Dicing sheet base film

Abstract

To provide a new dicing sheet base film that can be separated into chips during an expanding process and stretches them uniformly.SOLUTION: A dicing sheet base film contains 80 to 95 mass% of a binary ionomer resin and 5 to 20 mass% of an α-olefin copolymer, has a 5% modulus of 6 MPa or more in both the MD and TD directions in a tensile test at -15°C, and does not show a yield point in both the MD and TD directions in a tensile test at -15°C, or when it shows a yield point, the minimum value of tensile stress (v) after passing the yield point is 90% or more of the tensile yield stress (p).SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a film that serves as a base material for a dicing sheet that is attached to a semiconductor wafer when semiconductor devices formed on the semiconductor wafer are diced into individual pieces. [Background technology]

[0002] In the semiconductor manufacturing process, a wafer with a circuit pattern formed on its surface is diced into individual chips with a stretchable dicing sheet attached to its backside. The dicing sheet is a resin substrate with an adhesive layer. Various dicing methods are used, including the half-cut method, which cuts the wafer while leaving a portion of its thickness intact, and the laser dicing method, which focuses laser light inside the wafer to form modified regions through multiphoton absorption. In the expanding process following the dicing process, a push-up member located inside the ring frame that holds the dicing sheet is raised to stretch the dicing sheet, separating the chips. The individual chips separated in the expanding process are then picked up one by one.

[0003] Dicing sheets are required to have various properties, such as being easily stretched without breaking during the expanding process, being able to expand uniformly without necking during the expanding process, having low friction with the push-up member during expansion, and being able to fully shrink any warped parts caused by heating before picking up. Ionomer resins, which have all of these properties, are often used as dicing sheet substrates.

[0004] For example, Patent Document 1 describes a resin composition for a dicing film substrate that contains an ionomer of an ethylene-unsaturated carboxylic acid-unsaturated carboxylic acid ester copolymer and an ethylene copolymer in a specific ratio and has a Vicat softening point of less than 50°C, and a dicing film substrate that includes at least one layer containing the composition, which is said to enable the dicing film substrate to achieve both high strength and high heat shrinkability.

[0005] Patent Document 2 describes a substrate for semiconductor wafer sheets containing a specific range of ratios of an ionomer resin in which a compound having a carboxyl group is crosslinked with a cation and an octene-containing copolymer, which is said to produce a sheet with excellent expansion balance in the MD (machine direction; direction of flow of the sheet) and TD (trans direction; width direction of the sheet) directions during expansion.

[0006] Patent Document 3 describes a substrate for a dicing sheet in which a layer mainly composed of a thermoplastic polyurethane resin and a layer mainly composed of an ionomer resin are laminated. Patent Document 4 describes a substrate film for a dicing sheet in which a layer mainly composed of an ionomer resin or an ethylene vinyl acetate resin, a layer mainly composed of an ether-based thermoplastic polyurethane resin, and a layer mainly composed of an ionomer resin or an ethylene vinyl acetate resin are laminated.

[0007] Furthermore, Patent Document 5 describes a uniformly expandable film that does not use an ionomer but is primarily composed of a random copolymer of propylene and ethylene and / or an α-olefin having 4 to 8 carbon atoms. In the examples, it is described that films that showed a yield point in a tensile test were unable to expand uniformly because necking occurred when the film was expanded, and that the film was plastically deformed, so that the film did not return to its original shape even after the tension was removed after expansion. [Prior art documents] [Patent documents]

[0008] [Patent Document 1] International Publication No. 2020 / 031928 [Patent Document 2] Japanese Patent Application Laid-Open No. 2000-345129 [Patent Document 3] JP 2019-179800 A [Patent Document 4] Patent Publication No. 2021-061325 [Patent Document 5] Patent Publication No. 2021-014557 Summary of the Invention [Problem to be solved by the invention]

[0009] When dividing chips during the expanding process, a high modulus of elasticity is required during the initial push-up, i.e., initial elongation, because the wafer attached to the dicing sheet is pulled in the planar direction to divide it. The ionomer described in Patent Document 1 was a ternary system. Furthermore, although not explicitly stated in Patent Document 2, the ionomer used in the examples was also a ternary system. Generally, ternary ionomers do not exhibit a yield point in a tensile test, or the peak of the yield point is small, making them less likely to exhibit necking, but they have the problem of having a lower modulus of elasticity than binary ionomers.

