Patent ID: 12243954

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 toFIGS.1A to7B.

As shown inFIG.1A, a substrate10includes a first surface11, and a second surface12at a side opposite to the first surface11. Multiple protrusions13are formed in the first surface11. The protrusions13may be, for example, circular conic or truncated circular conic.

As shown inFIG.1B, a semiconductor structure20that includes a light-emitting layer20ais formed on the first surface11of the substrate10in which the multiple protrusions13are formed. For example, the semiconductor structure20is epitaxially grown on the first surface11of the substrate10by MOCVD (metal organic chemical vapor deposition). The thickness of the semiconductor structure20is, for example, not less than 5 μm and not more than 15 μm.

The substrate10is light-transmitting to light emitted by the light-emitting layer20a. The substrate10is, for example, a sapphire substrate. The first surface11is, for example, a c-plane of the sapphire. The first surface11may be tilted from the c-plane in a range in which the semiconductor structure20can be formed with good crystallinity. The dislocation density of the semiconductor structure20can be reduced by forming the semiconductor structure20on the first surface11in which the multiple protrusions13are provided. Also, by providing the multiple protrusions13, the light that is emitted by the light-emitting layer20acan easily enter through the first surface11.

For example, the semiconductor structure20is 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 InxAlyGa1-x-yN (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 inFIG.1B, the semiconductor structure20includes an n-side semiconductor layer20nand a p-side semiconductor layer20p. As shown inFIG.7B, an n-electrode21nthat conducts to the n-side semiconductor layer20nis formed, a p-electrode21pthat conducts to the p-side semiconductor layer20pis formed, and the light-emitting layer20ais caused to emit light by applying a voltage between the n-electrode21nand the p-electrode21p. For example, the p-electrode21pthat is provided at the upper surface of the p-side semiconductor layer20pincludes a metal material such as silver, aluminum, etc., that has a high reflectance to the light from the light-emitting layer20a.

For example, the light-emitting layer20ahas 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 layer20ais, for example, not less than 360 nm and not more than 650 nm.

After forming the semiconductor structure20on the substrate10, a portion of the semiconductor structure20is removed as shown inFIG.2A. After forming a mask91on the upper surface of the semiconductor structure20, a portion of the semiconductor structure20, which is a nitride semiconductor layer including gallium, is etched in the thickness direction. The mask91includes, for example, a resist film formed by photolithography. The removal of the semiconductor structure20includes, for example, dry etching using a SiCl4gas.

As shown inFIG.2A, the portion of the semiconductor structure20that is not covered with the mask91is removed, and an exposed region32is formed in which the first surface11of the substrate10is exposed from under the semiconductor structure20.

Multiple exposed regions32are formed in a mutually-orthogonal street configuration in a plane parallel to the first surface11. As shown inFIG.3A, the multiple exposed regions32divide the semiconductor structure20into multiple light-emitting portions31. The width of the exposed region32is, for example, not less than 10 μm and not more than 100 μm.

The protrusions13that are formed in the first surface11are exposed in the exposed region32. The protrusions13that are exposed in the exposed region32are etched. The etching of the protrusions13exposed in the exposed region32is performed using the same mask91as the formation of the exposed region32as-is, or by etching in a state in which the light-emitting portion31is covered by re-forming another mask. For example, the protrusions13that are exposed in the exposed region32are removed by dry etching using a BCl3gas.

As shown inFIG.2B, the protrusions13that are exposed in the exposed region32are etched, and the heights of the protrusions13become less than the heights of the protrusions13that are not etched. Also, the spacing between two adjacent protrusions13becomes greater than the spacing of two adjacent protrusions13that are not etched. For example, the heights of the protrusions13before the etching shown inFIG.2Aare not less than about 1 μm and not more than about 2 μm, and the heights of the protrusions13after the etching shown inFIG.2Bare not less than about 0.1 μm and not more than about 0.5 μm. Or, the protrusions13may be completely consumed by the etching. Thereby, the arithmetic average roughness of the first surface11in the exposed region32is less than the arithmetic average roughness of the first surface11in the region in which the light-emitting portion31is formed.

Also, not only the protrusions13but also the first surface11in the exposed region32is etched, and the first surface11in the exposed region32recedes further toward the second surface12side than the first surface11in the region in which the light-emitting portion31is formed. Accordingly, a level difference is formed between the first surface11in the region in which the light-emitting portion31is formed and the first surface11in the exposed region32.

