Aln monocrystal substrate and device

Abstract

Provided is an AlN monocrystal substrate exhibiting a high transmittance (i.e., a low absorption constant) in the ultraviolet region (e.g., a wavelength of 265 nm). This AlN monocrystal substrate is composed of AlN monocrystals and measures at least 100 μm in thickness. In a cathodoluminescence (CL) spectrum measured at a temperature of 30K, the ratio IB / IA of the peak intensity IB observed at 270-370 nm to the peak intensity IA observed at 200-230 nm is less than 4300. When a Raman spectrum corresponding to a depth position relative to the surface of the AlN monocrystal substrate is acquired by laser Raman spectroscopy, the difference between the wave number at which the E2 H peak is given in the Raman spectrum at a position 40 μm deep from the surface of the AlN monocrystal substrate and the wave number at which the E2 H peak is given in the Raman spectrum at a position 5 μm deep from the surface of the AlN monocrystal substrate is 0.40 cm-1 or less.

Description

AlN single crystal substrate and device

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

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

[0003] Patent Document 1 (JP 2012-188344 A) discloses an AlN single crystal with good ultraviolet light transmittance. This AlN single crystal is an AlN single crystal containing oxygen atoms and carbon atoms, and the concentration of oxygen atoms is [O]cm －３ , the concentration of carbon atoms is [C] cm －３ When this is set, the condition of the formula [O]-[C]>0 is satisfied.

[0004] Patent Document 2 (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 ρ is the electrical resistivity (Ω cm) of the AlN single crystal substrate at 25°C, and T is the average transmittance (%) in the transmission spectrum of the AlN single crystal substrate from 640 to 660 nm. 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.

[0005] JP 2012-188344 A

[0006] A website article titled "Reflectance and transmittance due to multiple reflections of light" in "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)

[0007] When an AlN single crystal substrate is used in 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 having a high transmittance in the ultraviolet region is desired.

[0008] The present inventors have now discovered that an AlN single crystal substrate can be provided that exhibits high transmittance (i.e., a low absorption constant) in the ultraviolet region (e.g., a wavelength of 265 nm) by satisfying predetermined peak intensity conditions in a cathodoluminescence (CL) spectrum measured at a temperature of 30 K and also satisfying predetermined peak conditions in a Raman spectrum that depends on the depth position from the surface.

[0009] Therefore, an object of the present invention is to provide an AlN single crystal substrate that exhibits high transmittance (i.e., low absorption constant) in the ultraviolet region (for example, wavelength 265 nm).

[0010] According to the present disclosure, the following aspects are provided: [Aspect 1] An AlN single crystal substrate made of an AlN single crystal and having a thickness of 100 μm or more, wherein a peak intensity I observed at 200 to 230 nm in a cathodoluminescence (CL) spectrum measured at a temperature of 30 K is Ａ The peak intensity I observed at 270 to 370 nm Ｂ Ratio to I Ｂ / I Ａ is less than 4300, and when Raman spectra according to depth positions from the surface of the AlN single crystal substrate are obtained by laser Raman spectroscopy, E is found in the Raman spectrum at a position 40 μm deep from the surface of the AlN single crystal substrate. ２ Ｈ The wave number giving the peak and the E in the Raman spectrum at a position 5 μm deep from the surface of the AlN single crystal substrate２ Ｈ The difference in wavenumber that gives the peak is 0.40 cm －１ [Aspect 2] An AlN single crystal substrate having an E in the Raman spectrum at any depth position from the surface of the AlN single crystal substrate to a depth of 50 μm. ２ Ｈ The wave number giving the peak is 657.0 to 660.2 cm －１ [Aspect 3] The AlN single crystal substrate according to Aspect 1 or 2, wherein the AlN single crystal substrate is in the form of a disk with a diameter of 100 mm or more. [Aspect 4] The AlN single crystal substrate according to Aspect 1, wherein the absorption coefficient at a wavelength of 265 nm is 25 cm －１ The AlN single crystal substrate according to any one of Aspects 1 to 3, wherein the thickness is less than 100 nm. [Aspect 5] A device comprising the AlN single crystal substrate according to any one of Aspects 1 to 4.

