Method for forming oxide semiconductor film

Abstract

The present invention is a film-formation method for performing film formation by heat-treating a misted raw material solution, the film-formation method being characterized by comprising: a step for generating mist by atomizing a raw material solution or by forming droplets therefrom; a step for conveying the mist to a film-formation part by means of a carrier gas; and a step for supplying the mist from a nozzle to a substrate and heat-treating the mist on the substrate to form a film in the film formation part, wherein, when the area of the opening surface of the nozzle is S [cm2], the longest distance among distances between points in the opening surface and the surface of the substrate is H [cm], and the flow rate of the carrier gas supplied from the nozzle is Q [L / minute], SH / Q≥0.015 is satisfied. Thus, a film-formation method for suppressing abnormal growth and forming a film having good surface smoothness is provided.

Description

[Technical Field]

[0001] The present invention relates to a film forming method for forming a film on a substrate using a mist-like raw material solution. [Background technology]

[0002] High-vacuum deposition equipment capable of realizing non-equilibrium conditions, such as pulsed laser deposition (PLD), molecular beam epitaxy (MBE), and sputtering, has been developed, enabling the fabrication of oxide semiconductors that were previously impossible using melt deposition and other methods. Furthermore, mist chemical vapor deposition (Mist CVD), which uses atomized raw materials to grow crystals on a substrate, has been developed, enabling the fabrication of corundum-structured gallium oxide (α-Ga2O3). As a wide-bandgap semiconductor, α-Ga2O3 is expected to be applied to next-generation switching devices, achieving high voltage resistance, low loss, and high heat resistance.

[0003] Regarding the mist CVD method, Patent Document 1 describes a tubular furnace type mist CVD apparatus. Patent Document 2 describes a fine channel type mist CVD apparatus. Patent Document 3 describes a linear source type mist CVD apparatus. Patent Document 4 describes a tubular furnace mist CVD apparatus, which differs from the mist CVD apparatus described in Patent Document 1 in that a carrier gas is introduced into the mist generator. Patent Document 5 describes a mist CVD apparatus in which a substrate is placed above a mist generator and a susceptor is a rotating stage mounted on a hot plate. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Publication No. 01-257337 [Patent Document 2] Japanese Patent Application Laid-Open No. 2005-307238 [Patent Document 3] Japanese Patent Application Laid-Open No. 2012-046772 [Patent Document 4] Patent No. 5397794 [Patent Document 5] Japanese Patent Application Laid-Open No. 2014-063973 Summary of the Invention [Problem to be solved by the invention]

[0005] Unlike other CVD methods, the mist CVD method allows film formation at relatively low temperatures and can also produce metastable phase crystal structures such as the corundum structure of α-Ga2O3. However, the inventors discovered that when films are formed using the mist CVD method, pits form on the film surface, resulting in poor surface smoothness. Furthermore, films containing many pits have the problem that the pits become killer defects, causing dielectric breakdown in semiconductor devices. Furthermore, removing pits by polishing increases the number of steps required to fabricate semiconductor devices. The present invention has been made to solve the above problems, and aims to provide a film that suppresses pits and has a good surface smoothness, and a film formation method for forming such a film. [Means for solving the problem]

[0006] The present invention has been made to achieve the above object, and provides an oxide semiconductor film containing gallium as a main component, the oxide semiconductor film having a corundum structure, and a surface density of the oxide semiconductor film being 10,000 / cm 2 The following oxide semiconductor film is provided.

[0007] Such an oxide semiconductor film can be obtained easily and inexpensively, and has excellent surface smoothness, making it suitable for use in semiconductor devices.

[0008] At this time, the number of pits on the surface of the oxide semiconductor film was 100 / cm 2 It can be the following:

[0009] This provides even better surface smoothness and makes the substrate even more suitable for use in semiconductor devices.

[0010] At this time, when the area of the oxide semiconductor film is 10 cm 2 It can be the above.

[0011] This results in a large-area oxide semiconductor film that has excellent surface smoothness and can be suitably used in a semiconductor device.

[0012] At this time, the pits on the surface of the oxide semiconductor film can have an opening diameter of 10 nm to 10 μm and a depth of 10 nm to 10 μm.

[0013] This results in a large-area oxide semiconductor film with even better surface smoothness that can be more suitably used in a semiconductor device.

[0014] In this case, a semiconductor device can include the above oxide semiconductor film.

[0015] This results in a semiconductor device with excellent characteristics.

[0016] The present invention also provides a film-forming method for forming a film by heat-treating a mist of a raw material solution, the method comprising: A step of atomizing or dropletizing the raw material solution to generate a mist; a step of transporting the mist to a film forming section by a carrier gas; a step of supplying the mist onto a substrate from a nozzle in the film forming unit and performing a heat treatment on the substrate to form a film; Including, The area of the nozzle opening is S [cm 2], the longest distance between a point in the opening plane and the surface of the substrate is H [cm], and the flow rate of the carrier gas supplied from the nozzle is Q [L / min], where SH / Q≧0.015. A film deposition method is provided.

[0017] According to this film forming method, pits on the surface are suppressed, and a film with excellent smoothness can be formed.

[0018] In this case, the raw material solution may contain gallium.

[0019] This suppresses the formation of pits on the surface, making it possible to form a gallium-containing film with excellent smoothness.

[0020] In this case, the raw material solution may contain a halogen.

[0021] This further suppresses pits on the surface, allowing the deposition of a film with better smoothness.

[0022] In this case, when the temperature of the heat treatment is T [° C.], ST / Q≧40 can be satisfied.

[0023] This further suppresses the formation of pits on the surface, allowing the deposition of a film with even better smoothness.

[0024] At this time, the mist can be supplied onto the substrate from the nozzle provided vertically above the substrate.

[0025] This further suppresses the formation of pits on the surface, allowing the deposition of a film with even better smoothness.

[0026] At this time, the substrate can be moved under the nozzle.

[0027] This allows a film with few pits on the surface and excellent smoothness to be formed over a large area.

[0028] At this time, the area of the surface of the substrate on which the film is formed is defined as A [cm 2 ], S / A≦0.3 can be achieved.

[0029] This allows a film with fewer surface pits and excellent smoothness to be formed over a large area.

[0030] In this case, the opening surface of the nozzle may be rectangular.

[0031] This allows a film with few pits on the surface and excellent smoothness to be formed over a large area.

[0032] In this case, when the major axis length of the nozzle opening surface is L [cm] and the maximum length in the major axis direction of the nozzle within the surface of the substrate on which the film is to be formed is R [cm], L / R≧1 can be satisfied.

[0033] This allows for easy deposition of a film with few surface pits and excellent smoothness over a large area.

[0034] In this case, the area of the substrate is 10 cm 2 It can be more than that.

