Stacked structure

Abstract

The stacked structure of the present invention is a stacked structure having a semiconductor film with a corundum-type crystal structure containing α-Ga2O3 or an α-Ga2O3 solid solution on a base substrate, wherein the average film thickness of the semiconductor film is greater than 10 μm, the semiconductor film is convexly or concavely warped, and the warping amount of the semiconductor film is greater than 20 μm and less than 64 μm.

Description

Technical Field

[0001] The present invention relates to a laminated structure. Background Art

[0002] Gallium oxide (Ga2O3) has recently attracted considerable attention as a semiconductor material. Gallium oxide is known to have five crystalline forms: α, β, γ, δ, and ε. α-Ga2O3, with its exceptionally large band gap of 5.3 eV, holds great promise as a power semiconductor material. However, α-Ga2O3 is a metastable phase, making it impractical for practical single-crystal substrates. Instead, it is typically grown heteroepitaxially on sapphire substrates.

[0003] For example, Patent Document 1 describes an example in which an α-(Al 0.02 Ga 0.98 )2O3 layers and α-Ga2O3 layers are alternately stacked as a buffer layer, and an α-Ga2O3 film is formed on the buffer layer as a crystalline oxide semiconductor film. In this example, the content of rotated domains in the crystalline oxide semiconductor film is 0.02% by volume or less, and warpage is reduced (specifically, the shortest distance between the shortest straight line passing through the two end points of a 5 mm interval and the vertex of the concave or convex portion is reduced to 0.21 μm).

[0004] Prior art literature

[0005] Patent Literature

[0006] Patent Document 1: Japanese Patent Application Laid-Open No. 2016-157878

[0007] Patent Document 2: Japanese Patent Application Laid-Open No. 2019-33271 Summary of the Invention

[0008] However, using the method of Patent Document 1, it is difficult to obtain a substantially crack-free α-Ga2O3-based semiconductor film over a large area. In particular, when a thick film of 10 μm or greater is produced, it is difficult to obtain a semiconductor film with sufficiently reduced cracks. In addition, when a film produced using this method is peeled off from a film-forming base substrate to make it self-supporting, or when the self-supporting film is transferred to another supporting substrate, cracks may sometimes be generated in the α-Ga2O3-based semiconductor film during peeling, or defects may be caused by poor peeling. Therefore, it is desirable to suppress the generation of cracks and poor peeling during the production of α-Ga2O3-based semiconductor films, thereby producing α-Ga2O3-based semiconductor films with a high yield.

[0009] Regarding the peeling method, for example, Patent Document 2 discloses a method of peeling by applying mechanical impact, a method of peeling by applying heat and utilizing thermal stress, a method of peeling by applying vibration such as ultrasonic waves, and a method of peeling by etching.

[0010] The present invention has been made to solve the above-mentioned problems, and its main object is to suppress the occurrence of cracks and delamination defects during the production of α-Ga 2 O 3 -based semiconductor films.

[0011] The stacked structure of the present invention is a stacked structure having a semiconductor film with a corundum-type crystal structure containing α-Ga2O3 or an α-Ga2O3 solid solution (hereinafter referred to as "α-Ga2O3 semiconductor film") on a base substrate, wherein the average film thickness of the semiconductor film is greater than 10 μm, the semiconductor film is convexly or concavely warped, and the warping amount of the semiconductor film is greater than 20 μm and less than 64 μm.

[0012] According to this stacked structure, cracks and peeling defects can be suppressed during the manufacture of α-Ga2O3-based semiconductor films. The mechanism is not yet clear, but it is believed that by keeping the warpage of the α-Ga2O3-based semiconductor film within an appropriate range, a moderate stress is applied to the semiconductor film, making it easy to peel off from the base substrate and less likely to crack. If the warpage is less than the lower limit of the appropriate range, the stress applied to the semiconductor film is sometimes insufficient, resulting in only partial peeling of the semiconductor film from the base substrate, or cracks when attempting to peel with a stronger force. If the warpage exceeds the upper limit of the appropriate range, the stress applied to the semiconductor film is sometimes too great, causing cracks in the semiconductor film on the base substrate.

[0013] In the present invention, the method for preparing a semiconductor film may include:

[0014] (a) forming a semiconductor film having a corundum-type crystal structure comprising α-Ga2O3 or an α-Ga2O3 solid solution on a base substrate by a spray CVD method or an HVPE method at a temperature of 300°C to 800°C, and then lowering the temperature to room temperature to obtain the above-mentioned stacked structure; and

[0015] (b) A step of peeling the semiconductor film of the stacked structure from the base substrate to obtain the semiconductor film.

[0016] According to this method for producing a semiconductor film, cracks and peeling defects are less likely to occur during the production of an α-Ga 2 O 3 -based semiconductor film, and therefore, the α-Ga 2 O 3 -based semiconductor film can be produced relatively easily with a good yield. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 1 and 2 are explanatory diagrams of the stacked structure 10 , wherein (a) is a plan view and (b) is an AA cross-sectional view.

[0018] Figure 2 It is an explanatory diagram regarding a method of measuring the warpage amount of the semiconductor film 14 .

[0019] Figure 3 It is an explanatory diagram regarding a method of measuring the warpage amount of the semiconductor film 14 .

[0020] Figure 4 It is an explanatory diagram regarding a method of measuring the warpage amount of the semiconductor film 14 .

[0021] Figure 5 It is an explanatory diagram regarding a method of measuring the warpage amount of the semiconductor film 14 .

[0022] Figure 6 It is an explanatory diagram regarding a method of measuring the warpage amount of the semiconductor film 14 .

[0023] Figure 7 It is a schematic cross-sectional view showing the structure of the spray CVD apparatus 20 .

[0024] Figure 8 It is a schematic cross-sectional view showing the structure of the vapor phase growth apparatus 60 .

[0025] Figure 9 It is a schematic cross-sectional view showing the structure of the AD device 40 .

[0026] Figure 10 This is a diagram showing the manufacturing process of a composite base substrate. DETAILED DESCRIPTION

[0027] [Laminated structure]

[0028] Figure 1 1 and 2 are explanatory diagrams of a stacked structure 10 according to the present embodiment, wherein (a) is a plan view and (b) is an AA cross-sectional view.

[0029] The stacked structure 10 is a plate-shaped component comprising a semiconductor film 14 on a base substrate 12. In this embodiment, the stacked structure 10 is circular when viewed from above. However, the stacked structure 10 is not limited to a circular shape and may be, for example, a polygonal shape (a quadrilateral such as a square or rectangle, a pentagon, a hexagon, etc.).

[0030] The base substrate 12 is preferably a substrate having a corundum structure, and is particularly preferably a substrate oriented along the c-axis and the a-axis (a biaxially oriented substrate). The biaxially oriented substrate may be a polycrystalline, a mosaic crystal (a collection of crystals with several crystal orientation deviations), or a single crystal. The base substrate 12 only needs to have a corundum structure and may be composed of a single material or a solid solution of multiple materials. The base substrate 12 may be a composite base substrate having a layer of a material having a corundum structure and a lattice constant closer to α-Ga2O3 than the material on a base substrate of a material having a corundum structure. The composite base substrate can be manufactured as follows: for example, (a) preparing a base substrate of a material having a corundum structure; (b) making an orientation precursor layer using a material having a lattice constant closer to α-Ga2O3 than the material of the base substrate; (c) heat-treating the orientation precursor layer on the base substrate to convert at least the portion near the base substrate into an orientation layer; and (d) applying grinding, polishing, or other processing as needed to expose the surface of the orientation layer. Examples of the base substrate 12 include a sapphire substrate and a composite base substrate including a layer of an oxide (such as α-Cr 2 O 3 or α-Fe 2 O 3 ) having a lattice constant closer to that of α-Ga 2 O 3 than that of sapphire on one surface of a sapphire substrate.

