JP7488678B2 - Protective sheet for semiconductor processing and method for manufacturing semiconductor device - Google Patents

Description

The present invention relates to a protective sheet for semiconductor processing and a method for manufacturing a semiconductor device. In particular, the present invention relates to a protective sheet for semiconductor processing that is suitable for use in a method for grinding the back surface of a semiconductor wafer having irregularities and dividing the semiconductor wafer into individual pieces using the resulting stress, and a method for manufacturing a semiconductor device that uses the protective sheet for semiconductor processing.

As various electronic devices become smaller and more multifunctional, the semiconductor chips mounted on them are also required to be smaller and thinner. In order to thin the chips, it is common to grind the backside of the semiconductor wafer to adjust the thickness. In order to obtain thin chips, a method called dicing before grinding (DBG) is sometimes used, in which grooves of a specified depth are formed on the front side of the wafer with a dicing blade, and then the wafer is ground from the backside, and the wafer is diced into individual pieces by grinding to obtain chips. With DBG, the backside grinding of the wafer and the dicing of the wafer can be performed simultaneously, allowing for efficient production of thin chips.

Traditionally, when grinding the backside of a semiconductor wafer or manufacturing chips using DBG, it is common to apply an adhesive tape called a backgrind sheet to the wafer surface to protect the circuits on the wafer surface and to hold the semiconductor wafer and semiconductor chips in place.

The backgrind sheet used in DBG is an adhesive tape that includes a substrate and an adhesive layer on one side of the substrate. As an example of such an adhesive tape, Patent Documents 1 and 2 disclose an adhesive tape that includes a substrate with a high Young's modulus, a buffer layer on one side of the substrate, and an adhesive layer on the other side.

In recent years, a method has been proposed as a variation of the dicing-before method, in which a modified region is created inside the wafer using a laser, and the wafer is divided into individual pieces by the stress generated during grinding the back surface of the wafer. Hereinafter, this method may be referred to as LDBG (Laser Dicing Before Grinding). In LDBG, the wafer is cut in the crystal direction starting from the modified region, so the occurrence of chipping can be reduced more than in the dicing-before method using a dicing blade. As a result, chips with excellent bending strength can be obtained, and this can contribute to further thinning of the chips. In addition, compared to DBG, in which a groove of a specified depth is formed on the wafer surface using a dicing blade, there is no area where the wafer is cut away by the dicing blade, that is, the kerf width is extremely small, so the chip yield is excellent.

On the other hand, when mounting a multi-pin LSI package used in an MPU, gate array, etc., on a printed wiring board, a flip-chip mounting method has been adopted in which a semiconductor chip with convex electrodes (bumps) made of eutectic solder, high-temperature solder, gold, etc., is formed on the connection pads, and these bumps are brought face-to-face and into contact with corresponding terminals on a chip-mounting substrate using the so-called face-down method, and melted/diffusion bonded.

International Publication No. 2015/156389 JP 2015-183008 A

The semiconductor chips used in this mounting method are obtained by dicing a semiconductor wafer having irregularities, such as a semiconductor wafer with convex electrodes formed thereon. Even when grinding such a semiconductor wafer having irregularities using DBG, as described above, a backgrind tape is attached to the circuit surface of the semiconductor wafer to protect the circuit surface during grinding and to prevent the chips from moving after the wafer is diced.

However, when the backgrind tapes described in Patent Documents 1 and 2 are applied to the circuit surface of a semiconductor wafer having irregularities and then ground using a DBG, the backgrind tapes described in Patent Documents 1 and 2 cannot adequately conform to the irregularities of the semiconductor wafer, causing problems such as water seeping into the circuit surface during grinding and chip movement (chip shift) after the wafer is diced.

The present invention was made in consideration of these circumstances, and aims to provide a protective sheet for semiconductor processing that can adequately conform to the unevenness of the wafer and suppress cracks in the chips after grinding, even when semiconductor wafers with unevenness are thinned using DBG or the like.

The aspects of the present invention are as follows.
[1] A protective sheet for semiconductor processing comprising a substrate, and an intermediate layer and a pressure-sensitive adhesive layer, in that order, on one main surface of the substrate, and satisfying the following (a) and (b):
(a) the loss tangent of the intermediate layer at 50°C measured at a frequency of 1 Hz is 0.40 or more and 0.65 or less; (b) the ratio [A/I] of the storage modulus A of the pressure-sensitive adhesive layer to the storage modulus I of the intermediate layer at 50°C measured at a frequency of 1 Hz is 0.80 or more and 3.50 or less.

[2] A semiconductor processing protective sheet according to [1], which has a buffer layer on the other main surface of the substrate.

[3] A protective sheet for semiconductor processing according to [1] or [2], in which the Young's modulus of the substrate is 1000 MPa or more.

[4] A protective sheet for semiconductor processing according to any one of [1] to [3], in which the thickness of the intermediate layer is 60 μm or more and 250 μm or less.

[5] A semiconductor processing protective sheet according to any one of [1] to [4], in which the adhesive layer is energy ray curable.

[6] A semiconductor processing protective sheet according to any one of [1] to [5], wherein the intermediate layer is energy ray curable.

[7] A semiconductor processing protective sheet according to any one of [1] to [6], which is attached to the surface of a semiconductor wafer in a process of grinding the back surface of a semiconductor wafer having grooves formed on the surface of the semiconductor wafer to separate the semiconductor wafer into semiconductor chips by grinding.

[8] A step of attaching the semiconductor processing protective sheet according to any one of [1] to [7] to a surface of a semiconductor wafer having projections and recesses;
forming a groove from a front surface side of the semiconductor wafer, or forming a modified region inside the semiconductor wafer from the front surface or rear surface of the semiconductor wafer;
A step of grinding a semiconductor wafer having a semiconductor processing protection sheet attached to a surface thereof and having grooves or modified regions formed thereon from a back surface thereof to separate the semiconductor wafer into a plurality of chips starting from the grooves or modified regions;
and peeling the protective sheet for semiconductor processing from the individual semiconductor chips.

The present invention provides a protective sheet for semiconductor processing that can adequately conform to the unevenness of the wafer and suppress cracks in the chips after grinding, even when the semiconductor wafer is thinned using DBG or the like.

FIG. 1A is a schematic cross-sectional view showing an example of a protective sheet for semiconductor processing according to this embodiment. FIG. 1B is a schematic cross-sectional view showing another example of the protective sheet for semiconductor processing according to this embodiment. FIG. 2 is a schematic cross-sectional view showing a state in which the protective sheet for semiconductor processing according to this embodiment is attached to the circuit surface of a semiconductor wafer.

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

Singulating a semiconductor wafer refers to dividing a semiconductor wafer into individual circuits to obtain semiconductor chips.

The "front side" of a semiconductor wafer refers to the side on which circuits, electrodes, etc. are formed, and the "back side" refers to the side on which circuits, etc. are not formed.

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

LDBG is a variation of DBG, in which a modified region is created inside the wafer using a laser, and the wafer is divided into individual pieces using stress generated during back grinding.

"Chip group" refers to multiple semiconductor chips that are held on the semiconductor processing protective sheet of the present invention after the semiconductor wafer is diced. These semiconductor chips as a whole form the same shape as the semiconductor wafer.

In this specification, for example, "(meth)acrylate" is used as a term to refer to both "acrylate" and "methacrylate," and the same applies to other similar terms.

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

(1. Protective sheet for semiconductor processing)
As shown in FIG. 1A, the protective sheet for semiconductor processing 1 according to this embodiment has a configuration in which an intermediate layer 20 and a pressure-sensitive adhesive layer 30 are laminated in this order on a substrate 10.

In this embodiment, the semiconductor processing protective sheet according to this embodiment is used by being attached to a semiconductor wafer having irregularities. An example of a semiconductor wafer having irregularities is a semiconductor wafer on which a convex electrode is formed.

For example, as shown in FIG. 2, the semiconductor processing protective sheet 1 according to this embodiment is used by attaching the main surface 30a of the adhesive layer 30 to the bump-forming surface 101a of a bumped semiconductor wafer in which bumps 102 serving as convex electrodes are formed on the semiconductor wafer 101. The bumps are formed so as to be electrically connected to the circuits formed on the semiconductor wafer, so the bump-forming surface 101a is the circuit surface.

In this embodiment, the bumped semiconductor wafer is singulated into multiple semiconductor chips by DBG or LDBG. That is, before or after the attachment of the semiconductor processing protective sheet, after grooves are formed on the front surface (circuit surface) or after modified regions are formed inside the semiconductor wafer, the back surface of the semiconductor wafer with the semiconductor processing protective sheet attached to the circuit surface is ground.

When unevenness such as convex electrodes is formed on a semiconductor wafer, the size of the unevenness relative to the thickness of the semiconductor wafer increases when the thickness of the semiconductor wafer is reduced by grinding. Therefore, if the unevenness is not properly embedded in the protective sheet for semiconductor processing, performing DBG or LDBG will cause the following problems to become more apparent. That is, problems such as water seeping into the circuit surface of the semiconductor wafer during back grinding, adhesive remaining on the kerf when the protective sheet for semiconductor processing is peeled off after grinding, and chips separated after grinding moving and colliding with each other, causing cracks in the chips, become apparent.

The semiconductor processing protective sheet according to this embodiment has an intermediate layer and an adhesive layer, which will be described later, and therefore can effectively prevent the above problems from occurring.

The semiconductor processing protective sheet is not limited to the configuration shown in FIG. 1A, and may have other layers as long as the effects of the present invention are obtained. That is, as long as the substrate, intermediate layer, and adhesive layer are laminated in this order, other layers may be formed, for example, between the substrate and intermediate layer, or other layers may be formed between the intermediate layer and adhesive layer.

In particular, in this embodiment, as shown in FIG. 1B, it is preferable that the substrate has a buffer layer 40 on the main surface 30b opposite to the main surface on which the adhesive layer is formed. By having the buffer layer 40, the occurrence of the above problems can be further suppressed.

The components of the semiconductor processing protective sheet 1 shown in Figure 1B are described in detail below.

(2. Substrate)
The substrate is not limited as long as it is made of a material capable of supporting a semiconductor wafer. For example, various resin films used as substrates for backgrinding tapes are exemplified. The substrate may be made of a single-layer film made of one resin film, or may be made of a multi-layer film made of a plurality of resin films laminated together.

(2.1 Physical properties of the substrate)
In this embodiment, the substrate preferably has high rigidity. The substrate has high rigidity, so that the semiconductor wafer can be held without being damaged even if the thickness of the wafer is reduced by grinding. Specifically, the substrate has a Young's modulus of preferably 1000 MPa or more, more preferably 1500 MPa or more, and even more preferably 2000 MPa or more.

In this embodiment, the thickness of the substrate is preferably 15 μm or more and 200 μm or less, and more preferably 40 μm or more and 150 μm or less.

(2.2 Substrate material)
The material of the substrate is preferably a material having a Young's modulus within the above range. In the present embodiment, examples of the material include polyesters such as polyethylene terephthalate, polyethylene naphthalate, polybutylene terephthalate, wholly aromatic polyester, polyamide, polycarbonate, polyacetal, modified polyphenylene oxide, polyphenylene sulfide, polysulfone, polyether ketone, biaxially oriented polypropylene, etc. Among these, polyesters are preferred, and polyethylene terephthalate is more preferred.

