AlN laminate

Abstract

This layered plate comprises an AlN polycrystal layer, an AlN single crystal layer formed over the AlN polycrystal layer, and a cavity-containing region which is in contact with the boundary portion between the AlN single crystal layer and the AlN polycrystal layer and into which a plurality of cavities have been introduced in a dispersed manner.

Description

Technical Field

[0001] The technology disclosed in this specification relates to a laminate in which an AlN single crystal layer and an AlN polycrystalline layer are laminated.

Background Art

[0002] An AlN single crystal plate may be used as a substrate for an ultraviolet light emitting device. For example, Non-Patent Document 1 discloses a method for manufacturing an ultraviolet light emitting device formed on an AlN single crystal plate. In Non-Patent Document 1, a functional layer of an ultraviolet light emitting device is formed on an AlN single crystal plate. After the functional layer is formed on the AlN single crystal plate, the AlN single crystal plate is thinned by mechanical polishing in order to improve the ultraviolet light transmittance.

Prior Art Documents

Non-Patent Documents

[0003]

Non-Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] In the ultraviolet light-emitting device described in Non-Patent Document 1, an AlN single-crystal plate is used as a substrate. In order to function as a support substrate when manufacturing an ultraviolet light-emitting device, a thick substrate is used, but a thick AlN single-crystal plate is expensive. Therefore, a laminated plate in which a support substrate is bonded to an AlN single-crystal plate may be used as a handling substrate for manufacturing an ultraviolet light-emitting device. Specifically, as the support substrate, an AlN polycrystalline plate having a thermal expansion coefficient close to that of the AlN single-crystal plate may be used. However, even when an AlN polycrystalline plate is used as the support substrate, its thermal expansion coefficient is not the same as that of the AlN single-crystal plate. Therefore, in the heat treatment process when manufacturing an ultraviolet light-emitting device, there is a risk that warping or cracking may occur in the AlN single-crystal plate.

[0005] This specification discloses a technique for making it difficult for warping or cracking to occur in an AlN single-crystal layer in a laminated plate in which an AlN single-crystal layer and an AlN polycrystalline layer are laminated.

Means for Solving the Problem

[0006] The laminated plate disclosed in this specification includes an AlN polycrystalline layer, an AlN single-crystal layer formed on the AlN polycrystalline layer, and a void-containing region that is in contact with an interface portion between the AlN single-crystal layer and the AlN polycrystalline layer and in which a plurality of voids are dispersedly introduced.

[0007] The above laminate is provided with a void-containing region in which a plurality of voids are dispersedly introduced at the interface between the AlN single crystal layer and the AlN polycrystalline layer, thereby relaxing the thermal expansion difference between the two based on the difference in the thermal expansion coefficients of the AlN single crystal layer and the AlN polycrystalline layer. That is, the void-containing region can absorb the strain caused by the difference in the thermal expansion coefficients of the AlN single crystal layer and the AlN polycrystalline layer, and reduce the force applied to the AlN single crystal layer. Therefore, even though the AlN single crystal layer and the AlN polycrystalline layer having different thermal expansion coefficients are laminated, it is possible to reduce the occurrence of warping and cracks in the AlN single crystal layer. Further, by providing the void-containing region, even when the AlN polycrystalline layer is removed by mechanical polishing after the production of the ultraviolet light-emitting device, the impact generated during the mechanical polishing is absorbed by the void-containing region, and it is possible to suppress the influence on the functional layer of the ultraviolet light-emitting device.

Brief Description of the Drawings

[0008]

Figure 1

Figure 2

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Figure 4

Modes for Carrying Out the Invention

[0009] The main features of the examples described below are listed. Note that the technical elements described below are each independent technical elements, which exhibit technical utility alone or in various combinations, and are not limited to the combinations described in the claims at the time of filing.

