Semiconductor Device

Abstract

Provided is a low-loss semiconductor device that is particularly useful for power devices, in which a leakage current is suppressed. Provided is a semiconductor device comprising at least a semiconductor layer, which contains an oxide semiconductor having a corundum structure as a main component, and a Schottky electrode, which includes a first electrode layer and a second electrode layer having a higher conductivity than the first electrode layer, wherein the outer end of the second electrode layer is electrically connected to the semiconductor layer via the first electrode layer, and the outer end of the first electrode layer is located outside the outer end of the electrically connected region of the second electrode layer that is electrically connected.

Description

[Technical field]

[0001] The present invention relates to a semiconductor device useful as a power device or the like. [Background technology]

[0002] Gallium oxide (Ga2O3) is a transparent semiconductor with a wide band gap of 4.8-5.3 eV at room temperature, which absorbs very little visible or ultraviolet light. Therefore, it is a promising material for use in optoelectronic devices and transparent electronics, particularly those operating in the deep ultraviolet region, and in recent years, photodetectors, light-emitting diodes (LEDs), and transistors based on Ga2O3 have been developed (see Non-Patent Document 1).

[0003] Gallium oxide (Ga2O3) has five crystal structures: α, β, γ, σ, and ε, and generally the most stable structure is β-Ga2O3. However, since β-Ga2O3 has a β-gallium structure, it is different from the crystal systems generally used in electronic materials and is not necessarily suitable for use in semiconductor devices. In addition, the growth of a β-Ga2O3 thin film requires a high substrate temperature and a high degree of vacuum, which increases the manufacturing cost. As described in Non-Patent Document 2, in β-Ga2O3, 19 / cm 3 Even a dopant (Si) of 1000 or more ions cannot be used as a donor unless it is annealed at high temperatures of 800°C to 1100°C after ion implantation. On the other hand, α-Ga2O3 has the same crystal structure as the widely used sapphire substrate, making it suitable for use in optical and electronic devices. Furthermore, since it has a wider band gap than β-Ga2O3, it is particularly useful in power devices. For these reasons, semiconductor devices using α-Ga2O3 as a semiconductor are eagerly awaited.

[0004] Patent Documents 1 and 2 describe semiconductor devices that use β-Ga2O3 as a semiconductor and, as electrodes that provide suitable ohmic characteristics, use two layers consisting of a Ti layer and an Au layer, three layers consisting of a Ti layer, an Al layer, and an Au layer, or four layers consisting of a Ti layer, an Al layer, a Ni layer, and an Au layer. Furthermore, Patent Document 3 describes a semiconductor device that uses β-Ga2O3 as a semiconductor and uses either Au, Pt, or a laminate of Ni and Au as an electrode that provides Schottky characteristics compatible with the semiconductor. However, when the electrodes described in Patent Documents 1 to 3 are applied to a semiconductor device using α-Ga2O3 as a semiconductor, there are problems such as the electrodes not functioning as Schottky electrodes or ohmic electrodes, the electrodes not being attached to the film, the semiconductor properties being impaired, etc. Furthermore, the electrode configurations described in Patent Documents 1 to 3 have problems such as leakage current occurring from the electrode end, and it has not been possible to obtain a semiconductor device that is satisfactory for practical use.

[0005] Patent Document 4 discusses a semiconductor device using α-Ga2O3 as a semiconductor and an electrode containing at least one metal selected from Groups 4 to 9 of the periodic table as a Schottky electrode. Patent Document 4 relates to a patent application filed by the present applicant. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] JP 2005-260101 A [Patent Document 2] JP 2009-81468 A [Patent Document 3] JP 2013-12760 A [Patent Document 4] JP 2018-60992 A [Non-patent literature]

[0007] [Non-Patent Document 1] Jun Liang Zhao et al, “UV and Visible Electroluminescence From a Sn:Ga2O3 / n+-Si Heterojunction by Metal-Organic Chemical Vapor Deposition”, IEEE TRANSACTIONS ON ELECTRON DEVICES, VOL. 58, NO.5 MAY 2011 [Non-Patent Document 2] Kohei Sasaki et al, “Si-Ion Implantation Doping in β-Ga2O3 and Its Application to Fabrication of Low-Resistance Ohmic Contacts”, Applied Physics Express 6 (2013) 086502 Summary of the Invention [Problem to be solved by the invention]

[0008] An object of the present invention is to provide a low-loss semiconductor device in which leakage current is suppressed. [Means for solving the problem]

[0009] As a result of intensive research into achieving the above-mentioned object, the present inventors have found that a semiconductor device comprising at least a semiconductor layer containing as a main component an oxide semiconductor having a corundum structure and a Schottky electrode, the Schottky electrode including a first electrode layer and a second electrode layer having a higher conductivity than the first electrode layer, wherein an outer end of the second electrode layer is electrically connected to the semiconductor layer via the first electrode layer, and the outer end of the first electrode layer is located outside the outer end of an electrical connection region of the electrically connected second electrode layer, can satisfactorily extend a depletion layer in the semiconductor layer and has a low loss with suppressed leakage current, and have found that the semiconductor device thus obtained can solve the above-mentioned conventional problems in one fell swoop. After obtaining the above findings, the inventors conducted further studies and completed the present invention.