[0035] This allows a film with few pits on the surface and excellent smoothness to be formed over a large area. [Effects of the Invention]

[0036] As described above, the oxide semiconductor film of the present invention has few pits and excellent surface smoothness, and is therefore suitable for use in semiconductor devices. Furthermore, according to the film forming method of the present invention, it is possible to form a film with few pits on the surface and excellent smoothness by a simple mist CVD method. [Brief explanation of the drawings]

[0037] [Figure 1] 1 is a schematic diagram showing an example of a film forming apparatus used in the present invention. [Figure 2]FIG. 2 is a diagram illustrating an example of a mist-forming unit used in the present invention. [Figure 3] FIG. 2 is a diagram illustrating an example of a film forming unit used in the present invention. [Figure 4] FIG. 2 is a diagram illustrating an example of a nozzle used in the present invention. [Figure 5] FIG. 2 is a diagram illustrating an example of a film forming unit equipped with a plurality of nozzles. [Figure 6] FIG. 10 is a diagram illustrating an example of a nozzle having a plurality of opening surfaces. [Figure 7] FIG. 2 is a diagram illustrating an example of a nozzle used in the present invention. [Figure 8] FIG. 2 is a diagram illustrating an example of a nozzle used in the present invention. [Figure 9] 1A and 1B are diagrams illustrating an example of a substrate moving mechanism used in the present invention. [Figure 10] 10A and 10B are diagrams illustrating an example of a moving mechanism that reciprocates under the nozzle. [Figure 11] 10A and 10B are diagrams illustrating an example of a rotational movement mechanism that moves in one direction below the nozzle. [Figure 12] FIG. 1 is a diagram showing the results of Test Example 1. [Figure 13] 10A and 10B are diagrams illustrating the structure of a semiconductor device produced in Test Example 2. [Figure 14] FIG. 10 is a diagram showing the results of Test Example 2. [Figure 15] FIG. [Figure 16] 1 is a diagram illustrating an example of an oxide semiconductor film of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0038] As described above, it has been desired to provide an oxide semiconductor film having few pits and excellent surface smoothness at low cost, and to provide a method for manufacturing an oxide semiconductor film by which an oxide semiconductor film having few pits and excellent surface smoothness can be formed simply and inexpensively using a low-temperature process.

[0039] As a result of extensive research into the above-described problems, the present inventors have discovered an oxide semiconductor film containing gallium as a main component, the oxide semiconductor film having a corundum structure, and a surface density of pits of 10,000 / cm. 2 The inventors have found that the following oxide semiconductor film can be obtained simply and inexpensively, has excellent surface smoothness, and can be suitably used in semiconductor devices, and have completed the present invention.

[0040] As a result of extensive research into the above-mentioned problems, the present inventors have discovered a film-forming method for forming a film by heat-treating a mist of a raw material solution, the method comprising the steps of: atomizing or dropletizing the raw material solution to generate mist; transporting the mist to a film-forming unit by a carrier gas; and supplying the mist from a nozzle onto a substrate in the film-forming unit and heat-treating the substrate to form a film; wherein the area of the opening surface of the nozzle is S [cm 2 ], the longest distance between a point in the opening plane and the surface of the substrate is H [cm], and the flow rate of the carrier gas supplied from the nozzle is Q [L / min]. It has been found that a film with few pits and excellent smoothness can be formed by a film formation method in which SH / Q≧0.015, and the present invention has been completed.

[0041] The present invention will be described in detail below, but the present invention is not limited thereto.

[0042] The following description will be made with reference to the drawings.

[0043] [Oxide semiconductor film] The oxide semiconductor film according to the present invention is mainly composed of gallium, has a corundum structure, and has pits of 10,000 / cm 2The oxide semiconductor film according to the present invention is characterized in the following points. Generally, an oxide semiconductor film is composed of a metal and oxygen, but the metal in the oxide semiconductor film according to the present invention is mainly composed of gallium. Here, "mainly composed" means that 50 to 100% of the metal components is gallium. Furthermore, "gallium-based" means that the metal component contains gallium. The metal component other than gallium may include, for example, one or more metals selected from iron, indium, aluminum, vanadium, titanium, chromium, rhodium, iridium, nickel, and cobalt.

[0044] 10,000 pits / cm 2 It is preferable that the density is less than 100 / cm 2 More preferably, it is 100 particles / cm or less. 2 It is more preferable that the number of pits is less than 0.01 / cm. There is no particular lower limit to the number of pits. 2 That's all there is to it.

[0045] The oxide semiconductor film can contain a dopant depending on the application. The dopant is not particularly limited. Examples include n-type dopants such as tin, germanium, silicon, titanium, zirconium, vanadium, and niobium, and p-type dopants such as copper, silver, tin, iridium, and rhodium. The dopant concentration is, for example, about 1.0×10 16 ~1.0×10 22 / cm 3 may be about 1.0 x 10 17 / cm 3 Even at low concentrations below this, the 20 / cm 3 A concentration higher than this may be used.

[0046] Here, the pits referred to in the present invention refer to depressions formed on the film surface as shown in Fig. 15, and can be observed using an optical microscope, SEM, TEM, etc. The opening diameter of the pits is about 10 nm to 10 µm, and the depth is 10 nm to 10 µm.

[0047] Although the details of why pits occur are unclear, it is thought that when the velocity component of the mist in the direction perpendicular to the substrate is large and the weight (moisture content) of the mist at the time of reaching the substrate is large, the impulse when the mist collides with the substrate becomes large, causing an excess amount of raw material components to be supplied locally, and unreacted components and by-reactants in the mist remain on the film. The presence of such residues on the film surface is thought to make it difficult for the film to grow locally. Therefore, it is thought that pit formation can be suppressed by reducing the velocity component of the mist in the direction perpendicular to the substrate and reducing the weight (moisture content) of the mist at the time of reaching the substrate under the conditions described below.

[0048] The oxide semiconductor film according to the present invention is not particularly limited in thickness, and may be, for example, 0.05 to 100 μm, preferably 0.1 to 50 μm, and more preferably 0.5 to 20 μm.

[0049] An oxide semiconductor film 180 according to the present invention is formed on a substrate 181 as shown in FIG.

[0050] Furthermore, another layer may be interposed between the substrate 181 and the oxide semiconductor film 180. The other layer is a layer having a different composition from the substrate 181 and the outermost oxide semiconductor film 180, and may be, for example, any of a crystalline oxide film, an insulating film, a metal film, or the like.

[0051] The area of the oxide semiconductor film is 10 cm 2 In the case of a circle, the diameter is preferably 2 inches (50 mm) or more. There is no particular upper limit to the area, but it is preferably 750 cm. 2 If circular, a diameter of 12 inches (300 mm) or less is preferred.

[0052] By appropriately designing the structure, the oxide semiconductor film according to the present invention can be used in semiconductor devices, such as Schottky barrier diodes (SBDs), metal semiconductor field effect transistors (MESFETs), high electron mobility transistors (HEMTs), metal oxide semiconductor field effect transistors (MOSFETs), static induction transistors (SITs), junction field effect transistors (JFETs), insulated gate bipolar transistors (IGBTs), and light emitting diodes (LEDs).

