JP2001074949A - Optical waveguide made of resin with protective layer, its production and optical parts - Google Patents

Abstract

PROBLEM TO BE SOLVED: To enhance the solvent resistance while having an upper clad made of a polyimide having a low refractive index by forming an upper clad layer from a fluorine-containing resin and a protective layer from a fluorine-free material. SOLUTION: A lower clad layer 15 is disposed on a silicon wafer substrate 14, a patterned core layer 16 is disposed on the clad layer 15 and coated with an upper clad layer 20 and the top of the clad layer 20 is coated with a protective layer 24. The lower and upper clad layers 15 and 20 are formed from fluorine introduced polyimide having a refractive index nearly equal to that of an optical fiber so as to enhance the efficiency of joining to the optical fiber. The protective layer 24 is formed from a fluorine-free polyimide. Since the fluorine-containing upper clad layer 20 having low adhesiveness and low solvent resistance is not exposed, optical parts can be bonded to the top of the resulting optical waveguide with high adhesive strength while using a solvent-containing adhesive.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

TECHNICAL FIELD The present invention relates to an optical waveguide,
In particular, the present invention relates to an optical waveguide whose cladding and core are made of resin.

[0002]

2. Description of the Related Art With the spread of personal computers and the Internet in recent years, the demand for information transmission has rapidly increased. For this reason, it is desired that optical transmission with a high transmission speed be spread to terminal information processing devices such as personal computers. To achieve this, it is necessary to manufacture high-performance optical waveguides for optical interconnection at low cost and in large quantities.

As materials for optical waveguides, inorganic materials such as glass and semiconductor materials and polymer materials are known. When an optical waveguide is manufactured from an inorganic material, a method is used in which an inorganic material film is formed by a film forming apparatus such as a vacuum evaporation apparatus or a sputtering apparatus, and the inorganic film is etched into a desired waveguide shape. . However, the vacuum evaporation apparatus and the sputtering apparatus require large-scale evacuation equipment, and are therefore large and expensive. In addition, since the evacuation step is required, the step becomes complicated.

On the other hand, when an optical waveguide is manufactured from a polymer material, the film formation process can be performed at atmospheric pressure by coating and heating, and thus there is an advantage that the apparatus and the process are simple. For example, Japanese Patent Application Laid-Open No. 9-40774
Japanese Patent Application Laid-Open Publication No. H11-139,086 discloses a method for manufacturing an optical waveguide using polyimide.

In the method of manufacturing an optical waveguide described in the above publication, first, a polyamic acid solution is spin-coated on a substrate such as silicon and heated and dried and cured to form a polyimide film. This is used as a lower cladding layer. Next, a polyimide film having a higher refractive index than the lower clad is formed by the same procedure, and this is used as a core layer. A predetermined mask is formed on the core layer with a resist, and processed into a desired core shape by reactive ion etching (RIE) or the like. Next, on this core, a polyamic acid solution was further spin-coated, heated and dried, and then further heated and cured to obtain a polyimide film having a lower refractive index than the core,
This is used as the upper cladding layer.

As an optical polymer constituting a core layer or a cladding layer of an optical waveguide, polymethyl methacrylate has been conventionally used, but a glass transition temperature (Tg) is used.
Is relatively low, so there are concerns about reliability. In addition, since the Tg is low, it cannot withstand a high-temperature process, so that an electric circuit cannot be soldered on the optical waveguide. Therefore, T
Polyimide having high g and excellent heat resistance is expected as a polymer material for an optical waveguide. When the optical waveguide is formed of polyimide, long-term reliability can be expected and it can withstand soldering. However, polyimide has a high refractive index due to the inclusion of an aromatic ring in the chemical structure, and it is difficult to obtain an optical waveguide that can be efficiently coupled to an optical fiber having a relatively low refractive index. Further, polyimide has a large propagation loss due to absorption since the light absorption edge is shifted to a longer wavelength side. Therefore, by introducing a fluorine atom,
Polyimides have been developed in which the refractive index is lowered and the absorption edge is shifted to the shorter wavelength side. For example, Japanese Patent Application Laid-Open No.
No. 9037, JP-A-4-328504, JP-A-4-328127, and JP-A-9-40774 disclose polyimides into which fluorine has been introduced.

[0007]

As described above, the polyimide into which fluorine is introduced has a low refractive index and a short absorption edge, so that an optical waveguide having high optical performance and easy coupling with an optical fiber is used. It can be formed. However, polyimide into which fluorine has been introduced has low solvent resistance and causes a problem in reliability. In addition, polyimide having fluorine introduced therein has a problem that adhesion is low due to the characteristics of fluorine, and it is difficult to bond other optical components and the like on the optical waveguide.

It is an object of the present invention to provide an optical waveguide having high solvent resistance while having a polyimide upper clad having a low refractive index.

[0009]

In order to achieve the above object, according to the present invention, the following optical waveguide is provided. That is, the substrate, and sequentially laminated on the substrate,
A lower clad layer, a core layer, an upper clad layer, and a protective layer disposed on the upper clad layer; the upper clad layer is made of a resin containing fluorine; and the protective layer is formed of the upper clad layer. An optical waveguide characterized in that the content of fluorine is smaller than that of the layer, or the optical waveguide is made of a resin containing no fluorine.

[0010]

DESCRIPTION OF THE PREFERRED EMBODIMENTS An optical waveguide according to an embodiment of the present invention will be described with reference to the drawings.

As shown in FIG. 4 (o), the optical waveguide of this embodiment includes a lower cladding layer 15 on a silicon wafer substrate 14, and a patterned core layer 16 on the lower cladding layer 15. Is arranged. The core layer 16
It is covered by the upper cladding layer 20. The upper surface of the upper cladding layer 20 is covered with a protective layer 24. The lower cladding layer 15 and the upper cladding layer 20 are made of fluorine-introduced polyimide having the same refractive index as the optical fiber in order to increase the coupling efficiency with the optical fiber. On the other hand, the protective layer 24 is formed from polyimide containing no fluorine.

