Method for manufacturing crystalline oxide semiconductor films

Abstract

The objective is to provide a method for producing crystalline oxide semiconductor films with low electrical resistance by promoting dopant activation and maximizing the activation rate. [Solution] A method for manufacturing a crystalline oxide semiconductor film, comprising the steps of: heating a substrate to 400°C or higher; supplying a mist containing a metal and a dopant to the substrate to form a crystalline oxide semiconductor film having a corundum structure containing the metal and the dopant on the substrate; stopping the heating of the substrate; and cooling the substrate, wherein in the step of cooling the substrate, the temperature of the substrate is reduced to 350°C or lower within 600 seconds after the heating of the substrate is stopped.

Description

[Technical Field]

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

[0002] In recent years, alpha-type gallium oxide (α-Ga2O3), which has a corundum structure, has attracted attention as a crystalline oxide semiconductor. For oxide semiconductor films like α-Ga2O3 to be used as semiconductor devices, low electrical resistivity is desirable. Therefore, it is important to promote dopant activation and maximize the activation rate.

[0003] Patent Document 1 measures the concentration of the dopant Ge and the carrier density in Ga2O3, and finds that they are 2.5 x 10⁻⁶ each. 19 / cm 3 (Figure 12 of Patent Document 1), 9.1x10 18 / cm 3 (Paragraph

[0054] of Patent Document 1) is described as follows. As can be seen from the relationship dopant concentration > carrier density, the entire amount of Ge, which is a dopant, is not activated and becomes a carrier source. [Prior art documents] [Patent Documents]

[0004] [Patent Document 1] Japanese Patent Publication No. 2019-034882 [Patent Document 2] Japanese Patent Publication No. 2023-174816 [Overview of the Initiative] [Problems that the invention aims to solve]

[0005] To increase the activation rate of the dopant, Patent Document 2 discloses an example in which equimolar amounts of hydrogen peroxide are mixed with Sn in an aqueous solution of SnCl2, which serves as the dopant source. This method increases the activation rate and reduces electrical resistance by promoting the oxidation of Sn. However, even this method was not sufficient to maximize the activation of Sn.

[0006] The present invention has been made to solve the above problems and aims to provide a method for producing a crystalline oxide semiconductor film with low electrical resistance by promoting dopant activation and maximizing the activation rate. [Means for solving the problem]

[0007] The present invention has been made to achieve the above objective, and provides a method for manufacturing a crystalline oxide semiconductor film, comprising the steps of: heating a substrate to 400°C or higher; supplying a mist containing a metal and a dopant to the substrate to form a crystalline oxide semiconductor film with a corundum structure containing the metal and the dopant on the substrate; stopping the heating of the substrate; and cooling the substrate, wherein in the step of cooling the substrate, the temperature of the substrate is reduced to 350°C or lower within 600 seconds after the heating of the substrate is stopped.

[0008] This method for manufacturing crystalline oxide semiconductor films promotes dopant activation and maximizes the activation rate, thereby enabling the production of crystalline oxide semiconductor films with low electrical resistance.

[0009] In this process, during the cooling of the substrate, the temperature of the substrate can be reduced to less than 400°C within 300 seconds of stopping the heating of the substrate.

[0010] This can further promote the activation of the dopant.

[0011] In this case, the dopant is preferably tin.

[0012] This makes it easier to obtain the effect of activating the dopant.

[0013] At this time, the metal is preferably gallium.

[0014] This enables the production of a gallium oxide film with low resistance.

[0015] At this time, in at least a part of the time period of the step of cooling the substrate, the mist containing the metal and the dopant may not be supplied to the substrate.

[0016] This enables the production of a semiconductor film with more excellent crystallinity.

[0017] At this time, as the substrate, one having a main surface area of 100 mm 2 or more, or a diameter of 50 mm (2 inches) or more can be used.

[0018] This enables the production of a semiconductor film with low resistance even for a large-area substrate.

Advantages of the Invention

[0019] As described above, according to the method for producing a crystalline oxide semiconductor film of the present invention, by promoting the activation of the dopant and maximizing the activation rate, it is possible to produce a crystalline oxide semiconductor film with low electrical resistance. In addition, since the cooling time after film formation is shortened, the throughput increases, which is effective during mass production.

