Semiconductor devices and semiconductor systems including semiconductor devices

Abstract

The present invention provides a semiconductor device, which is a normally closed semiconductor device and includes an oxide semiconductor film, wherein the oxide semiconductor film has a corundum structure or contains gallium oxide or a mixture thereof as the main component, and the threshold voltage of the semiconductor device is above 3V.

Description

Technical Field

[0001] The present invention relates to a semiconductor device that can be used as a power device, etc., and a semiconductor system including said semiconductor device. Background Technology

[0002] As a new generation of switching components capable of achieving high withstand voltage, low loss, and high heat resistance, gallium oxide (Ga2O3) semiconductor devices with a large bandgap have attracted attention, and their application in power semiconductor devices such as inverters is anticipated. Furthermore, due to its wide bandgap, it is expected to be used in light-emitting devices such as LEDs or sensors. According to Non-Patent Document 1, the bandgap of gallium oxide can be controlled by mixing it separately with indium and aluminum, or by combining indium and aluminum with gallium oxide, thus forming a highly attractive material system as an InAlGaO-based semiconductor. Here, InAlGaO-based semiconductor refers to In... X Al Y Ga Z O3 (0≦X≦2, 0≦Y≦2, 0≦Z≦2, X+Y+Z=1.5~2.5) stands out as a similar material system containing gallium oxide.

[0003] Next, recent studies have focused on gallium oxide-based p-type semiconductors. For example, Patent Document 1 describes how β-Ga₂O₃ crystals can be formed using MgO (a p-type dopant source) via a floating zone (FZ) method, yielding a substrate exhibiting p-type conductivity. Furthermore, Patent Document 2 describes the formation of α-(Al₂O₃) crystals using molecular beam epitaxy (MBE). x Ga 1-x P-type semiconductors are formed by ion implantation of a single-crystal O2 film to dope it with p-type dopants. However, it is difficult to manufacture p-type semiconductors using these methods (Non-Patent Document 2), and there are no reports of successful p-type semiconductor fabrication using these methods. Therefore, a method for manufacturing a realizable p-type oxide semiconductor is currently desired.

[0004] Furthermore, as described in Non-Patent Documents 3 and 4, although studies have been conducted on using Rh₂O₃ or ZnRh₂O₄ for p-type semiconductors, the concentration of Rh₂O₃ becomes particularly low during film formation, which affects film formation. Even with the use of organic solvents, it is difficult to fabricate Rh₂O₃ single crystals. Moreover, even when Hall effect measurements are performed, it is impossible to determine if it is p-type, and the measurement itself cannot be performed. Furthermore, regarding measured values, for example, the Hall coefficient can only be measured within the limit (0.2 cm⁻¹). 3The following conditions ( / C) cause practical problems. Furthermore, ZnRh2O4 has low mobility and a narrow bandgap, making it unsuitable for use in LEDs and power devices; these technologies do not meet current requirements.

[0005] As wide bandgap semiconductors, besides Rh₂O₃ and ZnRh₂O₄, various studies have also been conducted on p-type oxide semiconductors. Patent document 3 describes the use of black copper iron ore and oxychalcogenides as p-type semiconductors. However, the mobility of these semiconductors is 1 cm⁻¹. 2 Its electrical properties are poor at or below / V·s, and it also has the problem of not being able to successfully perform pn bonding with next-generation n-type oxide semiconductors such as α-Ga2O3.

[0006] Furthermore, Patent Document 4 describes the use of Ir₂O₃ as an iridium catalyst. Patent Document 5 describes the use of Ir₂O₃ as a dielectric. Patent Document 6 describes the use of Ir₂O₃ as an electrode. However, it is not known that anyone has used Ir₂O₃ as a p-type semiconductor, but until recently, there have been documents describing the applicant's research and development using Ir₂O₃ as a p-type semiconductor (Patent Document 7).

[0007] Therefore, research and development of p-type semiconductors continue to advance, and there is a prospect of a semiconductor device that can achieve high voltage resistance, low loss and high heat resistance by effectively using excellent semiconductor materials such as gallium oxide (Ga2O3).

[0008] [Patent Document 1] Japanese Patent Application Publication No. 2005-340308

[0009] [Patent Document 2] Japanese Patent Application Publication No. 2013-58637

[0010] [Patent Document 3] Japanese Patent Application Publication No. 2016-25256

[0011] [Patent Document 4] Japanese Patent Application Publication No. 9-25255

[0012] [Patent Document 5] Japanese Patent Application Publication No. 8-227793

[0013] [Patent Document 6] Japanese Patent Application Publication No. 11-21687

[0014] [Patent Document 7] International Publication No. 2018 / 043503

[0015] [Non-Patent Literature 1] Kentaro Kaneko, Growth and Physical Properties of Corundum-Structured Gallium Oxide-Based Mixed Crystal Thin Films, Doctoral Dissertation of Kyoto University, March 2013 (Kentaro Kaneko, "Growth and Physical Properties of Corundum-Structured Gallium Oxide-Based Mixed Crystal Thin Films", Doctoral Dissertation of Kyoto University, March 2013)

[0016] [Non-Patent Literature 2] Tatsuya Takemoto, "Gallium Oxide Power Semiconductor" on EE Times Japan: Moving toward practical application by overcoming challenges including thermal conductivity and P-type conductivity, [Online], February 27, 2014, ITmedia Inc., [Retrieved on June 21, 2016], URL<URL: http: / / eetimes.jp / ee / articles / 1402 / 27 / news028_2.html> (Tatsuya Takemoto, "Gallium Oxide Power Semiconductor" on EE Times Japan: Moving toward practical application by overcoming challenges including thermal conductivity and P-type conductivity, [online], February 27, 2014, ITmedia Inc., [Retrieved on June 21, 2016], Internet<URL: http: / / eetimes.jp / ee / articles / 1402 / 27 / news028_2.html>)

[0017] [Non-Patent Literature 3] F. P. KOFFYBERG et al., "Optical Bandgaps and Electron Affinities of Semiconducting Rh₂O₃(I) and Rh₂O₃(III)", Journal of Physics and Chemistry of Solids, Vol. 53, No. 10, pp. 1285-1288, 1992 (F.P.KOFFYBERG et al.,"optical bandgaps and electron affinities of semiconducting Rh2O3(I)andRh2O3(III)",J.Phys.Chem.Solids Vol.53,No.10,pp.1285-1288,1992)

