Method for manufacturing a substrate for epitaxial growth and substrate for epitaxial growth

Abstract

To provide a method for manufacturing an epitaxial growth substrate more suitable for single crystal epitaxial growth.SOLUTION: A method for manufacturing an epitaxial growth substrate comprises steps of: cleaving a single crystal body represented by the general formula RAMO4 to obtain a substrate having a cleavage surface as an epitaxial growth surface; and colliding charged particles having energy on the cleavage surface to form a step terrace structure (a terrace width being an interval between steps is 0.2-100 μm) having periodicity on the cleavage surface, where in the general formula, R represents at least one kind of trivalent elements selected from a group consisting of Sc, In, Y and lanthanoids; A represents at least one kind of trivalent elements selected from a group consisting of Fe(III), Ga and Al; and M represents at least one kind of bivalent elements selected from a group consisting of Mg, Mn, Fe(II), Co, Cu, Zn and Cd.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a method for manufacturing a substrate for epitaxial growth and a substrate for epitaxial growth.

Background Art

[0002] Single crystals represented by the general formula RAMO4 (in the general formula, R represents at least one trivalent element selected from the group consisting of Sc, In, Y, and lanthanoid elements, A represents at least one trivalent element selected from the group consisting of Fe(III), Ga, and Al, and M represents at least one divalent element selected from the group consisting of Mg, Mn, Fe(II), Co, Cu, Zn, and Cd.) are known. For example, the ScAlMgO4 substrate is used as a substrate for epitaxial growth of nitride semiconductors such as GaN (see Non-Patent Document 1).

Prior Art Documents

Non-Patent Documents

[0003]

Non-Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] As described in Non-Patent Document 1, the polished substrate of ScAlMgO4 has many steps, and three types of flat terraces on the c-plane coexist corresponding to the three cleavage planes existing within the unit cell. Therefore, for example, when a single crystal such as GaN is epitaxially grown on a polished substrate, many through dislocations occur from the boundary between terraces of different types. On the other hand, since the cleavage substrate of ScAlMgO4 has extremely few steps, when a single crystal such as GaN is similarly epitaxially grown, the growth nuclei of the crystal are insufficient and island-shaped and uneven crystals grow.

[0005] The present invention has been made in view of the above circumstances, and an object thereof is to provide a method for manufacturing a substrate for epitaxial growth suitable for epitaxial growth of a single crystal. Another object of the present invention is to provide a substrate for epitaxial growth suitable for epitaxial growth of a single crystal.

Means for Solving the Problems

[0006] A method for manufacturing a substrate for epitaxial growth according to one aspect of the present invention includes a step of cleaving a single crystal represented by the general formula RAMO4 to obtain a substrate having a cleavage plane as an epitaxial growth plane, and colliding charged particles having energy with the cleavage plane to form a step-terrace structure having periodicity on the cleavage plane. The width of the terrace, which is the interval between steps, is 0.2 to 100 μm. In the general formula, R represents at least one trivalent element selected from the group consisting of Sc, In, Y, and lanthanoid elements, A represents at least one trivalent element selected from the group consisting of Fe(III), Ga, and Al, and M represents at least one divalent element selected from the group consisting of Mg, Mn, Fe(II), Co, Cu, Zn, and Cd.

[0007] In one embodiment of the above manufacturing method, the collision of charged particles with the cleavage plane may be performed by irradiating the cleavage plane with an ion beam. At this time, the ion beam is preferably an Ar ion beam, and it is preferable to irradiate the ion beam so as to satisfy at least one of the following conditions. The number of particle collisions of Ar ions is 10 8 / cm 2 or less. The particle energy of Ar ions is 1 keV or less. The beam current value of Ar ions is 0.05 μA or less.

[0008] The substrate for epitaxial growth according to one aspect of the present invention has a cleavage plane of a single crystal represented by the general formula RAMO4 as an epitaxial growth surface, the cleavage plane has a stepped terrace structure having periodicity, and the width of the terrace, which is the interval between steps, is 0.2 to 100 μm.

[0009] In one embodiment of the above substrate, it is preferable that the height of the step is an integer multiple of the unit lattice length of the single crystal.

