Method for inspecting group-iii element nitride substrate, method for producing group-iii element nitride substrate, and method for producing semiconductor element

Abstract

Provided is a group-III element nitride substrate that is capable of having an improved yield. A method for inspecting a group-III element nitride substrate according to an embodiment of the present invention comprises: preparing a group-III element nitride substrate that is doped with an element other than group-III elements; irradiating the group-III element nitride substrate with excitation energy; and measuring the full width at half maximum of the band edge emission in an emission spectrum obtained by the irradiation.

Description

Method for inspecting a group III element nitride substrate, method for manufacturing a group III element nitride substrate, and method for manufacturing a semiconductor device

[0001] The present invention relates to a method for inspecting a group III element nitride substrate, a method for manufacturing a group III element nitride substrate, and a method for manufacturing a semiconductor device.

[0002] Group III element nitrides have a wide direct transition band gap, a high dielectric breakdown field, and a high saturated electron velocity, and therefore are being actively developed as semiconductor materials for, for example, high-frequency / high-power electronic devices.

[0003] For example, as described in Patent Document 1, depending on the application, it is desirable that the above-mentioned Group III element nitrides have high resistance.

[0004] Patent No. 5451085

[0005] Semiconductor devices obtained from the above-mentioned high-resistivity Group III element nitride substrates may not have sufficient uniformity in quality, and an improvement in yield is desired.

[0006] In view of the above, a main object of the present invention is to provide a Group III element nitride substrate that can improve yield.

[0007] 1. A method for inspecting a Group III element nitride substrate according to an embodiment of the present invention includes preparing a Group III element nitride substrate doped with an element other than a Group III element, irradiating the Group III element nitride substrate with excitation energy, and measuring the half-width of band edge emission in the emission spectrum obtained by the irradiation. 2. In the inspection method described in item 1 above, the irradiation with the excitation energy may be performed by irradiating at least one of ultraviolet light and an electron beam. 3. In the inspection method described in item 1 or 2 above, the excitation energy may be irradiated at a plurality of locations on the main surface of the Group III element nitride substrate. 4. In the inspection method described in any one of items 1 to 3 above, the element other than a Group III element may include a transition element. 5. In the inspection method described in item 4 above, the transition element may include at least one of iron and manganese. 6. In the inspection method described in any one of items 1 to 5 above, the Group III element nitride substrate may include gallium nitride. 7. In the inspection method according to any one of 1 to 6 above, the Group III element nitride substrate has a resistivity of 1×10 determined from the change in charge amount over time. ５Ω·cm or more. 8. In the inspection method according to any one of 1 to 7 above, the half width is a full width at half maximum. 9. In the inspection method according to any one of 1 to 7 above, the half width is a half width at half maximum. 10. A method for manufacturing a Group III element nitride substrate according to another embodiment of the present invention comprises carrying out the method for inspecting a Group III element nitride substrate according to any one of 1 to 7 above, and selecting the Group III element nitride substrate based on the half width at half maximum of the band edge emission. 11. In the manufacturing method according to 10 above, the Group III element nitride substrate may be selected for which the full width at half maximum of the band edge emission is 6.5 nm or less. 12. In the manufacturing method according to 10 above, the Group III element nitride substrate may be selected for which the half width at half maximum on the long wavelength side of the band edge emission is 4.2 nm or less. 13. 13. In the manufacturing method according to any one of items 10 to 12, preparing the Group III element nitride substrate may include preparing a seed crystal substrate having a sapphire substrate with upper and lower surfaces facing each other and a seed crystal film formed on the upper surface of the sapphire substrate, and growing a Group III element nitride crystal doped with an element other than a Group III element on the seed crystal film of the seed crystal substrate, and the off-angle of the sapphire substrate may be 0.58° or less. 14. In the manufacturing method according to item 13, the off-angle of the sapphire substrate may be 0.20° or more and 0.42° or less.

[0008] 15. A method for manufacturing a semiconductor device according to yet another embodiment of the present invention includes irradiating a Group III nitride substrate doped with an element other than a Group III element with excitation energy and measuring the half-width of the band-edge emission of the emission spectrum obtained by the irradiation; forming a channel layer and a barrier layer on the Group III nitride substrate to obtain a stacked structure; and providing a source electrode, a drain electrode, and a gate electrode on the stacked structure. 16. In the manufacturing method described in 15 above, the Group III nitride substrate may be irradiated with energy higher than the band gap energy of a material constituting the channel layer. 17. In the manufacturing method described in 15 or 16 above, a semiconductor device may be obtained that includes the Group III nitride substrate whose half-width satisfies a predetermined value. 18. In the manufacturing method described in any of 15 to 17 above, the stacked structure may be obtained by epitaxial growth.

[0009] 19. A Group III element nitride substrate according to yet another embodiment of the present invention is a Group III element nitride substrate doped with an element other than a Group III element, wherein the band edge emission in the emission spectrum obtained by irradiation with excitation energy has a half width at half maximum of 6.5 nm or less. 20. A Group III element nitride substrate according to yet another embodiment of the present invention is a Group III element nitride substrate doped with an element other than a Group III element, wherein the band edge emission in the emission spectrum obtained by irradiation with excitation energy has a half width at half maximum on the long wavelength side of 4.2 nm or less. 21. In the Group III element nitride substrate according to any one of the above items 19 to 20, the Group III element nitride substrate may contain gallium nitride. 22. In the Group III element nitride substrate according to any one of the above items 19 to 21, the element other than a Group III element may contain a transition element. 23. In the Group III element nitride substrate according to the above item 22, the transition element may contain at least one of iron and manganese. 24. 24. A method for producing a Group III element nitride substrate according to yet another embodiment of the present invention is the method for producing a Group III element nitride substrate according to any one of paragraphs 19 to 23 above, and may include the steps of: preparing a seed crystal substrate having a sapphire substrate with upper and lower surfaces facing each other and a seed crystal film formed on the upper surface of the sapphire substrate; and growing a Group III element nitride crystal doped with an element other than a Group III element on the seed crystal film of the seed crystal substrate, wherein the off-angle of the sapphire substrate may be 0.58° or less. 25. In the method for production according to paragraph 24 above, the Group III element nitride crystal may be grown by a flux method.

