JPH103016A - Manufacturing method of waveguide type optical component - Google Patents

Abstract

(57) [Problem] To provide a method of manufacturing a waveguide-type optical component that can safely and efficiently fill hydrogen in a core without deforming the core. SOLUTION: Since the sputtering method is a film forming method without a thermal vaporization / evaporation mechanism, it is easy to perform sputtering in a vacuum chamber 10 by mixing H ₂ gas with a sputtering gas such as Ar. Hydrogen can be incorporated into the core glass film. Since the film formation method by sputtering is not one which is exposed to a very high temperature atmosphere, hydrogen once taken into the core glass film hardly diffuses outside or disappears. Therefore, the same amount of hydrogen as in the case of the hydrogen loading method or the frame brushing method can be safely and efficiently filled in the core glass. In addition, hydrogen-filled SiO
By irradiating the _2- GeO ₂ core glass with ultraviolet light, a photo-induced refractive index change can be caused with high sensitivity.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a method for manufacturing an optical component, and more particularly to a method for manufacturing a waveguide type optical component.

[0002]

2. Description of the Related Art With the spread of communication systems using light, development of optical components with lower loss and higher reliability has been actively pursued. In particular, a planar optical waveguide type optical component has attracted the most attention as a highly integrated optical circuit device because it can form a complicated circuit on a substrate in addition to its low loss property.

In these planar optical waveguide type optical components, a light propagation region called a core having a high refractive index is formed on a Si substrate or a quartz substrate provided with a thermal oxide film, and the core is further covered with a cladding region having a low refractive index. In general, the structure is adopted. In particular, the material composition of the core region is excellent in matching with the optical fiber,
Germanium (hereinafter referred to as G
Silicon oxide glass to which e ") is added is said to be effective.

[0004] On the other hand, studies are being actively conducted to locally change the refractive index of the core by irradiating ultraviolet rays using a Ge-doped quartz optical fiber. Although the mechanism of the change in refractive index due to ultraviolet irradiation is still largely unknown,
The following two points can be considered as causes of the refractive index change.

[0005] 1) First, in silicon oxide glass to which Ge is added, Si is more easily oxidized than Ge, so that it cannot bond with oxygen, and an oxygen deficiency defect in which part of Ge is weakly bonded between Ges is formed. When this portion is irradiated with high-energy ultraviolet rays, the bonds between Ges are broken, and Ge electrons move from the valence band to the conduction band. Then, the electrons move to absorb light having a wavelength different from the absorption wavelength of germanium oxide, and the refractive index changes according to the Kramers-Kronig relationship.

[0006] However, this theory alone cannot explain a change in the refractive index of as much as 10 ^-3 .

2) Therefore, recently, it is generally considered that the influence of the density change due to the defect change is the main mechanism. That is, the bonding of oxygen-deficient defects weakly bonded between Ges is broken by ultraviolet absorption, and the network structure of the glass in the vicinity thereof shrinks and the density locally increases. As a result, it is considered that the refractive index increases by the amount of the density change.

If a refractive index is periodically changed in the core, the core becomes a grating (diffraction grating) and can be used as a filter that reflects only a specific wavelength. Such an optical component is called a fiber grating, and is extremely small in size as compared with a conventional bulk type diffraction grating, and can be easily connected to another optical fiber. If this technology is applied, it can be used as an optical component having various functions such as a single-frequency oscillation laser, optical pulse compression / shaping, and dispersion compensation, in addition to the function as a filter for simply separating wavelengths. In addition to the field of optical communication, it is considered to be widely applied in the fields of measurement and information processing as sensors and memories.

[0009]

However, the above-mentioned prior art has the following problems.

First, the natural photosensitivity of a Ge-doped silicon oxide glass waveguide (fiber) is too small to provide the photo-induced refractive index change Δn (> 10 ⁻³ ) required for application. Therefore, methods such as a hydrogen loading method and a frame brushing method have been proposed to increase the photosensitivity inherent in optical fibers.

All of these methods increase the photosensitivity by diffusing or filling hydrogen inside the core.

The hydrogen loading method is a method in which hydrogen is diffused and filled in an optical fiber by exposing the optical fiber to a high-pressure, high-purity hydrogen atmosphere for a long period of time. This method usually has to maintain the optical fiber at 100 to 200 atmospheres for about one week, so that the production efficiency is low and it must be performed carefully for safety.

