TW202336852A - Method for manufacturing protective sheet for workpiece processing and workpiece individualized article wherein protective sheet for workpiece processing includes a buffer layer whose stress relaxation rate at 23 DEG C is 50% or less, and whose Young's modulus at 23 DEG C is 400 MPa or more - Google Patents

Abstract

In a workpiece processing protective sheet having a laminated structure of the adhesive layer 12/base material 11/buffer layer 13, grinding chips generated during workpiece processing are prevented from adhering to the buffer layer. A protective sheet for workpiece processing is a protective sheet for workpiece processing having a base material 11, a buffer layer 13 provided on one side of the base material 11, and an adhesive layer 12 provided on the other side of the base material 11. The stress relaxation rate of the buffer layer 13 at 23 DEG C is 50% or less, and the Young's modulus of the buffer layer 13 at 23 DEG C is 400 MPa or more.

Description

Method for manufacturing protective sheet for workpiece processing and individualized workpiece

The present invention relates to a protective sheet for workpiece processing and a method for manufacturing individualized workpieces. In particular, the present invention relates to a protective sheet for workpiece processing that can be suitably used in a method of grinding the back surface of a workpiece and individualizing the workpiece by its stress, and a method of manufacturing an individualized workpiece using the protective sheet for workpiece processing.

As various electronic devices continue to be miniaturized and multifunctional, semiconductor chips mounted on them are also required to be miniaturized and thinned. In order to make the wafer thinner, the back surface of the semiconductor wafer is usually ground to adjust the thickness. Furthermore, in order to obtain a thinner wafer, a process called Dicing Before Grinding (DBG) is sometimes used. This process uses a dicing blade to form a trench of a predetermined depth from the front side of the wafer, and then The wafer is ground from the back side, and the wafer is individualized by grinding to obtain a wafer. In DBG, wafer backside grinding and wafer individualization can be performed simultaneously, so thinner wafers can be manufactured efficiently.

In addition, in recent years, as a modification of the pre-dicing method, a method has been proposed in which a modified region is provided inside the wafer using a laser and the wafer is individualized based on stress during grinding of the back surface of the wafer. Hereinafter, this method is sometimes described as Laser Dicing Before Grinding (LDBG: Laser Dicing Before Grinding). In LDBG, the wafer is cut along the crystallographic direction starting from the modified region, so the occurrence of chipping can be reduced compared with the pre-cutting method using a dicing blade. As a result, a wafer having excellent flexural strength can be obtained, and further, it can contribute to further thinning of the wafer. In addition, compared with DBG, which uses a dicing blade to form a trench of a predetermined depth on the front side of the wafer, there is no area that will be removed from the wafer by the dicing blade, that is, the kerf width is extremely small, so the wafer yield is very Excellent.

In the past, when grinding the backside of workpieces such as semiconductor wafers, or when individualizing workpieces using DBG, LDBG, etc., in order to protect the workpiece or its individualized items and to retain the workpiece and individualized items, the workpiece was usually placed on the workpiece. A protective sheet for workpiece processing called a back polishing sheet is attached. After grinding the back surface, an adhesive tape with an adhesive layer or a protective film-forming tape for forming a protective film is attached to the ground surface. Thereafter, the protective sheet for workpiece processing attached to the front surface of the workpiece is peeled off after the adhesive force is reduced by irradiation with energy rays such as ultraviolet rays. Through such steps, an adhesive layer, a protective film forming layer, etc. can be formed on the individual workpiece.

As a protective sheet for workpiece processing, a laminated protective sheet including a base material, an adhesive layer, and a buffer layer is sometimes used. Specific examples of such a protective sheet for workpiece processing are described in, for example, Patent Document 1 (Japanese Patent Application Laid-Open No. 2015-183008). The buffer layer is designed to absorb vibrations generated during grinding of the workpiece and alleviate unevenness caused by foreign matter to stably keep the workpiece flat. [Prior Technical Document] [Patent Document]

[Patent Document 1] Japanese Patent Application Laid-Open No. 2015-183008

[Problem to be solved by the invention]

As semiconductor equipment becomes smaller, the final thickness of individual workpieces such as wafers tends to become thinner. However, as the thinning of individualized workpieces continues to progress, the phenomenon of so-called "collapse" in which individualized workpieces are damaged increases. As a result of intensively searching for the cause, the inventor of this case made the following findings.

When grinding the back surface of a workpiece such as a semiconductor wafer, the above-mentioned protective sheet for workpiece processing is temporarily adhered to the circuit surface of the workpiece, and the back surface of the workpiece (opposite to the circuit surface) is ground while spraying water. By spraying water, the frictional heat generated during back grinding is removed, and the grinding chips and abrasive grain fragments of the workpiece generated by grinding are washed away. Hereinafter, grinding chips of the workpiece, fragments of abrasive grains, etc. may be collectively referred to as "grinding chips". Furthermore, the water sprayed during grinding is sometimes described as "grinding water". During back grinding, the surface of the workpiece processing protective sheet on the buffer layer side is held on the suction table.

After the backside grinding is completed, release the suction force of the suction table and remove the workpiece processing protective sheet from the suction table. The protective sheet for workpiece processing and the individual workpiece held on it are transported to the next step. When the suction force of the suction table is released, the space between the suction table and the surface of the workpiece processing protective sheet on the buffer layer side is in a negative pressure state. Therefore, part of the grinding water penetrates between the adsorption table and the buffer layer, and the grinding water comes into contact with the buffer layer. Since the grinding water contains grinding chips, when the suction force of the suction table is released, the grinding chips may adhere to the surface of the workpiece processing protective sheet on the buffer layer side.

The workpiece processing protective sheet holding the individualized workpiece is transported to the next step, and various processing is performed on the individualized workpiece. For example, when the individualized workpiece is a semiconductor wafer, an adhesive film for die bonding, a protective film for protecting the back surface of the wafer, etc. can be formed on the grinding surface. During these steps, the buffer layer side of the workpiece processing protective sheet is fixed to the workbench. If grinding chips adhere to the buffer layer, there will be foreign matter between the buffer layer and the workbench. In this state, if pressure is applied when attaching an adhesive film or a protective film, a large force is locally exerted on the individual workpiece near the foreign matter, which may cause the foreign matter (shavings) to serve as a fulcrum. bending and breakage of individual workpieces.

Therefore, in a workpiece processing protective sheet having a laminated structure of an adhesive layer/base material/buffer layer, it is necessary to prevent grinding chips generated during workpiece processing from adhering to the buffer layer. [Means used to solve problems]

The gist of this invention which aims at solving such a problem is as follows. (1) A protective sheet for workpiece processing, which has a base material, a buffer layer provided on one side of the base material, and an adhesive layer provided on the other side of the base material, Wherein, the stress relaxation rate of the buffer layer at 23°C is 50% or less, and the Young's modulus of the buffer layer at 23°C is 400 MPa or more. (2) The protective sheet for workpiece processing according to (1), wherein the Young's modulus of the base material at 23° C. is 1000 MPa or more. (3) The protective sheet for workpiece processing according to (1) or (2), wherein the buffer layer is a cured product of a buffer layer-forming composition containing an energy-beam polymerizable compound. (4) The protective sheet for workpiece processing according to any one of (1) to (3), which is obtained by grinding the back surface of a workpiece having grooves formed on the front surface or a modified area formed inside the workpiece. In the step of personalizing the workpiece, it is attached to the front of the workpiece and used. (5) A method of manufacturing an individualized workpiece, including the step of affixing the workpiece processing protective sheet according to any one of the above (1) to (4) on the front surface of the workpiece, The step of forming a groove from the front side of the above-mentioned workpiece, or forming a modified area inside the workpiece from the front or back side of the above-mentioned workpiece, and A step of grinding the workpiece with the protective sheet attached on the front and having the groove or the modified area formed thereon from the back side, and individualizing the workpiece into a plurality of individualized workpieces using the groove or the modified area as a starting point. [Invention effect]

The protective sheet for workpiece processing of the present invention can prevent grinding chips generated during workpiece processing from adhering to the buffer layer. Therefore, even if the individualized workpiece is processed including pressurization in the next step, damage to the individualized workpiece caused by grinding chips can be reduced.

[Form used to implement the invention]

Hereinafter, the protective sheet for workpiece processing of the present invention will be described in detail. First, the main terms used in this manual will be explained.

The workpiece refers to a plate-shaped object to which the workpiece processing protective sheet of the present embodiment is attached and then individualized. Examples of workpieces include circular wafers (including those with oriented planes), rectangular panel-level packages, strips (rectangular substrates) with molded resin packages, etc. Among them, this issue is easily obtained from From the perspective of effect, wafer is better. The wafer may be, for example, a semiconductor wafer such as silicon wafer, gallium arsenide wafer, silicon carbide wafer, gallium nitride wafer, indium phosphide wafer, etc.; glass wafer, lithium tantalate wafer , insulator wafers such as lithium niobate wafers, etc. Furthermore, it may also be a reprocessed wafer formed of resin and semiconductor used in the production of fan-out packages. From the viewpoint of easily obtaining the effects of the present invention, a semiconductor wafer or an insulator wafer is preferred as the wafer, and a semiconductor wafer is more preferred.

Individualization of workpieces means dividing the workpiece into individual circuits to obtain individualized workpieces. For example, when the workpiece is a semiconductor wafer, the workpiece individualization is a semiconductor wafer, and when the workpiece is a panel-level package or a strip (rectangular substrate) sealed with molded resin, the workpiece individualization is a semiconductor package.

The "front" of the workpiece refers to the surface where circuits, electrodes, etc. are formed, and the "back" of the workpiece refers to the surface where circuits, etc. are not formed. The electrode may be a convex electrode such as a bump.

DBG refers to a method in which a groove of a predetermined depth is formed on the front side of the workpiece and then ground from the back side of the workpiece to individualize the workpiece through grinding. The groove formed on the front side of the workpiece can be formed by blade cutting, laser cutting, plasma cutting, etc.

