AlN single crystal

Abstract

The present invention provides an AlN single crystal which is not susceptible to the occurrence of chipping if subjected to grinding or polishing. With respect to the transmission spectrum of this AlN single crystal, the average of transmittances in the range from 640 nm to 660 nm is lower than the average of transmittances in the range from 540 nm to 560 nm and the average of transmittances in the range from 780 nm to 800 nm; and the average of transmittances in the range from 640 nm to 660 nm is lower than the average of transmittances in the range from 780 nm to 800 nm by 5 to 20 percent points (%pt).

Description

Technical Field

[0001] The present invention relates to an AlN single crystal.

Background Art

[0002] In recent years, aluminum nitride (AlN) single crystals have attracted attention as a substrate for deep ultraviolet light emitting devices using AlN-based semiconductors. For example, as AlN-based semiconductors, AlN, AlGaN, etc. are used. Since these AlN-based semiconductors have a direct transition type band structure, they are suitable for light emitting devices and can be applied to LEDs (Light Emitting Diodes) and LDs (Laser Diodes) in the deep ultraviolet region.

[0003] As methods for producing AlN single crystals, the HVPE method (halide vapor phase growth method), mist CVD (chemical vapor deposition), sublimation method, etc. are known. For example, Non-Patent Document 1 (Hiroyuki Kamata et al., "Aluminum Nitride Single Crystal", Fujikura Technical Report, 2008, Vol. 2, No. 114, pp. 42-47) discloses a method of growing an AlN single crystal on a seed substrate using the sublimation method.

[0004] In addition, the surface of the produced AlN single crystal is flattened and polished by subsequent grinding and polishing. For example, Patent Document 1 (Japanese Patent No. 4511801) discloses a polishing method for obtaining a high-quality substrate for a GaN single crystal belonging to the same group 13 element nitride as AlN.

Prior Art Documents

Patent Documents

[0005]

Patent Document 1

Non-Patent Documents

[0006]

Non-Patent Document 1

Summary of the Invention

[0007] However, in the AlN single crystal produced by the production method as disclosed in Non-Patent Document 1, chipping (defects such as chips and cracks) is likely to occur in the grinding process, and there is a problem that the yield of the AlN single crystal decreases. Also, there is a similar problem in the polishing process (i.e., the mechanical polishing process and the chemical mechanical polishing (CMP) process) for mirror-finishing the surface of the AlN single crystal. Patent Document 1 discloses a polishing method for a GaN single crystal as described above, but there is no mention of suppressing the occurrence of chipping, and it is not disclosed for an AlN single crystal either. Therefore, when polishing an AlN single crystal, it is desired to suppress chipping that occurs in the AlN single crystal.

[0008] The present inventors have now found that by giving an AlN single crystal a characteristic in which the transmittance decreases at a certain rate in a specific wavelength range in the transmission spectrum, an AlN single crystal in which chipping is less likely to occur when ground or polished can be provided.

[0009] Therefore, an object of the present invention is to provide an AlN single crystal in which chipping is less likely to occur when ground or polished.

[0010] According to the present invention, the following aspects are provided. [Aspect 1] An AlN single crystal, wherein in the transmission spectrum of the AlN single crystal, the average value of the transmittance at 640 to 660 nm is lower than each of the average value of the transmittance at 540 to 560 nm and the average value of the transmittance at 780 to 800 nm, and the average value of the transmittance at 640 to 660 nm is 5 to 20 percentage points (%pt) lower than the average value of the transmittance at 780 to 800 nm. [Aspect 2] In the transmission spectrum of the AlN single crystal, there is an absorption peak with a half-value width of 50 to 150 nm within the wavelength range of 540 to 800 nm, wherein the half-value width is defined as the width of the wavelength range that gives a transmittance lower than the transmittance calculated from (ii) T2 + (T1 - T2) / 2, where T1 is the smaller value of the average value of the transmittance at 540 to 560 nm and the average value of the transmittance at 780 to 800 nm, and T2 is the average value of the transmittance at 640 to 660 nm, for the AlN single crystal according to Embodiment 1. [Embodiment 3] The AlN single crystal according to Embodiment 1 or 2, wherein the average value of the transmittance at 640 to 660 nm in the transmission spectrum of the AlN single crystal is 1 to 10%pt lower than the average value of the transmittance at 540 to 560 nm. [Embodiment 4] The AlN single crystal according to any one of Embodiments 1 to 3, wherein the average value of the transmittance at 640 to 660 nm in the transmission spectrum of the AlN single crystal is 6 to 18%pt lower than the average value of the transmittance at 780 to 800 nm. [Embodiment 5] The AlN single crystal according to any one of Embodiments 2 to 4, wherein the half-value width is 70 to 120 nm. [Embodiment 6] The AlN single crystal according to Embodiment 3, wherein the average value of the transmittance at 640 to 660 nm in the transmission spectrum of the AlN single crystal is 3 to 8%pt lower than the average value of the transmittance at 540 to 560 nm.

