JP2011162439A - Nitride semiconductor free-standing substrate and light emitter - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a nitride semiconductor free-standing substrate whose warpage is reduced, and a light emitter using the same. <P>SOLUTION: The nitride semiconductor free-standing substrate is the one composed of continuously grown nitride semiconductor crystals, wherein the inside of the nitride semiconductor free-standing substrate is provided with inversion domains at density of 10 to 600 pieces/cm<SP>2</SP>in the cross-section parallel to the surface of the substrate, the surface of the substrate has inversion domains at density of 0 to 200 pieces/cm<SP>2</SP>, and the density of the inversion domains arriving at the surface of the substrate is lower than that of the inversion domains at the inside of the nitride semiconductor free-standing substrate. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a nitride semiconductor free-standing substrate and a light emitting device. In particular, the present invention relates to a nitride semiconductor free-standing substrate with reduced warpage of the free-standing substrate and a light emitting device using the same.

  As a conventional method for producing a GaN single crystal substrate as a nitride semiconductor free-standing substrate, for example, nitriding using a vapor phase growth method on a heterogeneous substrate different from a nitride semiconductor such as a sapphire substrate, a silicon substrate, or a gallium arsenide substrate. There is a method of forming a nitride semiconductor self-supporting substrate by heteroepitaxially growing a nitride semiconductor layer and then removing the heterogeneous substrate using means such as polishing, etching, or peeling to leave only the nitride semiconductor layer. For example, see Patent Document 1). In this method of manufacturing a GaN single crystal substrate, a mask having dotted windows arranged at a certain interval in the [11-2] direction and shifted by a half pitch in the [−110] direction is formed on the (111) GaAs substrate. After the GaN buffer layer is grown on the formed mask, a GaN crystal is epitaxially grown on the GaN buffer layer, and then the GaAs substrate and the mask are removed to form a GaN free-standing substrate.

Japanese Patent No. 3788041

  However, in the method for manufacturing a GaN single crystal substrate described in Patent Document 1, a nitride semiconductor crystal is grown on a heterogeneous substrate having a lattice constant that is significantly different from the lattice constant of the nitride semiconductor. Many defects occur in the early stages of growth. Therefore, when the heterogeneous substrate and the nitride semiconductor crystal are separated, a defect density difference which is a difference between the defect density on the front surface and the defect density on the back surface of the nitride semiconductor crystal is generated. When the defect density difference occurs, internal stress remains in the nitride semiconductor crystal. As a result, the nitride semiconductor free-standing substrate after the dissimilar substrate is separated is warped.

  The nitride semiconductor free-standing substrate having such a warp is not oriented in a plane with a uniform plane orientation. Therefore, even when this nitride semiconductor free-standing substrate is processed flat by polishing or the like, the in-plane off-angle varies. When a light emitting device is formed from a nitride semiconductor free-standing substrate having variations in the in-plane off angle, the wavelength of light emitted from the light emitting device varies due to the variation in off angle. Furthermore, there is a disadvantage that the yield of the light emitting device that emits light of a desired wavelength is lowered.

  Accordingly, an object of the present invention is to provide a nitride semiconductor free-standing substrate with reduced warpage of the free-standing substrate and a light emitting device using the same.

In order to achieve the above object, the present invention provides a nitride semiconductor free-standing substrate made of continuously grown nitride semiconductor crystals, wherein the nitride semiconductor free-standing substrate has 10 / cm ² or more in a cross section parallel to the substrate surface. The nitride semiconductor free-standing substrate has inversion domains at a density of 600 pieces / cm ² or less, and the substrate surface has an inversion domain at a density of 0 pieces / cm ² or more to 200 pieces / cm ² or less. A nitride semiconductor free-standing substrate is provided in which the density of inversion domains reaching the substrate surface is smaller than the inversion domains inside.

  In the nitride semiconductor free-standing substrate, the off-angle variation in the substrate surface is preferably 0.1 ° to 0.75 °.

  In the light emitting device of the present invention, a plurality of semiconductor layers including an active layer are formed on one surface side of the nitride semiconductor free-standing substrate, an upper electrode is formed on the semiconductor layer, and the other side of the nitride semiconductor free-standing substrate is formed. It is fabricated by forming a lower electrode on the surface side.

   The light emitting device preferably has a variation in emission wavelength of 9 nm to 18 nm.

  According to the nitride semiconductor free-standing substrate and the method for manufacturing a nitride semiconductor free-standing substrate of the present invention, a nitride semiconductor free-standing substrate with reduced warpage of the free-standing substrate can be provided, and the nitride semiconductor free-standing substrate with less warpage can be provided. Can be manufactured.

[First Embodiment]
FIG. 1 is a schematic view of an HVPE furnace used in the method for manufacturing a nitride semiconductor free-standing substrate according to the first embodiment of the present invention.

(Structure of HVPE furnace 10)
An HVPE reactor 10 as a halide vapor phase epitaxy (HVPE) apparatus used in the method for manufacturing a nitride semiconductor free-standing substrate according to the first embodiment includes a quartz reaction tube 100 formed of quartz, quartz A quartz boat 120 which is installed at a predetermined position inside the reaction tube 100 and mounts the raw material of the nitride semiconductor free-standing substrate; an HCl introduction tube 130 as a halogen gas introduction tube disposed at a position close to the quartz boat 120; A substrate holder 150 for holding a heterogeneous substrate 1 on which a single crystal of a nitride semiconductor is formed, and an NH ₃ introduction tube 140 as an N (nitrogen) source supply tube disposed at a position close to the heterogeneous substrate 1; Is provided. Further, the HVPE furnace 10 includes a heater 110 that surrounds the periphery of the quartz reaction tube 100 and supplies heat to the inside of the quartz reaction tube 100.

