JPH07102088A - Processing method for polyimide film, and polyimide optical waveguide - Google Patents

Abstract

PURPOSE:To provide the method for simply and conveniently changing the refractive index of a polyimide film and to obtain a new polyimide optical waveguide free from problems with differences in thermal characteristics and birefringence between a core and a clad. CONSTITUTION:A polyimide film is irradiated with a radiation light. A polyimide optical waveguide comprises a polyimide clad and a polyimide core irradiated with a radiation light. A suitable polyimide film is a fluorinated one. Thus the steps and time for production are reduced, and the waveguide is produced simply and conveniently.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a polyimide optical waveguide in which the refractive index of polyimide is easily changed, and more particularly to an optical waveguide using a polyimide having a controlled refractive index as a core.

[0002]

2. Description of the Related Art Since polyimide has excellent heat resistance, electrical properties, and mechanical properties, it is widely used as an electronic material such as an insulating film for electronic parts and flexible printed wiring boards. On the other hand, with the development of optical communication systems, development of various high-performance and high-performance optical components is expected, and optical materials having performances suitable for each optical component are required. So far, quartz, which is also a material for optical fibers, has been mainly studied as an optical material for optical communication, and various optical parts have been developed. However, since a high temperature of 1000 ° C. or higher is required to manufacture an optical component using a silica-based optical material, the substrates that can be manufactured are limited, and there are drawbacks such as lack of flexibility, and so it is not a universal optical material. It is expected that a plastic optical material which is excellent in flexibility and manufacturability with respect to an inorganic optical material typified by quartz, particularly a plastic optical material which is excellent in heat resistance from the viewpoint of reliability and process compatibility. Since quartz has an extremely good optical transparency as has been proved with an optical fiber, even when used as a waveguide, a low optical loss of 0.1 dB / cm or less is achieved at a wavelength of 1.3 μm. However, there are problems in manufacturing, such as requiring a long time for manufacturing the optical waveguide, requiring high temperature during manufacturing, and making it difficult to increase the area. On the other hand, a plastic optical waveguide such as polymethylmethacrylate (PMMA) can be molded at a low temperature and has an advantage that a low price can be expected, but has a drawback that it is inferior in heat resistance. Therefore, a plastic optical waveguide having excellent heat resistance has been expected. On the other hand, polyimide, which is excellent in heat resistance, is often used as an insulating material for electronic parts, electronic materials such as flexible printed wiring boards, etc., but to date it has hardly been applied to optical parts such as optical waveguides.

From these viewpoints, the present inventors are conducting research and development on polyimide optical materials. In applying polyimide as an optical material, it is particularly important that it has excellent light transmittance and that the refractive index can be freely controlled. The inventors of the present invention have disclosed in JP-A-3-72528 that it is possible to control the refractive index necessary for forming an optical waveguide, for example, by copolymerizing a fluorinated polyimide. Regarding optical waveguides using this fluorinated polyimide, JP-A-4-9807 and 4-
No. 235505 and No. 4-235506. In these optical waveguides, the difference in the refractive index between the core having a role of transmitting light and the clad having a role of confining light is controlled by adjusting the content of fluorine contained in the polyimide. That is, two types of fluorinated polyimides having different refractive indexes for the core and the clad are used. Therefore, there may be a problem in some kinds of optical waveguides such as different thermal characteristics between the core and the clad and different birefringence. If the same polyimide can be used to freely control the refractive index, it is possible to form a polyimide optical waveguide that has never existed before. In addition, the conventional method of manufacturing a polyimide optical waveguide is mainly the method of using reactive ion etching (RIE) used in the semiconductor manufacturing process, and there are many manufacturing processes and there is a drawback that it takes a long time for manufacturing. . There is a demand for a method of manufacturing an optical waveguide that can be manufactured in a short time with a small number of manufacturing steps instead of these methods of manufacturing a polyimide optical waveguide.

[0004]

SUMMARY OF THE INVENTION An object of the present invention is to provide a method for simply changing the refractive index of a polyimide film, and to provide a novel polyimide optical fiber which does not have the problem of thermal characteristic difference and birefringence difference between the core and the clad. It is to provide a waveguide.

