Polyimide resin, polyimide varnish, polyimide film, and temporary fixing material composition

Abstract

Provided are a polyimide resin, a polyimide film, a polyimide varnish containing the polyimide resin, and a temporary fixing material composition containing the polyimide resin, the polyimide resin having a low elastic modulus, a low glass transition temperature, heat resistance, and excellent chemical resistance, and dissolving in a safer solvent than NMP or the like at room temperature. A polyimide resin according to the present invention has a structural unit A derived from a tetracarboxylic acid dianhydride and a structural unit B derived from a diamine. The structural unit A includes a structural unit derived from a compound represented by formula (A1), and the structural unit B includes a structural unit derived from a compound represented by formula (B1). (X is a single bond, a hydrocarbon group, -O-, -S-, -SO2-, or -CO-, Y is a C1-7 divalent hydrocarbon group, a divalent substituent represented by the following structural formula, -O-, -S-, -SO2-, or -CO.)

Description

Polyimide resin, polyimide varnish, polyimide film, and temporary fixing material composition

[0001] The present invention relates to a polyimide resin, a polyimide varnish, a polyimide film, and a temporary fixing material composition.

[0002] In recent years, semiconductor electronic components have become lighter and thinner. In 2.5-dimensional and 3-dimensional semiconductor packaging, technological developments are underway to thin semiconductor chips and stack them in multiple layers while connecting them via through silicon vias (TSVs) to achieve higher integration and higher density of semiconductor elements. Furthermore, in the field of power semiconductors, efforts are being made to thin semiconductor electronic circuit boards to reduce conduction loss for energy conservation. One method for thinning semiconductor wafers involves grinding the non-circuit-forming surface (backside) of the semiconductor wafer. Conventionally, during the grinding process, backgrinding tape (protective tape) is applied to the side opposite the grinding surface to prevent damage during grinding. However, backgrinding tape has insufficient heat resistance and is not suitable for the high-temperature processes used in the TSV and power semiconductor fields. Therefore, a method has been proposed in which a semiconductor wafer is fixed to a support substrate such as a silicon wafer or glass substrate that has supportability via a temporary fixing material (adhesive layer), and then grinding and backside circuit formation processing are performed, and then the processed semiconductor circuit formation substrate is peeled off from the support substrate.

[0003] Polyimide adhesives are known as temporary fixing materials for fixing a support substrate to a semiconductor wafer. For example, Patent Document 1 reports a polyimide resin composition for temporary fixing materials containing a polar solvent and a polyimide resin having a viscosity-average molecular weight η of 0.6 to 1.60. Patent Document 2 reports a polyamic acid varnish that does not have an ester bond, an amide bond, or an ether bond, but has a linear alkylene group. Patent Document 3 proposes a temporary fixing material composition in which a support substrate is pressure-bonded to a semiconductor wafer using a temporary bonding adhesive containing a low-volatility, highly polar solvent, followed by heat treatment at 300°C or higher, and then solvent peeling the support substrate and temporary bonding adhesive with a volatile solvent.

[0004] International Publication No. 2013 / 183293 International Publication No. 2023 / 074534 Patent No. 7183840

[0005] Temporary fixing materials for fixing support substrates to semiconductor wafers are required to have heat resistance, peelability, low-temperature drying, and low-temperature adhesion sufficient to withstand the manufacturing process of semiconductor electronic components. In particular, in the field of power semiconductors, heat resistance of 350°C or higher is required for the annealing process and backmetal process after ion implantation. Easy peeling is also required after the heat treatment process is completed. Furthermore, it is preferable to use a solvent with low toxicity for film formation and peeling of temporary fixing materials. Patent Documents 1 to 3 use polyimide varnish or polyamic acid varnish dissolved in N-methyl-2-pyrrolidone (NMP), but it is desirable to use a solvent with a lower environmental impact. Meanwhile, to save energy and improve productivity in the process, it is preferable to be able to perform film formation and adhesion of temporary fixing materials at lower temperatures. Patent Document 3 describes imidization at a high temperature of 400°C for one hour to form a temporary adhesive film on a support substrate. Therefore, there is a need for a temporary fixing material that can be formed into a film at low temperatures and that can bond a semiconductor wafer and a support substrate, that can be passed through a manufacturing process for semiconductor electronic components that involves heat treatment at 350°C or higher, and that can be peeled off without leaving any residue.An object of the present invention is to provide a polyimide resin that has a low elastic modulus, a low glass transition temperature and heat resistance, excellent chemical resistance, and that dissolves in solvents that are safer than NMP and the like at room temperature, a polyimide film, a polyimide varnish containing the polyimide resin, and a temporary fixing material composition containing the polyimide resin.

[0006] The present inventors have discovered that a polyimide resin containing a combination of structural units derived from a specific tetracarboxylic dianhydride and structural units derived from a specific diamine can solve the above problems, and have thus completed the present invention.

[0007] That is, the present invention relates to the following items <1> to <8>: <1> A polyimide resin having a structural unit A derived from a tetracarboxylic dianhydride and a structural unit B derived from a diamine, wherein the structural unit A includes a structural unit (A1') derived from a compound represented by the following formula (A1), and the structural unit B includes a structural unit (B1') derived from a compound represented by the following formula (B1): (In the formula, X represents a single bond, a divalent hydrocarbon group having 1 to 5 carbon atoms, -O-, -S-, -SO2-, or -CO-; and each Y represents independently a divalent hydrocarbon group having 1 to 7 carbon atoms, a divalent substituent represented by the following structural formula, -O-, -S-, -SO2-, or -CO-.) <2> The polyimide resin according to <1>, wherein the compound represented by formula (A1) is a compound represented by the following formula (a1): <3> The polyimide resin according to <1> or <2>, wherein the structural unit B further contains a structural unit (B2') derived from a compound represented by the following formula (B2), and the proportion of the structural unit (B2') within the structural unit B is greater than 0 mol% and not more than 70 mol%: (In the formula, each Z is independently —O—, —COO—, —OCO—, —C(CH3)2—, or —C(CF3)2—.) <4> The polyimide resin according to <3>, wherein the compound represented by formula (B1) is a compound represented by the following formula (b1), and the compound represented by formula (B2) is a compound represented by the following formula (b2): <5> A polyimide varnish containing the polyimide resin according to any one of <1> to <4> and an organic solvent. <6> A polyimide film containing the polyimide resin according to any one of <1> to <4>. <7> A temporary fixing material composition containing the polyimide resin in any one of <1> to <4>. <8> A method for thinning a semiconductor wafer, comprising: Step 1 of applying the temporary fixing material composition according to <7> to a semiconductor wafer or a support substrate to form an adhesive layer for temporary fixing; Step 2 of temporarily fixing the support substrate to the semiconductor wafer via the adhesive layer; Step 3 of grinding the back surface of the semiconductor wafer while the support substrate is temporarily fixed to the semiconductor wafer via the adhesive layer; and Step 4 of peeling off the support substrate.

