JP2017149633A - Ramo4 substrate and method for manufacturing the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a higher quality substrate.SOLUTION: An RAMOsubstrate consists of a single crystal body represented by a general formula RAMO(where, R represents one or more trivalent elements selected from a group consisting of Sc, In, Y and lanthanoid elements; A represents one or more trivalent elements selected from a group consisting of Fe(III), Ga and Al; and M represents one or more divalent elements selected from a group consisting of Mg, Mn, Fe(II), Co, Cu, Zn and Cd) and has an epitaxial growth surface on at least one surface. The epitaxial growth surface has a plurality of cleaved surfaces distributed with regularity and separated from each other.SELECTED DRAWING: Figure 12

Description

The present invention relates to a RAMO ₄ substrate and a manufacturing method thereof.

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. A ScAlMgO ₄ substrate is known as one of RAMO ₄ substrates composed of one or more divalent elements selected from the group consisting of: The ScAlMgO ₄ substrate is used as a growth substrate for a nitride semiconductor such as GaN (see, for example, Patent Document 1). FIG. 1 shows an example of a conventional method for manufacturing a ScAlMgO ₄ substrate described in Patent Document 1. As shown in FIG. 1, a conventional ScAlMgO ₄ substrate has been manufactured by cleaving a ScAlMgO ₄ bulk material.

JP-A-2015-178448

However, it has been difficult to obtain a RAMO ₄ substrate having a desired surface shape only by cleavage. Therefore, a higher quality substrate is required. That is, the present disclosure aims to provide a higher quality substrate.

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), a RAMO ₄ substrate that represents one or more divalent elements selected from the group consisting of Co, Cu, Zn, and Cd, and has an epitaxial growth surface on at least one surface, A RAMO ₄ substrate is provided in which an epitaxial growth surface has a plurality of cleaved surfaces separated from each other distributed regularly.

According to the present disclosure, a higher quality RAMO ₄ substrate can be provided.

Diagram of manufacturing process of conventional ScAlMgO ₄ substrate 2A is a side view of a conventional ScAlMgO ₄ substrate, and FIG. 2B is a plan view of the ScAlMgO ₄ substrate. Figure of flatness measurement result of epitaxial growth surface formed only by conventional cleavage Diagram of manufacturing process of ScAlMgO ₄ substrate according to the embodiment of the present disclosure The figure of the flatness measurement result when using a 2 μm diamond slurry and polishing the cleaved surface of ScAlMgO ₄ The figure of the flatness measurement result when the ScAlMgO ₄ cleaved surface is polished using a 0.125 μm diamond slurry Figure of flatness measurement results when the colloidal silica is used to polish the cleaved surface of ScAlMgO ₄ Figure of flatness measurement result when polishing the ScAlMgO ₄ cleaved surface using 0.5 μm diamond fixed abrasive processing The figure of the flatness measurement result after grinding by the unevenness formation process in the embodiment of the present disclosure The figure of the flatness measurement result after the cleavage plane formation process in the embodiment of the present disclosure FIG. _{4 is} a diagram of AFM measurement results of a ScAlMgO ₄ substrate having a single cleaved surface of the present disclosure FIG. 12A is a plan view of an epitaxial growth surface having a plurality of cleavage planes of the ScAlMgO ₄ substrate of this embodiment, and FIG. 12B is a side view of the ScAlMgO ₄ substrate. Explanatory diagram of force applied when forming epitaxial growth surface Figure of AFM measurement results of ScAlMgO ₄ substrate embodiment of the present disclosure X direction cross-sectional enlarged view of two adjacent cleavage planes Illustration of ScAlMgO ₄ substrate with matte shape Partial enlarged sectional view of a ScAlMgO ₄ substrate having a matte shape

  Hereinafter, embodiments of the present disclosure will be described with reference to the drawings.

First, the knowledge that led to the present disclosure will be described. As shown in the cited document 1, conventionally, the ScAlMgO ₄ substrate was produced by cleaving the ScAlMgO ₄ bulk material. However, only by cleavage, a step having a height of 500 nm or more was likely to occur on the epitaxial growth surface for GaN growth of the ScAlMgO ₄ substrate. 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.

Next, details of the conventional ScAlMgO ₄ substrate having a level difference of 500 nm or more and the problem will be described. FIG. 2A is a side view of a conventional ScAlMgO ₄ substrate 001, and FIG. 2B is a plan view of the substrate 001. As shown in FIGS. 2A and 2B, a stepped portion 003 is formed on the epitaxial growth surface 002 of the ScAlMgO ₄ substrate 001. Here, the height of the stepped portion 003 is 500 nm or more. FIG. 3 shows measurement data of the flatness of the epitaxial growth surface 002 of the ScAlMgO ₄ substrate 001 formed by the conventional manufacturing method, that is, cleavage. 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 in the same plane of the φ40 mm ScAlMgO ₄ substrate 001. In FIG. 3, the portion indicated by the arrow is a concavo-convex portion of 500 nm or more. 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.

