Adhesive composition and adhesive tape

Abstract

To eliminate adhesive residue on workpieces such as semiconductor chips and wafers and poor edge appearance in adhesive tapes used as backgrinding tapes and dicing tapes. The pressure-sensitive adhesive composition according to the present invention has a storage modulus G'(23) at 23°C of 1.0 x 10 5 Pa or more, and the storage modulus G'(50) at 50°C is 2.5 × 10 5 The elastic modulus of the acrylic resin is 0.5 or more at 60°C, and the tan δ of the dynamic viscoelasticity at 60°C is 0.5 or more. The elastic modulus of the acrylic resin is 0.5 or more at 60°C.

Description

[Technical Field]

[0001] The present invention relates to an adhesive tape preferably used as a workpiece processing tape to which a workpiece such as a semiconductor wafer (hereinafter sometimes referred to as "workpiece") is attached and held when the workpiece is subjected to temporary surface protection, polishing, dicing, etc. The present invention also relates to an adhesive composition preferably used for the adhesive tape. [Background technology]

[0002] Semiconductor wafers, such as silicon and gallium arsenide, are manufactured in large diameters. After circuits are formed on the surface of the semiconductor wafer, the backside is ground to a specified thickness, and the wafer is cut and separated (diced) into small element pieces (semiconductor chips), before being transferred to the next process, the bonding process. Various types of adhesive tapes are used in this series of processes.

[0003] In the backgrinding process, an adhesive tape called backgrind tape is used to hold the wafer during grinding and protect the circuit surface from grinding debris. Following the backgrinding process, circuit formation may also be performed on the ground surface, and in this case, the wafer is protected and fixed with adhesive tape. Surface protection tapes used during backgrinding, such as backgrind tape, consist of a substrate and an adhesive layer with pressure-sensitive adhesive properties. To reliably protect the circuit surface, adhesive tapes with relatively soft adhesives that have high stress relaxation properties are sometimes used.

[0004] The adhesive tape used in the dicing process, also known as dicing tape, consists of a substrate and a pressure-sensitive adhesive layer, and is used to fix a workpiece such as a semiconductor wafer when dicing the workpiece and to hold the chips after dicing. After dicing, adhesive tapes with a relatively soft substrate are sometimes used to facilitate expansion to space the chips apart.

[0005] In recent years, semiconductor chips with protrusions as three-dimensional structures have become commonplace, in addition to semiconductor chips with two-dimensional circuit patterns. For example, in the manufacture of semiconductor devices, a technique called wireless bonding is used to mount individual chips diced onto a substrate. This technique establishes electrical connections between the chip and the substrate without using thin metal wires. For example, electrical connections are established by contacting protruding electrodes called bumps on the chip circuit surface with electrodes on the substrate. This mounting method, known as face-down mounting or flip-chip mounting, contributes to the miniaturization of devices.

[0006] In one example of a method for manufacturing chips with such protrusions, a circuit is formed on the surface of a semiconductor wafer, protrusions are formed on the circuit surface, a backgrinding tape is applied to the surface, the back surface is ground to adjust the thickness, and the semiconductor wafer is then held on a dicing tape and diced into individual chips.

[0007] On the surface of a semiconductor wafer, protrusions cause minute unevenness of about 5 to 100 μm. Backgrinding tape is required to be able to conform to these uneven surfaces and reliably protect the circuit surface. If the conformability of the backgrinding tape is insufficient, grinding debris may penetrate the circuit surface during backgrinding, contaminating or damaging the circuit. Therefore, backgrinding tape is required to be able to embed fine uneven surfaces.

[0008] As a backgrinding tape for semiconductor wafers with such unevenness, a pressure-sensitive adhesive tape consisting of a substrate, an intermediate layer, and an adhesive layer is known (Patent Documents 1 and 2). In this pressure-sensitive adhesive tape, the intermediate layer absorbs the unevenness of the wafer surface and conforms to the circuit surface. However, in the above-mentioned documents, most of the intermediate layers are made of polyolefin polymers, and most of the adhesive layers are made of acrylic polymers. Polyolefin polymers and acrylic polymers generally have low affinity. For this reason, when peeling the backgrinding tape from the circuit surface of the semiconductor wafer, peeling occurs between the intermediate layer and the adhesive layer, which can cause the problem of the adhesive remaining on the circuit surface of the semiconductor wafer.

[0009] Also known as backgrinding tapes are adhesive tapes with a two-layer structure consisting of a substrate and an adhesive layer. For such adhesive tapes, thickening the adhesive layer or making the adhesive layer relatively soft is considered in order to conform to the irregularities on the semiconductor wafer surface. However, such adhesive tapes can cause problems such as poor appearance and adhesive residue remaining on the circuit surface of the semiconductor wafer.

[0010] Adhesive tapes are generally wound into rolls for storage and transport. During this process, pressure is applied to the tape, causing the adhesive layer and some of the intermediate layer to leak onto the edge of the roll. This leakage of resin components becomes particularly pronounced during summer storage or transport at sea, where the tape may be exposed to temperatures of approximately 40°C. Resin components leaking onto the edge of the roll can cause poor edge appearance and lead to the adhesion of dust and other particles, potentially contaminating semiconductor wafers. Furthermore, making the adhesive layer relatively soft improves its ability to conform to the irregularities on the semiconductor wafer surface. However, when the adhesive tape is peeled off from the semiconductor wafer surface, the adhesive layer stretches and breaks, leaving some of the adhesive (glue residue) on the wafer circuit surface, potentially contaminating the circuit surface. [Prior art documents] [Patent documents]

[0011] [Patent Document 1] Patent No. 3773358 [Patent Document 2] Patent No. 4918181 Summary of the Invention [Problem to be solved by the invention]

[0012] The present invention aims to eliminate adhesive residue on a workpiece and poor appearance at the edge of an adhesive tape used as a backgrinding tape or dicing tape. [Means for solving the problem]

[0013] Generally, when applying an adhesive tape to an uneven surface, the adhesive tape is heated to approximately 40 to 60°C to improve the fluidity and embedding ability of the adhesive layer (or intermediate layer) before application. Meanwhile, leakage of the adhesive (or intermediate layer) during storage, which is a cause of poor edge appearance, is caused by the fluidity of the adhesive (or intermediate layer) at room temperature to approximately 40°C. Therefore, the present inventors conducted a detailed study on the viscoelastic behavior of the adhesive composition constituting the adhesive layer (or intermediate layer). As a result, they found that the above-mentioned problems could be solved if an acrylic polymer could be realized that has elasticity to the extent that fluidity is suppressed at room temperature to approximately 40°C, and that has appropriate fluidity and shape retention under heating, leading to the completion of the present invention. The gist of the present invention, which aims to solve these problems, is as follows.

[0014] (1) The storage modulus G'(23) at 23°C is 1.0 × 10 5 Pa or more, Storage modulus G'(50) at 50°C is 2.5×10 5 Pa or less, The dynamic viscoelasticity tanδ at 60°C is 0.5 or more, A pressure-sensitive adhesive composition comprising an acrylic polymer as a main component. (2) The pressure-sensitive adhesive composition according to (1), wherein the ratio of the storage modulus G'(60) at 60°C to the storage modulus G'(23) at 23°C, G'(60) / G'(23), is 0.1 to 0.7. (3) An adhesive tape comprising a substrate and an adhesive layer, the adhesive layer comprising the adhesive composition according to (1) or (2). (4) A pressure-sensitive adhesive tape comprising a substrate, a pressure-sensitive adhesive layer, and an intermediate layer between the substrate and the pressure-sensitive adhesive layer, wherein the intermediate layer comprises the pressure-sensitive adhesive composition according to (1) or (2). [Effects of the Invention]

[0015] Acrylic polymers used in adhesives and the like generally exhibit a peak tan δ in the low-temperature range of approximately -50 to 0°C, and tan δ decreases as the temperature increases. Furthermore, the modulus of elasticity decreases as the temperature increases. The present inventors conducted extensive research into the viscoelasticity of acrylic polymers, which are the main component of adhesive compositions, and succeeded in designing an acrylic polymer that has sufficient elasticity to suppress fluidity at room temperature to approximately 40°C, but has adequate fluidity and shape retention at elevated temperatures. The use of such an acrylic polymer as the main component of the adhesive composition facilitates control of the fluidity of the adhesive layer (or intermediate layer) during application and storage, providing an adhesive tape that conforms to the uneven surface of a workpiece during application and exhibits minimal leakage of the adhesive composition during storage. DETAILED DESCRIPTION OF THE INVENTION

[0016] The pressure-sensitive adhesive tape according to the present invention will be specifically described below. First, the main terms used in this specification will be explained. In this specification, for example, "(meth)acrylate" is used as a term indicating both "acrylate" and "methacrylate," and the same applies to other similar terms.

[0017] The term "adhesive tape" refers to a laminate comprising a substrate and a pressure-sensitive adhesive layer, and does not preclude the inclusion of other constituent layers. For example, the tape may have an intermediate layer between the substrate and the pressure-sensitive adhesive layer. A primer layer may be formed on the substrate surface on the pressure-sensitive adhesive layer side for the purposes of improving adhesion between the substrate surface and the pressure-sensitive adhesive layer or between the substrate surface and the intermediate layer, or preventing migration of low-molecular-weight components. A release film may be laminated on the surface of the pressure-sensitive adhesive layer to protect the pressure-sensitive adhesive layer until use. The substrate may be a single layer, or may be a multilayer comprising a functional layer such as a buffer layer. The pressure-sensitive adhesive composition of the present invention described below is preferably used in the pressure-sensitive adhesive layer or intermediate layer of a pressure-sensitive adhesive tape.

[0018] Backgrind tape refers to an adhesive tape used to protect the circuit surface of a semiconductor wafer during backgrinding. Dicing tape refers to an adhesive tape used to hold a wafer and chips together when the wafer is diced into individual chips for each circuit. The "front surface" of a semiconductor wafer refers to the surface on which circuits are formed, and the "back surface" refers to the surface on which no circuits are formed.

[0019] (Adhesive composition) The adhesive composition of the present invention contains an acrylic polymer and satisfies the following viscoelastic behavior. The viscoelasticity of the adhesive composition is based on the solid component, and when the adhesive composition is in solution form, it means the viscoelasticity of the adhesive substance obtained by drying the solution. When the adhesive composition consists only of an acrylic polymer, it means the properties of the acrylic polymer itself. When the adhesive composition is energy ray-curable, the following physical properties refer to the physical properties before the adhesive composition is cured by energy ray irradiation.

[0020] The storage modulus G'(23) of the adhesive composition at 23°C is preferably 1.0 x 10 5 Pa or more, and more preferably 1.2 × 10 5 Pa or more, more preferably 1.3×10 5 ~8.0×10 5Pa, and particularly preferably 1.7 × 10 5 ~7.0×10 5 It is Pa.

[0021] When the storage modulus G'(23) of the pressure-sensitive adhesive composition is within the above range, the fluidity is suppressed at room temperature to about 40° C. As a result, even when the pressure-sensitive adhesive tape is stored and transported in a roll form, the pressure-sensitive adhesive composition does not leak from the end faces of the roll, and the appearance of the end faces of the roll can be maintained in good condition.

