PROTECTIVE SHEET FOR WORK PROCESSING AND METHOD FOR PRODUCING WORK INDUCED PRODUCT

Abstract

To provide a protection sheet for workpiece processing that can reduce defects in the singulated workpieces after grinding even when the singulated workpieces are obtained by grinding the workpieces by LDBG.SOLUTION: A workpiece processing protection sheet includes a base material and an adhesive layer disposed on one main surface of the base material, the shear storage modulus of the adhesive layer at 55°C is 40,000 Pa or more, the shear stress relaxation rate of the adhesive layer after 1 second at 55°C is 30% or more, and at 23°C, the elongation of the workpiece processing protection sheet is 2.5% or less when the tensile load reaches 30 N / 15 mm after starting to apply the tensile load to the workpiece processing protection sheet.SELECTED DRAWING: Figure 1A

Description

[Technical Field]

[0001] The present invention relates to a protective sheet for workpiece processing and a method for manufacturing singulated workpieces, particularly to a protective sheet for workpiece processing suitable for use in a method of grinding the back surface of a workpiece and using the resulting stress to singulate the workpiece, and a method for manufacturing singulated workpieces using the protective sheet for workpiece processing. [Background technology]

[0002] As various electronic devices become smaller and more multifunctional, the semiconductor chips used in them are also required to be smaller and thinner. To thin chips, the backside of the semiconductor wafer is typically ground to adjust the thickness. To obtain thin chips, a process called dicing before grinding (DBG) is sometimes used. This involves forming grooves of a specified depth on the front side of the wafer with a dicing blade, then grinding the wafer from the backside, dicing the wafer into individual chips. DBG allows for the efficient production of thin chips by simultaneously grinding the backside of the wafer and dicing the wafer.

[0003] Conventionally, when grinding the backside of a workpiece such as a semiconductor wafer or when manufacturing individual workpieces such as semiconductor chips using DBG, it is common to apply an adhesive tape called a backgrind sheet to the surface of the workpiece to protect the circuits on the surface of the workpiece and to hold the workpiece and the individual workpieces in place.

[0004] The backgrinding sheet used in DBG is an adhesive tape comprising a substrate and an adhesive layer provided on one side of the substrate. As an example of such an adhesive tape, Patent Document 1 discloses an adhesive tape comprising a substrate with a high Young's modulus, an adhesive layer provided on one side of the substrate, and a buffer layer provided on the other side.

[0005] In recent years, a variation of the dicing-before method has been proposed: a modified region is created inside the wafer using a laser, and the wafer is then singulated using stress generated during back-grinding. Hereinafter, this method may be referred to as LDBG (Laser Dicing Before Grinding). In LDBG, the wafer is cut in the crystal direction starting from the modified region, which reduces chipping compared to the dicing-before method using a dicing blade. Furthermore, compared to DBG, which creates grooves of a predetermined depth on the wafer surface using a dicing blade, LDBG does not remove any area of ​​the wafer with the dicing blade, meaning the kerf width is extremely small, resulting in superior chip yield. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Japanese Patent Application Laid-Open No. 2015-183008 Summary of the Invention [Problem to be solved by the invention]

[0007] However, when the adhesive tape described in Patent Document 1 is used to singulate workpieces such as wafers by LDBG, the shear force applied to the workpieces, such as chips, causes the workpieces to move slightly, resulting in contact with each other. As a result, cracks (unintended cracks) occur in the workpieces. As mentioned above, the tendency for cracks to occur is also due to the extremely small kerf width. In particular, if a crack occurs in the workpiece, it directly leads to defective workpieces and significantly affects the yield of the workpieces.

[0008] The present invention has been made in consideration of the above-described circumstances, and aims to provide a protective sheet for workpiece processing that can reduce defects in the workpiece segments after grinding, even when the workpiece is ground using LDBG to obtain individual workpiece segments. [Means for solving the problem]

[0009] The aspects of the present invention are as follows.

[0010] [1] A protective sheet for workpiece processing having a substrate and an adhesive layer disposed on one main surface of the substrate, The pressure-sensitive adhesive layer has a shear storage modulus of 40,000 Pa or more at 55°C, and the pressure-sensitive adhesive layer has a shear stress relaxation rate of 30% or more after 1 second at 55°C. This is a workpiece processing protection sheet in which, at 23°C, when a tensile load is applied to the workpiece processing protection sheet and the tensile load reaches 30 N / 15 mm, the elongation of the workpiece processing protection sheet is 2.5% or less.

[0011] [2] The protective sheet for workpiece processing according to [1], wherein a buffer layer is disposed on the other main surface of the substrate.

[0012] [3] The protective sheet for workpiece processing according to [1] or [2], wherein the protective sheet for workpiece processing has a tensile stress relaxation rate of less than 40% after 1 minute at 23°C.

[0013] [4] The adhesive layer is made of an energy ray-curable acrylic adhesive, The acrylic adhesive is a protective sheet for workpiece processing according to any one of [1] to [3], which contains a polymer in which an energy ray-curable group is bonded to an acrylic polymer, and an energy ray-curable compound.

[0014] [5] A protective sheet for workpiece processing according to any one of [1] to [4], which is attached to the surface of a workpiece in a process of dividing the workpiece into individual workpieces by grinding the back surface of the workpiece having a modified region formed therein.

[0015] [6] A step of attaching the workpiece processing protection sheet according to any one of [1] to [5] to the surface of the workpiece; forming a modified region inside the workpiece from the front or rear surface of the workpiece; a step of grinding the workpiece, which has a workpiece processing protection sheet attached to its surface and a modified region formed thereon, from its back surface side to separate the workpiece into a plurality of workpiece individual pieces starting from the modified region; The method for manufacturing the individual workpieces includes a step of peeling off the protective sheet for workpiece processing from the individualized workpieces. [Effects of the Invention]

[0016] According to the present invention, it is possible to provide a protective sheet for workpiece processing that can reduce defects in the workpiece segments after grinding, even when the workpiece is ground using LDBG to obtain individual workpiece segments. [Brief explanation of the drawings]

[0017] [Figure 1A] FIG. 1A is a cross-sectional view showing an example of a protection sheet for workpiece processing according to this embodiment. [Figure 1B] FIG. 1B is a cross-sectional view showing another example of the protection sheet for workpiece processing according to this embodiment. [Figure 2] FIG. 2 is a schematic cross-sectional view showing a state in which the protection sheet for workpiece processing according to this embodiment is attached to the surface of a workpiece. DETAILED DESCRIPTION OF THE INVENTION

[0018] The present invention will be described in detail below based on specific embodiments with reference to the accompanying drawings. First, the main terms used in this specification will be explained.

[0019] The term "workpiece" refers to a plate-shaped body to which the protective sheet for workpiece processing according to this embodiment is attached and then singulated. Examples of workpieces include circular wafers (including those with an orientation flat), rectangular panel-level packages, and strips (rectangular substrates) sealed with molded resin. Among these, wafers are preferred because they facilitate the attainment of the effects of the present invention. Examples of wafers include semiconductor wafers such as silicon wafers, gallium arsenide wafers, silicon carbide wafers, gallium nitride wafers, and indium phosphide wafers, as well as insulator wafers such as glass wafers, lithium tantalate wafers, and lithium niobate wafers. They may also be reconstructed wafers made of resin and semiconductors used in the manufacture of fan-out packages, etc. Because they facilitate the attainment of the effects of the present invention, semiconductor wafers or insulator wafers are preferred, with semiconductor wafers being more preferred.

[0020] Singulation of a workpiece refers to dividing the workpiece into individual circuits to obtain individual workpieces. For example, if the workpiece is a wafer, the individual workpieces are chips, and if the workpiece is a panel-level package or a strip (rectangular substrate) sealed with molded resin, the individual workpieces are semiconductor packages.

[0021] The "surface" of a workpiece refers to the surface on which circuits, electrodes, etc. are formed, and the "back" of a workpiece refers to the surface on which no circuits, etc. are formed. The electrodes may be convex electrodes such as bumps.

[0022] DBG is a method in which grooves of a specified depth are formed on the surface of a workpiece, and then the workpiece is ground from the back side to separate the workpiece. The grooves formed on the surface of the workpiece are formed by methods such as blade dicing, laser dicing, and plasma dicing.

[0023] LDBG is a variation of DBG, and refers to a method in which a fragile modified area is created inside a workpiece (e.g., a wafer) using a laser, and cracks originating from the modified area are propagated by stresses, etc., generated during back grinding of the workpiece, thereby dividing the workpiece into individual pieces.

[0024] A "group of individual workpieces" refers to a plurality of individual workpieces held on the protective sheet for workpiece processing according to the present invention after the workpiece has been singulated. These individual workpieces collectively form a shape similar to that of the workpiece. Furthermore, a "group of chips" refers to a plurality of chips held on the protective sheet for workpiece processing according to the present invention after the wafer serving as the workpiece has been singulated. These chips collectively form a shape similar to that of the wafer.

[0025] The term "(meth)acrylate" is used to refer to both "acrylate" and "methacrylate," and similar terms.

[0026] "Energy rays" refers to ultraviolet rays, electron beams, etc., and is preferably ultraviolet rays.

[0027] Unless otherwise specified, the "weight average molecular weight" is a polystyrene equivalent value measured by gel permeation chromatography (GPC). Measurements by this method are performed, for example, using a high-speed GPC device "HLC-8120GPC" manufactured by Tosoh Corporation, with a high-speed column "TSK guard column H" XL -H", "TSK Gel GMH XL ", "TSK Gel G2000 H XL (All products of Tosoh Corporation) connected in this order are used, and the column temperature is 40°C, the liquid flow rate is 1.0 mL / min, and the detector is a differential refractometer.

[0028] The release sheet is a sheet that supports the pressure-sensitive adhesive layer in a releasable manner. The term "sheet" is not limited to a specific thickness, and is used to include films.

[0029] The mass ratios in the descriptions of compositions such as the pressure-sensitive adhesive layer composition are based on the active ingredient (solid content), and do not include the solvent unless otherwise specified.