  Therefore, the present disclosure provides a manufacturing method including a step of removing a step having a height of 500 nm or more. In particular, the present invention provides a manufacturing method including a step of forming a plurality of cleaved surfaces separated from each other and distributed regularly on an epitaxial growth surface.

FIG. 4 shows a manufacturing process of the ScAlMgO ₄ substrate according to the present embodiment. In the manufacturing method of the present disclosure, a step of preparing a ScAlMgO ₄ bulk material (bulk material preparation step), a step of dividing the substrate by cleavage to form a substrate (cleavage step), and processing a surface corresponding to the epitaxial growth surface of the substrate (Steps for forming irregularities and cleaving surface forming steps).

For example, in the bulk material preparation step, a single crystal ScAlMgO ₄ ingot manufactured using a high-frequency induction heating type Czochralski furnace is prepared. As an ingot production method, for example, Sc ₂ O ₃ , Al ₂ O ₃ and MgO having a purity of 4N (99.99%) are blended as a starting material at a predetermined molar ratio. Then, 3400 g of the starting material is put into an iridium crucible having a diameter of 100 mm. Next, the crucible charged with the raw material is put into a growth furnace of a high-frequency induction heating type Czochralski furnace, and the inside of the furnace is evacuated. Thereafter, nitrogen is introduced, and heating of the crucible is started when the inside of 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. Then, the seed crystal is gradually lowered while rotating at a constant rotational speed, and the seed crystal is pulled at a speed of 0.5 mm / h while the tip is brought into contact with the melt and the temperature is gradually lowered. The crystal is grown by raising it (raising in the 0001 axis direction). Thereby, a single crystal ingot having a diameter of 50 mm and a length of the straight body portion of 50 mm is obtained.

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. Utilizing this characteristic, a step of cleaving the bulk material by cleavage and preparing a plate state (cleavage step) can be performed.

However, the properties related to the cleavage of the ScAlMgO ₄ single crystal make it easy to carry out the cleavage process, but make it difficult to process the cleavage plane by a conventional processing method. That is, with the conventional processing method, the unevenness with a height of 500 nm or more formed on the cleavage plane could not be removed. The reason will be explained. In the description, an example will be introduced in which processing is performed on a ScAlMgO ₄ substrate, which is generally considered to have a surface roughness of less than 500 nm for a semiconductor substrate such as GaN. The processing area is 10 mm square.

First, FIG. 5 shows the result of lapping the cleaved surface of ScAlMgO ₄ using a diamond slurry (abrasive grains) having a diameter of 2 μm used in conventional rough polishing. FIG. 5 shows the result of measuring the flatness of the cross-sectional shape of the processed surface in the X direction with the laser reflection type length measuring device. As shown in FIG. 5, it can be seen that when the processing is performed, irregularities of 500 nm or more are generated on the surface. In the lapping process, the diamond slurry rolls on the surface of the ScAlMgO ₄ so that the material of the rolled part is removed minutely. However, since the single crystal ScAlMgO ₄ is a laminate of a large number of ScO ₂ layers and AlMgO ₂ layers, it is considered that peeling occurs partially in a deep layer due to variations in processing force. Therefore, as shown in FIG. 5, it is considered that unevenness of 500 nm or more occurred.

Usually, in order to reduce such variation in processing force, it is effective to make the abrasive grain size smaller than the size of the irregularities that can be tolerated. Thus, FIG. 6 shows the result of lapping the cleaved surface of ScAlMgO ₄ using a diamond slurry having a diameter of 0.125 μm as abrasive grains. The measurement method of the flatness in the X direction at this time was the same as that in the case of polishing using a diamond slurry having a diameter of 2 μm. As shown in FIG. 6, even when the abrasive grain size was made smaller than the allowable uneven size (500 nm), unevenness of 500 nm or more was generated.

  On the other hand, the hardness and shape of the abrasive grains also affect the surface shape of the surface to be polished. Accordingly, FIG. 7 shows the result of polishing using colloidal silica abrasive grains that are softer than diamond and have a shape closer to a sphere. The polishing process was performed at a pressure of 1000 Pa when processing a general GaN single crystal. The measurement method of the flatness in the X direction at this time was the same as that in the case of polishing using a diamond slurry having a diameter of 2 μm. As shown in FIG. 7, according to the method, although the minute unevenness could be removed, the unevenness of 500 nm or more could not be removed.

