Patent Application
20230122494
The present disclosure relates to a method of manufacturing a semiconductor laser element, the semiconductor laser element, and a semiconductor laser device including the semiconductor laser element.
Semiconductor laser elements, which have advantages such as long life, high efficiency, and small size, are used as light sources for various applications, including image display devices such as projectors, and their applications are expanding to, for example, automotive headlamps and light sources for laser processing devices.
In recent years, semiconductor laser elements have been required to be further high-powered. For example, semiconductor laser elements used as light sources for laser processing devices are required to have high optical output power exceeding 1 watt.
In such cases, if a high-output laser beam is emitted from a single emitter (light emitter), the optical density at the front end surface from which the laser beam is emitted becomes too high, which could result in catastrophic optical damage (COD) on the front end surface.
In view of the above, there has been proposed a semiconductor laser element which has a multi-emitter structure in which a plurality of emitters are integrated to allow a single semiconductor laser element to emit a high-output laser beam (for example, Patent Literature (PTL) 1). This type of semiconductor laser element is configured as, for example, a laser bar including a plurality of waveguides.
PTL 1: Japanese Unexamined Patent Application Publication No. 2007-073669
A semiconductor laser element including a plurality of waveguides is formed by dividing a substrate (wafer) on which a semiconductor stacking structure made of, for example, a semiconductor material such as a nitride-based semiconductor material is formed. In this case, by laser scribing, grooves for division are formed on the substrate on which the semiconductor stacking structure is formed, and the substrate is divided into a plurality of pieces by cutting and cleaving the substrate using these grooves for division.
At this time, the substrate and the semiconductor material such as a nitride crystal are melted by laser scribing and a spatter is thereby generated, so processing waste called “debris” is deposited in and around the regions in which the laser scribing has been performed.
However, the grooves for division and the debris remaining in a mounting region of the semiconductor laser element cause such defects as follows when mounting the semiconductor laser element on, for example, a submount. The defects include, for example, that the semiconductor laser element is tilted and cannot be mounted in a predetermined orientation, and that the properties of the semiconductor laser element degrade.
The basic structure of a semiconductor laser element, such as waveguides and a semiconductor stacking structure, is usually formed on the front surface side (for example, the p-side) of the substrate. On the other hand, only electrodes (for example, n-electrodes) are formed on the back surface side of the substrate. The patterning of the electrodes on the back surface side is performed by mask alignment to the shape on the front surface side (for example, the p-electrode pattern). Therefore, a misalignment occurs between the basic structure of the semiconductor laser element on the front surface side and the electrode pattern on the back surface side within the mask alignment accuracy. As will be described later, the end surface of a laser resonator produced by cleavage is desired to be formed according to the basic structure of the semiconductor laser element as accurately as possible. Therefore, it is better for the laser scribing necessary for cleavage to be performed according to the pattern on the front surface side rather than the pattern on the back surface side having a mask misalignment.
In the case of junction-down mounting (face-down mounting) the semiconductor laser element on, for example, a submount with the p-side surface of the semiconductor laser element serving as the mounting surface, the defects as described above occur during mounting if the grooves for division or debris are present in the mounting region on the p-side surface of the semiconductor laser element as a result of the laser scribing performed on the p-side surface of the semiconductor laser element. However, in order to accurately produce the resonator according to the basic structure of the semiconductor laser element, laser scribing is desired on the p-side surface. Therefore, there is a conflict between the requirements of the mounting process and the requirements of the chip processing.
The present disclosure has been conceived to solve such a problem, and has an object to provide, for example, a method of manufacturing a semiconductor laser element that can inhibit the occurrence of defects when the semiconductor laser element is mounted on, for example, a submount.
In order to achieve the above object, a method of manufacturing a semiconductor laser element according to an aspect of the present disclosure is a method of manufacturing a semiconductor laser element that includes a plurality of waveguides, the method including: first dividing a substrate in a first direction parallel to a first main surface of the substrate to produce a plurality of divided substrates each including a plurality of waveguides spaced apart in a second direction orthogonal to the first direction and parallel to the first main surface, the substrate being a substrate on which a nitride-based semiconductor laser stacking structure is formed, the nitride-based semiconductor laser stacking structure including a plurality of waveguides each extending in the first direction; cleaving, in the second direction, one divided substrate included in the plurality of divided substrates produced by the first dividing, to produce a plurality of semiconductor laser elements each including a plurality of waveguides; and second dividing, in the first direction, one semiconductor laser element included in the plurality of semiconductor laser elements produced by the cleaving, to remove at least one end portion of the one semiconductor laser element in the second direction, wherein the cleaving includes: forming a cleavage lead-in groove on the one divided substrate, the cleavage lead-in groove extending in the second direction; and cleaving the one divided substrate in the second direction using the cleavage lead-in groove, and in the second dividing, a portion including the cleavage lead-in groove is removed as the at least one end portion of the one semiconductor laser element in the second direction.
In addition, a method of manufacturing a semiconductor laser element according to another aspect of the present disclosure is a method of manufacturing a semiconductor laser element that includes a plurality of waveguides, the method including: first dividing a substrate in a first direction parallel to a first main surface of the substrate to produce a plurality of divided substrates each including a plurality of waveguides spaced apart in a second direction orthogonal to the first direction and parallel to the first main surface, the substrate being a substrate on which a nitride-based semiconductor laser stacking structure is formed, the nitride-based semiconductor laser stacking structure including a plurality of waveguides each extending in the first direction; and cleaving, in the second direction orthogonal to the first direction and parallel to the first main surface, one divided substrate included in the plurality of divided substrates produced by the first dividing, to produce a plurality of semiconductor laser elements each including a plurality of waveguides, wherein each of the plurality of semiconductor laser elements includes a first side surface parallel to the first direction and a second side surface on an opposite side relative to the first side surface, and in the semiconductor laser element, a second distance is greater than a first distance which is a shortest distance among distances between two adjacent waveguides included in the plurality of waveguides, the second distance being a distance between the first side surface and one waveguide located closest to the first side surface among the plurality of waveguides.
