JP3771034B2 - Manufacturing method of optical waveguide - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a method for manufacturing an optical waveguide, and more particularly to a method for manufacturing a silica-based optical waveguide.
[0002]
[Prior art]
A conventional method for manufacturing a silica-based waveguide is shown in “NTT R & D Vol. 43, No. 11, 1994, Nos. 101 to 108”. Hereinafter, a conventional method for manufacturing a silica-based optical waveguide will be described with reference to FIG.
[0003]
First, silicon oxide glass fine particles (particle size 0.1 μm or less) obtained by heating and hydrolyzing the same gaseous raw material as the optical fiber (main component: silicon tetrachloride) in an oxyhydrogen flame using an oxyhydrogen torch 37 Is sprayed on the silicon substrate 31 to form. At this time, by changing the composition of the silicon oxide glass fine particles (GeO dopant concentration), the entire upper surface of the silicon substrate 31 is SiO 2. ₂ Fine particles 32 'are formed and SiO ₂ The entire upper surface of the fine particle 32 'is SiO. ₂ -GeO ₂ Fine particles 33 ′ are formed (see FIG. 5A).
[0004]
Next, the silicon oxide glass fine particle film is heated at a high temperature of 1250 ° C. or higher in an electric furnace to form a transparent silicon oxide glass film covering the upper surface of the silicon substrate 31. As described above, by changing the composition of the silicon oxide glass fine particles (GeO dopant concentration), an optical waveguide film having a two-layer structure of the lower cladding layer 32 and the core layer 33 is obtained (see FIG. 5B).
[0005]
Next, after a predetermined pattern is transferred to the core layer 33 by the photomask 38, unnecessary portions of the core layer 33 are removed by reactive ion etching (RIE), and the line width is increased to 4 to 10 μm. A ridge-shaped core 35 having a length of 4 to 10 μm is formed (see FIG. 5C). Finally, SiO2 fine particles 36 ′ are formed by a flame forming method (FHD: Frame Hydrolysis Deposition) so as to cover the core 35 (see FIG. 5D), and further made transparent to form the upper clad layer 36. Embedded SiO ₂ -GeO ₂ A system single-mode optical waveguide is completed (see FIG. 5E).
[0006]
[Problems to be solved by the invention]
By the way, when manufacturing an optical waveguide used for a Y-branch circuit, a directional coupler, a Mach-Zehnder interferometer, etc., it is processed so that the minimum distance between the core and the other core is 4 μm or less. However, when the upper cladding layer is formed, as shown in FIG. 7, when the distance w between the cores is smaller than the core height h, the core height h is particularly larger than the distance w between the cores. When the core is large (for example, when the core height h is 8 μm and the distance w between the cores is 4 μm or less), there is a problem that it is not easy to embed the inter-core 36 a with the upper cladding 36.
[0007]
In addition, since the optical waveguide usually needs to have a refractive index of the core relatively higher than that of the surrounding cladding, the optical waveguide is doped with impurities for the purpose of controlling the refractive index of the core and the cladding. In the above process, it is necessary to make transparent by heating at a high temperature of 1250 ° C. or higher after forming the silicon oxide glass fine particles. However, since the thermal stress is generated when the temperature is returned to room temperature, the birefringence of the optical waveguide is induced. There was a problem that the polarization characteristics deteriorated. Further, when a high-temperature heat treatment is performed after doping an impurity for controlling the refractive index, there is a problem that the impurity moves due to thermal diffusion and a desired refractive index distribution cannot be obtained.
[0008]
The present invention has been made in view of the above-mentioned problems of the conventional optical waveguide manufacturing method, and the object of the present invention is easy even when the ratio of the core height to the distance between the cores is large. It is an object of the present invention to provide a new and improved method of manufacturing an optical waveguide that can embed an upper clad in the substrate and can manufacture a highly accurate optical waveguide.
[0009]
Furthermore, another object of the present invention is to provide a new and improved optical waveguide manufacturing method capable of preventing the loss of the optical waveguide due to high-temperature heat treatment and increasing the yield.
