Optical connection structure and method for manufacturing the same

Abstract

To provide a method for manufacturing a mirror part of an optical connection structure which can form a mirror surface inclined to a substrate surface by using an imprint process with an accurate height position from the substrate.SOLUTION: There is provided a method for manufacturing an optical connection structure in which a part of a wall surface of a recess formed on the surface of an optical resin layer on an optical substrate is used as a mirror surface. The method includes: a height guide formation step of providing a height guide having a predetermined height on an optical substrate such as to surround a part where the recess is formed; an optical resin imparting step of filling the inside of the height guide with an optical resin; a transfer step of bringing a mold having a projection where the mirror surface is transferred into close contact with surface of the mold substrate, pushing the projection into the optical resin, and arranging the surface of the mold substrate on the height guide; a curing step of curing the optical resin; and a removal step of removing the mold.SELECTED DRAWING: Figure 2

Description

Technical Field

[0001] The present invention relates to a method for manufacturing an optical connection structure using an imprint process, and particularly to a method for manufacturing a mirror portion of an optical connection structure.

Background Art

[0002] Copackaging, in which an LSI (Large-Scale Integrated circuit) and an optical IC (optical integrated circuit) are formed on a single Si substrate, has been proposed. In the manufacture of such an optical IC structural portion, a silicon electronic device manufacturing technique called silicon photonics can be used.

[0003] For example, Patent Document 1 discloses that, for an optical input / output (optical I / O) port that inputs light from the outside to an optical circuit, patterning by photolithography is used particularly for manufacturing a mirror surface that changes the optical path in a direction (upward) substantially perpendicular to the surface of a substrate. It is described that when a resin layer is exposed with a mask whose light transmittance distribution varies depending on position and then developed, a mirror surface with a part of the surface of the resin layer inclined can be obtained depending on the difference in the amount of irradiated light.

[0004] Further, Patent Document 2 discloses that an imprint process is used for forming a mirror surface that receives light from an optical waveguide inside a cavity. It is described that an imprint mold having an outer shape matching the inner wall surface of the cavity is pressed against the laminated structure of a core layer and a clad layer made of resin to perform molding.

Prior Art Documents

Patent Documents

[0005]

Patent Document 1

Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0006] In contrast to the lower mirrors having an upwardly inclined mirror surface described in Patent Documents 1 and 2 above, an upper mirror having a downwardly inclined mirror surface can be used to change the optical path of light traveling upward (in a direction perpendicular to the surface) from the substrate surface to a horizontal direction (in a direction along the surface). If the height position of such an upper mirror is not precisely formed, it will not match the height position of the waveguide guided after the optical path has been changed. On the other hand, in the imprint process, molding is performed by pressing a mold (imprint mold) toward the substrate, so it becomes difficult to control the substrate direction, i.e., the height position, as it depends on the pressing pressure, etc.

[0007] The present invention has been made in view of the above-described circumstances, and its object is to provide a method for manufacturing a mirror portion of an optical connection structure that can accurately form an inclined mirror surface, particularly an upper mirror, on the substrate surface using an imprint process, at a height relative to the substrate. [Means for solving the problem]

[0008] The present invention relates to a method for manufacturing an optical connection structure in which a part of the wall surface of a recess formed on the surface of an optical resin layer on an optical substrate is a mirror surface, and is characterized by comprising: a height guide forming step of providing a height guide of a predetermined height on the optical substrate so as to surround the portion that forms the recess; an optical resin application step of filling the inside of the height guide with optical resin; a transfer step of bringing a mold having a convex portion for transferring the mirror surface close to the substrate and pressing the convex portion into the optical resin, thereby positioning the surface of the mold substrate on the height guide; a curing step of curing the optical resin; and a detachment step of detaching the mold.

[0009] According to the above-described features, a mirror surface, such as an upper mirror that is inclined with respect to the surface of the optical substrate, can be precisely formed at a height relative to the substrate. [Brief explanation of the drawing]

[0010] [Figure 1] This is a cross-sectional view of an optical connection structure manufactured according to an embodiment of the present invention. [Figure 2] This is a flowchart of a method for manufacturing an optical connection structure as an embodiment of the present invention. [Figure 3] This is a cross-sectional view showing each step in the manufacturing process of an optical connection structure. [Figure 4] (a) A side cross-sectional view and (a) a top view during the height guide formation process of the optical connection structure. [Figure 5] (a) Side cross-sectional view of the structure and mold used in the manufacturing experiment, and (b) Top view of the structure. [Figure 6] This graph shows a comparison between the cross-sectional profile of the concave portion and the shape of the convex portion, obtained through manufacturing experiments. [Modes for carrying out the invention]

[0011] Below, a method for manufacturing an optical connection structure, which is one embodiment of the present invention, will be described with reference to Figures 1 to 4.

