JP7724072B2 - Workpiece processing sheet - Google Patents

Description

The present invention relates to a workpiece processing sheet used for processing workpieces such as semiconductor wafers.

Semiconductor wafers, such as silicon and gallium arsenide, and various packages are manufactured in large diameters, cut into chips (diced), peeled off (picked up), and then moved to the next process, the mounting process. During this process, the semiconductor wafer or other workpiece is stacked on an adhesive sheet (hereinafter sometimes referred to as the "workpiece processing sheet") that has a base material and an adhesive layer, and undergoes processing such as backgrinding, dicing, cleaning, drying, expanding, picking up, and mounting.

When the specified processing steps are completed, the workpiece processing sheet is peeled off from the processed workpiece. At this time, static electricity known as peeling electrification can occur between the workpiece processing sheet and the adherend. This static electricity can cause dust and other particles to adhere to the workpiece or equipment, and can also cause damage to the workpiece. For this reason, workpiece processing sheets are required to have antistatic properties.

Patent Documents 1 and 2 disclose the use of a substrate containing a specific antistatic agent in order to provide a workpiece processing sheet with antistatic properties.

JP 2012-211314 A Japanese Patent Application Laid-Open No. 2008-244377

However, workpiece processing sheets with a base material containing the above-mentioned antistatic agent have the problem of their adhesive strength easily decreasing during storage. Furthermore, some antistatic agents contain alkali metal ions, and when such antistatic agents are used, the alkali metal ions can leak out of the base material and adhere to and affect the workpiece or the equipment used to handle the workpiece processing sheets.

The present invention was made in light of these circumstances, and aims to provide a workpiece processing sheet that exhibits excellent antistatic properties while suppressing changes in adhesive strength over time and the leakage of alkali metal ions.

To achieve the above object, the present invention first provides a workpiece processing sheet comprising a substrate and an adhesive layer laminated on one side of the substrate, wherein the substrate comprises a surface layer located proximal to the adhesive layer, a back layer located distal to the adhesive layer, and an intermediate layer located between the surface layer and the back layer, each of which contains an antistatic agent, the antistatic agent contained in the surface layer having a melt flow rate (MFR) of 15 g/10 min or less as measured in accordance with ASTM D1238 (190°C, 21.18 N), and the antistatic agent contained in the back layer having a melt flow rate (MFR) of 14 g/10 min or more as measured in accordance with ASTM D1238 (190°C, 21.18 N) (Invention 1).

The workpiece processing sheet according to the above invention (Invention 1) has a base material with the three layers described above, of which the front and back layers contain an antistatic agent, thereby exhibiting excellent antistatic properties. Meanwhile, because the melt flow rates of the antistatic agents contained in the front and back layers are within the above-mentioned ranges, changes in adhesive strength over time are effectively suppressed, and the leakage of alkali metal ions into the workpiece, equipment, etc. is effectively suppressed.

In the above invention (Invention 1), it is preferable that the thickness of the surface layer is 0.5 μm or more and less than 8 μm (Invention 2).

In the above inventions (Inventions 1 and 2), it is preferable that the antistatic agent is a polyether polyolefin block copolymer (Invention 3).

In the above inventions (Inventions 1 to 3), it is preferable that the sheet be a dicing sheet (Invention 4).

The workpiece processing sheet of the present invention exhibits excellent antistatic properties while suppressing changes in adhesive strength over time and the leakage of alkali metal ions.

1 is a cross-sectional view of a workpiece processing sheet according to one embodiment of the present invention.

Hereinafter, an embodiment of the present invention will be described.
A cross-sectional view of a workpiece processing sheet according to one embodiment is shown in Fig. 1. The workpiece processing sheet 1 shown in Fig. 1 includes a substrate 11 and an adhesive layer 12 laminated on one side of the substrate 11.

As shown in FIG. 1, the substrate 11 includes a surface layer 111 located proximal to the adhesive layer 12, a back layer 113 located distal to the adhesive layer 12, and an intermediate layer 112 located between the surface layer 111 and the back layer 113. Each of the surface layer 111 and the back layer 113 contains an antistatic agent.

As described above, by providing the substrate 11 with a layer containing an antistatic agent, the workpiece processing sheet 1 according to this embodiment has excellent antistatic properties. This effectively suppresses peeling static electricity when separating the release sheet or workpiece from the workpiece processing sheet 1.

Furthermore, in the substrate 11 of this embodiment, the antistatic agent contained in the surface layer 111 has a melt flow rate (MFR) measured in accordance with ASTM D1238 (190°C, 21.18N) of 15 g/10 min or less, and the antistatic agent contained in the back layer 113 has a melt flow rate (MFR) measured in accordance with ASTM D1238 (190°C, 21.18N) of 14 g/10 min or more.

The antistatic agent contained in the surface layer 111 has a relatively low MFR of 15 g/10 min or less, which gives the antistatic agent a high viscosity on its own and makes it less likely to leak out of the surface layer 111. This prevents the antistatic agent from migrating from the surface layer 111 to the adhesive layer 12, effectively preventing changes in the adhesive strength of the workpiece processing sheet 1 according to this embodiment from changing over time.

From this perspective, the MFR of the antistatic agent contained in the surface layer 111 is more preferably 13 g/10 min or less, and particularly preferably 10 g/10 min or less. There are no particular restrictions on the lower limit of the MFR, and it may be, for example, 1 g/10 min or more, and particularly 2 g/10 min or more.

On the other hand, the MFR of the antistatic agent contained in the backing layer 113 is 14 g/10 min or higher as described above. When the MFR is relatively high, the amount of alkali metal ions contained in the antistatic agent tends to be small. By containing an antistatic agent with this MFR in the backing layer 113, the outflow of alkali metal ions from the workpiece processing sheet 1 according to this embodiment is effectively suppressed. In particular, when dicing is performed, alkali metal ions often leak into the cutting water or the rinse water after dicing. However, the workpiece processing sheet 1 according to this embodiment can effectively suppress this outflow into the cutting water or the rinse water. This effectively suppresses the migration of alkali metal ions to the workpiece or various devices used to handle the workpiece processing sheet 1, thereby reducing the impact of alkali metal ions.

From this perspective, the MFR of the antistatic agent contained in the backing layer 113 is more preferably 14 g/10 min or more, and particularly preferably 17 g/10 min or more. There are no particular restrictions on the lower limit of the MFR, and it may be, for example, 30 g/10 min or less, and particularly 25 g/10 min or less.

Details of the method for measuring the above MFR are as described in the test examples below.

1. Structure of Workpiece Processing Sheet (1) Substrate As described above, the substrate 11 in this embodiment includes the surface layer 111, the intermediate layer 112, and the back layer 113. The composition of these layers is not particularly limited as long as the surface layer 111 and the back layer 113 each contain an antistatic agent exhibiting the above-mentioned MFR.

The materials other than the antistatic agent in each layer constituting the substrate 11 are not particularly limited as long as they are capable of forming those layers, and it is preferable to use a resin, for example. In particular, from the perspective of easily achieving the performance required of a workpiece processing sheet, such as expandability and reduction of cutting chips, it is preferable to use at least one of polyolefin resin and thermoplastic elastomer as the main material. Note that the surface layer 111 and the back layer 113 may have different compositions or may have the exact same composition.

