. 1(a). The sheet 1a can be used as at least one of the buffer layer 12 and the adhesive layer 13, and further has an adhesive sheet of the release sheet.

The adhesive sheet 1b shown in Fig. 1(b) has a configuration in which the release sheets 14a and 14b are provided on the surfaces on both sides of the cushion layer 12 and the adhesive layer 13, but the adhesive sheet of the present invention may be a buffer layer only. 12 and one side of the adhesive layer 13 are provided with a peeling sheet.

Further, the adhesive sheet of the present invention is shown in Figs. 1 (a) and (b). The adhesive sheets 1a and 1b can be used as an adhesive sheet which is easy to adhere to the layer between the rigid substrate 11 and the buffer layer 12 and between the rigid substrate 11 and the adhesive layer 13.

The adhesive sheets 1c, 1d shown in Figs. 1 (c) and (d) are formed with respect to the adhesive sheets 1a, 1b, and further between the rigid substrate 11 and the buffer layer 12, and the rigid substrate 11 and the adhesive layer. Between 13 has a configuration in which the easy-to-adhere layers 15a and 15b are separately provided. Further, the adhesive sheet of the present invention may have a configuration in which only the side of the easy-adhesion layers 15a, 15b is provided.

Further, the adhesive sheet 1d shown in Fig. 1(d) has the release sheets 14a, 14b provided on the surfaces of both the buffer layer 12 and the adhesive layer 13, respectively. Although the adhesive sheet of the present invention may be provided only on one side of the buffer layer 12 and the adhesive layer 13, a release sheet may be provided.

Hereinafter, each layer constituting the adhesive sheet of the present invention will be described in detail.

<rigid substrate>

The rigid substrate of the adhesive sheet of the present invention is a rigid substrate having a Young's modulus of 1000 MPa or more. When a substrate having a Young's modulus of less than 1000 MPa is used, when the obtained adhesive sheet is attached to a semiconductor wafer, since the elongation of the substrate is large, stress is easily generated because the semiconductor to which the adhesive sheet is attached is easily generated. The warpage of the wafer is not good.

Further, in the adhesive sheet of the present invention, even when a semiconductor substrate having a Young's modulus of 1000 MPa or more is used, when the semiconductor wafer is attached, since the elongation of the substrate is small, warpage can be suppressed. For example, even if the surface of the semiconductor wafer is on the surface of the semiconductor wafer, warpage of the organic film is likely to occur, and since the entire adhesive sheet has rigidity, warping of the semiconductor wafer can be suppressed.

Young's mode as a rigid substrate used in the present invention When the obtained adhesive sheet is attached to a semiconductor wafer, the viewpoint of suppressing the warpage of the semiconductor wafer and the workability (mechanical suitability) when attaching the adhesive sheet to the semiconductor wafer are improved. It is preferably 1000 to 30000 MPa, more preferably 1300 to 20000 MPa, still more preferably 1600 to 15000 MPa, and even more preferably 1800 to 10000 MPa.

Further, the Young's modulus of the rigid substrate of the present invention means a value measured by the method described in the examples.

The thickness of the rigid substrate is the Young's modulus of the rigid substrate. The range is not particularly limited, but the workability (mechanical suitability) when the adhesive sheet of the present invention is attached to a semiconductor wafer is improved, and when the adhesive sheet is peeled off from the semiconductor wafer (wafer), From the viewpoint of stress, it is preferably from 10 to 1000 μm, more preferably from 20 to 400 μm, still more preferably from 25 to 150 μm, still more preferably from 30 to 120 μm.

As a rigid substrate used in the present invention, if Young's modulus The above range is not particularly limited, but a resin film is preferred from the viewpoint of water resistance and heat resistance.

Examples of the resin constituting the resin film include polyesters such as polyethylene terephthalate, polyethylene naphthalate, polybutylene terephthalate, and wholly aromatic polyester, and polyamine. , polyimine, polyacetal, polycarbonate, modified polyphenylene ether, polysulfurized benzene, polyfluorene, polyether ketone, biaxially drawn polypropylene and the like.

Among these resins, one or more selected from the group consisting of polyester, polyamine, polyimide, and biaxially drawn polypropylene, more preferably polyester, more preferably polyterephthalic acid. Ethylene glycol ester.

Further, the rigid substrate used in the present invention may be a single-layer film selected from a resin film composed of one or two or more kinds of resins described above, or a resin film in which two or more types are laminated. Laminated film.

Moreover, the rigid substrate used in the present invention does not damage the present In the range of the effects of the invention, a filler, a colorant, an antistatic agent, an antioxidant, an organic lubricant, a catalyst, or the like may be contained.

Moreover, the substrate may be transparent, may be opaque, and may be desired as desired. Coloring or evaporation.

Further, in the surface of at least one of the rigid substrates used in the present invention, in order to improve the adhesion to the buffer layer and/or the adhesive layer, a subsequent treatment such as corona treatment may be performed, or a later-described process may be provided. Easy to layer.

<buffer layer>

The buffer layer of the adhesive sheet of the present invention is a layer formed of a buffer layer forming composition containing an energy ray polymerizable compound, and has a triangular hammer shape indenter having a tip end radius of curvature of 100 nm and an interangle angle of 115°. The apex is adjusted to a layer of 2.5 μm or more at a speed of 10 μm/min, and the compression depth (X) (hereinafter referred to as "crowding depth (X)") required for the compression load to reach 2 mN when the buffer layer is squeezed into the buffer layer is adjusted to a layer of 2.5 μm or more. .