In addition, a semiconductor laser element according to an aspect of the present disclosure is a semiconductor laser element including: a substrate including a first main surface and a second main surface on an opposite side relative to the first main surface; a nitride-based semiconductor laser stacking structure provided above the first main surface of the substrate and including a plurality of waveguides extending in a first direction parallel to the first main surface; a first side surface orthogonal to the first main surface and parallel to the first direction, a second side surface on an opposite side relative to the first side surface, and a third side surface orthogonal to the first main surface and orthogonal to the first direction; a first region in which waveguides included in the plurality of waveguides are formed and a second region that is interposed between the first region and the first side surface; and a stepped portion provided on the first side surface, the stepped portion being recessed inwardly from a surface of the semiconductor laser element on a second main surface side when the semiconductor laser element is viewed in the first direction.
In addition, a semiconductor laser element according to another aspect of the present disclosure is a semiconductor laser element including: a substrate including a first main surface and a second main surface on an opposite side relative to the first main surface; a nitride-based semiconductor laser stacking structure provided above the first main surface of the substrate and including a plurality of waveguides extending in a first direction parallel to the first main surface; a first side surface orthogonal to the first main surface and parallel to the first direction, a second side surface on an opposite side relative to the first side surface, and a third side surface orthogonal to the first main surface and orthogonal to the first direction; and a first region in which waveguides included in the plurality of waveguides are formed and a second region that is interposed between the first region and the first side surface, wherein a second distance is greater than a first distance which is a shortest distance among distances between two adjacent waveguides included in the plurality of waveguides, the second distance being a distance between the first side surface and one waveguide located closest to the first side surface among the plurality of waveguides.
In addition, a semiconductor laser device according to an aspect of the present disclosure includes any one of the semiconductor laser elements described above and a submount on which the semiconductor laser element is mounted, and the semiconductor laser element is mounted on the submount with a surface of the semiconductor laser element on a first main surface side facing the submount.
According to the present disclosure, it is possible to inhibit occurrence of defects when a semiconductor laser element is mounted on, for example, a submount.
These and other advantages and features will become apparent from the following description thereof taken in conjunction with the accompanying Drawings, by way of non-limiting examples of embodiments disclosed herein.
Hereinafter, an embodiment of the present disclosure will be described with reference to the drawings. Note that the embodiment described below illustrates a specific example of the present disclosure. Thus, the numerical values, shapes, materials, constituent elements, the arrangement and connection of the constituent elements, steps (processes), the processing order of the steps, etc., illustrated in the following embodiment are mere examples, and are not intended to limit the present disclosure.
Note also that the drawings are represented schematically and are not necessarily precise illustrations. Thus, the scales of the drawings, for example, are not necessarily precise. In the drawings, essentially the same constituent elements are given the same reference signs, and duplicate descriptions thereof are omitted or simplified.
In the present specification and the drawings, the X axis, Y axis, and Z axis represent the three axes of a three-dimensional orthogonal coordinate system. In the present embodiment, the Z axis direction represents the vertical direction, and the direction perpendicular to the Z axis (direction parallel to the XY plane) represents the horizontal direction. The X axis and Y axis are orthogonal to each other, and are both orthogonal to the Z axis. In the present embodiment, the Y axis direction is a first direction, and the X axis direction is a second direction. The Y axis direction, which is the first direction, and the X axis direction, which is the second direction, are in-plane directions of substrate 10. That is to say, the Y axis direction, which is the first direction, and the X axis direction, which is the second direction, are parallel to first main surface 11 and second main surface 12 of substrate 10. Also, the direction in which waveguides 21 of semiconductor laser element 1 extend (the direction of the laser resonator length) is the Y axis direction. Note that the directions of arrows of the X axis, Y axis, and Z axis are their respective positive directions.
First, a configuration of semiconductor laser element 1 manufactured by a method of manufacturing semiconductor laser element 1 according to the present embodiment will be described with reference to
Note that in
Semiconductor laser element 1 according to the present embodiment is a semiconductor laser having a multi-emitter structure in which a plurality of emitters are integrated in a single element. Semiconductor laser element 1 emits a plurality of laser beams. Specifically, semiconductor laser element 1 is a nitride-based semiconductor laser made of a nitride-based semiconductor material, and emits, for example, blue laser beams.
As illustrated in
Substrate 10 includes first main surface 11 and second main surface 12. Second main surface 12 is a surface on an opposite side relative to first main surface 11, and faces away from first main surface 11. In the present embodiment, first main surface 11 is the p-side surface, which is the front surface, and second main surface 12 is the n-side surface, which is the back surface.
For example, a semiconductor substrate such as a nitride semiconductor substrate is used as substrate 10. In the present embodiment, a hexagonal n-type GaN substrate is used as substrate 10.
Nitride-based semiconductor laser stacking structure 20 is a nitride semiconductor layer stacking body in which a plurality of nitride semiconductor layers each made of a nitride-based semiconductor material are stacked. Nitride-based semiconductor laser stacking structure 20 is formed above first main surface 11 of substrate 10. For example, nitride-based semiconductor laser stacking structure 20 has a configuration formed by sequentially stacking, on first main surface 11 of substrate 10, an n-type cladding layer made of n-type AlGaN, an active layer made of undoped InGaN, a p-type cladding layer made of p-type AlGaN, and a p-type contact layer made of p-type GaN.
Note that, in addition to these nitride semiconductor layers, nitride-based semiconductor laser stacking structure 20 may include other nitride semiconductor layers such as an optical guide layer and an overflow inhibition layer. Also, an insulating film having openings at positions corresponding to waveguides 21 may be formed on the surface of nitride-based semiconductor laser stacking structure 20.
Nitride-based semiconductor laser stacking structure 20 includes a plurality of waveguides 21 each extending in the Y axis direction (the first direction parallel to first main surface 11) in the plane of substrate 10. The plurality of waveguides 21 are spaced apart in the X axis direction (the direction orthogonal to the first direction and parallel to first main surface 11). Specifically, the plurality of waveguides 21 are parallel to each other and formed at a predetermined pitch in the X axis direction.
Each of the plurality of waveguides 21 functions as a current injection region and an optical waveguide in semiconductor laser element 1. The plurality of waveguides 21 correspond one-to-one with a plurality of emitters that emit laser beams. The plurality of waveguides 21 are formed in, for example, the p-type cladding layer of nitride-based semiconductor laser stacking structure 20. As an example, the plurality of waveguides 21 have a ridge stripe structure and are formed as a plurality of ridge portions in the p-type cladding layer. In this case, the p-type contact layer may be a plurality of semiconductor layers formed individually on each of the plurality of ridge portions, or may be a single semiconductor layer formed continuously to cover the plurality of ridge portions.
