JP7035377B2 - Semiconductor laser device - Google Patents

Description

The present invention relates to a semiconductor laser device including a submount substrate.

A semiconductor laser chip emits laser light and generates heat during operation. In general, since the output characteristics and reliability of a semiconductor laser chip are improved at low temperatures, it is important to efficiently dissipate the heat generated by the semiconductor laser chip. As the heat sink for heat dissipation, a member made of a high heat dissipation metal material (for example, Cu) is used. However, a heat sink made of a high heat dissipation metal material has a larger linear expansion coefficient than a semiconductor laser chip, so that it is difficult to directly bond the heat sink. Therefore, the semiconductor laser chip is bonded to a submount having a linear expansion coefficient intermediate between the heat sink and the semiconductor laser chip or a value close to that of the semiconductor laser chip, and the submount is bonded to the heat sink. Is common.
The submount substrate is configured by selecting an appropriate substance in consideration of the linear expansion coefficient and the thermal conductivity. Typically, AlN, SiC and the like are used. Patent Document 1 discloses that a single crystal SiC having good heat dissipation is used as a submount of a semiconductor laser device.

Japanese Unexamined Patent Publication No. 2014-225660

In recent years, it has been desired to increase the output of semiconductor laser devices, and it is desired to further improve the heat dissipation of submount substrates.
Therefore, it is an object of the present invention to provide a semiconductor laser device using a submount substrate having better heat dissipation.

In order to solve the above problems, one aspect of the semiconductor laser apparatus according to the present invention is a first crystal plane whose normal direction is the first crystal axis and a second crystal plane having a higher thermal conductivity than the first crystal axis. A single crystal conductive submount substrate having a crystal structure including a second crystal plane whose crystal axis is the normal direction, and a single crystal conductive submount substrate bonded to the first surface side of the submount substrate, having a rated output of 1 W or more. A semiconductor laser chip is provided, and the first crystal plane is inclined with respect to the first surface of the submount substrate, and the first conductive layer provided on the first surface side and the submount substrate are provided. An insulating film made of aluminum nitride that insulates between the second conductive layer provided on the second surface side is provided , and the thickness of the insulating film is 10 μm or less.
In this way, using a submount substrate composed of a material having anisotropy in thermal conductivity, the first crystal axis with respect to the normal direction of the first surface, which is the surface on the side to which the semiconductor laser chip is bonded. And the second crystal axis is uniformly tilted. As a result, for example, compared with the case where the normal direction of the first surface coincides with the direction of the first crystal axis and the angle formed by the normal direction of the first surface and the direction of the second crystal axis is 90 °. Therefore, the heat dissipation path (heat conduction path) generated by the semiconductor chip can be formed in a direction close to the normal direction of the first surface. That is, it is possible to further improve the heat dissipation in the normal direction of the first surface of the submount substrate by utilizing the crystal axis having high thermal conductivity. Therefore, the heat generated by the semiconductor laser chip bonded to the first surface side can be efficiently dissipated.

Further, in the above-mentioned semiconductor laser apparatus, the submount substrate may be made of any one of SiC, GaN and AlN single crystals. As described above, by using a material such as single crystal SiC, single crystal GaN, and single crystal AlN whose thermal conductivity has different anisotropy for each crystal orientation, the effect of improving the heat dissipation of the submount substrate is appropriately obtained. Obtainable.
Further, in the above-mentioned semiconductor laser apparatus, the first crystal plane may be the c-plane and the second crystal plane may be the a-plane. In this case, the submount substrate can be a submount substrate in which the c-plane is inclined with respect to the first surface, which is the surface on which the semiconductor laser chip is bonded.

Further, in the above-mentioned semiconductor laser apparatus, the angle formed by the first surface of the submount substrate and the first crystal plane may be 4 ° or more and 20 ° or less. This makes it possible to appropriately improve the heat dissipation of the submount substrate. It is considered that the heat dissipation can be maximized by using, for example, a submount substrate in which a SiC single crystal is grown in the direction of the second crystal plane, but such a submount substrate with good crystallinity has not been realized yet. Not available. Therefore, in a submount substrate in which a SiC single crystal is grown in the direction of the first crystal plane, it is realistic to set the angle formed by the first surface and the first crystal plane of the submount substrate in the above range as described above. be.

