Light emitting element and method for manufacturing the same

Abstract

To obtain a light emitting element having excellent adhesion between a protective film and a semiconductor layer.SOLUTION: A light emitting element according to the present invention is a flip-chip type light-emitting element including a buffer layer formed on a main surface of a substrate, an n-type AlGaN layer formed on the buffer layer, and a light-emitting layer and a p-type AlGaN layer formed in that order on at least a portion of the n-type AlGaN layer, the light-emitting element has an exposed surface of the substrate at an end portion on the main surface of the substrate, and in a cross-section of the light-emitting element, the exposed surface is inclined at an acute angle θs of 45° or less with respect to the horizontal line of the interface between the substrate and the buffer layer.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to GaN-based and AlGaN-based light-emitting devices and methods for manufacturing the same. [Background technology]

[0002] GaN-based and AlGaN-based Group III nitride semiconductors are used in light-emitting devices that emit light in the ultraviolet wavelength ranges of 200 nm to 280 nm (UVC), 280 to 320 nm (UVB), and 320 nm to 400 nm (UVA).

[0003] For example, Patent Document 1 describes that at least one of the end faces of the light emitting layer or the outer surface of the insulating film in contact with the end face of the light emitting layer is inclined with respect to a plane parallel to the light emitting layer so that the angle between the normal of the end face and the plane parallel to the light emitting layer is a predetermined angle or more. This is because when the end face of the light emitting layer of the light emitting element is inclined with respect to the plane parallel to the light emitting layer, reflected light that would not normally be extracted at the light extraction surface can be extracted by end face reflection.

[0004] Furthermore, in a conventional flip-chip type light emitting element, after etching is performed to expose the n-type semiconductor layer in order to form the n-type electrode, etching is performed to form the street region.

[0005] In Patent Document 2, a mask is formed to expose the n-type semiconductor layer, and reactive ion etching (RIE) is performed using SiCl4 gas and Cl2 gas. After removing the mask, a mask with a pattern that will result in a predetermined chip size is placed, and etching is performed by RIE until the sapphire substrate is exposed, forming a street region. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] JP 2003-347589 A [Patent Document 2] JP 2000-4066 A Summary of the Invention [Problem to be solved by the invention]

[0007] In recent years, there has been a demand for further improvement in the light emitting efficiency of light emitting devices as well as an improvement in the reliability of light emitting devices. Light emitting devices often have an insulating film such as SiO2 or SiN as a protective film for suppressing leakage current and protecting the device from moisture and the like, so as to completely cover the group III nitride semiconductor. If such a protective film peels off or cracks, the adhesion between the protective film and the semiconductor layer deteriorates, and the reliability of the device may be impaired.

[0008] Patent Document 1 shows that the substrate has an exposed surface at the edge of the main surface thereof, and the exposed surface is also covered with a protective film. However, peeling of the protective film and inclination of the exposed surface of the substrate are not taken into consideration. Patent Document 2 also does not take the protective film into consideration.

[0009] An object of the present invention is to provide a light emitting device in which peeling and cracks in a protective film are unlikely to occur, and a method for manufacturing the light emitting device. [Means for solving the problem]

[0010] As a result of intensive research conducted by the present inventors to achieve the above-mentioned object, they have found that the angle at which the protective film contacts the semiconductor layer at the surface where the substrate and the semiconductor layer contact is important in order to prevent peeling of the protective film and cracks, etc. Furthermore, the present inventors have found that in order to provide such an angle, it is appropriate to perform etching down to the substrate in order to form the street region, and then to perform etching to expose the n-type semiconductor layer in order to form the n-type electrode.

[0011] That is, the gist of the present invention is as follows. (1) A flip-chip type light-emitting element comprising a buffer layer formed on a principal surface of a substrate, an n-type AlGaN layer formed on the buffer layer, and a light-emitting layer and a p-type AlGaN layer formed in that order on at least a portion of the n-type AlGaN layer, the light-emitting element having an exposed surface of the substrate at an end portion on the principal surface of the substrate, the exposed surface having an inclined portion inclined at an acute angle θs of 45° or less with respect to a horizontal line of an interface between the substrate and the buffer layer in a cross section of the light-emitting element.

[0012] (2) The light-emitting element according to (1) above, wherein the acute angle θs is 2°<θs<30°.

[0013] (3) The light-emitting element according to (1) or (2) above, wherein, when the angle formed between the interface and a side surface of the buffer layer within the buffer layer is θb, θs<30°≦θb≦75° and θs+(180°−θb) is 120° or more.

[0014] (4) The light-emitting device according to any one of (1) to (3) above, wherein an end portion where the exposed surface of the n-type AlGaN layer and a side surface of the n-type AlGaN layer intersect is formed in the shape of an R-plane.

