JP7779787B2 - PROTECTIVE SHEET FOR WORK PROCESSING AND METHOD FOR PRODUCING WORK INDUCED PRODUCT - Google Patents

Description

The present invention relates to a protective sheet for workpiece processing and a method for manufacturing singulated workpieces. In particular, it relates to a protective sheet for workpiece processing that can reduce the total thickness variation (TTV) of a workpiece after backside grinding, and a method for manufacturing singulated workpieces using the protective sheet for workpiece processing.

Chips with circuits formed on them, such as semiconductor chips, are obtained as singulated workpieces by singulating a workpiece, such as a wafer, with multiple circuits formed on it. With the rapid progress in miniaturization and multi-functionality of electronic devices incorporating such chips, there is a demand for chips to be smaller, thinner, and more dense. To make chips smaller and thinner, it is common to form circuits on the surface of the workpiece, and then grind the backside of the workpiece to reduce the thickness of the chip.

When grinding the backside of a workpiece, a protective sheet called backgrind tape is applied to the surface of the workpiece to temporarily protect the circuits on the surface and to hold the workpiece in place.

The surface of the workpiece is formed with a protective film to protect the circuit, and convex electrodes such as bump electrodes to electrically connect the chip to electrodes on the substrate, resulting in height differences on the surface of the workpiece.

The protective sheet attached to the surface of the workpiece follows the shape of the workpiece's surface, so these height differences are reflected in the protective sheet. If the backside of the workpiece is ground when there are height differences, the pressure applied to the workpiece during grinding will be uneven on the grinding surface, resulting in an uneven thickness of the workpiece after grinding.

The difference between the maximum thickness of the workpiece after grinding and the minimum thickness of the workpiece after grinding is called the TTV (Total Thickness Variation), and is used as a standard for the thickness accuracy of the workpiece after grinding. If the thickness of the workpiece after grinding is uneven, the TTV will increase, making the workpiece more susceptible to cracks and causing problems when the workpiece is separated into individual pieces.

To address this issue, Patent Documents 1 and 2 describe a method of attaching an adhesive sheet to the surface of a semiconductor wafer, grinding the outermost surface of the adhesive sheet, and then grinding the backside of the semiconductor wafer, which results in improved thickness accuracy for the semiconductor wafer after grinding.

Patent No. 4261260 JP 2014-175334 A

In Patent Documents 1 and 2, the tensile modulus of the outermost surface of the adhesive sheet that is ground before the backside of the semiconductor wafer is ground is set within a specified range.

However, the inventors have discovered that the TTV of a workpiece depends not on the tensile modulus of elasticity of the outermost surface of the protective sheet attached to the workpiece, but on another parameter. In other words, the inventors have discovered that the dynamic friction coefficient and tensile breaking stress of the outermost surface to be ground affect the TTV of the workpiece more than the tensile modulus of elasticity of the outermost surface of the protective sheet.

The present invention was made in consideration of these circumstances, and aims to provide a protective sheet for workpiece processing that can reduce the total thickness variation (TTV) of a workpiece after backside grinding. It also aims to provide a method for producing individual workpieces obtained by singulating a workpiece using the protective sheet for workpiece processing.

Aspects of the present invention are as follows:

[1] A protective sheet for workpiece processing having a support material and an adhesive layer disposed on one main surface of the support material,
The other main surface of the support material constitutes the outermost surface of the workpiece processing protection sheet, and the dynamic friction coefficient between the outermost surface of the workpiece processing protection sheet and sandpaper having a grit size of 1200 is 1.40 or less;
This is a protection sheet for workpiece processing, in which the tensile breaking stress of the support material is 250 MPa or less.

[2] A protective sheet for workpiece processing according to [1], in which the support material is composed of two or more layers.

[3] The workpiece processing protective sheet according to [2], wherein the support material has a rigid layer and a soft layer that is softer than the rigid layer, and one main surface of the soft layer constitutes the outermost surface of the workpiece processing protective sheet.

[4] A protective sheet for workpiece processing according to any one of [1] to [3], in which the adhesive layer is attached to the surface of the workpiece, and the outermost surface of the protective sheet for workpiece processing is ground prior to the process of grinding the back surface of the workpiece having a front and back surface.

[5] A protective sheet for workpiece processing according to [4], used in a process of dividing a workpiece into individual workpieces by grinding the back surface of the workpiece having grooves formed on its surface or modified regions formed inside the workpiece.

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

[7] A step of attaching the adhesive layer of the protective sheet for workpiece processing according to any one of [1] to [6] to the surface of a workpiece having a front and back surface;
A step of grinding the back surface of the workpiece;
and a step of dividing the workpiece into individual pieces to obtain a plurality of individual workpieces.

[8] The workpiece processing protective sheet according to [4] or [5], further comprising a step of grinding the outermost surface of the workpiece processing protective sheet,
The method for producing individual workpieces according to [7], wherein the step of grinding the back surface of the workpiece is carried out after the step of grinding the outermost surface of the protective sheet for workpiece processing.

[9] The method further includes a step of forming a groove on the surface of the workpiece, or a step of forming a modified region inside the workpiece from the surface or back surface of the workpiece,
A method for manufacturing a workpiece singulation according to [7] or [8], wherein in the step of grinding the back surface of the workpiece, the workpiece is singulated into a plurality of workpiece singulations starting from grooves or modified regions.

[10] A method for manufacturing a workpiece singulated product according to any one of [7] to [9], further comprising a step of peeling off the workpiece processing protection sheet from the workpiece singulated product.

The present invention provides a protective sheet for workpiece processing that can reduce the total thickness variation (TTV) of a workpiece after backside grinding. The present invention also provides a method for producing individual workpieces obtained by singulating a workpiece using the protective sheet for workpiece processing.

FIG. 1A is a schematic cross-sectional view showing an example of a protection sheet for workpiece processing according to this embodiment. FIG. 1B is a cross-sectional view showing another example of the protection sheet for workpiece processing according to this embodiment. FIG. 1C is a schematic cross-sectional view showing another example of the protection sheet for workpiece processing according to this embodiment. FIG. 2 is a schematic cross-sectional view illustrating a process of attaching the workpiece processing protection sheet according to this embodiment to the workpiece. FIG. 3 is a cross-sectional view illustrating a process of grinding the outermost surface of the protective sheet for workpiece processing according to this embodiment. FIG. 4 is a schematic cross-sectional view illustrating a process of grinding the back surface of a workpiece using the protective sheet for workpiece processing according to this embodiment.

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

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

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

The "front surface" of a workpiece refers to the surface on which circuits, electrodes, etc. are formed, and the "back surface" of a workpiece refers to the surface on which circuits, etc. are not formed. Electrodes may be convex electrodes such as bumps.

DBG is a method in which grooves of a specified depth are formed on the front side of a workpiece, and then the workpiece is ground from the back side, resulting in individual pieces being cut into individual pieces. Grooves formed on the front side of the workpiece are made using methods such as blade dicing, laser dicing, and plasma dicing.

