Method for producing 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

AlN single crystal substrate manufacturing method and AlN single crystal substrate

[0001] The present disclosure relates to a method for manufacturing an AlN single crystal substrate and an AlN single crystal substrate.

[0002] In recent years, AlN single crystal substrates have been developed as base substrates for deep-ultraviolet LEDs. Sublimation deposition has been considered as a method for producing AlN single crystals. For example, Patent Document 1 (JP 2019-19042 A) discloses a method for producing AlN single crystals by using sublimation deposition to grow an AlN single crystal on a SiC seed substrate in at least two separate stages.

[0003] Japanese Patent Application Laid-Open No. 2019-19042

[0004] As described above, when producing an AlN single crystal by sublimation, cracks may occur due to the difference in thermal expansion coefficient 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 has been considered to perform sublimation using an AlN single crystal with a diameter of 50.8 mm (2 inches) instead of a SiC seed substrate. That is, the sublimation method has the characteristic that the size of the AlN single crystal increases gradually with each sublimation process. By utilizing this characteristic, it is possible to increase the diameter of the AlN single crystal substrate. However, this method requires repeated sublimation processes, for example, to produce an AlN single crystal with a diameter of 50.8 mm the first time, 60 mm the second time, 70 mm the third time, and so on, resulting in low productivity.

[0005] The present inventors have now discovered that by growing an AlN single crystal using an AlN bonded body 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 cracks, while still being a method suitable for increasing the diameter.

[0006] Therefore, an object of the present invention is to provide a method that is suitable for increasing the diameter and that is capable of producing AlN single crystal substrates with high productivity without causing cracks.

[0007] The present disclosure provides the following aspects. [Aspect 1] A method for producing an AlN single crystal substrate, comprising the steps of: preparing an AlN bonded body composed of an AlN seed crystal and an AlN sintered body; and growing an AlN single crystal from the AlN seed crystal by heat-treating the AlN bonded body. [Aspect 2] The method for producing an AlN single crystal substrate according to Aspect 1, wherein the AlN sintered body is prepared by a method comprising the steps of: (a1) mixing AlN powder with a powder containing at least one rare earth element to produce a mixed powder having an AlN content of 95% by weight or more, (a2) molding the mixed powder into a predetermined shape to produce a compact, and (a3) ​​sintering the compact to produce an AlN sintered body having an average crystal grain size of 1 to 40 μm. [Aspect 3] The method for producing an AlN single crystal substrate according to Aspect 1 or 2, wherein the step of growing an AlN single crystal from the AlN seed crystal comprises growing the AlN single crystal throughout the AlN sintered body. [Aspect 4] An AlN single crystal substrate produced by the method according to any one of Aspects 1 to 3. [Aspect 5] The AlN single crystal substrate according to Aspect 4, wherein the AlN single crystal substrate has a diameter of 100 mm or more. [Aspect 6] The AlN single crystal substrate according to Aspect 4 or 5, wherein the X-ray rocking curve half-width for 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 Aspects 4 to 6, wherein the X-ray rocking curve half-width for 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 x 10 ３ ~1.0 x 10 ７ cm －２ The AlN single crystal substrate according to any one of Aspects 4 to 7. [Aspect 9] A device comprising the AlN single crystal substrate according to any one of Aspects 4 to 8.

[0008] 1A to 1C are process diagrams showing an outline of a method for manufacturing an AlN single crystal substrate according to the present 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 bonded body 16 composed of an AlN seed crystal 12 and an AlN sintered body 14, and heat treating the AlN bonded body 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, yet is capable of manufacturing an AlN single crystal substrate 20 with high productivity and without causing cracks.