Furthermore, LDBG is a modification of DBG. It refers to using a laser to set up a relatively fragile modified area inside the workpiece (for example, a wafer), and starting from the modified area through the stress during back grinding. A method of individualizing workpieces by propagating cracks.

The "workpiece individualized object group" refers to a plurality of workpiece individualized objects held on the workpiece processing protective sheet of the present invention after the workpiece is individualized. These individualized objects are arranged as a whole in the same shape as the workpiece. In addition, the "wafer group" refers to a plurality of wafers held on the protective sheet for workpiece processing of the present invention after the wafers as workpieces are individualized. These wafers are arranged as a whole in the same shape as the wafer.

"(Meth)acrylate" is a term that refers to both "acrylate" and "methacrylate", and the same applies to other similar terms.

"Energy ray" refers to ultraviolet rays, electron rays, etc., preferably ultraviolet rays.

Unless otherwise stated, "weight average molecular weight" refers to a polystyrene-converted value measured by gel permeation chromatography (GPC). For measurement by this method, for example, high-speed column "TSK guard column H _XL -H", "TSK Gel GMH _XL ", "TSK Gel G2000 H _XL " (all of the above are manufactured by Tosoh Corporation) Following this procedure, it was connected to the high-speed GPC device "HLC-8120GPC" manufactured by Tosoh Corporation, and the conditions were column temperature: 40°C, liquid feed rate: 1.0 mL/min, and a differential refractometer was used as the detector. .

A release sheet is a sheet that supports the adhesive layer in a peelable manner. The term "sheet" is not limited to thickness and is used to include the concept of film.

The mass ratios in descriptions of compositions such as adhesive layer compositions are calculated based on the active ingredients (solid content), and solvents are not included unless otherwise stated.

Hereinafter, the structure of each component of the protective sheet for workpiece processing of the present invention will be described in more detail. In addition, the protective sheet for workpiece processing of the present invention may be simply called a "protective sheet".

In this embodiment, as shown in FIG. 1 , the protective sheet 10 refers to a laminated body including a base material 11 and an adhesive layer 12 . The protective sheet 10 has a buffer layer 13 on the surface of the base material 11 opposite to the adhesive layer 12 . In addition, other structural layers other than these may be included. For example, a primer layer may be formed on the surface of the base material on the side of the adhesive layer, or a peeling sheet may be layered on the surface of the adhesive layer to protect the adhesive layer until use. Furthermore, the base material may be a single layer or multiple layers. The same goes for the adhesive layer and buffer layer. Hereinafter, the structure of each component of the workpiece processing protective sheet of this embodiment will be described in more detail.

[Substrate 11] As the base material 11, various resin films conventionally used as base materials of protective sheets for semiconductor processing can be used without particular limitation. From the viewpoint of more reliably holding workpieces such as wafers and wafers, the Young's modulus of the base material 11 at 23° C. is preferably 1000 MPa or more. If a base material with a Young's modulus of less than 1000 MPa is used, the protective sheet's ability to hold the workpiece will be reduced, and it will not be able to suppress vibration during backside grinding, making chips and damage to the workpiece prone to occur. On the other hand, by setting the Young's modulus of the base material at 23°C to 1000 MPa or more, the protective sheet's ability to hold the workpiece can be improved, vibrations during backside grinding, etc. can be suppressed, and chipping, damage, etc. of the workpiece can be prevented. . Furthermore, the stress when peeling off the protective sheet from the workpiece can be reduced, and chipping, damage, etc. of the workpiece that may occur when the tape is peeled off can be prevented. In addition, the workability when attaching the protective sheet to the workpiece can be improved. From such a viewpoint, the Young's modulus of the base material at 23° C. is more preferably 1,800 to 30,000 MPa, and further more preferably 2,500 to 6,000 MPa.

The thickness of the base material is not particularly limited, but it is preferably 110 μm or less, more preferably 15 to 110 μm, and still more preferably 20 to 105 μm. By setting the thickness of the base material to 110 μm or less, the peeling force of the protective sheet can be easily controlled. Furthermore, if the thickness is 15 μm or more, the base material can easily function as a support for the protective sheet.

The material of the base material is not particularly limited as long as it satisfies the above-mentioned physical properties, and various resin films can be used. Here, examples of the base material having a Young's modulus at 23° C. of 1000 MPa or more include, for example, polyethylene terephthalate, polyethylene naphthalate, and polyterephthalate. Polyesters such as butylene glycol ester and fully aromatic polyester, polyimide, polyamide, polycarbonate, polyacetal, modified polyphenylene ether, polyphenylene sulfide, polypropylene, polyetherketone , biaxially stretched polypropylene and other resin films.

Among these resin films, it is preferable to include one or more films selected from the group consisting of polyester film, polyamide film, polyimide film, and biaxially stretched polypropylene film, and it is more preferable to include a polyester film. It is further more preferable to include an ethylene terephthalate film.

Furthermore, the base material may contain plasticizers, lubricants, infrared absorbers, ultraviolet absorbers, fillers, colorants, antistatic agents, antioxidants, catalysts, etc. within the scope that does not impair the effects of the present invention. Furthermore, the substrate can be transparent or opaque, and can be colored or evaporated as desired.

Furthermore, at least one surface of the base material may be subjected to an adhesion treatment such as corona treatment to improve adhesion with one of the buffer layer and the adhesive layer. Furthermore, the base material may have the above-mentioned resin film and a primer layer coated on at least one surface of the resin film.

The primer layer-forming composition for forming the primer layer is not particularly limited, and examples thereof include polyester resins, urethane resins, polyester urethane resins, acrylic resins, and the like. composition. The composition for forming a primer layer may optionally contain a crosslinking agent, a photopolymerization initiator, an antioxidant, a softener (plasticizer), a filler, a rust inhibitor, a pigment, a dye, and the like.

The thickness of the primer layer is preferably 0.01 to 10 μm, more preferably 0.03 to 5 μm. In addition, since the thickness of the primer layer in the embodiment of the present application is smaller than the thickness of the base material, the thickness of the resin film having the primer layer is substantially the same as the thickness of the base material. Furthermore, since the material of the primer layer is soft, it has little impact on the Young's modulus. The Young's modulus of the base material, even when there is a primer layer, is essentially the same as the Young's modulus of the resin film. The above is the same.

For example, the Young's modulus of the base material can be controlled by the selection of the resin composition, the addition of a plasticizer, the stretching conditions during the production of the resin film, etc. Specifically, when a polyethylene terephthalate film is used as a base material, the Young's modulus of the base material tends to decrease as the content ratio of the ethylene component in the copolymer component increases. Furthermore, if the compounding amount of the plasticizer is increased relative to the resin composition constituting the base material, the Young's modulus of the base material tends to decrease.

[Adhesive layer 12] The adhesive layer 12 is not particularly limited as long as it has moderate pressure-sensitive adhesiveness at room temperature, but the shear storage modulus at 23° C. is preferably 0.05 to 0.50 MPa. When the workpiece is a semiconductor wafer, the surface of the workpiece is usually uneven due to the formation of circuits and the like. By setting the shear storage modulus of the adhesive layer within the above range, when the protective sheet is attached to a wafer surface that has unevenness, the unevenness on the wafer surface can be fully contacted with the adhesive layer, and the adhesive layer can be properly Expand the adhesion of the adhesive layer. Therefore, the protective sheet can be reliably fixed to the semiconductor wafer, and the wafer surface can be appropriately protected during backside grinding. From these viewpoints, the shear storage modulus of the adhesive layer is preferably 0.12 to 0.35 MPa. Furthermore, when the adhesive layer is formed of an energy ray-curable adhesive, the shear storage modulus of the adhesive layer refers to the shear storage modulus before curing by energy ray irradiation.

The shear storage modulus can be determined by the following method. The measurement sample is obtained by punching an adhesive layer with a thickness of approximately 0.5 to 1 mm into a circular object with a diameter of 7.9 mm. Using the dynamic viscoelasticity measuring device ARES manufactured by Rheometric Corporation, the elastic modulus of the measurement sample was measured when the temperature was changed from -30°C to 150°C at a frequency of 1 Hz and a heating rate of 3°C/min. The elastic modulus at the measurement temperature of 23°C was defined as the shear storage modulus at 23°C.

The thickness of the adhesive layer is preferably less than 100 μm, more preferably 5 to 60 μm, and further preferably 10 to 50 μm. By making the adhesive layer so thin in this way, the generation of chips when cutting the protective sheet is suppressed, and it is easier to further prevent cracking of the individual workpiece that occurs during back grinding.

The adhesive layer can be formed of, for example, an acrylic adhesive, a urethane adhesive, a rubber adhesive, a silicone adhesive, etc., with an acrylic adhesive being preferred. Furthermore, the adhesive layer is preferably formed of an energy ray-curable adhesive. By forming the adhesive layer from an energy ray curable adhesive, the shear storage modulus at 23°C can be set within the above range before energy ray irradiation and curing, and the peeling force after curing can be easily set to 1000 mN/50 mm or less.

Hereinafter, specific examples of the adhesive will be described in detail, but these are non-limiting examples, and the adhesive layer in the present invention should not be construed as being limited thereto.

[Adhesive composition] As the energy ray curable adhesive used to form the adhesive layer, for example, in addition to the non-energy ray curable adhesive resin (also referred to as "adhesive resin I"), adhesive resins other than the adhesive resin can also be used. An energy-ray-curable adhesive composition of an energy-ray-curable compound (hereinafter, also referred to as "X-type adhesive composition"). Furthermore, as the energy ray curable adhesive, an energy ray curable adhesive resin containing an unsaturated group introduced into the side chain of a non-energy ray curable adhesive resin (hereinafter also referred to as " An adhesive composition (hereinafter, also referred to as a "Y-type adhesive composition") that contains "adhesive resin II") as a main component and does not contain an energy ray curable compound other than the adhesive resin.

