Method for producing crystalline oxide semiconductor film and method for producing raw material solution

Abstract

This invention provides a method for manufacturing crystalline oxide semiconductor films that promotes dopant activation, enabling the stable production of crystalline oxide semiconductor films with lower resistance values, while also increasing the film deposition rate. [Solution] A method for producing a crystalline oxide semiconductor film having a corundum structure, comprising supplying a atomized raw material solution together with a carrier gas to a heated substrate, wherein a first aqueous solution containing at least one metal element and at least one halogen, and a second aqueous solution containing at least Sn(II), the dissolved oxygen in the first aqueous solution is measured, an amount of oxidizing agent corresponding to the measured amount of dissolved oxygen is mixed into the second aqueous solution, and at least a portion of the second aqueous solution containing the oxidizing agent is mixed into the first aqueous solution to obtain a raw material solution.

Description

[Technical Field]

[0001] This invention relates to a method for producing a crystalline oxide semiconductor film and a method for producing a raw material solution. [Background technology]

[0002] In recent years, α-type gallium oxide (α-Ga2O3), which has a corundum structure, has attracted attention as a crystalline oxide semiconductor. Examples of using tin (Sn) as a dopant to exhibit conductivity are disclosed, for example, in Patent Documents 1 and 2. These methods involve depositing α-Ga2O3 films using the mist CVD method.

[0003] Patent Document 1 discloses that Sn(II) is oxidized to Sn(IV) by hydrogen peroxide, and that this Sn(IV) contributes to conductivity, and also discloses an example in which 0.5% hydrogen peroxide (H2O2) is mixed with the raw materials. According to this example, the concentration of H2O2 added to the raw materials appears to be a high concentration of about 43-51 mmol / L.

[0004] Patent Document 2 discloses an example in which equimolar amounts of H2O2 are mixed with a 1% aqueous solution of SnCl2. The final H2O2 concentration in the raw materials in Patent Document 2 is 0.2 mmol / L, which is lower than that in Patent Document 1. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Application Laid-Open No. 2013-028480 [Patent Document 2] Japanese Patent Application Publication No. 2023-174816 [Overview of the Initiative] [Problem to be solved by the invention]

[0006] As described above, when using Sn(II) as a dopant source, it is necessary to oxidize it to Sn(IV). On the other hand, for metal sources such as gallium, halides are preferred from the viewpoint of impurities remaining in the film and the film formation rate. However, as also mentioned in Patent Document 2, when a halogen-containing solution is oxidized, the halogen is also oxidized, and elemental halogens are released into the solution, which is a problem.

[0007] In fact, the metal source disclosed in Patent Document 1 is gallium acetylacetonate, but if this is replaced with, for example, a halide such as gallium iodide, the oxidation of iodine proceeds, which leads to problems such as the film not growing.

[0008] On the other hand, while the method described in Patent Document 2 allows for relatively stable film growth and relatively stable resistance values, it was not sufficient.

[0009] The present invention has been made to solve the above problems, and aims to provide a method for manufacturing a crystalline oxide semiconductor film that promotes dopant activation, enabling the stable production of a crystalline oxide semiconductor film with a lower resistance value, and increasing the film deposition rate. [Means for solving the problem]

[0010] The present invention has been made to achieve the above objective, and provides a method for producing a crystalline oxide semiconductor film having a corundum structure by supplying a atomized raw material solution together with a carrier gas to a heated substrate, characterized in that a first aqueous solution containing at least one metal element and at least one halogen and a second aqueous solution containing at least Sn(II) are prepared, the dissolved oxygen in the first aqueous solution is measured, an amount of oxidizing agent corresponding to the measured amount of dissolved oxygen is mixed into the second aqueous solution, and at least a portion of the second aqueous solution mixed with the oxidizing agent is mixed into the first aqueous solution to obtain a raw material solution.

[0011] This allows for the pre-oxidation of excess Sn(II) in the second aqueous solution by mixing an amount of oxidizing agent corresponding to the amount of dissolved oxygen in the first aqueous solution with the second aqueous solution. This pre-oxidizes the excess Sn(II) in the second aqueous solution to Sn(IV), and then, when the second aqueous solution is mixed with the first aqueous solution to form the raw material solution, the dissolved oxygen in the first aqueous solution reacts with the appropriate amount of remaining Sn(II) in the second aqueous solution to convert it all to Sn(IV), thus maintaining a balance so that neither Sn(II) nor dissolved oxygen remains in the raw material solution. As a result, the above raw material solution (a raw material solution containing Sn(IV) but free of Sn(II) and dissolved oxygen) can be supplied to the heated substrate as a mist along with a carrier gas. This promotes dopant activation, enabling the stable production of crystalline oxide semiconductor films with a corundum structure and lower resistance values. Furthermore, by not using excess oxidizing agent, halogen oxidation is suppressed, providing a method for producing crystalline oxide semiconductor films with a fast growth rate and high film deposition rate.

[0012] Preferably, the at least one halogen is bromine or iodine.

[0013] This allows for faster growth rates and lower resistance values ​​with less film-to-film variation.

[0014] The oxidizing agent is preferably hydrogen peroxide.

[0015] This ensures a faster growth rate, a lower resistance value with less variation between films, and a reduced amount of impurities in the film.

[0016] Preferably, the at least one metal element is gallium.

[0017] This allows the growth rate to be increased when manufacturing crystalline gallium oxide semiconductor films, which have been attracting attention in recent years, and makes it possible to obtain lower resistance values ​​with less variation between films.

[0018] Furthermore, the substrate has an area of ​​100 mm². 2 It is preferable to use the above, or one with a diameter of 2 inches (50 mm) or more.