Further, in the above-mentioned semiconductor laser apparatus, the submount substrate has a second surface which is a surface to which the heat radiating portion is joined, and has a normal direction of the first surface and a normal direction of the second surface. May match. In this case, the semiconductor laser chip is bonded to one surface (the surface on the first surface side) of the submount substrate, and the heat sink is attached to the other surface (the surface on the second surface side) facing the one surface of the submount substrate. When the heat radiating portion such as the portion is joined, the thermal conductivity in the direction from the semiconductor laser chip to the heat sink portion can be improved. As a result, the heat generated by the semiconductor laser chip can be efficiently dissipated through the heat radiating portion such as the heat sink portion.

Further, in the above-mentioned semiconductor laser apparatus, the rated output of the semiconductor laser chip may be 1 W or more. In such a semiconductor laser chip having a large output, the need for heat dissipation is even higher. Therefore, there is a great merit in using the above-mentioned submount board for the submount.
Further, in the semiconductor laser apparatus, the number of micropipes per wafer of the submount substrate may be 30 pieces / cm ² or less. In this case, the submount substrate after being divided for the semiconductor laser chip can have no or almost no micropipes.

According to the present invention, it is possible to obtain a semiconductor laser device using a submount substrate having better heat dissipation.

It is a figure which shows the structural example of the semiconductor laser apparatus in this embodiment. It is a figure which shows the structure of a submount. It is a figure which shows the direction of the crystal axis of a submount substrate. It is a figure which shows the direction of the crystal axis of the submount substrate of the comparative example. It is a figure explaining the difference of the heat conduction path between this embodiment and a comparative example. It is a figure which shows the structure of the submount provided with an insulating film.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.
FIG. 1 is a diagram showing a configuration example of the semiconductor laser device 100 according to the present embodiment. The semiconductor laser device 100 includes a submount substrate 10, a semiconductor laser chip (hereinafter referred to as “LD chip”) 20, and a heat sink (base) 30.
The submount substrate 10 constitutes a submount on which the LD chip 20 is mounted. In the present embodiment, the case where the submount substrate 10 is a SiC substrate made of single crystal SiC will be described. The SiC substrate may be a conductive single crystal SiC substrate or an insulating single crystal SiC substrate. For example, a SiC substrate with an impurity content of 1 × 10 ¹⁴ / cm ³ or more is defined as a “conductive” SiC substrate, and a SiC substrate with an impurity content of less than 1 × 10 ¹⁴ / cm ³ is defined as “insulating”. Can be defined as a SiC substrate.

Although not shown in particular, the LD chip 20 includes a semiconductor layer. The semiconductor layer may have a structure in which at least a first conductive semiconductor layer, an active layer, and a second conductive semiconductor layer are laminated in this order on a substrate. For example, the substrate can be a substrate made of any of a GaAs-based material, an InP-based material, and a GaN-based material. The LD chip 20 is supplied with a predetermined injection current and emits a laser beam having a predetermined oscillation wavelength. Here, the rated output of the LD chip 20 can be 1 W or more. The oscillation wavelength of the laser beam emitted by the LD chip 20 is not particularly limited.

A submount on which the LD chip 20 is placed is joined to the heat sink portion 30. The heat sink portion 30 is provided in the vicinity of the central portion of the circular surface of the disk-shaped stem 41. For example, the submount is joined to the heat sink portion 30 so that the emission direction of the laser beam emitted from the LD chip 20 coincides with the direction perpendicular to the circular surface of the stem 41. Further, at this time, the submount may be joined to the heat sink portion 30 so that the light emitting point of the LD chip 20 is located at the center of the circular surface of the stem 41.
Further, the submount, the LD chip 20, and the heat sink portion 30 including the submount substrate 10 are covered with a cylindrical cap 42 together with peripheral lead pins and wires. The cap 42 is attached for the purpose of protecting the LD chip 20, the wire, and the like. A light extraction window 43 is provided in the opening formed in the central portion of the upper surface of the cap 42, and the laser light emitted from the LD chip 20 passes through the light extraction window 43 and is emitted to the outside of the stem 41. Will be done.
The heat sink portion 30 is made of a high heat dissipation metal material (for example, Cu), and the heat generated by the LD chip 20 at the time of light emission is transferred to the heat sink portion 30 via the submount including the submount substrate 10. It is transmitted and dissipated.

