JP2001174651A - Optical waveguide substrate - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an optical waveguide substrate which is formed with an organic system optical waveguide with sufficient adhesion strength on an aluminum nitride substrate. SOLUTION: This optical waveguide substrate is constituted by forming the optical waveguide of the organic system having a layer consisting of an organic optical material having a hydroxyl group or alkyl group as a lower clad layer 3 on the aluminum oxide substrate 1 via an intermediate layer 2 consisting of silicon nitride or silicon interposed therebetween. Since the hydroxyl group at the terminal of the intermediate layer 2 surface and the hydroxyl group or alkyl group of the lower clad layer 3 are bonded by dehydration polymerization or dealcohol polymerization, the high adhesion strength may be obtained and the formation of the organic system optical waveguide on the aluminum nitride substrate with the sufficient adhesion strength is made possible.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical waveguide substrate used for an optical communication module or the like, and more particularly, to an optical waveguide formed on a substrate made of an aluminum nitride sintered body having excellent thermal conductivity. The present invention relates to an optical waveguide substrate.

[0002]

2. Description of the Related Art Conventionally, optical communication modules and the like have been used in which various optical devices are mounted on an optical waveguide substrate in which an electric circuit and an optical waveguide are formed on a silicon substrate. Further, there is an optical waveguide substrate in which an optical waveguide is formed on a ceramic circuit substrate which is superior in electrical high-frequency characteristics and mechanical strength as compared with a silicon substrate, and can realize a high electric wiring density by multilayering.

[0003] Above all, an optical waveguide substrate in which an optical waveguide is formed on a substrate made of an aluminum nitride sintered body (hereinafter, abbreviated as aluminum nitride substrate) can form a multilayer electric circuit and has a higher electric frequency than a silicon substrate. Since it uses a substrate made of aluminum nitride sintered body that has excellent characteristics and high thermal conductivity comparable to that of a silicon substrate, optical devices and electrical devices that drive and process optical devices and signal processing Is promising in that many and high-density electrical devices can be mounted at high density.

On the other hand, as an optical waveguide, for example, a silica-based optical waveguide in which a three-dimensional clad portion and a core portion are formed using a silica film formed by a flame deposition method on a quartz glass substrate or a silicon substrate, There is an optical waveguide or the like in which a lithium niobate single crystal substrate is used as a clad portion and titanium is thermally diffused on the substrate to form a core portion in a three-dimensional waveguide shape.

[0005] However, since a high-temperature heat treatment of about 1000 ° C. or more is required to form these silica-based optical waveguides and the like, they form a base when an optical circuit using these optical waveguides is formed on an electric circuit board. The electric circuit board will be damaged.

On the other hand, instead of these conventional silica-based optical waveguides and the like which require high-temperature processing during fabrication, optical waveguides made of organic optical materials that can be formed at a low temperature are being studied.
Organic optical materials used for this optical waveguide include P
MMA (polymethyl methacrylate), polycarbonate, polyimide, polysiloxane, BCB (benzocyclobutene), fluorine resin, and the like are being studied.

As a method of manufacturing an optical waveguide made of these organic optical materials, a lower cladding layer is formed on a silicon substrate or a glass substrate, and then a core layer having a higher refractive index than the lower cladding layer is formed. Then, the core layer is processed by RIE (reactive ion etching) or the like using a thin film microfabrication technique to form a core portion, and then the upper cladding layer having a lower refractive index than the core portion is covered to form a three-dimensional structure. A method of forming an optical waveguide having a shape has been performed.

[0008]

However, when an optical waveguide made of an organic optical material is to be formed on an aluminum nitride substrate, the adhesion strength between the organic optical material for the optical waveguide and the aluminum nitride substrate is low, and the optical waveguide is not provided. In a post-process such as a waveguide manufacturing process and a subsequent device mounting process, there was a problem that a lower cladding layer made of an organic optical material for an optical waveguide was peeled off from an aluminum nitride substrate and cracks were generated in the lower cladding layer. .

