JPH11211927A - Production of optical waveguide - Google Patents

Abstract

PROBLEM TO BE SOLVED: To easily produce an optical waveguide having a core region of a desired width (more particularly a very fine width). SOLUTION: A glass film for the core is formed on a glass layer by a step S10 and an etching mask is formed on the glass film for the core by steps S11 and S12. The glass film for the core is etched by gaseous c-C4 F8 via the etching mask and the core region is formed by a step S13. At the time of the etching, the gaseous c-C4 F8 is cracked and C2 F4 which is radical species is formed. The polymerized film of the C2 F4 is adhered to the flank of the core region as well. The polymerized film acts also as a protective film against etching.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for manufacturing an optical waveguide.

[0002]

2. Description of the Related Art With the development of optical communication technology, various optical devices have been developed. In addition, various optical devices are often formed on an optical waveguide. This is because the optical waveguide made of silica glass has a low loss, a small connection loss with an optical fiber as a transmission medium of signal light, and is excellent in mass productivity and reliability.

In such an optical waveguide, a high-refractive-index core glass film (eg, SiO ₂ —TiO ₂ ) is formed on a low-refractive-index substrate (eg, SiO ₂ ), and further formed on the core glass film. An etching mask having a predetermined shape is formed, and C ₂ F ₆
The glass film for the core is etched into a predetermined shape by using a mixed gas of CH ₂ and CHF _3, and a core region having a rectangular cross section and transmitting light is formed on the substrate (for example, see Japanese Unexamined Patent Application Publication No. No. 33106).

[0004]

[SUMMARY OF THE INVENTION However, in the etching in the above conventional example, since it is a mixed gas of C ₂ F ₆ and CHF _3, easy side of the core region is etched, created by etching The width of the core region is smaller than the width of the etching mask. Therefore,
It is difficult to manufacture an optical waveguide having a core region of a desired width, that is, an optical waveguide having a desired performance.

Further, since the width of the core region formed by etching becomes smaller by about 1 μm to 2 μm than the width of the etching mask, it is impossible to manufacture an optical waveguide having a core region having such a width.

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned problem, and an optical waveguide manufacturing method capable of easily manufacturing an optical waveguide having a core region having a desired width (particularly, a fine width) is provided. The purpose is to provide.

[0007]

According to the present invention, there is provided a method for manufacturing an optical waveguide, comprising: (1) a first step of forming a core glass film to be a core region on a glass layer; A second step of forming an etching mask on the glass film;
(3) The core glass film is c-C ₄
A third step of forming a core region by etching using F ₈ gas. The glass layer may be a substrate or a buffer glass film formed on the substrate.

According to this optical waveguide manufacturing method, a core glass film is formed on a glass layer in the first step,
In the second step, an etching mask is formed on the core glass film, and in the third step, the core glass film is etched by c-C ₄ F ₈ gas through the etching mask to form a core region. Is formed. In this etching, it is decomposed c-C ₄ F ₈ gas, C ₂ F ₄ is a radical species are generated, polymerization film of C ₂ F ₄ adheres to the side surface of the core region. This polymer film functions as a protective film against etching.

[0009]

Embodiments of the present invention will be described below in detail with reference to the accompanying drawings. In the description of the drawings, the same elements will be denoted by the same reference symbols, without redundant description.

(First Embodiment) First, a first embodiment will be described with reference to FIGS. 1 and 2. FIG. FIG. 1 is a flowchart illustrating an optical waveguide manufacturing method according to the first embodiment. FIG. 2 is a cross-sectional view after each step in the optical waveguide manufacturing method according to the first embodiment.

First, a substrate 11 is prepared. This substrate 1
1 is made of, for example, SiO ₂ . In step S10, a high refractive index core glass film 13 is formed on one surface of the substrate 11 (FIG. 2A). That is, glass particles having a predetermined composition are mixed with FHD (Flame hydrolysis depositio).
n) Deposition by the method, and this is carried out at 1300 ° C. to 1500 ° C.
The transparentized glass is used as a core glass film 13. For example, this core glass film 1
3 has a composition of SiO ₂ —GeO ₂ —B ₂ O ₃ —P ₂ O ₅ ,
The film thickness is 8 μm.

