JP4487297B2 - Resin optical waveguide provided with protective layer, method for manufacturing the same, and optical component - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an optical waveguide, and more particularly, to an optical waveguide whose cladding and core are made of resin.
[0002]
[Prior art]
With the recent spread of personal computers and the Internet, information transmission demand is rapidly increasing. For this reason, it is desired to spread optical transmission having a high transmission speed to an end information processing apparatus such as a personal computer. To realize this, it is necessary to manufacture a high-performance optical waveguide at low cost and in large quantities for optical interconnection.
[0003]
As materials for optical waveguides, inorganic materials such as glass and semiconductor materials, and polymer materials are known. In the case of manufacturing an optical waveguide 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 deposition apparatus or a sputtering apparatus, and this is etched into a desired waveguide shape. . However, the vacuum vapor deposition apparatus and the sputtering apparatus require a vacuum exhaust equipment, so that the apparatus is large and expensive. Moreover, since a vacuum exhaust process is required, the process becomes complicated.
[0004]
On the other hand, when an optical waveguide is manufactured from a polymer material, the film forming process can be performed at atmospheric pressure by application and heating, and thus there is an advantage that the apparatus and the process are simple. For example, Japanese Patent Laid-Open No. 9-40774 discloses a method of manufacturing an optical waveguide from polyimide.
[0005]
The manufacturing method of the optical waveguide described in the above publication first obtains a polyimide film by spin-coating a polyamic acid solution on a substrate such as silicon, and heating and drying and curing it. This is the lower clad layer. Next, in the same procedure, a polyimide film having a higher refractive index than that of the lower clad is formed, and this is used as the 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, a polyamic acid solution is further spin-coated on the core, and after heating and drying, a polyimide film having a refractive index lower than that of the core is obtained by further heating and curing. The upper cladding layer.
[0006]
As an optical polymer constituting the core layer and cladding layer of the optical waveguide, polymethyl methacrylate has been conventionally used. However, since the glass transition temperature (Tg) is relatively low, there is a concern about reliability. Moreover, since Tg is low, it cannot endure a high temperature process and an electric circuit cannot be soldered on an optical waveguide. Therefore, polyimide having high Tg and excellent heat resistance is expected as a polymer material for optical waveguides. When an optical waveguide is formed from polyimide, long-term reliability can be expected and it can withstand soldering. However, since polyimide contains an aromatic ring in its chemical structure, it is difficult to obtain an optical waveguide that can be coupled with an optical fiber having a high refractive index and a relatively low refractive index with high efficiency. Moreover, since the absorption edge of light is shifted to the long wavelength side, polyimide has a large propagation loss due to absorption. Therefore, a polyimide having a refractive index lowered and a absorption edge shifted to the short wavelength side by introducing fluorine atoms has been developed. For example, JP-A-4-239037, JP-A-4-328504, JP-A-4-328127, JP-A-9-40774, etc. disclose polyimides into which fluorine is introduced.
[0007]
[Problems to be solved by the invention]
As described above, since a polyimide into which fluorine is introduced has a low refractive index and a short absorption edge, it is possible to form an optical waveguide that is optically high-performance and easy to couple with an optical fiber. However, polyimide introduced with fluorine has low solvent resistance and causes a problem in reliability. Further, polyimide introduced with fluorine has a problem of low adhesion due to the characteristics of fluorine, and it is difficult to bond other optical components on the optical waveguide.
[0008]
An object of the present invention is to provide an optical waveguide having a high solvent resistance while having an upper clad made of polyimide having a low refractive index.
[0009]
[Means for Solving the Problems]
In order to achieve the above object, according to the present invention, the following optical waveguide is provided. That is,
A substrate, a lower clad layer, a core layer, an upper clad layer, and a protective layer disposed on the upper clad layer, which are sequentially laminated on the substrate;
The upper clad layer is made of a resin containing fluorine, and the protective layer is made of a material having less fluorine than the upper clad layer or a material not containing fluorine. It is.