(1-1) Polyolefin Resin Specific examples of the polyolefin resin described above are not particularly limited. In this specification, the polyolefin resin refers to a homopolymer or copolymer containing an olefin as a monomer, or a copolymer containing an olefin and a molecule other than an olefin as monomers, in which the mass ratio of the portion based on the olefin unit in the polymerized resin is 1.0 mass% or more.

The polymers constituting the polyolefin resins may be linear or may have side chains. Furthermore, the polymers may have aromatic or aliphatic rings.

Examples of olefin monomers that make up polyolefin-based resins include olefin monomers having 2 to 8 carbon atoms, α-olefin monomers having 3 to 18 carbon atoms, and olefin monomers having a cyclic structure. Examples of olefin monomers having 2 to 8 carbon atoms include ethylene, propylene, 2-butene, and octene. Examples of α-olefin monomers having 3 to 18 carbon atoms include propylene, 1-butene, 4-methyl-1-pentene, 1-hexene, 1-octene, 1-decene, 1-dodecene, 1-tetradecene, and 1-octadecene. Examples of olefin monomers having a cyclic structure include norbornene, cyclopentadiene, cyclohexadiene, dicyclopentadiene, tetracyclododecene, and derivatives thereof.

Polyolefin resins can be used alone or in combination of two or more.

Among the specific examples of polyolefin resins mentioned above, it is preferable to use at least one of polyethylene containing ethylene as the main polymerization unit and polypropylene containing propylene as the main polymerization unit.

As the polypropylene, for example, homopolypropylene, random polypropylene, and block polypropylene are preferably used. These can be used alone or in combination of two or more. In particular, it is preferable to use a mixture of homopolypropylene and random polypropylene.

The homopolypropylene, random polypropylene, and block polypropylene mentioned above may each be commercially available products. Examples of commercially available homopolypropylenes include Prime Polypro E111G, Prime Polypro E-100GV, Prime Polypro E-100GPL, and Prime Polypro E-200GP, all manufactured by Prime Polymer Co., Ltd. Examples of commercially available random polypropylenes include Prime Polypro B221WA, Prime Polypro B241, Prime Polypro E222, and Prime Polypro E-333GV, all manufactured by Prime Polymer Co., Ltd. Examples of commercially available block polypropylene products include Prime Polypro E701G, Prime Polypro E702G, and Prime Polypro E702MG, all manufactured by Prime Polymer Co., Ltd.

The polyethylene may be any of high-density polyethylene, medium-density polyethylene, low-density polyethylene, very-low-density polyethylene, and linear low-density polyethylene, or a mixture of two or more of these.

In particular, it is preferable to use low-density polyethylene as the polyethylene, and examples of commercially available products include "Novatec LL" manufactured by Mitsubishi Chemical Corporation, and the Neozex series and Ultraozex series manufactured by Prime Polymer Co., Ltd.

When any of the layers constituting the substrate 11 contains a polyolefin resin, the content of the polyolefin resin in that layer is preferably 10% by mass or more, particularly preferably 15% by mass or more, and even more preferably 20% by mass or more. Furthermore, the content is preferably 100% by mass or less, particularly preferably 95% by mass or less, and even more preferably 90% by mass or less. By keeping the polyolefin resin content within the above range, the workpiece processing sheet 1 according to this embodiment is more likely to have good expandability.

(1-2) Thermoplastic Elastomer The thermoplastic elastomer is not particularly limited as long as it is other than the polyolefin-based resins and can be used to form the substrate 11. Examples of the thermoplastic elastomer include olefin-based elastomers, rubber elastomers, urethane-based elastomers, styrene-based elastomers, acrylic-based elastomers, and vinyl chloride-based elastomers. These may be used alone or in combination of two or more.

Among the elastomers mentioned above, olefin-based elastomers are preferred because they are easier to expand. In particular, it is preferable that at least one of the surface layer 111 and the back layer 113 contains an olefin-based elastomer. In this specification, "olefin-based elastomer" refers to a copolymer containing structural units derived from olefin or its derivatives (olefin-based compounds), and is a material that has rubber-like elasticity and thermoplasticity in a temperature range including room temperature.

Examples of olefin-based elastomers include those containing at least one resin selected from the group consisting of ethylene-propylene copolymer, ethylene-α-olefin copolymer, propylene-α-olefin copolymer, butene-α-olefin copolymer, ethylene-propylene-α-olefin copolymer, ethylene-butene-α-olefin copolymer, propylene-butene-α-olefin copolymer, and ethylene-propylene-butene-α-olefin copolymer. Of these, ethylene-propylene copolymer is preferred.

If any of the layers constituting the substrate 11 contains an olefin-based elastomer, the content of the olefin-based elastomer in that layer is preferably 1% by mass or more, particularly preferably 10% by mass or more, and even more preferably 15% by mass or more. Furthermore, the content is preferably 90% by mass or less, particularly preferably 80% by mass or less, and even more preferably 70% by mass or less. By ensuring that the olefin-based elastomer content is within the above range, the workpiece processing sheet 1 according to this embodiment is more likely to achieve better expandability.

Furthermore, from the viewpoint of easily achieving good expandability, it is also preferable to use a styrene-based elastomer. In particular, it is preferable that the intermediate layer 112 contains a styrene-based elastomer. Note that, in this specification, "styrene-based elastomer" refers to a copolymer containing structural units derived from styrene or its derivatives (styrene-based compounds), and is a material that has rubber-like elasticity and thermoplasticity in a temperature range including room temperature.

Styrenic elastomers include styrene-conjugated diene copolymers and styrene-olefin copolymers, with styrene-conjugated diene copolymers being preferred. Specific examples of styrene-conjugated diene copolymers include unhydrogenated styrene-conjugated diene copolymers such as styrene-butadiene copolymer, styrene-butadiene-styrene copolymer (SBS), styrene-butadiene-butylene-styrene copolymer, styrene-isoprene copolymer, styrene-isoprene-styrene copolymer (SIS), and styrene-ethylene-isoprene-styrene copolymer; and hydrogenated styrene-conjugated diene copolymers such as styrene-ethylene/propylene-styrene copolymer (SEPS: hydrogenated styrene-isoprene-styrene copolymer) and styrene-ethylene-butylene-styrene copolymer (SEBS: hydrogenated styrene-butadiene copolymer). Styrenic thermoplastic elastomers may be hydrogenated or unhydrogenated, with hydrogenated products being preferred. Among the above, hydrogenated styrene-conjugated diene copolymers are preferred, with styrene-ethylene-butylene-styrene copolymer (SEBS) being particularly preferred, as they are more likely to provide good expandability.

The content of structural units derived from styrene or styrene-based compounds in the styrene-based elastomer (styrene ratio) is preferably 1% by mass or more, particularly preferably 5% by mass or more, and even more preferably 10% by mass or more. Furthermore, from the perspective of easily achieving excellent film-forming properties, the content of the above structural units is preferably 80% by mass or less, particularly preferably 70% by mass or less, and even more preferably 60% by mass or less. This makes it easier to achieve excellent expandability.

