JP7409790B2 - Oxide semiconductor film and semiconductor device - Google Patents

Description

The present invention relates to an oxide semiconductor film containing gallium as a main component, a method for adjusting electrical resistivity of an oxide semiconductor film, and a method for manufacturing an oxide semiconductor film.

Conventionally, high-vacuum film-forming equipment that can realize non-equilibrium conditions has been developed, such as pulsed laser deposition (PLD), molecular beam epitaxy (MBE), and sputtering. It has become possible to manufacture oxide semiconductors, which were impossible to manufacture using methods such as the melt method. In addition, a mist chemical vapor deposition method (hereinafter also referred to as "mist CVD method") has been developed, in which crystals are grown on a substrate using an atomized mist-like raw material. It has become possible to produce gallium oxide (α-Ga ₂ O ₃ ) having a corundum structure. As a semiconductor with a large band gap, α-Ga ₂ O ₃ is expected to be applied to next-generation switching elements that can realize high breakdown voltage, low loss, and high heat resistance.

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

Patent Document 6 discloses that when gallium oxide produced by the mist CVD method is formed to a thickness of about 300 nm, the problem of high resistance of the conductive thin film occurs when a heating process is performed, and that crystalline oxide It is stated that if the thin film is formed to a thickness of 1 μm or more, it is possible to suppress the increase in resistance of the conductive thin film when a heating step is performed.

Japanese Patent Application Publication No. 1-257337 JP2005-307238A Japanese Patent Application Publication No. 2012-46772 Patent No. 5397794 JP2014-63973A Japanese Patent Application Publication No. 2015-199648

In order to utilize an oxide semiconductor film such as α-Ga ₂ O ₃ as a semiconductor device, control of electrical resistance is important. However, when trying to obtain a thick film using the mist CVD method, fine control is difficult due to a balance with throughput, and the electrical resistivity of the obtained film has considerable variation. As a result, this has been a cause of variations in the characteristics of the resulting semiconductor devices.

In addition, in the method disclosed in the example of Patent Document 6, since a large amount of tin is mixed into the raw material solution, tin is incorporated into the crystal lattice, resulting in poor crystallinity of the obtained film. There was also the problem that the

The present invention has been made to solve the above problems, and an object of the present invention is to provide an oxide semiconductor film whose electrical resistivity can be adjusted even after film formation, and a method for manufacturing the oxide semiconductor film. Another object of the present invention is to provide a method for adjusting the electrical resistivity of an oxide semiconductor film, which can adjust the electrical resistivity to a desired value after film formation.

The present invention has been made to achieve the above object, and provides an oxide semiconductor film containing gallium as a main component, containing at least gallium as a dopant element and a metal, and having a film thickness of 1 μm or more, An oxide semiconductor film whose electrical resistivity increases by heat treatment is provided.

According to such an oxide semiconductor film, electrical resistivity can be easily and reliably adjusted.

At this time, the temperature of the heat treatment can be 350° C. or higher.

Thereby, the electrical resistivity of the obtained film can be increased more reliably.

At this time, the dopant element may include tin (Sn).

Thereby, the electrical resistivity of the obtained film can be increased more reliably.

At this time, the area of the oxide semiconductor film can be 100 mm ² or more.

This results in a large-area oxide semiconductor film whose electrical resistance can be easily and reliably adjusted.

At this time, a semiconductor device including the above oxide semiconductor film can be provided.

The present invention further provides a method for adjusting the electrical resistivity of an oxide semiconductor film containing gallium as a main component, the oxide semiconductor film having a thickness of 1 μm or more and containing at least gallium as a dopant element and a metal. Provided is a method for adjusting the electrical resistivity of an oxide semiconductor film in which the electrical resistivity is increased to a desired value by performing heat treatment on the oxide semiconductor film.

According to such a method for adjusting the electrical resistivity of an oxide semiconductor film, the electrical resistivity can be adjusted even after film formation, so even if the film is manufactured with a lower electrical resistivity than the desired one, heat treatment can be performed. This makes it possible to increase the resistance and adjust it within a desired range, thereby improving yield. Further, it is also possible to suppress fluctuations in electrical resistivity due to thermal history during subsequent processes.

At this time, the temperature of the heat treatment can be 350° C. or higher.

If heat treatment is performed in such a temperature range, the electrical resistivity of the oxide semiconductor film can be increased more reliably in a relatively short time.

At this time, the dopant element may include tin (Sn).

Thereby, the electrical resistivity of the oxide semiconductor film can be increased more reliably.

At this time, the oxide semiconductor film can have an area of 100 mm ² or more.

Thereby, the electrical resistivity of a large-area oxide semiconductor film can be easily and reliably adjusted.

