Components for forming optical waveguides

Abstract

The objective of this invention is to provide a composition that can eliminate the mutually exclusive relationships of patternability, film-forming properties, and high refractive index required for a composition used in optical waveguide formation, and thus satisfy these properties. The solution is a composition for optical waveguide formation comprising: an epoxy compound (A) containing a cyclohexane skeleton, 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 aforementioned compound (A), and a photoacid generator (D), and an optical waveguide comprising a hardened form of the composition for optical waveguide formation; (in formula [1], L1 and L2 each independently represent a naphthyl group that may have substituents, and m and n each independently represent integers from 0 to 10).

Description

Technical Field

[0001] This invention relates to a composition for forming an optical waveguide, particularly an epoxy resin composition, and also to an optical waveguide formed from the composition. Prior Technology

[0002] In a broad sense, optical waveguides refer to the transmission path of light used in communication. Currently, optical fibers, formed from quartz glass or plastic, have been put into practical use as transmission paths for light traveling to distant places, and have become indispensable for high-speed and high-precision transmission in communication.

[0003] Furthermore, the industry has been researching optical waveguides (hereinafter referred to as optical waveguides) as the transmission paths that carry light within optical circuits and are formed on substrates using microfabrication techniques. To achieve higher-speed communication, the industry has begun to put into practical use what is known as optical interconnects. These optical interconnects convert the electrical signals generated by metal wiring transmission paths, which are currently used for short-distance transmission within package substrates or between devices, directly into optical signals by the CPU or LSI, and then transmit these optical signals through optical waveguides within the substrate.

[0004] In recent years, a technique has been proposed that uses photolithography to create organic polymer optical waveguides made of photosensitive materials. This technique employs photolithography in all the formation steps of the bottom cladding layer (serving as the base), the core phase (serving as the waveguide portion of the light), and the top cladding layer covering the core phase to complete the wiring within the packaging substrate. This technique has attracted much attention. In addition to the desired high refractive index, photosensitive materials used for optical waveguide formation also require film-forming properties (film flatness, etc.), patterning properties, and stability that prevents the formation of precipitates or phase separation in order to form fine optical waveguides on a substrate.

[0005] As a photosensitive material for forming the aforementioned optical waveguide, a photosensitive epoxy resin composition for forming an optical waveguide has been proposed. This composition uses a multifunctional epoxy resin with a bisphenol A-type backbone, a solid semi-aliphatic difunctional epoxy resin, and other difunctional epoxy resins as resin components, and contains a photocationic polymerization initiator (for example, see Patent Document 1). [Previous Technical Documents] [Patent Literature]

[0006] [Patent Document 1] Japanese Patent Application Publication No. 2020-20927 Summary of the Invention

[0007] [The problem that the invention aims to solve] Photosensitive materials used for optical waveguide formation require the above-mentioned properties of patternability, film-forming ability, and high refractive index, but it is not easy to satisfy these properties simultaneously. For example, when using multifunctional resins or compounds to improve patternability, the increased molecular weight leads to a significant increase in material viscosity, which may hinder film formation or film flatness. Using resins or compounds with fewer than two functionalities, or low molecular weight compounds, to improve film formation at a lower viscosity may result in a decrease in refractive index or poorer patternability. Using high-density compounds, such as those containing aromatic rings, to achieve a high refractive index can cause a deterioration in compatibility with other resins / compounds, potentially leading to precipitates that negatively impact film formation. For example, in the aforementioned patent document 1, patternability is also evaluated and high refractive index is mentioned; on the other hand, the preservation stability or film-forming properties resulting from the use of high molecular weight components are not mentioned, indicating that it has not yet achieved the elimination of all mutual exclusions. Thus, improving patternability, improving film formation, and increasing refractive index are mutually compensating for each other. So far, none of the technologies proposed in the aforementioned literature can satisfy all of these requirements.

[0008] The present invention aims to provide a composition that can eliminate the mutually exclusive relationships of patternability, film-forming properties, and high refractive index required for components used in optical waveguide formation, and thus satisfy these properties. [Methods for solving problems]

[0009] In addressing the aforementioned issues, the inventors of this invention have discovered through their research that a composition comprising at least three epoxide compounds, including a difunctional fumonisin oxide compound containing a naphthalene ring, an alicyclic epoxide compound with less than two functions, and an aromatic epoxide compound with less than two functions other than the aforementioned fumonisin oxide compound, can solve the aforementioned issues, thus ultimately completing this invention.