(3. Middle Class)
The intermediate layer is a layer disposed between the substrate and the adhesive layer. In this embodiment, the intermediate layer, together with the adhesive layer, can sufficiently follow the unevenness formed on the surface of the semiconductor wafer, and the unevenness can be embedded in the adhesive layer and the intermediate layer. As a result, even when the semiconductor wafer is ground very thin and a force is applied to the convex electrodes, the adhesive layer and the intermediate layer can sufficiently protect the convex electrodes. In addition, when the convex electrodes break through the adhesive layer, the intermediate layer embeds and protects the convex electrodes. The intermediate layer may be composed of one layer (single layer), or may be composed of two or more layers.

The thickness of the intermediate layer 20 may be set taking into consideration the size of the unevenness of the semiconductor wafer, for example, the height of the convex electrodes. In this embodiment, the thickness of the intermediate layer 20 is preferably 60 μm or more and 250 μm or less, and more preferably 100 μm or more and 200 μm or less. The thickness of the intermediate layer means the thickness of the entire intermediate layer. For example, the thickness of an intermediate layer composed of multiple layers means the total thickness of all the layers that make up the intermediate layer.

In this embodiment, the intermediate layer has the following physical properties:

(3.1 Loss tangent at 50°C)
In this embodiment, the loss tangent (tan δ) of the intermediate layer is within a range of 0.40 or more and 0.65 or less at 50° C. The loss tangent is defined as “loss modulus/storage modulus” and is a value measured by a dynamic viscoelasticity measuring device based on the response to a stress applied to an object.

By having the loss tangent of the intermediate layer at 50°C be 0.40 or more, the irregularities formed on the surface of the wafer are sufficiently embedded in the semiconductor processing protective sheet, thereby preventing water from penetrating during grinding. In addition, by having the loss tangent of the intermediate layer at 50°C be 0.65 or less, chip shift after the wafer is singulated can be prevented.

In this embodiment, if the intermediate layer is energy ray curable, the loss tangent of the intermediate layer at 50°C is the loss tangent before energy ray curing.

The loss tangent of the intermediate layer at 50°C is preferably 0.42 or more. Also, the loss tangent of the intermediate layer at 50°C is preferably 0.64 or less.

The loss tangent of the intermediate layer at 50°C may be measured by a known method. In this embodiment, the intermediate layer is treated as a sample of a predetermined size, and a dynamic viscoelasticity measuring device is used to apply strain to the sample at a frequency of 1 Hz within a predetermined temperature range to measure the elastic modulus, and the loss tangent can be calculated from the measured elastic modulus.

(3.2 Ratio of storage modulus I of intermediate layer to storage modulus A of pressure-sensitive adhesive layer)
In this embodiment, when the storage modulus (G') of the intermediate layer at 50°C is defined as storage modulus I and the storage modulus (G') of the pressure-sensitive adhesive layer described below is defined as storage modulus A, the ratio of storage modulus I to storage modulus A ([A/I]) is 0.80 or more and 3.50 or less.

By having an [A/I] of 0.80 or more at 50°C, the protective sheet for semiconductor processing can adequately conform to the unevenness of the semiconductor wafer, allowing the unevenness of the semiconductor wafer to be properly embedded in the protective sheet for semiconductor processing. As a result, it is possible to suppress the intrusion of water during grinding. In addition, by having an [A/I] of 3.50 or less at 50°C, it is possible to suppress adhesion of the adhesive to the kerf when the protective sheet for semiconductor processing is peeled off.

In this embodiment, if the intermediate layer is energy ray curable, the storage modulus I is the storage modulus before energy ray curing.

The storage modulus I is not particularly limited as long as it satisfies the above range of [A/I]. In this embodiment, the storage modulus I is preferably 0.03 MPa or more and 0.08 MPa or less.

The storage modulus of the intermediate layer at 50°C (storage modulus I) may be measured by a known method. For example, the intermediate layer is treated as a sample of a given size, and a dynamic viscoelasticity measuring device is used to apply strain to the sample at a frequency of 1 Hz within a given temperature range to measure the modulus, and the storage modulus I can be calculated from the measured modulus.

(3.3 Intermediate layer composition)
The composition of the intermediate layer is not particularly limited as long as the intermediate layer has the above physical properties, but in this embodiment, the intermediate layer is preferably composed of a composition containing a resin (intermediate layer composition). Specifically, the intermediate layer composition preferably contains an acrylic polymer (A) having a weight average molecular weight of 300,000 to 1,500,000 and an energy ray curable acrylic polymer (B) having a weight average molecular weight of 50,000 to 250,000. The acrylic polymer (A) is non-energy ray curable or energy ray curable, but in this embodiment, it is preferably non-energy ray curable.

In this specification, the term "weight average molecular weight" refers to a polystyrene-equivalent value measured by gel permeation chromatography (GPC) unless otherwise specified. Measurements by such a method are carried out, for example, using a high-speed GPC apparatus "HLC-8120GPC" manufactured by Tosoh Corporation, connected in this order to high-speed columns "TSK guard column H _XL -H", "TSK Gel GMH _XL ", and "TSK Gel G2000 H _XL " (all manufactured by Tosoh Corporation), under conditions of a column temperature of 40°C, a liquid delivery rate of 1.0 mL/min, and a differential refractometer as a detector.

(3.3.1 Acrylic polymer (A))
As described above, the acrylic polymer (A) may be energy ray curable or non-energy ray curable. In this embodiment, the case where the acrylic polymer (A) is non-energy ray curable will be described. The acrylic polymer (A) is preferably a non-energy ray curable polymer having a structural unit derived from (meth)acrylate. Specifically, the acrylic polymer (A) is more preferably an acrylic copolymer having a structural unit derived from an alkyl (meth)acrylate (a1) and a structural unit derived from a functional group-containing monomer (a2).

As the alkyl (meth)acrylate (a1), an alkyl (meth)acrylate having an alkyl group with 1 to 18 carbon atoms is used. Specific examples include methyl (meth)acrylate, ethyl (meth)acrylate, propyl (meth)acrylate, n-butyl (meth)acrylate, n-pentyl (meth)acrylate, n-hexyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, isooctyl (meth)acrylate, n-decyl (meth)acrylate, n-dodecyl (meth)acrylate, n-tridecyl (meth)acrylate, myristyl (meth)acrylate, palmityl (meth)acrylate, and stearyl (meth)acrylate.

Among these, the alkyl (meth)acrylate (a1) is preferably an alkyl (meth)acrylate having an alkyl group with 4 to 8 carbon atoms. Specifically, n-butyl (meth)acrylate is preferred. The alkyl (meth)acrylate (a1) may be used alone or in combination of two or more.

The content of the structural units derived from alkyl (meth)acrylate (a1) in the acrylic polymer (A) is preferably 50 to 99.5% by mass, more preferably 60 to 99% by mass, and even more preferably 80 to 95% by mass, based on the total structural units (100% by mass) of the acrylic polymer (A).

If this content is 50% by mass or more, the retention performance of the adhesive sheet is improved, and it becomes easier to improve the conformability to an adherend with a large unevenness. Also, if it is 99.5% by mass or less, a certain amount or more of the structural unit derived from component (a2) can be secured.

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

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

Examples of carboxyl group-containing monomers include (meth)acrylic acid, maleic acid, fumaric acid, and itaconic acid.

Epoxy-containing monomers include epoxy group-containing (meth)acrylic acid esters and non-acrylic epoxy group-containing monomers. Epoxy group-containing (meth)acrylic acid esters include, for example, glycidyl (meth)acrylate, β-methylglycidyl (meth)acrylate, (3,4-epoxycyclohexyl)methyl (meth)acrylate, 3-epoxycyclo-2-hydroxypropyl (meth)acrylate, and the like. Non-acrylic epoxy group-containing monomers include, for example, glycidyl crotonate, allyl glycidyl ether, and the like.

The functional group-containing monomer (a2) may be used alone or in combination of two or more.

Among the functional group-containing monomers (a2), carboxy group-containing monomers are more preferred, and among these, (meth)acrylic acid is even more preferred, and acrylic acid is most preferred. When a carboxy group-containing monomer is used as the functional group-containing monomer (a2), the cohesive strength of the intermediate layer is increased, and the retention performance of the intermediate layer is more easily improved.

The content of the structural units derived from the functional group-containing monomer (a2) in the acrylic polymer (A) is preferably 0.5 to 40% by mass, more preferably 3 to 20% by mass, and even more preferably 5 to 15% by mass, based on the total structural units (100% by mass) of the acrylic polymer (A).

If the content of the structural units derived from the (a2) component is 0.5% by mass or more, the cohesive strength of the intermediate layer will be high, and compatibility with the (B) component will also be easily improved. On the other hand, if the content is 40% by mass or less, a certain amount or more of the structural units derived from the (a1) component can be secured.

The acrylic polymer (A) may be a copolymer of an alkyl (meth)acrylate (a1) and a functional group-containing monomer (a2), or may be a copolymer of the (a1) component, the (a2) component, and a monomer (a3) other than the (a1) and (a2) components.

Examples of other monomers (a3) include (meth)acrylates having a cyclic structure such as cyclohexyl (meth)acrylate, benzyl (meth)acrylate, isobornyl (meth)acrylate, dicyclopentanyl (meth)acrylate, dicyclopentenyl (meth)acrylate, and dicyclopentenyloxyethyl (meth)acrylate, as well as vinyl acetate and styrene. The other monomers (a3) may be used alone or in combination of two or more.

The content of the structural units derived from the other monomer (a3) in the acrylic polymer (A) is preferably 0 to 20% by mass, more preferably 0 to 10% by mass, and even more preferably 0 to 5% by mass, based on the total structural units (100% by mass) of the acrylic polymer (A).

The weight average molecular weight (Mw) of the acrylic polymer (A) is preferably 300,000 to 1,500,000, more preferably 400,000 to 1,100,000, and even more preferably 450,000 to 900,000. By setting the Mw to be equal to or less than these upper limits, the acrylic polymer (A) has good compatibility with the acrylic polymer (B). In addition, by setting the Mw within the above range, the retention performance of the pressure-sensitive adhesive sheet is easily improved.

The content of the acrylic polymer (A) in the intermediate layer composition is preferably 40 to 95% by mass, more preferably 45 to 90% by mass, based on the total amount (100% by mass) of the intermediate layer composition.

When the intermediate layer composition is diluted with a diluent such as an organic solvent as described below, the total amount of the intermediate layer composition means the total amount of solids excluding the diluent. The same applies to the pressure-sensitive adhesive layer composition described below.

(3.3.2 Acrylic polymer (B))
The acrylic polymer (B) is an acrylic polymer having energy ray curability due to the introduction of an energy ray polymerizable group. The acrylic polymer (B) has a weight average molecular weight (Mw) of 50,000 to 250,000. In the present invention, by using the (B) component in the intermediate layer, the convex electrode is sufficiently embedded during grinding of the back surface of the semiconductor wafer before energy ray curing, and then the intermediate layer is cured with energy ray after grinding, thereby preventing cohesive failure of the intermediate layer and allowing good peeling from the semiconductor chip.

The weight average molecular weight (Mw) of the acrylic polymer (B) is preferably 60,000 to 220,000, more preferably 70,000 to 200,000, and even more preferably 85,000 to 150,000.

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

The acrylic polymer (B) is preferably a reaction product obtained by reacting an acrylic copolymer (B0) having a structural unit derived from an alkyl (meth)acrylate (b1) and a structural unit derived from a functional group-containing monomer (b2) with a polymerizable compound (Xb) having an energy ray-polymerizable group.

As the alkyl (meth)acrylate (b1), an alkyl (meth)acrylate having an alkyl group with 1 to 18 carbon atoms is used, and specific examples thereof include those exemplified as component (a1). Among these, the alkyl (meth)acrylate (b1) is preferably an alkyl (meth)acrylate having an alkyl group with 4 to 8 carbon atoms. Specifically, n-butyl (meth)acrylate is preferred. These may be used alone or in combination of two or more.