[0019] This allows for faster growth rates when manufacturing crystalline oxide semiconductor films on large-area substrates, resulting in lower resistance values ​​with less variation between films. [Effects of the Invention]

[0020] As described above, the present invention provides a method for producing a crystalline oxide semiconductor film. By mixing an amount of oxidizing agent corresponding to the amount of dissolved oxygen in the first aqueous solution with the second aqueous solution, excess Sn(II) in the second aqueous solution can be oxidized to Sn(IV) beforehand. Subsequently, when the second aqueous solution is mixed with the first aqueous solution to form the raw material solution, the dissolved oxygen in the first aqueous solution reacts with just the right amount of remaining Sn(II) in the second aqueous solution to convert it all to Sn(IV), thus maintaining a balance so that neither Sn(II) nor dissolved oxygen remains in the raw material solution. As a result, the above raw material solution (a raw material solution containing Sn(IV) and no Sn(II) or dissolved oxygen) can be supplied to the heated substrate as a mist along with a carrier gas. This promotes dopant activation, enabling the stable production of a crystalline oxide semiconductor film with a corundum structure having a lower resistance value. Furthermore, by not using excess oxidizing agent, halogen oxidation is suppressed, providing a method for producing a crystalline oxide semiconductor film with a fast growth rate and high film deposition rate. [Brief explanation of the drawings]

[0021] [Figure 1] This is a schematic diagram showing an example of a semiconductor device having a crystalline oxide semiconductor film according to the present invention. [Figure 2] This is a schematic diagram showing an example of a film deposition apparatus (mist CVD apparatus) suitably used for manufacturing crystalline oxide semiconductor films according to the present invention. [Figure 3] This diagram illustrates an example of a misting section used in a film deposition apparatus (mist CVD apparatus). DETAILED DESCRIPTION OF THE INVENTION

[0022] The present invention will be described in detail below, but the present invention is not limited thereto.

[0023] As described above, there was a need for a method for manufacturing crystalline oxide semiconductor films that could promote dopant activation, stably produce crystalline oxide semiconductor films with lower resistance values, and increase the film deposition rate.

[0024] The inventors of this invention have diligently studied the above-mentioned problems and, as a result, have discovered that the amount of dissolved oxygen in the raw material is related to the film formation rate and resistance value, thereby completing the present invention.

[0025] That is, the present invention provides a method for producing a crystalline oxide semiconductor film having a corundum structure by supplying a mist of a raw material solution together with a carrier gas to a heated substrate, the method comprising the steps of: preparing a first aqueous solution containing at least one metal element and at least one halogen; and a second aqueous solution containing at least Sn(II); measuring the dissolved oxygen in the first aqueous solution; mixing an oxidizing agent into the second aqueous solution in an amount corresponding to the measured amount of dissolved oxygen; and mixing at least a portion of the second aqueous solution mixed with the oxidizing agent into the first aqueous solution to obtain a raw material solution.

[0026] (Crystalline oxide semiconductor film) The crystalline oxide semiconductor film according to the present invention has at least a corundum structure. Ideally, a unit cell of the corundum structure contains 12 metal atoms and 18 oxygen atoms. Substances having a corundum structure include, but are not limited to, Al2O3, Ga2O3, Cr2O3, Fe2O3, In2O3, Rh2O3, V2O3, Ti2O3, and Ir2O3. A solid solution of two or more of these may also be used. While polycrystalline films are acceptable, single crystals or uniaxially oriented films are preferred. A single crystal or uniaxially oriented film can be determined by the appearance of specific peaks in X-ray diffraction.

[0027] Furthermore, the crystalline oxide semiconductor film is not particularly limited, but it is preferable that it has gallium as its main component. "Having gallium as its main component" means that 50 to 100% (atomic percent) of the metal component is gallium. Other metal components may include, for example, one or more metals selected from iron, indium, aluminum, vanadium, titanium, chromium, rhodium, iridium, nickel, and cobalt.

[0028] Furthermore, the crystalline oxide semiconductor film contains at least tin as a dopant element for adjusting electrical resistivity. While not particularly limited, other dopants such as germanium, silicon, titanium, zirconium, vanadium, or niobium may also be included. The dopant concentration is not particularly limited, but for example, it is about 1 × 10⁻⁶. 16 / cm 3 ~1×10 22 / cm 3 It may be approximately 1 × 10 17 / cm 3 Even at the following low concentrations, approximately 1 × 10 20 / cm 3 Even higher concentrations are acceptable.

[0029] Furthermore, the thickness of the crystalline oxide semiconductor film is not particularly limited, but is preferably 1 μm or more. The upper limit of the film thickness is not particularly limited, but may be, for example, 100 μm or less, preferably 50 μm or less, and more preferably 20 μm or less.

[0030] Furthermore, the size of the crystalline oxide semiconductor film is not particularly limited, but the surface area of ​​the crystalline oxide semiconductor film is 100 mm². 2 If the diameter is 2 inches (50 mm) or larger, a large-area film with good crystallinity can be obtained, which is preferable.

[0031] (Laminated structure) In the manufacturing method according to the present invention, the crystalline oxide semiconductor film is manufactured on a substrate (base substrate), and therefore the substrate and the crystalline oxide semiconductor film can be collectively called a stacked structure.