In addition, as the energy ray curable adhesive, X type and a combination type with the Y type can also be used, that is, in addition to the energy ray curable adhesive resin II, an energy ray curable compound other than the adhesive resin can also be used. energy ray curable adhesive composition (hereinafter, also referred to as "XY type adhesive composition").

Among them, it is preferable to use an XY type adhesive composition. By using an XY-type adhesive composition, it is possible to have sufficient adhesive properties before curing, and on the other hand, after curing, the peel strength to the workpiece or workpiece individualized product can be sufficiently reduced.

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

In addition, in the following description, "adhesive resin" is used as a term to refer to one or both of the above-mentioned adhesive resin I and adhesive resin II. Specific examples of the adhesive resin include, for example, acrylic adhesives, urethane adhesives, rubber adhesives, silicone adhesives, etc., with acrylic adhesives being preferred. Hereinafter, an acrylic adhesive using an acrylic resin as an adhesive resin will be described in more detail.

As the acrylic resin, an acrylic acid polymer can be used. The acrylic polymer is obtained by polymerizing a monomer containing at least (meth)acrylic acid alkyl ester, and contains a structural unit derived from (meth)acrylic acid alkyl ester. Examples of alkyl (meth)acrylate include those having an alkyl group having 1 to 20 carbon atoms, and the alkyl group may be linear or branched. Specific examples of alkyl (meth)acrylate include methyl (meth)acrylate, ethyl (meth)acrylate, isopropyl (meth)acrylate, n-propyl (meth)acrylate, (meth)acrylate n-Butyl methacrylate, 2-ethylhexyl (meth)acrylate, n-octyl (meth)acrylate, isooctyl (meth)acrylate, nonyl (meth)acrylate, (meth) Decyl acrylate, undecyl (meth)acrylate, dodecyl (meth)acrylate, etc. Alkyl (meth)acrylate can be used alone or in combination of two or more.

Furthermore, from the viewpoint of improving the adhesive force of the adhesive layer, the acrylic polymer preferably contains a structural unit derived from an alkyl (meth)acrylate having 4 or more carbon atoms in an alkyl group. The number of carbon atoms of the alkyl (meth)acrylate is preferably 4 to 12, and more preferably 4 to 6. Furthermore, the (meth)acrylic acid alkyl ester in which the alkyl group has 4 or more carbon atoms is preferably an acrylic acid alkyl ester.

In an acrylic polymer, the content of alkyl (meth)acrylate having an alkyl group with 4 or more carbon atoms is relative to the total amount of monomers constituting the acrylic polymer (hereinafter referred to as "total monomer amount"). )100 parts by mass, preferably 40 to 98 parts by mass, more preferably 45 to 95 parts by mass, still more preferably 50 to 90 parts by mass.

Acrylic polymers, in addition to the structural units derived from alkyl (meth)acrylate with a carbon number of 4 or more in the alkyl group, contain other components derived from alkyl (meth)acrylate in order to adjust the modulus, adhesive properties, etc. of the adhesive layer. A copolymer of a structural unit of alkyl (meth)acrylate whose alkyl group has 1 to 3 carbon atoms is preferred. Moreover, the above-mentioned alkyl (meth)acrylate is preferably an alkyl (meth)acrylate having a carbon number of 1 or 2, more preferably methyl (meth)acrylate, and methyl methacrylate for the best. In the acrylic polymer, the content of alkyl (meth)acrylate having 1 to 3 carbon atoms in the alkyl group is preferably 1 to 30 parts by mass based on 100 parts by mass of the total monomer amount, and more preferably 1 to 30 parts by mass. The amount is 3 to 26 parts by mass, and more preferably 6 to 22 parts by mass.

In addition to the above-mentioned structural units derived from alkyl (meth)acrylate, the acrylic polymer preferably has structural units derived from functional group-containing monomers. Examples of the functional group of the functional group-containing monomer include a hydroxyl group, a carboxyl group, an amino group, an epoxy group, and the like. The functional group-containing monomer may react with a cross-linking agent described below to become a cross-linking starting point, or may react with an unsaturated group-containing compound to introduce an unsaturated group into the side chain of the acrylic polymer.

Examples of functional group-containing monomers include hydroxyl group-containing monomers, carboxyl group-containing monomers, amine group-containing monomers, and epoxy group-containing monomers. In this embodiment, hydroxyl group-containing monomers, carboxyl group-containing monomers, amine group-containing monomers, epoxy group-containing monomers, etc. may be used alone or in combination of two or more. Among them, it is preferable to use a hydroxyl group-containing monomer and a carboxyl group-containing monomer, and it is more preferable to use a hydroxyl group-containing monomer.

Examples of the hydroxyl-containing monomer include 2-hydroxyethyl acrylate, 2-hydroxyethyl methacrylate, 2-hydroxypropyl (meth)acrylate, 3-hydroxypropyl (meth)acrylate, ( Hydroxyalkyl (meth)acrylate, such as 2-hydroxybutyl methacrylate, 3-hydroxybutyl (meth)acrylate, 4-hydroxybutyl (meth)acrylate, etc.; vinyl alcohol, allyl alcohol Unsaturated alcohols, etc.

Examples of the carboxyl group-containing monomer include, for example, ethylenically unsaturated monocarboxylic acids such as (meth)acrylic acid and crotonic acid; ethylenically unsaturated monocarboxylic acids such as fumaric acid, itaconic acid, maleic acid, and citraconic acid. Saturated dicarboxylic acid and its anhydride, 2-carboxyethyl methacrylate, etc.

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 still more preferably 6 to 30 parts by mass relative to 100 parts by mass of the total monomers constituting the acrylic polymer. share. Furthermore, in addition to the above, the acrylic polymer may also contain structural units derived from monomers copolymerizable with the acrylic monomers, for example, styrene, α-methylstyrene, vinyltoluene , vinyl formate, vinyl acetate, acrylonitrile, acrylamide, etc.

As the above-mentioned acrylic polymer, non-energy ray curable adhesive resin I (acrylic resin) can be used. Examples of the energy ray-curable acrylic resin include, for example, a compound having a photopolymerizable unsaturated group (also referred to as an unsaturated group-containing compound) and a functional group of the above-mentioned acrylic polymer. And get something.

The unsaturated group-containing compound is a compound that has both a substituent that can be bonded to the functional group of the acrylic polymer and a photopolymerizable unsaturated group. Examples of the photopolymerizable unsaturated group include (meth)acrylyl group, vinyl group, allyl group, vinylbenzyl group, etc., with (meth)acrylyl group being preferred. In addition, examples of the substituent that the unsaturated group-containing compound has and can be bonded to a functional group include an isocyanate group, an epoxypropyl group, and the like. Therefore, examples of the unsaturated group-containing compound include (meth)acryloxyethyl isocyanate, (meth)acrylyl isocyanate, (meth)epoxypropyl acrylate, and the like.

Furthermore, it is preferable that the unsaturated group-containing compound reacts with a part of the functional groups of the acrylic polymer. Specifically, it is preferable that the unsaturated group-containing compound reacts with 50 to 98 of the functional groups of the acrylic polymer. The molar % reaction is more preferably 55 to 93 mol% of the functional groups of the unsaturated group-containing compound and the acrylic polymer. In this way, in the energy-beam-curable acrylic resin, part of the functional groups remains without reacting with the unsaturated group-containing compound, thereby facilitating crosslinking by the crosslinking agent. Moreover, 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, still more preferably 500,000 to 1,200,000.

(Energy ray curable compound) The energy ray curable compound contained in the X-type or XY-type adhesive composition is preferably a monomer or oligomer that has an unsaturated group in the molecule and can be polymerized and cured by energy ray irradiation. Examples of such energy ray curable compounds include trimethylolpropane tri(meth)acrylate, neopentylerythritol (meth)acrylate, neopentylerythritol tetra(meth)acrylate, Polyvalent (meth)acrylates such as dineopentaerythritol hexa(meth)acrylate, 1,4-butanediol di(meth)acrylate, and 1,6-hexanediol (meth)acrylate, Oligomers such as urethane (meth)acrylate, polyester (meth)acrylate, polyether (meth)acrylate, epoxy (meth)acrylate, etc.

Among them, urethane (meth)acrylate oligomer is preferred because the molecular weight is relatively high and the shear storage modulus of the adhesive layer is not easily reduced. 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, still more preferably 400 to 8,000, and particularly preferably 600 to 6,000.

The content of the energy ray curable compound in the X-type adhesive composition is preferably 40 to 200 parts by mass, more preferably 50 to 150 parts by mass, and further more preferably 60 parts by mass relative to 100 parts by mass of the adhesive resin. ~90 parts by mass. On the other hand, the content of the energy ray curable compound in the XY-type adhesive composition is preferably 1 to 30 parts by mass, more preferably 2 to 20 parts by mass based on 100 parts by mass of the adhesive resin. More preferably, it is 3 to 15 parts by mass. In the XY-type adhesive composition, since the adhesive resin is energy ray curable, even if the content of the energy ray curable compound is small, the peel strength can be sufficiently reduced after energy ray irradiation.

(cross-linking agent) The adhesive composition preferably further contains a cross-linking agent. For example, the cross-linking agent reacts with a functional group derived from a functional group-containing monomer possessed by the adhesive resin to cross-link the adhesive resins with each other. Examples of the cross-linking agent include isocyanate-based cross-linking agents such as toluene diisocyanate, hexamethylene diisocyanate, and adducts thereof; and epoxy-based cross-linking agents such as ethylene glycol epoxypropyl ether. Agent; aziridine cross-linking agent such as hexa[1-(2-methyl)-aziridinyl]triphosphatriazine; aluminum chelate Chelates such as compounds are cross-linking agents; etc. These cross-linking agents can be used alone or in combination of two or more.

