A method for producing a crystalline micro-textured structure made of an oxide or nitride of a group 13 element, and a structure having the crystalline micro-textured structure on its surface.

Abstract

This invention provides a method for producing a crystalline micro-textured structure, composed of oxides or nitrides of Group 13 elements and formed into a desired shape or pattern, and a structure having this crystalline micro-textured structure on its surface, by a low-temperature and low-toxicity process. [Solution] A precursor thin film made of amorphous oxide or nitride of a group 13 element is deposited on a substrate, and a laser is selectively irradiated onto its surface to crystallize the laser-irradiated area and synthesize a crystalline oxide or nitride of a group 13 element. Next, the amorphous oxide or nitride in the non-irradiated area is removed by etching to construct a crystalline micro-textured structure.

Description

[Technical Field]

[0001] This invention relates to a low-temperature and low-toxicity method for producing a crystalline micro-textured structure made of oxides or nitrides of Group 13 elements and formed into a desired shape or pattern. It also relates to a structure having this crystalline micro-textured structure on its surface, suitable for applications such as medium- and high-voltage power devices and optical devices. [Background technology]

[0002] Wide-bandgap semiconductor materials possess high voltage resistance and high transmittance in the ultraviolet and visible light regions, and have been put into practical use as power devices, transparent conductive thin films, and light-emitting devices. For the past several decades, materials such as GaN and SiC have had bandgap (E) of about 3 eV. g Research and development have been conducted, from fundamental physics to implementation, focusing on the materials of ).

[0003] In recent years, in order to realize higher-performance electronic devices, E g Research into semiconductor materials with E is actively underway. For example, gallium oxide (Ga2O3) is E g The temperature exceeds 4 eV, and aluminum nitride (AlN) is E g It is attracting attention as a wide-bandgap semiconductor with a voltage of approximately 6 eV.

[0004] In wide-bandgap semiconductor devices, improving crystallinity and orientation is crucial, alongside controlling semiconductor properties through impurity doping. Taking Ga2O3-based semiconductor devices as an example, the thermodynamically stable β-phase and the metastable α-phase of Ga2O3 have traditionally been fabricated under high-temperature conditions of 500°C or higher in various deposition processes. There are few reports on crystal growth in the low-temperature range below 500°C.

[0005] Furthermore, the formation of microstructures such as trenches and fins on the surface of Ga2O3 thin films is crucial for the construction of semiconductor devices and for improving their performance. Because crystalline Ga2O3 has a high melting point and high cleavage, making microfabrication difficult, the formation of microstructures on thin film surfaces has mainly been done by high-temperature etching using highly toxic gases or high-concentration acids. There are few reports of fabrication using low-toxicity and low-temperature processes.

[0006] For example, Patent Document 1 discloses a trench MOS type Schottky diode that includes a semiconductor layer made of a Ga2O3-based single crystal having trenches, and has an insulating dry-etched damage layer with a thickness of 0.8 μm or less in the region including the inner surface of the trenches, thereby suppressing an abnormal increase in on-resistance caused by the trench MOS structure. [Prior art documents] [Patent Documents]

[0007] [Patent Document 1] Japanese Patent Publication No. 2019-153645 [Non-patent literature]

[0008] [Non-Patent Document 1] Taishi Shiojiri, Satoshi Kaneko, et al., "Room-temperature laser annealing for solid-phase epitaxial crystallization of β-Ga2O3 thin films," Applied Physics Express, Volume 9, Number 10, 2016.10, 105502-1-105502-4 [Overview of the project] [Problems that the invention aims to solve]

[0009] However, in the trench MOS Schottky diode described in Patent Document 1, trenches in the Ga2O3 semiconductor layer are formed by plasma etching, and the resulting damaged layer is thinned by annealing at temperatures above 700°C. This requires dry etching under harsh conditions using toxic chlorine-based gases and high-temperature annealing, raising concerns about safety and environmental impact.

[0010] As described above, conventional gallium oxide thin film manufacturing requires a high-temperature annealing process to synthesize crystalline gallium oxide. Furthermore, surface microfabrication of crystalline gallium oxide thin films requires harsh etching processes, such as plasma etching using toxic gases. Currently, there is no low-temperature, low-toxicity manufacturing method for creating finely textured structures from crystalline gallium oxide that solves these problems.

[0011] The present invention has been made in view of the above problems, and aims to provide a method for synthesizing crystalline oxides or nitrides of Group 13 elements by a room temperature process, and then for producing a finely textured structure made of crystalline oxides or nitrides by a low-toxicity, room-temperature process. Furthermore, it aims to provide a structure having a finely textured surface made of crystalline oxides or nitrides of Group 13 elements, suitable for applications such as medium- and high-voltage power devices and optical devices.

[0012] As disclosed in Non-Patent Document 1, the present inventors have been conducting research on a technique for synthesizing highly oriented β-Ga2O3 thin films from amorphous Ga2O3 thin films deposited on an α-Al2O3 substrate using the excimer laser annealing (ELA) method. Using this technique, β-Ga2O3 thin films with excellent properties as wide-bandgap semiconductor materials can be synthesized by a room-temperature process.

[0013] By applying this technology, the inventors have found that by selectively irradiating the surface of an amorphous gallium oxide thin film with a laser, the laser-irradiated portion can be selectively crystallized. Further, by removing the remaining amorphous portion of the non-laser-irradiated portion by etching under mild conditions, it has been found that a crystalline fine concavo-convex structure made of gallium oxide can be produced. As a result of further research, the present invention has been completed.

[0014] That is, the present invention is a method for producing a crystalline fine concavo-convex structure made of a Group 13 element oxide, including the following steps. (a1) A step of depositing an oxide of a Group 13 element on the surface of a substrate by physical or chemical vapor deposition to form a precursor thin film made of an amorphous oxide of a Group 13 element. (b1) A step of selectively irradiating the surface of the precursor thin film with a laser to selectively crystallize the amorphous oxide in the laser-irradiated portion and synthesize a crystalline oxide of a Group 13 element, and / or (c1) When the substrate is transparent to the laser, irradiating the laser selectively to the interface between the substrate and the precursor thin film through the substrate from the opposite surface of the surface of the substrate on which the precursor thin film is formed, to selectively crystallize the amorphous oxide in the laser-irradiated portion and synthesize a crystalline oxide of a Group 13 element, and (1d) A step of removing the amorphous oxide in the non-laser-irradiated portion of the precursor thin film by etching to form fine concavo-convexities made of the crystalline oxide on the surface of the substrate.

