Method for manufacturing an AlN single crystal substrate and AlN single crystal substrate

Abstract

Provided is a method by which an AlN single crystal substrate can be produced with high productivity, which is suitable for enlarging the diameter without causing cracks. This method for producing an AlN single crystal substrate comprises: a step for preparing an AlN bonded body composed of an AlN seed crystal and an AlN sintered body; and a step for implementing heat treatment on the AlN bonded body to grow an AlN single crystal from the AlN seed crystal.

Description

[Technical Field]

[0001] This disclosure relates to a method for manufacturing an AlN single crystal substrate and to an AlN single crystal substrate. [Background technology]

[0002] In recent years, AlN single crystal substrates have been developed as underlayment substrates for deep ultraviolet LEDs. Sublimation is being investigated as a method for producing AlN single crystals. For example, Patent Document 1 (Japanese Patent Application Publication No. 2019-19042) discloses a method for producing AlN single crystals in which an AlN single crystal is grown on a SiC substrate in at least two stages using sublimation. [Prior art documents] [Patent Documents]

[0003] [Patent Document 1] Japanese Patent Publication No. 2019-19042 [Overview of the Initiative]

[0004] As mentioned above, when manufacturing AlN single crystals by sublimation, cracking can occur due to the difference in thermal expansion coefficients between the SiC substrate and the AlN single crystal. This problem becomes more pronounced as the substrate size increases. To address this problem, it is conceivable to use a 50.8 mm (2 inch) diameter AlN single crystal instead of a SiC substrate when performing the sublimation process. In other words, since the sublimation process has the characteristic of slightly increasing the size of the AlN single crystal with each sublimation, this characteristic can be utilized to increase the diameter of the AlN single crystal substrate. However, this method has low productivity because it requires repeating the sublimation process many times, for example, if the size (diameter) of the AlN single crystal is 50.8 mm the first time, 60 mm the second time, 70 mm the third time, and so on.

[0005] The present inventors have now discovered that by growing an AlN single crystal using an AlN bond composed of an AlN seed crystal and an AlN sintered body, it is possible to manufacture an AlN single crystal substrate with high productivity without causing cracking, while being a method suitable for increasing the diameter.

[0006] Therefore, the object of the present invention is to provide a method that is suitable for increasing the diameter of AlN single crystal substrates, yet can manufacture AlN single crystal substrates with high productivity without causing cracking.

[0007] The following aspects are provided according to this disclosure. [Aspect 1] A step to prepare an AlN bond composed of an AlN seed crystal and an AlN sintered body, A step of subjecting the AlN bond to heat treatment to grow an AlN single crystal from the AlN seed crystal, A method for manufacturing an AlN single crystal substrate, including [the specified component]. [Aspect 2] The AlT sintered body is (a1) A step of mixing AlN powder with a powder containing at least one rare earth element to produce a mixed powder with an AlN content of 95% by weight or more, (a2) A step of forming the mixed powder into a predetermined shape to produce a molded body, (a3) A step of firing the molded body to produce an AlN sintered body with an average crystal grain size of 1 to 40 μm, A method for manufacturing an AlN single crystal substrate according to embodiment 1, which is prepared by a method including the following. [Aspect 3] A method for manufacturing an AlN single crystal substrate according to embodiment 1 or 2, wherein the step of growing an AlN single crystal from the AlN seed crystal includes growing an AlN single crystal throughout the entire AlN sintered body. [Aspect 4] An AlN single crystal substrate manufactured by the method described in any one of embodiments 1 to 3. [Aspect 5] The AlN single crystal substrate according to embodiment 4, wherein the AlN single crystal substrate has a size of 100 mm or more in diameter. [Aspect 6] The AlN single crystal substrate according to embodiment 4 or 5, wherein the X-ray rocking curve full width at half maximum of the (002) plane of the AlN single crystal on at least one surface of the AlN single crystal substrate is 20 to 350 arcsec. [Aspect 7] The AlN single crystal substrate according to any one of embodiments 4 to 6, wherein the full width at half maximum of the X-ray rocking curve of the (102) plane of the AlN single crystal on at least one surface of the AlN single crystal substrate is 20 to 500 arcsec. [Aspect 8] The defect density on at least one surface of the AlN single crystal substrate is 1.0 × 10⁻¹⁴ 3 ~1.0×10 7 cm -2 An AlN single crystal substrate according to any one of embodiments 4 to 7. [Aspect 9] A device comprising an AlN single crystal substrate according to any one of embodiments 4 to 8. [Brief explanation of the drawing]