The frame brushing method is a method in which hydrogen is diffused in an optical fiber by brushing the optical fiber with a flame of an oxyhydrogen burner. This method can perform hydrogen diffusion and filling in a short time, but the core itself is deformed due to exposure to high temperature,
Alternatively, Ge, which is a dopant, diffuses into the peripheral portion due to heat, which may cause a significant change in the refractive index distribution of the core. In the optical waveguide having such a configuration, the loss increases or desired characteristics cannot be obtained.

By filling hydrogen in the core using the hydrogen loading method or the frame brushing method, it is possible to obtain a practically sufficient photoinduced refractive index change. However, these hydrogen treatment methods have problems such as productivity, safety, and deformation as described above.

It is an object of the present invention to solve the above-mentioned problems and to provide a method of manufacturing a waveguide-type optical component that can safely and efficiently fill hydrogen in a core without deforming the core. It is in.

[0016]

SUMMARY OF THE INVENTION In order to achieve the above object, the present invention relates to a method of forming a substrate comprising SiO ₂ , GeO _2, or SiO ₂ and Ge.
Using a mixture with O ₂ as a sputtering target material,
S on a substrate having a low refractive index layer by sputtering
forming a core glass film having an iO ₂ -GeO ₂ composition, and processing the core glass film into a core having a substantially rectangular cross-sectional shape by photolithography and dry etching;
Covering the entire core on the substrate with a low-refractive-index clad glass film, wherein the core glass film is formed by a sputtering method using a mixed gas of an inert gas and hydrogen gas. It is done inside.

In addition to the above constitution, the step of forming the core glass film by the sputtering method of the present invention may be such that the mixing ratio of hydrogen gas in the total amount of gas introduced during sputtering is 3 to 30.
%, And the gas pressure during sputtering is set to 0.0%.
It is preferable to set the pressure in the range of 1 to 1 Pa while applying bias power to the substrate.

In the present invention, in addition to the above configuration, it is preferable that at least a part of the core is irradiated with ultraviolet light to change the refractive index of the core.

Since the sputtering method is a film forming method that does not involve a thermal vaporization / evaporation mechanism, by mixing a sputtering gas such as argon with a hydrogen gas and performing sputtering, hydrogen can easily be contained in the core glass film. Can be taken. The film formation method by sputtering
Since it is not exposed to a very high temperature atmosphere, hydrogen once taken into the core glass film hardly diffuses outside or disappears. Therefore, the same amount of hydrogen as in the case of the hydrogen loading method or the frame brushing method can be safely and efficiently filled in the core glass.

As described above, the filling of the core with hydrogen according to the present invention eliminates a manufacturing step which requires a long-term and careful attention for safety and a manufacturing step of overheating which deteriorates the optical characteristics of the waveguide. can do. In addition, filling hydrogen at the time of forming a core film by a sputtering method is performed by using Ge.
Oxygen deficiency defects weakly bonded to each other can be efficiently formed. Therefore, it is more effective in enhancing photosensitivity than a method of filling with hydrogen as a post-treatment such as a hydrogen loading method and a frame brushing method. Si filled with hydrogen in this way
By irradiating the O ₂ —GeO ₂ core glass with ultraviolet light, a photo-induced refractive index change Δn can be caused with high sensitivity.

Here, the composition ratio and the refractive index of the formed core film can be controlled mainly by the mixing ratio of the SiO ₂ oxide powder and the GeO ₂ oxide powder, and greatly depends on the hydrogen content. Therefore, mixing hydrogen gas during sputtering does not become a major obstacle in controlling the refractive index of the core.

The SiO ₂ -GeO ₂ core film formed by the sputtering method has an extremely low film formation rate when excessively introducing hydrogen for the purpose of promoting hydrogen filling. Is not suitable. For this reason, when forming the SiO ₂ —GeO ₂ core film by the above-described method, it is preferable to set the mixing ratio of the hydrogen gas in the total amount of the introduced gas to be in the range of 3 to 30%. .

Further, the gas pressure during sputtering is
It is an important parameter for controlling the film formation rate, the film density, and the hydrogen content in the film together with the amount of the sputtering gas such as argon or the hydrogen gas introduced.

According to the results of the study by the present inventors, SiO ₂ -Ge
A suitable pressure range for forming the O ₂ core film is 0.01
１1 Pa. Outside this range, the film had a low density, and only a film having a large variation in the refractive index, the film thickness, and the amount of warpage of the substrate was obtained.

