Semiconductor device

Abstract

Provided is a semiconductor device having low loss and suppressed leakage current, which is particularly useful for power devices. A semiconductor device having at least a semiconductor layer containing an oxide semiconductor having a rutile structure as a main component and a Schottky electrode containing a first electrode layer and a second electrode layer having higher conductivity than the first electrode layer, wherein an outer end portion of the second electrode layer is electrically connected to the semiconductor layer via the first electrode layer, and an outer end portion of the first electrode layer is located at a position further outside than an outer end portion of an electrically connected region of the second electrode layer.

Description

Technical Field

[0001] The present invention relates to semiconductor devices that are useful as power devices and the like. Background Technology

[0002] Gallium oxide (Ga2O3) has a wide bandgap of 4.8–5.3 eV at room temperature and is a transparent semiconductor that absorbs almost no visible light or ultraviolet light. Therefore, it is a promising material for use in optical devices, electrical devices, and transparent electronics that operate in the deep ultraviolet region. In recent years, development of gallium oxide (Ga2O3)-based photodetectors, light-emitting diodes (LEDs), and transistors has been underway (see Non-Patent Literature 1).

[0003] Furthermore, gallium oxide (Ga2O3) exhibits five crystal structures: α, β, γ, σ, and ε, with β-Ga2O3 typically being the most stable. However, β-Ga2O3 has a β-gallia structure, which differs from crystal systems commonly used in electronic materials and may not be suitable for semiconductor devices. Additionally, the growth of β-Ga2O3 thin films requires high substrate temperatures and high vacuum levels, leading to increased manufacturing costs. Moreover, as described in Non-Patent Document 2, even at high concentrations (e.g., 1 × 10⁻⁶), β-Ga2O3... 19 / cm 3 The dopants (Si) mentioned above cannot be used as donors if they are not annealed at a high temperature of 800℃~1100℃ after ion implantation.

[0004] On the other hand, α-Ga2O3 has the same crystal structure as the already common sapphire substrate, so it is suitable for use in optical devices and electrical devices. Furthermore, due to its wider band gap than β-Ga2O3, it is particularly useful for power devices. Therefore, it is expected that α-Ga2O3 will be used as a semiconductor device.

[0005] In Patent Documents 1 and 2, as electrodes that use β-Ga2O3 as a semiconductor and obtain ohmic characteristics suitable therefor, semiconductor devices using 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 and a Ni layer and an Au layer are described.

[0006] Furthermore, in Patent Document 3, a semiconductor device using any one of Au, Pt, or a stack of Ni and Au is described as an electrode that uses β-Ga2O3 as a semiconductor and obtains Schottky characteristics suitable therefor.

[0007] However, when the electrodes described in Patent Documents 1-3 are applied to semiconductor devices using α-Ga2O3 as a semiconductor, problems arise such as the electrodes failing to function as Schottky or Ohmic electrodes, the electrodes not adhering to the film, and damage to semiconductor properties. Furthermore, the electrode structures described in Patent Documents 1-3 can generate leakage current from the electrode ends, and thus cannot provide a practically satisfactory electrode structure for use in semiconductor devices.

[0008] Patent Document 4 describes a semiconductor device that uses α-Ga₂O₃ as a semiconductor and employs an electrode comprising at least one metal selected from Groups 4 to 9 of the periodic table as a Schottky electrode. Furthermore, Patent Document 4 relates to the applicant's patent application.

[0009] Patent Document 1: Japanese Patent Application Publication No. 2005-260101

[0010] Patent Document 2: Japanese Patent Application Publication No. 2009-81468

[0011] Patent Document 3: Japanese Patent Application Publication No. 2013-12760

[0012] Patent Document 4: Japanese Patent Application Publication No. 2018-60992

[0013] [Non-Patent Literature 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 (Zhao Junliang 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)

[0014] [Non-Patent Literature 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

[0015] The purpose of this invention is to provide a low-loss semiconductor device that suppresses leakage current.

[0016] In order to achieve the above-mentioned objectives, the inventors conducted in-depth research and discovered the following: A semiconductor device comprising at least a semiconductor layer and a Schottky electrode, wherein the semiconductor layer comprises an oxide semiconductor having a corundum structure as the main component, and the Schottky electrode comprises a first electrode layer and a second electrode layer with 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 further outward than the outer end of the electrically connected region of the electrically connected second electrode layer. This semiconductor device can effectively extend the depletion layer into the semiconductor layer and is a low-loss semiconductor device that suppresses leakage current. The semiconductor device obtained in this way can solve the above-mentioned existing problems in one fell swoop.

[0017] Furthermore, after obtaining the above insights, the inventors conducted further and repeated research and finally completed this invention.

[0018] That is, the present invention relates to the following technical methods.

[0019] [1] A semiconductor device comprising at least a semiconductor layer and a Schottky electrode, wherein the semiconductor layer comprises an oxide semiconductor having a corundum structure as the main component, and the Schottky electrode comprises 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 at a position further outward than the outer end of the electrically connected region of the electrically connected second electrode layer.