[0008] According to the present invention, it is possible to provide a polyimide resin that has a low elastic modulus, a low glass transition temperature, and heat resistance, is excellent in chemical resistance, and is soluble in safer solvents at room temperature; a polyimide film; a polyimide varnish containing the polyimide resin; and a temporary fixing material composition containing the polyimide resin.

[0009] [Polyimide Resin] The polyimide resin of the present invention is a polyimide resin having a structural unit A derived from a tetracarboxylic dianhydride and a structural unit B derived from a diamine, in which the structural unit A includes a structural unit (A1′) derived from a compound represented by the following formula (A1), and the structural unit B includes a structural unit (B1′) derived from a compound represented by the following formula (B1): (In the formula, X is a single bond, a divalent hydrocarbon group having 1 to 5 carbon atoms, —O—, —S—, —SO—, or —CO—.) (In the formula, each Y is independently a divalent hydrocarbon group having 1 to 7 carbon atoms, a divalent substituent represented by the following structural formula, -O-, -S-, -SO2-, or -CO-.)

[0010] The polyimide resin of the present invention has a low elastic modulus, a low glass transition temperature, and heat resistance, and exhibits excellent solvent solubility. This is believed to be due to the fact that the polyimide resin contains structural units derived from a specific tetracarboxylic dianhydride having an alicyclic structure that can suppress intermolecular interactions due to CT complex formation while maintaining a certain degree of rigidity, and structural units derived from a specific aromatic diamine having a nonlinear sulfonyl group. This allows the polyimide resin to achieve the contradictory properties of a high weight loss temperature and a low glass transition temperature, and also provides the solvent solubility required for application to a semiconductor wafer or a support substrate, temporary fixation to the support substrate, and subsequent peeling during the semiconductor wafer thinning process. The polyimide resin is described in detail below.

[0011] <Structural Unit A> The structural unit A is a structural unit derived from a tetracarboxylic dianhydride contained in a polyimide resin. The structural unit A includes a structural unit (A1') derived from a compound represented by the following formula (A1). (In the formula, X is a single bond, a divalent hydrocarbon group having 1 to 5 carbon atoms, —O—, —S—, —SO—, or —CO—.)

[0012] When the structural unit A contains the structural unit (A1'), the polyimide resin has a low elastic modulus, a low glass transition temperature, and excellent thermal decomposition resistance, and is excellent in solvent solubility. It is believed that the structural unit A particularly contributes to achieving both high thermal decomposition resistance and a low glass transition temperature, as well as good solvent solubility and visible light transmittance.

[0013] The divalent hydrocarbon group having 1 to 5 carbon atoms is a chain hydrocarbon group such as an alkylene group, an alkenylene group, or an alkynylene group. Examples of the alkylene group include a methylene group, an ethylene group, a propylene group, an isopropylene group, a butylene group, and an isobutylene group. Examples of the alkenylene group include a vinylene group, an arylene group, a 1-butenylene group, a 2-butenylene group, and a pentenylene group. Examples of the alkynylene group include an ethynylene group, a 1-propynylene group, a 2-propynylene group, a butynylene group, and a pentynylene group.

[0014] Examples of the compound represented by formula (A1) include dicyclohexyl-3,4,3',4'-tetracarboxylic dianhydride (H-BPDA), 2,2-propylidene-4,4'-bis(cyclohexane-1,2-dicarboxylic acid) dianhydride, and oxy-4,4'-bis(cyclohexane-1,2-dicarboxylic acid) dianhydride.

[0015] Among these, the compound represented by the formula (A1) is preferably a compound represented by the following formula (a1), that is, dicyclohexyl-3,4,3',4'-tetracarboxylic dianhydride (H-BPDA).

[0016] That is, it is preferable that the structural unit A contains a structural unit (a1') derived from a compound represented by formula (a1). The compound represented by formula (a1) has an alicyclic structure that can suppress interactions due to intermolecular CT complex formation while maintaining a certain degree of rigidity. By including such a structural unit (a1') in the structural unit A, the polyimide resin of the present invention has a low glass transition temperature despite high heat resistance, and can also be provided with the solvent solubility required for the thinning process of semiconductor wafers.

[0017] Among the compounds represented by the formula (A1), commercially available products include dicyclohexyl-3,4,3',4'-tetracarboxylic dianhydride (H-BPDA) manufactured by Tokyo Chemical Industry Co., Ltd.

[0018] The proportion of the structural unit (A1') within the structural unit A is preferably 80 mol% or more, more preferably 90 mol% or more, and preferably 100 mol% or less. Within the structural unit (A1'), the proportion of the structural unit (a1') is preferably 80 mol% or more, more preferably 90 mol% or more, and preferably 100 mol% or less.