Brief Description of the Drawings

[0020] [Figure 1] An example of the process flow of the method for producing a crystalline oxide semiconductor film according to the present invention is shown. [Figure 2] It is a schematic configuration diagram showing an example of a semiconductor device using the laminated structure according to the present invention. [Figure 3] A schematic diagram of an example of a film forming apparatus preferably used in the present invention is shown. [Figure 4] A schematic diagram of an example of a misting section of a film-forming apparatus suitably used in the present invention is shown. [Modes for carrying out the invention]

[0021] The present invention will be described in detail below, but the present invention is not limited to these descriptions.

[0022] As mentioned above, there was a need for a method to produce crystalline oxide semiconductor films with low electrical resistance by promoting dopant activation and maximizing the activation rate.

[0023] As a result of diligent study on the above problems, the present inventors have found that a method for manufacturing a crystalline oxide semiconductor film, comprising the steps of: heating a substrate to 400°C or higher; supplying a mist containing a metal and a dopant to the substrate to form a crystalline oxide semiconductor film with a corundum structure containing the metal and the dopant on the substrate; stopping the heating of the substrate; and cooling the substrate, wherein in the step of cooling the substrate, the temperature of the substrate is reduced to 350°C or lower within 600 seconds after stopping the heating of the substrate, thereby promoting dopant activation and maximizing the activation rate, making it possible to manufacture a crystalline oxide semiconductor film with low electrical resistance; and furthermore, because the cooling time after film formation is shortened, throughput is increased, which is effective in mass production, and thus the present invention has been completed.

[0024] Furthermore, the activation rate defined by the following formula is a useful indicator of dopant activation. Activation rate (%) = Carrier density ÷ Dopant concentration in the membrane x 100

[0025] [Crystalline oxide semiconductor film] The crystalline oxide semiconductor film according to the present invention has at least a corundum structure. Ideally, the unit cell of the corundum structure contains 12 metal atoms and 18 oxygen atoms.

[0026] Examples of substances having a corundum structure include Al2O3, Ga2O3, Cr2O3, Fe2O3, In2O3, Rh2O3, V2O3, Ti2O3, Ir2O3, etc. In the present application, two or more solid solutions selected from these may be used.

[0027] Also, it may be polycrystalline, but it is preferably a single crystal or a uniaxially oriented film. Whether it is a single crystal or a uniaxially oriented film can be determined by the appearance of only specific peaks by X-ray diffraction.

[0028] The crystalline oxide semiconductor film according to the present invention preferably contains gallium as a main component. "Containing gallium as a main component" means that 50 to 100% of the metal components are gallium. As metal components other than gallium, for example, one or more metals selected from iron, indium, aluminum, vanadium, titanium, chromium, rhodium, iridium, nickel, and cobalt may be included.

[0029] The crystalline oxide semiconductor film according to the present invention contains a dopant element for adjusting the electrical resistivity. The dopant element is preferably tin. In addition to tin, germanium, silicon, titanium, zirconium, vanadium, niobium, etc. may be included.

[0030] The concentration of the dopant is, for example, about 1×10 16 / cm 3 ~1×10 22 / cm 3 and may be, or may be a low concentration of about 1×10 17 / cm 3 or less, or a high concentration of about 1×10 20 / cm 3 or more.

[0031] The film thickness of the crystalline oxide semiconductor film is not particularly limited, but is preferably 1 μm or more. The upper limit value is not particularly limited. For example, it may be 100 μm or less, preferably 50 μm or less, and more preferably 20 μm or less.

[0032] There are no particular restrictions on the size of the crystalline oxide semiconductor film, 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.

[0033] (Laminated structure) In the method for producing a crystalline oxide semiconductor film according to the present invention, the crystalline oxide semiconductor film may form a laminated structure together with a substrate (hereinafter also simply referred to as "substrate").

[0034] Furthermore, another layer may be interposed between the substrate and the crystalline oxide semiconductor film. This other layer is a layer with a different composition from the substrate and the outermost crystalline oxide semiconductor film, and is also called a buffer layer.