[0011] FIG. 1 is a conceptual diagram for explaining the transmittance of multiple reflections when light is absorbed. FIG. 2 is a schematic cross-sectional view showing the configuration of a heat treatment apparatus used to prepare AlN raw material powder. FIG. 3 is a schematic cross-sectional view showing the configuration of a crystal growth apparatus used in sublimation. FIG. 4 is a graph showing the CL spectra of the AlN single crystal substrates obtained in Examples 1, 2, and 7. FIG. 5 is a graph showing an enlarged view of the peaks due to band edge emission in the CL spectrum of the AlN single crystal substrate obtained in Example 1. FIG. 6 is a graph showing an enlarged view of the peaks due to band edge emission in the CL spectrum of the AlN single crystal substrate obtained in Example 7. ２ Ｈ 1 is an example of a Raman spectrum including a peak. The E of the Raman spectrum in a region 20 μm wide from the surface to a depth of 50 μm of the AlN single crystal substrate obtained in Examples 1, 2, and 7. ２ Ｈ 1 is a mapping image showing the wave numbers giving peaks in the Raman spectrum in a region 20 μm wide from the surface to a depth of 50 μm of the AlN single crystal substrates obtained in Examples 1 and 8. ２ Ｈ 1 is a mapping image showing the wave numbers that give peaks.

[0012] AlN single crystal substrate The AlN single crystal substrate according to the present invention is a substrate made of AlN single crystal and having a thickness of 100 μm or more. This AlN single crystal substrate has a peak intensity I observed at 200 to 230 nm in a cathodoluminescence (CL) spectrum measured at a temperature of 30 K. Ａ The peak intensity I observed at 270 to 370 nm Ｂ Ratio to I Ｂ / I Ａ In addition, when Raman spectra are obtained by laser Raman spectroscopy according to the depth position from the surface of the AlN single crystal substrate, the E ２ Ｈ The wave number giving the peak and the E in the Raman spectrum at a position 5 μm deep from the surface of the AlN single crystal substrate ２ Ｈ The difference in wavenumber that gives the peak is 0.40 cm －１ In this way, by satisfying the predetermined peak intensity condition in the CL spectrum measured at a temperature of 30 K and also satisfying the predetermined peak condition in the Raman spectrum according to the depth position from the surface, it is possible to provide an AlN single crystal substrate that exhibits high transmittance (i.e., a low absorption constant) in the ultraviolet region (for example, a wavelength of 265 nm).

[0013] Therefore, the AlN single crystal substrate has an absorption coefficient of 25 cm for ultraviolet light with a wavelength of 265 nm. －１ Preferably it is less than 20 cm －１ More preferably, 15 cm or less －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. The lower limit of the absorption coefficient is not particularly limited, but is typically 1 cm －１ or more, more typically 3 cm －１ That's all.

[0014] 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).

[0015] 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 will be provided below just to be sure. Figure 1 shows a conceptual diagram for explaining multiple reflections when light is absorbed. Note that in Figure 1, light is depicted as being incident obliquely on the surface of a material for convenience, but it is assumed that light is incident perpendicularly. In Figure 1 and the following explanation, I ０ is the intensity of the incident light, R １ is the reflectance of the substrate surface, R ２ is the reflectance of the rear 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. 1, the sum I of the light intensities of the transmitted light is expressed by the following formula: In the above formula, (1 + R １ R ２ e －２αｌ +R １ ２ R ２ ２ e －４αｌ +...) with the first term 1 and the common ratio R １ R ２ e －２αｌ When calculated as the sum of the geometric progression of: The transmittance T is the sum of the light intensities of the transmitted light I and the light intensity of the incident light I ０ Since it is a ratio to Therefore, in the above formula (3), the total light transmittance is substituted for T, the thickness of the AlN single crystal substrate is substituted for l, and R １ and R ２ The absorption coefficient α can be calculated by substituting the reflectances of the front and back surfaces of the AlN single crystal substrate as

[0016] The AlN single crystal substrate exhibits a peak intensity I observed at 200 to 230 nm in the cathodoluminescence (CL) spectrum measured at a temperature of 30 K. Ａ The peak intensity I observed at 270 to 370 nm Ｂ Ratio to I Ｂ / I Ａ is less than 4300. That is, when a CL spectrum is obtained for an AlN single crystal substrate at room temperature, no peak is observed in the 200-230 nm wavelength range, but in a CL spectrum obtained at a low temperature of 30 K, peaks are observed in both the 200-230 nm wavelength range and the 270-370 nm wavelength range. The inventors then calculated the relative ratio I Ｂ / I Ａ It has been found that when the ratio I is within a predetermined range, it contributes to improving the transmittance or absorption constant in the ultraviolet region. Ｂ / I Ａ is less than 4300, preferably 4200 or less, for example 4000 or less. Ｂ / I Ａ The lower limit of the ratio I Ｂ / I Ａ is typically 0.001 or more, more typically 0.010 or more, for example 100 or more, 500 or more, 1000 or more, or 3000 or more.