[0010] According to an embodiment of the present invention, a Group III element nitride substrate capable of improving yield can be provided.

[0011] 3A is a schematic cross-sectional view showing the general configuration of a group III element nitride substrate according to one embodiment of the present invention; FIG. 4 is a plan view of the group III element nitride substrate shown in FIG. 1; FIG. 5 is a view showing a manufacturing process of a group III element nitride substrate according to one embodiment; FIG. 6 is a view continuing from FIG. 3A; FIG. 7 is a view continuing from FIG. 3B; FIG. 8 is a schematic cross-sectional view showing the general configuration of a semiconductor device according to one embodiment of the present invention; FIG. 9 is a view for explaining a method for measuring the emission spectrum of a substrate; FIG. 10 is an emission spectrum near the band edge of the gallium nitride substrate of Experimental Example 1; FIG. 11 is an emission spectrum near the band edge of the gallium nitride substrate of Experimental Example 1;

[0012] Hereinafter, embodiments of the present invention will be described with reference to the drawings, but the present invention is not limited to these embodiments. In addition, in order to clarify the description, the drawings may show the width, thickness, shape, etc. of each part more schematically than in the embodiments, but these are merely examples and do not limit the interpretation of the present invention.

[0013] A. Group III Element Nitride Substrate Fig. 1 is a schematic cross-sectional view showing the general configuration of a Group III element nitride substrate according to one embodiment of the present invention, and Fig. 2 is a plan view of the Group III element nitride substrate shown in Fig. 1. The Group III element nitride substrate 10 is plate-shaped and has a first main surface 11 and a second main surface 12 that face each other and are connected via a side surface 13.

[0014] In the illustrated example, the group III element nitride substrate is disk-shaped (wafer), but is not limited thereto and may be any suitable shape. The size of the group III element nitride substrate may be appropriately set depending on the purpose. The diameter of the disk-shaped group III element nitride substrate is, for example, 50 mm or more and 200 mm or less. The thickness of the group III element nitride substrate is, for example, 250 μm or more and 800 μm or less.

[0015] In one embodiment, the resistivity of the group III nitride substrate is, for example, 1×10 ５ Ω・cm or more 1×10 １２ Ω cm or less, preferably 1×10 ６ Ω cm or more, more preferably 1×10 ７The resistivity is Ω cm or more. Such a semi-insulating Group III element nitride substrate can be suitably used, for example, as a substrate for a high electron mobility transistor (HEMT) device. Specifically, a channel layer and a barrier layer can be formed on the Group III element nitride substrate, and the resulting substrate can be used as a HEMT device.

[0016] The resistivity of the Group III element nitride substrate can be determined from the change in charge over time. This change in charge over time allows the resistivity to be determined without destroying the Group III element nitride substrate. Specifically, the Group III element nitride substrate is inserted into a capacitor consisting of a probe and a stage, a pulse voltage is applied, the change in charge over time of the Group III element nitride substrate is measured, and the resistivity is calculated from the measured value. Since the probe does not contact the Group III element nitride substrate, the resistivity can be determined without forming an ohmic contact electrode. The spatial resolution of the probe can be approximately 1 mm to 10 mm. The method for determining resistivity is described, for example, in the non-patent document "R. Stibal et al., "Contactless evaluation of semi-insulating GaAs wafer resistivity using the time-dependent charge measurement," Semiconductor Science and Technology, 6, p. 995 (1991)."

[0017] The group III element nitride substrate is composed of group III element nitride crystals. Examples of group III elements that make up the group III element nitride include aluminum (Al), gallium (Ga), and indium (In). These may be used alone or in combination of two or more. Specific examples of group III element nitrides include aluminum nitride (Al ｘ N), gallium nitride (Ga ｙ N), indium nitride (In ｚ N), aluminum gallium nitride (Al ｘ Ga ｙ N), gallium indium nitride (Ga ｙ In ｚ N), aluminum indium nitride (Alｘ In ｚ N), aluminum gallium indium nitride (Al ｘ Ga ｙ In ｚ In each chemical formula in parentheses, typically, x+y+z=1.

[0018] The group III element nitride is doped with an element other than a group III element. Specifically, the group III element nitride contains an element other than a group III element as a dopant. By being doped with an element other than a group III element, a group III element nitride substrate (semi-insulating group III element nitride substrate) that satisfies the above-mentioned resistivity can be obtained. As the dopant, preferably, a transition element such as iron (Fe), manganese (Mn), vanadium (V), chromium (Cr), cobalt (Co), or nickel (Ni) is used. These elements may be used alone or in combination of two or more. Preferably, the transition element includes at least one of iron or manganese. The amount of the transition element present in the group III element nitride substrate is, for example, 5×10 １６ atoms / cm ３ 1x10 or more ２０ atoms / cm ３ The following is the result.