[0030] (1. Protective sheet for workpiece processing) The protective sheet for workpiece processing 1 according to this embodiment has a substrate 10 and a pressure-sensitive adhesive layer 20 disposed on the substrate 10, as shown in FIG. 1A.

[0031] In this embodiment, as shown in Fig. 2, the protective sheet for workpiece processing 1 is used by attaching the main surface 20a of the adhesive layer to the surface 100a of the workpiece 100 (e.g., a wafer). The surface 100a of the workpiece 100 is a surface having circuits, electrodes, etc. The surface having the circuits may be a surface on which the circuits are exposed, or may be the main surface of a protective layer formed on the circuits to protect them. Furthermore, convex electrodes such as bumps may be formed on the circuits.

[0032] In this embodiment, the workpiece to which the protective sheet for workpiece processing is attached is divided into a plurality of workpiece pieces after backside grinding. Although DBG may be adopted as a method for dividing the workpiece, the protective sheet for workpiece processing 1 according to this embodiment is preferably used for dividing the workpiece by LDBG.

[0033] Specifically, after a modified region is formed inside the workpiece, the workpiece 100, on whose surface 100a the protective sheet for workpiece processing 1 is attached, has its back surface 100b, which is the main surface opposite to the surface 100a, ground.

[0034] As grinding progresses, the workpiece becomes thinner, and at the same time, the shear force and pressure applied to the modified region formed inside the workpiece cause cracks to form in the modified region and propagate to both sides of the workpiece. As a result, the workpiece is singulated. In LDBG singulation, almost no area is removed from the workpiece, so the distance between adjacent workpieces (kerf width) in the workpiece singulation (group of workpiece singulations) is very small.

[0035] Furthermore, the workpieces are not singulated simultaneously; grinding continues from the moment a portion of the workpiece begins to be singulated until the entire workpiece is singulated. Therefore, the shear force of the grinding wheel continues to be applied to the workpiece singulations. Because the uneven grinding wheel surface is constantly rotating and in contact with the group of workpiece singulations, the same shear force is not applied to all workpiece singulations at the same time, and the shear force applied to each workpiece singulation varies. Therefore, the movement of each individual workpiece singulation occurs independently in the direction parallel to the workpiece plane (i.e., the plane of the group of workpiece singulations), and because the kerf width is small, the workpiece singulations may come into contact with each other. When this contact occurs, cracks are likely to occur in the workpiece singulations. In particular, large cracks that lead to defective workpiece singulations are likely to occur in the workpiece singulations. The occurrence of such large cracks poses a problem of reduced yield of the workpiece singulations. When the thickness of the workpiece and the group of workpiece individual pieces after grinding is less than 20 μm, the workpiece individual pieces become more fragile than when the thickness is 20 μm or more, and large cracks are more likely to occur.

[0036] To address this issue, a hard protective sheet for workpiece processing can be used to firmly hold the workpieces in place, preventing the workpieces from moving during grinding. However, hardness alone cannot withstand shear forces, and instead, shear stress caused by shear forces can cause the workpieces to collide with each other, increasing the number of cracks in the workpieces. Therefore, for example, in addition to the substrate and adhesive layer, a layer with high stress relaxation properties has been used to alleviate shear stress. However, the problem of such layers not being sufficient to alleviate shear stress has become apparent.

[0037] To address this problem, the present inventors came up with the idea of ​​imparting stress relaxation properties to the adhesive layer that is closest to and in contact with the workpiece. The most important function of the adhesive layer is to adhere the workpiece to the protective sheet for workpiece processing, and the idea of ​​imparting stress relaxation properties to such an adhesive layer had not previously existed.

[0038] The inventors have discovered that by imparting stress relaxation properties to the adhesive layer, described below, while maintaining the original functions of the adhesive layer, it is possible to suppress the occurrence of large cracks that lead to defects in the workpiece singulation.

[0039] The components of the protection sheet for workpiece processing 1 shown in FIG. 1A will be described in detail below.

[0040] (2. Base material) The substrate is a component that provides the rigidity of the workpiece processing protection sheet. The substrate is not limited as long as it is made of a material that can support the workpiece. For example, various resin films used as substrates for backgrinding tapes are exemplified. By using such a resin film, the workpiece can be held without being damaged even if the thickness of the workpiece becomes thin due to grinding. The substrate may be made of a single-layer film made of one resin film, or may be made of a multi-layer film in which multiple resin films are laminated.

[0041] (2.1 Base Material) In this embodiment, examples of the material for the substrate include polyesters such as polyethylene terephthalate, polyethylene naphthalate, polybutylene terephthalate, wholly aromatic polyester, polyamide, polycarbonate, polyacetal, modified polyphenylene oxide, polyphenylene sulfide, polysulfone, polyether ketone, biaxially oriented polypropylene, etc. Among these, polyester is preferred, and polyethylene terephthalate is more preferred.

[0042] The thickness of the substrate affects the rigidity of the workpiece processing protective sheet, so it may be set according to the material of the substrate. For example, the thickness of the substrate may be set so that the physical properties of the workpiece processing protective sheet fall within the ranges described below. In this embodiment, the thickness of the substrate is preferably 25 μm or more and 200 μm or less, more preferably 35 μm or more and 150 μm or less, and even more preferably 40 μm or more and 150 μm or less.

[0043] At least one main surface of the substrate may be subjected to an adhesion treatment such as a corona treatment in order to improve adhesion with a layer formed on the main surface. Also, at least one main surface of the substrate may have an easy-adhesion layer formed thereon in order to improve adhesion with a layer formed on the main surface.

[0044] (3. Adhesive Layer) The adhesive layer is attached to the surface of the workpiece (i.e., the surface on which circuits, electrodes, etc. are formed). The adhesive layer protects the surface and supports the workpiece until it is peeled off from the surface.

[0045] The pressure-sensitive adhesive layer may be composed of one layer (single layer) or two or more layers. When the pressure-sensitive adhesive layer has multiple layers, these multiple layers may be the same or different, and the combination of layers constituting these multiple layers is not particularly limited.

[0046] In this embodiment, the adhesive layer has the following physical properties, which reduce collisions between the individual workpieces, thereby suppressing the occurrence of cracks, particularly large cracks, in the individual workpieces due to collisions between the individual workpieces.

[0047] (3.1. Shear storage modulus of adhesive layer) In this embodiment, the shear storage modulus (G') of the adhesive layer at 55°C is 40,000 Pa or more. During backgrinding of the workpiece, heat is generated on the grinding surface, and this heat is also transmitted to the adhesive layer. As a result, the temperature of the adhesive layer rises, for example, to approximately 50 to 60°C. Since the shear storage modulus of the adhesive layer at 55°C is within the above range, the adhesive layer remains relatively hard even during backgrinding of the workpiece. Therefore, even if shear forces applied to the workpiece during backgrinding are transmitted to the adhesive layer, deformation of the adhesive layer is suppressed. As a result, the movement amount of the group of workpiece individual pieces held by the adhesive layer is reduced, and collisions between the workpiece individual pieces are suppressed.

[0048] The shear storage modulus of the pressure-sensitive adhesive layer at 55°C is preferably 45,000 Pa or more, more preferably 50,000 Pa or more, and even more preferably 55,000 Pa or more.

[0049] From the viewpoint of easily achieving both the numerical range of the shear storage modulus of the pressure-sensitive adhesive layer and the numerical range of the shear stress relaxation rate of the pressure-sensitive adhesive layer described below, the shear storage modulus of the pressure-sensitive adhesive layer at 55°C is preferably 200,000 Pa or less, more preferably 150,000 Pa or less, and even more preferably 100,000 Pa or less.

[0050] The shear storage modulus of the pressure-sensitive adhesive layer at 55°C can be measured as follows. First, a measurement sample of a predetermined size is prepared from the material constituting the pressure-sensitive adhesive layer. Using a dynamic viscoelasticity measuring device, the measurement sample is twisted at a predetermined frequency within a predetermined temperature range to apply shear strain to the measurement sample, and the elastic modulus of the measurement sample is measured. The shear storage modulus of the pressure-sensitive adhesive layer at 55°C is calculated from the measured elastic modulus. Details of the measurement will be explained in the Examples.

[0051] (3.2. Shear stress relaxation rate of adhesive layer) In this embodiment, the shear stress relaxation rate of the adhesive layer after 1 second at 55°C is 30% or more. As grinding of the workpiece progresses and the workpiece begins to be divided into multiple individual workpieces, uneven shear force applied to each individual workpiece by the grinding wheel may occur when the connected workpiece before division and the individual workpieces after division are mixed together. As described above, the high shear storage modulus of the adhesive layer relatively suppresses deformation of the adhesive layer due to shear force, etc. However, among the individual workpieces where the applied shear force is uneven, the adhesive layer may deform in the individual workpieces located in areas where the shear force is temporarily high. If the shear stress relaxation rate of the adhesive layer at 55°C is not controlled within the above range, the time required for the individual workpieces to return to their normal, undeformed state when the temporarily high shear force is no longer applied is short, making it more likely that adjacent individual workpieces will collide more strongly. However, by controlling the shear stress relaxation rate of the adhesive layer at 55°C within the above range, even if the adhesive layer is deformed by a temporary high shear force, the shear stress is relaxed in a short time, and the time required for the adhesive layer to return to its normal, undeformed state when the temporary high shear force is no longer applied can be extended. Therefore, the acceleration of the group of workpiece individual pieces held by the adhesive layer is suppressed, and relatively strong collisions between the workpiece individual pieces are suppressed.

[0052] The shear stress relaxation rate of the pressure-sensitive adhesive layer at 55°C is preferably 35% or more, and more preferably 38% or more.

[0053] The upper limit of the shear stress relaxation rate of the pressure-sensitive adhesive layer at 55°C is not particularly limited as long as the effects of the present invention can be obtained. In this embodiment, the upper limit of the shear stress relaxation rate of the pressure-sensitive adhesive layer at 55°C is preferably 65%, more preferably 60%, from the viewpoint of achieving compatibility with other physical properties of the pressure-sensitive adhesive layer.