The present invention has been devised in view of the above-mentioned problems of the prior art, and has as its object to provide an optical waveguide substrate having an organic optical waveguide formed on an aluminum nitride substrate with sufficient adhesion strength. It is in.

[0010]

According to the optical waveguide substrate of the present invention, a layer made of an organic optical material having a hydroxyl group or an alkyl group is formed on an aluminum nitride substrate with an intermediate layer made of silicon oxide or silicon interposed therebetween. An organic optical waveguide serving as a cladding layer is formed.

The optical waveguide substrate according to the present invention is characterized in that, in the above-mentioned structure, the organic optical material is a siloxane-based polymer.

An optical waveguide substrate according to the present invention is an organic waveguide substrate having an interlayer made of silicon oxide or silicon on an aluminum nitride substrate, and a layer made of an organic optical material having a hydroxyl group or an alkyl group as a lower cladding layer. By forming the optical waveguide, the hydroxyl group at the surface end of the intermediate layer and the hydroxyl group or the alkyl group of the lower cladding layer of the optical waveguide are strongly bonded by dehydration polymerization or dealcoholization polymerization.
An optical waveguide substrate having an organic optical waveguide formed on an aluminum nitride substrate with sufficient adhesion strength can be obtained.

[0013]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, an optical waveguide substrate according to the present invention will be described with reference to the drawings.

FIG. 1 is a sectional view showing an example of an embodiment of an optical waveguide according to the present invention. In FIG. 1, 1 is a substrate, 2 is an intermediate layer, 3 is a lower cladding layer made of an organic optical material for an optical waveguide, 4 is a core portion of the optical waveguide, and 5 is an upper cladding layer of the optical waveguide.

The substrate 1 is a substrate made of an aluminum nitride sintered body. An aluminum nitride substrate alone, an aluminum nitride electric circuit substrate having an electric circuit formed on its surface, and a multilayer electric circuit substrate formed inside the aluminum nitride substrate are provided. A substrate or the like can be used.

The intermediate layer 2 is a layer made of silicon oxide or silicon. As a method for forming the intermediate layer 2, a sputtering method, an electron beam evaporation method, an ion beam evaporation method, a laser ablation film formation method, a CVD method, or the like can be used. Among them, the sputtering method and the ion beam evaporation method are preferable because the adhesion effect between the intermediate layer 2 and the substrate 1 is increased by the anchor effect because the effect of implanting the film-forming material particles on the surface of the substrate 1 is large.

The reason why silicon oxide or silicon is used as the intermediate layer 2 in the present invention is that the adhesion strength between the intermediate layer 2 and the lower cladding layer 3 formed thereon can be sufficiently increased. The reason is that the surface of the intermediate layer 2 made of silicon oxide or silicon can be terminated with a hydroxyl group, and the lower clad layer 3 made of an organic optical material contains a hydroxyl group or an alkyl group. This is because a hydroxyl group on the surface and a hydroxyl group or an alkyl group of the lower cladding layer 3 are firmly bonded by dehydration polymerization or dealcoholization polymerization, and a large adhesion strength is obtained between the two layers.

Even if the lower cladding layer 3 made of an organic optical material does not contain a hydroxyl group or an alkyl group, if the underlying layer is silicon oxide or silicon, a well-known silane coupling material is used. Thereby, a hydroxyl group or an alkyl group bonded to the intermediate layer 2 with the intermediate layer 2 and an organic functional group having a large adhesion strength with the lower cladding layer 3 can be obtained, and a large adhesion strength can be obtained. be able to. As such a silane coupling material, glycidoxypropyltrimethoxysilane, hexamethoxydimethylsilazane, methacryloxypropyltrimethoxysilane, trimethoxysilylpropylethylenediamine, or the like can be used.

The thickness of the intermediate layer 2 is not problematic in principle as long as silicon oxide or silicon has several molecular layers or several atomic layers, but the surface of the aluminum nitride substrate generally has a surface roughness of 10 nm or more. Therefore, in order to obtain sufficient coverage with the intermediate layer 2, the thickness is preferably 10 nm or more.