[0015] (5) The light-emitting device according to any one of (1) to (4) above, wherein the substrate includes a sapphire substrate, and the buffer layer includes at least an undoped AlN buffer layer.

[0016] (6) The light-emitting device according to any one of (1) to (5) above, further comprising a protective film covering at least the side surfaces of the p-type AlGaN layer, the light-emitting layer, the n-type AlGaN layer, and the buffer layer, and covering at least the inclined portion.

[0017] (7) A method for manufacturing a light-emitting element, comprising: a first step including a step of forming a buffer layer on a main surface of a substrate, a step of forming an n-type AlGaN layer on the buffer layer, and a step of forming a light-emitting layer and a p-type AlGaN layer in that order on the n-type AlGaN layer; a second step of etching at least a part of the p-type AlGaN layer, the light-emitting layer, the n-type AlGaN layer, and the buffer layer down to the substrate to form street regions in the substrate; and a third step of exposing a part of the n-type AlGaN layer by again etching the p-type AlGaN layer and the light-emitting layer after the second step, wherein in a cross section after the third step, the street regions of the substrate have an inclined portion that is inclined at an acute angle θs of 45° or less with respect to a horizontal line of the interface between the substrate and the buffer layer.

[0018] (8) A method for manufacturing a light-emitting element according to (7) above, further comprising a fourth step of forming at least a protective film on each side surface of the p-type AlGaN layer, the light-emitting layer, the n-type AlGaN layer, and the buffer layer formed by etching in the second step and the third step, and forming at least a protective film on the inclined portion of the street region of the substrate. Effect of the Invention

[0019] According to the present invention, it is possible to provide a light emitting device in which peeling and cracks in a protective film are unlikely to occur, and a method for manufacturing the light emitting device. [Brief description of the drawings]

[0020] [Figure 1] 4 is a schematic cross-sectional view illustrating an angle θs and an angle θb in the present invention. FIG. [Diagram 2] 1 is a schematic cross-sectional view showing a structure of a light-emitting element according to the present invention. [Figure 3A] FIG. 2 is a first process diagram illustrating a method for manufacturing a light-emitting element according to the present invention. [Figure 3B] FIG. 4 is a second process diagram illustrating the method for manufacturing the light-emitting element according to the present invention. [Figure 3C]FIG. 4 is a third process diagram illustrating the method for manufacturing the light-emitting element according to the present invention. [Figure 4A] FIG. 2 is a first process diagram illustrating a manufacturing method for manufacturing a light-emitting device similar to that of the present invention by a conventional manufacturing method. [Figure 4B] FIG. 2 is a second process diagram illustrating a manufacturing method for manufacturing a light emitting device similar to that of the present invention by a conventional manufacturing method. [Figure 4C] FIG. 11 is a third process diagram illustrating a manufacturing method for manufacturing a light emitting device similar to that of the present invention by a conventional manufacturing method. [Diagram 5] 3 is a diagram showing a cross-sectional SEM image of the light-emitting element according to Example 1. FIG. [Figure 6] FIG. 11 is a cross-sectional SEM image of the light-emitting element according to Example 2. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0021] Prior to describing the embodiments of the present invention, the following points will be explained in advance.

[0022] 1 is a partial cross-sectional view of the light-emitting device in this embodiment. A buffer layer 20 and an n-type AlGaN layer 30 are laminated in this order on a substrate 10, and an n-type electrode 130 is formed on a part of the n-type AlGaN layer 30. A protective film is formed on the exposed surface of the substrate 10, the side of the buffer layer 20, the side of the n-type AlGaN layer 30, the upper surface of the n-type AlGaN layer 30, and the side and upper periphery of the n-type electrode 130, except for the vicinity of the center of the upper surface of the n-type electrode 130 and the vicinity of the planned separation location of the substrate 10. The back side of the substrate 10 is the light extraction surface.

[0023] <Angle θs> The angle θs is an angle BAC when the contact point between the exposed substrate 10 and the buffer layer 20 in FIG. 1 is A, an arbitrary point on the inclined portion on the exposed substrate 10 (exposed surface) is B, and an arbitrary point outside the light emitting device on the horizontal line of the interface between the substrate 10 and the buffer layer 20 is C. The exposed surface of the substrate 10 is inclined toward the light extraction surface side from the horizontal line of the interface between the substrate 10 and the buffer layer 20 in FIG. 1. If the inclination of the exposed surface on the substrate 10 is a straight line, the point B may be any point on the straight line, but if the inclination of the exposed surface on the substrate 10 is a broken line or a curved line, the point B may be set at a position where a straight line tangent to the exposed surface of the substrate 10 can be drawn starting from the contact point A. The substrate 10 being exposed includes a state where it is covered with a protective film, and refers to a state where no semiconductor layer exists between the protective film and the substrate 10. However, the protective film is not illustrated in FIG. 2 and subsequent figures. The inclined portion in FIG. 1 (between A and B in the figure) is called the inclined portion.

