Composition for forming optical waveguide

Abstract

[Problem] To provide a composition that satisfies patterning properties, film-forming properties, and a high refractive index which are required for a composition for forming an optical waveguide by overcoming a trade-off therebetween. [Solution] A composition for forming an optical waveguide, comprising: a fluorene backbone-containing epoxy compound (A) represented by formula [1]; a monofunctional or bifunctional alicyclic epoxy compound (B); a monofunctional or bifunctional aromatic epoxy compound (C) different from the compound (A); and a photoacid generator (D). An optical waveguide comprising a cured product of the composition for forming an optical waveguide. (In formula [1], L1 and L2 each independently represent a naphthalenediyl group optionally having a substituent, and m and n each independently represent an integer of 0-10.)

Description

Composition for optical waveguide formation

[0001] The present invention relates to a composition for forming an optical waveguide, particularly an epoxy resin composition, and also to an optical waveguide formed from said composition.

[0002] In a broad sense, an optical waveguide refers to a transmission path that uses light for communication. Currently, optical fibers made of quartz glass or plastic are already in practical use as transmission paths for transmitting light over long distances, and are essential for increasing the speed and precision of communication transmissions.

[0003] Furthermore, research is being conducted on transmission paths that transmit light within optical circuits and are formed on substrates using microfabrication technology, which are conventionally referred to as optical waveguides (hereinafter referred to as optical waveguides in this specification). In order to achieve even higher speeds, progress is being made in the practical application of so-called optical interconnects, in which electrical signal transmission via metal wiring transmission paths, which has been used so far for relatively short-distance transmission within package substrates or between devices, is converted into optical signals directly from CPUs or LSIs and transmitted as optical signals through optical waveguides from within the substrate.

[0004] In recent years, organic polymer optical waveguides formed from photosensitive materials using photolithography have been proposed, and attention has been drawn to a technology that uses photolithography in all steps of forming the underlying undercladding layer, the core layer that is the optical waveguide portion, and the top cladding layer that covers the core layer to complete the wiring within the package substrate. In addition to being required to have a desired high refractive index, the photosensitive material used to form the optical waveguide is also required to have film-forming properties (such as film flatness), patterning properties, and stability that prevents precipitation and phase separation in order to form a fine optical waveguide on the substrate.

[0005] As the photosensitive material for forming the optical waveguide, a photosensitive epoxy resin composition for forming an optical waveguide, which contains a polyfunctional epoxy resin having a bisphenol A skeleton, a solid semi-aliphatic bifunctional epoxy resin, or other bifunctional epoxy resin as a resin component, and which also contains a photocationic polymerization initiator, has been proposed (see, for example, Patent Document 1).

[0006] Japanese Patent Application Laid-Open No. 2020-20927

[0007] As mentioned above, photosensitive materials for forming optical waveguides are required to have patterning properties, film-forming properties, and a high refractive index. However, it is difficult to simultaneously satisfy all of these requirements. For example, if a multifunctional resin or compound is used to improve patterning properties, the molecular weight increases, significantly increasing the viscosity of the material, which can hinder film-forming properties and film planarization. If a resin or compound with less than two functionalities, or a low-molecular-weight compound, is used to reduce the viscosity of the material to improve film-forming properties, it can result in a decrease in refractive index and a decrease in patterning properties. If a high-density compound, such as a compound containing an aromatic ring, is used to achieve a high refractive index, its rigidity and density can cause poor compatibility with other resins, compounds, etc., resulting in the formation of precipitates and adversely affecting film-forming properties. For example, Patent Document 1, mentioned above, evaluates patterning properties and also mentions the increase in refractive index, but does not mention the storage stability or film-forming properties that result from the use of high-molecular-weight components. It appears that all tradeoffs have not been resolved. As described above, improvements in patterning properties, film-forming properties, and a high refractive index are in a trade-off relationship with one another, and there has been no report to date that any of the techniques proposed so far, such as those listed in the above-mentioned documents, can satisfy all of these requirements.

[0008] An object of the present invention is to provide a composition that can resolve the trade-off between patterning ability, film-forming ability, and high refractive index required of a composition for forming an optical waveguide, and that can satisfy these performance requirements.

[0009] As a result of intensive research into solving the above-mentioned problems, the present inventors have found that the above-mentioned problems can be solved by a composition containing at least three epoxy compounds, namely, a difunctional fluorene epoxy compound having a naphthalene ring, a difunctional or lower alicyclic epoxy compound, and a difunctional or lower aromatic epoxy compound other than the fluorene epoxy compound, thereby completing the present invention.

