JPH09297238A - Production of optical waveguide - Google Patents

Abstract

PROBLEM TO BE SOLVED: To flatten the surface of a substrate where a core is to be formed or a buffer layer and to prevent deterioration in the transmission loss by coating a substrate with a resist layer and removing the surface of the resist layer and the surface of the substrate by dry etching to flatten the substrate surface. SOLUTION: A planar quartz substrate 10 is prepared (a). An almost flat resist layer 1 is formed on the surface of the quartz substrate 10 (b). The surface of the resist layer 1 is etched to an etching face 93 where scratches or rugged state on the surface of the quartz substrate 10 appear (c). Then the quartz substrate 10 and the resist layer 1 are etched at the same time. If etching is carried out under conditions to give different etching rates for the quartz glass and the resist, it increases rugged state. Therefore, conditions to give an equal etching rate for both are selected so that etching is continued while a flat surface is maintained. As a result, the surface of the quartz substrate 10 can be flattened (d).

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a method for manufacturing an optical waveguide used in an optical communication system.

[0002]

2. Description of the Related Art FIG. 7 shows a flow of a typical method of manufacturing a conventional optical waveguide. First, glass particles 102 ′ are deposited on a substrate 101 such as quartz or silicon by a flame deposition method (FIG. 10A), and then heated at a temperature of 1200 ° C. or higher to make the deposited glass particle layer transparent. The glass is vitrified to form the buffer layer 102 (FIG. 2B / glass composition: SiO2-B2O3-P2O5). Next, a glass fine particle layer 103 ′ for core is deposited on the buffer layer 102 by the flame deposition method (FIG. 6C), and then 1 again.
This glass fine particle layer 10 is heated at a temperature of 200 ° C. or higher.
3'is made into a transparent glass to form the core layer 103 (FIG. 2 (d) / glass composition: SiO2-B2O3-P2O5-
GeO2). Next, a mask pattern is formed on the core layer 103 by a photolithography technique, and then etching is performed using this as a mask to form an optical waveguide 103a having a desired pattern ((e) in the figure). Then, a glass fine particle layer 104 'is again deposited thereon by the flame deposition method (FIG. 6 (f)), and then made into a transparent glass to form the overclad layer 104 (FIG. 6 (g) / glass composition: SiO2).
-B2 O3 -P2 O5).

[0003]

However, the optical waveguide thus formed may also have irregularities due to scratches or distortion on the substrate, and even if a buffer layer is provided on the substrate, its surface is Scratches and irregularities appear again on. As described above, there is a problem that the transmission loss increases because the core layer is not uniformly formed on the uneven surface. Therefore, an object of the present invention is to provide a method for manufacturing an optical waveguide in which the surface of a substrate forming a core or a buffer layer is formed flat and the deterioration of transmission loss can be prevented.

[0004]

A method of manufacturing an optical waveguide according to the present invention comprises a first step of finishing the surface of a substrate to be flat, and an additive for increasing the refractive index of glass is supplied to a flame burner to flatten the surface. A second step of depositing a first glass fine particle layer for the core on the surface of the substrate, a third step of sintering the first glass fine particle layer to form a transparent glass, and the first transparent glass forming step. A fourth step of patterning the glass fine particle layer into a predetermined core shape; a fifth step of depositing a second glass fine particle layer for overcladding on the patterned first glass fine particle layer; Two
A sixth step of sintering the glass fine particle layer to obtain a transparent glass, in the first step, the substrate is once coated with a resist layer, and then the resist layer and the surface of the substrate are removed by a dry etching method. The feature is that the surface of the substrate is finished flat.

Further, in another method of manufacturing an optical waveguide according to the present invention, a first step of forming a buffer layer on a substrate, a second step of finishing the surface of the buffer layer to be flat, and a refractive index of glass are increased. The third step of supplying the additive to the flame burner and depositing the first glass fine particle layer for the core on the flattened surface of the buffer layer, and sintering the first glass fine particle layer to obtain transparent vitrification. And a fifth step of patterning the transparent vitrified first glass fine particle layer into a predetermined core shape, and a second glass fine particle layer for overcladding on the patterned first glass fine particle layer. And a seventh step of sintering the deposited second glass fine particle layer into a transparent glass, and in the second step, a resist layer is once coated on the buffer layer, Ide, characterized in that to finish the surface of the resist layer and the buffer layer to flatten the surface of the buffer layer is removed by dry etching.

[0006]

Embodiments of the present invention will be described below in detail with reference to the accompanying drawings. 1 and 2 are views showing a manufacturing process of the optical waveguide of the present embodiment. First,
A flat quartz substrate 10 having a thickness of 1 mm is prepared (see FIG.
(A)), the surface was ultrasonically cleaned in an acetone solution.

