JPH09297239A - Production of optical waveguide - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a production method of an optical waveguide with low loss and high production yield. SOLUTION: A SiO2 -GeO2 compact prepared by mixing a SiO2 powder and a GeO2 powder and pressing, or a SiO2 -GeO2 sintered body prepared by successively sintering the SiO2 -GeO2 compact is used as sputtering targets 4-1 to 4-4, and sputtering without thermal vaporization mechanism is carried out on a substrate 3. Therefore, no boiling due to the vapor pressure of the mixed material is caused or clusters do not intrude in the film. The core film can be produced without using phosphorus or boron as an additive to control the temp. to obtain a transparent film, so that increase in the scattering loss due to additives or deformation of the core when the core is heat-treated can be prevented. Thereby, an optical waveguide with low loss and high production yield can be obtd.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method of manufacturing an optical waveguide having low loss and high reliability, which is suitable for the fields of communication, measurement and information processing.

[0002]

2. Description of the Related Art With the spread of communication systems utilizing light, development of optical components with lower loss and higher reliability is under way. In particular, waveguide-type optical components that use quartz-based materials
In addition to its low loss property, it is possible to form complex circuits on a flat substrate all at once, so it has attracted the most attention.

These waveguide type optical components are made of Si having a low refractive index layer called a buffer layer (lower clad layer).
In general, a structure in which a light propagation region called a core having a high refractive index is formed on a substrate or a quartz substrate and the core is further covered with a clad layer having a low refractive index is adopted. Particularly, as the material composition of the core portion, a SiO ₂ —GeO ₂ composition glass that has been proven as a low-loss core material of an optical fiber is considered to be effective.

A conventional example of an optical waveguide having a core of SiO ₂ —GeO ₂ composition will be described below with reference to FIGS. 4 and 5.

The method of manufacturing an optical waveguide shown in FIG. 4 is an example of forming a film for a waveguide by utilizing fine particle formation by flame hydrolysis reaction and transparent vitrification by high temperature heat treatment.
First, P (phosphorus) or B is added to SiO ₂ on the Si substrate 3-1.
The fine particle layer 6 for the low refractive index layer (lower clad layer) to which (boron) is added and the fine particle layer 7 for the core film to which P, B, Ga, etc. are added are deposited by flame hydrolysis reaction, and these are deposited. The transparent lower clad glass layer and the core glass film 9 are sintered at a high speed, and then the unnecessary portion of the core glass film 9 is removed by dry etching to form a ridge-shaped core 10 and finally flame flame Fine particle layer 11 for low refractive index film (upper clad layer) to which P or B is added by decomposition reaction
Is deposited and sintered to form a transparent upper clad glass film 12, and a buried optical waveguide is obtained.

Here, P is added mainly for the purpose of lowering the softening rate of glass or the transparent vitrification temperature, and B is added for the purpose of lowering the refractive index of the film and at the same time adjusting the thermal expansion coefficient. Ge is added for the purpose of increasing the refractive index.

The optical waveguide manufacturing method shown in FIG. 5 is an example of forming a SiO ₂ —GeO ₂ waveguide using an electron beam evaporation method.

A core material composed of SiO ₂ and GeO _{2 is} evaporated on a quartz substrate 3-2 by an electron beam evaporation method to form a core film 13 of SiO ₂ —GeO ₂ composition on the surface of the substrate. Then, the core film 13 is formed by dry etching.
Is removed to form a ridge-shaped core 14, and finally, a fine particle layer 15 for a cladding film is deposited by a flame hydrolysis reaction, and this is sintered to form a transparent upper cladding film 16. A waveguide is obtained. In addition,
In this conventional example, the quartz substrate 3-2 itself plays the role of the lower clad film.

[0009]

However, the above-mentioned conventional techniques have the following problems.

In the conventional method for manufacturing an optical waveguide shown in FIG. 4, it is necessary to sinter each layer at a temperature equal to or lower than the heat resistant temperature of a Si substrate or a quartz substrate so as to obtain a transparent glass. For this reason, P must be added to each layer to reduce the softened skin. Further, the coefficient of thermal expansion and the refractive index of the film must be adjusted by adding B. The structure of oxide glass formed by adding P or B is SiO ₂ or GeO.
_Since it is fundamentally different from the structure of the _two glasses, phase separation is likely to occur after transparent vitrification, which may cause a scattering of the propagating light. Further, after forming a ridge-shaped core by etching, it is necessary to again perform fine glass deposition for forming a cladding layer and transparent vitrification treatment by high temperature sintering. Therefore, the core pattern is likely to be deformed by the high temperature heat treatment. In addition, there is a problem that P is likely to be diffused in the film thickness direction when the fine particle deposition layer is vitrified, and it is difficult to obtain a film having a uniform composition in the film thickness direction.