[0010] That is, a first aspect of the present invention relates to a composition for forming an optical waveguide, comprising: a fluorene skeleton-containing epoxy compound (A) represented by the following formula [1]; a monofunctional or difunctional alicyclic epoxy compound (B); a monofunctional or difunctional aromatic epoxy compound (C) different from the compound (A); and a photoacid generator (D). (In formula [1], L １ and L ２ each independently represent a naphthalenediyl group which may have a substituent, and m and n each independently represent an integer of 0 to 10.) A second aspect relates to the composition for forming an optical waveguide according to the first aspect, in which the alicyclic epoxy compound (B) is a liquid alicyclic epoxy compound. A third aspect relates to the composition for forming an optical waveguide according to the first or second aspect, in which the aromatic epoxy compound (C) is a bifunctional aromatic epoxy compound. A fourth aspect relates to the composition for forming an optical waveguide according to any one of the first to third aspects, in which the alicyclic epoxy compound (B) is a bifunctional alicyclic epoxy compound and the aromatic epoxy compound (C) is a bifunctional aromatic epoxy compound. A fifth aspect relates to the composition for forming an optical waveguide according to any one of the first to fourth aspects, in which the alicyclic epoxy compound (B) is a compound represented by the following formula [2]: (In formula [2], R １ and R ２ each independently represents a hydrogen atom, a linear or branched alkyl group having 1 to 6 carbon atoms which may have an ester group or an ether group, or a cyclic alkyl group having 3 to 6 carbon atoms, or a combination of the linear or branched alkyl group and the cyclic alkyl group, wherein the linear alkyl group having 2 or more carbon atoms, the branched alkyl group having 3 or more carbon atoms, or the cyclic alkyl group may form an epoxy ring together with adjacent carbon atoms, or R １ and R ２may be bonded to each other to form a ring having 4 to 6 carbon atoms, and in this case, adjacent carbon atoms constituting the ring may be taken together to form an epoxy ring.) A sixth aspect relates to the composition for forming an optical waveguide according to any one of the first to fifth aspects, in which the aromatic epoxy compound (C) is an epoxy compound having a bisphenol A type skeleton or a bisphenol F type skeleton. A seventh aspect relates to the composition for forming an optical waveguide according to any one of the first to sixth aspects, in which the fluorene skeleton-containing epoxy compound (A) is a compound represented by formula [3]. According to an eighth aspect, the present invention relates to the composition for forming an optical waveguide according to any one of the first to seventh aspects, in which the alicyclic epoxy compound (B) is at least one compound represented by the following formulas [4], [5], and [6]: As a ninth aspect, the present invention relates to a cured product that is a polymer of the optical waveguide forming composition according to any one of the first to eighth aspects. As a tenth aspect, the present invention relates to an optical waveguide comprising a cured product of the optical waveguide forming composition according to any one of the first to eighth aspects. As an eleventh aspect, the present invention relates to the optical waveguide according to claim 10, comprising a clad layer made of a cured product of the optical waveguide forming composition according to any one of the first to eighth aspects.

[0011] The optical waveguide-forming composition of the present invention can produce a cured product useful as a material for forming an optical waveguide, which has a high refractive index of 1.54 or more, good film-forming properties free from unevenness, phase separation, and aggregates, high patterning properties, and high storage stability. Furthermore, the optical waveguide-forming composition of the present invention has a viscosity that is sufficiently manageable even in a solvent-free form, and therefore can be provided as a material for forming an optical waveguide without the need for additional processes due to the addition of a solvent, or concerns about health hazards and corrosion of peripheral equipment due to the solvent.

[0012] Fig. 1 is a view showing a microscope photograph taken from the end face direction of a cured film after photolithography using the composition of Example 1. Fig. 2 is a view showing a microscope photograph taken from the end face direction of a cured film after photolithography using the composition of Comparative Example 2.

[0013] <<Optical Waveguide Forming Composition>> The optical waveguide forming composition of the present invention comprises a fluorene skeleton-containing epoxy compound (A), a monofunctional or difunctional alicyclic epoxy compound (B), a monofunctional or difunctional aromatic epoxy compound (C) different from compound (A), and a photoacid generator (D). In this specification, the above epoxy compounds (A) to (C) as well as other epoxy compounds described below are collectively referred to as the "resin component," and "monofunctional or difunctional" means that the composition contains one or two epoxy groups as functional groups.

[0014] [Fluorene Skeleton-Containing Epoxy Compound (A)] The fluorene skeleton-containing epoxy compound (A) used in the present invention is a compound represented by the following formula [1]. In the above formula [1], L １ and L ２ each independently represents a naphthalenediyl group which may have a substituent; m and n each independently represent an integer of 0 to 10;

[0015] L １ and L ２ Examples of the substituent on the naphthalenediyl group (on the naphthalene ring) in L include alkyl groups having 1 to 6 carbon atoms, such as methyl, ethyl, propyl, isopropyl, butyl, and t-butyl. １ and L ２ The number of substituents in the naphthalenediyl group in each group is independently 0 to 6, preferably 0 to 2, more preferably 0 or 1, and most preferably 0. １ and L ２ The types of the substituents in may be the same or different. When the same naphthalene ring has two or more substituents, they may be the same or different.

