Composite substrates and devices

Abstract

A composite substrate in which an AlN single crystal layer having a high crystal quality is firmly bonded to a support substrate is inexpensively provided. This composite substrate comprises a support substrate and an AlN single crystal layer bonded to the support substrate. At the exposed surface on the side opposite from the support substrate, the AlN single crystal layer has an X-ray rocking curve half-value width for the (0002) plane of 20-350 arcsec, an X-ray rocking curve half-value width for the (10-12) plane of 20-500 arcsec, and a defect density of 1.0 × 103-1.0 × 107 cm-2.

Description

[Technical Field]

[0001] The present disclosure relates to composite substrates and devices that include AlN single crystal layers. [Background technology]

[0002] In recent years, aluminum nitride (AlN) single crystals have been attracting attention as a base substrate for deep ultraviolet light-emitting devices that use AlN-based semiconductors. For example, AlN and AlGaN are used as AlN-based semiconductors. These AlN-based semiconductors have a direct transition band structure, making them suitable for light-emitting devices, and can be applied to deep ultraviolet light-emitting diodes (LEDs) and laser diodes (LDs) that can be used for sterilization and other purposes.

[0003] In order to achieve high luminous efficiency in such light-emitting devices, a high-quality base substrate with high crystallinity is required.

[0004] Therefore, AlN substrates with high crystallinity are being developed as base substrates. Patent Document 1 (Japanese Patent No. 6872074) discloses an AlN substrate that satisfies the following relationship: c1 > 97.5% and c2 / c1 < 0.995, where c1 is the c-plane orientation degree, and c2 is the c-plane orientation degree, where c1 is the ratio of the diffraction intensity of the (002) plane to the sum of the diffraction intensity of the (002) plane and the diffraction intensity of the (100) plane when the surface layer is subjected to X-ray diffraction measurement in the thickness direction, and c2 is the c-plane orientation degree, where c2 is the ratio of the diffraction intensity of the (002) plane to the sum of the diffraction intensity of the (002) plane and the diffraction intensity of the (100) plane when a portion other than the surface layer is subjected to X-ray diffraction measurement in the thickness direction. Patent Document 2 (Japanese Patent No. 6872075) discloses an AlN substrate in which the above c1 and c2 satisfy the relational expressions of c1>97.5% and c2>97.0%, while also satisfying the relational expressions of w1<2.5° and w1 / w2<0.995, where w1 is the half-width in the X-ray rocking curve profile of the (102) plane of the surface layer and w2 is the half-width in the X-ray rocking curve profile of the (102) plane of a portion other than the surface layer.

[0005] In addition, AlN substrates with low defect densities are being developed as base substrates. Patent Document 3 (JP 2017-117972 A) describes a substrate in which the front and back surfaces are Al polarity planes and the dislocation density is 10 6 cm -2 The following AlN single crystal laminate has been disclosed. This AlN single crystal laminate was manufactured by forming an AlN single crystal layer by HVPE (hydride vapor phase epitaxy) on the N-polarity surface of an AlN single crystal substrate manufactured by sublimation. Note that a high number of defects means a high number of dislocations.

[0006] Meanwhile, a bonded substrate of a support substrate and a group 13 element nitride crystal substrate has been proposed. For example, Patent Document 4 (Japanese Patent No. 7295351) discloses a bonded substrate of a support substrate and a group 13 element nitride crystal substrate, and discloses that the bonding surfaces of the group 13 element nitride crystal substrate and the support substrate are activated by irradiating them with a neutral atomic beam, thereby directly bonding the support substrate and the group 13 element nitride crystal substrate. [Prior art documents] [Patent documents]

[0007] [Patent Document 1] Patent No. 6872074 [Patent Document 2] Patent No. 6872075 [Patent Document 3] Japanese Patent Application Laid-Open No. 2017-117972 [Patent Document 4] Patent No. 7295351 [Patent Document 5] WO2022 / 190465 [Patent Document 6] Japanese Patent Application Laid-Open No. 2014-086400 Summary of the Invention

[0008] There are several possible methods for forming a functional film using an AlN single crystal as a base substrate or base layer. For example, a first method involves forming a functional film several microns thick on an AlN single crystal substrate approximately 400 to 600 μm thick, and then grinding the AlN single crystal substrate to a thickness of 100 μm. This method allows the functional film to be formed on an AlN single crystal substrate with high crystalline quality, resulting in the formation of a functional film with high crystalline quality. However, since thick AlN single crystal substrates are unnecessary for devices, it is desirable to thin them by grinding (for example, to improve the transmittance of LEDs). Furthermore, AlN single crystal substrates are expensive, which increases costs. On the other hand, a second method involves forming an AlN single crystal layer several microns thick on an inexpensive sapphire substrate, and then forming a functional film on the AlN single crystal layer. In this case, the lattice constant mismatch between the sapphire substrate and the AlN single crystal layer results in poor crystalline quality for both the AlN single crystal layer and the functional film. Therefore, although this method is inexpensive, it results in poor device performance. In light of these circumstances, there is a demand for AlN wafers that are both high in crystal quality and inexpensive.

[0009] The present inventors have now discovered that by bonding an AlN single crystal layer, whose X-ray rocking curve half-width for the (0002) plane, X-ray rocking curve half-width for the (10-12) plane, and defect density each fall within predetermined numerical ranges, to a support substrate, it is possible to provide an inexpensive composite substrate in which an AlN single crystal layer with high crystalline quality is firmly bonded to a support substrate.

[0010] Therefore, an object of the present invention is to provide, at low cost, a composite substrate in which an AlN single crystal layer with high crystal quality is firmly bonded to a support substrate.

