JPH0659147A - Optical waveguide and its production - Google Patents

Abstract

PURPOSE:To provide the glass waveguide which has the small warpage and the low loss by forming a core of an approximately rectangular shape on a substrate and covering the core with a material having a lower refractive index. CONSTITUTION:The core 2 having the approximately rectangular shape is formed by a plasma CVD method using SiOx (X=1.5 to 1.9) having the refractive index within 1.46 to 1.60 range on the substrate 1 and the core 2 is coated with a low-refractive index material (clad) 3 consisting of the material having the refractive index lower than the refractive index of the core 2. In such a case, the core 2 may be formed of the core 2 without contg. additives and any of glass, ferroelectric substance, magnetic material or semiconductor may be used for the substrate 1. The low-refractive index material 3 may be formed of SiO2 or a material formed by adding at least one kind of the additives for controlling the refractive index, such as B, F, P and Ge to the SiO2. Further the low-refractive index material 3 may be formed of a high-polymer material. The difference in the refractive index between the core 2 and the clad 3 is increased by constituting the optical waveguide in such a manner.

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 a method for manufacturing the same, and more particularly to a glass waveguide having a large refractive index difference between the core and the clad, a small warpage, a low loss, and a low-cost manufacturing thereof. It is about the method.

[0002]

2. Description of the Related Art With the progress of optical fiber communication, optical devices have 1) miniaturization, 2) mass productivity, 3) high reliability,
4) No adjustment of coupling, 5) Automatic assembly, 6) Reduction of loss, etc. are required, and waveguide type optical devices have been attracting attention in order to solve these problems. .

Among the optical waveguides, the silica glass optical waveguide has a low loss and the connection loss with the optical fiber is very small, so that it is regarded as a promising optical waveguide in the future. Conventionally, the flame deposition method shown in FIG. 9 is known as a method for manufacturing a silica glass optical waveguide. This is because (a) a silica glass porous film (buffer layer) is formed on a silicon substrate and a refractive index control additive (Ti or Ge) is formed on the film.
Etc.) containing a quartz glass porous film (core layer),
(B) Forming a planar optical waveguide film by heating and making it transparent,
(C) and (d) formation of a three-dimensional optical waveguide by patterning, (e) formation of a silica glass porous film (clad layer) on the above three-dimensional optical waveguide, and (f) realization by heating and transparency. (Miyashita: Optical Waveguide, 1. Recent Optical Waveguide Technology, Oplus E, No.78, P.59-67).

[0004]

The method of manufacturing the silica glass optical waveguide shown in FIG. 9 has the following problems.

(1) When a core glass film having a high refractive index is formed on a buffer layer in order to manufacture a glass waveguide having a large refractive index difference between the core and the clad, the entire substrate is affected by a difference in thermal expansion coefficient. Warping occurs, and it is difficult to pattern an optical circuit with high dimensional accuracy.

(2) In addition to the reason (1), it has been found that the above manufacturing method has a limit in the difference in refractive index between the core and the clad due to the following reasons. That is, even if the porous film for core having a high refractive index is deposited, the additive for controlling the refractive index is volatilized in the sintering process (b), and it is difficult to realize the core layer having a high refractive index.

(3) When the core layer containing a large amount of the refractive index controlling additive is patterned by the dry etching process as shown in (d), etching is performed due to the difference in etching rate between SiO ₂ and the additive. There is a problem that the side surface is roughened to increase scattering loss.

(4) Since the sintering process is performed twice, it takes time, the utility cost is high, and the cost reduction is difficult.

An object of the present invention is to solve the above-mentioned drawbacks of the prior art, and to provide a glass waveguide having a large refractive index difference between the core and the clad, a small warpage, and a low loss. Another object of the present invention is to provide a method for manufacturing a low cost glass waveguide.

[0010]

In order to achieve the above object, the present invention provides a SiOx (x = x = x) film having a refractive index of 1.46 to 1.60 on a substrate by a plasma CVD method.
1.5-1.9) is used to form a substantially rectangular core, and the core is covered with a low refractive index material made of a material having a refractive index lower than that of the core.

