JP2001154044A - Optical waveguide substrate - Google Patents

Abstract

PROBLEM TO BE SOLVED: To solve the problems that peelings or cracks are easily generated owing to the concentration of stresses in corner parts of the outside surface of the clad part in an optical waveguide, consisting of siloxane group polymer formed on a substrate and the reliability for the optical waveguide substrate is low. SOLUTION: In this optical waveguide substrate 6, where a three-dimensional waveguide shaped optical waveguide 4 provided with a clad part 2 made of siloxane group polymer having the outside surface nearly orthogonal to the upper surface and a core part 3 made of siloxane group polymer in the clad part 2 is formed on the upper surface of the substrate 1, the clad part 2 is provided with 2 μm or larger width between the outside surface and the core part 3, and respective corner parts 2a, 2b of the outside surface are provided with 20 μm or larger radius of curvature. Thus, stresses for the corner parts 2a, 2b of the clad part 2 are dispersed effectively and satisfacorily, and a highly reliable optical waveguide substrate 6, in which the film peeling from the corner parts 2a, 2b of the clad part 2 or cracks are difficult to generate, is obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical communication connection between optoelectronic circuit boards such as an optical communication system and a computer or an optical signal conversion area between optoelectronic elements in an optoelectronic circuit board. With respect to the optical waveguide substrate having a waveguide formed thereon, in particular, stress concentration on the cladding portion of the optical waveguide using a siloxane-based polymer as an optical material is relieved, and peeling and cracking of the cladding portion from the substrate are less likely to occur. The present invention relates to a highly reliable optical waveguide substrate.

[0002]

2. Description of the Related Art In response to demands for high-speed and large-capacity information processing in optical communication systems, computers, and the like, there is a limitation on the transmission capacity of information only with electric signals and the speed-up due to electromagnetic induction or the like. For signal transmission between circuit elements, between circuit boards on which they are mounted, or between boards on which a plurality of circuit boards are integrated, the use of optical signal transmission has been actively promoted. In this case, since the processing of the transmitted signal is performed by electronic components, it is necessary to perform signal conversion between an optical signal and an electric signal for information processing using optical signal transmission.

[0003] In such a signal conversion region between an optical signal and an electric signal, a transmission path of an optical signal by an optical fiber or an optical waveguide, an optoelectronic conversion element such as a laser diode or a photodiode, an optoelectronic conversion element and an electronic circuit are provided. High-speed driving of integrated circuit elements and electronic components such as combined OEICs (optical integrated circuits), optical ICs that process information only with optical signals, and ICs and LSIs for controlling electronic elements and processing electrical signals. High frequency electric circuits and the like are mixed.

Conventionally, a module assembled from individual optical components and electronic components has been used in such a signal conversion region between an optical signal and an electric signal. In order to achieve further high-density mounting of optical components and electronic components and high efficiency of optical connection, a photoelectric conversion element such as a light emitting / receiving element and an optical waveguide, a light emitting / receiving control LSI and an OEIC.
Research on practical use of opto-electronic mixed board called OE-MCM, in which integrated circuit elements such as optical IC / OEIC control LSIs and high-frequency electric circuits are mixed. Development is underway.

As an optical waveguide having a three-dimensional waveguide shape used in the OE-MCM, an optical waveguide made of an inorganic optical material, for example, a silica film formed on a quartz glass substrate or a silicon substrate by a flame volume method is conventionally used. Using a silica-based optical waveguide or a lithium niobate single crystal as a cladding part with a three-dimensional cladding and core part formed by using it, titanium is thermally diffused on this three-dimensional waveguide on this substrate to form a core part. Optical waveguides and the like are used.

However, such an optical waveguide made of an inorganic optical material has a problem that it requires a heat treatment at a high temperature of 1000 ° C. or more at the time of production, so that it is not easy to produce and there is a great restriction on a substrate material and the like. Therefore, use of an optical waveguide made of an organic optical material capable of forming a film at low temperature on various substrates is being studied instead of the optical waveguide made of the inorganic optical material. As such organic optical materials, siloxane-based polymers, polyimides, benzocyclobutenes, PMMA (polymethyl methacrylate), and the like have been studied. Among them, siloxane-based polymers have excellent optical properties and costs, and are practically used. Expected.