[0024] <Angle θb> 1, angle θb is the angle between the interface between substrate 10 and buffer layer 20 and the side surface of buffer layer 20. When the side surface of buffer layer 20 is a straight line, the angle θb with respect to the straight line may be used, and when the side surface of buffer layer 20 is a broken line or a curved line, a straight line is drawn starting from junction A and tangent to the side surface of buffer layer 20, and the angle θb with respect to the straight line may be used.

[0025] In this embodiment, the above-mentioned inclination angles (θs, θb) are evaluated by forming a cross section of the light-emitting element using a focused ion beam (FIB) or the like, obtaining a cross-sectional SEM (scanning electron microscope) image, and measuring the angles of the image. For example, a cross-sectional SEM image at 20,000 times magnification is obtained, a horizontal line is drawn on the image at the interface between the substrate 10 and the buffer layer 20, a straight line starting from the contact point A and tangent to the exposed surface of the substrate 10, and a straight line tangent to the side surface of the buffer layer 20 are drawn, and their angles are measured.

[0026] In this embodiment, the adhesion of the protective film is evaluated by obtaining a cross-sectional SEM image and checking the presence or absence of cracks, voids, or peeling of the protective film on the image. For example, the adhesion is checked near contact A using a cross-sectional SEM image at 20,000 magnification.

[0027] In this embodiment, "AlGaN" is Al a Ga 1―a N. The value of the Al composition ratio a of AlGaN in this embodiment is specified from the wavelength observed by photoluminescence measurement performed on the surface of each layer when each layer is grown. The Al composition ratio a is 0 to 1 unless otherwise specified. As a method for specifying the Al composition ratio from the cross section of the light-emitting device, for example, EDS (energy dispersive X-ray spectroscopy) can be used.

[0028] In this embodiment, the main surface of the semiconductor layer refers to the plane that is most suitable for crystal growth among the crystal plane orientations.

[0029] In the present invention, the dopant concentration is a value measured by SIMS (secondary ion mass spectrometry). In this specification, a layer that does not function electrically as p-type or n-type because a specific impurity such as Si or Mg is not intentionally added is called "i" type or "undoped". An undoped layer may contain unavoidable impurities during the manufacturing process. Specifically, the dopant density is small and close to the lower limit of detection by SIMS (for example, 4×10 16 / cm 3 In the present specification, when the doped polymer has a molecular weight of less than 1000, the doped polymer is considered to be "undoped."

[0030] In this embodiment, the crystallinity is evaluated by the full width at half maximum (arcsec) of the X-ray rocking curve obtained by an X-ray diffractometer. The full width at half maximum may be calculated automatically by application software attached to the X-ray diffractometer.

[0031] Hereinafter, one embodiment of the present invention will be described.

[0032] (Light emitting element) The light emitting device obtained by this embodiment will be described. The light emitting device according to this embodiment is a flip-chip type light emitting device 100 including a buffer layer 20 formed on the main surface 10A of the substrate 10, an n-type AlGaN layer 30 formed on the buffer layer 20, and a light emitting layer 40 and a p-type AlGaN layer 50 formed in this order on at least a part of the n-type AlGaN layer 30.

[0033] 2, the buffer layer 20 preferably includes an AlN buffer layer 21, and may include a first buffer layer 22 or a second buffer layer 23 made of AlGaN. In addition, a p-type cladding layer 60 or a p-type contact layer 70 may be formed in this order on the p-type AlGaN layer 50.

[0034] In the light-emitting device 100, the substrate 10 has an exposed surface at an end portion on the main surface 10A, and this exposed surface is characterized by having an inclined portion that is inclined at an acute angle θs of 45° or less with respect to the horizontal line of the interface between the substrate 10 and the buffer layer 20. Furthermore, the substrate 10 is preferably a sapphire substrate. The entire exposed surface may be an inclined portion, or a portion of the exposed surface may not be inclined. When a portion of the exposed surface is not inclined, the non-inclined portion may be horizontal.

[0035] The angle θs is preferably 2°<θs<30°, and more preferably 5°≦θs≦15°. The angle θb is preferably 30°≦θb≦75°, and more preferably 45°≦θb≦65°. Furthermore, the relationship between the angle θs and the angle θb is preferably such that θs+(180°-θb) is 120° or more, and more preferably 125° or more.

[0036] In the light emitting device 100, the end where the exposed surface on the primary surface of the n-type AlGaN layer 30 intersects with the side surface of the n-type AlGaN layer 30 inclined at an angle θb is preferably formed in the shape of an R-plane.