As described above, the unevenness of the epitaxial growth surface of the ScAlMgO ₄ substrate could not be made less than 500 nm by polishing using any loose abrasive grains.

  Therefore, grinding was performed using diamond fixed abrasive grains having a diameter of 0.5 μm. The result is shown in FIG. The method for measuring the flatness in the X direction was the same as that for polishing using a diamond slurry having a diameter of 2 μm. As shown in FIG. 8, irregularities of 500 nm or more were generated even when fixed abrasive grains were used.

From these results, it can be seen that the conventional processing method cannot process the surface of the ScAlMgO ₄ substrate into a smooth surface that does not include irregularities of 500 nm or more. Even if it is going to remove the unevenness | corrugation which arose by cleavage, when the ratio of the flat surface which occupies for the whole is large, when processing a flat surface, it will become easy to concentrate processing load on one part area | region (unevenness | corrugation). Then, cracks due to cleavage occur not inside the surface but inside deeper from the surface. And it is thought that a new unevenness | corrugation is formed by removing a crack part. Moreover, 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.

Therefore, in the present disclosure, in view of the characteristics of the ScAlMgO ₄ material, a processing method (an unevenness forming step and a cleavage plane forming step) described in detail below is adopted. 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 (concave / convex formation step). Next, the absolute amount of variation in the applied pressure during polishing is reduced by gradually reducing the applied pressure during polishing. Then, while preventing internal cleavage, the uneven shape having a certain height formed in the unevenness forming step is gradually reduced to form a plurality of cleavage surfaces separated from each other (cleavage surface forming step).

That is, in the manufacturing method of the present disclosure, a step of preparing a ScAlMgO ₄ plate obtained by cleaving a ScAlMgO ₄ single crystal in the (0001) plane (cleaving step), and a ScAlMgO ₄ plate with a thickness of 500 nm or more A step of forming irregularities (irregularity forming step) and a step of polishing the irregularities of 500 nm or more to form a plurality of cleaved surfaces separated from each other (irregularities of less than 500 nm) distributed regularly. Forming step).

In the present disclosure, in the unevenness forming process, the area of the region where the height of the unevenness is continuously 500 nm or less (hereinafter, also referred to as “flat portion”) present in the region to be the epitaxial growth surface after the process is finished. The uneven shape is distributed over the entire epitaxial growth surface so as to be 1 mm ² or less. This is because if a flat portion larger than 1 mm ^{2 is} formed in the unevenness forming step, the cleavage surface forming step is cleaved inside due to concentration of processing load, and unevenness having a height of more than 500 nm is generated. Moreover, it is preferable that the difference in height between the convex portions of the plurality of concave and convex portions formed in the concave and 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 reduced by the cleavage plane forming process, and separated into areas to be epitaxial growth surfaces A plurality of cleavage planes can be formed.

  Specifically, in the unevenness forming step, unevenness of 500 nm or more is formed using the first abrasive grains. In the cleavage plane forming step, irregularities (a plurality of cleavage planes) of less than 500 nm are formed using the second abrasive grains having a hardness lower than that of the first abrasive grains.

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 grains, 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 roughening 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), It is preferable that the processing removal amount is 1 μm or more and 300 μm or less (preferably 20 μm) at a processing speed of 0.01 μm / second or more and 1 μm / second or less (preferably 0.3 μm / second). FIG. 9 shows a flat cross-sectional shape when machining with # 600 diamond abrasive grains, grinding wheel rotation speed 1800 min ⁻¹ , ScAlMgO ₄ substrate rotation speed 100 min ⁻¹ , machining speed 0.3 μm / second, machining removal amount 20 μm. The result of measuring the degree is shown. FIG. 9 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. 9, when the unevenness forming step is performed, a flat portion of 1 mm ² or more (a portion where the unevenness height is 500 nm or less is continuous 1 mm ² or more) does not occur in the region to be the epitaxial growth surface, Regular irregularities can be formed.

Next, a process of gradually removing the unevenness formed in the unevenness forming process will be described. By performing polishing with stepwise weakening of the applied pressure, it is possible to form unevenness with a height of less than 500 nm while removing unevenness with a height of 500 nm or more formed by the above-described unevenness forming step. Here, the removal of the height 500nm or more irregularities, 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 amount 0. It can be performed by using a nonwoven fabric pad as a polishing pad at a rate of 02 ml / min to 2 ml / min (preferably 0.5 ml / min). Since the processing force tends to concentrate selectively on the convex portion when there are many irregularities, the initial pressure is in the range of 10,000 Pa to 20,000 Pa in the initial stage, and is 5000 Pa to less than 10,000 Pa as the convex portion becomes flat. In particular, the range of the applied pressure is preferably less than 5000 Pa. 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. At this time, if the final pressure is 1000 Pa or more and less than 5000 Pa, only a single cleaved surface is likely to be formed on the epitaxial growth surface.

