Free-standing substrate for epitaxial crystal growth and functional element

Abstract

On the basis of a self-supporting substrate for epitaxial crystal growth containing a Group 13 element nitride crystal selected from gallium nitride, aluminum nitride, indium nitride, or a mixed crystal thereof, cracking of the self-supporting substrate or the epitaxial crystal in a process of growing the epitaxial crystal is prevented. A self-supporting substrate for epitaxial crystal growth (21) containing a Group 13 element nitride crystal selected from gallium nitride, aluminum nitride, indium nitride, or a mixed crystal thereof has a nitrogen-polarity face (21a) and a Group 13 element-polarity face (21b). The nitrogen-polarity face (21a) is convexly curved, and a chamfered portion (21c) is provided at an outer peripheral portion (22) of the nitrogen-polarity face (21a).

Description

Technical Field

[0001] This invention relates to a self-standing substrate and functional elements for epitaxial crystal growth. Background Technology

[0002] As light-emitting devices such as light-emitting diodes (LEDs) that utilize single-crystal substrates, various gallium nitride (GaN) layers are known to be formed on sapphire (α-alumina single crystal). For example, a light-emitting device with the following structure has been mass-produced: an n-type GaN layer, a multiple quantum well (MQW) layer, and a p-type GaN layer are sequentially stacked on a sapphire substrate, wherein the MQW layer is obtained by alternating layers of quantum well layers containing InGaN layers and barrier layers containing GaN layers. Furthermore, a stacked substrate suitable for this application has been proposed.

[0003] It is known that a gallium nitride (GaN) layer is formed on a substrate such as a sapphire substrate, and the substrate is separated using techniques such as laser lift-off (LLO) to obtain a self-standing substrate containing GaN. Functional layers such as GaN, AlGaN, and InGaN are then deposited on this self-standing substrate to manufacture light-emitting elements and power devices such as LEDs. Recently, for ultra-high brightness LEDs and power devices, there has been a pursuit of large-diameter substrates of 4 inches and 6 inches.

[0004] However, after the gallium nitride (GaN) layer is peeled off from the substrate, it can sometimes warp significantly due to factors such as the stress distribution within the GaN crystal and the dislocation density difference between the surface and back of the GaN layer. If this occurs, the angular distribution on the surface of the GaN layer becomes larger, and therefore, the function of the functional layer deposited on this surface can sometimes change depending on its location. For example, in the case of light-emitting elements, the deviation in the emission wavelength can sometimes increase depending on the location within the substrate surface.

[0005] As a solution to the above problems, the solutions described in Patent Documents 1 to 3 have been proposed.

[0006] That is, Patent Document 1 attempts to make the polar surface of Group 13 elements the film-forming surface (growth surface), thereby keeping the atomic step density of the growth interface approximately constant, thereby reducing the deviation of the emission wavelength.

[0007] Patent document 2 attempts to reduce the deviation of the emission wavelength by processing the crystal growth surface according to the deviation of the crystal axis of the crystal growth surface.

[0008] In Patent Document 3, a flat portion is provided in the center of the substrate on the crystal growth surface, and a curved portion is provided on its outer periphery, so that the angular distribution of the flat portion is smaller, thereby reducing the angular distribution of the entire substrate.

[0009] Existing technical documents

[0010] Patent documents

[0011] Patent Document 1: Japanese Patent 4696935

[0012] Patent Document 2: Japanese Patent Application Publication No. 2009-126727

[0013] Patent Document 3: Japanese Patent Application Publication No. 2009-94230 Summary of the Invention

[0014] Using the structures described in Patent Documents 1-3, the angular distribution of the crystal growth surface (group 13 element polar surface) of the self-standing substrate can be reduced, thereby reducing the wavelength deviation of the light-emitting element. However, during the process of forming a film of the light-emitting element structure and other functional element structures on the group 13 element polar surface of the self-standing substrate, cracks can sometimes easily occur within the self-standing substrate and the functional element structure.

[0015] The objective of this invention is to prevent cracking of the substrate during epitaxial crystal growth, based on a self-standing substrate for epitaxial crystal growth containing group 13 element nitride crystals.

[0016] This invention relates to a self-standing substrate for epitaxial crystal growth, specifically a self-standing substrate comprising nitride crystals of group 13 elements selected from gallium nitride, aluminum nitride, indium nitride, or mixtures thereof.

[0017] The characteristic of the self-standing substrate for epitaxial crystal growth is that...

[0018] The self-standing substrate has a nitrogen polar surface and a group 13 element polar surface. The nitrogen polar surface is convex and warped, and a chamfer is provided on the outer periphery of the nitrogen polar surface.

[0019] In addition, the present invention relates to a functional element, characterized in that it comprises: the self-standing substrate for epitaxial crystal growth; and a functional layer disposed on the polar surface of the group 13 element of the self-standing substrate.

[0020] Invention Effects

[0021] The inventors of this invention have conducted various studies on the causes of cracking during the epitaxial crystal growth process on a self-standing substrate containing crystals of nitrides of Group 13 elements selected from gallium nitride, aluminum nitride, indium nitride, or mixed crystals thereof, and have obtained the following insights.

[0022] That is, functional components such as light-emitting elements are deposited on the group 13 element polar surface of a self-standing substrate. Therefore, during film deposition, the nitrogen polar surface of the self-standing substrate is placed on a substrate, and the self-standing substrate is transferred and held. Here, in order to ensure uniform film thickness for the functional components, it is necessary to ensure uniform temperature distribution on the group 13 element polar surface of the self-standing substrate. Therefore, it is common technical knowledge to make the nitrogen polar surface of the self-standing substrate flat.