Among them, isocyanate-based crosslinking agents are preferred from the viewpoint of improving cohesion and adhesion, and being easy to obtain. From the viewpoint of promoting the cross-linking reaction, the blending amount of the cross-linking agent is preferably 0.01 to 10 parts by mass, more preferably 0.03 to 7 parts by mass, and further more preferably 0.05 to 4 parts by mass relative to 100 parts by mass of the adhesive resin. parts by mass.

(Photopolymerization initiator) Furthermore, when the adhesive composition is energy-ray curable, the adhesive composition preferably further contains a photopolymerization initiator. By containing a photopolymerization initiator, the curing reaction of the adhesive composition can be sufficiently advanced even if low-energy energy rays such as ultraviolet rays are irradiated.

Examples of the photopolymerization initiator include benzoin compounds, acetophenone compounds, acylphosphine oxide compounds, titanocene compounds, thioxanthone compounds, peroxide compounds, amines, quinones, and the like. Photosensitizers etc., more specifically, for example, 1-hydroxycyclohexyl phenyl ketone, 2-hydroxy-2-methyl-1-phenyl-propan-1-one, benzoin, benzoin, etc. Indium methyl ether, benzoin ethyl ether, benzoin isopropyl ether, benzyl phenyl sulfide, tetramethyl thiuram monosulfide, azobisisobutyronitrile, bibenzyl (dibenzyl), diacetyl, 8-chloroanthraquinone, bis(2,4,6-trimethylbenzyl)phenylphosphine oxide, 2,2-dimethoxy-2-benzene acetophenone, etc.

These photopolymerization initiators can be used alone or in combination of two or more. The blending amount of the photopolymerization initiator is preferably 0.01 to 10 parts by mass, more preferably 0.03 to 5 parts by mass, and still more preferably 0.05 to 5 parts by mass relative to 100 parts by mass of the adhesive resin.

(Other additives) The adhesive composition may contain other additives within the scope 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, and the like. When these additives are blended, the blending amount of the additive is preferably 0.01 to 6 parts by mass relative to 100 parts by mass of the adhesive resin.

Furthermore, from the viewpoint of improving the coating properties on the base material, buffer layer, and release sheet, the adhesive composition can be further diluted with an organic solvent to form a solution of the adhesive composition. Examples of the organic solvent include methyl ethyl ketone, acetone, ethyl acetate, tetrahydrofuran, dioxane, cyclohexane, n-hexane, toluene, xylene, n-propanol, isopropanol, and the like. In addition, these organic solvents can be directly used as organic solvents used in the synthesis of the adhesive resin, or one or more organic solvents other than the organic solvents used in the synthesis can be added to make the solution of the adhesive resin uniform. ground coating.

[Buffer layer 13] The protective sheet 10 of this embodiment has a buffer layer 13 . An adhesive layer 12 is provided on one surface of the base material 11 , and a buffer layer 13 is provided on the other surface of the base material 11 .

The buffer layer relieves the stress during workpiece processing, for example, the stress during backside grinding of a semiconductor wafer, and prevents cracks and chips from occurring in the semiconductor wafer. After the protective sheet is attached to the workpiece, the workpiece is placed on the chuck platform through the protective sheet and the back side is ground. The protective sheet has a buffer layer as a constituent layer, which makes it easier to properly hold the workpiece on the chuck platform. superior. Furthermore, even if there is foreign matter on the chuck table, the unevenness of the foreign matter can be absorbed by the deformation of the buffer layer, and the workpiece can be ground smoothly and with a uniform thickness.

The protective sheet of this embodiment has the characteristic that even when the polishing debris comes into contact with the buffer layer, the polishing debris hardly adheres to the buffer layer. In order to exhibit this characteristic, the buffer layer material is designed to have specific viscoelasticity, and the stress relaxation rate of the buffer layer at 23°C and the Young's modulus at 23°C are controlled within a specific range.

The stress relaxation rate of the buffer layer at 23° C. is 50% or less, preferably 15 to 49%, more preferably 30 to 48%, and particularly preferably 38 to 47%. Furthermore, the Young's modulus of the buffer layer at 23° C. is 400 MPa or more, preferably 450 MPa or more, and more preferably 500 MPa or more.

The stress relaxation rate of the buffer layer is less than 50% and has the properties of rubber elasticity, but the Young's modulus is more than 400 MPa, which can satisfy the opposite property of being relatively hard. Since the buffer layer is relatively hard, even if it comes into contact with the grinding chips, the grinding chips will not be embedded in the buffer layer, and the adhesion of the grinding chips can be prevented. Furthermore, due to the properties of rubber elasticity, even if the grinding chips are embedded in the buffer layer, the elastic behavior of the rubber can restore the buffer layer to its original shape and push out the embedded grinding chips, thereby preventing the grinding chips from being dislodged. Attach.

The buffer layer is a layer obtained by curing a buffer layer-forming composition described below, and the viscoelasticity can be adjusted by selecting the composition of the buffer layer-forming composition.

The thickness of the buffer layer is preferably 15 to 80 μm, and more preferably 20 to 70 μm. By setting the thickness of the buffer layer within the above range, the buffer layer can appropriately relax the stress during back surface grinding.

The composition of the buffer layer is not limited as long as it satisfies the above-mentioned stress relaxation rate and Young's modulus. From the viewpoint of easy control of viscoelasticity, a cured product of a buffer layer-forming composition containing an energy-beam polymerizable compound is preferred. . Hereinafter, each component contained in a layer formed of a buffer layer-forming composition containing an energy-beam polymerizable compound will be described in order.

<Layer formed from a buffer layer-forming composition containing an energy-beam polymerizable compound> The composition for forming a buffer layer containing an energy ray polymerizable compound can be cured by irradiating energy rays. Furthermore, more specifically, the buffer layer forming composition containing an energy ray polymerizable compound preferably contains urethane (meth)acrylate (a1). Furthermore, in addition to the above (a1), the buffer layer forming composition contains a polymerizable compound (a2) having an alicyclic group or a heterocyclic group with 6 to 20 ring atoms and/or a polymer having a functional group. The sexual compound (a3) is more preferred. Furthermore, the buffer layer forming composition preferably contains the polyfunctional polymerizable compound (a4) in addition to the above-mentioned components (a1) to (a3). In addition, the composition for forming a buffer layer preferably contains a photopolymerization initiator, but may contain other additives, resin components, etc. within a range that does not impair the effects of the present invention. Hereinafter, each component contained in the buffer layer-forming composition containing an energy-beam polymerizable compound will be described.

(Urethane (meth)acrylate (a1)) Urethane (meth)acrylate (a1) refers to a compound having at least a (meth)acrylyl group and a urethane bond, and is a substance that has the property of polymerization and curing by energy ray irradiation. . Urethane (meth)acrylate (a1) is an oligomer or polymer.

The weight average molecular weight (Mw) of the component (a1) is preferably 1,000 to 100,000, more preferably 2,000 to 60,000, still more preferably 10,000 to 30,000. Furthermore, the number of (meth)acrylyl groups in component (a1) (hereinafter also referred to as "the number of functional groups") may be monofunctional, bifunctional, or trifunctional or more. Better.

Component (a1) can be obtained, for example, by reacting a terminal isocyanate urethane prepolymer obtained by reacting a polyol compound and a polyvalent isocyanate compound and a (meth)acrylate having a hydroxyl group. Moreover, component (a1) can be used individually or in combination of 2 or more types.

The polyol compound used as the raw material of component (a1) is not particularly limited as long as it is a compound having two or more hydroxyl groups. Specific polyol compounds include, for example, alkylene glycols, polyether polyols, polyester polyols, polycarbonate polyols, and the like. Among them, polyester polyol or polycarbonate polyol is preferred.

In addition, the polyol compound may be any of a bifunctional diol, a trifunctional triol, and a tetrafunctional or higher polyol. Bifunctional diols are preferred, and polyester type diols are preferred. Polyols or polycarbonate diols are more preferred.

Examples of the polyvalent isocyanate compound include aliphatic polyisocyanates such as tetramethylene diisocyanate, hexamethylene diisocyanate, and trimethylhexamethylene diisocyanate; isophorone diisocyanate, Norbornane diisocyanate, dicyclohexylmethane-4,4'-diisocyanate, dicyclohexylmethane-2,4'-diisocyanate, ω,ω'-diisocyanate, dimethylcyclohexane, etc. Alicyclic diisocyanates; 4,4'-diphenylmethane diisocyanate, toluene diisocyanate, xylylenedimethyl diisocyanate, benzolidine diisocyanate, tetramethylene xylylenedimethyl diisocyanate, naphthalene -Aromatic diisocyanates such as 1,5-diisocyanate, etc. Among them, isophorone diisocyanate, hexamethylene diisocyanate, and xylylene diisocyanate are preferred.

Urethane (meth)acrylate can be obtained by reacting a terminal isocyanate urethane prepolymer obtained by reacting the polyol compound and a polyvalent isocyanate compound with a (meth)acrylate having a hydroxyl group. (a1). The (meth)acrylate having a hydroxyl group is not particularly limited as long as it is a compound having at least a hydroxyl group and a (meth)acrylyl group in one molecule.

Specific (meth)acrylates having a hydroxyl group include, for example, 2-hydroxyethyl (meth)acrylate, 2-hydroxypropyl (meth)acrylate, and 4-hydroxybutyl (meth)acrylate. , 4-hydroxycyclohexyl (meth)acrylate, 5-hydroxycyclooctyl (meth)acrylate, 2-hydroxy-3-phenoxypropyl (meth)acrylate, neopenterythritol tri(methyl) ) acrylate, polyethylene glycol mono(meth)acrylate, polypropylene glycol mono(meth)acrylate, and other hydroxyalkyl (meth)acrylates; N-hydroxymethyl (meth)acrylamide, etc. Hydroxyl-containing (meth)acrylamide; vinyl alcohol, vinylphenol, reaction products obtained by reacting diepoxypropyl ester of bisphenol A with (meth)acrylic acid; etc. Among them, hydroxyalkyl (meth)acrylate is preferred, and 2-hydroxyethyl (meth)acrylate is more preferred.

