JP2021172552A - Crystal film - Google Patents

Abstract

To provide a high-quality crystal film useful for a semiconductor device or the like and having impurities such as Si reduced.SOLUTION: In a production method of a crystal film for forming a crystal film on a substrate by crystal growth from a raw material, the raw material contains GaCl3 and a rugged part composed of concavities or protrusions is formed directly or with another layer in-between on the substrate for crystal growth. A crystal film is then formed on the rugged part under the crystal growth condition of a partial pressure of the raw material of 1 kPa or higher. The crystal film contains gallium-containing crystalline metal oxide as its main component and has an Si content of 2×1015 cm-3 or less.SELECTED DRAWING: None

Description

The present invention relates to a crystal film useful for semiconductor devices.

As a next-generation switching element capable of achieving high withstand voltage, low loss, and high heat resistance, _{semiconductor devices using gallium oxide (Ga 2} O ₃ ) having a large bandgap are attracting attention, and are used for power semiconductor devices such as inverters. Expected to be applied. Further, it is expected to be widely applied as a light receiving / receiving device such as an LED or a sensor due to a wide band gap. In particular, among gallium oxide, α-Ga ₂ O _{3 and the} like having a corundum structure can be bandgap controlled by mixing indium and aluminum, respectively, or in combination, according to Non-Patent Document 1. It constitutes an extremely attractive material system as an InAlGaO-based semiconductor. Here InAlGaO based semiconductor and the _{In X Al Y Ga Z O 3} (0 ≦ X ≦ 2,0 ≦ Y ≦ 2,0 ≦ Z ≦ 2, X + Y + Z = 1.5~2.5) indicates (Patent Document 9 Etc.), it can be overlooked as the same material system containing gallium oxide.

However, since the most stable phase of gallium oxide has a β-Galia structure, it is difficult to form a crystal film having a corundum structure, which is a metastable phase, unless a special film forming method is used. _{Further, α-Ga 2} O ₃ having a corundum structure is a metastable phase, and a bulk substrate due to melt growth cannot be used. Therefore, at present, sapphire having the same crystal structure as _{α-Ga 2} O _{3 is used as a substrate.} However, since α-Ga ₂ O ₃ and sapphire have a large lattice mismatch _{, the crystal film of α-Ga 2} O ₃ heteroepitaxially grown on the sapphire substrate tends to have a high dislocation density. In addition to the crystal film having a corundum structure, there are still many problems in improving the film formation rate and crystal quality, suppressing cracks and abnormal growth, suppressing twins, and cracking the substrate due to warpage. Under such circumstances, some studies are currently being conducted on the film formation of crystalline semiconductors having a corundum structure.

Patent Document 1 describes a method for producing an oxide crystal thin film by a mist CVD method using a bromide or iodide of gallium or indium. Patent Documents 2 to 4 describe a multilayer structure in which a semiconductor layer having a corundum-type crystal structure and an insulating film having a corundum-type crystal structure are laminated on a base substrate having a corundum-type crystal structure. .. Further, as in Patent Documents 5 to 7, film formation by mist CVD using an ELO substrate or void formation is also being studied. However, none of these methods is still satisfactory in terms of film formation rate, and a film formation method having an excellent film formation rate has been desired.
Patent Document 8 describes that at least a gallium oxide raw material and an oxygen raw material are used to form a gallium oxide having a corundum structure by a halide vapor deposition method (HVPE method). However, since α-Ga ₂ O ₃ is a metastable phase, _{it is difficult to form a film like β-Ga 2} O ₃ , and there are still many problems in the industry. Further, Patent Documents 10 and 11 describe that ELO crystal growth is carried out using a PSS substrate to obtain a crystal film having ^{a surface area of 9 μm 2} or more and a dislocation density of 5 × 10 ⁶ cm- ^2. There is. However, in order to fully demonstrate the performance of gallium oxide as a power device, not only the dislocation density but also impurities such as Si should be reduced, that is, the Si content should be 1 × 10 ¹⁶ cm ^-3 or less. It is necessary to do so, and a method capable of easily producing such an impurity-free crystal film is desired.
All of Patent Documents 1 to 11 are publications relating to patents or patent applications by the applicants, and are still under study.

