Protective sheet for work processing and method for producing individualized work pieces

Abstract

To provide a protective sheet for work processing which enables reliable protection of high-bump wafers, exhibits superior antistatic performance, and prevents contamination of the work as the adherend.SOLUTION: A protective sheet for work processing 1 according to the present invention comprises a base material 10 having antistatic properties, an intermediate layer 20 disposed on the base material, and a pressure-sensitive adhesive layer 30 disposed on the intermediate layer, wherein the intermediate layer 20 contains an antistatic agent.SELECTED DRAWING: Figure 1

Description

[Technical Field]

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

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

[0003] Conventionally, when grinding the back surface of a workpiece such as a semiconductor wafer or when manufacturing individual workpieces such as semiconductor chips using DBG, it is common to apply a backgrinding tape, which is a protective sheet for workpiece processing and is composed of at least a base material and an adhesive layer, to the surface of the workpiece in order to protect the circuits on the surface of the workpiece and to hold the workpiece and multiple individual workpieces (i.e., a group of individual workpieces).

[0004] As an example of a backgrind tape, Patent Documents 1 and 2 disclose an adhesive tape having a substrate with a high Young's modulus, a buffer layer on one side of the substrate, and an adhesive layer on the other side.

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

[0006] On the other hand, when mounting a multi-pin LSI package used in an MPU, gate array, etc. on a printed wiring board, a semiconductor chip with convex electrodes (bumps) made of eutectic solder, high-temperature solder, gold, etc. formed on its connection pads has been used, and the so-called face-down method has been used to bring these bumps face-to-face with and into contact with corresponding terminals on the chip-mounting substrate, thereby performing melt / diffusion bonding. This flip-chip mounting method has been adopted. [Prior art documents] [Patent documents]

[0007] [Patent Document 1] International Publication No. 2015 / 156389 [Patent Document 2] Japanese Patent Application Laid-Open No. 2015-183008 [Patent Document 3] International Publication No. 2018 / 021145 [Patent Document 4] International Publication No. 2017 / 011134 Summary of the Invention [Problem to be solved by the invention]

[0008] It is known that charging occurs when processing a wafer, which is an example of a workpiece (for example, during dicing, back grinding, cleaning, peeling off backgrinding tape, etc.). When charging occurs, cut dust generated when cutting the backgrinding tape, minute foreign matter present in the environment, etc., tend to adhere to the wafer or chips, which are an example of individual workpieces.

[0009] For example, if cutting dust or foreign matter adheres to the wafer during backgrinding, the pressure generated during backgrinding can concentrate on the foreign matter, potentially causing damage to the wafer. In particular, when performing DBG or LDBG, which aim to thin the wafer, even a slight concentration of pressure can easily cause wafer damage. Furthermore, as wafers become thinner, their volume also decreases, increasing the impact of static electricity on the circuits formed on the wafer and making them more susceptible to electrostatic breakdown. Furthermore, excessive electrostatic charge generated during peeling of the backgrinding tape from the wafer can lead to damage to the circuits formed on the wafer. Therefore, it is necessary to suppress the electrostatic charge generated during wafer processing.

[0010] In order to suppress static electricity generated during wafer processing, an antistatic layer is provided on the backgrinding tape. Patent Document 3 discloses an adhesive tape having a substrate, an antistatic layer, and an adhesive layer containing a conductive additive. When this adhesive tape is used to grind the backside of a semiconductor wafer, the circuit side of the semiconductor wafer is fixed to the adhesive layer containing the conductive additive. Static electricity generated during backgrinding and when the adhesive tape is peeled off is removed to the outside via the adhesive layer containing the conductive additive. However, when the adhesive tape is peeled off, the conductive additive contained in the adhesive layer may be transferred to the circuit side. Adhesion of the conductive additive to the circuit side can cause a short circuit and reduce product yield.

[0011] Furthermore, the adhesive layer of the backgrinding tape adheres strongly to the surface of the wafer during backgrinding, providing adequate protection for the circuits, etc. However, when the backgrinding tape is peeled off from the wafer after backgrinding, it is required that the adhesive layer be peeled off without remaining on the wafer.

[0012] However, if the adhesive layer attached to the surface of the wafer does not adhere well to the antistatic layer, the adhesive layer may not peel off from the wafer together with the substrate when the backgrinding tape is peeled off, and may remain on the surface of the wafer as a residue (adhesive residue). The generation of such residues necessitates an extra step such as cleaning the wafer, which reduces production efficiency.

[0013] The semiconductor chips used in the flip-chip mounting method described above are obtained by dividing a semiconductor wafer having irregularities such as convex electrodes (hereinafter, sometimes referred to as a "high-bump wafer"). Even when grinding such a semiconductor wafer having irregularities by DBG, as described above, a backgrind tape is attached to the circuit surface of the semiconductor wafer to protect the circuit surface during grinding and to prevent the chips from moving after the wafer is divided.

[0014] However, when the backgrinding tapes described in Patent Documents 1 and 2 are applied to the circuit surface of a semiconductor wafer having irregularities and then ground using DBG, the backgrinding tapes described in Patent Documents 1 and 2 are unable to adequately conform to the irregularities of the semiconductor wafer, resulting in problems such as water penetration into the circuit surface during grinding and chip shift after wafer singulation. To accommodate the irregularities in such backgrinding tapes, it has also been proposed to provide a soft intermediate layer. Patent Document 4 discloses an adhesive tape having a substrate, an antistatic layer, an intermediate layer, and an adhesive layer. This adhesive tape has an intermediate layer that absorbs the irregularities on the wafer surface and an antistatic layer that suppresses static buildup during wafer processing, making it useful for singulating high-bump wafers. Furthermore, the presence of the intermediate layer between the antistatic layer and the adhesive layer enhances adhesion between the intermediate layer and the adhesive layer, thereby preventing the aforementioned adhesive residue.

[0015] In a high-bump wafer, when the height of the convex electrodes increases, the thickness of the intermediate layer must also be increased to absorb the difference in height. However, in an adhesive tape with the above layer configuration, when the thickness of the intermediate layer is increased, the distance between the antistatic layer and the surface of the adhesive layer increases. In other words, since the distance between the antistatic layer and the wafer surface increases, it becomes difficult to discharge static electricity on the wafer surface to the outside through the antistatic layer, and sufficient antistatic function may not be obtained.

[0016] An object of the present invention is to provide a protective sheet for workpiece processing that can reliably protect even high-bump wafers, has high antistatic properties, and is also capable of suppressing contamination of the workpiece to be adhered. [Means for solving the problem]

[0017] The aspects of the present invention are as follows. (1) A protective sheet for workpiece processing having an antistatic substrate, an intermediate layer disposed on the substrate, and an adhesive layer disposed on the intermediate layer, The intermediate layer is a protective sheet for workpiece processing that contains an antistatic agent. (2) The substrate has a support material and an antistatic agent-containing coating layer, The protective sheet for workpiece processing according to (1), wherein the intermediate layer is disposed on the antistatic agent-containing coating layer. (3) A protective sheet for workpiece processing described in (1) that is attached to the surface of a workpiece in a process of dividing a workpiece into individual workpieces by grinding the back surface of the workpiece having a groove formed on the surface or a modified region formed inside. (4) The protective sheet for workpiece processing according to (1), which has a buffer layer on the side opposite to the intermediate layer of the substrate. (5) The protective sheet for workpiece processing according to (1), wherein the distance between the surface of the adhesive layer that is attached to the workpiece and the surface of the substrate on the intermediate layer side is 50 μm or more. (6) The protective sheet for workpiece processing according to (1), wherein the intermediate layer contains an acrylic polymer. (7) A step of attaching the workpiece processing protection sheet according to any one of (1) to (6) to the surface of a workpiece having a front and back surface; forming a groove on the surface of the workpiece or forming a modified region inside the workpiece; a step of grinding the workpiece, on the surface of which the workpiece processing protection sheet is attached and on which the grooves or modified regions are formed, from the back side to separate the workpiece into a plurality of workpiece individual pieces, starting from the grooves or modified regions; and a step of peeling off the workpiece processing protection sheet from the plurality of workpieces. (8) The method for producing a workpiece singulated according to (7), wherein the workpiece has an uneven structure on its surface with a height difference of 20 μm or more. [Effects of the Invention]

[0018] According to the present invention, it is possible to provide a protective sheet for workpiece processing that sufficiently suppresses charging that occurs during processing of a workpiece, etc. (i.e., a workpiece or a group of individual workpieces), and that suppresses adhesive residue on the workpiece, etc. when the protective sheet for workpiece processing is peeled off from the workpiece, etc., and to provide a method for manufacturing individual workpieces using the protective sheet for workpiece processing. In particular, the protective sheet for workpiece processing of the present invention can reliably protect the surface of the workpiece, even when the workpiece is a high-bump wafer, and can also suppress charging and adhesive residue. [Brief explanation of the drawings]

[0019] [Figure 1] FIG. 1 is a cross-sectional view showing an example of a protection sheet for workpiece processing according to this embodiment. [Figure 2] FIG. 2 is a cross-sectional view showing an example in which a buffer layer is provided on the protective sheet for workpiece processing according to this embodiment. [Figure 3] FIG. 3 is a cross-sectional view showing a state in which the protection sheet for workpiece processing according to this embodiment is attached to the circuit surface of a semiconductor wafer. [Figure 4] FIG. 4 shows the positional relationship of the devices when measuring peel electrification voltage in the examples and comparative examples. DETAILED DESCRIPTION OF THE INVENTION

[0020] The present invention will be described in detail below based on specific embodiments with reference to the accompanying drawings. First, the main terms used in this specification will be explained.

[0021] The term "workpiece" refers to a plate-like body to which a surface protection sheet is attached and then singulated. Examples of workpieces include circular wafers (including those with an orientation flat), rectangular panel-level packages, and strips (rectangular substrates) sealed with molded resin. Among these, wafers are preferred because they facilitate the attainment of the effects of the present invention. Examples of wafers include semiconductor wafers such as silicon wafers, gallium arsenide wafers, silicon carbide wafers, gallium nitride wafers, and indium phosphide wafers, as well as insulator wafers such as glass wafers, lithium tantalate wafers, and lithium niobate wafers. They may also be reconstructed wafers made of resin and semiconductors used in the manufacture of fan-out packages, etc. Because they facilitate the attainment of the effects of the present invention, semiconductor wafers or insulator wafers are preferred, with semiconductor wafers being more preferred.

[0022] Singulation of a workpiece refers to dividing the workpiece into individual circuits to obtain individual workpieces. For example, if the workpiece is a wafer, the individual workpieces are chips, and if the workpiece is a panel-level package or a strip (rectangular substrate) sealed with molded resin, the individual workpieces are semiconductor packages.

[0023] The "surface" of a workpiece refers to the surface on which a circuit or the like is formed or is planned to be formed, and the "back side" of a workpiece refers to the surface on which no circuit or the like is formed or is not planned to be formed. The uneven structure of the workpiece surface refers to a structure with height differences formed by convex electrodes (bumps) or the like.

[0024] DBG (Dicing Before Grinding) is a method in which grooves of a specified depth are formed on the surface of a wafer as a workpiece, and then the wafer is ground from the backside to separate the wafer. The grooves formed on the surface of the wafer are formed by methods such as blade dicing, laser dicing, and plasma dicing.

[0025] LDBG (Laser Dicing Before Grinding) is a modified version of DBG, in which a modified region is created inside a wafer as a workpiece using a laser, and the wafer is diced into individual pieces using stress generated when grinding the backside of the wafer.

[0026] A "group of individual workpieces" refers to a plurality of individual workpieces held on the protective sheet for workpiece processing according to the present invention after the workpiece has been singulated. These individual workpieces collectively form a shape similar to that of the workpiece. Furthermore, a "group of chips" refers to a plurality of chips held on the protective sheet for workpiece processing according to the present invention after the wafer serving as the workpiece has been singulated. These chips collectively form a shape similar to that of the wafer.

[0027] The term "(meth)acrylate" is used to refer to both "acrylate" and "methacrylate," and similar terms.

[0028] "Energy rays" refers to ultraviolet rays, electron beams, etc., and is preferably ultraviolet rays.

[0029] Unless otherwise specified, the "weight average molecular weight" is a polystyrene equivalent value measured by gel permeation chromatography (GPC). Measurements by this method are performed, for example, using a high-speed GPC device "HLC-8120GPC" manufactured by Tosoh Corporation, with a high-speed column "TSK guard column H" XL -H", "TSK Gel GMH XL ", "TSK Gel G2000 H XL (All products of Tosoh Corporation) connected in this order are used, and the column temperature is 40°C, the liquid flow rate is 1.0 mL / min, and the detector is a differential refractometer.

[0030] Mass ratios in the description of compositions such as pressure-sensitive adhesive compositions are based on the active ingredient (solid content), and do not include the solvent unless otherwise specified.

[0031] (Workpiece processing protection sheet 1) The protective sheet for workpiece processing is used when processing a workpiece or the like (i.e., a workpiece or a group of individual workpieces) that has a circuit or the like formed on one side (front side) and no circuit or the like formed on the other side (back side). The front side of the workpiece or the like may be the side on which the circuit is exposed, or may be 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.

[0032] An example of processing a workpiece is back grinding of the workpiece. Grinding the back surface of the workpiece can reduce the thickness of the individual workpieces obtained by dividing the workpiece.

[0033] The workpiece processing protective sheet is temporarily attached to the surface of the workpiece before backside grinding to protect the surface of the workpiece. The backside of the workpiece is ground with the workpiece processing protective sheet attached to the surface of the workpiece. After grinding is completed, the workpiece processing protective sheet is peeled off from the workpiece or the group of individual workpieces.