[0010] That is, the present invention relates to the following inventions. [1] A semiconductor device comprising at least a semiconductor layer containing as a main component an oxide semiconductor having a corundum structure and a Schottky electrode, the Schottky electrode including a first electrode layer and a second electrode layer having a higher electrical conductivity than the first electrode layer, wherein an outer end of the second electrode layer is electrically connected to the semiconductor layer via the first electrode layer, and the outer end of the first electrode layer is located outside an outer end of an electrical connection region of the second electrode layer to which it is electrically connected. [2] The semiconductor device according to [1], wherein the oxide semiconductor contains at least one metal selected from the group consisting of aluminum, indium and gallium. [3] The semiconductor device according to [1] or [2], wherein the oxide semiconductor contains at least gallium. [4] The semiconductor device according to any one of [1] to [3] above, wherein the first electrode layer contains at least one metal selected from Groups 4 to 10 of the periodic table. [5] The semiconductor device according to any one of [1] to [4] above, wherein the first electrode layer contains at least one metal selected from Groups 4 and 9 of the periodic table. [6] The semiconductor device according to any one of [1] to [5] above, wherein the first electrode layer is made up of two or more layers having different compositions. [7] The semiconductor device according to any one of [1] to [6], wherein at least a portion of the portion of the first electrode layer that protrudes outward beyond the outer end of the second electrode layer has a tapered region in which the film thickness decreases toward the outside of the semiconductor device. [8] The semiconductor device according to any one of [1] to [7] above, wherein the second electrode layer contains at least one metal selected from silver, copper, gold and aluminum. [9] The semiconductor device according to any one of the above [1] to [8], wherein the first electrode layer is thinner than the second electrode layer.

[10] The semiconductor device according to any one of [1] to [9], further comprising a field insulating film, an outer end of the first electrode layer being located on the field insulating film.

[11] The semiconductor device according to any one of [1] to

[10] above, which is a Schottky barrier diode.

[12] The semiconductor device according to any one of [1] to

[11] above, which is a power device.

[13] A semiconductor system including a semiconductor device, the semiconductor device being the semiconductor device described in any one of [1] to

[12] above. Effect of the Invention

[0011] The semiconductor device of the present invention has a suppressed leakage current and low loss. [Brief description of the drawings]

[0012] [Figure 1] 1 is a diagram showing a schematic diagram of a preferred embodiment of a Schottky barrier diode (SBD) of the present invention. [Diagram 2] 1 is a diagram showing a schematic diagram of a preferred embodiment of a Schottky barrier diode (SBD) of the present invention. [Diagram 3] 1A to 1C are diagrams illustrating a preferred manufacturing process for a Schottky barrier diode (SBD) according to the present invention. [Figure 4] 1 is a diagram showing a schematic diagram of a preferred embodiment of a Schottky barrier diode (SBD) of the present invention. [Diagram 5] FIG. 1 is a configuration diagram of a mist CVD apparatus used in an embodiment of the present invention. [Figure 6] FIG. 1 is a diagram illustrating a preferred example of a power supply system. [Figure 7] FIG. 1 is a diagram illustrating a preferred example of a system device. [Figure 8] FIG. 1 is a diagram illustrating a preferred example of a power supply circuit diagram of a power supply device. [Figure 9] 1 is a diagram showing the results of IV measurement in an example and a comparative example, in which the vertical axis indicates current and the horizontal axis indicates voltage. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0013] The semiconductor device of the present invention is a semiconductor device including at least a semiconductor layer containing an oxide semiconductor having a corundum structure as a main component and a Schottky electrode, the Schottky electrode including a first electrode layer and a second electrode layer having a higher conductivity than the first electrode layer, the outer end of the second electrode layer is electrically connected to the semiconductor layer through the first electrode layer, and the outer end of the first electrode layer is located outside the outer end of the electrical connection region of the second electrode layer to which it is electrically connected. Here, "electrically connected" may be in direct contact or in contact through a conductive film or a semiconductor film. The outer end of the electrical connection region may be the outer end of the second electrode layer, or may be the outer end of the region in the second electrode layer that is electrically connected to the first electrode layer. Hereinafter, the "outer end of the second electrode layer" will be described as an example of the "outer end of the electrical connection region", but the present invention is not limited to these examples.

[0014] The semiconductor layer is not particularly limited as long as it contains an oxide semiconductor having a corundum structure as a main component. Examples of the oxide semiconductor having a corundum structure include metal oxides containing one or more metals selected from aluminum, gallium, indium, iron, chromium, vanadium, titanium, rhodium, nickel, cobalt, and iridium. In the present invention, the oxide semiconductor preferably contains at least one metal selected from aluminum, indium, and gallium, more preferably contains at least gallium, and is most preferably α-Ga2O3 or a mixed crystal thereof. Note that the term "main component" means that the oxide semiconductor having the corundum structure is preferably contained in an atomic ratio of 50% or more, more preferably 70% or more, and even more preferably 90% or more of the total components of the semiconductor layer, and may be 100%. The thickness of the semiconductor layer is not particularly limited, and may be 1 μm or less, or may be 1 μm or more, but in the present invention, it is preferably 10 μm or more. The surface area of ​​the semiconductor film is not particularly limited, but is preferably 1 mm 2 May be more than 1mm 2 May be less than 10mm 2 ~300cm 2 Preferably, 100 mm 2 ~100cm 2 It is more preferable that the semiconductor layer is a multilayer film including at least a first semiconductor layer and a second semiconductor layer. When a Schottky electrode is provided on the first semiconductor layer, the semiconductor layer is preferably a multilayer film in which the carrier density of the first semiconductor layer is smaller than the carrier density of the second semiconductor layer. In this case, the second semiconductor layer usually contains a dopant, and the carrier density of the semiconductor layer can be appropriately set by adjusting the doping amount.