[0016] The fluorene skeleton-containing epoxy compound (A) is preferably a compound represented by the following formula [3]:

[0017] The fluorene skeleton-containing epoxy compound (A) can be a commercially available product. Examples include OGSOL (registered trademark) CG-500 and EG-280 (manufactured by Osaka Gas Chemicals Co., Ltd.). Such fluorene skeleton-containing epoxy compounds having a naphthalene ring can be used alone or in combination of two or more. Furthermore, from the viewpoint of the solubility and refractive index of the resin component, for example, OGSOL (registered trademark) CG-500 can be used alone.

[0018] The fluorene skeleton-containing epoxy compound (A) is preferably contained in an amount of, for example, 5 to 50 parts by mass, more preferably 10 to 40 parts by mass, relative to the total amount of the epoxy compounds (100 parts by mass in total). If the amount of the fluorene skeleton-containing epoxy compound (A) is too small, it is difficult to obtain a sufficient refractive index, whereas if it is too large, precipitation occurs, resulting in deterioration of storage stability and deterioration of film-formability.

[0019] [Monofunctional or bifunctional alicyclic epoxy compound (B)] The monofunctional or bifunctional alicyclic epoxy compound (B) used in the present invention is not particularly limited as long as it is a compound having one or two alicyclic epoxy groups. In a preferred embodiment, the alicyclic epoxy compound (B) is a liquid embodiment, and from the viewpoint of patterning properties (exposure sensitivity), a compound having two epoxy groups introduced into an alicyclic skeleton can be mentioned.

[0020] The alicyclic epoxy compound (B) may be, for example, a compound represented by the following formula [2]: In formula [2], R １ and R ２ each independently represents a hydrogen atom, a linear or branched alkyl group having 1 to 6 carbon atoms which may have an ester group or an ether group, or a cyclic alkyl group having 3 to 6 carbon atoms, or a combination of the linear or branched alkyl group and the cyclic alkyl group, in which the linear alkyl group having 2 or more carbon atoms, the branched alkyl group having 3 or more carbon atoms, or the cyclic alkyl group may combine with adjacent carbon atoms to form an epoxy ring, or R １ and R ２may be bonded to each other to form a ring having 4 to 6 carbon atoms, and in this case, adjacent carbon atoms constituting the ring may be joined together to form an epoxy ring.

[0021] Examples of the linear or branched alkyl group having 1 to 6 carbon atoms include a methyl group, an ethyl group, an n-propyl group, an isopropyl group, an n-butyl group, an isobutyl group, a sec-butyl group, a tert-butyl group, an n-pentyl group, a 1-methylbutyl group, a 2-methylbutyl group, a 3-methylbutyl group, a 1,1-dimethylpropyl group, a 1,2-dimethylpropyl group, a 2,2-dimethylpropyl group, a 1-ethylpropyl group, an n-hexyl group, a 1-methylpentyl group, a 2-methylpentyl group, a 3-methylpentyl group, a 4-methylpentyl group, a 1,1-dimethylbutyl group, a 1,2-dimethylbutyl group, a 1,3-dimethylbutyl group, a 2,2-dimethylbutyl group, a 2,3-dimethylbutyl group, a 3,3-dimethylbutyl group, a 1-ethylbutyl group, a 2-ethylbutyl group, a 1,1,2-trimethylpropyl group, a 1,2,2-trimethylpropyl group, a 1-ethyl-1-methylpropyl group, and a 1-ethyl-2-methylpropyl group. Examples of the cyclic alkyl group having 3 to 6 carbon atoms include a cyclopropyl group, a cyclobutyl group, a cyclopentyl group, and a cyclohexyl group.

[0022] In a preferred embodiment, the alicyclic epoxy compound (B) may be a compound represented by the following formulas [4], [5], or [6]. These compounds have a low molecular weight and are liquid, and are suitable not only for patterning properties but also for adjusting the viscosity of the composition.