[0034] To achieve this function, the protective sheet for workpiece processing usually has a substrate and an adhesive layer. During back grinding of the workpiece, the substrate supports the workpiece, and the adhesive layer adheres to the workpiece to fix the protective sheet for workpiece processing to the workpiece.

[0035] As described above, when processing a workpiece, for example, when grinding the backside of the workpiece, charging occurs on the workpiece or a group of individual workpieces. Furthermore, charging (peeling charging) also occurs, for example, when peeling off a protective sheet for workpiece processing. If such charging is not alleviated, it can lead to the adhesion of foreign matter to the workpiece (i.e., the workpiece or a group of individual workpieces), which can cause damage or cracks to the workpiece. It can also lead to the destruction of circuits formed on the workpiece.

[0036] Therefore, in order to suppress such peeling charge, antistatic properties have been imparted to the workpiece processing protection sheet. That is, in this embodiment, the substrate has antistatic properties. The configuration of such a substrate is not particularly limited, but it may be a substrate having a support material rigid enough to support the workpiece and an antistatic agent-containing coating layer formed on at least one surface of the support material, or a substrate in which an antistatic agent is kneaded into the resin material constituting the support material.

[0037] To accommodate workpieces with uneven surfaces, such as high-bump wafers, it has been proposed to provide a soft intermediate layer. Such an intermediate layer is provided between the substrate and the adhesive layer. Because such an intermediate layer is made of a relatively soft resin, it has good adhesion to the adhesive layer and does not transfer the adhesive layer to the workpiece, thereby preventing the aforementioned adhesive residue.

[0038] Therefore, the protective sheet for workpiece processing according to this embodiment contains an antistatic agent in the intermediate layer, which allows the protective sheet for workpiece processing to have sufficient antistatic properties even when the intermediate layer is thick.

[0039] The configuration of the workpiece processing protection sheet according to this embodiment, which has such effects, will be described below.

[0040] The protective sheet for workpiece processing according to this embodiment has an antistatic substrate, an intermediate layer disposed on the substrate, and an adhesive layer disposed on the intermediate layer, and the intermediate layer contains an antistatic agent.

[0041] In this embodiment, as shown in FIG. 1, the protective sheet 1 for workpiece processing has an antistatic substrate 10, an intermediate layer 20 disposed on the substrate, and an adhesive layer 30 disposed on the intermediate layer, and the intermediate layer 20 contains an antistatic agent.

[0042] The configuration of the antistatic substrate 10 is not particularly limited, but as shown in FIG. 1, it may be a substrate having a support material 10a that is rigid enough to support a workpiece and an antistatic agent-containing coating layer 10b formed on at least one surface of the support material 10a, or the substrate 10 may be one in which an antistatic agent is kneaded into the resin material that constitutes the support material.

[0043] The protective sheet for workpiece processing is not limited to the configuration shown in Fig. 1 and may have other layers as long as the effects of the present invention are obtained. That is, as long as the substrate, intermediate layer, and adhesive layer are laminated in this order, other layers may be formed, for example, between the substrate and the intermediate layer, or between the intermediate layer and the adhesive layer. In particular, in this embodiment, as shown in Fig. 2, it is preferable that the substrate has a buffer layer 40 on the main surface opposite to the main surface on which the adhesive layer is formed.

[0044] In this embodiment, as shown in Fig. 3, the protective sheet for workpiece processing 1 is used by attaching the adhesive layer 30 to the surface 100a of the workpiece 100 (e.g., a wafer). The surface 100a of the workpiece 100 is a surface having circuits, electrodes, etc. The surface having the circuits may be a surface on which the circuits are exposed, or may be the main surface of a protective layer formed on the circuits to protect them. Furthermore, convex electrodes such as bumps may be formed on the circuits.

[0045] The components of the protection sheet for workpiece processing will be described in detail below.

[0046] (Base material 10) The substrate 10 is a member that provides the rigidity and antistatic properties of the protection sheet for workpiece processing. In this embodiment, as shown in Fig. 1, the substrate may be a substrate having a support material 10a and an antistatic agent-containing coating layer 10b formed on at least one surface of the support material 10a, or the substrate 10 may be a substrate in which an antistatic agent is kneaded into the resin material that constitutes the support material. The components of the substrate, namely, the support material, the antistatic agent-containing coating layer, and the antistatic agent, will be described below.

[0047] (Support material 10a) The support material 10a is a film-like member that provides the rigidity of the substrate. Therefore, the support material must have enough rigidity to suppress vibrations and the like during back grinding of the workpiece and to stably support the workpiece. In this embodiment, the rigidity of the support material is evaluated by Young's modulus. Specifically, the Young's modulus of the support material at 23°C is preferably 500 MPa or more.

[0048] By having the Young's modulus of the support material within the above range, the support and holding performance of the workpiece, etc. (i.e., the workpiece or a group of individual workpieces) is improved, and damage and cracks to the workpiece, etc. are reduced. In addition, the workability when attaching the workpiece processing protection sheet to the workpiece is improved.

[0049] The Young's modulus of the support material at 23° C. is more preferably 750 MPa or more, even more preferably 1000 MPa or more, and particularly preferably 3000 MPa or more. There is no upper limit to the Young's modulus, but it may be 5500 MPa or less.

[0050] The Young's modulus of the support material at 23°C is measured in accordance with JIS K 7127. That is, it is measured in the same manner as the measurement method specified in JIS K 7127, but the measurement conditions may be different. The specific measurement method will be explained in the examples.

[0051] In this embodiment, the thickness of the support material is preferably 10 μm or more and 80 μm or less, more preferably 22 μm or more and 65 μm or less, and even more preferably 25 μm or more and 60 μm or less.

[0052] The material of the support material may be selected depending on the desired application. For example, various resin films are exemplified. The support material may be composed of a single-layer film made of one resin film, or may be composed of a multi-layer film in which multiple resin films are laminated.

[0053] In this embodiment, examples of resin films include polyethylene terephthalate, polyethylene naphthalate, polybutylene terephthalate, polyesters such as wholly aromatic polyesters, polyimides, polyamides, polycarbonates, polyacetals, modified polyphenylene oxides, polyphenylene sulfides, polysulfones, polyether ketones, and high-density polyethylene (HDPE, density: 942 kg / m 3 Examples include films of the above-mentioned materials, biaxially oriented polyolefins, etc. Among these, films of one or more types selected from polyester, polyamide, polyimide, high-density polyethylene, and biaxially oriented polyolefins are preferred, polyester or high-density polyethylene films are more preferred, and polyethylene terephthalate films are even more preferred.

[0054] The support material may also contain a plasticizer, a lubricant, an infrared absorber, an ultraviolet absorber, a filler, an antistatic agent, an antioxidant, a catalyst, etc., within the scope of not impairing the effects of the present invention. The support material may be transparent or opaque, and may contain a colorant and be colored. Furthermore, a colored layer may be formed on the support material.

[0055] At least one of the main surfaces of the support material may be subjected to a surface treatment such as corona treatment in order to improve adhesion to other layers and members.

[0056] (Antistatic agent-containing coating layer 10b) The antistatic agent-containing coating layer 10b is a thin film that has the effect of dissipating static electricity to the outside on the surface of the support material 10a. The thickness of the antistatic agent-containing coating layer 10b is not particularly limited, but is preferably 50 nm to 5000 nm, more preferably 60 nm to 1000 nm, and particularly preferably 70 nm to 200 nm.

[0057] The material constituting the antistatic agent-containing coating layer may be any material that contains an antistatic agent and can be formed into a thin film.

[0058] The antistatic agent in the antistatic agent-containing coating layer is not particularly limited, and known antistatic agents can be used. Examples of such antistatic agents include conductive polymers, conductive fillers, anionic or cationic compounds, and compounds having a quaternary ammonium base in the main chain or side chain of the molecule, which are easily mixed with the resin described below.

[0059] Examples of the conductive polymer include polythiophene-based, polyaniline-based, and polypyrrole-based conductive polymers. Examples of polythiophene-based conductive polymers include polythiophene, poly(3-alkylthiophene), poly(3-thiophene-β-ethanesulfonic acid), and a mixture of polyalkylenedioxythiophene and polystyrene sulfonate. Examples of polyalkylenedioxythiophenes include polyethylenedioxythiophene, polypropylenedioxythiophene, and poly(ethylene / propylene)dioxythiophene. Examples of polyaniline-based conductive polymers include polyaniline, polymethylaniline, and polymethoxyaniline. Examples of polypyrrole-based conductive polymers include polypyrrole, poly(3-methylpyrrole), and poly(3-octylpyrrole). These conductive polymer compounds may be used alone or in combination of two or more. These conductive polymers are preferably dispersed in water and used in the form of an aqueous solution.

[0060] Examples of conductive fillers include particles of gold, silver, copper, nickel, aluminum, stainless steel, carbon, conductive ceramics, tin oxide, antimony-doped tin oxide (ATO), indium oxide-tin oxide (ITO), zinc oxide, antimony pentoxide, and the like.

[0061] Examples of anionic and cationic compounds include ionic liquids, ionic solids, anionic surfactants, alkali metal salts, cationic surfactants, and nonionic surfactants. Examples of ionic liquids and ionic solids include nitrogen-containing onium salts, sulfur-containing onium salts, and phosphorus-containing onium salts. Examples of alkali metal salts include lithium salts and potassium salts. These may be used alone or in combination of two or more.

[0062] Specific examples of compounds having a quaternary ammonium base include pyrrolidium rings, quaternized alkylamines, copolymers thereof with acrylic acid or methacrylic acid, quaternized N-alkylaminoacrylamides, vinylbenzyltrimethylammonium salts, and 2-hydroxy-3-methacryloxypropyltrimethylammonium salts.

[0063] The compound having a quaternary ammonium salt group is preferably a polymeric compound. The number-average molecular weight of the compound having a quaternary ammonium salt group is preferably 1,000 or more, particularly preferably 2,000 or more, and even more preferably 5,000 or more. In addition, the upper limit of the number-average molecular weight is preferably 500,000 or less, from the viewpoint of preventing the viscosity of the coating liquid containing the conductive material from becoming too high. In this specification, the number-average molecular weight is a value measured by gel permeation chromatography (GPC) in terms of standard polystyrene.

[0064] In this embodiment, from the viewpoint of facilitating the formation of the antistatic agent-containing coating layer, the composition for forming the antistatic agent-containing coating layer preferably contains a resin binder. Examples of resin binders include acrylic resins, silicone resins, urethane resins, epoxy resins, phenolic resins, urea resins, alkyd resins, vinyl acetate resins, vinyl chloride resins, amide resins, imide resins, chloroprene rubber, nitrile rubber, styrene-butadiene rubber, nylon, polycarbonate, polypropylene, etc. Among these, acrylic resins are preferably used because of their excellent adhesion to the support material.

[0065] The adhesive resin is preferably curable. By using a curable resin as the raw material, it is easy to apply before curing and can form a relatively hard coating after curing.

[0066] Examples of the curable resin include a thermosetting resin and an energy ray curable resin, and the energy ray curable resin is preferred.

[0067] The antistatic agent-containing coating layer-forming composition contains the above-mentioned antistatic agent and a resin component. The proportion of the antistatic agent in the antistatic agent-containing coating layer-forming composition varies depending on the antistatic agent used, but generally, the antistatic agent is used in a proportion of preferably 1 to 30 parts by mass, more preferably 1.5 to 25 parts by mass, and particularly preferably 3 to 20 parts by mass, per 100 parts by mass of the total amount of the antistatic agent-containing coating layer-forming composition. If the blending proportion of the antistatic agent is too low, the required antistatic properties may not be obtained, while if it is too high, the shape retention of the antistatic agent-containing coating layer may be reduced.

[0068] The antistatic agent-containing coating layer-forming composition may contain, in addition to the antistatic agent and the resin component, general components that are blended into coating film-forming compositions. When the resin component is an energy ray-curable resin, it preferably contains a photopolymerization initiator, and when the resin component is a thermosetting resin, it preferably contains a thermal polymerization initiator. In addition, it may contain an acrylic or polyester adhesive, or may contain a crosslinking agent.

[0069] As shown in FIG. 1, the antistatic agent-containing coating layer 10b is formed on at least one surface of the support material 10a, and may be formed on both surfaces of the support material 10a.

[0070] The means for forming the antistatic agent-containing coating layer 10b may be determined depending on the material used to form the antistatic agent-containing coating layer. For example, when forming the antistatic agent-containing coating layer using a curable resin, a means for applying a liquid resin before curing can be used. Specifically, coating devices such as die coaters, curtain coaters, spray coaters, slit coaters, and knife coaters; printing devices such as screen printing and inkjet printing; and dripping devices such as dispensers can be used.

[0071] The antistatic substrate 10 may be a substrate obtained by kneading the antistatic agent into the resin material constituting the support material. The antistatic substrate can be obtained by kneading the resin material and the antistatic agent and forming the mixture into a film using a T-die or the like. The kneading ratio of the resin material and the antistatic agent is not particularly limited, but the blending ratio of the antistatic agent is preferably about 5 to 50 parts by mass per 100 parts by mass of the total solid content constituting the substrate. The thickness of the substrate having such a configuration is the same as that of the support material 10a. A polymeric antistatic agent is preferably used as the antistatic agent kneaded into the substrate. Examples of polymeric antistatic agents include copolymers having 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.

[0072] (Middle class 20) The workpiece processing protective sheet according to this embodiment has an intermediate layer 20 containing an antistatic agent disposed on the substrate. When the substrate includes a support material and an antistatic agent-containing coating layer, the intermediate layer is preferably formed on the antistatic agent-containing coating layer. The intermediate layer is a component that performs antistatic functions and reduces the effects of stress and foreign matter on the workpiece during back grinding. By incorporating an antistatic agent into the intermediate layer, the workpiece processing protective sheet can be provided with sufficient antistatic performance even when the intermediate layer is thick. Furthermore, even when the workpiece surface has large height differences, the intermediate layer absorbs the height differences, allowing the workpiece to be kept flat and the back surface of the workpiece to be processed with high precision.

