Patent Application
20210296511
The disclosure relates to a semiconductor device that is useful for a power device and a semiconductor system that including the semiconductor device.
A semiconductor device including a Schottky barrier electrode that is arranged on a semiconductor substrate is known, and various Schottky barrier electrodes have been studied for the purposes of, for example, increasing a reverse direction withstand voltage or decreasing a forward direction turn-on voltage.
Patent Literature 1 describes to provide a first metal on a central portion of a semiconductor and forming a Schottky contact of a second metal and the semiconductor at a peripheral portion of the semiconductor. Here, barrier height between the first metal and the semiconductor is lower and barrier height between the second metal and the semiconductor is higher, in order to increase a reverse direction withstand voltage and to decrease a forward direction turn-on voltage.
Further, it has been also studied on a combination of a Schottky electrode and an Ohmic electrode. For example, Patent Literature 2 describes a wide band gap semiconductor device including a Schottky electrode made of a metal and an Ohmic electrode made of the same type of metal with the Schottky electrode that are arranged on a substrate, and describes that such a configuration enables to improve a thermal breakdown resistance in case that a high current such as a surge current flows in a forward direction. However, there is a problem in an adhesion at an interface of a Schottky junction and an Ohmic junction, an electrode material has to be limited, or there is a problem that barrier height changes depending on a temperature, and it is not necessarily satisfactory. Therefore, a semiconductor device with a low turn-on voltage and an enhanced thermal stability has been expected.
Patent Literature 3 describes a semiconductor device including electrically conductive guard ring that is connected to a main junction bonded on a Schottky electrode, via a short circuit portion, and describes that such a semiconductor device alleviates an electric field concentration and contributes to improving a withstand voltage. However, even when arranging a large number of guard rings, there is a problem of deteriorating a withstand voltage on the contrary because the guard rings are shorted to the main junction.
Patent Literature 1 JP-52-101970 discloses
Patent Literature 2 JP-A-2014-78660
Patent Literature 3 JP-A-2014-107408
An object of the disclosure is to provide a semiconductor device with enhanced semiconductor properties.
As a result of earnest examination to achieve the above object, the inventors found that, a semiconductor device, including: an n-type semiconductor layer; an electrode; two or more p-type semiconductors provided between the n-type semiconductor layer and the electrode, the n-type semiconductor layer containing a corundum-structured crystallin oxide semiconductor as a major component, a number of the two or more p-type semiconductor that is equal to or more than three, and the two or more p-type semiconductors that are embedded in the n-type semiconductor layer enables to reduce a contact resistance, suppressing electric field concentration, and also to enhance withstand voltage of the semiconductor device. The inventors also found that the semiconductor device can solve the above-mentioned problem.
In addition, after learning the above findings, the inventors have made further research to complete the disclosure.
That is, the disclosure relates to the followings.
[1] A semiconductor device, including: an n-type semiconductor layer; an electrode; two or more p-type semiconductors provided between the n-type semiconductor layer and the electrode, the n-type semiconductor layer containing a corundum-structured crystallin oxide semiconductor as a major component, a number of the two or more p-type semiconductor that is equal to or more than three, and the two or more p-type semiconductors that are embedded in the n-type semiconductor layer.
[2] The semiconductor device according to [1] above, wherein the two or more p-type semiconductors are protruded in the electrode.
[3] The semiconductor device according to [1] or [2] above, wherein the crystalline oxide semiconductor contains gallium.
[4] The semiconductor device according to any one of [1] to [3] above, wherein the crystalline oxide semiconductor is α-Ga2O3 or a mixed crystal of α-Ga2O3.
[5] The semiconductor device according to any one of [1] to [4] above, wherein the two or more p-type semiconductors are the oxide semiconductors containing one or more metals selected from Group 13 and Group 9 of the periodic table.
[6] The semiconductor device according to any one of [1] to [5] above, wherein the two or more p-type semiconductors are oxide semiconductors containing gallium.
[7] The semiconductor device according to any one of [1] to [6] above, wherein the two or more p-type semiconductors is crystalline oxide semiconductors, and wherein the crystalline oxide semiconductors have a corundum structure or a hexagonal structure.
[8] The semiconductor device according to any one of [1] to [7] above, wherein the number of the two or more p-type semiconductors is equal to or more than 10.
[9] The semiconductor device according to any one of [1] to [8] above, wherein the p-type semiconductor is epitaxially grown on the n-type semiconductor layer.
[10] The semiconductor device according to any one of [1] to [9] above, wherein the two or more p-type semiconductors include a lateral-growth area.
[11] The semiconductor device according to any one of [1] to [10] above, wherein the semiconductor device is a diode.