[0010] In one embodiment of the above substrate, it is preferable that the width of the terrace is 0.3 to 30 μm.

Advantages of the Invention

[0011] According to the present invention, it is possible to provide a method for manufacturing a substrate for epitaxial growth more suitable for epitaxial growth of a single crystal. Further, according to the present invention, it is possible to provide a substrate for epitaxial growth more suitable for epitaxial growth of a single crystal. The substrate for epitaxial growth can be obtained by the above manufacturing method. According to the present invention, for example, when epitaxially growing a single crystal such as GaN, it is possible to provide an excellent substrate for epitaxial growth that suppresses the generation of threading dislocations and suppresses the growth of the single crystal in an island shape.

Brief Description of the Drawings

[0012]

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DETAILED DESCRIPTION OF THE INVENTION

[0013] Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings as appropriate. However, the present invention is not limited to the following embodiments.

[0014] <Method for manufacturing a substrate for epitaxial growth> The method for manufacturing a substrate for epitaxial growth includes a step of cleaving a single crystal represented by the general formula RAMO4 to obtain a substrate having a cleavage plane as an epitaxial growth surface (cleavage step), and a step of colliding charged particles having energy with the cleavage plane to form a step-terrace structure having periodicity on the cleavage plane (step-terrace formation step).

[0015] (Cleavage step) Examples of the single crystal represented by the general formula RAMO4 (in the general formula, R represents at least one trivalent element selected from the group consisting of Sc, In, Y, and lanthanoid elements, A represents at least one trivalent element selected from the group consisting of Fe(III), Ga, and Al, and M represents at least one divalent element selected from the group consisting of Mg, Mn, Fe(II), Co, Cu, Zn, and Cd.) include ScAlMgO4, LuGaMgO4, InGaMgO4, YFeFeO4, YFeMnO4, and the like. The type of single crystal may be selected from the viewpoint of lattice constant matching with the crystal to be grown.

[0016] Taking ScAlMgO4 as an example to explain the general structure of RAMO4, ScAlMgO4 has a structure in which ScO2 layers with a rock-salt structure and AlMgO2 layers with a hexagonal graphite structure (h-BN) are alternately stacked. Since the binding force between the AlMgO2 layers existing at three positions within the unit cell is weak, the ScAlMgO4 single crystal can be cleaved perpendicular to the c-axis between the AlMgO2 layers. The unit cell length of ScAlMgO4 is 25.160 Å.

[0017] A substrate having a cleavage plane as an epitaxial growth plane can be obtained by cutting a high-quality RAMO4 single crystal without small-angle grain boundaries, which is obtained by a known method such as the pulling method, into a block shape, and then applying a blade parallel to the c-plane to the corner of the block and applying pressure to cleave it.

[0018] (Step-terrace formation process) By uniformly colliding charged particles having energy with the cleavage plane of the substrate obtained in the cleavage process, the crystal structure on the surface of the cleavage plane can be reconstructed. On the cleavage plane obtained by mechanical force, terraces with an unstable and atomically flat surface state are generated. By colliding charged particles having energy with this terrace under appropriate conditions, thermally stable steps can be formed. The purpose of colliding charged particles is to raise the temperature of the surface of the cleavage plane and form irregularities that become steps on the flat cleavage plane surface. When charged particles having energy hit the surface of the crystal, generally, surface atoms are knocked off, or atoms move due to the energy given to surrounding atoms and becoming high temperature. When colliding charged particles, in order to heat the surface of the cleavage plane, plasma or laser light irradiation may be used in combination.

[0019] In addition to the method using charged particles, methods for modifying the substrate surface include simply heating the substrate in air and chemically etching the substrate using hot phosphoric acid. However, in the former method, the crystal becomes cloudy at 1400 °C, and it is difficult to increase the steps at temperatures below this. Also, in the latter method, only dislocations and steps are etched deeply, and it is difficult to form uniform growth nuclei.