[0011] According to the present disclosure, the following aspects are provided. [Aspect 1] A composite substrate comprising a support substrate and an AlN single crystal layer bonded to the support substrate, The AlN single crystal layer has, on an exposed surface opposite to the support substrate, The X-ray rocking curve half-width of the (0002) plane is 20 to 350 arcsec, The X-ray rocking curve half-width of the (10-12) plane is 20 to 500 arcsec. Defect density is 1.0×10 3 ~1.0×10 7 cm -2 This is a composite substrate. [Aspect 2] 2. The composite substrate of embodiment 1, wherein the composite substrate has a size of 50 mm or more in diameter. [Aspect 3] 3. The composite substrate according to aspect 1 or 2, wherein the support substrate is made of one material selected from the group consisting of aluminum nitride polycrystalline, sapphire, silicon carbide, quartz, and a Si substrate. [Aspect 4] 4. The composite substrate according to any one of aspects 1 to 3, wherein the AlN single crystal layer is directly bonded to the support substrate. [Aspect 5] The composite substrate according to any one of aspects 1 to 3, further comprising a bonding layer between the support substrate and the AlN single crystal layer, whereby the AlN single crystal layer is indirectly bonded to the support substrate. [Aspect 6] 6. The composite substrate of embodiment 5, wherein the bonding layer comprises at least one selected from the group consisting of aluminum nitride, alumina, silicon carbide, silicon dioxide, and tantalum pentoxide. [Aspect 7] 5. The composite substrate according to aspect 4, wherein the support substrate and the AlN single crystal layer contain Ar in a layered region including a bonding interface therebetween. [Aspect 8] A device comprising the composite substrate according to any one of embodiments 1 to 7. [Aspect 9] 1. A method for manufacturing a composite substrate comprising a support substrate and an AlN single crystal layer bonded to the support substrate, the method comprising: preparing an AlN composite material including an AlN single crystal substrate as a seed substrate and an AlN single crystal layer grown on the AlN single crystal substrate; a step of implanting hydrogen ions from the exposed surface of the AlN single crystal layer to a predetermined depth in the AlN single crystal layer to form a hydrogen embrittlement portion; a step of bonding the AlN composite material including the hydrogen embrittlement portion to the support substrate to produce a bonded body; a step of heating the bonded body to separate the AlN single crystal layer together with the support substrate from the hydrogen embrittlement portion, thereby obtaining a composite substrate including the support substrate and the AlN single crystal layer; A method for manufacturing a composite substrate, comprising: [Brief explanation of the drawings]

[0012] [Figure 1] 1 is a schematic cross-sectional view showing an example of a composite substrate according to the present invention. [Figure 2] 2A to 2C are schematic cross-sectional views showing the manufacturing process of the composite substrate shown in FIG. [Figure 3] FIG. 2 is a schematic cross-sectional view showing another example of a composite substrate according to the present invention. [Figure 4] 1 is a schematic cross-sectional view showing the configuration of a vapor phase growth apparatus for forming a film by the HVPE method. DETAILED DESCRIPTION OF THE INVENTION

[0013] Composite PCB 1 shows an example of a composite substrate 10 of the present invention. The composite substrate 10 includes a support substrate 12 and an AlN single crystal layer 14 bonded to the support substrate 12. The AlN single crystal layer 14 has, on the exposed surface opposite the support substrate 12, an X-ray rocking curve half width (hereinafter referred to as XRC half width) of the (0002) plane of 20 to 350 arcsec, an XRC half width of the (10-12) plane of 20 to 500 arcsec, and a defect density of 1.0×10 3 ~1.0×10 7 cm -2By bonding an AlN single crystal layer 14 having the XRC half width at (0002) plane, the XRC half width at (10-12) plane, and the defect density each falling within the above-mentioned ranges to a support substrate 12 in this way, it is possible to provide a composite substrate 10 in which an AlN single crystal layer 14 with high crystal quality is firmly bonded to a support substrate 12 at low cost.

[0014] As mentioned above, several methods are possible for forming functional films using AlN single crystal as a base substrate or base layer. For example, the first method involves forming a functional film on a thick AlN single crystal substrate and then grinding the AlN single crystal substrate. This allows the functional film to be formed on an AlN single crystal substrate with high crystalline quality, but since the thick AlN single crystal substrate is unnecessary for devices, it is desirable to thin it by grinding it. Furthermore, AlN single crystal substrates are expensive, which increases costs. On the other hand, the second method involves forming an AlN single crystal layer on an inexpensive sapphire substrate and then forming a functional film on the AlN single crystal layer, resulting in poor crystalline quality for both the AlN single crystal layer and the functional film. Therefore, although this method is inexpensive, it results in poor device performance. In light of these circumstances, there is a demand for AlN wafers that are both high in crystalline quality and available at low cost.

[0015] Therefore, as a third method, as shown in FIG. 2 , an AlN single crystal substrate 16 is prepared (step (a)), an AlN single crystal layer 14 is formed on one of the surfaces (Al face or N face) of the AlN single crystal substrate 16 (step (b)), and the AlN single crystal layer 14 is then transferred to a support substrate 12 (which may be less expensive than the AlN single crystal substrate 16) (step (c)). This method makes it possible to produce an AlN single crystal layer 14 with high crystal quality while keeping costs down. That is, because the AlN single crystal layer 14 is formed on the AlN single crystal substrate 16, there is no lattice constant mismatch, and therefore an AlN single crystal layer 14 with high crystal quality can be achieved. Furthermore, by transferring the AlN single crystal layer 14 to the inexpensive support substrate 12 and simultaneously peeling off the AlN single crystal substrate 16 instead of grinding it, it is possible to reuse the expensive AlN single crystal substrate 16. This allows costs to be reduced. However, when the composite substrate 10 thus obtained is used in the manufacture of a device, the AlN single crystal layer 14 bonded to the support substrate 12 may peel off. This peeling is particularly likely to occur in high-temperature processes (e.g., 1000°C or higher). The present invention successfully solves this problem. That is, when the XRC half-width of the (0002) plane, the XRC half-width of the (10-12) plane, and the defect density of the AlN single crystal layer 14 satisfy the above-mentioned numerical ranges, the bonding strength with the support substrate 12 is increased. This effect is more pronounced as the size (diameter) of the composite substrate 10 increases. As a result, the present invention makes it possible to provide, at low cost, a composite substrate 10 in which a high-crystal-quality AlN single crystal layer 14 is firmly bonded to the support substrate 12 (e.g., is particularly resistant to peeling, even in high-temperature processes).