[0031] The semiconductor film 14 is a film having a corundum-type crystal structure, containing α-Ga2O3 or an α-Ga2O3-based solid solution, that is, an α-Ga2O3-based semiconductor film. α-Ga2O3 belongs to the trigonal crystal group and has a corundum-type crystal structure. An α-Ga2O3-based solid solution is a material formed by dissolving other components in α-Ga2O3, maintaining a corundum-type crystal structure. Examples of other components include Al2O3, In2O3, Cr2O3, Fe2O3, Rh2O3, V2O3, and Ti2O3.

[0032] The semiconductor film 14 is warped in a convex or concave shape. In all cases, the warping amount is in the range of 20 μm to 64 μm, preferably 30 μm to 64 μm, and more preferably 30 μm to 50 μm. The convex warping of the semiconductor film 14 means: Figure 3 and Figure 4 As shown in FIG. 1 , when observing a cross section of the semiconductor film 14 cut along the thickness direction, the film surface of the semiconductor film 14 (the surface on the side opposite to the base substrate 12) is convex. The concave warping of the semiconductor film 14 means: Figure 5 and Figure 6 As shown, when observing a cross section of the semiconductor film 14 cut along the thickness direction, the film surface of the semiconductor film 14 (the surface on the side opposite to the base substrate 12 side) is concave.

[0033] The following uses Figures 2 to 6 , the warping amount of the semiconductor film 14 is described. Figure 2 As shown, in the top view of the semiconductor film 14 (here, a circle), two straight lines X and Y are drawn that pass through point G, which is the center of gravity of the top view, and are perpendicular to each other. Two points A and B are determined on the straight line X, each 20 mm away from point G. Two points C and D are determined on the straight line Y, each 20 mm away from point G. Next, when the semiconductor film 14 is warped in a convex shape, as shown in FIG. Figure 3 As shown, the point P with the longest distance to the line segment AB among any points on the curve AB between point A and point B on the surface 14a of the semiconductor film 14 is determined; when the semiconductor film 14 is warped in a concave shape, as shown in FIG. Figure 5 As shown in FIG. 1 , a point P having the longest distance to the line segment AB among any points on the curve AB between point A and point B on the surface 14a of the semiconductor film 14 is determined. The distance between the line segment AB and the point P is defined as the warpage amount α. In addition, when the semiconductor film 14 is warped in a convex shape, as shown in FIG. Figure 4 As shown, the point R with the longest distance to the line segment CD among any points on the curve CD between the point C and the point D on the surface 14a of the semiconductor film 14 is determined; when the semiconductor film 14 is warped in a concave shape, as shown in FIG. Figure 6 As shown, among any points on the curve CD between points C and D on the surface 14a of the semiconductor film 14, point R is determined, which has the longest distance to the line segment CD. The distance between the line segment CD and point R is then defined as the warp amount β. The warp amounts α and β are defined as the warp amount of the semiconductor film 14. Both warp amounts α and β fall within the range of 20 μm to 64 μm. The smaller of the warp amounts α and β is preferably 50% to 100% of the larger, and more preferably 85% to 100%.

[0034] The method for measuring the warpage α and β is not particularly limited, and known methods can be used. For example, the warpage α and β can be measured using a high-precision laser measuring instrument (LT-9010M, manufactured by Keyence Co., Ltd.). Specifically, the warpage α can be measured by using a high-precision laser measuring instrument to measure the distance between a point on curve AB and line segment AB at 1 mm intervals between line segment AB. The same applies to the warpage β.

[0035] In addition, if Figure 3 and Figure 4 ,or, Figure 5 and Figure 6As shown, when point O corresponding to point G is determined on the surface 14a of the semiconductor film 14, the lengths of line segments PO and RO are preferably 10 mm or less to prevent cracking and delamination of the Ga2O3-based semiconductor film. These lengths are more preferably 5 mm or less, and even more preferably 3 mm or less. In particular, by setting the length to 5 mm or less, the warped shape of the Ga2O3-based semiconductor film becomes closer to a true sphere, reducing the number of areas where stress concentrates, making cracking less likely.

[0036] The average film thickness of the semiconductor film 14 is 10 μm or more, preferably 12 μm or more, and more preferably 14 μm or more. The upper limit of the average film thickness of the semiconductor film 14 is not particularly limited, and is, for example, 1000 μm or less. The method for measuring the film thickness of the semiconductor film 14 is not particularly limited, and a known method can be used. For example, an ellipsometer (M-2000D manufactured by JA Woollam Japan) can be used to measure the film thickness of the semiconductor film 14. The average film thickness of the semiconductor film 14 can be calculated as follows: Figure 2 The film thickness of the semiconductor film 14 is measured at five points, namely, G, A, B, C, and D, and the average value thereof is set as the average film thickness of the semiconductor film 14.

[0037] The surface area of the semiconductor film 14 is substantially equal to the area of the base substrate 12. The surface area of the semiconductor film 14 is preferably 20 cm 2 More than 70cm, more preferably 2 More than 170cm 2 By increasing the area of the semiconductor film 14 in this way, multiple semiconductor elements can be obtained from one semiconductor film 14, thereby reducing manufacturing costs. The upper limit of the size of the semiconductor film 14 is not particularly limited, and typically, a single side is 700 cm 2 the following.

[0038] The semiconductor film 14 can be formed at 1.0×10 16 ~1.0×10 21 / cm 3 The proportion of Group 14 elements as dopants is 1.0×10 16 ~1.0×10 21 / cm 3 , more preferably 1.0×10 17 ~1.0×10 19 / cm 3These dopants are uniformly distributed in the film, and the dopant concentrations on the surface and back surface of the semiconductor film 14 are preferably approximately the same.

[0039] Furthermore, the semiconductor film 14 is preferably an oriented film oriented in a specific plane orientation. The orientation of the semiconductor film 14 can be investigated using known methods, such as electron backscatter diffraction (EBSD) inverse pole figure imaging. For example, the semiconductor film may be oriented along the c-axis, or along the c-axis and also oriented in the in-plane direction.

[0040] [Method for producing semiconductor films]

[0041] The method for producing the semiconductor film 14 includes: (a) a step of obtaining the stacked structure 10 ; and (b) a step of peeling the semiconductor film 14 from the base substrate 12 .

[0042] (a) Step of Obtaining the Laminated Structure 10

[0043] The stacked structure 10 is formed by forming a semiconductor film 14 on a base substrate 12 using an α-Ga2O3-based material. The film formation method is not particularly limited, and known methods can be used. Preferred film formation methods include spray CVD, HVPE, MBE, MOCVD, sputtering, and hydrothermal methods, with spray CVD and HVPE being particularly preferred.

[0044] The film formation method and film formation conditions of the stacked structure 10 are not particularly limited as long as the amount of convex or concave warping of the semiconductor film 14 is within an appropriate range (20 μm to 64 μm) and the average film thickness of the semiconductor film 14 is within an appropriate range (10 μm or more). Furthermore, the amount of convex or concave warping of the semiconductor film 14 can be appropriately controlled by the film formation method, film formation conditions, film thickness, etc.

