AlN SINGLE CRYSTAL SUBSTRATE AND DEVICE

Abstract

To provide an AlN single crystal substrate having a low absorption coefficient at a wavelength of 265 nm and hardly causing a chipping.SOLUTION: An AlN single crystal substrate is composed of an AlN single crystal, and has a disk-like shape with a diameter of 50 mm or more. The AlN single crystal substrate is specified when at least one first virtual line with a length of 40 mm can be drawn on a surface of the AlN single crystal substrate such that a maximum absorption coefficient at all measurement points is 25 cm-1 or less and a difference between the maximum value and a minimum value of the absorption coefficient in all measurement points is 5 cm-1 or less when the absorption coefficient is measured with a wavelength of 265 nm at multiple measurement points at a 4 mm interval on the first virtual line, and an above condition is satisfied when at least one second virtual line that is orthogonal to the first virtual line and 40 mm in length can be drawn on a surface of the AlN single crystal substrate when the absorption coefficient is measured with a wavelength of 265 nm at multiple measurement points at a 4 mm interval on the second virtual line.SELECTED DRAWING: Figure 1

Description

[Technical Field]

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

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

[0003] Patent Document 1 (WO2023 / 181258) discloses an AlN single crystal substrate that is less likely to crack when processed. This AlN single crystal substrate has a thermal conductivity (W / m K) at 25°C of λ 25 , the thermal conductivity (W / m K) of the AlN single crystal substrate at 200°C is λ 200 , the electrical resistivity (Ω·cm) of the AlN single crystal substrate at 25°C is ρ, and the average transmittance (%) in the range of 640 to 660 nm in the transmission spectrum of the AlN single crystal substrate is T 640-660 The average transmittance (%) in the transmission spectrum from 260 to 280 nm is T 260-280 Then, 5≦[(λ 25 -λ 200 )×log 10 ρ] / (T 640-660 -T 260-280 )≦50. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] WO2023 / 181258A1 [Non-patent literature]

[0005] [Non-Patent Document 1] A website article titled "Reflectance and transmittance due to multiple reflections of light" from "Basic Terms in Optical Technology - A website explaining terms related to light and optics" (available as of February 20, 2024 at the URL: https: / / www.optics-words.com / kogaku_kiso / multiple_reflection.html) Summary of the Invention

[0006] When using an AlN single crystal substrate for an LED that emits light in the ultraviolet region, a high transmittance (i.e., a low absorption coefficient) in the ultraviolet region is desired. Therefore, an AlN single crystal substrate with a low absorption coefficient in the ultraviolet region is desired. However, to increase the device yield in LED manufacturing, the AlN single crystal substrate must not only have a low absorption coefficient, but also have little chipping (defects such as chips and cracks).

[0007] The present inventors have now discovered that an AlN single crystal substrate in which the absorption coefficient at a wavelength of 265 nm measured at multiple measurement points spaced 4 mm apart on two imaginary line segments that intersect at right angles satisfies certain conditions is less likely to suffer from chipping (defects such as chips and cracks).

[0008] Therefore, an object of the present invention is to provide an AlN single crystal substrate that has a low absorption constant at a wavelength of 265 nm and is resistant to chipping (defects such as chips and cracks).