The present invention also provides a method for producing an oxide semiconductor film containing gallium as a main component, which comprises producing a first aqueous solution containing at least a dopant element and a second aqueous solution containing at least gallium as a metal. , a third aqueous solution is prepared by mixing the prepared first aqueous solution and the prepared second aqueous solution, and the mist generated by atomizing or dropletizing the third aqueous solution is mixed with a carrier gas. Provided is a method for manufacturing an oxide semiconductor film, in which the mist is transported to a substrate using an oxide semiconductor film, and the oxide semiconductor film is formed by thermally reacting the mist on the substrate.

According to such a method for manufacturing an oxide semiconductor film, it is possible to finely control the amount of dopant in the solution, and the reproducibility of the characteristics of the obtained oxide semiconductor film is increased. Further, an oxide semiconductor film with good film quality can be obtained. Furthermore, when an oxide semiconductor film having a thickness of 1 μm or more is formed, an oxide semiconductor film whose electrical resistivity increases can be obtained by heat treatment.

At this time, an oxide semiconductor film having a thickness of 1 μm or more can be formed by thermal reaction.

Thereby, an oxide semiconductor film with good film quality that can increase the electrical resistivity when subjected to heat treatment can be obtained.

At this time, tin (Sn) can be used as a dopant element.

Thereby, an oxide semiconductor film whose electrical resistivity can be more reliably increased when heat-treated can be obtained.

At this time, a substrate having a film-forming surface area of 100 mm ² or more can be used as the substrate.

Thereby, the electrical resistivity can be easily and reliably adjusted, and a large-area oxide semiconductor film with good film quality can be obtained.

As described above, according to the oxide semiconductor film of the present invention, the electrical resistivity can be easily and reliably adjusted after film formation, and variations in the electrical resistivity can be reduced. Furthermore, according to the method for adjusting the electrical resistivity of an oxide semiconductor film of the present invention, the electrical resistivity can be adjusted even after film formation, so even if the film is manufactured with a lower electrical resistivity than the desired one. By heat treatment, it becomes possible to increase the resistance and adjust it within a desired range, thereby reducing variations, improving yield, and suppressing fluctuations in electrical resistivity due to thermal history in subsequent processes. Further, according to the method for manufacturing an oxide semiconductor film of the present invention, it is possible to manufacture an oxide semiconductor film with a thickness of 1 μm or more whose electrical resistivity increases by heat treatment, and the characteristics of the obtained film can be improved. It is possible to improve reproducibility and obtain an oxide semiconductor film with good film quality.

1 is a schematic configuration diagram showing an example of a film forming apparatus used in a method for manufacturing an oxide semiconductor film according to the present invention. FIG. 2 is a diagram illustrating an example of a misting section in a film forming apparatus.

Hereinafter, the present invention will be explained in detail, but the present invention is not limited thereto.

As described above, in order to reduce variations in electrical resistivity of an oxide semiconductor film, an oxide semiconductor film whose electrical resistivity can be adjusted even after film formation, a method for manufacturing the oxide semiconductor film, and an oxide semiconductor film are provided. There was a need for a method for adjusting electrical resistivity.

As a result of intensive studies on the above-mentioned problems, the present inventors have found that an oxide semiconductor film containing gallium as a main component, containing at least gallium as a dopant element and a metal, having a thickness of 1 μm or more, and being heat treated. The inventors have discovered that the electrical resistivity can be easily and reliably adjusted by using an oxide semiconductor film, which increases the electrical resistivity by increasing the electrical resistivity, and has completed the present invention.

The present inventor also provides a method for adjusting the electrical resistivity of an oxide semiconductor film containing gallium as a main component, the oxide semiconductor having a film thickness of 1 μm or more and containing at least gallium as a dopant element and a metal. Electrical resistivity can be adjusted even after film formation by using an electrical resistivity adjustment method for oxide semiconductor films that increases the electrical resistivity to a desired value by heat-treating the film. Even if the electrical resistivity is lower than the desired one, it is possible to increase the resistance through heat treatment and adjust it within the desired range, improving yield and reducing electrical resistance due to the thermal history received in subsequent processes. The present invention was completed based on the discovery that it is possible to suppress fluctuations in resistivity.

The present inventor further provides a method for manufacturing an oxide semiconductor film containing gallium as a main component, in which a first aqueous solution containing at least a dopant element and a second aqueous solution containing at least gallium as a metal are prepared. The prepared first aqueous solution and the prepared second aqueous solution are mixed to prepare a third aqueous solution, and the mist generated by atomizing or dropletizing the third aqueous solution is transferred to a carrier. The oxide semiconductor film is transported to a substrate using gas, and subjected to heat treatment by a method for producing an oxide semiconductor film in which the mist is thermally reacted on the substrate to form the oxide semiconductor film having a thickness of 1 μm or more. It is possible to manufacture an oxide semiconductor film with a thickness of 1 μm or more that increases the electrical resistivity, it is possible to improve the reproducibility of the properties of the obtained film, and it is also possible to obtain an oxide semiconductor film with good film quality. The present invention was completed based on the discovery that the following is true.

