JP2017126784A - Multi-beam semiconductor laser device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent short-circuit defect between solder materials between beams of a multi-beam semiconductor laser device.SOLUTION: Surface electrodes 15 of a laser chip 11 and submount electrodes 27 of a submount 10 are electrically connected by welding connection between solder materials 18 and second Au plating layers 17. The second Au plating layers 17 are in contact with the solder materials 18 above one of a pair of concave grooves 21 formed on a p-type second cladding layer 25 of both sides of ridge portions 20, and width of the second Au plating layers 17 is narrower than width of the solder materials 18, so that the ridge portions 20 are not planarly overlapped with the solder materials 18, thereby having a structure providing a space between the ridge portions 20 and the submount 10.SELECTED DRAWING: Figure 2

Description

  The present invention relates to a multi-beam semiconductor laser device, and more particularly to a semiconductor laser device in which a semiconductor chip on which a plurality of laser diodes are formed is mounted on a support substrate by junction down.

  A laser diode (LD) used as a light source of an optical communication system or a light source of an information processing device is provided with a stripe-shaped active layer in a semiconductor chip, and upper and lower semiconductor layers sandwiching the active layer. One of these is a first conductivity type (n-type) semiconductor layer and the other is a second conductivity type (p-type) semiconductor layer to form a pn junction. Various structures such as a ridge structure are employed to form a resonator (optical waveguide) for laser oscillation.

  The semiconductor chip on which the laser diode as described above is formed is composed of a solder material and Au plating on a support substrate made of a material with good thermal conductivity called a submount (for example, AlN, SiC, CuW, etc.) disposed in a package. Connected through layers. Further, in order to efficiently dissipate the heat generated when the laser diode emits light to the outside, a junction down method is often employed in which the pn junction that is a heat generation source is fixed in the state of being close to the submount (for example, Patent Document 1).

JP 2011-108932 A

  A semiconductor laser device adopting a junction down method melt-bonds an Au plating layer formed on a ridge portion located above a light emitting portion and a conductive solder material formed on an electrode of a submount. Therefore, heat dissipation and energization are performed.

  In the case of a multi-beam semiconductor laser device, a plurality of light emitting portions are provided in a semiconductor chip, and each ridge portion is formed with an electrode that is electrically isolated from each other. A plurality of solder materials having strip-like planar patterns corresponding to the plurality of electrodes are formed on the submount side, and a method of joining to the submount is common.

  However, when the above method is adopted, the distance between the beams is narrow (for example, 30 μm to 50 μm), and the width of the Au plating layer that is a part of the electrode on the semiconductor chip side is the solder material pattern on the submount side. When the width is larger than the width of the solder, the solder concentrates locally at the time of fusion bonding, and solder balls are generated. As a result, a short circuit between the solder materials may occur between the plurality of electrodes of the semiconductor chip, which makes it impossible to drive the beam alone, which may cause a decrease in assembly yield.

  In addition, the multi-beam semiconductor laser device is required to have a small characteristic difference between the beams. However, the multi-beam semiconductor laser device is caused by a difference in thermal expansion coefficient between the Au electrode material and the semiconductor material on the semiconductor chip side and the solder material and the submount material on the submount side when the semiconductor chip and the submount are assembled. There is a problem that a polarization angle characteristic defect occurs due to the stress generated by the reaction reaching the ridge portion.

  The polarization angle characteristic refers to the characteristic of the angle of polarization of light emitted from the light emitting section, and this polarization preferably vibrates in a plane along the main surface of the semiconductor chip. Irradiation with light whose polarization plane is inclined with respect to the main surface of the semiconductor chip deteriorates the polarization angle characteristic. When a semiconductor chip having a deteriorated polarization angle characteristic is used, there arises a problem that the amount of light decreases when passing through an optical component such as a lens. In the case of a multi-beam semiconductor laser device, if the polarization angle is different between the beams, a difference between the beams is generated, which is a particular problem.

  An object of the present invention is to suppress short-circuit defects between solder materials between beams of a multi-beam semiconductor laser device.