[0073] The thickness of the intermediate layer 20 may be set taking into consideration the difference in elevation on the work surface, for example, the height of the convex electrode. In this embodiment, the thickness of the intermediate layer 20 is preferably 60 μm or more and 350 μm or less, more preferably 70 μm or more and 200 μm or less, and particularly preferably 60 μm or more and 150 μm or less. The thickness of the intermediate layer refers to the thickness of the entire intermediate layer. For example, the thickness of an intermediate layer composed of multiple layers refers to the total thickness of all layers that make up the intermediate layer.

[0074] The intermediate layer 20 is not particularly limited in composition as long as it contains an antistatic agent and has flexibility sufficient to absorb the height differences on the work surface, but it preferably contains a relatively soft material to provide appropriate flexibility. That is, the intermediate layer-forming composition preferably contains a soft material and an antistatic agent.

[0075] The soft material is a member softer than the support material. Specifically, the Young's modulus at 23°C of the intermediate layer containing the soft material is lower than the Young's modulus at 23°C of the support material. The soft material in the intermediate layer can alleviate the stress applied to the workpiece, etc. (i.e., the workpiece or a group of individual workpieces) during backgrinding, thereby preventing damage to the workpiece, etc., and cracking. Furthermore, before backgrinding of the workpiece, the workpiece to which the workpiece processing protection sheet is attached is fixed to the suction table. Even if foreign matter, etc., is attached to the suction table at this time, the intermediate layer can embed the foreign matter, etc., and prevent damage to the workpiece, etc., and cracking caused by the foreign matter, etc., during backgrinding.

[0076] The Young's modulus at 23° C. of the intermediate layer containing a soft material is preferably 50 MPa or more and 1000 MPa or less, more preferably 100 MPa or more and 750 MPa or less, and even more preferably 120 MPa or more and 450 MPa or less.

[0077] The Young's modulus at 23°C of the intermediate layer can be measured in the same manner as the Young's modulus at 23°C of the support material.

[0078] In this embodiment, the intermediate layer is preferably made of a resin composition containing an antistatic agent and a soft material. The intermediate layer may have a single layer structure or a multi-layer structure.

[0079] The soft material is not particularly limited, but is preferably an energy ray-curable composition that can be easily formed into a film, and preferably contains an acrylic polymer, particularly an energy ray-curable acrylic polymer. Hereinafter, the intermediate layer composition will be described using an energy ray-curable composition as an example.

[0080] In this embodiment, the composition for intermediate layer preferably contains an acrylic polymer (A) having a weight-average molecular weight of 300,000 to 1,500,000 and an energy ray-curable acrylic polymer (B) having a weight-average molecular weight of 50,000 to 250,000. The acrylic polymer (A) may be non-energy ray-curable or energy ray-curable, but in this embodiment, the non-energy ray-curable acrylic polymer is preferred.

[0081] The acrylic polymer (A) may be energy ray curable or non-energy ray curable. In this embodiment, a case where the acrylic polymer (A) is non-energy ray curable will be described. The acrylic polymer (A) is preferably a non-energy ray curable polymer having a structural unit derived from a (meth)acrylate. Specifically, the acrylic polymer (A) is more preferably an acrylic copolymer having a structural unit derived from an alkyl (meth)acrylate (a1) and a structural unit derived from a functional group-containing monomer (a2).

[0082] As the alkyl(meth)acrylate (a1), an alkyl(meth)acrylate having an alkyl group with a carbon number of 1 to 18 is used. Specific examples include methyl(meth)acrylate, ethyl(meth)acrylate, propyl(meth)acrylate, n-butyl(meth)acrylate, n-pentyl(meth)acrylate, n-hexyl(meth)acrylate, 2-ethylhexyl(meth)acrylate, isooctyl(meth)acrylate, n-decyl(meth)acrylate, n-dodecyl(meth)acrylate, n-tridecyl(meth)acrylate, myristyl(meth)acrylate, palmityl(meth)acrylate, and stearyl(meth)acrylate.

[0083] Among these, the alkyl(meth)acrylate (a1) is preferably an alkyl(meth)acrylate in which the alkyl group has 4 to 8 carbon atoms. Specifically, n-butyl(meth)acrylate is preferred. The alkyl(meth)acrylate (a1) may be used alone or in combination of two or more.

[0084] The content of the structural units derived from alkyl (meth)acrylate (a1) in the acrylic polymer (A) is preferably 50 to 99.5 mass%, more preferably 60 to 99 mass%, and even more preferably 80 to 95 mass%, based on the total structural units (100 mass%) of the acrylic polymer (A).

[0085] If this content is 50% by mass or more, the retention performance of the intermediate layer is improved, and it becomes easier to improve the conformability to adherends with large irregularities. Also, if it is 99.5% by mass or less, a certain amount or more of the structural units derived from component (a2) can be ensured.

[0086] The functional group-containing monomer (a2) is a monomer having a functional group such as a hydroxy group, a carboxy group, an epoxy group, an amino group, a cyano group, a nitrogen atom-containing cyclic group, an alkoxysilyl group, etc. Among the above, the functional group-containing monomer (a2) is preferably at least one selected from the group consisting of a hydroxy group-containing monomer, a carboxy group-containing monomer, and an epoxy group-containing monomer.

[0087] Examples of hydroxy group-containing monomers include hydroxyalkyl (meth)acrylates such as 2-hydroxyethyl (meth)acrylate, 2-hydroxypropyl (meth)acrylate, 3-hydroxypropyl (meth)acrylate, 2-hydroxybutyl (meth)acrylate, 3-hydroxybutyl (meth)acrylate, and 4-hydroxybutyl (meth)acrylate; and unsaturated alcohols such as vinyl alcohol and allyl alcohol.

[0088] Examples of the carboxy group-containing monomer include (meth)acrylic acid, maleic acid, fumaric acid, and itaconic acid.

[0089] Examples of epoxy-containing monomers include epoxy group-containing (meth)acrylic acid esters and non-acrylic epoxy group-containing monomers. Examples of epoxy group-containing (meth)acrylic acid esters include glycidyl (meth)acrylate, β-methylglycidyl (meth)acrylate, (3,4-epoxycyclohexyl)methyl (meth)acrylate, and 3-epoxycyclo-2-hydroxypropyl (meth)acrylate. Examples of non-acrylic epoxy group-containing monomers include glycidyl crotonate and allyl glycidyl ether.

[0090] The functional group-containing monomer (a2) may be used alone or in combination of two or more kinds.

[0091] Among the functional group-containing monomers (a2), carboxy group-containing monomers are more preferred, among which (meth)acrylic acid is even more preferred, and acrylic acid is most preferred. When a carboxy group-containing monomer is used as the functional group-containing monomer (a2), the cohesive strength of the intermediate layer is increased, and the retention performance of the intermediate layer is more likely to be improved.

[0092] The content of the structural units derived from the functional group-containing monomer (a2) in the acrylic polymer (A) is preferably 0.5 to 40 mass%, more preferably 3 to 20 mass%, and even more preferably 5 to 15 mass%, relative to all structural units (100 mass%) of the acrylic polymer (A).

[0093] If the content of the structural units derived from component (a2) is 0.5% by mass or more, the cohesive strength of the intermediate layer will be high and compatibility with component (B) will also be likely to be good. On the other hand, if the content is 40% by mass or less, a certain amount or more of the structural units derived from component (a1) can be ensured.

[0094] The acrylic polymer (A) may be a copolymer of an alkyl (meth)acrylate (a1) and a functional group-containing monomer (a2), or may be a copolymer of the (a1) component, the (a2) component, and a monomer (a3) ​​other than the (a1) and (a2) components.

[0095] Examples of the other monomer (a3) ​​include (meth)acrylates having a cyclic structure such as cyclohexyl (meth)acrylate, benzyl (meth)acrylate, isobornyl (meth)acrylate, dicyclopentanyl (meth)acrylate, dicyclopentenyl (meth)acrylate, and dicyclopentenyloxyethyl (meth)acrylate, as well as vinyl acetate and styrene. The other monomer (a3) ​​may be used singly or in combination of two or more.

[0096] The content of the structural units derived from the other monomer (a3) ​​in the acrylic polymer (A) is preferably 0 to 20 mass%, more preferably 0 to 10 mass%, and even more preferably 0 to 5 mass%, relative to all structural units (100 mass%) of the acrylic polymer (A).

[0097] The weight-average molecular weight (Mw) of the acrylic polymer (A) is preferably 300,000 to 1,500,000, more preferably 400,000 to 1,100,000, and even more preferably 450,000 to 900,000. By setting Mw to the upper limit or less, the compatibility between the acrylic polymer (A) and the acrylic polymer (B) is improved. Furthermore, by setting Mw within the above range, the retention performance of the pressure-sensitive adhesive sheet is easily improved.

[0098] The content of the acrylic polymer (A) in the intermediate layer composition is preferably 40 to 95 mass%, more preferably 45 to 92 mass%, and even more preferably 60 to 90 mass% or more, relative to the total amount (100 mass%) of the resin components of the intermediate layer composition.

[0099] In addition, when the intermediate layer composition is diluted with a diluent such as an organic solvent as described below, the total amount of the intermediate layer composition means the total amount of solids excluding the diluent. The same applies to the pressure-sensitive adhesive layer composition described below.

[0100] The acrylic polymer (B) is an acrylic polymer that has energy ray curability due to the introduction of energy ray-polymerizable groups. The acrylic polymer (B) has a weight average molecular weight (Mw) of 50,000 to 250,000. In the present invention, by using the (B) component in the intermediate layer, the convex electrodes are sufficiently embedded during back grinding of the semiconductor wafer before energy ray curing, and by curing with energy ray after grinding, cohesive failure of the intermediate layer is prevented and good peeling from the semiconductor chip is facilitated.

[0101] The weight average molecular weight (Mw) of the acrylic polymer (B) is preferably from 60,000 to 220,000, more preferably from 70,000 to 200,000, and even more preferably from 85,000 to 150,000.

[0102] The acrylic polymer (B) is an acrylic polymer having an energy ray-polymerizable group introduced therein and a structural unit derived from (meth)acrylate. The energy ray-polymerizable group of the acrylic polymer (B) is preferably introduced into a side chain of the acrylic polymer. The energy ray-polymerizable group may be any group containing an energy ray-polymerizable carbon-carbon double bond, and examples thereof include a (meth)acryloyl group and a vinyl group, with a (meth)acryloyl group being preferred.

[0103] The acrylic polymer (B) is preferably a reaction product obtained by reacting an acrylic copolymer (B0) having a structural unit derived from an alkyl(meth)acrylate (b1) and a structural unit derived from a functional group-containing monomer (b2) with a polymerizable compound (Xb) having an energy ray-polymerizable group.

[0104] As the alkyl(meth)acrylate (b1), an alkyl(meth)acrylate having an alkyl group with 1 to 18 carbon atoms is used, and specific examples thereof include those exemplified as the component (a1). Among these, the alkyl(meth)acrylate (b1) is preferably an alkyl(meth)acrylate having an alkyl group with 4 to 8 carbon atoms. Specifically, n-butyl(meth)acrylate is preferred. These may be used alone or in combination of two or more.

[0105] The content of the structural units derived from alkyl (meth)acrylate (b1) in the acrylic copolymer (B0) is preferably 50 to 95% by mass, more preferably 60 to 85% by mass, and even more preferably 65 to 80% by mass, based on the total structural units (100% by mass) of the acrylic copolymer (B0). If this content is 50% by mass or more, the shape of the formed intermediate layer can be sufficiently maintained. Furthermore, if it is 95% by mass or less, a certain amount of structural units derived from component (b2), which serve as reaction sites with the polymerizable compound (Xb), can be secured.

[0106] The functional group-containing monomer (b2) may be any of the monomers having the functional group exemplified in the functional group-containing monomer (a2) described above, and is preferably at least one selected from the group consisting of hydroxyl group-containing monomers, carboxyl group-containing monomers, and epoxy group-containing monomers. Specific examples of these compounds include the same compounds as those exemplified as component (a2).

[0107] The functional group-containing monomer (b2) is preferably a hydroxy group-containing monomer, and more preferably various hydroxyalkyl (meth)acrylates such as 2-hydroxyethyl (meth)acrylate. The use of a hydroxyalkyl (meth)acrylate makes it relatively easy to react the acrylic copolymer (B0) with the polymerizable compound (Xb).

[0108] Furthermore, the functional groups in the functional group-containing monomer (a2) used in the acrylic polymer (A) and the functional group-containing monomer (b2) used in the acrylic polymer (B) may be the same or different, but are preferably different. That is, for example, if the functional group-containing monomer (a2) is a carboxyl group-containing monomer, the functional group-containing monomer (b2) is preferably a hydroxyl group-containing monomer. When the functional groups are different, for example, the acrylic polymer (B) can be preferentially crosslinked with a crosslinking agent described below, which makes it easier to improve the retention performance of the pressure-sensitive adhesive sheet.

[0109] The content of the structural units derived from the functional group-containing monomer (b2) in the acrylic copolymer (B0) is preferably 10 to 45% by mass, more preferably 15 to 40% by mass, and even more preferably 20 to 35% by mass, based on the total structural units (100% by mass) of the acrylic copolymer (B0). A content of 10% by mass or more ensures a relatively large number of reaction sites with the polymerizable compound (Xb), facilitating the introduction of energetic polymerizability into the side chains. Furthermore, a content of 45% by mass or less ensures that the shape of the intermediate layer formed can be adequately maintained.

