JP2001004858A - Optical waveguide and its manufacture - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an optical waveguide having high heat resistance, in particular, and excellent cost efficiency and being manufacturable with a relatively simple and easy manufacturing process. SOLUTION: This optical waveguide is formed on a substrate 1, and has a core 3 and clads (a lower clad 2 and an upper clad 4) having smaller refractive indexes than the core 3. The core 3 or both the core 3 and the clads (the lower clad 2 and the upper clad 4 are formed with an epoxy acrylate resin having a fluorene skeleton.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical waveguide, and more particularly to an optical waveguide which has high heat resistance, is economical, and can be manufactured using a relatively simple manufacturing process, and a method for manufacturing the same.

[0002]

2. Description of the Related Art Optical exchanges, optical interconnection devices, and the like have been actively researched and developed in order to realize large-capacity and high-speed communication. These devices are composed of an electric signal processing section and an optical signal processing section, and optical waveguides are often used as optical circuits in the optical signal processing section.

[0003] Among the optical waveguides, an optical waveguide made of a resin can be formed on various substrates because it can be formed at a low temperature process and at low cost, and the cost of the entire optical module can be reduced. Research and development.

For example, F. Shimokawa et al .: In Pr43rd
ECTC (1993), p.705-p.710, Toru Matsuura et al., MES'97 (No. 7)
Microelectronics Symposium), p.77-p.
80 discloses an example in which fluorinated polyimide is used as a material for forming an optical waveguide.

According to this document, the fluorinated polyimide is applied to a substrate and then heated to 300 to 400 ° C. to form a film. Then, using the reactive ion etching method,
The optical waveguide core is processed into a desired shape. The refractive index can be adjusted by changing the ratio of copolymerization of the two kinds of polyimides. The glass transition temperature of the fluorinated polyimide is about 300 ° C.

Further, K. Enbutsu et al., MOC / GRIN '97
Tech Digest, P3, p.394, Proceedings of the 1998 IEICE Electronics Society Conference Examples have been disclosed.

As shown in this document, the use of an ultraviolet curing resin has the advantage that the core can be formed into a desired shape by irradiating ultraviolet rays only to the core portion of the optical waveguide to cure the core. The refractive index can be adjusted by changing the main component of the ultraviolet curable resin. The glass transition temperature of the ultraviolet curable resin is about 250 ° C.

In Japanese Patent Application Laid-Open No. 10-170738, an optical waveguide is formed using an asymmetric spiro ring-containing epoxy acrylate resin as a material.

[0009]

However, when fluorinated polyimide is used as the material of the optical waveguide, the reactive ion etching method is used in the step of forming the optical waveguide core into a desired shape. As a result, it has been difficult to produce easily. Further, applicable substrates are limited due to process factors such as a high film forming temperature. Furthermore, the fluorinated polyimide has a disadvantage that the material cost is high.

On the other hand, when an ultraviolet curable resin is used, the core can be formed simply by irradiating it with ultraviolet light, so that the core can be easily manufactured. However, since the resolution is low and a fine pattern cannot be formed, only the multi-mode optical waveguide having a width and height of the optical waveguide core section of about several tens μm is applied, and the width and height of the optical waveguide core section are several No single-mode optical waveguide of about μm is applied. Furthermore, the UV-curable resins disclosed in the above-mentioned prior arts have a glass transition temperature of about 2
An optical element mounting step (about 300 ° C.) using a gold / tin-based solder (melting point: 280 ° C.) having a self-alignment effect (effect that the optical element is pulled to a target position by the surface tension of the solder ball) at 50 ° C. There was a problem that it could not withstand.

[0011]

SUMMARY OF THE INVENTION The present invention provides an optical waveguide having a core and a clad having a smaller refractive index than the core, wherein the core is formed using an epoxy acrylate resin containing a fluorene skeleton. The present invention relates to an optical waveguide characterized by:

It is preferable that the cladding is formed using an epoxy acrylate resin containing a fluorene skeleton having a smaller refractive index than the core.

The core formed by using the epoxy acrylate resin containing the fluorene skeleton, or both the core and the clad, have a glass transition temperature of 260 ° C. or higher and a light propagation loss of 1.3 μm at a wavelength of 0.3 μm. 5dB /
cm or less, and the light propagation loss at a wavelength of 1.55 μm is preferably 0.5 dB / cm or less.