[0023] The alicyclic epoxy compound (B) can be a commercially available product. Examples of the bifunctional alicyclic epoxy compound (B) include diepoxybicyclohexyl (e.g., Celloxide (registered trademark) 8000 and 8010, manufactured by Daicel Corporation), 3,4-epoxycyclohexylmethyl-3',4'-epoxycyclohexenecarboxylate (e.g., Celloxide (registered trademark) 2021P, manufactured by Daicel Corporation), epsilon-caprolactone-modified 3,4-epoxycyclohexylmethyl-3',4'-epoxycyclohexanecarboxylate (e.g., Celloxide (registered trademark) 2081, manufactured by Daicel Corporation), bis(3,4-epoxycyclohexylmethyl)adipate, and diepoxidized tetrahydroindene (e.g., Epocalic (registered trademark) THI-DE, manufactured by ENEOS Corporation). Furthermore, for example, as the monofunctional alicyclic epoxy compound, 3,4-epoxycyclohexylmethyl methacrylate (e.g., Cyclomer (registered trademark) M-100, manufactured by Daicel Corporation), 3,4-epoxycyclohexylmethyl methacrylate, 1,2-epoxy-4-vinylcyclohexane (e.g., Celloxide (registered trademark) 2000, manufactured by Daicel Corporation), 1,2,8,9-diepoxylimonene (e.g., Celloxide (registered trademark) 3000, manufactured by Daicel Corporation), and the like can be used.

[0024] The alicyclic epoxy compound (B) is preferably contained in an amount of, for example, 10 parts by mass to 80 parts by mass, more preferably 20 parts by mass to 70 parts by mass, relative to the total amount of epoxy compounds (100 parts by mass in total). If the amount of alicyclic epoxy compound (B) is too small, it becomes difficult to obtain sufficient patterning properties, and conversely, if it is too large, it becomes difficult to obtain a sufficient refractive index.

[0025] [Monofunctional or difunctional aromatic epoxy compound (C)] The present invention also includes a monofunctional or difunctional aromatic epoxy compound (C) different from the epoxy compound (A). In a preferred embodiment, the aromatic epoxy compound (C) is a compound having two epoxy groups from the viewpoint of patterning properties (exposure sensitivity). Among these, an epoxy compound having a bisphenol A skeleton or a bisphenol F skeleton is preferred.

[0026] Commercially available aromatic epoxy compounds (C) can be used. Examples of bifunctional aromatic epoxy compounds (C) include jER (registered trademark) 806, a bisphenol F type epoxy compound manufactured by Mitsubishi Chemical Corporation, and jER (registered trademark) 828, a bisphenol A type epoxy compound manufactured by Mitsubishi Chemical Corporation. Examples of monofunctional aromatic epoxy compounds (C) include phenyl glycidyl ether (e.g., Denacol (registered trademark) EX-141, manufactured by Nagase ChemteX Corporation), phenol (EO) 5 glycidyl ether (e.g., Denacol (registered trademark) EX-145, manufactured by Nagase ChemteX Corporation), and p-tert-butylphenyl glycidyl ether (e.g., Denacol (registered trademark) EX-146, manufactured by Nagase ChemteX Corporation).

[0027] The aromatic epoxy compound (C) is preferably contained in an amount of, for example, 5 to 60 parts by mass, more preferably 10 to 50 parts by mass, relative to the total amount (100 parts by mass) of the epoxy compounds. If the amount of aromatic epoxy compound (C) is too small, it becomes difficult to obtain a sufficient refractive index or a uniform film, and conversely, if it is too large, it becomes difficult to obtain sufficient patterning properties.

[0028] [Other Epoxy Compounds] The optical waveguide-forming composition of the present invention may contain other epoxy compounds in addition to the epoxy compounds (A) to (C) above, as long as the effects of the present invention are not impaired. Examples include heterocycle-containing epoxy compounds such as triglycidyl isocyanurate, and aliphatic epoxy compounds. Specific examples of the aliphatic epoxy compounds include monofunctional epoxy compounds such as glycidyl ethers of aliphatic alcohols and glycidyl esters of alkylcarboxylic acids, and polyglycidyl ethers of aliphatic polyhydric alcohols or their alkylene oxide adducts. Representative examples of these compounds include glycidyl ethers of monoalcohols such as allyl glycidyl ether, butyl glycidyl ether, 2-ethylhexyl glycidyl ether, and C12-13 mixed alcohol glycidyl ether; glycidyl ethers of polyhydric alcohols such as 1,4-butanediol diglycidyl ether, 1,6-hexanediol diglycidyl ether, glycerin triglycidyl ether, trimethylolpropane triglycidyl ether, sorbitol tetraglycidyl ether, dipentaerythritol hexaglycidyl ether, polyethylene glycol diglycidyl ether, and polypropylene glycol diglycidyl ether; and polyglycidyl ethers of polyether polyols, which are adducts of one or more alkylene oxides with aliphatic polyhydric alcohols such as propylene glycol, trimethylolpropane, and glycerin. These other epoxy compounds can be included in an amount of, for example, 0 to 20 parts by mass relative to the total amount (100 parts by mass) of epoxy compounds.

