Patent Publication Number: US-2021193867-A1

Title: Method for manufacturing light-emitting element

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application claims priority to Japanese Patent Application No. 2019-231153, filed on Dec. 23, 2019, the disclosure of which is hereby incorporated by reference in its entirety. 
     BACKGROUND 
     The present disclosure relates to a method for manufacturing a light-emitting element. 
     Japanese Patent No. 5556657 discusses a method for dicing a wafer in which a semiconductor structure including a light-emitting layer is formed on a substrate, in which modified regions are formed by concentrating a laser beam in the substrate interior, and the wafer is cleaved by using cracks extending from the modified regions as starting points. Also, there is a method in which a semiconductor structure including a light-emitting layer is grown on a surface of a substrate including multiple protrusions. 
     SUMMARY 
     When collectively cleaving a substrate and a light-transmitting body including a fluorescer after the light-transmitting body is bonded to the back surface of the substrate, it is difficult to concentrate a laser beam inside the substrate via the light-transmitting body from the backside of the substrate. Therefore, it is necessary to form modified regions inside the substrate by irradiating the laser beam from the front side of the substrate in which multiple protrusions are formed. However, in such a case, the laser beam is scattered by the multiple protrusions, and there is a risk that it may be difficult to form the modified regions inside the substrate. 
     The present disclosure is directed to a method for manufacturing a light-emitting element in which modified regions can be formed by efficiently concentrating a laser beam inside a substrate including multiple protrusions, so that a bonded body, which includes the substrate and a light-transmitting body including a fluorescer, can be singulated along the modified regions. 
     According to one embodiment of the present disclosure, a method for manufacturing a light-emitting element includes forming a semiconductor structure including a light-emitting layer on a first surface of a substrate, the substrate including the first surface and a second surface at a side opposite to the first surface, the first surface including a plurality of protrusions; dividing the semiconductor structure into a plurality of light-emitting portions by forming an exposed region by removing a portion of the semiconductor structure, the first surface being exposed from under the semiconductor structure in the exposed region; etching the protrusions formed in the exposed region; forming a bonded body by bonding the substrate and a light-transmitting body by bonding the light-transmitting body to the second surface, the light-transmitting body including a fluorescer; forming a plurality of modified regions along the exposed region inside the substrate by irradiating a laser beam on the exposed region from the first surface side after the bonding of the light-transmitting body to the second surface; removing the light-transmitting body that overlaps a portion in which the plurality of modified regions is formed in a plan view after the forming of the plurality of modified regions; and singulating the bonded body along the modified regions. 
     According to another embodiment of the present disclosure, a method for manufacturing a light-emitting element includes forming a semiconductor structure including a light-emitting layer on a first surface of a substrate, the substrate including the first surface and a second surface at a side opposite to the first surface, the first surface including a first region and a second region, the first region including a plurality of protrusions, a surface of the second region having a smaller arithmetic average roughness than a surface of the first region; dividing the semiconductor structure into a plurality of light-emitting portions by forming an exposed region by removing a portion of the semiconductor structure, the second region being exposed from under the semiconductor structure in the exposed region; forming a bonded body by bonding the substrate and a light-transmitting body by bonding the light-transmitting body to the second surface, the light-transmitting body including a fluorescer; forming a plurality of modified regions along the exposed region inside the substrate by irradiating a laser beam on the exposed region from the first surface side after the bonding of the light-transmitting body to the second surface; removing the light-transmitting body that overlaps a portion in which the plurality of modified regions is formed in a plan view after the forming of the plurality of modified regions; and singulating the bonded body along the modified regions. 
