Group iii element nitride substrate, semiconductor element, method for processing group iii element nitride substrate, and method for manufacturing semiconductor element

Abstract

This invention provides a group III element nitride substrate excellent in workability. The group III element nitride substrate is doped with a transition element and has an absorption coefficient of 22 cm -1 or more for light with a wavelength λ of 400 nm or more.

Description

Group III element nitride substrate, semiconductor device, method for processing group III element nitride substrate, and method for manufacturing semiconductor device

[0001] The present invention relates to a Group III element nitride substrate, a semiconductor device, a method for processing 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] The above-mentioned Group III element nitride substrate may not be easily cut using a laser (for example, the process of dividing the substrate into individual pieces).

[0006] In view of the above, a primary object of the present invention is to provide a Group III element nitride substrate that is highly workable.

[0007] 1. A Group III element nitride substrate according to an embodiment of the present invention is a Group III element nitride substrate doped with a transition element, and has an absorption coefficient of 22 cm for light with a wavelength λ of 400 nm or more. －１ 2. The Group III element nitride substrate described in 1 above has an oxygen concentration of 7×10 １５ cm －３ 3. In the Group III element nitride substrate described in 1 or 2 above, the manganese concentration may be 6×10 or more. １７ cm －３ 4. The Group III element nitride substrate according to any one of the above items 1 to 3 may have an oxygen concentration of 8×10 or more. １６ cm －３ 5. In the Group III element nitride substrate according to any one of 1 to 4 above, the manganese concentration may be 1×10 or less. １９ cm －３or less. 6. In the Group III element nitride substrate according to any one of the above items 1 to 5, the wavelength λ may be in the range of 770 nm to 830 nm. 7. The Group III element nitride substrate according to any one of the above items 1 to 6 may contain gallium nitride. 8. The Group III element nitride substrate according to any one of the above items 1 to 7 may have a resistivity of 1×10, determined from the change in charge amount over time. ５ 9. The Group III element nitride substrate according to any one of 1 to 8 above may have a dislocation density of 1×10 ７ cm －２ 10. A semiconductor device according to another embodiment of the present invention comprises the Group III element nitride substrate according to any one of 1 to 9 above, a stacked layer structure including a channel layer and a barrier layer in this order, and a source electrode, a drain electrode, and a gate electrode provided on the stacked layer structure.

[0008] 11. A method for processing a Group III element nitride substrate according to another embodiment of the present invention includes temporarily fixing the Group III element nitride substrate according to any one of 1 to 9 above to a processing sheet, and irradiating the Group III element nitride substrate with laser light having a wavelength of 400 nm or more along planned division lines while the Group III element nitride substrate is temporarily fixed to the processing sheet. 12. In the method for processing a Group III element nitride substrate according to 11 above, the adhesive strength of the processing sheet may be reduced by irradiation with light having a wavelength of less than 400 nm. 13. A method for manufacturing a semiconductor device according to another embodiment of the present invention includes forming a channel layer and a barrier layer on the Group III nitride substrate described in any one of items 1 to 9 above to obtain a stacked structure, providing a source electrode, a drain electrode, and a gate electrode on the stacked structure, temporarily fixing the Group III nitride substrate to a processing sheet, and irradiating the Group III nitride substrate with laser light having a wavelength of 400 nm or more along planned division lines while the Group III nitride substrate is temporarily fixed to the processing sheet. 14. In the method for manufacturing a semiconductor device described in item 13 above, the stacked structure may be obtained by epitaxial growth. 15. In the method for manufacturing a semiconductor device described in item 13 or 14 above, the adhesive strength of the processing sheet may be reduced by irradiation with light having a wavelength of less than 400 nm.

[0009] According to an embodiment of the present invention, a Group III element nitride substrate with excellent processability can be provided.

[0010] 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 cross-sectional view showing the general configuration of a group III element nitride substrate according to one embodiment. FIG. 10 is a view continuing from FIG. 11. FIG. 12 is a view continuing from FIG. 13. FIG. 13 is a view showing the optical transmittance measurement result of a gallium nitride substrate of Sample 5 of Experimental Example 1.