If any of the layers constituting the substrate 11 contains a styrene-based elastomer, the content of the styrene-based elastomer in that layer is preferably 1% by mass or more, particularly preferably 10% by mass or more, and even more preferably 15% by mass or more. Furthermore, the content is preferably 90% by mass or less, particularly preferably 80% by mass or less, and even more preferably 70% by mass or less. By keeping the styrene-based elastomer content within the above range, the workpiece processing sheet 1 according to this embodiment is more likely to achieve better expandability.

(1-3) Antistatic Agent The antistatic agent in this embodiment is not particularly limited, and known antistatic agents can be used. Examples of the antistatic agent include low-molecular-weight antistatic agents and polymer-type antistatic agents. However, polymer-type antistatic agents are preferred from the viewpoints that they can easily suppress the generation of chips, are less likely to bleed out from the substrate 11, and thus can easily suppress changes in adhesive strength over time.

Examples of polymer-type antistatic agents include copolymers containing polyether units, such as polyether ester amides and polyether polyolefin block copolymers. These copolymers may contain metal salts, such as alkali metal salts and alkaline earth metal salts, or ionic liquids. Among these, polyether polyolefin block copolymers are preferred from the standpoint of easily suppressing changes in adhesive strength over time while still achieving sufficient antistatic properties.

A polyether polyolefin block copolymer is a copolymer containing both polyether and polyolefin units. The polyether units exhibit ionic conductivity, providing antistatic properties, while the polyolefin units provide excellent dispersibility in polyolefin resins.

Commercially available examples of polyether polyblock olefin copolymers include "Pelestat 300," "Pelestat 230," "Pelestat PVH," "Pelestat PVL," "Pelestat HS," "Pelestat 201," and "Pelestat UC," all manufactured by Sanyo Chemical Industries, Ltd., as well as "Sankonol TBX-310," manufactured by Sanko Chemical Industries, Ltd.

Of these polyether polyolefin block copolymer antistatic agents, those suitable for use in the surface layer 111 (with an MFR of 15 g/10 min or less) include products such as "Pelectron PVH" (MFR: 9.8 g/10 min), "Pelestat 230" (MFR: 9 g/10 min), and "Pelectron UC" (MFR: 14 g/10 min). Furthermore, those suitable for use in the back layer 113 (with an MFR of 14 g/10 min or more) include products such as "Pelectron PVL" (MFR: 19 g/10 min).

Furthermore, when a sample solution obtained by mixing 1 g of the antistatic agent with 20 ml of pure water is heated at 121°C for 24 hours, the amount of lithium ions extracted into the pure water is preferably 50 ppm or less, more preferably 30 ppm or less, and even more preferably 10 ppm or less. Having this extraction amount of 50 ppm or less makes it easier to effectively suppress the leakage of lithium ions from the workpiece processing sheet 1 according to this embodiment. The lower limit of this extraction amount is not particularly limited, and may be, for example, 0.0001 ppm or more, and particularly 0.001 ppm or more. Details of the method for measuring the extraction amount are as described in the test examples below.

Furthermore, when a sample solution obtained by mixing 1 g of the antistatic agent with 20 ml of pure water is heated at 121°C for 24 hours, the amount of sodium ions extracted into the pure water is preferably 150 ppm or less, more preferably 50 ppm or less, and even more preferably 10 ppm or less. Having this extraction amount of 150 ppm or less makes it easier to effectively suppress the outflow of sodium ions from the workpiece processing sheet 1 according to this embodiment. The lower limit of this extraction amount is not particularly limited, and may be, for example, 0.0001 ppm or more, and particularly 0.001 ppm or more. Details of the method for measuring the extraction amount are as described in the test examples below.

In the substrate 11 of this embodiment, as described above, the surface layer 111 and the back layer 113 contain an antistatic agent, but the intermediate layer 112 may also contain an antistatic agent. However, from the perspective of easily suppressing the generation of chips during dicing, it is preferable that the intermediate layer 112 does not contain an antistatic agent, or that the intermediate layer 112 contains an antistatic agent in a content (unit: mass %) lower than that of each of the surface layer 111 and the back layer 113. In this way, by having the intermediate layer 112 containing no or a low amount of antistatic agent between the surface layer 111 and the back layer 113, the generation of chips from the intermediate layer 112 can be effectively suppressed when a dicing blade reaches the intermediate layer 112 during dicing.

The content of the antistatic agent in the surface layer 111 is preferably 3% by mass or more, particularly preferably 5% by mass or more, and even more preferably 10% by mass or more. An antistatic agent content of 3% by mass or more facilitates the exertion of good antistatic properties. Furthermore, the content of the antistatic agent in the surface layer 111 is preferably 40% by mass or less, particularly preferably 35% by mass or less, and even more preferably 30% by mass or less. An antistatic agent content of 40% by mass or less facilitates the suppression of changes over time in the pressure-sensitive adhesive layer 12.

The content of the antistatic agent in the back layer 113 is preferably 10% by mass or more, particularly preferably 20% by mass or more, and even more preferably 30% by mass or more. An antistatic agent content of 10% by mass or more facilitates the exhibiting of good antistatic properties. Furthermore, the content of the antistatic agent in the back layer 113 is preferably 50% by mass or less, particularly preferably 45% by mass or less, and even more preferably 40% by mass or less. An antistatic agent content of 50% by mass or less facilitates the suppression of the outflow of alkali metal ions.

As mentioned above, it is preferable that the intermediate layer 112 does not contain an antistatic agent, or that the intermediate layer 112 contains an antistatic agent in a content (unit: mass %) that is lower than that of each of the front layer 111 and the back layer 113. If the intermediate layer 112 contains an antistatic agent, the content thereof in the intermediate layer 112 is preferably 10 mass % or less, particularly preferably 5 mass % or less, and even more preferably 3 mass % or less. By ensuring that the content of the antistatic agent in the intermediate layer 112 is 10 mass % or less, it becomes easier to suppress the generation of cutting chips. The lower limit of the above content may be, for example, 0.01 mass % or more.

(1-4) Acid-Modified Resin It is also preferable that each layer constituting the substrate 11 contains an acid-modified resin. In particular, it is preferable that the surface layer 111 contains an acid-modified resin. In this specification, "acid-modified resin" means a resin in which a structure derived from an acid component is added to a polymer chain. The structure derived from the acid component may be in the form of an acid anhydride or may have a carboxy group. When the surface layer 111 contains an acid-modified resin as described above, the adhesion between the substrate 11 and the adhesive layer 12 is further improved, and it is possible to further prevent the adhesive from remaining on the chip side during pick-up.

Preferred examples of the main chain of the acid-modified resin include ethylene-acrylic copolymers such as ethylene-(meth)acrylic acid copolymer and ethylene-(meth)acrylic acid ester copolymer. Such resins facilitate improved adhesion between the surface layer 111 and the pressure-sensitive adhesive layer 12. Note that, in this specification, "(meth)acrylic acid" refers to both acrylic acid and methacrylic acid. The same applies to other similar terms.