[0018] [Non-Patent Literature 4] Hideo Hosono, "Functional Exploration of Oxide Semiconductors", Studies on Physical Properties · Electronic Version Vol.3, No.1, 031211 (Combined Issue of November 2013 and February 2014) (Hideo Hosono, "Functional Exploration of Oxide Semiconductors", Studies on Physical Properties · Electronic Version Vol.3, No.1, 031211 (Combined Issue of November 2013 and February 2014))

[0019] An object of the present invention is to provide a semiconductor device having excellent semiconductor characteristics. Summary of the Invention

[0020] As a result of in-depth research to achieve the above objectives, the inventors of this invention discovered that, as a first aspect of the invention, by configuring a crystalline oxide semiconductor film, wherein the crystals include gallium oxide, and by configuring an oxide film containing at least phosphorus on the oxide semiconductor film, a semiconductor device with a threshold voltage of 3V or higher can be obtained. Furthermore, as a second aspect of the invention, by configuring a crystalline oxide semiconductor film, wherein the crystals include gallium oxide having a corundum structure, and by configuring an oxide semiconductor film containing at least phosphorus, a semiconductor device with a threshold voltage of 3V or higher can be obtained. Moreover, as a third aspect of the invention, the inventors of this invention discovered a normally closed semiconductor device comprising an oxide semiconductor film having a corundum structure, or containing gallium oxide or a mixture thereof as the main component, wherein the threshold voltage of the semiconductor device is 3V or higher. Through repeated research, the inventors of this invention successfully demonstrated for the first time in the world that a transistor made of gallium oxide semiconductor could function. Following the above discoveries, the inventors of this invention further researched and completed this invention.

[0021] That is, the present invention relates to the following technical solutions.

[0022] [1]. A semiconductor device, characterized in that it is a normally closed semiconductor device, the semiconductor device comprising an oxide semiconductor film having a corundum structure, or containing gallium oxide or a mixture thereof as the main component, the semiconductor device having a threshold voltage of 3V or above.

[0023] [2]. The semiconductor device according to the aforementioned [1], wherein the oxide semiconductor film contains α-Ga2O3 or a mixture thereof as the main component.

[0024] [3]. The semiconductor device described in [2] above, wherein the semiconductor device is a MOSFET and the threshold voltage is the gate threshold voltage.

[0025] [4]. The semiconductor device according to the aforementioned [3], wherein the oxide semiconductor film includes a reverse channel region, a gate electrode is disposed on the reverse channel region via a gate insulating film, and a hydrogen diffusion prevention film is formed between the reverse channel region and the gate insulating film, the hydrogen diffusion prevention film being composed of an oxide film containing at least one element of Group 15 of the periodic table.

[0026] [5]. The semiconductor device according to [4] above, wherein the element is phosphorus.

[0027] [6]. The semiconductor device according to [4] or [5] above, wherein the reverse channel region is a p-type semiconductor layer.

[0028] [7]. The semiconductor device according to any one of [1] to [6] above, wherein the threshold voltage is 7V or more.

[0029] [8]. The semiconductor device according to any one of [1] to [7] above is a power device.

[0030] [9]. A semiconductor system comprising a semiconductor device, wherein the semiconductor device is a semiconductor device according to any one of the preceding [1] to [8].

[0031]

[10] . A semiconductor device having an oxide semiconductor film containing crystals and a threshold voltage of 3V or higher, said crystals comprising gallium oxide having a corundum structure.

[0032]

[11] . A semiconductor device having an oxide semiconductor film containing crystals and a threshold voltage of 3V or higher, said crystals comprising gallium oxide.

[0033]

[12] . The semiconductor device according to

[10] or

[11] above, wherein the crystal is a mixed crystal.

[0034]

[13] . The semiconductor device according to

[10] or

[11] above, wherein the semiconductor device is a normally closed semiconductor device.

[0035]

[14] . The semiconductor device according to

[10] or

[11] above, wherein the oxide semiconductor film includes a reverse channel region, a gate electrode is disposed on the reverse channel region via a gate insulating film, and a hydrogen diffusion prevention film is formed between the reverse channel region and the gate insulating film, the hydrogen diffusion prevention film being composed of an oxide film containing at least one element of Group 15 of the periodic table.

[0036]

[15] . The semiconductor device according to the preceding

[14] , wherein the element is phosphorus.

[0037] The semiconductor device of the present invention has excellent semiconductor characteristics such as high voltage resistance, low loss and high heat resistance. Attached Figure Description

[0038] Figure 1 A schematic structural diagram of a film-forming apparatus (atomizing CVD apparatus) used in embodiments of the present invention and suitable for forming oxide semiconductor films is shown.

[0039] Figure 2 As an example of the semiconductor device of the present invention, a cross-sectional view of one embodiment of a MOSFET is schematically shown.

[0040] Figure 3A photograph showing the MOSFET manufactured in the embodiment, viewed from above.

[0041] Figure 4 This is a graph showing the IV measurement results in the embodiment.

[0042] Figure 5 This is a graph showing the SIMS measurement results in the embodiment.

[0043] Figure 6 This is a diagram that schematically illustrates an example of a power supply system.

[0044] Figure 7 This is a diagram that schematically illustrates an example of a system device.

[0045] Figure 8 This is a schematic diagram illustrating an example of a power supply circuit diagram for a power supply device.

[0046] Figure 9 As an example of the semiconductor device of the present invention, a partial perspective view (600a') of a vertical semiconductor device viewed from the first surface side with the source electrode and a portion of the insulating layer under the source electrode removed from the first surface side is shown; and a partial cross-sectional view (600c) of the semiconductor device including the source electrode and the insulating layer under the source electrode on the first surface side is shown. Detailed Implementation

[0047] The semiconductor device according to the present invention is a normally closed semiconductor device, comprising an oxide semiconductor film having a corundum structure, or containing gallium oxide or a mixture thereof as the main component, wherein the threshold voltage of the semiconductor device is 3V or higher. In this invention, the semiconductor device is preferably a MOSFET. Furthermore, the threshold voltage here refers to the gate threshold voltage. In this invention, for convenience, the threshold voltage can be obtained from the IV characteristics of the semiconductor device.

[0048] The oxide semiconductor film has a corundum structure, or may contain gallium oxide or a mixture thereof as the main component, without particular limitation. Preferably, in this invention, it contains α-Ga2O3 or a mixture thereof as the main component.

[0049] Hereinafter, as a preferred embodiment of the present invention, a semiconductor device comprising at least a reverse channel region is given as an example, wherein the reverse channel region is composed of an oxide semiconductor film containing gallium oxide or a mixture thereof as the main component, to illustrate the present invention in more detail, but the present invention is not limited to these examples.