First, polishing is performed for 3 minutes at a pressure of 15000 Pa, then polishing is performed for 5 minutes with the pressure reduced to 8000 Pa, and finally polishing is performed for 10 minutes with the pressure reduced to 1000 Pa. FIG. Shown in FIG. 10 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. 11 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. 11, there is no unevenness of 500 nm or more in the range of 10 μm square, and no unevenness of 50 nm or more is observed such that Rmax indicating the maximum height is 6.42 nm. Rq is 0.179 nm. From FIG. 11 in which the shape analysis was performed in more detail, it can be seen that an extremely smooth surface having a surface roughness Ra of 0.139 nm and an unevenness of 50 nm or more can be formed in a minute region of 100 μm ² . The surface roughness Ra in the range of 100 μm ² of the ScAlMgO ₄ substrate formed by the above method is 0.08 nm or more and 0.5 nm or less. The surface roughness Ra is a value measured in accordance with ISO 13565-1 with a Dimension Icon from BRUKER.

In order to eliminate the unevenness caused by cleavage in this way and obtain a smooth surface, the smooth surface formed by cleavage is intentionally processed into a regular uneven shape (irregularity forming step), and then a little processing is performed without cleavage. This can be achieved by removing them one by one. That is, according to the present disclosure, it is possible to obtain a ScAlMgO ₄ substrate having an epitaxial growth surface that has an uneven height of less than 500 nm and an uneven height of 50 nm or less, which could not be realized by a conventional method. The surface roughness Ra within the range of 10 μm square (100 μm ² ) on the surface of the substrate obtained by the above method is 0.08 nm or more and 0.5 nm or less. For example, when the LED light emitting layer is formed on the epitaxial growth surface of the substrate, there are no problems such as the change in composition as described above, the light emission unevenness of the LED element, and the decrease in luminance. Furthermore, since the height of the unevenness is 50 nm or less, for example, formation defects (such as etching residue at the step portion) due to the unevenness are suppressed during electrode formation after the LED light emitting layer is formed on the epitaxial growth surface. The production yield of devices such as LEDs manufactured using this substrate is improved.

Here, as described above, a single (0001) plane (cleavage plane) may be formed on the epitaxial growth surface of the ScAlMgO ₄ substrate. However, incidental crystal growth such as defects and foreign substances may occur on the epitaxial growth surface. If there is a seed portion, Ga atoms may collect in the seed of the accidental crystal growth and cause local non-uniform growth when performing vapor phase growth of GaN on the epitaxial growth surface by, for example, MOCVD. . Therefore, in the present disclosure, in order to prevent this, it is preferable to perform the above processing so that the epitaxial growth surface has a plurality of cleaved surfaces that are regularly separated from each other by steps.

The advantage of having a plurality of regularly distributed cleavage planes on the epitaxial growth surface will be described below. When vapor phase growth of GaN is carried out on the ScAlMgO ₄ substrate by MOCVD, the Ga raw material moves (migrates) the (0001) plane which is the cleavage plane of the epitaxial growth plane in a state of being partially bonded to the methyl group. If there is a stable position, it stops at that position, breaks the bond with the methyl group, bonds with N, and grows epitaxially. Therefore, the epitaxial growth can be stabilized by forming a plurality of cleavage planes on the epitaxial growth surface and utilizing the step portions of the cleavage surfaces adjacent to each other as the stable position. In addition, by regularly forming a plurality of cleavage planes, there is an advantage that uniform and clean growth can be performed when epitaxial growth is performed on the epitaxial growth surface by the MOCVD method.

FIG. 12A shows a plan view of the ScAlMgO ₄ substrate 001 having an epitaxial growth surface 002 having a plurality of cleavage planes 060, and FIG. 12B shows a side view of the ScAlMgO ₄ substrate 001. As shown in FIG. 12A, the cleavage plane 060 has an elongated shape, and the plurality of cleavage planes are preferably formed regularly in parallel with the epitaxial growth plane 002. The width in the X direction of the cleavage plane 060 is the cleavage plane width 061, and the height of the step between adjacent cleavage planes is the height between cleavage planes 062.