Specifically, both the lower cladding layer 15 and the upper cladding layer 20 are polyimide films formed by using OPI-N1005 (trade name) manufactured by Hitachi Chemical Co., Ltd. This polyimide contains fluorine, and its content is about 19 mol%. The refractive indices of the lower cladding layer 15 and the upper cladding layer 20 are:
52 to 1.53. The thickness of the lower cladding layer 15 is
The thickness of the upper cladding layer 20 is about 15 μm. The core layer 16 is made of OPI- manufactured by Hitachi Chemical Co., Ltd.
It is a polyimide film formed using N3205 (trade name), and has a thickness of about 8 μm and a width of about 8 μm. The refractive index of the core layer 16 is about 0.5% greater than the lower and upper cladding layers 15,20.

The protective layer 24 is a polyimide film formed using PIX-6400 (trade name) manufactured by Hitachi Chemical DuPont Microsystems. This polyimide is
Does not contain fluorine. The film thickness is about 7 μm at an end portion away from the core layer 16.

Next, a method of manufacturing the optical waveguide shown in FIG.

First, the silicon wafer substrate 1 shown in FIG.
An extremely thin adhesive layer (not shown) for improving the adhesiveness with the lower cladding layer 15 is formed on the upper surface of the substrate 4. The above-mentioned OPI-N1005 (resin concentration: 15% by weight) is spin-coated thereon to form a material solution film. Thereafter, the solvent is evaporated by heating in a dryer at 100 ° C. for 30 minutes and then at 200 ° C. for 30 minutes, followed by curing by heating at 370 ° C. for 60 minutes to form a polyimide film having a thickness of about 7 μm. Formed. Thereby, the lower cladding layer 15 was formed.

On the lower cladding layer 15, the above-mentioned O
PI-N3205 (resin concentration 15% by weight) is spin-coated to form a material solution film. Then, in a dryer, 100
The solvent was evaporated by heating at 30 ° C. for 30 minutes and then at 200 ° C. for 30 minutes, followed by curing by heating at 350 ° C. for 60 minutes to form a polyimide film having a thickness of about 8 μm. Was formed (FIG. 1B).

Next, as a resist on the core layer 16,
RU-1600P (manufactured by Hitachi Chemical Co., Ltd.) was spin-coated, dried at 100 ° C., and exposed and developed with a mercury lamp to form a resist pattern layer 17 (FIG. 1C). The resist pattern layer 17 as a mask, reactive ion etching ₍₀ 2 -R oxygen
IE) was performed to pattern the core layer 16 into a desired optical waveguide shape. (FIG. 1 (d)). Thereafter, the resist was stripped (FIG. 1 (e)).

Furthermore, the above-mentioned OPI-N10
05 (resin concentration 25% by weight) was spin-coated to form a material solution film 18 (FIG. 2 (f)). This material solution film 1
Although the upper surface of 8 was flat as shown in FIG. 2 (f), it was heated in a dryer at 100 ° C. for 30 minutes and then at 200 ° C. for 30 minutes to evaporate the solvent to form a precursor film 19. Since the film thickness was reduced at a substantially constant reduction ratio, the upper surface of the precursor film 19 became convex along the shape of the core layer 16 (FIG. 2 (g)). Subsequent to this drying step, the polyamide acid in the precursor film 19 is imidized by heating at 350 ° C. for 60 minutes to be cured, thereby forming an upper clad layer 20 of a polyimide film having a thickness of 15 μm (FIG. 2
(H)). The upper cladding layer 20 substantially maintained the shape of the precursor film 19, and the upper surface was convex along the shape of the core layer 16.

Next, in the present embodiment, a protective layer 24 of a polyimide film containing no fluorine is formed on the upper surface of the upper clad layer 20.

First, the material solution film 21 was formed on the upper clad layer 20 by spin-coating the above-mentioned PIX-6400 (density of tree finger: 35.5% by weight) (FIG. 2 (i)).
The upper surface of the material solution film 21 is formed by spin coating, as shown in FIG.
It was flat as in (i). Then, in a dryer, 100
After heating at 30 ° C. for 30 minutes and then at 200 ° C. for 30 minutes to evaporate the solvent to obtain a precursor film 23, the shape of the precursor film 23 becomes convex along the upper surface of the upper cladding layer 20. (FIG. 3 (j)). However, following this drying process, the polyamide acid in the precursor film 23 was imidized and cured by heating at 350 ° C. for 60 minutes.
As shown in (k), a protective layer 24 of a polyimide film having a substantially flat upper surface and a thickness of 7 μm was obtained.

Next, a silicon oxide film 25 is formed on the protective layer 24 by a spin-on-glass (SOG) process (FIG. 3A). Next, RU-1600P manufactured by Hitachi Chemical Co., Ltd. was spin-coated as a resist film,
After drying at ° C, exposure and development were performed with a mercury lamp to form a resist pattern layer 26 (FIG. 4 (m)). Using the resist pattern layer 26 as a mask, reactive ion etching (F-RIE) was performed with fluorine gas to pattern the silicon oxide film 25 (FIG. 4 (n)). further,
The silicon oxide film 25 of oxygen subjected to reactive ion etching _(O 2 -RlE) in as a mask, to process the lower and upper cladding layers 20 and 21 into a desired shape. Thereafter, the silicon oxide film 25 was removed (FIG. 4 (o)). As a result, an optical waveguide (FIG. 4 (o)) including the protective layer 24 of the present embodiment was obtained.