The content of the structural units derived from alkyl (meth)acrylate (b1) in the acrylic copolymer (B0) is preferably 50 to 95% by mass, more preferably 60 to 85% by mass, and even more preferably 65 to 80% by mass, relative to the total structural units (100% by mass) of the acrylic copolymer (B0). If this content is 50% by mass or more, the shape of the intermediate layer formed can be sufficiently maintained. Also, if it is 95% by mass or less, a certain amount of structural units derived from the (b2) component that serve as reaction sites with the polymerizable compound (Xb) can be secured.

The functional group-containing monomer (b2) may be a monomer having a functional group exemplified in the functional group-containing monomer (a2) described above, and is preferably one or more selected from a hydroxy group-containing monomer, a carboxy group-containing monomer, and an epoxy group-containing monomer. Specific examples of these compounds include the same compounds exemplified as the component (a2).

As the functional group-containing monomer (b2), a hydroxy group-containing monomer is preferred, and among them, various hydroxyalkyl (meth)acrylates such as 2-hydroxyethyl (meth)acrylate are more preferred. By using a hydroxyalkyl (meth)acrylate, it becomes relatively easy to react the acrylic copolymer (B0) with the polymerizable compound (Xb).

The functional groups in the functional group-containing monomer (a2) used in the acrylic polymer (A) and the functional group-containing monomer (b2) used in the acrylic polymer (B) may be the same or different, but are preferably different. That is, for example, if the functional group-containing monomer (a2) is a carboxyl group-containing monomer, the functional group-containing monomer (b2) is preferably a hydroxyl group-containing monomer. In this way, when the functional groups are different from each other, for example, it becomes possible to preferentially crosslink the acrylic polymer (B) with a crosslinking agent described later, which makes it easier to improve the retention performance of the pressure-sensitive adhesive sheet described above.

The content of the structural unit derived from the functional group-containing monomer (b2) in the acrylic copolymer (B0) is preferably 10 to 45% by mass, more preferably 15 to 40% by mass, and even more preferably 20 to 35% by mass, based on the total structural units (100% by mass) of the acrylic copolymer (B0). If it is 10% by mass or more, a relatively large number of reaction points with the polymerizable compound (Xb) can be secured, making it easier to introduce energetic polymerizability into the side chain. Also, if it is 45% by mass or less, the shape of the intermediate layer formed can be sufficiently maintained.

The acrylic copolymer (B0) may be a copolymer of an alkyl (meth)acrylate (b1) and a functional group-containing monomer (b2), but may also be a copolymer of the (b1) component, the (b2) component, and a monomer (b3) other than the (b1) and (b2) components.

Other examples of monomer (b3) include those exemplified above as monomer (a3).

The content of the structural units derived from the other monomer (b3) in the acrylic copolymer (B0) is preferably 0 to 30% by mass, more preferably 0 to 10% by mass, and even more preferably 0 to 5% by mass, relative to the total structural units (100% by mass) of the acrylic copolymer (B0).

The polymerizable compound (Xb) is a compound having an energy ray polymerizable group and a substituent (hereinafter simply referred to as a "reactive substituent") that can react with a functional group in the structural unit derived from the (b2) component of the acrylic copolymer (B0).

As described above, examples of the energy ray polymerizable group include a (meth)acryloyl group and a vinyl group, with a (meth)acryloyl group being preferred. In addition, the polymerizable compound (Xb) is preferably a compound having 1 to 5 energy ray polymerizable groups per molecule.

The reactive substituent in the polymerizable compound (Xb) may be appropriately changed depending on the functional group possessed by the functional group-containing monomer (b2), but examples thereof include an isocyanate group, a carboxyl group, an epoxy group, etc., and from the viewpoint of reactivity, etc., an isocyanate group is preferred. When the polymerizable compound (Xb) has an isocyanate group, for example, when the functional group of the functional group-containing monomer (b2) is a hydroxyl group, it becomes possible for the polymerizable compound (Xb) to easily react with the acrylic copolymer (B0).

Specific examples of the polymerizable compound (Xb) include (meth)acryloyloxyethyl isocyanate, meta-isopropenyl-α,α-dimethylbenzyl isocyanate, (meth)acryloyl isocyanate, allyl isocyanate, glycidyl (meth)acrylate, (meth)acrylic acid, etc. These polymerizable compounds (Xb) may be used alone or in combination of two or more.

Among these, (meth)acryloyloxyethyl isocyanate is preferred from the viewpoint that it is a compound that has an isocyanate group suitable as the reactive substituent and has an appropriate distance between the main chain and the energy ray polymerizable group.

Of the total amount (100 equivalents) of functional groups derived from the functional group-containing monomer (b2) in the acrylic polymer (B), preferably 40 to 98 equivalents, more preferably 60 to 90 equivalents, and even more preferably 70 to 85 equivalents of the polymerizable compound (Xb) are reacted with the functional groups.

In the intermediate layer composition, the content of the acrylic polymer (B) is preferably 5 to 60 parts by mass, and more preferably 10 to 50 parts by mass, per 100 parts by mass of the acrylic polymer (A). By making the content of the (B) component relatively small in this manner, the intermediate layer can easily conform to the irregularities of the semiconductor wafer.

3.3.3 Crosslinking Agents
The intermediate layer composition preferably further contains a crosslinking agent. Examples of the crosslinking agent include isocyanate-based crosslinking agents, epoxy-based crosslinking agents, aziridine-based crosslinking agents, and metal chelate-based crosslinking agents, and among these, isocyanate-based crosslinking agents are preferred. When an isocyanate-based crosslinking agent is used, for example, when component (B) has a hydroxyl group, the crosslinking agent preferentially crosslinks the acrylic polymer (B).

The intermediate layer composition is crosslinked by the crosslinking agent, for example by heating after application. The intermediate layer is formed by crosslinking the acrylic polymer, particularly the low molecular weight acrylic polymer (B), etc., so that the coating film is properly formed and the intermediate layer can easily function.

The content of the crosslinking agent is preferably 0.1 to 10 parts by mass, more preferably 0.5 to 7 parts by mass, and even more preferably 1 to 5 parts by mass, per 100 parts by mass of the acrylic polymer (A).

Examples of isocyanate crosslinking agents include polyisocyanate compounds. Specific examples of polyisocyanate compounds include aromatic polyisocyanates such as tolylene diisocyanate, diphenylmethane diisocyanate, and xylylene diisocyanate, aliphatic polyisocyanates such as hexamethylene diisocyanate, and alicyclic polyisocyanates such as isophorone diisocyanate and hydrogenated diphenylmethane diisocyanate. Other examples include biuret and isocyanurate forms of these compounds, as well as adducts that are reaction products with low-molecular-weight active hydrogen-containing compounds such as ethylene glycol, propylene glycol, neopentyl glycol, trimethylolpropane, and castor oil.

These may be used alone or in combination of two or more. Among the above, adducts of aromatic polyisocyanates such as tolylene diisocyanate with polyhydric alcohols (e.g., trimethylolpropane, etc.) are preferred.

Epoxy crosslinking agents include, for example, 1,3-bis(N,N'-diglycidylaminomethyl)cyclohexane, N,N,N',N'-tetraglycidyl-m-xylylenediamine, ethylene glycol diglycidyl ether, 1,6-hexanediol diglycidyl ether, trimethylolpropane diglycidyl ether, diglycidylaniline, diglycidylamine, etc. These may be used alone or in combination of two or more.

Examples of metal chelate crosslinking agents include compounds in which acetylacetone, ethyl acetoacetate, tris(2,4-pentanedionate), etc. are coordinated to polyvalent metals such as aluminum, iron, copper, zinc, tin, titanium, nickel, antimony, magnesium, vanadium, chromium, and zirconium. These may be used alone or in combination of two or more.

Examples of aziridine crosslinking agents include diphenylmethane-4,4'-bis(1-aziridinecarboxamide), trimethylolpropane tri-β-aziridinylpropionate, tetramethylolmethane tri-β-aziridinylpropionate, toluene-2,4-bis(1-aziridinecarboxamide), triethylenemelamine, bisisophthaloyl-1-(2-methylaziridine), tris-1-(2-methylaziridine)phosphine, trimethylolpropane tri-β-(2-methylaziridine)propionate, and hexa[1-(2-methyl)-aziridinyl]triphosphatriazine.

(3.3.4 Photopolymerization initiator)
The intermediate layer composition preferably further contains a photopolymerization initiator. By containing the photopolymerization initiator, the intermediate layer composition is easily cured by energy rays such as ultraviolet rays.

Examples of photopolymerization initiators include acetophenone, 2,2-diethoxybenzophenone, 4-methylbenzophenone, 2,4,6-trimethylbenzophenone, Michler's ketone, benzoin, benzoin methyl ether, benzoin ethyl ether, benzoin isopropyl ether, benzoin isobutyl ether, benzyl diphenylsulfide, tetramethylthiuram monosulfide, benzyl dimethyl ketal, dibenzyl, diacetyl, 1-chloroanthraquinone, 2-chloroanthraquinone, 2-ethylanthraquinone, 2,2-dimethoxy-1,2-diphenylethane-1-one, 1 1-Hydroxycyclohexyl phenyl ketone, 2-methyl-1-[4-(methylthio)phenyl]-2-morpholinopropanone-1,2-benzyl-2-dimethylamino-1-(4-morpholinophenyl)-butanone-1,2-hydroxy-2-methyl-1-phenyl-propan-1-one, diethylthioxanthone, isopropylthioxanthone, low molecular weight polymerization initiators such as 2,4,6-trimethylbenzoyldiphenyl-phosphine oxide, and oligomerized polymerization initiators such as oligo{2-hydroxy-2-methyl-1-[4-(1-methylvinyl)phenyl]propanone}. These may be used alone or in combination of two or more. Among these, 1-hydroxycyclohexyl phenyl ketone is preferred.

The content of the photopolymerization initiator is preferably 1 to 10 parts by mass, more preferably 2 to 8 parts by mass, per 100 parts by mass of the acrylic polymer (A) so that curing can proceed sufficiently even with a small content of the acrylic polymer (B).

The intermediate layer composition may contain other additives as long as the effects of the present invention are not impaired. Examples of other additives include antioxidants, softeners (plasticizers), fillers, rust inhibitors, pigments, dyes, and tackifiers. When these additives are contained, the content of each additive is preferably 0.01 to 6 parts by mass, and more preferably 0.01 to 2 parts by mass, per 100 parts by mass of the acrylic polymer (A).

The storage modulus and loss tangent of the intermediate layer can be adjusted, for example, when an acrylic polymer (B) is used, by adjusting the type and amount of monomers constituting the acrylic polymer (B) and the amount of energy ray polymerizable groups introduced into the acrylic polymer (B). For example, increasing the amount of energy ray polymerizable groups tends to increase the storage modulus. Furthermore, the storage modulus and loss tangent can be appropriately adjusted by adjusting the amount of crosslinking agent and the amount of photopolymerization initiator blended into the intermediate layer.

(4. Pressure-sensitive adhesive layer)
The adhesive layer is attached to the circuit surface of the semiconductor wafer, and protects the circuit surface and supports the semiconductor wafer until it is peeled off from the circuit surface. In this embodiment, the adhesive layer, together with the intermediate layer, can sufficiently follow the unevenness formed on the surface of the semiconductor wafer, and the unevenness can be embedded in the protective sheet for semiconductor processing. As a result, even if the semiconductor wafer is ground very thin and a force is applied to the convex electrodes, the protective sheet for semiconductor processing can sufficiently protect the convex electrodes, etc. Furthermore, even if the semiconductor wafer is divided into individual pieces, contact between the semiconductor chips can be suppressed. In addition, the adhesive layer may be composed of one layer (single layer), or may be composed of two or more layers.

