WO2021064803A1

WO2021064803A1 - α-Ga2O3 SEMICONDUCTOR FILM

Info

Publication number: WO2021064803A1
Application number: PCT/JP2019/038558
Authority: WO
Inventors: 福井　宏史; 守道渡邊; 吉川　潤
Original assignee: 日本碍子株式会社
Priority date: 2019-09-30
Filing date: 2019-09-30
Publication date: 2021-04-08
Also published as: JP7221410B2; JPWO2021064803A1

Abstract

This α-Ga₂O₃ semiconductor film has a nunchuck structure 20 which is observed in a planar TEM bright-field image taken with an electron beam incident in parallel with the <001> direction, and has, at both ends of a thin line-like region 22, rod-like regions 24, 24 wider than the thin line-like region 22.

Description

α-Ga2O3 series 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 has a very large bandgap of 5.3 eV and power. It is expected as a material for semiconductors. However, since α-Ga ₂ O ₃ has a forward stable phase, a single crystal substrate has not been put into practical use, and it is generally formed by heteroepitaxial growth on a sapphire substrate.

For example, Patent Document 1 discloses a semiconductor device including 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, and a sapphire substrate. An example in which an _{α-Ga 2} O ₃ film is formed as a semiconductor layer is described above. Further, Patent Document 2 describes an n-type semiconductor layer containing a crystalline oxide semiconductor having a corundum structure as a main component, a p-type semiconductor layer containing an inorganic compound having a hexagonal crystal structure as a main component, and an electrode. A semiconductor device comprising the above is disclosed. _{In the embodiment of Patent Document 2, an α-Ga 2} O ₃ film having a corundum structure which is a semi-stable phase as an n-type semiconductor layer is formed on a c-plane sapphire substrate, and a hexagonal crystal structure is used as a p-type semiconductor layer. It is disclosed that a diode is produced by forming an α-Rh ₂ O _{3 film having.}

By the way, there is a problem that cracks and crystal defects occur when the _{α-Ga 2} O _{3 film is crystal-grown on a dissimilar substrate.} When forming an InAlGaO-based semiconductor film, which is a mixed crystal of α-Ga ₂ O ₃ and a dissimilar corundum material, crystals usually grow on the dissimilar substrate, which causes problems such as cracks in the epitaxial film. It is happening. As a technique for dealing with this problem, Patent Document 3 discloses that an _{α-Ga 2} O _{3 film having few cracks is produced.} _{Further, Patent Document 4 discloses that an α-Ga 2} O ₃ film having reduced cracks is produced by including voids when the epitaxial film is formed.

Japanese Unexamined Patent Publication No. 2014-72533 Japanese Unexamined Patent Publication No. 2016-25256 Japanese Unexamined Patent Publication No. 2016-100592 Japanese Unexamined Patent Publication No. 2016-100593

Although various α-Ga ₂ O ₃ films have been produced in this way, it has been desired to develop a _{useful α-Ga 2} O _{3 system semiconductor film different from the conventional ones.}

The present invention has been made to solve such a problem, and an object of the present invention is to provide a novel α-Ga ₂ O ₃ system semiconductor film.

The α-Ga ₂ O ₃ system semiconductor film of the present invention has a width wider than that of the fine line region at both ends of the fine line region in a plane TEM bright-field image when an electron beam is incident in parallel in the <001> direction. A nunchaku-type tissue with a large rod-like region is observed.

This α-Ga ₂ O ₃ system semiconductor film is a novel one that has not been known so far, and the occurrence of cracks is suppressed.

It is explanatory drawing of the laminated structure 10, (a) is a plan view, (b) is a sectional view of AA. Explanatory drawing of Nunchaku type organization 20. Explanatory drawing of Nunchaku type organization 20. The schematic cross-sectional view which shows the structure of the mist CVD apparatus 40. The schematic cross-sectional view which shows the structure of the vapor phase growth apparatus 60. FIG. 6 is a schematic cross-sectional view showing a cutout position of a test piece for plane TEM observation. A photograph of a bright-field image of a plane TEM observation. A photograph of a bright-field image of a plane TEM observation. An enlarged photograph of a part of FIG. 7. A photograph of a BF-STEM image near the nunchaku-shaped tissue shown in FIG. Photograph of HAADF-STEM image of rod-shaped region A. A photograph of the HAADF-STEM image of the thin linear region B.