[0035] The buffer layer can be any of the following: a crystalline oxide film, a semiconductor film, an insulating film, a metal film, etc. Suitable materials include, for example, Al2O3, Ga2O3, Cr2O3, Fe2O3, In2O3, Rh2O3, V2O3, Ti2O3, Ir2O3, etc. Two or more solid solutions selected from these may also be used. The thickness of the buffer layer is preferably 0.1 μm to 2 μm.

[0036] (Substrate) The substrate in the laminated structure according to the present invention is not particularly limited as long as it serves as a support for the crystalline oxide semiconductor film described above. The material is not particularly limited, and known substrates can be used, and may be organic compounds or inorganic compounds. Examples 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.

[0037] In addition to these, single-crystal substrates such as silicon, sapphire, lithium tantalate, lithium niobate, SiC, GaN, iron oxide, and chromium oxide are also used, and such single-crystal substrates are desirable in the laminated structure according to the present invention. These allow for the acquisition of higher quality crystalline oxide semiconductor films. In particular, sapphire substrates, lithium tantalate substrates, and lithium niobate substrates are relatively inexpensive and industrially advantageous.

[0038] The thickness of the substrate is not particularly limited, but is preferably 10 to 2000 μm, and 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.

[0039] The substrate area is 100mm². 2 The above is preferable, and more preferably the diameter is 2 inches (50 mm) or more.

[0040] (Example of semiconductor device configuration) Figure 2 shows a schematic configuration diagram of an example of a semiconductor device using a multilayer structure according to the present invention. In the example of the semiconductor device 100 shown in Figure 2, the multilayer structure 110 includes a base substrate 101 and a crystalline oxide semiconductor film 103 formed on the base substrate 101. The crystalline oxide semiconductor film 103 may include an insulating thin film 103a and a conductive thin film 103b that are stacked in order from the base substrate 101 side.

[0041] A gate insulating film 105 is formed on the conductive thin film 103b. A gate electrode 107 is formed on the gate insulating film 105. In addition, source and drain electrodes 109 are formed on the conductive thin film 103b so as to sandwich the gate electrode 107.

[0042] With this configuration, the depletion layer formed on the conductive thin film 103b can be controlled by the gate voltage applied to the gate electrode 107, enabling transistor operation (FET device).

[0043] Semiconductor devices formed using the multilayer structure according to the present invention include transistors such as MIS, HEMT, and IGBT, TFTs, Schottky barrier diodes utilizing semiconductor-metal junctions, PN or PIN diodes combined with other P layers, and light-emitting / receiving elements. The multilayer structure according to the present invention is useful for improving the characteristics of these devices.

[0044] The aforementioned layered structures can be formed by the mist CVD method. The method for producing a crystalline oxide semiconductor film according to the present invention is described below. Here, "mist" as used in this invention refers to a general term for fine liquid particles dispersed in a gas, and includes what are called fog, droplets, etc.

[0045] [Film forming equipment] Figure 3 shows an example of a film-forming apparatus (mist CVD apparatus) suitably used in the method for producing a crystalline oxide semiconductor film according to the present invention. The film-forming apparatus 201 includes at least a misting unit 220 that atomizes a raw material solution 204a to generate mist, a carrier gas supply unit 230 that supplies a carrier gas to transport the mist, a supply pipe 209 that connects the misting unit 220 and the film-forming chamber 207 and through which the mist is transported by the carrier gas, and a film-forming chamber 207 that heat-treats the mist supplied from the supply pipe 209 together with the carrier gas to form a film on a substrate (underlayment substrate) 210.

[0046] (Misting section) In the misting unit 220, the raw material solution 204a is atomized to generate mist. The misting means is not particularly limited as long as it can atomize the raw material solution 204a, and any known misting means may be used, but it is preferable to use a misting means using ultrasonic vibration, because it can atomize more stably.

[0047] An example of the misting unit 220 is shown in Figure 4. The misting unit 220 may include a mist generating source 204 containing a raw material solution 204a, a container 205 containing a medium capable of transmitting ultrasonic vibrations, such as water 205a, and an ultrasonic transducer 206 attached to the bottom of the container 205. More specifically, the mist generating source 204, which consists of a container containing the raw material solution 204a, can be housed in the container 205 containing the water 205a using a support (not shown).