Patent No. 5397794 Patent No. 5343224 Patent No. 5397795 Japanese Unexamined Patent Publication No. 2014-72533 Japanese Unexamined Patent Publication No. 2016-100592 Japanese Unexamined Patent Publication No. 2016-98166 Japanese Unexamined Patent Publication No. 2016-100593 Japanese Unexamined Patent Publication No. 2016-155714 International Publication No. 2014/050793 US Publication No. 2019/0057865 Japanese Unexamined Patent Publication No. 2019-034883

Kentaro Kaneko, "Growth and Physical Properties of Corundum Structure Gallium Oxide Mixed Crystal Thin Film", Doctoral Dissertation, Kyoto University, March 2013

An object of the present invention is to provide a high-quality crystal film useful for semiconductor devices and the like.

As a result of diligent studies to achieve the above object, the present inventors have _{formed Ga 2} O ₃ at a partial pressure of 1 kPa or more using _{GaCl 3} , and the Si content is 2 × 10 ¹⁵ cm ^-3 or less. We have found that a crystal film can be easily obtained, and found that such a crystal film can solve the above-mentioned conventional problems at once.

In addition, after obtaining the above findings, the present inventors have further studied and completed the present invention.

That is, the present invention relates to the following invention.
[1] A crystal film containing a crystalline metal oxide containing gallium as a main component, wherein the Si content is 2 × 10 ¹⁵ cm ^-3 or less.
[2] The crystal film according to the above [1], wherein the crystalline metal oxide has a corundum structure.
[3] The crystal film according to the above [1] or [2], wherein the C content is 5 × 10 ¹⁶ cm ^{-3 or less.}
[4] The crystal film according to any one of the above [1] to [3], which has a film thickness of 10 μm or more.
[5] The crystal film according to any one of the above [1] to [4], which has a film thickness of 25 μm or more.
[6] The crystal film according to any one of the above [1] to [5], which has a surface area of 10 cm ^{2 or more.}
[7] The crystal film according to any one of [1] to [6] above, wherein the crystal film is a semiconductor film.
[8] A semiconductor device including a crystal film, wherein the crystal film is the crystal film according to any one of the above [1] to [7].
[9] The semiconductor device according to the above [8], which is a power device.
[10] A semiconductor system including a semiconductor device, wherein the semiconductor device is the semiconductor device according to the above [8] or [9].

The crystal film of the present invention is a high-quality crystal film useful for semiconductor devices and the like.

It is a figure explaining the halide vapor deposition (HVPE) apparatus preferably used in this invention. It is a figure which shows typically the surface of the concavo-convex portion formed on the surface of the substrate which is preferably used in this invention. It is a schematic diagram which shows typically the surface of the concavo-convex portion formed on the surface of the substrate which is preferably used in this invention. It is a schematic diagram which shows one aspect of the concavo-convex portion formed on the surface of the substrate which is preferably used in this invention. It is a figure which shows the photograph of the crystal film in an Example. It is a figure which shows the SEM observation result in the comparative example. It is a figure which shows the SEM observation result in the comparative example. It is a figure which shows the SEM observation result in an Example. It is a figure which shows typically a preferable example of a power-source system. It is a figure which shows typically a preferable example of a system apparatus. It is a figure which shows typically a preferable example of the power supply circuit diagram of a power supply device.

The crystal film of the present invention is a crystal film containing a crystalline metal oxide containing gallium as a main component, and is characterized by having a Si content of 2 × 10 ¹⁵ cm ^-3 or less. The Si content is a value measured by SIMS. In the present invention, it is preferable that the crystalline metal oxide has a corundum structure. Further, in the present invention, the C content ^{is preferably 5 × 10 16} cm ^-3 or less. The C content is a value measured by SIMS. In the present invention, the film thickness of the crystal film is preferably 10 μm or more, and more preferably 25 μm or more. The surface area of the crystal film ^{is preferably 10 cm 2} or more, and more preferably 20 cm ² or more. Further, in the present invention, it is preferable that the crystal film is a semiconductor film.

The above-mentioned preferable crystal film is a method for producing a crystal film containing a crystalline metal oxide containing gallium as a main component on a substrate by crystal growth from the raw material, wherein the raw material _{contains GaCl 3} and is described above. It can be easily obtained by carrying out crystal growth under the crystal growth conditions of the raw material having a partial pressure of 1 kPa or more. Hereinafter, a preferable method for producing the crystal film will be described.

In the present invention, it is preferable that the crystal growth is carried out by the HVPE method. Further, in the present invention, it is preferable to carry out the above-mentioned crystal growth under a crystal growth condition of a film formation rate of 90 μm / hour or more, and more preferably to carry out the crystal growth under a crystal growth condition of a film formation rate of 100 μm / hour or more. In the present invention, for example, when the crystal growth is carried out by the HVPE method, _{the partial pressure of the raw material gas (GaCl 3} gas, its precursor gas, etc.) is 1 kPa or more, and the partial pressure of the oxygen-containing raw material gas is 1.25 kPa or more. Is preferable. Further, in the present invention, it is preferable to carry out the above-mentioned crystal growth in an oxygen-containing atmosphere.

