Laminate

Abstract

Provided are a laminate and a method for manufacturing the laminate. The laminate has a support substrate having a step, and a polyimide resin layer on the support substrate, wherein a polyimide resin constituting the polyimide resin layer has a structural unit of general formula (1) and has a glass transition temperature of at least 300°C. The method comprises the steps of: applying a polyimide resin varnish or a polyimide resin precursor varnish on a support substrate having a step; and heating the resultant to obtain a polyimide resin layer, wherein the polyimide resin or the polyimide resin precursor has a structural unit of general formula (1).

Description

Laminate

[0001] The present invention relates to a laminate and a method for manufacturing the laminate.

[0002] As semiconductors become more highly integrated, it has become important to planarize the insulating film on the wafer surface in semiconductor processes in order to improve patterning accuracy in higher definition, miniaturization, and multilayer wiring, and to improve the accuracy of wafer-to-wafer bonding. Polyimide resins have excellent mechanical properties, heat resistance, and insulating properties, and various applications have been considered in fields such as electrical and electronic components, and their use as the insulating film has also been attempted. For example, Patent Document 1 discloses a planarization process for forming an insulating film by applying a composition containing a fully imidized polyimide polymer and a solvent to a substrate having a conductive metal pattern, with the aim of forming an insulating film with good planarization properties.

[0003] Special Publication No. 2022-550611

[0004] Although polyimide resins have the excellent properties described above, there are several issues that must be addressed before they can be used as insulating films, particularly planarization films, in the semiconductor field. For example, silicon wafers used in the semiconductor field have few functional groups on their surfaces, making them less likely to exhibit adhesion to resins or step-filling properties. Furthermore, polishing solutions are used in the planarization (polishing) process, but there are concerns that water absorption, in particular, can reduce the resin's adhesion and deteriorate its heat resistance. Furthermore, it is extremely difficult to simultaneously satisfy all of these performance requirements. For example, increasing the resin's fluidity to improve planarization properties, filling properties, adhesion, etc., can result in a deterioration in heat resistance. The present invention was made in light of these circumstances, and its objective is to provide a laminate that is excellent in heat resistance, adhesion, step-filling properties, and planarization.

[0005] The present inventors have found that the above-mentioned problems can be solved by a laminate having a polyimide resin layer having a specific structural unit and a glass transition temperature of 300°C or higher, which is formed on a supporting substrate having a step, and have thereby completed the invention.

[0006] That is, the present invention relates to the following [1] to

[10] : [1] A laminate comprising a supporting substrate having a step and a polyimide resin layer on the supporting substrate, wherein the polyimide resin constituting the polyimide resin layer has a structural unit represented by the following general formula (1) and has a glass transition temperature of 300°C or higher: [2] The laminate according to [1] above, having a silicon-containing inorganic film on the polyimide resin layer. [3] The laminate according to [1] or [2] above, wherein the step height of the supporting substrate is 0.1 to 50 μm. [4] The laminate according to any one of [1] to [3] above, wherein the polyimide resin layer has a film thickness of 0.5 to 300 μm. [5] The laminate according to any one of [2] to [4] above, wherein the inorganic film is silicon oxide or silicon nitride. [6] The laminate according to any one of [2] to [5] above, wherein the inorganic film has a thickness of 1 to 1,000 nm. [7] The laminate according to any one of [1] to [6] above, wherein the supporting substrate is silicon, silicon carbide, gallium nitride, gallium oxide, aluminum nitride, or diamond. [8] A method for producing a laminate, comprising the steps of applying a polyimide resin varnish or a polyimide resin precursor varnish to a supporting substrate having a step, and heating the applied varnish to obtain a polyimide resin layer, wherein the polyimide resin or the polyimide resin precursor has a structural unit represented by the following general formula (1): [9] The method for producing the laminate according to [8], further comprising a step of polishing the surface of the polyimide resin layer opposite to the surface in contact with the support substrate.

[10] The method for producing the laminate according to [8] or [9], further comprising a step of laminating an inorganic film on the laminate.

[0007] According to the present invention, a laminate having excellent heat resistance, adhesion, step-filling ability, and flatness can be provided. Because the laminate of the present invention has the above-mentioned properties, it is useful as a laminate in semiconductor processes.

[0008] [Laminate] The laminate of the present invention is a laminate having a supporting substrate having a step and a polyimide resin layer on the supporting substrate, wherein the polyimide resin constituting the polyimide resin layer has a structural unit represented by the following general formula (1) and has a glass transition temperature of 300°C or higher:

[0009] <Support substrate having steps> The laminate of the present invention has a support substrate having steps. The support substrate is preferably silicon, silicon carbide, gallium nitride, gallium oxide, aluminum nitride, or diamond, and more preferably silicon. When the support substrate is silicon, the film-forming property and heat resistance are excellent. Furthermore, silicon is excellent in yield during the crystallization process and in raw material availability, making it an excellent support substrate in the present invention.

[0010] The height of the step in the support substrate is preferably 0.1 to 50 μm, more preferably 1 to 40 μm, even more preferably 1 to 20 μm, even more preferably 1 to 15 μm, and even more preferably 1 to 10 μm. The step in the support substrate occurs because the laminate of the present invention is a laminate for 2.x-dimensional or 3-dimensional mounting. That is, the lower level of the support substrate is the substrate (surface portion) on which the chip is placed directly, and the upper level of the support substrate (the portion narrower than the lower level of the support substrate) is the upper surface of the chip placed on the substrate. The substrate may be a substrate on which a silicon oxide layer, a silicon nitride layer, or an interlayer insulating layer (low-k film) is formed. Furthermore, if the substrate is a silicon substrate, it may be a silicon substrate on which an interlayer insulating layer (low-k film) is formed. The polyimide resin layer described below functions as a planarizing film to fill the step and flatten the surface. It also functions as an insulating film.

[0011] The laminate of the present invention has a polyimide resin layer on the supporting substrate. The polyimide resin constituting the polyimide resin layer has a structural unit represented by the following general formula (1) and has a glass transition temperature of 300° C. or higher:

[0012] The film thickness of the polyimide resin layer is preferably 0.5 to 300 μm, more preferably 1 to 100 μm, even more preferably 1 to 50 μm, even more preferably 1 to 30 μm, and even more preferably 1 to 25 μm. In particular, in order to fill the steps of the support substrate, it is preferable that the film thickness of the polyimide resin layer in the upper and lower parts of the support substrate is different. The difference in film thickness of the polyimide resin layer in the upper and lower parts of the support substrate is preferably 0.1 to 50 μm, more preferably 1 to 40 μm, even more preferably 1 to 20 μm, even more preferably 1 to 15 μm, and even more preferably 1 to 10 μm. In the present invention, the "film thickness of the polyimide resin layer" refers to the film thickness of the polyimide resin layer on the upper part of the support substrate of a support substrate having a step (the film thickness of the polyimide resin layer on the upper part of the support substrate). In other words, the "film thickness of the polyimide resin layer" refers to the thinner film thickness of the polyimide resin layer on the support substrate having a step. The film thickness of the polyimide resin layer on the lower portion of a supporting substrate having a step is referred to as the "film thickness of the polyimide resin layer on the lower portion of the supporting substrate." In other words, the "film thickness of the polyimide resin layer on the lower portion of the supporting substrate" refers to the thicker film thickness of the polyimide resin layers on the supporting substrate having a step. The film thickness of the polyimide resin layer on the lower portion of the supporting substrate is preferably 0.5 to 350 μm, more preferably 1 to 150 μm, even more preferably 1 to 100 μm, and still more preferably 1 to 50 μm.

[0013] The polyimide resin has a structural unit of the following general formula (1) and has a glass transition temperature of 300° C. or higher.

[0014] The polyimide resin has a glass transition temperature of 300°C or higher. The polyimide resin has a glass transition temperature of preferably 350°C or higher, more preferably 380°C or higher, even more preferably 400°C or higher, still more preferably 420°C or higher, still more preferably 430°C or higher, and still more preferably 440°C or higher. There is no upper limit, but it is preferably 550°C or lower. When the glass transition temperature of the polyimide resin is in the above range, the laminate of the present invention has excellent heat resistance and is useful as a laminate in semiconductor processes.

[0015] The reason why the laminate of the present invention has excellent heat resistance, adhesion, step-filling ability, and flatness is unclear, but it is thought to be as follows. The polyimide resin precursor of the present invention, which is applied to a support substrate having steps, contains a structure derived from a specific diamine having an ester skeleton that is highly linear and exhibits relatively low water absorption, and it is thought that the resin obtained after thermal imidization has excellent heat resistance. Furthermore, since the polyimide resin precursor of the present invention contains the above structure, it is thought that the resin obtained is less likely to absorb moisture that inhibits adhesion. Therefore, it is thought that the laminate has excellent adhesion and fillability, and has strong adhesion that does not peel off from the support substrate even during a flattening process such as polishing.

[0016] The polyimide resin has a structural unit of formula (1), preferably at least one structural unit selected from the group consisting of a structural unit of formula (1a) below and a structural unit of formula (1b) below, and more preferably a structural unit of formula (1b) below:

[0017] The polyimide resin having the structural unit of formula (1a) more preferably contains at least one selected from the group consisting of a repeating unit represented by formula (2a) below and a repeating unit represented by formula (3a) below, even more preferably contains a repeating unit represented by formula (2a) below, and even more preferably contains a repeating unit represented by formula (2a) below and a repeating unit represented by formula (3a) below.