[0005]

The present invention will be summarized. The first invention of the present invention relates to a method for processing a polyimide, and is characterized in that the polyimide is irradiated with radiant light. A second invention of the present invention relates to a polyimide optical waveguide, and is characterized in that a polyimide whose refractive index is controlled by irradiation of radiant light is used as a core thereof.

In view of the above situation, the inventors of the present invention have conducted extensive studies and found that the refractive index of polyimide is changed by irradiating the polyimide with radiant light, and the present invention has been completed.

The polyimide used in the present invention can be produced, for example, from the following tetracarboxylic acid or its derivative and a diamine, and contains a simple substance of polyimide, a polyimide copolymer, a polyimide mixture and, if necessary, additives and the like. Some are added.

The acid anhydrides, acid chlorides, ester compounds and the like as tetracarboxylic acids and their derivatives include the following. Here, an example of tetracarboxylic acid will be given. (Trifluoromethyl) pyromellitic acid, di (trifluoromethyl) pyromellitic acid, di (heptafluoropropyl) pyromellitic acid, pentafluoroethylpyromellitic acid, bis {3,5-di (trifluoromethyl) phenoxy} Pyromellitic acid, 2, 3,
3 ', 4'-biphenyltetracarboxylic acid, 3,3',
4,4'-tetracarboxydiphenyl ether, 2,
3,3 ', 4'-tetracarboxydiphenyl ether, 3,3', 4,4'-benzophenone tetracarboxylic acid, 2,3,6,7-tetracarboxynaphthalene,
1,4,5,7-tetracarboxynaphthalene, 1,
4,5,6-tetracarboxynaphthalene, 3,3 ',
4,4'-tetracarboxydiphenylmethane, 3,
3 ', 4,4'-tetracarboxydiphenyl sulfone, 2,2-bis (3,4-dicarboxyphenyl) propane, 2,2-bis (3,4-dicarboxyphenyl) hexafluoropropane, 5,5 '-Bis (trifluoromethyl) -3,3', 4,4'-tetracarboxybiphenyl, 2,2 ', 5,5'-tetrakis (trifluoromethyl) -3,3', 4,4'- Tetracarboxybiphenyl, 5,5'-bis (trifluoromethyl) -3,3 ', 4,4'-tetracarboxydiphenyl ether, 5,5'-bis (trifluoromethyl)-
3,3 ′, 4,4′-tetracarboxybenzophenone, bis {(trifluoromethyl) dicarboxyphenoxy} benzene, bis {(trifluoromethyl) dicarboxyphenoxy} (trifluoromethyl) benzene,
Bis (dicarboxyphenoxy) (trifluoromethyl) benzene, bis (dicarboxyphenoxy) bis (trifluoromethyl) benzene, bis (dicarboxyphenoxy) tetrakis (trifluoromethyl) benzene, 3,4,9,10-tetra Carboxyperylene,
2,2-bis {4- (3,4-dicarboxyphenoxy) phenyl} propane, butanetetracarboxylic acid, cyclopentanetetracarboxylic acid, 2,2-bis {4-
(3,4-dicarboxyphenoxy) phenyl} hexafluoropropane, bis {(trifluoromethyl) dicarboxyphenoxy} biphenyl, bis {(trifluoromethyl) dicarboxyphenoxy} bis (trifluoromethyl) biphenyl, bis {( Trifluoromethyl)
Dicarboxyphenoxy} diphenyl ether, bis (dicarboxyphenoxy) bis (trifluoromethyl) biphenyl, bis (3,4-dicarboxyphenyl) dimethylsilane, 1,3-bis (3,4-dicarboxyphenyl) tetramethyldi Siloxane, difluoropyromellitic acid, 1,4-bis (3,4-dicarboxytrifluorophenoxy) tetrafluorobenzene,
1,4-bis (3,4-dicarboxytrifluorophenoxy) octafluorobiphenyl and the like.

