JP3607129B2 - Spot size conversion optical waveguide manufacturing method - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a method for manufacturing a spot size conversion optical waveguide at a connection portion of an optical waveguide.
[0002]
[Prior art]
The problem with the coupling between the optical waveguide connected to the optical device and the optical fiber is the spot size. Usually, the mode field diameter of the single mode fiber is 8 to 10 μm. On the other hand, in order to reduce the chip size of the optical device, an optical waveguide with a large refractive index difference between the core layer and the cladding layer is used. However, the spot size of an optical waveguide with a single mode high refractive index difference is It is approximately 4 μm or less. Therefore, in order to make a low-loss connection between the optical waveguide and the optical fiber, it is necessary to convert the spot size. Therefore, a structure for converting the spot size to the optical fiber side or the optical waveguide side is required.
[0003]
Therefore, it is possible to change the spot size of the light by processing the tip of the optical fiber to reduce the diameter of the core of the optical fiber or to have a lens structure like a photosphere fiber. However, each optical fiber must be processed individually. In addition, since the spot size is converted externally, the light is greatly deviated by a slight axial shift of the lens, and the manufacturing tolerance is deteriorated. Therefore, it is desirable to provide a spot size conversion structure on the optical waveguide side.
[0004]
When a spot size conversion structure is provided on the optical waveguide side, processing in a direction parallel to the substrate (optical waveguide substrate) can be easily produced by using a semiconductor photolithographic technique, but in a direction perpendicular to the substrate. Processing is not easy. As a conventional method for manufacturing a spot size conversion optical waveguide for converting the spot size in the direction perpendicular to the substrate, the following method is known.
[0005]
FIG. 5 is an explanatory diagram of a conventional method for manufacturing a spot size conversion optical waveguide. As shown in the figure, first, a refractive index changing material 22 made of a material whose refractive index increases when an electron beam is irradiated onto the substrate 21 is formed. Next, the core layer 23 of the optical waveguide composed of a belt-like high refractive index region is formed by sweeping an electron beam on the refractive index changing material 22 in the direction of the arrow.
[0006]
In the spot size conversion optical waveguide manufactured by the manufacturing method described with reference to FIG. 5, the change in the refractive index of the core layer 23 depends on the irradiation amount of the electron beam, and as shown in FIG. Is sufficient, the difference in refractive index between the core layer 23 and the clad layer is large, so that light is strongly confined in the core layer 23 and the spot size is small. Since the refractive index difference between the layer 23 and the cladding layer is small, the confinement of the core layer 23 is weak and the spot size is large. By utilizing this property, the spot size converter gradually reduces the electron beam dose in the sweep direction, thereby reducing the refractive index difference between the core layer 23 and the clad layer and weakening the light confinement. The diameter of the spot size can be expanded.
[0007]
FIGS. 7A and 7B are explanatory views of another conventional spot size conversion optical waveguide manufacturing method. FIG. 7A is a front view and FIG. 7B is a bottom view. As shown in the figure, after forming an etching stop layer 32 between core materials to be the core layer 31, the core material is etched to form a multi-layer core layer 31 to have a tapered structure.
[0008]
[Problems to be solved by the invention]
However, in the method of manufacturing the spot size conversion optical waveguide described with reference to FIG. 5, it is necessary to finely control the amount of electron beam irradiation, and beam irradiation must be performed on each optical waveguide, so that the throughput is poor. There is a problem.
[0009]
In addition, in the method of manufacturing the spot size conversion optical waveguide described with reference to FIG. 7, in order to make the core layer 31 multi-layered, there are problems that the manufacturing process is complicated and complicated, resulting in a burden on the process. is there.
[0010]
The present invention has been made to solve the above-described problems, and an object thereof is to provide a method for producing a spot size conversion optical waveguide capable of forming a spot size conversion optical waveguide having high coupling efficiency by a simple process. And
[0011]
[Means for Solving the Problems]
In order to achieve the above object, according to the present invention, a first step of forming a first lower cladding layer thin film on a substrate, and an optical connection portion by selectively etching the first lower cladding layer thin film. The second step of removing the first lower clad layer thin film in the vicinity, the third step of applying the lower clad layer thin film material, and the thermal curing treatment of the lower clad layer thin film material can achieve a flattening rate. A fourth step of forming a second lower cladding layer thin film having a taper structure in a direction that is low and perpendicular to the substrate, a fifth step of forming a core layer thin film having a high planarization rate, and the core layer thin film At least six steps of a sixth step of selectively etching to form a core layer having a tapered structure in a direction parallel to the substrate are performed.