[0009] According to the present disclosure, the following aspects are provided. [Aspect 1] An AlN single crystal substrate that is made of AlN single crystal and has a disk shape with a diameter of 50 mm or more, When at least one first imaginary line segment having a length of 40 mm is formed on the surface of the AlN single crystal substrate and the absorption coefficient at a wavelength of 265 nm is measured at a plurality of measurement points spaced 4 mm apart on the first imaginary line segment, the maximum absorption coefficient at all measurement points is 25 cm -1The difference between the maximum and minimum absorption coefficients among all measurement points is 5cm or less. -1 It can be drawn so that it is within When a second imaginary line segment having a length of 40 mm, which is perpendicular to the at least one first imaginary line segment, is formed on the surface of the AlN single crystal substrate, and the absorption coefficient at a wavelength of 265 nm is measured at a plurality of measurement points spaced 4 mm apart on the second imaginary line segment, the maximum value of the absorption coefficient at all measurement points is 25 cm -1 The difference between the maximum and minimum absorption coefficients among all measurement points is 5cm or less. -1 The AlN single crystal substrate can be identified by its ability to be drawn within the specified range. [Aspect 2] The difference between the maximum and minimum absorption coefficients among all the measurement points on the first virtual line segment is 3 cm. -1 and the difference between the maximum and minimum absorption coefficients among all the measurement points on the second virtual line segment is 3 cm or less. -1 2. The AlN single crystal substrate according to embodiment 1, wherein the AlN single crystal substrate is within the range of 0.1 to 1.5 μm. [Aspect 3] The maximum absorption coefficient at all measurement points on the first virtual line segment is 15 cm -1 or less, and the maximum value of the absorption coefficient at all measurement points on the second virtual line segment is 15 cm -1 3. The AlN single crystal substrate according to aspect 1 or 2, wherein: [Aspect 4] 4. The AlN single crystal substrate according to any one of aspects 1 to 3, wherein the AlN single crystal substrate is in the shape of a disk having a diameter of 100 mm or more. [Aspect 5] A device comprising the AlN single crystal substrate according to any one of embodiments 1 to 4. [Brief explanation of the drawings]

[0010] [Figure 1] 1 is a schematic top view showing a virtual first virtual line segment and a virtual second virtual line segment on an AlN single crystal substrate. FIG. [Figure 2] FIG. 10 is a conceptual diagram for explaining the transmittance of multiple reflections when light is absorbed. [Figure 3]FIG. 1 is a schematic cross-sectional view showing the configuration of a heat treatment apparatus used to produce AlN raw material powder. [Figure 4] FIG. 1 is a schematic cross-sectional view showing the configuration of a crystal growth apparatus used in a sublimation method. DETAILED DESCRIPTION OF THE INVENTION

[0011] AlN single crystal substrate The AlN single crystal substrate according to the present invention is a disk-shaped substrate made of AlN single crystal and having a diameter of 50 mm or more. Figure 1 shows an example of an AlN single crystal substrate. As shown in Figure 1, when the AlN single crystal substrate 1 has at least one first imaginary line segment L1 with a length of 40 mm on its surface 1a, and the absorption coefficient at a wavelength of 265 nm is measured at a plurality of measurement points on the first imaginary line segment L1 at 4 mm intervals, (a1) the maximum value of the absorption coefficient at all measurement points is 25 cm -1 (a2) The difference between the maximum and minimum absorption coefficients among all measurement points is 5 cm or less. -1 Furthermore, when at least one second imaginary line segment L2 having a length of 40 mm that is perpendicular to the first imaginary line segment L1 is drawn on the same surface 1a of the AlN single crystal substrate 1 and the absorption coefficient at a wavelength of 265 nm is measured at a plurality of measurement points spaced 4 mm apart on the second imaginary line segment L2, (b1) the maximum value of the absorption coefficient at all measurement points is 25 cm -1 (b2) The difference between the maximum and minimum absorption coefficients among all measurement points is 5 cm or less. -1 In this way, if the AlN single crystal substrate has an absorption coefficient at a wavelength of 265 nm that satisfies the specified conditions, measured at multiple measurement points spaced 4 mm apart on two imaginary line segments L1 and L2 that are perpendicular to each other, it will have a low absorption constant at a wavelength of 265 nm and will be less susceptible to chipping (defects such as chips and cracks).