[0054] In this embodiment, the shear stress relaxation rate of the pressure-sensitive adhesive layer can be measured as follows. The material constituting the pressure-sensitive adhesive layer is used as a measurement sample of a predetermined size. The measurement sample, which is at a temperature of 55°C, is twisted using a dynamic viscoelasticity measuring device to apply shear strain to the measurement sample. In this embodiment, taking into account that the shear stress is relaxed in a short period of time, the shear stress relaxation rate is calculated from the shear stress immediately after the application of strain and the shear stress 1 second after the application of strain begins. Details of the measurement will be explained in the Examples.

[0055] (3.3. Composition of Adhesive Layer) The adhesive layer is not particularly limited as long as it is made of an adhesive that satisfies the above-mentioned physical properties. In this embodiment, the adhesive layer is preferably formed from an energy ray-curable adhesive. By forming the adhesive layer of the workpiece processing protective sheet from an energy ray-curable adhesive, it adheres to the workpiece with high adhesive strength when attached to the workpiece, and when peeled from the workpiece, the adhesive strength can be reduced by irradiating it with energy rays. Therefore, while appropriately protecting the workpiece's circuits, etc., when peeling off the workpiece processing protective sheet, damage to the circuits, electrodes, etc. on the workpiece surface and adhesion of the adhesive to the workpiece are prevented.

[0056] As a composition for an adhesive layer that constitutes an energy ray-curable adhesive, for example, a composition for an energy ray-curable adhesive layer (hereinafter also referred to as an "X-type adhesive layer composition") that contains a non-energy ray-curable adhesive resin (also referred to as "adhesive resin I") as a main component and contains an energy ray-curable compound other than the adhesive resin can be used.

[0057] In addition, as a composition for adhesive layer constituting the energy ray-curable adhesive, a composition for energy ray-curable adhesive layer (hereinafter also referred to as "Y-type composition for adhesive layer") may also be used which contains, as a main component, an energy ray-curable adhesive resin (hereinafter also referred to as "adhesive resin II") in which an unsaturated group has been introduced into the side chain of a non-energy ray-curable adhesive resin, and does not contain any energy ray-curable compound other than the adhesive resin.

[0058] Furthermore, as the composition for adhesive layer constituting the energy ray-curable adhesive, a combination of X type and Y type may be used, i.e., a composition for energy ray-curable adhesive layer containing an energy ray-curable adhesive resin II as a main component and also containing an energy ray-curable compound other than the adhesive resin (hereinafter also referred to as an "XY-type composition for adhesive layer").

[0059] However, the pressure-sensitive adhesive layer may be formed from a non-energy ray-curable pressure-sensitive adhesive that does not cure even when irradiated with energy rays. The pressure-sensitive adhesive layer composition constituting the non-energy ray-curable pressure-sensitive adhesive contains at least the non-energy ray-curable pressure-sensitive adhesive resin I, but does not contain the above-mentioned energy ray-curable pressure-sensitive adhesive resin II or energy ray-curable compound.

[0060] In this embodiment, in order to achieve the above-mentioned physical properties of the pressure-sensitive adhesive layer, it is preferable to use an XY-type pressure-sensitive adhesive layer composition as the energy ray-curable pressure-sensitive adhesive. By using an XY-type composition, the polymer structure of the pressure-sensitive adhesive resin II contains a flowable energy ray-curable compound, making it easier to control stress relaxation properties within a range that does not affect the shear storage modulus. Furthermore, while the composition has sufficient adhesive properties before energy ray curing, it is easier to sufficiently reduce the peel strength against the workpiece after energy ray curing.

[0061] In the following description, the term "adhesive resin" refers to one or both of the above-mentioned adhesive resin I and adhesive resin II. Specific examples of adhesive resins include acrylic resins, urethane resins, rubber resins, and silicone resins. In this embodiment, acrylic adhesives are preferred from the viewpoints of easily controlling the shear storage modulus and shear stress relaxation rate of the adhesive layer within the above-mentioned ranges and reducing costs.

[0062] The acrylic adhesive in which an acrylic resin is used as the adhesive resin will be described in more detail below.

[0063] (3.3.1. Acrylic Polymers) An acrylic polymer is used for the acrylic resin. The acrylic polymer is obtained by polymerizing a monomer containing at least an alkyl(meth)acrylate, and contains a structural unit derived from the alkyl(meth)acrylate. Examples of the alkyl(meth)acrylate include those having an alkyl group with 1 to 20 carbon atoms, and the alkyl group may be linear or branched. Specific examples of the alkyl(meth)acrylate include methyl(meth)acrylate, ethyl(meth)acrylate, isopropyl(meth)acrylate, n-propyl(meth)acrylate, n-butyl(meth)acrylate, 2-ethylhexyl(meth)acrylate, n-octyl(meth)acrylate, isooctyl(meth)acrylate, nonyl(meth)acrylate, decyl(meth)acrylate, undecyl(meth)acrylate, and dodecyl(meth)acrylate. The alkyl(meth)acrylates may be used alone or in combination of two or more.

[0064] Furthermore, from the viewpoint of improving the adhesive strength of the pressure-sensitive adhesive layer and facilitating control of the shear stress relaxation rate of the pressure-sensitive adhesive layer within the above-mentioned range, the acrylic polymer preferably contains a structural unit derived from an alkyl(meth)acrylate in which the alkyl group has 4 or more carbon atoms. The number of carbon atoms in the alkyl(meth)acrylate is preferably 4 to 12, more preferably 4 to 6. Furthermore, the alkyl(meth)acrylate in which the alkyl group has 4 or more carbon atoms is preferably an alkyl acrylate. Examples of such alkyl acrylates include n-butyl acrylate, 2-ethylhexyl acrylate, and dodecyl acrylate.

[0065] In the acrylic polymer, the content of alkyl (meth)acrylate in which the alkyl group has 4 or more carbon atoms is preferably 40 to 98 parts by mass, more preferably 45 to 95 parts by mass, and even more preferably 50 to 90 parts by mass, relative to 100 parts by mass of the total amount of monomers constituting the acrylic polymer (hereinafter simply referred to as "total amount of monomers").

[0066] The acrylic polymer is preferably a copolymer containing, in addition to structural units derived from alkyl (meth)acrylates in which the alkyl group has 4 or more carbon atoms, structural units derived from monomers that, when polymerized to form a homopolymer, yield a polymer with a relatively high glass transition temperature (Tg), from the viewpoints of reducing adhesive residue in the pressure-sensitive adhesive layer, increasing adhesive strength, and facilitating control of the shear storage modulus and shear stress relaxation rate of the pressure-sensitive adhesive layer within the above-mentioned ranges. Specifically, monomers that, when polymerized to form a homopolymer, have a glass transition temperature of 50°C or higher are preferred, monomers with a glass transition temperature of 70°C or higher are more preferred, and monomers with a glass transition temperature of 90°C to 150°C are even more preferred. The Tg of the homopolymer can be determined from values ​​listed in the Polymer Data Handbook, Adhesive Handbook, Polymer Handbook, or the like.

[0067] Examples of such monomers include dimethylacrylamide, methyl methacrylate, acryloylmorpholine, etc. Among these, dimethylacrylamide and methyl methacrylate are preferred, and dimethylacrylamide is more preferred.

[0068] In the acrylic polymer, the content of the monomer having a glass transition temperature of 50°C or higher when forming a homopolymer is preferably 2 to 40 parts by mass, more preferably 5 to 30 parts by mass, and even more preferably 8 to 25 parts by mass, relative to 100 parts by mass of the total amount of monomers.

[0069] The acrylic polymer preferably has a structural unit derived from a functional group-containing monomer in addition to the structural units described above. Examples of the functional group of the functional group-containing monomer include a hydroxyl group, a carboxyl group, an amino group, and an epoxy group. The functional group-containing monomer can react with a crosslinking agent described below to serve as a crosslinking origin, or can react with an unsaturated group-containing substance described below to introduce an unsaturated group into the side chain of the acrylic polymer.

[0070] Examples of functional group-containing monomers include hydroxyl group-containing monomers, carboxyl group-containing monomers, amino group-containing monomers, and epoxy group-containing monomers, which may be used alone or in combination of two or more. Among these, it is preferable to use hydroxyl group-containing monomers and carboxyl group-containing monomers, and it is more preferable to use hydroxyl group-containing monomers.

[0071] Examples of hydroxyl group-containing monomers include hydroxyalkyl (meth)acrylates such as 2-hydroxyethyl acrylate, 2-hydroxyethyl methacrylate, 2-hydroxypropyl (meth)acrylate, 3-hydroxypropyl (meth)acrylate, 2-hydroxybutyl (meth)acrylate, 3-hydroxybutyl (meth)acrylate, and 4-hydroxybutyl (meth)acrylate; and unsaturated alcohols such as vinyl alcohol and allyl alcohol.

[0072] Examples of carboxy group-containing monomers include ethylenically unsaturated monocarboxylic acids such as (meth)acrylic acid and crotonic acid; ethylenically unsaturated dicarboxylic acids such as fumaric acid, itaconic acid, maleic acid and citraconic acid, and anhydrides thereof; and 2-carboxyethyl methacrylate.

[0073] The content of the functional group-containing monomer is preferably 1 to 35 parts by mass, more preferably 3 to 32 parts by mass, and even more preferably 6 to 30 parts by mass, relative to 100 parts by mass of the total amount of the monomers constituting the acrylic polymer.

[0074] In addition to the above, the acrylic polymer may also contain structural units derived from monomers copolymerizable with the above acrylic monomers, such as styrene, α-methylstyrene, vinyltoluene, vinyl formate, vinyl acetate, and acrylonitrile.

[0075] The acrylic polymer can be used as the non-energy ray-curable adhesive resin I. The energy ray-curable adhesive resin II can be obtained by reacting a substance having an energy ray-curable group (also referred to as an unsaturated group-containing substance) with the functional group of the non-energy ray-curable acrylic polymer to bond the same.

[0076] The unsaturated group-containing substance is a substance having both a substituent capable of bonding to the functional group of the acrylic polymer and an energy ray-curable group. Examples of the energy ray-curable group include a (meth)acryloyl group, a vinyl group, an allyl group, and a vinylbenzyl group, with a (meth)acryloyl group being preferred. Furthermore, examples of the substituent possessed by the unsaturated group-containing substance and capable of bonding to the functional group of the acrylic polymer include an isocyanate group and a glycidyl group. Therefore, examples of the unsaturated group-containing substance include (meth)acryloyloxyethyl isocyanate, (meth)acryloyl isocyanate, and glycidyl (meth)acrylate.