[0010] The laminate disclosed in this specification is a laminate of an AlN single crystal layer and an AlN polycrystalline layer. Single crystal AlN, for example, compared with sapphire, Al x Ga yThe nitride semiconductor such as N(0≦x≦1, 0<y≦1) has a lattice constant that is close to or the same as that of the AlN single crystal layer of the laminate disclosed in this specification. Therefore, the AlN single crystal layer of the laminate disclosed in this specification is useful as a growth substrate for an ultraviolet light-emitting device (UV LED) having a nitride semiconductor as a functional layer. Further, the laminate disclosed in this specification is useful as a handling substrate when manufacturing an ultraviolet light-emitting device. When using an AlN single crystal plate as a handling substrate when manufacturing an ultraviolet light-emitting device, it is necessary to use a thick AlN single crystal plate to ensure strength, but thick AlN single crystal plates are expensive. The laminate disclosed in this specification has an AlN polycrystalline layer provided on the back side of the AlN single crystal layer (the side where the functional layer of the ultraviolet light-emitting device is not provided). The AlN polycrystalline layer can be obtained (or manufactured) at a relatively low cost. Therefore, by laminating the AlN single crystal layer and the AlN polycrystalline layer, it is possible to realize a growth substrate with a relatively close lattice constant to that of the nitride semiconductor and high strength without using an expensive thick AlN single crystal plate.

[0011] In addition, the laminate disclosed in this specification has a void-containing region in which voids are dispersed and introduced at the interface between the AlN single crystal layer and the AlN polycrystalline layer. Although the thermal expansion coefficient of single crystal AlN and the thermal expansion coefficient of polycrystalline AlN are relatively close, they are slightly different. Therefore, when the AlN single crystal layer and the AlN polycrystalline layer are laminated, during heat treatment or the like, a force may be applied from the AlN polycrystalline layer to the AlN single crystal layer based on the difference in thermal expansion coefficients between the two. As a result, warping or cracking may occur in the AlN single crystal layer. The laminate disclosed in this specification is provided with a void-containing region at the interface between the AlN single crystal layer and the AlN polycrystalline layer, thereby being able to absorb the strain generated at the interface due to the difference in thermal expansion coefficients between the AlN single crystal layer and the AlN polycrystalline layer. Specifically, the void-containing region can be physically deformed to relieve the force applied to the AlN crystal layer. Therefore, it is possible to reduce the occurrence of warping and cracking in the AlN single crystal layer.

[0012] In addition, the laminate disclosed in this specification is provided with a void-containing region, so that when removing the AlN polycrystalline layer by mechanical polishing, the impact can be reduced from reaching the AlN single-crystalline layer due to the void-containing region. That is, the void-containing region absorbs the impact generated during mechanical polishing. Therefore, the force (vibration) applied to the functional layer of the ultraviolet light-emitting device can be reduced, and the influence on the functional layer can be reduced. The laminate disclosed in this specification is not particularly limited, but the thickness (the distance between the front and back surfaces including the AlN single-crystalline layer and the AlN polycrystalline layer) may be 0.5 to 10.0 mm. Further, the void-containing region may be provided at a portion in contact with the interface between the AlN single-crystalline layer and the AlN polycrystalline layer. That is, the void-containing region may be provided within the AlN single-crystalline layer, may be provided within the AlN polycrystalline layer, or may be provided across both the AlN single-crystalline layer and the AlN polycrystalline layer.

[0013] In the laminate disclosed in this specification, the thickness of the void-containing region may be 0.1 μm or more and 5.0 μm or less. That is, in the thickness direction from the front surface to the back surface of the laminate, the void-containing region is provided locally. If the thickness of the void-containing region is 0.1 μm or more, the effect of alleviating the influence of the difference in thermal expansion coefficient between the AlN single-crystalline layer and the AlN polycrystalline layer can be obtained, and the impact generated during mechanical polishing can be sufficiently absorbed. Also, if it is 5.0 μm or less, since the thickness of the void-containing region is sufficiently thin with respect to the thickness of the laminate, a thickness that substantially functions as the AlN single-crystalline layer and the AlN polycrystalline layer is sufficiently ensured, and the mechanical strength of the laminate can be maintained. The thickness of the void-containing region may be 0.2 μm or more, may be 0.3 μm or more, may be 0.5 μm or more, may be 0.7 μm or more, may be 1.0 μm or more, or may be 1.5 μm or more. Also, the thickness of the void-containing region may be 4.5 μm or less, may be 4.0 μm or less, may be 3.5 μm or less, or may be 3.0 μm or less.