[0011] 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 order to clarify the description, the drawings may schematically show the width, thickness, shape, etc. of each part compared to the embodiments, but these are merely examples and do not limit the interpretation of the present invention. Furthermore, in the drawings, the same or equivalent elements are given the same reference numerals, and redundant explanations may be omitted.

[0012] 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.

[0013] 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.

[0014] In one embodiment, the resistivity of the group III nitride substrate is, for example, 1×10 ５ Ω・cm or more 1×10 １４ Ω cm or less, preferably 1×10 ６ Ω cm or more, more preferably 1×10 ７ The 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.

[0015] 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)."

[0016] In one embodiment, the group III element nitride substrate can absorb light having a wavelength of 400 nm or more. Specifically, the absorption coefficient of the group III element nitride substrate for light having a wavelength λ of 400 nm or more is, for example, 22 cm －１ More than 25 cm, preferably －１ That is all. By having such light absorption characteristics, it is possible to process the substrate using a laser beam with a wavelength of 400 nm or more. Typically, it is possible to divide the substrate using a laser beam with a wavelength of 400 nm or more. On the other hand, the absorption coefficient of a group III element nitride substrate for light with a wavelength λ of 400 nm or more is, for example, 35 cm －１ less than 30 cm －１ It may be the following:

[0017] The wavelength λ of 400 nm or more is preferably 700 nm or more, and may be, for example, approximately 800 nm. Specifically, the wavelength λ of 400 nm or more may be in the range of 770 nm to 830 nm. In this case, the wavelength λ may be the wavelength that exhibits the lowest light transmittance within the range of 770 nm to 830 nm. Note that a Group III element nitride substrate may exhibit high absorptivity for light having a wavelength equal to or shorter than the wavelength corresponding to its band gap energy. For example, a gallium nitride substrate may exhibit high absorptivity for light having a wavelength of 365 nm or shorter.

[0018] The dislocation density of the Group III element nitride substrate evaluated by cathodoluminescence is, for example, 1×10 ８ cm －２ or less, preferably 5 × 10 ７ cm －２ or less, more preferably 1×10 ７ cm －２ or less, and more preferably 6×10 ６ cm －２ It is particularly preferably 2 × 10 ６ cm －２ On the other hand, the dislocation density of the group III element nitride substrate evaluated by cathodoluminescence is, for example, 1×10 ４ cm －２ It could be more than that.

[0019] 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 ｚN), aluminum gallium indium nitride (Al ｘ Ga ｙ In ｚ In each chemical formula in parentheses, typically, x+y+z=1.

[0020] 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, manganese is used as the dopant.

[0021] The group III element nitride substrate may contain manganese. By containing manganese, it is possible to obtain a group III element nitride substrate that satisfies the above-mentioned light absorption characteristics. The amount of manganese present in the group III element nitride substrate (unit: atoms / cm ３ The amount of manganese present in the group III element nitride substrate (unit: atoms / cm ３ ) will be simply referred to as the manganese concentration (unit: cm －３ The manganese concentration is, for example, 6 × 10 １７ cm －３ or more, preferably 7×10 １７ cm －３ More preferably, 8×10 １７ cm －３ or more, and more preferably 9 × 10 １７ cm －３ More preferably, it is 1×10 １８ cm －３ That's all.

[0022] The manganese concentration is, for example, 1×10 ２０ cm －３ or less, preferably 5 × 10１９ cm －３ or less, and more preferably 3×10 １９ cm －３ or less, and more preferably 1×10 １９ cm －３ With such a manganese concentration, it is possible to obtain a Group III element nitride substrate that satisfies the above-mentioned resistivity and / or dislocation density.

[0023] The group III element nitride substrate may contain oxygen. By containing oxygen, it is possible to obtain a group III element nitride substrate that satisfies the above-mentioned light absorption characteristics. The amount of oxygen present in the group III element nitride substrate (unit: atoms / cm ３ ) can be set to any appropriate value. The amount of oxygen present in the Group III element nitride substrate (unit: atoms / cm ３ ) will be simply referred to as the oxygen concentration (unit: cm －３ The oxygen concentration is, for example, 6×10 １５ cm －３ That is 7 x 10 １５ cm －３ or more, 8 × 10 １５ cm －３ It may be 9×10 or more. １５ cm －３ or more, and may be 1×10 １６ cm －３ or more, and may be 2×10 １６ cm －３ It may be more than that.