[0050] In this invention, an oxide film is disposed on an oxide semiconductor film (where the oxide semiconductor film may also be referred to as an oxide semiconductor layer) to form a stacked structure, which is then used in a semiconductor device. This allows for the easy acquisition of a semiconductor device with a threshold voltage of 3V or higher, and preferably a semiconductor device with a threshold voltage of 7V or higher.

[0051] Preferably, the aforementioned oxide film is a hydrogen diffusion prevention film for preventing hydrogen diffusion, and is an oxide film containing at least one element from Group 15 of the periodic table. More preferably, in this invention, the oxide film includes at least one element from Group 15 of the periodic table and one or more metals from Group 13 of the periodic table. Examples of such elements include nitrogen, phosphorus, antimony, and bismuth, with nitrogen or phosphorus being preferred, and phosphorus being more preferred. Examples of such metals include aluminum (Al), gallium (Ga), and indium (In), with Ga and / or Al being preferred, and Ga being more preferred. Furthermore, the oxide film is preferably a thin film, more preferably with a film thickness of 100 nm or less, and most preferably with a film thickness of 50 nm or less. Methods for forming the oxide film include, for example, known methods, and more specifically, dry or wet methods, preferably surface treatment with phosphoric acid on the reverse channel region, and more preferably surface treatment with phosphoric acid on gallium oxide or its mixed crystals. As described above, a high-quality passivation film can be obtained by forming an oxide film containing at least one of the elements in Group 15 of the periodic table.

[0052] An oxide film containing at least one element from Group 15 of the periodic table is stacked on the reverse channel region. This prevents hydrogen diffusion into the oxide semiconductor film and further reduces interface states, thus imparting superior semiconductor characteristics to semiconductor devices, particularly wide-bandgap semiconductor devices. Moreover, by stacking such an oxide film, gate leakage current can be suppressed more effectively, and semiconductor characteristics can be further improved.

[0053] Preferably, the reverse channel region uses an oxide semiconductor film comprising gallium oxide or a mixture thereof as the main component. Preferably, an oxide semiconductor film having a corundum structure is used. The oxide semiconductor film can be a p-type semiconductor film or an n-type semiconductor film. Examples of gallium oxide include α-Ga₂O₃, β-Ga₂O₃, and ε-Ga₂O₃, with α-Ga₂O₃ being preferred. As a mixture of the aforementioned gallium oxide, a mixture of gallium oxide and one or more metal oxides can be used. Preferred examples of the metal oxide include aluminum oxide, indium oxide, iridium oxide, rhodium oxide, and iron oxide.

[0054] Furthermore, oxide semiconductor films with corundum structures typically contain metal oxides as the main component. Examples of such metal oxides include aluminum oxide, indium oxide, iridium oxide, rhodium oxide, and iron oxide.

[0055] Furthermore, "main component" refers to, for example, when the oxide semiconductor film contains α-Ga₂O₃ as the main component, α-Ga₂O₃ is contained in a proportion where the atomic ratio of gallium in the metal elements of the oxide semiconductor film is 0.5 or more. In this invention, the atomic ratio of gallium in the metal elements of the oxide semiconductor film is preferably 0.7 or more, more preferably 0.8 or more. Additionally, even when the crystal is a mixed crystal, the main component of the oxide semiconductor film is preferably gallium oxide. For example, even when the oxide semiconductor film contains α-(AlGa)₂O₃ as the main component, it can be contained in a proportion where the atomic ratio of gallium in the metal elements of the oxide semiconductor film is 0.5 or more. In this invention, the atomic ratio of gallium in the metal elements of the oxide semiconductor film is preferably 0.7 or more, more preferably 0.8 or more.

[0056] The reverse channel region is typically a single-phase region, but it may also have a second semiconductor region composed of different semiconductor phases, or other equivalent phases, provided that the purpose of the invention is not compromised. Furthermore, the semiconductor region is typically film-like and may be a semiconductor film. The thickness of the oxide semiconductor film in the semiconductor region is not particularly limited and may be less than 1 μm or more than 1 μm. In this invention, it is preferably more than 1 μm, more preferably 1 μm to 40 μm, and most preferably 1 μm to 25 μm. The surface area of ​​the oxide semiconductor film is not particularly limited, but may be 1 mm. 2 The above can also be 1mm. 2 Furthermore, the oxide semiconductor film is typically monocrystalline, but can also be polycrystalline. Additionally, the oxide semiconductor film can be a single-layer film or a multilayer film.

[0057] The oxide semiconductor film preferably contains a dopant. The dopant is not particularly limited and can be any known dopant. Examples of dopant include n-type dopants such as tin, germanium, silicon, titanium, zirconium, vanadium, or niobium, or p-type dopants such as Mg, Zn, or Ca. In this invention, the dopant is preferably Sn, Ge, or Si. Regarding the dopant content, in the composition of the oxide semiconductor film, it is preferably 0.00001 atomic% or more, more preferably 0.00001 atomic% to 20 atomic%, and even more preferably 0.00001 atomic% to 10 atomic%.

[0058] In this invention, the reverse channel region is preferably at least a portion of a p-type semiconductor layer, and is a channel region that reverses to n-type when a voltage is applied. More preferably, the p-type semiconductor layer is composed of an oxide semiconductor film containing gallium oxide or a mixture thereof as its main component. The oxide semiconductor film is preferably a p-type semiconductor film, and more preferably contains the p-type dopant. Moreover, the p-type dopant is not particularly limited as long as it can enable the oxide semiconductor film to provide conductivity as a p-type semiconductor film, and can be a known dopant. Examples of p-type dopants include Mg, H, Li, Na, K, Rb, Cs, Fr, Be, Ca, Sr, Ba, Ra, Mn, Fe, Co, Ni, Pd, Cu, Ag, Au, Zn, Cd, Hg, Tl, Pb, N, P, and two or more elements selected from these elements. In this invention, the p-type dopant is preferably Mg, Zn, or Ca.

[0059] The oxide semiconductor film can be obtained by forming a film using an epitaxial growth method. The epitaxial growth method is not particularly limited as long as it does not impair the purpose of the present invention, and can be a known method. Examples of such epitaxial growth methods include CVD, MOCVD, MOVPE, atomized CVD, atomized epitaxial growth, MBE, HVPE, or pulsed growth methods. In the present invention, the epitaxial growth method is preferably atomized CVD or atomized epitaxial growth.

[0060] In this invention, preferably, the droplets are made to float by atomizing a raw material solution containing metal (atomization process), and the atomized droplets are carried to the vicinity of the substrate by a carrier gas (transportation process), and then the atomized droplets are subjected to thermal reaction (film formation process) to form a film.