[0077] Furthermore, the unsaturated group-containing substance preferably reacts with a portion of the functional groups of the acrylic polymer. Specifically, the unsaturated group-containing substance is preferably reacted with 50 to 98 mol %, more preferably 55 to 93 mol %, of the functional groups of the acrylic polymer. In this way, in the energy ray-curable acrylic resin, some of the functional groups remain unreacted with the unsaturated group-containing substance, making it easier to crosslink with a crosslinking agent. The weight-average molecular weight (Mw) of the acrylic resin is preferably 300,000 to 1,600,000, more preferably 400,000 to 1,400,000, and even more preferably 500,000 to 1,200,000.

[0078] (3.3.2. Energy ray curable compounds) The energy ray-curable compound contained in the X-type or XY-type pressure-sensitive adhesive layer composition is preferably a monomer or oligomer having an unsaturated group in the molecule and capable of being polymerized and cured by energy ray irradiation. 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 urethane (meth)acrylate, polyester (meth)acrylate, polyether (meth)acrylate, and epoxy (meth)acrylate.

[0079] Among these, urethane (meth)acrylate oligomers are preferred from the viewpoint of having a relatively high molecular weight and being less likely to reduce the shear storage modulus of the pressure-sensitive adhesive layer. The molecular weight (weight average molecular weight in the case of an oligomer) of the energy ray-curable compound is preferably 100 to 12,000, more preferably 200 to 10,000, even more preferably 400 to 8,000, and particularly preferably 600 to 6,000.

[0080] The content of the energy ray-curable compound in the X-type composition for adhesive layer is preferably 40 to 200 parts by mass, more preferably 50 to 150 parts by mass, and even more preferably 60 to 90 parts by mass, per 100 parts by mass of the adhesive resin.

[0081] On the other hand, the content of the energy ray-curable compound in the XY-type pressure-sensitive adhesive layer composition is preferably 4 to 90 parts by mass, more preferably 7 to 50 parts by mass, and even more preferably 9 to 25 parts by mass, relative to 100 parts by mass of the pressure-sensitive adhesive resin. By setting the content of the energy ray-curable compound within the above range, it becomes easier to control the shear stress relaxation rate of the pressure-sensitive adhesive layer. Furthermore, in the XY-type pressure-sensitive adhesive layer composition, because the pressure-sensitive adhesive resin is energy ray-curable, even if the content of the energy ray-curable compound is small, it is possible to sufficiently reduce the peel strength after energy ray irradiation.

[0082] (3.3.3. Crosslinking Agents) From the viewpoint of more easily increasing the shear storage modulus of the pressure-sensitive adhesive layer, it is preferable that the composition for a pressure-sensitive adhesive layer further contains a crosslinking agent. The crosslinking agent reacts with functional groups of the pressure-sensitive adhesive resin to crosslink the resins together, for example.

[0083] Examples of crosslinking agents include isocyanate-based crosslinking agents (crosslinking agents having an isocyanate group) such as tolylene diisocyanate, hexamethylene diisocyanate, xylylene diisocyanate, and adducts of these diisocyanates; epoxy-based crosslinking agents (crosslinking agents having a glycidyl group) such as ethylene glycol glycidyl ether; aziridine-based crosslinking agents (crosslinking agents having an aziridinyl group) such as hexa[1-(2-methyl)-aziridinyl]triphosphatriazine; metal chelate-based crosslinking agents (crosslinking agents having a metal chelate structure) such as aluminum chelate; and isocyanurate-based crosslinking agents (crosslinking agents having an isocyanuric acid skeleton). These crosslinking agents may be used alone or in combination of two or more.

[0084] From the viewpoint of improving the cohesive strength of the adhesive and reducing adhesive residue when the adhesive layer is peeled off from the individual workpiece, increasing the shear storage modulus of the adhesive layer and making it easier to control it within the above-mentioned range, and being easy to obtain, it is preferable that the crosslinking agent be an isocyanate-based crosslinking agent.

[0085] The amount of the crosslinking agent to be added 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 4 parts by mass, relative to 100 parts by mass of the adhesive resin, from the viewpoint of promoting the crosslinking reaction.

[0086] (3.3.4. Photopolymerization initiator) When the composition for pressure-sensitive adhesive layer is energy ray-curable, it is preferable that the composition for pressure-sensitive adhesive layer further contains a photopolymerization initiator. By containing the photopolymerization initiator in the composition for pressure-sensitive adhesive layer, the curing reaction proceeds sufficiently even when irradiated with relatively low-energy energy rays such as ultraviolet rays.

[0087] Examples of photopolymerization initiators include photoinitiators such as benzoin compounds, acetophenone compounds, acylphosphine oxide compounds, titanocene compounds, thioxanthone compounds, and peroxide compounds, and photosensitizers such as amines and quinones. Specific examples include α-hydroxycyclohexyl phenyl ketone, benzoin, benzoin methyl ether, benzoin ethyl ether, benzoin isopropyl ether, benzyl diphenyl sulfide, benzyl dimethyl ketal, tetramethylthiuram monosulfide, azobisisobutyronitrile, dibenzyl, diacetyl, β-chloroanthraquinone, bis(2,4,6-trimethylbenzoyl)phenylphosphine oxide, and 2,4,6-trimethylbenzoyldiphenylphosphine oxide. These photopolymerization initiators may be used alone or in combination of two or more.

[0088] The amount of the photopolymerization initiator to be added 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 5 parts by mass, relative to 100 parts by mass of the adhesive resin.

[0089] (3.3.5. Other Additives) The composition for pressure-sensitive adhesive layer may contain other additives within the range that does not impair the effects of the present invention. Examples of other additives include antistatic agents, antioxidants, softeners (plasticizers), fillers, rust inhibitors, pigments, dyes, etc. When these additives are added, the amount of the additives added is preferably 0.01 to 6 parts by mass per 100 parts by mass of the pressure-sensitive adhesive resin.

[0090] (3.4. Glass transition temperature of adhesive layer) In this embodiment, the glass transition temperature (Tg) of the adhesive layer is preferably −50°C or higher and 30°C or lower. As described above, during backside grinding, the workpiece (including the case where the workpiece is a group of individualized workpieces) is heated to approximately 50 to 60°C due to grinding heat. Heating is not performed at the same temperature rise rate across the entire surface of the workpiece, and as grinding progresses, temperature non-uniformity may occur within the grinding surface of the workpiece. Along with this heating, the adhesive layer in direct contact with the workpiece is also heated to a similar temperature. On the other hand, when the adhesive layer is made of an adhesive resin, the physical properties of the adhesive resin tend to change significantly near the glass transition temperature of the adhesive resin.

[0091] For example, if the glass transition temperature of the adhesive layer is higher than the above range, the physical properties of the adhesive layer are likely to change as the backgrinding proceeds. In particular, as described above, if the temperature of the workpiece becomes non-uniform within the surface, the physical properties of the adhesive layer are likely to become non-uniform within the surface. As a result, cracks tend to occur more easily in the individual workpieces. Therefore, to prevent significant changes in the physical properties of the adhesive layer during backgrinding, it is preferable that the glass transition temperature of the adhesive layer be away from the temperature (50 to 60°C) to which the adhesive layer is heated during backgrinding.

[0092] As described above, in this embodiment, the composition for pressure-sensitive adhesive layer preferably contains a monomer having a high homopolymer glass transition temperature, for the purposes of reducing adhesive residue in the pressure-sensitive adhesive layer and increasing adhesive strength, etc. Therefore, even when the composition for pressure-sensitive adhesive layer contains a monomer having a high homopolymer glass transition temperature, it is preferable to control the glass transition temperature of the pressure-sensitive adhesive layer within the above range.

[0093] The glass transition temperature of the pressure-sensitive adhesive layer is more preferably −40° C. or higher, even more preferably −30° C. or higher, even more preferably −20° C. or higher, and particularly preferably −10° C. or higher. On the other hand, the glass transition temperature of the pressure-sensitive adhesive layer is more preferably 20° C. or lower, even more preferably 10° C. or lower, and particularly preferably less than 0° C.

[0094] The glass transition temperature of the pressure-sensitive adhesive layer can be measured as follows. First, a measurement sample of a predetermined size is prepared from the material constituting the pressure-sensitive adhesive layer. Using a dynamic viscoelasticity measuring device, the measurement sample is twisted at a predetermined frequency within a predetermined temperature range to apply shear strain to the measurement sample, and the storage modulus and loss modulus of the measurement sample are measured, and the loss tangent (tan δ) at each temperature is calculated. The peak temperature of the measured loss tangent is taken as the glass transition temperature (Tg) of the pressure-sensitive adhesive layer. Details of the measurement will be explained in the Examples.

[0095] In this embodiment, the thickness of the adhesive layer is preferably less than 50 μm, more preferably 45 μm or less, and even more preferably 40 μm or less. By keeping the thickness of the adhesive layer within the above range, minute movements of the workpiece pieces due to pressure applied to the workpiece or the group of workpiece pieces during grinding can be suppressed. As a result, the probability of contact between the workpiece pieces is reduced, and the crack occurrence rate can be further suppressed.

[0096] On the other hand, from the viewpoint of embedding circuits, electrodes, etc. formed on the workpiece in the adhesive layer, the thickness of the adhesive layer is preferably 10 μm or more.

[0097] The thickness of the pressure-sensitive adhesive layer refers to the thickness of the entire pressure-sensitive adhesive layer. For example, the thickness of a pressure-sensitive adhesive layer composed of multiple layers refers to the total thickness of all layers constituting the pressure-sensitive adhesive layer.

[0098] (4. Physical properties of protective sheets for workpiece processing) In this embodiment, in addition to the physical properties of the adhesive layer described above, the physical properties of the protective sheet for workpiece processing are controlled as follows.