[0007]

However, for an optical waveguide made of a siloxane-based polymer as described above, the support substrate is generally made of single-crystal silicon, quartz glass, or ceramics. It has a smaller coefficient of thermal expansion as compared with the base polymer. Au-Sn solder is generally used for mounting optical components,
At the time of mounting, it is about 50 ° C higher than its melting point of about 280 ° C33
Since the optical waveguide substrate is heated to about 0 ° C., the thermal stress between the substrate and the optical waveguide increases due to the difference in the coefficient of thermal expansion accompanying the heat treatment at the time of this mounting. The four corners of the outer surface of the vertically formed optical waveguide layer and the outer surface corners of the four corners of the opening provided in the optical waveguide layer for mounting elements such as optical components on the optoelectronic mixed substrate are included. In addition, thermal stress concentrates on the tip of the corner, and there is a problem that the optical waveguide layer is easily peeled from this portion or cracks of the optical waveguide layer are easily generated.

The present invention has been devised in view of the above-mentioned problems in the prior art, and has as its object to concentrate stress on a corner of an outer surface of an optical waveguide made of a siloxane-based polymer formed on a substrate. It is an object of the present invention to provide a highly reliable optical waveguide substrate having a structure in which film peeling or cracking of an optical waveguide layer is less likely to occur.

[0009]

According to the present invention, there is provided an optical waveguide substrate comprising a siloxane-based polymer clad portion having an outer surface substantially perpendicular to the upper surface of the substrate, and a siloxane-based polymer in the clad portion. Having a core part made of
In the optical waveguide substrate formed with a two-dimensional waveguide shape optical waveguide, the clad portion has a width of 20 μm or more between the outer surface and the core portion, and each corner of the outer surface has a width of 20 μm. It is characterized by having the above radius of curvature.

[0010]

DESCRIPTION OF THE PREFERRED EMBODIMENTS According to the optical waveguide substrate of the present invention,
In an optical waveguide substrate in which an optical waveguide made of a siloxane-based polymer is formed on a support substrate of an optical waveguide layer, an outer surface of the cladding portion of the waveguide layer that is substantially perpendicular to the substrate and an outer surface of the cladding portion and the core portion Between the outer surface of the cladding portion and the outer end of the cladding portion, the radius of curvature of which is 20 μm or more. With the addition of, stress on each of these corners is dispersed,
As a result, a highly reliable optical waveguide substrate in which an optical waveguide made of a siloxane-based polymer in which film peeling or cracking from corners is less likely to be formed is formed.

Hereinafter, an optical waveguide substrate according to the present invention will be described with reference to the drawings.

FIG. 1 is a perspective view showing an example of an embodiment of an optical waveguide substrate according to the present invention, and FIG.
(B) is a sectional view thereof. In these figures, a clad 2 made of a siloxane polymer and having different refractive indices and a clad 2 are formed on a substrate 1 as a support substrate.
An optical waveguide 4 having a core portion 3 formed therein is formed, and an optical signal is transmitted through the core portion 3. The optical waveguide 4 is provided with an opening 5 in the middle of the core 3 for inputting / outputting an optical signal and mounting an optoelectronic element or the like (not shown) for controlling the input / output. .
In FIG. 1, a part of the cladding part 2 is seen through, and the substrate 1 and the core part 3 in that part are shown by broken lines. These constitute the optical waveguide substrate 6 of the present invention.

In the optical waveguide substrate 6 according to the present invention, the clad portion 2 has an outer surface substantially perpendicular to the upper surface of the substrate 1, and the clad portion 2 is formed between the core portion 3 and the outer surface surrounding the core portion. In addition, each of the corners 2a of the outer surface on the outer peripheral side and each of the corners 2b of the outer surface on the opening 5 side in this example.
Are characterized in that each of them has an arc shape having a radius of curvature of 20 μm or more. Thus, when each corner is substantially right angle as in the conventional case, the concentration of stress on the corner is remarkable, but the stress can be dispersed and relieved, and each corner of the clad portion 2 can be relaxed. Peeling from 2a and 2b and generation of cracks can be effectively prevented.