  In the present embodiment, the quartz boat 120 is loaded with Ga metal as one of the raw materials for the nitride semiconductor crystal. Then, the Ga metal is melted by the heating of the heater 110 to become a Ga melt 2. In addition, the heterogeneous substrate 1 according to the present embodiment is, for example, a sapphire substrate having a diameter of 2 inches and having a (0001) plane, that is, a c-plane. The sapphire substrate is fixed on the substrate holder 150 so that the surface thereof is perpendicular to the longitudinal direction of the quartz reaction tube 100. The position where the substrate holder 150 is disposed is adjusted so that the surface of the sapphire substrate is disposed at a position away from the quartz boat 120 by a predetermined distance.

Further, the nitride semiconductor free-standing substrate produced by the production method of a nitride semiconductor free-standing substrate according to the present embodiment, as an _{example, In x Al y Ga 1-} xy N (0 ≦ x, 0 ≦ y, x + y ≦ 1 Is a free-standing substrate formed of a nitride semiconductor represented by: The nitride semiconductor free-standing substrate according to this embodiment is, for example, a GaN free-standing substrate.

  FIG. 2 shows a flow of manufacturing the nitride semiconductor free-standing substrate according to the first embodiment of the present invention.

(Nitride semiconductor free-standing substrate manufacturing method)
First, a sapphire substrate is introduced into the HVPE furnace 10 (S100). Specifically, a sapphire substrate is fixed on the substrate holder 150. Subsequently, the quartz boat 120 on which the Ga metal is mounted is heated to 900 ° C. to melt the Ga metal to obtain a Ga melt 2. Further, a predetermined region where the sapphire substrate is disposed is heated to 1100 ° C., and the surface of the sapphire substrate is cleaned in a hydrogen carrier gas atmosphere for 10 minutes (S110). After completion of cleaning, the temperature of a predetermined region where the sapphire substrate is disposed is lowered to 500 ° C.

Subsequently, HCl gas is introduced from the HCl introduction pipe 130 together with the hydrogen carrier gas. When HCl gas is introduced from the HCl introduction pipe 130, the Ga melt 2 in the quartz boat 120 and the HCl gas react to generate GaCl. The generated GaCl is supplied onto the sapphire substrate together with the hydrogen carrier gas. On the other hand, nitrogen carrier gas and NH ₃ gas are supplied from the NH ₃ introduction tube 140 onto the sapphire substrate. Thereby, a low-temperature buffer layer formed of GaN grows on the sapphire substrate (S120). As an example, the low-temperature buffer layer is grown to a thickness of 30 nm.

After growing the low-temperature buffer layer, a predetermined region where the sapphire substrate is disposed is heated to 1050 ° C. Then, supplies GaCl with hydrogen carrier gas, is supplied to the low-temperature buffer layer through the HCl inlet tube 130, NH ₃ gas with nitrogen carrier gas from NH ₃ inlet tube 140. For example, GaCl and NH ₃ are supplied under the condition that the growth rate of GaN is 100 μm / hour. As an example, GaN is grown for 8 hours, and a GaN crystal having a predetermined film thickness of 800 μm is grown on the low-temperature buffer layer (S130). Thereby, an epitaxial wafer in which a low-temperature buffer layer and a GaN crystal having a predetermined thickness are formed on a sapphire substrate is obtained.

  Subsequently, the obtained epitaxial wafer is taken out from the HVPE furnace 10 (S140). Then, the extracted epitaxial wafer is transferred to a polishing apparatus. Next, the epitaxial wafer transferred to the polishing apparatus is polished using a diamond abrasive. Specifically, the sapphire substrate side is lapped to remove the sapphire substrate and the low-temperature buffer layer (S150). Accordingly, the GaN substrate as the GaN free-standing substrate having a thickness of about 800 μm and a diameter of about 50 mm as the nitride semiconductor free-standing substrate manufactured by the method for manufacturing a nitride semiconductor free-standing substrate according to the first embodiment of the present invention is sapphire. Separated from the substrate (S160).

  The GaN free-standing substrate obtained by the method for manufacturing a nitride semiconductor free-standing substrate according to the first embodiment had a warped shape so that the back surface became a convex surface. The difference between the GaN free-standing substrate and the height of the back surface of the outer periphery of the GaN free-standing substrate, that is, the amount of warpage was about 100 μm when measured using a laser displacement meter. Subsequently, the front and back surfaces of the obtained GaN free-standing substrate were polished to form a flat GaN free-standing substrate having a thickness of 400 μm. When the off-angle of the obtained 400 μm-thick GaN free-standing substrate was measured, the variation in the off-angle of the GaN free-standing substrate was (maximum−minimum) = 0.7 degrees.