[0008] [Figure 1] This is a schematic process diagram showing the manufacturing method of an AlN single crystal substrate according to the present invention. [Modes for carrying out the invention]

[0009] The present invention relates to a method for manufacturing an AlN single crystal substrate. As shown in Figure 1, this method includes the steps of preparing an AlN bond 16 composed of an AlN seed crystal 12 and an AlN sintered body 14, and the step of heat-treating the AlN bond 16 to grow an AlN single crystal 18 from the AlN seed crystal 12. This method is suitable for increasing the diameter of the substrate, and allows for the high-productivity manufacturing of an AlN single crystal substrate 20 without causing cracks.

[0010] In other words, as described above, when manufacturing AlN single crystals by sublimation, cracking may occur due to the difference in thermal expansion coefficients between the SiC seed substrate and the AlN single crystal. This problem becomes more pronounced as the substrate size increases. To address this problem, it is conceivable to use an AlN single crystal with a diameter of 50.8 mm (2 inches) instead of a SiC seed substrate when performing the sublimation process. However, this method requires repeating the sublimation process many times to increase the substrate size, resulting in low productivity. In this respect, the method of the present invention can avoid such low-productivity repetition of the sublimation process, thereby improving productivity. For example, the sublimation process is performed only to produce the AlN seed crystal 12, and then the AlN seed crystal 12 is transferred to an AlN sintered body, and an AlN single crystal is grown from the AlN seed crystal in the region of the AlN sintered body. In this way, the AlN seed crystal 12 only needs to be precipitated by sublimation to a thickness that does not cause cracking even in large sizes (e.g., diameter of 100 mm or more), and the subsequent growth of the AlN single crystal 18 from the AlN seed crystal 12 is carried out not by sublimation, but by the conversion of the AlN sintered body 14 (AlN polycrystalline body) into the AlN single crystal 18. In this case, since the thermal expansion coefficients of the AlN seed crystal 12 and the AlN single crystal 18 are remarkably similar, the possibility of cracking due to differences in thermal expansion coefficients, as is the case when using a SiC seed substrate, is extremely low. For this reason, according to the present invention, a large-sized (e.g., diameter of 100 mm or more) AlN single crystal substrate 20 can be obtained with good quality without going through processes that are prone to cracking.

[0011] Therefore, the size of the AlN single crystal substrate 20 is 100 mm or more in diameter, preferably 150 mm or more or 200 mm or more in diameter. According to the method of the present invention, if the AlN seed crystal 12 and the AlN sintered body 14 are made large in size, the diameter of the AlN single crystal 18 can be increased without difficulty. For this reason, the upper limit of the diameter of the AlN single crystal substrate 20 is not particularly limited, but the diameter of the AlN single crystal substrate 20 is typically 300 mm or less, more typically 250 mm or less. The AlN single crystal substrate 20 typically has a circular shape. In this specification, the "circular shape" does not necessarily need to be a perfect circular shape, and may be a substantially circular shape that can be generally recognized as circular as a whole. For example, a shape in which a part of the circle is cut out for specifying the crystal orientation or other purposes (for example, a circular shape including an Orientation Flat or a notch) may be used.

[0012] Each step of the method for manufacturing an AlN single crystal substrate will be described below.