The thickness of the adhesive layer is not particularly limited as long as it is thick enough to sufficiently support a semiconductor wafer. In this embodiment, the thickness of the adhesive layer is preferably 5 μm or more and 500 μm or less, and more preferably 8 μm or more and 100 μm or less. The thickness of the adhesive layer means the thickness of the entire adhesive layer. For example, the thickness of an adhesive layer composed of multiple layers means the total thickness of all layers that make up the adhesive layer.

In this embodiment, the adhesive layer has the following physical properties:

(4.1 Storage Modulus A of Pressure-Sensitive Adhesive Layer)
As described above, the storage modulus (G') of the pressure-sensitive adhesive layer at 50°C is represented by the storage modulus A. The storage modulus A is not particularly limited as long as it satisfies the above range of [A/I]. In this embodiment, the storage modulus A is preferably 0.03 MPa or more and 0.15 MPa or less. In addition, the storage modulus A is more preferably 0.04 MPa or more, and even more preferably 0.12 MPa or more. In addition, the storage modulus A is more preferably 0.05 MPa or less, and even more preferably 0.10 MPa or less. In this embodiment, when the pressure-sensitive adhesive layer has energy ray curing properties, the storage modulus A is the storage modulus before energy ray curing.

The storage modulus of the adhesive layer at 50°C (storage modulus A) may be measured by a known method. For example, the adhesive layer is treated as a sample of a given size, and a dynamic viscoelasticity measuring device is used to apply strain to the sample at a frequency of 1 Hz within a given temperature range to measure the modulus, and the storage modulus A can be calculated from the measured modulus.

(4.2 Pressure-sensitive adhesive layer composition)
The adhesive layer is not particularly limited in composition as long as it has the above physical properties, but in this embodiment, it is preferable that the adhesive layer is composed of a composition having a resin (adhesive layer composition). Specifically, it is preferable that the adhesive layer composition is energy ray curable. Since the adhesive layer composition is energy ray curable, it has a high adhesive strength that can sufficiently hold the semiconductor wafer before the energy ray irradiation, but after the energy ray irradiation, the adhesive layer is cured and the adhesive strength is reduced, and even if the semiconductor wafer, which is the adherend, is singulated, it becomes easy to peel it off from the singulated semiconductor chip.

The adhesive layer composition that forms the adhesive layer contains, for example, acrylic polymers, polyurethanes, rubber-based polymers, polyolefins, silicones, etc., as adhesive components (adhesive resins) that can impart adhesive properties to the adhesive layer. Of these, acrylic polymers are preferred.

The adhesive layer composition forming the adhesive layer may have energy ray curability by blending an energy ray curable compound separately from the adhesive resin, but it is preferable that the above-mentioned adhesive resin itself has energy ray curability. When the adhesive resin itself has energy ray curability, an energy ray polymerizable group is introduced into the adhesive resin, but it is preferable that the energy ray polymerizable group is introduced into the main chain or side chain of the adhesive resin.

In addition, when an energy ray curable compound is blended separately from the adhesive resin, a monomer or oligomer having an energy ray polymerizable group is used as the energy ray curable compound. The oligomer is an oligomer having a weight average molecular weight (Mw) of less than 10,000, such as urethane (meth)acrylate. In addition, even if the adhesive resin itself is energy ray curable, the adhesive layer composition may also contain an energy ray curable compound in addition to the adhesive resin.

Hereinafter, a more detailed explanation will be given of the case where the energy ray-curable adhesive resin contained in the adhesive layer composition is an acrylic polymer (hereinafter also referred to as "acrylic polymer (C)").

(4.2.1 Acrylic polymer (C))
The acrylic polymer (C) is an acrylic polymer having an energy ray polymerizable group introduced therein and a structural unit derived from a (meth)acrylate. The energy ray polymerizable group is preferably introduced into a side chain of the acrylic polymer.

The acrylic polymer (C) is preferably a reaction product obtained by reacting an acrylic copolymer (C0) having a structural unit derived from an alkyl (meth)acrylate (c1) and a structural unit derived from a functional group-containing monomer (c2) with a polymerizable compound (Xc) having an energy ray-polymerizable group.

As the alkyl (meth)acrylate (c1), an alkyl (meth)acrylate having an alkyl group with 1 to 18 carbon atoms is used, and specific examples thereof include those exemplified as component (a1). Among these, the alkyl (meth)acrylate (c1) is preferably an alkyl (meth)acrylate having an alkyl group with 4 to 8 carbon atoms. Specifically, 2-ethylhexyl (meth)acrylate and n-butyl (meth)acrylate are preferred, and n-butyl (meth)acrylate is more preferred. These may be used alone or in combination of two or more.

From the viewpoint of improving the adhesive strength of the pressure-sensitive adhesive layer to be formed, the content of the structural units derived from alkyl (meth)acrylate (c1) in the acrylic copolymer (C0) is preferably 50 to 99% by mass, more preferably 60 to 97% by mass, and even more preferably 70 to 96% by mass, based on the total structural units (100% by mass) of the acrylic copolymer (C0).

For example, the alkyl (meth)acrylate (c1) may contain ethyl (meth)acrylate and methyl (meth)acrylate in addition to the above-mentioned 2-ethylhexyl (meth)acrylate and n-butyl (meth)acrylate. By including these monomers, it becomes easier to adjust the adhesive performance of the adhesive layer to the desired one.

The functional group-containing monomer (c2) may be a monomer having a functional group exemplified as the functional group-containing monomer (a2) described above, and specifically, it is preferably one or more selected from a hydroxy group-containing monomer, a carboxy group-containing monomer, and an epoxy group-containing monomer. Specific examples of these compounds include the same compounds exemplified as the component (a2).

As the functional group-containing monomer (c2), among the above, a hydroxy group-containing monomer is more preferable, among which a hydroxyalkyl (meth)acrylate is more preferable, 2-hydroxyethyl (meth)acrylate and 4-hydroxybutyl (meth)acrylate are even more preferable, and 4-hydroxybutyl (meth)acrylate is particularly preferable.

By using a hydroxyalkyl (meth)acrylate as component (c2), it becomes relatively easy to react the acrylic copolymer (C0) with the polymerizable compound (Xc). In addition, by using 4-hydroxybutyl (meth)acrylate, the tensile strength of the intermediate layer increases, making it easier to prevent adhesive residue.

The content of the structural units derived from the functional group-containing monomer (c2) in the acrylic copolymer (C0) is preferably 1 to 40% by mass, more preferably 2 to 35% by mass, and even more preferably 3 to 30% by mass, based on the total structural units (100% by mass) of the acrylic copolymer (C0).

If the content is 1% by mass or more, a certain amount of functional groups that become reaction sites with the polymerizable compound (Xc) can be secured. Therefore, the adhesive layer can be appropriately cured by irradiation with energy rays, so that the adhesive strength after irradiation with energy rays can be reduced. Furthermore, it becomes easier to improve the interlayer strength between the adhesive layer and the intermediate layer after irradiation with energy rays. In addition, if the content is 40% by mass or less, a sufficient pot life can be secured when applying a solution of the adhesive layer composition to form an adhesive layer.

The acrylic copolymer (C0) may be a copolymer of an alkyl (meth)acrylate (c1) and a functional group-containing monomer (c2), but may also be a copolymer of the (c1) component, the (c2) component, and a monomer (c3) other than the (c1) and (c2) components.

Other examples of monomer (c3) include those exemplified above as monomer (a3).

The content of the structural units derived from the other monomer (c3) in the acrylic copolymer (C0) is preferably 0 to 30% by mass, more preferably 0 to 10% by mass, and even more preferably 0 to 5% by mass, relative to the total structural units (100% by mass) of the acrylic copolymer (C0).

The polymerizable compound (Xc), like the above-mentioned polymerizable compound (Xb), is a compound having an energy ray-polymerizable group and a substituent (reactive substituent) capable of reacting with a functional group in the structural unit derived from the component (c2) of the acrylic copolymer (C0), and is preferably a compound having 1 to 5 energy ray-polymerizable groups per molecule.

Specific examples of the reactive substituent and the energy ray polymerizable group are the same as those of the polymerizable compound (Xb), and therefore the reactive substituent is preferably an isocyanate group, and the energy ray polymerizable group is preferably a (meth)acryloyl group.

Specific examples of the polymerizable compound (Xc) include those exemplified as the polymerizable compound (Xb) described above, with (meth)acryloyloxyethyl isocyanate being preferred. The polymerizable compound (Xc) may be used alone or in combination of two or more kinds.

Of the total amount (100 equivalents) of functional groups derived from the functional group-containing monomer (c2) in the acrylic copolymer (C0), preferably 30 to 98 equivalents, more preferably 40 to 95 equivalents, of the polymerizable compound (Xc) are reacted with the functional groups.

The weight average molecular weight (Mw) of the acrylic polymer (C) is preferably 100,000 to 1,500,000, more preferably 250,000 to 1,000,000, and even more preferably 350,000 to 800,000. Having such an Mw makes it possible to impart appropriate adhesiveness to the pressure-sensitive adhesive layer.

Even if the adhesive resin has energy ray curability, it is preferable that the adhesive layer composition contains an energy ray curable compound other than the adhesive resin. Such an energy ray curable compound is preferably a monomer or oligomer that has an unsaturated group in the molecule and can be polymerized and cured by energy ray irradiation.

Specific examples include polyvalent (meth)acrylate monomers such as trimethylolpropane tri(meth)acrylate, pentaerythritol (meth)acrylate, pentaerythritol tetra(meth)acrylate, dipentaerythritol hexa(meth)acrylate, 1,4-butylene glycol di(meth)acrylate, and 1,6-hexanediol (meth)acrylate, as well as oligomers such as urethane (meth)acrylate, polyester (meth)acrylate, polyether (meth)acrylate, and epoxy (meth)acrylate.

Among these, urethane (meth)acrylate oligomers are preferred because they have a relatively high molecular weight and are less likely to reduce the elastic modulus of the adhesive layer.

4.2.2 Crosslinking Agents
The pressure-sensitive adhesive layer composition preferably further contains a crosslinking agent. The pressure-sensitive adhesive layer composition is crosslinked by the crosslinking agent, for example, by heating after application. The pressure-sensitive adhesive layer is formed by appropriately forming a coating film by crosslinking the acrylic polymer (C) with the crosslinking agent, and is easily able to function as a pressure-sensitive adhesive layer.

Examples of crosslinking agents include isocyanate-based crosslinking agents, epoxy-based crosslinking agents, aziridine-based crosslinking agents, and chelate-based crosslinking agents. Of these, isocyanate-based crosslinking agents are preferred. The crosslinking agents may be used alone or in combination of two or more. Specific examples of isocyanate-based crosslinking agents include those exemplified as crosslinking agents that can be used in the intermediate layer composition, and the preferred compounds thereof are the same.

The content of the crosslinking agent is preferably 0.01 to 10 parts by mass, more preferably 0.1 to 7 parts by mass, and even more preferably 0.3 to 4 parts by mass, per 100 parts by mass of the acrylic polymer (C).

(4.2.3 Photopolymerization initiator)
The pressure-sensitive adhesive layer composition preferably further contains a photopolymerization initiator. Examples of the photopolymerization initiator include those exemplified as the photopolymerization initiator used in the intermediate layer composition described above. The photopolymerization initiator may be used alone or in combination of two or more kinds. Among the above, 2,2-dimethoxy-1,2-diphenylethan-1-one and 1-hydroxycyclohexyl phenyl ketone are preferred.