[0015] The semiconductor layer preferably contains a dopant. The dopant is not particularly limited and may be a known one. Examples of the dopant include n-type dopants such as tin, germanium, silicon, titanium, zirconium, vanadium, or niobium, or p-type dopants such as magnesium, calcium, or zinc. In the present invention, the n-type dopant is preferably Sn, Ge, or Si. The content of the dopant in the composition of the semiconductor layer is preferably 0.00001 atomic % or more, more preferably 0.00001 atomic % to 20 atomic %, and most preferably 0.00001 atomic % to 10 atomic %. More specifically, the concentration of the dopant is usually about 1×10 16 / cm 3 ~1×10 22 / cm 3 Alternatively, the concentration of the dopant may be, for example, about 1×10 17 / cm 3 In accordance with the present invention, the dopant may be present in a concentration as low as about 1×10 20 / cm 3 In the present invention, the concentration of 1×10 17 / cm 3 It is preferable that the carrier concentration is equal to or higher than this.

[0016] The semiconductor layer may be formed by using a known means. Examples of the means for forming the semiconductor layer include a CVD method, an MOCVD method, an MOVPE method, a mist CVD method, a mist epitaxy method, an MBE method, an HVPE method, a pulse growth method, and an ALD method. In the present invention, the means for forming the semiconductor layer is preferably a mist CVD method or a mist epitaxy method. In the mist CVD method or the mist epitaxy method, for example, a mist CVD apparatus shown in FIG. 5 is used to atomize a raw material solution (atomization step), suspend the droplets, and after atomization, the obtained atomized droplets are transported to a substrate by a carrier gas (transport step), and then the atomized droplets are thermally reacted near the substrate to laminate a semiconductor film containing a crystalline oxide semiconductor as a main component on the substrate (film formation step), thereby forming the semiconductor layer.

[0017] (Atomization process) In the atomization step, the raw solution is atomized. The atomization means for the raw solution is not particularly limited as long as it can atomize the raw solution, and may be a known means, but in the present invention, an atomization means using ultrasonic waves is preferable. The atomized droplets obtained using ultrasonic waves have an initial velocity of zero and are preferably suspended in the air, and are very suitable because they are not sprayed like a spray, but are mist that can be suspended in space and transported as a gas, and therefore are not damaged by collision energy. The droplet size is not particularly limited, and may be droplets of about several mm, but is preferably 50 μm or less, and more preferably 100 nm to 10 μm.

[0018] (Raw material solution) The raw material solution is not particularly limited as long as it can be atomized or turned into droplets and contains a raw material capable of forming a semiconductor film, and may be an inorganic material or an organic material. In the present invention, the raw material is preferably a metal or a metal compound, and more preferably contains one or more metals selected from aluminum, gallium, indium, iron, chromium, vanadium, titanium, rhodium, nickel, cobalt, and iridium.

[0019] In the present invention, the raw material solution can be suitably used in which the metal is dissolved or dispersed in an organic solvent or water in the form of a complex or salt. Examples of the complex include acetylacetonate complexes, carbonyl complexes, ammine complexes, and hydride complexes. Examples of the salt include organic metal salts (e.g., metal acetates, metal oxalates, and metal citrates), metal sulfides, metal nitrates, metal phosphates, and metal halides (e.g., metal chlorides, metal bromides, and metal iodides).

[0020] In addition, it is preferable to mix additives such as hydrohalogenated acid and oxidizing agents into the raw material solution. Examples of the hydrohalogenated acid include hydrobromic acid, hydrochloric acid, and hydroiodic acid. Among them, hydrobromic acid and hydroiodic acid are preferable because they can more efficiently suppress the generation of abnormal grains. Examples of the oxidizing agent include peroxides such as hydrogen peroxide (H2O2), sodium peroxide (Na2O2), barium peroxide (BaO2), and benzoyl peroxide (C6H5CO)2O2, hypochlorous acid (HClO), perchloric acid, nitric acid, ozone water, and organic peroxides such as peracetic acid and nitrobenzene.

[0021] The raw material solution may contain a dopant. By adding a dopant to the raw material solution, doping can be performed well. The dopant is not particularly limited as long as it does not impede the object of the present invention. Examples of the dopant include n-type dopants such as tin, germanium, silicon, titanium, zirconium, vanadium, or niobium, and p-type dopants such as Mg, H, Li, Na, K, Rb, Cs, Fr, Be, Ca, Sr, Ba, Ra, Mn, Fe, Co, Ni, Pd, Cu, Ag, Au, Zn, Cd, Hg, Ti, Pb, N, or P. The content of the dopant is appropriately set by using a calibration curve showing the relationship between the concentration of the dopant in the raw material and the desired carrier density.