[0020] [2] According to the semiconductor device of [1], wherein the oxide semiconductor comprises at least one metal selected from aluminum, indium and gallium.

[0021] [3] The semiconductor device according to [1] or [2], wherein the oxide semiconductor comprises at least gallium.

[0022] [4] The semiconductor device according to any one of [1] to [3], wherein the first electrode layer comprises at least one metal selected from Group 4 to Group 10 of the periodic table.

[0023] [5] The semiconductor device according to any one of [1] to [4], wherein the first electrode layer comprises at least one metal selected from Group 4 and Group 9 of the periodic table.

[0024] [6] The semiconductor device according to any one of [1] to [5], wherein the first electrode layer is composed of two or more layers with different compositions.

[0025] [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 extending outward beyond the outer end of the second electrode layer has a tapered region with a reduced film thickness toward the outside of the semiconductor device.

[0026] [8] The semiconductor device according to any one of [1] to [7], wherein the second electrode layer comprises at least one metal selected from silver, copper, gold and aluminum.

[0027] [9] The semiconductor device according to any one of [1] to [8], wherein the thickness of the first electrode layer is thinner than the thickness of the second electrode layer.

[0028]

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

[0029]

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

[10] , wherein it is a Schottky barrier diode.

[0030]

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

[11] , wherein it is a power device.

[0031]

[13] A semiconductor system comprising a semiconductor device, wherein the semiconductor device is any one of the semiconductor devices described in [1] to

[12] .

[0032] The semiconductor device of the present invention suppresses leakage current and has low loss. Attached Figure Description

[0033] Figure 1 This is a schematic diagram illustrating a preferred embodiment of the Schottky barrier diode (SBD) of the present invention.

[0034] Figure 2 This is a schematic diagram illustrating a preferred embodiment of the Schottky barrier diode (SBD) of the present invention.

[0035] Figure 3 This is a schematic diagram illustrating preferred manufacturing processes of the Schottky barrier diode (SBD) of the present invention.

[0036] Figure 4 This is a schematic diagram illustrating a preferred embodiment of the Schottky barrier diode (SBD) of the present invention.

[0037] Figure 5 This is a structural diagram of the atomizing CVD device used in an embodiment of the present invention.

[0038] Figure 6 This is a diagram schematically illustrating a preferred example of a power supply system.

[0039] Figure 7 This is a diagram schematically illustrating a preferred example of the system device.

[0040] Figure 8 This is a diagram schematically illustrating a preferred example of a power supply circuit diagram of a power supply device.

[0041] Figure 9 This is a graph showing the results of IV measurements in the embodiments and comparative examples. The vertical axis represents current, and the horizontal axis represents voltage. Detailed Implementation

[0042] The semiconductor device of the present invention includes at least a semiconductor layer and a Schottky electrode. The semiconductor layer comprises an oxide semiconductor having a corundum structure as its main component. The Schottky electrode comprises a first electrode layer and a second electrode layer with a higher conductivity than the first electrode layer. The device is characterized in that 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 further outward than the outer end of the electrically connected region of the electrically connected second electrode layer. Here, "electrical connection" can refer to direct contact or contact via a conductive film or semiconductor film, etc. The outer end of the electrically connected region can be the outer end of the second electrode layer or the outer end of the region electrically connected to the first electrode layer within the second electrode layer. Hereinafter, the "outer end of the second electrode layer" will be described as an example of the "outer end of the electrically connected region," but the present invention is not limited to these examples.

[0043] The semiconductor layer is not particularly limited as long as it contains an oxide semiconductor with a corundum structure as its main component. Examples of the oxide semiconductor with 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 this invention, preferably, the oxide semiconductor contains at least one metal selected from aluminum, indium, and gallium; more preferably, it contains at least gallium; and most preferably, it is α-Ga₂O₃ or a mixture thereof. Furthermore, "main component" refers to the total composition of the oxide semiconductor with a corundum structure relative to the semiconductor layer, preferably containing 50% or more atomically, more preferably 70% or more, further preferably 90% or more, and possibly 100%. Additionally, the thickness of the semiconductor layer is not particularly limited and can be less than 1 μm or more, but in this invention, it is preferably 10 μm or more. The surface area of ​​the semiconductor film is not particularly limited and can be 1 mm. 2 The above can also be 1mm. 2 The following is preferred: 10mm 2 ~300cm 2 More preferably 100mm 2 ~100cm 2 Furthermore, the semiconductor layer is typically single-crystal, but can also be polycrystalline. Preferably, the semiconductor layer is a multilayer film comprising at least a first semiconductor layer and a second semiconductor layer. If a Schottky electrode is disposed on the first semiconductor layer, the semiconductor layer is a multilayer film where the carrier density of the first semiconductor layer is less than the carrier density of the second semiconductor layer. In this case, the second semiconductor layer typically contains a dopant, and the carrier density of the semiconductor layer can be appropriately set by adjusting the doping amount.

