JPH05294653A - Production of optical waveguide - Google Patents

Abstract

PURPOSE:To provide an optical waveguide as a component of optical integrated circuits, with its refractive index controllable easily and accurately. CONSTITUTION:The surface of a SiO2 layer 2-bearing substrate 1 is provided with an Al alloy film 3 containing a dopant Si for controlling refractive index, and part of this film 3 is eliminated to form an optical waveguide pattern followed by anodizing to convert the ridge 4 of the Al alloy containing said dopant Si to a transparent oxide ridge 5, thus forming a core as optical transmission region.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION The present invention relates to an optical integrated circuit (OEIC:
Opto Electronic Integrated Circuits).

[0002]

2. Description of the Related Art Conventionally, SiO ₂ or a region having a high refractive index (core) and a region having a low refractive index (clad) is added as a basic element constituting an optical integrated circuit by adding SiO ₂ or some kind of dopant.
Research on optical waveguides that form a matrix and propagate light by confining light in the core region is being rapidly advanced.

As a manufacturing method for forming such an optical waveguide, there is one using a flame deposition method (VAD method).
In this method, SiO ₂ or soot containing this as a main component is deposited on a glass or silicon substrate by an oxyhydrogen burner and then sintered to form a glass film. In this case, in order to make the refractive index higher than that of SiO ₂ , TiO ₂ , Al ₂ O ₃ , GeO ₂ , P ₂ O ₅ , Ta ₂
In order to lower the refractive index of O _{3 and the} like, B ₂ O ₃ , S
iF ₄ or the like is used as a dopant. The glass film in the core region having a high refractive index is three-dimensionally processed by the photolithography method. The optical waveguide thus formed has a height and a width of about 10 μm when coupled with a single-mode optical fiber.

Further, as a method for forming the glass film, a CVD method, an electron beam evaporation method, or a sputtering method can be used in addition to the flame deposition method. Although there is no limitation on the material of the film to be formed by these forming methods, the film forming speed is slow and it is suitable for forming a thin film having a thickness of several μm or less.

[0005]

By the way, as the characteristics of the optical waveguide which is a basic element of the optical integrated circuit, it is important that the optical waveguide has a low loss and a large refractive index difference (Δn) between the core and the glad, By increasing Δn, the light is strongly confined in the core, and the bending loss is small even if the optical waveguide is bent with a small curvature, and as a result, the size of the device can be reduced.

However, it is difficult to apply the above-mentioned conventional flame deposition method to a material other than SiO ₂ or a material containing it as a main component, and it is possible to obtain a core having a high refractive index. Can not. Further, if an excessive amount of dopant is doped to increase the refractive index, many clusters and cracks occur in the film, and it becomes impossible to obtain a film with low loss. On the other hand, according to the CVD method, the electron beam evaporation method or the sputtering method, the material is not limited as compared with the flame deposition method.

[0007]

In order to solve the above problems, the present invention forms an Al alloy film containing a dopant for controlling the refractive index on a substrate having a low refractive index layer. After the portion was removed to form an optical waveguide pattern, the Al alloy film containing the refractive index controlling dopant was converted into a transparent film by anodic oxidation to form a core which is a light propagation region to form an optical waveguide.

[0008]

By mixing Al and the refractive index controlling dopant at the same time to form a film, a waveguide core with a controlled refractive index can be obtained by an easy method, and the concentration of the refractive index controlling dopant can be changed. As a result, the refractive index can be finely adjusted easily, and the versatility of the Al ₂ O ₃ waveguide can be enhanced. Further, by converting the alloy film into an oxide film by anodic oxidation, conversion can be performed in a short time.

[0009]

Embodiments of the present invention will be described below with reference to the accompanying drawings. Here, FIG. 1 is an explanatory view showing a manufacturing process of an optical waveguide according to the present invention, and FIGS. 2 and 3 are conceptual views of an electron beam vapor deposition apparatus and a sputtering apparatus used for forming an Al film.

First, as shown in FIG. 1A, the Si substrate 1
On the low refractive index layer ₂ containing SiO ₂ as a main component, an Al film 3 having a refractive index control dopant Si added thereto by an electron beam evaporation method as shown in FIG.
μm. Here, the film formation by the electron beam evaporation method was performed by the two evaporation source method in which the Al tablet 11 and the Si tablet 12 as the refractive index controlling dopant are evaporated from different evaporation sources as shown in FIG.

In this case, the vapor deposition method is not limited to the electron beam vapor deposition method, and when a material having a low melting point is vapor deposited, a resistance heating method of energizing filamentary Al can be used. By using these electron beam evaporation method and resistance heating method, the concentration of the refractive index controlling dopant in Al can be controlled with good controllability.

Al containing a dopant for controlling the refractive index
The formation of the film is not limited to high vacuum vapor deposition such as electron beam vapor deposition, but sputtering can also be used. As the sputtering device, for example, a load lock type device as shown in FIG. 3 is used. In this sputtering apparatus, a preparation chamber 14 and an extraction chamber 15 are arranged at both ends of a tunnel type housing 13, and the cathode electrode 1 is provided inside the housing 13.
6, 16 are provided, an Al target 17 and a Si target 18 which is a dopant for controlling the refractive index are attached to the cathode electrodes 16, respectively, and a film is formed by simultaneous sputtering or cross sputtering. The film can also be formed by single sputtering using an alloy or a sintered body in which a desired amount of the refractive index controlling dopant is mixed in the Al film as a sputtering source.

Next, as shown in FIG. 1C, a waveguide pattern is formed on the Al film 3 formed as described above by using the photolithography method. The width of this waveguide pattern was 10 μm, which is the same as the film thickness. Partial etching of the Al film 3 to which Si is added can be easily performed with caustic soda or phosphoric acid, but a dry process can also be used. Wet etching is advantageous in that it does not require expensive equipment, and dry etching is excellent in accurately forming a waveguide pattern. Here, the height of the Al ridge portion 4 is 1 as in the waveguide width.
It was set to 0 μm.