[0018] The "repeating unit" in the polyimide resin refers to an imide unit containing a structural unit derived from one tetracarboxylic dianhydride and a structural unit derived from one diamine. The ratio of the repeating unit represented by formula (2a) to the sum of the repeating units represented by formula (2a) and formula (3a) is preferably 30 to 100 mol%, and from the viewpoint of transparency, it is more preferably 40 to 100 mol%, even more preferably 50 to 100 mol%, even more preferably 60 to 100 mol%, even more preferably 70 to 100 mol%, even more preferably 80 to 100 mol%, even more preferably 90 to 100 mol%, and may even be 100 mol%. Furthermore, from the viewpoint of heat resistance and strength, it is more preferably 30 to 90 mol%, even more preferably 30 to 80 mol%, even more preferably 30 to 70 mol%, even more preferably 30 to 60 mol%, and even more preferably 30 to 50 mol%.

[0019] From the viewpoint of heat resistance and mechanical strength, the sum of the repeating units represented by formula (2a) and the repeating units represented by formula (3a) is preferably 50 mol% or more and 100 mol% or less, more preferably 70 mol% or more and 100 mol% or less, even more preferably 80 mol% or more and 100 mol% or less, still more preferably 90 mol% or more and 100 mol% or less, still more preferably 95 mol% or more and 100 mol% or less, still more preferably 99 mol% or more and 100 mol% or less, and may be 100 mol%, with 100 mol% being even more preferred from the viewpoint of heat resistance and mechanical strength.

[0020] From the viewpoint of transparency, the repeating unit represented by formula (2a) preferably accounts for 40 mol% or more, more preferably 50 mol% or more, even more preferably 60 mol% or more, still more preferably 70 mol% or more, still more preferably 80 mol% or more, and still more preferably 90 mol% or more of all repeating units of the polyimide resin, with the upper limit being 100 mol% or less.

[0021] The polyimide resin may contain repeating units other than the repeating units represented by formula (2a) and the repeating units represented by general formula (3a). The content of repeating units other than the repeating units represented by formula (2a) and the repeating units represented by general formula (3a) is preferably 50 mol% or less, more preferably 30 mol% or less, even more preferably 20 mol% or less, still more preferably 10 mol% or less, still more preferably 5 mol% or less, still more preferably 1 mol% or less, still more preferably 0 mol%, and even more preferably zero, based on the total repeating units of the polyimide resin.

[0022] The polyimide resin having the structural unit of formula (1b) further preferably contains a repeating unit represented by the following formula (2b):

[0023] From the viewpoint of heat resistance and mechanical strength, the repeating unit represented by formula (2b) is preferably 50 mol% or more and 100 mol% or less, more preferably 70 mol% or more and 100 mol% or less, even more preferably 80 mol% or more and 100 mol% or less, still more preferably 90 mol% or more and 100 mol% or less, still more preferably 95 mol% or more and 100 mol% or less, still more preferably 99 mol% or more and 100 mol% or less, and may be 100 mol%, with 100 mol% being even more preferred from the viewpoint of heat resistance and adhesion.

[0024] The polyimide resin may contain a repeating unit other than the repeating unit represented by formula (2b). The content of repeating units other than the repeating unit represented by formula (2b) is preferably 50 mol% or less, more preferably 30 mol% or less, even more preferably 20 mol% or less, still more preferably 10 mol% or less, still more preferably 5 mol% or less, still more preferably 1 mol% or less, still more preferably 0 mol%, and even more preferably zero, based on the total repeating units of the polyimide resin.

[0025] As described above, the polyimide resin more preferably contains at least one repeating unit selected from the group consisting of a repeating unit represented by formula (2a), a repeating unit represented by formula (3a), and a repeating unit represented by formula (2b), and even more preferably contains a repeating unit represented by formula (2b). By containing the repeating unit represented by formula (2b), the polyimide resin can be dissolved in any solvent when preparing a varnish, and is particularly preferred because it can be well dissolved in an ester-based solvent.

[0026] <Structural Units of Polyimide Resin> The polyimide resin has a structural unit A derived from a tetracarboxylic dianhydride and a structural unit B derived from a diamine. In the polyimide resin, structural unit A and structural unit B form an imide structure. The structural unit A preferably includes at least one selected from the group consisting of a structural unit (A1) derived from a compound represented by formula (a1) below, a structural unit (A2) derived from a compound represented by formula (a2) below, and a structural unit (A3) derived from a compound represented by formula (a3) ​​below. The structural unit B preferably includes at least one selected from the group consisting of a structural unit (B1) derived from a compound represented by formula (b1) below, a structural unit (B2) derived from a compound represented by formula (b2) below, and a structural unit (B3) derived from a compound represented by formula (b3) below.

[0027] (Structural Unit A) The structural unit A is a structural unit derived from a tetracarboxylic dianhydride, and preferably includes at least one selected from the group consisting of the structural unit (A1) derived from a compound represented by formula (a1), the structural unit (A2) derived from a compound represented by formula (a2), and the structural unit (A3) derived from a compound represented by formula (a3), and more preferably includes the structural unit (A3) derived from a compound represented by formula (a3). When the structural unit (A1) derived from a compound represented by formula (a1) is included, it is even more preferable that the structural unit (A1) derived from a compound represented by formula (a1) and the structural unit (A2) derived from a compound represented by formula (a2) are included. The compound represented by formula (a1) is 4,4'-oxydiphthalic anhydride (ODPA). By using the structural unit (A1) derived from a compound represented by formula (a1) as a structural unit of a polyimide resin, the polyimide resin will have excellent heat resistance and strength. The compound represented by formula (a2) is 3,3',4,4'-biphenyltetracarboxylic dianhydride (s-BPDA). By using the structural unit (A2) derived from the compound represented by formula (a2) as a structural unit of the polyimide resin, it is possible to further improve heat resistance and strength. The compound represented by formula (a3) ​​is 3,3',4,4'-diphenylsulfonetetracarboxylic dianhydride (DSDA). By using the structural unit (A3) derived from the compound represented by formula (a3) ​​as a structural unit of the polyimide resin, it is possible to further improve heat resistance and adhesion.

[0028] The total ratio of the structural unit (A1), the structural unit (A2), and the structural unit (A3) in the structural unit A is preferably 50 mol% or more and 100 mol% or less, more preferably 70 mol% or more and 100 mol% or less, even more preferably 80 mol% or more and 100 mol% or less, even more preferably 90 mol% or more and 100 mol% or less, still more preferably 95 mol% or more and 100 mol% or less, even more preferably 99 mol% or more and 100 mol% or less, and may be 100 mol%, with 100 mol% being even more preferred from the viewpoint of heat resistance and mechanical strength.

[0029] When the structural unit A contains the structural unit (A1) and the structural unit (A2), the total ratio of the structural unit (A1) and the structural unit (A2) in the structural unit A is preferably 50 mol% or more and 100 mol% or less, more preferably 70 mol% or more and 100 mol% or less. Even more preferably 80 mol% or more and 100 mol% or less, even more preferably 90 mol% or more and 100 mol% or less, even more preferably 95 mol% or more and 100 mol% or less, even more preferably 99 mol% or more and 100 mol% or less, and may be 100 mol%, and 100 mol% is even more preferable from the viewpoint of heat resistance and mechanical strength.

[0030] The ratio of the structural unit (A1) to the total of the structural unit (A1) and the structural unit (A2) is preferably 30 to 100 mol%, and from the viewpoint of heat resistance and strength, it is more preferably 40 to 100 mol%, even more preferably 50 to 100 mol%, even more preferably 60 to 100 mol%, even more preferably 70 to 100 mol%, even more preferably 80 to 100 mol%, even more preferably 90 to 100 mol%, or even 100 mol%. Also, from the viewpoint of heat resistance and strength, it is more preferably 30 to 90 mol%, even more preferably 30 to 80 mol%, even more preferably 30 to 70 mol%, even more preferably 30 to 60 mol%, and even more preferably 30 to 50 mol%.

[0031] From the viewpoint of heat resistance and strength, the proportion of the structural unit (A1) in the structural unit A is preferably 40 mol% or more, more preferably 50 mol% or more, even more preferably 60 mol% or more, still more preferably 70 mol% or more, still more preferably 80 mol% or more, and still more preferably 90 mol% or more, with the upper limit being 100 mol% or less.

[0032] When the structural unit A contains the structural unit (A3), the proportion of the structural unit (A3) in the structural unit A is preferably 50 mol% or more and 100 mol% or less, more preferably 70 mol% or more and 100 mol% or less, even more preferably 80 mol% or more and 100 mol% or less, even more preferably 90 mol% or more and 100 mol% or less, still more preferably 95 mol% or more and 100 mol% or less, even more preferably 99 mol% or more and 100 mol% or less, and may be 100 mol%, with 100 mol% being even more preferred from the viewpoint of heat resistance and adhesion.

[0033] The structural unit A may contain a structural unit other than the structural unit (A1), the structural unit (A2), and the structural unit (A3). Such structural units are not particularly limited, but include structural units derived from aromatic tetracarboxylic dianhydrides other than the structural unit (A1), the structural unit (A2), and the structural unit (A3), structural units derived from alicyclic tetracarboxylic dianhydrides, and structural units derived from aliphatic tetracarboxylic dianhydrides.