     According to certain embodiments of the method for manufacturing the light-emitting element of the present disclosure, the modified regions can be formed by efficiently concentrating the laser beam inside the substrate including the multiple protrusions, so that the bonded body, which includes the substrate and the light-transmitting body including the fluorescer, can be singulated along the modified regions. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1A  to  FIG. 4B  are schematic cross-sectional views showing a method for manufacturing a light-emitting element according to one embodiment of the invention; 
         FIG. 5A  is a schematic plan view showing the method for manufacturing the light-emitting element according to one embodiment of the invention; 
         FIG. 5B  to  FIG. 6B  are schematic cross-sectional views showing the method for manufacturing the light-emitting element according to one embodiment of the invention; 
         FIG. 7A  is a schematic plan view showing the method for manufacturing the light-emitting element according to one embodiment of the invention; 
         FIG. 7B  is a schematic plan view of the light-emitting element according to one embodiment of the invention; 
         FIG. 8A  and  FIG. 8B  are schematic cross-sectional views showing a method for manufacturing a light-emitting element according to another embodiment of the invention; 
         FIG. 9  is a schematic plan view showing the method for manufacturing the light-emitting element according to another embodiment of the invention; 
         FIG. 10A  and  FIG. 10B  are schematic cross-sectional views showing the method for manufacturing the light-emitting element according to another embodiment of the invention; and 
         FIG. 11A  to  FIG. 12B  are schematic cross-sectional views showing a method for manufacturing a light-emitting element according to still another embodiment of the invention. 
     
    
    
     DETAILED DESCRIPTION 
     Embodiments will now be described with reference to the drawings. The same components in the drawings are labeled with the same reference numerals. 
     A method for manufacturing a light-emitting element of one embodiment of the invention will now be described with reference to  FIGS. 1A to 7B . 
     As shown in  FIG. 1A , a substrate  10  includes a first surface  11 , and a second surface  12  at a side opposite to the first surface  11 . Multiple protrusions  13  are formed in the first surface  11 . The protrusions  13  may be, for example, circular conic or truncated circular conic 
     As shown in  FIG. 1B , a semiconductor structure  20  that includes a light-emitting layer  20   a  is formed on the first surface  11  of the substrate  10  in which the multiple protrusions  13  are formed. For example, the semiconductor structure  20  is epitaxially grown on the first surface  11  of the substrate  10  by MOCVD (metal organic chemical vapor deposition). The thickness of the semiconductor structure  20  is, for example, not less than 5 μm and not more than 15 μm. 
     The substrate  10  is light-transmitting to light emitted by the light-emitting layer  20   a.  The substrate  10  is, for example, a sapphire substrate. The first surface  11  is, for example, a c-plane of the sapphire. The first surface  11  may be tilted from the c-plane in a range in which the semiconductor structure  20  can be formed with good crystallinity. The dislocation density of the semiconductor structure  20  can be reduced by forming the semiconductor structure  20  on the first surface  11  in which the multiple protrusions  13  are provided. Also, by providing the multiple protrusions  13 , the light that is emitted by the light-emitting layer  20   a  can easily enter through the first surface  11 . 
     For example, the semiconductor structure  20  is formed of a nitride semiconductor layer including gallium. For example, GaN, InGaN, AlGaN, etc., are examples of the nitride semiconductor layer including gallium. In the specification, “nitride semiconductor” includes all compositions of semiconductors of the chemical formula In x Al y Ga 1-x-y N (0≤x≤1, 0≤y≤1, and x+y≤1) for which the composition ratio x and y are changed within the ranges respectively. As shown in  FIG. 1B , the semiconductor structure  20  includes an n-side semiconductor layer  20   n  and a p-side semiconductor layer  20   p.  As shown in  FIG. 7B , an n-electrode  21   n  that conducts to the n-side semiconductor layer  20   n  is formed, a p-electrode  21   p  that conducts to the p-side semiconductor layer  20   p  is formed, and the light-emitting layer  20   a  is caused to emit light by applying a voltage between the n-electrode  21   n  and the p-electrode  21   p.  For example, the p-electrode  21   p  that is provided at the upper surface of the p-side semiconductor layer  20   p  includes a metal material such as silver, aluminum, etc., that has a high reflectance to the light from the light-emitting layer  20   a.    