Further, in the conventional method for manufacturing an optical waveguide shown in FIG. 5, since the core can be composed of only SiO ₂ and GeO ₂ , the deformation of the core pattern due to the high temperature heat treatment is extremely small. However, SiO ₂ and GeO ₂ with different vapor pressures
Since the mixed material with and is heated and evaporated by an electron beam, the bumping phenomenon (SiO ₂
Since the vapor pressure of GeO ₂ is higher than that of GeO ₂ , the phenomenon that GeO ₂ vaporizes first and bubbles are generated in the material) is more likely to occur. Therefore, due to this bumping phenomenon, the material pops off and mixes into the film as clusters (mass) of several μm to several tens of μm. The materials mixed in these films cause waveguide breakage and increase the waveguide loss. Further, since the shrinkage of the film during the high temperature heat treatment is large, the warp of the substrate is increased, and the subsequent patterning process cannot be performed, or the film itself is cracked.

Therefore, an object of the present invention is to solve the above problems and to provide a method of manufacturing an optical waveguide with low loss and high yield.

[0013]

In order to achieve the above object, the present invention provides a method of mixing or pressing SiO ₂ powder and GeO ₂ powder to form a SiO ₂ —GeO ₂ compact or pressing. Subsequent sintering to form a SiO ₂ —GeO ₂ sintered body, and a SiO ₂ —GeO ₂ composition on a flat substrate having a low refractive index layer by a sputtering method using a compact or a sintered body as a sputtering target. To form a core glass film, heat treating the entire flat substrate at a high temperature, processing the core glass film into a core having a substantially rectangular cross section by photolithography and dry etching, and And a step of coating a clad glass film having a low refractive index.

In addition to the above structure, the present invention is based on GeO ₂ for SiO ₂ powder in a sputter target made of a sintered body.
It is preferable to control the refractive index of the core glass film formed by changing the mixing ratio of the powder within the range of 50 mol% or less.

In the present invention, in addition to the above constitution, it is preferable that the particle diameters of the SiO ₂ powder and the GeO ₂ powder are each 10 μm or less.

In addition to the above constitution, in the present invention, it is preferable that the purity of the sputter target made of a sintered body is 99.9% or more.

In addition to the above constitution, in the present invention, the density of the sputter target made of a sintered body is preferably 70% or more.

In addition to the above-mentioned constitution, the present invention, in forming the core glass film by the sputtering method, applies RF high frequency power to at least two or more sputtering targets at the same time,
It is preferable to deposit a material sputtered from a sputter target on a flat substrate attached to a substrate holder having a rotating mechanism.

According to the present invention, in addition to the above structure, the core glass film is formed by a sputtering method in a mixed gas of argon and oxygen which is a sputtering gas, and the mixing ratio of oxygen gas in the total amount of introduced gas is 3 to 30. It is preferably within the range of%.

In addition to the above structure, in the present invention, it is preferable that the core glass film is formed by the sputtering method at a gas pressure of 0.01 to 1 Pa during sputtering.

In addition to the above-mentioned constitution, the present invention is such that the high frequency power applied to each sputter target during the formation of the core glass film by the sputtering method is 2 to 10 W / c.
It is preferable to set it in the range of m ² .

In addition to the above structure, the present invention performs the high temperature heat treatment after forming the core glass film in oxygen at 700 to 1200 ° C.
It is preferable to carry out at a temperature in the range.

In the above method, the sputtering method is a film forming method that does not involve a thermal vaporization / evaporation mechanism.
The bumping phenomenon depending on the vapor pressure of the mixed material, which is a problem in the vapor deposition method, does not occur. Therefore, clusters (lumps of material) are not mixed in the film. In addition, as in the method that uses fine particle formation by flame hydrolysis reaction and transparent vitrification by high temperature heat treatment, it is used for cores without adding phosphorus or boron, which is an additive for adjusting the clearing temperature, to the core glass. Since the film can be formed, there is no concern about an increase in scattering loss due to the additive and deformation of the core when the core is heat-treated.

