AlN TEMPLATE SUBSTRATE AND METHOD FOR PRODUCING SAME

Abstract

The present invention improves the characteristics of an AlN template substrate. An AlN template substrate according to the present invention is characterized in that: the AlN template substrate has an AlN layer formed on a main surface of a sapphire substrate; the main surface of the sapphire substrate has a C-plane inclined at an off angle of 0.02°-0.35°; and a step linear rate is at least 90%, the step linear rate being obtained by dividing the linear distance connecting a first contact point which is between a ridge line of a step in an AFM image of a surface of the AlN layer and an edge of the AFM image, and a second contact point by the length of the ridge line of the step extending from the first contact point to the second contact point.

Description

AlN template substrate and method of manufacturing same

[0001] The present invention relates to an AlN template substrate and a method for manufacturing the same, and more particularly to an AlN template substrate that can have excellent light-emitting efficiency when used in the fabrication of a group III nitride semiconductor device, and a method for manufacturing the same.

[0002] Group III nitride semiconductors made of compounds of N with Al, Ga, In, etc. have been widely used as materials for light-emitting elements or elements for electronic devices. In particular, Group III nitride semiconductors made of AlGaN with an Al composition ratio of 50% or more are used as active layers (also referred to as "light-emitting layers") of deep ultraviolet light-emitting devices (DUV-LEDs) that emit light at wavelengths of 300 nm or less.

[0003] Group III nitride semiconductors have high melting points and high nitrogen dissociation pressures, making bulk single crystal growth difficult. Therefore, they are usually formed as Group III nitride semiconductor layers by epitaxial growth on a heterogeneous sapphire substrate.

[0004] In general, the better the crystallinity of the group III nitride semiconductor layer, the better the light-emitting properties of the group III nitride semiconductor light-emitting device that can be fabricated. It is known that epitaxial growth of a group III nitride semiconductor on a sapphire substrate as described above results in lattice mismatch between the sapphire substrate and the group III nitride semiconductor, which contributes to deterioration of crystallinity. To alleviate the lattice strain caused by this lattice mismatch, AlN template substrates, in which an AlN layer is epitaxially grown on a sapphire substrate, have come into use. Because the characteristics of a group III nitride semiconductor light-emitting device are affected by the surface characteristics of the AlN layer, various attempts have been made in recent years to improve the characteristics of AlN template substrates epitaxially grown on sapphire substrates.

[0005] For example, according to Patent Document 1, a group III nitride semiconductor epitaxial substrate is made of a sapphire single crystal substrate whose main surface has a crystal orientation tilted by 0.35° to 0.55° from the C-axis direction, i.e., a C-plane sapphire single crystal substrate with an off-angle of 0.35° to 0.55°, and the thickness of the AlN layer epitaxially grown on the main surface is controlled to 0.3 μm to 0.7 μm, followed by heat treatment, thereby improving the crystallinity and flatness of the AlN layer epitaxially grown on the sapphire substrate.

[0006] Furthermore, Patent Document 2 describes that using only hydrogen gas as the carrier gas for the raw material trimethylaluminum (TMA) gas and using only hydrogen gas as the carrier gas for ammonia gas makes it possible to promote the lateral growth of AlN crystals and improve the flatness of the surface of the AlN layer, compared to when at least one of the carrier gases is nitrogen gas or a mixture of nitrogen gas and hydrogen gas.

[0007] JP 2016-064928 A JP 2017-139253 A

[0008] The technology described in Patent Document 1 improves the surface flatness and crystallinity of an AlN layer on a C-plane sapphire substrate with an off-angle of 0.35° to 0.55°. On the other hand, the characteristics of an AlN layer on a sapphire substrate with an off-angle of less than 0.35° are insufficient. However, when the back surface of the sapphire substrate is used as the light extraction surface, it may be desirable to use a sapphire substrate with an off-angle of less than 0.35°. The primary purpose of forming an excellent AlN layer is to improve the characteristics of a Group III nitride semiconductor layer formed on the AlN layer, and further improved techniques are desired.

[0009] Therefore, an object of the present invention is to improve the characteristics of an AlN template substrate when a sapphire substrate having an off-angle of 0.02° or more and less than 0.35° is used.

[0010] The present inventors have conducted extensive research into ways to solve the above-mentioned problems. While Patent Document 1 uses crystallinity and flatness as evaluation parameters for AlN template substrates, the present inventors have focused on a new parameter called step linearity and optimized it to complete an AlN template substrate with better characteristics. As proposed in Patent Document 2, it has been conventionally believed that using only hydrogen gas as a carrier gas is preferable. However, through detailed research, the present inventors have found that, when using a sapphire substrate with an off-angle of 0.02° or more and less than 0.35°, using a mixed gas of hydrogen gas and nitrogen gas can optimize the step linearity and improve the light output of a light-emitting device composed of a group III nitride semiconductor layer formed on an AlN layer. This finding led to the completion of the present invention.

[0011] That is, the gist of the present invention is as follows: (1) An AlN template substrate comprising a sapphire substrate and an AlN layer formed on a primary surface of the sapphire substrate, wherein the primary surface of the sapphire substrate is a C-plane inclined at an off-angle of 0.02° or more and less than 0.35°, and wherein a step linearity ratio, which is calculated by dividing the linear distance connecting a first contact point on one side of a ridge line of a step in an AFM image of the surface of the AlN layer and an edge of the AFM image to a second contact point on the other side, by the length of the ridge line of the step extending from the first contact point to the second contact point, is 90% or more.

[0012] (2) The AlN template substrate according to (1) above, wherein the AlN layer has a surface flatness Ra of 1.1 nm or less.

