Polymer and protective film agent for laser dicing

Abstract

Provided is a polymer that has excellent heat resistance and that, when being blended in a protective film agent for use in laser dicing processing of a semiconductor wafer or the like, hardly causes deterioration in the protective film agent.　This polymer includes a structural unit represented by formula (1) (in formula (1), R1-R5 each represent a hydrogen atom, or an alkyl group or a hydroxyalkyl group having 1-8 carbon atoms), has a weight average molecular weight of less than 1,000,000, and is (i) a homopolymer of said structural unit or (ii) a copolymer of said structural unit and a structural unit derived from at least one monomer (referred to as another monomer) selected from the group consisting of N-vinylcarboxylic acid amide, unsaturated carboxylic acid monomers, salts of the unsaturated carboxylic acid monomers, unsaturated carboxylic acid ester monomers, vinylester monomers, and unsaturated nitrile monomers.

Description

Polymers, protective coatings for laser dicing

[0001] This invention relates to a polymer with excellent acid resistance and a heat-resistant protective film agent for laser dicing using the polymer.

[0002] A known method exists for processing a substrate (for example, glass, semiconductor wafers, or resin molded products) by forming a protective film on the substrate surface to protect unprocessed areas during processing, and then removing the protective film after processing.

[0003] Such methods are used, for example, in the processing of semiconductor wafers. A semiconductor wafer is a laminate in which an insulating film and a functional film are layered on the surface of a semiconductor substrate such as silicon. Semiconductor chips are manufactured by creating grooves in this semiconductor wafer by irradiating it with laser light, and then cutting along the grooves. However, when laser light is irradiated onto a semiconductor wafer, the laser light is absorbed by the semiconductor substrate, generating molten material and thermal decomposition products from the semiconductor substrate. These molten materials and thermal decomposition products adhere to the surface of the semiconductor wafer or semiconductor chip as processing debris.

[0004] Therefore, a method is known in which a protective film that can be removed by washing with water is formed on the surface of a semiconductor wafer, and processing is performed by irradiating it with laser light (laser dicing). By irradiating with laser light through the protective film, debris is made to adhere to the surface of the protective film, and the debris can be removed together with the protective film by washing with water.

[0005] Such protective film agents generally contain a water-soluble polymer and a water-soluble laser light absorber having an absorbance within a specific range.

[0006] Conventional blade dicing is unsuitable for relatively brittle Low-k materials, so laser processing is used for these materials. Laser processing is broadly divided into two types: continuous wave operation (CW operation) and pulsed operation. Pulsed operation is mainly used for the dicing of semiconductor substrates because it can suppress thermal effects, but even with suppressed thermal effects, considerable heat is still applied locally.

[0007] Generally, to facilitate the cleaning of processing debris generated in such processes, a protective film using a water-soluble polymer is applied to the processed area before the cutting process, as described above. However, because the scattered debris is at high temperatures, the water-soluble polymer in the protective film can undergo crosslinking or thermal degradation, making it difficult to clean with water, which could significantly affect product quality and performance.

[0008] For example, Patent Document 1 (Japanese Patent Publication No. 2023-41313) uses a water-soluble polymer such as polyvinyl alcohol, polyvinylpyrrolidone, hydroxypropyl cellulose, or polyoxazoline, and a light absorber having a flavonoid structure, a flavonol structure, or an isoflavone structure.

[0009] Furthermore, Patent Document 2 (Japanese Unexamined Patent Publication No. 2020-066667) proposes a protective film agent comprising a polyvinylpyrrolidone resin, a solvent, and a laser light absorber.

[0010] Furthermore, Patent Document 3 (Japanese Patent Application Publication No. 2016-066768) proposes a protective film composition containing a water-soluble polymer made of polyvinyl alcohol or polyvinylpyrrolidone, a resin capsule containing a laser light absorber, and an aqueous solvent.

[0011] Furthermore, Patent Document 4 (Japanese Unexamined Patent Publication No. 2015-134373) discloses a protective film agent for laser processing containing poly-N-vinylacetamide. In addition, Patent Document 5 (Japanese Unexamined Patent Publication No. 2019-12807) discloses a protective film agent for laser processing that is a blend of polyvinyl alcohol and poly-N-vinylacetamide.

[0012] Japanese Patent Publication No. 2023-41313, Japanese Patent Publication No. 2020-066667, Japanese Patent Publication No. 2016-066768, Japanese Patent Publication No. 2015-134373, Japanese Patent Publication No. 2019-12807

[0013] However, Patent Document 1 had the problem that the heat resistance of the resin used was not very high, leading to thermal crosslinking and thermal degradation, which made washing with water difficult. Furthermore, Patent Documents 2 and 3 did not describe the heat resistance of polyvinylpyrrolidone, and although polyvinylpyrrolidone has a high thermal decomposition point according to TG / DTA measurement, it had problems with degradation and insolubilization when heated strongly in an aqueous solution. In addition, no consideration was given to the degradation of the resin by laser irradiation.