[0024] The oxygen concentration is, for example, 1×10 １８ cm －３ or less, preferably 3×10 １７ cm －３ or less, more preferably 1×10 １７ cm －３ or less, and more preferably 8×10 １６ cm －３ The following is the result.

[0025] 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 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.

[0026] B. 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.

[0027] 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.

[0028] 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.

[0029] Any suitable substrate can be used as the base substrate. The base substrate is typically made of a single crystal. Examples of materials that can be used for the base substrate include sapphire, crystal-oriented alumina, silicon, gallium oxide, aluminum gallium nitride, gallium arsenide, and silicon carbide (SiC).

[0030] The thickness of the seed crystal film is, for example, 0.2 μm or more. From the viewpoint of preventing meltback or disappearance during growth of the Group III nitride crystal, 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.

[0031] Any appropriate material can be used as the material for the seed crystal film. A typical material for the seed crystal film is a group III element nitride. Details of the group III element nitride are as described above.

[0032] 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.

[0033] 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.

[0034] 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.

[0035] 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.

[0036] 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 high-pressure nitrogen gas, a turntable that can rotate within the pressure-resistant vessel, and an outer vessel placed on the turntable.

[0037] 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.

[0038] 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.

[0039] 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.

[0040] 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.

[0041] The pressure of the atmosphere during growth may be set to any appropriate pressure. For example, the pressure of the atmosphere during growth may be 1 MPa or more, 2 MPa or more, or 3 MPa or more, from the viewpoint of preventing evaporation of the flux. On the other hand, the pressure of the atmosphere during growth may be 50 MPa or less, or 10 MPa or less, from the viewpoint of preventing the growth apparatus from becoming large-scale.

[0042] The temperature of the atmosphere during growth can be set to any appropriate temperature. The temperature of the atmosphere during growth is preferably 700°C to 1000°C, and more preferably 800°C to 900°C. In one embodiment, the desired oxygen concentration can be achieved by adjusting the temperature of the atmosphere during growth.

[0043] The growth is preferably carried out while rotating the base substrate (crucible) from the viewpoint of, for example, promoting dissolution of high-pressure nitrogen gas into the melt composition. For example, the crucible with a lid is placed in the outer container of the crystal production apparatus and placed on a turntable, and the turntable is rotated (for example, on its axis) in this state to rotate the crucible.

[0044] After growth of the group III element nitride crystal, as shown in FIG. 3C , the base substrate 21 is removed from the group III element nitride crystal (group III element nitride crystal layer 16) 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 layer 16 and a seed crystal film 22. For example, the free-standing substrate 32 is obtained by separating the group III element nitride crystal layer 16 from the base substrate 21. 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 a method of spontaneously separating the group III element nitride crystal 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, a separation method using chemical etching, and a laser lift-off method using laser light irradiation. Alternatively, the free-standing substrate may be obtained by, for example, grinding and removing the base substrate 21, or by slicing the base substrate using a wire saw or the like.

[0045] 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.

[0046] 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).

[0047] 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).

[0048] Furthermore, for example, processing performed on the freestanding substrate includes chamfering the outer peripheral edge, removing a process-affected layer formed on the surface by grinding or polishing, and removing residual stress that may be caused by the process-affected layer.

[0049] C. Applications The Group III element nitride substrate can be typically applied to any suitable semiconductor device. Specifically, any suitable upper structural layer can be formed on the Group III element nitride substrate.

[0050] 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. HEMT device 40 includes a group III element nitride substrate 10, a stacked structure 43 including a channel layer 41 and a barrier layer 42, in that order, and a source electrode 44, a drain electrode 45, and a gate electrode 46 provided on stacked structure 43. These electrodes may be metal electrodes each having a thickness of about 10-15 nm.

[0051] Each layer of the stacked structure 43 can be obtained by heterogrowth. 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. 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.

[0052] 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.

[0053] 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 MOCVD. When the channel layer 41 and the barrier layer 42 are formed by MOCVD, 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 MOCVD, 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.

[0054] 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.

[0055] The Group III element nitride substrate can be divided into individual pieces, specifically, before, after, or during the formation of an upper structural layer including various layers such as an epitaxial growth layer, a passivation film, and electrodes.