Particularly preferred examples of the epoxy acrylate resin having a fluorene skeleton include a compound represented by the following chemical formula (1).

[0015]

Embedded image (In the chemical formula (1), the chemical structure X represents a chemical structure represented by the following chemical formula (2). However, in the benzene ring of the chemical structure X, * represents a bond to the compound represented by the chemical formula (1). And the bonding position * may be independently any of ortho, meta and para positions with respect to the bonding position between the benzene ring and the fluorene skeleton, and Y is hydrogen or methyl. In addition, R1 to R16
Each independently represents hydrogen, alkyl, alkoxy, alkoxycarbonyl, aryl or aralkyl. N represents an integer of 0 or more. )

[0016]

Embedded image Further, the present invention provides a first step of forming a lower clad layer on a substrate and a second step of forming an epoxy acrylate resin layer containing a fluorene skeleton on the lower clad layer.
And a third step of exposing and etching the epoxy acrylate resin layer containing the fluorene skeleton to form a core, and a fourth step of post-baking the substrate on which the core is formed. In the first step relating to the method for manufacturing an optical waveguide, characterized in that when forming an epoxy acrylate resin containing a fluorene skeleton as the lower cladding layer, forming an epoxy acrylate resin layer containing a fluorene skeleton, Next, by controlling the refractive index of the lower cladding layer to be smaller than the refractive index of the core by exposing with an exposure amount larger than the exposure amount that is exposed when forming the core, then the lower cladding layer is exposed. The formed substrate is post-baked.

In the case where an epoxy acrylate resin containing a fluorene skeleton is formed as an upper cladding layer covering the core layer after the fourth step, an epoxy acrylate resin layer containing a fluorene skeleton is formed. By controlling the refractive index of the upper clad layer to be smaller than the refractive index of the core by exposing with an exposure amount larger than the exposure amount to be exposed when forming the core, then the upper clad layer is formed. Post-baked substrate.

It is preferable that the post-baking is performed in a temperature range of 160 to 250 ° C.

[0019]

BEST MODE FOR CARRYING OUT THE INVENTION The optical waveguide of the present invention comprises at least a core and a clad, and the structure thereof is not particularly limited. The optical waveguide may be a buried type optical waveguide or a ridge type optical waveguide. Is also good.

The epoxy acrylate resin having a fluorene skeleton used in the present invention has a fluorene skeleton represented by the following chemical formula (3), and further includes an epoxy acrylate (including epoxy methacrylate) which is a UV-curable functional group. Compound.

[0021]

Embedded image Such a resin is particularly used as a material for an optical waveguide because, firstly, by having both a fluorene skeleton and an epoxy acrylate, it is possible to form a film at a low temperature, but to have high heat resistance. Second, it has a small optical propagation loss at the communication wavelength of 1.3 μm or 1.55 μm and is very effective as a material for the optical waveguide. At the time of formation, it is necessary to control the refractive index of the core layer and the cladding layer, but this is because the control can be performed by a simple method simply by changing the exposure amount.

Particularly preferred epoxy acrylate resins having a fluorene skeleton include compounds represented by the following chemical formula (1).

[0023]

Embedded image (In the chemical formula (1), the chemical structure X represents a chemical structure represented by the following chemical formula (2). However, in the benzene ring of the chemical structure X, * represents a bond to the compound represented by the chemical formula (1). And the bonding position * may be independently any of ortho, meta and para positions with respect to the bonding position between the benzene ring and the fluorene skeleton, and Y is hydrogen or methyl. In addition, R1 to R16
Each independently represents hydrogen, alkyl, alkoxy, alkoxycarbonyl, aryl or aralkyl. N represents an integer of 0 or more. )

[0024]

Embedded image The substituent of R1 to R16 is, for example, an alkyl group having 1 to 1 carbon atoms such as methyl, ethyl, propyl, and butyl.
8 alkyl groups. As the alkoxy group,
Examples thereof include alkoxy groups having 1 to 8 carbon atoms such as methoxy, ethoxy, propoxy and butoxy groups. Examples of the alkoxycarbonyl group include methoxycarbonyl,
An ethoxycarbonyl, propoxycarbonyl, butoxycarbonyl and the like include an alkoxycarbonyl group having 2 to 9 carbon atoms. Examples of the aryl group include phenyl,
Tolyl, xylyl, mesityl, cumenyl, naphthyl, anthracenyl groups and the like. As the aralkyl group, benzyl, phenethyl, 1-phenylethyl, 1-
Methyl-1-phenylethyl, methylbenzyl group and the like. In the compounds exemplified above, for example, C ₄
When there is a branched structure as in the above alkyl group and the like, isomers thereof are also included in the present invention.