[0037] When a protective film is formed to cover the light emitting element 100, it is preferable that peeling, cracks, etc. do not occur in the protective film. The protective film is preferably formed so as to cover the side surfaces of the buffer layer 20, the n-type AlGaN layer 30, the light emitting layer 40, the p-type AlGaN layer 50, the p-type cladding layer 60, and the p-type contact layer 70, and the inclined portion of the substrate 10. In addition, it is preferable that the protective film is not formed at least in the central portion (bonding region) of the upper surface of the p-side electrode and the n-type electrode, but may cover the outer periphery of the p-side electrode and the n-type electrode.

[0038] By forming a protective film on the light-emitting device 100 according to the present invention, it is possible to obtain a light-emitting device in which the protective film is less likely to peel off, crack, etc. Hereinafter, each component will be described in detail through an embodiment of a manufacturing method for obtaining the light-emitting device 100 and an explanation of each step thereof.

[0039] (Method of manufacturing light-emitting element) 3A to 3C are process diagrams of a method for manufacturing the above-mentioned light-emitting element 100. As shown in Fig. 3A to 3C, the method for manufacturing the light-emitting element 100 according to the present invention includes a first step (Fig. 3A) of epitaxially growing and depositing each semiconductor layer on the main surface 10A of the substrate 10, a second step (Fig. 3B) of dry-etching the semiconductor layer deposited in the first step down to the substrate 10 to form street regions, and a third step (Fig. 3C) of exposing the main surface of the n-type AlGaN layer 30 by dry-etching again.

[0040] <<First step>> In the first step, first, a substrate 10 is prepared. The substrate 10 may be one manufactured according to a conventional method. The substrate 10 preferably includes a sapphire substrate.

[0041] A buffer layer 20, an n-type AlGaN layer 30, a light-emitting layer 40, and a p-type AlGaN layer 50 are sequentially formed on the substrate 10 to form a light-emitting device 100 on the substrate 10 (FIG. 3A). Each layer constituting the light-emitting device 100 will be briefly described below.

[0042] First, the buffer layer 20 is epitaxially grown on the substrate 10. The buffer layer 20 can be formed by, for example, metal organic chemical vapor deposition (MOCVD). The buffer layer 20 preferably includes an AlN buffer layer 21, and a first buffer layer 22 or a second buffer layer 23 made of AlGaN may be stacked on the AlN buffer layer 21 in this order. The thickness of the AlN buffer layer 21 is preferably 0.3 μm or more and 0.7 μm or less. The AlN buffer layer 21 is preferably undoped. The Al composition ratios of the AlGaN of the first buffer layer 22 and the second buffer layer 23 may be the same or different. When the Al composition ratios of the first buffer layer 22 and the second buffer layer 23 are different, it is preferable that the Al composition ratio of the first buffer layer 22 is higher. The thickness of the first buffer layer 22 is preferably 10 nm or more and 50 nm or less, and the thickness of the second buffer layer 23 is preferably 200 nm or more and 2000 nm or less. Furthermore, the first buffer layer 22 and the second buffer layer 23 are preferably undoped.

[0043] Next, an n-type AlGaN layer 30 is laminated on the buffer layer 20. The thickness of the n-type AlGaN layer 30 is sufficient to supply carriers, and is preferably, for example, 300 nm to 3000 nm. Here, an element to be doped into the n-type AlGaN layer 30 is, for example, Si.

[0044] Next, the light emitting layer 40 is laminated on the n-type AlGaN layer 30. The light emitting layer 40 is preferably a layer including a layer made of AlGaN. The light emitting layer 40 may have a single layer structure or a multiple quantum well structure in which multiple barrier layers and well layers are alternately laminated. In the figures of this embodiment, a multiple quantum well structure is illustrated as an example. Although not illustrated, an undoped AlGaN layer having a thickness of 1 nm to 5 nm may be provided on the light emitting layer 40 so as to be in contact therewith.

[0045] Next, a p-type AlGaN layer 50 is laminated on the light emitting layer 40. Furthermore, a p-type cladding layer 60 may be provided on the p-type AlGaN layer 50. The p-type cladding layer 60 is made of p-type AlGaN, and preferably has a lower Al composition ratio than the p-type AlGaN layer 50. Elements doped into the p-type AlGaN layer 50 and the p-type cladding layer 60 include Mg and the like. A p-type contact layer 70 made of p-type AlGaN may be provided on the p-type cladding layer 60 to facilitate electrode formation. The p-type contact layer is preferably made of a p-type GaN layer, and elements doped therewith include Mg and the like.

[0046] <<Second process>> In the second step, it is preferable to first form an insulating film on the entire surface of the p-type contact layer 70 using a CVD (Chemical Vapor Deposition) device. Examples of insulating films that can be used include SiO2 and SiN. In this embodiment, the insulating film is described as a SiO2 layer. This SiO2 layer can serve as a mask during RIE, which will be described later.