[0010] The present invention has been made in consideration of the above, and aims to provide a new substrate film for a dicing sheet that can be divided into chips during the expanding process and that stretches uniformly. [Means for solving the problem]

[0011] The substrate film for a dicing sheet of the present invention contains 80 to 95 mass% of a binary ionomer resin and 5 to 20 mass% of an α-olefin copolymer, and in a tensile test at -15°C, the 5% modulus in both the MD and TD directions is 6 MPa or more, preferably 10 MPa or more, and in a tensile test at -15°C, the film does not show a yield point in both the MD and TD directions, or if it shows a yield point, the minimum tensile stress after passing the yield point is 90% or more of the tensile yield stress.

[0012] In this specification, the tensile test refers to a tensile test in accordance with JIS K7127, except that the tensile speed is 1 m / min.

[0013] Another substrate film for a dicing sheet of the present invention contains 80 to 95 mass% of a binary ionomer resin and 5 to 20 mass% of an α-olefin copolymer, and in a tensile test at room temperature, the 5% modulus is 6 MPa or more in both the MD and TD directions, and in a tensile test at room temperature, the film does not show a yield point in both the MD and TD directions, or if it shows a yield point, the minimum tensile stress after passing the yield point is 90% or more of the tensile yield stress. The room temperature is about 23°C.

[0014] Preferably, in any of the above substrate films for dicing sheets, the ionomer resin is a zinc ion-crosslinked ethylene-(meth)acrylic acid binary copolymer, where "(meth)acrylic acid" is a term used to encompass both "acrylic acid" and "methacrylic acid."

[0015] Preferably, in any of the above substrate films for a dicing sheet, the α-olefin copolymer is an ethylene-1 butene random copolymer. [Effects of the Invention]

[0016] The substrate for a dicing sheet of the present invention has a tensile modulus at the initial stage of elongation that is large enough to separate chips in the expanding step, and is elongated uniformly. [Brief explanation of the drawings]

[0017] [Figure 1] 1 is a stress / strain curve from a tensile test. DETAILED DESCRIPTION OF THE INVENTION

[0018] The structure of one embodiment of the substrate film for a dicing sheet of the present invention will be described first. Note that the substrate film for a dicing sheet may be simply referred to as the "substrate film" below.

[0019] The substrate film for a dicing sheet of this embodiment is a single-layer film containing 80 to 95 mass % of a binary ionomer resin and 5 to 20 mass % of an α-olefin copolymer.

[0020] An ionomer is a resin in which polymer chains such as an ethylene-(meth)acrylic acid copolymer are crosslinked with cations. Ionomers combine the basic properties required of a dicing sheet substrate, such as high elongation, low friction with a push-up member, and sufficient shrinkage upon heating after elongation. The ionomer used in this embodiment is a binary system. Binary ionomers are preferred because they have a higher initial modulus of elasticity when elongated than ternary ionomers. The ionomer is preferably an ethylene-(meth)acrylic acid binary copolymer crosslinked with cations, and more preferably an ethylene-(meth)acrylic acid binary copolymer crosslinked with Zn ions.

[0021] Ionomers vary in modulus of elasticity at the initial stage of elongation depending on the grade. In this regard, the flexural rigidity of the ionomer according to JIS K7106:1995 is preferably 160 MPa or more, more preferably 200 MPa or more. Although the flexural rigidity is not a mechanical property of a thin film such as a substrate film, the use of an ionomer with such physical properties makes it possible to obtain a substrate film that is harder and has a high modulus of elasticity at the initial stage of elongation. On the other hand, the flexural rigidity of the ionomer is preferably 300 MPa or less. If the flexural rigidity is too high, the substrate film is likely to exhibit a high yield point. The flexural rigidity of the ionomer usually does not exceed 400 MPa.

[0022] α-olefin copolymers are blended to eliminate the yield point of the ionomer or to lower the peak of the yield point. Binary ionomers have a high modulus of elasticity at the beginning of elongation, but are prone to yielding. Even within the same binary ionomer, those with a higher modulus of elasticity at the beginning of elongation are more likely to exhibit large yielding. The α-olefin copolymer is preferably an ethylene-1-butene random copolymer.

