JP2893093B2 - Fabrication method of optical waveguide with fiber guide - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a simple optical waveguide-optical fiber connection technology which is a key technology for realizing an optical waveguide circuit.

[Conventional technology]

In order to realize an optical waveguide circuit, there is a demand for the development of a simple optical fiber connection technology to an optical waveguide. A method of forming an optical fiber alignment guide at the same time as forming an optical circuit on a silica-based optical waveguide substrate and using this guide to connect the fibers [Japanese Patent Application Laid-Open No. 60-17406] is simple and reliable. It is expected as a high optical fiber connection technology. FIG. 10 is an explanatory view of this connection method, in which 11 is an optical circuit board, 12 is a ridge-shaped optical waveguide, 12b is its buffer layer, 12a is a core layer, and 12c is a cladding layer. . 13 is a fiber guide, 14 is an optical fiber, and 14a is its core layer. Since the width and the depth of the guide groove surrounded by the guide 13 are appropriately set, the alignment between the optical fiber and the optical waveguide can be realized only by inserting the optical fiber 14 into the guide. Moreover, since the position of the optical fiber 14 is mechanically determined by the guide 13, even if the temperature of the use environment fluctuates after the optical fiber is fixed, no positional displacement occurs, and therefore, a highly reliable fiber Connection can be realized.

[Problems to be solved by the invention]

By the way, it has been conventionally difficult to apply the above-described guide groove connection method to an embedded optical waveguide (an optical waveguide having a structure in which a core layer is embedded by forming a thick clad layer). The reason for this is that, in the case of manufacturing a buried optical waveguide, conventionally, a guide and an optical waveguide cannot be formed simultaneously using one photomask, and for example, they were manufactured in a process shown in FIG. It is. First, a core portion 12a of an optical waveguide 12 is formed on a substrate 11 as shown in FIG. 11 (a), buried with a cladding layer 12c, and a mask formed on the upper surface of the cladding layer as shown in FIG. 11 (b). The material 15 is patterned using a photomask 16 on which a guide pattern is drawn. Next, as shown in FIG. 3C, the unnecessary portion of the cladding layer 12c was etched to form the fiber guide 13.
In such a process, it is necessary to pattern the guide pattern with an alignment accuracy of 1 μm or less with respect to the position of the optical waveguide 12 already formed. However, since the optical waveguide 12 formed in the lower layer is transparent for both the core layer and the cladding layer, it has been extremely difficult to realize precise alignment.

As described above, the conventional guide groove connection method has a problem that it is difficult to apply the method to a buried optical waveguide. SUMMARY OF THE INVENTION An object of the present invention is to provide a method of manufacturing an optical waveguide with a fiber guide, which can be applied to an embedded optical waveguide.

[Means for solving the problem]

The method for manufacturing an optical waveguide with a fiber guide portion of the present invention comprises the steps of: forming a buffer layer on a Si substrate having a concave portion and a convex portion formed on a surface thereof, forming a silica-based optical waveguide buffer layer; and polishing the substrate surface. A polishing step of exposing the surface of the convex portion of the Si substrate, and adjusting the height of the surface of the silica-based optical waveguide buffer layer formed on the concave portion of the Si substrate to the height of the convex portion of the Si substrate; A core layer forming step of forming a waveguide core layer, a single photomask in which a guide core layer pattern and an optical waveguide pattern are simultaneously drawn, and the guide is formed on the surface of the core layer on the upper surface of the convex portion of the Si substrate. A first photolithography step in which a core layer pattern is formed, and the optical waveguide pattern is formed so as to be formed on the core layer surface on the upper surface of the concave portion of the Si substrate to pattern the mask material; Except for the optical waveguide core layer Then, a core layer etching step of exposing the surface of the convex portion of the Si substrate, an embedding step of forming a clad layer on the substrate, and a mask material covering an area where the optical waveguide pattern is formed on the upper surface of the clad layer. A second photolithography step for patterning, a cladding layer etching step for removing unnecessary portions of the cladding layer and exposing the convex portions of the Si substrate while leaving the guide / core layer pattern formed of the core layer, The method is characterized by comprising a Si substrate etching step of forming a fiber guide groove by etching a Si substrate protrusion using the guide / core layer pattern as a mask.