[0015] Further, the present invention is a method for producing a crystalline fine concavo-convex structure made of a Group 13 element nitride, including the following steps. (a2) A step of depositing a nitride of a Group 13 element on the surface of a substrate by physical or chemical vapor deposition to form a precursor thin film made of an amorphous nitride of a Group 13 element (b2) A step of selectively irradiating the surface of the precursor thin film with a laser to selectively crystallize the amorphous nitride in the laser-irradiated portion and synthesize a crystalline nitride of a Group 13 element, and / or (c2) When the substrate is transparent to the laser, the laser is selectively irradiated through the substrate from the opposite surface of the surface of the substrate on which the precursor thin film is formed to a position at the interface between the substrate and the precursor thin film, and the amorphous nitride in the laser-irradiated portion is selectively crystallized to synthesize a crystalline nitride of a group 13 element, and (d2) A step of removing the amorphous nitride in the non-laser-irradiated portion of the precursor thin film by etching to form fine irregularities made of the crystalline nitride on the surface of the substrate.

[0016] The manufacturing method of the present invention selectively irradiates a laser to a precursor thin film made of an amorphous oxide or nitride of a group 13 element formed by physical vapor deposition or the like, thereby selectively crystallizing the amorphous oxide or nitride in the laser-irradiated portion, and efficiently synthesizing a crystallization region having a desired shape or pattern made of a crystalline oxide or nitride of a group 13 element by a room-temperature process.

[0017] Next, by removing the remaining amorphous oxide or nitride in the non-laser-irradiated portion by etching under mild conditions such as room-temperature wet etching, a fine irregular structure having a desired shape or pattern made of a crystalline oxide or nitride of a group 13 element can be efficiently manufactured with low toxicity and low environmental load by a room-temperature process.

[0018] Furthermore, the present invention is a method for manufacturing a crystalline fine irregular structure made of an oxide of a group 13 element, including the following steps. (3a) A step of forming a precursor thin film by coating an inorganic polymer synthesized by a sol-gel method using an alkoxide of a group 13 element as a raw material on the surface of a substrate. (3b) A step of selectively irradiating a laser on the surface of the precursor thin film to selectively crystallize the inorganic polymer in the laser-irradiated portion to synthesize a crystalline oxide of a group 13 element, and / or (3c) If the substrate is transparent to the laser, a step of positionally irradiating the interface between the substrate and the precursor thin film with the laser from the opposite side of the surface of the substrate on which the precursor thin film has been deposited, thereby positionally crystallizing the inorganic polymer in the laser-irradiated portion to synthesize a crystalline oxide of a group 13 element, and (3d) A step of removing the inorganic polymer in the non-irradiated portion of the precursor thin film by etching to form fine irregularities made of the crystalline oxide on the surface of the substrate.

[0019] In the manufacturing method of the present invention, an inorganic polymer can be synthesized using an alkoxide of a group 13 element as a raw material by the sol-gel method to prepare a sol, which can then be coated onto the surface of a substrate to gel and form a precursor thin film. Since the sol-gel method requires simple equipment and does not require reduced pressure, combining it with laser annealing makes it possible to carry out all processes at atmospheric pressure and room temperature.

[0020] Furthermore, the present invention comprises a substrate and fine irregularities formed on its surface, which consist of crystalline oxides or nitrides of Group 13 elements, wherein the Group 13 elements are one or more selected from the group consisting of gallium, aluminum, and indium, and the area of ​​the region on the surface of the substrate where the fine irregularities are formed is 150 mm². 2 The above describes a structure having a crystalline micro-rough structure on its surface, which is made of an oxide or nitride of a group 13 element, wherein the average height of the micro-roughness is 100 nm or more, and the band gap of the crystalline oxide or nitride is 4.0 eV or more.

[0021] The structure of the present invention is composed of crystalline oxides or nitrides of Group 13 elements and has a surface with a fine uneven structure formed in a desired shape or pattern. It is expected to have excellent properties as a wide-bandgap semiconductor material and is suitable for applications such as the manufacture of medium-voltage or high-voltage power devices and optical devices. [Effects of the Invention]

[0022] According to the present invention's method for manufacturing crystalline micro-textured structures, micro-textured structures composed of crystalline oxides or nitrides of Group 13 elements, formed into desired shapes and patterns, can be manufactured with high production efficiency and reduced environmental impact through a low-temperature and low-toxicity process.

[0023] Furthermore, the structure having the crystalline micro-roughness structure of the present invention on its surface is expected to exhibit excellent properties as a wide-bandgap semiconductor material and is suitable for applications such as medium- and high-voltage power devices and optical devices. [Brief explanation of the drawing]

[0024] [Figure 1] This is an explanatory diagram illustrating the schematic method for producing the crystalline gallium oxide micro-textured structure of the present invention. [Figure 2] (a) An image obtained by electron microscope (SEM) of a sapphire substrate having a β-type gallium oxide micro-texture on its surface, prepared in Example 1, and (b) an image showing the measurement results of a stylus-type step meter in the PP line in the observed image. [Figure 3] These are the diffraction patterns obtained by X-ray diffraction (XRD) of amorphous gallium oxide thin films and β-type gallium oxide thin films crystallized by excimer laser annealing (ELA). [Figure 4] (a) An amorphous gallium oxide thin film, and (b) a β-type gallium oxide thin film crystallized with ELA, observed by reflection high-energy electron diffraction (RHEED). [Figure 5] These are atomic force microscope (AFM) images of amorphous gallium oxide thin films and β-type gallium oxide thin films crystallized with ELA. [Figure 6] This graph shows the relationship between laser fluence and grain size for β-type gallium oxide thin films crystallized using ELA from amorphous gallium oxide thin films of three different thicknesses. [Figure 7] This graph shows the relationship between laser fluence, film thickness, and crystal morphology for β-type gallium oxide thin films crystallized using ELA from three different amorphous gallium oxide thin films of varying thicknesses. [Figure 8]This is a graph of Tauc plots used to calculate the band gap of amorphous gallium oxide thin films and β-type gallium oxide thin films crystallized by ELA. [Modes for carrying out the invention]

[0025] The following describes in detail a method for producing a crystalline micro-textured structure made of an oxide or nitride of a group 13 element according to the present invention, and a structure having such a crystalline micro-textured structure on its surface. Note that material compositions, shapes, structures, manufacturing methods, etc., that are not described here may be the same as or substantially the same as those known to those skilled in the art.