[0110] The acrylic copolymer (B0) may be a copolymer of an alkyl (meth)acrylate (b1) and a functional group-containing monomer (b2), or may be a copolymer of the (b1) component, the (b2) component, and a monomer (b3) other than the (b1) and (b2) components.

[0111] Examples of the other monomer (b3) include those exemplified above as the monomer (a3).

[0112] The content of the structural units derived from the other monomer (b3) in the acrylic copolymer (B0) is preferably 0 to 30% by mass, more preferably 0 to 10% by mass, and even more preferably 0 to 5% by mass, relative to all structural units (100% by mass) of the acrylic copolymer (B0).

[0113] The polymerizable compound (Xb) is a compound having an energy ray-polymerizable group and a substituent (hereinafter simply referred to as a "reactive substituent") that can react with a functional group in a structural unit derived from the component (b2) of the acrylic copolymer (B0).

[0114] As described above, examples of the energy ray-polymerizable group include a (meth)acryloyl group and a vinyl group, with a (meth)acryloyl group being preferred. The polymerizable compound (Xb) is preferably a compound having 1 to 5 energy ray-polymerizable groups per molecule.

[0115] The reactive substituent in the polymerizable compound (Xb) may be appropriately changed depending on the functional group possessed by the functional group-containing monomer (b2), and examples thereof include an isocyanate group, a carboxyl group, an epoxy group, etc., with an isocyanate group being preferred from the viewpoint of reactivity, etc. When the polymerizable compound (Xb) has an isocyanate group, for example, when the functional group of the functional group-containing monomer (b2) is a hydroxy group, it can easily react with the acrylic copolymer (B0).

[0116] Specific examples of the polymerizable compound (Xb) include (meth)acryloyloxyethyl isocyanate, meta-isopropenyl-α,α-dimethylbenzyl isocyanate, (meth)acryloyl isocyanate, allyl isocyanate, glycidyl (meth)acrylate, (meth)acrylic acid, etc. These polymerizable compounds (Xb) may be used alone or in combination of two or more.

[0117] Among these, (meth)acryloyloxyethyl isocyanate is preferred from the viewpoint that it is a compound having a suitable isocyanate group as the reactive substituent and having an appropriate distance between the main chain and the energy ray-polymerizable group.

[0118] The polymerizable compound (Xb) reacts with the functional group in an amount of preferably 40 to 98 equivalents, more preferably 60 to 90 equivalents, and even more preferably 70 to 85 equivalents, of the total amount (100 equivalents) of functional groups derived from the functional group-containing monomer (b2) in the acrylic polymer (B).

[0119] In the intermediate layer composition, the content of the acrylic polymer (B) is preferably 5 to 60 parts by mass, and more preferably 10 to 35 parts by mass, per 100 parts by mass of the acrylic polymer (A). By making the content of the (B) component relatively low in this manner, the intermediate layer can more easily conform to the irregularities of the semiconductor wafer.

[0120] The intermediate layer composition preferably further contains a crosslinking agent. Examples of crosslinking agents include isocyanate-based crosslinking agents, epoxy-based crosslinking agents, aziridine-based crosslinking agents, and metal chelate-based crosslinking agents. Among these, isocyanate-based crosslinking agents are preferred. When an isocyanate-based crosslinking agent is used, for example, when component (B) has a hydroxy group, the crosslinking agent preferentially crosslinks the acrylic polymer (B).

[0121] The composition for the intermediate layer is crosslinked by the crosslinking agent, for example, by heating after application. The acrylic polymer, particularly the low-molecular-weight acrylic polymer (B), etc., is crosslinked, so that the intermediate layer is properly formed as a coating film and is more likely to function as an intermediate layer.

[0122] The content of the crosslinking agent is preferably 0.1 to 10 parts by mass, more preferably 0.5 to 7 parts by mass, and even more preferably 1 to 5 parts by mass, based on 100 parts by mass of the acrylic polymer (A).

[0123] Examples of isocyanate crosslinking agents include polyisocyanate compounds. Specific examples of polyisocyanate compounds include aromatic polyisocyanates such as tolylene diisocyanate, diphenylmethane diisocyanate, and xylylene diisocyanate, aliphatic polyisocyanates such as hexamethylene diisocyanate, and alicyclic polyisocyanates such as isophorone diisocyanate and hydrogenated diphenylmethane diisocyanate. Examples of the polyisocyanate compounds include biuret compounds and isocyanurate compounds of these compounds, as well as adducts obtained by reaction with low-molecular-weight active hydrogen-containing compounds such as ethylene glycol, propylene glycol, neopentyl glycol, trimethylolpropane, and castor oil.

[0124] These may be used alone or in combination of two or more. Among the above, an adduct of an aromatic polyisocyanate such as tolylene diisocyanate with a polyhydric alcohol (for example, trimethylolpropane) is preferred.

[0125] Examples of epoxy crosslinking agents include 1,3-bis(N,N'-diglycidylaminomethyl)cyclohexane, N,N,N',N'-tetraglycidyl-m-xylylenediamine, ethylene glycol diglycidyl ether, 1,6-hexanediol diglycidyl ether, trimethylolpropane diglycidyl ether, diglycidylaniline, diglycidylamine, etc. These may be used alone or in combination of two or more.

[0126] Examples of metal chelate crosslinking agents include compounds in which acetylacetone, ethyl acetoacetate, tris(2,4-pentanedionate), etc. are coordinated with polyvalent metals such as aluminum, iron, copper, zinc, tin, titanium, nickel, antimony, magnesium, vanadium, chromium, and zirconium. These may be used alone or in combination of two or more.

[0127] Examples of aziridine crosslinking agents include diphenylmethane-4,4'-bis(1-aziridinecarboxamide), trimethylolpropane tri-β-aziridinylpropionate, tetramethylolmethane tri-β-aziridinylpropionate, toluene-2,4-bis(1-aziridinecarboxamide), triethylenemelamine, bisisophthaloyl-1-(2-methylaziridine), tris-1-(2-methylaziridine)phosphine, trimethylolpropane tri-β-(2-methylaziridine)propionate, and hexa[1-(2-methyl)-aziridinyl]triphosphatriazine.

[0128] The intermediate layer composition preferably further contains a photopolymerization initiator. By containing the photopolymerization initiator, the intermediate layer composition can be more easily cured by energy rays such as ultraviolet rays.

[0129] Examples of the photopolymerization initiator include acetophenone, 2,2-diethoxybenzophenone, 4-methylbenzophenone, 2,4,6-trimethylbenzophenone, Michler's ketone, benzoin, benzoin methyl ether, benzoin ethyl ether, benzoin isopropyl ether, benzoin isobutyl ether, benzyl diphenylsulfide, tetramethylthiuram monosulfide, benzil dimethyl ketal, dibenzyl, diacetyl, 1-chloroanthraquinone, 2-chloroanthraquinone, 2-ethylanthraquinone, 2,2-dimethoxy-1,2-diphenylethan-1-one, 1 Examples of suitable initiators include low-molecular-weight initiators such as 1-hydroxycyclohexyl phenyl ketone, 2-methyl-1-[4-(methylthio)phenyl]-2-morpholinopropanone-1,2-benzyl-2-dimethylamino-1-(4-morpholinophenyl)-butanone-1,2-hydroxy-2-methyl-1-phenyl-propan-1-one, diethylthioxanthone, isopropylthioxanthone, and 2,4,6-trimethylbenzoyldiphenylphosphine oxide, and oligomerized initiators such as oligo{2-hydroxy-2-methyl-1-[4-(1-methylvinyl)phenyl]propanone}. These initiators may be used alone or in combination. Among these, 1-hydroxycyclohexyl phenyl ketone is preferred.

[0130] The content of the photopolymerization initiator is preferably 1 to 10 parts by mass, more preferably 2 to 8 parts by mass, per 100 parts by mass of the acrylic polymer (A), so that curing can proceed sufficiently even with a small content of the acrylic polymer (B).

[0131] The intermediate layer composition contains an antistatic agent in addition to the energy ray-curable acrylic polymer and other components.

[0132] The antistatic agent contained in the intermediate layer composition is not particularly limited, and known antistatic agents can be used. Examples of the antistatic agent include ionic liquids, low molecular weight antistatic agents, and high molecular weight antistatic agents. Ionic liquids are preferably used because they are easily mixed with the resin constituting the intermediate layer and have excellent antistatic properties.

[0133] Ionic liquids are a type of salt that contains cationic (positive ion) compounds and anionic (negative ion) compounds, and are in a liquid state below 100°C. Ionic liquids exhibit high electrical conductivity, which allows them to exhibit excellent antistatic properties.

[0134] Examples of cations constituting an ionic liquid include triethylpentylammonium, cyclohexyltrimethylammonium, methyltri-n-octylammonium, tetrabutylammonium, tetrabutylphosphonium, tributylhexadecylphosphonium, tributyl(2-methoxyethyl)phosphonium, tributylmethylammonium, tributylmethylphosphonium, triethylsulfonium, trimethylpropylammonium, 1-butyl-1-methylpiperidinium, hydroxyethylpiperazine, 2-methylpiperazine, N-ethylmorpholine, N-N-dimethylethanolamine, N-N-dimethylethanolamine, N-methylethanolamine, N-methyldiethanolamine, N-ethylethanolamine, N-ethyldiethanolamine, N-(β-aminoethyl)ethanolamine, Nn-butyldiethanolamine, Examples of such an amine include diethanolamine, Nt-butyldiethanolamine, N,N-diethylisopropanolamine, 1-butyl-2,3-dimethylimidazolium, 1-butyl-3-methylimidazolium, 1,3-dimethylimidazolium, 1,2-dimethyl-3-propylimidazolium, 1-ethyl-2,3-dimethylimidazolium, 1-ethyl-3-methylimidazolium, 1-hexyl-3-methylimidazolium, 1-methyl-3-n-octylimidazolium, 1-methyl-3-propylimidazolium, 1-butyl-4-methylpyridinium, 1-butyl-3-methylpyridinium, 1-butylpyridinium, 1-ethyl-3-(hydroxymethyl)pyridinium, 1-ethyl-3-methylpyridinium, 1-ethylpyridinium, 1-butyl-1-methylpyrrolidinium, and 1-methyl-1-propylpyrrolidinium.

[0135] The cation is not limited in any way as long as it can constitute an ionic liquid, and cations other than those exemplified above can also be used.

[0136] As with the above cations, the anions constituting the ionic liquid are not limited in any way, and anions other than those exemplified below can also be used.

[0137] Examples of anions that constitute ionic liquids include AlCl4 - , Al2Cl7 - , BF4 - , PF6 - , F(HF)n - , CF3COO - , CH3CH2OSO3 - , CF3SO3 - (TfO), (CF3SO2)2N - (TFSI), (CF3SO2)3C - (TFSM), HN(Tf)2 - , NO3 - , (NC)2N - , CH3COO - , Br - , Cl - , I - , (CH3O)2OPO - Other examples include sulfonic acid (sulfonate) anions such as linear alkylbenzenesulfonic acid, dialkyl succinate sulfonic acid, α-sulfofatty acid methyl ester, α-olefin sulfonic acid, and alkanesulfonic acid; fatty acid anions such as higher fatty acids; sulfate ester (sulfate) anions such as alkyl sulfate ester, glycol ether sulfate ester, and alkyl ether sulfate ester; and phosphate ester (phosphate) anions such as (mono)alkyl phosphate ester.

[0138] Examples of ionic liquids include ionic liquids containing N-ethylethanolamine and alkylbenzenesulfonic acid, N-ethylethanolamine and glycol ether sulfate, and N-ethylethanolamine and dialkylsuccinatesulfonic acid. Ionic liquids may be used alone or in combination. Furthermore, the ionic liquid may contain two or more types of cations and / or two or more types of anions.

[0139] Examples of ionic liquid products include AS100, AS200, AS300, and AS400 from Nippon Nyukazai Co., Ltd., and the IL-P series, IL-A series, IL-C series, IL-IM series, and IL-AP series from Koei Chemical Industry Co., Ltd.

[0140] Furthermore, the ionic liquid may have a reactive site. Examples of ionic liquids having a reactive site include RE3000MA, JI62J01, and JI62G01 from Nippon Nyukazai Co., Ltd., the IL-MA series and IL-S series from Koei Chemical Industry Co., Ltd., and FC-4400 from 3M Japan Limited.

[0141] Examples of polymeric antistatic agents include copolymers having polyether units, such as polyether ester amides and polyether polyolefin block copolymers.

[0142] The intermediate layer composition contains the antistatic agent and a resin component. The proportion of the antistatic agent in the intermediate layer composition varies depending on the antistatic agent used, but generally, the antistatic agent is used in a proportion of preferably 0.3 to 5.0 parts by mass, more preferably 0.4 to 4.5 parts by mass, and particularly preferably 0.5 to 4.0 parts by mass per 100 parts by mass (solids) of the total amount of the intermediate layer composition. If the blending proportion of the antistatic agent is too low, the required antistatic properties may not be obtained. If the blending proportion is too high, the intermediate layer may whiten or its shape retention may be reduced. Furthermore, if the amount of antistatic agent is too high, depending on the composition and thickness of the pressure-sensitive adhesive layer, the antistatic agent may migrate to the wafer during wafer attachment, causing wafer contamination.

[0143] The means for forming the intermediate layer 20 may be determined depending on the material used to form the intermediate layer. When forming an antistatic agent-containing coating layer using the energy ray-curable resin, a means for applying a liquid resin before curing can be used. Specifically, a coating device such as a die coater, curtain coater, spray coater, slit coater, or knife coater; a printing device such as a screen printer or inkjet printer; or a dropping device such as a dispenser can be used.