[0010] That is, the first aspect of the present invention relates to a composition for forming an optical waveguide, comprising: The following formula [1] represents an epoxy compound (A) containing a fusiform skeleton. Monofunctional or difunctional alicyclic epoxides (B) Monofunctional or difunctional aromatic epoxy compounds (C) that differ from the aforementioned compound (A), and Photoacid generator (D); (in formula [1], L1 and L2 represent naphthyl dimethyl groups that can have substituents, respectively. m and n each independently represent integers from 0 to 10. The second point concerns the composition for forming an optical waveguide as described in the first point, wherein the aforementioned alicyclic epoxy compound (B) is a liquid alicyclic epoxy compound. The third viewpoint relates to the composition for forming optical waveguides as described in the first or second viewpoint, wherein the aforementioned aromatic epoxy compound (C) is a difunctional aromatic epoxy compound. The fourth viewpoint is a composition for forming an optical waveguide as described in any one of the first to third viewpoints, wherein the aforementioned alicyclic epoxy compound (B) is a difunctional alicyclic epoxy compound, and the aforementioned aromatic epoxy compound (C) is a difunctional aromatic epoxy compound. The fifth point concerns the composition for forming an optical waveguide as described in any of the first to fourth points, wherein the aforementioned alicyclic epoxy compound (B) is a compound represented by the following formula [2]: (in formula [2], R1 and R2 respectively represent a hydrogen atom, a straight-chain or branched alkyl group with 1 to 6 carbon atoms that may have an ester or ether group, a cyclic alkyl group with 3 to 6 carbon atoms, or a combination of the aforementioned straight-chain or branched alkyl group and the aforementioned cyclic alkyl group; in this case, the aforementioned straight-chain alkyl group with 2 or more carbon atoms, the aforementioned branched alkyl group with 3 or more carbon atoms, or the aforementioned cyclic alkyl group may form an epoxy ring together with adjacent carbon atoms. Alternatively, R1 and R2 can bond together to form a ring with 4 to 6 carbon atoms, which can then form an epoxy ring together with the adjacent carbon atoms that constitute the aforementioned ring. The sixth point concerns a composition for forming an optical waveguide, as described in any of the first to fifth points, wherein the aforementioned aromatic epoxy compound (C) is an epoxy compound having a bisphenol A-type backbone or a bisphenol F-type backbone. The seventh point concerns the composition for forming an optical waveguide as described in any of the first to sixth points, wherein the aforementioned epoxy compound (A) containing a fusiform skeleton is a compound represented by formula [3]: . The eighth point concerns a composition for forming an optical waveguide as described in any of the first to seventh points, wherein the aforementioned alicyclic epoxy compound (B) is at least one compound represented by the following formulas [4], [5], and [6]: . The ninth point concerns a hardened material, which is a polymer of an optical waveguide forming composition as described in any of the first to eighth points. The 10th point relates to an optical waveguide comprising a hardened material of an optical waveguide forming component as described in any of the 1st to 8th points. The 11th point concerns an optical waveguide as described in the 10th point, which includes a cladding layer composed of a hardened material of an optical waveguide forming component as described in any of the 1st to 8th points. [Effects of the Invention]

[0011] The composition for forming optical waveguides of the present invention can be made into a hardened material with a high refractive index of 1.54 or higher, no inhomogeneity or phase separation, good film-forming properties of condensates, high patternability, and even high storage stability, which can be used as a forming material for optical waveguides. Furthermore, the composition for forming optical waveguides of the present invention has a viscosity that allows for sufficient handling even in a solvent-free form. Therefore, it can be provided as a material for forming optical waveguides that does not require the addition of solvents or does not raise concerns about health hazards or corrosion of peripheral equipment caused by solvents. Simple Explanation of the Diagram

[0012] [Figure 1] is a microscopic photograph showing the hardened film after photolithography using the composition of Example 1, viewed from the end face direction. [Figure 2] is a microscopic photograph showing the hardened film after photolithography of the composition of Comparative Example 2, viewed from the end face direction. Implementation

[0013] [Forms of Invention Implementation] Components for forming optical waveguides The composition for forming an optical waveguide of the present invention comprises: an epoxy compound (A) containing a cyclohexane framework, a monofunctional or difunctional alicyclic epoxy compound (B), a monofunctional or difunctional aromatic epoxy compound (C) different from the aforementioned compound (A), and a photoacid generator (D). Furthermore, in this specification, the epoxy compounds included in (A) to (C) above, and other epoxy compounds mentioned below, are referred to as "resin components", and "monofunctional or difunctional" means containing one or two epoxy groups as functional groups.