[0013] (1) Preparation of an AlN bonded body As shown in FIG. 1(ii), an AlN bonded body 16 composed of an AlN seed crystal 12 and an AlN sintered body 14 is prepared. The AlN sintered body 14 is an AlN polycrystal, and is therefore a ceramic material composed of a plurality of AlN crystal particles bonded to each other. The diameter of the AlN bonded body 16 is preferably 100 mm or more, more preferably 150 mm or more or 200 mm or more. The diameter of the AlN bonded body 16 is typically 300 mm or less, more typically 250 mm or less. The thickness of the AlN seed crystal 12 is not particularly limited, but is preferably 0.1 to 700 μm, more preferably 0.5 to 450 μm, and still more preferably 1 to 5 μm. The thickness of the AlN sintered body 14 is not particularly limited, but is preferably 200 to 700 μm, more preferably 250 to 650 μm, and still more preferably 350 to 550 μm.

[0014] The AlN bonded body 16 can be prepared by any method as long as it is composed of an AlN seed crystal 12 and an AlN sintered body 14. Preferably, the AlN bonded body 16 is prepared by the method shown in the following steps (a) to (c) and in Figures 1(i) and (ii). The order of steps (a) and (b) may be reversed.

[0015] (a) Preparation of AlN sintered body The AlN sintered body 14 is prepared. For example, the AlN sintered body 14 can be produced by mixing AlN powder with a sintering aid, molding the resulting mixed powder, and firing the resulting molded body. Specifically, the preparation step (step (a)) for the AlN sintered body 14 is preferably carried out by (a1) preparing the mixed powder, (a2) preparing the molded body, and (a3) ​​sintering the molded body, as described below. Note that the AlN sintered body 14 is not limited to the method including the following steps (a1) to (a3), and may be prepared by various known methods.

[0016] (a1) Preparation of mixed powder First, AlN powder and a powder containing at least one rare earth element are mixed to produce a mixed powder with an AlN content of 95% by weight or more. While AlN powder is the main component of the mixed powder, the powder containing the rare earth element is used as a sintering aid. Preferred examples of rare earth elements include Y, La, Ce, Sm, Eu, Gd, Dy, and Yb. These rare earth elements are preferably included in the powder in the form of oxides, carbonides, hydroxides, or composite oxides. Furthermore, the sintering aid is not limited to powders containing rare earth elements, but may also be powders containing alkaline earth elements such as Mg and Ca. The AlN content in the mixed powder is 95% by weight or more, typically 96% by weight or more, more typically 97% by weight or more, and even more typically 98% by weight or more. The content of the sintering aid in the mixed powder is not particularly limited, but is preferably 0.1 to 5.0% by weight, more preferably 0.2 to 4.0% by weight, even more preferably 0.4 to 3.0% by weight, and most preferably 0.5 to 2.0% by weight.

[0017] (a2) Fabrication of molded body The resulting mixed powder is molded into a predetermined shape to produce a molded body. The molding method is not particularly limited and may be performed by press molding (e.g., uniaxial press molding) or by sheet molding (e.g., doctor blade method).

[0018] (a3) Sintering of the molded body The obtained molded body is fired to produce an AlN sintered body 14 having an average crystal grain size of 1 to 40 μm. This firing is preferably carried out by hot press firing, which includes holding the molded body at a predetermined firing temperature and pressure for a predetermined time. The firing temperature in hot press firing is preferably 1500 to 2000°C, more preferably 1600 to 1900°C, and even more preferably 1650 to 1800°C. The holding time at the above firing temperature (i.e., firing time) is preferably 1 to 10 hours, more preferably 2 to 8 hours, and even more preferably 4 to 6 hours. The press load during hot press firing is preferably 0 to 30 MPa, more preferably 0 to 20 MPa, and even more preferably 0 to 10 MPa. The average crystal grain size of the AlN sintered body 14 (the average crystal grain size of the multiple AlN crystal particles constituting the AlN sintered body 14) is 1 to 40 μm, preferably 2 to 25 μm, and even more preferably 3 to 10 μm. This average crystal grain size can be measured based on the method described in the examples below.

[0019] (b) Preparation of the AlN template As shown in Figure 1(i), an AlN template 13 is prepared. The AlN template 13 is a composite material comprising an AlN seed crystal 12 and a substrate 10 that supports the AlN seed crystal 12. Preferably, the substrate 10 is capable of forming a film of AlN seed crystal 12 on it. Preferred examples of such a substrate 10 include a SiC substrate, a sapphire substrate, a Si substrate, etc. The AlN seed crystal 12 is preferably formed on the substrate 10 by a vapor phase method. Examples of vapor phase methods include sublimation, chemical vapor deposition (CVD), sputtering, and hydride vapor deposition (HVPE), with sublimation being preferred.