[0012] As shown in Figure 1, the optical connection structure 10 manufactured by the manufacturing method of this embodiment has a structure in which a resin layer 2 made of optical resin is formed on an optical substrate 1. Near the bottom of the resin layer 2, a lower waveguide 3 is formed as a first waveguide extending from left to right in the plane of the paper, and light that has passed through the inside of the lower waveguide 3 can be guided out from its tip to a lower mirror portion 4 in the resin layer 2. The lower mirror portion 4 is provided so as to cross the lower waveguide 3, and the lower mirror 4a placed inside it can reflect the light guided out from the lower waveguide 3 (see dotted arrow in the figure) vertically upward to the surface of the optical substrate 1.

[0013] On the other hand, above the lower mirror 4a, a mirror surface 5 is formed that slopes upward to the right. The mirror surface 5 receives light that travels along the lower waveguide 3 and is reflected upward by the lower mirror 4a, and can reflect this light toward the right of the paper. To the right of the mirror surface 5, an upper waveguide 6 is formed as a second waveguide to guide the reflected light. The upper waveguide 6 is formed, for example, by laminating a core material and a cladding material made of resin. In this way, the optical connection structure 10 guides light from the lower waveguide 3, which is formed in the direction of optical propagation (from left to right of the paper), to the upper waveguide 6, which is formed along the direction of optical propagation at a position greater from the optical substrate 1 than the lower waveguide 3.

[0014] Here, the mirror surface 5 is formed on a part of the wall surface of the recess 7 formed in the resin layer 2. In other words, the recess 7 must have the mirror surface 5 positioned to reflect light from the lower mirror portion 4 formed at the bottom of its base to the right and guide it to the upper waveguide 6. Therefore, the recess 7, including the mirror surface 5, must be precisely formed at a height relative to the optical substrate 1.

[0015] The following describes a method for manufacturing an optical connection structure 10 that can accurately form the height position of the mirror surface 5. The description will primarily focus on the formation of the recess 7 and the resulting formation of the mirror surface 5. Since the formation methods for the lower mirror section 4 and the waveguide are well known, their explanation will be omitted here.

[0016] Referring to Figure 2 and also to Figure 3, first, height guides 11 (11a, 11b) having a predetermined height from the surface of the optical substrate 1 are formed on both sides of the optical substrate 1 along the longitudinal direction of a waveguide (not shown) (S1: height guide formation process, see Figure 3(a)). The height guides 11 are formed to determine the height from the optical substrate 1 when a plate-shaped mold, described later, is pressed into it. Furthermore, from the viewpoint of the moldability of the mold itself, it is preferable to use a flexible material with lower rigidity than a hard material for the mold. On the other hand, the mold will also be more prone to bending, so the upper ends of the height guides 11, which are provided as multiple planes parallel to the surface of the optical substrate 1, are used to maintain the parallelism of the flat plate shape when the mold is pressed into the optical substrate 1. For example, the proximity height guides 11a are positioned to surround the portion that forms the recess 7, and the wide-area height guides 11b are positioned spaced apart from them to maintain the height and flat plate shape of the mold. Note that the lower mirror section 4, lower waveguide 3, upper waveguide 6, etc., are already in place before the height guide 11 is formed, but are not shown in the diagram.

[0017] Next, the optical resin 12 is applied by a spin coating method or the like to fill the interior of the proximity height guide 11a (S2: optical resin application step, see Figure 3(b)). The interior of the proximity height guide 11a is the part that forms the recess 7. As the optical resin 12, a resin that can be molded with a mold described later is used before curing. For example, a photocurable resin can be suitably used.

