Composite substrate and device

Abstract

The present application provides a composite substrate in which a high-quality AlN single crystal layer is firmly bonded to a support substrate. The composite substrate includes a support substrate and an AlN single crystal layer bonded to the support substrate. The AlN single crystal layer has a (0002) plane with an X-ray rocking curve half-value width of 20 to 350 arcsec, a (10-12) plane with an X-ray rocking curve half-value width of 20 to 500 arcsec, and a defect density of 1.0 x 10 3 cm 7 -1.0 x 10 －2 cm

Description

Technical Field

[0001] This invention relates to composite substrates and devices comprising AlN single crystal layers. Background Technology

[0002] In recent years, aluminum nitride (AlN) single crystals have attracted much attention as substrates for deep ultraviolet light-emitting devices using 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 enabling applications in LEDs (Light Emitting Diodes) and LDs (Laser Diodes) in the deep ultraviolet region, which can be used for purposes such as sterilization.

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

[0004] Therefore, AlN substrates with improved crystallinity are being developed as substrates. Patent Document 1 (Japanese Patent No. 6872074) discloses an AlN substrate in which the orientation degree c1 is defined as the ratio of the diffraction intensity of the (002) plane to the total diffraction intensity of the (002) plane and the diffraction intensity of the (100) plane when X-ray diffraction is performed on the surface layer from the thickness direction, and the orientation degree c2 is defined as the ratio of the diffraction intensity of the (002) plane to the total diffraction intensity of the (002) plane and the diffraction intensity of the (100) plane when X-ray diffraction is performed on the parts other than the surface layer from the thickness direction, and the relationship c1 > 97.5% and c2 / c1 < 0.995 is satisfied. Patent document 2 (Japanese Patent No. 6872075) discloses an AlN substrate in which the relationships c1 and c2 satisfy c1 > 97.5% and c2 > 97.0%. On the other hand, when the half-width of the X-ray rocking curve profile of the (102) surface of the surface is set to w1 and the half-width of the X-ray rocking curve profile of the (102) surface of the part other than the surface is set to w2, the relationships w1 < 2.5° and w1 / w2 < 0.995 are satisfied.

[0005] Furthermore, AlN substrates with reduced defect density are being developed as substrates. Patent Document 3 (Japanese Patent Application Publication No. 2017-117972) discloses an AlN single-crystal laminate in which both the surface and back sides are Al polar surfaces, and the dislocation density is 10⁻⁶. 6 cm －2 The AlN single-crystal stack is fabricated by forming an AlN single-crystal layer on the N-polar surface of an AlN single-crystal substrate manufactured using the sublimation method via HVPE (hydride vapor phase growth). It should be noted that a high number of defects indicates a high number of dislocations.

[0006] However, a bonding substrate for a support substrate and a group 13 nitride crystal substrate has been proposed. For example, Patent Document 4 (Japanese Patent No. 7295351) discloses a bonding substrate for a support substrate and a group 13 nitride crystal substrate, and discloses that: the bonding surface of the group 13 nitride crystal substrate and the bonding surface of the support substrate are irradiated with a neutral atom beam to activate them, and the support substrate and the group 13 nitride crystal substrate are directly bonded.

[0007] Existing technical documents

[0008] Patent documents

[0009] Patent Document 1: Japanese Patent No. 6872074

[0010] Patent Document 2: Japanese Patent No. 6872075

[0011] Patent Document 3: Japanese Patent Application Publication No. 2017-117972

[0012] Patent Document 4: Japanese Patent No. 7295351

[0013] Patent Document 5: WO2022 / 190465

[0014] Patent Document 6: Japanese Patent Application Publication No. 2014-086400 Summary of the Invention

[0015] However, several methods can be considered when using AlN single crystals as substrates or base layers to form functional films. For example, a first method could involve forming a functional film several μm thick on an AlN single crystal substrate with a thickness of approximately 400–600 μm, and then grinding the AlN single crystal substrate to a thickness of 100 μm. This method allows the formation of a functional film on an AlN single crystal substrate with good crystal quality, thus achieving a functional film with good crystal quality. However, since a thicker AlN single crystal substrate is not required in devices, it is desirable to thin it using grinding (e.g., to improve transmittance in LEDs). Furthermore, AlN single crystal substrates are expensive, thus constituting a major reason for increased costs. On the other hand, a second method could be considered: forming an AlN single crystal layer several μm thick on an inexpensive sapphire substrate, and then forming the functional film on the AlN single crystal layer. In this case, due to the lattice constant mismatch between the sapphire substrate and the AlN single crystal layer, the crystal quality of both the AlN single crystal layer and the functional film deteriorates. Therefore, while this method is inexpensive, the device performance is reduced. Given these circumstances, there is a need for AlN wafers that have high crystal quality and are available at a low cost.

[0016] The inventors of this invention recently discovered that by bonding an AlN single crystal layer with the X-ray rocking curve half-width of the (0002) plane, the X-ray rocking curve half-width of the (10-12) plane, and the defect density respectively within a specified numerical range to a support substrate, it is possible to provide a composite substrate inexpensively in which a high-quality AlN single crystal layer is firmly bonded to the support substrate.

[0017] Therefore, the object of the present invention is to provide, at a low cost, a composite substrate on which a high-crystal-quality AlN single crystal layer is firmly bonded to a supporting substrate.

[0018] According to the present invention, the following solution is provided.

[0019] [Option 1]

[0020] A composite substrate comprising a support substrate and an AlN single-crystal layer bonded to the support substrate.

[0021] The composite substrate is characterized in that...

[0022] Regarding the AlN single crystal layer, the exposed surface on the side opposite to the supporting substrate,

[0023] The half-width of the X-ray rocking curve of the (0002) plane is 20–350 arcsec.