[0023] However, the inventors of this invention believe that because the nitrogen polar surface of the self-standing substrate is made flat, when the substrate is held and transported using tweezers or a robotic arm, tiny scratches are easily generated on the nitrogen polar surface of the self-standing substrate, thus causing cracking. Therefore, they conceived of chamfering the outer periphery of the nitrogen polar surface of the self-standing substrate.

[0024] However, even when the nitrogen polar surface of the outer periphery of the self-standing substrate is chamfered, small gaps and chipping sometimes occur due to the hardness of group 13 nitride crystals, making it difficult to completely suppress cracking during the manufacturing process.

[0025] Therefore, in addition to chamfering the outer periphery of the nitrogen polar surface of the self-standing substrate, the inventors of this invention also attempted to make the nitrogen polar surface convex and warped. This attempt is difficult to imagine from the conventional viewpoint of uniform heat transfer from the substrate to the self-standing substrate. However, it was found that when epitaxially crystallizing a film on the self-standing substrate, cracking of both the self-standing substrate and the epitaxial crystallization was significantly reduced. That is, it was found that although it seems unlikely that substrate cracking would occur when the nitrogen polar surface of the self-standing substrate is concave, the reality is the opposite.

[0026] Furthermore, according to the present invention, by reducing notches, chipping, and minor scratches on the back side of the substrate end face, it is expected that the substrate cracking effect can be reduced not only in the functional layer epitaxial growth process on the self-standing substrate, but also in the device formation process after the functional layer is formed, the thinning process using grinding, fine grinding, and lapping, the transport between processes, and the mechanical transport in the device equipped with an automatic transport mechanism. Attached Figure Description

[0027] Figure 1 In the diagram, (a) is a schematic diagram showing the self-supporting substrate 21 according to an embodiment of the present invention, and (b) is a schematic diagram showing the self-supporting substrate 24 of the reference example.

[0028] Figure 2 This is a bottom view of the self-standing substrate 21.

[0029] Figure 3 In the diagram, (a) is a schematic diagram showing the outer periphery of the self-supporting substrate 21 according to an embodiment of the present invention, and (b) is a schematic diagram showing the outer periphery of the self-supporting substrate 21G.

[0030] Figure 4 In the diagram, (a), (b), and (c) represent the outer periphery of the self-standing substrates 21A, 21B, and 21C, respectively.

[0031] Figure 5 In the diagram, (a), (b), and (c) represent the outer periphery of the self-standing substrates 21D, 21E, and 21F, respectively.

[0032] Figure 6 In the diagram, (a) and (b) are schematic diagrams representing the self-standing substrates 30A and 30B of the comparative examples, respectively.

[0033] Figure 7 In the diagram, (a) indicates a state in which a seed film 2 and a gallium nitride layer 3 are disposed on a substrate 1, (b) indicates a state in which the gallium nitride layer 3 is separated from the substrate, and (c) indicates a state in which a functional layer is disposed on the gallium nitride layer 3A.

[0034] Figure 8 In the diagram, (a) represents the crystal axis of the substrate 1, the seed film 2, and the gallium nitride layer 3, and (b) represents the state of laser A being irradiated from the substrate side.

[0035] Figure 9 In the diagram, (a) represents the state in which the gallium nitride layer 13 and the seed film 12 are separated from the substrate, (b) represents the surface of the gallium nitride layer 13 and the surface to which the back side processing is performed, and (c) represents the self-standing substrate 14 obtained by surface and back side processing.

[0036] Figure 10 This is a schematic front view of the self-supporting substrate involved in an embodiment of the present invention, showing that the warping of the group 13 element polar surface 17a is different from the warping of the nitrogen polar surface 17b. Detailed Implementation

[0037] The elements of the present invention will be further described below.

[0038] This invention relates to a self-standing substrate for epitaxial crystal growth comprising nitride crystals of group 13 elements selected from gallium nitride, aluminum nitride, indium nitride, or mixtures thereof. In this invention, "self-standing substrate" refers to a substrate that will not deform or break under its own weight during operation and can be operated as a solid material. The self-standing substrate of this invention can be used as a substrate for various semiconductor devices such as light-emitting elements.

[0039] The nitrides that make up the crystalline layers of group 13 element nitrides are gallium nitride, aluminum nitride, indium nitride, or mixtures thereof. Specifically, they are GaN, AlN, InN, and Ga... x Al 1-x N(1>x>0),Ga x In 1-x N(1>x>0), Alx In 1-x N(1>x>0),Ga x Al y In z N (1 > x > 0, 1 > y > 0, x + y + z = 1) can be doped using various n-type or p-type dopants. Preferred examples of p-type dopants include at least one from the group consisting of beryllium (Be), magnesium (Mg), strontium (Sr), and cadmium (Cd). Preferred examples of n-type dopants include at least one from the group consisting of silicon (Si), germanium (Ge), tin (Sn), and oxygen (O).

[0040] In this invention, for example, such as Figure 1 As shown in (a), the self-standing substrate 21 has a group 13 element polar surface 21b and a nitrogen polar surface 21a. In addition, a side surface 21e is provided on the self-standing substrate 21. Epitaxial crystal growth is performed on the group 13 element polar surface 21b, and the nitrogen polar surface 21a can be held and transferred by a substrate or the like.