On the other hand, when silicon oxide or silicon is formed by a sputtering method, an electron beam evaporation method, an ion beam evaporation method, a laser ablation film formation method, a CVD method, or the like,
Usually, the film stress is 100 MPa or more. When the thickness of the layer is large, there is a problem that the substrate is largely warped by the film stress, the layer is peeled off from the substrate surface, and cracks are generated. On the other hand, the thickness of the intermediate layer 2 is 50
When the thickness is 0 nm or less, the film stress can be suppressed to the same level as that of the lower cladding layer 3 made of an organic optical material.

The optical waveguide formed on the substrate 1 is a three-dimensional waveguide-shaped optical waveguide in which a core portion 4 is formed in cladding portions 3 and 5 comprising a lower cladding layer 3 and an upper cladding layer 5. As the forming material, for example, polyimide, fluorinated polyimide, siloxane-based polymer, PMMA
(Polymethylmethacrylate) An optical waveguide made of an olefin resin or the like and made of an organic optical material having a hydroxyl group or an alkyl group as a terminal group is used.

As a method of manufacturing the optical waveguide, first, the lower clad layer 3 is formed. To this, an organic solvent solution of an organic optical material such as polyimide, fluorinated polyimide, siloxane-based polymer, PMMA, olefin-based resin, etc.
Is formed on the substrate 1 on which is formed a predetermined thickness by a spin coating method or the like and heat-treated.

The core part 4 has a polyimide / fluorinated polyimide / siloxane-based polymer / PMM on the lower cladding layer 3.
A: An organic solvent solution of an organic optical material such as an olefin resin is applied to the substrate 1 on which the intermediate layer 2 is formed to a predetermined thickness by, for example, a spin coating method or the like, and heat-treated to form a layer. What is necessary is just to form in a predetermined shape using well-known thin film microfabrication techniques, such as RIE.
Here, the core portion 4 is made of a material having a higher refractive index than the lower cladding layer 3.

After the core 4 is formed, the upper clad layer 4 is coated with an organic solvent solution of an organic optical material such as polyimide, fluorinated polyimide, siloxane-based polymer, PMMA, or olefin-based resin. The substrate 4 on which the substrate 4 is formed is formed by applying a predetermined thickness by, for example, a spin coating method or the like, and performing heat treatment.

Here, the height, width, and refractive index of the core portion 4, the thickness and refractive index of the lower cladding layer 3, and the thickness and refractive index of the upper cladding layer 4 are set to desired values using a known optical waveguide theory. What is necessary is just to design by specification.

As described above, an optical waveguide having a buried three-dimensional waveguide shape is manufactured.

In the optical waveguide substrate of the present invention, when a siloxane-based polymer is used as the organic optical material for forming the lower cladding layer 3, for example, an organic solvent of the siloxane-based polymer is applied to the substrate 1 by spin coating or the like. After that, the lower cladding layer 3 can be formed by low-temperature heat treatment at about 100 ° C. to 300 ° C., and a metal-containing siloxane-based polymer can be easily produced by mixing a metal alkoxide to control the refractive index. Since the refractive index can be controlled to a desired refractive index with high accuracy, the fabrication of the optical waveguide becomes easy. Further, since the shrinkage during the formation of the layer is small, the surface of the layer formed on the surface of the substrate 1 is excellent in flatness and smoothness, and the substrate 1 has large undulations due to a substrate or wiring having a large surface roughness. Even when an electric wiring board is used, an optical waveguide can be manufactured thereon with high accuracy.

Since the siloxane-based polymer has a siloxane bond, an optical waveguide having excellent thermal stability can be formed. Further, it is easy to make a hydroxyl group or an alkyl group a terminal group, and when a film serving as the lower cladding layer 3 is formed on the intermediate layer 2, dehydration polymerization or dealcoholization polymerization with hydroxyl groups on the surface of the intermediate layer 2 is performed. Thereby, a large adhesion strength with the intermediate layer 2 is obtained.