[0019] The structural unit A may include a structural unit other than the structural unit (A1′). Compounds that provide such structural units include, but are not limited to, aromatic tetracarboxylic acid dianhydrides and aliphatic tetracarboxylic acid dianhydrides. Examples of aromatic tetracarboxylic dianhydrides include 3,3',4,4'-diphenylsulfonetetracarboxylic dianhydride (DSDA), 4,4'-(hexafluoroisopropylidene)diphthalic anhydride (6FDA), pyromellitic anhydride (PMDA), 4,4-bis(1,3-dioxo-1,3-dihydroisobenzofuran-5-ylcarbonyloxy)biphenyl (BP-TME), 9,9-bis[4-(3,4-dicarboxyphenoxy)phenyl]fluorene dianhydride (BPF-PA), 2,3,6,7-naphthalenetetracarboxylic 2,3:6,7-dianhydride (NTCDA), 3,3',4,4'-benzophenonetetracarboxylic dianhydride (BTDA), 9,9-bis(trifluoromethyl)-9H-xanthene-2, Examples of suitable dianhydrides include 3,6,7-tetracarboxylic dianhydride (6FCDA), 2,2-bis[4-(3,4-dicarboxyphenoxy)phenyl]hexafluoropropane dianhydride, 4,4'-oxydiphthalic anhydride (ODPA), 2,2-bis(3,4-dicarboxyphenyl)-propane dianhydride, 3,3',4,4'-biphenyltetracarboxylic dianhydride (s-BPDA), 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), and p-phenylene bis(trimellitate) dianhydride (TAHQ). Examples of aliphatic tetracarboxylic dianhydrides include 1,2,3,4-butanetetracarboxylic dianhydride. In this specification, an aromatic tetracarboxylic dianhydride refers to a tetracarboxylic dianhydride containing one or more aromatic rings, and an aliphatic tetracarboxylic dianhydride refers to a tetracarboxylic dianhydride containing neither an aromatic ring nor an alicyclic ring. The structural unit A may optionally contain one type of structural unit, or two or more types of structural units.

[0020] <Structural Unit B> The structural unit B includes a structural unit (B1′) derived from a compound represented by the following formula (B1). (In the formula, each Y is independently a divalent hydrocarbon group having 1 to 7 carbon atoms, a divalent substituent represented by the following structural formula, -O-, -S-, -SO2-, or -CO-.)

[0021] The polyimide resin of the present invention, by containing the structural unit (B1'), can achieve both a low glass transition temperature and high thermal decomposition resistance, and can also be provided with the solvent solubility required for the thinning process of semiconductor wafers. In particular, the rigid and non-linear structural unit (B1') having a sulfonyl group and multiple aromatic rings is thought to contribute to the polyimide resin's high thermal decomposition resistance and the low elastic modulus required for adhesiveness.

[0022] In formula (B1), each Y independently represents a divalent hydrocarbon group having 1 to 7 carbon atoms, a divalent substituent represented by the above structural formula, -O-, -S-, -SO2-, or -CO-. Examples of bisphenylfluorene groups include 9,9'-bisphenylfluorene-2,7-diyl and 9,9'-bisphenylfluorene-3,6-diyl groups. Examples of divalent hydrocarbon groups having 1 to 7 carbon atoms include chain hydrocarbon groups such as alkylene groups, alkenylene groups, and alkynylene groups. Examples of the alkylene groups include methylene, ethylene, propylene, isopropylene (-C(CH3)2-), butylene, isobutylene, hexylene, and heptylene groups. Examples of the alkenylene group include a vinylene group, an arylene group, a 1-butenylene group, a 2-butenylene group, a pentenylene group, a hexenylene group, and a heptenylene group. Examples of the alkynylene group include an ethynylene group, a 1-propynylene group, a 2-propynylene group, a butynylene group, a pentynylene group, a hexynylene group, and a heptynylene group. Y is preferably at least one selected from the group consisting of -O- and an isopropylene group (-C(CH3)2-), and more preferably -O-.

[0023] The compound represented by the formula (B1) is preferably a compound represented by the following formula (b1), that is, bis[4-(3-aminophenoxy)phenyl]sulfone (BAPS-M).

[0024] The proportion of the structural unit (B1') in the structural unit B is preferably 30 mol% or more, more preferably 50 mol% or more, and from the standpoints of thermal decomposition resistance and solubility, is even more preferably 70 mol% or more, still more preferably 80 mol% or more, even more preferably 90 mol% or more, still more preferably 95 mol% or more, and preferably 100 mol% or less. In other words, the structural unit B may be composed solely of the structural unit (B1').

[0025] The structural unit B may consist solely of the structural unit (B1′), or may contain, in addition to the structural unit (B1′), a structural unit (B2′) derived from a compound represented by the following formula (B2): (In the formula, each Z is independently -O-, -COO-, -OCO-, -C(CH3)2-, or -C(CF3)2-.) Specific examples of the compound represented by formula (B2) include 1,3-bis(3-aminophenoxy)benzene (TPE-M), 1,3-bis(4-aminophenoxy)benzene (TPE-R), 1,3-bis[2-(3-aminophenyl)-2-propyl]benzene, and 1,3-bis[2-(3-aminophenyl)-2-hexafluoropropyl]benzene. Of these, the compound represented by the following formula (b2), i.e., 1,3-bis(3-aminophenoxy)benzene (TPE-M), is more preferred.

[0026] In the polyimide resin of the present invention, the structural unit B preferably includes a structural unit (B1') derived from a compound represented by formula (B1) above and a structural unit (B2') derived from a compound represented by formula (B2) above, and the compound represented by formula (B1) above is a compound represented by formula (b1) below, and the compound represented by formula (B2) above is a compound represented by formula (b2) below.

[0027] When the structural unit B contains the structural unit (B1') and the structural unit (B2'), the proportion of the structural unit (B2') in the structural unit B is preferably 50 mol% or more, more preferably 60 mol% or more, and preferably 70 mol% or less.

[0028] When the structural unit B comprises the structural unit (B1') and the structural unit (B2'), the molar ratio of the structural unit (B1') to the structural unit (B2') within the structural unit B [(B1') / (B2')] is preferably 30 / 70 to 90 / 10, more preferably 30 / 70 to 80 / 20, and from the viewpoint of reducing the elastic modulus and improving the adhesive properties and thermal decomposition resistance, it is even more preferably 30 / 70 to 50 / 50, and still more preferably 30 / 70 to 40 / 60.