[0016] The AlN single crystal layer 14 has an XRC half-width of the (0002) plane of 20 to 350 arcsec, preferably 100 to 300 arcsec, and more preferably 100 to 280 arcsec, on the exposed surface (Al face or N face) opposite the support substrate 12. Having an XRC half-width of the (0002) plane within this range offers the advantage that, when a device is fabricated, dislocations are not introduced into the deposited film, resulting in good performance. Furthermore, the AlN single crystal layer 14 has an XRC half-width of the (10-12) plane of 20 to 500 arcsec, preferably 200 to 450 arcsec, and more preferably 200 to 400 arcsec, on the exposed surface (Al face or N face) opposite the support substrate 12. Having an XRC half-width of the (10-12) plane within this range offers the advantage that, when a device is fabricated, dislocations are not introduced into the deposited film, resulting in good performance. It is preferable that both surfaces (the Al surface and the N surface) of the AlN single crystal layer 14 have an XRC half-width of the (10-12) plane and an XRC half-width of the (0002) plane within the above-mentioned ranges. However, since it is not practical to measure the XRC half-width of the AlN single crystal layer 14 at the interface between the AlN single crystal layer 14 and the support substrate 12, it is sufficient to measure the XRC half-width of the exposed surface opposite the support substrate 12, as this can be said to represent the crystalline quality of the AlN single crystal layer 14. The XRC profiles of the (0002) plane and the (10-12) plane of the AlN single crystal layer 14 can be measured using a general XRD device (e.g., D8 DISCOVER, manufactured by Bruker-AXS) and accompanying XRD analysis software (e.g., "LEPTOS" Ver. 4.03, manufactured by Bruker-AXS) according to the procedure described in the Examples below.

[0017] The AlN single crystal layer 14 has a defect density of 1.0×10 on the exposed surface (Al surface or N surface) opposite to the support substrate 12. 3 ~1.0×10 7 cm -2 and preferably 1.0 × 10 6 ~8.0×10 6 cm -2 , more preferably 1.0 × 10 6 ~6.0×10 6 cm -2Within this range, there is an advantage that the deposited film will not introduce dislocations and will have good performance when fabricated into a device. It is preferable that both surfaces (the Al surface and the N surface) of the AlN single crystal layer 14 have a defect density within the above range. However, since it is not practical to measure the defect density at the interface between the AlN single crystal layer 14 and the support substrate 12, measuring the defect density on the exposed surface opposite the support substrate 12 is sufficient because it can be said to represent the crystal quality of the AlN single crystal layer 14. The defect density is preferably measured over the entire exposed surface, and can be performed by reflection X-ray topography measurement or etch pit evaluation using KOH molten etching. Etch pit evaluation can be performed by measuring the etched surface with an optical microscope, laser microscope, SEM, or the like. Note that the applicable defect density range of each defect evaluation method is limited, and when the defect density is high, evaluation by TEM observation is preferred. Because it is difficult to measure the entire surface area in TEM observation, defects can be evaluated by sampling a 50 μm × 50 μm area, including the center of gravity of the AlN single crystal substrate, from the surface exposed by polishing and measuring it with TEM. The method for measuring such defect density distribution is not particularly limited; for example, X-ray topography can be used to measure a tomographic topography, or section X-ray topography can be used to measure the defect density distribution within the AlN single crystal substrate. In this specification, defects include threading screw dislocations (TSDs), threading edge dislocations (TEDs), basal plane dislocations (BPDs), and mixed dislocations. "Threading" means that the dislocation line is approximately parallel to the

[0001] axis of the hexagonal crystal system. "Basal" means that the dislocation line is within the basal hexagonal crystal system (0001) plane.

[0018] The AlN single crystal layer 14 is preferably an oriented layer oriented in both the c-axis and a-axis directions, and may contain mosaic crystals. Mosaic crystals are a collection of crystals that do not have clear grain boundaries but whose orientation slightly differs from one or both of the c-axis and a-axis. Such an oriented layer has a structure in which the crystal orientation is generally aligned in the approximately normal direction (c-axis direction) and the in-plane direction (a-axis direction). This structure makes it possible to form a semiconductor layer with excellent quality, particularly excellent orientation, on top of it.

[0019] The method for evaluating the orientation of the AlN single crystal layer 14 is not particularly limited, and known analytical techniques such as EBSD (Electron Backscatter Diffraction Patterns) and X-ray pole figures can be used. For example, when using EBSD, inverse pole figure mapping and crystal orientation mapping of the surface of the AlN single crystal layer 14 or a cross section perpendicular to the sheet surface are measured. The obtained inverse pole figure mapping can be defined as being oriented in two axes, namely, the approximately normal direction and the approximately sheet surface direction, when the following four conditions are met: (A) the AlN single crystal layer 14 is oriented in a specific direction (first axis) approximately normal to the sheet surface; (B) the AlN single crystal layer 14 is oriented in a specific direction (second axis) approximately in-plane and perpendicular to the first axis; and (C) the AlN single crystal layer 14 has tilt angles within ±10° from the first axis; and (D) the AlN single crystal layer 14 has tilt angles within ±10° from the second axis. In other words, when the above four conditions are met, the AlN single crystal layer 14 can be determined to be oriented in two axes, namely, the c-axis and the a-axis. For example, if the approximately normal direction to the plate surface is oriented along the c-axis, the approximately in-plane direction may be oriented along a specific direction (e.g., the a-axis) perpendicular to the c-axis. The AlN single crystal layer 14 may be oriented along two axes, the approximately normal direction and the approximately in-plane direction, but it is preferable that the approximately normal direction be oriented along the c-axis. The smaller the tilt angle distribution in the approximately normal direction and / or the approximately in-plane direction, the less mosaic the AlN single crystal substrate will be, and the closer it is to zero, the closer it will be to a perfect single crystal. Therefore, from the perspective of the crystallinity of the AlN single crystal substrate, it is preferable that the tilt angle distribution be small in both the approximately normal direction and the approximately in-plane direction; for example, ±5° or less is preferable, and ±3° or less is even more preferable.

