JPH06140620A - Optical waveguide and manufacture thereof - Google Patents

Abstract

PURPOSE:To provide a high performance and compact optical waveguide which can integrate monolithic electronic(circuits and optical circuits on the same substrate and can form multilayered waveguide thereon and a method of manufacturing the same. CONSTITUTION:In an optical waveguide comprising an oxide silicon layer 2 formed on a silicon substrate 1 and an optical waveguide layer 3a on the layer 2, a low refractive index layer 4 having the end portion formed like a sloped layer is provided at an upper part of the optical waveguide layer and the entire surface including such upper part is over-coated with a layer 3b having the refractive index equal to that of the lower optical waveguide layer.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical waveguide used for an optical element of an optical head used for recording / reproducing an optical disk, an optical thin film component having an isolator function in an optical circuit, and a method for manufacturing the same.

[0002]

2. Description of the Related Art An optical waveguide is capable of controlling a large amount of information at high speed and without being affected by surrounding electromagnetic waves, with respect to an electric circuit that controls the flow of electrons, which is currently the mainstream. It is a circuit that guides light necessary for realizing a circuit using light that is possible.

A conventional optical waveguide will be described below with reference to the drawings. FIG. 3 shows a basic configuration of a conventional optical waveguide type isolator.

In FIG. 3, 11 is a single crystal substrate such as LiNbO ₃ , 12 is a Ti diffusion region, 13 is a Ti non-diffusion region, 14 is a light input / output end, 15 is a light input / output end, and 16 is a light output. The end portion 17 is a Y-shaped branch portion.

The operation of the optical waveguide having the above structure will be described below.

Since the Ti diffused region 12 formed on the LiNbO ₃ single crystal substrate 11 has a larger refractive index than the non-diffused region 13, the light incident from the light incident end portion 14 has T
The light does not spread to the non-diffusion region 13 of i, is guided while being confined in the Ti diffusion region 12, and is emitted from the light input / output end portion 15. Similarly, the light incident from the light input / output end portion 15 is guided to the light output / end portion 16 while being confined in the Ti diffusion region 12. At this time, due to the waveguide loss due to the shape of the Y-shaped branch portion 17, almost no light is guided to the light input end portion 14 as compared to the light output end portion 16. Furthermore, this L
The element using iNbO ₃ can realize various optical device functions due to the acousto-optic effect by adding electrodes.

[0007]

However, in the above-mentioned conventional configuration, the function as a device cannot be exhibited unless the units such as the semiconductor laser and the photodetector which are the light source are configured separately from the optical waveguide circuit. Further, an optical component such as a prism for introducing and extracting light to the optical waveguide is required, and a very high precision alignment technique is required in terms of assembling.

Further, there is a problem that it is difficult to reduce the size and weight of the device because the optical circuit has to be formed only within the two-dimensional region on the substrate surface.

The present invention solves the above-mentioned conventional problems. It is possible to monolithically integrate an electronic circuit and an optical circuit on a single substrate. An object is to provide an optical waveguide which is compact in function and a manufacturing method thereof.

[0010]

In order to achieve this object, an optical waveguide of the present invention has a silicon oxide layer on a silicon substrate, and an optical waveguide layer made of a silicon compound thereon.
Furthermore, it has a low-refractive-index aluminum oxide layer with a slanted end formed in a part of its upper part, and has a structure in which the entire surface including the upper part is overcoated with the same high-refractive-index silicon compound as the lower part. ing. Further, as a manufacturing method thereof, the optical waveguide layer and the low refractive index layer are formed by a thin film using a vacuum process, a resist is applied on the low refractive index layer, and after exposure patterning by low temperature baking, phosphoric acid-based It is characterized in that wet etching is performed with the etching solution.

[0011]

With this structure, since the optical waveguide can be formed on the Si substrate, the semiconductor laser serving as the light source and the photodetector can be built on the same substrate.

If the optical waveguide layer made of a silicon compound is formed directly on the Si substrate, the refractive index of the Si substrate becomes larger than that of the optical waveguide layer, and it becomes impossible to confine light. Since the silicon oxide layer on the Si substrate has a smaller refractive index than the silicon compound, it serves as an optical buffer layer.