Conditions for reacting the terminal isocyanate urethane prepolymer and the (meth)acrylate having a hydroxyl group include reaction 1 to 4 at 60 to 100°C in the presence of a solvent and a catalyst added as necessary. Hours of conditions are better.

The content of component (a1) in the buffer layer forming composition is preferably 10 to 70 parts by mass, more preferably 20 to 60 parts by mass relative to the total amount of the buffer layer forming composition (100 parts by mass).

(Polymerizable compound (a2) having an alicyclic group or heterocyclic group with 6 to 20 ring atoms) Component (a2) is a polymerizable compound having an alicyclic group or a heterocyclic group having 6 to 20 ring atoms. More preferably, it is a compound having at least one (meth)acrylyl group, and more preferably A compound having one (meth)acrylyl group. By using component (a2), the film-forming property of the obtained buffer layer forming composition can be improved.

Furthermore, although the definition of component (a2) overlaps with the definition of component (a3) described later, the overlapping portion is included in component (a3). For example, a compound having at least one (meth)acrylyl group, an alicyclic group or a heterocyclic group with 6 to 20 ring atoms, and a functional group such as a hydroxyl group, an epoxy group, a amide group, or an amino group, Although it is included in the definitions of both component (a2) and component (a3), in the present invention, this compound is included in component (a3).

The number of ring atoms of the alicyclic group or heterocyclic group contained in component (a2) is preferably 6 to 20, more preferably 6 to 18, still more preferably 6 to 16, and particularly preferably 7 to 12. Examples of atoms forming the ring structure of the heterocyclic group include carbon atoms, nitrogen atoms, oxygen atoms, sulfur atoms, and the like.

In addition, the number of ring-forming atoms refers to the number of atoms constituting the ring itself in a compound in which atoms are bonded to form a ring structure. The atoms that do not constitute the ring (for example, hydrogen atoms bonded to the atoms constituting the ring), when When the ring is substituted by a substituent, the atoms included in the substituent are not included in the number of ring atoms.

Specific components (a2) include, for example, isobornyl (meth)acrylate, dicyclopentenyl (meth)acrylate, dicyclopentyl (meth)acrylate, and dicyclopentenyl (meth)acrylate. Alicyclic group-containing (meth)acrylates such as cyclopentenoxy ester, cyclohexyl (meth)acrylate, adamantyl (meth)acrylate, etc.; tetrahydrofuran methyl (meth)acrylate, mofeline Heterocyclic group-containing (meth)acrylates such as (meth)acrylate, cyclic trimethylolpropane formal acrylate, etc.; etc.

Moreover, component (a2) can be used individually or in combination of 2 or more types. Among the alicyclic group-containing (meth)acrylates, isobornyl (meth)acrylate is preferred.

The content of component (a2) in the buffer layer forming composition is preferably 10 to 80 parts by mass, more preferably 30 to 70 parts by mass relative to the total amount of the buffer layer forming composition (100 parts by mass).

(Polymerizable compound (a3) having a functional group) Component (a3) is a polymerizable compound containing a functional group such as a hydroxyl group, an epoxy group, a amide group, an amine group, or the like. More preferably, it is a compound having at least one (meth)acrylyl group, and more preferably It is a compound having one (meth)acrylyl group.

The component (a3) and the component (a1) have good compatibility, and it is relatively easy to adjust the viscosity of the buffer layer forming composition to an appropriate range. Furthermore, even if the buffer layer becomes relatively thin, the buffering performance is still good.

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

Examples of hydroxyl-containing (meth)acrylates include 2-hydroxyethyl (meth)acrylate, 2-hydroxypropyl (meth)acrylate, 3-hydroxypropyl (meth)acrylate, and (meth)acrylate. 2-hydroxybutyl acrylate, 3-hydroxybutyl (meth)acrylate, 4-hydroxybutyl (meth)acrylate, phenylhydroxypropyl (meth)acrylate, 2-hydroxy-3-benzene acrylate Oxypropyl ester, etc.

Examples of the epoxy group-containing compound include, for example, glycidyl (meth)acrylate, methylglycidyl (meth)acrylate, allylglycidyl ether, etc. Among them, ( Epoxy group-containing (meth)acrylates such as glycidyl methacrylate and methylglycidyl (meth)acrylate are preferred.

Examples of the amide group-containing compound include (meth)acrylamide, N,N-dimethyl(meth)acrylamide, N-butyl(meth)acrylamide, and N-hydroxyacrylamide. Methyl(meth)acrylamide, N-hydroxymethylpropane(meth)acrylamide, N-methoxymethyl(meth)acrylamide, N-butoxymethyl(methyl) Acrylamide, etc.

Examples of the amino group-containing (meth)acrylates include primary amino group-containing (meth)acrylates, secondary amino group-containing (meth)acrylates, and tertiary amino group-containing (meth)acrylates. wait.

Among them, hydroxyl-containing (meth)acrylate is preferred, and hydroxyl-containing (meth)acrylate having an aromatic ring such as phenylhydroxypropyl (meth)acrylate is more preferred. Moreover, component (a3) can be used individually or in combination of 2 or more types.

The content of component (a3) in the buffer layer forming composition is preferably 0 to 40 parts by mass, more preferably 0 to 35 parts by mass, relative to the total amount of the buffer layer forming composition (100 parts by mass). More preferably, it is 0 to 30 parts by mass.

(Polyfunctional polymerizable compound (a4)) A polyfunctional polymerizable compound refers to a compound having two or more photopolymerizable unsaturated groups. The photopolymerizable unsaturated group is a functional group containing a carbon-carbon double bond, and examples thereof include (meth)acrylyl group, vinyl group, allyl group, vinylbenzyl group, and the like. Two or more types of photopolymerizable unsaturated groups may be combined. By reacting the photopolymerizable unsaturated group in the polyfunctional polymerizable compound with the (meth)acrylyl group in the component (a1), or reacting the photopolymerizable unsaturated groups in the component (a4) with each other, A three-dimensional network structure (cross-linked structure) can be formed. When a polyfunctional polymerizable compound is used, it is easier to increase the crosslinked structure formed by energy ray irradiation than when a compound containing only one photopolymerizable unsaturated group is used.

Moreover, although the definition of component (a4) has overlapping parts with the definitions of component (a2), component (a3), etc. mentioned above, the overlapping parts are included in component (a4). For example, compounds having an alicyclic group or heterocyclic group with 6 to 20 ring atoms and two or more (meth)acrylyl groups are included in both component (a4) and component (a2) , but in the present invention, this compound is included in ingredient (a4). Furthermore, compounds containing functional groups such as hydroxyl group, epoxy group, amide group, and amine group, and having two or more (meth)acrylyl groups are included in component (a4) and component (a3) in both definitions, but in the present invention this compound is included in ingredient (a4).

From the above viewpoint, the number of photopolymerizable unsaturated groups (number of functional groups) in the polyfunctional polymerizable compound is preferably 2 to 10, and more preferably 3 to 6.

Furthermore, the weight average molecular weight of component (a4) is preferably 30 to 40,000, more preferably 100 to 10,000, and still more preferably 200 to 1,000.

Specific components (a4) include, for example, ethylene glycol di(meth)acrylate, diethylene glycol di(meth)acrylate, triethylene glycol di(meth)acrylate, and tetraethylene glycol di(meth)acrylate. Diol di(meth)acrylate, polyethylene glycol di(meth)acrylate with the number of repeating units derived from diol being 200 to 800, neopentyl glycol di(meth)acrylate, 1,6-hexanediol di(meth)acrylate, trimethylolpropane tri(meth)acrylate, neopentylerythritol tri(meth)acrylate, neopentylerythritol tetra(meth)acrylate Ester, dipenterythritol hexa(meth)acrylate, divinylbenzene, vinyl (meth)acrylate, divinyl adipate, N,N'-methylene bis(meth)acrylamide Amines etc. Polyethylene glycol di(meth)acrylate is generally expressed by placing the number of ethylene glycol units in brackets. For example, when the number of ethylene glycol units is 600, it is expressed as polyethylene glycol (600) di(meth)acrylate. Acrylate. Moreover, component (a4) can be used individually or in combination of 2 or more types. Among them, polyethylene glycol diacrylate and neopentyl glycol di(meth)acrylate are preferred.

The content of component (a4) in the buffer layer forming composition is preferably 2 to 40 parts by mass, more preferably 3 to 20 parts by mass relative to the total amount of the buffer layer forming composition (100 parts by mass). More preferably, it is 5 to 15 parts by mass.

(Polymerizable compound (a5) other than components (a1) to (a4)) The buffer layer forming composition may contain a polymerizable compound (a5) other than the above-mentioned components (a1) to (a4) within a range that does not impair the effects of the present invention.

Examples of the component (a5) include alkyl (meth)acrylate having an alkyl group having 1 to 20 carbon atoms; styrene, hydroxyethyl vinyl ether, hydroxybutyl vinyl ether, N- Vinyl compounds such as vinylformamide, N-vinylpyrrolidone, N-vinylcaprolactam, etc.; etc. Moreover, component (a5) can be used individually or in combination of 2 or more types.

The content of component (a5) in the buffer layer forming composition is preferably 0 to 20 parts by mass, more preferably 0 to 10 parts by mass, relative to the total amount of the buffer layer forming composition (100 parts by mass). More preferably, it is 0 to 5 parts by mass, and particularly preferably 0 to 2 parts by mass.

(Photopolymerization initiator) From the viewpoint of shortening the polymerization time of light irradiation when forming the buffer layer and reducing the amount of light irradiation, the buffer layer forming composition preferably further contains a photopolymerization initiator.