[0032] Although not particularly limited, another layer may be interposed between the substrate and the crystalline oxide semiconductor film. The other layer, which has a different composition from the substrate and the outermost crystalline oxide semiconductor film, is also called a buffer layer. The buffer layer may be a crystalline oxide semiconductor film, a semiconductor film, an insulating film, a metal film, or the like. The material for the buffer layer is not particularly limited, but examples thereof include Al2O3, Ga2O3, Cr2O3, Fe2O3, In2O3, Rh2O3, V2O3, Ti2O3, and Ir2O3. A solid solution of two or more of these may also be used. Although not particularly limited, the thickness of the buffer layer is preferably 0.1 μm to 2 μm.

[0033] (Substrate (base substrate)) The base substrate used in the above-described stacked structure is not particularly limited as long as it can serve as a support for the crystalline oxide semiconductor film. The substrate material is not particularly limited, and known substrates can be used, and may be organic or inorganic compounds. Examples of suitable substrates include polysulfone, polyethersulfone, polyphenylene sulfide, polyetheretherketone, polyimide, polyetherimide, fluororesin, metals such as iron, aluminum, stainless steel, and gold, quartz, glass, calcium carbonate, gallium oxide, and ZnO. Other examples include single-crystal substrates such as silicon, sapphire, lithium tantalate, lithium niobate, SiC, GaN, iron oxide, and chromium oxide.

[0034] The base substrate used for the above-described stacked structure is not particularly limited, but is preferably a single-crystal substrate. This allows a crystalline oxide semiconductor film of better quality to be obtained. In particular, a sapphire substrate, a lithium tantalate substrate, or a lithium niobate substrate is relatively inexpensive and industrially advantageous.

[0035] The thickness of the base substrate is not particularly limited, but is preferably 10 to 2000 μm, more preferably 50 to 800 μm. Within this range, handling is easy and thermal resistance during film formation can be suppressed, making it easier to obtain a high-quality film.

[0036] Furthermore, although not particularly limited, the substrate may have an area of ​​100 mm 2 It is preferable to use one with a diameter of 2 inches (50 mm) or more.

[0037] (Configuration example of semiconductor device) 1 shows an example of a semiconductor device having a crystalline oxide semiconductor film according to the present invention. In the semiconductor device 100, a crystalline oxide semiconductor film 103 is formed on a substrate (base substrate) 101. The crystalline oxide semiconductor film 103 is configured by laminating an insulating thin film 103a and a conductive thin film 103b in this order from the base substrate 101 side. The base substrate 101 and the crystalline oxide semiconductor film 103 can be collectively referred to as a stacked structure 110.

[0038] A gate insulating film 105 is formed on the conductive thin film 103b, and a gate electrode 107 is formed on the gate insulating film 105. Source-drain electrodes 109 are formed on the conductive thin film 103b so as to sandwich the gate electrode 107. With this configuration, it becomes possible to control the depletion layer formed in the conductive thin film 103b by applying a gate voltage to the gate electrode 107, thereby realizing transistor operation (FET device).

[0039] 1 can be used as a device, but is not limited to, transistors such as MIS, HEMT, and IGBT, TFTs, Schottky barrier diodes using semiconductor-metal junctions, PN or PIN diodes combined with other P layers, light-emitting and receiving elements, etc. The crystalline oxide semiconductor film according to the present invention is useful for improving the characteristics of these devices.

[0040] The crystalline oxide semiconductor film described above can be formed by, but is not limited to, a mist CVD method. Therefore, a method for manufacturing a crystalline oxide semiconductor film using the mist CVD method will be described below. Here, the term "mist" as used in the present invention refers to a general term for liquid particles dispersed in a gas, and includes what are called fog, droplets, etc.

[0041] (Film forming equipment) An example of a film formation apparatus (mist CVD apparatus) used in the mist CVD method suitable for producing a crystalline oxide semiconductor film according to the present invention is shown in Fig. 2. Film formation apparatus 201 can include mist-forming unit 220 that generates mist by turning raw material solution 204a into mist, carrier gas supply unit 230 that supplies a carrier gas that transports the mist, supply pipe 209 that connects mist-forming unit 220 and film formation chamber 207 and through which the mist is transported by the carrier gas, and film formation chamber 207 that heat-treats the mist supplied from supply pipe 209 together with the carrier gas to form a film on substrate (base substrate) 210.

[0042] (Mist generating section) In the mist generating section 220, the raw solution 204a is turned into mist to generate mist. The mist generating means is not particularly limited as long as it can turn the raw solution 204a 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.

[0043] An example of such a mist-generating unit 220 is shown in Figure 3. The mist-generating unit 220 may include a mist generation source 204 that contains raw solution 204a, a medium capable of transmitting ultrasonic vibrations, such as a container 205 that contains water 205a, and an ultrasonic vibrator 206 attached to the bottom of the container 205. In detail, the mist generation source 204, which is a container that contains raw solution 204a, can be housed in the container 205 that contains water 205a using a support (not shown).

[0044] The ultrasonic vibrator 206 attached to the bottom of the container 205 may be connected to an oscillator 216. When the oscillator 216 is activated, the ultrasonic vibrator 206 vibrates, and ultrasonic waves are propagated into the mist generation source 204 via the water 205a, thereby turning the raw material solution 204a into mist.

[0045] (Raw material solution) The raw material solution 204a contains a metal element and a halogen, and the solvent can be water, although it is not particularly limited. The method for preparing the raw material solution will be described later.

[0046] Although not particularly limited, it is preferable that at least one metal element is gallium. Furthermore, although not particularly limited, it is preferable that the metal element is ionized. Furthermore, in addition to gallium, the metal element may also include, but is not particularly limited to, one or more metals selected from the group consisting of iron, indium, aluminum, vanadium, titanium, chromium, rhodium, nickel, and cobalt. Although not particularly limited, the metal concentration in the raw material solution 204a can be, for example, 0.005 to 1 mol / L.