[0020] (c) Bonding of the AlN sintered body to the AlN seed crystal and removal of the underlying substrate As shown in Figures 1(i) and (ii), the AlN sintered body 14 is bonded to the AlN seed crystal 12 of the obtained AlN template 13, and the base substrate 10 is removed to obtain an AlN bonded body 16. This bonding may be performed by a surface activation method or by plasma bonding. In the case of the surface activation method, bonding can be preferably performed by the following procedure. First, the surface of the AlN sintered body 14 is mirror polished. Next, the surface of the AlN seed crystal 12 and the surface of the AlN sintered body 14 are activated. Surface activation can be performed by irradiation with a carbonation beam such as an Ar beam. Then, the AlN template 13 and the AlN sintered body 14 are stacked on top of each other so that the activated surfaces of the AlN seed crystal 12 and the AlN sintered body 14 are in contact with each other to form a laminate. This laminate is bonded by applying a load of 100 to 20000 N under vacuum. After bonding, the unnecessary base substrate 10 is removed to expose the AlN seed crystal 12, thereby obtaining an AlN bonded body 16 composed of the AlN seed crystal 12 and the AlN sintered body 14. The base substrate 10 can be removed using known methods such as grinding or reactive ion etching (RIE).

[0021] When performing surface activation using the neutralizing beam described above, an inert gas is introduced into the chamber, and a high voltage is applied from a DC power supply to the electrodes placed inside the chamber. In this configuration, electrons move due to the electric field generated between the electrode (positive electrode) and the chamber (negative electrode), generating a beam of atoms and ions from the inert gas. Of the beam that reaches the grid, the ion beam is neutralized at the grid, so a beam of neutral atoms is emitted from the high-speed atomic beam source. The atomic species constituting the beam are preferably inert gas elements (e.g., Ar, Ne, Kr, He, N, or Xe). The voltage during activation by beam irradiation is, for example, 0.5 to 2.0 kV, and the current is, for example, 50 to 200 mA.

[0022] In the illustrated example, the AlN sintered body 14 is bonded to only one side of the AlN seed crystal 12, but the AlN sintered body 14 may be bonded to both sides of the AlN seed crystal 12.

[0023] (2) Growth of AlN single crystals As shown in Figures 1(ii) and (iii), the AlN bonded body 16 is heat-treated to grow an AlN single crystal 18 from the AlN seed crystal 12. That is, by heat-treating the AlN bonded body 16, the AlN sintered body 14 is gradually converted into an AlN single crystal 18 from the portion in contact with the AlN seed crystal 12, resulting in the growth of the AlN single crystal 18. Unlike the sublimation method, which is prone to cracking because it uses a SiC substrate with a different coefficient of thermal expansion from the AlN single crystal, this method allows for the growth of an AlN single crystal 18 to a desired thickness without worrying about cracking, even at large sizes (e.g., diameter of 100 mm or more), because the coefficients of thermal expansion of the AlN seed crystal 12 and the AlN single crystal 18 are remarkably similar. This heat treatment is preferably carried out in an inert gas atmosphere such as nitrogen. The preferred firing temperature in the heat treatment is preferably 2000 to 2300°C, more preferably 2100 to 2250°C, and even more preferably 2150 to 2200°C. The holding time at the above firing temperature (i.e., firing time) is preferably 1 to 50 hours, more preferably 3 to 45 hours, and even more preferably 5 to 40 hours. This heat treatment may be carried out by atmospheric pressure firing or by hot press firing. The press load during heat treatment is preferably 0 to 30 MPa, more preferably 0 to 20 MPa, and even more preferably 0 to 10 MPa. Two AlN bonded bodies 16 may be stacked and subjected to heat treatment.