[12] The semiconductor device according to any one of [1] to [11] above, wherein the semiconductor device is a Junction barrier Schottky diode.
[13] The semiconductor device according to any one of [1] to [12] above, wherein the semiconductor device is a power device.
[14] A semiconductor system, including: a semiconductor device according to any one of [1] to [13] above.
The semiconductor device according to the disclosure has enhanced semiconductor properties.
The semiconductor device according to an embodiment of the disclosure is A semiconductor device, including: an n-type semiconductor layer; an electrode; two or more p-type semiconductors provided between the n-type semiconductor layer and the electrode, the n-type semiconductor layer containing a corundum-structured crystallin oxide semiconductor as a major component, a number of the two or more p-type semiconductor that is equal to or more than three, and the two or more p-type semiconductors that are embedded in the n-type semiconductor layer. According to an embodiment of the disclosure, it is preferable that the part of two or more p-type semiconductors is protruded in the electrode. The two or more p-type semiconductors may be embedded in the n-type semiconductor layer, by embedding the part of the two or more p-type semiconductors in the n-type semiconductor layer by using a known method. According to such a preferred embodiment, electric field concentration would be more suppressed and a contact resistance would be reduced more.
The electrode is not particularly limited and may be a known electrode. A material of the electrode is not particularly limited as long as the material can be used as an electrode. The material of the electrode may be an electrically conductive inorganic material or may be an electrically conductive organic material. According to an embodiment of the disclosure, the material of the electrode layer is preferably a metal. The metal is not particularly limited. Examples of the metal include at least one metal selected from groups 4 to 11 of the Periodic Table. Examples of a metal of group 4 of the Periodic Table include titanium (Ti), zirconium (Zr), and hafnium (Hf). Among them, Ti is preferred. Examples of a metal of group 5 of the Periodic Table include vanadium (V), niobium (Nb) and tantalum (Ta). Examples of a metal of group 6 of the Periodic Table include one or more metals selected from chromium (Cr), molybdenum (Mo) and tungsten (W) According to an embodiment of the disclosure, the metal of group 6 of the periodic table is preferably Cr. By using such a preferred metal, more enhanced semiconductor properties such as switching characteristics may be realized. Examples of a metal of group 7 of the Periodic Table include manganese (Mn), technetium (Tc), and rhenium (Re) Examples of a metal of group 8 of the Periodic Table include iron (Fe), ruthenium (Ru), and osmium (Os). Examples of a metal of group 9 of the Periodic Table include cobalt (Co), rhodium (Rh), and iridium (Ir). Examples of a metal of group 10 of the Periodic Table include nickel (Ni), palladium (Pd), and platinum (Pt). Among them, Pt is preferred. Examples of a metal of group 11 of the periodic table include copper (Cu), silver (Ag), and gold (Au). Examples of the method of forming the electrode include a known method. The method of forming the electrode, more specifically, for example, is a dry method or a wet method. The dry method may be, for example, a known method such as sputtering, vacuum deposition, and CVD. The wet method may be, for example, screen printing, and die coating. According to an embodiment of the disclosure, the electrode is preferably a barrier electrode (Schottky electrode) that forms a Schottky barrier having a certain barrier height at an interface between the n-type semiconductor layer and the electrode.
The n-type semiconductor layer is not particularly limited as long as the n-type semiconductor includes a corundum structured crystalline oxide semiconductor as a major component. Examples of the corundum-structured crystalline oxide semiconductor includes aluminum oxide, gallium oxide, indium oxide, chromium oxide, iron oxide, titanium oxide, vanadium oxide, cobalt oxide and a mixed crystal thereof. According to an embodiment of the disclosure, the crystalline oxide semiconductor preferably contains one or more metals selected from aluminum, indium and gallium, and more preferably contains at least gallium. According to an embodiment of the disclosure, the crystalline oxide semiconductor is most preferably α-Ga2O3 or a mixed crystal of α-Ga2O3. “major component” herein means, for example, when the crystalline oxide semiconductor is α-Ga2O3, α-Ga2O3 is contained in the n-type semiconductor layer at an atomic ratio of gallium in all the metal element contained in the n-type semiconductor layer that is equal to or more than 0.5. According to an embodiment of the disclosure, it is preferable that the atomic ratio of gallium in all the metal element contained in the n-type semiconductor layer is equal to or more than 0.7, and more preferably equal to or more than 0.8. A thickness of the semiconductor layer is not particularly limited. The thickness of the semiconductor layer may be equal to or less than 1 μm and may be equal to or more than 1 μm. According to an embodiment of the disclosure, the thickness of the semiconductor layer may be preferably in a range of from 1 μm to 40 μm. According to an embodiment of the disclosure, the thickness of the semiconductor layer may be more preferably in a range of from 1 μm to 25 μm. A surface area of the n-type semiconductor layer is not particularly limited. The surface area of the n-type semiconductor layer may be equal to or more than 1 mm2, and may be equal to or less than 1 mm2. The crystalline oxide semiconductor is usually a single crystal, but may be polycrystalline. Also, the n-type semiconductor layer may be a single layer film, or may be a multilayer film. When the n-type semiconductor layer is a multilayer film, the multilayer film preferably has a film thickness that is equal to or less than 40 μm. In case that the n-type semiconductor layer is a multilayer film including at least a first semiconductor layer and a second semiconductor layer and the Schottky electrode is provided on the first semiconductor layer, a carrier concentration of the first semiconductor layer is preferably smaller than a carrier concentration of the second semiconductor layer. In this case, the second semiconductor layer usually contains a dopant. The carrier concentration of the semiconductor layer may be appropriately set by adjusting an amount of the dopant. Also, an orientation of a main surface of the n-type semiconductor layer is not particularly limited. Examples of the orientation of the main surface of the n-type semiconductor layer include a c-plane, m-plane, a-plane, and r-plane. According to an embodiment of the disclosure, it is preferable that the plane orientation of the main surface of the n-type semiconductor layer is m-plane.