[0014] Although the poly-N-vinylacetamide used in Patent Documents 4 and 5 showed improved heat resistance compared to the aforementioned polymers, it was not necessarily sufficient.

[0015] Thus, conventional protective film agents had a problem: the water-soluble polymers used as protective films during laser dicing of semiconductor wafers had insufficient heat resistance, leading to degradation of the protective film and making it difficult to remove the protective film, which should have been washed away with water.

[0016] In this context, we discovered that a homopolymer (hereinafter sometimes referred to as PDMA) composed of monomers such as N,N-dimethylacrylamide, or a copolymer with other monomers, can withstand high-temperature laser irradiation and does not degrade even under high-temperature thermal conditions, and maintains good resolubility in water after the thermal treatment. This led to the present invention. The structure of the present invention is as follows.

[0017] [1] Includes a constituent unit represented by the following formula (1), (In formula (1), R １ ~R ５ (i) a homopolymer of the constituent units, or (ii) a copolymer of the constituent units and a constituent unit derived from at least one monomer selected from the group consisting of N-vinyl carboxylic acid amide, unsaturated carboxylic acid monomer, salt of an unsaturated carboxylic acid monomer, unsaturated carboxylic acid ester monomer, vinyl ester monomer, and unsaturated nitrile monomer (referred to as "other monomer"), wherein the weight-average molecular weight is less than 1 million.

[0018] [2] The polymer of [1], wherein the viscosity of a 10% by mass aqueous solution is 100 mPa·s or more and 15000 mPa·s or less. [3] The polymer of [1] or [2], wherein the content of the other monomer constituent units is 90 mol% or less in 100 mol% of the total constituent units of the polymer. [4] The polymer of [1] to [3], wherein the weight-average molecular weight is in the range of more than 30000 and less than 1,000000. [5] A protective film agent containing the polymer of [1] to [4]. [6] The protective film agent of [5], further comprising a light absorber. [7] A protective film using the protective film agent of [5] or [6].

[0019] The polymer of the present invention has high heat resistance and can withstand high-temperature laser irradiation, such as that used in laser dicing. Therefore, when used as a protective film agent, it does not degrade, does not leave any residue when washed with water, and can be easily removed.

[0020] The FT-IR transmission spectra of the polymer of Example 2 before and after heating at 250°C are shown. The FT-IR transmission spectra of the polymer of Comparative Example 2 before and after heating at 250°C are shown. The photographs show the changes in appearance of the samples from the examples and comparative examples before and after heating at 250°C for 1 hour.

[0021] The embodiments of the present invention will be described below, but these embodiments are not limited to the description below.

[0022] (1) Polymer This embodiment is a polymer containing a constituent unit represented by the following formula (1).

[0023] (In formula (1), R１ ~R ５ is a hydrogen atom, an alkyl group having 1 to 8 carbon atoms or a hydroxyalkyl group). Such a polymer is a water-soluble polymer and exhibits amphiphilicity.

[0024] The polymer of the present embodiment is either (i) a homopolymer of the above-mentioned structural unit or (ii) a copolymer of the above-mentioned structural unit and a structural unit derived from at least one monomer selected from the group consisting of N-vinylcarboxylic acid amide, unsaturated carboxylic acid monomer, salt of unsaturated carboxylic acid monomer, unsaturated carboxylic acid ester monomer, vinyl ester monomer, and unsaturated nitrile monomer (hereinafter referred to as other monomers). The other monomers are more preferably (meth)acrylic acid and its salts, and even more preferably sodium acrylate. In this specification, "(meth)acrylic acid" means acrylic acid and methacrylic acid.

[0025] In the polymer of the present embodiment, among 100 mol% of all the structural units of the polymer, the structural units other than the structural unit represented by the formula (1) (that is, other monomer structural units) are preferably 90 mol% or less, and more preferably 80 mol% or less. With this ratio, solubility in water can be obtained, which is preferable. It is even more preferable that the ratio of the other structural units is 0. Therefore, the polymer of the present embodiment is preferably a homopolymer composed of the structural unit of the formula (1).

[0026] In the general formula (1), R １ ~R ３ is a hydrogen atom, R ４ and R ５ are both alkyl groups having 1 to 6 carbon atoms, the structural unit I-II, R ４ is a hydrogen atom and R ５ is an alkyl group having 1 to 8 carbon atoms, the structural unit I-II, R ４ is a hydrogen atom and R ５ is a hydroxyalkyl group having 1 to 2 carbon atoms, and it is preferably at least one selected from the group consisting of the structural unit I-III. R ４ and R ５It is preferable that both are a methyl group or an ethyl group, and more preferably a methyl group. The polymer of the present embodiment has a weight average molecular weight of 1.3 million or less, further 1 million or less, preferably more than 30,000 and less than 1,000,000. Such a polymer has high solubility in water, high heat resistance, and can withstand high-temperature laser irradiation used in laser dicing and the like.