In addition, when the 400 μm-thick GaN free-standing substrate obtained by the method for manufacturing a nitride semiconductor free-standing substrate according to the first embodiment is cleaved and the cleavage plane is observed with a TEM, a streak region considered to be an inversion domain Was observed. An inversion domain is a region having a different polarity. Further, when the polarity of the GaN free-standing substrate was determined by CBED (Convergent Beam Electron Diffraction), it was confirmed that the streaky region was an inversion domain. The density of the inversion domain of the GaN free-standing substrate according to the first embodiment is found to be present in the substrate at a density of 100 / cm ² in a cross section parallel to the surface of the GaN free-standing substrate. In addition, it was confirmed to be present on the substrate surface at a density of 100 / cm ² .

  The details of the method for measuring the density of the inversion domain inside the GaN free-standing substrate are as follows. That is, a cross section parallel to the substrate surface (or back surface) is formed at a position 50 μm high from the back surface (surface opposite to the growth surface) of the GaN free-standing substrate. Then, the density of the inversion domain is measured in the formed cross section.

  Note that it is impossible to epitaxially grow a nitride semiconductor crystal on a heterogeneous substrate such as sapphire having a lattice constant greatly different from that of the nitride semiconductor in a state in which the lattice structure of the heterogeneous substrate is inherited. Therefore, when a nitride semiconductor crystal grows on a heterogeneous substrate, an initial nucleus of the nitride semiconductor crystal is generated at an arbitrary position on the heterogeneous substrate, and the nitride semiconductor crystal starts from the generated initial nucleus. Growing up. Then, adjacent crystals are fused to grow into a crystal film that is planar and continuous. In such a heteroepitaxial crystal, many crystal defects are generated at the early stage of the growth stage, and an inversion domain is generated at the stage of initial nucleation depending on the growth conditions. In the present embodiment, a condition for actively generating inversion domains during crystal growth is employed.

(Comparative example)
In the method for manufacturing a nitride semiconductor free-standing substrate according to the comparative example, after the surface of the sapphire substrate is cleaned (S110), the temperature of a predetermined region where the sapphire substrate is disposed is lowered to 500 ° C. The method is the same as that of the nitride semiconductor self-supporting substrate manufacturing method according to the first embodiment except that a nitriding step is further provided. Therefore, a detailed description is omitted except for differences. The step of nitriding the surface of the sapphire substrate is a step performed for the purpose of preventing the occurrence of inversion domains in the GaN crystal layer formed on the sapphire substrate.

Nitriding of the surface of the sapphire substrate is performed as follows. That is, first, NH ₃ gas is supplied onto the sapphire substrate at 1 L / min from an NH ₃ introduction tube 140 serving as an N source supply tube located in the vicinity of the sapphire substrate, and a predetermined region including the surface of the sapphire substrate is NH. A mixed atmosphere of ₃ and hydrogen. Then, the surface of the sapphire substrate is nitrided by exposing the surface of the sapphire substrate to a mixed atmosphere of NH ₃ and hydrogen for 3 minutes. Subsequently, a low-temperature buffer layer of GaN is formed on the surface of the nitrided sapphire substrate as in the first embodiment. Subsequent steps are the same as those in the first embodiment.

  The GaN substrate obtained by the method for manufacturing a nitride semiconductor self-supporting substrate according to the comparative example had a warped shape so that the back surface became a convex surface. The amount of warpage of the GaN substrate formed by the method for manufacturing a nitride semiconductor free-standing substrate according to the comparative example was about 150 μm when measured using a laser displacement meter. Subsequently, the front and back surfaces of the obtained GaN substrate according to the comparative example were polished to form a flat GaN substrate having a thickness of 400 μm. When the off-angle of the 400 μm-thick GaN substrate according to the comparative example was measured, the variation in the off-angle of the GaN substrate was (maximum−minimum) = 0.9 degrees.

(Effects of the first embodiment)
The difference between the comparative example and the first embodiment is whether or not the surface of the sapphire substrate is nitrided. In the first embodiment, the low temperature buffer layer is formed on the sapphire substrate without nitriding the growth conditions of the nitride semiconductor crystal in which inversion domains are likely to occur, that is, the surface of the sapphire substrate. Thereby, according to the method for manufacturing a nitride semiconductor free-standing substrate according to the first embodiment, a nitride semiconductor free-standing substrate having an inversion domain can be formed. The nitride semiconductor free-standing substrate formed in the first embodiment has a smaller warp than the nitride semiconductor free-standing substrate according to the comparative example formed through the step of nitriding the surface of the sapphire substrate.

  In the present embodiment, the inventor has obtained knowledge that one of the growth conditions in which inversion domains are likely to occur in the initial stage of growth of a nitride semiconductor crystal is that the surface of the heterogeneous substrate 1 is not nitrided. It is applied.

  As described above, in the nitride semiconductor free-standing substrate according to the first embodiment, the variation in the off-angle of the free-standing substrate is smaller than that of the free-standing substrate according to the comparative example. Therefore, when a light emitting device such as an LED or LD is manufactured from the nitride semiconductor free-standing substrate obtained in the first embodiment, variation in the wavelength of light emitted by the manufactured light emitting device can be reduced. Furthermore, according to the first embodiment, it is possible to greatly contribute to the improvement of the yield when manufacturing the light emitting device.

[Second Embodiment]
FIG. 3 shows a flow of manufacturing a nitride semiconductor free-standing substrate according to the second embodiment of the present invention.