The buffer layer is a layer formed of a buffer layer-forming composition containing an energy ray-polymerizable compound, and it is relatively easy to adjust the viscoelasticity by selecting the composition of the buffer layer-forming composition. Therefore, for example, when the adhesive sheet is used as a BG sheet, vibration due to grinding of the semiconductor wafer cannot be alleviated, and occurrence of cracks or cracks in the semiconductor wafer or floating of the back surface of the adhesive sheet from the vacuum holder can be suppressed.

Moreover, the present inventors have found that in the configuration of the adhesive sheet, the foreign matter adsorption property is improved by providing a buffer layer having the above-described extrusion depth (X) adjusted to 2.5 μm or more, for example, the adhesive sheet of the present invention is used as a semiconductor crystal. When the rounded BG sheet is used, it is possible to effectively prevent cracking of the semiconductor wafer.

In addition, the viscosity of the buffer layer having the extrusion depth (X) of less than 2.5 μm When the sheet is used, the foreign matter adsorption property cannot be sufficiently improved, and when the adhesive sheet is used as a BG sheet for grinding a semiconductor wafer, the semiconductor wafer tends to be broken.

The above-mentioned penetration depth (X), the adhesive sheet obtained from the lifting The viewpoint of the foreign matter adsorption property is preferably 2.5 to 20.0 μm, more preferably 2.8 to 15.0 μm, still more preferably 3.0 to 10.0 μm, still more preferably 3.2 to 7.0 μm.

Further, in the present invention, the depth of penetration (X) means a value measured by the method described in the examples.

In addition, the extrusion depth (X) can be adjusted within the above range by appropriately changing the type or content of the component contained in the buffer layer forming composition for forming the buffer layer, the degree of curing of the buffer layer, and the like.

The most dynamic tantropic δ of the buffer layer at -5 to 120 °C The large value (hereinafter also referred to simply as "the maximum value of tan δ") is preferably 0.5 or more, more preferably 0.8 or more, still more preferably 1.0 or more, and still more preferably 1.2 or more.

When the maximum value of tan δ of the buffer layer is 0.5 or more, in the first dicing method, the obtained adhesive sheet is attached to the wafer group, and when the inner surface of the wafer group is subjected to grinding, the buffer layer absorbs vibration of the abrasive grains or The effect of the punching is higher, and even if the wafer group is ground to 100 μm or less, the corner crack and the grinding surface discoloration can be suppressed.

Further, tan δ is called loss tangent, and is defined as "loss elastic modulus / storage elastic modulus", which is a dynamic viscoelasticity measuring device, which responds to stress such as tensile stress or torsional stress with respect to the object to be applied. Determination The value, specifically, means the value measured by the method described in the examples.

Moreover, the maximum value of tan δ of this buffer layer does not depend on the above-described penetration depth (X).

The adhesive layer of the adhesive sheet of the present invention is provided by a package A layer formed of a buffer layer forming composition containing an energy ray polymerizable compound.

The energy ray-polymerizable compound to be contained in the buffer layer-forming composition is not particularly limited as long as it can form a buffer layer having a depth of penetration (X) within the above range, and for example, photocurability can be used. Resin or monomer.

However, from the viewpoint of adjusting the extrusion depth (X) to the above range, the energy ray polymerizable compound preferably contains ethyl urethane (meth) acrylate (a1) and has a ring formation. A composition for forming a buffer layer of a polymerizable compound (a2) having an alicyclic group or a heterocyclic group having 6 to 20 atoms and a polymerizable compound (a3) having a functional group.

Moreover, it is preferable that the composition for forming a buffer layer contains a photopolymerization initiator, and may contain other additives or resin components in the range which does not impair the effect of this invention.

Hereinafter, each component contained in the buffer layer-forming composition will be described.

(Aminoethyl methacrylate (meth) acrylate (a1))

Amino methacrylate (meth) acrylate used as the present invention (a1) is a compound having at least a (meth) acrylonitrile group and an urethane bond, and has a property of performing polymerization hardening by energy ray irradiation.

The ethyl urethane (meth) acrylate (a1) may be any of an oligomer, a high molecular weight body, or a mixture thereof, but is preferably an ethyl urethane (meth) acrylate oligo. Polymer.

The mass average molecular weight (Mw) of the component (a1) is preferably 1,000. ~100,000, more preferably 2,000 to 60,000, and even more preferably 3,000 to 20,000.

Further, the number of (meth)acrylonitrile groups (hereinafter also referred to as "functional group number") in the component (a1) may be monofunctional, bifunctional or trifunctional or higher, but is preferably monofunctional or 2. Functional.

The component (a1) can be, for example, a polyol compound, and a polyvalent The terminal isocyanate urethane prepolymer obtained by the reaction of a cyanate compound is obtained by reacting a hydroxyl group-containing (meth) acrylate.

In addition, the component (a1) can be used individually or in combination of 2 or more types.

The polyol compound which is a raw material of the component (a1) is not particularly limited as long as it is a compound having two or more hydroxyl groups.

Specific examples of the polyhydric alcohol compound include an alkylene glycol, a polyether polyol, a polyester polyol, and a polycarbonate polyol.

Among these, a polyester polyol is preferred.

Further, the polyol compound may be any of a bifunctional diol, a trifunctional triol, and a tetrafunctional or higher polyhydric alcohol, but is preferably a bifunctional diol, more preferably a polyester bis. alcohol.