[0034] Examples of aromatic tetracarboxylic dianhydrides that provide structural units derived from aromatic tetracarboxylic dianhydrides other than the structural unit (A1), the structural unit (A2), and the structural unit (A3) include pyromellitic anhydride (PMDA), 3,3',4,4'-benzophenonetetracarboxylic dianhydride (BTDA), 9,9-bis(trifluoromethyl)-9H-xanthene-2,3,6,7-tetracarboxylic dianhydride (6FCDA), 2,2-bis[4-( 3,4-dicarboxyphenoxy)phenyl]hexafluoropropane dianhydride, 2,3,3',4'-biphenyltetracarboxylic dianhydride (a-BPDA), 9,9'-bis(3,4-dicarboxyphenyl)fluorene dianhydride (BPAF), hydroquinone diphthalic anhydride (HQDEA), ethylene glycol bis(trimellitate) dianhydride (TMEG), p-phenylene bis(trimellitate) dianhydride (TAHQ), 4,4 '-(Hexafluoroisopropylidene)diphthalic anhydride (6FDA), 2,2',3,3',5,5'-hexamethyl[1,1'-biphenyl]-4,4'-diyl bis(1,3-dioxo-1,3-dihydro-2-benzofuran-5-carboxylate) (TMPBP-TME), 2,2-bis(3,4-dicarboxyphenyl)-propane dianhydride, spiro[11H-difuro[3,4-b:3',4'-i]xanthene-11, Examples of suitable structural units include 9'-[9H]fluorene]-1,3,7,9-tetrone (SFDA), 4,4'-thiodiphthalic anhydride, 5-[4-(1,3-dioxo-2-benzofuran-5-yl)phenyl]-2-benzofuran-1,3-dione, 5-[3-(1,3-dioxo-2-benzofuran-5-yl)phenyl]-2-benzofuran-1,3-dione, and p-biphenylenebis(trimellitic acid monoester acid anhydride) (BP-TME). Among these, pyromellitic anhydride (PMDA) is preferred. By including a structural unit derived from PMDA as structural unit A, a laminate having excellent adhesion, step-filling properties, flatness, and heat resistance can be obtained.

[0035] Examples of alicyclic tetracarboxylic dianhydrides that provide structural units derived from alicyclic tetracarboxylic dianhydrides include cyclohexane-1,2,4,5-tetracarboxylic dianhydride (HPMDA), cyclohexane-1,2,3,4-tetracarboxylic dianhydride, 1,2,3,4-cyclobutanetetracarboxylic dianhydride, 1,2,3,4-cyclopentanetetracarboxylic dianhydride, 1,2,4,5-cyclopentanetetracarboxylic dianhydride, 3,3',4,4'-bicyclohexyltetracarboxylic dianhydride, 1,2,3,4-tetramethyl-1,2,3,4-cyclobutanetetracarboxylic dianhydride, decahydro-1,4:5,8-dimethanonaphthalene-2,3,6,7-tetracarboxylic dianhydride (DNDA), 5,5'-(1,4-phenylene)-bis[hexahydro-4,7- Methanoisobenzofuran-1,3-dione], 5,5'-bis-2-norbornene-5,5',6,6'-tetracarboxylic acid-5,5',6,6'-dianhydride, norbornane-2-spiro-α-cyclopentanone-α'-spiro-2''-norbornane-5,5',6,6'-tetracarboxylic acid anhydride (CpODA), 2,2-propylidene-4,4'-bis(cyclohexane Examples of aliphatic tetracarboxylic acid dianhydrides that provide structural units derived from aliphatic tetracarboxylic acid dianhydrides include 1,2,3,4-butanetetracarboxylic acid dianhydride, ... In this specification, the term "aromatic tetracarboxylic acid dianhydride" refers to a tetracarboxylic acid dianhydride containing one or more aromatic rings, the term "alicyclic tetracarboxylic acid dianhydride" refers to a tetracarboxylic acid dianhydride containing one or more alicyclic rings but no aromatic rings, and the term "aliphatic tetracarboxylic acid dianhydride" refers to a tetracarboxylic acid dianhydride containing neither an aromatic ring nor an alicyclic ring.

[0036] (Structural Unit B) Structural unit B is a structural unit derived from a diamine, and preferably includes at least one selected from the group consisting of structural unit (B1) derived from a compound represented by formula (b1), structural unit (B2) derived from a compound represented by formula (b2), and structural unit (B3) derived from a compound represented by formula (b3). More preferably, it includes at least one selected from the group consisting of structural unit (B1) derived from a compound represented by formula (b1) and structural unit (B2) derived from a compound represented by formula (b2). Even more preferably, it includes structural unit (B1) derived from a compound represented by formula (b1). The compound represented by formula (b1) is 4-aminophenyl-4-aminobenzoate (4-BAAB). By including structural unit (B1) in structural unit B, the resulting polyimide resin has excellent heat resistance and can also have improved adhesion. The compound represented by formula (b2) is bis(4-aminophenyl)terephthalate (APTP). When the structural unit B includes the structural unit (B2), the heat resistance of the resulting polyimide resin is excellent, and the adhesion of the polyimide resin can also be improved. The compound represented by formula (b3) is 1,4-bis(4-aminobenzoyloxy)benzene. When the structural unit B includes the structural unit (B3), the heat resistance of the resulting polyimide resin is excellent, and the adhesion of the polyimide resin can also be improved.

[0037] The total ratio of the structural unit (B1), the structural unit (B2), and the structural unit (B3) in the structural unit B is preferably 30 to 100 mol%, more preferably 70 to 100 mol%, even more preferably 90 to 100 mol%, still more preferably 95 to 100 mol%, or even 100 mol%, and the structural unit B may consist of only at least one selected from the group consisting of the structural unit (B1), the structural unit (B2), and the structural unit (B3). The ratio of the structural unit (B1) in the structural unit B is preferably 30 to 100 mol%, more preferably 70 to 100 mol%, even more preferably 90 to 100 mol%, still more preferably 95 to 100 mol%, or even 100 mol%, and the structural unit B may consist of only the structural unit (B1). The proportion of the structural unit (B2) in the structural unit B is preferably 30 to 100 mol%, more preferably 70 to 100 mol%, even more preferably 90 to 100 mol%, still more preferably 95 to 100 mol%, or even 100 mol%, and the structural unit B may consist solely of the structural unit (B2). The proportion of the structural unit (B3) in the structural unit B is preferably 30 to 100 mol%, more preferably 70 to 100 mol%, even more preferably 90 to 100 mol%, still more preferably 95 to 100 mol%, or even 100 mol%, and the structural unit B may consist solely of the structural unit (B3). When the proportions of the structural unit (B1), the structural unit (B2), and the structural unit (B3) are within the above ranges, the resulting polyimide resin has excellent heat resistance, and the coatability of the varnish and the adhesion of the polyimide resin are also improved.

[0038] The structural unit B may contain structural units other than the structural unit (B1), the structural unit (B2), and the structural unit (B3). Diamines that provide such structural units are not particularly limited, but include aromatic diamines, alicyclic diamines, and aliphatic diamines excluding the compounds represented by formula (b1), the compounds represented by formula (b2), and the compounds represented by formula (b3). Examples of aromatic diamines include 2,2'-bis(trifluoromethyl)-4,4'-diaminodiphenyl ether (6FODA), 2,2'-bis(trifluoromethyl)-4,4'-diaminobiphenyl (2,2'-TFMB), 3,3'-bis(trifluoromethyl)-4,4'-diaminobiphenyl, 2,2'-bis(trifluoromethyl)-5,5'-diaminobiphenyl, 2,2-bis(4-aminophenyl)hexafluoropropane (HFDA), 2 , 2-bis(3-amino-4-methylphenyl)hexafluoropropane, 2,2-bis[4-(4-aminophenoxy)phenyl]hexafluoropropane (HFBAPP), 4,4'-diaminodiphenyl ether (4,4'-ODA), 3,4'-diaminodiphenyl ether, 4,4'-diaminodiphenylmethane (DDM), 4,4'-diaminodiphenyl sulfone (4,4'-DDS), 3,3'-diaminodiphenyl sulfone (3,3'-DDS ), 4,4'-diamino-2,2'-dimethylbiphenyl (mTB), 9,9-bis(4-aminophenyl)fluorene (BAFL), 4,4'-diaminobiphenyl (benzidine), 4,4'-diamino-3,3'-dimethylbiphenyl, 4,4'-diaminodiphenyl sulfide, 4,4'-diaminobenzophenone, 2,2-bis(3-aminophenyl)propane, 2,2-bis(4-aminophenyl)propane, 5-amino-1,3,3-trimethyl -1-(4-aminophenyl)-indan (5-TMDM), 6-amino-1,3,3-trimethyl-1-(4-aminophenyl)-indan (6-TMDM), 1,3-bis(3-amino-α,α-dimethylbenzyl)benzene, 1,3-bis(4-amino-α,α-dimethylbenzyl)benzene (BisAM), 1,4-bis(4-amino-α,α-dimethylbenzyl)benzene (BisAP), 4,4'-bis(3-aminophenoxy)biphenyl, 4,4'-bis(4-aminophenoxy)biphenyl (BODA), 1,1-bis[4-(4-aminophenoxy)phenyl]cyclohexane, 2,2-bis[4-(4-aminophenoxy)phenyl]propane (BAPP), 1,4-bis(3-aminophenoxy)benzene, 1,4-bis(4-aminophenoxy)benzene, 1,3-bis(3-aminophenoxy)benzene, 1,3-bis(4-aminophenoxy)benzene, bis[4-(3-aminophenoxy)phenyl]ketone, bis[4-(4-aminophenoxy)phenyl]ketone [4-(4-aminophenoxy)phenyl]ketone, bis[4-(3-aminophenoxy)phenyl]sulfide, bis[4-(4-aminophenoxy)phenyl]sulfide, bis[4-(3-aminophenoxy)phenyl]ether, bis[4-(4-aminophenoxy)phenyl]ether, bis[4-(3-aminophenoxy)phenyl]sulfone, bis[4-(4-aminophenoxy)phenyl]sulfone, 4,4-diaminobenzanilide, 4-aminobenzoate-4-aminophenyl, 3,4-diaminobenzanilide, and the like. Examples of alicyclic diamines include 1,3-bis(aminomethyl)cyclohexane (1,3-BAC), 1,4-bis(aminomethyl)cyclohexane, 1,3-cyclohexyldiamine, 1,4-cyclohexyldiamine, isophoronediamine, bis(aminomethyl)norbornane, 4,4'-diaminodicyclohexylmethane, 4,4'-diaminodicyclohexyl ether, and 2,2-bis(4-aminocyclohexyl)propane. Examples of aliphatic diamines include ethylenediamine and hexamethylenediamine. In this specification, aromatic diamine refers to a diamine containing one or more aromatic rings, alicyclic diamine refers to a diamine containing one or more alicyclic rings but no aromatic rings, and aliphatic diamine refers to a diamine containing neither an aromatic ring nor an alicyclic ring. The structural units other than the structural units (B1), (B2), and (B3) optionally contained in the structural unit B may be one type, or two or more types.