Examples of the photopolymerization initiator include benzoin compounds, acetophenone compounds, acylphosphine oxide compounds, titanocene compounds, thioxanthone compounds, peroxide compounds, amines, quinones, and the like. Photosensitizers etc., more specifically, for example, 1-hydroxycyclohexyl phenyl ketone, 2-hydroxy-2-methyl-1-phenyl-propan-1-one, benzoin, benzoin, etc. Indium methyl ether, benzoin ethyl ether, benzoin isopropyl ether, benzyl phenyl sulfide, tetramethylthiuram monosulfide, azobisisobutyronitrile, bibenzyl, diacetyl, 8-chloroanthraquinone, bis(2,4,6-trimethylbenzyl)phenylphosphine oxide, etc.

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

The content of the photopolymerization initiator in the buffer layer forming composition is preferably 0.05 to 15 parts by mass, more preferably 0.1 to 10 parts by mass relative to the total amount of energy ray polymerizable compounds (100 parts by mass). More preferably, it is 0.3 to 5 parts by mass.

(Other additives) The buffer layer forming composition 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, and the like. When these additives are blended, the content of each additive in the buffer layer forming composition is preferably 0.01 to 6 parts by mass, more preferably 0.1 to 6 parts by mass relative to the total amount of the energy ray polymerizable compound (100 parts by mass). 3 parts by mass.

(resin component) The buffer layer-forming composition may contain a resin component within a range that does not impair the effects of the present invention. Examples of the resin component include polyene/thiol-based resins, polyolefin-based resins such as polybutene, polybutadiene, and polymethylpentene, and thermoplastic resins such as styrene-based copolymers.

The content of these resin components in the buffer layer forming composition is preferably 0 to 20 parts by mass, more preferably 0 to 10 parts by mass relative to the total amount of the buffer layer forming composition (100 parts by mass), and further More preferably, it is 0 to 5 parts by mass, and particularly preferably 0 to 2 parts by mass.

A buffer layer formed from a buffer layer forming composition containing an energy ray polymerizable compound is obtained by polymerizing and curing the buffer layer forming composition having the above composition by irradiation with energy rays. That is, this buffer layer is a cured product of the buffer layer forming composition.

Therefore, this buffer layer contains polymerized units derived from component (a1). Furthermore, the buffer layer preferably contains polymerized units derived from component (a2) and/or polymerized units derived from component (a3). In addition, a polymerized unit derived from component (a4) and/or a polymerized unit derived from component (a5) may be contained. The content ratio of each polymer unit in the buffer layer usually matches the ratio (feed ratio) of each component constituting the buffer layer-forming composition. For example, when the content of the component (a1) in the buffer layer-forming composition is 10 to 70 parts by mass relative to the total amount of the buffer layer-forming composition (100 parts by mass), the buffer layer contains the component (a1). ) of polymerized units 10 to 70 parts by mass. Furthermore, when the content of the component (a2) in the buffer layer-forming composition is 10 to 80 parts by mass relative to the total amount of the buffer layer-forming composition (100 parts by mass), the buffer layer contains the component (a2) derived from the component (a2). 10 to 80 parts by mass of polymerized units of a2). The same applies to components (a3) to (a5).

(Control of viscoelasticity of buffer layer) The buffer layer can be obtained by curing the above buffer layer forming composition. The viscoelasticity of the buffer layer can be adjusted by selecting the composition of the buffer layer forming composition. Therefore, in order to control the stress relaxation rate, Young's modulus, etc. of the buffer layer within the above-mentioned ranges, the types, contents, etc. of the above-mentioned components constituting the buffer layer-forming composition can be adjusted. In the following, guidelines for adjusting the type and content of each ingredient will be explained.

For example, when the number of (meth)acryl groups of urethane (meth)acrylate (a1) is large, the cross-linked structure in the buffer layer increases, the buffer layer becomes hard, and the Young's modulus increases. Therefore, by adjusting the amount of components involved in the formation of the cross-linked structure, the Young's modulus can be controlled within an appropriate range. Examples of components that participate in the formation of a cross-linked structure include the (meth)acryl group of urethane (meth)acrylate (a1) and the polyfunctional polymerizable compound (a4). In particular, the polyfunctional polymerizable compound (a4) is a component that is easy to use and useful for forming a cross-linked structure.

By adding the polyfunctional polymerizable compound (a4), the movement of molecules inside the cured product can be hindered, so that the stress relaxation property can be designed to be low and the Young's modulus can be designed to be high. That is, by increasing the addition amount of the polyfunctional polymerizable compound (a4), the above-mentioned physical properties can be easily exhibited. As the stress relaxation rate decreases, urethane (meth)acrylate (a1), components involved in the formation of long-chain structures, etc., will play a role in easing the embrittlement of the buffer layer.

The above buffer layer may contain additives such as plasticizers, lubricants, infrared absorbers, ultraviolet absorbers, fillers, colorants, antistatic agents, antioxidants, catalysts, etc. within the scope that does not impair the effects of the present invention. Furthermore, the above-mentioned buffer layer may be transparent or opaque, and may be colored or evaporated as needed.

[Peel-off sheet] A release sheet can be attached to the surface of the protective sheet. Specifically, the release sheet is attached to the surface of the adhesive layer of the protective sheet. Attach the release sheet to the surface of the adhesive layer to protect the adhesive layer during transportation and storage. The release sheet is peelably attached to the protective sheet, and is peeled off and removed from the protective sheet before using the protective sheet (that is, before attaching the workpiece). As the release sheet, a release sheet that has been subjected to release treatment on at least one surface is used. Specific examples thereof include a release sheet coated with a release agent on the surface of a release sheet base material.

As the base material for the release sheet, a resin film is preferred. Examples of the resin constituting the resin film include polyethylene terephthalate resin, polybutylene terephthalate resin, and polynaphthalene resin. Polyester resin films such as ethylene diformate resin, polyolefin resin films such as polypropylene resin and polyethylene resin, etc. Examples of the release agent include rubber-based elastomers such as silicone-based resins, olefin-based resins, isoprene-based resins, butadiene-based resins, long-chain alkyl-based resins, alkyd-based resins, fluorine-based resins, etc. System resin, etc. The thickness of the release sheet is not particularly limited, but is preferably 10 to 200 μm, more preferably 20 to 150 μm.

[Manufacturing method of protective sheet] There is no particular limitation on the manufacturing method of the protective sheet of the present invention, and it can be manufactured by a known method. For example, a method for manufacturing a protective sheet having a base material, an adhesive layer provided on one side of the base material, and a buffer layer provided on the other side of the base material is as described below.

When the buffer layer is formed from a buffer layer-forming composition containing an energy-beam polymerizable compound, the buffer layer formed by applying and curing the buffer layer-forming composition on a release sheet is bonded to the base material, and then removed and peeled off. sheets, whereby a laminate of the buffer layer and the base material can be obtained.

Then, the adhesive layer provided on the release sheet can be bonded to the base material side of the laminate to produce a protective sheet in which the release sheet is attached to the surface of the adhesive layer. The release sheet attached to the surface of the adhesive layer can be appropriately peeled off and removed before use of the protective sheet.

As a method of forming an adhesive layer on a release sheet, the adhesive (adhesive composition) can be directly applied on the release sheet by a known coating method, and the coated film can be heated and dried to form an adhesive layer.

Furthermore, the adhesive (adhesive composition) can also be directly coated on one side of the base material to form an adhesive layer. As the adhesive coating method, as shown in the manufacturing method of the buffer layer, for example, spray coating method, rod coating method, blade coating method, roller coating method, blade coating method, Mold coating method, gravure coating method, etc.

As a method of forming the buffer layer on the release sheet, a known coating method can be used to directly apply the buffer layer-forming composition on the release sheet to form a coating film, and then irradiate the coating film with energy rays to form the buffer layer. . Furthermore, the buffer layer-forming composition may be directly coated on one side of the substrate, and the buffer layer may be formed by heating and drying or irradiating the coated film with energy rays.

Examples of the coating method of the buffer layer forming composition include spray coating, rod coating, knife coating, roller coating, blade coating, die coating, and gravure coating. Coating method, etc. Furthermore, in order to improve the coatability, an organic solvent may be added to the composition for forming a buffer layer, and the composition may be in the form of a solution and be applied on the release sheet.

When the buffer layer-forming composition contains an energy-beam polymerizable compound, it is preferable to form the buffer layer by irradiating the coating film of the buffer layer-forming composition with energy rays for curing. The buffer layer can be cured in one curing process or multiple times. For example, the coating film on the release sheet may be completely cured to form a buffer layer and then attached to the base material; or the coating film may not be completely cured to form a buffer layer-forming film in a semi-cured state, and the buffer layer-forming film may be formed After being bonded to the base material, it is irradiated with energy rays again to completely solidify and form a buffer layer. As the energy ray to be irradiated in this curing process, ultraviolet rays are preferred. In addition, during curing, the coating film of the buffer layer forming composition may be in an exposed state, but it is preferable to cover the coating film with a release sheet, a base material, etc., and irradiate the energy ray in a state where the coating film is not exposed. solidify.

Furthermore, a method for manufacturing a protective sheet having buffer layers provided on both sides of a base material may be, for example, obtaining a laminate in which a buffer layer, a base material, and a buffer layer are sequentially laminated by the above method, and then, one buffer layer Adhesive layer is formed on the side.

[Method for manufacturing individual workpieces] The protective sheet of the present invention can be used to temporarily hold workpieces during processing of semiconductor wafers, semiconductor wafers, glass, ceramics, etc. The processing of the workpiece includes, but is not limited to, cutting and grinding. Among these applications, a method for manufacturing individual workpieces such as semiconductor wafers and the like by attaching them to the front side of a workpiece such as a semiconductor wafer and grinding the backside of the workpiece is particularly preferred. More preferably, the protective sheet of the present invention is used in a DBG that simultaneously performs backside grinding of workpieces such as semiconductor wafers and individualization of the workpieces. Particularly preferably, the protective sheet of the present invention is used in an LDBG that can obtain a wafer group with a small kerf width when individualizing semiconductor wafers. In addition, the "wafer group" refers to a plurality of semiconductor wafers held on the protective sheet of the present invention and arranged in a wafer shape. As a non-limiting use example of using a protective sheet, a manufacturing method of a semiconductor device will be further described in more detail below.