[0022] The solvent of the raw material solution is not particularly limited, and may be an inorganic solvent such as water, an organic solvent such as alcohol, or a mixed solvent of an inorganic solvent and an organic solvent. In the present invention, the solvent preferably contains water, and more preferably is water or a mixed solvent of water and alcohol.

[0023] (Transportation process) In the transport step, the atomized droplets are transported into the film-forming chamber by a carrier gas. The carrier gas is not particularly limited as long as it does not impede the object of the present invention, and suitable examples include inert gases such as oxygen, ozone, nitrogen, and argon, and reducing gases such as hydrogen gas and forming gas. The type of carrier gas may be one type, but may be two or more types, and a dilution gas with a reduced flow rate (for example, a 10-fold dilution gas, etc.) may be further used as a second carrier gas. The number of supply points of the carrier gas may be not only one but also two or more. The flow rate of the carrier gas is not particularly limited, but is preferably 0.01 to 20 L / min, and more preferably 1 to 10 L / min. In the case of a dilution gas, the flow rate of the dilution gas is preferably 0.001 to 2 L / min, and more preferably 0.1 to 1 L / min.

[0024] (Film forming process) In the film-forming step, the mist droplets are thermally reacted in the vicinity of the substrate to form the semiconductor film on the substrate. The thermal reaction may be performed as long as the mist droplets react with heat, and the reaction conditions are not particularly limited as long as the object of the present invention is not hindered. In this step, the thermal reaction is usually performed at a temperature equal to or higher than the evaporation temperature of the solvent, but is preferably not too high (for example, 1000°C) or lower, more preferably 650°C or lower, and most preferably 300°C to 650°C. In addition, the thermal reaction may be performed under any atmosphere, such as a vacuum, a non-oxygen atmosphere (for example, an inert gas atmosphere), a reducing gas atmosphere, or an oxygen atmosphere, as long as the object of the present invention is not hindered, but is preferably performed under an inert gas atmosphere or an oxygen atmosphere. In addition, the thermal reaction may be performed under any condition, such as atmospheric pressure, pressurized, or reduced pressure, but in the present invention, it is preferable to perform the thermal reaction under atmospheric pressure. The film thickness can be set by adjusting the film-forming time.

[0025] (Base) The substrate is not particularly limited as long as it can support the semiconductor film. The material of the substrate is not particularly limited as long as it does not impede the object of the present invention, and may be a known substrate, an organic compound, or an inorganic compound. The substrate may have any shape, and is effective for any shape, such as a plate shape such as a flat plate or a disk, a fiber shape, a rod shape, a column shape, a prism shape, a tube shape, a spiral shape, a sphere shape, a ring shape, etc., but in the present invention, a substrate is preferred. The thickness of the substrate is not particularly limited in the present invention.

[0026] The substrate is not particularly limited as long as it is plate-shaped and serves as a support for the semiconductor film. It may be an insulating substrate, a semiconductor substrate, a metal substrate, or a conductive substrate, but the substrate is preferably an insulating substrate, and is also preferably a substrate having a metal film on its surface. Examples of the substrate include a substrate containing a substrate material having a corundum structure as a main component, a substrate containing a substrate material having a β-gallium structure as a main component, and a substrate containing a substrate material having a hexagonal crystal structure as a main component. Here, the term "main component" means that the substrate material having the specific crystal structure is preferably contained in an atomic ratio of 50% or more, more preferably 70% or more, and even more preferably 90% or more of the total components of the substrate material, and may be 100%.

[0027] The substrate material is not particularly limited, and may be any known material, so long as it does not impede the object of the present invention. Suitable examples of the substrate material having the corundum structure include α-Al2O3 (sapphire substrate) or α-Ga2O3, and more suitable examples include a-plane sapphire substrate, m-plane sapphire substrate, r-plane sapphire substrate, c-plane sapphire substrate, and α-type gallium oxide substrate (a-plane, m-plane, or r-plane). Examples of the base substrate mainly made of a substrate material having a β-gallium structure include a β-Ga2O3 substrate, or a mixed crystal substrate containing Ga2O3 and Al2O3, with Al2O3 being more than 0 wt% and 60 wt% or less. Examples of the base substrate mainly made of a substrate material having a hexagonal structure include a SiC substrate, a ZnO substrate, and a GaN substrate.

[0028] In the present invention, an annealing treatment may be performed after the film formation step. The annealing temperature is not particularly limited as long as it does not impede the object of the present invention, and is usually 300°C to 650°C, and preferably 350°C to 550°C. The annealing time is usually 1 minute to 48 hours, preferably 10 minutes to 24 hours, and more preferably 30 minutes to 12 hours. The annealing may be performed in any atmosphere as long as it does not impede the object of the present invention. It may be a non-oxygen atmosphere or an oxygen atmosphere. Examples of the non-oxygen atmosphere include an inert gas atmosphere (e.g., a nitrogen atmosphere) or a reducing gas atmosphere, and in the present invention, an inert gas atmosphere is preferable, and a nitrogen atmosphere is more preferable.