[0026] In this specification, "consisting of" means essentially or substantially consisting of the element or compound in question, and allows for the inclusion of trace amounts of other elements or compounds. For example, it may include dopants intentionally added to impart semiconductor properties.

[0027] Furthermore, "abbreviated" is not limited to cases where the product is strictly identical, but rather includes errors or modifications that do not result in a loss of identity. For example, "abbreviated whole" is not limited to cases where the product is strictly whole, but includes forms that can be considered equivalent to the whole from the perspective of their effects and benefits.

[0028] The present invention provides a method for producing a crystalline micro-textured structure made from oxides or nitrides of elements belonging to Group 13 of the periodic table. Gallium oxide (Ga2O3), aluminum oxide (Al2O3), and indium oxide (In2O3) are preferred examples of oxides, while gallium nitride (GaN) and aluminum nitride (AlN) are preferred examples of nitrides.

[0029] First, in steps (a1) and (a2), an amorphous oxide or nitride precursor thin film is formed on the surface of the substrate that will serve as the support by physical or chemical vapor deposition.

[0030] The substrate material and its thickness are not limited as long as they have sufficient strength, heat resistance, etching resistance, etc., as a support, and exhibit the desired properties for the application of the crystalline micro-texture structure of the present invention. Examples of materials include quartz glass, alumina, sapphire (α-Al2O3), gallium oxide (α or β-Ga2O3), and silicon. It may be a single-layer or multi-layer structure. As a substrate for semiconductor devices, it is desirable to have excellent electrical insulation and thermal conductivity.

[0031] The method for depositing oxides or nitrides of group 13 elements on the surface of a substrate is not limited to any method that can deposit smooth, uniform amorphous thin films with high throughput and low cost. Examples of physical vapor deposition (PVD) include pulsed laser deposition (PLD), vacuum deposition methods such as ion plating (IP), and sputtering, while examples of chemical vapor deposition (CVD) include thermal CVD and plasma CVD. Pulsed laser deposition is preferred in terms of high-quality and stable film deposition and room-temperature deposition, while ion plating and sputtering are preferred in terms of uniform and large-area film deposition and room-temperature deposition.

[0032] In the physical or chemical vapor deposition method used in the present invention, multiple Group 13 elements may be used as raw materials simultaneously. The raw materials may be individual Group 13 elements or oxides or nitrides of a desired composition. Higher purity is preferable to prevent contamination with impurities. Specifically, two or more individual raw materials or compound raw materials selected from Ga, Al, and In are placed in the film deposition apparatus as an evaporation source or target to perform film deposition. When individual raw materials are used, reactive film deposition is performed by introducing an oxidizing gas such as O2 gas, plasma-formed O2 gas, and ozone (O3) gas, or a nitriding gas such as N2 gas or plasma-formed N2 gas.

[0033] Furthermore, in the manufacturing method of the present invention, instead of physical or chemical vapor deposition, in step (a3), an inorganic polymer may be synthesized using a alkoxide of a group 13 element as a raw material by a liquid phase method called the sol-gel method, and this may be coated onto the surface of a substrate that serves as a support to form a precursor thin film.

[0034] When forming films using the sol-gel method, inorganic polymers are synthesized using alkoxides such as ethoxides and isopropoxides of Group 13 elements as raw materials. Specifically, metal alkoxides such as gallium, aluminum, and indium (M(OR)) n A metal (M: metal, R: hydrocarbon group) is dissolved in water or an organic solvent, and hydrolysis and dehydration condensation are carried out using an acid or base as a catalyst to synthesize an inorganic polymer (polymetalloxane) with a repeating metalloxane (MO) bond as the main chain skeleton.

[0035] This colloidal suspension (sol) of inorganic polymer is uniformly coated onto the substrate surface by a method such as spin coating. The solvent is evaporated or dehydration condensation is promoted to increase the degree of polymerization and gel, thereby forming a precursor thin film mainly composed of inorganic polymer. This gelled precursor thin film of inorganic polymer is amorphous and porous, containing trace amounts of water and solvent, and retaining organic functional groups and hydroxyl groups in the main chain. It is believed that crystallization is possible by applying sufficient energy with laser annealing to remove the water, solvent, and residual functional groups. The term "main component" means that it contains a sufficient amount of inorganic polymer to be crystallized by laser annealing. Furthermore, the amorphous and porous portion is thought to have an etching rate orders of magnitude larger than that of the crystalline portion.

[0036] The shape and size of the substrate and the precursor thin film deposited on its surface are not limited as long as the crystalline micro-texture structure of the present invention can be manufactured uniformly and stably. Vacuum deposition and sputtering methods allow for industrially large-area film deposition, and it is considered possible to deposit large-area precursor thin films with a diameter of 4 to 6 inches or more. Larger substrate and precursor thin film areas are preferable because they reduce the manufacturing cost of semiconductor devices. For rectangular substrates, 150 mm is preferable. 2 Preferably, the above (10 x 15 mm square or larger) is preferred, and for a roughly circular substrate, 20 cm 2 A diameter of 2 inches or more is preferable.

[0037] The thickness of the precursor thin film is not limited as long as the crystalline micro-texture structure of the present invention can be manufactured uniformly and stably. In the examples described later, changes in the particle size and crystalline state of in-plane grains of the solid-phase epitaxially grown β-Ga2O3 thin film were observed depending on the thickness of the precursor thin film and the laser irradiation intensity. The thickness of the precursor thin film is set considering the irradiation conditions such as laser irradiation intensity, the crystalline morphology of the synthesized crystalline oxide or nitride, and the shape and application of the micro-texture structure to be manufactured. Examples of precursor thin film thicknesses deposited in one cycle include a range of several tens of nanometers to 1 μm.