[0010]
[Means for Solving the Problems]
To solve the above problems, The present invention According to the present invention, there is provided a method of manufacturing an optical waveguide in which a core and a cladding layer surrounding the core are formed on an upper portion of a substrate, the step of forming a lower cladding layer on the substrate, and the core layer on the entire upper surface of the lower cladding layer. Forming the core, forming the core from the core layer, forming the first upper cladding layer having a predetermined thickness on the entire upper surface of the lower cladding layer and the core, and formed between the cores There is provided a method for manufacturing an optical waveguide, comprising: a step of forming a buffer film in the groove; and a step of forming a second upper clad layer on the entire upper surface of the first upper clad layer and the buffer film. . The buffer film is , S An OG (Spin on Glass) film may be used.
[0011]
According to this manufacturing method, after forming the first upper cladding layer between the cores, the SOG film having high fluidity is formed as the buffer film. Therefore, it is possible to reduce the inclination of the side wall portion while reducing the ratio of the width and height of the groove forming the second upper cladding layer. Therefore, the second upper cladding layer can be easily formed.
[0012]
Further, the structure in which the SOG film is sandwiched between the first upper clad layer and the second upper clad layer can reduce water absorption into the SOG film and reduce water release from the SOG film. It is. Water causes a Si—OH group having an absorptivity in the vicinity of a wavelength of 1.39 μm, and there is a risk of reducing light propagation loss for an optical waveguide using a wavelength band of 1.3 μm. Therefore, it is possible to prevent a decrease in light propagation loss by reducing the concentration of Si—OH groups as in the present manufacturing method.
[0013]
More preferably , S The OG film is also formed on the side wall of the groove. According to such a manufacturing method, about 7 × 10 ⁸ A quartz film as a clad layer having a compressive stress of Pa, and about 3 × 10 ⁸ Since the SOG film having a tensile stress of Pa is formed not only on the bottom of the groove but also on the side wall of the groove, the stress is relaxed, the birefringence is reduced, and the polarization characteristics are reduced. It is possible to improve.
[0014]
More preferably , Number The upper cladding layer 2 is formed by plasma treatment. According to this manufacturing method, since the SOG film is exposed to plasma in the step of forming the second upper cladding layer, F radicals and F ions in the plasma gas decomposed from the processing gas C2F6 are applied to the SOG film. Spread. Therefore, the refractive index of the upper clad can be uniformly set to about 1.452.
[0015]
In particular, the present invention , Ko The ratio between the minimum distance between the cores and the height of the core is 2/3 or less And also , Ko The present invention is suitably applied to the production of an optical waveguide having a minimum interval of 5 μm or less and a core height of 4 to 12 μm. According to the manufacturing method of the present invention, the distance between the cores is small compared to the height of the core, and even an optical waveguide having a shape that has been considered difficult in the conventional optical waveguide manufacturing method is easily manufactured. It is possible.
[0016]
DETAILED DESCRIPTION OF THE INVENTION
Exemplary embodiments of an optical waveguide manufacturing method according to the present invention will be described below in detail with reference to the accompanying drawings. In the present specification and drawings, components having substantially the same functional configuration are denoted by the same reference numerals, and redundant description is omitted.
[0017]
(First embodiment)
In this embodiment, as shown in FIGS. 1 and 2, a silicon substrate 11 is used as a substrate, and a lower clad layer 12, a core material 13, a first upper clad layer 16, and An example of a method for manufacturing an optical waveguide manufactured by forming the quartz film to be the second upper cladding layer 18 and the SOG film 17 will be described. A plasma chemical vapor deposition (hereinafter, referred to as “plasma CVD (Chemical Vapor Deposition)”) method is used to form the quartz film and the SOG film. First, as an example of an apparatus used for the plasma CVD method, a plasma CVD apparatus 100 for forming a quartz film shown in FIG. 3 will be described.
[0018]
In the processing chamber 110 of the plasma CVD apparatus 100 for forming a quartz film, a lower electrode 120 for mounting an object to be processed, for example, a silicon substrate 130 is accommodated. Temperature adjusting means is provided inside the lower electrode 120 so that the silicon substrate 130 on the lower electrode 120 can be maintained at a predetermined temperature (for example, a maximum of 500 degrees).