By using a radical initiator for this resin, photopolymerization can proceed. As the radical initiator, although not particularly limited, a known peroxide initiator,
An azobis-based initiator or the like can be used. For example, peroxide initiators include methyl ethyl ketone peroxide, isobutyl peroxide, cumene hydroperoxide and the like, and azobis initiators such as 1,1′-
Azobiscyclohexane-1-carbonitrile, 4,
4'-azobis- (4-cyanovaleic acid) and the like.

For forming a layer, a coating solution in which an epoxy acrylate resin having a fluorene skeleton containing these compositions is dissolved in a solvent is prepared and applied to a predetermined substrate. Next, pre-heating is performed to evaporate and remove the solvent to form a dried coating film.

The solvent is preferably one that uniformly dissolves the epoxy acrylate resin having a fluorene skeleton, or one that does not completely dissolve the epoxy acrylate resin, but is uniformly dispersed, and can be appropriately selected in consideration of the boiling point and the like. For example, it dissolves in a liquid photopolymerizable compound such as a low molecular weight epoxy (meth) acrylate at room temperature within a range that does not impair properties such as an organic solvent such as cellosolve or an optical waveguide such as heat resistance, refractive index, and light propagation loss. Or it can be dispersed.

The concentration at the time of dissolution or uniform dispersion can be appropriately selected depending on the designed film thickness and the like.

Examples of the substrate to be coated include a silicon substrate, a ceramic substrate, a printed substrate and the like.

When this coating film is used as a core, a predetermined core-shaped portion is cured by ultraviolet light by partial exposure using a mask. At this time, the refractive index of the core is determined by the amount of exposure of the irradiated ultraviolet light. Further, the core is formed by developing and etching the unexposed portion by, for example, immersion in an amine-based alkali developing solution.

When this coating film is used as a cladding layer, the refractive index of the cladding is made smaller than the refractive index of the core by irradiating an ultraviolet ray having an exposure amount larger than a predetermined exposure amount to the core portion. Adjust so that

Table 1 shows an example of the relationship between the amount of exposure and the refractive index.

[0033]

[Table 1] The data in Table 1 was measured by the following method. A solution obtained by dissolving an epoxy acrylate resin having a fluorene skeleton represented by the following chemical formula (4) is spin-coated at 800 rpm, 10 seconds + 4000 rpm, and 3 rpm.
The coating was performed on the substrate under the condition of 0 sec to obtain a coating film. Then 7
After preliminary drying at 5 ° C. for about 10 minutes, exposure was performed, and heat treatment (post-baking) was performed at 230 ° C. for about 30 minutes in a nitrogen atmosphere to obtain a uniform film having a thickness of 4.7 μm. The exposure amount was set under three conditions of 0, 100, and 800 mJ / cm ² , three types of samples were prepared, and the refractive index was measured using the prism coupler method.

In the chemical formula (4), the chemical structure X
₁ shows a chemical structure represented by the following chemical formula (5). As shown in this structure, the bonding position in the chemical structure X ₁ *
Are para to the fluorene skeleton at both positions.

[0035]

Embedded image

[0036]

Embedded image The above method of controlling the refractive index by changing the amount of ultraviolet light exposure is most preferable, but in the cladding layer and the core layer, the type of epoxy acrylate resin having a fluorene skeleton is changed, or the epoxy having a fluorene skeleton is changed. The refractive index can be controlled by changing the mixing ratio of the composition containing the acrylate resin.

Thus, the core or the core and the clad are formed by the epoxy acrylate resin having a fluorene skeleton.

Further, as post-baking (post-heating step), temperature conditions are 160 to 250 ° C., preferably 230 to 250 ° C.
By heating at 250 ° C. for about 30 to 90 minutes, the crosslinking density is increased, and further heat resistance is imparted.

For example, the relationship between the glass transition temperature of the compound represented by the chemical formula (4) and the post-bake temperature is as follows.
When the temperature is 50 ° C and the post-bake temperature is 210 ° C, the glass transition temperature is 260 ° C, and when the post-bake temperature is 230 to 250 ° C, the glass transition temperature is about 300 ° C.