[0041] Here, the nitrogen polar surface 21a of the self-standing substrate 21 is convexly warped. This means that when the self-standing substrate is viewed from the nitrogen polar surface side, the nitrogen polar surface warps in a way that it protrudes from the self-standing substrate. Furthermore, a chamfered portion 21c is provided on the outer periphery 22 of the nitrogen polar surface 21a. In addition, in this example, a chamfered portion 21d is provided on the outer periphery 23 of the group 13 element polar surface 21b. Moreover, the group 13 element polar surface 21b warps in a direction that is recessed when viewed from the self-standing substrate.

[0042] From the perspective of this invention, the radius of curvature of the warping of the nitrogen polar surface is preferably +5m or more and +65m or less, more preferably +7m or more and +32m or less. Wherein, when the nitrogen polar surface is convex, the radius of curvature is set to a positive value (+), and when the nitrogen polar surface is concave, the radius of curvature is set to a negative value (-).

[0043] On the other hand, the polar facets of Group 13 elements, when viewed from a self-standing substrate, can be convex, concave, or flat. However, from the viewpoint of suppressing angular deviation of the polar facets of Group 13 elements, it is preferable that the convex / concave orientation of the polar facets of Group 13 elements is opposite to that of the nitrogen polar facets, that is, concave when viewed from a self-standing substrate. Accordingly, the angular deviation of the polar facets of Group 13 elements can be reduced. In this case, the radius of curvature of the polar facets of Group 13 elements is preferably -3 μm or less, and more preferably -7 μm or less from the viewpoint of ease of grinding. Wherein, when the polar facets of Group 13 elements are convex, the value of the radius of curvature is set to a positive value (+), and when the polar facets of Group 13 elements are concave, the value of the radius of curvature is set to a negative value (-).

[0044] Furthermore, in a preferred embodiment, the absolute value of the radius of curvature of the warping of the Group 13 element polar surface is smaller than the absolute value of the radius of curvature of the warping of the nitrogen polar surface. This means that the warping of the Group 13 element polar surface is steeper than the warping of the nitrogen polar surface. Accordingly, the angular deviation of the nitrogen polar surface can be reduced. In this embodiment, the ratio of (absolute value of the radius of curvature of the warping of the Group 13 element polar surface) to (absolute value of the radius of curvature of the warping of the nitrogen polar surface) is more preferably 0.7 or less, and more preferably 0.5 or less. In addition, the ratio of (absolute value of the radius of curvature of the warping of the Group 13 element polar surface) to (absolute value of the radius of curvature of the warping of the nitrogen polar surface) is typically 0.01 or more.

[0045] For example, Figure 1 (b) The reference example's self-standing substrate 24 has a group 13 element polar surface 24b and a nitrogen polar surface 24a. A chamfered portion 24d is provided on the outer periphery 23 of the group 13 element polar surface 24b, and a chamfered portion 24c is provided on the outer periphery 22 of the nitrogen polar surface 24a. The group 13 element polar surface is convexly warped relative to the self-standing substrate, and its radius of curvature is positive. The nitrogen polar surface 24a is concavely warped relative to the self-standing substrate, and its radius of curvature is negative. 24e is a side surface.

[0046] Furthermore, in a preferred embodiment, the polar surface of group 13 elements is a mirror-finished surface. A mirror-finished surface refers to a surface on which, after processing, the roughness and undulations of the substrate surface are reduced to a level that allows for visually identifiable light reflection, enabling objects to be reflected onto the processed surface. In other words, a mirror-finished surface is a surface where the roughness and undulations of the processed substrate surface are reduced to a level that is negligible relative to the wavelength of visible light. Performing this mirror-finishing process allows for sufficient epitaxial crystal growth on the substrate.

[0047] Furthermore, in a preferred embodiment, the angular distribution of the polar planes of group 13 elements is 0.25° or less, thereby suppressing crystallinity deviations in epitaxial crystallization and thus suppressing characteristic deviations in the functional layer containing the epitaxial crystallization. More preferably, the angular distribution of the polar planes of group 13 elements is 0.1° or less. In addition, it is more common for the angular distribution of the polar planes of group 13 elements to be 0.02° or more.

[0048] The warpage of the polar surfaces of Group 13 elements and the nitrogen polar surface was measured, and the radius of curvature was calculated based on the warpage. The warpage measurements are as follows.

[0049] First, the warping of the polar surfaces of group 13 elements and nitrogen polar surfaces can be measured using a laser displacement meter. A laser displacement meter is a device that measures the displacement of each surface by irradiating it with a laser. With the laser wavelength set to 655 nm, the measurement method can be determined based on the surface roughness, using a confocal method, a triangulation method, or an optical interference method.

[0050] Here, regarding the nitrogen polar surface, a waveform is obtained, excluding a 3mm width range measured from the substrate end. Next, an approximate curve for this waveform is obtained using the least squares method of a quadratic function. The difference between the highest and lowest values ​​of this approximate curve is measured along two orthogonal axes on the substrate surface, and the average of the two values ​​is taken as the warp. Furthermore, based on this warp value, the radius of curvature R is calculated using the following formula.

[0051] [Mathematical Expression 1]

[0052]

[0053] (The units for radius of curvature, substrate diameter, and warpage here are [m])

[0054] Furthermore, regarding the polar surface of group 13 elements, a waveform was obtained, excluding a 3mm width range measured from the substrate end. Next, an approximate curve for this waveform was obtained using the least squares method of quadratic functions. The difference between the highest and lowest values ​​of this approximate curve was measured along two orthogonal axes on the substrate surface, and the average of the two values ​​was taken as the warp. Additionally, based on this warp value, the radius of curvature R was calculated in the same manner as for the nitrogen polar surface.

