TWI517509B - Multi - beam semiconductor laser device - Google Patents

Description

Multi-beam semiconductor laser device

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

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

The semiconductor wafer forming the above-described laser diode is connected to a support substrate made of a material having good thermal conductivity (for example, AlN, SiC, CuW, etc.) called a susceptor which is disposed in a package through solder and an Au plating layer. on. In addition, in order to efficiently radiate heat generated when the laser diode emits light to the outside, a contact-down manner in which the pn junction serving as a heat generating source is fixed close to the susceptor is generally used (for example, patent document) 1).

[Previous Technical Literature] [Patent Literature]

Patent Document 1 Japanese Patent Laid-Open Publication No. 2011-108932

The semiconductor laser device having the contact-down type is formed by heat-dissipating and energizing the Au plating layer formed on the ridge portion of the upper portion of the light-emitting portion and the conductive solder formed on the susceptor electrode by fusion bonding.

In the case of a multi-beam semiconductor laser device, a plurality of light-emitting portions are provided in a semiconductor wafer, and each of the raised portions forms an electrode that is electrically insulated. Further, it is common to form a plurality of solders having a short-side planar pattern corresponding to the plurality of electrodes on the susceptor side and to be bonded to the susceptor.

However, in the case of the above-described method, the width of the Au plating layer which is a part of the electrode on the semiconductor wafer side is narrower than the width of the solder pattern on the base side by the narrow gap (for example, 30 μm to 50 μm) between the beams, and is fusion-bonded at the time of fusion bonding. The solder is partially concentrated to produce a solder ball. As a result, a short circuit between the solders is generated between the plurality of electrodes of the semiconductor wafer, and driving by the beam alone cannot be performed, which may cause a decrease in assembly yield.

In addition, multi-beam semiconductor laser devices require a small difference in characteristics between beams. However, when the semiconductor wafer and the susceptor are assembled, the multi-beam semiconductor laser device generates stress due to a reaction caused by a difference in thermal expansion coefficients between the Au electrode material on the semiconductor wafer side and the semiconductor material, the solder on the pedestal side, and the susceptor material. Since it is spread over the ridge, there is a problem that the polarization angle characteristics are poor.

The polarization angle characteristic is a characteristic of an angle of a polarization of light irradiated from the light-emitting portion, and the polarized wave is preferably vibrated in the plane along the principal surface of the semiconductor wafer. The irradiation of light in which the polarization surface is rotated obliquely with respect to the main surface of the semiconductor wafer causes deterioration in polarization characteristics. Further, when a semiconductor wafer having deteriorated polarization angle characteristics is used, when an optical component such as a lens is transmitted, a problem such as a reduction in the amount of light is generated. In the case of a multi-beam semiconductor laser device, it is a problem that the beam-to-beam difference is different between beams when the polarization angles are different.

It is an object of the present invention to suppress short-circuit defects between solders between beams of a multi-beam semiconductor laser device.

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

The above and other objects and novel features of the present invention will become apparent from the description and appended claims.

In the invention disclosed in the present application, a brief description of a more representative manner is as follows.

A multi-beam semiconductor laser device includes: a semiconductor wafer including three or more beams; and a support substrate on which the semiconductor wafer is mounted; wherein the semiconductor wafer has a first conductive type cladding layer formed on a semiconductor substrate The active layer is formed on the upper portion of the first conductive type coating layer; the second conductive type coating layer is formed on the upper portion of the active layer; and three or more raised portions each include the second portion a conductive coating layer and a second conductive type contact layer formed on the upper portion of the second conductive type coating layer; and a pair of grooves formed on the second conductive type coating layer on both sides of each of the raised portions; The electrode is electrically connected to each of the ridges so as to cover an upper portion of each of the ridges and an upper portion of the pair of grooves formed on both sides thereof; the first conductive layer is formed on the surface An upper portion of the electrode; the second conductive layer is formed on an upper portion of the first conductive layer, and has a smaller area than the first conductive layer; and the back surface electrode is formed on the semiconductor substrate a back surface; a first electrode having the same number as the raised portion on the wafer mounting surface of the support substrate; a solder formed on a surface of each of the first electrodes; and the semiconductor substrate is fused to the second conductive layer The solder is mounted on the wafer mounting surface of the support substrate; the second conductive layer is in contact with the solder on at least one of the pair of grooves formed on both sides of the raised portion; and along the raised portion The width of the second conductive layer in the array direction is narrower than the width of the solder.

The effects of the present invention are as follows.

In the invention disclosed in the present application, the effects obtained by the representative methods will be briefly described as follows.

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

It is possible to reduce the polarization between the beams of the multi-beam semiconductor laser device and the relative difference between the beams of the polarization angle.