P-side electrodes 30 are formed on nitride-based semiconductor laser stacking structure 20. P-side electrodes 30 each include, for example, Pd, Pt, and Au. P-side electrodes 30 are formed on, for example, the p-type contact layer of nitride-based semiconductor laser stacking structure 20. As illustrated in part (a) of
N-side electrodes 40 are formed on second main surface 12 of substrate 10. N-side electrodes 40 each include, for example, Ti, Pt, and Au. As illustrated in part (b) of
As illustrated in parts (a) through (c) of
First side surface 1a is one end surface in the long-side direction of semiconductor laser element 1, and second side surface 1b is the other end surface in the long-side direction of semiconductor laser element 1. In other words, second side surface 1b is a surface on an opposite side relative to first side surface 1a, and faces away from first side surface 1a. The long-side direction of semiconductor laser element 1 is the X axis direction that is orthogonal to the long-side direction of waveguides 21.
In the present embodiment, first side surface 1a and second side surface 1b are surfaces orthogonal to first main surface 11 of substrate 10 and parallel to the Y axis direction (the first direction). Specifically, first side surface 1a and second side surface 1b are surfaces parallel to the YZ plane.
Third side surface 1c is one end surface in the short-side direction of semiconductor laser element 1, and fourth side surface 1d is the other end surface in the short-side direction of semiconductor laser element 1. In other words, fourth side surface 1d is a surface on an opposite side relative to third side surface 1c, and faces away from third side surface 1c. The short-side direction of semiconductor laser element 1 is the Y axis direction that is parallel to waveguides 21.
In the present embodiment, third side surface 1c and fourth side surface 1d are surfaces orthogonal to first main surface 11 of substrate 10 and orthogonal to the Y axis direction (the first direction). In other words, third side surface 1c and fourth side surface 1d are surfaces parallel to the X axis direction (the second direction). Specifically, third side surface 1c and fourth side surface 1d are surfaces parallel to the XZ plane and perpendicular to first side surface 1a and second side surface 1b.
In the present embodiment, third side surface 1c and fourth side surface 1d are resonator end surfaces of semiconductor laser element 1. Specifically, third side surface 1c is the front end surface of semiconductor laser element 1. In other words, the laser beams are emitted from third side surface 1c. Fourth side surface 1d is the rear end surface of semiconductor laser element 1. Although not illustrated in the diagram, third side surface 1c and fourth side surface 1d are coated with an end surface coating film as a reflective film.
Although the details will be described later, first side surface 1a, second side surface 1b, third side surface 1c, and fourth side surface 1d are division surfaces at the time of producing semiconductor laser element 1 from a wafer. Specifically, first side surface 1a and second side surface 1b are division surfaces at the time of division in the Y axis direction, and third side surface 1c and fourth side surface 1d are division surfaces at the time of division in the X axis direction. Note that third side surface 1c and fourth side surface 1d are cleavage surfaces formed by cleavage. Therefore, the flatness of third side surface 1c is greater than the flatness of each of first side surface 1a and second side surface 1b. Likewise, the flatness of fourth side surface 1d is greater than the flatness of each of first side surface 1a and second side surface 1b. This allows light to resonate efficiently in waveguides 21 between third side surface 1c and fourth side surface 1d, and laser beams can be thereby obtained.
When semiconductor laser element 1 is viewed in the X axis direction, stepped portion 50 which is recessed inwardly from a surface of semiconductor laser element 1 on the second main surface 12 side is formed on first side surface 1a. Likewise, stepped portion 50 which is recessed inwardly from the surface of semiconductor laser element 1 on the second main surface 12 side is formed on second side surface 1b as well. In other words, stepped portion 50 is formed to be depressed into the positive direction of the Z axis direction from the surface of semiconductor laser element 1 on the second main surface 12 side, that is, the back surface of semiconductor laser element 1.
As illustrated in
As illustrated in part (b) of
As illustrated in
In the present embodiment, in second region 120 and third region 130, p-side electrodes 30 and n-side electrodes 40 are formed but waveguides 21 are not formed. Therefore, second region 120 and third region 130 are regions that do not function as semiconductor lasers, and the laser beams are not emitted from second region 120 or third region 130.
Given that: first distance d1 is the shortest distance among distances between two adjacent waveguides 21 included in the plurality of waveguides 21 of semiconductor laser element 1; second distance d2 is the distance between first side surface 1a and waveguide 21 located closest to first side surface 1a among the plurality of waveguides 21 of semiconductor laser element 1; and third distance d3 is the distance between second side surface 1b and waveguide 21 located closest to second side surface 1b among the plurality of waveguides 21 of semiconductor laser element 1, second distance d2 and third distance d3 are greater than first distance d1.
In the present embodiment, first distance d1 is in first region 110. Specifically, all waveguides 21 in first region 110 are formed at the same pitch. That is to say, all waveguides 21 in first region 110 are formed at equal distances, and the distances between two adjacent waveguides 21 in first region 110 are all the same at first distance d1.
Second distance d2 is the width of second region 120 in the X axis direction, and third distance d3 is the width of third region 130 in the X axis direction. In the present embodiment, second distance d2 and third distance d3 are the same, but are not limited to being the same.
As an example, the width of semiconductor laser element 1 (length in the X axis direction) is 9200 μm, and the length of semiconductor laser element 1 in the resonator length direction (length in the Y axis direction) is 1200 μm. In this case, first distance d1 is d1=400 μm, and second distance d2 and third distance d3 are d2=d3=600 μm. In other words, second region 120 and third region 130 each having a width of 600 μm are located at the two end portions of semiconductor laser element 1 in the long-side direction as regions in which waveguides 21 are not present. Note that in first region 110, there are twenty-one waveguides 21 formed at distances of 400 μm, and each waveguide 21 has a width of 30 μm centered on the dash-dot-dash line.
Next, a method of manufacturing semiconductor laser element 1 according to the embodiment will be described with reference to
The method of manufacturing semiconductor laser element 1 according to the present embodiment is a method of manufacturing semiconductor laser element 1 that includes a plurality of waveguides 21.
