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

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

[Technical Field]

[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. [Background technology]

[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. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Patent No. 5451085 Summary of the Invention [Problem to be solved by the invention]

[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. [Means for solving the problem]

[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 detecting band edge luminescence in the emission spectrum obtained by the irradiation.peak and measuring the half-width of the peak. 2. In the inspection method described in 1 above, the irradiation of the excitation energy may be carried out by irradiating at least one of ultraviolet light and an electron beam. 3. In the inspection method described in 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 according to any one of 1 to 3 above, the elements other than the group III elements may include transition elements. 5. In the inspection method described in 4 above, the transition element may include at least one of iron and manganese. 6. In the inspection method according to any one of the above items 1 to 5, the Group III element nitride substrate may contain gallium nitride. 7. In the inspection method according to any one of the above items 1 to 6, the Group III element nitride substrate has a resistivity of 1×10 5 It may be Ω·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 half width at half maximum. 10. A method for manufacturing a Group III element nitride substrate according to another embodiment of the present invention includes carrying out the method for inspecting a Group III element nitride substrate according to any one of the above items 1 to 7, and detecting the band edge luminescence. peak and selecting the Group III element nitride substrate based on the half width of the peak intensity distribution. 11. In the manufacturing method according to the above item 10, the band edge emission peak Alternatively, the Group III element nitride substrate may be selected such that the full width at half maximum of the reflection spectrum is 6.5 nm or less. 12. In the manufacturing method according to the above item 10, the band edge emission peak Alternatively, the Group III element nitride substrate may be selected such that the half width at half maximum on the long wavelength side is 4.2 nm or less. 13. In the manufacturing method according to any one of 10 to 12 above, 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 3 above, the sapphire substrate may have an off-angle of 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 element nitride substrate doped with an element other than a Group III element with excitation energy, and obtaining band edge emission in the emission spectrum obtained by the irradiation. peak forming a channel layer and a barrier layer on the Group III element 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 according to 15 above, the Group III element nitride substrate may be irradiated with energy higher than the band gap energy of the material constituting the channel layer. 17. In the manufacturing method according to 15 or 16 above, a semiconductor device may be obtained that includes the Group III element nitride substrate whose half-width satisfies a predetermined value. 18. In the manufacturing method according to any one of the above items 15 to 17, the laminated 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, and has a band edge emission in the emission spectrum obtained by irradiation with excitation energy. peak The half-width of the peak is 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, and has a band edge emission in the emission spectrum obtained by irradiation with excitation energy. peak The half width at half maximum on the long wavelength side is 4.2 nm or less. 21. In the Group III element nitride substrate according to the above item 19 or 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 elements other than the Group III elements may include a transition element. 23. In the Group III element nitride substrate according to 22 above, the transition element may include at least one of iron and manganese. 24. A method for manufacturing a Group III element nitride substrate according to yet another embodiment of the present invention is the method for manufacturing a Group III element nitride substrate according to any one of 19 to 23 above, and 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, wherein the off-angle of the sapphire substrate may be 0.58° or less. 25. In the manufacturing method described in 24 above, the Group III element nitride crystal may be grown by a flux method. [Effects of the Invention]

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

[0011] [Figure 1] 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. [Figure 2] FIG. 2 is a plan view of the group III element nitride substrate shown in FIG. [Figure 3A]1A to 1C are diagrams illustrating a manufacturing process of a group III element nitride substrate according to one embodiment. [Figure 3B] This is a continuation of Figure 3A. [Figure 3C] This is a continuation of Figure 3B. [Figure 4] 1 is a schematic cross-sectional view showing the general configuration of a semiconductor element according to one embodiment of the present invention. [Figure 5] FIG. 10 is a diagram for explaining a method for measuring the emission spectrum of a substrate. [Figure 6] 1 shows an emission spectrum near the band edge of the gallium nitride substrate of Experimental Example 1. [Figure 7] 1 shows an emission spectrum near the band edge of the gallium nitride substrate of Experimental Example 1. DETAILED DESCRIPTION OF THE INVENTION

[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 disc-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 disc-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 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, and more preferably 1×10 7 The resistivity is Ω·cm or more. Such a semi-insulating Group III 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 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. By measuring the change in charge over time, the resistivity can 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 the 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 (Al x In z N), aluminum gallium indium nitride (Al x Ga y In z N). In each chemical formula in parentheses, typically, x+y+z=1.

[0018] The above-mentioned Group III element nitride is doped with an element other than Group III elements. Specifically, the Group III element nitride contains an element other than Group III elements as a dopant. By doping with an element other than Group III elements, 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 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 More than 1×10 20 atoms / cm 3 The following is the result.