[0020] The charged particles are made to collide with the cleavage plane so that the width of the terrace, which is the interval between steps, becomes 0.2 to 100 μm. As a result, steps are formed on the cleavage plane at an appropriate density, and it is possible to suppress the generation of through dislocations and suppress the growth of single crystals in an island shape. From this perspective, it is more preferable that the width of the terrace is 0.3 to 30 μm. The width of the terrace can be adjusted by the energy intensity of the charged particles to be collided, the number of collisions, etc. Note that the width of the terrace on the cleavage plane of a cleavage substrate with extremely few steps is generally more than 100 μm. The width of the terrace on the polished surface of a polished substrate with extremely many steps is generally 0.15 μm or less.

[0021] The charged particles are preferably made to collide with the cleavage plane so that the height of the step is an integer multiple of the unit lattice length. When epitaxially growing a crystal on a substrate, the crystal grows parallel to the terrace from the step as a growth nucleus for crystal growth, and then the growth proceeds in the vertical direction after covering the terrace (step flow growth). When growing in the vertical direction, it collides with the crystal layer grown on the adjacent terrace. At this time, since the height of the step at the boundary between the terraces is an integer multiple of the unit lattice length, the lattice mismatch can be reduced and the generation of through dislocations can be suppressed. The height of the step can be adjusted by changing the energy intensity of the charged particles.

[0022] Figure 1 is a diagram showing step flow growth using a substrate for epitaxial growth. In the figure, H represents the height of the step, W represents the width of the terrace, the arrow Gp represents the growth direction of the crystal on the terrace, and the arrow Gv represents the growth direction of the crystal after covering the terrace.

[0023] Charged particles having energy are preferably irradiated so as to reduce three types of steps that are originally present on the cleavage plane and are integer multiples of 1 / 3 times the unit lattice length, and increase steps that are integer multiples of the unit lattice length. By minimizing the total number of the three types of steps originally present, the generation of through dislocations can be further suppressed. The total number of steps originally present on the cleavage plane can be adjusted by changing the energy intensity of the charged particles.

[0024] As a method of colliding charged particles having energy with the cleavage plane, for example, a method of irradiating the cleavage plane with an ion beam, a method of treating the cleavage plane with plasma (however, charged particles such as ions in the plasma are adjusted to the same conditions (energy intensity, number of collisions, etc.) as the charged particles in the above ion beam irradiation), and the like can be mentioned. In any method, a desired step-terrace structure can be formed by treating the surface of the cleavage plane under very weak conditions.

[0025] If it does not chemically react with the substrate, the ion species used for the ion beam is not particularly limited. Examples of the ion species include Ar, N2, He, O2, etc. As long as the surface heating necessary to achieve the purpose of forming steps that are integer multiples of the lattice constant with a uniform density on a flat surface at the atomic level and the destruction of the surface due to the collision of particles are possible, the type of particles does not matter.

[0026] The ions contained in the ion beam are not particularly limited as long as the ion beam can be irradiated with a uniform density, and may be single ions or cluster ions (gas cluster ion beam). By appropriately adjusting the ion species of the irradiated ions, the energy of the ion beam, the number of particles of the irradiated ions, the irradiation density, etc., a homogeneous single-type step having a desired density and a terrace having a desired width can be formed on the cleavage plane.

[0027] As the ion beam, an Ar ion beam can be used from the viewpoint that the ions are inert and have a certain mass. Further, it is preferable to irradiate the ion beam so as to satisfy at least one of the following conditions. The number of particle collisions of Ar ions is 10 8 / cm 2 or less. The particle energy of Ar ions is 1 keV or less. The beam current value of Ar ions is 0.05 μA or less. Any of the conditions means treating the cleavage plane surface with an ion beam under very weak conditions. To adjust the height of the step or reduce the steps originally present on the cleavage plane, various conditions may be adjusted within the above ranges.

[0028] Note that there is no particular limitation as long as steps can be formed, but the irradiation conditions of the ion beam can be set, for example, as follows. The number of particle collisions of Ar ions is 10 3 / cm 2 or more. The particle energy of Ar ions is 10 eV or more. The beam current value of Ar ions is 1 pA or more.

