WO2020261355A1 - Semiconductor film - Google Patents

Abstract

This semiconductor film: has a corundum crystal structure comprising α–Ga₂O₃ or an α–Ga₂O₃-based solid solution; has a film surface area of at least 19 cm²; and has a minimum film thickness that is 50%–95% of the maximum film thickness.

Description

Semiconductor film

The present invention relates to a 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 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, so that there is a problem that the epitaxial film cracks. 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.

Patent Document 5 discloses an example in which a crystalline oxide semiconductor film having a large area and substantially free of cracks is obtained by using a film-forming base substrate on which two or more oxide layers are formed. Has been done. However, it is necessary to form a plurality of layers on the base substrate, which complicates the work and is disadvantageous in terms of cost. Further, when the film produced by this method is separated from the film-forming base substrate to be self-supporting, or when it is reprinted on another support substrate, cracks and the like are still likely to occur. Therefore, an α-Ga ₂ O ₃ semiconductor film and a method for producing the same are desired, in which cracks and the like are less likely to occur not only at the time of film formation but also after self-supporting.

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 JP-A-2018-2544

By the way, in order to produce a low-cost power semiconductor device, it is preferable to form an α-Ga ₂ O ₃ system semiconductor film on a large-diameter substrate, but when the area of the film surface becomes large, the semiconductor film cracks. There was a problem that it was easy to occur. For example, in Patent Documents 3 and 4, since a square crystal growth substrate having a side of 10 mm is used to form an α-Ga ₂ O ₃ system semiconductor film on the substrate, the film surface of the obtained semiconductor film is obtained. The area of the semiconductor film was only about 1 cm ^2, which was a condition in which cracks were unlikely to occur in the semiconductor film.

The present invention has been made to solve such a problem, and an object of the present invention is to provide an α-Ga ₂ O ₃ system semiconductor film having a large film surface area but few cracks. ..

The semiconductor film of the present invention is a semiconductor film (α-Ga ₂ O ₃ system semiconductor film) having a collane type crystal structure composed of an α-Ga ₂ O ₃ or α-Ga ₂ O ₃ system solid solution. The surface area is 19 cm ² or more, and the minimum film thickness is 50% or more and 95% or less of the maximum film thickness.

According to this semiconductor film, cracks are reduced even though the area of the film surface is large. The mechanism is not clear, but it is presumed that stress concentration in the film is less likely to occur in the α-Ga ₂ O ₃ system semiconductor film by setting the film thickness distribution within a certain range.

It is explanatory drawing of the film thickness measurement position of a semiconductor film. It is a schematic cross-sectional view which shows the structure of the mist CVD apparatus 10.

[Semiconductor film]
The semiconductor film of the present embodiment has a corundum-type crystal structure composed of an α-Ga ₂ O ₃ or α-Ga ₂ O ₃ system solid solution. Such a semiconductor film is referred to as 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 . The plan view figure when the semiconductor film is viewed in a plan view is not particularly limited, and may be, for example, a circular shape or a polygon (a quadrangle such as a square or a rectangle, a pentagon or a hexagon). You may.

The area of the film surface of the semiconductor film is preferably 19 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 in this way, it is possible to obtain a large number of semiconductor elements from one semiconductor film, and it is possible to reduce the manufacturing cost. The upper limit of the size of the semiconductor film is not particularly limited, but is typically 700 cm ² or less on one side.

The minimum film thickness of the semiconductor film is preferably 50% or more and 95% or less of the maximum film thickness. It is presumed that stress concentration in the semiconductor film is less likely to occur by setting the film thickness distribution within this range. If the minimum film thickness is less than 50% or more than 95% of the maximum film thickness, the number of cracks increases, which is not preferable.