In addition, large-scale SiO ₂ --GeO _{2 has been used} so far.
Since a sputtering target made of glass could not be obtained, a core glass film having a composition of SiO ₂ —GeO ₂ could not be prepared by the sputtering method.

However, in the present invention, the SiO ₂ powder and the GeO ₂ powder are mixed and pressed to form a compact, or subsequently sintered to form a sintered body, which is then formed. Since it is used as a sputter target, it is possible to form a sputter target at low cost and with good reproducibility, and a highly reliable SiO ₂ —GeO ₂ core film can be reproduced.

Here, the composition ratio and the refractive index of the formed core film can be controlled by the mixing ratio of the SiO ₂ powder and the GeO ₂ powder. Refractive index The more GeO ₂ powder content for SiO ₂ powder is higher, the refractive index difference between the core and the cladding ([Delta] n) becomes large. The larger the refractive index difference Δn, the smaller the loss due to the bending of the optical waveguide, and the smaller device can be realized. However excessive G
The addition of eO ₂ not only increases the internal stress and scattering loss, but also deteriorates the matching between the optical waveguide and the ordinary optical fiber and causes a large coupling loss. Therefore, the content of the GeO ₂ powder with respect to the SiO ₂ powder is preferably 50 mol% or less.

Further, the uniformity of the composition depends on the SiO _{2 to be} mixed.
It depends on the particle size of the powder and GeO ₂ powder. In order to obtain a uniform composition film, it is necessary to use a powder raw material having a particle size of at least 10 μm or less. When a material having a particle size exceeding 10 μm is used, the compositional change in the film thickness direction becomes significantly large.

Further, the loss of the film increases due to the inclusion of impurities. It was confirmed that this increase in loss becomes remarkable when the amount of impurities exceeds 0.1%. It was also found that the refractive index also changes when the content exceeds 0.1%. Therefore, the purity of the sputter target made of a sintered body is preferably 99.9% or more.

Further, in order to improve the use efficiency and life of the sputter target itself, it is preferable that the sintered density be 70% or more. In the case of SiO ₂ —GeO ₂ sintered body,
A sputter target having a density lower than 70% undergoes remarkable volume contraction during sputtering, which is considered to be due to an increase in the surface temperature. This shrinkage rate depends on the plasma density (temperature) on the surface of the sputter target. If the difference in shrinkage ratio on the sputter target is large, cracks are likely to occur. Further, it has been confirmed that when the density is lower than 70%, the amount of the inert gas or water adsorbed becomes remarkable.

The thickness of the glass film for the waveguide core is preferably set to 6 to 10 μm which is substantially equal to the core diameter of the optical fiber in consideration of coupling with the optical fiber. Further, in order to reduce the manufacturing cost, it is necessary to uniformly form a film on a large number of substrates or large substrates. Therefore, RF high frequency power is simultaneously applied to at least two or more sputter targets, and the material sputtered from the sputter targets is deposited at high speed and uniformly on the substrate while being attached to the substrate holder having the rotating mechanism.

Here, the SiO ₂ —GeO ₂ core film formed by the above-mentioned sputtering method needs to be subsequently heat-treated at a high temperature in an oxygen atmosphere in order to stabilize the composition and refractive index of the film.

However, when the film immediately after film formation is in an oxygen-deficient state, volume expansion of the film occurs due to oxidation during heat treatment, and cracks due to stress change occur. Further, if oxygen is excessively introduced for the purpose of accelerating the oxidation, the film forming rate will be extremely reduced, and therefore it is not suitable as a film forming method of the micron order. Therefore, when the SiO ₂ —GeO ₂ core film is formed by the above method, it is preferable to set the mixing ratio of oxygen gas in the total amount of introduced gas to be within the range of 3 to 30%.

The gas pressure at the time of sputtering is an important parameter for controlling the film formation rate, the film density and the film oxidation state together with the gas introduction amount such as argon gas or oxygen gas. According to the examination results of the present inventors, SiO ₂ —GeO ₂
A suitable pressure range for forming the core film is 0.01 to 1
Pa. Outside this range, the film becomes an oxygen-deficient state or has a low density, and only a film having large fluctuations in the refractive index, the film thickness, and the warp amount of the substrate during the high temperature heat treatment was obtained.