LDBG is a variation of DBG, and refers to a method in which a weak modified region is created inside a workpiece (e.g., a wafer) using a laser, and cracks originating from the modified region are propagated by stress during back grinding of the workpiece, thereby dividing the workpiece into individual pieces.

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

The term "(meth)acrylate" is used to refer to both "acrylate" and "methacrylate," and similarly applies to other similar terms.

"Energy rays" refers to ultraviolet rays, electron beams, etc., with ultraviolet rays being preferred.

Unless otherwise specified, the "weight average molecular weight" is a polystyrene-equivalent value measured by gel permeation chromatography (GPC). Measurements by this 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 flow rate of 1.0 mL/min, and a differential refractometer as a detector.

A release sheet is a sheet that supports the adhesive layer in a releasable manner. The term "sheet" does not limit thickness, and is used to include films.

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

(1. Protective sheet for workpiece processing)
The protective sheet for workpiece processing is used when processing a workpiece having a circuit or the like formed on one side (front side) and no circuit or the like formed on the other side (back side). Examples of workpiece processing include backside grinding of the workpiece. Grinding the backside of the workpiece can reduce the thickness of the individual workpieces obtained by dividing the workpiece.

The workpiece processing protection sheet is applied to the surface of the workpiece before back grinding. The surface of the workpiece may be the surface on which the circuit is exposed, or the main surface of a protective layer formed on the circuit to protect the circuit. Also, convex electrodes such as bumps may be formed on the circuit. Therefore, differences in elevation usually occur on the surface of the workpiece due to the elements formed on the surface of the workpiece.

As a result, these height differences are also reflected in the workpiece processing protective sheet attached to the surface of the workpiece. After the workpiece is attached, the workpiece processing protective sheet is adsorbed to a grinding table such as a chuck table, and the backside of the workpiece is ground. However, if there are height differences in the workpiece processing protective sheet, gaps are formed between the workpiece processing protective sheet and the chuck table, and the force applied during backside grinding may not be transmitted evenly to the workpiece. As a result, there are areas on the backside of the workpiece where grinding has progressed sufficiently and areas where grinding has not progressed sufficiently. This difference in the degree of grinding progress causes unevenness in the workpiece thickness after grinding. In other words, the presence of areas where the workpiece is thick after grinding and areas where the workpiece is thin after grinding tends to increase the TTV after grinding.

As mentioned above, if the TTV becomes large, problems such as cracks becoming more likely to occur in the workpiece and problems occurring when the workpiece is singulated can occur.

As mentioned above, one known approach to addressing this issue is to improve TTV by grinding the outermost surface of the workpiece processing protection sheet attached to the workpiece. In this approach, the tensile modulus of elasticity of the outermost surface of the workpiece processing protection sheet is set within a specified range.

However, the inventors focused on the dynamic friction coefficient and tensile breaking stress of the outermost surface of the protective sheet for workpiece processing and discovered that optimizing these parameters has a positive effect on the backside grinding of the workpiece and can reduce the total thickness variation (TTV) of the workpiece after backside grinding.

The following describes in detail the protective sheet for workpiece processing according to this embodiment.

As shown in FIG. 1A, the protective sheet for workpiece processing 1 according to this embodiment includes a support material 10 and an adhesive layer 20 disposed on the support material 10. As shown in FIG. 2, the protective sheet for workpiece processing 1 is attached such that the main surface 20a of the adhesive layer 20 is attached to the surface 100a of the workpiece 100 (e.g., a wafer).

In the protective sheet for workpiece processing 1 according to this embodiment, before grinding the back surface 100b of the workpiece 100, the main surface 10b of the support material 10 of the protective sheet for workpiece processing 1, opposite the main surface 10a on which the adhesive layer 20 is disposed, is ground. Therefore, the main surface 10b constitutes the outermost surface of the protective sheet for workpiece processing 1.

(1.1. Support material)
The support material is a member that supports the adhesive layer and supports the workpiece after the workpiece processing protection sheet is attached to the workpiece. Therefore, it is preferable that the support material has rigidity. In this embodiment, the support material has the following physical properties.

(1.2. Coefficient of Dynamic Friction)
In this embodiment, the coefficient of dynamic friction between the main surface of the support material constituting the outermost surface of the workpiece processing protective sheet and sandpaper with a grit size of 1200 is 1.40 or less. The coefficient of dynamic friction is the proportional coefficient of the dynamic friction force acting in the opposite direction to the direction of movement at the contact surface when two objects are in contact and moving relative to each other. A large coefficient of dynamic friction indicates a large force attempting to stop the moving object. The sandpaper is intended as a grinding means (e.g., a grinding wheel) that grinds the main surface of the support material, and the above-mentioned coefficient of dynamic friction is an indicator of the resistance force experienced by the grinding means that grinds the main surface of the support material.

By having the dynamic friction coefficient within the above range, the outermost surface of the workpiece processing protection sheet does not adhere to the grinding means, and grinding of the outermost surface is carried out properly, improving the smoothness of the outermost surface after grinding. If the backside of the workpiece is ground after the outermost surface has been properly ground, the backside of the workpiece is also ground properly, making it possible to reduce the total thickness variation (TTV) of the workpiece after grinding. In particular, grinding of the outermost surface is carried out properly even when the adhesive layer is relatively soft.

The above-mentioned dynamic friction coefficient is preferably 1.38 or less, more preferably 1.35 or less, and even more preferably 1.30 or less. Furthermore, from the viewpoint of enabling grinding with a grinding wheel, the above-mentioned dynamic friction coefficient is preferably 0.1 or more.

The above-mentioned dynamic friction coefficient can be measured by known methods. For example, it can be measured in accordance with JIS K 7125. That is, it is measured in the same manner as the measurement method specified in JIS K 7125, but the measurement conditions may be different. Specific measurement methods are explained in the examples.

(1.3. Tensile Breaking Stress)
In this embodiment, the support material has a tensile breaking stress of 250 MPa or less. The tensile breaking stress is the stress at which the sample breaks when it is continuously pulled. The tensile breaking stress is an index showing whether the support material is susceptible to grinding.

When the tensile breaking stress is within the above range, the outermost surface of the workpiece processing protection sheet is easily ground, the grinding of the outermost surface is carried out appropriately, and the smoothness of the outermost surface after grinding is improved. If the backside of the workpiece is ground after the outermost surface has been properly ground, the backside of the workpiece is also properly ground, and the TTV of the workpiece after grinding can be reduced. In particular, the outermost surface is properly ground even when the adhesive layer is relatively soft.

As described below, if the support material is composed of two or more layers, the above tensile breaking stress is the tensile breaking stress of the layer that constitutes the outermost surface of the workpiece processing protection sheet.

The above tensile breaking stress is preferably 240 MPa or less, and more preferably 230 MPa or less. Furthermore, from the perspective of preventing breakage during manufacturing, the above tensile breaking stress is preferably 1 MPa or more.

