JP2000338346A - Optical waveguide element and its production - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain an optical waveguide element which allows the exact control of its shape and dimensions by providing the element with a single crystal ground surface layer and an optical waveguide which consists of magnetic garnet of a single crystal and is formed on the single crystal ground surface layer, providing optical waveguide with a forward tapered cross-sectional shape and constituting the flanks of optical waveguide of planes. SOLUTION: A resist layer 2 is formed on a garnet substrate 1 which is the single crystal ground surface layer. This resist layer is patterned by using a lithography technique. Next, for example, metal is deposited by evaporation as a thin film, by which a metallic layer 3 is formed. The resist layer 2 is removed by a lift-off process. As a result, apertures meeting the patterns of the resist layer 2 are formed at the metallic layer 3. The magnetic garnet layer 4 is thereafter deposited by liquid phase epitaxy on the surface of the substrate 1 on which surface the metallic layer 3 is formed. The optical waveguide element having the optical waveguide 5 composed of the magnetic garnet layer 4 in the manner described above is obtained. The formed optical waveguide 5 has the forward tapered cross-sectional shape and its flanks are composed of the planes.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to an optical waveguide device and a method of manufacturing the same, and more particularly, to an optical waveguide device having an optical waveguide formed of a magnetic garnet and a method of manufacturing the same.

[0002]

2. Description of the Related Art In a waveguide type optical non-reciprocal device such as an optical isolator or an optical circulator, an optical waveguide made of a magnetic garnet is indispensable. Such an optical waveguide can be formed, for example, by the following method.

[0003] First, a magnetic garnet layer is formed on a single crystal substrate made of garnet by liquid phase epitaxy. Next, a metal pattern is formed on the magnetic garnet layer. Further, the magnetic garnet layer is dry-etched using the metal pattern as a mask. Thus, an optical waveguide made of a magnetic garnet is obtained.

According to this method, an optical waveguide can be formed with a relatively small number of steps. However, it has been found that when a metal pattern is used as a mask during dry etching of the magnetic garnet layer, light loss of the optical waveguide increases. Therefore, usually, the magnetic garnet optical waveguide is formed by the method shown in FIG.

FIGS. 5A to 5F are cross-sectional views schematically showing a conventional method for forming a magnetic garnet optical waveguide. According to the conventional method, first, as shown in FIG. 5A, a magnetic garnet layer 12 is formed on a single crystal substrate 11 made of garnet by liquid phase epitaxy.

Next, a silicon oxide layer 13 is formed on the magnetic garnet layer 12 as shown in FIG. After a resist layer 14 is formed on the silicon oxide layer 13, an opening corresponding to the waveguide pattern is formed in the resist layer 14 by using a photolithography technique, as shown in FIG.

After that, the resist layer 14 of the single crystal substrate 11 is
A metal is deposited on the surface on which is formed, and the resist layer 14 is lifted off to form a metal pattern 15 shown in FIG. Next, reactive ion etching or the like is performed using the metal pattern 15 as a mask. Thereby, as shown in FIG. 5E, the silicon oxide layer 13 is patterned, and the metal pattern 15 is further removed.

Next, using the patterned silicon oxide layer 13 as a mask, the magnetic garnet layer 12 is patterned by dry etching as shown in FIG. As described above, an optical waveguide made of a magnetic garnet is obtained.

According to the above-described method, since the patterned silicon oxide layer 13 is used as an etching mask for the magnetic garnet layer, light loss in the optical waveguide is smaller than when a metal pattern is used.

However, according to this method, since the magnetic garnet layer 12 is patterned by dry etching, the side wall of the optical waveguide is damaged. That is, roughness of the side wall of the optical waveguide, which is a cause of the light scattering loss, occurs. Also, this method requires an extremely large number of steps, as is clear from the above.

On the other hand, when the magnetic garnet layer is patterned by wet etching, the light loss does not become excessive even if a metal pattern is used as the etching mask. Therefore, in this case, the optical waveguide can be formed with a relatively small number of steps.