[0010] That is, as described above, when producing an AlN single crystal by sublimation, cracks may occur due to the difference in thermal expansion coefficient 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 has been considered to perform sublimation using an AlN single crystal with a diameter of 50.8 mm (2 inches) instead of the SiC seed substrate. However, this method requires repeated sublimation to increase the substrate size, resulting in low productivity. In this regard, the method of the present invention makes it possible to avoid such repeated sublimation processes with low productivity, thereby improving productivity. For example, sublimation is performed only to produce the AlN seed crystal 12, and then the AlN seed crystal 12 is transferred to an AlN sintered compact, and an AlN single crystal is grown from the AlN seed crystal in the region of the AlN sintered compact. In this way, it is sufficient to deposit the AlN seed crystal 12 by sublimation to a thickness large enough to prevent cracking even when the crystal is large (e.g., 100 mm or larger in diameter), and the subsequent growth of the AlN single crystal 18 from the AlN seed crystal 12 is achieved not by sublimation but by converting the AlN sintered body 14 (AlN polycrystalline body) into the AlN single crystal 18. Since the thermal expansion coefficients of the AlN seed crystal 12 and the AlN single crystal 18 are very similar, the possibility of cracking occurring due to differences in thermal expansion coefficients, as occurs when a SiC seed substrate is used, is extremely low. Therefore, according to the present invention, a large-sized (e.g., 100 mm or larger in diameter) AlN single crystal substrate 20 can be obtained with good quality without undergoing any process that is 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, the diameter of the AlN single crystal 18 can be reasonably increased. Therefore, although there is no particular upper limit on the diameter of the AlN single crystal substrate 20, 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 term "circular shape" does not necessarily mean a perfect circle, but may refer to a substantially 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).

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

[0013] (1) Preparation of 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 polycrystalline body and, therefore, a ceramic material composed of a plurality of AlN crystal grains 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 even 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 even more preferably 350 to 550 μm.

[0014] The AlN bonded body 16 may be prepared by any method as long as it is composed of the AlN seed crystal 12 and the 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)) of the AlN sintered body 14 is preferably carried out through (a1) preparation of the mixed powder, (a2) preparation of a molded body, and (a3) ​​sintering of the molded body, as described below. Note that the AlN sintered body 14 is not limited to a 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 prepare a mixed powder with an AlN content of 95 wt% or more. While the 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 contained in the powder in the form of oxide, carbonate, hydroxide, or composite oxide. Furthermore, the sintering aid is not limited to powder containing a rare earth element, but may also be powder containing an alkaline earth element such as Mg or Ca. The AlN content in the mixed powder is 95 wt% or more, typically 96 wt% or more, more typically 97 wt% or more, and even more typically 98 wt% 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 particularly preferably 0.5 to 2.0% by weight.

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

[0018] (a3) Sintering of the Molded Body The resulting molded body is sintered to produce an AlN sintered body 14 having an average crystal grain size of 1 to 40 μm. This sintering is preferably performed by hot-press sintering, which involves holding the molded body at a predetermined sintering temperature and under a predetermined pressure for a predetermined time. The sintering temperature in the hot-press sintering 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 sintering temperature (i.e., the sintering 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 the hot-press sintering 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 grain size of the multiple AlN crystal grains 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 may be measured based on the method described in the examples below.

[0019] (b) Preparation of AlN Template As shown in FIG. 1( i), an AlN template 13 is prepared. The AlN template 13 is a composite material including an AlN seed crystal 12 and a base substrate 10 supporting the AlN seed crystal 12. The base substrate 10 is preferably one on which the AlN seed crystal 12 can be grown. Preferred examples of such a base substrate 10 include a SiC substrate, a sapphire substrate, and a Si substrate. The AlN seed crystal 12 is preferably grown on the base substrate 10 by a vapor deposition method. Examples of vapor deposition methods include sublimation deposition, chemical vapor deposition (CVD), sputtering, and hydride vapor phase epitaxy (HVPE), with sublimation deposition being preferred.

[0020] (c) Bonding of the AlN Sintered Body to the AlN Seed Crystal and Removal of the Underlying Substrate As shown in FIGS. 1(i) and 1(ii), the AlN sintered body 14 is bonded to the AlN seed crystal 12 of the obtained AlN template 13, and the undersubstrate 10 is removed to obtain an AlN bonded body 16. This bonding may be performed by surface activation or 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 surfaces of the AlN seed crystal 12 and the AlN sintered body 14 are activated. The surface activation can be performed by irradiating them with a neutralizing beam such as an Ar beam. Then, the AlN template 13 and the AlN sintered body 14 are stacked 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 20,000 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 by a known method such as grinding or reactive ion etching (RIE).

