JPH07119848B2 - Manufacturing method of quartz optical waveguide - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION Overview A method for manufacturing a silica-based optical waveguide on a silicon substrate, which has a thickness of 1.0 μm or more previously formed on the silicon substrate in order to form a transparent glass film on the silicon substrate with good mass productivity. The transparent glass film is always stably obtained by forming the porous glass film for the cladding and the core on the thermal oxide film after forming the thermal oxide film.

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for manufacturing an optical waveguide used for an optical communication device or the like, particularly an optical waveguide formed of silica glass.

With the progress of optical communication in recent years, optical branching / coupling circuits and optical demultiplexing
It is required to supply optical components such as multiplexers in large quantities at low cost. Conventionally, a bulk type optical component composed of a combination of these optical components has been used. However, since these bulk type optical components require a long time for assembly and adjustment, the productivity is poor, the cost of the optical components is increased, and the miniaturization is difficult, which hinders the development of various fields of the optical communication system. It had been. Recently, as a method of solving the above problems, an optical waveguide is formed on a flat substrate, and a light emitting element is formed on the flat substrate.
An optical module has been developed which is equipped with various functional elements such as a light receiving element and which couples an end portion of an optical waveguide with an optical fiber.
Since the usage of the optical waveguide has been developed more and more recently in recent years, there is a demand for an optical waveguide manufacturing method capable of efficiently manufacturing the optical waveguide.

Conventional Technology As a conventional glass film forming method for a silica-based optical waveguide,
There are known a method of directly forming a glass film on a silicon substrate and a method of forming a porous glass film and then heating the porous glass film to sinter it to form a transparent glass film.

As an example of the former method, first, a silicon substrate is heated in a steam atmosphere to be thermally oxidized to a thickness of 4.5.
After forming a cladding glass having a thickness of μm, a SiO ₂ glass containing Ti is formed thereon by sputtering to form a core glass film. In order to obtain an optical waveguide, the glass film formed on the silicon substrate as described above is patterned by lithography to form a laminated glass film for cladding and core into a predetermined shape, and then the SiO ₂ glass is used to form the pattern. An optical waveguide is obtained by forming a cladding glass on the above by a CVD method or the like.

In the latter method, a device as shown in FIG. 2 is used. In FIG. 2, 6 is a turntable, which is intermittently rotated in the direction of the arrow shown. A plurality of silicon substrates 1 are placed on the turntable 6, and source gases such as H ₂ , O ₂ and SiCl ₄ are sprayed and deposited on the silicon substrate 1 by a flame hydrolysis burner 5. First, a porous glass film for cladding is deposited on the silicon substrate 1, and then a porous glass film for core is deposited by changing the composition. Then, the silicon substrate 1 is heated to about 1300 ° C. to sinter the porous glass film into transparent glass. In order to form an optical waveguide, the transparent glass film thus formed on the silicon substrate is patterned into a predetermined shape by lithography, and subsequently SiO ₂ glass is formed on this pattern by a CVD method or the like as a clad glass, A quartz glass optical waveguide is obtained.

Problems to be Solved by the Invention Among the conventional glass film forming methods, in the method of directly forming a glass film on a silicon substrate, a glass film with good transparency can be formed relatively easily, but workability is poor. was there. For example, it takes about 25 hours to form a cladding glass having a thickness of 4.5 μm, and the deposition rate of the core glass is very low.

In the method in which porous glass is first formed on a silicon substrate and then made into transparent glass, it takes about 2 hours to form a transparent clad glass with a thickness of 4.5 μm and a transparent core glass with a thickness of 45 μm. Is enough. However, this method requires strict control of transparent vitrification conditions.

For example, when a porous glass composed of SiO ₂ —P ₂ O ₅ —B ₂ O ₃ was formed on a silicon substrate and heated at 1260 ° C. for 15 minutes,
Although a transparent glass film could be formed on a part of the silicon substrate, sintering was not completed and it was opaque on a part. When subsequently heated at the same temperature for 15 minutes, the glass where the transparent glass film was previously made contained many bubbles, and the previously opaque place became the transparent glass film. Was observed.

Further, when glass having the same composition was heated at 1290 ° C. for 15 minutes, it was observed that a part thereof also contained bubbles and a part thereof became a transparent glass film. As described above, this method has a problem that it is difficult to stably form a transparent glass film on a silicon substrate.

The present invention has been made in view of the above circumstances, and its purpose is to provide a method for manufacturing a silica-based optical waveguide that has good workability and can stably form a transparent glass film on a silicon substrate. Is to provide.

Means for Solving the Problems According to the present invention, in forming a glass film for an optical waveguide on the silicon substrate 1, by blowing water vapor onto the heated silicon substrate 1, the process shown in FIG. So that the thickness in advance
A thermal oxide film (SiO ₂ ) 2 having a thickness of 1.0 μm or more is formed. After that, a porous glass film 3 for cladding and a porous glass film 4 for core are formed on the thermal oxide film 2, and these are heated to a high temperature and sintered to obtain a transparent glass film.