[0048] An ultrasonic transducer 206 may be installed at the bottom of the container 205, and the ultrasonic transducer 206 may be connected to an oscillator 216. When the oscillator 216 is activated, the ultrasonic transducer 206 vibrates, and ultrasonic waves are transmitted through the water 205a into the mist source 204, causing the raw material solution 204a to be atomized.

[0049] (Raw material solution) The raw material solution 204a contains at least a first metal element. The metal element is preferably gallium. This makes it possible to manufacture gallium oxide films with low resistance.

[0050] In addition to gallium, it may also contain one or more metals selected from, for example, iron, indium, aluminum, vanadium, titanium, chromium, rhodium, nickel, and cobalt.

[0051] The metal concentration in the raw material solution 204a is not particularly limited, but can be, for example, 0.005 to 1 mol / L. The metal can preferably be used in the form of a complex or salt, dissolved or dispersed in a solvent such as water. Examples of complexes include acetylacetonate complexes, carbonyl complexes, ammine complexes, and hydride complexes. Examples of salts include metal chloride salts, metal bromide salts, and metal iodide salts.

[0052] The solvent can be atomizable and contain dissolved or dispersed metal elements; for example, water, alcohols, or mixtures thereof. An acid may be included to promote the dissolution of the metal elements. Examples of acids include hydrobromic acid, hydrochloric acid, and hydroiodic acid.

[0053] Furthermore, the raw material solution 204a contains a dopant source. Tetravalent tin is preferred as the dopant source. This makes it easier to obtain the effect of dopant activation.

[0054] In addition to tin, other dopant sources such as germanium, silicon, titanium, zirconium, vanadium, or niobium may also be included.

[0055] The concentration of the dopant source can usually be around 0.01 to 1 mmol / L. Tin can exist in both divalent and tetravalent states, but it can be converted to the tetravalent state by dissolved oxygen in the solvent or an oxidizing agent. Suitable oxidizing agents include hydrogen peroxide, chloric acid, bromic acid, iodic acid, chlorous acid, bromic acid, iodic acid, hypochlorous acid, hypobromic acid, hypoiodic acid, perchloric acid, perbromic acid, and periodic acid. From the viewpoint of not leaving impurities in the film, hydrogen peroxide is preferred.

[0056] (Carrier gas supply department) As shown in Figure 3, the carrier gas supply unit 230 has a carrier gas source 202a for supplying carrier gas. In this case, it may also be equipped with a flow control valve 203a for adjusting the flow rate of carrier gas discharged from the carrier gas source 202a.

[0057] Furthermore, the system may also be equipped with a dilution carrier gas source 202b for supplying dilution carrier gas as needed, and a flow control valve 203b for adjusting the flow rate of dilution carrier gas discharged from the dilution carrier gas source 202b.

[0058] The type of carrier gas is not particularly limited and can be appropriately selected depending on the film to be deposited. Examples include inert gases such as oxygen, ozone, nitrogen, and argon, or reducing gases such as hydrogen gas and foaming gas.

[0059] Furthermore, there may be one type of carrier gas or two or more types. For example, as the second carrier gas, a dilution gas may be used, which is the same gas as the first carrier gas but diluted with another gas (for example, diluted 10 times), or air may be used.

[0060] The carrier gas flow rate is not particularly limited. For example, when depositing a film on a substrate with a diameter of 2 inches (approximately 50 mm), the carrier gas flow rate is preferably 0.05 to 50 L / min, and more preferably 5 to 20 L / min.

[0061] (supply pipe) The film-forming apparatus 201 has a supply pipe 209 connecting the atomizing section 220 and the film-forming chamber 207. In this case, the mist is transported from the mist source 204 of the atomizing section 220 via the supply pipe 209 by a carrier gas and supplied into the film-forming chamber 207. The supply pipe 209 can be, for example, a quartz tube, a glass tube, or a resin tube.

[0062] (film forming room) A substrate 210 is placed inside the film deposition chamber 207. The film deposition chamber 207 may be equipped with a heater 208 for heating the substrate 210. The heater 208 may be located outside the film deposition chamber 207, as shown in Figure 3, or it may be located inside the film deposition chamber 207.

[0063] The mist supplied from the supply pipe 209 passes through the piping in the film-forming chamber 207 and is ejected from the nozzle towards the substrate 210 along with the carrier gas. In addition, an exhaust port 212 for exhaust gas may be provided in the film-forming chamber 207 at a location that does not affect the supply of mist to the substrate 210.