[0056] 5A and 5B are cross-sectional views schematically illustrating a method for processing a group III-nitride substrate according to one embodiment, in which an upper structural layer that may be formed on the group III-nitride substrate is omitted.

[0057] 5A shows a state in which a group III element nitride substrate 10 is temporarily fixed to a processing sheet 50. A sheet (e.g., dicing tape) whose adhesive strength can be reduced by irradiation with light is typically used as the processing sheet 50. Thereafter, as shown in FIG. 5B , with the group III element nitride substrate 10 temporarily fixed to the processing sheet 50, the group III element nitride substrate 10 is irradiated with laser light 51. By irradiating with the laser light 51, a processing groove 52 can be formed in the group III element nitride substrate 10. By irradiating with the laser, the processing groove can be formed while suppressing the generation of dust due to processing.

[0058] The wavelength of the laser light 51 is preferably 400 nm or more, more preferably 700 nm or more. For example, the laser light 51 may be a visible light laser and / or an infrared light laser. Irradiating the Group III element nitride substrate 10 temporarily fixed to the processing sheet 50 with light having a wavelength of less than 400 nm (e.g., ultraviolet light having a wavelength of 200 nm or more but less than 400 nm) may reduce the adhesive strength of the processing sheet 50. For example, irradiation with light having a wavelength of less than 400 nm may harden the adhesive layer (not shown) of the processing sheet 50, reducing its adhesive strength. Specifically, the adhesive strength of the processing sheet 50 may be reduced at the irradiation point of the light having a wavelength of less than 400 nm and at the surrounding area that may be affected by the scattered light. A reduction in the adhesive strength of the processing sheet 50 may cause, for example, the Group III element nitride substrate 10 to lift off the processing sheet 50, reducing processing accuracy, or the Group III element nitride substrate 10 to peel off from the processing sheet 50 during processing, reducing processability. As described above, the group III element nitride substrate 10 can absorb light with a wavelength of 400 nm or more, so by setting the wavelength of the laser light 51 to 400 nm or more, the group III element nitride substrate 10 can be well processed even when temporarily fixed to the processing sheet 50 without reducing the adhesive strength of the processing sheet 50. Furthermore, the use of the group III element nitride substrate 10 can also contribute to improving yield.

[0059] As a light source (processing laser) of laser light with a wavelength of 400 nm or more, for example, titanium sapphire (Ti:Al ２ O ３ ) laser, a solid-state laser (DPSS: Diode Pumped Solid State) laser using a semiconductor laser as excitation light, and an erbium-doped fiber laser.

[0060] The laser beam 51 may typically be applied along the planned dividing line. In the illustrated example, the laser beam 51 is applied from the group III element nitride substrate 10 side (upper side in FIG. 5B ), but it may also be applied from the processing sheet 50 side (lower side in FIG. 5B ). The conditions for applying the laser beam 51 may be set to any appropriate conditions. In one embodiment, the grooves 52 in the group III element nitride substrate 10 formed by laser irradiation may penetrate the group III element nitride substrate 10. Specifically, if the individual pieces obtained by dividing the group III element nitride substrate do not require cleavage planes (crystal planes) for high-precision alignment (e.g., alignment during electrode formation), the group III element nitride substrate does not need to be cleaved along the grooves. For example, when manufacturing semiconductor devices for high-frequency applications, the group III element nitride substrate does not need to be cleaved along the grooves.

[0061] The present invention will be specifically explained below with reference to examples, but the present invention is not limited to these examples.

[0062] Experimental Example 1 (Preparation of Seed Crystal Substrate) A plurality of c-plane sapphire substrates having a diameter of 4 inches were prepared, and a gallium nitride film having a thickness of 2 μm was formed on each of the sapphire substrates 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 vessel capable of supplying high-pressure nitrogen gas, a turntable rotatable within the pressure-resistant vessel, an outer vessel placed on the turntable, and a crystal growth furnace for placing the outer vessel under a desired temperature environment. 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 0.01 g to 0.10 g of manganese as a doping element were each 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 vessel, which was then placed in a stainless steel outer vessel capable of accommodating the inner vessel, and the outer vessel was closed with a lid equipped with a nitrogen inlet pipe. In this state, the outer vessel was placed on a turntable located within the crystal manufacturing apparatus, and the pressure-resistant vessel of the crystal manufacturing apparatus was sealed with a lid. Next, the heater unit was operated to heat the crystal growth furnace in the crystal manufacturing apparatus to a uniform temperature of 850°C, while nitrogen gas was introduced from a nitrogen gas cylinder into the pressure-resistant container until the pressure reached 4 MPa, and the outer container was rotated horizontally. This state was maintained for 35 hours, allowing gallium nitride crystal to grow. After that, the container was naturally cooled to room temperature and reduced 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 4 inches and a thickness of 1 mm was obtained.