[0039] The polyimide resin may contain a structure other than a polyimide chain (a structure formed by imide bonding between structural unit A and structural unit B) as long as it does not impair the present invention. Examples of structures other than polyimide chains that can be contained in a polyimide resin include structures containing amide bonds. It is preferable that the polyimide resin contains a polyimide chain (a structure formed by imide bonding between structural unit A and structural unit B) as its main structure. Therefore, the proportion of polyimide chains in the polyimide resin is preferably 80% by mass or more, more preferably 90% by mass or more, even more preferably 99% by mass or more, and even more preferably 100% by mass.

[0040] <Method for Producing Polyimide Resin> The polyimide resin may be produced by any method, but is preferably produced by the following method. The polyimide resin may be produced by polymerizing a diamine (hereinafter also referred to as a diamine component) and a tetracarboxylic dianhydride (hereinafter also referred to as a tetracarboxylic acid component) to directly obtain a polyimide. Alternatively, the polyimide resin may be produced by polymerizing a diamine and a tetracarboxylic dianhydride to obtain a polyamic acid or an imide-amic acid copolymer, which is a precursor of the polyimide resin (polyimide resin precursor), and then imidizing the polyimide resin when producing a laminate. However, a method in which a polyimide resin precursor is obtained and imidized when producing a laminate is preferred. Here, we will explain the method for producing the imide-amic acid copolymer, which is a polyimide resin precursor, and polyamic acid, as well as the method for producing a polyimide resin directly. Note that the polyimide resin precursor and polyimide resin may also be collectively referred to as a polymer.

[0041] (Method for producing imide-amic acid copolymer, which is a polyimide resin precursor) A preferred method for producing a polymer containing both imide units and amic acid units (hereinafter also referred to as imide-amic acid copolymer) comprises the following steps 1 and 2: Step 1: A step of reacting a tetracarboxylic dianhydride with a diamine in the presence of a solvent to obtain an imide oligomer; Step 2: A step of mixing the imide oligomer obtained in step 1 with at least one of a tetracarboxylic dianhydride and a diamine, and polymerizing the mixture.

[0042] [Step 1] Step 1 is a step of reacting a tetracarboxylic dianhydride constituting an imide moiety with a diamine in the presence of a solvent to obtain an imide oligomer. In Step 1, the ratio of the diamine to the tetracarboxylic dianhydride is preferably 1.01 to 2 mol, more preferably 1.05 to 1.9 mol, and even more preferably 1.1 to 1.7 mol.

[0043] There are no particular limitations on the method for reacting a tetracarboxylic dianhydride with a diamine to obtain an imide oligomer in step 1, and known methods can be used. Specific reaction methods include: (1) a method in which a tetracarboxylic dianhydride, a diamine, and a solvent are charged into a reactor, and the mixture is stirred at 10 to 110°C for 0.5 to 30 hours, and then the temperature is raised to carry out an imidization reaction; (2) a method in which a diamine and a solvent are charged into a reactor and dissolved, and then a tetracarboxylic dianhydride is charged, and the mixture is stirred at 10 to 110°C for 0.5 to 30 hours as needed, and then the temperature is raised to carry out an imidization reaction; and (3) a method in which a tetracarboxylic dianhydride, a diamine, and a solvent are charged into a reactor, and the temperature is immediately raised to carry out an imidization reaction.

[0044] The imidization reaction is preferably carried out while removing water generated during the production using a Dean-Stark apparatus, etc. By performing such an operation, the degree of polymerization and the imidization rate can be further increased.

[0045] In the imidization reaction, a known imidization catalyst can be used. Examples of the imidization catalyst include base catalysts and acid catalysts. Examples of the base catalyst include organic base catalysts such as pyridine, quinoline, isoquinoline, α-picoline, β-picoline, 2,4-lutidine, 2,6-lutidine, trimethylamine, triethylamine, tripropylamine, tributylamine, triethylenediamine, imidazole, N,N-dimethylaniline, and N,N-diethylaniline; and inorganic base catalysts such as potassium hydroxide, sodium hydroxide, potassium carbonate, sodium carbonate, potassium bicarbonate, and sodium bicarbonate. Examples of the acid catalyst include crotonic acid, acrylic acid, trans-3-hexenoic acid, cinnamic acid, benzoic acid, methylbenzoic acid, hydroxybenzoic acid, terephthalic acid, benzenesulfonic acid, paratoluenesulfonic acid, and naphthalenesulfonic acid. The imidization catalysts described above may be used alone or in combination of two or more. Of the above, from the viewpoint of ease of handling, a base catalyst is preferred, an organic base catalyst is more preferred, one or more selected from triethylamine and triethylenediamine is even more preferred, and triethylamine is even more preferred.

[0046] The temperature of the imidization reaction is preferably 120 to 250° C., more preferably 160 to 200° C., from the viewpoint of the reaction rate and suppression of gelation, etc. The reaction time is preferably 0.5 to 10 hours after the start of distillation of the produced water.

[0047] The above method provides a solution containing an imide oligomer dissolved in a solvent. The solution containing the imide oligomer obtained in step 1 may contain at least a portion of the components used as the tetracarboxylic dianhydride or diamine in step 1 as unreacted monomers, as long as the effects of the present invention are not impaired.

[0048] [Step 2] Step 2 is a step of mixing the imide oligomer obtained in step 1 with at least one of a tetracarboxylic dianhydride and a diamine, followed by polymerization.

[0049] In the entire process of steps 1 and 2, the ratio of the diamine component to the tetracarboxylic acid component is preferably 0.9 to 1.1 moles.

[0050] In step 2, the method for polymerizing the imide oligomer, tetracarboxylic dianhydride, and diamine obtained in step 1 is not particularly limited, and known methods can be used. Specific reaction methods include (1) a method in which the imide oligomer and at least one of the tetracarboxylic dianhydride and diamine are charged into a reactor and stirred at 0 to 120°C, preferably 5 to 80°C, for 1 to 72 hours, and (2) a method in which the imide oligomer and a solvent are charged into a reactor and dissolved, and then at least one of the tetracarboxylic dianhydride and diamine is charged and stirred at 0 to 120°C, preferably 5 to 80°C, for 1 to 72 hours. When the reaction is carried out at 80°C or below, the molecular weight of the copolymer obtained in step 2 does not vary depending on the temperature history during polymerization, and the progress of thermal imidization can be suppressed, allowing the copolymer to be produced stably.

[0051] The concentration of the copolymer in the resulting solution is preferably 1 to 50% by mass, more preferably 3 to 35% by mass, and even more preferably 5 to 30% by mass.

[0052] (Method for Producing Polyamic Acid, a Polyimide Resin Precursor) When the polyimide resin precursor is polyamic acid, a preferred method for producing the polyimide resin precursor is to react a tetracarboxylic dianhydride with a diamine in the presence of a solvent to obtain a polyamic acid. There are no particular limitations on the method for polymerizing the tetracarboxylic dianhydride and the diamine, and known methods can be used. Specific reaction methods include charging a solution containing the diamine and a solvent and the tetracarboxylic dianhydride into a reactor and stirring at 0 to 120°C, preferably 5 to 80°C, for 1 to 72 hours. The ratio of the diamine component to the tetracarboxylic acid component is preferably 0.9 to 1.1 moles. When the reaction is carried out at 80°C or below, the molecular weight of the polyamic acid does not vary depending on the temperature history during polymerization, and the progress of thermal imidization can be suppressed, allowing for stable production of the polyamic acid.

[0053] The concentration of the polyamic acid in the resulting solution is preferably 1 to 50% by mass, more preferably 3 to 35% by mass, and even more preferably 5 to 30% by mass.

[0054] (Method for Producing Polyimide Resin) A preferred method for directly obtaining a polyimide resin is a method in which a tetracarboxylic dianhydride and a diamine are reacted in the presence of a solvent to obtain a polyimide resin.

[0055] The method for polymerizing the tetracarboxylic dianhydride and the diamine is not particularly limited, and any known method can be used. Specific reaction methods include (1) a method in which a solution containing the diamine and a solvent and the tetracarboxylic dianhydride are charged into a reactor, and the mixture is stirred at 10 to 110°C for 0.5 to 30 hours as needed, and then the temperature is raised to carry out the imidization reaction, and (2) a method in which a solution containing the diamine and a solvent and the tetracarboxylic dianhydride are charged into a reactor, and the temperature is immediately raised to carry out the imidization reaction.

