JP2008270689A - GaN-BASED LIGHT EMITTING DIODE ELEMENT AND MANUFACTURING METHOD THEREOF - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a GaN-based light emitting diode element constituted by forming an LED structure comprising a GaN-based semiconductor on a surface of a semiconductor, while forming irregularities desirable for the purpose of improving light extraction efficiency on the surface of the substrate. <P>SOLUTION: The GaN-based light emitting diode element 10 includes the substrate 11 and the GaN-based semiconductor 12. A region 11A in which the irregularities capable of scattering the light are formed is partially provided to the surface of the substrate 11. The GaN-based semiconductor 12 includes a GaN system semiconductor crystal film which has laterally grown from a region 11B where no irregularity is formed on the surface of the substrate 11 to the region 11A where the irregularities are formed. In a desirable manufacturing method, a part of the surface of the substrate having a mirror-polished surface is etched to form the irregularities capable of scattering the light, and the GaN-based semiconductor crystal film is laterally grown from the region where no irregularity is formed to the region where the irregularities are formed. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

The present invention uses a GaN-based semiconductor represented by the chemical formula Al _a In _b Ga _1-ab N (0 ≦ a ≦ 1, 0 ≦ b ≦ 1, 0 ≦ a + b ≦ 1) to form a light emitting diode structure (hereinafter referred to as “light emitting diode structure”). In particular, an LED structure made of a GaN-based semiconductor on a substrate having irregularities capable of scattering light formed on a surface thereof. The present invention relates to a GaN-based light-emitting diode element formed by forming and a manufacturing method thereof.

In a GaN-based light emitting diode element, it has been practiced to improve the light extraction efficiency by forming irregularities for scattering light on the surface of a substrate (Patent Documents 1 to 3). As a method for forming irregularities, there is a method in which fine particulate matter is randomly deposited on the surface of a substrate to be processed, and the surface is etched using the particulate matter as a mask (random etching mask). . As one form of such an etching process, there is known an etching process for a substrate surface that is performed using a dry etching apparatus so that etching and deposition occur simultaneously (Patent Document 1).
JP 2006-100518 A JP 2003-218383 A JP 2005-354020 A

From the viewpoint of improving the light extraction efficiency of the light-emitting diode element, the unevenness formed on the surface of the substrate should not have a flat surface portion parallel to the layer direction of the layered GaN-based semiconductor constituting the LED structure. In addition, (b) it is desired that the periodicity of the shape is low. According to the etching process using a random etching mask, it is possible to preferably form irregularities having such properties. However, there is a problem that it is difficult to form a single crystal layer of a GaN-based semiconductor by epitaxial growth on the surface of the substrate having such irregularities, that is, it is difficult to form an LED structure.

The present invention has been made in view of such circumstances, and its main object is to form an LED structure made of a GaN-based semiconductor on the substrate surface while forming preferable irregularities on the substrate surface in order to improve light extraction efficiency. It is an object to provide a GaN-based light emitting diode element formed. Another object of the present invention is to provide a preferred method for producing such a GaN-based light emitting diode element.

The following invention is disclosed as a suitable means for achieving the above object.
(1) It has a substrate and a GaN-based semiconductor formed on the substrate, and the surface of the substrate is partially provided with a region on which irregularities capable of scattering light are formed, the GaN-based semiconductor The semiconductor includes a GaN-based light-emitting diode element, wherein the semiconductor includes a GaN-based semiconductor crystal film laterally grown on a region where the unevenness is formed from a region where the unevenness is not formed on the surface of the substrate.
(2) The GaN-based light-emitting diode element according to (1), wherein the unevenness is an unevenness formed by an etching process using a random etching mask.
(3) The GaN-based light-emitting diode element according to (1) or (2), wherein the convex portions included in the concave and convex portions have a cone shape.
(4) The GaN-based light-emitting diode element according to any one of (1) to (3), wherein the height difference of the unevenness is 0.1 μm to 3 μm.
(5) a step of etching a part of the surface of the substrate having a mirror-polished surface to form unevenness capable of scattering light; and a GaN-based semiconductor crystal film is formed with the unevenness on the surface of the substrate. And a step of laterally growing on the region where the projections and depressions are formed from a region that is not formed, a method for manufacturing a GaN-based light-emitting diode element.
(6) The manufacturing method according to (5), wherein the etching process is an etching process using a random etching mask.
(7) The manufacturing method according to (6), wherein the etching process is an etching process performed using a dry etching apparatus so that etching and deposition occur simultaneously.
(8) The manufacturing method in any one of said (5)-(7) whose convex part contained in the said unevenness is a cone shape.
(9) The manufacturing method according to any one of (5) to (8), wherein a height difference of the unevenness is 0.1 μm to 3 μm.