[Laminated structure]
1A and 1B are explanatory views of the laminated structure 10, FIG. 1A is a plan view, and FIG. 1B is a cross-sectional view taken along the line AA.

The laminated structure 10 is a plate-shaped member, and has a semiconductor film 14 on a base substrate 12. The plan view figure when the laminated structure 10 is viewed in a plan view is circular in the present embodiment. 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. Further, the plan view figure of the laminated structure 10 is not limited to a circle, and may be, for example, a polygon (a quadrangle such as a square or a rectangle, a pentagon, a hexagon, or the like).

The base substrate 12 preferably has a layer of an oxide (α-Cr ₂ O ₃ , α-Fe ₂ O _3, etc.) whose lattice constant is closer to α-Ga ₂ O ₃ _{than sapphire, and α-Cr 2} Those provided with a single crystal layer of O ₃ or α-Cr ₂ O _{3 system solid solution are more preferable.}

The semiconductor film 14 is a semiconductor film _{having a corundum-type crystal structure composed of an α-Ga 2} O ₃ or α-Ga ₂ O ₃ system solid solution, that is, an α-Ga ₂ O ₃ system semiconductor film. α-Ga ₂ O ₃ belongs to a trigonal crystal group and has a corundum-type crystal structure. 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. Examples of other components include Al ₂ O ₃ , In ₂ O ₃ , Cr ₂ O ₃ , Fe ₂ O ₃ , Rh ₂ O ₃ , V ₂ O ₃ , and Ti ₂ O ₃ .

In the semiconductor film 14, the nunchaku-shaped structure 20 shown in FIG. 2 is observed in a flat TEM bright-field image when an electron beam is incident parallel to the <001> direction. The nunchaku-shaped structure 20 is a structure having rod-

shaped areas

24, 24 wider than the fine line-shaped area 22 at both ends of the thin line-shaped area 22. The nunchaku-type tissue 20 appears as a dark part in a plane TEM bright-field image. The observation of the plane TEM bright-field image is performed as follows. That is, the sample is cut out so as to include a surface having a depth of about 0.04 μm from the surface of the semiconductor film 14 (the surface opposite to the surface on the base substrate 12 side), and the thickness of the portion of the sample that serves as the measurement field of view. Is processed by ion milling so that the value is 200 nm. Then, an electron beam is incident on the portion to be the measurement field of view in parallel with the <001> direction at an acceleration voltage of 300 kV, and the TEM bright field image is observed.