Examples of the diamine include the following. m-phenylenediamine, 2,4-diaminotoluene, 2,4-diaminoxylene, 2,4-diaminodurene, 4- (1H, 1H, 11H-eicosafluoroundecanoxy) -1,3-diaminobenzene, 4-
(1H, 1H-perfluoro-1-butanoxy) -1,
3-diaminobenzene, 4- (1H, 1H-perfluoro-1-heptanoxy) -1,3-diaminobenzene,
4- (1H, 1H-perfluoro-1-octanoxy)
-1,3-diaminobenzene, 4-pentafluorophenoxy-1,3-diaminobenzene, 4- (2,3,
5,6-Tetrafluorophenoxy) -1,3-diaminobenzene, 4- (4-fluorophenoxy) -1,3
-Diaminobenzene, 4- (1H, 1H, 2H, 2H-
Perfluoro-1-hexanoxy) -1,3-diaminobenzene, 4- (1H, 1H, 2H, 2H-perfluoro-1-dodecanoxy) -1,3-diaminobenzene,
p-phenylenediamine, 2,5-diaminotoluene,
2,3,5,6-tetramethyl-p-phenylenediamine, 2,5-diaminobenzotrifluoride, bis (trifluoromethyl) phenylenediamine, diaminotetra (trifluoromethyl) benzene, diamino (pentafluoroethyl) benzene 2,5-diamino (perfluorohexyl) benzene, 2,5-diamino (perfluorobutyl) benzene, benzidine, 2,2′-
Dimethylbenzidine, 3,3′-dimethylbenzidine,
3,3'-dimethoxybenzidine, 2,2'-dimethoxybenzidine, 3,3 ', 5,5'-tetramethylbenzidine, 3,3'-diacetylbenzidine, 2,2'-
Bis (trifluoromethyl) -4,4′-diaminobiphenyl, octafluorobenzidine, 3,3′-bis (trifluoromethyl) -4,4′-diaminobiphenyl, 4,4′-diaminodiphenyl ether, 4,4 '
-Diaminodiphenylmethane, 4,4'-diaminodiphenyl sulfone, 2,2-bis (p-aminophenyl)
Propane, 3,3'-dimethyl-4,4'-diaminodiphenyl ether, 3,3'-dimethyl-4,4'-diaminodiphenylmethane, 1,2-bis (anilino) ethane, 2,2-bis (p- Aminophenyl) hexafluoropropane, 1,3-bis (anilino) hexafluoropropane, 1,4-bis (anilino) octafluorobutane, 1,5-bis (anilino) decafluoropentane, 1,7-bis (anilino) ) Tetradecafluoroheptane, 2,2'-bis (trifluoromethyl) -4,
4'-diaminodiphenyl ether, 3,3'-bis (trifluoromethyl) -4,4'-diaminodiphenyl ether, 3,3 ', 5,5'-tetrakis (trifluoromethyl) -4,4'-diaminodiphenyl ether , 3,3'-bis (trifluoromethyl) -4,4 '
-Diaminobenzophenone, 4,4 "-diamino-p
-Terphenyl, 1,4-bis (p-aminophenyl)
Benzene, p-bis (4-amino-2-trifluoromethylphenoxy) benzene, bis (aminophenoxy)
Bis (trifluoromethyl) benzene, bis (aminophenoxy) tetrakis (trifluoromethyl) benzene, 4,4 ′ ″-diamino-p-quarterphenyl, 4,4′-bis (p-aminophenoxy) biphenyl, 2 , 2-bis {4- (p-aminophenoxy) phenyl} propane, 4,4'-bis (3-aminophenoxyphenyl) diphenyl sulfone, 2,2-bis {4-
(4-Aminophenoxy) phenyl} hexafluoropropane, 2,2-bis {4- (3-aminophenoxy)
Phenyl} hexafluoropropane, 2,2-bis {4
-(2-Aminophenoxy) phenyl} hexafluoropropane, 2,2-bis {4- (4-aminophenoxy) -3,5-dimethylphenyl} hexafluoropropane, 2,2-bis {4- (4- Aminophenoxy)-
3,5-ditrifluoromethylphenyl} hexafluoropropane, 4,4′-bis (4-amino-2-trifluoromethylphenoxy) biphenyl, 4,4′-bis (4-amino-3-trifluoromethylphenoxy) ) Biphenyl, 4,4'-bis (4-amino-2-trifluoromethylphenoxy) diphenyl sulfone, 4,4 '
-Bis (3-amino-5-trifluoromethylphenoxy) diphenyl sulfone, 2,2-bis {4- (4-amino-3-trifluoromethylphenoxy) phenyl}
Hexafluoropropane, bis {(trifluoromethyl) aminophenoxy} biphenyl, bis [{(trifluoromethyl) aminophenoxy} phenyl] hexafluoropropane, diaminoanthraquinone, 1,5-diaminonaphthalene, 2,6-diaminonaphthalene, Bis {2-[(aminophenoxy) phenyl] hexafluoroisopropyl} benzene, bis (2,3,5,6-tetrafluoro-4-aminophenyl) ether, bis (2,3,5,6-tetrafluoro- 4-aminophenyl) sulfide, 1,3-bis (3-aminopropyl)
Tetramethyldisiloxane, 1,4-bis (3-aminopropyldimethylsilyl) benzene, bis (4-aminophenyl) diethylsilane, 1,3-diaminotetrafluorobenzene, 1,4-diaminotetrafluorobenzene, 4, 4′-bis (tetrafluoroaminophenoxy) octafluorobiphenyl and the like.