The minimum film thickness and the maximum film thickness of the semiconductor film can be set as follows, for example. FIG. 1 is an explanatory diagram of a semiconductor film thickness measurement position. First, in a plan view figure when a semiconductor film is viewed in a plan view, four straight lines are drawn every 90 ° from a point G, which is the center of gravity of the plan view figure, and a point P at which each straight line intersects the outer edge of the semiconductor film. , Q, R, S. Then, the points that divide the lengths of the line segments GP, GQ, GR, and GS from the point G to 8: 2 are defined as points A, B, C, and D, and the film thickness Gt at the points G, A, B, C, and D, The minimum value of At, Bt, Ct, and Dt is set to the minimum film thickness, and the maximum value is set to the maximum film thickness. The film thickness can be measured, for example, by TEM observation of the cross section. The film thickness Gt is preferably larger than the average value AVt of the film thicknesses At, Bt, Ct, and Dt, and preferably larger than any of the film thicknesses At, Bt, Ct, and Dt. Further, the outer peripheral minimum value, which is the minimum value among the film thicknesses At, Bt, Ct, and Dt, is 80% or more of the outer peripheral maximum value, which is the maximum value among the film thicknesses At, Bt, Ct, and Dt. It is preferably 90% or more, more preferably 95% or more. From the viewpoint of reducing the number of cracks, it is preferable that the film thicknesses Gt, At, and Ct satisfy the following equations. In the following formula, AC is the length of the line segment AC, and Const is a constant. Const is preferably 8.0 × 10 ^-6 , more preferably 5.0 × 10 ^-6 , and even more preferably 2.5 × 10 ^-6 . The semiconductor film preferably has a circular shape in a plan view. Even if the film thickness At is replaced with the film thickness Bt, the film thickness Ct is replaced with the film thickness Dt, and the AC is replaced with BD (the length of the line segment BD) in the following formula, it is preferable to satisfy the relationship of the following formula. ..
Z = (| At-Gt | + | Ct-Gt |) / AC <Const

The number of cracks per 20 cm ² of the film surface of the semiconductor film is preferably 20 or less, more preferably 15 or less, still more preferably 10 or less, and particularly preferably 5 or less. The number of cracks can be counted using an industrial microscope (ECLIPSE LV150N manufactured by Nikon). The eyepiece is set to 10 times, the objective lens is set to 5 times, the entire film surface is observed in the polarization / differential interference contrast mode, and if cracks are confirmed, the objective lens is changed to 10 times to acquire an image. In this embodiment, only cracks having a length of 50 μm or more are counted as cracks. If the distance from one crack to another is 500 μm or less, it is regarded as one crack. Regardless of the size of the semiconductor film, the number of cracks on the entire surface of the film is measured and converted to a film area of 20 cm ² .

The semiconductor film can contain a Group 14 element as a dopant at a ratio of 1.0 × 10 ¹⁵ to 1.0 × 10 ²¹ / cm ³ . Here, the Group 14 elements are 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 dopant can be appropriately changed according to the desired characteristics, but is preferably 1.0 × 10 ¹⁵ 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 are about the same.

Further, the semiconductor film is preferably an alignment film oriented in a specific plane orientation. The orientation of the semiconductor film can be investigated by a known method, but it can be investigated, 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.

The average film thickness of the semiconductor film may be appropriately adjusted from the viewpoint of cost and required characteristics. That is, if it is too thick, it takes time to form a film, so it is preferable that the film is not extremely thick from the viewpoint of cost. Further, when a device that requires a particularly high dielectric strength is manufactured, a thick film is preferable. On the other hand, when manufacturing a device that requires conductivity in the vertical direction (thickness direction), a thin film is preferable. As described above, the average film thickness may be appropriately adjusted according to the desired characteristics, but is typically 0.1 to 50 μm, preferably 0.2 to 20 μm, and more preferably 0.2 to 10 μm. By setting the film thickness in such a range, it is possible to achieve both cost and semiconductor characteristics. When a self-supporting semiconductor film is required, the average film thickness may be increased, for example, 50 μm or more, preferably 100 μm or more, and there is no particular upper limit unless there is a cost limitation.