Brief Description of the Drawings

[0011]

Figure 1

Figure 2

Figure 3

Figure 4

BEST MODE FOR CARRYING OUT THE INVENTION

[0012] AlN single crystal In the transmission spectrum of the AlN single crystal according to the present invention, the average value of the transmittance (%) at 640 to 660 nm is lower than each of the average value of the transmittance (%) at 540 to 560 nm and the average value of the transmittance (%) at 780 to 800 nm. Further, in this AlN single crystal, the average value of the transmittance (%) at 640 to 660 nm is 5 to 20 percentage points (%pt) lower than the average value of the transmittance (%) at 780 to 800 nm. Thus, by giving the AlN single crystal a characteristic in which the transmittance decreases at a constant rate in a specific wavelength range in the transmission spectrum, it is possible to provide an AlN single crystal in which chipping hardly occurs when ground or polished. Therefore, by subjecting such an AlN single crystal to polishing or the like, an AlN single crystal substrate can be manufactured with a high yield. That is, as described above, for the AlN single crystal, the surface of the AlN single crystal is flattened and mirror-finished by subsequent grinding and polishing. However, in conventional AlN single crystals, there has been a problem that chipping easily occurs in the AlN single crystal after passing through the grinding or polishing process. In this regard, according to the AlN single crystal of the present invention, this problem can be conveniently solved.

[0013] Here, the "average value of the transmittance" in a specific wavelength range in the transmission spectrum is obtained by dividing the sum of the transmittances (%) of each wavelength (nm) measured in a specific wavelength range (for example, 540 to 560 nm, 640 to 660 nm, 780 to 800 nm, etc.) by the number of measurement points. For example, when the transmittance is measured at 1 nm intervals in the region of 540 to 560 nm and the sum of those transmittances is 1050, the average value of the transmittance (for example, 1050 / 21 = 50%) can be obtained by dividing the sum of the transmittances by the number of measurement points, which is 21. Also, the transmittance at this time is the transmittance T when the thickness of the AlN single crystal is converted to 100 μm. 100μmIt is preferable to use this. This is because if there is variation in the thickness of the AlN single crystal to be measured, the transmittance will also change accordingly. For example, when the AlN single crystal is thick, the transmittance is low, and when the AlN single crystal is thin, the transmittance is high.

[0014] The transmittance in the transmission spectrum can be obtained, for example, by the calculation method shown below. The total light transmittance T of the AlN single crystal a is measured using a spectrophotometer. T a The measured value of and the theoretical transmittance T of the AlN single crystal t are used to obtain the absorption coefficient α of the AlN single crystal. Then, the transmittance T when the thickness of the AlN single crystal is converted to 100 μm 100μm is calculated. At this time, α and T 100μm are given by the following formula: α = -1 / t × ln(T a / T t ), and T 100μm = exp(-α / 100) (where t represents the actual thickness (cm) of the AlN single crystal sample) can be obtained. For AlN single crystal samples with low transmittance and difficult calculation of the absorption coefficient α, the actual thickness can be reduced to measure the total light transmittance T a . In this way, a transmission spectrum based on the transmittance T when the thickness is converted to 100 μm 100μm can be obtained.