Further, the high frequency power applied to each sputter target during film formation is a factor controlling the film formation rate, but when forming a SiO ₂ —GeO ₂ core film, the internal stress and refractive index are also increased. It changes depending on the applied power. In order to form a film with little fluctuation during the high temperature heat treatment, it is preferable to form the film with an electric power in the range of ^{2 to} 10 W / cm ² per sputter target. When the electric power is lower than ² W / cm ² , the film formation rate is slow and it is not practical. Also, 1
When the electric power is higher than 0 W / cm ^{2, the} film has large internal stress fluctuation during high temperature heat treatment.

Further, after the core film is formed, it is preferable to perform a heat treatment at a high temperature in an oxygen atmosphere in order to promote the oxidation of the film, densify the film, and stabilize the refractive index. In this case, it is necessary to select a temperature at which changes in the refractive index and the film thickness are saturated and the internal stress of the film is minimized.

In particular, a film having a large internal stress causes a large amount of warpage of the flat substrate, so that the subsequent patterning by photolithography cannot be performed accurately. As a result of various examinations by the present inventors on variations in the refractive index, film thickness, and internal stress with respect to the heat treatment temperature, the optimum temperature is 700 to 120.
It was found to be in the range of 0 ° C.

[0037]

Embodiments of the present invention will be described below in detail with reference to the accompanying drawings.

FIG. 1 is a plan view showing an embodiment of a sputtering apparatus to which the method for manufacturing an optical waveguide of the present invention is applied.

In FIG. 1, 1 is a vacuum container, 2 is a substrate holder, 3 is a flat substrate (substrate), and 4-1 to 4-4 are Si.
O ₂ —GeO ₂ sintered target (target), 5-
Reference numerals 1 to 5-4 are high frequency power supplies for supplying power to the targets 4-1 to 4-4, respectively.

Here, the substrate 3 is attached to the outer peripheral side surface of the substrate holder 2 having a rotatable polyhedral shape. Targets 4-1 to 4-4 are provided on the inner wall of the vacuum container 1 facing the substrate 3 and each target 4-
High frequency power supplies 5-1 to 5-4 for supplying electric power to each of them are connected to 1 to 4-4.

The present inventors initially set targets 4-1 to 4-4.
As -4, it was considered to use SiO ₂ —GeO ₂ bulk glass. However, it was difficult to obtain a product having a uniform composition, and it was easily cracked, so that a large-scale product for a mass production device could not be produced.

Therefore, in the present embodiment, SiO ₂ powder and GeO ₂ powder are mixed and pressed, and then 1
A sintered body formed by sintering at a high temperature of 000 ° C. or higher and having a density of 70% or higher was used as a target.

The refractive index of the core film is SiO ₂ powder and GeO ₂
It can be easily controlled by changing the mixing ratio with the powder, but in the present embodiment, the mixing ratio of GeO ₂ was set to 10 mol%.

Here, in order to improve the use efficiency and the life of the target itself, the sintering temperature is preferably 70% or more. In the case of a SiO ₂ —GeO ₂ sintered body, GeO
A target having a mixture ratio of ₂ lower than 70% had a remarkable volume shrinkage during sputtering, which is considered to be due to an increase in the surface temperature of the target. This shrinkage rate depends on the plasma density (temperature) of the target surface. If the difference in shrinkage ratio increases on the target, cracks are likely to occur. Further, when the mixing ratio of GeO ₂ was lower than 70%, the amount of adsorbed impurity gas and water became remarkable.

The particle diameters of the raw materials composed of SiO ₂ powder and GeO ₂ powder were 10 μm or less in order to ensure the uniformity of the composition. Particle size is 10
When a material having a thickness of more than μm was used, the compositional change in the film thickness direction was significantly increased.

When an amount of impurities exceeding 0.1% is mixed in the film, the increase in loss and the change in refractive index due to the impurities become remarkable, which is not desirable as a core film for a waveguide. Therefore, the purity of the target made of a sintered body is 99.9%.
It was above.

Next, in the actual core film formation, the substrate 3 such as a quartz substrate or a Si substrate having a low refractive index layer is attached to the outer peripheral side of the substrate holder 2 provided in the vacuum container 1, and the vacuum container 1 is attached. The inside is evacuated to a vacuum degree of 1 × 10 ⁻⁵ Pa or less.