[Manufacturing method of semiconductor film]
The method for producing a semiconductor film of the present embodiment is not particularly limited as long as the above-mentioned semiconductor film can be produced. For example, mist CVD, HVPE, MBE, MOCVD, sputtering and the like can be used, of which mist CVD and HVPE are preferable, and mist CVD is more preferable. In mist CVD, the distribution of the film thickness of the semiconductor film can be controlled by the number of rotations of the base substrate for crystal formation, the distance between the upper end of the nozzle for ejecting mist and the lower surface of the base substrate, and the like. In HVPE, it can be controlled by the ratio of the substrate size to the width of the gas flow path, the shape of the jig on which the substrate is placed, the rectifying plate that controls the gas flow, the presence or absence of rotation of the substrate, and in sputtering. It can be controlled by the shape of the jig on which the gas is placed, the size relationship and positional relationship between the target and the substrate, the application of a mask, and the like. The mist CVD will be described in detail below.

FIG. 2 is a schematic cross-sectional view showing the configuration of the mist CVD apparatus 10. The mist CVD apparatus 10 includes a mist generator 12, a mist supply pipe 18, and a growth chamber 20. The mist generator 12 generates mist by oscillating the raw material solution stored in the mist generator 12 with ultrasonic waves by operating the ultrasonic vibrator 14 provided on the bottom surface. A gas introduction port 16 is provided on the side surface of the mist generator 12. The gas introduction port 16 can introduce carrier gas into the mist generator 12 from the outside. The mist supply pipe 18 connects the mist generator 12 and the growth chamber 20. The lower end of the mist supply pipe 18 penetrates the ceiling surface of the mist generator 12 and communicates with the inside of the mist generator 12. The upper end of the mist supply pipe 18 communicates with the nozzle 22 attached to the floor surface of the growth chamber 20. Therefore, the mist generated in the mist generator 12 is supplied into the growth chamber 20 via the mist supply pipe 18. The growth chamber 20 is a cylindrical container, which is provided with a gas discharge port 24 on the upper side surface and a rotating stage 26 on the ceiling surface. The rotating stage 26 is a disk-shaped rotating body, and rotates as the rotating shaft 26a is rotated by a motor (not shown). A base substrate 28 for crystal growth is detachably held on the lower surface of the rotating stage 26. A heater 30 for heating the base substrate 28 held by the rotary stage 26 is provided on the ceiling surface of the growth chamber 20.

A case where the semiconductor film of the present embodiment is formed by using the mist CVD apparatus 10 will be described. The raw material solution used in the mist CVD method is not limited as long as it is a solution that can obtain a semiconductor film composed of an α-Ga ₂ O ₃ or α-Ga ₂ O ₃ solid solution, but is not limited, for example, Ga and / or Examples thereof include an organic metal complex of a metal forming a solid solution with Ga and a halide dissolved in a solvent. Further, the metal Ga may be dissolved with an acid. Examples of the organometallic complex include an acetylacetonate complex. When adding a dopant to the semiconductor film, 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. The prepared raw material solution is put into the mist generator 18. A sapphire substrate which is α-Al ₂ O ₃ as a base substrate 28 is detachably held on the lower surface of the rotating stage 26. At this time, the distance d (see FIG. 2) between the upper end of the nozzle 22 and the lower surface of the base substrate 28 is set to an appropriate value (for example, 100 mm or more and 200 mm or less). Then, the rotation stage 26 is rotated at a desired rotation speed (for example, 5 rpm or more and 100 rpm or less). Further, the heater 30 heats the rotary stage 26 to a desired temperature (for example, 300 ° C. or higher and 800 ° C. or lower, preferably 400 ° C. or higher and 700 ° C. or lower). Then, in the mist generator 18, the raw material solution is atomized by the ultrasonic vibrator 14 to generate mist. The mist generated by the mist generator 18 passes through the mist supply pipe 18 together with the carrier gas (for example, N ₂ or rare gas) introduced from the gas introduction port 16 and is provided on the floor surface of the growth chamber 20. Is supplied upward from the inside of the growth chamber 20. As a result, gallium halide in the raw material solution is thermally decomposed into gallium oxide, which grows heteroepitaxially on the lower surface of the underlying substrate 28 to form an α-Ga ₂ O ₃ system semiconductor film. The growth time may be appropriately set according to the design value of the film thickness of the semiconductor film. The obtained semiconductor film can be formed as it is or divided into semiconductor elements. Alternatively, the semiconductor film may be peeled from the base substrate 28 to form a single film, or the peeled semiconductor film may be reprinted on a support substrate made of a material different from that of the base substrate 28.