[0044] Preferably, the semiconductor layer comprises 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 magnesium, calcium, or zinc. In this invention, the n-type dopant is preferably Sn, Ge, or Si. Regarding the dopant content, in the composition of the semiconductor layer, it 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 dopant concentration is typically about 1 × 10⁻⁶. 16 / cm 3 ~1×10 22 / cm 3 Alternatively, the concentration of the dopant can be set, for example, to approximately 1 × 10⁻⁶. 17 / cm 3The following low concentrations. Furthermore, according to the present invention, it is also possible to achieve a concentration of approximately 1 × 10⁻⁶. 20 / cm 3 The above high concentrations contain dopants. In this invention, a concentration of 1×10⁻⁶ is preferred. 17 / cm 3 The above carrier concentrations contain...

[0045] The semiconductor layer can be formed using known methods. Examples of methods for forming the semiconductor layer include CVD, MOCVD, MOVPE, atomized CVD, atomized / epitaxial growth, MBE, HVPE, pulsed growth, and ALD. In this invention, the semiconductor layer is preferably formed using atomized CVD or atomized / epitaxial growth. In the atomized CVD or atomized / epitaxial growth method, for example, by using… Figure 5 The atomizing CVD apparatus shown atomizes the raw material solution (atomization process), causing the droplets to float. After atomization, the atomized droplets are transported to the substrate by a carrier gas (transportation process). Then, the atomized droplets undergo a thermal reaction near the substrate, thereby forming the semiconductor layer by stacking a semiconductor film containing a crystalline oxide semiconductor as the main component on the substrate (film formation process).

[0046] (Atomization process)

[0047] In the atomization process, the raw material solution is atomized. The atomization method for the raw material solution is not particularly limited as long as it can atomize the solution; any known method may be used. In this invention, an ultrasonic atomization method is preferred. Since the atomized droplets obtained using ultrasound have an initial velocity of zero and float in the air, it is preferable that, because it is not sprayed like a mist but floats in space and is transported as a gas, there is no damage caused by collision energy, making it very suitable. The droplet size is not particularly limited and can be droplets of about a few millimeters, preferably less than 50 μm, and more preferably 100 nm to 10 μm.

[0048] (Raw material solution)

[0049] The raw material solution is not particularly limited as long as it contains raw materials that can be atomized or dropletized and form a semiconductor film; it can be inorganic or organic materials. In this invention, the raw material is preferably a metal or metal compound, and more preferably contains one or more metals selected from aluminum, gallium, indium, iron, chromium, vanadium, titanium, rhodium, nickel, cobalt, and iridium.

[0050] In this invention, the raw material solution can be a substance that dissolves or disperses the metal in an organic solvent or water in the form of a complex or salt. Examples of complex forms include acetylacetone complexes, carbonyl complexes, amine complexes, and hydride complexes. Examples of salt forms include organometallic salts (e.g., metal acetates, metal oxalates, metal citrates, etc.), sulfide metal salts, nitrate metal salts, metal phosphates, and halide metal salts (e.g., metal chlorides, metal bromides, metal iodides, etc.).

[0051] Furthermore, it is preferable to mix additives such as hydrohalic acid and oxidizing agents into the raw material solution. Examples of hydrohalic acid include hydrobromic acid, hydrochloric acid, and hydroiodic acid, among which hydrobromic acid or hydroiodic acid is preferred for the purpose of more effectively suppressing the generation of abnormal particles. Examples of oxidizing agents include peroxides such as hydrogen peroxide (H₂O₂), sodium peroxide (Na₂O₂), barium peroxide (BaO₂), and benzoyl peroxide ((C₆H₅CO)₂O₂), as well as organic peroxides such as hypochlorous acid (HClO), perchloric acid, nitric acid, ozone water, peracetic acid, and nitrobenzene.

[0052] The raw material solution may also contain dopants. By including dopants in the raw material solution, doping can be performed effectively. The dopants are not particularly limited as long as they do not hinder the purpose of the invention. Examples of dopants include n-type dopants such as tin, germanium, silicon, titanium, zirconium, vanadium, or niobium, or 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 dopants is appropriately set using a calibration line that shows the relationship between the concentration of the dopant in the raw material and the desired carrier density.

[0053] The solvent for the raw material solution is not particularly limited; it can be an inorganic solvent such as water, an organic solvent such as ethanol, or a mixture of inorganic and organic solvents. In this invention, preferably, the solvent contains water, more preferably water or a mixture of water and ethanol.

[0054] (Transportation process)

[0055] In the transport process, the atomized droplets are transported to the film-forming chamber by a carrier gas. The carrier gas is not particularly limited as long as it does not hinder the purpose of the invention; suitable examples include inert gases such as oxygen, ozone, nitrogen, or argon, or reducing gases such as hydrogen or synthesis gases. Furthermore, the carrier gas can be one type, or two or more types, and a dilution gas with a reduced flow rate (e.g., a 10-fold dilution gas) can be used as a second carrier gas. Additionally, there can be more than one carrier gas supply point. The flow rate of the carrier gas is not particularly limited, but is preferably 0.01 L / min to 20 L / min, more preferably 1 L / min to 10 L / min. When a dilution gas is present, the flow rate of the dilution gas is preferably 0.001 L / min to 2 L / min, more preferably 0.1 L / min to 1 L / min.