In the optical waveguide substrate 6 of the present invention, the substrate 1
Serves as a support substrate for the optical waveguide 4, and various substrates used as substrates for handling optical signals, such as an optical integrated circuit substrate and a photoelectric mixed substrate, such as a silicon substrate, an alumina ceramic substrate, a glass ceramic substrate, and a multilayer A ceramic wiring board or the like can be used.

The cladding 2 and the core 3 of the optical waveguide 4
Is formed from a siloxane-based polymer. For example, the siloxane-based polymer film forming solution used for the preparation may be a siloxane-based polymer having a phenyl group or a methyl group at an end group, an alkyl group such as a butyl group or a propyl group, or a phenyl group.・ Synthesis of siloxane-based polymer having an aryl group such as a tolyl group, a functional group partially substituted with fluorine, a hydroxyl group, etc. at the end group with propylene glycol monoether or 3methoxy-3-methyl-1-butanol / ethylene glycol monomethyl ether It is preferable to use a mixed solution.

As the metal alkoxide to be added to the siloxane-based polymer film forming solution, for example, tetra-n
-Butoxytitanium, tetramethoxytitanium, tetrapropoxytitanium, tetramethoxygermanium, tetraethoxygermanium, tetraethoxygermanium, trimethoxyerbium, among which alcoholates of the same metal type have a large number of C (carbon). When it is used, it is preferable because it has better chemical stability than those having a small number of C, and hardly causes gelation upon mixing and can be easily mixed.

The amount of addition of the metal alkoxide is determined by measuring the refractive index of the polymer film with respect to the amount of addition of the metal alkoxide in advance with respect to the siloxane-based polymer film forming solution obtained by combining each of the raw materials. What is necessary is just to set to a desired addition amount.

As a method and conditions for adding the metal alkoxide, for example, the alcoholate may be diluted with a sufficient amount of alcohol and mixed with the siloxane-based polymer film forming solution while refluxing. The alcohol used at this time is preferably the same as the alcohol of the alcoholate.

By adding the metal alkoxide to the siloxane-based polymer film forming solution as described above, the metal alkoxide is mixed at an arbitrary ratio into the siloxane-based polymer film forming solution to form a metal-containing siloxane-based polymer film. And the refractive index of the optical waveguide can be controlled.

After the siloxane-based polymer film forming solution is applied onto a substrate by a coating method such as a spin coating method, a dip coating method, or a roller coating method, a heat treatment at about 270 ° C. is performed using, for example, an oven or a hot plate. By carrying out the thermal polymerization, the crosslinking reaction of the siloxane bond proceeds to obtain a silica-based siloxane-based polymer film.

In order to form the optical waveguide 4 from such a siloxane-based polymer, the dimensions of the core portion 3 are usually determined in consideration of the connection between the core portion 3 and an optical fiber for exchanging optical signals with an external optical circuit. About 3 μm or more is required. Also,
To reduce light leakage, the overall thickness is about 10 μm
It is good to do above.

The siloxane-based polymer film obtained as described above usually has an internal stress of about 20 MPa, and the thickness of the clad portion made of the siloxane-based polymer is about 10 μm.
In the above case, that is, when the total stress is about 200 N / m or more, if the corner of the outer surface of the clad part 2 is substantially perpendicular,
The stress overcomes the adhesive strength between the clad portion 2 and the substrate 1, causing film peeling and cracking at the tip of the corner. Actually, when the corners of the outer surface of the cladding part 2 are substantially perpendicular, stress is concentrated more than about 200 N / m, and as a result of performing a numerical calculation by the finite element method, about 325 N / m Since film peeling and cracks occur at m, it is estimated that more stress is concentrated.

When the corners of the cladding 2 are perpendicular to each other, the concentration of stress on the tip of the corners is caused by the fact that one side forming the corners on the plane of the film of the cladding 2 is perpendicular to the side. And the same force is also generated on the other side, and the two forces are applied to the vertices of the corners. It is to be noted that such stress concentration on the corner portion is caused by a force for compressing the corner portion 2a at a portion such as the corner portion 2a of the clad portion 2 having a tip facing outward on the outer surface. Peeling tends to occur. On the other hand, in a portion such as the corner 2b corresponding to the opening corner of the opening 5 on the outer surface, a pulling force acts on the corner 2b.
Cracks tend to occur, and thereafter, peeling is likely to occur from the cracked portions.