[0015] In the transmission spectrum of the AlN single crystal, it is preferable that the average value of the transmittance at 640 - 660 nm is 1 - 10%pt lower than the average value of the transmittance at 540 - 560 nm, and more preferably 3 - 8%pt lower. Also, in the transmission spectrum of the AlN single crystal, it is preferable that the average value of the transmittance at 640 - 660 nm is 5 - 20%pt lower than the average value of the transmittance at 780 - 800 nm, and more preferably 6 - 18%pt lower, and even more preferably 8 - 13%pt lower.

[0016] The AlN single crystal of the present invention preferably has an absorption peak with a half-value width of 50 to 150 nm within a wavelength range of 540 to 800 nm in the transmission spectrum, more preferably a half-value width of 70 to 120 nm. This "absorption peak" means an absorption band in which the transmittance is minimized (i.e., the absorption rate is maximized) within the wavelength range of 540 to 800 nm in the transmission spectrum with the horizontal axis being the wavelength (nm) and the vertical axis being the transmittance (%). In such an absorption band, the shape of the transmission spectrum is concave downward (e.g., valley-shaped). This half-value width is defined as the width of the wavelength range that gives a transmittance lower than the transmittance calculated from (ii) T2+(T1-T2) / 2, where T1 is the smaller value of the average value of the transmittance at 540 to 560 nm and the average value of the transmittance at 780 to 800 nm, and T2 is the average value of the transmittance at 640 to 660 nm.

[0017] The AlN single crystal in the present invention is preferably an oriented layer oriented in both the c-axis direction and the a-axis direction, and may contain mosaic crystals. Mosaic crystals refer to a collection of crystals that do not have distinct grain boundaries but have a slightly different crystal orientation from one or both of the c-axis and the a-axis. Such an oriented layer has a structure in which the crystal orientations are generally aligned in the substantially normal direction (c-axis direction) and the in-plane direction (a-axis direction). By having such a structure, it becomes possible to form a semiconductor layer with excellent quality, particularly excellent orientation, thereon. That is, when forming a semiconductor layer 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 use the semiconductor film formed on the AlN single crystal as an oriented film.

[0018] The method for evaluating the orientation of the AlN single crystal in the present invention is not particularly limited. For example, known analysis methods such as the EBSD (Electron Back Scatter Diffraction Patterns) method or X-ray pole figures can be used. For example, when using the EBSD method, inverse pole figure mapping and crystal orientation mapping of the surface (plate surface) of the AlN single crystal or a cross-section perpendicular to the plate surface are measured. In the obtained inverse pole figure mapping, (A) being oriented in a specific orientation (first axis) in the substantially normal direction of the plate surface, (B) being oriented in a specific orientation (second axis) in the substantially in-plane direction of the plate surface perpendicular to the first axis, in the obtained crystal orientation mapping, (C) the inclination angle from the first axis being distributed within ±10°, (D) the inclination angle from the second axis being distributed within ±10°. When these four conditions are satisfied, it can be defined that the AlN single crystal is oriented in two axes of the substantially normal direction and the substantially plate surface direction. In other words, when the above four conditions are satisfied, it can be determined that the AlN single crystal is oriented in two axes of the c-axis and the a-axis. For example, when the substantially normal direction of the plate surface is oriented in the c-axis, the substantially in-plane direction of the plate surface may be oriented in a specific orientation (for example, the a-axis) perpendicular to the c-axis. The AlN single crystal only needs to be oriented in two axes of the substantially normal direction and the substantially in-plane direction of the plate surface, but it is preferably that the substantially normal direction is oriented in the c-axis. The smaller the inclination angle distribution in the substantially normal direction and / or the substantially in-plane direction, the smaller the mosaicity of the AlN single crystal, and the closer it is to zero, the closer it is to a perfect single crystal. Therefore, from the viewpoint of the crystallinity of the AlN single crystal, it is preferable that the inclination angle distribution is small in both the substantially normal direction and the substantially plate surface direction. For example, ±5° or less is preferable, and ±3° or less is more preferable.