[0056] (Film forming process)

[0057] In the film-forming process, the semiconductor film is formed on the substrate by subjecting the atomized droplets to a thermal reaction near the substrate. Regarding the thermal reaction, any reaction caused by heat is acceptable, and the reaction conditions are not particularly limited as long as they do not hinder the purpose of this invention. In this process, the thermal reaction is typically carried out at a temperature above the solvent's evaporation temperature, preferably below a temperature not too high (e.g., 1000°C), more preferably below 650°C, and most preferably between 300°C and 650°C. Furthermore, the thermal reaction can be carried out under any atmosphere, such as a vacuum, a non-oxygen atmosphere (e.g., an inert gas atmosphere), a reducing gas atmosphere, or an oxygen atmosphere, as long as it does not hinder the purpose of this invention; preferably under an inert gas atmosphere or an oxygen atmosphere. Additionally, it can be carried out under any conditions, including atmospheric pressure, pressurized conditions, and depressurized conditions; in this invention, atmospheric pressure is preferred. Furthermore, the film thickness can be set by adjusting the film-forming time.

[0058] (Matrix)

[0059] 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 hinder 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; all shapes are effective. For example, it can be plate-shaped, fibrous, rod-shaped, cylindrical, square-prism-shaped, tubular, spiral-shaped, spherical, or annular, etc. However, in this invention, a substrate is preferred. The thickness of the substrate is not particularly limited in this invention.

[0060] The substrate is plate-shaped, and its use as a support for the semiconductor film is not particularly limited. It can be an insulating substrate, a semiconductor substrate, a metal substrate, or a conductive substrate. Preferably, the substrate is an insulating substrate, and even more preferably, it is a substrate with a metal film on its surface. Examples of substrates include a substrate containing a substrate material with a corundum structure as its main component, a substrate containing a substrate material with a β-gallia structure as its main component, or a substrate containing a substrate material with a hexagonal crystal structure as its main component. Here, "main component" refers to the total composition of the substrate material having the specific crystal structure relative to the total composition of the substrate material, preferably containing 50% or more in atomic ratio, more preferably 70% or more, even more preferably 90% or more, and possibly 100%.

[0061] The substrate material is not particularly limited as long as it does not hinder the purpose of this invention, and can be any known substrate material. Examples of substrate materials with a corundum structure include α-Al₂O₃ (sapphire substrate) or α-Ga₂O₃, and more suitable examples include 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, for example, β-Ga₂O₃ substrates, or mixed crystal substrates containing Ga₂O₃ and Al₂O₃, where Al₂O₃ is greater than 0 wt% and less than 60 wt%. Furthermore, examples of substrates with a substrate material having a hexagonal crystal structure as the main component include, for example, SiC substrates, ZnO substrates, and GaN substrates.

[0062] In this invention, an annealing process can be performed after the film-forming step. The annealing temperature is not particularly limited as long as it does not hinder the purpose of this invention; it 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. Furthermore, the annealing process can be performed in any atmosphere as long as it does not hinder the purpose of this invention. It can be performed in a non-oxygen atmosphere or an oxygen atmosphere. Examples of non-oxygen atmospheres include an inert gas atmosphere (e.g., a nitrogen atmosphere) or a reducing gas atmosphere; in this invention, an inert gas atmosphere is preferred, and a nitrogen atmosphere is more preferred.

[0063] Furthermore, in this invention, the semiconductor film can be formed directly on the substrate, or it can be formed via other layers such as a stress relaxation layer (e.g., a buffer layer, an ELO layer, etc.) or a release sacrificial layer. The method for forming each layer is not particularly limited and can be a known method; however, in this invention, atomization CVD is preferred.

[0064] In this invention, the semiconductor layer can be used as a semiconductor layer in a semiconductor device after using a known method such as peeling the semiconductor film from the substrate, or it can be used directly as a semiconductor layer in a semiconductor device.

[0065] The first electrode layer is not particularly limited to any electrode layer that is conductive but has a lower conductivity than the second electrode layer, as long as it does not hinder the purpose of the present invention. The constituent material of the first electrode layer can be a conductive inorganic material or a conductive organic material. In the present invention, the material of the first electrode layer is preferably a metal. As the metal, examples include at least one metal selected from Groups 4 to 10 of the periodic table. Examples of Group 4 metals include titanium (Ti), zirconium (Zr), and hafnium (Hf). Examples of Group 5 metals include vanadium (V), niobium (Nb), and tantalum (Ta). Examples of Group 6 metals include chromium (Cr), molybdenum (Mo), and tungsten (W). Examples of Group 7 metals include manganese (Mn), technetium (Tc), and rhenium (Re). Examples of Group 8 metals include iron (Fe), ruthenium (Ru), and osmium (Os). Examples of metals belonging to Group 9 of the periodic table include cobalt (Co), rhodium (Rh), and iridium (Ir). Examples of metals belonging to Group 10 of the periodic table include nickel (Ni), palladium (Pd), and platinum (Pt). In this invention, preferably, the first electrode layer comprises at least one metal selected from Groups 4 and 9 of the periodic table, more preferably, it comprises a metal from Group 9. The thickness of the first electrode layer is not particularly limited, preferably 0.1 nm to 10 μm, more preferably 5 nm to 500 nm, and most preferably 10 nm to 200 nm. Furthermore, in this invention, preferably, the thickness of the first electrode layer is thinner than that of the second electrode layer. Additionally, in this invention, the first electrode layer is preferably composed of two or more layers with different compositions. By setting the first electrode layer to such a preferred structure, not only can a semiconductor device with superior Schottky characteristics be obtained, but leakage current suppression can also be better achieved.

