WO2020261574A1 - Semiconductor film - Google Patents

Abstract

The present invention provides an α-Ga₂O₃ semiconductor film which is capable of making the device characteristics uniform. This α-Ga₂O₃ semiconductor film has, as the main phase, a crystal having a corundum crystal structure that is composed of α-Ga₂O₃ or an α-Ga₂O₃-based solid solution. This semiconductor film has a circular shape that has a diameter of 5.08 cm (2 inches) or more, and if an X-ray diffraction (XRD) ϕ scanning measurement is performed with respect to the (104) plane of the crystal on the center point X of the surface and four points A, B, C and D on the outer periphery of the semiconductor film, the ratio of the peak intensity of a sub peak assigned to a rotation domain to the peak intensity of the main peak is 1.00% or less. The points A, B, C and D on the outer periphery are determined so that (i) the straight line connecting the points A and C on the outer periphery and the straight line connecting the points B and D on the outer periphery are at right angles to each other at the center point X, and (ii) the respective shortest distances of the points A, B, C and D on the outer periphery from the outer edge of the semiconductor film is 1/5 of the radium of the semiconductor film.

Description

Semiconductor film

The present invention relates to an α-Ga ₂ O ₃ system semiconductor film.

In recent years, gallium oxide (Ga ₂ O ₃ ) has been attracting attention as a material for semiconductors. Gallium oxide is known to have five crystal forms of α, β, γ, δ and ε. Among them, α-Ga ₂ O ₃ which is a semi-stable phase has a band gap of 5.3 eV. It is very large and is expected as a material for power semiconductors.

For example, Patent Document 1 (Japanese Unexamined Patent Publication No. 2014-72533) describes a semiconductor provided with a base substrate having a corundum-type crystal structure, a semiconductor layer having a corundum-type crystal structure, and an insulating film having a corundum-type crystal structure. The apparatus is disclosed, and an example in which an α-Ga ₂ O ₃ film is formed as a semiconductor layer on a sapphire substrate is described. Further, Patent Document 2 (Japanese Unexamined Patent Publication No. 2016-25256) contains an n-type semiconductor layer containing a crystalline oxide semiconductor having a corundum structure as a main component and an inorganic compound having a hexagonal crystal structure as a main component. A semiconductor device including a p-type semiconductor layer and an electrode is disclosed. The examples of Patent Document 2, on a c-plane sapphire substrate, the alpha-Ga ₂ O ₃ film having a corundum structure metastable phase as an n-type semiconductor layer, hexagonal as p-type semiconductor layer crystal structure It is disclosed that a diode is produced by forming an α-Rh ₂ O ₃ film having.

By the way, the α-Ga ₂ O ₃ film has a corundum-type crystal structure, and while the c-plane of the corundum-type crystal structure is three-fold symmetric, the rotation domain rotated by 60 ° with the c-axis as the rotation axis is partially. There is a problem that it occurs in the device and deteriorates the device characteristics. In this regard, a method for producing a film having a low content of rotating domains by introducing a buffer layer has been proposed. For example, in Patent Document 3 (Japanese Unexamined Patent Publication No. 2016-156073), a first layer containing an oxide having a corundum structure as a main component and a second layer containing an oxide containing aluminum as a main component are provided. Quantum well structures stacked alternately are disclosed, and it is described that such quantum well structures are useful as a buffer layer capable of reducing rotational domains and warpage. Further, in Patent Document 4 (Japanese Unexamined Patent Publication No. 2016-157878), a crystalline oxide semiconductor film containing an oxide semiconductor having a corundum structure as a main component and having a rotation domain content of 0.02% by volume or less. Is disclosed, and it is also described that a quantum well structure having the same configuration as that of Patent Document 3 is used as a buffer layer.

Japanese Unexamined Patent Publication No. 2014-72533 Japanese Unexamined Patent Publication No. 2016-25256 Japanese Unexamined Patent Publication No. 2016-156073 Japanese Unexamined Patent Publication No. 2016-157878

However, in the prior art as disclosed in Patent Documents 3 and 4, when an α-Ga ₂ O ₃ film is formed using a large-diameter substrate having a diameter of 5.08 cm (2 inches) or more, the central portion of the film is formed. It has been difficult to form an α-Ga ₂ O ₃ system semiconductor film that substantially does not contain a rotation domain over a wide range from to the outer peripheral portion.

The present inventors have now can form a substantially α-Ga ₂ O ₃ based semiconductor film that does not contain rotational domain over a wide range from the center of the film up to the outer peripheral portion, whereby alpha-Ga knowledge was obtained with characteristics of devices fabricated can be made uniform to using ₂ O ₃ based semiconductor film.

Therefore, an object of the present invention is to provide an α-Ga ₂ O ₃ system semiconductor film capable of making device characteristics uniform.

According to one aspect of the present invention, a semiconductor film as a main phase crystals having alpha-Ga 2 _{O 3,} or alpha-Ga ₂ O corundum type crystal structure composed of _three solid solution,
The semiconductor film has a circular shape with a diameter of 5.08 cm (2 inches) or more.
When X-ray diffraction (XRD) φ scan measurement is performed on the (104) plane of the crystal at each of the center point X and the four outer peripheral points A, B, C and D of the surface of the semiconductor film, The ratio of the peak intensity of the sub-peak due to the rotation domain to the peak intensity of the main peak is 1.00% or less.
The outer peripheral points A, B, C and D are i) The straight line connecting the outer peripheral point A and the outer peripheral point C and the straight line connecting the outer peripheral point B and the outer peripheral point D intersect at a right angle at the center point X. And ii) Provided is a semiconductor film in which the shortest distances of the outer peripheral points A, B, C and D from the outer edge of the semiconductor film are determined to be 1/5 of the radius of the semiconductor film.

According to another aspect of the present invention, there is provided a composite material comprising a circular support substrate having a diameter of 5.08 cm (φ2 inch) or more and the semiconductor film formed on the support substrate. Will be done.

It is a figure for demonstrating the position of the center point X and four outer peripheral points A, B, C and D on the surface of the semiconductor film of this invention. It is a schematic cross-sectional view which shows the structure of the mist CVD (chemical vapor deposition) apparatus. It is a schematic cross-sectional view which shows the structure of an aerosol deposition (AD) apparatus. It is a schematic cross-sectional view which shows the layer structure of the Schottky barrier diode produced in Examples 1-9.