The above-mentioned tensile breaking stress can be measured by known methods. For example, it can be measured in accordance with JIS K 7161:1994 and JIS K 7127:1999. That is, it is measured in the same manner as the measurement methods specified in these standards, but the measurement conditions may be different. Specific measurement methods are explained in the examples.

(1.4. Configuration of Support Material)
The structure of the support material is not particularly limited as long as it has the above-mentioned physical properties. Below, a case where the support material is composed of one layer and a case where the support material is composed of two or more layers will be described.

(1.5. When the support material is composed of one layer)
When the support material is composed of a single layer, it is necessary that the support material be composed of a material that can support and hold the adhesive layer and the workpiece during processing of the workpiece in addition to satisfying the above physical properties. Therefore, when the support material is composed of a single layer, it is preferable that the tensile breaking stress of the support material is within the above range and that the rigidity of the support material is relatively high.

When the support material is composed of a single layer, examples of the support material include polyethylene terephthalate, polybutylene terephthalate, polyimide, polyamide, low-density polyethylene, high-density polyethylene, and biaxially oriented polypropylene. Of these, polyethylene terephthalate is preferred. On the other hand, when the support material is composed of a single layer, materials such as polyethylene naphthalate, polycarbonate, ethylene-vinyl acetate copolymer (EVA), and ethylene/methacrylic acid copolymer are not preferred. Note that the above examples are general examples, and the same material may satisfy the physical properties of the support material described above depending on the manufacturing method.

(1.6. When the support material is composed of two or more layers)
In this embodiment, the support material preferably comprises two or more layers. When the support material comprises two or more layers, it preferably has a rigid layer and a soft layer. In this case, it is preferable that the main surface of the soft layer constitutes the outermost surface of the workpiece processing protective sheet 1. For example, as shown in FIG. 1B, the support material 10 comprises a rigid layer 11 and a soft layer 12, and the main surface 12b of the soft layer 12 constitutes the outermost surface of the workpiece processing protective sheet 1. Also, as shown in FIG. 1C, the support material 10 comprises a rigid layer 11, a first soft layer 12, and a second soft layer 13, and the main surface 12b of the first soft layer 12 constitutes the outermost surface of the workpiece processing protective sheet 1.

(1.6.1. Rigid layer)
The rigid layer is a layer that provides the rigidity of the support material and is not limited as long as it is made of a material that can support the adhesive layer and the workpiece. For example, various resin films used as the substrate of backgrinding tape are exemplified. By using such a resin film, the workpiece can be held without being damaged even if the thickness of the workpiece is reduced by grinding. The rigid layer may be made of a single-layer film made of one resin film, or may be made of a multi-layer film made of multiple resin films laminated together.

In this embodiment, examples of materials for the rigid layer include polyesters such as polyethylene terephthalate, polyethylene naphthalate, polybutylene terephthalate, wholly aromatic polyesters, polyamides, polycarbonates, polyacetals, modified polyphenylene oxides, polyphenylene sulfides, polysulfones, polyether ketones, and biaxially oriented polypropylenes. Among these, polyesters are preferred, and polyethylene terephthalate is more preferred.

The thickness of the rigid layer is not particularly limited, but since it affects the rigidity of the workpiece processing protection sheet, it should be set according to the material of the rigid layer. In this embodiment, the thickness of the rigid layer is preferably 10 μm or more and 200 μm or less, more preferably 15 μm or more and 150 μm or less, and even more preferably 20 μm or more and 130 μm or less.

At least one of the main surfaces of the rigid layer may be subjected to an adhesion treatment such as corona treatment to improve adhesion with a layer formed on that main surface. Furthermore, at least one of the main surfaces of the rigid layer may have an easy-adhesion layer formed thereon to improve adhesion with a layer (e.g., a soft layer) formed on that main surface.

(1.6.2. Soft layer)
The soft layer is made of a material softer than the rigid layer. In this embodiment, the soft layer is preferably the layer that forms the outermost surface of the workpiece processing protective sheet on the support material. That is, after the workpiece processing protective sheet is attached to the surface of the workpiece, the soft layer is ground before the backside of the workpiece is ground. This is because a relatively soft material is more likely to satisfy the physical properties of the support material than a relatively hard material.

(1.6.3 Soft Layer Material)
In this embodiment, the soft layer may be made of a soft resin film, or may be formed using a soft layer composition containing an energy ray-curable compound.

Examples of soft resin films include low-density polyethylene (LDPE), high-density polyethylene (HDPE), linear low-density polyethylene (LLDPE), biaxially oriented polypropylene, polyurethane acrylate, and other resin films. Among these, low-density polyethylene (LDPE), linear low-density polyethylene (LLDPE), polyurethane acrylate, and other resin films are preferred. On the other hand, ethylene-vinyl acetate copolymer (EVA), ethylene-(meth)acrylic acid copolymer, vinyl chloride, and other soft resin films are not preferred. Note that the above examples are general examples, and the same material may satisfy the physical properties of the support material described above depending on the manufacturing method.

(1.6.4. Composition for soft layer)
In this embodiment, the soft layer composition preferably contains a urethane (meth)acrylate (d1) and a polymerizable compound (d2) having an alicyclic group or heterocyclic group having 6 to 20 ring atoms and/or a polyfunctional polymerizable compound (d3). The soft layer composition may contain a polymerizable compound (d4) having a functional group in addition to the components (d1) to (d3). The soft layer composition may also contain a photopolymerization initiator in addition to the above components. Furthermore, the soft layer composition may contain other additives and resin components within a range that does not impair the above-described effects.

The following describes in detail each component contained in the energy ray-curable compound-containing soft layer composition.

(1.6.4.1 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. Furthermore, the number of (meth)acryloyl groups (hereinafter also referred to as "functionality") in component (d1) 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 produce an isocyanate-terminated urethane prepolymer, followed by a (meth)acrylate having a hydroxyl group. Component (d1) may be used alone or in combination of two or more types.

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

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

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

Specific examples of component (d2) include alicyclic group-containing (meth)acrylates such as isobornyl (meth)acrylate; heterocyclic group-containing (meth)acrylates such as tetrahydrofurfuryl (meth)acrylate; and the like. Component (d2) may be used alone or in combination of two or more types.

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

(1.6.4.3. Polyfunctional polymerizable compound (d3))
The term "polyfunctional polymerizable compound" refers to a compound having two or more energy ray-curable groups. The energy ray-curable group is a functional group containing a carbon-carbon double bond, such as a (meth)acryloyl group, a vinyl group, an allyl group, or a vinylbenzyl group. Two or more types of energy ray-curable groups may be used in combination. A three-dimensional network structure (crosslinked structure) is formed by a reaction between an energy ray-curable group in the polyfunctional polymerizable compound and a (meth)acryloyl group in component (d1), or by a reaction between energy ray-curable groups in component (d3). When a polyfunctional polymerizable compound is used, the number of crosslinked structures formed by energy ray irradiation increases compared to when a compound containing only one energy ray-curable group is used. This results in the soft layer exhibiting unique viscoelasticity, making it easier for the outermost surface to have an appropriate dynamic friction coefficient and tensile break stress.