[0029] The proportion of the structural unit (B2') within the structural unit B is preferably 0 to 70 mol%, more preferably 20 to 70 mol%, even more preferably 30 to 70 mol%, and still more preferably 40 to 70 mol%. The total proportion of the structural unit (B1') and the structural unit (B2') within the structural unit B is preferably 50 mol% or more, more preferably 70 mol% or more, even more preferably 90 mol% or more, and preferably 100 mol% or less. The structural unit B may be composed only of the structural unit (B1') and the structural unit (B2').

[0030] The structural unit B may contain structural units other than the structural unit (B1') and the structural unit (B2'). Diamines that provide such structural units are not particularly limited, but include aromatic diamines, alicyclic diamines, and aliphatic diamines excluding both the compounds represented by formula (B1) and the compounds represented by formula (B2). Examples of aromatic diamines include 4-aminophenyl-4-aminobenzoate (4-BAAB), bis(4-aminophenyl)terephthalate (APTP), 1,4-bis(4-aminobenzoyloxy)benzene, 2,2'-bis(trifluoromethyl)-4,4'-diaminodiphenyl ether (6FODA), 2,2'-bis(trifluoromethyl)-4,4'-diaminobiphenyl (2,2'-TFMB), 3,3 ... Aminobiphenyl, 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'-di Aminobenzophenone, 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), 1,4-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, bis[4-(3-aminophenoxy)phenyl]ketone, bis[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-(4-aminophenoxy)phenyl]sulfone, 4,4-diaminobenzanilide, 4-aminobenzoic acid-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 unit optionally contained in structural unit B may be one type or two or more types.

[0031] <Characteristics of Polyimide Resin> The number-average molecular weight of the polyimide resin is preferably 5,000 to 300,000 from the viewpoints of thermal decomposition resistance, solubility, and mechanical strength of the resulting polyimide film. The number-average molecular weight of the polyimide resin can be determined, for example, by gel filtration chromatography using a standard polymethyl methacrylate (PMMA) equivalent value.

[0032] 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). Examples of structures other than a polyimide chain that may be contained in the polyimide resin include a structure containing an amide bond. The polyimide resin preferably 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 50% by mass or more, more preferably 70% by mass or more, even more preferably 90% by mass or more, even more preferably 99% by mass or more, and preferably 100% by mass or less. In other words, the polyimide resin of the present invention may be composed solely of polyimide chains.

[0033] [Method for Producing Polyimide Resin] The method for producing the polyimide resin of the present invention is not particularly limited, but a method for obtaining a polyimide resin by reacting the compound (tetracarboxylic acid component) that provides the above-mentioned structural unit A with the compound (diamine component) that provides the above-mentioned structural unit B. By this method, a polyimide resin can be obtained directly from the tetracarboxylic acid component and the diamine component.

[0034] In this production method, the polyimide resin can be produced by reacting a tetracarboxylic acid component containing a compound that provides the above-mentioned structural unit (A1′) with a diamine component that contains a compound that provides the above-mentioned structural unit (B1′).

[0035] Examples of compounds that provide the structural unit (A1') include, but are not limited to, compounds represented by formula (A1), and derivatives thereof may also be used as long as they provide the same structural unit. Examples of such derivatives include tetracarboxylic acids corresponding to the tetracarboxylic acid dianhydrides represented by formula (A1) and alkyl esters of such tetracarboxylic acids. The compound represented by formula (A1) is preferably a tetracarboxylic acid dianhydride.

[0036] Examples of compounds that provide the structural unit (B1') include, but are not limited to, compounds represented by formula (B1), and may also be derivatives thereof that provide the same structural unit. Examples of such derivatives include diisocyanates that correspond to the compound (diamine) represented by formula (B1).

[0037] The diamine component may contain a structural unit other than the structural unit (B1'), and preferably may contain a structural unit (B2') derived from a compound represented by formula (B2). When the diamine component contains the structural unit (B2'), examples of compounds that provide the structural unit (B2') include, but are not limited to, compounds represented by formula (B2), and may also be derivatives thereof as long as they provide the same structural unit. Examples of such derivatives include diisocyanates corresponding to the compound (diamine) represented by formula (B2).

[0038] Within the diamine component, the molar ratio of the compound that provides the structural unit (B1') to the compound that provides the structural unit (B2') [(B1') / (B2')] is preferably from 30 / 70 to 90 / 10, and more preferably from 30 / 70 to 80 / 20, from the viewpoint of reducing the elastic modulus and improving the adhesive properties and thermal decomposition resistance; and is even more preferably from 30 / 70 to 50 / 50, and still more preferably from 30 / 70 to 40 / 60, from the viewpoint of reducing the elastic modulus and improving the adhesive properties and thermal decomposition resistance.

[0039] The proportion of the compound that provides the structural unit (B1') in the diamine component is preferably 30 mol% or more, more preferably 50 mol% or more, even more preferably 70 mol% or more, even more preferably 80 mol% or more, even more preferably 90 mol% or more, even more preferably 95 mol% or more, and preferably 100 mol% or less. When the diamine component contains a compound that provides the structural unit (B2'), the proportion of the compound that provides the structural unit (B2') in the diamine component is preferably 50 mol% or more, more preferably 60 mol% or more, and preferably 70 mol% or less. The total proportion of the compound that provides the structural unit (B1') and the compound that provides the structural unit (B2') in the diamine component is preferably 50 mol% or more, more preferably 70 mol% or more, even more preferably 90 mol% or more, and preferably 100 mol% or less. The diamine component may consist solely of a compound that provides the structural unit (B1') and a compound that provides the structural unit (B2').