[0010]
DETAILED DESCRIPTION OF THE INVENTION
An optical waveguide according to an embodiment of the present invention will be described with reference to the drawings.
[0011]
The optical waveguide of the present embodiment includes a lower cladding layer 15 on a silicon wafer substrate 14 and a patterned core layer 16 is disposed on the lower cladding layer 15 as shown in FIG. ing. The core layer 16 is covered with the upper cladding layer 20. The upper surface of the upper cladding layer 20 is covered with a protective layer 24. The lower clad layer 15 and the upper clad layer 20 are made of polyimide into which fluorine is introduced and has a refractive index comparable to that of the optical fiber in order to increase the coupling efficiency with the optical fiber. On the other hand, the protective layer 24 is made of polyimide that does not contain fluorine.
[0012]
Specifically, the lower clad layer 15 and the upper clad layer 20 are both 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 indexes of the lower cladding layer 15 and the upper cladding layer 20 are 1.52 to 1.53. The thickness of the lower cladding layer 15 is about 7 μm, and the thickness of the upper cladding layer 20 is about 15 μm. The core layer 16 is a polyimide film formed using OPI-N3205 (trade name) manufactured by Hitachi Chemical Co., Ltd., and has a film thickness of about 8 μm and a width of about 8 μm. The refractive index of the core layer 16 is about 0.5% larger than that of the lower and upper cladding layers 15 and 20.
[0013]
The protective layer 24 is a polyimide film formed using PIX-6400 (trade name) manufactured by Hitachi Chemical DuPont Microsystems. This polyimide does not contain fluorine. The film thickness is about 7 μm at the end portion away from the core layer 16.
[0014]
Next, a method for manufacturing the optical waveguide shown in FIG.
[0015]
First, an extremely thin adhesive layer (not shown) is formed on the upper surface of the silicon wafer substrate 14 in FIG. On top of that, the above-mentioned OPI-N1005 (resin concentration 15% by weight) is spin-coated to form a material solution film. Thereafter, the solvent is evaporated by heating at 100 ° C. for 30 minutes in a dryer, then at 200 ° C. for 30 minutes, and subsequently cured 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.
[0016]
On the lower clad layer 15, the above-mentioned OPI-N3205 (resin concentration: 15% by weight) is spin-coated to form a material solution film. Thereafter, the solvent is evaporated by heating at 100 ° 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. Then, the core layer 16 was formed (FIG. 1B).
[0017]
Next, RU-1600P (manufactured by Hitachi Chemical Co., Ltd.) is spin-coated on the core layer 16 as a resist, dried at 100 ° C., exposed and developed with a mercury lamp to form a resist pattern layer 17. (FIG. 1 (c)). Using this resist pattern layer 17 as a mask, reactive ion etching (02-R1E) was performed with oxygen to pattern the core layer 16 into a desired optical waveguide shape. (FIG. 1 (d)). Thereafter, the resist was peeled off (FIG. 1 (e)).
[0018]
Further, the above-mentioned OPI-N1005 (resin concentration 25% by weight) was spin-coated thereon to form a material solution film 18 (FIG. 2 (f)). The upper surface of the material solution film 18 was flat as shown in FIG. 2 (f), but the solvent was evaporated by heating at 100 ° C. for 30 minutes and then at 200 ° C. for 30 minutes in a dryer, and the precursor film. 19, since the film thickness was reduced at a substantially constant reduction rate, the upper surface of the precursor film 19 became a convex shape along the shape of the core layer 16 (FIG. 2G). Subsequent to this drying step, the polyamic acid in the precursor film 19 is imidized by heating at 350 ° C. for 60 minutes to cure and form an upper clad layer 20 of a polyimide film having a thickness of 15 μm (see FIG. 2 (h)). The upper clad layer 20 substantially maintained the shape of the precursor film 19, and the upper surface was a convex shape along the shape of the core layer 16.
