JP6365992B2 - Group III nitride crystal manufacturing method and RAMO4 substrate - Google Patents

Description

The present invention relates to a group III nitride crystal manufacturing method and a RAMO ₄ substrate.

A substrate represented by the general formula RAMO ₄ (in the general formula, R represents one or more trivalent elements selected from the group consisting of Sc, In, Y, and lanthanoid elements, and A represents Fe. (III) represents one or more trivalent elements selected from the group consisting of Ga, and Al, and M is a group consisting of Mg, Mn, Fe (II), Co, Cu, Zn, and Cd As an example, a ScAlMgO ₄ substrate is known. The ScAlMgO ₄ substrate is used as a growth substrate for a nitride semiconductor such as GaN (see, for example, Patent Document 1). FIG. 11 is a diagram showing the steps of the conventional ScAlMgO ₄ substrate manufacturing method described in Patent Document 1. In the formation of the single crystal in step S201, a bulk material of ScAlMgO ₄ is formed. The substrate is formed by cleaving the bulk material in the growth substrate production in step S202. In the GaN layer formation in S203, a GaN layer is formed on the substrate. In the growth substrate removal of S204 step, ScAlMgO ₄ substrate is a growth substrate, or is removed by etching using buffered hydrofluoric acid or the like, after cleaving a portion of ScAlMgO ₄ substrate, further growth substrate by etching or polishing is removed Or By performing these steps, a GaN substrate is finally formed.

JP-A-2015-178448

As described above, in Patent Document 1, when manufacturing a GaN substrate, the RAMO ₄ substrate is removed by etching or polishing in step S204. Further, when a part of the RAMO ₄ substrate is removed by cleavage, the removed RAMO ₄ substrate is reused by dissolving the removed RAMO ₄ substrate once and making it into a single crystal again. However, in recent years, it has been required to easily reuse the removed RAMO ₄ substrate in consideration of the cost of manufacturing the GaN substrate, the manufacturing efficiency, and the like. That is, an object of the present disclosure is to provide a method for improving the use efficiency of the RAMO ₄ substrate, which is a growth substrate, when manufacturing a group III nitride.

To achieve the above object, the present disclosure provides a single crystal represented by the general formula RAMO ₄ (in the general formula, R is one selected from the group consisting of Sc, In, Y, and a lanthanoid element) Or A represents a plurality of trivalent elements, A represents one or more trivalent elements selected from the group consisting of Fe (III), Ga, and Al, and M represents Mg, Mn, Fe ( II), representing one or more divalent elements selected from the group consisting of Co, Cu, Zn, and Cd), and preparing a RAMO ₄ substrate having a notch on the side, and growing a group III nitride crystal RAMO ₄ on a substrate, and a step for cleaving the RAMO ₄ substrate the notch starting point, to provide a group III nitride crystal manufacturing method.
Further, the present disclosure provides a single crystal represented by the general formula RAMO ₄ (in the general formula, R is one or more trivalent selected from the group consisting of Sc, In, Y, and a lanthanoid element) A represents an element, A represents one or more trivalent elements selected from the group consisting of Fe (III), Ga, and Al, and M represents Mg, Mn, Fe (II), Co, Cu A RAMO ₄ substrate having a notch on a side portion thereof is provided. The RAMO ₄ substrate is a RAMO ₄ substrate composed of one or more divalent elements selected from the group consisting of Zn, Cd, and Cd.

According to the present disclosure, the RAMO ₄ substrate easily reused, it provides a method and RAMO ₄ substrate to produce a group III nitride.

FIG. 6 is a diagram of a manufacturing process of the group III nitride substrate in the first embodiment of the present disclosure Figure 2A represents a perspective view showing the shape after the outer shape processing ScAlMgO ₄ ingot of the first embodiment of the present disclosure, FIG. 2B, FIG. 2C is the shape of the notch ScAlMgO ₄ ingot according to the first embodiment of the present disclosure Side view, FIG. 2D is a top view of the ScAlMgO ₄ ingot according to the first embodiment of the present disclosure. 3A and 3B show the shape of the blade used for cleavage in the first embodiment of the present disclosure. Figure of flatness measurement result of epitaxial growth surface formed only by conventional cleavage 5A is a plan view and a side view of a notched ScAlMgO ₄ substrate after cleavage in Embodiment 1 of the present disclosure, and FIG. 5B is a side view in which a GaN layer is formed on the ScAlMgO ₄ substrate in Embodiment 1. FIG. FIG. 5D is a side view when the ScAlMgO ₄ substrate in the first embodiment is removed, and FIG. 5D is a side view of the GaN substrate formed in the first embodiment. The figure of the flatness measurement result after the rough uneven | corrugated formation process in Embodiment 1 of this indication The figure of the flatness measurement result after the micro unevenness formation process in Embodiment 1 of this indication The figure of the AFM measurement result after the micro unevenness formation process in Embodiment 1 of this indication FIG. 7 is a diagram of a manufacturing process of the group III nitride substrate in the second embodiment of the present disclosure 10A is a side view in which a GaN layer is formed on a ScAlMgO ₄ substrate in Embodiment 2, and FIG. 10B is a side view of the substrate in which a device in Embodiment 2 is formed. Diagram of manufacturing process of conventional ScAlMgO ₄ substrate

Hereinafter, embodiments of the present invention will be described with reference to FIGS. In the embodiment, the group III nitride is GaN, and the RAMO ₄ substrate is ScAlMgO ₄ .