[0017] When a Raman spectrum according to the depth position from the surface of the AlN single crystal substrate is obtained by laser Raman spectroscopy, the Raman spectrum at a position 40 μm deep from the surface of the AlN single crystal substrate has E ２ Ｈ Wave number P giving the peak ２ and E in the Raman spectrum at a depth of 5 μm from the surface of the AlN single crystal substrate. ２ Ｈ Wave number P giving the peak １ The difference ΔP (= |P ２ -P １ |) is 0.40 cm －１ That is, according to the findings of the present inventors, in the Raman spectrum of an AlN single crystal substrate, －１ E observed in２ Ｈ The position of the peak (wave number) tends to shift depending on the stress state, such as compressive stress or tensile stress. In other words, the shift is small when the stress is small, and the shift is large when the stress is large. It is thought that small stress leads to fewer defects and higher transmittance, while large stress leads to more defects and lower transmittance. In this regard, stress or defects generated near the substrate surface due to processing such as surface grinding tend to remain at a depth of 5 μm from the surface of the AlN single crystal substrate, and such stress or the like can affect E ２ Ｈ While the peak position is shifted relatively significantly, at a depth of 40 μm from the surface of the AlN single crystal substrate, the influence of processing such as surface grinding is small, so stress or defects are unlikely to occur. ２ Ｈ It can be said that the peak position shifts little and is stable. ２ Ｈ Wave number P giving the peak ２ and E at a depth of 5 μm ２ Ｈ Wave number P giving the peak １ By focusing on the difference ΔP between the wavelengths of the light and the wavelengths of the light, it was found that controlling the difference ΔP within a predetermined range contributes to improving the transmittance or absorption constant in the ultraviolet region. －１ less than or equal to 0.35 cm －１ Less than or equal to 0.30 cm, more preferably －１ Less than 0.25 cm, more preferably －１ Below, most preferably 0 m －１ The following is the result.

[0018] The AlN single crystal substrate exhibits E in the Raman spectrum at any depth position from the surface of the AlN single crystal substrate to a depth of 50 μm. ２ Ｈ The wave number giving the peak is 657.0 to 660.2 cm －１ Preferably, the thickness is in the range of 658.0 to 660.2 cm －１ , more preferably 659.0 to 660.2 cm －１, particularly preferably 659.6 to 660.1 cm －１ , most preferably 659.9 to 660.1 cm －１ is within the range.

[0019] The size of the AlN single crystal substrate is 100 mm or more in diameter, preferably 150 mm or more or 200 mm or more in diameter. Increasing the area of ​​the AlN single crystal substrate in this manner allows for a larger area of ​​the semiconductor layer formed thereon. Therefore, it becomes 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).

[0020] 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.

[0021] 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 the 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 the AlN single crystal substrate as an oriented film.

[0022] Manufacturing Method The AlN single crystal substrate of the present invention can be manufactured by various methods as long as the above-mentioned 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 manufactured 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 any of vapor-phase deposition, liquid-phase deposition, and 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, pulsed laser deposition (PLD), etc., with sublimation or HVPE being preferred. Examples of liquid phase deposition methods include solution growth methods (e.g., flux deposition). Furthermore, even without directly depositing an AlN single crystal on a seed substrate, it is also possible to obtain an AlN single crystal substrate by a step of forming an orientation precursor layer, a step of converting the orientation precursor layer into an AlN single crystal layer by heat treatment, and a step of grinding and removing the seed substrate. Examples of methods for forming the alignment precursor layer include the AD (aerosol deposition) method and the HPPD (supersonic plasma particle deposition) method.

[0023] 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 and removing the seed substrate and polishing the surface of the AlN single crystal layer.

[0024] (a) Heat Treatment of AlN Polycrystalline Powder This step involves heat treating AlN polycrystalline powder to obtain AlN raw material powder. As shown in FIG. 2, AlN powder 12 as a raw material for AlN single crystal is placed in a sheath 10. ２ At this time, the graphite powder 14 and the metal oxide (Y) are placed in the sheath 10 so as not to come into direct contact with the AlN powder 12. ２ O ３ , CaO, CeO ２ , Yb ２ O ３ , Sm ２ O ３ The powders 15 are placed in separate crucibles 16 and 17. These crucibles 16 and 17 are large enough to fit inside the sheath 10. By appropriately adjusting the contents of graphite and metal oxide, an AlN single crystal substrate satisfying the aforementioned relationships regarding transmittance, thermal conductivity, and electrical resistivity can be produced. The pressure inside the furnace of 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 the sheath and crucible include tantalum carbide, tungsten, molybdenum, and boron nitride (BN), with BN being more preferred.