     For example, the light-emitting layer  20   a  has a multi-quantum well structure that includes multiple well layers and multiple barrier layers. The peak wavelength of the light emitted by the light-emitting layer  20   a  is, for example, not less than 360 nm and not more than 650 nm. 
     After forming the semiconductor structure  20  on the substrate  10 , a portion of the semiconductor structure  20  is removed as shown in  FIG. 2A . After forming a mask  91  on the upper surface of the semiconductor structure  20 , a portion of the semiconductor structure  20 , which is a nitride semiconductor layer including gallium, is etched in the thickness direction. The mask  91  includes, for example, a resist film formed by photolithography. The removal of the semiconductor structure  20  includes, for example, dry etching using a SiCl 4  gas. 
     As shown in  FIG. 2A , the portion of the semiconductor structure  20  that is not covered with the mask  91  is removed, and an exposed region  32  is formed in which the first surface  11  of the substrate  10  is exposed from under the semiconductor structure  20 . 
     Multiple exposed regions  32  are formed in a mutually-orthogonal street configuration in a plane parallel to the first surface  11 . As shown in  FIG. 3A , the multiple exposed regions  32  divide the semiconductor structure  20  into multiple light-emitting portions  31 . The width of the exposed region  32  is, for example, not less than 10 μm and not more than 100 μm. 
     The protrusions  13  that are formed in the first surface  11  are exposed in the exposed region  32 . The protrusions  13  that are exposed in the exposed region  32  are etched. The etching of the protrusions  13  exposed in the exposed region  32  is performed using the same mask  91  as the formation of the exposed region  32  as-is, or by etching in a state in which the light-emitting portion  31  is covered by re-forming another mask. For example, the protrusions  13  that are exposed in the exposed region  32  are removed by dry etching using a BCI 3  gas. 
     As shown in  FIG. 2B , the protrusions  13  that are exposed in the exposed region  32  are etched, and the heights of the protrusions  13  become less than the heights of the protrusions  13  that are not etched. Also, the spacing between two adjacent protrusions  13  becomes greater than the spacing of two adjacent protrusions  13  that are not etched. For example, the heights of the protrusions  13  before the etching shown in  FIG. 2A  are not less than about 1 μm and not more than about 2 μm, and the heights of the protrusions  13  after the etching shown in  FIG. 2B  are not less than about 0.1 μm and not more than about 0.5 μm. Or, the protrusions  13  may be completely consumed by the etching. Thereby, the arithmetic average roughness of the first surface  11  in the exposed region  32  is less than the arithmetic average roughness of the first surface  11  in the region in which the light-emitting portion  31  is formed. 
     Also, not only the protrusions  13  but also the first surface  11  in the exposed region  32  is etched, and the first surface  11  in the exposed region  32  recedes further toward the second surface  12  side than the first surface  11  in the region in which the light-emitting portion  31  is formed. Accordingly, a level difference is formed between the first surface  11  in the region in which the light-emitting portion  31  is formed and the first surface  11  in the exposed region  32 . 
     After etching the exposed region  32 , the substrate  10  is thinned from the second surface  12  side as shown in  FIG. 3B . For example, a third surface  14  is formed by thinning the substrate  10  from a second surface side by CMP (Chemical Mechanical Polishing) and by mirror polishing. For example, the thickness of the substrate  10  that was about 200 μm before thinning is reduced to 50 μm or less. 
     By singulating into the multiple light-emitting portions  31  on the substrate  10  by removing a portion of the semiconductor structure  20  before thinning the substrate  10 , the stress of the semiconductor structure  20  on the substrate  10  can be relaxed, and warpage of the wafer made of the substrate  10  and the semiconductor structure  20  can be suppressed. 
     After thinning the substrate  10 , a bonded body  50  in which the substrate  10  and a light-transmitting body  40  are bonded is formed by bonding the light-transmitting body  40  to the third surface  14  of the substrate  10  as shown in  FIG. 4A . The light-transmitting body  40  is directly bonded to the third surface  14  that has been mirror-polished. The method for bonding the light-transmitting body  40  to the bonded body  50  includes, for example, surface-activated bonding. 