[0012] That is, as mentioned above, there is a demand for an AlN single crystal substrate that has a low absorption coefficient in the ultraviolet region. However, in order to increase the yield of devices in LED manufacturing, an AlN single crystal substrate is required to have not only a low absorption coefficient but also little chipping (defects such as chips and cracks). In this regard, the present invention overcomes such problems and provides an AlN single crystal substrate that has a low absorption coefficient and is less likely to suffer from chipping (defects such as chips and cracks). That is, the above-mentioned conditions (a1) and (b1) are satisfied when, for each of a first imaginary line segment L1 and a second imaginary line segment L2 that are perpendicular to each other, when the absorption coefficient at a wavelength of 265 nm is measured at multiple measurement points on the imaginary line segment L1 or L2 at 4 mm intervals, the maximum absorption coefficient at all measurement points on each imaginary line segment L1 or L2 is 25 cm. -1 The above conditions (a2) and (b2) are satisfied when the difference between the maximum and minimum values ​​of the absorption coefficients among all measurement points on the first imaginary line segment L1 and the second imaginary line segment L2, which are perpendicular to each other, is 5 cm or less. -1 This means that the absorption coefficient is within the specified range, which leads to a small in-plane variation in the absorption coefficient. Furthermore, according to the findings of the present inventors, a small in-plane variation in the absorption coefficient reduces chipping. For example, this reduces the probability of cracking or chipping occurring in later processes (such as in the LED manufacturing process) using an AlN single crystal substrate. In this regard, an AlN single crystal substrate with a low absorption coefficient means that it has few defects, and if there are many defects, it can be said that cracking is more likely to occur. Therefore, by using an AlN single crystal substrate with a low absorption coefficient and a small in-plane variation in the absorption coefficient, it is possible to increase the yield of devices in LED manufacturing.

[0013] As described above, the AlN single crystal substrate according to the present invention is characterized by the fact that at least one first imaginary line segment L1 having a length of 40 mm and a second imaginary line segment L2 having a length of 40 mm that intersects the at least one first imaginary line segment L1 at right angles can be virtually drawn on the surface 1a of the AlN single crystal substrate 1 so as to satisfy the above conditions (a1), (a2), (b1), and (b2). The above conditions (a1), (a2), (b1), and (b2) are based on the results of measuring the absorption coefficient at a wavelength of 265 nm at multiple measurement points spaced 4 mm apart on the first imaginary line segment L1 or the second imaginary line segment L2, both of which are orthogonal to each other and have a length of 40 mm.

[0014] Condition (a1) is that the maximum value of the absorption coefficient at all measurement points on the first virtual line segment L1 is 25 cm -1 It is preferably 20cm or less. -1 Less than 15cm, more preferably -1 Such a low absorption coefficient at a wavelength of 265 nm makes it possible to achieve high transmittance in the ultraviolet region. Therefore, the lower the absorption coefficient at a wavelength of 265 nm, the better. There is no particular lower limit, but it is typically 1 cm -1 Over 3 cm, more typically -1 That's all.

[0015] Condition (a2) is that the difference between the maximum and minimum absorption coefficients among all measurement points on the first virtual line segment L1 is 5 cm. -1 Within 3cm, preferably -1 Such a small difference between the maximum and minimum values ​​of the absorption coefficient, coupled with the similar condition (b2) for the second imaginary line segment L2, leads to small in-plane variations in the absorption coefficient, resulting in less chipping.

[0016] Condition (b1) is that the maximum value of the absorption coefficient at all measurement points on the second virtual line segment L2 is 25 cm -1 It is preferably 20cm or less. -1 Less than 15cm, more preferably -1Such a low absorption coefficient at a wavelength of 265 nm makes it possible to achieve high transmittance in the ultraviolet region. Therefore, the lower the absorption coefficient at a wavelength of 265 nm, the better. There is no particular limit to the lower limit, but it is typically 1 cm -1 Over 3 cm, more typically -1 That's all.

[0017] Condition (b2) is that the difference between the maximum and minimum absorption coefficients among all measurement points on the second virtual line segment L2 is 5 cm. -1 Within 3cm, preferably -1 Such a small difference between the maximum and minimum values ​​of the absorption coefficient, coupled with the similar condition (a2) regarding the first imaginary line segment L1, leads to small in-plane variations in the absorption coefficient, resulting in less chipping.

[0018] The absorption coefficient at a wavelength of 265 nm can be calculated by measuring the total light transmittance and total reflectance of the AlN single crystal substrate with a spectrophotometer, measuring the thickness of the AlN single crystal substrate, and then using the obtained measurement results while taking multiple reflections (see, for example, Non-Patent Document 1) into consideration.