Semiconductor film The semiconductor film according to the present invention has a crystal having a corundum-type crystal structure as a main phase, and this corundum-type crystal structure is composed of an α-Ga ₂ O ₃ or an α-Ga ₂ O ₃ system solid solution. To. Therefore, the semiconductor film according to the present invention can be referred to as an α-Ga ₂ O ₃ system semiconductor film. This semiconductor film has a circular shape with a diameter of 5.08 cm (2 inches) or more. Then, when X-ray diffraction (XRD) φ scan measurement is performed on the (104) plane of the crystal at each of the center point X and the four outer peripheral points A, B, C and D of the surface of the semiconductor film, The ratio of the peak intensity of the sub-peak due to the rotation domain to the peak intensity of the main peak is 1.00% or less. Like the semiconductor film 10 shown in FIG. 1, the outer peripheral points A, B, C and D are centered on i) a straight line connecting the outer peripheral points A and the outer peripheral point C and a straight line connecting the outer peripheral points B and the outer peripheral point D. It is determined so that the points X intersect at right angles and ii) the shortest distances of the outer peripheral points A, B, C and D from the outer edge of the semiconductor film are 1/5 of the radius of the semiconductor film. Thus α-Ga ₂ O ₃ based semiconductor film is the ratio of the peak intensity of the secondary peak due to the rotation domains 1.00% or less in five points well away from each other, the outer peripheral portion from the central portion of the film It can be said that the rotation domain is substantially not contained (the content of the rotation domain is extremely low) over a wide range, and the characteristics of the device manufactured by using such a semiconductor film can be made uniform. “Homogeneous device characteristics” means that even when a plurality of devices are manufactured from different parts of the same semiconductor film, there is little variation in device characteristics among the plurality of devices obtained (device homogenization). It means that it has been done). As described above, in the prior art, when an α-Ga ₂ O ₃ film is formed using a large-diameter substrate having a diameter of 5.08 cm (2 inches) or more, the film extends from the central portion to the outer peripheral portion. It has been difficult to form an α-Ga ₂ O ₃ system semiconductor film that substantially does not contain a rotation domain over a wide range, but according to the present invention, such a problem can be solved and the characteristics of the device can be made uniform. It is possible to provide an α-Ga ₂ O ₃ system semiconductor film that substantially does not contain a rotating domain over a wide range.

As described above, the semiconductor film of the present invention has a crystal having a corundum-type crystal structure as a main phase. In the present specification, "having a crystal having a corundum-type crystal structure as a main phase" means that the crystal having a corundum-type crystal structure is 80% by weight or more, preferably 90% by weight or more, and more preferably 95% by weight of the semiconductor film. As described above, it means that it occupies 97% by weight or more, particularly preferably 99% by weight or more, and most preferably 100% by weight. This corundum-type crystal structure is composed of α-Ga ₂ O ₃ or α-Ga ₂ O ₃ system solid solution. α-Ga ₂ O ₃ belongs to a trigonal crystal group, has a corundum-type crystal structure, and its c-plane is three-fold symmetric. Further, the α-Ga ₂ O ₃ system solid solution is a solid solution of other components in α-Ga ₂ O ₃ , and the corundum type crystal structure is maintained. For example, the semiconductor film of the present invention contains α-Ga ₂ O ₃ , Cr ₂ O ₃ , Fe ₂ O ₃ , Ti ₂ O ₃ , V ₂ O ₃ , Ir ₂ O ₃ , Rh ₂ O ₃ , and In ₂ O. It can be composed of an α-Ga ₂ O ₃ system solid solution in which one or more components selected from the group consisting of ₃ and Al ₂ O ₃ are solid-dissolved. All of these components have a corundum-type crystal structure and have relatively close lattice constants to each other. Therefore, the metal atoms of these components easily replace Ga atoms in the solid solution. Further, by dissolving these components in solid solution, it becomes possible to control the band gap, electrical characteristics, and / or lattice constant of the semiconductor film. The solid solution amount of these components can be appropriately changed according to the desired characteristics.

The semiconductor film of the present invention has a circular shape having a diameter of 5.08 cm (2 inches) or more, and may have a size of 10.0 cm or more. The upper limit of the size of the semiconductor film is not particularly limited, but is typically 30.0 cm or less in diameter, and more typically 20.0 cm or less in diameter. In the present specification, the "circular shape" does not have to be a perfect circular shape, and may be a substantially circular shape that can be generally recognized as a circular shape. For example, a part of the circle may be cut out for the purpose of specifying the crystal orientation or for other purposes.

The semiconductor film of the present invention was subjected to X-ray diffraction (XRD) φ scan measurement on the (104) plane of the crystal at each of the center point X and the four outer peripheral points A, B, C and D of the surface thereof. In some cases, the ratio of the peak intensity of the sub-peak due to the rotation domain to the peak intensity of the main peak is 1.00% or less, preferably 0.50% or less, and more preferably 0.10% or less. From the viewpoint of homogenizing the device characteristics, the smaller the number of rotation domains, the better. Therefore, the lower limit of the ratio of the peak intensity of the sub-peak due to the rotation domain is not particularly limited, and is ideally 0%.

In the semiconductor film of the present invention, the ratio of the peak intensity of the sub-peak due to the rotation domain to the peak intensity of the main peak measured at the center point X is _IX %, and the outer peripheral points A, B, C and D in to the peak intensity of the measured main peak, the arithmetic mean value of the ratio of the peak intensity of the secondary peak due to the rotation domain when the I _M%, | a relationship ≦ 0.20 _| I X _-I M it is preferable to satisfy, more preferably _{| I X -I M | ≦ 0.10} , more preferably _| satisfies the relationship of ≦ 0.05, and most preferably _{| | I X -I M I X} -I M | = Satisfy the relationship of 0. Since these relationships mean that the difference in the content of the rotating domain is small between the central portion and the outer peripheral portion of the semiconductor film, it is possible to more effectively achieve uniform device characteristics.

From the viewpoint of homogenizing the device characteristics, the semiconductor film of the present invention preferably has an arithmetic mean value of the film thickness measured at the center point X and the outer peripheral points A, B, C and D of 2.0 μm or more. It is more preferably 3.0 μm or more, still more preferably 5.0 μm or more. When the film thickness is large as described above, it is possible to avoid deterioration of the device characteristics due to the occurrence of cracks during device fabrication, and it is possible to more effectively achieve uniform device characteristics. Conventionally, when trying to increase the film thickness, a rotation domain is particularly likely to occur, and it is difficult to achieve both an increase in the film thickness and a decrease in the rotation domain. However, the semiconductor film of the present invention has such a problem. The film thickness can be increased. The upper limit of the film thickness is not particularly limited and may be appropriately adjusted from the viewpoint of cost and required characteristics, but is, for example, 50 μm or less, 20 μm or less, or 10 μm or less. When a self-supporting semiconductor film is required, a thick film may be used. From this point of view, it is, for example, 50 μm or more, or 100 μm or more, and there is no particular upper limit unless there is a cost limitation.

The semiconductor film of the present invention preferably has a volume resistivity of 0.10 Ω · cm or less, more preferably 0.0001 to 0, as measured at the center point X and the outer peripheral points A, B, C and D. It is .10 Ω · cm, more preferably 0.0005 to 0.05 Ω · cm, and particularly preferably 0.001 to 0.03 Ω · cm. As described above, the low volume resistivity over a wide range from the central portion to the outer peripheral portion of the film makes it possible to more effectively achieve uniform device characteristics. Conventionally, when trying to reduce the volume resistivity, a rotational domain is particularly likely to occur, and it has been difficult to achieve both a decrease in the volume resistivity and a reduction in the rotational domain. However, the semiconductor film of the present invention solves such a problem. The volume resistivity can be lowered without accompanying.