[0040] In the present invention, in addition to the tetracarboxylic acid component and diamine component described above, a terminal blocking agent may be used in the production of the polyimide resin. Monoamines or dicarboxylic acids are preferred as terminal blocking agents. The amount of terminal blocking agent to be introduced is preferably 0.0001 to 0.1 mol, more preferably 0.001 to 0.06 mol, per mol of the tetracarboxylic acid component. Examples of monoamine terminal blocking agents include methylamine, ethylamine, propylamine, butylamine, benzylamine, 4-methylbenzylamine, 4-ethylbenzylamine, 4-dodecylbenzylamine, 3-methylbenzylamine, 3-ethylbenzylamine, aniline, 3-methylaniline, and 4-methylaniline, with benzylamine and aniline being preferred. Dicarboxylic acids are preferred as dicarboxylic acid terminal blocking agents, and a portion of these may be ring-closed. Examples include phthalic acid, phthalic anhydride, 4-chlorophthalic acid, tetrafluorophthalic acid, 2,3-benzophenonedicarboxylic acid, 3,4-benzophenonedicarboxylic acid, cyclohexane-1,2-dicarboxylic acid, cyclopentane-1,2-dicarboxylic acid, and 4-cyclohexene-1,2-dicarboxylic acid, with phthalic acid and phthalic anhydride being preferred.

[0041] The method for reacting the tetracarboxylic acid component and the diamine component is not particularly limited, and known methods can be used. Examples include (1) a method in which the tetracarboxylic acid component, the diamine component, and the reaction solvent are charged into a reactor, stirred at 0 to 80°C for 0.5 to 30 hours, and then heated to carry out the imidization reaction, (2) a method in which the diamine component and the reaction solvent are charged into a reactor and dissolved, and then the tetracarboxylic acid component is charged, stirred at room temperature to 80°C for 0.5 to 30 hours as needed, and then heated to carry out the imidization reaction, and (3) a method in which the tetracarboxylic acid component, the diamine component, and the reaction solvent are charged into a reactor, and immediately heated to carry out the imidization reaction.

[0042] The organic solvent (reaction solvent) used in the production of the polyimide resin may be any solvent that does not inhibit the imidization reaction and can dissolve the resulting polyimide resin at room temperature, such as aprotic solvents, phenolic solvents, ether solvents, and carbonate solvents.

[0043] Specific examples of the aprotic solvent include amide solvents such as N,N-dimethylformamide, N,N-dimethylacetamide, N-methylcaprolactam, 1,3-dimethylimidazolidinone, tetramethylurea, 3-methoxy-N,N-dimethylpropanamide, and 3-butoxy-N,N-dimethylpropanamide; lactone solvents such as γ-butyrolactone (GBL) and γ-valerolactone; glycol solvents such as diethylene glycol dimethyl ether, triethylene glycol, and triethylene glycol dimethyl ether; phosphorus-containing amide solvents such as hexamethylphosphoric amide and hexamethylphosphine triamide; sulfur-containing solvents such as dimethyl sulfone, dimethyl sulfoxide, and sulfolane; ketone solvents such as acetone, cyclopentanone, cyclohexanone, and methylcyclohexanone; amine solvents such as picoline and pyridine; and ester solvents such as 2-methoxy-1-methylethyl acetate.

[0044] 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 reaction solvents, aprotic solvents are preferred, with amide-based solvents and lactone-based solvents being more preferred, and lactone-based solvents being more preferred from the viewpoints of low toxicity and low environmental impact. The above reaction solvents may be used alone or in combination of two or more.

[0045] 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.

[0046] 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 (TEA), 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. Among the above, from the viewpoint of ease of handling, it is preferable to use a base catalyst, it is more preferable to use an organic base catalyst, and it is even more preferable to use at least one selected from the group consisting of triethylamine and triethylenediamine.

[0047] 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.

[0048] [Polyimide Varnish and Temporary Fixing Material Composition] The polyimide varnish of the present invention is obtained by dissolving the polyimide resin of the present invention in an organic solvent. The organic solvent is not particularly limited as long as it is capable of dissolving the polyimide resin, but it is preferable to use the compounds described above as reaction solvents used in the production of polyimide resins, either alone or in combination of two or more. The polyimide varnish of the present invention may be a polyimide solution itself in which a polyimide resin obtained by a polymerization method is dissolved in a reaction solvent, or may be a polyimide solution diluted by further adding a solvent.

[0049] Because the polyimide resin of the present invention is solvent-soluble, it can be made into a highly concentrated varnish that is stable at room temperature. The polyimide varnish of the present invention preferably contains 5 to 40% by mass, more preferably 10 to 30% by mass, of the polyimide resin of the present invention. The viscosity of the polyimide varnish is preferably 1 to 200 Pa·s, more preferably 1 to 100 Pa·s. The viscosity of the polyimide varnish is measured at 25°C using an E-type viscometer. The polyimide varnish of the present invention 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 resin and temporary fixing material. The method for producing the polyimide varnish of the present invention is not particularly limited, and known methods can be used.

[0050] The temporary fixing material composition of the present invention contains the polyimide resin. Therefore, the polyimide varnish can also be used as a temporary fixing material composition. The temporary fixing material composition of the present invention is preferably a composition in which the polyimide resin of the present invention is dissolved in an organic solvent. The organic solvent is not particularly limited as long as it dissolves the polyimide resin, but it is preferable to use the compounds described above as reaction solvents used in producing polyimide resins, either alone or in combination of two or more. The temporary fixing material composition of the present invention may be a polyimide solution itself in which a polyimide resin obtained by a polymerization method is dissolved in a reaction solvent, or may be a polyimide solution diluted by further adding a solvent to the polyimide solution.

[0051] Because the polyimide resin of the present invention is solvent-soluble, it can be made into a high-concentration temporary fixing material composition that is stable at room temperature. The temporary fixing material composition of the present invention preferably contains 5 to 40 mass %, and more preferably 10 to 30 mass %, of the polyimide resin of the present invention. The viscosity of the temporary fixing material composition is preferably 1 to 200 Pa·s, and more preferably 1 to 100 Pa·s. The viscosity of the temporary fixing material composition is a value measured at 25°C using an E-type viscometer. In addition, the temporary fixing material composition of the present invention may contain various additives, such as inorganic fillers, adhesion promoters, release agents, flame retardants, UV stabilizers, surfactants, leveling agents, antifoaming agents, fluorescent brightening agents, crosslinking agents, polymerization initiators, and photosensitizers, within ranges that do not impair the required properties of the polyimide resin and temporary fixing material.

