JP2013228691A - Optical module and manufacturing method of optical module - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an optical module with high performance that prevents curvature of an optical element in surface activation joint to a substrate of the optical element, and a manufacturing method of the optical module.SOLUTION: In an optical module in which a wavelength conversion element 20 to be an optical element is mounted on a silicon substrate 10, the silicon substrate 10 has a junction 41 of a micro-bump structure composed of Au, and the wavelength conversion element 20 is joined to the junction 41 by a surface activation joint technology. The micro-bump structure of the junction 41 has a different constitution in a bump area per unit area from a micro-bump 46 positioned at a place A1 in the vicinity of both ends of the wavelength conversion element 20 and a micro-bump 46 positioned at a place A2 in the vicinity of a center part of the wavelength conversion element 20. Consequently, curvature of the wavelength conversion element 20 is prevented, and an optical module with high performance that surely performs optical coupling and reduces transmission loss can be attained.

Description

  The present invention relates to an optical module in which an optical element is mounted on a substrate and an optical module manufacturing method.

Blue, green, and other short wavelength laser light sources are being widely developed in fields such as laser projectors and high-density optical storage devices. This short wavelength laser light source is an SHG (Second
There is a method called Harmonic Generation (second harmonic generation), which outputs laser light such as blue or green by a wavelength conversion element that converts fundamental infrared light oscillated by a semiconductor laser into second harmonic It is.

  As this SHG type short wavelength laser light source, there has been proposed an optical device in which a laser element and a wavelength conversion element are bonded on a silicon substrate by a surface activated bonding technique using micro bumps (see, for example, Patent Document 1).

[Description of Configuration and Operation of Short Wavelength Laser Light Source Using Conventional SHG Method: FIG. 1]
Hereinafter, an example of the configuration of a conventional short wavelength laser light source based on the SHG method according to Patent Document 1 will be described with reference to FIG. FIG. 1 is an external perspective view schematically showing an optical module which is a short wavelength laser light source of Patent Document 1. In FIG. 1, the optical module 1 includes a plate-like silicon substrate 10 and a silicon substrate 10 on the silicon substrate 10. The laser element 3 is a mounted optical element, and the wavelength conversion element 20 is an optical element mounted on a silicon substrate 10 that is optically coupled to the laser element 3.

  The laser element 3 is a chip-type semiconductor laser that emits infrared light or the like, and the wavelength conversion element 20 has a thin long plate shape and has an optical waveguide 30 (shown by a broken line) inside. As an example, the optical waveguide 30 is made of a ferroelectric single crystal material LN (lithium niobate: LiNbO3) as a main component and added with MgO, and is formed along the longitudinal direction of the approximate center of the wavelength conversion element 20. The

  Next, an outline of the operation of the conventional short wavelength laser light source by the SHG method will be described. In FIG. 1, when the laser element 3 is supplied with a drive current from the silicon substrate 10 by means (not shown), it emits infrared light L1 that is a fundamental wave. The wavelength conversion element 20 makes the infrared light L 1 from the laser element 3 incident on the optical waveguide 30, converts it into a harmonic by the optical waveguide 30, and converts the green or blue laser light L 2 to the opposite side of the optical waveguide 30. The light is emitted from the exit port. The laser light L2 emitted from the optical light guide 30 is transmitted to an external optical system through an optical fiber (not shown).

  Here, if the positional relationship between the laser element 3 and the wavelength conversion element 20 is not adjusted with high accuracy, the optical coupling becomes insufficient, and the infrared light L1 from the laser element 3 is converted into the light of the wavelength conversion element 20. Since the light cannot enter the waveguide 30 efficiently, the alignment of the laser element 3 and the wavelength conversion element 20 is extremely important. Further, since the wavelength conversion element 20 has a thin long plate shape, it has a characteristic that it is easily bent when an unnecessary stress is applied when it is mounted on the silicon substrate 10. When the wavelength conversion element 20 is bent, the internal optical waveguide 30 is also bent, and the transmission loss of the incident infrared light L1 increases, causing a problem that the wavelength conversion element 20 cannot sufficiently function.

[Description of Optical Device Mounting Method of Short Wavelength Laser Light Source Using Conventional SHG Method: FIG. 2]
Next, the outline of the mounting method of the optical element in the conventional short wavelength laser light source will be described with reference to the exploded perspective view of FIG. In FIG. 2, joints 40 and 41 for mounting the laser element 3 and the wavelength conversion element 20 are formed on the surface of the silicon substrate 10. The joint portions 40 and 41 have a micro bump structure made of Au.

  Here, an Au film (not shown) is formed on the lower surface of the laser element 3, and the laser element 3 is surface-activated by placing and pressing the laser element 3 at a predetermined position on the joint 40. Bonded to the silicon substrate 10 by a bonding technique. Similarly, an Au film (not shown) is also formed on the lower surface of the wavelength conversion element 20, and the wavelength conversion element 20 is applied to the surface of the silicon substrate 10 by applying pressure on a predetermined position on the joint 41. Joined by activated joining technology. The junction 41 is formed as two parallel elongated patterns avoiding the portion of the optical waveguide 30.