[0019] Calculation of the absorption coefficient α taking multiple reflections into account is common technical knowledge, as detailed in general literature such as Non-Patent Document 1, but a supplementary explanation is provided below just to be sure. Figure 2 shows a conceptual diagram for explaining multiple reflections when light is absorbed. Note that in Figure 2, for convenience, light is depicted as being incident obliquely on the surface of the material, but it is assumed that the light is incident perpendicularly. In Figure 2 and the following explanation, I0 is the intensity of the incident light, R1 is the reflectance of the surface of the substrate, R2 is the reflectance of the back surface of the substrate, l is the thickness of the substrate (cm), and α is the absorption coefficient (cm -1 As can be seen from FIG. 2, the sum I of the light intensities of the transmitted light is expressed by the following formula:

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[0020] The size of the AlN single crystal substrate is 50 mm or more in diameter, preferably 100 mm or more, and more preferably 150 mm or more or 200 mm or more in diameter. Increasing the area of ​​the AlN single crystal substrate in this way allows for a larger area of ​​the semiconductor layer formed thereon. This makes it possible to obtain a large number of semiconductor devices from a single semiconductor layer, which is expected to reduce manufacturing costs. While there is no particular upper limit on the diameter of the AlN single crystal substrate, the diameter of the AlN single crystal substrate is typically 300 mm or less, more typically 250 mm or less. AlN single crystal substrates typically have a circular shape. In this specification, the term "circular shape" does not necessarily refer to a perfect circle, but may refer to a roughly circular shape that can be recognized as a circle overall. For example, the shape may be a shape in which a portion of the circle is cut out for identifying the crystal orientation or for other purposes (e.g., a circular shape including an orientation flat or a notch).

[0021] The thickness of the AlN single crystal substrate is 100 μm or more, preferably 200 to 700 μm, more preferably 250 to 680 μm, and even more preferably 300 to 650 μm.

[0022] The AlN single crystal substrate of the present invention is preferably an oriented layer oriented in both the c-axis and a-axis directions, and may contain mosaic crystals. Mosaic crystals are a collection of crystals that do not have clear grain boundaries but whose orientation slightly differs from one or both of the c-axis and a-axis. Such an oriented layer has a structure in which the crystal orientation is generally aligned in the approximately normal direction (c-axis direction) and the in-plane direction (a-axis direction). This structure makes it possible to form a semiconductor layer thereon with excellent quality, particularly excellent orientation. In other words, when a semiconductor layer is formed on an oriented layer, the crystal orientation of the semiconductor layer generally follows the crystal orientation of the oriented layer. Therefore, it is easy to form a semiconductor film on an AlN single crystal substrate as an oriented film.

[0023] Manufacturing method The AlN single crystal substrate of the present invention can be produced by various methods as long as the aforementioned CL spectrum and Raman spectrum conditions are met. A seed substrate may be prepared and epitaxially grown thereon, or an AlN single crystal substrate may be produced directly by spontaneous nucleation without using a seed substrate. The seed substrate used may be an AlN substrate to achieve homoepitaxial growth, or a different substrate may be used for heteroepitaxial growth. While vapor-phase deposition, liquid-phase deposition, or solid-phase deposition may be used to grow the single crystal, vapor-phase deposition is preferred, followed by grinding away the seed substrate as needed to obtain the desired AlN single crystal substrate. Examples of vapor-phase deposition methods include various CVD (chemical vapor deposition) methods (e.g., thermal CVD, plasma CVD, MOVPE, etc.), sputtering, hydride vapor phase epitaxy (HVPE), molecular beam epitaxy (MBE), sublimation, and pulsed laser deposition (PLD), with sublimation and HVPE being preferred. Examples of liquid-phase deposition methods include solution growth (e.g., flux deposition). It is also possible to obtain an AlN single crystal substrate without directly depositing an AlN single crystal on a seed substrate by forming an oriented precursor layer, converting the oriented precursor layer into an AlN single crystal layer by heat treatment, and polishing the seed substrate. Examples of methods for forming the oriented precursor layer include aerosol deposition (AD) and supersonic plasma particle deposition (HPPD).