In the semiconductor film of the present invention, the maximum value R _max and the minimum value R _{min of} the volume resistivity measured at the center point X and the outer peripheral points A, B, C and D are set to [(R _max −R _min ) / R _max. ] ≤ 0.20, more preferably [(R _max −R _min ) / R _max ] ≦ 0.10, and even more preferably [(R _max −R _min ) / R _max ] ≦ 0. 0.05, ideally satisfying the relationship [(R _max −R _min ) / R _max ] = 0. As described above, since the variation in volume resistivity is small over a wide range from the central portion to the outer peripheral portion of the film, it is possible to more effectively achieve uniform device characteristics.

The semiconductor film of the present invention can contain a Group 14 element as a dopant. Here, the Group 14 element is the Group 14 element according to the periodic table formulated by the IUPAC (International Union of Pure and Applied Chemistry). Specifically, carbon (C), silicon (Si), and germanium (Ge). ), Tin (Sn) and lead (Pb). The content of the dopant (Group 14 element) in the semiconductor film is preferably 1.0 × 10 ¹⁶ to 1.0 × 10 ²¹ / cm ³ , more preferably 1.0 × 10 ¹⁷ to 1.0 × 10 ¹⁹ /. It is cm ³ . It is preferable that these dopants are uniformly distributed in the film and the dopant concentrations on the front surface and the back surface of the semiconductor film are about the same. Conventionally, when a dopant is added, a rotational domain is particularly likely to be generated, and it is difficult to achieve both the addition of the dopant and the reduction of the rotational domain. However, according to the semiconductor film of the present invention, the dopant is added without such a problem. can do.

The semiconductor film of the present invention may be in the form of a self-supporting film of the film alone, or may be formed on a support substrate. In the latter case, the semiconductor film of the present invention is preferably formed on a circular support substrate having a diameter of 5.08 cm (2 inches) or more. That is, according to a preferred embodiment of the present invention, there is provided a composite material including a circular support substrate having a diameter of 5.08 cm (2 inches) or more and a semiconductor film formed on the support substrate. .. The size of the support substrate may be 10.0 cm or more, like the size of the semiconductor film, and the upper limit is not particularly limited, but is typically 30.0 cm or less in diameter, and more typically 20 in diameter. It is 0.0 cm or less.

The support substrate preferably has a corundum structure and is oriented in two axes of the c-axis and the a-axis (biaxially oriented substrate). By using a biaxially oriented substrate having a corundum structure as the support substrate, it is possible to serve as a seed crystal for heteroepitaxial growth of the semiconductor film. The biaxially oriented substrate may be a polycrystal or a mosaic crystal (a set of crystals whose crystal orientations are slightly deviated), or may be a single crystal such as sapphire or Cr ₂ O ₃ . As long as it has a corundum structure, it may be composed of a single material or a solid solution of a plurality of materials. The main components of the support substrate are α-Cr ₂ O ₃ , α-Fe ₂ O ₃ , α-Ti ₂ O ₃ , α-V ₂ O ₃ , α-Rh ₂ O ₃ , and α-Al ₂ O _3. Materials selected from the group consisting of α-Al ₂ O ₃ , α-Cr ₂ O ₃ , α-Fe ₂ O ₃ , α-Ti ₂ O ₃ , α-V ₂ O ₃ , and α-Rh ₂ O. A solid solution containing two or more selected from the group consisting of ₃ is preferable. Among them, sapphire (α-Al ₂ O ₃ single crystal) is particularly preferable in that it has excellent thermal conductivity and a large-area and high-quality substrate is easily available commercially, and α-Cr ₂ is particularly preferable from the viewpoint of reducing crystal defects. O _3, or a solid solution of _α-Cr 2 _{O 3} and heterogeneous materials are especially preferred.

Further, as a seed crystal for the support substrate and heteroepitaxial growth, sapphire, on corundum single crystal such as Cr ₂ O _3, a material having a corundum type crystal structure having a-axis length and / or c-axis length larger than the sapphire A composite base substrate on which the configured alignment layer is formed can also be used. The alignment layer is a material selected from the group consisting of α-Cr ₂ O ₃ , α-Fe ₂ O ₃ , α-Ti ₂ O ₃ , α-V ₂ O ₃ , and α-Rh ₂ O ₃ , or α. -Al ₂ O ₃ , α-Cr ₂ O ₃ , α-Fe ₂ O ₃ , α-Ti ₂ O ₃ , α-V ₂ O ₃ , and α-Rh ₂ O ₃ selected from the group. Includes a solid solution containing the above.

Alternatively, the semiconductor film formed on the film-forming substrate may be separated and reprinted on another support substrate. The material of the other support substrate is not particularly limited, but a suitable material may be selected from the viewpoint of material physical characteristics. For example, from the viewpoint of thermal conductivity, a metal substrate such as Cu, a ceramic substrate such as SiC or AlN, or the like is preferable. It is also preferable to use a substrate having a coefficient of thermal expansion of 6 to 13 ppm / K at 25 to 400 ° C. By using a support substrate having such a coefficient of thermal expansion, the difference in thermal expansion from the semiconductor film can be reduced, and as a result, cracks and peeling of the semiconductor film due to thermal stress can be suppressed. An example of such a support substrate is a substrate made of a Cu—Mo composite metal. The composite ratio of Cu and Mo can be appropriately selected in consideration of the coefficient of thermal expansion matching with the semiconductor film, the thermal conductivity, the conductivity and the like.

Semiconductor film manufacturing method of the present invention the semiconductor film, using a sapphire substrate or a composite base substrate as a base substrate, forming a α-Ga ₂ O ₃ based material thereon (alignment layer in the case of a composite base substrate) It can be manufactured by doing so. Known methods are possible for forming the semiconductor layer, but preferred examples are the mist CVD method (mist chemical vapor deposition method), the HVPE method (halide vapor deposition method), and the MBE method (molecular beam epitaxy method). ), And the mist CVD method or the HVPE method is particularly preferable. Α-Ga ₂ O ₃ based semiconductor film containing no rotating domain substantially over a wide range up to the outer peripheral portion from the central portion of the film, or the film is formed while rotating the sapphire substrate, or a composite base substrate It can be realized by this.

That is, when a sapphire substrate is used as the substrate, the film is formed while rotating the substrate 36 in the in-plane direction as in the apparatus shown in FIG. 2 described later. At this time, by setting appropriate conditions, it is possible to prevent the rotation domain from being included even with a larger substrate size and film thickness. By rotating the substrate to generate centrifugal force, the airflow in the vicinity of the substrate 36 can be conveniently controlled so as to bring about membrane uniformity.