[0013] (3) The AlN template substrate according to (1), wherein the X-ray rocking curve of the (0002) plane of the AlN layer has a half-width of 100 seconds or less, and the X-ray rocking curve of the (10-12) plane has a half-width of 300 seconds or less.

[0014] (4) A method for manufacturing an AlN template substrate, comprising: a first step of epitaxially growing an AlN layer on a primary surface of a sapphire substrate; and a second step of heat-treating the AlN layer, wherein the primary surface of the sapphire substrate is a C-plane inclined at an off-angle of 0.02° or more and less than 0.35°, a carrier gas used in the first step is a mixed gas of hydrogen gas and nitrogen gas, and the heat treatment in the second step is performed in an atmosphere containing nitrogen element.

[0015] (5) The method for manufacturing an AlN template substrate according to (4) above, wherein the temperature inside the furnace during the heat treatment in the second step is higher than the temperature inside the furnace in the first step.

[0016] (6) The method for producing an AlN template substrate according to (4) or (5) above, wherein the ratio of nitrogen gas in the carrier gas is 1% or more and 10% or less.

[0017] According to the present invention, it is possible to provide an AlN template substrate that, when used in the fabrication of a Group III nitride semiconductor device, can provide a Group III nitride semiconductor device having excellent light-emitting efficiency, and a method for fabricating the same.

[0018] FIG. 1 is an AFM diagram illustrating a step linearity in the present invention. FIG. 2 is a cross-sectional schematic diagram illustrating an AlN template substrate according to the present invention. FIG. 3 is a flowchart illustrating a manufacturing method of an AlN template substrate according to the present invention. FIG. 4 is a schematic diagram illustrating an off-angle of a sapphire substrate surface according to the present invention. FIG. 5 is a schematic diagram illustrating the crystal orientation of a sapphire single crystal. FIG. 6 is a schematic diagram of an MOCVD apparatus when growing an AlN layer according to the present invention. FIG. 7 is a cross-sectional schematic diagram showing the layer structure of a light-emitting device according to the present embodiment. FIG. 8 is an AFM image of an AlN template substrate according to Example 1. FIG. 9 is an AFM image of an AlN template substrate according to Example 2. FIG. 10 is an AFM image of an AlN template substrate according to a comparative example.

[0019] Prior to describing the embodiments according to the present invention, the following points will be explained in advance.

[0020] <Step Linearity> The step linearity in the present invention will be described with reference to FIG. 1 . An AFM (atomic force microscope) image of the surface of the AlN layer is acquired, and the contact points between the step ridge E1 in the AFM image and the edges of the AFM image (the upper end E2 and lower end E3 of the observation range) are designated as the first contact point A and the second contact point B, respectively. The step linearity in the present invention is defined as d / L, which is the linear distance d connecting the first contact point A and the second contact point B divided by the length L of the step ridge E1 extending from the first contact point A to the second contact point B. Note that FIG. 1 shows an AFM image acquired within a rectangular area measuring 5.0 μm × 2.5 μm. The step linearity in the present invention is measured within the same rectangular area measuring 5.0 μm × 2.5 μm as in FIG. 1 , using an AFM image captured so that the linear distance d is approximately 2.5 μm to 2.8 μm. Then, of all the step ridgelines E1 observed extending from the first contact point A to the second contact point B, the one with the smallest d / L is selected, and the minimum value of d / L is calculated.

[0021] The flatness (Ra) value in this embodiment can be determined by automatic calculation using application software attached to the AFM device based on the surface profile obtained by AFM measurement, in accordance with JIS (B0601-2001). In the examples of this specification, the flatness was determined by performing AFM measurement on a rectangular area of ​​5.0 μm × 2.5 μm.

[0022] In this embodiment, the crystallinity is evaluated by the value of the half-width (arcsec) of the X-ray rocking curve obtained by an X-ray diffractometer. The half-width may be automatically calculated using application software attached to the X-ray diffractometer. In this embodiment, X-rays are irradiated onto each of the (0002) plane and the (10-12) plane to be evaluated, and the resulting diffraction profiles are evaluated. In particular, the measurement results for the (10-12) plane serve as an index of the threading dislocation density (mixed screw and edge-like dislocations) within the crystal. Note that a bar representing a negative number in the Miller indices is represented by placing a minus sign before the negative number.

[0023] The thickness of the AlN layer is non-uniform on a microscopic scale at the atomic size level. Therefore, in this specification, the thickness of the AlN layer refers to the thickness of the AlN layer at the wafer center (hereinafter referred to as the "center thickness"). In this embodiment, the thickness of the AlN layer was measured using a Nanospec M6100A optical interference film thickness measuring instrument manufactured by Nanometrics, Inc., and the thickness at the wafer center was taken as the center thickness, with the average value of film thicknesses measured at 25 equally spaced locations on the wafer surface taken as the average thickness.

[0024] In this embodiment, the thickness of each layer of the light-emitting layer formed by epitaxial growth on the AlN template substrate can be calculated from cross-sectional observation of the grown layer using a TEM-EDS (transmission electron microscope).

[0025] In this embodiment, "AlGaN" is Al ａ Ga １―ａ N. In this embodiment, the value of the Al composition ratio a of AlGaN is determined from the wavelength observed in photoluminescence measurements performed on the surface of each layer when the layer is grown. Unless otherwise specified, the Al composition ratio a is 0 to 1. As a method for determining the Al composition from the cross section of the light-emitting element 100, for example, EDS (energy dispersive X-ray spectroscopy) can be used.

