JP5648726B2 - GaN substrate and manufacturing method thereof, epitaxial substrate, and semiconductor device - Google Patents

Description

  The present invention relates to a group III nitride semiconductor substrate, an epitaxial substrate, and a semiconductor device.

  In recent years, semiconductors, including compound semiconductors, have expanded their application range by taking advantage of their various characteristics. For example, a compound semiconductor is useful as a base substrate for stacking epitaxial layers, and is used in semiconductor devices such as light emitting diodes and laser diodes.

  When a semiconductor substrate is used as the base substrate, the surface of the semiconductor substrate needs to be a mirror surface without distortion. Therefore, a semiconductor single crystal ingot is subjected to pre-processing (for example, cutting, lapping, etching) to obtain a semiconductor substrate, and then the surface of the semiconductor substrate is subjected to mirror polishing.

  As the semiconductor substrate, for example, those described in Patent Documents 1 to 3 below are known. In Patent Document 1, a semiconductor substrate obtained by cutting a crystalline group III-V nitride (e.g., (Al, Ga, In) -N) grown by vapor phase epitaxy (VPE) and then performing pre-processing. Is disclosed. Patent Document 1 discloses that as a pre-processing, after the surface of a semiconductor substrate is mechanically polished, chemical polishing (CMP) is performed to remove surface damage caused by the mechanical polishing.

In Patent Document 2, the surface of an Al _x Ga _y In _z N (0 <y ≦ 1, x + y + z = 1) wafer is polished by CMP so that the RMS standard surface roughness is less than 0.15 nm. A semiconductor substrate with reduced defects and contamination is disclosed. Patent Document 2 discloses that when performing CMP, Al ₂ O ₃ or SiO ₂ is used as abrasive grains, and an oxidizing agent is added to a polishing liquid to adjust pH.

Patent Document 3 discloses that Si piled up (accumulated) at the interface between the epitaxial layer and the semiconductor substrate deteriorates the characteristics of the device, and Si at the interface between the epitaxial layer and the semiconductor substrate. A semiconductor substrate having a concentration of 8 × 10 ¹⁷ cm ⁻³ or less is disclosed.

US Pat. No. 6,596,079 US Pat. No. 6,488,767 Japanese Patent No. 3183335

  However, in a semiconductor device using a stacked body in which an epitaxial layer (well layer) is arranged on the semiconductor substrate described in Patent Documents 1 to 3, there is a limit to improving light emission intensity and yield. . For this reason, development of a semiconductor substrate capable of highly balancing the emission intensity and yield of a semiconductor device is strongly desired.

  The present invention has been made to solve the above-described problems, and provides a group III nitride semiconductor substrate, an epitaxial substrate, and a semiconductor device capable of highly balancing the emission intensity and yield of a semiconductor device. Objective.

  As a result of diligent research, the present inventors have found that when impurities such as C (carbon) are present on the surface of the semiconductor substrate, C is piled up at the interface when an epitaxial layer is formed on the surface of the semiconductor substrate. It has been found that a layer having high electrical resistance (hereinafter referred to as “high resistance layer”) is formed at the layer / semiconductor substrate interface. It has also been found that the formation of a high resistance layer increases the electrical resistance at the epitaxial layer / semiconductor substrate interface, thereby reducing the emission intensity and yield.

  Furthermore, the present inventors have found that in a group III nitride semiconductor substrate used for a semiconductor device, a certain amount of sulfide and oxide are present on the substrate surface, so that C is piled up at the interface between the epitaxial layer and the semiconductor substrate. It was found that it is possible to suppress the increase. Thus, by suppressing the pile-up of C, formation of the high resistance layer at the interface between the epitaxial layer and the semiconductor substrate is suppressed. Thereby, the electrical resistance at the interface between the epitaxial layer and the semiconductor substrate can be reduced, and the crystal quality of the epitaxial layer can be improved. Therefore, the emission intensity and yield of the semiconductor device can be improved.

That is, the present invention is a group III nitride semiconductor substrate (GaN substrate) used for a semiconductor device, having a surface layer on the surface of the group III nitride semiconductor substrate, and the surface layer is 30 × 10 in terms of S. ¹⁰ sulfide / cm ^{2 to} 2000 × 10 ¹⁰ sulfide / cm ² sulfide and 2 at% to 20 at% oxide in terms of O are included. Here, in the surface layer, sulfides of 30 × 10 ¹⁰ pieces / cm ^{2 to} 2000 × 10 ¹⁰ pieces / cm ² in terms of S are measured by TXRF (total reflection fluorescent X-ray analysis), and 2 at% to in terms of O 20 at% oxide is a layer having a thickness that can be measured by AES (Auger Electron Spectroscopy).

The surface layer preferably contains 40 × ^{10 10} pieces ^/ cm 2 to 1500 × ^{10 10} pieces / cm ² sulfides S terms. In this case, the formation of the high resistance layer at the interface between the epitaxial layer and the semiconductor substrate can be further suppressed, and the emission intensity and yield of the semiconductor device can be further improved.

  Moreover, it is preferable that a surface layer contains the oxide of 3at%-16at% in O conversion. In this case, the formation of the high resistance layer at the interface between the epitaxial layer and the semiconductor substrate can be further suppressed, and the emission intensity and yield of the semiconductor device can be further improved.

  Furthermore, the present inventors further suppress the formation of the high resistance layer at the interface between the epitaxial layer and the semiconductor substrate by the presence of the specific amount of chloride or the specific amount of silicon compound on the substrate surface, and the semiconductor It has been found that the emission intensity and yield of the device can be further improved.

That is, the surface layer preferably contains 40 × 10 ¹⁰ pieces / cm ^{2 to} 15000 × 10 ¹⁰ pieces / cm ² of chloride in terms of Cl. The surface layer preferably contains 100 × ^{10 10} pieces ^/ cm 2 ^~12000 × ^{10 10} pieces / cm ² of silicon compound calculated as Si.

  Furthermore, the present inventors further suppress the formation of a high resistance layer at the interface between the epitaxial layer and the semiconductor substrate by setting the content of the carbon compound on the substrate surface to a specific amount or less, and the emission intensity of the semiconductor device and It has been found that the yield can be further improved.

  That is, the content of the carbon compound in the surface layer is preferably 22 at% or less in terms of C.

  In addition, the present inventors have found that the copper compound on the substrate surface contributes to the formation of the high resistance layer. Furthermore, by making the content of the copper compound on the substrate surface below a specific amount, the formation of a high resistance layer at the interface between the epitaxial layer and the semiconductor substrate is further suppressed, and the light emission intensity and yield of the semiconductor device are further improved. I found that I can do it.