[0061] (Raw material solution)

[0062] The raw material solution contains a metal as a film-forming material, and there are no particular restrictions as long as it can be atomized. It can contain both inorganic and organic materials. The aforementioned metal can be a metal monomer or a metal compound, and there are no particular restrictions as long as it does not hinder the purpose of this invention. Examples include one or more metals selected from gallium (Ga), iridium (Ir), indium (In), rhodium (Rh), aluminum (Al), gold (Au), silver (Ag), platinum (Pt), copper (Cu), iron (Fe), manganese (Mn), nickel (Ni), palladium (Pd), cobalt (Co), ruthenium (Ru), chromium (Cr), molybdenum (Mo), tungsten (W), tantalum (Ta), zinc (Zn), lead (Pb), rhenium (Re), titanium (Ti), tin (Sn), gallium (Ga), magnesium (Mg), calcium (Ca), and zirconium (Zr). In this invention, preferably, the aforementioned metal contains at least one or more metals from periods 4 to 6 of the periodic table; more preferably, it contains at least gallium, indium, aluminum, rhodium, or iridium; and most preferably, it contains at least gallium. By using this preferred metal, it is possible to form epitaxial films suitable for semiconductor devices and the like.

[0063] In this invention, the raw material solution is appropriately used as a solution in which the metal is dissolved or dispersed in an organic solvent or water in the form of a complex or salt. Examples of complex forms include acetylacetone complexes, carbonyl complexes, ammonia complexes, and hydride complexes. Examples of salt forms include organometallic salts (e.g., metal acetates, metal oxalates, metal citrates), sulfide metal salts, nitrate metal salts, phosphate metal salts, and halide metal salts (e.g., metal chloride salts, metal bromide salts, metal iodide salts, etc.).

[0064] The solvent for the raw material solution is not particularly limited, as long as it does not impair the purpose of the present invention. It can be an inorganic solvent such as water, an organic solvent such as ethanol, or a mixture of inorganic and organic solvents. In the present invention, it is preferred that the solvent contains water.

[0065] Furthermore, additives such as hydrohalic acid or oxidizing agents can be mixed into the raw material solution. Examples of hydrohalic acid include hydrobromic acid, hydrochloric acid, and hydroiodic acid. Examples of oxidizing agents include peroxides such as hydrogen peroxide (H2O2), sodium peroxide (Na2O2), barium peroxide (BaO2), and benzoyl peroxide (C6H5CO)2O2; and organic oxides such as hypochlorous acid (HClO), perchloric acid, nitric acid, ozone water, peracetic acid, and nitrobenzene. The mixing ratio of the additives is not particularly limited, but is preferably 0.001 vol% to 50 vol% relative to the raw material solution, more preferably 0.01 vol% to 30 vol%.

[0066] The raw material solution may contain a dopant. The dopant is not particularly limited as long as it does not impair the purpose of the invention. Examples of dopant include the aforementioned n-type or p-type dopant. The concentration of the dopant is typically about 1 × 10⁻⁶. 16 / cm 3 ~1×10 22 / cm 3 And the concentration of the dopant can be, for example, about 1 × 10⁻⁶. 17 / cm 3 The following low concentrations. Furthermore, according to the present invention, it is possible to achieve concentrations of approximately 1 × 10⁻⁶. 20 / cm 3 The above high concentrations contain dopants.

[0067] (Atomization process)

[0068] In the atomization process, a raw material solution containing metal is adjusted and atomized, causing the atomized droplets to float and generate atomized droplets. The mixing ratio of the metal is not particularly limited, but preferably, it is 0.0001 mol / L to 20 mol / L relative to the overall raw material solution. The atomization method is not particularly limited as long as it can atomize the raw material solution; any known atomization method can be used. However, in this invention, an ultrasonic vibration atomization method is preferred. The fog used in this invention is fog that floats in the air, preferably, for example, not sprayed like a mist, but with an initial velocity of zero, floating in space and capable of being transported as a gas. The droplet size of the fog is not particularly limited; it can be droplets of about several millimeters, but preferably less than 50 μm, more preferably 1 μm to 10 μm.

[0069] (Conveying process)

[0070] In the delivery process, the atomized droplets are delivered to the substrate using the carrier gas. There are no particular limitations on the type of carrier gas, as long as it does not impair the purpose of the invention, and suitable examples include oxygen, ozone, inert gases (e.g., nitrogen and argon), or reducing gases (hydrogen, synthesis gases, etc.). Furthermore, the carrier gas can be of one type, or two or more types, and a dilution gas with a different concentration (e.g., a gas diluted 10 times) can be used as a second carrier gas. Moreover, the carrier gas can be supplied from two or more locations, not just one. The flow rate of the carrier gas is not particularly limited, but is preferably a flow rate that allows for supply speed control of the delivery, more specifically 1 LPM or less, and more preferably 0.1 LPM to 1 LPM.

[0071] (Film forming process)

[0072] In the film-forming process, the atomized droplets are reacted to form a film on the substrate. The reaction is not particularly limited as long as it involves the formation of a film from the atomized droplets; however, in this invention, a thermal reaction is preferred. The thermal reaction is simply a reaction caused by heat to react the atomized droplets, and the reaction conditions are not particularly limited as long as they do not impair the purpose of this invention. In this process, the thermal reaction is generally carried out at a temperature above the evaporation temperature of the solvent in the raw material solution, but preferably below a temperature that is not too high, more preferably below 650°C. Furthermore, the thermal reaction can be carried out in any atmosphere, including vacuum, non-oxygen atmosphere, reducing atmosphere, and oxygen atmosphere, as long as it does not impair the purpose of this invention. Moreover, it can be carried out under atmospheric pressure, pressurized, or depressurized conditions. However, in this invention, considering the simplicity of calculating the evaporation temperature and the simplification of equipment, it is preferred to carry out the reaction under atmospheric pressure. Furthermore, the film thickness can be set by adjusting the film-forming time.

[0073] (Matrix)

[0074] The substrate is not particularly limited as long as it can support the semiconductor film. The material of the substrate is also not particularly limited as long as it does not impair the purpose of the invention; it can be a known substrate, an organic compound, or an inorganic compound. The shape of the substrate can be any shape, and all shapes are effective, such as plate-shaped (e.g., flat or circular), fibrous, rod-shaped, cylindrical, prismatic, tubular, spiral, spherical, or ring-shaped. In this invention, a substrate is preferred. The thickness of the substrate is not particularly limited in this invention.