[0022] The storage modulus G'(50) of the adhesive composition at 50°C is preferably 2.5 × 10 5 Pa or less, and more preferably 2.4 × 10 5 Pa or less, and more preferably 7.0 × 10 4 ~2.3×10 5 Pa, and particularly preferably 8.0×10 4 ~2.2×10 5 It is Pa.

[0023] When the storage modulus G'(50) of the adhesive composition is within the above range, the adhesive tape has appropriate fluidity when heated to about 40 to 60°C and applied, and the adhesive composition has improved embedding properties into the irregularities on the semiconductor wafer surface.

[0024] The tan δ of the dynamic viscoelasticity of the adhesive composition at 60°C (hereinafter sometimes referred to as "tan δ(60)") is preferably 0.5 or more, more preferably 0.51 or more, even more preferably 0.52 to 0.8, and particularly preferably 0.53 to 0.75.

[0025] The tan δ of the pressure-sensitive adhesive composition is obtained as follows: a sample of a predetermined shape is obtained from the pressure-sensitive adhesive composition, a strain of 1 Hz frequency is applied to this sample, the storage modulus G' and the loss modulus G'' are measured at each measurement temperature, and the loss tangent tan δ (G'' / G') at 60°C is calculated from these values ​​to obtain tan δ(60).

[0026] By having tan δ(60) within the above range, the adhesive layer or intermediate layer, once deformed, tends to maintain its shape after deformation. As a result, the adhesive layer or intermediate layer embedded in the irregularities on the semiconductor wafer surface maintains its shape, preventing the penetration of cutting water into the wafer surface and reducing contamination and damage to the circuit.

[0027] Furthermore, the pressure-sensitive adhesive composition of the present invention preferably satisfies the following viscoelasticity. The ratio of the storage modulus G'(60) at 60°C to the storage modulus G'(23) at 23°C of the pressure-sensitive adhesive composition, G'(60) / G'(23), is preferably 0.1 to 0.7, more preferably 0.2 to 0.6, even more preferably 0.21 to 0.45, and particularly preferably 0.23 to 0.41.

[0028] When G'(60) / G'(23) is in the above range, the adhesive layer or intermediate layer does not become excessively fluid even when heated, so the adhesive composition does not penetrate into the fine structure of the circuit surface. Therefore, even when the adhesive tape is peeled off after the specified process is completed, the adhesive composition does not remain on the fine structure of the circuit surface.

[0029] Furthermore, the adhesive composition has multiple, preferably two, maximum values ​​of tan δ of dynamic viscoelasticity. When the zwitterion-containing acrylic polymer described below is used as the acrylic polymer that is the main component of the adhesive composition, the polymer contains both a moiety corresponding to a normal adhesive polymer and a moiety derived from a zwitterion-containing unit. It is believed that the multiple maximum values ​​of tan δ appear because the viscoelastic behavior of the two polymers is different. In a preferred embodiment, the maximum value of tan δ on the low temperature side appears in the range of -50 to 0°C, and the maximum value of tan δ on the high temperature side appears in the range of 10 to 60°C.

[0030] Because it has a maximum value of tan δ at low temperatures, it has excellent adhesive strength at room temperature, especially initial adhesive strength. Furthermore, because it has a maximum value of tan δ at high temperatures, the adhesive layer maintains its deformation after heating the adhesive tape to about 40-60°C and embedding the adhesive into the irregularities on the semiconductor wafer surface, reducing contamination and damage to the circuit surface caused by cutting water.

[0031] The adhesive composition according to the present invention contains an acrylic polymer as a main component. The acrylic polymer is a polymer whose main component is a repeating unit derived from (meth)acrylic acid or an ester derivative thereof, and may be a modified polymer. The physical properties of the adhesive composition described above are mainly attributable to the acrylic polymer. Therefore, the adhesive composition of the present invention can be obtained by selecting an acrylic polymer with appropriate viscoelasticity. Acrylic polymers that are preferably used are described below, but these are non-limiting examples, and the acrylic polymer of the present invention is not limited to those described below. Other acrylic polymers that can be used in the present invention can be obtained by appropriately adjusting the polymer structure based on the following description and common technical knowledge.

[0032] The pressure-sensitive adhesive composition according to the present invention preferably contains, as the acrylic polymer, an acrylic polymer having a repeating unit containing a zwitterion structure and a repeating unit derived from a (meth)acrylic monomer. Hereinafter, the repeating unit containing the zwitterion structure will be referred to as a "zwitterion-containing unit," the repeating unit derived from a (meth)acrylic monomer will be referred to as a "(meth)acrylic unit," and a polymer containing these repeating units will be referred to as a "zwitterion-containing acrylic polymer."

[0033] (Zwitterion-containing acrylic polymer) The zwitterion-containing acrylic polymer contains a repeating unit containing a zwitterion structure. Here, the zwitterion structure refers to a polar structure containing a positive charge and a negative charge. The zwitterion-containing acrylic polymer preferably has a zwitterion structure in the side chain of the polymer. The zwitterion structure is not particularly limited as long as it has a polar structure. However, from the viewpoint of convenience in production, the positive charge is preferably a positive charge derived from a quaternary ammonium, a nitrogen-containing heterocycle, or a quaternary phosphonium, and the negative charge is a sulfo residue (SO3) derived from a sultone. - ) The structure of the main chain of the polymer is not particularly limited, but preferably comprises a carbon skeleton. Therefore, a preferred zwitterion-containing unit is represented by the following formula (1). In the following, an example in which the positive charge is derived from a quaternary ammonium will be described, but the positive charge may also be derived from a nitrogen-containing heterocycle or a quaternary phosphonium.

[0034] [ka]

[0035] In formula (1), R 1 represents a hydrogen atom or a methyl group, and R 2 , R 3 R each independently represents a hydrogen atom, an alkyl group having 1 to 10 carbon atoms with or without an ether bond, a cyanoalkyl group having 2 to 11 carbon atoms with or without an ether bond, an alkenyl group having 2 to 10 carbon atoms with or without an ether bond, or an aryl group having 6 to 20 carbon atoms with or without a substituent. 2 and R 3 may be bonded to each other to form a ring. m is an integer of 2 to 5, preferably 3 or 4.

[0036] R 2 , R 3The number of carbon atoms in the alkyl group having 1 to 10 carbon atoms, which may or may not have an ether bond, is preferably 1 to 8, and more preferably 1 to 5. Examples of the alkyl group not having an ether bond include a methyl group, an ethyl group, an n-propyl group, an n-butyl group, an n-pentyl group, and an n-hexyl group. Examples of the alkyl group having an ether bond include groups represented by the following formula (2) or (3).

[0037] [ka]

[0038] In formula (2), R 4 represents an alkyl group having 1 to 8 carbon atoms, and Z 1 represents an alkylene group having 2 to 9 carbon atoms, and R 4 and Z 1 The total number of carbon atoms is 3 to 10. * represents a bond. In formula (3), R 5 represents an alkyl group having 1 to 6 carbon atoms, and Z 2 represents an alkylene group having 2 to 7 carbon atoms, and Z 3 represents an alkylene group having 2 to 7 carbon atoms, and R 5 , Z 2 , Z 3 The total number of carbon atoms is 5 to 10. * represents a bond.

[0039] R 2 , R 3 The number of carbon atoms in the cyanoalkyl group having 2 to 11 carbon atoms, which may or may not have an ether bond, is preferably 2 to 9, and more preferably 2 to 6. Examples of the cyanoalkyl group not having an ether bond include a cyanomethyl group, a 2-cyanoethyl group, a 3-cyanopropyl group, a 4-cyanobutyl group, and a 6-cyanohexyl group. Examples of the cyanoalkyl group having an ether bond include groups represented by the following formula (4) or (5).

[0040] [ka]

[0041] In formula (4), R 6 represents a cyanoalkyl group having 2 to 9 carbon atoms, and Z 4 represents an alkylene group having 2 to 9 carbon atoms, and R 6 and Z 4 The total number of carbon atoms is 4 to 11. * represents a bond. In formula (5), R 7 represents a cyanoalkyl group having 2 to 7 carbon atoms, and Z 5 represents an alkylene group having 2 to 7 carbon atoms, and Z 6 represents an alkylene group having 2 to 7 carbon atoms, and R 7 , Z 5 , Z 6 The total number of carbon atoms is 6 to 11. * represents a bond.

[0042] R 2 , R 3 The number of carbon atoms in the alkenyl group having 2 to 10 carbon atoms, which may or may not have an ether bond, is preferably 2 to 9, and more preferably 2 to 6. Examples of the alkenyl group not having an ether bond include a vinyl group, an allyl group, a 1-butenyl group, a 2-butenyl group, and a 1-pentenyl group. Examples of the alkenyl group having an ether bond include groups represented by the following formula (6) or (7).

[0043] [ka]

[0044] In formula (6), R 8 represents an alkenyl group having 2 to 8 carbon atoms, and Z 7 represents an alkylene group having 2 to 8 carbon atoms, and R 8 and Z 7 The total number of carbon atoms is 4 to 10. * represents a bond. In formula (7), R 9 represents an alkenyl group having 2 to 6 carbon atoms, and Z 8represents an alkylene group having 2 to 6 carbon atoms, and Z 9 represents an alkylene group having 2 to 6 carbon atoms, and R 9 , Z 8 , Z 9 The total number of carbon atoms is 6 to 10. * represents a bond.

[0045] R 2 , R 3 The aryl group having 6 to 20 carbon atoms, which may or may not have a substituent, preferably has 6 to 10 carbon atoms. Examples of the unsubstituted aryl group include a phenyl group, a 1-naphthyl group, and a 2-naphthyl group. Examples of the substituent of the aryl group having a substituent include an alkyl group having 1 to 6 carbon atoms, such as a methyl group or an ethyl group; an alkoxy group having 1 to 6 carbon atoms, such as a methoxy group or an ethoxy group; and a halogen atom, such as a fluorine atom or a chlorine atom.

[0046] R 2 and R 3 Examples of the ring formed by bonding include a pyrrolidine ring, a piperidine ring, and a morpholine ring. In formula (1), A 1 represents a divalent group represented by any one of the following formulas (8) to (10).

[0047] [ka]

[0048] In formulas (8) to (10), A 2 and A 3 each independently represents an alkylene group having 1 to 10 carbon atoms, and n represents an integer of 1 to 10. *1 represents a bond to a carbon atom, and *2 represents a bond to a nitrogen atom.

[0049] A 2 , A 3 The alkylene group having 1 to 10 carbon atoms preferably has 1 to 8 carbon atoms, and more preferably has 1 to 6 carbon atoms. Examples of the alkylene group having 1 to 10 carbon atoms include linear alkylene groups such as methylene, ethylene, trimethylene, tetramethylene, and pentamethylene; and branched alkylene groups such as propane-1,2-diyl and butane-1,3-diyl. n is an integer of 1 to 10, and an integer of 1 to 5 is preferred.

[0050] In addition, when the positive charge of the zwitterion structure is derived from a nitrogen-containing heterocycle or a quaternary phosphonium, the quaternary ammonium moiety (N + R 2 R 3 ) is substituted with the structures of the following formulae (11) to (14).