On the other hand, when a composite substrate is used as the substrate, it is not always necessary to rotate the substrate to form a film, but it may be rotated. In any case, by setting appropriate rotation conditions and / or film formation conditions, it is possible to prevent the rotation domain from being included even with a larger substrate size, a thick film thickness, or a low resistivity.

Hereinafter, the mist CVD method, which is one of the particularly preferable film forming methods, will be described.

In the mist CVD method, the raw material solution is atomized or dropletized to generate mist or droplets, and the mist or droplet is conveyed to a film forming chamber equipped with a substrate using a carrier gas, and the mist or droplet is transferred in the film forming chamber. It is a method of forming and growing a film on a substrate by thermally decomposing and chemically reacting droplets, and it is possible to prepare a large amount of samples in a short time without requiring a vacuum process. FIG. 2 shows an example of a mist CVD apparatus. The mist CVD apparatus 20 shown in FIG. 2 forms a semiconductor film 38 through a mist generation chamber 22 that generates mist M from a carrier gas G and a raw material solution L, and a mist M that is sprayed onto a substrate 36 through thermal decomposition and a chemical reaction. It has a film forming chamber 30 to be formed. The mist generation chamber 22 contains a carrier gas introduction port 24 into which the carrier gas G is introduced, an ultrasonic vibrator 26 provided in the mist generation chamber 22, and a mist M generated in the mist generation chamber 22 in a film forming chamber 30. It is provided with a duct 28 for transporting to. The raw material solution L is housed in the mist generation chamber 22. The ultrasonic vibrator 26 is configured to be able to generate mist M together with the carrier gas G by applying ultrasonic vibration to the raw material solution L. The film forming chamber 30 is provided with a nozzle 32 for spraying the mist M introduced through the duct 28 onto the substrate 36, a rotary stage 34 to which the substrate 36 is fixed, and a rotary stage near the back surface of the rotary stage 34. A heater 42 for heating the 34 and the substrate 36, and an exhaust port 44 for discharging the carrier gas G are provided. The rotary stage 34 is configured to be rotatable in the in-plane direction when the mist M is sprayed onto the substrate 36. By forming the semiconductor film 38 while rotating the substrate 36 with such a configuration, even when the semiconductor film 38 is formed using a large-diameter substrate having a diameter of 5.08 cm (2 inches) or more, the semiconductor film 38 is formed from the center of the film. It is possible to form an α-Ga ₂ O ₃ system semiconductor film that substantially does not contain a rotation domain over a wide range up to the outer peripheral portion.

The raw material solution L used in the mist CVD method is not limited as long as it is a solution that can obtain an α-Ga ₂ O ₃ system semiconductor film, but is, for example, a metal that forms a solid solution with Ga and / or Ga. Examples thereof include those obtained by dissolving an organic metal complex or a halide in a solvent. Examples of organometallic complexes include acetylacetonate complexes. When adding a dopant to the semiconductor layer, a solution of the dopant component may be added to the raw material solution. Further, an additive such as hydrochloric acid may be added to the raw material solution. Water, alcohol or the like can be used as the solvent.

Next, the obtained raw material solution L is atomized or dropletized to generate mist M or droplets. A preferred example of the method of atomizing or atomizing is a method of vibrating the raw material solution L using the ultrasonic vibrator 26. Then, the obtained mist M or droplets is conveyed to the film forming chamber 30 using the carrier gas G. The carrier gas G is not particularly limited, but one or more of an inert gas such as oxygen, ozone and nitrogen, and a reducing gas such as hydrogen can be used.

The film forming chamber 30 is provided with a substrate 36. The mist M or droplets conveyed to the film forming chamber 30 are thermally decomposed and chemically reacted there to form a semiconductor film 38 on the substrate 36. The reaction temperature varies depending on the type of the raw material solution L, but is preferably 300 to 800 ° C, more preferably 400 to 700 ° C. The atmosphere in the film forming chamber 30 is not particularly limited as long as a desired semiconductor film can be obtained, and typically, an oxygen gas atmosphere, an inert gas atmosphere, a vacuum atmosphere, a reducing atmosphere, and an air atmosphere. It is selected from one of.

The semiconductor film thus obtained can be formed as it is or divided into semiconductor elements. Alternatively, the semiconductor film may be peeled off from the composite substrate to form a single film. In this case, in order to facilitate peeling from the composite base substrate, a peeling layer may be provided in advance on the alignment layer surface (deposition surface) of the composite base substrate. Examples of such a release layer include those provided with a C injection layer and an H injection layer on the surface of the composite substrate. Further, C or H may be injected into the film at the initial stage of film formation of the semiconductor film to provide a release layer on the semiconductor film side. Further, a support substrate (mounting substrate) different from the composite substrate is adhered and bonded to the surface of the semiconductor film formed on the composite substrate (that is, the surface opposite to the composite substrate), and then the semiconductor film is formed. It is also possible to peel off the composite substrate from the substrate. As such a support substrate (mounting substrate), a substrate having a coefficient of thermal expansion at 25 to 400 ° C. of 6 to 13 ppm / K, for example, a substrate composed of a Cu—Mo composite metal can be used. Further, as an example of the method of adhering and bonding the semiconductor film and the support substrate (mounting substrate), known methods such as brazing, soldering, and solid phase bonding can be mentioned. Further, an electrode such as an ohmic electrode or a Schottky electrode, or another layer such as an adhesive layer may be provided between the semiconductor film and the support substrate.

Method for manufacturing composite base substrate For the above-mentioned composite base substrate, (a) a sapphire substrate is prepared, (b) a predetermined orientation precursor layer is prepared, and (c) the orientation precursor layer is heat-treated on the sapphire substrate. It can be preferably produced by converting at least a portion near the sapphire substrate into an alignment layer and, if desired, performing processing such as (d) grinding or polishing to expose the surface of the alignment layer. This alignment precursor layer becomes an alignment layer by heat treatment, and is a material having a corundum-type crystal structure whose a-axis length and / or c-axis length is larger than sapphire, or a-axis length and / or c-axis by heat treatment described later. Includes materials with a corundum-type crystal structure longer than sapphire. Further, the orientation precursor layer may contain trace components in addition to the material having a corundum-type crystal structure. According to such a manufacturing method, the growth of the alignment layer can be promoted by using the sapphire substrate as a seed crystal. That is, the high crystallinity and crystal orientation orientation peculiar to a single crystal of a sapphire substrate are inherited by the alignment layer.

(A) Preparation of sapphire substrate To prepare a base substrate, first, a sapphire substrate is prepared. The sapphire substrate used may have any orientation plane. That is, it may have a-plane, c-plane, r-plane, and m-plane, and may have a predetermined off-angle with respect to these planes. For example, when c-plane sapphire is used, since it is c-axis oriented with respect to the surface, it is possible to easily heteroepitaxially grow an oriented layer oriented c-axis on it. It is also possible to use a sapphire substrate to which a dopant has been added in order to adjust the electrical characteristics. Known dopants can be used as such dopants.