Here, it is preferable to set the cleavage plane width 061 so that the Ga source can be migrated to the stepped portion of the cleavage plane where the Ga material is stable when epitaxial growth is performed using the MOCVD method. Specifically, when performing GaN crystal epitaxial growth using the MOCVD method, a uniform epitaxial film can be formed on the entire epitaxial growth surface when the cleavage plane width is in the range of 1.5 nm to 500 nm. This is because when the cleavage plane width is less than 1.5 nm, the stable position of the Ga raw material when epitaxially growing is very close to the raw material molecule size. Therefore, step flow growth in which a uniform epitaxial film is obtained (a growth mode in which a uniform epitaxial film is obtained in which epitaxial growth progresses laterally from each stepped portion) may not be realized. Further, if the cleavage plane width is 500 nm or more, the width is the migration distance on the GaN surface of the Ga raw material by the MOCVD method (the NH ₃ molecule that is the N raw material after the Ga raw material molecules adhere to the surface of the epitaxial growth surface). This is because step flow growth cannot be realized in the same manner because the distance is much larger than the distance traveled by the Ga source molecules on the surface of the epitaxial growth surface until it becomes GaN by reacting with. Furthermore, when the cleavage plane width is in the range of 5 nm or more and 150 nm or less, a good epitaxial film with uniform crystal concentration variation and uniform impurity concentration can be formed uniformly on the entire epitaxial growth surface. This is because when the cleavage plane width is in the range of 5 nm to 150 nm, the migration distance on the GaN surface of the Ga raw material in the MOCVD method matches the GaN surface, so that most of the Ga raw material molecules attached to the surface are the cleavage plane. Migrate to the step part. This is because step flow growth proceeds well over the entire epitaxial growth surface of the ScAlMgO ₄ substrate, and a uniform epitaxial film is grown while maintaining the underlying crystal orientation.

  In the present disclosure, a method (cleaved surface forming step) for processing the cleaved surface width 061 to be 1.5 nm or more and 500 nm or less will be described. FIG. 13 shows a processing state when processing a surface composed of a plurality of cleavage planes. FIG. 13 is a cross-sectional view of the epitaxial growth surface 002 in the X direction. The direction of the force applied to the abrasive grain 070 during processing is a resultant force composed of a combined vector of the force that moves the abrasive grain 070 in the X direction and the force that moves in the Z direction. In this case, an angle can be formed between the abrasive grain moving direction and the cleavage plane. When viewed on the entire epitaxial growth surface 002, the processing state varies depending on the size of the inclination angle such that the vector of force applied to the abrasive grain 070 is easy to process in a certain direction and difficult to process in a certain direction. Therefore, in order not to make unevenness on each cleaved surface 060, it is necessary to set the pressing force in consideration of a state where the cleaving direction which is the most difficult to process and the opening angle θ in the vector direction of the force applied to the abrasive grains are large. Therefore, it is necessary to perform final processing at a lower pressure than in the case where the cleavage plane is not separated into a plurality. Specifically, in the step of gradually removing the unevenness, a plurality of cleavage planes can be formed by setting the final pressure range to 20 Pa or more and 3000 Pa or less.

That is, the plurality of cleavage surfaces, in the step of gradually removing the aforementioned irregularities, using a polishing pad made from the slurry and the nonwoven fabric composed mainly of colloidal silica, the rotational speed 10min ^-1 or more 1000min ^-1 or less of the polishing pad The slurry is supplied at a rate of 0.02 ml / min to 2 ml / min and a pressure of 1000 Pa to 20000 Pa. More specifically, in the step of gradually removing the above-described unevenness, the plurality of cleaved surfaces are subjected to a pressure so that the pressure is 10,000 Pa or more and 20000 Pa or less, 5000 Pa or more and less than 10,000 Pa, 20 Pa or more and 3000 Pa or less. It is formed by weakening in order.

FIG. 14 shows the result of performing polishing for 10 minutes with the last applied pressure lowered to 200 Pa in the step of gradually removing the unevenness. Except for the final pressing condition, the conditions are the same as those for obtaining the ScAlMgO ₄ substrate shown in FIG. FIG. 14 shows the surface shape measurement result measured by AFM in the range of 10 μm square (100 μm ² ). As shown in FIG. 14, it can be seen that the epitaxial growth surface 002 is formed of a plurality of elongated cleavage surfaces.

  Here, the final pressing force when the cleavage plane width 061 is set to 1.5 nm or more and 500 nm or less is set in a range of 20 Pa or more and 3000 Pa or less. Since the opening angle θ between the resultant vector and the cleavage direction becomes small, the final pressure should be set in the range of 100 Pa to 2800 Pa. That is, when the cleavage plane width 061 is 5 nm or more and 150 nm or less, it is formed such that the applied pressure is reduced as the processing proceeds in the order of 10,000 Pa to 20000 Pa, 5000 Pa to less than 10,000 Pa, and 100 Pa to 2800 Pa.