[0024] The half-width of the X-ray rocking curve for the (10-12) plane is 20–500 arcsec.

[0025] The defect density is 1.0 × 10⁻⁶. 3 ~1.0×10 7 cm －2 .

[0026] [Option 2]

[0027] The composite substrate according to Scheme 1 is characterized in that,

[0028] The composite substrate has a diameter of 50 mm or more.

[0029] [Option 3]

[0030] The composite substrate according to scheme 1 or 2 is characterized in that,

[0031] The supporting substrate is composed of one material selected from the group consisting of polycrystalline aluminum nitride, sapphire, silicon carbide, quartz, and Si substrates.

[0032] [Option 4]

[0033] The composite substrate according to any one of claims 1 to 3 is characterized in that,

[0034] The AlN single crystal layer is directly bonded to the supporting substrate.

[0035] [Option 5]

[0036] The composite substrate according to any one of claims 1 to 3 is characterized in that,

[0037] A bonding layer is also provided between the supporting substrate and the AlN single crystal layer, thereby indirectly bonding the AlN single crystal layer to the supporting substrate.

[0038] [Option 6]

[0039] The composite substrate according to Scheme 5 is characterized in that,

[0040] The bonding layer comprises at least one selected from the group consisting of aluminum nitride, aluminum oxide, silicon carbide, silicon dioxide, and tantalum pentoxide.

[0041] [Option 7]

[0042] The composite substrate according to Scheme 4 is characterized in that...

[0043] The supporting substrate and the AlN single crystal layer contain Ar in the layered region including their bonding interface.

[0044] [Option 8]

[0045] A device comprising a composite substrate as described in any one of embodiments 1 to 7.

[0046] [Option 9]

[0047] A method for manufacturing a composite substrate, the composite substrate comprising a support substrate and an AlN single crystal layer bonded to the support substrate.

[0048] The method for manufacturing the composite substrate is characterized by comprising the following steps:

[0049] Prepare an AlN composite material having an AlN single crystal substrate as a seed substrate and an AlN single crystal layer grown on the AlN single crystal substrate.

[0050] Hydrogen ions are injected from the exposed surface of the AlN single crystal layer to a predetermined depth of the AlN single crystal layer to form a hydrogen embrittlement region;

[0051] The AlN composite material, including the hydrogen-embrittled portion, and the supporting substrate are joined to form a bond; and

[0052] By heating the bonding body, the AlN single crystal layer and the supporting substrate are peeled off together from the hydrogen embrittlement portion to obtain a composite substrate having the supporting substrate and the AlN single crystal layer. Attached Figure Description

[0053] Figure 1 This is a simplified cross-sectional view showing an example of the composite substrate involved in the present invention.

[0054] Figure 2 It is shown Figure 1 A simplified cross-sectional view of the manufacturing process of the composite substrate shown.

[0055] Figure 3 This is a simplified cross-sectional view showing another example of the composite substrate involved in the present invention.

[0056] Figure 4 This is a simplified cross-sectional view showing the configuration of a vapor phase growth apparatus for performing HVPE-based film formation. Detailed Implementation

[0057] Composite substrate

[0058] Figure 1 An example of the composite substrate 10 of the present invention is shown. The composite substrate 10 includes a support substrate 12 and an AlN single crystal layer 14 bonded to the support substrate 12. Furthermore, regarding the AlN single crystal layer 14, on the exposed surface opposite to the support substrate 12, the X-ray rocking curve half-width (hereinafter referred to as XRC half-width) of the (0002) surface is 20 to 350 arcsec, the XRC half-width of the (10-12) surface is 20 to 500 arcsec, and the defect density is 1.0 × 10⁻¹⁰. 3 ~1.0×10 7 cm －2 By bonding an AlN single crystal layer 14 with XRC half-width of the (0002) plane, XRC half-width of the (10-12) plane, and defect density respectively within the above-mentioned numerical range to a support substrate 12, a composite substrate 10 with a high-crystal-quality AlN single crystal layer 14 firmly bonded to the support substrate 12 can be provided cheaply.

[0059] In other words, as described above, several methods can be considered when forming functional films using AlN single crystals as substrates or substrate layers. For example, in the first method, where a functional film is formed on a thicker AlN single crystal substrate followed by grinding, the functional film can be formed on an AlN single crystal substrate with good crystal quality. However, a thicker AlN single crystal substrate is not required in devices, so grinding is desired to thin it. Furthermore, AlN single crystal substrates are expensive, thus constituting a major reason for increased costs. On the other hand, in the second method, where a functional film is formed on an inexpensive sapphire substrate after forming an AlN single crystal layer, the crystal quality of both the AlN single crystal layer and the functional film deteriorates. Therefore, while this method is inexpensive, the device performance is reduced. In view of these circumstances, it is desirable to have AlN wafers with high crystal quality that are also inexpensive to provide.