As described above, the optical waveguide of this embodiment is
Since the protective layer 24 containing no fluorine is provided, the upper surface of the upper clad layer 20 can be covered with the protective layer 24. As a result, since the upper cladding layer 20 containing fluorine and having low adhesiveness and low solvent resistance is not exposed on the upper surface, the optical component can be adhered to the upper portion with a strong adhesive strength using an adhesive or the like using a solvent. . Further, since the upper clad layer 20 is not exposed to the outside, the corrosion resistance is improved, and the reliability of the optical waveguide is improved.

On the other hand, the upper and lower cladding layers 20
As for No. 15, since a polyimide containing fluorine is used, the refractive index can be as low as 1.52 to 1.53, and the input / output characteristics such as the numerical aperture of the optical fiber can be realized. Therefore,
The optical waveguide of the present embodiment can be coupled with an optical fiber with high efficiency. The upper and lower cladding layers 20, 1
As No. 5, since a polyimide containing fluorine is used, the absorption edge is very short at around 400 nm, and the transmittance is high over a wide wavelength range from visible light to infrared. Therefore, an optical waveguide with low propagation loss in a wide wavelength range can be provided.

In the optical waveguide according to the present embodiment, since all layers from the lower cladding layer 15 to the protective layer 24 are formed of polyimide, Tg is higher than that of polymethyl methacrylate or the like. High temperature process. In the optical waveguide of the present embodiment, the layers of the upper and lower claddings 20 and 15 and the core layer 16 related to light propagation are formed of polyimide having a Tg of 270 ° C. or higher. For this reason, they are particularly excellent in heat resistance and can maintain the propagation characteristics even at high temperatures.

In the above-described manufacturing process, the upper cladding layer 20 and the lower cladding layer 15 are etched as shown in FIG. 4 (o), but the core layer 16 is not etched and the core layer 16 is flattened as shown in FIG. Can be used as a plate-shaped optical waveguide embedded in the clad layers 20 and 15. In the case of this flat optical waveguide, the upper clad layer 20 has a large upper surface area. However, in the configuration of FIG. 5, the upper clad layer 20 can be covered with the protective layer 24 having high solvent resistance and high adhesiveness. It becomes an optical waveguide having high solvent resistance and high adhesiveness. In the case of the configuration shown in FIG. 4 (o), not only the upper surfaces but also the side surfaces of the upper and lower claddings 20 and 15 can be shaped to be covered with the protective film 24. In this case, the protective film 24
However, since the upper and lower claddings 20 and 15 can be protected from the side surfaces, the solvent resistance of the optical waveguide is further improved.

Since the polyimide of the upper cladding layer 20 and the polyimide of the protective layer 24 have good adhesiveness, even if the upper cladding layer 20 contains fluorine, the protective layer 24 is hardly peeled off. However, when a polyimide having a fluorine content of more than 19 mol% is used as the upper cladding layer 20, the solvent resistance of the polyimide becomes too low, and the above-described FIG.
When the material solution film 21 of the protective layer 24 is formed in the step (i), the solvent in the material solution film 21 dissolves the upper clad layer 20. For this reason, it is desirable that the fluorine content of the upper cladding layer 20 be 19 mol% or less.

In this embodiment, a polyimide containing no fluorine is used as the protective layer 24. However, if the fluorine content of the polyimide of the protective layer 24 is smaller than that of the upper clad layer 20, the polyimide of the protective layer 24 may be used. Perform the function of However, in consideration of practical solvent resistance and adhesion, if the fluorine content of the protective layer 24 exceeds 11 mol%, the protective layer 24 is not sufficient as a practical protective layer 24.
It is desirable to use polyimide having a fluorine content of 11 mol% or less as the polyimide constituting the protective layer 24. On the other hand, the higher the fluorine content of the polyimide constituting the upper cladding layer 20, the lower the refractive index can be suppressed. Therefore, in order to suppress the refractive index to the same level as an optical fiber and reduce the loss due to light absorption, it is desirable to use a fluorine content of 14 mol% or more. Therefore, the preferred range of the fluorine content of the upper cladding layer 20 is 14 mol
% Or more and 19 mol% or less.

The optical waveguide of this embodiment is similar to that of FIG.
(O), as shown in FIG. 5, the protective layer 24 is
The upper surface has a flat shape by embedding the convex shape of 0. Thus, when bonding an optical component, laminating another optical waveguide, or forming a wiring pattern on the protective layer 24, it can be handled in the same manner as a flat substrate. As a result, good adhesive properties can be obtained, and an optical waveguide to be laminated can be formed into a good film. Further, there is no possibility that the wiring pattern may be disconnected due to the step. In addition, when the surface step of the protective layer 24 of the present embodiment was measured by a contact step meter, it was 1 μm or less.

The reason why the protective layer 24 having a flat upper surface is obtained is as follows. Upper cladding layer 20
Both the protective layer 24 and the protective layer 24 are made of polyimide, but have different structural formulas. The polyimide of the upper cladding layer 20 formed of OPI-N1005 has a glass transition temperature (Tg) of 325.
On the other hand, the protective layer 24 formed of PIX-6400 has a glass transition temperature (Tg) of 270 ° C., which is lower than that of the upper cladding layer 20. In the manufacturing process of the present embodiment, when the precursor film 19 of the upper cladding layer 20 is cured to form a polyimide film, and when the precursor film 23 of the protective layer 24 is cured to form a polyimide film, Is the same 35
It is 0 ° C. Accordingly, the polyimide film of the upper cladding layer 20 is heated at a glass transition temperature (Tg) + 25 ° C., while the polyimide film of the protective layer 24 is heated at a glass transition temperature (Tg) + 80 ° C. Generally, resins such as polyimide have fluidity at a temperature equal to or higher than the glass transition temperature (Tg), and the fluidity increases as the temperature difference from the glass transition temperature increases. Therefore, when heated to the same 350 ° C., the protective layer 24 has a higher fluidity and flows more easily than the upper clad layer 20, so that the protective layer 24 flows from a raised portion to a lower portion, and the upper surface becomes flat.