[0029] [Photoacid Generator (D)] The composition for forming an optical waveguide of the present invention contains a photoacid generator (D). Specific examples of the photoacid generator (D) include onium salts such as iodonium salts, sulfonium salts, phosphonium salts, and selenium salts, metallocene complex compounds, iron arene complex compounds, disulfone-based compounds, sulfonic acid derivative compounds, triazine-based compounds, acetophenone derivative compounds, and diazomethane-based compounds.

[0030] Among the onium salts, examples of iodonium salts include diaryliodonium salts such as chloride, bromide, mesylate, tosylate, trifluoromethanesulfonate, tetrafluoroborate, tetrakis(pentafluorophenyl)borate, hexafluorophosphate, hexafluoroarsenate, and hexafluoroantimonate of diaryliodonium such as diphenyliodonium, 4,4'-dichlorodiphenyliodonium, 4,4'-dimethoxydiphenyliodonium, 4,4'-di-tert-butyldiphenyliodonium, 4-methylphenyl(4-(2-methylpropyl)phenyl)iodonium, 3,3'-dinitrophenyliodonium, 4-(1-ethoxycarbonylethoxy)phenyl(2,4,6-trimethylphenyl)iodonium, and 4-methoxyphenyl(phenyl)iodonium.

[0031] Examples of the sulfonium salts include triarylsulfonium salts such as chlorides, bromides, trifluoromethanesulfonates, tetrafluoroborate, hexafluorophosphate, hexafluoroarsenate, and hexafluoroantimonates of triarylsulfonium such as triphenylsulfonium, diphenyl(4-tert-butylphenyl)sulfonium, tris(4-tert-butylphenyl)sulfonium, diphenyl(4-methoxyphenyl)sulfonium, tris(4-methylphenyl)sulfonium, tris(4-methoxyphenyl)sulfonium, tris(4-ethoxyphenyl)sulfonium, diphenyl(4-(phenylthio)phenyl)sulfonium, and tris(4-(phenylthio)phenyl)sulfonium.

[0032] Examples of the phosphonium salt include arylphosphonium salts such as chlorides, bromides, tetrafluoroborates, hexafluorophosphates, and hexafluoroantimonates of triarylphosphoniums or tetraarylphosphoniums such as tetraphenylphosphonium, ethyltriphenylphosphonium, tetra(p-methoxyphenyl)phosphonium, ethyltri(p-methoxyphenyl)phosphonium, and benzyltriphenylphosphonium.

[0033] The selenium salts include triarylselenium salts such as triphenylselenium hexafluorophosphate.

[0034] Examples of the iron arene complex compounds include bis(η5-cyclopentadienyl)(η6-isopropylbenzene)iron(II) hexafluorophosphate.

[0035] Among these, iodonium salts, sulfonium salts, etc. can be preferably used as the photoacid generator. Commercially available products can be used, and examples thereof include triarylsulfonium salts such as CPI-310FG and CPI-101A.

[0036] These photoacid generators (D) can be used alone or in combination of two or more. The photoacid generator (D) is typically contained in an amount of, for example, preferably 0.1 to 10 parts by mass, more preferably 0.2 to 5 parts by mass, per 100 parts by mass of the total mass of the epoxy compound (resin component). If the amount of the photoacid generator (D) is less than 0.1 parts by mass, there is a risk that the photocuring reaction will not proceed sufficiently. On the other hand, if it exceeds 10 parts by mass, there is a risk that the degree of polymerization of the polymer will decrease, making the polymer brittle and prone to cracking.

[0037] [Organic Solvent] The optical waveguide-forming composition of the present invention may contain an organic solvent. When the prepared composition has a low viscosity, the addition of an organic solvent is not necessary, enabling good film formation. In this case, the solvent-free composition has the advantage of eliminating the need for a process to volatilize the organic solvent after film formation, such as by heat treatment. Furthermore, the absence of an organic solvent significantly reduces concerns about health hazards caused by inhalation by the organic solvent during its evaporation and corrosion of surrounding equipment. Because the optical waveguide-forming composition of the present invention has a relatively low viscosity, the inclusion of an organic solvent is not essential. However, even if an organic solvent is included, it can be added in any proportion without impairing the above-described effects of the present invention. There are no particular restrictions on the organic solvent that can be used in the present invention, as long as it is an organic solvent commonly used in the technical field. However, it is desirable to avoid the use of extremely high-polarity or low-polarity solvents, such as water or hydrocarbon solvents such as hexane, due to the risk of precipitation or phase separation. Furthermore, caution is required when adding a large amount of organic solvent, as this may prevent a sufficient film thickness from being achieved during film formation.