The n-type semiconductor layer preferably contains a dopant. The dopant is not particularly limited and may be a known dopant. Examples of the dopant include n-type dopants such as tin, germanium, silicon, titanium, zirconium, vanadium and niobium. According to an embodiment of the disclosure, the dopant is preferably Sn, Ge or Si. The content of the dopant in a composition of the semiconductor layer is preferably equal to or more than 0.00001 atomic %, more preferably in a range of from 0.00001 atomic % to 20 atomic %, and most preferably in a range of 0.00001 atomic % to 10 atomic %. According to an embodiment of the disclosure, when the n-type semiconductor layer is a multilayer film including a first semiconductor layer and a second semiconductor layer, it is preferable that the dopant used for the first semiconductor layer is germanium, silicon, titanium, zirconium, vanadium or niobium, and the dopant used for the second semiconductor layer is tin. Such a preferred configuration enables to further enhance semiconductor properties without impairing the adhesion.
The n-type semiconductor layer is formed, for example, by using a method such as mist CVD method, and more specifically, the n-type semiconductor layer may be preferably obtained by a method including, turning a raw material solution into atomized droplets (atomization step), carrying the obtained atomized droplets to a base with a carrier gas (carrying step), then, depositing a semiconductor film containing a crystalline oxide semiconductor as a major component on the base by thermally reacting the atomized droplets in the deposition chamber (deposition step).
At an atomization step, the raw material solution is turned into atomized droplets. A method of forming atomized droplets from the raw material solution is not particularly limited, as long as the raw material solution is able to be turned into atomized droplets, and may be a known method. According to one or more embodiments of the disclosure, a method of forming atomized droplets using ultrasonic vibration is preferable. Atomized droplets including mist particles and obtained by using ultrasonic vibration and floating in the space have the initial velocity that is zero. Since atomized droplets floating in the space is carriable as a gas, the atomized droplets floating in the space are preferable to avoid damage caused by the collision energy without being blown like a spray. The droplet size is not particularly limited and may be a droplet of about several millimeters, but is preferably 50 μm or less, and more preferably 100 nm to 10 μm.
The raw material solution is not particularly limited as long as the atomized droplets can be formed from the raw material solution and as long as the raw material solution includes a raw material capable of forming the n-type semiconductor layer. The raw material may be an inorganic material or an organic material. According to one or more embodiments of the disclosure, the raw material is preferably a metal or a metal compound, and more preferably contains one or more metals selected from among gallium, iron, indium, aluminum, vanadium, titanium, chromium, rhodium, nickel, cobalt, zinc, magnesium, calcium, silicon, yttrium, strontium and barium.
According to one or more embodiments of the disclosure, a raw material solution containing at least one metal, in a form of complex or salt, dissolved or dispersed in an organic solvent or water may be used. Examples of the form of the complex include an acetylacetonate complex, a carbonyl complex, an ammine complex and a hydride complex. Examples of the form of the salt includes an organic metal salt (e.g., metal acetate, metal oxalate, metal citrate, etc.), metal sulfide, metal nitrate, phosphorylated metal and metal halide (e.g., metal chloride, metal bromide, metal iodide, etc.).
Further, raw material solution may contain a hydrohalic acid and/or an oxidant as an additive. Examples of the hydrohalic acid include hydrobromic acid, hydrochloric acid and hydroiodic acid. Among all, hydrobromic acid or hydroiodic acid may be preferable for a reason to obtain a film of better quality. Examples of the oxidant include hydrogen peroxide (H2O2), sodium peroxide (Na2O2), barium peroxide (BaO2), a peroxide including benzoyl peroxide (C6H5CO)2O2, hypochlorous acid (HClO), perchloric acid, nitric acid, ozone water, and an organic peroxide such as peracetic acid and nitrobenzene.