The base substrate 28 is preferably a substrate having a corundum structure, and particularly preferably a substrate oriented in two axes of the c-axis and the a-axis (biaxially oriented substrate). The biaxially oriented substrate may be a polycrystal, a mosaic crystal (a set of crystals whose crystal orientations are slightly deviated), or a single crystal. The base substrate 28 may be composed of a single material or a solid solution of a plurality of materials as long as it has a corundum structure. The base substrate 28 may be a composite base substrate having a layer of a material having a lattice constant closer to α-Ga ₂ O ₃ than the base substrate of a material having a corundum structure. For the composite base substrate, for example, (a) a base substrate made of a material having a corundum structure is prepared, and (b) an orientation precursor layer is used using a material having a lattice constant closer to α-Ga ₂ O ₃ than the material of the base substrate. (C) The alignment precursor layer is heat-treated on the base substrate to convert at least a portion near the base substrate into an alignment layer, and if desired, processing such as (d) grinding or polishing is performed to perform the alignment layer. It can be manufactured by exposing the surface of the. The base substrate 28 is, for example, a sapphire substrate or a layer of an oxide (α-Cr ₂ O ₃ or α-Fe ₂ O ₃ or the like) having a lattice constant closer to α-Ga ₂ O ₃ than sapphire on one surface of the sapphire substrate. For example, a composite base substrate provided with.

It is needless to say 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.

The present invention will be described in more detail with reference to the following examples. The present invention is not limited to the following examples.

[Example 1]
1. 1. Preparation of film (1) Preparation of raw material solution Metal Ga was added to hydrochloric acid, and the mixture was stirred at room temperature for 3 weeks to obtain a gallium chloride solution having a gallium ion concentration of 3 mol / L. Water was added to the obtained gallium chloride solution to adjust the aqueous solution so that the gallium ion concentration was 40 mmol / L. Further, ammonium hydroxide was added to adjust the pH to 4.0 to prepare a raw material solution.

(2) Preparation for film formation In the mist CVD apparatus 10 having the configuration shown in FIG. 2, the raw material solution of (1) above was housed in the mist generator 12. Next, a c-plane sapphire substrate having a diameter of 50.8 mm (area 20.3 cm ² ) was set as the base substrate 28, and the distance d between the upper end of the nozzle 22 and the lower surface of the base substrate 28 was set to 150 mm. The temperature of the rotary stage 26 was raised to 500 ° C. by the heater 30 and held for 30 minutes for temperature stabilization. Next, a flow rate control valve (not shown) provided in the gas introduction port 16 is opened to supply carrier gas to the inside of the mist generator 12 and the film forming chamber 20, and the atmosphere of the mist generator 12 and the film forming chamber 20 is changed to the carrier. After sufficient replacement with gas, the flow rate of the carrier gas was adjusted to 1.0 L / min. Here, nitrogen gas was used as the carrier gas.

(3) Film formation The rotation speed of the rotation stage 26 is set to 5 rpm, the raw material solution is atomized by the ultrasonic vibrator 14, the generated mist is introduced into the film formation chamber 20 by the carrier gas, and the reaction occurs in the film formation chamber 20. A circular film was formed on the lower surface of the base substrate 28. The film formation temperature was 500 ° C., and the film formation time was 1 hour. Area of the film, from the area of the base substrate 28, was 19.3Cm ² obtained by subtracting the area of 1 cm ² was covered with a jig for holding the base substrate 28 on the rotary stage 26.