[0014] In the laminated board disclosed in this specification, within the void-containing region, the distance between adjacent voids may be 1 μm or more and 300 μm or less. In other words, the gap between voids may be 1 μm or more and 300 μm or less. According to such a configuration, if it is 1 μm or more, the problem (deterioration of the AlN single crystal layer 12) caused by the difference in the thermal expansion coefficients of the AlN single crystal layer and the AlN polycrystalline layer can be reduced. Also, if it is 300 μm or less, the distance between voids becomes sufficiently small, and the mechanical strength of the laminated board can be maintained. Note that "adjacent voids" means voids adjacent in a direction (substantially parallel) along the end face in the thickness direction of the AlN polycrystalline layer. The distance between voids within the adjacent void-containing region may be 2 μm or more, 5 μm or more, 10 μm or more, 20 μm or more, or 25 μm or more. Also, the distance between void components within the void-containing region may be 275 μm or less, 250 μm or less, 200 μm or less, 150 μm or less, or 100 μm or less.

[0015] In the laminated board disclosed in this specification, the shape of the void (that is, the shape surrounding the space provided by the void) may have an aspect ratio greater than 1 and less than or equal to 10. In this case, within the void-containing region, the long side of the void may be present (substantially parallel) along the first surface (or the first surface and the second surface). Specifically, the long side of the void may be arranged to form an angle of less than 20 degrees with respect to the first surface. If the aspect ratio of the void is greater than 1, the problem (deterioration of the AlN single crystal layer 12) caused by the difference in the thermal expansion coefficients of the AlN single crystal layer and the AlN polycrystalline layer can be reduced. Also, if the aspect ratio is less than or equal to 10, the mechanical strength of the laminated board can be maintained. Note that the aspect ratio may be 0.5 or more, 1.0 or more, 1.5 or more, or 2.0 or more. Also, the aspect ratio may be 8 or less, 7 or less, 5 or less, or 3 or less.

[0016] Also, in the void-containing region, the ratio of voids (void ratio) to the total volume (AlN matrix + voids) may be 1 to 10 vol%. If the void ratio is 1 vol% or more, the effect of absorbing the strain generated in the above-described interface portion and the effect of absorbing the impact generated during mechanical polishing can be sufficiently obtained. Also, if it is 10 vol% or less, the strength of the laminated plate is sufficiently ensured. Further, when the volume of voids is less than 1 vol% with respect to the total volume in the range of 0.1 μm in the thickness direction for specific voids, such voids are different from the voids constituting the void-containing region. That is, the laminated plate disclosed in this specification may contain a small amount of voids in the AlN single crystal layer or the AlN polycrystalline layer in addition to the void-containing region. By the ratio of voids in the void-containing region being 1 to 10 vol%, the effect of absorbing the strain generated in the interface portion due to the difference in the coefficient of thermal expansion and the effect of absorbing the impact generated during mechanical polishing are sufficiently exhibited.

Example

[0017] (Example 1) Hereinafter, the laminated plate 10 according to the example will be described. The laminated plate 10 is used as a handling substrate for manufacturing the ultraviolet light-emitting device 1. Therefore, before explaining the laminated plate 10 in detail, the ultraviolet light-emitting device 1 using the laminated plate 10 as a handling substrate will be briefly explained.

[0018] The ultraviolet light-emitting device 1 is an ultraviolet light-emitting diode (UV LED), and includes an AlN single crystal layer 12, an n-type nitride semiconductor layer 2, a p-type nitride semiconductor layer 3, and a light-emitting layer 4. The n-type nitride semiconductor layer 2 is provided on the surface of the AlN single crystal layer 12. The light-emitting layer 4 is provided on a part (the right side in FIG. 1) of the surface of the n-type nitride semiconductor layer 2. Therefore, a part of the surface of the n-type nitride semiconductor layer 2 is provided with the light-emitting layer 4, and the other parts are exposed. On the surface of the light-emitting layer 4, a p-type nitride semiconductor layer 3 is provided. That is, the light-emitting layer 4 is provided between the n-type nitride semiconductor layer 2 and the p-type nitride semiconductor layer 3. Electrodes (not shown) are respectively provided on the surface of the p-type nitride semiconductor layer 3 and the exposed part of the surface of the n-type nitride semiconductor layer 2. Although not shown in the figure, actually, the n-type nitride semiconductor layer 2 may be formed of a plurality of layers, the p-type nitride semiconductor layer 3 may be formed of a plurality of layers, and the light-emitting layer 4 may be formed of a plurality of layers. The materials and the number of layers of each layer of the n-type nitride semiconductor layer 2, each layer of the p-type nitride semiconductor layer 3, and each layer of the light-emitting layer 4 can be appropriately selected according to the use of the ultraviolet light-emitting device 1.