The reason why the flowability of the protective layer 24 is large is not only the temperature difference between the glass transition temperature (Tg) and the heating temperature, but also the polyimide formed from PIX-6400 and the polyimide formed from OPI-N1005. It is thought that the difference in the chemical composition of the phenol also influences this.

The protective layer 24 is made of a material solution, PI
The resin concentration of X-6400 is 35.5%, which is higher than OPI-N1005 (resin concentration 25% by weight) of the material solution of the upper cladding layer 20. For this reason, the degree of reduction when the material solution film 21 of the protective layer 24 changes to the precursor film 23 due to drying depends on the degree of reduction when the material solution film 18 of the upper cladding layer 20 changes to the precursor film 19. Not as big. Therefore, when the precursor film 23 is formed, the step is smaller than the step on the upper surface of the upper clad layer 20. As described above, the fact that the material having a higher concentration of the material solution than the upper clad layer 20 is used for the protective layer 24 is also considered to be a factor that can effectively reduce the step of the upper clad layer 20.

The optical waveguide shown in FIG. 4 (o) and the optical waveguide shown in FIG. 5 according to the present embodiment can be used as optical components for optical interconnection for connecting between an optical module and an optical fiber. . Further, by making the pattern shape of the core layer 16 of the optical waveguide of the present embodiment a predetermined shape, it is possible to configure an optical component such as an optical path conversion element, an optical path branching element, and a directional coupler.

In the method of manufacturing an optical waveguide according to the present embodiment, all of the lower clad layer 15, the core layer 16, the upper clad layer 20, and the protective layer 24 are subjected to simple steps of spin coating, drying and curing. To form a film at atmospheric pressure,
It is suitable as a method for producing a large amount of optical waveguides at low cost. In addition, in the configuration of the optical waveguide, the protective layer 24 has almost no effect on the propagation of light in the core layer 16, so that the material can be selected from the fluorine content without considering the refractive index and the like. it can.

In the above-described embodiment, FIG.
Although the silicon oxide film 25 is removed in the step, since the silicon oxide film 25 does not affect the propagation of light, it can be left as it is.

In the above embodiment, the heating temperature for curing the upper cladding layer 20 and the heating temperature for curing the protective layer 24 are the same.
It is not necessary that the temperature be the same. The heating temperature can be determined in consideration of the fluidity of the resin during heating.

In the above-described embodiment, the core layer 16, the upper and lower clad layers 15, 20 and the protective layer 24 are formed of polyimide films having different structures as described above. The material that can be used for the waveguide is not limited to polyimide. Not only polyimide but also polymers into which fluorine has been introduced tend to have lower solvent resistance and lower adhesiveness than polymers into which fluorine has not been introduced. Therefore, as the material of the protective layer 24, a polymer having a lower fluorine content than the upper cladding layer 20 or a polymer containing no fluorine can be used. For example, the upper cladding layer 20 is formed of fluorinated polyimide, and the protective layer 24 is formed of a resin containing no fluorine (for example,
Polymethyl methacrylate, polycarbonate, polystyrene, styrene copolymer, styrene-acrylonitrile copolymer, vinyl chloride, epoxy resin, polyolefin, polyether, polyester, polyurethane, silicone resin, polyamide, acrylic resin including alicyclic acrylic resin, (Olefin resin containing an alicyclic olefin resin) or the like.

The protective layer 24 is not limited to the resin described above, but may be formed of an inorganic material such as SiO ₂ . When the protective layer 24 is formed as an inorganic film, the protective layer 24 can be formed by a known film forming method such as a CVD method and an evaporation method. Also, it can be formed by a solution coating method like SOG.

[0038]

As described above, according to the present invention,
An optical waveguide having high solvent resistance can be provided while having a polyimide upper clad having a low refractive index.

[Brief description of the drawings]

FIGS. 1A to 1E are cross-sectional views showing steps of manufacturing an optical waveguide according to an embodiment of the present invention.

FIGS. 2F to 2I are cross-sectional views showing steps of manufacturing an optical waveguide according to one embodiment of the present invention.

FIGS. 3 (j) to (l) are cross-sectional views showing steps of manufacturing an optical waveguide according to an embodiment of the present invention.

FIGS. 4 (m) to (n) are cross-sectional views showing steps of manufacturing an optical waveguide according to an embodiment of the present invention, and (o) are cross-sectional views of the optical waveguide according to an embodiment of the present invention.

FIG. 5 is a cross-sectional view showing the shape of the optical waveguide when the upper and lower claddings 20 and 15 are not processed according to the embodiment of the present invention.

[Explanation of symbols]

14 silicon wafer substrate, 15 lower clad layer, 16 core layer, 17 resist pattern layer, 18 material solution film, 19 precursor film, 20
... upper clad layer, 21 ... material solution film, 23
..Precursor film, 24 ... protective layer, 25 ... silicon oxide film, 26 ... resist pattern layer.

────────────────────────────────────────────────── ───

[Procedure amendment]

[Submission date] October 21, 1999 (1999.10.
21)

[Procedure amendment 1]

[Document name to be amended] Statement

[Correction target item name] Full text

[Correction method] Change

[Correction contents]

[Document Name] Statement

Patent application title: RESIN OPTICAL WAVEGUIDE WITH PROTECTIVE LAYER, ITS MANUFACTURING METHOD, AND OPTICAL COMPONENT

[Claims]

DETAILED DESCRIPTION OF THE INVENTION

[0001]

TECHNICAL FIELD The present invention relates to an optical waveguide,
In particular, the present invention relates to an optical waveguide whose cladding and core are made of resin.

[0002]

2. Description of the Related Art With the spread of personal computers and the Internet in recent years, the demand for information transmission has rapidly increased. For this reason, it is desired that optical transmission with a high transmission speed be spread to terminal information processing devices such as personal computers. To achieve this, it is necessary to manufacture high-performance optical waveguides for optical interconnection at low cost and in large quantities.