(B) Preparation of orientation precursor layer A material having a corundum-type crystal structure whose a-axis length and / or c-axis length is larger than sapphire, or a corundum-type crystal structure whose a-axis length and / or c-axis length is larger than sapphire by heat treatment. An orientation precursor layer containing the material to be used is prepared. The method for forming the orientation precursor layer is not particularly limited, and a known method can be adopted. Examples of methods for forming the orientation precursor layer include AD (aerosol deposition) method, sol-gel method, hydrothermal method, sputtering method, thin-film deposition method, various CVD (chemical vapor deposition) methods, PLD method, and CVT (chemical vapor deposition) method. Examples include the vapor deposition method and the sublimation method. Examples of the CVD method include a thermal CVD method, a plasma CVD method, a mist CVD method, an MO (organic metal) CVD method, and the like. Alternatively, a method may be used in which a molded product of the orientation precursor is prepared in advance and the molded product is placed on a sapphire substrate. Such a molded product can be produced by molding the material of the orientation precursor by a method such as tape molding or press molding. Further, it is also possible to use a method in which a polycrystal prepared in advance by various CVD methods or sintering is used as the orientation precursor layer and placed on a sapphire substrate.

However, the aerosol deposition (AD) method, various CVD methods, or sputtering methods are preferable. By using these methods, it is possible to form a dense orientation precursor layer in a relatively short time, and it becomes easy to cause heteroepitaxial growth using a sapphire substrate as a seed crystal. In particular, the AD method does not require a high vacuum process and has a relatively high film formation rate, and is therefore preferable in terms of manufacturing cost. When the sputtering method is used, it is possible to form a film using a target made of the same material as the alignment precursor layer, but it is also possible to use a reactive sputtering method in which a metal target is used to form a film in an oxygen atmosphere. it can. A method of placing the molded product prepared in advance on sapphire is also preferable as a simple method, but since the orientation precursor layer is not dense, a process of densification is required in the heat treatment step described later. The method using a polycrystal prepared in advance as the orientation precursor layer requires two steps, a step of preparing the polycrystal and a step of heat-treating on the sapphire substrate. Further, in order to improve the adhesion between the polycrystal and the sapphire substrate, it is necessary to take measures such as keeping the surface of the polycrystal sufficiently smooth. Although known conditions can be used for either method, a method of directly forming an orientation precursor layer using the AD method and a method of placing a prefabricated molded product on a sapphire substrate will be described below. ..

The AD method is a technology in which fine particles and fine particle raw materials are mixed with gas to form an aerosol, and this aerosol is jetted at high speed from a nozzle to collide with a substrate to form a film, which is said to be able to form a dense film at room temperature. It has characteristics. FIG. 3 shows an example of a film forming apparatus (aerosol deposition (AD) apparatus) used in such an AD method. The film forming apparatus 50 shown in FIG. 3 is configured as an apparatus used in the AD method of injecting raw material powder onto a substrate in an atmosphere of atmospheric pressure lower than atmospheric pressure. The film forming apparatus 50 includes an aerosol generation unit 52 that generates an aerosol of a raw material powder containing a raw material component, and a film forming unit 60 that injects the raw material powder onto a sapphire substrate 51 to form a film containing the raw material component. There is. The aerosol generation unit 52 includes an aerosol generation chamber 53 that stores raw material powder and receives a carrier gas supply from a gas cylinder (not shown) to generate an aerosol, and a raw material supply pipe 54 that supplies the generated aerosol to the film forming unit 60. The aerosol generation chamber 53 and the aerosol in the aerosol are provided with a vibration exciter 55 that vibrates at a frequency of 10 to 100 Hz. The film forming section 60 includes a film forming chamber 62 that injects aerosols onto the sapphire substrate 51, a substrate holder 64 that is arranged inside the film forming chamber 62 and fixes the sapphire substrate 51, and the substrate holder 64 on the X-axis-Y axis. It is equipped with an XY stage 63 that moves in a direction. Further, the film forming section 60 includes an injection nozzle 66 in which a slit 67 is formed at the tip thereof and ejects aerosol to the sapphire substrate 51, and a vacuum pump 68 for reducing the pressure in the film forming chamber 62.

It is known that the AD method can control the film thickness, film quality, etc. depending on the film forming conditions. For example, the form of the AD film is easily affected by the collision rate of the raw material powder with the substrate, the particle size of the raw material powder, the aggregated state of the raw material powder in the aerosol, the injection amount per unit time, and the like. The collision speed of the raw material powder with the substrate is affected by the differential pressure between the film forming chamber 62 and the injection nozzle 66, the opening area of the injection nozzle, and the like. If appropriate conditions are not used, the coating may become a powder or pores, so it is necessary to control these factors appropriately.

When a molded product in which the orientation precursor layer is prepared in advance is used, the raw material powder of the orientation precursor can be molded to prepare the molded product. For example, when press molding is used, the orientation precursor layer is a press molded body. The press-molded product can be produced by press-molding the raw material powder of the orientation precursor based on a known method. For example, the raw material powder is placed in a mold, preferably 100 to 400 kgf / cm ² , more preferably 150. It may be produced by pressing at a pressure of about 300 kgf / cm ² . The molding method is not particularly limited, and in addition to press molding, tape molding, casting molding, extrusion molding, doctor blade method, and any combination thereof can be used. For example, when tape molding is used, additives such as a binder, a plasticizer, a dispersant, and a dispersion medium are appropriately added to the raw material powder to form a slurry, and the slurry is passed through a narrow slit-shaped discharge port to form a sheet. It is preferable to discharge and mold. The thickness of the molded product formed into a sheet is not limited, but is preferably 5 to 500 μm from the viewpoint of handling. Further, when a thick orientation precursor layer is required, a large number of these sheet molded products may be stacked and used as a desired thickness.

In these molded bodies, the portion near the sapphire substrate becomes an orientation layer by the subsequent heat treatment on the sapphire substrate. As described above, in such a method, it is necessary to sinter and densify the molded product in the heat treatment step described later. For this reason, the molded product may contain trace components such as a sintering aid in addition to the material having or bringing about a corundum-type crystal structure.