Here, the height between cleavage surfaces 062 will be described. FIG. 15 shows an enlarged cross-sectional view in the X direction of two adjacent cleavage planes. In FIG. 15, in the ScAlMgO ₄ substrate composed of the MgAlO ₂ atomic layer 081 and the ScO ₂ atomic layer 082, the ScO ₂ atomic layer 082 is one layer, whereas the MgAlO ₂ layer 081 is overlapped, and the MgAlO ₂ layer 081 is overlapped. Between the layers is a cleavage plane. Therefore, the outermost surface is formed of one layer of the MgAlO ₂ layer 081. The height between cleavage planes 062 is the smallest unit of thickness for two layers of MgAlO ₂ atomic layers 081 and one layer of ScO ₂ atomic layers 082 based on the characteristics of the cleavage portion considered from the ScAlMgO ₄ atomic arrangement. That is, this is the minimum unit of the height between cleavage planes 062 in FIG. 11, specifically about 0.8 nm.

In addition, when performing GaN crystal epitaxial growth using the MOCVD method, it is desirable that the height between the cleavage planes is not more than a certain height in order to suppress epitaxial growth from the wall surface of the stepped portion. The wall surface of the step portion has a crystal orientation different from that of the cleavage plane. Therefore, the crystal epitaxially grown on the wall surface has a problem that the impurity concentration is different from that of the crystal epitaxially grown on the cleavage plane, or the yield of epitaxial growth is reduced due to the generation of polycrystals. Because. Specifically, when the height between the cleavage planes is in the range of 1 to 10 times the minimum unit, the generation of polycrystal is suppressed and the yield of epitaxial growth is improved. That is, the cleavage plane height 062 is preferably 0.8 nm or more and 8 nm or less. In order to form the cleavage plane height 062 between 0.8 nm and 8 nm, the range of 100 μm ² is measured by AFM with respect to the epitaxial growth surface obtained as a result of processing with the final pressure, and the surface roughness Ra is 0. It is processed and formed to have a thickness of 08 nm to 1.5 nm.

Furthermore, when the height between the cleavage planes is in the range of 1 to 4 times the minimum unit, a good epitaxial film having a uniform impurity concentration over the entire epitaxial growth surface can be obtained in addition to the polycrystal suppression. That is, the cleavage plane height 062 is more preferably 0.8 nm or more and 3.2 nm or less. In order to form the cleavage plane height of 062 between 0.8 nm and 3.2 nm, the range of 100 μm ² is measured by AFM with respect to the epitaxial growth surface as a result of processing with the final pressure, and the surface roughness Ra is Processed and formed to be 0.08 nm or more and 1.0 nm or less.

Here, the details of this method are summarized. In the unevenness forming step, the unevenness of 500 nm or more is formed under the following processing conditions using a grindstone to which diamond abrasive grains of # 300 or more and # 2000 or less are attached. Grindstone rotation speed 500 min ^-1 or more 50000Min ^-1 or less, ScAlMgO ₄ plate member rotational speed 10min ^-1 or 300 min ^-1 or less, the processing speed of 0.01 [mu] m / sec or more 1 [mu] m / sec, machining removal amount is more than 1 [mu] m 300 μm or less. In the cleavage plane forming step, a plurality of cleavage planes (irregularities of less than 500 nm) are formed under the following processing conditions using a polishing pad made of a slurry mainly composed of colloidal silica and a nonwoven fabric. Rotational speed of the polishing pad 10min ^-1 or more 1000min ^-1 or less, the slurry feed rate 0.02 ml / min to 2 ml / min or less, pressure is not more than 20000Pa than 20 Pa. Furthermore, a plurality of cleavage planes (the unevenness of less than 500 nm) can be formed more accurately by weakening the pressing force in the order of 10,000 Pa to 20,000 Pa or less, 5000 Pa to 10000 Pa, 20 Pa to 3000 Pa in order. In addition, when forming a single cleavage plane, the final applied pressure in the cleavage plane formation step is set to 1000 Pa or more and less than 5000 Pa.

  Note that the epitaxial growth surface may be formed only on one surface (surface). By polishing only one surface (surface), the process can be simplified. In this case, the other surface (back surface) side is left with an unevenness of 500 nm or more formed. However, an epitaxial growth surface may be formed on both sides. In this case, nitride semiconductor such as GaN can be epitaxially grown on both sides.