[0014] [Epoxy compound (A) containing a chromium skeleton] The epoxy compound (A) containing a fusiform skeleton used in this invention is a compound represented by the following formula [1]: In the above formula [1], L1 and L2 represent naphthyl dimethyl groups that can have substituents, and m and n represent integers from 0 to 10.

[0015] Examples of substituents for the naphthyl group (on the naphthalene ring) in L1 and L2 include alkyl groups with 1 to 6 carbon atoms, such as methyl, ethyl, propyl, isopropyl, butyl, and tributyl. Furthermore, the number of substituents of the naphthyl dimethyl group in L1 and L2 is independently 0 to 6, preferably 0 to 2, more preferably 0 or 1, and most preferably 0. Furthermore, the types of substituents in L1 and L2 can be the same or different. When there are more than two substituents in the same naphthalene ring, they can be the same or different.

[0016] Epoxy compounds (A) containing a fusiform skeleton are preferred, and examples of compounds represented by the following formula [3] are given:

[0017] The aforementioned epoxy compound (A) containing a fusiform skeleton can be commercially available. Examples include OGSOL (registered trademark) CG-500 and EG-280 (manufactured by Osaka Gas Chemicals Co., Ltd.). Such epoxy compounds containing a naphthalene ring and a naphthalene skeleton can be used alone or in combination with two or more; and based on the solubility or refractive index of the resin components, such as the aforementioned OGSOL (registered trademark) CG-500 can be used alone.

[0018] The epoxy compound (A) containing the epoxide skeleton is preferably contained in a proportion of, for example, 5 to 50 parts by mass relative to the total amount of epoxy compounds (total 100 parts by mass), more preferably 10 to 40 parts by mass. If the amount of epoxy compound (A) containing the epoxide skeleton is too small, it is difficult to obtain a sufficient refractive index; conversely, if the amount is too large, precipitation will cause deterioration of storage stability or reduction of film-forming properties.

[0019] [Monofunctional or difunctional alicyclic epoxides (B)] The monofunctional or difunctional alicyclic epoxy compound (B) used in this invention is not particularly limited as long as it has one or two alicyclic epoxy groups. In a preferred embodiment, the alicyclic epoxy compound (B) is in a liquid state, and from the viewpoint of patternability (exposure sensitivity), compounds having two epoxy groups introduced into the alicyclic skeleton can be cited.

[0020] Examples of the above-mentioned alicyclic epoxy compounds (B) include compounds represented by the following formula [2]: In formula [2], R1 and R2 respectively represent hydrogen atoms, straight-chain or branched alkyl groups with 1 to 6 carbon atoms that may have ester or ether groups, or cyclic alkyl groups with 3 to 6 carbon atoms, or combinations of the aforementioned straight-chain or branched alkyl groups and the aforementioned cyclic alkyl groups; at this time, the aforementioned straight-chain alkyl groups with 2 or more carbon atoms, the aforementioned branched alkyl groups with 3 or more carbon atoms, or the aforementioned cyclic alkyl groups may form an epoxy ring together with adjacent carbon atoms, or R1 and R2 may bond together to form a ring with 4 to 6 carbon atoms, at which time they may form an epoxy ring together with adjacent carbon atoms constituting the aforementioned ring.

[0021] Examples of straight-chain or branched alkyl groups with 1 to 6 carbon atoms include methyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl, dibutyl, tributyl, n-pentyl, 1-methylbutyl, 2-methylbutyl, 3-methylbutyl, 1,1-dimethylpropyl, 1,2-dimethylpropyl, 2,2-dimethylpropyl, 1-ethylpropyl, n-hexyl, 1-methylpentyl, 2-methylpentyl, 3-methylpentyl, 4-methylpentyl, 1,1-dimethylbutyl, 1,2-dimethylbutyl, 1,3-dimethylbutyl, 2,2-dimethylbutyl, 2,3-dimethylbutyl, 3,3-dimethylbutyl, 1-ethylbutyl, 2-ethylbutyl, 1,1,2-trimethylpropyl, 1,2,2-trimethylpropyl, 1-ethyl-1-methylpropyl, and 1-ethyl-2-methylpropyl. Furthermore, examples of the cyclic alkyl groups with 3 to 6 carbon atoms mentioned above include cyclopropyl, cyclobutyl, cyclopentyl, and cyclohexyl.

