Bonding structure, photonic integrated circuit, and method for actively aligning the optical axis of a semiconductor optical device and the optical axis of an optical circuit on a substrate

Abstract

A bonding structure (100) and method for actively aligning the optical axis (OAX1) of a semiconductor optical device (20) with the optical axis (OAX2) of an optical circuit (30) on a substrate (10), and a photonic integrated circuit (110). The bonding structure (100) includes at least one first bonding member (11) on the substrate (10) for initially bonding the semiconductor optical device (20) to the substrate (10), and the first bonding member (11) is made of a material such as a porous metal that exhibits plastic deformation to enable deformation of the at least one first bonding member (11) during active alignment. Further, the bonding structure (100) includes at least one second bonding member (12) on the substrate (10) for secondarily bonding the semiconductor optical device (20) to the substrate (10) upon completion or after active alignment.

Description

Technical Field

[0001] The present invention generally relates to photonic devices, and more specifically, to a bonding structure for bonding a semiconductor optical device onto a substrate. In particular, but not limited thereto, the present invention relates to a bonding structure for actively aligning the optical axis of a semiconductor optical device with the optical axis of an optical circuit on a substrate.

Background Art

[0002] In known photonic devices, the optical circuit is designed and adapted such that its optical axis aligns with that of the semiconductor optical device when the semiconductor optical device is disposed, for example, bonded onto a substrate having the optical circuit. Ideally, the alignment of the axes is appropriate as designed. However, in practice, this is not always the case.

[0003] For example, when a laser is emitted from a semiconductor optical device, a difference may occur between the actual spot and the expected spot, which then causes misalignment with the optical axis of the optical circuit. On the other hand, there is also a possibility of bonding errors due to, for example, particles, squeeze or slip of the bonding material. Further, for example, tilting due to process problems or defects on the facet due to the influence of the thickness of the antireflection coating. Furthermore, there may be other process or design errors during manufacturing or bonding. Thus, even if the device is carefully designed to ensure correct alignment after bonding the components to the substrate, there are numerous factors that can cause misalignment of the optical axis in actual applications.

Summary of the Invention

Problems to be Solved by the Invention

[0004] An object of the present invention is to provide a bonding structure for actively aligning the optical axis of a semiconductor optical device and the optical axis of an optical circuit on a substrate, a photonic integrated circuit, and a method for actively aligning the optical axis of a semiconductor optical device and the optical axis of an optical circuit on a substrate. Another object of the present invention is that the bonding structure, the photonic integrated circuit, and the method improve the alignment of the optical axis between the semiconductor optical device and the optical circuit designed to operate the device.

[0005] The object of the present invention is achieved by a bonding structure for actively aligning the optical axis of a semiconductor optical device and the optical axis of an optical circuit on a substrate, a photonic integrated circuit, and a method for actively aligning the optical axis of a semiconductor optical device and the optical axis of an optical circuit on a substrate, each defined by an independent claim.

[0006] According to a first aspect, a bonding structure for actively aligning the optical axis of a semiconductor optical device and the optical axis of an optical circuit on a substrate is provided. The bonding structure comprises at least one first bonding member on the substrate for initially bonding the semiconductor optical device to the substrate. The first bonding member is made of a material that exhibits plastic deformation in order to enable deformation of at least one first bonding member during active alignment, and the material is a porous metal. Further, the bonding structure comprises at least one second bonding member on the substrate for bonding the semiconductor optical device to the substrate upon completion or after active alignment. Preferably, the second bonding member(s) can be debonded from the device before the active alignment is completed, thereby not interfering with the alignment process.

[0007] As used herein, plastic deformation refers to the ability of the first bonding member(s) of a solid material to undergo permanent deformation, i.e., an irreversible change in shape, in response to an applied force. Thus, after the force is removed, the first bonding member(s) will not return to its previous shape, at least to a significant extent.

[0008] The porous metal can be selected from the group consisting of porous copper, porous aluminum, and porous gold.

[0009] At least one second joining member can be a solder material or a eutectic joining material.