In the ScAlMgO ₄ substrate of the present disclosure, as shown in FIG. 16, one surface, that is, the back surface of the epitaxial growth surface 002 may have a matte shape 090. FIG. 16 shows a ScAlMgO ₄ substrate 001 having a satin shape 090. ScAlMgO ₄ on the rear surface of the substrate by the presence of satin shape 090, it is possible to identify the front and back of ScAlMgO ₄ substrate 001. Further, when the ScAlMgO ₄ substrate 001 is transported, the matte shape 090 acts as a slip stopper, and it is possible to suppress scratches and chips caused by the ScAlMgO ₄ substrate 001 slipping and colliding during transport. The matte shape 090 has a surface roughness Ra larger than that of the epitaxial growth surface 002, and even when a plurality of cleaved surfaces 060 are formed on the epitaxial growth surface 002, the surface texture 090 has the largest surface roughness. Specifically, the surface roughness Ra of the epitaxial growth surface 002 composed of a single cleavage plane is usually 0.08 nm or more and 0.5 nm or less, and when having a plurality of cleavage planes, 0.08 nm or more and 1.5 nm or less. It is. On the other hand, the surface roughness of the satin-shaped 090 is 500 nm or more and 8000 nm or less. These surface roughnesses are measured values in a region of 100 μm ² . FIG. 17 shows an enlarged view of the satin shape 090.

Furthermore, the epitaxial growth surface 001 preferably has a concavo-convex shape height of 500 nm or less, whereas the satin shape 090 preferably has a concavo-convex shape height of 500 nm or more. The uneven height is a value measured by the above-described laser reflection type length measuring machine. When the back surface of the epitaxial growth surface of the ScAlMgO ₄ substrate is not a matte shape having a concavo-convex height of 500 nm or more, the ScAlMgO ₄ substrate is transparent when performing an exposure process for forming a pattern of a device structure or a wiring structure on the epitaxial growth surface side. As a result, light may be reflected from the back surface, affecting exposure. In addition, there may be a problem that it is difficult to discriminate between the front and the back during handling, and that the substrate is likely to slip when placed on a flat surface such as a stage of a manufacturing apparatus.

The satin shape 090 can be formed by a processing method that uniformly forms irregularities on the surface. Specifically, it can be formed by grinding using diamond fixed abrasive grains having a large abrasive grain size. As abrasive grains, diamond abrasive grains of # 100 or more and # 2000 or less are used. More preferably, # 600 diamond abrasive grains are used. That is, a substrate having a satin shape 090 includes a step of preparing a ScAlMgO ₄ plate obtained by cleaving a ScAlMgO ₄ single crystal at a (0001) plane, and one surface (surface) of the ScAlMgO ₄ plate. And polishing the surface to form an epitaxial growth surface, and processing the surface (back surface) opposite to the epitaxial growth surface to form a textured surface having a surface roughness larger than that of the epitaxial growth surface. It is done. Mat surface, using the attached grindstone ♯100 more ♯2000 following diamond abrasive grains, grinding wheel rotational speed 500 min ^-1 or more 50000Min ^-1 or less, ScAlMgO ₄ plate member rotation speed 10min ^-1 or 300 min ^-1 or less, It is formed under processing conditions of a processing speed of 0.01 μm / second to 1 μm / second and a processing removal amount of 1 μm to 300 μm. Preferably, the difference in unevenness can be further reduced by # 600 diamond abrasive grains. As preferable processing conditions, the processing is performed so that the processing removal amount becomes 20 μm at a grinding wheel rotational speed of 1800 min ⁻¹ , ScAlMgO ₄ substrate rotational speed of 100 min ⁻¹ , a processing speed of 0.3 μm / second.

  Moreover, in order to remove the influence of the work-affected layer due to processing, grinding or blasting for forming the work-affected layer may be performed.

  Here, the epitaxial growth surface is a surface on which another crystal is epitaxially grown on the crystal to be the substrate, and can be, for example, a region 5 mm or more inside from the outer periphery of the substrate. Epitaxial growth is a crystal growth mode in which crystals are newly aligned with the crystal plane of the underlying substrate. On this epitaxial growth surface, a group III nitrogen compound is formed by a vapor phase growth method such as MOCVD method, MOVPE (Metal-Organic Vapor Phase Epitaxy) method, HVPE (Hydride Vapor Phase Epitaxy) method, or liquid phase growth method such as flux method. The compound semiconductor crystal can be grown.

Although GaN MOCVD growth has been described as a method for epitaxial growth on a ScAlMgO ₄ substrate, AlGaInN-based crystal growth in which Al or In is added to GaN has the same effect.

  Further, the growth method is not limited to MOCVD, and other HVPE growth, or HVPE growth after MOCVD growth may be used together. After growing the AlGaInN buffer layer at a low temperature of about 500 to 600 ° C., the GaN crystal may be grown at a high temperature of 1000 ° C. or higher.

  A light emitting device, a power device, or the like may be formed by forming an AlGaInN heterojunction on the AlGaInN crystal layer.