[0023] The blending ratio of the ionomer to the α-olefin copolymer is 80:20 to 95:5 by mass. If the amount of the α-olefin copolymer is too small, the effect of suppressing the yielding of the ionomer is small. On the other hand, if the amount of the α-olefin copolymer is too large, the slipperiness of the ionomer is impaired, increasing friction with the push-up member during expansion and resulting in non-uniform elongation.

[0024] The thickness of the substrate film for the dicing sheet is preferably 40 μm or more. If the substrate film is too thin, the warpage of the wafer cannot be sufficiently corrected. On the other hand, the thickness of the substrate film is preferably 200 μm or less. If the substrate film is too thick, the rigidity increases, which deteriorates the workability of the process of attaching the substrate to the wafer.

[0025] The substrate film for a dicing sheet of this embodiment conforms to JIS K7127:1999, but has a 5% modulus of 6 MPa or more in both the MD and TD directions in a tensile test at a tensile speed of 1 m / min. The 5% modulus is the tensile stress when the film elongates by 5% in the tensile test and serves as an index of the initial modulus of elasticity. The expanding process may be performed at room temperature or at a low temperature of approximately -15°C. Therefore, the 5% modulus is the value obtained in a tensile test at room temperature or at -15°C, depending on the temperature at which the expanding process is performed. In addition, the expanding process at low temperatures is often performed in the hope of achieving a higher initial modulus of elasticity, taking advantage of the fact that the modulus of elasticity of resin films increases with decreasing temperature. In consideration of this, the 5% modulus in a tensile test at -15°C is preferably 10 MPa or more. On the other hand, the 5% modulus is preferably 25 MPa or less, more preferably 20 MPa or less. Although there is no particular problem if the 5% modulus is large, this is because a large force is required to widen the gap between the chips after they are cut in the expanding step.

[0026] Furthermore, as an indicator of the degree of yield, the substrate film for dicing sheets of this embodiment does not exhibit a yield point in the MD and TD directions in a tensile test at a tensile speed of 1 m / min, or if it does exhibit a yield point, the minimum value of the tensile stress after passing the yield point is 90% or more of the tensile yield stress.

[0027] The substrate film for a dicing sheet of this embodiment can be produced by kneading and melting pellets of an ionomer and an α-olefin copolymer, extruding the mixture from a T-die, and passing it between a pair of cooling rolls to form a film.

[0028] A dicing sheet can be produced by providing an adhesive layer on the surface of this base film. The adhesive that constitutes the adhesive layer is not particularly limited, and various known adhesives can be used. In many cases, adhesives that are cured by exposure to ultraviolet (UV) light, such as UV-curable acrylic adhesives, are used. If the adhesive layer is too thick, the wafer may shake during expansion, easily causing chipping defects, while if it is too thin, the adhesive strength may be insufficient and cohesive failure may occur during peeling. The thickness of the adhesive layer is generally about 8 to 20 μm.

[0029] In preparing the dicing sheet, other layers such as an antistatic layer may be provided on the surface of the substrate film opposite to the adhesive layer or between the substrate film and the adhesive layer. [Example]

[0030] Pellets of various ionomers and α-olefin copolymers were kneaded and melted, extruded through a T-die, and passed through a pair of cooling rolls to form a film with a thickness of 90 μm, to prepare the substrate films of the examples and comparative examples.

[0031] The ionomers used were as follows: A: Mitsui Dow Polychemicals Co., Ltd., Himilan 1705, ethylene-acrylic acid copolymer, zinc crosslinked, tensile strength at break 31 MPa, flexural modulus 200 MPa, Vicat softening temperature 65°C B: Mitsui Dow Polychemicals Co., Ltd., Himilan 1702, ethylene-methacrylic acid copolymer, Zn cross-linked, tensile strength at break 27 MPa, flexural modulus 170 MPa, Vicat softening temperature 63°C C: Mitsui Dow Polychemicals Co., Ltd., Himilan 1650, ethylene-methacrylic acid copolymer, Zn cross-linked, tensile strength at break 30 MPa, flexural modulus 250 MPa, Vicat softening temperature 63°C D: Mitsui Dow Polychemicals Co., Ltd., Himilan 1652, ethylene-methacrylic acid copolymer, Zn cross-linked, tensile strength at break 24 MPa, flexural modulus 160 MPa, Vicat softening temperature 80°C E: Mitsui Dow Polychemicals Co., Ltd., Himilan 1855, ethylene-methacrylic acid-acrylic acid ester terpolymer, zinc crosslinked, tensile strength at break 32 MPa, flexural modulus 92 MPa, Vicat softening temperature 56°C F: Mitsui Dow Polychemicals Co., Ltd., Himilan 1707, ethylene-methacrylic acid copolymer, sodium crosslinked, tensile strength at break 33 MPa, flexural modulus 310 MPa, Vicat softening temperature 60°C