[0022] In a preferred form, the aforementioned alicyclic epoxy compounds (B) can be exemplified by compounds represented by the following formulas [4], [5], and [6]. These are low molecular weight liquid compounds, which are also suitable from the viewpoints of graphical properties and adjusting the viscosity of the composition.

[0023] The above-mentioned alicyclic epoxy compound (B) can be commercially available. Examples of difunctional alicyclic epoxides (B) include diepoxycyclohexyl (e.g., manufactured by DAICL, CELLOXIDE 8000, and 8010), 3,4-epoxycyclohexylmethyl-3',4'-epoxycyclohexane carboxylates (e.g., manufactured by DAICL, CELLOXIDE 2021P), ε-caprolactone-modified 3,4-epoxycyclohexylmethyl-3',4'-epoxycyclohexane carboxylates (e.g., manufactured by DAICL, CELLOXIDE 2081), bis(3,4-epoxycyclohexylmethyl) adipate, and diepoxytetrahydroindene (e.g., manufactured by ENEOS, EPOCHALIC THI-DE). For example, monofunctional alicyclic epoxy compounds can use 3,4-epoxycyclohexylmethyl methacrylate (e.g., DAICL (stock) manufacture, CYCLOMER (registered trademark) M-100), 3,4-epoxycyclohexylmethyl methacrylate, 1,2-epoxy-4-vinylcyclohexane (e.g., DAICL (stock) manufacture, CELLOXIDE (registered trademark) 2000), 1,2,8,9-diepoxylimonene (e.g., DAICL (stock) manufacture, CELLOXIDE (registered trademark) 3000), etc.

[0024] The alicyclic epoxy compound (B) preferably contains, for example, 10 to 80 parts by mass, and more preferably 20 to 70 parts by mass, relative to the total amount of the epoxy compound (total 100 parts by mass). If the amount of alicyclic epoxy compound (B) is too small, sufficient patternability is difficult to obtain; conversely, if the amount is too large, sufficient refractive index is difficult to obtain.

[0025] [Monofunctional or difunctional aromatic epoxides (C)] This invention also includes monofunctional or difunctional aromatic epoxy compounds (C) that differ from the aforementioned epoxy compound (A). From a patterning (exposure sensitivity) perspective, the aromatic epoxy compound (C) preferably comprises a compound having two epoxy groups. Preferably, it is an epoxy compound having a bisphenol A-type backbone or a bisphenol F-type backbone.

[0026] Aromatic epoxy compounds (C) can be commercially available. Examples of difunctional aromatic epoxy compounds (C) include Mitsubishi Chemical (Stock) jER (registered trademark) 806, a bisphenol F type epoxy compound, and Mitsubishi Chemical (Stock) jER (registered trademark) 828, a bisphenol A type epoxy compound. Furthermore, examples of monofunctional aromatic epoxy compounds (C) include phenyl glycidyl ethers (e.g., manufactured by Nagase ChemteX, DENACOL EX-141, a registered trademark), phenol (EO)5 glycidyl ethers (e.g., manufactured by Nagase ChemteX, DENACOL EX-145, a registered trademark), and p-tert-butylphenyl glycidyl ethers (e.g., manufactured by Nagase ChemteX, DENACOL EX-146, a registered trademark).

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

[0028] [Other Epoxy Compounds] The composition for forming the optical waveguide of the present invention may also include other epoxy compounds besides those in (A) to (C) above, without compromising the effect of the present invention. Examples include heterocyclic or aliphatic epoxy compounds such as triglycidyl isocyanurate. Specific examples of the aforementioned aliphatic epoxy compounds include monofunctional epoxy compounds such as glycidyl ethers of aliphatic alcohols and glycidyl esters of alkyl carboxylic acids, or polyglycidyl ethers of aliphatic polyols or their alkyl oxidants. Representative specific compounds include allyl glycidyl ether; glycidyl ethers of monohydric alcohols such as 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, triglycidyl ether of glycerol, trimethylolpropane triglycidyl ether, tetraglycidyl ether of sorbitol, hexaglycidyl ether of dipentaerythritol, diglycidyl ether of polyethylene glycol, and diglycidyl ether of polypropylene glycol; and polyglycidyl ethers of polyether polyols containing one or more epoxide adducts of aliphatic polyols such as propylene glycol, trimethylolpropane, and glycerol. These other epoxy compounds are contained, for example, in a proportion of 0 to 20 parts by mass relative to the total amount of epoxy compounds (100 parts by mass).