Note that while there is some overlap between the definition of component (d3) and the definition of component (d4) described below, the overlapping portions are included in component (d3). For example, a compound containing a functional group such as a hydroxyl group, epoxy group, amide group, or amino group and having two or more (meth)acryloyl groups is included in the definitions of both component (d3) and component (d4), and in this embodiment, such a compound is considered to be included in component (d3).

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

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

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

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

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

Component (d4) has good compatibility with component (d1), making it easier to adjust the viscosity of the soft layer composition within an appropriate range. Furthermore, good cushioning performance is achieved even when the soft layer is 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. Of these, hydroxyl group-containing (meth)acrylates are preferred.

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

(1.6.4.5 Polymerizable compound (d5) other than components (d1) to (d4))
The soft layer-forming composition may contain a polymerizable compound (d5) other than the above components (d1) to (d4) as long as the above-mentioned effects are not impaired.

Examples of component (d5) include alkyl (meth)acrylates having an alkyl group with 1 to 20 carbon atoms; vinyl compounds, etc.

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

1.6.4.6 Photoinitiators
The composition for the soft layer preferably further contains a photopolymerization initiator from the viewpoint of shortening the polymerization time by light irradiation and reducing the amount of light irradiation when forming the soft 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 specific examples include 1-hydroxycyclohexyl phenyl ketone and 2-hydroxy-2-methyl-1-phenyl-propan-1-one. These photopolymerization initiators can be used alone or in combination of two or more.

The content of the photopolymerization initiator in the soft 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-curable compounds.

1.6.4.7 Other Additives
The soft layer composition may contain other additives as long as the above-described effects are not impaired. 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 soft layer composition is preferably 0.01 to 6 parts by mass, more preferably 0.1 to 3 parts by mass, per 100 parts by mass of the total amount of the energy ray-curable compounds.

A soft layer formed from a soft layer composition containing an energy ray-curable compound is obtained by polymerizing and curing the soft layer composition having the above-described composition by irradiating it with energy rays. In other words, the soft layer is a product obtained by curing the soft layer composition.

The thickness of the soft material is not particularly limited, but is preferably 5 μm or more and 100 μm or less, more preferably 10 μm or more and 90 μm or less, and even more preferably 15 μm or more and 80 μm or less.

(2. Pressure-sensitive adhesive layer)
The adhesive layer is attached to the surface of the workpiece (i.e., the surface on which circuits, electrodes, etc. are formed) and protects the surface and supports the workpiece until it is peeled off from the surface. The adhesive layer may be composed of one layer (single layer), or may be composed of two or more layers. When the adhesive layer has multiple layers, these multiple layers may be the same or different from each other, and the combination of layers constituting these multiple layers is not particularly limited.

In this embodiment, the adhesive layer is not particularly limited as long as it has appropriate pressure-sensitive adhesive properties at room temperature, and may be a single layer or multiple layers. The thickness of the adhesive layer is not particularly limited, but is preferably 5 μm or more and 200 μm or less, and more preferably 10 μm or more and 190 μm or less.

The thickness of an adhesive layer refers to the thickness of the entire adhesive layer. For example, the thickness of an adhesive layer composed of multiple layers refers to the total thickness of all layers that make up the adhesive layer.

The composition of the adhesive layer is not limited as long as it has enough adhesiveness to protect the surface of the workpiece. In this embodiment, the adhesive layer is preferably composed of, for example, an acrylic adhesive, a urethane adhesive, a rubber adhesive, a silicone adhesive, or the like.

The adhesive layer is preferably formed from an energy ray-curable adhesive. By forming the adhesive layer of the workpiece processing protective sheet from an energy ray-curable adhesive, the sheet adheres to the workpiece with high adhesive strength when attached to the workpiece, and the adhesive strength can be reduced by irradiating it with energy rays when peeling it off from the workpiece. Therefore, while adequately protecting the workpiece's circuits, etc., damage to the circuits, electrodes, etc. on the workpiece surface and adhesion of the adhesive to the workpiece are prevented when the workpiece processing protective sheet is peeled off. In other words, the energy ray-curable adhesive layer improves the peelability of the workpiece processing protective sheet.

In this embodiment, the energy ray-curable adhesive is preferably composed of an adhesive composition containing an acrylic adhesive. The acrylic adhesive contains an acrylic polymer.

The acrylic polymer may be any known acrylic polymer, but in this embodiment, a functional group-containing acrylic polymer is preferred. The functional group-containing acrylic polymer may be a homopolymer formed from one type of acrylic monomer, a copolymer formed from multiple types of acrylic monomers, or a copolymer formed from one or more types of acrylic monomers and a monomer other than an acrylic monomer.

In this embodiment, the functional group-containing acrylic polymer is preferably an acrylic copolymer obtained by copolymerizing an alkyl (meth)acrylate and a functional group-containing monomer.

Examples of alkyl (meth)acrylates include methyl (meth)acrylate, ethyl (meth)acrylate, n-propyl (meth)acrylate, isopropyl (meth)acrylate, n-butyl (meth)acrylate, isobutyl (meth)acrylate, t-butyl (meth)acrylate, n-pentyl (meth)acrylate, n-hexyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, isooctyl (meth)acrylate, and n-octyl (meth)acrylate.

The functional group-containing monomer is a monomer that contains a reactive functional group. The reactive functional group is a functional group that can react with other compounds, such as the crosslinking agent described below. Examples of functional groups in the functional group-containing monomer include a hydroxyl group, a carboxyl group, and an epoxy group, with a hydroxyl group being preferred.

Examples of hydroxyl group-containing monomers include hydroxyalkyl (meth)acrylates such as hydroxymethyl (meth)acrylate, 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 non-(meth)acrylic unsaturated alcohols (unsaturated alcohols without a (meth)acryloyl skeleton) such as vinyl alcohol and allyl alcohol.

The acrylic polymer is preferably an energy ray-curable acrylic polymer having an energy ray-curable group, obtained by reacting (e.g., by addition reaction) an energy ray-curable substance having an energy ray-curable group with a functional group possessed by the acrylic polymer. The energy ray-curable substance having an energy ray-curable group is preferably a compound having, in addition to the energy ray-curable group, one or more groups selected from an isocyanate group, an epoxy group, and a carboxy group, and more preferably a compound having an isocyanate group. The isocyanate group can undergo an addition reaction with a hydroxyl group of the functional group-containing acrylic polymer.

Examples of compounds containing an isocyanate group include 2-methacryloyloxyethyl isocyanate, meta-isopropenyl-α,α-dimethylbenzyl isocyanate, methacryloyl isocyanate, allyl isocyanate, 1,1-(bisacryloyloxymethyl)ethyl isocyanate; acryloyl monoisocyanate compounds obtained by reacting a diisocyanate compound or polyisocyanate compound with hydroxyethyl (meth)acrylate; and acryloyl monoisocyanate compounds obtained by reacting a diisocyanate compound or polyisocyanate compound with a polyol compound and hydroxyethyl (meth)acrylate.