[0051] [ka]

[0052] (In the formula, R 10 represents an alkyl group having 1 to 10 carbon atoms, which may or may not have an ether bond, a cyanoalkyl group having 2 to 11 carbon atoms, which may or may not have an ether bond, or an alkenyl group having 2 to 10 carbon atoms, which may or may not have an ether bond; R 11 represents a hydrogen atom or an alkyl group having 1 to 10 carbon atoms, which may or may not have an ether bond, provided that R 10 or R 11 Either atom or group is absent and is in a radical state, representing a bond to A1. * represents (CH2) m represents a bond to .)

[0053] [ka]

[0054] (In the formula, R 12 ~R 16 each independently represents a hydrogen atom or an alkyl group having 1 to 10 carbon atoms and having or not having an ether bond, provided that R12 ~R 16 Any one of the atoms or groups is absent and is in a radical state, representing a bond to A1. * represents (CH2) m represents a bond to .)

[0055] [ka]

[0056] (In the formula, R 17 ~R 21 each independently represents a hydrogen atom or an alkyl group having 1 to 10 carbon atoms and having or not having an ether bond, provided that R 17 ~R 21 Any one of the atoms or groups is absent and is in a radical state, representing a bond to A1. * represents (CH2) m represents a bond to .)

[0057] [ka]

[0058] (In the formula, R 22 represents an alkyl group having 1 to 10 carbon atoms, which may or may not have an ether bond, a cyanoalkyl group having 2 to 11 carbon atoms, which may or may not have an ether bond, an alkenyl group having 2 to 10 carbon atoms, which may or may not have an ether bond, or a substituted or unsubstituted aryl group having 6 to 20 carbon atoms. 23 , R 24 each independently represents a hydrogen atom, an alkyl group having 1 to 10 carbon atoms with or without an ether bond, a cyanoalkyl group having 2 to 11 carbon atoms with or without an ether bond, an alkenyl group having 2 to 10 carbon atoms with or without an ether bond, or a substituted or unsubstituted aryl group having 6 to 20 carbon atoms, provided that R 22 ~R 24 Any one of the atoms or groups is absent and is in a radical state, representing a bond to A1. * represents (CH2) m represents a bond to .)

[0059] The zwitterion-containing acrylic polymer contains the zwitterion-containing units and (meth)acrylic units described above. The proportion of zwitterion-containing units in the zwitterion-containing acrylic polymer is less than 100% by mass, preferably 30% by mass or less, more preferably 15% by mass or less, particularly preferably 0.1 to 10% by mass, and most preferably 0.5 to 5.0% by mass, based on the total mass of the zwitterion-containing acrylic polymer. If the proportion of zwitterion-containing units in the zwitterion-containing acrylic polymer is too low, the properties of the adhesive composition derived from the zwitterion-containing units are less likely to be exhibited, resulting in poor embedding ability into uneven surfaces and poor edge appearance. On the other hand, if the proportion of zwitterion-containing units is too high, sufficient adhesiveness may not be obtained.

[0060] Examples of the (meth)acrylic unit include a repeating unit derived from a (meth)acrylic acid ester, a repeating unit derived from (meth)acrylic acid, a repeating unit derived from (meth)acrylamide, etc. The proportion of the (meth)acrylic unit is greater than 0% by mass, preferably 70% by mass or more, more preferably 85% by mass or more, particularly preferably 90 to 99.9% by mass, and most preferably 95 to 99.5% by mass, based on the total mass of the zwitterion-containing acrylic polymer.

[0061] The (meth)acrylic acid ester is preferably an alkyl (meth)acrylate. Examples of the alkyl (meth)acrylate include those having an alkyl group with 1 to 20 carbon atoms, and the alkyl group may be linear or branched. Specific examples of the alkyl (meth)acrylate include methyl (meth)acrylate, ethyl (meth)acrylate, isopropyl (meth)acrylate, n-propyl (meth)acrylate, n-butyl (meth)methacrylate, 2-ethylhexyl (meth)acrylate, n-octyl (meth)acrylate, isooctyl (meth)acrylate, nonyl (meth)acrylate, decyl (meth)acrylate, undecyl (meth)acrylate, and dodecyl (meth)acrylate. The alkyl (meth)acrylates may be used alone or in combination of two or more.

[0062] Furthermore, from the viewpoint of improving the adhesive strength of the adhesive composition, it is preferable that the adhesive composition contains a repeating unit derived from an alkyl(meth)acrylate in which the alkyl group has 4 or more carbon atoms. The number of carbon atoms in the alkyl(meth)acrylate is preferably 4 to 12, and more preferably 4 to 6. Furthermore, the alkyl(meth)acrylate in which the alkyl group has 4 or more carbon atoms is preferably an alkyl acrylate.

[0063] In the zwitterion-containing acrylic polymer, the proportion of repeating units derived from alkyl (meth)acrylate in which the alkyl group has 4 or more carbon atoms is preferably 40 to 98 mass%, more preferably 45 to 95 mass%, and even more preferably 50 to 90 mass%, based on the total amount of the zwitterion-containing acrylic polymer.

[0064] The zwitterion-containing acrylic polymer may be a copolymer containing, in addition to repeating units derived from an alkyl(meth)acrylate in which the alkyl group has 4 or more carbon atoms, repeating units derived from an alkyl(meth)acrylate in which the alkyl group has 1 to 3 carbon atoms in order to adjust the elastic modulus and adhesive properties of the adhesive composition. The alkyl(meth)acrylate is preferably an alkyl(meth)acrylate in which the alkyl group has 1 to 2 carbon atoms, more preferably methyl(meth)acrylate, and most preferably methyl methacrylate. In the zwitterion-containing acrylic polymer, the proportion of repeating units derived from an alkyl(meth)acrylate in which the alkyl group has 1 to 3 carbon atoms is preferably 0 to 30% by mass, more preferably 0 to 26% by mass, and even more preferably 0 to 22% by mass, based on the total amount of the zwitterion-containing acrylic polymer.

[0065] Zwitterion-containing acrylic polymers can be obtained by copolymerizing a zwitterion-containing polymerizable monomer with a (meth)acrylic monomer. Alternatively, zwitterion-containing acrylic polymers can be obtained by copolymerizing a polymerizable monomer having a structure capable of introducing a zwitterion structure with a (meth)acrylic monomer and then reacting the resulting copolymer with a sultone compound or the like. Furthermore, when synthesizing these polymers, other monomers copolymerizable with the zwitterion-containing polymerizable monomer or the polymerizable monomer having a structure capable of introducing a zwitterion structure and the (meth)acrylic monomer may be copolymerized.

[0066] First, we will explain the copolymerization of a zwitterion-containing polymerizable monomer with a (meth)acrylic monomer to obtain a zwitterion-containing acrylic polymer. The zwitterion-containing polymerizable monomer used to synthesize the zwitterion-containing acrylic polymer refers to a compound having a polymerizable carbon-carbon double bond and the aforementioned polar structure in its molecule. Examples of the (meth)acrylic monomer include the aforementioned (meth)acrylic acid esters, (meth)acrylic acid, and (meth)acrylamide.

[0067] In the present invention, the zwitterion-containing polymerizable monomer can be appropriately selected depending on the desired zwitterion-containing acrylic polymer. For example, a zwitterion-containing acrylic polymer having a repeating unit represented by the above formula (1) can be synthesized using a zwitterion-containing polymerizable monomer represented by the following formula (1a). Note that the quaternary ammonium moiety (N + R 2 R 3 ) may be substituted into the structures of the formulae (11) to (14).

[0068] [ka]

[0069] In formula (1a), R 1 , R 2 , R 3 , A 1 , and m have the same meanings as above. The method for synthesizing the zwitterion-containing polymerizable monomer represented by formula (1a) is not particularly limited. For example, as shown in the following formula, the zwitterion-containing polymerizable monomer represented by formula (1a) can be obtained by reacting the corresponding amine compound (1b) with a sultone compound (1c).

[0070] [ka]

[0071] (In the above formula, R 1 ~R 3 , A 1 has the same meaning as above, and p is (m-2). The amine compound (1b) can be produced and obtained by a known method. In addition, in the amine compound (1b), the amine moiety (NR 2 R 3 ) can also be used with a structure capable of introducing zwitterions, as shown in the following formulas (15) to (18).

[0072] [ka]

[0073] (In the formula, R 10 ~R 24 has the same meaning as above, except that R 10 or R 11 Either atom or group of R is in an absent radical state and represents a bond to A1. 12 ~R 16 Any one atom or group of R is in an absent radical state and represents a bond to A1. 17 ~R 21 Any one atom or group of R is in an absent radical state and represents a bond to A1. 22 ~R 24 Any one of the atoms or groups is absent and is in a radical state, representing a bond to A1.

[0074] Examples of the sultone compound (1c) include 1,2-ethane sultone, 1,3-propane sultone, 1,4-butane sultone, 2,4-butane sultone, and 1,5-pentane sultone. These are known compounds and can be produced and obtained by known methods, or commercially available products can also be used.

[0075] In the reaction of amine compound (1b) with sultone compound (1c), the amount of sultone compound (1c) used is preferably 0.8 to 1.2 equivalents, more preferably 0.9 to 1.1 equivalents, relative to amine compound (1b). By using the sultone compound (1c) in the above range, the step of removing unreacted compounds can be omitted or the time required for removal can be shortened.

[0076] The reaction of the amine compound (1b) with the sultone compound (1c) may be carried out in the absence of a solvent or in the presence of an inert solvent. Examples of the inert solvent to be used include ether solvents such as tetrahydrofuran and diglyme; nitrile solvents such as acetonitrile and propionitrile; ketone solvents such as acetone and methyl ethyl ketone; aromatic hydrocarbon solvents such as toluene and xylene; and halogenated hydrocarbon solvents such as chloroform.

[0077] When an inert solvent is used, the amount used is not particularly limited, but is usually 1 to 100 parts by mass per part by mass of the amine compound (1b). The reaction temperature is not particularly limited, but is usually in the range of 0 to 200° C., preferably 10 to 100° C., and more preferably 20 to 60° C. The reaction may be carried out under normal pressure (atmospheric pressure) or under pressurized conditions.

[0078] The reaction time is not particularly limited, but is usually 12 to 332 hours, preferably 24 to 168 hours. The reaction is preferably carried out in an inert gas atmosphere such as nitrogen gas or argon gas to prevent a decrease in yield due to oxidation by oxygen or hydrolysis of the sultone compound (1c) due to moisture in the air. The progress of the reaction can be confirmed by conventional analytical means such as gas chromatography, high-performance liquid chromatography, thin-layer chromatography, NMR, and IR.

[0079] After the reaction is complete, the desired zwitterion-containing polymerizable monomer can be isolated by performing typical post-treatment procedures in organic synthetic chemistry, and optionally purifying the resulting product by known purification methods such as recrystallization and column chromatography. In the present invention, commercially available products may also be used as the zwitterion-containing polymerizable monomer. Furthermore, compounds in which the amine of the amine compound (1b) is substituted with a structure capable of incorporating a zwitterion structure, such as those of formulas (15) to (18), can also be reacted with a sultone compound (1c) in the same manner as in the case of using the amine compound (1b), to obtain a zwitterion-containing polymerizable monomer.