[0029] In the present invention, the semiconductor film may be provided directly on the substrate, or may be provided via another layer such as a stress relaxation layer (e.g., a buffer layer, an ELO layer, etc.), a peeling sacrificial layer, etc. The means for forming each layer is not particularly limited and may be a known means, but in the present invention, a mist CVD method is preferred.

[0030] In the present invention, the semiconductor film may be used as the semiconductor layer in a semiconductor device after being peeled off from the base or the like by a known means, or may be used as the semiconductor layer in a semiconductor device as it is.

[0031] The first electrode layer is not particularly limited as long as it has conductivity and has a lower conductivity than the second electrode layer, as long as it does not impede the object of the present invention. The material of the first electrode layer may be a conductive inorganic material or a conductive organic material. In the present invention, the material of the first electrode is preferably a metal. The metal is preferably at least one metal selected from Groups 4 to 10 of the periodic table. Examples of metals in Group 4 of the periodic table include titanium (Ti), zirconium (Zr), and hafnium (Hf). Examples of metals in Group 5 of the periodic table include vanadium (V), niobium (Nb), and tantalum (Ta). Examples of metals in Group 6 of the periodic table include chromium (Cr), molybdenum (Mo), and tungsten (W). Examples of metals in Group 7 of the periodic table include manganese (Mn), technetium (Tc), and rhenium (Re). Examples of metals in Group 8 of the periodic table include 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). In the present invention, the first electrode layer preferably contains at least one metal selected from Groups 4 and 9 of the periodic table, and more preferably contains a metal in Group 9 of the periodic table. The thickness of the first electrode layer is not particularly limited, but is preferably 0.1 nm to 10 μm, more preferably 5 nm to 500 nm, and most preferably 10 nm to 200 nm. In the present invention, the thickness of the first electrode layer is preferably thinner than the thickness of the second electrode layer. In the present invention, the first electrode layer is preferably composed of two or more layers having different compositions, which not only provides a semiconductor device with better Schottky characteristics but also provides a better effect of suppressing leakage current.

[0032] The second electrode layer is not particularly limited as long as it is conductive and has a higher conductivity than the first electrode layer, as long as it does not impede the object of the present invention. The material of the second electrode layer may be a conductive inorganic material or a conductive organic material. In the present invention, the material of the second electrode is preferably a metal. In the present invention, the material of the second electrode is preferably a metal. The metal is preferably at least one metal selected from Groups 8 to 13 of the periodic table. Examples of the metal of Groups 8 to 10 of the periodic table include the metals exemplified as the metals of Groups 8 to 10 of the periodic table in the description of the first electrode layer. Examples of the metal of Group 11 of the periodic table include copper (Cu), silver (Ag), and gold (Au). Examples of the metal of Group 12 of the periodic table include zinc (ZN) and cadmium (Cd). Examples of metals in Group 13 of the periodic table include aluminum (Al), gallium (Ga), and indium (In). In the present invention, the second electrode layer preferably contains at least one metal selected from metals in Groups 11 and 13 of the periodic table, and more preferably contains at least one metal selected from silver, copper, gold, and aluminum. The thickness of the second electrode layer is not particularly limited, but is preferably 1 nm to 500 μm, more preferably 10 nm to 100 μm, and most preferably 0.5 μm to 10 μm.

[0033] The means for forming the first electrode layer or the second electrode layer is not particularly limited and may be a known means. Specific examples of the means for forming the first electrode layer or the second electrode layer include a dry method and a wet method. Examples of the dry method include sputtering, vacuum deposition, and CVD. Examples of the wet method include screen printing and die coating.

[0034] The outer end of the first electrode layer is not particularly limited as long as it is located outside the outer end of the second electrode layer, but in the present invention, it is preferable that the distance between the outer end of the first electrode layer and the outer end of the second electrode layer is 1 μm or more because it can further suppress the leakage current. In addition, in the present invention, it is also preferable that at least a part of the part of the first electrode layer that protrudes outward from the outer end of the second electrode layer (hereinafter also referred to as the "protruding part") has a tapered region in which the film thickness decreases toward the outside of the semiconductor device, because the pressure resistance of the semiconductor device can be improved. In addition, by combining such a preferable electrode configuration with the above-mentioned preferable constituent material of the semiconductor layer, a semiconductor device with a lower loss in which the leakage current is more effectively suppressed can be obtained. Note that the reduction rate of the film thickness in the tapered region is not particularly limited, and for convenience, if it can be said that the film thickness decreases toward the outside of the semiconductor device from any two points, the inner film thickness and the outer film thickness, it may be the tapered region.

[0035] In the present invention, it is also preferable that the semiconductor layer further has a field insulating film. In this case, it is more preferable that the outer end of the first electrode layer is located on the field insulating film, since the depletion layer is more effectively formed in the semiconductor layer. The material of the field insulating film is not particularly limited as long as it does not impede the object of the present invention, and may be a known material. Examples of the field insulating film include SiO2 film, polysilicon film, phosphorus-added SiO2 film (PSG film), boron-added SiO2 film, phosphorus-boron-added SiO2 film (BPSG film), etc. Examples of the means for forming the field insulating film include CVD method, atmospheric pressure CVD method, plasma CVD method, mist CVD method, thermal oxidation method, etc. In the present invention, it is preferable that the means for forming the field insulating film is mist CVD method or atmospheric pressure CVD method.