[0032] The α-olefin copolymers used were as follows: a: Mitsui Chemicals, Inc., Tafmer A4085S, ethylene-1 butene random copolymer b: Mitsui Chemicals, Toughmer PN2060, propylene-olefin copolymer

[0033] Tensile tests were conducted in accordance with JIS K7127:1999 on 10 mm wide, 50 mm gauge spacing test pieces at a tensile speed of 1 m / min. This tensile speed is higher than the recommended range of JIS K7161, which JIS K7127 cites, but is closer to the conditions of the expanding process. Tensile tests were conducted at room temperature (23°C) and -15°C.

[0034] Table 1 shows the results of the tensile test at room temperature, and Table 2 shows the results of the tensile test at -15°C. The tensile test results shown in Tables 1 and 2 are the average of the results of three tests. In Tables 1 and 2, "mod." means modulus. "v / p" refers to the ratio of the minimum tensile stress (v) after the yield point to the tensile yield stress (p), as shown in Figure 1. For samples that did not show a yield point in the tensile test, the v / p value was set to 1.

[0035] In Tables 1 and 2, substrate films with a 5% modulus of 6 MPa or more and a v / p of 0.9 or more are examples, and the rest are comparative examples.

[0036] [Table 1]

[0037] [Table 2]

[0038] The results in Table 1 show that in tensile tests at room temperature, samples 6, 7, and 10 showed good results for 5% modulus and v / p. For samples 6 to 8, a clear tendency for the 5% modulus to decrease and the TD v / p to increase as the blending ratio of α-olefin copolymer increases is evident. It was found that excellent properties can be obtained with ionomer C by blending α-olefin copolymer preferably in an amount of 5 to 19 mass%. Sample 1, which was a ternary ionomer alone, did not show yield, but had a small 5% modulus value.

[0039] The results in Table 2 show that the 5% modulus was generally higher in the tensile tests at -15°C compared to the tensile tests at room temperature, and good results were obtained for 5% modulus and v / p in samples 2-4, 6, 8-10, 12-14, and 16. In samples 12-15, there is a clear tendency for the 5% modulus to decrease and the v / p to increase as the blending ratio of α-olefin copolymer increases. It was found that excellent properties can be obtained by blending α-olefin copolymer with ionomer A in an amount of preferably 5-18% by mass, more preferably 12-18% by mass. Sample 1 did not show yield but had a small 5% modulus, similar to the results in Table 1.

[0040] The present invention is not limited to the above-described embodiments and examples, and various modifications are possible within the scope of the technical concept thereof.

Claims

1. The composition contains 80 to 95% by mass of a binary ionomer resin and 5 to 20% by mass of an α-olefin copolymer, In a tensile test at -15°C, the 5% modulus is 6 MPa or more in the MD and TD directions, In a tensile test at -15°C, the material does not exhibit a yield point in the MD or TD direction, or if it exhibits a yield point, the minimum value of the tensile stress after passing the yield point is 90% or more of the tensile yield stress. Base film for dicing sheets.

2. The composition contains 80 to 95% by mass of a binary ionomer resin and 5 to 20% by mass of an α-olefin copolymer, In a tensile test at room temperature, the 5% modulus is 6 MPa or more in the MD direction and the TD direction, In a tensile test at room temperature, the material does not exhibit a yield point in the MD direction or the TD direction, or if a yield point is exhibited, the minimum value of the tensile stress after the yield point is 90% or more of the tensile yield stress. Base film for dicing sheets.

3. The ionomer resin is a zinc ion-crosslinked ethylene-(meth)acrylic acid binary copolymer. The substrate film for a dicing sheet according to claim 1 or 2.

4. The α-olefin copolymer is an ethylene-1 butene random copolymer. The substrate film for a dicing sheet according to claim 1 or 2.

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