Next, as shown in FIG. 3, a cleaned quartz substrate 10 is fixed on a disk 5 of a rotating device, and a resist made of an organic substance such as novolac resin is fixed on the quartz substrate 10 through a nozzle 7 of a dropping device. At the same time, the disk 5 was rotated at high speed to form a substantially flat resist layer 1 on the surface of the substrate 10 (FIG. 1).
(B)). The thickness of the resist layer 1 is determined by the viscosity and rotation speed of the resist, and is set to a thickness sufficient to cover scratches or irregularities on the quartz substrate 10. Viscosity is 10 to 300 cp
s, the rotation speed was adjusted in the range of 500 to 5000 rpm.

Next, as shown in FIG. 4, the quartz substrate 10 is fixed to one side of the electrode 4 arranged in the vacuum chamber 8, and an etching gas of CF4 gas and O2 gas is blown between the electrodes 4. The surface of the quartz substrate 10 was etched. Etching gas flow rate: 200 (sccm), pressure: 1.0 (Pa), plasma generation power: 1.0 (k
W) and accelerating voltage: 100 (V) or less, 50 μm was etched (FIG. 1C). As shown in FIG. 5, the etching rate is generally different between quartz glass and resist, and also changes depending on the ratio of CF4 gas and O2 gas fed between the electrodes.

By the way, when the surface of the resist layer 1 provided on the substrate 10 is etched, first, as shown in FIG.
As shown in 91 and 92 in (c), the entire surface is resist, but when it reaches 93, scratches or irregularities appearing on the surface of the substrate 10 appear. In this state, the quartz substrate 1
0 and the resist layer 1 are simultaneously etched.
When the etching is performed under the condition that the etching rates of the quartz glass and the resist are different from each other as described above, the unevenness is more and more emphasized due to the difference in the etching rate. Therefore, as shown in FIG. 5, the condition that both etching rates are equal / x% for CF4 gas and (1-x)% for O2 gas
By selecting, it is possible to continue etching while maintaining a flat surface. As a result, the surface of the substrate 10 can be flatly etched as shown in FIG.

Next, the substrate 1 whose surface is flatly etched
0 is used to form an optical waveguide according to the process shown in FIG. In the oxyhydrogen flame, SiCl4 as a source gas,
BCl3 and GeCl4 were introduced, and by flame hydrolysis reaction, B2, P and Ge added SiO2 particles were generated and deposited on the quartz substrate 10 (FIG. 2 (a)). The deposited core glass fine particle layer 11 ′ was sintered at 1500 ° C. for 4 hours to form a core layer 11 having a thickness of 8 μm (FIG. 2).
(B)).

Next, a photosensitive resist layer 20 having a thickness of 1 μm is formed on the core layer 11 (FIG. 2 (c)). The resist layer 20 is strip-shaped and its width is selected to be equal to the dimensions of the core.

Next, reactive ionization is performed using the resist layer 20 as an etching mask to remove the exposed portion of the core layer 11 until the upper surface of the substrate 10 is exposed (FIG. 2).
(D)). As a result, the columnar core member 11a is formed on the quartz substrate 10.

Next, in the oxyhydrogen flame, S is used as a source gas.
iCl4, BCl3, and POCl3 were introduced, and flame hydrolysis reaction was performed to generate and deposit SiO2 particles to which B and P were added (FIG. 2 (e)). The deposited overclad fine particle layer 12 ′ was sintered at 1200 ° C. for 4 hours to obtain an overclad layer 12 having a thickness of 30 μm (FIG. 2).
(F)). The waveguide structure has a core cross-sectional shape of 8 μm × 8.
μm and the relative refractive index difference was 0.3%. The quartz substrate 10 and the over clad layer 12 are integrated to form a clad layer, and the waveguide is fixed while being embedded in the clad layer. The waveguide loss of the linear optical waveguide manufactured through the above steps is 0.06 ± 0.0
It was 3 dB / cm.

<Comparative Example> An optical waveguide was manufactured in the same manner as in the above-described embodiment, but in the comparative example, the first step of flattening the substrate 10 was not performed, and the step shown in FIG. The core layer 11 and the overclad layer 12 were formed by. Unevenness of about 1 μm was present on the entire surface of the substrate. The waveguide loss of the fabricated linear optical waveguide is 0.6 ±
It was 0.1 dB / cm.