First, as illustrated in
For example, a hexagonal n-type GaN substrate is used as substrate 10. Therefore, in the present embodiment, as illustrated in
To produce semiconductor stacking substrate 2, first, a wafer of a 2-inch n-type GaN substrate is prepared as substrate 10, and next, a plurality of nitride semiconductor layers are epitaxially grown sequentially on the entire surface of first main surface 11 of substrate 10. For example, metal organic chemical vapor deposition (MOCVD) is used to sequentially form, on first main surface 11 of substrate 10, an n-type cladding layer made of n-type AlGaN, an active layer made of undoped InGaN, a p-type cladding layer made of p-type AlGaN, and a p-type contact layer made of p-type GaN. Thereafter, the plurality of nitride semiconductor layers stacked are subjected to photolithography and etching to form ridge stripes that serve as the plurality of waveguides 21. Note that each of the plurality of waveguides 21 is formed in the direction [1-100]. As a result, nitride-based semiconductor laser stacking structure 20 that includes the plurality of waveguides 21 can be formed on substrate 10. Thereafter, an insulating film is formed to partially cover nitride-based semiconductor laser stacking structure 20, and furthermore, p-side electrodes 30 are formed on the ridge stripes of nitride-based semiconductor laser stacking structure 20. Next, substrate 10 is thinned by grinding and polishing the back surface of substrate 10. As an example, the back surface of substrate 10 is polished until semiconductor stacking substrate 2 that is 400 μm in thickness becomes 85 μm in thickness. Thereafter, n-side electrodes 40 are formed on second main surface 12 which is the back surface of thinned substrate 10. As a result, semiconductor stacking substrate 2 can be produced.
Next, as a wafer shaping process, semiconductor stacking substrate 2 illustrated in
In the present embodiment, four divided substrates 3 are produced as illustrated in
Note that the regions surrounded by dashed lines in
When the thickness of semiconductor stacking substrate 2 is 85 μm, the depth of scribed grooves formed by laser scribing is approximately 50 μm from the surface of semiconductor stacking substrate 2 on the first main surface 11 side, and the width of the scribed grooves in top view is approximately 5 μm. In this case, as illustrated in the enlarged view in
In such a manner, in the first division process, substrate 10 on which nitride-based semiconductor laser stacking structure 20 including a plurality of waveguides 21 spaced apart in the X axis direction and extending in the Y axis direction are formed is divided in the Y axis direction, to produce the plurality of divided substrates 3 each including a plurality of waveguides 21 spaced apart in the X axis direction.
Note that the laser scribing in the first division process is performed on the surface (the front surface) of semiconductor stacking substrate 2 on the first main surface 11 side of substrate 10, but the present disclosure is not limited to this. That is to say, the laser scribing in the first division process may be performed on the surface (the back surface) of semiconductor stacking substrate 2 on the second main surface 12 side of substrate 10. In this case, however, since debris 3D is deposited on the surface of semiconductor stacking substrate 2 on the second main surface 12 side of substrate 10 (that is, the surface on the n-side electrode 40 side), debris 3D may become an obstacle in the next process (a cleavage process). Therefore, it is better to perform the laser scribing of the first division process on the surface (the front surface) of semiconductor stacking substrate 2 on the first main surface 11 side of substrate 10.
Next, one divided substrate 3 included in the plurality of divided substrates 3 produced by the first division process described above is cleaved in the X axis direction to produce a plurality of semiconductor laser elements 5 each including a plurality of waveguides 21 (the cleavage process (also referred to as “cleaving”)).
In the present embodiment, the cleavage process includes a first cleavage process of forming, on divided substrate 3, cleavage lead-in grooves 4 extending in the X axis direction (the first cleavage process is also referred to as “forming a cleavage lead-in groove”) and a second cleavage process of cleaving divided substrates 3 in the long-side direction of cleavage lead-in grooves 4 (the second cleavage process is also referred to as “cleaving the one divided substrate”). The long-side direction of cleavage lead-in grooves 4 is the X axis direction that is orthogonal to waveguides 21.
The first cleavage process is a pre-process for cleaving divided substrate 3, and is a process of forming cleavage lead-in grooves 4 as the starting points of cleavage. That is to say, cleavage lead-in grooves 4 are guide grooves for when cleaving and dividing divided substrate 3, and function as grooves for division that are used for dividing divided substrate 3 into a plurality of pieces.
Specifically, in the first cleavage process, as illustrated in
In the present embodiment, the laser scribing is performed on the surface of divided substrate 3 on the first main surface 11 side of substrate 10 (that is, the front surface on the p-side electrode 30 side). This is because cleavage lead-in grooves 4 need to be accurately aligned with the shape of nitride-based semiconductor laser stacking structure 20 (that is, a mask pattern).
In this case, as illustrated in the enlarged view in
Note that cleavage lead-in grooves 4 formed by the first cleavage process are formed in positions corresponding to second region 120 of semiconductor laser element 1 illustrated in
After the first cleavage process, the second cleavage process is performed. The second cleavage process is a process for cleaving divided substrate 3, and is a process of dividing divided substrate 3 by cleavage with cleavage lead-in grooves 4 used as the starting points. Specifically, as illustrated in
Specifically, in the second cleavage process, a Teflon (registered trademark) blade is pressed into a portion which is on the surface (that is, the back surface) of divided substrate 3 on the second main surface 12 side of substrate 10 and which corresponds to a position opposite cleavage lead-in groove 4. As a result, cleavage occurs from cleavage lead-in groove 4 as the starting point, causing divided substrate 3 to be naturally cut and divided in the direction [1-100] indicated by the dash-dot-dash lines in
Note that in the second cleaving process, if debris 3D generated by the laser scribing performed in the first division process is deposited on the back surface of divided substrate 3 (the surface on the n-side electrode 40 side), debris 3D will be an obstacle when pressing the blade. Therefore, as described above, in the first division process, the laser scribing is performed on the front surface of semiconductor stacking substrate 2 (the surface on the p-side electrode 30 side) so that debris 3D is deposited on the front surface of semiconductor stacking substrate 2.