[0020] The thickness of the AlN single crystal layer 14 is not particularly limited, but is preferably 0.1 to 200 μm, more preferably 0.5 to 150 μm, and even more preferably 1.0 to 120 μm.

[0021] The support substrate 12 is not particularly limited as long as it can be firmly bonded to the AlN single crystal layer 14, but is preferably a substrate that is less expensive than the AlN single crystal substrate 16 and has a thermal expansion coefficient close to that of the AlN single crystal. Alternatively, the support substrate 12 is preferably a substrate having high light transmittance and a low refractive index. From this perspective, the support substrate 12 is preferably made of one material selected from the group consisting of aluminum nitride polycrystal, sapphire, silicon carbide, quartz, and a Si substrate. The thickness of the support substrate 12 is not particularly limited, but is preferably 200 to 2000 μm, more preferably 300 to 1500 μm, and even more preferably 400 to 1000 μm.

[0022] The size of the composite substrate 10 is 50 mm or more in diameter, preferably 100 mm or more or 150 mm or more in diameter. The larger the diameter of the composite substrate 10, the more likely it is to exhibit the effect of improving the bonding strength between the support substrate 12 and the AlN single crystal layer 14. There is no particular upper limit to the diameter of the composite substrate 10, but the diameter of the composite substrate 10 is typically 300 mm or less, more typically 250 mm or less. The composite substrate 10 typically has a circular shape. In this specification, the term "circular shape" does not necessarily mean a perfect circle, but may also mean a roughly circular shape that can be recognized as a circle overall. For example, the shape may be a shape in which a portion of the circle is cut out for identifying the crystal orientation or for other purposes (e.g., a circular shape including an orientation flat or a notch).

[0023] According to a preferred embodiment of the present invention, the AlN single crystal layer 14 is directly bonded to the support substrate 12. In this case, it is preferable to enhance the bond strength by irradiating each bonding surface with a neutral atomic beam such as an Ar beam to activate the surface, as proposed in Patent Document 4 (Japanese Patent No. 7295351). Consequently, it is preferable from the viewpoint of high bond strength that the support substrate 12 and the AlN single crystal layer 14 contain Ar in a layered region including their bonding interface. This layered region containing Ar can be identified by elemental analysis of a cross section of the composite substrate 10 using SEM-EDX (energy dispersive X-ray analyzer (EDX) attached to a scanning electron microscope (SEM)). Alternatively, the bond strength may be enhanced by irradiating each bonding surface with a plasma such as nitrogen gas plasma to activate the surface (plasma activation method), as proposed in Patent Document 5 (WO2022 / 190465).

[0024] According to another preferred embodiment of the present invention, as in the composite substrate 10′ shown in FIG. 3, a bonding layer 18 may be provided between the support substrate 12 and the AlN single crystal layer 14, thereby indirectly bonding the AlN single crystal layer 14 to the support substrate 12. This can achieve even higher bonding strength. From the viewpoint of high bonding strength, the bonding layer 18 preferably contains at least one material selected from the group consisting of aluminum nitride, alumina, silicon carbide, silicon dioxide, and tantalum pentoxide. After forming the bonding layer 18, a bonded body of the support substrate 12, bonding layer 18, and AlN single crystal layer 14 can be obtained with high bonding strength by performing the same process as the direct bonding described above.

[0025] Manufacturing method As shown in FIG. 2, the composite substrate 10 of the present invention can be manufactured by preparing an AlN single crystal substrate 16 (step (a)), depositing an AlN single crystal layer 14 on either surface (Al face or N face) of this AlN single crystal substrate 16 (step (b)), and transferring the AlN single crystal layer 14 to a support substrate 12 (step (c)).

[0026] (a) Preparation of AlN single crystal substrate The AlN single crystal substrate 16 may be any known or commercially available AlN single crystal substrate, and is not particularly limited.

[0027] (b) Deposition of an AlN single crystal layer The AlN single crystal layer 14 is formed on either surface of the AlN single crystal substrate 16. Therefore, the AlN single crystal layer 14 may be formed on the Al face of the AlN single crystal substrate 16, or on the N face of the AlN single crystal substrate 16. The AlN single crystal layer 14 is typically formed by epitaxially growing an AlN single crystal on the surface of the AlN single crystal substrate 16 used as a seed crystal. Any of vapor phase deposition, liquid phase deposition, and solid phase deposition may be used to grow the single crystal, but it is preferable to form the AlN single crystal layer 14 using vapor phase deposition. Examples of vapor phase film deposition methods include various CVD (chemical vapor deposition) methods (e.g., thermal CVD, plasma CVD, MOVPE, etc.), sputtering, hydride vapor phase epitaxy (HVPE), molecular beam epitaxy (MBE), sublimation, pulsed laser deposition (PLD), etc., with HVPE being preferred. Examples of liquid phase film deposition methods include solution growth methods (e.g., flux deposition). Known conditions can be used for any of the solid phase film deposition method, vapor phase film deposition method, and liquid phase film deposition method.

[0028] An example of a method for fabricating an AlN single crystal layer 14 using the HVPE method is described below. In this method, the AlN single crystal layer 14 is fabricated through the steps of (i) forming the AlN single crystal layer 14 on an AlN single crystal substrate 16, and (ii) polishing the surface of the AlN single crystal layer 14.