[0024] Although known conditions can be used for any of the above-mentioned solid-phase deposition, vapor-phase deposition, and liquid-phase deposition methods, the following describes a method for producing an AlN single crystal substrate using, for example, sublimation deposition. Specifically, the substrate is produced by (a) heat-treating AlN polycrystalline powder, (b) depositing an AlN single crystal layer, and (c) grinding off the seed substrate and polishing the surface of the AlN single crystal layer.

[0025] (a) Heat treatment of AlN polycrystalline powder This process heat-treats AlN polycrystalline powder to obtain AlN raw material powder. As shown in FIG. 3, AlN powder 12, the raw material for AlN single crystal, is placed in sheath 10 and heat-treated in a N2 atmosphere. At this time, graphite powder 14 and metal oxide (Y2O3, CaO, CeO2, Yb2O3, Sm2O3, etc.) powder 15 are placed in separate crucibles 16 and 17 so as not to directly contact the AlN powder 12. These crucibles 16 and 17 are large enough to fit within sheath 10. By appropriately adjusting the contents of graphite and metal oxide, an AlN single crystal substrate satisfying the aforementioned relationships for transmittance, thermal conductivity, and electrical resistivity can be fabricated. The pressure inside the sheath 10 is preferably 0.1 to 10 atmospheres, more preferably 0.5 to 5 atmospheres. The heat treatment temperature is preferably 1900°C to 2300°C, more preferably 2000 to 2200°C. Preferred examples of materials for forming the sheath and the crucible include tantalum carbide, tungsten, molybdenum, and boron nitride (BN), and more preferred is BN.

[0026] (b) Deposition of an AlN single crystal layer This process is a process of forming an AlN single crystal film on a seed substrate in a crystal growth apparatus. An example of a crystal growth apparatus used in the sublimation method is shown in FIG. 4. The film formation apparatus 20 shown in FIG. 4 includes a crucible 22, a heat insulator 24 for insulating the crucible 22, and a coil 26 for heating the crucible 22 to a high temperature. The crucible 22 contains AlN raw material powder 28 in its lower part and includes a seed substrate 30 on which a sublimate of the AlN raw material powder 28 is deposited in its upper part. The interior of the crucible 22 is pressurized in an N2 atmosphere, and the crucible 22 is heated by the coil 26 to sublimate the AlN raw material powder 28. The pressure is preferably 10 to 100 kPa, and more preferably 20 to 90 kPa. At this time, a temperature gradient is created so that the temperature in the vicinity of the seed substrate 30 in the upper part of the crucible 22 is lower than the temperature in the vicinity of the AlN raw material powder 28 in the lower part of the crucible 22. For example, the portion of the crucible 22 near the AlN raw material powder 28 is preferably heated to 1900 to 2250°C, more preferably 2000 to 2200°C, and the portion of the crucible 22 near the seed substrate 30 is preferably heated to 1400 to 2150°C, more preferably 1500 to 2050°C. At this time, the temperature of the portion near the seed substrate 30 is preferably 100 to 500°C lower than the portion near the AlN raw material powder 28, more preferably 200 to 400°C. The heating is preferably maintained for 2 to 100 hours, more preferably 4 to 90 hours. Temperature control can be performed by measuring the temperatures of the upper and lower parts of the crucible 22 with radiation thermometers (not shown) through holes in the heat insulating material 24 covering the crucible 22 and feeding the measured temperatures back into the temperature control. In this way, a SiC single crystal is placed as the seed substrate 30, and AlN is re-precipitated on its surface to form an AlN single crystal layer 32.

[0027] (c) Grinding and removing the seed substrate and polishing the surface of the AlN single crystal layer This process includes a grinding step to remove the seed substrate and expose the AlN single crystal layer, and a polishing step to remove irregularities and defects on the AlN single crystal surface. Since the AlN single crystal layer fabricated using a SiC substrate as the seed substrate through steps (a) and (b) still contains residual SiC single crystals, the surface of the AlN single crystal layer is exposed by grinding. To achieve a mirror finish on the surface of the deposited AlN single crystal layer, the substrate surface is smoothed by lapping using diamond abrasive grains, followed by chemical mechanical polishing (CMP) using colloidal silica or similar. The CMP removal amount (the reduction in AlN thickness due to CMP) is preferably 0.2 μm or more, more preferably 0.5 to 5 μm. Increasing the CMP removal amount in this way sufficiently reduces residual stress or defects near the surface, resulting in a reduction in the absorption coefficient in the ultraviolet range, a reduction in the in-plane variation in the absorption coefficient, and ultimately, the suppression of chipping. In this way, an AlN single crystal substrate can be fabricated.

