JPH11237518A - Manufacture of optical waveguide - Google Patents

Abstract

PROBLEM TO BE SOLVED: To make reducible the number of processes without damaging a core layer by exposing a poly methyl methacrylate(PMMA) layer to deep ultraviolet light by using a mask and then forming an optical waveguide layer by directly etching the exposed part of the PMMA layer by using etching gas. SOLUTION: The PMMA layer 12 is formed on a base 10 and a glass substrate for instance is used as the base 10. Then, the mask 14 for patterning is used and the PMMA layer 12 is exposed to the deep ultraviolet light. In this case, the mask pattern 14 is tightly adhered to the PMMA layer 12 and exposure is performed. Then, the exposed part of the PMMA layer 12 is etched and removed by using methyl methacrylate. For that, for instance, the glass substrate 10 is carried into a gas etching furnace and the PMMA layer 12 is etched. As a result, an optical waveguide 16 composed of the remaining PMMA layer 12 is formed. Then, a clad layer 18 is formed on the upper surface of the glass substrate 10 provided with a core pattern 16.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a method for manufacturing an optical waveguide.

[0002]

2. Description of the Related Art An optical waveguide device used for optical communication is for branching and coupling an optical path. As such an optical waveguide device, an optical fiber coupling element or a flat plate optical circuit (PLC) made of quartz is currently used. Optical waveguides used in these devices are required to have low propagation loss and heat resistance. In recent years, attention has been paid to an optical waveguide using a polymer material to meet such a demand.

As an example of an optical waveguide using a polymer material, see, for example, Document I (IEICE Technical Report, TECHNICAL).
REPORT OF 1EICE. , OME97-8
5, OPE97-74 (1997-10). According to Document I, a UV-curable epoxy resin or deuterated polymethyl methacrylate (abbreviation: d-PMMA) is used as a core layer. In a conventional optical waveguide using an epoxy resin for a core layer, a core pattern is formed by etching a core layer by a photolithography technique using a resist film.

[0004]

However, according to the conventional method of manufacturing an optical waveguide, there is a problem that the core layer is easily damaged by photolithography or the O ₂ -RIE.

In the case where a core pattern is formed using the above-described resist film, a step of forming a resist mask by photolithography is required, so that the number of steps is increased. For this reason, the cost was increased.

Therefore, there has been a demand for an optical waveguide manufacturing method capable of reducing the number of steps without damaging the core layer.

[0007]

Therefore, according to the method of manufacturing an optical waveguide of the present invention, a step of forming a polymethyl methacrylate (PMMA) layer on a base, and a step of deepening the polymethyl methacrylate layer using a mask. Ultraviolet light (D
(e.g., deep UV light) and a step of etching away the exposed portion of the polymethyl methacrylate layer using methyl methacrylate (MMA) gas.

As described above, the PMMA layer is exposed to the deep UV light using the mask, and then the exposed portion of the PMMA layer is directly etched using the etching gas to form the optical waveguide layer (core pattern). Only two steps are required to form the optical waveguide layer. For this reason, the number of steps can be significantly reduced as compared with the related art. Further, since the present invention does not use the photolithography technology or the reactive ion etching technology as in the related art, the PMMA layer serving as the core layer is not damaged.

[0009]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of a method for manufacturing an optical waveguide according to the present invention will be described below with reference to the drawings. It should be noted that the drawings merely schematically show the size, shape, and arrangement relationship of each component to the extent that the present invention can be understood. Therefore, the present invention is not limited to the illustrated examples. Absent.

Referring to FIG. 1, a method of manufacturing an optical waveguide according to the present invention will be described. FIGS. 1A, 1B, and 1C are views for explaining a manufacturing process of the optical waveguide of the present invention, and show a cut at a position cut along a direction orthogonal to the optical waveguide. FIG.

In the present invention, first, a polymethyl methacrylate (PMMA) layer 12 is formed on a base 10. In this example, a glass substrate is used as the base 10. Here, a commercially available substrate (trade name: 7059, manufactured by Corning Incorporated) is used as the glass substrate 10.

In this embodiment, as a coating material of the PMMA layer 12, PMA is applied so that 15 wt% of PMMA is obtained.
MMA is dissolved in, for example, 2-methoxyethyl acetate (solvent). This PMMA coating solution is applied on the glass substrate 10 by using a spin coating method. Thereafter, the glass substrate 10 is heated at a temperature of about 80 ° C. to dry the PMMA layer 12. Here, the thickness of the PMMA layer 12 may be a thickness that functions as an optical waveguide. In this example, this film thickness is about 5.5 μm. In this example, the optimum film thickness was 5.5 μm, but a preferable film thickness is 4 to 6 μm.
It is sufficient if it is within the range.

Next, in the present invention, the PMMA layer 12 is exposed to deep ultraviolet light using a patterning mask (also referred to herein as a pattern mask) 14. In FIG. 1A, the pattern mask 14 is formed by PMMA.
Although drawn separately from the layer 12, in practice, exposure is performed with the mask pattern 14 in close contact with the PMMA film 12.
A high-pressure mercury lamp is used as a light source for exposure. As the exposure light at this time, deep ultraviolet light (Deep) from a high-pressure mercury lamp was used.
UV light). The exposure wavelength of this lamp is 200 to 300 nm. And
Deep UV light is applied to the PMMA layer 12 for 15 minutes (FIG. 1A). Such Deep UV light is converted to PMM
By irradiating the A layer 12, the polymer of the PMMA layer 12 is decomposed.

Next, in the present invention, the exposed portion of the PMMA layer 12 is removed by etching using methyl methacrylate. For this reason, in this example, the glass substrate 10 is carried into a gas etching furnace (a reduced-pressure bell jar), and the PMMA layer 12 is etched. The etching conditions at this time are as follows.