[0036] Preferred embodiments of the present invention will now be described in more detail with reference to the drawings, but the present invention is not limited to these embodiments.

[0037] FIG. 1 shows a main part of a Schottky barrier diode (SBD) according to a preferred embodiment of the present invention. The SBD in FIG. 1 includes an ohmic electrode 102, an n-type semiconductor layer 101a, an n+ type semiconductor layer 101b, and a Schottky electrode 103. The Schottky electrode 103 is composed of a metal layer 103a, a metal layer 103b, and a metal layer 103c. In the semiconductor device in FIG. 1, the outer end of the metal layer 103b and / or the metal layer 103c as the first electrode layer is located outside the outer end of the metal layer 103a as the second electrode layer, so that the leakage current can be suppressed more effectively. Furthermore, the part of the metal layer 103b and / or the metal layer 103c that protrudes outward from the outer end of the metal layer 103a has a tapered region in which the film thickness decreases toward the outside of the semiconductor device, so that the device has a configuration with better voltage resistance.

[0038] Examples of the material of the metal layer 103a include the metals exemplified above as the material of the second electrode layer. Examples of the material of the metal layer 103b and the metal layer 103c include the metals exemplified above as the material of the first electrode layer. The means for forming each layer in FIG. 1 is not particularly limited as long as it does not impede the object of the present invention, and may be a known means. For example, a means for forming a film by a vacuum deposition method, a CVD method, a sputtering method, or various coating techniques, followed by patterning by a photolithography method, or a means for directly patterning by a printing technique, etc., may be used.

[0039] Fig. 2 shows the main part of a Schottky barrier diode (SBD) which is another preferred embodiment of the present invention. The SBD in Fig. 2 differs from the SBD in Fig. 1 in that it further includes a field insulating film 104 and the outer ends of metal layer 103b and / or metal layer 103c are located on field insulating film 104. With this configuration, the breakdown voltage characteristics of the semiconductor device can be improved.

[0040] 2 may be formed by any known means without particular limitation as long as it does not impede the object of the present invention, for example, by forming a film by vacuum deposition, CVD, sputtering, or various coating techniques, followed by patterning by photolithography, or by directly patterning using a printing technique.

[0041] The present invention will now be described in more detail with reference to a preferred example of manufacturing the semiconductor device shown in FIG.

[0042] FIG. 3(a) shows a laminate in which an n+ type semiconductor layer 101b and an n- type semiconductor layer 101a are formed in this order on an ohmic electrode 102, and a field insulating film 104 is formed on the n- type semiconductor layer. The means for forming the field insulating film 104 is not particularly limited as long as it does not impede the object of the present invention. Examples of the means for forming the field insulating film 104 include a sputtering method, a vacuum deposition method, a coating method, a CVD method, an atmospheric pressure CVD method, a plasma CVD method, a mist CVD method, and a thermal oxidation method. In the present invention, the mist CVD method or the atmospheric pressure CVD method is preferable. In addition, an opening for the first electrode layer is formed in the field insulating film 4 so that at least a part of the n- type semiconductor layer 101a is exposed. The means for forming the opening is not particularly limited and may be a known etching means. In addition, a tapered portion in which the film thickness decreases from the outside to the inside of the semiconductor device is formed in the field insulating film 104. The means for forming the tapered portion is not particularly limited as long as it does not impede the object of the present invention, and may be a known means.

[0043] Next, metal layers 103a, 103b, and 103c are formed on the laminate of FIG. 3(a) using the dry method or the wet method, to obtain the laminate of FIG. 3(b). After that, excess portions of the metal layers 103a, 103b, and 103c are removed using a known etching technique to obtain the laminate of FIG. 3(c). In this etching, for example, it is preferable to form the outer end of the first electrode to have a tapered shape by etching while retracting the resist. The semiconductor device obtained in this manner has a configuration that suppresses leakage current and has excellent pressure resistance.

[0044] FIG. 4 shows a main part of a Schottky barrier diode (SBD) according to another preferred embodiment of the present invention. The SBD in FIG. 4 differs from the SBD in FIG. 2 in that a protective metal layer 105 is further provided around the outer end of the first metal layer. The protective metal layer 105 is provided so as to cover at least the end of the field insulating film 104. The material of the protective metal layer is not particularly limited, and may be the same as the metals exemplified as the material of the metal layer. With this configuration, the metal layers 103a, 103b, and 103c can be formed more efficiently, and the breakdown voltage characteristics can be improved while the reliability of the semiconductor device can be improved.

[0045] The means for forming each layer in Fig. 4 is not particularly limited as long as it does not impede the object of the present invention, and may be any known means, such as a means for forming a film by a vacuum deposition method, a CVD method, a sputtering method, or various coating techniques, followed by patterning by a photolithography method, or a means for directly patterning by a printing technique.

[0046] The semiconductor device is particularly useful as a power device. Examples of the semiconductor device include diodes (e.g., PN diodes, Schottky barrier diodes, junction barrier Schottky diodes, etc.) and transistors (e.g., MOSFETs, MESFETs, etc.), among which diodes are preferred, and Schottky barrier diodes (SBDs) are more preferred.