The core may be formed of a core containing no additive.

Any one of glass, ferroelectric, magnetic substance or semiconductor may be used for the substrate.

The low refractive index material may be SiO ₂ or SiO ₂ .
₂ B, F, P, may be at least one is added to the materials for refractive index control additives such as Ge.

The low refractive index material may be a polymer material.

Further, the manufacturing method thereof includes a step of forming a SiOx film on a substrate made of a low refractive index material by a plasma CVD method, and a step of patterning the SiOx film into a substantially rectangular shape by photolithography and dry etching. And a step of coating the surface of this pattern with a low refractive index material.

The step of coating the low refractive index material on the surface of the pattern may be carried out by first depositing a thin layer of the low refractive index material by plasma CVD and then coating another low refractive index material thereon. Good.

When the SiOx film is formed by the plasma CVD method, the refractive index of the SiOx film may be set by changing the degree of vacuum during film formation or the substrate heating temperature.

[0018]

With the above structure, the refractive index is 1.46 to 1.60.
Since a substantially rectangular core is formed by using SiOx (x = 1.5 to 1.9) within the range, the core is covered with a low refractive index material made of a material having a lower refractive index than that. , The refractive index difference between the core and the clad becomes large.

In addition, in the core of the optical waveguide, the conventional refractive index control additives (Ge, P, Ti, Al, Z) are used.
(n, Na, K, etc.) are not added, there is almost no change in refractive index due to volatilization of the above additives during the manufacturing process of the optical waveguide. Further, the coefficient of thermal expansion of the core layer is not so different from that of the buffer layer, the clad layer or the substrate, so that the core layer hardly warps. As a result, an optical circuit with high dimensional accuracy can be patterned.

The method of manufacturing the optical waveguide of the present invention is
The optical waveguide can be manufactured at a low cost for the reasons that 1) it is not necessary to add an expensive refractive index controlling additive in the core layer, and 2) the sintering process is required only once. .

[0021]

EXAMPLE FIG. 1 is a sectional view of an optical waveguide of the present invention. In this, SiO ₂ glass is used for the substrate 1, and a SiOx (x = 1.5 to 1.9) glass film formed by the plasma CVD method (CVD method; vapor phase chemical vapor deposition method) is used for the core 2. The refractive index nw of the core 2 is 1.
It is created so as to fall within the range of 46 to 1.60. As the clad 3, SiO ₂ or SiO ₂ containing at least one additive for controlling the refractive index such as B, P and F is used. This clad 3 is formed by plasma CVD method, atmospheric pressure CVD
Method, sputtering method, electron beam evaporation method, flame deposition method or the like, and the value of the refractive index nc thereof is selected to be lower than the value of nw. For example, normal pressure C
When the SiO ₂ film is formed by the VD method, the value of nc is about 1.458, and the relative refractive index difference between the core 2 and the clad 3 (or the substrate 1) reaches about 8.8% at maximum. be able to. In other words, in the conventional method, the difference in relative refractive index was limited to about 1% at most, but in the configuration of the present invention, it can be made as large as about 8.8 times that of the conventional method. Moreover, since the SiO _x core film has a value close to the thermal expansion coefficient of the SiO ₂ substrate 1 and the clad 3, there is almost no substrate warpage during film formation, and it is possible to pattern an optical circuit with high dimensional accuracy. You can Further, in the core 2, as in the conventional case, P, Ge, Al and T are added as refractive index controlling additives.
Since i, B, etc. are not included, the refractive index of the core 2 does not decrease during the optical waveguide manufacturing process. Further, since the core 2 does not contain the refractive index controlling additive, it can be etched at a substantially constant speed when processed into a substantially rectangular structure by a dry etching process, and the side surface of the core having less side surface roughness can be formed. Can be realized.

