JP2003014966A - Method for manufacturing optical waveguide - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for manufacturing an optical waveguide by which an optical waveguide having a core pattern formed on a substrate and suitable to be used as an optical integrated circuit having large difference in the refractive index between the clad and core can be easily manufactured without performing complicated processes of forming and removing a resist pattern and etching. SOLUTION: After a film of a photosensitive material, for example, consisting of a mixture of polymethyl silazane and a photoacid producing agent is formed on a substrate of quartz or the like, the film is exposed by using a photomask having the core pattern of the optical waveguide and then developed to form the core pattern consisting of a photosensitive material on the substrate. Then the photosensitive material constituting the core pattern is heat-treated, for example, at about 900 deg.C in an argon atmosphere to stabilize and increase the refractive index to form the optical waveguide.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical waveguide in which a core pattern is formed on a substrate and which can be suitably used as an optical integrated circuit, and a manufacturing method thereof.

[0002]

2. Description of the Related Art An optical integrated circuit is an integrated circuit in which a plurality of optical devices are organically connected on the same substrate.
It is a compact, stable and efficient development of excellent performance or function that cannot be obtained by a single device. In manufacturing an optical integrated circuit, it is indispensable to form an optical waveguide in which a core having a refractive index higher than those of these materials is arranged on or in a substrate, and such an optical waveguide is made of glass. In many cases, a material layer having a different refractive index is formed on the surface of a substrate such as a plate, and the layer is finely processed by dry etching using a resist pattern formed by a lithography method or the like. For example, in the flame deposition method, which is known as a typical method for manufacturing an amorphous optical waveguide, which plays an important role in forming a hybrid optical integrated circuit by combining other optical elements, Porous film for buffer made of quartz glass,
After forming a core porous film made of quartz glass containing a refractive index control additive in this order, heat treatment to make it transparent,
A three-dimensional optical waveguide is formed by forming a resist mask having a waveguide pattern on the core layer by lithography, forming a substantially rectangular core by dry etching, and peeling off the resist mask remaining on the core. .

In the method of manufacturing an optical waveguide by the flame deposition method, it takes time and labor to form a resist mask pattern and remove the resist mask pattern after processing, and the accuracy of dimensional conversion from the mask pattern to the waveguide material pattern is high. Advanced technology such as control of is required. Further, the refractive index difference Δ between the core and the clad (coating of the core made of a material having a lower refractive index than the core) of the optical waveguide formed by the flame deposition method.
Was at most about 1%, and it was difficult to increase the difference.

As a method of solving the problem of the difference in the refractive index, Japanese Patent Laid-Open No. 6-258538 focuses on a SiO _x N _y H _z material whose refractive index greatly changes depending on the nitrogen content, and uses 0 as a cladding material. 2 to 2 atomic% of SiO _x N _y H _z as a core material and nitrogen content of 3 to
Methods using 25 atomic% SiO _x N _y H _z each are disclosed. Then, according to this method, it is possible to increase the refractive index difference Δ to about 6%.

[0005]

However, in the above method, not only the plasma CVD method which requires a special apparatus for forming the SiO _x N _y H _z film to be the clad and the core but also the optical waveguide of the optical waveguide is used. Similar to the flame deposition method, the formation includes the steps of forming / peeling a resist mask pattern, etching, etc., and there is a problem in terms of simplicity.

Therefore, the present invention provides a method for easily manufacturing an optical waveguide in which a core pattern having a large difference in refractive index with a clad and a finely and precisely controlled core pattern is formed on a substrate. With the goal.

[0007]

Means for Solving the Problems The inventors of the present invention formed the core pattern itself with a photosensitive material and then stabilized the photosensitive material without forming / peeling a resist pattern or dry etching. Based on the original idea that an optical waveguide can be formed, the inventors have made earnest studies to solve the above problems. As a result, a photosensitive material obtained by adding a photoacid generator to polymethylsilazane or polymethylsilsesquiazane having a property of being decomposed by an acid to have a low molecular weight has a high refractive index when heat-treated at a high temperature. A highly stable core material is changed into a suitable substance, and further, a decomposed product of the above photosensitive material which is decomposed by an acid to have a low molecular weight is obtained as described above when subjected to heat treatment at high temperature after moisture absorption treatment. The present invention has been completed by finding that the material can be changed to a material that can be used as a clad material having a lower refractive index than a material suitable as a core.