     The light-transmitting body  40  includes a fluorescer. The fluorescer is excited by the light emitted by the light-emitting layer  20   a  and emits light of a different wavelength from the wavelength of the light emitted by the light-emitting layer  20   a.  The light-transmitting body  40  includes a fluorescer in, for example, glass or a resin such as a silicone resin, etc. The light-transmitting body  40  may be a sintered body including a fluorescer. The fluorescer includes, for example, a cerium-activated yttrium-aluminum-garnet-based fluorescer (YAG:Ce), a cerium-activated lutetium-aluminum-garnet-based fluorescer (LAG:Ce), etc. The thickness of the light-transmitting body  40  is thicker than the substrate  10  and greater than the total thickness of the substrate  10  and the semiconductor structure  20 . The thickness of the light-transmitting body  40  is, for example, not less than 70 μm and not more than 120 μm. 
     After forming the bonded body  50  in which the substrate  10  and the light-transmitting body  40  are bonded, a laser beam L is irradiated on the substrate  10  of the exposed region  32  from the first surface  11  side as shown in  FIG. 4B . By bonding the light-transmitting body  40  to the substrate  10 , the substrate  10  is supported by the light-transmitting body  40 ; in this state, the irradiation of the laser beam on the substrate  10  can be stably performed. The strength easily becomes insufficient in the process of thinning the substrate  10 , and it is favorable to increase the strength by bonding the light-transmitting body  40  to the substrate  10 . 
     The laser beam is emitted in pulses. For example, a Nd:YAG laser, a titanium sapphire laser, a Nd:YVO 4  laser, a Nd:YLF laser, or the like is used as the laser light source. The wavelength of the laser beam is the wavelength of the light passing through the substrate  10 . For example, the laser beam has a peak wavelength in the range not less than 800 nm and not more than 1200 nm. 
       FIG. 5A  is an enlarged schematic top view of the portion in which the laser beam is irradiated.  FIG. 5B  is a schematic enlarged cross-sectional view of the portion in which the laser beam is irradiated. 
     The laser beam is concentrated at a position at a designated depth inside the substrate  10 ; the energy of the laser beam concentrates at the position, and modified regions  60  are formed inside the substrate  10  as shown in  FIG. 5B . The modified regions  60  are more embrittled than the portion of the substrate  10  where the laser beam is not concentrated. 
     The laser beam is scanned along the direction in which the exposed region  32  extends, and the multiple modified regions  60  are formed along the direction in which the exposed region  32  extends as shown in  FIG. 5A . The multiple modified regions  60  may be separated from each other along the direction in which the exposed region  32  extends or may partially overlap each other. 
     The modified regions  60  that are formed by the irradiation of the laser beam generate stress, and the stress causes cracks to occur inside the substrate  10 . As shown in  FIG. 5B , a crack c occurs in the thickness direction of the substrate  10  from the modified region  60 , and reaches the first surface  11  and the third surface  14 . The crack c reaches the light-transmitting body  40  that is bonded to the third surface  14 . 
     The modified regions  60  may be formed at positions of different depths inside the substrate  10 . For example, multiple first modified regions  60  may be formed along the direction in which the exposed region  32  extends at a first depth, and multiple second modified regions  60  may be formed along the direction in which the exposed region  32  extends at a second depth that is different from the first depth. In such a case, the multiple first modified regions  60  and the multiple second modified regions  60  are formed to overlap in a plan view. 
     According to the embodiment, the heights of the protrusions  13  in the exposed region  32  on which the laser beam is irradiated are less than the heights of the protrusions  13  in the region in which the light-emitting portion  31  is formed, or the protrusions  13  in the exposed region  32  on which the laser beam is irradiated are consumed. In other words, the arithmetic average roughness of the first surface  11  in the exposed region  32  is less than the arithmetic average roughness of the first surface  11  in the region in which the light-emitting portion  31  is formed. Therefore, when irradiating the laser beam from the first surface  11  side, the scattering of the laser beam by the protrusions  13  is suppressed, and the modified regions  60  can be formed inside the substrate  10  by efficiently concentrating the laser beam. If the laser beam is irradiated from the third surface  14  side, it is necessary to concentrate the laser beam inside the substrate  10  via the light-transmitting body  40 . However, because the fluorescer, etc., are included in the light-transmitting body  40 , the laser beam is scattered by the fluorescer and cannot be easily concentrated inside the substrate  10 . 