[0053] [Film forming equipment] 1 shows an example of a film formation apparatus 101 that can be used in the film formation method according to the present invention. The film formation apparatus 101 includes a mist-forming unit 120 that generates mist by misting a raw material solution, a carrier gas supply unit 130 that supplies a carrier gas that transports the mist, a film formation unit 140 that heat-treats the mist to form a film on a substrate, and a transport unit 109 that connects the mist-forming unit 120 and the film formation unit 140 and transports the mist by the carrier gas. The operation of the film formation apparatus 101 may also be controlled by including a control unit (not shown) that controls all or part of the film formation apparatus 101. Here, the term "mist" as used in the present invention refers to a general term for fine particles of liquid dispersed in a gas, and includes what is called fog, droplets, and the like.

[0054] (Mist generating section) In the mist generating section 120, the raw material solution is turned into mist to generate mist. The mist generating means is not particularly limited as long as it can turn the raw material solution into mist, and any known mist generating means may be used, but it is preferable to use a mist generating means that uses ultrasonic vibrations, as this allows for more stable mist generation.

[0055] An example of such a mist-generating unit 120 is shown in FIG. 2. For example, the mist-generating unit 120 may include a mist source 104 that contains raw solution 104a, a container 105 that contains a medium capable of transmitting ultrasonic vibrations, such as water 105a, and an ultrasonic vibrator 106 attached to the bottom of the container 105. More specifically, the mist source 104, which is a container that contains the raw solution 104a, is housed in the container 105 that contains the water 105a using a support (not shown). The bottom of the container 105 is equipped with an ultrasonic vibrator 106, which is connected to an oscillator 116. When the oscillator 116 is activated, the ultrasonic vibrator 106 vibrates, and ultrasonic waves propagate through the water 105a into the mist source 104, turning the raw solution 104a into mist.

[0056] (Carrier gas supply unit) The carrier gas supply unit 130 has a carrier gas source 102a that supplies a carrier gas, and may also be equipped with a flow rate control valve 103a for adjusting the flow rate of the carrier gas delivered from the carrier gas source 102a. Furthermore, the carrier gas supply unit 130 may also be equipped with a dilution carrier gas source 102b that supplies a dilution carrier gas as needed, and a flow rate control valve 103b for adjusting the flow rate of the dilution carrier gas delivered from the dilution carrier gas source 102b. The number of carrier gas supply locations may be two or more, rather than just one.

[0057] (Film forming part) In the film forming section 140, the mist is heated and heat-treated to form a film on a part or all of the surface of the substrate 110. The film forming section 140 may be partially or entirely enclosed, or may not be enclosed. For example, as shown in FIG. 1, the film forming section 140 may be entirely enclosed to form a film forming chamber 107. The film forming section 140 has a substrate 110 placed therein and may be provided with a hot plate 108 for heating the substrate 110. The hot plate 108 may be provided inside the film forming chamber 107 as shown in FIG. 1, or may be provided outside the film forming chamber 107. The film forming section 140 may also be provided with a moving stage 161a. Details will be described later.

[0058] Furthermore, the film forming unit 140 is equipped with a nozzle 150 for supplying mist to the substrate 110, as shown in Fig. 3. An example of the nozzle 150 is shown in Fig. 4. The nozzle 150 includes a connection part 151 that connects the transfer part 109 and the nozzle 150, and a nozzle opening surface 152 for spraying the mist. The position at which the nozzle 150 is equipped is not particularly limited. As shown in Fig. 3, the substrate 110 may be installed on the lower surface of the film forming chamber 107, with the nozzle 150 installed vertically above the substrate, in a face-up position. Alternatively, the substrate 110 may be installed on the upper surface of the film forming chamber 107, with the nozzle 150 installed vertically below the substrate, in a face-down position.

[0059] The number of nozzles and the number of nozzle openings are not particularly limited as long as they are at least 1. As shown in Figure 5, multiple nozzles 150a and 150b may be provided, and as shown in Figure 6, nozzle 150c may have multiple openings.

[0060] Furthermore, the angle formed between the plane including the nozzle opening surface 152 and the plane including the substrate 110 is not particularly limited. As shown in Fig. 7, a nozzle 150d may be provided having a nozzle opening surface 152 that is inclined so that the mist flows more easily in a specific direction, or as shown in Fig. 8, a nozzle 150e may be provided in which a portion of the nozzle opening surface is inclined, but it is preferable that the nozzle opening surface is parallel to the substrate 110, as shown in Fig. 4. This is because a film with fewer pits and excellent smoothness can be formed with a simpler structure.

[0061] In addition, the film forming section 140 may be equipped with a position adjustment mechanism (not shown) that can appropriately adjust the longest distance H [cm] between a point within the nozzle opening surface 152 and the surface of the substrate 110 within the range described below. Furthermore, the nozzle 150 may be constructed by assembling a plurality of members, and the area of the nozzle opening may be adjusted appropriately by adjusting the size of the members.

[0062] The shape of the nozzle opening surface 152 is not particularly limited. Possible shapes include polygonal, circular, elliptical, etc., but a square shape is preferable, and a rectangle is more preferable.

[0063] 9, the film forming unit 140 may include a moving mechanism 160 that moves the substrate 110 below the nozzle 150. The direction in which the substrate is moved is not particularly limited. FIGS. 10 and 11 show the film forming unit 140, including moving mechanisms 160a and 160b, viewed vertically above the substrate 110. As shown in FIG. 10, a moving stage 161a on which the substrate 110 and hot plate 108 are placed is provided, and the substrate 110 and hot plate 108 move back and forth below the nozzle 150. Alternatively, as shown in FIG. 11, a moving stage 161b on which the substrate 110 and hot plate 108 are placed rotates the substrate 110 and hot plate 108 below the nozzle 150. Alternatively, a mechanism for rotating the substrate may be provided to rotate the substrate.

[0064] When a substrate moving mechanism is provided, the speed and range of substrate movement are not particularly limited, but the number of times a substrate passes under the nozzle per minute should be 0.1 or more, preferably 0.5 or more, and more preferably 1 or more. If the number of times is 0.1 or more, there will be no areas where the gas supply is locally excessive (i.e., the SH / Q will not decrease locally), so pits will not increase and a film with good surface smoothness will be obtained. Furthermore, while there is no particular upper limit to the number of times, as the number of times increases, the fixation of the substrate will become unstable due to inertial forces, so it is best to use 120 times or less, and preferably 60 times or less.

[0065] More specifically, in the case of a moving mechanism such as that shown in FIG. 10, where v [mm / min] is the substrate moving speed and D [mm] is the width of the substrate movement, v / D is preferably 0.1 / min or more, preferably 0.5 / min to 120 / min, and more preferably 1 to 60 / min. D is not particularly limited, and is preferably equal to or greater than the diameter R [mm] of the substrate (100 mm or more for a 4-inch substrate), with no particular upper limit. Increasing D allows for deposition on a large number of substrates per nozzle. However, since the deposition rate per substrate decreases, it is preferable to limit the number of substrates per nozzle to 1000 mm or less for superior productivity. v is not particularly limited. It is preferably 10 mm / min to 30,000 mm / min, more preferably 30 mm / min to 12,000 mm / min, and more preferably 60 mm / min to 6,000 mm / min. In the case of a rotary type moving mechanism such as that shown in FIG. 11, the rotation speed is preferably 0.1 rpm or more, more preferably 0.5 to 120 rpm, and even more preferably 1 to 60 rpm.

