JPH0534527A - Formation of optical waveguide - Google Patents

Abstract

PURPOSE:To provide the method for forming the optical waveguide which facilitates the control of the amts. of additive and the control of the regions for addition. CONSTITUTION:This method for forming the optical waveguide has a stage for forming a protective mask pattern consisting of a metallic film on silica glass added with a functional compd. produced by a sol-gel method and a stage for forming the optical waveguide by subjecting the silica glass formed with this protective mask pattern to anisotropic etching by reactive gases. The more particularly preferable embodiemnt includes the use of >=1 selected from rare earth element ions, semiconductor particles and org. compds. having a nonlinear optical effect as the functional compd. The control of the amts. of the additives and the control of the regions for addition are easy and the control of the core diameter at 0.1mum order and a refractive index difference at 0.01% level is possible. The optical waveguide having the precise structure is thus formed.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a novel optical waveguide forming method.

[0002]

2. Description of the Related Art Conventionally, as an optical waveguide manufactured by using the sol-gel method, for example, the method proposed in Japanese Patent Laid-Open No. 61-156007 is well known. That is, the metal alkoxide solution is gelled and dried to form a porous glass body, and after the mask is attached to the porous glass body, the porous glass body is placed in an atmosphere containing atoms that can change the refractive index of the glass. It is a method of immersing the body and diffusing atoms that can change the refractive index of glass into the unmasked doped portion. According to this method, the atoms to be added are in a solution state or in a gas phase state, and a refractive index distribution can be formed in the porous glass body by the diffusion phenomenon into the porous glass body.

[0003]

The refractive index distribution for forming an optical waveguide is required to have high accuracy. In the case of a single mode waveguide, the core diameter is 8 ± 0.1 μm and the refractive index difference is 0. It is about 33 ± 0.05%. In the case of the conventional method, the addition amount and the addition region are controlled by controlling the concentration of diffusion atoms, the diffusion temperature and the diffusion time. However, with this method, it is difficult to control the core diameter on the order of 0.1 μm and the refractive index difference at the level of 0.01%. In view of the above situation, an object of the present invention is to provide an optical waveguide forming method in which it is easy to control the amount of an additive and the region of addition.

The present invention which achieves the above-mentioned object comprises a step of forming a protective mask pattern made of a metal film on a silica-based glass containing a functional compound prepared by a sol-gel method, and a silica-based glass on which the protective mask pattern is formed. And forming an optical waveguide by anisotropically etching glass with a reactive gas. The silica glass produced by the sol-gel method,
It is possible to fabricate functional optical devices such as optical switches and optical amplifiers by adding at least one of rare earth ions, semiconductor fine particles, organic compounds having a nonlinear optical effect (hereinafter abbreviated as nonlinear organic compounds), and the like. Become.

[0005]

The sol-gel method is a process for synthesizing glass by hydrolyzing a metal alkoxide in an alcohol solution and condensing silica bonds. This process is characterized in that it is a liquid phase reaction and that it can be vitrified at a low temperature of about 1000 ° C. Therefore, it is easy to add optical functional materials such as rare earth element ions, semiconductor fine particles, and non-linear organic compounds. The glass to which these photofunctional compounds are added is very useful as a functional glass. For example, glass doped with rare earth element ions is used as a laser glass or an optical amplifier, and glass added with semiconductor fine particles or a nonlinear organic compound exhibits a large nonlinear optical effect, and is applied to a nonlinear switch or the like.
Optical waveguide forming technology is very important for these devices.