Specifically, the method of manufacturing an individualized workpiece includes at least the following steps 1 to 3. Step 1: Attach the above protective film to the front of the workpiece Step 2: The step of forming a groove from the front side of the workpiece, or forming a modified area inside the workpiece from the front or back side of the workpiece Step 3: The workpiece with the protective sheet attached on the front and the above-mentioned groove or modified area formed thereon is ground from the back side and individualized into a plurality of individual workpieces using the groove or modified area as a starting point.

Hereinafter, each step of the above-described method of manufacturing a semiconductor device will be described in detail. (step 1) In step 1, the protective sheet of the present invention is attached to the front side of the workpiece through an adhesive layer. The protective sheet can be pre-cut to roughly the same shape as the workpiece, or a larger protective sheet can be attached to the workpiece and then cut along the periphery of the workpiece.

This step may be performed before step 2 described below, or may be performed after step 2. For example, when forming a modified region in a workpiece, it is preferable to perform step 1 before step 2. On the other hand, when a groove is formed on the front surface of the workpiece by a cutting blade or the like, step 1 is performed after step 2. That is, in step 1, the protective sheet is attached to the front surface of the workpiece having the groove formed in step 2, which will be described later.

The workpiece used in this manufacturing method may be a silicon wafer, or may be a wafer or glass crystal of gallium arsenide, silicon carbide, lithium tantalate, lithium niobate, gallium nitride, indium phosphide, etc. Circle etc. The thickness of the workpiece before grinding is not particularly limited, but is usually about 500 to 1000 μm. Furthermore, when the workpiece is a semiconductor wafer, circuitry is typically formed on its front side. The circuit can be formed on the front surface of the wafer by various methods including etching, lift-off, and other commonly used methods.

(step 2) In step 2, a groove is formed from the front side of the workpiece, or a modified area is formed inside the workpiece from the front or back side of the workpiece. The groove formed in this step has a depth shallower than the thickness of the workpiece. The trenches can be formed by using a conventionally known wafer dicing device and the like with a dicing blade. Furthermore, in step 3 described below, the workpiece is individualized into a plurality of individualized workpieces along the groove.

Furthermore, the modified area is a brittle part in the workpiece, and the workpiece becomes thinner due to grinding during the grinding step, or the workpiece is damaged due to the force caused by grinding, and the workpiece is individualized into workpieces. The area where the individuation starts. That is, the grooves and modified regions in step 2 are formed along the dividing lines when the workpiece is divided and individualized into individualized workpieces in step 3 described below.

The modified region is formed by irradiating a laser focused on the inside of the workpiece, and the modified region can be formed inside the workpiece. Laser irradiation can be performed from the front side or the back side of the workpiece. In addition, in the aspect of forming the modified region, when Step 2 is performed after Step 1 to perform laser irradiation from the front of the workpiece, the laser is irradiated to the workpiece through the protective sheet.

The workpiece with a protective sheet attached and formed with grooves or modified areas is placed on the chuck platform, and is adsorbed and held by the chuck platform. At this time, the buffer layer of the protective sheet is arranged on the platform side and is adsorbed.

(step 3) After steps 1 and 2, the back surface of the workpiece on the chuck platform is ground and the workpiece is individualized into a plurality of individualized workpieces. In order to remove frictional heat, grinding chips, etc. generated during grinding, grinding is performed while spraying grinding water.

Here, when forming a groove in a workpiece, back grinding is performed in such a manner that the workpiece is thinned at least to a position where it reaches the bottom of the groove. By this backside grinding, the grooves become incisions that penetrate the workpiece, and the workpiece is divided and individualized into individual workpieces through the incisions.

On the other hand, when the modified area is formed, the grinding surface (the back side of the wafer) produced by grinding can reach the modified area, or the modified area does not need to be reached accurately. That is, it is sufficient to grind to a position close to the modified region, break the workpiece using the modified region as a starting point, and individualize the workpiece into individualized products. For example, actual individualization of workpiece individualization products can be performed by attaching a pick-up tape to be described later and then extending the pick-up tape.

The shape of the individualized workpiece may be a square or an elongated shape such as a rectangle. Furthermore, the thickness of the individualized workpiece is not particularly limited, but is preferably about 5 to 100 μm, more preferably about 10 to 45 μm. According to LDBG, when a modified area is provided inside a workpiece by laser and the workpiece is individualized by stress during grinding on the back side of the workpiece, etc., the thickness of the individualized workpiece is set to 50 μm or less. is relatively easy, and it is better to set it to 10 to 45 μm. Furthermore, the size of the individualized workpiece is not particularly limited, but the wafer size is preferably less than 600 mm ² , more preferably less than 400 mm ² , and still more preferably less than 300 mm ² . Prior to pick-up of the wafer, dry grinding may be performed. Dry polishing refers to a step of mirror polishing the back surface of an individualized wafer using dry abrasive grains. After this process, the broken layer on the back of the wafer can be reduced and the bending strength can be improved.

After the above steps, an individualized workpiece can be obtained on the protective sheet, and when the workpiece is a semiconductor wafer, a plurality of semiconductor wafers arranged in the shape of the wafer before cutting can be obtained. Remove the protective sheet with the workpiece individualization attached from the chuck platform and move it to the next step. When the protective sheet is removed from the chuck platform, the suction force is released, and part of the grinding water infiltrates between the buffer layer of the protective sheet and the platform, and grinding chips may adhere to the buffer layer.

After the back surface grinding is completed, the film-like adhesive, protective film (or its precursor film), etc. used in the subsequent die bonding step can be attached to the grinding surface. When forming a film-like adhesive, protective film, etc., the resin film forming the adhesive, protective film, etc. is pressurized and adhered to the back surface of the wafer.

When the resin film is pressed against the backside of the wafer, pressure is applied to the wafer group. At this time, if foreign matter such as grinding chips is present on the surface of the buffer layer of the protective sheet, the wafer near the foreign matter will be subjected to a large local stress, and the wafer may be damaged using the foreign matter as a starting point.

In the protective sheet of the present invention, since the material is designed so that the buffer layer has specific viscoelasticity as described above, even when abrasive debris comes into contact with the buffer layer, the abrasive debris is less likely to adhere to the buffer layer. Buffer layer properties. Therefore, during pressure bonding of the resin film, damage to the wafer caused by shavings can be prevented.

Then, the protective sheet for workpiece processing is peeled off from the individualized workpieces (that is, a plurality of individualized workpieces). This step is performed by, for example, the following method.

First, when the adhesive layer of the protective sheet is formed of an energy ray-curable adhesive, the adhesive layer is cured by irradiating energy rays. Then, the pick-up tape is attached to the back side of the individualized workpiece, and the position and direction are adjusted so that the workpiece can be picked up. At this time, the annular frame arranged on the outer peripheral side of the individualized workpiece is also bonded to the pickup tape, and the outer peripheral edge portion of the pickup tape is fixed to the annular frame. The individualized workpiece and the ring frame can be bonded to the pickup tape at the same time, or the individualized workpiece and the ring frame can be bonded to the pickup tape at different points in time. Then, the protective sheet is peeled off from the plurality of individual workpieces held on the pickup tape.

Afterwards, a plurality of individual workpieces located on the pickup tape are picked up. When the individualized workpiece is a semiconductor wafer, the individualized workpiece is fixed on a substrate for a semiconductor device or the like to manufacture a semiconductor device. In addition, the pick-up tape is not particularly limited. For example, it may be composed of a base material and an adhesive tape having an adhesive layer provided on at least one surface of the base material.

Alternatively, adhesive tape can be used instead of pick-up tape. Examples of the adhesive tape include a laminate of a film adhesive and a release sheet, a laminate of a dicing tape and a film adhesive, and an adhesive layer and a release sheet that have the functions of both a dicing tape and a die bonding tape. Formed dicing and die bonding tapes, etc. That is, this embodiment may include a step of affixing the dicing and die bonding tape to the back surface of the workpiece. Furthermore, before attaching the pick-up tape, a film-like adhesive may be attached to the back side of the individualized workpiece. When a film adhesive is used, the film adhesive may have the same shape as the wafer.

When an adhesive tape is used, or when a film-like adhesive is applied to the back side of an individualized workpiece before attaching the pick-up tape, a plurality of individual workpieces on the adhesive tape or pick-up tape are divided into workpieces. Individual adhesive layers of the same shape are picked together. Then, the individualized workpiece is fixed on a substrate or the like via an adhesive layer to manufacture a semiconductor device. The adhesive layer can be divided by laser, expansion, etc. In addition, a protective film forming tape for forming a protective film on the back surface of the wafer may be used instead of the adhesive tape.

The above describes an example in which the protective sheet of the present invention is used in a method of individualizing workpieces by DBG or LDBG. However, the protective sheet of the present invention can also be used for general backside grinding. Furthermore, it can also be used Used to temporarily hold the workpiece when processing glass, ceramics, etc. Furthermore, it can also be used as various removable protective sheets. [Example]

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

The measurement method and evaluation method are as follows.

[Measurement of stress relaxation rate] The single-layer film composed only of the buffer layer produced in the Examples and Comparative Examples was cut into a width of 15 mm and a length of 150 mm, and was laminated so that the thickness became 0.1 mm to obtain a test piece. This test piece was mounted on a precision universal testing machine (Autograph AG-IS manufactured by Shimadzu Corporation) with a distance between chucks of 100 mm, and stretched at a speed of 200 mm/min. According to the stress at 10% elongation A. Calculate the stress relaxation rate of the buffer layer by (A-B)/A×100 (%) with the stress B after the elongation stops for 1 minute. In addition, the measurement was performed in an environment of 23°C and 50%RH.