[0029] [Photoacid Generator (D)] The composition system for forming the optical waveguide of the present invention includes a photoacid generator (D). Specific examples of photoacid generators (D) include onium salts such as monazite, strontium salts, phosphonium salts, and selenium salts; metallocene complexes; iron aromatic complexes; disulfonic acid derivatives; triazine derivatives; acetophenone derivatives; and diazomethanes.

[0030] Among the aforementioned onium salts, examples of diaryl iron salts include diphenyliron, 4,4'-dichlorodiphenyliron, 4,4'-dimethoxydiphenyliron, 4,4'-di-tert-butyldiphenyliron, 4-methylphenyl(4-(2-methylpropyl)phenyl)iron, 3,3'-dinitrophenyliron, 4-(1-ethoxycarbonylethoxy)phenyl(2,4,6-trimethylphenyl)iron, 4-methoxyphenyl(phenyl)iron, and their chlorides, bromides, methanesulfonates, toluenesulfonates, trifluoromethanesulfonates, tetrafluoroborates, tetra(pentafluorophenyl)borates, hexafluorophosphates, hexafluoroarsenates, and hexafluoroantimonates.

[0031] Examples of the aforementioned strontium salts include triphenylstrontium, diphenyl(4-tert-butylphenyl)strontium, triphenyl(4-tert-butylphenyl)strontium, diphenyl(4-methoxyphenyl)strontium, triphenyl(4-methylphenyl)strontium, triphenyl(4-methoxyphenyl)strontium, triphenyl(4-ethoxyphenyl)strontium, diphenyl(4-(phenylthio)phenyl)strontium, and triphenyl(4-(phenylthio)phenyl)strontium, as well as their chlorides, bromides, trifluoromethane sulfonates, tetrafluoroborates, hexafluorophosphates, hexafluoroarsenates, and hexafluoroantimonates.

[0032] Examples of the aforementioned phosphonium salts include aryl phosphonium salts such as tetraphenylphosphonium, ethyltriphenylphosphonium, tetra(p-methoxyphenyl)phosphonium, ethyltri(p-methoxyphenyl)phosphonium, benzyltriphenylphosphonium, etc., as well as their chlorides, bromides, tetrafluoroborates, hexafluorophosphates, hexafluoroantimonates, etc.

[0033] Examples of the aforementioned selenium salts include triphenylselenophosphate and other triaryl selenium salts.

[0034] Examples of the aforementioned iron-aromatic complexes include bis(n5-cyclopentadienyl)(n6-isopropylbenzene)iron(II)hexafluorophosphate.

[0035] Among these, strontium salts and other similar salts are preferred as photoacid generators. Commercially available products can be used, such as triarylstrontium salts like CPI-310FG and CPI-101A.

[0036] These photoacid generators (D) can be used alone or in combination of two or more. The photopolymer generating agent (D) is typically contained in an amount, for example, 0.1 to 10 parts by mass, more preferably 0.2 to 5 parts by mass, relative to 100 parts by mass of the aforementioned epoxy compound (resin component). If the amount of photopolymer generating agent (D) is less than 0.1 parts by mass, the photocuring reaction may not be sufficiently carried out. Furthermore, if it exceeds 10 parts by mass, the degree of polymerization of the polymer may decrease, leading to embrittlement and increased susceptibility to cracking.

[0037] [Organic solvents] The composition for forming the optical waveguide of the present invention can also be mixed with organic solvents. When the prepared composition has low viscosity, it can form a film well without the addition of organic solvents. In this case, since it is solvent-free, there is no need for heat treatment or other procedures to evaporate the organic solvents after film formation, which is also an advantage. Furthermore, since no organic solvents are mixed in, concerns about health hazards to workers due to inhalation or corrosion of surrounding equipment caused by the evaporation of organic solvents are significantly reduced. Since the composition for forming the optical waveguide of the present invention forms a composition with low viscosity, there is no need to mix in organic solvents. However, even if organic solvents are contained, the above-mentioned effects of the present invention will not be lost, and they can be added in any proportion. The organic solvents that can be used in this invention are not particularly limited, as long as they are conventional organic solvents in this technical field; however, if extremely highly polar to low polar solvents such as water or hexane are used, precipitates or phase separation may occur, and their use should be cautious. Furthermore, when adding a large amount of organic solvent, there is a risk that sufficient film thickness cannot be ensured during film formation, and this should be noted.