[0026] The dopant concentration in the present invention is a value measured by SIMS (secondary ion mass spectrometry). In this specification, a layer that is not intentionally doped with a specific impurity such as Zn, Te, or Si and does not function electrically as a p-type or n-type is referred to as "i" type or "undoped." An undoped layer may contain unavoidable impurities during the manufacturing process, and specifically, a layer with a small carrier density (e.g., 4×10 １６ / cm ３ If the thickness is less than 100 nm, the polymer will be treated as "undoped" in this specification.

[0027] Hereinafter, embodiments of the present invention will be described with reference to the drawings. For ease of explanation, the aspect ratios of the substrate and each layer are exaggerated from their actual ratios in Fig. 2, Fig. 3, and Fig. 4. For simplicity of illustration, Fig. 2 and Fig. 3 do not show the off-angle θ of the sapphire substrate 10. Instead, Fig. 4 shows an enlarged schematic diagram for explaining the off-angle θ.

[0028] (AlN Template Substrate) The AlN template substrate obtained by the present invention will now be described. As shown in FIG. 2, the AlN template substrate 1 according to the present invention has an AlN layer formed on a primary surface 10A of a sapphire substrate 10. The primary surface 10A of the sapphire substrate 10 is characterized in that the C-plane is inclined at an off-angle of 0.02° or more and less than 0.35°, and the step linearity is 90% or more. The crystal axis orientation of the inclination direction at which the off-angle is provided may be either the m-axis direction or the a-axis direction, but the m-axis direction is preferred. The off-angle is preferably 0.04° or more and 0.30° or less, and more preferably 0.06° or more and 0.19° or less. The step linearity is more preferably 95% or more, with the theoretical upper limit being 100%, but may be 99.9% or less in consideration of productivity. The thickness of the AlN layer 20 is preferably 0.3 μm or more and 0.7 μm or less.

[0029] The surface flatness Ra of the AlN layer 20 is preferably 1.1 nm or less, and more preferably 0.21 nm or less.

[0030] Furthermore, it is preferable that the half width of the X-ray rocking curve of the (0002) plane of the AlN layer 20 is 100 seconds or less, and the half width of the X-ray rocking curve of the (10-12) plane is 300 seconds or less.

[0031] When the AlN template substrate 1 according to the present invention is used to fabricate a Group III nitride semiconductor device, the resulting device has excellent light emission efficiency. Hereinafter, each component will be described in detail through an embodiment of a manufacturing method for obtaining the AlN template substrate 1 and each step thereof.

[0032] <Method for Manufacturing AlN Template Substrate> FIG. 3 is a flowchart of a method for manufacturing the above-described AlN template substrate 1. As shown in FIG. 3, the method for manufacturing the AlN template substrate 1 according to the present invention includes a first step ( FIGS. 3A and 3B ) of epitaxially growing an AlN layer 20 on the primary surface 10A of a sapphire substrate 10, and a second step ( FIG. 3C ) of heat-treating the AlN layer 20 formed in the first step. Here, as described above, the primary surface 10A of the sapphire substrate 10 is a C-plane inclined at an off-angle of 0.02° or more and less than 0.35° ( FIG. 4 ). θ in FIG. 4 is the same angle as the off-angle. Furthermore, the carrier gas used in the first step is a mixed gas of hydrogen gas and nitrogen gas, and the heat treatment in the second step is performed in an atmosphere containing nitrogen element.

[0033] <<First Step>> In the first step, a sapphire substrate 10 is first prepared as shown in FIG. 3A . In the present invention, a sapphire substrate 10 is used whose main surface 10A is a plane inclined at an off angle of 0.02° or more and less than 0.35° from the C-plane. Hereinafter, in this specification, such an inclination angle of the C-plane is simply referred to as the "off angle" or "off angle θ" of the sapphire substrate 10. The crystal axis orientation of the inclination direction for providing the off angle θ may be either the m-axis direction or the a-axis direction, but the m-axis direction is more preferable. Hereinafter, FIG. 4 is an enlarged schematic diagram of the main surface 10A. The terrace width W and step height H on the main surface 10A are appropriately determined depending on the off angle θ and the axis orientation. FIG. 5 is a schematic diagram showing the crystal orientation of a typical hexagonal sapphire single crystal, illustrating the a-axis, m-axis, and C-plane of the sapphire single crystal. The off-angle θ, terrace width W, and step height H are measured by X-ray diffraction measurement, AFM, or the like.

[0034] The sapphire substrate 10 may be manufactured according to a conventional method. The off-angle θ of the sapphire substrate 10 involves an unavoidable error in the manufacturing process of the sapphire substrate. Therefore, in the present invention, angles within an error range of 8% from the upper and lower limits of the off-angle θ are considered to be included in the scope of the present invention. Other specifications of the sapphire substrate 10, such as the thickness and width, may be appropriately designed depending on the application of the AlN template substrate 1.

[0035] Next, as shown in FIG. 3B , an AlN layer 20 is epitaxially grown on the sapphire substrate 10. Here, in the present invention, the thickness T of the AlN layer 20 is preferably 0.3 μm or more and 0.7 μm or less. The AlN layer 20 can be formed, for example, by metal organic chemical vapor deposition (MOCVD). In the present invention, when epitaxially growing the AlN layer 20 on the sapphire substrate 10, as will be described later, it is preferable to use ammonia gas and liquid trimethylaluminum (TMA) as raw materials, and further, a mixed gas of hydrogen gas and nitrogen gas is used as the carrier gas. Here, in the present invention, it is preferable that the proportion of nitrogen gas in the carrier gas is 1% or more and 10% or less. The proportion of nitrogen gas is determined by the flow rate N of the nitrogen gas. ２ [sccm] is the total carrier gas flow rate (N ２ +H ２ ) [sccm] is used.