[0045] For achieving a convex warping amount that exceeds the range that can be achieved by the film forming method, film forming conditions, etc., for example, a base substrate 12 having a convex warping is used, or the base substrate 12 is treated to produce a convex warping during film forming. As a method for obtaining such a base substrate 12, for example, there can be cited a method of preparing a material (high thermal expansion material) with a higher thermal expansion coefficient than that of the base substrate 12 and forming a film of the material on the back of the base substrate 12 at a specified temperature. In this case, when the specified temperature for forming the high thermal expansion material is lowered to room temperature, the base substrate 12 can be caused to produce a convex warping by thermal stress. With regard to the warping amount of the base substrate 12, the desired warping amount can be achieved by controlling the thermal expansion coefficient and thickness of the base substrate 12 and the high thermal expansion material respectively. There is no particular limitation on the film forming method of the high thermal expansion material, and examples include: AD, HVPE, sputtering, evaporation, CVD, etc., preferably HVPE, sputtering, and CVD. In addition, the high thermal expansion material can be pasted to the base substrate at a specified temperature instead of film forming. There are no particular limitations on the pasting method, and examples include: a method using an adhesive, a method of sintering, and the like. A protective layer may be formed in advance on the surface of the base substrate 12 where the semiconductor film 14 is to be formed, so that the high thermal expansion material does not adhere to or form a film. As a combination of the above-mentioned base substrate 12 and the high thermal expansion material, for example, the base substrate 12 may include sapphire or Cr2O3 single crystal, and the high thermal expansion material may include transition metals, MgAl2O4, MgO, and the like. Furthermore, for Al2O3, the thermal expansion coefficient of the c-axis is greater than that of the a-axis, and therefore, the thermal expansion coefficient of polycrystalline is greater than that of the a-axis. Therefore, when c-plane sapphire is used as the base substrate 12, polycrystalline Al2O3 may be used as the high thermal expansion material.

[0046] In addition, when the amount of convex warping of the semiconductor film 14 exceeds the appropriate range due to the film forming method and film forming conditions, for example, a thicker base substrate 12 can be used to increase the rigidity, or the thickness of the semiconductor film 14 can be thinned within a range of not less than 10 μm, so that the film forming method and film forming conditions are adopted and the warping amount falls within the appropriate range. Alternatively, a base substrate 12 with concave warping can be used, or the base substrate 12 can be treated to produce concave warping during film forming. As a method for obtaining the above-mentioned base substrate 12, for example, there can be cited a method of preparing a material (low thermal expansion material) with a lower thermal expansion coefficient than that of the base substrate 12 and forming a film of the material on the back side of the base substrate 12 at a specified temperature. In this case, when the specified temperature for forming the low thermal expansion material is lowered to room temperature, the base substrate 12 can be caused to produce concave warping due to thermal stress. Regarding the warping amount of the base substrate 12, the desired warping amount can be achieved by controlling the thermal expansion coefficient and thickness of the base substrate 12 and the low thermal expansion material respectively. There are no particular restrictions on the film-forming method of the low thermal expansion material, and examples thereof include AD, HVPE, sputtering, vapor deposition, CVD, etc., preferably HVPE, sputtering, and CVD. In addition, the low thermal expansion material can be pasted to the base substrate at a specified temperature instead of forming a film. There are no particular restrictions on the pasting method, and examples thereof include a method using an adhesive, a method of sintering it, etc. Among them, a protective layer can be pre-formed on the surface of the base substrate 12 where the semiconductor film 14 is to be formed, so that the low thermal expansion material does not adhere to and form a film. As a combination of the above-mentioned base substrate 12 and the low thermal expansion material, the base substrate 12 can include sapphire and Cr2O3 single crystal, and the low thermal expansion material can include metals such as AlN, SiC, W, and Mo.

[0047] Another method for reducing the convex warpage of the semiconductor film 14 is to form a process-degraded layer on the back side of the base substrate 12 and utilize the stress caused by the Tyman effect to reduce the warpage. The process-degraded layer can be formed using known methods, such as grinding and sandblasting. It should be noted that grinding the front or back side of the base substrate 12 for purposes such as thickness adjustment or removal of defects or dirt can sometimes form a process-degraded layer on the base substrate 12, causing unintended warping of the base substrate 12. In such cases, the formed process-degraded layer can be removed by, for example, mirror polishing or annealing at a specified temperature. When removing the process-degraded layer by mirror polishing, the polishing can be performed to a thickness greater than the thickness of the formed process-degraded layer, which is difficult to be introduced into the process-degraded layer. For example, the process-degraded layer can be removed by grinding to a #6000 grindstone, then fine-grinding with diamond abrasive grains, and then chemical mechanical polishing (CMP) using colloidal silica.

[0048] To achieve a concave warpage amount that exceeds the range achievable by the film formation method, film formation conditions, etc., for example, it is sufficient to use a base substrate 12 having concave warpage or to treat the base substrate 12 to produce concave warpage during film formation. The method for obtaining such a base substrate 12 can be the same as the method described above for obtaining a base substrate 12 having a warpage amount within an appropriate range using a film formation method and film formation conditions when the convex warpage amount of the semiconductor film 14 exceeds an appropriate range due to the film formation method and film formation conditions.

[0049] Another method for increasing the concave warpage of the semiconductor film 14 is to form a process-induced deterioration layer on the back surface of the base substrate 12 and utilize the stress caused by the Thyman effect to increase the warpage. The process-induced deterioration layer can be formed using known methods, such as grinding and sandblasting.

[0050] Furthermore, if the amount of concave warpage of the semiconductor film 14 exceeds the appropriate range due to the film formation method or film formation conditions, for example, a thicker base substrate 12 may be used to increase rigidity, or the thickness of the semiconductor film 14 may be increased so that the warpage falls within the appropriate range using the film formation method and film formation conditions. Alternatively, a base substrate 12 having convex warpage may be used, or the base substrate 12 may be treated to produce convex warpage during film formation. The method for obtaining the above-described base substrate 12 can be the same as the method for obtaining the base substrate 12 for achieving a convex warpage amount exceeding the range achievable using the film formation method, film formation conditions, etc.

[0051] Figure 7This is a simplified cross-sectional diagram showing the structure of the spray CVD apparatus 20. The spray CVD apparatus 20 includes a spray generator 22, a spray supply pipe 28, and a growth chamber 30. The spray generator 22 operates an ultrasonic vibrator 24 disposed on the bottom surface, ultrasonically vibrating the raw material solution stored in the spray generator 22 to generate a spray. A gas inlet 26 is disposed on the side of the spray generator 22. The gas inlet 26 allows a carrier gas to be introduced into the spray generator 22 from the outside. The spray supply pipe 28 connects the spray generator 22 and the growth chamber 30. The lower end of the spray supply pipe 28 passes through the top surface of the spray generator 22 and communicates with the interior of the spray generator 22. The upper end of the spray supply pipe 28 communicates with a nozzle 32 mounted on the bottom surface of the growth chamber 30. Thus, the spray generated by the spray generator 22 is supplied into the growth chamber 30 through the spray supply pipe 28. The growth chamber 30 is a cylindrical container having a gas exhaust port 34 on the upper side and a disc-shaped work table 36 on the top surface. A base substrate 12 for crystal growth is removably held on the bottom surface of the work table 36. A heater 38 is provided on the top surface of the growth chamber 30 for heating the base substrate 12 held on the work table 36.