     After forming the multiple modified regions  60  inside the substrate  10 , a trench  41  is formed in the light-transmitting body  40  as shown in  FIG. 6A . The trench  41  is formed in the light-transmitting body  40  from the surface on the side opposite to the bonding surface with the substrate  10 . For example, the trench  41  is formed by blade dicing, etc. 
     The trench  41  is formed by removing a portion of the light-transmitting body  40  that overlaps the portion in which the multiple modified regions  60  are formed in a plan view. The trench  41  is formed along the multiple modified regions  60 . The trench  41  may reach the substrate  10 . It is favorable to form the trench  41  not to reach the substrate  10 . For example, damage of the substrate  10  that may occur when the trench  41  is formed to reach the substrate  10  by blade dicing is suppressed thereby. The thickness of the light-transmitting body  40  that remains between the trench  41  and the substrate  10  is, for example, not less than 20 μm and 50 μm. For example, when the thickness of the light-transmitting body  40  is about 180 μm, about 30 μm of the light-transmitting body  40  will remain between the trench  41  and the substrate  10 . The width of the trench  41  is, for example, not less than 30 μm and not more than 60 μm. Because the trench  41  is formed after the irradiation process of the laser beam described above, breakage of the light-transmitting body  40  of the irradiation process of the laser beam can be inhibited. 
     After forming the trench  41  in the light-transmitting body  40 , for example, a force is applied to the bonded body  50  by using a pressing member, and the bonded body  50  is singulated along the trench  41  and the modified regions  60  as shown in  FIG. 6B . When singulating the bonded body  50 , the substrate  10  and the light-transmitting body  40  are collectively cleaved. For example, if the modified regions  60  are not formed inside the substrate  10  and a crack is not produced in the substrate  10 , singulation is difficult even when a force is applied to the bonded body  50 . Even if the bonded body  50  can be singulated, there is a risk that the substrate  10  may break in an unintended direction, and the yield can be reduced due to chipping of the substrate  10 , etc. By presetting the substrate  10  to be thin, e.g., 50 μm thick or less, the substrate  10  can be singulated while further suppressing the chipping of the substrate  10 . 
     As shown in  FIG. 7A , the bonded body  50  is singulated along the trench  41  and the modified regions  60  in the wafer state and is singulated into multiple light-emitting elements  1 .  FIG. 7B  is a schematic plan view of one singulated light-emitting element  1 . 
     As shown in  FIGS. 6B and 7B , the light-emitting element  1  includes the substrate  10 , the semiconductor structure  20  that is provided on the first surface  11  of the substrate  10 , and the light-transmitting body  40  that includes the fluorescer and is bonded to the third surface  14  of the substrate  10 . 
     The first surface  11  of the substrate  10  includes a first region  71  in which the multiple protrusions  13  are formed, and a second region  72  that is positioned at the outer perimeter of the first region  71  and has a smaller arithmetic average roughness than the surface of the first region  71 . 
     The semiconductor structure  20  is provided in the first region  71 , and the second region  72  is exposed from under the semiconductor structure  20 . Also, the first surface  11  of the substrate  10  includes a level difference between the first region  71  and the second region  72 . 