[0029] In the present disclosure, a method of forming unevenness in the form of steps on a flat cleavage plane surface by colliding charged particles having energy with the cleavage plane is adopted. However, the cleavage plane surface may be treated by other methods such as chemical etching, thermal etching, or laser ablation that can roughen a flat surface at the atomic level.

[0030] <Substrate for epitaxial growth> The substrate for epitaxial growth has a cleavage plane of a single crystal represented by the general formula RAMO4 as an epitaxial growth surface, the cleavage plane has a stepped terrace structure having periodicity, and the width of the terrace, which is the interval between steps, is 0.2 to 100 μm.

[0031] The above-described substrate for epitaxial growth can be obtained by the method for manufacturing a substrate for epitaxial growth described above.

[0032] On the substrate for epitaxial growth, crystals of group III-V semiconductors, group II-VI semiconductors, and other compound semiconductors can be grown. Examples of group III-V semiconductors include AlN, GaN, InN, and solid solutions thereof. Examples of group II-VI semiconductors include ZnO, ZnS, etc. Examples of other compound semiconductors include Ga2O3, etc.

[0033] For example, a substrate for epitaxial growth obtained by processing ScAlMgO4 can be particularly preferably used for the crystal growth of GaN from the viewpoint of lattice matching. ScAlMgO4 has a lattice mismatch rate with GaN that is 10 times smaller than that of sapphire, and can significantly reduce the threading dislocation density.

[0034] For example, for the crystal growth of GaN, the MOVPE method can be employed as described in Non-Patent Document 1. In the MOVPE method, gaseous organometal (Ga) and ammonia (NH3) react near the surface of a substrate heated to a high temperature, and GaN is adsorbed onto the substrate. Atomic GaN moves along the substrate surface and deposits on steps, and epitaxially grows in the lateral direction parallel to the substrate along terraces.

Examples

[0035] Hereinafter, the present invention will be described in detail using examples, but the present invention is not limited to only the following examples.

[0036] (Growth of ScAlMgO4 single crystal) Scandium oxide Sc2O3, magnesium oxide MgO, and aluminum oxide Al2O3 powder were weighed and mixed as raw materials to obtain a mixed powder. The obtained mixed powder was placed in an alumina crucible, fired at 1400 °C, cooled, and then the fired powder was placed in an Ir crucible in a single crystal growth furnace. The crucible made of Ir was heated by high-frequency heating, and the fired powder was melted in nitrogen containing a small amount of oxygen. A single crystal was pulled up by bringing a seed into contact with the melt from above and solidifying it. After separating the grown single crystal from the melt and cooling it, it was taken out of the furnace. As described above, a ScAlMgO4 single crystal was obtained.

[0037] (Fabrication of cleavage substrate of ScAlMgO4 single crystal) The ScAlMgO4 single crystal obtained as described above was cut into a block shape. Then, by applying a blade parallel to the c-plane to the corner of the block and applying pressure, a cleavage substrate of the ScAlMgO4 single crystal was obtained. No step observable with the naked eye was found on the cleavage plane of the cleavage substrate.

[0038] The AFM images of the cleavage plane of the cleavage substrate are shown in FIGS. 2 and 3.

[0039] FIG. 2 is an AFM image of the terrace portion of the cleavage plane. As shown in the figure, it can be seen that there are terraces that are flat at the atomic level on the cleavage plane.

[0040] FIG. 3 is an AFM image of the step portion of the cleavage plane. Most of the cleavage plane is composed of terraces, but there are steps in a part of it. The height of the step is about 8 Å (0.8 nm), and in the figure, it constitutes the step between terraces arranged neatly in several steps. The height of the step corresponds to approximately 1 / 3 of the unit cell, which is consistent with the fact that it is pointed out that there are three planes (cleavage planes) with weak bonds in the unit cell.