[0019] In the above-mentioned Group III element nitride crystal, typically, <0001> The <1-100> 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 III-nitride substrate 10 is parallel or approximately parallel to the c-axis, the first main surface 11 is a III-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 tilt angle of the second main surface 12 with respect to the (000-1) plane is, for example, 10° or less, may be 5° or less, 2° or less, or may be 1° or less.

[0020] B. Inspection Method The Group III element nitride substrate has a resistivity determined by the change in the amount of charge over time of 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 nitride substrate. Specifically, impurity elements such as oxygen may segregate into crystal defects such as dislocations in the Group III nitride crystal, affecting conductivity. Donor impurities such as oxygen are likely to be mixed into the crystal defects, affecting resistivity. Therefore, it is conceivable that crystal defects may be concentrated in a small region of, for example, φ10 μm to 200 μm within the plane of the Group III nitride substrate. On the other hand, the diameter of the measurement probe used in the method for measuring resistivity using the charge amount versus time change may be, for example, φ1 mm to 10 mm. Resistivity measurement using the charge amount versus time change assumes that resistivity is uniform at least within this range of the measurement probe diameter, making it difficult to accurately measure the resistivity of a region containing a small region of locally low resistivity. Furthermore, semiconductor devices obtained in regions of low resistivity may be of low quality. For example, HEMT devices obtained in regions of low resistivity may exhibit current leakage.

[0021] A method for inspecting a group III element nitride substrate according to one embodiment of the present invention includes irradiating the prepared group III element nitride substrate with excitation energy, and detecting band edge luminescence (BEL) of the emission spectrum obtained by the irradiation. peak and measuring the half-width of the peak.

[0022] The excitation energy irradiation can be performed by, for example, irradiation with 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 a HEMT device.

[0023] The ultraviolet light is irradiated using a light source capable of emitting laser light with a wavelength shorter than the band edge. Typical examples of laser light sources include He-Cd lasers and excimer lasers. Furthermore, ultraviolet light can also be irradiated using deep ultraviolet (DUV) lamps such as low-pressure mercury lamps and deuterium lamps.

[0024] The electron beam is irradiated using an electron beam source (for example, an electron gun) with an energy of about 0.5 KeV to 10 KeV. Examples of the electron beam source include a cold cathode field emission electron source, a photocathode electron source, and 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 therefore may be irradiated with an electron beam.

[0026] The emission spectrum obtained by irradiating the Group III nitride substrate with excitation energy can be measured, typically by measuring the intensity of light at 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] Band-edge emission from the measured emission spectrum peakThe half-width of the measured half-width satisfies a predetermined value (having a value equal to or less than the predetermined value), thereby enabling the production of a semiconductor device with excellent quality. For example, a HEMT device with suppressed leakage current can be obtained. Furthermore, by selecting and using a Group III element nitride substrate that satisfies the predetermined half-width, the yield of semiconductor device production 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 band edge emission of the measured emission spectrum is peak In another embodiment, the full width at half maximum of the band edge emission of the measured emission spectrum is preferably 6.5 nm or less. peak The half width at half maximum on the long wavelength side 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 (for example, a Group III element nitride substrate not doped with elements other than Group III elements) with excitation energy, and is more likely to be affected by the surface flatness of the substrate and the presence or absence of a process-affected layer. However, the present inventors have carefully investigated the relationship between the emission spectrum of the semi-insulating Group III element nitride substrate and the quality of the resulting semiconductor device, and have found that the band-edge emission peak We found that there is a correlation between the half-width of the band edge and the quality of the resulting semiconductor device. In Group III nitrides with good semi-insulating properties, the band edge intensity of the emission spectrum can be weak, but the half-width can appear narrower because the emission via various levels near the band edge is relatively reduced. On the other hand, for example, when donor impurities such as oxygen are incorporated into Group III nitride crystals, the emission intensity near the band edge increases, and the half-width can widen.

[0029] Band-edge emission peak The quality of a Group III nitride substrate can be easily determined by measuring at room temperature based on the half-width of the band edge. Strictly speaking, the emission spectrum may contain various levels of emission near the band edge, and can only be observed separately at extremely low temperatures. peak The half-width of the band edge emission can be measured at room temperature. peak Measurement of the half-width of the ion beam 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 a plurality of locations on the main surface of the Group III nitride substrate. peak By mapping the half-width of the peak, it is possible to predict that regions that do not satisfy a predetermined value will be regions where the quality of the resulting semiconductor device is low (for example, defective regions with large leakage current). For example, excitation energy is irradiated at predetermined intervals (for example, 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 where semiconductor devices are to be formed may be selected based on the mapping data within the substrate plane.