(Embodiment 1)
FIG. 5 shows each step of the method for producing a group III nitride according to the first embodiment of the present disclosure. This method comprises a step of preparing a ScAlMgO ₄ substrate 10 made of a ScAlMgO ₄ single crystal and having a notch 2b on the side (FIG. 5A), and a step of growing a group III nitride crystal 4 on the ScAlMgO ₄ substrate 10 ( 5B) and a step (FIG. 5C) of cleaving the ScAlMgO ₄ substrate 10 starting from the notch 2b (FIG. 5C).

Top view of FIG. 5A is a diagram viewed from above the main surface of ScAlMgO ₄ substrate 10, below is a side view in the thickness direction of ScAlMgO ₄ substrate 10, in particular, a portion of the side of ScAlMgO ₄ substrate 10 FIG. The main surface of the ScAlMgO ₄ substrate 10 is a cleavage plane of the ScAlMgO ₄ single crystal, and the notch 2b is arranged on the side portion of the ScAlMgO ₄ substrate 10 substantially in parallel with the cleavage surface. In the step of FIG. 5B, a group III nitride crystal is grown on the main surface of the ScAlMgO ₄ substrate 10 as a seed substrate. Thereafter, the ScAlMgO ₄ substrate 10 is easily separated into the side 10b where the group III nitride crystal is formed and the side 10a where the group III nitride crystal is not formed starting from the notch 2b. For this reason, the side 10a on which the group III nitride crystal is not formed can be easily reused. For example, the side 10a where the group III nitride crystal is not formed may be reused to grow the group III nitride crystal on the main surface.

Next, details of a method for producing a group III nitride crystal including a method for producing the ScAlMgO ₄ substrate 10 will be described. In the description, GaN (gallium nitride) is exemplified as the group III nitride.

Details of this method, as shown in FIG. 1, has a ScAlMgO ₄ ingot preparing step of generating a single crystal ScAlMgO _4, processed outline of the single crystal ScAlMgO ₄ ingot, a plurality of notches 2a to the side, the 2b ScAlMgO ₄ ingot outer shape processing step for preparing a cylindrical ScAlMgO ₄ ingot 1, ScAlMgO ₄ substrate preparation step for processing the ingot 1 into a substrate and preparing a ScAlMgO ₄ substrate 10 having a notch 2b on the side, and a ScAlMgO substrate ₄ origin and uneven removal step of removing the unevenness of the surface (main surface) corresponding to the epitaxial growth surface of the substrate 10, a GaN crystal growth step of growing a GaN layer 4 on the main surface of ScAlMgO ₄ substrate 10, a notch 2b and ScAlMgO ₄ removing step of removing the ScAlMgO ₄ substrate, Ga Including a GaN substrate processing step of processing epiready face the main surface of the substrate 4a, a. Hereinafter, details of each process will be described.

In the ScAlMgO ₄ ingot preparation step, for example, a single crystal ScAlMgO ₄ ingot manufactured using a high-frequency induction heating type Czochralski furnace is prepared. As an example of the ingot manufacturing method, a method of generating an ingot having a diameter of 50 mm will be described. First, Sc ₂ O ₃ , Al ₂ O ₃ and MgO having a purity of 4N (99.99%) are blended in a predetermined molar ratio as starting materials. Then, 3400 g of the starting material is put into an iridium crucible having a diameter of 100 mm. Next, the crucible containing the raw materials is put into a high-frequency induction heating type Czochralski furnace (growing furnace), and the inside of the furnace is evacuated. Thereafter, nitrogen is introduced into the furnace, and heating of the crucible is started when the pressure in the furnace reaches atmospheric pressure. Then, the material is melted by gradually heating over 12 hours until the melting point of ScAlMgO ₄ is reached. Next, the ScAlMgO ₄ single crystal cut in the (0001) direction is used as a seed crystal, and the seed crystal is lowered to near the melt in the crucible. The seed crystal is gradually lowered while rotating at a constant rotation speed, and the seed crystal is raised at a speed of 0.5 mm / h while gradually lowering the temperature by bringing the tip of the seed crystal into contact with the melt. (Raised in the direction of the 0001 axis) to grow crystals. Thereby, a single crystal ingot having a diameter of 50 mm and a length of the straight body portion of 50 mm is obtained.

In the ScAlMgO ₄ ingot outer shape processing step, the pulled ingot is processed into a cylindrical shape, and further, a notch process is performed on the side of the column. First, both ends (top and tail) of the ingot are cut using a band saw, a slicer with an inner peripheral blade or an outer peripheral blade, a single wire saw, or the like. Since the pulled ScAlMgO ₄ ingot is not in the form of a regular circle, it is subjected to outer peripheral grinding using a diamond wheel or the like and polishing with a polishing cloth to form a cylinder. A perspective view of the columnar ScAlMgO ₄ ingot 1 is shown in FIG. 2A.