[0029] (i) Deposition of an AlN single crystal layer on an AlN single crystal substrate This step is a step of forming an AlN single crystal layer 14 on an AlN single crystal substrate 16 serving as a seed substrate. Figure 4 shows a vapor phase growth apparatus (hereinafter referred to as an HVPE apparatus) for performing film formation by the HVPE method. The HVPE apparatus includes a reactor 40, a susceptor 44, a carrier gas supply source 46, an Al source material supply source 48, a metallic Al powder source 50 disposed within the Al source material supply source 48, a heater 52, and a gas outlet 54. The AlN single crystal substrate 16 is placed on the susceptor 44, and AlCl gas obtained by supplying HCl gas to the heated Al source material supply source 48 and NH gas from the carrier gas supply source 46 are mixed and supplied to the AlN single crystal substrate 16. The heating temperature of the Al source material supply source 48 is preferably 500 to 700°C, more preferably 550 to 650°C. The flow rate ratio of AlCl3 gas to NH3 gas is preferably 1:1 to 1:500, more preferably 1:10 to 1:200. The pressure inside the reaction furnace 40 is preferably 1 to 100 Torr, more preferably 10 to 30 Torr. The growth temperature is preferably 1100 to 1400°C, more preferably 1150 to 1250°C.

[0030] (ii) Polishing the surface of the AlN single crystal layer The surface of the obtained AlN single crystal layer 14 is then mirror-finished. This mirror-finishing is preferably carried out by smoothing the plate surface by lapping using diamond abrasive grains, followed by polishing using chemical mechanical polishing (CMP) using colloidal silica or the like. In this way, an AlN composite material is obtained comprising a mirror-finished AlN single crystal layer 14 on the AlN single crystal substrate 16.

[0031] (c) Transfer of the AlN single crystal layer to the support substrate The AlN single crystal layer 14 is transferred from the obtained AlN composite material to the support substrate 12. This support substrate 12 can be a cheaper substrate than the AlN single crystal substrate 16, thereby reducing costs. Furthermore, because the transfer of the AlN single crystal layer 14 to the support substrate 12 involves peeling off the AlN single crystal substrate 16, it becomes possible to reuse the expensive AlN single crystal substrate 16, which also contributes to cost reduction. That is, if the AlN single crystal substrate 16 is removed by grinding, the shape of the AlN single crystal substrate 16 is lost and the AlN single crystal substrate 16 cannot be reused. However, if the AlN single crystal substrate 16 is removed by peeling, the shape of the AlN single crystal substrate 16 can be maintained, allowing the AlN single crystal substrate 16 to be reused.

[0032] Transferring the AlN single crystal layer 14 to the support substrate 12 involves bonding the AlN single crystal layer 14 to the support substrate 12 and peeling off the AlN single crystal substrate 16. While bonding the AlN single crystal layer 14 to the support substrate 12 may be performed after peeling off the AlN single crystal substrate 16, it is preferable to peel off the AlN single crystal substrate 16 after bonding the AlN single crystal layer 14 to the support substrate 12. Examples of peeling techniques include cutting with a wire saw, laser lift-off (LLO), laser slicing, hydrogen ion implantation peeling (also known as smart cut or ion cut), and sacrificial layer etching. Furthermore, peeling can be facilitated by interposing a peeling layer made of graphene, hexagonal boron nitride (h-BN), or the like between the AlN single crystal substrate 16 and the AlN single crystal layer 14.

[0033] For example, when using the hydrogen ion implantation delamination method, the delamination is preferably performed as follows. First, a hydrogen ion beam is irradiated onto the surface of the AlN single crystal layer 14 using an ion implanter to implant hydrogen ions into the AlN single crystal layer 14. Next, the AlN single crystal layer 14 implanted with hydrogen ions is bonded to the support substrate 12 (the bonding method will be described later). The resulting bonded body is heat-treated at 400 to 600°C to delaminate the AlN single crystal substrate 16 and the AlN single crystal layer 14 at the depth where the hydrogen ions were implanted. At this time, the portions of the AlN single crystal layer 14 implanted with hydrogen ions are hydrogen-embrittled, so that they can be easily delaminated by heating. However, instead of heating the AlN single crystal substrate 16 and the AlN single crystal layer 14, mechanical delamination may be performed by inserting a blade into the hydrogen-embrittled portions where the hydrogen ions were implanted. Finally, the surfaces of the delaminated AlN single crystal substrate 16 and the AlN single crystal layer 14 may be polished as necessary.

[0034] As described above, the AlN single crystal layer 14 and the support substrate 12 can be bonded by direct bonding. In this case, it is preferable to enhance the bond strength by irradiating the bonding surfaces of the AlN single crystal layer 14 and the support substrate 12 with a neutral atomic beam such as an Ar beam for surface activation (see, for example, Patent Document 4 (Japanese Patent No. 7295351)). Surface activation using a neutral atomic beam is preferably performed by generating a neutral atomic beam using a known device such as that disclosed in Patent Document 6 (Japanese Patent Laid-Open Publication No. 2014-086400). Specifically, a saddlefield fast atom beam source is used as the beam source. An inert gas is introduced into the chamber, and a high voltage is applied to the electrode from a DC power supply. A saddlefield electric field generated between the electrode (positive electrode) and the housing (negative electrode) causes electrons to move, generating a beam of atoms and ions from the inert gas. Of the beams that reach the grid, the ion beam is neutralized by the grid, and a neutral atomic beam is emitted from the fast atom beam source. The atomic species constituting the beam are preferably inert gas (argon, nitrogen, etc.). The voltage during activation by beam irradiation is preferably 0.5 to 2.0 kV, and the current is preferably 50 to 200 mA. Next, the activated bonding surfaces are brought into contact with each other in a vacuum atmosphere, thereby bonding the AlN single crystal layer 14 and the support substrate 12. The bonding temperature may be room temperature, but specifically, is preferably 40°C or less, more preferably 30°C or less, and even more preferably 20 to 25°C. The pressure load during bonding is preferably 100 to 20,000 N. Furthermore, the flatter the bonding surfaces of the AlN single crystal layer 14 and the support substrate 12, the higher the bonding strength can be. Alternatively, as previously mentioned, the bonding strength may be increased by surface activation (plasma activation method) using plasma such as nitrogen gas plasma on the bonding surfaces, as proposed in Patent Document 5 (WO2022 / 190465).