[0018] Next, the shape of the convex portion 22 provided on the mold 20 is transferred to the optical resin 12 (S3: transfer step, see FIG. 3(c)). Specifically, the substantially flat plate-shaped mold 20 having the convex portion 22 is brought close to the optical substrate 1, and the convex portion 22 is pressed into the optical resin 12 provided inside the proximity height guide 11a. The mold 20 includes a plate-shaped mold substrate 21 and the convex portion 22 provided on a surface 21a of the mold substrate 21. Then, the surface 21a of the mold substrate 21 is placed on the height guide 11, and the surface 21a and the height guide 11 are brought into contact with each other. Alternatively, the optical resin 12 having a predetermined thickness may be left between the surface 21a and the height guide 11. Thereby, the shape of the convex portion 22 is transferred to the optical resin 12. The convex portion 22 has a height lower than a sum of the above-described predetermined height and the predetermined thickness of the optical resin 12. That is, the height of the convex portion 22 from the surface 21a is lower than the height of the height guide 11 from the surface of the optical substrate 1. Therefore, when the shape of the convex portion 22 is transferred to the optical resin 12, the bottom portion of the formed recess 7 is positioned away from the surface of the optical substrate 1, so that the convex portion 22 does not interfere with the lower mirror 4a or the like disposed therebetween. Further, one of the side surfaces of the convex portion 22 is formed as an inclined surface, and the mirror surface 5 is formed by transfer of the inclined surface.

[0019] Note that when the mold 20 is made of a flexible material as described above, it is easy to precisely form the mold into a shape including the convex portion 22 and the like. For example, silicone elastomers typified by polydimethylsiloxane (PDMS) can be suitably used. Many of these materials have excellent gas permeability, and can facilitate removal of air bubbles from the optical resin 12.

[0020] Next, while the convex portion 22 of the mold 20 is pressed into the optical resin 12, the optical resin 12 is cured (S4: Curing step, see FIG. 3(d)). When the optical resin 12 is a photocurable resin, it is cured by irradiating light through the mold 20. That is, in this case, a material transparent to the light irradiated for curing the optical resin 12 is used as the material of the mold 20. For example, ultraviolet rays are used as the irradiation light. In this regard, the above-mentioned PDMS can be suitably used as the material of the mold 20. Note that other known curing methods such as thermosetting may also be used within a range that does not adversely affect the lower mirror portion 4, the waveguide, and the like.

[0021] Finally, the mold 20 is released (S5: Release step, see FIG. 3(e)). As a result, the recess 7 having the mirror surface 5 is formed in the optical resin 12. Note that the dimensional accuracy in the height direction of the formed mirror surface 5 can be at most 15 μm or less. Note that the position of the recess 7 in the horizontal direction (left-right direction and depth direction on the paper surface of FIG. 3) can be set to an accurate position by a known technique, such as providing alignment marks at a plurality of positions on both the mold 20 and the optical substrate 1 and aligning these marks in the transfer step (S3).

[0022] As shown in FIG. 4(a), as the height guide 11, the surrounding structure of the portion where the recess 7 is formed may be used as it is. For example, the cross section of the upper waveguide 6 is exposed on the end face of the space 13 where the optical resin 12 is applied for forming the recess 7, and the resin layer 2 around the upper waveguide 6 is used as the height guide. Accordingly, when the optical resin 12 is applied into the space 13 to form the recess 7, the cross section of the upper waveguide 6 is exposed on a part of the side surface of the recess 7, and light from the mirror surface 5 of the recess 7 can be guided to the upper waveguide 6.

[0023] Furthermore, as shown in Figure (b), it is also preferable to connect a relief portion 14 of the optical resin 12 to the space 13. The relief portion 14 is, for example, connected to the space 13 above the lower mirror portion 4, and extends towards the right side of the paper along both sides of the upper waveguide 6, passing between the height guides 11. When the optical resin 12 before curing is applied to the space 13, and the mold 20 is brought close in the transfer process (S3) to press the convex portion 22 into the optical resin 12, the excess optical resin 12 relative to the space 13 flows into the relief portion 14, and air bubbles can be trapped in the relief portion 14. This allows the shape of the convex portion 22 to be accurately transferred and the recess 7 to be formed.

[0024] [Manufacturing experiment] Next, we will explain the experimental results of actually forming the recess 7 using the method described above, with reference to Figures 5 and 6.

[0025] As shown in Figure 5, a height guide 11 was provided on an optical substrate 1 made of a Si wafer by a resin layer 2, and a space 13 and a relief section 14 were formed between them to obtain an experimental structure 50. In this structure, the lower mirror section 4 and waveguide, which are unnecessary for the experiment, were not formed. The height of the convex portion 22 of the mold 20 was 26 μm, and the height from the upper end surface of the height guide 11 to the surface of the optical substrate 1 was 44 μm. The dimensions of the space 13 in the direction of light propagation (left to right on the paper) were 271 μm, and the width was 700 μm. The relief section 14 was roughly wedge-shaped when viewed from above, but the wedge shape was more open towards the inside than towards the outside.