[0013]
A first step of forming a first lower clad layer thin film on the substrate; and selectively etching the first lower clad layer thin film to remove the first lower clad layer thin film in the vicinity of the optical connecting portion. The remaining second step, the third step of applying the lower clad layer thin film material, and the lower clad layer thin film material is heat-cured so that the flattening rate is low and the taper structure is formed in the direction perpendicular to the substrate. A fourth step of forming a second lower cladding layer thin film, a fifth step of forming a core layer thin film having a high planarization rate, and a direction parallel to the substrate by selectively etching the core layer thin film At least six steps of the sixth step of forming a core layer having a tapered structure are performed.
[0014]
In these cases, an upper clad layer may be formed on the core layer.
[0015]
In these cases, the planarization rate of the second lower cladding layer thin film may be 70% or less, and the planarization rate of the core layer thin film may be 90% or more.
[0016]
In these cases, the material of the second lower cladding layer thin film is fluorinated polyimide or photosensitive benzocyclobutene, the material of the core layer thin film is benzocyclobutene or an epoxy-based ultraviolet curable resin, and the material of the upper cladding layer is May be fluorinated benzocyclobutene or epoxy-based ultraviolet curable resin.
[0017]
DETAILED DESCRIPTION OF THE INVENTION
FIG. 1 is an explanatory view of a method for producing a spot size conversion optical waveguide according to the present invention. First, as shown in FIG. 1 (a), a fluorinated polyimide stock solution is applied onto a substrate 1 by a spin coater, and then heat-cured (cured) at 380 ° C. for 1 hour, whereby a fluorinated polyimide is obtained. A first lower clad layer thin film 2-1 having a thickness of 10 μm is formed (first step). Next, as shown in FIG. 1B, a resist 3 is applied onto the lower clad layer thin film 2-1, photolithography is performed, and the lower clad layer thin film 2-1 is formed by reactive ion etching (RIE). A step (step-like structure) is formed by selectively etching to remove the lower cladding layer thin film 2-1 in the vicinity of the optical connecting portion, that is, the left side of FIG. 1 (form a groove). That is, a step is formed in the spot size conversion portion formation scheduled region (second step). Next, as shown in FIG. 1 (c), after removing the resist 3, a fluorinated polyimide stock solution 2-2a, which is a lower clad layer thin film material, is formed on the substrate 1 and the lower clad layer thin film 2-1 by a spin coater. Apply again (third step). Next, as shown in FIG.1 (d), the 2nd lower clad layer thin film 2-2 is formed by thermosetting the fluorinated polyimide stock solution 2-2a on conditions of 380 degreeC and 1 hour. In this case, since the fluorinated polyimide has a large shrinkage ratio in the thermosetting process, the flattening rate of the lower cladding layer thin film 2-2 is lowered during the thermosetting process, and the lower cladding layer thin film 2-2 is perpendicular to the substrate 1. A taper structure (slope structure) is formed in such a direction that is perpendicular to the surface of the substrate 1. At this time, the taper length can be adjusted from the film thickness and viscosity of the re-coated fluorinated polyimide stock solution 2-2a, and the taper length can be controlled to 1 mm or less. Further, by forming the lower clad layer thin film 2-2 having a thickness of 10 μm, a taper structure in a direction perpendicular to the substrate 1 having a length of 100 μm and a height difference of 8 μm can be obtained. At this time, the lower clad layer thin film 2 -2 ({1- (a / b)} × 100 (%) in FIG. 2) is 20% (a = 8 μm, b = 10 μm) (fourth step). Next, as shown in FIG. 1 (e), benzoate is formed on the lower clad layer 2 composed of the lower clad layer thin film 2-1 and the lower clad layer thin film 2-2 having the tapered structure by a spin coater. After applying cyclobutene, heat curing treatment is performed at 210 ° C. for 30 minutes, and the core layer thin film having a flat portion thickness of 2 μm on the right side of FIG. 1 is made of benzocyclobutene, which is a material with a high flattening rate. 4a is formed (fifth step). In this case, benzocyclobutene undergoes reflow during the thermosetting treatment, and the core layer thin film 4a having a high flattening rate is formed. The flattening rate of the core layer thin film 4a is 96%. Next, as shown in FIG. 1F, a resist 5 is applied on the core layer thin film 4a, and the resist 5 is tapered in a direction parallel to the substrate 1, that is, in a direction parallel to the surface of the substrate 1, using photolithography. After patterning into the structure, as shown in FIG. 1 (g), the core layer thin film 4a is selectively etched by reactive ion etching so that the spot size conversion portion has a taper structure in a direction parallel to the substrate 1 4 is formed (sixth step). Next, as shown in FIG. 1H, after the resist 5 is removed, an upper clad layer 6 made of fluorinated benzocyclobutene is formed on the core layer 4 to produce a buried optical waveguide.