The raw material solution may contain a dopant. By adding a dopant into the raw material solution, it is possible to preferably perform doping. The dopant is not particularly limited unless it deviates from an object of the disclosure. Examples of the dopant include n-type dopants. The n-type dopants may include tin, germanium, silicon, titanium, zirconium, vanadium or niobium. Also, examples of the dopant include p-type dopants. The dopant concentration in general may be approximately in a range of from 1×1016/cm3 to 1×1022/cm3. The dopant concentration may be at a lower concentration of, for example, approximately equal to or less than 1×1017/cm3. According to one or more embodiments of the disclosure, the dopant may be contained at a high concentration of, for example, approximately equal to or more than 1×1020/cm3. According to one or more embodiments of the disclosure, it is preferable that the dopant is contained in a carrier concentration of equal to or more than 1×1017/cm3.
A solvent of the raw material solution is not particularly limited unless it deviates from an object of the disclosure. The solvent may be an inorganic solvent such as water. The solvent may be an organic solvent such as alcohol. Also, the solvent may be a mixed solvent of the inorganic solvent and the organic solvent. According to one or more embodiments of the disclosure, the solvent preferably includes water. According to one or more embodiments of the disclosure, the solvent is more preferably water or a mixed solvent of water and alcohol.
At a carrying step, the atomized droplets are delivered to a deposition chamber by using a carrier gas. The carrier gas is not particularly limited unless it deviates from an object of the disclosure. Examples of the carrier gas includes oxygen, ozone, an inert gas such as nitrogen or argon and a reduction gas such as hydrogen gas or a forming gas. Further, the carrier gas may contain one or two or more gasses. Also, a diluted gas (e.g., 10-fold diluted carrier gas) and the like may be further used as a second carrier gas. The carrier gas may be supplied from one or more locations. A flow rate of the carrier gas is not particularly limited. The flow rate of the carrier gas is preferably in a range of from 0.01 L/min to 20 L/min and more preferably in a range of from 1 L/min to 10 L/min. For the diluted carrier gas, a flow rate of the dilute carrier gas may be preferably in a range of from 0.001 L/min to 2 L/min, and more preferably in a range of from 0.1 L/min to 1 L/min.
At a deposition step, the semiconductor film is deposited on the base by a thermal reaction of the atomized droplets in a deposition chamber. The thermal reaction is not particularly limited as long as the atomized droplets react with heat. Reaction conditions and the like are not particularly limited unless it deviates from an object of the disclosure. In the deposition step, the thermal reaction is in general carried out at an evaporation temperature of the solvent of the raw material solution or at a higher temperature than the evaporation temperature. The temperature during the thermal reaction is equal to or less than a too high temperature (for example, 1000° C.), and preferably equal to or less than 650° C., and more preferably in a range of from 300° C. to 650° C. Further, the thermal reaction may be conducted, unless it deviates from an object of the disclosure, in any atmosphere of a vacuum, a non-oxygen atmosphere, a reducing gas atmosphere and an oxygen atmosphere. According to an embodiment of the disclosure, the thermal reaction may be preferably conducted in a non-oxygen atmosphere or an oxygen atmosphere. Further, the thermal reaction may be conducted in any conditions of under atmospheric pressure, under increased pressure, and under a reduced pressure. According to one or more embodiments of the disclosure, the thermal reaction may be preferably conducted under an atmospheric pressure. Further, a film thickness can be set by adjusting a deposition time.
A base is not particularly limited as long as the base can support the semiconductor film. A material of the base is not particularly limited unless it deviates from an object of the disclosure, and may be a known base. The base may be an organic compound, or may be an inorganic compound. The base may be in any shape, and can perform for any shape. Examples of the shape of the base includes plate such as flat plate or a disc, fibrous, bar, columnar, prismatic, cylindrical, spiral, spherical and annular. According to one or more embodiments of the disclosure, the base is preferably a substrate. A thickness of the substrate is not particularly limited according to one or more embodiments of the disclosure.