The pressure-sensitive adhesive composition preferably contains an energy ray-curable compound in addition to the acrylic polymer. The energy ray-curable compound is preferably a monomer or oligomer that has an unsaturated group in its molecule and can be polymerized and cured by energy ray irradiation.

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

Of these, urethane (meth)acrylate oligomers are preferred.

The molecular weight of the energy ray-curable compound (weight average molecular weight in the case of an oligomer) is preferably 100 to 12,000, more preferably 200 to 10,000, even more preferably 400 to 8,000, and particularly preferably 600 to 6,000.

The content of the energy ray-curable compound in the pressure-sensitive adhesive composition is preferably 5 to 100 parts by mass, more preferably 10 to 70 parts by mass, and even more preferably 15 to 40 parts by mass, per 100 parts by mass of the acrylic polymer.

The pressure-sensitive adhesive composition preferably further contains a crosslinking agent. The crosslinking agent, for example, reacts with functional groups to crosslink resins contained in the functional group-containing acrylic polymer.

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

From the viewpoint of improving the cohesive strength of the adhesive and thereby improving the adhesive strength of the adhesive layer, and from the viewpoint of ease of availability, it is preferable that the crosslinking agent be an isocyanate-based crosslinking agent.

The pressure-sensitive adhesive composition may further contain a photopolymerization initiator. By containing a photopolymerization initiator, the curing reaction proceeds sufficiently even when irradiated with relatively low-energy energy rays such as ultraviolet light.

Examples of photopolymerization initiators include the photopolymerization initiators described in the soft layer composition.

(3. Manufacturing method of protective sheet for workpiece processing)
The method for producing the protection sheet for workpiece processing according to this embodiment may be any known method.

First, prepare the support material. If the support material is composed of one layer, simply prepare a resin film or other material that will make up the support material. If the support material is composed of two or more layers, for example, the support material is manufactured by laminating a resin film that will make up a rigid layer and a resin film that will make up a soft layer.

An example of a method for laminating resin films is dry lamination, in which one resin film (e.g., a resin film constituting a rigid layer) is laminated to another resin film (e.g., a resin film constituting a flexible layer) via an easy-adhesion layer formed on one main surface of the other resin film.

In the dry lamination method, a resin film with an easy-adhesion layer may be used, or a resin film on which an easy-adhesion layer has been formed by applying an easy-adhesion layer-forming composition to a surface that has been subjected to an adhesion treatment such as corona treatment may be used.

Another example is a method in which the resin that makes up the soft material is melted and kneaded using a T-die film-forming machine or the like, and the molten resin is extruded onto one side of the support material while moving the support material at a constant speed to laminate it. Another example is a method in which the soft material is directly laminated onto the support material by heat sealing or the like.

When a soft layer is formed on one main surface of the rigid layer using a soft layer composition, the soft layer composition or a composition obtained by diluting the soft layer composition with a solvent (these two compositions are collectively referred to as the "soft layer coating agent") is prepared. The prepared soft layer coating agent is applied to the release surface of the release film, dried as needed to form a coating film on the release film, and the coating film is cured (e.g., by irradiation with energy rays) to form the soft layer. Then, one main surface of the rigid layer and the soft layer are bonded together. If this soft layer still has energy ray curability, it may be further cured (e.g., by irradiation with energy rays) as needed.

After producing the support material, a composition for forming the adhesive layer is prepared. For example, an adhesive layer composition that constitutes the adhesive layer, or a composition obtained by diluting the adhesive layer composition with a solvent (these two compositions are collectively referred to as an "adhesive layer coating agent"). The prepared adhesive layer coating agent is applied to the release surface of a release film and dried as necessary to form an adhesive layer on the release film. The adhesive layer is then bonded to the main surface of the support material opposite the main surface whose dynamic friction coefficient with sandpaper is controlled within the above-mentioned range, resulting in a protective sheet for workpiece processing in which an adhesive layer is formed on one main surface of the support material. Alternatively, the prepared adhesive layer coating agent may be directly applied to the main surface of the support material opposite the main surface whose dynamic friction coefficient with sandpaper is controlled within the above-mentioned range to form an adhesive layer.

(4. Manufacturing method of workpiece singulation)
As described above, the protective sheet for workpiece processing according to this embodiment is suitable for use in back grinding of a workpiece having circuits or the like formed on one side (front surface) and no circuits or the like formed on the other side (back surface), and during or after back surface grinding, the workpiece is singulated to obtain a plurality of workpiece singulations (a group of workpiece singulations).

As a non-limiting example of how the protective sheet for workpiece processing can be used, a method for producing individual workpieces (e.g., chips) is specifically described below.

Specifically, the method for manufacturing the workpiece singulation preferably includes at least the following steps 1 to 4.
Step 1: A step of attaching the above-mentioned workpiece processing protection sheet to the surface of the workpiece. Step 2: A step of grinding the main surface of the support material that constitutes the outermost surface of the workpiece processing protection sheet. Step 3: A step of grinding the back surface of the workpiece. Step 4: A step of dividing the workpiece into individual pieces to obtain a plurality of workpiece individual pieces.

The following describes in detail each step of the manufacturing method for the above-mentioned workpiece singulation. In the explanation, a wafer is used as an example of the workpiece, and a chip is used as an example of the workpiece singulation.

(4.1. Process 1)
In step 1, the adhesive layer of the protective sheet for workpiece processing according to this embodiment is attached to the surface of the wafer, as shown in Fig. 2. By attaching the protective sheet for workpiece processing to the surface of the wafer, the surface of the wafer is sufficiently protected.

The thickness of the wafer used in this manufacturing method before grinding is not particularly limited, but is usually around 500 to 1000 μm. Furthermore, a circuit is formed on the surface of the wafer. Forming the circuit on the wafer surface can be done by a variety of methods, including conventional methods such as etching and lift-off.

The formed circuit may be exposed, or a circuit protection layer may be formed to protect the circuit. The circuit protection layer is usually formed by applying a composition that constitutes the circuit protection layer and then thermally curing it. Furthermore, convex electrodes such as bumps and pillars may be formed on the circuit.

(4.2. Process 2)
Step 2 is performed after step 1. In step 2, as shown in Fig. 3, the main surface 10b (12b) constituting the outermost surface of the protective sheet for workpiece processing 1 is ground on the support material. The main surface constituting the outermost surface of the protective sheet for workpiece processing is main surface 10b in the protective sheet for workpiece processing shown in Fig. 1A, and is main surface 12b in the protective sheets for workpiece processing shown in Fig. 1B and Fig. 1C.

From the perspective of streamlining and simplifying step 2, the equipment used for grinding is preferably a grinding device that grinds the backside of the wafer. In such a grinding device, as shown in FIG. 3, the backside 100b of the wafer 100 is held on a chuck table 60 so that the grinding wheel 50 and the main surface 10b (12b) that forms the outermost surface of the protective sheet 1 for workpiece processing face each other. The grinding wheel 50 then comes into contact with the wafer 100 and the protective sheet 1 for workpiece processing while rotating relative to each other, and the main surface 10b (12b) is ground by the abrasive grains of the grinding wheel 50.