[0064] Thereafter, the surface of the gallium nitride crystal that had been separated from the sapphire substrate and the opposite surface were polished and flattened using diamond abrasive grains to obtain a Mn-doped gallium nitride substrate having a diameter of 4 inches and a thickness of 0.43 mm.

[0065] Experimental Example 2 A Mn-doped gallium nitride substrate was obtained in the same manner as in Experimental Example 1, except that the set temperature of the crystal growth furnace was changed from 850°C to within the range of 820°C to 900°C.

[0066] <Evaluation> The following evaluations were carried out on the gallium nitride substrates obtained in Experimental Examples 1 and 2. Table 1 shows the evaluation results for the gallium nitride substrate obtained in Experimental Example 1, and Table 2 shows the evaluation results for the gallium nitride substrate obtained in Experimental Example 2 together with the evaluation results for the gallium nitride substrate obtained in Experimental Example 1. FIG. 6 shows the measurement results for the light transmittance of the gallium nitride substrate of Sample 5 in Experimental Example 1 as a representative. Samples 1 to 10 in Table 1 differ in the amount of manganese filled in the growth of the gallium nitride crystal.

[0067] 1. Laser Processing Test Dicing tape was attached to the bottom surface of the obtained substrate, and the substrate was irradiated with laser light from the top surface side of the substrate. The laser light was irradiated so that chips with a size of 20 mm x 20 mm were obtained. For the laser irradiation, titanium sapphire (Ti:Al ２ O ３ ) laser (center wavelength: 820 nm) with an irradiation fluence of 0.5 J / cm ２ The laser irradiation did not change the adhesive strength of the dicing tape, and the substrate remained fixed to the dicing tape even after the laser irradiation. (Evaluation criteria) Good: The substrate was cut by the laser irradiation Fairly good: A groove was formed by the laser irradiation, but the substrate could not be separated (divided into chips) Poor: No substantial groove formation was confirmed by the laser irradiation

[0068] 2. Manganese Concentration and Oxygen Concentration A measurement sample measuring 20 mm x 20 mm was cut out from the obtained substrate, and the manganese concentration and oxygen concentration were determined by secondary ion mass spectrometry (SIMS). The measurement conditions were as follows: (Measurement conditions) Type of secondary ion mass spectrometer: magnetic sector type Type of primary ion: O ２ ＋ (when measuring manganese), Cs ＋ (When measuring oxygen) Measurement range: from the surface to a depth of 5 μm Information depth: average value from a depth of 1 μm to a depth of 5 μm from the surface Detection limit: 4 × 10 １４ cm －３ (Manganese measurement), 7 x 10 １５ cm －３(When measuring oxygen)

[0069] 3. Light absorption characteristics The light absorption characteristics of the obtained substrate were evaluated. Specifically, a measurement sample measuring 20 mm x 20 mm was cut out from the obtained substrate, and the light transmittance was measured at room temperature using an ultraviolet-visible-near-infrared spectrophotometer ("UH4150" manufactured by Hitachi High-Techno Science Corporation). The measurement conditions were as follows: (Measurement conditions) Starting wavelength: 300 nm Ending wavelength: 1300 nm Sampling interval: 2 nm Scan speed: 300 nm / min Slit width (resolution): 1 nm From the obtained measurement data of light transmittance, the absorption coefficient α (unit: cm) at a peak wavelength around 820 nm (815 nm to 825 nm) was calculated. －１ ) was calculated using the following formula: I = I ０ ×exp(-αt) (I ０ : incident light intensity, I: transmitted light intensity, t: thickness of the measurement sample)