[0018]
In the method of manufacturing the spot size conversion optical waveguide described with reference to FIG. 1, first, a step serving as a basis for a taper structure is formed, and a lower clad layer thin film 2-2 having a taper structure reflecting the step is formed thereon. Then, the core layer 4 having a high flattening rate that does not depend on the structure of the lower cladding layer 2 is formed. As a result, a spot size conversion structure can be provided only by adding one process to the production of a normal optical waveguide, and a tapered structure in a direction perpendicular to the substrate 1 is compared with a conventional method for manufacturing a spot size conversion optical waveguide. Since it can be formed by a simple process, a manufacturing method of a spot size conversion optical waveguide that can be easily manufactured and mass-produced can be realized, and a spot size conversion optical waveguide having high coupling efficiency can be formed. Further, the upper cladding layer 6 made of fluorinated benzocyclobutene, which is a material having a high flattening rate, is formed. Since the flattening rate of the upper clad layer 6 is high, the optical wiring can be multilayered. Further, the fluorinated benzocyclobutene of the material of the upper cladding layer 6 has a refractive index as small as 1.481 with respect to light having a wavelength of 1.5 μm, and the refractive index of the benzocyclobutene of the material of the core layer 4 is 1.543. Therefore, the upper clad layer 6 and the core layer 4 have a high refractive index difference (about 4%). By using this refractive index difference, it is possible to manufacture an optical waveguide having a passive functional element having a curvature radius of 600 μm or less. Therefore, it is particularly effective when applied to a semiconductor substrate on which an optical device or an electronic device is formed. Since the lower cladding layer 2 is made of fluorinated polyimide, the core layer 4 is made of benzocyclobutene, and the upper cladding layer 6 is made of fluorinated benzocyclobutene, the lower cladding layer 2, the core layer 4 and the upper cladding layer 6 are made. Is made of an organic thin film, so optical waveguides with a high refractive index difference can be fabricated compared to the currently mainstream glass-based optical waveguides. On-chip optical wiring can be made possible.