  Here, although the optical module 1 which is a short wavelength laser light source shown in FIG.1 and FIG.2 is shown as a prior art example, the external basic structure of this optical module 1 is the same as that of the optical module of this invention. Therefore, an embodiment of the present invention, which will be described later, will also be described with reference to the optical module 1 shown in FIGS. This is because the present invention relates to a micro-bump structure of a joint for joining optical elements, and the basic configuration as an optical module is the same as that of the conventional example.

[Description of Surface Activated Bonding of Conventional Short Wavelength Laser Light Source: FIG. 3 (a)]
Next, an outline of surface activated bonding in a conventional short wavelength laser light source will be described with reference to FIG. FIG. 3A is a cross-sectional view of the silicon substrate 10 and the wavelength conversion element 20 obtained by cutting the above-described optical module 1 of FIG. 1 along the cutting line AA ′. In FIG. 3A, bonding portions 41 are formed on the surface of the silicon substrate 10, and a large number of micro bumps 45 having a predetermined diameter are formed on the surface of the bonding portion 41 at a predetermined pitch. An Au film 21 is formed on the lower surface of the wavelength conversion element 20.

  Here, before bonding, the bonding portion 41 of the silicon substrate 10 and the Au film 21 on the bonding surface of the wavelength conversion element 20 are cleaned by argon plasma to activate the respective surfaces. Then, when the wavelength conversion element 20 is adsorbed by a pressure tool (not shown), placed on the bonding portion 41 of the silicon substrate 10 and a load K is applied at room temperature without heating, the wavelength conversion between the microbump 45 of the bonding portion 41 and the wavelength conversion is performed. The Au film 21 on the lower surface of the element 20 comes into contact, the micro bumps 45 are slightly crushed, and the wavelength conversion element 20 is bonded by surface activation bonding.

JP 2011-242436 A (page 8, FIG. 5)

[Bending problem caused by conventional surface activated bonding: FIG. 3B]
However, in the conventional surface activated bonding described with reference to FIG. 3A, as shown in FIG. 3B, even if the wavelength conversion element 20 is uniformly loaded for bonding, the center of the wavelength conversion element 20 is not affected. A stronger load is applied in the vicinity of both ends than in the vicinity of the portion, the amount of crushing of the microbump 45 near the center is small, and the amount of crushing of the microbump near the both ends is increased.

  This is because the bumps in the center part also have bumps around, but the bumps at both ends have no bumps outside them, and the number of bumps per unit area is more at the both ends than at the center part. This is probably because the load applied to each bump increases as it reaches both ends. Thereby, the wavelength conversion element 20 is bonded to the silicon substrate 10 in a state where the vicinity of the center is raised and curved.

Thus, when the wavelength conversion element 20 is joined in a curved state, the position (particularly the height) of the wavelength conversion element 20 with respect to the laser element 3 varies, and the optical coupling between the laser element 3 and the wavelength conversion element 20 occurs. Is not normal, and there is a problem that optical loss increases. Further, when the wavelength conversion element 20 is curved, the internal optical waveguide 30 is also curved, and even if the infrared light L1 (see FIG. 1) from the laser element 3 is incident, transmission loss inside the optical waveguide 30 increases. There arises a problem that the wavelength conversion element 20 cannot function sufficiently. Such bending of the optical element at the time of joining is a serious problem because it appears conspicuously when joining thin and long parts such as the wavelength conversion element 20 in particular.

[Peeling problem due to conventional surface activated bonding: FIG. 4]
As shown in FIG. 4A, when the wavelength conversion element 20 is bonded to the silicon substrate 10 in a state where the vicinity of the center is raised and curved, the wavelength conversion element 20 is released after the load is released. Then, a force k1 is generated to return to the vicinity of both curved ends of the wavelength conversion element 20. Due to the force k1 for returning to the original state, the bonding strength in the vicinity of both ends of the wavelength conversion element 20 is lowered.

  Moreover, as shown in FIG.4 (b), it is assumed that the vicinity of the both ends of the wavelength conversion element 20 in which the joint strength has decreased is in a peeled state in the worst case (indicated by a dashed ellipse). As described above, the bonding strength in the vicinity of both end portions of the wavelength conversion element 20 is reduced, and when the wavelength conversion element 20 is peeled off, not only does the optical coupling between the laser element 3 and the wavelength conversion element 20 cause a problem, but the The reliability of this will be greatly impaired.

  SUMMARY OF THE INVENTION An object of the present invention is to solve the above-mentioned problems and to provide a high-performance optical module and a method for manufacturing the optical module by preventing the bending of the optical element in surface activated bonding of the optical element to the substrate.

  In order to solve the above-described problems, the optical module and the method for manufacturing the optical module of the present invention employ the following configurations and methods.

  The optical module of the present invention is an optical module in which an optical element is mounted on a substrate, the substrate has a joint part of a microbump structure made of a metal material, and the optical element is joined to the joint part by a surface activation joining technique, The micro bumps at the junction are characterized in that the micro bumps located near both ends of the optical element and the micro bumps located near the central part of the optical element have different bump areas per unit area.

  Further, the bump pitch of the micro bumps located near both ends of the optical element may be narrow, and the bump pitch of the micro bumps located near the center part of the optical element may be wide.

  Moreover, the bump diameter of the micro bump located near the both ends of the optical element may be large, and the bump diameter of the micro bump located near the center of the optical element may be small.