That is, in the first aspect of the present invention, a film made of a photosensitive material is formed on a substrate, an optical waveguide core pattern is exposed on the film, and then the photosensitive material which becomes the core pattern is stabilized. It is a method of manufacturing an optical waveguide.

According to the manufacturing method of the present invention described above, for example, the film is exposed to the optical waveguide core pattern and then developed without requiring a complicated operation such as formation / peeling of a resist pattern and dry etching. By forming an optical waveguide core pattern made of the photosensitive material or a derivative thereof on the substrate, and then stabilizing the photosensitive material or a derivative thereof constituting the core pattern,
It is possible to manufacture an optical waveguide having a core with a fine and complicated pattern. After exposing the film to the optical waveguide core pattern, stabilize the photosensitive material or its derivative in a portion of the film that does not become the optical waveguide core pattern, and stabilize the photosensitive material or its derivative to become the optical waveguide core pattern. Before, after, or at the same time as the stabilization, by converting to a material having a lower refractive index than the material obtained by the stabilization, the development process can be omitted and the cladding layer is formed on the side surface of the core pattern. The obtained optical waveguide can be obtained.

In particular, when a composition containing a polymeric silicon compound containing silicon atoms and nitrogen atoms as constituent elements and capable of decomposing upon contact with an acid, and a photoacid generator are used as the photosensitive material. Can be easily obtained by stabilizing it by, for example, heat treatment. Further, as the substrate, a substrate in which the surface on which the core pattern is formed at least on the substrate is made of a substance having a refractive index lower than that of the photosensitive material after stabilization, such as aluminum nitride or aluminum nitride. When using a substrate with a part of the surface of a high heat conductive ceramic base material such as a ceramic base material as the main component coated with quartz etc., a core pattern is formed on the coated part and aluminum nitride etc. By mounting an electronic element such as a semiconductor element on the exposed portion, an optoelectronic integrated circuit having excellent heat dissipation can be obtained. Further, the surface of the core (the upper surface and the side surface of the core in the case of the above-mentioned method of developing treatment, and the upper surface of the core in the case of the above-mentioned method of not developing) is lower in refractive index than the constituent material of the core. The cladding layer that also serves as a protective film can be easily formed by coating with a substance having

The second invention is an optical waveguide manufactured by the manufacturing method of the first invention. The core of the optical waveguide of the present invention is obtained, for example, by heat-treating the above-described high molecular silicon compound, and it is difficult to specify its composition or structure, but the refractive index is disclosed in the above publication. It is much higher than the above-mentioned SiO _x N _y H _{z and the} like (the refractive index is about 1.58 or less according to FIG. 2 of the publication), and not only the manufacturing method is excellent, but also itself. It can be said that this is an excellent optical waveguide that has never been seen before.

Furthermore, a third aspect of the present invention is a method for manufacturing an optical integrated circuit, characterized in that the optical waveguide according to the second aspect of the present invention is used, and a fourth aspect of the present invention is the second aspect of the present invention. An optical integrated circuit including the optical waveguide of the present invention as a constituent element. The optical integrated circuit referred to in the present invention is a concept including an optoelectronic integrated circuit.

Furthermore, a fifth aspect of the present invention is to provide an optical waveguide core on a portion of the surface of a ceramic base material coated with a substance having a refractive index lower than that of the core material of the optical waveguide. The optoelectronic integrated circuit is characterized in that an electronic element is mounted on a portion of the ceramic base material which is not covered with a substance having a refractive index lower than that of the photosensitive material and which forms a pattern.

[0014]

DETAILED DESCRIPTION OF THE INVENTION The present invention will be described in detail below with reference to the drawings. FIG. 1 is a diagram showing a typical manufacturing process flow of the manufacturing method of the present invention. In the manufacturing process flow shown in FIG. 1, first, the film 12 made of a photosensitive material is formed on the substrate 110.
0 is formed {FIG. 1, step (1)}.