FIG. 2 is a diagram showing a configuration of a submount in the present embodiment. FIG. 2 shows a joint portion between the submount substrate 10, the LD chip 20, and the heat sink portion 30.
The submount substrate 10 has a first surface 11 and a second surface 12 facing the first surface 11. The first surface 11 and the second surface 12 are arranged so as to face each other in a direction perpendicular to the emission direction of the laser beam from the LD chip 20. Further, in the present embodiment, it is assumed that the normal directions of the first surface 11 and the second surface 12 are the same.

The first conductive layer 13 is provided on the first surface 11 of the submount substrate 10, and the second conductive layer 14 is provided on the second surface 12 of the submount substrate 10. Here, the first conductive layer 13 and the second conductive layer 14 can be made of any one or more substances of Ti, Ni, Pt, Mo, and Au, respectively. The LD chip 20 is bonded onto the first conductive layer 13 via the bonding layer 51. Further, the second conductive layer 14 is bonded to the heat sink portion 30 via the bonding layer 52. Here, the bonding layer 51 and the bonding layer 52 can be made of AuSn solder, respectively.

In the present embodiment, the thickness direction of the submount substrate 10 (vertical direction in FIG. 2) is uniformly inclined with respect to the crystal axis of the submount substrate 10. The submount substrate 10 is a crystal including a c-axis which is a first crystal axis and an a-axis (a1 axis, a2 axis, a3 axis) which is a second crystal axis having a higher thermal conductivity than the first crystal axis. Has a structure. Here, when the submount substrate 10 is composed of a single crystal SiC substrate, the thermal conductivity of the c-axis is 390 W / m · K, whereas the thermal conductivity of the a-axis is 490 W / m · K. be.

As shown in FIG. 3A, the submount substrate 10 in the present embodiment has a structure in which the first crystal plane (c plane) is inclined with respect to the first plane 11 of the submount substrate 10. Here, the plane having the first crystal axis (c-axis) in the normal direction is the first crystal plane (c-plane), and the plane having the second crystal axis (a-axis) in the normal direction is the second crystal plane (a). Face). Further, in the following description, the normal direction of the first surface 11 of the submount board 10 is referred to as "board normal direction". In the case of the submount substrate 10 using a single crystal SiC having a hexagonal crystal structure, as shown in FIG. 3B, the c-plane appearing perpendicular to the c-axis is the first surface of the submount substrate 10. And tilt. Note that FIG. 3B is an example in which the a-axis in FIG. 3A is the a3 axis. Here, the angle formed by the first plane 11 and the first crystal plane (c plane) can be, for example, 4 ° or more and 20 ° or less.

As described above, the single crystal of a specific substance has a different thermal conductivity depending on the crystal orientation (the thermal conductivity has anisotropy). For example, in the case of a SiC single crystal, as described above, the a-axis thermal conductivity is larger than the c-axis thermal conductivity, and the heat dissipation (thermal conductivity) in the a-axis direction is superior to that in the c-axis direction. Therefore, by inclining the c-plane of the submount substrate 10 uniformly with respect to the first surface 11, a component in the a-axis direction having high thermal conductivity can be imparted in the normal direction of the substrate. Therefore, the heat dissipation in the normal direction of the substrate can be improved as compared with the case where the c-plane of the submount substrate 10 and the first surface 11 are parallel (when the c-axis direction and the normal direction of the substrate match). can.

4 (a) and 4 (b) are views showing a submount substrate 10'as a comparative example. The submount substrate 10'has a structure in which the first surface 11 and the c surface of the submount substrate 10'are parallel to each other.
In this submount substrate 10', the conduction path of the heat generated by the LD chip 20 in the submount substrate 10'is higher in thermal conductivity than in the c-axis direction, as shown by arrow A in FIG. 5 (a). It becomes closer to the a-axis direction. That is, it becomes closer to the substrate surface direction.

On the other hand, the submount substrate 10 in the present embodiment has a structure in which the first crystal plane (c plane) is inclined with respect to the first plane 11. By inclining the c-plane of the submount substrate 10 with respect to the first surface 11 in this way, the conduction path of the heat generated by the LD chip 20 in the submount substrate 10 is shown by the arrow B in FIG. 5 (b). As shown in, it can be approached in the direction normal to the substrate.