It is particularly preferable to use a fluorinated polyimide obtained by binding a fluorine atom to either or both of an acid dianhydride and a diamine.

By irradiating a polyimide film formed on a substrate such as a silicon wafer with radiant light, a polyimide film having a changed refractive index can be obtained.
The linear absorption coefficient of the radiant light absorbed by the polyimide film in the irradiation direction of the radiant light is determined by the composition of the polyimide and the energy of the radiated light, and the refractive index also changes according to the composition of the polyimide, the energy of the radiated light, and the intensity of the radiated light. However, the degree of change in the refractive index depends on the chemical structure of the polyimide.

The value of the linear absorption coefficient of the polyimide film varies greatly depending on the energy of the emitted light, for example, 300e.
When the energy is about V, it becomes about 1 μm ⁻¹ , and the refractive index change region is up to about 1 μm. Moreover, when the energy becomes higher, the value of the linear absorption coefficient becomes smaller, and the refractive index changes to a deep region. Moreover, when the irradiation amount is increased, the change in the refractive index is correspondingly increased. However, if the irradiation dose is too high, material destruction may occur depending on the chemical structure of polyimide. Thus the chemical structure of polyimide,
By controlling the energy and the irradiation amount of the radiated light, it is possible to change the refractive index so that the region where the refractive index changes has various profiles.

Several methods can be considered as a method of manufacturing the optical waveguide. Most simply, the core can be formed by using an X-ray mask. That is, first, a polyamide acid solution is spin-coated on a substrate such as silicon and then cured by heating to obtain a polyimide film. Next, this is irradiated with radiant light through an X-ray mask so as to have a predetermined refractive index and a predetermined size. After spin-coating the same polyamic acid solution on this film, heat curing,
It is peeled off from the silicon substrate to obtain a two-layered polyimide film having a core layer. This polyimide film is brought into close contact with the silicon substrate with the radiation light irradiation film side facing upward. Finally, the same polyamic acid solution as the upper clad is spin-coated and then heated and cured to obtain an embedded optical waveguide. The embedded waveguide can also be formed by sandwiching a polyimide film serving as a clad from above and below the core layer film and bonding them by pressure bonding or by interposing a very thin adhesive layer. As the optical waveguide structure, it is possible to manufacture a slab type, a ridge type, and various other generally manufactured optical waveguide structures. Both single mode and multimode light propagation modes can be manufactured by controlling the refractive index difference between the core and the clad.