As the cladding layer etching step, the guide
By utilizing the difference in film thickness between the core layer pattern formation part and other parts and the difference in etching rate between the core layer and clad layer,
The guide / core layer pattern formed by the core layer can be left.

In the buffer layer forming step, a (100) plane crystal is used as the Si substrate, and in the first photolithography step, the guide / core layer pattern is changed to the Si substrate [110].
A guide groove having high dimensional accuracy can be easily formed by performing the Si substrate anisotropic etching in the Si substrate etching step.

The difference between the prior art and the present invention is that the conventional optical waveguide with a fiber guide groove is formed on a flat Si substrate, whereas the concave and convex portions are formed on the surface in the present invention. The difference is that it is formed on a Si substrate. Although the conventional manufacturing method cannot use a photomask in which a waveguide pattern and a guide pattern are simultaneously drawn, the present invention is greatly different in that it is possible.

〔Example〕

Embodiment 1 FIG. 1 is a perspective view showing an optical waveguide with a fiber guide section manufactured by a manufacturing method according to a first embodiment of the present invention. Reference numeral 1 denotes a Si substrate, 1a denotes its convex portion, and 1b denotes its concave portion. A quartz optical waveguide 2 is provided in the concave portion 1b of the Si substrate 1, and the quartz optical waveguide 2 includes a core layer 2a, a buffer layer 2b, and a cladding layer 2c. The buffer layer 2b and the cladding layer 2c have the same refractive index,
The value is lower than the refractive index of 2a. Also, the buffer layer
The height of the upper surface of 2b is equal to the upper surface of the convex portion 1a of the Si substrate 1. The optical waveguide of the first embodiment is
This is a structure in which the core layer 2c is embedded in the buffer layer 2b and the cladding layer 2c that are sufficiently thick, and such a structure is called “embedded optical waveguide”.

Further, a fiber guide portion is provided on the convex portion 1a of the Si substrate 1. This fiber guide section
It comprises a guide core layer pattern 3 and a fiber guide groove 4. The feature of this structure is that the fiber guide core layer pattern 3 is provided directly on the convex portion 1a of the Si substrate 1 using the same glass layer as the core layer 2a of the optical waveguide. That is. That is, as described above,
The core layer is formed on the concave portion 1b of the substrate 1 through the thick buffer layer 2b.
2a is formed, whereas a buffer layer is formed on the protrusion 1a.
The fiber guide core layer pattern 3 is formed directly without the interposition of 2b. Then, using the fiber guide core layer pattern 3 as a mask, a groove is formed in a part of the convex portion 1a of the Si substrate 1, and the groove is formed in the fiber guide groove 4.
It has become.

FIG. 2 is a cross-sectional view for explaining the function of the optical waveguide. 5 is an optical fiber and 5a is its core layer. The optical fiber 5 and the fiber guide groove 4 are in contact at three points A, B, and C. Where A and B are fiber
At the midpoint in the thickness direction of the guide / core layer pattern 3, AC
Is substantially intersected with the center O of the waveguide core layer. B is a point on the bottom surface of the fiber guide groove. Assuming that the dimensions of the guide groove are: fiber radius R, guide groove width W, and guide groove depth (from the center O of the waveguide core to the bottom of the guide) D, D ≒ R and W ≒ 2R are set. Alignment between the fiber and the waveguide can be realized only by inserting it into the groove.

Such a guided optical waveguide can be manufactured by the method shown in FIG. FIG. 2A shows a step of forming a silica-based optical waveguide buffer layer 2b on a Si substrate 1 having a concave portion 1b and a convex portion 1a to form an optical waveguide substrate. In this example, the flame deposition method [M. Kawachi et.al., Jan. J. Appl. Phys.,
Vol.22, (1983), p.1392]. That is, SiCl ₄ ,
After depositing a glass fine particle film on the Si substrate 1 using a flame hydrolysis reaction of a glass forming raw material gas such as TiCl ₄ or the like, the glass fine particle film is formed by heating to a transparent vitrification in an electric furnace. I do. At this time, the thickness of the buffer layer 2b is Si
It was formed so as to be thicker than the step between the concave and convex portions of the substrate.

FIG. 3B shows a step of exposing the surface of the convex portion of the Si substrate and flattening the surface by polishing the surface of the optical waveguide substrate. FIG. 3C shows a step of forming an optical waveguide core layer 2c on the optical circuit board. Here, the flame deposition method was used again.