[0060] Therefore, as a third method, we can consider: Figure 2 As shown, an AlN single-crystal substrate 16 is prepared (step (a)), an AlN single-crystal layer 14 is formed on any surface (Al surface or N surface) of the AlN single-crystal substrate 16 (step (b)), and the AlN single-crystal layer 14 is transferred to a support substrate 12 (which is cheaper than the AlN single-crystal substrate 16) (step (c)). According to this method, it is possible to produce an AlN single-crystal layer 14 with high crystal quality while suppressing costs. That is, since the AlN single-crystal layer 14 is formed on the AlN single-crystal substrate 16, there is no lattice constant mismatch, thus enabling the realization of a high-crystal-quality AlN single-crystal layer 14. Furthermore, by transferring the AlN single-crystal layer 14 to the cheaper support substrate 12, and simultaneously peeling off the AlN single-crystal substrate 16 instead of grinding it, the high-cost AlN single-crystal substrate 16 can be reused. Therefore, costs can be suppressed. However, when the composite substrate 10 obtained in this way is used for device manufacturing, the AlN single-crystal layer 14 bonded to the support substrate 12 is sometimes peeled off. In particular, this peeling is prone to occur in high-temperature processes (e.g., above 1000°C). According to the present invention, this problem can be effectively eliminated. That is, the AlN single-crystal layer 14 satisfies the aforementioned numerical ranges for the XRC half-width of the (0002) plane, the XRC half-width of the (10-12) plane, and the defect density, thereby improving the bonding strength with the support substrate 12. The larger the size (diameter) of the composite substrate 10, the easier it is to achieve this effect. As a result, according to the present invention, it is possible to provide, at a low cost, a composite substrate 10 in which a high-quality AlN single-crystal layer 14 (particularly resistant to peeling even in high-temperature processes) is firmly bonded to the support substrate 12.

[0061] Regarding the AlN single crystal layer 14, on the exposed surface (Al or N surface) opposite to the supporting substrate 12, the XRC half-width of the (0002) surface is 20 to 350 arcsec, preferably 100 to 300 arcsec, and more preferably 100 to 280 arcsec. If the XRC half-width of the (0002) surface is within such a range, it has the advantage that no dislocations are generated in the formed film during device fabrication, resulting in good performance. Furthermore, regarding the AlN single crystal layer 14, on the exposed surface (Al or N surface) opposite to the supporting substrate 12, the XRC half-width of the (10-12) surface is 20 to 500 arcsec, preferably 200 to 450 arcsec, and more preferably 200 to 400 arcsec. If the XRC half-width of the (10-12) surface is within such a range, it has the advantage that no dislocations are generated in the formed film during device fabrication, resulting in good performance. It should be noted that, preferably, both sides (Al side and N side) of the AlN single crystal layer 14 have XRC half-widths within the range of the (10-12) side and the (0002) side. However, it is not practical to measure the XRC half-width at the interface between the AlN single crystal layer 14 and the support substrate 12. Therefore, it is sufficient to measure the XRC half-width on the exposed surface opposite to the support substrate 12 to represent the crystal quality of the AlN single crystal layer 14. The XRC profiles of the (0002) side and (10-12) side of the AlN single crystal layer 14 can be measured using a conventional XRD apparatus (e.g., a Bruker-AXS D8 DISCOVER) and its accompanying XRD analysis software (e.g., a Bruker-AXS "LEPTOS" Ver4.03) based on the steps described in the embodiments described later.

[0062] Regarding the AlN single crystal layer 14, the defect density on the exposed surface (Al surface or N surface) opposite to the supporting substrate 12 is 1.0 × 10⁻⁶. 3 ~1.0×10 7 cm －2 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 are advantages such as no dislocations being generated in the film during device fabrication, resulting in good performance. It is preferable that both sides (Al and N sides) of the AlN single-crystal layer 14 have the defect density within the aforementioned range. However, measuring the defect density at the interface between the AlN single-crystal layer 14 and the support substrate 12 is impractical. Therefore, measuring the defect density on the exposed surface opposite to the support substrate 12 is sufficient 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 using reflective X-ray morphology measurement or pit evaluation using KOH melt etching. In pit evaluation, the pit density can be determined by measuring the etched surface using an optical microscope, laser microscope, SEM, etc. It should be noted that the method of defect evaluation limits the range of applicable defect densities; when the defect density is high, TEM observation is preferred for evaluation. In TEM observation, measuring the entire surface area is difficult. Therefore, a 50μm × 50μm region, including the centroid, of the AlN single-crystal substrate exposed by grinding is taken out and TEM is performed to evaluate defects. There are no particular limitations on the method for measuring such defect density distribution; for example, X-ray topography can be used to measure tortuous morphologies, or segmental X-ray topography can be used to measure the defect density distribution inside the AlN single-crystal substrate. It should be noted that in this specification, the term "defect" includes: through-screw dislocations (TSDs), through-edge dislocations (TEDs), base plane dislocations (BPDs), and mixed dislocations. "Through" means that the dislocation line is approximately parallel to the

[0001] axis of the hexagonal crystal system. "Base plane" means that the dislocation line lies within the (0001) plane of the hexagonal crystal system.

[0063] The AlN single crystal layer 14 is preferably an orientation layer oriented along both the c-axis and the a-axis, and may contain mosaic crystals. Mosaic crystals refer to a collection of crystals whose orientation is slightly different from one or both of the c-axis and a-axis, although there are no clearly defined grain boundaries. Such an orientation layer has the following configuration: the crystal orientation is approximately aligned with the normal direction (c-axis direction) and the in-plane direction (a-axis direction). By configuring it in this way, a semiconductor layer of excellent quality, especially with excellent orientation, can be formed on the AlN single crystal layer 14.

[0064] There is no particular limitation on the method for evaluating the orientation of the AlN single crystal layer 14. Known analytical methods such as EBSD (Electron Back Scatter Diffraction Patterns) and X-ray pole figures can be used. For example, when using EBSD, the inverse pole figure mapping and crystal orientation mapping of the AlN single crystal layer 14 at a cross section orthogonal to the surface or plate plane are measured. An orientation can be defined as two axes: approximately normal and approximately plate plane, when the following four conditions are met: In the obtained inverse pole figure mapping, (A) a specific orientation (first axis) along the approximately normal direction of the plate plane; (B) a specific orientation (second axis) along a direction approximately in-plane orthogonal to the first axis; In the obtained crystal orientation mapping, (C) the tilt angle relative to the first axis is within ±10°; (D) the tilt angle relative to the second axis is within ±10°. In other words, when the above four conditions are met, the orientation can be determined to be along the c-axis and a-axis. For example, if the approximate normal direction of the substrate is oriented along the c-axis, the approximate in-plane direction can be oriented along a specific orientation orthogonal to the c-axis (e.g., the a-axis). The AlN single crystal layer 14 can be oriented along both the approximate normal direction and the approximate in-plane direction, with the approximate normal direction preferably oriented along the c-axis. When the tilt angle distribution in the approximate normal direction and / or the approximate in-plane direction is small, the mosaicism of the AlN single crystal substrate decreases; the closer it is to zero, the closer it is to a complete single crystal. Therefore, from the viewpoint of the crystallinity of the AlN single crystal substrate, the tilt angle distribution is preferably small in both the approximate normal direction and the approximate in-plane direction, for example, preferably ±5° or less, and more preferably ±3° or less.