[0031] C. Manufacturing method A method for manufacturing 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 illustrating a manufacturing process for a group III nitride substrate according to one embodiment. Fig. 3A illustrates a state in which a seed crystal film 22 is formed on an upper surface 21a of a base substrate 21 having an upper surface 21a and a lower surface 21b 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 the production of a group III nitride substrate having the desired shape and size. 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 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 means the inclination angle of the main 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 vapor phase growth. Specific examples of vapor phase growth methods include metal organic chemical vapor deposition (MOCVD), hydride vapor phase epitaxy (HVPE), pulsed photoexcitation deposition (PXD), molecular beam epitaxy (MBE), evaporation, and sublimation. Among these, MOCVD 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. There are no particular limitations on the method for growing Group III element nitride crystals, as long as it is a method that can achieve a crystal orientation that roughly matches 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 photoexcitation 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.

[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 a growth method 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 equipped with a pressure-resistant container capable of supplying pressurized nitrogen gas, a turntable that can rotate within the pressure-resistant container, and an outer container 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 covered and placed under a nitrogen-containing atmosphere at a predetermined pressure and temperature for the growth process.

[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, 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 materials for the crucible include alumina, yttria, and YAG (yttrium aluminum garnet). The crucible material can be a single crystal or a polycrystalline (ceramic). The ceramics can be made translucent by increasing the relative density through HIP treatment or the like.

[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 to 1000°C, more preferably 800 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 the 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 base substrate and the group III element nitride crystal 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 21b side 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 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 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 nitride substrate 10, a stacked 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 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 channel layer 41 has a thickness of, for example, 50 nm to 5 μm. The barrier layer 42 has a thickness of, 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 that make up 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 deposition of the channel layer, and may contain the material that constitutes the channel layer.

[0060] Band-edge emission of III-group nitride substrate 10 peak When the full width at half maximum 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. [Example]

[0061] The present invention will be described in more detail below with reference to examples, but the present invention is not limited to these examples. The resistivity is a value measured by the following measurement method. <Resistivity> The resistivity within the substrate surface was measured by a non-contact method based on the change in the amount of charge over time. Specifically, the substrate was placed on a capacitor stage consisting of a probe and a stage, and the probe was brought close to the substrate, a pulse voltage with a pulse width of 100 ns was applied, and the change in the amount of charge 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 substrate) Three-inch diameter c-plane sapphire substrates 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°) were prepared. A 2 μm-thick gallium nitride film was deposited on each sapphire substrate by MOCVD to prepare seed crystal substrates.

[0063] (Gallium nitride crystal growth) The gallium nitride crystal was grown using a crystal manufacturing apparatus equipped with 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. 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. 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 that could accommodate 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 a crystal manufacturing apparatus that had been vacuum-baked in advance, and the pressure-resistant container of the crystal manufacturing apparatus was sealed with a lid. Next, the heating units (upper heater, middle heater, and lower heater) were operated to heat the heating space to 850°C, while nitrogen gas was introduced into the pressure vessel from a nitrogen gas cylinder until the pressure reached 4 MPa, and the outer vessel was rotated horizontally. This state was maintained for 35 hours to grow gallium nitride crystals. After that, the container was allowed to cool naturally to room temperature and the pressure was reduced to atmospheric pressure. When the lid of the alumina crucible was opened, the grown gallium nitride crystal was found to have naturally separated from the sapphire substrate, yielding a gallium nitride crystal with a diameter of 3 inches and a thickness of 1 mm.

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

[0065] [Experimental Example 2] The same procedure as in Experimental Example 1 was used except that the doping element was changed to Mn instead of Fe (0.1 g of manganese was filled in the crucible), and a diameter of 3 inches, thickness of 0.5 mm, and resistivity of 1 × 10 7 Mn-doped gallium nitride substrates with a resistivity of over Ω·cm were obtained.