That is, the content of the copper compound in the surface layer is preferably 150 × 10 ¹⁰ pieces / cm ² or less in terms of Cu.

  Further, the surface roughness of the surface layer is preferably 5 nm or less on the basis of RMS. In this case, the crystal quality of the epitaxial layer can be further improved, and the emission intensity and yield of the semiconductor device can be further improved.

The dislocation density of the surface layer is preferably 1 × 10 ⁶ pieces / cm ² or less. In this case, since the crystal quality of the epitaxial layer can be further improved, the emission intensity and yield of the semiconductor device can be further improved.

  Further, the inclination angle of the surface normal axis with respect to the c-axis is preferably 10 ° to 81 °. In this case, since the piezoelectric field can be reduced and the dislocation density of the epitaxial layer can be reduced, the emission intensity and yield of the semiconductor device can be further improved.

  The surface orientations of the surface are {20-21} plane, {10-11} plane, {20-2-1} plane, {10-1-1} plane, {11-22} plane, {22- 43} plane, {11-21} plane, {11-2-2} plane, {22-4-3} plane, and {11-2-1} plane are preferred. In this case, since the indium (In) incorporation efficiency of the epitaxial layer can be improved, good light emission characteristics can be obtained.

  An epitaxial substrate according to the present invention has the above group III nitride semiconductor substrate and an epitaxial layer formed on the surface layer of the group III nitride semiconductor substrate, and the epitaxial layer includes a group III nitride semiconductor.

  Since the epitaxial substrate according to the present invention includes the group III nitride semiconductor substrate, it is possible to suppress the pile-up of C at the interface between the epitaxial layer and the semiconductor substrate. Therefore, the formation of the high resistance layer at the interface between the epitaxial layer and the semiconductor substrate can be suppressed, and the emission intensity and yield of the semiconductor device can be improved.

  Moreover, it is preferable that the epitaxial substrate has an active layer in which the epitaxial layer has a quantum well structure, and the active layer is provided so as to generate light having a wavelength of 430 nm to 550 nm.

  A semiconductor device according to the present invention includes the epitaxial substrate.

  Since the semiconductor device according to the present invention includes the above-described epitaxial substrate, it is possible to suppress C from being piled up at the interface between the epitaxial layer and the semiconductor substrate. Therefore, the formation of the high resistance layer at the interface between the epitaxial layer and the semiconductor substrate can be suppressed, and the emission intensity and yield of the semiconductor device can be improved.

  ADVANTAGE OF THE INVENTION According to this invention, the group III nitride semiconductor substrate, epitaxial substrate, and semiconductor device which can make the light emission intensity and yield of a semiconductor device highly compatible are provided.

It is a schematic sectional drawing which shows the group III nitride semiconductor substrate which concerns on 1st Embodiment. It is a figure which shows the apparatus which can be used for dry etching. It is a figure which shows the apparatus which can be used for polishing. 1 is a schematic cross-sectional view showing an epitaxial substrate according to a first embodiment. It is a schematic sectional drawing which shows the epitaxial substrate which concerns on 2nd Embodiment. It is a top view which shows the epitaxial substrate which concerns on 3rd Embodiment. It is the figure which showed the procedure which produces the epitaxial substrate which concerns on 3rd Embodiment. It is a top view which shows the modification of the epitaxial substrate which concerns on 3rd Embodiment. 1 is a schematic cross-sectional view showing a semiconductor device according to a first embodiment. It is a schematic sectional drawing which shows the semiconductor device which concerns on 2nd Embodiment.

  Hereinafter, preferred embodiments of a group III nitride semiconductor substrate, an epitaxial substrate, and a semiconductor device according to the present invention will be described in detail with reference to the drawings.

(Group III nitride semiconductor substrate)
FIG. 1 is a schematic cross-sectional view showing a group III nitride semiconductor substrate 10 according to the first embodiment. As shown in FIG. 1, group III nitride semiconductor substrate 10 (hereinafter referred to as “nitride substrate 10”) has a front surface 10a and a back surface 10b facing each other. Is formed.

  The constituent material of the nitride substrate 10 is preferably a crystal having a wurtzite structure, and examples thereof include GaN, AlN, InN, AlGaN, and InGaN. The nitride substrate 10 made of GaN can be manufactured by the HVPE method, the flux method, or the like. The nitride substrate 10 made of AlN can be produced by HVPE method, sublimation method or the like. The nitride substrate 10 made of InN, AlGaN, or InGaN can be produced by the HVPE method or the like.

  The nitride substrate 10 can epitaxially grow a desired semiconductor layer (epitaxial layer) on the surface 10a. The quality of the surface 10a is preferably suitable for forming an epitaxial layer. Unlike the crystal quality in the bulk portion inside the substrate, the quality of the surface 10a is easily affected by the surface composition, roughness, and work-affected layer.

  Here, the work-affected layer refers to a layer in which the crystal lattice formed in the surface side region of the crystal is disturbed by crystal grinding or polishing. The work-affected layer can be confirmed in its presence and thickness by observing a cross section of the crystal fractured at the cleavage plane by SEM observation, TEM observation, or CL (cathode luminescence) observation. The thickness of the work-affected layer is preferably 20 nm or less, and more preferably 10 nm or less. If the thickness of the work-affected layer is large, the morphology and crystallinity of the epitaxial layer tend to decrease.

  CL observation refers to observing visible light emitted from the III nitride semiconductor crystal or light having a wavelength close to the visible wavelength region by making an electron beam incident on the III nitride semiconductor crystal as excitation light. When CL observation of a group III nitride semiconductor crystal is performed, light is observed in a crystal region having a good surface state, light is not observed in a region of a work-affected layer where the crystal is disordered, and is observed as a black linear shadow. The

  When the nitride substrate 10 is used for a semiconductor device, it is preferable to suppress the formation of a high resistance layer at the interface between the nitride substrate 10 and the epitaxial layer. If the electrical resistance at the interface is increased due to the presence of the high resistance layer, the light emission efficiency of the semiconductor device is lowered. In particular, when a large current is injected into a semiconductor device, the light emission efficiency is significantly reduced.

  From the viewpoint of suppressing the formation of such a high resistance layer, the surface layer 12 includes sulfides and oxides.