As the substrate 110 used in the manufacturing method of the present invention, a structure having a flat surface on the surface of which a core is formed,
There is no particular limitation as long as it is a plate-like body, and a substrate made of a known substrate material can be used, but in order to allow light to propagate in the core layer, at least the surface underlying the core is the core. It must be composed of a material having a lower refractive index than the substance. Examples of the substrate material that can be preferably used in the present invention include quartz, quartz-based glass, various other glass materials, and materials used as substrates for ordinary optical waveguides such as LiNbO ₃ , ZnO, and sapphire. Among these, quartz or a glass material containing silicon dioxide as a main component is used when a heat treatment is adopted as a treatment for stabilizing a high molecular silicon compound such as polymethylsilazane described below as a photosensitive material.
It can be used particularly preferably because it has good compatibility with respect to the heat treatment and the thermal expansion coefficient of the high molecular silicon compound and the heat treated product thereof. Also, a ceramic material such as aluminum nitride, beryllia, silicon carbide, or alumina can be used by coating the surface thereof with the above material. For example, FIG. 2 shows a schematic cross-sectional view of a typical optical integrated circuit (optical electronic integrated circuit) of the present invention in which not only a core pattern but also an electronic element 140 such as a semiconductor element is mounted on the same substrate. The substrate of the electronic element 140
In order to efficiently dissipate the heat generated in, a substrate having a structure in which a part of a base material 111 having a high thermal conductivity such as aluminum nitride is covered with a layer 112 made of a low refractive index material such as quartz is used. ing. An optical waveguide core pattern 123 (the core may be covered with a film 130 made of the same or different low refractive index material as 111) is formed on the layer 112 of the substrate to form an optical waveguide. Base material 11
By mounting the electronic element 140 on the exposed portion of 1 through a metallization layer (not shown), a heat sink function can be provided, and high density can be sufficiently dealt with. At this time, in order to enhance the effect of dissipating the heat generated from the electronic element, a diamond film may be formed between the underlying ceramic substrate on which the electronic element is mounted and the metallized layer. In forming the layer 112, a method of applying alkoxysilane, silica sol or the like and baking, a method of applying polymethylsilsesquiazane and exposing the entire surface to moisture absorption and heating, a method of applying perhydropolysilazane and oxygen. Or a method of heating in the presence of moisture,
It can be formed by a CVD method using a silane-based gas, a sputtering method using silicon dioxide as a target, an ion plating method using silicon dioxide as a raw material, or the like.

The photosensitive material used in the manufacturing method of the present invention is
It is a material that can be formed into a film and is photosensitive, that is, it has the property of being polymerized or condensed by irradiation of light or electron beams, or conversely decomposed. The material is not particularly limited as long as it is a so-called positive type (a type in which the irradiated portion of light is decomposed, in other words, it is changed to a derivative to be solubilized) and a negative type (the irradiated portion of light is cross-linked and insolubilized). It is possible to use a photosensitive material of a type, that is, a type that is changed to a derivative). However, from the viewpoint of light confinement effect when used as a core and the viewpoint of abundance of clad materials that can be used, the refractive index after stabilization is
It is preferable to use one having a ratio of 1.57 or more, particularly 1.65 or more. A polymer silicon compound containing a silicon atom and a nitrogen atom as constituent elements and capable of decomposing by contact with an acid (for example, a polymer silicon compound in which -Si-NH- units are linked) and a photoacid generator are contained. The composition not only has a low molecular weight when exposed to light and becomes soluble in a solvent (has photosensitivity), but is also easily stabilized by heat treatment and has a high light-transmitting property (mainly silicon nitride). It is particularly preferable to use such a composition as a photosensitive material in the present invention, since it becomes a component material). Examples of the above-mentioned polymeric silicon compound include polyorganosilazane {J. Am. Ceram. Soc., 66, C-132 (198
4)}, polyalkylsilsesquiazane {Tec.Dig.-Int.
Electron Device Meet. (2000), 253-256}, in addition to Si, Al, Ga, In, Si, Ge, Ti, Zr, Hf,
Polymerizable multi-element azan containing elements such as V, Nd, Ta, Cr, Mo and W (JP-A-6-340744), alkylpoly (polysilyl) azane preceramic polymer (JP-A-5-59178), Examples thereof include perhydropolysilazane, and their derivatives. From the viewpoint of easy availability, it is particularly preferable to use polymethylsilazane, polymethylsilsesquiazane, perhydropolysilazane, or their derivatives. The photoacid generator is not particularly limited as long as it can generate Bronstedt acid or Lewis acid by irradiation with light or electron beam, and is not particularly limited, and it is a halomethyl group-substituted-s-triazine derivative, diphenyliodonium salt compound, sulfonium salt compound, sulfone. In addition to acid ester compounds, disulphone compounds, diazonium salt compounds, and the like, known photoacid generators can be used without limitation. Further, a sensitizer such as a sensitizing dye may be added to the above composition.