[0064] Alternatively, the substrate 210 may be placed on the upper surface of the film deposition chamber 207 to form a face-down configuration, or the substrate 210 may be placed on the bottom surface of the film deposition chamber 207 to form a face-up configuration.

[0065] [Method for manufacturing crystalline oxide semiconductor films] Next, the method for manufacturing a crystalline oxide semiconductor film according to the present invention will be described with reference to Figures 1 and 3. Figure 1 shows an example of the process flow for manufacturing a crystalline oxide semiconductor film according to the present invention.

[0066] As shown in Figure 1, the method for manufacturing a crystalline oxide semiconductor film according to the present invention includes the steps of: heating a substrate 210 to 400°C or higher (S1); supplying a mist containing a metal and a dopant to the substrate 210 to form a crystalline oxide semiconductor film with a corundum structure containing a metal and a dopant on the substrate 210 (S2); stopping the heating of the substrate 210 (S3); and cooling the substrate 210 (S4).

[0067] In the step of cooling the substrate 210 (S4), the temperature of the substrate 210 is reduced to 350°C or below within 600 seconds after the heating of the substrate 210 is stopped, thereby manufacturing a crystalline oxide semiconductor film.

[0068] This method for manufacturing crystalline oxide semiconductor films promotes dopant activation and maximizes the activation rate, thereby enabling the production of crystalline oxide semiconductor films with low electrical resistance.

[0069] (Step of heating the substrate to over 400°C: S1) The raw material solution 204a containing the first metal element and dopant source described above is placed inside the mist generator 204. The substrate 210 is placed inside the film deposition chamber 207, and the heater 208 is activated to heat the substrate 210 to over 400°C.

[0070] The substrate 210 has a main surface area of ​​100 mm². 2 You may use one of the above, or one with a diameter of 50 mm (2 inches) or more. This makes it possible to manufacture semiconductor films with low resistance even on large-area substrates.

[0071] Next, flow control valves 203a and 203b are opened to supply carrier gas from carrier gas source 202a and dilution carrier gas source 202b into the film formation chamber 207. After the atmosphere in the 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.

[0072] Next, the ultrasonic transducer 206 is vibrated, and the vibrations are transmitted to the raw material solution 204a through the water 205a, thereby atomizing the raw material solution 204a and generating a mist containing the first metal element and the dopant source.

[0073] Next, a carrier gas for transporting the mist is supplied to the atomizing unit 220, and the mist is transported from the atomizing unit 220 to the film-forming chamber 207 via a supply pipe 209 connecting the atomizing unit 220 and the film-forming chamber 207 using the carrier gas.

[0074] (Step S2: Supplying a mist containing metal and dopant to a substrate, and forming a crystalline oxide semiconductor film with a corundum structure containing metal and dopant on the substrate) Next, the mist transported to the film deposition chamber 207 is heated to induce a thermal reaction, thereby depositing a film on part or all of the surface of the substrate 210. The thermal reaction requires that the gallium and other elements contained in the mist be activated by heating. For this reason, the surface temperature of the substrate 210 during the reaction must be at least 400°C.

[0075] Unlike other CVD methods, mist CVD requires the raw materials to reach the substrate surface in a mist-like liquid state. Therefore, the substrate surface temperature drops significantly. Consequently, the substrate surface temperature during the reaction generally differs from the temperature set in the apparatus.

[0076] While it is preferable to measure and control the temperature of the substrate surface during the reaction, if this is difficult, the reaction can be simulated by introducing only a carrier gas or a water mist without solute, and the temperature can be measured as a substitute.

[0077] Furthermore, the thermal reaction also depends on the ambient temperature around the substrate. Therefore, it is desirable that the temperature of the nozzle and the inner wall of the deposition chamber be higher than room temperature, as this stabilizes the thermal reaction. For example, the nozzle temperature can be set to 50-250°C.

[0078] The thermal reaction may be carried out under any of the following conditions: vacuum, non-oxygen atmosphere, reducing gas atmosphere, air atmosphere, or oxygen atmosphere, and should be set appropriately depending on the material to be deposited.