[0021] To perform surface activation using the neutralization beam described above, an inert gas is introduced into the chamber and a high voltage is applied from a DC power supply to an electrode disposed within the chamber. With this configuration, an electric field generated between the electrode (positive electrode) and the chamber (negative electrode) causes electrons to move, generating a beam of atoms and ions from the inert gas. Of the beams reaching the grid, the ion beam is neutralized by the grid, resulting in a beam of neutral atoms being emitted from the fast atom 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 Crystal As shown in Figures 1(ii) and 1(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 the 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 uses a SiC seed substrate with a different thermal expansion coefficient from the AlN single crystal and is therefore prone to cracking, this method of growing the AlN single crystal 18 uses a SiC seed substrate with a different thermal expansion coefficient from the AlN single crystal, but because the thermal expansion coefficients of the AlN seed crystal 12 and the AlN single crystal 18 are significantly closer, the AlN single crystal 18 can be grown to a desired thickness without worrying about cracking, even when the crystal is large (e.g., 100 mm or larger in diameter). This heat treatment is preferably performed in an inert gas atmosphere such as nitrogen. The preferred firing temperature in the heat treatment is 2000 to 2300°C, more preferably 2100 to 2250°C, and even more preferably 2150 to 2200°C. The holding time at the 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 performed by atmospheric firing or hot press firing. The press load during the 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 the heat treatment.

[0024] 1(ii) and 1(iii), it is preferable to grow the AlN single crystal 18 over the entire AlN sintered body 14, as this more effectively prevents cracks from occurring. However, as long as cracks do not occur, the AlN single crystal 18 may be grown partway through 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 manner, a free-standing 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 above-described method is also provided. Even when fabricated in a large size (e.g., a diameter of 100 mm or more), this AlN single crystal substrate 20 is not only free from cracks but also has good crystallinity and a low defect density. As described above, the size of the AlN single crystal substrate 20 is preferably 100 mm or more in diameter, more preferably 150 mm or more or 200 mm or more in diameter. While there is no particular upper limit to the diameter of the AlN single crystal substrate 20, 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. Although there is no particular limit to the thickness of the AlN single crystal substrate 20, 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 X-ray rocking curve (hereinafter referred to as XRC) profile of the (002) or (102) plane of the AlN single crystal and measuring the half-width. Specifically, the XRC half-width 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. An XRC half-width of the (002) plane within this range has the advantage that, when a device is fabricated, the formed film does not introduce dislocations and therefore has good performance. Furthermore, the XRC half-width 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. An XRC half-width of the (102) plane within this range has the advantage that, when a device is fabricated, the formed film will not introduce dislocations and will have good performance. It is preferable that the surface having the XRC half-width of the (102) plane within the above range is the same surface as the surface having the XRC half-width of the (002) plane within the above range. It is also preferable that both surfaces of the AlN single crystal substrate 20 have the XRC half-width of the (102) plane within the above range and / or the XRC half-width of the (002) plane within the above range. Measurement of the XRC profiles of the (002) and (102) planes of the AlN single crystal can be performed using a common 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) based on the procedures described in the Examples below.

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

[0028] 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, making it suitable for use in a variety of devices. Therefore, according to a preferred embodiment of the present invention, a device including the AlN single crystal substrate 20 is provided. Preferred examples of such devices include deep ultraviolet LEDs, ultraviolet lasers, power devices, MEMS devices, and HMETs (high electron mobility transistors).

[0029] The present invention will be explained in more detail by the following examples, but the present invention is not limited to the following examples.

[0030] Examples 1 to 11 (1) Preparation of AlN Sintered Body Aluminum nitride powder (Tokuyama Corporation, F grade), yttrium oxide powder (Shin-Etsu Chemical Co., Ltd.), dysprosium oxide powder (Shin-Etsu Chemical Co., Ltd.), and samarium oxide powder (Nippon Yttrium Co., Ltd.) were prepared. Aluminum nitride powder was mixed with yttrium oxide powder (Examples 1 to 6 and 9 to 11), dysprosium oxide powder (Example 7), or samarium oxide powder (Example 8) in the weight ratios shown in Table 1 to obtain blended powders. This blended powder was subjected to uniaxial press molding, followed by heating and pressurization to the maximum temperature and maximum pressure shown in Table 1, and hot-press sintering was performed by holding the maximum temperature and maximum pressure for the time shown in Table 1. Both sides of the obtained hot-press sintered body were mirror-polished to obtain a plate-shaped AlN sintered body (AlN polycrystalline).