[0038] [Other Additives] The optical waveguide-forming composition of the present invention may contain other additives commonly used in the art, as long as the effects of the present invention are not impaired. Examples of other additives include antireflection agents, UV absorbers, antioxidants, light stabilizers, sensitizers, surfactants, crosslinking agents, leveling agents, and silane coupling agents. When these other additives are used, they are typically blended in an amount of 10 parts by mass or less per 100 parts by mass of the total mass of the epoxy compound (resin component).

[0039] [Optical Waveguide Forming Composition] As will be described later, the optical waveguide forming composition of the present invention can be suitably used as a material for forming an optical waveguide, and in particular as a material for forming the cladding layer of an optical waveguide. The method for preparing the optical waveguide forming composition of this embodiment is not particularly limited. Examples of the preparation method include a method in which components (A), (B), (C), and (D), as well as other epoxy compounds and other additives as necessary, are further added and mixed to form a uniform solution, or a method in which a conventional organic solvent is further used in addition to these components. In the optical waveguide-forming composition of the present invention, the blending amounts of each component can be, for example, 10 to 40 parts by mass of the fluorene skeleton-containing epoxy compound (A), 20 to 70 parts by mass of the alicyclic epoxy compound (B), 10 to 50 parts by mass of the aromatic epoxy compound (C), and 0 to 20 parts by mass of other epoxy compounds, assuming a total mass of 100 parts by mass of the epoxy compounds (resin components). The photoacid generator (D) can be 0.2 to 5 parts by mass, and other additives can be 0 to 10 parts by mass, relative to 100 parts by mass of the total mass of the epoxy compounds (resin components). When the organic solvent is used, the solids content of the optical waveguide-forming composition is not particularly limited as long as each component is uniformly dissolved in the organic solvent, but can be, for example, 60% by mass or more, or 70% by mass or more. Preferably, the solids content of the composition can be, for example, 75% to 100% by mass. Here, the solids content refers to all components of the optical waveguide-forming composition excluding the organic solvent component.

[0040] The composition for forming an optical waveguide is preferably used after being filtered using a filter having a pore size of 0.05 to 5 μm.

[0041] The composition for forming an optical waveguide of the present invention preferably has a viscosity that is excellent in workability when forming an optical waveguide. For example, the viscosity of the composition for forming an optical waveguide can be set to 100 to 10,000 mPa·s at 25°C.

[0042] <<Optical Waveguide>> The optical waveguide of the present invention includes a cured product of the optical waveguide-forming composition, and preferably includes a clad layer made of the cured product of the optical waveguide-forming composition. For example, in one embodiment, the optical waveguide of the present invention includes a core and a clad layer surrounding the entire periphery of the core and having a refractive index lower than that of the core, and the clad layer may be made of the cured product of the optical waveguide-forming composition. The core may be formed of a material having a refractive index higher than that of the formed clad layer. The optical waveguide of the present invention may be of any of the following types: a graded-index (GI) type in which the refractive index of the core changes continuously in the radial direction; a multi-step-index (MI) type in which the refractive index of the core changes stepwise in the radial direction; and a step-index (SI) type in which the refractive index changes discontinuously only at the interface between the core and the clad.

[0043] The present invention will be described in more detail below with reference to examples, but the present invention is not limited to the following examples.

[0044] The compounds and their abbreviations used in the examples are as follows: [Fluorene skeleton-containing diepoxy compounds] CG-500: OGSOL (registered trademark) CG-500, manufactured by Osaka Gas Chemicals Co., Ltd. PG-100: OGSOL (registered trademark) PG-100, manufactured by Osaka Gas Chemicals Co., Ltd. [Bifunctional alicyclic epoxy compounds] CEL-8010: Celloxide (registered trademark) 8010, manufactured by Daicel Corporation THI-DE: Epocalic (registered trademark) THI-DE, manufactured by ENEOS Corporation CEL-2021P: Celloxide (registered trademark) 2021P (3',4'-epoxycyclohexylmethyl 3,4-epoxycyclohexanecarboxylate), manufactured by Daicel Corporation [Bifunctional aromatic epoxy compounds] jER806: jER (registered trademark) bisphenol F epoxy resin, manufactured by Mitsubishi Chemical Corporation jER828: jER (registered trademark) bisphenol A epoxy resin, manufactured by Mitsubishi Chemical Corporation [Other bifunctional epoxy compounds] YX-8000: hydrogenated bisphenol A epoxy resin, manufactured by Mitsubishi Chemical Corporation [Monofunctional alicyclic epoxy compounds] M-100: Cyclomer (registered trademark) M-100 (3,4-epoxycyclohexylmethyl methacrylate), manufactured by Daicel Corporation [Monofunctional aromatic epoxy compounds] EX-141: Denacol (registered trademark) EX-141 (phenyl glycidyl ether), manufactured by Nagase ChemteX Corporation [Polyfunctional alicyclic epoxy compounds] GT-401: Epolead (registered trademark) GT-401 (butanetetracarboxylic acid tetra(3,4-epoxycyclohexylmethyl) modified ε-caprolactone), manufactured by Daicel Corporation [Other polyfunctional epoxy compounds] EHPE-3150: 1,2-epoxy-4-(2-oxiranyl)cyclohexane adduct of 2,2-bis(hydroxymethyl)-1-butanol, manufactured by Daicel Corporation [Photoacid generator] CPI-310FG: triarylsulfonium salt-type photoacid generator, manufactured by San-Apro Co., Ltd. [Organic solvent] PGMEA: propylene glycol monomethyl ether acetate, manufactured by Showa Denko K.K.

