JPH1062638A - Optical waveguide and its manufacture - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve the uniformity or flatness and reduce the cost by forming a part or all of a core area, a clad area and a buffer layer by use of a glass film using a thermosetting inorganic polymer precursor as starting material. SOLUTION: Since a base 1 is formed of a quartz base, a core area 2 can be formed directly on the base 1 without particularly requiring a buffer layer. The base 1 also functions as a clad area 3 for surrounding the lower part of the core area 2. The base 1 is spin-coated by use of polysilazane precursor as a thermosetting inorganic polymer, and a preliminary heating is performed at a relatively low temperature near the boiling point of a solvent to evaporate the solvent. The baking temperature and baking atmosphere which are thermal treatment conditions for vitrification by thermal decomposition are selected, whereby the contents of nitrogen and oxygen in the glass film are controlled to provide a glass film having a wide refractive index range of 1.44-2.0. A film excellent in uniformity and step coverage can be formed with an inexpensive device.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical waveguide, and more particularly to a novel optical waveguide made of a thermosetting inorganic high molecular polymer in which a glass film can be easily formed by spinner coating or vapor phase growth, and a method of manufacturing the same. is there.

[0002]

2. Description of the Related Art An optical waveguide generally comprises a region having a high refractive index called a core and a region having a lower refractive index called a cladding surrounding the core on a flat substrate. Propagation is confined to. In addition, a buffer layer for optically isolating the light propagation region and the substrate from each other is formed as necessary in order to avoid the influence of light absorption and deflection dependence by the substrate.

[0003] Optical waveguides are typically manufactured using glass materials useful in the field of communications or information processing. In an optical waveguide using a glass material, as a method of forming a glass film constituting a core region, a cladding region, and a buffer region, a flame deposition method, a CVD (Chemical Vapor Deposition) method,
Various forming methods such as a sputtering method and a vapor deposition method have been conventionally studied.

The flame deposition method is widely used for forming a buffer layer formed on a substrate and an upper cladding region covering a core region since a thick and flat glass film can be obtained. Further, the CVD method, the sputtering method, the vapor deposition method and the like are effective at forming a glass film having a relatively low temperature and a uniform film thickness.

On the other hand, recently, SOG (Spin On Glas)
A simple glass film formation method using s) has attracted attention. Particularly, it is widely used as a method for forming an interlayer insulating film of a multilayer wiring in an electronic device. This SOG forms a high-quality glass film only by applying a precursor on a substrate by spin coating and applying heat treatment. As described above, various methods have been studied for forming a glass film for forming an optical waveguide.

[0006]

As described above, various methods for forming a glass film have been studied. However, each of the film forming methods has the following problems.

First, the flame deposition method requires a heat treatment at a high temperature exceeding 1000 ° C. in the step of forming a transparent glass, so that there is a concern that the shape of the substrate or the waveguide may be deformed. Further, the CVD method, the sputtering method, the vapor deposition method and the like are not suitable for forming a flat film and for covering a step, that is, for forming a cladding film above a core region having a step due to difficulty in step coverage.

Further, a SiH ₄ gas or TE
When a glass film is formed using an OS-based material, components such as an OH group and a SiH group that cause a loss of the waveguide easily remain in the formed film. That is, it is difficult to manufacture a low-loss optical waveguide.

The sputtering method has a low film forming rate and requires a considerable time to form a micron-order film. Each of the CVD method, sputtering method, and vapor deposition method described above requires an expensive film forming apparatus.
That is, there is a problem that the manufacturing cost of the optical waveguide is high.

On the other hand, a glass film using SOG can be formed by an inexpensive apparatus. However, in the conventional SOG, a vitreous forming material and an organic binder are added to a silicon compound, and a precursor solution obtained by dissolving these in an organic solvent is used. Is used. Such an SOG contains a large amount of OH groups and CH groups, and the film is greatly shrunk by thermal decomposition in the heat treatment step to cause cracks. Therefore, it is difficult to form a thick glass film. Further, since the CH group is incorporated as a constituent element of the glass film, transmission loss in a wavelength band used for communication increases.

Accordingly, an object of the present invention is to solve the above-mentioned problems of the prior art, and to provide an optical waveguide excellent in uniformity and flattening and low in loss, and a method of manufacturing the same.

[0012]

According to the present invention, there is provided an optical waveguide formed on a substrate made of any one of a semiconductor, a glass and a polymer resin. An optical waveguide was used in which a core region, a cladding region, and a part or all of a buffer layer having a substantially rectangular cross section were formed by a glass film using a thermosetting inorganic high molecular polymer precursor as a starting material.

The thermosetting inorganic polymer precursor is applied by a spin coating method, and thereafter, the thermosetting inorganic polymer precursor is thermally decomposed by heat treatment to be vitrified and applied at least once or heat treated. It is preferable to use a manufacturing method in which the above steps are repeated.