[0014]

EXAMPLES The present invention will be described in detail below with reference to some examples. The present invention is not limited to these examples.

Example 1 88.8 g of 2,2-bis (3,4-dicarboxyphenyl) hexafluoropropane dianhydride in an Erlenmeyer flask
(0.2 mol) and 2,2'-bis (trifluoromethyl) -4,4'-diaminobiphenyl 64.0 g (0.
2 mol) and N, N-dimethylacetamide 1000
g was added. This mixture was stirred at room temperature for 3 days under a nitrogen atmosphere to obtain a polyamic acid solution having a concentration of about 15 wt%. This polyamic acid solution was spin-coated on a silicon wafer and then heated in an oven at 70 ° C. for 2 hours, 160 ° C. for 1 hour, 250 ° C. for 30 minutes, and 350 ° C. for 1 hour.
Imidization was performed to obtain a polyimide film having a thickness of 10 μm. 27 on the polyimide film on this silicon substrate
Irradiation light of 200 eV to 1000 eV having a peak at 5 eV was irradiated for 5 minutes. As a result of measuring the change in the refractive index of this polyimide film, the average in the film thickness direction was 0.3%.

Example 2 88.8 g of 2,2-bis (3,4-dicarboxyphenyl) hexafluoropropane dianhydride in an Erlenmeyer flask
(0.2 mol) and 2,2'-bis (trifluoromethyl) -4,4'-diaminobiphenyl 64.0 g (0.
2 mol) and N, N-dimethylacetamide 1000
g was added. This mixture was stirred at room temperature for 3 days under a nitrogen atmosphere to obtain a polyamic acid solution having a concentration of about 15 wt%. This polyamic acid solution was spin-coated on a silicon wafer with an oxide film and then at 70 ° C. for 2 hours in an oven for 1 hour.
The film was heated at 60 ° C. for 1 hour, 250 ° C. for 30 minutes, and 380 ° C. for 1 hour for imidization to obtain a polyimide film having a thickness of 10 μm. The polyimide film on the silicon substrate is irradiated with synchrotron radiation of 200 to 1000 eV having a peak at 275 eV through an X-ray mask for 5 minutes to form a core (1
A one-layer polyimide optical waveguide having a 0 μm square) formed by irradiation with radiant light was obtained. The manufacturing process is shown in FIG. The change in refractive index of this core was 0.3%. When light having a wavelength of 1320 nm was passed through this waveguide and observed from a light emitting end face with a microscope equipped with an infrared camera, it was confirmed that the light was confined. This polyimide optical waveguide could be manufactured in two steps. Fig. 3 shows the optical energy of the emitted light (horizontal axis, e
V) and luminance (vertical axis, photons / s / mrad ² / mA / 0.
1% -bw) is shown as a graph.

Example 3 A polyimide film prepared in the same manner as in Example 1 was irradiated with an X-ray mask as shown in FIG. 2 under the same conditions as in Example 1 for 5 minutes. As a result of measuring the change in the refractive index of the portion where the refractive index of this polyimide film changed, the average was 0.8% in the film thickness direction.

Example 4 A polyimide film prepared in the same manner as in Example 1 was irradiated for 15 minutes under the same conditions as in Example 1. As a result of measuring the change in the refractive index of this polyimide film, the average in the film thickness direction was 0.8%.

Example 5 A polyimide film prepared in the same manner as in Example 1 was irradiated for 30 minutes under the same conditions as in Example 1. As a result of measuring the change in the refractive index of this polyimide film, the average in the film thickness direction was 1.3%.

Example 6 A polyimide film produced in the same manner as in Example 1 was irradiated with radiant light through an X-ray stencil mask in which a substrate was hollowed out into a predetermined shape. When the X-ray stencil mask was softly contacted with the polyimide film and irradiated with radiant light for 5 minutes under the same conditions as in Example 1, as a result, only the refractive index of the X-ray transmissive part was changed, and the shape of the transmissive part of the stencil mask was changed. A refractive index change range having is obtained.