[0019] When manufacturing the ultraviolet light-emitting device 1, first, an n-type nitride semiconductor layer 2 is formed on the surface of the laminate 10 of the present embodiment (specifically, the surface of the AlN single crystal layer 12). Next, a light-emitting layer 4 is formed on the surface of the formed n-type nitride semiconductor layer 2, and a p-type nitride semiconductor layer 3 is formed on the surface of the formed light-emitting layer 4. Then, a part of the light-emitting layer 4 and the p-type nitride semiconductor layer 3 is removed to expose a part of the surface of the n-type nitride semiconductor layer 2. In order to form high-quality nitride semiconductor layers 2, 3, and 4, the nitride semiconductor layers 2, 3, and 4 are formed on the surface of the laminate 10 (the surface of the AlN single crystal layer 12). Further, in order to facilitate the film formation and processing of the n-type nitride semiconductor layer 2, the p-type nitride semiconductor layer 3, and the light-emitting layer 4, a thick laminate 10 is used as a handling substrate when manufacturing the ultraviolet light-emitting device 1. On the other hand, since the AlN single crystal layer 12 and the AlN polycrystalline layer 14 are laminated on the laminate 10, if the laminate 10 is used as it is as the substrate of the ultraviolet light-emitting device 1, it becomes difficult for the light emission (ultraviolet light) to pass through the laminate 10 due to the AlN polycrystalline layer 14. Therefore, after the film formation of the n-type nitride semiconductor layer 2, the p-type nitride semiconductor layer 3, and the light-emitting layer 4, the laminate 10 is thinned to a required thickness. That is, the AlN polycrystalline layer 14, which is an unnecessary part, is removed from the laminate 10 so that only the necessary AlN single crystal layer 12 remains as the substrate. Hereinafter, the n-type nitride semiconductor layer 2, the p-type nitride semiconductor layer 3, and the light-emitting layer 4 may be collectively referred to as a "functional layer".

[0020] As shown in Fig. 2, the laminated plate 10 includes an AlN single crystal layer 12 and an AlN polycrystalline layer 14. The AlN single crystal layer 12 is composed of single crystal AlN. The AlN polycrystalline layer 14 is composed of polycrystalline AlN. In this embodiment, for example, single crystal AlN and polycrystalline AlN are defined as follows. Using an XRD apparatus (D8-DISCOVER manufactured by Bruker-AXS), under the conditions of using CuKα ray, voltage 40 kV, current 40 mA, collimator diameter 0.5 mm, anti-scattering slit 3 mm, ω step width 0.01°, measure the XRC profile of the (002) plane of the AlN single crystal layer with a counting time of 1 second. Then, perform the measurement using the full width at half maximum based on the obtained XRC profile. Those with a measured value less than 10000 arcsec are referred to as single crystal AlN, and those with a measured value of 10000 arcsec or more are referred to as polycrystalline AlN. Both the AlN single crystal layer 12 and the AlN polycrystalline layer 14 can be formed, for example, by the sublimation method. Note that the formation methods of the AlN single crystal layer 12 and the AlN polycrystalline layer 14 are not particularly limited, and the AlN single crystal layer 12 and the AlN polycrystalline layer 14 can be formed, for example, by vapor deposition methods such as CVD method, HVPE method, MBE method, sputtering method, liquid phase deposition methods such as hydrothermal method, Na flux method, or other methods such as room temperature bonding in which single crystal AlN and polycrystalline AlN are bonded using a surface activation method.

[0021] In addition, the laminated plate 10 includes a void-containing region 16 provided between the front surface 20 and the back surface 22. Specifically, the void-containing region 16 is disposed at the interface portion between the AlN single-crystal layer 12 and the AlN polycrystalline layer 14 (hereinafter, also simply referred to as the "interface portion"). In this embodiment, the void-containing region 16 is disposed across both the AlN single-crystal layer 12 and the AlN polycrystalline layer 14 in the interface portion. In this embodiment, when manufacturing the ultraviolet light-emitting device 1 using the laminated plate 10 as a handling substrate in the laminated plate 10, the surface on which the functional layer is formed (that is, the exposed surface of the AlN single-crystal layer 12 in the thickness direction) is referred to as the front surface 20, and the opposite surface (that is, the exposed surface of the AlN polycrystalline layer 14 in the thickness direction) is referred to as the back surface 22. The void-containing region 16 is locally provided in the thickness direction of the laminated plate 10 and is provided substantially parallel to the back surface 14.