[0010] In some embodiments, at least one second joining member can be arranged with respect to the first joining member such that, upon melting of the second joining member, the material of the second joining member penetrates the porous metal of at least one first joining member, thereby forming an intermetallic compound. Further, at least one second joining member can be arranged adjacent to the first joining member on the substrate.

[0011] The first joining member(s) is / are porous at least during active alignment and prior to the second joining.

[0012] Alternatively or additionally, the end portion of at least one first joining member on the side opposite to the substrate can extend beyond the end portion of at least one second joining member on the side opposite to the substrate. Thus, when the semiconductor optical device is arranged in contact with the joining structure, it first comes into contact with at least one first joining member.

[0013] In various embodiments, at least one second joining member can be arranged to act as a stopper during or at the completion of active alignment. Thus, the semiconductor optical device can come into contact with at least one second joining member when it approaches the substrate sufficiently during alignment.

[0014] The joining structure can include a plurality of first joining members. The plurality of first joining members can be arranged on the opposite side or different sides of at least one second joining member on the substrate. In some embodiments, for example, there can be four first joining members arranged to contact the four corner portions of the semiconductor optical device.

[0015] At least one first joining member or a plurality of first joining members may have a longitudinal shape in a direction away from the substrate.

[0016] According to a second aspect, a photonic integrated circuit is provided. The photonic integrated circuit includes, on a substrate, an optical circuit such as a sensing device, and a semiconductor optical device that is aligned with the optical circuit and is joined to the substrate by a joining structure according to the first aspect described above in this specification.

[0017] The semiconductor optical device may be one selected from the group consisting of a semiconductor optical amplifier, a photodiode, and a laser diode.

[0018] According to a third aspect, a method for actively aligning the optical axis of a semiconductor optical device and the optical axis of an optical circuit on a substrate is provided. The method includes providing at least one first joining member on the substrate to initially or initially join the semiconductor optical device to the substrate, the first joining member being made of a material that exhibits plastic deformation to enable deformation of the at least one first joining member, and the material being a porous metal, providing at least one second joining member on the substrate to secondarily or finally join the semiconductor optical device to the substrate, joining the semiconductor optical device to the at least one first joining member, aligning the optical axis of the semiconductor optical device with the optical axis of the optical circuit by applying a force to the semiconductor optical device to deform the at least one first joining member, and joining the aligned semiconductor optical device by the at least one second joining member.

[0019] Furthermore, the alignment may include applying a force by a flip chip bonder head or arm that holds the semiconductor optical device during active alignment.

[0020] Furthermore, the method may include melting at least one second joining member in a reflow soldering process.

[0021] The present invention provides a joining structure, a photonic integrated circuit, and a method for actively aligning the optical axis of a semiconductor optical device and the optical axis of an optical circuit on a substrate. The present invention provides advantages over known solutions in that a highly reliable joining of components with good optical alignment is achieved. The optical alignment can be actively controlled using the joining structure so that proper alignment between the optical axes is obtained.

[0022] Based on the following detailed description, various other advantages will become apparent to those skilled in the art.

[0023] The expression "a plurality of" can refer to any positive integer starting from two (2), i.e., at least two, 2, at least three, 3, etc.

[0024] The terms "first", "second", and "third" are used herein to distinguish one element from another and, unless otherwise explicitly stated, do not specifically prioritize or order them.

[0025] The exemplary embodiments of the present invention presented herein should not be construed as limiting the applicability of the appended claims. The verb "comprising" is used herein as an open limitation that does not exclude the presence of unenumerated features. The features recited in the claims can be freely combined with each other unless specifically stated otherwise.

[0026] The novel features considered characteristic of the present invention are particularly set forth in the appended claims. However, the invention itself, both as to its construction and the manner of its operation, together with further objects and advantages thereof, will be best understood from the following description of specific embodiments when read in conjunction with the accompanying drawings.

[0027] Some embodiments of the present invention are shown by way of example in the figures of the accompanying drawings without limitation.