In the semiconductor film 14, a plurality of linear structures are observed in a cross-sectional TEM bright-field image when an electron beam is incident in parallel in the <1-10> direction. Among the linear structures observed in this bright-field image, there is a structure that does not disappear in either the dark-field image g * = 110 or the dark-field image g * = 00-6 of the same cross-sectional TEM. The tissue observed as a linear dark part in the TEM bright-field image is generally recognized as a dislocation. For blade-shaped dislocations and spiral dislocations, the dark-field image g * = 110 and dark-field image g * = 00-6 of the cross-sectional TEM can be observed, and the attribution of blade-shaped dislocations and spiral dislocations can be determined by whether or not they disappear. However, such an indelible linear structure is not attributed to either blade dislocations or spiral dislocations. Further, even if the planar STEM observation in which the electron beam is incident parallel to the Nunchak-shaped structure 20 observed in the planar TEM image of the semiconductor film 14 in the <001> direction is performed, the planar STEM bright-field image is captured by the planar TEM. A dark area corresponding to the image appears. Even if the Ga atomic image is magnified to a level where it can be recognized (for example, at a magnification of 4 million times or more) in the plane STEM, the increase or decrease of the atomic plane and the large deviation of the atomic arrangement do not occur in any region of the nunchaku-type structure 20. I can't confirm. In the case of dislocations and surface defects (stacking defects, grain boundaries, etc.), the atomic planes increase or decrease or shift in the Ga atomic image, so the Nunchak-type structure is not only blade-shaped dislocations and spiral dislocations, but also mixed dislocations and basal plane dislocations. In addition, it is not attributed to surface defects such as stacking defects and grain boundaries. The plane STEM bright-field image is observed as follows. That is, the sample is cut out so as to include a surface having a depth of about 0.04 μm from the surface of the semiconductor film 14 (the surface opposite to the surface on the base substrate 12 side), and the thickness of the portion of the sample that serves as the measurement field of view. Is processed by ion milling so that the value is 70 nm. Then, an electron beam is incident parallel to the measurement field of view in the <001> direction at an acceleration voltage of 200 kV, and the STEM bright field image is observed. From the above, although the nunchak-type structure 20 contained in the semiconductor film 14 is observed as a dark part in the plane TEM bright-field image, dislocations (blade dislocations, spiral dislocations, mixed dislocations, basal plane dislocations) and stacking defects , Not attributed to surface defects such as grain boundaries. Further, STEM-EDS analysis and electron diffraction analysis of TEM were carried out in the region where the nunchaku-type structure 20 was detected, but no heterogeneous phase or agglutination of foreign substances was observed. Therefore, the nunchak-type structure 20 observed in the planar TEM image of the semiconductor film 14 is considered to be a crystal defect that is not attributed to blade-like dislocations, spiral dislocations, mixed dislocations, basal plane dislocations, and surface defects such as stacking defects and grain boundaries. .. The structure of the nunchaku-type structure 20 is unknown, but in the planar STEM image, the Ga atomic image is slightly unclear compared to the peripheral part (non-defect part), so it is considered that the Ga atomic arrangement is slightly overlooked. It is speculated that the atomic position may have been replaced by O.

The density of the nunchaku-type structure 20 of the semiconductor film 14 is preferably as low as possible from the viewpoint of crystallinity, specifically, 1.0 × 10 ¹⁰ / cm ² or less, and 1.0 × 10 ⁹ / cm ² or less. Is more preferable, and 1.0 × 10 ⁸ / cm ² or less is further preferable. On the other hand, the density of the nunchaku-type structure 20 of the semiconductor film 14 is preferably a certain density from the viewpoint of crack suppression, specifically, 1.0 × 10 ⁴ / cm ² or more, and 1.0 × 10 ⁵ / cm ² or more is more preferable, and 1.0 × 10 ⁶ / cm ² or more is further preferable. Therefore, in order to achieve both crystallinity and crack suppression, the density of the nunchaku-type structure of the semiconductor film 14 is preferably 1.0 × 10 ⁶ / cm ² or more and 1.0 × 10 ⁸ / cm ² or less.

The total length of the nunchaku-shaped structure 20 of the semiconductor film 14, that is, the length of the line segment connecting the outer ends of the rod-shaped

regions

24 and 24 is not particularly limited, but is typically 100 to 800 nm. The length of the thin linear region 22 is not particularly limited, but is typically 50 to 500 nm. The length of the rod-shaped region 24 is not particularly limited, but is typically 20 to 150 nm.

The nunchaku-shaped structure 20 of the semiconductor film 14 may have a part of the thin linear region 22 bent (see FIG. 3A) or may be substantially linear (see FIG. 3B). .. In terms of numbers, the former tends to be larger than the latter. It is considered that the former is more effective in dispersing the stress in the semiconductor film 14, and is therefore preferable in terms of suppressing cracks and warpage of the semiconductor film.

The nunchaku-shaped structure 20 of the semiconductor film 14 may have the two rod-shaped

regions

24 and 24 substantially parallel in the longitudinal direction (see FIG. 3C) or may have an angle (FIG. 3). (D), (e)). In terms of numbers, the former tends to be larger than the latter. It is considered that the former is more effective in dispersing the stress in the semiconductor film 14, and is therefore preferable in terms of suppressing cracks and warpage of the semiconductor film.