Preferred examples of the (meth)acrylic acid ester include alkyl (meth)acrylate esters in which the alkyl group has 1 to 4 carbon atoms. Examples include methyl (meth)acrylate, ethyl (meth)acrylate, propyl (meth)acrylate, and n-butyl (meth)acrylate. Among these, ethyl (meth)acrylate is more preferred, with ethyl acrylate being particularly preferred.

The content of structures derived from (meth)acrylic acid ester in the ethylene-(meth)acrylic acid ester copolymer is preferably 1% by mass or more, and particularly preferably 3% by mass or more. Furthermore, this content is preferably 20% by mass or less, particularly preferably 15% by mass or less, and even more preferably 10% by mass or less.

To acid-modify the resin, it is preferable to react the resin with an unsaturated carboxylic acid. Examples of unsaturated carboxylic acids include maleic acid, fumaric acid, itaconic acid, citraconic acid, glutaconic acid, tetrahydrophthalic acid, aconitic acid, maleic anhydride, itaconic anhydride, glutaconic anhydride, citraconic anhydride, aconitic anhydride, norbornene dicarboxylic anhydride, and tetrahydrophthalic anhydride. These can be used alone or in combination of two or more. Of the above, maleic anhydride is particularly preferred from the viewpoint of adhesion to the pressure-sensitive adhesive layer 12.

The amount of acid components (amount of structures derived from acid components) in the acid-modified resin is preferably 1% by mass or more, and particularly preferably 2% by mass or more. Furthermore, the amount of acid components is preferably 7% by mass or less, and particularly preferably 5% by mass or less. Having the amount of acid components in the above range further improves the adhesion between the surface layer 111 and the pressure-sensitive adhesive layer 12.

When the surface layer 111 contains an acid-modified resin, the content of the acid-modified resin in the surface layer 111 is preferably 5% by mass or more, and particularly preferably 10% by mass or more. This further improves the adhesion between the surface layer 111 and the pressure-sensitive adhesive layer 12. Furthermore, the content is preferably 30% by mass or less, particularly preferably 25% by mass or less, and even more preferably 20% by mass or less.

(1-5) Other Components The layers constituting the substrate 11 may contain components other than the above-described components. In particular, the resin composition may contain components used in the substrate of a general workpiece processing sheet.

Examples of such components include various additives such as flame retardants, plasticizers, lubricants, antioxidants, colorants, infrared absorbers, ultraviolet absorbers, and ion scavengers. The amount of these additives contained is not particularly limited, but it is preferable to set it within a range that allows the substrate to exhibit the desired functions.

(1-6) Surface Treatment of Substrate The surface of the substrate 11 on which the pressure-sensitive adhesive layer 12 is laminated may be subjected to surface treatment such as primer treatment, corona treatment, plasma treatment, roughening treatment (matt finish), etc. in order to improve adhesion to the pressure-sensitive adhesive layer 12. Examples of roughening treatment include embossing and sandblasting. Of these, corona treatment is preferred.

(1-7) Method for Producing Substrate The method for producing the substrate 11 in this embodiment is not particularly limited, and for example, melt extrusion methods such as a T-die method or a round die method; a calendar method; a solution method such as a dry method or a wet method, etc. Among these, from the viewpoint of efficiently producing the substrate, it is preferable to employ the melt extrusion method, and it is particularly preferable to employ the T-die method.

When the substrate 11 is manufactured by melt extrusion, the components constituting each layer are mixed together, and then the resulting mixture is extruded directly or after pellets have been produced into pellets using a known extruder to simultaneously extrude multiple layers to form a film.

(1-8) Physical Properties of the Substrate In this embodiment, when 1 g of the substrate 11 is mixed with 20 ml of pure water and the resulting sample solution is heated at 121°C for 24 hours, the amount of lithium ions extracted into the pure water is preferably 1 ppm or less, more preferably 0.5 ppm or less, and even more preferably 0.3 ppm or less. Having this amount of extraction of 1 ppm or less makes it easier to effectively suppress the leakage of lithium ions from the workpiece processing sheet 1 according to this embodiment. The lower limit of this amount of extraction is not particularly limited and may be, for example, 0.001 ppm or more, particularly 0.01 ppm or more. Details of the method for measuring the amount of extraction are as described in the test examples below.

Furthermore, in this embodiment, when 1 g of the substrate 11 is mixed with 20 ml of pure water to obtain a sample solution and heated at 121°C for 24 hours, the amount of sodium ions extracted into the pure water is preferably 1 ppm or less, more preferably 0.5 ppm or less, and even more preferably 0.3 ppm or less. Having this extraction amount of 1 ppm or less makes it easier to effectively suppress the outflow of sodium ions from the workpiece processing sheet 1 according to this embodiment. The lower limit of this extraction amount is not particularly limited, and may be, for example, 0.001 ppm or more, and particularly 0.01 ppm or more. Details of the method for measuring the extraction amount are as described in the test examples below.

In this embodiment, the surface resistivity of the surface of the surface layer 111 side of the substrate 11 is preferably 1.0 x 10 ¹³ Ω/□ or less, particularly preferably 1.0 x 10 ¹² Ω/□ or less, and even more preferably 1.0 x 10 ¹¹ Ω/□ or less. When the surface resistivity is 1.0 x 10 ¹³ Ω/□ or less, the workpiece processing sheet 1 according to this embodiment is likely to have good antistatic properties. The lower limit of the surface resistivity is not particularly limited, and may be, for example, 1.0 x 10 ⁸ Ω/□ or more, particularly 1.0 x 10 ⁹ Ω/□ or more. Details of the method for measuring the surface resistivity are as described in the test examples below.

In this embodiment, the thickness of the surface layer 111 is preferably 0.5 μm or more, more preferably 1 μm or more, particularly preferably 2 μm or more, and even more preferably 4 μm or more. Furthermore, the thickness of the surface layer 111 is preferably less than 8 μm, particularly preferably 4 μm or less. Having the thickness of the surface layer 111 within this range makes it easier for the workpiece processing sheet 1 to have excellent antistatic properties. Furthermore, having the thickness of the surface layer 111 less than 8 μm makes it easier to suppress changes in the adhesive strength of the workpiece processing sheet 1 over time.

In this embodiment, the thickness of the intermediate layer 112 is preferably 40 μm or more, particularly preferably 50 μm or more, and even more preferably 60 μm or more. Furthermore, the thickness of the intermediate layer 112 is preferably 100 μm or less, particularly preferably 90 μm or less, and even more preferably 80 μm or less. Having the thickness of the intermediate layer 112 within the above range makes it easier for the workpiece processing sheet 1 to achieve excellent expandability and also makes it easier to impart the desired performance to the workpiece processing sheet 1.