Gas pressure: about 6.7 Pa (50 × 10 ⁻³ Torr) Etching gas: methyl methacrylate (MMA) Processing time: about 60 minutes Temperature: room temperature (about 25 ° C.) The above etching conditions are optimal. It is a condition, and as a preferable range, the gas pressure is 6.7 to 40.2 Pa.
(50 to 300 mTorr). With such a gas pressure, the pattern accuracy does not substantially deteriorate. Also, the processing time is only an optimal example,
It is necessary to change the processing time depending on the line width or etching depth of the core pattern.

By such an etching process, the PMM
The exposed area of the A layer 12 is etched away. As a result, an optical waveguide layer 16 made of the remaining PMMA layer is formed (FIG. 1B). Here, the optical waveguide layer 1
6 is also called a core pattern.

Next, the core pattern 16 is formed by a known technique.
The cladding layer 18 is formed on the upper surface of the glass substrate 10 containing (FIG. 1C).

The optical waveguide is completed through the steps described above.

Next, referring to FIGS. 1, 2 and 3,
The difference between the manufacturing method of the present invention and the conventional manufacturing method will be described. FIG. 2 and FIG. 3 are cross-sectional views of the cut surface at positions cut along a direction orthogonal to the optical waveguide for explaining a conventional process.

In the conventional process, a silicon (Si) substrate 5
The lower clad layer 52 and the core layer 54 are formed on the lower layer 0. As the core layer 54, a UV curable epoxy resin is used. Next, a resist film 56 is formed on the core layer 54 to form an etching mask. Note that a well-known process is used as a process for forming the resist film 56.

That is, any suitable resist is selected,
This resist is applied on the core layer 54 by using a spin coating method. Thereafter, the resist film 56 is dried (about 80
C.) (FIG. 2A).

Next, using a mask 58 similar to that of the present invention, a resist mask 6 is formed by photolithography.
0 (FIGS. 2B and 2C). In this photolithography step, exposure and development are required.
Next, a baking process is performed to remove the solvent of the resist mask 60.

Next, oxygen reactive ion etching (O ₂
The core layer 54 is etched by (RIE etching) to remove the exposed core layer 54 other than the resist mask 60 (FIG. 3A). At this time, a core pattern 62 is formed on the lower surface of the resist mask 60. After that, the resist mask 60 is removed using any suitable solvent (FIG. 3B). Thus, a stripe-shaped core pattern 62 is formed on the lower cladding layer 52.

Next, an upper clad layer 64 is formed on the lower clad layer 52 including the core pattern 62 to complete the optical waveguide (FIG. 3C).

A comparison between the process of the present invention and the conventional process shows that, in the conventional process, the UV-curable epoxy resin is used as the core layer, whereas the PMMA layer 12 is used as the core layer of the present invention. Used. Further, the same mask is used as the pattern mask 14 (FIG. 1A) used in the present invention and the pattern mask 58 (FIG. 2B) used in the conventional photolithography process.

As can be understood from the conventional process and the process of the present invention, conventionally, a resist mask 60 is formed and a core layer 54 is formed.
Although it was necessary to perform patterning,
Since the PMMA layer is used, a core pattern can be formed only by performing UV light exposure and gas etching using an MMA gas. Therefore, conventionally, as described above, the core pattern 62 is formed through seven steps of resist coating, resist drying, resist exposure, development, resist mask baking, oxygen reactive ion etching, and resist mask removal. Was. On the other hand, according to the present invention, the core pattern 16 can be formed by two steps of UV light exposure and gas etching of the PMMA layer.

Therefore, comparing the numbers of steps of the two, according to the present invention, it is possible to reduce the number of steps to about 30% as compared with the prior art.

According to the results of microscopic observation by the inventors of the present invention, when a 50 μm stripe-shaped core pattern 16 is formed on the glass substrate 10, the accuracy of ± 1 μm or less with respect to the design value is obtained. Have been obtained.

In the above-described embodiment, a glass substrate is used as a substrate material. However, the present invention is not limited to this material. For example, a base having a silicon oxide film formed on a silicon substrate may be used. .

Further, the concentration or solvent of PMMA used in the embodiment is merely an example, and the concentration of PMMA may be arbitrarily changed in order to obtain a predetermined thickness of the PMMA layer.

[0031]

As is clear from the above description, according to the method for manufacturing an optical waveguide of the present invention, an optical waveguide layer can be formed by two steps of exposure and gas etching. Thus, the number of steps can be significantly reduced. Further, in the process of the present invention, since a photolithography technique or a reactive ion etching technique is not used as in the related art, damage to the core layer can be reduced.

[Brief description of the drawings]

FIGS. 1A to 1C are cross-sectional views for explaining a method for manufacturing an optical waveguide of the present invention.

FIGS. 2A to 2C are cross-sectional views for explaining a process of manufacturing a conventional optical waveguide.

3 (A) to 3 (C) are cross-sectional views provided to explain a conventional process following the process of FIG. 2;

[Explanation of symbols]

 10: Glass substrate 12: PMMA layer 14: Mask 16: Optical waveguide layer (core pattern) 18: Cladding layer

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Katsuaki Kaifu 1-7-12 Toranomon, Minato-ku, Tokyo Oki Electric Industry Co., Ltd.

Claims (1)

[Claims] 1. A step of (a) forming a polymethyl methacrylate (PMMA) layer on a base, (b) exposing the polymethyl methacrylate layer to deep ultraviolet light using a mask, and (c) methacrylic Etching the exposed portion of the polymethyl methacrylate layer using an acid methyl gas.