[0036] In the manufacturing method of the present invention, a mixture of hydrogen gas and nitrogen gas is used as the carrier gas. While it has been conventionally considered preferable to use only hydrogen gas as the carrier gas, the inventors have conducted extensive research and found that using a mixture of hydrogen gas and nitrogen gas, which was previously considered undesirable, increases the step linearity and, as shown in the examples described below, increases the light output of an LED formed on the AlN layer 20. It is believed that the linearity of the step ridges reduces fluctuations in the Al composition in the in-plane direction in, for example, an n-type semiconductor layer or a light-emitting layer formed on the AlN layer 20, improving the compositional abruptness of the interface in the light-emitting layer and improving the light-emitting efficiency.

[0037] The growth temperature of the AlN layer 20 is preferably 1270° C. or higher and 1350° C. or lower, and more preferably 1290° C. or higher and 1330° C. or lower. This temperature range ensures improved crystallinity of the AlN layer 20 after heat treatment in the subsequent second step. The growth pressure in the chamber is not intended to be limited, but can be, for example, 5 Torr to 20 Torr, and more preferably 8 Torr to 15 Torr.

[0038] In addition, ammonia (NH ３ The molar ratio of Group V element to Group III element (hereinafter referred to as V / III ratio) calculated based on the growth gas flow rates of Group V element gas such as HCl (HClO) gas and Group III element gas such as trimethylaluminum (TMA) gas is not intended to be limited, but the V / III ratio can be, for example, in the range of 130 to 190, and more preferably in the range of 140 to 180. Note that, since an appropriate V / III ratio exists depending on the growth temperature and growth pressure, it is preferable to appropriately set the growth gas flow rate.

[0039] Referring to FIG. 6 , an MOCVD apparatus 50 used to epitaxially grow the AlN layer 20 will be described. In the MOCVD apparatus 50, a source material and a carrier gas are supplied to a reactor 55 from an ammonia gas supply source 51, a nitrogen gas supply source 52, a hydrogen gas supply source 53, and a TMA supply source 54, respectively. Since TMA is bubbled using hydrogen gas, the hydrogen gas supply source 53 is connected to the TMA supply source 54. The hydrogen gas, TMA gas vaporized by bubbling, and nitrogen gas join at the outlet of the TMA supply source 54 and are supplied to the reactor 55. In this embodiment, TMA is bubbled with hydrogen gas, but the method of mixing the source material and carrier gas is not limited to this. Furthermore, ammonia gas is supplied to the reactor 55 together with a mixed gas of nitrogen gas and hydrogen gas. The reactor 55 includes a susceptor for placing the sapphire substrate on which the AlN layer 20 has been grown, support legs for supporting and rotating the susceptor, and a heater located directly below the susceptor, and is capable of adjusting the temperature and pressure inside the reactor 55 to epitaxially grow the AlN layer 20. A vacuum pump 56 is connected to the outside of the reactor 55 to exhaust gases inside the reactor.

[0040] <<Second Step>> In the subsequent second step, the AlN layer 20 on the sapphire substrate 10 obtained as described above is preferably subjected to a heat treatment at a temperature higher than the growth temperature in the first step. The second step is performed in an atmosphere containing nitrogen elements so as to prevent decomposition of the AlN layer 20. The nitrogen-containing atmosphere may have a nitrogen partial pressure higher than the nitrogen partial pressure at which AlN decomposes at the heating temperature described below. The gas used in the atmosphere may be nitrogen gas or ammonia gas, but nitrogen gas is preferred. This heat treatment can be performed using a known heat treatment furnace. The high-temperature heat treatment can reduce the half-width of the X-ray rocking curve of the (0002) plane and the half-width of the X-ray rocking curve of the (10-12) plane of the AlN layer 20 after the heat treatment. The nitrogen-containing atmosphere described above is suitable for sapphire (Al ２ O ３ In order to control the decomposition of the hydroxyl group, a gas containing oxygen may be contained.

[0041] In the second step, it is preferable to perform heat treatment at a temperature higher than the growth temperature in the first step in order to improve the crystallinity of the AlN layer 20. In the second step, it is more preferable to set the heating temperature during the heat treatment to 1580°C or higher and 1730°C or lower. This is because a temperature of 1580°C or higher can sufficiently reduce the dislocation density, and a temperature of 1730°C or lower can suppress the phenomenon of the surface roughening caused by the decomposition of part of the AlN layer on the surface. Furthermore, by setting the heat treatment temperature to 1600°C or higher and 1700°C or lower, it is possible to reliably improve the crystallinity of the AlN layer 20.

[0042] Furthermore, the heating time in the second step is preferably 3 hours or more and 12 hours or less. Heat treatment for 3 hours or more can sufficiently reduce the dislocation density. Furthermore, a heat treatment time of 12 hours or less can suppress the phenomenon in which part of the AlN on the surface decomposes, causing the surface to become rough. In order to reliably improve the crystallinity of the AlN layer 20, it is more preferable to set the heat treatment time to 4 hours or more and 10 hours or less.

[0043] 7 , a light-emitting device 100 formed on the fabricated AlN template substrate 1 will be described. For example, the light-emitting device 100 can be formed on the AlN template substrate 1 by sequentially depositing an undoped first buffer layer 101, a second buffer layer 102, an n-type semiconductor layer 103, an n-type guide layer 104, a light-emitting layer 105, an i-type guide layer 106, a p-type electron blocking layer 107, a p-type cladding layer 108, and a p-type contact layer 109 on the AlN layer 20. Each layer constituting the light-emitting device 100 will be described below.