[0052] [Polyimide Film] The polyimide film of the present invention contains the polyimide resin described above, and therefore has a low elastic modulus, a low glass transition temperature, heat resistance, and excellent solvent solubility.

[0053] The polyimide film of the present invention preferably has the following physical properties: the glass transition temperature is preferably 240°C or lower, more preferably 230°C or lower, and even more preferably 220°C or lower; the 1% weight loss temperature is preferably 420°C or higher, more preferably 435°C or higher, and even more preferably 445°C or higher; the weight loss rate when held at 350°C for 1 hour is preferably 1.0% or lower, more preferably 0.7% or lower, and even more preferably 0.4% or lower; and the tensile modulus according to JIS K7127:1999 is preferably 4.0 GPa or lower, more preferably 3.5 GPa or lower, and even more preferably 3.0 GPa or lower.

[0054] The polyimide film of the present invention is soluble at room temperature in low-water-absorbency solvents such as gamma-butyrolactone (GBL). Therefore, a low-water-absorbency solvent can be used to peel the polyimide film, making it less susceptible to humidity and moisture during the semiconductor manufacturing process. GBL is a solvent with a lower environmental impact than NMP.

[0055] Therefore, the polyimide film of the present invention can be suitably used as a temporary fixing material by forming the polyimide film of the present invention on a semiconductor wafer by the following method. The above-mentioned physical property values ​​in the present invention can be specifically measured by the methods described in the Examples.

[0056] There are no particular restrictions on the thickness of the polyimide film of the present invention, but when used as a temporary fixing material, it is preferably 1 to 250 μm, more preferably 5 to 100 μm, even more preferably 8 to 80 μm, and even more preferably 10 to 80 μm. The thickness of the polyimide film can be easily controlled by adjusting the solids concentration and viscosity of the polyimide varnish. Therefore, when using the polyimide film as a temporary fixing material, the thickness can be easily controlled by adjusting the solids concentration and viscosity of the temporary fixing material composition.

[0057] The method for producing the polyimide film of the present invention is not particularly limited, and known methods can be used. For example, a method in which the polyimide varnish of the present invention is applied to a support and heated is exemplified. Specifically, a method in which the polyimide varnish is applied to a smooth support such as a glass plate, a metal plate, or plastic, and then organic solvents contained in the polyimide varnish, such as reaction solvents and dilution solvents, are removed by heating is exemplified. A polyimide varnish containing the polyimide resin of the present invention is suitably used as a raw material for a temporary fixing material. When the polyimide film of the present invention is used as a temporary fixing material, it is applied to a semiconductor wafer or a support.

[0058] Examples of the coating method include known coating methods such as spin coating, slit coating, and blade coating. Among these, spin coating is preferred from the viewpoints of improving film uniformity and workability. A preferred method for removing the organic solvent contained in the polyimide varnish by heating is to evaporate the organic solvent at a temperature of 150°C or less to make it tack-free, and then dry it at a temperature equal to or higher than the boiling point of the organic solvent used (preferably 200 to 350°C, but not particularly limited thereto). Drying is also preferred in an air atmosphere or a nitrogen atmosphere. The pressure of the drying atmosphere may be reduced, normal pressure, or increased pressure. The method for peeling the polyimide film formed on the support from the support is not particularly limited, but examples include laser lift-off, a method using a sacrificial layer for peeling (a method in which a release agent is applied to the surface of the support in advance), a method using a release agent, solvent peeling, and mechanical peeling. When the polyimide film of the present invention is used as a temporary fixing material, methods for peeling it from a laminate consisting of a semiconductor wafer, a temporary fixing material, and a support substrate include a method in which a support substrate having a porous structure is used and the temporary fixing material is dissolved with a solvent; a method in which a laser is irradiated from the support substrate side to peel it off; a method in which a blade is inserted into the interface between the support substrate and the temporary fixing material to mechanically peel it off; and a method in which the temporary fixing material is softened by heat and then slid to peel it off.

[0059] [Method for Thinning a Semiconductor Wafer] The method for thinning a semiconductor wafer of the present invention includes Step 1 of applying the temporary fixing material composition to a semiconductor wafer or a supporting substrate to form an adhesive layer for temporary fixing; Step 2 of temporarily fixing the supporting substrate to the semiconductor wafer via the adhesive layer; Step 3 of grinding the back surface of the semiconductor wafer in a state in which the supporting substrate is temporarily fixed to the semiconductor wafer via the adhesive layer; and Step 4 of peeling off the supporting substrate.

[0060] Step 1 is a step of applying the temporary fixing material composition to a semiconductor wafer or a supporting substrate to form an adhesive layer for temporary fixing. In this step, the adhesive layer is preferably formed by the method described in the manufacturing method of the polyimide film. Specific examples include a method of applying the temporary fixing material composition to a semiconductor wafer or a supporting substrate and heating it. More specific examples include a method of applying the temporary fixing material composition to a semiconductor wafer or a supporting substrate and then removing organic solvents, such as reaction solvents and dilution solvents, contained in the temporary fixing material composition by heating.

[0061] Examples of the coating method include known coating methods such as spin coating, slit coating, and blade coating. Among these, spin coating is preferred from the viewpoints of improving film uniformity and workability. A preferred method for removing the organic solvent contained in the temporary fixing material composition by heating is to evaporate the organic solvent at a temperature of 150°C or less to make it tack-free, and then dry it at a temperature equal to or higher than the boiling point of the organic solvent used (not particularly limited, but preferably 200 to 350°C). Furthermore, drying is preferably performed in an air atmosphere or a nitrogen atmosphere. The pressure of the drying atmosphere may be reduced pressure, normal pressure, or increased pressure.