[0038] [Other Additives] The composition for forming the optical waveguide of the present invention may also include other additives commonly used in the art, to the extent that the effects of the present invention are not impaired. Other additives include, for example, antireflective agents, ultraviolet absorbers, antioxidants, photostable agents, sensitizers, surfactants, crosslinking agents, leveling agents, silane coupling agents, etc. When using these other additives, they can usually be blended in proportions of 10 parts by mass or less relative to the total mass of the aforementioned epoxy compound (resin component) of 100 parts by mass.

[0039] [Components for forming optical waveguides] As will be described later, the aforementioned composition for forming optical waveguides of the present invention can be used as a forming material for optical waveguides, and in particular as a forming material for the cladding layer of optical waveguides. The modulation method for the components used in forming the optical waveguide in this embodiment is not particularly limited. Examples of modulation methods include adding components (A), (B), (C), and (D), and, if necessary, adding other epoxy compounds or other additives to form a homogeneous solution, or using conventional organic solvents in addition to these components. In the composition for forming the optical waveguide of the present invention, the mixing amount of each component, for example, when the total mass of the epoxy compounds is set to 100 parts by mass, can be 10-40 parts by mass of epoxy compound (A) containing a cycloaliphatic skeleton, 20-70 parts by mass of alicyclic epoxy compound (B), 10-50 parts by mass of aromatic epoxy compound (C), and 0-20 parts by mass of other epoxy compounds. Relative to the total mass of the aforementioned epoxy compounds (resin components) of 100 parts by mass, the ratio can be 0.2-5 parts by mass of photoacid generator (D) and 0-10 parts by mass of other additives. When using the aforementioned organic solvent, the proportion of solid components in the composition for forming the optical waveguide is not particularly limited, provided that all components are uniformly dissolved in the organic solvent; for example, it may be 60% by mass or more, or 70% by mass or more. Preferably, the proportion of solid components in the composition is, for example, 75% by mass to 100% by mass. The solid components referred to herein are substances remaining after removing the organic solvent components from all components of the composition for forming the optical waveguide.

[0040] Furthermore, it is preferable to use the constituent systems for forming optical waveguides after filtering them with filters or similar materials with apertures of 0.05 to 5 μm.

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

[0042] Optical Waveguide The optical waveguide of the present invention comprises a hardened form of the above-mentioned composition for forming an optical waveguide, and preferably comprises a cladding layer formed by the hardened form of the composition for forming an optical waveguide. For example, in one embodiment, the optical waveguide of the present invention is an optical waveguide consisting of a core and a cladding layer surrounding its entire periphery with a refractive index lower than that of the core. The cladding layer may be a hardened form of the aforementioned components for forming the optical waveguide. The core may be formed of a material having a refractive index greater than that of the formed cladding layer. Furthermore, the optical waveguide of the present invention can be any one of the following: a graded refractive index (GI) type in which the refractive index of the core changes continuously in the radial direction; a multimode step-variable refractive index (MI) type in which the refractive index of the core changes in stages in the radial direction; or a step-variable refractive index (SI) type in which the refractive index changes discontinuously only at the interface between the core and the cladding layer. [Example]

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

[0044] In addition, the compounds and their abbreviations used in the examples are as follows: [Contains a diepoxide compound with a fusiform skeleton] CG-500: OGSOL (registered trademark) CG-500, manufactured by Osaka Gas Chemicals (stock). PG-100: OGSOL (registered trademark) PG-100, manufactured by Osaka Gas Chemicals (stock). [Difunctional alicyclic epoxides] CEL-8010: CELLOXIDE (registered trademark) 8010, manufactured by DAICL (stock). THI-DE:EPOCHALIC (registered trademark) THI-DE, ENEOS (stock) CEL-2021P: CELLOXIDE (registered trademark) 2021P (3',4'-epoxycyclohexylmethyl 3,4-epoxycyclohexane carboxylate), manufactured by DAICL (stock). [Difunctional aromatic epoxides] jER806: jER (registered trademark) bisphenol F type epoxy resin, manufactured by Mitsubishi Chemical Co., Ltd. jER828: jER (registered trademark) bisphenol A type epoxy resin, manufactured by Mitsubishi Chemical Co., Ltd. [Other difunctional epoxides] YX-8000: Hydrogenated bisphenol A type epoxy resin, manufactured by Mitsubishi Chemical Co., Ltd. [Monofunctional alicyclic epoxides] M-100: CYCLOMER (registered trademark) M-100 (3,4-epoxycyclohexylmethyl methacrylate), DAICEL (stock company) [Monofunctional aromatic epoxides] EX-141: DENACOL (registered trademark) EX-141 (phenyl glycidyl ether), manufactured by Nagase ChemteX (stock). [Multifunctional alicyclic epoxides] GT-401: EPOLEAD (registered trademark) GT-401 (butanetetracarboxylic acid tetra(3,4-epoxycyclohexylmethyl) modified ε-caprolactone), manufactured by DAICL (stock). [Other multifunctional epoxy compounds] EHPE-3150: 1,2-epoxy-4-(2-epoxyethylene)cyclohexane adduct of 2,2-bis(hydroxymethyl)-1-butanol, manufactured by DAICEL (stock). [Photoacid Generator] CPI-310FG: Triaryl strontium salt type photoacid generator, manufactured by San-Apro (stock). [Organic solvents] PGMEA: Propylene Glycol Monomethyl Ether Acetate, manufactured by Showa Denko (stock).