[0075] The substrate is plate-shaped and is not particularly limited as long as it serves as a support for the semiconductor film. It can be an insulating substrate, a semiconductor substrate, a metal substrate, or a conductive substrate. However, the substrate is preferably an insulating substrate, and more preferably a substrate with a metal film on its surface. Examples of preferred substrates include: a substrate containing a substrate material having a corundum structure as its main component; a substrate containing a substrate material having a β-gallia structure as its main component; a substrate containing a substrate material having a hexagonal crystal structure as its main component, etc. Here, "main component" refers to the substrate material having the specific crystal structure, which, in atomic ratio, is preferably 50% or more, more preferably 70% or more, and even more preferably 90% or more, and may also be 100% relative to all components of the substrate material.

[0076] The substrate material is not particularly limited as long as it does not impair the purpose of this invention, and can be any known material. Examples of substrate materials with a corundum structure include, for instance, α-Al₂O₃ (sapphire substrate) or α-Ga₂O₃, and more preferably, a-plane sapphire substrates, m-plane sapphire substrates, r-plane sapphire substrates, c-plane sapphire substrates, and α-type gallium oxide substrates (a-plane, m-plane, or r-plane). Examples of substrates with a substrate material having a β-gallia structure as the main component include β-Ga₂O₃ substrates; or mixed-crystal substrates containing Ga₂O₃ and Al₂O₃, wherein Al₂O₃ is greater than 0 wt% and less than 60 wt%, etc. Furthermore, examples of substrates with a substrate material having a hexagonal crystal structure as the main component include SiC substrates, ZnO substrates, and GaN substrates.

[0077] In this invention, annealing can be performed after the film-forming process. The annealing temperature is not particularly limited as long as it does not impair the purpose of this invention, and is typically 300°C to 650°C, preferably 350°C to 550°C. The annealing time is typically 1 minute to 48 hours, preferably 10 minutes to 24 hours, and more preferably 30 minutes to 12 hours. Annealing can be performed in any atmosphere as long as it does not hinder the purpose of this invention, but is preferably in a non-oxygen atmosphere, and more preferably in a nitrogen atmosphere.

[0078] In this invention, the semiconductor film can be directly deposited on the substrate, or it can be deposited via other layers such as a buffer layer or a stress relaxation layer. The method for forming each layer is not particularly limited and can be a known method; however, in this invention, atomization CVD or atomization epitaxy is preferred.

[0079] The film-forming apparatus 19, which is suitable for atomization CVD or atomization epitaxial growth, will be described below with reference to the accompanying drawings. Figure 1 The film-forming apparatus 19 includes: a carrier gas source 22a for supplying carrier gas; a flow regulating valve 23a for regulating the flow rate of the carrier gas supplied from the carrier gas source 22a; a carrier gas (dilution) source 22b for supplying carrier gas (dilution); a flow regulating valve 23b for regulating the flow rate of the carrier gas (dilution) supplied from the carrier gas (dilution) source 22b; a mist generating source 24 for storing the raw material solution 24a; a container 25 for holding water 25a; an ultrasonic transducer 26 mounted on the bottom surface of the container 25; a film-forming chamber 30; a quartz supply pipe 27 connected from the mist generating source 24 to the film-forming chamber 30; and a hot plate (heater) 28 mounted inside the film-forming chamber 30. A substrate 20 is disposed on the hot plate 28.

[0080] like Figure 1As shown, the raw material solution 24a is contained in the mist generation source 24. Next, using the substrate 20, the substrate 20 is placed on the hot plate 28, and the hot plate 28 is activated to raise the temperature inside the film formation chamber 30. Next, the flow regulating valves 23 (23a, 23b) are opened to supply carrier gas from the carrier gas source 22 (22a, 22b) into the film formation chamber 30, and the atmosphere inside the film formation chamber 30 is fully replaced with the carrier gas. Then, the flow rates of the carrier gas and the carrier gas (dilution) are adjusted respectively. Next, the ultrasonic transducer 26 is vibrated, and the vibration is propagated to the raw material solution 24a through the water 25a, thereby atomizing the raw material solution 24a into microparticles and generating atomized droplets 24b containing mist. The atomized droplets 24b are introduced into the film formation chamber 30 by the carrier gas and transported to the substrate 20. Then, the atomized droplets 24b undergo a thermal reaction in the film formation chamber 30 under atmospheric pressure, thereby forming a film on the substrate 20.

[0081] In this invention, the film obtained in the film-forming process can be used in a semiconductor device as is, or it can be used in a semiconductor device after being peeled off from the substrate using known methods.

[0082] The oxide semiconductor film, a preferred p-type semiconductor film used in this invention, can be obtained, for example, by adding a p-type dopant and hydrobromic acid to a metal-containing feed solution using a fogging CVD method. Importantly, hydrobromic acid is added to the feed solution as an additive. Furthermore, the steps, methods, and conditions of the fogging CVD method are the same as those described above for the fogging / dropleting steps, transport steps, and film formation steps, methods, and conditions. The resulting p-type semiconductor film exhibits good pn bonding with the n-type semiconductor and is suitable for the reverse channel region.

[0083] The reverse channel region is typically disposed between semiconductor regions exhibiting different types of conductivity. For example, when the reverse channel region is disposed in a p-type semiconductor layer, it is typically disposed within a p-type semiconductor layer between semiconductor regions composed of n-type semiconductors, and when the reverse channel region is disposed within an n-type semiconductor layer, it is typically disposed within an n-type semiconductor layer between semiconductor regions composed of p-type semiconductors. Furthermore, the method for forming each semiconductor region can be the same as the method for forming an oxide semiconductor film.

[0084] In this invention, preferably, an oxide film containing at least one element from Group 15 of the periodic table is stacked on the reverse channel region. Examples of such elements include nitrogen (N) and phosphorus (P). In this invention, nitrogen (N) or phosphorus (P) is preferred, and phosphorus (P) is more preferred. For example, by stacking an oxide film containing at least phosphorus on the reverse channel region between the gate insulating film and the reverse channel region, hydrogen diffusion into the oxide semiconductor film can be prevented, and the interface states can be further reduced. Therefore, superior semiconductor characteristics can be imparted to semiconductor devices, especially wide-bandgap semiconductor devices, and normally closed semiconductor devices with a threshold voltage of 3V or higher can be realized. Furthermore, in this invention, more preferably, the oxide film contains at least one element from Group 15 of the periodic table and one or more metals from Group 13 of the periodic table. Examples of such metals include aluminum (Al), gallium (Ga), and indium (In). Ga and / or Al are preferred, and Ga is more preferred. Furthermore, the oxide film is preferably a thin film, more preferably with a thickness of 100 nm or less, and most preferably with a thickness of 50 nm or less. By stacking such an oxide film, gate leakage current can be suppressed more effectively, and semiconductor characteristics can be improved. Known methods can be cited as methods for forming the oxide film. More specifically, these include, for example, dry and wet methods, and preferably, the reverse channel region is surface-treated with phosphoric acid or the like.