FIG. 2 shows another embodiment of the optical waveguide of the present invention. This figure shows a cross-sectional view of the optical waveguide.
An i substrate is used, and the low refractive index layer 4 (refractive index n
b <nw) is provided, and the core 2 surrounded by the cladding 3 is formed in a substantially rectangular shape on the low refractive index layer 4. The material of the low refractive index layer 4 may be the same as the material of the clad 3, and its refractive index nb is the refractive index n of the clad 3.
It may be about the same as c, or nb> nc and nb <nc.

FIG. 3 shows still another embodiment of the optical waveguide of the present invention. This figure also shows a cross-sectional view of the optical waveguide. In this structure, a thin layer 15 having a refractive index nt (nt ≦ nb) is provided on the low refractive index layer 4 and the core 2, and the cladding 3 is formed thereon. This thin layer 15
Can be formed by a method similar to the method of forming the clad 3. By providing this thin layer 15, the confinement of light in the core 2 can be further strengthened.

FIG. 4 shows a method of manufacturing the optical waveguide of the present invention. First, SiO ₂ on the substrate 1, as described below, to deposit a SiOx film serving as the core layer 2 'by a plasma CVD method. The film thickness of this SiO _x is several μm to 20 μm when a single mode optical waveguide is realized, and 1 μm to 100 μm when a multimode optical waveguide is realized.
Within the range (FIG. 4 (a)). Next, FIG. 4 (b)
As shown in FIG. 5, a rectangular core 2 is processed by dry etching using a reactive ion etching device. After that, the film of the clad 3 is deposited by the plasma CVD method, the atmospheric pressure CVD method, the flame deposition method, or the like. The cladding 3 may have a film thickness of 5 μm or more. When the cladding 3 is formed by the plasma CVD method, the low pressure CVD method, or the like, a transparent glass film can be formed, so that the subsequent high temperature heat treatment step may be omitted. When the film of the clad 3 is formed by the flame deposition method, the atmospheric pressure CVD method, or the like, the film is porous, so that a high temperature heat treatment step is required thereafter.

FIG. 5 shows a schematic view of a method of depositing a core film on the substrate 1 by the plasma CVD method of the present invention. In the plasma CVD apparatus 5, two parallel plate electrodes 6 and 7 are provided on the upper and lower sides, and the high frequency power source 1 is provided between these electrodes.
The high frequency voltage is applied from 2. And this device 5
The inside is evacuated to a vacuum by a vacuum exhaust device 61.
The substrate 1 is placed on the lower electrode 7, and a voltage 11 is applied to the heater 10 below the electrode 7 to bring the temperature to several hundred degrees Celsius.
Is heated to. The upper electrode 6 has a shower electrode structure for uniformly ejecting the gas sent from the direction of arrow 9-1 between the parallel plate electrodes 6 and 7. The shower electrode 6 is formed by the insulator 13 into the plasma CVD device 5
Insulated. Plasma CVD from the direction of arrow 9-1
The gas fed into the device 5 is Si (OC ₂ H ₅ ) ₄ , S
i (OCH ₃ ) _{4 and} other metal alcohol oxide vapors are converted into O ₂
A gas carrier is used, or a vapor of a silicon compound such as SiH ₄ is carried by O ₂ gas.
Further, O ₂ gas is fed into the plasma atmosphere 8 from the outside as shown by an arrow 14. With such a device structure, the SiO _x film is formed on the substrate 1. here,
An example of film forming conditions for realizing the above-described core refractive index of 1.46 to 1.60 will be described.

FIG. 6 shows the degree of vacuum and refraction during film formation when an experiment was conducted using the above-mentioned Si (OC ₂ H ₅ ) ₄ and O ₂ gas as the gas introduced in the direction of arrow 9-1. The relationship between the rate and the film formation rate is shown. In this graph,
The refractive index is shown by a broken line, and the liquid film formation rate is shown by a solid line. Body Si
The temperature of (OC ₂ H ₅ ) ₄ was set to 17 ° C.
₂ gas 40SCCM is sent and bubbling is performed, and Si (O
C ₂ H ₅ ) ₄ vapor and O ₂ gas were introduced from the direction of arrow 9-1. Further, 50 SCCM of O ₂ gas was introduced from the direction of arrow 14. Then, the substrate 1 was heated to 350 ° C. by the heater 10 and the power of the high frequency power source was set to 100 W to form a film. The refractive index shows that the desired value of 1.46 to 1.60 can be achieved. The higher the vacuum, the lower the refractive index and the faster the film formation rate. On the contrary, when the degree of vacuum is poor, the refractive index is high, but the film formation rate tends to be low.