[0019] In the above-described Group III element nitride crystal, typically, the <0001> direction is the c-axis direction, the <1-100> direction is the m-axis direction, and the <11-20> direction is the a-axis direction. The crystal plane perpendicular to the c-axis is the c-plane, the crystal plane perpendicular to the m-axis is the m-plane, and the crystal plane perpendicular to the a-axis is the a-plane. In one embodiment, the thickness direction of the Group III element nitride substrate 10 is parallel or approximately parallel to the c-axis, the first main surface 11 is a Group III element polar plane on the (0001) plane side, and the second main surface 12 is a nitrogen polar plane on the (000-1) plane side. The first main surface 11 may be parallel to the (0001) plane or may be inclined with respect to the (0001) plane. The inclination angle of the first main surface 11 with respect to the (0001) plane is, for example, 10° or less, 5° or less, 2° or less, or 1° or less. The second main surface 12 may be parallel to the (000-1) plane or may be inclined with respect to the (000-1) plane. The inclination angle of the second main surface 12 with respect to the (000-1) plane is, for example, 10° or less, 5° or less, 2° or less, or 1° or less.

[0020] B. Inspection Method The Group III element nitride substrate is inspected to determine whether the resistivity determined from the change in the amount of charge over time is a predetermined value (for example, 1×10 ５Even when the resistivity (Ω·cm or more) is satisfied, it is believed that there may be regions of low resistivity within the plane of the Group III element nitride substrate. Specifically, impurity elements such as oxygen may segregate into crystal defects such as dislocations in the Group III element nitride crystal, affecting conductivity. Donor impurities such as oxygen are likely to be mixed into the crystal defects, affecting resistivity. Therefore, it is believed that crystal defects may be concentrated in a minute region of, for example, φ10 μm to 200 μm within the plane of the Group III element nitride substrate. On the other hand, the diameter of the measurement probe used in the method of measuring resistivity based on the change in charge amount over time may be, for example, φ1 mm to 10 mm. Resistivity measurement based on the change in charge amount over time assumes that the resistivity is uniform at least within this range of the measurement probe diameter, and it is therefore believed difficult to accurately measure the resistivity of a region that includes a minute region with locally low resistivity. Furthermore, semiconductor devices obtained corresponding to low resistivity regions may be of low quality. For example, HEMT devices obtained corresponding to low resistivity regions may suffer from current leakage.

[0021] A method for inspecting a Group III-nitride substrate according to one embodiment of the present invention includes irradiating a prepared Group III-nitride substrate with excitation energy and measuring the half-width of band-edge emission in an emission spectrum obtained by the irradiation.

[0022] The excitation energy can be irradiated by, for example, at least one of ultraviolet light and an electron beam. In one embodiment, the Group III nitride substrate is irradiated with energy higher than the band gap energy of the material constituting the channel layer. By irradiating with such energy, for example, it is possible to accurately predict the occurrence of current leakage in the HEMT device.

[0023] The ultraviolet light is emitted from a light source capable of emitting laser light with a wavelength shorter than the band edge. Typical examples of the laser light source include a He—Cd laser and an excimer laser. Alternatively, a deep ultraviolet (DUV) lamp such as a low-pressure mercury lamp or a deuterium lamp can be used for the ultraviolet light irradiation.

[0024] The electron beam is irradiated using an electron beam source (e.g., an electron gun) with an energy of about 0.5 KeV to 10 KeV, such as a cold cathode field emission electron source, a photocathode electron source, or a Schottky electron source.

[0025] For example, a Group III element nitride substrate made of gallium nitride may be irradiated with ultraviolet light having a wavelength of 364 nm or less. A Group III element nitride substrate made of aluminum gallium nitride, which has a higher band gap energy than gallium nitride, may require higher energy and may be irradiated with an electron beam.

[0026] The emission spectrum obtained by irradiating the Group III element nitride substrate with excitation energy can be measured, typically by measuring the intensity of light of a given wavelength separated by a spectrometer using any appropriate ultraviolet detector. Examples of ultraviolet detectors include a Si photodiode and a photomultiplier tube (PMT). Another example of an ultraviolet detector is an array-type spectrometer detector that combines a small grating with a CCD / CMOS / NMOS image sensor.

[0027] The half-width of the band-edge emission is obtained from the measured emission spectrum. By ensuring that the measured half-width satisfies a predetermined value (i.e., is equal to or less than the predetermined value), a semiconductor device with excellent quality can be obtained. For example, a HEMT device with suppressed leakage current can be obtained. Furthermore, by selecting and using a Group III nitride substrate that satisfies the predetermined half-width, the yield of semiconductor device manufacturing can be significantly improved. Here, the half-width includes the full-width at half maximum (FWHM) and the half-width at half maximum (HWHM). In one embodiment, the full-width at half maximum of the band-edge emission of the measured emission spectrum is preferably 6.5 nm or less. In another embodiment, the half-width at half maximum on the long-wavelength side of the band-edge emission of the measured emission spectrum is preferably 4.2 nm or less.

[0028] The intensity of the emission spectrum obtained by irradiating the semi-insulating Group III element nitride substrate with excitation energy may be weaker than the intensity of the emission spectrum obtained by irradiating a conductive Group III element nitride substrate (e.g., a Group III element nitride substrate not doped with elements other than Group III elements) with excitation energy, and is furthermore easily affected by the surface flatness of the substrate and the presence or absence of a process-affected layer. However, the inventors have carefully investigated the relationship between the emission spectrum of a semi-insulating Group III element nitride substrate and the quality of the resulting semiconductor device and have found that there is a correlation between the half-width of the band-edge emission and the quality of the resulting semiconductor device. In a Group III element nitride with good semi-insulating properties, the band-edge intensity of the emission spectrum may be weak, but the half-width may appear narrower due to a relative decrease in emission via various levels near the band edge. On the other hand, for example, when donor impurities such as oxygen are incorporated into the Group III element nitride crystal, the emission intensity near the band edge may increase, and the half-width may widen.