[0144] The intermediate layer may be directly coated onto the substrate 10, or may be coated onto another release sheet or the like and then transferred onto the substrate.

[0145] The intermediate layer may contain other additives as long as the effects of the present invention are not impaired. Examples of other additives include antioxidants, softeners (plasticizers), fillers, rust inhibitors, pigments, dyes, and tackifiers. When these additives are contained, the content of each additive is preferably 0.01 to 6 parts by mass, more preferably 0.01 to 2 parts by mass, based on the total solid content constituting the intermediate layer.

[0146] The above has been described in detail with respect to the case where the resin component constituting the intermediate layer contains an energy ray-curable acrylic polymer, but the resin component constituting the intermediate layer is not limited to this and may be a polyolefin resin. Examples of polyolefin resins include very low density polyethylene (VLDPE, density: 880 kg / m 3 More than 910kg / m 3 less than 910 kg / m 3 Above, 942kg / m 3 less than 942 kg / m 3 Examples of suitable polyolefin resins include polyethylene resins (such as those mentioned above), polypropylene resins, polyethylene-polypropylene copolymers, olefin elastomers (TPO), cycloolefin resins, polyvinyl chloride (PVC), ethylene-vinyl acetate copolymers (EVA), ethylene-vinyl acetate-maleic anhydride copolymers, ethylene-(meth)acrylic acid copolymers, ethylene-(meth)acrylic acid ester copolymers, ethylene-(meth)acrylic acid ester-maleic anhydride copolymers, and ionomer resins. These polyolefin resins can be used alone or in combination of two or more.

[0147] At least one of the main surfaces of the intermediate layer may be subjected to a surface treatment such as a corona treatment in order to improve adhesion to other layers and members.

[0148] (Adhesive layer 30) The adhesive layer 30 is attached to the surface of a workpiece having a front and back surface (i.e., the surface on which circuits, electrodes, etc. are formed), and protects the surface and supports the workpiece or a group of individual workpieces until it is peeled off from the surface. In this embodiment, the adhesive layer is preferably composed of one layer (single layer). This is because if the adhesive layer has multiple layers, when the protective sheet for workpiece processing is peeled off, the adhesive layers may peel off from each other, with one adhesive layer remaining on the protective sheet for workpiece processing and the other adhesive layer remaining on the workpiece, potentially leaving residue on the workpiece.

[0149] The thickness of the adhesive layer is preferably 20 μm or more and 210 μm or less, and more preferably 25 μm or more and 60 μm or less. When the thickness of the adhesive layer is within the above range, the adhesive layer can fully exhibit its adhesive properties, and further, can fully conform to irregularities (electrodes, grooves, etc.) present on the surface of the workpiece, making it easy to fill the irregularities, and can also make it easy to subsequently peel off from the workpiece, etc.

[0150] The thickness of the pressure-sensitive adhesive layer refers to the thickness of the entire pressure-sensitive adhesive layer. For example, the thickness of a pressure-sensitive adhesive layer composed of multiple layers refers to the total thickness of all layers constituting the pressure-sensitive adhesive layer.

[0151] The composition of the adhesive layer is not limited as long as it has enough adhesiveness to protect the surface of the workpiece or the group of individual workpieces. In this embodiment, the adhesive layer is composed of an adhesive composition, and is preferably composed of, for example, an acrylic adhesive composition, a urethane adhesive composition, a rubber adhesive composition, a silicone adhesive composition, or the like.

[0152] Furthermore, the adhesive layer is preferably an energy ray-curable adhesive layer composed of an energy ray-curable adhesive composition. Since the adhesive layer of the protective sheet for workpiece processing is an energy ray-curable adhesive layer, when attached to a workpiece, it adheres to the workpiece with high adhesive strength, and when peeled from the workpiece or a group of individual workpieces, the adhesive strength can be reduced by irradiating with energy rays. Therefore, while appropriately protecting the circuits, etc. of the workpiece or a group of individual workpieces, when the protective sheet for workpiece processing is peeled off, damage to the circuits, electrodes, etc. on the surface of the workpiece or a group of individual workpieces is prevented.

[0153] In this embodiment, the energy ray-curable pressure-sensitive adhesive composition is preferably composed of an acrylic pressure-sensitive adhesive composition, which contains an acrylic polymer.

[0154] 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 multiple types of acrylic monomers and a monomer other than the acrylic monomer.

[0155] In this embodiment, the functional group-containing acrylic polymer is preferably an acrylic copolymer obtained by copolymerizing alkyl (meth)acrylate and a functional group-containing monomer.

[0156] 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.

[0157] The functional group-containing monomer is a monomer containing a reactive functional group. The reactive functional group is a functional group capable of reacting with other compounds such as a crosslinking agent, which will be described later. Examples of the functional group in the functional group-containing monomer include a hydroxyl group, a carboxyl group, and an epoxy group, with a hydroxyl group being preferred.

[0158] 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 not having a (meth)acryloyl skeleton) such as vinyl alcohol and allyl alcohol.

[0159] The acrylic polymer is preferably an energy ray-curable acrylic polymer having an energy ray-curable group, obtained by reacting (e.g., adding) an energy ray-curable substance having an energy ray-curable group with a functional group of 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 be added to a hydroxyl group of the functional group-containing acrylic polymer.

[0160] Examples of compounds having 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 a polyisocyanate compound with hydroxyethyl (meth)acrylate; and acryloyl monoisocyanate compounds obtained by reacting a diisocyanate compound or a polyisocyanate compound with a polyol compound and hydroxyethyl (meth)acrylate.

[0161] The pressure-sensitive adhesive composition preferably contains, in addition to the acrylic polymer, an energy ray-curable compound. The energy ray-curable compound is preferably a monomer or oligomer having an unsaturated group in the molecule and capable of being polymerized and cured by energy ray irradiation.

[0162] Examples of such energy ray-curable compounds include polyvalent (meth)acrylate monomers such as trimethylolpropane tri(meth)acrylate, pentaerythritol (meth)acrylate, pentaerythritol tetra(meth)acrylate, dipentaerythritol hexa(meth)acrylate, 1,4-butylene glycol di(meth)acrylate, and 1,6-hexanediol (meth)acrylate, and oligomers such as urethane (meth)acrylate, polyester (meth)acrylate, polyether (meth)acrylate, and epoxy (meth)acrylate.

[0163] Among these, urethane (meth)acrylate oligomers having a relatively high molecular weight are preferred.

[0164] 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, still more preferably 400 to 8,000, and particularly preferably 600 to 6,000.

[0165] The content of the energy ray-curable compound in the pressure-sensitive adhesive composition is preferably 3 to 100 parts by mass, more preferably 5 to 70 parts by mass, and even more preferably 7 to 40 parts by mass, relative to 100 parts by mass of the acrylic polymer.

[0166] The pressure-sensitive adhesive composition preferably further contains a crosslinking agent, which reacts with the functional groups to crosslink molecules contained in the functional group-containing acrylic polymer, for example.

[0167] 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).

[0168] From the viewpoint of improving the cohesive strength of the pressure-sensitive adhesive and thereby improving the adhesive strength of the pressure-sensitive adhesive layer, and from the viewpoint of ease of availability, the crosslinking agent is preferably an isocyanate-based crosslinking agent.

[0169] The pressure-sensitive adhesive composition may further contain a photopolymerization initiator. When the pressure-sensitive adhesive composition contains a photopolymerization initiator, the curing reaction proceeds sufficiently even when irradiated with relatively low-energy energy rays such as ultraviolet rays.

[0170] Examples of the photopolymerization initiator include photoinitiators such as benzoin compounds, acetophenone compounds, acylphosphine oxide compounds, titanocene compounds, thioxanthone compounds, and peroxide compounds, and photosensitizers such as amines and quinones. Specific examples include α-hydroxycyclohexyl phenyl ketone, benzoin, benzoin methyl ether, benzoin ethyl ether, benzoin isopropyl ether, benzyl diphenyl sulfide, benzil dimethyl ketal, tetramethylthiuram monosulfide, azobisisobutyronitrile, dibenzyl, diacetyl, β-chloroanthraquinone, and 2,4,6-trimethylbenzoyldiphenylphosphine oxide.

[0171] The pressure-sensitive adhesive composition may contain other additives as long as the effects of the present invention are not impaired. Examples of other additives include tackifiers, antioxidants, softeners (plasticizers), fillers, rust inhibitors, pigments, dyes, etc. When these additives are contained, the content of each additive is preferably 0.01 to 6 parts by mass, more preferably 0.02 to 2 parts by mass, per 100 parts by mass of the acrylic polymer.

[0172] From the viewpoint of preventing contamination of the workpiece, it is preferable that the pressure-sensitive adhesive composition does not contain an antistatic agent.

[0173] (Buffer layer 40) The protective sheet for workpiece processing 1 is not limited to the configuration shown in Fig. 1 and may have other layers as long as the effects of the present invention are obtained. That is, as long as the substrate, intermediate layer, and adhesive layer are laminated in this order, other layers may be formed, for example, between the substrate and the intermediate layer, or between the intermediate layer and the adhesive layer.

[0174] In particular, in this embodiment, as shown in Figure 2, it is preferable that the substrate has a buffer layer 40 on the main surface opposite to the main surface on which the adhesive layer is formed. The buffer layer 40 is a layer softer than the substrate and relieves stress during backgrinding of the semiconductor wafer, preventing cracks and chips from occurring in the semiconductor wafer. Furthermore, the semiconductor wafer with the workpiece processing protective sheet attached is placed on a vacuum table via the workpiece processing protective sheet during backgrinding, and the presence of the buffer layer as a constituent layer of the workpiece processing protective sheet makes it easier to properly hold the wafer on the vacuum table.

[0175] The thickness of the buffer layer is preferably 1 to 100 μm, more preferably 5 to 80 μm, and even more preferably 10 to 60 μm. By setting the thickness of the buffer layer within the above range, the buffer layer can appropriately relieve stress during back grinding.

[0176] The buffer layer may be a layer formed from a buffer layer composition containing an energy ray-polymerizable compound, or may be a film such as a polypropylene film, an ethylene-vinyl acetate copolymer film, an ionomer resin film, an ethylene-(meth)acrylic acid copolymer film, an ethylene-(meth)acrylic acid ester copolymer film, an LDPE film, or an LLDPE film.

[0177] The buffer layer is laminated on one or both sides of the substrate.

[0178] The composition for forming the buffer layer (hereinafter referred to as the buffer layer composition) preferably contains an energy ray-polymerizable compound. The buffer layer composition containing the energy ray-polymerizable compound can be cured by being irradiated with energy rays.

[0179] More specifically, the buffer layer composition containing the energy ray-polymerizable compound preferably contains a urethane (meth)acrylate (d1) and a polymerizable compound (d3) having an alicyclic or heterocyclic group with 6 to 20 ring atoms. The buffer layer composition may contain a polyfunctional polymerizable compound (d2) and / or a polymerizable compound (d4) having a functional group, in addition to the components (d1) and (d3). The buffer layer composition may also contain a photopolymerization initiator in addition to the above components. The buffer layer composition may also contain other additives and resin components, as long as they do not impair the effects of the present invention.

[0180] Hereinafter, each component contained in the buffer layer composition containing the energy ray-polymerizable compound will be described in detail.

[0181] 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.

[0182] The weight-average molecular weight (Mw) of component (d1) is preferably 1,000 to 100,000, more preferably 2,000 to 60,000, and even more preferably 3,000 to 20,000. The number of (meth)acryloyl groups (hereinafter also referred to as "number of functional groups") in component (d1) may be monofunctional, bifunctional, or trifunctional or higher, but is preferably monofunctional or bifunctional.

[0183] Component (d1) can be obtained, for example, by reacting a polyol compound with a polyvalent isocyanate compound to obtain a terminal isocyanate urethane prepolymer, and then reacting the resulting prepolymer with a (meth)acrylate having a hydroxyl group. Component (d1) may be used alone or in combination of two or more.

[0184] The polyol compound used as the raw material for component (d1) is not particularly limited as long as it has two or more hydroxy groups. It may be a bifunctional diol, a trifunctional triol, or a polyol with four or more functional groups, but a bifunctional diol is preferred, and a polyester diol or a polycarbonate diol is more preferred.

[0185] Examples of polyisocyanate compounds include aliphatic polyisocyanates such as tetramethylene diisocyanate, hexamethylene diisocyanate, and trimethylhexamethylene diisocyanate; alicyclic diisocyanates such as isophorone diisocyanate, norbornane diisocyanate, dicyclohexylmethane-4,4'-diisocyanate, dicyclohexylmethane-2,4'-diisocyanate, and ω,ω'-diisocyanatodimethylcyclohexane; and aromatic diisocyanates such as 4,4'-diphenylmethane diisocyanate, tolylene diisocyanate, xylylene diisocyanate, tolidine diisocyanate, tetramethylene xylylene diisocyanate, and naphthalene-1,5-diisocyanate.

[0186] Among these, isophorone diisocyanate, hexamethylene diisocyanate, and xylylene diisocyanate are preferred.

[0187] The urethane (meth)acrylate (d1) can be obtained by reacting a (meth)acrylate having a hydroxy group with a terminal isocyanate urethane prepolymer obtained by reacting the above-mentioned polyol compound with a polyisocyanate compound. The (meth)acrylate having a hydroxy group is not particularly limited as long as it is a compound having a hydroxy group and a (meth)acryloyl group in at least one molecule.