The GaN-based light-emitting diode device according to the embodiment of the present invention has preferable irregularities on the substrate surface for improving light extraction efficiency, and an LED structure made of a GaN-based semiconductor is formed on the substrate surface. It exhibits high luminous efficiency and can be suitably used for various applications that require high output, including lighting applications and display applications.

According to the method for manufacturing a GaN-based light-emitting diode element according to the embodiment of the present invention, the substrate surface has preferable irregularities for improving light extraction efficiency, and an LED structure made of a GaN-based semiconductor is formed on the substrate surface. The manufactured GaN-based light emitting diode element can be easily manufactured.

A GaN-based light-emitting diode element according to a preferred embodiment of the present invention includes a substrate and a GaN-based semiconductor formed on the substrate, and unevenness capable of scattering light is formed on the surface of the substrate. The GaN-based semiconductor is formed by laterally growing a GaN-based semiconductor crystal film on a region where the irregularities are formed from a region where the irregularities are not formed on the surface of the substrate. Contains. FIG. 1 is a cross-sectional view showing a structural example of a GaN-based light emitting diode element configured as described above. A GaN light-emitting diode element 10 shown in FIG. 1 has a substrate 11 and a GaN-based semiconductor 12 formed on the substrate. The surface of the substrate 11 on the side where the GaN-based semiconductor 12 is formed has a first region 11A, which is a region where irregularities capable of scattering light are formed, and a second region 11B, which is a mirror-like flat region. is doing. The GaN-based semiconductor 12 has a base layer part 121 provided on the substrate 11 side and an LED structure forming part 122 provided thereon. The base layer portion 121 completely covers the surface of the substrate 11, and the upper surface thereof is a flat surface. The base layer portion 121 includes, in part, a GaN-based semiconductor crystal film that is laterally grown from the second region 11B on the substrate surface to the first region 11A. The LED structure forming part 122 includes a first conductivity type layer 1221 and a second conductivity type layer 1222 in order from the base layer part 121 side. The first conductivity type layer 1221 and the second conductivity type layer 1222 form a pn junction that can emit light by carrier injection. A lower electrode 13 is formed on the first conductivity type layer 1221, and an upper electrode 14 is formed on the second conductivity type layer 1222.

A preferred configuration of each part of the GaN-based light emitting diode element 10 will be described.

(substrate)
The substrate 11 may be any substrate that can be used for epitaxial growth of GaN-based semiconductor crystals. Sapphire, SiC, GaN, AlGaN, AlN, Si, GaAs, GaP, spinel, ZnO, NGO (NdGaO ₃ ), LGO (LiGaO ₂ ) A single crystal substrate made of a material such as LAO (LaAlO ₃ ), ZrB ₂ , or TiB ₂ can be preferably used. A template (a substrate having a multilayer structure) having a single crystal layer made of these materials as a surface layer on the crystal growth surface side may be used. Whether it is a single crystal substrate or a template, the substrate 11 is preferably transparent to light emitted from the element.

The unevenness of the first region 11A on the substrate surface is preferably an unevenness formed by an etching process using a random etching mask. That is, the unevenness is formed by randomly depositing fine particulate matter on the surface of the substrate and etching the surface using the particulate matter as a mask. The unevenness formed in this way exhibits a strong light scattering action because the periodicity of the shape is low. Furthermore, if the convex portions included in the concaves and convexes are conical, the light scattering action by the concaves and convexes can be particularly strengthened. This is because the flat surface parallel to the layer direction of the layered GaN-based semiconductor 12 included in the unevenness is reduced. The height difference of the unevenness in the first region 11A (the height of the top of the convex portion viewed from the bottom of the concave portion) can be, for example, 0.05 μm to 5 μm, preferably 0.1 μm to 3 μm, More preferably, it is 0.3 μm to 1 μm. If the height difference of the unevenness is too small compared to the wavelength of light, the light scattering effect is weakened because the interaction between the light wave and the unevenness is reduced. When the height difference of the unevenness is excessively increased, the light scattering effect is weakened because the distribution density of the protrusions and recesses is lowered.