The content of the photopolymerization initiator is preferably 0.5 to 15 parts by mass, more preferably 1 to 12 parts by mass, and even more preferably 4.5 to 10 parts by mass, per 100 parts by mass of the acrylic polymer (C).

The adhesive layer composition may contain other additives as long as the effects of the present invention are not impaired. Examples of other additives include tackifiers, antioxidants, softeners (plasticizers), fillers, rust inhibitors, pigments, dyes, etc. When these additives are contained, the content of each additive is preferably 0.01 to 6 parts by mass, more preferably 0.02 to 2 parts by mass, per 100 parts by mass of the acrylic polymer (C).

The storage modulus and loss tangent of the adhesive layer can be adjusted, for example, when an acrylic polymer (C) is used, by the type and amount of monomers constituting the acrylic polymer (C) and the amount of energy ray polymerizable groups introduced into the acrylic polymer (C). For example, increasing the amount of energy ray polymerizable groups tends to increase the elastic modulus. Furthermore, the storage modulus and loss tangent can be appropriately adjusted by the amount of crosslinking agent and photopolymerization initiator blended into the adhesive layer.

5. Buffer Layer
As shown in Fig. 1B, the buffer layer is formed on the main surface of the substrate opposite to the main surface on which the adhesive layer is formed. The buffer layer 40 is a soft layer compared to the substrate, and relieves stress during back grinding of the semiconductor wafer, preventing cracks and chips from occurring in the semiconductor wafer. In addition, the semiconductor wafer with the semiconductor processing protective sheet attached thereto is placed on a vacuum table via the semiconductor processing protective sheet during back grinding, and the presence of the buffer layer as a constituent layer of the semiconductor processing protective sheet makes it easier to properly hold the semiconductor wafer on the vacuum table.

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

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

A substrate having a buffer layer can be obtained by laminating a buffer layer on one or both sides of a substrate.

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

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

Below, we will explain in detail each component contained in the buffer layer composition containing the energy ray-polymerizable compound.

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

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

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

The polyol compound used as the raw material for component (d1) is not particularly limited as long as it has two or more hydroxyl groups. It may be a difunctional diol, a trifunctional triol, or a polyol having four or more functional groups, but a difunctional diol is preferred, and a polyester type diol or a polycarbonate type diol is more preferred.

Examples of polyisocyanate compounds include aliphatic polyisocyanates such as tetramethylene diisocyanate, hexamethylene diisocyanate, and trimethylhexamethylene diisocyanate; alicyclic diisocyanates such as isophorone diisocyanate, norbornane diisocyanate, dicyclohexylmethane-4,4'-diisocyanate, dicyclohexylmethane-2,4'-diisocyanate, and ω,ω'-diisocyanate dimethylcyclohexane; and aromatic diisocyanates such as 4,4'-diphenylmethane diisocyanate, tolylene diisocyanate, xylylene diisocyanate, tolidine diisocyanate, tetramethylene xylylene diisocyanate, and naphthalene-1,5-diisocyanate.

Among these, isophorone diisocyanate, hexamethylene diisocyanate, and xylylene diisocyanate are preferred.

The above-mentioned polyol compound is reacted with a polyisocyanate compound to give a terminal isocyanate urethane prepolymer, which is then reacted with a (meth)acrylate having a hydroxyl group to give a urethane (meth)acrylate (d1). The (meth)acrylate having a hydroxyl group is not particularly limited as long as it is a compound having a hydroxyl group and a (meth)acryloyl group in at least one molecule.

Specific examples of (meth)acrylates having a hydroxy group include hydroxyalkyl (meth)acrylates such as 2-hydroxyethyl (meth)acrylate, 2-hydroxypropyl (meth)acrylate, 4-hydroxybutyl (meth)acrylate, 4-hydroxycyclohexyl (meth)acrylate, 5-hydroxycyclooctyl (meth)acrylate, 2-hydroxy-3-phenyloxypropyl (meth)acrylate, pentaerythritol tri(meth)acrylate, polyethylene glycol mono(meth)acrylate, and polypropylene glycol mono(meth)acrylate; hydroxy group-containing (meth)acrylamides such as N-methylol (meth)acrylamide; and reaction products obtained by reacting diglycidyl esters of vinyl alcohol, vinylphenol, and bisphenol A with (meth)acrylic acid; and the like.

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

The conditions for reacting the isocyanate-terminated urethane prepolymer and the (meth)acrylate having a hydroxyl group are preferably 60 to 100°C for 1 to 4 hours in the presence of a solvent and a catalyst, which are added as necessary.

The content of component (d1) in the buffer layer composition is preferably 10 to 70 mass%, more preferably 20 to 60 mass%, and even more preferably 25 to 55 mass%, based on the total amount (100 mass%) of the buffer layer composition.

(5.1.2 Polyfunctional polymerizable compound (d2))
The 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 a (meth)acryloyl group, a vinyl group, an allyl group, and a vinylbenzyl group. Two or more types of photopolymerizable unsaturated groups may be combined. A three-dimensional network structure (crosslinked structure) is formed by reacting a photopolymerizable unsaturated group in the polyfunctional polymerizable compound with a (meth)acryloyl group in component (d1) or by reacting photopolymerizable unsaturated groups in component (d2) with each other. When a polyfunctional polymerizable compound is used, the number of crosslinked structures formed by energy beam irradiation increases compared to when a compound containing only one photopolymerizable unsaturated group is used, and therefore the buffer layer exhibits unique viscoelasticity, making it easier to relieve stress during back grinding.

Note that the definition of component (d2) overlaps with the definitions of components (d3) and (d4) described below, but the overlapping parts are included in component (d2). For example, a compound having an alicyclic or heterocyclic group with 6 to 20 ring atoms and two or more (meth)acryloyl groups is included in the definitions of both components (d2) and (d3), but in the present invention, such a compound is included in component (d2). In addition, a compound containing a functional group such as a hydroxyl group, an epoxy group, an amide group, or an amino group and having two or more (meth)acryloyl groups is included in the definitions of both components (d2) and (d4), but in the present invention, such a compound is included in component (d2).

From the above viewpoints, 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.

The weight average molecular weight of component (d2) is preferably 30 to 40,000, more preferably 100 to 10,000, and even more preferably 200 to 1,000.

Specific examples of component (d2) include diethylene glycol di(meth)acrylate, ethylene glycol di(meth)acrylate, tetraethylene glycol di(meth)acrylate, neopentyl glycol di(meth)acrylate, 1,6-hexanediol di(meth)acrylate, trimethylolpropane tri(meth)acrylate, pentaerythritol tri(meth)acrylate, pentaerythritol tetra(meth)acrylate, dipentaerythritol hexa(meth)acrylate, divinylbenzene, vinyl (meth)acrylate, divinyl adipate, and N,N'-methylenebis(meth)acrylamide. Among these, dipentaerythritol hexa(meth)acrylate is preferred. Component (d2) may be used alone or in combination of two or more.

The content of component (d2) in the buffer layer composition is preferably 0 to 40 mass%, more preferably 3 to 20 mass%, and even more preferably 5 to 15 mass%, based on the total amount (100 mass%) of the buffer layer composition.

(5.1.3 Polymerizable compound (d3) having an alicyclic group or heterocyclic group having 6 to 20 ring atoms)
Component (d3) is a polymerizable compound having an alicyclic group or heterocyclic group with 6 to 20 ring atoms, and is preferably a compound having at least one (meth)acryloyl group, more preferably a compound having one (meth)acryloyl group. By using component (d3), the film-forming property of the obtained buffer layer composition can be improved.

Note that there is some overlap between the definition of component (d3) and the definition of component (d4) described below, but the overlapping portion is included in component (d4). For example, a compound having at least one (meth)acryloyl group, an alicyclic or heterocyclic group having 6 to 20 ring atoms, and a functional group such as a hydroxyl group, an epoxy group, an amide group, or an amino group is included in the definitions of both component (d3) and component (d4), but in the present invention, such a compound is considered to be included in component (d4).

Specific examples of component (d3) include alicyclic group-containing (meth)acrylates such as isobornyl (meth)acrylate, dicyclopentenyl (meth)acrylate, dicyclopentanyl (meth)acrylate, dicyclopentenyloxy (meth)acrylate, cyclohexyl (meth)acrylate, and adamantane (meth)acrylate; heterocyclic group-containing (meth)acrylates such as tetrahydrofurfuryl (meth)acrylate and morpholine (meth)acrylate; and the like. In addition, component (d3) may be used alone or in combination of two or more kinds.

Among the alicyclic group-containing (meth)acrylates, isobornyl (meth)acrylate is preferred, and among the heterocyclic group-containing (meth)acrylates, tetrahydrofurfuryl (meth)acrylate is preferred.

The content of component (d3) in the buffer layer composition is preferably 10 to 80 mass%, more preferably 20 to 70 mass%, and even more preferably 25 to 60 mass%, based on the total amount (100 mass%) of the buffer layer composition.

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

Component (d4) has good compatibility with component (d1), making it easier to adjust the viscosity of the buffer layer composition to an appropriate range. In addition, the buffer layer has good buffer performance even if it is made relatively thin.

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

Examples of hydroxyl group-containing (meth)acrylates include 2-hydroxyethyl (meth)acrylate, 2-hydroxypropyl (meth)acrylate, 3-hydroxypropyl (meth)acrylate, 2-hydroxybutyl (meth)acrylate, 3-hydroxybutyl (meth)acrylate, 4-hydroxybutyl (meth)acrylate, phenylhydroxypropyl (meth)acrylate, and 2-hydroxy-3-phenoxypropyl acrylate. Among these, hydroxyl group-containing (meth)acrylates having an aromatic ring, such as phenylhydroxypropyl (meth)acrylate, are more preferred. Component (d4) may be used alone or in combination of two or more.

The content of component (d4) in the buffer layer composition is preferably 0 to 40 mass %, more preferably 7 to 35 mass %, and even more preferably 10 to 30 mass %, relative to the total amount (100 mass %) of the buffer layer composition in order to improve the film-forming properties of the buffer layer composition.

(5.1.5 Polymerizable compound (d5) other than components (d1) to (d4))
The buffer layer composition may contain a polymerizable compound (d5) other than the above components (d1) to (d4) as long as the effect of the present invention is not impaired.

Examples of component (d5) include alkyl (meth)acrylates having an alkyl group with 1 to 20 carbon atoms; vinyl compounds such as styrene, hydroxyethyl vinyl ether, hydroxybutyl vinyl ether, N-vinyl formamide, N-vinyl pyrrolidone, and N-vinyl caprolactam. Component (d5) may be used alone or in combination of two or more kinds.

The content of component (d5) in the buffer layer forming composition is preferably 0 to 20% by mass, more preferably 0 to 10% by mass, even more preferably 0 to 5% by mass, and particularly preferably 0 to 2% by mass.

(5.1.6 Photopolymerization initiator)
It is preferable that the buffer layer composition further contains a photopolymerization initiator from the viewpoint of shortening the polymerization time by light irradiation and reducing the amount of light irradiation when forming the buffer layer.

Examples of photopolymerization initiators include benzoin compounds, acetophenone compounds, acylphosphinoxide compounds, titanocene compounds, thioxanthone compounds, peroxide compounds, and photosensitizers such as amines and quinones. More specifically, examples of photopolymerization initiators include 1-hydroxycyclohexyl phenyl ketone, 2-hydroxy-2-methyl-1-phenyl-propan-1-one, benzoin, benzoin methyl ether, benzoin ethyl ether, benzoin isopropyl ether, benzyl phenyl sulfide, tetramethylthiuram monosulfide, azobisisobutyrolnitrile, dibenzyl, diacetyl, 8-chloroanthraquinone, and bis(2,4,6-trimethylbenzoyl)phenylphosphine oxide. These photopolymerization initiators can be used alone or in combination of two or more.