[0188] Specific examples of (meth)acrylates having a hydroxy group include hydroxyalkyl (meth)acrylates such as 2-hydroxyethyl (meth)acrylate, 2-hydroxypropyl (meth)acrylate, 4-hydroxybutyl (meth)acrylate, 4-hydroxycyclohexyl (meth)acrylate, 5-hydroxycyclooctyl (meth)acrylate, 2-hydroxy-3-phenyloxypropyl (meth)acrylate, pentaerythritol tri(meth)acrylate, polyethylene glycol mono(meth)acrylate, and polypropylene glycol mono(meth)acrylate; hydroxy group-containing (meth)acrylamides such as N-methylol (meth)acrylamide; and reaction products obtained by reacting a diglycidyl ester of vinyl alcohol, vinylphenol, or bisphenol A with (meth)acrylic acid.

[0189] Among these, hydroxyalkyl (meth)acrylate is preferred, and 2-hydroxyethyl (meth)acrylate is more preferred.

[0190] The conditions for reacting the isocyanate-terminated urethane prepolymer and the (meth)acrylate having a hydroxy group are preferably such that the reaction is carried out at 60 to 100° C. for 1 to 4 hours in the presence of a solvent and a catalyst, which are added as needed.

[0191] The content of component (d1) in the buffer layer composition is preferably 10 to 70 mass %, more preferably 20 to 60 mass %, and even more preferably 25 to 55 mass %, relative to the total amount (100 mass %) of the buffer layer composition.

[0192] The multifunctional polymerizable compound (d2) refers to a compound having two or more photopolymerizable unsaturated groups. The photopolymerizable unsaturated group is a functional group containing a carbon-carbon double bond, such as a (meth)acryloyl group, a vinyl group, an allyl group, or a vinylbenzyl group. Two or more types of photopolymerizable unsaturated groups may be combined. A three-dimensional network structure (crosslinked structure) is formed by the reaction of the photopolymerizable unsaturated group in the multifunctional polymerizable compound with the (meth)acryloyl group in component (d1) or by the reaction of the photopolymerizable unsaturated groups in component (d2) with each other. The use of a multifunctional polymerizable compound increases the number of crosslinked structures formed by energy beam irradiation compared to the use of a compound containing only one photopolymerizable unsaturated group. This results in the buffer layer exhibiting unique viscoelasticity and facilitating stress relief during backgrinding.

[0193] Although the definition of component (d2) overlaps with the definitions of components (d3) and (d4) described below, the overlapping portions are included in component (d2). For example, a compound having an alicyclic or heterocyclic group with 6 to 20 ring atoms and two or more (meth)acryloyl groups is included in the definitions of both component (d2) and component (d3), but in the present invention, such a compound is included in component (d2). Furthermore, 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 (d2) and component (d4), but in the present invention, such a compound is included in component (d2).

[0194] From the above viewpoints, the number of photopolymerizable unsaturated groups (number of functional groups) in the polyfunctional polymerizable compound is preferably 2 to 10, and more preferably 3 to 6.

[0195] The weight average molecular weight of the component (d2) is preferably 30 to 40,000, more preferably 100 to 10,000, and even more preferably 200 to 1,000.

[0196] Specific examples of component (d2) include diethylene glycol di(meth)acrylate, ethylene glycol di(meth)acrylate, tetraethylene glycol di(meth)acrylate, neopentyl glycol di(meth)acrylate, 1,6-hexanediol di(meth)acrylate, trimethylolpropane tri(meth)acrylate, pentaerythritol tri(meth)acrylate, pentaerythritol tetra(meth)acrylate, dipentaerythritol hexa(meth)acrylate, divinylbenzene, vinyl (meth)acrylate, divinyl adipate, and N,N'-methylenebis(meth)acrylamide. Among these, dipentaerythritol hexa(meth)acrylate is preferred. Component (d2) may be used alone or in combination of two or more.

[0197] The content of component (d2) in the buffer layer composition is preferably 2 to 40 mass %, more preferably 3 to 20 mass %, and even more preferably 5 to 15 mass %, relative to the total amount (100 mass %) of the buffer layer composition.

[0198] The polymerizable compound (d3) is a polymerizable compound having an alicyclic group or a heterocyclic group with 6 to 20 ring atoms, and is preferably a compound having at least one (meth)acryloyl group, more preferably a compound having one (meth)acryloyl group. The use of component (d3) can improve the film-forming properties of the resulting buffer layer composition.

[0199] Although the definition of component (d3) overlaps with the definition of component (d4) described below, the overlapping portion is included in component (d4). For example, a compound having at least one (meth)acryloyl group, an alicyclic or heterocyclic group having 6 to 20 ring atoms, and a functional group such as a hydroxyl group, an epoxy group, an amide group, or an amino group is included in the definitions of both component (d3) and component (d4), and in the present invention, such a compound is considered to be included in component (d4).

[0200] Specific examples of component (d3) include alicyclic group-containing (meth)acrylates such as isobornyl (meth)acrylate, dicyclopentenyl (meth)acrylate, dicyclopentanyl (meth)acrylate, dicyclopentenyloxy (meth)acrylate, cyclohexyl (meth)acrylate, and adamantane (meth)acrylate; heterocyclic group-containing (meth)acrylates such as tetrahydrofurfuryl (meth)acrylate and morpholine (meth)acrylate; etc. Component (d3) may be used alone or in combination of two or more.

[0201] Among the alicyclic group-containing (meth)acrylates, isobornyl (meth)acrylate is preferred, and among the heterocyclic group-containing (meth)acrylates, tetrahydrofurfuryl (meth)acrylate is preferred.

[0202] The content of component (d3) in the buffer layer composition is preferably 10 to 70 mass %, more preferably 20 to 60 mass %, and even more preferably 25 to 55 mass %, relative to the total amount (100 mass %) of the buffer layer composition.

[0203] The content ratio of component (d2) to component (d3) in the buffer layer composition [(d2) / (d3)] is preferably 0.1 to 3.0, more preferably 0.15 to 2.0, and even more preferably 0.18 to 1.0.

[0204] The polymerizable compound (d4) having a functional group 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.

[0205] Component (d4) has good compatibility with component (d1), making it easier to adjust the viscosity of the buffer layer composition within an appropriate range, and also ensuring good buffer performance even when the buffer layer is relatively thin.

[0206] Examples of component (d4) include hydroxyl group-containing (meth)acrylates, epoxy group-containing compounds, amide group-containing compounds, amino group-containing (meth)acrylates, etc. Among these, hydroxyl group-containing (meth)acrylates are preferred.

[0207] Examples of hydroxyl group-containing (meth)acrylates include 2-hydroxyethyl (meth)acrylate, 2-hydroxypropyl (meth)acrylate, 3-hydroxypropyl (meth)acrylate, 2-hydroxybutyl (meth)acrylate, 3-hydroxybutyl (meth)acrylate, 4-hydroxybutyl (meth)acrylate, phenylhydroxypropyl (meth)acrylate, and 2-hydroxy-3-phenoxypropyl acrylate. Among these, hydroxyl group-containing (meth)acrylates having an aromatic ring, such as phenylhydroxypropyl (meth)acrylate, are more preferred. Component (d4) may be used alone or in combination of two or more.

[0208] In order to improve the film-forming properties of the buffer layer composition, the content of component (d4) in the buffer layer composition is preferably 5 to 40 mass %, more preferably 7 to 35 mass %, and even more preferably 10 to 30 mass %, relative to the total amount (100 mass %) of the buffer layer composition.

[0209] The content ratio of component (d3) to component (d4) in the buffer layer composition [(d3) / (d4)] is preferably 0.5 to 3.0, more preferably 1.0 to 3.0, and even more preferably 1.3 to 3.0.

[0210] The buffer layer-forming composition may contain a polymerizable compound (d5) other than the above components (d1) to (d4) within the range that does not impair the effects of the present invention.

[0211] Examples of component (d5) include alkyl (meth)acrylates having an alkyl group having 1 to 20 carbon atoms, and vinyl compounds such as styrene, hydroxyethyl vinyl ether, hydroxybutyl vinyl ether, N-vinyl formamide, N-vinyl pyrrolidone, and N-vinyl caprolactam. Component (d5) may be used alone or in combination of two or more.

[0212] The content of component (d5) in the buffer layer composition is preferably 0 to 20 mass %, more preferably 0 to 10 mass %, even more preferably 0 to 5 mass %, and particularly preferably 0 to 2 mass %.

[0213] The buffer layer composition preferably further contains a photopolymerization initiator from the viewpoint of shortening the polymerization time by light irradiation and reducing the amount of light irradiation when forming the buffer layer.

[0214] 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, 2-hydroxy-2-methyl-1-phenyl-propan-1-one, benzoin, benzoin methyl ether, benzoin ethyl ether, benzoin isopropyl ether, benzyl phenyl sulfide, tetramethylthiuram monosulfide, azobisisobutyrolnitrile, dibenzyl, diacetyl, 8-chloroanthraquinone, bis(2,4,6-trimethylbenzoyl)phenylphosphine oxide, etc. These photopolymerization initiators can be used alone or in combination of two or more.

[0215] The content of the photopolymerization initiator in the composition for the buffer layer is preferably 0.05 to 15 parts by mass, more preferably 0.1 to 10 parts by mass, and even more preferably 0.3 to 5 parts by mass, relative to 100 parts by mass of the total amount of the energy ray-polymerizable compounds.

[0216] The buffer layer composition may contain other additives as long as the effects of the present invention are not impaired. Examples of other additives include antistatic agents, antioxidants, softeners (plasticizers), fillers, rust inhibitors, pigments, and dyes. When these additives are added, the content of each additive in the buffer layer composition is preferably 0.01 to 6 parts by mass, and more preferably 0.1 to 3 parts by mass, per 100 parts by mass of the total amount of the energy ray-polymerizable compounds.

[0217] The buffer layer formed from the buffer layer composition containing the energy ray-polymerizable compound is obtained by polymerizing and curing the buffer layer composition having the above-described composition by energy ray irradiation. In other words, the buffer layer is a product obtained by curing the buffer layer composition.

[0218] Therefore, the buffer layer preferably contains polymerization units derived from component (d1) and polymerization units derived from component (d3). The buffer layer may also contain polymerization units derived from component (d2) and / or polymerization units derived from component (d4), or may contain polymerization units derived from component (d5). The content ratio of each polymerization unit in the buffer layer usually corresponds to the ratio (feed ratio) of each component constituting the buffer layer composition.

[0219] (Release sheet) A release sheet may be attached to the surface of the workpiece processing protective sheet. Specifically, the release sheet is attached to the surface of the adhesive layer of the workpiece processing protective sheet. By being attached to the surface of the adhesive layer, the release sheet protects the adhesive layer during transportation and storage. The release sheet is removably attached to the workpiece processing protective sheet, and is peeled off and removed from the workpiece processing protective sheet before the workpiece processing protective sheet is used (i.e., before attaching a wafer).

[0220] The release sheet used is a release sheet having at least one surface subjected to a release treatment, and specifically includes a release sheet substrate having a release agent applied to the surface thereof.

[0221] The substrate for the release sheet is preferably a resin film, and examples of the resin constituting the resin film include polyester resin films such as polyethylene terephthalate resin, polybutylene terephthalate resin, and polyethylene naphthalate resin, and polyolefin resins such as polypropylene resin and polyethylene resin. Examples of the release agent include rubber elastomers such as silicone resins, olefin resins, isoprene resins, and butadiene resins, long-chain alkyl resins, alkyd resins, and fluorine-based resins.

[0222] The thickness of the release sheet is not particularly limited, but is preferably 10 to 200 μm, more preferably 20 to 150 μm.

[0223] (Method of manufacturing protective sheet for workpiece processing) A method for producing the above-mentioned workpiece processing protection sheet is described below. First, an antistatic substrate is prepared. As described above, such a substrate can be obtained by providing an antistatic agent-containing coating layer on a support material. Alternatively, an antistatic agent can be mixed with the resin components constituting the support material, and the mixture can be formed into a sheet to obtain an antistatic substrate.

[0224] Next, an intermediate layer and a pressure-sensitive adhesive layer are formed on one main surface of the substrate. This method is not particularly limited, and any known method may be used. In addition, when the substrate has a structure in which an antistatic agent-containing coating layer is formed on a support material, the intermediate layer is formed on the antistatic agent-containing coating layer. In addition, a buffer layer may be formed on the other main surface of the substrate. The following will be explained using the case in which a buffer layer is included as an example.

[0225] First, as a composition for forming an intermediate layer, for example, a composition for intermediate layer containing the components described above, or a composition obtained by diluting the composition for intermediate layer with a solvent, etc. is prepared. Similarly, as a composition for pressure-sensitive adhesive layer for forming a pressure-sensitive adhesive layer, for example, a composition for pressure-sensitive adhesive layer containing the components described above, or a composition obtained by diluting the composition for pressure-sensitive adhesive layer with a solvent, etc. is prepared. Similarly, as a composition for buffer layer for forming a buffer layer, for example, a composition for buffer layer containing the components described above, or a composition obtained by diluting the composition for pressure-sensitive adhesive layer with a solvent, etc. is prepared.

[0226] Examples of the solvent include organic solvents such as methyl ethyl ketone, acetone, ethyl acetate, tetrahydrofuran, dioxane, cyclohexane, n-hexane, toluene, xylene, n-propanol, and isopropanol.

[0227] The buffer layer composition is then applied to the release-treated surface of the first release sheet by a known method such as spin coating, spray coating, bar coating, knife coating, roll coating, blade coating, die coating, or gravure coating to form a coating film, which is then semi-cured to form a buffer layer film on the release sheet. The buffer layer film formed on the release sheet is then attached to a substrate and completely cured to form the buffer layer.

[0228] In this embodiment, the coating film is preferably cured by irradiation with energy rays. The coating film may be cured in a single curing treatment or in multiple steps.