  In the second embodiment, a void-formed separation method (VAS method) is used. The VAS method is a method of performing crystal growth by forming a thin film of titanium nitride (TiN) having a network structure between a sapphire substrate and a GaN growth layer. A GaN epitaxial layer is grown on the sapphire substrate using the VAS method, and then the sapphire substrate is removed to obtain a GaN free-standing substrate.

Specifically, first, as an example, an impurity is formed on a sapphire substrate having a diameter of 2 inches and having a c-plane using a metal organic vapor phase epitaxy (MOVPE) method. An undoped undoped GaN layer is formed (S200). Trimethylgallium (TMG) and NH ₃ are used as raw materials for the GaN layer to be formed. In addition, the film thickness of the undoped GaN layer to be formed is 300 nm as an example.

Next, as an example, Ti having a thickness of 20 nm is vapor-deposited on the formed GaN layer using a vacuum vapor deposition method to form a Ti layer as a Ti thin film (S210). Then, the sapphire substrate having the GaN layer on which the Ti layer is formed is transferred to an electric furnace. Subsequently, the sapphire substrate having the GaN layer on which the Ti layer is formed is subjected to a heat treatment at 1050 ° C. for 20 minutes with the inside of the electric furnace as a mixed gas atmosphere of 20% NH ₃ and 80% H ₂ (S220). . As a result, a part of the undoped GaN layer is etched to form a void-formed GaN layer having high-density voids, and the Ti layer is nitrided. The nitrided Ti layer changes to a hole-formed TiN layer in which fine openings of the order of submicron are formed at a high density on the surface.

  Subsequently, a sapphire substrate having a void-formed GaN layer and a hole-formed TiN layer is mounted on the substrate holder 150 of the HVPE furnace 10. Then, on this sapphire substrate, the V / III ratio, which is the ratio of the Group V raw material to the Group III raw material at the start of growth, is adjusted to a predetermined value to form GaN having a predetermined thickness (S230). Specifically, the V / III ratio at the start of growth is set to 20, and 800 μm thick GaN is formed on a sapphire substrate having a void-formed GaN layer and a hole-formed TiN layer.

Here, the formation conditions of GaN are as follows. First, the quartz boat 120 on which the Ga metal is mounted is heated to 900 ° C., and the substrate holder 150 side is heated to 1100 ° C. Further, a mixed gas of 5% H ₂ and 95% N ₂ is used as a carrier gas, and GaCl gas and NH ₃ gas generated by reacting HCl gas and Ga metal are used as source gases. The source gas is set so that the V / III ratio at the start of GaN growth is 20. The NH ₃ gas is supplied onto the sapphire substrate simultaneously with the GaCl gas.

  The growth of GaN proceeds as follows. First, the GaN crystal nucleus grows in a three-dimensional island shape on the TiN layer. Next, the GaN crystals grow in the lateral direction on the surface of the sapphire substrate starting from each of the island-shaped crystals and are bonded to each other. Thereby, planarization of the surface of the GaN crystal proceeds. The progress of the growth of the GaN crystal was confirmed by observing the surface and cross section of the sapphire substrate taken out of the HVPE furnace 10 for each growth time under various microscopes.

  After the growth of the GaN crystal is completed, the inside of the HVPE furnace 10 is cooled (S240). In the process of cooling the inside of the HVPE furnace 10, the GaN layer formed on the TiN layer naturally peels from the boundary with the void-formed GaN layer (S250). Thereby, a GaN free-standing substrate as a nitride semiconductor free-standing substrate having a thickness of 800 μm is formed.

  The GaN self-supporting substrate formed in the second embodiment had a large number of indentations on the surface and a warped shape so that the back surface was a convex surface. When the amount of warpage of the GaN free-standing substrate formed in the second embodiment was measured using a laser displacement meter, it was about 10 μm. Subsequently, the front and back surfaces of the obtained GaN free-standing substrate were polished until there was no dent on the front surface to form a flat GaN free-standing substrate having a thickness of 400 μm. When the off-angle of the GaN free-standing substrate was measured, the variation in the off-angle of the GaN free-standing substrate was (maximum−minimum) = 0.2 degrees.

Further, when the obtained GaN free-standing substrate was cleaved and the cleaved surface was observed with a TEM, a large number of streaky regions considered to be inversion domains were confirmed on the cleaved surface. Many of these streaks have reached the surface of the GaN free-standing substrate. And when the polarity determination by CBED was implemented, it was confirmed that this area | region is an inversion domain. Then, regarding the density of the inversion domain of the GaN free-standing substrate according to the second embodiment, it is recognized that it exists inside the substrate at a density of 300 / cm ² in a cross section parallel to the surface of the GaN free-standing substrate. In addition, it was confirmed to be present on the substrate surface at a density of 300 / cm ² .

(Effect of the second embodiment)
In the second embodiment, the growth conditions in which inversion domains are likely to occur, that is, the V / III ratio is set high. Thereby, according to the method for manufacturing a nitride semiconductor free-standing substrate according to the second embodiment, a nitride semiconductor free-standing substrate having an inversion domain can be formed.

  In the present embodiment, one of the growth conditions in which inversion domains are likely to occur at the initial growth stage of the nitride semiconductor crystal is to increase the V / III ratio, while the conditions in which the inversion domains tend to disappear are V The knowledge obtained by the inventor that the ratio / III is to be lowered is applied.