[0024] At this time, as shown in Figures 1(ii) and (iii), it is preferable to grow the AlN single crystal 18 over the entire AlN sintered body 14 in order to more effectively prevent the occurrence of cracks. However, as long as no cracks occur, the AlN single crystal 18 may be grown up to a certain point in the AlN sintered body 14, leaving a portion of the AlN sintered body 14 (in this case, it is desirable to remove the remaining portion of the AlN sintered body 14 by grinding or the like). By grinding and polishing the surface of the AlN single crystal 18 obtained in this way, a self-supporting AlN single crystal substrate 20 can be obtained.

[0025] AlN single crystal substrate According to a preferred embodiment of the present invention, an AlN single crystal substrate 20 manufactured by the method described above is also provided. This AlN single crystal substrate 20, even when manufactured in a large size (e.g., 100 mm or more in diameter), is not only free from cracks but also possesses good crystallinity and a low defect density. As mentioned above, the size of the AlN single crystal substrate 20 is preferably 100 mm or more in diameter, and more preferably 150 mm or more or 200 mm or more in diameter. There is no particular upper limit to the diameter of the AlN single crystal substrate 20, but the diameter of the AlN single crystal substrate 20 is typically 300 mm or less, and more typically 250 mm or less. The AlN single crystal substrate 20 is typically circular in shape. There is no particular limit to the thickness of the AlN single crystal substrate 20, but it is preferably 200 to 700 μm, more preferably 250 to 680 μm, and even more preferably 300 to 650 μm.

[0026] Good crystallinity can be evaluated by measuring the profiles of the X-ray rocking curves (hereinafter referred to as XRC) of the (002) plane and (102) plane of the AlN single crystal and using their full width at half maximum. Specifically, the XRC full width at half maximum of the (002) plane of the AlN single crystal on at least one surface of the AlN single crystal substrate 20 is preferably 20 to 350 arcsec, more preferably 100 to 300 arcsec, and even more preferably 100 to 280 arcsec. When a device is fabricated with the XRC full width at half maximum of the (002) plane within such a range, there is an advantage that the deposited film has no dislocations and good performance. Also, the XRC full width at half maximum of the (102) plane of the AlN single crystal on at least one surface of the AlN single crystal substrate 20 is preferably 20 to 500 arcsec, more preferably 200 to 450 arcsec, and even more preferably 200 to 400 arcsec. When a device is fabricated with the XRC full width at half maximum of the (102) plane within such a range, there is an advantage that the deposited film has no dislocations and good performance. The surface having the XRC full width at half maximum of the (102) plane within the above range is preferably the same surface as the surface having the XRC full width at half maximum of the (002) plane within the above range. Also, it is preferable that both surfaces of the AlN single crystal substrate 20 have the XRC full width at half maximum of the (102) plane and / or the XRC full width at half maximum of the (002) plane within the above range. The measurement of the XRC profiles of the (002) plane and (102) plane of the AlN single crystal can be performed based on the procedures described in the examples below using a general XRD apparatus (for example, D8 DISCOVER manufactured by Bruker-AXS) and the accompanying XRD analysis software (for example, "LEPTOS" Ver4.03 manufactured by Bruker-AXS).

[0027] The defect density on at least one surface of the AlN single crystal substrate 20 is 1.0×10 3 ~1.0×10 7 cm -2 which is preferably, more preferably is 1.0×10 6 ~8.0×10 6 cm -2 and even more preferably is 1.0×10 6 ~6.0×10 6 cm -2This is the case. Within this range, there is an advantage that when a device is fabricated, dislocations do not enter the deposited film, resulting in good performance. Preferably, the surface having a defect density within the above range is the same surface of the AlN single crystal substrate 20 as the surface having the XRC full width at half maximum of the (102) plane within the aforementioned numerical range and the surface having the XRC full width at half maximum of the (002) plane within the aforementioned numerical range. Furthermore, it is preferable that both sides of the AlN single crystal substrate 20 have a defect density within the above numerical range. The defect density can be measured based on the procedure described in the examples below.