[0025] (b) Deposition of AlN Single Crystal Layer This step is a step of depositing an AlN single crystal 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. 3. The deposition apparatus 20 shown in FIG. 3 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 the lower part, and includes a seed substrate 30 in the upper part on which a sublimate of the AlN raw material powder 28 is deposited. The interior of the crucible 22 is filled with N ２Pressurization is applied under atmospheric pressure, 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, 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 in the portion near the seed substrate 30 is preferably 100 to 500°C lower, more preferably 200 to 400°C, than the portion near the AlN raw material powder 28. 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 a radiation thermometer (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 manner, 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.

[0026] (c) Grinding and Removal of Seed Substrate and Polishing of AlN Single Crystal Layer Surface This process includes a grinding step in which the seed substrate is ground and removed to expose the AlN single crystal layer, and a polishing step in which irregularities and defects on the AlN single crystal surface are removed. Since the AlN single crystal layer fabricated using a SiC substrate as the seed substrate through the above steps (a) and (b) still contains residual SiC single crystals, the surface of the AlN single crystal layer is exposed by grinding. Furthermore, to mirror-finish the surface of the AlN single crystal layer after deposition, the plate surface is smoothed by lapping using diamond abrasive grains, and then polished by chemical mechanical polishing (CMP) using colloidal silica or the like. At this time, the amount of polishing by CMP (the thickness of the AlN reduced by CMP) is preferably 0.2 μm or more, more preferably 0.5 to 5 μm. By increasing the amount of CMP polishing in this way, stresses or defects that may remain near the surface are sufficiently reduced, resulting in E at a depth of 40 μm. ２ Ｈ Wave number P giving the peak ２and E at a depth of 5 μm ２ Ｈ Wave number P giving the peak １ The difference ΔP (= |P ２ -P １ |) becomes smaller, which is thought to lead to a reduction in the absorption coefficient in the ultraviolet region, as described above. In this way, an AlN single crystal substrate can be produced.

[0027] The AlN single crystal substrate of the present invention exhibits high transmittance in the ultraviolet region and can therefore be suitably used in a variety of devices. Therefore, according to a preferred embodiment of the present invention, a device including an AlN single crystal substrate is provided. Preferred examples of such devices include deep ultraviolet LEDs, ultraviolet lasers, power devices, MEMS devices, and HMETs (high electron mobility transistors).

[0028] The present invention will be explained in more detail by the following examples, but the present invention is not limited to the following examples.

[0029] Examples 1 to 9 (1) Preparation of AlN Single Crystal Substrate In each example, an AlN single crystal substrate was prepared by sublimation deposition as follows.

[0030] (1a) Heat Treatment of AlN Polycrystalline Powder As shown in FIG. 2, 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 a BN sheath 10. Commercially available graphite powder 14 with an average particle size of 1 μm was placed in a 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 a 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 the BN sheath 10 so as not to come into direct contact with the AlN powder 12. The BN crucibles 16 and 17 were sized to fit within the BN sheath 10. This BN sheath 10 was heated in a graphite heater furnace with N ２ The heat treatment was carried out in an atmosphere of 0.1 to 10 atmospheres at 2200° C. In this way, the AlN powder 12, which was AlN polycrystalline powder, was heat treated to produce AlN raw material powder.

[0031] (1b) Formation of AlN Single Crystal Layer A film formation apparatus 20 shown in FIG. 3 was prepared. This film formation apparatus 20 was equipped with a heat insulating material 24 for insulating a crucible 22, which is a crystal growth container, and a coil 26 for heating the crucible 22. Inside this film formation apparatus 20, the crucible 22 containing the AlN raw material powder 28 prepared in (1a) above was placed. In the upper part of the film formation apparatus 20, a SiC substrate was placed as a seed substrate 30 for precipitating a sublimate of the AlN raw material powder 28, so as not to come into contact with the AlN raw material powder 28. Next, the crucible 22 was heated with N ２ A pressure of 50 kPa was applied in an 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 the AlN single crystal layer 32 on the SiC substrate. The maintenance time was 10 hours.