As the polyvalent isocyanate compound, for example, four Asians can be cited. An aliphatic polyisocyanate such as methyl diisocyanate, hexamethylene diisocyanate or trimethyl hexamethylene diisocyanate; isophorone diisocyanate, norbornane diisocyanate, dicyclohexylmethane-4, 4'-diisocyanate, dicyclohexylmethane-2,4'-diisocyanate, ω,ω'-diisocyanate dimethylcyclohexane or the like, alicyclic diisocyanate; 4,4'-diphenyl Aromatic compounds such as methane diisocyanate, methylphenyl diisocyanate, benzodimethyl diisocyanate, tolidine diisocyanate, tetramethylene dimethyl diisocyanate, naphthalene-1,5-diisocyanate It is a diisocyanate or the like.

Among these, isophorone diisocyanate, hexamethylene diisocyanate, and benzodimethyl diisocyanate are preferable.

For the above polyol compound, and polyvalent isocyanate The terminal isocyanate urethane prepolymer obtained by the reaction of the compound is subjected to a reaction of a hydroxyl group-containing (meth) acrylate to obtain an ethyl urethane (meth) acrylate (a1).

The (meth) acrylate having a hydroxyl group is not particularly limited as long as it has a hydroxyl group and a (meth)acryl fluorenyl group in at least one molecule.

As a (meth) acrylate having a specific hydroxyl group, for example, Listed 2-hydroxyethyl (meth) acrylate, 2-hydroxypropyl (meth) acrylate, 4-hydroxybutyl (meth) acrylate, 4-hydroxycyclohexyl (meth) acrylate, 5 -Hydroxycyclooctyl (meth) acrylate, 2-hydroxy-3-phenyloxypropyl (meth) acrylate, pentaerythritol tri (meth) acrylate, polyethylene glycol mono (meth) acrylate a hydroxyalkyl (meth) acrylate such as polypropylene glycol mono(meth)acrylate; or a hydroxyl group such as N-hydroxymethyl (meth) acrylamide (Meth) acrylamide; a reaction product obtained by reacting vinyl glycerol, bisphenol glycidyl bisphenol A with (meth)acrylic acid, and the like.

Among these, a hydroxyalkyl (meth) acrylate is preferred, and 2-hydroxyethyl (meth) acrylate is more preferred.

As a terminal isocyanate urethane prepolymer and The reaction conditions of the hydroxyl group-containing (meth) acrylate are preferably carried out at 60 to 100 ° C for 1 to 4 hours in the presence of a solvent or a catalyst to be added, if necessary.

The content of the component (a1) in the composition for forming a buffer layer, The total amount (100% by mass) of the composition for forming a buffer layer is preferably from 10 to 70% by mass, more preferably from 20 to 60, from the viewpoint of forming a buffer layer having a depth of penetration (X) in the above range. The mass %, more preferably 25 to 55 mass%, and even more preferably 30 to 50 mass%.

(Polymerizable compound (a2) having an alicyclic group or a heterocyclic group having 6 to 20 ring atoms)

The component (a2) used in the present invention is preferably a polymerizable compound having an alicyclic group or a heterocyclic group having 6 to 20 ring atoms, and a compound having at least one (meth)acryl fluorenyl group. By using this component (a2), the film-forming property of the obtained buffer layer-forming composition can be improved.

The ring of the alicyclic group or the heterocyclic group which the component (a2) has is formed to have an atomic number, preferably 6 to 20, more preferably 6 to 18, still more preferably 6 to 16, and still more preferably 7 ~12.

Examples of the atom forming the ring structure of the heterocyclic group include a carbon source. A nitrogen atom, an oxygen atom, a sulfur atom or the like.

Further, in the present invention, the ring-forming atomic number is a number of atoms constituting the ring itself of a compound in which a bond is bonded to a ring, and does not constitute an atom of a ring (for example, a hydrogen atom bonded to an atom constituting the ring). Or the atom contained in the substituent when the ring is substituted by a substituent is not included in the number of ring forming atoms.

As a specific component (a2), an isodecyl group (A Acrylate, dicyclopentenyl (meth) acrylate, dicyclopentyl (meth) acrylate, dicyclopentenyloxy (meth) acrylate, cyclohexyl (meth) acrylate, (A) alicyclic group-containing (meth) acrylate such as adamantane (meth) acrylate; heterocyclic group such as tetrahydroindenyl (meth) acrylate or morpholine (meth) acrylate (methyl group) ) acrylate; and so on.

In addition, the component (a2) can be used individually or in combination of 2 or more types.

Among these, a (meth) acrylate containing an alicyclic group is preferred, and an isodecyl (meth) acrylate is more preferred.

The content of the component (a2) in the composition for forming a buffer layer, The total amount (100% by mass) of the composition for forming a buffer layer is obtained from the viewpoint of forming a buffer layer having a depth of penetration (X) in the above range and a film forming property of the buffer layer-forming composition obtained. Preferably, it is 10 to 70% by mass, more preferably 20 to 60% by mass, still more preferably 25 to 55% by mass, and still more preferably 30 to 50% by mass.

(Polymerizable compound (a3) having a functional group)

The component (a3) used in the present invention contains a hydroxyl group, an epoxy group, and a decylamine. The polymerizable compound having a functional group such as a group or an amine group is preferably a compound having at least one (meth)acryl fluorenyl group.