[0022] The void-containing region 16 is disposed across both the AlN single-crystal layer 12 and the AlN polycrystalline layer 14 at the interface between the AlN single-crystal layer 12 and the AlN polycrystalline layer 14. In the void-containing region 16, a plurality of voids (pores) are dispersed and introduced into the AlN single-crystal layer 12 and the AlN polycrystalline layer 14. Specifically, the voids in the void-containing region 16 have an aspect ratio greater than 1 and adjusted to 10 or less, and the long sides are arranged along the front surface 12 and the back surface 14. Further, each void is arranged at intervals such that the distance between adjacent voids is 1 μm to 300 μm. Also, the density of the voids (pores) in the void-containing region 16 (the ratio of the voids to the total volume) is adjusted to 1 to 10 vol%. The method for introducing voids into the void-containing region 16 is not particularly limited. For example, when manufacturing the laminated plate 10 by a vapor-phase growth method such as the sublimation method, the deposition rate is increased by increasing the raw material heating temperature or increasing the supply rate of the raw material (raw material gas) at the timing of forming the void-containing region 16, and a layer with voids introduced (void-containing region 16) can be formed. Also, when manufacturing the laminated plate 10 by room-temperature bonding such as bonding single-crystal AlN and polycrystalline AlN using a surface activation method, a layer with voids introduced (void-containing region 16) can be formed by intentionally forming irregularities on the surface of the polycrystalline AlN and then bonding.

[0023] Although the single-crystalline AlN that constitutes the AlN single-crystalline layer 12 and the polycrystalline AlN that constitutes the AlN polycrystalline layer 14 have relatively close coefficients of thermal expansion, they are slightly different. Therefore, in the heat treatment process when manufacturing the ultraviolet light-emitting device 1, a difference occurs in the amount of deformation (elongation amount) between the AlN single-crystalline layer 12 and the AlN polycrystalline layer 14. When the void-containing region 16 does not exist, strain occurs at the interface portion between the AlN single-crystalline layer 12 and the AlN polycrystalline layer 14, and the AlN single-crystalline layer 12 may deteriorate (warping or cracking may occur). The laminated plate 10 of the present embodiment includes a void-containing region 16 at the interface portion. Thereby, the strain at the interface portion due to the difference in the coefficients of thermal expansion between the AlN single-crystalline layer 12 and the AlN polycrystalline layer 14 can be relaxed. Therefore, the deterioration of the AlN single-crystalline layer 12 can be suppressed. Since the ultraviolet light-emitting device 1 can be formed on the surface of the high-quality AlN single-crystalline layer 12, the adverse effect on the functional layer of the ultraviolet light-emitting device 1 can be reduced. Further, the laminated plate 10 of the present embodiment includes the void-containing region 16, so that the impact is absorbed by the voids during mechanical polishing. Therefore, the force (vibration) applied to the functional layer of the ultraviolet light-emitting device 1 can be reduced, and the adverse effect on the functional layer can be reduced.

[0024] In this embodiment, for example, the thickness L1 of the laminate 10 is adjusted to be 0.5 mm to 10.0 mm, and the thickness L2 of the void-containing region 16 is adjusted to be 0.1 μm to 0.5 μm. The thickness L1 of the laminate 10 is the length between the front surface 20 and the back surface 22, and indicates the length in the direction perpendicular to the front surface 20 and the back surface 22. In other words, the thickness L1 of the laminate 10 is the length from the exposed surface of the AlN single crystal layer 12 through the interface portion to the exposed surface of the AlN polycrystalline layer 14. Also, the thickness L2 of the void-containing region 16 also indicates the length in the direction perpendicular to the front surface 20 and the back surface 22. By setting the thickness L2 of the void-containing region 16 to be 0.1 μm or more, it is possible to more surely obtain the effect of reducing the problem (deterioration of the AlN single crystal layer 12) caused by the difference in the thermal expansion coefficients of the AlN single crystal layer 12 and the AlN polycrystalline layer 14. Further, by setting the thickness L2 to be 0.1 μm or more, the void-containing region 16 can sufficiently absorb the impact when the laminate 10 is mechanically polished. Also, by setting the thickness L2 to be 0.5 μm or less, the ratio of the void-containing region 16 to the total thickness of the laminate 10 can be lowered. Typically, when a void-containing region is provided in the AlN layer (AlN single crystal layer 12 or AlN polycrystalline layer 14), the mechanical strength of the AlN layer decreases. However, if the thickness L2 is 0.5 μm or less, it is possible to suppress a decrease in the mechanical strength of the laminate 10 and sufficiently ensure the mechanical strength of the laminate 10.