  The nitride semiconductor free-standing substrate formed in the second embodiment is a nitride semiconductor free-standing substrate according to a comparative example formed with a V / III ratio in the initial stage of growth lower than that of the second embodiment. The warpage is very small. Therefore, the nitride semiconductor free-standing substrate formed by the method for manufacturing a nitride semiconductor free-standing substrate according to the second embodiment has a smaller off-angle variation of the free-standing substrate than the free-standing substrate according to the comparative example. The nitride semiconductor free-standing substrate obtained in the second embodiment can produce light-emitting elements such as LEDs and LDs with small variations in emission wavelength, and can greatly contribute to the improvement of yield in production. .

[Third Embodiment]
FIG. 4 shows a flow of manufacturing a nitride semiconductor free-standing substrate according to the third embodiment of the present invention.

  The nitride semiconductor free-standing substrate manufacturing method according to the third embodiment is different from the nitride semiconductor free-standing substrate manufacturing method according to the second embodiment when the growth of GaN crystals on the TiN layer is started. Except that the V / III ratio is changed to a different V / III ratio after GaN having a predetermined thickness is formed. Therefore, a detailed description is omitted except for differences.

In the third embodiment, the V / III ratio at the start of growth, which is one of the growth conditions for the GaN crystal grown on the TiN layer, is adjusted to be 15. As an example, after growing a GaN crystal having a thickness of 500 μm, the NH ₃ flow rate is changed and adjusted so that the V / III ratio is 12 as an example, and the GaN crystal is continuously grown. Other processes and growth conditions are the same as those in the second embodiment. As a result, a GaN free-standing substrate having a thickness of 800 μm and a flat surface can be obtained unlike the GaN free-standing substrate according to the second embodiment.

Specifically, first, an undoped GaN layer is formed on a sapphire substrate using the MOVPE method (S300). Next, Ti having a thickness of 20 nm is deposited on the formed GaN layer by a vacuum deposition method to form a Ti thin film (S310). Then, the sapphire substrate having the GaN layer on which the Ti thin film is formed is transferred to an electric furnace, and the inside of the electric furnace is made a mixed gas atmosphere of 20% NH ₃ and 80% H ₂ . Then, the sapphire substrate having the GaN layer on which the Ti thin film is formed is subjected to a heat treatment at 1050 ° C. for 20 minutes (S320).

Subsequently, a sapphire substrate having a void-formed GaN layer and a hole-formed TiN layer is mounted on the substrate holder 150 of the HVPE furnace 10. Then, on this sapphire substrate, the V / III ratio, which is the ratio of the Group V material and the Group III material at the start of growth, is adjusted to 15 to form 500 μm thick GaN (S330). Subsequently, the V / III ratio is changed to 12, and a GaN crystal is continuously grown to a thickness of 800 μm on the GaN formed to a thickness of 500 μm (S340).
After the growth of the GaN crystal is completed, the inside of the HVPE furnace 10 is cooled (S350). In the process of cooling the inside of the HVPE furnace, the GaN layer formed on the TiN layer naturally peels from the boundary with the void-formed GaN layer (S360). Thereby, a GaN free-standing substrate as a nitride semiconductor free-standing substrate having a thickness of 800 μm is formed.

  The GaN free-standing substrate obtained by the method for manufacturing a nitride semiconductor free-standing substrate according to the third embodiment is warped so that the back surface is a convex surface, and the amount of warpage is measured using a laser displacement meter. , About 120 μm. Further, 50 μm on the surface of the obtained GaN free-standing substrate and 350 μm on the back surface were polished to form a flat GaN free-standing substrate having a thickness of 400 μm. When the off-angle of the GaN free-standing substrate was measured, the variation in the off-angle of the GaN free-standing substrate was (maximum−minimum) = 0.75 degrees.

Furthermore, the GaN free-standing substrate obtained by the method for manufacturing a nitride semiconductor free-standing substrate according to the third embodiment was cleaved, and the cleavage plane was observed by TEM. As a result, a large number of streak regions thought to be inversion domains were observed. When polarity determination by CBED was performed, it was confirmed that many of these regions were inversion domains. It should be noted that the inversion domain density of the GaN free-standing substrate according to the third embodiment is found to be present in the substrate at a density of 10 / cm ² in a cross section parallel to the surface of the GaN free-standing substrate. In addition, it was confirmed that the density was 0 / cm ^{2 on} the substrate surface.

  Note that the GaN free-standing substrate to be formed preferably has a diameter of 20 mm or more and a thickness of 200 μm. This is because it is necessary to secure a thickness that can be handled as a nitride semiconductor free-standing substrate. Further, if the formed GaN free-standing substrate is warped with the same curvature, the smaller the diameter, the smaller the warping amount, and the smaller the off-angle variation due to the warping of the substrate. That is, when the diameter of the substrate is small, the effect of using the nitride semiconductor free-standing substrate manufacturing method according to the first to third embodiments of the present invention is small.