The substrate is not particularly limited as long as the substrate is in the shape of plate and can support the semiconductor film. The substrate may be an insulator substrate or a semiconductor substrate. The substrate may be an insulator substrate, a semiconductor substrate, a metal substrate or a conductive substrate. According to an embodiment of the disclosure, the substrate is preferably an insulator substrate. It is also preferable that the substrate may have a metal film on a surface thereof. Examples of the substrate include a substrate including a substrate material with a corundum structure as a major component, a substrate including a substrate material with a β-Gallia structure as a major component or a substrate including a substrate material with a hexagonal structure as a major component. The term “major component” herein means that the substrate preferably contains a substrate material with a particular crystalline structure at an atomic ratio of 50% or more to all components of a substrate material contained in the substrate. The substrate preferably contains the substrate material with the particular crystalline structure at an atomic ratio of 70% or more to all components of the substrate material contained in the substrate and more preferably contains at an atomic ratio of 90% or more. The substrate may contain the substrate material with the particular crystalline structure at an atomic ratio of 100% to all components of the substrate material contained in the substrate.
The substrate material is not particularly limited as long as it deviates from an object of the disclosure, and may be a known substrate material. Examples of the substrate material with the corundum structure include α-Al2O3 (sapphire substrate) or α-Ga2O3. Also, preferable examples of the substrate material with the corundum structure include an a-plane sapphire substrate, an m-plane sapphire substrate, an r-plane sapphire substrate, a c-plane sapphire substrate and an α-type gallium oxide substrate (a-plane, m-plane or r-plane). Examples of the substrate including the substrate material with the β-Gallia structure as a major component include a β-Ga2O3 substrate or a mixed crystal substrate containing Al2O3 and Ga2O3 where Al2O3 is more than 0 wt % and equal to or less than 60 wt %. Examples of the substrate including the substrate material with a hexagonal structure include a SiC substrate, a ZnO substrate and a GaN substrate. According to an embodiment of the disclosure, the sapphire substrate is preferably an m-plane sapphire substrate.
According to one or more embodiments of the disclosure, annealing may be performed after the deposition step. An annealing temperature is not particularly limited unless it deviates from an object of the disclosure. The annealing temperature may be generally in a range of from 300° C. to 650° C., and may be preferably in a range of from 350° C. to 550° C. An annealing time is generally in a range of from 1 minute to 48 hours, preferably in a range of from 10 minutes to 24 hours, and more preferably in a range of from 30 minutes to 12 hours. The annealing may be performed in any atmosphere unless it deviates from an object of the disclosure. According to an embodiment of the disclosure, the thermal reaction is preferably performed in a non-oxygen atmosphere, more preferably performed in a nitrogen atmosphere
According to one or more embodiments of the disclosure, the semiconductor film may be provided directly on the base, or may be provided via another layer such as a buffer layer or a stress relief layer. A forming method of each layer is not particularly limited and may be a known method, however, a mist CVD method is preferred according to one or more embodiments of the disclosure.
Also, according to one or more embodiments of the disclosure, the semiconductor film that is separated from the base and the like by use of a known method may be used as the semiconductor region. The semiconductor film may be used as the semiconductor region, as it is.
The p-type semiconductor (the two or more p-type semiconductors) is not particularly limited unless it deviates from an object of the disclosure. Examples of the p-type semiconductor include a crystalline oxide semiconductor that is p-type doped by use of a p-type dopant (preferably Mg, Zn or Ca). In addition to Mg, Zn and Ca, examples of the p-type dopant include, one or more elements selected from H, Li, Na, K, Rb, Cs, Fr, Be, Sr, Ba, Ra, Mn, Fe, Co, Ni, Pd, Cu, Ag, Au, Cd, Hg, Tl, Pb, N, and P. The p-type semiconductor preferably has a corundum structure or a hexagonal structure, and more preferably has a corundum structure. According to an embodiment of the disclosure, the p-type semiconductor is preferably an oxide semiconductor containing one or more metals selected from Group 9 and Group 13 of the periodic table. Examples of a metal of group 9 of the Periodic Table include cobalt, rhodium and iridium. According to embodiment of the disclosure, the iridium is preferred. Examples of a metal of group 13 of the Periodic Table include aluminum, gallium and indium. According to one or more embodiments of the disclosure, the p-type semiconductor more is preferably an InAlGaO-based semiconductor, and is the most preferably α-Ga2O3 or a mixed crystal of α-Ga2O3. Examples of the mixed crystals of the alpha-Ga2O3 include a mixed crystal of α-Ga2O3 and one or more of metal oxides. Preferable examples of the metal oxide include aluminum oxide, indium oxide, iridium oxide, rhodium oxide and iron oxide. According to an embodiment of the disclosure, the mixed crystal of α-Ga2O3 is preferably a mixed crystal of the α-Ga2O3 and α-Ir2O3. The p-type semiconductor may be obtained by, for example, mist-CVD method using a raw material solution including a metal and additionally including the p-type dopant and hydrobromic acid. Each step and each condition of the mist CVD method may be the same as each step and each condition of the atomization step, the carrying step and the deposition step. A number of the two or more p-type semiconductors embedded in the n-type semiconductor layer not particularly limited as long as the number is equal to three or more. According to an embodiment of the disclosure, the number of the two or more p-type semiconductors is preferably equal to or more than four. Such a preferred configuration enables to suppress the electric field concentration more effectively. Also, such a preferred configuration enables to further enhance the electrical properties of the semiconductor device. According to an embodiment of the disclosure, the number of the two or more p-type semiconductors is more preferably equal to or more than ten, most preferably equal to or more than forty. According to such a preferred embodiment, a threshold voltage of the semiconductor device may be further lowered and temperature stability of the semiconductor device may be more enhanced. Also, such a preferred embodiment enables to further enhance withstand voltage of the semiconductor device.