[0080] The method for synthesizing the zwitterion-containing acrylic polymer is not particularly limited. For example, the zwitterion-containing acrylic polymer can be synthesized by carrying out a polymerization reaction of a monomer mixture containing a zwitterion-containing polymerizable monomer, a (meth)acrylic monomer, and, if necessary, a monomer copolymerizable with the zwitterion-containing polymerizable monomer, in the presence of a radical polymerization initiator.

[0081] Examples of the radical polymerization initiator include organic peroxides and azo compounds. Examples of organic peroxides include diacyl peroxides such as lauroyl peroxide and benzoyl peroxide; peroxyketals such as 1,1-bis(t-butylperoxy)cyclohexane and 1,1-bis(t-butylperoxy)3,3,5-trimethylcyclohexane; peroxydicarbonates such as diisopropyl peroxydicarbonate and di-2-ethylhexyl peroxydicarbonate; and peroxyesters such as t-butylperoxy-2-ethylhexanoate and t-butylperoxyisobutyrate.

[0082] Examples of azo compounds include 2,2'-azobisisobutyronitrile, 2,2'-azobis(2-methylbutyronitrile), 1,1'-azobis(cyclohexane-1-carbonitrile), 2,2'-azobis(2,4-dimethylvaleronitrile), 2,2'-azobis(2,4-dimethyl-4-methoxyvaleronitrile), dimethyl 2,2'-azobis(2-methylpropionate), 4,4'-azobis(4-cyanovaleric acid), 2,2'-azobis(2-hydroxymethylpropionitrile), and 2,2'-azobis[2-(2-imidazolin-2-yl)propane]. These may be used alone or in combination of two or more.

[0083] The amount of radical polymerization initiator used is usually 0.0001 to 0.1000 mol, preferably 0.0005 to 0.0050 mol, per mol of monomer used in the polymerization reaction (however, in the case of a copolymer, the total moles of monomers).

[0084] The conditions for the radical polymerization reaction are not particularly limited as long as the desired polymerization reaction proceeds. The heating temperature is usually 40 to 150° C., and the reaction time can be appropriately set within the range of 1 minute to 24 hours. The resulting reaction solution may be used as it is for preparing a pressure-sensitive adhesive composition, or the zwitterion-containing acrylic polymer may be isolated and purified according to a conventional method.

[0085] As described above, the zwitterion-containing acrylic polymer can also be obtained by copolymerizing a polymerizable monomer having a structure capable of introducing a zwitterion structure with a (meth)acrylic monomer, and then reacting the resulting copolymer with a sultone compound or the like.

[0086] Examples of structures into which a zwitterion structure can be introduced include amino groups, nitrogen-containing heterocycles, and phosphines. The aforementioned amine compound (1b) is preferably used as a polymerizable monomer having a structure into which a zwitterion structure can be introduced. Copolymerization of the amine compound (1b) with a (meth)acrylic monomer can be carried out under the same conditions as those for the copolymerization of the zwitterion-containing polymerizable monomer with a (meth)acrylic monomer. During copolymerization, if necessary, a polymerization reaction of a monomer mixture containing the amine compound (1b) and a monomer copolymerizable with the (meth)acrylic monomer can be carried out to synthesize an acrylic polymer having a structure into which a zwitterion structure can be introduced.

[0087] Next, the zwitterion-containing acrylic polymer is obtained by reacting the sultone compound (1c) with the structure of the obtained acrylic polymer that can introduce a zwitterion structure. The reaction of a functional group such as an amino group with the sultone compound can be carried out under the same conditions as the reaction of the amine compound (1b) with the sultone compound (1c). Instead of the amine compound (1b), the amine moiety (NR 2 R 3 ) can also be used as a compound in which the zwitterionic structure of the formulae (15) to (18) can be introduced.

[0088] The zwitterion-containing acrylic polymer may contain, in addition to the repeating units described above, repeating units derived from functional group-containing monomers. Examples of the functional group of the functional group-containing monomer include hydroxyl groups, carboxyl groups, amino groups, and epoxy groups. The functional group-containing monomer can react with a crosslinking agent described below to serve as a crosslinking initiator, or can react with an unsaturated group-containing compound to introduce an unsaturated group into the side chain of the zwitterion-containing acrylic polymer.

[0089] Examples of functional group-containing monomers include hydroxyl group-containing monomers, carboxyl group-containing monomers, amino group-containing monomers, and epoxy group-containing monomers. These monomers may be used alone or in combination of two or more. Among these, hydroxyl group-containing monomers and carboxyl group-containing monomers are preferred, and hydroxyl group-containing monomers are more preferred.

[0090] Examples of hydroxyl group-containing monomers include hydroxyalkyl (meth)acrylates such as 2-hydroxyethyl (meth)acrylate, 2-hydroxypropyl (meth)acrylate, 3-hydroxypropyl (meth)acrylate, 2-hydroxybutyl (meth)acrylate, 3-hydroxybutyl (meth)acrylate, and 4-hydroxybutyl (meth)acrylate; and unsaturated alcohols such as vinyl alcohol and allyl alcohol.

[0091] Examples of the carboxy group-containing monomer include ethylenically unsaturated monocarboxylic acids such as crotonic acid; ethylenically unsaturated dicarboxylic acids such as fumaric acid, itaconic acid, and citraconic acid, and anhydrides thereof; and 2-carboxyethyl methacrylate.

[0092] The proportion of repeating units derived from functional group-containing monomers is 70% by mass or less, and preferably 50% by mass or less, based on the total amount of the zwitterion-containing acrylic polymer.

[0093] In addition to the above, the zwitterion-containing acrylic polymer may also contain repeating units derived from monomers copolymerizable with the above acrylic monomers, such as styrene, α-methylstyrene, vinyltoluene, vinyl formate, vinyl acetate, acrylonitrile, and acrylamide.

[0094] The glass transition temperature (Tg) of the resulting zwitterion-containing acrylic polymer is preferably −60 to −20°C, and more preferably −50 to −22°C. The Tg of the zwitterion-containing acrylic polymer refers to the temperature at which the loss tangent (tanδ) reaches its maximum value in the −60 to 50°C range when a sample made of the zwitterion-containing acrylic polymer is subjected to dynamic viscoelasticity measurement at a frequency of 1 Hz. If the Tg of the zwitterion-containing acrylic polymer is too low, adhesive residue is likely to occur. On the other hand, if the Tg is too high, the ability to embed the unevenness of the circuit surface may be reduced.

[0095] The glass transition temperature of the zwitterion-containing acrylic polymer tends to decrease when the proportion of repeating units derived from alkyl (meth)acrylates in which the alkyl group has 4 or more carbon atoms is increased, for example.

[0096] The mass-average molecular weight (Mw) of the zwitterion-containing acrylic polymer is preferably 10,000 to 300,000, and more preferably 20,000 to 200,000. In this specification, the mass-average molecular weight is a value measured by gel permeation chromatography in terms of standard polystyrene. If the Mw of the zwitterion-containing acrylic polymer is too low, adhesive residue is likely to occur. If the Mw is too high, the ability to embed the irregularities on the circuit surface may be reduced.

[0097] The weight average molecular weight of the zwitterion-containing acrylic polymer tends to decrease, for example, when the amount of radical polymerization initiator used in producing the zwitterion-containing acrylic polymer is increased. Furthermore, the weight average molecular weight tends to increase when the polymerization reaction time is increased, whereas the weight average molecular weight tends to decrease when the polymerization reaction temperature is increased.

[0098] The molecular weight distribution (Mw / Mn, where Mn is the number average molecular weight) of the zwitterion-containing acrylic polymer is preferably 15 or less, and more preferably 2 to 11. If the molecular weight distribution of the zwitterion-containing acrylic polymer is too broad, adhesive residue is more likely to occur.

[0099] The molecular weight distribution of zwitterion-containing acrylic polymers can be narrowed by preparing them using living radical polymerization, which uses tellurium-containing compounds as radical polymerization initiators. Narrowing of the molecular weight distribution can also be achieved by polymerization techniques such as atom transfer radical polymerization (ATRP) and reversible addition / fragmentation chain transfer polymerization (RAFT).

[0100] (Components of adhesive composition) The adhesive composition of the present invention contains an acrylic polymer, preferably a zwitterion-containing acrylic polymer. When a zwitterion-containing acrylic polymer is used, one type may be used alone, or two or more types may be used in combination. The adhesive composition may be formed solely from the zwitterion-containing acrylic polymer, or may contain components other than the zwitterion-containing acrylic polymer. The proportion of the zwitterion-containing acrylic polymer in the adhesive composition of the present invention is preferably 80% by mass or more, more preferably 85% by mass or more, and even more preferably 90% by mass or more, based on the total amount of the adhesive composition.

[0101] The pressure-sensitive adhesive composition of the present invention may contain, in addition to the acrylic polymer, for example, an energy ray-curable compound, a crosslinking agent, a photopolymerization initiator, a pressure-sensitive adhesive polymer other than the zwitterion-containing acrylic polymer, and other additives.

[0102] (energy ray curable compound) The energy ray-curable compound is preferably a monomer or oligomer that has an unsaturated group in the molecule and can be polymerized and cured by irradiation with energy rays. 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.

[0103] Among these, urethane (meth)acrylate oligomers are preferred from the viewpoint of having a relatively high molecular weight and being less likely to reduce the modulus of elasticity of the pressure-sensitive adhesive layer. The molecular weight of the energy ray-curable compound (mass 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.

[0104] When an energy ray-curable compound is used in the adhesive composition, the blending ratio thereof is preferably 1 to 99 mass %, more preferably 10 to 85 mass %, and even more preferably 20 to 80 mass %, based on the total amount of the adhesive composition.

[0105] (Crosslinking agent) The pressure-sensitive adhesive composition may further contain a crosslinking agent. The crosslinking agent reacts with, for example, a functional group derived from a functional group-containing monomer possessed by the acrylic polymer, thereby crosslinking the acrylic polymers together. Examples of crosslinking agents include isocyanate-based crosslinking agents such as tolylene diisocyanate, hexamethylene diisocyanate, and their adducts; epoxy-based crosslinking agents such as ethylene glycol glycidyl ether and 1,3-bis(N,N'-diglycidylaminomethyl)cyclohexane; aziridine-based crosslinking agents such as hexa[1-(2-methyl)-aziridinyl]triphosphatriazine; and chelating crosslinking agents such as aluminum chelate. These crosslinking agents may be used alone or in combination of two or more.

[0106] Among these, isocyanate-based crosslinking agents are preferred from the viewpoints of increasing cohesive strength and improving adhesive strength, and from the viewpoints of availability. When a crosslinking agent is used in the adhesive composition, the blending ratio thereof is preferably 0.01 to 20 mass%, more preferably 0.05 to 15 mass%, and even more preferably 0.1 to 10 mass%, based on the total amount of the adhesive composition, from the viewpoint of promoting the crosslinking reaction.

[0107] (Photopolymerization initiator) In addition, when the pressure-sensitive adhesive composition is energy ray-curable, the pressure-sensitive adhesive composition preferably further contains a photopolymerization initiator, which allows the curing reaction of the pressure-sensitive adhesive composition to proceed sufficiently even with relatively low-energy energy rays such as ultraviolet rays.