[0047] In addition to the above, the semiconductor device of the present invention can be suitably used as a power module, inverter, or converter by using known means, and these semiconductor devices are also included in the present invention. The semiconductor device of the present invention can also be suitably used in, for example, a semiconductor system using a power supply device. The power supply device can be manufactured from or as the semiconductor device by connecting to a wiring pattern or the like using known means. FIG. 6 shows an example of a power supply system. FIG. 6 shows a power supply system using a plurality of the power supplies and a control circuit. The power supply system can be used in a system device in combination with an electronic circuit as shown in FIG. 7. FIG. 8 shows an example of a power supply circuit diagram of a power supply device. FIG. 8 shows a power supply circuit of a power supply device consisting of a power circuit and a control circuit, in which a DC voltage is switched at high frequency by an inverter (composed of MOSFETs: A to D) to convert it to AC, then insulated and transformed by a transformer, rectified by a rectifier MOSFET (A to B'), smoothed by a DCL (smoothing coils L1, L2) and a capacitor, and a DC voltage is output. At this time, a voltage comparator compares the output voltage with a reference voltage, and a PWM control circuit controls the inverter and rectifier MOSFET so as to obtain a desired output voltage. EXAMPLES

[0048] Examples of the present invention will be described below, but the present invention is not limited to these.

[0049] Example 1 1. Formation of n-type semiconductor layer 1-1. Film deposition equipment The mist CVD apparatus 1 used in this embodiment will be described with reference to FIG. 5. The mist CVD apparatus 1 includes a carrier gas source 2a for supplying a carrier gas, a flow rate control valve 3a for adjusting the flow rate of the carrier gas sent from the carrier gas source 2a, a carrier gas (dilution) source 2b for supplying a carrier gas (dilution), a flow rate control valve 3b for adjusting the flow rate of the carrier gas (dilution) sent from the carrier gas (dilution) source 2b, a mist source 4 for containing a raw material solution 4a, a container 5 for containing water 5a, an ultrasonic vibrator 6 attached to the bottom surface of the container 5, a film formation chamber 7, a supply pipe 9 connecting the mist source 4 to the film formation chamber 7, a hot plate 8 installed in the film formation chamber 7, and an exhaust port 11 for discharging mist, droplets, and exhaust gas after the thermal reaction. A substrate 10 is installed on the hot plate 8.

[0050] 1-2. Preparation of raw solution Tin bromide was mixed with a 0.1 M aqueous solution of gallium bromide to prepare an aqueous solution such that the atomic ratio of tin to gallium was 1:0.0008. At this time, hydrobromic acid was added to the aqueous solution so that the volume ratio was 20%. This was used as a raw material solution.

[0051] 1-3. Preparation for film deposition The raw material solution 4a obtained in 1-2 above was placed in the mist generating source 4. Next, as the substrate 10, an m-plane sapphire substrate with a non-doped α-Ga2O3 layer formed on the surface as a buffer layer was placed on the hot plate 8, and the hot plate 8 was operated to raise the temperature in the film formation chamber 7 to 470°C. Next, the flow rate control valves 3a and 3b were opened to supply carrier gas from the carrier gas supply sources 2a and 2b, which are carrier gas sources, into the film formation chamber 7, and the atmosphere in the film formation chamber 7 was sufficiently replaced with the carrier gas, and the flow rate of the carrier gas was adjusted to 1.2 L / min and the flow rate of the carrier gas (dilution) was adjusted to 1.0 L / min, respectively. Nitrogen was used as the carrier gas.

[0052] 1-4. Formation of crystalline oxide semiconductor film Next, the ultrasonic vibrator 6 was vibrated at 2.4 MHz, and the vibration was propagated to the raw material solution 4a through the water 5a, thereby atomizing the raw material solution 4a to generate mist 4b. This mist 4b was introduced into the film formation chamber 7 through the supply pipe 9 by the carrier gas, and the mist was thermally reacted in the film formation chamber 7 at 615°C under atmospheric pressure to form a film on the substrate 10. The film formation time was 6 hours.

[0053] 1-5.Evaluation When the phase of the film obtained in 1-4 above was identified using an XRD diffractometer, it was found to be α-Ga2O3.

[0054] 2. Formation of n+ type semiconductor layer As a raw material solution, tin bromide was mixed into a 0.1M aqueous solution of gallium bromide to prepare an aqueous solution with an atomic ratio of tin to gallium of 1:0.24, and a crystalline oxide semiconductor film was formed in the same manner as in 1 above, except that an aqueous solution containing 20% ​​hydrobromic acid by volume was used and the film formation time was set to 2 hours. The phase of the obtained film was identified using an XRD diffractometer, and the obtained film was found to be α-Ga2O3.

[0055] 3. Formation of Ohmic Electrodes A Ti layer and an Au layer were each laminated by sputtering on the n+ type semiconductor layer of the laminate obtained in the above step 2. The Ti layer had a thickness of 70 nm, and the Au layer had a thickness of 30 nm.

[0056] 4. Substrate removal A temporary wafer was temporarily bonded onto the ohmic electrode of the laminate obtained in the above step 3, and then the substrate 10 was polished using a grinder and a CMP device to remove the sapphire substrate and the buffer layer.