  The optical module manufacturing method of the present invention is a method for manufacturing an optical module in which an optical element is mounted on a substrate, a bonding portion forming step for forming a bonding portion of a microbump structure made of a metal material on the substrate, and bonding the optical element. An optical element bonding step for bonding to the portion by surface activated bonding technology, and the bonding portion forming step includes a micro bump located near both ends of the optical element, and a micro bump located near the center of the optical element. Is characterized in that the joints are formed so that the bump areas per unit area are different.

  Further, the bonding portion forming step may form a bonding portion in which the bump pitch of the micro bumps located near both ends of the optical element is narrow and the bump pitch of the micro bumps located near the central portion of the optical element is wide.

  Further, the bonding portion forming step may form a bonding portion where the bump diameter of the micro bump located near both ends of the optical element is large and the bump diameter of the micro bump located near the center portion of the optical element is small.

  According to the present invention, the bump per unit area of the micro-bump for surface activated bonding between the junction of the substrate located near both ends of the optical element and the junction of the substrate located near the center of the optical element. Due to the difference in area, the amount of crushing of the micro bumps can be made uniform, and the bending of the optical element during bonding can be reduced.

  In addition, the bump area per unit area of the micro-bump for surface activated bonding between the bonding portion of the substrate positioned near both ends of the optical element and the bonding portion of the substrate positioned near the central portion of the optical element is By forming the joint portions differently, it is possible to provide a manufacturing method capable of making the crushing amount of the micro bumps uniform and reducing the curvature of the optical element at the time of joining.

  In addition, since the optical element is bonded to the substrate using surface activation bonding technology that does not require heating, the functional deterioration of the component due to thermal stress does not occur, and distortion due to the difference in thermal expansion coefficient is caused by the microbump structure. It has many advantages such as prevention of occurrence.

It is a perspective view which shows the external appearance of the optical module of the conventional and embodiment of this invention. It is a disassembled perspective view of the optical module of the conventional and embodiment of this invention. It is typical sectional drawing explaining the curved state of the wavelength conversion element by the surface activation joining of the conventional optical module. It is typical sectional drawing explaining the peeling state of the wavelength conversion element by the surface activation joining of the conventional optical module. It is sectional drawing of the optical module of the 1st Embodiment of this invention. It is process drawing explaining the junction part formation process of the optical module of the 1st Embodiment of this invention. It is a perspective view which shows the microbump structure of the junction part of the optical module of the 1st Embodiment of this invention. It is explanatory drawing explaining the optical element joining process of the optical module of the 1st Embodiment of this invention. It is sectional drawing of the optical module of the 2nd Embodiment of this invention. It is a top view which shows the micro bump arrangement | positioning of the junction part of the optical module of 3rd Embodiment of this invention. It is drawing showing the simple model of the heat conduction path | route used for calculation of the thermal resistance of the optical module of the 3rd Embodiment of this invention.

[Surface activated bonding technology]
Next, before explaining the embodiments of the present invention, the outline of the surface activated bonding technique will be described as it is known but helps to understand the present invention. Surface activated bonding technology is activated by removing inactive layers such as oxide film and dust (contamination) covering the material surface by plasma treatment, etc., and bringing atoms with high surface energy into contact with each other. This is a technique for joining using force. However, even in this technique, in joining between flat joining surfaces, joining cannot be performed unless heating is applied to some extent (100 to 150 ° C.). In the present invention, in order to lower the bonding temperature, bonding at normal temperature is possible by forming micro bumps made of a material of Au that is easily plastically deformed on one side of the bonding surface, that is, the bonding portion of the silicon substrate.

  Here, the principle of surface activated bonding will be described. An oxide film and contamination are present on the actual surface (such as a junction). For this reason, plasma cleaning or sputter etching using an ion beam is performed to activate the surface of the junction, and the junction is brought into an active state in which atoms having bonds are exposed. Thereby, it is possible to perform interatomic bonding simply by bringing the Au film on the lower surface of the laser element or wavelength conversion element to be bonded into contact with the bonding portion.

According to this surface activated bonding, since it is a non-heated bonding, it has the following advantages.
1. No component breakage due to residual stress due to difference in thermal expansion coefficient.
2. There is no thermal stress on the parts, and functional deterioration of the parts does not occur.
3. Since there is no heating and solid phase bonding, there is no positional deviation during mounting.
4). There is no thermal effect on other parts.
5. Due to the direct bonding of atoms, the bonding layer does not deteriorate with time.

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.
[Features of each embodiment]
The feature of the first embodiment is that the joint located near both ends of the optical element and the joint located near the center of the optical element have a micro-bump structure with different bump pitches. The feature of the second embodiment is that the joint located near both ends of the optical element and the joint located near the center of the optical element have a micro-bump structure with different bump diameters. .

[Description of Joint Part of Optical Module of First Embodiment: FIG. 5]
The configuration of the joint portion of the optical module of the first embodiment will be described with reference to FIG. Since the basic configuration of the optical module of the first embodiment is the same as that of the conventional optical module 1 described above with reference to FIGS. 1 and 2, the overall configuration of the optical module of the first embodiment is shown in FIGS. 2, the same elements are assigned the same numbers, and duplicate descriptions are omitted.