[0047] Although not particularly limited, the halogen may be any one of fluorine, chlorine, bromine, and iodine, or two or more selected from these. Although not particularly limited, it is preferable that at least one halogen is bromine or iodine. Furthermore, although not particularly limited, it is preferable that the halogen is ionized.

[0048] The raw material solution also contains Sn(IV) as a dopant source, which is obtained by oxidizing Sn(II). The dopant source may also contain, but is not limited to, other elements than Sn, such as germanium, silicon, titanium, zirconium, vanadium, or niobium. The concentration of the dopant source is not particularly limited, but may be about 0.01 to 1 mmol / L.

[0049] (Carrier gas supply unit) 2, the carrier gas supply unit 230 has a carrier gas source 202a that supplies a carrier gas. In this case, although not particularly limited, a flow rate control valve 203a for adjusting the flow rate of the carrier gas sent from the carrier gas source 202a may be provided. Furthermore, if necessary, a dilution carrier gas source 202b for supplying a dilution carrier gas and a flow rate control valve 203b for adjusting the flow rate of the dilution carrier gas sent from the dilution carrier gas source 202b may also be provided.

[0050] The type of carrier gas is not particularly limited and can be selected appropriately depending on the film to be produced. 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 or more. 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 used as the second carrier gas, or air may be used.

[0051] The flow rate of the carrier gas is not particularly limited. For example, when forming a film on a substrate with a diameter of 2 inches (approximately 50 mm), the flow rate of the carrier gas is preferably 0.05 to 50 L / min, and more preferably 5 to 20 L / min.

[0052] (supply pipe) 2 may have, but is not limited to, a supply pipe 209 connecting the mist-generating unit 220 and the film-forming chamber 207. In this case, the mist obtained by generating mist from the raw material solution may be transported by a carrier gas from the mist generating source 204 of the mist-generating unit 220 via the supply pipe 209 and supplied into the film-forming chamber 207. The supply pipe 209 may be, but is not limited to, a quartz tube, a glass tube, a resin tube, or the like.

[0053] (Film forming chamber) 2, a substrate (base substrate) 210 is placed inside the film formation chamber 207, and since the substrate 210 needs to be heated, it may be provided with, for example, but not limited to, a heater 208. The heater 208 may be provided outside the film formation chamber 207 as shown in FIG. 2, or may be provided inside the film formation chamber 207. The mist supplied from the supply pipe 209 passes through piping inside the film formation chamber 207 and is sprayed from a nozzle toward the substrate 210 together with the carrier gas.

[0054] Furthermore, the film formation chamber 207 may be provided with an exhaust gas outlet 212, although this is not particularly limited, at a position that does not affect the supply of mist to the substrate 210. Furthermore, the substrate 210 may be placed face-down, for example, on the top surface of the film formation chamber 207, or may be placed face-up, for example, on the bottom surface of the film formation chamber 207.

[0055] (Method for preparing raw material solution) In a method for producing a crystalline oxide semiconductor film according to the present invention, a first aqueous solution containing at least one metal element and at least one halogen, and a second aqueous solution containing at least Sn(II) are prepared, the dissolved oxygen in the first aqueous solution is measured, an oxidizing agent in an amount corresponding to the measured amount of dissolved oxygen is mixed into the second aqueous solution, and at least a portion of the second aqueous solution mixed with the oxidizing agent is mixed into the first aqueous solution to prepare a raw material solution.

[0056] Although not particularly limited, at least one metal element is preferably gallium, and although not particularly limited, one or more metals selected from the group consisting of iron, indium, aluminum, vanadium, titanium, chromium, rhodium, iridium, nickel, and cobalt may also be included.

[0057] Furthermore, although not particularly limited, a metal in the form of a complex or salt dissolved or dispersed in water can be suitably used. Examples of the complex form include, but are not particularly limited to, an acetylacetonate complex, a carbonyl complex, an ammine complex, and a hydride complex. Examples of the salt form include, but are not particularly limited to, metal chloride salts, metal bromide salts, and metal iodide salts.

[0058] Although not particularly limited, the above metals can also be dissolved in hydrobromic acid, hydrochloric acid, hydroiodic acid, etc. to form aqueous salt solutions. The solute metal concentration is not particularly limited, but is preferably 0.005 to 1 mol / L. The temperature during mixing and dissolution is not particularly limited, but is preferably 20°C or higher.

[0059] The first aqueous solution also contains at least one halogen. While not particularly limited, the halogen may be selected from fluorine, chlorine, bromine, and iodine, or two or more of them may be used. Although not particularly limited, it is more preferable that the at least one halogen is bromine or iodine. Furthermore, although not particularly limited, it is preferable that these halogens are dissolved in water as anions. For example, if the above-mentioned metal chloride salts, metal bromide salts, metal iodide salts, etc. are used, or if hydrobromic acid, hydrochloric acid, hydroiodic acid, etc. are used, the halogens can exist as anions.

[0060] In the present invention, it is necessary to measure the amount of dissolved oxygen in the first aqueous solution. The amount of dissolved oxygen is not particularly limited, but can be measured by known methods such as chemical analysis ("titration method"), electrochemical analysis ("diaphragm electrode method"), and photochemical analysis ("fluorescence method"). The solution temperature during measurement is not particularly limited, but is preferably 15 to 30°C. In addition, because the reaction between dissolved oxygen and halogen is slow, the dissolved oxygen in the solvent water used to prepare the solution can also be considered to be the dissolved oxygen in the first aqueous solution. The amount of dissolved oxygen obtained by such a method is referred to as DO [mg / L].