[0052] The following describes the case where the stacked structure 10 of this embodiment is produced using the spray CVD apparatus 20. A gallium halide solution is prepared as a raw material solution and placed in the spray generator 22. A sapphire substrate of α-Al2O3 is held on the lower surface of the workbench 36 in a detachable manner as the base substrate 12. At this time, the distance d between the upper end of the nozzle 32 and the lower surface of the base substrate 12 is set to 0 (refer to FIG. 1 ). Figure 7) is set to an appropriate value (for example, 100 mm or more and 200 mm or less). In addition, the workbench 36 is heated to the desired temperature by the heater 38. Then, in the spray generator 22, the raw material solution is atomized by the ultrasonic vibrator 24 to generate a spray. The spray generated in the spray generator 22 is supplied upward into the growth chamber 30 through the spray supply pipe 28 from the nozzle 32 provided on the bottom surface of the growth chamber 30 together with the carrier gas (for example, N2, rare gas, etc.) introduced from the gas inlet 26. As a result, the gallium halide in the raw material solution is thermally decomposed to generate gallium oxide, which is heteroepitaxially grown on the lower surface of the base substrate 12 to form the semiconductor film 14 (α-Ga2O3-based semiconductor film). The temperature of the workbench 36 is set so that the semiconductor film 14 is formed and the warpage α and β of the formed semiconductor film 14 fall within the range of 20 μm or more and 64 μm or less. Specifically, it is preferably 300°C or more and 800°C or less, and more preferably 400°C or more and 700°C or less. The growth time is set so that the average film thickness of the semiconductor film 14 reaches 10 μm or greater. Thus, a stacked structure 10 is obtained. The temperature of the stacked structure 10 is then lowered to room temperature (e.g., 10° C. to 40° C.), thereby obtaining a stacked structure 10 in which the warpage and average film thickness of the semiconductor film 14 fall within the desired numerical ranges.

[0053] Figure 8 1 is a schematic cross-sectional view showing the structure of a vapor phase growth apparatus 60 using HVPE. The vapor phase growth apparatus 60 includes a reaction vessel 62 and a heater 64 .

[0054] Reaction vessel 62 is made of a material (e.g., quartz) that is non-reactive with the various raw materials and products. A carrier gas supply pipe 66, an oxidizing gas supply pipe 68, and a raw material supply pipe 70 are attached to one of a pair of opposing side surfaces of reaction vessel 62, while an exhaust pipe 74 is attached to the other side. Carrier gas supply pipe 66 supplies a carrier gas (e.g., nitrogen, a rare gas, etc.) into reaction vessel 62. Oxidizing gas supply pipe 68 supplies oxygen as an oxidizing gas into reaction vessel 62. In addition to oxygen, oxidizing gases such as water vapor and nitrous oxide can also be supplied. In raw material supply pipe 70, halogen gas (e.g., chlorine) or hydrogen halide gas (e.g., hydrogen chloride) supplied from a gas supply source reacts with metallic gallium within a storage section 72 located midway within raw material supply pipe 70 to produce gallium halide. Therefore, raw material supply pipe 70 supplies gallium halide gas as the raw material gas into reaction vessel 62. Halogen gas or hydrogen halide gas can be supplied together with a carrier gas such as nitrogen or a rare gas. A susceptor 76 is provided downstream of each supply pipe 66, 68, and 70 in the reaction vessel 62 to detachably hold the base substrate 12. An exhaust pipe 74 exhausts unreacted gas from the reaction vessel 62. A vacuum pump can be connected to the exhaust pipe 74, and the vacuum level within the reaction vessel 62 can be adjusted using the vacuum pump. This can suppress gas phase reactions and improve the growth rate distribution.

[0055] The heater 64 is arranged so as to surround the periphery of the reaction container 62. As the heater 64, for example, a resistance heating type heater or the like can be used.

[0056] The following describes the case where the stacked structure 10 of this embodiment is produced using a vapor phase growth apparatus 60. In the reaction vessel 62, oxygen supplied from the oxidizing gas supply pipe 68 reacts with the raw material gas (gallium halide gas) supplied from the raw material supply pipe 70, thereby forming a semiconductor film 14 (α-Ga2O3 film) on the base substrate 12. The film formation temperature is set so that the semiconductor film 14 is formed and the warpage α and β of the formed semiconductor film 14 fall within the range of 20 μm to 64 μm. Specifically, the film formation temperature is preferably 300°C to 800°C, more preferably 400°C to 700°C. The partial pressures of oxygen and raw material gas are not particularly limited. For example, the partial pressure of the raw material gas can be in the range of 0.05 kPa to 10 kPa, and the partial pressure of oxygen can be in the range of 0.25 kPa to 50 kPa. The growth time is set so that the average film thickness of the semiconductor film 14 reaches 10 μm or more. In this way, the stacked structure 10 is obtained. Thereafter, the temperature of the stacked structure 10 is lowered to room temperature (eg, 10° C. to 40° C.), thereby obtaining a stacked structure 10 in which the warpage amount and average film thickness of the semiconductor film 14 fall within desired numerical ranges.

[0057] (b) Step of peeling the semiconductor film 14 from the base substrate 12

[0058] The method for peeling the semiconductor film 14 from the base substrate 12 of the room-temperature stacked structure 10 obtained as described above is not particularly limited, and known methods can be employed. Examples of peeling methods include methods employing mechanical impact, methods employing heat to utilize thermal stress, and methods employing vibrations such as ultrasonic waves. By peeling, the semiconductor film 14 can be obtained as a free-standing film. Alternatively, the semiconductor film 14 can be transferred to another supporting substrate.

[0059] The semiconductor film 14 thus obtained as a self-standing film preferably has no defects and preferably has a film surface area of 20 cm 2 The number of cracks is preferably 20 or less. Although not particularly limited, for example, an industrial microscope (ECLIPSE LV150N manufactured by Nikon) can be used to count the number of cracks. At this time, the eyepiece can be set to 10 times, the objective lens can be set to 5 times, and the entire film surface can be observed in polarized differential interference mode. When cracks are confirmed, the objective lens is changed to 10 times to obtain an image. In this embodiment, only cracks with a length of more than 50 μm are counted as cracks. In addition, the situation where the distance from a crack to another crack is less than 500 μm is regarded as one crack. Regardless of the size of the semiconductor film 14, the number of cracks on the entire surface of the film is measured and converted to per 20 cm of film area. 2 The number of cracks.

[0060] According to the stacked structure 10 of the present embodiment described above, it is possible to suppress cracks and poor peeling during the manufacture of α-Ga2O3-based semiconductor films, and thus it is possible to manufacture α-Ga2O3-based semiconductor films with a good yield. The mechanism is not yet clear, but it is believed that by making the warping of the semiconductor film 14 within an appropriate range (above 20 μm and below 64 μm), a moderate stress is applied to the semiconductor film 14, making it easy to peel off from the base substrate 12, and even if the film is thickened to more than 10 μm, it is not easy to crack. If the warping is less than the lower limit of the appropriate range, the stress applied to the semiconductor film 14 is sometimes insufficient, resulting in the semiconductor film 14 only partially peeling off from the base substrate 12, or cracks when trying to peel it with a stronger force. If the warping exceeds the upper limit of the appropriate range, the stress applied to the semiconductor film 14 is sometimes too great, resulting in cracks in the semiconductor film 14 on the base substrate 12.