[0066] Furthermore, when the film forming unit 140 is enclosed, the exhaust gas outlet 111 may be provided at a position that does not affect the supply of mist to the substrate 110. The exhaust outlet 111 may be provided in one location or in two or more locations as long as it does not affect the supply of mist.

[0067] (Transportation section) The transfer unit 109 connects the mist generation unit 120 and the film formation unit 140. Mist is transferred by a carrier gas from the mist generation source 104 of the mist generation unit 120 to the nozzle 150 of the film formation unit 140 via the transfer unit 109. The transfer unit 109 can be, for example, a supply pipe 109a. The supply pipe 109a can be, for example, a quartz pipe or a resin tube.

[0068] [Film forming method] Next, a film forming method according to the present invention will be described. The present invention is a film forming method for forming a film by heat-treating a mist of a raw material solution, and includes the steps of: atomizing or dropletizing the raw material solution to generate a mist; transporting the mist to a film forming unit by a carrier gas; and supplying the mist from a nozzle onto a substrate in the film forming unit and heat-treating the substrate to form a film; and the area of the opening surface of the nozzle is set to S [cm 2 ], the longest distance between a point in the opening plane and the surface of the substrate is H [cm], and the flow rate of the carrier gas supplied from the nozzle is Q [L / min], where SH / Q≧0.015.

[0069] (Process for generating mist) First, the raw material solution 104a is atomized or converted into droplets to generate a mist. This process can be performed using the mist-generating unit 120 described above. The raw material solution (aqueous solution) 104a is not particularly limited as long as it contains a material that can be converted into a mist, and may be an inorganic or organic material. A solution of a metal or metal compound is preferably used as the raw material solution, and one or more metals selected from gallium, iron, indium, aluminum, vanadium, titanium, chromium, rhodium, nickel, and cobalt can be used. Among these, a solution containing gallium is particularly preferred, as it can suppress pitting and form a gallium-containing film with excellent smoothness.

[0070] The raw material solution is not particularly limited as long as it can mist a solution of the metal (compound). A suitable raw material solution is one in which the metal is dissolved or dispersed in an organic solvent or water in the form of a complex or salt. Examples of complexes include acetylacetonate complexes, carbonyl complexes, ammine complexes, and hydride complexes. Examples of salts include metal chlorides, metal bromides, and metal iodides. Furthermore, solutions in which the metals are dissolved in hydrobromic acid, hydrochloric acid, hydroiodic acid, or the like can also be used as aqueous salt solutions. The solute concentration is preferably 0.01 to 1 mol / L. Among these, those containing halogens are particularly preferred, as they can further suppress pitting and form films with better smoothness.

[0071] The raw material solution may also contain additives such as hydrohalic acid and oxidizing agents. Examples of hydrohalic acids include hydrobromic acid, hydrochloric acid, and hydroiodic acid, with hydrobromic acid and hydroiodic acid being preferred. Examples of oxidizing agents include peroxides such as hydrogen peroxide (HO), sodium peroxide (NaO), barium peroxide (BaO), and benzoyl peroxide (CHCO)O, as well as hypochlorous acid (HClO), perchloric acid, nitric acid, ozone water, and organic peroxides such as peracetic acid and nitrobenzene.

[0072] Furthermore, the raw material solution may contain a dopant. The dopant is not particularly limited. Examples of the dopant include n-type dopants such as tin, germanium, silicon, titanium, zirconium, vanadium, and niobium, and p-type dopants such as copper, silver, tin, iridium, and rhodium. The dopant concentration is, for example, about 1.0 × 10 -9 It may be up to 1.0 mol / L, and may be about 1.0 × 10 -7 The concentration may be as low as 0.01 mol / L or less, or as high as about 0.01 mol / L or more.

[0073] (Process of transporting mist) Next, the generated mist is transported to the film forming section by a carrier gas. The type of carrier gas is not particularly limited and can be selected appropriately depending on the film to be formed. Examples include inert gases such as oxygen, ozone, nitrogen, and argon, and reducing gases such as hydrogen gas and forming gas. The type of carrier gas may be one type or two or more types. For example, a dilution gas obtained by diluting the same gas as the first carrier gas with another gas (e.g., diluted 10 times) may be further used as the second carrier gas, or air may be used.

[0074] The flow rate Q [L / min] of the carrier gas according to the present invention represents the total flow rate of the carrier gas. For example, when a dilution carrier gas is used in addition to the carrier gas, the total flow rate of the carrier gas and the dilution carrier gas is designated as Q. Note that Q is a value measured at 20°C. When measured at other temperatures or when a different type of flow rate (such as mass flow rate) is measured, Q can be converted to a volumetric flow rate at 20°C using the gas state equation.

[0075] The flow rate of the carrier gas (total flow rate when multiple types of gases are used) is not particularly limited as long as it satisfies the conditions described below. For example, when forming a film on a substrate with a diameter of 4 inches (100 mm), the flow rate is preferably 1 to 80 L / min, and more preferably 4 to 40 L / min.

[0076] (Film formation process) Next, in the film forming section, the mist is supplied onto a substrate from a nozzle, and a film is formed on the substrate by heat treatment. Here, the area of the nozzle opening surface 152 is S [cm 2], the flow rate of the carrier gas is Q [L / min], and the longest distance between a point in the nozzle opening surface 152 and the surface of the substrate 110 is H [cm], then SH / Q should be 0.015 or more, preferably 0.1 or more and 20 or less. If SH / Q is less than 0.015, the film will have many pits and poor surface smoothness. In addition, the velocity of the carrier gas in the direction perpendicular to the substrate at the nozzle opening surface 152 should be 0.01 m / s or more and less than 8.0 m / s, preferably 0.1 m / s or more and less than 2.5 m / s.

[0077] In addition, the area S of the nozzle opening surface 152 is 0.1 cm 2 More than 400cm 2 The shortest distance H between the nozzle opening surface 152 and the substrate 110 is preferably 0.1 cm or more and 6.0 cm or less, and more preferably 0.2 cm or more and 3.0 cm or less.

[0078] The area of the nozzle opening 152 is S [cm 2 ], the area of the substrate is A [cm 2 ], S / A≦0.3 is preferable, and 0.004≦S / A≦0.15 is more preferable. If S / A≦0.3, the film will have fewer pits and have better surface smoothness. In this case, the area A of the substrate is 10 cm 2 It is preferable that the diameter of the substrate is 2 inches (50 mm) or more, and if the substrate is circular, it is preferable that the diameter is 2 inches (50 mm) or more. This is because a film with good surface smoothness can be formed over a larger area. There is no particular upper limit for A. The larger the area of the substrate, the larger the area of the film that can be formed in one film formation, making it suitable for mass production.