[0028] device The AlN single crystal substrate of the present invention has a low absorption coefficient at a wavelength of 265 nm and is resistant to chipping (defects such as chips and cracks), making it suitable for use in a variety of devices. Therefore, a preferred embodiment of the present invention provides a device equipped with the AlN single crystal substrate. Preferred examples of such devices include deep-ultraviolet LEDs, ultraviolet lasers, power devices, MEMS devices, and HMETs (high electron mobility transistors). [Example]

[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 1-9 (1) Preparation of AlN single crystal substrate In each example, an AlN single crystal substrate was produced by sublimation deposition as follows.

[0031] (1a) Heat treatment of AlN polycrystalline powder As shown in FIG. 3, commercially available AlN powder 12 with an average particle size of 1 μm, used as a raw material for AlN single crystals, was placed in BN sheath 10. Commercially available graphite powder 14 with an average particle size of 1 μm was placed in BN crucible 16 at a ratio of 6 parts by weight per 100 parts by weight of the AlN powder. Furthermore, BN powder 15 with an average particle size of 3 μm was placed in BN crucible 17 at a ratio (parts by weight) shown in Table 1 per 100 parts by weight of the AlN powder. These BN crucibles 16 and 17 were placed in BN sheath 10 so as not to directly contact AlN powder 12. BN crucibles 16 and 17 were sized to fit within BN sheath 10. This BN sheath 10 was heat-treated in a graphite heater furnace at 2200°C in a N2 atmosphere at 0.1 to 10 atmospheres. In this way, AlN powder 12, which is AlN polycrystalline powder, was heat treated to produce AlN raw material powder.

[0032] (1b) Deposition of AlN single crystal layer A film formation apparatus 20 shown in FIG. 4 was prepared. This film formation apparatus 20 included a heat insulator 24 for insulating a crucible 22, which was a crystal growth container, and a coil 26 for heating the crucible 22. The crucible 22, containing the AlN raw material powder 28 prepared in (1a) above, was placed inside the film formation apparatus 20. A SiC substrate was placed in the upper part of the film formation apparatus 20 so as not to come into contact with the AlN raw material powder 28 as a seed substrate 30 for precipitating a sublimate of the AlN raw material powder 28. Next, the crucible 22 was pressurized to 50 kPa in an N atmosphere, and the portion of the crucible 22 near the AlN raw material powder was heated to 2100°C by high-frequency induction heating using the coil 26. Meanwhile, the portion of the crucible 22 near the SiC substrate was heated to a lower temperature (temperature difference of 200°C) and maintained at that temperature, thereby re-precipitating an AlN single crystal layer 32 on the SiC substrate. The maintenance time was 10 hours.

[0033] (1c) Grinding and removal of SiC substrate and polishing of AlN single crystal layer surface The SiC substrate on which AlN was reprecipitated, obtained in (1b) above, was ground using a grinding wheel with a grit size up to #2000 until the AlN single crystal was exposed, and then the plate surface was further smoothed by lapping using diamond abrasive grains. The plate surface was then mirror-finished by chemical mechanical polishing (CMP) using colloidal silica. In this series of steps, the surface of the AlN single crystal that had been in contact with the SiC substrate and the surface of the AlN single crystal that had not been in contact with the SiC substrate were each lapped using diamond abrasive grains, and subsequent CMP was performed to achieve the CMP polishing amounts (the thickness of AlN reduced by CMP) shown in Table 1. Thus, a substrate with a diameter of 100 mm and an area of ​​7850 mm was obtained. 2 A circular AlN single crystal substrate having a thickness of 0.5 mm was fabricated.