After etching the exposed region32, the substrate10is thinned from the second surface12side as shown inFIG.3B. For example, a third surface14is formed by thinning the substrate10from a second surface side by CMP (Chemical Mechanical Polishing) and by mirror polishing. For example, the thickness of the substrate10that was about 200 μm before thinning is reduced to 50 μm or less.

By singulating into the multiple light-emitting portions31on the substrate10by removing a portion of the semiconductor structure20before thinning the substrate10, the stress of the semiconductor structure20on the substrate10can be relaxed, and warpage of the wafer made of the substrate10and the semiconductor structure20can be suppressed.

After thinning the substrate10, a bonded body50in which the substrate10and a light-transmitting body40are bonded is formed by bonding the light-transmitting body40to the third surface14of the substrate10as shown inFIG.4A. The light-transmitting body40is directly bonded to the third surface14that has been mirror-polished. The method for bonding the light-transmitting body40to the bonded body50includes, for example, surface-activated bonding.

The light-transmitting body40includes a fluorescer. The fluorescer is excited by the light emitted by the light-emitting layer20aand emits light of a different wavelength from the wavelength of the light emitted by the light-emitting layer20a. The light-transmitting body40includes a fluorescer in, for example, glass or a resin such as a silicone resin, etc. The light-transmitting body40may 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 body40is thicker than the substrate10and greater than the total thickness of the substrate10and the semiconductor structure20. The thickness of the light-transmitting body40is, for example, not less than 70 μm and not more than 120 μm.

After forming the bonded body50in which the substrate10and the light-transmitting body40are bonded, a laser beam L is irradiated on the substrate10of the exposed region32from the first surface11side as shown inFIG.4B. By bonding the light-transmitting body40to the substrate10, the substrate10is supported by the light-transmitting body40; in this state, the irradiation of the laser beam on the substrate10can be stably performed. The strength easily becomes insufficient in the process of thinning the substrate10, and it is favorable to increase the strength by bonding the light-transmitting body40to the substrate10.

The laser beam is emitted in pulses. For example, a Nd:YAG laser, a titanium sapphire laser, a Nd:YVO4laser, 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 substrate10. For example, the laser beam has a peak wavelength in the range not less than 800 nm and not more than 1200 nm.

FIG.5Ais an enlarged schematic top view of the portion in which the laser beam is irradiated.FIG.5Bis 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 substrate10; the energy of the laser beam concentrates at the position, and modified regions60are formed inside the substrate10as shown inFIG.5B. The modified regions60are more embrittled than the portion of the substrate10where the laser beam is not concentrated.

The laser beam is scanned along the direction in which the exposed region32extends, and the multiple modified regions60are formed along the direction in which the exposed region32extends as shown inFIG.5A. The multiple modified regions60may be separated from each other along the direction in which the exposed region32extends or may partially overlap each other.

The modified regions60that are formed by the irradiation of the laser beam generate stress, and the stress causes cracks to occur inside the substrate10. As shown inFIG.5B, a crack c occurs in the thickness direction of the substrate10from the modified region60, and reaches the first surface11and the third surface14. The crack c reaches the light-transmitting body40that is bonded to the third surface14.

The modified regions60may be formed at positions of different depths inside the substrate10. For example, multiple first modified regions60may be formed along the direction in which the exposed region32extends at a first depth, and multiple second modified regions60may be formed along the direction in which the exposed region32extends at a second depth that is different from the first depth. In such a case, the multiple first modified regions60and the multiple second modified regions60are formed to overlap in a plan view.

According to the embodiment, the heights of the protrusions13in the exposed region32on which the laser beam is irradiated are less than the heights of the protrusions13in the region in which the light-emitting portion31is formed, or the protrusions13in the exposed region32on which the laser beam is irradiated are consumed. In other words, the arithmetic average roughness of the first surface11in the exposed region32is less than the arithmetic average roughness of the first surface11in the region in which the light-emitting portion31is formed. Therefore, when irradiating the laser beam from the first surface11side, the scattering of the laser beam by the protrusions13is suppressed, and the modified regions60can be formed inside the substrate10by efficiently concentrating the laser beam. If the laser beam is irradiated from the third surface14side, it is necessary to concentrate the laser beam inside the substrate10via the light-transmitting body40. However, because the fluorescer, etc., are included in the light-transmitting body40, the laser beam is scattered by the fluorescer and cannot be easily concentrated inside the substrate10.

After forming the multiple modified regions60inside the substrate10, a trench41is formed in the light-transmitting body40as shown inFIG.6A. The trench41is formed in the light-transmitting body40from the surface on the side opposite to the bonding surface with the substrate10. For example, the trench41is formed by blade dicing, etc.