[0061] In the present invention, the second aqueous solution must contain at least Sn(II). The Sn source is not particularly limited, but examples include SnCl2, SnBr2, SnI2, and hydrates thereof, which can be dissolved by mixing with an acid. The Sn concentration is not particularly limited, but can be 0.01 to 10 wt %. This is converted to a molar concentration, C [mol / L]. In this case, since the amount of Sn is excessive compared to the amount of dissolved oxygen, most of the Sn in the second aqueous solution is not oxidized and remains Sn(II).

[0062] Furthermore, in the present invention, a portion of the second aqueous solution is mixed with the first aqueous solution to prepare a raw solution, and the Sn concentration after mixing is s [mmol / L], which is lower than the above C. The range of s is not particularly limited, but is approximately 0.01 to 1, and it is particularly preferable to set s to 0.06 DO or more. Here, the coefficient 0.06 has the dimension of [mol / g]. When mixed in this manner, dissolved oxygen reacts with Sn(II), all of the dissolved oxygen is consumed, and at least a portion of the Sn(II) is converted to Sn(IV). In order to stabilize the doping, it is preferable to convert all Sn to Sn(IV). For this purpose, the excess Sn(II) in the second aqueous solution is oxidized to Sn(IV) in advance, and an appropriate amount of Sn(II) is left unreacted relative to the dissolved oxygen. After mixing, the dissolved oxygen reacts with the appropriate amount of unreacted Sn(II), consuming all the dissolved oxygen and converting all of the Sn(II) to Sn(IV).

[0063] The concentration of this unreacted Sn(II) is obtained at (1-0.06DO / s)·C, and by adding an equivalent amount of oxidizing agent to the second aqueous solution and allowing the oxidation of Sn(II) to proceed, all of the Sn in the final raw solution after mixing can be converted to Sn(IV). The solution obtained through this procedure can be used as the raw solution.

[0064] The oxidizing agent is not particularly limited, but hydrogen peroxide, chloric acid, bromic acid, iodic acid, chlorous acid, bromous acid, iodic acid, hypochlorous acid, hypobromous acid, hypoiodic acid, perchloric acid, perbromic acid, periodic acid, etc. can be used. Although not particularly limited, hydrogen peroxide is preferably used as the oxidizing agent. Hydrogen peroxide is particularly advantageous in that it does not leave impurities in the film.

[0065] (Film forming method) The process of the mist CVD method using a film formation apparatus such as that shown in Figure 2 roughly consists of a mist generation process in which a raw material solution is turned into mist in a mist-forming section to generate mist; a carrier gas supply process in which a carrier gas for transporting the mist is supplied to the mist-forming section; a transport process in which the mist is transported from the mist-forming section to the film formation chamber by the carrier gas via a supply pipe connecting the mist-forming section to the film formation chamber; and a film formation process in which the transported mist is heat-treated to form a film on the base substrate.

[0066] Therefore, in the present invention, prior to the mist generating step, raw material solution 204a prepared in advance based on the above (method of preparing raw material solution) is placed in mist generating source 204 shown in Fig. 2. Next, substrate 210 is placed in film formation chamber 207, and heater 208 is activated. Next, flow rate control valves 203a and 203b are opened to supply carrier gas from carrier gas source 202a and dilution carrier gas source 202b into film formation chamber 207, and after the atmosphere in film formation chamber 207 has been sufficiently replaced with carrier gas, the flow rates of the carrier gas and dilution carrier gas are adjusted, respectively.

[0067] Next, in the mist generating step, the ultrasonic vibrator 206 is vibrated, and the vibration is propagated to the raw material solution 204a through the water 205a, thereby turning the raw material solution 204a into mist and generating the mist.

[0068] Next, in the carrier gas supply step, a carrier gas for transporting the mist is supplied to the mist-forming section 220.

[0069] Next, in the transport step, the mist is transported by a carrier gas from the mist-generating section 220 to the film-forming chamber 207 via the supply pipe 209 connecting the mist-generating section 220 and the film-forming chamber 207.

[0070] Next, in the film formation process, the mist transported to the film formation chamber 207 is heated to cause a thermal reaction, thereby forming a film on a part or the entire surface of the substrate 210 .

[0071] (thermal reaction) The thermal reaction accelerates the reaction of, for example, gallium contained in the mist by heating. Therefore, the temperature of the substrate surface during the reaction is preferably, but not limited to, at least 400°C or higher. Unlike other CVD methods, the mist CVD method requires the raw material to reach the substrate surface in a mist-like liquid state, so the temperature of the substrate surface drops significantly due to the influence of the mist temperature. Therefore, the temperature of the substrate surface during the thermal reaction may differ from the temperature set in the device.

[0072] Therefore, it is preferable to heat the substrate during the thermal reaction and control the temperature by measuring the temperature of the substrate surface. However, if it is difficult to measure during production, it is also possible to simulate the state of the thermal reaction by separately introducing only a carrier gas or a water mist that does not contain solute, and measure the temperature, and use this temperature as a substitute.

[0073] Furthermore, the thermal reaction also depends on the temperature of the environment around the substrate. Therefore, it is desirable that the temperature of the nozzle and the inner wall of the film formation chamber be higher than room temperature. This is because the smaller the difference between the environmental temperature and the temperature of the substrate during the thermal reaction, the more stable the thermal reaction (the less the temperature varies). Therefore, although not particularly limited, the nozzle temperature can be set to, for example, 50 to 250°C.

[0074] The thermal reaction 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 produced. The reaction pressure is also not particularly limited, and may be carried out under any of atmospheric pressure, pressure, or reduced pressure, but atmospheric pressure is preferred because it simplifies the device configuration.