[0085] In this invention, it is preferred that the gate electrode be disposed on the reverse channel region and the oxide film via the gate insulating film as needed. The gate insulating film is not particularly limited as long as it does not impair the purpose of this invention and can be any known insulating film. Preferred examples of the gate insulating film are oxide films, which can be oxide films comprising at least, for example, SiO2, Si3N4, Al2O3, GaO, AlGaO, InAlGaO, AlInZnGaO4, AlN, Hf2O3, SiN, SiON, MgO, GdO, and phosphorus oxides. The method for forming the gate insulating film can be a known method; examples of such known forming methods include, for example, dry methods and wet methods. Dry methods include, for example, known methods such as sputtering, vacuum evaporation, CVD, and PLD. Wet methods include, for example, coating methods such as screen printing and die coating.

[0086] The gate electrode can be a known gate electrode, and the electrode material can be a conductive inorganic material or a conductive organic material. In this invention, the electrode material is preferably a metal. There are no particular limitations on the metal, but at least one metal selected from Groups 4-11 of the periodic table is preferred. Examples of Group 4 metals include titanium (Ti), zirconium (Zr), and hafnium (Hf), with Ti being preferred. Examples of Group 5 metals include vanadium (V), niobium (Nb), and tantalum (Ta). Examples of Group 6 metals include one or more metals selected from, for example, chromium (Cr), molybdenum (Mo), and tungsten (W). In this invention, Cr is preferred because its semiconductor properties, such as switching characteristics, are improved. Examples of Group 7 metals include, for example, manganese (Mn), technetium (Tc), and rhenium (Re). Examples of Group 8 metals include, for example, iron (Fe), ruthenium (Ru), and osmium (Os). Examples of metals in Group 9 of the periodic table include cobalt (Co), rhodium (Rh), and iridium (Ir). Examples of metals in Group 10 of the periodic table include nickel (Ni), palladium (Pd), and platinum (Pt), with Pt being preferred. Examples of metals in Group 11 of the periodic table include copper (Cu), silver (Ag), and gold (Au). Methods for forming the gate electrode include known methods, more specifically, dry methods and wet methods. Dry methods include known methods such as sputtering, vacuum evaporation, and CVD. Wet methods include methods such as screen printing and die coating.

[0087] In this invention, not only is a gate electrode provided, but also a source electrode and a drain electrode are typically provided. Similar to the gate electrode, either the source electrode or the drain electrode can be a known electrode, and the electrode forming method can also be a known method.

[0088] The semiconductor device is particularly suitable for power devices. Examples of semiconductor devices include transistors, with MOSFETs being preferred.

[0089] (MOSFET)

[0090] Figure 2 A preferred example is shown where the semiconductor device of the present invention is a MOSFET. Figure 2The MOSFET is a lateral MOSFET and includes: an n+ type semiconductor layer (n+ type source layer) as a first semiconductor region 1a; an n+ type semiconductor layer (n+ type drain layer) as a second semiconductor region 1b; a p-type semiconductor layer as an oxide semiconductor film 2; and a reverse channel region 2a located within the p-type semiconductor layer and having a phosphorus-containing oxide film formed on its surface; a metal oxide film layer 3; an insulating film 4a (gate insulating film); an insulating film 4b (field insulating film); a gate electrode as a third electrode 5a; a source electrode as a first electrode 5b; a drain electrode as a second electrode 5c; and a substrate 9. The metal oxide layer 3 contains gallium oxide. The metal oxide layer 3 may contain gallium oxide as its main component. Furthermore, the metal oxide layer 3 is preferably a film with a higher resistivity than the oxide semiconductor film 2, and is preferably a layer without dopants.

[0091] exist Figure 2 In the MOSFET's on-state, when a voltage is applied between the source electrode 5b and the drain electrode 5c, providing a positive voltage to the source electrode 135b and the gate electrode 5a, an n-type reverse channel region is formed in the reverse channel region 2a portion within the p-type semiconductor layer 2, thus turning on. In the off-state, the voltage at the gate electrode is set to 0V, thereby preventing it from becoming a reverse channel region, thus turning off.

[0092] Figure 9As an example of the semiconductor device of the present invention, a partial perspective view (600a') of a first surface side 600a of a vertically oriented semiconductor device is shown, in which a first electrode 5b and a portion of the insulating layer 4a below the first electrode 5b are removed; and a partial cross-sectional view (600c) of the semiconductor device 600 is shown. For ease of observation, the partial perspective view 600a' viewed from the first surface side 600a does not include the second semiconductor region 1b and the second electrode 5c located on the second surface side 600b, but the partial cross-sectional view 600c includes the first electrode 5b and the insulating layer 4a, as well as the second semiconductor region 1b and the second electrode 5c. The semiconductor device 600 of this embodiment shows a vertically oriented device structure in which electrodes are arranged on the first surface side 600a and the second surface side 600b of the semiconductor device 600. The semiconductor device 600 includes an oxide semiconductor film 2, which includes at least a crystal containing gallium oxide and includes an oxide film 2b, and the semiconductor device 600 has a reverse channel region 2a at a location in contact with the oxide film 2b. Furthermore, the semiconductor device 600 includes a first electrode 5b, a second electrode 5c, and a third electrode 5a. The first electrode 5b is disposed on the first surface side of the oxide semiconductor film 2. The second electrode 5c is disposed on the second surface side of the oxide semiconductor film 2. The third electrode 5a is located on the first surface side of the oxide semiconductor film 2 and, in a cross-sectional view, is at least partially located between the first electrode 5b and the second electrode 5c. Additionally, the third electrode 5a, as... Figure 9As shown in figure 600c, the first electrode 5b is separated from the insulating film 4a, and the third electrode 5a is located at a position separated from the second electrode 5c via a plurality of layers. The semiconductor device in this embodiment can be used as a vertical MOSFET. For example, when the oxide semiconductor film 2 is a p-type semiconductor film and has a reverse channel region 2a on which a phosphorus-containing oxide film 2b is disposed, the first electrode 5b is the source electrode. The second electrode 5c is the drain electrode, and the third electrode 5a is the gate electrode. Furthermore, the semiconductor device 600 includes: a first semiconductor region 1a buried in the oxide semiconductor film 2; a third semiconductor region 6 in which at least a portion of the oxide semiconductor film 2 is buried; a second semiconductor region 1b in contact with the second surface of the third semiconductor region 6; and a second electrode 5c in contact with the second semiconductor region 1b. Additionally, reference numeral 50b indicates the contact surface of the first electrode, which is in partial contact with the oxide semiconductor film 2 and the first semiconductor region 1a buried in the oxide semiconductor film 2. The second electrode 5c is located on the second surface side 600b of the semiconductor device 600. In this embodiment, the first semiconductor region 1a is an n+ type semiconductor layer (n+ type source layer). Furthermore, the second semiconductor region 1b is an n+ type semiconductor layer (n+ type drain layer). In this embodiment, the oxide semiconductor film 2 is a p-type semiconductor film, and it is disposed within the oxide semiconductor film 2, contacting the reverse channel region 2a, and a phosphorus-containing oxide film 2b is formed near the third electrode 5a (gate electrode). Using this structure, gate leakage current can be suppressed more effectively. Suppressing the gate leakage current solves the problem of difficulty in forming the reverse channel region due to gate leakage current, and a semiconductor device 600 with superior semiconductor characteristics can be obtained. Furthermore, by configuring the semiconductor device as a vertical type, with the first electrode (source electrode) disposed on the first surface side 600a and the second electrode (drain electrode) disposed on the second surface side 600b, compared to a lateral type semiconductor device, which places the first electrode (source electrode) and the second electrode (drain electrode) on one side (first surface side 600a or second surface side 600b) of the semiconductor device, miniaturization of the semiconductor device can be achieved. Moreover, when a vertical type semiconductor device is used in combination with a vertical type device including a diode, the circuit can be easily designed because they are both identical vertical type devices.