[0065] 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.

[0066] The support substrate 12 can be any substrate capable of firmly bonding with the AlN single crystal layer 14, and is not particularly limited. Preferably, it is a substrate that is cheaper than the AlN single crystal substrate 16 and has a coefficient of thermal expansion close to that of AlN single crystal. Alternatively, the support substrate 12 is preferably a substrate with high light transmittance and low refractive index. From this viewpoint, the support substrate 12 is preferably composed of one substrate selected from the group consisting of polycrystalline aluminum nitride, sapphire, silicon carbide, quartz, and Si substrates. The thickness of the support substrate 12 is not particularly limited, but is preferably 200–2000 μm, more preferably 300–1500 μm, and even more preferably 400–1000 μm.

[0067] Regarding the dimensions of the composite substrate 10, the diameter is 50 mm or more, preferably 100 mm or more or 150 mm or more. The larger the diameter of the composite substrate 10, the easier it is to achieve an improved 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; typically, the diameter is 300 mm or less, and more typically, 250 mm or less. The composite substrate 10 typically has a circular shape. In this specification, "circular shape" does not need to be a complete circle; it can be a generally circular shape that can be identified as substantially circular overall. For example, it can be a shape obtained by cutting away a portion of a circle for specific crystal orientation or other purposes (including, for example, an orientation flat, or a circular shape with a cut).

[0068] 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 perform surface activation on each bonding surface by irradiation with a neutral atom beam such as an Ar beam, as proposed in Patent Document 4 (Japanese Patent No. 7295351), thereby improving the bonding strength. As a result, it is ideal from the viewpoint that the support substrate 12 and the AlN single crystal layer 14 contain Ar in the layered region including their bonding interface. This Ar-containing layered region can be determined by performing elemental analysis on the cross section of the composite substrate 10 using SEM-EDX (energy dispersive X-ray analysis device (EDX) attached to a scanning electron microscope (SEM)). Alternatively, as proposed in Patent Document 5 (WO2022 / 190465), surface activation (plasma activation method) can be performed on each bonding surface by irradiation with a plasma such as nitrogen plasma, thereby improving the bonding strength.

[0069] According to another preferred embodiment of the invention, like Figure 3 As shown in the composite substrate 10', a bonding layer 18 can 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 allows for a higher bonding strength. Ideally, the bonding layer 18 should contain at least one material selected from the group consisting of aluminum nitride, aluminum oxide, silicon carbide, silicon dioxide, and tantalum pentoxide, as this is desirable from the viewpoint of high bonding strength. By performing the same process as the direct bonding described above after forming the bonding layer 18, a bond of support substrate 12 / bonding layer 18 / AlN single crystal layer 14 can be obtained with high bonding strength.

[0070] Manufacturing method

[0071] The composite substrate 10 of the present invention can be manufactured as follows: Figure 2As shown, an AlN single crystal substrate 16 is prepared (step (a)), an AlN single crystal layer 14 is formed on any surface (Al surface or N surface) of the AlN single crystal substrate 16 (step (b)), and the AlN single crystal layer 14 is transferred to a support substrate 12 (step (c)).

[0072] (a) Preparation of AlN single crystal substrate

[0073] The AlN single crystal substrate 16 can be any known or commercially available AlN single crystal substrate, and there are no particular limitations.

[0074] (b) Film formation of AlN single crystal layer

[0075] An AlN single-crystal layer 14 is formed on any surface of the AlN single-crystal substrate 16. Therefore, the AlN single-crystal layer 14 can be formed on either the Al or N-plane of the AlN single-crystal substrate 16. Typically, an AlN single crystal is epitaxially grown on the surface of the AlN single-crystal substrate 16, which serves as a seed crystal, thereby forming the AlN single-crystal layer 14. The single crystal can be grown using any of the following methods: vapor phase deposition, liquid phase deposition, and solid phase deposition; preferably, vapor phase deposition is used to form the AlN single-crystal layer 14. Examples of vapor-phase film formation methods include various CVD (chemical vapor deposition) methods (such as thermal CVD, plasma CVD, MOVPE, etc.), sputtering, hydride vapor phase epitaxy (HVPE), molecular beam epitaxy (MBE), sublimation, and pulsed laser deposition (PLD), with HVPE being the preferred method. Examples of liquid-phase film formation methods include solution growth methods (such as flux methods). All methods in solid-phase, vapor-phase, and liquid-phase film formation can use known conditions.

[0076] The following describes an example of a method for fabricating an AlN single crystal layer 14 using the HVPE method. In this method, the AlN single crystal layer 14 is fabricated by (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.