[0061] It should be noted that the present invention is not limited to the above-described embodiment and can be implemented in various forms as long as they fall within the technical scope of the present invention.

[0062] Example

[0063] The present invention will be further described in detail with reference to the following examples, but it should be noted that the present invention is not limited to the following examples.

[0064] [Example 1] (Spray CVD)

[0065] 1. Fabrication of laminated structures

[0066] (1) Preparation of raw material solution

[0067] Metallic Ga was added to hydrochloric acid and stirred at room temperature for four weeks to obtain a gallium chloride solution with a gallium ion concentration of 3 mol / L. Water was added to the resulting gallium chloride solution to adjust the aqueous solution to a gallium ion concentration of 65 mmol / L. Ammonium hydroxide was then added to adjust the pH to 4.0 to prepare a raw material solution.

[0068] (2) Film preparation

[0069] In having Figure 7 In the spray CVD apparatus 20 of the structure shown in the figure, the raw material solution (1) is stored in the spray generator 22. Next, a φ2 inch (area 20.3 cm) 2 ) c-plane sapphire substrate (thickness 0.43 mm), and the distance d between the upper end of the nozzle 32 and the lower surface of the base substrate 12 is set to 150 mm. The temperature of the workbench 36 is raised to 520°C using the heater 38 and maintained for 30 minutes to stabilize the temperature. Next, the flow control valve (not shown) provided in the gas inlet 26 is opened to supply carrier gas to the interior of the spray generator 22 and the growth chamber 30. After the atmosphere in the spray generator 22 and the growth chamber 30 is fully replaced with the carrier gas, the flow rate of the carrier gas is adjusted to 1.8 L / min. Here, nitrogen gas is used as the carrier gas.

[0070] (3) Film formation

[0071] The raw material solution was atomized by ultrasonic oscillator 24, and the resulting mist was introduced into growth chamber 30 using a carrier gas. Reactions occurred within growth chamber 30, thereby forming a circular semiconductor film 14 on the lower surface of base substrate 12, ultimately yielding stacked structure 10. The surface area of semiconductor film 14 matched that of base substrate 12. The film formation temperature was 520°C, and the film formation time was 300 minutes. The temperature of stacked structure 10 was then lowered to room temperature.

[0072] 2. Membrane Evaluation

[0073] (1) Surface EDX

[0074] EDX measurement of the surface of the obtained film revealed that only Ga and O were detected. This indicates that the obtained semiconductor film 14 is a Ga oxide.

[0075] (2)EBSD

[0076] EBSD analysis of the semiconductor film 14 was performed. The resulting inverse pole figure image revealed that the semiconductor film 14 had a biaxially oriented corundum-type crystal structure with the c-axis oriented in the substrate normal direction and also oriented in the in-plane direction. This indicates the formation of an oriented film containing α-Ga2O3.

[0077] (3) Warpage measurement

[0078] The warp amount α, warp amount β, length of line segment PO, and length of line segment RO of the semiconductor film 14 were measured using the method described in the "Detailed Description of the Invention" section. The results are shown in Table 1. Table 1 also shows the warp magnitude ratio (the ratio of the smaller of the warp amounts α and β to the larger of the warp amounts α and β).

[0079] (4)Film thickness

[0080] The average film thickness of the semiconductor film 14 was calculated by the method described in the [Detailed Description of the Invention] section. Specifically, the film thickness was measured using an ellipsometer (M-2000D manufactured by JA Woollam Japan). The measurement position was set to Figure 2 The film thickness was measured at 5 points, namely G, A, B, C, and D. The average value of the film thickness measured at the 5 points was defined as the average film thickness. The results are shown in Table 1.

[0081] (5) Evaluation of peeling yield, crack yield and overall yield

[0082] The semiconductor film 14 of the stacked structure 10 is peeled off from the base substrate 12 using ultrasonic vibration (frequency 45kHz). Products that are completely peeled off are defined as good products, products that are not peeled off or only partially peeled off are defined as defective products, and the peeling yield is calculated by the formula: peeling yield [%] = number of good peeling products / (number of good peeling products + number of defective peeling products) × 100. The peeling yield results are shown in Table 1. In addition, for the peeled semiconductor film 14 (however, only good peeling products), the cracks are observed using the method described in the [Specific Implementation] section to evaluate the crack yield. That is, an industrial microscope (Nikon ECLIPSE LV150N) is used, the eyepiece is set to 10 times, the objective lens is set to 5 times, and the entire film surface is observed in polarized differential interference mode. When cracks are confirmed, the objective lens is changed to 10 times to obtain an image. In addition, only cracks with a length of 50 μm or more are counted as cracks. In addition, a situation where the distance from a crack to another crack is less than 500 μm is considered to be one crack. Regardless of the size of the semiconductor film 14, the number of cracks on the entire surface of the film is measured, and the number of cracks per 20 cm of film area is calculated. 2 For conversion, the membrane area is calculated as2 Products with 20 or fewer cracks were considered good, and products with more than 20 cracks were considered defective. The crack yield was calculated using the formula: Crack yield [%] = number of good cracks / (number of good cracks + number of defective cracks) × 100. The crack yield results are shown in Table 1. Furthermore, the overall yield was calculated using the formula: Overall yield [%] = peeling yield × crack yield / 100, resulting in a total yield of 75%.

[0083] [Example 2] (Spray CVD)

[0084] As the base substrate 12, a 2-inch c-plane sapphire substrate with a polycrystalline Al2O3 layer formed on its back surface and mirror-finished to be convexly curved was used. The following describes a method for producing the substrate.

[0085] Al2O3 powder (AKP-20 manufactured by Sumitomo Chemical) was used as the raw material powder, and sapphire (diameter 50.8 mm (2 inches), thickness 1.00 mm, c-plane, off-angle 0.2°) was used as the substrate. Figure 9 The AD (aerosol deposition) device 40 shown forms an AD film containing Al 2 O 3 on a seed substrate (sapphire substrate). Figure 9 The AD device 40 shown is configured as an apparatus used in an AD method that sprays a raw material powder onto a substrate in an atmosphere at a pressure lower than atmospheric pressure. The AD device 40 includes an aerosol generating unit 42 that generates an aerosol of raw material powder containing a raw material component, and a film forming unit 50 that sprays the raw material powder onto a sapphire substrate 41 to form a film containing the raw material component. The aerosol generating unit 42 includes an aerosol generating chamber 43 that stores the raw material powder and receives a carrier gas from a gas cylinder (not shown) to generate an aerosol; a raw material supply pipe 44 that supplies the generated aerosol to the film forming unit 50; and an exciter 45 that vibrates the aerosol generating chamber 43 and the aerosol therein at a frequency of 10 to 100 Hz. The film forming unit 50 includes a film forming chamber 52 in which aerosol is sprayed toward the sapphire substrate 41; a substrate holder 54 disposed within the film forming chamber 52 to secure the sapphire substrate 41; and an X-Y stage 53 for moving the substrate holder 54 along the X-axis and Y-axis directions. The film forming unit 50 also includes a spray nozzle 56 with a slit 57 formed at its tip for spraying the aerosol toward the sapphire substrate 41; and a vacuum pump 58 for depressurizing the film forming chamber 52.