[0029] The FWHM of the band-edge emission can be used to easily determine the quality of a Group III nitride substrate by measuring it at room temperature. Strictly speaking, an emission spectrum may contain various levels of emission near the band edge, which can only be separated and observed at extremely low temperatures. However, the FWHM of the band-edge emission can be measured at room temperature. Furthermore, the measurement of the FWHM of the band-edge emission tends to be less dependent on the measurement device. Specifically, there is no need to adjust the intensity of the irradiated excitation energy to a constant value or to check the reproducibility using a calibration sample.

[0030] The excitation energy may be irradiated at multiple locations on the principal surface of the Group III nitride substrate. By irradiating multiple locations and mapping the half-width of the band-edge emission within the substrate plane, it is possible to predict that regions that do not satisfy a predetermined value will be regions of low quality in the resulting semiconductor device (e.g., defective regions with large leakage current). For example, excitation energy is irradiated at predetermined intervals (e.g., intervals of 0.01 mm to 1 mm) in both the vertical and horizontal directions within the plane of the disk-shaped substrate shown in FIG. 2. Mapping data can be obtained from the obtained data. The locations for forming the semiconductor device may be selected based on the mapping data within the substrate plane.

[0031] C. Manufacturing Method A manufacturing method of a Group III element nitride substrate according to one embodiment of the present invention includes preparing a seed crystal substrate having a base substrate and a seed crystal film, and growing a Group III element nitride crystal doped with an element other than a Group III element on the seed crystal film of the seed crystal substrate.

[0032] 3A to 3C are diagrams showing a manufacturing process for a group III nitride substrate according to one embodiment, in which a seed crystal film 22 is formed on an upper surface 21 a of a base substrate 21 having an upper surface 21 a and a lower surface 21 b facing each other, thereby completing a seed crystal substrate 20.

[0033] The base substrate may be, for example, a substrate having a shape and size that allows a Group III nitride substrate having the desired shape and size to be produced. Typically, the base substrate is disk-shaped with a diameter of 50 mm to 200 mm. The thickness of the base substrate is, for example, 200 μm to 800 μm.

[0034] Any suitable substrate can be used as the base substrate. The base substrate is preferably made of a single crystal having a hexagonal crystal structure. For example, it is preferable to use a sapphire substrate made of single crystal alumina as the base substrate.

[0035] The off-angle of the sapphire substrate can be set to any appropriate angle. The off-angle of the sapphire substrate is preferably 0.58° or less, more preferably 0.48° or less, and even more preferably 0.42° or less. By using a sapphire substrate having such an off-angle, it is possible to obtain, for example, a Group III element nitride substrate that can produce high-quality semiconductor devices with a good yield (e.g., a high yield). On the other hand, the off-angle of the sapphire substrate is preferably 0.20° or more. By using a sapphire substrate having such an off-angle, it is possible to grow, for example, a Group III element nitride crystal well. Here, the off-angle of the sapphire substrate refers to the inclination angle of the primary surface of the sapphire substrate with respect to the reference crystal plane (c-plane).

[0036] The thickness of the seed crystal film is, for example, 0.2 μm or more. From the viewpoint of preventing meltback or disappearance during film formation, the thickness of the seed crystal film is preferably 1 μm or more, more preferably 2 μm or more. On the other hand, from the viewpoint of productivity, the thickness of the seed crystal film is preferably 10 μm or less, more preferably 5 μm or less.

[0037] Any appropriate material can be used as the material for forming the seed crystal film. A group III element nitride is typically used as the material for forming the seed crystal film. Details of the group III element nitride are as described above. In one embodiment, gallium nitride is used. Preferably, gallium nitride that exhibits a yellow luminescence effect is used by fluorescence microscopy. In such gallium nitride, in addition to band-to-band exciton transitions (UV), a peak (yellow luminescence (YL) or yellow band (YB)) is observed in the range of 2.2 eV to 2.5 eV.

[0038] The seed crystal film can be formed by any appropriate method. A typical method for forming the seed crystal film is a vapor phase growth method. Specific examples of the vapor phase growth method include metal organic chemical vapor deposition (MOCVD), hydride vapor phase epitaxy (HVPE), pulsed excited deposition (PXD), molecular beam epitaxy (MBE), evaporation, and sublimation. Among these, the MOCVD method is preferably used.

[0039] The formation of the seed crystal film by the MOCVD method includes, for example, a first formation step and a second formation step, in this order. Specifically, in the first formation step, a first layer (low-temperature grown buffer layer) (not shown) is formed on a base substrate at a temperature T1 (e.g., 450°C to 550°C), and in the second formation step, a second layer (not shown) is formed at a temperature T2 (e.g., 1000°C to 1200°C) higher than temperature T1. The thickness of the first layer is, for example, 20 nm to 50 nm. The thickness of the second layer is, for example, 1 μm to 5 μm.

[0040] Next, a group III element nitride crystal is grown on the seed crystal film 22 of the seed crystal substrate 20 to form a group III element nitride crystal layer 16, thereby obtaining a layered substrate 30 as shown in FIG. 3B . The degree of growth of the group III element nitride crystal (the thickness of the group III element nitride crystal layer 16) can be adjusted depending on the desired thickness of the group III element nitride substrate. Any appropriate direction can be selected as the growth direction of the group III element nitride crystal depending on the application, purpose, etc. Specific examples include the normal directions to the c-plane, a-plane, and m-plane, and the normal directions to planes inclined relative to the c-plane, a-plane, and m-plane.