[0077] (i) Deposition of AlN single crystal layer on AlN single crystal substrate

[0078] This process is: forming an AlN single crystal layer 14 on an AlN single crystal substrate 16, which serves as a seed substrate. Figure 4The diagram shows a vapor phase growth apparatus (hereinafter referred to as an HVPE apparatus) for film formation based on the HVPE method. The HVPE apparatus includes: a reactor 40, a base 44, a carrier gas supply source 46, an Al raw material supply source 48, metallic Al powder raw material 50 disposed within the Al raw material supply source 48, a heater 52, and a gas exhaust section 54. An AlN single crystal substrate 16 is disposed on the base 44, and AlCl3 gas obtained by supplying HCl gas to the heated Al raw material supply source 48 and NH3 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 raw material supply source 48 is preferably 500–700°C, more preferably 550–650°C. Furthermore, 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 within the reactor 40 is preferably 1–100 Torr, more preferably 10–30 Torr. The preferred growth temperature is 1100–1400℃, and more preferably 1150–1250℃.

[0079] (ii) Grinding of AlN single crystal layer surface

[0080] The surface of the obtained AlN single crystal layer 14 is subjected to mirror finishing. Preferably, this mirror finishing involves smoothing the surface using diamond abrasives, followed by polishing using chemical mechanical polishing (CMP) with colloidal silica or similar materials. This yields an AlN composite material having a mirror-finished AlN single crystal layer 14 on an AlN single crystal substrate 16.

[0081] (c) Transfer of AlN single crystal layer toward the supporting substrate

[0082] 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, thus reducing costs. Furthermore, the transfer of the AlN single crystal layer 14 to the support substrate 12 is accompanied by the peeling off of the AlN single crystal substrate 16, thus enabling the reuse of 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, its shape is lost, making reuse impossible. However, if removal is based on peeling, the shape of the AlN single crystal substrate 16 can be maintained, thus enabling its reuse.

[0083] The transfer of the AlN single crystal layer 14 toward the support substrate 12 is accompanied by the bonding of the AlN single crystal layer 14 and the support substrate 12, and the peeling off of the AlN single crystal substrate 16. The bonding of the AlN single crystal layer 14 and the support substrate 12 can be performed after the AlN single crystal substrate 16 is peeled off; however, it is preferable to peel off the AlN single crystal substrate 16 after the bonding of the AlN single crystal layer 14 and the support substrate 12. Examples of peeling methods include: wire saw cutting, laser lift-off (LLO) processing, laser slicing, hydrogen ion implantation lift-off (also known as smart cutting or ion cutting), and sacrificial layer etching. Furthermore, by placing a peeling layer composed of graphene, hexagonal boron nitride (h-BN), etc., between the AlN single crystal substrate 16 and the AlN single crystal layer 14, peeling can be facilitated.

[0084] For example, when using the hydrogen ion implantation stripping method, the stripping is preferably performed as follows: First, using an ion implanter, a hydrogen ion beam is irradiated onto the surface of the AlN single crystal layer 14 to implant hydrogen ions into the AlN single crystal layer 14. Next, the hydrogen-implanted AlN single crystal layer 14 is bonded to the support substrate 12 (the bonding method will be described below). The resulting bond is heat-treated at 400–600°C, and the AlN single crystal substrate 16 or the AlN single crystal layer 14 is peeled off at the depth where hydrogen ions were implanted. At this time, the hydrogen-implanted portion of the AlN single crystal layer 14 becomes hydrogen-embrittled, and therefore, it can be easily peeled off by heating. However, instead of heating the AlN single crystal substrate 16 and the AlN single crystal layer 14, a knife or similar tool can be inserted into the hydrogen-embrittled portion to mechanically peel off the material. Finally, the surfaces of the peeled AlN single crystal substrate 16 and the AlN single crystal layer 14 can be polished as needed.

[0085] The bonding of the AlN single crystal layer 14 and the support substrate 12 can be performed using direct bonding as described above. In this case, it is preferable to perform surface activation on each bonding surface of the AlN single crystal layer 14 and the support substrate 12 by irradiation with a neutral atomic beam such as an Ar beam, thereby improving the bonding strength (see, for example, Patent Document 4 (Japanese Patent No. 7295351)). Surface activation based on a neutral atomic beam preferably uses a known device as disclosed in Patent Document 6 (Japanese Unexamined Patent Application Publication No. 2014-086400) to generate a neutral atomic beam and irradiate each bonding surface. That is, a saddle-type high-speed atomic beam source is used as the beam source. Furthermore, an inactive gas is introduced into the chamber, and a high voltage is applied to the electrodes from a DC power supply. As a result, due to the saddle-type electric field generated between the electrode (positive electrode) and the shell (negative electrode), electrons move, generating a beam of atoms and ions based on the inactive gas. In the beam reaching the gate, the ion beam is neutralized at the grid, thus a beam of neutral atoms is emitted from the high-speed atomic beam source. The atomic species constituting the beam are preferably inactive gases (argon, nitrogen, etc.). The activation voltage based on beam irradiation is preferably 0.5–2.0 kV, and the current is preferably 50–200 mA. Next, in a vacuum atmosphere, the activated bonding surfaces are brought into contact with each other, thereby bonding the AlN single crystal layer 14 and the support substrate 12. The bonding temperature is room temperature, specifically preferably below 40°C, more preferably below 30°C, and even more preferably 20–25°C. The pressure load applied during bonding is preferably 100–20000 N. Furthermore, the flatter the bonding surfaces of the AlN single crystal layer 14 and the support substrate 12, the better the bonding strength. Alternatively, as mentioned above, surface activation (plasma activation method) based on plasma irradiation such as nitrogen plasma can be applied to each joint surface, as proposed in Patent Document 5 (WO2022 / 190465), thereby improving the joint strength.

[0086] The bonding of the AlN single crystal layer 14 and the support substrate 12 can also be performed using indirect bonding as described above. In this case, like Figure 3 As shown in the composite substrate 10', the bonding layer 18 is positioned between the support substrate 12 and the AlN single crystal layer 14. Otherwise, bonding can be performed in the same manner as the direct bonding described above. The bonding layer 18 is preferably formed using a vapor phase deposition method such as sputtering. By performing the same process as the direct bonding described above after the formation of the bonding layer 18, a bond of support substrate 12 / bonding layer 18 / AlN single crystal layer 14 can be obtained with high bonding strength.