[0028] device The AlN single crystal substrate 20 obtained by the manufacturing method of the present invention has the above-mentioned good crystallinity and low defect density, and is also suitable for large sizes, so it can be suitably used in various devices. Accordingly, according to a preferred embodiment of the present invention, a device equipped with the AlN single crystal substrate 20 is provided. Preferred examples of such devices include deep ultraviolet LEDs, ultraviolet lasers, power devices, MEMS devices, HMETs (high electron mobility transistors), and the like. [Examples]

[0029] The present invention will be further described in detail by the following examples. However, the present invention is not limited to the following examples.

[0030] Examples 1-11 (1) Fabrication of AlN sintered body Aluminum nitride powder (manufactured by Tokuyama Corporation, F grade), yttrium oxide powder (manufactured by Shin-Etsu Chemical Co., Ltd.), dysprosium oxide powder (manufactured by Shin-Etsu Chemical Co., Ltd.), and samarium oxide powder (manufactured by Nippon Yttrium Co., Ltd.) were prepared. The aluminum nitride powder was mixed with yttrium oxide powder (Examples 1-6 and 9-11), dysprosium oxide powder (Example 7), or samarium oxide powder (Example 8) in the weight ratios shown in Table 1 to obtain a blended powder. After uniaxial press molding of this blended powder, it was heated and pressurized to the maximum temperature and pressure shown in Table 1, and held at the maximum temperature and pressure for the time shown in Table 1 to perform hot press firing. Both sides of the obtained hot press fired body were mirror polished to obtain a plate-shaped AlN sintered body (AlN polycrystalline).

[0031] The average grain size of the obtained AlN sintered body was measured using the following procedure, and the results shown in Table 1 were obtained. (Measurement of average crystal grain size) The grain size of the sintered body was determined by mirror-polishing the cross-section of the sintered body, observing the microstructure in a 64 μm × 48 μm area at 2000x magnification using a SEM (JEOL Ltd., JSM-IT500LA), and determining it using the intercept method. Specifically, on the SEM image of the polished surface of the sintered body, any number of line segments with a length of 40 μm or more were drawn on the scale of the SEM image, and the number of crystal grains n intersected by these line segments was determined. If the end of a line segment was located within a crystal grain, that crystal grain was counted as 1 / 2. The average grain size (i.e., average intercept length) I was obtained by dividing the length L of the line segment by n, and the average sintered grain size was obtained by multiplying I by a coefficient of 1.5.

[0032] (2) Preparation of AlN templates by sublimation method A SiC substrate was placed in a crucible, which served as a crystal growth vessel, and AlN raw material powder was added so as not to come into contact with the SiC substrate. The growth vessel was pressurized at 50 kPa under an N2 atmosphere, and the portion of the growth vessel near the AlN raw material powder was heated to 2100°C by high-frequency induction heating, while the portion of the growth vessel near the SiC substrate was heated to a temperature 200°C lower (i.e., 1900°C). By holding the vessel at the above heating temperatures for 30 minutes, an AlN seed crystal was deposited on the SiC substrate. The surface of this AlN seed crystal was made mirror-finished to obtain a SiC substrate with an AlN seed crystal attached, which served as an AlN template.

[0033] (3) Bonding of the AlN sintered body to the AlN seed crystal and removal of the substrate The surfaces of the AlN sintered body and the AlN seed crystal side of the AlN template were activated by irradiating them with a high-speed Ar neutral atomic beam (acceleration voltage: 1kV, Ar flow rate: 60 sccm) for 70 seconds. The AlN sintered body and the AlN template were placed on top of each other so that the AlN sintered body and the AlN seed crystal were in contact, and a load of 1000N was applied under vacuum to bond the AlN sintered body and the AlN template. After removing the SiC substrate from the resulting bonded body by grinding with a #2000 grit grinding wheel, the surface was further smoothed by lapping with diamond abrasive grains to obtain an AlN bonded body consisting of the AlN sintered body and the AlN seed crystal. The AlN bonded body was disc-shaped, with a diameter of 100 mm in Examples 1-8 and 150 mm in Examples 9 and 10. The thickness of the AlN seed crystal was 2 μm in Examples 1-10 and 4 μm in Example 11. In all of Examples 1-11, the thickness of the AlN sintered body was 400 μm.