[0041] Group III element nitride crystals can be grown by any appropriate method. The method for growing Group III element nitride crystals is not particularly limited, as long as it is a method that can achieve a crystal orientation that roughly follows the crystal orientation of the seed crystal film. Specific examples of methods for growing Group III element nitride crystals include vapor phase growth methods such as metal organic chemical vapor deposition (MOCVD), hydride vapor phase epitaxy (HVPE), pulsed excited deposition (PXD), molecular beam epitaxy (MBE), and sublimation; and liquid phase growth methods such as flux deposition, ammonothermal deposition, hydrothermal deposition, and sol-gel deposition. These methods can be used alone or in combination of two or more.

[0042] Preferably, a flux method (e.g., a Na flux method) is employed as a method for growing Group III element nitride crystals. Details of such growth methods are described, for example, in Japanese Patent No. 5451085, and growth may be performed by adjusting various conditions of the described growth method as appropriate. Specifically, Group III element nitride crystals can be grown by adjusting various conditions using a crystal manufacturing apparatus that includes a pressure-resistant vessel capable of supplying pressurized nitrogen gas, a turntable that can rotate within the pressure-resistant vessel, and an outer vessel placed on the turntable.

[0043] Growth of Group III nitride crystals by the flux method is typically carried out using a crucible as a growth container. Specifically, the seed crystal substrate is placed at a predetermined position in the crucible, and the crucible is then filled with raw materials. The crucible containing the seed crystal substrate is typically placed with a lid on in a nitrogen-containing atmosphere at a predetermined pressure and temperature for growth.

[0044] The raw material is, for example, a melt composition containing a flux, a Group III element, and a dopant. The flux preferably contains at least one of an alkali metal and an alkaline earth metal, and more preferably metallic sodium. Typically, the flux and a metal source material are mixed together. As the metal source material, an elemental metal, an alloy, a metal compound, etc. can be used, but from the viewpoint of handling, an elemental metal is preferably used.

[0045] The crucible (including the lid) can be made of any suitable material that can be used in the flux method. Examples of the crucible material include alumina, yttria, and YAG (yttrium aluminum garnet). The crucible material may be a single crystal or a polycrystal (ceramic). The ceramic may have a high relative density, such as by HIP treatment, to give it translucency.

[0046] As described above, the growth can be carried out in a nitrogen-containing atmosphere. The growth atmosphere can contain other gases in addition to nitrogen. The other gases are preferably inert gases such as argon, helium, and neon.

[0047] The pressure of the atmosphere during growth can be set to any appropriate pressure. For example, from the viewpoint of preventing evaporation of the flux, the pressure of the atmosphere during growth is preferably 10 atmospheres or more, more preferably 30 atmospheres or more. On the other hand, for example, from the viewpoint of preventing the growth apparatus from becoming large-scale, the pressure of the atmosphere during growth is preferably 2000 atmospheres or less, more preferably 500 atmospheres or less.

[0048] The temperature of the atmosphere during growth can be set to any appropriate temperature, preferably 700°C to 1000°C, more preferably 800°C to 900°C.

[0049] The growth is preferably carried out while rotating the crucible. For example, the crucible with a lid is placed in the outer container and placed on the turntable, and the crucible is rotated by rotating the turntable.

[0050] After growth of the group III element nitride crystal, as shown in FIG. 3C , the group III element nitride crystal (group III element nitride crystal layer 16) is separated from the base substrate 21 to obtain a free-standing substrate 32. Typically, as shown in the figure, the free-standing substrate 32 may include the group III element nitride crystal 16 and a seed crystal film 22. The group III element nitride crystal may be separated from the base substrate by any appropriate method. Examples of methods for separating the group III element nitride crystal include spontaneous separation from the base substrate by utilizing the difference in thermal contraction between the group III element nitride crystal and the base substrate during a cooling step after growth of the group III element nitride crystal, separation by chemical etching, and laser lift-off using laser light irradiation. When separating the group III element nitride crystal by laser lift-off, typically, laser light is irradiated from the lower surface 21 b of the base substrate 21 of the laminated substrate 30. Alternatively, the free-standing substrate may be obtained by grinding or cutting using a cutting machine such as a wire saw.

[0051] The free-standing substrate 32 can be used as the above-mentioned Group III element nitride substrate as it is, but typically, the free-standing substrate 32 is subjected to any appropriate processing to obtain the above-mentioned Group III element nitride substrate.

[0052] One example of processing performed on the free-standing substrate is grinding of the peripheral portion (e.g., grinding using a diamond grinding wheel). Typically, the free-standing substrate is ground to have the desired shape and size (e.g., a disk shape having a desired diameter).

[0053] Other examples of processing performed on the freestanding substrate include grinding and polishing (e.g., lapping and chemical mechanical polishing (CMP)) of the main surfaces (upper and lower surfaces). Typically, the substrate is thinned and flattened to a desired thickness by grinding and polishing. In one embodiment, the seed crystal film 22 is removed by processing the main surface, leaving only the group III element nitride crystal layer 16 (only a single crystal growth layer).

[0054] Furthermore, examples of processing performed on the freestanding substrate include chamfering the outer peripheral edge, removing a process-affected layer, and removing residual stress that may result from the process-affected layer.

[0055] D. Applications The above-described Group III element nitride substrate can be applied to any appropriate semiconductor device. FIG. 4 is a schematic cross-sectional view showing the general configuration of a semiconductor device according to one embodiment of the present invention, taking a HEMT device as an example. A HEMT device 40 includes a Group III element nitride substrate 10, a stacked layer structure 43 including a channel layer 41 and a barrier layer 42, in this order, and a source electrode 44, a drain electrode 45, and a gate electrode 46 provided on the stacked layer structure 43. These electrodes may each be metal electrodes having a thickness of approximately 10-15 nm.