[0087] Devices

[0088] Devices can also be fabricated using the composite substrate 10 or the AlN single crystal layer 14 of the present invention. That is, it is preferable to provide a device having the composite substrate 10 or the AlN single crystal layer 14. Examples of such devices include: deep ultraviolet laser diodes, deep ultraviolet diodes, power electronic devices, high-frequency devices, heat sinks, etc. The manufacturing method for devices using the composite substrate 10 or the AlN single crystal layer 14 is not particularly limited, and can be manufactured using known methods.

[0089] Example

[0090] The invention will be further illustrated by the following examples. However, the invention is not limited to these examples.

[0091] Examples 1 to 20

[0092] (1) Fabrication of AlN single crystal layers

[0093] As seed crystals for growing AlN single crystal layers, disc-shaped AlN single crystals (of various known crystal qualities) with a thickness of 600 μm (Examples 1-12) or 400 μm (Examples 13-20) and a diameter of 100 mm (Examples 1-5 and 7-12), 150 mm (Example 6), or 50 mm (Examples 13-20) are prepared. Figure 4 The HVPE apparatus shown grows an AlN single crystal layer on an AlN single crystal (seed crystal) using the HVPE method. Specifically, the HVPE apparatus includes: a reactor 40, a substrate 44, a carrier gas supply source 46, an Al raw material supply source 48, metallic Al powder raw material 50 disposed within the Al raw material supply source 48, a heater 52, and a gas exhaust section 54. In this HVPE apparatus, an AlN single crystal substrate 16 (seed crystal) is disposed on the substrate 44 with either the N-side (Examples 1-7 and 9-20) or the Al-side (Example 8) exposed. AlCl3 gas obtained by supplying HCl gas to the Al raw material supply source 48 heated to 600°C and NH3 gas from the carrier gas supply source 46 are mixed and supplied to the AlN single crystal substrate 16, and an AlN single crystal layer is grown under the following conditions. Thus, a composite material (hereinafter referred to as AlN composite material) with an AlN single crystal layer formed on the AlN single crystal (seed crystal) is obtained.

[0094] <HVPE conditions>

[0095] AlCl3 supply partial pressure: 4.0 × 10 －4 atm

[0096] • NH3 supply partial pressure: 2.0 × 10 －4 atm

[0097] • AlN growth temperature (film formation temperature): 1450℃ (Examples 1-8 and 12-20) or 1100℃ (Examples 9-11)

[0098] • Film formation time: The time required for the AlN single crystal layer to reach a thickness of 1 μm or more (Example 13), 2 μm or more (Examples 1-6, 8-12 and 14-20), or 100 μm or more (Example 7).

[0099] To achieve a mirror finish on the surface of the obtained AlN single crystal layer, the surface was smoothed using a diamond abrasive, and then polished using chemical mechanical polishing (CMP) with colloidal silica. This resulted in an AlN single crystal substrate with a mirror-finished surface.

[0100] (2) Transfer of AlN single crystal layer

[0101] The AlN single crystal layer was peeled off by ion implantation (Examples 1-6 and 8-12) or by wire (Example 7), and bonded to a support substrate by direct bonding (Examples 1-11) or by indirect bonding using 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 substrates used were 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 order is as follows.

[0102] (Examples 1-6 and 8-11)

[0103] First, using an ion implanter, a hydrogen ion beam is irradiated onto the surface of the AlN single crystal layer, injecting hydrogen ions to the target depth. This causes hydrogen embrittlement of the AlN single crystal layer at a specified depth. Next, the surfaces of the AlN single crystal layer and the supporting substrate are irradiated with a high-speed Ar neutral atom beam (accelerating voltage: 1 kV, Ar flow rate: 60 sccm) for 70 seconds to activate their surfaces. The AlN composite material and the supporting substrate are then overlapped in contact, and a load of 1000 N is applied under vacuum to bond the AlN composite material (especially the AlN single crystal layer) to the supporting substrate. By heating the resulting bond to 500°C, the AlN single crystal layer, along with the supporting substrate, is peeled off from the AlN single crystal (seed crystal) at the hydrogen ion implanted portion. This transfers the AlN single crystal layer onto the supporting substrate. The surface of the resulting composite material is then smoothed using precision grinding with diamond abrasives and chemical mechanical polishing (CMP) with colloidal silica, resulting in a composite substrate composed of the supporting substrate and the AlN single crystal layer. The composite substrate is in the shape of a disc, with a diameter of 100 mm in Examples 1-5 and 8-11, and 150 mm in Example 6. In addition, the thickness of the AlN seed layer is 2 μm in Examples 1-6 and 8-11, and the thickness of the composite substrate is 602 μm in Examples 1-6 and 8-11.

[0104] (Example 7)

[0105] The surfaces of the AlN single crystal layer and the supporting substrate were irradiated with a high-speed Ar neutral atom beam (accelerating voltage: 1 kV, Ar flow rate: 60 sccm) for 70 seconds to activate their surfaces. The AlN composite material and the supporting substrate were then overlapped in contact, and a load of 1000 N was applied under vacuum to bond the AlN composite material (especially the AlN single crystal layer) to the supporting substrate. Next, using a diamond wire saw, the AlN single crystal layer, along with the supporting substrate, was peeled off from the AlN single crystal (seed crystal). This transferred the AlN single crystal layer to the supporting substrate. The surface of the resulting composite material was then smoothed using precision grinding with diamond abrasives and chemical mechanical polishing (CMP) with colloidal silica, resulting in a composite substrate composed of the supporting substrate and the AlN single crystal layer. The composite substrate is a circular plate with a diameter of 100 mm. In addition, the AlN seed layer has a thickness of 100 μm, and the composite substrate has a thickness of 700 μm.