When cleaving and dividing divided substrate 3 into a plurality of semiconductor laser elements 5, the order in which divided substrate 3 is cleaved may be a sequential order as illustrated in
As described, the end portions, in the long-side direction, of semiconductor laser element 5 produced by the cleavage process (the first cleavage process and the second cleavage process) have debris 3D and 4D deposited thereon. Specifically, debris 3D and 4D are deposited on the surface of semiconductor laser element 5 on the first main surface 11 side of substrate 10. That is to say, debris 3D and 4D are deposited on the surface (the front surface) of semiconductor laser element 5 on the p-side electrode 30 side.
In view of this, after the cleavage process (the first cleavage process and the second cleavage process), semiconductor laser element 5 is divided to remove the portions of semiconductor laser element 5 where debris 3D and 4D are deposited (a second division process (also referred to as “second dividing”)).
In the second division process, one semiconductor laser element 5 included in the plurality of semiconductor laser elements 5 produced by the cleavage process is divided in the Y axis direction to remove at least one of the end portions of semiconductor laser element 5 in the long-side direction.
In the present embodiment, as illustrated in
As illustrated in
In such a manner, not only the end portion of semiconductor laser element 5 on the first end surface 3a side, but the end portion of semiconductor laser element 5 on the second end surface 3b side is also removed. In other words, each of the two ends of semiconductor laser element 5 in the long-side direction is removed.
Specifically, to remove the end portion of semiconductor laser element 5 on the first end surface 3a side and the end portion of semiconductor laser element 5 on the second end surface 3b side, first, by laser scribing, division grooves 6 are formed on the surface of semiconductor laser element 5 on the second main surface 12 side of substrate 10, as illustrated in
In the groove forming process, division grooves 6 extending in the Y axis direction are formed on the surface (the back surface) of semiconductor laser element 5 on the second main surface 12 side of substrate 10. In the present embodiment, laser scribing is performed to form division grooves 6 on semiconductor laser element 5. Therefore, division grooves 6 are laser-scribed grooves formed by laser scribing.
Since division grooves 6 are formed by performing laser scribing on the back surface (the surface on the n-side electrode 40 side) of semiconductor laser element 5 in the above manner, even if debris 6D is generated by the laser scribing, debris 6D is deposited on the back surface of semiconductor laser element 5, and is not deposited on the front surface (the surface on the p-side electrode 30 side) of semiconductor laser element 5. In this case, as illustrated in the enlarged view in
In the present embodiment, division grooves 6 do not reach third side surface 1c or fourth side surface 1d formed on semiconductor laser element 5 by the second cleavage process described above. In other words, one end portion of each division groove 6 in the Y axis direction is set back from third side surface 1c, and the other end portion of each division groove 6 is set back from fourth side surface 1d. With this configuration, it is possible to inhibit the debris generated during the formation of division grooves 6 by laser scribing from attaching to third side surface 1c and fourth side surface 1d which are the resonator end surfaces of semiconductor laser element 5.
The depth of each division groove 6 formed by laser scribing is approximately 50 μm from the surface (the back surface) of semiconductor laser element 5 on the second main surface 12 side, and in top view, the width of each division groove 6 is approximately 5 μm and the length of each division groove 6 is approximately 1100 μm.
In the present embodiment, in order to remove each of the two end portions of semiconductor laser element 5 in the long-side direction, division groove 6 is formed at each of the end portion of semiconductor laser element 1 on the first end surface 3a side and the end portion of semiconductor laser element 1 on the second end surface 3b side. Specifically, division groove 6 at the end portion on the first end surface 3a side is formed at the position 600 μm away from first end surface 3a. Also, division groove 6 at the end portion on the second end surface 3b side is formed at the position 200 μm away from second end surface 3b.
Next, after forming division grooves 6 on semiconductor laser element 5 by the groove forming process, semiconductor laser element 5 is divided along division grooves 6 to remove the portion including cleavage lead-in grooves 4.
Specifically, a Teflon (registered trademark) blade is pressed into a portion which is on the surface (that is, the front surface) of semiconductor laser element 5 on the first main surface 11 side of substrate 10 and which corresponds to a position opposite division groove 6. As a result, semiconductor laser element 5 is cut along division groove 6. In the present embodiment, since division groove 6 is formed at each of the two ends of semiconductor laser element 1 in the long-side direction, semiconductor laser element 5 is cut along two division grooves 6, and end portion 5a of semiconductor laser element 5 on the first end surface 3a side and end portion 5a of semiconductor laser element 5 on the second end surface 3b side are separated and removed from semiconductor laser element 5 as illustrated in
At this time, since debris 3D and 4D and cleavage lead-in grooves 4 are present at end portion 5a of semiconductor laser element 5 on the first end surface 3a side, removal of end portion 5a of semiconductor laser element 5 on the first end surface 3a side allows removal of debris 3D and 4D and cleavage lead-in grooves 4 from semiconductor laser element 5. Also, since debris 3D is present at end portion 5a of semiconductor laser element 5 on the second end surface 3b side, removal of end portion 5a of semiconductor laser element 5 on the second end surface 3b side allows removal of debris 3D from semiconductor laser element 5. Specifically, all debris 3D and 4D and all cleavage lead-in grooves 4 are removed from semiconductor laser element 5. In such a manner, semiconductor laser element 1 illustrated in
An SEM image of first side surface 1a of semiconductor laser element 1 produced in the above manner is illustrated in
Note that after the removal of debris 3D and 4D and cleavage lead-in grooves 4, an end surface coating films is formed on each resonator end surface of semiconductor laser element 1 (an end surface coating process). For example, an end surface coating film having a reflectance of 16% is formed on third side surface 1c which is the front end surface of semiconductor laser element 1, and an end surface coating film having a reflectance of at least 95% is formed on fourth side surface 1d which is the rear end surface of semiconductor laser element 1. A dielectric multilayer film can be used as the end surface coating film.
As described above, the method of manufacturing semiconductor laser element 1 according to the present embodiment includes: a first division process of dividing substrate 10 in the Y axis direction (the first direction) to produce a plurality of divided substrates 3 each including a plurality of waveguides 21, substrate 10 being a substrate on which nitride-based semiconductor laser stacking structure 20 is formed, nitride-based semiconductor laser stacking structure 20 including a plurality of waveguides 21 each extending in the Y axis direction; a cleavage process of cleaving, in the X axis direction (the second direction), one divided substrate 3 included in the plurality of divided substrates 3 produced by the first division process, to produce a plurality of semiconductor laser elements 5 each including a plurality of waveguides 21; and a second division process of dividing, in the Y axis direction, one semiconductor laser element 5 included in the plurality of semiconductor laser elements 5 produced by the cleavage process, to remove at least one end portion of one semiconductor laser element 5 in the long-side direction (the second direction orthogonal to waveguides 21). The cleavage process includes: a first cleavage process of forming cleavage lead-in groove 4 on one divided substrate 3, cleavage lead-in groove 4 extending in the X axis direction; and a second cleavage process of cleaving one divided substrate 3 in the long-side direction (the second direction orthogonal to waveguides 21) using cleavage lead-in groove 4, and in the second division process, a portion including cleavage lead-in groove 4 is removed as the at least one end portion of one semiconductor laser element 5 in the long-side direction.