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

(5.1.7 Other Additives)
The buffer layer 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, etc. When these additives are blended, the content of each additive in the buffer layer composition is preferably 0.01 to 6 parts by mass, more preferably 0.1 to 3 parts by mass, based on 100 parts by mass of the total amount of the energy ray-polymerizable compounds.

The buffer layer formed from the buffer layer composition containing the energy ray-polymerizable compound is obtained by polymerizing and curing the buffer layer composition having the above composition by irradiating it with energy rays. In other words, the buffer layer is a product obtained by curing the buffer layer composition.

Therefore, the buffer layer preferably contains polymerization units derived from component (d1) and polymerization units derived from component (d3). The buffer layer may also contain polymerization units derived from component (d2) and/or polymerization units derived from component (d4), or may contain polymerization units derived from component (d5). The content ratio of each polymerization unit in the buffer layer usually corresponds to the ratio (feed ratio) of each component constituting the buffer layer composition.

(6. Release Sheet)
A release sheet may be attached to the surface of the semiconductor processing protective sheet. The release sheet is specifically attached to the surface of the adhesive layer of the semiconductor processing protective sheet. The release sheet is attached to the surface of the adhesive layer to protect the adhesive layer during transportation and storage. The release sheet is releasably attached to the semiconductor processing protective sheet, and is peeled off and removed from the semiconductor processing protective sheet before the semiconductor processing protective sheet is used (i.e., before the wafer is attached).

The release sheet used is one that has at least one surface that has been subjected to a release treatment, specifically, one in which a release agent is applied to the surface of the release sheet substrate.

The substrate for the release sheet is preferably a resin film, and examples of the resin constituting the resin film include polyester resin films such as polyethylene terephthalate resin, polybutylene terephthalate resin, and polyethylene naphthalate resin, and polyolefin resins such as polypropylene resin and polyethylene resin. Examples of the release agent include rubber-based elastomers such as silicone-based resins, olefin-based resins, isoprene-based resins, and butadiene-based resins, long-chain alkyl-based resins, alkyd-based resins, and fluorine-based resins.

There are no particular limitations on the thickness of the release sheet, but it is preferably 10 to 200 μm, and more preferably 20 to 150 μm.

(7. Manufacturing method of protective sheet for semiconductor processing)
The method for manufacturing the semiconductor processing protective sheet of this embodiment is not particularly limited as long as it is a method that can form an intermediate layer and an adhesive layer on one main surface of the substrate and a buffer layer on the other main surface of the substrate, and any known method may be used.

First, as a composition for forming an intermediate layer, for example, a composition for an intermediate layer containing the above-mentioned components, or a composition obtained by diluting the composition for an intermediate layer with a solvent or the like is prepared. Similarly, as a composition for an adhesive layer for forming an adhesive layer, for example, a composition for an adhesive layer containing the above-mentioned components, or a composition obtained by diluting the composition for an adhesive layer with a solvent or the like is prepared. Similarly, as a composition for a buffer layer for forming a buffer layer, for example, a composition for a buffer layer containing the above-mentioned components, or a composition obtained by diluting the composition for an adhesive layer with a solvent or the like is prepared.

Examples of the solvent include organic solvents such as methyl ethyl ketone, acetone, ethyl acetate, tetrahydrofuran, dioxane, cyclohexane, n-hexane, toluene, xylene, n-propanol, and isopropanol.

Then, the buffer layer composition is applied to the release-treated surface of the first release sheet by a known method such as spin coating, spray coating, bar coating, knife coating, roll coating, blade coating, die coating, or gravure coating to form a coating film, and this coating film is semi-cured to form a buffer layer film on the release sheet. The buffer layer film formed on the release sheet is attached to a substrate, and the buffer layer film is completely cured to form a buffer layer.

In this embodiment, the coating film is preferably cured by irradiation with energy rays. The coating film may be cured in a single curing process or in multiple steps.

Next, the intermediate layer composition is applied to the release-treated surface of the second release sheet by a known method and then heated and dried to form an intermediate layer on the second release sheet. After that, the intermediate layer on the second release sheet is bonded to the surface of the substrate on which the buffer layer is not formed, and the second release sheet is removed.

Next, a composition for the adhesive layer is applied to the release-treated surface of the third release sheet by a known method, and then heated and dried to form an adhesive layer on the third release sheet. Thereafter, the adhesive layer on the third release sheet and the intermediate layer are bonded together to obtain a semiconductor processing protective sheet in which the intermediate layer and adhesive layer are formed in this order on one main surface of the substrate, and a buffer layer is formed on the other main surface of the substrate. The third release sheet can be removed when the semiconductor processing protective sheet is used.

(8. Manufacturing Method of Semiconductor Device)
The protective sheet for semiconductor processing according to the present invention is preferably used in DBG when it is attached to the surface of a semiconductor wafer and the back grinding of the wafer is performed. In particular, the protective sheet for semiconductor processing according to the present invention is preferably used in LDBG, which obtains a group of chips with a small kerf width when the semiconductor wafer is singulated.

As a non-limiting example of the use of the protective sheet for semiconductor processing, a method for manufacturing a semiconductor device is described in more detail below.

Specifically, the method for manufacturing a semiconductor device includes at least the following steps 1 to 4.
Step 1: A step of attaching the above-mentioned protective sheet for semiconductor processing to the surface of a semiconductor wafer having projections and recesses. Step 2: A step of forming a groove from the front side of the semiconductor wafer, or a step of forming a modified region inside the semiconductor wafer from the front or back side of the semiconductor wafer. Step 3: A step of grinding the semiconductor wafer with the protective sheet for semiconductor processing attached to the front side and the above-mentioned groove or modified region formed therein from the back side to separate the semiconductor wafer into a plurality of chips starting from the groove or modified region. Step 4: A step of peeling off the protective sheet for semiconductor processing from the separated semiconductor wafer (i.e., a plurality of semiconductor chips).

Each step of the manufacturing method for the semiconductor device is described in detail below.

(Step 1)
In step 1, the semiconductor processing protective sheet of the present invention is attached to the uneven semiconductor wafer surface via an adhesive layer. This step may be performed before step 2 described later, or after step 2. For example, when forming a modified region on a semiconductor wafer, it is preferable to perform step 1 before step 2. On the other hand, when forming a groove on the semiconductor wafer surface by dicing or the like, step 1 is performed after step 2. That is, in this step 1, the semiconductor processing protective sheet is attached to the surface of the wafer having the groove formed in step 2 described later.

The semiconductor wafer used in this manufacturing method may be a silicon wafer, or may be a wafer of gallium arsenide, silicon carbide, lithium tantalate, lithium niobate, gallium nitride, indium phosphide, or the like, or a glass wafer. The thickness of the semiconductor wafer before grinding is not particularly limited, but is usually about 500 to 1000 μm. In addition, the semiconductor wafer usually has a circuit formed on its surface. The formation of the circuit on the wafer surface can be performed by various methods including conventionally widely used methods such as an etching method and a lift-off method. In particular, in this embodiment, a convex electrode (bump) is formed on the circuit surface of the semiconductor wafer. As a result, there are irregularities on the circuit surface of the semiconductor wafer compared to a semiconductor wafer without a convex electrode. The height of the convex electrode is not particularly limited, but is usually 5 to 200 μm.

(Step 2)
In step 2, a groove is formed from the front surface side of the semiconductor wafer, or a modified region is formed inside the semiconductor wafer from the front surface or rear surface of the semiconductor wafer.

The grooves formed in this process are shallower than the thickness of the semiconductor wafer. The grooves can be formed by dicing using a conventionally known wafer dicing device. In step 3, which will be described later, the semiconductor wafer is divided into multiple semiconductor chips along the grooves.

The modified region is a brittle portion of the semiconductor wafer, and is the region that becomes the starting point for breaking the semiconductor wafer and dicing it into semiconductor chips due to the thinning of the semiconductor wafer caused by grinding in the grinding process or the application of grinding force. That is, the grooves and modified region in step 2 are formed so as to follow the parting lines that will be formed when the semiconductor wafer is divided and diced into semiconductor chips in step 3, which will be described later.

The modified region is formed by irradiating a laser focused on the inside of the semiconductor wafer, and the modified region is formed inside the semiconductor wafer. The laser may be irradiated from either the front side or the back side of the semiconductor wafer. In the embodiment in which the modified region is formed, when step 2 is performed after step 1 and the laser is irradiated from the front side of the wafer, the laser is irradiated onto the semiconductor wafer through the semiconductor processing protective sheet.

The semiconductor wafer with the semiconductor processing protective sheet attached and the grooves or modified regions formed therein is placed on the chuck table and adsorbed to the chuck table. At this time, the semiconductor wafer is adsorbed with the front side placed on the table side.

(Step 3)
After steps 1 and 2, the back surface of the semiconductor wafer on the chuck table is ground to separate the semiconductor wafer into a plurality of semiconductor chips.

Here, when grooves are formed in the semiconductor wafer, back grinding is performed so as to thin the semiconductor wafer at least to the position that reaches the bottom of the groove. This back grinding turns the grooves into cuts that penetrate the wafer, and the semiconductor wafer is divided by the cuts and singulated into individual semiconductor chips.

On the other hand, when a modified region is formed, the grinding surface (back surface of the wafer) may reach the modified region by grinding, but it is not necessary to reach the modified region strictly. In other words, grinding may be performed to a position close to the modified region so that the semiconductor wafer is destroyed and singulated into semiconductor chips starting from the modified region. For example, the actual singulation of the semiconductor chips may be performed by applying a pick-up tape, which will be described later, and then stretching the pick-up tape.

After back grinding is complete, dry polishing may be performed prior to picking up the chips.

The shape of the individualized semiconductor chip may be square or may be elongated such as rectangular. The thickness of the individualized semiconductor chip is not particularly limited, but is preferably about 5 to 100 μm, more preferably 10 to 45 μm. According to LDBG, which provides a modified region inside the wafer with a laser and performs individualization of the wafer by stress during wafer back grinding, it is easy to make the thickness of the individualized semiconductor chip 50 μm or less, more preferably 10 to 45 μm. The size of the individualized semiconductor chip is not particularly limited, but the chip size is preferably less than 600 mm ² , more preferably less than 400 mm ² , and even more preferably less than 120 mm ² .

By using the semiconductor processing protective sheet of the present invention, even in the case of thin and/or small semiconductor chips like this, cracks are prevented from occurring in the semiconductor chips when grinding the back surface (step 3) and when peeling off the semiconductor processing protective sheet (step 4).

(Step 4)
Next, the protective sheet for semiconductor processing is peeled off from the individual semiconductor wafer (i.e., a plurality of semiconductor chips). This step is performed, for example, by the following method.

First, when the adhesive layer of the semiconductor processing protective sheet is formed from an energy ray curable adhesive, the adhesive layer is cured by irradiating it with energy rays. Next, a pick-up tape is attached to the back side of the individualized semiconductor wafer, and the position and direction are adjusted so that pick-up is possible. At this time, a ring frame arranged on the outer periphery of the wafer is also attached to the pick-up tape, and the outer edge of the pick-up tape is fixed to the ring frame. The wafer and ring frame may be attached to the pick-up tape at the same time, or may be attached at different times. Next, the semiconductor processing protective sheet is peeled off from the multiple semiconductor chips held on the pick-up tape.