[0019]
Next, in the present embodiment, a polyimide film protective layer 24 containing no fluorine is formed on the upper surface of the upper clad layer 20.
[0020]
First, the above-mentioned PIX-6400 (resin concentration 35.5 wt%) was spin-coated on the upper clad layer 20 to form a material solution film 21 (FIG. 2 (i)). The upper surface of the material solution film 21 was flat as shown in FIG. 2 (i) because of spin coating. Thereafter, the precursor film 23 was obtained by evaporating the solvent by heating at 100 ° C. for 30 minutes and then at 200 ° C. for 30 minutes to obtain the precursor film 23. It became a convex shape along (Fig. 3 (j)). However, following this drying step, heating was performed at 350 ° C. for 60 minutes to imidize and cure the polyamic acid in the precursor film 23. As a result, the top surface was almost flat as shown in FIG. A protective layer 24 of a polyimide film having a thickness of 7 μm was obtained.
[0021]
Next, a silicon oxide film 25 is formed on the protective layer 24 by a spin-on-glass (SOG) process (FIG. 3L). Next, RU-1600P manufactured by Hitachi Chemical Co., Ltd. was spin-coated as a resist film, dried at 100 ° C., exposed and developed with a mercury lamp to form a resist pattern layer 26 (FIG. 4 (m)). . Using this 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, reactive ion etching (O2-RlE) was performed with oxygen using the silicon oxide film 25 as a mask, and the lower and upper cladding layers 20 and 15 and the protective layer 24 were processed into desired shapes. Thereafter, the silicon oxide film 25 was removed (FIG. 4 (o)). Thereby, the optical waveguide (FIG. 4 (o)) provided with the protective layer 24 of this Embodiment was obtained.
[0022]
Thus, since the optical waveguide of the present embodiment includes the protective layer 24 that does not contain fluorine, the upper surface of the upper cladding layer 20 can be covered with the protective layer 24. Thereby, since the upper clad layer 20 containing fluorine and having low adhesiveness and low solvent resistance is not exposed on the upper surface, an optical component can be bonded to the upper part with an adhesive using a solvent or the like with strong adhesive strength. . 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 increased.
[0023]
On the other hand, since the upper and lower cladding layers 20 and 15 are made of polyimide containing fluorine, the refractive index can be lowered to 1.52 to 1.53, and the input / output characteristics such as the numerical aperture equivalent to that of an optical fiber. Can be realized. Therefore, the optical waveguide of the present embodiment can be coupled to the optical fiber with high efficiency. Further, since polyimide containing fluorine is used for the upper and lower cladding layers 20 and 15, 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, it is possible to provide an optical waveguide with a low propagation loss over a wide wavelength range.
[0024]
Moreover, since all the layers from the lower clad layer 15 to the protective layer 24 are made of polyimide, the optical waveguide of the present embodiment has a high Tg compared to polymethyl methacrylate and the like, and a high temperature process such as soldering. Can also withstand. In the optical waveguide of the present embodiment, the layers related to the light propagation of the upper and lower claddings 20 and 15 and the core layer 16 are formed of polyimide having a Tg of 270 ° C. or more. For this reason, they are particularly excellent in heat resistance and can maintain propagation characteristics even at high temperatures.
[0025]
In the above manufacturing process, the upper clad layer 20 and the lower clad layer 15 are etched as shown in FIG. 4 (o), but without etching, the core layer 16 is flattened as shown in FIG. It can be used as a flat optical waveguide embedded with the 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. 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 adhesion. It becomes an optical waveguide with high solvent resistance and high adhesiveness. In the case of the configuration shown in FIG. 4 (o), the protective film 24 can cover not only the upper surfaces of the upper and lower claddings 20 and 15 but also the side surfaces thereof. In this case, since the protective film 24 can protect the upper and lower clads 20 and 15 from the side surfaces, the solvent resistance of the optical waveguide is further improved.