[0035] As described above, the AlN single crystal layer 14 and the support substrate 12 can also be bonded by indirect bonding. In this case, as in the composite substrate 10′ shown in FIG. 3, bonding can be performed in the same manner as the direct bonding described above, except that a bonding layer 18 is interposed between the support substrate 12 and the AlN single crystal layer 14. The bonding layer 18 is preferably formed by a vapor deposition method such as sputtering. After forming the bonding layer 18, a bonded body of the support substrate 12, bonding layer 18, and AlN single crystal layer 14 can be obtained with high bonding strength by performing the same process as the direct bonding described above.

[0036] device Devices can also be fabricated using the composite substrate 10 or AlN single crystal layer 14 of the present invention. That is, devices preferably comprising the composite substrate 10 or AlN single crystal layer 14 are provided. Examples of such devices include deep ultraviolet laser diodes, deep ultraviolet diodes, power electronic devices, high-frequency devices, heat sinks, etc. The method for manufacturing devices using the composite substrate 10 or AlN single crystal layer 14 is not particularly limited, and they can be manufactured by known methods. [Example]

[0037] The present invention will be explained in more detail by the following examples, but the present invention is not limited to the following examples.

[0038] Examples 1-20 (1) Fabrication of AlN single crystal layer As a seed crystal for growing an AlN single crystal layer, a disk-shaped AlN single crystal (of various known crystal qualities) with a thickness of 600 μm (Examples 1 to 12) or 400 μm (Examples 13 to 20) and a diameter of 100 mm (Examples 1 to 5 and 7 to 12), 150 mm (Example 6) or 50 mm (Examples 13 to 20) was prepared. Using the HVPE apparatus shown in Fig. 4, an AlN single crystal layer was grown on the AlN single crystal (seed crystal) by the HVPE method. Specifically, the HVPE apparatus includes a reaction furnace 40, a susceptor 44, a carrier gas supply source 46, an Al raw material supply source 48, a metallic Al powder raw material 50 disposed in the Al raw material supply source 48, a heater 52, and a gas discharge part 54. In this HVPE apparatus, the AlN single crystal substrate 16 (seed crystal) was placed on the susceptor 44 such that the N face (Examples 1 to 7 and 9 to 20) or the Al face (Example 8) was the exposed surface. The AlCl3 gas obtained by supplying HCl gas to the Al raw material supply source 48 heated to 600 °C and the NH3 gas from the carrier gas supply source 46 were mixed and supplied to the AlN single crystal substrate 16, and an AlN single crystal layer was grown under the following conditions. Thus, a composite material (hereinafter referred to as an AlN composite material) in which an AlN single crystal layer was formed on the AlN single crystal (seed crystal) was obtained. <HVPE Conditions> a ·AlCl3 supply partial pressure: 4.0×10 -4 atm ·NH3 supply partial pressure: 2.0×10 -4 atm ·Growth temperature of AlN (film formation temperature): 1450 °C (Examples 1 to 8 and 12 to 20) or 1100 °C (Examples 9 to 11) ·Film formation time: The time until the thickness of the AlN single crystal layer becomes 1 μm or more (Example 13), 2 μm or more (Examples 1 to 6, 8 to 12 and 14 to 20) or 100 μm or more (Example 7)

[0039] In order to mirror-polish the surface of the obtained AlN single crystal layer, the plate surface was smoothed by lapping using diamond abrasive grains, and then polished by chemical mechanical polishing (CMP) using colloidal silica or the like. Thus, an AlN single crystal substrate with a mirror-polished surface was obtained.

[0040] (2) Transfer of the AlN single crystal layer This AlN single crystal layer was peeled off by ion implantation (Examples 1-6 and 8-12) or wire (Example 7) and directly bonded to a support substrate (Examples 1-11), or indirectly bonded via SiO2 (Examples 12-14 and 18), Al2O3 (Example 15), SiC (Examples 16 and 19), or Ta2O5 (Examples 17 and 20). As shown in Table 1, the support substrate used was a 600 μm thick polycrystalline AlN substrate (Examples 1-3 and 7-12), a 600 μm thick sapphire substrate (Examples 4, 6, and 18-20), a 600 μm thick silicon substrate (Example 5), or a 400 μm thick quartz substrate (Examples 13-17). The specific procedure is as follows.

[0041] (Examples 1-6 and 8-11) First, a hydrogen ion beam was irradiated onto the surface of the AlN single crystal layer using an ion implanter to implant hydrogen ions to the desired depth. This resulted in hydrogen embrittlement of the AlN single crystal layer to the desired depth. Next, a high-speed Ar neutral atom beam (acceleration voltage: 1 kV, Ar flow rate: 60 sccm) was irradiated onto the surface of the AlN single crystal layer and the surface of the support substrate for 70 seconds to activate these surfaces. The AlN composite and the support substrate were then superimposed so that the AlN single crystal layer and the support substrate were in contact, and a load of 1000 N was applied under vacuum to bond the AlN composite (particularly the AlN single crystal layer) to the support substrate. The resulting bonded body was heated to 500°C, which separated the AlN single crystal layer and the support substrate from the AlN single crystal (seed crystal) at the hydrogen ion-implanted area. In this way, the AlN single crystal layer was transferred to the support substrate. The surface of the obtained composite material was smoothed by lapping using diamond abrasive grains or chemical mechanical polishing (CMP) using colloidal silica or the like to obtain a composite substrate consisting of a support substrate and an AlN single crystal layer. The composite substrate was disk-shaped, with a diameter of 100 mm in Examples 1 to 5 and 8 to 11, and 150 mm in Example 6. The thickness of the AlN seed crystal layer was 2 μm in all Examples 1 to 6 and 8 to 11, and the thickness of the composite substrate was 602 μm in Examples 1 to 6 and 8 to 11.