[0099] (4.1. Elongation of protective sheet for workpiece processing) In this embodiment, the elongation of the protection sheet for workpiece processing is 2.5% or less at 23° C. This elongation is the elongation when the tensile load first reaches 30 N / 15 mm after starting to pull both ends of the protection sheet for workpiece processing.

[0100] This parameter assumes a situation in which the workpiece processing protection sheet is attached to the workpiece while tension is being applied to it. Since the atmosphere in which the workpiece processing protection sheet is attached to the workpiece is usually room temperature, the elongation of the workpiece processing protection sheet at 23°C is specified as the parameter.

[0101] By ensuring that the elongation of the workpiece processing protective sheet at 23°C is within the above range, deformation of the workpiece processing protective sheet during back grinding caused by tensile stress due to tension applied when the workpiece processing protective sheet is attached can be suppressed, thereby suppressing shifting of the workpiece individual pieces caused by deformation of the workpiece processing protective sheet.

[0102] The elongation of the protection sheet for workpiece processing at 23°C is preferably 2.1% or less, more preferably 1.8% or less, and even more preferably 1.5% or less.

[0103] The elongation of the protection sheet for workpiece processing at 23° C. can be measured using a tensile tester. Details of the measurement will be explained in the Examples.

[0104] (4.2. Tensile stress relaxation rate of protective sheet for workpiece processing) In this embodiment, the tensile stress relaxation rate of the workpiece processing protection sheet is preferably less than 40% at 23° C. This tensile stress relaxation rate is calculated from the stress at the point when both ends of the workpiece processing protection sheet are pulled and the sheet is stretched by 10% from the length before pulling, and the stress one minute after pulling is stopped at the point when the sheet is stretched by 10%.

[0105] By keeping the tensile stress relaxation rate within the above range, the workpiece processing protection sheet is supported and fixed to the suction table without deformation as a whole during backside grinding, which in turn reduces the amount of movement of the workpiece (single workpiece group) held by the workpiece processing protection sheet, thereby further reducing cracks caused by collisions between the single workpieces.

[0106] The tensile stress relaxation rate of the protection sheet for workpiece processing at 23°C is more preferably 38% or less, even more preferably 36% or less, and particularly preferably 34% or less.

[0107] Furthermore, the lower limit of the tensile stress relaxation rate of the workpiece processing protection sheet at 23°C is not particularly limited, but from the viewpoints of ease of application of the workpiece processing protection sheet and cost, it is preferably 5% or more, and more preferably 10% or more.

[0108] The tensile stress relaxation rate of the protection sheet for workpiece processing at 23° C. can be measured using a tensile tester. Details of the measurement will be explained in the Examples.

[0109] (5.Buffer layer) 1A, the protective sheet for workpiece processing may have other layers as long as the effects of the present invention are obtained. That is, as long as the protective sheet has a configuration in which the pressure-sensitive adhesive layer 20 is disposed on the substrate 10, for example, other layers may be formed between the substrate 10 and the pressure-sensitive adhesive layer 20, or a release sheet may be disposed on the main surface 20a of the pressure-sensitive adhesive layer 20 to protect the pressure-sensitive adhesive layer 20 until it is attached to the adherend.

[0110] 1B, the protective sheet for workpiece processing 1 preferably has a buffer layer 30 in addition to the substrate 10 and the adhesive layer 20. The buffer layer 30 is formed on the main surface 10b of the substrate opposite to the main surface 10a on which the adhesive layer 20 is formed.

[0111] Furthermore, a layer that exhibits a desired function may be formed on the outermost surface of the protection sheet for workpiece processing shown in FIGS. 1A and 1B, if necessary.

[0112] The buffer layer 30 is a softer layer than the base material, and may further reduce the stress generated during back grinding of the workpiece, thereby further preventing cracks from occurring in the workpiece. Furthermore, the workpiece to which the workpiece processing protective sheet is attached is placed on the suction table via the workpiece processing protective sheet during back grinding, and the inclusion of the buffer layer as a constituent layer of the workpiece processing protective sheet makes it easier to properly hold the workpiece on the suction table.

[0113] On the other hand, from the viewpoint of reducing the cost of raw materials and reducing the risk of thickness variations occurring during the production of the protection sheet for workpiece processing due to an increase in the number of thick layers that constitute it, it is preferable to have substantially no buffer layer 30. "Substantially no buffer layer" means that there is no buffer layer at all or that the thickness is less than 1 μm.

[0114] The thickness of the buffer layer is preferably 1 to 100 μm, more preferably 5 to 80 μm, and even more preferably 10 to 60 μm. By setting the thickness of the buffer layer within the above range, the buffer layer can appropriately relieve stress during back grinding.

[0115] The buffer layer may be a layer formed from a buffer layer composition containing an energy ray-polymerizable compound, or may be a film such as a polypropylene film, an ethylene-vinyl acetate copolymer film, an ionomer resin film, an ethylene-(meth)acrylic acid copolymer film, an ethylene-(meth)acrylic acid ester copolymer film, an LDPE film, or an LLDPE film.

[0116] The substrate having a buffer layer can be obtained by laminating a buffer layer onto a substrate.

[0117] (5.1 Composition for buffer layer) The buffer layer composition containing the energy ray-polymerizable compound can be cured by being irradiated with energy rays.

[0118] More specifically, the buffer layer composition containing the energy ray-polymerizable compound preferably contains a urethane (meth)acrylate (d1) and a polymerizable compound (d2) having an alicyclic or heterocyclic group with 6 to 20 ring atoms and / or a polyfunctional polymerizable compound (d3). The buffer layer composition may contain a polymerizable compound (d4) having a functional group in addition to the components (d1) to (d3). The buffer layer composition may also contain a photopolymerization initiator in addition to the above components. The buffer layer composition may also contain other additives and resin components within the range that does not impair the effects of the present invention.

[0119] Hereinafter, each component contained in the buffer layer composition containing the energy ray-polymerizable compound will be described in detail.

[0120] (5.1.1 Urethane (meth)acrylate (d1)) The urethane (meth)acrylate (d1) is a compound having at least a (meth)acryloyl group and a urethane bond, and has the property of being polymerized and cured by irradiation with energy rays. The urethane (meth)acrylate (d1) is an oligomer or a polymer.

[0121] The weight-average molecular weight (Mw) of component (d1) is preferably 1,000 to 100,000, more preferably 2,000 to 60,000, and even more preferably 3,000 to 20,000. The number of (meth)acryloyl groups (hereinafter also referred to as "number of functional groups") in component (d1) may be monofunctional, bifunctional, or trifunctional or higher, but is preferably monofunctional or bifunctional.

[0122] Component (d1) can be obtained, for example, by reacting a polyol compound with a polyvalent isocyanate compound to obtain a terminal isocyanate urethane prepolymer, and then reacting the resulting prepolymer with a (meth)acrylate having a hydroxyl group. Component (d1) may be used alone or in combination of two or more.

[0123] The content of component (d1) in the buffer layer composition is preferably 10 to 70 parts by mass, more preferably 20 to 60 parts by mass, and even more preferably 25 to 55 parts by mass, per 100 parts by mass of the buffer layer composition.

[0124] (5.1.2. Polymerizable Compound (d2) Having an Alicyclic or Heterocyclic Group with 6 to 20 Ring Atoms) Component (d2) is a polymerizable compound having an alicyclic or heterocyclic group with 6 to 20 ring atoms, and is preferably a compound having at least one (meth)acryloyl group, more preferably a compound having one (meth)acryloyl group. Use of component (d2) can improve the film-forming properties of the resulting buffer layer composition.

[0125] Although the definition of component (d2) overlaps with the definitions of components (d3) and (d4) described below, the overlapping portions are included in component (d3) or component (d4). For example, a compound having at least one (meth)acryloyl group, an alicyclic or heterocyclic group having 6 to 20 ring atoms, and a functional group such as a hydroxyl group, an epoxy group, an amide group, or an amino group is included in the definitions of both component (d2) and component (d4), and in the present invention, such a compound is considered to be included in component (d4).

[0126] Specific examples of component (d2) include alicyclic group-containing (meth)acrylates such as isobornyl (meth)acrylate, heterocyclic group-containing (meth)acrylates such as tetrahydrofurfuryl (meth)acrylate, etc. Component (d2) may be used alone or in combination of two or more.

[0127] The content of component (d2) in the buffer layer composition is preferably 10 to 70 parts by mass, more preferably 20 to 60 parts by mass, and even more preferably 25 to 55 parts by mass, per 100 parts by mass of the buffer layer composition.

[0128] (5.1.3. Polyfunctional polymerizable compound (d3)) A polyfunctional polymerizable compound refers to a compound having two or more energy ray-curable groups. The energy ray-curable group is a functional group containing a carbon-carbon double bond, such as a (meth)acryloyl group, a vinyl group, an allyl group, or a vinylbenzyl group. Two or more types of energy ray-curable groups may be combined. A three-dimensional network structure (crosslinked structure) is formed by reaction between the energy ray-curable group in the polyfunctional polymerizable compound and the (meth)acryloyl group in component (d1), or by reaction between the energy ray-curable groups in component (d3). When a polyfunctional polymerizable compound is used, the crosslinked structure formed by energy ray irradiation increases compared to when a compound containing only one energy ray-curable group is used. This results in the buffer layer exhibiting unique viscoelasticity and making it easier to relieve stress during backgrinding.

[0129] Although the definition of component (d3) overlaps with the definition of component (d4) described below, the overlapping portion is included in component (d3). For example, a compound containing a functional group such as a hydroxyl group, an epoxy group, an amide group, or an amino group and having two or more (meth)acryloyl groups is included in the definitions of both component (d3) and component (d4), and in the present invention, such a compound is considered to be included in component (d3).

[0130] From the above viewpoints, the number of energy ray-curable groups (number of functional groups) in the polyfunctional polymerizable compound is preferably 2 to 10, and more preferably 3 to 6.

[0131] The weight average molecular weight of the component (d3) is preferably 30 to 40,000, more preferably 100 to 10,000, and even more preferably 200 to 1,000.