[0026]
Further, since the polyimide of the upper clad layer 20 and the polyimide of the protective layer 24 have good adhesion, even if the upper clad layer 20 contains fluorine, the protective layer 24 does not easily peel off. However, if polyimide having a fluorine content exceeding 19 mol% is used as the upper clad layer 20, the solvent resistance of the polyimide becomes too low, and the material solution film 21 of the protective layer 24 is formed in the step of FIG. At this time, the upper clad layer 20 is dissolved by the solvent in the material solution film 21. For this reason, the fluorine content of the upper cladding layer 20 is desirably 19 mol% or less.
[0027]
In the present embodiment, polyimide that does not contain fluorine is used as the protective layer 24, but the polyimide of the protective layer 24 functions as the protective layer 24 as long as the fluorine content is lower than that of the upper cladding layer 20. Fulfill. However, in consideration of practical solvent resistance and adhesiveness, if the fluorine content of the protective layer 24 exceeds 11 mol%, it is not sufficient as a practical protective layer 24. Therefore, as a polyimide constituting the protective layer 24, Is preferably used with a fluorine content of 11 mol% or less. On the other hand, the polyimide constituting the upper clad layer 20 can be suppressed to have a smaller refractive index as the fluorine content increases. Therefore, in order to suppress the refractive index at the same level as the optical fiber and reduce the loss due to light absorption, it is desirable to use a fluorine content of 14 mol% or more. Therefore, a preferable range of the fluorine content of the upper cladding layer 20 is 14 mol% or more and 19 mol% or less.
[0028]
Further, in the optical waveguide of the present embodiment, as shown in FIGS. 4O and 5, the protective layer 24 embeds the convex shape of the upper clad 20 and has a flat upper surface. Thereby, when an optical component is bonded on the protective layer 24, another optical waveguide is laminated, or a wiring pattern is formed, it can be handled in the same manner as a flat substrate. As a result, good adhesive properties can be obtained, and the laminated optical waveguide can be satisfactorily formed. Further, there is no risk of disconnection or the like in the wiring pattern due to the step. In addition, when the surface level | step difference of the protective layer 24 of this Embodiment was measured with the contact level meter, it was 1 micrometer or less.
[0029]
The reason why the protective layer 24 having a flat upper surface is obtained is as follows. Both the upper clad layer 20 and the protective layer 24 are polyimides, but both have different structural formulas. The polyimide of the upper clad layer 20 formed from OPI-N1005 has a glass transition temperature (Tg) of 325 ° C. The protective layer 24 formed from 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, both when the precursor film 19 of the upper cladding layer 20 is cured to be a polyimide film, and when the precursor film 23 of the protective layer 24 is cured to be a polyimide film, Is the same 350 ° C. Therefore, the upper clad layer 20 is heated at a glass transition temperature (Tg) + 25 ° C. while the protective layer 24 is heated at a glass transition temperature (Tg) + 80 ° C. Generally, a resin such as polyimide has 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 higher fluidity than the upper clad layer 20 and flows more easily, so that it flows from a raised portion to a lower portion, and the upper surface becomes flat.
[0030]
The reason why the fluidity 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 chemical structure of the polyimide formed from PIX-6400 and the polyimide formed from OPI-N1005. It is thought that this difference also has an effect.
[0031]
Further, the protective layer 24 has a resin concentration of PIX-6400, which is a material solution, of 35.5% by weight , and the concentration is higher than that of OPI-N1005 (resin concentration of 25% by weight) of the material solution of the upper clad layer 20. high. For this reason, the degree of reduction when the material solution film 21 of the protective layer 24 changes to the precursor film 23 by drying is the degree of reduction when the material solution film 18 of the upper cladding layer 20 changes to the precursor film 19. Not so big. Therefore, when the precursor film 23 is formed, the step is smaller than the step on the upper surface of the upper cladding layer 20. Thus, the use of a material having a material solution concentration higher than that of the upper clad layer 20 for the protective layer 24 also seems to be a factor that can effectively reduce the level difference of the upper clad layer 20.