As materials for optical waveguides, inorganic materials such as glass and semiconductor materials and polymer materials are known. When an optical waveguide is manufactured from an inorganic material, a method is used in which an inorganic material film is formed by a film forming apparatus such as a vacuum evaporation apparatus or a sputtering apparatus, and the inorganic film is etched into a desired waveguide shape. . However, the vacuum evaporation apparatus and the sputtering apparatus require large-scale evacuation equipment, and are therefore large and expensive. In addition, since the evacuation step is required, the step becomes complicated.

On the other hand, when an optical waveguide is manufactured from a polymer material, the film formation process can be performed at atmospheric pressure by coating and heating, and thus there is an advantage that the apparatus and the process are simple. For example, Japanese Patent Application Laid-Open No. 9-40774
Japanese Patent Application Laid-Open Publication No. H11-139,086 discloses a method for manufacturing an optical waveguide using polyimide.

In the method of manufacturing an optical waveguide described in the above publication, first, a polyamic acid solution is spin-coated on a substrate such as silicon and heated and dried and cured to form a polyimide film. This is used as a lower cladding layer. Next, a polyimide film having a higher refractive index than the lower clad is formed by the same procedure, and this is used as a core layer. A predetermined mask is formed on the core layer with a resist, and processed into a desired core shape by reactive ion etching (RIE) or the like. Next, on this core, a polyamic acid solution was further spin-coated, heated and dried, and then further heated and cured to obtain a polyimide film having a lower refractive index than the core,
This is used as the upper cladding layer.

As an optical polymer constituting a core layer or a cladding layer of an optical waveguide, polymethyl methacrylate has been conventionally used, but a glass transition temperature (Tg) is used.
Is relatively low, so there are concerns about reliability. In addition, since the Tg is low, it cannot withstand a high-temperature process, so that an electric circuit cannot be soldered on the optical waveguide. Therefore, T
Polyimide having high g and excellent heat resistance is expected as a polymer material for an optical waveguide. When the optical waveguide is formed of polyimide, long-term reliability can be expected and it can withstand soldering. However, polyimide has a high refractive index due to the inclusion of an aromatic ring in the chemical structure, and it is difficult to obtain an optical waveguide that can be efficiently coupled to an optical fiber having a relatively low refractive index. Further, polyimide has a large propagation loss due to absorption since the light absorption edge is shifted to a longer wavelength side. Therefore, by introducing a fluorine atom,
Polyimides have been developed in which the refractive index is lowered and the absorption edge is shifted to the shorter wavelength side. For example, Japanese Patent Application Laid-Open No.
No. 9037, JP-A-4-328504, JP-A-4-328127, and JP-A-9-40774 disclose polyimides into which fluorine has been introduced.

[0007]

As described above, the polyimide into which fluorine is introduced has a low refractive index and a short absorption edge, so that an optical waveguide having high optical performance and easy coupling with an optical fiber is used. It can be formed. However, polyimide into which fluorine has been introduced has low solvent resistance and causes a problem in reliability. In addition, polyimide having fluorine introduced therein has a problem that adhesion is low due to the characteristics of fluorine, and it is difficult to bond other optical components and the like on the optical waveguide.

It is an object of the present invention to provide an optical waveguide having high solvent resistance while having a polyimide upper clad having a low refractive index.

[0009]

In order to achieve the above object, according to the present invention, the following optical waveguide is provided. That is, the substrate, and sequentially laminated on the substrate,
A lower clad layer, a core layer, an upper clad layer, and a protective layer disposed on the upper clad layer; the upper clad layer is made of a resin containing fluorine; and the protective layer is formed of the upper clad layer. An optical waveguide characterized in that the content of fluorine is smaller than that of the layer, or the material is made of a material not containing fluorine.

[0010]

DESCRIPTION OF THE PREFERRED EMBODIMENTS An optical waveguide according to an embodiment of the present invention will be described with reference to the drawings.

As shown in FIG. 4 (o), the optical waveguide of this embodiment includes a lower cladding layer 15 on a silicon wafer substrate 14, and a patterned core layer 16 on the lower cladding layer 15. Is arranged. The core layer 16
It is covered by the upper cladding layer 20. The upper surface of the upper cladding layer 20 is covered with a protective layer 24. The lower cladding layer 15 and the upper cladding layer 20 are made of fluorine-introduced polyimide having the same refractive index as the optical fiber in order to increase the coupling efficiency with the optical fiber. On the other hand, the protective layer 24 is formed from polyimide containing no fluorine.

Specifically, both the lower cladding layer 15 and the upper cladding layer 20 are polyimide films formed by using OPI-N1005 (trade name) manufactured by Hitachi Chemical Co., Ltd. This polyimide contains fluorine, and its content is about 19 mol%. The refractive indices of the lower cladding layer 15 and the upper cladding layer 20 are:
52 to 1.53. The thickness of the lower cladding layer 15 is
The thickness of the upper cladding layer 20 is about 15 μm. The core layer 16 is made of OPI- manufactured by Hitachi Chemical Co., Ltd.
It is a polyimide film formed using N3205 (trade name), and has a thickness of about 8 μm and a width of about 8 μm. The refractive index of the core layer 16 is about 0.5% greater than the lower and upper cladding layers 15,20.

The protective layer 24 is a polyimide film formed using PIX-6400 (trade name) manufactured by Hitachi Chemical DuPont Microsystems. This polyimide is
Does not contain fluorine. The film thickness is about 7 μm at an end portion away from the core layer 16.

Next, a method of manufacturing the optical waveguide shown in FIG.

First, the silicon wafer substrate 1 shown in FIG.
An extremely thin adhesive layer (not shown) for improving the adhesiveness with the lower cladding layer 15 is formed on the upper surface of the substrate 4. The above-mentioned OPI-N1005 (resin concentration: 15% by weight) is spin-coated thereon to form a material solution film. Thereafter, the solvent is evaporated by heating in a dryer at 100 ° C. for 30 minutes and then at 200 ° C. for 30 minutes, followed by curing by heating at 370 ° C. for 60 minutes to form a polyimide film having a thickness of about 7 μm. Formed. Thereby, the lower cladding layer 15 was formed.