This will be explained below with reference to the drawings.

(Oxide semiconductor film)
The oxide semiconductor film according to the present invention is an oxide semiconductor film containing gallium as a main component, has a thickness of 1 μm or more, and has an electrical resistivity that is increased by heat treatment. Generally, an oxide semiconductor film is composed of metal and oxygen, but in the oxide semiconductor film according to the present invention, gallium may be the main component of the metal. In the present invention, "containing gallium as a main component" means that 50 to 100% of the metal component is gallium. The metal component other than gallium may include, for example, one or more metals selected from iron, indium, aluminum, vanadium, titanium, chromium, rhodium, iridium, nickel, and cobalt.

The oxide semiconductor film contains a dopant element for adjusting electrical resistivity. Examples include n-type dopants such as tin, germanium, silicon, titanium, zirconium, vanadium, or niobium, and p-type dopants such as copper, silver, tin, iridium, and rhodium. The dopant is not particularly limited, but it is particularly preferable to use tin (Sn) because it can more reliably increase the electrical resistivity of the obtained film. The concentration of ^the dopant may be, for example, about 1×10 ¹⁶ /cm ³ to 1×10 ²² /cm ³ , even as low as about 1×10 ¹⁷ /cm ³ or less. The concentration may be as high as cm ³ or higher.

The oxide semiconductor film may be single crystal or polycrystalline. The crystal structure is not particularly limited, and may be a β-gallium structure, a corundum structure, or a mixture of a plurality of crystal structures. Further, it may be amorphous.

In the oxide semiconductor film according to the present invention, the thickness of the oxide semiconductor film is 1 μm or more, but the upper limit 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. Furthermore, the oxide semiconductor film may be a free-standing film without a substrate, or may be a laminate with a substrate. In the case of a stacked body, another layer may be interposed between the substrate and the oxide semiconductor film. Another layer is a layer having a composition different from that of the substrate and the outermost oxide semiconductor film, and may be, for example, an oxide semiconductor film, an insulating film, a metal film, or the like.

(Heat treatment)
The oxide semiconductor film according to the present invention has an increased electrical resistivity when subjected to heat treatment. At this time, the conditions of the heat treatment are not particularly limited. The temperature of the heat treatment is preferably 350°C or higher. In such a temperature range, the electrical resistivity can be increased in a short time of several minutes to several tens of minutes. The upper limit of the heat treatment temperature is not particularly limited, but it is preferably lower than the maximum temperature in the subsequent semiconductor device manufacturing process. For example, the temperature can be 1100°C or less, but the higher the temperature, the longer the total time required for heat treatment, so it is preferably 1000°C or less, and more preferably 700°C or less.

The atmosphere for the heat treatment is not particularly limited either, and the electrical resistivity of the oxide semiconductor film can be increased in any atmosphere. For example, heat treatment in an air (atmosphere) atmosphere is preferable because the heat treatment can be performed extremely easily using a hot plate or the like. Further, it is preferable to use an inert gas atmosphere because there is no fear of change in film quality.

The heat treatment time is also not particularly limited, but the heat treatment time is preferably 1 minute or more, and more preferably 5 minutes or more because the electrical resistivity can be reliably increased. The upper limit is not particularly limited. For example, it can be 60 minutes or less.

For heat treatment to increase the electrical resistivity, a simple heating device such as a hot plate or an oven can be used, but it goes without saying that a heat treatment device that heat-treats a semiconductor substrate (for example, an RTA device, etc.) can also be used. stomach.

The phenomenon in which electrical resistivity increases due to heat treatment can be qualitatively understood as follows. Electrons contributing to electrical conduction are generated when dopant atoms such as tin (Sn) replace lattice positions of gallium atoms. This state is considered to be a relatively unstable state in which the bond between the dopant atom and the oxygen atom does not follow the stoichiometric ratio. When this is heat-treated, the dopant atoms and oxygen atoms bond in accordance with the stoichiometric ratio, and as a result, conduction electrons are bound near the oxygen atoms, which is thought to increase the electrical resistivity.

Note that the electrical resistivity of the oxide semiconductor film is obtained as the product of sheet resistance and film thickness. Sheet resistance can be measured with a four-probe resistivity meter or the like. Further, the film thickness can be measured not only optically using an ellipsometer or an interference-type film thickness meter, but also directly by observing a stylus-type step meter or a cross section of the film using an electron microscope or the like.