Here, the ScAlMgO ₄ single crystal will be described. The ScAlMgO ₄ single crystal has a structure in which a rock salt structure (111) -plane ScO ₂ layer and a hexagonal (0001) -plane AlMgO ₂ layer are alternately stacked. The hexagonal (0001) plane two layers are planar compared to the wurtzite structure, and the bond between the upper and lower layers is about 0.03 nm longer than the in-plane bond. The power is weak. For this reason, the ScAlMgO ₄ single crystal can be cleaved in the (0001) plane. Using this characteristic, the columnar ScAlMgO ₄ ingot 1 is formed into a substrate having a predetermined thickness in the ScAlMgO ₄ substrate preparation step. In this case, since a starting point for cleaving is necessary, the notches 2a and 2b are formed in the side portions of the ingot in the ScAlMgO ₄ ingot outer shape processing step. A method of forming the starting point will be described with reference to FIGS. 2B and 2C.

As shown in FIGS. 2B and 2C, in the ScAlMgO ₄ substrate preparation step, when the final thickness of the ScAlMgO ₄ substrate is t1, notches 2a that are the starting points are formed at intervals of t1. Further, in order to form a substrate with a notch 2b, a notch is provided at a position away from t2 in the same direction by t2. The notch 2a is a starting point of cleavage when the ingot is turned into a substrate, and the notch 2b is a starting point of cleavage when the ScAlMgO ₄ substrate is reused. For example, t1 = 500 μm and t2 = 100 μm.

Next, a method for forming notches will be described. FIG. 2B shows a notch shape formed by dicing or laser processing. When dicing, for example, a blade having a diameter of 100 mm, a grindstone particle size of 30 μm, and a particle size of # 600 is rotated at 1800 min ⁻¹ for processing. In the case of laser processing, a laser having a wavelength of 400 nm or less and a pulse width of 100 nsec or less can be used as long as the YAG laser has a pulse width of nanoseconds. In addition, an infrared or visible laser can be used as long as the pulse width is an ultrashort pulse laser of 1 nsec or less. As shown in FIG. 2B, the notch formed by dicing or laser processing has a sharp shape at the tip of the notch when viewed macroscopically. On the other hand, FIG. 2C shows a notch shape when processed with a wire saw. A single wire saw is used when forming notches one by one with a wire saw, and a multi-wire saw is used when machining a plurality of locations at the same time. As the wire diameter of the wire used is thinner, a narrow notch shape can be formed. For the wire saw, for example, a fixed abrasive wire electrodeposited with a diamond having a core diameter of 80 μm and an abrasive grain size of 8 to 16 μm can be used. When forming a notch using a multi-wire saw, first, a plurality of notches 2a are formed at a pitch of t1, and then the ingot or wire position is shifted by a distance of t2 to form the notches 2b. As shown in FIG. 2C, the notch formed by the wire saw has an R shape at the tip of the notch when viewed macroscopically.

FIG. 2D is a view of the ScAlMgO ₄ ingot 1 as seen from a circular surface (upper surface). As for the depth d of the notch shown in FIG. 2D and the width w in the circumferential direction, d is preferably 0.1 mm to 5 mm, and w is preferably 0.1 mm to 15 mm. For example, when the ScAlMgO ₄ ingot 1 is a cylinder of 2 inches (diameter 50 mm), if the notch depth d is 0.1 mm, the circumferential width w is geometrically determined to be 4.46 mm. . In addition, when the ScAlMgO ₄ ingot 1 is a 4 inch (diameter 100 mm) cylinder, if the notch depth d is 0.1 mm, the circumferential width w is 6.32 mm. When the ScAlMgO ₄ ingot 1 is not a cylinder, the notch depth d and width w are determined according to the shape. If the notch depth d is too deep, the effective area of the substrate is reduced, so that the effective area of the substrate is allowed. Specifically, the allowable range (notch depth d) of the effective area of the substrate is 5 mm or less. In the case of a cylinder, when the depth is determined as described above, the width is also geometrically determined. For this reason, w becomes 15 mm or less.

When the ScAlMgO ₄ ingot 1 is actually cleaved, the shape of the blade 3 shown in FIG. 3 is cleaved into the notches 2a and 2b. Therefore, it is preferable that the shape of the notch is a shape in which the cutting edge is sharply inserted, and as shown in FIG. 2B, the tip of the notch (the tip on the inner side of the ingot 1) is preferably a sharp shape. .
Although it is conceivable to provide a plurality of cutouts 2b in the same plane, if the cleavage is performed from a plurality of locations with insufficient alignment, a step is generated on the cleavage plane. Accordingly, when a plurality of cutouts are provided in the same plane, alignment at the atomic level is necessary, which is substantially difficult.

Next, the ScAlMgO ₄ substrate preparation process will be described. In this step, in order to obtain the ScAlMgO ₄ substrate 10 having a notch, the blade 3 shown in FIG. 3 is applied to the notch 2a, and cleavage is performed by applying a force in the cleavage direction, so that the thickness t1 from the cylindrical ingot 1 is increased. ScAlMgO ₄ substrate 10 is obtained. The material of the blade 3 is made of steel. A typical shape of the blade 3 is shown in FIGS. 3A and 3B. As shown in FIG. 3A, the blade 3 may be a single blade, or may be a double blade as shown in FIG. 3B. The angle of the blade edge of the blade 3 (the angle represented by θ1 in FIG. 3A and θ2 in FIG. 3B) is desirably 30 ° or less. The shape of the blade 3 is not limited to the shape shown in FIGS. 3A and 3B. For example, in the case of both blades, the angle indicated by θ2 in FIG. 3B may be asymmetric from the center of the blade edge, and a plurality of angles are provided. It may be.