The pattern formed by the first region 11A and the second region 11B on the surface of the substrate 11 is a pattern in which the first region 11A and the second region 11B are alternately arranged along at least one direction. As one pattern, a pattern in which each of the first region and the second region is formed in a stripe shape and arranged in parallel and alternately is exemplified. In this case, the stripe width of the second region can be, for example, 0.5 μm to 20 μm, preferably 1 μm to 10 μm, more preferably 2 μm to 5 μm. As another pattern, a plurality of isolated island-like first regions are separated by the second region, and conversely, a plurality of isolated island-like second regions are separated by the first region. Patterns. In addition, a pattern in which a plurality of first regions and second regions are formed in an annular shape surrounding a certain point and the like are exemplified. In any case, the area ratio of the first region 11A in the surface of the substrate is preferably 40% to 90%, more preferably 50% to 85%, and still more preferably 60% to 80%. When the area ratio of the first region 11A is too small, the effect of improving the light extraction efficiency due to the unevenness formed in the region is not sufficiently exhibited. If the area ratio of the first region 11A is too large, in other words, if the contact area between the substrate 11 and the GaN-based semiconductor 12 (≈the area of the second region) is too small, the substrate 11 and the GaN-based material due to thermal stress. There is a possibility that peeling occurs with the semiconductor 12. In any case, any boundary between the first region 11A and the second region 11B on the substrate surface is formed in a direction parallel to the A plane of the GaN-based semiconductor single crystal epitaxially grown on the substrate. It is preferable to do. With such a configuration, since the lateral growth of the GaN-based semiconductor crystal from the first region 11A to the second region 11B is accelerated, even when the area of the first region is set large, the GaN-based semiconductor crystal is grown on the wide first region. It becomes easy to cover with a system semiconductor crystal.

(Base layer)
The base layer portion 121 of the GaN-based semiconductor 12 is not an essential component for the LED structure, but by providing this layer, the crystal quality of the LED structure forming portion 122 formed thereon is improved, and as a result, the luminous efficiency ( (Internal quantum efficiency) can be improved. For this purpose, the thickness of the base layer portion 121 is preferably 1 μm or more, more preferably 2 μm or more, and further preferably 3 μm or more. In order to improve the crystallinity of the base layer portion 121, it is preferable to interpose a buffer layer between the substrate 11 and the base layer portion 121, and further, no impurity should be added to the base layer portion 121. Is preferred. However, since the addition of Mg (magnesium) has an effect of promoting lateral growth of the GaN-based semiconductor crystal, when the area of the first region 11A on the surface of the substrate 11 is set to be large, the base layer portion 121 is initially grown. When Mg is added, it becomes easy to form the base layer portion 121 covering the wide first region. Since the GaN-based semiconductor crystal film laterally grown on the first region 11A of the substrate 11 has a low transition defect density, the GaN-based semiconductor crystal grown thereon has a particularly high quality. The composition of the GaN-based semiconductor crystal constituting the base layer part 121 is not limited, but for the purpose of improving the crystallinity of the LED structure forming part 122, the base layer part 121 is a GaN (gallium nitride) layer having a thickness of several μm or more. It is preferable to contain. In that case, the base layer portion 121 may be composed only of the GaN layer. In addition, a strained superlattice structure is formed in the base layer portion 121 in order to suppress the penetration transition caused by lattice mismatch at the interface between the substrate 11 and the base layer portion 121 from propagating upward in the base layer portion 121. May be provided.

(LED structure forming part)
Any one of the first conductivity type layer 1221 and the second conductivity type layer constituting the LED structure forming portion 122 may be a layer including an n-type semiconductor and the other including a p-type semiconductor. Preferably, the first conductivity type layer 1221 to be grown first is formed using an n-type semiconductor. When an active layer is provided at the junction between the first conductivity type layer 1221 and the second conductivity type layer 1222 to form a double heterostructure, the light emission efficiency is dramatically improved. The active layer preferably has a multiple quantum well structure.