[0056] The stacked structure 43 can be obtained by heterojunction of each layer. For example, the channel layer 41 and the barrier layer 42 can be formed by epitaxial growth on the group III element nitride substrate 10. This stacked structure may be referred to as an epitaxial substrate. The thickness of the channel layer 41 is, for example, 50 nm to 5 μm. The thickness of the barrier layer 42 is, for example, 2 nm to 40 nm.

[0057] The channel layer 41 and the barrier layer 42 may each be made of a Group III element nitride crystal. Examples of Group III elements constituting the Group III element nitride include Ga (gallium), Al (aluminum), and In (indium). These may be used alone or in combination. In one embodiment, the Group III element nitride substrate 10 may be made of gallium nitride doped with an element other than Ga. In this case, the channel layer 41 is preferably made of gallium nitride. The barrier layer 42 is preferably made of at least one selected from aluminum gallium nitride, aluminum indium nitride, and aluminum indium gallium nitride.

[0058] The channel layer 41 and the barrier layer 42 may each be formed by any appropriate method. In one embodiment, the channel layer 41 and the barrier layer 42 may each be formed by an MOCVD method. When the channel layer 41 and the barrier layer 42 are formed by an MOCVD method, a metal-organic (MO) precursor gas may be used as a Group III element source. For example, when a gallium nitride layer is formed as the channel layer 41 and an aluminum gallium nitride layer is formed as the barrier layer 42 by an MOCVD method, trimethylgallium (TMG) and trimethylaluminum (TMA) may be used as the Ga source and the Al source, respectively. Ammonia gas may be used as the nitrogen source. At least one of hydrogen gas and nitrogen gas may be used as the carrier gas.

[0059] Although not shown, a buffer layer may be disposed between the group III element nitride substrate 10 and the channel layer 41. For example, the buffer layer may be formed during the deposition of the channel layer, and may contain the material that constitutes the channel layer.

[0060] When the half width at half maximum of the band edge emission of the group III nitride substrate 10 satisfies a predetermined value, for example, leakage current can be effectively suppressed in the HEMT device 40. The predetermined value may be, for example, a full width at half maximum of 6.5 nm or less, or a half width at half maximum on the long wavelength side of 4.2 nm or less.

[0061] The present invention will be described in detail below with reference to examples, but the present invention is not limited to these examples. Resistivity values ​​were measured using the following measurement method. <Resistivity> Resistivity within the substrate surface was measured by a non-contact method based on the change in charge amount over time. Specifically, the substrate was placed on a capacitor stage consisting of a probe and a stage, the probe was brought close to the substrate, a pulse voltage with a pulse width of 100 ns was applied, and the change in charge amount over time on the substrate was measured for 1 second at room temperature (25°C), and the resistivity was calculated.

[0062] Experimental Example 1 (Preparation of Seed Crystal Substrates) Three-inch diameter c-plane sapphire substrates were prepared with various off-angles (0.20°, 0.28°, 0.36°, 0.39°, 0.42°, 0.43°, 0.44°, 0.46°, 0.48°, 0.52°, 0.56°, 0.58°, and 0.60°). A 2 μm-thick gallium nitride film was formed on each sapphire substrate by MOCVD to prepare seed crystal substrates.

[0063] (Growth of Gallium Nitride Crystals) Gallium nitride crystals were grown using a crystal manufacturing apparatus equipped with a pressure-resistant container capable of supplying pressurized nitrogen gas, a turntable rotatable within the pressure-resistant container, and an outer container placed on the turntable. The obtained seed crystal substrate was placed in an alumina crucible in a nitrogen atmosphere glove box. Next, 40 g of metallic gallium, 80 g of metallic sodium, and 0.1 g of iron as a doping element were melted in the glove box and filled into the crucible, and the seed crystal substrate was immersed in the flux melt and covered with an alumina plate. In this state, the crucible was placed in a stainless steel inner container, which was then placed in a stainless steel outer container capable of accommodating the inner container, and the outer container was closed with a lid equipped with a nitrogen inlet pipe. In this state, the outer container was placed on a turntable installed in the heating section of the crystal manufacturing apparatus, which had been vacuum-baked in advance, and the pressure-resistant container of the crystal manufacturing apparatus was sealed with a lid. Next, the heating section (upper heater, middle heater, and lower heater) was operated to heat the temperature of the heating space to 850°C, while nitrogen gas was introduced from a nitrogen gas cylinder into the pressure vessel until the pressure reached 4 MPa, and the outer vessel was rotated horizontally. This state was maintained for 35 hours, allowing gallium nitride crystal to grow. After that, the vessel was naturally cooled to room temperature and depressurized to atmospheric pressure, and the lid of the alumina crucible was opened, revealing that the grown gallium nitride crystal had naturally peeled off from the sapphire substrate. In this way, a gallium nitride crystal with a diameter of 3 inches and a thickness of 1 mm was obtained.

[0064] Thereafter, the surface of the gallium nitride crystal separated from the sapphire substrate and the opposite surface were polished and flattened using diamond abrasive grains, resulting in a 3-inch diameter, 0.5 mm thick, and 1×10 resistivity. ７ An Fe-doped gallium nitride substrate with a resistivity of Ω·cm or more was obtained.