The surface layer 12 includes 30 × 10 ¹⁰ pieces / cm ^{2 to} 2000 × 10 ¹⁰ pieces / cm ² of sulfide in terms of S and 2 at% to 20 at% of oxide in terms of O. The content of sulfide is preferably 40 × 10 ¹⁰ pieces / cm ^{2 to} 1500 × 10 ¹⁰ pieces / cm ^{2 in} terms of S, and more preferably 100 × 10 ¹⁰ pieces / cm ^{2 to} 500 × 10 ¹⁰ pieces / cm ^2. . The content of the oxide is preferably 3 at% to 16 at% in terms of O, and more preferably 4 at% to 12 at%. When the sulfide content is less than 30 × 10 ¹⁰ pieces / cm ² or the oxide content is less than 2 at%, a high resistance layer is formed at the interface between the semiconductor substrate and the epitaxial layer, and the interface height is high. Resistivity reduces the yield of semiconductor devices. If the sulfide content exceeds 2000 × 10 ¹⁰ pieces / cm ² , or the oxide content exceeds 20 at%, the crystal quality of the epitaxial layer deteriorates, and the PL (photoluminescence) method in the epitaxial layer The intensity of emitted light (PL intensity) decreases.

It is preferable that the surface layer 12 contains 120 × 10 ¹⁰ pieces / cm ^{2 to} 15000 × 10 ¹⁰ pieces / cm ² of chloride in terms of Cl. The chloride content is more preferably 350 × 10 ¹⁰ pieces / cm ^{2 to} 10,000 × 10 ¹⁰ pieces / cm ^{2 in} terms of Cl, and further 1000 × 10 ¹⁰ pieces / cm ^{2 to} 5000 × 10 ¹⁰ pieces / cm ^2. preferable. When the chloride content is less than 120 × 10 ¹⁰ pieces / cm ² , a high resistance layer is easily formed at the interface between the semiconductor substrate and the epitaxial layer, and the yield of the semiconductor device is lowered due to the increase in resistance at the interface. Tend. If the chloride content exceeds 15000 × 10 ¹⁰ pieces / cm ² , the crystal quality of the epitaxial layer tends to deteriorate, and the PL strength of the epitaxial layer tends to decrease.

It is preferable that the surface layer 12 contains 100 × 10 ¹⁰ pieces / cm ^{2 to} 12000 × 10 ¹⁰ pieces / cm ² of silicon compound in terms of Si. The content of the silicon compound, 500 × ^{10 10} pieces in terms of Si ^/ cm 2 ^~8000 × ^{10 10} pieces / cm ^2, more preferably, 1000 × ^{10 10} pieces ^/ cm 2 ~ 5000 × ^{10 10} pieces / cm ² is further preferable. When the content of the silicon compound is less than 100 × 10 ¹⁰ pieces / cm ² , a high resistance layer is easily formed at the interface between the semiconductor substrate and the epitaxial layer, and the yield of the semiconductor device is reduced due to the increase in resistance at the interface. Tend. When the content of the silicon compound exceeds 12000 × 10 ¹⁰ pieces / cm ² , the crystal quality of the epitaxial layer tends to be lowered, and the PL strength of the epitaxial layer tends to be lowered.

  The surface layer 12 may contain a carbon compound. The content of the carbon compound in the surface layer 12 is preferably 22 at% or less, more preferably 18 at% or less, and further preferably 15 at% or less in terms of C. When the content of the carbon compound exceeds 22 at%, the crystal quality of the epitaxial layer is liable to deteriorate, the PL strength of the epitaxial layer tends to decrease, and a high resistance layer is formed at the interface between the semiconductor substrate and the epitaxial layer. The yield of semiconductor devices tends to decrease due to the increase in resistance at the interface.

The surface layer 12 may contain a copper compound. The content of the copper compound in the surface layer 12 is preferably 150 × 10 ¹⁰ pieces / cm ² or less in terms of Cu, more preferably 100 × 10 ¹⁰ pieces / cm ² or less, and further 50 × 10 ¹⁰ pieces / cm ² or less. preferable. When the content of the copper compound exceeds 150 × 10 ¹⁰ pieces / cm ² , the crystal quality of the epitaxial layer tends to be lowered, and the PL strength of the epitaxial layer tends to be lowered, and at the interface between the semiconductor substrate and the epitaxial layer. High resistance layers are easily formed, and the yield of semiconductor devices tends to decrease due to the increased resistance of the interface.

  The composition of the surface layer 12 can be quantified by TXRF (total reflection X-ray fluorescence analysis) for S, Si, Cl and Cu. TXRF evaluates the composition from the depth of X-ray penetration to about 5 nm from the surface. O and C can be quantified by AES (Auger electron spectroscopy). AES has a resolution of 0.1%. AES evaluates a composition of about 5 nm from the surface from the escape depth of Auger electrons. In addition, the surface layer 12 is a layer which has a thickness which can measure a content component by TXRF or AES, for example, has a thickness of about 5 nm.

  The difference in composition between the surface layer 12 and the bulk portion inside the nitride substrate 10 can be evaluated by performing analysis in the depth direction by SIMS (secondary ion mass spectrometry). Further, the difference in composition inside the nitride substrate 10, the interface between the nitride substrate 10 and the epitaxial layer, and the inside of the epitaxial layer can also be evaluated by SIMS.

  The surface roughness of the surface layer 12 in the nitride substrate 10 is preferably 5 nm or less, preferably 3 nm or less on the RMS basis, from the viewpoint of further improving the crystal quality of the epitaxial layer and further improving the integrated intensity of device emission. More preferred is 1 nm or less. Further, from the viewpoint of achieving both excellent productivity and crystal quality of the epitaxial layer, the surface roughness is preferably 1 nm to 3 nm. Here, the RMS-based surface roughness (root mean square roughness) can be measured using an AFM (Atomic Force Microscope) as a 10 μm square region of the surface 10a.

The dislocation density of the surface layer 12 is preferably 1 × 10 ⁶ pieces / cm ² or less, more preferably 1 × 10 ⁵ pieces / cm ² or less, and still more preferably 1 × 10 ⁴ pieces / cm ² or less. When the dislocation density exceeds 1 × 10 ⁶ pieces / cm ² , the crystal quality of the epitaxial layer tends to be lowered, and the emission intensity of the semiconductor device tends to be lowered. On the other hand, the dislocation density is preferably 1 × 10 ² pieces / cm ² or more from the viewpoint of excellent cost and productivity at the time of crystal production. The dislocation density can be calculated by performing CL observation and counting the number of non-light emitting points in the 10 μm square region of the surface layer 12.

  The plane orientation of the surface 10a of the nitride substrate 10 is the wurtzite structure {20-21} plane, {10-11} plane, {20-2-1} from the viewpoint of improving the indium incorporation efficiency of the epitaxial layer. } Plane, {10-1-1} plane, {11-22} plane, {22-43} plane, {11-21} plane, {11-2-2} plane, {22-4-3} plane And {11-2-1} plane. The plane orientation of the surface 10a can be measured using, for example, an X-ray diffractometer.

