JP2001185800A - Optical module - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an optical module for solving the problem that the active region of an element is made adjacent to a bonding member such as soldering, and a function such as the element is damaged when an optical semiconductor element is flip chip mounted by a simple constitution, and for higher precisely and hardly fixing the optical semiconductor element. SOLUTION: An optical semiconductor element 11 and an optical waveguide body 15 to be optically coupled with the optical semiconductor element 11 are arranged on a substrate 12, and at least either the substrate 12 or the optical semiconductor element 11 is provided with at least one recessed part 18 for leading adhesive 14 for bonding the both of them so that an optical module can be constituted.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical module used for optical fiber communication, and more particularly to an optical module having an optical semiconductor element such as a light emitting semiconductor element such as a semiconductor laser and a light receiving semiconductor element such as a photodiode. is there.

[0002]

2. Description of the Related Art In recent years, plans for introducing optical subscriber systems in optical fiber communication have been advanced. An optical module used for such an optical fiber communication optically couples (optically couples) a minute light emitting semiconductor element or a light receiving semiconductor element with an optical fiber. In the optical module on the transmitting side, the light emitted from the light emitting semiconductor element driven by modulation is coupled to the transmission optical fiber, and the optical signal transmitted in the optical fiber is converted into an electric signal by the light receiving semiconductor element of the optical module on the transmitting side. You.

The optical fiber and each optical semiconductor element used here are required to be aligned on the order of μm. 2. Description of the Related Art Conventionally, a technique called active alignment is used for positioning a light emitting semiconductor element for optical communication and an optical fiber. Active alignment is a method of driving a light-emitting semiconductor element, changing the position of the optical fiber to be aligned, monitoring the amount of light incident on the optical fiber, and fixing the optical fiber in the best coupling state. Therefore, it was difficult to mass produce.

As shown in FIG. 5, for example, an optical fiber 42 is fixed on a V-shaped groove 43 on a mount 41 serving as a support base. The optical semiconductor element 44 is precisely positioned with respect to the V groove 43 on the mount 41 using a marker 45 or the like, and is flip-chip mounted on an electrode pad 46 on the mount 41 using solder or the like.

[0005] According to this method, the relative positions of the marker 45 and the electrode pad 46 can be accurately formed by photolithography of the V-shaped groove 43. The optical axes of the optical semiconductor element 44 and the optical fiber 42 are automatically aligned with the pattern accuracy of the electrode pads 46. This eliminates the need for driving the optical semiconductor device, grasping the optical coupling rate, and adjusting the relative position between the optical fiber and the optical semiconductor device by feedback, etc., so that submicron mounting can be performed in a short time. Becomes possible. Such a technique that does not drive the optical semiconductor element is called a passive alignment technique.

As shown in FIGS. 6 and 7, an optical semiconductor element used in an optical module is a minute element having a length and width of about 100 μm and a thickness of about 100 μm. The active region 51 of the optical semiconductor element is precisely formed at a depth 52 of several μm from one side. It is necessary to precisely design the height of the active region, that is, the height from the mounting surface of the optical semiconductor to be passively mounted. Therefore, in the passive alignment mounting, the electrode 55 formed on the active region surface 54 of the optical semiconductor element is connected to the bonding material 5 such as solder.
6, the active area surface 5 of the optical semiconductor element is mounted on the mount 53.
Normally, mounting is performed in a face-down manner as shown in FIG.

[0007]

However, the method of mounting the optical semiconductor device face down on a mount by passive alignment technology as described above has the following disadvantages. When the optical semiconductor device is flip-chip mounted, as shown in FIG.
Will come close to the bonding material 56 such as solder. As a result, as shown in FIG. 8, a bonding material 56 such as solder adheres so as to electrically bypass the active region 51 of the element and becomes inoperable, or adheres to the emission end 58 of the optical waveguide 57 of the optical semiconductor element. For example, there is a possibility that the function as an element cannot be achieved.