However, since wet etching proceeds isotropically, an undercut occurs due to side etching below the etching mask, and it is difficult to accurately control the shape of the optical waveguide. Further, since the etch rate is easily affected by the environment such as temperature, the above-described method cannot form an optical waveguide with high reproducibility. On the other hand, side etching does not easily occur in dry etching, but the edges of the etch mask are gradually etched as the etching proceeds, and the mask width is reduced, so that an optical waveguide cannot be formed with high reproducibility. That is, according to the method using etching, it is difficult to accurately control the dimensions of the optical waveguide.

[0013]

SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned problems, and has an optical waveguide composed of a magnetic garnet, in which the shape and dimensions can be accurately controlled. An object of the present invention is to provide an optical waveguide device and a method for manufacturing the same.

Another object of the present invention is to provide an optical waveguide device having an optical waveguide composed of a magnetic garnet and capable of being manufactured in a small number of steps, and a method of manufacturing the same.

[0015]

In order to solve the above-mentioned problems, the present invention provides a single crystal underlayer and an optical waveguide substantially formed of a single crystal magnetic garnet and formed on the single crystal underlayer. The optical waveguide element is characterized in that the optical waveguide has a forward tapered cross-sectional shape, and the side surface of the optical waveguide is formed as a plane.

Further, according to the present invention, there is provided a step of forming a metal layer having an opening of a predetermined pattern on a single crystal underlayer, and a step of forming a liquid phase epitaxy on an exposed surface of the single crystal underlayer having the metal layer formed thereon. Forming a magnetic waveguide substantially consisting of the magnetic garnet by causing crystal growth of the magnetic garnet, thereby producing a method of manufacturing an optical waveguide device.

[0017]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, the present invention will be described in more detail with reference to the drawings. 1 (a) to 1 (c)
3A to 3C are cross-sectional views schematically showing a method for manufacturing an optical waveguide device according to one embodiment of the present invention.

In manufacturing an optical waveguide device, first,
As shown in FIG. 1A, a resist layer 2 is formed on a garnet substrate 1, which is a single crystal underlayer, and is patterned using a lithography technique such as a photolithography technique. The pattern of the resist layer 2 corresponds to the pattern of the optical waveguide finally formed.

Next, as shown in FIG. 1B, a metal layer 3 is formed as a thin film, for example, by depositing a metal, and the resist layer 2 is removed by a lift-off process. Thus, an opening corresponding to the pattern of the resist layer 2 is formed in the metal layer 3.

Thereafter, a magnetic garnet layer 4 is formed on the surface of the substrate 1 on which the metal layer 3 is formed by liquid phase epitaxy. Since the crystal growth of the magnetic garnet selectively occurs on the exposed surface of the substrate 1, the magnetic garnet layer 4 is formed in a pattern corresponding to the pattern of the opening of the metal layer 3.

Since the liquid phase epitaxy is performed at a high temperature, the metal layer 3 usually melts with the passage of time and eventually disappears. Therefore, the magnetic garnet layer 4
Is not necessarily formed only in the opening of the metal layer 3.

However, the metal layer 3 functions as a mask at least at the beginning of liquid phase epitaxy. Therefore, in the early stage of the liquid phase epitaxy, the crystal growth of the magnetic garnet selectively occurs on the surface of the substrate 1 exposed in the opening of the metal layer 3.

The interface between the metal layer 3 and the substrate 2 is roughened during liquid phase epitaxy. Therefore, the magnetic garnet that grows there does not become a single crystal, but becomes a polycrystal in which amorphous (amorphous) and a small amount of crystals are mixed. Normal,
The growth rate differs between a single crystal and a polycrystal.