FIG. 7 shows the dependence of the refractive index on the substrate temperature, and it can be seen that the refractive index of 1.46 or more and 1.60 or less can be realized. In addition, this result is (0.
4 torr) characteristic example.

FIG. 8 shows the results of measuring the in-plane distribution of the film thickness and the refractive index of the core layer 2'when the core layer 2'of FIG. 4 (a) is formed. The table shows the measurement results at five measurement positions 0 to 4 provided on the plan view of the substrate 1. The characteristics before the heat treatment are those after film formation, and the characteristics after the heat treatment are 1000 ° C. after the film formation and O ₂ atmosphere (O ₂ gas flow rate: 3 l / min).
3) shows the characteristics after heat treatment for 3 hours. As described above, since the core layer 2'does not contain the refractive index controlling additive, the refractive index characteristics before and after the heat treatment change only to the extent of difference due to the change in density. That is, unlike the prior art, the heat treatment does not significantly reduce the refractive index due to volatilization of the refractive index control additive. Further, the warp of the substrate was several μm or less, which was a value that caused almost no problem.

[0029]

As described above, the optical waveguide and the method for manufacturing the same of the present invention have the following effects.

(1) Since the optical waveguide having a high relative refractive index difference can be realized, the performance of the optical waveguide can be improved as much as possible.

(2) Since the warp of the substrate hardly occurs, the patterning accuracy is improved.

(3) When the core is patterned into a rectangular shape by the dry etching process, the roughness of etching on the side surface of the core is extremely small, so that scattering loss is reduced.

(4) Since the number of sintering processes is at most once, the utility cost is low.

(5) Since the amount of expensive additive for controlling the refractive index can be greatly reduced (only for the clad and not for the core), the cost can be reduced.

[Brief description of drawings]

FIG. 1 is a sectional view of an optical waveguide showing an embodiment of the present invention.

FIG. 2 is a cross-sectional view of an optical waveguide showing another embodiment of the present invention.

FIG. 3 is a sectional view of an optical waveguide showing another embodiment of the present invention.

FIG. 4 is a process drawing showing the method of manufacturing the optical waveguide of the present invention.

FIG. 5 is a schematic view of a method of depositing a core film on a substrate by the plasma CVD method of the present invention.

FIG. 6 is a characteristic diagram showing a graph showing the relationship between the degree of vacuum during film formation, the refractive index, and the film formation rate in the present invention.

FIG. 7 is a characteristic diagram showing a graph showing the substrate temperature dependence of the refractive index in the present invention.

FIG. 8 is a plan view of the substrate showing positions for measuring the in-plane distribution of the film thickness and the refractive index of the core layer 2 ′ when the core layer 2 ′ of FIG. 4A is formed, and a table showing the results. is there.

FIG. 9 is a process diagram of a flame deposition method showing a conventional example.

[Explanation of symbols]

 1 substrate 2 core 3 clad

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[Procedure amendment]

[Submission date] March 29, 1993

[Procedure Amendment 1]

[Document name to be amended] Statement

[Correction target item name] Full text

[Correction method] Change

[Correction content]

[Document name] Statement

Title: Optical waveguide and method for manufacturing the same

[Claims]

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical waveguide and a method for manufacturing the same, and more particularly to a glass waveguide having a large refractive index difference between the core and the clad, a small warpage, a low loss, and a low-cost manufacturing thereof. It is about the method.