The component (a3) is excellent in compatibility with the component (a1), and the viscosity of the buffer layer-forming composition can be adjusted to an appropriate range, and the modulus of the buffer layer formed of the composition can be adjusted to an appropriate range. Therefore, by using this component (a3), a buffer layer having a depth of penetration (X) of the above range can be formed.

Examples of the component (a3) include a hydroxyl group-containing (meth) acrylate, an epoxy group-containing (meth) acrylate, a guanamine group-containing compound, and an amine group-containing (meth) acrylate.

As the hydroxyl group-containing (meth) acrylate, for example, 2-Hydroxyethyl (meth) acrylate, 2-hydroxypropyl (meth) acrylate, 3-hydroxypropyl (meth) acrylate, 2-hydroxybutyl (meth) acrylate, 3- Hydroxybutyl (meth) acrylate, 4-hydroxybutyl (meth) acrylate, phenyl hydroxypropyl (meth) acrylate, and the like.

Examples of the epoxy group-containing (meth) acrylate include glycidyl (meth) acrylate, methyl glycidyl (meth) acrylate, and allyl glycidyl ether.

Examples of the guanamine-containing compound include (meth) acrylamide, N, N-dimethyl (meth) acrylamide, N-butyl (meth) acrylamide, and N-hydroxyl (meth) acrylamide, N-methylolpropane (meth) acrylamide, N-methoxymethyl (meth) acrylamide, N-butoxymethyl (meth) propylene Amidoxime and the like.

Examples of the amino group-containing (meth) acrylate include (meth) acrylate containing a first-stage amine group and (meth) acrylate containing a second-order amine group. An ester, a (meth) acrylate containing a third-order amine group, or the like.

In addition, the component (a3) can be used individually or in combination of 2 or more types.

Among these, from the formation of the penetration depth (X) to the above range From the viewpoint of the buffer layer, a hydroxyl group-containing (meth) acrylate, preferably a phenyl hydroxypropyl (meth) acrylate or the like having a hydroxy group-containing (meth) acrylate having an aromatic ring is preferable. .

The content of the component (a3) in the composition for forming a buffer layer, The total amount (100% by mass) of the composition for forming a buffer layer is obtained from the viewpoint of forming a buffer layer having a depth of penetration (X) in the above range and a film forming property of the buffer layer-forming composition obtained. Preferably, it is 5 to 40% by mass, more preferably 7 to 35% by mass, still more preferably 10 to 30% by mass, and still more preferably 13 to 25% by mass.

Further, the content ratio of the component (a2) to the component (a3) in the buffer layer-forming composition [(a2)/(a3)] is preferably from 0.5 to 3.0, more preferably from 1.0 to 3.0, still more preferably 1.3~3.0, and even better, 1.5~2.8.

When the content ratio is 0.5 or more, the film forming property of the obtained buffer layer-forming composition can be improved. Further, when the content ratio is 3.0 or less, a buffer layer having a depth of penetration (X) in the above range can be formed.

(polymerizable compound other than the components (a1) to (a3))

In the composition for forming a buffer layer, a polymerizable compound other than the above components (a1) to (a3) may be contained in a range that does not impair the effects of the present invention.

Examples of the other polymerizable compound include carbon numbers 1 to 20 Alkyl alkyl (meth) acrylate; styrene, hydroxyethyl vinyl ether, hydroxybutyl vinyl ether, N-vinyl formamide, N-vinyl pyrrolidone, N-vinyl caprolactone A vinyl compound such as an amine: and the like.

In addition, these other polymerizable compounds may be used alone or in combination of two or more.

Other polymerizable compound in the buffer layer forming composition The content is preferably 0 to 20% by mass, more preferably 0 to 10% by mass, still more preferably 0 to 5% by mass, and still more preferably 0 to 2% by mass.

(photopolymerization initiator)

In the case of forming a buffer layer in the buffer layer-forming composition, it is preferable to further contain a photopolymerization initiator from the viewpoint of shortening the polymerization time by light irradiation and reducing the amount of light irradiation.

The photopolymerization initiator may, for example, be a photopolymerization initiator such as a benzoin compound, an acetophenone compound, an acylphosphine oxide compound, a titanocene compound, a thioxanthone compound or a peroxide compound. A photosensitizer or the like of an amine or hydrazine, and more specifically, for example, 1-hydroxycyclohexyl phenyl ketone, 2-hydroxy-2-methyl-1-phenyl-propan-1-one, benzoin, benzoin A Ethyl ether, benzoin ethyl ether, benzoin isopropyl ether, and the like.

These photopolymerization initiators can be used alone or in combination of two or more.

The content of the photopolymerization initiator in the buffer layer forming composition The amount is preferably 0.05 to 15 parts by mass, more preferably 0.1 to 10 parts by mass, still more preferably 0.3 to 5 parts by mass, per 100 parts by mass of the total amount of the energy ray polymerizable compound.

(other additives)

The buffer layer-forming composition may contain other additives insofar as it does not impair the effects of the present invention.

Examples of other additives include an antioxidant, a softener (plasticizer), a filler, a rust preventive, a pigment, a dye, and the like.

When the additive is blended, the content of each additive in the buffer layer-forming composition is preferably 0.01 to 6 parts by mass, more preferably 0.1 to 3 parts by mass based on 100 parts by mass of the total amount of the energy ray polymerizable compound. Parts by mass.

(resin component)

In the composition for forming a buffer layer, a resin component may be contained in a range that does not impair the effects of the present invention.