[0032] (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 grindstone 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 subjected to lapping using diamond abrasive grains, and subsequent CMP was performed to achieve the CMP polishing amounts (thickness of AlN reduced by CMP) shown in Table 1.In this way, a SiC 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.

[0033] (2) Evaluation of AlN Single Crystal Substrate The AlN single crystal substrate obtained in (1c) above was evaluated as follows.

[0034] (2a) CL spectrum measurement CL mapping measurement was performed on the surface of the AlN single crystal substrate (the side that was not in contact with the SiC substrate) at a cryogenic temperature of 30 K using a CL spectrometer (spectroscope: iHR-320 manufactured by Horiba, Ltd., SEM: Schottky emission type SEM JSM-7100F / TTLS manufactured by JEOL Ltd.) in a field of view of 5 μm × 5 μm to obtain a CL spectrum. The conditions for this CL mapping measurement were as follows:

[0035] <CL mapping measurement conditions> Detector: CCD (Jobin Yvon) Spectrometer diffraction grating: 100 gr / mm, blaze wavelength 450 nm Number of CL image pixels: 51 x 51 s CL spectrum integration time: 10 ms x 1 Measurement temperature: 30 K Exposure current: 4.8 nA Acceleration voltage: 15 kV W.D.: 10.3 mm Number of SEM image pixels: 250 x 250

[0036] In this way, CL spectra were obtained for the AlN single crystal substrates of each example. In each CL spectrum, peaks were observed in the wavelength range of 200 to 230 nm and in the wavelength range of 270 to 370 nm. The peak in the wavelength range of 200 to 230 nm is considered to be due to band edge emission. Table 1 shows the peak intensity I observed in the range of 200 to 230 nm. Ａ , peak intensity I observed at 270 to 370 nm Ｂ , and ratio I Ｂ / I Ａ 4 shows the CL spectra of the AlN single crystal substrates obtained in Examples 1, 2, and 7. In the CL spectra of Examples 1 and 7 shown in FIG. 4, the peaks observed in the range of 200 to 230 nm are too small to be visually recognized, but from the enlarged spectra of the low wavelength range of the CL spectra of Examples 1 and 7 shown in FIGS. 5 and 6, it can be seen that the CL spectra of these examples also have peaks in the range of 200 to 230 nm due to band edge emission.

[0037] (2b) Raman Spectrum The Raman spectrum of the AlN single crystal substrate was measured using a laser Raman spectrometer (LabRAM HR Evolution, manufactured by HORIBA, Ltd.) under the following conditions for a region 20 μm wide in the substrate surface direction (X direction) from the substrate surface (the side that was not in contact with the SiC substrate) to a position 50 μm in the depth direction (Z direction), and a Raman spectrum was obtained for each XZ position. <Laser Raman spectroscopy measurement conditions> Optical system: Czerny-Turner spectroscopy system (focal length: 800 mm), backscattering method Light source: semiconductor pumped solid-state laser (DPSS, 532 nm) Detector: EMCCD (1600 x 200 pixels) Objective lens magnification: x100 Diffraction grating: 1800 gr / mm Reference light source lamp: Ne Measurement area: measurement of a range of -10 to 10 μm (width 20 μm) in the X direction (substrate surface direction) and 0 to -50 μm in the Z direction (depth direction)

[0038] An example of the Raman spectrum measured in Example 1 is shown in Figure 7. As indicated by the arrows in Figure 7, the Raman spectrum obtained contains E ２ Ｈ A peak is observed. ２ Ｈ A mapping image was created from the substrate surface to a depth of 50 μm, in which the positions (wave numbers) where the peaks appeared were color-coded. ２ Ｈ The wave number giving the peak (cm －１ Based on the results obtained in this way, the E at a depth of 5 μm from the surface of the AlN single crystal substrate was calculated. ２ Ｈ Wave number P giving the peak １ and E at a depth of 40 μm from the surface of the AlN single crystal substrate ２ Ｈ Wave number P giving the peak ２ Identify and P ２ From P １ The value ΔP (= P ２ -P １As can be seen from the mapping image, various peak positions are obtained over a 20 μm wide region in the substrate surface direction even at the same depth. １ or P ２ The average value of the wave number data at the depth position was adopted as a representative value for the . The results are shown in Table 1. In Examples 1 to 6, the E ２ Ｈ The wave number giving the peak is 659.9 to 660.1 cm －１ was within the range.