  FIG. 5 is a cross-sectional view of the silicon substrate 10 and the wavelength conversion element 20 obtained by cutting the optical module 1 of FIG. 1 along the cutting line AA ′. In FIG. 5, bonding portions 41 are formed on the surface of the silicon substrate 10, and a large number of micro bumps 46 having a predetermined diameter are formed on the surface of the bonding portion 41. An Au film 21 is formed on the lower surface of the wavelength conversion element 20 as an optical element. When this wavelength conversion element 20 is placed on the bonding portion 41 of the silicon substrate 10 and pressed with a predetermined load, the Au film 21 on the lower surface of the wavelength conversion element 20 comes into contact, and the microbumps 46 slightly change. The wavelength conversion element 20 is crushed and bonded by surface activated bonding.

  Here, the microbumps 46 of the joint portion 41 have different bump pitches between the microbumps 46 located near the both ends A1 of the wavelength conversion element 20 and the microbumps 46 located near the center A2 of the wavelength conversion element 20. Formed. Specifically, the microbumps 46 located near the both ends A1 of the wavelength conversion element 20 form a narrow bump pitch P1, and the microbumps 46 located near the center A2 form a wide bump pitch P2. That is, the bump pitch in the vicinity A1 of both ends in the longitudinal direction of the joining portion 41, which is a long and narrow pattern, is narrowed, and the bump pitch in the vicinity of the central portion A2 is widened. Note that it is not always necessary to reduce the bump pitch at both ends in the short direction of the joint portion 41.

By forming the micro bumps 46 in this way, even when a load is applied in the vicinity of both ends A1 to the vicinity of the center A2 of the wavelength conversion element 20 in the application of the load in the surface activation bonding, both ends are applied. Since the microbumps 46 near the portion A1 have a narrow pitch and a large number, the bump area per unit area increases, and the microbumps 46 can withstand a load and are not crushed so that the amount of crushing is appropriate. Further, the load in the vicinity of the center portion A2 of the wavelength conversion element 20 is smaller than the load in the vicinity of both end portions A1, but the micro bumps 46 in the vicinity of the center portion A2 have a wide pitch and a small number. The area is reduced and the amount of crushing is appropriate for the load.

  As a result, the amount of crushing of the microbumps 46 can be made uniform in the vicinity of both ends A1 and in the vicinity of the center A2, so that the bending of the wavelength conversion element 20 in the surface activated bonding can be prevented. Thereby, since alignment with respect to the laser element 3 can be performed with high accuracy, the optical coupling between the laser element 3 and the wavelength conversion element 20 can be reliably performed. Further, since the bending of the wavelength conversion element 20 can be prevented, a high-performance optical module can be provided while minimizing transmission loss inside the optical waveguide 30. Moreover, since the bending of the wavelength conversion element 20 can be prevented, it is possible to provide a highly reliable optical module by preventing a decrease in bonding strength and peeling of the bonding surface in the vicinity A1 of both ends. It should be noted that the specific pitch widths near the both ends A1 and near the center A2 may be adjusted so that the bumps are uniformly crushed when a predetermined load is applied.

[Explanation of Joining Step of Optical Module of First Embodiment: FIG. 6]
Next, an example of a process for forming a joint portion of the optical module according to the first embodiment will be described with reference to the process diagram of FIG. 6 is a cross-sectional view of the silicon substrate 10 shown in FIG. 2 cut in the longitudinal direction. The silicon substrate 10 has a laser element mounting region 11 in which the laser element 3 is mounted, and a wavelength conversion element. A wavelength conversion element mounting region 12 on which 20 is mounted is provided.

  In the process of FIG. 6A, a gold Au film 13 which is a metal material is formed on the surface of the silicon substrate 10 flattened through the CMOS-LSI formation process.

  Next, in the step of FIG. 6B, a resist film 14 for leaving the Au film 13 as an electrode is formed in the laser element mounting area 11 and the wavelength conversion element mounting area 12 described above. That is, this region becomes the joints 40 and 41 on the silicon substrate 10.

  Next, in the step of FIG. 6C, etching is performed to remove the Au film 13 in a region not covered with the resist film 14, thereby forming an electrode. Thereby, the Au film 13 is formed as an electrode in the laser element mounting area 11 and the wavelength conversion element mounting area 12.

  Next, in the step of FIG. 6D, after the resist film 14 is removed, a resist film for micro bumps is formed on the surface of the electrode of the Au film 13 formed in the laser element mounting region 11 and the wavelength conversion element mounting region 12. 15 is formed. The resist film 15 is formed, for example, as a pattern in which a large number of small substantially circular dots are arranged in a plan view. Here, the difference between the bump pitch of the microbump 46 near the both ends A1 of the wavelength conversion element 20 and the bump pitch of the microbump 46 near the center A2 is formed by the pattern of the resist film 15.

  Next, in the step of FIG. 6E, half etching is performed to form a groove 13 a having a predetermined depth in the Au film 13 in the dot-like gap of the resist film 15.

Next, in the step of FIG. 6F, the resist film 15 is removed. As a result, a large number of micro bumps 46 are formed on the surface of the Au film 13 in the laser element mounting region 11 and the wavelength conversion element mounting region 12 and are arranged in a dot shape by the grooves 13a. Note that the Au film 13 remains in the gap between the micro bumps 46, that is, the bottom of the groove 13a (see FIG. 6E), whereby the lower portion of each micro bump 46 is connected by the Au film 13. Therefore, the entire laser element mounting area 11 and the wavelength conversion element mounting area 12 are in a conductive state as electrodes. Thus, the laser element mounting area 11 and the wavelength conversion element mounting area 1 in which a large number of microbumps 46 are formed.
The two two regions are the joint portions 40 and 41.