[0031] The average crystal grain size of the obtained AlN sintered body was measured using the following procedure, and the results are shown in Table 1. (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 an area of ​​64 μm × 48 μm at 2000x magnification using an SEM (JSM-IT500LA, manufactured by JEOL Ltd.), and using the intercept method. Specifically, an arbitrary number of line segments 40 μm or longer in length were drawn on the scale of an SEM image of the polished surface of the sintered body, and the number n of crystal grains crossed by these line segments was determined. Note that if the end of a line segment was located within a crystal grain, that crystal grain was counted as 1 / 2. The value obtained by dividing the length L of the line segment by n was defined as the average crystal grain size (i.e., the average intercept length) I, and the value obtained by multiplying I by a coefficient of 1.5 was defined as the average sintered grain size.

[0032] (2) Preparation of AlN template by sublimation method A SiC substrate was placed as a base material in a crucible serving as a crystal growth vessel, and AlN raw material powder was placed therein so as not to come into contact with the SiC substrate. ２ The pressure was increased to 50 kPa under atmospheric pressure, 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). The above heating temperature was maintained for 30 minutes, thereby forming an AlN seed crystal on the SiC substrate. The surface of this AlN seed crystal was polished to a mirror finish, and an AlN seed crystal-attached SiC substrate was obtained as an AlN template.

[0033] (3) Bonding of the AlN sintered body to the AlN seed crystal and removal of the base substrate. The surface of the AlN sintered body and the surface of the AlN seed crystal side of the AlN template 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 sintered body and the AlN template were overlapped so that the AlN sintered body and the AlN seed crystal were in contact, and a load of 1000 N was applied under vacuum to bond the AlN sintered body and the AlN template. The SiC substrate was removed from the resulting bonded body by grinding using a #2000 grindstone, and the surface was further smoothed by lapping using 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 disk-shaped, with a diameter of 100 mm in Examples 1 to 8 and 150 mm in Examples 9 and 10. The thickness of the AlN seed crystal was 2 μm in Examples 1 to 10 and 4 μm in Example 11. In all of Examples 1 to 11, the thickness of the AlN sintered body was 400 μm.

[0034] (4) Growth of AlN single crystals. ２ The AlN single crystal was grown from the AlN seed crystal over the entire AlN sintered body by performing hot press sintering for 40 hours under conditions of 2160° C. and 13 MPa in an atmosphere.

[0035] (5) Post-Processing (Grinding and Polishing) In Examples 1 to 5 and 7 to 10, the surface of the obtained AlN single crystal was ground and polished by a predetermined amount to obtain a free-standing AlN single crystal substrate having a thickness of 0.3 mm. In Example 6, the surface of the AlN single crystal was ground and polished in the same manner as above to obtain a free-standing AlN single crystal substrate having a thickness of 0.3 mm, but cracks occurred. In Example 11, the AlN single crystal cracked during the growth process, so grinding and polishing were not performed.

[0036] (6) Evaluation of AlN Single Crystal The obtained AlN single crystal was evaluated as follows.

[0037] (6a) Evaluation of AlN single crystal substrate fabrication The state of the AlN single crystal was observed during the AlN single crystal growth process ((4) above) and the post-process ((5) above), and was evaluated based on the following criteria. The results are shown in Table 1. - Evaluation A: The AlN single crystal grew without cracking. Furthermore, 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 during the post-process (grinding and polishing), but it was determined that the cracks could be prevented by changing the conditions for the post-process to milder conditions. - Evaluation C: The AlN single crystal cracked during growth, and a free-standing AlN single crystal substrate could not be obtained.