[0079] It is preferable to use a nozzle with a rectangular opening, where L [cm] is the long axis length of the nozzle opening 152 and R [cm] is the maximum length of the substrate in the nozzle long axis direction, and L / R≧1 is desirable. If L / R≧1, a film with good smoothness can be easily formed on a large-area substrate. Here, the long axis refers to the long side of the rectangle. There is no particular upper limit to L / R, but the larger the L / R, the more mist is not supplied to the substrate, so it is preferable to set it to 3 or less.

[0080] The heat treatment is not particularly limited as long as the mist reacts by heating. The reaction conditions can be appropriately set depending on the raw material and the film to be formed. For example, the heating temperature is in the range of 120 to 600°C, preferably in the range of 200 to 600°C, and more preferably in the range of 300 to 550°C. The heating temperature is T [°C], and the area of the nozzle opening surface 152 is S [cm 2 ] and the flow rate of the carrier gas is Q [L / min], ST / Q is preferably 40 or more, and more preferably 100 or more and 2000 or less. If ST / Q≧40, the number of pits will be further reduced, resulting in a film with even better surface smoothness.

[0081] The heat treatment may be carried out under any of the following atmospheres: vacuum, non-oxygen atmosphere, reducing gas atmosphere, air atmosphere, and oxygen atmosphere, and may be appropriately set depending on the film to be formed. The reaction pressure may be atmospheric pressure, pressurized pressure, or reduced pressure, but film formation under atmospheric pressure is preferred because it simplifies the device configuration.

[0082] The substrate 110 is not particularly limited as long as it can be used to form a film and can support the film. The material of the substrate 110 is also not particularly limited, and any known substrate can be used, and it may be an organic compound or an inorganic compound. Examples of materials include, but are not limited to, polysulfone, polyethersulfone, polyphenylene sulfide, polyetheretherketone, polyimide, polyetherimide, fluororesin, metals such as iron, aluminum, stainless steel, and gold, silicon, sapphire, quartz, glass, gallium oxide, lithium niobate, and lithium tantalate. The thickness of the substrate is not particularly limited, but is preferably 10 to 2000 μm, and more preferably 50 to 800 μm.

[0083] The film formation may be performed directly on the substrate, or may be laminated on an intermediate layer formed on the substrate. The intermediate layer is not particularly limited, and for example, it can be mainly composed of an oxide containing any one of aluminum, titanium, vanadium, chromium, iron, gallium, rhodium, indium, and iridium. More specifically, they are Al2O3, Ti2O3, V2O3, Cr2O3, Fe2O3, Ga2O3, Rh2O3, In2O3, Ir2O3. Also, when two elements selected from the above metal elements are defined as A and B, (A x B 1-x )2O3 (0 < x < 1), a binary metal oxide represented thereby, or when three elements selected from the above metal elements are defined as A, B, and C, (A x B y C 1-x-y )2O3 (0 < x < 1, 0 < y < 1, 0 < x + y < 1), a ternary metal oxide represented thereby can be used.

[0084] In the present invention, annealing treatment may be performed after film formation. The temperature of the annealing treatment is not particularly limited, but is preferably 600 °C or lower, and more preferably 550 °C or lower, in order not to impair the crystallinity of the film. The treatment time of the annealing treatment is not particularly limited, but is preferably 10 seconds to 10 hours, and more preferably 10 seconds to 1 hour.

[0085] (Peeling) The substrate 110 may be peeled from the oxide semiconductor film. The peeling means is not particularly limited, and known means may be used. For example, means for peeling by applying mechanical impact, means for peeling by applying heat and utilizing thermal stress, means for peeling by applying vibrations such as ultrasonic waves, means for peeling by etching, laser lift-off, etc. can be mentioned. By the above peeling, the oxide semiconductor film can be obtained as a self-supporting film.

[0086] (Electrode) Electrodes required for constructing a semiconductor device can be formed using conventional methods. Examples include vapor deposition, sputtering, CVD, plating, and printing methods, such as bonding with resins. Electrode materials include metals such as Al, Ag, Ti, Pd, Au, Cu, Cr, Fe, W, Ta, Nb, Mn, Mo, Hf, Co, Zr, Sn, Pt, V, Ni, Ir, Zn, In, and Nd; conductive metal oxide films such as tin oxide, zinc oxide, indium oxide, indium tin oxide (ITO), and indium zinc oxide (IZO); and organic conductive compounds such as polyaniline, polythiophene, and polypyrrole. These materials may also be alloys or mixtures of two or more of these. The electrode thickness is preferably 1 to 1,000 nm, more preferably 10 to 500 nm.

[0087] [Film deposition system] Next, a film forming system according to the present invention will be described. The present invention is a film forming system that forms a film by heat-treating a mist of a raw material solution, and includes a mechanism for atomizing or dropletizing the raw material solution to generate mist, a mechanism for transporting the mist to a film forming unit by a carrier gas, and a mechanism for supplying the mist from a nozzle onto a substrate in the film forming unit and heat-treating the substrate to form a film, and the area of the opening surface of the nozzle is S [cm 2 ], the longest distance between a point in the opening plane and the surface of the substrate is H [cm], and the flow rate of the carrier gas supplied from the nozzle is Q [L / min], where SH / Q≧0.015.

[0088] (Mist generating mechanism) First, the raw material solution 104a is atomized or converted into droplets to generate a mist. This mechanism can be performed using the mist-generating unit 120 described above. The raw material solution (aqueous solution) 104a is not particularly limited as long as it contains a material that can be converted into a mist, and may be an inorganic or organic material. A solution of a metal or metal compound is preferably used as the raw material solution, and one or more metals selected from gallium, iron, indium, aluminum, vanadium, titanium, chromium, rhodium, nickel, and cobalt can be used. Among these, a solution containing gallium is particularly preferred, as it can suppress pitting and form a gallium-containing film with excellent smoothness.

[0089] The raw material solution is not particularly limited as long as it can mist a solution of the metal (compound). A suitable raw material solution is one in which the metal is dissolved or dispersed in an organic solvent or water in the form of a complex or salt. Examples of complexes include acetylacetonate complexes, carbonyl complexes, ammine complexes, and hydride complexes. Examples of salts include metal chlorides, metal bromides, and metal iodides. Furthermore, solutions in which the metals are dissolved in hydrobromic acid, hydrochloric acid, hydroiodic acid, or the like can also be used as aqueous salt solutions. The solute concentration is preferably 0.01 to 1 mol / L. Among these, those containing halogens are particularly preferred, as they can further suppress pitting and form films with better smoothness.