  When forming a wiring pattern other than micro bumps on the surface of the first silicon substrate 10, the resist film 14 formed in the step of FIG. 6B is patterned in accordance with the wiring pattern to be formed, A wiring pattern or the like can be formed by etching in the step of FIG. Moreover, the bump pitch of the micro bumps 46 of the joint portion 40 on which the laser element 3 is mounted may be changed between the both end portions and the central portion as necessary.

  According to the joint formation process described above, joints having a microbump structure made of Au, a wiring pattern, and the like can be efficiently manufactured collectively on the surface of the silicon substrate 10. Note that the pitch of the micro bumps 46 of the joint portion 41 is different between the both end portions and the central portion as described above, but the description of the difference in pitch is omitted in FIG.

[Description of Micro Bump Structure at Joint: FIG. 7]
Next, the structure of the micro bumps of the joint portions 40 and 41 formed in the joint portion forming step will be described with reference to FIG. FIG. 7 is an enlarged perspective view of a part of the joint portion 41. In FIG. 7, the micro bumps 46 have a substantially cylindrical shape made of Au, and are formed with a diameter of about 8 μm and a height of about 2 μm as an example. Since the Au film 13 exists in the gaps between the micro bumps 46, that is, the bottom surfaces of the grooves 13a as described above, the micro bumps 46 are mechanically and electrically connected by the Au film 13 and integrated. It is configured as a structured electrode.

  In addition, the bump pitch of each micro bump 46 is defined as a pitch Px in the X-axis direction and a pitch Py in the Y-axis direction in the drawing. Here, as described above, the pitches Px and Py of the microbumps 46 of the joint portion 41 located in the vicinity A1 of both ends of the wavelength conversion element 20 are narrowed by a predetermined width so as to be near the center A2 of the wavelength conversion element 20. By forming the pitches Px and Py of the micro-bumps 46 of the joint portion 41 positioned to be wide by a predetermined width, the crushing amount of the micro-bumps 46 can be made uniform at both ends A1 and near the center A2.

  Note that the pitches Px and Py near both ends A1 and near the center A2 may be changed in both the X-axis direction and the Y-axis direction, or may be changed only in one axis. For example, if the longitudinal direction of the wavelength conversion element 20 is the X-axis direction, only the pitch Px in the X-axis direction may be changed between both end portions A1 and the central portion A2.

[Description of optical element joining process of optical module: FIG. 8]
Next, a bonding process for mounting the laser element, which is the optical element of the first embodiment, and the wavelength conversion element by the surface activated bonding technique described above will be described with reference to FIG. FIG. 8 is a side view of the optical module 1 for explaining a bonding process in which a laser element and a wavelength conversion element are mounted on a silicon substrate.

  In FIG. 8A, joint portions 40 and 41 are formed on the silicon substrate 10, and a large number of micro bumps 46 are formed in the joint portions 40 and 41 by the joint portion forming process described above. In this state, the laser element 3 and the wavelength conversion element 20 are bonded by the surface activation bonding described above. Before the bonding, the bonding portions 40 and 41 of the silicon substrate 10, the laser element 3 of the optical element, and the wavelength conversion element 20 are bonded. The electrodes on the bonding surfaces are cleaned with argon plasma to activate the respective surfaces. Note that an Au film 3 a is formed as an electrode on the bonding surface on the lower surface of the laser element 3, and an Au film 21 is also formed on the bonding surface on the lower surface of the wavelength conversion element 20.

Next, in FIG. 8B, the Au film 3a of the laser element 3 is positioned at the bonding portion 40 of the silicon substrate 10, and the Au film 21 on the lower surface of the wavelength conversion element 20 is positioned at the bonding portion 41. Surface activation bonding in a normal temperature state is performed by contacting and pressurizing a predetermined load K. At this time, the laser element 3 is caused to emit light by means (not shown) so that the laser element 3 and the wavelength conversion element 20 are optically coupled, and the laser light L2 is detected from the exit 30b of the optical waveguide 30 of the wavelength conversion element 20. While detecting with (not shown), the load K is adjusted and the surface activation bonding is performed while performing precise positioning, thereby completing the optical module 1.

  Here, as described above, the joint 41 that joins the wavelength conversion element 20 has a narrow bump pitch in the microbumps 46 located near both ends of the wavelength conversion element 20 and the microbumps 46 located in the vicinity of the center part. Since the bump pitch is widely formed, the amount of crushing of the micro bumps 46 becomes uniform, and the flatness of the wavelength conversion element 20 at the time of bonding can be maintained. Thereby, since alignment between the laser element 3 and the wavelength conversion element 20 can be precisely adjusted, the optical coupling between the laser element 3 and the wavelength conversion element 20 can be surely adjusted. In addition, since the bending of the wavelength conversion element 20 can be prevented, the transmission loss inside the optical waveguide 30 can be minimized, and the joining surface can be prevented from being peeled, thereby providing an optical module with high performance and excellent reliability.