In the semiconductor laser device 100 of the present embodiment, the normal direction of the first surface 11 on the side where the LD chip 20 is joined and the normal direction of the second surface 12 on the side where the heat sink portion 30 is joined are one. I am doing it. That is, the LD chip 20 and the heat sink portion 30 are arranged so as to face each other in the direction normal to the substrate. Therefore, the shortest heat conduction path from the LD chip 20 to the heat sink portion 30 is the path in the normal direction of the first surface 11 and the second surface 12, that is, the path in the normal direction of the substrate. Therefore, as shown in FIG. 5B, by bringing the heat conduction path generated by the LD chip 20 closer to the substrate normal direction, the heat dissipation property via the heat sink portion 30 can be improved.

As described above, in the submount substrate 10 of the present embodiment, in order to improve the heat dissipation of the heat from the LD chip 20 via the heat sink portion 30, the c-plane is set with respect to the first surface 11 which is the substrate surface. It has a structure that is intentionally tilted. As described above, by utilizing the fact that the thermal conductivity has anisotropy, it is possible to further improve the heat dissipation property of the submount substrate 10 in the substrate normal direction. As a result, the heat generated by the LD chip 20 at the time of light emission can be efficiently released to the heat sink portion 30 arranged to face the LD chip 20 in the normal direction of the substrate.
Further, in order to enhance the effect of improving heat dissipation in the substrate normal direction of the submount substrate 10, it is preferable that the angle formed by the first surface 11 and the first crystal plane (c surface) is 4 ° or more. Further, the closer the angle between the first plane 11 and the first crystal plane (c plane) direction is to 90 °, the more the substrate normal direction and the second crystal axis (any of a1 axis, a2 axis, and a3 axis). Since the angle formed by the above direction approaches 0 °, the effect of improving heat dissipation in the normal direction of the substrate is high, but due to manufacturing restrictions and the like, the directions of the first plane 11 and the first crystal plane (c plane). The angle between the two and may be 20 ° or less.

It is considered that the heat dissipation can be maximized by using a submount substrate in which a SiC single crystal is grown on the second crystal plane (a plane), but such a submount substrate with good crystallinity is still realized. In reality, high quality substrates are not available. Therefore, in the submount substrate in which the SiC single crystal is grown on the first crystal plane (c plane), the angle formed by the first plane 11 and the first crystal plane (c plane) of the submount substrate 10 is formed as described above. It is realistic to set the range to 4 ° or more and 20 ° or less.

Further, in order to increase the thermal conductivity of the submount substrate, it is preferable that the number of hollow pipe-shaped defects called micropipes is small. In the present embodiment, the number of micropipes per wafer of the submount substrate is 30 pieces / cm ² or less, 10 pieces / cm ² or less, preferably 5 pieces / cm ² or less, and more preferably 1 piece / cm ² . It is preferable that the micropipe is substantially zero (zero or substantially zero) in the submount for the semiconductor laser element after being divided for the semiconductor laser chip. As described above, by using the submount substrate having substantially zero micropipes, the thermal conductivity of the submount substrate can be effectively increased and the heat dissipation can be improved.

Further, when the single crystal SiC substrate constituting the submount substrate 10 is conductive, the first conductive layer 13 and the second conductive layer 14 are insulated in order to secure the insulating property of the submount substrate 10. It is preferable to provide an insulating film. The position where the insulating film is provided can be, for example, at least one of the first surface 11 and the second surface 12 of the submount substrate 10. This insulating film can be made of, for example, aluminum nitride (AlN). The material and film thickness of the insulating film can be set as appropriate. For example, the film thickness of the insulating film can be 0.2 μm or more and 10 μm or less.

FIG. 6 is a diagram showing a configuration of a submount when an insulating film 15a is provided on the first surface 11 of a submount substrate 10 which is a conductive single crystal SiC substrate.
As shown in FIG. 6, by providing the insulating film 15a on the first surface 11 of the submount substrate 10 (hereinafter referred to as “SiC substrate 10”), the surface of the SiC substrate 10 (the surface on the first surface 11 side) is provided. ) And the back surface (the surface on the second surface 12 side), respectively, it is possible to prevent a short circuit between the first conductive layer 13 and the second conductive layer 14. That is, although the SiC substrate 10 is a conductive substrate, the conductive member (first conductive layer 13, LD chip 20) to be bonded to the first surface 11 side of the SiC substrate 10 and the second of the SiC substrate 10. It is possible to appropriately insulate the conductive member (second conductive layer 14, heat insulating portion 30) to be joined to the surface 12 side.