[0019]
Further, an upper electrode 140 provided with an ejection hole for supplying a processing gas is provided above the processing chamber 110. A mass flow controller MFC for controlling the flow rate of the processing gas and a processing gas source 170 are sequentially connected to the upper electrode 140, and a jet provided in the upper electrode 140 is further connected from the processing gas source 170 through the muffs controller MFC. A predetermined processing gas such as O is introduced into the processing chamber 110 through the outlet. ₂ , C ₂ F ₆ , N ₂ , Tetraethoxysilane (hereinafter referred to as “TEOS”), triethoxysilane (hereinafter referred to as “TRIES”), and the like can be introduced at a predetermined flow rate. Further, an exhaust pipe 180 is connected to the lower side of the processing chamber 110, and the exhaust pipe 180 communicates with an exhaust system 190 including a turbo molecular pump, a rotary pump, etc. (not shown) via a butterfly valve BB. The inside of the processing chamber 110 is, for example, 1 × 10 ^-3 The pressure can be reduced to Pa.
[0020]
The lower electrode 120 is configured to be supplied with power from a high-frequency power source 150 that outputs high-frequency power of a predetermined frequency, for example, 13.56 MHz, through the matching unit 160. With this configuration, a desired film forming process can be performed on the silicon substrate 130 placed on the lower electrode 120.
[0021]
Below, the manufacturing method of the optical waveguide using the plasma CVD apparatus 100 mentioned above is demonstrated, referring FIG.1 and FIG.2.
[0022]
(1. Substrate cleaning process)
First, the silicon substrate 11 is washed for about 5 minutes with a solution having a temperature of about 85 ° C. in which sulfuric acid and hydrogen peroxide are mixed at a ratio of about 3: 1 by a predetermined cleaning apparatus, and then cleaned with pure water. Next, after washing with a hydrofluoric acid solution diluted to about 1% with pure water for about 20 seconds, it is washed with pure water.
[0023]
(2. Lower cladding layer formation process)
Next, a quartz film to be the lower cladding layer 12 is formed using the plasma CVD apparatus 100.
[0024]
The cleaned silicon substrate 11 is placed on the lower electrode 120 in the processing chamber 110 of the plasma CVD apparatus 100. The silicon substrate 11 is heated until the temperature reaches about 400 ° C. The inside of the processing chamber 110 is exhausted by a rotary pump (not shown) until the pressure becomes about 1 Pa. Next, the pressure is about 1 × 10 5 by a turbo molecular pump (not shown). ^-3 The processing chamber 110 is evacuated until Pa is reached. TRIE or TEOS is introduced into the processing chamber 110 from the upper electrode at a flow rate of about 12 sccm, oxygen of about 400 sccm, and C 2 F 6 of about 10 sccm. TRIE or TEOS is vaporized at a temperature of about 80 ° C. in advance.
[0025]
C ₂ F ₆ In order to form a clad for a non-doped core, doping is performed for the purpose of making the refractive index of the clad about 0.3% smaller than the refractive index of the core. C ₂ F ₆ Is also used for cleaning the processing chamber 110 to remove the film formed in the processing chamber 110 other than on the silicon substrate 11. Oxygen is also used for cleaning fluorine-based organic substances generated in the processing chamber 110.
[0026]
The pressure in the processing chamber 110 is maintained at about 30 Pa, and a high frequency of about 13.56 MHz is applied between the upper electrode 140 and the lower electrode 120 with a power density of about 1.6 W / cm. ² Apply with. Plasma is generated in the processing chamber, and a quartz film that forms the lower cladding layer 12 having a film thickness of about 25 μm and a refractive index of about 1.452 is formed on the silicon substrate 11 in about 3 hours and 30 minutes (see FIG. 1B). thing). After film formation, the application of high-frequency power is stopped.
[0027]
(3. Core layer forming step)
Next, a quartz film serving as the core layer 13 is formed on the entire upper surface of the lower cladding layer 12 using the plasma CVD apparatus 100. The silicon substrate 11 is placed on the lower electrode 120 in the processing chamber 110 of the plasma CVD apparatus 100. The silicon substrate 11 is heated until the temperature reaches about 400 ° C. The processing chamber 110 is evacuated to a pressure of about 1 Pa by a rotary pump (not shown). Subsequently, the pressure is about 1 × 10 by a turbo molecular pump (not shown). ^-3 Exhaust to Pa.