[0093] The semiconductor device of the present invention, preferably, in addition to the above-described aspects, can be used as a power module, inverter, or converter using known methods, and is even more preferably used in, for example, semiconductor systems using power supply devices. The power supply device can be manufactured from the semiconductor device by connecting it to a wiring pattern, etc., using known methods; or the power supply device can be manufactured as a semiconductor device.Figure 6 A power system 170 is shown, comprising multiple power supply devices 171 and 172 and a control circuit 173. For example... Figure 7 As shown, by combining electronic circuit 181 and power supply system 182, power supply system 170 can be used in system device 180. Furthermore, Figure 8 An example of a power supply circuit diagram for a power supply device is shown. Figure 8 This diagram shows the power supply circuit of a power supply device consisting of a power circuit and a control circuit, utilizing an inverter 192 (MOSFET: with The inverter 192 and rectifier 194 are configured to switch DC voltage at a high frequency to AC voltage. A transformer 193 provides insulation and voltage transformation, rectifier MOSFETs (A-B') rectify the voltage, and DCLs (smoothing coils L1 and L2) 195 and capacitors smooth the output DC voltage. A voltage comparator 197 compares the output voltage with a reference voltage, and a PWM control circuit 196 controls the inverter 192 and rectifier MOSFETs 194 to generate the desired output voltage.

[0094] Example

[0095] (Example 1) Figure 2 The fabrication of the MOSFET shown.

[0096] 1. Forming a p-type semiconductor layer

[0097] 1-1. Film-forming equipment

[0098] use Figure 1 The film-forming device 19 in the middle.

[0099] 1-2. Preparation of raw material solution

[0100] A raw material solution was obtained by adding Mg at a ratio of 1% by volume to a 0.1M gallium bromide aqueous solution containing 20% ​​by volume of hydrobromic acid.

[0101] 1-3. Film Formation Preparation

[0102] The raw material solution 24a obtained in steps 1-2 above is collected in the mist generation source 24. Next, as substrate 20, a sapphire substrate with an undoped α-Ga2O3 film formed on its surface is placed on a hot plate 28, and the hot plate 28 is activated to raise the temperature in the film formation chamber 30 to 520°C. Next, flow control valves 23a and 23b are opened, and carrier gas is supplied from carrier gas supply devices 22a and 22b, which serve as carrier gas sources, into the film formation chamber 30. After the atmosphere in the film formation chamber 30 is fully replaced with carrier gas, the flow rate of the carrier gas is adjusted to 1 LPM, and the flow rate of the carrier gas (diluted) is also adjusted to 1 LPM. Nitrogen gas is used as the carrier gas.

[0103] 1-4. Formation of Semiconductor Films

[0104] Next, the ultrasonic transducer 26 is vibrated at 2.4 MHz, and this vibration is propagated through water 25a to the raw material solution 24a, thereby atomizing the raw material solution 24a to generate mist. The mist is then introduced into the film-forming chamber 30 using a carrier gas, and reacted within the chamber 30 at atmospheric pressure and 520°C to form a semiconductor film on the substrate 20. The film thickness is 0.6 μm, and the film formation time is 15 minutes.

[0105] 1-5. Evaluation

[0106] When the phase of the film obtained in 1-4 above was identified using an XRD diffraction apparatus, it was found that the obtained film was α-Ga2O3.

[0107] 2. Formation of n+ type semiconductor region

[0108] A 0.1M gallium bromide aqueous solution containing 10% hydrobromic acid and 8% tin bromide (by volume) was used as the raw material solution. The film deposition temperature was set to 580°C, and the film deposition time was set to 5 minutes. Except for the steps described above, all other steps were the same as in step 1., and an n+ type semiconductor film was deposited on the p-type semiconductor layer obtained in step 1. When the phase of the resulting film was identified using XRD diffraction, the film was determined to be α-Ga₂O₃.

[0109] 3. Formation of insulating film and electrodes

[0110] The n+ type semiconductor layer (between 1a and 1b) corresponding to the gate region is etched with phosphoric acid and further treated with phosphoric acid to form an oxide film containing at least phosphorus on the semiconductor film. Then, a SiO2 film is formed by sputtering. Additionally, photolithography, etching, electron beam evaporation, and other processes are performed. Figure 2 As shown, the MOSFET was fabricated. Furthermore, Ti was used for both electrodes. Additionally, regarding the obtained MOSFET, for reference only, a photograph viewed from above is shown. Figure 3 middle.

[0111] (evaluate)

[0112] IV measurements were performed on the obtained MOSFETs. The IV measurement results are shown in... Figure 4 From Figure 4 It can be clearly seen that a reverse channel region is formed, and the gallium oxide semiconductor MOSFET functions well as a transistor, which is the first time this has been empirically demonstrated in the world. Furthermore, the gate threshold voltage derived from the obtained IV characteristics is 7.9V.