[0019]
FIG. 3 is an explanatory view of another method for manufacturing a spot size conversion optical waveguide according to the present invention. First, as shown in FIG. 3A, after applying a fluorinated polyimide stock solution on a substrate 11 by a spin coater, a thermosetting treatment is performed at 380 ° C. for 1 hour, and the thickness of the fluorinated polyimide is increased. A 10 μm first lower cladding layer thin film 12-1 is formed (first step). Next, as shown in FIG. 3B, a resist 13 is applied on the lower cladding layer thin film 12-1, photolithography is performed, and the lower cladding layer thin film 12-1 is selectively etched by reactive ion etching. Then, by leaving the lower cladding layer thin film 12-1 in the vicinity of the optical connecting portion, that is, the left side of FIG. 3 (forming a protruding portion), a step having a height of 6 μm is formed. That is, a step is formed in the spot size conversion portion formation scheduled region (second step). Next, as shown in FIG. 3 (c), after removing the resist 13, a fluorinated polyimide stock solution 12-2a, which is a lower clad layer thin film material, is applied onto the substrate 11 and the lower clad layer thin film 12-1 by a spin coater. Apply again (third step). Next, as shown in FIG.3 (d), the 2nd lower clad layer thin film 12-2 is formed by thermosetting the fluorinated polyimide stock solution 12-2a on condition of 380 degreeC and 1 hour. In this case, since the fluorinated polyimide has a large shrinkage ratio in the thermosetting process, the flattening rate of the lower cladding layer thin film 12-2 is lowered during the thermosetting process, and the lower cladding layer thin film 12-2 is perpendicular to the substrate 11. Tapered structures are formed in various directions. At this time, the taper length can be adjusted from the film thickness and viscosity of the re-coated fluorinated polyimide stock solution 12-2a, and the taper length can be controlled to 1 mm or less. Further, by forming the lower clad layer thin film 12-2 having a thickness of 10 μm, a taper structure in a direction perpendicular to the substrate 11 having a length of 100 μm and a height difference of 2 μm is obtained. −2 ({1− (a / b)} × 100 (%) in FIG. 4) is 67% (a = 2 μm, b = 6 μm) (fourth step). Next, as shown in FIG. 3 (e), benzoate is formed on the lower clad layer 12 composed of the lower clad layer thin film 12-1 and the lower clad layer thin film 12-2 having the tapered structure by a spin coater. After applying cyclobutene, heat curing treatment is performed at 210 ° C. for 30 minutes, and a core layer having a flat portion on the right side of FIG. 3 made of benzocyclobutene, which is a material having a high flattening rate, is about 2 μm. The thin film 14a is formed (fifth step). In this case, benzocyclobutene causes reflow during thermosetting, and the core layer thin film 14a having a high flattening rate is formed. The flattening rate of the core layer thin film 14a is 96%. Next, as shown in FIG. 3 (f), a resist 15 is applied on the core layer thin film 14a, and the resist 15 is patterned into a tapered structure in a direction parallel to the substrate 11 by using photolithography, and then FIG. As shown in (g), the core layer thin film 14a is selectively etched by reactive ion etching to form the core layer 14 having a taper structure in the direction parallel to the substrate 11 in the spot size conversion portion (sixth sixth). Process). Next, as shown in FIG. 3H, after the resist 15 is removed, an upper clad layer 16 made of fluorinated benzocyclobutene is formed on the core layer 14 to produce a buried optical waveguide.
[0020]
In the manufacturing method of the spot size conversion optical waveguide described with reference to FIG. 3, the taper structure in the direction perpendicular to the substrate 11 can be manufactured by a simple process compared to the conventional manufacturing method of the spot size conversion optical waveguide, and high coupling is achieved. An efficient spot size converting optical waveguide can be formed.
[0021]
In the above-described embodiment, the flattening rates of the lower cladding layer thin films 2-2 and 12-2 are 20% and 67%, respectively, and the flattening rates of the core layer thin films 4a and 14a are 96%. If the flattening rate of the second lower cladding layer thin film is 70% or less and the flattening rate of the core layer thin film is 90% or more, a taper structure in a direction perpendicular to the substrate can be formed satisfactorily. It is desirable that the flattening rate of the second lower cladding layer thin film is 50% or less and the flattening rate of the core layer thin film is 95% or more. In the above-described embodiment, the lower clad layer thin films 2-1, 2-2, 12-1, 12-2 made of fluorinated polyimide are formed. The first and second thin films made of photosensitive benzocyclobutene or the like are used. Two lower cladding layer thin films may be formed. In the above-described embodiment, the core layer thin films 4a and 14a made of benzocyclobutene are formed. However, a core layer thin film made of epoxy-based ultraviolet curable resin or the like may be formed. When a core layer thin film made of an epoxy-based ultraviolet curable resin is formed, the core layer can be directly processed in the same process as that for processing a resist, so that an etching process for forming the core layer is omitted. Can do. In the above-described embodiment, the upper cladding layers 6 and 16 made of fluorinated benzocyclobutene are formed. However, an upper cladding layer made of an epoxy-based ultraviolet curable resin may be formed. In addition, the parameter values such as the film thickness, temperature, and time described in the above embodiment are merely examples, and the invention described in the claims is not limited thereto.
[0022]
【The invention's effect】
As described above, in the method for manufacturing a spot size conversion optical waveguide according to the present invention, a spot size conversion optical waveguide having high coupling efficiency can be formed by a simple process.