The optical waveguide forming method of the present invention will be described in detail.
First, a silica-based glass is produced by a sol-gel method, and this step may be performed by a known technique in this field, for example, silicon alkoxide such as silicon methoxide and ethoxide, alcohol such as water, methanol, ethanol and propanol, and the like. If necessary, an acid or alkali catalyst is mixed to prepare a hydrolysis solution, the hydrolysis reaction is allowed to proceed under appropriate conditions to cause gelation, and the obtained gel is dried, or dried and heated. After making porous glass,
Further, after sintering to make transparent glass, a glass pattern is formed by an etching process described later to form an optical waveguide. To add the functional compound to the glass by the sol-gel method, the functional compound or a salt thereof is simply added to the sol-gel solution as an aqueous solution or an alcohol solution (in the case of rare earth element ions or organic compounds), or the functional compound. Various other means can be adopted, such as adding an aqueous salt solution or alcohol solution of (1) to make particles by a chemical reaction (in the case of semiconductor fine particles). Examples of the above-mentioned rare earth element ions include lanthanoid rare earth element ions such as Pr, Nd, Sm, Er and Yb. The addition amount of these is not particularly limited, but is generally about 10 ppm to 5% by weight. Is. Examples of the semiconductor fine particles include S
i, Ge, PbS, CdS, CdSSe, CdSe, C
uCl, CuBr, GaAs, etc. may be mentioned. The addition amount of these is not particularly limited, but is generally 1 to 20% by weight. Examples of the organic compound include xylizanin, para-nitroaniline, 2-methyl-4-nitroaniline and various other functional organic compounds, and the addition amount thereof is not particularly limited, but is 1 to 20% by weight. Is common.

Next, the gas obtained as described above is subjected to the steps shown in FIG.
Lath (dry gel or transparent glass) is processed into a waveguide.
First, the silica-based gas containing the functional compound obtained above is added.
A protective mask pattern made of a metal film is formed on the lath 1.
It Specifically, for silica glass 1 produced by the sol-gel method
Amorpha is formed by sputtering, vacuum deposition, CVD, etc.
Si, Si₃N_FourA metal film 2 of Al, Al, Mo, etc.
To do. The figure shows the case of Al as a representative of metals. next
A photo resist is formed on the metal film 2 by using a photo process technology.
Forming a strike pattern. Resist film 3 on metal film 2
After coating and drying, attach a waveguide-shaped mask to it and
Irradiate. Resist can be either negative or positive.
Yes. Then, dip it in the developer to remove unnecessary parts.
Then, the resist pattern 4 is formed. Etching this
Put it in the equipment and use the etching gas as a photoresist pattern
The metal film is used as a mask to etch the metal film
The metal film in the area without the strike film is etched and the metal pattern
A layer (Al pattern 5 in FIG. 1) can be formed. Then money
Silica-based glass is etched using the metal film as a protective mask.
The glass pattern 6 is formed by chemical etching with a glass.
Particularly preferably, anisotropic etching is performed. CF _FourSuch
Fluorine radicals when plasma is generated using the reactive gas
Occurs. It is chemically very active and can
Reacts with the gas and etches. At this time,
Then, when a vertical electric field is formed, the fluorine radicals are perpendicular to the sample.
It is incident and the etching proceeds only in the vertical direction. This is anisotropic
This is referred to as property etching. Then the photoresist pattern,
The metal film is removed. In this way, width 2-10 μm, depth
Optical waveguide having an arbitrary shape within the range of 1 to 10 μm
Can be produced. FIG. 2 shows an optical waveguide formed by the present invention.
A specific example of In addition, silica added with a functional compound
The thickness of the system glass is not particularly limited, but is about 1 to 2 mm,
The thickness of the metal film is about 1 to 2 μm. Reactive ion
By changing the type of etching gas during
Greatly change the etching rate of metal and silica
Therefore, the metal film is used as a protective mask. Siri
The mask that can etch the mosquito around 8 μm is gold
Genus is common. For example, the etching gas is CF_FourPlace
In the case of silica and Al, the relative etching rate is 8
0: 1 and etching gas is BCl₃In Case of
It is 1:15. Therefore, CF_FourSilica only
Is etched and BCl₃If you use
Be ching. Here, the etching gas is CC
l_Four, BCl₃, CF_Four, C₂F₆Chlorine gas such as
And fluorine gas, depending on the type of metal film
You can choose. Generally chlorine-based gas etches metal
The fluorine-based gas is used for glass. Etch
The ing gas concentration is usually 100%.