Further, even if the flow rate or mixing ratio of the hydrogen gas introduced into the vacuum chamber is the same, more hydrogen can be taken into the core film by applying a bias voltage to the substrate. That is, by adjusting the bias voltage applied to the substrate, the film can be formed while controlling the rate of taking in hydrogen into the film. As described above, the sputtering conditions are important for maintaining the production efficiency and the optical performance of the waveguide and for efficiently filling the core film with hydrogen.

[0026]

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

FIG. 1 is a schematic plan view of a sputtering apparatus to which the method of manufacturing a waveguide type optical component according to the present invention is applied.

As shown in FIG. 1, a dodecagonal (but not limited to a dodecagonal in the figure) substrate holder 11 is provided in a vacuum chamber 10 so as to be rotatable around a central axis 12. A plurality (12 but not limited to 12 in the figure) of substrates 13 are attached to the outer peripheral side surface of the substrate 11. Four inner walls of the vacuum chamber 10 are provided with sputtering targets (hereinafter, “targets”) 14a, 1
4b, 14c, and 14d are attached, and each target is connected to a high-frequency power supply 15a, 15b, 15c, 1 respectively.
5d.

A method of manufacturing a waveguide type optical component using such a sputtering apparatus will be described.

First, the inside of the vacuum chamber 10 is set to 1 × 10 ⁻⁵ Pa
Evacuate to the following degree of vacuum. Although a quartz substrate is used as the substrate 13, an Si substrate or the like having a low refractive index layer may be used.

Next, an argon gas (hereinafter referred to as “Ar gas”), which is a sputtering gas, is introduced into the vacuum chamber 10 for 100 times.
sccm and hydrogen gas (hereinafter “H ₂ gas”) at 10 sc
cm, and the gas pressure in the vacuum chamber 10 is 0.3 P
a, and while rotating the substrate holder 11 in the direction of arrow A (or vice versa), each of the targets 14a, 14b,
The high-frequency power supplies 15a, 15b, 15
A high frequency power of 8 W / cm ² was supplied from c and 15d to form a film.

Here, each target 14a, 14b, 14
Although c and 14d are all SiO ₂ plates of the same shape containing 10 mol% of GeO ₂ , in the case of an apparatus in which a plurality of targets 14a, 14b, 14c and 14d can be mounted as in the present embodiment, If a high-frequency voltage is independently applied to each target using a target of 100% GeO ₂ or SiO _2, the refractive index of the core film formed on the substrate can be adjusted to an arbitrary value.

In the present embodiment, the thickness of the glass film for the waveguide core is set to 6 μm which is substantially equal to the core diameter of the optical fiber in consideration of the coupling with the optical fiber.

The SiO ₂ -GeO ₂ core film formed by the above-mentioned sputtering method has an extremely low H ₂ gas for the purpose of promoting hydrogen filling. It is not suitable as a film deposition method. Therefore, according to the above-described method, SiO ₂ -Ge
In the case of forming an O ₂ core film, H
The mixing ratio of the _two gases was set to be in the range of 3 to 30%.

The gas pressure during sputtering is Ar
It is an important parameter for controlling the film formation rate, the film density, and the oxidation state of the film together with the amount of gas or H ₂ gas introduced. As a result of the study, an appropriate pressure range for forming the SiO ₂ —GeO ₂ core film was 0.01 to 1 Pa. Outside this range, the film had a low density, and only a film having a large variation in the refractive index, the film thickness, and the amount of warpage of the substrate could be obtained.

Further, the high-frequency voltage applied to each target at the time of film formation is a factor for directly controlling the film formation speed, but when forming a SiO ₂ —GeO ₂ core film,
The internal stress and the refractive index also change according to the applied voltage. In order to form a film with less internal stress and less change in refractive index during high-temperature heat treatment, it is preferable to form the film with a power of ^{2 to} 10 (W / cm ² ) per target.

FIG. 2 is a process chart showing a method of manufacturing a waveguide type optical component according to the present invention.