When an insulating single crystal SiC substrate is used, since there are many micropipes, a conductive member such as a solder material easily enters the micropipes, and the insulating property of the single crystal SiC substrate tends to decrease. Therefore, in order to suppress this, there is a method of closing the micropipe with an insulating material, but such a step is complicated. On the other hand, if the insulating film 15a is provided on the first surface 11 of the SiC substrate 10 to ensure the insulating property, the complicated process of closing the micropipe with the insulating material as described above is unnecessary. be.
Further, since the content of the micropipe of the SiC substrate 10 is extremely small as described above, the electrode material does not enter the micropipe very much. Therefore, the film thickness of the insulating film 15a at the time of formation on the SiC substrate 10 is 4 μm. Sufficient insulation can be ensured if there are also the following. In this case, the time required to form the insulating film can be shortened, and the decrease in heat dissipation due to the formation of the insulating film 15a can be minimized. Therefore, the thickness of the insulating film 15a is particularly preferably 4 μm or less.

Further, since the SiC substrate 10 has no or almost no micropipes, the insulating film 15a is not embedded in the micropipes. Therefore, the surface of the insulating film 15a does not undulate due to the micropipe, and a polishing step for flattening the surface is unnecessary. Therefore, the manufacturing process of the submount substrate can be simplified.
As described above, in the conductive single crystal SiC substrate, it is possible to secure the insulating property while taking advantage of the advantages of excellent heat dissipation and low cost. Therefore, it is possible to obtain a semiconductor laser device 100 utilizing a single crystal SiC substrate that ensures good heat dissipation and insulation.
Further, the rated output of the LD chip 20 can be 1 W or more. Since the LD chip 20 having such a large output has a higher need for heat dissipation, there is a great merit in using the SiC substrate as in the present embodiment for the submount.

(Modification example)
In the above embodiment, the case where the submount substrate 10 is composed of a single crystal of SiC has been described, but any material having anisotropy in thermal conductivity may be used, and for example, a single crystal of GaN or AlN is used. You can also do it.
Further, in the above embodiment, the can type semiconductor laser device 100 has been described, but the semiconductor laser device to which the present invention is applicable is not limited to the can type.

100 ... semiconductor laser device, 10 ... SiC substrate, 11 ... first surface, 12 ... second surface, 13 ... first conductive layer, 14 ... second conductive layer, 20 ... semiconductor laser chip (LD chip), 30 ... heat sink Part, 51, 52 ... Bonding layer

Claims (7)

A single crystal structure having a first crystal plane whose normal direction is the first crystal axis and a second crystal plane whose normal direction is the second crystal axis having a higher thermal conductivity than the first crystal axis. With a crystalline conductive submount substrate,
A semiconductor laser chip having a rated output of 1 W or more, which is bonded to the first surface side of the submount substrate, is provided.
The first crystal plane is inclined with respect to the first surface of the submount substrate, and the first conductive layer provided on the first surface side and the second surface side of the submount substrate are provided. A semiconductor laser apparatus comprising an insulating film made of aluminum nitride that insulates between the second conductive layer and the insulating film, and the thickness of the insulating film is 10 μm or less . The semiconductor laser device according to claim 1, wherein the submount substrate is made of any one of SiC, GaN, and AlN single crystals. The semiconductor laser apparatus according to claim 1 or 2, wherein the first crystal plane is the c-plane and the second crystal plane is the a-plane. The semiconductor laser apparatus according to any one of claims 1 to 3, wherein the angle formed by the first surface of the submount substrate and the first crystal plane is 4 ° or more and 20 ° or less. The submount substrate has a second surface which is a surface to which the heat radiating portion is joined.
The semiconductor laser apparatus according to any one of claims 1 to 4, wherein the normal direction of the first surface and the normal direction of the second surface coincide with each other. The semiconductor laser device according to any one of claims 1 to 5, wherein the rated output of the semiconductor laser chip is 1 W or more. The semiconductor laser apparatus according to any one of claims 1 to 6, wherein the number of micropipes in a wafer unit of the submount substrate is 30 pieces / cm ² or less.

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