The refractive index of the glass film starting from the thermosetting inorganic high molecular polymer precursor is determined by setting the atmosphere during the thermal decomposition in the heat treatment to nitrogen, oxygen, or a mixture of nitrogen and oxygen. And the content of oxygen.

[0015]

FIG. 1 is a sectional view of an optical waveguide according to a first embodiment of the present invention. 1 denotes a substrate, 2 denotes a core region, and 3 denotes a cladding region. Since the substrate 1 uses a quartz substrate, optical effects such as absorption loss and polarization dependence of the substrate are small, and no buffer layer is particularly required. Therefore, the core region 2 can be formed directly on the substrate 1. The substrate 1 also functions as a cladding region surrounding the lower part of the core region.

In the first embodiment, perhydropolysilazane (manufactured by Tonen), which is a ceramic precursor shown in Chemical formula 1, was used as the thermosetting inorganic high molecular polymer. This polymer is completely inorganic without C or O in composition,
It is composed only of Si, N and H, and is soluble in most organic solvents such as aromatics and esters. Therefore, it can be applied by the same method as the organic resin.

[0017]

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Furthermore, this material starts to thermally decompose at a relatively low temperature and is easy to vitrify. Further, since it does not contain an OH group or a CH group, there is no absorption by those groups, and a low-loss optical waveguide can be realized.

Unlike conventional SOG (Spin On Glass) in which the organic binder in the precursor is vitrified while evaporating, N and H are vitrified while substituting O in the external atmosphere, so that the glass is thermally decomposed. Volume shrinkage rate when forming Therefore, it is possible to form a high-quality thick glass layer free from defects such as cracks and voids. In addition, since it is a polymer, it can be formed on various substrates such as a semiconductor, glass, and a polymer resin, and an optical waveguide formed by combining these various materials is also possible.

The polysilazane precursor is applied to the substrate 1 by a spin coating method, and after evaporating the solvent by preheating, it is vitrified at a firing temperature of 600 ° C. in an electric furnace. Thus, a core layer having a thickness of about 3 μm is obtained. This core layer is processed into a core region 2 having a rectangular cross section by patterning of a waveguide by photolithography and dry etching.

The core region 2 must have a relatively higher refractive index than the surrounding region. Therefore, the firing atmosphere during firing was a mixed gas atmosphere with oxygen containing 20% nitrogen. This gives a refractive index of 1.49 at a wavelength of 632.8 nm.
Was able to be formed.

FIG. 2 shows the dependence of the refractive index of the perhydropolysilazane film on the heat treatment. A polysilazane precursor diluted with a xylene solvent is spin-coated on a substrate, and then preheated at a relatively low temperature near the boiling point of the solvent to evaporate the solvent. Next, heat treatment is performed in an appropriate temperature and atmosphere to vitrify by thermal decomposition. By selecting a firing temperature and a firing atmosphere, which are heat treatment conditions at this time, a glass film having a wide range of refractive index from 1.44 to 2.0 can be obtained. 500 ° C especially in oxygen atmosphere
At a relatively low temperature below, a glass film having a refractive index substantially equal to that of a SiO ₂ film formed by thermal oxidation of Si can be obtained. By selecting the atmosphere during the heat treatment as described above, the contents of nitrogen and oxygen in the glass film can be controlled and the refractive index can be changed.

What is important in forming the core region is to form a dense glass film. If the core film is not dense enough, not only does the scattering loss increase, but also the pattern width of the waveguide is greatly reduced when the core region is processed by dry etching, and the dimensional accuracy according to the mask pattern cannot be obtained. The density of the core film formed in the present example is 2.2 g / cm ^3, which is a sufficient density.

FIG. 3 is a sectional view of an optical waveguide according to a second embodiment of the present invention. 1 denotes a substrate, 2 denotes a core region, 3 denotes a cladding region, and 4 denotes a buffer layer. The second embodiment is an example in which the present invention is applied to a buffer layer provided between an optical waveguide and a substrate in order to suppress optical effects of the substrate such as absorption loss and deflection dependence.

The optical waveguide is formed by optically connecting the substrate 1, the core region 2 having a higher refractive index than the cladding region 3, the cladding region 3 having a lower refractive index than the core region 2, and the light propagation region and the substrate 1. It is composed of a buffer layer 4 which is isolated from the outside. When a material made of a lossy medium such as a semiconductor substrate or an organic polymer film is used as the substrate, the buffer layer 4 is indispensable. The polysilazane precursor is applied on the substrate 1 in multiple layers by spin coating, preheated to evaporate the solvent, and then vitrified at 450 ° C. in an electric furnace. Thus, a buffer layer 4 having a thickness of 10 μm was obtained.