10‧‧‧ Pedestal

11‧‧‧Laser Wafer

12‧‧‧GaAs substrate

13‧‧‧Back electrode

14‧‧‧passivation film

15‧‧‧ surface electrode

16‧‧‧1Au plating

17‧‧‧2Au plating

18‧‧‧ solder

20‧‧‧ Uplift

21‧‧‧ Groove

22‧‧‧n type cladding

23‧‧‧Active layer

24‧‧‧p type first cladding

25‧‧‧p type second cladding

26‧‧‧p type contact layer

27‧‧‧Base electrode

28‧‧‧Insulation

29‧‧‧identification mark

30‧‧‧ handle

31‧‧‧ Cover

32‧‧‧Flange

33‧‧‧ glass plate

34‧‧‧ round hole

35‧‧‧ Heat sink

36‧‧‧Au wire

37‧‧‧Au wire

38‧‧‧Au wire

39a‧‧‧Wire

39b‧‧‧Wire

39c‧‧‧Wire

39d‧‧‧Wire

39e‧‧‧Wire

39f‧‧‧Wire

40‧‧‧Photodiode wafer

1 is a partially cutaway perspective view showing an overall configuration of a multi-beam semiconductor laser device according to an embodiment of the present invention.

2 is a cross-sectional view showing the main parts of a multibeam semiconductor laser device according to an embodiment of the present invention.

Fig. 3(a) is a plan view showing a principal surface of the laser wafer, and Fig. 3(b) is a plan view showing a back surface of the laser wafer.

Fig. 4 is a cross-sectional view showing the main part of another example of the multibeam semiconductor laser device of the present invention.

Fig. 5 is a cross-sectional view showing the main part of still another example of the multibeam semiconductor laser device of the present invention.

Hereinafter, embodiments of the present invention will be described in detail based on the drawings. In the drawings, the same reference numerals will be given to the parts having the same functions, and the overlapping description will be omitted. In addition, in the embodiment, the same or the same portions are not repeatedly described in principle unless otherwise necessary. Further, in the drawings for explaining the embodiment, in order to make the structure easy to understand, a hatching may be also indicated in a plan view, and a cross-sectional view may be omitted.

(implementation type)

The present embodiment is applied to a 4-beam semiconductor laser device having a convex ridge portion, and FIG. 1 is a cross-sectional perspective view showing a main portion of the overall structure of the 4-beam semiconductor laser device.

The four-beam semiconductor laser device of the present embodiment has, for example, a disk-shaped shank 30 made of a Fe alloy having a diameter of about 5.6 mm and a thickness of about 1.0 mm, and a CAN package having a cover 31 covering the upper surface of the shank 30. (closed container) structure.

The flange portion 32 provided on the outer periphery of the bottom of the cover 31 is fixed to the upper surface of the shank 30. Further, a circular hole 34 into which a glass plate 33 for transmitting a laser beam is transmitted is provided at a central portion of the upper surface of the lid 31.

Installed near the central portion of the upper surface of the shank 30 covered by the cover 31 There is a heat sink 35 made of a metal having good thermal conductivity such as Cu. The heat sink 35 is joined to the upper surface of the shank 30 by solder (not shown), and the susceptor (support substrate) 10 is fixed to the surface by solder (not shown).

The susceptor 10 is made of a ceramic such as AlN, SiC or CuW, and a laser wafer (semiconductor wafer) 11 in which four laser diodes are formed is mounted on one surface thereof by a contact point. The susceptor 10 also serves as a heat dissipation plate for dissipating heat generated when the laser diode emits light to the outside of the laser wafer 11, and a substrate for supporting the laser wafer 11. The back surface electrode 13 which will be described later on the laser wafer 11 is electrically connected to the heat sink 35 through the Au wire 37.

The laser wafer 11 mounted on the susceptor 10 emits a laser beam from its both end faces (the upper end face and the lower end face in Fig. 1). Therefore, the susceptor 10 supporting the laser wafer 11 is fixed to the heat sink 35 with its wafer mounting surface facing in a direction perpendicular to the upper surface of the shank 30. The laser beam (front light) emitted from the upper end surface of the laser wafer 11 is emitted to the outside through the circular hole 34 of the cover 31. Further, the laser beam (rear light) emitted from the lower end surface of the laser wafer 11 is received by the photodiode wafer 40 mounted near the central portion of the upper surface of the shank 30, and is converted into a current.