[0002]

2. Description of the Related Art With the progress of optical fiber communication, optical devices have 1) miniaturization, 2) mass productivity, 3) high reliability,
4) No adjustment of coupling, 5) Automatic assembly, 6) Reduction of loss, etc. are required, and waveguide type optical devices have been attracting attention in order to solve these problems. .

Among the optical waveguides, the silica glass optical waveguide has a low loss and the connection loss with the optical fiber is very small, so that it is regarded as a promising optical waveguide in the future. Conventionally, the flame deposition method shown in FIG. 9 is known as a method for manufacturing a silica glass optical waveguide. This is because (a) a silica glass porous film (buffer layer) is formed on a silicon substrate and a refractive index control additive (Ti or Ge) is formed on the film.
Etc.) containing a quartz glass porous film (core layer),
(B) Forming a planar optical waveguide film by heating and making it transparent,
(C) and (d) formation of a three-dimensional optical waveguide by patterning, (e) formation of a silica glass porous film (clad layer) on the above three-dimensional optical waveguide, and (f) realization by heating and transparency. (Miyashita: Optical Waveguide, 1. Recent Optical Waveguide Technology, Oplus E, No.78, P.59-67).

[0004]

The method of manufacturing the silica glass optical waveguide shown in FIG. 9 has the following problems.

(1) When a core glass film having a high refractive index is formed on a buffer layer in order to manufacture a glass waveguide having a large refractive index difference between the core and the clad, the entire substrate is affected by a difference in thermal expansion coefficient. Warping occurs, and it is difficult to pattern an optical circuit with high dimensional accuracy.

(2) In addition to the reason (1), it has been found that the above manufacturing method has a limit in the difference in refractive index between the core and the clad due to the following reasons. That is, even if the porous film for core having a high refractive index is deposited, the additive for controlling the refractive index is volatilized in the sintering process (b), and it is difficult to realize the core layer having a high refractive index.

(3) When the core layer containing a large amount of the refractive index controlling additive is patterned by the dry etching process as shown in (d), etching is performed due to the difference in etching rate between SiO ₂ and the additive. There is a problem that the side surface is roughened to increase scattering loss.

(4) Since the sintering process is performed twice, it takes time, the utility cost is high, and the cost reduction is difficult.

An object of the present invention is to solve the above-mentioned drawbacks of the prior art, and to provide a glass waveguide having a large refractive index difference between the core and the clad, a small warpage, and a low loss. Another object of the present invention is to provide a method for manufacturing a low cost glass waveguide.

[0010]

In order to achieve the above object, the present invention provides a SiOx (x = x = x) film having a refractive index of 1.46 to 1.60 on a substrate by a plasma CVD method.
1.5-1.9) is used to form a substantially rectangular core, and the core is covered with a low refractive index material made of a material having a refractive index lower than that of the core.

The core may be formed of a core containing no additive.

Any one of glass, ferroelectric, magnetic substance or semiconductor may be used for the substrate.

The low refractive index material may be SiO ₂ or SiO ₂ .
₂ B, F, P, may be at least one is added to the materials for refractive index control additives such as Ge.

The low refractive index material may be a polymer material.

Further, the manufacturing method is a step of forming a SiOx film on a substrate made of a low refractive index material by a plasma CVD method, and a step of patterning the SiOx film into a substantially rectangular shape by photolithography and dry etching. And a step of coating the surface of this pattern with a low refractive index material.

The step of coating the low refractive index material on the surface of the pattern may be carried out by first depositing a thin layer of the low refractive index material by plasma CVD and then coating another low refractive index material thereon. Good.

When the SiOx film is formed by the plasma CVD method, the refractive index of the SiOx film may be set by changing the degree of vacuum during film formation or the substrate heating temperature.

[0018]

With the above structure, the refractive index is 1.46 to 1.60.
Since a substantially rectangular core is formed by using SiOx (x = 1.5 to 1.9) within the range, the core is covered with a low refractive index material made of a material having a lower refractive index than that. , The refractive index difference between the core and the clad becomes large.