(substrate)
The substrate is usually a crystalline substrate. The crystal substrate is not particularly limited as long as it is a substrate containing a crystal as a main component, and may be a known substrate. It may be an insulator substrate, a conductive substrate, or a semiconductor substrate. It may be a single crystal substrate or a polycrystalline substrate. Examples of the crystal substrate include a substrate containing a crystal having a corundum structure as a main component, a substrate containing a crystal having a β-Galia structure as a main component, and a substrate containing a crystal having a hexagonal structure as a main component. And so on. The "main component" refers to a composition ratio in the substrate containing 50% or more of the crystals, preferably 70% or more, and more preferably 90% or more.

Examples of the substrate containing a crystal having a corundum structure as a main component include a sapphire substrate and an α-type gallium oxide substrate. Examples of the substrate containing the crystal having a β-gallia structure as a main component include a β-Ga ₂ O ₃ substrate or a mixed crystal substrate containing β-Ga ₂ O ₃ and Al ₂ O _3. .. As the mixed crystal substrate containing β-Ga ₂ O ₃ and Al ₂ O ₃ , for example, a mixed crystal substrate containing Al ₂ O ₃ in an atomic ratio of more than 0% and 60% or less is preferable. Is listed as. Examples of the substrate having the hexagonal structure include a SiC substrate, a ZnO substrate, and a GaN substrate. Examples of other crystal substrates include Si substrates.

In the present invention, the crystal substrate is preferably a sapphire substrate. Examples of the sapphire substrate include a c-plane sapphire substrate, an m-plane sapphire substrate, and an a-plane sapphire substrate. Further, the sapphire substrate may have an off angle. The off angle is not particularly limited, but is preferably 0 ° to 15 °. The thickness of the crystal substrate is not particularly limited, but is preferably 50 to 2000 μm, and more preferably 200 to 800 μm.

In the present invention, it is preferable to form a concavo-convex portion composed of concave or convex portions on the substrate directly or via another layer, and then form the crystal film on the concavo-convex portion. .. The concavo-convex portion is not particularly limited as long as it is composed of a concave portion or a convex portion, and may be a concavo-convex portion composed of a concave portion or a concavo-convex portion composed of a convex portion. Further, the uneven portion may be formed from a regular concave portion or a convex portion, or may be formed from an irregular concave portion or a convex portion. In the present invention, it is preferable that the uneven portion is formed periodically, and it is more preferable that the uneven portion is periodically and regularly patterned. The shape of the uneven portion is not particularly limited, and examples thereof include a striped shape, a dot shape, a mesh shape, and a random shape. In the present invention, the dot shape or the striped shape is preferable. When the uneven portion is patterned periodically and regularly, the pattern shape of the uneven portion is a polygonal shape such as a triangle, a quadrangle (for example, a square, a rectangle or a trapezoid), a pentagon or a hexagon. The shape is preferably circular or elliptical. When forming the uneven portion in a dot shape, the lattice shape of the dots is preferably a lattice shape such as a square lattice, an orthorhombic lattice, a triangular lattice, or a hexagonal lattice, and the lattice shape of the triangular lattice is used. Is more preferable. The cross-sectional shape of the concave or convex portion of the uneven portion is not particularly limited, and is, for example, U-shaped, U-shaped, inverted U-shaped, corrugated, or triangular, quadrangular (for example, square, rectangular, trapezoidal, etc.). ), Polygons such as pentagons and hexagons, etc.

The constituent material of the convex portion is not particularly limited and may be a known material. It may be an insulator material, a conductor material, or a semiconductor material. Further, the constituent material may be amorphous, single crystal, or polycrystalline. Examples of the constituent material of the convex portion include oxides such as Si, Ge, Ti, Zr, Hf, Ta, Sn, nitrides or carbides, carbon, diamond, metal, and a mixture thereof. More specifically, _{a Si-containing compound containing SiO 2} , SiN or polycrystalline silicon as a main component, a metal having a melting point higher than the crystal growth temperature of the crystalline oxide (for example, platinum, gold, silver, palladium, etc.) Precious metals such as rhodium, iridium, and ruthenium) and the like. The content of the constituent material is preferably 50% or more, more preferably 70% or more, and most preferably 90% or more in the convex portion in terms of composition ratio.