According to an embodiment of the disclosure, a distance from a first p-type semiconductor to a second p-type semiconductor that is adjacent to the first p-type semiconductor is not particularly limited unless it deviates from an object of the disclosure. According to an embodiment of the disclosure, the distance between the first p-type semiconductor and the second p-type semiconductor may be preferably in a range of from 0.125 μm to 4 μm. Further, the p-type semiconductor is preferably embedded in the n-type semiconductor layer. A depth of the p-type semiconductor embedded in the n-type semiconductor layer is not particularly limited unless it deviates from an object of the disclosure. According to an embodiment of the disclosure the depth of the p-type semiconductor embedded in the n-type semiconductor layer is preferably in a range of from 0.125 μm to 4 μm. Also, according to an embodiment of the disclosure, the p-type semiconductor is preferably epitaxially-grown on the n-type semiconductor layer. According to an embodiment of the disclosure, it is also preferable that the p-type semiconductor includes a lateral-growth region. By using such a preferred p-type semiconductor, even when the crystalline oxide semiconductor contains gallium, it is possible to achieve a better performance as a junction barrier Schottky diode (JBS).
When the p-type semiconductor is an oxide semiconductor containing iridium, the p-type semiconductor may be formed, for example, by using a metal oxide gas as a raw material, and conducting a crystal growth on a base having a corundum structure. In more detail, for example, a solid substance (e.g., powder) of the metal oxide gas is sublimed (sublimation step), and then crystal growth is conducted on the base having the corundum structure, using the obtained metal oxide gas (crystal growth step).
At the sublimation step, a solid substance of the metal oxide gas (e.g., powder) is sublimed to form a gaseous state and to, thereby obtaining a metal oxide gas. Examples of the metal oxide gas include a gaseous oxide of a metal that is contained in the p-type oxide semiconductor film. A valence and the like of the metal oxide is not particularly limited unless it deviates from an object of the disclosure. The valence of the metal oxide may be monovalent and may be divalent. The valence of the metal oxide may be trivalent or tetravalent. According to an embodiment of the disclosure, the metal oxide preferably contains a metal of group 9 of the periodic table, and more preferably contains iridium. When the p-type oxide semiconductor contains a mixed crystal, it is also preferable that the metal oxide contains iridium and a metal of group 9 of the periodic table other than iridium, or a metal of group 13 of the periodic table. By using a preferred metal oxide as described above, a p-type semiconductor that has a band gap of equal to or more than 2.4 eV. Therefore, it is possible to exhibit a wider band gap and enhanced electrical properties in the p-type semiconductor.
According to one or more embodiments of the disclosure, when the p-type oxide semiconductor is an oxide semiconductor containing iridium, IrO2 gas is preferably used as the metal oxide gas. Examples of the sublimation method include heating method. A heating temperature is not particularly limited, but is preferably in a range of from 600° C. to 1200° C., more preferably in a range of from 800° C. to 1000° C. According to one or more embodiments of the disclosure, it is preferable that the metal oxide gas obtained by sublimation is transported to a base by a carrier gas. A type of the carrier gas is not particularly limited unless it deviates from an object of the disclosure. Examples of the carrier gas include oxygen, ozone, an inert gas such as nitrogen, or argon, or a reducing gas such as a hydrogen gas or a forming gas. In an embodiment of the present invention, oxygen is preferably used as the carrier gas. According to one or more embodiments of the disclosure, it is preferable to use oxygen as the carrier gas. Examples of the carrier gas that uses oxygen include air, oxygen gas, ozone gas, and in particular, oxygen gas and/or ozone gas are preferable. Further, the carrier gas may contain one or two or more gasses. Also, a diluted gas (e.g., 10-fold diluted carrier gas) and the like may be further used as a second carrier gas. The carrier gas may be supplied from one or more locations. While a flow rate of the carrier gas is not particularly limited, but may be preferably in a range of from 0.01 L/min to 20 L/min and more preferably in a range of from 1 L/min to 10 L/min.