(Film forming equipment)
Next, manufacturing of the oxide semiconductor film according to the present invention will be described. First, a film forming apparatus capable of manufacturing an oxide semiconductor film according to the present invention will be described. FIG. 1 shows an example of a film forming apparatus 101 that can be used in the method for manufacturing an oxide semiconductor film according to the present invention. The film forming apparatus 101 includes a misting section 120 that turns a raw material solution into a mist to generate mist, a carrier gas supply section 130 that supplies a carrier gas for transporting the mist, and a mist forming section 130 that heat-processes the mist to form a film on a substrate 110. The mist-forming unit 120 and the film-forming unit 140 are connected to each other, and a transport unit 109 is configured to transport the mist using a carrier gas. Further, the operation of the film forming apparatus 101 may be controlled by including a control unit (not shown) that controls the whole or a part of the film forming apparatus 101.

Note that the term "mist" as used in the present invention refers to a general term for fine particles of liquid dispersed in gas, and includes what are called mist, droplets, and the like.

(Raw material solution)
The raw material solution 104a is a material that can be made into a mist and contains at least gallium as a metal source and a dopant element for adjusting electrical resistivity. Details of the raw material solution 104a will be explained in the method for producing a raw material solution, which will be described later.

(Misting department)
In the misting section 120, the raw material solution 104a is adjusted, and the raw material solution 104a is made into mist to generate mist. The misting means is not particularly limited as long as it can make the raw material solution 104a into a mist, and may be any known misting means, but it is preferable to use a misting means using ultrasonic vibration. This is because mist can be formed more stably.

An example of such a misting section 120 is shown in FIG. For example, it may include a mist generation source 104 containing a raw material solution 104a, a container 105 containing a medium capable of transmitting ultrasonic vibrations, such as water 105a, and an ultrasonic vibrator 106 attached to the bottom of the container 105. good. Specifically, a mist generation source 104 made of a container containing a raw material solution 104a is housed in a container 105 containing water 105a using a support (not shown). An ultrasonic transducer 106 is provided at the bottom of the container 105, and the ultrasonic transducer 106 and an oscillator 116 are connected. When the oscillator 116 is activated, the ultrasonic vibrator 106 vibrates, and the ultrasonic wave propagates into the mist generation source 104 through the water 105a, so that the raw material solution 104a becomes a mist.

(Transportation section)
The transport section 109 connects the misting section 120 and the film forming section 140. The mist is transported by carrier gas from the mist generation source 104 of the mist forming section 120 to the film forming chamber 107 of the film forming section 140 via the transport section 109 . The conveyance section 109 can be, for example, a supply pipe 109a. As the supply pipe 109a, for example, a quartz tube or a resin tube can be used.

(Film forming section)
In the film forming section 140, the mist is heated to cause a thermal reaction, and a film is formed on part or all of the surface of the substrate 110. The film forming unit 140 includes, for example, a film forming chamber 107, a substrate 110 is installed in the film forming chamber 107, and a hot plate 108 for heating the substrate 110. The hot plate 108 may be provided outside the film forming chamber 107 as shown in FIG. 1, or may be provided inside the film forming chamber 107. Furthermore, an exhaust gas exhaust port 112 may be provided in the film forming chamber 107 at a position that does not affect the supply of mist to the substrate 110.

Further, the substrate 110 may be placed on the top surface of the film forming chamber 107, so as to be placed face down, or the substrate 110 may be placed on the bottom surface of the film forming chamber 107, and may be placed face up.

(substrate)
The substrate 110 is not particularly limited as long as it can form a film and support a film. The material of the substrate 110 is not particularly limited either, and a known substrate can be used, and it may be an organic compound or an inorganic compound. For example, polysulfone, polyethersulfone, polyphenylene sulfide, polyetheretherketone, polyimide, polyetherimide, fluororesin, metals such as iron, aluminum, stainless steel, gold, silicon, sapphire, quartz, glass, gallium oxide, etc. These include, but are not limited to. The thickness of the substrate 110 is not particularly limited, but is preferably 10 to 2000 μm, more preferably 50 to 800 μm. Further, the area of the substrate 110 is preferably 100 mm ² or more, and more preferably the diameter is 2 inches (50 mm) or more.

(Carrier gas supply section)
The carrier gas supply unit 130 includes a carrier gas source 102a that supplies carrier gas, and a flow rate adjustment valve 103a for adjusting the flow rate of the carrier gas (hereinafter referred to as "main carrier gas") sent out from the carrier gas source 102a. may be provided. Further, a dilution carrier gas source 102b that supplies a dilution carrier gas as needed, and a flow rate adjustment valve 103b for adjusting the flow rate of the dilution carrier gas sent out from the dilution carrier gas source 102b can also be provided. .