[0055] In the cases of nitrogen polar surface and group 13 element polar surface, the least squares approximation of quadratic function is used. When the waveform is convex, the value of the radius of curvature is set to a positive value (+), and when the waveform is concave, the value of the radius of curvature is set to a negative value (-).

[0056] In this invention, a chamfered portion is provided on the outer periphery of the nitrogen polar surface. Preferably, for example, as shown below... Figure 2 As shown, a chamfered portion 21c is provided around the entire circumference of the outer periphery 22 of the nitrogen polar surface 21a of the self-standing substrate 21. However, the chamfered portion 21c does not need to be provided around the entire circumference of the outer periphery of the nitrogen polar surface; it can be provided on the portion that is contacted by the transport member (tweezers, robot, etc.) of the self-standing substrate. For example, Figure 2 When the conveyor contacts region H in the outer periphery 22 of the self-supporting substrate, a chamfered portion 21c can be provided on the outer periphery 22 of these regions H.

[0057] Furthermore, the chamfer can be provided across the entire width of the outer periphery of the nitrogen polar surface, or it can be provided only on a portion of the outer periphery. The width of the chamfer can be greater than the width of the outer periphery.

[0058] Furthermore, when a chamfer is provided on the outer periphery of the Group 13 element polar surface, it is preferable that the chamfer 21d is provided on the entire periphery of the outer periphery 23 of the Group 13 element polar surface 21b, similar to the nitrogen polar surface. However, the chamfer 21d does not need to be provided on the entire periphery of the outer periphery 23 of the Group 13 element polar surface; it is preferable that it is provided on 50% or more of the outer periphery 23 of the Group 13 element polar surface.

[0059] Additionally, the chamfer can be set across the entire width of the outer perimeter of the polar face of a Group 13 element, or it can be set only on a portion of the outer perimeter. The width of the chamfer can be greater than the width of the outer perimeter.

[0060] The outer periphery of the polar facet of group 13 elements refers to a 1 mm wide strip-shaped region including the outer edge of the polar facet of group 13 elements. Similarly, the outer periphery of the nitrogen polar facet refers to a 1 mm wide strip-shaped region including the outer edge of the nitrogen polar facet.

[0061] (Explanation of the shape of the chamfered part)

[0062] Figure 3 , Figure 4 The shape of the chamfered portion at each outer perimeter is further illustrated.

[0063] Figure 3 In the self-standing substrate 21 shown in (a), a chamfered portion 21c is provided on the outer periphery 22 of the nitrogen polar surface 21a, and a chamfered portion 21d is provided on the outer periphery 23 of the group 13 element polar surface 21b. In this example, each chamfered portion is a flat surface, and each flat surface is inclined relative to the group 13 element polar surface, the nitrogen polar surface, and the side surface 21e. In addition, the side surface 21e is a flat surface.

[0064] Figure 3 In the self-standing substrate 21G shown in (b), a chamfered portion 21c is provided on the outer periphery 22 of the nitrogen polar surface 21a, and a chamfered portion 21d is provided on the outer periphery 23 of the group 13 element polar surface 21b. In this example, each chamfered portion is a protruding curved surface, and each curved surface converges at the outer periphery edge, leaving no flat side surface.

[0065] The reference example involves Figure 4 In the self-standing substrate 21A shown in (a), no chamfered portions are provided on the outer periphery 22 of the nitrogen polar surface 21a and the outer periphery 23 of the group 13 element polar surface 21b. Therefore, the side surface 21e is flat overall.

[0066] Figure 4In the self-standing substrate 21B shown in (b), a chamfered portion 21c is provided on the outer periphery 22 of the nitrogen polar surface 21a, and a chamfered portion 21d is provided on the outer periphery 23 of the group 13 element polar surface 21b. The chamfered portions 21c and 21d are inclined relative to the group 13 element polar surface, the nitrogen polar surface, and the side surface 21e. In addition, the side surface 21e is a flat surface.

[0067] Figure 4 In the self-standing substrate 21C shown in (c), a chamfered portion 21c is provided on the outer periphery 22 of the nitrogen polar surface 21a, and a chamfered portion 21d is provided on the outer periphery 23 of the group 13 element polar surface 21b. In this example, each chamfered portion is a curved surface that protrudes outward (so-called R-chamfer). The side surface 21e is a flat surface.

[0068] Figure 5 In the self-standing substrate 21D shown in (a), a chamfered portion 21c is provided on the outer periphery 22 of the nitrogen polar surface 21a, and a chamfered portion 21d is provided on the outer periphery 23 of the group 13 element polar surface 21b. In this example, the chamfered portion 21d is a flat surface that is inclined relative to the group 13 element polar surface 21b. In addition, the chamfered portion 21c is a curved surface that protrudes outward (so-called R-chamfer). The side surface 21e is a flat surface.

[0069] Figure 5 In the self-standing substrate 21E shown in (b), a chamfered portion 21c is provided on the outer periphery 22 of the nitrogen polar surface 21a, and a chamfered portion 21d is provided on the outer periphery 23 of the group 13 element polar surface 21b. In this example, the chamfered portions 21c and 21d are flat surfaces. In addition, the side surface 21e is a curved surface that protrudes outward.

[0070] Figure 5 In the self-standing substrate 21F shown in (c), a chamfered portion 21c is provided on the outer periphery 22 of the nitrogen polar surface 21a, and a chamfered portion 21d is provided on the outer periphery 23 of the group 13 element polar surface 21b. In this example, the chamfered portions 21c and 21d are curved surfaces that protrude outwards (so-called R-surfaces). In addition, the side surface 21e is also a curved surface that protrudes outwards.