In addition, in the core of the optical waveguide, the conventional refractive index control additives (Ge, P, Ti, Al, Z) are used.
(n, Na, K, etc.) are not added, there is almost no change in refractive index due to volatilization of the above additives during the manufacturing process of the optical waveguide. Further, the coefficient of thermal expansion of the core layer is not so different from that of the buffer layer, the clad layer or the substrate, so that the core layer hardly warps. As a result, an optical circuit with high dimensional accuracy can be patterned.

The method of manufacturing the optical waveguide of the present invention is
The optical waveguide can be manufactured at a low cost for the reasons that 1) it is not necessary to add an expensive refractive index controlling additive in the core layer, and 2) the sintering process is required only once. .

[0021]

EXAMPLE FIG. 1 is a sectional view of an optical waveguide of the present invention. In this, SiO ₂ glass is used for the substrate 1, and a SiOx (x = 1.5 to 1.9) glass film formed by the plasma CVD method (CVD method; vapor phase chemical vapor deposition method) is used for the core 2. The refractive index nw of the core 2 is 1.
It is created so as to fall within the range of 46 to 1.60. As the clad 3, SiO ₂ or SiO ₂ containing at least one additive for controlling the refractive index such as B, P and F is used. This clad 3 is formed by plasma CVD method, atmospheric pressure CVD
Method, sputtering method, electron beam evaporation method, flame deposition method or the like, and the value of the refractive index nc thereof is selected to be lower than the value of nw. For example, normal pressure C
When the SiO ₂ film is formed by the VD method, the value of nc is about 1.458, and the relative refractive index difference between the core 2 and the clad 3 (or the substrate 1) reaches about 8.8% at maximum. be able to. In other words, in the conventional method, the difference in relative refractive index was limited to about 1% at most, but in the configuration of the present invention, it can be made as large as about 8.8 times that of the conventional method. Moreover, since the SiO _x core film has a value close to the thermal expansion coefficient of the SiO ₂ substrate 1 and the clad 3, there is almost no substrate warpage during film formation, and it is possible to pattern an optical circuit with high dimensional accuracy. You can Further, in the core 2, as in the conventional case, P, Ge, Al and T are added as refractive index controlling additives.
Since i, B, etc. are not included, the refractive index of the core 2 does not decrease during the optical waveguide manufacturing process. Further, since the core 2 does not contain the refractive index controlling additive, it can be etched at a substantially constant speed when processed into a substantially rectangular structure by a dry etching process, and the side surface of the core having less side surface roughness can be formed. Can be realized.

FIG. 2 shows another embodiment of the optical waveguide of the present invention. This figure shows a cross-sectional view of the optical waveguide.
An i substrate is used, and the low refractive index layer 4 (refractive index n
b <nw) is provided, and the core 2 surrounded by the cladding 3 is formed in a substantially rectangular shape on the low refractive index layer 4. The material of the low refractive index layer 4 may be the same as the material of the clad 3, and its refractive index nb is the refractive index n of the clad 3.
It may be about the same as c, or nb> nc and nb <nc.

FIG. 3 shows still another embodiment of the optical waveguide of the present invention. This figure also shows a cross-sectional view of the optical waveguide. In this structure, a thin layer 15 having a refractive index nt (nt ≦ nb) is provided on the low refractive index layer 4 and the core 2, and the cladding 3 is formed thereon. This thin layer 15
Can be formed by a method similar to the method of forming the clad 3. By providing this thin layer 15, the confinement of light in the core 2 can be further strengthened.