In order to solve these problems, a method as shown in FIG. 9 has been proposed (for example, see Japanese Patent Application Laid-Open No. H11-38244). In this proposal, a projection 73 is provided on the active region 72 side of the optical semiconductor element 71.
Is formed. Electrode 7 formed on the surface of protrusion 73
5 and the bonding material 76 such as solder, the optical semiconductor element 71 is mounted face down on the mount 74,
Since the distance between the active region 72 and the solder joint can be made constant, the above-described problem is less likely to occur.

However, in order to use such a method, it is necessary to make the height of the projection 73 greater than the thickness of the solder, and it is generally necessary to make a step of about several μm to 10 μm. Further, in the production process of the optical semiconductor element, it is necessary to grow and form a new projection of about 10 μm after the production of a normal optical semiconductor element. As disclosed in Japanese Unexamined Patent Publication No. Hei 11-38244, it is necessary to control the sub-μm, and it takes a lot of time to manufacture. Although the above method can prevent the bonding material such as solder from adhering to the waveguide end surface 77 of the optical semiconductor element, the bonding material such as solder is applied to the active region as shown in FIG. There is a risk of adhesion.

Accordingly, an object of the present invention is to provide an optical module capable of solving such a problem with a simple configuration and fixing an optical semiconductor element with high accuracy and rigidity.

[0011]

An optical module according to the present invention comprises an optical semiconductor device and an optical waveguide for optically coupling to the optical semiconductor device on a substrate, and at least one of the substrate and the optical semiconductor device. On the other hand, one or more recesses for drawing in an adhesive for joining the two are provided.

In particular, the present invention is characterized in that a plurality of recesses are formed, and the recesses comprise shallow and deep recesses.
In addition, a plurality of recesses are formed and are arranged substantially symmetrically with respect to the optical axis of the optical waveguide.

According to the optical module having the above configuration, when the adhesive such as solder is heated and melted at the joint surface between the optical semiconductor element and the substrate, the solder moves so as to collect in the concave portion formed at the boundary surface.

The reason for the above configuration will be described below. When mounting an optical semiconductor device on a substrate, in order to prevent oxidation of a metal such as solder in particular, it is customary to blow outside air with a gas that blocks oxygen such as N2.
The temperature of the outer peripheral portions of the optical semiconductor element and the substrate is lower than that of the inside of the element. On the other hand, the part where the optical semiconductor and the substrate are bonded is kept at a high temperature because it is separated from the outside air. The solder that has been heated and melted at the time of mounting has a low viscosity, so it will try to flow out,
Cools and solidifies when exposed to outside air. Adhesive material such as molten solder is supplied to the solidified portion from the surroundings, and is applied to the previously solidified portion and gradually grows into a large mass. Since this mass occurs around the optical semiconductor,
As described above, this results in attachment to the side surface of the optical semiconductor device so as to bypass the optical semiconductor active region.

However, in the present invention, there is a concave portion at the interface between the optical semiconductor element and the substrate, and since the interface is not exposed to the outside air, the concave portion functions as a solder pool in which the temperature is kept high. That is, since there is an adhesive such as high-temperature solder in the concave portion, the temperature of the adhesive such as solder around the concave portion also rises, and the adhesive gathers so as to be drawn into the high-temperature concave portion. By reducing the amount of adhesive such as solder flowing out to the outside,
It is possible to eliminate the above-mentioned problem caused by the adhesion to the side surface of the optical semiconductor element.

Further, by using a silicon substrate as the substrate in the present invention, it is possible to use an anisotropic etching technique capable of performing precision processing in forming the concave portion, so that the depth and shape of the concave portion can be more precisely determined. Can be controlled.

Further, by controlling the depth, shape, quantity and the like of the concave portions formed in the present invention, it is possible to design the distribution of the adhesive such as solder in the plane. Since the collecting force of the adhesive such as solder changes as the shape of the concave portion changes, the amount of the adhesive such as solder can be adjusted without a joint surface. For example, depending on the shape of the optical semiconductor element, when there is less adhesive around the element,
By arranging a shallow and small concave portion in the center of the element and a deep and large concave portion in the outer periphery of the element, a quantitative arrangement of the adhesive in the element surface, which has been impossible in the past, is designed.

[0018]

Embodiments of the present invention will be described below in detail with reference to the drawings.