[0086] The AD film formation conditions are as follows. Specifically, the carrier gas is N2, and a ceramic nozzle with a slit measuring 5 mm long and 0.3 mm short is used. The nozzle scanning conditions are as follows: at a scanning speed of 0.5 mm / s, the nozzle moves 55 mm in a forward direction perpendicular to the long side of the slit, 5 mm in a return direction perpendicular to the long side of the slit, and 5 mm in a direction opposite to the initial position along the long side of the slit. This scanning is repeated. At the point where the nozzle has moved 55 mm from the initial position along the long side of the slit, it scans in the opposite direction and returns to the initial position. This cycle is considered one, and 400 cycles are repeated. During one cycle of film formation at room temperature, the set pressure of the transport gas is adjusted to 0.06 MPa, the flow rate is adjusted to 5 L / min, and the pressure in the chamber is adjusted to below 100 Pa. The thickness of the AD film formed in this way is approximately 70 μm.

[0087] The sapphire substrate with the AD film formed on it was removed from the AD device and annealed at 1650°C for 4 hours in a nitrogen atmosphere, forming a polycrystalline Al2O3 layer on the back side of the sapphire substrate. The resulting substrate was fixed to a ceramic platen, and the surface with the AD film was ground to #6000 using a grindstone to flatten the plate surface. Next, diamond abrasives were used for lapping to smooth the plate surface. The abrasive grain size was gradually reduced from 3μm to 0.5μm to improve flatness. Chemical mechanical polishing (CMP) was then performed using colloidal silica to mirror-finish the polycrystalline Al2O3 layer. The thickness of the mirror-finished polycrystalline Al2O3 layer was 20μm. The substrate was then fixed to a ceramic platen, and the surface of the sapphire substrate was ground to #6000 using a grindstone to flatten the plate surface. Next, diamond abrasives were used for lapping to smooth the plate surface. The abrasive grain size was gradually reduced from 3μm to 0.5μm to improve flatness. Then, chemical mechanical polishing (CMP) was performed using colloidal silica to provide a mirror finish. The substrate thickness after polishing was 0.80 mm.

[0088] In Example 2, film formation and evaluation were performed in the same manner as in Example 1, except that the convexly warped substrate prepared as described above was used as the base substrate 12 and the film formation time was set to 450 minutes. The results are shown in Table 1. It was found that the semiconductor film 14 obtained in Example 2 was also a Ga oxide as determined by EDX, and an oriented film having a biaxially oriented corundum-type crystal structure as determined by EBSD. Furthermore, the overall yield was calculated as described above and found to be 93%.

[0089] [Example 3] (Spray CVD)

[0090] As the base substrate 12, a polycrystalline Al2O3 layer was formed on the back surface of a 2-inch c-plane sapphire substrate, and the back surface was ground to introduce a work-degraded layer to warp convexly. The following is a method for producing the substrate.

[0091] Al2O3 powder (AKP-20 manufactured by Sumitomo Chemical) was used as the raw material powder, and sapphire (diameter 50.8 mm (2 inches), thickness 1.00 mm, c-plane, off-angle 0.2°) was used as the substrate. Figure 9 The AD device 40 shown in the figure forms an AD film containing Al2O3 on a seed substrate (sapphire substrate). The AD film forming conditions are the same as those in the second embodiment.

[0092] The sapphire substrate with the AD film formed on it was removed from the AD device and annealed at 1650°C for 4 hours in a nitrogen atmosphere, thereby forming a polycrystalline Al2O3 layer on the back of the sapphire substrate. The substrate thus obtained was fixed to a ceramic platform, and the surface on the side with the AD film formed was ground to #325 using a grindstone, introducing a processed deteriorated layer into the polycrystalline Al2O3 layer. The thickness of the polycrystalline Al2O3 layer after #325 grinding was 20μm. After that, the substrate was fixed to a ceramic platform, and the surface of the sapphire substrate was ground to #6000 using a grindstone to make the plate surface flat. Next, diamond abrasives were used for fine grinding to smooth the plate surface. The size of the abrasive grains was gradually reduced from 3μm to 0.5μm to improve flatness. After that, chemical mechanical polishing (CMP) was performed using colloidal silica to achieve mirror finishing. The thickness of the substrate after grinding was 0.45mm.

[0093] In Example 3, film formation and evaluation were performed in the same manner as in Example 1, except that a convexly warped substrate prepared as described above was used as the base substrate 12. The results are shown in Table 1. EDX analysis revealed that the semiconductor film 14 obtained in Example 3 was also a Ga oxide, and EBSD analysis revealed that it was an oriented film having a biaxially oriented corundum-type crystal structure. Furthermore, the overall yield was calculated as described above and found to be 85%.

[0094] [Example 4] (Spray CVD)

[0095] As the base substrate 12, a 2-inch (φ) c-plane sapphire substrate (thickness 0.43 mm) with its backside ground to #325 and a processed altered layer introduced to form a concave warp was used. Film formation and evaluation were performed in the same manner as in Example 1. The results are shown in Table 1. It was found that the semiconductor film 14 obtained in Example 4 was also a Ga oxide as determined by EDX, and an oriented film having a biaxially oriented corundum-type crystal structure as determined by EBSD. Furthermore, the overall yield was calculated as described above and found to be 76%.

[0096] [Example 5] (Spray CVD)

[0097] Film formation and evaluation were performed in the same manner as in Example 1, except that a 2-inch (φ) c-plane sapphire substrate (0.43 mm thick) was used as the base substrate 12, using Fujirundum WA (grain number 100, manufactured by Fuji Seisakusho) as the abrasive, by sandblasting the back surface to introduce a processed altered layer and cause concave warping. The results are shown in Table 1. It was found that the semiconductor film 14 obtained in Example 5 was also a Ga oxide as determined by EDX, and an oriented film having a biaxially oriented corundum-type crystal structure as determined by EBSD. Furthermore, the overall yield was calculated as described above and found to be 92%.

[0098] [Example 6] (Spray CVD)

[0099] As the base substrate 12 , a substrate having a concave warping shape was used by forming an AlN film on the back surface of a 2-inch c-plane sapphire substrate (thickness 1.00 mm) by HVPE. The following is a method for producing the substrate.

[0100] A 5μm AlN film is formed on the back of the sapphire substrate using HVPE at 1200°C. After the AlN film is formed, the substrate is fixed to a ceramic platform and the surface of the sapphire substrate is ground to #6000 using a grindstone to make the plate surface flat. Next, fine grinding is performed using diamond abrasives to smooth the plate surface. The abrasive grain size is gradually reduced from 3μm to 0.5μm to improve flatness. After that, chemical mechanical polishing (CMP) is performed using colloidal silica to achieve a mirror finish. The substrate thickness after grinding is 0.435mm.

[0101] In Example 6, film formation and evaluation were performed in the same manner as in Example 1, except that the base substrate 12 prepared as described above and having a concave warp was used. The results are shown in Table 1. EDX analysis revealed that the semiconductor film 14 obtained in Example 6 was also a Ga oxide, and EBSD analysis revealed that it was an oriented film having a biaxially oriented corundum-type crystal structure. Furthermore, the overall yield was calculated as described above and found to be 85%.

[0102] [Example 7] (Spray CVD)

[0103] A composite base substrate of 2 inches in diameter was used as the base substrate 12. A method for producing the composite base substrate is described below.