FIG. 4 shows a method of manufacturing the optical waveguide of the present invention. First, SiO ₂ on the substrate 1, as described below, to deposit a SiOx film serving as the core layer 2 'by a plasma CVD method. The film thickness of this SiO _x is several μm to 20 μm when a single mode optical waveguide is realized, and 1 μm to 100 μm when a multimode optical waveguide is realized.
Within the range (FIG. 4 (a)). Next, FIG. 4 (b)
As shown in FIG. 5, a rectangular core 2 is processed by dry etching using a reactive ion etching device. After that, the film of the clad 3 is deposited by the plasma CVD method, the atmospheric pressure CVD method, the flame deposition method, or the like. The cladding 3 may have a film thickness of 5 μm or more. When the cladding 3 is formed by the plasma CVD method, the low pressure CVD method, or the like, a transparent glass film can be formed, so that the subsequent high temperature heat treatment step may be omitted. When the film of the clad 3 is formed by the flame deposition method, the atmospheric pressure CVD method, or the like, the film is porous, so that a high temperature heat treatment step is required thereafter.

FIG. 5 shows a schematic view of a method of depositing a core film on the substrate 1 by the plasma CVD method of the present invention. In the plasma CVD apparatus 5, two parallel plate electrodes 6 and 7 are provided on the upper and lower sides, and the high frequency power source 1 is provided between these electrodes.
The high frequency voltage is applied from 2. And this device 5
The inside is evacuated to a vacuum by a vacuum exhaust device 61.
The substrate 1 is placed on the lower electrode 7, and a voltage 11 is applied to the heater 10 below the electrode 7 to bring the temperature to several hundred degrees Celsius.
Is heated to. The upper electrode 6 has a shower electrode structure for uniformly ejecting the gas sent from the direction of arrow 9-1 between the parallel plate electrodes 6 and 7. The shower electrode 6 is formed by the insulator 13 into the plasma CVD device 5
Insulated. Plasma CVD from the direction of arrow 9-1
The gas fed into the device 5 is Si (OC ₂ H ₅ ) ₄ , S
i (OCH ₃ ) _{4 and} other metal alcohol oxide vapors are converted into O ₂
A gas carrier is used, or a vapor of a silicon compound such as SiH ₄ is carried by O ₂ gas.
Further, O ₂ gas is fed into the plasma atmosphere 8 from the outside as shown by an arrow 14. With such a device structure, the SiO _x film is formed on the substrate 1. here,
An example of film forming conditions for realizing the above-described core refractive index of 1.46 to 1.60 will be described.

FIG. 6 shows the degree of vacuum and refraction during film formation when an experiment was conducted using the above-mentioned Si (OC ₂ H ₅ ) ₄ and O ₂ gas as the gas introduced in the direction of arrow 9-1. The relationship between the rate and the film formation rate is shown. In this graph,
The refractive index is shown by a broken line, and the liquid film formation rate is shown by a solid line. Body Si
The temperature of (OC ₂ H ₅ ) ₄ was set to 17 ° C.
₂ gas 40SCCM is sent and bubbling is performed, and Si (O
C ₂ H ₅ ) ₄ vapor and O ₂ gas were introduced from the direction of arrow 9-1. Further, 50 SCCM of O ₂ gas was introduced from the direction of arrow 14. Then, the substrate 1 was heated to 350 ° C. by the heater 10 and the power of the high frequency power source was set to 100 W to form a film. The refractive index shows that the desired value of 1.46 to 1.60 can be achieved. The higher the vacuum, the lower the refractive index and the faster the film formation rate. On the contrary, when the degree of vacuum is poor, the refractive index is high, but the film formation rate tends to be low.

FIG. 7 shows the dependence of the refractive index on the substrate temperature, and it can be seen that the refractive index of 1.46 or more and 1.60 or less can be realized. In addition, this result is (0.
4 torr) characteristic example.

[0028] Figure 4 result of measuring the in-plane distribution of the film thickness and refractive index of the core layer 2 'in the case of forming the core layer 2' of (a) a
explain. As shown in FIG. 8, measurement was performed at five measurement positions 0 to 4 provided on the plan view of the substrate 1 . So
The results are shown in Table 1 .