  Another object of the present invention is to reduce polarization angle rotation between beams of a multi-beam semiconductor laser device and a relative difference between polarization angles.

  The above and other objects and novel features of the present invention will be apparent from the description of this specification and the accompanying drawings.

  Of the inventions disclosed in the present application, the outline of typical ones will be briefly described as follows.

A semiconductor chip with an even number of beams of four or more;
A support substrate on which the semiconductor chip is mounted;
A multi-beam semiconductor laser device comprising:
The semiconductor chip is
A first conductivity type cladding layer formed on the main surface of the semiconductor substrate;
An active layer formed on the first conductivity type cladding layer;
A second conductivity type cladding layer formed on the active layer;
4 pieces having a convex cross-sectional shape each including the second conductivity type cladding layer and a second conductivity type contact layer formed thereon, and arranged so that the distance between the beams is 30 μm to 50 μm An even number of ridges, and
A surface electrode electrically connected to each of the ridge portions and formed to cover the top of each of the ridge portions;
A first conductive layer formed on the surface electrode;
A second conductive layer formed in a region above the first conductive layer and excluding the top of the ridge portion, and having a smaller area than the first conductive layer;
A back electrode formed on the back surface of the semiconductor substrate,
The surface electrode, the first conductive layer, and the second conductive layer are formed in the same number as the ridge portions, respectively.
The same number of first electrodes as the ridge portions are formed on the chip mounting surface of the support substrate,
A solder material is formed on each surface of the first electrode,
The semiconductor substrate is mounted on the chip mounting surface of the support substrate by melting and bonding the second conductive layer and the solder material,
The second conductive layer is in contact with the solder material at one upper portion on both sides of the ridge portion,
The same number of joint portions as the number of the ridge portions between the second conductive layer and the solder material are disposed outside the center of the even number of the beams,
The width of the second conductive layer along the arrangement direction of the ridge portions is narrower than the width of the solder material.

  The effects obtained by typical ones of the inventions disclosed in the present application will be briefly described as follows.

  It is possible to suppress short-circuit defects between solder materials between beams of the multi-beam semiconductor laser device.

  The polarization angle rotation between the beams of the multi-beam semiconductor laser device and the relative difference between the beams of the polarization angle can be reduced.

1 is a fragmentary perspective view showing an overall configuration of a multi-beam semiconductor laser device according to an embodiment of the present invention. It is principal part sectional drawing of the multi-beam semiconductor laser apparatus which is embodiment of this invention. (A) is a top view which shows the main surface of a laser chip, (b) is a top view which shows the back surface of a laser chip. It is principal part sectional drawing which shows another example of the multi-beam semiconductor laser apparatus of this invention.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. Note that components having the same function are denoted by the same reference symbols throughout the drawings for describing the embodiments, and the repetitive description thereof will be omitted. In the embodiments, the description of the same or similar parts will not be repeated in principle unless particularly necessary. Furthermore, in the drawings for describing the embodiments, hatching may be applied even in a plan view or hatching may be omitted even in a cross-sectional view for easy understanding of the configuration.

(Embodiment)
The present embodiment is applied to a four-beam semiconductor laser device having a convex ridge portion, and FIG. 1 is a fragmentary perspective view showing the entire configuration of the four-beam semiconductor laser device.

  The four-beam semiconductor laser device of the present embodiment includes a disk-shaped stem 30 made of an Fe alloy having a diameter of about 5.6 mm and a thickness of about 1.0 mm, and a cap 31 that covers the upper surface of the stem 30. It has a CAN package (sealing container) structure.

  A flange portion 32 provided on the outer periphery of the bottom portion of the cap 31 is fixed to the upper surface of the stem 30. In addition, a circular hole 34 is provided at the center of the upper surface of the cap 31 to which a glass plate 33 that transmits a laser beam is bonded.

  Near the center of the upper surface of the stem 30 covered with the cap 31, a heat sink 35 made of a metal having good thermal conductivity such as Cu is mounted. The heat sink 35 is joined to the upper surface of the stem 30 via a brazing material (not shown), and a submount (support substrate) 10 is fixed to the one surface via solder (not shown). Yes.