Examples of the resin component include a polyene thiol resin, a polyolefin resin such as polybutene, polybutadiene, and polymethylpentene, and a thermoplastic resin such as a styrene copolymer.

The content of the resin component in the buffer layer forming composition is preferably from 0 to 20% by mass, more preferably from 0 to 10% by mass, still more preferably from 0 to 5% by mass, still more preferably from 0 to 5% by mass. 2% by mass.

<Adhesive layer>

As the adhesive for forming the adhesive layer of the adhesive sheet of the present invention, the type of the adhesive is not limited as long as it is an adhesive having moderate removability with respect to the semiconductor wafer or the like.

Examples of such an adhesive include an acrylic adhesive, an urethane-based adhesive, an anthrone-based adhesive, a rubber-based adhesive, a polyester-based adhesive, an energy ray-curable adhesive, and a heat-foaming. Type of adhesive, water swelling adhesive, and the like.

These adhesives can be used individually or in combination of 2 or more types.

Further, as the energy ray-curable adhesive, for example, The adhesive described in, for example, Japanese Laid-Open Patent Publication No. Hei. No. 60-223139, and the like is preferably an ultraviolet curable adhesive.

The mass average molecular weight (Mw) of the resin contained in the adhesive is preferably 20,000 to 1,500,000, more preferably 50,000 to 1.2 million, and still more preferably 100,000 to 1,000,000.

Moreover, such an adhesive may contain an energy ray-curable resin, a hardener, a crosslinking agent, a photopolymerization initiator, an antioxidant, a softener (plasticizer), a filler, a rust preventive agent, if necessary. Pigments, dyes, etc.

The thickness of the adhesive layer can be made into a semiconductor The shape of the bump of the wafer, the surface state, and the polishing method are appropriately set, but it is preferably 5 to 500 μm, more preferably 10 to 300 μm, still more preferably 15 to 100 μm.

<easy layer>

The adhesive sheet of the present invention can be between the rigid substrate and the buffer layer and between the rigid substrate and the adhesive layer from the viewpoint of improving the adhesion between the rigid substrate and the buffer layer and/or the adhesive layer. An easy-to-layer layer is provided on at least one side.

The composition for forming an easy-to-adhere layer which forms an easy-adhesion layer is not particularly limited, and examples thereof include a polyester resin, a urethane resin, a polyester urethane resin, and an acrylic resin. A composition such as a resin.

Further, the composition for forming an easy-contact layer may contain a crosslinking agent, a photopolymerization initiator, an antioxidant, a softener (plasticizer), a filler, a rust preventive, a pigment, a dye, and the like, if necessary.

The thickness of the easy-adhesion layer is preferably 0.01 to 10 μm, more preferably 0.03 to 5 μm.

Further, since the thickness of the easy-to-adhere layer is small and the material is soft relative to the rigid substrate, the Young's modulus of the rigid substrate which is easy to adhere to the layer, and only the rigid base where the easy-to-attach layer is not provided The difference in Young's modulus of the material is extremely small.

Therefore, in the present invention, it is considered that "the Young's modulus of the rigid substrate on which the adhesion layer is provided" = "Young's modulus of the rigid substrate".

<Peeling sheet>

The release sheet to be used in the present invention may be a release sheet which has been subjected to a release treatment on both sides, a release sheet which has been subjected to a release treatment on one side, or the like, and a release agent is applied to the surface of the substrate for release sheet.

The base material for a release sheet is preferably a resin film, and examples of the resin constituting the resin film include polyethylene terephthalate resin, polybutylene terephthalate resin, and polyethylene naphthalate. Polyester resin film such as ester resin, polyolefin resin such as polypropylene resin or polyethylene resin Wait.

Examples of the release agent include a rubber-based elastomer such as an anthrone-based resin, an olefin-based resin, an isoprene-based resin, and a butadiene-based resin, a long-chain alkyl-based resin, an alkyd-based resin, and a fluorine-based resin. Wait.

The thickness of the release sheet is not particularly limited, but is preferably 10 to 200 μm, more preferably 20 to 150 μm.

[Method of Manufacturing Adhesive Sheet]

The method for producing the adhesive sheet of the present invention is not particularly limited and can be produced by a known method.

For example, on the surface of the rigid substrate, if the buffer layer provided on the release sheet and the adhesive layer provided on the release sheet can be bonded together, the adhesive sheet 1b shown in Fig. 1(b) can be produced.

Further, if the two release sheets can be removed from the adhesive sheet 1b shown in Fig. 1(b), the adhesive sheet 1a shown in Fig. 1(a) can be obtained.

Further, after the easy-to-adhere layer is formed on the surface of the rigid substrate to be used, if the buffer layer provided on the release sheet and the adhesive layer provided on the release sheet can be bonded, the sheet of Fig. 1(a) can be produced. The adhesive sheet 1c is shown.

As a buffer layer or an adhesive layer formed on the release sheet The method can be directly applied to form a coating film by a coating composition for forming a buffer layer or an adhesive by a known coating method, and the coating film can be dried and/or irradiated with an energy ray to form a buffer layer or an adhesive. The layer is on the release sheet.

Examples of the coating method include a spin coating method, a spray coating method, a bar coating method, a knife coating method, a roll coating method, a knife coating method, a die coating method, and a gravure coating method.

Moreover, in order to improve the coating property, the buffer layer forming group is used. A product or an adhesive, which is blended with an organic solvent, can be applied to the release sheet as a form of a solution.

