JPH09297237A - Production of optical waveguide - Google Patents

Abstract

PROBLEM TO BE SOLVED: To decrease the number of production processes and to shorten a production time by rapidly shaving the surface of a quartz substrate formed with a core to form a clean surface and then forming a waveguide thereon without forming a buffer layer on the quartz substrate. SOLUTION: The surface of a quartz substrate 10 is removed by ICP method (a). SiO2 fine particles with addition of B, P, Ge are produced by flame hydrolysis reaction and are deposited on the quartz substrate 10 (b). The fine particle layer 11' of the core glass deposited is sintered to form a core layer 11 (c). Then a photosensitive resist layer 20 is formed on the core layer 11 (d). Reactive ion mask is carried out by subjecting the photosensitive resist layer 20 to an etching mask to form a columnar core member 11a on the quartz substrate 10 (e). SiO2 fine particles with addition of B, P are produced by flame hydrolysis and deposited (f). The deposited fine particle layer 12' for an overclad layer is sintered to form an overclad layer 12 (g).

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 The use of a wide range of optical communication technology is expected with the development of advanced information or the era, and in order to realize this, it is possible to reduce the cost of optical passive components having the functions of processing and controlling optical signals. A technique that can be easily manufactured is desired. As a component commonly used in this field, there is an optical waveguide in which an optical switch, an optical coupler and the like are formed on a substrate.

The flow of a typical method for manufacturing these optical waveguides is shown in FIG. 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. Vitrification is performed to form the buffer layer 102 (FIG. 2B / glass composition: SiO2-B2O3-P2O5). Next, the glass fine particle layer 103 'for core is deposited on the buffer layer 102 by the flame deposition method (FIG. 7C), 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 ((d) in the figure / glass composition: SiO2-B2O3-P2O5-Ge).
O2). Next, after forming a mask pattern on the core layer 103 by photolithography, etching is performed using this as a mask to form the optical waveguide 1 having a desired pattern.
03a is formed ((e) in the figure). Then, a glass fine particle layer 104 'is again deposited thereon by the flame deposition method ((f) in the same figure), and then made into a transparent glass to form the overclad layer 1
No. 04 is formed ((g) in the figure / glass composition: SiO2-
B2O3-P2O5).

[0004]

However, it is not preferable to form the optical waveguide through such many steps in terms of manufacturing time and manufacturing cost. On the other hand, when a quartz substrate is used, the vicinity of the surface of the substrate can be made to have a function as a clad, so that the manufacturing process of the buffer layer 102 can be omitted. However, if the core layer is formed directly on the quartz substrate, there is a problem that the waveguide loss increases due to impurities existing near the surface of the substrate. Therefore, an object of the present invention is to provide a method for manufacturing a low-loss optical waveguide in which the surface of a quartz substrate forming a core is promptly removed to form a clean surface and a waveguide is formed thereon.

[0005]

A method of manufacturing an optical waveguide according to the present invention is a method of manufacturing an optical waveguide on a quartz substrate, which comprises a first step of removing the surface of the quartz substrate and a refractive index of glass. A second step of supplying a flame burner with an additive that enhances the temperature, and depositing a first glass fine particle layer for the core on the surface of the removed substrate; and sintering the first glass fine particle layer to form a transparent glass. And a fourth 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 sixth step of sintering the deposited second glass fine particle layer into a transparent vitrification, the first step comprising dry etching using CF4 gas on the surface of the substrate. 1 ˜50 μm is removed, and the plasma electron density of dry etching is 10 10 /
It is characterized by being at least cm3.

[0006]

Embodiments of the present invention will be described below in detail with reference to the accompanying drawings. FIG. 1 is a diagram showing a manufacturing process of the optical waveguide of the present embodiment. First, a 1 mm thick quartz substrate 10 having a flat surface was prepared, and the surface was ultrasonically cleaned in an acetone solution (not shown).

On the other hand, the inventor of the present invention, regarding various quartz substrates,
The surfaces were etched, and the influence of impurities was examined from the relationship between the etching depth and the waveguide loss of the waveguide formed on the surface. As a result, as shown in FIG.
It was found that the waveguide loss has no practical effect when etched by 50 μm, preferably 10-50 μm.