(C) Heat treatment of the alignment precursor layer on the sapphire substrate The sapphire substrate on which the alignment precursor layer is formed is heat-treated at a temperature of 1000 ° C. or higher. By this heat treatment, at least a portion of the alignment precursor layer near the sapphire substrate can be converted into a dense alignment layer. Further, this heat treatment makes it possible to grow the oriented layer heteroepitaxially. That is, by forming the alignment layer with a material having a corundum-type crystal structure, heteroepitaxial growth occurs in which the material having a corundum-type crystal structure grows as a seed crystal using a sapphire substrate during heat treatment. At that time, the crystals are rearranged, and the crystals are arranged according to the crystal plane of the sapphire substrate. As a result, the crystal axes of the sapphire substrate and the alignment layer can be aligned. For example, when a c-plane sapphire substrate is used, the sapphire substrate and the alignment layer can both be oriented in the c-axis with respect to the surface of the base substrate. Moreover, this heat treatment makes it possible to form an inclined composition region in a part of the alignment layer. That is, during the heat treatment, a reaction occurs at the interface between the sapphire substrate and the alignment precursor layer, and the Al component in the sapphire substrate diffuses into the alignment precursor layer and / or the component in the alignment precursor layer is in the sapphire substrate. Diffuses into a sapphire composition region composed of a solid solution containing α-Al ₂ O ₃ .

It is known that various CVD methods, sputtering methods, PLD methods, CVT methods, sublimation methods, and the like may cause heteroepitaxial growth on the sapphire substrate without undergoing heat treatment at 1000 ° C. or higher. However, the orientation precursor layer is in a non-oriented state at the time of its production, that is, it is an amorphous or non-oriented polycrystal, and it is preferable to cause crystal rearrangement using sapphire as a seed crystal during this heat treatment step. By doing so, the crystal defects reaching the surface of the alignment layer can be effectively reduced. The reason for this is not clear, but it is thought that the crystal defects generated in the lower part of the alignment layer are likely to be annihilated.

The heat treatment is not particularly limited as long as a corundum-type crystal structure is obtained and heteroepitaxial growth using a sapphire substrate as a seed occurs, and the heat treatment can be carried out in a known heat treatment furnace such as a tube furnace or a hot plate. Further, in addition to these heat treatments under normal pressure (pressless), pressure heat treatments such as hot press and HIP, and combinations of normal pressure heat treatments and pressure heat treatments can also be used. The heat treatment conditions can be appropriately selected depending on the material used for the alignment layer. For example, the heat treatment atmosphere can be selected from air, vacuum, nitrogen and an inert gas atmosphere. The preferred heat treatment temperature also varies depending on the material used for the alignment layer, but is preferably 1000 to 2000 ° C, more preferably 1200 to 2000 ° C, for example. The heat treatment temperature and holding time are related to the thickness of the alignment layer generated by heteroepitaxial growth and the thickness of the inclined composition region formed by diffusion with the sapphire substrate, and are related to the type of material, the target alignment layer, and the thickness of the inclined composition region. It can be adjusted as appropriate depending on the size. However, when a prefabricated molded product is used as an orientation precursor layer, it is necessary to sinter and densify it during heat treatment, and atmospheric firing at high temperature, hot pressing, HIP, or a combination thereof is preferable. .. For example, when using a hot press, the surface pressure is preferably 50 kgf / cm ² or more, more preferably 100 kgf / cm ² or more, particularly preferably 200 kgf / cm ² or more, the upper limit is not particularly limited. The firing temperature is also not particularly limited as long as sintering, densification, and heteroepitaxial growth occur, but is preferably 1000 ° C. or higher, more preferably 1200 ° C. or higher, further preferably 1400 ° C. or higher, and particularly preferably 1600 ° C. or higher. The firing atmosphere can also be selected from atmosphere, vacuum, nitrogen and an inert gas atmosphere. As the firing jig such as a mold, those made of graphite or alumina can be used.

(D) Exposure of the surface of the oriented layer On the oriented layer formed near the sapphire substrate by heat treatment, an oriented precursor layer or a surface layer having poor or unoriented orientation may exist or remain. In this case, it is preferable that the surface derived from the alignment precursor layer is subjected to processing such as grinding or polishing to expose the surface of the alignment layer. By doing so, the material having excellent orientation is exposed on the surface of the alignment layer, so that the semiconductor layer can be effectively epitaxially grown on the material. The method for removing the orientation precursor layer and the surface layer is not particularly limited, and examples thereof include a method for grinding and polishing and a method for ion beam milling. Polishing of the surface of the alignment layer is preferably performed by lapping using abrasive grains or chemical mechanical polishing (CMP).

The present invention will be described more specifically by the following examples.

Example 1
(1) Preparation of α-Ga ₂ O ₃ system semiconductor film by mist CVD method (1a) Preparation of raw material solution A 0.05 mol / L gallium acetylacetonate aqueous solution was prepared, and 1.5% of the aqueous solution was prepared. 12N concentrated hydrochloric acid was added by volume. Tin (II) chloride was added to the obtained mixed solution to a concentration of 0.001 mol / L to prepare a raw material solution.

(1b) Preparation for film formation A mist CVD apparatus 20 having the configuration shown in FIG. 2 was prepared. The configuration of the mist CVD apparatus 20 is as described above. In the mist CVD apparatus 20, the raw material solution L obtained in (1a) above was housed in the mist generation chamber 22. A c-plane sapphire substrate having a diameter of 5.08 cm (2 inches) was set on the rotating stage 34 as the substrate 36, and the distance between the tip of the nozzle 32 and the substrate 36 was set to 120 mm. The temperature of the rotary stage 34 was raised to 480 ° C. by the heater 42 and held for 30 minutes for temperature stabilization. The flow rate control valve (not shown) was opened to supply nitrogen gas as the carrier gas G into the film forming chamber 30 via the mist generation chamber 22, and the atmosphere of the film forming chamber 30 was sufficiently replaced with the carrier gas G. After that, the flow rate of the carrier gas G was adjusted to 2.0 L / min.

(1c) Film formation The raw material solution L is atomized by vibrating the ultrasonic vibrator 26 at 2.4 MHz while rotating the rotary stage 34 at a rotation speed of 60 rpm, and the generated mist M is deposited with the carrier gas G. It was introduced in the room 30. The semiconductor film 38 was formed on the substrate 36 for 1 hour by reacting the mist M in the film forming chamber 30, particularly on the surface of the substrate 36 (specifically, the sapphire substrate). In this way, a composite material 40 composed of the substrate 36 and the semiconductor film 38 formed on the substrate 36 was obtained.

(2) Evaluation of semiconductor film (2a) Surface EDX
As a result of composition analysis by energy dispersive X-ray analysis (EDX) on the surface of the obtained semiconductor film 38, only Ga and O were detected. From this, it was found that the semiconductor film 38 is composed of Ga oxide.

(2b) XRD
Using an X-ray diffraction (XRD) device (D8-DISCOVER, manufactured by Bruker-AXS Co., Ltd.), a colland type is used at the center point X of the surface of the semiconductor film and the outer peripheral points A, B, C and D shown in FIG. A φ scan was performed on the (104) plane of the Ga oxide film under the following conditions. That is, in the XRD measurement at each of the above points, after adjusting 2θ, ω, χ and φ and arranging the shaft so that the peak of the (104) plane of α-Ga ₂ O ₃ appears, the tube voltage is 40 kV and the tube is used. The current was 40 mA, the collimator diameter was 0.5 mm, the anti-scattering slit was 3 mm, the ω = 0 to 360 ° range, the ω step width was 0.005 °, and the counting time was 0.5 seconds. The peak top values of the three detected main peaks were averaged to obtain the peak intensity of the main peaks. In addition, the peak top values of the three sub-peaks caused by the rotation domain detected at ω deviated from the main peak by 60 ° were averaged to obtain the peak intensity of the sub-peak caused by the rotation domain.