[0047] Next, it is preferable to use a mask pattern formed by resist for the SiO2 layer on the p-type contact layer 70, and then etch and remove the SiO2 layer in a well-shaped region (street region, street width range: 50 to 150 μm) having a street width sufficient to position a line to be separated by a laser scribe later near the center, and then remove the resist. Thereafter, as shown in FIG. 3B, the III nitride layer in the street region not covered by the SiO2 layer is entirely etched using an RIE device to expose the substrate 10 in the street region. FIG. 3B is a schematic diagram at the end of etching, and shows a state in which the III nitride layer is etched in the depth direction and side-etched, resulting in a slope being formed on the side of the III nitride layer and an eaves being formed on the SiO2 layer mask. The vertical and horizontal dimensions of the figure do not show the actual ratio, but are exaggerated for easy understanding. The same applies to FIG. 3C, FIG. 4B, and FIG. 4C.

[0048] <<3rd process>> In the third step, as shown in FIG. 3C, the main surface of the n-type AlGaN layer 30 is exposed in order to form an n-type electrode later. First, it is preferable to use a mask pattern formed with a resist to leave the SiO2 layer on the p-type contact layer 70 in the region (light-emitting region) of the p-type semiconductor layer (p-type contact layer 70, p-type cladding layer 60, and p-type AlGaN layer 50) and the light-emitting layer 40 that is to be left, and to remove the other SiO2 layers by etching. Then, as shown in FIG. 3C, an RIE device is used to expose the n-type AlGaN layer 30 in the range not covered by the SiO2 layer. By having the third step after the second step, the substrate 10 in the street region exposed in the street formation step is subjected to a second etching.

[0049] During the street formation process in the second step, the p-type contact layer 70, the p-type cladding layer 60, the p-type AlGaN layer 50, the light emitting layer 40, the n-type AlGaN layer 30, and the buffer layer 20 must all be etched, and since the etching depth is deep, at several thousand nm or more, it is preferable to use a combination of gases that increases the etching rate of AlGaN. For example, a combination of (Cl2 gas, BCl3 gas) can be used. The depth of the group III nitride etched by this etching can be determined depending on the thickness of the epitaxially grown light emitting device.

[0050] On the other hand, in the third step of exposing the n-type AlGaN layer 30, the p-type contact layer 70, the p-type cladding layer 60, the p-type AlGaN layer 50, and the light-emitting layer 40 may be etched, and the etching depth is about several tens to several hundreds of nm, so it is preferable to use a combination of gases that will result in a smaller etching rate for AlGaN than that in the street formation step. For example, a combination of (Cl2 gas, SiCl4 gas) may be used. This also advances the formation of the angle θs in the substrate 10 that is already exposed and is away from the mask, forming an inclined portion in the street region. The depth of the III nitride etched by this etching may be determined depending on the thickness of the epitaxially grown light-emitting element, and it is preferable to proceed with the etching to a depth at which a part of the n-type AlGaN layer 30 on the light-emitting layer side is etched, thereby reliably exposing the surface of the n-type AlGaN layer 30.

[0051] Furthermore, by optimizing the etching conditions in the RIE apparatus in the second and third steps to obtain a low aspect ratio, and the etching conditions for the SiO2 layer in the third step, it is preferable that the end where the exposed surface of the principal surface of the n-type AlGaN layer 30 intersects with the side surface of the n-type AlGaN layer 30 has an R-shaped end.

[0052] After exposing a portion of the n-type AlGaN layer 30 as described above, the SiO2 layer on the p-type contact layer 70 may be removed by etching. It is preferable to remove at least the SiO2 layer in the position where the p-side electrode 120 described later is to be formed.

[0053] It is preferable to form a p-side electrode 120 on the p-type contact layer 70. The p-side electrode 120 is preferably a known electrode that can be used for the p-type contact layer 70, and is preferably a reflective electrode. For example, a first metal (Ni) and a second metal (Rh), or a conductive metal nitride can be used as the p-side electrode 120.

[0054] Furthermore, it is preferable to form an n-type electrode 130 on a portion of the exposed n-type AlGaN layer 40. As the n-type electrode 130, a known electrode may be selected, and for example, a first metal (Ti) and a second metal (Al), or a conductive metal nitride may be used.

[0055] A known film formation method, such as a sputtering method, can be used to laminate the p-side electrode 120 and the n-type electrode 130. In addition, it is preferable to use a lift-off method using a resist to form the electrode patterns of the p-side electrode 120 and the n-type electrode 130.