[0008]

EXAMPLES The present invention will be specifically described below with reference to examples, but the present invention is not limited thereto. Example 1 30 ml of silicon methoxide and 30 water as glass raw materials
60 ml of ethyl alcohol is added to and mixed with ml to prepare a uniform sol-gel solution. Next, 0.28 g of erbium chloride as a functional compound was added to this sol-gel solution,
Dissolve. The sol-gel solution is poured into a disk-shaped container, sealed with an aluminum sheet, and kept at 80 ° C. for 2 days for gelation. Next, several 1 mmφ holes are made in the aluminum sheet and dried at 150 ° C. for 1 week. 1 for the obtained gel
The temperature was raised to 200 ° C. to make transparent glass. This glass contains 1% by weight of erbium (Er), which has laser oscillation characteristics.
Contains. Next, using this glass as a substrate, Al was vapor-deposited to a thickness of 1 μm by a sputtering method and patterned by a photoresist. This sample was etched with CCl ₄ gas using a reactive ion etching apparatus to provide a patterned Al layer on glass. Next, the underlying Er-doped glass was etched by about 8 μm with CF ₄ gas using the patterned Al as a mask. As a result, an 8 μm square waveguide could be formed on the Er glass.

Example 2 30 ml of silicon methoxide and 30 parts of water as glass raw materials
60 ml of ethyl alcohol was added to and mixed with 1.5 ml of lead chloride. The solution prepared above was poured into a container, sealed with an aluminum sheet, and kept at 80 ° C. for 2 days for gelation. The aluminum sheet is perforated with several 1 mmφ holes for drying, the temperature is raised to 150 ° C. over 100 hours, and the temperature is maintained for 30 hours. The obtained dried gel is heated in a vacuum sintering furnace to 300 ° C. for 5 hours and kept for 1 hour, and then heated to 800 ° C. for 10 hours and kept for 1 hour.
The obtained porous glass is dipped in a sodium sulfide aqueous solution to generate fine particles of lead sulfide in the porous glass. This glass contains 1% by weight of lead sulfide having a nonlinear optical effect. Next, using this glass as a substrate, amorphous silicon was formed by the PCVD method, and a resist pattern was formed thereon by the photolithography method. C
BrF ₃ is used as an etching gas to pattern the amorphous silicon by reactive ion etching. Next, using amorphous silicon as a mask, CHF
_The lead sulfide-added glass is patterned by reactive ion etching using ₃ as an etching gas. After that, the resist is removed by oxygen plasma, and the mask of amorphous silicon is removed using CBrF ₃ as an etching gas. As a result, a waveguide was formed on the glass containing lead sulfide.

Example 3 As a glass raw material, 30 ml of silicon methoxide and 2 parts of water were used.
Add 0 ml and 60 ml of ethyl alcohol, mix, and mix.
Add 1.2 g of -methyl-4-nitroaniline to make a homogeneous solution. After transferring to a container, it was sealed with an aluminum sheet and kept at 80 ° C. for 2 days for gelation. A few 1 mmφ holes are opened in an aluminum sheet and dried, and the temperature is raised to 150 ° C. over 100 hours and kept for 30 hours to obtain a dried gel. Tungsten silicide is deposited on the dried gel by a sputtering method and patterned by a photoresist. The tungsten silicide is etched by reactive ion etching using NF ₃ gas. Next, using the patterned tungsten silicide as a mask, the 2-methyl-4-nitroaniline-added gel is etched using C ₃ F ₈ . After that, the resist is removed by oxygen plasma, and the tungsten silicide is removed by etching with NF ₃ gas. As a result, a waveguide was formed on the gel doped with 2-methyl-4-nitroaniline.

[0011]

As described above, according to the present invention, it is possible to perform a high degree of fine processing on a functional glass produced by the sol-gel method at each stage of dry gel, porous body and transparent glass. It is possible to produce an excellent optical waveguide in which the core diameter can be controlled in the order of 0.1 μm and the refractive index difference can be controlled at the level of 0.01%.

[Brief description of drawings]

FIG. 1 is a schematic diagram illustrating an optical waveguide forming step of the present invention.

FIG. 2 is a diagram showing a specific example of an optical waveguide produced by the present invention.

[Explanation of symbols]

1 Er-doped glass 2 Al 3 resist 4 Resist pattern 5 Al pattern 6 glass patterns

Claims (2)

[Claims] 1. A step of forming a protective mask pattern made of a metal film on silica-based glass containing a functional compound added by a sol-gel method, and a step of reacting the silica-based glass on which the protective mask pattern is formed with a reactive gas. And a step of forming an optical waveguide by performing anisotropic etching. 2. The method for forming an optical waveguide according to claim 1, wherein the functional compound is one or more selected from rare earth element ions, semiconductor fine particles, and organic compounds having a nonlinear optical effect.