<Another Embodiment> In order to avoid the influence of transmission loss due to impurities on the substrate, the first glass fine particle layer 1 for core is provided after the buffer layer 13 is provided as shown in FIG.
1 ′ may be deposited (FIG. 6 (a)). Even if the buffer layer 13 is provided, if a scratch or the like is present on the substrate, unevenness due to the scratch also appears on the surface of the buffer layer 13. Therefore, it is necessary to make the surface of the buffer layer 13 flat. Also in this case, the surface of the buffer layer 13 is dry-etched flat by a method similar to that of FIG. At this time,
Etching is performed under the condition that the etching rate of the buffer layer 13 is equal to the etching rate of the resist layer. Hereinafter, the buffer layer 1 etched according to the process shown in FIG.
3, the core layer 11 is formed (FIG. 3B), and the overclad layer 12 is provided (FIG. 3F) to form an optical waveguide. The buffer layer 13 is formed by depositing glass particles on the substrate 10 and then heating the glass particles at a temperature of 1200 ° C. or higher to make the deposited glass particle layer transparent vitrified (glass composition: SiO 2 —B 2 O 3 —P 2 O 5). ).

[0016]

The present invention is embodied in the form described above and has the following effects.

Even if irregularities due to scratches or distortion occur on the substrate, since the waveguide is formed after finishing the surface of the substrate flat, it is possible to prevent the deterioration of transmission loss due to the irregularities.

Since the irregularities due to scratches or strains generated on the substrate are removed by dry etching, impurities on the surface are removed at the same time as the irregularities, so that the transmission loss is greatly improved.

[Brief description of drawings]

FIG. 1 is a diagram showing a first half manufacturing process of an optical waveguide according to the present embodiment.

FIG. 2 is a diagram showing a manufacturing process of the latter half of the optical waveguide according to the present embodiment.

FIG. 3 is a diagram showing a method of manufacturing a resist layer.

FIG. 4 is a diagram showing a dry etching method.

FIG. 5 is a diagram showing characteristics relating to an etching rate.

FIG. 6 is a diagram showing another manufacturing process of the optical waveguide according to the present embodiment.

FIG. 7 is a diagram showing a manufacturing process of a conventional optical waveguide.

[Explanation of symbols]

 1: Resist layer 2: Dry etching gas 3: Exhaust gas 4: Electrode 5: Acceleration power supply 6: Disk of rotating device 7: Nozzle of dropping device 8: Vacuum chamber 9: Direction of dry etching 91, 92 ・ ・: Etching Surface 10: Substrate 11: Core Layer 11 ': Glass Particulate Layer of Core Part 12: Overclad Layer 12': Glass Particulate Layer of Overclad Part 13: Buffer Layer 13 ': Glass Particulate Particle Layer of Buffer Part 20: Photosensitive Resist layer

Claims (4)

[Claims] 1. A first step of finishing the surface of a substrate to be flat, and an additive for increasing a refractive index of glass are supplied to a flame burner,
A second step of depositing a first glass fine particle layer for a core on the flattened surface of the substrate, a third step of sintering the first glass fine particle layer to make it a transparent vitrification, and a transparent vitrification A fourth step of patterning the first glass fine particle layer into a predetermined core shape, a fifth step of depositing a second glass fine particle layer for overcladding on the patterned first glass fine particle layer, and And a sixth step of sintering the second glass fine particle layer into a transparent glass, and in the first step, the substrate is once coated with a resist layer, and then the resist layer and the surface of the substrate are dry-etched. A method for manufacturing an optical waveguide, characterized in that the surface of the substrate is flattened by removing it by a method. 2. The method of manufacturing an optical waveguide according to claim 1, wherein the dry etching is performed under the condition that the etching rates of the substrate and the resist layer are equal to each other. 3. A first step of forming a buffer layer on a substrate, a second step of flattening the surface of the buffer layer, and an additive for increasing the refractive index of glass are supplied to a flame burner,
A third step of depositing a first glass fine particle layer for the core on the flattened surface of the buffer layer, a fourth step of sintering the first glass fine particle layer to make it a transparent vitrification, and a transparent vitrification A fifth step of patterning the first glass fine particle layer into a predetermined core shape, and a sixth step of depositing a second glass fine particle layer for overcladding on the patterned first glass fine particle layer, 7th step of sintering the second glass fine particle layer thus formed into a transparent glass, and in the second step, a resist layer is once coated on the buffer layer, and then the resist layer and the surface of the buffer layer are coated. Is removed by dry etching to finish the surface of the buffer layer flat. 4. The method of manufacturing an optical waveguide according to claim 3, wherein the dry etching is performed under the condition that the etching rates of the buffer layer and the resist layer are equal.