The main surface of the support material that forms the outermost surface of the workpiece processing protection sheet has the physical properties described above, so during grinding, this main surface is easily ground and does not easily adhere to the grinding wheel. As a result, this main surface is ground properly, resulting in a surface with minimal irregularities.

(4.3. Process 3)
In step 3, as shown in FIG. 4 , the main surface 10b (12b) of the support material ground in step 2 is held on a chuck table 60, and then the back surface 100b of the wafer 100 is ground by a grinding wheel 50. Because the main surface 10b (12b) of the support material ground in step 2 has little unevenness, almost no gap is formed between the support material of the workpiece processing protection sheet 1 and the chuck table 60. Therefore, the force applied during back surface grinding is evenly transmitted to the back surface 100b of the wafer 100, and the back surface 100b of the wafer 100 is ground uniformly. As a result, the wafer thickness after grinding is less uneven, and the total thickness variation (TTV) of the wafer after grinding can be reduced.

(4.4. Process 4)
In step 4, the wafer is divided into individual chips (chip groups). The wafer may be divided into individual chips after step 3 or during step 3.

If the wafer is singulated after step 3, for example, the suction between the support material and the chuck table is released, and the wafer is transported to the dicing step with the workpiece processing protection sheet attached. In the dicing step, the wafer is singulated into multiple chips. Any known method can be used for singulation. For example, a rotary blade such as a dicer is used to form grooves that penetrate the front and back surfaces of the wafer, thereby cutting the wafer into multiple singulated chips.

In this embodiment, step 4 is preferably a step of singulating by DBG or LDBG. In this case, step 4 is performed in step 3.

When singulating using DBG or LDBG, in addition to steps 1 to 4 above, there is also a step of forming grooves from the front side of the workpiece (step 5a), or a step of forming modified regions inside the workpiece from the front or back side of the workpiece (step 5b).

(4.5. Step 5a)
Step 5a is performed before steps 1 to 3. The grooves formed in step 5a are shallower than the thickness of the wafer. The grooves can be formed by dicing using a conventionally known wafer dicing device or the like. These grooves serve as starting points for dividing the wafer. In other words, the grooves are formed so as to follow the dividing lines that will be used when the wafer is divided into individual chips in step 3.

(4.6. Step 5b)
Step 5b is performed before step 3. Step 5b may be performed before steps 1 and 2, or after step 1 and before step 2, or after steps 1 and 2. In this embodiment, step 5b is preferably performed after steps 1 and 2.

The modified region formed in step 5b is an embrittled portion of the wafer. In the modified region, cracks are likely to occur due to the shear force and pressure applied to the wafer during backside grinding. These cracks become the starting point for dividing the wafer. In other words, the modified region is formed so as to follow the dividing line when the wafer is divided into individual chips in step 3.

The modified region is formed by irradiating the wafer with a laser focused on the interior of the wafer. Therefore, the modified region is formed inside the wafer. The laser can be irradiated from either the front or back side of the wafer. Note that if step 5b is performed after step 1 and the laser is irradiated from the front side of the wafer, the laser will be irradiated onto the wafer through the workpiece processing protective sheet.

Step 3 is performed after step 5a or step 5b. That is, after grooves or modified regions are formed in the wafer, the backside of the wafer is ground to separate the wafer into multiple chips. In other words, step 4 is performed in step 3.

In step 3, which follows step 5a, backside grinding is performed to thin the wafer at least to the point where it reaches the bottom of the groove. This backside grinding turns the groove into a notch that penetrates the wafer, and the wafer is divided by the notch into individual chips.

In step 3 after step 5b, back grinding may be performed until the ground surface (wafer back surface) reaches the modified region, but the grinding surface does not have to reach the modified region exactly. That is, grinding may be performed to a position close to the modified region so that the wafer is divided starting from the modified region and individual chips are obtained. For example, grinding may be performed to a position close to the modified region, and the wafer may be completely singulated using cracks that appear in the modified region. Alternatively, the wafer may be partially singulated using cracks that appear in the modified region, and then the wafer may be completely singulated by applying a pickup tape (described below) and stretching the pickup tape. Alternatively, the wafer may be completely singulated by stretching the pickup tape.

Furthermore, after backside grinding using a grinding wheel is completed, stress relief such as dry polishing may be performed.

The shape of the chips singulated through step 4 may be square or elongated, such as rectangular. The thickness of the singulated chips is not particularly limited, but is preferably about 5 to 100 μm, and more preferably 10 to 45 μm. LDBG facilitates the thickness of the singulated chips to be 50 μm or less, and more preferably 10 to 45 μm. The size of the singulated chips is not particularly limited. For example, the chip area is preferably less than 600 mm ² , more preferably less than 400 mm ² , and even more preferably less than 120 mm ² .

(4.7. Process 6)
In this embodiment, the method for manufacturing the workpiece singulation preferably includes a step (step 6) of peeling off the workpiece processing protection sheet from the singulated workpiece (i.e., the plurality of workpiece singulations). Step 6 is performed after step 4. Step 6 is performed, for example, by the following method.

First, if the adhesive layer of the workpiece processing protection sheet is formed from an energy ray-curable adhesive, a step (step 6a) is performed in which the adhesive layer is cured by irradiating it with energy rays. As described above, step 6a is a step in which the adhesive strength of the adhesive layer is reduced by irradiating it with energy rays. By performing step 6a, the workpiece processing protection sheet can be peeled from the surface of the wafer, which has been sufficiently protected by the adhesive strength of the adhesive layer in steps 1 to 5, while preventing damage to the circuits, electrodes, etc. on the workpiece surface and adhesion of the adhesive to the workpiece.

On the other hand, since energy ray-curable adhesive layers are cured by irradiation with energy rays, it is preferable for the adhesive layer to be hard when grinding the backside of the wafer, from the perspective of stably grinding the backside of the wafer and improving the thickness accuracy of the wafer after grinding.

In other words, there is a trade-off between the thickness accuracy of the wafer after grinding and the removability of the workpiece processing protection sheet.

In this embodiment, even if the curable adhesive layer is uncured or the non-curable adhesive layer is relatively soft, the main surface of the support material that constitutes the outermost surface of the workpiece processing protective sheet has the above-mentioned physical properties, so that the main surface can be properly ground, resulting in a surface with minimal irregularities. As a result, even if the adhesive layer is relatively soft, the total thickness variation (TTV) of the wafer after grinding can be reduced. In other words, it is possible to achieve both high thickness accuracy of the wafer after grinding and good removability when peeling off the workpiece processing protective sheet.

Thus, step 6a may be performed after step 1, step 2, or step 5b, but is preferably performed after step 3.

The conditions for energy ray irradiation are preferably, for example, an illuminance of the energy ray of 120 to 280 mW/cm ² and a light amount of the energy ray of 100 to 1000 mJ/cm ^2. The energy ray is preferably ultraviolet light.