In this embodiment, the thickness of the back layer 113 is preferably 2 μm or more, particularly preferably 4 μm or more, and even more preferably 8 μm or more. Having a thickness of 2 μm or more for the back layer 113 makes it easier for the workpiece processing sheet 1 to have excellent antistatic properties. Furthermore, the thickness of the back layer 113 is preferably 40 μm or less, particularly preferably 30 μm or less, and even more preferably 25 μm or less. Having a thickness of 40 μm or less for the back layer 112 makes it easier to suppress the outflow of alkali metal ions from the workpiece processing sheet 1.

(2) Pressure-sensitive adhesive layer In this embodiment, the pressure-sensitive adhesive constituting the pressure-sensitive adhesive layer 12 is not particularly limited as long as it can exert sufficient adhesive strength to the adherend (particularly, adhesive strength to the workpiece sufficient for processing the workpiece). Examples of pressure-sensitive adhesives constituting the pressure-sensitive adhesive layer 12 include acrylic pressure-sensitive adhesives, rubber pressure-sensitive adhesives, silicone pressure-sensitive adhesives, urethane pressure-sensitive adhesives, polyester pressure-sensitive adhesives, polyvinyl ether pressure-sensitive adhesives, etc. Among these, it is preferable to use acrylic pressure-sensitive adhesives because they can easily exert the desired adhesive strength.

In this embodiment, the adhesive constituting the adhesive layer 12 may be an adhesive that is not active energy ray curable, but is preferably an adhesive that is active energy ray curable (hereinafter, sometimes referred to as an "active energy ray curable adhesive"). By having the adhesive layer 12 composed of an active energy ray curable adhesive, the adhesive layer 12 can be cured by irradiation with active energy rays, easily reducing the adhesive strength of the workpiece processing sheet 1 to the adherend. In particular, irradiation with active energy rays makes it possible to easily separate the processed workpiece from the workpiece processing sheet 1.

The active energy ray-curable adhesive constituting the adhesive layer 12 may be one whose main component is a polymer that is active energy ray-curable, or one whose main component is a mixture of a non-active energy ray-curable polymer (a polymer that is not active energy ray-curable) and a monomer and/or oligomer that has at least one active energy ray-curable group. The active energy ray-curable adhesive may also be a mixture of a polymer that is active energy ray-curable and a monomer and/or oligomer that has at least one active energy ray-curable group.

The active energy ray-curable polymer is preferably a (meth)acrylic acid ester polymer (hereinafter sometimes referred to as an "active energy ray-curable polymer") having an active energy ray-curable functional group (active energy ray-curable group) introduced into its side chain. This active energy ray-curable polymer is preferably obtained by reacting an acrylic polymer having a functional group-containing monomer unit with an unsaturated group-containing compound having a functional group bonded to the functional group. In this specification, (meth)acrylic acid refers to both acrylic acid and methacrylic acid. The same applies to other similar terms. Furthermore, the term "polymer" also includes the concept of "copolymer."

The acrylic polymer having the above-mentioned functional group-containing monomer unit may be obtained by polymerizing other monomers together with the functional group-containing monomer. Such functional group-containing monomers and other monomers, as well as the above-mentioned unsaturated group-containing compounds, may be known compounds, such as those disclosed in WO 2018/084021.

The weight-average molecular weight of the above-mentioned active energy radiation-curable polymer is preferably 10,000 or more, particularly preferably 150,000 or more, and even more preferably 200,000 or more. Furthermore, the weight-average molecular weight is preferably 1,500,000 or less, particularly preferably 1,000,000 or less. Note that the weight-average molecular weight (Mw) in this specification is a value measured by gel permeation chromatography (GPC) in terms of standard polystyrene.

As the non-active energy ray-curable polymer component, for example, the above-mentioned acrylic polymer can be used before being reacted with the unsaturated group-containing compound.

The weight-average molecular weight of the acrylic polymer serving as the non-active energy ray-curable polymer component is preferably 10,000 or more, particularly preferably 150,000 or more, and even more preferably 200,000 or more. Furthermore, the weight-average molecular weight is preferably 1.5 million or less, particularly preferably 1 million or less.

Furthermore, examples of the monomers and/or oligomers having at least one active energy ray-curable group that can be used include esters of polyhydric alcohols and (meth)acrylic acid.

When ultraviolet rays are used as the active energy rays to cure an active energy ray-curable adhesive, it is preferable to add a photopolymerization initiator to the adhesive. Furthermore, the adhesive may also contain a non-active energy ray-curable polymer component or oligomer component, a crosslinking agent, etc.

In this embodiment, the thickness of the adhesive layer 12 is preferably 1 μm or more, particularly preferably 3 μm or more, and even more preferably 5 μm or more. Furthermore, the thickness of the adhesive layer 12 is preferably 70 μm or less, particularly preferably 30 μm or less, and even more preferably 15 μm or less. By ensuring that the thickness of the adhesive layer 12 is within the above-mentioned range, the workpiece processing sheet 1 according to this embodiment is more likely to exhibit the desired adhesiveness.

(3) Release sheet In the workpiece processing sheet 1 according to this embodiment, a release sheet may be laminated on the side of the adhesive layer 12 opposite the substrate 11 (hereinafter sometimes referred to as the "adhesive side") in order to protect that side until it is attached to the workpiece.

The release sheet may be made of any material, including plastic films that have been treated with a release agent. Specific examples of such plastic films include polyester films such as polyethylene terephthalate, polybutylene terephthalate, and polyethylene naphthalate, and polyolefin films such as polypropylene and polyethylene. Silicone-based, fluorine-based, and long-chain alkyl-based release agents can be used, with silicone-based release agents being preferred due to their low cost and stable performance.

There are no particular restrictions on the thickness of the release sheet, and it may be, for example, 16 μm or more and 250 μm or less.

(4) Others: In the workpiece processing sheet 1 according to this embodiment, an adhesive layer may be laminated on the surface of the adhesive layer 12 opposite the substrate 11. In this case, the workpiece processing sheet 1 according to this embodiment can be used as a dicing/die bonding sheet. By attaching a workpiece to the adhesive layer on the surface opposite the adhesive layer 12 and dicing the adhesive layer together with the workpiece, a chip can be obtained in which the individual adhesive layers are laminated. The individual adhesive layers allow the chip to be easily fixed to the target on which it is to be mounted. Materials constituting the adhesive layer described above are preferably those containing a thermoplastic resin and a low-molecular-weight thermosetting adhesive component, or those containing a B-stage (semi-cured) thermosetting adhesive component.

In addition, in the workpiece processing sheet 1 according to this embodiment, a protective film forming layer may be laminated on the adhesive surface of the adhesive layer 12. In this case, the workpiece processing sheet 1 according to this embodiment can be used as a sheet for both protective film formation and dicing. With such a sheet, a workpiece is attached to the surface of the protective film forming layer opposite the adhesive layer 12, and the protective film forming layer is diced together with the workpiece to obtain a chip on which an individual protective film forming layer is laminated. It is preferable that the workpiece has a circuit formed on one side. In this case, the protective film forming layer is typically laminated on the surface opposite the surface on which the circuit is formed. By curing the individual protective film forming layer at a predetermined time, a protective film with sufficient durability can be formed on the chip. The protective film forming layer is preferably made of an uncured curable adhesive.