[0027] In one aspect, the polymer of the present embodiment has a viscosity at 20°C of a 10% by mass aqueous solution of 100 mPa·s or more. The polymer of the present embodiment has a viscosity at 20°C of a 10% by mass aqueous solution of 15,000 mPa·s or less. A polymer in such an aspect can be obtained by the following production method.

[0028] (2) Production method of polymer The production method of the polymer of the present embodiment is to carry out radical polymerization of a monomer represented by the following formula (2) in an aqueous solution using an aqueous medium.

[0029] (In formula (2), R １ ~R ５ represent a hydrogen atom, an alkyl group having 1 to 8 carbon atoms, or a hydroxyalkyl group.)

[0030] As the monomer represented by the general formula (2), similar to the formula (1), at least one monomer selected from the group consisting of a monomer in which R ４ and R ５ are both alkyl groups having 1 to 6 carbon atoms (where they may be the same or different), a monomer in which R ４ is a hydrogen atom and R ５ is an alkyl group having 1 to 8 carbon atoms, and a monomer in which R ４ is a hydrogen atom and R ５ is a hydroxyalkyl group having 1 to 2 carbon atoms is preferable.

[0031] Among these, a monomer in which R ４ is a hydrogen atom and R ５ is a methyl group or an ethyl group is preferable, and a methyl group is more preferable. R ４ is a hydrogen atom and R ５When it is a methyl group or an ethyl group, the hydrogen bond is appropriate, the cohesive force is appropriate, and it is preferable as a coating agent. R ４ and R ５ The compound in which is bonded by a covalent bond is not included in the monomer of formula (2).

[0032] Examples of the monomer represented by the general formula (2) include N-methylacrylamide (MAA), N-ethylacrylamide, N-propylacrylamide, N-isopropylacrylamide (NIPAM), N-butylacrylamide, N-isobutylacrylamide, N-tert-butylacrylamide, N-heptylacrylamide, N-octylacrylamide, N-tert-octylacrylamide, N-methylolacrylamide, N-hydroxyethylacrylamide (HEAA), N,N-dimethylacrylamide (DMAA), N,N-diethylacrylamide (DEAA), N,N-dipropylacrylamide, N,N-diisopropylacrylamide, N,N-dibutylacrylamide, N,N-diisobutylacrylamide, N,N-diheptylacrylamide, N,N-dioctylacrylamide, N,N-dimethylolacrylamide, N,N-dihydroxyethylacrylamide, and the like. These can be used alone or in combination of two or more. Among these monomers, N-isopropylacrylamide, N-hydroxyethylacrylamide, N,N-dimethylacrylamide, and N,N-diethylacrylamide are preferable, and N-hydroxyethylacrylamide and N,N-diethylacrylamide are more preferable.

[0033] It may contain a monomer copolymerizable with the above monomer (hereinafter sometimes referred to as "other monomer"). The other monomer is at least one monomer selected from the group consisting of an unsaturated carboxylic acid monomer, a salt of an unsaturated carboxylic acid monomer, an unsaturated carboxylic acid ester monomer, a vinyl ester monomer, and an unsaturated nitrile monomer. Among these, (meth)acrylic acid and its salts are more preferable, and sodium acrylate is even more preferable. In the present specification, "(meth)acrylic acid" means acrylic acid and methacrylic acid.

[0034] For polymerization, general radical polymerization methods are applicable. Solution polymerization and dropwise polymerization are applicable, with radical polymerization in an aqueous solution using a water-soluble radical polymerization initiator and a water medium with low chain transfer activity being suitable. For high-viscosity products, a batch polymerization method in which the monomers are mixed in an aqueous solution and polymerization proceeds is preferred. For medium to low-viscosity products, a dropwise polymerization method in which one or both monomers are added dropwise is preferred.

[0035] It is preferable to include a solvent during polymerization. A more preferable solvent is water, and pure water treated with an ionic resin is preferable. Even more preferable is the use of ultrapure water.

[0036] During polymerization, it is preferable to carry out the polymerization while stirring. More preferably, the stirring is performed using a device equipped with a motor, shaft, and stirring blades to mix the reaction system, and it is particularly preferable that the stirring speed can be varied according to the progress of the polymerization reaction. Regarding the shape of the stirring blades, there are turbine blades, paddle blades, propeller blades, anchor blades, and three-bladed swept-back blades. While the appropriate blade can be used in each case, for medium to low viscosity polymers like those in this embodiment, three-bladed swept-back blades are preferred. By incorporating stirring during the production of the polymer of the present invention, it is preferable to obtain a polymer with a uniform and appropriate molecular weight distribution.