FIG. 4 shows flatness measurement data of the cleavage plane (epitaxial growth surface of the ScAlMgO ₄ substrate) when the ScAlMgO ₄ bulk material is cleaved. The data is data obtained by using a laser reflection type length measuring device (NH-3MA manufactured by Mitaka Kogyo Co., Ltd.) with XY axes orthogonal to each other in the same plane of a φ40 mm ScAlMgO ₄ substrate. In FIG. 4, as shown by the arrows, there are uneven portions of 500 nm or more on the cleaved surface obtained by cleaving the bulk material. In the ScAlMgO ₄ substrate, the peeling force in the cleavage direction at the time of cleavage varies, so that cleavage in the same atomic layer does not occur, and as a result, an uneven portion having a step of 500 nm or more is generated. If a stepped portion having a height of 500 nm or more exists on the epitaxial growth surface, a problem occurs when a crystal is epitaxially grown on the substrate. An adverse effect when a step having a height of 500 nm or more exists on the epitaxial growth surface of the substrate will be described. When a crystal such as GaN is formed on an epitaxial growth surface having a step having a height of 500 nm or more, different crystal orientations are formed in the step portion having a height of 500 nm or more. For example, when an InGaN layer used for an LED light emitting layer is formed on the epitaxial growth surface by a MOCVD (Metal-Organic Chemical Vapor Deposition) method, the composition of indium changes between the stepped portion and the flat portion. When the composition of indium changes, the emission wavelength and brightness of the LED element change. As a result, light emission unevenness occurs as the LED element, resulting in a decrease in luminance.

It is not easy to remove unevenness of 500 nm or more generated by cleavage. In particular, it is difficult to process the cleaved surface of the ScAlMgO ₄ substrate. Even if it is intended to remove the irregularities generated by cleaving, if the ratio of the flat surface to the whole is large, a certain area ( The processing load tends to concentrate on the unevenness, and cracks due to cleavage occur not inside the surface but inside deeper from the surface. Therefore, it is considered that new irregularities are formed by removing the cracked portion. Further, when the ratio of the flat surface is high, the unevenness generated in the cleavage process can hardly be removed only by applying a load that does not cleave inside.

Accordingly, in view of the characteristics of the ScAlMgO ₄ material, a processing method (a rough unevenness forming step and a fine unevenness forming step) described in detail below was found. This is the unevenness removing step of the present disclosure. Specifically, a concavo-convex shape having a certain height is formed over the entire region of the ScAlMgO ₄ substrate as an epitaxial growth surface (rough concavo-convex forming step). Next, by gradually reducing the applied pressure, the uneven amount of the constant height formed on the entire surface is gradually reduced while decreasing the absolute amount of applied pressure variation and preventing internal cleavage. (Small unevenness forming step). That is, the ScAlMgO ₄ single crystal body is cleaved at the cleavage plane starting from the notch 2a to prepare the ScAlMgO ₄ substrate 10 shown in the upper diagram of FIG. 5A. Then, a rough unevenness forming step for forming unevenness with a height of 500 nm or more on the main surface of the ScAlMgO ₄ substrate 10, and a fine unevenness forming step for polishing unevenness with a height of 500 nm or more to form unevenness with a height of less than 500 nm. And at least do.

In the rough unevenness forming step, unevenness is formed on the entire surface of the region to be the epitaxial growth surface so that the area of the region having a surface roughness of 500 nm or less (hereinafter also referred to as “flat portion”) is 1 mm ² or less. Distribute the shape. This is because if a flat portion larger than 1 mm ^{2 is} formed in the rough unevenness forming step, the fine unevenness forming step is cleaved inside due to the concentration of processing load, and unevenness larger than 500 nm is generated. Moreover, it is preferable that the difference in height of the convex portions of the plurality of concaves and convexes formed in the rough concave-convex forming step is within a range of ± 0.5 μm or less. By forming unevenness with a uniform height over the entire surface so that the variation in height falls within this range, the height of the unevenness can be gradually lowered by the minute unevenness forming process, and a uniform flat portion is formed in the surface. Can be formed.

  Specifically, in the rough unevenness forming step, the unevenness having a height of 500 nm or more is formed using the first abrasive grains, and in the fine unevenness forming process, the unevenness having a height of less than 500 nm is formed more than the first abrasive grains. It forms using the 2nd abrasive grain with low hardness.