The area of the film surface of the semiconductor film 14 substantially coincides with the area of the underlying substrate 12. The area of the film surface of the semiconductor film 14 is preferably 20 cm ² or more, more preferably 70 cm ² or more, and further preferably 170 cm ² or more. By increasing the area of the semiconductor film 14 in this way, it is possible to obtain a large number of semiconductor elements from one semiconductor film 14, and it is possible to reduce the manufacturing cost. The upper limit of the size of the semiconductor film 14 is not particularly limited, but is typically 700 cm ² or less on one side. The average film thickness of the semiconductor film 14 is preferably 3 μm or more, more preferably 5 μm or more, still more preferably 8 μm or more.

The semiconductor film 14 can contain a Group 14 element as a dopant at a ratio of ^{1.0 × 10 16} to 1.0 × 10 ²¹ / cm ^3. Here, the Group 14 elements are the Group 14 elements according to the periodic table formulated by the IUPAC (International Union of Pure and Applied Chemistry). Specifically, carbon (C), silicon (Si), germanium (Ge), and so on. It is either tin (Sn) or lead (Pb). The amount of the dopant can be appropriately changed according to the desired characteristics, but is preferably 1.0 × 10 ¹⁶ to 1.0 × 10 ²¹ / cm ³ , and more preferably 1.0 × 10 ¹⁷ to 1.0. × 10 ¹⁹ / 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 14 are about the same.

Further, the semiconductor film 14 is preferably an alignment film oriented in a specific plane orientation. The orientation of the semiconductor film 14 can be examined by a known method, and can be examined, for example, by performing reverse pole map orientation mapping using an electron backscatter diffraction device (EBSD). For example, the semiconductor film may be c-axis oriented, or may be c-axis oriented and also oriented in the in-plane direction.

[Manufacturing method of semiconductor film]
The method for producing the semiconductor film 14 includes (a) a step of obtaining the laminated structure 10 and (b) a step of peeling the semiconductor film 14 from the base substrate 12.

(A) Step of obtaining the laminated structure 10 The laminated structure 10 has an oxide (α-Cr ₂ O ₃ , α-Fe ₂ O ₃ , α-Cr _{) whose lattice constant is closer to α-Ga 2} O _{3 than that of sapphire.} the base substrate 12, such as ₂ O ₃ solid solution), is obtained by forming a semiconductor film 14. Examples of the base substrate 12 include a Cr ₂ O ₃ single crystal substrate. The film forming method is not particularly limited, and a known method can be adopted. As the film forming method, mist CVD, HVPE, MBE, MOCVD, sputtering, and hydrothermal method are preferable, mist CVD and HVPE are more preferable, and mist CVD is further preferable.

FIG. 4 is a schematic cross-sectional view showing the configuration of the mist CVD apparatus 40. The mist CVD apparatus 40 includes a susceptor 50 on which the base substrate 12 is placed, a dilution gas source 42a, a carrier gas source 42b, and a flow rate control valve 43a for adjusting the flow rate of the dilution gas sent out from the dilution gas source 42a. On the bottom of the container 45, the flow control valve 43b for adjusting the flow rate of the carrier gas sent out from the carrier gas source 42b, the mist generation source 44 containing the raw material solution 44a, the container 45 containing the water 45a, and the bottom surface of the container 45. It includes an attached ultrasonic transducer 46, a quartz tube 47 serving as a film forming chamber, a heater 48 installed around the quartz tube 47, and an exhaust port 51. The susceptor 50 is made of quartz, and the surface on which the base substrate 12 is placed is inclined from the horizontal plane.