[0071] In a preferred embodiment, as described above, the nitrogen polar surface is convexly warped, while the group 13 element polar surfaces are concavely warped. This further suppresses the angular deviation of the group 13 element polar surfaces. The advantages of this will be further explained.

[0072] Typically, such as Figure 7As shown in (a), a seed film 2 is formed on the surface 1a of a substrate 1, and a group 13 element nitride layer 3 is formed on the group 13 element polar facet 2a of the seed film 2. Next, the group 13 element nitride layer is separated from the substrate 1 to obtain a self-standing substrate 3. A laser can be irradiated from the back side 1b of the substrate 1, as shown by arrow A, and a laser lift-off method can be used, such as... Figure 7 (b) shows the separation of the group 13 nitride layer to obtain a self-standing substrate; alternatively, the self-standing substrate 3 can be obtained by spontaneous separation using the difference in thermal shrinkage during cooling after the formation of the group 13 nitride layer, or by slicing the group 13 nitride layer using a wire saw or similar method.

[0073] Next, after adjusting the shape to a circle using grinding, the nitrogen polar facet of the self-standing substrate is adhered to the processing platform. During adhesion, the wax thickness is changed by adjusting the load applied to the self-standing substrate, or a jig is clamped between the self-standing substrate and the processing platform, thereby changing the surface shape of the self-standing substrate. Next, the group 13 element polar facet 3a is removed through grinding, fine lapping, and polishing processes, thereby thinning and planarizing the surface to the desired thickness, forming the self-standing substrate.

[0074] Next, the polar facets of the group 13 elements of the self-standing substrate are bonded to the processing platform. During bonding, the wax thickness is changed by adjusting the load applied to the self-standing substrate, or the surface shape of the self-standing substrate is changed by clamping the fixture between the self-standing substrate and the processing platform.

[0075] Next, the nitrogen polar surface is removed through grinding, finishing, and lapping processes, thereby thinning the substrate to the desired thickness and planarizing the surface to obtain a self-standing substrate. Here, the group 13 element polar surface is finished first, followed by the nitrogen polar surface; however, the order can be reversed.

[0076] Next, the outer periphery of the self-standing substrate is chamfered by grinding to obtain the final self-standing substrate 3A.

[0077] Next, epitaxial growth of crystals is performed on the group 13 element polar plane 3a of the self-standing substrate 3A, such as... Figure 7 (c) Figure 2 As shown, functional layer 4 is deposited to obtain functional element 5. 3b is the nitrogen polar surface.

[0078] Here, the problems associated with the warping of self-standing substrates are further explained. Typically, substrates with an angled tilt, where the crystallization axis on the seed film surface is tilted relative to the a-axis, m-axis, and c-axis of the wurtzite structure, are more common. However, for ease of understanding, a substrate with a 0° tilt angle (JUST substrate) will be used here for explanation. Figure 8As shown in (a), in the substrate 1, the crystallization axes are oriented in a certain direction, as indicated by arrow B. Typically, crystallization axis B is the a-axis, m-axis, and c-axis of a wurtzite structure. In the seed film 2, the crystallization axes grow in accordance with the crystal orientation of the substrate, as indicated by arrow C. Then, when the group 13 nitride layer 3 is formed, the crystallization axes grow in accordance with the crystal orientation of the seed film, as indicated by arrow D.

[0079] In this state, a laser is irradiated as shown by arrow A, causing the group 13 nitride layer to peel off from the substrate. Figure 8 (b)). Therefore, as Figure 9 (a) Schematic illustration shows that the group 13 nitride layer 13 and the seed film 12 are warped. This warping is caused by, for example, internal stress resulting from the difference in defect density between the group 13 polar facet 13a and the nitrogen polar facet 13b of the gallium nitride layer, or differences in crystal growth modes. Correspondingly, the orientation of the crystal axis E in the group 13 nitride layer 13 also changes overall.

[0080] For example, such as Figure 9 As shown in (b), by adjusting the pressure applied to the group 13 element nitride layer, and while retaining some degree of warping in the gallium nitride layer, the layer is adhered to a processing platform. The gallium nitride layer is then ground and polished to achieve a thinner sheet, with a pair of planes X forming the surface and back of the substrate. In this case, the desired result is... Figure 9 (c) shows the self-standing substrate 14. However, on the Group 13 element polar surface 14a of this self-standing substrate 14, the angle of the crystal axis E varies significantly depending on the position. The angle of the Group 13 element polar surface refers to the tilt angle of the crystal axis E relative to the normal L orthogonal to the Group 13 element polar surface. If the angle distribution of the Group 13 element polar surface becomes larger, the composition and crystallinity of the functional layer epitaxially grown on this surface are affected, thus causing performance changes depending on the position. For example, when a light-emitting element is formed on the Group 13 element polar surface, the emission wavelength changes depending on the position, resulting in a lower yield. It should be noted that 14b is the nitrogen polar surface.

[0081] The inventors of this invention differentiated the warpage amounts of the group 13 element polar side and the nitrogen polar side of the self-standing substrate. Even with warpage on the nitrogen polar side, by reducing the angular distribution on the group 13 element polar side, they successfully further homogenized the performance of the functional layer formed on the group 13 element polar side. That is, as... Figure 10As illustrated schematically, for example, by relatively increasing the warpage WU of the group 13 element polar surface 17a of the self-supporting substrate 17, the angular distribution of the group 13 element polar surface 17a can be reduced. Meanwhile, the warpage of the group 13 element polar surface 17a of the self-supporting substrate 1 is different from the warpage of the nitrogen polar surface 17b. It is believed that by relatively reducing the warpage WB of the nitrogen polar surface 17b, the temperature distribution of the group 13 element polar surface can be reduced, suppressing changes in the composition and crystallinity of the functional layer caused by this, and suppressing the generation of micro-scratches on the nitrogen polar surface that may occur when the substrate is handled and transported using tweezers or a robotic arm. 17c and 17d are chamfered portions.