More specifically, in the concavo-convex forming step of processing a concavo-convex shape having a constant height, grinding using diamond fixed abrasive grains having a large abrasive grain size is performed. As the abrasive grain size, diamond abrasive grains of # 300 or more and # 20000 or less (preferably # 600) are used. According to processing using diamond abrasive grains having a size in this range, the difference in height of the unevenness on the processed surface can be kept within a range of ± 5 μm or less. The processing conditions in the crude irregularities forming step, the grinding wheel rotational speed 500 min ^-1 or more 50000Min ^-1 or less (preferably 1800 min ^-1), ScAlMgO ₄ substrate rotational speed 10min ^-1 or 300 min ^-1 or less (preferably 100 min ^-1) The processing speed is preferably 0.01 μm / second or more and 1 μm / second or less (preferably 0.3 μm / second), and the processing removal amount is 1 μm or more and 300 μm or less (preferably 20 μm). FIG. 6 shows the result of processing using # 600 diamond abrasive grains at a grinding wheel rotational speed of 1800 min ⁻¹ , a ScAlMgO ₄ substrate rotational speed of 100 min ⁻¹ , a processing speed of 0.3 μm / sec, and a processing removal amount of 20 μm. FIG. 6 shows the result of measuring the flatness in the X direction of the processed surface by the same method as described above. As shown in FIG. 6, a flat portion of 1 mm ² or more (a portion where the height of the unevenness is 500 nm or less is continuous 1 mm ² or more) does not occur in the region to be the epitaxial growth surface, and a regular uneven shape is formed. Is made.

Next, the micro unevenness | corrugation formation process which removes the unevenness | corrugation formed at the rough unevenness | corrugation formation process gradually is demonstrated. In the fine unevenness forming step, the unevenness with a height of less than 500 nm is formed by polishing with gradually decreasing pressure while removing the unevenness with a height of 500 nm or more. The fine irregularities forming step, using a slurry composed mainly of colloidal silica as abrasive grains, the rotational speed 10min ^-1 or more 1000min ^-1 or less (preferably 60min ^-1), the slurry supply rate 0.02 ml / min to 2 ml / min In the following (preferably 0.5 ml / min), the polishing pad is preferably a non-woven pad. The amount of slurry supplied varies depending on the substrate area. Specifically, it is preferable to increase the slurry supply amount as the substrate area increases. When there are many irregularities, the processing force tends to concentrate selectively on the convex portions. Therefore, the amount of pressurization is in the range of 10,000 Pa to 20,000 Pa at the beginning of the micro unevenness forming process, and is set to 5000 Pa to less than 10,000 Pa as the convex portion becomes flat, and finally in the range of 1000 Pa to 5000 Pa. It is preferable. By reducing the applied pressure stepwise in this way, it is possible to remove unevenness having a height of 500 nm or more from the region to be the epitaxial growth surface without causing internal cleavage.

In the minute unevenness forming process, first, polishing is performed for 3 minutes at a pressure of 15000 Pa, then polishing is performed for 5 minutes by lowering the pressure to 8000 Pa, and finally polishing is performed for 10 minutes by reducing the pressure to 1000 Pa. The results are shown in FIG. FIG. 7 shows the surface shape measurement result obtained by measuring the flatness in the X direction of the epitaxially grown surface after processing by the same method as described above. Further, FIG. 8 shows the surface shape measurement result measured by AFM (atomic force microscope) in the range of 10 μm square of the epitaxial growth surface. As shown in FIG. 8, there is no unevenness with a height of 500 nm or more in the range of 10 μm square, and no unevenness with a height of 50 nm or more is observed such that Rmax indicating the maximum height is 6.42 nm. Rq is 0.179 nm. FIG. 8 obtained by further detailed shape analysis shows that an extremely smooth surface having a surface roughness Ra of 0.139 nm and no irregularities of 50 nm or more can be formed in a minute region of 100 μm ² . Here, the surface roughness Ra of the obtained epitaxial growth surface is 0.08 nm or more and 0.5 nm or less. The surface roughness Ra was measured with a Dimension Icon from BRUKER in accordance with ISO13565-1. Thus, the ScAlMgO ₄ substrate 10 having the epi-ready surface is prepared.

  Next, the GaN crystal growth process will be described. The GaN single crystal growth method includes a vapor phase growth method for reacting and synthesizing group V and group III source gases, and a liquid phase growth method using a solution or a melt. As the vapor phase growth method, a HVPE (Hydride Vapor Phase Epitaxy) method or an OVPE (Oxide Vapor Phase Epitaxy) method can be used. As a liquid phase growth method, a Na flux (Sodium Flux) method or the like can be used.

The HVPE method uses GaCl as a group III source. Specifically, GaCl gas is generated by reacting metal Ga and HCl gas in a raw material gas generating section in a quartz tube furnace. When the reaction efficiency at this time is increased, almost 100% of HCl reacts to generate GaCl gas. The GaCl gas is transported to the growth part where the seed substrate (ScAlMgO ₄ substrate 10) is installed. Then, GaCl gas, by reaction with NH ₃ gas at approximately 1000 to 1100 ° C., GaN is generated. A feature of the HVPE method is that GaN can be grown at a high speed, and a GaN free-standing substrate having a thickness of several hundred nm to several mm can be formed. In the present disclosure, using the ScAlMgO ₄ substrate 10 as a seed substrate, the GaN layer 4 can be formed on the ScAlMgO ₄ substrate 10 as shown in FIG. 5B.