Therefore, the shape of the opening of the metal layer 3 is reflected in the shape of the magnetic garnet layer 4 finally formed. That is, the rib waveguide structure shown in FIG. 1C can be obtained. According to the method according to the present embodiment, an optical waveguide element having the optical waveguide 5 constituted by the magnetic garnet layer 4 is obtained as described above. The optical waveguide device obtained in this way can be further processed into a waveguide type optical non-reciprocal device such as an optical isolator or an optical circulator by subjecting it to a predetermined processing.

According to the above-described method, it is possible to form the optical waveguide 5 without etching the magnetic garnet. Therefore, the sidewall of the optical waveguide 5 is not damaged by the etching. Therefore, according to this method, the optical waveguide 5 with reduced light scattering loss can be formed.

In the present method, since the metal layer 3 is formed by depositing a metal in the opening formed by the resist layer 2, the resist layer is hardly etched during the pattern formation, as a matter of course. . In addition, the line width of the resist pattern formed by the resist layer 2 can be controlled with high accuracy by using a known photolithography technique or the like. Therefore, according to the present method, the size and shape of the metal layer 3 can be controlled with extremely high accuracy.

In the present method, since the magnetic garnet layer 4 is formed by liquid phase epitaxy, the optical waveguide 5
Has an extremely high correlation with the size of the opening of the metal layer 3 in the initial stage of its formation. That is, in the present method, even if the metal layer 3 is melted in the liquid phase epitaxy, the influence on the width of the optical waveguide 5 is extremely small. Therefore, according to the method described above, the width of the optical waveguide 5 can be controlled with high accuracy.

Further, in the present method, the optical waveguide 5 is formed by liquid phase epitaxy, which is one of the selective growth methods. As is known, according to the selective growth method, it is possible to control the film thickness with extremely high accuracy. Therefore, according to the present method, the height of the optical waveguide 5 can be controlled with high accuracy.

As described above, according to the above-described method, both the width and the height of the optical waveguide 5 can be controlled with high accuracy. That is, according to the present method, the dimensions of the optical waveguide 5 can be accurately controlled.

Optical waveguide 5 formed by the method described above
Has a forward tapered cross-sectional shape, and its side surface is a flat surface. Here, the forward tapered cross-sectional shape means, for example, an isosceles trapezoid or an isosceles triangle as shown in FIG.

When a thin film is formed by liquid phase epitaxy, the thin film has a forward tapered cross section regardless of its size. Also, in this case, since a specific crystal plane appears on the side surface of the thin film, the side surface becomes planar. Such a cross-sectional shape is observed even when a conventional method of patterning a thin film formed by liquid phase epitaxy is used.

For example, as shown in FIG.
When the magnetic garnet layer 12 is formed on the entire surface of the substrate 1 by liquid phase epitaxy, the cross-sectional shape of the magnetic garnet layer 12 is extremely flat, but is macroscopically forward-tapered, and its side surface is flat.

However, when the magnetic garnet layer 12 is formed on the entire surface of the substrate 11, it is necessary to perform patterning using an etching method. Therefore, in such a case, the characteristic cross-sectional shape formed by liquid phase epitaxy is not left in the finally formed optical waveguide.
That is, the cross-sectional shape of the finally formed optical waveguide is
Determined by the etching process.

When the magnetic garnet layer 12 is patterned using dry etching or wet etching, the cross-sectional shape of the obtained optical waveguide varies depending on the etching conditions and the like. However, in these methods, since the exposed portion of the magnetic garnet layer 12 is isotropically etched, the side surface of the optical waveguide obtained by the method is considered to be a curved surface.

In addition, since reactive ion etching has high directivity, it is suitable for obtaining a rectangular cross-sectional shape. However, it is considered difficult to obtain a forward tapered cross-sectional shape by reactive ion etching.

Therefore, it is a feature of the present method that the optical waveguide 5 having the side surface constituted by the forward tapered cross-sectional shape and the plane, more specifically, the side surface constituted by a predetermined crystal plane is obtained. You can say that.