Then, multiple semiconductor chips on the pickup tape are picked up and fixed onto a substrate or the like to manufacture a semiconductor device.

The pickup tape is not particularly limited, but may be, for example, composed of a substrate and an adhesive sheet having an adhesive layer provided on one side of the substrate.

The above describes an example of the semiconductor processing protective sheet according to the present invention being used in a method for singulating semiconductor wafers by DBG or LDBG, but the semiconductor processing protective sheet according to the present invention can be preferably used for LDBG, which produces a group of thinner chips with a smaller kerf width when the semiconductor wafer is singulated.

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

The invention will be explained in more detail below using examples, but the invention is not limited to these examples.

The measurement and evaluation methods used in this example are as follows:

(Loss tangent and storage modulus of the intermediate layer)
The intermediate layer composition described below was applied using a knife coater to form a 50 μm thick intermediate layer with a polyethylene terephthalate (PET) film-based release film (product name "SP-PET381031", thickness 38 μm, manufactured by Lintec Corporation) attached to both sides.

Multiple intermediate layers formed in this manner were prepared, and the PET release films were peeled off and the release surfaces were aligned and laminated in sequence to prepare an intermediate layer laminate (thickness 1,000 μm).

Next, the resulting laminate of intermediate layers was punched out into a circle with a diameter of 10 mm to obtain a sample for measuring viscoelasticity.

A viscoelasticity measuring device (product name "ARES", manufactured by TA Instruments) was used to apply a strain of 1 Hz to the above sample, and the storage modulus (G') was measured from -30 to 120°C at a heating rate of 10°C/min. From the measured values, the loss tangent (tan δ) at 50°C and the storage modulus (G') at 50°C were calculated. The calculated storage modulus value was taken as the storage modulus I.

(Loss tangent and storage modulus of adhesive layer)
Using a composition for adhesive layer described below, an adhesive layer having a thickness of 50 μm was formed using a knife coater, with a polyethylene terephthalate (PET) film-based release film (product name "SP-PET381031", thickness 38 μm, manufactured by Lintec Corporation) attached to both sides.

Multiple adhesive layers formed in this manner were prepared, and the PET release films were peeled off and the release surfaces were aligned and laminated in sequence to prepare an adhesive layer laminate (thickness 1,000 μm).

Next, the resulting laminate of adhesive layers was punched out into a circle with a diameter of 10 mm to obtain a sample for measuring viscoelasticity.

A viscoelasticity measuring device (product name "ARES", manufactured by TA Instruments) was used to apply a strain of 1 Hz to the above sample, and the storage modulus was measured from -30 to 120°C at a heating rate of 10°C/min. The storage modulus (G') at 50°C was calculated from the measured value, and this value was taken as the storage modulus A.

(DBG Chip Crack Evaluation)
After forming grooves on the wafer surface of a 12-inch diameter silicon wafer, the semiconductor processing protective sheet produced in the examples and comparative examples was attached to the wafer surface, and the wafer was divided by back grinding, and the wafer was divided into chips with a thickness of 50 μm and a chip size of 5 mm square by a first dicing method. Thereafter, without peeling off the semiconductor processing protective sheet, the corners of the chips divided from the wafer grinding surface were observed with a digital microscope (product name "VHX-1000", manufactured by KEYENCE Co., Ltd.) to observe the presence or absence of cracks in each chip, and the crack occurrence rate in 700 chips was measured and evaluated according to the following evaluation criteria.
A: Less than 1.0%, B: 1.0-2.0%, C: More than 2.0%

(LDBG Chip Crack Evaluation)
The semiconductor processing protective sheets prepared in the Examples and Comparative Examples were attached to a silicon wafer having a diameter of 12 inches and a thickness of 775 μm using a backgrind tape laminator (manufactured by Lintec Corporation, device name "RAD-3510F/12"). A lattice-shaped modified region was formed on the wafer using a laser saw (manufactured by Disco Corporation, device name "DFL7361"). The lattice size was 5 mm x 5 mm.

Then, a back grinding machine (manufactured by Disco, machine name "DGP8761") was used to grind (including dry polish) the wafer down to a thickness of 50 μm, and the wafer was divided into multiple chips.

After the grinding process, energy rays (ultraviolet rays) were irradiated, a dicing tape (Adwill D-176, manufactured by Lintec Corporation) was attached to the surface opposite to the attached surface of the protective sheet for semiconductor processing, and the protective sheet for semiconductor processing was peeled off. Thereafter, the individualized chips were observed with a digital microscope (product name "VHX-1000", manufactured by KEYENCE Corporation), the number of chips with cracks was counted, and the crack occurrence rate in 700 chips was measured and evaluated according to the following evaluation criteria.
A: Less than 1.0%, B: 1.0-2.0%, C: More than 2.0%

(Evaluation of kerf application)
The protective sheets for semiconductor processing with release sheets prepared in the examples and comparative examples were set in a tape laminator (manufactured by Lintec Corporation, product name "RAD-3510") while removing the release sheet, and attached to a 12-inch silicon wafer (thickness 760 μm) with grooves formed on the wafer surface by a pre-dicing method under the following conditions.
Roll height: 0 mm, roll temperature: 23° C. (room temperature), table temperature: 23° C. (room temperature)

The silicon wafer with the semiconductor processing protective sheet obtained was cut into individual pieces with a thickness of 50 μm and a chip size of 5 mm square by back grinding (first dicing method). The individualized semiconductor processing protective sheet with chips was irradiated with ultraviolet light (conditions: 230 mW/cm, 380 mJ/cm) from the tape side using a dicing tape mounter (manufactured by Lintec Corporation, product name "RAD-2700") to harden the adhesive. Then, in the same RAD-2700 device, a pickup tape (manufactured by Lintec Corporation, product name "D-510T") was attached from the chip side. At this time, a jig called a ring frame used in the pickup process was also attached to the pickup tape. Next, the hardened semiconductor processing protective sheet was peeled off in the RAD-2700 device. After removing the semiconductor processing protective sheet, 700 chips were observed with a digital microscope (product name "VHX-1000", manufactured by KEYENCE) to check for the presence or absence of glue residue near the kerf, with a mark of "○" if there was none and a mark of "×" if there was.

(Bump Absorption Evaluation)
The semiconductor processing protection sheets prepared in the following examples and comparative examples were attached to a wafer (8-inch wafer, manufactured by Waltz) with spherical bumps made of Sn-3Ag-0.5Cu alloy with bump height of 80 μm, pitch of 200 μm, and diameter of 100 μm, using a laminator (product name "RAD-3510F/12", manufactured by Lintec Corporation). During attachment, the temperature of the lamination table and lamination roll of the device was set to 50° C.

After lamination, the diameter of the circular voids that appeared around the bumps was measured from the substrate side using a digital optical microscope (product name "VHX-1000", manufactured by KEYENCE).

The smaller the diameter of the voids, the higher the bump absorption of the semiconductor processing protection sheet. The superiority or inferiority of the bump absorption was judged according to the following criteria.
A: The diameter of the void is less than 150 μm.
×: The diameter of the void is 150 μm or more.

Example 1
(1) Substrate As a substrate, a PET film with adhesive layers on both sides (Cosmoshine A4300, manufactured by Toyobo Co., Ltd., thickness: 50 μm, Young's modulus at 23° C.: 2550 MPa) was prepared.

(2) Buffer layer (synthesis of urethane acrylate oligomer)
A urethane acrylate oligomer (UA-2) having a weight average molecular weight (Mw) of about 9,000 was obtained by reacting 2-hydroxyethyl acrylate with a terminal isocyanate urethane prepolymer obtained by reacting a polyester diol with isophorone diisocyanate.

(Preparation of Buffer Layer Composition)
A buffer layer composition was prepared by blending 40 parts by mass of the urethane acrylate oligomer (UA-2) synthesized above, 20 parts by mass of isobornyl acrylate (IBXA), 20 parts by mass of tetrahydrofurfuryl acrylate (THFA), and 20 parts by mass of morpholine acrylate (ACMO), and further blending 2.0 parts by mass of 2-hydroxy-2-methyl-1-phenyl-propan-1-one (manufactured by BASF Japan, product name "Irgacure 1173") as a photopolymerization initiator.

(Creating a substrate with a buffer layer)
The buffer layer composition was applied to the release-treated surface of another release sheet (manufactured by Lintec Corporation, product name "SP-PET381031") to form a coating film. Next, the coating film was irradiated with ultraviolet light to semi-cure the coating film, thereby forming a buffer layer-forming film with a thickness of 53 μm.

The above ultraviolet irradiation was performed using a belt conveyor type ultraviolet irradiation device (manufactured by I-Graphics, device name "US2-0801") and a high-pressure mercury lamp (manufactured by I-Graphics, device name "H08-L41") under irradiation conditions of a lamp height of 230 mm, output of 80 mW/cm, illuminance of 90 mW/ ^cm2 at a light wavelength of 365 nm, and irradiation dose of 50 mJ/ ^cm2 .

The surface of the buffer layer-forming film thus formed was then bonded to a substrate, and the buffer layer-forming film was again irradiated with ultraviolet light from the release sheet side to completely harden the buffer layer-forming film, forming a buffer layer having a thickness of 53 μm. The ultraviolet light irradiation was performed using the above-mentioned ultraviolet light irradiation device and high-pressure mercury lamp under irradiation conditions of a lamp height of 220 mm, a conversion output of 120 mW/cm, a light wavelength of 365 nm, an illuminance of 160 mW/cm ² , and an irradiation dose of 650 mJ/cm ² .

(3) Substrate A with intermediate layer
A non-energy ray curable acrylic copolymer (a) (Mw: 600,000) was obtained by copolymerizing 91 parts by mass of n-butyl acrylate (BA) and 9 parts by mass of acrylic acid (AA).

Separately from the acrylic copolymer (a), 62 parts by mass of n-butyl acrylate (BA), 10 parts by mass of methyl methacrylate (MMA), and 28 parts by mass of 2-hydroxyethyl acrylate (2HEA) were copolymerized to obtain an acrylic polymer, which was then reacted with 2-methacryloyloxyethyl isocyanate (MOI) so as to add to 80 equivalents of the hydroxyl groups of the total hydroxyl groups (100 equivalents) of the acrylic polymer, to obtain an energy beam-curable acrylic copolymer (b) (Mw: 100,000).

13 parts by weight of energy ray curable acrylic copolymer (b) was added to 100 parts by weight of this non-energy ray curable acrylic copolymer (a), 2.79 parts by weight of an isocyanate crosslinking agent (manufactured by Tosoh Corporation, product name "Coronate L") was added as a crosslinking agent, and 3.71 parts by weight of 1-hydroxycyclohexyl phenyl ketone (manufactured by BASF, Irgacure 184) was added as a photoinitiator, and the solid content was adjusted to 37% using toluene. The mixture was stirred for 30 minutes to prepare a composition for the intermediate layer.

Then, the prepared solution of the intermediate layer composition was applied to a PET-based release film (SP-PET381031, manufactured by Lintec Corporation, thickness 38 μm) and dried to form an intermediate layer with a thickness of 60 μm. This was then attached to the side of the substrate with the buffer layer opposite the side on which the buffer layer was formed, and the solution of the adhesive layer composition was further applied to the PET-based release film (SP-PET381031, manufactured by Lintec Corporation, thickness 38 μm). This was repeated twice to form a substrate A with an intermediate layer with a thickness of 180 μm.