[0056] The imidization reaction is preferably carried out while removing water generated during the production using a Dean-Stark apparatus, etc. By performing such an operation, the degree of polymerization and the imidization rate can be further increased.

[0057] In the imidization reaction, a known imidization catalyst can be used. Examples of the imidization catalyst include base catalysts and acid catalysts. Examples of the base catalyst include organic base catalysts such as pyridine, quinoline, isoquinoline, α-picoline, β-picoline, 2,4-lutidine, 2,6-lutidine, trimethylamine, triethylamine, tripropylamine, tributylamine, triethylenediamine, imidazole, N,N-dimethylaniline, and N,N-diethylaniline; and inorganic base catalysts such as potassium hydroxide, sodium hydroxide, potassium carbonate, sodium carbonate, potassium bicarbonate, and sodium bicarbonate. Examples of the acid catalyst include crotonic acid, acrylic acid, trans-3-hexenoic acid, cinnamic acid, benzoic acid, methylbenzoic acid, hydroxybenzoic acid, terephthalic acid, benzenesulfonic acid, paratoluenesulfonic acid, and naphthalenesulfonic acid. The imidization catalysts described above may be used alone or in combination of two or more. Of the above, from the viewpoint of ease of handling, a base catalyst is preferred, an organic base catalyst is more preferred, one or more selected from triethylamine and triethylenediamine is even more preferred, and triethylamine is even more preferred.

[0058] The temperature of the imidization reaction is preferably 120 to 250° C., more preferably 160 to 200° C., from the viewpoint of the reaction rate and suppression of gelation, etc. The reaction time is preferably 0.5 to 10 hours after the start of distillation of the produced water.

[0059] The concentration of the polyimide in the resulting solution is preferably 1 to 50% by mass, more preferably 3 to 35% by mass, and even more preferably 5 to 30% by mass.

[0060] Next, raw materials used in the production methods of the imide-amic acid copolymer, polyamic acid, and polyimide resin will be described.

[0061] [Tetracarboxylic acid dianhydride] The tetracarboxylic acid dianhydride used as a raw material in the production method is preferably the tetracarboxylic acid dianhydride described in the structural unit A of the polyimide resin. Examples of tetracarboxylic acid dianhydrides include, but are not limited to, acid dianhydrides, and may be derivatives thereof as long as they provide the structural unit A. Examples of such derivatives include tetracarboxylic acids (free acids) and alkyl esters of the tetracarboxylic acids. Of these, acid dianhydrides are preferred.

[0062] [Diamine] The diamine used as a raw material in the production method is preferably the diamine described above for the structural unit B of the polyimide resin. Examples of diamines include, but are not limited to, diamines, and may be derivatives thereof as long as they provide the structural unit B in the polymer. Examples of such derivatives include diisocyanates corresponding to the diamines. Among these, diamines are preferred.

[0063] [End-capping Agent] In addition to the tetracarboxylic acid component and diamine component described above, a terminal-capping agent may also be used in the production of the polymer. In the production of the imide-amidic acid copolymer, the terminal-capping agent is preferably used in step 2. Preferred terminal-capping agents are acid anhydrides, monoamines, or dicarboxylic acids. The amount of terminal-capping agent introduced is preferably 0.0001 to 20 mol, more preferably 0.1 to 10 mol, and even more preferably 0.5 to 5 mol, per mol of the tetracarboxylic acid component. Recommended monoamine terminal-capping agents include, for example, methylamine, ethylamine, propylamine, butylamine, benzylamine, 4-methylbenzylamine, 4-ethylbenzylamine, 4-dodecylbenzylamine, 3-methylbenzylamine, 3-ethylbenzylamine, aniline, 3-methylaniline, 4-methylaniline, o-aminophenol, m-aminophenol, p-aminophenol, o-aminobenzoic acid, m-aminobenzoic acid, and p-aminobenzoic acid. Of these, benzylamine, aniline, o-aminophenol, m-aminophenol, p-aminophenol, o-aminobenzoic acid, m-aminobenzoic acid, and p-aminobenzoic acid are preferably used. As the dicarboxylic acid end-capping agent, dicarboxylic acids are preferred, and a portion of the dicarboxylic acid may be ring-closed. For example, phthalic acid, phthalic anhydride, 4-chlorophthalic acid, tetrafluorophthalic acid, 2,3-benzophenonedicarboxylic acid, 3,4-benzophenonedicarboxylic acid, cyclopentane-1,2-dicarboxylic acid, 4-cyclohexene-1,2-dicarboxylic acid, trimellitic anhydride, and the like are recommended. Of these, phthalic acid, phthalic anhydride, and trimellitic anhydride are preferably used.

[0064] [Solvent] The solvent used in the method for producing a polymer may be any solvent capable of dissolving the polymer to be produced, such as an aprotic solvent, a phenolic solvent, an ether solvent, or a carbonate solvent.

[0065] Specific examples of aprotic solvents include amide solvents such as cyclic amides and chain amides, phosphorus-containing amide solvents, sulfur-containing solvents, ketone solvents, and ester solvents including cyclic esters. Examples of cyclic amides include N-methylpyrrolidone, N-methylcaprolactam, and 1,3-dimethylimidazolidinone, with N-methylpyrrolidone being preferred. Examples of chain amides include N,N-dimethylformamide, N,N-dimethylacetamide, and tetramethylurea. Examples of cyclic esters include γ-butyrolactone and γ-valerolactone. Other examples of ester solvents include 2-methoxy-1-methylethyl acetic acid. Examples of phosphorus-containing amide solvents include hexamethylphosphoric amide and hexamethylphosphine triamide. Examples of sulfur-containing solvents include dimethyl sulfone, dimethyl sulfoxide, and sulfolane. Examples of ketone solvents include acetone, methyl ethyl ketone, cyclohexanone, and methylcyclohexanone.

[0066] Specific examples of phenol-based solvents include phenol, o-cresol, m-cresol, p-cresol, 2,3-xylenol, 2,4-xylenol, 2,5-xylenol, 2,6-xylenol, 3,4-xylenol, and 3,5-xylenol. Specific examples of ether-based solvents include 1,2-dimethoxyethane, bis(2-methoxyethyl)ether, 1,2-bis(2-methoxyethoxy)ethane, bis[2-(2-methoxyethoxy)ethyl]ether, tetrahydrofuran, and 1,4-dioxane. Specific examples of carbonate-based solvents include diethyl carbonate, methyl ethyl carbonate, ethylene carbonate, and propylene carbonate. Among the above solvents, preferred are solvents that contain at least one selected from the group consisting of cyclic amides, linear amides, and cyclic esters, more preferred are solvents that contain at least one selected from the group consisting of cyclic amides and cyclic esters, and even more preferred are solvents that contain cyclic esters. More specifically, the solvent contains at least one selected from the group consisting of N-methylpyrrolidone and γ-butyrolactone, and even more preferably γ-butyrolactone. The above solvents may be used alone or in combination of two or more.

[0067] (Polyimide Resin Precursor) In the method for producing a polyimide resin and the method for producing a laminate described below, the polyimide resin precursor used as a raw material for the polyimide resin preferably has a structural unit of the following general formula (1).

[0068] The polyimide resin precursor preferably has a structural unit of formula (1), more preferably has at least one structural unit selected from the group consisting of a structural unit of formula (1a) below and a structural unit of formula (1b) below, and even more preferably has a structural unit of formula (1b) below:

[0069] The polyimide resin precursor having the structural unit of formula (1a) more preferably contains at least one selected from the group consisting of a repeating unit represented by formula (4a) below and a repeating unit represented by formula (5a) below, still more preferably contains a repeating unit represented by formula (4a) below, and still more preferably contains a repeating unit represented by formula (4a) below and a repeating unit represented by formula (5a) below. (In formula (4a) and formula (5a), X 1 and X 2 are each independently a hydrogen atom, an alkyl group having 1 to 6 carbon atoms, or an alkylsilyl group having 3 to 9 carbon atoms.

[0070] The "repeating unit" in the polyimide resin precursor is an amic acid unit containing a structural unit derived from one tetracarboxylic dianhydride and a structural unit derived from one diamine. 1 and X 2 are each independently at least one selected from the group consisting of a hydrogen atom, an alkyl group having 1 to 6 carbon atoms, and an alkylsilyl group having 3 to 9 carbon atoms, preferably at least one selected from the group consisting of a hydrogen atom and an alkyl group having 1 to 6 carbon atoms, more preferably a hydrogen atom. The ratio of the repeating unit represented by formula (4a) to the total of the repeating unit represented by formula (4a) and the repeating unit represented by formula (5a) is preferably 30 to 100 mol%, and from the viewpoint of transparency, more preferably 40 to 100 mol%, even more preferably 50 to 100 mol%, still more preferably 60 to 100 mol%, still more preferably 70 to 100 mol%, still more preferably 80 to 100 mol%, still more preferably 90 to 100 mol%, or even 100 mol%. Furthermore, from the viewpoint of heat resistance and strength, it is more preferably 30 to 90 mol%, even more preferably 30 to 80 mol%, still more preferably 30 to 70 mol%, even more preferably 30 to 60 mol%, and still more preferably 30 to 50 mol%.