At the crystal growth step, a crystal growth is conducted in a vicinity of a surface of the base to form a film on a part or all of the surface of the base. A temperature of the crystal growth is preferably lower than the heating temperature in the sublimation step, more preferably equal to or less than 900° C. or less, and most preferably in a range of from 500° C. to 900° C. The crystal growth may be conducted in any atmosphere of a vacuum, a non-oxygen, atmosphere, a reducing gas atmosphere and an oxygen atmosphere, unless it deviates from an object of the disclosure. The crystal growth may be conducted in any conditions of under an atmospheric pressure, under an increased pressure, and under a reduced pressure, unless it deviates from an object of the disclosure According to one or more embodiments of the disclosure, it is preferable that the crystal growth is conducted under an oxygen atmosphere, preferably under an atmospheric pressure, and more preferably under an oxygen atmosphere and at atmospheric pressure. “Oxygen atmosphere” is not particularly limited as long as the oxygen atmosphere is an atmosphere in which a crystal of the metal oxide or a mixed crystal of the metal oxide can be formed and is an atmosphere in which oxygen or a compound including oxygen are present. The oxygen atmosphere may be formed, for example, by using a carrier gas including oxygen or by using an oxidant. Further, a film thickness can be set by adjusting a deposition time. According to one or more embodiments of the disclosure, the metal oxide gas may contain a p-type dopant to make the p-type semiconductor to be doped by the p-type dopant. Examples of the p-type dopant include Mg, H, Li, Na, K, Rb, Cs, Fr, Be, Ca, Sr, Ba, Ra, Mn, Fe, Co, Ni, Pd, Cu, Ag, Au, Zn, Cd, Hg, Tl, Pb, N, P, and two or more elements thereof. According to one or more embodiments of the disclosure, the p-type dopant is preferably a metal of Group 1 in the periodic table or a metal of Group 2 in the periodic table, more preferably a metal of Group 2 in the periodic table, and most preferably magnesium. Further, according to one or more embodiments of the disclosure, the p-type oxide semiconductor film obtained by the crystal growth process may be annealed.
The semiconductor device according to an embodiment of the disclosure generally includes an Ohmic electrode. The Ohmic electrode is not particularly limited unless it deviates from an object of the disclosure and may be a known electrode material. According to an embodiment of the disclosure, the Ohmic electrode may contain a metal of the Group 4 and/or Group 11 of the periodic table. Preferred metal of the Group 4 and/or Group 11 of the periodic table used for the Ohmic electrode may be same as the metal contained in the Schottky electrode. Also, the Ohmic electrode may be a single metal layer or may include two or more metal layers. A method of forming the Ohmic electrode is not particularly limited. Examples of the method of forming the Ohmic electrode include a known method such as a vacuum evaporation method or a sputtering method. The metal contained in the Ohmic electrode may be an alloy. According to one or more embodiments of the disclosure, the Ohmic electrode preferably contains Ti and/or Au.
Hereinafter, although preferable embodiments of the disclosure are described, the disclosure is not limited to these embodiments.
A method of forming each layer included in the semiconductor device of
Hereinafter, with reference to
A material with high barrier height is in general used as the guard ring. Examples of the material used as the guard ring include a conductive material with barrier height of equal to or more than 1 eV. The material used as the guard ring may be the same material as the electrode material described above. According to one or more embodiments of the disclosure, the material used in the guard ring is preferably the above-mentioned metal, for a reason that larger flexibility in a design of a withstand-voltage structure can be provided, a large number of guard rings can be provided, and a withstand voltage can be flexibly made improved. A shape of the guard ring is not particularly limited, but may be square-shape, circular, channel-shape, L-shape or band-shape. While a number of the guard rings is not particularly limited, a number of the guard rings may be preferably three or more and more preferably six or more. While the semiconductor device of
Hereinafter, with reference to
Then, removing a part of the barrier electrode 2 and a part of the n-type semiconductor layer 3 of the multilayer structure of
In the above description, the guard ring 5 is formed at the end of the process, however, according to one or more embodiments of the disclosure, it is also preferable to forming the guard ring 5 prior to form the barrier electrode 2, for a reason that it is possible to suppress affecting by metal at the time of forming electrodes.
Examples of a method of forming each layer of the semiconductor device of
Hereinafter, with reference to
The semiconductor device is particularly useful for power devices. Examples of the semiconductor device include a diode or transistor (e.g., MESFET, etc.). Among all, a diode is preferable and a junction barrier Schottky diode (JBS) is more preferable.
In addition, the semiconductor device according to the disclosure may be used as a power module, an inverter, and/or a converter in combination with a known structure. Also, a semiconductor device according to the disclosure may be used in a semiconductor system including a power source, to which the semiconductor device may be electrically connected by a known structure and/or method. The semiconductor device may be electrically connected to a wiring pattern in the semiconductor system.