In step S11, the core glass film 13
A resist film 14 is applied on the substrate (FIG. 2B). The thickness of the resist film 14 is, for example, 10 μm. In step S12, the resist film 14 is exposed and developed using a general photolithography technique to form an etching mask 14A (FIG. 2C).

In step S13, the core glass film 13 is dry-etched through the etching mask 14A to form a core region 13A (FIG. 2D). In this etching, a c-C ₄ F ₈ gas having a ring structure is used as an etching gas. By this etching, a portion of the core glass film 13 below the etching mask 14A remains and becomes the core region 13A, and the other portions are removed. Further, by using c-C ₄ F ₈ gas as the etching gas, the amount of etching on the side surface of the core region 13A, that is, the amount of core thinning becomes small.

In step S14, the etching mask 1
The resist film remaining as 4A is removed (FIG. 2).
(E)). Then, in step S15, the cladding glass film 15 having a low refractive index is formed by the FHD method.
(F)). For example, the cladding glass film 15 has a composition of SiO ₂ and a thickness of 50 μm. The optical waveguide manufactured as described above has a core region 13A having a high refractive index embedded in a cladding region composed of a substrate 11 having a low refractive index and a glass film 15 for cladding.

Next, the optical waveguide manufacturing methods according to the present embodiment and the prior art will be compared. FIG. 3 is a table summarizing etching conditions and results in the optical waveguide manufacturing methods of the first embodiment and the prior art.

The etching conditions in the optical waveguide manufacturing method according to the prior art are as follows. The etching gas is C ₂ F ₆ (90 sc).
cm) and CHF ₃ (10 sccm), the power of the high-frequency electric field is 150 W, and the pressure of the etching gas is 4.0 Pa. When etching was performed under these conditions, the etch rate for SiO ₂ was 0.06 μm / min, and the core thinning amount was 2.0 μm.
Met.

On the other hand, the etching conditions in the optical waveguide manufacturing method according to the present embodiment are such that the etching gas is c-C ₄ F _8.
(100 sccm) and the power of the high-frequency electric field is 20
0 W, and the pressure of the etching gas is 5.0 Pa. When etching was performed under these conditions, SiO 2
_The etch rate for No. ₂ was 0.04 μm / min, and the core thinning amount was 0.25 μm. in this way,
According to the optical waveguide manufacturing method according to the present embodiment, as compared with the optical waveguide manufacturing method according to the related art, the core thinning amount is significantly reduced.

This can be explained as follows. That is, when c-C ₄ F ₈ gas is used as an etching gas, as shown in FIG. 4, the c-C ₄ F ₈ gas is decomposed in a high-frequency electric field to generate C ₂ F ₄ as a radical species. Is done.
This C ₂ F ₄ is easily polymerized to form a fluorocarbon film, and as shown in FIG. 5, the polymerized film also adheres to the side surface of the core region 13A. Since this polymer film acts as a protective film against etching, the core region 13A
The amount of etching on the side surface of is reduced, and the amount of core thinning is reduced.

(Second Embodiment) Next, a second embodiment will be described with reference to FIGS. The optical waveguide manufacturing method according to this embodiment is different from the first embodiment in that a buffer glass film is formed between a substrate and a core region. FIG. 6 is a flowchart for explaining the optical waveguide manufacturing method according to the second embodiment.
FIG. 7 is a cross-sectional view after each step in the optical waveguide manufacturing method according to the second embodiment.