[0028]
TRIE or TEOS is introduced into the processing chamber 110 from the upper electrode 140 at a flow rate of about 12 sccm and oxygen of about 400 sccm. TRIE or TEOS is vaporized at a temperature of about 80 ° C. in advance. The pressure in the processing chamber 110 is maintained at about 30 Pa, and a high frequency of about 13.56 MHz is applied between the upper electrode 140 and the lower electrode 120 with a power density of about 1.6 W / cm. ² Apply with. Plasma is generated in the processing chamber 110, and a quartz film serving as the core layer 13 having a film thickness of about 8 μm and a refractive index of about 1.456 is formed on the lower cladding layer 12 in about 1 hour and 10 minutes (FIG. 1C See)). The high-frequency discharge and gas introduction are stopped, and a rotary pump (not shown) and a turbo molecular pump (not shown) are used in this order, and the pressure in the processing chamber 110 is about 1 × 10 ^-3 Exhaust to Pa. After evacuation, nitrogen is introduced into the processing chamber 110 to bring it to atmospheric pressure, and then the silicon substrate 11 is removed.
[0029]
(4. Resist pattern formation process)
Next, a resist pattern 14 for forming the core 15 is formed on the silicon substrate 11 by a commonly used exposure method using a mask (not shown) on which an optical waveguide pattern is formed. First, a resist is applied on the silicon substrate 11 by spin coating to a thickness of about 1.4 μm. Next, the silicon substrate 11 coated with the resist is held in a constant temperature bath at a temperature of about 90 ° C. for about 10 minutes, and then the mask and the silicon substrate 11 are set in a reduction projection exposure machine using i-line. Next, the resist on the silicon substrate 11 is irradiated with i-line with a predetermined exposure amount. Next, the resist pattern 14 of the optical waveguide is formed on the silicon substrate 11 by holding in a constant temperature bath at a post-development temperature of about 80 ° C. for about 10 minutes (see FIG. 1D).
[0030]
(5. Core formation process)
Next, the core layer 13 is processed. A silicon substrate 11 on which a resist pattern 14 of an optical waveguide is formed is placed in a processing chamber 110 of a generally used RIE (Reactive Ion Etching) apparatus. After exhausting the pressure in the processing chamber 110 to about 1 Pa by a rotary pump (not shown), the pressure is about 1 × 10 10 by a turbo molecular pump (not shown). ^-3 Exhaust to Pa. Next, CHF _Three Is introduced into the processing chamber 110 at a flow rate of about 100 sccm. The pressure in the processing chamber 110 is maintained at about 2 Pa, and a high frequency with a frequency of about 13.56 MHz is about 1 W / cm. ² Apply at a power density of. Using the resist pattern 14 as a mask, the core layer 13 is etched. After about 40 minutes, high frequency discharge and CHF _Three The rotary chamber (not shown) and the turbo molecular pump (not shown) are used in this order, and the pressure in the processing chamber 110 is about 1 × 10 × 10. ^-3 Exhaust to Pa. After evacuation, nitrogen is introduced into the processing chamber 110 to bring it to atmospheric pressure, and then the silicon substrate 11 is removed. The resist is stripped by a generally used oxygen plasma asher method and subsequent cleaning with a solution at a temperature of about 85 ° C. in which sulfuric acid and hydrogen peroxide are mixed at a ratio of about 3: 1. Subsequently, it is washed with pure water. Through the above steps, the core 15 having a height h of about 8 μm, a width s of about 8 μm, and a minimum distance w between the cores 15 of about 3 μm is formed (see FIG. 1E).
[0031]
(6. First upper clad layer forming step)
Next, a part of a quartz film to be an upper clad layer (hereinafter referred to as “first upper clad layer”) is formed using the plasma CVD apparatus 100. In the processing chamber 110 of the plasma CVD apparatus 100, the silicon substrate 11 on which the core 15 is formed is installed. The silicon substrate 11 is heated until the temperature reaches about 400 ° C. The processing chamber 110 is evacuated to a pressure of about 1 Pa by a rotary pump (not shown). Next, the pressure is about 1 × 10 5 by a turbo molecular pump (not shown). ^-3 The processing chamber 110 is evacuated until Pa is reached. About 12 sccm for TRIE or TEOS, about 400 sccm for oxygen, C ₂ F ₆ Is introduced into the processing chamber 110 from the upper electrode 140 at a flow rate of about 10 sccm. TRIE or TEOS is vaporized at a temperature of about 80 ° C. in advance.