[Description of Joint Part of Optical Module of Second Embodiment: FIG. 9]
Next, the structure of the joint part of the optical module of the second embodiment will be described with reference to FIG. The basic configuration of the optical module of the second embodiment is the same as that of the conventional optical module 1 described above with reference to FIGS. 1 and 2, and therefore the configuration of the optical module of the second embodiment is as shown in FIGS. The same elements are assigned the same reference numerals, and duplicate descriptions are omitted.

  FIG. 9 is a cross-sectional view of the silicon substrate 10 and the wavelength conversion element 20 obtained by cutting the optical module 1 of FIG. 1 along the cutting line AA ′. In FIG. 9, the bonding portion 41 is formed on the surface of the silicon substrate 10, and many micro bumps 47 are formed on the surface of the bonding portion 41. An Au film 21 is formed on the lower surface of the wavelength conversion element 20. When the wavelength conversion element 20 is placed on the bonding portion 41 of the silicon substrate 10 and pressed with a predetermined load, the Au film 21 on the lower surface of the wavelength conversion element 20 comes into contact with the microbump 47 slightly. The wavelength conversion element 20 is crushed and bonded by surface activated bonding.

  Here, the microbump 47 of the joint portion 41 has a bump diameter of the microbump 47 located near the both ends A1 of both ends of the wavelength conversion element 20 and the microbump 47 located near the center A2 of the wavelength conversion element 20. Are formed differently. Specifically, the microbump 47 positioned near both ends A1 of the wavelength conversion element 20 has a large bump diameter D1, and the microbump 47 positioned near the center A2 has a small bump diameter D2.

  By forming the micro bumps 47 in this way, even when a load is applied in the vicinity of both ends A1 to the vicinity of the center portion A2 of the wavelength conversion element 20 in the application of the load in the surface activation bonding, both ends are applied. Since the microbump 47 near the portion A1 has a large bump diameter, the area of the bump per unit area increases, and the microbump 47 can withstand the load and have an appropriate amount of crushing. Further, the load in the vicinity of the center portion A2 of the wavelength conversion element 20 is smaller than the load in the vicinity of both end portions A1, but since the microbump 47 in the vicinity of the center portion A2 has a small bump diameter, the bump area per unit area is small. Therefore, the amount of crushing is appropriate for the load.

  As a result, the amount of crushing of the micro bumps 47 can be made uniform in the vicinity of both end portions A1 and the vicinity of the central portion A2, so that the bending of the wavelength conversion element 20 at the time of bonding can be reduced. Thereby, the same effects as those of the first embodiment can be obtained, and a high-performance optical module can be provided.

Further, the bump pitch is changed in the first embodiment and the bump diameter is changed in the second embodiment, but both the bump pitch and the bump diameter may be changed. That is, the micro bumps 47 located near the both ends A1 of the wavelength conversion element 20 are formed with a narrow bump pitch and a large bump diameter, and the micro bumps 47 located near the center part A2 of the wavelength conversion element 20 are bumps. The pitch may be increased and the bump diameter may be reduced. Thereby, the flatness of the wavelength conversion element 20 can be improved by further finely adjusting the amount of crushing of the micro bumps near both ends A1 and near the center A2.

  In the first and second embodiments, the bump pitch is narrow or wide in two steps and the bump diameter is large or small in two steps. However, the bump structure may be different in two or more steps. For example, a medium bump pitch is formed in the region between both end vicinity A1 and center vicinity A2 in the first embodiment, and a medium bump diameter is formed in the second embodiment. You may do it. Thus, the flatness of the wavelength conversion element 20 can be improved by changing the bump structure in multiple stages to finely adjust the crushing amount of the microbump.

  As described above, according to the present invention, the bump pitch or the bump diameter of the microbump of the bonding portion for surface activation bonding of the optical element is made different between the vicinity of both ends and the central portion of the optical element to be bonded, It is possible to provide a high-performance optical module in which the crushing amount of the bumps is made uniform to prevent the optical element from being bent, optical coupling is ensured, and transmission loss is minimized. In particular, when the optical element is thin and elongated like a wavelength conversion element, the present invention can exert an extremely large effect.

[Description of Joint Part of Optical Module of Third Embodiment: FIG. 10]
Next, the configuration of the joint portion of the optical module of the third embodiment will be described with reference to FIG. The basic configuration of the optical module of the third embodiment is the same as that of the conventional optical module 1 described above with reference to FIGS. 1 and 2, and therefore the configuration of the optical module of the third embodiment is shown in FIGS. The same elements are assigned the same reference numerals, and duplicate descriptions are omitted.

  FIG. 10 is a view of the silicon substrate 10 of the optical module 1 of FIG. 2 as viewed from above, and particularly shows the vicinity where the wavelength conversion element 20 and the laser element 3 are mounted. A bonding portion 41 is formed on the surface of the silicon substrate 10, and a number of micro bumps 48 (hereinafter sometimes simply referred to as bumps) are formed on the surface of the bonding portion 41. Bonded by surface activated bonding. Similarly, the laser element 3 is bonded to the bonding portion 40.