[0108] Examples of the photopolymerization initiator include benzoin compounds, acetophenone compounds, acylphosphinoxide compounds, titanocene compounds, thioxanthone compounds, peroxide compounds, and further 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, and bis(2,4,6-trimethylbenzoyl)phenylphosphine oxide.

[0109] These photopolymerization initiators may be used alone or in combination of two or more. When a photopolymerization initiator is used, the blending ratio is preferably 0.1 to 10 mass %, more preferably 0.3 to 8.0 mass %, and even more preferably 0.5 to 5 mass %, based on the total amount of the energy ray-curable components.

[0110] (Other adhesive polymers) The adhesive composition may contain, in addition to the zwitterion-containing acrylic polymer, an adhesive polymer other than the zwitterion-containing acrylic polymer. Examples of such adhesive polymers include acrylic adhesive polymers without a zwitterion structure, urethane adhesive polymers, rubber adhesive polymers, and silicone adhesive polymers, which are commonly used as the main material for adhesives. In particular, acrylic adhesives are preferred from the viewpoints of compatibility and affinity. These adhesive polymers may be used alone or in combination of two or more.

[0111] (Other additives) The pressure-sensitive adhesive composition may contain other additives within the range that does not impair the effects of the present invention, such as antistatic agents, antioxidants, tackifiers, softeners (plasticizers), fillers, rust inhibitors, pigments, dyes, etc.

[0112] In addition, from the viewpoint of improving the coating properties on the substrate or release film, the pressure-sensitive adhesive composition may be further diluted with an organic solvent to form a solution of the pressure-sensitive adhesive composition. Examples of the organic solvent include methyl ethyl ketone, acetone, ethyl acetate, tetrahydrofuran, dioxane, cyclohexane, n-hexane, toluene, xylene, n-propanol, and isopropanol.

[0113] These organic solvents may be the same as those used during synthesis of the adhesive composition, or one or more organic solvents other than those used during synthesis may be added to enable the adhesive composition solution to be applied uniformly.

[0114] (Control of viscoelasticity of adhesive composition) The storage modulus G'(23) of the adhesive composition can be controlled, for example, by the monomer composition of the zwitterion-containing acrylic polymer. As the content of repeating units derived from alkyl (meth)acrylates, in which the alkyl group has four or more carbon atoms, increases, the storage modulus G'(23) tends to decrease. Furthermore, as the content of zwitterion-containing units increases, a relatively rigid structure is formed at temperatures around 23°C due to the association of zwitterion structures. This is thought to be due to the formation of ionic bonds between the negatively charged moieties of one zwitterion structure and the positively charged moieties of another zwitterion structure. As a result, the storage modulus G'(23) tends to increase.

[0115] The storage modulus G'(50) of the adhesive composition can be controlled, for example, by the monomer composition of the zwitterion-containing acrylic polymer. As the content of repeating units derived from alkyl (meth)acrylates, in which the alkyl group has four or more carbon atoms, increases, the storage modulus G'(50) tends to decrease. Furthermore, as the content of zwitterion-containing units increases, a relatively rigid structure is formed at temperatures around 50°C due to the association of zwitterion structures. This is thought to be due to the formation of ionic bonds between the negatively charged moieties of one zwitterion structure and the positively charged moieties of another zwitterion structure. As a result, the storage modulus G'(50) tends to increase.

[0116] Tan δ(60) can be controlled, for example, by the monomer composition of the zwitterion-containing acrylic polymer. As the content of zwitterion-containing units increases, energy is consumed in the cleavage of the association sites between zwitterion structures at temperatures around 60°C, which is thought to increase the loss modulus G''. As a result, the deformation of the adhesive layer or intermediate layer is maintained when the adhesive tape is heated, reducing contamination and damage to the circuit surface due to cutting water.

[0117] The G'(60) / G'(23) ratio of the adhesive composition can be controlled, for example, by the monomer composition of the zwitterion-containing acrylic polymer. The storage modulus G'(23) tends to decrease as the content of repeating units derived from alkyl (meth)acrylates, whose alkyl groups have four or more carbon atoms, increases. Furthermore, the storage modulus G'(23) tends to increase as the content of zwitterion-containing units increases.

[0118] As the content of repeating units derived from alkyl (meth)acrylates with alkyl groups having four or more carbon atoms increases, the storage modulus G'(60) tends to decrease. The content of zwitterion-containing units does not have a significant effect on the storage modulus G'(60), but because some of the zwitterion structures remain associated with each other even at temperatures around 60°C, excessive decreases in the storage modulus G'(60) are suppressed.

[0119] The temperature at which the maximum value of tan δ appears can be controlled, for example, by the monomer composition of the zwitterion-containing acrylic polymer. As the content of zwitterion-containing units increases, both the low-temperature peak and the high-temperature peak at which the maximum value of tan δ appears shift toward higher temperatures. Therefore, by controlling the monomer composition of the zwitterion-containing acrylic polymer, it is possible to achieve good embedding properties and shape retention at a desired application temperature.

[0120] (adhesive tape) The adhesive tape according to the present invention has an adhesive layer or intermediate layer containing the above-mentioned adhesive composition. The use of the adhesive tape is not particularly limited, and it can be used, for example, as a backgrinding tape, a dicing tape, or a tape for transferring chips after pick-up. The adhesive tape may be pre-cut to fit the shape of the object to which it is to be attached. For example, when used for backgrinding a semiconductor wafer, it may be cut to the shape of the semiconductor wafer. When used as a dicing tape, it may be cut to fit the shape of a ring frame. The following description focuses on the use as a backgrinding tape (semiconductor wafer surface protection tape) or a dicing tape. Hereinafter, a pressure-sensitive adhesive tape having a pressure-sensitive adhesive layer containing the pressure-sensitive adhesive composition will be described as a first embodiment, and a pressure-sensitive adhesive tape having an intermediate layer containing the pressure-sensitive adhesive composition will be described as a second embodiment.

[0121] (Adhesive tape according to the first embodiment) The pressure-sensitive adhesive tape according to the first embodiment comprises a substrate and a pressure-sensitive adhesive layer, and the pressure-sensitive adhesive layer comprises the pressure-sensitive adhesive composition.

[0122] (base material) The substrate of the pressure-sensitive adhesive tape according to the first embodiment is not particularly limited in terms of its constituent material, as long as the pressure-sensitive adhesive tape functions properly in desired processes such as dicing and backgrinding. It is usually composed of a film primarily made of a resin-based material. Specific examples of such films include ethylene-based copolymer films such as ethylene-vinyl acetate copolymer film, ethylene-(meth)acrylic acid copolymer film, and ethylene-(meth)acrylic acid ester copolymer film; polyethylene films such as low-density polyethylene (LDPE) film, linear low-density polyethylene (LLDPE) film, and high-density polyethylene (HDPE) film; polyolefin films such as polypropylene film, polybutene film, polybutadiene film, polymethylpentene film, ethylene-norbornene copolymer film, and norbornene resin film; polyvinyl chloride films such as polyvinyl chloride film and vinyl chloride copolymer film; polyester films such as polyethylene terephthalate film and polybutylene terephthalate film; polyurethane films; polyimide films; polystyrene films; polycarbonate films; and fluororesin films. Modified films such as crosslinked films and ionomer films of these films may also be used. The substrate may be a film made of one of these materials, or may be a laminated film made of a combination of two or more of these materials.

[0123] The film constituting the substrate preferably comprises at least one of an ethylene-based copolymer film and a polyolefin-based film. The mechanical properties of an ethylene-based copolymer film can be easily controlled over a wide range by changing the copolymerization ratio, for example. Therefore, a substrate comprising an ethylene-based copolymer film is likely to satisfy the mechanical properties required for the substrate of the pressure-sensitive adhesive tape according to this embodiment. Furthermore, since the ethylene-based copolymer film has relatively high adhesion to the pressure-sensitive adhesive layer, peeling at the interface between the substrate and the pressure-sensitive adhesive layer is unlikely to occur when used as a pressure-sensitive adhesive tape.

[0124] Some films, such as polyvinyl chloride films, contain many components that adversely affect the properties of adhesive tapes. For example, in polyvinyl chloride films, the plasticizer contained in the film migrates from the substrate to the adhesive layer and is distributed on both the side of the adhesive layer facing the substrate and the opposite side, which can reduce the adhesiveness of the adhesive layer to the workpiece (such as a semiconductor wafer or chip). However, ethylene copolymer films and polyolefin films contain a small amount of components that adversely affect the properties of adhesive tapes, so problems such as reduced adhesiveness of the adhesive layer to the workpiece are unlikely to occur. In other words, ethylene copolymer films and polyolefin films have excellent chemical stability.

[0125] The substrate may contain various additives, such as colorants such as pigments, flame retardants, plasticizers, antistatic agents, lubricants, and fillers, within the film primarily made of the resin-based material. Examples of pigments include titanium dioxide and carbon black. Examples of fillers include organic materials such as melamine resin, inorganic materials such as fumed silica, and metal materials such as nickel particles. The content of these additives is not particularly limited, but should be within a range that allows the substrate to perform the desired functions without losing smoothness and flexibility.

[0126] When the pressure-sensitive adhesive layer is energy ray curable, the substrate preferably has transparency to predetermined energy rays such as ultraviolet rays and electron beams.

[0127] The surface of the substrate facing the adhesive layer (hereinafter also referred to as the "substrate adhesion surface") may be subjected to a corona treatment or provided with a primer layer in order to improve adhesion to the adhesive layer. The surface of the substrate opposite to the substrate adhesion surface may be provided with various coating films.

[0128] The thickness of the substrate is not limited as long as the adhesive tape can function appropriately in the desired process, and is preferably in the range of 20 to 450 μm, more preferably 25 to 400 μm, and particularly preferably 50 to 350 μm.

[0129] (Adhesive layer) A pressure-sensitive adhesive layer containing the pressure-sensitive adhesive composition is formed on one surface of the substrate. When the pressure-sensitive adhesive tape is used as a dicing tape, the thickness of the pressure-sensitive adhesive layer is preferably 5 to 50 μm, particularly preferably 7 to 40 μm, and even more preferably 10 to 20 μm. If the thickness of the pressure-sensitive adhesive layer is less than 5 μm, problems such as large variations in the adhesiveness of the pressure-sensitive adhesive layer may occur.

[0130] When the adhesive tape is used as a backgrinding tape, the adhesive layer only needs to have a thickness that allows it to fill the irregularities on the semiconductor wafer surface. Therefore, when the adhesive tape is applied to the surface of a semiconductor wafer on which bumps are formed, the thickness of the adhesive layer only needs to be greater than the height of the bumps. Specifically, the thickness of the adhesive layer is preferably at least 1.0 times the height of the bumps, more preferably 1.2 to 3 times, and even more preferably 1.4 to 2 times. The bump height here refers to the maximum height of the bumps formed on the semiconductor wafer. Specifically, the thickness of the adhesive layer in this case is preferably 20 to 300 μm, more preferably 30 to 200 μm, and even more preferably 40 to 150 μm.