The type of carrier gas is not particularly limited, and can be appropriately selected depending on the film to be formed. Examples include oxygen, ozone, inert gases such as nitrogen and argon, and reducing gases such as hydrogen gas and forming gas. Furthermore, the number of types of carrier gas may be one or two or more types. For example, a diluted gas obtained by diluting the same gas as the first carrier gas with another gas (for example, 10 times diluted) may be further used as the second carrier gas, or air may also be used.

Note that in this specification, the carrier gas flow rate Q refers to the total flow rate of the carrier gas. In the above example, the flow rate Q of the carrier gas is the total amount of the flow rate of the main carrier gas sent out from the carrier gas source 102a and the flow rate of the dilution carrier gas sent out from the dilution carrier gas source 102b.

The flow rate Q of the carrier gas is appropriately determined depending on the size of the film forming chamber and the substrate, but is usually 1 to 20 L/min, preferably 2 to 10 L/min.

Next, a method for manufacturing an oxide semiconductor film according to the present invention will be described.

(Method for preparing raw material solution)
In the method for manufacturing an oxide semiconductor film according to the present invention, a first aqueous solution containing at least a dopant element and a second aqueous solution containing at least gallium are separately produced, and the first aqueous solution produced The method is characterized in that a third aqueous solution is prepared by mixing the aqueous solution of 1 and the prepared second aqueous solution.

The first aqueous solution contains at least a dopant element. Examples include n-type dopants such as tin, germanium, silicon, titanium, zirconium, vanadium, or niobium, and p-type dopants such as copper, silver, tin, iridium, and rhodium. The dopant is not particularly limited, but is preferably tin (Sn). Further, it is preferable that the dopant element is ionized. Therefore, an acid may be mixed into the first aqueous solution to promote dissolution of the dopant element. Examples of the acid include hydrogen halides such as hydrobromic acid, hydrochloric acid, and hydroiodic acid, hypochlorous acid, chlorous acid, hypobromous acid, bromous acid, hypoiodic acid, and iodic acid. Examples include halogen oxoacids, carboxylic acids such as formic acid, nitric acid, and the like. Note that heating or applying ultrasonic waves is also effective for promoting dissolution. The solute concentration is preferably 0.01 to 10%. When the solute is divalent tin (Sn(II)), an oxidation reaction can be performed by mixing hydrogen peroxide, and it can be changed into tetravalent tin (Sn(IV)). Furthermore, by adjusting the amount of hydrogen peroxide, the amounts of Sn(II) and Sn(IV) can be controlled.

The second aqueous solution is not particularly limited as long as it contains at least gallium. That is, in addition to gallium, it may contain one or more metals selected from, for example, iron, indium, aluminum, vanadium, titanium, chromium, rhodium, iridium, nickel, and cobalt. Metals dissolved or dispersed in water in the form of complexes or salts can be suitably used. Examples of the form of the complex include an acetylacetonate complex, a carbonyl complex, an ammine complex, and a hydride complex. Examples of the salt form include metal chlorides, metal bromides, metal iodides, and the like. Further, the above metals dissolved in hydrobromic acid, hydrochloric acid, hydroiodic acid, etc. can also be used as an aqueous salt solution. The solute concentration is preferably 0.01 to 1 mol/L.

Then, a separately prepared first aqueous solution is mixed with the second aqueous solution so that the dopant element has a desired concentration to obtain a third aqueous solution. The third aqueous solution obtained in this way is the raw material solution 104a. Since the amount of dopant used is extremely small compared to the amount of gallium, if the raw material solution is prepared in this way, precise concentration adjustment becomes easy and reliable. That is, an oxide semiconductor film whose electrical resistivity increases by heat treatment can be manufactured, and furthermore, the accuracy of the electrical resistivity of the obtained film, the reproducibility of the properties of the obtained film, and the film quality are improved. Furthermore, when an oxidizing agent such as hydrogen peroxide is mixed into a solution, reducing substances such as hydrogen iodide and hydrogen bromide are oxidized, causing a problem that solutes are no longer dispersed. In the method for manufacturing a semiconductor film, as described above, hydrogen peroxide can be mixed and reacted in the first aqueous solution stage, and this problem does not occur. Therefore, the stability of the raw material solution is improved, and it is also possible to suppress problems in supplying raw materials during film formation, stabilize the quality of the obtained film, and improve productivity and yield.

(Film forming method)
First, the raw material solution 104a prepared as described above is accommodated in the mist generation source 104 of the mist forming section 120, and the substrate 110 is placed on the hot plate 108 directly or through the wall of the film forming chamber 107, Activate hot plate 108.