  Here, the bumps 48 of the joint portion 41 are formed and arranged so that the bump diameters are different between the vicinity of the central waveguide 30 and the outer end portion with respect to the short direction of the wavelength conversion element 20 to be joined. Specifically, the one arranged along the waveguide 30 of the wavelength conversion element 20 reduces the bump diameter, increases the bump diameter as the distance from the waveguide 30 increases, and aligns along the end in the short direction. The bump 48 has the largest bump diameter.

Now, let us consider the heat conduction that is transmitted from the laser element 3 to the wavelength conversion element 20 via the bumps 48. The laser element 3 is used as a heat source, and the temperature change caused in the waveguide 30 of the wavelength conversion element 20 by this will be considered.
As a simple model, the heat source is in the vicinity of the center of the laser element 3, a heat conduction path passing through the bump 48 is determined for one point of the waveguide 30, and its thermal resistance is calculated and compared with the conventional configuration. .
As a conventional model for comparison, it is assumed that the areas of the bumps 48 are the same and are arranged almost uniformly in the joint portion 41. On the other hand, in the present embodiment, the area of the bump 48 differs depending on the distance from the waveguide 30, and the area of the bump 48 increases as the distance in the perpendicular direction to the waveguide 30 increases. .
In addition, in order not to change the bonding strength and bonding balance of the wavelength conversion element 20 to the silicon substrate 10, the total area of the bumps 48 and the center position of the bumps 48 are the same as those of the conventional model.

Here, when the bump 48 of this embodiment is joined to the wavelength conversion element 20, the bump 48a is located near the waveguide 30, the bump 48c is located far from the waveguide 30, and the bump 48a is between the bump 48a and the bump 48c. The bump located at a distance of 48b was designated as 48b.
Further, it is assumed that the bumps arranged along the longitudinal direction of the wavelength conversion element 20 have the same diameter, and here, from the bumps 48a, 48b, and 48c, a predetermined point on the waveguide 30 is changed to the waveguide 30. An operation was performed for each of the bump diameters on the vertical line.
The bump area S and the heat conduction path length L from the laser element 3 to the waveguide 30 via each bump are defined as Sa and La for the bump 48a, Sb and Lb for the bump 48b, and the bump 48c, respectively. For Sc and Lc, respectively.

FIG. 11 collectively shows the above-described conditions for a simple model calculated by the configuration of the present embodiment.
In the silicon substrate 10, each of the diameters 48 a, 48 b, and 48 c arranged in the direction perpendicular to the waveguide 30 from B to a predetermined point B of the waveguide 30, using the vicinity A of the center of the junction region of the laser element 3 as a heat source. Heat conduction paths La, Lb, and Lc passing through each bump are determined.
Here, assuming that the bump diameters of the bumps 48a, 48b, and 48c are Da, Db, and Dc, the relationship of Da <Db <Dc is established, and the length relationship of the heat conduction path lengths L is La <Lb <Lc. It has become.
Incidentally, in the conventional configuration, the diameters of the bumps are the same (Da = Db = Dc), but the heat conduction path lengths La, Lb, and Lc have the above-described short-and-long relationship as in the present embodiment. Yes.

The thermal resistance is calculated under these conditions, and compared with the conventional configuration.
First, the thermal resistance Ra from the laser element 3 to the waveguide 30 via the bump 48a is given by the following equation.

  Ra = (1 / λ) · (La / Sa) (1)

Here, λ is the thermal conductivity, and Sa is the cross-sectional area of the heat conduction path.
Similarly, the thermal resistances Rb and Rc of the path through the bumps 48b and 48c are given by the following equations, respectively.

Rb = (1 / λ) · (Lb / Sb) (2)
Rc = (1 / λ) · (Lc / Sc) (3)

  On the other hand, the thermal resistance in the conventional configuration is given as follows when the cross-sectional area of the heat conduction path is S because each bump diameter D is the same.

ra = (1 / λ) · (La / S) (4)
rb = (1 / λ) · (Lb / S) (5)
rc = (1 / λ) · (Lc / S) (6)

Next, the equation is modified in order to see the difference in thermal resistance between the configuration of the present embodiment and the conventional configuration.
Here, for simplification, the following replacement is performed.

Sb = S (7)
Sa = S−α (8)
Sc = S + α (9)

Equation (7) above assumes that the bump diameter Db is the same size as the bump diameter D of the conventional configuration, and the cross-sectional area Sb of the heat transfer path passing through the bump 48b is calculated by dividing the heat transfer path of the conventional configuration. The area S is replaced.
Further, the above formula (8) is expressed assuming that the bump diameter Da is smaller than the bump diameter Db by α, and the formula (9) is assumed assuming that the bump diameter Dc is larger than the bump diameter Db by α. is there.
Since the bump shape is substantially circular, the bump area is proportional to the square of the bump diameter. In addition, assuming that the cross-sectional area of the heat conduction path is almost proportional to the bump diameter, the size relationship of the bump diameter remains the same as the cross-sectional area of the heat conduction path, with the main purpose of obtaining a thermal resistance magnitude relationship with the conventional configuration. It was assumed that this was the case.

  Now, the total R of thermal resistance through the bumps 48a, 48b and 48c given by the above formulas (1) to (3) can be obtained from the following formula.

  R = 1 / (1 / Ra + 1 / Rb + 1 / Rc) (10)

By substituting the equations (1) to (3) into the equation (10) and replacing them with the equations (7) to (9), the following equation is obtained.
R = A (1 / (B + C)) (11)

  Here, A, B, and C were placed as follows.