[0131] (others) An intermediate layer made of various soft polymers may be provided between the substrate and the pressure-sensitive adhesive layer. The configuration of the intermediate layer in the first embodiment is optional and not necessarily required. For example, when a zwitterion-containing acrylic polymer is used as the main component of the pressure-sensitive adhesive composition, the intermediate layer is preferably made of a soft acrylic polymer. By providing such an intermediate layer, adhesion between the pressure-sensitive adhesive layer and the intermediate layer is improved, preventing delamination. When an intermediate layer is provided, the thickness of the pressure-sensitive adhesive layer may be smaller than the bump height. In other words, it is sufficient if the two layers, the intermediate layer and the pressure-sensitive adhesive layer, can fill in the irregularities on the semiconductor wafer surface. In this case, the thickness of the intermediate layer is preferably 30 to 500 μm, more preferably 50 to 300 μm, and even more preferably 80 to 250 μm. The thickness of the pressure-sensitive adhesive layer laminated with the intermediate layer is preferably 5 to 50 μm, particularly preferably 7 to 40 μm, and further preferably 10 to 20 μm.

[0132] Furthermore, the adhesive tape may have a release film laminated on the surface of the adhesive layer opposite the substrate side for the purpose of protecting the adhesive layer until the adhesive layer is attached to the workpiece. The release film may have any configuration, and examples thereof include plastic films that have been treated with a release agent or the like. Specific examples of plastic films include polyester films such as polyethylene terephthalate, polybutylene terephthalate, and polyethylene naphthalate, and polyolefin films such as polypropylene and polyethylene. Silicon-based, fluorine-based, and long-chain alkyl-based release agents can be used, but among these, silicone-based ones are preferred because they are inexpensive and provide stable performance. There are no particular limitations on the thickness of the release film, but it is usually about 20 to 250 μm.

[0133] (Adhesive tape according to the second embodiment) The pressure-sensitive adhesive tape according to a second embodiment includes a substrate, a pressure-sensitive adhesive layer, and an intermediate layer provided therebetween, the intermediate layer containing the pressure-sensitive adhesive composition. The pressure-sensitive adhesive tape of this embodiment is particularly preferably used as a backgrinding tape. The substrate is the same as that explained in the first embodiment, and the surface of the substrate on the intermediate layer side (substrate adhesion surface) may be subjected to the same treatment as above.

[0134] (middle class) An intermediate layer containing the pressure-sensitive adhesive composition is formed on one side of the substrate. When the pressure-sensitive adhesive tape is used as a backgrinding tape, the total thickness of the pressure-sensitive adhesive layer and the intermediate layer need only be thick enough to fill the irregularities on the surface of a semiconductor wafer. Therefore, when the pressure-sensitive adhesive tape is applied to the surface of a semiconductor wafer having bumps, the total thickness of the pressure-sensitive adhesive layer and the intermediate layer need only be greater than the height of the bumps. Specifically, the total thickness is preferably at least 1.0 times the height of the bumps, more preferably 1.2 to 3 times, and even more preferably 1.4 to 2 times. The height of the bumps referred to here refers to the maximum height of the bumps formed on the semiconductor wafer. In this case, the total thickness of the pressure-sensitive adhesive layer and the intermediate layer is preferably 20 to 300 μm, more preferably 30 to 200 μm, and even more preferably 40 to 150 μm.

[0135] (Adhesive layer) The adhesive is not particularly limited as long as it has adequate pressure-sensitive adhesive properties at room temperature, but a storage modulus of 0.05 to 0.50 MPa at 23°C is preferred. Semiconductor wafers typically have uneven surfaces due to the formation of circuits and the like. When the adhesive tape has a storage modulus within the above range, it ensures sufficient contact between the adhesive layer and the unevenness of the wafer surface when applied to the uneven wafer surface, allowing the adhesive layer to adequately exhibit its adhesive properties. This ensures reliable fixation of the adhesive tape to the semiconductor wafer and adequate protection of the wafer surface during backgrinding. From these perspectives, the storage modulus of the adhesive is more preferably 0.10 to 0.35 MPa. Note that, when the adhesive layer is formed from an energy ray-curable adhesive, the storage modulus of the adhesive refers to the storage modulus before curing by energy ray irradiation.

[0136] The thickness of the adhesive layer is preferably less than 40 μm, more preferably 5 to 35 μm, and even more preferably 10 to 30 μm. Making the adhesive layer this thin reduces the proportion of low-rigidity areas in the adhesive tape, improving grinding accuracy and making it easier to prevent chipping of semiconductor chips during backgrinding. It also reduces adhesive residue on the surface of the semiconductor wafer.

[0137] The adhesive layer is formed from, for example, an acrylic adhesive, a urethane adhesive, a rubber adhesive, a silicone adhesive, or the like, with an acrylic adhesive being preferred. The pressure-sensitive adhesive layer is preferably formed from an energy ray-curable pressure-sensitive adhesive, which allows the pressure-sensitive adhesive layer to have an elastic modulus at 23°C within the above range before curing by energy ray irradiation, and a peel strength of 1000 mN / 50 mm or less after curing.

[0138] (others) In the adhesive tape of the second form, as in the first form, a release film may be laminated on the surface of the adhesive layer opposite the substrate side in order to protect the adhesive layer until the adhesive layer is attached to the workpiece.

[0139] (Method of manufacturing adhesive tape) The method for producing the pressure-sensitive adhesive tape 10 of the present invention is not particularly limited, and it can be produced by a known method. For example, the pressure-sensitive adhesive tape according to the first embodiment can be produced by laminating a pressure-sensitive adhesive layer provided on a release film to one side of a substrate and then laminating a release film on the surface of the pressure-sensitive adhesive layer. The release film affixed to the surface of the pressure-sensitive adhesive layer can be peeled off and removed as appropriate before using the pressure-sensitive adhesive tape.

[0140] Alternatively, an adhesive tape according to the second embodiment can be produced by laminating an intermediate layer provided on a release film to one side of a substrate, peeling off the release film, and then laminating a pressure-sensitive adhesive layer provided on the release film onto the exposed intermediate layer. The release film attached to the surface of the pressure-sensitive adhesive layer can be peeled off and removed as appropriate before using the pressure-sensitive adhesive tape. A simple method for forming a pressure-sensitive adhesive layer or intermediate layer on a release film is to directly apply the pressure-sensitive adhesive composition of the present invention to the release film using a known application method, and then heat-dry the coating to volatilize the solvent from the coating film.

[0141] Alternatively, the pressure-sensitive adhesive layer or intermediate layer may be formed by directly applying the pressure-sensitive adhesive composition to one surface of the substrate. Examples of methods for applying the pressure-sensitive adhesive composition include spin coating, spray coating, bar coating, knife coating, roll coating, blade coating, die coating, and gravure coating.

[0142] (How to use adhesive tape) The pressure-sensitive adhesive tape of the present invention is preferably used as a dicing tape or a backgrinding tape. As a dicing tape, it can be preferably used for dicing semiconductor wafers, BGA type packages, etc. It is particularly suitable as a dicing tape for semiconductor wafers and BGA type packages that have large irregularities on the surface that comes into contact with the dicing tape. The dicing method is not particularly limited, and may be blade dicing using a rotary circular blade or dicing using laser light.

[0143] Next, a method for grinding the backside of a wafer using the adhesive tape of the present invention will be described. In the backside grinding of a wafer, an adhesive tape is applied to the circuit surface of a semiconductor wafer having a circuit formed on its surface to protect the circuit surface, while the backside of the wafer is ground to a predetermined thickness.

[0144] The semiconductor wafer may be a silicon wafer or a compound semiconductor wafer such as a gallium arsenide wafer. Forming a circuit on the wafer surface can be performed by various methods, including conventionally used methods such as etching and lift-off. A predetermined circuit is formed in the circuit formation process on the semiconductor wafer. Bumps may also be formed on the surface of the semiconductor wafer. The thickness of such a wafer before grinding is not particularly limited, but is usually about 500 to 1000 μm. The surface shape of the semiconductor wafer is not particularly limited, but the adhesive tape of the present invention is preferably used for protecting the surface of a wafer having bumps formed on the circuit surface.

[0145] The pressure-sensitive adhesive tape of the present invention has a pressure-sensitive adhesive layer or intermediate layer that exhibits the above-mentioned unique elastic behavior, and exhibits viscoelasticity that can sufficiently conform to the unevenness of bumps under heated conditions. When applying the pressure-sensitive adhesive tape of the present invention, it is preferable to do so in a state where the storage modulus of the pressure-sensitive adhesive layer or intermediate layer is reduced. Therefore, it is preferable to apply the pressure-sensitive adhesive tape to a semiconductor wafer at a temperature of about 40 to 60°C. If the temperature during application is too high, the intermediate layer or pressure-sensitive adhesive layer may become excessively softened and fluid, resulting in leakage from the side of the pressure-sensitive adhesive tape.

[0146] When the adhesive tape is applied under heating, the adhesive layer or intermediate layer is embedded in the wafer surface on which the bumps are formed, eliminating unevenness. Furthermore, by allowing the tape to cool after application, the elastic modulus of the adhesive layer or intermediate layer recovers, increasing the elastic modulus of the adhesive layer or intermediate layer, thereby maintaining the wafer in a flat state. Furthermore, the adhesive tape of the present invention has high conformability to the surface shape of the wafer, and since the adhesive layer or intermediate layer is relatively hard under normal conditions, even when the adhesive tape is wound into a roll, the adhesive does not leak to the edges, reducing poor edge appearance.

[0147] The backside grinding is performed by a known method using a grinder and a suction table for fixing the wafer while the adhesive tape is still attached. After the backside grinding process, a process for removing the fractured layer generated by grinding may be performed. The thickness of the semiconductor wafer after backside grinding is not particularly limited, but is preferably about 10 to 400 μm, and particularly preferably about 25 to 300 μm.

[0148] After the backside grinding step, the adhesive tape is peeled off from the circuit side. The adhesive tape of the present invention can securely hold the wafer during backside grinding and can also prevent cutting water from penetrating into the circuit side.

[0149] Furthermore, the pressure-sensitive adhesive tape of the present invention is preferably used in chipping a bumped wafer by a so-called pre-dicing method, specifically, A process of grinding a back surface of a semiconductor wafer having grooves or modified regions formed on a surface thereof to separate the semiconductor wafer into semiconductor chips by the grinding, forming a groove having a depth shallower than the thickness of the semiconductor wafer from the surface of the semiconductor wafer having the bumps, or forming a modified region from the surface or back surface of the semiconductor wafer into the interior of the semiconductor wafer; The adhesive tape is applied to the circuit-formed surface as a surface protection tape, The semiconductor wafer having the adhesive tape attached to its surface and the grooves or modified regions formed thereon is ground from its back surface to separate the wafer into a plurality of chips (chip assemblies) starting from the grooves or modified regions. It is preferably used in the manufacturing method of semiconductor chips.

[0150] The preferred embodiment of the adhesive tape is the same as that described above. By using the adhesive tape of the present invention, high adhesion can be obtained between the wafer (chip) and the adhesive layer, so that grinding water does not penetrate into the circuit surface, and contamination of the chip can be prevented.