[0044] The first buffer layer 101 and the second buffer layer 102 are stacked layers of AlGaN layers with different Al compositions, and the first buffer layer 101 preferably has a thickness of 10 nm to 100 nm, and the second buffer layer 102 preferably has a thickness of 500 nm to 2000 nm. The first buffer layer 101 and the second buffer layer 102 are preferably undoped. The first buffer layer 101 and the second buffer layer 102 are positioned between the AlN layer 20 and the n-type semiconductor layer 103, which have different lattice constants, thereby enabling the formation of a flat n-type semiconductor layer 103 with good crystallinity and also alleviating strain caused by the difference in lattice constant between the AlN layer 20 and the n-type semiconductor layer 103. Furthermore, the Al composition of the second buffer layer 102 is preferably lower than that of the first buffer layer 101.

[0045] The n-type semiconductor layer 103 is an Al layer having an Al composition ratio x. ｘ Ga １－ｘ The doping element is preferably N. Here, examples of the doping element include Si, Te, S, Ge, Sn, and Se. The impurity concentration when SIMS analysis was performed was 1.0×10 １８ / cm ３ Above 5.0 x 10 １９ / cm ３ It is preferable that the temperature is about the same or less.

[0046] The average surface roughness (Ra) of the surface of the n-type semiconductor layer 103 within a rectangular area of ​​5.0 μm × 2.5 μm is preferably 1 nm or less. A flat surface of the n-type semiconductor layer 103 allows the layers grown thereon to maintain flatness.

[0047] The full width at half maximum of the X-ray rocking curve of the (10-12) plane of the n-type semiconductor layer 103 is preferably 350 seconds or less, more preferably 300 seconds or less. The Al composition ratio of the n-type semiconductor layer 103 is preferably 0.2 or more and 0.35 or less, which is greater than the Al composition ratio w of the well layer 1052 described below, with w<x.

[0048] The thickness of the n-type semiconductor layer 103 is sufficient to supply carriers, and is preferably, for example, 300 nm or more and 3000 nm or less.

[0049] As will be described later, an n-type electrode 192 is formed on a portion of the exposed n-type semiconductor layer 103. As a modification, an AlGaN layer having an Al composition of 0 or more and 0.2 or less, which is lower than that of the n-type semiconductor layer 103, may be provided between the n-type semiconductor layer 103 and the n-type electrode 192.

[0050] An n-type guide layer 104 may be formed on the n-type semiconductor layer 103. The n-type guide layer 104 is an AlGaN layer having the same Al composition ratio as the n-type semiconductor layer 103, but containing an n-type dopant, and functions as an n-type semiconductor. The n-type guide layer 104 may be thinner than the n-type semiconductor layer 103. Examples of elements that may be doped into the n-type guide layer 104 include Si, Te, S, Ge, Sn, and Se. The thickness of the n-type guide layer 104 is preferably 10 nm or more and 300 nm or less.

[0051] The light-emitting layer 105 is preferably a layer including a layer made of AlGaN. In this embodiment, the light-emitting layer 105 has a plurality of barrier layers 1051 and a plurality of well layers 1052, and although the light-emitting layer 105 is illustrated as a multiple quantum well layer in which these layers are alternately stacked, the light-emitting layer 105 may have a single-layer structure. In this embodiment, the light-emitting layer 105 preferably has well layers 1052 and barrier layers 1051 having an Al composition ratio corresponding to the central emission wavelength, and has a configuration in which one or more pairs of the barrier layers 1051 and the well layers 1052 are repeated.

[0052] The well layer 1052 of this embodiment is an Al well layer having an Al composition ratio w ｗ Ga １－ｗ It is preferable that the well layer 1052 is a layer made of N. The Al composition ratio w is preferably w<0.3 when the central emission wavelength is set to exceed 320 nm. The well layer 1052 preferably has w≦0.15 when the central emission wavelength is set to 331 nm or more, and preferably has w<0.07 when the central emission wavelength is set to 349 nm or less. The well layer 1052 preferably has a film thickness of 1 nm or more and 5 nm or less, and is preferably undoped.

[0053] The barrier layer 1051 is an Al layer having an Al composition ratio b. ｂ Ga １－ｂIt is preferable that the barrier layer 1051 is a layer made of N. The Al composition ratio b of the barrier layer 1051 is preferably in the range of w+0.05≦b≦w+0.3. The barrier layer 1051 may be undoped or n-type doped with an n-type dopant. In this case, elements doped into the barrier layer 1051 include Si, Te, S, Ge, Sn, and Se.

[0054] The i-type guide layer 106 is preferably made of AlGaN having a higher Al composition ratio than the barrier layer 1051 and is an i-type layer having a film thickness of 0.7 nm to 1.3 nm. The Al composition ratio of the i-type guide layer 106 is preferably higher than the Al composition ratio y of the p-type electron blocking layer 107 described below, and is most preferably AlN.

[0055] There are two methods for manufacturing the i-type guide layer 106. One is a method of directly forming the i-type guide layer 106 having the above-mentioned film thickness and Al composition. The other is a method of forming an AlGaN layer having a thickness equal to or greater than the above-mentioned film thickness, and then changing the carrier gas from nitrogen gas to hydrogen gas. In the process, the nitrogen partial pressure decreases, causing Ga in the AlGaN layer to volatilize and the Al composition to increase, resulting in the i-type guide layer 106 having the above-mentioned film thickness and Al composition. Either method can be adopted in this embodiment.