A = LaLbLc / λ (12)
B = SLbLc + SLaLc + SLaLb (13)
C = αLb (−Lc + La) (14)

  Similarly, the total thermal resistance r of the conventional configuration is as follows.

  r = 1 / (1 / ra + 1 / rb + 1 / rc) (15)

Substituting the equations (4) to (6) into the equation (15) and placing A and B as in the equations (12) and (13), the following equation is obtained.
r = A (1 / B) (16)

Now, since the length relationship of each heat conduction path length L is La <Lb <Lc, from the above equation (14), C = αLb (−Lc + La) <0, and C may be a negative number. Recognize.
Therefore, the following relationship is established.

  A (1 / (B + C))> A (1 / B) (17)

Since the left side of the formula (17) is R and the right side is r, R> r, and it can be seen that the thermal resistance R according to the configuration of this example is larger than the thermal resistance r of the conventional configuration.
That is, heat is less likely to flow than in the conventional configuration, and the influence of heat generated by the laser element 3 is less likely to reach the waveguide 30 of the wavelength conversion element 20.
This is because the bump diameter near the center near the waveguide 30 is reduced, and the heat conduction path with a shorter distance from the laser element 3 serving as the heat source to the waveguide 30 becomes narrower, and heat is not easily transmitted. You can understand qualitatively.

In this way, by reducing the bump diameter near the center of the wavelength conversion element 20 and increasing the bump diameter near the outer end, the overall bump area remains unchanged and the bonding strength is maintained, compared to the conventional case. Since the heat resistance is increased, it becomes difficult for heat to be transmitted, and the heat generated by the laser element 3 is less affected by the temperature rise on the waveguide 30, so that the temperature characteristics of the wavelength conversion element 20 are improved and the wavelength conversion efficiency is increased. Therefore, a light source capable of obtaining a stable output with high efficiency even in continuous operation for a long time is realized.
This is a configuration that produces the excellent effect of eliminating the external factors affecting the performance of the wavelength conversion element 20 in combination with the reduction of the bending at the time of applying the load, as shown in the second embodiment. It represents that.

  In Example 3, the bump diameter is increased in the vicinity of the outer end portion of the wavelength conversion element 20. However, since the same effect is produced if the bump area per unit area is large, the bump pitch is set at both outer end portions of the wavelength conversion element 20. A narrowing configuration may be used.

  Further, in Example 3, the bumps arranged along the longitudinal direction of the wavelength conversion element 20 have the same diameter, but as in the previous example, the bump diameter near both ends in the longitudinal direction is increased. Alternatively, the micro bumps may be arranged so as to narrow the bump pitch. In that case, the effect of improving the temperature characteristics of the present embodiment and the effect of reducing the curvature of the optical element can be obtained together as described in the previous embodiment.

  Note that the configuration diagrams, process diagrams, and the like shown in the embodiments of the present invention are not limited thereto, and may be arbitrarily changed as long as they satisfy the gist of the present invention. In the embodiments, the optical element mounted on the silicon substrate has been described as a laser element and a wavelength conversion element. However, the present invention is not limited to this, and any optical element to be mounted is applicable.

  The optical module of the present invention can be widely used in various fields such as a laser projector, an illumination device using laser light, and optical tweezers as a short wavelength laser light source of blue, green and the like.

DESCRIPTION OF SYMBOLS 1 Optical module 3 Laser element 10 Silicon substrate 20 Wavelength conversion element 21 Au film 30 Optical waveguide 40, 41 Joint part 46, 47 Micro bump L1 Infrared light L2 Laser light

Claims (6)

In an optical module in which an optical element is mounted on a substrate,
The substrate has a joint portion of a micro bump structure made of a metal material,
The optical element is bonded to the bonding portion by surface activated bonding technology,
The micro-bumps of the joint are the micro-bumps located near both ends of the optical element and the micro-bumps located near the central part of the optical element.
An optical module having different bump areas per unit area.   2. The optical module according to claim 1, wherein a bump pitch of the micro bumps located near both ends of the optical element is narrow and a bump pitch of the micro bumps located near the center part of the optical element is wide. .   2. The optical module according to claim 1, wherein a bump diameter of the micro bump located near both ends of the optical element is large, and a bump diameter of the micro bump located near the center of the optical element is small. . In the manufacturing method of the optical module in which the optical element is mounted on the substrate,
A bonding portion forming step of forming a bonding portion of a microbump structure made of a metal material on the substrate;
An optical element bonding step of bonding the optical element to the bonding portion by a surface activated bonding technique;
With
In the bonding part forming step, the bonding is performed so that the micro bumps located near both ends of the optical element and the micro bumps located near the center part of the optical element have different bump areas per unit area. Forming an optical module.   The bonding portion forming step forms the bonding portion where the bump pitch of the micro bumps located near both ends of the optical element is narrow and the bump pitch of the micro bumps located near the central portion of the optical element is wide. The method of manufacturing an optical module according to claim 4. The bonding portion forming step forms the bonding portion where the bump diameter of the micro bump located near both ends of the optical element is large and the bump diameter of the micro bump located near the central portion of the optical element is small. The method of manufacturing an optical module according to claim 4.

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