  On the other hand, as the substrate has a larger diameter, the amount of warpage at the outer peripheral portion of the substrate increases and the variation in off-angle due to warping of the substrate also increases. Therefore, nitriding according to the first to third embodiments of the present invention. This is because the effect of using the method for manufacturing a physical semiconductor free-standing substrate is very large. That is, even if the GaN free-standing substrate to be formed has a diameter of 20 mm or more, the nitride semiconductor free-standing substrate manufacturing method according to the first to third embodiments of the present invention is used. Thus, a nitride semiconductor free-standing substrate with little warpage can be formed.

(Effect of the third embodiment)
The difference between the third embodiment and the second embodiment is that the V / III ratio at the time of starting the growth of the GaN crystal on the TiN layer is maintained at a predetermined value from the start of the growth to the predetermined film thickness. Whether or not the V / III ratio is changed after growing a GaN crystal having a predetermined thickness. In the third embodiment, after a GaN crystal having a predetermined thickness is grown, the growth conditions in which inversion domains are less likely to occur, that is, the V / III ratio is set low.

  That is, in the method for manufacturing a nitride semiconductor free-standing substrate according to the third embodiment, a growth condition that easily generates an inversion domain is applied at the initial growth stage of nitride semiconductor crystal growth, and at the time of growth on the surface side of the substrate. Apply growth conditions that are unlikely to cause inversion domains. Thereby, a nitride semiconductor free-standing substrate having an inversion domain inside the nitride semiconductor crystal and few inversion domains reaching the surface of the nitride semiconductor crystal can be formed.

  Therefore, according to the method for manufacturing the nitride semiconductor free-standing substrate according to the third embodiment, the warpage of the nitride semiconductor free-standing substrate after the dissimilar substrate 1 is peeled off is very small, and the warpage of the free-standing substrate is caused. Since the variation in the off-angle can be reduced, the variation in the wavelength of light emitted from the light-emitting element formed using the self-supporting substrate can be reduced. In addition, the yield of light-emitting elements manufactured using the self-supporting substrate can be improved.

  The inversion domain once generated has a property of extending to the surface of the crystal growth layer while maintaining a predetermined region when the growth conditions are kept constant. If a semiconductor layer of a light-emitting device is formed by epitaxial growth on a free-standing substrate in which the inversion domain reaches the crystal surface, the surface of the region where the inversion domain exists becomes rough. To do. Therefore, conventionally, crystal growth conditions have been selected such that inversion domains do not occur in the growth layer.

  However, the method for manufacturing a nitride semiconductor free-standing substrate according to the first to third embodiments has been made by the inventors with the following knowledge. That is, as a first finding, if an inversion domain exists in a nitride semiconductor crystal, the internal stress is relieved by shifting the crystal lattice in the thickness direction of the nitride semiconductor, and the warpage of the nitride semiconductor free-standing substrate is reduced. The inventors have found that it is suppressed. As a second finding, it has been found that when the number of inversion domains per unit area is large and the inversion domains extend to the vicinity of the crystal surface, the warpage of the free-standing substrate decreases. Furthermore, as a third finding, when the inversion domain reaches the outermost surface of the free-standing substrate, the surface of the free-standing substrate is roughened, so the inversion domain does not reach the surface of the free-standing substrate and does not reach the surface of the free-standing substrate. The inventors have found that it is desirable to stop the inversion domain at a position to form a free-standing substrate.

  Therefore, in the first embodiment and the second embodiment, a method for manufacturing a nitride semiconductor free-standing substrate in which the inversion domain exists inside the substrate will be described, and the superiority of the free-standing substrate having the inversion domain will be described. explained. Furthermore, in the third embodiment, as the best manufacturing method of the nitride semiconductor free-standing substrate according to the present invention, the manufacture of a free-standing substrate that has an inversion domain inside and the inversion domain does not reach the substrate surface. It explains the method.

Note that the manufacturing method of the nitride semiconductor free-standing substrate shown in the first to third embodiments is not limited as long as the inversion domain is generated in the nitride semiconductor free-standing substrate. Furthermore, it is not necessary for the inversion domain to remain in the finally obtained nitride semiconductor free-standing substrate, and it is sufficient that the inversion domain is generated during the manufacturing process. That is, in the method for manufacturing a nitride semiconductor free-standing substrate, after forming a region having an inversion domain and a region having no inversion domain, at least a part of the region having an inversion domain is removed by polishing, etching, or the like. Thus, a nitride semiconductor free-standing substrate may be formed.

  Further, an ingot of a nitride semiconductor crystal can be formed by growing a nitride semiconductor crystal having an inversion domain to a thickness of several millimeters on a different substrate. A plurality of nitride semiconductor crystal free-standing substrates can be obtained by slicing the formed nitride semiconductor crystal ingot.

[Fourth Embodiment]
The nitride semiconductor free-standing substrate manufacturing method according to the fourth embodiment is different from the nitride semiconductor free-standing substrate manufacturing method according to the third embodiment when the growth of GaN crystals on the TiN layer is started. When the V / III ratio is changed to a different V / III ratio after GaN having a predetermined film thickness is formed, substantially the same steps are provided except that the values of the respective V / III ratios are different. Therefore, detailed description is omitted.

In the fourth embodiment, the V / III ratio at the start of growth, which is one of the growth conditions for the GaN crystal grown on the TiN layer, is adjusted to be 20. As an example, after growing a GaN crystal having a thickness of 500 μm, the NH ₃ flow rate is adjusted so that the V / III ratio becomes 12, and the GaN crystal is continuously grown. Other processes and growth conditions are the same as those of the third embodiment.