The optical waveguide 5 formed by the above method
Is not particularly limited, but is usually in the range of the order of submicrons to several tens of μm. The height of the optical waveguide 5 is not particularly limited, but is usually in the order of submicron to 10 μm.

The range of the angle between the side surface of the optical waveguide 5 and the main surface of the single crystal underlayer 1 differs depending on the material used for the magnetic garnet layer 4 and the like. Typically, this angle is greater than 0 ° and less than 90 °.

As described above, the optical waveguide 5 formed by the present method has an isosceles trapezoidal shape or a cross-sectional shape of an isosceles triangle. The cross-sectional shape of the optical waveguide 5 is determined according to the width and height of the optical waveguide 5 and the angle between the side surface of the optical waveguide 5 and the main surface of the single crystal underlayer 1. For example, the optical waveguide 5 has an isosceles trapezoidal cross section when its width is wide, and has an isosceles triangular cross section when its width is narrow.

The material constituting the single crystal underlayer 1 is as follows.
There is no particular limitation as long as the magnetic garnet layer 4 can be lattice-matched with the magnetic garnet layer 4 and the magnetic garnet layer 4 is formed during the liquid phase epitaxy. For example, garnet such as Gd ₃ Ga ₅ O ₁₂ can be used. Can be. Usually, the single crystal underlayer 1 is a single crystal substrate.

The magnetic garnet constituting the optical waveguide 5 is not particularly limited as long as it can be grown on the single crystal underlayer 1 by liquid phase epitaxy.
(LuNdBi) ₃ (FeAl) ₅ O _{12 and the} like.

The material of the resist layer 2 is not particularly limited, and a photoresist or the like generally used in photolithography can be used. In addition, the metal layer 3
Examples of the material include metals such as Ti.

[0043]

Embodiments of the present invention will be described below. 2A to 2E are cross-sectional views schematically illustrating a method for manufacturing an optical waveguide device according to an embodiment of the present invention.
The optical waveguide device shown in FIG. 2E was manufactured by the following method.

First, as shown in FIG. 2A, Gd ₃ G
a ₅ O ₁₂ on a garnet substrate 1 having a composition represented by, OEBR-100 is a positive resist of the electron beam exposure
0 was applied by a spinner to form a coating film having a thickness of 0.5 μm. This coating film was baked at 180 ° C. for 30 minutes to form a resist layer 2.

Next, as shown in FIG. 2B, a thickness of about 0.2 μm was formed on the resist layer 2 by using a vacuum evaporation apparatus.
Was formed. The Al film 6 prevents the substrate 1 from being charged during electron beam exposure described later.

After the formation of the Al film 6, a region of the resist layer 2 where the optical waveguide is not formed was exposed to an electron beam. After the exposure, the Al film 6 was removed using a NaOH aqueous solution. Thereafter, the resist layer 2 was developed with a developing solution obtained by mixing methyl isobutyl ketone and isopropyl alcohol (IPA) at a ratio of 1: 1 and rinsed with IPA. Further, undesired resist slightly remaining after the development was removed by O ₂ plasma ashing. The ashing was performed for 45 seconds at an incident power of 50 W. As described above,
A resist pattern composed of the resist layer 2 shown in FIG. 2C was formed.

Next, a Ti film 3 having a thickness of about 90 nm was formed on the substrate 1 using the resist pattern as a mask.
Note that the Ti film 3 was formed using E-gun, that is, by a vapor deposition method using an electron beam.

After forming the Ti film 3, the substrate 1 was immersed in acetone to perform lift-off. The Ti film 3 formed on the resist layer 2 was removed together with the resist, and only the Ti film 3 formed on the substrate 1 remained. As a result, the structure shown in FIG. 2D was obtained.

Next, using the Ti film 3 as a mask, FIG.
(LuNdBi) on the substrate 1 as shown in FIG.
_An optical waveguide 5 made of a magnetic garnet having a composition represented by ₃ (FeAl) ₅ O ₁₂ was formed by a liquid phase epitaxial growth method. The growth temperature was 755 ° C. and the growth time was 3
0 second to 1 minute. In addition, the Ti film 3 dissolved in the melt used for the liquid crystal epitaxial growth of the magnetic garnet during the growth of the magnetic garnet and disappeared from the substrate 1.