First, a substrate 21 is prepared. This substrate 2
1 is made of, for example, SiO ₂ . In step S20, a low refractive index buffer glass film 22 is formed on one surface of the substrate 21. That is, glass fine particles having a predetermined composition are deposited by the FHD method,
The transparentized glass is heat-treated at 500 ° C., and the transparentized glass is used as the buffer glass film 22. For example, the composition of the buffer glass film 22 is SiO ₂ . In the following step S21, a core glass film 23 having a high refractive index is formed on the buffer glass film 22 (FIG. 7A). At this time, similarly, the core glass film 23 is formed by deposition of glass fine particles by the FHD method and transparency by the heat treatment.
For example, the core glass film 23 has a composition of SiO ₂ —GeO.
_2- B ₂ O ₃ -P ₂ O ₅ , and the film thickness is 8 μm.

In step S22, the core glass film 23
A resist film 24 is applied on the substrate (FIG. 7B). The thickness of the resist film 24 is, for example, 10 μm. In step S23, the resist film 24 is exposed and developed using a general photolithography technique to form an etching mask 24A (FIG. 7C).

In step S24, the core glass film 23 is dry-etched through the etching mask 24A to form a core region 23A (FIG. 7D). In this etching, a c-C ₄ F ₈ gas is used as an etching gas. By this etching, a portion of the core glass film 23 below the etching mask 24A remains and becomes the core region 23A, and other portions are removed. Also, by using c-C ₄ F ₈ gas as an etching gas,
The etching amount on the side surface of the core region 23A, that is, the core thinning amount is small.

In step S25, the etching mask 2
The resist film remaining as 4A is removed (FIG. 7).
(E)). Then, in step S26, a low refractive index clad glass film 25 is formed by the FHD method.
(F)). For example, the cladding glass film 25 has a composition of SiO ₂ and a thickness of 50 μm. The optical waveguide manufactured in this manner has a core region 23A having a high refractive index embedded in a cladding region composed of a buffer glass film 22 and a cladding glass film 25 having a low refractive index.

A comparison between the optical waveguide manufacturing method according to the present embodiment and the optical waveguide manufacturing method according to each of the prior arts shows that the optical waveguide manufacturing method according to the present embodiment has a sufficient The amount of thinning was significantly reduced.

[0025]

As described in detail above, according to the present invention, the core glass film is formed on the glass layer in the first step, and the core glass film is formed in the second step. An etching mask is formed thereon, and in the third step, the glass film for the core is c-
The core region is formed by etching with the C ₄ F ₈ gas. In this etching, it is decomposed c-C ₄ F ₈ gas, C ₂ F ₄ is a radical species are generated, polymerization film of C ₂ F ₄ adheres to the side surface of the core region. This polymer film functions as a protective film against etching. Therefore, the etching amount on the side surface of the core region is reduced, and the core thinning amount is reduced. That is, an optical waveguide having a core region having a desired width (particularly, a fine width) can be easily manufactured.

[Brief description of the drawings]

FIG. 1 is a flowchart illustrating an optical waveguide manufacturing method according to a first embodiment.

FIG. 2 is a cross-sectional view after each step in the optical waveguide manufacturing method according to the first embodiment.

FIG. 3 is a table summarizing etching conditions and results in the optical waveguide manufacturing methods of the first embodiment and the conventional technology.

FIG. 4 is a diagram illustrating decomposition of c-C ₄ F ₈ gas into C ₂ F ₄ .

FIG. 5 is a diagram illustrating the formation of a C ₂ F ₄ polymerized film.

FIG. 6 is a flowchart illustrating an optical waveguide manufacturing method according to a second embodiment.

FIG. 7 is a cross-sectional view after each step in an optical waveguide manufacturing method according to a second embodiment.

[Explanation of symbols]

11: substrate, 13: glass film for core, 13A: core region, 14: resist film, 14A: etching mask, 1
5: clad glass film, 21: substrate, 22: buffer glass film. 23: core glass film, 23A: core region, 24: resist film, 24A: etching mask, 2
5 ... Glass film for cladding.

Claims (2)

[Claims] 1. A first step of forming a core glass film to be a core region on a glass layer, a second step of forming an etching mask on the core glass film, and the etching mask Through the core glass film c-
A third step of forming a core region by etching using a C ₄ F ₈ gas. 2. The method according to claim 1, wherein the glass layer is a buffer glass film formed on a substrate.