     A portion of the light emitted by the light-emitting layer  20   a  passes through the substrate  10 , enters the light-transmitting body  40 , and excites the fluorescer in the light-transmitting body  40 . In the light-emitting element  1  of the embodiment, the color of the light obtained is a mixture of the color of the light of the light-emitting layer  20   a  and the color of the light emitted by the fluorescer. In the light-emitting element  1  of the embodiment, light is externally extracted mainly from the surface of the light-transmitting body  40  on the side opposite to the bonding surface with the substrate  10 . The protrusions  13  of the desired heights exist at the interface between the substrate  10  and the semiconductor structure  20  in the region in which the light-emitting portion  31  is formed; therefore, the incidence efficiency of the light from the semiconductor structure  20  on the substrate  10  can be increased, and the light extraction efficiency of the light-emitting element  1  can be increased. 
     A method for manufacturing a light-emitting element of another embodiment of the invention will now be described with reference to  FIGS. 8A to 10B . 
     As shown in  FIG. 8A , masks  94   a  and  95  are selectively formed at the first surface  11  of the substrate  10 . The mask  95  covers a region of the first surface  11  in which the protrusions are not formed. The mask  94   a  covers a portion of the region of the first surface  11  in which the protrusions are formed. The first surface  11  is etched in this state. In the region of the first surface  11  in which the protrusions are formed, the mask  94   a  is provided to correspond to the region in which the protrusions  13  are formed. The thickness of the mask  95  in the region of the first surface  11  in which the protrusions are not formed is greater than the thickness of the mask  94   a  in the region of the first surface  11  in which the protrusions are formed. In the region of the first surface  11  in which the protrusions are not formed, the mask  95  has a stacked structure in which an insulating film  92  and a resist film  94   b  are stacked from the first surface  11  side. The insulating film  92  includes, for example, silicon oxide, silicon nitride, etc. The mask  94   a  is a resist film. The etching rate of the insulating film  92  for the etchant that etches the first surface  11  is less than those of the mask  94   a  and the resist film  94   b,  which are resist films. 
     By etching the first surface  11  by using the masks  94   a  and  95  as shown in  FIG. 8B , the multiple protrusions  13  are formed in the first region  71  of the first surface  11  that is not covered with the masks  94   a  and  95 . The portion of the first surface  11  that is not covered with the mask  94   a  is etched in the first region  71 , while the mask  94   a  is etched in the portion of the first surface  11  that is covered with the mask  94   a.  The first region  71  in which the multiple protrusions  13  are provided is formed by such etching. Although the resist film  94   b  is etched in the second region  72  of the first surface  11  covered with the mask  95 , protrusions are not formed because the insulating film  92  remains. Accordingly, in the first surface  11 , the first region  71  that includes the multiple protrusions  13  is formed, and the second region  72  that does not include the protrusions  13  and has a smaller arithmetic average roughness than the surface of the first region  71  is formed. The insulating film  92  that remains in the second region  72  is removed by etching, etc., and the surface of the second region  72  is exposed. 
     The first surface  11  in the first region  71  that is etched recedes further toward the second surface  12  side than the first surface  11  in the second region  72 . Accordingly, a level difference is formed between the first surface  11  in the first region  71  and the first surface  11  in the second region  72 . 
       FIG. 9  is a top view of the first surface  11  of the substrate  10  in which the first region  71  and the second region  72  are formed. 
     As shown in  FIG. 9 , the multiple second regions  72  are formed in a street configuration orthogonal to each other in a plane parallel to the first surface  11 . The multiple first regions  71  in which the protrusions  13  are formed are divided by the second regions  72 . The width of the second region  72  is, for example, not less than 10 μm and not more than 100 μm. 
     As shown in  FIG. 10A , the semiconductor structure  20  is formed on the first surface  11  of the substrate  10 . The semiconductor structure  20  is epitaxially grown by MOCVD on the first surface  11  including the first region  71  and the second region  72 . 
     Subsequently, similarly to the embodiments described above, the semiconductor structure  20  is etched in a state in which the upper surface of the semiconductor structure  20  is selectively covered with a mask. Specifically, a mask that covers the upper surface of the semiconductor structure  20  that overlaps the first region  71  in a plan view is formed on the upper surface of the semiconductor structure  20 . Thereby, as shown in  FIG. 10B , a portion of the semiconductor structure  20  on the second region  72  is removed, and the exposed region  32  is formed in which the first surface  11  in the second region  72  is exposed from under the semiconductor structure  20 . The exposed region  32  divides the semiconductor structure  20  into the multiple light-emitting portions  31 . 