[0066] The second electrode layer is not particularly limited as long as it does not hinder the purpose of the present invention, provided that it is a conductive electrode layer with a higher conductivity than the first electrode layer. The constituent material of the second electrode layer can be a conductive inorganic material or a conductive organic material. In the present invention, the material of the second electrode layer is preferably a metal. As such a metal, at least one metal selected from Groups 8 to 13 of the periodic table is preferred. As metals from Groups 8 to 10 of the periodic table, the metals exemplified in the description of the first electrode layer as metals from Groups 8 to 10 of the periodic table can be cited. As metals from Group 11 of the periodic table, examples include copper (Cu), silver (Ag), and gold (Au). As metals from Group 12 of the periodic table, examples include zinc (Zn) and cadmium (Cd). Furthermore, as metals from Group 13 of the periodic table, examples include aluminum (Al), gallium (Ga), and indium (In). In this invention, the second electrode layer preferably comprises at least one metal selected from Group 11 and Group 13 of the periodic table, more preferably at least one metal selected from silver, copper, gold, and aluminum. Furthermore, 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.

[0067] The method for forming the first electrode layer or the second electrode layer is not particularly limited and can be a known method. Specifically, examples of methods for forming the first electrode layer or the second electrode layer include dry methods and wet methods. Examples of dry methods include sputtering, vacuum evaporation, and CVD. Examples of wet methods include screen printing or mold coating.

[0068] It is not particularly limited if the outer end of the first electrode layer is located further outward than the outer end of the second electrode layer. However, in this invention, the distance between the outer ends of the first electrode layer and the outer ends of the second electrode layer is 1 μm or more, which can better suppress leakage current, and is therefore preferred. Furthermore, in this invention, at least a portion of the portion of the first electrode layer that extends further outward than the outer end of the second electrode layer (hereinafter also referred to as the "extended portion") has a tapered region where the film thickness decreases towards the outside of the semiconductor device, which can also improve the withstand voltage of the semiconductor device, and is therefore preferred. In addition, by combining such a preferred electrode structure with the aforementioned preferred semiconductor layer constituent materials, a semiconductor device with better leakage current suppression and lower losses can be obtained. Furthermore, the reduction rate of film thickness in the tapered region is not particularly limited. For convenience, it can be said that the tapered region is defined as the film thickness decreasing towards the outside of the semiconductor device from any two points of film thickness on the inner and outer sides.

[0069] Furthermore, in this invention, it is preferable to further provide a field insulating film on the semiconductor layer. In this case, the outer end of the first electrode layer is located on the field insulating film, which allows for a better formation of a depletion layer within the semiconductor layer, and is therefore more preferable. The material constituting the field insulating film is not particularly limited as long as it does not impede the purpose of this invention, and can be any known material. Examples of the field insulating film include SiO2 films, polycrystalline silicon films, phosphorus-added SiO2 films (PSG films), boron-added SiO2 films, and phosphorus-boron-added SiO2 films (BPSG films). Examples of methods for forming the field insulating film include CVD, atmospheric pressure CVD, plasma CVD, atomization CVD, and thermal oxidation. In this invention, the method for forming the field insulating film is preferably atomization CVD or atmospheric pressure CVD.

[0070] The preferred embodiments of the present invention will now be described in more detail with the aid of the accompanying drawings, but the present invention is not limited to these embodiments.

[0071] Figure 1 The main parts of a Schottky barrier diode (SBD), which is one of the preferred embodiments of the present invention, are shown. Figure 1 The SBD includes: an ohmic electrode 102, an n-type semiconductor layer 101a, an n+ type semiconductor layer 101b, and a Schottky electrode 103. Furthermore, the Schottky electrode 103 includes metal layers 103a, 103b, and 103c. Figure 1 In the semiconductor device, the outer ends of the metal layers 103b and / or 103c, which serve as the first electrode layer, are located further outward than the outer ends of the metal layer 103a, which serves as the second electrode layer, thus better suppressing leakage current. Furthermore, in the metal layers 103b and / or 103c, the portion extending further outward than the outer ends of the metal layer 103a has a tapered region with a reduced film thickness towards the outside of the semiconductor device, thus creating a structure with even better withstand voltage.