[0037] The polymerization initiator can be any of those commonly used in the radical polymerization of vinyl compounds, without being limited to any specific type. Examples include redox polymerization initiators, azo compound polymerization initiators, and peroxide polymerization initiators. These may be used individually or in combination of two or more. In some cases, molecular weight adjustment may be performed using a chain transfer agent.

[0038] Examples of redox polymerization initiators include combinations of ammonium persulfate with sodium thiosulfate, sodium bisulfate, trimethylamine, or tetramethylethylenediamine, or combinations of t-butyl hydroperoxide with sodium thiosulfate or sodium bisulfate.

[0039] Examples of peroxide-based polymerization initiators include persulfates such as sodium, potassium, and ammonium, and organic peroxides such as benzoyl peroxide, lauroyl peroxide, caproyl peroxide, t-butyl peroctoate, and diacetyl peroxide.

[0040] Examples of azo compound polymerization initiators include 2,2'-azobis(2-methylbutyronitrile), 2,2'-azobis(2,4-dimethylvaleronitrile), dimethyl-2,2'-azobis(isobutyrate), dimethyl-2,2'-azobis(2-methylbutyrate), and dimethyl-2,2'-azobis(2,4-dimethylpentanoate), 2,2'-azobis(2-amidinopropane) dihydrochloride, and 2,2' Examples include azobis[2-(2-imidazolin-2-yl)propane] dihydrochloride, 2,2'-azobis[N-(2-carboxyethyl)-2-methylpropionamidin] n hydrate, 2,2'-azobis{2-[N-(2-carboxyethyl)amidino]propane} n hydrate, 2,2'-azobis(2-methylpropionic acid)dimethyl, 2,2'-azobis(2-methylpropionic acid)dimethyl, etc.

[0041] Among the polymerization initiators mentioned above, in polymerization methods using water as the solvent, considering the impact of halogen residues in the polymer on coatings and electronic devices, heat resistance, and especially thermal discoloration performance, azo compound-based polymerization initiators that do not contain halogens are preferred, and it is even more preferable to use 2,2'-azobis[N-(carboxyethyl)-2-methylpropionamidine]tetrahydrate (trade name: VA-057, azo compound-based polymerization initiator manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.).

[0042] The amount of radical polymerization initiator used is preferably 0.05 parts by mass or more and 2.0 parts by mass or less, more preferably 0.1 parts by mass or more and 0.8 parts by mass or less, and even more preferably 0.4 parts by mass or more and 0.7 parts by mass or less, per 100 parts by mass of all monomers, in the case of azo compound polymerization initiators. In the case of redox polymerization initiators, the amount is preferably 0.001 parts by mass or more and 0.03 parts by mass or less, more preferably 0.003 parts by mass or more and 0.01 parts by mass or less, and even more preferably 0.004 parts by mass or more and 0.009 parts by mass or less, per 100 parts by mass of all monomers. If the amount of radical polymerization initiator used is within the above range, both the polymerization rate and the molecular weight of the copolymer tend to be favorable.

[0043] In such a manufacturing method, it is preferable to polymerize by dropwise adding a solution containing at least a polymerization initiator to an aqueous medium solution of the monomer. Furthermore, if a copolymer component is present, it is preferable to dropwise add the aqueous medium solution constituting the copolymer to the aqueous medium solution of the monomer.

[0044] Within limits that do not impair the objectives of the present invention, chain transfer agents may be used during copolymerization for the purpose of adjusting the degree of polymerization of the polymer or introducing modifying groups to the ends of the copolymer. Examples of chain transfer agents include aldehyde compounds such as acetaldehyde and propionaldehyde, ketone compounds such as acetone and methyl ethyl ketone, thiol compounds such as 2-hydroxyethanethiol, 3-mercaptopropionic acid, dodecanethiol, and thioacetic acid, halogenated hydrocarbon compounds such as carbon tetrachloride, trichloroethylene, and perchloroethylene, and phosphinate salts such as sodium phosphinate monohydrate. Among these, thiol compounds, aldehyde compounds, and ketone compounds are preferably used. The amount of chain transfer agent added is preferably 0.1% by mass or more and 2.0% by mass or less, based on 100 parts by mass of the total amount of all monomers. Within this range, the objectives of adjusting the degree of polymerization and introducing modifying groups to the ends of the polymer can be sufficiently achieved.

[0045] Furthermore, the mixing method may involve stirring and mixing within the tank, or it may be added during the formulation process and mixed as part of the mixture.

[0046] The polymerization temperature is preferably 30 to 100°C, more preferably 60 to 98°C, and most preferably 70 to 95°C.

[0047] The resulting polymer can also be dried and converted into a powder. Specifically, powdering can be done by freeze-drying, drying and solidification grinding, or spray-drying, but spray-drying is the most preferred method.

[0048] (3) Protective film agent The protective film agent of this embodiment includes the polymer. Furthermore, it may optionally include a solvent and additives such as a light absorber.