[0057] 5. Formation of insulating film A SiO2 film was formed by plasma CVD on the n-type semiconductor layer of the laminate obtained in the above step 4. After that, an opening was formed in the SiO2 film by etching so that a part of the n-type semiconductor layer was exposed.

[0058] 6. Formation of Schottky electrodes On the n-type semiconductor layer of the laminate obtained in 5. above, a Co film (thickness 100 nm), a Ti film (50 nm), and an Al film (thickness 5 μm) were formed by EB deposition, respectively, to form a Schottky electrode. Then, the Co film, the Ti film, and the Al film were removed by etching. When the outer end of the obtained Schottky electrode was observed by SEM, it was confirmed that the Ti film and the Co film protruded outward by about 10 μm at the periphery of the Al film, and that the outer ends of the Ti film and the Co film were located outside the outer end of the Al film. The outer ends of the Ti film and the Co film were in contact with the n-type semiconductor layer. The sheet resistance of the protruding Co film was 1.3 Ω.

[0059] Comparative Example 1 An SBD was fabricated in the same manner as in Example 1, except that the Schottky electrodes were formed so that the outer ends of the Al film, Co film, and Ti film were located on the SiO2 film (the outer end of the Al film as the second electrode layer was not electrically connected to the semiconductor layer) and the outer ends of the Al film, Ti film, and Co film were in approximately the same position.

[0060] Example 2 An SBD was fabricated in the same manner as in Example 1, except that the n-semiconductor layer was formed using a 0.1 M gallium bromide aqueous solution containing 10% hydrobromic acid by volume as the raw material solution, and the Schottky electrode was formed so that the Al film was electrically connected to the n-type semiconductor layer via the Co film and the Ti film, and the outer ends of the Co film and the Ti film were located on the SiO2 film. An IV measurement was performed on the obtained SBD, and it was found to have the same leakage current reduction effect as the SBD of Example 1.

[0061] (IV measurement) IV measurements were performed on the SBDs obtained in Example 1, Comparative Example 1, and Example 2. The results of Example 2 and Comparative Example 1 are shown in FIG. 9. As is clear from FIG. 9, the SBD of Example 2 has a significantly reduced leakage current compared to the SBD of Comparative Example 1. Furthermore, the SBD of Example 1 had the same leakage current suppression effect as the SBD of Example 2. [Industrial Applicability]

[0062] The semiconductor device of the present invention can be used in a wide variety of fields, including semiconductors (eg, compound semiconductor electronic devices), electronic components, electrical equipment components, optical and electrophotographic related devices, and industrial materials, but is particularly useful as a power device. [Explanation of symbols]

[0063] 1. Film forming equipment (mist CVD equipment) 2a Carrier gas source 2b Carrier gas (dilution) source 3a Flow control valve 3b Flow control valve 4. Mist Source 4a Raw material solution 4b Raw material fine particles 5 containers 5a water 6 Ultrasonic transducer 7 Deposition chamber 8. Hot Plate 9 Supply pipe 10 Substrate 101a n-type semiconductor layer 101b n+ type semiconductor layer 102 Ohmic electrode 103 Schottky electrode 103a Metal layer 103b Metal layer 103c metal layer 104 Insulating film (field insulating film) 105 Protective metal layer

Claims

1. 1. A semiconductor device comprising: at least a semiconductor layer containing as a main component an oxide semiconductor having a corundum structure; and a Schottky electrode, the Schottky electrode including a first electrode layer and a second electrode layer having a higher electrical conductivity than the first electrode layer, wherein an outer end of the second electrode layer is electrically connected to the semiconductor layer via the first electrode layer, and the outer end of the first electrode layer is located outside an outer end of an electrical connection region of the second electrode layer to which it is electrically connected.

2. 2. The semiconductor device according to claim 1, wherein the oxide semiconductor contains at least one metal selected from the group consisting of aluminum, indium, and gallium.

3. The semiconductor device according to claim 1 , wherein the oxide semiconductor contains at least gallium.

4. 4. The semiconductor device according to claim 1, wherein the first electrode layer contains at least one metal selected from Groups 4 to 10 of the periodic table.

5. 5. The semiconductor device according to claim 1, wherein the first electrode layer contains at least one metal selected from the elements of Groups 4 and 9 of the periodic table.

6. 6. The semiconductor device according to claim 1, wherein the first electrode layer is made up of two or more layers having different compositions.

7. 7. The semiconductor device according to claim 1, wherein at least a portion of the first electrode layer that protrudes outward beyond the outer end of the second electrode layer has a tapered region in which the thickness decreases toward the outside of the semiconductor device.

8. 8. The semiconductor device according to claim 1, wherein the second electrode layer contains at least one metal selected from the group consisting of silver, copper, gold and aluminum.

9. 9. The semiconductor device according to claim 1, wherein the first electrode layer has a thickness smaller than that of the second electrode layer.

10. 10. The semiconductor device according to claim 1, further comprising a field insulating film, an outer end of said first electrode layer being located on said field insulating film.

11. 11. The semiconductor device according to claim 1, which is a Schottky barrier diode.

12. 12. The semiconductor device according to claim 1, which is a power device.

13. A semiconductor system comprising a semiconductor device, the semiconductor device being the semiconductor device according to any one of claims 1 to 12.

Images