[0072] Examples of materials that constitute metal layer 103a include the aforementioned metals, which are examples of materials that constitute the second electrode layer. Similarly, examples of materials that constitute metal layers 103b and 103c include the aforementioned metals, which are examples of materials that constitute the first electrode layer. Figure 1 The method for forming each layer is not particularly limited as long as it does not hinder the purpose of the present invention, and can be a known method. For example, methods such as forming a film by vacuum evaporation, CVD, sputtering, various coating techniques and then patterning it by photolithography, or directly patterning it using printing technology, etc., can be cited.

[0073] Figure 2The main portion of a Schottky barrier diode (SBD) is shown as one of the other preferred embodiments of the present invention. Figure 2 The SBD further has a field insulating film 104, and the outer ends of the metal layer 103b and / or metal layer 103c are located on the field insulating film 104, which is consistent with... Figure 1 This differs from the SBD. By adopting such a structure, the voltage withstand characteristics of the semiconductor device can be improved.

[0074] Figure 2 The method for forming each layer is not particularly limited as long as it does not hinder the purpose of the present invention, and can be a known method. For example, methods such as forming a film by vacuum evaporation, CVD, sputtering, various coating techniques and then patterning it by photolithography, or directly patterning it using printing technology, etc., can be cited.

[0075] The following uses manufacturing Figure 2 Preferred examples of semiconductor devices are described in more detail below.

[0076] Figure 3 (a) shows a stacked structure in which an n+ type semiconductor layer 101b and an n- type semiconductor layer 101a are sequentially formed on an ohmic electrode 102, and a field insulating film 104 is formed on the n- type semiconductor layer. The method for forming the field insulating film 104 is not particularly limited as long as it does not impede the purpose of the present invention. Examples of methods for forming the field insulating film 104 include sputtering, vacuum evaporation, coating, CVD, atmospheric pressure CVD, plasma CVD, atomization CVD, and thermal oxidation. In the present invention, atomization CVD or atmospheric pressure CVD is preferred. Furthermore, an opening for the first electrode layer is formed on the field insulating film 4, exposing at least a portion of the n- type semiconductor layer 101a. The method for forming the opening is not particularly limited and can be a known etching method. Additionally, a tapered portion is formed in the field insulating film 104, with the film thickness decreasing from the outside to the inside of the semiconductor device. The method of forming the tapered portion is not particularly limited as long as it does not hinder the purpose of the present invention, and can be a known method.

[0077] Next, in Figure 3 On the laminate of (a), metal layers 103a, 103b and 103c are formed using the dry method or the wet method to obtain Figure 3 The stack of (b) is then processed by removing excess portions of metal layers 103a, 103b, and 103c using a known etching technique to obtain... Figure 3The stack of (c) is further characterized by a tapered shape at the outer end of the first electrode layer, for example, by etching while simultaneously retracting the resist. The semiconductor device obtained as described above exhibits excellent breakdown voltage while suppressing leakage current.

[0078] Figure 4 The main portion of a Schottky barrier diode (SBD) is shown as one of the other preferred embodiments of the present invention. Figure 4 The SBD has a protective metal layer 105 further provided around the outer end of the first metal layer, which is consistent with... Figure 2 Unlike the SBD, the protective metal layer 105 is configured to at least cover the ends of the field insulating film 104. The material of the protective metal layer is not particularly limited and can be the same as the metal used as an example of the material of the metal layer described above. By adopting such a structure, the metal layers 103a, 103b and 103c can be formed more efficiently, and the reliability of the semiconductor device can be improved while further enhancing the withstand voltage characteristics.

[0079] Figure 4 The method for forming each layer is not particularly limited as long as it does not hinder the purpose of the present invention, and can be a known method. For example, methods such as forming a film by vacuum evaporation, CVD, sputtering, various coating techniques and then patterning it by photolithography, or directly patterning it using printing technology, etc., can be cited.

[0080] The semiconductor device is particularly useful for power devices. Examples of such semiconductor devices include diodes (e.g., PN diodes, Schottky barrier diodes, junction barrier Schottky diodes, etc.) or transistors (e.g., MOSFETs, MESFETs, etc.), with diodes being preferred, and Schottky barrier diodes (SBDs) being more preferred.

[0081] In addition to the foregoing, the semiconductor device of the present invention further utilizes known methods and is preferably used as a power module, inverter, or converter, which are also included in the present invention. Furthermore, the semiconductor device of the present invention is further preferably used, for example, in a semiconductor system using a power supply device. The power supply device is connected to a wiring pattern, etc., using known methods, thereby enabling it to be manufactured from or as the semiconductor device. Figure 6 An example of a power supply system is shown. Figure 6 A power system is constructed using multiple power supply devices and control circuits. For example... Figure 7 As shown, the power supply system can be combined with electronic circuits for use in system devices. Furthermore, Figure 8 An example of a power supply circuit diagram for a power supply device is shown. Figure 8The diagram illustrates the power supply circuit of a power supply device consisting of a power circuit and a control circuit. An inverter (composed of MOSFETs A to D) converts DC voltage to AC at a high frequency. A transformer provides insulation and voltage transformation. After rectification by rectifier MOSFETs (A to B'), the voltage is smoothed by a DCL (smoothing coils L1 and L2) and a capacitor, resulting in an output DC voltage. A voltage comparator compares the output voltage with a reference voltage. A PWM control circuit controls the inverter and rectifier MOSFETs to achieve the desired output voltage.