[0038] Next, in steps (b1), (b2), and (b3), a laser is regioselectively irradiated onto a portion or most of the surface of the precursor thin film to regioselectively crystallize the inorganic polymer synthesized from amorphous oxides or nitrides of Group 13 elements and alkoxides of Group 13 elements in the laser-irradiated area, thereby synthesizing crystalline oxides or nitrides of Group 13 elements. Regioselective irradiation and crystallization means that, without particular limitations within the region of the surface of the precursor thin film, the desired position, shape, and pattern can be freely selected from a plan view from directly above or directly below, or from a viewpoint in the direction of irradiation, for irradiation and crystallization.

[0039] The medium, wavelength, pulse width, etc., of the laser used for irradiation are not limited as long as sufficient energy can be applied to efficiently crystallize amorphous oxides or nitrides and inorganic polymers at low energy. Both pulsed lasers and continuous-wave (CW) lasers may be used. Examples of media include solids, gases, and semiconductors; wavelengths include visible light, ultraviolet light, and X-rays; and pulse widths include nanoseconds, picoseconds, and phetoseconds.

[0040] From the viewpoint of microfabrication and irradiation costs, visible light lasers (wavelengths 380-780 nm) and ultraviolet lasers (wavelengths less than 380 nm) are preferred. Examples of visible light lasers include semiconductor lasers, helium-neon (HeNe) lasers, and lasers obtained by wavelength conversion of infrared solid-state lasers such as YAG and YLF, while examples of ultraviolet lasers include excimer lasers, semiconductor lasers, and lasers obtained by wavelength conversion of infrared solid-state lasers such as YAG and YLF.

[0041] Among these, an excimer laser, which is a widely used irradiation device and has proven results in laser annealing in the semiconductor field, is more preferable. The medium may be any of argon fluoride (ArF, wavelength 193 nm), krypton fluoride (KrF, wavelength 248 nm), xenon chloride (XeCl, wavelength 308 nm), and xenon fluoride (XeF, wavelength 351 nm). ArF and KrF, which have short oscillation wavelengths and enable microfabrication, are preferable, and KrF, which has a low irradiation cost, is even more preferable.

[0042] In the laser annealing of the precursor thin film, irradiation conditions such as pulse energy (mJ), pulse width, repetition frequency (Hz), number of shots, and fluence of energy density (mJ / cm 2 ) are set in consideration of the balance between the characteristics of the resulting group 13 element crystalline oxide or nitride and the manufacturing cost. Also, as described above, the laser irradiation conditions are adjusted in consideration of the film thickness of the precursor thin film, the crystal structure and morphology of the synthesized crystalline oxide or nitride, and the shape and use of the fine uneven structure to be manufactured. The laser fluence is exemplified in the range of 100 to 500 mJ / cm 2 . If it is less than 300 mJ / cm 2 , crystal growth in the solid phase proceeds, and if it is 300 mJ / cm 2 or more, a tendency is recognized that the irradiated portion melts and crystal growth in the liquid phase proceeds.

[0043] The region irradiated with the laser is a part or most of the surface of the precursor thin film in plan view. "Part" means an area of less than 50%, and "most" means an area of 50% or more to almost all. In order to make the most of the substrate, for a rectangular substrate, the laser is irradiated by setting the region so that as many chips as possible can be placed in almost all regions, and for a substantially circular substrate, the region is set so that as many chips as possible can be placed. By moving the laser irradiation light source or the substrate, or by scanning the laser using a galvano mirror and irradiating sequentially, crystallization of a large-area amorphous thin film with a diameter of 4 to 6 inches or more is considered possible.

[0044] The laser irradiation direction may be directly above or below the substrate, or it may be irradiated at an angle. Lasers with the same or different irradiation conditions may be superimposed. The spot shape of the laser beam is set considering the energy application required for crystallization and production efficiency, and examples include rectangles with sides of several hundred μm to 20 mm or circles with a diameter of several hundred μm to 20 mm. Examples of shot counts include 250 to 20,000 shots, and examples of repetition frequency include 1 Hz to 300 Hz. A line-shaped laser (line laser) may be irradiated continuously.

[0045] One method for positionally irradiating a precursor thin film is a simple method with fewer steps, in which a laser focused on the surface of the precursor thin film is irradiated along a fine pattern for forming fine irregularities. Another method, which allows for irradiation of a wide area at once and is highly efficient, involves forming or placing a mask on or near the surface of the precursor thin film to transfer a fine pattern for forming fine irregularities, and then irradiating the surface of the precursor thin film with a laser through the mask.

[0046] As for the mask, there are methods that use only a photomask to transfer the fine pattern, and methods that use a combination of a photomask and a photoresist to transfer the fine pattern. Alternatively, a fine pattern of inorganic or organic material may be directly formed on the surface of the precursor thin film via a mask using vapor deposition or other vapor phase growth methods similar to those used for depositing the precursor thin film.

[0047] Existing photomasks and photoresists used in the semiconductor field can be used. Examples of photomasks include contact-type photomasks that are in close contact with the precursor thin film for exposure, proximity-type photomasks that are close to the precursor thin film with a print gap for exposure, and single-projection or segmented-projection photomasks that project fine patterns completely non-contact. The photoresist used can be either a positive or negative resist.

[0048] After laser irradiation, the photomask is detached from or near the surface of the precursor thin film. Masks such as photoresists directly formed on the surface of the precursor thin film are removed by a wet or dry process. They may also be removed simultaneously with amorphous oxides or nitrides during the etching process described later.

[0049] In the manufacturing method of the present invention, steps (c1), (c2), and (c3) may be performed together with or instead of the above steps (b1), (b2), and (b3), in which a laser is irradiated from the opposite side of the surface of the substrate on which the precursor thin film has been deposited, through the substrate, to selectively crystallize the amorphous oxide or nitride and inorganic polymer in the laser-irradiated area, thereby synthesizing a crystalline oxide or nitride. Since crystallization proceeds from the interface between the substrate and the precursor thin film, the amorphous portion can be crystallized even if the laser is irradiated from the opposite side.

[0050] In this case, the substrate must be transparent to the laser. Transparency means it must be approximately transparent; the important thing is that enough energy can be applied to the substrate when the laser is shone through it to crystallize the amorphous portion of the laser-irradiated area. Specifically, an example is when a laser is incident on a substrate formed from a predetermined material and having a predetermined thickness, and the transmittance T(I / I0) of the transmitted light I relative to the incident light I0 is in the range of 75-95%.