[0032]
The pressure in the processing chamber 110 is maintained at about 30 Pa, and a high frequency of about 13.56 MHz is applied between the upper electrode 140 and the lower electrode 120 with a power density of about 1.6 W / cm. ² Apply with. Plasma is generated in the processing chamber 110, and a quartz film serving as the first upper cladding layer 16 having a film thickness of about 5 μm and a refractive index of about 1.452 is deposited on the flat surface of the core 15 in about 30 minutes (FIG. 1). (See (F)). After film formation, the application of high-frequency power is stopped. At this time, the quartz film is also deposited on the side wall of the core 15, but the thickness t of the quartz film is about 1.2 μm at the thickest portion, and the gap between the cores 15 is not completely filled, and the groove 16 a is formed. Has been. If the formation is continued in this state, the film is overhanged at the upper part of the core 15, and a gap is formed between the cores 15.
[0033]
(7. SOG film formation process)
Next, an inorganic SOG (Spin on Glass) film 17 is formed in the groove 16a between the cores. Inorganic SOG 17 is a material containing Si and O atoms and is dissolved in an organic solvent so that the viscosity becomes 1.1 cP. The silicon substrate 11 on which the first upper clad layer 16 is formed is placed on a spinner that is widely used in general. After about 1 cc of inorganic SOG 17 is dropped on the sample surface, the inorganic SOG 17 is applied at a rotation speed of about 2000 rpm and a rotation time of about 20 seconds. Next, the silicon substrate 11 is placed in a thermostat and heated at a temperature of about 90 ° C. for about 30 minutes. The solvent evaporates by this heat treatment. Next, baking is performed at a temperature of about 450 ° C. for about 1 hour. As a result, an inorganic SOG film 17 having a refractive index of 1.457 having a film thickness of about 0.13 μm and a wavelength of 1.3 μm is formed on the first upper cladding layer 16 of the groove 16a. At the same time, an inorganic SOG film 17 is also formed in the concave portion of the first upper clad layer 16 existing around the core 15 to promote flattening.
[0034]
(8. Second upper clad layer forming step)
Subsequently, a second upper clad layer (hereinafter referred to as “second upper clad layer”) is formed by the same method as the formation of the first upper clad layer 16. In about 165 minutes, a quartz film serving as the second upper cladding layer 18 having a film thickness of about 15 μm and a refractive index of 1.452 is formed on the inorganic SOG film 17 (see FIG. 2H). The high-frequency discharge and gas introduction were stopped, and a rotary pump (not shown) and a turbo molecular pump (not shown) were used in this order, and the pressure inside the processing chamber 110 was 1 × 10. ^-3 Exhaust to Pa. After evacuation, nitrogen is introduced into the processing chamber 110 to bring it to atmospheric pressure, and then the silicon substrate is taken out. Through the above upper clad formation process, the upper clad is also embedded between the cores 15. (See Fig. 2 (H))
[0035]
As described above, according to the first embodiment, after forming the first upper cladding layer 16 between the cores 15, the inorganic SOG film 17 having high fluidity is formed as a buffer. Therefore, it is possible to reduce the ratio of the width and height of the groove 16a that forms the second upper clad layer 18, and to reduce the inclination of the side wall portion. Therefore, it is possible to easily form the second upper cladding layer 18. Furthermore, since the optical waveguide can be formed at a temperature of 500 ° C. or less, the distribution of impurities for controlling the refractive index can be made steep.
[0036]
Furthermore, the structure in which the inorganic SOG film 17 is sandwiched between the first upper clad layer 16 and the second upper clad layer 18 reduces the water absorption of the inorganic SOG film 17 and the water from the inorganic SOG film 17. Can be reduced. Water causes a Si—OH group having an absorptivity in the vicinity of a wavelength of about 1.39 μm, and there is a risk of reducing light propagation loss for an optical waveguide using a wavelength of about 1.3 μm. Therefore, it is possible to prevent a decrease in light propagation loss by reducing the concentration of Si—OH groups as in the present manufacturing method.