2. 2. Evaluation of membrane (1) Surface EDX
As a result of performing EDX measurement on the surface of the obtained film, only Ga and O were detected. From this, it was found that the obtained film was a Ga oxide.

(2) EBSD
The EBSD measurement of the Ga oxide film was performed. 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.

(3) Film thickness The film thickness can be evaluated by TEM observation of the cross section. It can be carried out using a general transmission electron microscope. For example, when using Hitachi H-90001UHR-I, TEM observation may be performed at an acceleration voltage of 300 kV. The test piece used for TEM observation may be produced by sampling the film and the substrate at the film thickness measurement site by FIB and thinning them by ion milling. The film thickness can be evaluated from the TEM image of the cross section of the test piece thus obtained. As for the film thickness, the film thickness Gt, At, Bt, Ct, and Dt were measured at five points on the substrate at points G, A, B, C, and D. Then, the average value of the film thicknesses At, Bt, Ct, and Dt was taken as the average film thickness AVt, and Gt / AVt was obtained. Further, the minimum and maximum values of the film thicknesses Gt, At, Bt, Ct, and Dt were set as the minimum film thickness and the maximum film thickness, respectively, and the minimum film thickness / maximum film thickness was determined. Further, the minimum value and the maximum value of the film thicknesses At, Bt, Ct, and Dt were set as the outer circumference minimum value and the outer circumference maximum value, respectively, and the outer circumference minimum value / outer circumference maximum value was obtained. In addition, the value of Z explained in the column of [Mode for carrying out the invention] was also obtained. The results are shown in Table 1.

(4) Number of cracks The number of cracks per 20 cm ² area of the film surface was counted by the method described in the column of [Mode for carrying out the invention]. That is, using an industrial microscope (Nikon ECLIPSE LV150N), the eyepiece is set to 10 times and the objective lens is set to 5 times, and the entire film surface is observed in the polarization / differential interference mode. If cracks are confirmed, the objective is used. The lens was changed to 10 times and an image was acquired. Then, only cracks having a length of 50 μm or more were counted as cracks. Further, when the distance from one crack to another is 500 μm or less, it is regarded as one crack. Regardless of the size of the film, the number of cracks on the entire surface of the film was measured and converted per 20 cm ^{2 of} the film area. The results are shown in Table 1.

[Example 2]
The film formation and evaluation were carried out in the same manner as in Example 1 except that the rotation speed of the rotation stage was set to 100 rpm. The results are shown in Table 1. The semiconductor film obtained in Example 2 was also found to be a Ga oxide from the EDX measurement and an alignment film having a biaxially oriented corundum-type crystal structure from the EBSD measurement.

[Example 3]
The film formation and evaluation were carried out in the same manner as in Example 1 except that the rotation speed of the rotation stage was set to 20 rpm. The results are shown in Table 1. The semiconductor film obtained in Example 3 was also found to be a Ga oxide from the EDX measurement and an alignment film having a biaxially oriented corundum-type crystal structure from the EBSD measurement.

[Example 4]
The film formation and evaluation were carried out in the same manner as in Example 1 except that the rotation speed of the rotation stage was 10 rpm and the size of the base substrate was φ100 mm (area 78.5 cm ² ). The results are shown in Table 1. The semiconductor film obtained in Example 4 was also found to be a Ga oxide from the EDX measurement and an alignment film having a biaxially oriented corundum-type crystal structure from the EBSD measurement.

[Comparative Example 1]
The film formation and evaluation were carried out in the same manner as in Example 1 except that the rotation speed of the rotation stage was set to 1000 rpm. The results are shown in Table 1. From the EDX measurement, it was found that the semiconductor film obtained in Comparative Example 1 was also a Ga oxide, and from the EBSD measurement, it was found to be an alignment film having a biaxially oriented corundum-type crystal structure.