[0056] Here, in the manufacturing method of the present invention, it is essential that the etching for exposing the n-type AlGaN layer 30 in the third step is performed after the etching for forming the street region in the second step. Conventionally, it was common to perform the etching for exposing the n-type semiconductor layer and then the etching for forming the street region. However, by performing the etching for exposing the n-type semiconductor layer after the etching for forming the street region, an angle θs can be formed between the exposed surface of the substrate 10 and the horizontal line of the interface between the substrate 10 and the buffer layer 20. Furthermore, the angle θb, which is the angle between the interface between the substrate 10 and the buffer layer 20 and the inclined surface of the buffer layer 20, becomes smaller than in the past. As a result, peeling and cracks of the protective film, which will be described later, are less likely to occur.

[0057] <<Step 4>> The protective film is formed at least in the area excluding the central part (bonding area) of the upper surface of the p-side electrode and the n-type electrode. In order to prevent the protective film from evaporating and reattaching due to the laser irradiation, which would contaminate the electrode surface and the protective film surface, it is preferable that the sapphire substrate is exposed without the protective film at the position irradiated with the laser by the laser scriber. The fourth step, which is a step of forming a protective film, is a step of forming a protective film on at least the side surfaces of the p-type AlGaN layer, the light emitting layer, the n-type AlGaN layer, and the buffer layer formed by etching in the above-mentioned second and third steps, as well as on at least the inclined portions of the street regions of the substrate. The thickness of the protective film may be 0.2 μm to 3 μm. The protective film is preferably made of SiO2, SiN, SiON or a combination thereof.

[0058] Finally, it is preferable to perform contact annealing using an infrared lamp annealing heating device, and then separate into individual rectangular elements with chip sizes of 500 μm×500 μm to 1500 μm×1500 μm using a laser scriber. In addition, the thickness of the sapphire substrate after element separation is preferably 100 μm to 600 μm.

[0059] The present invention will be described in more detail below using examples, but the present invention is not limited to the following examples in any way.

[0060] [Example 1] (Experimental Example 1) A sapphire substrate (diameter: 2 inches, thickness: 430 μm, surface orientation (0001), off-angle θ in the m-axis direction: 0.5°) was prepared, and an AlN buffer layer with a central thickness of 600 nm was grown on the sapphire substrate by MOCVD at a growth temperature of 1200° C. Then, it was heated in a heat treatment furnace at 1650° C. for 4 hours in a nitrogen gas atmosphere.

[0061] The half-width of the X-ray rocking curve of (10-12) measured with an X-ray diffractometer (D8 DISCOVER AUTOWAFS; manufactured by Bruker AXS, CuKα1 radiation) of the AlN layer of the AlN template substrate was 288 seconds, which was less than 300 seconds.

[0062] After obtaining the AlN template substrate, undoped Al was grown on the AlN template substrate by MOCVD at a growth temperature of 1200°C. 0.40 Ga 0.60A first buffer layer of 30 nm thick made of N is formed, followed by an undoped Al 0.25 Ga 0.75 A second buffer layer having a thickness of 1000 nm was formed and made of N. The total thickness of the undoped first buffer layer and second buffer layer measured from a cross-sectional SEM image was 1030 nm.

[0063] Next, Si-doped Al 0.25 Ga 0.75 An n-type semiconductor layer made of N and having a thickness of 2400 nm was formed on the second buffer layer. Furthermore, after changing the growth temperature from 1200° C. to 1100° C., a Si-doped Al 0.25 Ga 0.75 An n-type guide layer made of N was formed to a thickness of 25 nm.

[0064] Next, Si-doped Al 0.25 Ga 0.75 A 12 nm thick barrier layer made of N and undoped Al 0.10 Ga 0.90 The formation of a 2.4 nm-thick well layer made of N was repeated three times to form a light-emitting layer with a quantum well structure.

[0065] Then, undoped Al was deposited on the light-emitting layer (on the third well layer). 0.25 Ga 0.75 A 3-nm-thick i-type guide layer made of N was then formed. After that, while continuing the supply of the group V source gas, the supply of the group III source gas was stopped, the nitrogen gas used as the carrier gas was stopped, and the carrier gas was changed to hydrogen gas. One minute after the start of the hydrogen gas supply, the supply of the group III source gas was started, and the Mg-doped Al 0.4 Ga 0.6 A p-type electron blocking layer of 22 nm thick was formed using Mg-doped AlN. 0.22 Ga 0.78A 64-nm-thick p-type cladding layer made of N was formed, followed by a 4-nm-thick p-type contact layer made of Mg-doped GaN (p-type GaN contact layer). With the change in carrier gas, the Ga component of the i-type guide layer volatilized and decomposed, and it changed into a 1.0-nm-thick i-type guide layer with an Al composition ratio of approximately 1.

[0066] A SiO2 layer was formed over the entire surface of the p-type contact layer using a CVD apparatus. This SiO2 layer acts as a mask during RIE.