[0065] [Experimental Example 2] A 3-inch diameter, 0.5 mm thick, and 1×10 resistivity sample was prepared in the same manner as in Experimental Example 1, except that the doping element was changed to Mn instead of Fe (0.1 g of manganese was filled in the crucible). ７ A Mn-doped gallium nitride substrate with a resistivity of Ω·cm or more was obtained.

[0066] <Evaluation> The gallium nitride substrates obtained in Experimental Examples 1 and 2 were evaluated as follows.

[0067] 1. Half-Width of Band-Edge Emission (Full Width at Half Maximum and Half Width at Half Maximum) The photoluminescence obtained by irradiating the resulting gallium nitride substrate with an ultraviolet laser was measured using a spectrometer to determine the half-width of the band-edge emission peak. Specifically, as shown in FIG. 5 , the resulting gallium nitride substrate (measurement substrate) 56 was fixed to a sample stage 55, and in this state, a He—Cd laser with a wavelength of 325 nm was irradiated onto the main surface of the substrate 56 from a laser device 51. The laser was irradiated onto the main surface of the substrate 56 at an angle of incidence of 45° via a chopper 52, a beam attenuation plate 53, and a condenser lens 54 with a focal length of 100 mm and a diameter of 50 mm. The photoluminescence from the substrate 56 was incident on a spectrometer 59 via condenser lenses 57 and 58 with a focal length of 100 mm and a diameter of 150 mm. Note that the arrow in FIG. 5 indicates the direction of the laser light. A photodetector (photomultiplier tube) 60 was attached to the spectrometer 59. The weak signal detected by the photodetector 60 was amplified by a lock-in amplifier 61 in synchronization with the chopper 52 to obtain an emission spectrum. The position of the sample stage 55, which fixed the substrate 56, was adjusted so that the detection intensity of the lock-in amplifier 61 was maximized. At this time, the diameter of the irradiated light on the substrate 56 was approximately 0.3 mm. The dashed lines in Figure 5 indicate the synchronization signal. By moving the sample stage 55, the band edge emission was measured at intervals of 1 mm within the substrate surface, the half-width of the peak value was calculated, and mapping data of the half-width of the band edge emission was obtained.

[0068] 2. Leakage Current (Fabrication of Epitaxial Substrate) A gallium nitride (GaN) layer and an aluminum gallium nitride (AlGaN) layer were epitaxially grown on the main surface of the obtained gallium nitride substrate by MOCVD to fabricate an epitaxial substrate. Specifically, the obtained gallium nitride substrate was placed on a susceptor in an MOCVD furnace. A mixed flow of hydrogen gas and nitrogen gas was introduced into the MOCVD furnace, and the temperature was raised to 1100°C at a furnace pressure of 0.3 atm. After reaching 1100°C, a 1 μm GaN layer was formed using ammonia gas and Ga source gas, and then an Al source gas was added to form a 20 nm AlGaN layer (Al:Ga composition ratio 0.2:0.8), thereby forming an epitaxial substrate. After the film formation, the substrate temperature was lowered to room temperature and the pressure was returned to atmospheric pressure, and then the epitaxial substrate was removed from the MOCVD furnace.

[0069] (Fabrication of Transistor Element) Next, a transistor element was fabricated using the epitaxial substrate. Prior to forming electrodes on the epitaxial substrate, a 10 nm thick silicon oxide film was formed on the obtained epitaxial substrate as a passivation film. Subsequently, the silicon oxide film was etched away by photolithography in the areas where the source electrode, drain electrode, and gate electrode were to be formed. Next, using photolithography and reactive ion etching (RIE), the AlGaN layer and GaN layer were etched away to a depth of approximately 400 nm at the boundaries of the resulting transistor elements. Next, a photoresist was applied to the AlGaN layer, and openings were formed by photolithography in the areas where the source electrode and drain electrode were to be formed. Metal films of Ti, Al, Ni, and Au were sequentially formed by vacuum deposition to thicknesses of 25 nm, 75 nm, 15 nm, and 100 nm, respectively, to form a multilayer structure. The substrate was then immersed in an organic solvent or a stripping solution, and the photoresist film was removed by lift-off to obtain source and drain electrodes. Next, to improve the ohmic properties of the source and drain electrodes, the substrate was subjected to a heat treatment at 850°C for 30 seconds in a nitrogen gas atmosphere. Subsequently, similar to the formation of the source and drain electrodes, Pt and Au metal films were sequentially deposited to thicknesses of 30 nm and 100 nm, respectively, using photolithography and vacuum deposition to form gate electrodes that could serve as Schottky metal patterns. In this way, a transistor element was fabricated, in which electrodes with a gate width of 1 mm, a source-to-gate spacing of 2 μm, a gate-to-drain spacing of 8 μm, and a gate length of 1 μm were formed.

[0070] The leakage current was measured for 15 randomly selected samples from the epitaxial substrate of the transistor devices fabricated as described above. A source-drain voltage of 10 V was applied, and the gate voltage was set to -4 V to turn the device off. The leakage current was the current flowing between the source and drain.

[0071] As an example, the evaluation results when a sapphire substrate with an off-angle of 0.43° in Experimental Example 1 was used are shown in Table 1 and Figures 6 and 7. Specifically, Table 1 summarizes the leakage current of 16 arbitrary elements in the substrate, and the full width at half maximum and half width at half maximum on the long wavelength side of the peak of band edge emission at the position in the substrate of each element calculated from the mapping data. In addition, the leakage current when off is small (4.57 × 10 －８ A / mm ２ The emission spectrum near the band edge (wavelength 364 nm) corresponding to the device is shown in FIG. 6(1), and the emission spectrum near the band edge (wavelength 364 nm) corresponding to the device with a large leakage current (6.85×10 －２ A / mm ２ The emission spectrum near the band edge corresponding to the device is shown in Figure 7 (2). The emission spectrum was normalized by the maximum value.