Six wires 39a, 39b, 39c, 39d, 39e, 39f are attached to the lower surface of the handle 30. Among the six wires 39a to 39f, four wires 39a, 39b, 39e, and 39f are electrically connected to the base electrode 27 (described later) of the susceptor 10 through the Au wire 36, respectively. Further, the wire 39c of the remaining two wires 39c, 39d is fixed to the lower surface of the shank 30, and is electrically connected to the shank 30 in an equipotential state. In addition, the wire 39d is transmitted through The Au wire 38 is electrically connected to the photodiode wafer 40.

Fig. 2 is a cross-sectional view showing a principal part of a four-beam semiconductor laser device according to the present embodiment, wherein Fig. 3(a) is a plan view showing a principal surface of the laser wafer 11, and Fig. 3(b) is a plan view showing a back surface of the laser wafer 11. .

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

The p-type second cladding layer 25 has a convex cross-sectional shape, and forms four ridges (protrusion types) 20 that extend in parallel with each other. The four ridges 20 correspond to one laser diode, respectively. FIG. 2 shows two ridges 20 of the four ridges 20.

Further, a p-type contact layer 26 is formed on the upper portion of each of the p-type second cladding layers 25 constituting the raised portion 20. That is, the raised 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 ridge portions 20 is a groove 21, and a passivation film 14 made of ruthenium oxide is formed on both side portions and the bottom portion of the groove 21.

A p-type surface electrode 15 ohmically connected to the 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. In addition, a first Au plating layer (first conductive layer) 16 for heat dissipation is formed on the upper surface of the surface electrode 15, and a second Au plating layer (second conductive layer) having a smaller area than the first Au plating layer 16 is formed on a part of the upper surface of the first Au plating layer 16 Layer) 17. On the other hand, an n-type rear surface electrode 13 is formed on the back surface of the GaAs substrate 12. Each of the surface electrode 15 and the back surface electrode 13 is configured by, for example, a multilayer metal film in which a Pt film and an Au film are sequentially laminated on a Ti film.

When the laser wafer 11 configured as described above injects a predetermined current into the front surface electrode 15 and the back surface electrode 13, the active layer 23 (light emitting portion) in the lower portion of each of the four raised portions 20 has, for example, an oscillation wavelength of 650 nm. The red laser beam oscillates. These red laser beams are emitted from both end faces of the laser wafer 11 orthogonal to the extending direction of the ridge portion 20, and the front light is emitted to the outside of the CAN package through the circular hole 34 of the cover 31 shown in Fig. 1 described above.

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

Further, a solder 18 made of, for example, an Au-Sn alloy is formed on the surface of each of the four base electrodes 27. In addition, in order to prevent short circuits of the pedestal electrodes 27, the susceptor electrodes 27 and the susceptor 10 are An insulating layer 28 composed of ruthenium oxide or the like is formed therebetween.

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 wafer 11 and the susceptor electrode 27 of the susceptor 10 are electrically connected to the second Au plating layer 17 via the fusion bonding solder 18. Further, when the laser wafer 11 is mounted on the susceptor 10 by the contact point downward, the identification mark 29 on the back surface of the laser wafer 11 shown in FIG. 3(b) and the laser (not shown) are provided on the laser. The same identification marks on the surface of the wafer 11 are aligned.

In the conventional conventional multi-beam semiconductor laser device, 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 formed on the surface of the susceptor electrode 27. Therefore, when the solder is melt-bonded to the Au plating layer, the solder balls are locally concentrated by the solder, and a solder short circuit occurs between the laser diodes.

On the other hand, in the four-beam semiconductor laser device of the present embodiment, as shown in FIG. 2, the width of the second Au plating layer 17 formed on the upper surface of the surface electrode 15 is larger than the solder 18 formed on the surface of the susceptor electrode 27. The width of the structure is narrow.

Thereby, the excess solder generated at the time of fusion bonding is pushed out to the outside of the laser wafer 11, and the width of the solder 18 is wide and is absorbed as a whole, so that it is difficult to generate a solder ball. Therefore, it is possible to effectively suppress the solder short circuit between the laser diodes. Further, in order to reliably suppress the solder short circuit between the laser diodes, the ratio of the width of the second Au plating layer 17 to the width of the solder 18 (the width of the second Au plating layer 17 or the width of the solder 18) is 0.7 or less. good.

Further, when the ratio of the width of the second Au plating layer 17 to the width of the solder 18 is too small, that is, when the ratio of the width of the second Au plating layer 17 is too small, the connection strength between the laser wafer 11 and the susceptor 10 may be caused ( The shear strength is lowered and the heat dissipation is lowered. Therefore, it is preferable that the ratio of the width of the second Au plating layer 17 to the width of the solder 18 is 0.5 or more.

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

Therefore, it is difficult for the stress generated during the assembly of the laser wafer 11 and the susceptor 10 to reach the ridge portion 20, so that it is possible to reduce the polarization angle rotation and the polarization angle between the beams due to the stress at the time of assembly. Relatively poor.