[0023]
Further, when the upper clad layer is formed on the core layer, the optical wiring can be multi-layered.
[0024]
Further, when the flattening rate of the second lower cladding layer thin film is 70% or less and the flattening rate of the core layer thin film is 90% or more, the taper structure in the direction perpendicular to the substrate can be satisfactorily formed. .
[0025]
In addition, the material of the second lower cladding layer thin film is fluorinated polyimide or photosensitive benzocyclobutene, the material of the core layer is benzocyclobutene or epoxy-based ultraviolet curable resin, and the material of the upper cladding layer is fluorinated benzocyclobutene. Alternatively, when the epoxy ultraviolet curable resin is used, the second lower clad layer thin film, the core layer, and the upper clad layer are formed of an organic thin film, so that an optical waveguide having a high refractive index difference can be produced.
[Brief description of the drawings]
FIG. 1 is an explanatory diagram of a method for producing a spot size conversion optical waveguide according to the present invention.
FIG. 2 is an explanatory diagram of a method for manufacturing the spot size conversion optical waveguide described with reference to FIG. 1;
FIG. 3 is an explanatory diagram of another method for manufacturing a spot size conversion optical waveguide according to the present invention.
4 is an explanatory diagram of a method for manufacturing the spot size conversion optical waveguide described with reference to FIG. 3;
FIG. 5 is an explanatory diagram of a conventional method for producing a spot size conversion optical waveguide.
6 is an explanatory diagram of a method for manufacturing the spot size conversion optical waveguide described with reference to FIG. 5. FIG.
FIG. 7 is an explanatory view of another conventional spot size conversion optical waveguide manufacturing method.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 ... Substrate 2-1 ... 1st lower clad layer thin film 2-2a ... Fluorinated polyimide stock solution 2-2 ... 2nd lower clad layer thin film 4a ... Core layer thin film 4 ... Core layer 6 ... Upper clad layer 11 ... Substrate 12-1 ... First lower clad layer thin film 12-2a ... Fluorinated polyimide stock solution 12-2 ... Second lower clad layer thin film 14a ... Core layer thin film 14 ... Core layer 16 ... Upper clad layer

Claims (5)

A first step of forming a first lower cladding layer thin film on the substrate; and selectively etching the first lower cladding layer thin film to remove the first lower cladding layer thin film in the vicinity of the optical connecting portion. A second step; a third step of applying a lower clad layer thin film material; and a thermosetting treatment of the lower clad layer thin film material to provide a low planarization rate and a taper structure in a direction perpendicular to the substrate. A fourth step of forming a lower clad layer thin film, a fifth step of forming a core layer thin film having a high planarization rate, and selectively etching the core layer thin film in a direction parallel to the substrate. A method for producing a spot size conversion optical waveguide, comprising at least six steps of a sixth step of forming a core layer having a tapered structure. A first step of forming a first lower cladding layer thin film on the substrate, and a first etching of the first lower cladding layer thin film to leave the first lower cladding layer thin film near the optical connecting portion. 2 and a third step of applying a lower clad layer thin film material, and a second structure having a taper structure in a direction perpendicular to the substrate with a low flattening rate by thermosetting the lower clad layer thin film material. A fourth step of forming the lower cladding layer thin film, a fifth step of forming the core layer thin film having a high flattening rate, and a taper in a direction parallel to the substrate by selectively etching the core layer thin film A method for producing a spot size conversion optical waveguide, comprising at least six steps of a sixth step of forming a core layer having a structure. 3. The method for producing a spot size conversion optical waveguide according to claim 1 , wherein an upper clad layer is formed on the core layer. 4. The spot size conversion according to claim 1, wherein the flattening rate of the second lower cladding layer thin film is 70% or less, and the flattening rate of the core layer thin film is 90% or more. Manufacturing method of optical waveguide. The material of the second lower cladding layer thin film is fluorinated polyimide or photosensitive benzocyclobutene, the material of the core layer thin film is benzocyclobutene or an epoxy-based ultraviolet curable resin, and the material of the upper cladding layer is a fluorinated benzoic benzoate. 5. The method for producing a spot size conversion optical waveguide according to claim 3, wherein cyclobutene or epoxy-based ultraviolet curable resin is used.

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