[0049] Specifically, the solvent is not particularly limited, but examples include water, alcohols and their derivatives, and esters. Examples of alcohols include monohydric alcohols such as methanol, ethanol, propanol, and butanol, and polyhydric alcohols such as ethylene glycol, diethylene glycol, and propylene glycol. Examples of alcohol derivatives include ethylene glycol monoalkyl ethers such as ethylene glycol monomethyl ether, ethylene glycol monoethyl ether, ethylene glycol monopropyl ether, and ethylene glycol monobutyl ether, ethylene glycol monoalkyl ether acetates such as ethylene glycol monomethyl ether acetate and ethylene glycol monoethyl ether acetate, propylene glycol monoalkyl ethers such as propylene glycol monomethyl ether, propylene glycol monoethyl ether, propylene glycol monopropyl ether, and propylene glycol monobutyl ether, propylene glycol monoalkyl ether acetates such as propylene glycol monomethyl ether acetate, propylene glycol monoethyl ether acetate, propylene glycol monopropyl ether acetate, and propylene glycol monobutyl ether acetate.

[0050] Examples of esters include methyl-3-methoxypropionate and ethyl-3-ethoxypropionate.

[0051] Among these, water, which offers high rinsing potential, is the most preferred. Note that one or more solvents may be used in combination.

[0052] Such protective coatings can be used as various types of protective coatings, for example, as protective coatings for laser processing. The protective coating can be applied to the surface of a substrate such as a wafer by a spin coater or spray. To prevent repulsion from the substrate surface, improve wettability and coating performance, and further enhance the storage stability of the solution, the protective coating may also contain a surfactant. Both nonionic and cationic surfactants can be used.

[0053] Examples of the nonionic surfactants mentioned above include nonylphenol-based, higher alcohol-based, polyhydric alcohol-based, polyoxyalkylene glycol-based, polyoxyethylene alkyl ester-based, polyoxyethylene alkyl ether-based, polyoxyethylene alkylphenol-based, and polyoxyethylene sorbitan alkyl ester-based surfactants.

[0054] Cationic surfactants include, for example, quaternary ammonium salts and amine salts; anionic surfactants include, for example, alkylbenzene sulfonic acid and its salts, alkyl sulfate ester salts, methyl taurate, and ether sulfonate; and amphoteric surfactants include, for example, imidazolinium betaine, amidopropyl betaine, and aminodipropionate. One or more of these surfactants can be appropriately selected and used. Typically, the surfactant is used as an active ingredient in an amount of 0.05% to 5% by mass relative to the total amount of the protective film agent.

[0055] The absorbent is not particularly limited and examples include ultraviolet absorbers and dyes, among which water-soluble ones are preferred.

[0056] Examples of UV absorbers include benzophenone-based UV absorbers {e.g., polyhydroxybenzophenone (e.g., 2,2',4,4'-tetrahydroxybenzophenone, 2,2'-dihydroxy-4,4'-dimethoxybenzophenone, 2,4-dihydroxybenzophenone, 2,2'-dihydroxy-4-methoxybenzophenone)}, benzotriazole-based UV absorbers (e.g., 2,2'-methylenebis[6-(benzotriazole-2-yl)-4-tert-octylphenol]), and ferulic acid.

[0057] Examples of pigments include food additive pigments {for example, red food colorings (e.g., Red No. 2, Red No. 40, Red No. 102, Red No. 104, Red No. 105, Red No. 106), yellow food colorings (e.g., Yellow NY, Yellow No. 4 tartrazine, Yellow No. 5), blue food colorings (e.g., Blue No. 1, Blue No. 2), and green food colorings (e.g., Green No. 3)}.

[0058] Furthermore, water-soluble compounds having a flavonoid structure, flavonol structure, or isoflavone structure can be used as absorbents. Typical examples of such compounds include isorhamnetin, flavonol, 4'-hydroxyflavone, 5-hydroxyflavone, acacetin, vogonoside, 3-hydroxy-4'-methoxyflavone, 7,8-dihydroxyflavone, epimedin C, quercetin, baicalin, nobiletin, fisetin, rutin, icariin, icaritine, 7-hydroxyflavone, morin, kaempferol, hesperidin, 6-hydroxyflavone, kaempferol, vogonin, isoorientin, 5-methoxyflavone, luteolin, myricitrin, 3-methylflavone-8-carboxylic acid, 6-methylflavone, apigenin, and 3-methoxy Examples include flavones, baicalein, 3,4'-dihydroxyflavone, orientin, 3',4'-dihydroxyflavone, methylhesperidin, chrysin, 6-methoxyflavone, tangeretin, diosmetin, galangin, flavones, eupatirin, diosmin, neodiosmin, troxerutin, 2-(2-amino-3-methoxyphenyl)chromone, flavonol-2'-sulfonic acid, flavoxate, genistein, tectoridin, ononine, demethyltexacin, ipriflavin, neobabaisoflavone, sophoricoside, irisflorentin, puerarin, biochanin A, formononetin, tectorigenin, 7-methoxy-5-methylisoflavonone, 4',6,7-trimethoxyisoflavonone, daidzein, dihydrodaidzein, and daidzin.