[0079] Furthermore, the reaction pressure may be carried out under atmospheric pressure, pressurized pressure, or reduced pressure, but film formation under atmospheric pressure is preferred because it simplifies the apparatus configuration.

[0080] Through this thermal reaction, a crystalline oxide semiconductor film containing a dopant, having a corundum structure, and containing the first metal is formed on the substrate 210.

[0081] (Step to stop heating the substrate: S3) The reaction time is determined appropriately depending on the desired film thickness, ranging from 5 minutes to 24 hours. Once the predetermined reaction time has elapsed, heating of the substrate is stopped.

[0082] (Step to cool the substrate: S4) Within 600 seconds of stopping the heating of the substrate 210, the temperature of the substrate 210 should be reduced to 350°C or below. The simplest cooling method is to remove the substrate 210 from the heater 208. Even if the substrate 210 remains on the heater 208, it can be cooled by known methods such as promoting heat exchange with the outside air with an air cooling fan, lowering the outside temperature with an air conditioner, supplying liquid nitrogen, or supplying water mist.

[0083] By performing rapid cooling in this manner, a state of high dopant activation can be achieved. Although the detailed mechanism is not fully understood, it is thought that a phase transition of the dopant occurs near the film deposition temperature, and that this phase transition reduces dopant activation, leading to increased film resistance. Rapid cooling is thought to suppress this phase transition, thereby maintaining a high activation rate.

[0084] It is preferable to lower the temperature of the substrate 210 to below 400°C within 300 seconds after stopping the heating of the substrate 210, as this can further promote dopant activation.

[0085] After heating is stopped, it is preferable to stop supplying mist to the substrate 210 to suppress unwanted deposits on the surface, but it is also acceptable to continue supplying it. Alternatively, the supply of raw materials may be stopped and a solute-free mist, such as water mist, may be supplied instead.

[0086] In other words, during at least a portion of the time period of the substrate cooling process (S4), mist containing metal and dopant may not be supplied to the substrate 210. This makes it possible to manufacture semiconductor films with superior crystallinity.

[0087] (Formation of a buffer layer) The present invention's method for manufacturing a crystalline oxide semiconductor film may include a step of providing a buffer layer between the substrate 210 and the crystalline oxide semiconductor film as appropriate.

[0088] The method for forming the buffer layer is not particularly limited, and it can be formed by known methods such as sputtering and vapor deposition. However, when using the mist CVD method described above, it is convenient because it can be formed simply by appropriately changing the raw material solution.

[0089] Specifically, one or more metals selected from aluminum, gallium, chromium, iron, indium, rhodium, vanadium, titanium, and iridium can be suitably used as the raw material aqueous solution by dissolving or dispersing them in water in the form of a complex or salt.

[0090] Examples of complex forms include acetylacetonate complexes, carbonyl complexes, ammine complexes, and hydride complexes. Examples of salt forms include metal chloride salts, metal bromide salts, and metal iodide salts. Furthermore, solutions of the above metals dissolved in hydrobromic acid, hydrochloric acid, hydroiodic acid, etc., can also be used as aqueous solutions of salts. In this case as well, the solute concentration is preferably 0.005 to 1 mol / L, and the dissolution temperature is preferably 20°C or higher.

[0091] For other conditions as well, the buffer layer can be formed by the same manufacturing method as described above. After forming a buffer layer of a predetermined thickness, a crystalline oxide semiconductor film can be formed using the method described above. This makes it possible to manufacture a multilayer structure including a substrate 210, a buffer layer, and a crystalline oxide semiconductor film.

[0092] (Heat treatment) Furthermore, the laminated structure described above according to the present invention may be heat-treated at 200 to 350°C. This removes unreacted species and other impurities from the film, resulting in a higher quality crystalline oxide semiconductor film.

[0093] The heat treatment may be carried out in air, an oxygen atmosphere, or under an inert gas atmosphere such as nitrogen or argon. The heat treatment time can be determined as appropriate, but for example, it can be 5 to 240 minutes.

[0094] (Peeling) In the laminated structure described above according to the present invention, the crystalline oxide semiconductor film may be peeled off from the underlying substrate. The peeling means is not particularly limited and may be a known means. Examples of peeling methods include peeling by applying mechanical impact, peeling by applying heat and utilizing thermal stress, peeling by applying vibration such as ultrasound, and peeling by etching. By such peeling, the crystalline oxide semiconductor film can be obtained as a self-supporting film. [Examples]

[0095] The present invention will be described in detail below with reference to examples, but this is not intended to limit the present invention.