The method of forming a film made of the above-mentioned photosensitive material on the substrate is not particularly limited, and for example, a solution obtained by dissolving the above-mentioned composition in a solvent is applied or spin-coated. After that, the solvent can be preferably removed by removing the solvent by a method such as solvent drying. At this time, the solution viscosity and the spin coating conditions may be adjusted so that the thickness of the film to be formed will be a desired core thickness in consideration of the volume change and the like due to the stabilization treatment or the like depending on the photosensitive material used.

In the manufacturing method of the present invention, with respect to the film 120 made of the photosensitive material formed as described above, a photomask (not shown) for printing an optical waveguide core pattern is used, or an electron beam drawing apparatus is used. Then, the film is exposed and developed to form a core pattern made of the photosensitive material on the substrate {FIG. 1, steps (2) and (3)}. For example, when a light-sensitive material made of a composition containing the above-described high molecular silicon compound is used and exposed to ultraviolet rays or electron beams, the light-irradiated portion 121 of the film 120 is decomposed to have a low molecular weight. However, since the unirradiated portion forming the core pattern does not change, the exposed portion 12 is irradiated with a solvent or an aqueous alkali solution.
By removing 1 (developing), the core pattern 122 made of the photosensitive material before the stabilization process can be formed. When exposing and developing, the light irradiation part 12
In order to facilitate the removal of 1, it is preferable to carry out an auxiliary reaction process such as sensitization / moisture absorption (steam treatment). Also, the film 1
In the film formation, exposure, and development of 20, by adopting the lithography technique in the LSI manufacture, it is possible to form a pattern having an extremely accurate film thickness and in-plane direction dimension.

As described above, in the manufacturing method of the present invention, it is not always necessary to perform development after exposure. For example, when a photosensitive material made of a composition containing the above-mentioned high molecular silicon compound is used, exposure That is, after the step (2) in FIG. 1, a moisture absorption treatment is performed, and the core pattern 122 is subjected to stabilization by a heat treatment as described below.
Is changed to the stabilized core 123 made of the photosensitive material, and at the same time, the light irradiation portion 121 is changed to a substance having a lower refractive index than the core 123 containing silicon oxide as a main component, so that the development process is omitted. As shown in FIG. 3, an optical waveguide having a clad layer on the side surface of the core can be easily manufactured.

In the manufacturing method of the present invention, after the core pattern 122 made of the photosensitive material is formed on the substrate as described above, the photosensitive material forming the core pattern or its derivative is stabilized to make it photosensitive. Not converted into a stable translucent material to form a final core pattern 123 {FIG. 1, step (4)}. The stabilizing method at this time may be a suitable chemical treatment or physical treatment depending on the photosensitive material used. For example, in the case of using a photosensitive material composed of a composition containing the above-mentioned polymeric silicon compound and a photoacid generator, for example, a photoacid generator is chemically deactivated by adding a base, or by heating. It can be stabilized by volatilizing or sublimating or decomposing the photo-acid generator. When the composition containing the above-mentioned high molecular silicon compound is used as the photosensitive material, it is possible to achieve such stabilization, as well as high strength, high refractive index, or transparency. Is preferably performed. The heat treatment conditions at this time may be appropriately determined according to the type of composition used (type of high molecular silicon compound and photoacid generator). The higher the heating temperature and the longer the treatment time, the higher the refractive index of the polymer silicon compound after treatment tends to be. Therefore, in the production method of the present invention, the refractive index of the core is controlled by adjusting the heat treatment conditions. can do. In order to obtain a suitable refractive index as a core material, 700 to 1
200 ° C., preferably 800-1100 ° C., especially 900
It is preferable to perform heat treatment at about 1000 ° C. for about 0.1 to 10 hours. The atmosphere at this time is not particularly limited, but in order to increase the refractive index, it is preferable to carry out under an inert gas atmosphere such as nitrogen gas or argon gas or under a reducing gas atmosphere such as ammonia. It should be noted that, depending on the type, the above-mentioned polymeric silicon compound may have a property of being converted into a substance containing silicon oxide as a main component when heated in an atmosphere in which oxygen or water exists. When a compound is used, it is also possible to control the degree of conversion to silicon oxide by controlling the partial pressure of oxygen or water vapor in the atmosphere, and thus the refractive index of the substance obtained after the treatment. Therefore, it is possible to perform the treatment in an atmosphere in which oxygen and water are present.