[0071] From the viewpoint of heat resistance and mechanical strength, the sum of the repeating units represented by formula (4a) and the repeating units represented by formula (5a) is preferably 50 mol% or more and 100 mol% or less, more preferably 70 mol% or more and 100 mol% or less, even more preferably 80 mol% or more and 100 mol% or less, still more preferably 90 mol% or more and 100 mol% or less, still more preferably 95 mol% or more and 100 mol% or less, still more preferably 99 mol% or more and 100 mol% or less, and may be 100 mol%, with 100 mol% being even more preferred from the viewpoint of heat resistance and mechanical strength.

[0072] From the viewpoint of transparency, the repeating unit represented by formula (4a) preferably accounts for 40 mol% or more, more preferably 50 mol% or more, even more preferably 60 mol% or more, still more preferably 70 mol% or more, still more preferably 80 mol% or more, and still more preferably 90 mol% or more of the total repeating units of the polyimide resin precursor, with the upper limit being 100 mol% or less.

[0073] The polyimide resin precursor may contain repeating units other than the repeating unit represented by formula (4a) and the repeating unit represented by general formula (5a). The content of repeating units other than the repeating unit represented by formula (4a) and the repeating unit represented by general formula (5a) is preferably 50 mol% or less, more preferably 30 mol% or less, more preferably 20 mol% or less, even more preferably 10 mol% or less, still more preferably 5 mol% or less, still more preferably 1 mol% or less, still more preferably 0 mol%, and even more preferably zero, based on the total repeating units of the polyimide resin precursor.

[0074] The polyimide resin precursor having the structural unit of formula (1b) preferably contains a repeating unit represented by the following formula (4b). (In formula (4b), X 1 and X 2 are each independently a hydrogen atom, an alkyl group having 1 to 6 carbon atoms, or an alkylsilyl group having 3 to 9 carbon atoms.

[0075] In the formula (4b), X 1 and X 2 are each independently at least one selected from the group consisting of a hydrogen atom, an alkyl group having 1 to 6 carbon atoms, and an alkylsilyl group having 3 to 9 carbon atoms, preferably at least one selected from the group consisting of a hydrogen atom and an alkyl group having 1 to 6 carbon atoms, more preferably a hydrogen atom. From the viewpoint of heat resistance and mechanical strength, the repeating unit represented by formula (4b) is preferably 50 mol% to 100 mol%, more preferably 70 mol% to 100 mol%, based on all repeating units of the polyimide resin precursor. Even more preferably, it is 80 mol% to 100 mol%, still more preferably 90 mol% to 100 mol%, still more preferably 95 mol% to 100 mol%, still more preferably 99 mol% to 100 mol%, and may be 100 mol%, with 100 mol% being even more preferred from the viewpoint of heat resistance and adhesion.

[0076] The polyimide resin precursor may contain a repeating unit other than the repeating unit represented by formula (4b). The content of repeating units other than the repeating unit represented by formula (4b) is preferably 50 mol% or less, more preferably 30 mol% or less, even more preferably 20 mol% or less, still more preferably 10 mol% or less, still more preferably 5 mol% or less, still more preferably 1 mol% or less, still more preferably 0 mol%, and even more preferably zero, based on the total repeating units of the polyimide resin precursor.

[0077] As described above, the polyimide resin precursor more preferably contains at least one repeating unit selected from the group consisting of a repeating unit represented by formula (4a), a repeating unit represented by formula (5a), and a repeating unit represented by formula (4b), and even more preferably contains a repeating unit represented by formula (4b). By containing the repeating unit represented by formula (4b), the polyimide resin precursor can be dissolved in any solvent when preparing a varnish, and is particularly preferred because it can be well dissolved in an ester-based solvent.

[0078] In addition, when the polyimide resin precursor is an imide-amic acid copolymer, it preferably contains the repeating units described in this section and the repeating units described in the section on polyimide resins. Specifically, the imide moiety preferably contains at least one selected from the group consisting of a repeating unit represented by formula (2b), a repeating unit represented by formula (2a), and a repeating unit represented by formula (3a), more preferably at least one selected from the group consisting of a repeating unit represented by formula (2b) and a repeating unit represented by formula (2a) below, and even more preferably a repeating unit represented by formula (2b). And, the amic acid moiety preferably contains at least one selected from the group consisting of a repeating unit represented by formula (4b), a repeating unit represented by formula (4a), and a repeating unit represented by formula (5a), more preferably at least one selected from the group consisting of a repeating unit represented by formula (4b) and a repeating unit represented by formula (4a) below, and even more preferably a repeating unit represented by formula (4b).

[0079] <Varnish> The laminate of the present invention is preferably obtained by a laminate manufacturing method including a step of applying a polyimide resin varnish or a polyimide resin precursor varnish to a supporting substrate having a step and heating the applied varnish to obtain a polyimide resin layer. The polyimide resin or the polyimide resin precursor has a structural unit of the general formula (1). The varnish used in the manufacture of the laminate will be described below. However, since the preferred varnish is the same for both a varnish containing a polyimide resin and an organic solvent that constitutes the polyimide resin layer and a varnish containing a polyimide resin precursor and an organic solvent that constitutes the polyimide resin layer, they will be collectively described below as "varnish."

[0080] The varnish contains the polyimide resin and an organic solvent, or a polyimide resin precursor and an organic solvent. The solvent is not particularly limited as long as it dissolves the polyimide resin or polyimide resin precursor. However, it is preferable to use the compounds described above as solvents used in the production of polyimide resins or polyimide resin precursors, either alone or in combination of two or more. Among the above solvents, the varnish preferably contains at least one selected from the group consisting of cyclic amides, linear amides, and cyclic esters, more preferably cyclic amides, and even more preferably N-methylpyrrolidone. The varnish may be the polyimide resin solution or polyimide resin precursor solution obtained by the above-described method for producing a polyimide resin or polyimide resin precursor, or a solution obtained by adding a solvent or a solution obtained by reducing the solvent content by concentration or the like.

[0081] In the case of a varnish containing a polyimide resin precursor, the varnish may further contain an imidization catalyst and a dehydration catalyst from the viewpoint of efficiently proceeding with the imidization of the amic acid moiety. The imidization catalyst may be an imidization catalyst having a boiling point of 40°C or higher and 180°C or lower, with amine compounds having a boiling point of 180°C or lower being preferred. An imidization catalyst having a boiling point of 180°C or lower prevents the polyimide film obtained from the laminate formed and drying at high temperatures from becoming discolored, which could impair its appearance. Furthermore, an imidization catalyst having a boiling point of 40°C or higher can prevent the polyimide film from volatilizing before the imidization has progressed sufficiently. Examples of amine compounds suitable for use as imidization catalysts include pyridine and picoline. The above imidization catalysts may be used alone or in combination of two or more. Examples of dehydration catalysts include acid anhydrides such as acetic anhydride, propionic anhydride, n-butyric anhydride, benzoic anhydride, and trifluoroacetic anhydride; carbodiimide compounds such as dicyclohexylcarbodiimide; and the like. These may be used alone or in combination of two or more.

[0082] The polyimide resin or polyimide resin precursor contained in the varnish is solvent-soluble, allowing for a high concentration varnish. The varnish preferably contains 1 to 40% by mass of the polyimide resin or polyimide resin precursor, more preferably 3 to 40% by mass, and even more preferably 5 to 30% by mass. The viscosity of the varnish is preferably 0.1 to 200 Pa·s, more preferably 1 to 20 Pa·s. The viscosity of the varnish is measured at 25°C using an E-type viscometer. The varnish may also contain various additives, such as inorganic fillers, adhesion promoters, release agents, flame retardants, UV stabilizers, surfactants, leveling agents, defoamers, fluorescent brighteners, crosslinking agents, polymerization initiators, and photosensitizers, as long as they do not impair the required properties of the polyimide film.

[0083] <Inorganic Film> The laminate of the present invention preferably comprises a supporting substrate having a step, a polyimide resin layer on the supporting substrate, and an inorganic film on the polyimide resin layer. The inorganic film preferably contains silicon. The inorganic film more preferably comprises at least one selected from the group consisting of silicon oxide and silicon nitride, and even more preferably comprises at least one selected from the group consisting of silicon oxide and silicon nitride. The inorganic film is even more preferably silicon oxide or silicon nitride, and even more preferably silicon nitride. When the inorganic film is silicon nitride, the effects of the present invention can be fully exhibited, and the film has excellent film-forming properties and heat resistance. Furthermore, silicon nitride has excellent barrier properties and chemical stability, making it an excellent inorganic film to be used in the laminate of the present invention. The inorganic film is an insulating film. That is, the inorganic film functions as an insulating film and a barrier film in the laminate, and also functions as a buffer film.

[0084] The thickness of the inorganic film is preferably 1 to 1,000 nm, more preferably 1 to 400 nm, even more preferably 10 to 300 nm, and even more preferably 20 to 200 nm.

[0085] [Method for Producing Laminate] The laminate of the present invention may be obtained by any production method as long as it has the above-mentioned configuration, but is preferably produced by the following method. Specifically, it is a method for producing a laminate comprising the steps of applying a polyimide resin varnish or a polyimide resin precursor varnish to a supporting substrate having a step and heating the applied varnish to obtain a polyimide resin layer, and the polyimide resin or the polyimide resin precursor is preferably produced by a method for producing a laminate in which the polyimide resin or the polyimide resin precursor has a structural unit represented by the following general formula (1):

[0086] In the present production method, the supporting substrate having a step, the polyimide resin varnish, the polyimide resin precursor varnish, the polyimide resin, and the polyimide resin precursor are as described above in this specification, and the preferred ranges are also as described above in this specification.