[0104] (1) Fabrication of composite base substrate

[0105] Cr2O3 powder (Colortherm green manufactured by LANXESS) was used as the raw material powder, and sapphire (diameter 50.8 mm (2 inches), thickness 2.00 mm, c-plane, off-angle 0.2°) was used as the substrate. Figure 9 The AD device 40 shown forms an AD film (alignment precursor layer) containing Cr2O3 on a seed substrate (sapphire substrate).

[0106] The AD film formation conditions are as follows. Specifically, the carrier gas is N2, and a ceramic nozzle with a slit measuring 5 mm long and 0.3 mm short is used. The nozzle scanning conditions are as follows: at a scanning speed of 0.5 mm / s, the nozzle moves 55 mm in a forward direction perpendicular to the long side of the slit, 5 mm in a return direction perpendicular to the long side of the slit, and 5 mm in a direction opposite to the initial position along the long side of the slit. This scanning is repeated. At the point where the nozzle has moved 55 mm from the initial position along the long side of the slit, it scans in the opposite direction and returns to the initial position. This cycle is considered one, and 500 cycles are repeated. During one cycle of film formation at room temperature, the set pressure of the transport gas is adjusted to 0.06 MPa, the flow rate is adjusted to 6 L / min, and the pressure in the chamber is adjusted to below 100 Pa. The thickness of the AD film formed in this way is approximately 100 μm.

[0107] The sapphire substrate with the AD film formed thereon is taken out from the AD device and annealed at 1700°C for 4 hours in a nitrogen atmosphere. The substrate thus obtained is fixed to a ceramic platform, and the surface on the side with the AD film formed thereon is ground to #6000 using a grindstone to make the plate surface flat. Next, diamond abrasives are used for fine grinding to smooth the plate surface. The size of the abrasive grains is gradually reduced from 3μm to 0.5μm to improve flatness. Thereafter, chemical mechanical polishing (CMP) is performed using colloidal silica to perform mirror finishing to obtain a composite base substrate. The arithmetic mean roughness Ra after processing is 0.1nm, the grinding and polishing amount is 50μm, and the thickness of the substrate after polishing is 2.05mm. It should be noted that the surface on the side with the AD film formed thereon is referred to as the "surface".

[0108] (2) Evaluation of Orientation Layer

[0109] (2a) Cross-sectional EDX

[0110] An energy dispersive X-ray analyzer (EDX) was used to perform composition analysis of a cross section perpendicular to the main surface of the substrate. As a result, only Cr and O were detected in the range from the surface of the composite base substrate to a depth of about 20 μm. The ratio of Cr to O hardly changed within a range of about 20 μm, indicating that a Cr oxide layer with a thickness of about 20 μm was formed. In addition, Cr, O, and Al were detected in the range from the Cr oxide layer to a depth of 30 μm, indicating that a Cr·Al oxide layer (gradient composition layer) of about 30 μm was formed between the Cr oxide layer and the sapphire substrate. Within the Cr·Al oxide layer, the ratio of Cr to Al was different, and it was confirmed that the Al concentration was higher on the sapphire substrate side and lower on the side close to the Cr oxide layer.

[0111] (2b) Surface EBSD

[0112] Inverse pole figure imaging of the substrate surface composed of the Cr oxide layer was performed using an SEM (SU-5000 manufactured by Hitachi High-Technologies Corporation) equipped with an electron backscatter diffraction (EBSD) device (Nordlys Nano manufactured by Oxford Instruments) in a field of view of 500 μm × 500 μm. The EBSD measurement conditions are as follows.

[0113] EBSD measurement conditions

[0114] Accelerating voltage: 15kV

[0115] Point Strength: 70

[0116] Working distance: 22.5mm

[0117] Step size: 0.5μm

[0118] Specimen tilt angle: 70°

[0119] ·Assay program: Aztec (version 3.3)

[0120] The obtained inverse pole figure imaging shows that the Cr oxide layer has a biaxially oriented corundum-type crystal structure with the c-axis oriented in the substrate normal direction and also oriented in the in-plane direction. This indicates that an oriented layer containing α-Cr2O3 is formed on the substrate surface. Based on this, if we schematically represent the production process of the composite base substrate, as shown below: Figure 10 As shown in (a) to (d).

[0121] (2c)XRD

[0122] XRD in-plain measurements of the substrate surface were performed using a multifunctional high-resolution X-ray diffractometer (Bullker Axe Co., Ltd., D8DISCOVER). Specifically, after adjusting the Z axis according to the height of the substrate surface, the Chi, Phi, ω, and 2θ axes were adjusted relative to the (11-20) plane, and 2θ-ω measurements were performed under the following conditions.

[0123] <XRD measurement conditions>

[0124] Tube voltage: 40kV

[0125] Tube current: 40mA

[0126] Detector: Triple Ge(220)Analyzer

[0127] CuKα rays obtained by parallel monochromation (half-value width 28 seconds) using a Ge(022) asymmetric reflection monochromator

[0128] Stride length: 0.001°

[0129] Scanning speed: 1.0 sec / step

[0130] The results show that the a-axis length of the orientation layer is

[0131] In Example 7, film formation and evaluation were performed in the same manner as in Example 1, except that the film was formed on the α-Cr2O3 oriented layer of the composite base substrate prepared above, and the film formation time was set to 450 minutes. The results are shown in Table 1. It can be seen that the semiconductor film 14 obtained in Example 7 was also a Ga oxide as determined by EDX, and an oriented film having a biaxially oriented corundum-type crystal structure as determined by EBSD. Furthermore, the overall yield was calculated as described above and was found to be 94%.

[0132] [Example 8] (HVPE)

[0133] Figure 8In the vapor phase growth apparatus 60 shown, a convexly warped substrate prepared in the same manner as in Example 2 was prepared as the base substrate 12. Hydrogen chloride gas was introduced into the raw material supply pipe 70, where metal Ga and the hydrogen chloride gas reacted to generate gallium chloride gas, which was then supplied from the raw material supply pipe 70 into the reaction vessel 62. Oxygen gas was used as the oxidizing gas, and N2 gas was used as the carrier gas. The growth temperature was 550°C, and the film formation time was 80 minutes. Thus, a stacked structure 10 having a semiconductor film 14 formed on the base substrate 12 was obtained. Subsequent evaluations were performed in the same manner as in Example 1. The results are shown in Table 1. It can be seen that the semiconductor film 14 obtained in Example 8 was also a Ga oxide as determined by EDX, and an oriented film having a biaxially oriented corundum-type crystal structure as determined by EBSD. Furthermore, the overall yield was calculated as described above and found to be 93%.

[0134] [Comparative Example 1] (Spray CVD)

[0135] Film formation and evaluation were performed in the same manner as in Example 1, except that the film formation time was set to 240 minutes. The results are shown in Table 1. It can be seen that the semiconductor film 14 obtained in Comparative Example 1 was also a Ga oxide as determined by EDX, and an oriented film having a biaxially oriented corundum-type crystal structure as determined by EBSD. The overall yield of Comparative Example 1 was calculated as described above and found to be 59%, which is inferior to that of Example 1.

[0136] [Comparative Example 2] (Spray CVD)

[0137] As the base substrate 12, a polycrystalline Al2O3 layer was formed on the back surface of a 2-inch c-plane sapphire substrate, and the back surface was mirror-finished to be convexly curved. The following is a method for producing the substrate.