[0106] (Examples 12 and 13)

[0107] First, using an ion implanter, a hydrogen ion beam is irradiated onto the surface of an AlN single crystal layer, injecting hydrogen ions to the target depth. This causes hydrogen embrittlement of the AlN single crystal layer at a specified depth. Next, a 1 μm thick SiO2 film is sputtered onto the surface of the AlN single crystal layer to prepare a SiO2 / AlN composite material. The surface of the SiO2 film is planarized using chemical mechanical polishing (CMP). The SiO2 / AlN composite material and a supporting substrate are placed in a plasma activation chamber, and the surfaces of the SiO2 film and the supporting substrate are activated at 30°C using nitrogen plasma. This surface activation is performed at an energy of 100 W for 40 seconds. The SiO2 / AlN composite material and the supporting substrate are then overlapped with their activated surfaces in contact, and heated at 130°C for 4 hours under a pressure of 0.3 MPa in a nitrogen atmosphere oven, thereby bonding the SiO2 / AlN composite material (especially the SiO2 film) to the supporting substrate. The resulting bond was heated to 500°C, thereby peeling the AlN single crystal layer and SiO2 film, along with the supporting substrate, from the AlN single crystal (seed crystal) in the hydrogen ion implanted portion. This transfers the AlN single crystal layer and SiO2 film together onto the supporting substrate. The surface of the resulting composite material was smoothed using diamond abrasive grinding, resulting in a composite substrate composed of the supporting substrate, SiO2 film (bonding layer), and AlN single crystal layer. The composite substrate is circular, with a diameter of 100 mm (Example 12) or 50 mm (Example 13). Furthermore, the thickness of the AlN seed layer is 2 μm, and the thickness of the composite substrate is 602 μm (Example 12) or 401 μm (Example 13).

[0108] (Examples 14~20)

[0109] First, using an ion implanter, a hydrogen ion beam is irradiated onto the surface of the AlN single crystal layer, injecting hydrogen ions to the target depth. This causes hydrogen embrittlement of the AlN single crystal layer at a specified depth. Next, a 1 μm thick SiO2 film (Examples 14 and 18), Al2O3 film (Example 15), SiC film (Examples 16 and 19), or Ta2O5 film (Examples 17 and 20) is formed on the surface of the AlN single crystal layer by sputtering, thus preparing SiO2 / AlN composite materials (Examples 14 and 18), Al2O3 / AlN composite materials (Example 15), SiC / AlN composite materials (Examples 16 and 19), or Ta2O5 / AlN composite materials (Examples 17 and 20). The surface of the SiO2 film, Al2O3 film, SiC film, or Ta2O5 film is planarized by chemical mechanical polishing (CMP). The surfaces of the SiO2, Al2O3, SiC, or Ta2O5 films of these composite materials, as well as the surfaces of the supporting substrates (quartz substrates (Examples 14-18) or sapphire substrates (Examples 18-20)), were irradiated with a high-speed Ar neutral atom beam (accelerating voltage: 1 kV, Ar flow rate: 60 sccm) for 70 seconds to activate their surfaces. The AlN composite material and the supporting substrate were then overlapped in a manner that brought the AlN single crystal layer into contact with the supporting substrate. Under vacuum, a load of 1000 N was applied to bond the AlN composite material (especially the AlN single crystal layer) to the supporting substrate. The resulting bond was heated to 500 °C, thereby bonding the AlN single crystal layer to the hydrogen-implanted portion. The crystalline layer, along with the supporting substrate, is peeled off from the AlN single crystal (seed crystal). This allows the AlN single crystal layer to be transferred onto the supporting substrate together with a SiO2 film, Al2O3 film, SiC film, or Ta2O5 film. The surface of the resulting composite material is smoothed using diamond abrasive grinding, resulting in a composite substrate consisting of a supporting substrate, a bonding layer (SiO2 film, Al2O3 film, SiC film, or Ta2O5 film), and an AlN single crystal layer. The composite substrate is circular with a diameter of 50 mm. Furthermore, the thickness of the AlN seed layer is 2 μm, and the thickness of the composite substrate is 402 μm (Examples 13-17) or 602 μm (Examples 18-20).

[0110] (3) Evaluation

[0111] The following evaluations were performed on the obtained composite substrate.

[0112] (3a) Half-width of X-ray rocking curve

[0113] XRC measurements were performed on the (0002) plane of the AlN single crystal layer (the surface opposite to the supporting substrate) using a multi-functional high-resolution X-ray diffractometer (D8 DISCOVER manufactured by Bruker-AXS). The conditions for this XRC measurement are as follows.

[0114] <XRD Measurement Conditions>

[0115] • Tube voltage: 40kV

[0116] Tube current: 40mA

[0117] • Detector: Tripple Ge (220) Analyzer

[0118] • Parallel monochromatic CuKα rays were obtained using a Ge(022) asymmetric reflection monochromator (half-value width 28 seconds).

[0119] • Step width: 0.001°

[0120] • Scanning speed: 0.5 seconds / step

[0121] In practice, after adjusting 2θ, ω, χ, and φ to establish the peak of the (0002) plane of the AlN single crystal, a 3mm anti-scattering slit was used, and the range of ω = 14.5–19.5° was measured. Using XRD analysis software (Bruker-AXS's "LEPTOS" Ver4.03), the profile was smoothed, and peak searching was performed to determine the half-width of the XRC profile of the (0002) plane of the AlN single crystal. The results are shown in Table 1.