The low-refractive-index aluminum oxide layer formed on the silicon compound acts as a clad layer because it has a lower refractive index than the optical waveguide layer, and it is possible to three-dimensionally split light. In addition, since the end portion is formed in a slanted shape, only by overcoating the optical waveguide layer on the upper portion,
The loss generated in the optical branch can be reduced, and the function as an isolator can be realized.

Further, by etching a ring-shaped grating lens on each optical waveguide layer having a multi-layer structure, it becomes possible to make a light input / output function and a light collecting function on the Si substrate.

By using a vacuum process such as sputtering or CVD as a method for producing the optical waveguide layer and the cladding layer, it is possible to change the required refractive index of the film by controlling the reactivity by the introduced gas. Becomes

A resist is applied on the low refractive index layer,
By performing exposure patterning by low-temperature baking with the baking temperature changed, the adhesive force between the resist and the low refractive index layer is controlled, and during wet etching, the etching solution is positively applied between the resist and the low refractive index layer. Let me in,
It becomes possible to proceed with the side etching, and it is possible to control the inclined shape of the end portion.

The phosphoric acid-based etching solution etches aluminum oxide in the low refractive index layer, but does not etch the silicon compound which is the optical waveguide layer, so that it is possible to selectively etch only the low refractive index layer. ,
It is possible to reduce the scattering loss due to the uneven surface shape in the portion where the optical waveguide layer is laminated.

[0018]

Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 is a perspective view of the optical waveguide of this embodiment. In FIG. 1, 1 is a silicon substrate, 2 is a silicon oxide film, 3a, 3b and 3c are silicon nitride films, and 4 is an aluminum oxide film.

The operation of the optical waveguide configured as described above will be described below. Silicon nitride film 3
Since b has a larger refractive index than the aluminum oxide film 4, light is guided while being confined in the silicon nitride film 3b. Similarly, since the silicon nitride film 3c has a larger refractive index than the silicon oxide film 2, light is guided while being confined in the silicon nitride film 3c. Further, since the silicon nitride film 3a has a larger refractive index than the silicon oxide film 2 and the aluminum oxide film 4, light is guided while being confined in the silicon nitride film 3a.

The incident light at this time is the same silicon substrate 1
Light from a semiconductor laser (not shown) built in above is formed in the silicon nitride film 3b by a ring-shaped grating lens or the like (not shown) formed by etching on the surface of the silicon nitride film 3b. Can be captured.

The light guided through the silicon nitride film 3b is
The light is guided to the silicon nitride film 3c. Then, a ring-shaped grating lens or the like (not shown), which is etched on the surface of the silicon nitride film 3c in the same manner as on the silicon nitride film 3b, allows light to be emitted to the outside and condensed at the same time. It is also possible to take in light from the outside and guide it in the silicon nitride film 3c by the same optical system.

The light guided in the silicon nitride film 3c is guided in the silicon nitride film 3a. At this time, since the end portion of the aluminum oxide film 4 is formed in a shape,
Light is hardly guided from the inside of the silicon nitride film 3c to the silicon nitride film 3b.

Considering only the silicon nitride films 3b and 3c, it has the function of an optical isolator. Further, the function as a three-dimensional optical directional coupler is realized as the entire configuration.

Next, a method of manufacturing the optical waveguide of the present invention will be described with reference to the drawings. 2A to 2G are sectional views showing the manufacturing process of the optical waveguide of the present embodiment.

Hereinafter, each process will be described with reference to FIGS. 2 (a) to 2 (g). First, as shown in FIG. 2 (a), sputtering or C
The silicon oxide film 2 is formed on the entire surface by a vacuum process such as the VD method. As a forming method at this time, a method such as a steam oxidation method is also possible. If a quartz substrate is used instead of the silicon substrate 1, this step can be omitted.

Next, as shown in FIG. 2B, a silicon nitride film 3a is formed on the entire surface of the silicon oxide film 2 by about 0.5 μm. At this time, targeting Si ₃ N ₄ ,
By the reactive sputtering method using Ar and N ₂ and O ₂ gas, the partial pressure of N ₂ and O ₂ gas is controlled, and the silicon nitride film 3
It is also possible to control the refractive index of a. Similarly, S
Plasma CV using iH ₄ , NH ₃ , N ₂ , N ₂ O gas, etc.
By the D method, it is possible to form a film with a controlled refractive index and waveguide loss.