[0019] One side of the AlN single crystal preferably has an area of 2 20 cm² or more, more preferably 2 70 cm² or more, and even more preferably 2 170 cm² or more. By increasing the area of the AlN single crystal substrate in this way, it becomes possible to increase the area of the semiconductor layer formed thereon. Therefore, it becomes possible to obtain a large number of semiconductor elements from a single semiconductor layer, and a reduction in manufacturing cost is expected. The upper limit of the size is not particularly limited, but typically, one side has an area of 2It is as follows.

[0020] Manufacturing method The AlN single crystal of the present invention can be manufactured by various methods as long as it is an AlN single crystal in which the transmittance decreases by a predetermined amount in a specific wavelength range in the transmission spectrum. An epitaxial film may be formed on a seed substrate, or an AlN single crystal may be directly manufactured by spontaneous nucleation without using a seed substrate. Further, as the seed substrate to be used, an AlN substrate may be used for homoepitaxial growth, or heteroepitaxial growth may be performed using other substrates. For the growth of the single crystal, any of a vapor phase deposition method, a liquid phase deposition method, and a solid phase deposition method may be used, but preferably, an AlN single crystal is formed by a vapor phase deposition method, and then, if necessary, the seed substrate portion is ground and removed to obtain an AlN single crystal having desired transmission spectrum characteristics. Examples of the vapor phase deposition method include MOVPE (metal organic vapor phase epitaxy) method, various CVD (chemical vapor deposition) methods (for example, thermal CVD method, plasma CVD method, etc.), sputtering method, hydride vapor phase epitaxy (HVPE) method, molecular beam epitaxy (MBE) method, sublimation method, and pulsed laser deposition (PLD) method, etc., and preferably the sublimation method or the HVPE method. Examples of the liquid phase deposition method include a solution growth method (for example, flux method). Further, even if an AlN single crystal is not directly formed on the seed substrate, it is also possible to obtain an AlN single crystal 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 the manufacturing method for forming the orientation precursor layer at that time include an AD (aerosol deposition) method and an HPPD (hypersonic plasma particle deposition) method.

[0021] Manufacturing process Any of the above-mentioned solid-phase film formation method, vapor-phase film formation method, and liquid-phase film formation method can use known conditions. For example, a method for producing an AlN single crystal using the sublimation method will be described below. Specifically, it is produced by (a) heat treatment of AlN polycrystalline powder, (b) film formation of an AlN single crystal layer, and (c) grinding and removal of a seed substrate and polishing of the surface of the AlN single crystal layer.

[0022] (a) Heat treatment of AlN polycrystalline powder This step is a step of obtaining AlN raw material powder by heat-treating AlN polycrystalline powder. As shown in FIG. 1, AlN powder 12 as a raw material for an AlN single crystal is placed in a sheath 10 made of boron nitride (BN) and heat-treated in an N2 atmosphere. At this time, a crucible 16 made of BN into which graphite powder 14 is introduced so as not to directly contact the AlN powder 12 is also placed in the sheath 10. This BN crucible 16 is sized to be accommodated in the sheath 10. The amount of graphite powder introduced is preferably 0.015 to 0.130 g, more preferably 0.020 to 0.120 g, per 100 g of AlN powder. When the amount of graphite powder introduced is within the above range, for example, it is possible to obtain an AlN single crystal in which the transmittance in a specific wavelength range in the transmission spectrum decreases by a predetermined amount. The furnace pressure of the sheath 10 is preferably 0.1 to 10 atmospheres, more preferably 0.5 to 5 atmospheres. The heat treatment temperature is preferably 2150°C to 2300°C, more preferably 2200 to 2250°C.