[0034] (4) Growth of AlN single crystals The resulting AlN bond was subjected to hot-press firing at 2160°C and 13 MPa for 40 hours in an N2 atmosphere, thereby growing AlN single crystals from AlN seed crystals throughout the entire AlN sintered body.

[0035] (5) Subsequent processes (grinding and polishing) Examples 1-5 and 7- 11In Example 0, by grinding and polishing the surface of the obtained AlN single crystal by a predetermined amount, a self-standing AlN single crystal substrate with a thickness of 0.3 mm was obtained. In Example 6, the surface of the AlN single crystal was also ground and polished in the same manner as above to obtain a self-standing AlN single crystal substrate with a thickness of 0.3 mm, but cracks occurred. In Example 12 In Example, the AlN single crystal cracked during the growth process, so grinding and polishing were not performed.

[0036] (6) Evaluation of AlN single crystal The following evaluations were performed on the obtained AlN single crystal.

[0037] (6a) Evaluation of production of AlN single crystal substrate The state of the AlN single crystal in the growth process (above (4)) and the post-process (above (5)) of the AlN single crystal was observed, and evaluation was performed based on the following criteria. The results were as shown in Table 1. · Evaluation A: The AlN single crystal grew without cracking. Also, the AlN single crystal did not crack in the post-process (grinding and polishing). · Evaluation B: The AlN single crystal grew without cracking. Cracks occurred in the AlN single crystal in the post-process (grinding and polishing), but it was judged that the cracks could be prevented by changing the conditions of the post-process to milder conditions. · Evaluation C: The AlN single crystal cracked during the growth process, and a self-standing AlN single crystal substrate could not be obtained.

[0038] (6b) X-ray rocking curve full width at half maximum Using a multifunctional high-resolution X-ray diffractometer (manufactured by Bruker-AXS, D8 DISCOVER), XRC measurement of the (002) plane of the surface of the AlN single crystal substrate (the surface opposite to the side where the AlN seed crystal was located) was performed. The conditions for this XRC measurement were as follows. [[ID=​​​​​​​​​CuKα lines converted to parallel monochromatic light (FWHM 28 arcseconds) using a Ge(O22) asymmetric reflection monochromator. Step width: 0.001° • Scan speed: 0.5 seconds / step

[0040] In practice, the AlN single crystal was oriented by adjusting 2θ, ω, χ, and φ to obtain peaks on the (002) plane. Then, measurements were taken in the range of ω = 14.5 to 19.5° using a 3 mm anti-scattering slit. The full width at half maximum (FWHM) of the obtained XRC profile of the (002) plane of the AlN single crystal was determined by performing a peak search after smoothing the profile using XRD analysis software (Bruker-AXS, "LEPTOS" Ver4.03). As a result, the FWHM of the (002) plane XRC profile on the surface of the AlN single crystal substrate is shown in Table 1.

[0041] XRC measurements were also performed on the (102) plane of the surface of the AlN single crystal substrate (the surface opposite to the side that was the AlN seed crystal). A Bruker-AXS D8-DISCOVER XRD system was used, and after adjusting 2θ, ω, χ, and φ to align the system so that the peak of the (102) plane of the AlN single crystal was obtained, measurements were taken with ω = 24.5 to 29.5°. Other conditions and analysis methods were the same as those for the (002) plane XRC measurements. As a result, the full width at half maximum of the (102) plane XRC profile of the surface of the AlN single crystal substrate is shown in Table 1.

[0042] (6c) Defect density The defect density of the obtained AlN single crystal substrate (on the surface opposite to the side that was the AlN seed crystal) was evaluated by measuring the entire surface area using X-ray topography (Rigaku Corporation, XRTmicron). Here, the defect density was 1.0 × 10⁻⁶. 5 cm -2In cases exceeding the above, accurate calculation of the number of etch pits is difficult using X-ray topography. Therefore, etch pit evaluation was performed using KOH melt etching, and the defect density on the surface of the AlN single crystal substrate was measured. Specifically, for etch pit evaluation, the surface of the AlN single crystal substrate was immersed for 5 minutes in a molten solution prepared by mixing KOH and NaOH in a weight ratio of 1:1 and heating it to 450°C. After etching, the defect density was measured using an optical microscope.