[0045] [Examples 1-5, Comparative Examples 1-7] As shown in Table 1, various epoxy compounds, photoacid generators (100 parts by mass) relative to the aforementioned epoxy compounds, and organic solvents as needed were placed into flasks and stirred at temperatures below 110°C until the solid components were completely dissolved. After cooling to room temperature, the mixture was pressurized and filtered in a cleanroom using a 3 μm SUS filter to prepare liquid components.

[0046] A 4-inch diameter circular silicon wafer substrate was patterned using a UV / ozone irradiator. The aforementioned composition was then deposited onto the patterned substrate, and a film was formed by spin coating to a thickness of 20 μm. The resulting film was subjected to photolithography to obtain a patterned hardened film. Specifically, a photomask aligner was used to expose the prepared film to light, exposing only the illuminated areas. After exposure, it was baked at 60°C for 1 minute, followed by development with PGMEA / IPA (2-propanol) (50 / 50 vol / vol%) using an organic solvent for 3 minutes. Finally, it was post-baked at 100°C for 2 minutes to obtain the patterned hardened film.

[0047] For each component, the following procedures are used to evaluate its film-forming properties during spin coating, the patternability of the hardened film, the refractive index of the component, and the storage stability of the component.

[0048] [1. Film-forming properties] The state of the film during spin coating (visual inspection) and after spin coating (visual inspection and microscopy) was observed and evaluated according to the following evaluation criteria. The results are shown in Table 1. A: The entire membrane has a uniform appearance, with no visible phase separation or bright spots indicating agglomeration. Microscopic cross-sectional observation shows that the membrane thickness is within ±1 μm of its flatness. B: Only slight inhomogeneities or phase separation and bright spots were observed in the membrane. The membrane thickness was slightly tilted from the center of the membrane toward the end face. C: Unable to form a uniform film, or with aggregates scattered within the film.

[0049] [2. Graphification] The hardened film after photolithography was observed under a microscope from the end face direction, and the exposure sensitivity (patternability) was evaluated according to the following evaluation criteria. The results are shown in Table 1. Microscopic photographs taken from the end face direction are shown in Figure 1 (Example 1) and Figure 2 (Comparative Example 2). A: Only the exposed areas harden, while the unexposed areas dissolve due to organic imaging. B: The shape is formed to some extent, but the unexposed areas are also slightly hardened, or the exposed areas are not fully hardened, so the shape will not be convex. C: The unexposed area hardens significantly, or the exposed area dissolves due to development.

[0050] [3. Refractive Index] The refractive index of each component at 589 nm was measured using an Abbe refractometer, and the following evaluation criteria were followed. The results are shown in Table 1. A: The refractive index is 1.54 or higher. C: The refractive index did not reach 1.54.

[0051] [4. Storage stability] After storing each component at room temperature (23±3℃) for one month, the properties and state of the components were visually observed, and the following evaluation criteria were followed. The results are shown in Table 1. A: No precipitates or phase separation were observed; the solution remained transparent and homogeneous. B: Only a slight cloudiness of the liquid, or precipitation at the bottom. C: A precipitate clearly forms, which cannot be dissolved even with stirring.

[0052]

[0053] As shown in Table 1, the components of Examples 1 to 5 have excellent film-forming properties, as shown in Figure 1. They also have good exposure sensitivity and a refractive index of 1.54 or higher, resulting in excellent storage stability.