[0090] The raw material solution may also contain additives such as hydrohalic acid and oxidizing agents. Examples of hydrohalic acids include hydrobromic acid, hydrochloric acid, and hydroiodic acid, with hydrobromic acid and hydroiodic acid being preferred. Examples of oxidizing agents include peroxides such as hydrogen peroxide (HO), sodium peroxide (NaO), barium peroxide (BaO), and benzoyl peroxide (CHCO)O, as well as hypochlorous acid (HClO), perchloric acid, nitric acid, ozone water, and organic peroxides such as peracetic acid and nitrobenzene.

[0091] Furthermore, the raw material solution may contain a dopant. The dopant is not particularly limited. Examples of the dopant include n-type dopants such as tin, germanium, silicon, titanium, zirconium, vanadium, and niobium, and p-type dopants such as copper, silver, tin, iridium, and rhodium. The dopant concentration is, for example, about 1.0 × 10 -9 It may be up to 1.0 mol / L, and may be about 1.0 × 10 -7 The concentration may be as low as 0.01 mol / L or less, or as high as about 0.01 mol / L or more.

[0092] (Mist transport mechanism) Next, the generated mist is transported to the film forming unit by a carrier gas. This mechanism can be performed using the transport unit 109 described above. The type of carrier gas is not particularly limited and can be selected appropriately depending on the film to be formed. Examples include inert gases such as oxygen, ozone, nitrogen, and argon, and reducing gases such as hydrogen gas and forming gas. The type of carrier gas may be one type or two or more types. For example, a dilution gas obtained by diluting the same gas as the first carrier gas with another gas (e.g., diluted 10 times) may be further used as the second carrier gas, or air may be used.

[0093] The flow rate Q [L / min] of the carrier gas according to the present invention represents the total flow rate of the carrier gas. For example, when a dilution carrier gas is used in addition to the carrier gas, the total flow rate of the carrier gas and the dilution carrier gas is designated as Q. Note that Q is a value measured at 20°C. When measured at other temperatures or when a different type of flow rate (such as mass flow rate) is measured, Q can be converted to a volumetric flow rate at 20°C using the gas state equation.

[0094] The flow rate of the carrier gas (total flow rate when multiple types of gases are used) is not particularly limited as long as it satisfies the conditions described below. For example, when forming a film on a substrate with a diameter of 4 inches (100 mm), the flow rate is preferably 1 to 80 L / min, and more preferably 4 to 40 L / min.

[0095] (Mechanism for film formation) Next, in the film forming unit 140, the mist is supplied from the nozzle onto the substrate, and a film is formed on the substrate by heat treatment. Here, the area of the nozzle opening surface 152 is S [cm 2 ], the flow rate of the carrier gas is Q [L / min], and the longest distance between a point in the nozzle opening surface 152 and the surface of the substrate 110 is H [cm], then SH / Q should be 0.015 or more, preferably 0.1 or more and 20 or less. If SH / Q is less than 0.015, the film will have many pits and poor surface smoothness. In addition, the velocity of the carrier gas in the direction perpendicular to the substrate at the nozzle opening surface 152 should be 0.01 m / s or more and less than 8.0 m / s, preferably 0.1 m / s or more and less than 2.5 m / s.

[0096] In addition, the area S of the nozzle opening surface 152 is 0.1 cm 2 More than 400cm 2 The shortest distance H between the nozzle opening surface 152 and the substrate 110 is preferably 0.1 cm or more and 6.0 cm or less, and more preferably 0.2 cm or more and 3.0 cm or less.

[0097] The area of the nozzle opening 152 is S [cm 2 ], the area of the substrate is A [cm 2 ], S / A≦0.3 is preferable, and 0.004≦S / A≦0.15 is more preferable. If S / A≦0.3, the film will have fewer pits and have better surface smoothness. In this case, the area A of the substrate is 10 cm 2 It is preferable that the diameter of the substrate is 2 inches (50 mm) or more, and if the substrate is circular, it is preferable that the diameter is 2 inches (50 mm) or more. This is because a film with good surface smoothness can be formed over a larger area. There is no particular upper limit for A. The larger the area of the substrate, the larger the area of the film that can be formed in one film formation, making it suitable for mass production.

[0098] It is preferable to use a nozzle with a rectangular opening, where L [cm] is the long axis length of the nozzle opening 152 and R [cm] is the maximum length of the substrate in the nozzle long axis direction, and L / R≧1 is desirable. If L / R≧1, a film with good smoothness can be easily formed on a large-area substrate. Here, the long axis refers to the long side of the rectangle. There is no particular upper limit to L / R, but the larger the L / R, the more mist is not supplied to the substrate, so it is preferable to set it to 3 or less.

[0099] The heat treatment is not particularly limited as long as the mist reacts by heating. The reaction conditions can be appropriately set depending on the raw material and the film to be formed. For example, the heating temperature is in the range of 120 to 600°C, preferably in the range of 200 to 600°C, and more preferably in the range of 300 to 550°C. The heating temperature is T [°C], and the area of the nozzle opening surface 152 is S [cm 2 ] and the flow rate of the carrier gas is Q [L / min], ST / Q is preferably 40 or more, and more preferably 100 or more and 2000 or less. If ST / Q≧40, the number of pits will be further reduced, resulting in a film with even better surface smoothness.

[0100] The heat treatment may be carried out under any of the following atmospheres: vacuum, non-oxygen atmosphere, reducing gas atmosphere, air atmosphere, and oxygen atmosphere, and may be appropriately set depending on the film to be formed. The reaction pressure may be atmospheric pressure, pressurized pressure, or reduced pressure, but film formation under atmospheric pressure is preferred because it simplifies the device configuration.

[0101] The substrate 110 is not particularly limited as long as it can be film-formed and support a film. The material of the substrate 110 is also not particularly limited, and known substrates can be used, which may be organic compounds or inorganic compounds. For example, polysulfone, polyethersulfone, polyphenylene sulfide, polyetheretherketone, polyimide, polyetherimide, fluororesin, metals such as iron, aluminum, stainless steel, gold, etc., silicon, sapphire, quartz, glass, gallium oxide, lithium niobate, lithium tantalate, etc. can be mentioned, but it is not limited thereto. The thickness of the substrate is not particularly limited, but preferably it is 10 to 2000 μm, more preferably 50 to 800 μm.

[0102] Film formation may be directly performed on the substrate, or may be laminated on an intermediate layer formed on the substrate. The intermediate layer is not particularly limited. For example, it can be mainly composed of an oxide containing any one of aluminum, titanium, vanadium, chromium, iron, gallium, rhodium, indium, and iridium. More specifically, they are Al2O3, Ti2O3, V2O3, Cr2O3, Fe2O3, Ga2O3, Rh2O3, In2O3, Ir2O3. Also, when two elements selected from the above metal elements are A and B, a binary metal oxide represented by (A x B 1-x )2O3 (0 < x < 1), or when three elements selected from the above metal elements are A, B, and C, a ternary metal oxide represented by (A x B y C 1-x-y )2O3 (0 < x < 1, 0 < y < 1, 0 < x + y < 1) can be used.