On the lower cladding layer 15, the above-mentioned O
PI-N3205 (resin concentration 15% by weight) is spin-coated to form a material solution film. Then, in a dryer, 100
The solvent was evaporated by heating at 30 ° C. for 30 minutes and then at 200 ° C. for 30 minutes, followed by curing by heating at 350 ° C. for 60 minutes to form a polyimide film having a thickness of about 8 μm. Was formed (FIG. 1B).

Next, as a resist on the core layer 16,
RU-1600P (manufactured by Hitachi Chemical Co., Ltd.) was spin-coated, dried at 100 ° C., and exposed and developed with a mercury lamp to form a resist pattern layer 17 (FIG. 1C). Using this resist pattern layer 17 as a mask, reactive ion etching (02-R
1E), the core layer 16 was patterned into a desired optical waveguide shape. (FIG. 1 (d)). Thereafter, the resist was stripped (FIG. 1 (e)).

Furthermore, the above-mentioned OPI-N10
05 (resin concentration 25% by weight) was spin-coated to form a material solution film 18 (FIG. 2 (f)). This material solution film 1
Although the upper surface of 8 was flat as shown in FIG. 2 (f), it was heated in a dryer at 100 ° C. for 30 minutes and then at 200 ° C. for 30 minutes to evaporate the solvent to form a precursor film 19. Since the film thickness was reduced at a substantially constant reduction ratio, the upper surface of the precursor film 19 became convex along the shape of the core layer 16 (FIG. 2 (g)). Subsequent to this drying step, the polyamide acid in the precursor film 19 is imidized by heating at 350 ° C. for 60 minutes to be cured, thereby forming an upper clad layer 20 of a polyimide film having a thickness of 15 μm (FIG. 2
(H)). The upper cladding layer 20 substantially maintained the shape of the precursor film 19, and the upper surface was convex along the shape of the core layer 16.

Next, in the present embodiment, a protective layer 24 of a polyimide film containing no fluorine is formed on the upper surface of the upper clad layer 20.

First, the above-mentioned PIX-6400 (resin concentration: 35.5% by weight) was spin-coated on the upper cladding layer 20 to form a material solution film 21 (FIG. 2 (i)).
The upper surface of the material solution film 21 is formed by spin coating, as shown in FIG.
It was flat as in (i). Then, in a dryer, 100
After heating at 30 ° C. for 30 minutes and then at 200 ° C. for 30 minutes to evaporate the solvent to obtain a precursor film 23, the shape of the precursor film 23 becomes convex along the upper surface of the upper cladding layer 20. (FIG. 3 (j)). However, following this drying process, the polyamide acid in the precursor film 23 was imidized and cured by heating at 350 ° C. for 60 minutes.
As shown in (k), a protective layer 24 of a polyimide film having a substantially flat upper surface and a thickness of 7 μm was obtained.

Next, a silicon oxide film 25 is formed on the protective layer 24 by a spin-on-glass (SOG) process (FIG. 3 (l)). Next, RU-1600P manufactured by Hitachi Chemical Co., Ltd. was spin-coated as a resist film,
After drying at ° C, exposure and development were performed with a mercury lamp to form a resist pattern layer 26 (FIG. 4 (m)). Using the resist pattern layer 26 as a mask, reactive ion etching (F-RIE) was performed with fluorine gas to pattern the silicon oxide film 25 (FIG. 4 (n)). further,
Using the silicon oxide film 25 as a mask, reactive ion etching (O2-RIE) was performed with oxygen to process the lower and upper cladding layers 20 , 15 and the protective layer 24 into desired shapes. Thereafter, the silicon oxide film 25 was removed (FIG. 4 (o)). As a result, an optical waveguide (FIG. 4 (o)) including the protective layer 24 of the present embodiment was obtained.

As described above, the optical waveguide of this embodiment is
Since the protective layer 24 containing no fluorine is provided, the upper surface of the upper clad layer 20 can be covered with the protective layer 24. As a result, since the upper cladding layer 20 containing fluorine and having low adhesiveness and low solvent resistance is not exposed on the upper surface, the optical component can be adhered to the upper portion with a strong adhesive strength using an adhesive or the like using a solvent. . Further, since the upper clad layer 20 is not exposed to the outside, the corrosion resistance is improved, and the reliability of the optical waveguide is improved.

On the other hand, the upper and lower cladding layers 20
As for No. 15, since a polyimide containing fluorine is used, the refractive index can be as low as 1.52 to 1.53, and the input / output characteristics such as the numerical aperture of the optical fiber can be realized. Therefore,
The optical waveguide of the present embodiment can be coupled with an optical fiber with high efficiency. The upper and lower cladding layers 20, 1
As No. 5, since a polyimide containing fluorine is used, the absorption edge is very short at around 400 nm, and the transmittance is high over a wide wavelength range from visible light to infrared. Therefore, an optical waveguide with low propagation loss in a wide wavelength range can be provided.

In the optical waveguide according to the present embodiment, since all layers from the lower cladding layer 15 to the protective layer 24 are formed of polyimide, Tg is higher than that of polymethyl methacrylate or the like. High temperature process. In the optical waveguide of the present embodiment, the layers of the upper and lower claddings 20 and 15 and the core layer 16 related to light propagation are formed of polyimide having a Tg of 270 ° C. or higher. For this reason, they are particularly excellent in heat resistance and can maintain the propagation characteristics even at high temperatures.