[0056] The p-type electron blocking layer 107 is made of Al having an Al composition ratio y. ｙ Ga １－ｙ The dopant of the p-type electron blocking layer 107 is preferably N. Examples of the dopant include Mg, Zn, C, and Be. The impurity concentration in the SIMS analysis was 1.0×10 １８ / cm ３ Above 5.0 x 10 １９ / cm ３ It is preferable that the temperature is about the same or less.

[0057] The Al composition ratio y of the p-type electron blocking layer 107 is preferably 0.35 or more and 0.45 or less. The thickness of the p-type electron blocking layer 107 is preferably 11 nm or more and 70 nm or less. By having such an Al composition ratio and thickness, the p-type electron blocking layer 107 can suppress deterioration of its surface roughness while fulfilling its role as an electron blocking layer, thereby improving the light emission output. A thickness of 60 nm or less is even more preferable for improving the light emission output.

[0058] The p-type cladding layer 108 is an Al layer having an Al composition ratio z. ｚ Ga １－ｚ The Al composition ratio z is preferably 0.17 or more and 0.27 or less. Dopants for the p-type cladding layer 108 include Mg, Zn, C, and Be. The impurity concentration when SIMS analysis was performed was 1.0×10 １８ / cm ３ Above 5.0 x 10 １９ / cm ３ It is preferable that the temperature is about the same or less.

[0059] Regarding the relationship between the Al composition ratio z of the p-type cladding layer 108 and the Al composition ratios of the other layers, the Al composition ratio z of the p-type cladding layer 108 is preferably less than the Al composition ratio y of the p-type electron blocking layer 107 (z<y). Furthermore, the Al composition ratio z of the p-type cladding layer 108 is preferably 0.48 to 0.60 times the Al composition ratio y of the p-type electron blocking layer 107. Hereinafter, the ratio of the Al composition ratio z of the p-type cladding layer 108 to the Al composition ratio y of the p-type electron blocking layer 107 may be referred to as the Al ratio. Furthermore, the Al composition ratio z is preferably less than or equal to the Al composition ratio x of the n-type semiconductor layer 103 (z≦x). Furthermore, the Al composition ratio z is preferably greater than the Al composition ratio w of the well layer 1052 (w<z).

[0060] The thickness of the p-type cladding layer 108 is preferably adjusted according to the thickness of the p-type electron blocking layer 107 as follows.

[0061] In determining the thickness of p-type cladding layer 108, the total thickness of p-type electron blocking layer 107 and p-type cladding layer 108 is preferably 73 nm or more and 100 nm or less in order to achieve both light emission output and flatness. Furthermore, in order to improve light emission output, the total thickness of p-type electron blocking layer 107 and p-type cladding layer 108 is preferably 79 nm or more.

[0062] Furthermore, when the total thickness of the p-type electron blocking layer 107 and the p-type cladding layer 108 is constant, a thinner electron blocking layer tends to result in a larger output. Therefore, the thickness of the electron blocking layer is preferably set to 11 nm or more and 60 nm or less in order to achieve a significant effect of improving the output.

[0063] The value obtained by dividing the thickness of the p-type cladding layer 108 by the thickness of the p-type electron blocking layer 107 (hereinafter, sometimes referred to as the layer thickness ratio) should be at least 0.1. In order to suppress the maximum surface roughness (Rmax) of the p-type contact layer 109, the layer thickness ratio is preferably 0.4 or more, and more preferably 0.5 or more. The upper limit of the layer thickness ratio can be 6.0 or less. Furthermore, if the layer thickness ratio is less than 0.4, the surface flatness of the p-type cladding layer 108 tends to deteriorate, and the Rmax of the p-type contact layer 109 tends to increase.

[0064] By setting the Al composition ratio of the p-type electron blocking layer 107 in the range of 0.35 to 0.45 and the layer thickness ratio to 0.55 or more, the maximum surface roughness of the p-type contact layer 109 described below can be set to less than 6.5 nm.

[0065] The p-type contact layer 109 is preferably made of a p-type semiconductor made of GaN. Examples of dopants used in the p-type contact layer 109 include Mg, Zn, C, and Be. The impurity concentration measured by SIMS analysis was 1.0×10 １９ / cm ３ Above 5.0 x 10 ２１ / cm ３ It is preferable that the temperature is about the same or less.

[0066] The thickness of the p-type contact layer 109 is preferably 2 nm or more and 15 nm or less, and more preferably 2 nm or more and 10 nm or less. By using the p-type electron blocking layer 107 and the p-type cladding layer 108 as described above, the flatness of the p-type contact layer 109 can be ensured even when the p-type contact layer 109 is made such a thin layer.

[0067] As the n-type electrode 192, it is preferable to expose the n-type semiconductor layer 103 by dry etching, form a layer made of AlGaN on the exposed n-type semiconductor layer 103, the Al composition ratio of which is lower than that of the n-type semiconductor layer 103 and is equal to or greater than 0 and equal to or less than 0.2, and then form the n-type electrode 192 on top of that.

[0068] A known electrode may be selected as the n-type electrode 192, and may be, for example, a first metal (Ti) and a second metal (Al), or a conductive metal nitride. Here, the film thickness of the first metal of the n-type electrode 192 is preferably 10 nm to 50 nm, and the film thickness of the second metal is preferably 50 nm to 300 nm.

[0069] As the p-type electrode 195, it is preferable to select a known electrode that can be used for the p-type contact layer 109, and it is more preferable to use a reflective electrode with a reflectance of 50% or more at the center wavelength of light emission. For example, a first metal (Ni) and a second metal (Rh), or a conductive metal nitride can be used as the p-type electrode 195. Here, the film thickness of the first metal of the p-type electrode 195 is preferably 5 nm or more and 10 nm or less, and the film thickness of the second metal is preferably 20 nm or more and 100 nm or less.