[0062] Step 2 is a step of temporarily fixing a support substrate to the semiconductor wafer via an adhesive layer. There are no limitations on the method of temporary fixing, but it is preferable to temporarily fix by pressing using a vacuum heat press or the like. The support substrate may be, but is not limited to, a glass substrate, a sapphire substrate, a ceramic substrate, or the like.

[0063] Step 3 is a step of grinding the back surface of the semiconductor wafer while the support substrate is temporarily fixed to the semiconductor wafer via the adhesive layer. The back surface of the semiconductor wafer is the surface of the wide flat surface of the semiconductor wafer opposite to the surface that contacts the adhesive layer. This step reduces the thickness of the semiconductor wafer. Grinding of the back surface of the semiconductor wafer is preferably performed using a grinder. Grinding is preferably performed while supplying grinding water or CMP slurry liquid. The thickness of the semiconductor wafer obtained by this step can be adjusted appropriately depending on the application, but is preferably 5 to 600 μm.

[0064] Step 4 is a step of peeling off the support substrate. In this step, the polyimide film is preferably peeled off by the method described in the manufacturing method. Specific examples include a laser lift-off method, a method using a sacrificial layer for peeling (a method in which a release agent is applied to the surface of the support in advance), and a method of adding a release agent. Methods that can be used include a method in which the adhesive layer is dissolved with a solvent using a support substrate with a porous structure, a method in which a laser is irradiated from the support substrate side to peel it off, a method in which a blade is inserted into the interface between the support substrate and the temporary fixing material to mechanically peel it off, and a method in which the temporary fixing material is softened by heat and slid to peel it off.

[0065] The present invention will be specifically explained below with reference to examples and comparative examples, but the present invention is not limited to these examples in any way.

[0066] <Physical Properties and Evaluation of Polyimide Resin (Polyimide Film)> The methods for measuring and evaluating the physical properties of the polyimide films of the Examples and Comparative Examples are shown below.

[0067] (1) Glass Transition Temperature (Tg) Using a differential scanning calorimeter "DSC 7000X" manufactured by Hitachi High-Tech Science Corporation, a polyimide film (test piece) was heated from 40°C to 220°C at a heating rate of 10°C / min, then cooled to 40°C at a heating rate of 40°C / min, and then heated again to 250°C at a heating rate of 10°C / min. The glass transition temperature (Tg) was calculated from the DSC curve observed during the second heating process.

[0068] (2) 1% Weight Loss Temperature (Td1%) A Hitachi High-Tech Science Corporation "NEXTA STA200RV" thermogravimetric differential thermal analyzer was used. The polyimide film (test piece) was heated from 40°C to 150°C at a heating rate of 10°C / min, held at 150°C for 30 minutes to remove moisture, and then heated to 500°C. The temperature at which the weight decreased by 1% compared to the weight after holding at 150°C for 30 minutes was defined as the 1% weight loss temperature.

[0069] (3) Weight loss rate (%) after heating at 350°C for 1 hour A simultaneous thermogravimetric and differential thermal analyzer "NEXTA STA200RV" manufactured by Hitachi High-Tech Science Corporation was used. The polyimide film (test piece) was heated from 40°C to 150°C at a heating rate of 10°C / min, held at 150°C for 30 minutes to remove moisture, and then heated to 350°C. The weight loss rate was calculated from the weight loss amount after holding at 350°C for 1 hour, based on the weight of the polyimide film when it reached 350°C.

[0070] (4) Tensile Modulus of Elasticity The tensile modulus of elasticity of the polyimide film (test piece) was measured in accordance with JIS K7127:1999 using a tensile tester "Strograph VG-1E" manufactured by Toyo Seiki Co., Ltd.

[0071] (5) Solvent Solubility (After Post-Bake) A silicon wafer spin-coated with polyimide varnish was placed on a hot plate and heated at 120°C for 20 minutes, and then heated in air in a hot air dryer at 250°C for 30 minutes to evaporate the solvent. The resulting polyimide film was used as a test specimen. The polyimide film (test specimen) was immersed in γ-butyrolactone (GBL) at room temperature (25°C) to a concentration of 0.2% (w / w) and stirred with a magnetic stirrer. The solubility of the polyimide film in GBL was evaluated visually. The evaluation method is as follows: A: Dissolved within 1 hour. B: Not dissolved within 1 hour, but dissolved within 24 hours. C: Not dissolved within 24 hours, but dissolved within 72 hours. D: Not dissolved within 72 hours (insoluble).

[0072] (6) Solvent Solubility (After Annealing at 350°C for 60 Minutes) A ​​polyimide film formed on a silicon wafer was used as a test specimen and heated in a hot air dryer at 350°C for 60 minutes under a nitrogen atmosphere. After air-cooling to room temperature (25°C), the test specimen was immersed in a GBL solvent and stirred with a magnetic stirrer to evaluate solubility. The size of the test specimen was 10 mm x 20 mm, and the amount of GBL was 50 mL. The evaluation method is as follows: A: Dissolved within 1 hour. B: Not dissolved within 1 hour, but dissolved within 24 hours. C: Not dissolved within 24 hours, but dissolved within 72 hours. D: Not dissolved within 72 hours (insoluble).

[0073] (7) Chemical Resistance A polyimide film formed on a silicon wafer was used as a test piece and immersed in butyl acetate at room temperature (25°C) for 30 seconds, and durability was evaluated visually. The size of the test piece was 10 mm x 20 mm, and the amount of butyl acetate was 50 mL. The evaluation method is as follows: A: No cracks were observed on the silicon wafer. D: Cracks were observed on the silicon wafer.