(4) Pressure-sensitive adhesive layer (Preparation of composition for pressure-sensitive adhesive layer)
An energy ray-curable acrylic copolymer (c) (Mw: 500,000) was obtained by reacting an acrylic polymer obtained by copolymerizing 52 parts by mass of n-butyl acrylate (BA), 20 parts by mass of methyl methacrylate (MMA), and 28 parts by mass of 2-hydroxyethyl acrylate (2HEA) with 2-methacryloyloxyethyl isocyanate (MOI) so as to be added to 90 equivalents of hydroxyl groups out of the total hydroxyl groups (100 equivalents) of the acrylic polymer.

100 parts by mass of this energy ray curable acrylic copolymer (c) was mixed with 12 parts by mass of a multifunctional urethane acrylate (manufactured by Mitsubishi Chemical Corporation, Shikoh UT-4332), which is an energy ray curable compound, 1.1 parts by mass of an isocyanate-based crosslinking agent (manufactured by Tosoh Corporation, product name "Coronate L"), and 1 part by mass of bis(2,4,6-trimethylbenzoyl)phenylphosphine oxide (manufactured by BASF, Irgacure TPO) as a photopolymerization initiator, and diluted with methyl ethyl ketone to prepare a coating liquid of a pressure-sensitive adhesive layer composition with a solids concentration of 34% by mass.

(Production of protective sheet for semiconductor processing)
The coating liquid of the adhesive layer composition obtained above was applied to the release-treated surface of a release sheet (manufactured by Lintec Corporation, product name "SP-PET381031") and dried by heating to form an adhesive layer with a thickness of 10 μm on the release sheet.

Then, an adhesive layer was attached to the surface of the intermediate layer-attached substrate A to produce a protective sheet for semiconductor processing. The type of substrate and the composition and thickness of the intermediate layer and adhesive layer are shown in Table 1.

Example 2
Except for the fact that the thickness of the intermediate layer was 120 μm, a protective sheet for semiconductor processing was obtained in the same manner as in Example 1. The type of substrate, and the composition and thickness of the intermediate layer and the pressure-sensitive adhesive layer are shown in Table 1.

Example 3
Except for changing the amount of the acrylic copolymer (b) added to the intermediate layer composition to 34 parts by mass, a protective sheet for semiconductor processing was obtained in the same manner as in Example 1. The type of substrate, and the composition and thickness of the intermediate layer and pressure-sensitive adhesive layer are shown in Table 1.

Example 4
Except for changing the amount of the acrylic copolymer (b) added to the intermediate layer composition to 67 parts by mass, a protective sheet for semiconductor processing was obtained in the same manner as in Example 1. The type of substrate, and the composition and thickness of the intermediate layer and pressure-sensitive adhesive layer are shown in Table 1.

Example 5
Except for changing the amount of the acrylic copolymer (b) added to the intermediate layer composition to 100 parts by mass, a protective sheet for semiconductor processing was obtained in the same manner as in Example 1. The type of substrate, and the composition and thickness of the intermediate layer and pressure-sensitive adhesive layer are shown in Table 1.

(Example 6)
A protective sheet for semiconductor processing was obtained in the same manner as in Example 1, except for the following two changes. The type of substrate, and the composition and thickness of the intermediate layer and pressure-sensitive adhesive layer are shown in Table 1.
(1) The thickness of the intermediate layer is 120 μm.
(2) An energy ray-curable acrylic copolymer (d) (Mw: 500,000) was obtained by reacting an acrylic polymer obtained by copolymerizing 60 parts by mass of 2-ethylhydroxyacrylate (2EHA), 15 parts by mass of ethyl acrylate (EA), 5 parts by mass of methyl methacrylate (MMA), and 20 parts by mass of 2-hydroxyethyl acrylate (2HEA) as a composition for a pressure-sensitive adhesive layer with 2-methacryloyloxyethyl isocyanate (MOI) so as to be added to 60 equivalents of hydroxyl groups out of the total hydroxyl groups (100 equivalents) of the acrylic polymer.

100 parts by mass of this energy ray-curable acrylic copolymer (d) was mixed with 1.2 parts by mass of an isocyanate-based crosslinking agent (manufactured by Tosoh Corporation, product name "Coronate L") and 7.29 parts by mass of 2,2-dimethoxy-2-phenylacetophenone (manufactured by BASF, Irgacure 651) as a photopolymerization initiator, and diluted with toluene to prepare a coating liquid for a pressure-sensitive adhesive layer composition with a solids concentration of 25% by mass.

(Example 7)
A protective sheet for semiconductor processing was obtained in the same manner as in Example 1, except for the following changes. The type of substrate, and the composition and thickness of the intermediate layer and pressure-sensitive adhesive layer are shown in Table 1.

As a composition for the adhesive layer, 75 parts by mass of n-butyl acrylate (BA), 10 parts by mass of i-butyl acrylate (iBA), 5 parts by mass of methyl methacrylate (MMA), and 10 parts by mass of 4-hydroxybutyl acrylate (4HBA) were copolymerized to obtain an acrylic polymer. 2-Methacryloyloxyethyl isocyanate (MOI) was then reacted with the acrylic polymer so that 90 equivalents of the total hydroxyl groups (100 equivalents) of the acrylic polymer were added to the acrylic polymer, to obtain an energy beam-curable acrylic copolymer (e) (Mw: 500,000).

100 parts by mass of this energy ray-curable acrylic copolymer (e) was mixed with 1.8 parts by mass of an isocyanate-based crosslinking agent (manufactured by Tosoh Corporation, product name "Coronate L") and 7.29 parts by mass of 2,2-dimethoxy-2-phenylacetophenone (manufactured by BASF, Irgacure 651) as a photopolymerization initiator, and diluted with toluene to prepare a coating liquid for a pressure-sensitive adhesive layer composition with a solids concentration of 25% by mass.

(Example 8)
Except for changing the substrate with the buffer layer to a PET substrate, a protective sheet for semiconductor processing was obtained in the same manner as in Example 2. The type of substrate, and the composition and thickness of the intermediate layer and pressure-sensitive adhesive layer are shown in Table 1.

(Comparative Example 1)
Except for changing the amount of the acrylic copolymer (b) added to the intermediate layer composition to 134 parts by mass, a protective sheet for semiconductor processing was obtained in the same manner as in Example 1. The type of substrate, and the composition and thickness of the intermediate layer and pressure-sensitive adhesive layer are shown in Table 1.

(Comparative Example 2)
A protective sheet for semiconductor processing was obtained in the same manner as in Example 1, except that the adhesive layer composition of Example 6 was used as the adhesive layer composition. The type of substrate, and the compositions and thicknesses of the intermediate layer and adhesive layer are shown in Table 1.

(Comparative Example 3)
Using the substrate D with intermediate layer prepared as described below, a protective sheet for semiconductor processing was obtained in the same manner as in Example 1, except that the adhesive layer composition of Example 6 was used as the adhesive layer composition. The type of substrate, and the composition and thickness of the intermediate layer and adhesive layer are shown in Table 1.

Substrate D with intermediate layer
A UV-curable resin composition was prepared by mixing 40 parts by mass (solid content ratio) of monofunctional urethane acrylate, 45 parts by mass (solid content ratio) of isobornyl acrylate (IBXA), 15 parts by mass (solid content ratio) of hydroxypropyl acrylate (HPA), 3.5 parts by mass (solid content ratio) of pentaerythritol tetrakis (3-mercaptobutyrate) (product name "Karrenz MT PE1", Showa Denko K.K., secondary tetrafunctional thiol-containing compound, solid content concentration 100 parts by mass%), 1.8 parts by mass of a UV-reactive thermal crosslinking agent, and 1.0 part by mass of 2-hydroxy-2-methyl-1-phenyl-propan-1-one (product name "Darocur 1173", BASF, solid content concentration 100 parts by mass%) as a photopolymerization initiator, and the UV-curable resin composition was applied to a polyethylene terephthalate (PET) film-based release film (SP-PET381031, Lintec Corporation). The coating was applied onto a substrate (thickness 38 μm) using a fountain die method so that the thickness after curing would be 400 μm. Then, ultraviolet light was irradiated from the coating side to form a semi-cured layer.

The ultraviolet irradiation was performed using a belt conveyor type ultraviolet irradiation device (product name "ECS-401GX", manufactured by iGraphics) as the ultraviolet irradiation device and a high pressure mercury lamp (H04-L41, manufactured by iGraphics) as the ultraviolet source under the following irradiation conditions: illuminance of 112 mW/cm ² at a light wavelength of 365 nm, and light quantity of 177 mJ/cm ² (measured with "UVPF-A1" manufactured by iGraphics).

A polyethylene terephthalate (PET) film (Toray Lumirror 75U403, thickness 75 μm) was laminated on the formed semi-cured layer, and ultraviolet light was further irradiated from the PET film side (using the above-mentioned ultraviolet light irradiation device and ultraviolet light source, irradiation conditions were illuminance 271 mW/ ^cm2 , light quantity 1200 mJ/ ^cm2 ) to completely cure the layer, forming a 400 μm thick intermediate layer on the PET film substrate.

The above measurements and evaluations were carried out on the obtained samples (Examples 1 to 8 and Comparative Examples 1 to 3). The results are shown in Table 2.

From Table 2, it was confirmed that when the AI ratio and the loss tangent of the intermediate layer are within the above-mentioned ranges, even when a wafer having irregularities is singulated using DBG and LDBG, the irregularities are sufficiently filled, the occurrence rate of cracks due to chip shift is low, and no glue residue is observed in the kerf.

Reference Signs List 1: Protective sheet for semiconductor processing 10: Substrate 20: Intermediate layer 30: Pressure-sensitive adhesive layer 40: Buffer layer

Claims (8)

A substrate, and an intermediate layer and a pressure-sensitive adhesive layer on one main surface of the substrate, in that order, and the following (a) and (b) are satisfied:
The protective sheet for semiconductor processing , wherein the intermediate layer does not contain a zwitterion-containing acrylic polymer .
(a) the loss tangent of the intermediate layer at 50°C measured at a frequency of 1 Hz is 0.40 or more and 0.65 or less; (b) the ratio [A/I] of the storage modulus A of the pressure-sensitive adhesive layer to the storage modulus I of the intermediate layer at 50°C measured at a frequency of 1 Hz is 0.80 or more and 3.50 or less. The semiconductor processing protective sheet according to claim 1, which has a buffer layer on the other main surface of the substrate. The semiconductor processing protective sheet according to claim 1 or 2, wherein the Young's modulus of the substrate is 1000 MPa or more. A protective sheet for semiconductor processing according to any one of claims 1 to 3, wherein the thickness of the intermediate layer is 60 μm or more and 250 μm or less. The semiconductor processing protective sheet according to any one of claims 1 to 4, wherein the adhesive layer is energy ray curable. The semiconductor processing protective sheet according to any one of claims 1 to 5, wherein the intermediate layer is energy ray curable. The semiconductor processing protective sheet according to any one of claims 1 to 6 is attached to the surface of a semiconductor wafer in a process of grinding the back surface of a semiconductor wafer having grooves formed on the surface of the semiconductor wafer, and dicing the semiconductor wafer into semiconductor chips by grinding. A step of attaching the semiconductor processing protective sheet according to any one of claims 1 to 7 to a surface of a semiconductor wafer having projections and recesses;
forming a groove from the front surface side of the semiconductor wafer, or forming a modified region inside the semiconductor wafer from the front surface or rear surface of the semiconductor wafer;
A step of grinding the semiconductor wafer having the semiconductor processing protective sheet attached to the front surface and the groove or the modified region formed thereon from the rear surface side to separate the semiconductor wafer into a plurality of chips starting from the groove or the modified region;
and peeling the protective sheet for semiconductor processing from each of the individual semiconductor chips.

Images