  The GaN free-standing substrate obtained by the method for manufacturing a nitride semiconductor free-standing substrate according to the fourth embodiment is warped so that the back surface becomes a convex surface, and the amount of warping is measured using a laser displacement meter. About 20 μm. Further, 50 μm on the surface of the obtained GaN free-standing substrate and 350 μm on the back surface were polished to form a flat GaN free-standing substrate having a thickness of 400 μm. When the off-angle of the GaN free-standing substrate was measured, the variation in the off-angle of the GaN free-standing substrate was (maximum−minimum) = 0.23 degrees.

Furthermore, the GaN free-standing substrate obtained by the method for manufacturing a nitride semiconductor free-standing substrate according to the fourth embodiment was cleaved, and the cleavage plane was observed by TEM. As a result, a large number of streak regions thought to be inversion domains were observed. When polarity determination by CBED was performed, it was confirmed that many of these regions were inversion domains. Then, regarding the density of the inversion domain of the GaN free-standing substrate according to the fourth embodiment, it is recognized that it exists in the substrate at a density of 300 / cm ² in a cross section parallel to the surface of the GaN free-standing substrate. In addition, it was confirmed that the density was 0 / cm ^{2 on} the substrate surface.

[Fifth Embodiment]
The nitride semiconductor free-standing substrate manufacturing method according to the fifth embodiment is different from the nitride semiconductor free-standing substrate manufacturing method according to the third embodiment when the growth of a GaN crystal on the TiN layer is started. When the V / III ratio is changed to a different V / III ratio after GaN having a predetermined film thickness is formed, substantially the same steps are provided except that the values of the respective V / III ratios are different. Therefore, detailed description is omitted.

In the fifth embodiment, the V / III ratio at the start of growth, which is one of the growth conditions for the GaN crystal grown on the TiN layer, is adjusted to be 40. As an example, after growing a GaN crystal having a thickness of 500 μm, the NH ₃ flow rate is adjusted so that the V / III ratio becomes 12, and the GaN crystal is continuously grown. Other processes and growth conditions are the same as those of the third embodiment.

  The GaN free-standing substrate obtained by the method for manufacturing a nitride semiconductor free-standing substrate according to the fifth embodiment is warped so that the back surface is a convex surface, and the amount of warpage is measured using a laser displacement meter. It was about 5 μm. Further, 50 μm on the surface of the obtained GaN free-standing substrate and 350 μm on the back surface were polished to form a flat GaN free-standing substrate having a thickness of 400 μm. When the off-angle of the GaN free-standing substrate was measured, the variation in the off-angle of the GaN free-standing substrate was (maximum−minimum) = 0.1 degrees.

Furthermore, the GaN free-standing substrate obtained by the method for manufacturing a nitride semiconductor free-standing substrate according to the fifth embodiment was cleaved, and the cleavage plane was observed by TEM. As a result, a large number of streak regions thought to be inversion domains were observed. When polarity determination by CBED was performed, it was confirmed that many of these regions were inversion domains. Then, regarding the density of the inversion domain of the GaN free-standing substrate according to the fifth embodiment, it is recognized that it exists in the substrate at a density of 600 / cm ² in a cross section parallel to the surface of the GaN free-standing substrate. In addition, it was confirmed that the density was 200 / cm ^{2 on} the substrate surface.

[Application example]
FIG. 5 shows a cross-sectional view of a light emitting device formed using a nitride semiconductor free-standing substrate manufactured in the method for manufacturing a nitride semiconductor free-standing substrate according to the first to fifth embodiments of the present invention.

  The light emitting device 20 according to the application example includes a GaN substrate 200 formed by the method for manufacturing a nitride semiconductor free-standing substrate according to the first to fifth embodiments, an n-type cladding layer 205 formed on the GaN substrate 200, and , An active layer 210 formed on the n-type cladding layer 205, a p-type cladding layer 215 formed on the active layer 210, and a p-type contact layer 220 formed on the p-type cladding layer 215, Is provided.

  Furthermore, the light-emitting device 20 includes a lower electrode 235 formed on substantially the entire surface of the GaN substrate 200 opposite to the surface on which the n-type cladding layer 205 is formed, and a p-type cladding layer 215 of the p-type contact layer 220. And an upper electrode 230 formed in a predetermined region on the opposite side of the surface in contact with the electrode. In addition, the active layer 210 according to the application example has a quantum well structure. As an example, the active layer 210 has a multiple quantum well structure including three well layers 212 and four barrier layers 214 sandwiching the well layers 212, respectively.

  Note that the quantum well structure of the active layer 210 can be formed of a single quantum well structure or a strained quantum well structure. Furthermore, the active layer 210 may be formed not from a quantum well structure but from a double heterostructure.

As an example, the plurality of semiconductor layers included in the light-emitting device 20 according to the application example can be formed by a metal organic chemical vapor deposition (MOCVD) method. As an example, the plurality of semiconductor layers can be formed by MOCVD using trimethylgallium (TMG), trimethylindium (TMI), or biscyclopentadienylmagnesium (Cp ₂ Mg), which are organic metal raw materials. Note that hydrogen and nitrogen are used as an example of the carrier gas supplied together with the organometallic raw material when forming the plurality of semiconductor layers.