[0229] Next, the intermediate layer composition is applied to the release-treated surface of the second release sheet by a known method and heated and dried to form an intermediate layer on the second release sheet.The intermediate layer on the second release sheet is then bonded to the surface of the substrate on which the buffer layer is not formed, and the second release sheet is removed.In addition, if the support material has an antistatic agent-containing coating layer, the intermediate layer is provided on the antistatic agent-containing coating layer.

[0230] Next, a composition for the adhesive layer is applied to the release-treated surface of the third release sheet by a known method, and then heated and dried to form an adhesive layer on the third release sheet.Then, the adhesive layer on the third release sheet and the intermediate layer are bonded together, so that the intermediate layer and the adhesive layer are formed in this order on one main surface of the substrate, and a buffer layer is formed on the other main surface of the substrate, resulting in a protective sheet for workpiece processing.The third release sheet can be removed when the protective sheet for workpiece processing is used.

[0231] According to the present invention, a protective sheet for workpiece processing can be obtained that sufficiently suppresses charging that occurs during processing of a workpiece, etc. (i.e., a workpiece or a group of individual workpieces). For example, after a semiconductor wafer is singulated into chips by the LDBG method, the peeling charging voltage that occurs when the protective sheet for workpiece processing is peeled off can be suppressed to 150 V or less. A method for measuring the peeling charging voltage will be described in detail in the Examples.

[0232] (Method of manufacturing individual workpieces) The protective sheet for workpiece processing according to the present invention is preferably used for surface protection during back grinding of the workpiece, and is particularly suitable for use in processing methods for dividing the workpiece into individual pieces by back grinding (DBG, LDBG, etc.). As a non-limiting example of use of the protective sheet for workpiece processing, a method for producing the divided workpieces will be described in more detail below.

[0233] Specifically, the method for manufacturing the workpiece singulation 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 a workpiece having a front surface and a back surface opposite to the front surface. Step 2: A step of forming a groove on the surface of the workpiece, or a step of forming a modified region inside the workpiece Step 3: A step of grinding the workpiece, on the surface of which the protective sheet for workpiece processing is attached and on which grooves or modified regions are formed, from the back side to separate the workpiece into a plurality of individual workpieces, starting from the grooves or modified regions. Step 4: A step of peeling off the workpiece processing protection sheet from a plurality of workpiece individual pieces (i.e., a group of workpiece individual pieces).

[0234] Each step of the method for manufacturing the above-mentioned workpiece singulation will be described in detail below, using a wafer as a specific example of the workpiece and a chip as a specific example of the workpiece singulation.

[0235] (Process 1) In step 1, as shown in FIG. 3, the adhesive layer 30 of the protective sheet for workpiece processing 1 according to this embodiment is attached to the surface 100a of the wafer 100. The wafer may be a silicon wafer, or may be a wafer made of gallium arsenide, silicon carbide, lithium tantalate, lithium niobate, gallium nitride, indium phosphide, or the like, or a glass wafer or a reconstructed wafer. In this embodiment, the wafer is preferably a silicon wafer. The thickness of the wafer before grinding is not particularly limited, but is typically about 500 to 1000 μm.

[0236] In addition, a circuit is formed on the surface of the wafer. 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 constituting the circuit protection layer and thermally curing it. In addition, convex electrodes such as bumps and pillars may be formed on the circuit. The protective sheet for workpiece processing of the present invention is particularly suitable for use in protecting the surface of a workpiece having an uneven structure with a large difference in height on its surface, as described above. The difference in height of the uneven structure on the workpiece surface may be 20 μm or more, or may be 40 μm or more.

[0237] By attaching the protective sheet for workpiece processing to the surface 100a of the wafer, the surface of the wafer is sufficiently protected. Note that the excess protective sheet for workpiece processing remaining on the periphery of the wafer can be cut to fit the shape of the wafer and removed as needed.

[0238] This step 1 may be performed before or after step 2, which will be described later. For example, when forming a modified region on a wafer, it is preferable to perform step 1 before step 2, from the viewpoint of reducing the risk of the wafer being unintentionally divided when the protective sheet for workpiece processing is attached. On the other hand, when grooves are formed on the wafer surface 100a by dicing or the like, step 1 is performed after step 2. In other words, the protective sheet for workpiece processing is attached to the surface of the wafer on which grooves have been formed in step 2, which will be described later.

[0239] (Process 2) In step 2, grooves are formed on the surface of the wafer. Alternatively, modified regions are formed inside the wafer. In step 2, the grooves and modified regions are formed so as to follow the dividing lines that will be used when the wafer is divided into individual chips in step 3, which will be described later.

[0240] The grooves formed in this step 2 have a depth shallower than the thickness of the wafer. The grooves can be formed by dicing using a conventionally known wafer dicing device or the like.

[0241] The modified region is a brittle part of the wafer, and is the starting point for the wafer to be broken down into individual chips when the wafer becomes thinner due to grinding in the grinding process or when grinding force is applied.

[0242] The modified region is formed by irradiating the wafer with a laser focused on the interior of the wafer, and the modified region is formed inside the wafer. The laser irradiation may be performed from the front surface 100a side of the wafer or the back surface 100b side. In the embodiment for forming the modified region, when step 2 is performed after step 1 and the laser irradiation is performed from the wafer front surface 100a, the laser is irradiated onto the wafer through the workpiece processing protection sheet.

[0243] The wafer with the workpiece processing protection sheet attached and the grooves or modified regions formed thereon is placed on the chuck table and held by suction on the chuck table. At this time, the wafer is placed with its front side facing the table and suctioned. If the workpiece processing protection sheet has a buffer layer, the influence of foreign matter, etc. can be suppressed.

[0244] (Step 3) After steps 1 and 2, the back surface 100b of the wafer on the chuck table is ground to separate the wafer into a plurality of chips, thereby obtaining a group of chips.

[0245] When a groove is formed in the wafer, back grinding is performed to thin the wafer at least to the bottom of the groove, which turns the groove into a cut that penetrates the wafer, and the wafer is divided by the cut into individual chips.

[0246] On the other hand, when a modified region is formed, the grinding surface (wafer back surface) may be ground to the modified region, but it does not have to be ground exactly to the modified region. That is, the wafer may be ground to a position close to the modified region so that the wafer is broken and singulated into chips starting from the modified region. Furthermore, the actual singulation of the chips may be performed by applying a pick-up tape (described later) and then stretching the pick-up tape.

[0247] After the backside grinding with the grinding stone is completed, dry polishing may be carried out before the chip is picked up.

[0248] The shape of the individual chips may be square or may be an elongated shape such as a rectangle. The thickness of the individual chips is not particularly limited, but is preferably 5 to 100 μm, more preferably 10 to 90 μm, and particularly preferably 20 to 80 μm. LDBG makes it easy to make the thickness of the individual chips 50 μm or less, more preferably 10 to 45 μm. The size of the individual chips is not particularly limited, but the chip size is preferably 600 mm. 2Less than 400mm, preferably 2 Less than 120mm, more preferably 2 is less than.

[0249] In the protective sheet for workpiece processing according to this embodiment, the base material and intermediate layer have antistatic properties, so that even for thin and / or small chips, charging is suppressed during wafer processing, and adhesion of cut dust and foreign matter is reduced, thereby preventing cracks from occurring in the chips.

[0250] (Step 4) Next, the protective sheet for workpiece processing is peeled off from the individual wafers (i.e., a plurality of chips). This step is carried out, for example, by the following method.

[0251] When the adhesive layer of the protective sheet for workpiece processing is an energy ray-curable adhesive layer, the adhesive layer is cured and shrunk by irradiating it with energy rays, thereby reducing the adhesive strength to the adherend (diced wafer). For example, the irradiance of the energy rays is 120 to 280 mW / cm. 2 The energy ray dose is 100-1000mJ / cm 2 Preferably, the energy beam is ultraviolet light. Next, a pickup tape is attached to the backside of the individualized wafer, and the wafer is positioned and oriented so that it can be picked up. At this time, a ring frame arranged 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 the ring frame may be attached to the pickup tape simultaneously or at different times. Next, a tape peeling mechanism provided in a predetermined device peels the workpiece processing protective sheet from the multiple chips (i.e., chip group) held on the pickup tape. Since the workpiece processing protective sheet according to this embodiment has the above-mentioned configuration, the charging voltage when peeling off the workpiece processing protective sheet is preferably reduced to 150 V or less, and more preferably reduced to 100 V or less.

[0252] Since the workpiece processing protective sheet of this embodiment has the above-described configuration, even when the workpiece processing protective sheet is peeled off from the wafer, excessive peeling electrification is suppressed, and the adhesive layer is prevented from peeling off from the workpiece processing protective sheet and remaining on the wafer (glue residue).

[0253] Then, the multiple chips on the pickup tape are picked up and fixed onto a substrate or the like, and the chips are mounted.

[0254] The pickup tape is not particularly limited, but may be composed of, for example, a substrate and an adhesive sheet having an adhesive layer provided on one surface of the substrate.

[0255] Although the embodiments of the present invention have been described above, the present invention is not limited to the above-described embodiments and may be modified in various ways within the scope of the present invention. [Example]

[0256] The present invention will be described in more detail below using examples, but the present invention is not limited to these examples.

[0257] (Measurement of peeling electrification voltage) The backside of the wafer was ground in the following three ways, and the peeling plate voltage when peeling off the protection sheet for workpiece processing was measured. (1) Backside grinding using silicon wafers (hereinafter referred to as "normal BG"). (2) Using a bump wafer, the backside is ground and the wafer is simultaneously divided into individual pieces by the DBG method. (3) Using a bump wafer, the backside is ground and the wafer is simultaneously divided by the LDBG method. Each aspect will be described in detail below.

[0258] (Peeling charge voltage: normal BG) The protective sheets for workpiece processing prepared in the examples and comparative examples were attached to a bump wafer (height 80 μm, width φ100 μm, pitch 200 μm) with a diameter of 12 inches (300 mm) and a thickness of 775 μm using a backgrinding tape laminator (manufactured by Lintec Corporation, device name "RAD-3510F / 12").

[0259] Next, using a back grinding device (manufactured by Disco Corporation, device name "DGP8761"), grinding (including dry polishing) was carried out until the thickness reached 30 μm.

[0260] After the grinding process, ultraviolet light (illuminance 220 mW / cm) was irradiated through the substrate. 2 , light intensity 380mJ / cm 2 ) irradiation, and dicing tape (Adwill D-175, manufactured by Lintec Corporation) was attached to the opposite side of the semiconductor processing protective sheet. The semiconductor processing protective sheet was peeled from the silicon wafer using a wafer mounter (product name "RAD-2700F / 12," manufactured by Lintec Corporation) at a peeling speed of 600 mm / min and a temperature of 40°C. While peeling, the voltage was measured using a Prostat PFM-711A peeling charge measuring instrument, as shown in Figure 4. A measuring instrument 50 was placed 25 mm above the wafer 60, 25 mm away from the peeling interface between the wafer 60 and the workpiece processing protective sheet 1, and the voltage was measured and used as the peeling charge voltage value. Note that no static eliminator, such as an ionizer, was used.

[0261] (Delamination voltage: DBG) Grooves 70 μm deep were formed from the surface side of a bump wafer (height 80 μm, width φ100 μm, pitch 200 μm) with a diameter of 12 inches (300 mm) and a thickness of 775 μm, with a grid size of 10 mm × 10 mm. The protective sheets for workpiece processing prepared in the examples and comparative examples were attached to the surface side of the silicon wafer using a back-grinding tape laminator (manufactured by Lintec Corporation, device name "RAD-3510F / 12").

[0262] Next, a back grinding device (manufactured by Disco, device name "DGP8761") was used to grind (including dry polishing) the wafer to a thickness of 50 μm, dividing the wafer into multiple chips, and a group of chips aligned in a wafer shape as a whole was obtained on a protective sheet for workpiece processing.

[0263] After the grinding process, ultraviolet light (illuminance 220 mW / cm) was irradiated through the substrate. 2 , light intensity 380mJ / cm 2 ) irradiation was performed, and dicing tape (Adwill D-485H, manufactured by Lintec Corporation) was attached to the opposite side of the protective sheet for workpiece processing. Using a wafer mounter (product name "RAD-2700F / 12," manufactured by Lintec Corporation), the protective sheet for workpiece processing was peeled off from the chip group at a peeling speed of 600 mm / min and a temperature of 40°C. While peeling, the voltage was measured using a Prostat PFM-711A peeling charge measuring instrument, as shown in Figure 4. A measuring instrument 50 was placed 25 mm above the chip group 60, 25 mm away from the peeling interface between the chip group 60 and the protective sheet for workpiece processing 1, and the voltage was measured and used as the peeling charge voltage value. Note that no static electricity eliminator, such as an ionizer, was used.

[0264] (Peeling voltage: LDBG) The protective sheets for workpiece processing prepared in the examples and comparative examples were attached to a 12-inch (300 mm) diameter, 775 μm thick bump wafer (height 80 μm, width φ100 μm, pitch 200 μm) using a backgrinding tape laminator (manufactured by Lintec Corporation, device name "RAD-3510F / 12"). A lattice-shaped modified region was formed on the wafer using a laser saw (manufactured by Disco Corporation, device name "DFL7361"). The lattice size was 10 mm x 10 mm.

[0265] Next, a back grinding device (manufactured by Disco, device name "DGP8761") was used to grind (including dry polishing) the wafer to a thickness of 50 μm, dividing the wafer into multiple chips, and a group of chips aligned in a wafer shape as a whole was obtained on a protective sheet for workpiece processing.