Examples of the organic solvent to be used include methyl ethyl ketone, acetone, ethyl acetate, tetrahydrofuran, dioxane, cyclohexane, n-hexane, toluene, xylene, n-propanol, and isopropanol. Wait.

In addition, as the organic solvent, the organic solvent used in the synthesis of the components contained in the composition may be used as it is, or one or more organic solvents other than the organic solvent may be added.

The buffer layer forming composition for forming a coating film is contained The energy ray polymerizable compound is cured by irradiation with an energy ray to form a buffer layer.

The hardening treatment can completely harden it at a time, and can be hardened by being divided into a plurality of times. That is, after the coating film on the release sheet is completely cured to form a buffer layer, it is bonded to the rigid substrate, and the coating film is not completely cured to form a buffer layer forming film in a semi-hardened state, and the buffer layer can be formed. After the film is attached to the rigid substrate, the energy line is again irradiated to completely harden to form a buffer layer.

As the energy line irradiated by the hardening treatment, it is preferably purple Outside line.

The amount of irradiation of the energy ray can be appropriately changed depending on the type of the energy ray. For example, when ultraviolet rays are used, the illuminance of the ultraviolet ray to be irradiated is preferably 50 to 500 mW/cm ² , more preferably 100 to 340 mW/cm ² , and the ultraviolet ray irradiation amount is preferably 80 to 2500 mJ/cm ² , more preferably 100 Å. 2000mJ/cm ² .

The adhesive sheet of the present invention is used for the manufacture of wafers for grinding It is suitable as a BG sheet for protecting the surface side of the wafer.

As a method for producing a wafer by using the adhesive sheet of the present invention, for example, a method for producing a finished wafer having the following steps (1A) to (3A) is preferable.

Step (1A): a step of attaching the adhesive layer of the adhesive sheet of the present invention to the surface side of the wafer to obtain a wafer with a buffer layer

Step (2A): a step of placing the buffer layer of the buffer layer of the buffer layer obtained in the step (1A) on the chuck holder of the grinding machine

Step (3A): grinding the inside of the wafer of the buffer layer of the wafer without the buffer layer, and obtaining the step of grinding the completed wafer

The adhesive sheet of the present invention is excellent in foreign matter adsorption property. Therefore, in the step (2A) of the above-described method for manufacturing a wafer to be completed, even if foreign matter adheres to the chuck holder, the buffer layer absorbs the thickness of the foreign matter, thereby suppressing the swelling of the inner surface of the wafer due to the presence of the foreign matter. .

As a result, according to the above-described manufacturing method, it is possible to prevent the wafer from being broken due to the cutting process due to the presence of the foreign matter, and it is possible to manufacture a wafer having a high yield and a finished film.

Moreover, the adhesive sheet of the present invention is also suitable for use as a borrow A BG sheet of a method of manufacturing a semiconductor wafer by a dicing method.

As a method of producing a semiconductor wafer using the adhesive sheet of the present invention, for example, a method of manufacturing a semiconductor wafer having the following steps (1B) to (3B) is preferable.

Step (1B): on the surface, the surface of the wafer to which the adhesive layer of the adhesive sheet of the present invention is attached to a specific depth groove is disposed in a specific configuration Step of obtaining a wafer with a buffer layer

Step (2B): a step of placing the buffer layer of the buffer layer of the buffer layer obtained in the step (1B) on the chuck holder of the grinding machine

Step (3B): a step of grinding the inside of the buffer layer of the buffer layer on which the buffer layer is not provided to a specific thickness, and dividing into the respective wafers

As described above, the buffer layer of the adhesive sheet of the present invention is excellent in foreign matter adsorption property, and can prevent the foreign matter adhering to the chuck holder from being broken due to the cutting process. As a result, according to the above production method, a semiconductor wafer having a high yield and a thin film can be manufactured.

[Examples]

The mass average molecular weight (Mw) of each component used in the following examples and comparative examples, and the Young's modulus of the rigid substrate were measured using the methods described below.

<mass average molecular weight (Mw)>

Using a gel permeation chromatography apparatus (manufactured by Tosoh Corporation, product name "HLC-8020"), the measurement was carried out under the following conditions, and the values measured in terms of standard polystyrene were used.

(measurement conditions)

. Pipe column: "TSK guard column HXL-H" "TSK gel GMHXL (×2)" "TSK gel G2000HXL" (made by Tosoh Co., Ltd.)

. Column temperature: 40 ° C

. Developing solvent: tetrahydrofuran

. Flow rate: 1.0mL/min

<Young's modulus of rigid substrate>

The Young's modulus of the rigid substrate was measured by a tensile test using a tensile tester, and was calculated from the obtained tensile strength and elongation chart. Specifically, the PET film having the adhesive layer on both sides of the production example 3 was cut into a size of 15 mm in width × 150 mm in length, and the stretching portion was set to 100 mm in a stretchable manner. Compression tester (manufactured by A & D Co., Ltd., product name "Tensilon"). Further, the measurement was carried out at a test speed of 200 mm/min, and the Young's modulus was calculated from the slope of the origin of the obtained graph.

Manufacturing example 1 (Synthesis of urethane acrylate oligomer (UA-1))

The 2-hydroxyethyl acrylate is reacted with a polyester diol and a terminal isocyanate urethane prepolymer obtained by reacting with isophorone diisocyanate to obtain a mass average molecular weight (Mw) of 5,000. Bifunctional urethane acrylate oligomer (UA-1).