In the above-described manufacturing process, the upper cladding layer 20 and the lower cladding layer 15 are etched as shown in FIG. 4 (o), but the core layer 16 is not etched and the core layer 16 is flattened as shown in FIG. Can be used as a plate-shaped optical waveguide embedded in the clad layers 20 and 15. In the case of this flat optical waveguide, the area of the upper surface of the upper clad layer 20 is large, but in the configuration of FIG. 5, the upper clad layer 20 can be covered with the protective layer 24 having high solvent resistance and high adhesiveness. It becomes an optical waveguide having high solvent resistance and high adhesiveness. In the case of the configuration shown in FIG. 4 (o), not only the upper surfaces but also the side surfaces of the upper and lower claddings 20 and 15 can be shaped to be covered with the protective film 24. In this case, the protective film 24
However, since the upper and lower claddings 20 and 15 can be protected from the side surfaces, the solvent resistance of the optical waveguide is further improved.

Since the polyimide of the upper cladding layer 20 and the polyimide of the protective layer 24 have good adhesiveness, even if the upper cladding layer 20 contains fluorine, the protective layer 24 is hardly peeled off. However, when a polyimide having a fluorine content of more than 19 mol% is used as the upper cladding layer 20, the solvent resistance of the polyimide becomes too low, and the above-described FIG.
When the material solution film 21 of the protective layer 24 is formed in the step (i), the solvent in the material solution film 21 dissolves the upper clad layer 20. For this reason, it is desirable that the fluorine content of the upper cladding layer 20 be 19 mol% or less.

In this embodiment, a polyimide containing no fluorine is used as the protective layer 24. However, if the fluorine content of the polyimide of the protective layer 24 is smaller than that of the upper clad layer 20, the polyimide of the protective layer 24 may be used. Perform the function of However, in consideration of practical solvent resistance and adhesion, if the fluorine content of the protective layer 24 exceeds 11 mol%, the protective layer 24 is not sufficient as a practical protective layer 24.
It is desirable to use polyimide having a fluorine content of 11 mol% or less as the polyimide constituting the protective layer 24. On the other hand, the higher the fluorine content of the polyimide constituting the upper cladding layer 20, the lower the refractive index can be suppressed. Therefore, in order to suppress the refractive index to the same level as an optical fiber and reduce the loss due to light absorption, it is desirable to use a fluorine content of 14 mol% or more. Therefore, the preferred range of the fluorine content of the upper cladding layer 20 is 14 mol
% Or more and 19 mol% or less.

The optical waveguide of this embodiment is similar to that of FIG.
(O), as shown in FIG. 5, the protective layer 24 is
The upper surface has a flat shape by embedding the convex shape of 0. Thus, when bonding an optical component, laminating another optical waveguide, or forming a wiring pattern on the protective layer 24, it can be handled in the same manner as a flat substrate. As a result, good adhesive properties can be obtained, and an optical waveguide to be laminated can be formed into a good film. Further, there is no possibility that the wiring pattern may be disconnected due to the step. In addition, when the surface step of the protective layer 24 of the present embodiment was measured by a contact step meter, it was 1 μm or less.

The reason why the protective layer 24 having a flat upper surface is obtained is as follows. Upper cladding layer 20
Both the protective layer 24 and the protective layer 24 are made of polyimide, but have different structural formulas. The polyimide of the upper cladding layer 20 formed of OPI-N1005 has a glass transition temperature (Tg) of 325.
On the other hand, the protective layer 24 formed of PIX-6400 has a glass transition temperature (Tg) of 270 ° C., which is lower than that of the upper cladding layer 20. In the manufacturing process of the present embodiment, when the precursor film 19 of the upper cladding layer 20 is cured to form a polyimide film, and when the precursor film 23 of the protective layer 24 is cured to form a polyimide film, Is the same 35
It is 0 ° C. Accordingly, the polyimide film of the upper cladding layer 20 is heated at a glass transition temperature (Tg) + 25 ° C., while the polyimide film of the protective layer 24 is heated at a glass transition temperature (Tg) + 80 ° C. Generally, resins such as polyimide have fluidity at a temperature equal to or higher than the glass transition temperature (Tg), and the fluidity increases as the temperature difference from the glass transition temperature increases. Therefore, when heated to the same 350 ° C., the protective layer 24 has a higher fluidity and flows more easily than the upper clad layer 20, so that the protective layer 24 flows from a raised portion to a lower portion, and the upper surface becomes flat.

The reason why the flowability of the protective layer 24 is large is not only the temperature difference between the glass transition temperature (Tg) and the heating temperature, but also the polyimide formed from PIX-6400 and the polyimide formed from OPI-N1005. It is thought that the difference in the chemical composition of the phenol also influences this.

The protective layer 24 is made of a material solution, PI
The resin concentration of X-6400 is 35.5% by weight , which is higher than that of OPI-N1005 (resin concentration 25% by weight) of the material solution of the upper cladding layer 20. For this reason, the degree of reduction when the material solution film 21 of the protective layer 24 changes to the precursor film 23 due to drying depends on the degree of reduction when the material solution film 18 of the upper cladding layer 20 changes to the precursor film 19. Not as big. Therefore, when the precursor film 23 is formed, the step is smaller than the step on the upper surface of the upper clad layer 20. In this way, a material having a concentration of the material solution higher than that of the upper cladding layer 20 is transferred to the protective layer 24.
Is considered to be a factor that can effectively reduce the step of the upper cladding layer 20.

The optical waveguide shown in FIG. 4 (o) and the optical waveguide shown in FIG. 5 according to the present embodiment can be used as optical components for optical interconnection for connecting between an optical module and an optical fiber. . Further, by making the pattern shape of the core layer 16 of the optical waveguide of the present embodiment a predetermined shape, it is possible to configure an optical component such as an optical path conversion element, an optical path branching element, and a directional coupler.