[0059] Furthermore, preservatives such as phenyl glycol can be added as needed to adjust the shelf life of the protective film. Plasticizers, organic acids, etc., can also be used as needed.

[0060] The proportion of polymer in the protective film agent is not particularly limited, but may be, for example, 1 to 30% by mass, preferably 1 to 25% by mass, more preferably 1 to 20% by mass, or 1 to 15% by mass.

[0061] In the protective film agent, the proportion of the solvent is not particularly limited, but is preferably, for example, 50 to 99% by mass, more preferably 50 to 95% by mass, 60 to 99% by mass, 60 to 95% by mass, 70 to 99% by mass, or 70 to 95% by mass.

[0062] In the protective film agent, the proportion of the light absorber is not particularly limited, but is preferably, for example, 0.01 to 5% by mass, and more preferably 0.01 to 3% by mass, 0.01 to 1% by mass, 0.01 to 0.5% by mass, or 0.05 to 0.5% by mass.

[0063] Furthermore, the surfactant should typically be present as an active ingredient in an amount ranging from 0.05% to 5% by mass relative to the total amount of the protective film agent.

[0064] The method for producing the protective film agent of the present invention is not particularly limited, but for example, a polymer, a solvent, and a light absorber may be mixed, and other components may be added as needed. Mixing may be carried out at room temperature or while heating. Mixing may also be carried out while stirring. The order in which each component is added is not particularly limited. The protective film of the present invention is formed using the protective film agent described above. Specifically, the protective film can be formed by applying the protective film agent to the surface of a substrate.

[0065] The substrate is not particularly limited and includes, for example, glass, synthetic quartz, resin molded products, and semiconductors (e.g., semiconductor wafers).

[0066] The coating method is not particularly limited and can be selected as appropriate depending on the type of substrate, but for example, it can be applied using a spin coater or spray coater, and uniform coating can be achieved in that process alone.

[0067] The thickness of the protective film is not particularly limited and can be appropriately selected depending on the application of the composition, but for example it is 0.01 to 50 μm (for example 0.01 to 30 μm), preferably 0.01 to 20 μm (for example 0.01 to 15 μm), and more preferably 0.01 to 10 μm.

[0068] By processing the substrate through the protective film formed on its surface as described above, the substrate can be processed while protecting the unprocessed areas.

[0069] The processing method is not particularly limited and can be selected as appropriate depending on the type of substrate, etc., but examples include machining (e.g., cutting, grinding) and laser processing (e.g., laser dicing).

[0070] After the above processing, the protective film can be removed by washing it. The washing method is not particularly limited, but the protective film formed with the composition of the present invention can be efficiently removed by washing with water {for example, water, hot water (for example, hot water at 40 to 90°C)}.

[0071] Furthermore, by cleaning such protective films, any deposits generated during processing (e.g., molten materials, thermal decomposition products, etc.) can be efficiently removed.

[0072] The embodiment will be described in more detail below with reference to examples, but these are illustrative and not limiting to these examples. The following evaluations were performed in the examples and comparative examples.

[0073] Viscosity Measurement: Immerse a poly bottle containing the sample in a circulating constant-temperature water bath heated to 20°C, and adjust the internal polymer aqueous solution temperature to 20°C ± 0.5°C. Once the temperature is reached, measure the viscosity using a Type B viscometer as specified in JIS K-7117-1-1999. Record the value after 5 minutes at 50 rpm as the measured value.

[0074] Each material for molecular weight measurement was dissolved in the eluent and allowed to stand for 20 hours. The solid content concentration in this solution was 0.1% by mass. This was filtered through a 0.45 μm membrane filter, and the weight-average molecular weight (Mw) of the filtrate was measured using GPC-MALS (multi-angle light scattering detector). MALS detector: Wyatt Technology Corporation, DAWN HELEOS 8+ Column: ResonaX Shodex (registered trademark) SB-G 8B, SB-807HQ x 2, SB-806M-HQ Column temperature: 40°C Eluent: 0.025 mol sodium bicarbonate pH adjusted to 9.0 with 0.025 mol sodium carbonate aqueous solution Flow rate: 0.7 mL / min Sample injection volume: 300 μL Laser wavelength: 633 nm Multi-angle fitting method: Zimm method

[0075] Survival Rate Test Using a 60 ml aluminum petri dish manufactured by Kenis Co., Ltd., the weight of the aluminum petri dish was measured in advance, and then 30 g of water-soluble polymer aqueous solution was added and the mass was measured. This was taken as the initial mass. The aluminum petri dish was placed in an oven preheated to 250°C and left to stand. After 1 hour, the aluminum petri dish was removed and allowed to cool. A DRA330DC oven manufactured by Advantec Toyo Co., Ltd. was used. After that, the aluminum petri dish was placed in a lidded plastic container containing 1000 g of water and left to stand at room temperature for 15 hours. After 15 hours, the aluminum petri dish was removed and placed in an oven preheated to 150°C. After 1 hour, the weight of the aluminum petri dish was measured.