With this configuration, it is possible to remove debris 3D deposited in the vicinity of the division interface and at the scratch on the division interface generated when substrate 10 is divided into divided substrates 3 in the first division process. In addition, it is possible to remove cleavage lead-in grooves 4 (grooves for division) themselves that are formed when divided substrate 3 is divided into semiconductor laser elements 5 in the cleavage process, and it is also possible to remove debris 4D deposited in the periphery of cleavage lead-in grooves 4 during the formation of cleavage lead-in grooves 4. As a result, it is possible to obtain semiconductor laser element 1 having no cleavage lead-in grooves 4 or debris 3D and 4D in the mounting region for mounting semiconductor laser element 1 on, for example, a submount. Accordingly, it is possible to inhibit occurrence of defects when mounting semiconductor laser element 1 on, for example, a submount.
Also, in the first cleaving process of the cleaving process included in the method of manufacturing semiconductor laser element 1 according to the present embodiment, cleavage lead-in grooves 4 are formed on the surface (the front surface) of divided substrate 3 on the first main surface 11 side of substrate 10.
With this configuration, cleavage lead-in grooves 4 can be formed by being accurately aligned with the shape of nitride-based semiconductor laser stacking structure 20 (that is, the mask pattern) formed on the first main surface 11 side of substrate 10. As a result, waveguides 21 can be produced at predetermined positions with accuracy.
In the groove forming process of forming division grooves 6 by laser scribing in the method of manufacturing semiconductor laser element 1 according to the present embodiment, division grooves 6 are formed on the surface (the back surface) of semiconductor laser element 5 on the second main surface 12 side, and in the second division process, a portion including cleavage lead-in grooves 4 is removed by dividing semiconductor laser element 5 along division groove 6.
As described, since division grooves 6 for removing cleavage lead-in grooves 4 and debris 3D and 4D are formed on the back surface of semiconductor laser element 5, cleavage lead-in grooves 4 and debris 3D and 4D do not remain on the front surface of semiconductor laser element 1 (the surface on the p-side electrode 30 side) that serves as the mounting surface of semiconductor laser element 1. As a result, it is possible to easily mount semiconductor laser element 1 on, for example, a submount by junction-down mounting with p-side electrodes 30 facing downward.
Also, in the groove forming process included in the method of manufacturing semiconductor laser element 1 according to the present embodiment, division grooves 6 are formed to extend in the Y axis direction, and division grooves 6 do not reach third side surface 1c formed on semiconductor laser element 5 by the second cleavage process.
With this configuration, it is possible to inhibit debris 6D generated during the formation of division grooves 6 by laser scribing from attaching to third side surface 1c which is a resonator end surface of semiconductor laser element 5.
If division grooves 6 are formed to reach third side surface 1c of semiconductor laser element 5, even the resin sheet on which semiconductor laser element 5 is placed may be cut when forming division grooves 6 by, for example, laser scribing, and the debris scattering from the resin sheet by this cutting may attach to third side surface 1c of semiconductor laser element 5. In contrast, by forming division grooves 6 not to reach third side surface 1c of semiconductor laser element 5 as in the present embodiment, it is possible to prevent debris from scattering from the resin sheet and prevent debris scattering from the resin sheet from attaching to third side surface 1c of semiconductor laser element 5.
In addition, in the method of manufacturing semiconductor laser element 1 according to the present embodiment, division grooves 6 do not reach fourth side surface 1d of semiconductor laser element 5 either.
With this configuration, it is possible to inhibit debris 6D generated during the formation of division grooves 6 by laser scribing from attaching to fourth side surface 1d which is a resonator end surface of semiconductor laser element 5. In addition, it is also possible to prevent debris scattering from the resin sheet on which semiconductor laser element 5 is placed from attaching to fourth side surface 1d of semiconductor laser element 5 during the formation of division grooves 6 by, for example, laser scribing.
Also, with the method of manufacturing semiconductor laser element 1 according to the present embodiment, since it is possible to form first side surface 1a and second side surface 1b of semiconductor laser element 1 at arbitrary positions using division grooves 6, it is also possible to arbitrarily and accurately set the distance between waveguide 21 and first side surface 1a of semiconductor laser element 1 and the distance between waveguide 21 and second side surface 1b of semiconductor laser element 1.
In this case, in semiconductor laser element 1 manufactured by the method of manufacturing semiconductor laser element 1 according to the embodiment, second distance d2, which is the distance between first side surface 1a and waveguide 21 located closest to first side surface 1a among the plurality of waveguides 21, is greater than first distance d1, which is the shortest distance among distances between two adjacent waveguides.
With this configuration, it is possible to obtain semiconductor laser element 1 having excellent heat dissipation property. This point will be described in comparison with semiconductor laser element ix of a comparative example with reference to
As illustrated in
In contrast, with semiconductor laser element 1 according to the present embodiment, second distance d2 is greater than first distance d1. That is to say, the distance between first side surface 1a and waveguide 21 located closest to first side surface 1a among the plurality of waveguides 21 is greater than the pitch of waveguides 21. With this, as illustrated in
Also, in semiconductor laser element 1 according to the present embodiment, third distance d3, which is a distance between second side surface 1b and waveguide 21 located closest to second side surface 1b among the plurality of waveguides 21, is greater than first distance d1.
With this, it is possible to ensure a sufficiently wide heat dissipation path for each of waveguides 21 located at the two end portions of semiconductor laser element 1 in the long-side direction. With this, it is possible to obtain semiconductor laser element 1 having further excellent heat dissipation property as a whole.