Manufacturing Example 2 (Production of peeling sheet with adhesive layer)

Blending 100 parts by mass with a composition derived from n-butyl acrylate (BA), methyl methacrylate (MMA) and 2-hydroxyethyl acrylate (2HEA) Acrylic copolymer of the unit (BA/MMA/2HEA=52/20/28 (% by mass), Mw=500,000), 6 parts by mass of a polyfunctional urethane acrylate-based ultraviolet curable resin, and 1 part by mass a diisocyanate-based hardener, and 1 part by mass of bis(2,4,6-trimethylbenzylidene)phenylphosphine oxide as a photopolymerization initiator, diluted with methyl ethyl ketone to prepare a solid content concentration A solution of 32% by mass of the adhesive.

Further, the release sheet (manufactured by Lintec Co., Ltd., trade name "SP-PET381031", polyethylene terephthalate (PET) film subjected to an oxime release treatment, thickness: 38 μm) was subjected to a release treatment, and the above-mentioned coating was applied. A solution of the adhesive composition was dried and a release sheet of an adhesive layer having an adhesive layer having a thickness of 20 μm was produced.

Manufacturing Example 3 (Production of PET film on both sides with easy adhesion layer)

The first easy-to-back layer of the PET film (manufactured by Toyobo Co., Ltd., trade name "PET50 A-4100") having a thickness of 50 μm, which is an easy-adhesion layer (the first easy-to-adhere layer), is provided on the surface provided on one side. On the side surface, a polyester coating agent (manufactured by Arakawa Chemical Co., Ltd.) was applied and dried, and a second easy-adhesion layer having a thickness of 2 μm was provided to obtain a double-sided layer having a thickness of 52 μm. Layer of PET film. The Young's modulus of the PET film on both sides of the adhesive layer was 2,500 MPa.

Examples 1 to 2 and Comparative Examples 1 to 4 (1) Modulation of a buffer layer forming composition

As the energy ray polymerizable compound, the urethane acrylate oligomer (UA-1), isodecyl acrylate (IBXA), and phenyl hydroxypropyl acrylate (HPPA) which will be synthesized in Production Example 1 are used. Incorporation of 2.0 parts by mass of 1-hydroxycyclohexyl phenyl ketone (manufactured by BASF Corporation, product name "Irgacure 184") and 0.2 parts by mass of ruthenium in an amount of the blending amount shown in Table 1 A cyanine pigment is used to prepare a composition for forming a buffer layer.

(2) Production of adhesive sheets

The peeled sheet (manufactured by Lintec Co., Ltd., trade name "SP-PET381031", polyethylene terephthalate (PET) film subjected to an oxime release treatment, thickness: 38 μm) was subjected to a release treatment, and the above was applied. The coating layer forming composition forms a coating film. Further, the coating film was irradiated with ultraviolet rays, and the coating film was semi-cured to form a buffer layer-forming film having a thickness of 43 μm.

In the above-mentioned ultraviolet irradiation, a belt conveyor type ultraviolet irradiation device (product name "ECS-401GX", manufactured by Eye Graphics Co., Ltd.) and a high-pressure mercury lamp (manufactured by H04-L41Eye Graphics Co., Ltd.: H04-L41) were used, and the lamp height was 150 mm. The output was carried out under the irradiation conditions of 3 kW (converted output 120 mW/cm), illuminance of light wavelength 365 nm of 120 mW/cm ² , and irradiation dose of 100 mJ/cm ² .

Further, the surface of the buffer layer forming film formed by bonding and the first easy-adhesion layer of the PET film having the adhesive layer formed on both sides of the production example 3 were irradiated with ultraviolet rays from the side of the release sheet on the buffer layer forming film. buffer The layer forming film was completely cured to form a buffer layer having a thickness of 43 μm.

In the above ultraviolet irradiation, the ultraviolet irradiation device and the high-pressure mercury lamp described above are used, and the illumination height is 150 mm, the lamp output is 3 kW (converted output 120 mW/cm), the illuminance at a light wavelength of 365 nm is 160 mW/cm ² , and the irradiation amount is 500 mJ/cm ² . Under the conditions.

Next, the adhesive layer of the release sheet of the adhesive layer prepared in the production example 2 was bonded to the second easy-to-adhere layer of the PET film on the both sides of the adhesive layer, and was adhered to the adhesive layer of FIG. 1(d). The sheet 1d has the same adhesive sheet.

For the adhesive sheets prepared as above, various physical properties The measurement and the evaluation of the characteristics were carried out by the methods described below. The results are shown in Table 1.

<Measurement of the penetration depth (X)>

Using a dynamic microhardness tester (manufactured by Shimadzu Corporation, product name "DUH-W201S"), and a triangular pyramid shape indenter with a radius of curvature of 100 nm at the tip of the indenter and an angle of 115° between the edges, at 23 ° C, 50 Measured under the environment of %RH (relative humidity).

Specifically, on the glass plate of the dynamic microhardness tester, the release sheet on the buffer layer of the prepared adhesive sheet is removed, and the buffer layer is provided in a manner of being described. For the buffer layer, the triangular pyramid shape indenter is used. The tip end was extruded at a rate of 10 μm/min to measure the depth of penetration (X) when the compression load reached 2 mN.

<Measurement of the maximum value of tan δ of the buffer layer>

In the same manner as described above, a buffer layer forming film having a thickness of 500 μm composed of the buffer layer forming compositions used in the respective examples and comparative examples was formed on the first release sheet, and further formed on the buffer layer. The second release sheet is bonded. The first and second release sheets used were the same as those used in the above examples and comparative examples.