Further, when the number of the laser diodes formed in the laser wafer 11 is an even number as in the four-beam semiconductor laser device of the present embodiment, it is used as a line with respect to the center of the plurality of laser diodes. By arranging the joint position of the second Au plating layer 17 and the solder 18 in a symmetrical manner, the relative difference between the beam rotation angle and the polarization angle of the polarization angle can be further reduced. In other words, 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, as shown in FIG. 2, the upper portion of the groove 21 located on the right side of each of the ridges 20 is provided. The second Au plating layer 17 is brought into contact with the solder 18 on the left side of the center of the four laser diodes, for example, as shown in FIG. As shown in the upper portion of the recess 21 on the left side of each of the raised portions 20, the second Au plating layer 17 is brought into contact with the solder 18.

The invention made by the inventors of the present invention has been specifically described above, but the present invention is not limited to the embodiments described above, and various modifications can be made without departing from the spirit and scope of the invention.

For example, when there is vacancy in the space of the adjacent laser diodes (the ridges 20), as shown in FIG. 5, in the upper portions of the grooves 21 formed on both sides of the ridges 20, The second Au plating layer 17 is brought into contact with the solder 18.

Further, in the foregoing embodiment, the present invention is applied to a 4-beam semiconductor laser device, but can of course be applied to a multi-beam semiconductor laser device such as a 2-beam semiconductor laser device or an 8-beam semiconductor laser device.

The present invention can be applied to a multi-beam semiconductor laser device employing a contact-down approach.

10‧‧‧ Pedestal

11‧‧‧Laser Wafer

12‧‧‧GaAs substrate

13‧‧‧Back electrode

14‧‧‧passivation film

15‧‧‧ surface electrode

16‧‧‧1Au plating

17‧‧‧2Au plating

18‧‧‧ solder

20‧‧‧ Uplift

21‧‧‧ Groove

22‧‧‧n type cladding

23‧‧‧Active layer

24‧‧‧p type first cladding

25‧‧‧p type second cladding

26‧‧‧p type contact layer

27‧‧‧Base electrode

28‧‧‧Insulation

Claims (7)

A multi-beam semiconductor laser device includes: a semiconductor wafer including three or more beams; and a support substrate on which the semiconductor wafer is mounted; wherein the semiconductor wafer has a first conductive type cladding layer formed on a semiconductor substrate The active layer is formed on the upper portion of the first conductive type coating layer; the second conductive type coating layer is formed on the upper portion of the active layer; and three or more raised portions each include the second portion a conductive coating layer and a second conductive type contact layer formed on the upper portion of the second conductive type coating layer; and a pair of grooves formed on the second conductive type coating layer on both sides of each of the raised portions; The electrode is electrically connected to each of the ridges so as to cover an upper portion of each of the ridges and an upper portion of the pair of grooves formed on both sides thereof; the first conductive layer is formed on the surface An upper portion of the electrode; the second conductive layer is formed on an upper portion of the first conductive layer, and has a smaller area than the first conductive layer; and the back surface electrode is formed on the semiconductor substrate a back surface; a first electrode having the same number as the raised portion on the wafer mounting surface of the support substrate; and a solder formed on a surface of each of the first electrodes; The semiconductor substrate is mounted on the wafer mounting surface of the support substrate by fusion bonding the second conductive layer and the solder, and the second conductive layer is formed on the pair of grooves formed on both sides of the raised portion. At least one of the upper portions is in contact with the solder; and the width of the second conductive layer along the direction in which the raised portions are arranged is narrower than the width of the solder. The multibeam semiconductor laser device of claim 1, wherein a ratio of a width of the second conductive layer to a width of the solder is 0.7 or less. The multibeam semiconductor laser device of claim 1, wherein a ratio of a width of the second conductive layer to a width of the solder is 0.5 or more. The multi-beam semiconductor laser device of claim 1, wherein the number of the beams is an even number, and the second conductive layer is in contact with the solder on an upper portion of the pair of grooves formed on both sides of the raised portion . The multiple beam semiconductor laser device of claim 1, wherein the number of the beams is an even number, and the raised portion and the second conductive layer are arranged in line symmetry with respect to a center of the even number of the beams. The multibeam semiconductor laser device according to claim 1, wherein the first and second conductive layers are made of Au, and the solder is formed of an Au-Sn alloy. The multi-beam semiconductor laser device of claim 1, wherein the semiconductor wafer is formed on the front surface and the back surface of the semiconductor wafer An identification mark for alignment when the body wafer is mounted on the aforementioned support substrate.