[0051] The method for selectively irradiating with a laser is the same as described above. When forming a mask by combining a photomask and a photoresist, or when forming a mask by vapor phase growth methods such as vapor deposition, the mask is formed directly on the surface opposite to the surface of the substrate on which the precursor thin film has been deposited.

[0052] The crystal structure and morphology of the crystalline micro-rough structure of the present invention are not limited as long as they exhibit the desired properties for their application and show sufficient etching resistance in the etching process described later. For example, gallium oxide (Ga2O3) is known to have five different crystalline polymorphisms: α, β, γ, δ, and ε, each with a different crystal structure. Furthermore, the crystalline morphology that grows differs depending on the surface properties of the substrate. If the substrate surface is a single crystal or a highly oriented crystal surface that has been planarized, highly oriented polycrystalline material will grow. On the other hand, if the substrate surface is random and untreated, randomly oriented polycrystalline material will grow.

[0053] For applications requiring high performance as a power semiconductor material, the crystal structure of Ga2O3 is preferably the thermodynamically most stable β phase (monoclinic) and the metastable α phase (rhombohedral). A highly oriented polycrystalline form is preferred. In this case, in order to epitaxially grow amorphous Ga2O3, the substrate surface (deposition plane) must be a single crystal with aligned crystal orientations, or a polycrystalline form with orientation in at least one axis perpendicular to the plane and in the in-plane direction. The deposition plane of the substrate may be planarized to prevent orientation growth in unintended or random directions, thereby forming a step-terrace structure.

[0054] The epitaxial growth method may be a solid-phase method in which a thin film is grown while maintaining its solid state, or a liquid-phase method in which the laser-irradiated area is dissolved and grown. Furthermore, it may be a heteroepitaxial method in which the crystalline oxide or nitride of the group 13 element to be synthesized is epitaxially grown on a crystal plane of a substrate with a different lattice constant, crystal orientation, or material composition, or a homoepitaxial method in which the crystalline oxide or nitride is epitaxially grown on a crystal plane of a substrate with the same lattice constant, crystal orientation, and material composition.

[0055] For heteroepitaxial structures using single-layer substrates, examples of substrate types include α-Al2O3 (sapphire) plane orientation (0001) single crystal substrates and Si plane orientation (100) single crystal substrates. From the viewpoint of similarity of atomic arrangement, ease of availability, and cost, α-Al2O3 (sapphire) plane orientation (0001) single crystal substrates are preferred. For homoepitaxial structures using single-layer substrates, the substrate is a single crystal substrate of an oxide or nitride of a group 13 element to be epitaxially grown. For example, in the case of gallium oxide, an example is a β-Ga2O3 plane orientation (001) single crystal substrate.

[0056] In heteroepitaxial systems using multilayer substrates, the uppermost layer (deposited surface) of the substrate may be a highly oriented polycrystalline surface composed of alumina, silicon, or oxides or nitrides of different Group 13 elements. In homoepitaxial systems using multilayer substrates, the uppermost layer (deposited surface) of the substrate may be a highly oriented polycrystalline surface composed of oxides or nitrides of the same Group 13 element.

[0057] In heteroepitaxial growth, a buffer layer may be provided between the substrate and the crystalline thin film to mitigate in-plane lattice mismatches and other defects such as misfit dislocations caused by in-plane lattice mismatches between the substrate crystal surface and the epitaxially grown crystalline thin film. Examples of buffer layers include NiO layers (111) laminated on the substrate crystal surface by vapor phase growth methods similar to those used for oxide or nitride thin films.

[0058] In the laser-irradiated portion of the precursor thin film, amorphous oxides or nitrides and inorganic polymers undergo regioselective crystallization, resulting in the synthesis of crystalline oxides or nitrides. On the other hand, areas not irradiated by the laser, such as those covered by a mask, do not undergo crystallization and remain amorphous. The amorphous portions have a random atomic arrangement and exhibit an etching rate orders of magnitude larger than that of the crystalline portions. In steps (d1), (d2), and (d3), these remaining amorphous portions are removed by etching.

[0059] Existing etching processes used in the semiconductor field can be used for the etching process, including wet etching using an etching solution and dry etching using an etching gas. Wet etching is preferred because it allows for the setting of mild conditions using a low-toxicity etching solution and causes less damage to the processed surface. Examples of etching solutions include aqueous phosphoric acid solution, aqueous sulfuric acid solution, and aqueous hydrofluoric acid solution. Preferably, etching is performed at room temperature to 100°C using an aqueous phosphoric acid solution of 60% by weight or less, and at room temperature using an aqueous hydrofluoric acid solution of 40% by weight or less. The etching rate may be increased by applying ultrasound in the direction of the film thickness being etched.

[0060] In the dry etching of amorphous portions of the present invention, milder conditions can be set compared to conventional dry etching of crystalline oxides, etc. In other words, in the dry etching used in the present invention, it is necessary to adjust the type of etching gas, gas concentration and flow rate, substrate temperature and plasma conditions, and etching time so that the crystalline portions are not etched. Examples of etching gases for dry etching include BCl3, Cl2, and CF4.

[0061] In steps (d1), (d2), and (d3), conditions such as the type and concentration of the etchant, and the etching temperature and time are set so that a sufficient etching rate is obtained in the amorphous region and the crystalline region is etched as little as possible. The etching rate of the amorphous region is preferably several Å / min or more, and more preferably several tens of Å / min or more. The etching rate of the crystalline region is preferably close to zero. In the room temperature wet etching using a 40 wt% phosphoric acid aqueous solution in the example described later, the etching rate of the amorphous Ga2O3 region was approximately 22 Å / min, and no etching was observed in the crystalline region.

[0062] The region where crystalline micro-irregularities consisting of oxides or nitrides of Group 13 elements are formed is a part or most of the surface of the deposited substrate in a plan view. The meaning of "part or most of the surface" is the same as described above. The region where crystalline micro-irregularities are formed includes both convex and concave regions, and also includes the form in which the substrate is exposed in the concave region. From the viewpoint of reducing the manufacturing cost of semiconductor devices, a larger area of ​​the region where micro-irregularities are formed on the substrate surface is preferable. For a rectangular substrate, 150 mm is preferable. 2 Preferably, the above (10 x 15 mm square or larger) is preferred, and for a roughly circular substrate, 20 cm 2 A diameter of 2 inches or more is preferable.