[0037]
Further, the second upper cladding layer 18 is formed by the plasma CVD apparatus 100. In the step of forming the second upper clad layer 18, the inorganic SOG film 17 is exposed to plasma, so that the process gas C ₂ F ₆ F radicals and F ions in the plasma gas decomposed from the gas diffuse into the inorganic SOG film 17. Therefore, the refractive index of the upper clad can be uniformly set to about 1.452.
[0038]
(Second Embodiment)
The manufacturing method of the optical waveguide according to the second embodiment is as follows. In the SOG film forming process, the optical waveguide manufacturing method according to the first embodiment is improved. In the following, 1. 1. substrate cleaning process; 2. Lower clad layer forming step, 3. core layer forming step; 4. resist pattern forming step; 5. Core formation process, First upper cladding layer forming step, 8. Since the second upper clad layer forming step is the same as that of the first embodiment, the description thereof will be omitted. The SOG film forming process will be described.
[0039]
(7. SOG film formation process)
An inorganic SOG film 27 is formed in the groove 26a between the cores. The inorganic SOG film 27 is made of the same material as that of the inorganic SOG film 17 according to the first embodiment. The silicon substrate 21 on which the first upper clad layer 26 is formed is installed on a spinner that is widely used in general. After about 1 cc of inorganic SOG is dropped onto the sample surface, the inorganic SOG is applied at a rotation speed of about 500 rpm and a rotation time of 20 seconds, unlike the first embodiment. Next, the silicon substrate 21 is placed in a fence temperature bath and heated at a temperature of about 90 ° C. for about 30 minutes. The solvent evaporates by this heat treatment. Next, baking is performed at a temperature of about 450 ° C. for about 1 hour. Thereby, on the flat first upper clad layer 26, the film thickness is about 0.8 μm, the refractive index is about 1.457 having a wavelength of about 1.3 μm, and the film stress is about 3 × unlike the first embodiment. 10 ⁸ An inorganic SOG film 27 having a tensile stress of Pa is formed. At the same time, an inorganic SOG film 27 is also formed on the side wall portion of the first upper cladding layer 26 existing around the core 15.
[0040]
As described above, according to the second embodiment, in forming the upper clad, after the first upper clad layer 26 is formed, the highly fluid inorganic SOG film 27 is formed as a buffering agent. Thus, the same effect as in the first embodiment can be obtained.
[0041]
Furthermore, according to the present embodiment, the inorganic SOG film 27 is also formed on the side wall of the groove 26a. Therefore, about 7 × 10 ⁸ A quartz film as a clad layer having a compressive stress of Pa, and about 3 × 10 ⁸ Since the inorganic SOG film 27 having a tensile stress of Pa is formed not only on the bottom of the groove 26a but also on the side wall of the groove 26a, the stress is relaxed and birefringence is reduced as compared with the case where only the quartz film is formed. It is possible to improve the characteristics.
[0042]
The preferred embodiments of the optical waveguide manufacturing method according to the present invention have been described above with reference to the accompanying drawings, but the present invention is not limited to such examples. It will be obvious to those skilled in the art that various changes or modifications can be conceived within the scope of the technical idea described in the claims, and these are naturally within the technical scope of the present invention. It is understood that it belongs.
[0043]
For example, although the above embodiment has been described with respect to an example in which a silicon substrate is used as the substrate, the present invention is not limited to such a case. Even when a glass substrate is used as the substrate, the present invention can be similarly applied.
[0044]
Further, in the above-described embodiment, an example in which a parallel plate type plasma chemical vapor deposition apparatus is used for forming a cladding layer has been described, but the present invention is not limited to this. Similarly, the present invention can be applied if an apparatus capable of forming a clad layer is used. Similarly, the RIE apparatus used in the core forming process is not limited to this.
[0045]
Furthermore, although the above embodiment has been described with respect to an example in which inorganic SOG is used as the SOG material, the present invention is not limited to this example. The present invention can be similarly applied even when organic SOG is used.
[0046]
Furthermore, in the above embodiment, an example in which the core material is etched using only the resist has been described, but the present invention is not limited to this case. The present invention is applicable even when a multilayer resist structure is formed in which a film of amorphous silicon, tungsten silicide, aluminum, chromium, or the like is formed under the resist and the core material is etched using the film as a mask.