(Electrodes and others)
For the material, structure, and the like of the lower electrode 13 formed on the first conductivity type layer 1221 and the upper electrode 14 formed on the second conductivity type layer 1222, well-known techniques can be referred to as appropriate. Specifically, the electrodes formed on the surface of the n-type GaN-based semiconductor are simple substances such as Ti (titanium), Al (aluminum), W (tungsten), V (vanadium), and Cr (chromium), or these It can form using the alloy containing 1 or more types of metals chosen from these. In addition, the electrode formed on the surface of the p-type GaN-based semiconductor may be a single substance such as Ni (nickel), Co (cobalt), platinum group (Pt, Pd, Rh, Ir, Os, Ru), Au (gold), or , And an alloy containing one or more metals selected from these. Conductive oxides such as indium oxide, tin oxide, zinc oxide, gallium oxide, ITO (indium tin oxide), IZO (indium zinc oxide), AZO (aluminum zinc oxide), FTO (fluorine-doped tin oxide) It can also be used as an electrode formed on any surface of an n-type GaN-based semiconductor and a p-type GaN-based semiconductor. Each of the lower electrode 13 and the upper electrode 14 has a surface layer of Ag (silver), Au (gold), Sn (tin), In (indium), Bi (so that it can be easily connected to an external electrode. It is preferable to provide a layer made of bismuth), Cu (copper), Zn (zinc), or the like. The upper electrode 14 may be composed of a full-surface electrode that covers substantially the entire upper surface of the second conductivity type layer 1222 and a pad electrode formed on a part of the full-surface electrode. What is necessary is just to provide the surface layer which consists of the said material in a pad electrode. The connection between the lower electrode 13 and the upper electrode 14 and the external electrode can be performed using a bonding wire made of Au or the like, or using a conductive bonding material such as solder, a eutectic alloy, or a conductive paste. You can also. In a preferred embodiment, the upper electrode 14 is composed of a light-transmitting full-surface electrode made of a conductive oxide and a pad electrode formed on a part thereof, and the light-emitting diode element 10 is flip-chip mounted. In flip-chip mounting, the lower electrode 13 and the upper electrode 14 are generally connected to an external electrode using a conductive bonding material.

Next, an example of a manufacturing method of the GaN-based light emitting diode element shown in FIG. 1 will be described.

(Board processing)
A C-plane sapphire substrate (single-side polished substrate) having a mirror-polished crystal growth surface and having a diameter of 2 inches is prepared. To form a line and space pattern. The line direction (longitudinal direction of the photoresist film patterned in a stripe shape) is the <11-20> direction of sapphire. This direction is parallel to the A plane of the GaN-based semiconductor crystal (C-axis oriented crystal) that is epitaxially grown on the C-plane sapphire substrate. Next, this substrate is loaded into the etching chamber of a reactive ion etching apparatus, and the portion of the crystal growth surface of the substrate that is not protected by the photoresist film is etched using conditions that cause etching and deposition simultaneously. To do. More specifically, trifluoromethane is used as the etching gas, the pressure in the chamber is 1.5 to 6.0 Pa, the ICP (inductively coupled plasma) power is 150 to 600 W, and the bias voltage is 300 W to 500 W. The etching time is 15 minutes to 40 minutes. By this treatment, conical convex portions having a height of 0.3 μm to 0.5 μm are formed on the surface of the sapphire substrate (the portion not protected by the photoresist film) at a density of 1 piece / μm ² to 70 pieces / μm ² . The unevenness can be formed. The shape and size of the unevenness can be changed by changing the ICP power, the bias voltage, the pressure in the chamber, and the etching time. After the treatment, the substrate is taken out from the reactive ion etching apparatus, the photoresist film is removed, and organic cleaning is performed.

(Formation of GaN-based semiconductors)
A GaN-based semiconductor having an LED structure is formed on the substrate on which the crystal growth surface is partially processed to form irregularities by using the MOVPE (organometallic compound vapor phase epitaxy) method. More specifically, first, the substrate mounted in the MOVPE apparatus is cleaned by heating to 1100 ° C. in a hydrogen stream. Next, the substrate temperature is lowered to 500 ° C. to 650 ° C., TMG (trimethylgallium), TMA (trimethylaluminum), and ammonia are used as raw materials, and the composition ratio of Al (aluminum) is higher than the composition ratio of Ga (gallium). A larger AlGaN buffer layer is formed to a thickness of about 30 nm. After the buffer layer is formed, the substrate temperature is raised to 1000 ° C. while supplying ammonia onto the substrate, and then GaN is formed to a thickness of about 4 μm using TMG and ammonia as raw materials. At this time, the ratio of the supply amount of TMG and ammonia supplied onto the substrate is adjusted to a ratio at which the lateral growth rate of the GaN crystal is sufficiently increased. Further, hydrogen gas and nitrogen gas are used as the raw material carrier gas. FIG. 2 schematically shows how the GaN crystal thus formed grows. FIG. 2A is a cross-sectional view of the sapphire substrate 21 before the GaN crystal is grown, and shows a cross section orthogonal to the longitudinal direction of the photoresist film patterned in the stripe shape used in the previous step. Looking at this cross section, the first region 21A in which irregularities are formed and the second region 21B in which irregularities are not formed are alternately arranged on the crystal growth surface of the substrate 21. FIG. 2B shows the initial growth state, and the GaN crystal 22 is formed only on the second region of the crystal growth surface (the buffer layer is not shown. FIG. 2C). The same applies to d). In FIG. 2 (c), where the growth has continued, the GaN crystal 22 has further grown in the vertical and lateral directions from the state shown in FIG. 2 (b). FIG. 2D shows a state where the growth has further continued from the state of FIG. 2C, and the GaN crystals grown from the two adjacent second regions are connected by lateral growth, and a layered structure having a flat upper surface is obtained. A state in which the GaN crystal 22 covers the entire crystal growth surface of the sapphire substrate 21 is achieved.