FIG. 2D shows a fiber guide core layer pattern 3 using a single photomask pattern in which a fiber guide core layer pattern 3 and an optical waveguide pattern 2a are simultaneously drawn.
Is positioned so that the mask material is on the convex part of the Si substrate.
This is a photolithography process for patterning 10. Here, an amorphous Si (a-Si) film was used as the mask material 10.

FIG. 4E shows a step of removing unnecessary portions of the quartz optical waveguide film by etching using the mask material 10 to form the optical waveguide core layer pattern 2a and the fiber guide core layer pattern 3. Here, reactive ion etching (RIE) using a fluorine-based etching gas was used as the etching means. The etching was performed until the unnecessary portion of the core layer was completely removed. At this time, the convex portion 1a of the Si substrate 1
Above, the upper surface of the projection 1a is exposed leaving the fiber guide core layer pattern 3. By this step, the optical waveguide core layer pattern 2a is formed on the buffer layer 2b, and the fiber guide core layer pattern 3 is placed on the convex portion 1a.
It is formed directly without the interposition of 2b, and this finally becomes a mask for forming the fiber guide groove 4. FIG. 1F shows a step of forming a cladding layer 2c and embedding a lower layer pattern, and FIG. 2G shows a step of patterning a mask material 10a so as to cover a region where an optical waveguide is formed on the upper surface of the cladding layer 2c. .

FIG. 7H shows a step of removing unnecessary portions of the cladding layer by etching to expose the fiber guide core layer pattern 3 and the Si substrate in the guide groove portion interposed therebetween. In this step, if the end of the etching is properly determined, the surface of the Si substrate in the region between the fiber guide core layer pattern 3 and the fiber guide core layer pattern 3 can be exposed. this is,
For the reason shown in FIG. That is, when the buried cladding layer is formed, the thickness of the former portion is larger than that of the latter portion in the portion where the core layer is not provided and in the portion where the core layer is not provided (FIG. 4a). In addition, the etching rate is slightly different between the cladding layer and the core layer, and the etching rate of the core layer is slightly lower (about 10 to 20%) than that of the cladding layer. Therefore,
In the case of the two-layer structure in which the core layer and the clad layer are formed on the convex portion of the Si substrate as in the present embodiment, since the required etching amount is small, the above-mentioned film thickness difference and slight etching rate difference cause The surface of the Si substrate can be exposed while leaving the core layer (FIGS. 4b and 4c). On the other hand, the flat S
In the case of a conventional optical waveguide in which a buffer layer, a core layer and a clad layer are formed on an i-substrate, deep etching up to the buffer layer is necessary to expose the Si substrate, and
In the buffer layer, since there is no difference in the etching rate between the two, the fiber guide core layer pattern becomes unclear as the etching proceeds, and a clear step cannot be formed as shown in FIG. Therefore, it is difficult to accurately determine the guide groove width.

Thereafter, using the fiber guide core layer pattern 3 remaining after the above etching step as a mask, the Si substrate is etched so as to satisfy the condition of the depth shown in FIG. 1a, a groove is formed on the first groove.
It becomes the fiber guide groove 4 shown in the figure.

As described above, in this embodiment, since the guide groove is formed on the upper surface of the convex portion of the Si substrate, the etching depth in FIG. 3 (h) can be reduced. As a result, the difference in the thickness of the optical waveguide and the slight difference in the etching rate between the core layer and the cladding layer can be used, and the fiber and the fiber can be used.
With the guide / core layer pattern 3 left,
The Si substrate surface can now be exposed. This fiber
A fiber guide groove can be formed by etching the Si substrate using the guide core layer pattern 3 as a mask.
Thus, in the present invention, when forming the guide groove in the embedded optical waveguide, the fiber guide groove and the optical waveguide can be formed using one photomask.

In the cladding layer etching step of FIG. 3 (h), in order to expose the Si substrate surface in the region between the fiber guide core layer patterns 3 while leaving the fiber guide core layer pattern 3, the method described in the present embodiment must be used. Other than the embedded mask method [Japanese
62-94936]. That is, in the embedding process shown in FIG.
In this method, the mask material 10 is buried on the core layer pattern 3 with the mask material 10 remaining, and the buried mask material 10 is used as a mask in the cladding layer etching step of FIG. However, as compared with this method, the manufacturing method of the present embodiment is advantageous in that the number of processes is small.