[0063] Furthermore, the height of the crystalline micro-roughness structure is not limited as long as the desired effect and function are achieved in the semiconductor device application. An example of an average height of 100 nm or more in a side view of the micro-roughness is provided. In a configuration in which a crystalline thin film is formed by the manufacturing method of the present invention and crystalline micro-roughness is constructed on it, the average height of the micro-roughness shall include the thickness of the thin film. The average height of the micro-roughness is calculated using, for example, the maximum height (Ry) or the ten-point average roughness (Rz) measured by a method compliant with JIS B0601-2013.

[0064] In the manufacturing method of the present invention, after the step of synthesizing a crystalline oxide or nitride by laser irradiation, a further step may be performed to remove a portion of the amorphous portion of the laser-unirradiated area of ​​the precursor thin film by etching, thereby forming crystalline fine irregularities on the surface of the substrate. Following this step, the steps of synthesizing a crystalline oxide or nitride, etching and removing the amorphous portion, etc., may be performed.

[0065] In this case, the etching conditions, such as the type and concentration of the etchant, and the etching temperature and time, are made milder to leave a portion of the amorphous region in the area not irradiated by the laser. This portion does not need to be almost entirely amorphous; the goal is simply to create crystalline micro-irradiations of the desired shape by a second, position-selective laser irradiation. Specifically, this is exemplified by a range of 25-75 volume percent of the amorphous region of the precursor thin film remaining after the first position-selective laser irradiation.

[0066] Furthermore, after the step of forming a precursor thin film, a step may be performed in which a laser is irradiated onto substantially the entire surface of the precursor thin film to crystallize substantially the entire precursor thin film and synthesize a crystalline thin film. Following this step, the process of forming a precursor thin film, the process of synthesizing a crystalline oxide or nitride, the process of etching away amorphous portions, etc., may be performed.

[0067] Furthermore, prior to the step of synthesizing crystalline oxides or nitrides by laser irradiation, a step may be performed to deposit a precursor thin film by selectively depositing amorphous oxides or nitrides onto the surface of the substrate using physical vapor phase growth or the like. Following this step, the steps for synthesizing crystalline oxides or nitrides, etching and removing amorphous portions, etc., are performed. In this case, a mask is formed or placed on or near the surface of the substrate or precursor thin film, similar to the selective laser irradiation described above, and amorphous oxides or nitrides are deposited selectively through the mask.

[0068] The steps (a1), (b1) and / or (c1) and (d1), (a2), (b2) and / or (c2) and (d2), and (a3), (b3) and / or (c3) and (d3) constitute one cycle, and these cycles may be repeated multiple times. In addition, the modified steps described above may be combined with these cycles. By combining these multiple cycles and steps, it becomes possible to construct fine irregularities with a greater thickness, an average height of 5 to 10 μm or more, film-like fine irregularities, and fine irregularities with more complex three-dimensional shapes, without being limited by irradiation conditions such as laser penetration depth and laser irradiation intensity.

[0069] The micro-textured structure of the present invention is a microstructure in which multiple micro-textured areas are formed in both plan view and side view. The shape and dimensions of each micro-textured area are not limited as long as the desired effect can be achieved in its application. Each textured unit may be the same shape or different shapes, may be symmetrical or asymmetrical in the front-to-back, left-to-right, up-to-down, and may be formed at equal or uneven intervals in the front-to-back, left-to-right, and down-to-down directions. Specifically, examples include a front-to-back or left-to-right width of each textured unit in plan view ranging from several hundred nm to several hundred μm, and a top-to-bottom height in side view ranging from several tens of nm to several tens of μm. Forming surface micro-textured areas of a desired shape or pattern made of crystalline oxide or nitride is important in the construction of high-performance wide-bandgap semiconductor devices. Preferred examples include trenches and fins in semiconductor elements, circuit patterns, and microlens arrays in optical elements.

[0070] The structures having a crystalline micro-rough surface according to the present invention are expected to be used in medium-voltage or high-voltage power devices or optical devices. The band gap of the crystalline oxide or nitride oxidation is preferably 4.0 eV or higher. Doping of impurities into the oxide or nitride is expected to be done by incorporating them into the amorphous oxide or nitride during the precursor thin film deposition process, or by incorporating them into the amorphous or crystalline oxide or nitride before or after the synthesis process of the crystalline oxide or nitride, or after the etching removal process of the amorphous portion, by ion diffusion, ion implantation, etc. [Examples]

[0071] The method for producing a crystalline micro-textured structure made of oxides or nitrides of Group 13 elements according to the present invention will be described in detail below with reference to examples and test examples. However, the present invention is not limited to these examples, and various modifications are possible without departing from the technical spirit of the present invention.

[0072] [Example 1] (Pulsed laser deposition method) Amorphous Ga2O3 precursor thin films were deposited on an α-Al2O3 (sapphire) substrate by pulsed laser deposition (PLD). A KrF excimer laser (wavelength 248 nm, laser fluence 1.5 J / cm²) was used.2 A pulse width of 20 nsec and a frequency of 5 Hz was focused and irradiated onto a target β-Ga2O3 sintered body, and the thin film was deposited onto an ultraplanarized α-Al2O3(0001) substrate for thin film deposition. The substrate size was 10 × 5 × 0.5 mm, the film thickness was 70 nm, and the deposition atmosphere was dilute O2(1.0 × 10) -5 Torr, base pressure 5×10 -9 Torr (below) and substrate temperature were set to room temperature (below 20°C, unheated).

[0073] (Excimer laser annealing) β-Ga2O3 was synthesized by excimer laser annealing (ELA). A circular Au mesh (diameter 5 mm, aperture width 200 μm, wire diameter 50 μm) was placed as a photomask in the center of an amorphous Ga2O3 precursor thin film. A KrF excimer laser (wavelength 248 nm) was irradiated across the entire surface of the amorphous Ga2O3 precursor thin film through this photomask to synthesize β-Ga2O3 through position-selective solid-phase epitaxial growth. Laser fluence: 150 mJ / cm² 2 The pulse width was 20 nsec, 10,000 pulses (non-focused, incident on the thin film surface), the repetition rate was 5 Hz, and the atmosphere was air (humidity 50% or less, 20°C or less).