Further, ultraviolet rays were again irradiated from the side of the first release sheet, and the buffer layer forming film was completely cured to form a test buffer layer having a thickness of 500 μm. In the above ultraviolet irradiation, the ultraviolet irradiation device and the high-pressure mercury lamp described above are used, and the illumination height is 150 mm, the lamp output is 3 kW (converted output 120 mW/cm), the illuminance at a light wavelength of 365 nm is 160 mW/cm ² , and the irradiation amount is 500 mJ/cm ² . Under the conditions.

After removing the double-faced release sheet on the prepared test buffer layer, the test piece cut into a specific size was used to measure the frequency in a dynamic viscoelastic device (manufactured by Orientec Co., Ltd., product name "Rheovibron DDV-II-EP1"). 11 Hz, loss elastic modulus and storage elastic modulus in the temperature range of -20 to 150 °C.

The value of the "loss elastic modulus / storage elastic modulus" of each temperature is calculated as tan δ of the temperature, and the maximum value of tan δ in the range of -5 to 120 ° C is described as "the maximum value of tan δ of the buffer layer" in Table 1. .

<Evaluation of foreign matter adsorption (whether or not wafer rupture)>

On the surface of the 700 μm thick fluorenone wafer, the adhesive layer of the release sheet on the adhesive layer of the adhesive sheet is removed, so that the adhesive layer is removed. The BG tape was bonded by a laminator (manufactured by Lintec Co., Ltd., product name "Laminator RAD-3500m/12").

After attaching the adhesive sheet to the fluorenone wafer, the release sheet on the buffer layer was removed, and on the surface of the buffer layer shown as a pseudo foreign matter, five tapes were attached (on a PET film having a thickness of 6 μm, a thickness of 3 μm was set. The adhesive layer composed of the acrylic adhesive, vertical: 1 cm, horizontal: 2 cm, thickness: 9 μm).

In addition, the inner surface of the adhesive sheet of the fluorene ketone wafer was not attached to the wafer surface grinding machine (product name "DFG-8540" manufactured by DISCO Corporation), and the thickness was 100 μm.

After the grinding, the presence or absence of rupture of the fluorene ketone wafer was visually observed, and the foreign matter adsorption property of the adhesive sheet was evaluated by the following criteria.

A: No cracking of the wafer was observed, and the foreign matter adsorption of the adhesive sheet was good.

F: The rupture of the wafer was observed, and the foreign matter adsorption of the adhesive sheet was poor.

From Table 1, it is understood that the adhesive sheets prepared in Examples 1 to 2 are excellent in adsorption property to foreign matters.

Further, the adhesive sheets produced in Comparative Examples 1 to 4 were used as the result of the foreign matter adsorption property during the grinding of the wafer, and the result was that the wafer was broken after the cutting.

[Industrial availability]

The adhesive sheet of the present invention is excellent in foreign matter adsorption property.

Therefore, the adhesive sheet of the present invention can be suitably used for polishing a semiconductor wafer, for example, as a BG sheet which serves as a surface side for protecting a semiconductor wafer, and can be used for this purpose to effectively prevent cracking of the semiconductor wafer.

1a, 1b, 1c, 1d‧‧‧ adhesive sheets

11‧‧‧Rigid substrate

12‧‧‧ Buffer layer

13‧‧‧Adhesive layer

14a, 14b‧‧‧ peeling sheets

15a, 15b‧‧‧Easy layer

Claims (9)

An adhesive sheet having a rigid substrate having a Young's modulus of 1000 MPa or more, a buffer layer provided on one side of the rigid substrate, and an adhesive layer provided on the other side of the rigid substrate The sheet is characterized in that the buffer layer is a layer formed of a buffer layer forming composition containing an energy ray-polymerizable compound, and a tip end of a triangular hammer-shaped indenter having a tip end radius of curvature of 100 nm and an inter-edge angle of 115° is used. At a speed of 10 μm/min, the compression depth (X) necessary for the compression load when the buffer layer is pushed into 2 mN is 2.5 μm or more. The adhesive sheet according to claim 1, wherein the buffer layer-forming composition contains the urethane (meth) acrylate (a1) and has a ring-forming atomic number of 6 to 20 as the energy ray-polymerizable compound. The polymerizable compound (a2) having an alicyclic group or a heterocyclic group, and the polymerizable compound (a3) having a functional group. The adhesive sheet according to claim 2, wherein the content ratio (a2)/(a3) of the component (a2) to the component (a3) in the buffer layer-forming composition is 0.5 to 3.0. An adhesive sheet according to claim 2 or 3, wherein the component (a2) is an alicyclic group-containing (meth) acrylate. The adhesive sheet according to any one of claims 2 to 4, wherein the component (a3) is a hydroxyl group-containing (meth) acrylate. The adhesive sheet according to any one of claims 1 to 5, wherein the buffer layer has a thickness of 5 to 100 μm. The adhesive sheet according to any one of claims 1 to 6, wherein a maximum value of tan δ of the dynamic viscoelasticity of the buffer layer at -5 to 120 ° C is 0.5 or more. The adhesive sheet according to any one of claims 1 to 7, wherein at least one of the rigid substrate and the buffer layer and the rigid substrate and the adhesive layer have an easy-adhesion layer. The adhesive sheet according to any one of claims 1 to 8, which is used for cutting a semiconductor wafer, and is used as a backside polished sheet for protecting the surface side of the semiconductor wafer.