Specifically, an n-type cladding layer 205 having a Si doping concentration of 1 × 10 ¹⁹ cm ⁻³ at 1050 ° C. is formed on the GaN substrate 200 formed in the first to fifth embodiments. The n-type GaN layer is formed. The film thickness of the n-type cladding layer 205 is 4 μm as an example. Subsequently, at 800 ° C., an InGaN-based active layer as an active layer 210 including a GaN barrier layer as three barrier layers 214 and an In _0.1 Ga _0.9 N well layer as four well layers 212 is formed. . The thickness of the In _0.1 Ga _0.9 N well layer is 3 nm as an example, and the thickness of the GaN barrier layer is 10 nm as an example.

Further, a p-type Al _0.1 Ga _0.9 N clad layer as the p-type clad layer 215 and a p-type GaN contact layer as the p-type contact layer 220 are formed in this order. As an example of the p-type dopant, Mg is used. Further, the upper electrode 230 and the lower electrode 235 are formed from a metal material containing Ti, Ni, Al, or the like.

  Table 1 shows the results of variations in the emission wavelength of light emitting devices formed using the nitride semiconductor free-standing substrate formed in the first to fifth embodiments and the nitride semiconductor free-standing substrate formed in the comparative example. Show.

  In Table 1, the meanings of symbols in the column of surface morphology are as follows. That is, the double circle “◎” is a substrate on which surface roughness was hardly observed. A single circle “◯” is a substrate on which surface roughness is slightly observed. Furthermore, the cross “X” is a substrate on which a lot of surface roughness was observed. Note that when the surface roughness is large, the yield of the light-emitting device decreases.

  The light emitting device shown in FIG. 5 was formed using the nitride semiconductor free-standing substrate formed in the first to fifth embodiments and the nitride semiconductor free-standing substrate formed in the comparative example. And the variation of the light emission wavelength was measured by EL measurement. As a result, a light emitting device having a small off-angle variation resulted in a small variation in emission wavelength. This is a result of using a self-supporting substrate having an inversion domain to reduce the warpage of the substrate and reduce the variation in off-angle within the substrate surface.

As seen with reference to Table 1, when the GaN free-standing substrate is, with free-standing substrate surface section parallel, i.e., the 10 / cm ² or more from 600 / cm ² or less in density in the inversion domains inside the substrate, The amount of warpage of the free-standing substrate can be reduced as compared with the comparative example. When the warpage of the free-standing substrate is small (for example, when the amount of warpage is 5 μm to 120 μm), the variation in the emission wavelength of the light emitting device can be in the range of 9 nm to 18 nm. Note that when the inversion domain is provided on the surface of the free-standing substrate at a density of 0 piece / cm ² or more to 200 pieces / cm ² or less, the morphology of the substrate surface can be improved.

  While the embodiments of the present invention have been described above, the embodiments described above do not limit the invention according to the claims. In addition, it should be noted that not all the combinations of features described in the embodiments are essential to the means for solving the problems of the invention.

It is the schematic of the HVPE furnace used for the manufacturing method of the nitride semiconductor self-supporting substrate which concerns on the 1st Embodiment of this invention. It is a figure which shows the flow of manufacture of the nitride semiconductor self-supporting substrate concerning the 1st Embodiment of this invention. It is a figure which shows the flow of manufacture of the nitride semiconductor self-supporting substrate concerning the 2nd Embodiment of this invention. It is a figure which shows the flow of manufacture of the nitride semiconductor self-supporting substrate concerning the 3rd Embodiment of this invention. FIG. 5 is a cross-sectional view of a light emitting device formed using a nitride semiconductor free-standing substrate manufactured in the method for manufacturing a nitride semiconductor free-standing substrate according to the first to fifth embodiments of the present invention.

1 heterologous substrate 2 Ga melt 10 HVPE furnace 20 light emitting device 100 quartz reaction tube 110 heaters 120 quartz boat 130 HCl inlet tube 140 NH ₃ inlet tube 150 substrate holder 200 GaN substrate 205 n-type cladding layer 210 an active layer 212 well layer 214 barrier Layer 215 p-type cladding layer 220 p-type contact layer 230 upper electrode 235 lower electrode

Claims (4)

In a nitride semiconductor free-standing substrate comprising a continuously grown nitride semiconductor crystal,
Inside of a nitride semiconductor free-standing substrate has inversion domains 600 / cm ² or less in a density from 10 / cm ² or more in a cross section that is parallel to the substrate surface, the substrate surface is 0 / cm ² or more Nitride semiconductor free-standing substrate having inversion domains at a density of 200 / cm ² or less and having a lower density of inversion domains reaching the substrate surface than inversion domains inside the nitride semiconductor free-standing substrate.   2. The nitride semiconductor free-standing substrate according to claim 1, wherein an in-plane variation in off-angle of the nitride semiconductor free-standing substrate is not less than 0.1 degrees and not more than 0.75 degrees.   A plurality of semiconductor layers including an active layer are formed on one side of the nitride semiconductor free-standing substrate according to claim 1, an upper electrode is formed on the semiconductor layer, and the other of the nitride semiconductor free-standing substrate A light-emitting device manufactured by forming a lower electrode on the surface side of the substrate.   A light emitting device having a variation in emission wavelength emitted from the light emitting device according to claim 3 of 9 nm or more and 18 nm or less.

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