[0082] Example

[0083] The following describes embodiments of the present invention, but the present invention is not limited to these embodiments.

[0084] (Example 1)

[0085] 1. Formation of n-type semiconductor layer

[0086] 1-1. Film forming apparatus

[0087] use Figure 5 The atomizing CVD apparatus 1 used in this embodiment will be described. The atomizing CVD apparatus 1 includes: a carrier gas source 2a for supplying carrier gas; a flow regulating valve 3a for adjusting the flow rate of the carrier gas supplied from the carrier gas source 2a; a carrier gas (dilution) source 2b for supplying carrier gas (dilution); a flow regulating valve 3b for adjusting the flow rate of the carrier gas (dilution) supplied from the carrier gas (dilution) source 2b; an atomizing source 4 for containing a raw material solution 4a; a container 5 for holding water 5a; an ultrasonic transducer 6 mounted on the bottom surface of the container 5; a film-forming chamber 7; a supply pipe 9 connecting the atomizing source 4 to the film-forming chamber 7; a hot plate 8 disposed within the film-forming chamber 7; and an outlet 11 for discharging the mist, droplets, and exhaust gas after the thermal reaction. Furthermore, a substrate 10 is disposed on the hot plate 8.

[0088] 1-2. Preparation of raw material solution

[0089] Tin bromide was mixed in a 0.1M aqueous solution of gallium bromide to prepare the aqueous solution with an atomic ratio of tin to gallium of 1:0.0008. The aqueous solution contained 20% hydrobromic acid by volume and was used as the raw material solution.

[0090] 1-3. Film Formation Preparation

[0091] The raw material solution 4a obtained from steps 1-2 above is contained within the atomization source 4. Next, an m-sided sapphire substrate is placed on the hot plate 8 as substrate 10, and an undoped α-Ga₂O₃ layer is formed on the surface of this m-sided sapphire substrate as a buffer layer. The temperature inside the film-forming chamber 7 is raised to 470°C by operating the hot plate 8. Then, flow control valves 3a and 3b are opened to supply carrier gas from carrier gas supply sources 2a and 2b, which serve as carrier gas sources, into the film-forming chamber 7. After the atmosphere in the film-forming chamber 7 is fully replaced by the carrier gas, the flow rate of the carrier gas is adjusted to 1.2 L / min, and the flow rate of the carrier gas (diluted) is adjusted to 1.0 L / min. Nitrogen is used as the carrier gas.

[0092] 1-4. Formation of crystalline oxide semiconductor films

[0093] Next, by vibrating the ultrasonic transducer 6 at 2.4 MHz and propagating this vibration through water 5a to the raw material solution 24a, the raw material solution 4a is atomized to generate mist 4b. This mist 4b is introduced into the film-forming chamber 7 via a carrier gas supply pipe 9. At atmospheric pressure and 615°C, the mist undergoes a thermal reaction within the film-forming chamber 7, forming a film on the substrate 10. Furthermore, the film-forming time is 6 hours.

[0094] 1-5. Evaluation

[0095] The phase of the film obtained by XRD diffraction was identified using the XRD diffraction apparatus described in steps 1-4 above, and the resulting film was identified as α-Ga2O3.

[0096] 2. Formation of n+ type semiconductor layer

[0097] As a raw material solution, tin bromide was mixed in a 0.1M aqueous solution of gallium bromide, and the aqueous solution was prepared with an atomic ratio of tin to gallium of 1:0.24. At this time, except that an aqueous solution containing 20% ​​hydrobromic acid by volume was used, and the film formation time was set to 2 hours, everything else was the same as in step 1 above, to form a crystalline oxide semiconductor film. The resulting film was identified by XRD diffraction, and the film was determined to be α-Ga₂O₃.

[0098] 3. Formation of Ohmic Electrodes

[0099] On the n+ type semiconductor layer of the stack obtained in step 2 above, a Ti layer and an Au layer are respectively deposited by sputtering. Furthermore, the thickness of the Ti layer is 70 nm, and the thickness of the Au layer is 30 nm.

[0100] 4. Substrate removal

[0101] On the ohmic electrode of the laminate obtained by step 3 above, a temporary wafer is temporarily bonded, and then the substrate 10 is ground using a grinding machine and a CMP apparatus to remove the sapphire substrate and buffer layer.

[0102] 5. Formation of the insulating film

[0103] On the n-type semiconductor layer of the laminate obtained in step 4 above, a SiO2 film is formed using plasma CVD. Then, an opening is formed in the SiO2 film by etching, exposing a portion of the n-type semiconductor layer.

[0104] 6. Formation of Schottky electrodes

[0105] On the n-type semiconductor layer of the laminate obtained in step 5 above, a Co film (100 nm thick), a Ti film (50 nm thick), and an Al film (5 μm thick) were formed by EB (electron beam) evaporation to serve as Schottky electrodes. Then, the Co, Ti, and Al films were removed by etching. SEM observation of the outer ends of the obtained Schottky electrodes confirmed that the Ti and Co films extended outwards by approximately 10 μm around the outer periphery of the Al film, with the outer ends of the Ti and Co films located further outwards than the outer end of the Al film. Furthermore, the outer ends of the Ti and Co films were in contact with the n-type semiconductor layer. Additionally, the thin film resistance of the extended Co film was 1.3 Ω.