Next, the flow rate control valves 103a and 103b are opened to supply carrier gas from the carrier gas sources 102a and 102b into the film forming chamber 107, and the atmosphere in the film forming chamber 107 is sufficiently replaced with the carrier gas, and the main carrier gas and the flow rate of the carrier gas for dilution are respectively adjusted to control the carrier gas flow rate Q.

In the process of generating mist, the ultrasonic vibrator 106 is vibrated and the vibration is propagated to the raw material solution 104a through the water 105a, thereby turning the raw material solution 104a into a mist to generate mist. Next, in the step of transporting the mist with the carrier gas, the mist is transported by the carrier gas from the mist forming section 120 to the film forming section 140 via the transport section 109 and introduced into the film forming chamber 107 . In the process of forming a film, the mist introduced into the film forming chamber 107 is heat-treated by the heat of the hot plate 108 in the film forming chamber 107 to cause a thermal reaction, and a film is formed on the substrate 110 .

An oxide semiconductor film with a thickness of 1 μm or more can be formed by thermal reaction. In this way, it is possible to obtain an oxide semiconductor film with good film quality and whose electrical resistivity can be increased when heat-treated. In the thermal reaction, the mist may react by heating, and the reaction conditions are not particularly limited. It can be set appropriately depending on the raw material and the film to be formed. For example, the heating temperature can be in the range of 100 to 600°C, preferably in the range of 200 to 600°C, and more preferably in the range of 300 to 550°C.

The thermal reaction may be performed in any of the following atmospheres: vacuum, non-oxygen atmosphere, reducing gas atmosphere, air atmosphere, and oxygen atmosphere, and may be appropriately set depending on the film to be formed. The reaction pressure may be atmospheric pressure, increased pressure, or reduced pressure; however, film formation under atmospheric pressure is preferable because the apparatus configuration can be simplified.

(Peeling)
When the formed oxide semiconductor film is used as a free-standing film, the substrate 110 used as a base can be separated from the oxide semiconductor film. The peeling means (method) is not particularly limited and may be any known means. The peeling means (methods) include, for example, peeling by applying mechanical shock, peeling by applying heat and using thermal stress, peeling by applying vibrations such as ultrasonic waves, and peeling by etching. methods, laser lift-off, etc. By the peeling, the oxide semiconductor film can be obtained as a free-standing film.

(How to adjust electrical resistivity)
In the method for adjusting the electrical resistivity of an oxide semiconductor film according to the present invention, the produced oxide semiconductor film having a thickness of 1 μm or more is subjected to heat treatment to increase the electrical resistivity to a desired value. Thereby, for example, even if a film with lower electrical resistivity than the desired one is obtained, the electrical resistivity can be adjusted by heat treatment, and an oxide semiconductor film having the desired electrical resistivity can be obtained. Furthermore, if the oxide semiconductor film is formed so that the electrical resistivity is lower than the desired value, and the electrical resistivity is brought within the desired range by heat treatment, subsequent processes such as semiconductor device manufacturing etc. It is also possible to suppress fluctuations in electrical resistivity due to thermal history. Note that the heat treatment for increasing the electrical resistivity is as already explained.

(semiconductor device)
The oxide semiconductor film according to the present invention can be used for a semiconductor device by appropriately designing the structure. For example, Schottky barrier diode (SBD), metal semiconductor field effect transistor (MESFET), high electron mobility transistor (HEMT), metal oxide semiconductor field effect transistor (MOSFET), static induction transistor (SIT), junction field effect Each semiconductor layer can be configured as a transistor (JFET), an insulated gate bipolar transistor (IGBT), a light emitting diode (LED), or the like.

(electrode)
A general method can be used to form the electrodes necessary for configuring the semiconductor device. That is, in addition to vapor deposition, sputtering, CVD, plating, and the like, any method such as a printing method for bonding together with resin or the like may be used. The electrode materials include Al, Ag, Ti, Pd, Au, Cu, Cr, Fe, W, Ta, Nb, Mn, Mo, Hf, Co, Zr, Sn, Pt, V, Ni, Ir, Zn, In. In addition to metals such as , Nd, metal oxide conductive films such as tin oxide, zinc oxide, indium oxide, indium tin oxide (ITO), and indium zinc oxide (IZO), organic conductive compounds such as polyaniline, polythiophene, or polypyrrole, Either one may be used, or an alloy or a mixture of two or more of these may be used. The thickness of the electrode is preferably 1 to 1000 nm, more preferably 10 to 500 nm.

EXAMPLES The present invention will be described in detail below with reference to Examples, but the present invention is not limited thereto.