[0041] (Ion beam irradiation on the cleavage substrate) The cleavage plane of the cleavage substrate obtained as described above was irradiated with an Ar ion beam using an irradiation apparatus manufactured by Showa Vacuum Co., Ltd. In this apparatus, low-pressure Ar gas ionized by a high-frequency electric field is made into an ion beam by a direct-current electric field. In this example, after narrowing the beam diameter with an aperture, it was irradiated on the cleavage plane. By irradiating with the ion beam, a step-terrace structure having periodicity could be formed on the cleavage plane. In the portion where the desired step was formed, the number of particle collisions of Ar ions was 108 / cm 2 The following conditions were met. At that time, the particle energy of the Ar ions was 1 keV or less, and the beam current value of the Ar ions was 0.05 μA or less.

[0042] Figure 4 is an AFM image of the step-terrace structure formed by ion beam irradiation on the cleavage plane of the cleaved substrate. Further, Figure 5 is a cross-sectional view of the AFM image of the step-terrace structure formed by ion beam irradiation on the cleavage plane of the cleaved substrate. The height of the steps in the formed step-terrace structure was an integer multiple of about 25 Å. Also, steps with a height of about 8 Å (1 / 3 of the unit cell c-axis) were not found. The width of the terraces was 10 μm.

[0043] As a comparison, an epitaxial lapped substrate of ScAlMgO4 single crystal is exemplified. Figure 6 is a cross-sectional view of the AFM image of the step-terrace structure on the lapped surface of the lapped substrate. The height of the steps in the step-terrace structure was about 8 Å (1 / 3 of the unit cell c-axis). The width of the terraces was about 0.14 μm.

[0044] The substrate obtained as described above can be said to be an epitaxial growth substrate suitable for epitaxial growth of single crystals such as GaN.

Industrial Applicability

[0045] The epitaxial growth substrate according to the present disclosure has appropriate steps that are fewer than those of an epitaxial lapped substrate and more than those of a mere cleaved substrate. Therefore, by using the epitaxial growth substrate according to the present disclosure, it is possible to reduce the penetration transition while suppressing the growth of single crystals in an island shape when epitaxially growing a single crystal. As a result, a nitride semiconductor such as GaN with a low defect density can be obtained.

Claims

1. General formula RAMO ４ A step of cleaving a single crystal represented by the formula to obtain a substrate having a cleavage plane as an epitaxial growth plane; A step of forming a periodic step-terrace structure having steps at the boundaries between terraces on the cleavage plane, wherein the width of the terraces, which is the interval between the steps, is 0.2 to 100 μm, and the height of the steps is an integral multiple of the unit lattice length of the single crystal, by colliding charged particles having energy with the cleavage plane, wherein the collision of the charged particles with the cleavage plane is performed by irradiating the cleavage plane with an ion beam, and a method for manufacturing a substrate for epitaxial growth comprising the same. [In the general formula, R represents at least one trivalent element selected from the group consisting of Sc, In, Y, and lanthanoid elements, A represents at least one trivalent element selected from the group consisting of Fe(III), Ga, and Al, and M represents at least one divalent element selected from the group consisting of Mg, Mn, Fe(II), Co, Cu, Zn, and Cd.]

2. The ion beam is an Ar ion beam, The manufacturing method according to claim 1, wherein the ion beam is irradiated so as to satisfy at least one of the following conditions. The number of particle collisions of Ar ions is 10 ８ / cm ２ or less. The particle energy of the Ar ions is 1 keV or less. The beam current value of the Ar ions is 0.05 μA or less.

3. The manufacturing method according to claim 1 or 2, wherein the width of the terraces is 0.3 to 30 μm.

4. General formula RAMO ４ having a cleavage plane of a single crystal represented by as an epitaxial growth surface, A substrate for epitaxial growth having a periodic step-terrace structure having steps at the boundaries between terraces, wherein the width of the terraces, which is the interval between the steps, is 0.2 to 100 μm, and the height of the steps is an integral multiple of the unit lattice length of the single crystal. [In the general formula, R represents at least one trivalent element selected from the group consisting of Sc, In, Y, and lanthanoid elements, A represents at least one trivalent element selected from the group consisting of Fe(III), Ga, and Al, and M represents at least one divalent element selected from the group consisting of Mg, Mn, Fe(II), Co, Cu, Zn, and Cd.]

5. The substrate according to claim 4, wherein the width of the terraces is 0.3 to 30 μm.

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