The raw material solution 44a 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, and is, for example, an organic metal complex of Ga, a halide of Ga, and a halide of Ga. Examples thereof include those in which one or more of organic metal complexes of Ga and a metal forming a solid solution are dissolved in a solvent. Examples of organometallic complexes include acetylacetonate complexes, and examples of halides include GaCl ₃ and GaBr ₃ . When a halide is used as a raw material and dissolved in a solvent, a halogen element is contained in the raw material solution. However, in order to facilitate the preparation of the solution, the halide may be directly dissolved in the solvent or hydrogen halide in water. The halide may be dissolved in a solution to which an acid (for example, hydrochloric acid) is added, or metal Ga may be dissolved in a solution of water and a hydrohalic acid. _{Further, when forming an α-Ga 2} O ₃ system semiconductor film containing a Group 14 element as a dopant, or forming a mixed crystal film with _{α-Ga 2} O ₃ containing an oxide of In or Al. In some cases, a solution containing these components may be added to the raw material solution. Further, even when the organometallic complex is used as a raw material, an additive such as hydrohalic 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 44a is atomized to generate mist 44b. A preferred example of the atomization method is a method of vibrating the raw material solution 44a using the ultrasonic vibrator 46. Then, the obtained mist 44b is conveyed to the film forming chamber using a carrier gas. The carrier gas is not particularly limited, but one or more kinds of an inert gas such as oxygen, ozone and nitrogen, and a reducing gas such as hydrogen can be used.

The film forming chamber (quartz tube 47) is provided with a base substrate 12. The mist 44b conveyed to the film forming chamber is thermally decomposed and chemically reacted there to form a film on the substrate 12. The reaction temperature varies depending on the type of the raw material solution, but is preferably 300 to 800 ° C, more preferably 350 to 700 ° C. The atmosphere in the film forming chamber is not particularly limited as long as a desired semiconductor film can be obtained, and may be an oxygen gas atmosphere, an inert gas atmosphere, a vacuum or a reducing atmosphere, but an air atmosphere is preferable. In addition, a droplet of the raw material solution 44a may be used in place of or in addition to the mist 44b.

FIG. 5 is a schematic cross-sectional view showing the configuration of the vapor deposition apparatus 60 using HVPE. The vapor phase growth apparatus 60 includes a reaction vessel 62 and a heater 64.

The reaction vessel 62 is a vessel made of a material (for example, quartz) that does not react with various raw materials and products. A carrier gas supply pipe 66, an oxidation gas supply pipe 68, and a raw material supply pipe 70 are attached to one side surface of the pair of side surfaces of the reaction vessel 62 facing each other, and an exhaust pipe 74 is attached to the other side surface. There is. The carrier gas supply pipe 66 supplies a carrier gas (for example, nitrogen, a rare gas, etc.) into the reaction vessel 62. The oxidation gas supply pipe 68 supplies oxygen gas as an oxidation gas into the reaction vessel 62. In addition to oxygen, water vapor, nitrous oxide, or the like may be supplied as the oxidation gas. In the raw material supply pipe 70, halogen gas (for example, chlorine gas) or hydrogen halide gas (for example, hydrogen chloride gas) supplied from the gas supply source and metallic gallium in the accommodating portion 72 provided in the middle of the raw material supply pipe 70. And react to form gallium halide. Therefore, the raw material supply pipe 70 supplies gallium halide gas as a raw material gas into the reaction vessel 62. The halogen gas or the hydrogen halide gas may be supplied together with a carrier gas such as nitrogen or a rare gas. A susceptor 76 for detachably holding the base substrate 12 is provided downstream of the

supply pipes

66, 68, 70 in the reaction vessel 62. The exhaust pipe 74 discharges the unreacted gas in the reaction vessel 62. A vacuum pump may be connected to the exhaust pipe 74, and the degree of vacuum in the reaction vessel 62 may be adjusted by the vacuum pump. Thereby, the gas phase reaction can be suppressed and the growth rate distribution can be improved.

The heater 64 is arranged so as to surround the reaction vessel 62. As the heater 64, for example, a resistance heating type heater or the like can be adopted.