[0075] (Buffer layer formation) As described above, a buffer layer may be provided between the substrate and the crystalline oxide semiconductor film as appropriate. The method for forming the buffer layer is not particularly limited, and the buffer layer can be formed by known methods such as sputtering and vapor deposition. However, when the mist CVD method as described above is used, different layers can be formed simply by changing the raw material solution as appropriate, which is convenient.

[0076] Although not particularly limited, specifically, a solution in which one or more metals selected from aluminum, gallium, chromium, iron, indium, rhodium, vanadium, titanium, and iridium are dissolved or dispersed in water in the form of a complex or salt can be suitably used as the raw material solution.

[0077] The form of the complex is not particularly limited, but examples thereof include an acetylacetonate complex, a carbonyl complex, an ammine complex, a hydride complex, etc. The form of the salt is not particularly limited, but examples thereof include a metal chloride salt, a metal bromide salt, a metal iodide salt, etc.

[0078] Although not particularly limited, a solution of the above metal dissolved in hydrobromic acid, hydrochloric acid, hydroiodic acid, or the like can also be used as the salt aqueous solution. In this case, the solute concentration is also not particularly limited, but is preferably 0.005 to 1 mol / L, and the dissolution temperature is also not particularly limited, but is preferably 20°C or higher. The buffer layer can be formed by maintaining the other conditions similar to those described above. After the buffer layer is formed to a predetermined thickness, a crystalline oxide semiconductor film can be produced by the above-mentioned method.

[0079] In a special case of the buffer layer formation method, the same material as that of the crystalline oxide semiconductor film may be used. In this case, the deposition temperature of the buffer layer may be, but is not limited to, higher than that of the crystalline oxide semiconductor film. For example, the buffer layer may be formed at 450° C. and the crystalline oxide semiconductor film may be formed at 400° C. Alternatively, the buffer layer may be formed at 500° C. and the crystalline oxide semiconductor film at 450° C. This further improves the crystallinity of the crystalline oxide semiconductor film.

[0080] (Heat treatment) 1 may be heat-treated at a temperature of 200 to 600°C, although this is not particularly limited. This removes unreacted species and the like in the film, thereby obtaining a crystalline oxide semiconductor film 103 of higher quality. The heat treatment may be performed in air, an oxygen atmosphere, or an inert gas atmosphere such as nitrogen or argon, although this is not particularly limited. The heat treatment time can be determined appropriately, but is not particularly limited, and may be, for example, 5 to 240 minutes.

[0081] (peeling) Furthermore, in the stacked layer structure 110, although not particularly limited, the crystalline oxide semiconductor film 103 may be peeled off from the base substrate 101. The peeling means is not particularly limited and may be a known means. Examples of the peeling means include a means for peeling off by applying a mechanical impact, a means for peeling off by applying heat and using thermal stress, a means for peeling off by applying vibration such as ultrasonic waves, and a means for peeling off by etching. By such peeling, the crystalline oxide semiconductor film 103 can be obtained as a free-standing film.

[0082] The key points and effects of the configuration of the embodiment described above will be summarized. The method for producing a crystalline oxide semiconductor film according to the present embodiment is a method for producing a crystalline oxide semiconductor film having a corundum structure by supplying a mist of raw material solution 204a together with a carrier gas to a heated substrate 210. The method includes the steps of: preparing a first aqueous solution containing at least one metal element and at least one halogen; and a second aqueous solution containing at least Sn(II); measuring the dissolved oxygen in the first aqueous solution; mixing an oxidizing agent into the second aqueous solution in an amount corresponding to the measured amount of dissolved oxygen; and mixing at least a portion of the second aqueous solution containing the oxidizing agent into the first aqueous solution to produce raw material solution 204a.

[0083] By mixing an oxidizing agent in an amount corresponding to the amount of dissolved oxygen in the first aqueous solution with the second aqueous solution, excess Sn(II) in the second aqueous solution can be oxidized to Sn(IV) in advance. When the second aqueous solution is then mixed with the first aqueous solution to prepare the raw material solution 204a, the dissolved oxygen in the first aqueous solution reacts with an appropriate amount of remaining Sn(II) in the second aqueous solution to convert all of the Sn(IV) to Sn(IV), achieving a balance such that neither Sn(II) nor dissolved oxygen remains in the raw material solution 204a. As a result, the mist-formed raw material solution 204a (a raw material solution containing Sn(IV) but free of Sn(II) and dissolved oxygen) can be supplied to the heated substrate 210 together with a carrier gas. This promotes dopant activation, enabling stable production of a crystalline oxide semiconductor film with a corundum structure and lower resistivity. Furthermore, the use of an excess oxidizing agent suppresses halogen oxidation, providing a method for producing a crystalline oxide semiconductor film with a high growth rate and a high film-forming rate.

[0084] Although not particularly limited, it is preferable that at least one halogen is bromine or iodine.

[0085] This allows for faster growth rates and lower resistance values ​​with less film-to-film variation.

[0086] Although not particularly limited, it is preferable to use hydrogen peroxide as the oxidizing agent.

[0087] This ensures a faster growth rate, a lower resistance value with less variation between films, and a reduced amount of impurities in the film.

[0088] Although not particularly limited, it is preferable that at least one metal element is gallium.

[0089] This allows the growth rate to be increased when manufacturing crystalline gallium oxide semiconductor films, which have been attracting attention in recent years, and makes it possible to obtain lower resistance values ​​with less variation between films.

[0090] Furthermore, the substrate is not particularly limited, but may be a substrate having an area of ​​100 mm 2 It is preferable to use one with a diameter of 2 inches (50 mm) or more.