[0038] (6b) X-ray rocking curve half-width: XRC measurement was performed on the (002) plane of the surface of the AlN single crystal substrate (the surface opposite to the AlN seed crystal) using a multifunctional high-resolution X-ray diffractometer (D8 DISCOVER, manufactured by Bruker-AXS). The conditions for this XRC measurement were as follows:

[0039] <XRD measurement conditions> Tube voltage: 40 kV Tube current: 40 mA Detector: Triple Ge (220) Analyzer CuKα rays collimated monochromated (half width 28 seconds) by a Ge (022) asymmetric reflection monochromator Step width: 0.001° Scan speed: 0.5 seconds / step

[0040] In practice, the axis was adjusted by adjusting 2θ, ω, χ, and φ so that the peak of the (002) plane of the AlN single crystal was obtained, and then measurements were made over the range of ω = 14.5 to 19.5° with an anti-scattering slit of 3 mm. The half-width of the XRC profile of the (002) plane of the obtained AlN single crystal was determined by smoothing the profile and then performing a peak search using XRD analysis software ("LEPTOS" Ver. 4.03, manufactured by Bruker-AXS). As a result, the half-width of the XRC profile of the (002) plane of the surface of the AlN single crystal substrate was as 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 was used as the XRD device, and after adjusting 2θ, ω, χ, and φ to obtain the peak of the (102) plane of the AlN single crystal, measurements were performed at ω = 24.5 to 29.5°. Other conditions and analytical methods were the same as those used in the XRC measurements of the (002) plane. As a result, the half-widths of the XRC profiles of the (102) plane of the AlN single crystal substrate surface were as shown in Table 1.

[0042] (6c) Defect Density The defect density of the obtained AlN single crystal substrate (the surface opposite to the side that was the AlN seed crystal) was evaluated by measuring the entire area of ​​the surface by X-ray topography (XRTmicron, manufactured by Rigaku Corporation). ５ cm －２ In cases where the number of etch pits was more than this, it was difficult to accurately calculate the number of etch pits using X-ray topography, so etch pit evaluation was performed using KOH melt etching to measure the defect density on the surface of the AlN single crystal substrate. Specifically, for the etch pit evaluation, the surface of the AlN single crystal substrate was immersed for 5 minutes in a melt prepared by mixing KOH:NaOH in a weight ratio of 1:1 and heating to 450°C, and then etching was performed, after which the defect density was measured using an optical microscope.

[0043] Example 12 (Comparative) An AlN single crystal was produced by sublimation as follows, and then evaluated in the same manner as in Examples 1 to 11. The results are shown in Table 1.

[0044] (Preparation of AlN Single Crystal Substrate) A SiC substrate having a diameter of 100 mm was placed as a base material in a crucible serving as a crystal growth vessel, and AlN raw material powder was placed therein so as not to come into contact with the SiC substrate. ２The pressure was increased to 50 kPa under atmospheric pressure, 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 maintaining this heating temperature for 10 hours, an AlN single crystal was precipitated and grown on the SiC substrate. A SiC substrate with an AlN single crystal was obtained. After cooling, the AlN single crystal was inspected and found to have cracks. Because there is a large difference in thermal expansion between the SiC substrate and the AlN single crystal, it is believed that the cracks were caused by thermal stress resulting from the difference in thermal expansion during cooling.

[0045]

Claims

1. A method for manufacturing an AlN single crystal substrate, comprising: a step of preparing an AlN bonded body composed of an AlN seed crystal and an AlN sintered body; and a step of subjecting the AlN bonded body to a heat treatment to grow an AlN single crystal from the AlN seed crystal.

2. The method for producing an AlN single crystal substrate according to claim 1, wherein the AlN sintered body is prepared by a method comprising the steps of: (a1) mixing AlN powder with a powder containing at least one rare earth element to produce a mixed powder having an AlN content of 95% by weight or more; (a2) forming the mixed powder into a predetermined shape to produce a molded body; and (a3) ​​sintering the molded body to produce an AlN sintered body having an average crystal grain size of 1 to 40 μm.

3. The method for producing 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 the AlN single crystal over the entire AlN sintered body.

4. An AlN single crystal substrate manufactured by the method according to any one of claims 1 to 3.

5. The AlN single crystal substrate according to claim 4, wherein the AlN single crystal substrate has a diameter of 100 mm or more.

6. The AlN single crystal substrate according to claim 4, wherein the X-ray rocking curve half-width 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. The AlN single crystal substrate according to claim 4, wherein the half-width of an 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 ３ ~1.0 x 10 ７ cm －２ The AlN single crystal substrate according to claim 4 , 9. A device comprising the AlN single crystal substrate according to claim 4.

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