A case where the laminated structure 10 of this embodiment is produced by using the vapor phase growth apparatus 60 will be described. In the reaction vessel 62, the oxygen gas supplied from the oxidation gas supply pipe 68 and the raw material gas (gallium halide gas) supplied from the raw material supply pipe 70 react with each other to form a semiconductor film 14 (gallium halide gas) on the base substrate 12. α-Ga ₂ O ₃ film) is formed. The film formation temperature is not particularly limited, and may be appropriately set in the range of, for example, 300 ° C. or higher and 800 ° C. or lower. The partial pressure of the oxygen gas or the raw material gas is not particularly limited. For example, the partial pressure of the raw material gas may be in the range of 0.05 kPa or more and 10 kPa or less, and the partial pressure of the oxygen gas is 0.25 kPa or more and 50 kPa or less. It may be a range. The growth time may be appropriately set according to the design value of the film thickness of the semiconductor film 14. As a result, the laminated structure 10 is obtained.

(B) Step of peeling the semiconductor film 14 from the base substrate 12 The method of peeling the semiconductor film 14 from the base substrate 12 of the laminated structure 10 at room temperature obtained as described above from the base substrate 12 is particularly limited. A known method can be used instead of the one. Examples of the peeling method include a method of peeling by applying a mechanical impact, a method of peeling by applying heat and utilizing thermal stress, and a method of peeling by applying vibration such as ultrasonic waves. By peeling, the semiconductor film 14 can be obtained as a self-supporting film. Alternatively, the semiconductor film 14 can be reprinted on another support substrate.

_{The α-Ga 2} O ₃ system semiconductor film of the present embodiment described above is a nunchaku having rod-shaped regions at both ends of a thin linear region in a flat TEM bright-field image when an electron beam is incident in parallel in the <001> direction. Type tissue is observed. Therefore, it is possible to suppress the occurrence of cracks in the α-Ga ₂ O _{3 system semiconductor film.}

It goes without saying that the present invention is not limited to the above-described embodiment, and can be implemented in various embodiments as long as it belongs to the technical scope of the present invention.

Hereinafter, examples of the present invention will be described. The following examples do not limit the present invention in any way.

[Example 1]
_{The α-Ga 2} O ₃ film (semiconductor film) was formed by the following method using the mist CVD apparatus 40 shown in FIG. As the base substrate 12, a commercially available Cr ₂ O ₃ single crystal (8 mm × 8 mm, thickness 0.5 mm, c-plane, no off-angle, hereinafter _{referred to as Cr 2} O ₃ substrate) was used.

(1) Formation of α-Ga ₂ O ₃ film by mist CVD method (1a) Preparation of raw material solution The aqueous solution was adjusted to 0.09 mol / L of gallium acetylacetonate. At this time, 36% hydrochloric acid was contained in a volume ratio of 1.5% to prepare a raw material solution 44a.

(1b) Preparation for film formation Next, the obtained raw material solution 44a was housed in the mist generation source 44 of the mist CVD apparatus 40 of FIG. The Cr ₂ O ₃ substrate was placed on the susceptor 50 as the base substrate 12, and the heater 48 was operated to raise the temperature inside the quartz tube 47 to 570 ° C. Next, the

flow control valves

43a and 43b are opened to supply the diluted gas and the carrier gas into the quartz tube 47 from the diluted gas source 42a and the carrier gas source 42b, and the atmosphere of the quartz tube 47 is sufficiently filled with the diluted gas and the carrier gas. After the replacement, the flow rate of the diluting gas was adjusted to 0.5 L / min, and the flow rate of the carrier gas was adjusted to 1 L / min. Nitrogen gas was used as the diluting gas and the carrier gas.

(1c) Membrane formation Next, the ultrasonic vibrator 46 is vibrated at 2.4 MHz, and the vibration is propagated to the raw material solution 44a through water 45a to mist the raw material solution 44a to generate mist 44b. did. This mist 44b is introduced into the quartz tube 47, which is a film forming chamber, by a diluting gas and a carrier gas, reacts in the quartz tube 47, and crystallizes on the base substrate 12 by a CVD reaction on the surface of the base substrate 12. The α-Ga ₂ O ₃ film (semiconductor film 14) was laminated. The film formation time was 40 minutes. In this way, a laminated structure 10 having a semiconductor film 14 on the base substrate 12 was obtained.