[0072] From Table 1, the leakage current is 1×10 －６ A / mm ２ When an off-angle of less than 0.43° is defined as a non-defective product, the rate of non-defective products when a sapphire substrate with an off-angle of 0.43° is used is 75%. Similarly, in Experimental Example 1, the yield rates of gallium nitride substrates fabricated using sapphire substrates with different off-angles were calculated. The calculation results are summarized in Table 2.

[0073] As an example, when a sapphire substrate with an off-angle of 0.43° in Experimental Example 2 was used, the evaluation results are shown in Table 3. Specifically, Table 3 summarizes the leakage currents of 16 arbitrary elements in the substrate, and the full width at half maximum and half width at half maximum on the long wavelength side of the band edge emission at the position in the substrate of each element determined from the above mapping data.

[0074] From Table 3, the leakage current is 1×10 －６ A / mm ２ If a substrate with an off-angle of less than 0.43° is considered a non-defective product, the rate of non-defective products when a sapphire substrate with an off-angle of 0.43° was used was 63%. Similarly, in Experimental Example 2, the yield rates of gallium nitride substrates fabricated using sapphire substrates with different off-angles were calculated. The calculation results are summarized in Table 4.

[0075] Group III nitride substrates according to embodiments of the present invention can be used, for example, as substrates for various semiconductor devices.

[0076] 10 Group III element nitride substrate, 11 First main surface, 12 Second main surface, 13 Side surface, 16 Group III element nitride crystal layer, 20 Seed crystal substrate, 21 Base substrate, 21a Upper surface, 21b Lower surface, 22 Seed crystal film, 30 Laminated substrate, 32 Freestanding substrate, 40 HEMT element, 41 Channel layer, 42 Barrier layer, 43 Laminated structure, 44 Source electrode, 45 Drain electrode, 46 Gate electrode, 51 Laser device, 52 Chopper, 53 Light-attenuating plate, 54 Condenser lens, 55 Sample stage, 56 Measurement substrate, 57 Condenser lens, 58 Condenser lens, 59 Spectrometer, 60 Photodetector, 61 Lock-in amplifier.

Claims

1. A method for inspecting a Group III element nitride substrate, the method comprising: preparing a Group III element nitride substrate doped with an element other than a Group III element; irradiating the Group III element nitride substrate with excitation energy; and measuring a half-width of a band edge emission peak of an emission spectrum obtained by the irradiation; and selecting the Group III element nitride substrate based on the half width of the band edge emission peak; a Group III element nitride substrate having a full width at half maximum of the band edge emission peak of 6.5 nm or less is selected.

2. A method for inspecting a Group III element nitride substrate, the method comprising: preparing a Group III element nitride substrate doped with an element other than a Group III element; irradiating the Group III element nitride substrate with excitation energy; and measuring a half-width of a band edge emission peak of an emission spectrum obtained by the irradiation; and selecting the Group III element nitride substrate based on the half width of the band edge emission peak; the method for producing a Group III element nitride substrate, selecting the Group III element nitride substrate having a half width at half maximum of 4.2 nm or less on the long wavelength side of the band edge emission peak.

3. Performing a method for inspecting a Group III element nitride substrate, the method comprising: preparing a Group III element nitride substrate doped with an element other than a Group III element; irradiating the Group III element nitride substrate with excitation energy; and measuring a half-width of a band edge emission peak of an emission spectrum obtained by the irradiation; and selecting the Group III element nitride substrate based on the half width of the band edge emission peak; Providing the Group III nitride substrate includes: preparing a seed crystal substrate having a sapphire substrate having upper and lower surfaces opposed to each other and a seed crystal film formed on the upper surface of the sapphire substrate; growing a Group III element nitride crystal doped with an element other than Group III elements on the seed crystal film of the seed crystal substrate; The off-angle of the sapphire substrate is 0.58° or less. A method for manufacturing a group III element nitride substrate.

4. The method for producing a Group III element nitride substrate according to claim 3 , wherein the off-angle of the sapphire substrate is not less than 0.20° and not more than 0.42°.

5. A group III element nitride substrate doped with an element other than a group III element, A Group III element nitride substrate, in which the full width at half maximum of a band edge emission peak of an emission spectrum obtained by irradiation with excitation energy is 6.5 nm or less.

6. A group III element nitride substrate doped with an element other than a group III element, A Group III element nitride substrate, in which the half width at half maximum on the long wavelength side of a band edge emission peak of an emission spectrum obtained by irradiation with excitation energy is 4.2 nm or less.

7. The Group III-nitride substrate according to claim 5 or 6, wherein the Group III-nitride substrate comprises gallium nitride.

8. The Group III element nitride substrate according to claim 5 , wherein the element other than the Group III element includes a transition element.

9. The group III-nitride substrate according to claim 8 , wherein the transition element includes at least one of iron and manganese.

10. The Group III element nitride substrate according to claim 5, wherein the resistivity determined from the charge amount versus time is 1×10 5 Ω·cm or more.

11. preparing a seed crystal substrate having a sapphire substrate having upper and lower surfaces opposed to each other and a seed crystal film formed on the upper surface of the sapphire substrate; growing a Group III element nitride crystal doped with an element other than Group III elements on the seed crystal film of the seed crystal substrate; The off-angle of the sapphire substrate is 0.58° or less.

7. The method for producing a Group III element nitride substrate according to claim 5 or 6.

12. The method for producing a Group III element nitride substrate according to claim 11 , wherein the Group III element nitride crystal is grown by a flux method.