Brief Description of the Drawings

[0028]

Figure 1

Figure 2A

Figure 2B

Figure 2C

Figure 2D

Figure 3A

Figure 3B

Figure 4

Figure 5A

Figure 5B

Figure 5C

Figure 6

Figure 7

Figure 8

Best Mode for Carrying Out the Invention

[0029] Figure 1 schematically shows a bonding structure 100. Also shown is a part of a semiconductor optical device 20 and an optical circuit 30 on a substrate 10 such as a silicon photonics platform. The bonding structure 100 in Figure 1 includes at least one first bonding member 11 on the substrate 10 for initially or initially bonding the semiconductor optical device 20 to the substrate 10. The first bonding member 11 is made of a material that exhibits plastic deformation to enable deformation of at least one first bonding member 11 during active alignment. Further, the bonding structure 100 includes at least one second bonding member 12 on the substrate 10 for secondarily or finally bonding the semiconductor optical device 20 to the substrate 10 upon completion or after active alignment. Preferably, at least one second bonding member 12 can be arranged adjacent to the first bonding member(s) 11 on the substrate 10.

[0030] Furthermore, the end portion of at least one first bonding member 11 on the opposite side of the substrate 10 preferably extends beyond the end portion of at least one second bonding member 12 on the opposite side of the substrate 10. Therefore, the semiconductor optical device 20 first contacts at least one first bonding member 11 when the device 20 is arranged towards the substrate 10 to be bonded, before coming into contact with the second bonding member(s) 12.

[0031] The second bonding member(s) 12 can be arranged to act as a stopper during or at the end of active alignment. Therefore, the movement of the semiconductor optical device 20 can be restricted to a specific position by the second bonding member(s) 12. A specific position is preferably a position where the alignment is sufficiently good, if not optimal.

[0032] As can be understood, the semiconductor optical device 20 defines a first optical axis, the optical axis OAX1, that is, the direction in which an optical signal such as light or a laser exits the device 20. On the other hand, the optical circuit 30 also defines an optical axis OAX2, which is a second optical axis related to the position / direction of the waveguide of the optical circuit 30. For proper functioning, the optical axis OAX1 of the semiconductor optical device 20 and the optical axis OAX2 of the optical circuit 30 must be arranged or positioned relative to each other such that the optical signal provided by the semiconductor optical device 20 can efficiently enter the optical circuit 30 and be further sufficiently transmitted. Therefore, the alignment of the axes OAX1 and OAX2 is most importantly related to the alignment of the exit point of the optical signal from the semiconductor optical device 20 and the entry point into the optical circuit 30, respectively.

[0033] Regarding the semiconductor optical device 20, it may be a semiconductor optical amplifier, a photodiode, or a laser diode, and may include an active layer 22 from which an optical signal is output. Further, the semiconductor optical device 20 may include a first contact layer 24, or a bottom contact layer or electrode, whereby the device 20 is connected to the substrate 10, such as by bonding. As is known to those skilled in the art, the semiconductor optical device 20 may include other layers, such as a second contact layer (such as an upper contact layer or electrode on the upper part of the device 20 in FIG. 1), as well as an antireflection layer(s) and a cladding layer.

[0034] Regarding the optical circuit 30, it may include a waveguide 32, such as a silicon waveguide, for transmitting an optical signal therethrough. As shown in FIG. 1, the optical circuit 30 may be part of a photonic integrated circuit 110, such as a silicon photonic device.

[0035] In FIG. 1, two first joining members 11 are shown, but there may be only one, or there may be more than two, such as four. The first joining member(s) 11 can preferably be made of a conductive material such as a conductive metal. Although not shown in FIG. 1, the first joining member(s) 11 may be provided on a specific contact pad(s) or region(s) provided on or defined by the substrate 10. The contact pad(s) or region(s) can then be further connected to other components or circuits of the device.

[0036] In addition, there may be only one second joining member 12, or there may be a plurality. The second joining member 12 can be provided on a specific contact pad(s) or region(s) provided on or defined by the substrate 10. The contact pad(s) or region(s) may be the same as or different from those used for the first joining member(s) 11.

[0037] In various embodiments, the material of the first joining member(s) 11 is substantially the same as the material of the first contact layer 24 of the semiconductor optical device 20 or comprises at least a majority of the same material.