Next, the surface of the substrate 10 is covered with ICP (I
(Nuditive Coupling Plasma)
It was removed by the method (FIG. 1 (a)). In the ICP method, as shown in FIG. 3, a quartz substrate 10 is placed in a vacuum chamber 6 in which a coil 4 is provided on the outer periphery, and CF 4 is placed in the chamber 6.
The surface of the quartz substrate 10 was etched by blowing gas. The flow rate of the etching gas 2 is 200 (sccm),
The pressure was 1.0 (Pa) and the power applied to the coil 4 was 2 kW or less. As a result, a plasma electron density of 1010 / cm3 could be stably generated. Under this condition, the time required to etch the surface of the substrate 10 by 50 μm was 50 minutes. On the other hand, the maximum plasma electron density that could be generated by the conventional reactive ion etching (RIE) method was 10 9 / cm 3. The etching rate depends on the plasma electron density, as shown in FIG.
In particular, it was found that there was a large change near 10 10 / cm 3.

Next, the substrate 1 whose surface is flatly etched
0 was used to form an optical waveguide. Introducing SiCl4, BCl3, and GeCl4 as source gases into the oxyhydrogen flame,
Si with B, P and Ge added by flame hydrolysis reaction
O2 fine particles were generated and deposited on the quartz substrate 10 (FIG. 1 (b)). 1 for the deposited core glass particle layer 11 '
The core layer 11 having a thickness of 8 μm was formed by sintering at 500 ° C. for 4 hours (FIG. 1C).

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

Then, reactive ion etching was 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 was exposed. As a result, the columnar core member 11a was formed on the quartz substrate 10 (FIG. 1E).

Next, in the oxyhydrogen flame, S is used as a raw material 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. 1 (f)). The deposited overclad particle layer 12 'was sintered at 1200 ° C. for 4 hours to obtain an overclad layer 12 having a thickness of 30 μm (FIG. 1).
(G)). 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 1 The core layer 11 and the overclad layer 12 were formed directly according to the process shown in FIG. 1 without removing the surface of the quartz substrate 10. The waveguide loss of the produced linear optical waveguide was 0.6 ± 0.1 dB / cm, and an optical waveguide with low loss could not be obtained.

Comparative Example 2 Further, the surface of the quartz substrate 10 was removed by the conventional RIE method using a capacitor instead of the ICP method, but the plasma electron density was 10 9 /
Since it could not be increased by more than 3 cm3, it took 10 hours to etch 50 μm, which was not suitable for the purpose of low cost production.

[0015]

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

Since no buffer layer is provided on the quartz substrate, the number of manufacturing steps is small and the manufacturing time is shortened.

When high density plasma is generated and dry etching is performed, the etching rate is remarkably increased and the manufacturing time is shortened.

[Brief description of drawings]

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

FIG. 2 is a diagram showing a relationship between etching depth and waveguide loss.

FIG. 3 is a diagram showing a configuration of etching by an ICP method.

FIG. 4 is a diagram showing a relationship between an etching rate and plasma electron density.

FIG. 5 is a diagram showing a manufacturing process of a conventional optical waveguide.

[Explanation of symbols]

 1: Direction of dry etching 11, 12 ...: Etching surface 2: Dry etching gas 3: Exhaust gas 4: Coil 5: Accelerating power supply 6: Vacuum chamber 10: Substrate 11: Core layer 11 ': Core part Glass fine particle layer 12: Overclad layer 12 ': Glass fine particle layer in overclad portion 13: Buffer layer 13': Glass fine particle layer in buffer portion 20: Photosensitive resist layer

Claims (1)

[Claims] 1. A method of manufacturing an optical waveguide on a quartz substrate, comprising: a first step of removing the surface of the quartz substrate; and an additive for increasing the refractive index of glass is supplied to a flame burner,
A second step of depositing a first glass fine particle layer for a core on the surface of the removed substrate, a third step of sintering the first glass fine particle layer to make it a transparent vitrification, and the transparent vitrification A fourth step of patterning the first glass fine particle layer into a predetermined core shape, and a fifth step of depositing a second glass fine particle layer for overcladding on the patterned first glass fine particle layer, A sixth step of sintering the second glass fine particle layer to obtain a transparent vitrification, the first step removing the surface of the substrate by 1 to 50 μm by dry etching using CF 4 gas, and Plasma electron density is 10 by ICP method
A method for manufacturing an optical waveguide, which is 10 / cm3 or more.