[0076] Based on the survival rate calculated using Equation 1, materials with a survival rate of 10% or higher were deemed unsuitable.

[0077] The initial state of the appearance change and the state after 250°C for a period of time were compared and judged according to the following criteria: ○: Little discoloration, no deterioration observed ×: Significant discoloration, deterioration observed

[0078] The uniformity of film spread on a silicon wafer was evaluated using a film-forming evaluation spin coater (Blue Ocean Technology Co., Ltd. AJC-300-BOT). The silicon wafer used was AKD Corporation 4-520P1FME. Conditions: 5000 rpm, 10 seconds per sheet. Sample: 0.5 g, 46φ. ○: Uniform, thin film state. ×: Non-uniform, thick film state.

[0079] <Overall Assessment> The overall assessment was made based on the following criteria: ○: Dissolution retention rate less than 10%, coating performance evaluation ○, appearance change ○ ×: Other

[0080] The evaluation was performed using the FT-IR Thermo Scientific Nicolet iS20.

[0081] [Example 1] Preparation of medium to high molecular weight PDMA polymers A 2L four-necked separable flask was fitted with a nitrogen gas inlet tube, stirrer, solvent dropper, thermometer, and nitrogen gas exhaust tube. 70g of N,N-dimethylacrylamide was added to 700g of deionized water in the separable flask and dissolved to prepare an aqueous solution.

[0082] Subsequently, while introducing nitrogen at a rate of 200 ml / min, heating was initiated and the internal temperature was adjusted to 58°C. Two hours after the start of heating, 20 g of an aqueous solution containing 0.48 g (0.6 mass by monomer) of 2,2'-azobis[N-(carboxyethyl)-2-methylpropionamidine]tetrahydrate (product name: VA-057, an azo compound polymerization initiator manufactured by Fujifilm Wako Pure Chemical Industries, Ltd., hereinafter also referred to as "initiator VA-057") was added by syringe, and polymerization was allowed to proceed for 4 hours with stirring at an internal temperature of 58.0 to 68.0°C. After that, the bath temperature was raised to 80°C and the internal temperature was maintained at 75°C for 1 hour. The outside of the container was then cooled with 23°C tap water, and the container was allowed to cool until the next day.

[0083] The obtained polymer (PDMA-103) was evaluated for its resolubility upon heating, appearance, and film-forming properties. The results are shown in Table 1.

[0084] [Example 2] Medium molecular weight PDMA A 1 L separable flask with four necks was fitted with a nitrogen gas inlet tube, stirrer, solvent dropper, thermometer, and nitrogen gas exhaust tube. 350 g of deionized water was placed in the separable flask, and heating was started to adjust the internal temperature to 68.0°C. At the same time, 65 g of N,N-dimethylacrylamide was placed in a 500 ml flask, followed by 204.3 g of deionized water, and mixed. Two hours after the start of heating, at an internal temperature of 68.0°C, 20 g of an aqueous solution containing 0.293 g of initiator VA-057 (0.45% by mass of monomer) was added to the 1 L flask by syringe, and then the N,N-dimethylacrylamide solution mixed in the 500 ml flask was added dropwise by pump.

[0085] Polymerization was carried out by dropwise addition while stirring at an internal temperature of 68.0–72.0°C for 2.5 hours. After that, the bath temperature was raised to 80°C and the internal temperature was maintained at 75°C for 1 hour. Dilution stirring was continued for about 1 hour, then the external temperature of the container was cooled with tap water, and then it was allowed to cool. The obtained polymer (PDMA-104) was evaluated in the same manner as in Example 1. For Example 2, the polymer after heating to 250°C was confirmed by FT-IR.

[0086] [Example 3] Low molecular weight PDMA A 1L four-neck separable flask was fitted with a nitrogen gas inlet tube, stirrer, solvent dropper, thermometer, and nitrogen gas exhaust tube. 600g of deionized water was placed in the separable flask, and while supplying nitrogen at a rate of 200ml / min, the heating was started and the internal temperature was adjusted to 90.0°C.

[0087] Simultaneously, 107 g of N,N-dimethylacrylamide was placed in a 500 ml flask, followed by 200 g of deionized water, and dissolved and mixed. Next, 3.2 g of initiator VA-057 (2.99% by mass of monomer) was weighed into a 200 ml beaker, and 100 g of deionized water was added and dissolved and mixed.