As shown in FIG. 1A, a semiconductor laser element 11 as an optical semiconductor element is bonded to an electrode 13 formed on a substrate 12 as a silicon platform by solder (Au--Sn alloy solder or lead) as an adhesive. (For example, alloy solder) or a conductive adhesive using resin. Hereinafter, a case where solder is used as the adhesive will be described. In the figure, reference numeral 15 denotes an optical fiber as an optical waveguide, which is fixed on a V-groove 16 formed on the substrate 12 by an adhesive or the like.
Instead of the optical fiber, an optical waveguide formed by directly diffusing a metal or the like into the substrate may be applied.

As shown in FIG. 1B, the semiconductor laser device 11 has a linear concave portion 18 (50 μm × 50 μm to 100 μm × 100 μm, depth: 10 to 30 μm) on the mounting surface 17 of the device. However, on both sides of the active layer of the semiconductor laser element 11, a depression 19 called a mesa (width:
(About 10 microns, depth: about several microns). That is, the concave portion 18 is arranged substantially symmetrically with respect to the optical axis of the optical fiber 15, whereby the semiconductor laser element 11 is accurately arranged on the substrate 12. Here, the depression 19
In general, there is a function of concentrating a current applied to a semiconductor laser device on an active layer portion on an optical waveguide. The electrode 1 is provided on the mounting surface on which the concave portion 18 is formed.
Although the electrode 10 is formed, the electrode 110 is formed up to the inside of the recess 18 so that the solder can flow into the recess 18.

FIG. 1C is a cross-sectional view taken along the line AA ′ of FIG. 1A, showing a state in which such a semiconductor laser device 11 is mounted. In FIG. 1C, the solder 14 on the substrate 12 is moved by heating so as to gather at the location of the concave portion 18 formed on the lower surface side of the semiconductor laser element 11. The direction of movement of the solder is indicated by arrows 111 and 113 in FIG.
12 will be suppressed as much as possible.

If the recess 18 is not provided, the solder may concentrate on the recess 19 of the semiconductor laser device described above for the same reason.
By forming 8, the movement of the solder moves in the direction of arrow 113. When the solder concentrates on the depression 19 of the mesa portion, the solder flows to the semiconductor laser waveguide end 114, so that the solder may adhere to the end 114 and stop functioning as a light emitting semiconductor element. By collecting the solder at 118, it is possible to prevent the solder from flowing out to 114, so that the function of the semiconductor laser is not impaired. Here, the recesses 118 are formed one on each side of the mesa, but this is not always optimal.

As another example, as shown in FIG.
By arranging a large number of grooves having different depths and areas such as the grooves 22 and the grooves 23, it is possible to perform better solder fixing.

That is, the method of collecting the solder tends to be able to collect a larger amount of solder as the groove is larger, so that the groove 21 is a small groove, the groove 22 is a large groove, and the groove 23 is a large groove.
Are arranged as small grooves, so that the solder can be collected at an intermediate point between the mesa portion of the semiconductor laser and the periphery of the element. Although not shown, by forming a similar groove shape distribution in a direction parallel to the optical waveguide, it becomes possible to prevent solder from adhering to the end face of the waveguide.

FIG. 3 is a perspective view showing a second embodiment of the present invention, in which a concave portion formed on the joint surface between the semiconductor laser element 11 and the substrate 12 is provided on the substrate 12 side. As shown in FIG. 3, the substrate 12 on which the semiconductor laser element 31 is mounted
A concave portion 32 is formed on the surface on which the semiconductor laser element 11 is mounted. Further, an electrode 33 is formed on the recess 32. Forming the recess 32 on the substrate 12 side is easier and more effective than forming the recess in the semiconductor laser device body.

The recess 32 is formed in the mesa 3 of the semiconductor laser device 11.
1 is formed in a direction perpendicular to the direction. As shown in FIG. 1, when forming a groove on the semiconductor laser element 11 side, the mesa 3 of the semiconductor laser element 11 indicated by 18 in FIG.
Although it is not possible to form a concave portion in a direction transverse to 1, the concave portion 33 formed on the substrate 12 side can provide a concave portion that is long in a direction perpendicular to the mesa of the semiconductor laser device.