[0045] Examples 1 to 5, Comparative Examples 1 to 7 In the amounts shown in Table 1, various epoxy compounds, and a photoacid generator relative to the epoxy compounds (100 parts by mass), and an organic solvent, if desired, were placed in a flask, and the solid components were completely dissolved by stirring under heating at 110° C. or less. After cooling to room temperature, the mixture was pressure-filtered using a 3 μm SUS filter in a clean room to prepare each liquid composition.

[0046] A 4-inch diameter round silicon wafer substrate was cleaned using a UV / ozone irradiator. The composition was dropped onto the cleaned substrate, and a film was formed by spin coating to a thickness of 20 μm. The obtained film was subjected to photolithography to obtain a patterned cured film. Specifically, the formed film was exposed to light using a mask aligner, and only the light-irradiated areas were exposed to light. After exposure, the film was baked at 60°C for 1 minute, and then developed with an organic solvent, PGMEA / IPA (2-propanol) (50 / 50 vol / vol%), for 3 minutes. Finally, the film was post-baked at 100°C for 2 minutes to obtain a patterned cured film.

[0047] Each composition was evaluated for film-forming properties during spin coating, patterning properties of the cured film, refractive index of the composition, and storage stability according to the following procedures.

[0048] [1. Film-forming properties] The state of the film was observed during spin-coating of the composition (visually) and after spin-coating (visually and with a microscope), and evaluated according to the following evaluation criteria. The results are shown in Table 1. A: The overall appearance of the film is uniform, no phase separation is observed, and no bright spots due to aggregates are found. When the cross section is observed with a microscope, the film thickness is flat with a thickness of ±1 μm or less. B: Slight unevenness, phase separation, or bright spots are observed in the film. A slight gradient in film thickness is observed from the center of the film toward the edge. C: A uniform film cannot be formed, or aggregates are found scattered throughout the film.

[0049] [2. Patterning Ability] The cured film after photolithography was observed from the edge direction under a microscope, and the exposure sensitivity (patterning ability) was evaluated according to the following evaluation criteria. The results are shown in Table 1. Microscope photographs observed from the edge direction are also shown in Figure 1 (Example 1) and Figure 2 (Comparative Example 2). A: Only the exposed areas were cured, and the unexposed areas were dissolved by organic development. B: A pattern was formed to some extent, but the unexposed areas were also slightly cured, or the exposed areas were not sufficiently cured, and the shape was not convex. C: The unexposed areas were significantly cured, or the exposed areas were dissolved by development.

[0050] [3. Refractive Index] The liquid refractive index of each composition at 589 nm was measured using an Abbe refractometer and evaluated according to the following criteria. The results are shown in Table 1. A: The refractive index is 1.54 or more. C: The refractive index is less than 1.54.

[0051] [4. Storage Stability] After storing each composition at room temperature (23±3°C) for one month, the properties of the composition were visually observed and evaluated according to the following evaluation criteria. The results are shown in Table 1. A: No precipitates or phase separation were observed, and the solution remained a clear, homogeneous solution. B: The solution became slightly cloudy, or a precipitate was found at the bottom. C: A clear precipitate was formed, and the precipitate did not redissolve even when stirred.

[0052]

[0053] As shown in Table 1, the compositions of Examples 1 to 5 each had excellent film-forming properties, and as shown in FIG. 1, the compositions had good exposure sensitivity. Furthermore, the compositions had a refractive index of 1.54 or more and were also excellent in storage stability.