[0038] FIGS. 2A - 2D schematically show some of the steps of aligning and joining the semiconductor optical device 20 with the optical circuit 30 on the substrate 10 using the joining structure 100. As seen in FIGS. 2A - 2D, the components / elements may be substantially similar to those shown in and described in relation to FIG. 1.

[0039] FIG. 2A shows the semiconductor optical device 20 while it is being brought near the substrate 10 and moving towards the joining structure 100 thereon.

[0040] Figure 2B shows a semiconductor optical device 20 that is initially or initially joined to the first joining member 11 by at least partially melting the first joining member 11 and / or the first contact layer 24 using, for example, a high temperature, thereby joining them to each other. Other joining techniques may alternatively be used. In Figure 2B, the first joining member 11 is shown blacked out to indicate that it is joined to the device 20.

[0041] Figure 2C shows a semiconductor optical device 20 that is moved vertically to align the optical axes OAX1 and OAX2. During this vertical movement during alignment, the first joining member 11 made of a material that exhibits plastic deformation is deformed by the force utilized to move the semiconductor optical device 20. If a sufficiently good alignment is obtained, the alignment is completed. This may involve the axes OAX1 and OAX2 being at a distance from each other that is less than a distance threshold, or it may be measured such that the optical signal is sufficiently coupled to the optical circuit 30, so that, for example, a silicon photonic device can function properly.

[0042] Figure 2D shows a semiconductor optical device 20 that is secondarily or finally joined to the substrate 10 by at least one second joining member 12. Also in this case, the second joining member 12 is shown blacked out to indicate that the joining has been performed. The joining by the second joining member(s) 12, for example, by soldering or a eutectic joining material, is preferably designed to provide a better joining to the substrate 10 than the first joining so that the semiconductor optical device 20 does not move easily later. Thus, the second joining member 12 preferably does not exhibit plastic deformation, but a material / composition that provides a more rigid joining is utilized, such as using a typical soldering or eutectic joining material. For example, a tin or tin-lead type material may be utilized for the second joining member 12. In this way, the second joining then fixes the semiconductor optical device 20 in its aligned position.

[0043] Figures 3A and 3B schematically show an example of the alignment between the optical axis OAX1 of the semiconductor optical device 20 and the optical axis of the optical circuit 30 on the substrate 10. In FIG. 3A, the semiconductor optical device 20 is being moved in the vertical direction, upward and / or downward. In FIG. 3A, it is shown that the width of the first joining member 11 can change during movement, or is actually exaggerated. For example, when the first joining member 11 is stretched longer, its width can become smaller, as shown on the upper right side of the figure. On the other hand, when the first joining member 11 is compressed against the substrate 10 to be shorter, the width of the first joining member 11 can become larger.

[0044] In FIG. 3B, the semiconductor optical device 20 is being moved in the horizontal direction, left and / or right. Since both ends of the first joining member 11 are joined to corresponding counterparts, a tilted or inclined first joining member 11 is produced by the horizontal movement. The tilt can be utilized to increase or, preferably, reduce the gap between the semiconductor optical device 20 and the optical circuit 30. Alternatively or additionally, the tilt can be utilized to move the semiconductor optical device 20 simultaneously in both the vertical and horizontal directions, and as a result, a rotational movement can be made about the joining point of the first joining member 11 with respect to the substrate 10. In this case, the width of the first joining member 11 can be maintained, but can also be changed.

[0045] FIG. 4 schematically shows the joining structure 100. In the joining structure 100 of FIG. 4, the material of the first joining member 11 is a porous metal. This is indicated by the small circles within the joining member 11, which suggests the porosity of the material. In various embodiments, the porous metal is porous copper, porous aluminum, or porous gold. In this case, the porosity of the first joining member(s) 11 imparts plastic deformation characteristics to the first joining member(s) 11.

[0046] In various embodiments, the material of the first contact layer 24 of the semiconductor optical device 20 may be the same as the material of the porous metal of the first joining member 11, but is preferably not porous. Thus, the material of the first contact layer 24 can be (at least mostly) copper, aluminum, or gold, respectively, with respect to the porous metal material of the first joining member(s) 11.