In the above embodiment, n-side electrodes 40 are formed on the entire back surface of semiconductor laser element 1, and second region 120 and third region 130 are regions that do not function as a semiconductor laser as a result of not forming waveguide 21 in second region 120 or third region 130. The present disclosure, however, is not limited to this. For example, as illustrated in
In this case, semiconductor laser element 5A (1A) according to the present variation can be manufactured by the same method as the method of manufacturing semiconductor laser element 5 (1) in the above embodiment. In this case, in the present variation too, division grooves 6 are formed on the back surface of semiconductor laser element 5A rather than on the front surface in the groove forming process as in the above embodiment, and thus, debris 6D generated during the formation of division grooves 6 by laser scribing is not present on the front surface of semiconductor laser element 5A.
However, since division grooves 6 are formed on the back surface of semiconductor laser element 5A, debris 6D generated during the formation of division grooves 6 is deposited on the back surface of semiconductor laser element 5A (the surface on the second main surface 12 side). Specifically, debris 6D is deposited at the periphery of division grooves 6, that is, debris 6D is deposited on second main surface 12 of substrate 10 in second region 120 and third region 130 which are in the vicinity of first side surface 1a and second side surface 1b and in which n-side electrodes 40 are not formed.
In view of this, with semiconductor laser element 5A (1A) according to the present variation, n-side electrodes 40 formed at more inward positions than the regions in which debris 6D is deposited are given a thickness greater than the height of debris 6D. As an example, since the height of debris 6D is 1 μm at maximum, the thickness of n-side electrode 40 is 1 μm or greater, and more preferably 2 μm or greater.
In this case, it is favorable to provide n-side electrodes 40 at a sufficient distance from division grooves 6 and debris 6D (for example, at a distance of 30 μm or greater from division grooves 6). With this, it is possible to inhibit deposition of debris 6D on the surfaces of n-side electrodes 40.
In such a manner, by forming n-side electrodes 40 away from the positions where debris 6D is deposited and making the thickness of n-side electrodes 40 greater than the height of debris 6D, it is possible to inhibit debris 6D deposited on the back surface of semiconductor laser element 1A from becoming an obstacle in the case of connecting also the surface of semiconductor laser element 1A on the n-side electrode 40 side to, for example, a heat sink to improve the heat dissipation.
Next, semiconductor laser devices that include semiconductor laser element 1 according to the embodiment will be described.
First, first semiconductor laser device 200 that includes semiconductor laser element 1 according to the embodiment will be described with reference to
As illustrated in
Submount 210 includes base 211 and electrode layer 212 stacked on the upper surface of base 211. It is favorable that base 211 include a material having a high thermal conductivity and a low thermal expansion coefficient. Possible materials of base 211 include, for example, SiC ceramic, AlN ceramic, semi-insulating SiC crystal, and artificial diamond. A metal material such as an alloy of Cu and W or an alloy of Cu and Mo may also be used for base 211. Electrode layer 212 includes, for example, Ti/Pt/Au in this order from the base 211 side.
In the present embodiment, semiconductor laser element 1 is mounted on submount 210 with the surface of semiconductor laser element 1 on the first main surface 11 side of substrate 10, facing submount 210. In other words, semiconductor laser element 1 is mounted junction-down on submount 210 with p-side electrodes 30, which are formed on the front surface side, facing submount 210.
Semiconductor laser element 1 is mounted on submount 210 via bonding layer 220. In the present embodiment, semiconductor laser element 1 is electrically connected to electrode layer 212 of submount 210. Therefore, for example, a metal bonding material such as AuSn solder is used as bonding layer 220.
Accordingly, since first semiconductor laser device 200 includes semiconductor laser element 1 described above, it is possible to mount semiconductor laser element 1 on submount 210 without any defects during mounting.
Next, second semiconductor laser device 201 that includes semiconductor laser element 1 according to the embodiment will be described with reference to
As illustrated in
Specifically, submount 210 on which semiconductor laser element 1 is mounted by a submount mounting process is disposed on heat sink 230 by a heat sink mounting process. For example, a water-cooled heat sink made of Cu can be used as heat sink 230. Submount 210 on which semiconductor laser element 1 is mounted is bonded to the upper surface of heat sink 230 using, for example, bonding material 240. As bonding material 240, it is possible to use, for example, an electrically-conductive bonding material having a high thermal conductivity such as SnAgCu solder (SAC solder).
With heat sink 230 serving as a positive electrode, second semiconductor laser device 201 according to the present embodiment further includes: negative electrode 260 provided on heat sink 230 via insulation layer 250; first metal wires 270; and second metal wires 280.
Specifically, by a wire bonding process, electrode layer 212 of submount 210 and heat sink 230 are connected by a plurality of first metal wires 270. Also, n-side electrodes 40 of semiconductor laser element 1 and negative electrode 260 are connected by a plurality of second metal wires 280. For example, gold wires can be used as first metal wires 270 and second metal wires 280. A Cu block can be used as negative electrode 260. Note that in the case where base 211 of submount 210 has electrical conductivity by including, for example, metal, first metal wires 270 are unnecessary.
As described, according to second semiconductor laser device 201, semiconductor laser element 1 is thermally connected to heat sink 230, and thus, the heat generated by semiconductor laser element 1 can be efficiently dissipated. This makes it possible to realize a semiconductor laser device capable of high-power operation.
Next, third semiconductor laser device 202 that includes semiconductor laser element 1 according to the embodiment will be described with reference to
As illustrated in
Note that in the present embodiment, two second semiconductor laser devices 201 are stacked; however, the present disclosure is not limited to this. For example, three or more second semiconductor laser devices 201 may be stacked. That is to say, second semiconductor laser devices 201 may be stacked sequentially.
As described, since third semiconductor laser device 202 includes a plurality of second semiconductor laser devices 201 illustrated in
Next, fourth semiconductor laser device 203 that includes semiconductor laser element 1 according to the embodiment will be described with reference to
As illustrated in
Heat dissipation plate 290 functions as a heat sink. Therefore, it is favorable that heat dissipation plate 290 be made of a material having a high thermal conductivity. Electrode layer 291 is formed on the surface of heat dissipation plate 290. Electrode layer 291 is, for example, an Au layer. Electrode layer 291 is electrically connected to n-side electrodes 40 of semiconductor laser element 1 by an electrically-conductive bonding material such as AuSn solder. Also, electrode layer 291 and negative electrode 260 are electrically connected by a solder bump. Use of the solder bump enables not only the electrical bonding of electrode layer 291 and negative electrode 260 but also absorption of the height difference between heat dissipation plate 290 and negative electrode 260.