[0082] If the warpage of the group 13 element polar facets differs from that of the nitrogen polar facet, a total thickness variation (TTV) occurs in the self-contained substrate. However, even with this TTV, the distribution of group 13 element polar facets during epitaxial growth of the functional layer on the self-contained substrate remains relatively small. This is because the high thermal conductivity of the gallium nitride crystals constituting the self-contained substrate is utilized. As a result, no morphological anomalies occur during functional layer deposition, and wavelength deviations are sufficiently suppressed.

[0083] The material of the substrate is not particularly limited, and examples include sapphire, crystalline oriented alumina, gallium oxide, and Al. x Ga 1-x N (0≤x≤1) and SiC are preferred examples.

[0084] Al can be used as a material for seed films. x Ga 1-x N(0≤x≤1), In x Ga 1-x N (0≤x≤1) is a preferred example, and gallium nitride is particularly preferred. The seed film is particularly preferred to be gallium nitride, which has been confirmed to have a yellow emission effect by observation using a fluorescence microscope. The so-called yellow emission, in addition to the interband exciton transition (UV), is also a peak appearing in the range of 2.2 to 2.5 eV (yellow emission (YL) or yellow band (YB)).

[0085] The preferred method for forming the seed film is vapor phase growth, such as metal-organic chemical vapor deposition (MOCVD), hydride vapor phase growth (HVPE), pulse-excited deposition (PXD), MBE, and sublimation. Metal-organic chemical vapor deposition is particularly preferred. Furthermore, the preferred growth temperature is 950–1200°C.

[0086] There is no particular limitation on the growth direction of gallium nitride crystals. It can be the normal direction of the c-plane of the wurtzite structure, or the normal direction of the a-plane and m-plane, or a plane that is inclined relative to the c-plane, a-plane, and m-plane.

[0087] There are no particular limitations on the methods for fabricating gallium nitride layers. Examples include: metal-organic chemical vapor deposition (MOCVD), hydride vapor deposition (HVPE), pulse-excited deposition (PXD), MBE, sublimation, and other vapor-phase methods; as well as ammonothermal methods, flux methods, and other liquid-phase methods.

[0088] As a preferred embodiment, the thickness of the self-standing substrate after grinding is preferably 300 μm or more, and more preferably 1000 μm or less.

[0089] There is no particular limitation on the size of the self-standing substrate, but 2 inches, 4 inches, and 6 inches are preferred, and it can also be 8 inches or larger.

[0090] On the nitrogen polar surface and the group 13 element polar surface, the width W of the chamfer (refer to...) Figures 3-5 There are no particular limitations. From the point of view of the present invention, the length is preferably one-twentieth or more and three times or less than the thickness of the self-supporting substrate, and more preferably one-tenth or more and less than one time the thickness of the self-supporting substrate.

[0091] On the nitrogen polar surface and the group 13 element polar surface, the height D of the chamfer (refer to...) Figures 3-5 Without particular limitation, from the viewpoint of the present invention, when the side surface 21e is a flat surface, the length is preferably more than one-twentieth and less than one-half of the thickness of the self-supporting substrate, more preferably more than one-tenth and less than two-fifths of the length; when the side surface 21e is a curved surface, the length is preferably more than one-twentieth and less than one-half of the thickness of the self-supporting substrate. The height D of the chamfer is the dimension in the thickness direction of the self-supporting substrate from the starting point of the chamfer to the end of the self-supporting substrate.

[0092] Furthermore, from the perspective of this invention, regarding the nitrogen polar plane and the group 13 element polar plane, Figure 3 The opening width H at the end of the self-supporting substrate shown is preferably 70 μm or more, more preferably 100 μm or more. Furthermore, the opening width H is preferably less than half the thickness of the self-supporting substrate, more preferably less than two-fifths. It should be noted that the opening width H refers to the height of each chamfer portion when viewed from the center O of each polarity surface 21a, 21b along the thickness direction of the self-supporting substrate.

[0093] Examples of epitaxial crystals grown on a self-contained substrate include gallium nitride, aluminum nitride, indium nitride, or mixtures thereof. Specifically, examples include GaN, AlN, InN, and Ga... x Al 1-x N(1>x>0),Ga x In 1-x N(1>x>0), Al x In 1- x N(1>x>0),Ga x Al y In z N(1>x>0, 1>y>0, x+y+z=1). In addition to the light-emitting layer, functional layers disposed on the self-standing substrate can include, for example, rectifier layers, switching elements, and power semiconductor layers, besides the light-emitting layer. Furthermore, after disposing of the functional layer on the group 13 element polar surface of the self-standing substrate, the nitrogen polar surface can be processed, for example, by grinding or lapping, to reduce the thickness and thickness distribution of the self-standing substrate.

[0094] Example

[0095] (Example 1)

[0096] Trial production Figure 1 (a) and Figure 3 (a) shows the self-standing substrate 21.

[0097] Specifically, a GaN template (2.5-inch substrate diameter) is fabricated by depositing a GaN seed film containing gallium nitride on a sapphire substrate. The seed film has a thickness of 2 μm.

[0098] Next, a 1 mm thick gallium nitride layer was formed using the sodium flux method. Then, the gallium nitride layer was removed using a laser lift-off method to obtain a 1 mm thick gallium nitride substrate. At this point, warping was observed on the gallium nitride substrate.