The means for forming the convex portion may be a known means, for example, a known patterning processing means such as photolithography, electron beam lithography, laser patterning, and subsequent etching (for example, dry etching or wet etching). Can be mentioned. In the present invention, the convex portion is preferably striped or dot-shaped, and more preferably dot-shaped. Further, in the present invention, it is also preferable that the crystal substrate is a PSS (Patterned Sapphire Substate) substrate. The pattern shape of the PSS substrate is not particularly limited and may be a known pattern shape. Examples of the pattern shape include a cone shape, a bell shape, a dome shape, a hemispherical shape, a square or triangular pyramid shape, and the like, but in the present invention, the pattern shape is preferably a cone shape. The pitch interval of the pattern shape is also not particularly limited, but in the present invention, it is preferably 5 μm or less, and more preferably 1 μm to 3 μm.
Further, in the present invention, it is preferable to form the convex portion by forming a mask layer on the crystal substrate. The mask layer is suitably formed by forming a film of a constituent material of the mask layer by a known film forming means such as a vacuum vapor deposition method, a CVD method or a sputtering method, and then processing the mask layer by a known patterning means described above. be able to. Examples of the constituent material of the mask layer include materials exemplified as the constituent material of the convex portion. In the present invention, when a crystal film is produced using the mask layer, forming the polycrystal on at least the mask layer provides a thicker film and a larger area of the crystalline oxide layer. It is preferable because it can be used.

The concave portion is not particularly limited, but may be the same as the constituent material of the convex portion, or may be a substrate. In the present invention, it is preferable that the recess is a void layer provided on the surface of the substrate. As the means for forming the concave portion, the same means as the means for forming the convex portion can be used. The void layer can be formed on the surface of the substrate by providing a groove on the substrate by a known groove processing means. In the present invention, the void layer can be suitably formed by, for example, providing a mask layer by sputtering and then patterning using a known patterning processing means such as photolithography. The groove width, groove depth, terrace width, etc. of the void layer are not particularly limited and can be appropriately set as long as the object of the present invention is not impaired.

Hereinafter, preferred embodiments of the crystal substrate preferably used in the present invention will be described with reference to the drawings.
FIG. 2 shows one aspect of the uneven portion provided on the crystal growth surface of the crystal substrate in the present invention. The uneven portion of FIG. 2 is composed of the crystal substrate 1 and the mask layer 4. FIG. 3 shows the surface of the uneven portion shown in FIG. 2 as viewed from the zenith direction. As can be seen from FIGS. 2 and 3, the mask layer 4 is formed on the crystal growth surface of the crystal substrate 1 and has holes in a dot shape. The crystal substrate 1 is exposed from the dot holes of the mask layer 4, and the dot-shaped recesses 2b are formed in a triangular lattice shape. The circles of the dots are provided at regular intervals a. The period a is not particularly limited, but in the present invention, it is preferably 1 μm to 1 mm, and more preferably 5 μm to 300 μm. Here, the period a refers to the distance between the ends of circles of adjacent dots. The mask layer 4 can be formed by forming a film of the constituent material of the mask layer 4 and then processing it into a predetermined shape using a known means such as photolithography. Examples of the constituent material of the mask layer 4 include oxides such as Si, Ge, Ti, Zr, Hf, Ta, Sn, and Al, nitrides or carbides, carbon, diamond, metal, or a mixture thereof. Can be mentioned. Further, the film forming means of the mask layer 4 is not particularly limited, and may be a known means. Examples of the film forming means for the mask layer 4 include a vacuum vapor deposition method, a CVD method, a sputtering method, and the like.

FIG. 4 shows an aspect of the uneven portion provided on the crystal growth surface of the crystal substrate in the present invention. FIG. 4 The uneven portion is composed of the crystal substrate 1 and the mask layer 4. The mask layer is formed in stripes on the crystal growth surface of the crystal substrate 1, and the recesses (grooves) 2b are formed in stripes by the mask layer 4. The mask layer 4 can be formed by using a known means such as photolithography. Examples of the constituent material of the mask layer 4 include oxides such as Si, Ge, Ti, Zr, Hf, Ta, Sn, and Al, nitrides or carbides, carbon, diamond, metal, or a mixture thereof. Can be mentioned.