On the undoped GaN layer grown as described above, an n-type contact layer composed of Si-doped GaN, an active layer having a multiple quantum well structure composed of an undoped GaN barrier layer and an undoped InGaN well layer, and Mg-doped AlGaN A p-type cladding layer and a p-type contact layer made of Mg-doped AlGaN are sequentially formed and laminated to obtain a wafer made of a substrate and a GaN-based semiconductor.

(Electrode formation, etc.)
An upper electrode and a lower electrode are formed on the wafer. The upper electrode is composed of a full-surface electrode made of an ITO film and a pad electrode formed on a part thereon. The lower electrode is formed on the n-type contact layer partially exposed by dry etching. After forming the electrode, the lower surface (non-polished surface) of the sapphire substrate is ground and polished to reduce the thickness of the substrate to 100 μm, and the wafer is divided using a known scribing method to obtain a chip-like light emitting diode element. obtain.

In the manufacturing method described above, in order to form irregularities on the substrate surface, a reactive ion etching apparatus is used to etch the substrate so that etching and deposition occur simultaneously. This reactive ion etching apparatus It is also possible to replace with a plasma etching apparatus. In such a method of etching a substrate so that etching and deposition occur at the same time using a dry etching apparatus, the etching gas and / or the workpiece (substrate) is a raw material for a random etching mask with fine particles. However, the method of processing the unevenness of the substrate surface is not limited to this method, and a method of dry etching treatment after forming a random etching mask in advance can also be adopted. As an example of a random etching mask in that case, after forming an Au thin film (film thickness of about 5 nm) on the substrate surface by vapor deposition, the substrate temperature is raised to about 180 ° C. to agglomerate the Au that had formed the thin film. And fine particles (Patent Document 3). In addition, the random etching mask is not limited to the one in which the particulate matter is deposited. For example, after the mask material layer is formed by applying a solution in which the block copolymer is dissolved, the mask material layer is annealed. The block copolymer may be phase-separated (Patent Document 2). In the case of using these random etching masks, a region of the substrate surface where the unevenness is not planned is covered with a protective film, the random etching mask is formed, and processing by dry etching is performed. The protective film may be any film that can prevent the surface of the substrate covered with the protective film from deforming into a non-mirror surface in the process of forming the random etching mask and the subsequent dry etching process.

The present invention is not limited to the embodiments explicitly described above, and various modifications can be made without departing from the spirit of the invention.

It is sectional drawing which shows the structure of the GaN-type light emitting diode element which concerns on embodiment of this invention. It is sectional drawing for demonstrating the manufacturing method of the GaN-type light emitting diode element which concerns on embodiment of this invention.

Explanation of symbols

10 GaN-based light-emitting diode element 11 Substrate 12 GaN-based semiconductor 13 Lower electrode 14 Upper electrode

Claims (9)

A substrate and a GaN-based semiconductor formed on the substrate;
The surface of the substrate is partially provided with a region where unevenness capable of scattering light is formed,
The GaN-based semiconductor includes a GaN-based semiconductor crystal film laterally grown on a region where the irregularities are formed from a region where the irregularities are not formed on the surface of the substrate.
GaN-based light emitting diode element. The GaN-based light emitting diode element according to claim 1, wherein the unevenness is an unevenness formed by an etching process using a random etching mask. The GaN-based light-emitting diode element according to claim 1, wherein the convex portion included in the concave and convex portions has a cone shape. The GaN-based light-emitting diode element according to any one of claims 1 to 3, wherein a height difference of the unevenness is 0.1 µm to 3 µm. A step of etching a part of the surface of the substrate having a mirror-polished surface to form light unevenness, and a region where the unevenness of the surface of the substrate is not formed in the GaN-based semiconductor crystal film And a step of laterally growing on the region where the irregularities are formed from above. The manufacturing method according to claim 5, wherein the etching process is an etching process using a random etching mask. The manufacturing method according to claim 6, wherein the etching process is an etching process performed so that etching and deposition occur simultaneously using a dry etching apparatus. The manufacturing method in any one of Claims 5-7 whose convex part contained in the said unevenness | corrugation is cone shape. The manufacturing method according to any one of claims 5 to 8, wherein a height difference of the unevenness is 0.1 µm to 3 µm.

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