[0103] In the present invention, annealing treatment may be performed after film formation. The temperature of the annealing treatment is not particularly limited, but preferably it is 600 °C or lower, more preferably 550 °C or lower. This is to avoid damaging the crystallinity of the film. The treatment time of the annealing treatment is not particularly limited, but preferably it is 10 seconds to 10 hours, more preferably 10 seconds to 1 hour.

[0104] (Peeling) The substrate 110 may be peeled off from the oxide semiconductor film. The peeling method is not particularly limited and may be any known method. Examples include peeling by applying a mechanical shock, peeling by applying heat and using thermal stress, peeling by applying vibration such as ultrasonic waves, peeling by etching, and laser lift-off. By peeling, the oxide semiconductor film can be obtained as a free-standing film.

[0105] (electrode) Electrodes required for constructing a semiconductor device can be formed using conventional methods. Examples include vapor deposition, sputtering, CVD, plating, and printing methods, such as bonding with resins. Electrode materials include metals such as Al, Ag, Ti, Pd, Au, Cu, Cr, Fe, W, Ta, Nb, Mn, Mo, Hf, Co, Zr, Sn, Pt, V, Ni, Ir, Zn, In, and Nd; conductive metal oxide films such as tin oxide, zinc oxide, indium oxide, indium tin oxide (ITO), and indium zinc oxide (IZO); and organic conductive compounds such as polyaniline, polythiophene, and polypyrrole. These materials may also be alloys or mixtures of two or more of these. The electrode thickness is preferably 1 to 1,000 nm, more preferably 10 to 500 nm. [Example]

[0106] EXAMPLES The present invention will be specifically explained below using examples and comparative examples, but the present invention is not limited to these.

[0107] Example 1 In this example, a film forming apparatus as shown in FIG. 1 was used. Tin chloride was mixed with a 0.05 mol / L aqueous solution of gallium iodide to prepare an aqueous solution with an atomic ratio of tin to gallium of 1:0.08, which was designated as raw material solution 104a. The raw material solution 104a obtained as described above was placed in the mist generating source 104. The temperature of the solution at this time was 25°C. Next, a 4-inch (100 mm diameter) c-plane sapphire substrate as substrate 110 was placed on hot plate 108 in film formation chamber 107, and hot plate 108 was operated to raise the temperature to 500°C. Next, the flow control valves 103a and 103b were opened to supply nitrogen gas as a carrier gas from the carrier gas sources 102a and 102b into the film formation chamber 107, and the atmosphere in the film formation chamber 107 was thoroughly replaced with the carrier gas, while the flow rates of the main carrier gas and the dilution carrier gas were adjusted to 12 L / min and 12 L / min, respectively. Next, the ultrasonic vibrator 106 was vibrated at 2.4 MHz, and the vibration was propagated to the raw material solution 104a through the water 105a, thereby turning the raw material solution 104a into mist and generating mist. This mist was supplied to the substrate 110 by the carrier gas through the supply pipe 109a and the nozzle 150. The nozzle 150 used had a rectangular opening surface 152, and the area of the nozzle opening surface 152 was S [cm 2 ], the flow rate of the carrier gas is Q [L / min], and the longest distance between a point in the nozzle opening surface 152 and the surface of the substrate 110 is H [cm]. In this case, S = 6.0, H = 2.0, and Q = 24. The mist was then heat-treated in the film-forming chamber 107 under atmospheric pressure and at 500° C. to form a thin film of gallium oxide (α-Ga2O3) having a corundum structure on the substrate 110. The film-forming time was 30 minutes. When the heat treatment temperature is T [℃], ST / Q = 40, and the area of the substrate is A [cm 2 ], S / A=0.024, the long axis length of the nozzle opening surface 152 is L [cm], and the maximum length of the substrate in the nozzle long axis direction is R [cm], so L / R=1.2. In this case, T=500, A=78.5, L=12, and R=10. The substrate and hot plate were moved back and forth at a speed of 15 cm / min by a moving mechanism as shown in Figure 10, so that they passed under the nozzle once per minute. Subsequently, an n-semiconductor film was laminated as a second layer on the n+ semiconductor film obtained as described above under the same conditions using the same source solution as above except that it did not contain tin chloride.

[0108] Example 2 The area S of the nozzle opening is 10.8 cm 2 Film formation was performed in the same manner as in Example 1, except that the total flow rate of the carrier gas was changed to 40 L / min and the film formation temperature T was changed to 550° C. At this time, SH / Q=0.54, ST / Q=149, and S / A=0.15.

[0109] Example 3 Film formation was performed in the same manner as in Example 2, except that the total flow rate of the carrier gas was changed to 20 L / min and the film formation temperature T was changed to 500° C. At this time, SH / Q=1.08, ST / Q=270, and S / A=0.15.

[0110] Example 4 Film formation was carried out in the same manner as in Example 2, except that the film formation temperature T was changed to 500° C. In this case, SH / Q=0.54, ST / Q=135, and S / A=0.15.

[0111] Example 5 The concentration of the raw material solution is 0.3 mol / L, and the nozzle opening area S is 1.2 cm 2 Film formation was performed in the same manner as in Example 1, except that the longest distance H between a point in the nozzle opening surface 152 and the surface of the substrate 110 was changed to 2.5 cm and the total flow rate of the carrier gas was changed to 14 L / min. At this time, SH / Q=0.21, ST / Q=42.9, and S / A=0.015.

[0112] Example 6 Film formation was performed in the same manner as in Example 5, except that the raw material solution was a 0.3 mol / L aqueous gallium bromide solution and the longest distance H between a point within nozzle opening surface 152 and the surface of substrate 110 was changed to 1.6 cm. At this time, SH / Q=0.14, ST / Q=42.9, and S / A=0.015.

[0113] Example 7 A 6-inch (150 mm diameter) sapphire substrate was used as the substrate 110, and the area S of the nozzle opening was 8.5 cm 2 Film formation was performed in the same manner as in Example 1, except that the longest distance H between a point in the nozzle opening surface 152 and the surface of the substrate 110 was changed to 0.2 cm and the total flow rate of the carrier gas was changed to 36 L / min. At this time, SH / Q=0.047, ST / Q=118, S / A=0.048, and L / R=1.1.

[0114] Example 8 The raw material solution used was a 0.05 mol / L aqueous solution of gallium acetylacetonate complex dissolved in water containing 1.5% by volume of hydrochloric acid. The nozzle opening area S was 1.2 cm 2 Film formation was performed in the same manner as in Example 1, except that the longest distance H between a point in the nozzle opening surface 152 and the surface of the substrate 110 was changed to 0.2 cm, the total flow rate of the carrier gas was changed to 10 L / min, and the film formation temperature T was changed to 450° C. At this time, SH / Q=0.024, ST / Q=54, and S / A=0.015.

[0115] Example 9 Film formation was performed in the same manner as in Example 6, except that the longest distance H between a point within the nozzle opening surface 152 and the surface of the substrate 110 was changed to 1.2 cm. At this time, SH / Q=0.1, ST / Q=42.9, and S / A=0.015.