[0113] In section 3 above, SIMS measurements were performed to confirm whether an oxide film containing at least phosphorus was formed between the p-type semiconductor layer and the gate insulating film (SiO2 film). The SIMS measurement results are shown in... Figure 5 .like Figure 5 As shown, a phosphorus-containing oxide film is formed between the p-type semiconductor layer and the gate insulating film, which can effectively prevent hydrogen from diffusing from the gate insulating film to the p-type semiconductor layer.

[0114] Industrial availability

[0115] The semiconductor device of the present invention can be used in various fields, such as semiconductors (e.g., compound semiconductor electronic components), electronic components / electromechanical components, optical / electrophotographic related devices, industrial components, etc., but is particularly suitable for power devices.

[0116] [Symbol Explanation]

[0117] 1a First semiconductor region

[0118] 1b Second Semiconductor Region

[0119] 2 oxide semiconductor film

[0120] 2a Reverse Channel Region

[0121] 2b oxide film

[0122] The second surface of 2c oxide semiconductor film

[0123] 3 metal oxide layers

[0124] 4a insulating film

[0125] 4b insulating film

[0126] 5a Third electrode

[0127] 5b First Electrode

[0128] 5c second electrode

[0129] 6 Third Semiconductor Region

[0130] 9 substrates

[0131] 19 Film Forming Device

[0132] 20 substrates

[0133] 22a Carrier Gas Source

[0134] 22b Carrier Gas (Dilution) Source

[0135] Flow regulating valve of 23a carrier air source

[0136] Flow control valve for 23b carrier gas (dilution) source

[0137] 24 Fog Sources

[0138] 24a raw material solution

[0139] 25 containers

[0140] 25a water

[0141] 26 ultrasonic transducers

[0142] 27 Supply Pipe

[0143] 28 hot plate

[0144] 29 exhaust ports

[0145] 50b first electrode contact surface

[0146] 100 Semiconductor Devices

[0147] 170 power system

[0148] 171 Power Supply Unit

[0149] 172 Power Supply Unit

[0150] 173 control circuit

[0151] 180 system equipment

[0152] 181 Electronic Circuits

[0153] 182 power system

[0154] 192 inverter

[0155] 193 Transformer

[0156] 194 MOSFET

[0157] 195 DCL

[0158] 196 PWM control circuit

[0159] 197 Voltage Comparator

[0160] 600 Semiconductor Devices

Claims

1. A semiconductor device, characterized in that, It is a normally closed semiconductor device, comprising an oxide semiconductor film having a corundum structure and containing gallium oxide, or the oxide semiconductor film containing gallium oxide or a mixture thereof as the main component. The oxide semiconductor film contains p-type dopants. The threshold voltage of the semiconductor device is above 3V. The atomic ratio of gallium in the metal element of the oxide semiconductor film is 0.5 or higher.

2. The semiconductor device according to claim 1, wherein, The oxide semiconductor film contains α-Ga2O3 or a mixture thereof as the main component.

3. The semiconductor device according to claim 1, wherein, The semiconductor device is a MOSFET, and the threshold voltage is a gate threshold voltage.

4. The semiconductor device according to claim 3, wherein, An oxide film is disposed on the oxide semiconductor film, and a gate electrode is disposed on the oxide film via a gate insulating film.

5. The semiconductor device according to claim 3, wherein, The oxide semiconductor film includes a reverse channel region. A gate electrode is disposed on the reverse channel region via a gate insulating film, and a hydrogen diffusion prevention film is formed between the reverse channel region and the gate insulating film. The hydrogen diffusion prevention membrane is composed of an oxide film containing at least one element from Group 15 of the periodic table.

6. The semiconductor device according to claim 5, wherein, The element in question is phosphorus.

7. The semiconductor device according to claim 5 or 6, wherein, The reverse channel region is a p-type semiconductor layer.

8. The semiconductor device according to any one of claims 1 to 6, wherein, The threshold voltage is above 7V.

9. The semiconductor device according to any one of claims 1 to 6, wherein, It is a power device.

10. A semiconductor system comprising a semiconductor device, wherein, The semiconductor device is the semiconductor device according to any one of claims 1 to 9.

11. A normally closed semiconductor device comprising an oxide semiconductor film containing crystals, said crystals comprising gallium oxide having a corundum structure, wherein, The oxide semiconductor film includes a reverse channel region that reverses to n-type when a voltage is applied, the oxide semiconductor film includes a p-type dopant, the normally closed semiconductor device has a threshold voltage of 3V or higher, and the atomic ratio of gallium in the metal element of the oxide semiconductor film is 0.5 or higher.

12. The semiconductor device according to claim 11, wherein, The semiconductor device is a MOSFET, the threshold voltage is a gate threshold voltage, the oxide semiconductor film includes a reverse channel region, a gate electrode is disposed on the reverse channel region via a gate insulating film, and an oxide film is formed between the reverse channel region and the gate insulating film.

13. A normally closed semiconductor device comprising an oxide semiconductor film containing crystals, said crystals comprising gallium oxide having a corundum structure, wherein, The oxide semiconductor film includes Mg, H, Li, Na, K, Rb, Cs, Fr, Be, Ca, Sr, Ba, Ra, Mn, Fe, Co, Ni, Pd, Cu, Ag, Au, Zn, Cd, Hg, Tl, Pb, N, or P, or two or more of these elements as p-type dopants. The normally closed semiconductor device has a threshold voltage of 3V or higher, and the atomic ratio of gallium in the metal elements of the oxide semiconductor film is 0.5 or higher.

14. The normally closed semiconductor device according to any one of claims 10 to 13, wherein, It crystallizes into a mixed crystal.

15. The semiconductor device according to claim 13, wherein, The semiconductor device is a MOSFET, the threshold voltage is the gate threshold voltage, an oxide film is disposed on the oxide semiconductor film, and a gate electrode is disposed on the oxide film via a gate insulating film.

16. The normally closed semiconductor device according to claim 11, wherein, A gate electrode is disposed on the reverse channel region via a gate insulating film, and a hydrogen diffusion prevention film is formed between the reverse channel region and the gate insulating film. The hydrogen diffusion prevention membrane is composed of an oxide film containing at least one element from Group 15 of the periodic table.

17. The normally closed semiconductor device according to claim 13, wherein, The oxide semiconductor film includes a reverse channel region. A gate electrode is disposed on the reverse channel region via a gate insulating film, and a hydrogen diffusion prevention film is formed between the reverse channel region and the gate insulating film. The hydrogen diffusion prevention membrane is composed of an oxide film containing at least one element from Group 15 of the periodic table.

18. The normally closed semiconductor device according to claim 16 or 17, wherein, The element in question is phosphorus.

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