  The inclination angle (off angle) of the normal axis of the surface 10a with respect to the c-axis is preferably 10 ° to 81 °, more preferably 17 ° to 80 °, and still more preferably 63 ° to 79 °. Since the piezo electric field due to the spontaneous polarization of the wurtzite structure is suppressed when the inclination angle is 10 ° or more, the PL intensity of the light emitting device can be improved. When the inclination angle is 81 ° or less, the dislocation density of the epitaxial layer (well layer) can be reduced, and the PL intensity of the semiconductor device can be improved.

  Next, a method for manufacturing the nitride substrate 10 will be described.

  First, after a group III nitride semiconductor crystal is grown in the c-axis direction or the m-axis direction by the HVPE method or the like, the crystal is subjected to outer periphery processing and shaped to obtain a group III nitride semiconductor ingot. Next, the obtained ingot is cut at a desired angle using a wire saw or a blade saw to obtain a nitride substrate 10 having a desired off-angle on the surface 10a. A semipolar substrate may be used as the base substrate, and a group III nitride semiconductor crystal may be grown on the semipolar substrate, and an ingot having a desired off angle on the surface may be used.

Next, in order to planarize the substrate surface, machining such as grinding (grinding) or lapping is performed. For grinding, a grindstone containing diamond, SiC, BN, Al ₂ O ₃ , Cr ₂ O ₃ , ZrO ₂ or the like as hard abrasive grains can be used. For lapping, a general abrasive containing diamond, SiC, BN, Al ₂ O ₃ , Cr ₂ O ₃ , ZrO ₂ or the like as hard abrasive grains can be used.

  The abrasive grains are appropriately selected in consideration of mechanical action and characteristics. For example, from the viewpoint of increasing the polishing rate, abrasive grains having a high hardness and a large particle diameter are used. From the viewpoint of smoothing the surface and suppressing the formation of a work-affected layer, abrasive grains having a low hardness and a small particle diameter are used. Further, from the viewpoint of shortening the polishing time and obtaining a smooth surface, multi-stage polishing in which the abrasive grains having a large particle size are changed to small abrasive grains as the polishing process proceeds is suitable.

  After the nitride substrate 10 is ground or lapped, the surface 10a is subjected to a surface finish such as dry etching or CMP in order to reduce the surface roughness of the surface 10a of the nitride substrate 10 or to remove the work-affected layer. Do. Note that dry etching may be performed before grinding or lapping.

  Dry etching includes RIE (reactive ion etching), inductively coupled plasma RIE (ICP-RIE), ECR (electron cyclotron resonance) -RIE, CAIBE (chemically assisted ion beam etching), RIBE (reactive ion beam etching), etc. Among them, reactive ion etching is preferable. For reactive ion etching, for example, a dry etching apparatus 16 shown in FIG. 2 can be used.

  The dry etching apparatus 16 includes a chamber 16a. In the chamber 16a, a parallel plate type upper electrode 16b and a lower electrode 16c, and a substrate support 16d disposed on the lower electrode 16c so as to face the upper electrode 16b are provided. A gas supply port 16e connected to a gas source and a gas exhaust port 16f connected to a vacuum pump are provided in the chamber 16a. A high frequency power source 16g connected to the lower electrode 16c is disposed outside the chamber 16a.

  In the dry etching apparatus 16, plasma can be generated in the chamber 16a by supplying gas from the gas supply port 16e into the chamber 16a and supplying high frequency power from the high frequency power supply 16g to the lower electrode 16c. By disposing the nitride substrate 10 on the substrate support 16d, the surface 10a of the nitride substrate 10 can be dry-etched.

By using a sulfur-based gas as the etching gas supplied from the gas supply port 16e, a high etching rate can be obtained and the sulfide content of the surface layer 12 can be adjusted. As the sulfur-based gas, for example, H ₂ S, SO ₂ , SF ₄ , SF _{6 and the} like can be used. Similarly, by using a chlorine-based gas as an etching gas, a high etching rate can be obtained and the chloride content of the surface layer 12 can be adjusted. As the chlorine-based gas, for example, Cl ₂ , HCl, CCl ₄ , BCl ₃ , SiCl ₄ , SiHCl ₃ can be used. The contents of the silicon compound and the carbon compound in the surface layer 12 can be adjusted by using, for example, SiCl ₄ , SiHCl ₃ , CH ₄ , or C ₂ H ₂ as an etching gas. It should be noted that the content of the components contained in the surface layer 12 can also be controlled by adjusting the type of gas, the gas flow rate, the pressure in the chamber, and the etching power.

In reactive ion etching, it is preferable to satisfy the following formula (1) when the pressure in the chamber is P (Pa), the gas flow rate is Q (sccm), and the chamber volume is V (L).
0.05 ≦ PV / Q ≦ 3.0 (1)
When PV / Q is smaller than 0.05, the surface roughness tends to increase. When PV / Q is larger than 3.0, the effect of surface modification tends to be small.

  For example, a polishing apparatus 18 shown in FIG. 3 can be used for the CMP. The polishing apparatus 18 includes a surface plate 18a, a polishing pad 18b, a crystal holder 18c, a weight 18d, and a slurry liquid supply port 18e.

  The polishing pad 18b is placed on the surface plate 18a. The surface plate 18a and the polishing pad 18b are rotatable about the central axis X1 of the surface plate 18a. The crystal holder 18c is a component for supporting the nitride substrate 10 on its lower surface. A load is applied to the nitride substrate 10 by a weight 18d placed on the upper surface of the crystal holder 18c. The crystal holder 18c is substantially parallel to the axis line X1 and has a center axis line X2 at a position displaced from the axis line X1, and is rotatable around the center axis line X2. The slurry liquid supply port 18e supplies the CMP solution slurry S onto the polishing pad 18b.

  According to this polishing apparatus 18, the surface plate 18a, the polishing pad 18b, and the crystal holder 18c are rotated, the slurry S is supplied onto the polishing pad 18b, and the surface 10a of the nitride substrate 10 is brought into contact with the polishing pad 18b. Thus, the CMP of the surface 10a can be performed.

The content of the components contained in the surface layer 12 can be adjusted by the additive of the CMP solution, pH, and redox potential. Abrasive grains can be added to the CMP solution. As the material of the abrasive grains, ZrO ₂ , SiO ₂ , CeO ₂ , MnO ₂ , Fe ₂ O ₃ , Fe ₃ O ₄ , NiO, ZnO, CoO, Co ₃ O ₄ , GeO ₂ , CuO, Ga ₂ O ₃ , At least one metal oxide selected from the group consisting of In ₂ O ₃ can be used. A compound such as Si, Cu, Cu—Zn alloy, Cu—Sn alloy, Si ₃ N ₄ , or SiAlON can also be used. The material of the abrasive grains is preferably a material having a high ionization tendency from the viewpoint of improving the cleaning property, and if the material has a higher ionization tendency than H, the removal efficiency by cleaning can be particularly improved. A CMP solution that does not contain abrasive grains may be used. By using Si, Si ₃ N ₄ , SiAlON, or the like as the abrasive grains, the content of the silicon compound in the surface layer 12 can be adjusted. By using Cu, Cu—Zn alloy, Cu—Sn alloy, or the like as the abrasive grains, the content of the copper compound in the surface layer 12 can be adjusted.