[0116] Example 10 The area of the nozzle opening, S, is 24 cm 2 Film formation was performed in the same manner as in Example 1, except that the longest distance H between a point in the nozzle opening surface 152 and the surface of the substrate 110 was changed to 0.2 cm, the total flow rate of the carrier gas was changed to 80 L / min, and the film formation temperature T was changed to 550° C. At this time, SH / Q=0.06, ST / Q=165, and S / A=0.30.

[0117] Example 11 The area of the nozzle opening, S, is 5.0 cm 2The longest distance H between a point in the nozzle opening surface 152 and the surface of the substrate 110 was set to 0.2 cm, and the total flow rate of the carrier gas was set to 60 L / min, and film formation was performed in the same manner as in Example 1. At this time, SH / Q=0.017, ST / Q=41.7, S / A=0.064, and L / R=1.0.

[0118] Example 12 Film formation was performed in the same manner as in Example 1, except that the shape of the nozzle opening surface was changed to a circle with a diameter of 4 inches (100 mm), the longest distance H between a point within the nozzle opening surface 152 and the surface of the substrate 110 was changed to 0.2 cm, the substrate was not moved, the flow rate of the carrier gas was changed to a total of 80 L / min, and the heating temperature was set to 550° C. At this time, SH / Q=0.20, ST / Q=540, S / A=1, and L / R=1.

[0119] Example 13 Film formation was performed in the same manner as in Example 6, except that the raw material solution was a 0.05 mol / L aqueous gallium bromide solution to which 10% by volume of bromide deuterium acid was added, the longest distance H between a point within nozzle opening surface 152 and the surface of substrate 110 was changed to 0.2 cm, and the film formation temperature T was changed to 470° C. At this time, SH / Q=0.017, ST / Q=40, and S / A=0.015.

[0120] Example 14 Film formation was performed in the same manner as in Example 6, except that the raw material solution was a 0.05 mol / L aqueous gallium iodide solution, the longest distance H between a point within the nozzle opening surface 152 and the surface of the substrate 110 was changed to 0.2 cm, the total flow rate of the carrier gas was changed to 16 L / min, and the film formation temperature T was changed to 450° C. At this time, SH / Q=0.015, ST / Q=33.8, and S / A=0.015.

[0121] (Comparative Example 1) Except for changing the total flow rate of the carrier gas to 20 L / min, film formation was carried out in the same manner as in Example 14. At this time, SH / Q=0.012, ST / Q=27, and S / A=0.015.

[0122] (Comparative Example 2) Except for changing the total flow rate of the carrier gas to 24 L / min, film formation was carried out in the same manner as in Example 14. At this time, SH / Q=0.01, ST / Q=22.5, and S / A=0.015.

[0123] (Comparative Example 3) Except for changing the total flow rate of the carrier gas to 48 L / min, film formation was carried out in the same manner as in Example 14. At this time, SH / Q=0.005, ST / Q=11.3, and S / A=0.015.

[0124] Comparative Example 4 Except for changing the total flow rate of the carrier gas to 60 L / min, film formation was carried out in the same manner as in Example 14. At this time, SH / Q=0.004, ST / Q=9, and S / A=0.015.

[0125] (Test Example 1) After deposition, the surface of the film was observed using an optical microscope. 2 The number of pits within the specimen was counted. The pit density was calculated by dividing the number of pits counted by the observation area, and is shown in Table 1. Figure 12 shows the results of plotting the pit density against SH / Q.

[0126] (Test Example 2) Using the semiconductor film obtained as described above, a semiconductor device 170 as shown in FIG. 13 was fabricated.

[0127] <Formation of Schottky electrode> A Pt layer, a Ti layer, and an Au layer were laminated on the n-type semiconductor layer 171a by electron beam evaporation, to form the Schottky electrode 172.

[0128] <Formation of ohmic electrodes> On the n+ type semiconductor layer 171b, a Ti layer and an Au layer were laminated by electron beam evaporation, to form an ohmic electrode 173.

[0129] <Evaluation> The current-voltage characteristics of the obtained semiconductor devices were evaluated. The voltage at which breakdown occurs was determined by measuring the reverse current-voltage characteristics. Semiconductor devices with a breakdown voltage of 300V or more were considered to be acceptable products, and the yield was calculated as the number of acceptable products / total number of semiconductor devices produced = yield [%]. The results are shown in Table 1. FIG. 14 shows a graph in which the yield is plotted against the pit density calculated in Test Example 1.

[0130] [Table 1]

[0131] From a comparison between Examples 1 to 14 and Comparative Examples 1 to 4, the nozzle opening area S [cm 2 ], the longest distance between a point in the opening plane and the surface of the substrate is H [cm], and the flow rate of the gas supplied from the nozzle is Q [L / min]. It was found that by forming a film using a film formation method in which SH / Q≧0.015, pits are suppressed and the film has excellent smoothness, and that semiconductor devices with high breakdown voltage can be manufactured with excellent yield.

[0132] The present invention is not limited to the above-described embodiments, which are merely examples, and anything that has substantially the same configuration as the technical idea described in the claims of the present invention and that provides similar effects is included within the technical scope of the present invention.

Claims

1. A film-forming method for forming a film by heat-treating a mist of a raw material solution, comprising: A step of atomizing or dropletizing the raw material solution to generate a mist; a step of transporting the mist to a film forming section by a carrier gas; a step of supplying the mist onto a substrate from a nozzle in the film forming unit and performing a heat treatment on the substrate to form a film; Including, The area of the opening of the nozzle is S [cm ２ ], the longest distance between a point in the opening plane and the surface of the substrate is H [cm], and the flow rate of the carrier gas supplied from the nozzle is Q [L / min], where SH / Q≧0.

015. A film forming method characterized by:

2. 2. The film forming method according to claim 1, wherein the raw material solution contains gallium.

3. 3. The film forming method according to claim 1, wherein the raw material solution contains a halogen.

4. 4. The film forming method according to claim 1, wherein ST / Q≧40 when the temperature of the heat treatment is T [° C.].

5. 5. The film forming method according to claim 1, wherein the mist is supplied onto the substrate from the nozzle provided vertically above the substrate.

6. 6. The film forming method according to claim 5, wherein the substrate is moved under the nozzle.

7. The area of the surface of the substrate on which the film is formed is defined as A [cm ２ 7. The film forming method according to claim 6, wherein S / A≦0.3 when

8. 8. The film forming method according to claim 1, wherein the nozzle has an opening surface that is rectangular.

9. 9. The film forming method according to claim 8, wherein L / R≧1 is satisfied, where L [cm] is the length of the major axis of the opening surface of the nozzle, and R [cm] is the maximum length of the nozzle in the major axis direction within the surface of the substrate on which the film is to be formed.

10. The area of the substrate is 10 cm ２ The film forming method according to any one of claims 1 to 9, wherein the film forming method is characterized by the above.

Images