The product obtained by performing such a stabilizing treatment can be sufficiently used as an optical waveguide by itself, but it is a stabilizer formed on a substrate for the purpose of reducing loss and protecting the core layer. It is preferable to coat the surface of the core 123 made of the photosensitive material with a core coating 130 made of a substance having a refractive index lower than that of the constituent substance of the core {FIG. 1, step (5)}. . As the coating material at this time, the same material as the material of the layer 112 in FIG. 2 can be preferably used. Further, the coating method is not particularly limited, and for example, the layer 1
It can be performed in the same manner as the formation of 12.

In the optical waveguide of the present invention manufactured in this manner, a structure having various functions such as electrodes is arranged on the optical waveguide, or the waveguide itself is further processed to have a special structure. By doing so, it is possible to provide an optical integrated circuit capable of performing various optical controls. Further, as shown in FIG. 2, it may be combined with various electronic elements to form an optoelectronic integrated circuit.

By the way, the optoelectronic integrated circuit of the present invention shown in FIG. 2 has a novel structure itself, and as described above, has a high ability to dissipate the heat generated from the electronic element, and the electronic element and the electric wiring are It has a feature not found in conventional optoelectronic devices that it can be used stably even if the density is increased. Therefore, the optical waveguide core pattern is formed on the coated portion of the substrate, which is the fifth aspect of the present invention, in which a part of the surface of the ceramic base material is coated with a substance having a refractive index lower than that of the core material of the optical waveguide. An optical waveguide core pattern in an optoelectronic integrated circuit according to the present invention, wherein an electronic device is mounted on a portion of the ceramic substrate which is not covered with a substance having a refractive index lower than that of the photosensitive material. As a method for forming the above, a known method for forming an optical waveguide pattern can be used without limitation.

[0024]

The present invention will be described in more detail with reference to examples, but the present invention is not limited to the examples.

Example A quartz glass substrate (thickness: about 0.7 mm, about 35 mm square, refractive index: 1.55) was prepared. This was washed with alcohol and dried, and the photosensitive material layer was spin-coated. Here, a propylene glycol monomethyl ether acetate (PGMEA) solution of photosensitive polymethylsilazane (manufactured by Clariant Japan) was spin-coated on a quartz glass substrate at 4000 rpm. 90 on a hot plate
It was heated at ℃ for 1 minute and dried.

The photosensitive material layer was exposed to deep ultraviolet light using a mask having an optical waveguide pattern. The exposure time depends on the sensitivity of the photosensitive polymethylsilazane, but typically,
It was set to 20 seconds. Then, hold the glass substrate together for 10 minutes in a case filled with water by slightly stretching water on the bottom,
The acid generator in the photosensitive polymethylsilazane was made to absorb moisture and sensitized.

Then, an ordinary commercially available organic alkaline aqueous solution (trimethylammonium hydride 2.38% aqueous solution,
The photosensitive material film was developed using Tokyo Ohka Co., Ltd., trade name NMD-3), and the exposed portion was removed. The glass plate on which the optical waveguide pattern was formed was heat-treated in an argon atmosphere at various temperatures for 1 to 2 hours to confirm the change in the refractive index.
As a result, the heat treatment at 700 ° C. or lower had a refractive index of about 1.5. However, when heat treatment was performed at 800 ° C. and 900 ° C., the photosensitive polymethylsilazane was changed to a material containing silicon nitride as a main component, The refractive index is about 1.7 (at
800 ° C.) and about 1.8 (at 900 ° C.). Since the optical waveguide pattern thus formed has a higher refractive index than the underlying quartz glass substrate, light can be propagated in the waveguide pattern due to the difference in the refractive index.