Next, 100 sccm of argon (Ar) gas which is a sputtering gas and 10 scm of oxygen (O ₂ ) gas which is a reaction gas are introduced into the vacuum container 1, and the vacuum container 1
While maintaining the gas pressure in the inside at 0.3 Pa and rotating the substrate holder 2, each of the sintered body targets 4-1 to 4-4 is supplied with 8 W / from the high frequency power sources 5-1 to 5-4.
A film was formed by supplying electric power of cm ² .

Here, the thickness of the glass film for the waveguide core is set to 6 to 10 μm, which is approximately equal to the core diameter of the optical fiber, in consideration of coupling with the optical fiber. Also,
In order to reduce the manufacturing cost, it is necessary to uniformly form a film on a large number of substrates or large substrates. Therefore, at least 2
High-frequency power is simultaneously applied to one or more targets 4-1 to 4-4, and the materials sputtered from the targets 4-1 to 4-4 are rapidly transferred onto the substrate 3 mounted on the substrate holder 2 having a rotation mechanism. It is preferable that the film can be formed uniformly.

Further, the SiO ₂ --GeO ₂ core film formed by the above-mentioned sputtering method needs to be subsequently heat-treated at a high temperature in an oxygen atmosphere in order to stabilize the composition and refractive index of the film.

However, when the film immediately after film formation is in an oxygen-deficient state, volume expansion of the film occurs due to oxidation during heat treatment, and cracks due to stress change occur. Further, if O ₂ gas is excessively introduced for the purpose of accelerating the oxidation, the film forming rate is extremely lowered, and therefore it is not suitable as a film forming method of the micron order. Therefore, when the SiO ₂ —GeO ₂ core film is formed by the above method, the mixing ratio of O ₂ gas in the total amount of introduced gas is 3 to 30.
It is preferable to set it within the range of%.

The gas pressure at the time of sputtering is an important parameter for controlling the film formation rate, the film density, and the softened state of the film together with the introduction amount of Ar gas or O ₂ gas. According to the examination result of the present inventors, the suitable pressure range for forming the SiO ₂ —GeO ₂ core film was 0.01 to 1 Pa. Outside this range, the film becomes an oxygen-deficient state or has a low density, and only a film having large fluctuations in the refractive index, the film thickness, and the warp amount of the substrate during the high temperature heat treatment was obtained.

Further, the high frequency power applied to each target during film formation is a factor for directly controlling the film formation rate, but in the case of forming the SiO ₂ —GeO ₂ core film,
The internal stress and refractive index also change depending on the applied power. In order to form a film with a small internal stress and a small change in refractive index during high temperature heat treatment, it is preferable to form the film with an electric power in the range of ^{2 to} 10 W / cm ² per target. High frequency power is 2W
If it is lower than / cm ² , the film formation rate is slow and not practical. When the high frequency power is higher than 10 W / cm ^{2, the} film has large internal stress fluctuation during high temperature heat treatment.

Next, the formed core film was heat-treated together with the substrate in an oxygen atmosphere at a temperature of about 900.degree.

After film formation, it is preferable to perform heat treatment at a high temperature in an oxygen atmosphere in order to promote oxidation of the film, densify the film, and stabilize the refractive index. In this case, it is necessary to select a temperature at which changes in the refractive index and the film thickness are saturated and the internal stress of the film is minimized. In particular, a film having a large internal stress also causes a large amount of warp of the substrate, so that subsequent patterning by photolithography cannot be performed accurately.

FIG. 2 shows the results of examining changes in the refractive index and the internal stress with respect to the heat treatment temperature.

FIG. 2 is a diagram showing the relationship between the amount of warpage and the refractive index of the substrate with respect to the heat treatment temperature of the present invention, where the horizontal axis represents temperature,
The left vertical axis shows the warp amount (internal stress) of the substrate, and the right vertical axis shows the refractive index. The white points indicate the warp amount (internal stress) of the substrate,
Black dots indicate the refractive index.

From the figure, it can be seen that the temperature range in which the refractive index is stable and the internal stress becomes approximately 0 exists in the range of 700 to 1200 ° C. That is, it is desirable to perform the heat treatment within this temperature range. In the figure, the warp amount of the substrate is
It is the amount of warpage of the substrate within ± 25 mm from the center of the substrate having a diameter of 3 inches.