[Measurement of Young’s modulus] The single-layer film composed only of the buffer layer produced in the Examples and Comparative Examples was cut into a width of 15 mm and a length of 150 mm, and was laminated so that the thickness became 0.1 mm to obtain a test piece. This test piece was mounted on a precision universal testing machine (Autograph AG-IS manufactured by Shimadzu Corporation) with a distance between chucks of 100 mm, stretched at a speed of 200 mm/min, and the Young's modulus was measured. In addition, the measurement was performed in an environment of 23°C and 50%RH.

[Evaluation method for the number of foreign matter adhesion] Micro silicon wafers were prepared instead of grinding chips, and the number of silicon wafers adhered to the buffer layer of the protective sheet was counted to evaluate the foreign matter adhesion of the buffer layer. Specifically, nine 300-μm-thick silicon wafers cut into 1 mm × 1 mm were arranged at approximately equal intervals on a mounting table of RAD-2700F/12 manufactured by Lintec (see FIG. 2 ). The protective sheet produced in the Example and Comparative Example was cut into a circle with a diameter of 12 inches, and static electricity was eliminated using an ionizer for 1 minute. The protective sheet was placed on the mounting table so that the buffer layer side surface was in contact with the silicon wafer. superior. In this state, apply the suction force (vacuum) of the mounting table, release the suction force after 20 seconds, and slowly lift the protective sheet with tweezers. The number of wafers attached to the buffer layer when lifted was measured. Carry out this operation 10 times, and take the average value as the number of foreign matter attachments. An average value of 0 to 2 is set as A; an average value of more than 2 and less than 4 is set as B; an average value of more than 4 and less than 6 is set as C; an average value of more than 6 and less than 9 is set as D.

The parts by mass in the following examples and comparative examples are all solid content conversion values. [Examples 1 to 6, Comparative Examples 1 to 5] (1)Substrate As a base material, a PET film (manufactured by Toyobo Co., Ltd., product name [COSMOSHINE A4300], thickness: 50 μm, Young's modulus at 23° C.: 2550 MPa) with coating layers on both sides was prepared.

(2)Adhesive layer An acrylic copolymer having structural units derived from n-butyl acrylate (BA), methyl methacrylate (MMA) and 2-hydroxyethyl acrylate (2HEA) (BA/MMA/2HEA = 65/20/15 (mass %) acrylic copolymer obtained by copolymerization), with 2-methacryloyloxyethyl by adding 80 mol% of all hydroxyl groups in the acrylic polymer isocyanate (MOI) reacts to obtain an energy-beam-curable acrylic resin (Mw: 500,000).

To 100 parts by mass of this energy-beam-curable acrylic resin, 6 parts by mass of polyfunctional urethane acrylate (trade name: Purple Light UT-4332, manufactured by Mitsubishi Chemical Industries, Ltd.) as an energy-beam-curable compound was added. , isocyanate cross-linking agent (manufactured by Tosoh Co., Ltd., trade name: Coronate L), 0.375 parts by mass based on solid content, bis(2,4,6-trimethylbenzyl)phenylphosphine oxide 1 part by mass of the photopolymerization initiator was diluted with a solvent to prepare a coating liquid of the adhesive composition. Then, on the release-treated surface of the release sheet (manufactured by Lintec, trade name "SP-PET381031", silicone release-treated polyethylene terephthalate (PET) film, thickness: 38 μm), The coating liquid of the above-mentioned adhesive composition was spread and dried to prepare a release sheet with an adhesive layer having an adhesive layer with a thickness of 20 μm.

(3)Buffer layer (Preparation of buffer layer forming composition) Urethane acrylate oligomer (CN8881), isobornyl acrylate (IBXA), polyethylene glycol (200) diacrylate, and polyethylene glycol (400) diacrylate purchased from Sartomer Company , polyethylene glycol (600) diacrylate, ethoxylated (3) trimethylolpropane triacrylate, ethoxylated (6) trimethylolpropane triacrylate, ethoxylated (9 ) Trimethylolpropane triacrylate was prepared in the amounts shown in Table 1 as the energy ray polymerizable compound, and 2-hydroxy-2-methyl-1-phenylpropan-1-one was prepared. (manufactured by IGM Resin, product name "Omnirad 1173") 2.0 parts by mass as a photopolymerization initiator to prepare a buffer layer forming composition.

On the release-treated surface of a release sheet (manufactured by Lintec, trade name "SP-PET381031", silicone release-treated polyethylene terephthalate (PET) film, thickness: 38 μm), apply the above The composition for forming a buffer layer is used to form a coating film. Then, the coating film was irradiated with ultraviolet rays to semi-cure the coating film to form a semi-cured film of a buffer layer with a thickness of 28 μm.

In addition, the above-mentioned ultraviolet irradiation uses a belt conveyor type ultraviolet irradiation device (product name "ECS-401GX", manufactured by Eyegraphics Co., Ltd.) and a high-pressure mercury lamp (product name "H04-L41", manufactured by Eyegraphics Co., Ltd.). It was carried out under the irradiation conditions of height 260 mm, output 80 W/cm, illumination 70 mW/cm ² , and irradiation dose 30 mW/cm ² .

Then, the surface of the formed semi-cured film is bonded to the first coating layer of the base material, and ultraviolet rays are irradiated from the release sheet side of the semi-cured film again to completely cure the semi-cured film to form a buffer with a thickness of 28 μm. layer. In addition, the second ultraviolet irradiation was performed using the above-mentioned ultraviolet irradiation device and high-pressure mercury lamp, under the irradiation conditions of lamp height 210 mm, output 120 W/cm, illumination 155 mW/cm ² , and irradiation amount 600 mW/cm ² proceed below. The stress relaxation rate and Young's modulus of the obtained buffer layer were measured. The results are shown in Table 2.

(4) Production of protective film Then, the adhesive layer of the release sheet with an adhesive layer is bonded to the second coating layer of the PET film with coating layers on both sides, thereby producing a protective sheet for workpiece processing. Using the obtained protective sheet for workpiece processing, the number of foreign matter adhesion was measured. The results are shown in Table 2.

[Table 1] Amount of the buffer layer forming composition (parts by mass) CN8881 IBXA PEG(200) PEG(400) PEG(600) 3TMPTA 6TMPTA 9TMPTA Example 1 50 50 Example 2 40 10 50 Example 3 40 10 50 Example 4 40 10 50 Comparative example 1 50 20 Comparative example 2 40 60 Comparative example 3 50 50 Comparative example 4 30 20 50 Example 5 40 40 20 Example 6 40 10 50 Comparative example 5 50 50

Abbreviations in Table 1 are as follows. CN8881: Urethane acrylate oligomer manufactured by Sartomer Corporation IBXA: Isobornyl acrylate PEG (200): Polyethylene glycol (200) diacrylate PEG (400): Polyethylene glycol (400) diacrylate PEG (600): Polyethylene glycol (600) diacrylate 3TMPTA: Ethoxylated (3) trimethylolpropane triacrylate 6TMPTA: Ethoxylated (6)trimethylolpropane triacrylate 9TMPTA: Ethoxylated (9) trimethylolpropane triacrylate

[Table 2] Young's modulus of buffer layer (MPa) Buffer layer stress relaxation rate (%) Evaluation results of the number of foreign matter adhesion Example 1 631 46.9 A Example 2 698 45.6 A Example 3 532 46.0 A Example 4 459 42.7 A Comparative example 1 52 3.4 D Comparative example 2 147 24.6 D Comparative example 3 287 40.7 C Comparative example 4 357 60.3 C Example 5 413 44.6 A Example 6 841 47.9 B Comparative example 5 975 72.3 C

From the above results, it can be seen that according to the protective sheet for workpiece processing of the present invention, since the buffer layer has specific viscoelasticity, even if the buffer layer comes into contact with foreign matter, foreign matter can be prevented from adhering to the buffer layer.

10:Protective film 11:Substrate 12:Adhesive layer 13: Buffer layer

[Fig. 1] is a schematic diagram showing the protective sheet for workpiece processing according to this embodiment. [Fig. 2] Fig. 2 is a diagram showing an example of foreign matter arrangement in the evaluation method of the number of foreign matter adhesion.

10:Protective film

11:Substrate

12:Adhesive layer

13: Buffer layer

Claims (5)

A protective sheet for workpiece processing, which is a protective sheet for workpiece processing having a base material, a buffer layer provided on one side of the base material, and an adhesive layer provided on the other side of the base material, Wherein, the stress relaxation rate of the buffer layer at 23°C is 50% or less, and the Young's modulus of the buffer layer at 23°C is 400 MPa or more. The protective sheet for workpiece processing according to claim 1, wherein the Young's modulus of the base material at 23° C. is 1000 MPa or more. The protective sheet for workpiece processing according to claim 1, wherein the buffer layer is a cured product of a buffer layer forming composition containing an energy ray polymerizable compound. The protective sheet for workpiece processing according to claim 1, which is attached in the step of individualizing the workpiece into an individualized workpiece by grinding the backside of the workpiece with grooves formed on the front side or a modified area formed inside. Used by attaching it to the front of the workpiece. A method of manufacturing an individualized workpiece, which includes the step of attaching a protective sheet for workpiece processing according to any one of claims 1 to 4 on the front side of the workpiece, The step of forming a groove from the front side of the above-mentioned workpiece, or forming a modified area inside the workpiece from the front or back side of the above-mentioned workpiece, and A step of grinding the workpiece with the protective sheet attached on the front and having the groove or the modified area formed thereon from the back side, and individualizing the workpiece into a plurality of individualized workpieces using the groove or the modified area as a starting point.