[0067] A resist mask pattern was formed on the SiO2 layer on the p-type contact layer, and the SiO2 layer in the strip-shaped street area (street width: 100 μm) including the line to be separated by a laser scribe was removed using buffered hydrofluoric acid, and the resist was also removed. Using an RIE device, etching was performed for 16 minutes using Cl2 gas and BCl3 gas as etching gas, and all of the III-nitride layer in the street area that was not covered by the SiO2 layer was etched, exposing the sapphire substrate in the street area.

[0068] Next, a mask pattern was formed using resist to leave the SiO2 layer on the p-type semiconductor layer (p-type contact layer, p-type cladding layer, and p-type electron blocking layer) and the area of ​​the light-emitting layer that was to be left (light-emitting area), and the rest of the SiO2 layer was removed using buffered hydrofluoric acid, after which the resist was also removed. Etching was performed for 9 minutes and 30 seconds using Cl2 gas and SiCl4 gas as etching gas using RIE, exposing the area of ​​the n-type semiconductor layer that was not covered by the SiO2 layer. The thickness from the interface between the AlN buffer layer and the first buffer layer to the surface of the exposed n-type semiconductor layer was measured from a cross-sectional SEM image and was found to be 3000 nm.

[0069] When exposing the n-type semiconductor layer, the sapphire substrate in the street area exposed during the street formation process was etched a second time, after which the SiO2 layer (mask) on the p-type contact layer was removed using buffered hydrofluoric acid.

[0070] Next, a 7 nm-thick Ni layer and a 50 nm-thick Rh layer were formed on the p-type contact layer to form a reflective electrode serving as a p-side electrode.

[0071] Furthermore, a Ti layer with a thickness of 20 nm and an Al layer with a thickness of 150 nm were formed on the exposed portion of the n-type semiconductor layer to serve as an n-type electrode.

[0072] The p-side electrode and n-type electrode were laminated using the sputtering method, and the electrode patterns of the p-side electrode and n-type electrode were formed using the lift-off method using a resist.

[0073] Further, after performing contact annealing at 550°C for 10 minutes using an infrared lamp annealing heating device, a protective film made of SiO2 with a target thickness of 1 μm was formed on the entire surface except for the planned separation line by the laser scriber and the central part (bonding area) of the upper surface of the p-side electrode and the n-type electrode. After that, the semiconductor device was separated into individual rectangular elements with a chip size of 1000 μm x 1000 μm using a laser scriber to produce an ultraviolet light emitting element (hereinafter sometimes referred to as a light emitting element) according to Example 1. The side surface of the sapphire substrate was perpendicular to the main surface, and the thickness of the sapphire substrate after element separation was 430 μm.

[0074] Example 2 A light-emitting device according to Example 2 was obtained in the same manner as in Example 1, except that the thickness of the second buffer layer was changed to 250 nm. The total thickness of the undoped first buffer layer and second buffer layer measured from a cross-sectional SEM image was 280 nm. At this time, the thickness from the interface between the AlN buffer layer and the first buffer layer to the surface of the exposed n-type semiconductor layer was measured from the cross-sectional SEM image and was 2050 nm.

[0075] (Comparative Example) 4A to 4C, a process diagram for fabricating a similar light-emitting device using a conventional method is shown. First, a semiconductor layer was epitaxially grown on a sapphire substrate to form a light-emitting device (FIG. 4A). This process is the same as the first process in the embodiment.

[0076] Next, a CVD apparatus was used to form an SiO2 layer on the entire surface of the p-type contact layer 70, and a resist mask pattern was used to leave the SiO2 layer on the p-type contact layer 70 in the region (light-emitting region) of the p-type semiconductor layer (p-type contact layer 70, p-type cladding layer 60, and p-type AlGaN layer 50) and the light-emitting layer 40 that was to be left, and the other SiO2 layers were removed by etching. After that, as shown in FIG. 4B, an RIE apparatus was used to expose the n-type AlGaN layer 30 in the region not covered by the SiO2 layer.

[0077] After exposing a part of the n-type semiconductor layer as described above, the street forming step was performed. In the street forming step, since the SiO2 layer other than the light emitting region has already been removed in the step of exposing the n-type semiconductor layer, the SiO2 layer was formed again to cover the region other than the street region, including the exposed upper surface of the n-type semiconductor layer. This SiO2 layer was used as a mask during RIE, and the etching time in the street forming step was changed from 16 minutes to 12 minutes, and all of the III nitride layers in the street region not covered by the SiO2 layer were etched to expose the sapphire substrate in the street region. Here, the light emitting device according to the comparative example was obtained in the same manner as in Example 1, except that the order of the street forming step and the step of exposing the n-type semiconductor layer was reversed and the etching time in the street forming step was changed. Unlike Example 1 or Example 2, the light emitting device according to the comparative example is etched only once in the street forming step, which is the etching of the sapphire substrate in the street region. In this case, as shown in FIG. 4C, no inclined portion is formed in the sapphire substrate in the street region.