Embodiment 2 FIG. 6 is a perspective view showing an optical waveguide with a fiber guide portion manufactured by a manufacturing method according to a second embodiment of the present invention. In the second embodiment, a (100) plane crystal is used as the Si substrate 1. The optical waveguide 2 is formed in the concave portion 1b of the Si substrate, and the guide groove 4 is provided in the convex portion 1a of the Si substrate in parallel with the [110] direction. The guide groove has a V-groove shape, and its side wall is formed of Si (11
1) It is formed by the surface 4a. This is formed by anisotropic etching of the Si substrate as described later. The optical waveguide end 20 has a shape protruding in a convex shape.

FIG. 7 is a cross-sectional view for explaining the function of the fiber guide groove in the optical waveguide. Guide groove side wall 4a
Is the angle θ with the substrate surface, the radius R of the optical fiber 5, and the thickness h of the waveguide core layer 2a, the interval W between the fiber guide core layer patterns 3 is W = 2 [(R / sin θ) − (H / (2tanθ))]. With such dimensions, the distance from the contact points A and B between the optical fiber 5 and the guide groove 4 to the center O of the optical waveguide core layer becomes R, so that the optical fiber 5 is simply inserted into the guide groove 4. The center of the optical waveguide core layer 2a and the center of the optical fiber core layer 5a coincide, and positioning between the fiber and the waveguide can be realized. In this embodiment, since the V-groove was formed by anisotropic etching of the Si substrate (100), θ = 54.74 °. Therefore, when the outer diameter of the optical fiber is 125 μm (R = 62.5 μm) and the thickness h of the waveguide core layer is 8 μm, the optimum distance W between the fiber guide core layer patterns 3 is 148 μm.

The fiber guide groove having such a structure can be manufactured basically by the same method as the manufacturing method of the first embodiment. That is, in forming the fiber guide core layer pattern 3, the same process as in FIG.
The substrate may be subjected to anisotropic etching. For anisotropic etching of the Si substrate, for example, an alkaline etching solution such as ethylenediamine pyrocatechol is used. If the optical waveguide substrate is immersed in an etchant, the Si substrate is etched using the fiber guide core layer pattern 3 made of a quartz glass film and the optical waveguide 2 as a mask to form a V-groove in the Si substrate.

An advantage of the manufacturing method of the second embodiment is that the processing accuracy of the guide groove can be easily increased as compared with the manufacturing method of the first embodiment. That is, when the above etching solution is used, the relationship between the Si crystal plane and the etching rate is (10
0): (110): (111) ≒ 50: 30: 3, so that when the (111) plane appears, it is no longer etched. For this reason, if even the interval W of the fiber guide core layer pattern 3 is formed with high accuracy, the guide groove dimension can be determined accurately, so that the control of the etching depth becomes unnecessary. In contrast, in the first embodiment, the fiber guide
It was necessary to precisely control the depth of the guide groove together with the interval W between the core layer patterns 3.

In this embodiment, the optical waveguide end 20 is projected from the Si substrate projection 1a as shown in FIG. 6 for the following reason. If the waveguide end 20 is flat, the (111) plane 4a also appears on the Si substrate immediately below the waveguide end 20 as shown in FIG. 8, and as a result, as shown in FIG. The end faces of the optical fiber 5 and the optical waveguide 2 cannot be brought into contact with each other.
When the waveguide end 20 protrudes from the convex portion of the Si substrate, as shown in FIG. 9, a liquid crystal surface 4a 'other than the (111) plane appears, and as a result, the Si substrate below the optical waveguide is etched. As shown in FIG. 4B, the fiber and the end of the waveguide can be brought into contact.

As described above, in the present embodiment, when the guide groove is provided in the convex portion of the Si substrate, the guide groove is formed in a V-groove shape by anisotropic etching. As a result, formation of the precision guide groove was facilitated.