[0023] (b) Film formation of an AlN single crystal layer This step is a step 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. 2. The film forming apparatus 20 shown in Fig. 2 includes a crucible 22, a heat insulating material 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 at its lower part and is provided with a seed substrate 30 for depositing the sublimated product of the AlN raw material powder 28 at its upper part. The inside of the crucible 22 is pressurized under an N2 atmosphere, and the crucible 22 is heated by the coil 26 to sublime 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 such that the temperature near the seed substrate 30 at the upper part of the crucible 22 is lower than the temperature near the AlN raw material powder 28 at the lower part of the crucible 22. For example, it is preferable to heat the part near the AlN raw material powder 28 of the crucible 22 to 1900 to 2250 °C, more preferably 2000 to 2200 °C, and it is preferable to heat the part near the seed substrate 30 of the crucible 22 to 1400 to 2150 °C, more preferably 1500 to 2050 °C. At this time, it is preferable that the temperature of the part near the seed substrate 30 is 100 to 500 °C lower than the temperature of the part near the AlN raw material powder 28, more preferably 200 to 400 °C. The above 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 the holes of the heat insulating material 24 covering the crucible 22 and feeding back the temperature adjustment. In this way, a SiC single crystal can be arranged as the seed substrate 30, and AlN can be redeposited on its surface to form an AlN single crystal layer 32.

[0024] (c) Grinding and removal of the seed substrate and polishing of the surface of the AlN single crystal layer This process includes a grinding process of grinding and removing the seed substrate to expose the AlN single crystal layer, and a polishing process of removing irregularities and defects on the surface of the AlN single crystal. Since SiC single crystals remain in the AlN single crystal layer fabricated through the above steps (a) and (b) using an SiC substrate as the seed substrate, grinding is performed to expose the surface of the orientation layer. Further, in order to mirror-finish the surface of the AlN single crystal layer after film formation, after smoothing the plate surface by lapping using diamond abrasive grains, polishing is performed by chemical mechanical polishing (CMP) using colloidal silica or the like. Thus, an AlN single crystal can be fabricated.

[0025] As a method other than the sublimation method, a method for fabricating an AlN single crystal using the HVPE method will be described below. As a specific example, it is fabricated by (d) forming an AlN single crystal layer on a seed substrate, (e) grinding and removing the seed substrate, (f) heat-treating the AlN single crystal layer, and (g) polishing the surface of the AlN single crystal layer.

[0026] (d) Forming an AlN Single Crystal Layer on a Seed Substrate This process is a process of forming an AlN single crystal layer on a seed substrate. Fig. 3 shows a vapor phase growth apparatus using the HVPE method. The vapor phase growth apparatus using the HVPE method includes a reaction furnace 40, a susceptor 44 on which a film-forming lower base substrate 42 is placed, a carrier gas supply source 46, an Al raw material supply source 48 and a metallic Al powder raw material 50 disposed in the Al raw material supply source 48, a heater 52, and a gas discharge part 54. It is preferable to use an SiC substrate as the film-forming lower base substrate 42. The substrate 42 is placed on the susceptor 44, and an AlCl3 gas obtained by supplying HCl gas to the heated Al raw material supply source 48 and an NH3 gas from the carrier gas supply source 46 are mixed and supplied to the film-forming lower base substrate 42. At this time, the heating temperature of the Al raw material supply source 48 is preferably 500 to 700°C, more preferably 550 to 650°C. Also, the flow rate ratio of the AlCl3 gas to the NH3 gas is preferably 1:1 to 1:500, more preferably 1:10 to 1:200. The pressure inside the reaction furnace 40 is preferably 1 to 100 Torr, more preferably 10 to 30 Torr. The growth temperature is preferably 1100 to 1400°C, more preferably 1150 to 1250°C.

[0027] (e) Grinding and removal of the seed substrate This step is a grinding process for grinding and removing the seed substrate to expose the AlN single crystal layer. Since SiC single crystals remain in the AlN single crystal layer produced through the step (d) using an SiC substrate as the seed substrate, grinding is performed to expose the surface of the orientation layer.

[0028] (f) Heat treatment of the AlN single crystal layer The AlN single crystal is placed in a BN sheath together with graphite powder and heat-treated in an N2 atmosphere. At this time, the furnace pressure is preferably 0.1 to 10 atmospheres, more preferably 0.5 to 5 atmospheres. The heat treatment temperature is preferably 2150°C to 2300°C, more preferably 2200 to 2250°C.