[0074] (Wet etching) After ELA, the Au mesh of the photomask was removed, and the remaining amorphous Ga2O3 in the non-irradiated areas was removed by wet etching. A laminate of Ga2O3 thin films, in which β-Ga2O3 was synthesized positionally, was immersed in a 40 wt% phosphoric acid aqueous solution and etched at room temperature for 30 minutes while applying ultrasound in the film thickness direction to form fine irregularities. After wet etching, the laminate was washed with water and the surface was observed to find that fine irregularities with the Au mesh pattern transferred onto the substrate had been formed. A schematic of the manufacturing method of the present invention is shown in Figure 1.

[0075] (Observation of micro-textures) Figure 2(a) shows an electron microscope (SEM) image of the fine surface texture of β-Ga2O3 formed on the surface of a sapphire substrate by position-selective solid-phase epitaxial growth using ELA and wet etching under mild conditions. Figure 2(b) shows the measurement results using a stylus-type step meter on the PP line in Figure 2(a). From the observation image in Figure 2(a), it can be seen that multiple rectangular fine surface textures with sharp edges and sides of approximately 180-190 μm have been formed in plan view. Furthermore, from the measurement results in Figure 2(b), it can be seen that multiple protrusions with sharp edges and a height of approximately 65 nm have been formed in cross-sectional view. The thickness of the amorphous thin film is slightly thinner than the original thickness of approximately 70 nm, which is thought to be due to shrinkage caused by ELA.

[0076] [Test Example 1] Various properties of amorphous Ga2O3 thin films and crystalline Ga2O3 thin films after ELA (electrolytic layer aging) were evaluated and analyzed using the same materials, equipment, and conditions as in Example 1. (X-ray diffraction and reflection high-speed electron diffraction analysis) Immediately after deposition of amorphous Ga2O3 precursor thin film and after ELA (fluence 250 mJ / cm²) 2 Figure 3 shows the diffraction patterns of β-Ga2O3 thin films obtained by X-ray diffraction (XRD) after 500 and 1000 shots. Additionally, the diffraction patterns of amorphous Ga2O3 precursor thin films immediately after deposition and after ELA (fluence 250 mJ / cm²) are shown. 2 Figures 4(a) and (b) show the observation images of β-Ga2O3 thin films (500 shots) obtained by reflection high-energy electron diffraction (RHEED).

[0077] In the XRD diffraction pattern of the precursor thin film in Figure 3, no diffraction attributed to Ga2O3 was observed, and in the RHEED observation image of the precursor thin film in Figure 4(a), a halo pattern was observed, indicating that it is amorphous. On the other hand, in the XRD diffraction pattern after ELA in Figure 3, four diffractions attributed to β-Ga2O3 were observed, and in the RHEED observation image after ELA in Figure 4(b), a clear diffraction streak pattern and six-fold symmetric in-plane anisotropy with the pattern changing every 30° were observed, confirming solid-phase epitaxial growth by ELA.

[0078] (Atomic force microscopy observation) Immediately after deposition of amorphous Ga2O3 precursor thin film, after ELA (fluence 250 mJ / cm²) 2 Figures 5(a) to (c) show the surface morphology of β-Ga2O3 thin films (500 and 1000 shots) as observed by atomic force microscopy (AFM).

[0079] In the AFM observation image of the amorphously deposited precursor thin film shown in Figure 5(a), an ultraflat plane reflecting the morphology of the α-Al2O3 substrate was observed. Furthermore, in the β-Ga2O3 thin films after ELA shown in Figures 5(b) and (c), no growth of coarse crystal grains was observed even after solid-phase epitaxial growth, and the flat surface was maintained.

[0080] (Analysis of grain size) The relationship between the irradiation intensity of a KrF excimer laser in the ELA method and the in-plane grain size of a β-Ga2O3 thin film after laser irradiation was investigated. The film thickness of the amorphous Ga2O3 precursor thin film was at three levels: 40, 70, and 100 nm, and the laser fluence was 100-250 mJ / cm². 2 The range was defined as follows. Figure 6 shows the relationship between laser irradiation intensity and average grain size. A tendency was observed for the in-plane grain size to increase as the thickness of the amorphous Ga2O3 thin film increased, and for film thicknesses of 70 nm or more, the maximum grain size after ELA was approximately 1 μm.

[0081] Grain size affects the properties of semiconductor materials; a larger grain size reduces grain boundaries and leakage, improving semiconductor properties, while a smaller grain size improves surface flatness. Figure 6 shows a relationship between laser fluence, precursor thin film thickness, and grain size. This suggests that by adjusting the laser fluence and precursor thin film thickness, it may be possible to control the grain size within a suitable range during solid-phase epitaxial growth by ELA.

[0082] (Analysis of crystal morphology) The relationship between the crystalline morphology of amorphous Ga2O3 precursor thin films, ELA conditions, and precursor thin film thickness was analyzed. The amorphous Ga2O3 precursor thin film thicknesses were at three levels: 40, 70, and 100 nm, and the laser fluence was 100–250 mJ / cm². 2 The range was set to 500 shots. Figure 7 shows the relationship between the crystal morphology of the precursor thin film, identified from the XRD diffraction pattern and RHEED observation image, and the ELA conditions and the precursor thin film thickness.

[0083] The results in Figure 7 show a relationship between laser fluence, precursor thin film thickness, and crystal morphology. This suggests that by adjusting the laser fluence and precursor thin film thickness, it may be possible to control the crystal morphology within a suitable range during solid-phase epitaxial growth by ELA.

[0084] (Calculation of the band gap) Immediately after deposition of amorphous Ga2O3 precursor thin film, after ELA (150 mJ / cm²) 2 The optical band gap was calculated using Tauc plots for β-Ga2O3 thin films (500 and 1000 shots). The Tauc plots are shown in Figure 8.