〔The invention's effect〕

According to the invention of claim 1, an Si substrate having a concave portion and a convex portion on a surface is used, and an optical waveguide including a buffer layer, a core layer, and a clad layer is formed in the concave portion,
Since the fiber guide groove is formed by etching the substrate protrusion using the guide / core layer pattern as a mask, the guide / core layer pattern and the optical waveguide pattern can be simultaneously patterned using one photomask. Therefore, the embedded optical waveguide with the fiber guide portion can be manufactured efficiently and accurately. Further, according to the invention of claim 2, the number of processes can be reduced as compared with other manufacturing methods. Further, according to the third aspect of the present invention, when forming the guide groove in the convex portion of the Si substrate, the guide groove is formed by anisotropic etching of the Si substrate. It is not necessary to control the size of the guide groove, and a guide groove having a high dimensional accuracy can be easily manufactured.

[Brief description of the drawings]

1 to 5 show a first embodiment of the method of the present invention. FIG. 1 is a perspective view of an embedded optical waveguide manufactured by the method of the first embodiment, and FIG. FIGS. 3 (a) to 3 (h) are explanatory views of the guide portion, FIGS. 3 (a) to 3 (h) are process diagrams of the method of the first embodiment, FIGS. 4 (a) to 4 (c) and 5 (a) to 5 (c). FIG. 3 is an explanatory view of a step of forming a guide / core layer pattern. 6 to 9 show a second embodiment of the method of the present invention. FIG. 6 is a perspective view of a buried optical waveguide manufactured by the method of the second embodiment, and FIG. FIGS. 8 (a) and (b) and FIGS. 9 (a) and 9 (b) are illustrations of the structure of the end of the optical waveguide. FIG. 10 is a perspective view of a conventional optical waveguide with a guide, and FIG. 11 is a process diagram showing a process of forming a guide in a buried optical waveguide by a conventional method. 1 ... Si substrate, 1a ... Si substrate convex, 1b ... Si substrate concave,
2 optical waveguide 2a optical waveguide core layer 2b optical waveguide buffer layer 2c optical waveguide clad layer 3 fiber guide core layer pattern 4 fiber guide groove 4a ... guide groove side wall (Si (111) surface), 5 ... optical fiber, 5a ... optical fiber core layer, 10, 10a ... mask material.

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-61-117513 (JP, A) JP-A-63-131104 (JP, A) JP-A-61-267010 (JP, A) (58) Field (Int.Cl. ⁶ , DB name) G02B ⁶ /00-6/54

Claims (3)

(57) [Claims] 1. A buffer layer forming step of forming a silica-based optical waveguide buffer layer on a Si substrate having a concave portion and a convex portion formed on a surface thereof, and polishing the substrate surface to expose the Si substrate convex portion surface. And,
A polishing step of making the height of the surface of the silica-based optical waveguide buffer layer formed on the concave portion of the Si substrate coincide with the height of the convex portion of the Si substrate, and a core layer forming step of forming an optical waveguide core layer on the substrate, Using a single photomask in which the guide core layer pattern and the optical waveguide pattern are simultaneously drawn, and the guide core layer pattern is formed on the core layer surface on the upper surface of the convex portion of the Si substrate,
A first photolithography step of aligning the optical waveguide pattern so as to be formed on the surface of the core layer on the upper surface of the concave portion of the Si substrate to pattern the mask material, and removing an unnecessary portion of the silica-based optical waveguide core layer. A core layer etching step of exposing the surface of the convex portion of the Si substrate, an embedding step of forming a clad layer on the substrate, and a mask material patterned so as to cover a region where the optical waveguide pattern is formed on the upper surface of the clad layer. A second photolithography step of forming a core layer, an unnecessary part of the clad layer, and a clad layer etching step of exposing the convex portion of the Si substrate leaving a guide / core layer pattern formed of the core layer; and a guide formed of the core layer. A silicon substrate etching step of etching the silicon substrate protrusions using the core layer pattern as a mask to form a fiber guide groove. Production method of de unit equipped optical waveguide. 2. In the cladding layer etching step,
Utilizing a difference in film thickness between the guide core layer pattern forming portion and other portions and a difference in etching rate between the core layer and the cladding layer, a guide core layer pattern formed of a core layer is left. The method for manufacturing an optical waveguide with a fiber guide section according to claim 1. 3. The method according to claim 1, wherein the (100) plane crystal is used as the Si substrate in the buffer layer forming step, and the guide / core layer pattern is changed to the Si substrate [11] in the first photolithography step.
0] direction, and the Si
3. The method of manufacturing an optical waveguide with a fiber guide according to claim 1, wherein anisotropic etching of the Si substrate is performed in the substrate etching step.