[0054] On the other hand, as shown in Table 1 and FIG. 2 , none of the compositions of Comparative Examples 1 to 7 satisfied all of the performance criteria for film-forming ability, exposure sensitivity, refractive index, and storage stability. Specifically, Comparative Example 7, which did not use a fluorene skeleton-containing epoxy compound (A), exhibited a lower refractive index than the Examples. Furthermore, even when a fluorene skeleton-containing epoxy compound was used, Comparative Example 1, which used an epoxy compound with a structure different from that of the compound (A) of the present invention, exhibited improved refractive index, but poor film-forming ability and storage stability. When the bifunctional or monofunctional alicyclic epoxy compound (B) was not included (Comparative Example 2), the composition exhibited poor film-forming ability and poor exposure sensitivity. Furthermore, when the bifunctional or monofunctional aromatic epoxy compound (C) was not included but a polyfunctional other epoxy compound was included instead (Comparative Example 5), the composition exhibited poor film-forming ability, exposure sensitivity, and storage stability. Adding an organic solvent to this composition (Comparative Example 6) slightly improved film-forming ability, exposure sensitivity, and storage stability, but did not achieve the A rating equivalent to the Examples. Furthermore, in the case where the bifunctional or monofunctional aromatic epoxy compound (C) was not contained but the monofunctional alicyclic epoxy compound (B), the polyfunctional alicyclic epoxy compound, and the other polyfunctional epoxy compound were contained (Comparative Example 3), the film-forming property, exposure sensitivity, and storage stability were also poor. By adding an organic solvent (Comparative Example 4), the film-forming property, exposure sensitivity, and storage stability were slightly improved, but this also did not reach the result of evaluation A corresponding to the Examples.

Claims

1. A fluorene skeleton-containing epoxy compound (A) represented by the following formula [1], A monofunctional or difunctional alicyclic epoxy compound (B), a monofunctional or difunctional aromatic epoxy compound (C) different from the compound (A); A photoacid generator (D), When the total mass of the epoxy compounds is 100 parts by mass, the epoxy compound (A) containing a fluorene skeleton is contained in an amount of 5 parts by mass to 50 parts by mass, the alicyclic epoxy compound (B) is contained in an amount of 10 parts by mass to 80 parts by mass, and the aromatic epoxy compound (C) is contained in an amount of 5 parts by mass to 60 parts by mass, A composition for forming an optical waveguide, comprising 0.1 to 10 parts by mass of the photoacid generator (D) based on a total of 100 parts by mass of epoxy compounds. 【Chemistry 1】 (In formula [1], L １ and L ２ each independently represents a naphthalenediyl group which may have a substituent, m and n each independently represent an integer of 0 to 10.

2. The composition for forming an optical waveguide according to claim 1 , wherein the alicyclic epoxy compound (B) is a liquid alicyclic epoxy compound.

3. The aromatic epoxy compound (C) is a difunctional aromatic epoxy compound. The composition for forming an optical waveguide according to claim 1 or 2.

4. The alicyclic epoxy compound (B) is a difunctional alicyclic epoxy compound, and The aromatic epoxy compound (C) is a difunctional aromatic epoxy compound. The composition for forming an optical waveguide according to claim 1 or 2.

5. The composition for forming an optical waveguide according to claim 1 or 2, wherein the alicyclic epoxy compound (B) is a compound represented by the following formula [2]: 【Chemistry 2】 (In formula [2], R １ and R ２ each independently represents a hydrogen atom, a linear or branched alkyl group having 1 to 6 carbon atoms which may have an ester group or an ether group, or a cyclic alkyl group having 3 to 6 carbon atoms, or a combination of the linear or branched alkyl group and the cyclic alkyl group, wherein the linear alkyl group having 2 or more carbon atoms, the branched alkyl group having 3 or more carbon atoms, or the cyclic alkyl group may form an epoxy ring together with adjacent carbon atoms, Or R １ and R ２ may be bonded to each other to form a ring having 4 to 6 carbon atoms, and in this case, may be bonded to adjacent carbon atoms constituting the ring to form an epoxy ring.

6. 3. The composition for forming an optical waveguide according to claim 1, wherein the aromatic epoxy compound (C) is an epoxy compound having a bisphenol A type skeleton or a bisphenol F type skeleton.

7. The composition for forming an optical waveguide according to claim 1 or 2, wherein the fluorene skeleton-containing epoxy compound (A) is a compound represented by formula [3]. 【Chemistry 3】

8. The composition for forming an optical waveguide according to claim 1 or 2, wherein the alicyclic epoxy compound (B) is at least one compound represented by the following formulas [4], [5], and [6]: 【Chemistry 4】

9. A cured product which is a polymer of the composition for forming an optical waveguide according to claim 1 or 2.

10. An optical waveguide comprising a cured product of the composition for forming an optical waveguide according to claim 1 or 2.

11. 11. The optical waveguide according to claim 10, comprising a clad layer made of a cured product of the composition for forming an optical waveguide according to claim 1 or 2.

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