[0096] [Examples] The film-forming apparatus 201 used in this embodiment will be described with reference to Figure 3. The film-forming apparatus 201 includes a carrier gas source 202a for supplying carrier gas, a flow control valve 203a for adjusting the flow rate of carrier gas discharged from the carrier gas source 202a, a dilution carrier gas source 202b for supplying dilution carrier gas, and a flow control valve 203b for adjusting the flow rate of dilution carrier gas discharged from the dilution carrier gas source 202b.

[0097] The apparatus also includes a mist generating source 204 containing the raw material solution 204a, a container 205 containing water 205a, an ultrasonic transducer 206 attached to the bottom of the container 205, a film-forming chamber 207 equipped with a heater 208, and a quartz supply pipe 209 connecting the mist generating source 204 to the film-forming chamber 207.

[0098] (Preparation of raw material solution) Ultrapure water was used as the solvent, and gallium bromide as the solute. The gallium bromide was dissolved at a concentration of 0.1 mol / L. SnCl2 dihydrate was used as the dopant source, and it was added to achieve a Sn concentration of 0.2 mmol / L. Furthermore, hydrogen peroxide at the same concentration as the Sn was added to oxidize the entire amount of Sn to the tetravalent state. This was then placed in the mist generator 204 as the raw material solution 204a.

[0099] (Film formation of gallium oxide film) A 4-inch (100 mm) c-plane sapphire substrate was prepared as substrate 210. This substrate was placed in the film deposition chamber 207, the heater 208 was set to 450°C, the temperature was raised, and it was left for 30 minutes to stabilize the temperature inside the film deposition chamber, including the nozzle.

[0100] Next, flow control valves 203a and 203b were opened to supply carrier gas from carrier gas source 202a and dilution carrier gas source 202b into the film-forming chamber 207. After the atmosphere in the film-forming chamber 207 was sufficiently replaced with 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.

[0101] Next, the ultrasonic transducer 206 was vibrated at 2.4 MHz, and the vibrations were propagated through water 205a to the raw material solution 204a, thereby atomizing the raw material solution 204a and generating a mist. This mist was introduced into the film formation chamber 207 via the supply pipe 209 using a carrier gas, and the mist was subjected to a thermal reaction on the substrate 210 to form a thin film of gallium oxide on the substrate 210.

[0102] After 30 minutes of film deposition, the gas supply was stopped and substrate heating was halted. A cooling fan was then activated to begin cooling the substrate. 600 seconds after the substrate heating was stopped, the substrate temperature was 309°C.

[0103] (evaluation) X-ray diffraction confirmed the formation of α-Ga2O3 in the thin film formed on substrate 210. Measurement of the rocking curve of the (006) plane of α-Ga2O3 revealed excellent crystallinity, with a full width at half maximum of 9 seconds. For the rocking curve measurement, a four-crystal monochromator, combining two channel-cut crystals, was used to enhance the monochromaticity of the X-rays and achieve higher precision.

[0104] Furthermore, the film thickness was measured using a FILMETRICS F-50 interferometer and found to be 1.6 μm. The sheet resistance was measured using a Napson RT-3000 / RG-80 four-probe resistivity meter and found to be 11 kΩ. The resistivity was calculated from the film thickness and sheet resistance to be 1.8 Ωcm.

[0105] [Comparative Example] In the example, cooling was not performed after the substrate heating was stopped. The substrate temperature 600 seconds after the substrate heating was stopped was 376°C. Film deposition and evaluation were performed under the same conditions as in the example.

[0106] As a result, the sheet resistance reached the upper limit of measurement (10 10 The resistance will be greater than Ω, and the resistivity will be 10 6 It is estimated to have a high resistance of Ωcm or more.

[0107] In the comparative example where cooling was not performed after stopping substrate heating, the resistance increased significantly compared to the example where cooling was performed. It is thought that a dopant phase transition occurred near the film deposition temperature, and that this phase transition reduced the activation of the dopant, resulting in a higher resistance film. In contrast, in the example where cooling was performed after stopping substrate heating, the phase transition was suppressed and a high activation rate was maintained, resulting in the acquisition of a crystalline oxide semiconductor film with low resistance.