The substrate 12 is formed by using anisotropic etching technology and it is easy to precisely control the width of the groove to be formed. It has the merit that it can be embedded. Also in this embodiment, by arranging concave shapes of various sizes similarly to the first embodiment, it becomes possible to design the arrangement of the solder.

Further, as shown in FIG.
By forming the concave portion 81 on the lower surface of the chip 1 in a direction perpendicular to the depression 19, the end is stopped inside the chip. Conventionally, the solder gathered in the dent 19 flows down the dent and flows in the direction of the end face 82 to adhere to the end face 82, thereby hindering the output of light. To the side surface, and adhesion to the end face 82 can be prevented as much as possible.

Although a surface-mount type optical module using a light emitting semiconductor laser element as an optical semiconductor element will be described, the present invention can be easily applied to a case where a light receiving element such as a photodiode is used as an optical semiconductor element. It is.

[0030]

As described in detail above, according to the present invention,
At least one of the substrate and the optical semiconductor element is provided with one or more recesses for drawing in an adhesive for bonding the two, so that the flow of the adhesive at the time of mounting is controlled, so that the flip chip of the optical semiconductor element is provided. At the time of mounting, the adhesion of the adhesive to the side surface of the element or the end surface of the waveguide can be suppressed as much as possible, and the distribution of the adhesive within the mounting surface can be optimally controlled.

Further, by controlling the adhesive distribution, it is possible to solve the problems such as insufficient fixing strength due to a decrease in the amount of adhesive around the element due to the inclination of the element, which existed conventionally, and the reliability was improved. Optical module with high performance. This effect is particularly remarkable when the recess is formed substantially symmetrically with respect to the optical axis of the optical waveguide.

Further, when the substrate used for flip-chip connection or the optical semiconductor element is made of a material that can be anisotropically etched, the concave portion can be formed easily and with high precision.

[Brief description of the drawings]

FIGS. 1A to 1C are diagrams schematically illustrating an embodiment of an optical module according to the present invention, in which FIG. 1A is a perspective view, and FIG. 1B is a bottom view of an optical semiconductor element. FIG. 2C is a cross-sectional view at a location where the optical semiconductor element is provided.

FIG. 2 is a perspective view schematically illustrating a state of a lower surface side of another optical semiconductor element according to the present invention.

FIG. 3 is an exploded perspective view schematically illustrating another embodiment of the optical module according to the present invention.

FIG. 4 is a perspective view schematically illustrating a state of a lower surface side of another optical semiconductor element according to the present invention.

FIG. 5 is a perspective view schematically illustrating passive alignment mounting.

FIG. 6 is a perspective view schematically illustrating the structure of a general optical semiconductor element.

FIG. 7 is a cross-sectional view schematically illustrating an example of a failure state when the optical semiconductor element is mounted.

FIG. 8 is a cross-sectional view schematically illustrating another example of a failure state when the optical semiconductor element is mounted.

FIG. 9 is a cross-sectional view schematically illustrating another example of a failure state when the optical semiconductor element is mounted.

[Explanation of symbols]

 11: Optical semiconductor element (semiconductor laser element) 12: Substrate 14: Adhesive (solder) 15: Optical waveguide (optical fiber) 18: Concave section 21, 22, 23: Groove (concave section) 32, 81: Concave section

Claims (4)

[Claims] An optical module in which an optical semiconductor element and an optical waveguide that is optically coupled to the optical semiconductor element are disposed on a substrate, wherein at least one of the substrate and the optical semiconductor element includes: An optical module, wherein one or more concave portions for drawing in an adhesive for joining the two are provided. 2. The optical module according to claim 1, wherein a plurality of the concave portions are formed, and the optical module includes a shallow concave portion and a deep concave portion. 3. The optical module according to claim 1, wherein a plurality of the concave portions are formed and arranged substantially symmetrically with respect to an optical axis of the optical waveguide. 4. The optical module according to claim 1, wherein the substrate or the optical semiconductor element is formed of a material that can be anisotropically etched.