The width and height of the convex portion (mask layer) of the uneven portion, the width and depth of the concave portion, the interval, and the like are not particularly limited, but in the present invention, the width of the convex portion (mask layer) is about 1 μm to about 1 mm. It is preferably about 5 μm to about 300 μm, more preferably about 10 μm to about 100 μm. Further, in the present invention, the height of the convex portion (mask layer) is preferably about 1 nm to about 10 μm, more preferably about 5 nm to about 1 μm, and more preferably about 10 nm to about 100 nm. Is the most preferable. Further, in the present invention, the width of the recess is preferably about 1 μm to about 300 μm, more preferably about 3 μm to about 100 μm, and most preferably about 5 μm to about 50 μm. Further, in the present invention, the depth of the recess is preferably about 1 nm to about 1 mm, more preferably about 10 nm to about 300 μm, and most preferably about 20 nm to about 100 μm. By making the uneven portion such a preferable one, a better crystal film can be obtained more easily. The uneven portion may be formed directly on the crystal substrate, or may be provided via another layer.

The crystal growth means is not particularly limited and may be a known means. Examples of the crystal growth means include a CVD method, a MOCVD method, a MOVPE method, a mist CVD method, a mist epitaxy method, an MBE method, an HVPE method, a pulse growth method, an ALD method, a sputtering method and the like. In the present invention, the crystal growth means is preferably a mist CVD method, a mist epitaxy method or an HVPE method, and more preferably an HVPE method.

Hereinafter, the present invention will be described in more detail by taking as an example the case where the crystal film is formed by using the HVPE method as the crystal growth means. Specifically, in the HVPE method, for example, a metal source containing gallium is gasified and, if desired, reacted with HCl gas to obtain GaCl ₃ gas, and then GaCl ₃ gas and an oxygen-containing raw material gas are combined in a reaction chamber. When supplying to the crystal substrate to form a film, it is preferable to supply the reactive gas onto the crystal substrate and perform the film formation under the flow of the reactive gas.

(Metal source)
The metal source is not particularly limited as long as it contains gallium and can be gasified, and may be a simple substance of a metal or a metal compound. In the present invention, it is most preferable that the metal source is gallium alone. Further, the metal source may be a gas, a liquid, or a solid, but in the present invention, the metal source is preferably a liquid.

The gasification means is not particularly limited and may be a known means as long as the object of the present invention is not impaired. In the present invention, the gasification means is preferably carried out by halogenating the metal source. The halogenating agent used for the halogenation is not particularly limited as long as the metal source can be halogenated, and may be a known halogenating agent. Examples of the halogenating agent include halogens and hydrogen halides. Examples of the halogen include fluorine, chlorine, bromine, iodine and the like. Examples of hydrogen halide include hydrogen fluoride, hydrogen chloride, hydrogen bromide, hydrogen iodide and the like. In the present invention, hydrogen halide is preferably used for the halogenation, and hydrogen chloride is more preferably used. In the present invention, the gasification is carried out by supplying halogen or hydrogen halide as a halogenating agent to the metal source and reacting the metal source with halogen or hydrogen halide at a temperature equal to or higher than the vaporization temperature of the metal halide. It is preferable to carry out the process by forming a metal halogenated gas. The halogenation reaction temperature is not particularly limited, but in the present invention, for example, when the metal source is gallium and the halogenating agent is HCl, the halogenation reaction temperature is preferably 900 ° C. or lower, preferably 700 ° C. or lower. More preferably, it is most preferably 400 ° C. to 700 ° C. The metal halide gas is not particularly limited as long as it is a gas containing a halide of gallium as the metal source. Examples of the metal halide gas include halides of gallium (fluoride, chloride, bromide, iodide, etc.).