[0029]

[Table 1]

In Table 1, the characteristics before heat treatment are those after film formation, and the characteristics after heat treatment are 1000 ° C. and O 2 after film formation.
_It shows the characteristics after heat treatment in ₂ atmospheres (O ₂ gas flow rate: 3 l / min) for 3 hours. As previously mentioned,
Since the core layer 2'does not contain the refractive index control additive, the refractive index characteristics before and after the heat treatment change only to the extent of difference due to the change in density. That is, unlike the prior art, the heat treatment does not significantly reduce the refractive index due to volatilization of the refractive index control additive. Further, the warp of the substrate was several μm or less, which was a value that caused almost no problem.

[0031]

As described above, the optical waveguide and the method for manufacturing the same of the present invention have the following effects.

(1) Since an optical waveguide having a high relative refractive index difference can be realized, the performance of the optical waveguide can be improved as much as possible.

(2) Since the substrate is hardly warped, the patterning accuracy is improved.

(3) When the core is patterned into a rectangular shape by the dry etching process, the etching roughness on the side surface of the core is extremely small, so that scattering loss is reduced.

(4) Since the number of sintering processes is at most once, the utility cost is low.

(5) Since the amount of expensive additive for controlling the refractive index can be greatly reduced (only for the clad, not for the core), the cost can be reduced.

[Brief description of drawings]

FIG. 1 is a sectional view of an optical waveguide showing an embodiment of the present invention.

FIG. 2 is a cross-sectional view of an optical waveguide showing another embodiment of the present invention.

FIG. 3 is a sectional view of an optical waveguide showing another embodiment of the present invention.

FIG. 4 is a process drawing showing the method of manufacturing the optical waveguide of the present invention.

FIG. 5 is a schematic view of a method of depositing a core film on a substrate by the plasma CVD method of the present invention.

FIG. 6 is a characteristic diagram showing a graph showing the relationship between the degree of vacuum during film formation, the refractive index, and the film formation rate in the present invention.

FIG. 7 is a characteristic diagram showing a graph showing the substrate temperature dependence of the refractive index in the present invention.

FIG. 8 shows the positions where the in-plane distributions of film thickness and refractive index are measured.
It is a top view of a substrate.

FIG. 9 is a process diagram of a flame deposition method showing a conventional example.

[Explanation of symbols] 1 substrate 2 core 3 clad

[Procedure Amendment 2]

[Document name to be corrected] Drawing

[Correction target item name] All drawings

[Correction method] Change

[Correction content]

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[Fig. 2]

[Figure 3]

[Figure 8]

[Figure 4]

[Figure 5]

[Figure 6]

[Figure 7]

[Figure 9]

Claims (8)

[Claims] 1. A SiOx film (x = x = x) having a refractive index of 1.46 to 1.60 on a substrate by plasma CVD.
1.5-1.9) is used to form a substantially rectangular core, and the core is covered with a low refractive index material made of a material having a refractive index lower than that of the core. 2. The optical waveguide according to claim 1, wherein the core is formed of a core containing no additive. 3. The optical waveguide according to claim 1, wherein the substrate is made of glass, ferroelectric, magnetic or semiconductor. 4. The low refractive index material is SiO ₂ or Si.
_2. The optical waveguide according to claim 1, wherein O ₂ is a material in which at least one kind of a refractive index controlling additive such as B, F, P and Ge is added. 5. The optical waveguide according to claim 1, wherein the low refractive index material is a polymer material. 6. A plasma C is formed on a substrate made of a low refractive index material.
The method comprises a step of forming a SiOx film by the VD method, a step of patterning the SiOx film into a substantially rectangular shape by photolithography and dry etching, and a step of coating the surface of the pattern with a low refractive index material. And a method for manufacturing an optical waveguide. 7. The step of coating the low refractive index material on the pattern surface is performed by first depositing a thin layer of the low refractive index material by plasma CVD and then coating another low refractive index material thereon. 7. The method of manufacturing an optical waveguide according to claim 6, wherein 8. When the SiOx film is formed by the plasma CVD method, the refractive index of the SiOx film is set by changing the degree of vacuum during film formation or the substrate heating temperature. The method for manufacturing an optical waveguide according to claim 6.