[0151] Thereafter, the chips are picked up by a predetermined method. Alternatively, prior to picking up the chips, the chip assembly may be transferred to another adhesive tape (pick-up tape), and then the chips may be picked up.

[0152] If the adhesive layer of the adhesive tape is energy ray curable, the adhesive layer is irradiated with energy rays to harden the adhesive layer. Next, a pickup tape is attached to the back side of the chip assembly, and the chip assembly is positioned and oriented so that it can be picked up. At this time, a ring frame arranged on the outer periphery of the chip assembly is also attached to the pickup tape, and the outer edge of the pickup tape is fixed to the ring frame. The chip assembly and the ring frame may be attached to the pickup tape simultaneously or at different times. Next, only the adhesive tape is peeled off, and the chip assembly is transferred onto the pickup tape.

[0153] Thereafter, the pickup tape is expanded as necessary to increase the distance between the chips, and the individual semiconductor chips on the pickup tape are picked up and fixed onto a substrate or the like to manufacture a semiconductor device.

[0154] The pickup tape is not particularly limited, but may be, for example, an adhesive tape comprising a substrate and an adhesive layer provided on one side of the substrate. The adhesive strength of the pickup tape should be greater than that of the backgrind tape during peeling. It is also preferable that the pickup tape has properties that allow for reduced adhesive strength when picking up chips from the pickup tape. Therefore, energy ray-curable adhesive tapes and foamable, easily peelable films are preferably used as pickup tapes.

[0155] Alternatively, an adhesive tape can be used instead of the pick-up tape. Examples of adhesive tape include a laminate of a film adhesive and a release film, a laminate of a dicing tape and a film adhesive, and a dicing / die bonding tape consisting of an adhesive layer and a release film that functions as both a dicing tape and a die bonding tape. Furthermore, a film adhesive may be attached to the backside of the individualized semiconductor wafer before the pick-up tape is applied. When a film adhesive is used, the film adhesive may have the same shape as the wafer.

[0156] When using adhesive tape or when a film adhesive is applied to the backside of a diced semiconductor wafer before application of a pickup tape, multiple semiconductor chips on the adhesive tape or pickup tape are picked up together with an adhesive layer divided into pieces with the same shape as the semiconductor chips. The semiconductor chips are then fixed onto a substrate or the like via the adhesive layer, thereby manufacturing a semiconductor device. The adhesive layer may be divided using a laser or an expander, or may be divided by tension during pickup.

[0157] The above has outlined the uses of the pressure-sensitive adhesive tape of the present invention as a dicing tape and a backgrinding tape, but the uses of the pressure-sensitive adhesive tape of the present invention are not particularly limited, and it can be used to hold or temporarily protect various workpieces having uneven surfaces. [Example]

[0158] The present invention will be described in more detail below based on examples, but the present invention is not limited to these examples.

[0159] The measurement and evaluation methods in the present invention are as follows. [Mass average molecular weight (Mw)] The mass average molecular weight (Mw) of the zwitterion-containing acrylic polymer was determined by gel permeation chromatography (GPC) under the following conditions. Column: TSKgel SuperAWM-H x 2 (6.0 mm I.D. x 15 cm) Column Lot No.: S0095, S0096 Flow rate: 6.0mL / min Detector: HLC-8320GPC built-in RI detector / UV-8320 (optional) Detector conditions: RI:Pol(+),Res(0.5s) / UV:λ(280nm).Pol(+),Res(0.5s) Sample concentration: 1.0 g / L Injection volume: 40μL Pressure: 2.84 MPa Column temperature: 40℃ System temperature: 40°C Eluent: 10mM LiBr+20mM TEA in DMAc

[0160] [Measurement of elastic modulus] The elastic modulus of each of the pressure-sensitive adhesive compositions prepared in the Examples and Comparative Examples was measured using the following apparatus and conditions. Sample preparation: Each pressure-sensitive adhesive composition was applied to a release film, dried, and then laminated with another release film. This resulted in a laminate with a 40 μm thick pressure-sensitive adhesive layer laminated between the release films. One of the release films from this laminate was removed, and the pressure-sensitive adhesive layers were repeatedly laminated together to prepare a measurement sample with a thickness of 2000 μm. Dynamic elastic modulus measuring device: TA Instruments, product name "ARES" Measurement start temperature: -60℃ Measurement end temperature: 120℃ Heating rate: 4°C / min Frequency: 1Hz

[0161] [Adhesive residue evaluation] The adhesive tapes prepared in Examples 1 to 4 and Comparative Examples 1 and 2 were cut into 25 mm wide strips and attached to the mirror-polished surface of a silicon wafer (6 inches in diameter) with one side mirror-polished. The adhesive tapes were attached at 23°C and 50% RH (relative humidity) by rolling a 2.5 kg roller back and forth once. After attachment, the adhesive tapes were left to stand for 20 minutes and then peeled off. Peeling was performed using a tensile tester (manufactured by Orientec Co., Ltd., product name "Tensilon") at a peeling speed of 300 mm / min and a peeling angle of 180°. After peeling, the wafer surface was visually inspected to determine whether or not any adhesive residue remained. Adhesive residue was evaluated according to the following criteria. A: No visible glue residue B: Visible glue residue

[0162] [Dicing] The adhesive tapes produced in Examples 1 to 4 and Comparative Examples 1 and 2 were used to dicing silicon wafers, and the number of chips that scattered was counted to evaluate the dicing properties. Adhesive tape was applied to the mirror-polished surface of a silicon wafer (6-inch diameter, 200 μm thick) with one side mirror-polished using a desktop laminator (FUJiPLA, product name "LPD3226Meister6"). Application conditions were a temperature of 23°C and an application speed of 0.4 m / min. With the adhesive tape attached to the silicon wafer, the silicon wafer was diced into 10 mm x 10 mm chips. A dicing machine (DISCO, product name "DFD-6361") was used, with the blade rotation speed set to 4500 rpm and the cutting speed set to 50 mm / sec. When square chips peeled off from the adhesive tape after dicing, the number of chips that peeled off was counted. In this case, chips at the edge of the wafer (triangular chips) that did not become products were not included in the number of chips scattered. Evaluation was performed on all square chips. Dicing properties were judged according to the following criteria. A: Less than 3 scattered chips B: Number of scattered chips: 3 or more but less than 10 C: 10 or more scattered chips

[0163] [Evaluation of embeddability (for small bumps)] Embeddability evaluation was performed using the adhesive tapes produced in Examples 5 to 8 and Comparative Examples 3 and 4. The adhesive tapes produced in Examples 5 to 8 and Comparative Examples 3 and 4 were applied to a wafer (manufactured by Waltz, 8-inch wafer, wafer material: Si) with Cu pillars 10 μm high, 30 to 100 μm pitch, and 42 μm diameter in plan view, using a laminator "RAD-3510F / 12" manufactured by Lintec Corporation. During application, the temperature of the laminating table of the device was set to 23°C, the laminating roller to 60°C, the roller pressure to 0.3 MPa, and the application speed to 10 mm / sec. After lamination, the diameter of the circular voids that appeared around the bumps was measured from the substrate side using a digital microscope (Keyence Corporation, product name "VHX-1000"), and the embeddability was evaluated according to the following criteria: The smaller the void diameter, the better the embeddability into the bumps. A: Diameter of voids less than 90 μm B: Diameter of voids: 90 μm or more and less than 100 μm C: Diameter of voids is 100 μm or more

[0164] [Evaluation of embeddability (for medium bumps)] The embeddability was evaluated in the same manner as for the small bumps described above, except that a wafer (manufactured by Waltz, 8-inch wafer, wafer material: Si) with Cu pillars 45 μm high, 30 to 100 μm pitch, and 42 μm diameter in plan view was used. The embeddability was evaluated according to the following criteria. A: Diameter of voids less than 120 μm B: Diameter of voids: 120 μm or more and less than 130 μm C: Diameter of voids is 130 μm or more

[0165] [End Appearance] The pressure-sensitive adhesive tapes produced in Examples 5 to 8 and Comparative Examples 3 and 4 were wound into rolls around cores with a diameter of 3 inches and left to stand for one week in an environment of 23°C and 50% RH (relative humidity). After standing, the side of the roll was examined using an optical digital microscope (magnification 100x) to evaluate whether or not any components had leaked from the pressure-sensitive adhesive layer or intermediate layer. A: No leakage of ingredients was observed B: Leakage of ingredients was observed

[0166] [Base material] In the following examples and comparative examples, Fanclair LEA type (thickness 120 μm, manufactured by Gunze Co., Ltd.), which is a low-density polyethylene polymer, was used as the substrate. The zwitterion-containing acrylic polymer was prepared as follows.

[0167] [Zwitterion-containing acrylic polymer 1] A reaction vessel equipped with a stirrer was charged with 93 parts by weight of n-butyl acrylate (BA), 5 parts by weight of dimethylaminoethyl acrylate (DMAEA), 2 parts by weight of 2-hydroxyethyl acrylate (HEA), azobisisobutyronitrile (AIBN) as an initiator, and 180 parts by weight of ethyl acetate as a solvent. Nitrogen was then introduced for 30 minutes while stirring. The reaction system was then heated to 60°C and stirred for 24 hours to obtain prepolymer solution 1 (weight average molecular weight 78,000) with a BA / DMAEA / HEA (mass ratio) of 93 / 5 / 2. The resulting prepolymer solution 1 was diluted with methyl ethyl ketone to a solids content of 30%. 3.88 parts by weight of propane sultone was slowly added dropwise at room temperature and stirred for 3 hours. The reaction system was heated to 60°C and then reacted for an additional 48 hours to obtain zwitterion-containing acrylic polymer 1, which had a glass transition temperature (Tg) of -30°C, a mass-average molecular weight (Mw) of 100300, a molecular weight distribution (Mw / Mn) of 10.4, maximum tanδ peaks at -30°C and 40°C, and a proportion of zwitterion-containing units of 3 mass%.

[0168] [Zwitterion-containing acrylic polymer 2] In a reaction vessel equipped with a stirrer, 95 parts by mass of n-butyl acrylate, 3 parts by mass of dimethylaminoethyl acrylate, 2 parts by mass of 2-hydroxyethyl acrylate, azobisisobutyronitrile, and 180 parts by mass of ethyl acetate were charged, and nitrogen was introduced for 30 minutes while stirring. The reaction system was then heated to 60°C and stirred for 24 hours to obtain prepolymer solution 2 (mass average molecular weight 128,000) with a BA / DMAEA / HEA (mass ratio) of 95 / 3 / 2. The resulting prepolymer solution 2 was diluted with methyl ethyl ketone to a solids content of 30%. 2.33 parts by mass of propane sultone was slowly added dropwise at room temperature, and the mixture was stirred for 3 hours. The reaction system was heated to 60°C and then reacted for an additional 48 hours to obtain zwitterion-containing acrylic polymer 2 having a Tg of -24°C, Mw of 165,000, Mw / Mn of 10.3, and maximum tanδ peaks at -24°C and 50°C, and a proportion of zwitterion-containing units of 3 mass%.