2. Physical Properties of the Workpiece Processing Sheet When 1 g of the workpiece processing sheet 1 according to this embodiment is mixed with 20 ml of pure water and heated at 121°C for 24 hours, the amount of lithium ions extracted into the pure water is preferably 1 ppm or less, more preferably 0.5 ppm or less, and even more preferably 0.3 ppm or less. Having an extractable amount of 1 ppm or less makes it easier to effectively suppress the leakage of lithium ions from the workpiece processing sheet 1 according to this embodiment. The lower limit of the extractable amount is not particularly limited and may be, for example, 0.001 ppm or more, particularly 0.01 ppm or more. Details of the method for measuring the extractable amount are described in the test examples below.

Furthermore, when 1 g of the workpiece processing sheet 1 according to this embodiment is mixed with 20 ml of pure water to obtain a sample liquid and heated at 121°C for 24 hours, the amount of sodium ions extracted into the pure water is preferably 1 ppm or less, more preferably 0.5 ppm or less, and even more preferably 0.3 ppm or less. Having this extraction amount of 1 ppm or less makes it easier to effectively suppress the outflow of sodium ions from the workpiece processing sheet 1 according to this embodiment. The lower limit of this extraction amount is not particularly limited, and may be, for example, 0.001 ppm or more, and particularly 0.01 ppm or more. Details of the method for measuring the extraction amount are as described in the test examples below.

Furthermore, when 1 g of the workpiece processing sheet 1 according to this embodiment is mixed with 20 ml of pure water to obtain a sample solution, and the resulting solution is heated at 121°C for 24 hours, the total amount of lithium ions and sodium ions extracted into the pure water is preferably 2 ppm or less, more preferably 1.5 ppm or less, and even more preferably 1 ppm or less. Having this amount of extraction of 2 ppm or less makes it easier to effectively suppress the outflow of lithium ions and sodium ions from the workpiece processing sheet 1 according to this embodiment. The lower limit of this amount of extraction is not particularly limited, and may be, for example, 0.001 ppm or more, and particularly 0.02 ppm or more. Details of the method for measuring the amount of extraction are as described in the test examples below.

In the workpiece processing sheet 1 according to this embodiment, the adhesive strength of the workpiece processing sheet to the mirror surface of a silicon wafer (adhesive strength before irradiation with active energy rays and before storage, as described below) (hereinafter sometimes referred to as "adhesive strength before storage") is preferably 3000 mN/25 mm or more, more preferably 4000 mN/25 mm or more, and even more preferably 5000 mN/25 mm or more. Having an adhesive strength before storage of 3000 mN/25 mm or more facilitates favorable fixation of the workpiece on the workpiece processing sheet 1. The upper limit of the adhesive strength before storage is not particularly limited, and may be 20,000 mN/25 mm or less, particularly 10,000 mN/25 mm or less, or even 8,000 mN/25 mm or less. Details of the method for measuring the adhesive strength before storage are as described in the test examples below.

Furthermore, in the workpiece processing sheet 1 according to this embodiment, the adhesive strength of the workpiece processing sheet to the mirror surface of a silicon wafer (adhesive strength before exposure to active energy rays) after storage for two days in a 60°C environment (hereinafter sometimes referred to as "adhesive strength after storage") is preferably 3000 mN/25 mm or more, more preferably 4000 mN/25 mm or more, and even more preferably 5000 mN/25 mm or more. Having an adhesive strength of 3000 mN/25 mm or more after storage facilitates favorable fixation of the workpiece on the workpiece processing sheet 1. The upper limit of the adhesive strength after storage is not particularly limited, and may be 20,000 mN/25 mm or less, particularly 10,000 mN/25 mm or less, or even 8,000 mN/25 mm or less. Details of the method for measuring the adhesive strength after storage are as described in the test examples below.

Furthermore, in the workpiece processing sheet 1 according to this embodiment, the ratio of the adhesive strength after storage to the adhesive strength before storage (hereinafter sometimes referred to as the "adhesive strength retention rate") is preferably 70 or more, particularly preferably 80 or more, and even more preferably 90 or more. As described above, the workpiece processing sheet 1 according to this embodiment has an antistatic agent in the surface layer 111 having the aforementioned MFR, and therefore exhibits good antistatic properties while achieving the high adhesive strength retention rate described above. The upper limit of the adhesive strength retention rate is not particularly limited and may be, for example, 100 or less, particularly 95 or less.

3. Manufacturing Method of Workpiece Processing Sheet There are no particular limitations on the manufacturing method of the workpiece processing sheet 1 according to this embodiment. For example, it is preferable to obtain the workpiece processing sheet 1 by forming the adhesive layer 12 on a release sheet, and then laminating one side of the substrate 11 on the surface of the adhesive layer 12 opposite the release sheet.

The pressure-sensitive adhesive layer 12 can be formed by a known method. For example, a coating liquid containing a pressure-sensitive adhesive composition for forming the pressure-sensitive adhesive layer 12 and, if desired, a solvent or dispersion medium is prepared. The coating liquid is then applied to the releasable surface of a release sheet (hereinafter sometimes referred to as the "release surface"). The resulting coating film is then dried to form the pressure-sensitive adhesive layer 12.

The coating liquid described above can be applied by known methods, such as bar coating, knife coating, roll coating, blade coating, die coating, and gravure coating. The nature of the coating liquid is not particularly limited as long as it allows application, and it may contain the components for forming the adhesive layer 12 as a solute or as a dispersoid. The release sheet may be peeled off as a processing material, or it may protect the adhesive layer 12 until it is attached to the adherend.

When the adhesive composition used to form the adhesive layer 12 contains the crosslinking agent described above, it is preferable to change the drying conditions (temperature, time, etc.) or to perform a separate heat treatment to promote the crosslinking reaction between the polymer component in the coating film and the crosslinking agent, thereby forming a crosslinked structure with the desired density within the adhesive layer 12. Furthermore, to promote the above-mentioned crosslinking reaction sufficiently, after bonding the adhesive layer 12 and the substrate 11 together, the resulting product may be cured by, for example, leaving it to stand for several days in an environment of 23°C and a relative humidity of 50%.

4. How to Use the Workpiece Processing Sheet The workpiece processing sheet 1 according to this embodiment can be used to process workpieces such as semiconductor wafers. That is, after the adhesive surface of the workpiece processing sheet 1 according to this embodiment is attached to the workpiece, the workpiece can be processed on the workpiece processing sheet 1. Depending on the processing, the workpiece processing sheet 1 according to this embodiment can be used as a backgrinding sheet, dicing sheet, expanding sheet, pickup sheet, etc. Examples of workpieces include semiconductor components such as semiconductor wafers and semiconductor packages, and glass components such as glass plates.

As mentioned above, the workpiece processing sheet 1 according to this embodiment has excellent antistatic properties while suppressing changes in adhesive strength over time and the outflow of alkali metal ions. In particular, the workpiece processing sheet 1 according to this embodiment can effectively suppress the outflow of alkali metal ions into the cutting water used during dicing and the rinse water after dicing. Therefore, the workpiece processing sheet 1 according to this embodiment is particularly suitable for use as a dicing sheet, among the workpiece processing sheets described above.