[0087] (Step of Obtaining a Polyimide Resin Layer) This production method first includes a step of applying a polyimide resin varnish or polyimide resin precursor varnish to a supporting substrate having a step, followed by heating to obtain a polyimide resin layer. This step results in a laminate in which a polyimide resin layer is laminated on a supporting substrate having a step. The heating temperature is preferably 300°C or higher, more preferably 300 to 500°C. The heating time is preferably 1 minute to 6 hours, more preferably 10 minutes to 3 hours, and even more preferably 20 minutes to 2 hours. In order to remove the solvent contained in the varnish, preheating at 60 to 250°C may be performed before heating to 300°C or higher. The preheating temperature is preferably 60 to 250°C, more preferably 70 to 180°C. The preheating time is preferably 1 minute to 6 hours, more preferably 5 minutes to 2 hours, and even more preferably 10 minutes to 1 hour. Preheating may be performed multiple times. Examples of the heating atmosphere include air gas, nitrogen gas, oxygen gas, hydrogen gas, and a nitrogen / hydrogen mixed gas. In order to suppress discoloration of the resulting polyimide resin, nitrogen gas having an oxygen concentration of 100 ppm or less and a nitrogen / hydrogen mixed gas containing a hydrogen concentration of 0.5% or less are preferred.

[0088] (Polishing Step) The laminate of the present invention has a polyimide resin layer on a supporting substrate having a step, and in order to increase the flatness of the laminate surface and improve the accuracy of bonding between wafers, the surface of the polyimide resin layer of the laminate obtained in the above step may be polished. That is, it is preferable that the method for producing a laminate of the present invention further includes, following the above step, a step of polishing the surface of the polyimide resin layer opposite to the surface that contacts the supporting substrate.

[0089] The polishing method used in this step is not particularly limited, but preferred polishing methods include mechanical polishing, chemical polishing, and chemical mechanical polishing. From the viewpoint of improving flatness, chemical mechanical polishing is more preferred, and two or more of these may be combined. The slurry used in chemical mechanical polishing (CMP) is preferably a slurry in which particles of an appropriate particle size are dispersed depending on the required flatness. As the slurry, an aqueous dispersion of alumina, silica, or silicon carbide is preferred, and an alumina slurry is more preferred, and two or more of these may be used. It is also more preferred to perform rough polishing with a large particle size and finish polishing with a small particle size, and the polishing process may be divided into three or more stages. The polishing pad may be selected appropriately depending on the size, application, slurry, etc. of the laminate, but a urethane pad is preferred. For mechanical polishing, abrasive paper, abrasive belt, grinder, etc. can be used. Diamond, alumina, etc. are preferred as abrasive grains fixed to the abrasive paper, etc.

[0090] (Step of Laminating Inorganic Film) The laminate of the present invention has a polyimide resin layer on a supporting substrate having a step, and may further have an inorganic film on the polyimide resin layer. When the laminate of the present invention has an inorganic film, it preferably further has a step of laminating an inorganic film after the step of obtaining the polyimide resin layer or the step of polishing. The inorganic film may be laminated by any method, but is preferably laminated by sputtering, CVD film formation, or vacuum deposition.

[0091] The present invention will be specifically described below with reference to examples, but the present invention is not limited to these examples in any way.

[0092] <Physical Properties of Polyimide Resin> (1) Glass Transition Temperature of Polyimide Resin The glass transition temperature of the polyimide resin constituting the polyimide resin layer in the laminates of the Examples and Comparative Examples was measured as follows: The polyamic acid varnish obtained in the Examples and Comparative Examples (Production of Polyamic Acid Varnish) was applied to a supporting substrate (4-inch silicon wafer), held at 100°C for 10 minutes on a hot plate, and then heated to 400°C at a heating rate of 5°C / min in a nitrogen atmosphere in a hot air dryer, and heated at 400°C for 30 minutes to evaporate the solvent and thermally imidize, thereby obtaining a polyimide film with a thickness of 10 μm. The obtained polyimide film was subjected to TMA measurement using a thermomechanical analyzer "TMA 7100C" manufactured by Hitachi High-Tech Science Corporation, with a sample size of 4 mm x 20 mm, in tensile mode, under conditions of a load of 50 mN and a heating rate of 10 ° C / min, with the temperature rising from 40 ° C to 500 ° C. The point at which an inflection point of elongation was observed was extrapolated to determine the glass transition temperature (Tg). The higher the glass transition temperature (Tg), the better the heat resistance. The glass transition temperatures of the polyimide resins are shown in Table 1.

[0093] <Process Evaluation> Process evaluation of the laminate was performed using the method shown below. (1) Adhesion The adhesion of the laminates (support substrate / polyimide resin layer having steps) obtained in the Examples and Comparative Examples was measured in accordance with ASTM D3359. Specifically, a cross-cut test was performed under the following conditions to evaluate adhesion. (Adhesion after Post-Bake) Using a cutter guide and a cutter knife, 10 x 10 cuts (100 squares (each square measuring 1 mm x 1 mm)) reaching the support substrate were made in the polyimide resin layer of the laminates (support substrate / polyimide resin layer having steps) obtained in the Examples and Comparative Examples. Tape (Cellotape (registered trademark), CT-24, manufactured by Nichiban Co., Ltd.) was applied evenly to the grid portion (cross-cut portion) over an area of ​​20 mm beyond the grid portion, ensuring that no air bubbles or the like were trapped. The applied tape was peeled off within 0.5 to 1 second, the state of the grid portion was observed, and the number of squares remaining without being peeled off was counted. The greater the number of remaining squares, the higher the adhesion. The evaluation criteria were as follows: A: The number of remaining squares was 80 or more out of 100 squares. B: The number of remaining squares was 50 or more but less than 80 out of 100 squares. D: The number of remaining squares was less than 50 out of 100 squares. (Adhesion after annealing) The laminates (support substrate / polyimide resin layer having steps) obtained in the examples and comparative examples were further heated and annealed at 400 ° C for 3 hours. After annealing, a cutter guide and a cutter knife were used to make 10 x 10 cuts (100 squares (1 square size 1 mm x 1 mm)) in the polyimide resin layer reaching the support substrate. Tape (Nichiban Co., Ltd., Cellotape (registered trademark), CT-24) was applied flat to the lattice portion (crosscut portion) created by the cuts over a range of 20 mm beyond the lattice portion to prevent the inclusion of air bubbles. The attached tape was peeled off within 0.5 to 1 second, the state of the grid portion was observed, and the number of squares remaining that were not peeled off was counted. The more squares remaining, the higher the adhesion. The evaluation criteria were as follows: A: The number of remaining squares was 80 or more out of 100 squares B: The number of remaining squares was 50 or more but less than 80 out of 100 squares D: The number of remaining squares was less than 50 out of 100 squares

[0094] (2) Embeddability The stepped portion of the laminate (support substrate / polyimide resin layer having a step) obtained in the examples and comparative examples was cut, and the corner portion of the lower step of the laminate was observed with a scanning electron microscope (SU8000, manufactured by Hitachi High-Technologies Corporation) at a magnification of 5000 times to evaluate the embeddability of the resin in the support substrate having a step. Evaluation was made according to the following criteria. A: No space was observed between the support substrate and the resin. D: Space was observed between the support substrate and the resin.

[0095] (3) Flatness The polyimide resin layer side of the laminates (support substrate / polyimide resin layer having a step) obtained in the Examples and Comparative Examples was polished by one of the following three methods. After polishing, the step portion of the laminate was cleaved, and the cross section was enlarged using a digital microscope VHX-7000 (manufactured by Keyence Corporation). The height difference between the thinnest part of the polyimide resin layer formed on the lower part of the step of the support substrate of the polyimide resin layer and the thickest part of the polyimide resin layer formed on the upper part of the step of the support substrate was measured and evaluated according to the following criteria. The "height" is the length from the plane formed on the surface of the lower part of the step of the support substrate to the surface of the polyimide resin layer in the vertical direction. The smaller the height difference, the better the flatness. Note that the polyimide resin layer had poor adhesion to the support substrate and the polyimide resin layer peeled off during polishing, which was rated D. A: The height difference between the bottom and top of the step was 1.0 μm or less. B: The height difference between the bottom and top of the step was more than 1.0 μm and less than 2.0 μm. C: The height difference between the bottom and top of the step was more than 2.0 μm. D: The step peeled off during polishing and could not be polished. (Polishing Method 1: Mechanical Polishing) The polyimide resin layer was polished using abrasive paper. Specifically, the polyimide resin layer was polished using "abrasive paper #2500 (6 μm) with a load of 100 g for 2 minutes," "diamond film (2 μm) with a load of 100 g for 2 minutes," and "diamond film (0.5 μm) with a load of 100 g for 2 minutes." (Polishing Method 2: CMP1) The polyimide resin layer was polished using an alumina slurry. Specifically, the polyimide resin layer was polished using "alumina slurry with a particle size of 1.5 μm, a polishing pressure of 5.3 psi, a rotation speed of 100 rpm, and 4 minutes 30 seconds." (Polishing Method 3: CMP2) The polyimide resin was polished using an alumina slurry. Specifically, the polyimide resin layer was polished using an alumina slurry with a particle size of 1.5 μm, a polishing pressure of 5.3 psi, a rotation speed of 100 rpm, and 1 minute 30 seconds, and a silica slurry with a particle size of 100 nm, a polishing pressure of 5.3 psi, a rotation speed of 100 rpm, and 5 minutes. (Polishing Method 4: Mechanical Polishing / Grinder) The polyimide resin was polished using a semiconductor wafer grinding device.Specifically, a blade having a roughness of #6000 was attached, and the polyimide resin layer was polished at a polishing speed of 0.1 μm / s, a spindle rotation speed of 2000 rpm, and a table rotation speed of 100 rpm.