  The submount 10 is made of ceramic such as AlN, SiC, or CuW, and a laser chip (semiconductor chip) 11 in which four laser diodes are formed is mounted on one surface thereof by a junction down method. The submount 10 serves both as a heat radiating plate for radiating heat generated when the laser diode emits light to the outside of the laser chip 11 and a substrate for supporting the laser chip 11. A back surface electrode 13 to be described later of the laser chip 11 is electrically connected to the heat sink 35 through an Au wire 37.

  The laser chip 11 mounted on the submount 10 emits a laser beam from both end faces (upper end face and lower end face in FIG. 1). Therefore, the submount 10 that supports the laser chip 11 is fixed to the heat sink 35 so that the chip mounting surface faces a direction perpendicular to the upper surface of the stem 30. The laser beam (front light) emitted from the upper end surface of the laser chip 11 is emitted to the outside through the round hole 34 of the cap 31. Further, the laser beam (back light) emitted from the lower end surface of the laser chip 11 is received by the photodiode chip 40 mounted in the vicinity of the center portion of the upper surface of the stem 30 and converted into a current.

  Six leads 39a, 39b, 39c, 39d, 39e, and 39f are attached to the lower surface of the stem 30. Of these six leads 39a to 39f, the four leads 39a, 39b, 39e, and 39f are electrically connected to a submount electrode 27 (described later) of the submount 10 through Au wires 36, respectively. Of the remaining two leads 39 c and 39 d, the lead 39 c is fixed to the lower surface of the stem 30 and is in an electrically equipotential state with respect to the stem 30. The lead 39d is electrically connected to the photodiode chip 40 via the Au wire 38.

  2 is a cross-sectional view of the main part of the four-beam semiconductor laser device of the present embodiment, FIG. 3A is a plan view showing the main surface of the laser chip 11, and FIG. FIG.

  As shown in FIG. 2, a plurality of semiconductor layers are stacked on the main surface of the GaAs substrate 12. The semiconductor layer is composed of, for example, an n-type cladding layer 22, an active layer 23, a p-type first cladding layer 24, a p-type second cladding layer 25, and a p-type contact layer 26 deposited by metal organic chemical vapor deposition (MOCVD). Become. Of these semiconductor layers, the n-type cladding layer 22 is made of AlGaInP. The active layer 23 has a multi quantum well (MQW) structure in which barrier layers made of AlGaInP and well layers made of GaInP layers are alternately stacked. The p-type first cladding layer 24 and the p-type second cladding layer 25 are each made of AlGaInP, and the p-type contact layer 26 is made of GaAs.

  The p-type second cladding layer 25 is formed with four ridges (mesa stripes) 20 having a convex cross-sectional shape and extending parallel to each other. Each of the four ridge portions 20 corresponds to one laser diode. FIG. 2 shows two ridge portions 20 out of the four ridge portions 20.

  A p-type contact layer 26 is formed on each of the p-type second cladding layers 25 constituting the ridge portion 20. That is, the ridge portion 20 has a two-layer structure of the p-type second cladding layer 25 and the p-type contact layer 26.

  The p-type second cladding layer 25 on both sides of each of the four ridges 20 is a concave groove 21, and a passivation film 14 made of silicon oxide is formed on both sides and the bottom of the concave groove 21. ing.

  A p-type surface electrode 15 ohmically connected to the p-type contact layer 26 is formed on the upper surface of the p-type contact layer 26 and the upper surface of the passivation film 14. Further, a first Au plated layer (first conductive layer) 16 for heat dissipation is formed on the upper surface of the surface electrode 15, and a part of the upper surface of the first Au plated layer 16 is more than the first Au plated layer 16. A second Au plating layer (second conductive layer) 17 having a small area is formed. On the other hand, an n-type back electrode 13 is formed on the back surface of the GaAs substrate 12. Each of the front surface electrode 15 and the back surface electrode 13 is composed of, for example, a multilayer metal film in which a Pt film and an Au film are sequentially laminated on a Ti film.