[0029] (g) Polishing of the AlN single crystal layer surface This step is a polishing process for mirror-finishing the surface of the AlN single crystal layer. In order to mirror-finish the surface of the AlN single crystal layer after heat treatment, 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. In this way, an AlN single crystal substrate can be produced.

Example

[0030] The present invention will be described more specifically by the following examples.

[0031] Example 1 (1) Production of AlN single crystal (1a) Heat treatment of AlN polycrystalline powder As shown in FIG. 1, in the BN sleeve 10, a commercially available AlN powder 12 (Tokuyama AlN powder, F grade) used as a raw material for the AlN single crystal was placed, and a BN crucible 16 charged with a commercially available graphite powder 14 (graphite powder manufactured by SEC Carbon, SGP grade) was placed so as not to directly touch the AlN powder 12. This BN crucible 16 is sized to be accommodated in the sleeve 10. This BN sleeve 10 was heat-treated at 2200° C. at 0.1 to 10 atmospheres in an N2 atmosphere in a graphite heater furnace. At this time, the graphite powder was charged at a ratio of 0.052 g per 100 g of the AlN powder. Thus, the AlN polycrystalline powder was heat-treated to produce an AlN raw material powder.

[0032] (1b) Film formation of AlN single crystal layer As shown in FIG. 2, a crucible 22 was used as a crystal growth container, and a SiC substrate was installed as a base material (seed substrate) 30 in this crucible, and the AlN raw material powder 28 produced in the above (1a) was put in so as not to contact it. The crucible 22 was pressurized at 50 kPa in an N2 atmosphere, and while heating the portion near the AlN raw material powder 28 in the crucible 22 to 2100° C. by high-frequency induction heating, the portion near the SiC substrate 30 in the crucible 22 was heated and held at a lower temperature (temperature difference of 200° C.) than that, whereby an AlN single crystal layer 32 was reprecipitated on the SiC substrate 30. The holding 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 the above (1b) was ground using a grinding wheel with a grit number up to #2000 until the AlN single crystal was exposed, and then the surface of the plate was further smoothed by lapping using diamond abrasive grains. Thereafter, mirror finishing was performed on the surface of the plate by chemical mechanical polishing (CMP) using colloidal silica. Thus, an AlN single crystal was produced.

[0034] (2) Evaluation of AlN single crystal (2a) EBSD measurement When EBSD measurement was performed on the front and back surfaces of the AlN single crystal, it was found that the AlN crystals were oriented in both the c-axis direction and the a-axis direction.

[0035] (2b) Transmission spectrum The total light transmittance T in the wavelength range of 200 to 800 nm for AlN single crystal a was measured using a spectrophotometer (UH4150, manufactured by Hitachi High-Technologies Corporation). T a The measured value of and the theoretical transmittance T of the AlN single crystal t After obtaining the absorption coefficient α of the AlN single crystal using the above, the transmittance T when the thickness of the AlN single crystal was converted to 100 μm 100μm was calculated. α and T 100μm are given by the following equations: α = -1 / t × ln(T a / T t ), and T 100μm = exp(-α / 100) (where t represents the actual thickness (cm) of the AlN single crystal sample) were obtained in this way. Based on this, a transmission spectrum based on the transmittance T when the thickness was converted to 100 μm 100μm was obtained. Based on the obtained transmission spectrum, the difference (%pt) (hereinafter referred to as Δ(T av640-660 -T av540-560 ) between the average value of the transmittance (%) at 640 to 660 nm and the average value of the transmittance (%) at 540 to 560 nm, and the difference (%pt) (hereinafter referred to as Δ(T av640-660 -T av540-560 ) between the average value of the transmittance (%) at 640 to 660 nm and the average value of the transmittance (%) at 780 to 800 nm were calculated. Also, within the wavelength range of 540 to 800 nm, the full width at half maximum (nm) of the absorption peak was determined. This full width at half maximum was determined by (i) determining the smaller value between the average value of the transmittance (%) at 540 to 560 nm and the average value of the transmittance (%) at 780 to 800 nm as T1, and determining the average value of the transmittance (%) at 640 to 660 nm as T2, and then (ii) reading the width of the wavelength range that gives a transmittance lower than the transmittance calculated from the equation: T2 + (T1 - T2) / 2 from the transmission spectrum. The results are shown in Table 1.