[0034] (2) Evaluation of AlN single crystal substrates The AlN single crystal substrate obtained in (1c) above was evaluated as follows.

[0035] (2a) Absorption coefficient For each of a first imaginary line segment L1 and a second imaginary line segment L2, each 40 mm long and perpendicular to each other, which were imaginarily set on the surface of the AlN single crystal substrate, the total light transmittance and total reflectance at a wavelength of 265 nm were measured at multiple measurement points spaced 4 mm apart on the imaginary line segment L1 or L2 using a spectrophotometer (UH4150, manufactured by Hitachi High-Tech Science) under the following measurement conditions. <Measurement conditions> Measurement equipment: Hitachi High-Tech Science, UH4150 Accessory: Integrating sphere (Φ60mm) Spectralon ·Measurement wavelength: 200~600nm Light source switching wavelength: 340nm Slit: 1nm Light source: Deuterium lamp (UV), Tungsten halogen lamp (Vis / NIR) Detector: PMT (photomultiplier tube) (UV / Vis), cooled PbS (NIR) Reference: Total Reflection Measurement: Al mirror ·Incident angle: Transmission measurement: 0°, total reflection measurement: 8°

[0036] The thickness of the AlN single crystal substrate was also measured. The measurement results were calculated using the following equation, which takes into account multiple reflections (see Non-Patent Document 1, for example): Therefore, the following formula:

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[0037] (2b) Check for chipping The surface of the AlN single crystal after grinding and polishing in (1c) above was observed under an optical microscope, and chips and cracks with a maximum length of 50 μm or more were considered to be chipping, and the presence or absence of chipping was confirmed. A total of 10 AlN single crystals were produced using the same method as in (1) above, and it was determined how many of them had chipping, and they were graded according to the evaluation criteria shown below. The results are shown in Table 1. <Evaluation criteria> - Evaluation A: 9 to 10 AlN single crystal substrates were chip-free - Evaluation B: 6 to 8 AlN single crystal substrates were chip-free - Evaluation C: 3 to 5 AlN single crystal substrates without chipping - Rating D: Chipping was observed on all AlN single crystal substrates

[0038] [Table 1]

Claims

1. An AlN single crystal substrate made of AlN single crystal and having a disk shape with a diameter of 50 mm or more, When at least one first virtual line segment having a length of 40 mm is formed on the surface of the AlN single crystal substrate and the absorption coefficient at a wavelength of 265 nm is measured at a plurality of measurement points spaced 4 mm apart on the first virtual line segment, the maximum absorption coefficient at all measurement points is 25 cm －１ or less, and the difference between the maximum and minimum absorption coefficients among all measurement points is 5 cm －１ It can be drawn so that it is within When a second virtual line segment having a length of 40 mm, which is perpendicular to the at least one first virtual line segment, is formed on the surface of the AlN single crystal substrate, and the absorption coefficient at a wavelength of 265 nm is measured at a plurality of measurement points spaced 4 mm apart on the second virtual line segment, the maximum absorption coefficient at all measurement points is 25 cm －１ or less, and the difference between the maximum and minimum absorption coefficients among all measurement points is 5 cm －１ An AlN single crystal substrate, characterized by being able to be drawn so as to be within.

2. The difference between the maximum and minimum absorption coefficients among all the measurement points on the first virtual line segment is 3 cm. －１ and the difference between the maximum and minimum absorption coefficients among all the measurement points on the second virtual line segment is 3 cm or less. －１ The AlN single crystal substrate according to claim 1 , wherein the thickness is within 100 μm.

3. The maximum value of the absorption coefficient at all the measurement points on the first virtual line segment is 15 cm －１ or less, and the maximum value of the absorption coefficient at all the measurement points on the second virtual line segment is 15 cm －１ 3. The AlN single crystal substrate according to claim 1, wherein:

4. 3. The AlN single crystal substrate according to claim 1, wherein the AlN single crystal substrate is in the shape of a disk having a diameter of 100 mm or more.

5. A device comprising the AlN single crystal substrate according to claim 1 or 2.

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