[0099] Next, the outer periphery of the gallium nitride substrate was ground to a diameter of 2 inches. Then, through grinding, finishing, and lapping, a self-standing substrate with a thickness of 400 μm and mirror-finished Group 13 element polar facets and nitrogen polar facets was obtained. At this point, by varying the bonding load on the processing platform and the amount of wax used for bonding, the warpage of the gallium and nitrogen polar facets was adjusted to the ranges shown in Table 1. Ten samples of each type were fabricated, and the warpage values ​​are expressed as the range of maximum and minimum values.

[0100] Furthermore, chamfered portions are formed on the outer peripheries of both the nitrogen-polar and gallium-polar surfaces. The width W of the chamfered portion is 200 μm, the opening width H of the chamfered portion is 100 μm, and the shape of the chamfered portion is as follows: Figure 4(b) shows the flat surface. Additionally, the height D of the chamfer is represented in Table 1 by the range of its maximum and minimum values.

[0101] The angular distribution of the gallium polar facet of the obtained self-standing substrate was evaluated. Next, an LED device structure was grown on the gallium polar facet of the self-standing substrate in the form of an epitaxial film using MOCVD, and the performance (surface morphology, emission wavelength) of the LED device structure was evaluated. These evaluation results are shown in Table 1.

[0102] The evaluation method is as follows.

[0103] (warping)

[0104] As described above, the warpage of the gallium polar surface and the nitrogen polar surface of the self-standing substrate was measured, and the radius of curvature was calculated.

[0105] (Method for determining the skewness distribution)

[0106] Five points within the substrate surface were measured using an energy-dispersive X-ray diffractometer (Bruker AXS D2 CRYSO). The five points were: the center of the substrate, and four points on the X and Y axes within 5 mm of the substrate end, with the center of the substrate as the origin. The "maximum value - minimum value" was set to an angular distribution.

[0107] For example, in the case of a self-standing substrate with a diameter of 50.8 mm, measurements were taken at five points: (0,0), (45.8,0), (-45.8,0), (0,45.8), and (0,-45.8).

[0108] (Morphology of the epitaxial film within the wafer plane)

[0109] In addition, the surface morphology of the obtained epitaxial film was observed to confirm whether any abnormalities were generated.

[0110] (Method for determining the emission wavelength distribution of LEDs)

[0111] In PL (photoluminescence) measurement, the emission peak wavelengths at 5 points with the same skew angle are measured. The "maximum wavelength - minimum wavelength" is set as the emission wavelength distribution.

[0112] (Any cracks)

[0113] For 10 self-standing substrates, as described above, an epitaxial film is formed, and the presence or absence of cracks in the self-standing substrates and the epitaxial film is observed to determine the cracking rate.

[0114] [Table 1]

[0115]

[0116] As shown in Table 1, in Example 1, chamfered portions were provided on the outer periphery of both the gallium polar surface and the nitrogen polar surface. The radius of curvature of the nitrogen polar surface ranged from +24.8 to 46.1 μm, and the radius of curvature of the gallium polar surface ranged from -46.1 to -24.8 μm. As a result, no abnormal morphology of the epitaxial film was observed, the emission wavelength distribution of the LED was 12 nm, and the yield of the crack-free self-standing substrate was 100%.

[0117] (Examples 2-4)

[0118] The self-standing substrate and LED structure were fabricated and evaluated in the same manner as in Example 1. The results are shown in Table 1.

[0119] That is, in Examples 2-4, chamfered portions are provided on the outer periphery of both the gallium polar surface and the nitrogen polar surface. The radii of curvature of the nitrogen polar surface and the gallium polar surface are shown in Table 1. However, the nitrogen polar surface is convexly warped, while the gallium polar surface is concavely warped. As a result, no abnormal morphology of the epitaxial film was observed, the emission wavelength distribution of the LED was relatively small, and the yield of the self-standing substrate without cracks was 100%.

[0120] (Comparative Examples 1-3)

[0121] The self-supporting substrate and LED structure for each example were fabricated and evaluated in the same manner as in Example 1. The results are shown in Table 2.

[0122] That is, in Comparative Examples 1 to 3, no chamfered portions were provided on the outer periphery of either the gallium polar surface or the nitrogen polar surface, and the nitrogen polar surface was convex and warped. As a result, no abnormal morphology of the epitaxial film was observed, and the emission wavelength distribution of the LED was relatively small. However, the yield of the self-standing substrate without cracks was significantly reduced to only 70%.

[0123] (Comparative Examples 4-5)

[0124] The self-supporting substrate and LED structure for each example were fabricated and evaluated in the same manner as in Example 1. The results are shown in Table 2.

[0125] That is, in Comparative Examples 4 and 5, chamfered portions were provided on the outer periphery of the gallium polar surface and the nitrogen polar surface, respectively; however, the nitrogen polar surface was concave and warped. As a result, no abnormal morphology of the epitaxial film was observed, and the emission wavelength distribution of the LED was relatively small. However, the yield of the uncracking self-standing substrate was significantly reduced to only 50%.

[0126] [Table 2]

[0127]

[0128] (Comparative Examples 6-7)

[0129] The self-supporting substrate and LED structure for each example were fabricated and evaluated in the same manner as in Example 1. The results are shown in Table 3.

[0130] Furthermore, in Comparative Examples 6 and 7, no chamfered portions were provided on the outer periphery of either the gallium polar surface or the nitrogen polar surface, and the nitrogen polar surface was concave and warped. As a result, no abnormal morphology portions of the epitaxial film were observed, and the emission wavelength distribution of the LED was relatively small. However, the yield of the crack-free self-standing substrate was significantly reduced to only 30%.