[0042] (Example 7) The surfaces of the AlN single crystal layer and the support substrate were activated by irradiating them with a high-speed Ar neutral atom beam (accelerating voltage: 1 kV, Ar flow rate: 60 sccm) for 70 seconds. The AlN composite and the support substrate were then superimposed so that the AlN single crystal layer and the support substrate were in contact with each other, and a load of 1000 N was applied under vacuum to bond the AlN composite (particularly the AlN single crystal layer) to the support substrate. Next, the AlN single crystal layer was peeled off from the AlN single crystal (seed crystal) together with the support substrate using a diamond wire saw. In this way, the AlN single crystal layer was transferred to the support substrate. The surface of the resulting composite material was smoothed by lapping with diamond abrasive grains or chemical mechanical polishing (CMP) using colloidal silica, etc., to obtain a composite substrate consisting of the support substrate and the AlN single crystal layer. The composite substrate was disk-shaped and had a diameter of 100 mm. The thickness of the AlN seed crystal layer was 100 μm, and the thickness of the composite substrate was 700 μm.

[0043] (Examples 12 and 13) First, a hydrogen ion beam was irradiated onto the surface of the AlN single crystal layer using an ion implanter to implant hydrogen ions to the target depth. This resulted in hydrogen embrittlement of the AlN single crystal layer to the specified depth. Next, a 1 μm-thick SiO2 film was formed on the surface of the AlN single crystal layer by sputtering to create an SiO2 / AlN composite. The surface of this SiO2 film was polished and planarized by chemical mechanical polishing (CMP). The SiO2 / AlN composite and supporting substrate were placed in a plasma activation chamber, and the surfaces of the SiO2 film and supporting substrate were activated with nitrogen gas plasma at 30 °C. This surface activation was carried out for 40 seconds with an energy of 100 W. The SiO2 / AlN composite and supporting substrate were then superimposed with their activated surfaces in contact, pressurized to 0.3 MPa, and heated in a nitrogen atmosphere oven at 130 °C for 4 hours to bond the SiO2 / AlN composite (particularly the SiO2 film) to the supporting substrate. The resulting bonded body was heated at 500°C, whereupon the AlN single crystal layer and SiO2 film were peeled off from the AlN single crystal (seed crystal) along with the support substrate at the hydrogen ion-implanted portions. Thus, the AlN single crystal layer was transferred to the support substrate together with the SiO2 film. The surface of the resulting composite material was smoothed by lapping using diamond abrasive grains to obtain a composite substrate consisting of the support substrate, SiO2 film (bonding layer), and AlN single crystal layer. The composite substrate was disk-shaped and had a diameter of 100 mm (Example 12) or 50 mm (Example 13). The AlN seed crystal layer was 2 μm thick, and the composite substrate was 602 μm (Example 12) or 401 μm (Example 13) thick.

[0044] (Examples 14-20) First, a hydrogen ion beam was irradiated onto the surface of the AlN single crystal layer using an ion implanter to implant hydrogen ions to the desired depth. This resulted in hydrogen embrittlement of the AlN single crystal layer to the desired depth. Next, a 1 μm-thick SiO film (Examples 14 and 18), AlO film (Example 15), SiC film (Examples 16 and 19), or TaO film (Examples 17 and 20) was formed on the surface of the AlN single crystal layer by sputtering to produce SiO / AlN composites (Examples 14 and 18), AlO / AlN composites (Example 15), SiC / AlN composites (Examples 16 and 19), or TaO / AlN composites (Examples 17 and 20). The surfaces of the SiO, AlO, SiC, or TaO films were polished and planarized by chemical mechanical polishing (CMP). The surfaces of the SiO2 film, Al2O3 film, SiC film, or Ta2O5 film of these composite materials, and the surface of the support substrate (quartz substrate (Examples 14 to 18) or sapphire substrate (Examples 18 to 20)) were irradiated with a high-speed Ar neutral atom beam (acceleration voltage: 1 kV, Ar flow rate: 60 sccm) for 70 seconds to activate these surfaces. The AlN composite material and the support substrate were overlapped so that the AlN single crystal layer and the support substrate were in contact, and a load of 1000 N was applied in a vacuum to bond the AlN composite material (particularly the AlN single crystal layer) to the support substrate. The resulting bonded body was heated at 500°C, and the AlN single crystal layer was supported at the hydrogen ion-implanted portion. The substrate was peeled off from the AlN single crystal (seed crystal). In this way, the AlN single crystal layer was transferred to the support substrate together with the SiO2 film, Al2O3 film, SiC film, or Ta2O5 film. The surface of the obtained composite material was smoothed by lapping using diamond abrasive grains to obtain a composite substrate consisting of the support substrate, bonding layer (SiO2 film, Al2O3 film, SiC film, or Ta2O5 film), and AlN single crystal layer. The composite substrate was disk-shaped and had a diameter of 50 mm. The thickness of the AlN seed crystal layer was 2 μm, and the thickness of the composite substrate was 402 μm (Examples 13 to 17) or 602 μm (Examples 18 to 20).

[0045] (3) Evaluation The resulting composite substrate was subjected to the following various evaluations.

[0046] (3a) X-ray rocking curve half-width XRD measurement of the (0002) plane on the surface of the AlN single crystal layer (the surface opposite to the support substrate) was performed using a multifunctional high-resolution X-ray diffractometer (manufactured by Bruker-AXS, D8 DISCOVER). The conditions for this XRD measurement were as follows.