The OVPE method, which is another method for forming the GaN layer 4, will be described. The OVPE method uses Ga ₂ O as a Ga source. In this method, Ga ₂ O gas is generated, and a GaN crystal is grown by reacting Ga ₂ O gas and NH ₃ in the growth part. In this method, since the by-product is hydrogen or water vapor, the exhaust system is not clogged, and in principle, continuous growth for a long time is possible.

In addition, if the apparatus by the HVPE method or the OVPE method is a type in which a gas flows from the lateral direction, it is preferable to install the ScAlMgO ₄ substrate 10 so that the notch 2b is on the downstream side of the gas flow.

Further, there is a Na flux method as another method for forming the GaN layer 4. In the Na flux method, nitrogen is dissolved in a high-temperature Ga—Na melt to cause a supersaturated state and grow GaN. The seed substrate (ScAlMgO ₄ substrate 10) and the crucible on which Ga and Na are placed are placed in a stainless steel tube and heated to 800 to 900 ° C. with a heater while applying a nitrogen pressure of 3 to 4 MPa. As nitrogen is dissolved in the heated Ga—Na melt, GaN crystals grow on the ScAlMgO ₄ substrate 10. A feature of the Na flux method is that the growth rate is slower than that of the HVPE method, but a high-quality GaN crystal with a small dislocation density and few defects can be obtained.

Next, the ScAlMgO ₄ removal step will be described. When a sapphire substrate is used as a seed substrate as in the prior art, the sapphire substrate and the GaN substrate are separated at the temperature lowering stage of the GaN crystal growth process due to expansion and contraction due to the difference in thermal expansion difference between the sapphire substrate and the GaN layer. The However, since the thermal expansion coefficients of ScAlMgO ₄ and GaN are close, in the present disclosure, the ScAlMgO ₄ substrate 10 and the GaN layer 4 are not separated even when the GaN crystal growth process is completed. Therefore, a separation process is necessary.

Since the outer peripheral shape of the GaN layer 4 generated in the GaN crystal growth step is distorted, cylindrical processing is performed to make the outer periphery circular. For example, in circular processing, grinding is performed using a rotating grindstone. Next, in order to remove a part of the ScAlMgO ₄ substrate (the portion indicated by 10a in FIG. 5), the notch 2b formed in the side portion of the ScAlMgO ₄ substrate 10 is shown in the blade 3 (shown in FIG. 3A or FIG. 3B). Apply the blade 3). Then, by applying a force in the cleavage direction of the ScAlMgO ₄ substrate 10 starting from the notch 2b, as shown in FIG. 5B, the ScAlMgO ₄ substrate 10 is replaced with the ScAlMgO ₄ substrate 10b including the GaN layer 4, and the ScAlMgO ₄ substrate. Separated into 10a. The separated ScAlMgO ₄ substrate 10a can be regenerated as a seed substrate again by performing the process described in the unevenness removal step.

Next, the GaN substrate processing step will be described. In this step, the Ga surface 20 which is the epitaxial growth surface of the GaN layer 4 and the N surface 21 where ScAlMgO ₄ is present are ground and polished to finish the GaN free-standing substrate 4a capable of epitaxial growth. Grinding is performed by grinding using fixed abrasive grains or lapping using loose abrasive grains. Polishing of the Ga surface 20 can be a method of removing a work-affected layer that is a crystal damage by CMP (Chemical Mechanical Polishing) after lapping with loose abrasive grains reduced. On the other hand, the N surface 21 is removed by grinding the ScAlMgO ₄ substrate 10b, and the N surface 21 is finished by polishing. Thereby, as shown in FIG. 5D, a GaN free-standing substrate 4a capable of epitaxial growth is formed.

In the present disclosure, the ScAlMgO ₄ substrate 10a separated in the ScAlMgO ₄ removal step can be used as the seed substrate by performing the unevenness removal step again on the ScAlMgO ₄ substrate 10a. That is, it is possible to form a GaN free-standing substrate by using the regenerated ScAlMgO ₄ substrate 10a again. Therefore, ScAlMgO ₄ can be used efficiently, and the material yield can be improved. Note that the notch 2b of the ScAlMgO ₄ substrate 10 does not have to be a single location, and a plurality of notches 2b may be formed in the thickness direction of the substrate in the ScAlMgO ₄ substrate preparation step having a notch according to the number of times of regeneration of the seed substrate. it can.

(Embodiment 2)
FIG. 9 shows each step of the method for producing a group III nitride according to the second embodiment of the present disclosure. Manufacturing method according to the second embodiment of the present disclosure, a ScAlMgO ₄ ingot preparing step of generating a single crystal ScAlMgO _4, to produce a cylindrical ingot from the single crystal ScAlMgO _4, further provided with a notch on the side of the ingot ScAlMgO ₄ ingot outer shape processing step, ScAlMgO ₄ substrate preparation step of preparing indented ScAlMgO ₄ substrate by processing ingot into substrate shape, and unevenness removal step of removing surface unevenness corresponding to epitaxial growth surface of ScAlMgO ₄ substrate And a group III nitride crystal growth step of epitaxially growing a group III nitride crystal (eg, GaN crystal) on the ScAlMgO ₄ substrate, and a device formation step of forming a device. The device formation step includes ScAlMgO ₄ removal for removing ScAlMgO ₄ from the notch.