In the present invention, the metal source containing gallium is gasified to obtain GaCl ₃ gas, and then the GaCl ₃ gas and the oxygen-containing raw material gas are supplied onto the substrate in the reaction chamber. In the present invention, the metal source containing gallium to those gasified may be a GaCl ₃ gas, for example, the GaCl gas e.g. reacted with HCl gas before feeding onto the substrate GaCl ₃ gas May be supplied on the substrate. Further, in the present invention, it is preferable to supply the reactive gas onto the substrate. The formation temperature of the crystal film is not particularly limited, but in the present invention, for example, when the metal source is gallium and the halogenating agent is HCl, the temperature is preferably 900 ° C. or lower, preferably 700 ° C. or lower. Is more preferable, and the temperature is most preferably 400 ° C. to 700 ° C. The oxygen-containing raw material gas may be, for example, one or more gases selected from _{O 2} gas, CO ₂ gas, NO gas, NO ₂ gas, N ₂ O gas, H ₂ O gas or O _{3 gas.} be. In the present invention, the oxygen-containing feed gas, O _{2, H} and even preferably one or more kinds of gas selected from 2 _O and N _{2 O} consisting of the group, and more preferably comprises an O ₂ .. The reactive gas is usually a reactive gas different from the metal halide gas and the oxygen-containing raw material gas, and does not include an inert gas. The reactive gas is not particularly limited, and examples thereof include an etching gas and the like. The etching gas is not particularly limited and may be a known etching gas as long as the object of the present invention is not impaired. In the present invention, the reactive gas is a halogen gas (for example, fluorine gas, chlorine gas, bromine gas, iodine gas, etc.), hydrogen halide gas (for example, hydrofluoric acid gas, hydrochloric acid gas, hydrogen bromide gas, or hydrogen bromide gas). (Hydrogen gas, etc.), hydrogen gas, or a mixed gas of two or more of these, and the like, preferably containing hydrogen halide gas, and most preferably containing hydrogen chloride. The metal halide gas, the oxygen-containing raw material gas, and the reactive gas may contain a carrier gas. Examples of the carrier gas include an inert gas such as nitrogen and argon. The partial pressure of the metal halide gas is not particularly limited, but in the present invention, the partial pressure is usually 1 kPa or more. The partial pressure of the oxygen-containing raw material gas is not particularly limited, but in the present invention, it is preferably 0.5 to 100 times the partial pressure of the metal halide gas, and 1 to 20 times the partial pressure. Is more preferable. The partial pressure of the reactive gas is also not particularly limited, but in the present invention, it is preferably 0.1 to 5 times, preferably 0.2 to 3 times, the partial pressure of the metal halide gas. Is more preferable.

In the present invention, it is also preferable to supply the dopant-containing raw material gas to the substrate. The dopant-containing raw material gas is not particularly limited as long as it contains a dopant. The dopant is also not particularly limited, but in the present invention, the dopant preferably contains one or more elements selected from germanium, silicon, titanium, zirconium, vanadium, niobium and tin, preferably germanium. It is more preferably containing silicon or tin, and most preferably it contains germanium. By using the dopant-containing raw material gas in this way, the conductivity of the obtained film can be easily controlled. The dopant-containing raw material gas preferably has the dopant in the form of a compound (for example, a halide, an oxide, etc.), and more preferably in the form of a halide. The partial pressure of the dopant-containing raw material gas is not particularly limited, but in the present invention, it is preferably 1 × 10 ^-7 times to 0.1 times the partial pressure of the metal-containing raw material gas, and is 2.5 ×. and more preferably 10 ^-6 times to 7.5 × ^{10 -2} times. In the present invention, it is preferable to supply the dopant-containing raw material gas together with the reactive gas onto the substrate.

(Crystal film)
The crystal film is a crystal film containing a crystalline metal oxide containing gallium as a main component, and is characterized by having a Si content of 2 × 10 ¹⁵ cm ^-3 or less. In the present invention, it is preferable that the crystal film contains a single crystal of the crystalline metal oxide as a main component. Further, in the present invention, the crystalline oxide may be a semiconductor. In the present invention, it is _{most preferable that the crystalline metal oxide is Ga 2} O ₃ or a mixed crystal thereof. The crystal structure of the crystalline metal oxide is not particularly limited. The crystal structure of the crystalline oxide includes, for example, a corundum structure, a β-gallia structure, a hexagonal structure (for example, ε-type structure, etc.), a rectangular structure (for example, a κ-type structure, etc.), a cubic structure, or a tetragonal structure. A crystal structure and the like can be mentioned. In the present invention, the crystalline oxide preferably has a corundum structure, a β-Galia structure or a hexagonal crystal (for example, an ε-type structure), and more preferably has a corundum structure. The "main component" contains the crystalline oxide in an atomic ratio of preferably 50% or more, more preferably 70% or more, still more preferably 90% or more with respect to all the components of the crystal film. It means that it may be 100%. The thickness of the crystal film is not particularly limited, but is preferably 10 μm or more, more preferably 25 μm or more, and most preferably 50 μm or more. The surface area of the crystal film is not particularly limited ^{, but is preferably 10 cm 2} or more, and more preferably 20 cm ² or more.