[0169] [Zwitterion-containing acrylic polymer 3] A reaction vessel equipped with a stirrer was charged with 50 parts by weight of n-butyl acrylate, 47 parts by weight of 2-ethylhexyl acrylate (2EHA), 3 parts by weight of dimethylaminoethyl acrylate, azobisisobutyronitrile, and 180 parts by weight of ethyl acetate. Nitrogen was then introduced for 30 minutes while stirring. The reaction system was then heated to 60°C and stirred for 24 hours to obtain prepolymer solution 3 (mass average molecular weight 86,000) with a BA / 2EHA / DMAEA (mass ratio) of 50 / 47 / 3. The resulting prepolymer solution 3 was diluted with methyl ethyl ketone to a solids content of 30%. 2.33 parts by weight of propane sultone was slowly added dropwise at room temperature, and the mixture was stirred for 3 hours. The reaction system was heated to 60°C and then reacted for an additional 48 hours to obtain zwitterion-containing acrylic polymer 3, which had a Tg of -40°C, an Mw of 110,500, an Mw / Mn of 11.2, and maximum tanδ peaks at -40°C and 70°C, and contained 5% by mass of zwitterion-containing units.

[0170] [Zwitterion-containing acrylic polymer 4] A reaction vessel equipped with a stirrer was charged with 97 parts by weight of n-butyl acrylate, 3 parts by weight of dimethylaminoethyl acrylate, azobisisobutyronitrile, and 180 parts by weight of ethyl acetate. Nitrogen was introduced for 30 minutes while stirring. The reaction system was then heated to 60°C and stirred for 24 hours to obtain prepolymer solution 4 (mass average molecular weight 111,000) with a BA / DMAEA (mass ratio) of 97 / 3. The resulting prepolymer solution 4 was diluted with methyl ethyl ketone to a solids content of 30%. 2.33 parts by weight of propane sultone was slowly added dropwise at room temperature and stirred for 3 hours. The reaction system was heated to 60°C and reacted for an additional 48 hours to obtain zwitterion-containing acrylic polymer 4, which had a Tg of -33°C, Mw of 142,700, Mw / Mn of 10.9, and maximum tanδ peaks at -30°C and 60°C, and a proportion of zwitterion-containing units of 4% by weight.

[0171] Adhesive polymers and intermediate layer compositions free of zwitterionic structures were prepared. [Adhesive polymer A] A solution of an acrylic copolymer resin (main adhesive, mass average molecular weight 720,000, solid content 35.0% by mass) consisting of 86 parts by mass of butyl acrylate (BA), 8 parts by mass of methyl methacrylate (MMA), 1 part by mass of acrylic acid (AA), and 5 parts by mass of 2-hydroxyethyl acrylate (2HEA) was prepared. To 100 parts by mass of this adhesive base, 0.2 parts by mass (solid content) of a polyisocyanate compound (product name "BHS-8515", manufactured by Toyochem Co., Ltd., solid content 37.5% by mass) was added as a crosslinking agent, and after stirring, adhesive polymer A was obtained.

[0172] [Adhesive polymer B] An acrylic copolymer resin solution (main adhesive, mass average molecular weight 700,000, solid content 35.0% by mass) consisting of 59.5 parts by mass of 2-ethylhexyl acrylate (2EHA), 30 parts by mass of vinyl acetate (Vac), 0.5 parts by mass of acrylic acid (AA), and 10 parts by mass of 2-hydroxyethyl acrylate (2HEA) was prepared. To 100 parts by mass of this adhesive base, 1.9 parts by mass (solid content) of a polyisocyanate compound (product name "BHS-8515", manufactured by Toyochem Co., Ltd., solid content 37.5% by mass) was added as a crosslinking agent, and after stirring, adhesive polymer B was obtained.

[0173] [Intermediate layer composition C] An acrylic acid ester copolymer having a mass average molecular weight of 600,000 and consisting of 91 parts by mass of butyl acrylate and 9 parts by mass of acrylic acid was prepared. Separately, a resin solution (solid content 35.0% by mass) was obtained by adding 2-isocyanatoethyl methacrylate (product name "Karenz MOI" (registered trademark), manufactured by Showa Denko K.K.) to an acrylic copolymer consisting of 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) at an addition rate of 80 mol% relative to 100 mol% of 2HEA. The resin solution was mixed in a ratio of 10 parts by mass (solid content) based on the solid content to 100 parts by mass (solid content) of the acrylic acid ester copolymer, to obtain a composition C for intermediate layer.

[0174] [Intermediate layer composition D] An acrylic acid ester copolymer consisting of 91 parts by mass of butyl acrylate and 9 parts by mass of acrylic acid and having a mass average molecular weight of 600,000 was prepared. Composition D for intermediate layer was obtained by adding 2 parts by mass (solid content) of di- to tri-functional urethane acrylate oligomer (product name "PU-5", manufactured by Dainichiseika Chemicals Co., Ltd.) to 100 parts by mass (solid content) of acrylic acid ester copolymer.

[0175] Zwitterion-containing acrylic polymers 1 to 4, adhesive polymers A and B, For middle layer The elastic moduli of Compositions C and D were measured. The storage moduli G' at 23°C, 40°C, 50°C, 60°C, 70°C, and 80°C, the dynamic viscoelasticity tan δ at the same temperatures, and the ratio of the storage modulus G'(60) at 60°C to the storage modulus G'(23) at 23°C, G'(60) / G'(23), are shown in the table below. [Table 1]

[0176] (Examples 1 to 4, Comparative Examples 1 and 2) Adhesive tapes having adhesive layers made of zwitterion-containing acrylic polymers 1 to 4 and adhesive polymers A and B were prepared. Zwitterion-containing acrylic polymers 1 to 4 and adhesive polymer A or B were applied to a polyethylene terephthalate (PET) release film (product name "SP-PET381031", thickness 38 μm, manufactured by Lintec Corporation) and dried to obtain an adhesive layer with a thickness of 20 μm. The adhesive layer and the substrate were bonded together to prepare an adhesive tape.

[0177] The adhesive tape thus obtained was evaluated for adhesive residue, dicing properties, embeddability (for small bumps), embeddability (for medium bumps), and edge appearance. The results are shown in Table 2.

[0178] [Table 2]

[0179] (Examples 5 to 8, Comparative Examples 3 and 4) Pressure-sensitive adhesive tapes having intermediate layers made of zwitterion-containing acrylic polymers 1 to 4 and intermediate layer compositions C and D were prepared.

[0180] (Creating the intermediate layer) Zwitterion-containing acrylic polymers 1 to 4 and intermediate layer composition C or D were applied to a polyethylene terephthalate (PET) release film (product name "SP-PET381031", thickness 38 μm, manufactured by Lintec Corporation) and dried to obtain a 45 μm thick resin layer. A 90 μm thick resin layer was obtained by laminating this with a similarly prepared 45 μm thick resin layer. The resin layer and the substrate were then laminated to produce a laminate of the resin layer and substrate. This resin layer would later become the intermediate layer.

[0181] (Preparation of adhesive layer) A resin solution (adhesive base, solids content 35.0% by mass) was prepared by adding 2-isocyanatoethyl methacrylate (product name "Karenz MOI" (registered trademark), manufactured by Showa Denko K.K.) to an acrylic copolymer consisting of 74 parts by mass of butyl acrylate (BA), 20 parts by mass of methyl methacrylate (MMA), and 6 parts by mass of 2-hydroxyethyl acrylate (2HEA) at an addition rate of 50 mol% relative to 100 mol% of 2HEA (main adhesive, solids content 35.0% by mass).

[0182] To 100 parts by weight of this adhesive base, 1.0 part by weight of 1-hydroxycyclohexylphenyl ketone (product name "Irgacure 184" manufactured by BASF) as a photopolymerization initiator and 0.2 parts by weight (solids) of a polyisocyanate compound (product name "Coronate L" manufactured by Tosoh Corporation) as a crosslinker were added, and after stirring, an adhesive composition was obtained. The adhesive composition was then applied to a polyethylene terephthalate (PET) release film (product name "SP-PET381031" manufactured by Lintec Corporation, 38 μm thick) and dried to form a 20 μm thick adhesive layer on the release film. This was then bonded to a polyethylene terephthalate (PET) release film (product name "SP-PET382150" manufactured by Lintec Corporation, 38 μm thick) to obtain a laminate with an adhesive layer.

[0183] (Preparation of adhesive tape) One PET film was removed from the laminate having the adhesive layer, and the PET film was attached to the resin layer surface of the laminate of the resin layer and the substrate. As a result, an adhesive tape consisting of PET film / adhesive layer / resin layer / substrate was obtained. The resin layer serves as an intermediate layer between the adhesive layer and the substrate.

[0184] The adhesive tape thus obtained was evaluated for adhesive residue, dicing properties, embeddability (for small bumps), embeddability (for medium bumps), and edge appearance. The results are shown in Table 3.

[0185] [Table 3]

[0186] As described above, the present invention uses a polymer, which is the main component of the adhesive composition, that has a moiety whose viscoelastic behavior changes depending on temperature, i.e., a polymer having a repeating unit containing a zwitterionic structure. This makes it easy to control the fluidity of the adhesive layer (or intermediate layer) during application and storage, and provides an adhesive tape that conforms to the uneven surface of a workpiece during application and that exhibits little leakage of the adhesive composition during storage.

Claims

1. It includes a substrate and a pressure-sensitive adhesive layer, The substrate is a resin film, The pressure-sensitive adhesive layer contains a pressure-sensitive adhesive composition, and the pressure-sensitive adhesive composition has a storage modulus G'(23) at 23°C of 1.0 x 10 5 Pa or more, Storage modulus G'(50) at 50°C is 2.5 x 10 5 Pa or less, The dynamic viscoelasticity tanδ at 60°C is 0.5 or more, An adhesive tape for workpiece processing, comprising an adhesive composition containing, as a main component, an acrylic polymer having a repeating unit containing a zwitterionic structure.

2. a substrate, a pressure-sensitive adhesive layer, and an intermediate layer between the substrate and the pressure-sensitive adhesive layer; The substrate is a resin film, The intermediate layer contains a pressure-sensitive adhesive composition, and the pressure-sensitive adhesive composition has a storage modulus G'(23) at 23°C of 1.0 x 10 5 Pa or more, Storage modulus G'(50) at 50°C is 2.5 x 10 5 Pa or less, The dynamic viscoelasticity tanδ at 60°C is 0.5 or more, An adhesive tape for workpiece processing, comprising an adhesive composition containing, as a main component, an acrylic polymer having a repeating unit containing a zwitterionic structure.

3. 3. The adhesive tape for workpiece processing according to claim 1, wherein the ratio of the storage modulus G'(60) at 60 ° C. to the storage modulus G'(23) at 23 ° C., G'(60) / G'(23), of the adhesive composition is 0.1 to 0.

7.

4. The adhesive tape for workpiece processing according to any one of claims 1 to 3, wherein the adhesive composition contains a crosslinking agent.

5. The adhesive tape for workpiece processing according to any one of claims 1 to 4, wherein the acrylic polymer has a repeating unit derived from at least one functional group-containing monomer selected from the group consisting of a hydroxyl group-containing monomer, a carboxyl group-containing monomer, an amino group-containing monomer, and an epoxy group-containing monomer.

Images