The refractive index of the epoxy acrylate resin having a fluorene skeleton is fixed at a constant value by performing the above-described post-baking. Therefore, when each optical waveguide layer is formed using an epoxy acrylate resin having a fluorene skeleton, it is preferable to perform post-baking before forming the next layer. By performing post-baking after forming each layer as described above, it is possible to suppress a change in the refractive index due to the subsequent ultraviolet exposure step and heating step.

[0041]

The present invention will be described in further detail below with reference to examples.

Example 1 FIG. 1 is a schematic sectional view of a buried optical waveguide according to one embodiment of the present invention. Substrate 1
The lower clad 2 and the core 3 were sequentially laminated on the upper, and the upper clad was formed on the lower clad 2 so as to cover the core 3. The upper and lower claddings need to have a lower refractive index than the core.

As the material of the lower clad 2 and the upper clad 4, in this embodiment, fluorinated polyimide having a refractive index of 1.560 was used.

The optical waveguide shown in this figure was prepared by using the steps shown in FIG.

In step a, a fluorinated polyimide was formed as a lower clad 22 on the substrate 21.

Next, in step b, a coating solution containing an epoxy acrylate resin having a fluorene skeleton is formed on the lower clad 22 by a spin coating method or a dip coating method, and further preheated (at 75 ° C. for 10 minutes). ), And the solvent was evaporated to obtain a core layer (epoxy acrylate resin layer having a fluorene skeleton) 23.

As the epoxy acrylate resin having a fluorene skeleton, a resin represented by the following chemical formula (4) was used. In the chemical formula (4), the chemical structure X ₁ represents a chemical structure represented by the following chemical formula (5). As shown in this structure, the bonding position * is the chemical structure X _1, which is para to the fluorene skeleton with two places.

[0048]

Embedded image

[0049]

Embedded image Next, in step c, exposure was performed through a glass mask having a predetermined pattern. The exposure wavelength at this time is 365n
m and the exposure amount was 300 mJ / cm ² .

Then, it is immersed in potassium hydroxide or an amine-based alkali developing solution to dissolve and develop the unexposed portion, and further subjected to a heat treatment (post-bake) at 230 ° C. for about 30 minutes in a nitrogen atmosphere. As a result, the exposed portion was post-cured to form the shape of the optical waveguide core 23a. At this time, a single mode optical waveguide having a core cross section having a height and width of about several μm, and a multimode optical waveguide having a core cross section having a height and width of about several tens μm can be manufactured.

The glass transition temperature of the core after the post-curing was 300 ° C., and the refractive index was 1.567. When the glass transition temperature is 300 ° C. or higher, sufficient heat resistance is obtained in the optical mounting process. As described above, by performing the heat treatment at a high temperature of 230 ° C. or more,
Glass transition temperatures of at least ℃ can be achieved.

Next, in step d, a film of fluorinated polyimide was formed as an upper clad 24 on the lower clad 22 so as to cover the core 23a, thereby completing an optical waveguide.

The wavelength of this optical waveguide is 1.3 μm and 1.5 μm.
When a light propagation loss of 5 μm was measured, it was 0.3 dB / c.
m and a good value.

The following method was used for measuring the light propagation loss. The light emitted from the laser was made incident on one side of the optical waveguide using an optical fiber, and the light propagating through the optical waveguide and emitted from the side opposite to the incident side was guided to the light receiving device using the optical fiber, and the light amount was measured. The same measurement was performed on the optical waveguide that was cut short, and the light propagation loss was determined from the relationship between the length of the optical waveguide and the amount of light measured by the light receiving device.

In this embodiment, the core material is
Since no fluorinated polyimide was used, there was no need to use reactive ion etching to form the core, and an optical waveguide having high heat resistance could be formed by a simple process.

Embodiment 2 In the optical waveguide having the same structure as that of FIG. 1 shown in Embodiment 1, an embodiment in which an epoxy acrylate resin having a fluorene skeleton is used for all of the core layer, lower cladding layer and upper cladding layer. This will be described with reference to FIG.

As the epoxy acrylate resin having a fluorene skeleton, the resin represented by the chemical formula (4) used in Example 1 was used.