  From the viewpoint of sufficiently suppressing abrasive grains from remaining on the surface 10a after CMP, a surfactant can be added to the CMP solution. Examples of the surfactant include a carboxylic acid type, a sulfonic acid type, a sulfate ester type, a quaternary ammonium salt type, an alkylamine salt type, an ester type, and an ether type.

  As a solvent for the CMP solution, a nonpolar solvent is preferred. Nonpolar solvents include hydrocarbons, carbon tetrachloride, diethyl ether and the like. By using a nonpolar solvent, solid contact between the abrasive grains, which are metal oxides, and the substrate can be promoted, so that the metal composition on the substrate surface can be efficiently controlled.

The chemical action (mechanochemical effect) of the CMP solution on the semiconductor substrate can be adjusted by the pH and redox potential of the CMP solution. The pH of the CMP solution is preferably 1 to 6 or 8.5 to 14, and more preferably 1.5 to 4 or 10 to 13. Examples of pH adjusters include inorganic acids such as hydrochloric acid, nitric acid, sulfuric acid and phosphoric acid, organic acids such as formic acid, acetic acid, citric acid, malic acid, tartaric acid, succinic acid, phthalic acid, maleic acid and fumaric acid, KOH, NaOH In addition to alkalis such as NH ₄ OH, organic alkalis and amines, salts such as sulfates, carbonates and phosphates can be used. By using an organic acid as a pH adjuster, the effect of removing impurities can be improved even at the same pH as compared with inorganic acids and inorganic salts. As the organic acid, dicarboxylic acid (divalent carboxylic acid) is preferable.

  Adjusting the content of sulfide in the surface layer 12 by using an acid containing a sulfur atom such as sulfuric acid, a sulfate such as sodium sulfate, or a thiosulfate such as sodium thiosulfate as a pH adjusting agent and an oxidizing agent. Can do. Acids containing chlorine atoms such as hydrochloric acid, salts such as potassium chloride, hypochlorite, sodium hypochlorite, hypochlorites such as calcium hypochlorite, chlorinated isocyanuric acids such as trichloroisocyanuric acid, dichloro By using a chlorinated isocyanurate such as sodium isocyanurate, the chloride content of the surface layer 12 can be adjusted. By using an organic acid such as carbonic acid, carbonate, citric acid, oxalic acid, fumaric acid, phthalic acid, malic acid, or an organic acid salt, the content of the carbon compound in the surface layer 12 can be adjusted.

  The oxidation-reduction potential of the CMP solution can be adjusted using an oxidizing agent. By increasing the oxidation-reduction potential by adding an oxidizing agent to the CMP solution, it is possible to improve the polishing rate while maintaining a high abrasive removal effect, and to adjust the oxide content of the surface layer 12. . The oxidizing agent is not particularly limited, but from the viewpoint of sufficiently increasing the oxidation-reduction potential, hypochlorite such as hypochlorous acid, sodium hypochlorite, calcium hypochlorite, trichloroisocyanuric acid, etc. Chlorinated oxidants such as chlorinated isocyanuric acid and chlorinated isocyanurates such as sodium dichloroisocyanurate, sulfur oxidants such as thiosulfates such as sulfuric acid and sodium thiosulfate, and permanganates such as potassium permanganate , Dichromates such as potassium dichromate, bromates such as potassium bromate, thiosulfates such as sodium thiosulfate, persulfates such as ammonium persulfate and potassium persulfate, nitric acid, hydrogen peroxide, ozone etc. Preferably used. Among these, by using a sulfur-based oxidizing agent or a chlorine-based oxidizing agent, the polishing rate is improved, and the content of sulfide or chloride in the surface layer 12 after polishing is adjusted to the above-mentioned preferable content. be able to.

Here, when the value of the pH of the CMP solution is x and the value of the oxidation-reduction potential is y (mV), the relationship between x and y preferably satisfies the following formula (2).
−50x + 1400 ≦ y ≦ −50x + 1900 (2)
If y exceeds the upper limit of formula (2), the corrosive action on the polishing pad and polishing equipment becomes strong, and it tends to be difficult to polish in a stable state, and the oxidation of the substrate surface proceeds excessively. Tend to. If y is less than the lower limit of the formula (2), the oxidizing action on the substrate surface tends to be weakened, and the polishing rate tends to decrease.

  By controlling the viscosity of the CMP solution, the content of the components contained in the surface layer 12 can be adjusted. The viscosity of the CMP solution is preferably 2 mPa · s to 30 mPa · s, and more preferably 5 mPa · s to 10 mPa · s. When the viscosity of the CMP solution is lower than 2 mPa · s, the content of the content component of the surface layer 12 tends to be higher than the desired value described above, and when it exceeds 30 mPa · s, the content of the content component of the surface layer 12 is included. The amount tends to be lower than the desired value described above. The viscosity of the CMP solution can be adjusted by adding a highly viscous organic compound such as ethylene glycol or an inorganic compound such as boehmite.

The sulfide content of the surface layer 12 can be adjusted by the concentration of sulfate ions in the CMP solution and the contact coefficient C. The contact coefficient C is “C = η × V / P” using the viscosity η (mPa · s) of the CMP solution, the peripheral speed V (m / s) during polishing, and the pressure P (kPa) during polishing. Defined by Contact Factor C is preferably ^{1.0 × 10 -6 m~2.0 × 10 -6} m. If the contact coefficient C is less than 1.0 × 10 ⁻⁶ m, the load on the semiconductor substrate in CMP tends to be strong, and the sulfide content of the surface layer 12 tends to be excessive, and 2.0 When it exceeds ^{x10 −6} m, the polishing rate tends to decrease and the sulfide content of the surface layer 12 tends to decrease.

  The pressure during polishing is preferably 3 kPa to 80 kPa, and more preferably 10 kPa to 60 kPa. When the pressure is less than 3 kPa, the polishing rate tends to be insufficient in practical use, and when it exceeds 80 kPa, the surface quality of the substrate tends to deteriorate.