[0032]
In addition, the optical waveguide of FIG. 4 (o) of this Embodiment and the optical waveguide of FIG. 5 can be used as an optical component for optical interconnection which connects between an optical module and an optical fiber. In addition, by making the pattern shape of the core layer 16 of the optical waveguide of the present embodiment a predetermined shape, optical components such as an optical path conversion element, an optical path branching element, and a directional coupler can be configured.
[0033]
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 atmospheric pressure by a simple process of spin coating, drying and curing. Therefore, it is suitable as a method for manufacturing optical waveguides in large quantities at a low cost. Further, in this optical waveguide configuration, the protective layer 24 hardly affects 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 or the like. it can.
[0034]
In the above-described embodiment, the silicon oxide film 25 is removed in the step of FIG. 4 (o). However, the silicon oxide film 25 does not affect the propagation of light and can be left as it is. It is.
[0035]
In the above-described embodiment, the heating temperature for curing the upper clad layer 20 and the heating temperature for curing the protective layer 24 are set to the same temperature. However, the heating temperature is not necessarily set to the same temperature. Absent. The heating temperature can be determined in consideration of the fluidity of the resin during heating.
[0036]
In the above-described embodiment, the core layer 16, the upper and lower cladding layers 15 and 20, and the protective layer 24 are formed by the polyimide films having different structures as described above. The material that can be used is not limited to polyimide. Not only polyimide but also polymers introduced with fluorine tend to have lower solvent resistance and lower adhesion than polymers without introduction. Therefore, as the material of the protective layer 24, a polymer having a fluorine content lower than that of the upper cladding layer 20 or a fluorine-free polymer can be used. For example, the upper clad layer 20 is formed of fluorinated polyimide, and the protective layer 24 is 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 containing alicyclic acrylic resin, olefin resin containing alicyclic olefin resin) and the like.
[0037]
The protective layer 24 is not limited to the resin described above, and can 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 formation method such as a CVD method or a vapor deposition method. It can also be formed by a solution coating method such as SOG.
[0038]
【The invention's effect】
As described above, according to the present invention, it is possible to provide an optical waveguide with high solvent resistance while having a low refractive index polyimide upper cladding.
[Brief description of the drawings]
FIGS. 1A to 1E are cross-sectional views illustrating steps of manufacturing an optical waveguide according to an embodiment of the present invention.
2 (f) to (i) are cross-sectional views showing a process for manufacturing an optical waveguide according to an 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.
4 (m) to (n) are cross-sectional views showing a process for manufacturing an optical waveguide according to an embodiment of the present invention, and (o) a cross-sectional view of the optical waveguide according to an embodiment of the present invention.
FIG. 5 is a cross-sectional view showing the shape of an optical waveguide when the upper and lower claddings 20 and 15 are not processed according to an embodiment of the present invention.
[Explanation of symbols]
DESCRIPTION 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.

Claims (2)

A first step of sequentially laminating a lower cladding layer and a core layer on a substrate;
A second step of forming an upper clad layer made of a resin film by applying a first resin material solution on the core layer, drying and curing the solution; and
A third step of applying a second resin material solution on the upper clad layer, and drying and curing to form a protective layer made of a resin film; and
The upper clad layer formed in the second step contains fluorine, and in the third step, the protective layer is made of a material containing less fluorine than the upper clad layer or containing no fluorine. Forming a layer,
The resin constituting the upper cladding layer and the material constituting the protective layer are both polyimide,
As the first resin material, a material in which the fluorine content of the resin film after curing is 14 mol% or more and 19 mol% or less,
The resin constituting the protective layer has a glass transition temperature lower than that of the resin constituting the upper cladding layer ,
The method for manufacturing an optical waveguide , wherein a resin content concentration in the second resin material is higher than a resin content concentration in the first resin material . 2. The method of manufacturing an optical waveguide according to claim 1 , wherein the second resin material is a material having a fluorine content of 11 mol% or less after curing. .

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