(2) Evaluation of semiconductor film (2a) Surface EDS
As a result of performing EDS measurement on the film surface on the film formation side of the obtained film, only Ga and O were detected, and it was found that the obtained film was a Ga oxide.
(2b) EBSD

Film surface on the film formation side composed of Ga oxide by SEM (Hitachi High-Technologies Corporation, SU-5000) equipped with an electron backscatter diffraction device (EBSD) (Nordlys Nano manufactured by Oxford Instruments). Inverse pole map orientation mapping was performed with a field of view of 500 μm × 500 μm. The conditions for this EBSD measurement were as follows.
<EBSD measurement conditions>
・ Acceleration voltage: 15kV
・ Spot intensity: 70
・ Working distance: 22.5mm
・ Step size: 0.5 μm
-Sample tilt angle: 70 °
-Measurement program: Aztec (version 3.3)
From the obtained reverse pole map orientation mapping, it was found that the Ga oxide film has a corundum-type crystal structure with c-axis orientation in the normal direction of the substrate and biaxial orientation with in-plane orientation. From these, it was shown that an alignment film composed of _{α-Ga 2} O _{3 was formed.}

(2c) Cross-section TEM
A cross-section test piece is cut out from the α-Ga ₂ O ₃ film so that both the film-forming side and _{the interface side between the Cr 2} O ₃ substrate are included and the sample thickness (T) around the measurement field of view is 200 nm. It was. Using the obtained test piece, a cross-sectional TEM observation (measuring device: Hitachi H-90001UHR-I) was carried out by injecting an electron beam in parallel in the <1-10> direction at an acceleration voltage of 300 kV. As a result of measuring the thickness of the _{α-Ga 2} O ₃ film from the obtained TEM image, it was 0.7 μm. In the bright field image of the cross-sectional TEM, a structure composed of a plurality of linear dark areas was observed. Among the linear tissues observed in this bright-field image, there was a tissue that did not disappear in both the dark-field image g * = 110 and the dark-field image g * = 00-6 of the same cross-sectional TEM. Such indelible structures are not attributed to either blade dislocations or spiral dislocations.

(2d) Flat surface TEM of the film-forming side surface
A test piece for flat TEM observation was cut out from the α-Ga ₂ O ₃ film so as to include a surface having a depth of about 0.04 μm just below the surface on the film formation side, and the thickness (T) of the test piece around the measurement field of view was increased. It was processed by ion milling so as to have a thickness of 70 nm. FIG. 6 shows a schematic cross-sectional view of the cutout position of the test piece. In order to evaluate the crystallinity of the α-Ga ₂ O ₃ film, a test piece for plane TEM observation was used, and an electron beam was incident parallel to the <001> direction at an acceleration voltage of 300 kV to observe the plane TEM (measuring device:: Hitachi H-90001UHR-I) was carried out. Actually, a TEM image having a plane measurement field of view of 4.0 μm × 2.6 μm was observed in two fields of view. The obtained two-field planar TEM observation bright-field images are shown in FIGS. 7 and 8, respectively. Further, FIG. 9 shows a bright field image in which a part of FIG. 7 is enlarged. As shown in FIG. 9, a nunchaku-type structure was observed in the bright-field image of the plane TEM observation. The nunchaku-type structure had rod-shaped regions A and A'at both ends of the fine linear region B.

In FIGS. 7 and 8, nunchaku-type tissues were observed at 7 sites. When the density of the nunchaku-type tissue was calculated from the area of the measurement field of view and the number of nunchaku-type tissues, it was 3.4 × 10 ⁷ / cm ² . The observed nunchak-shaped structure had a total length (the length of the line segment connecting the points of the outer ends of the rod-shaped region) of 376 to 645 nm, a rod-shaped region of 82 nm to 131 nm (average 107 nm), and a fine linear region. The length (the length of the line segment connecting both ends of the thin linear region) was 245 nm to 408 nm (average 352 nm).

(2e) Flat surface STEM on the film formation side
In order to evaluate the state of the nunchaku-type tissue of the α-Ga ₂ O ₃ membrane, a planar STEM observation (plan view) near the structure shown in FIG. 9 was performed. STEM observation was performed at an acceleration voltage of 200 kV using a field emission transmission electron microscope (ARM-200F Dual-X manufactured by JEOL). An electron beam was incident and observed in parallel with the <001> direction.