The crystal film may contain a dopant. The dopant is not particularly limited and may be a known one, and may be an n-type dopant or a p-type dopant. Examples of the n-type dopant include tin, germanium, silicon, titanium, zirconium, vanadium, niobium, two or more elements thereof, and the like. Examples of the p-type dopant include Mg, H, Li, Na, K, Rb, Cs, Fr, Be, Ca, Sr, Ba, Ra, Mn, Fe, Co, Ni, Pd, Cu, Ag and Au. , Zn, Cd, Hg, Ti, Pb, N, P or two or more of these elements. The content of the dopant is also not particularly limited, but is preferably 0.00001 atomic% or more, more preferably 0.00001 atomic% to 20 atomic%, and 0.00001 atomic% in the crystal film. Most preferably, it is 10 atomic%.

The crystal film can be particularly preferably used for semiconductor devices, and is particularly useful for power devices. Semiconductor devices formed using the crystal film include transistors and TFTs such as MIS, HEMT, and MOS, Schottky barrier diodes using semiconductor-metal junctions, PN or PIN diodes combined with other P layers, and receivers. A light emitting element can be mentioned. In the present invention, the crystal film may be used as it is in a semiconductor device or the like together with the substrate, or may be applied to a semiconductor device or the like after using a known means such as peeling from the substrate or the like.

In addition to the above items, the semiconductor device is suitably used as a power module, an inverter or a converter by using known means, and these semiconductor devices are also included in the present invention. Further, the semiconductor device is further preferably used for, for example, a semiconductor system using a power supply device. The power supply device can be manufactured from the semiconductor device or as the semiconductor device by connecting to a wiring pattern or the like using a known means. FIG. 9 shows an example of a power supply system. In FIG. 9, a power supply system is configured by using the plurality of power supply devices and control circuits. As shown in FIG. 10, the power supply system can be used in a system device in combination with an electronic circuit. An example of the power supply circuit diagram of the power supply device is shown in FIG. FIG. 11 shows a power supply circuit of a power supply device including a power circuit and a control circuit. A DC voltage is switched at a high frequency by an inverter (MOSFET: composed of A to D), converted to AC, and then insulated and transformed by a transformer. This is performed, rectified by a rectifying MOSFET (A to B'), smoothed by a DCL (smoothing coils L1 and L2) and a capacitor, and a DC voltage is output. At this time, the output voltage is compared with the reference voltage by the voltage comparator, and the inverter and the rectifying MOSFET are controlled by the PWM control circuit so as to obtain the desired output voltage.

Hereinafter, examples of the present invention will be described, but the present invention is not limited thereto.

(Example 1)
1. 1. Formation of ELO mask A sapphire substrate (c-plane, off-angle 0.25 °) having an _{α-Ga 2} O ₃ layer formed on its surface is used as a substrate, and a mask made of _{SiO 2 is used on the substrate by a sputtering method.} A layer was formed, and then the formed mask layer was processed into a mask having a predetermined shape by using a photolithography method. Specifically, the mask layer was processed so that the openings (dots) (diameter: 5 μm) were arranged on the substrate in a triangular lattice pattern with a period (distance between the ends of adjacent dots) of 5 μm.

2. Formation of crystal film 2-1. HVPE device The halide vapor deposition (HVPE) device 50 used in this embodiment will be described with reference to FIG. The HVPE apparatus 50 includes a reaction chamber 51, a heater 52a for heating the metal source 57, and a heater 52b for heating the substrate fixed to the substrate holder 56, and further supplies an oxygen-containing raw material gas into the reaction chamber 51. It includes a pipe 55b, a reactive gas supply pipe 54b, and a board holder 56 on which a board is installed. A metal-containing raw material gas (metal halide gas) supply pipe 53b is provided in the reactive gas supply pipe 54b to form a double pipe structure. The oxygen-containing raw material gas supply pipe 55b is connected to the oxygen-containing raw material gas supply source 55a, and the oxygen-containing raw material gas is transferred from the oxygen-containing raw material gas supply source 55a via the oxygen-containing raw material gas supply pipe 55b to the substrate holder. The flow path of the oxygen-containing raw material gas is configured so that it can be supplied to the substrate fixed to 56. Further, the reactive gas supply pipe 54b is connected to the reactive gas supply source 54a, and the reactive gas is fixed to the substrate holder 56 from the reactive gas supply source 54a via the reactive gas supply pipe 54b. The flow path of the reactive gas is configured so that it can be supplied to the substrate. The metal-containing raw material gas supply pipe 53b is connected to the halogen-containing raw material gas supply source 53a, and the halogen-containing raw material gas is supplied to the metal source to become the metal-containing raw material gas, and the metal-containing raw material gas is fixed to the substrate holder 56. It is supplied to the substrate. The reaction chamber 51 is provided with a gas discharge unit 59 for exhausting used gas, and further, a protective sheet 58 for preventing precipitation of reactants is provided on the inner wall of the reaction chamber 51.