[0132] Specific examples of component (d3) include diethylene glycol di(meth)acrylate, ethylene glycol di(meth)acrylate, tetraethylene glycol di(meth)acrylate, neopentyl glycol di(meth)acrylate, 1,6-hexanediol di(meth)acrylate, trimethylolpropane tri(meth)acrylate, pentaerythritol tri(meth)acrylate, pentaerythritol tetra(meth)acrylate, dipentaerythritol hexa(meth)acrylate, divinylbenzene, vinyl (meth)acrylate, divinyl adipate, and N,N'-methylenebis(meth)acrylamide. Among these, neopentyl glycol di(meth)acrylate and dipentaerythritol hexa(meth)acrylate are preferred. Component (d3) may be used alone or in combination of two or more.

[0133] The content of component (d3) in the buffer layer composition is preferably 2 to 40 parts by mass, more preferably 3 to 20 parts by mass, and even more preferably 5 to 15 parts by mass, per 100 parts by mass of the buffer layer composition.

[0134] (5.1.4 Polymerizable compound having a functional group (d4)) Component (d4) is a polymerizable compound containing a functional group such as a hydroxyl group, an epoxy group, an amide group, or an amino group, and is preferably a compound having at least one (meth)acryloyl group, more preferably a compound having one (meth)acryloyl group.

[0135] Component (d4) has good compatibility with component (d1), making it easier to adjust the viscosity of the buffer layer composition within an appropriate range, and also ensuring good buffer performance even when the buffer layer is relatively thin.

[0136] Examples of component (d4) include hydroxyl group-containing (meth)acrylates, epoxy group-containing compounds, amide group-containing compounds, amino group-containing (meth)acrylates, etc. Among these, hydroxyl group-containing (meth)acrylates are preferred.

[0137] In order to improve the film-forming properties of the buffer layer composition, the content of component (d4) in the buffer layer composition is preferably 5 to 40 parts by mass, more preferably 7 to 35 parts by mass, and even more preferably 10 to 30 parts by mass, per 100 parts by mass of the buffer layer composition.

[0138] (5.1.5 Polymerizable Compound (d5) Other Than Components (d1) to (d4)) The buffer layer-forming composition may contain a polymerizable compound (d5) other than the above components (d1) to (d4) within the range that does not impair the effects of the present invention.

[0139] Examples of the component (d5) include alkyl (meth)acrylates having an alkyl group with 1 to 20 carbon atoms; vinyl compounds, and the like.

[0140] The content of component (d5) in the buffer layer composition is preferably 0 to 20 parts by mass, more preferably 0 to 10 parts by mass, and even more preferably 0 to 5 parts by mass, per 100 parts by mass of the buffer layer composition.

[0141] 5.1.6 Photoinitiators The buffer layer composition preferably further contains a photopolymerization initiator from the viewpoint of shortening the polymerization time by light irradiation and reducing the amount of light irradiation when forming the buffer layer.

[0142] Examples of the photopolymerization initiator include benzoin compounds, acetophenone compounds, acylphosphinoxide compounds, titanocene compounds, thioxanthone compounds, peroxide compounds, and further photosensitizers such as amines and quinones, and more specific examples include 1-hydroxycyclohexyl phenyl ketone, 2-hydroxy-2-methyl-1-phenyl-propan-1-one, etc. These photopolymerization initiators can be used alone or in combination of two or more.

[0143] The content of the photopolymerization initiator in the composition for the buffer layer is preferably 0.05 to 15 parts by mass, more preferably 0.1 to 10 parts by mass, and even more preferably 0.3 to 5 parts by mass, relative to 100 parts by mass of the total amount of the energy ray-polymerizable compounds.

[0144] (5.1.7 Other additives) The buffer layer composition may contain other additives as long as the effects of the present invention are not impaired. Examples of other additives include antistatic agents, antioxidants, softeners (plasticizers), fillers, rust inhibitors, pigments, and dyes. When these additives are added, the content of each additive in the buffer layer composition is preferably 0.01 to 6 parts by mass, and more preferably 0.1 to 3 parts by mass, per 100 parts by mass of the total amount of the energy ray-polymerizable compounds.

[0145] The buffer layer formed from the buffer layer composition containing the energy ray-polymerizable compound is obtained by polymerizing and curing the buffer layer composition having the above-described composition by energy ray irradiation. In other words, the buffer layer is a product obtained by curing the buffer layer composition.

[0146] (6. Manufacturing method of protective sheet for workpiece processing) The method for producing the protective sheet for workpiece processing according to this embodiment may be any known method. For example, a protective sheet for workpiece processing having a substrate and a pressure-sensitive adhesive layer formed on one main surface of the substrate may be produced as follows.

[0147] First, a composition for forming the adhesive layer is prepared, for example, a composition for the adhesive layer that constitutes the adhesive layer, or a composition obtained by diluting the composition for the adhesive layer with a solvent (these two compositions are referred to as "adhesive layer coating agent"). The prepared adhesive layer coating agent is applied to the release surface of a release film and dried as necessary to form an adhesive layer on the release film. Then, one main surface of the substrate and the adhesive layer are bonded together to obtain a protective sheet for workpiece processing in which the adhesive layer is formed on one main surface of the substrate. Alternatively, the prepared adhesive layer coating agent may be applied directly to one main surface of the substrate to form the adhesive layer.

[0148] In addition, a protective sheet for workpiece processing having a substrate, an adhesive layer formed on one main surface of the substrate, and a buffer layer formed on the other main surface of the substrate may be manufactured as follows.

[0149] Similarly to the above, a coating agent for a pressure-sensitive adhesive layer for forming a pressure-sensitive adhesive layer is prepared. Subsequently, as a composition for forming a buffer layer, for example, a buffer layer composition constituting the buffer layer, or a composition obtained by diluting the buffer layer composition with a solvent (these two compositions are referred to as "buffer layer coating agent"). The prepared buffer layer coating agent is applied to the release surface of a release film, dried as necessary to form a coating film on the release film, and the coating film is cured (for example, by irradiation with energy rays) to form a buffer layer. Thereafter, one main surface of the substrate and the buffer layer are bonded together. If this buffer layer still has energy ray curability, it may be further cured (for example, by irradiation with energy rays) as necessary.

[0150] In addition, the prepared adhesive layer coating agent is applied to the release surface of the release film, and if necessary, dried to form an adhesive layer on the release film.Then, the main surface of the substrate on which the buffer layer is not formed is bonded to the adhesive layer, so that the adhesive layer is formed on one main surface of the substrate, and the buffer layer is formed on the other main surface of the substrate to obtain a workpiece processing protection sheet.Similar to the case of forming the above-mentioned adhesive layer, the buffer layer coating agent can be directly applied to one main surface of the substrate to form a buffer layer.

[0151] (7. Manufacturing method of workpiece singulation) As described above, the protective sheet for workpiece processing according to the present invention is suitably used in a method for dividing a workpiece into individual pieces using LDBG.

[0152] As a non-limiting example of the use of the protection sheet for workpiece processing, a method for producing individual workpieces (for example, chips) using LDBG will be specifically described below.

[0153] Specifically, the method for manufacturing the workpiece singulation includes at least the following steps 1 to 4. Step 1: A process of attaching the above-mentioned workpiece processing protection sheet to the surface of the workpiece. Step 2: A step of forming a modified region inside the workpiece from the front or back surface of the workpiece. Step 3: A step of grinding the workpiece, on whose surface a protective sheet for workpiece processing has been attached and on which a modified region has been formed, from the back side to separate the workpiece into a plurality of individual workpieces, starting from the modified region. Step 4: A step of peeling off the workpiece processing protection sheet from the divided workpieces (i.e., multiple divided workpieces) Each step of the method for manufacturing the above-mentioned workpiece singulation will be described in detail below, using a wafer as a specific example of the workpiece and a chip as a specific example of the workpiece singulation.

[0154] (Process 1) In step 1, the adhesive layer of the protective sheet for workpiece processing according to this embodiment is applied to the wafer surface. At this time, tension is applied to the protective sheet for workpiece processing. However, since the tensile stress relaxation rate of the protective sheet for workpiece processing is within the above-mentioned range, the protective sheet for workpiece processing is not deformed during back grinding and is sufficiently fixed to the suction table. As a result, chip movement during back grinding is suppressed, and cracks are suppressed. This step may be performed after step 2 described below, but is preferably performed before step 2 to reduce the risk of unintentional separation of the wafer when the protective sheet for workpiece processing is applied.

[0155] In addition, a circuit is formed on the surface of the wafer. Formation of the circuit on the wafer surface can be carried out by various methods including conventionally widely used methods such as etching and lift-off.

[0156] The formed circuit may be exposed, or a circuit protection layer may be formed to protect the circuit. Furthermore, convex electrodes such as bumps and pillars may be formed on the circuit.

[0157] (Process 2) In step 2, a modified region is formed inside the wafer from the front or back surface of the wafer.

[0158] The modified region formed in this process is an embrittled portion of the wafer. The modified region is prone to cracking due to shear forces and pressure applied to the wafer. Such cracks become the starting point for dividing the wafer. In other words, the modified region in process 2 is formed so as to follow the dividing line that will be formed when the wafer is divided into individual chips in process 3, which will be described later.

[0159] The modified region is formed by irradiating a laser focused on the inside of the wafer. Therefore, the modified region is formed inside the wafer. The laser irradiation may be performed from the front side or the back side of the wafer. Note that when step 2 is performed after step 1 and the laser is irradiated from the front side of the wafer, the laser is irradiated onto the wafer through a workpiece processing protection sheet.

[0160] The wafer with the workpiece processing protection sheet attached and the modified region formed thereon is placed on the suction table and held by the suction table, with the front side of the wafer positioned on the suction table via the workpiece processing protection sheet and adsorbed.

[0161] (Step 3) After steps 1 and 2, the backside of the wafer on the suction table is ground to separate the wafer into a plurality of chips.

[0162] Here, the backside grinding may be performed until the grinding surface (wafer backside) reaches the modified region, but the grinding surface does not have to reach the modified region strictly. That is, the grinding may be performed to a position close to the modified region so that the wafer is divided starting from the modified region to obtain individual chips.

[0163] After the backside grinding using the grinding wheel is completed, stress relief such as dry polishing may be carried out.