[0043] Example 12 (comparison) AlN single crystals were prepared by sublimation as described below, and then evaluated in the same manner as in Examples 1 to 11. The results are shown in Table 1.

[0044] (Fabrication of AlN single crystal substrates) A 100 mm diameter SiC substrate was placed in a crucible used as a crystal growth vessel, and AlN raw material powder was added so as not to come into contact with the SiC substrate. The growth vessel was pressurized at 50 kPa in an N2 atmosphere, and the portion of the growth vessel near the AlN raw material powder was heated to 2100°C by high-frequency induction heating, while the portion of the growth vessel near the SiC substrate was heated to a lower temperature of 200°C (i.e., 1900°C). By maintaining the above heating temperature for 10 hours, an AlN single crystal was deposited and grown on the SiC substrate. A SiC substrate with an AlN single crystal was obtained. After cooling, the AlN single crystal was examined and found to have cracks. Given the large difference in thermal expansion between the SiC substrate and the AlN single crystal, it is thought that the cracks occurred due to thermal stress caused by the difference in thermal expansion that occurred during cooling.

[0045] [Table 1]

Claims

1. A step of preparing an AlN bond composed of an AlN seed crystal and an AlN sintered body, A step of subjecting the AlN bond to heat treatment to grow an AlN single crystal from the AlN seed crystal, Includes, The step of preparing the AlN bond is, (a) A step of preparing an AlN sintered body, (b) A step of preparing an AlN template comprising an AlN seed crystal and a base substrate for supporting the AlN seed crystal, (c) A step of bonding the AlN sintered body to the AlN seed crystal of the AlN template, and removing the base substrate to obtain the AlN bonded body, A method for manufacturing an AlN single crystal substrate, including the method described above.

2. The AlN sintered body is (a1) A step of mixing AlN powder with a powder containing at least one rare earth element to produce a mixed powder with an AlN content of 95% by weight or more, (a2) A step of forming the mixed powder into a predetermined shape to produce a molded body, (a3) A step of firing the molded body to produce an AlN sintered body having an average crystal grain size of 1 to 40 μm, A method for manufacturing an AlN single crystal substrate according to claim 1, which is prepared by a method including the following.

3. The method for manufacturing an AlN single crystal substrate according to claim 2, wherein the average crystal grain size of the AlN sintered body is 1 to 10 μm.

4. The method for manufacturing an AlN single crystal substrate according to claim 1, wherein the step of growing an AlN single crystal from the AlN seed crystal includes growing an AlN single crystal throughout the entire AlN sintered body.

5. The method for manufacturing an AlN single crystal substrate according to any one of claims 1 to 4, wherein the AlN single crystal substrate has a diameter of 100 mm or more.

6. A method for manufacturing an AlN single crystal substrate according to any one of claims 1 to 4, wherein the full width at half maximum of the X-ray rocking curve of the (002) plane of the AlN single crystal on at least one surface of the AlN single crystal substrate is 20 to 350 arcsec.

7. A method for manufacturing an AlN single crystal substrate according to any one of claims 1 to 4, wherein the full width at half maximum of the X-ray rocking curve of the (102) plane of the AlN single crystal on at least one surface of the AlN single crystal substrate is 20 to 500 arcsec.

8. The defect density on at least one surface of the AlN single crystal substrate is 1.0 × 10⁻¹⁶ ３ ~1.0 x 10 ７ cm －２ The method for manufacturing an AlN single crystal substrate according to any one of claims 1 to 4.

9. The method for manufacturing an AlN single crystal substrate according to any one of claims 1 to 4, wherein the AlN seed crystal and the AlN sintered body in the AlN bonded body have the same diameter.

10. A method for manufacturing an AlN single crystal substrate according to any one of claims 1 to 4, wherein after performing steps (a), (b), and (c) in this order to prepare the AlN bond, the AlN bond is subjected to the heat treatment to grow the AlN single crystal from the AlN seed crystal.

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