[0026] As shown in Figure 6, the optical resin 12 was applied, and the cross-sectional profile of the recess 7 (see Figure 3) obtained after transfer, curing, and detachment by the mold 20 was measured and compared with the shape of the convex portion 22 of the mold 20. The recess 7 was formed twice, and in both cases the shape was very close to that of the convex portion 22. In other words, the height position of the mirror surface 5 formed in the recess 7 from the optical substrate 1 was accurately formed.

[0027] Although embodiments and modifications based thereon have been described above, the present invention is not necessarily limited thereto, and those skilled in the art will be able to find various alternative embodiments and modifications without departing from the spirit of the invention or the scope of the attached claims. [Explanation of symbols]

[0028] 1 Optical board 2 resin layers 3 Lower waveguide 4. Lower mirror section 4a Lower mirror 5 Mirror surface 7 recesses 10 Optical connection structure S1 Height guide formation process

Claims

1. A method for manufacturing an optical connection structure in which a part of the wall surface of a recess formed on the surface of an optical resin layer on an optical substrate is made into a mirror surface, A height guide forming step involves providing a height guide of a predetermined height on the optical substrate so as to surround the portion that forms the recess, The process of applying optical resin to fill the inside of the height guide with optical resin, A transfer step in which a mold having a convex portion for transferring the mirror surface is brought close to the optical substrate and the convex portion is pressed into the optical resin, and the surface of the mold substrate is placed on the height guide, A curing step for curing the optical resin, The process includes a detachment step of removing the mold, The lower part of the bottom of the recess has a lower mirror portion that is provided across a first waveguide formed in the direction of light propagation inside the optical substrate and has a lower mirror disposed inside, and a second waveguide is laminated on the optical substrate along the direction of light propagation. A method for manufacturing an optical connection structure, characterized in that the height guide exposes the cross-section of the second waveguide on a part of its side surface, and has a relief portion that allows the optical resin to flow from the upper part of the lower mirror portion along the side of the second waveguide when the mold is brought close during the transfer process.

2. The method for manufacturing an optical connection structure according to claim 1, characterized in that the transfer step involves the convex portion having a height lower than the predetermined height, and the surface of the molded substrate being brought into contact with the height guide.

3. The method for manufacturing an optical connection structure according to Claim 1, characterized in that the height guide forming step and the transfer step are performed to form the mirror surface at a position where it receives and reflects light that has progressed along the optical substrate in the first waveguide and reflected upward by the lower mirror, and guides it to the second waveguide.

4. The method for manufacturing an optical connection structure according to claim 1, wherein the optical resin is a photocurable resin, and the curing step is characterized by curing the optical resin by irradiating it with light through the mold.

5. An optical connection structure in which a part of the wall surface of a recess formed on the surface of an optical resin layer on an optical substrate is used as a mirror surface, The optical resin layer is A first optical resin portion having the recess formed therein, which includes the mirror surface inclined with respect to the substrate surface of the optical substrate, It includes a second optical resin portion that surrounds the first optical resin portion and has an upper waveguide formed thereon that extends parallel to the surface of the substrate, The first optical resin portion is formed to extend from the recess along both sides of the upper waveguide when viewed from a direction perpendicular to the substrate surface. An optical connection structure characterized in that, within the first optical resin portion, light traveling away from the substrate surface in the direction normal to the substrate surface is directed to the upper waveguide by the mirror surface.

6. The optical connection structure according to claim 5, characterized in that the first optical resin portion is made of a photo- or thermosetting resin.

7. The optical connection structure according to claim 5 or 6, characterized in that the second optical resin portion has a lower waveguide formed on the opposite side of the mirror surface, parallel to the substrate surface, such that it is in a straight line with the upper waveguide when the substrate surface is viewed in the direction normal to the substrate surface, and the lower waveguide is closer to the substrate surface than the upper waveguide.

8. The optical connection structure according to claim 7, characterized in that the first optical resin part is provided with a lower mirror that directs light from the lower waveguide towards the mirror surface.

9. The optical connection structure according to claim 5 or 6, characterized in that the recess of the first optical resin portion has an inclined surface facing the mirror surface so as to narrow the aperture area on the substrate surface side.

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