[0047] Figures 5A - 5C schematically show some of the steps of aligning and bonding the semiconductor optical device 20 with the optical circuit 30 on the substrate 10 using the bonding structure 100. Again, the material of the first joining member(s) 11 is porous metal. As shown in Figure 5A, the second joining member 12 (which may alternatively be just one) is disposed adjacent to the first joining member 11. In Figure 5A, the semiconductor optical device 20 is bonded using the first joining member 11. In Figure 5B, a force is applied to move the semiconductor optical device 20 such that the length of the first joining member 11 becomes shorter. This is shown in Figure 5B by the ellipse (corresponding to the small circle in Figure 5A) within the first joining member 11 and further by the decrease in the height of the joining member 11.

[0048] Figure 5C shows that, upon melting of the second joining member 12, the material of the second joining member 12 penetrates the corresponding porous metal of at least one of the first joining members 11, thereby forming an intermetallic compound, with the second joining member 12 disposed with respect to the first joining member 11. This is emphasized in Figure 5C by the blackened color of the ellipse within the joining member 11. Thereafter, due to the penetration of the material of the second joining member 12, the first joining member 11 becomes at least somewhat non - porous, if not completely, thereby becoming more rigid, and thus the semiconductor optical device 20 is fixed in its aligned position. Figure 5C shows a small "tail" drawn beside the first joining member 11 simply to show that the material of the second joining member 12 penetrates the first joining member 11. However, in reality, a small amount of material may be left to form such a tail.

[0049] FIG. 6 schematically shows a flip-chip bonding device 40 or an arm 40 that can be used for aligning the optical axis OAX1 of the semiconductor optical device 20 and the optical axis OAX2 of the optical circuit 30 on the substrate 10. The flip-chip bonding device 40 or the arm 40 can be used to move the semiconductor optical device 20, and thus to generate a force for aligning the optical axes OAX1 and OAX2. The flip-chip bonding device 40 or the arm 40 can be used to move the semiconductor optical device 20 in the vertical direction and / or the horizontal direction, or basically in all directions. Thus, the force can have an arbitrary direction.

[0050] FIG. 7 schematically shows a photonic integrated circuit 110 as viewed from above. The photonic integrated circuit 110 includes an optical circuit 30 and a semiconductor optical device 20 on the substrate 10. Further, the semiconductor optical device 20 is bonded to the substrate 10 by four first bonding members 11 disposed at the corner portions of the semiconductor optical device 20. Also, at the center of the four first bonding members 11, there is one second bonding portion 12 to which the semiconductor optical device 20 is also bonded to the substrate 10 after the alignment of the optical axes OAX1 and OAX2. Thus, the plurality of first bonding members 11 can be disposed on the opposite side of at least one second bonding member 12 on the substrate 10. For clarity, the optical axis OAX1 is omitted from FIG. 7. The number of the first bonding members 11 and / or the second bonding members 12 can easily differ from that in FIG. 7.

[0051] FIG. 8 shows a flow diagram of the method. Item (or method step) 210 refers to an optional general start stage of the method. Suitable devices and components are obtained, and the system is assembled and configured to operate.

[0052] Item 210 refers to providing at least one first bonding member 11 on the substrate 10 for initially or initially bonding the semiconductor optical device 20 to the substrate 10, and the first bonding member 11, or member 11, is made of a material that exhibits plastic deformation to enable deformation of at least one first bonding member 11.

[0053] Item 220 refers to providing at least one second bonding member 12 on the substrate 10 for second or final bonding of the semiconductor optical device 120 to the substrate 10.

[0054] In various embodiments, the order of Item 210 and Item 220 may be different, or further, they may be executed substantially simultaneously.

[0055] Item 230 refers to bonding the semiconductor optical device 20 to at least one first bonding member 11. This can be done by using high temperature to at least partially melt the surfaces that will come into contact with each other during bonding.

[0056] Item 240 refers to aligning the optical axis OAX1 of the semiconductor optical device 20 and the optical axis OAX2 of the optical circuit 30 by applying a force to the semiconductor optical device 20 by means of a flip-chip bonder head or arm, etc., and deforming at least one first bonding member 11.