The trench41is formed by removing a portion of the light-transmitting body40that overlaps the portion in which the multiple modified regions60are formed in a plan view. The trench41is formed along the multiple modified regions60. The trench41may reach the substrate10. It is favorable to form the trench41not to reach the substrate10. For example, damage of the substrate10that may occur when the trench41is formed to reach the substrate10by blade dicing is suppressed thereby. The thickness of the light-transmitting body40that remains between the trench41and the substrate10is, for example, not less than 20 μm and 50 μm. For example, when the thickness of the light-transmitting body40is about 180 μm, about 30 μm of the light-transmitting body40will remain between the trench41and the substrate10. The width of the trench41is, for example, not less than 30 μm and not more than 60 μm. Because the trench41is formed after the irradiation process of the laser beam described above, breakage of the light-transmitting body40of the irradiation process of the laser beam can be inhibited.

After forming the trench41in the light-transmitting body40, for example, a force is applied to the bonded body50by using a pressing member, and the bonded body50is singulated along the trench41and the modified regions60as shown inFIG.6B. When singulating the bonded body50, the substrate10and the light-transmitting body40are collectively cleaved. For example, if the modified regions60are not formed inside the substrate10and a crack is not produced in the substrate10, singulation is difficult even when a force is applied to the bonded body50. Even if the bonded body50can be singulated, there is a risk that the substrate10may break in an unintended direction, and the yield can be reduced due to chipping of the substrate10, etc. By presetting the substrate10to be thin, e.g., 50 μm thick or less, the substrate10can be singulated while further suppressing the chipping of the substrate10.

As shown inFIG.7A, the bonded body50is singulated along the trench41and the modified regions60in the wafer state and is singulated into multiple light-emitting elements1.FIG.7Bis a schematic plan view of one singulated light-emitting element1.

As shown inFIGS.6B and7B, the light-emitting element1includes the substrate10, the semiconductor structure20that is provided on the first surface11of the substrate10, and the light-transmitting body40that includes the fluorescer and is bonded to the third surface14of the substrate10.

The first surface11of the substrate10includes a first region71in which the multiple protrusions13are formed, and a second region72that is positioned at the outer perimeter of the first region71and has a smaller arithmetic average roughness than the surface of the first region71.

The semiconductor structure20is provided in the first region71, and the second region72is exposed from under the semiconductor structure20. Also, the first surface11of the substrate10includes a level difference between the first region71and the second region72.

A portion of the light emitted by the light-emitting layer20apasses through the substrate10, enters the light-transmitting body40, and excites the fluorescer in the light-transmitting body40. In the light-emitting element1of the embodiment, the color of the light obtained is a mixture of the color of the light of the light-emitting layer20aand the color of the light emitted by the fluorescer. In the light-emitting element1of the embodiment, light is externally extracted mainly from the surface of the light-transmitting body40on the side opposite to the bonding surface with the substrate10. The protrusions13of the desired heights exist at the interface between the substrate10and the semiconductor structure20in the region in which the light-emitting portion31is formed; therefore, the incidence efficiency of the light from the semiconductor structure20on the substrate10can be increased, and the light extraction efficiency of the light-emitting element1can be increased.

A method for manufacturing a light-emitting element of another embodiment of the invention will now be described with reference toFIGS.8A to10B.

As shown inFIG.8A, masks94aand95are selectively formed at the first surface11of the substrate10. The mask95covers a region of the first surface11in which the protrusions are not formed. The mask94acovers a portion of the region of the first surface11in which the protrusions are formed. The first surface11is etched in this state. In the region of the first surface11in which the protrusions are formed, the mask94ais provided to correspond to the region in which the protrusions13are formed. The thickness of the mask95in the region of the first surface11in which the protrusions are not formed is greater than the thickness of the mask94ain the region of the first surface11in which the protrusions are formed. In the region of the first surface11in which the protrusions are not formed, the mask95has a stacked structure in which an insulating film92and a resist film94bare stacked from the first surface11side. The insulating film92includes, for example, silicon oxide, silicon nitride, etc. The mask94ais a resist film. The etching rate of the insulating film92for the etchant that etches the first surface11is less than those of the mask94aand the resist film94b, which are resist films.