[0088] Two hours after the start of heating, the initiator VA-057, dissolved and mixed in a 1 L flask at an internal temperature of 90.0°C, was supplied dropwise by pump, followed by the supply of N-vinylacetamide solution mixed in a 500 ml flask dropwise by pump. Polymerization was carried out by dropwise addition while stirring at an internal temperature of 90.0–95.0°C for 2.5 hours. After stirring and holding at 90.0–95.0°C for 30 minutes, a solution of 0.5 g of initiator VA-057 dissolved in 55 g of deionized water was supplied by pump, and stirring and holding at 90.0–95.0°C for 30 minutes. The external temperature of the container was cooled with tap water, and then allowed to cool. The obtained polymer (PDMA-107) was evaluated in the same manner as in Example 1.

[0089] [Comparative Example 1] High molecular weight type PDMA (weight-average molecular weight: 1.5 to 4 million) A 2L separable flask with four necks was equipped with a nitrogen gas inlet tube, stirrer, solvent dropper, thermometer, and nitrogen gas exhaust tube. 708.0 g of deionized water was added to the separable flask, and 66.1 g of N,N-dimethylacrylamide was dissolved to prepare an aqueous solution.

[0090] Subsequently, heating was initiated and the internal temperature was adjusted to 53.5°C. 10 g of an aqueous solution containing 0.053 g of polymerization initiator (VA-057) (0.08% monomer ratio) was added by syringe, and polymerization was carried out for 4 hours with stirring at an internal temperature of 50.0 to 62.0°C. After that, the bath temperature was raised to 80°C and the internal temperature was maintained at 75°C for 1 hour, at which point 865.4 g of deionized water for dilution was added, stirring was continued for about 1 hour, and then the container was cooled with tap water at 23°C and allowed to cool. The obtained polymer (PDMA-043) was evaluated in the same manner as in Example 1.

[0091] [Comparative Example 2-5] The following polymers were used and adjusted to the concentrations shown in Table 1, and evaluated in the same manner as in Example 1. For Comparative Example 2, the polymer after heating at 250°C was confirmed by FT-IR.

[0092] Comparative Example 2: Polyvinyl alcohol (PVA) POVAL PVA 124 5% by mass aqueous solution Kuraray Co., Ltd. Comparative Example 3: Polyvinylpyrrolidone (PVP) K-90 10% by mass aqueous solution Nippon Shokubai Co., Ltd. Comparative Example 4: Carboxymethylcellulose sodium salt (CMC) Sunrose (CMC) 350HC 2% by mass aqueous solution Nippon Paper Industries Co., Ltd. Comparative Example 5: Polyethylene glycol (PEG) PEG 500000 reagent 10% by mass aqueous solution Fujifilm Wako Pure Chemical Industries, Ltd.

[0093]

[0094] For Examples 1 to 3, the residual rate was 10% or less in all cases, and the change in the material's appearance after the test was minimal. For Comparative Example 1, it is considered that there was no degradation based on its resolubility and change in appearance, but its high viscosity resulted in poor film-forming properties. On the other hand, Comparative Examples 2, 3, and 4 showed high residual rates and significant changes in appearance. Comparative Example 5 is considered to have decomposed because it continued to evaporate even after the water had disappeared during the 250°C heating test.

[0095] Furthermore, the state of the polymers in Example 2 and Comparative Example 2 after heating at 250°C was confirmed by FT-IR. In Example 2, no change was observed, similar to the appearance, but in Comparative Example 2, approximately 1600-1700 cm² was observed. －１ A significant increase in the surrounding C=O bond sites was observed, confirming a substantial acceleration of oxidative degradation.

Claims

1. Includes the constituent unit represented by the following formula (1), (In formula (1), R １ ~R ５ (i) a homopolymer of the constituent units, or (ii) a copolymer of the constituent units and a constituent unit derived from at least one monomer selected from the group consisting of N-vinyl carboxylic acid amide, unsaturated carboxylic acid monomer, salt of an unsaturated carboxylic acid monomer, unsaturated carboxylic acid ester monomer, vinyl ester monomer, and unsaturated nitrile monomer (referred to as "other monomer"), wherein the weight-average molecular weight is less than 1 million.

2. The polymer according to claim 1, wherein the viscosity of a 10% by mass aqueous solution is 100 mPa·s or more and 15000 mPa·s or less.

3. The polymer according to claim 1, wherein the content of the other monomer constituent units is 90 mol% or less of the total constituent units of the polymer in 100 mol%.

4. The polymer according to claim 1, wherein the weight-average molecular weight is in the range of more than 30,000 and less than 1,000,000.

5. A protective film agent comprising the polymer according to any one of claims 1 to 4.

6. The protective film agent according to claim 5, further comprising a light absorber.

7. A protective film using the protective film agent of claim 6.

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