When the workpiece processing sheet 1 according to this embodiment is provided with the adhesive layer described above, the workpiece processing sheet 1 can be used as a dicing/die bonding sheet. Furthermore, when the workpiece processing sheet 1 according to this embodiment is provided with the protective film forming layer described above, the workpiece processing sheet 1 can be used as a protective film forming/dicing sheet.

Furthermore, when the adhesive layer 12 in the workpiece processing sheet 1 according to this embodiment is composed of the aforementioned active energy ray-curable adhesive, it is also preferable to irradiate it with active energy rays as follows during use. That is, when processing of a workpiece on the workpiece processing sheet 1 is completed and the processed workpiece is to be separated from the workpiece processing sheet 1, it is preferable to irradiate the adhesive layer 12 with active energy rays before the separation. This hardens the adhesive layer 12, effectively reducing the adhesive strength of the adhesive sheet to the processed workpiece, making it easier to separate the processed workpiece.

The above-described embodiments have been described to facilitate understanding of the present invention, and are not intended to limit the scope of the present invention. Therefore, each element disclosed in the above embodiments is intended to include all design modifications and equivalents that fall within the technical scope of the present invention.

For example, in the workpiece processing sheet 1 according to this embodiment, other layers may be laminated between the base material 11 and the adhesive layer 12, or on the surface of the base material 11 opposite the adhesive layer 12. Furthermore, other layers may be laminated on the surface of the surface layer 111 opposite the intermediate layer 112, between the surface layer 111 and the intermediate layer 112, between the intermediate layer 112 and the back layer 113, and on the surface of the back layer 113 opposite the intermediate layer 112.

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

Example 1
(1) Preparation of substrate 28 parts by mass of random polypropylene resin (manufactured by Japan Polypropylene Corporation, product name "Novatec FX3B"), 47 parts by mass of olefin-based thermoplastic elastomer (manufactured by Japan Polypropylene Corporation, product name "Welnex RFX4V"), and 25 parts by mass of antistatic agent (manufactured by Sanyo Chemical Industries, Ltd., product name "Pelectron PVH", melt flow rate: 9.8 g/10 min) were dried and then kneaded in a twin-screw kneader to obtain pellets for the surface layer.

Furthermore, 80 parts by mass of random polypropylene resin (manufactured by Japan Polypropylene Corporation, product name "Novatec FX3B") and 20 parts by mass of olefin-based thermoplastic elastomer (manufactured by Japan Polypropylene Corporation, product name "Wellnex RFX4V") were dried and then kneaded in a twin-screw kneader to obtain pellets for the intermediate layer.

Furthermore, 70 parts by weight of an olefin-based thermoplastic elastomer (manufactured by Japan Polypropylene Corporation, product name "Wellnex RFX4V") and 30 parts by weight of an antistatic agent (manufactured by Sanyo Chemical Industry Co., Ltd., product name "Pelectron UC", melt flow rate: 14 g/10 min) were each dried and then kneaded in a twin-screw kneader to obtain pellets for the back layer.

The three types of pellets obtained as described above were co-extruded using a small T-die extruder (manufactured by Toyo Seiki Seisaku-sho, product name "Labo Plastomill") to obtain a three-layer substrate consisting of a 2 μm thick surface layer, a 70 μm thick middle layer, and an 8 μm thick back layer laminated in that order.

The melt flow rate values of the antistatic agents mentioned above were measured as described in Test Example 1 below.

(2) Preparation of Pressure-Sensitive Adhesive Composition 62 parts by mass of n-butyl acrylate, 10 parts by mass of methyl methacrylate, and 28 parts by mass of 2-hydroxyethyl acrylate were polymerized by solution polymerization to obtain a (meth)acrylic acid ester polymer. Subsequently, 2-methacryloyloxyethyl isocyanate (MOI) was added in an amount equivalent to 80 mol % of the 2-hydroxyethyl acrylate constituting the (meth)acrylic acid ester polymer, and dibutyltin dilaurate (DBTDL) as a tin-containing catalyst was added in an amount of 0.025 parts by mass per 100 parts by mass of the (meth)acrylic acid ester polymer. The mixture was then allowed to react at 50°C for 24 hours to obtain a (meth)acrylic acid ester polymer having active energy ray-curable groups introduced into its side chains. The weight-average molecular weight of the active energy ray-curable polymer was measured using the method described below and found to be 500,000.

100 parts by weight (solids equivalent, same below) of the (meth)acrylic acid ester polymer obtained above with active energy ray-curable groups introduced into its side chains, 2 parts by weight of 2-hydroxy-1-{4-[4-(2-hydroxy-2-methyl-propionyl)-benzyl]phenyl}-2-methyl-propan-1-one (manufactured by BASF, product name "Omnirad 127") as a photopolymerization initiator, and 5.71 parts by weight of trimethylolpropane-modified tolylene diisocyanate (manufactured by Tosoh Corporation, product name "Coronate L") as a crosslinking agent were mixed in a solvent to obtain a coating solution of an adhesive composition.

(3) Formation of Pressure-Sensitive Adhesive Layer The coating solution of the pressure-sensitive adhesive composition obtained in step (2) above was applied to the release surface of a release sheet (manufactured by Lintec Corporation, product name "SP-PET381031") which was made by forming a silicone-based release agent layer on one side of a 38 μm thick polyethylene terephthalate film, and dried at 90°C for 1 minute, thereby obtaining a laminate in which a pressure-sensitive adhesive layer of 5 μm thickness was formed on the release sheet using a comma coater.

(4) Preparation of workpiece processing sheet After corona treatment was performed on the surface of the surface layer side of the substrate obtained in the above step (1), the corona-treated surface was bonded to the surface of the adhesive layer side of the laminate obtained in the above step (3), thereby obtaining a workpiece processing sheet.

Here, the weight average molecular weight (Mw) is a weight average molecular weight measured by gel permeation chromatography (GPC) under the following conditions (GPC measurement) and converted into standard polystyrene.
<Measurement conditions>
Measuring device: Tosoh Corporation, HLC-8320
GPC columns (passed in the following order): TSK gel super H-H manufactured by Tosoh Corporation
TSK gel superHM-H
TSK gel superH2000
Measurement solvent: tetrahydrofuran Measurement temperature: 40°C

[Examples 2 to 6, Comparative Examples 1 to 3]
A workpiece processing sheet was obtained in the same manner as in Example 1, except that the composition of the pellets for forming each layer of the substrate and the thickness of each layer were changed as shown in Table 1.

Comparative Example 4
An 80 μm thick EMAA film was obtained by extrusion molding ethylene-methacrylic acid copolymer (EMAA) (manufactured by DuPont-Mitsui Polychemicals, product name "Nucrel N0903HC") using a small T-die extruder (manufactured by Toyo Seiki Seisakusho, product name "Labo Plastomill"), and a workpiece processing sheet was obtained in the same manner as in Example 1, except that the EMAA film was used as the substrate.