By etching the first surface11by using the masks94aand95as shown inFIG.8B, the multiple protrusions13are formed in the first region71of the first surface11that is not covered with the masks94aand95. The portion of the first surface11that is not covered with the mask94ais etched in the first region71, while the mask94ais etched in the portion of the first surface11that is covered with the mask94a. The first region71in which the multiple protrusions13are provided is formed by such etching. Although the resist film94bis etched in the second region72of the first surface11covered with the mask95, protrusions are not formed because the insulating film92remains. Accordingly, in the first surface11, the first region71that includes the multiple protrusions13is formed, and the second region72that does not include the protrusions13and has a smaller arithmetic average roughness than the surface of the first region71is formed. The insulating film92that remains in the second region72is removed by etching, etc., and the surface of the second region72is exposed.

The first surface11in the first region71that is etched recedes further toward the second surface12side than the first surface11in the second region72. Accordingly, a level difference is formed between the first surface11in the first region71and the first surface11in the second region72.

FIG.9is a top view of the first surface11of the substrate10in which the first region71and the second region72are formed.

As shown inFIG.9, the multiple second regions72are formed in a street configuration orthogonal to each other in a plane parallel to the first surface11. The multiple first regions71in which the protrusions13are formed are divided by the second regions72. The width of the second region72is, for example, not less than 10 μm and not more than 100 μm.

As shown inFIG.10A, the semiconductor structure20is formed on the first surface11of the substrate10. The semiconductor structure20is epitaxially grown by MOCVD on the first surface11including the first region71and the second region72.

Subsequently, similarly to the embodiments described above, the semiconductor structure20is etched in a state in which the upper surface of the semiconductor structure20is selectively covered with a mask. Specifically, a mask that covers the upper surface of the semiconductor structure20that overlaps the first region71in a plan view is formed on the upper surface of the semiconductor structure20. Thereby, as shown inFIG.10B, a portion of the semiconductor structure20on the second region72is removed, and the exposed region32is formed in which the first surface11in the second region72is exposed from under the semiconductor structure20. The exposed region32divides the semiconductor structure20into the multiple light-emitting portions31.

Subsequently, the process ofFIG.3Band subsequent processes are continued as described above. Protrusions are not formed in the first surface11in the exposed region32on which the laser beam is irradiated. Therefore, the scattering of the laser beam in the exposed region32is suppressed, and the modified regions60can be formed inside the substrate10by efficiently concentrating the laser beam. In the embodiment, the laser beam can be more efficiently concentrated inside the substrate10because the exposed region32is 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 toFIGS.11A to12B.

As shown inFIG.11A, the multiple protrusions13are formed in the entire surface of the first surface11of the substrate10. Then, a mask93is selectively formed on the first surface11. The mask93covers the first region71of the first surface11but does not cover the second region72of the first surface11.

Then, the protrusions13that are provided in the second region72that is not covered with the mask93are etched. As shown inFIG.11B, the heights of the protrusions13of the second region72are caused to be less than the heights of the protrusions13of the first region71by the etching using the mask93. Also, the spacing between two adjacent protrusions13in the second region72is greater than the spacing between two adjacent protrusions13in the first region71. Alternatively, the protrusions13of the second region72may be completely consumed. Thereby, the arithmetic average roughness of the first surface11in the second region72is caused to be less than the arithmetic average roughness of the first surface11in the first region71.

Not only the protrusions13but also the first surface11in the second region72is etched, and the first surface11in the second region72recedes further toward the second surface12side than the first surface11in the first region71. Accordingly, a level difference is formed between the first surface11in the first region71and the first surface11in the second region72.

After etching the protrusions13of the second region72, the semiconductor structure20is formed on the first surface11of the substrate10as shown inFIG.12A. The semiconductor structure20is epitaxially grown by MOCVD on the first and second regions71and72.

Subsequently, similarly to the embodiments described above, the semiconductor structure20is etched in a state in which the upper surface of the semiconductor structure20is selectively covered with a mask. Specifically, a mask that covers the upper surface of the semiconductor structure20that overlaps the first region71in a plan view is formed on the upper surface of the semiconductor structure20. Thereby, as shown inFIG.12B, a portion of the semiconductor structure20on the second region72is removed, and the exposed region32is formed in which the first surface11in the second region72is exposed from under the semiconductor structure20. The exposed region32divides the semiconductor structure20into the multiple light-emitting portions31.

Subsequently, the process ofFIG.3Band subsequent processes are continued as described above. In the embodiment as well, the arithmetic average roughness of the first surface11in the exposed region32on which the laser beam is irradiated is less than the arithmetic average roughness of the first surface11in the first region71in which the light-emitting portion31is formed. Therefore, the scattering of the laser beam in the exposed region32is suppressed, and the modified regions60can be formed by efficiently concentrating the laser beam inside the substrate10.

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.