According to the nitride substrate 10, 30 × 10 ¹⁰ pieces / cm ^{2 to} 2000 × 10 ¹⁰ pieces / cm ² of sulfide in terms of S and 2 at% to 20 at% of oxide in terms of O are formed on the surface layer 12. By being present, it is possible to suppress the pile-up of C at the interface between the epitaxial layer and the nitride substrate 10. Thus, by suppressing the pile-up of C, formation of the high resistance layer at the interface between the epitaxial layer and the nitride substrate 10 is suppressed. Thereby, the electrical resistance at the interface between the epitaxial layer and the nitride substrate 10 can be reduced, and the crystal quality of the epitaxial layer can be improved. Therefore, the emission intensity and yield of the semiconductor device can be improved.

(Epitaxial substrate)
FIG. 4 is a schematic cross-sectional view showing the epitaxial substrate 20 according to the first embodiment. As shown in FIG. 4, the epitaxial substrate 20 has the nitride substrate 10 as a base substrate and an epitaxial layer 22 laminated on the surface 10 a of the nitride substrate 10.

  The epitaxial layer 22 includes, for example, a group III nitride semiconductor. As the group III nitride semiconductor, a crystal having a wurtzite structure is preferable, and examples thereof include GaN, AlN, InN, AlGaN, and InGaN. The epitaxial layer 22 can be formed by vapor phase growth methods such as HVPE method, MOCVD method, VOC method, MBE method, and sublimation method. By providing the epitaxial layer 22 on the nitride substrate 10, the PL strength can be improved.

  FIG. 5 is a schematic cross-sectional view showing an epitaxial substrate 30 according to the second embodiment. As shown in FIG. 5, the epitaxial substrate 30 has an epitaxial layer 32 composed of a plurality of layers formed on the surface 10 a of the nitride substrate 10. By providing the epitaxial layer 32 on the nitride substrate 10, the PL strength can be improved.

The epitaxial layer 32 includes a first semiconductor region 32a, a second semiconductor region 32b, and an active layer 32c provided between the first semiconductor region 32a and the second semiconductor region 32b. The first semiconductor region 32a includes one or a plurality of n-type semiconductor layers, and includes, for example, an n-type GaN layer 32d having a thickness of 1 μm and an n-type Al _0.1 Ga _0.9 N layer 32e having a thickness of 150 nm. The second semiconductor region 32b includes one or a plurality of p-type semiconductor layers, and includes, for example, a p-type Al _0.2 Ga _0.8 N layer 32f having a thickness of 20 nm and a p-type GaN layer 32g having a thickness of 150 nm. In the epitaxial layer 32, an n-type GaN layer 32d, an n-type Al _0.1 Ga _0.9 N layer 32e, an active layer 32c, a p-type Al _0.2 Ga _0.8 N layer 32f, and a p-type GaN layer 32g are formed on the nitride substrate 10. Laminated in order.

The active layer 32c is provided so as to generate light having a wavelength of 430 nm to 550 nm, for example. The active layer 32c has, for example, a multiple quantum well structure (MQW) in which four barrier layers and three well layers are formed, and the barrier layers and the well layers are alternately stacked. The barrier layer is, for example, a GaN layer having a thickness of 10 nm. The well layer is, for example, a Ga _0.85 In _0.15 N layer having a thickness of 3 nm.

The epitaxial layer 32 is formed, for example, by MOCVD (metal organic chemical vapor deposition), using an n-type GaN layer 32d, an n-type Al _0.1 Ga _0.9 N layer 32e, an active layer 32c, a p-type Al _0.2 Ga _0.8 N layer 32f and p. The type GaN layer 32g can be formed by epitaxial growth on the nitride substrate 10 sequentially.

  FIG. 6 is a plan view showing an epitaxial substrate 40 according to the third embodiment. As shown in FIG. 6, epitaxial substrate 40 has an epitaxial layer 42 arranged on surface 10 a of nitride substrate 10.

The epitaxial layer 42 has a plurality of low dislocation density regions 44A having a dislocation density smaller than a predetermined dislocation density, and a plurality of high dislocation density regions 44B having a dislocation density larger than the predetermined dislocation density. This predetermined dislocation density is, for example, 8 × 10 ⁷ cm ⁻² .

  Each of the low dislocation density region 44A and the high dislocation density region 44B extends in a stripe shape substantially parallel to each other in the plane direction (Y direction in FIG. 6) of the surface 10a of the nitride substrate 10, and the back surface of the epitaxial layer 42 To the surface. The epitaxial layer 42 has a stripe structure in which low dislocation density regions 44A and high dislocation density regions 44B are alternately arranged. The epitaxial layer 42 is made of, for example, GaN, and the dislocation density in the crystal is reduced by the stripe structure. The low dislocation density region 44A and the high dislocation density region 44B can be confirmed by CL observation using a scanning electron microscope (for example, S-4300 manufactured by Hitachi, Ltd.).

Next, the manufacturing method of the epitaxial substrate 40 is demonstrated using FIG. First, as shown in FIG. 7A, a striped mask layer 46 is formed by patterning on the surface 10a of the nitride substrate 10 serving as a base substrate so as to extend in the Y direction of FIG. 7A, for example. The mask layer 46 is made of, for example, SiO ₂ .

  Next, as shown in FIG. 7B, the epitaxial layer 42 is facet grown by vapor phase epitaxy on the surface 10a on which the mask layer 46 is formed. As the vapor phase growth method, an HVPE method, an MOCVD method, a VOC method, an MBE method, a sublimation method, or the like can be used. When the epitaxial layer 42 is grown thickly by facet growth, the mask layer 46 is covered with the epitaxial layer 42, and a high dislocation density region 44B is formed in a portion located on the mask layer 46.

  The high dislocation density region 44B is not only the stripe structure, but also a square structure in which the stripe-shaped high dislocation density regions 44B are orthogonal to each other as shown in FIG. 8A, or as shown in FIG. A dot structure in which the dot-like high dislocation density regions 44B are regularly arranged at a predetermined interval may be used. Such a high dislocation density region 44B having a square structure or a dot structure can be obtained by patterning the epitaxial layer 42 using the mask layer 46, similarly to the stripe structure.

(Semiconductor device)
FIG. 9 is a schematic cross-sectional view showing the semiconductor device 100 according to the first embodiment. As shown in FIG. 9, the semiconductor device 100 includes an epitaxial substrate 20, an electrode 90 </ b> A that covers the entire surface 23 of the epitaxial layer 22, and an electrode 90 </ b> B that covers the entire back surface 10 b of the nitride substrate 10. And have. The electrodes 90A and 90B are formed by metal vapor deposition, for example. The formation positions of the electrodes 90A and 90B can be appropriately changed as necessary. If the electrode 90B is electrically connected to the nitride substrate 10 and the electrode 90A is electrically connected to the epitaxial layer 22 Good.

