JPS6366511A - Production of quartz optical waveguide - Google Patents

Abstract

PURPOSE:To obviate the generation of foam at the boundary between a silicon substrate and glass film by forming the glass film having a high viscosity at a high temp. on the substrate, then forming the porous glass films for a clad and core on said glass film and heating the glass films to a high temp. to sinter the glass films. CONSTITUTION:The glass film having the high viscosity at a high temp. is preliminarily formed on the Si substrate 1 to form the glass film for an optical waveguide on the Si substrate 1. The porous glass film 3 for the clad and the porous glass film 4 for the core are thereafter formed on the glass film 2 and these glass films are heated at a high temp. and are sintered to form the transparent glass films. The glass films having the coefft. of thermal expansion larger than the coefft. of thermal expansion of the glass film 2 and have the low vitrifying temp. are used for the two glass films 3, 4. The glass film 2 having the high viscosity on the Si substrate 1 suppresses the expansion of the foam generated between said film and the substrate 1. Since the two glass films 3, 4 are formed on the glass film 2, the splintering of the Si substrate 1 by the stress is obviated and the transparent glass film is stably formable over the entire surface of the Si substrate 1.

Description

Detailed Description of the Invention - I A method for manufacturing a quartz-based optical waveguide on a silicon substrate, in which a transparent glass film is formed on a silicon substrate with high productivity by pre-heating the silicon substrate at a high temperature. After forming a highly viscous glass film, porous glass films for cladding and core are formed on top of it, and these glass films are heated to a high temperature and sintered, thereby producing stable transparent glass at all times. membrane can be obtained.

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical waveguide used in optical communication devices, and more particularly to a method for manufacturing an optical waveguide made of silica glass.

In recent years, with the progress of optical communications, optical branching/coupling circuits, optical demultiplexing/
There is a demand for supplying optical components such as multiplexers in large quantities and at low cost. Traditionally, these optical components include prisms,
Bulk type optical components consisting of a combination of lenses, filters, etc. have been used. However, these bulk optical components require a long time to assemble and adjust, resulting in poor productivity (
This led to higher prices for optical components, and it was also difficult to miniaturize, which hindered the development of optical communication systems in various fields. Recently, as a method to solve the above problem, an optical waveguide has been created on a flat substrate, and various 81-function elements such as a light emitting element and a light receiving element are mounted on this flat substrate, and the end of the optical waveguide is connected to an optical waveguide. An optical module has been developed that can be combined with As the usage of optical waveguides has been developing more and more recently, there is a demand for an optical waveguide manufacturing method that can efficiently manufacture optical waveguides.

The conventional method for forming a glass film for a silica optical waveguide is as follows:
Two methods are known: one method is to form a glass film directly on a silicon substrate, and the other method is to form a porous glass film and then heat it to a temperature of 20°C to sinter it to form a transparent glass film.

To give an example of the former method, first, a silicon substrate is heated in a steam atmosphere to thermally oxidize it to a thickness of 4.5 mm.
After forming a 5 μm cladding glass, Ti
5i02 glass doped with is formed by sputtering to form a core glass crotch. In order to form an optical waveguide, the glass film formed on the silicon substrate as described above is patterned into a predetermined shape using lithography, and then 5i02 glass is formed on the pattern. An optical waveguide is obtained by forming a clad glass by a CVD method or the like.

In the latter method, an apparatus 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 in the figure.

A plurality of silicon substrates 1 are placed on a turntable 6, and source gases such as H2,02 and 5IC)4 are blown onto the silicon substrates 1 by a flame hydrolysis burner 5 to deposit them. First, a porous glass film for the cladding is deposited on the silicon substrate 1, and then a porous glass film for the core is deposited with a different composition. Subsequently, the silicon substrate 1 is heated to about 1300° C. to sinter the porous glass film into transparent glass. In order to make an optical waveguide, the transparent glass film thus formed on the silicon substrate is patterned into a predetermined shape by lithography, and then SiO2 glass is formed on this pattern by CVD method etc., and quartz is used as cladding glass. A glass-based leading waveguide is obtained.

Problems to be Solved by the Invention Among the conventional glass film forming methods, the method of directly forming a glass film on a silicon substrate can form a glass film with good transparency relatively easily, but it has the disadvantage of poor workability. was there. For example, it takes about 25 hours to form a cladding glass with a thickness of 4°5 μm, and the core glass jI
The L stacking velocity is also very small.

In the method of first forming porous glass on a silicon substrate and converting it into transparent glass from C, it takes about 2 hours to form transparent rad glass with a thickness of 4.5 μm and transparent core glass with a thickness of 45 μm. It is enough. However, this method requires strict control of the transparent vitrification conditions.

For example, conventionally, a glass film made of SiO-P205-[3203 or a glass film made only of 5tO2 was formed as a clad glass film on a silicon substrate, but the following problems occurred at this time. .

When using glass made of S i 02-P2O3-8203 for cladding, it is difficult to stably form a transparent and homogeneous glass film over the entire surface of the silicon substrate. 12 glasses
When heated at 60° C. for 15 minutes, a transparent glass film was formed on a portion of the substrate, but sintering was not yet completed on other portions and the film remained opaque. When heated at 1,290°C, a transparent glass film was similarly formed in some parts, but in some parts, bubbles were generated in the glass, contrary to what happened when heated to 1,260°C. It was confirmed that these bubbles were generated from the interface between the silicon substrate and the glass film. These phenomena are thought to arise from the non-uniformity of the composition of the porous glass deposited on the silicon substrate and the large change in viscosity of this ternary glass at high temperatures.