[0091] This increases the growth rate even when a crystalline oxide semiconductor film is manufactured on a large-area substrate, and makes it possible to obtain a lower resistance value with less variation between films. [Example]

[0092] The present invention will be specifically explained below with reference to examples, but the present invention is not limited to these examples.

[0093] [Example 1] 2, a film formation apparatus 201 used in this example will be described. The film formation apparatus 201 includes a carrier gas source 202a for supplying a carrier gas, a flow rate control valve 203a for adjusting the flow rate of the carrier gas delivered from the carrier gas source 202a, a dilution carrier gas source 202b for supplying a dilution carrier gas, a flow rate control valve 203b for adjusting the flow rate of the dilution carrier gas delivered from the dilution carrier gas source 202b, a mist generation source 204 containing a raw material solution 204a, a container 205 containing water 205a, an ultrasonic vibrator 206 attached to the bottom of the container 205, a film formation chamber 207 equipped with a heater 208, and a quartz supply pipe 209 connecting the mist generation source 204 to the film formation chamber 207.

[0094] (Preparation of raw material solution) First aqueous solution: Ultrapure water was used as the solvent, and gallium bromide was used as the solute. The gallium bromide concentration was 0.1 mol / L. The amount of dissolved oxygen in this solution (dissolved oxygen concentration) was measured using a dissolved oxygen concentration meter MM41DP / MM4DDO manufactured by Toa DKK Corporation. The result was that the dissolved oxygen concentration was 2.3 mg / L.

[0095] Second aqueous solution: The solvent was ultrapure water, and the solute was SnCl2 dihydrate. The solute concentration was 0.2 wt% (8.9 mmol / L), and 0.82 wt% hydrochloric acid was added to dissolve the solute. Furthermore, hydrogen peroxide was added as an oxidant in an amount corresponding to the measured amount of dissolved oxygen, so that the solution reached 2.8 mmol / L, and mixed. This amount of hydrogen peroxide (2.8 mmol / L) was calculated by substituting the measured amount of dissolved oxygen (dissolved oxygen concentration) DO = 2.3 [mg / L], the Sn concentration before mixing (equivalent to molar concentration) C = 8.9 [mmol / L], and the target Sn concentration after mixing (equivalent to molar concentration) s = 0.2 [mmol / L] into the formula (1-0.06 DO / s)·C for the concentration of unreacted Sn(II). (1-0.06DO / s) C=(1-0.06×2.3 / 0.2)×8.9 =2.8 [mmol / L] This was calculated as follows.

[0096] Therefore, the second aqueous solution was weighed and added to the first aqueous solution so that the Sn concentration in the first aqueous solution would be 0.2 mmol / L after mixing with the second aqueous solution, and this was contained in the mist generating source 204 as raw material solution 204a.

[0097] (Gallium oxide film formation) A 4-inch (100 mm) c-plane sapphire substrate was prepared as the substrate 210. This substrate was placed in the film formation chamber 207, and the heater 208 was set to 450° C., the temperature was raised, and the substrate was left for 30 minutes to stabilize the temperature inside the film formation chamber 207, including the nozzle.

[0098] Subsequently, the flow rate control valves 203a and 203b were opened to supply carrier gas from the carrier gas sources 202a and 202b into the film formation chamber 207. After the atmosphere in the film formation chamber 207 was sufficiently replaced with the carrier gas, the flow rate of the carrier gas was adjusted to 2 L / min and the flow rate of the dilution carrier gas was adjusted to 6 L / min. Nitrogen was used as the carrier gas.

[0099] Next, ultrasonic vibrator 206 was vibrated at 2.4 MHz, and the vibrations were propagated to raw material solution 204a through water 205a, thereby misting raw material solution 204a to generate mist. This mist was introduced into film formation chamber 207 via supply pipe 209 by a carrier gas, and the mist was thermally reacted on substrate 210 to form a thin film of gallium oxide, which is a crystalline oxide semiconductor film having a corundum structure, on substrate 210. The film formation time was 30 minutes.

[0100] (evaluation) The formation of α-Ga2O3 was confirmed by X-ray diffraction for the thin film formed on the substrate 210. When the rocking curve of the (006) plane of α-Ga2O3 was measured, the half-width was 9 seconds, indicating extremely good crystallinity. In addition, when measuring the rocking curve, a four-crystal monochromator combining two channel-cut crystals was used to increase the monochromaticity of the X-rays, allowing for more accurate measurements.

[0101] The film thickness was measured using an interference film thickness meter F-50 manufactured by FILMETRICS, and was found to be 1.6 μm. The film formation rate was 3.5 μm / hour.

[0102] The sheet resistance was measured using a Napson four-probe resistivity meter RT-3000 / RG-80 and was found to be 11 kΩ / □. The resistivity was calculated from the film thickness and sheet resistance to be 1.8 Ωcm. The value obtained near the center of the substrate was used as the representative value.

[0103] The film formation and evaluation were repeated eight times under the same conditions. In particular, the dissolved oxygen in the first aqueous solution was measured each time, and the amount of hydrogen peroxide added to the second aqueous solution was adjusted accordingly.

[0104] [Comparative Example 1] The difference from Example 1 is that no oxidizing agent, not just hydrogen peroxide, was added to the raw material solutions including the second aqueous solution. Other than this, film formation and evaluation were repeated eight times under the same conditions as Example 1.

[0105] Comparative Example 2 The difference from Example 1 is that the value was not set according to the amount of dissolved oxygen in the first aqueous solution, but rather hydrogen peroxide was added as an oxidizing agent to the second aqueous solution in an excess amount to achieve the same concentration as Sn, 8.9 mmol / L. Except for this, film formation and evaluation were repeated eight times under the same conditions as Example 1.