Test Example 1 (Measurement of MFR of antistatic agent)
The melt flow rates (MFR) (g/10 min) of the antistatic agents used in the examples and comparative examples were measured according to ASTM D1238 (190°C, 21.18 N) using a flow tester (manufactured by Shimadzu Corporation, product name "CFT-100D"). The results are shown in Table 2.

Test Example 2 (Measurement of the amount of extracted ions from the antistatic agent)
A sample solution was prepared by mixing 1 g of the antistatic agent used in the Examples and Comparative Examples with 20 ml of pure water. The sample solution was placed in a Teflon (registered trademark) container for ion concentration measurement, sealed, and heated at 121°C for 24 hours to extract alkali metal ions. The concentrations (ppm) of lithium ions and sodium ions in the resulting extract were measured using an ion chromatograph (manufactured by Thermo Fisher Scientific, product name "DIONEX ICS-2100"). The results are shown in Table 2.

Test Example 3 (Measurement of extracted ions from the substrate alone and the sheet)
A 1-g portion was cut out from each of the substrates prepared in the Examples and Comparative Examples and mixed with 20 ml of pure water to prepare a sample solution. This sample solution was placed in a Teflon (registered trademark) container for ion concentration measurement, sealed, and heated at 121°C for 24 hours to extract alkali metal ions. The concentrations (ppm) of lithium ions and sodium ions in the resulting extract were measured using an ion chromatograph (manufactured by Thermo Fisher Scientific, product name "DIONEX ICS-2100"). The results are shown in Table 3. Table 3 also shows the total amount of these ions.

Furthermore, for the workpiece processing sheets produced in the Examples and Comparative Examples, sample solutions were prepared in the same manner as above, and the concentrations (ppm) of lithium ions and sodium ions in the extracts were measured. The results are shown in Table 3. The total amount of these ions is also shown in Table 3. Note that the notation "N.D." in the table indicates that the sodium ion concentration was less than 0.002 ppm and the lithium ion concentration was less than 0.0005 ppm.

[Test Example 4] (Measurement of adhesive strength)
The workpiece processing sheets produced in the Examples and Comparative Examples were cut into 25 mm wide strips. The release sheet was peeled off from the resulting strips, and the exposed adhesive surface of the pressure-sensitive adhesive layer was attached to the mirror-finished surface of a silicon wafer using a 2 kg rubber roller at a temperature of 23°C and a relative humidity of 50%, and then left to stand for 20 minutes to prepare measurement samples.

The obtained measurement sample was used to peel the workpiece processing sheet from the silicon wafer using a universal tensile tester (manufactured by Orientec Co., Ltd., product name "Tensilon UTM-4-100") at a peeling speed of 300 mm/min and a peeling angle of 180°. The adhesive strength (mN/25 mm) to the silicon wafer was measured using the 180° peeling method in accordance with JIS Z0237:2009. The adhesive strength obtained in this way is shown in Table 3 as the adhesive strength before storage.

Additionally, measurement samples prepared in the same manner as above were stored in an environment at 60°C for two days. After this storage, the adhesive strength (mN/25 mm) of the measurement samples was measured in the same manner as above. The adhesive strength thus obtained is shown in Table 3 as the adhesive strength after storage at 60°C for two days.

Furthermore, the ratio of the adhesive strength after storage to the adhesive strength before storage was calculated. This value is shown in Table 3 as the adhesive strength retention rate.

Test Example 5 (Measurement of surface resistivity)
The substrates produced in the examples and comparative examples were conditioned at 23°C and 50% relative humidity for 24 hours, and then the surface resistivity of the surface layer side was measured using a DIGITAL ELECTROMETER (manufactured by ADVANTEST Co., Ltd.) at an applied voltage of 100 V. The results are shown in Table 3.

Test Example 6 (Evaluation of Antistatic Properties)
One side of a 6-inch silicon wafer was ground to a thickness of 350 μm using a grinder (manufactured by Disco Corporation, product name "DFG8540"), and the exposed surface of the pressure-sensitive adhesive layer exposed by peeling the release sheet from the workpiece processing sheet produced in the Examples and Comparative Examples was attached to the ground surface using a laminator.

Twenty minutes after the attachment, the silicon wafer was diced into individual chips using a dicing device (manufactured by Disco Corporation, product name "DFD6362") under the following dicing conditions.
Dicing conditions Chip size: 10mm x 10mm
Cutting height: 60 μm
Blade: Product name "ZH05-SD2000-Z1-90 CC"
Blade rotation speed: 35,000 rpm
Cutting speed: 60 mm/sec
Cutting water amount: 1.0L/min
Cutting water temperature: 20℃

After dicing, the workpiece processing sheet was fixed to the spinner table by suction, and the resulting chips were washed and dried as described above. The electrostatic charge (V) of the workpiece processing sheet immediately after lifting it from the spinner table was measured using a measuring device (manufactured by Prostat, product name "PFK-100"). The antistatic properties were evaluated based on the following criteria. The electrostatic charge and evaluation results are shown in Table 3.
⊚: The charging voltage was 100V or less.
Good: The charging voltage was more than 100V and 500V or less.
×: The charging voltage was more than 500V.

As is clear from Table 3, the workpiece processing sheets produced in the examples had good antistatic properties, while also exhibiting a high adhesive strength retention rate and minimizing the amount of alkali metal ion leakage.

The workpiece processing sheet of the present invention can be suitably used for processing workpieces such as semiconductor wafers.

DESCRIPTION OF SYMBOLS 1...Workpiece processing sheet 11...Base material 111...Surface layer 112...Intermediate layer 113...Back surface layer 12...Adhesive layer

Claims (3)

A workpiece processing sheet comprising a substrate and an adhesive layer laminated on one side of the substrate,
the substrate comprises a surface layer located proximal to the pressure-sensitive adhesive layer, a back layer located distal to the pressure-sensitive adhesive layer, and an intermediate layer located between the surface layer and the back layer;
each of the front surface layer and the back surface layer contains an antistatic agent;
the antistatic agent is a polyether polyolefin block copolymer,
the antistatic agent has an extractable amount of lithium ions in pure water of 0.0001 ppm or more and 50 ppm or less when a sample liquid obtained by mixing 1 g of the antistatic agent with 20 ml of pure water is heated at 121°C for 24 hours;
the antistatic agent has an extractable amount of sodium ions in pure water of 0.0001 ppm or more and 150 ppm or less when a sample liquid obtained by mixing 1 g of the antistatic agent with 20 ml of pure water is heated at 121°C for 24 hours;
all of the antistatic agents contained in the surface layer have a melt flow rate (MFR) of 13 g/10 min or less, as measured in accordance with ASTM D1238 (190°C, 21.18 N);
A workpiece processing sheet characterized in that the melt flow rate (MFR) of all of the antistatic agents contained in the back layer, measured in accordance with ASTM D1238 (190°C, 21.18N), is 14 g/10 min or more. The workpiece processing sheet according to claim 1, characterized in that the thickness of the surface layer is 0.5 μm or more and less than 8 μm. 3. The workpiece processing sheet according to claim 1, which is a dicing sheet.