[0131] [Table 3]

[0132]

[0133] (Comparative Examples 8-10)

[0134] The self-supporting substrate and LED structure for each example were fabricated and evaluated in the same manner as in Example 1. The results are shown in Table 3.

[0135] In Comparative Examples 8 and 10, chamfered portions were provided on the outer periphery of the gallium polar surface and the nitrogen polar surface, respectively; however, the nitrogen polar surface was flat. As a result, no abnormal morphology of the epitaxial film was observed, and the emission wavelength distribution of the LED was relatively small; however, the yield of the self-standing substrate without cracks was significantly reduced.

[0136] In Comparative Example 9, no chamfered portions were provided on the outer peripheries of either the gallium polar surface or the nitrogen polar surface. Furthermore, the nitrogen polar surface was flat. As a result, no abnormal morphology of the epitaxial film was observed, and the emission wavelength distribution of the LED was relatively small. However, the yield of the crack-free self-standing substrate was significantly reduced.

[0137] (Comparative Example 11)

[0138] The self-standing substrate and LED structure were fabricated and evaluated in the same manner as in Example 1. The results are shown in Table 3.

[0139] Among them, as a self-standing substrate, a prototype was fabricated. Figure 6 (a) shows the form of the self-supporting substrate 30A. This self-supporting substrate is substantially the same as the self-supporting substrate described in Patent Document 3. That is, Figure 6 (a) The nitrogen polar surface 30a of the self-standing substrate 30A is flat, and the gallium polar surface 30b is also flat. However, a concave curved surface 32 is provided on the outer periphery 31 (5 mm wide) of the gallium polar surface 30b. The side surface 30c of the self-standing substrate is also flat. No chamfered portion is provided.

[0140] As a result, abnormal morphology of the epitaxial film was mainly observed in the raised parts of the outer periphery, the emission wavelength distribution of the LED was particularly large in the curved parts of the outer periphery, and the yield of the self-standing substrate without cracks was greatly reduced.

[0141] (Comparative Example 12)

[0142] The self-standing substrate and LED structure were fabricated and evaluated in the same manner as in Example 1. The results are shown in Table 3.

[0143] Among them, as a self-standing substrate, a prototype was fabricated. Figure 6 (b) shows the form of the self-standing substrate 30B. Specifically, the side surface 30c of the self-standing substrate 30B is flat, and the gallium polar surface 30b is also flat. However, a concave curved surface 32 is provided on the outer periphery 31 (3 mm wide) of the gallium polar surface 30b. Furthermore, the nitrogen polar surface 30d is convex and warped, with a radius of curvature ranging from +24.8 to 46.1 μm. No chamfered portion is provided.

[0144] As a result, abnormal morphology of the epitaxial film was mainly observed in the raised parts of the outer periphery, the emission wavelength distribution of the LED was particularly large in the curved parts of the outer periphery, and the yield of the self-standing substrate without cracks was greatly reduced.

Claims

1. A self-standing substrate for epitaxial crystal growth, comprising crystals of group 13 element nitrides selected from gallium nitride, aluminum nitride, indium nitride, or mixtures thereof, for epitaxial crystal growth. The characteristic of the self-standing substrate for epitaxial crystal growth is that... The self-standing substrate has a nitrogen polar surface and a group 13 element polar surface. The nitrogen polar surface is convex and warped, and a chamfered portion is provided on the outer periphery of the nitrogen polar surface. The absolute value of the radius of curvature of the warped polar surface of the group 13 elements is smaller than the absolute value of the radius of curvature of the warped polar surface of nitrogen.

2. The self-standing substrate for epitaxial crystal growth according to claim 1, characterized in that, The radius of curvature of the warped nitrogen polar surface is greater than +5m and less than +65m.

3. The self-standing substrate for epitaxial crystal growth according to claim 1, characterized in that, The chamfered portion is provided around the entire circumference of the outer periphery of the nitrogen polar surface.

4. The self-standing substrate for epitaxial crystal growth according to any one of claims 1 to 3, characterized in that, A chamfered portion is provided on the outer periphery of the polar surface of the group 13 elements.

5. The self-standing substrate for epitaxial crystal growth according to any one of claims 1 to 3, characterized in that, The polar surfaces of the 13 group elements are concave and warped.

6. The self-standing substrate for epitaxial crystal growth according to any one of claims 1 to 3, characterized in that, The skew angle distribution of the polar surfaces of the 13 group elements is less than 0.25°.

7. The self-standing substrate for epitaxial crystal growth according to any one of claims 1 to 3, characterized in that, The polar surfaces of the group 13 elements are mirror-finished.

8. The self-standing substrate for epitaxial crystal growth according to any one of claims 1 to 3, characterized in that, The opening width of the nitrogen polar surface end of the self-standing substrate is 70 μm or more and less than half the thickness of the self-standing substrate.

9. The self-standing substrate for epitaxial crystal growth according to any one of claims 1 to 3, characterized in that, The height of the chamfer at the outer periphery of the nitrogen polar surface of the self-standing substrate is more than one-twentieth and less than one-half of the thickness of the self-standing substrate.

10. A functional element, characterized in that, have: The self-standing substrate for epitaxial crystal growth according to any one of claims 1 to 9; and A functional layer disposed on the polar surface of the group 13 elements of the self-standing substrate.

11. The functional element according to claim 10, characterized in that, The functional element has a light-emitting function.

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