When using SiO□ glass for cladding, the following problems arose. When 5i02 porous glass was heated at 1350°C, a transparent glass film was formed, but 5i
02 There is a large mismatch in the thermal expansion coefficients of glass and silicon substrate, and the vitrification temperature is S i 02-P2
Since it is higher than 05-8203 glass, there was a problem that the silicon substrate would break during the time it was cooled to room temperature after being made into transparent glass. In addition, the silicon substrate and 3i02
Bubbles were generated at the interface with the glass, but due to the high viscosity of 5i02, these bubbles remained small, and 5i02
The transparency of the glass was not affected.

As described above, when Si02-P205-[3203 glass or 5i02 glass was used as the cladding glass, there was a problem in that a transparent glass film could not be formed over the entire surface of the silicon substrate.

The present invention has been made in view of these points, 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. It is to provide.

Means for Solving the Problems According to the present invention, in order to form a glass film for an optical waveguide on a silicon substrate 1, a highly viscous glass g! is applied on the silicon substrate 1 in advance at high temperature. form 2.

After that, a porous glass film 3 for cladding is placed on the glass film 2,
A transparent glass film is obtained by forming a core porous glass film 4 and heating it to a high temperature to sinter it. The porous glass W for the cladding 43 and the porous glass film 4 for the core are made to have a larger thermal expansion coefficient than the glass m2 and have a lower transparent vitrification humidity.

[-1 plate The highly viscous glass film 2 formed on the silicon substrate 1 functions to suppress the expansion of air bubbles generated between it and the substrate 1. For this inhibiting effect, it is sufficient that the glass film 2, which is highly viscous at high temperatures, has a thickness of about 1 μm. According to the present invention, the porous glass film 3 for the cladding and the porous glass film 4 for the core, which have a large thermal expansion coefficient and a low transparent vitrification temperature, are formed on the glass film 2, so that stress can cause the silicon The board 1 will not be broken,
A transparent glass film can be stably formed over the entire surface of the silicon substrate 1.

Example Examples of the present invention will be described in detail below.

Using a porous glass film deposition apparatus as shown in FIG. 2, a porous glass film of SiO2 was deposited on a silicon L (plate 1) by a flame hydrolysis burner 5.Then, a silicon substrate was deposited. A transparent 5ho2 glass film having a thickness of approximately 1 μm was formed over the entire surface of the silicon substrate by heating at 1350° C. for 15 minutes.This silicon substrate did not crack even when cooled to room temperature.

followed by 5iO2-P, using similar equipment.

Porous glass for cladding consisting of 05-8203, S
i02-Gem2-P20 was sequentially deposited and then heated at 1290°C, and the glass became transparent without containing any air bubbles. Obtained over the entire substrate.

FIG. 1 is a cross-sectional view of the glass film formed on the silicon substrate F as described above.
．． A 0 μm SiO2 glass film 2 is formed,
A cladding glass film 3 and a core glass film 4 are laminated on this glass film 2.

In this example, the thickness of the cladding glass film 3 is 5 μm.
The thickness of the glass film 4 for m1 core was 47 μm. This silicon substrate did not crack even when cooled to room temperature.

The cladding glass film 3 and the core glass film 4 used in this example had a larger coefficient of thermal expansion and a lower transparent vitrification temperature than the Sio2 glass film 2.

In this example, a silicon substrate is used as the substrate, and the silicon substrate has good thermal conductivity, and has the advantage of good heat dissipation when a GaAs-based optical semiconductor element is used in combination with an optical waveguide. This is because there is.

In this way, the Si02 glass film 2 is deposited on the silicon substrate 1.
After forming the glass film 3 for cladding and the glass film for core, in order to form an optical waveguide, the glass film 3 for cladding and the glass film 4 for core are patterned into a predetermined shape by lithography, and then 3i02 is formed on this pattern. An optical waveguide was formed by forming glass using a CVD method to form clad glass.

Effects of the Invention As detailed above, the present invention forms a highly viscous glass film at high temperature on a silicon substrate, and forms a cladding glass film and a core glass film on this glass film. Silicon does not generate bubbles at the interface between the substrate and the glass film on it, and the stress acting between the substrate and the glass on it due to mismatching of thermal expansion coefficients is small, so the substrate does not break. substrate"
- It is possible to stably form a glass film for an optical waveguide. Furthermore, since porous glass is first formed and the porous glass is made transparent by sintering, productivity is improved compared to the method of forming a 111-contact glass film on a silicon substrate.

[Brief explanation of drawings]

FIG. 1 is a sectional view of a glass film for an optical waveguide formed according to the present invention, and FIG. 2 is a schematic diagram of a porous glass film deposition apparatus. 1...Silicon substrate, 2...Glass film with high temperature and high viscosity (Sin,...),
3... Glass membrane for cladding, 4... Glass membrane for core, 5... Burner for flame hydrolysis, 6... Turntable. 1: ＞Recon No. 4: Tsuagari Orashira (Fig. 1)

Claims (1)

[Claims] A porous glass film for cladding (3) on a silicon substrate (1).
) and a porous glass membrane for the core (4) are formed in this order,
These glass films (3, 4) are heated to a high temperature and sintered to form a transparent glass film, and then the laminated transparent glass films for cladding and core are patterned into a predetermined shape by lithography, and then the pattern is In a method for manufacturing a silica-based optical waveguide in which a clad glass is laminated thereon, a glass film (2) with high viscosity is formed at high temperature on the silicon substrate (1), and then porous holes for cladding are formed on the glass film (2). quality glass membrane (3)
A method for producing a silica-based optical waveguide, which comprises forming a core porous glass film (4), and heating and sintering these porous glass films (3, 4) to a high temperature.