The difference from the first embodiment is that a group III nitride crystal is epitaxially grown on a ScAlMgO ₄ substrate to further form a device. Since the unevenness removing step is the same as that in the first embodiment, the group III nitride crystal growth step and subsequent steps will be described. However, the uneven removal step, the epitaxial growth surface in the first embodiment, ScAlMgO ₄ may be formed only on one surface of the substrate (front side), but in the second embodiment, the epitaxial growth surface on both sides of ScAlMgO ₄ substrate It may be formed. In this case, a group III nitride crystal such as GaN (group III nitride semiconductor) can be epitaxially grown on both sides. Further, by using the above-described processing technique, for example, when an LED light emitting layer is formed on the epitaxial growth surface of the substrate, problems such as the above-described change in composition, light emission unevenness of the LED element, and luminance decrease due to the change are not caused. . Furthermore, by forming the unevenness on the epitaxial growth surface of the ScAlMgO ₄ substrate to 50 nm or less by the unevenness removal step, for example, when forming an electrode after forming the LED light emitting layer on the epitaxial growth surface, formation defects (steps due to the unevenness) Etching residue etc. at the part) is suppressed. Therefore, the manufacturing yield of devices such as LEDs manufactured using this substrate is improved.

In the crystal growth process of the second embodiment, the group III nitride crystal layer 5 shown in FIG. 10A is formed on the epitaxial growth surface of the ScAlMgO ₄ substrate 10 by vapor phase growth of group III nitride, for example, by MOCVD. When the vapor phase growth of the group III nitride is performed on the ScAlMgO ₄ substrate by, for example, the MOCVD method, the group III nitride raw material moves (migrate) on the (0001) plane that is the cleavage plane of the epitaxial growth surface. If there is a stable position, it stops at that position and grows epitaxially.

In the group III nitride crystal layer forming step, for example, a group III nitride crystal layer 5 (light emitting layer of the LED device) formed of a laminate of an n-type nitride semiconductor layer, an active layer, and a p-type nitride semiconductor layer is formed. Can do. The n-type nitride semiconductor layer is a layer formed from, for example, an n-type Al _u Ga _v In _w N (where u + v + w = 1, u ≧ 0, v ≧ 0, w ≧ 0) semiconductor. be able to. For example, silicon (Si) may be used as the n-type dopant. As the n-type dopant, for example, oxygen (O) or the like may be used in addition to Si. As the active layer, for example, a Ga _1-x In _x N well layer having a thickness of about 3 nm to 20 nm (where 0 <x <1), a GaN barrier layer having a thickness of about 5 nm to 30 nm, Can be a layer (well layer) having a multiple quantum well (MQW) structure made of GaInN / GaN in which are alternately stacked. The wavelength of light emitted from the LED device depends on the size of the band gap of the nitride semiconductor constituting the active layer, specifically, the In composition x in the Ga _1-x In _x N semiconductor, which is the semiconductor composition of the well layer. Determined. p-type nitride semiconductor layer is, for example, p-type _Al s _Ga t N (where, s + t = 1, a s ≧ 0, t ≧ 0. ) may be a layer formed from a semiconductor. As the p-type dopant, for example, magnesium (Mg) can be used. In addition to Mg, for example, zinc (Zn), beryllium (Be), or the like may be used as the p-type dopant.

  Next, a device formation process will be described. In the device formation step, the group III nitride crystal layer 5 stacked in the group III nitride crystal growth step is processed into a desired shape by a lithography method, a dry etching method, or the like. For example, the recess 6 from which a part of the p-type nitride semiconductor layer, the active layer, and the n-type nitride semiconductor is removed is formed so that an electrode can be formed. Then, an n-side electrode 8 electrically connected to the n-type nitride semiconductor layer and a p-side electrode 7 electrically connected to the p-type nitride semiconductor layer are formed. The n-side electrode 8 is formed of, for example, a laminated structure (Ti / Pt) composed of a titanium (Ti) layer and a platinum (Pt) layer. In addition, a laminated structure (Ti / Al) composed of a titanium (Ti) layer and an aluminum (Al) layer may be used. The p-side electrode 7 is formed of, for example, a laminated structure (Pd / Pt) composed of a palladium (Pd) layer and a platinum (Pt) layer. In addition, a silver (Ag) layer may be used.

Next, the ScAlMgO ₄ 10a formed on the side opposite to the crystal growth surface of the group III nitride crystal layer 5 is removed. Specifically, ScAlMgO ₄ against the blade to the side the formed notch 2b of the substrate 10, starting from the notch 2b, by applying a force to the cleavage direction of ScAlMgO ₄ substrate 10, the ScAlMgO ₄ substrate 10 Then, the substrate is separated into a ScAlMgO ₄ substrate 10b and a ScAlMgO ₄ substrate 10a including a device structure including the group III nitride crystal layer 5 and electrodes shown in FIG. 10B. The separated ScAlMgO ₄ substrate 10a can be regenerated as a seed substrate again by performing the unevenness removing step described in the first embodiment. Therefore, also in the present embodiment, ScAlMgO ₄ can be used efficiently and the material yield can be improved. It is not necessary notch 2b of ScAlMgO ₄ substrate 10 is one place, in accordance with the views of ScAlMgO ₄ substrate 10 may be a plurality of locations formed in the thickness direction of the ScAlMgO ₄ substrate 10. That is, in the ScAlMgO ₄ substrate preparation step, the ScAlMgO ₄ substrate 10 can be used a plurality of times by forming notches at a plurality of locations. When the ScAlMgO ₄ substrate 10a is regenerated, polishing is performed so that the ScAlMgO ₄ substrate 10a has a predetermined thickness. Furthermore, the light extraction efficiency can be improved by forming a fine concavo-convex structure in the micro concavo-convex formation step of the concavo-convex removal step.