[0078] The cross-sectional SEM images of Examples 1 and 2 are shown in Figs. 5 and 6, respectively. In the figures, the horizontal line of the interface between the sapphire substrate and the AlN buffer layer on the AlN template substrate, the value of the angle (θs) between the horizontal line and the inclined portion of the sapphire substrate, and the value of the angle (θb) between the horizontal line and the AlN buffer layer are written. In Example 1, θs was 7° and θb was 61°. In Example 2, θs was 5° and θb was 55°. Here, in both Examples 1 and 2, the sapphire substrate is inclined from the contact point between the sapphire substrate and the side surface of the AlN layer to 2 μm horizontally to the right on the cross-sectional SEM image. Beyond 2 μm horizontally to the right, it is flat. On the other hand, in the comparative example, the angle (θs) between the horizontal line and the inclined portion of the sapphire substrate was zero, and no inclined portion was generated. In addition, the angle (θb) between the boundary line and the AlN buffer layer was 82°.

[0079] Table 1 shows the evaluation of θs, θb, θs+(180°-θb) and the adhesion between the protective film and the semiconductor layer in Examples 1 and 2 and Comparative Example. θs+(180°-θb) is the angle at which the protective film contacts the semiconductor layer on the surface where the sapphire substrate and the side of the AlN layer contact. The value of θs+(180°-θb) was 126° in Example 1 and 130° in Example 2, and since the angle was sufficiently large, no voids or cracks were observed between the protective film and the semiconductor layer, and the adhesion was sufficient. On the other hand, in the Comparative Example, the angle was close to a right angle of 98°, and voids or cracks were sometimes observed in some parts where the protective film contacted.

[0080] [Table 1]

[0081] From the above results, by controlling the angles θs and θb and setting θs+(180°-θb) to 120° or more, it was possible to obtain a semiconductor element in which the protective film is less susceptible to peeling and cracks. [Explanation of symbols]

[0082] 100 Light emitting element 10 Sapphire substrate 20 Buffer Layer 30 n-type AlGaN layer 40 Light-emitting layer 50 p-type AlGaN layer 60 p-type cladding layer 70 p-type contact layer 120 p side electrode 130 n-type electrode

Claims

1. a buffer layer formed on a major surface of a substrate; an n-type AlGaN layer formed on the buffer layer; a light emitting layer and a p-type AlGaN layer formed in this order on at least a portion of the n-type AlGaN layer; A flip-chip type light emitting device comprising: an exposed surface of the substrate at an end portion on a main surface of the substrate; In a cross section of the light emitting device, the exposed surface has an inclined portion inclined at an acute angle θs of 45° or less with respect to a horizontal line of the interface between the substrate and the buffer layer. Light emitting element.

2. The acute angle θs is 2°<θs<30°. The light-emitting device according to claim 1 .

3. When the angle formed between the interface and the side surface of the buffer layer within the buffer layer is θb, θs<30°≦θb≦75° and θs+(180°−θb) is 120° or more; The light-emitting device according to claim 1 .

4. an end portion where an exposed surface of the n-type AlGaN layer and a side surface of the n-type AlGaN layer intersect is formed in the shape of an R-plane; The light-emitting device according to claim 1 .

5. the substrate comprises a sapphire substrate; The buffer layer includes at least an undoped AlN buffer layer. The light-emitting device according to claim 1 .

6. a protective film that covers at least each of the side surfaces of the p-type AlGaN layer, the light emitting layer, the n-type AlGaN layer, and the buffer layer, and that covers at least the inclined portion; The light-emitting device according to claim 1 .

7. forming a buffer layer on a major surface of a substrate; forming an n-type AlGaN layer on the buffer layer; A first step including a step of sequentially forming a light emitting layer and a p-type AlGaN layer on the n-type AlGaN layer; a second step of etching at least a portion of the p-type AlGaN layer, the light emitting layer, the n-type AlGaN layer, and the buffer layer down to the substrate to form street regions in the substrate; a third step of etching the p-type AlGaN layer and the light emitting layer again after the second step to expose a part of the n-type AlGaN layer; Including, In a cross section after the third step, the street region of the substrate has an inclined portion inclined at an acute angle θs of 45° or less with respect to a horizontal line of the interface between the substrate and the buffer layer. A method for manufacturing a light-emitting device.

8. 8. The method for manufacturing a light-emitting element according to claim 7, further comprising a fourth step of forming at least a protective film on each side surface of the p-type AlGaN layer, the light-emitting layer, the n-type AlGaN layer, and the buffer layer formed by etching in the second step and the third step, and forming at least a protective film on the inclined portion in the street region of the substrate.

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