When the thermal oxide film 2 is formed on the silicon substrate 1 as described above, the thermal oxide film 2 and the porous glass film for cladding 3 are made of the same material and have substantially the same thermal expansion coefficient.
No bubbles are generated at this interface during sintering. Therefore, even if the porous glass is heated at a high temperature for a long time, bubbles are not generated in the glass, and the transparent vitrification of the porous glass can be easily achieved.

Examples Hereinafter, examples of the present invention will be described in detail.

The silicon substrate was heated in a water vapor atmosphere at 1200 ° C. for 100 minutes to form a 1.0 μm thick SiO ₂ thermal oxide film on the silicon substrate. Then use the device as shown in FIG. 2 on the substrate, cladding porous glass made of _{SiO 2 -P 2 O 5 -B 2} O 3 , and _{SiO 2 -P 2 O 5 -B 2} O 3 Porous glass for cores made of -TiO ₄ was sequentially formed. Then, the silicon substrate on which the porous glass film was thus formed was heated at 1300 ° C. for 30 minutes to sinter the porous glass to form a transparent clad glass film and a core glass film. It was confirmed that these glass films were composed of a transparent glass film containing no bubbles and having no cloudiness. FIG. 1 is a cross-sectional view of the glass film formed on the silicon substrate as described above, in which the thermal oxide film 2 having a thickness of 1.0 μm is formed on the silicon substrate 1, and the thermal oxide film 2 is formed on the thermal oxide film. The clad glass film 3 and the core glass film 4 are laminated. In this embodiment,
The cladding glass film 3 had a thickness of 4.5 μm, and the core glass film 4 had a thickness of 45 μm.

As a result of various experiments, if the thickness of the thermal oxide film was 1.0 μm or more, a transparent glass film for the clad and the core could be easily obtained in the same manner as in the above-mentioned embodiment. When the thickness is even thinner, for example, 0.8 μm, when trying to heat the porous glass into a transparent glass, bubbles are formed in the glass film as in the case where the thermal oxide film is not formed at all. Therefore, the thickness of the thermal oxide film is
1.0 μm or more is a necessary condition, and there is no particular critical value as the upper limit, but 2.0 μm or less is desirable.

When the thermal oxide film SiO ₂ is previously formed on the Si substrate in this manner, the porous glass film for cladding contains SiO ₂ as a main component as described above, so that the thermal oxide film and the porous glass for cladding are formed. Since the film and the film are made of the same material, they have substantially the same thermal expansion coefficient, so that no bubbles are generated between the thermal oxide film and the glass film for cladding during sintering.
That is, it is considered that the thermal oxide film plays the role of a cushioning material, reduces strain on the glass film for cladding during sintering, and prevents generation of cracks. However, if the thermal oxide film is too thin, the thermal oxide film cannot serve as a buffer material, and cracks may occur.

In this embodiment, a silicon substrate is used as the substrate, but the silicon substrate has good heat conduction and has the advantage of good heat dissipation when using a GaAs optical semiconductor element in combination with an optical waveguide. is there.

After the thermal oxide film 2, the cladding glass film 3 and the core glass film 4 are formed on the silicon substrate 1 in this way, the cladding glass film 3 and the core glass film 4 are lithographically processed to form an optical waveguide. Then, an optical waveguide was formed by patterning into a predetermined shape by, and then forming SiO ₂ glass on this pattern by a CVD method to form a clad glass.

EFFECTS OF THE INVENTION As described in detail above, according to the present invention, a thermal oxide film is formed on a silicon substrate, and a clad glass film and a core glass film are formed on the thermal oxide film. Since the glass film for cladding has approximately the same thermal expansion coefficient, no bubbles are generated between the glass film for cladding and the thermal oxide film, and the thermal oxide film serves as a buffer material during sintering. This has an effect that a transparent glass film can be easily formed. Furthermore, since the porous glass is first formed and the porous glass is made transparent by sintering, there is also an effect that the productivity is good as compared with the method of directly forming the glass film on the silicon substrate.

[Brief description of drawings]

FIG. 1 is a sectional view of a glass film for an optical waveguide formed by the present invention, and FIG. 2 is a schematic configuration diagram of a porous glass film deposition apparatus. 1 ...... silicon substrate, 2 ...... thermal oxide film (SiO _2), 3 ......
Glass film for clad, 4 ... Glass film for core, 5 ... Burner for flame hydrolysis, 6 ... Turntable.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Koji Okamura 1015 Kamiodanaka, Nakahara-ku, Kawasaki-shi, Kanagawa Fujitsu Limited (56) References JP-A-60-39605 (JP, A)

Claims (1)

[Claims] 1. A porous glass film (3) for cladding and a porous glass film (4) for core are formed in this order on a silicon substrate (1), and these glass films (3, 4) are heated to a high temperature. And then sintering to form a transparent glass film, and then patterning the transparent glass film for cladding and core laminated by lithography into a predetermined shape, and then laminating a cladding glass on the pattern In the method, after forming a thermal oxide film (2) having a thickness of 1.0 μm or more on the silicon substrate (1), a porous glass film (3) for cladding is formed on the thermal oxide film (2).
And a porous glass film (4) for a core, and heating the porous glass film (3, 4) to a high temperature to sinter the silica glass optical waveguide manufacturing method.