[0057] Item 250 refers to bonding the aligned semiconductor optical device 20 by means of at least one second bonding member 12.

[0058] In some embodiments, the method may include melting at least one second bonding member 12 in a reflow soldering process. In the reflow soldering process, the second bonding member(s) 12 can then bond and fix the semiconductor optical device 20 in its aligned position. This can be done as shown in FIGS. 2A - 2D or FIGS. 5A - 5C.

[0059] The execution of the method can be stopped at Item 299.

Claims

1. A junction structure (100) on a substrate (10) for active alignment of an optical axis (OAX1) of a semiconductor optical device (20) with an optical axis (OAX2) of an optical circuit (30) on the substrate (10), the junction structure (100) comprising: at least one first bonding member (11) on the substrate (10) for initially bonding the semiconductor optical device (20) to the substrate (10), the first bonding member (11) being made of a material that exhibits plastic deformation to allow deformation of the at least one first bonding member (11) during the active alignment, the material being a porous metal; and at least one second bonding member (12) on the substrate (10) for secondly bonding the semiconductor optical device (20) to the substrate (10) upon completion or after the active alignment.

2. The joint structure (100) of claim 1, wherein the porous metal is selected from the group consisting of porous copper, porous aluminum, and porous gold.

3. The joining structure (100) of claim 1, wherein the at least one second joining member (12) is a solder or eutectic joining material.

4. 2. The joining structure (100) of claim 1, wherein the at least one second joining member (12) is positioned relative to the first joining member (11) such that, upon melting of the second joining member (12), material of the second joining member penetrates the porous metal of the at least one first joining member (11), thereby forming an intermetallic compound.

5. The joint structure (100) of claim 4, wherein the at least one second joint member (12) is disposed adjacent to the first joint member (11) on the substrate (10).

6. 2. The joining structure (100) of claim 1, wherein an opposite end of the at least one first joining member (11) relative to the substrate (10) extends beyond an opposite end of the at least one second joining member (12) relative to the substrate (10).

7. The joining structure (100) of claim 1, wherein the at least one second joining member (12) is positioned to act as a stop during or upon completion of the active alignment.

8. The joint structure (100) according to claim 1, comprising a plurality of first joint members (11) disposed on the substrate (10) opposite the at least one second joint member (12).

9. The joining structure (100) according to claim 8, wherein the at least one first joining member (11) or the plurality of first joining members (11) have an elongated shape in a direction away from the substrate (10).

10. A photonic integrated circuit (110) comprising: an optical circuit (30) on a substrate (10); A photonic integrated circuit (110) comprising: a semiconductor optical device (20) aligned with the optical circuit (30) and bonded to the substrate (10) by the bonding structure (100) according to any one of claims 1 to 9.

11. The photonic integrated circuit (110) of claim 10, wherein the semiconductor optical device (20) is one selected from the group consisting of a semiconductor optical amplifier, a photodiode, and a laser diode.

12. A method for active alignment of an optical axis (OAX1) of a semiconductor optical device (20) with an optical axis (OAX2) of an optical circuit (30) on a substrate (10), the method comprising: providing (210) at least one first bonding member (11) on the substrate (10) for initially bonding the semiconductor optical device (20) to the substrate (10), the first bonding member (11) being made of a material that exhibits plastic deformation to allow deformation of the at least one first bonding member (11), the material being a porous metal; providing (220) at least one second bonding member (12) on the substrate (10) for secondly bonding the semiconductor optical device (20) to the substrate (10); bonding (230) the semiconductor optical device (20) to the at least one first bonding member (11); a step of aligning (240) the optical axis (OAX1) of the semiconductor optical device (20) with the optical axis (OAX2) of the optical circuit (30) by applying a force to the semiconductor optical device (20) to deform the at least one first joining member (11); and bonding (250) the aligned semiconductor optical device (20) with the at least one second bonding member (12).

13. The method of claim 12, wherein the aligning (240) comprises applying the force by a flip-chip bonder head (40) or arm (40) that holds the semiconductor optical device (20) during the active alignment.

14. 14. The method according to claim 12 or 13, comprising the step of melting the at least one second joining member (12) in a reflow soldering process.

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