[0106] The results are shown in Table 1.

[0107] [Table 1]

[0108] Compared to Example 1, Comparative Example 1, in which no oxidizing agent was added, had a resistance value (average resistivity) that was more than four times higher, and its variation (standard deviation of resistivity) was 33 times larger. This is thought to be because, since there was no oxidizing agent in Comparative Example 1, the oxidation of Sn did not proceed sufficiently with dissolved oxygen alone, and much of the Sn(II) could not be converted to Sn(IV), and the dopant was not activated.

[0109] Furthermore, in Comparative Example 2, in which an excess amount of oxidizing agent was uniformly added, the film formation rate was 15% lower, and the resistance value (average resistivity) and its variation (standard deviation of resistivity) were slightly larger than in Example 1. This is thought to be because the excess oxidizing agent in Comparative Example 2 accelerated the oxidation of halogens together with the dissolved oxygen, making it difficult for the film to grow.

[0110] On the other hand, Example 1, in which an oxidizing agent was mixed in an amount corresponding to the measured amount of dissolved oxygen, had the highest film-forming rate and the lowest resistance value (average resistivity) and its variation (standard deviation of resistivity), resulting in favorable results. This is thought to be because, in Example 1, mixing an oxidizing agent in an amount corresponding to the measured amount of dissolved oxygen promoted dopant activation, enabling stable production of a crystalline oxide semiconductor film with a corundum structure and lower resistance value, and also because no excess oxidizing agent was used, suppressing halogen oxidation and realizing a method for producing a crystalline oxide semiconductor film with a high growth rate and a high film-forming rate.

[0111] The present specification includes the following aspects. [1]: A method for producing a crystalline oxide semiconductor film having a corundum structure by supplying a mist of a raw material solution together with a carrier gas to a heated substrate, the method comprising the steps of: preparing a first aqueous solution containing at least one metal element and at least one halogen; and a second aqueous solution containing at least Sn(II); measuring the dissolved oxygen in the first aqueous solution; mixing an oxidizing agent into the second aqueous solution in an amount corresponding to the measured amount of dissolved oxygen; and mixing at least a portion of the second aqueous solution containing the oxidizing agent into the first aqueous solution to obtain a raw material solution. [2]: The method for producing a crystalline oxide semiconductor film according to [1] above, wherein the at least one halogen is bromine or iodine. [3]: The method for producing a crystalline oxide semiconductor film according to [1] or [2] above, wherein the oxidizing agent is hydrogen peroxide. [4]: The method for producing a crystalline oxide semiconductor film according to any one of [1] to [3] above, wherein the at least one metal element is gallium. [5]: The substrate has an area of ​​100 mm 2 The method for producing a crystalline oxide semiconductor film according to any one of the above [1] to [4], characterized in that the above or a diameter of 2 inches (50 mm) or more is used.

[0112] The present invention is not limited to the above-described embodiments. The above-described embodiments 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 exhibits similar effects is included within the technical scope of the present invention. [Explanation of symbols]

[0113] 100... semiconductor device, 101... substrate (base substrate), 103...crystalline oxide semiconductor film, 103a...insulating thin film, 103b...conductive thin film, 105...gate insulating film, 107...gate electrode, 109...source / drain electrode, 110...laminated structure, 201...film forming apparatus, 202a...carrier gas source; 202b...dilution carrier gas source; 203a, 203b...flow control valve, 204...mist generation source, 204a...raw material solution, 205...container, 205a...water, 206... ultrasonic vibrator, 207... film formation chamber, 208... heater, 209...supply pipe, 210...substrate (base substrate), 216...oscillator, 212...exhaust port, 220...mist generating section, 230...carrier gas supply section.

Claims

1. A manufacturing method for manufacturing a crystalline oxide semiconductor film having a corundum structure by supplying a mist of a raw material solution together with a carrier gas onto a heated substrate, the method comprising: A first aqueous solution containing at least one metal element and at least one halogen and a second aqueous solution containing at least Sn(II) are prepared; measuring the dissolved oxygen in the first aqueous solution; mixing an oxidizing agent in an amount corresponding to the measured amount of dissolved oxygen into the second aqueous solution; A method for producing a crystalline oxide semiconductor film, comprising mixing at least a part of the second aqueous solution containing the oxidizing agent with the first aqueous solution to obtain a raw material solution.

2. 2. The method for producing a crystalline oxide semiconductor film according to claim 1, wherein the at least one halogen is bromine or iodine.

3. 2. The method for producing a crystalline oxide semiconductor film according to claim 1, wherein the oxidizing agent is hydrogen peroxide.

4. 2. The method for producing a crystalline oxide semiconductor film according to claim 1, wherein the at least one metal element is gallium.

5. The substrate has an area of ​​100 mm ２ 5. The method for producing a crystalline oxide semiconductor film according to claim 1, wherein a diameter of 2 inches (50 mm) or more is used.

6. A method for producing a raw material solution for producing a crystalline oxide semiconductor film having a corundum structure by supplying a mist of the raw material solution together with a carrier gas to a heated substrate, the method comprising: A first aqueous solution containing at least one metal element and at least one halogen and a second aqueous solution containing at least Sn(II) are prepared; measuring the dissolved oxygen in the first aqueous solution; mixing an oxidizing agent in an amount corresponding to the measured amount of dissolved oxygen into the second aqueous solution; A method for producing a raw material solution, comprising mixing at least a portion of the second aqueous solution containing the oxidizing agent with the first aqueous solution to obtain a raw material solution.

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