2-2. Preparation for film formation A gallium (Ga) metal source 57 (purity 99.99999% or more) is arranged inside the metal-containing raw material gas supply pipe 53b, and the above 1. The sapphire substrate with the mask layer obtained in the above was installed. After that, the heaters 52a and 52b were operated to raise the temperature in the reaction chamber 51 to 570 ° C (near the Ga metal source) and 520 ° C (near the substrate holder).

2-3. Hydrogen chloride (HCl) gas (purity 99.999% or more) was supplied from the halogen-containing raw material gas supply source 53a to the gallium (Ga) metal 57 arranged inside the film-forming metal raw material-containing gas supply pipe 53b. _{Gallium chloride (GaCl / GaCl 3} ) was produced by a chemical reaction between a Ga metal and hydrogen chloride (HCl) gas. The obtained gallium chloride (GaCl / GaCl _{3 ) and O 2} gas (purity 99.99995% or more) supplied from the oxygen-containing raw material gas supply source 55a are supplied onto the substrate through the reactive gas supply pipe 54b. bottom. Then, under the flow of HCl gas, gallium chloride (GaCl / GaCl ₃ ) and O ₂ gas were reacted on the substrate at atmospheric pressure at 520 ° C. to form a film on the substrate. Here, the flow rate of the HCl gas supplied from the halogen-containing raw material gas supply source 53a is 1 kPa, the flow rate of the HCl gas supplied from the reactive gas supply source 54a is 1 kPa, and the flow rate of the HCl gas supplied from the oxygen-containing raw material gas supply source 55a is O. _{The flow rates of the two} gases were maintained at 2.5 kPa, respectively.

2-4. Evaluation 2-3. The crystal film obtained in 1) was observed by SEM. The results are shown in FIG. A photograph of the obtained crystal film is shown in FIG. In addition, SIMS measurement was performed on the obtained crystal film. The measurement results are shown in Table 1. As is clear from Table 1, the content of Si and the like in the example product was lower than the detection limit value as compared with the comparative example product.

(Comparative Example 1)
A crystal film was prepared in the same manner as in Example 1 except that the conditions shown in Table 2 were met. The obtained crystal film was observed by SEM. The results are shown in FIG.

(Comparative Example 2)
A crystal film was prepared in the same manner as in Example 1 except that the conditions shown in Table 2 were met. The obtained crystal film was observed by SEM. The results are shown in FIG.

The crystal film of the present invention can be used in all fields such as semiconductors (for example, compound semiconductor electronic devices, etc.), electronic parts / electrical equipment parts, optical / electrophotographic-related devices, industrial parts, etc., but is particularly useful for semiconductor devices and the like. Is.

a period 1 substrate (crystal substrate)
1a Substrate surface 2b Recess 4 Mask layer 50 Halide vapor growth (HVPE) device 51 Reaction chamber 52a Heater 52b Heater 53a Halogen-containing raw material gas supply source 53b Metal-containing raw material gas (metal halide gas) supply pipe 54a Reactive gas supply Source 54b Reactive gas supply pipe 55a Oxygen-containing raw material gas supply source 55b Oxygen-containing raw material gas supply pipe 56 Substrate holder 57 Metal source 58 Protective sheet 59 Gas discharge part

Claims (10)

A crystal film containing a crystalline metal oxide containing gallium as a main component, wherein the Si content is 2 × 10 ¹⁵ cm ^-3 or less. The crystal film according to claim 1, wherein the crystalline metal oxide has a corundum structure. The crystal film according to claim 1 or 2, wherein the C content is 5 × 10 ¹⁶ cm ^{-3 or less.} The crystal film according to any one of claims 1 to 3, wherein the film thickness is 10 μm or more. The crystal film according to any one of claims 1 to 4, wherein the film thickness is 25 μm or more. The crystal film according to any one of claims 1 to 5, which has a surface area of 10 cm ^{2 or more.} The crystal film according to any one of claims 1 to 6, wherein the crystal film is a semiconductor film. A semiconductor device including a crystal film, wherein the crystal film is the crystal film according to any one of claims 1 to 7. The semiconductor device according to claim 8, which is a power device. A semiconductor system including a semiconductor device, wherein the semiconductor device is the semiconductor device according to claim 8 or 9.

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