[0138] Al2O3 powder (AKP-20 manufactured by Sumitomo Chemical) was used as the raw material powder, and sapphire (diameter 50.8 mm (2 inches), thickness 1.00 mm, c-plane, off-angle 0.2°) was used as the substrate. Figure 9 The AD device 40 shown in the figure forms an AD film containing Al2O3 on a seed substrate (sapphire substrate). The AD film forming conditions are the same as those in the second embodiment.

[0139] The sapphire substrate with the AD film formed on it was removed from the AD device and annealed at 1650°C for 4 hours in a nitrogen atmosphere, forming a polycrystalline Al2O3 layer on the back side of the sapphire substrate. The resulting substrate was fixed to a ceramic platen, and the surface with the AD film formed was ground to #6000 using a grindstone to flatten the plate surface. Next, diamond abrasives were used for lapping to smooth the plate surface. The abrasive grain size was gradually reduced from 3μm to 0.5μm to improve flatness. Chemical mechanical polishing (CMP) was then performed using colloidal silica to mirror-finish the polycrystalline Al2O3 layer. The thickness of the mirror-finished polycrystalline Al2O3 layer was 20μm. The substrate was then fixed to a ceramic platen, and the surface of the sapphire substrate was ground to #6000 using a grindstone to flatten the plate surface. Next, diamond abrasives were used for lapping to smooth the plate surface. The abrasive grain size was gradually reduced from 3μm to 0.5μm to improve flatness. Then, chemical mechanical polishing (CMP) was performed using colloidal silica to provide a mirror finish. The substrate thickness after polishing was 0.45 mm.

[0140] In Comparative Example 2, film formation and evaluation were performed in the same manner as in Example 1, except that a convexly warped substrate prepared as described above was used as the base substrate 12. The results are shown in Table 1. EDX analysis revealed that the semiconductor film 14 obtained in Comparative Example 2 was also a Ga oxide, and EBSD analysis revealed that the film was an oriented film having a biaxially oriented corundum-type crystal structure. The overall yield of Comparative Example 2 was calculated as described above and found to be 58%, which is lower than that of Example 1.

[0141] [Comparative Example 3] (Spray CVD)

[0142] As the base substrate 12, a 2-inch (φ) c-plane sapphire substrate (thickness 0.43 mm) with its backside ground to #325 and a processed deteriorated layer introduced to form a concave warp was used. Film formation and evaluation were performed in the same manner as in Example 1, except that the film formation time was set to 360 minutes. The results are shown in Table 1. It can be seen that the semiconductor film 14 obtained in Comparative Example 3 was also a Ga oxide as determined by EDX, and an oriented film having a biaxially oriented corundum-type crystal structure as determined by EBSD. The overall yield of Comparative Example 3 was calculated as described above and found to be 58%, which is inferior to that of Example 1.

[0143] [Comparative Example 4] (Spray CVD)

[0144] As the base substrate 12, a 2-inch (φ) c-plane sapphire substrate (thickness 1.00 mm) was used, on the back side of which an AlN film was formed by HVPE and then ground to introduce a processed altered layer into the AlN film, resulting in concave warping. Film formation and evaluation were performed in the same manner as in Example 1, except that a substrate was used. The following describes the method for preparing the substrate.

[0145] An AlN film is formed on the back of a sapphire substrate at 1200°C using HVPE. After the AlN film is formed, the substrate is fixed to a ceramic platform and the AlN film-formed surface is ground to #325 using a grindstone to introduce a processed deteriorated layer. The thickness of the AlN film after grinding is 5μm. Thereafter, the surface of the sapphire substrate is ground to #6000 using a grindstone to make the plate surface flat. Next, diamond abrasives are used for fine grinding to smooth the plate surface. The size of the abrasive grains is gradually reduced from 3μm to 0.5μm to improve flatness. Thereafter, chemical mechanical polishing (CMP) is performed using colloidal silica to perform mirror finishing. The thickness of the substrate after mirror finishing is 0.435mm.

[0146] In Comparative Example 4, film formation and evaluation were performed in the same manner as in Example 1, except that the base substrate 12 prepared as described above and having a concave warp was used. The results are shown in Table 1. EDX analysis revealed that the semiconductor film 14 obtained in Comparative Example 4 was also a Ga oxide, and EBSD analysis revealed that the film was an oriented film having a biaxially oriented corundum-type crystal structure. The overall yield of Comparative Example 4 was calculated as described above and found to be 59%, which is inferior to that of Example 1.

[0147] Table 1

[0148]

[0149] This application claims priority based on Japanese Patent Application No. 2020-159611 filed on September 24, 2020, the entire contents of which are incorporated herein by reference.

[0150] Industrial applicability

[0151] The present invention can be utilized in, for example, materials for power semiconductors.

[0152] Explanation of symbols

[0153] 10 stacked structure, 12 base substrate, 14 semiconductor film, 14a surface, 20 spray CVD device, 22 spray generator, 24 ultrasonic vibrator, 26 gas inlet, 28 spray supply pipe, 30 growth chamber, 32 nozzle, 34 gas exhaust port, 36 workbench, 38 heater, 40 AD device, 41 sapphire substrate, 42 aerosol generating unit, 43 aerosol generating chamber, 44 raw material supply pipe, 45 exciter, 50 film forming unit, 52 film forming chamber, 53 X-Y workbench, 54 substrate holder, 56 injection nozzle, 57 slit, 58 vacuum pump, 60 vapor phase growth device, 62 reaction container, 64 heater, 66 carrier gas supply pipe, 68 oxidizing gas supply pipe, 70 raw material supply pipe, 72 storage unit, 74 exhaust pipe, 76 base.

Claims

1. A laminated structure, wherein: A semiconductor film having a corundum-type crystal structure and containing α-Ga2O3 or an α-Ga2O3 solid solution is provided on a base substrate. The stacked structure is characterized in that The semiconductor film has an average film thickness of 10 μm or greater, and the semiconductor film is warped in a convex or concave shape. In a top view of the semiconductor film, two straight lines X and Y are drawn that pass through point G, which is the center of gravity of the top view, and are orthogonal to each other. Two points A and B are determined on straight line X, each 20 mm away from point G. Two points C and D are determined on straight line Y, each 20 mm away from point G. A point P is determined, among any points on a curve AB between points A and B on the surface of the semiconductor film, that has the longest distance to a line segment AB. A point R is determined, among any points on a curve CD between points C and D on the surface of the semiconductor film, that has the longest distance to a line segment CD. Assuming the distance between line segment AB and point P is a warping amount α, and the distance between line segment CD and point R is a warping amount β, and assuming the warping amounts α and β are the warping amount of the semiconductor film, the warping amount of the semiconductor film is 20 μm or greater and 64 μm or less.

2. The laminated structure according to claim 1, wherein When point O corresponding to point G is determined on the surface of the semiconductor film, the length of line segment PO and the length of line segment RO are equal to or less than 10 mm.

3. The laminated structure according to claim 1, wherein The smaller of the warpage amounts α and β is not less than 50% and not more than 100% of the larger one.

4. The laminated structure according to claim 2, wherein: The smaller of the warpage amounts α and β is not less than 50% and not more than 100% of the larger one.

5. The laminated structure according to any one of claims 1 to 4, characterized in that The warping amount of the semiconductor film is not less than 30 μm and not more than 64 μm.

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