     Subsequently, the process of  FIG. 3B  and subsequent processes are continued as described above. Protrusions are not formed in the first surface  11  in the exposed region  32  on which the laser beam is irradiated. Therefore, the scattering of the laser beam in the exposed region  32  is suppressed, and the modified regions  60  can be formed inside the substrate  10  by efficiently concentrating the laser beam. In the embodiment, the laser beam can be more efficiently concentrated inside the substrate  10  because the exposed region  32  is not patterned and is a flat surface. 
     A method for manufacturing a light-emitting element of another embodiment of the invention will now be described with reference to  FIGS. 11A to 12B . 
     As shown in  FIG. 11A , the multiple protrusions  13  are formed in the entire surface of the first surface  11  of the substrate  10 . Then, a mask  93  is selectively formed on the first surface  11 . The mask  93  covers the first region  71  of the first surface  11  but does not cover the second region  72  of the first surface  11 . 
     Then, the protrusions  13  that are provided in the second region  72  that is not covered with the mask  93  are etched. As shown in  FIG. 11B , the heights of the protrusions  13  of the second region  72  are caused to be less than the heights of the protrusions  13  of the first region  71  by the etching using the mask  93 . Also, the spacing between two adjacent protrusions  13  in the second region  72  is greater than the spacing between two adjacent protrusions  13  in the first region  71 . Alternatively, the protrusions  13  of the second region  72  may be completely consumed. Thereby, the arithmetic average roughness of the first surface  11  in the second region  72  is caused to be less than the arithmetic average roughness of the first surface  11  in the first region  71 . 
     Not only the protrusions  13  but also the first surface  11  in the second region  72  is etched, and the first surface  11  in the second region  72  recedes further toward the second surface  12  side than the first surface  11  in the first region  71 . Accordingly, a level difference is formed between the first surface  11  in the first region  71  and the first surface  11  in the second region  72 . 
     After etching the protrusions  13  of the second region  72 , the semiconductor structure  20  is formed on the first surface  11  of the substrate  10  as shown in  FIG. 12A . The semiconductor structure  20  is epitaxially grown by MOCVD on the first and second regions  71  and  72 . 
     Subsequently, similarly to the embodiments described above, the semiconductor structure  20  is etched in a state in which the upper surface of the semiconductor structure  20  is selectively covered with a mask. Specifically, a mask that covers the upper surface of the semiconductor structure  20  that overlaps the first region  71  in a plan view is formed on the upper surface of the semiconductor structure  20 . Thereby, as shown in  FIG. 12B , a portion of the semiconductor structure  20  on the second region  72  is removed, and the exposed region  32  is formed in which the first surface  11  in the second region  72  is exposed from under the semiconductor structure  20 . The exposed region  32  divides the semiconductor structure  20  into the multiple light-emitting portions  31 . 
     Subsequently, the process of  FIG. 3B  and subsequent processes are continued as described above. In the embodiment as well, the arithmetic average roughness of the first surface  11  in the exposed region  32  on which the laser beam is irradiated is less than the arithmetic average roughness of the first surface  11  in the first region  71  in which the light-emitting portion  31  is formed. Therefore, the scattering of the laser beam in the exposed region  32  is suppressed, and the modified regions  60  can be formed by efficiently concentrating the laser beam inside the substrate  10 . 
     Embodiments of the present invention have been described with reference to specific examples. However, the present invention is not limited to these specific examples. Based on the above-described embodiments of the present invention, all embodiments that can be implemented with appropriately design modification by one skilled in the art are also within the scope of the present invention as long as the gist of the present invention is included. Further, within the scope of the spirit of the present invention, one skilled in the art can conceive various modifications, and the modifications fall within the scope of the present invention.