[0025] (Example 2) In the above-described Example 1, the void-containing region 16 was disposed in both the AlN single crystal layer 12 and the AlN polycrystalline layer 14, but the configuration is not limited to this. The void-containing region may be disposed at the interface portion between the AlN single crystal layer 12 and the AlN polycrystalline layer 14. For example, as shown in FIG. 3, the void-containing region 116 may be disposed in the AlN single crystal layer 12. In this embodiment, the void-containing region 116 is different from the void-containing region 16 of Example 1, and the other configurations are substantially the same. Therefore, the description of the same configuration as that of the laminate 10 of Example 1 is omitted.

[0026] As shown in FIG. 3, the void-containing region 116 of the laminated plate 110 is disposed in the AlN single crystal layer 12. That is, the voids are introduced into the AlN single crystal layer 12 at the interface between the AlN single crystal layer 12 and the AlN polycrystalline layer 14. Note that the size and density of the voids introduced into the void-containing region 116 and the thickness L2 of the void-containing region 116 are the same as those of the void-containing region 16 in Example 1, and thus detailed description thereof is omitted.

[0027] Also in this embodiment, since the void-containing region 116 is provided at the interface portion, the void-containing region 116 can reduce the problems caused by the difference in the coefficient of thermal expansion between the AlN single crystal layer 12 and the AlN polycrystalline layer 14. As a result, deterioration of the AlN single crystal layer 12 can be suppressed. Further, since the laminated plate 110 includes the void-containing region 116, the laminated plate 110 can sufficiently absorb the impact generated when the laminated plate 110 is mechanically polished to remove the AlN polycrystalline layer 14.

[0028] (Example 3) Further, the void-containing region may be disposed at the interface between the AlN single crystal layer 12 and the AlN polycrystalline layer 14. For example, as shown in FIG. 4, the void-containing region 216 may be disposed in the AlN polycrystalline layer 14. In this embodiment, the void-containing region 216 is different from the void-containing region 16 in Example 1, and the other configurations are substantially the same. Therefore, the description of the same configuration as that of the laminated plate 10 in Example 1 is omitted.

[0029] As shown in FIG. 4, the void-containing region 216 of the laminated plate 210 is disposed in the AlN polycrystalline layer 14. That is, the voids are introduced into the AlN polycrystalline layer 14 at the interface between the AlN single crystal layer 12 and the AlN polycrystalline layer 14. Note that the size and density of the voids introduced into the void-containing region 216 and the thickness L2 of the void-containing region 116 are the same as those of the void-containing region 16 in Example 1, and thus detailed description thereof is omitted.

[0030] Also in this embodiment, since the void-containing region 216 is provided in the interface portion, the void-containing region 216 can reduce the problems caused by the difference in the coefficient of thermal expansion between the AlN single crystal layer 12 and the AlN polycrystalline layer 14. As a result, the deterioration of the AlN single crystal layer 12 can be suppressed. Further, by including the void-containing region 216, the laminated plate 210 can sufficiently absorb the impact generated when the laminated plate 210 is mechanically polished to remove the AlN polycrystalline layer 14.

[0031] As described above, specific examples of the technology disclosed in this specification have been described in detail, but these are merely examples and do not limit the scope of the claims. The technology described in the claims includes various modifications and changes of the specific examples illustrated above. Further, the technical elements described in this specification or the drawings exhibit technical utility alone or in various combinations, and are not limited to the combinations described in the claims at the time of filing.

Claims

1. an AlN polycrystalline layer; an AlN single-crystalline layer formed on the AlN polycrystalline layer; a void-containing region that is in contact with an interface portion between the AlN single-crystalline layer and the AlN polycrystalline layer and in which a plurality of voids are dispersedly introduced; and the thickness of the void-containing region is 0.1 μm or more and 5.0 μm or less; a laminate in which, within the void-containing region, the distance between adjacent voids is 1 μm or more and 300 μm or less.

2. The laminate according to claim 1, wherein the voids have an aspect ratio greater than 1 and 10 or less and are present such that their long sides are along the end faces in the thickness direction of the AlN polycrystalline layer.

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