[0036] (2c) Confirmation of chipping The surface of the AlN single crystal after grinding and polishing in (1c) above was observed with an optical microscope, and chips and cracks with a maximum length of 50 μm or more were regarded as chipping, and the presence or absence of such chipping was confirmed. A total of 10 AlN single crystals were produced by the same method as in (1) above, and it was confirmed how many of the AlN single crystals had chipping, and grading evaluation was performed 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 without chipping - Evaluation B: 6 to 8 AlN single crystal substrates without chipping - Evaluation C: 3 to 5 AlN single crystal substrates without chipping - Evaluation D: Chipping was observed in all AlN single crystal substrates

[0037] Examples 2 to 6 In (1a) above, AlN single crystals were produced and evaluated in the same manner as in Example 1, except that the amount of graphite powder input during the heat treatment of the AlN polycrystalline powder was the amount shown in Table 1. Also, when EBSD measurement was performed on the front and back surfaces of the AlN single crystal, it was found that the AlN crystals were oriented in both the c-axis direction and the a-axis direction. The results are shown in Table 1.

[0038] Examples 7 and 8 (Comparison) In (1a) above, AlN single crystals were produced and evaluated in the same manner as in Example 1, except that the amount of graphite powder input during the heat treatment of the AlN polycrystalline powder was the amount shown in Table 1. Also, when EBSD measurement was performed on the front and back surfaces of the AlN single crystal, it was found that the AlN crystals were oriented in both the c-axis direction and the a-axis direction. The results are shown in Table 1.

[0039] Example 9 (Comparison) An AlN single crystal was produced and evaluated in the same manner as in Example 1, except that commercially available AlN powder (Tokuyama AlN powder, F grade) was used as the AlN raw material powder without going through the step of (1a) above. Further, when EBSD measurement was carried out on the front and back surfaces of the AlN single crystal, it was found that the AlN crystals were oriented in both the c-axis direction and the a-axis direction. The results are shown in Table 1.

[0040]

Table 1

Claims

Claim 1: An AlN single crystal containing carbon, wherein in the transmission spectrum of the AlN single crystal, the average value of the transmittance at 640 to 660 nm is lower than each of the average value of the transmittance at 540 to 560 nm and the average value of the transmittance at 780 to 800 nm, and the average value of the transmittance at 640 to 660 nm is 5 to 20 percentage points (%pt) lower than the average value of the transmittance at 780 to 800 nm.

2. In the transmission spectrum of the AlN single crystal, it has an absorption peak with a half-width of 50 to 150 nm within the wavelength range of 540 to 800 nm. The half-value width is defined as the width of a wavelength range that gives a transmittance lower than the transmittance calculated from (i) the smaller value of the average value of the transmittances at 540 to 560 nm and the average value of the transmittances at 780 to 800 nm, taken as T １ and (ii) when the average value of the transmittances at 640 to 660 nm is taken as T ２ the AlN single crystal according to claim 1, defined as the width of a wavelength range that gives a transmittance lower than the transmittance calculated from T ２ + (T １ - T ２ ) / 2

3. The AlN single crystal according to claim 1 or 2, wherein in the transmission spectrum of the AlN single crystal, the average value of the transmittance at 640 to 660 nm is 1 to 10%pt lower than the average value of the transmittance at 540 to 560 nm.

4. The AlN single crystal according to claim 1 or 2, wherein in the transmission spectrum of the AlN single crystal, the average value of the transmittance at 640 to 660 nm is 6 to 18%pt lower than the average value of the transmittance at 780 to 800 nm.

5. The AlN single crystal according to claim 2, wherein the half-width is 70 to 120 nm.

6. The AlN single crystal according to claim 3, wherein in the transmission spectrum of the AlN single crystal, the average value of the transmittance at 640 to 660 nm is 3 to 8%pt lower than the average value of the transmittance at 540 to 560 nm.

Images