Example 7 A reflection type X-ray mask having an X-ray reflecting portion and an absorbing portion was used on a polyimide film prepared in the same manner as in Example 1, and a pattern image on the X-ray mask was formed on the polyimide surface. Irradiation with synchrotron radiation was performed as described above. As a result of irradiation with radiant light for 5 minutes under the same conditions as in Example 1, it was possible to selectively change the refractive index only in the portion corresponding to the X-ray reflection portion.

Example 8 The same polyamic acid solution as in Example 2 was spin-coated on the upper part of the one-layer optical waveguide of Example 2 and then at 70 ° C. in an oven.
2 hours, 160 ° C for 1 hour, 250 ° C for 30 minutes, 38
It was heated at 0 ° C. for 1 hour for imidization to obtain a buried waveguide in which the lower clad was SiO ₂ and the upper clad was polyimide. Light of wavelength 1320 nm is passed through this waveguide,
Observation with a microscope equipped with an infrared camera confirmed that light was confined from the exit end face.

Example 9 The waveguide prepared in Example 8 was separated from the Si wafer,
The surface of the radiant light irradiation film is faced up, and the same polyamic acid solution is spin-coated on the film.
It was heated at 0 ° C. for 1 hour for imidization to form an upper clad. In this way, a buried waveguide having the same polyimide for the core, the upper clad, and the lower clad was obtained. When light having a wavelength of 1320 nm was passed through this waveguide and observed through a microscope with an infrared camera from the emission end face, it was confirmed that the light was confined.

Comparative Example 1 FIG. 4 shows a manufacturing process of a conventional ridge type polyimide optical waveguide using RIE. A total of 5 strokes are required.

[0025]

As described above, it is possible to change the refractive index of polyimide by irradiation with radiant light, and the amount of change in refractive index can be changed by changing the irradiation amount of radiant light. Therefore, an optical waveguide or the like can be freely formed by changing the refractive index into a predetermined shape using an X-ray mask. In addition, it is possible to provide a refractive index distribution by selecting the energy of the emitted light, and it is possible to expect an effect that a graded index type optical waveguide or a planar lens can be formed. Further, in an optical waveguide using a polyimide core whose refractive index is controlled by irradiation of synchrotron radiation, the core and the clad are made of the same material, and the problems of thermal characteristic difference and birefringence difference caused by the difference in material can be solved. effective. Further, in the present invention, the polyimide optical waveguide has the effects of reducing the manufacturing process, shortening the manufacturing time, and easily forming the polyimide optical waveguide.

[Brief description of drawings]

FIG. 1 is a process drawing showing a manufacturing process of a ridge type polyimide optical waveguide using radiant light irradiation according to the present invention.

FIG. 2 is a process drawing showing the steps of the method for irradiating polyimide with radiant light in the present invention.

FIG. 3 is a graph showing the relationship between photon energy of emitted light and brightness.

FIG. 4 is a process diagram showing a manufacturing process of a ridge-type polyimide optical waveguide using conventional RIE.

 ─────────────────────────────────────────────────── ─── Continuation of front page (72) Inventor Toshiyuki Horiuchi 1-1-6 Uchisaiwaicho, Chiyoda-ku, Tokyo Nihon Telegraph and Telephone Corporation (72) Instructor Tsuneyuki Haga 1-1-6 Uchiyuki-cho, Chiyoda-ku, Tokyo No. Japan Telegraph and Telephone Corp. (72) Inventor Hiroo Kinoshita 1-1-6 Uchisaiwaicho, Chiyoda-ku, Tokyo Nihon Telegraph and Telephone Corp.

Claims (4)

[Claims] 1. A method for processing a polyimide film, which comprises irradiating the polyimide film with radiant light. 2. A method for processing a polyimide film, wherein a fluorinated polyimide film is used as the polyimide film. 3. A polyimide optical waveguide having a core and a clad made of polyimide, wherein the core is a polyimide irradiated with radiant light. 4. A polyimide optical waveguide having a core and a clad made of polyimide, wherein the core is a fluorinated polyimide irradiated with radiant light.