[0047]
【The invention's effect】
As described above, according to the present invention, after the first upper cladding layer is formed between the cores, the SOG film having high fluidity is formed as a buffer. Therefore, it is possible to reduce the inclination of the side wall portion while reducing the ratio of the width and height of the space forming the second upper cladding layer. Therefore, the second upper cladding layer can be easily formed. Furthermore, it is possible to prevent loss of the optical waveguide due to high-temperature heat treatment and increase the yield.
[0048]
Further, the structure in which the SOG film is sandwiched between the first upper clad layer and the second upper clad layer can reduce water absorption into the SOG film and reduce water release from the SOG film. It is. Water causes a Si—OH group having an absorptivity in the vicinity of a wavelength of 1.39 μm, and there is a risk of reducing light propagation loss for an optical waveguide using a wavelength band of 1.3 μm. Therefore, it is possible to prevent a decrease in light propagation loss by reducing the concentration of Si—OH groups as in the present manufacturing method.
[0049]
further , S The OG film is also formed on the side wall of the groove. According to such a manufacturing method, about 7 × 10 ⁸ A quartz film as a clad layer having a compressive stress of Pa, and about 3 × 10 ⁸ Since the SOG film having a tensile stress of Pa is formed not only on the bottom of the groove but also on the side wall of the groove, the stress is relaxed, the birefringence is reduced, and the polarization characteristics are reduced. It is possible to improve.
[0050]
further , Number The upper cladding layer 2 is formed by plasma treatment. According to this manufacturing method, since the SOG film is exposed to plasma in the step of forming the second upper cladding layer, F radicals and F ions in the plasma gas decomposed from the processing gas C2F6 are applied to the SOG film. Spread. Accordingly, the refractive index of the upper clad can be uniformly set to 1.452.
[Brief description of the drawings]
1A and 1B are process diagrams of an optical waveguide manufacturing method according to the present invention, in which FIG. 1A shows a silicon substrate, FIG. 1B shows a state in which a lower cladding is formed, and FIG. ) Represents a state in which a core layer is formed, FIG. 1D represents a state in which a resist pattern is formed, and FIG. 1E represents a state in which a core is formed.
FIG. 2 is a process diagram of a method of manufacturing an optical waveguide according to the present invention, where FIG. 2 (F) shows a state in which a first upper cladding layer is formed, and FIG. 2 (G) shows an SOG film formed. FIG. 2H shows a state in which the second upper clad layer is formed.
FIG. 3 is a block diagram showing an outline of a plasma CVD apparatus.
FIG. 4 is another process chart of the method of manufacturing an optical waveguide according to the present invention. FIG. 4 (F) shows a state in which a first upper cladding layer is formed, and FIG. 4 (G) shows an SOG film. FIG. 4H shows a state in which the second upper cladding layer is formed.
FIG. 5 is a process diagram of a conventional method for manufacturing an optical waveguide.
6A and 6B are explanatory views showing a state in which a resist pattern is formed in a manufacturing process of a conventional optical waveguide, FIG. 6A is a plan view, and FIG. 6B is a cross-sectional view.
FIG. 7 is an explanatory view showing a state in which a core is formed in a manufacturing process of a conventional optical waveguide.
[Explanation of symbols]
11 Silicon substrate
12 Lower cladding layer
13 Core layer
14 resist pattern
15 core
16 First upper cladding layer
16a groove
17 Inorganic SOG membrane
18 Second upper cladding layer

Claims (3)

A manufacturing method using plasma enhanced chemical vapor deposition of an optical waveguide in which a core and a cladding layer surrounding the core are formed on a substrate,
Forming a lower cladding layer on the substrate;
Forming a core layer over the entire top surface of the lower cladding layer;
Forming a core from the core layer;
Forming a first upper cladding layer having a predetermined thickness on the entire upper surface of the lower cladding layer and the core;
Forming a buffer film made of an SOG (Spin on Glass) film on the side wall and bottom of the groove between the core on which the first upper cladding layer is formed ;
Forming a second upper cladding layer on the entire upper surface of the first upper cladding layer and the buffer film;
A method for manufacturing an optical waveguide, comprising: And the minimum spacing between the cores, and the ratio of the height of the core is 2/3 or less, a method of manufacturing an optical waveguide according to claim 1. The method for manufacturing an optical waveguide according to claim 2 , wherein a minimum interval between the cores is 5 μm or less, and a height of the core is 4 to 12 μm.

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