(Comparative example 1)
A film of gallium oxide (α-Ga ₂ O ₃ ) having a corundum structure was formed based on the film formation method described above.

Specifically, first, a 1% tin chloride aqueous solution was prepared as the first aqueous solution. Since tin chloride is poorly soluble in water, 2% of 35% hydrochloric acid was mixed with it to prepare a first aqueous solution. As the second aqueous solution, an aqueous solution containing 0.1 mol/L of gallium bromide was prepared, and a 48% hydrobromic acid solution was further added to the solution at a volume ratio of 10%. 2.2 mL of the first aqueous solution was mixed with 0.5 L of the second aqueous solution, and this was used as a raw material solution 104a.

The raw material solution 104a obtained as described above was contained in the mist generation source 104. Next, a 4-inch (diameter 100 mm) c-plane sapphire substrate as the substrate 110 is installed adjacent to the hot plate 108 in the film forming chamber 107, and the hot plate 108 is activated to raise the temperature to 500°C. did.

Subsequently, the flow control valves 103a and 103b are opened to supply nitrogen gas as a carrier gas into the film forming chamber 107 from the carrier gas sources 102a and 102b, and the atmosphere in the film forming chamber 107 is sufficiently replaced with the carrier gas. The flow rate of the main carrier gas was adjusted to 2 L/min, and the flow rate of the diluting carrier gas was adjusted to 5 L/min. That is, the carrier gas flow rate Q was set to 7 L/min.

Next, the ultrasonic vibrator 106 was vibrated at 2.4 MHz, and the vibration was propagated to the raw material solution 104a through the water 105a, thereby turning the raw material solution 104a into a mist. This mist was introduced into the film forming chamber 107 via the supply pipe 109a using a carrier gas. Then, the mist was thermally reacted in the film forming chamber 107 at 500° C. under atmospheric pressure to form a thin film of gallium oxide (α-Ga ₂ O ₃ ) having a corundum structure on the substrate 110 . The film forming time was 15 minutes.

The thickness of the obtained α-Ga ₂ O ₃ thin film was measured using an interferometric film thickness meter F-50 manufactured by FILMETRICS, and the film thickness was 0.8 μm. Further, when the sheet resistance was measured using a four-probe resistivity meter RT-3000/RG-80 manufactured by Napson, the sheet resistance was 11.6 MΩ. Therefore, the electrical resistivity was calculated to be 928 Ωcm.

The obtained α-Ga ₂ O ₃ thin film was heat-treated at 350° C. for 10 minutes in an air atmosphere. Thereafter, when the sheet resistance was measured and the electrical resistivity was calculated, it was found to be 4680 Ωcm, which confirmed that the electrical resistivity was approximately 5 times higher.

(Example 1)
Film formation and evaluation were performed under the same conditions as in Comparative Example 1, except that the film formation time was 30 minutes. As a result, the film thickness was 1.7 μm. The electrical resistivities before and after the heat treatment were 1.6 Ωcm and 8.1 Ωcm, respectively, and an approximately 5-fold increase in electrical resistivity was confirmed in this case as well.

(Example 2)
Film formation and evaluation were performed under the same conditions as in Example 1, except that the heat treatment temperature and time were 400° C. and 5 minutes. The electrical resistivities before and after the heat treatment were 1.8 Ωcm and 8.8 Ωcm, respectively.

(Example 3)
Film formation and evaluation were performed under the same conditions as in Example 1, except that the heat treatment temperature and time were 500° C. and 2 minutes. The electrical resistivities before and after the heat treatment were 1.7 Ωcm and 8.3 Ωcm, respectively.

(Example 4)
As the first aqueous solution, a 5% aqueous solution of germanium oxide was prepared. To promote dissolution of germanium oxide, 10% of 48% hydrogen bromide was mixed thereto to prepare a first aqueous solution. As the second aqueous solution, an aqueous solution containing 0.1 mol/L of gallium bromide was prepared, and a 48% hydrobromic acid solution was further added thereto to give a volume ratio of 10%. 5.0 mL of the first aqueous solution was mixed with 0.5 L of the second aqueous solution, and this was used as a raw material solution 104a. Thereafter, film formation and evaluation were performed under the same conditions as in Example 1. As a result, the film thickness was 1.7 μm. The electrical resistivities before and after the heat treatment were 9.7 Ωcm and 52 Ωcm, respectively.

(Example 5)
Film formation and evaluation were performed under the same conditions as in Example 4, except that the film formation time was 60 minutes. As a result, the film thickness was 3.3 μm. The electrical resistivities before and after the heat treatment were 0.065 Ωcm and 0.31 Ωcm, respectively.