[0028]

According to the manufacturing method of the present invention, it is possible to control an optical waveguide which has a core having a large difference in refractive index from the clad and whose shape is finely and accurately controlled on the substrate. It can be easily manufactured without using a complicated etching method.

[Brief description of drawings]

FIG. 1 is a diagram showing a typical manufacturing process flow of a manufacturing method of the present invention.

FIG. 2 is a schematic cross-sectional view of a typical optical integrated circuit (optoelectronic integrated circuit) of the present invention.

FIG. 3 is a schematic cross-sectional view of a typical optical waveguide of the present invention.

[Explanation of symbols]

110: substrate 111: Base material having high thermal conductivity 112: Layer made of low refractive index material 120: Film made of photosensitive material 121: Light irradiation part 122: Core pattern made of photosensitive material before stabilization processing 123: Core pattern 130: Core coating 140: Electronic element

   ─────────────────────────────────────────────────── ─── Continued front page    (72) Inventor Junichi Murota             23, 1-6, Tohiga, Aoba-ku, Sendai-shi, Miyagi Prefecture             403 (72) Inventor Kenichiro Miyahara             1-1 Mikagecho, Tokuyama City, Yamaguchi Prefecture             In Kuyama (72) Inventor Toru Nonaka             1-1 Mikagecho, Tokuyama City, Yamaguchi Prefecture             In Kuyama (72) Inventor Yuichiro Minabe             1-1 Mikagecho, Tokuyama City, Yamaguchi Prefecture             In Kuyama F term (reference) 2H047 KA04 PA22 PA24 PA28 QA05                       QA07

Claims (12)

[Claims] 1. A film comprising a photosensitive material is formed on a substrate, an optical waveguide core pattern is exposed to the film, and then the photosensitive material or its derivative to be the core pattern is stabilized. A method for manufacturing an optical waveguide. 2. An optical waveguide core pattern made of the photosensitive material or a derivative thereof is formed on the substrate by exposing the film made of the photosensitive material to an optical waveguide core pattern and then developing the film. The method according to claim 1, wherein the photosensitive material or its derivative constituting the material is stabilized. 3. After exposing a film made of the photosensitive material with an optical waveguide core pattern, a portion of the film which is not the optical waveguide core pattern is treated with the photosensitive material or its derivative as an optical waveguide core pattern. 2. The method according to claim 1, wherein the functional material or its derivative is converted into a substance having a lower refractive index than the substance obtained by the stabilization, before or after the stabilization, or simultaneously with the stabilization. . 4. The photosensitive material comprises a composition containing a silicon atom and a nitrogen atom as constituent elements and containing a polymeric silicon compound decomposable by contact with an acid, and a photoacid generator. The manufacturing method according to any one of claims 1 to 3, which is characterized. 5. A substrate is used, wherein at least a surface of the substrate on which the core pattern is formed is made of a substance having a refractive index lower than that of the photosensitive material after stabilization. The manufacturing method according to claim 1. 6. The manufacturing method according to claim 1, wherein the method for stabilizing the photosensitive material is a heat treatment. 7. The surface of a core made of the stabilized photosensitive material formed on a substrate is coated with a substance having a refractive index lower than that of the constituent substance of the core. 7. The method according to any one of 6 to 6. 8. An optical waveguide manufactured by the manufacturing method according to claim 1. 9. A method of manufacturing an optical integrated circuit, wherein the optical waveguide according to claim 8 is used. 10. An optical integrated circuit including the optical waveguide according to claim 9 as a constituent element. 11. A core pattern is formed on the coated portion of a substrate in which a part of the surface of a ceramic substrate is coated with a substance having a refractive index lower than that of the photosensitive material after stabilization, and the ceramic is formed. The optical integrated circuit according to claim 11, wherein an electronic element is mounted on a portion of the base material which is not covered with a substance having a refractive index lower than that of the photosensitive material. 12. An optical waveguide core pattern is formed on the coated portion of a substrate in which a part of the surface of a ceramic base material is coated with a substance having a refractive index lower than that of a core material of the optical waveguide, and the ceramic substrate is formed. An optical integrated circuit in which an electronic element is mounted on a portion of the material which is not covered with a substance having a refractive index lower than that of the photosensitive material.