[0266] After the grinding process, ultraviolet light (illuminance 220 mW / cm) was irradiated through the substrate. 2 , light intensity 380mJ / cm 2 ) irradiation was performed, and dicing tape (Adwill D-485H, manufactured by Lintec Corporation) was attached to the opposite side of the semiconductor processing protective sheet. Using a wafer mounter (product name "RAD-2700F / 12," manufactured by Lintec Corporation), the workpiece processing protective sheet was peeled off from the chip group at a peeling speed of 600 mm / min and a temperature of 40°C. While peeling, the voltage was measured using a Prostat peeling charge measuring instrument PFM-711A, as shown in Figure 4. A measuring instrument 50 was placed 25 mm away from the peeling interface between the chip group 60 and the workpiece processing protective sheet 1, 25 mm above the chip group 60, and the voltage was measured and used as the peeling charge voltage value. Note that no static electricity eliminator, such as an ionizer, was used.

[0267] (embeddability) A workpiece processing protection sheet was attached to a bump wafer on which convex electrodes (height 80 μm, width φ100 μm, pitch 200 μm) were formed using a laminator RAD-3510 at an attachment speed of 5 mm / sec, at room temperature, and under a pressure of 0.3 MPa. The presence or absence of air bubbles between the bumps was confirmed using a digital microscope (product name "VHX-1000", manufactured by KEYENCE Corporation) and evaluated according to the following criteria. Good: No bubbles observed Pass: Bubbles are found at the base of the bump, but they are not connected to the bubbles at the base of adjacent bumps (the bubbles exist independently). Poor: Air bubbles are found at the base of the bump and are connected to the air bubbles at the base of the adjacent bump (air bubbles are continuous).

[0268] (Wafer contamination) The individual chips obtained from the above evaluation of peeling electrification voltage (DGB and LDBG) were observed with a digital microscope (product name "VHX-1000", manufactured by KEYENCE Corporation) to check for the presence or absence of contamination by adhesive or antistatic agent on the chip surface. When no contamination was found in either DBG or LDBG, the chip was evaluated as "good."

[0269] (Intermediate layer compatibility) The state of the intermediate layer was visually checked, and when there was no whitening, it was evaluated as "good."

[0270] Example 1 (1) Preparation of a substrate with a coating layer containing an antistatic agent A 50 μm thick PET (polyethylene terephthalate) film (Toyobo Cosmoshine A4300) with a primer layer on both sides was used as the support material. The antistatic layer-forming composition "UVH515" was applied to one side of the support material so that the thickness after drying would be 150 nm. After drying at 50°C for 1 minute, the film was exposed to ultraviolet light (light intensity: 100 mJ / cm). 2 ) to obtain a substrate with an antistatic agent-containing coating layer. Note that "UVH515" is a polythiophene-containing ultraviolet-curable resin composition (manufactured by Idemitsu Technofine Co., Ltd.), which contains poly(3,4-ethylenedioxythiophene) as an antistatic agent and an acrylic ultraviolet-curable resin as a resin binder.

[0271] (2) Creating a buffer layer (Synthesis of urethane acrylate oligomers) A urethane acrylate oligomer (UA-1) with a weight-average molecular weight (Mw) of approximately 5,000 was obtained by reacting a terminal isocyanate urethane prepolymer obtained by reacting a polyester diol with isophorone diisocyanate with 2-hydroxyethyl acrylate.

[0272] (Preparation of buffer layer composition) A buffer layer composition was prepared by blending 50 parts by mass of the urethane acrylate oligomer (UA-1) synthesized above, 40 parts by mass of isobornyl acrylate (IBXA), and 20 parts by mass of 2-hydroxy-3-phenoxypropyl acrylate (HPPA), and further blending 1.0 part by mass of 2-hydroxy-2-methyl-1-phenyl-propan-1-one (manufactured by IGM Resin, product name "Omnirad1173") as a photopolymerization initiator.

[0273] (Creating a substrate with a buffer layer) The buffer layer composition was applied to the release-treated surface of a release sheet (manufactured by Lintec Corporation, product name "SP-PET381031") to form a coating film. Next, the coating film was irradiated with ultraviolet light to semi-cure the coating film, forming a buffer layer-forming film with a thickness of 30 μm.

[0274] The ultraviolet irradiation was performed using a belt conveyor type ultraviolet irradiation device (manufactured by Eye Graphics, device name "US2-0801") and a high-pressure mercury lamp (manufactured by Eye Graphics, device name "H08-L41"), with a lamp height of 230 mm, an output of 80 mW / cm, a light wavelength of 365 nm, and an illuminance of 90 mW / cm. 2 , irradiation amount 50mJ / cm 2 The irradiation conditions were as follows:

[0275] The surface of the buffer layer-forming film thus formed was then bonded to the support side of the substrate with the antistatic agent-containing coating layer, and ultraviolet light was again irradiated from the release sheet side of the buffer layer-forming film to completely harden the buffer layer-forming film and form a buffer layer having a thickness of 30 μm. The ultraviolet light irradiation was carried out using the above-mentioned ultraviolet light irradiation device and high-pressure mercury lamp, with a lamp height of 220 mm, an equivalent output of 120 mW / cm, and an illuminance of 160 mW / cm at a light wavelength of 365 nm. 2 , irradiation amount 650mJ / cm 2 The irradiation conditions were as follows:

[0276] (3) Formation of the middle class A non-energy ray curable acrylic copolymer (a) (Mw: 600,000) was obtained by copolymerizing 91 parts by mass of n-butyl acrylate (BA) and 9 parts by mass of acrylic acid (AA).

[0277] Separately from the acrylic copolymer (a), an energy ray-curable acrylic copolymer (b) (Mw: 100,000) was obtained by copolymerizing 62 parts by mass of n-butyl acrylate (BA), 10 parts by mass of methyl methacrylate (MMA), and 28 parts by mass of 2-hydroxyethyl acrylate (2HEA). This acrylic polymer was then reacted with 2-methacryloyloxyethyl isocyanate (MOI) so that it was added to 80 equivalents of the total hydroxyl groups (100 equivalents) of the acrylic polymer.

[0278] To 100 parts by mass of non-energy ray curable acrylic copolymer (a), 3 parts by mass of energy ray curable acrylic copolymer (b) was added, 3.36 parts by mass of an isocyanate crosslinking agent (manufactured by Tosoh Corporation, product name "Coronate L") was added as a crosslinking agent, 3.71 parts by mass of 1-hydroxycyclohexyl phenyl ketone (manufactured by IGM Resin, Omnirad 184) was added as a photoinitiator, and 2.74 parts by mass of an antistatic agent (manufactured by Nippon Nyukazai Co., Ltd., AS100) was added, and the mixture was adjusted to 37% solids with toluene and stirred for 30 minutes to prepare a composition for an intermediate layer.

[0279] Next, the prepared solution of the intermediate layer composition was applied to a PET-based release film (SP-PET381031, manufactured by Lintec Corporation, thickness 38 μm) and dried to form a 50 μm-thick intermediate layer, which was then bonded to the antistatic agent-containing coating layer of the substrate, and the solution of the intermediate layer composition was further applied to a PET-based release film (SP-PET381031, manufactured by Lintec Corporation, thickness 38 μm) again and bonded to the above intermediate layer, thereby forming a substrate A with an intermediate layer, thickness 100 μm.

[0280] (4) Formation of adhesive layer (Preparation of Composition for Pressure-Sensitive Adhesive Layer) An energy ray-curable acrylic copolymer (c) (Mw: 500,000) was obtained by reacting an acrylic polymer obtained by copolymerizing 52 parts by mass of n-butyl acrylate (BA), 20 parts by mass of methyl methacrylate (MMA), and 28 parts by mass of 2-hydroxyethyl acrylate (2HEA) with 2-methacryloyloxyethyl isocyanate (MOI) so that it added to 90 equivalents of the total hydroxyl groups (100 equivalents) of the acrylic polymer.

[0281] 100 parts by mass of this energy ray-curable acrylic copolymer (c) was blended with 12 parts by mass of a multifunctional urethane acrylate (manufactured by Mitsubishi Chemical Corporation, Shikoh UT-4332), which is an energy ray-curable compound, 1.1 parts by mass of an isocyanate-based crosslinking agent (manufactured by Mitsui Chemicals, Inc., product name Takenate D-101E), and 1 part by mass of bis(2,4,6-trimethylbenzoyl)phenylphosphine oxide (manufactured by IGM Resin, Omnirad TPO) as a photopolymerization initiator, and the blend was diluted with methyl ethyl ketone to prepare a coating liquid of a pressure-sensitive adhesive layer composition with a solids concentration of 34% by mass.

[0282] (5) Preparation of protective sheet for workpiece processing The coating liquid of the adhesive layer composition obtained above was applied to the release-treated surface of a release sheet (manufactured by Lintec Corporation, product name "SP-PET381031") and dried by heating to form an adhesive layer 10 μm thick on the release sheet.

[0283] Thereafter, a pressure-sensitive adhesive layer was attached to the surface of the intermediate layer-attached substrate A to prepare a protective sheet for workpiece processing. The obtained protective sheet for workpiece processing was evaluated as described above. The results are shown in Table 1.

[0284] Example 2 The same operations as in Example 1 were carried out, except that 34 parts by mass of the energy ray-curable acrylic copolymer (b) was added to 100 parts by mass of the non-energy ray-curable acrylic copolymer (a) in "3. Preparation of intermediate layer" of Example 1. The results are shown in Table 1.

[0285] Example 3 The same operations as in Example 1 were carried out except that in "3. Preparation of intermediate layer" of Example 1, a 50 μm thick intermediate layer was laminated only once instead of twice, and the thickness of the intermediate layer was set to 50 μm. The results are shown in Table 1.

[0286] Example 4 In "3. Preparation of intermediate layer" of Example 1, the same procedure as in Example 1 was carried out except that the intermediate layer having a thickness of 50 μm was laminated six times instead of twice, and the thickness of the intermediate layer was set to 300 μm. The results are shown in Table 1.

[0287] Comparative Example 1 The same operations as in Example 1 were carried out except that the pressure-sensitive adhesive layer was not provided and the operations up to (3) above were carried out and a wafer was attached onto the intermediate layer. The results are shown in Table 1.

[0288] Comparative Example 2 The same procedure as in Example 1 was carried out, except that no antistatic agent-containing coating layer was provided and the amount of antistatic agent added to the intermediate layer was 6 parts by mass. The results are shown in Table 1.

[0289] Comparative Example 3 The same procedure as in Example 1 was carried out, except that the intermediate layer was not provided and the pressure-sensitive adhesive layer was directly attached to the antistatic agent-containing coating layer. The results are shown in Table 1.

[0290] Comparative Example 4 The same operations as in Example 1 were carried out except that no antistatic agent was added to the intermediate layer and a substrate not having an antistatic agent-containing coating layer was used. The results are shown in Table 1.

[0291] Comparative Example 5 The same procedure as in Example 1 was carried out, except that no antistatic agent was added to the intermediate layer in Example 1. The results are shown in Table 1.

[0292] Comparative Example 6 In Example 1, the substrate was not provided with an antistatic agent-containing coating layer, but an intermediate layer was provided on the substrate. Next, Idemitsu Kosan's "UVH515" was applied to the release-treated surface of a release sheet (manufactured by Lintec Corporation, product name "SP-PET381031") so that the thickness after drying would be 3 μm, and after drying at 50°C for 1 minute, it was irradiated with ultraviolet light (light intensity: 100 mJ / cm 2 The same operations as in Example 1 were carried out, except that the antistatic agent-containing coating layer obtained by the above-mentioned procedure was laminated to the intermediate layer, and then a pressure-sensitive adhesive layer was laminated on top of that. The results are shown in Table 1.

[0293] Comparative Example 7 The same procedure as in Comparative Example 5 was carried out, except that the thickness of the intermediate layer not containing an antistatic agent was set to 300 μm. The results are shown in Table 1.

[0294] [Table 1] [Explanation of symbols]

[0295] 1...Protection sheet for workpiece processing 10...Base material 10a...Support material 10b...Antistatic agent-containing coating layer 20...Middle class 30...Adhesive layer 40...Buffer layer 50...Charged voltage measuring device 60... Wafer or group of chips

Claims

1. A protective sheet for workpiece processing having an antistatic substrate, an intermediate layer disposed on the substrate, and an adhesive layer disposed on the intermediate layer, The intermediate layer is a protective sheet for workpiece processing that contains an antistatic agent.

2. the substrate has a support material and an antistatic agent-containing coating layer, 2. The protective sheet for workpiece processing according to claim 1, wherein the intermediate layer is disposed on the antistatic agent-containing coating layer.

3. A protective sheet for workpiece processing as described in claim 1, which is attached to the surface of a workpiece in a process of dividing a workpiece into individual workpieces by grinding the back surface of the workpiece having a groove formed on the surface or a modified region formed inside.

4. The protective sheet for workpiece processing according to claim 1 , further comprising a buffer layer on the side opposite to the intermediate layer of the substrate.

5. 2. The protective sheet for workpiece processing according to claim 1, wherein the distance between the surface of the adhesive layer that is attached to the workpiece and the surface of the base material that faces the intermediate layer is 50 [mu]m or more.

6. The protective sheet for workpiece processing according to claim 1 , wherein the intermediate layer contains an acrylic polymer.

7. A step of attaching the workpiece processing protection sheet according to any one of claims 1 to 6 to the surface of a workpiece having a front and back surface; forming a groove on the surface of the workpiece or forming a modified region inside the workpiece; a step of grinding the workpiece, on the surface of which the workpiece processing protection sheet is attached and on which the grooves or modified regions are formed, from the back side to separate the workpiece into a plurality of workpiece individual pieces, starting from the grooves or modified regions; and a step of peeling off the workpiece processing protection sheet from the plurality of workpieces.

8. The method for producing individual workpieces according to claim 7 , wherein the workpiece has an uneven structure on the surface with a height difference of 20 μm or more.

Images