In order to reduce such concentration of stress,
By making the structure of the corner portion of the outer surface of the clad portion 2 an arc shape having a predetermined radius of curvature, it is possible to prevent stress from being concentrated at one point of the corner vertex and to disperse the stress. Becomes FIG. 3 is a diagram showing the results of numerical calculations performed on such a model.

In FIG. 3, the abscissa represents the radius of curvature R (unit: μm) of the arc portion provided at the corner of the outer surface of the cladding portion 2 made of a siloxane polymer, and the ordinate represents the corner at that time. The maximum value (unit: N / m) of the calculated total stress is shown, and a black square and a solid line connecting them indicate a change in the total stress with respect to the radius of curvature R. From the results shown in FIG. 3, it can be seen that the stress is dispersed and the total stress becomes smaller as the radius of curvature R of the corner becomes larger. In particular, by setting the radius of curvature to 20 μm or more, the total stress becomes 300 N / m, which is smaller than about 325 N / m, which is the total stress at which peeling or cracking occurs in the cladding portion made of the siloxane-based polymer.

Also, from the examples described below, the outer corners of the cladding portion of the optical waveguide having a thickness of 10 μm or more made of a siloxane-based polymer are formed in an arc shape, and the radius of curvature R is set to 20 μm or more. By doing so, it was found that the concentration of stress on the corners was alleviated, and peeling and cracking of the clad could be effectively prevented.

Further, in order to ensure sufficient adhesion of the clad portion 2 to the upper surface of the substrate 1, the corner portion of the outer surface has a radius of curvature of 20 μm or more, and the outer surface and the core portion When a plurality of core portions are formed, it is preferable to secure a width between the outermost core portion and the outermost core portion of 20 μm or more, whereby the cladding portion made of a siloxane-based polymer is separated from the substrate. It has been found that the generation of cracks and cracks can be more effectively prevented, and a highly reliable optical waveguide substrate can be obtained.

If the width between the outer surface of the clad portion and the core portion is not less than 20 μm, it does not particularly affect the concentration of stress on the corners. Therefore, depending on the purpose and specifications of the optical waveguide substrate, In addition, a necessary dimension may be used so that each corner of the clad has a desired radius of curvature.

The radius of curvature of each corner of the cladding is:
If it is 20 μm or more, the occurrence of peeling and cracks is sufficiently suppressed, and from the results shown in FIG. 3, the total stress applied to the corners decreases as the radius of curvature increases, and becomes saturated when the radius of curvature exceeds a certain level. It can be seen that the value approaches a certain value. Normally, if the radius of curvature is 500 μm or more, there is almost no change in the reduction of the total stress, which is negligible in practical use. Accordingly, it is sufficient that the radius of curvature of each corner of the cladding is 20 μm or more and up to about 500 μm.

[0030]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, specific examples of the optical waveguide substrate of the present invention will be described.

First, a siloxane-based polymer solution was applied on an alumina support substrate, and heat-treated at 85 ° C./30 minutes and 270 ° C./30 minutes to form a 15 μm-thick cladding layer (refractive index 1.44).
05, λ = 1.3 μm).

Next, a siloxane-based polymer and tetra-n-
A 6 μm-thick core layer (refractive index: 1.4450, λ = 1.3 μm) was formed using a mixed solution with butoxytitanium.

Subsequently, an aluminum film having a thickness of 0.5 μm serving as a mask when processing the core portion is formed by a sputtering method, and a line width 3 serving as a pattern of the core portion is formed thereon.
A μm resist pattern was formed by photolithography.

Next, the aluminum film was etched with a mixed solution of phosphoric acid-acetic acid-nitric acid to obtain an aluminum pattern to which a resist pattern was transferred.

Next, after removing the resist, RIE
The core portion was patterned by the (reactive ion etching) method. Here, the RIE condition is oxygen 60
Sccm, pressure 5 Pa, output 600 W, and a substantially rectangular core section were formed.

Thereafter, the aluminum pattern is removed,
In the same manner as above, the cladding layer (refractive index 1.4405, λ = 1.3
μm).