The siloxane-based polymer used for the cladding portions 3 and 5 and the core portion 4 of such an optical waveguide may be basically a resin containing a siloxane bond in the polymer skeleton, such as polyphenylsilyl. Sesquioxane, polydiphenylsilsesquioxane, polymethylphenylsilsesquioxane, and the like can be used.

[0030]

Next, a specific example of the optical waveguide substrate of the present invention will be described.

Example 1 An organic solvent solution of polymethylphenylsilsesquioxane was applied by a spin coating method on an aluminum nitride substrate on which an intermediate layer made of a silicon oxide layer having a thickness of 10 nm was formed by a sputtering method. hand,
A heat treatment at 250 ° C. was performed to form a 5 μm-thick siloxane polymer film made of polymethylphenylsilsesquioxane as a lower cladding layer of the optical waveguide. When the adhesion strength between the siloxane polymer film and the aluminum nitride substrate was measured, it was about 15.7 N / mm ² .

On the other hand, the adhesion strength of the siloxane polymer film to the aluminum nitride substrate on which the silicon oxide layer is not formed is as follows:
It was about 5.9 N / mm ² or less. That is, the adhesion strength of the lower cladding layer in the embodiment of the present invention is a value that is 2.5 times or more as compared with the conventional one that does not use the intermediate layer as in the present invention. It was a sufficient value.

<Example 2> On an aluminum nitride substrate on which an intermediate layer made of a silicon oxide layer having a thickness of 10 nm was formed by a sputtering method, a cladding portion was made of a siloxane-based polymer and a core portion was made of a titanium-containing siloxane-based polymer. A step index optical waveguide was formed. At this time, the refractive indices of the core portion and the cladding portion were 1.444 and 1.440, respectively.
The width of the core portion was 8 μm, the height was 8 μm, and the thickness of the upper cladding layer above the core portion was 4 μm. The thickness of the lower cladding layer between the substrate and the core is 12μ.
m.

At this time, no peeling or cracking of the optical waveguide layer was observed during the fabrication. Also, in the chip separation by dicing after the formation of the optical waveguide, peeling of the optical waveguide layer was not observed. Further, no problem was found in the waveguide characteristics of the optical waveguide.

As described above, according to the present invention, it was confirmed that an optical waveguide substrate capable of fabricating an organic optical waveguide with sufficient adhesion strength on an aluminum nitride substrate could be provided.

It should be noted that the present invention is not limited to the above examples, and various changes and improvements can be made without departing from the spirit of the present invention.

[0037]

As described above, according to the optical waveguide substrate of the present invention, an organic optical material having a hydroxyl group or an alkyl group is formed on an aluminum nitride substrate with an intermediate layer made of silicon oxide or silicon interposed therebetween. By forming an organic optical waveguide using the layer as the lower cladding layer, the hydroxyl group at the end of the intermediate layer surface and the hydroxyl or alkyl group of the lower cladding layer constituting the optical waveguide are bonded by dehydration polymerization or dealcoholization polymerization. Thus, an optical waveguide substrate having an organic optical waveguide formed on an aluminum nitride substrate with sufficient adhesion strength was obtained.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view showing an example of an embodiment of an optical waveguide substrate according to the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Substrate 2 ... Intermediate layer 3 ... Lower cladding layer of optical waveguide 4 ... Core part of optical waveguide 5 ... Upper cladding layer of optical waveguide

Claims (2)

[Claims] 1. An optical waveguide comprising a substrate made of an aluminum nitride sintered body, an intermediate layer made of silicon oxide or silicon interposed, and a layer made of an organic optical material having a hydroxyl group or an alkyl group as a lower cladding layer. An optical waveguide substrate, wherein a waveguide is formed. 2. The optical waveguide substrate according to claim 1, wherein said organic optical material is a siloxane polymer.