[0096] (4) Inorganic film formability (evaluation of film formability) An inorganic film of SiN, 1000 Å thick, was formed by sputtering on the polyimide resin layer of the laminate (support substrate / polyimide resin layer having steps) obtained in the examples and comparative examples. The presence or absence of cracks in the inorganic film of the laminate after film formation was evaluated visually. As a result of evaluation without using a microscope, those for which no cracks were observed were further evaluated using a microscope (magnification 100x). The smaller the crack size, the fewer defects there are during film formation, the higher the heat resistance, and the better the film. Those for which there are no cracks are fewer defects during film formation, the higher the heat resistance, and the better the film. A: No cracks are observed in the inorganic film even when magnified 100x with a microscope. D: No cracks are observed in the inorganic film with the naked eye, but cracks are observed in the inorganic film when magnified 100x with a microscope. E: Cracks are observed in the inorganic film with the naked eye.

[0097] (5) Annealing resistance (evaluation of heat resistance) An inorganic film of SiN, 1000 Å, was formed by sputtering on the polyimide resin layer of the laminate (support substrate / polyimide resin layer having steps) obtained in the examples and comparative examples, and the resulting laminate (support substrate / polyimide resin layer / inorganic film) was heated and annealed at 400 ° C. for 3 hours. The presence or absence of cracks in the inorganic film of the laminate (support substrate / polyimide resin / inorganic film) after the annealing treatment was visually evaluated. Evaluation was performed visually and under a microscope. As a result of evaluation without using a microscope, those in which no cracks were observed were further evaluated under a microscope (magnification 100 times). The smaller the size of the cracks, the fewer defects there were during film formation, and the higher the heat resistance, which is good. Those in which there were no cracks were free of defects during film formation, and the higher the heat resistance, which is good. A: No cracks were observed in the inorganic film even under a microscope at 100 times magnification. D: No cracks are visible in the inorganic film with the naked eye, but cracks are visible in the inorganic film when magnified 100 times with a microscope. E: Cracks are visible in the inorganic film with the naked eye.

[0098] The tetracarboxylic acid components and diamine components used in the examples and comparative examples, as well as their abbreviations, are as follows: <Tetracarboxylic acid components> ODPA: 4,4'-oxydiphthalic anhydride (manufactured by Manac Corporation; compound represented by formula (a1)) s-BPDA: 3,3',4,4'-biphenyltetracarboxylic dianhydride (manufactured by Mitsubishi Chemical Corporation; compound represented by formula (a2)) DSDA: 3,3',4,4'-diphenylsulfonetetracarboxylic dianhydride (manufactured by ChinaTech Chemical (Tianjin) Co., Ltd.; compound represented by formula (a3)) PMDA: pyromellitic anhydride (manufactured by Tokyo Chemical Industry Co., Ltd.) <Diamine components> 4-BAAB: 4-aminophenyl-4-aminobenzoate (manufactured by Nihon Junryo Pharmaceutical Co., Ltd.; compound represented by formula (b1)) APTP: bis(4-aminophenyl)terephthalate (manufactured by Tokyo Chemical Industry Co., Ltd.; compound represented by formula (b2)) PPD: p-phenylenediamine

[0099] The abbreviations for the solvents and catalysts used in the examples and comparative examples are as follows: NMP: N-methyl-2-pyrrolidone (manufactured by Tokyo Pure Chemical Industries, Ltd.) GBL: γ-butyrolactone (manufactured by Mitsubishi Chemical Corporation)

[0100] <Production of Laminate (Support Substrate / Polyimide Resin Layer)> Example 1 (Production of Polyamic Acid Varnish) A 1 L five-necked round-bottom flask equipped with a stainless steel crescent-shaped stirring blade, a nitrogen inlet tube, a Dean-Stark condenser, a thermometer, and a glass end cap was charged with 34.836 g (0.100 mol) of APTP and 294.927 g of NMP, and the system was stirred at 50 ° C. under a nitrogen atmosphere at a rotation speed of 200 rpm to obtain a solution. To this solution, 15.511 g (0.050 mol) of ODPA, 14.711 g (0.050 mol) of s-BPDA, and 73.732 g of NMP were added all at once, and the mixture was stirred for 3 hours while maintaining the temperature at 50 ° C. with a mantle heater. Then, 108.429 g of NMP was added to obtain a polyamic acid varnish having a solids concentration of 12% by mass.

[0101] (Production of Polyimide Resin Layer and Laminate) Next, the obtained polyamic acid varnish was applied to a supporting substrate having a step (a 4-inch silicon wafer (step: 10 μm, distance below the step: 280 μm) and a 4-inch silicon wafer on which a SiN film was formed (step: 10 μm, distance below the step: 280 μm)) and held at 80° C. for 20 minutes on a hot plate. Thereafter, the temperature was increased to 400° C. at a rate of 5° C. / min in a nitrogen atmosphere in a hot air dryer. The mixture was heated at 400° C. for 60 minutes to evaporate the solvent and induce thermal imidization, forming a polyimide resin layer on the supporting substrate and obtaining a laminate. The evaluation results of the obtained laminate are shown in Table 1.

[0102] Example 2 A polyamic acid varnish having a solids concentration of 5% by mass was obtained, and a polyimide resin layer was formed on a supporting substrate to obtain a laminate in the same manner as in Example 1, except that the ODPA and s-BPDA were changed to 294.22 g (0.100 mol) of s-BPDA and the amount of NMP used for dilution was changed. The evaluation results of the obtained laminate are shown in Table 1.

[0103] Example 3 A polyamic acid varnish having a solids concentration of 12 mass% was obtained, and a polyimide resin layer was formed on a supporting substrate to obtain a laminate in the same manner as in Example 1, except that ODPA and s-BPDA were changed to 35.828 g (0.100 mol) of DSDA, APTP was changed to 22.825 g (0.100 mol) of 4-BAAB, and the amount of NMP used for dilution was changed. The evaluation results of the obtained laminate are shown in Table 1.

[0104] Example 4 A polyamic acid varnish having a solids concentration of 12% by mass was obtained, and a polyimide resin layer was formed on a support substrate to obtain a laminate in the same manner as in Example 1, except that ODPA and s-BPDA were changed to 25.080 g (0.070 mol) of DSDA and 6.544 g (0.030 mol) of PMDA, APTP was changed to 22.825 g (0.100 mol) of 4-BAAB, and the amount of NMP used for dilution was changed. The evaluation results of the obtained laminate are shown in Table 1.

[0105] Example 5 A polyamic acid varnish having a solids concentration of 12 mass% was obtained, and a polyimide resin layer was formed on a support substrate to obtain a laminate in the same manner as in Example 1, except that ODPA and s-BPDA were changed to 17.914 g (0.050 mol) of DSDA and 10.906 g (0.050 mol) of PMDA, APTP was changed to 22.825 g (0.100 mol) of 4-BAAB, and the amount of NMP used for dilution was changed. The evaluation results of the obtained laminate are shown in Table 1.

[0106] Comparative Example 1 A polyamic acid varnish having a solids concentration of 12 mass% was obtained, and a polyimide resin layer was formed on a supporting substrate to obtain a laminate in the same manner as in Example 1, except that the ODPA and s-BPDA were changed to 294.22 g (0.100 mol) of s-BPDA and the APTP was changed to 10.814 g (0.100 mol) of PPD. The evaluation results of the obtained laminate are shown in Table 1.

[0107]

[0108] As shown in Table 1, the laminates of the examples are excellent in heat resistance, adhesion, step-filling ability, and flatness. Therefore, the laminates of the present invention have the above-mentioned properties and are therefore useful as laminates in semiconductor processes.

Claims

1. A laminate comprising a support substrate having a step and a polyimide resin layer on the support substrate, wherein the polyimide resin constituting the polyimide resin layer has a structural unit of the following general formula (1) and a glass transition temperature of 300°C or higher. 【Chemistry 1】

2. The laminate according to claim 1, further comprising an inorganic film containing silicon on the polyimide resin layer.

3. The laminate according to claim 1 or 2, wherein the height of the step of the support substrate is 0.1 to 50 μm.

4. The laminate according to claim 1 or 2, wherein the thickness of the polyimide resin layer is 0.5 to 300 μm.

5. The laminate according to claim 2, wherein the inorganic film is silicon oxide or silicon nitride.

6. The laminate according to claim 2, wherein the thickness of the inorganic film is 1 to 1,000 nm.

7. The laminate according to claim 1 or 2, wherein the supporting substrate is silicon, silicon carbide, gallium nitride, gallium oxide, aluminum nitride, or diamond.

8. A method for manufacturing a laminate comprising the steps of applying a polyimide resin varnish or a polyimide resin precursor varnish to a support substrate having steps, and heating to obtain a polyimide resin layer, wherein the polyimide resin or polyimide resin precursor has a structural unit of the following general formula (1). 【Chemistry 2】

9. The method for manufacturing a laminate according to claim 8, further comprising the step of polishing the surface of the polyimide resin layer opposite to the surface in contact with the support substrate.

10. A method for manufacturing a laminate according to claim 8 or 9, further comprising the step of laminating an inorganic film on the laminate.

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