  FIG. 10 is a schematic cross-sectional view showing a semiconductor device 200 according to the second embodiment. As shown in FIG. 10, the semiconductor device 200 includes an epitaxial substrate 30, a first electrode (p-side electrode) 92 </ b> A formed so as to cover the entire surface 33 of the epitaxial layer 32, and a back surface 10 b of the nitride substrate 10. And a second electrode (n-side electrode) 92B formed so as to cover a part of the electrode. The size of the semiconductor device 200 is, for example, 400 μm square or 2 mm square. The conductor 91A is electrically connected to the electrode 92A through the solder layer 93. The conductor 91B is electrically connected to the electrode 92B through the wire 94.

  The semiconductor device 200 can be manufactured by the following procedure. First, the nitride substrate 10 is obtained by the method described above. Next, the epitaxial layer 32 is laminated on the surface 10 a of the nitride substrate 10. Furthermore, an electrode 92 A is formed on the surface 33 of the epitaxial layer 32 and an electrode 92 B is formed on the back surface 10 b of the nitride substrate 10. Subsequently, the electrode 92A is electrically connected to the conductor 91A by the solder layer 93, and the electrode 92B is electrically connected to the conductor 91B by the wire 94.

  The present invention is not limited to the above embodiment. The plane orientations of {20-21} plane, M plane, A plane and the like described in the above description include not only those specified by the description itself but also crystallographically equivalent planes and orientations. For example, the {20-21} plane is not only the {20-21} plane, but also the (02-21) plane, the (0-221) plane, the (2-201) plane, the (−2021) plane, (− 2201) plane.

  EXAMPLES Hereinafter, although an Example explains in full detail this invention, the scope of the present invention is not limited to these Examples.

(1) Production of GaN substrate First, an n-type GaN crystal (dopant: O) was grown in the c-axis direction by the HVPE method. Next, the GaN crystal was sliced perpendicularly to the c-axis to obtain a GaN substrate having a (0001) plane and a diameter of 50 mm and a thickness of 0.5 mm.

Subsequently, dry etching was performed on the surface of the GaN substrate and the back surface opposite to the surface to remove the work-affected layer. For dry etching, an RIE apparatus having the same configuration as that shown in FIG. 2 was used. The volume (V) of the vacuum chamber was 20L. The material of the substrate support was SiC. The etching gas was Cl ₂ or CH ₄ and the gas flow rate (Q) was 30 sccm. Dry etching was performed at a pressure (P) of 4.0 Pa and a power of 50 W to 200 W (PV / Q = 2.67).

(2) Wrapping of GaN substrate surface The back surface ((000-1) surface) of the GaN substrate was attached to a ceramic crystal holder with wax. A surface plate having a diameter of 380 mm was installed in the lapping apparatus, and the surface plate was rotated about its rotation axis while supplying slurry in which diamond abrasive grains were dispersed from the slurry supply port to the surface plate. Next, the surface of the n-type GaN crystal was lapped by rotating the GaN substrate around the rotation axis of the crystal holder while pressing the GaN substrate against the surface plate by placing a weight on the crystal holder.

Lapping was performed under the following conditions. As the surface plate, a copper surface plate and a tin surface plate were used. As the abrasive grains, three kinds of diamond abrasive grains having an abrasive grain size of 9 μm, 3 μm, and 2 μm were prepared, and with the progress of lapping, abrasive grains having a small abrasive grain size were used step by step. Polishing pressure was ^{100g / cm 2 ~500g / cm 2} , the rotational speed of the GaN substrate and the surface plate were both 30 times / Min～60 times / min. It was confirmed that the surface of the GaN crystal substrate became a mirror surface by the above lapping.

(3) CMP of GaN substrate surface
CMP of the surface of the GaN substrate was performed using a polishing apparatus having the same configuration as in FIG. CMP was performed under the following conditions. As the polishing pad, a polyurethane suede pad (Supreme RN-R, manufactured by Nitta Haas Co., Ltd.) was used. As the surface plate, a circular stainless steel surface plate having a diameter of 380 mm was used. Contact coefficient between GaN substrate and the polishing pad C was a ^{1.0 × 10 -6 m~2.0 × 10 -6} m. The polishing pressure was 10 kPa to 80 kPa, and the rotation speeds of the GaN substrate and the polishing pad were both 30 times / min to 120 times / min. In the slurry (CMP solution), silica particles having a particle size of 200 nm were dispersed as 20% by mass in water as abrasive grains. To the slurry, citric acid and H ₂ SO ₄ were added as pH adjusting agents, and sodium dichloroisocyanurate was added as an oxidizing agent to adjust the pH and redox potential of the slurry to the range of the following formula (3) ( x: pH, y: redox potential (mV)).
−50x + 1400 ≦ y ≦ −50x + 1900 (3)

  GaN substrates having different surface compositions were produced by appropriately changing the dry etching and CMP conditions. The content of sulfide, silicon compound, chloride and copper compound on the surface of the GaN substrate was evaluated by TXRF, and the content of oxide and carbon compound was evaluated by AES. For TXRF, a W-encapsulated X-ray tube was used as the X-ray source, the X-ray output was 40 kV, the current was 40 mA, and the incident angle was 0.05 °. AES was measured at an acceleration voltage of 10 keV. The RMS-based surface roughness on the surface of the GaN substrate was evaluated by AFM observation within a range of 10 μm × 10 μm on the surface of the GaN substrate. The dislocation density was evaluated by cathodoluminescence. Tables 1 to 7 show the surface composition, surface roughness, and dislocation density of the GaN substrate.

(4) Fabrication of a semiconductor device including a GaN substrate A GaN substrate is placed in an MOCVD apparatus, and an MOCVD method is used to form an n-type GaN layer (dopant: Si) having a thickness of 1 μm and an n-type Al _0.1 Ga _0.9 having a thickness of 150 nm. An N layer (dopant: Si), an active layer, a p-type Al _0.2 Ga _0.8 N layer (dopant: Mg) with a thickness of 20 nm, and a p-type GaN layer (dopant: Mg) with a thickness of 150 nm on the surface side of the GaN substrate Then, an epitaxial layer was formed on the GaN substrate. Here, the active layer has four barrier layers and three well layers, and has a multiple quantum well structure in which barrier layers and well layers are alternately stacked. The barrier layer was a GaN layer having a thickness of 10 nm, and the well layer was a Ga _0.85 In _0.15 N layer having a thickness of 3 nm.

  The PL strength of the epitaxial layer formed as described above was evaluated. The PL intensity was evaluated by using a He—Cd laser having a wavelength of 325 nm as an excitation light source and evaluating the intensity at a wavelength of 460 nm. The measurement results of PL intensity are shown in Tables 1-7.