(Other)
In the first and second embodiments described above, the substrate obtained from the single crystal of ScAlMgO ₄ has been described among the substrates formed of the single crystal represented by the general formula RAMO _4. It is not limited. Specifically, a substrate typified by ScAlMgO ₄ of the present disclosure is composed of a substantially single crystal material represented by the general formula RAMO ₄ . In the above general formula, R represents one or more trivalent elements selected from Sc, In, Y, and a lanthanoid element (atomic number 67-71), and A represents Fe (III), Ga And one or more trivalent elements selected from Al, and M is one or more divalent elements selected from Mg, Mn, Fe (II), Co, Cu, Zn, Cd Represents. Note that the almost single crystal material includes 90 at% or more of RAMO ₄ constituting the epitaxial growth surface, and when attention is paid to an arbitrary crystal axis, the direction is the same in any part of the epitaxial growth surface. A crystalline solid. However, those in which the orientation of the crystal axis is locally changed and those containing local lattice defects are also treated as single crystals. O is oxygen. However, as described above, it is desirable that R is Sc, A is Al, and M is Mg.

Further, the group III nitride crystal grown on the single crystal substrate is not limited to GaN, n-type nitride semiconductor layer, active layer, p-type nitride semiconductor layer, or the like. Gallium (Ga) is the best Group III element metal constituting the Group III nitride, but other examples of Group III element metals include aluminum (Al), indium (In), and thallium (Tl). In the group III nitride, the group III element metal may be used alone or in combination of two or more. For example, at least one selected from the group consisting of aluminum (Al), gallium (Ga), and indium (In) may be used as the group III element metal. In this case, the composition of the III-nitride crystal to be _produced, expressed in _{Al s Ga t In {1- (} s + t)} N ( However, 0 ≦ s ≦ 1,0 ≦ t ≦ 1, s + t ≦ 1) In the first embodiment, GaN is preferably a group III nitride. An example of a ternary or higher nitride crystal produced using two or more Group III element metals is a Ga _x In _1-x N (0 <x <1) crystal.

  In manufacturing an LED element by growing an LED light emitting layer on a substrate during MOCVC vapor phase growth, by using the substrate according to the present disclosure, the material efficiency of the seed substrate material is improved, and light emission unevenness is generated as the LED element. It is possible to prevent a decrease in luminance.

1 Ingot 2a, 2b Notch 3 Blade 4 GaN layer (Group III nitride crystal layer)
5 Group III nitride crystal layer 6 Recess 7 P-side electrode 8 N-side electrode 10, 10a, 10b ScAlMgO ₄ substrate 20 Ga surface (epitaxial growth surface)
21 N side

Claims (7)

A single crystal represented by the general formula RAMO ₄ (in the general formula, R represents one or more trivalent elements selected from the group consisting of Sc, In, Y, and lanthanoid elements; Represents one or more trivalent elements selected from the group consisting of Fe, (III), Ga, and Al, and M represents Mg, Mn, Fe (II), Co, Cu, Zn, and Cd. Preparing a RAMO ₄ substrate having a notch on the side portion, which represents one or more divalent elements selected from the group consisting of:
Growing a group III nitride crystal on the RAMO ₄ substrate;
Cleaving the RAMO ₄ substrate,
The group III nitride crystal manufacturing method, wherein a plurality of the notches are provided in a thickness direction of the RAMO ₄ substrate. The group III nitride crystal manufacturing method according to claim 1, wherein the RAMO ₄ substrate is a ScAlMgO ₄ substrate. The method for producing a group III nitride crystal according to claim 1 or 2 , wherein the group III nitride crystal is GaN. A single crystal represented by the general formula RAMO ₄ (in the general formula, R represents one or more trivalent elements selected from the group consisting of Sc, In, Y, and lanthanoid elements; Represents one or more trivalent elements selected from the group consisting of Fe, (III), Ga, and Al, and M represents Mg, Mn, Fe (II), Co, Cu, Zn, and Cd. In a RAMO ₄ substrate consisting of one or more divalent elements selected from the group consisting of:
Has a notch on the side,
The RAMO ₄ substrate, wherein a plurality of the notches are provided in the thickness direction of the RAMO ₄ substrate. The RAMO ₄ substrate according to claim 4 , further comprising a group III nitride crystal on the surface. The RAMO ₄ substrate according to claim 4 or 5 , wherein the single crystal is ScAlMgO ₄ . The RAMO ₄ substrate according to claim 5 or 6 , wherein the group III nitride crystal is GaN.