(Example 6)
A 10% tin bromide aqueous solution was prepared as the first aqueous solution. This was mixed with 10% of 48% hydrogen bromide to form a first aqueous solution. As the second aqueous solution, an aqueous solution containing 0.1 mol/L of gallium bromide was prepared, and a 48% hydrobromic acid solution was further added to the solution at a volume ratio of 10%. 10.0 mL of the first aqueous solution was mixed with 0.5 L of the second aqueous solution, and this was used as a raw material solution 104a. Thereafter, film formation and evaluation were performed under the same conditions as in Example 1. As a result, the film thickness was 1.7 μm. The electrical resistivities before and after the heat treatment were 0.052 Ωcm and 0.34 Ωcm, respectively.

(Example 7)
Film formation and evaluation were performed under the same conditions as in Example 6, except that the film formation time was 60 minutes. As a result, the film thickness was 3.4 μm. The electrical resistivities before and after the heat treatment were 0.074 Ωcm and 0.49 Ωcm, respectively.

(Example 8)
A 1% tin chloride aqueous solution was prepared as the first aqueous solution. 10% of 48% hydrogen bromide and hydrogen peroxide were mixed in equimolar amounts with tin to form a first aqueous solution. As the second aqueous solution, an aqueous solution containing 0.1 mol/L of gallium iodide was prepared, and a 57% hydroiodic acid solution was further added to the solution at a volume ratio of 10%. 2.2 mL of the first aqueous solution was mixed with 0.5 L of the second aqueous solution, and this was used as a raw material solution 104a. Thereafter, film formation and evaluation were performed under the same conditions as in Example 1. As a result, the film thickness was 3.2 μm. The electrical resistivities before and after the heat treatment were 2.1 Ωcm and 9.9 Ωcm, respectively.

(Comparative example 2)
An aqueous solution containing a dopant and an aqueous solution containing gallium were not prepared separately, but were mixed from the beginning. As raw material solution 104a, 10% of 48% hydrogen bromide and tin chloride were mixed in an aqueous solution of 0.1 mol/L of gallium iodide so that the atomic ratio with gallium was the same as in Example 8. Furthermore, when hydrogen peroxide and tin were mixed in an equimolar amount, the solution changed from colorless to brown, and a precipitate was also observed. A film formation process similar to that in Example 8 was performed using this solution, but no film was formed.

The results of Examples 1-8 and Comparative Examples 1 and 2 are shown in Table 1.

As shown in Table 1, in Comparative Example 1 in which the film thickness was 0.8 μm, the electrical resistivity of the film was increased by heat treatment, as also described in Patent Document 6. On the other hand, in Examples 1-8, even in the case of a film having a thickness of 1 μm or more, where heat treatment is said to reduce electrical resistivity in Patent Document 6, the electrical resistivity could be increased by heat treatment.

In Comparative Example 2, since the aqueous solution containing the dopant and the aqueous solution containing gallium were not prepared separately, the dispersibility of the raw material solution decreased due to the mixing of hydrogen peroxide, resulting in the inability to form a film itself. . In Example 8, in which an aqueous solution containing a dopant and an aqueous solution containing gallium were prepared separately, the dispersibility of the raw material solution was maintained. According to the method for manufacturing an oxide semiconductor film according to the present invention, it is also possible to use hydrogen peroxide.

Note that the present invention is not limited to the above embodiments. The above-mentioned embodiments are illustrative, and any embodiment that has substantially the same configuration as the technical idea stated in the claims of the present invention and has similar effects is the present invention. covered within the technical scope of

101... Film forming apparatus, 102a... Carrier gas source,
102b...Dilution carrier gas source, 103a...Flow rate control valve,
103b...flow control valve, 104...mist generation source, 104a...raw material solution,
105... Container, 105a... Water, 106... Ultrasonic vibrator, 107... Film forming chamber,
108... Hot plate, 109... Conveyance section, 109a... Supply pipe,
110... Substrate, 112... Exhaust port, 116... Oscillator, 120... Mist forming section,
130... Carrier gas supply section, 140... Film forming section.

Claims (4)

An oxide semiconductor film with a corundum structure containing gallium as a main component,
a dopant element and at least gallium as a metal;
The film thickness is 1 μm or more,
When heat treated at a temperature of 350°C or higher and 500°C or lower for 2 minutes or more and 10 minutes or less , the electrical resistivity obtained as the product of sheet resistance and film thickness increases by 4.7 times or more and 6.6 times or less. An oxide semiconductor film characterized by the following. The oxide semiconductor film according to claim 1, wherein the dopant element contains tin (Sn). The oxide semiconductor film according to claim 1 or 2, wherein the oxide semiconductor film has an area of 100 mm ² or more. A semiconductor device comprising the oxide semiconductor film according to claim 1 .

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