[0164] The shape of the individual chips may be square or may be elongated, such as rectangular. The thickness of the individual chips is not particularly limited, but is preferably about 5 to 100 μm, more preferably 10 to 45 μm. LDBG makes it easy to make the thickness of the individual chips 50 μm or less, more preferably 10 to 45 μm. The size of the individual chips is not particularly limited. For example, the chip area is preferably 600 mm 2 Less than 400mm, preferably 2 Less than 120mm, more preferably 2 is less than.

[0165] By using the protection sheet for workpiece processing according to this embodiment, large cracks that lead to chip defects are reduced in chips after backside grinding (step 3) is completed.

[0166] (Step 4) Next, the protective sheet for workpiece processing is peeled off from the individual wafer (i.e., the group of chips). This step is performed, for example, by the following method.

[0167] First, when the adhesive layer of the protection sheet for workpiece processing is formed from an energy ray-curable adhesive, the adhesive layer is cured by irradiating it with energy rays. For example, the irradiance of the energy rays is 120 to 280 mW / cm 2 The energy ray dose is 100-1000mJ / cm 2 Preferably, the energy beam is ultraviolet light. Next, a pickup tape is attached to the back side of the group of chips, and the chips are positioned and oriented so that they can be picked up. At this time, a ring frame located on the outer periphery of the wafer is also attached to the pickup tape, and the outer edge of the pickup tape is fixed to the ring frame. The wafer and ring frame may be attached to the pickup tape simultaneously, or they may be attached at different times. Next, the workpiece processing protection sheet is peeled off from the multiple chips held on the pickup tape.

[0168] The chips are then picked up from the pickup tape. The chips are then fixed onto a substrate or the like for a device to manufacture the device. For example, if the chips are semiconductors, the chips are fixed onto a substrate or the like for a semiconductor device to manufacture the semiconductor device.

[0169] The pickup tape is not particularly limited, but may be, for example, an adhesive sheet including a substrate and an adhesive layer provided on one surface of the substrate.

[0170] Although the embodiments of the present invention have been described above, the present invention is not limited to the above-described embodiments and may be modified in various ways within the scope of the present invention. [Example]

[0171] The present invention will be described in more detail below using examples, but the present invention is not limited to these examples.

[0172] The measurement and evaluation methods in the present examples are as follows.

[0173] (Shear storage modulus of adhesive layer) In the Examples and Comparative Examples described below, a pressure-sensitive adhesive layer was formed on a release film using a pressure-sensitive adhesive layer composition. A plurality of pressure-sensitive adhesive layers thus formed were prepared, and the release films were peeled off, and the layers were laminated together with their release surfaces facing each other to produce a pressure-sensitive adhesive layer laminate having a thickness of 1 mm.

[0174] The obtained laminate of the pressure-sensitive adhesive layer was punched out into a cylindrical shape with a diameter of 8 mm, which was used as a sample for measuring the shear storage modulus.

[0175] The shear storage modulus (G') of the pressure-sensitive adhesive layer was measured using an Anton Paar MCR302 rheometer. Both ends of the sample in the thickness direction were sandwiched between parallel plates, and the shear storage modulus was measured by twisting the sample around the thickness direction as the axis of rotation under the following conditions: measurement temperature -40 to 100°C, heating rate 3°C / min, gap 1 mm, strain 0.05 to 0.5%, and angular frequency 1 Hz, applying shear force to the sample. The shear storage modulus (G') at 55°C was calculated from the obtained measurements.

[0176] (Shear stress relaxation rate of adhesive layer) A sample for measuring the shear stress relaxation rate was prepared in the same manner as the sample for measuring the shear storage modulus. The shear stress relaxation rate of the pressure-sensitive adhesive layer was measured using an Anton Paar MCR302 rheometer. While heating the sample and maintaining it at 55°C, the sample was twisted around the thickness direction of the sample as the axis of rotation under conditions of a gap of 1 mm and an angular frequency of 1 Hz, applying shear stress to the sample. The stress at the moment (0 seconds) when the sample reached 5% strain (angle 18°) was defined as A0, and the stress generated 1 second later while maintaining 5% strain was defined as A1. The shear stress relaxation rate was calculated using the following formula: Shear stress relaxation rate = {(A0-A1) / A0} x 100 (%)

[0177] (Glass transition temperature (Tg) of adhesive layer) Samples for measuring the glass transition temperature (Tg) were prepared in the same manner as the samples for measuring the shear storage modulus. The glass transition temperature of the pressure-sensitive adhesive layer was measured using an Anton Paar MCR302 rheometer. Both ends of the sample in the thickness direction were sandwiched between parallel plates, and the sample was twisted around the thickness direction of the sample under the following conditions: a measurement temperature of -40 to 100°C, a heating rate of 3°C / min, a gap of 1 mm, a strain of 0.05 to 0.5%, and an angular frequency of 1 Hz. A shear force was applied to the sample by twisting the sample. The loss modulus was measured, and the loss tangent tanδ at each temperature was calculated using the loss modulus and the shear storage modulus. The peak temperature was determined from the resulting tanδ chart at each temperature, and this was taken as the glass transition temperature (Tg) of the pressure-sensitive adhesive layer.

[0178] (Elongation and tensile stress relaxation rate of protective sheets for workpiece processing) The protective sheets for workpiece processing prepared in the examples and comparative examples were cut to a size of 140 mm in length and 15 mm in width to obtain samples for measuring elongation and tensile stress relaxation rate. Using a universal tensile tester (Shimadzu Corporation, Autograph (registered trademark) AG-10kNIS), both ends of the sample in the longitudinal direction were gripped with 20 mm of gripping tools (i.e., the initial gripping distance was 100 mm), and the sample was stretched in the longitudinal direction at a rate of 200 mm / min in an environment of 23 °C while recording the tensile load. The elongation of the sample was measured when the tensile load first reached 30 N / 15 mm.

[0179] The specimen was stretched in the longitudinal direction under the above conditions, and the tension was stopped when the specimen was stretched by 10% (i.e., the distance between the grippers was 110 mm). The maximum stress from the start to the end of tension was defined as A (N / m 2 ) and the stress B (N / m 2 The tensile stress relaxation rate was calculated from the measured values ​​of stress A and stress B using the following formula. Tensile stress relaxation rate = {(AB) / A} x 100 (%)

[0180] (Crack occurrence rate) Using a backgrinding tape laminator (Rintec Corporation, RAD-3510F / 12), the workpiece processing protection sheets prepared in the examples and comparative examples were attached to a silicon mirror wafer as a workpiece with a diameter of 300 mm and a thickness of 780 μm. The attachment temperature was 50°C. Next, using a stealth dicing device (Disco Corporation, DFL7361), stealth dicing was performed on the wafer to form a lattice-shaped modified region. The lattice size was 10 mm x 10 mm.

[0181] Next, using a back grinding machine (DISCO Corporation, DGP8761), the surface opposite to the surface on which the workpiece processing protective sheet was attached of the wafer on which the modified region was formed was ground (including dry polishing) to a thickness of 18 μm, and the wafer was divided into multiple chips to form a chip group. After the grinding process, in order to make it easier to observe cracks that had occurred in the chips, dicing tape (Lintec Corporation, D-175D) was attached to the chip group side of the chip group with the workpiece processing protective sheet (i.e., the ground surface) and to the 12-inch ring frame using a wafer mounter (Lintec Corporation, RAD-2510F / 12).

[0182] Next, the workpiece processing protection sheet was irradiated with energy rays (ultraviolet rays), and the workpiece processing protection sheet was peeled off to expose the surface of the wafer (group of chips). Using an infrared camera built into a stealth dicing machine (DISCO DFL7361), cracks in the chips were observed and counted from the wafer surface side. The observation range was a radius of 145 mm from the center of the wafer (290 mm diameter). The observed cracks were classified based on their length as shown below. A crack whose longest length is less than 10 μm is defined as a small crack. A crack whose longest length is between 10 μm and 20 μm is defined as a medium crack. A crack whose longest length is 20 μm or more is defined as a large crack.

[0183] Using the classified crack types, the crack score was calculated according to the following formula. Crack score = 0 x number of small cracks + 1 x number of medium cracks + 10 x number of large cracks In this example, a crack score of 0 or more and 20 or less was rated as A, a crack score of 21 or more and 40 or less was rated as B, a crack score of 41 or more and 55 or less was rated as C, and a crack score of 56 or more was rated as D. Samples rated as A and B were deemed to have passed.

[0184] Example 1 (1) Base material First, a PET film with an easy-adhesion coating layer on both sides (thickness: 50 μm, Young's modulus at 23° C.: 4000 MPa) was prepared as a substrate.

[0185] (2) Adhesive layer (Preparation of Composition for Pressure-Sensitive Adhesive Layer) An acrylic polymer was obtained by copolymerizing 52 parts by mass of n-butyl acrylate (BA), 20 parts by mass of dimethylacrylamide (DMAA), and 28 parts by mass of 2-hydroxyethyl acrylate (HEA). 2-Methacryloyloxyethyl isocyanate (MOI) was then reacted with this polymer so that 90 equivalents of the total hydroxyl groups (100 equivalents) of the acrylic polymer were added to the hydroxyl groups. This gave an energy beam-curable acrylic copolymer (Mw: approximately 750,000) (BA / DMAA / HEA (MOI) = 52 / 20 / 28 (90 mol%) (A-1).

[0186] 100 parts by mass of this energy ray-curable acrylic copolymer was blended with 12 parts by mass of a multifunctional urethane acrylate (Mitsubishi Chemical Corporation, Shikoh UT-4332) which is an energy ray-curable resin, 1.07 parts by mass of an isocyanate-based crosslinking agent (Tosoh Corporation, Coronate L), and 1.4 parts by mass of bis(2,4,6-trimethylbenzoyl)phenylphosphine oxide as a photopolymerization initiator, and the mixture was diluted with methyl ethyl ketone to prepare a coating agent for a pressure-sensitive adhesive layer composition with a solids concentration of 34% by mass.