[0070] A known film formation method, such as sputtering, can be used to laminate the n-type electrode 192 and the p-type electrode 195. Furthermore, it is preferable to use a lift-off method using a resist to form the electrode patterns of the n-type electrode 192 and the p-type electrode 195.

[0071] The MOCVD method can be used as a method for epitaxially growing each layer. For the epitaxial growth of each layer, trimethylaluminum gas (TMA gas), trimethylgallium gas (TMG gas), and ammonia gas (NH ３ It is preferable to use a source gas consisting of Al and V groups (V / III gases). The growth temperature is preferably 1000°C or higher and 1400°C or lower, depending on the Al composition ratio. The growth pressure in the chamber can be set to, for example, 10 Torr to 760 Torr. Note that, since there is an optimal molar ratio of group V elements to group III elements (V / III ratio) depending on the growth temperature and growth pressure, it is preferable to appropriately set the flow rate of the source gas.

[0072] When singulating the wafer into individual light-emitting element 100 chips, it is preferable to remove each layer on the substrate at the intended separation position using dry etching or the like. At this time, mesas (inclined portions) may be formed on the side surfaces of each layer. The chip size of the light-emitting element 100 may be a square, rectangle, or hexagon with a side length of 200 μm to 2000 μm. Scribe or laser dicing can be used to singulate the substrate. The thickness of the substrate may be adjusted by grinding or the like before singulation.

[0073] 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.

[0074] Experimental Example 1 (Example 1) An AlN template substrate according to Example 1 was fabricated according to the flowchart shown in FIG. 3 . First, a sapphire substrate (diameter: 2 inches, thickness: 430 μm, surface orientation: (0001), off-angle θ in the m-axis direction: 0.11°) was prepared ( FIG. 3A ). Next, an AlN layer with a center thickness of 0.60 μm was grown on the sapphire substrate by MOCVD at a growth temperature of 1330° C. and a growth pressure in the chamber of 10 Torr. The flow rates of the source gases were 250 sccm for Group V gas (ammonia gas) and 43 sccm for Group III gas (TMA gas). A mixture of hydrogen and nitrogen gases was used as the carrier gas, with the hydrogen gas flow rates set to 9507 sccm and nitrogen gas flow rate set to 400 sccm (4.04% of the nitrogen gas in the mixture). As described above, the AlN film thickness was measured at a total of 25 equally spaced locations, including the center of the wafer, using an optical interference film thickness measuring device (Nanospec M6100A; manufactured by Nanospec Co., Ltd.).

[0075] Next, the AlN template substrate on which the AlN layer had been formed was introduced into a heat treatment furnace, and after reducing the pressure to 10 Pa, the nitrogen gas was purged to atmospheric pressure to create a nitrogen gas atmosphere inside the furnace. The temperature inside the furnace was then raised to perform a heat treatment on the AlN template substrate. The heating temperature was 1620° C. and the heating time was 5 hours. In this manner, the AlN template substrate according to Example 1 was produced.

[0076] The AlN layer of the AlN template substrate had a (10-12) X-ray rocking curve half width of 247 seconds and a (0002) X-ray rocking curve half width of 51 seconds, measured using an X-ray diffractometer (D8 DISCOVER AUTOWAFS; manufactured by Bruker AXS, CuKα1 ray).

[0077] Furthermore, when the surface roughness of the AlN template substrate was measured using an AFM in a rectangular area of ​​5.0 μm×2.5 μm around the center of the wafer, the average surface roughness (Ra) was 0.15 nm.

[0078] On the prepared AlN template substrate, undoped Al was deposited by MOCVD. ０．４０ Ga０．６０ A first buffer layer of 30 nm thick made of N and undoped Al ０．２５ Ga ０．７５ A second buffer layer of 1000 nm thick made of N was then formed at a growth temperature of 1200°C.

[0079] Next, a Si-doped n-type semiconductor layer having a thickness of 2400 nm was formed on the second buffer layer. The Si concentration of the n-type semiconductor layer was measured by SIMS and found to be 1.0×10 １９ atoms / cm ３ It was.

[0080] Next, the growth temperature was changed from 1200° C. to 1100° C., and undoped Al was grown on the n-type semiconductor layer. ０．２５ Ga ０．７５ An n-type guide layer of 25 nm thick made of N was formed. ０．２５ Ga ０．７５ A barrier layer of 12 nm thick 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.

[0081] Next, 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. Thereafter, while continuing to supply 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 ０．４０ Ga ０．６０ A p-type electron blocking layer of 22 nm thick made of N was formed. ０．２２ Ga ０．７８ A p-type cladding layer made of N and having a thickness of 64 nm was formed, and a p-type contact layer made of Mg-doped GaN (p-type GaN contact layer) and having a thickness of 4 nm was formed thereon.

[0082] The semiconductor device formed on the AlN template substrate was analyzed using SIMS, and the Mg concentrations in the p-type electron blocking layer, p-type cladding layer, and p-type contact layer were found to be 1.0×10 １９ atoms / cm ３ , 5.0 × 10 １９ atoms / cm ３ , 2.0 × 10 ２０ atoms / cm ３ It was.

[0083] Furthermore, estimation of the Al composition ratio by photoluminescence measurement and film thickness measurement by TEM revealed that, as a result of the change in carrier gas after the formation of the i-guide layer, the Ga component of the i-guide layer volatilized and decomposed, resulting in a transformation into an i-guide layer with a film thickness of 1.0 nm and an Al composition ratio of approximately 1.