[0039] FIG. 9 shows the E measured in Examples 1 and 8. ２ Ｈ The mapping image of the peak position is shown. Since the amount of BN added is the same in Examples 1 and 8, it is understood that these are examples in which only the processed state of the surface differs due to the difference in the amount of CMP polishing. Specifically, in Example 1, the amount of CMP polishing of the AlN single crystal on the side that was not in contact with the SiC substrate was large at 3 μm, whereas in Example 8, which is a comparative example, the amount of CMP polishing on the same side was small at 0.1 μm. As a result, in Example 8, where the amount of CMP polishing was small, the E ２ Ｈ It can be seen that the wave number of the peak is significantly smaller than that of Example 1, in which the CMP polishing amount is large. For example, as shown in Table 1, at a position 5 μm deep from the surface, in Example 1, E ２ Ｈ Peak position P １ is 659.95 cm －１ In Comparative Example 8, １ is 659.52 cm －１ As a result, E at a depth of 40 μm ２ Ｈ Peak position P ２ and E at a depth of 5 μm ２ Ｈ Peak position P １ The difference ΔP (= P ２ -P １) was significantly larger than that of Example 1. This is thought to be because in Comparative Example 8, in which the amount of polishing by CMP was small, stress or defects generated near the substrate surface due to processing such as surface grinding were not sufficiently removed by CMP and remained. It is thought that such stress or defects lead to a decrease in transmittance (i.e., an increase in the absorption coefficient). On the other hand, in Example 1, it is thought that the large amount of polishing by CMP sufficiently removed or reduced stress or defects (which would have been present near the surface before CMP polishing). In other words, it can be seen that the wavenumber difference ΔP can be reduced by increasing the amount of polishing by CMP.

[0040] (2c) Absorption Coefficient The total light transmittance and total reflectance of the AlN single crystal substrate, including the ultraviolet region, were measured using a spectrophotometer (UH4150, manufactured by Hitachi High-Tech Science) under the following measurement conditions. <Measurement Conditions> - Measurement device: UH4150, manufactured by Hitachi High-Tech Science - Accessory device: Spectralon integrating sphere (Φ60 mm) - Measurement wavelength: 200 to 600 nm - Light source switching wavelength: 340 nm - Slit: 1 nm - 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°

[0041] 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): (i.e., T is the total light transmittance, l is the thickness of the AlN single crystal substrate, R １ and R ２ The absorption coefficient of AlN at a wavelength of 265 nm was calculated by substituting the reflectances of the front and back surfaces of the AlN single crystal substrate as . The results are shown in Table 1. From the results shown in Table 1, the ratio I Ｂ / I Ａ is less than 4300, and the wave number difference ΔP (= P ２ -P １ ) is 0.40 cm －１It can be seen that the substrates that satisfy the following conditions have a significantly lower absorption coefficient at a wavelength of 265 nm, i.e., an absorption coefficient in the ultraviolet region, compared to substrates that do not satisfy these conditions.

[0042]

Claims

1. An AlN single crystal substrate made of AlN single crystal and having a thickness of 100 μm or more, wherein the peak intensity I observed at 200 to 230 nm in the cathodoluminescence (CL) spectrum measured at a temperature of 30 K is Ａ The peak intensity I observed at 270 to 370 nm Ｂ Ratio to I Ｂ / I Ａ is less than 4300, and when Raman spectra according to depth positions from the surface of the AlN single crystal substrate are obtained by laser Raman spectroscopy, E is found in the Raman spectrum at a position 40 μm deep from the surface of the AlN single crystal substrate. ２ Ｈ The wave number giving the peak and the E in the Raman spectrum at a position 5 μm deep from the surface of the AlN single crystal substrate ２ Ｈ The difference in wavenumber that gives the peak is 0.40 cm －１ The following is an AlN single crystal substrate.

2. At any depth position from the surface of the AlN single crystal substrate to a depth of 50 μm, E ２ Ｈ The wave number giving the peak is 657.0 to 660.2 cm －１ 2. The AlN single crystal substrate according to claim 1, wherein the surface roughness is in the range of 0.1 to 1.0 μm.

3. The AlN single crystal substrate according to claim 1 or 2, wherein the AlN single crystal substrate is in the form of a disk having a diameter of 100 mm or more.

4. The absorption coefficient at a wavelength of 265 nm is 25 cm －１ The AlN single crystal substrate according to claim 1 or 2, wherein the SiO 2 content is less than 100%.

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

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