In step a, a coating solution containing an epoxy acrylate resin having a fluorene skeleton is formed on the substrate 21 by a spin coating method, a dip coating method, or the like.
(5 ° C. for about 10 minutes) and the solvent was evaporated to obtain a lower clad (epoxy acrylate resin layer having a fluorene skeleton) 22.

Then, exposure was performed at 800 mJ / cm ² to adjust the refractive index of the lower cladding 22 to 1.5667.

Then, the exposed portion was cured by a heat treatment (post-bake) at 230 ° C. for about 30 minutes in a nitrogen atmosphere, and the refractive index was fixed.

In step b, on the lower cladding 22,
A core layer (epoxy acrylate resin layer having a fluorene skeleton) 23 was obtained in exactly the same manner as in Example 1 except that the amount of exposure was changed. Exposure is 100mJ / cm
² , and the refractive index was 1.5678.

Next, in step c, the optical waveguide core 23a was formed in exactly the same manner as in Example 1.

Next, in step d, the lower cladding 22
On top, an epoxy acrylate resin layer having a fluorene skeleton is formed so as to cover the core 23a,
Exposure was performed at 800 mJ / cm ² to adjust the refractive index of the upper cladding 24 to 1.5667. In a nitrogen atmosphere 2
Post-baking was performed at 30 ° C. for 30 minutes to complete the optical waveguide.

The glass transition temperature of the core and clad portions is 3
00 ° C.

The wavelength of this optical waveguide is 1.3 μm and 1.5 μm.
When a light propagation loss of 5 μm was measured, it was 0.3 dB / c.
m and a good value.

In this example, both the core and the clad were formed using an epoxy acrylate resin having a fluorene skeleton. In particular, the feature of the present embodiment lies in that the clad and the core are formed using the same material and only by the difference in the amount of exposure to ultraviolet light. By employing such a process, an optical waveguide can be manufactured more easily than in the first embodiment.

In addition to the buried type optical waveguide structure shown in FIG. 1, a substrate 31 and a lower clad 32 are sequentially formed as shown in FIG. May be adopted, and any optical waveguide structure may be adopted. Further, the optical waveguide may be formed by a dry process such as a reactive ion etching method or the like, and can be etched by a known process.

[0068]

The present invention has the following effects.

First, as a material property, a communication wavelength of 1.3 is used.
Good light transmittance at μm or 1.55 μm.

Second, the glass transition temperature is 260 ° C. or higher, and the heat resistance is high.

Third, since it has an epoxy acrylate group, it has the property of being cured by ultraviolet irradiation,
A core shape having a height and width of several μm to several tens μm can be formed in the cross-sectional shape of the core by exposure and development of ultraviolet rays, so that core formation is easy.

Fourth, since the epoxy acrylate resin having a fluorene skeleton can control the refractive index in an appropriate range by controlling the amount of exposure, a layer is formed using the same material. After that, the cladding and the core can be formed only by adjusting the exposure amount.

Fifth, unlike fluorinated polyimide, a high temperature is not required for film formation, so that a low-temperature process is possible.

As described above, when an epoxy acrylate resin having a fluorene skeleton is used as a material of an optical waveguide, an optical waveguide having heat resistance can be easily formed.

[Brief description of the drawings]

FIG. 1 is a schematic sectional view of a buried optical waveguide according to an embodiment of the present invention.

FIG. 2 is a process sectional view of a buried optical waveguide according to an embodiment of the present invention.

FIG. 3 is a sectional view of a ridge type optical waveguide.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Substrate 2 Lower clad 3 core 4 Upper clad 21 Substrate 22 Lower clad 23 Core layer 23a core 24 Upper clad 31 Substrate 32 Lower clad 33 core

 ────────────────────────────────────────────────── ─── Continuing on the front page (72) Inventor Yuzo Shimada 5-7-1 Shiba, Minato-ku, Tokyo F-term in NEC Corporation 2H047 KA04 PA17 PA28 QA05 TA16 TA31 TA43

Claims (15)