In this embodiment, the buffer layer 4 not only functions to isolate the optical waveguide from the optical influence from the substrate 1 but also functions as a cladding layer surrounding the lower part of the core region 2. Therefore, the firing atmosphere for vitrification is oxygen 10
0%. As a result, the refractive index of the buffer layer 4 becomes
A glass film having a refractive index of 1.45 at 32.8 nm and substantially equal to the refractive index of SiO ₂ due to thermal oxidation could be obtained.

What is important in forming the buffer layer 4 is the adhesive force between the buffer layer 4 and the substrate 1. In the buffer layer 4 according to the second embodiment, the substrate is a semiconductor, glass,
In each case, good adhesion was exhibited. Although the buffer layer 4 was formed using a substrate having a flat surface,
According to the present invention, a glass layer having a flat surface can be formed even on a substrate having an uneven surface. Therefore, the present invention can be applied to the formation of an optical waveguide having a multilayer structure.

FIG. 4 is a sectional view of an optical waveguide according to a third embodiment of the present invention. 1 denotes a substrate, 2 denotes a core region, and 3 denotes a cladding region. A quartz substrate is used as the substrate 1, and the substrate 1
After the core region 2 is formed thereon, the polysilazane precursor is applied many times by spin coating, the solvent is evaporated by preheating, and then vitrified at a firing temperature of 450 ° C. in an electric path. Thereby, a cladding region 3 having a thickness of about 10 μm covering the upper portion of the core region 2 is obtained.

The refractive index of the cladding region 3 is set at a firing temperature of 45.
1.45 was achieved by setting the firing atmosphere to oxygen at 0 ° C. This refractive index is lower than that of the core region 2. However, it is a value at a wavelength of 632.8 nm. Core area 2
What is important in forming the cladding region 3 covering the upper part of the substrate is that the core region having a step is excellent in coverage, that is, excellent in step coverage. If the step coverage is poor, a gap is formed between the core region 2 and the cladding region 3, which significantly increases transmission loss.

Hereinafter, other embodiments will be described.
The present invention can be applied to a case where a material other than glass, for example, a thermosetting organic high molecular polymer is used as the material of the core region 2. As the organic polymer, a material having a particularly large nonlinear optical effect can be easily obtained, and there are many important materials for forming an active optical waveguide.

However, the organic high molecular polymer has a disadvantage that it has a high hygroscopicity and is generally inferior in long-term reliability to a glass waveguide, and it is difficult to form a clad region in the conventional technology. However, according to the present invention, the cladding region can be formed even with a waveguide using such an organic polymer as the core region, and the water vapor transmission rate can be suppressed to about 0.6 g / m ² / day. However, it is a value at 1 atm and a film thickness of 0.6 μm. For this reason, it can also serve to protect the core region made of the organic high molecular polymer from the external environment.

Further, according to the present invention, the surface shape of the clad layer covering the upper portion of the core is flattened. Therefore, in order to further increase the thickness of the clad region, after forming the clad region 3 according to the present invention, a CVD method or a vapor deposition method is used. Alternatively, a film may be additionally formed by a conventional method such as a sputtering method.

In the first and third embodiments, the substrate 1 is a quartz substrate. As described above, when a lossy material such as a semiconductor or a polymer resin film is used as the substrate, a buffer layer is required to optically isolate the light propagation region from the substrate. In the first and third embodiments, the case where the present invention is applied only to the core region and the cladding region has been described. However, the present invention may be applied to all of the core, cladding, and buffer layers. The invention may be applied, and an optical waveguide may be formed in other regions by using a glass layer formed by a conventional method such as a CVD method, a vapor deposition method, or a sputtering method.

Regarding the control of the refractive index, in the above-described embodiment, the case where the control is performed by the gas atmosphere at the time of firing using perhydropolysilazane composed of only Si, N and H has been described. The refractive index can be changed not only by the gas atmosphere at the time of firing but also by adding a dopant for controlling the refractive index to the polysilazane precursor. For example, at least one of dopants P, Al, Ge, Ti, Zn, and Zr for increasing the refractive index is added to the polysilazane precursor used for the core region. Alternatively, a dopant B or F for reducing the refractive index is added to the polysilazane precursor used for the cladding region. Thereby, when firing the core region and the cladding region, the refractive index of the core region becomes higher than that of the cladding region even if the gas atmosphere is the same.

Further, in the above embodiment, all the films are formed by spinner coating. However, the thermosetting inorganic high molecular polymer is vaporized by bubbling, and this is used as a raw material gas by heat or plasma. Vitrification can also be achieved by phase growth. In this case, the refractive index of the formed glass film can be controlled by changing the gas used during bubbling to nitrogen or oxygen.