SiO ₂ -G produced according to this embodiment
GeO _{2 in} sintered body target of eO ₂ core glass film
FIG. 3 shows the results of examining the powder mixture amount and the refractive index after heat treatment at 1200 ° C. in an oxygen atmosphere.

FIG. 3 shows the mixture amount of GeO ₂ powder in the sintered body target to which the optical waveguide manufacturing method of the present invention is applied and the refraction when the formed film is heat-treated at a temperature of 1200 ° C. in an oxygen atmosphere. FIG. 3 is a diagram showing the relationship of the indices, where the horizontal axis represents the amount of GeO ₂ powder mixed and the vertical axis represents the refractive index.

From the figure, it can be seen that the refractive index changes linearly by changing the mixing amount of the GeO ₂ powder.
That is, the refractive index of the film could be controlled by the amount of the GeO ₂ powder mixed. In addition, in the range of the GeO ₂ powder content of 50 mol% or less (more preferably 30 mol% or less), no inclusion of foreign matter such as clusters or generation of cracks was confirmed. Furthermore, when the composition in the film thickness direction and in-plane were analyzed, it was confirmed that Ge was uniformly dispersed.

Next, as described above, the SiO ₂ —GeO ₂ film produced on the substrate having the low refractive index layer and heat-treated is formed.
A pattern for a waveguide was formed on the core glass film having the composition by photolithography. At this time, according to the present invention, the internal stress of the core glass film (warpage of the substrate) is controlled to be extremely small, so that the pattern can be formed with good reproducibility.

Next, based on these waveguide patterns, CH
The core glass film was processed into a core having a substantially rectangular cross section by reactive ion etching (dry etching) using F ₃ gas.

Further, fine particles for a glass film having a low refractive index are deposited by a flame hydrolysis reaction on the entire core processed into a substantially rectangular sectional shape on the substrate, and the particles are sintered at a high temperature of 1300 ° C. The fine particles were subjected to transparent vitrification to form an upper clad layer.

As a result of evaluating the SiO ₂ —GeO ₂ waveguide having a core size of 6 μm × 6 μm manufactured according to the present embodiment, a low loss waveguide having a transmission loss of 0.05 dB / cm or less can be obtained with good reproducibility. I found out. Moreover, as a result of observing the end face of the waveguide, it was confirmed that the core shape did not change due to the high temperature heat treatment.

In the above, since the present invention applies the sputtering method without the thermal vaporization / evaporation mechanism as the waveguide manufacturing method, it depends on the vapor pressure of the mixed material, which is a problem in the vapor deposition method. The bumping phenomenon does not occur. Therefore, clusters (hardness of material) are not mixed in the film. In addition, as in the method that utilizes fine particle formation by flame hydrolysis reaction and transparent vitrification by high temperature heat treatment, it is used for cores without adding phosphorus or boron, which is an additive for adjusting the clearing temperature, to the core glass. Since this film can be formed, there is no concern about an increase in scattering loss due to this additive and deformation of the core shape when the core is heat-treated. In addition, SiO
₂ powder and GeO ₂ powder are mixed and pressed, or the sintered body produced by subsequent sintering is used as a target, so that the target is less likely to be cracked during sputtering and low in It is possible to manufacture a large-sized target with good cost and reproducibility.

Further, O ₂ gas within the range of 3 to 30% is A
2 to 10 W / c per target by mixing with r gas and setting the gas pressure in the sputtering container within the range of 0.01 Pa.
The above-mentioned SiO ₂ —GeO ₂ target is sputtered with a high-frequency power of m ² to form a core film, so that characteristics such as film thickness, composition, and internal stress during high temperature heat treatment do not fluctuate and a SiO ₂ — A GeO ₂ core film is obtained.

The produced core film was subjected to 70% oxygen atmosphere.
By performing the heat treatment at a temperature of 0 to 1200 ° C., the internal stress of the film can be reduced and the amount of warpage of the substrate can be reduced. As a result, the subsequent patterning by photolithography can be performed with high accuracy, and thus the yield of waveguide fabrication can be greatly improved.