[0070] 4. Resistivity The resistivity within the substrate surface was measured using a non-contact method based on the change in charge amount over time. Specifically, the substrate was placed on a stage, and a probe was brought close to the substrate (with a gap of 1 mm to 2 mm) to form a capacitor. A pulse voltage with a pulse width of 100 ns was applied, and the change in the charge amount over time on the substrate was measured for 1 second at room temperature (25°C) to calculate the resistivity, and the magnitude of the resistivity was judged according to the following criteria. (Judgment Criteria) A: Resistivity is 1 x 10 ７ Ω cm or more B: Resistivity is 1 x 10 ５ Ω・cm or more 1×10 ７ C: Resistivity less than 1 x 10 ５ Less than Ω cm

[0071] 5. Dislocation Density The dislocation density of the obtained semi-insulating (high-resistivity) gallium nitride substrate was determined by acquiring a cathodoluminescence (CL) image. Here, the CL image was acquired by epitaxially growing a Si-doped GaN layer (2 μm thick) on the gallium nitride substrate, which would have a dislocation density equivalent to that of the semi-insulating substrate, in order to enhance the CL image emission, and then photographing a CL image of the epitaxial layer. Specifically, a scanning electron microscope (Hitachi High-Technologies Corporation, "S-3400N") was used to acquire the CL image as a monochrome image under conditions of an acceleration voltage of 15 kV and an emission current of 100 μA, using a photomultiplier tube (PMT) as a detector. The dislocation density was then calculated by counting dark spots in a predetermined area of ​​the obtained image.

[0072]

[0073]

[0074] Group III nitride substrates according to embodiments of the present invention can be used, for example, as substrates for various semiconductor devices.

[0075] 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, 50 Processing sheet, 51 Laser light, 52 Processing groove.

Claims

1. A group III nitride substrate doped with a transition element, having an absorption coefficient of light with a wavelength λ of 400 nm or more of 22 cm －１ or more, a group III nitride substrate.

2. The concentration of oxygen is 7×10 １５ cm －３ or more, the group III nitride substrate according to claim 1.

3. The concentration of manganese is 6×10 １７ cm －３ or more, and the group III nitride substrate according to claim 1.

4. The concentration of oxygen is 8×10 １６ cm －３ or less. The group III nitride substrate according to claim 1.

5. The concentration of manganese is 1×10 １９ cm －３ or less, and the group III nitride substrate according to claim 1.

6. The group-III nitride substrate according to claim 1, wherein the wavelength λ is in the range of 770 nm to 830 nm.

7. The group-III nitride substrate according to claim 1, which contains gallium nitride.

8. The resistivity obtained from the change in the amount of charge over time is 1 × 10 ５ Ω·cm or more, and the group III nitride substrate according to claim 1.

9. The III-nitride substrate according to claim 1, wherein the dislocation density is 1 × 10 ７ cm －２ or less.

10. A semiconductor device comprising: a stacked structure including, in this order, the group-III nitride substrate according to any one of claims 1 to 9, a channel layer, and a barrier layer; and a source electrode, a drain electrode, and a gate electrode provided on the stacked structure.

11. A method for processing a group-III nitride substrate, comprising temporarily fixing the group-III nitride substrate according to any one of claims 1 to 9 to a processing sheet, and irradiating the group-III nitride substrate with laser light having a wavelength of 400 nm or more along a planned division line in a state where the group-III nitride substrate is temporarily fixed to the processing sheet.

12. The method for processing a group-III nitride substrate according to claim 11, wherein the processing sheet has an adhesive force that decreases when irradiated with light having a wavelength of less than 400 nm.

13. A method for manufacturing a semiconductor device, comprising: forming a channel layer and a barrier layer on the group-III nitride substrate according to any one of claims 1 to 9 to obtain a stacked structure; providing a source electrode, a drain electrode, and a gate electrode on the stacked structure; temporarily fixing the group-III nitride substrate to a processing sheet; and irradiating the group-III nitride substrate with laser light having a wavelength of 400 nm or more along a planned division line in a state where the group-III nitride substrate is temporarily fixed to the processing sheet.

14. The method for manufacturing a semiconductor device according to claim 13, wherein the stacked structure is obtained by epitaxial growth.

15. The method for manufacturing a semiconductor device according to claim 13, wherein the processing sheet has an adhesive force that decreases when irradiated with light having a wavelength of less than 400 nm.

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