The outer peripheral points A, B, C and D are i) the straight line connecting the outer peripheral points A and the outer peripheral point C and the straight line connecting the outer peripheral points B and the outer peripheral point D intersect at a right angle at the center point X, and ii) The shortest distances of the outer peripheral points A, B, C and D from the outer edge of the semiconductor film are set to be 1/5 of the radius of the semiconductor film. Center point X, and the outer peripheral point A, B, in C and D, to the peak intensity of the main peak, the ratio _I x of the peak intensity of the secondary peak due to rotation _domain, I _A, I B, the _{I C} and _{I D} Each was calculated. _Also, I _A, I _B, the arithmetic average value _{I M} and _{I C} and _{I D |} was calculated | I X -I _M. The results were as shown in Table 1.

(2c) Film thickness The film thickness was evaluated by TEM observation of the cross section. The test piece used for the TEM observation is a composite material 40 separately prepared by the same method as in (1) above, from the center point X shown in FIG. 1 and the vicinity of the outer peripheral points A, B, C and D. , FIB, and sliced by ion milling. A cross-sectional observation was performed at an acceleration voltage of 300 kV using a Hitachi transmission electron microscope H-90001UHR-I, the film thickness was measured for each sample, and the average value of the film thicknesses of the five samples was taken as the thickness of the semiconductor film. The results were as shown in Table 1.

(2d) Volume resistivity The volume resistivity of the semiconductor film 38 was measured by a four-probe method using a resistivity meter (manufactured by Mitsubishi Chemical Corporation, Loresta GP, MCP-T610 type). Specifically, the center point X shown in FIG. 1, and the outer peripheral point A, B, in C and D, the volume resistivity _R x of the semiconductor film _38, R _A, R B, respectively measured _{R C} and _{R D} did. Further, among the values of R _x , R _A , R _B , _RC and R _D , the maximum value was R _max and the minimum value was R _min, and the value of (R _max −R _min ) / R _max was calculated. The results were as shown in Table 1.

(2e) Device homogeneity (fabrication of device)
The composite material 40 obtained in (1c) above is cut into 10 mm squares so that the center point X and the outer peripheral points A, B, C and D are substantially centered, and the five composite material pieces 40 'Get. As shown in FIG. 4, the composite material piece 40'consists of the substrate 36 and the semiconductor film 38, and the substrate 36 is used as the base substrate 72 and the semiconductor film 38 is used as the n ⁺ layer 74 in manufacturing the device. Use. On the surface of the composite material piece 40'on the semiconductor film 38 (n ⁺ layer 74) side, a region of 2 mm × 10 mm from the end was masked with a sapphire substrate (not shown), and then the n ⁻ layer 76 was formed. The formation of the n ^- layer 76 did not include the addition of a dopant (specifically, tin (II) chloride) in the preparation of the raw material solution in (1a) above, and did not rotate the rotary stage 34 in (1c) above. The same procedure as in (1) above was carried out except that the film was formed for 30 minutes. After the n ^- layer 76 was formed, the sapphire substrate (not shown) as masking was removed to expose the n ⁺ layer 74. A Ti electrode 78 (ohmic electrode) was formed in the exposed region of the n ⁺ layer 74, while a Pt electrode 80 (shotkey electrode) was formed on the n ⁻ layer. Forming a Pt electrode 80 in a layer on the ^- Ti electrode 78 and n. In this way, a horizontal Schottky barrier diode 70 as shown in FIG. 4 was produced.

(Device evaluation)
For the Schottky barrier diode 70, the current (ON current) I _ON that flows when a voltage of 10 V is applied in the forward direction and the current (OFF current) I _OFF that flows when a voltage of 10 V is applied in the reverse direction are measured. , The ratio of the OFF current I _OFF to the ON current I _ON (that is, I _ON / I _OFF ) was defined as the P value. In this case, the center point X, and the outer peripheral point A, B, by measuring the P value for each of the Schottky barrier diode 70 that corresponds to C and D, respectively _{P X,} P _A, P B, _{P C} and It was designated as _PD . The value logP _X their common logarithm, when the logP _A, logP _B, the arithmetic mean value of logP _C and logP _D was _{M P, | M P -logP X} |, | M P -logP A |, | _{M P -logP B |, | M} P -logP C | and _| M P _{-logP D |} of the five values, and the number of those of 0.5 or less and S, (S / 5) × 100 [% ] Was used as an index indicating the homogeneity of the device. The results were as shown in Table 1.

In this example, the Schottky barrier diode 70 is in the form of a horizontal device in order to easily evaluate the homogeneity of the device, but this example is also used in a vertical device manufactured by removing the base substrate 72. Shows the same tendency as the horizontal device of.

Example 2
Except that the concentration of tin (II) chloride was set to 0.01 mol / L in the preparation of the raw material solution of (1a) above, and the film forming conditions in (1c) above were changed as shown in Table 1. , A semiconductor film was prepared and various evaluations were carried out in the same manner as in Example 1. The results were as shown in Table 1.

Example 3
A semiconductor film was prepared and various evaluations were carried out in the same manner as in Example 2 except that the apparatus and film forming conditions of the above (1b) and (1c) were changed as shown in Table 1. The results were as shown in Table 1.

Example 4
Same as Example 2 except that the raw material solution of (1a) was prepared as follows, and the apparatus and film forming conditions of (1c) and (1d) were changed as shown in Table 1. The semiconductor film was prepared and various evaluations were performed. The results were as shown in Table 1.

(Preparation of raw material solution)
An aqueous raw material solution containing gallium bromide and germanium oxide in a substance amount ratio of 100: 5 was prepared. This aqueous solution contained 10% by volume of a 48% hydrobromic acid solution. The concentration of germanium (IV) oxide was 5.0 × ^10-3 mol / L.

Example 5
The apparatus and film forming conditions of the above (1b) and (1c) were changed as shown in Table 1, and the composite base substrate produced as the substrate 36 in the above (1c) film formation as follows was used. A semiconductor film was prepared and various evaluations were carried out in the same manner as in Example 2 except that it was used. The results were as shown in Table 1.