Thereafter, the three-dimensionally processed Si-added Al ridge portion 4 is converted into a transparent oxide ridge portion 5 by an anodic oxidation method as shown in FIG. 1D. Anodization is a method in which a voltage is applied by using an Al substrate or the like immersed in an electrolytic solution such as sulfuric acid or oxalic acid as an anode and a carbon plate or a platinum plate as a cathode to convert the surface into Al ₂ O ₃ .

Here, the ridge portion 4 of Al containing Si is used as an anode, the platinum plate is used as a cathode, and a liquid temperature 2 is used as an electrolytic solution.
Anodization was carried out in sulfuric acid having a concentration of 20% at 0 ° C. As a result, when the current density is 30 mA / cm ² , about 45 μm /
The Al ridge portion 13 to which Si was added at the rate of h was oxidized and converted into a transparent oxide ridge portion 5.

Then, as shown in FIG. 3E, the oxide ridge portion 5 anodized was covered with the SiO ₂ glad layer 6 by the flame deposition method to form a waveguide. As a result, it was possible to obtain a stable optical waveguide that is not easily affected by the roughness of the side surface of the ridge portion or the external environment. This SiO ₂
Some kind of dopant may be added to the glad layer 6 in order to adjust the refractive index or stress.

The refractive index of Al ₂ O ₃ thus formed is
1.75 at a wavelength of 1.3μm vicinity sufficiently larger than the refractive index 1.45 of SiO _2, SiO ₂ cladding material
When using, a large refractive index difference Δn can be obtained, and an optical waveguide with a small bending loss can be realized.

By using the anodic oxidation method, the alloy film can be made into a transparent oxide film in a short time.
Taking the case of only 1 as an example, conversion into Al ₂ O ₃ becomes possible at a speed of about 1 μm / min. On the other hand, Al ₂
When the O ₃ film is formed directly on the substrate and three-dimensional patterning is performed, the film formation rate and the etching rate are both Al.
₂ O ₃ is much slower than Al and requires expensive film forming and fine processing equipment. As described above, the formation of the optical waveguide until patterning is performed in the state of Al, and then conversion to Al ₂ O ₃ also significantly improves the manufacturing efficiency.

In addition to Si, the refractive index dopant is B.
A material having a refractive index lower than that of Al ₂ O ₃ by anodic oxidation such as Mg or Mg can be used. Further, the dopant concentration is preferably 10 mol% or less so that the anodic oxidation is not suppressed by the mixture of the dopant. The oxide film may be colored by mixing a large amount of dopant,
In such a case, a transparent film can be formed by annealing at 1300 ° C. in an O ₂ atmosphere.

In the embodiment, a Si substrate having a low refractive index layer containing SiO ₂ as a main component is used as the substrate,
This is effective when integrating elements such as a light source and a light receiving element in an optical integrated circuit, but an optical waveguide can be formed by using the same process even if SiO ₂ is used as the substrate.

[0021]

As described above, according to the present invention,
An Al alloy film containing a dopant for controlling the refractive index is formed on a substrate having a low refractive index layer, a part of the Al alloy film is removed to form an optical waveguide pattern, and then the refractive index is controlled by anodic oxidation. The optical alloy is manufactured by converting the Al alloy film containing the dopant for use into a transparent glass film to form a core which is a light propagation region, so that the dopant for controlling the refractive index can be easily used as the waveguide core layer. The optical waveguide can be placed inside and the controllability thereof can be performed with high precision, and an optical waveguide having a wide range of application can be efficiently formed.

Further, since the loss is low and the refractive index difference between the core and the clad can be increased, the bending loss is small and the element can be miniaturized.

[Brief description of drawings]

FIG. 1 is an explanatory view showing a manufacturing process of an optical waveguide according to the present invention.

FIG. 2 is a conceptual diagram of an electron beam vapor deposition apparatus used for carrying out the method of the present invention.

FIG. 3 is a conceptual diagram of a sputtering apparatus used for carrying out the method of the present invention.

[Explanation of symbols]

1 ... Substrate, 2 ... SiO ₂ layer, 3 ... Al with Si added
Alloy layer, 4 ... Al alloy ridge, 5 ... Si oxide added ridge, 6 ... SiO ₂ clad layer.

Claims (6)

[Claims] 1. A low refractive index layer is formed on a substrate, an Al alloy film containing a dopant for controlling the refractive index is formed on the low refractive index layer, and a part of the Al alloy film is removed. After forming an optical waveguide pattern, the Al alloy film containing the refractive index controlling dopant is converted into a transparent film by anodic oxidation to form a core which is a light propagation region, and a method of manufacturing an optical waveguide. .. 2. Al containing the dopant for controlling the refractive index
The method of manufacturing an optical waveguide according to claim 1, wherein the alloy film is formed by an electron beam evaporation method having at least two evaporation sources. 3. Al containing the refractive index controlling dopant
The alloy film is formed by a sputtering method using a refractive index control dopant and an Al alloy target, or a co-sputtering method using a refractive index control dopant target and an Al target. Manufacturing method of optical waveguide of. 4. The optical waveguide according to claim 1, wherein the refractive index control dopant is a material having a lower refractive index after oxidation than Al ₂ O _{3 obtained} by oxidizing Al. Waveguide manufacturing method. 5. The refractive index control dopant is Si,
5. The method for manufacturing an optical waveguide according to claim 1, further comprising at least one of B and Mg elements. 6. The method of manufacturing an optical waveguide according to claim 1, wherein the core waveguide is covered with a film having a refractive index lower than that of the core waveguide.