After the adhesive layer has hardened, a pickup tape is attached to the backside of the multiple workpieces, and they are positioned and oriented so that they can be picked up. At this time, the ring frame located on the outer periphery of the wafer is also attached to the pickup tape, and the outer edge of the pickup tape is fixed to the ring frame. The wafer and ring frame may be attached to the pickup tape at the same time, or they may be attached at different times. Next, the workpiece processing protective sheet is peeled off from the multiple chips held on the pickup tape.

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

This embodiment has been described above, but the present invention is not limited to the above embodiment and may be modified in various ways within the scope of the present invention.

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

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

(Coefficient of dynamic friction between support material and sandpaper)
The support materials prepared in the Examples and Comparative Examples were cut to a length of 200 mm and a width of 80 mm to obtain test samples for measuring the coefficient of dynamic friction. The test sample was placed on sandpaper with a grit size of 1200. A sliding piece with a side length of 63 mm and a felt surface in contact with the test sample was placed on the test sample. A weight was then placed on the sliding piece so that the total mass of the sliding piece and the weight was 1000 g. The test sample was pulled in the longitudinal direction of the test sample at a rate of 100 mm/min. The average load from the start of relative shear movement between the contact surfaces of the test sample and the sandpaper to the point of movement of 60 mm was taken as the kinetic friction force, without taking into account the load at the time the test sample began to move. The coefficient of dynamic friction was calculated by dividing the obtained kinetic friction force by the normal force generated by the total mass of the sliding piece and the weight. The results are shown in Table 1.

(Tensile breaking stress of support material)
The support materials prepared in the Examples and Comparative Examples were cut to a size of 140 mm in length and 15 mm in width to obtain measurement samples for measuring tensile stress at break. Film tension labels were attached to 20 mm sections on both ends of the obtained measurement samples to prepare samples with a measurement area of 15 mm x 100 mm. The tensile stress at break of the samples was measured using a tensile tester (Shimadzu Corporation, product name "Autograph AG-IS 1kN") under conditions of a chuck distance of 100 mm and a tensile speed of 200 mm/min. The results are shown in Table 1. In Examples 1 to 3 and 5 and Comparative Examples 1, 3 and 4, where the support material was composed of two or more layers, the tensile stress at break of the layer constituting the outermost surface of the workpiece processing protection sheet, i.e., the soft layer, was measured as the tensile stress at break.

(TTV evaluation of wafer after grinding)
In Examples 1 to 4 and Comparative Examples 1 to 4, the protective sheets for workpiece processing 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 back-grinding tape laminator (manufactured by Lintec Corporation, device name "RAD-3510F/12"). Next, the outermost surface of the protective sheet for workpiece processing was ground by 12 μm using a grinder (manufactured by Disco Corporation, device name "DGP8760").

Next, a back grinding machine (manufactured by Disco Corporation, model number "DGP8761") was used to grind (including dry polish) the substrate until it reached a thickness of 30 μm.

In Example 5, as described above, a workpiece processing protective sheet was attached to a silicon wafer, and the top surface of the workpiece processing protective sheet was ground by 12 μm. After that, a laser saw (manufactured by Disco Corporation, device name "DFL7361") was used to form a modified region on the wafer with a grid size of 10 mm x 10 mm. Next, as described above, the backside of the wafer was ground to a thickness of 30 μm, and the wafer was divided into multiple chips.

The thickness of the ground wafer or the entire surface of each of the individual chips was measured at a measurement pitch of 10 mm using a wafer thickness mapping system (manufactured by Hamamatsu Photonics K.K., device name "C8870-02"), and the TTV of the ground wafer was calculated from the maximum and minimum thickness values and evaluated according to the following criteria. The results are shown in Table 1.
◎: The outermost surface of the workpiece processing protection sheet can be ground, and the TTV is less than 5 μm. ○: The outermost surface of the workpiece processing protection sheet can be ground, and the TTV is 5 μm or more and less than 10 μm. ×: The outermost surface of the workpiece processing protection sheet can be ground, and the TTV is 10 μm or more. XX: The outermost surface of the workpiece processing protection sheet cannot be ground.

Example 1
(1) Support Material First, a polyethylene terephthalate (PET) film (thickness: 50 μm) was prepared as a rigid layer.

Next, low-density polyethylene was melted and extruded using a T-die method. The extrudate was then biaxially stretched using a cooling roll to obtain a 25 μm-thick LDPE film (tensile modulus: 420 MPa). A 2.5 μm-thick easy-adhesion layer was formed on one side of the prepared PET film, and the resulting LDPE film was bonded to the soft layer using a dry lamination method. Next, a 2.5 μm-thick easy-adhesion layer was formed on the other side of the PET film, and the resulting LDPE film was bonded to the soft layer using a dry lamination method to obtain a support material composed of a three-layer structure: soft layer/rigid layer/soft layer, in which a rigid layer and a soft layer were laminated. The support material had a thickness of 105 μm.

(2) Pressure-sensitive adhesive layer (Preparation of composition for pressure-sensitive adhesive layer)
An energy ray-curable acrylic copolymer (Mw: 500,000) was obtained by reacting an acrylic polymer obtained by copolymerizing 65 parts by mass of n-butyl acrylate (BA), 20 parts by mass of methyl methacrylate (MMA), and 15 parts by mass of 2-hydroxyethyl acrylate (2HEA) with 2-methacryloyloxyethyl isocyanate (MOI) so that MOI was added to 80 equivalents of hydroxyl groups out of all hydroxyl groups (100 equivalents) of the acrylic polymer.

100 parts by weight of this energy ray-curable acrylic copolymer was blended with 10 parts by weight of a multifunctional urethane acrylate ultraviolet-curable compound (manufactured by Mitsubishi Chemical Corporation, product name "UT-4332"), 0.38 parts by weight of an isocyanate-based crosslinking agent (manufactured by Tosoh Corporation, product name "Coronate L"), and 1 part by weight of bis(2,4,6-trimethylbenzoyl)phenylphosphine oxide as a photopolymerization initiator, and diluted with methyl ethyl ketone to prepare a coating agent for a pressure-sensitive adhesive layer composition with a solids concentration of 34% by weight.

(Production of protective sheet for workpiece processing)
The adhesive layer composition obtained above was applied to the silicone 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 20 μm on the release sheet.

Then, one of the soft layers of the support material was bonded to the adhesive layer to produce a workpiece processing protection sheet. In other words, the workpiece processing protection sheet shown in Figure 1C was produced.

Example 2
The protection sheet for workpiece processing shown in FIG. 1B was produced in the same manner as in Example 1, except that a support material composed of two layers, a soft layer/a rigid layer, was produced as follows.

A PET film (thickness: 50 μm) was prepared as the rigid layer. Next, a soft layer composition for forming the soft layer was prepared as follows.