[0074] Example 1 Into a 500 mL five-neck round-bottom flask equipped with a stainless steel half-moon stirring blade, a nitrogen inlet tube, a Dean-Stark stirrer fitted with a condenser, a thermometer, and a glass end cap, 24.495 g (0.057 mol) of bis[4-(3-aminophenoxy)phenyl]sulfone (BAPS-M; manufactured by Seika Corporation) (a compound represented by formula (b1)) and 70.008 g of GBL were added, and the mixture was stirred under a nitrogen atmosphere at a system temperature of 70°C and a rotation speed of 200 rpm to obtain a solution. To this solution, 17.350 g (0.057 mol) of dicyclohexyl-3,4,3',4'-tetracarboxylic dianhydride (H-BPDA; manufactured by Tokyo Chemical Industry Co., Ltd.) (a compound represented by formula (a1)) and 18.687 g of γ-butyrolactone (GBL; manufactured by Mitsubishi Chemical Corporation) were added all at once, and then 0.287 g of triethylamine (TEA; manufactured by Kanto Chemical Co., Ltd.) as an imidization catalyst and 4.667 g of GBL were added. The mixture was heated with a mantle heater, and the temperature inside the reaction system was raised to 190°C over approximately 20 minutes. The temperature inside the reaction system was maintained at 190°C and refluxed for 3 hours while collecting the components that were distilled off. Thereafter, the temperature inside the reaction system was cooled to 50°C, and a polyimide varnish containing a polyimide resin was obtained. The resulting polyimide varnish was then spin-coated onto a silicon wafer, held on a hot plate at 120°C for 20 minutes, and then heated in an air atmosphere in a hot air dryer at 250°C for 30 minutes to evaporate the solvent, yielding a polyimide film. The physical properties and evaluation results of the film are shown in Table 1.

[0075] Example 2 A solution containing a polyimide resin was obtained in the same manner as in Example 1, except that 18.494 g (0.043 mol) of BAPS-M and 23.271 g (0.079 mol) of 1,3-bis(3-aminophenoxy)benzene (TPE-M; manufactured by Seika Corporation) (a compound represented by formula (b2)) were used instead of 24.495 g (0.057 mol) of BAPS-M as the diamine component, and 37.628 g (0.122 mol) of H-BPDA was used as the acid dianhydride component. The types and blending ratios of the tetracarboxylic acid component and the diamine component are shown in Table 1. A polyimide varnish containing a polyimide resin was obtained in the same manner as in Example 1, and then a polyimide film was obtained. The physical properties and evaluation results of the polyimide film are shown in Table 1.

[0076] Comparative Example 1 A solution containing a polyimide resin was obtained in the same manner as in Example 1, except that 27.077 g (0.093 mol) of TPE-M was used as the diamine component instead of 24.495 g (0.057 mol) of BAPS-M, and 28.598 g (0.093 mol) of H-BPDA was used as the acid dianhydride component. The types and blending ratios of the tetracarboxylic acid component and diamine component are shown in Table 1. A polyimide varnish containing a polyimide resin was obtained in the same manner as in Example 1, and then a polyimide film was obtained. The physical properties and evaluation results of the polyimide film are shown in Table 1.

[0077]

[0078] As shown in Table 1, when the polyimide resin of Comparative Example 1, which does not contain a structural unit derived from BAPS-M, is compared with the polyimide resins of Examples 1 and 2, the glass transition temperature and 1% weight loss temperature are both higher for Examples 1 and 2. The weight loss rate after heating at 350°C for 1 hour was also higher for the polyimide resins of Examples 1 and 2 than for the polyimide resin of Comparative Example 1, demonstrating that the polyimides of the present invention have excellent heat resistance. Compared to the polyimide film (polyimide resin) of Comparative Example 1, the polyimide films (polyimide resins) of Examples 1 and 2 have a lower elastic modulus and superior adhesion. Furthermore, the polyimide films (polyimide resins) of the Examples exhibited excellent solubility in GBL. Because the polyimide films of the present invention are soluble in low-water-absorbent solvents such as GBL, they can be used in the peeling process and are less susceptible to humidity and moisture during peeling. Furthermore, the polyimide resins of the Examples exhibited excellent chemical resistance. As described above, the polyimide resins of the present invention can be suitably used as temporary fixing materials, and temporary fixing material compositions containing the polyimide resins possess the excellent properties described above.

Claims

1. A polyimide resin having a structural unit A derived from a tetracarboxylic dianhydride and a structural unit B derived from a diamine, wherein structural unit A contains a structural unit (A1') derived from a compound represented by the following formula (A1), and structural unit B contains a structural unit (B1') derived from a compound represented by the following formula (B1): (In the formula, X represents a single bond, a divalent hydrocarbon group having 1 to 5 carbon atoms, -O-, -S-, -SO2-, or -CO-; and each Y represents independently a divalent hydrocarbon group having 1 to 7 carbon atoms, a divalent substituent represented by the following structural formula, -O-, -S-, -SO2-, or -CO-.) 2. The polyimide resin according to claim 1, wherein the compound represented by formula (A1) is a compound represented by the following formula (a1):

3. The polyimide resin according to claim 1, wherein the structural unit B further contains a structural unit (B2') derived from a compound represented by the following formula (B2), and the proportion of the structural unit (B2') in the structural unit B is greater than 0 mol % and not more than 70 mol %. (In the formula, each Z is independently —O—, —COO—, —OCO—, —C(CH3)2—, or —C(CF3)2—.) 4. The polyimide resin according to claim 3, wherein the compound represented by formula (B1) is a compound represented by the following formula (b1), and the compound represented by formula (B2) is a compound represented by the following formula (b2):

5. A polyimide varnish containing the polyimide resin according to any one of claims 1 to 4 and an organic solvent.

6. A polyimide film comprising the polyimide resin according to any one of claims 1 to 4.

7. A temporary fixing material composition comprising a polyimide resin according to any one of claims 1 to 4.

8. A method for thinning a semiconductor wafer, comprising: Step 1 of applying the temporary fixing material composition according to claim 7 to a semiconductor wafer or a support substrate to form an adhesive layer for temporary fixing; Step 2 of temporarily fixing the support substrate to the semiconductor wafer via the adhesive layer; Step 3 of grinding the back surface of the semiconductor wafer while the support substrate is temporarily fixed to the semiconductor wafer via the adhesive layer; and Step 4 of peeling off the support substrate.

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