[0036]

According to the present invention, a part or all of the core region, the cladding region, and the buffer layer are formed of a glass film starting from a thermosetting inorganic high molecular polymer precursor. The use of the optical waveguide, the thermosetting inorganic polymer precursor was applied by spin coating, and thereafter the thermosetting inorganic polymer precursor was thermally decomposed by heat treatment to vitrify, and at least one time Using a manufacturing method characterized by repeating the steps of coating or heat treatment, and the refractive index of a glass film starting from a thermosetting inorganic high molecular polymer precursor, the atmosphere during the thermal decomposition in the heat treatment Nitrogen, oxygen, or a mixture of nitrogen and oxygen, and using a production method characterized by controlling the content of nitrogen and oxygen, the following excellent effects are obtained. It exerts a result.

It is possible to form a glass layer having a wide range of refractive index applicable from the core region to the cladding region only by changing the gas atmosphere when heat-treating the thermosetting inorganic high molecular polymer precursor.

It is possible to form a film with excellent uniformity and step coverage with an inexpensive apparatus.

It is possible to form a flat and thick glass film,
In particular, it is suitable for forming a clad region covering the upper part of the core region.

The vitrification can be performed at a relatively low temperature, and the deformation of the substrate and the shape of the waveguide due to heat can be suppressed.

The optical waveguide can be formed on various substrates such as semiconductor, glass, and polymer resin, and an optical waveguide made of such various composite materials can be formed.

[Brief description of the drawings]

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

FIG. 2 is a graph showing a heat treatment temperature dependency of a refractive index according to the first embodiment.

FIG. 3 is a sectional view of an optical waveguide according to a second embodiment of the present invention.

FIG. 4 is a sectional view of an optical waveguide according to a third embodiment of the present invention.

[Explanation of symbols]

 Reference Signs List 1 substrate 2 core region 3 cladding region 4 buffer layer

Claims (11)

[Claims] In an optical waveguide formed on a substrate made of a semiconductor, glass, or a polymer resin, one of a core region, a cladding region, and a buffer layer, each of which has a substantially rectangular cross section, which constitutes the optical waveguide. An optical waveguide characterized in that part or all of the optical waveguide is formed by a glass film using a thermosetting inorganic high molecular polymer precursor as a starting material. 2. The refractive index of the glass film starting from the thermosetting inorganic high molecular weight polymer precursor is controlled by the contents of nitrogen and oxygen. 2. The optical waveguide according to claim 1, wherein the optical waveguide has a high core area. 3. The refractive index of the glass film starting from the thermosetting inorganic high molecular polymer precursor is controlled by the contents of nitrogen and oxygen. The optical waveguide according to claim 1, wherein the optical waveguide has a low cladding region. 4. The clad region covering the core region having a substantially rectangular cross section is partially or entirely formed of a glass film starting from a thermosetting inorganic high molecular polymer precursor, and the clad region is formed by the glass film. 2. The optical waveguide according to claim 1, wherein the shape of the upper part of the core region is flattened. 5. The core region is made of a thermosetting organic high molecular polymer, and the cladding region covering the upper part of the core region is partially or entirely made of a thermosetting inorganic high molecular polymer precursor as a starting material. 2. The optical waveguide according to claim 1, wherein the optical waveguide is formed of a glass film. 6. The thermosetting inorganic high-molecular polymer is polysilazane, or P, B, F, Ti,
2. The optical waveguide according to claim 1, wherein at least one of Ge, Al, Zr, and Zn is added. 7. A method for forming an optical waveguide comprising a buffer layer, a core region, and a clad region on a substrate, wherein a part or all of the core region, the clad region, and the buffer layer are formed by a thermosetting inorganic high molecular polymer precursor. A method for manufacturing an optical waveguide, comprising forming a glass film using a body as a starting material. 8. The thermosetting inorganic polymer precursor is applied by a spin coating method, and thereafter the thermosetting inorganic polymer precursor is thermally decomposed by heat treatment to be vitrified and applied at least once. 8. The method for manufacturing an optical waveguide according to claim 7, wherein the step of heat treatment is repeated. 9. The refractive index of a glass film starting from the thermosetting inorganic high molecular weight polymer precursor is determined by setting the atmosphere during thermal decomposition in the heat treatment to nitrogen, oxygen, or a mixture of nitrogen and oxygen. 8. The method for manufacturing an optical waveguide according to claim 7, wherein the control is performed by controlling the oxygen content. 10. The thermosetting inorganic high molecular weight polymer precursor is vaporized by bubbling and vitrified by vapor phase growth using heat or plasma.
The manufacturing method of the optical waveguide described. 11. The refractive index of a glass film starting from the thermosetting inorganic polymer precursor is determined by using nitrogen, oxygen, or a mixed gas of nitrogen and oxygen. 8. The method for manufacturing an optical waveguide according to claim 7, wherein the body is vaporized by bubbling and controlled by the contents of nitrogen and oxygen.