(Preparation of composite substrate)
(A) Preparation of Orientation Precursor Layer To 100 parts by weight of commercially available Cr ₂ O ₃ powder, 2.4 parts by weight of TiO ₂ powder is added and wet-mixed, and the obtained mixed powder is pulverized with a pot mill to obtain grains. A Cr ₂ O ₃ / TiO ₂ mixed powder having a diameter D50 of 0.4 μm was obtained as a raw material powder. Using this raw material powder and sapphire as a seed substrate (diameter 5.08 cm (2 inches), thickness 0.43 mm, c-plane, off-angle 0.2 °), the aerosol deposition (AD) shown in FIG. ) The AD film was formed on the seed substrate (sapphire substrate) by the apparatus 50. The configuration of the aerosol deposition (AD) device 50 is as described above.

The AD film formation conditions were as follows. That is, the carrier gas was N _2, and a ceramic nozzle having a slit having a long side of 5 mm and a short side of 0.3 mm was used. The scanning conditions of the nozzle are 1 mm / s scanning speed, 55 mm movement in the direction perpendicular to the long side of the slit and in the forward direction, 5 mm movement in the long side direction of the slit, and vertical and return direction to the long side of the slit. The scan is repeated with 55 mm movement, 5 mm movement in the long side direction of the slit and in the direction opposite to the initial position, and when 55 mm is moved from the initial position in the long side direction of the slit, scanning is performed in the opposite direction. The cycle of returning to the initial position was set as one cycle, and this was repeated for 300 cycles. In one cycle of film formation at room temperature, the set pressure of the transport gas was adjusted to 0.06 MPa, the flow rate was adjusted to 6 L / min, and the pressure in the chamber was adjusted to 100 Pa or less. The thickness of the AD film (alignment precursor layer) thus formed was about 60 μm.

(B) Heat Treatment of Orientation Precursor Layer The sapphire substrate on which the AD film (alignment precursor layer) was formed was taken out from the AD apparatus and annealed at 1600 ° C. for 4 hours in a nitrogen atmosphere.

(C) Measurement of Crystal Growth Thickness An AD film (alignment precursor layer) separately prepared by the same method as in (a) and (b) above is prepared and passes through the center of the substrate in a direction orthogonal to the plate surface. I cut it like this. The cross section of the cut sample was smoothed by lapping with diamond abrasive grains, and mirror-finished by chemical mechanical polishing (CMP) using colloidal silica. The obtained cross section was photographed with a scanning electron microscope (SU-5000, manufactured by Hitachi High-Technologies Corporation). When observing the reflected electron image of the cross section after polishing, the orientation precursor layer (hereinafter referred to as the polycrystal part) remaining as polycrystalline and the alignment layer can be identified by the channeling contrast due to the difference in crystal orientation. Was made. As a result of estimating the thickness of each layer in this way, the film thickness of the oriented layer was about 50 μm, and the film thickness of the polycrystalline portion was about 10 μm.

(D) Grinding and polishing The surface of the obtained substrate on the side derived from the AD film is ground with a grindstone having a count of up to # 2000 until the alignment layer is exposed, and then lap processing using diamond abrasive grains is performed. , The plate surface was further smoothed. Then, it was mirror-finished by chemical mechanical polishing (CMP) using colloidal silica to obtain a composite base substrate having an orientation layer on the sapphire substrate. The surface of the substrate on the side derived from the AD film was designated as the "surface". The amount of grinding and polishing was about 30 μm including the polycrystalline portion and the alignment layer, and the thickness of the alignment layer formed on the composite base substrate was about 30 μm.

Example 6
The equipment and film formation conditions of (1b) and (1c) above were changed as shown in Table 1, a 10.0 cm composite substrate was prepared and used, and film formation by the AD method was used. A semiconductor film was prepared and various evaluations were carried out in the same manner as in Example 5 except that the range was expanded to a 110 mm square area. The results were as shown in Table 1.

Examples 7 and 8 (comparison)
A semiconductor film was prepared and various evaluations were carried out in the same manner as in Example 1 except that the film forming conditions of (1c) above were changed as shown in Table 1 (for example, the stage rotation speed was set to 0 rpm). The results were as shown in Table 1.

Example 9 (comparison)
In the preparation of the raw material solution of (1a) above, the concentration of tin (II) chloride was set to 0.02 mol / L, and the film formation conditions of (1c) above were changed as shown in Table 1 (for example, stage rotation). A semiconductor film was prepared and various evaluations were carried out in the same manner as in Example 1 except that the number was 0 rpm). The results were as shown in Table 1.

 

Claims (8)

1. A semiconductor film having a crystal having a corundum-type crystal structure composed of α-Ga ₂ O ₃ or α-Ga ₂ O ₃ solid solution as a main phase.
   The semiconductor film has a circular shape with a diameter of 5.08 cm (2 inches) or more.
   When X-ray diffraction (XRD) φ scan measurement is performed on the (104) plane of the crystal at each of the center point X and the four outer peripheral points A, B, C and D of the surface of the semiconductor film, The ratio of the peak intensity of the sub-peak due to the rotation domain to the peak intensity of the main peak is 1.00% or less.
   The outer peripheral points A, B, C and D are i) The straight line connecting the outer peripheral point A and the outer peripheral point C and the straight line connecting the outer peripheral point B and the outer peripheral point D intersect at a right angle at the center point X. And ii) A semiconductor film in which the shortest distances of the outer peripheral points A, B, C and D from the outer edge of the semiconductor film are defined to be 1/5 of the radius of the semiconductor film.
2. The ratio of the peak intensity of the sub-peak due to the rotation domain to the peak intensity of the main peak measured at the center point X is _IX %, and the measurement is performed at the outer peripheral points A, B, C and D. to the peak intensity of the main peak, the arithmetic mean value of the ratio of the peak intensity of the secondary peak caused by the rotation domain when the I _M%, | satisfy a relationship of ≦ 0.20 _| I X _-I M , The semiconductor film according to claim 1.
3. The semiconductor film according to claim 1 or 2, wherein the arithmetic mean value of the thickness of the semiconductor film measured at the center point X and the outer peripheral points A, B, C and D is 2.0 μm or more.
4. The semiconductor film according to any one of claims 1 to 3, wherein the volume resistivity measured at the center point X and the outer peripheral points A, B, C and D is 0.10 Ω · cm or less.
5. The maximum value R _max and the minimum value R _{min of} the volume resistivity measured at the center point X and the outer peripheral points A, B, C and D are [(R _max −R _min ) / R _max ] ≦ 0.20. The semiconductor film according to any one of claims 1 to 4, which satisfies the above relationship.
6. The semiconductor film according to any one of claims 1 to 5, wherein the semiconductor film contains a Group 14 element as a dopant at a ratio of 1.0 × 10 ¹⁶ to 1.0 × 10 ²¹ / cm ³ .
7. The semiconductor film according to any one of claims 1 to 6, wherein the semiconductor film is formed on a circular support substrate having a diameter of 5.08 cm (φ2 inch) or more.
8. A composite material comprising a circular support substrate having a diameter of 5.08 cm (φ2 inch) or more and the semiconductor film according to any one of claims 1 to 6 formed on the support substrate.

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