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

A soft layer composition was prepared by blending 50 parts by weight of the urethane acrylate oligomer (UA-1) synthesized above, 45 parts by weight of isobornyl acrylate (IBXA), and 5 parts by weight of polyethylene glycol 600 diacrylate as energy ray-curable compounds, and further blending in 2 parts by weight of 1-hydroxycyclohexyl phenyl ketone (manufactured by IGM Resins, product name "OMNIRAD1173") as a photopolymerization initiator.

The above-mentioned soft layer composition was applied to the silicone release-treated surface of a release sheet (SP-PET381031, manufactured by Lintec Corporation, thickness: 38 μm) to form a coating film. The coating film was then semi-cured by irradiating it with ultraviolet light, forming a semi-cured soft layer film with a thickness of 55 μm.

The ultraviolet irradiation was carried out using a belt conveyor-type ultraviolet irradiation device (ECS-401GX, manufactured by iGraphics) and a high-pressure mercury lamp (H04-L41, manufactured by iGraphics) under irradiation conditions of a lamp height of 260 mm, an output of 80 W/cm, an illuminance of 70 mW/cm ² , and an irradiation amount of 30 mW/cm ^2. The surface of the formed semi-cured film was then bonded to one main surface of a PET film serving as a rigid layer, and ultraviolet light was irradiated again from the release sheet side of the semi-cured film to completely cure the semi-cured film and form a soft layer with a thickness of 55 μm.

Example 3
The protective sheet for workpiece processing shown in Figure 1C was produced in the same manner as in Example 1, except that a 25 μm-thick linear low-density polyethylene (LLDPE) was formed as the soft layer in a support material composed of three layers: soft layer/rigid layer/soft layer. The LLDPE was obtained by melting the linear low-density polyethylene, extruding the melt using a T-die method, and biaxially stretching the extrudate using a chill roll. The tensile modulus of the LLDPE was 90 MPa.

Example 4
A workpiece processing protection sheet was produced in the same manner as in Example 1, except that a support material consisting of one layer of PET film (manufactured by Toray Advanced Materials Co., Ltd., product name "XG7PH8", thickness: 50 μm) was used. That is, the workpiece processing protection sheet shown in FIG. 1A was produced.

Example 5
A protection sheet for workpiece processing was produced in the same manner as in Example 2.

(Comparative Example 1)
A protective sheet for workpiece processing shown in FIG. 1B was produced in the same manner as in Example 2, except that the soft layer was formed using the soft layer composition shown below in a support material composed of two layers: a soft layer/a rigid layer.

A urethane acrylate oligomer (UA-2) with a weight-average molecular weight (Mw) of approximately 25,000 was obtained by reacting 2-hydroxyethyl acrylate with a terminal isocyanate urethane prepolymer obtained by reacting polycarbonate diol with isophorone diisocyanate.

A soft layer composition was prepared by blending 25 parts by weight of the urethane acrylate oligomer (UA-2) synthesized above, 65 parts by weight of isobornyl acrylate (IBXA), and 10 parts by weight of phenylhydroxypropyl acrylate (HPPA) as energy ray-curable compounds, and further blending 2.0 parts by weight of 2-hydroxy-2-methyl-1-phenyl-propan-1-one (manufactured by IGM Resins, product name "Omnirad 1173") as a photopolymerization initiator.

(Comparative Example 2)
A protection sheet for workpiece processing was produced in the same manner as in Example 4, except that a support material consisting of one layer of polyethylene naphthalate (PEN) film (thickness: 50 μm) was used.

(Comparative Example 3)
The protective sheet for workpiece processing shown in FIG. 1C was produced in the same manner as in Example 1, except that a colorless and transparent ethylene-methacrylic acid copolymer having a thickness of 25 μm was formed as the soft layer in a support material composed of three layers: soft layer/rigid layer/soft layer.

(Comparative Example 4)
A protective sheet for workpiece processing shown in FIG. 1C was produced in the same manner as in Example 1, except that a colorless and transparent ethylene-vinyl acetate copolymer having a thickness of 25 μm was formed as the soft layer in a support material composed of three layers: soft layer/rigid layer/soft layer.

The above measurements and evaluations were performed on the obtained samples (Examples 1 to 5 and Comparative Examples 1 to 4). The results are shown in Table 1.

Table 1 shows that when the coefficient of dynamic friction between the support material and sandpaper and the tensile breaking stress of the support material are within the above-mentioned ranges, grinding the main surface of the support material that forms the outermost surface of the workpiece processing protection sheet and then backgrinding the wafer results in a small TTV of the wafer after backgrinding.

DESCRIPTION OF SYMBOLS 1...protective sheet for workpiece processing 10...support material 11...rigid layer 12...soft layer 20...adhesive layer

Claims (10)

A protective sheet for workpiece processing having a support material and an adhesive layer disposed on one main surface of the support material,
The other main surface of the support material constitutes the outermost surface of the workpiece processing protection sheet, and the dynamic friction coefficient between the outermost surface of the workpiece processing protection sheet and sandpaper having a grit size of 1200 is 1.40 or less;
A protective sheet for workpiece processing, wherein the support material has a tensile breaking stress of 250 MPa or less. The protective sheet for workpiece processing according to claim 1, wherein the support material is composed of two or more layers. The workpiece processing protective sheet according to claim 2, wherein the support material has a rigid layer and a soft layer that is softer than the rigid layer, and one main surface of the soft layer forms the outermost surface of the workpiece processing protective sheet. A protective sheet for workpiece processing according to any one of claims 1 to 3, in which the adhesive layer is attached to the surface of a workpiece having a front and back surface, and the outermost surface of the protective sheet for workpiece processing is ground before use, prior to the process of grinding the back surface of the workpiece. The protective sheet for workpiece processing described in claim 4 is used in a process of dividing a workpiece into individual workpieces by grinding the back surface of the workpiece having grooves formed on the surface or modified regions formed inside the workpiece. A protective sheet for workpiece processing according to any one of claims 1 to 5, wherein the adhesive layer is energy ray curable. A step of attaching the adhesive layer of the protective sheet for workpiece processing according to any one of claims 1 to 6 to the surface of a workpiece having a front and back surfaces;
grinding the back surface of the workpiece;
and a step of dividing the work into individual pieces to obtain a plurality of individual work pieces. The workpiece processing protective sheet according to claim 4 or 5, further comprising a step of grinding the outermost surface of the workpiece processing protective sheet,
The method for producing individual workpieces according to claim 7, wherein the step of grinding the back surface of the workpiece is carried out after the step of grinding the outermost surface of the protection sheet for workpiece processing. The method further includes a step of forming a groove on the surface of the workpiece, or a step of forming a modified region inside the workpiece from the surface or back surface of the workpiece,
The method for manufacturing a workpiece singulation product according to claim 7 or 8, wherein in the step of grinding the back surface of the workpiece, the workpiece is singulated into a plurality of workpiece singulation products starting from the groove or the modified region. The method for manufacturing a workpiece singulated product according to any one of claims 7 to 9, further comprising a step of peeling off the workpiece processing protection sheet from the workpiece singulated product.