(Other embodiments)
In the above-described embodiment, the substrate obtained from the single crystal of ScAlMgO ₄ is described among the substrates formed of the single crystal represented by the general formula RAMO _4. However, the present disclosure is not limited to this.

Note that the substrate of the present disclosure is made 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, wherein M is one or more divalent elements selected from Mg, Mn, Fe (II), Co, Cu, Zn, and Cd Represents an element. 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.

  When the LED light emitting layer is grown on the substrate and the LED light emitting layer is grown to manufacture the LED element, by using the substrate according to the present disclosure, the light emitting unevenness is generated as the LED element, and the luminance can be prevented from being lowered. .

001 ScAlMgO ₄ substrate 002 Epitaxial growth surface 003 Stepped portion 060 Cleaved surface 061 Cleaved surface width 062 Cleaved surface height 070 Abrasive grain 081 MgAlO ₂ atomic layer 082 ScO ₂ atomic layer 090 Pear-like shape

Claims (15)

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. A RAMO ₄ substrate comprising one or more divalent elements selected from the group consisting of:
Having an epitaxial growth surface on at least one surface;
The RAMO ₄ substrate, wherein the epitaxial growth surface has a plurality of cleaved surfaces separated from each other distributed with regularity. Each of the plurality of cleavage planes has an elongated shape.
The RAMO ₄ substrate according to claim 1. The width of each cleavage plane is 1.5 nm or more and 500 nm or less,
The RAMO ₄ substrate according to claim 2. The width of each cleavage plane is 5 nm or more and 150 nm or less,
The RAMO ₄ substrate according to claim 2. The adjacent cleavage planes are separated by 0.8 nm or more and 8 nm or less,
The RAMO ₄ substrate according to claim 3 or 4. The surface roughness Ra in the region of 100 μm ² in the cleavage plane is 0.08 nm or more and 1.5 nm or less.
The RAMO ₄ substrate according to any one of claims 1 to 5. R in the general formula is Sc, A is Al, and M is Mg.
The RAMO ₄ substrate according to any one of claims 1 to 6. Between adjacent cleaved surfaces, an AlMgO ₂ layer is exposed,
The RAMO ₄ substrate according to claim 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. Cleaving at (0001) plane to prepare a RAMO ₄ plate-like body, which represents one or more divalent elements selected from the group consisting of:
An unevenness forming step of forming unevenness having a height of 500 nm or more on the RAMO ₄ plate;
Cleaving the irregularities having a height of 500 nm or more to form a plurality of cleaved surfaces separated from each other and distributed with regularity; and
A method for manufacturing a RAMO ₄ substrate. The concavo-convex forming step is a step of grinding the RAMO ₄ plate with the first abrasive grains,
The cleavage plane forming step is a step of polishing the unevenness having a height of 500 nm or more with a second abrasive grain having a hardness lower than that of the first abrasive grain.
The method for manufacturing the RAMO ₄ substrate according to claim 9. In the cleavage plane forming step, the plurality of cleavage planes are formed by gradually reducing the pressure applied during polishing.
The method for producing a RAMO ₄ substrate according to claim 9 or 10. In the irregularity forming step,
Using a grindstone with diamond abrasive grains of # 300 or more and # 2000 or less,
The number of revolutions of the grindstone is 500 min ⁻¹ or more and 50000 min ⁻¹ or less,
The RAMO ₄ plate body rotational speed 10min ^-1 or 300 min ^-1 or less,
Processing speed 0.01 μm / second or more and 1 μm / second or less, and processing removal amount 1 μm or more and 300 μm or less,
Grinding under the conditions of
In the cleavage plane forming step,
Using a polishing pad made of a slurry and non-woven fabric based on colloidal silica,
Rpm 10min ^-1 or more of the polishing pad 1000min ^-1 or less,
Slurry supply rate 0.02 ml / min or more and 2 ml / min or less, and pressing force 1000 Pa or more and 20000 Pa or less,
Polishing under the conditions of
The manufacturing method of the RAMO ₄ board | substrate as described in any one of Claims 9-11. In the cleavage plane forming step, the applied pressure is gradually reduced in the order of 10,000 Pa to 20000 Pa, 5000 Pa to less than 10,000 Pa, 20 Pa to 3000 Pa,
The manufacturing method of the RAMO ₄ board | substrate of Claim 11 or 12. In the cleavage plane forming step, the applied pressure is gradually reduced in the order of 10,000 Pa to 20000 Pa, 5000 Pa to less than 10,000 Pa, 100 Pa to 2800 Pa.
The manufacturing method of the RAMO ₄ board | substrate of Claim 11 or 12. R in the general formula is Sc, A is Al, and M is Mg.
The manufacturing method of the RAMO ₄ board | substrate as described in any one of Claims 9-14.