As described, according to fourth semiconductor laser device 203, heat dissipation plate 290 provides an additional heat dissipation path for the heat generated by semiconductor laser element 1 as compared to second semiconductor laser device 201 illustrated in
Note that with regard to semiconductor laser element 1 illustrated in
Although a method of manufacturing a semiconductor laser element, the semiconductor laser element, and a semiconductor laser device according to the present disclosure have been described above based on an embodiment, the present disclosure is not limited to the above embodiment.
For example, in the above embodiment, twenty-one waveguides 21 each having a width of 30 μm are formed at distances of 400 μm in semiconductor laser element 1 having a width of 9200 μm in the long-side direction and a length of 1200 μm in the resonator length direction; however, the present disclosure is not limited to this. Specifically, thirty-seven waveguides 21 each having a width of 30 μm may be formed at distances of 225 μm (=d1) in a semiconductor laser having a width of 9200 μm in the long-side direction and a length of 1200 μm in the resonator length direction. In this case, second distance d2 and third distance d3 are, for example, d2=d3=550 μm.
Alternatively, fifty-six waveguides 21 each having a width of 30 μm may be formed at distances of 150 μm (=d1) in a semiconductor laser having a width of 9200 μm in the long-side direction and a length of 1200 μm in the resonator length direction. In this case, second distance d2 and third distance d3 are, for example, d2=d3=475 μm.
The distances between the plurality of waveguides 21 and the width of the plurality of waveguides 21 need not be the same for all waveguides 21. The widths and positions of the individual waveguides are determined according to the designed output of the semiconductor laser element and the design of the heat dissipation circuit.
Further, in the above embodiment, second region 120 and third region 130 are regions that do not function as a semiconductor laser as a result of not forming waveguide 21 in second region 120 or third region 130. The present disclosure, however, is not limited to this. For example, even if p-side electrodes 30 and waveguides 21 are formed in second region 120 and third region 130, second region 120 and third region 130 may be regions that do not function as a semiconductor laser as a result of making separation between p-side electrodes 30 and waveguides 21 with an insulating film so that second region 120 and third region 130 are electrically not connected.
In the above embodiment, waveguides 21 in semiconductor laser element 1 have a ridge stripe structure, but the present disclosure is not limited to this. For example, waveguides 21 may have an electrode stripe structure including only electrodes that are divided without forming ridge stripes, or waveguides 21 may have, for example, a current narrowing structure that includes a current blocking layer.
In the above embodiment, the long-side direction of semiconductor laser element 1 has been described as the direction orthogonal to waveguides 21; however, when the number of waveguides is small, the direction parallel to the laser resonator length may be the long-side direction of semiconductor laser element 1. For example, it is possible to form semiconductor laser element 1 in which two waveguides 21 each having a length of 1200 μm in the resonator length direction are formed at distances of 150 μm (=d1) and second distance d2 and third distance d3 on the respective outer sides of the two waveguides 21 are 475 μm. In this case, the length in the resonator length direction, which is 1200 μm, is greater than the width of semiconductor laser element, which is 1100 μm (475 μm+150 μm+475 μm).
As long as the distances between waveguides 21 of semiconductor laser element 1 are appropriate and a heat sink with a good heat dissipation property and its cooling mechanism are provided, it is possible to obtain a total optical output of semiconductor laser element 1 close to an optical output calculated by multiplying an optical output extractable from one waveguide 21 by a total number of waveguides. For example, with a semiconductor laser element having a maximum of sixty waveguides or less can achieve: an optical output of at least 60 W and at most 300 W in the case of a semiconductor laser having a wavelength in a range of from 365 nm to 390 nm; an optical output of at least 180 W and at most 600 W in the case of a semiconductor laser having a wavelength in a range of from 390 nm to 420 nm; an optical output of at least 360 W and at most 900 W in the case of a semiconductor laser having a wavelength in a range of from 420 nm to 460 nm; and an optical output of at least 180 W and at most 900 W in the case of a semiconductor laser having a wavelength in a range of from 460 nm to 500 nm.
In addition, although the above embodiment has illustrated the case where the nitride-based semiconductor material is used in semiconductor laser element 1, the present disclosure is not limited to this. For example, the present disclosure is also applicable to the case where a semiconductor material other than the nitride-based semiconductor material is used. In this case, semiconductor laser element 1 includes, rather than nitride-based semiconductor laser stacking structure 20, a semiconductor laser stacking structure in which another semiconductor material is used.
Although the above embodiment has illustrated the case of manufacturing a semiconductor laser element which is a laser bar including a plurality of waveguides 21, semiconductor laser element 1 which is a laser bar including a plurality of waveguides 21 may be further divided into a plurality of pieces to produce single-emitter semiconductor laser elements each including one waveguide 21.
The present disclosure also encompasses other forms achieved by making various modifications conceivable to those skilled in the art to the embodiment, as well as forms resulting from arbitrary combinations of constituent elements and functions from different embodiments that do not depart from the essence of the present disclosure.
Although only an exemplary embodiment of the present disclosure has been described in detail above, those skilled in the art will readily appreciate that many modifications are possible in the exemplary embodiment without materially departing from the novel teachings and advantages of the present disclosure. Accordingly, all such modifications are intended to be included within the scope of the present disclosure.
The semiconductor laser element according to the present disclosure is useful as a light source for various applications, including a light source for image display devices such as projectors and displays, a light source for automotive headlamps, a light source for illumination devices, and a light source for various industrial equipment such as laser welding devices, thin-film annealing devices, and laser processing devices.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2020-107450 | Jun 2020 | JP | national |
This is a continuation application of PCT International Application No. PCT/JP2021/021099 filed on Jun. 2, 2021, designating the United States of America, which is based on and claims priority of Japanese Patent Application No. 2020-107450 filed on Jun. 23, 2020. The entire disclosures of the above-identified applications, including the specifications, drawings and claims are incorporated herein by reference in their entirety.
| Number | Date | Country | |
|---|---|---|---|
| Parent | PCT/JP2021/021099 | Jun 2021 | US |
| Child | 18084327 | US |