That is, according to the present invention, a low loss optical waveguide of SiO ₂ —GeO ₂ composition suitable for mass production can be produced with good reproducibility.

In this embodiment, the target is SiO 2.
_{Although the} explanation was made using the _2- GeO ₂ sintered body,
SiO pressed after mixing ₂ powder and GeO ₂ powder
_{A 2-} GeO ₂ molded body may be used.

[0071]

In summary, according to the present invention, the following excellent effects are exhibited.

Mix SiO ₂ powder and GeO ₂ powder,
A SiO ₂ —GeO ₂ compact obtained by pressing or a SiO ₂ —GeO ₂ sintered body obtained by subsequent sintering was used as a target, and a sputtering method without a thermal vaporization / evaporation mechanism was used. Therefore, it is possible to provide a method for manufacturing an optical waveguide with low loss and high yield.

[Brief description of drawings]

FIG. 1 is a plan view showing an embodiment of a sputtering apparatus to which an optical waveguide manufacturing method of the present invention is applied.

FIG. 2 is a diagram showing a relationship between a warp amount and a refractive index of a substrate with respect to a heat treatment temperature of the present invention.

FIG. 3 shows a mixture amount of GeO ₂ powder in a sintered body target to which the method for producing an optical waveguide of the present invention and a refractive index when the formed film is heat-treated at a temperature of 1200 ° C. in an oxygen atmosphere. It is a figure which shows a relationship.

FIG. 4 is a diagram showing a conventional example of a method of manufacturing an optical waveguide.

FIG. 5 is a diagram showing another conventional example of a method for manufacturing an optical waveguide.

[Explanation of symbols]

1 Vacuum Container 2 Substrate Holder 3 Flat Substrate (Substrate) 4-1 to 4-4 SiO ₂ -GeO ₂ Sintered Target (Target) 5-1 to 5-4 High Frequency Power Supply

Claims (10)

[Claims] 1. A mixture of SiO ₂ powder and GeO ₂ powder, which is then pressed to form a SiO ₂ —GeO ₂ compact or is pressed and sintered to form a SiO ₂ —GeO ₂ sintered body. A step of forming, a step of forming a core glass film of SiO ₂ —GeO ₂ composition on a flat substrate having a low refractive index layer by a sputtering method using the molded body or the sintered body as a sputtering target, and the whole substrate. At a high temperature, a step of processing the core glass film into a core having a substantially rectangular cross section by photolithography and dry etching, and a step of coating the entire core on the planar substrate with a clad glass film having a low refractive index. And a method of manufacturing an optical waveguide. _2. The mixing ratio of the GeO ₂ powder to the SiO ₂ powder in the sputter target made of the above sintered body is 5%.
The method for producing an optical waveguide according to claim 1, wherein the refractive index of the core glass film formed is controlled by changing it within the range of 0 mol% or less. 3. The method for producing an optical waveguide according to claim 1, wherein the particle diameters of the SiO ₂ powder and the GeO ₂ powder are each 10 μm or less. 4. The method for producing an optical waveguide according to claim 1, wherein the purity of the sputter target made of the sintered body is 99.9% or more. 5. The method for manufacturing an optical waveguide according to claim 1, wherein the density of the sputter target made of the sintered body is 70% or more. 6. In the core glass film formation by the sputtering method, RF high frequency power is simultaneously applied to at least two or more sputter targets to sputter from a sputter target on a flat substrate attached to a substrate holder having a rotating mechanism. The method for manufacturing an optical waveguide according to claim 1, wherein the formed material is formed into a film. 7. The core glass film is formed by the sputtering method in a mixed gas of argon and oxygen which is a sputtering gas, and the mixing ratio of oxygen gas in the total amount of introduced gas is within the range of 3 to 30%. The method for manufacturing an optical waveguide according to claim 1. 8. The method of manufacturing an optical waveguide according to claim 1, wherein the core glass film is formed by the sputtering method within a gas pressure range of 0.01 to 1 Pa during sputtering. 9. The production of an optical waveguide according to claim 1, wherein the core glass film is formed by the sputtering method such that the high frequency power applied to each sputtering target during film formation is in the range of ² to 10 W / cm ^2. Method. 10. The method of manufacturing an optical waveguide according to claim 1, wherein the high temperature heat treatment after forming the core glass film is performed in oxygen at a temperature in the range of 700 to 1200 ° C.