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

[0067] 1. Band-edge emission peak Half-width (full width at half maximum and half width at half maximum) The photoluminescence obtained by irradiating the obtained gallium nitride substrate with an ultraviolet laser was measured by a spectrometer, and the half-width of the peak of the band edge emission was determined. Specifically, as shown in Fig. 5, the obtained 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 from a laser device 51 onto the main surface of the substrate 56. The laser was irradiated onto the main surface of the substrate 56 at an incident angle of 45° via a chopper 52, a light-reducing plate 53, and a condenser lens 54 with a focal length of 100 mm and a diameter of 50 mm. 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. The arrow in Fig. 5 indicates the direction of the laser light. A photodetector (photomultiplier tube) 60 is attached to the spectrometer 59. The weak signal detected by the photodetector 60 is 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 to which the substrate 56 is fixed is adjusted so that the detection intensity of the lock-in amplifier 61 is maximized. At this time, the diameter of the irradiated light on the substrate 56 was approximately 0.3 mm. The dashed line in Figure 5 indicates the synchronization signal. By moving the sample stage 55, the band edge emission is measured at intervals of 1 mm on the substrate surface, and the half width of the peak value is calculated. peak Mapping data of the half-width of the peak was obtained.

[0068] 2. Leakage current (Epitaxial substrate fabrication) We fabricated epitaxial substrates by epitaxially growing gallium nitride (GaN) and aluminum gallium nitride (AlGaN) layers on the primary surfaces of the resulting gallium nitride substrates using the MOCVD method. Specifically, the resulting gallium nitride substrates were placed on a susceptor in an MOCVD furnace. A mixed flow of hydrogen and nitrogen gases was introduced into the MOCVD furnace, and the furnace was heated to 1100°C at a furnace pressure of 0.3 atm. After reaching 1100°C, a 1 μm GaN layer was grown using ammonia gas and Ga precursor gas. Then, Al precursor gas was added to grow a 20 nm AlGaN layer (Al:Ga composition ratio 0.2:0.8), forming an epitaxial substrate. After deposition, the substrate temperature was lowered to room temperature and the pressure was restored to atmospheric pressure, after which the epitaxial substrate was removed from the MOCVD furnace.

[0069] (Fabrication of transistor elements) 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 resulting epitaxial substrate as a passivation film. Subsequently, the silicon oxide film was etched away using photolithography from the locations where the source, drain, and gate electrodes were to be formed. Next, using photolithography and reactive ion etching (RIE), the AlGaN layer and the GaN layer were etched away to a depth of about 400 nm at the boundary between 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 and drain electrodes would be formed. Metal films of Ti, Al, Ni, and Au were then deposited sequentially 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 stripper, and the photoresist film was removed by lift-off to obtain the source and drain electrodes. To improve the ohmic properties of the source and drain electrodes, the substrate was then heat-treated in a nitrogen gas atmosphere at 850°C for 30 seconds. Next, similar to the formation of the source electrode and drain electrode, 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 were formed with a gate width of 1 mm, a source-to-gate distance of 2 μm, a gate-to-drain distance of 8 μm, and a gate length of 1 μm.

[0070] Among the transistor elements fabricated as described above, an arbitrarily selected region in the epitaxial substrate was 16 The leakage current of the sample was measured by applying a source-drain voltage of 10 V and setting the gate voltage to -4 V to turn off the device.

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

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

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

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

[0075] The group III nitride substrate according to the embodiment of the present invention can be used, for example, as a substrate for various semiconductor devices. [Explanation of symbols]

[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 free-standing 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 the half-width of a band edge emission peak of an emission spectrum obtained by the irradiation; and selecting the Group III nitride substrate based on the half width of the band-edge emission peak, a method for producing a Group III element nitride substrate, wherein the Group III element nitride substrate has a full width at half maximum of the band edge emission peak of 6.5 nm or less;

2. 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 the half-width of a band edge emission peak of an emission spectrum obtained by the irradiation; and selecting the Group III nitride substrate based on the half width of the band-edge emission peak, a method for producing a Group III element nitride substrate, wherein the Group III element nitride substrate has 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 the half-width of a band edge emission peak of an emission spectrum obtained by the irradiation; and selecting the Group III nitride substrate based on the half width of the band-edge emission peak, Providing the Group III element nitride substrate includes: preparing a seed crystal substrate having a sapphire substrate with an upper surface and a lower surface facing each other, and a seed crystal film formed on the upper surface of the sapphire substrate; growing a Group III nitride crystal doped with an element other than a Group III element 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 0.20° or more and 0.42° or less.

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 the band edge emission peak of the 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 the band edge emission peak of the emission spectrum obtained by irradiation with excitation energy is 4.2 nm or less.

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

8. The Group III element nitride substrate according to claim 5 or 6, wherein the elements other than Group III elements include transition elements.

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 or 6, wherein the resistivity determined by the change in charge amount over time is 1×10 5 Ω·cm or more.

11. preparing a seed crystal substrate having a sapphire substrate with an upper surface and a lower surface facing each other, and a seed crystal film formed on the upper surface of the sapphire substrate; growing a Group III nitride crystal doped with an element other than a Group III element 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.

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