[0108] As described above, according to the embodiments of the present invention, it was possible to produce a crystalline oxide semiconductor film with low electrical resistance by promoting dopant activation and maximizing the activation rate. Furthermore, the cooling time after film formation was shortened, which increased throughput and was confirmed to be effective in mass production.

[0109] This specification includes the following embodiments: [1]: A method for manufacturing a crystalline oxide semiconductor film, comprising the steps of: heating a substrate to 400°C or higher; supplying a mist containing a metal and a dopant to the substrate to form a crystalline oxide semiconductor film having a corundum structure containing the metal and the dopant on the substrate; stopping the heating of the substrate; and cooling the substrate, wherein in the step of cooling the substrate, the temperature of the substrate is reduced to 350°C or lower within 600 seconds after the heating of the substrate is stopped. [2]: A method for producing a crystalline oxide semiconductor film according to [1], comprising the step of cooling the substrate, wherein the temperature of the substrate is reduced to less than 400°C within 300 seconds after the heating of the substrate is stopped. [3]: A method for producing a crystalline oxide semiconductor film according to [1] or [2], comprising the dopant being tin. [4]: A method for producing a crystalline oxide semiconductor film according to [1], [2], or [3], wherein the metal is gallium. [5]: A method for producing a crystalline oxide semiconductor film according to [1], [2], [3], or [4], comprising not supplying a mist containing the metal and dopant to the substrate for at least a portion of the time period of the step of cooling the substrate. [6]: The substrate has a main surface area of ​​100 mm² 2 A method for producing a crystalline oxide semiconductor film according to [1], [2], [3], [4], or [5] above, including using a film with a diameter of 50 mm (2 inches) or more.

[0110] It should be noted that the present invention is not limited to the embodiments described above. The embodiments described above are illustrative, and any configuration that is substantially identical to the technical idea described in the claims of the present invention and achieves similar effects is included within the technical scope of the present invention. [Explanation of symbols]

[0111] 100... Semiconductor equipment, 101... Substrate, 103... Crystalline oxide semiconductor film 103a...Insulating thin film, 103b...Conductive thin film, 105...Gate insulating film, 107...Gate electrode, 109...Source / drain electrodes, 110...Laminated structure, 201...Film deposition equipment, 202a...Carrier gas source, 202b... Dilution carrier gas source, 203a, 203b... Flow control valves, 204...Mist source, 204a...Raw material solution, 205...Container, 205a...Water 206... Ultrasonic transducer, 207... Film deposition chamber, 208... Heater, 209... Supply pipe, 210... Circuit board (base circuit board), 212... Exhaust vent, 216... Oscillator, 220...Misting unit, 230...Carrier gas supply unit.

Claims

1. A method for manufacturing a crystalline oxide semiconductor film, A process of heating the substrate to over 400°C, A step of supplying a mist containing a metal and a dopant to the substrate, and forming a crystalline oxide semiconductor film with a corundum structure containing the metal and the dopant on the substrate, A step of stopping the heating of the substrate, The process includes a step of cooling the substrate, A method for manufacturing a crystalline oxide semiconductor film, characterized in that, in the step of cooling the substrate, the temperature of the substrate is reduced to 350°C or less within 600 seconds after the heating of the substrate is stopped.

2. The method for producing a crystalline oxide semiconductor film according to claim 1, characterized in that, in the step of cooling the substrate, the temperature of the substrate is reduced to less than 400°C within 300 seconds after the heating of the substrate is stopped.

3. The method for producing a crystalline oxide semiconductor film according to claim 1, characterized in that the dopant is tin.

4. The method for producing a crystalline oxide semiconductor film according to claim 1, characterized in that the metal is gallium.

5. The method for producing a crystalline oxide semiconductor film according to claim 1, characterized in that a mist containing the metal and dopant is not supplied to the substrate during at least a portion of the time period of the step of cooling the substrate.

6. The substrate has a main surface area of ​​100 mm². ２ A method for producing a crystalline oxide semiconductor film according to any one of claims 1 to 5, characterized in that a material with a diameter of 50 mm (2 inches) or more is used.

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