[0085] The optical band gap of the amorphous Ga2O3 precursor thin film, determined by Tauc plotting, was 4.2 eV, absorbing a KrF excimer laser (wavelength 248 nm, equivalent to 5 eV). On the other hand, the β-Ga2O3 thin film after ELA treatment yielded optical band gaps of approximately 4.8 eV (500 shots) and 4.9 eV (1000 shots). These values ​​are comparable to those of single-crystal β-Ga2O3 and β-Ga2O3 thin films epitaxially grown at high temperatures above 500°C. [Industrial applicability]

[0086] The manufacturing method of the present invention allows for the production of crystalline micro-rough structures composed of oxides or nitrides of Group 13 elements, formed into desired shapes and patterns, using a low-temperature, low-toxicity, highly efficient, and environmentally friendly process. Furthermore, the structures of the present invention are expected to exhibit excellent properties as wide-bandgap semiconductors and optical device materials, making them suitable for applications such as the manufacture of medium-voltage or high-voltage power devices and optical devices.

[0087] Therefore, the method for manufacturing a crystalline micro-textured structure of the present invention, and the structure having this crystalline micro-textured structure on its surface, are particularly important in the fields of power electronics such as field-effect transistors (FETs) and optoelectronics such as optical elements equipped with microlens arrays, and are expected to be applied to high-voltage, high-power devices and light-emitting / absorbing devices in the deep ultraviolet region.

Claims

1. A method for producing a crystalline micro-textured structure made of oxides of Group 13 elements, including the following steps: (a1) A step of depositing an oxide of a group 13 element on the surface of a substrate by physical or chemical vapor deposition to form a precursor thin film consisting of an amorphous oxide of a group 13 element. (b1) A step of positionally irradiating the surface of the precursor thin film with a laser to positionally crystallize the amorphous oxide in the laser-irradiated portion to synthesize a crystalline oxide of a group 13 element, and / or (c1) When the substrate is transparent to the laser, a step of positionally irradiating the interface between the substrate and the precursor thin film with the laser from the opposite side of the surface of the substrate on which the precursor thin film has been deposited, thereby positionally crystallizing the amorphous oxide in the laser-irradiated portion to synthesize a crystalline oxide of a group 13 element, and (d1) A step of removing the amorphous oxide in the non-irradiated portion of the precursor thin film by etching to form fine irregularities made of the crystalline oxide on the surface of the substrate.

2. A method for producing a crystalline micro-textured structure made of nitrides of Group 13 elements, including the following steps: (a2) A step of depositing a nitride of a group 13 element on the surface of a substrate by physical or chemical vapor deposition to form a precursor thin film consisting of amorphous nitride of a group 13 element. (b) A step of positionally irradiating the surface of the precursor thin film with a laser to positionally crystallize the amorphous nitride in the laser-irradiated portion to synthesize a crystalline nitride of a group 13 element, and / or (c2) When the substrate is transparent to the laser, a step of positionally irradiating the interface between the substrate and the precursor thin film with the laser from the opposite side of the surface of the substrate on which the precursor thin film has been deposited, thereby positionally crystallizing the amorphous nitride in the laser-irradiated portion to synthesize a crystalline nitride of a group 13 element, and (d2) A step of removing the amorphous nitride in the non-irradiated portion of the precursor thin film by etching, thereby forming fine irregularities made of the crystalline nitride on the surface of the substrate.

3. A method for producing a crystalline micro-textured structure made of oxides of Group 13 elements, including the following steps: (a3) A step of forming a precursor thin film by coating the surface of a substrate with an inorganic polymer synthesized by the sol-gel method using an alkoxide of a group 13 element as a raw material. (b3) A step of positionally irradiating the surface of the precursor thin film with a laser to positionally crystallize the inorganic polymer in the laser-irradiated portion to synthesize a crystalline oxide of a group 13 element, and / or (c3) When the substrate is transparent to the laser, a step of positionally irradiating the interface between the substrate and the precursor thin film with the laser from the opposite side of the surface of the substrate on which the precursor thin film has been deposited, thereby positionally crystallizing the inorganic polymer in the laser-irradiated portion to synthesize a crystalline oxide of a group 13 element, and (d3) A step of removing the inorganic polymer in the non-irradiated portion of the precursor thin film by etching to form fine irregularities made of the crystalline oxide on the surface of the substrate.

4. A method for producing a crystalline micro-textured structure according to any one of claims 1 to 3, wherein the group 13 element is one or more selected from the group consisting of gallium, aluminum, and indium.

5. A method for producing a crystalline micro-textured structure according to any one of claims 1 to 3, wherein the process from forming the precursor thin film to forming the micro-textured surface is defined as one cycle, and this cycle is repeated multiple times.

6. A method for manufacturing a crystalline micro-rough structure according to any one of claims 1 to 3, wherein the laser is a visible light laser or an ultraviolet laser.

7. A method for producing a crystalline micro-rough structure according to any one of claims 1 to 3, wherein the etching is wet etching.

8. A method for producing a crystalline micro-rough structure according to any one of claims 1 to 3, wherein the surface of the substrate on which the precursor thin film is deposited is a single crystal or a highly oriented polycrystalline surface, and the regioselective crystallization is crystallization by solid-phase or liquid-phase epitaxial growth.

9. The method for producing a crystalline thin film according to claim 8, wherein the oxide of the group 13 element is gallium oxide, and the epitaxial growth is homoepitaxial growth.

10. The method for producing a crystalline thin film according to claim 8, wherein the oxide of the group 13 element is gallium oxide, and the epitaxial growth is heteroepitaxial growth.

11. The method for producing a crystalline micro-textured structure according to claim 8, wherein the crystalline oxide of the group 13 element is β-type gallium oxide.

12. The device comprises a substrate and fine irregularities formed on its surface, which consist of crystalline oxides or nitrides of group 13 elements. The aforementioned Group 13 element is one or more elements selected from the group consisting of gallium, aluminum, and indium. The area of ​​the region on the surface of the substrate where the fine irregularities are formed is 150 mm². ２ That's all. The average height of the aforementioned fine irregularities is 100 nm or more. The band gap of the crystalline oxide or nitride is 4.0 eV or greater. A structure having a crystalline micro-rough surface made of oxides or nitrides of Group 13 elements.

13. A structure having a crystalline micro-rough surface according to claim 12, wherein its application is to medium-voltage or high-voltage power devices and optical devices.

Images