Next, as shown in FIG. 2C, an aluminum oxide film 4 is formed on the entire surface of the silicon nitride film 3a to a thickness of about 1.
Form a film with a thickness of μm. At this time, the refractive index of the aluminum oxide film 4 is made lower than that of the silicon nitride film 3a.

Then, a resist 5 is applied to the upper surface of the aluminum oxide film 4 by a spin coater and baked at a temperature lower than a normal baking temperature. Further, a mask (not shown) having a desired pattern shape is aligned and overlapped, and UV light is exposed on the mask. Then, by developing the resist with a developing solution, the resist 5 is partially formed as shown in FIG.

Next, the work in the state of FIG. 2D is introduced with a phosphoric acid-based etching solution to wet-etch the aluminum oxide film 4 where the resist 5 is not formed thereon. At this time, since the etching liquid also permeates the interface between the aluminum oxide film 4 and the resist 5 and side etching is performed, the aluminum oxide film 4 having a shape as shown in FIG. 2E is processed. At this time, since the silicon nitride film 3a is not etched by phosphoric acid, only the aluminum oxide film 4 is selectively etched. It should be noted that films and etching solutions of other materials may be used as long as they satisfy the conditions of the combination of the selectively etchable film and the etching solution and the refractive index.

After cleaning and drying, the resist 5 is removed by ashing to expose the aluminum oxide film 4 as shown in FIG. 2 (f).

Finally, the silicon nitride film 3b is formed on the entire upper surface by about 0.5 by the same process as that of forming the silicon nitride film shown in FIG.
A film of about μm is formed and overcoating is performed. At this time, the silicon nitride film 3c is formed under the condition that the refractive index of the silicon nitride film 3b is the same as that of the silicon nitride film 3a.
It can be formed as in (g).

[0033]

As described above, according to the present invention, a silicon oxide layer is formed on a silicon substrate, and an optical waveguide layer made of a silicon nitride film is formed on the silicon oxide layer. By forming a low-refractive-index aluminum oxide layer and then overcoating the entire surface including the upper part with the same high-refractive-index silicon nitride film as the lower part, electronic circuits and optical circuits are monolithically integrated on one substrate. Further, it is possible to provide a highly functional and compact optical waveguide in which the waveguide layers are formed in multiple layers. Further, as a manufacturing method thereof, the optical waveguide layer and the low refractive index layer are formed by a thin film using a vacuum process, a resist is applied on the low refractive index layer, and after exposure patterning by low temperature baking, phosphoric acid-based By wet-etching with the above-mentioned etching solution, a production method using a conventional semiconductor manufacturing process can be realized.

[Brief description of drawings]

FIG. 1 is a perspective view of an optical waveguide according to an embodiment of the present invention.

FIG. 2 is a sectional view for explaining the manufacturing process of the optical waveguide according to the embodiment of the invention

FIG. 3 is a basic configuration diagram of a conventional optical waveguide.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Silicon substrate 2 Silicon oxide film 3a Silicon nitride film (base film) 3b Silicon nitride film (overcoat film) 3c Silicon nitride film (composite film of 3a and 3b) 4 Aluminum oxide film

Claims (3)

[Claims] 1. An optical waveguide having a silicon oxide layer on a silicon substrate, and an optical waveguide layer on the silicon oxide layer, wherein a low-end portion having an inclined end portion is formed only on a part of an upper portion of the optical waveguide layer. An optical waveguide having a structure having a refractive index layer and further having an entire surface including an upper portion thereof overcoated with a layer having the same refractive index as that of the lower optical waveguide layer. 2. The optical waveguide according to claim 1, wherein the optical waveguide layer is a silicon compound, and the low-refractive index layer having inclined end portions is aluminum oxide. 3. The optical waveguide according to claim 2, wherein the optical waveguide layer and the low refractive index layer are formed by a thin film using a vacuum process, a resist is applied on the low refractive index layer, and exposure patterning is performed by low temperature baking. After that, wet etching is performed with a phosphoric acid-based etching solution, which is a method for manufacturing an optical waveguide.