The thickness of the optical waveguide 5 of the optical waveguide device shown in FIG.
It was 62 μm, and the refractive index for light having a wavelength of 1.55 μm was about 2.25 to 2.26 (the film thickness and the refractive index were measured by the m-line method). Further, the exposed surface of the optical waveguide 5 was flat and constituted of a crystal plane.

FIGS. 3 and 4 are electron micrographs of the optical waveguide device manufactured as described above. In the optical waveguide device shown in FIG. 3, the optical waveguide 5 has a cross-sectional shape of an equilateral trapezoid. On the other hand, in the optical waveguide device shown in FIG. 4, the optical waveguide 5 has an isosceles triangular cross section. The optical waveguide device shown in FIG. 3 was obtained when the line width of the resist pattern was made wider, and the optical waveguide device shown in FIG. 4 was obtained when the line width of the resist pattern was made narrower. is there. From the above, it was confirmed that the cross-sectional shape and dimensions of the optical waveguide 5 could be controlled according to the opening width of the metal mask 3.

Further, it was confirmed that the side surface of the optical waveguide 5 made an angle of about 22 ° with the main surface of the substrate 1 and corresponded to the (3 2 1) plane.

Further, it was confirmed that the optical waveguide device had extremely low optical loss because the sidewall of the optical waveguide was not damaged by etching.

[0054]

As described above, according to the present invention,
The optical waveguide is formed by causing crystal growth on a single-crystal underlayer on which a metal layer having a predetermined pattern of openings is formed. Therefore, unlike the case where etching is used, the shape and dimensions can be accurately controlled, and the optical waveguide element can be manufactured in a small number of steps.

That is, according to the present invention, there is provided an optical waveguide device having an optical waveguide composed of a magnetic garnet and capable of accurately controlling its shape and dimensions, and a method of manufacturing the same. Further, according to the present invention, there is provided an optical waveguide element having an optical waveguide constituted by a magnetic garnet and capable of being manufactured in a small number of steps, and a method of manufacturing the same.

[Brief description of the drawings]

1A to 1C are cross-sectional views schematically illustrating a method for manufacturing an optical waveguide device according to an embodiment of the present invention.

FIGS. 2A to 2E are cross-sectional views schematically illustrating a method for manufacturing an optical waveguide device according to an embodiment of the present invention.

FIG. 3 is an electron micrograph of an optical waveguide device according to an example of the present invention.

FIG. 4 is an electron micrograph of an optical waveguide device according to an example of the present invention.

5A to 5F are cross-sectional views schematically showing a conventional method for forming a magnetic garnet optical waveguide.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1, 11 ... Substrate 2, 14 ... Resist layer 3 ... Metal layer 4, 12 ... Magnetic garnet layer 5 ... Optical waveguide 6 ... Al film 13 ... Silicon oxide layer 15 ... Metal pattern

[Procedure amendment]

[Submission date] March 24, 2000 (200.3.2.
4)

[Procedure amendment 1]

[Document name to be amended] Statement

[Correction target item name] Claims

[Correction method] Change

[Correction contents]

[Claims]

Claims (2)

[Claims] 1. An optical waveguide substantially comprising a single crystal underlayer and a single crystal magnetic garnet and formed on the single crystal underlayer, wherein the optical waveguide has a forward tapered cross-sectional shape. And a side surface of the optical waveguide is formed as a plane. 2. A step of forming a metal layer having an opening of a predetermined pattern on a single crystal underlayer, and forming a magnetic garnet by liquid phase epitaxy on an exposed surface of the single crystal underlayer on which the metal layer is formed. Forming an optical waveguide substantially consisting of magnetic garnet by crystal growth.