[0122] In addition, XRC measurements were performed on the (10-12) plane of the AlN single crystal layer surface (the surface opposite to the supporting substrate). A Bruker-AXS D8-DISCOVER was used as the XRD apparatus. After adjusting 2θ, ω, χ, and φ to establish the axis so that the peaks of the (10-12) plane of the AlN single crystal appeared, measurements were performed at ω = 24.5–29.5°. Other conditions and analytical methods were performed under the same conditions as for the (0002) plane XRC measurements. The half-widths of the (10-12) plane XRC profiles of the AlN single crystal substrate surface are shown in Table 1.

[0123] (3b) Defect density

[0124] The defect density on the surface of the obtained AlN single crystal layer (the surface opposite to the supporting substrate) was evaluated by measuring the entire surface area using X-ray topology (XRTmicron manufactured by Rigaku Corporation). Here, the defect density was 1.0 × 10⁻⁶. 5 cm －2Under the above circumstances, it is difficult to accurately calculate the number of etch pits using X-ray morphology. Therefore, an evaluation of etch pits using KOH melt etching was conducted to determine the defect density on the surface of the AlN single crystal layer. Specifically, for the etch pit evaluation, a KOH:NaOH mixture with a weight ratio of 1:1 was used. The surface of the AlN single crystal layer was immersed in a melt heated to 450°C for 5 minutes. After etching, the defect density was measured using an optical microscope. The results are shown in Table 1.

[0125] (3c) Peelability evaluation

[0126] For each example, a total of 10 composite substrates were fabricated in the same manner as in (1) and (2) above. These composite substrates were heated at 1000°C for 5 minutes in a N2 atmosphere, and the presence of self-supporting substrate peeling off the AlN single crystal layer was investigated. The number of composite substrates that peeled off was counted out of the 10 composite substrates, and the results were evaluated according to the following criteria. The results are shown in Table 1.

[0127] • Evaluation A: The number of composite substrates that did not peel off was 7 to 10.

[0128] • Evaluation B: The number of composite substrates that did not peel off is 1 to 6.

[0129] • Evaluation C: The number of composite substrates that did not peel off is 0 (peeling occurred in all composite substrates).

[0130] As shown in Table 1, the XRC half-width of the (0002) facet is in the range of 20–350 arcsec, the XRC half-width of the (10–12) facet is in the range of 20–500 arcsec, and the defect density is 1.0 × 10⁻⁶. 3 ~1.0×10 7 cm －2 In Examples 1-8 and 12-20, the peel quality was rated A or B, resulting in a composite substrate with a high-quality AlN single crystal layer firmly bonded to an inexpensive support substrate. In contrast, in Examples 9-11, where HVPE was applied at a film-forming temperature of 1100°C, an AlN single crystal layer with poor crystallinity and defect density was formed. This poor-quality AlN single crystal layer was transferred to the support substrate, resulting in a poor peel quality rating of C. It should be noted that the crystallinity varied primarily by using AlN single crystals (seed crystals) of various crystal qualities in Examples 1-8 and 12-20, and by varying the HVPE film-forming temperature in Examples 9-11.

[0131] Table 1

[0132]

[0133] Explanation of reference numerals in the attached figures

[0134] 10' 10' composite substrate

[0135] 12 Supporting substrate

[0136] 14 AlN monocrystalline layer

[0137] 16 AlN single crystal substrate

[0138] 18 Bonding Layer

[0139] 40 Reactor

[0140] 44 Base

[0141] 46 Carrier Gas Supply Source

[0142] 48 Al raw material supply sources

[0143] 50 Metallic Al Powder Raw Material

[0144] 52 Heater

[0145] 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 composite substrate is characterized in that... Regarding the AlN single crystal layer, the exposed surface on the side opposite to the supporting substrate, The half-width of the X-ray rocking curve of the (0002) plane is 20–350 arcsec. The half-width of the X-ray rocking curve for the (10-12) plane is 20–500 arcsec. The defect density is 1.0 × 10⁻⁶. 3 ~1.0×10 7 cm －2 .

2. The composite substrate according to claim 1, characterized in that, The composite substrate has a diameter of 50 mm or more.

3. The composite substrate according to claim 1, characterized in that, The supporting substrate is composed of one material selected from the group consisting of polycrystalline aluminum nitride, sapphire, silicon carbide, quartz, and Si substrates.

4. The composite substrate according to claim 1, characterized in that, The AlN single crystal layer is directly bonded to the supporting substrate.

5. The composite substrate according to claim 1, characterized in that, A bonding layer is also provided between the supporting substrate and the AlN single crystal layer, thereby indirectly bonding the AlN single crystal layer to the supporting substrate.

6. The composite substrate according to claim 5, characterized in that, The bonding layer comprises at least one selected from the group consisting of aluminum nitride, aluminum oxide, silicon carbide, silicon dioxide, and tantalum pentoxide.

7. The composite substrate according to claim 4, characterized in that, The supporting substrate and the AlN single crystal layer contain Ar in the layered region including their bonding interface.

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

9. A method for manufacturing a composite substrate, the composite substrate comprising a support substrate and an AlN single crystal layer bonded to the support substrate, The method for manufacturing the composite substrate is characterized by comprising the following steps: Prepare an AlN composite material having an AlN single crystal substrate as a seed substrate and an AlN single crystal layer grown on the AlN single crystal substrate. Hydrogen ions are injected from the exposed surface of the AlN single crystal layer to a predetermined depth of the AlN single crystal layer to form a hydrogen embrittlement region; The AlN composite material, including the hydrogen-embrittled portion, and the supporting substrate are joined to form a bond; and By heating the bonding body, the AlN single crystal layer and the supporting substrate are peeled off together from the hydrogen embrittlement portion to obtain a composite substrate having the supporting substrate and the AlN single crystal layer.

Images