[0047] <XRD Measurement Conditions> · Tube voltage: 40 kV · Tube current: 40 mA · Detector: Tripple Ge(220) Analyzer · Monochromatic parallel light (half-value width 28 seconds) of CuKα ray using a Ge(022) asymmetric reflection monochromator · Step width: 0.001° · Scan speed: 0.5 seconds / step

[0048] Actually, after adjusting 2θ, ω, χ, and φ to align the axis so that the peak of the (0002) plane of the AlN single crystal appears, the range of ω = 14.5 to 19.5° was measured with an anti-scattering slit of 3 mm. The half-value width of the XRC profile of the (0002) plane of the obtained AlN single crystal was determined by performing peak search after smoothing the profile using XRD analysis software (manufactured by Bruker-AXS, "LEPTOS" Ver4.03). As a result, the half-value width of the (0002) plane XRC profile on the surface of the AlN single crystal substrate was as shown in Table 1.

[0049] Also, XRD measurement of the (10-12) plane on the surface of the AlN single crystal layer (the surface opposite to the support substrate) was performed. As the XRD apparatus, D8-DISCOVER manufactured by Bruker-AXS was used, and after adjusting 2θ, ω, χ, and φ to align the axis so that the peak of the (10-12) plane of the AlN single crystal appears, the measurement was performed with ω = 24.5 to 29.5°. Other conditions and analysis methods were the same as those for the XRD measurement of the (0002) plane. As a result, the half-value width of the (10-12) plane XRC profile on the surface of the AlN single crystal substrate was as shown in Table 1.

[0050] (3b) Defect density The defect density of the surface of the resulting AlN single crystal layer (the surface opposite to the support substrate) was evaluated by measuring the entire surface area using X-ray topography (XRTmicron, manufactured by Rigaku Corporation). 5 cm -2 In cases where the number of etch pits was above this level, it was difficult to accurately calculate the number of etch pits using X-ray topography, so an etch pit evaluation was performed using KOH molten etching to measure the defect density on the surface of the AlN single crystal layer. Specifically, for the etch pit evaluation, the surface of the AlN single crystal layer was immersed for 5 minutes in a molten mixture of KOH and NaOH in a weight ratio of 1:1, heated to 450°C, and then etched, after which the defect density was measured using an optical microscope. The results are shown in Table 1.

[0051] (3c) Peelability evaluation A total of 10 composite substrates were fabricated for each example in the same manner as in (1) and (2) above. These composite substrates were heated at 1000°C for 5 minutes in an N2 atmosphere and examined for the presence or absence of peeling of the AlN single crystal layer from the support substrate. The number of composite substrates that exhibited peeling was counted among the 10 composite substrates and evaluated according to the following criteria. The results are shown in Table 1. Evaluation A: The number of composite substrates that did not peel off was 7 to 10. Evaluation B: The number of composite substrates that did not peel off was 1 to 6 Evaluation C: The number of composite substrates on which peeling did not occur was 0 (peel-off occurred on all composite substrates).

[0052] As shown in Table 1, the XRC half-width of the (0002) plane is in the range of 20 to 350 arcsec, the XRC half-width of the (10-12) plane is in the range of 20 to 500 arcsec, and the defect density is 1.0 × 10 3 ~1.0×10 7 cm -2In Examples 1 to 8 and 12 to 20, which were within this range, the delamination evaluation was A or B, and composite substrates were obtained in which a high-crystallinity AlN single crystal layer was firmly bonded to an inexpensive support substrate. In contrast, in Examples 9 to 11, in which HVPE was performed at a film formation temperature of 1100°C, an AlN single crystal layer poor in crystallinity and defect density was formed, and when this poor-quality AlN single crystal layer was transferred to a support substrate, the delamination evaluation was also poor, with a rating of C. Note that between Examples 1 to 8 and 12 to 20 (Examples), the crystallinity was changed mainly by using AlN single crystals (seed crystals) of various crystallinity qualities, and between Examples 1 to 8 and 12 to 20 (Examples) and Examples 9 to 11 (Comparative Examples), the crystallinity was changed by changing the HVPE film formation temperature.

[0053] [Table 1] [Explanation of symbols]

[0054] 10,10' composite board 12 Support substrate 14 AlN single crystal layer 16 AlN single crystal substrate 18 Bonding layer 40 Reactor 44 Susceptor 46 Carrier gas supply source 48 Al raw material supply source 50 Metal Al powder raw material 52 Heater 54 Gas exhaust section

Claims

1. A composite substrate comprising a support substrate and an AlN single crystal layer bonded to the support substrate, The AlN single crystal layer has, on an exposed surface opposite to the support substrate, The X-ray rocking curve half width of the (0002) plane is 20 to 350 arcsec, The X-ray rocking curve half width of the (10-12) plane is 20 to 500 arcsec, The defect density is 1.0 × 10 ３ ~1.0 x 10 ７ cm －２ and The composite substrate further comprises a bonding layer between the support substrate and the AlN single crystal layer, the bonding layer containing at least one selected from the group consisting of aluminum nitride, alumina, silicon carbide, silicon dioxide, and tantalum pentoxide, thereby indirectly bonding the AlN single crystal layer to the support substrate.

2. The composite substrate according to claim 1 , wherein the composite substrate has a diameter of 50 mm or more.

3. 2. The composite substrate according to claim 1, wherein the support substrate is made of one material selected from the group consisting of aluminum nitride polycrystalline, sapphire, silicon carbide, quartz, and a Si substrate.

4. A composite substrate comprising a support substrate and an AlN single crystal layer bonded to the support substrate, The AlN single crystal layer has, on an exposed surface opposite to the support substrate, The X-ray rocking curve half width of the (0002) plane is 20 to 350 arcsec, The X-ray rocking curve half width of the (10-12) plane is 20 to 500 arcsec, the defect density is 1.0×10 3 to 1.0×10 7 cm −2 , The AlN single crystal layer is directly bonded to the support substrate, and the support substrate and the AlN single crystal layer contain Ar in a layered region including the bonding interface therebetween.

5. A composite substrate as described in claim 4, wherein the composite substrate has a diameter of 50 mm or more.

6. A composite substrate as described in claim 4, wherein the support substrate is composed of one type selected from the group consisting of aluminum nitride polycrystalline, sapphire, silicon carbide, quartz, and Si substrate.

7. A device comprising the composite substrate according to any one of claims 1 to 6.

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