[0187] (3)Buffer layer (Preparation of buffer layer-forming composition) A buffer layer-forming composition was prepared by blending 50 parts by mass (component d1) of a urethane acrylate oligomer (CN8888, manufactured by Sartomer Corporation), 40 parts by mass (component d2) of isobornyl acrylate (IBXA), and 10 parts by mass (component d3) of neopentyl glycol diacrylate as energy ray-polymerizable compounds, and further blending 2.0 parts by mass of 2-hydroxy-2-methyl-1-phenyl-propan-1-one (Omnirad 1173, manufactured by BASF) as a photopolymerization initiator.

[0188] The buffer layer-forming composition was applied to the silicone release-treated surface of a release sheet (manufactured by Lintec Corporation, SP-PET381031, thickness: 38 μm) to form a coating film, which was then semi-cured by irradiating the coating film with ultraviolet light to form a semi-cured buffer layer film with a thickness of 30 μm.

[0189] The ultraviolet irradiation was performed using a belt conveyor type ultraviolet irradiation device (Eye Graphics, ECS-401GX) and a high-pressure mercury lamp (Eye Graphics, H04-L41), with a lamp height of 260 mm, output of 80 W / cm, and illuminance of 70 mW / cm. 2 , irradiation amount 30mW / cm 2 The surface of the semi-cured film thus formed was then bonded to the first coating layer of the substrate, and ultraviolet light was again irradiated from the release sheet side of the semi-cured film to completely cure the semi-cured film and form a buffer layer having a thickness of 30 μm.

[0190] (Production of protective sheets for workpiece processing) The adhesive layer composition was applied to the silicone release-treated surface of a release sheet (Lintec Corporation, SP-PET381031, thickness: 38 μm) and dried by heating to form an adhesive layer with a thickness of 20 μm on the release sheet. The glass transition temperature (Tg) of the adhesive layer was 7.4°C.

[0191] Next, the adhesive layer of the release sheet with the adhesive layer was attached to the second coating layer of the double-sided coated PET film to produce a protective sheet for workpiece processing, i.e., the protective sheet for workpiece processing shown in Figure 1B was produced.

[0192] Example 2 A protective sheet for workpiece processing was obtained in the same manner as in Example 1, except that the acrylic copolymer obtained below was used as the acrylic copolymer and the amount of isocyanate crosslinking agent (Coronate L, manufactured by Tosoh Corporation) added was changed to 0.27 parts by mass. The glass transition temperatures of the pressure-sensitive adhesive layers are shown in Table 1.

[0193] An acrylic polymer was obtained by copolymerizing 70 parts by mass of n-butyl acrylate (BA), 20 parts by mass of methyl methacrylate (MMA), and 10 parts by mass of 2-hydroxyethyl acrylate (HEA). 2-Methacryloyloxyethyl isocyanate (MOI) was then reacted with this polymer so that 70 equivalents of the total hydroxyl groups (100 equivalents) of the acrylic polymer were added to obtain an energy beam-curable acrylic copolymer (Mw: approximately 750,000) (BA / MMA / HEA (MOI) = 70 / 20 / 10 (70 mol%) (A-4).

[0194] Example 3 A protection sheet for workpiece processing was obtained in the same manner as in Example 2, except that the amount of isocyanate-based crosslinking agent (Coronate L, manufactured by Tosoh Corporation) added was changed to 0.54 parts by mass. The glass transition temperature of the pressure-sensitive adhesive layer is shown in Table 1.

[0195] Example 4 A protection sheet for workpiece processing was obtained in the same manner as in Example 2, except that the amount of isocyanate-based crosslinking agent (Coronate L, manufactured by Tosoh Corporation) added was changed to 1.07 parts by mass. The glass transition temperature of the pressure-sensitive adhesive layer is shown in Table 1.

[0196] Example 5 A protective sheet for workpiece processing was obtained in the same manner as in Example 1, except that the acrylic copolymer obtained below was used as the acrylic copolymer and the amount of isocyanate crosslinking agent (Coronate L, manufactured by Tosoh Corporation) added was changed to 0.27 parts by mass. The glass transition temperatures of the pressure-sensitive adhesive layers are shown in Table 1.

[0197] An acrylic polymer was obtained by copolymerizing 80 parts by mass of n-butyl acrylate (BA), 10 parts by mass of methyl methacrylate (MMA), and 10 parts by mass of 2-hydroxyethyl acrylate (HEA). 2-methacryloyloxyethyl isocyanate (MOI) was then reacted with this polymer so that 70 equivalents of the total hydroxyl groups (100 equivalents) of the acrylic polymer were added to obtain an energy beam-curable acrylic copolymer (Mw: approximately 750,000) (BA / MMA / HEA (MOI) = 80 / 10 / 10 (70 mol%) (A-3).

[0198] Example 6 Except for not forming a buffer layer, a protection sheet for workpiece processing was produced in the same manner as in Example 1. The glass transition temperatures of the adhesives are shown in Table 1.

[0199] Example 7 Except for not forming a buffer layer, a protection sheet for workpiece processing was produced in the same manner as in Example 2. The glass transition temperatures of the adhesives are shown in Table 1.

[0200] Example 8 Except for not forming a buffer layer, a protection sheet for workpiece processing was produced in the same manner as in Example 3. The glass transition temperatures of the adhesives are shown in Table 1.

[0201] Example 9 Except for not forming a buffer layer, a protection sheet for workpiece processing was produced in the same manner as in Example 4. The glass transition temperatures of the adhesives are shown in Table 1.

[0202] Example 10 Except for not forming a buffer layer, a protection sheet for workpiece processing was produced in the same manner as in Example 5. The glass transition temperatures of the adhesives are shown in Table 1.

[0203] (Comparative Example 1) A protective sheet for workpiece processing was obtained in the same manner as in Example 1, except that the acrylic copolymer obtained below was used as the acrylic copolymer and the amount of isocyanate crosslinking agent (Coronate L, manufactured by Tosoh Corporation) added was changed to 0.27 parts by mass. The glass transition temperatures of the pressure-sensitive adhesive layers are shown in Table 1.

[0204] An energy beam-curable acrylic copolymer (Mw: approximately 750,000) was obtained by copolymerizing 90 parts by mass of n-butyl acrylate (BA) and 10 parts by mass of 2-hydroxyethyl acrylate (HEA). 2-methacryloyloxyethyl isocyanate (MOI) was then reacted with the acrylic polymer so that 70 equivalents of the total hydroxyl groups (100 equivalents) of the acrylic polymer were added. (BA / HEA (MOI) = 90 / 10 (70 mol%) (A-2).

[0205] (Comparative Example 2) A protection sheet for workpiece processing was obtained in the same manner as in Example 1, except that the acrylic copolymer obtained below was used as the acrylic copolymer. The glass transition temperatures of the pressure-sensitive adhesive layers are shown in Table 1.

[0206] An acrylic polymer was obtained by copolymerizing 85 parts by mass of n-butyl acrylate (BA), 5 parts by mass of methyl methacrylate (MMA), and 10 parts by mass of 2-hydroxyethyl acrylate (HEA). 2-Methacryloyloxyethyl isocyanate (MOI) was then reacted with this polymer so that 70 equivalents of the total hydroxyl groups (100 equivalents) of the acrylic polymer were added to obtain an energy beam-curable acrylic copolymer (Mw: approximately 750,000) (BA / MMA / HEA (MOI) = 85 / 5 / 10 (70 mol%) (A-5).

[0207] (Comparative Example 3) A protection sheet for workpiece processing was obtained in the same manner as in Comparative Example 1, except that the amount of isocyanate-based crosslinking agent (Coronate L, manufactured by Tosoh Corporation) added was changed to 4 parts by mass. The glass transition temperatures of the pressure-sensitive adhesives are shown in Table 1.

[0208] Comparative Example 4 Except for changing the thickness of the substrate to 20 μm, a protection sheet for workpiece processing was obtained in the same manner as in Example 2. Table 1 shows the glass transition temperatures of the adhesives.

[0209] The above measurements and evaluations were carried out on the obtained samples (Examples 1 to 10 and Comparative Examples 1 to 4). The results are shown in Table 1.

[0210] [Table 1]

[0211] From Table 1, it was confirmed that when the shear storage modulus and shear stress relaxation rate of the adhesive and the elongation of the workpiece processing protective sheet are within the above-mentioned ranges, even when the wafer is diced by LDBG, large cracks that lead to chip defects (i.e., defective workpiece diced products) are unlikely to occur. [Explanation of symbols]

[0212] 1...Protection sheet for workpiece processing 10...Base material 20...Adhesive layer 30...Buffer layer

Claims

1. A protective sheet for workpiece processing having a substrate and an adhesive layer disposed on one main surface of the substrate, the pressure-sensitive adhesive layer has a shear storage modulus of 40,000 Pa or more at 55°C and a shear stress relaxation rate after 1 second of 30% or more at 55°C; A protective sheet for workpiece processing, wherein the elongation of the protective sheet for workpiece processing is 2.5% or less when a tensile load reaches 30 N / 15 mm after starting to apply the tensile load to the protective sheet for workpiece processing at 23°C.

2. 2. The protective sheet for workpiece processing according to claim 1, further comprising a buffer layer disposed on the other main surface of the substrate.

3. 3. The workpiece processing protection sheet according to claim 1, wherein the tensile stress relaxation rate of the workpiece processing protection sheet after 1 minute at 23°C is less than 40%.

4. the pressure-sensitive adhesive layer is made of an energy ray-curable acrylic pressure-sensitive adhesive, The protective sheet for workpiece processing according to claim 1 , wherein the acrylic adhesive comprises a polymer in which an energy ray-curable group is bonded to an acrylic polymer, and an energy ray-curable compound.

5. A protective sheet for workpiece processing described in any one of claims 1 to 4, which is attached to the surface of a workpiece in a process of dividing a workpiece into individual workpieces by grinding the back surface of the workpiece having a modified region formed therein.

6. A step of attaching the workpiece processing protection sheet according to any one of claims 1 to 5 to a surface of a workpiece; forming a modified region inside the workpiece from the front or rear surface of the workpiece; a step of grinding the workpiece, on which the workpiece processing protection sheet is attached on its surface and the modified region is formed, from its back surface side to separate the workpiece into a plurality of workpiece individual pieces starting from the modified region; and a step of peeling off the workpiece processing protection sheet from the workpiece after it has been singulated.

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