[0054] On the other hand, as shown in Table 1 and Figure 2, the compositions of Comparative Examples 1 to 7 failed to meet all performance requirements for film formation, exposure sensitivity, refractive index, and storage stability. In detail, Comparative Example 7, which did not use an epoxy compound (A) containing a fusiform skeleton, showed a lower refractive index compared to the examples. Furthermore, when using an epoxy compound containing a fusiform skeleton, as in Comparative Example 1, which used an epoxy compound with a structure different from the compound (A) of this invention, although the refractive index was improved, the result lacked film-forming properties and storage stability. When there is no difunctional or monofunctional alicyclic epoxy compound (B) (Comparative Example 2), it lacks film-forming properties and has poor exposure sensitivity. Furthermore, when the product does not contain difunctional or monofunctional aromatic epoxy compounds (C) but instead contains other polyfunctional epoxy compounds (Comparative Example 5), the film-forming properties, exposure sensitivity, and storage stability are poorer. By adding an organic solvent to this composition (Comparative Example 6), the film-forming properties, exposure sensitivity, and storage stability are slightly improved, but the results do not reach the level of evaluation A of the examples. Furthermore, when the film-forming properties, exposure sensitivity, and storage stability are poor, the film-forming properties, exposure sensitivity, and storage stability are also poor, as is the case with the addition of an organic solvent (Comparative Example 4). The film-forming properties, exposure sensitivity, and storage stability are slightly improved by adding an organic solvent (Comparative Example 4), but the results do not reach the level of evaluation A of the examples.

Claims

1. A composition for forming an optical waveguide, comprising: an epoxy compound (A) containing a cyclohexane skeleton, a monofunctional or difunctional alicyclic epoxy compound (B), a monofunctional aromatic epoxy compound and a difunctional aromatic epoxy compound (C) different from the aforementioned compound (A), and a photoacid generator (D); wherein, relative to 100 parts by mass of the total mass of the epoxy compound, the aforementioned epoxy compound (A) containing a cyclohexane skeleton comprises 5 to 50 parts by mass; the aforementioned alicyclic epoxy compound (B) comprises 10 to 80 parts by mass; the aforementioned aromatic epoxy compound (C) comprises 5 to 60 parts by mass; and the aforementioned photoacid generator (D) comprises 0.1 to 10 parts by mass, (in formula [1], L1 and L2 independently represent naphthyl dimethyl groups that may have substituents, and m and n independently represent integers from 0 to 10).

2. The composition for forming an optical waveguide as claimed in claim 1, wherein the aforementioned alicyclic epoxy compound (B) is a liquid alicyclic epoxy compound.

3. The composition for forming an optical waveguide as claimed in claim 1 or 2, wherein the aforementioned alicyclic epoxy compound (B) is a difunctional alicyclic epoxy compound.

4. The composition for forming an optical waveguide as claimed in claim 1 or 2, wherein the aforementioned alicyclic epoxy compound (B) is a compound represented by the following formula [2]: (In formula [2], R1 and R2 respectively independently represent a hydrogen atom, a straight-chain or branched alkyl group having 1 to 6 carbon atoms that 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 aforementioned straight-chain or branched alkyl group and the aforementioned cyclic alkyl group; in this case, the aforementioned straight-chain alkyl group having 2 or more carbon atoms, the aforementioned branched alkyl group having 3 or more carbon atoms, or the aforementioned cyclic alkyl group may form an epoxy ring together with adjacent carbon atoms, or R1 and R2 may be bonded to each other to form a ring having 4 to 6 carbon atoms, in which case they may form an epoxy ring together with adjacent carbon atoms constituting the aforementioned ring).

5. The composition for forming an optical waveguide as claimed in claim 1 or 2, wherein the aforementioned aromatic epoxy compound (C) is an epoxy compound having a bisphenol A-type backbone or a bisphenol F-type backbone.

6. The composition for forming an optical waveguide as claimed in claim 1 or 2, wherein the aforementioned epoxy compound (A) containing the epoxide skeleton is a compound represented by formula [3]: .

7. The composition for forming an optical waveguide as claimed in claim 1 or 2, wherein the aforementioned alicyclic epoxy compound (B) is at least one compound represented by the following formulas [4], [5], [6]:

8. A hardened material, which is a polymer of the composition for forming an optical waveguide as claimed in any one of claims 1 to 7.

9. An optical waveguide comprising a hardened component of an optical waveguide forming composition as claimed in any one of claims 1 to 7.

10. The optical waveguide of claim 9, comprising a cladding layer made of a hardened component of an optical waveguide forming composition of any one of claims 1 to 7.

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