In the method of manufacturing an optical waveguide according to the present embodiment, all of the lower clad layer 15, the core layer 16, the upper clad layer 20, and the protective layer 24 are subjected to simple steps of spin coating, drying and curing. To form a film at atmospheric pressure,
It is suitable as a method for producing a large amount of optical waveguides at low cost. In addition, in the configuration of the optical waveguide, the protective layer 24 has almost no effect on the propagation of light in the core layer 16, so that the material can be selected from the fluorine content without considering the refractive index and the like. it can.

In the above-described embodiment, FIG.
Although the silicon oxide film 25 is removed in the step, since the silicon oxide film 25 does not affect the propagation of light, it can be left as it is.

In the above embodiment, the heating temperature for curing the upper cladding layer 20 and the heating temperature for curing the protective layer 24 are the same.
It is not necessary that the temperature be the same. The heating temperature can be determined in consideration of the fluidity of the resin during heating.

In the above-described embodiment, the core layer 16, the upper and lower clad layers 15, 20 and the protective layer 24 are formed of polyimide films having different structures as described above. The material that can be used for the waveguide is not limited to polyimide. Not only polyimide but also polymers into which fluorine has been introduced tend to have lower solvent resistance and lower adhesiveness than polymers into which fluorine has not been introduced. Therefore, as the material of the protective layer 24, a polymer having a lower fluorine content than the upper cladding layer 20 or a polymer containing no fluorine can be used. For example, the upper cladding layer 20 is formed of fluorinated polyimide, and the protective layer 24 is formed of a resin containing no fluorine (for example,
Polymethyl methacrylate, polycarbonate, polystyrene, styrene copolymer, styrene-acrylonitrile copolymer, vinyl chloride, epoxy resin, polyolefin, polyether, polyester, polyurethane, silicone resin, polyamide, acrylic resin including alicyclic acrylic resin, (Olefin resin containing an alicyclic olefin resin) or the like.

The protective layer 24 is not limited to the resin described above, but may be formed of an inorganic material such as SiO2. When the protective layer 24 is formed as an inorganic film, the protective layer 24 can be formed by a known film forming method such as a CVD method and an evaporation method. Also, it can be formed by a solution coating method like SOG.

[0038]

As described above, according to the present invention,
An optical waveguide having high solvent resistance can be provided while having a polyimide upper clad having a low refractive index.

[Brief description of the drawings]

FIGS. 1A to 1E are cross-sectional views showing steps of manufacturing an optical waveguide according to an embodiment of the present invention.

FIGS. 2F to 2I are cross-sectional views showing steps of manufacturing an optical waveguide according to one embodiment of the present invention.

FIGS. 3 (j) to (l) are cross-sectional views showing steps of manufacturing an optical waveguide according to an embodiment of the present invention.

FIGS. 4 (m) to (n) are cross-sectional views showing steps of manufacturing an optical waveguide according to an embodiment of the present invention, and (o) are cross-sectional views of the optical waveguide according to an embodiment of the present invention.

FIG. 5 is a cross-sectional view showing the shape of the optical waveguide when the upper and lower claddings 20 and 15 are not processed according to the embodiment of the present invention.

[Description of Signs] 14 silicon wafer substrate 15 lower clad layer 16 core layer 17 resist pattern layer 18 material solution film 19 precursor Membrane, 20
... upper clad layer, 21 ... material solution film, 23
..Precursor film, 24 ... protective layer, 25 ... silicon oxide film, 26 ... resist pattern layer.

Claims (14)

[Claims] An upper cladding layer comprising: a substrate; a lower cladding layer, a core layer, an upper cladding layer, and a protective layer disposed on the upper cladding layer, which are sequentially stacked on the substrate. Is a resin containing fluorine, and the protective layer is made of a material having a lower fluorine content than the upper cladding layer or a material not containing fluorine. 2. An optical waveguide according to claim 1, wherein said material forming said protective layer is a resin. 3. The optical waveguide according to claim 2, wherein the fluorine content of the resin constituting the protective layer is 11 mol%.
An optical waveguide characterized by the following. 4. The optical waveguide according to claim 1, wherein said upper cladding layer has a fluorine content of 14%.
mol% or more. 5. The optical waveguide according to claim 1, wherein said upper cladding layer has a fluorine content of:
An optical waveguide characterized by being at most 19 mol%. 6. The optical waveguide according to claim 1, wherein said upper cladding layer is made of polyimide. 7. The optical waveguide according to claim 2, wherein said protective layer is made of polyimide. 8. The optical waveguide according to claim 1, wherein the resin forming the upper cladding layer and the resin forming the protective layer are both polyimide. 9. The optical waveguide according to claim 1, wherein the core layer is disposed only on a part of the lower clad layer,
The optical waveguide, wherein the upper clad layer has a convex shape on the upper surface along the shape of the core layer, and the protective layer has a flat upper surface by embedding the convex shape of the upper surface of the upper clad layer. 10. The optical waveguide according to claim 9, wherein the resin forming the protective layer has a lower glass transition temperature than the resin forming the upper cladding layer. 11. An optical component using the optical waveguide according to claim 1, 2, 3, 9, or 10. 12. A first step of sequentially laminating a lower clad layer and a core layer on a substrate, and applying a first resin material solution on the core layer, drying and curing the resin film to form a resin film. A second step of forming an upper clad layer comprising: and a third step of forming a protective layer on the upper clad layer, wherein the material constituting the protective layer is more than the upper clad layer. A method for producing an optical waveguide, wherein the content of fluorine is small or the material does not contain fluorine. 13. The method of manufacturing an optical waveguide according to claim 12, wherein said third step includes forming a second protective film on said second protective film.
A method of manufacturing an optical waveguide, comprising forming a resin film using a tree material. 14. The method of manufacturing an optical waveguide according to claim 13, wherein a material having a fluorine content of 11 mol% or less in the cured resin film is used as the second resin material. A method for manufacturing an optical waveguide, wherein a material having a fluorine content of 14 mol% or more and 19 mol% or less of a cured resin film is used as the resin material.