  Next, a laminate composed of a 200 nm thick Ti layer, a 1000 nm thick Al layer, a 200 nm thick Ti layer, and a 2000 nm thick Au layer is formed on the back surface ((000-1) surface) of the GaN substrate. Formed. The laminated body was heated in a nitrogen atmosphere to form an n-side electrode (first electrode) having a diameter of 100 μm. Further, on the p-type GaN layer, a laminate composed of a Ni layer having a thickness of 4 nm and an Au layer having a thickness of 4 nm was formed. The laminated body was heated in a nitrogen atmosphere to form a p-side electrode (second electrode). The laminate obtained by the above process was processed into a 2 mm square. Further, the p-side electrode was bonded to a conductor with a solder layer formed of AuSn, and the n-side electrode and the conductor were bonded with a wire to obtain an LED.

  Using an integrating sphere, the light output (PL intensity) of the LED was measured under the condition of an injection current of 4A. The light output of the LED was measured by injecting a predetermined current into the LED placed in the integrating sphere and measuring the light collected from the LED with a detector. In addition, the yield of 200 LEDs was calculated using an LED having a light output of 2 W or more as a semiconductor device that was successfully fabricated. The element yield of LED is shown in Tables 1-7.

As shown in Tables 1 to 7, Examples 1-1 to 1-8, 2-1 to 2-9, 3-1 to 3-8, 4-1 to 4-6, and 5-1 to 5- 6, 6-1 to 6-5 and 7-1 to 7-6 have a sulfide content in the range of 30 × 10 ¹⁰ pieces / cm ^{2 to} 2000 × 10 ¹⁰ pieces / cm ² in terms of S. Since the oxide content is in the range of 2 at% to 20 at% in terms of O, good light output and device yield were obtained. On the other hand, in Comparative Examples 1-1 to 1-6, since the content of at least one of sulfide and oxide was out of the above range, it was confirmed that the light output and the device yield were lowered.

Further, as shown in Table 2, in Examples 2-2 to 2-8 in which the chloride content is 120 × 10 ¹⁰ pieces / cm ^{2 to} 15000 × 10 ¹⁰ pieces / cm ² in terms of Cl, It was confirmed that both the output and the device yield were particularly excellent. As shown in Table 3, in Examples 3-2-3-7 in which the content of silicon compound is 100 × 10 ¹⁰ pieces / cm ^{2 to} 12000 × 10 ¹⁰ pieces / cm ² in terms of Si, the light output and All of the device yields were confirmed to be particularly excellent. As shown in Table 4, in Examples 4-1 to 4-5 in which the content of the carbon compound is 22 at% or less in terms of C, it is confirmed that both the light output and the device yield are particularly excellent. It was done. As shown in Table 5, in Examples 5-1 to 5-5 in which the content of the copper compound is 150 × 10 ¹⁰ pieces / cm ² or less in terms of Cu, both the light output and the element yield are particularly high. It was confirmed to be excellent. As shown in Table 6, in Examples 6-1 to 6-4 having a surface roughness of 5 nm or less, it was confirmed that both the light output and the device yield were particularly excellent. As shown in Table 7, in Examples 7-1 to 7-5 in which the dislocation density is 1 × 10 ⁶ pieces / cm ² or less, it is confirmed that both the optical output and the device yield are particularly excellent. It was done.

  DESCRIPTION OF SYMBOLS 10 ... Nitride substrate (Group III nitride semiconductor substrate), 10a ... Surface, 12 ... Surface layer, 20, 30, 40 ... Epitaxial substrate, 22, 32, 42, 52 ... Epitaxial layer, 32c, 52e ... Active layer, 100, 200: Semiconductor device.

Claims (15)

A GaN substrate used in a semiconductor device,
A surface layer on the surface of the GaN substrate;
A GaN substrate in which the surface layer includes 30 × 10 ¹⁰ pieces / cm ^{2 to} 2000 × 10 ¹⁰ pieces / cm ² of sulfide in terms of S and 2 at% to 20 at% of oxide in terms of O. ^2. The GaN substrate according to claim 1, wherein the surface layer contains 40 × 10 ¹⁰ pieces / cm ^{2 to} 1500 × 10 ¹⁰ pieces / cm ² of the sulfide in terms of S. 3.   The GaN substrate according to claim 1, wherein the surface layer contains 3 at% to 16 at% of the oxide in terms of O. The GaN substrate according to any one of claims 1 to 3, wherein the surface layer includes a silicon compound of 100 × 10 ¹⁰ pieces / cm ^{2 to} 12000 × 10 ¹⁰ pieces / cm ² in terms of Si.   The GaN substrate according to claim 1, wherein the surface layer has a surface roughness of 5 nm or less on an RMS basis.   The GaN substrate according to any one of claims 1 to 5, wherein a thickness of the work-affected layer on the surface is 20 nm or less. The GaN substrate according to claim 1, wherein a dislocation density of the surface layer is 1 × 10 ⁶ pieces / cm ² or less.   The GaN substrate according to claim 1, wherein an inclination angle of the normal axis of the surface with respect to the c-axis is 10 ° to 81 °.   The surface orientation of the surface is {20-21} plane, {10-11} plane, {20-2-1} plane, {10-1-1} plane, {11-22} plane, {22-43 } Surface, any one of {11-21} surface, {11-2-2} surface, {22-4-3} surface, and {11-2-1} surface. The GaN substrate according to claim 1.   The GaN substrate according to claim 1, wherein the surface orientation of the surface is a (0001) plane. A GaN substrate used in a semiconductor device,
A surface layer on the surface of the GaN substrate;
The surface layer includes 30 × 10 ¹⁰ pieces / cm ² to 2000 × 10 ¹⁰ pieces / cm ² of sulfide in terms of S, and 2 at% to 20 at % of oxide in terms of O;
A GaN substrate, wherein the carbon compound content in the surface layer is 22 at% or less in terms of C. A method for producing a GaN substrate according to any one of claims 1 to 11,
A method for manufacturing a GaN substrate, wherein the surface of a GaN crystal is planarized by grinding or polishing, and then surface finish is performed by dry etching or CMP.   An epitaxial substrate comprising: the GaN substrate according to claim 1; and an epitaxial layer formed on the surface layer of the GaN substrate, wherein the epitaxial layer includes a group III nitride semiconductor. . The epitaxial layer has an active layer having a quantum well structure;
The epitaxial substrate according to claim 13, wherein the active layer is provided to generate light having a wavelength of 430 nm to 550 nm.   A semiconductor device comprising the epitaxial substrate according to claim 13.

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