Subsequently, a 0.5 μm-thick aluminum film serving as a mask was formed by sputtering in the same manner as in the core processing when the opening was processed, and a resist pattern in the opening was formed by photolithography. And
Each of the corners of the cladding portion made of a siloxane-based polymer is provided with an arc shape, and the radius of curvature is
30 μm, 25 μm, 20 μm, 15 μm, 10 μm, 5 μm and right angles were prepared. The opening size of the opening was 1000 μm × 300 μm.

Next, the aluminum film was etched with a mixed solution of phosphoric acid-acetic acid-nitric acid to obtain an aluminum pattern to which a resist pattern was transferred.

Next, after removing the resist, patterning was performed by the RIE method. Here, the RIE conditions were oxygen 60 sccm, pressure 5 Pa, output 600 W, and a core part having a substantially rectangular cross section was formed.

As described above, the size of the core portion is 3 μm × 3
μm, the refractive index of the core is 1.4450, and the refractive index of the cladding is
Each sample of an embedded optical waveguide made of a siloxane-based polymer having a total thickness of 1.4405 and a cladding of 10 μm was prepared. The width of the clad between the outer surface of the clad and the core was about 3 mm.

A heat resistance test was conducted using these samples. As a test method, the optical waveguide substrate was placed on a hot plate, a thermocouple was placed on the hot plate, and the temperature was monitored to 330 ° C while monitoring the temperature. Was evaluated by observing with a binocular microscope. The results are as shown in Table 1.

[0042]

[Table 1]

As can be seen from the results shown in Table 1, cracks were generated at the corners of the clad portion in the samples having the curvature radii of right angles, 5 μm and 10 μm, and film peeling was observed around the corners.
At 15 μm, there was slight but partial film peeling and cracking, and the reliability of the optical waveguide substrate was insufficient. On the other hand, if the radius of curvature is 20 μm or more,
No cracks were seen.

From the above results, for the optical waveguide having a cladding portion made of a siloxane-based polymer having a thickness of 10 μm or more, the shape of the corner of the outer surface of the cladding portion substantially perpendicular to the substrate has a curvature radius R of 20 μm. In the case of the above, it was confirmed that the concentration of stress on the corners was reduced, and the occurrence of film peeling and cracking at the corners on the outer surface of the clad portion could be effectively prevented.

It should be noted that the above is merely an example of the embodiment of the present invention, and the present invention is not limited to the embodiment. Various modifications and improvements may be made without departing from the gist of the present invention. No problem.

[0046]

As described above, according to the optical waveguide substrate of the present invention, a cladding portion made of a siloxane-based polymer having an outer surface substantially perpendicular to the upper surface of the substrate is formed on the upper surface of the substrate. An optical waveguide substrate comprising a three-dimensional optical waveguide having a core portion made of a siloxane-based polymer having a width of at least 20 μm between the outer surface and the core portion. In addition, since each corner of the outer surface has a radius of curvature of 20 μm or more, stress on the corner of the outer surface of the cladding is effectively and sufficiently dispersed, and as a result, the outer portion of the cladding is It is possible to provide a highly reliable optical waveguide substrate in which peeling or cracking does not easily occur from the corners of the side surface.

[Brief description of the drawings]

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

FIGS. 2A and 2B are a plan view and a cross-sectional view of the optical waveguide substrate shown in FIG. 1, respectively.

FIG. 3 is a diagram showing a relationship between a radius of curvature R and a total stress at a corner of an outer surface of a clad portion of the optical waveguide.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Substrate 2 ... Cladding part 2a, 2b ... Corner part 3 ... Core part 4 ... Optical waveguide 5 ... Opening 6 ... Optical waveguide board

Claims (1)

[Claims] 1. A three-dimensional waveguide comprising, on an upper surface of a substrate, a siloxane-based polymer clad portion having an outer surface substantially perpendicular to the upper surface, and a siloxane-based polymer core portion in the clad portion. In the optical waveguide substrate formed with a shaped optical waveguide, the clad portion has a width of 20 μm or more between the outer surface and the core portion,
An optical waveguide substrate, wherein each corner of the outer surface has a radius of curvature of 20 μm or more.