[0106] (Comparative Example 1)

[0107] The Schottky electrode was formed with the outer ends of the Al film, Co film and Ti film located on the SiO2 film (the outer end of the Al film, which serves as the second electrode layer, is not electrically connected to the semiconductor layer), and the outer ends of the Al film, Ti film and Co film were located in approximately the same position. Otherwise, the SBD was fabricated in the same manner as in Example 1.

[0108] (Example 2)

[0109] The n-semiconductor layer was formed as follows: An aqueous solution containing 10% hydrobromic acid by volume in a 0.1M gallium bromide aqueous solution was used as the raw material solution. The Schottky electrode was formed by electrically connecting an Al film to the n-type semiconductor layer via a Co film and a Ti film, with the outer ends of the Co and Ti films located on a SiO2 film. Except as described above, the SBD was fabricated in the same manner as in Example 1. IV measurements were performed on the obtained SBD, and the results showed that it exhibited the same leakage current reduction effect as the SBD of Example 1.

[0110] (IV measurement)

[0111] IV measurements were performed on the SBDs obtained from Example 1, Comparative Example 1, and Example 2. Figure 9 The results of Example 2 and Comparative Example 1 are shown. From... Figure 9It is evident that the SBD of Example 2 significantly reduces leakage current compared to the SBD of Comparative Example 1. Furthermore, the SBD of Example 1 exhibits the same leakage current suppression effect as the SBD of Example 2.

[0112] Industrial availability

[0113] The semiconductor device of the present invention can be used in all fields, including semiconductors (e.g., compound semiconductor electronic devices), electronic components and electrical equipment components, optical and electronic photographic devices, and industrial components, and is particularly useful for power devices.

[0114] Symbol Explanation

[0115] 1. Film-forming device (atomized CVD device)

[0116] 2a Carrier gas source

[0117] 2b Carrier gas (dilution) source

[0118] 3a Flow regulating valve

[0119] 3b Flow regulating valve

[0120] 4. Atomization source

[0121] 4a Raw material solution

[0122] 4b Raw material particles

[0123] 5 containers

[0124] 5a Water

[0125] 6. Ultrasonic transducer

[0126] 7 Film-forming chamber

[0127] 8 Hot Plate

[0128] 9. Supply Management

[0129] 10 substrate

[0130] 101a n-type semiconductor layer

[0131] 101b n+ type semiconductor layer

[0132] 102 Ohm Electrode

[0133] 103 Schottky electrode

[0134] 103a metal layer

[0135] 103b metal layer

[0136] 103c metal layer

[0137] 104 Insulating Film (Field Insulation Film)

[0138] 105 Protective Metal Layer

Claims

1. A semiconductor device comprising at least a semiconductor layer and a Schottky electrode, the semiconductor layer containing an oxide semiconductor having a rutile structure as a main component, the Schottky electrode containing a first electrode layer and a second electrode layer having higher conductivity than the first electrode layer, characterized in that, An outer end portion of the second electrode layer is electrically connected to the semiconductor layer via the first electrode layer, and an outer end portion of the first electrode layer is positioned further outward than an outer end portion of an electrically connected region of the second electrode layer, At least a part of a portion of the first electrode layer that extends further outward than the outer end portion of the second electrode layer has a tapered region in which the film thickness decreases toward the outside of the semiconductor device.

2. The semiconductor device according to claim 1, wherein The oxide semiconductor includes at least one metal selected from aluminum, indium, and gallium.

3. The semiconductor device according to claim 1 or 2, wherein The oxide semiconductor includes at least gallium.

4. The semiconductor device according to claim 1 or 2, wherein The first electrode layer includes at least one metal selected from Group 4 to Group 10 of the periodic table.

5. The semiconductor device according to claim 1 or 2, wherein The first electrode layer includes at least one metal selected from Group 4 and Group 9 of the periodic table.

6. The semiconductor device according to claim 1 or 2, wherein The first electrode layer is composed of two or more layers whose compositions are different from each other.

7. The semiconductor device according to claim 1 or 2, wherein The second electrode layer includes at least one metal selected from silver, copper, gold, and aluminum.

8. The semiconductor device according to claim 1 or 2, wherein The layer thickness of the first electrode layer is thinner than the layer thickness of the second electrode layer.

9. The semiconductor device according to claim 1 or 2, wherein Further provided is a field insulating film, and an outer end portion of the first electrode layer is positioned on the field insulating film.

10. The semiconductor device according to claim 1 or 2, wherein It is a Schottky barrier diode.

11. The semiconductor device according to claim 1 or 2, wherein It is a power device.

12. A semiconductor system provided with a semiconductor device, characterized by comprising: The semiconductor device is the semiconductor device according to any one of claims 1 to 11.

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