[Comparative Example 2]
Film formation and evaluation were performed in the same manner as in Example 2 except that the distance between the nozzle tip and the substrate was 50 mm. The results are shown in Table 1. From the EDX measurement, it was found that the semiconductor film obtained in Comparative Example 2 was also a Ga oxide, and from the EBSD measurement, it was found to be an alignment film having a biaxially oriented corundum-type crystal structure.

[Discussion]
In Examples 1 to 4, since the minimum film thickness / maximum film thickness was 50% or more and 95% or less, the number of cracks per 20 cm ^{2 of} the film surface was 20 or less. On the other hand, in Comparative Example 1, the minimum film thickness / maximum film thickness was more than 95%, and in Comparative Example 2, the minimum film thickness / maximum film thickness was less than 50%, so the number of cracks per 20 cm ^{2 of} the film surface was 100. Beyond.

Of Examples 1 to 4, in Examples 1, 3 and 4, the film thickness Gt was larger than the average film thickness AVt (that is, Gt / AVt> 1), and therefore, as compared with Example 2, which is not so. The number of cracks was small. Further, in Examples 1, 3 and 4, since the film thickness Gt was larger than any of the film thicknesses At, Bt, Ct, and Dt, the number of cracks was smaller than that in Example 2, which was not the case. Further, among Examples 1, 3 and 4, since the outer peripheral minimum value was 80% or more of the outer peripheral maximum value in Examples 3 and 4, the number of cracks was smaller than that in Example 1 which was not so. Of Examples 3 and 4, in Example 3, Z was less than 8.0 × 10 ^-6 , so that the number of cracks was smaller than in Example 4, which was not.

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

10 mist CVD device, 12 mist generator, 14 ultrasonic oscillator, 16 gas inlet, 18 mist supply pipe, 20 growth chamber, 22 nozzle, 24 gas outlet, 26 rotary stage, 26a rotary shaft, 28 base substrate, 30 heater.

Claims (7)

1. A semiconductor film having a corundum-type crystal structure composed of an α-Ga ₂ O ₃ or α-Ga ₂ O ₃ solid solution.
   The area of the film surface is 19 cm ² or more,
   The minimum film thickness is 50% or more and 95% or less of the maximum film thickness.
   Semiconductor film.
2. The number of cracks per 20 cm ^{2 of the} film surface area is 20 or less.
   The semiconductor film according to claim 1.
3. In the plan view figure when the semiconductor film is viewed in a plan view, four straight lines are drawn every 90 ° from the point G which is the center of gravity of the plan view figure, and the points where each straight line intersects the outer edge of the plan view figure are pointed. When P, Q, R, S and the points that divide the lengths of the line segments GP, GQ, GR, GS from the point G to 8: 2 are the points A, B, C, D, the points G, A, B , C, D, the minimum value among the film thicknesses Gt, At, Bt, Ct, and Dt is set to the minimum film thickness, and the maximum value is set to the maximum film thickness.
   The semiconductor film according to claim 1 or 2.
4. The film thickness Gt is larger than the average value of the film thickness At, Bt, Ct, and Dt.
   The semiconductor film according to claim 3.
5. The film thickness Gt is larger than any of the film thicknesses At, Bt, Ct, and Dt.
   The semiconductor film according to claim 3 or 4.
6. The minimum value among the film thicknesses At, Bt, Ct and Dt is 80% or more of the maximum value among the film thicknesses At, Bt, Ct and Dt.
   The semiconductor film according to any one of claims 3 to 5.
7. The film thicknesses Gt, At, Ct are
   Z = (| At-Gt | + | Ct-Gt |) / AC <8.0 × 10 ^-6
   (In the formula, AC is the length of the line segment AC)
   Meet,
   The semiconductor film according to any one of claims 1 to 6.

Images