[Claims] 1. An optical waveguide having a core and a clad having a smaller refractive index than the core, wherein the core is formed by using an epoxy acrylate resin having a fluorene skeleton. . 2. The method according to claim 1, wherein the cladding is formed using an epoxy acrylate resin containing a fluorene skeleton having a lower refractive index than the core.
An optical waveguide as described. 3. The glass transition temperature of the core or both of the core and the clad formed using the epoxy acrylate resin containing the fluorene skeleton is 260 ° C. or higher. Optical waveguide. 4. A core formed by using the epoxy acrylate resin having a fluorene skeleton, or a light propagation loss at a wavelength of 1.3 μm of both the core and the clad is 0.5 dB / cm or less. Claim 1
4. The optical waveguide according to any one of items 1 to 3. 5. A core formed by using the epoxy acrylate resin containing a fluorene skeleton, or a light propagation loss at a wavelength of 1.55 μm of both the core and the clad is 0.5 dB / cm or less. The optical waveguide according to claim 1. 6. The optical waveguide according to claim 1, wherein the epoxy acrylate resin having a fluorene skeleton is a compound represented by the following chemical formula (1). Embedded image (In the chemical formula (1), the chemical structure X represents a chemical structure represented by the following chemical formula (2). However, in the benzene ring of the chemical structure X, * represents a bond to the compound represented by the chemical formula (1). And the bonding position * may be independently any of ortho, meta and para positions with respect to the bonding position between the benzene ring and the fluorene skeleton, and Y is hydrogen or methyl. In addition, R1 to R16
Each independently represents hydrogen, alkyl, alkoxy, alkoxycarbonyl, aryl or aralkyl. N represents an integer of 0 or more. ) 7. A first step of forming a clad layer (hereinafter, referred to as a lower clad layer) on a substrate, and a second step of forming an epoxy acrylate resin layer containing a fluorene skeleton on the lower clad layer. And a third step of exposing and etching the epoxy acrylate resin layer containing the fluorene skeleton to form a core, and a fourth step of post-baking the substrate on which the core is formed. A method for manufacturing an optical waveguide. 8. In the first step, when an epoxy acrylate resin containing a fluorene skeleton is formed as the lower cladding layer, an epoxy acrylate resin layer containing a fluorene skeleton is formed, and then the core is formed. By controlling the refractive index of the lower cladding layer to be smaller than the refractive index of the core by exposing with an exposure amount larger than the exposure amount to be exposed at the time of, then the substrate on which the lower cladding layer is formed 8. The method for manufacturing an optical waveguide according to claim 7, wherein post-baking is performed. 9. After the fourth step, as a clad layer (hereinafter referred to as an upper clad layer) covering the core layer,
When forming an epoxy acrylate resin containing a fluorene skeleton, forming an epoxy acrylate resin layer containing a fluorene skeleton, and then exposing with a light exposure larger than the light exposure when forming the core. 9. The optical waveguide according to claim 7, wherein the refractive index of the upper cladding layer is controlled to be smaller than the refractive index of the core, and then the substrate on which the upper cladding layer is formed is post-baked. Production method. 10. The post-baking is performed at 160 to 250.
The method according to any one of claims 7 to 9, wherein the method is performed in a temperature range of ° C. 11. The method according to claim 11, wherein the post-baking is performed at 230 to 250.
The method according to claim 10, wherein the method is performed in a temperature range of ° C. 12. The glass transition temperature of a core formed using the epoxy acrylate resin containing a fluorene skeleton or both of the core and the clad is 260 ° C.
The method for manufacturing an optical waveguide according to any one of claims 7 to 11, wherein: 13. A core formed by using the epoxy acrylate resin containing a fluorene skeleton, or a light propagation loss at a wavelength of 1.3 μm of both the core and the clad is 0.5 dB / cm or less. The method for manufacturing an optical waveguide according to any one of claims 7 to 12. 14. A core formed by using the epoxy acrylate resin containing a fluorene skeleton, or a light propagation loss at a wavelength of 1.55 μm of both the core and the clad is 0.5 dB / cm or less. The method for manufacturing an optical waveguide according to any one of claims 7 to 13. 15. The method of manufacturing an optical waveguide according to claim 7, wherein the epoxy acrylate resin having a fluorene skeleton is a compound represented by the following chemical formula (1). Embedded image (In the chemical formula (1), the chemical structure X represents a chemical structure represented by the following chemical formula (2). However, in the benzene ring of the chemical structure X, * represents a bond to the compound represented by the chemical formula (1). And the bonding position * may be independently any of the ortho, meta and para positions with respect to the bonding position between the benzene ring and the fluorene skeleton, and Y is hydrogen or methyl. In addition, R1 to R16
Each independently represents hydrogen, alkyl, alkoxy, alkoxycarbonyl, aryl or aralkyl. N represents an integer of 0 or more. )