  In the laser chip 11 configured as described above, when a predetermined current is injected into the front surface electrode 15 and the back surface electrode 13, the active layer 23 (light emitting portion) below each of the four ridge portions 20 For example, a red laser beam having an oscillation wavelength of 650 nm oscillates. These red laser beams are emitted from both end faces of the laser chip 11 orthogonal to the extending direction of the ridge portion 20, and the forward light is emitted to the outside of the CAN package through the round holes 34 of the cap 31 shown in FIG. The

  On the other hand, on the chip mounting surface of the submount 10, for example, four submount electrodes (first electrodes) 27 made of a multilayer metal film in which a Pt film and an Au film are sequentially laminated on a Ti film are formed. These submount electrodes 27 are disposed so as to face the ridge portion 20 of the laser chip 11 when the laser chip 11 is mounted on the submount 10.

  Further, a solder material 18 made of, for example, an Au—Sn alloy is formed on the surface of each of the four submount electrodes 27. Further, an insulating layer 28 made of silicon oxide or the like is formed between the submount electrode 27 and the submount 10 in order to prevent a short circuit between the submount electrodes 27.

  In the case of the four-beam semiconductor laser device of the present embodiment configured as described above, the surface electrode 15 of the laser chip 11 and the submount electrode 27 of the submount 10 melt the solder material 18 and the second Au plating layer 17. It is electrically connected by joining. When the laser chip 11 is mounted on the submount 10 by the junction down method, the recognition mark 29 on the back surface of the laser chip 11 shown in FIG. 3B and the surface of the laser chip 11 are not shown. Both of them are aligned using the same recognition mark provided in the above.

  The conventional general multi-beam semiconductor laser device has a structure in which the width of the Au plating layer formed on the upper surface of the surface electrode 15 is wider than the width of the solder material formed on the surface of the submount electrode 27. . For this reason, when the solder material and the Au plating layer are melt-bonded, the solder material is locally concentrated and solder balls are generated, so that a solder short may occur between the laser diodes.

  In contrast, in the four-beam semiconductor laser device of the present embodiment, the width of the second Au plating layer 17 formed on the upper surface of the surface electrode 15 is formed on the surface of the submount electrode 27 as shown in FIG. The structure is narrower than the width of the solder material 18 formed.

  As a result, excess solder generated at the time of fusion bonding is pushed out of the laser chip 11, but is absorbed as a whole by the wide width of the solder material 18, so that solder balls are hardly generated. Therefore, a solder short between the laser diodes can be effectively suppressed. In order to reliably suppress solder shorts between laser diodes, the ratio of the width of the second Au plating layer 17 to the width of the solder material 18 (the width of the second Au plating layer 17 / the width of the solder material 18) is set to 0. .7 or less is preferable.

  Further, when the ratio of the width of the second Au plating layer 17 to the width of the solder material 18 becomes too small, that is, when the ratio of the width of the second Au plating layer 17 becomes too small, the space between the laser chip 11 and the submount 10. There is a risk that the connection strength (shearing strength) of the steel will be reduced and the heat dissipation will be reduced. Therefore, the ratio of the width of the second Au plating layer 17 to the width of the solder material 18 is preferably 0.5 or more.

  Further, in the four-beam semiconductor laser device of the present embodiment, as shown in FIG. 2, the second Au plating layer 17 formed on the upper surface of the surface electrode 15 has the p-type second cladding layer 25 on both sides of the ridge portion 20. The solder material 18 is in contact with the upper part of one of the pair of concave grooves 21 formed in. In other words, the ridge portion 20 and the solder material 18 do not overlap in a plan view, and have a structure in which there is a gap between the ridge portion 20 and the submount 10.

  This makes it difficult for the stress generated during assembly of the laser chip 11 and the submount 10 to reach the ridge portion 20, thereby reducing the polarization angle rotation and the relative difference between the beams of the polarization angle due to the stress during assembly, which has been a problem in the past. It becomes possible to do.