The BF-STEM image near the nunchaku-type tissue shown in FIG. 9 is shown in FIG. In FIG. 10, a nunchaku-shaped structure having rod-shaped regions A and A'at both ends of the thin line-shaped region B was observed. The HAADF-STEM images obtained by enlarging the rod-shaped region A and the thin line-shaped region B are shown in FIGS. 11 and 12, respectively. The vicinity of the arrow in FIG. 11 corresponds to the rod-shaped region A, and the vicinity of the arrow in FIG. 12 corresponds to the thin line region B. The white dots in the figure indicate the cation atom image (Ga atom). Since the atomic image is a little unclear, it is considered that the Ga atomic arrangement is disturbed, but no increase or decrease in the atomic plane was confirmed at any of the locations. In the case of dislocations (blade-shaped dislocations, spiral dislocations, mixed dislocations, basal plane dislocations, etc.), an increase or decrease is confirmed on the atomic surface. Was also found not to be attributed.

(2f) Appearance evaluation of semiconductor film Using an industrial microscope (Nikon ECLIPSE LV150N), the appearance of the obtained semiconductor film was set to 10 times for the eyepiece and 5 times for the objective lens, and the film was set in the polarization / differential interference contrast mode. The entire surface was observed, but no cracks were observed.

[Comparative Example 1]
_{As the base substrate 12, an α-Ga 2} O ₃ film was formed in the same manner as in Example 1 except that a sapphire substrate having a diameter of 5.08 cm (2 inches), a thickness of 0.65 mm, a c-plane, and no off-angle was used. It was formed and various evaluations were carried out. As a result of performing EDS measurement on the film surface on the film formation side of the obtained film, only Ga and O were detected, and it was found that the obtained film was a Ga oxide. From the reverse pole map orientation mapping of the film surface on the film formation side, it was found that the Ga oxide film has a corundum-type crystal structure in which the Ga oxide film is oriented in the c-axis direction in the normal direction of the substrate and is also oriented in the plane. From these, it was shown that an alignment film composed of _{α-Ga 2} O _{3 was formed.} When the plane TEM observation of the surface on the film-forming side was carried out, no nunchaku-type structure was observed from the bright-field image. When the appearance of the obtained semiconductor film was observed using an industrial microscope, many cracks were observed.

The present invention can be used, for example, as a material for power semiconductors.

10 laminated structure, 12 base substrate, 14 semiconductor film, 20 nunchak type structure, 22 fine linear region, 24 rod-shaped region, 40 mist CVD device, 42a diluted gas source, 42b carrier gas source, 43a flow control valve, 43b flow control Valve, 44 mist source, 44a raw material solution, 44b mist, 45 container, 45a water, 46 ultrasonic transducer, 47 quartz tube, 48 heater, 50 susceptor, 51 exhaust port, 60 gas phase growth device, 62 reaction vessel, 64 heaters, 66 carrier gas supply pipes, 68 oxide gas supply pipes, 70 raw material supply pipes, 72 accommodating parts, 74 exhaust pipes, 76 susceptors.

Claims

In a flat TEM bright-field image when an electron beam is incident parallel to the <001> direction, a nunchaku-shaped structure having rod-shaped regions wider than the fine-wired region is observed at both ends of the fine-wired region, α. -Ga 2 O 3 system semiconductor film.
The nunchaku-type structure is a structure that is not attributed to any of blade-shaped dislocations, spiral dislocations, mixed dislocations, basal plane dislocations, and surface defects.
The α-Ga 2 O 3 system semiconductor film according to claim 1.
The density of the nunchaku-type tissue is 1.0 × 10 6 / cm 2 or more and 1.0 × 10 8 / cm 2 or less.
The α-Ga 2 O 3 system semiconductor film according to claim 1 or 2.
The total length of the nunchaku-type structure is 100 nm or more and 800 nm or less.
The α-Ga 2 O 3 system semiconductor film according to any one of claims 1 to 3.