First, a core glass film 16a having a SiO ₂ —GeO ₂ composition is formed on a substrate 13 by using the sputtering apparatus shown in FIG. After a pattern for a waveguide is formed on the core glass film 16a by photolithography, the core glass film 16a is substantially formed by reactive ion etching (dry etching) using CHF ₃ gas based on the pattern of the waveguide. It is processed into a core 16 having a rectangular cross section. Further, an upper cladding layer 17 was formed by laminating a low refractive index SiO ₂ glass film containing no Ge on the entire core 16 processed into a substantially rectangular cross-sectional shape on the substrate 13 by a plasma CVD method or a sputtering method.

In the above, the size of the core 16 is 6 μm ×
As a result of evaluating a 6 μm SiO ₂ —GeO ₂ waveguide, it was confirmed that a low loss waveguide type optical component with a transmission loss of 0.05 dB / cm or less can be realized.

As a result, it was found that, even if hydrogen was filled during the formation of the core film, transmission loss was not significantly affected according to the present embodiment.

FIG. 3 is a schematic view showing a method of causing a light-induced refractive index change in a waveguide-type optical component formed by the apparatus shown in FIG.

In the method shown in FIG. 1, a grating is formed by irradiating the waveguide type optical component 20 with ultraviolet rays (excimer laser light) 21. A phase mask 22 on which a grating pattern is written is placed on the waveguide type optical component 20 having the structure and material composition as described above,
From above, an excimer laser beam 21 having a wavelength of 248 nm, shaped into an appropriate beam shape by a lens 23, is irradiated. The grating length obtained by the change in the refractive index due to the exposure is adjusted by moving the mirror 24 and the lens 23 to scan the excimer laser light 21 or moving the waveguide type optical component 20. As a result of forming a grating on the core of the waveguide type optical component 20 in this way, the length was 5 m.
m, the reflectance at a wavelength of 1535 nm is 99.8% or more;
A grating having a photo-induced refractive index change Δn of 10 ⁻³ or more was obtained.

As described above, according to the present invention, there is no need for hydrogen loading or hydrogen filling by frame brushing or the like in order to increase the refractive index change due to ultraviolet irradiation. As a result, there is no need for a manufacturing step that requires long-term and careful attention for safety or an overheating manufacturing step that deteriorates the optical characteristics of the waveguide. Further, according to the present invention, since a bias voltage is applied to the substrate, the amount of oxygen deficiency defects that contribute to a change in the refractive index during irradiation with ultraviolet light can also be controlled. Further, the present invention can be achieved by a conventional manufacturing apparatus, and can be easily applied to a planar optical waveguide type optical component having various functions.

[0044]

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

By forming the core glass film by the sputtering method in a mixed gas of an inert gas and hydrogen gas, the core can be safely and efficiently filled with hydrogen without deforming the core. A method for manufacturing a waveguide-type optical component can be provided.

[Brief description of the drawings]

FIG. 1 is a schematic plan view of a sputtering apparatus to which a method of manufacturing a waveguide optical component according to the present invention is applied.

FIG. 2 is a process chart showing a method of manufacturing a waveguide-type optical component according to the present invention.

FIG. 3 is a schematic view showing a method of causing a light-induced refractive index change in a waveguide type optical component formed by the apparatus shown in FIG.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 10 Vacuum chamber 11 Substrate holder 13 Substrate 14a, 14b, 14c, 14d Sputtering target (target) 15a, 15b, 15c, 15d High frequency power supply

Claims (3)

[Claims] 1. A SiO _2, GeO ₂ or SiO ₂ and G
using a mixture with eO ₂ as a sputtering target material, forming a SiO ₂ -GeO ₂ composition core glass film on a substrate having a low refractive index layer by a sputtering method, and subjecting the core glass film to photolithography and dry etching. In a method of manufacturing a waveguide-type optical component, comprising a step of processing a core having a substantially rectangular cross-sectional shape and a step of coating the entire core on a substrate with a low-refractive-index clad glass film, A method for manufacturing a waveguide-type optical component, wherein the formation is performed in a mixed gas of an inert gas and a hydrogen gas. 2. The step of forming a core glass film by the sputtering method, wherein the mixing ratio of hydrogen gas in the total amount of gas introduced at the time of sputtering is in the range of 3 to 30%,
2. The method for manufacturing a waveguide-type optical component according to claim 1, wherein the gas pressure during sputtering is set in a range of 0.01 to 1 Pa and the bias power is applied to the substrate. 3. The method according to claim 1, wherein the refractive index of the core is changed by irradiating at least a part of the core with ultraviolet light.