  When the number of laser diodes formed on the laser chip 11 is an even number as in the four-beam semiconductor laser device of the present embodiment, the bonding position between the second Au plating layer 17 and the solder material 18 is determined. By arranging them so as to be line symmetric with respect to the centers of the plurality of laser diodes, it becomes possible to further reduce the polarization angle rotation and the relative difference between the beams of the polarization angle. That is, in the case of the four-beam semiconductor laser device of the present embodiment, on the right side of the center of the four laser diodes, for example, on the upper part of the concave groove 21 positioned on the right side of each ridge portion 20 as shown in FIG. When the second Au plating layer 17 and the solder material 18 are brought into contact with each other, on the left side of the center of the four laser diodes, for example, as shown in FIG. The plating layer 17 and the solder material 18 are brought into contact with each other.

  As mentioned above, the invention made by the present inventor has been specifically described based on the embodiment. However, the present invention is not limited to the embodiment, and various modifications can be made without departing from the scope of the invention. Needless to say.

  In the above embodiment, the present invention is applied to a four-beam semiconductor laser device, but it is needless to say that the present invention can be applied to a multi-beam semiconductor laser device such as a two-beam semiconductor laser device or an eight-beam semiconductor laser device.

  The present invention can be used in a multi-beam semiconductor laser device that employs a junction down system.

10 Submount (support substrate)
11 Laser chip (semiconductor chip)
12 GaAs substrate 13 Back electrode 14 Passivation film 15 Front electrode 16 First Au plating layer (first conductive layer)
17 Second Au plating layer (second conductive layer)
18 Solder material 20 Ridge part (mesa stripe)
21 concave groove 22 n-type cladding layer 23 active layer 24 p-type first cladding layer 25 p-type second cladding layer 26 p-type contact layer 27 submount electrode (first electrode)
28 Insulating layer 29 Recognition mark 30 Stem 31 Cap 32 Flange portion 33 Glass plate 34 Round hole 35 Heat sink 36, 37, 38 Au wire 39a, 39b, 39c, 39d, 39e, 39f Lead 40 Photodiode chip

Claims (3)

A semiconductor chip with an even number of beams of four or more;
A support substrate on which the semiconductor chip is mounted;
A multi-beam semiconductor laser device comprising:
The semiconductor chip is
A first conductivity type cladding layer formed on the main surface of the semiconductor substrate;
An active layer formed on the first conductivity type cladding layer;
A second conductivity type cladding layer formed on the active layer;
4 pieces having a convex cross-sectional shape each including the second conductivity type cladding layer and a second conductivity type contact layer formed thereon, and arranged so that the distance between the beams is 30 μm to 50 μm An even number of ridges, and
A surface electrode electrically connected to each of the ridge portions and formed to cover the top of each of the ridge portions;
A first conductive layer formed on the surface electrode;
A second conductive layer formed in a region above the first conductive layer and excluding the top of the ridge portion, and having a smaller area than the first conductive layer;
A back electrode formed on the back surface of the semiconductor substrate,
The surface electrode, the first conductive layer, and the second conductive layer are formed in the same number as the ridge portions, respectively.
The same number of first electrodes as the ridge portions are formed on the chip mounting surface of the support substrate,
A solder material is formed on each surface of the first electrode,
The semiconductor substrate is mounted on the chip mounting surface of the support substrate by melting and bonding the second conductive layer and the solder material,
The second conductive layer is in contact with the solder material at one upper portion on both sides of the ridge portion,
The same number of joint portions as the number of the ridge portions between the second conductive layer and the solder material are disposed outside the center of the even number of the beams,
The multi-beam semiconductor laser device according to claim 1, wherein a width of the second conductive layer along the arrangement direction of the ridge portions is narrower than a width of the solder material.   2. The multi-beam semiconductor laser device according to claim 1, wherein a ratio of a width of the second conductive layer to a width of the solder material is 0.7 or less.   3. The multi-beam semiconductor laser device according to claim 1, wherein a ratio of a width of the second conductive layer to a width of the solder material is 0.5 or more.

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