[0084] The Al composition ratio, dopant type, and film thickness of each layer of the semiconductor layer fabricated in Example 1 are shown in Table 1. Here, the Al composition ratio was estimated from the wavelength observed by photoluminescence measurement, the dopant type was based on the SIMS analysis results, and the film thickness was based on the TEM measurement results.

[0085]

[0086] Furthermore, a mask was formed on the p-type contact layer, and mesa etching was performed by dry etching to expose a part of the n-type semiconductor layer, and then the mask on the p-type contact layer was removed.

[0087] Next, a 7 nm thick Ni layer and a 50 nm thick Rh layer were formed in this order on the p-type contact layer to form a reflective electrode as a p-side electrode.

[0088] Furthermore, a 20 nm thick Ti layer and a 150 nm thick Al layer were formed in this order on the exposed portion of the n-type semiconductor layer to form an n-type electrode.

[0089] The p-side electrode and n-type electrode were laminated using a sputtering method, and the electrode patterns were formed using a lift-off method using a resist.

[0090] Furthermore, contact annealing was performed for 10 minutes at 550°C using an infrared lamp annealing heating device, and then the substrate was separated into individual rectangular elements with a chip size of 1000 μm × 1000 μm using a laser scriber to produce ultraviolet light-emitting elements (hereinafter referred to as light-emitting elements) according to Example 1. After element separation, the side surfaces of the sapphire substrate were perpendicular to the main surface, and the thickness of the sapphire substrate was 430 μm.

[0091] Example 2 An AlN template substrate was fabricated in the same manner as in Example 1, except that the flow rate of hydrogen gas in step 1 was changed to 9707 sccm and the flow rate of nitrogen gas was changed to 200 sccm.

[0092] Comparative Example An AlN template substrate was fabricated in the same manner as in Example 1, except that the flow rate of hydrogen gas in step 1 was changed to 9907 sccm and the flow rate of nitrogen gas was changed to 0 sccm.

[0093] 8, 9, and 10 show AFM images of a 5.0 μm × 2.5 μm rectangular area of ​​the AlN layer surface on the AlN template substrate obtained in Example 1, Example 2, and Comparative Example, respectively. Furthermore, the flatness, step linearity, and crystallinity of the AlN layer surface on the AlN template substrate obtained in Example 1, Example 2, and Comparative Example were measured. A current of 350 mA was applied to the light-emitting device stacked on this AlN template substrate using a constant current voltage source, and the device was inserted into an integrating sphere with the sapphire substrate side facing the center of the sphere, and the total luminous output (Po) was measured. The results are shown in Table 2.

[0094]

[0095] From the above results, it was confirmed that the step linearity of the AlN layer surface increases as the proportion of nitrogen gas in the carrier gas during AlN layer growth increases, and the light output of the light-emitting device formed on the AlN template substrate increases. Although the comparative example, in which nitrogen gas is not included in the carrier gas, has superior crystallinity compared to examples 1 and 2, in which nitrogen gas is included in the carrier gas, the fact that examples 1 and 2 have higher light output suggests that the step linearity is an important evaluation parameter for AlN layers.

[0096] According to the present invention, an AlN template substrate with a large step linearity and a method for manufacturing the same can be provided by using a mixed gas of nitrogen gas and hydrogen gas as a carrier gas when forming an AlN layer.

[0097] REFERENCE SIGNS LIST 1 AlN template substrate 10 Sapphire substrate 10A Primary surface of sapphire substrate 20 AlN layer 50 MOCVD apparatus 51 Ammonia gas supply source 52 Nitrogen gas supply source 53 Hydrogen gas supply source 54 TMA supply source 55 Reactor 56 Vacuum pump 100 Light emitting element 101 First buffer layer 102 Second buffer layer 103 n-type semiconductor layer 104 n-type guide layer 105 Light emitting layer 1051 Barrier layer 1052 Well layer 106 i-type guide layer 107 P-type electron blocking layer 108 P-type cladding layer 109 P-type contact layer 192 N-type electrode 195 P-type electrode

Claims

1. An AlN template substrate comprising: a sapphire substrate; and an AlN layer formed on a primary surface of the sapphire substrate, wherein the primary surface of the sapphire substrate is a C-plane inclined at an off angle of 0.02° or more and less than 0.35°, and wherein a step linearity ratio, calculated by dividing a straight-line distance connecting a first contact point on one side between an edge of a step in an AFM image of the surface of the AlN layer and an edge of the AFM image and a second contact point on the other side, by the length of the edge of the step extending from the first contact point to the second contact point, is 90% or more.

2. The AlN template substrate according to claim 1, wherein the AlN layer has a surface flatness Ra of 1.1 nm or less.

3. The AlN template substrate according to claim 1, wherein the half-width of an X-ray rocking curve of the (0002) plane of the AlN layer is 100 arc seconds or less, and the half-width of an X-ray rocking curve of the (10-12) plane is 300 arc seconds or less.

4. A method for manufacturing an AlN template substrate, comprising: a first step of epitaxially growing an AlN layer on a primary surface of a sapphire substrate; and a second step of heat-treating the AlN layer, wherein the primary surface of the sapphire substrate is a C-plane inclined at an off-angle of 0.02° or more and less than 0.35°, the carrier gas used in the first step is a mixed gas of hydrogen gas and nitrogen gas, and the heat treatment in the second step is performed in an atmosphere containing nitrogen element.

5. The method for producing an AlN template substrate according to claim 4, wherein the temperature inside the furnace during the heat treatment in the second step is higher than the temperature inside the furnace in the first step.

6. The method for producing an AlN template substrate according to claim 4, wherein the ratio of nitrogen gas in the carrier gas is 1% or more and 10% or less.

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