In a reference example 1, an adjustment of barrier height by using a p-type semiconductor was evaluated.
1-1. Deposition of a p-Type Semiconductor Layer
With reference to
Gallium bromide and magnesium bromide were mixed in ultrapure water to be a raw material solution such that the atomic ratio of magnesium to gallium is 1:0.01 and gallium bromide is 0.1 mol/L, and the raw material solution contains hydrohalic acid to be 20% by volume ratio.
The raw material solution 24a obtained at 1-1-2. was set in the mist generator 24. Then, as the substrate 20, a sapphire substrate, that has an n+-type semiconductor layer (α-Ga2O3) formed by mist CVD on its surface, was placed on the susceptor 21, and the heater 28 was activated to raise a temperature in the deposition chamber 27 up to 520° C. The flow control valves 23a and 23b were opened to supply a carrier gas from the carrier gas supply devices 22a and 22b that are carrier gas source into the deposition chamber 27 to replace an atmosphere in the deposition chamber with the carrier gas. After the atmosphere in the deposition chamber 27 was sufficiently replaced with the carrier gas, a flow rate of the carrier gas was adjusted at 1 L/min and a flow rate of the carrier gas (diluted) was adjusted at 1 L/min. In this embodiment, nitrogen was used as the carrier gas.
The ultrasonic transducer 26 was then vibrated at 2.4 MHz, and the vibration propagated through the water 25a to the raw material solution 24a, to atomize the raw material solution 24a to form a mist. The mist was introduced into the deposition chamber 27 by the carrier gas. The mist reacted at 520° C. under an atmospheric pressure to deposit a semiconductor film on the substrate 20. A deposition time was 60 minutes.
The obtained film at 1-1-4. was identified by X-ray diffraction device and revealed to be α-Ga2O3.
In order to confirm whether magnesium works properly as a p-type dopant in a p-type semiconductor layer, I-V measurement was conducted on the α-Ga2O3 film obtained in at 1-1. The result is illustrated in
In a reference example 2, an adjustment of barrier height by using a p-type semiconductor was evaluated.
2-1. Deposition of a p-Type Semiconductor Layer
With reference to
As a raw material 5, IrO2 powder was placed on the raw material mount 4, and as a substrate 6, a sapphire substrate was placed on the susceptor 7. Next, a temperature of the heater 3 was raised up to 850° C., and by heating IrO2 powder placed on the raw material mount 4 sublimating IrO2 powder to produce a gaseous iridium oxide.
A carrier gas was supplied into the quartz cylinder 52 from a carrier gas supply source while maintaining the temperature of the heater 53 at 850° C., to supply the metal oxide gas (gaseous iridium oxide) generated in the above 52. to the substrate 56 through the quartz cylinder 52. The flow rate of the carrier gas was 1.0 L/min, and oxygen was used as the carrier gas. The metal oxide gas was reacted in a vicinity of a surface of the substrate 6 under atmospheric pressure, and a film was formed on the substrate. A deposition time was 120 minutes.
The obtained film at 2-1. was identified by X-ray diffraction device and revealed to be α-Ir2O3. After forming an n−-type semiconductor layer (α-Ga2O3) and an n+-type semiconductor layer (α-Ga2O3) by mist CVD method, I-V measurement was conducted. As a result, excellent rectifying property was observed and the n+-type semiconductor layer and the p-type semiconductor layer formed a good PN junction. Since magnesium works properly as a p-type dopant it was revealed that barrier height may be adjusted by forming a p-type semiconductor.
1. Formation of an n+-Type Semiconductor Layer
With reference to
Tin bromide was mixed to a 0.1 M aqueous gallium bromide solution, and the aqueous gallium bromide solution containing tin bromide was prepared to have an atomic ratio of tin to gallium that is 1:0.12, and at this point, hydrobromic acid was contained in the aqueous gallium bromide solution containing tin bromide to have a volume ratio of 15% of the aqueous solution that would be a raw-material solution.
The raw material solution 24a obtained at 2. was set in the mist generator 24. Then, as the substrate 20, an m-plane sapphire substrate that has an undoped α-Ga2O3 buffer layer on its surface was placed on the hot plate 28, and the hot plate 28 was activated to raise a temperature of the substrate up to 600° C. The flow control valve 23a and 23b were opened to supply a carrier gas from the carrier gas supply device 22a and 22b that are the carrier gas source into the deposition chamber 30 to replace the atmosphere in the deposition chamber 30 with the carrier gas. After the atmosphere in the deposition chamber 30 is sufficiently replaced with the carrier gas, a flow rate of the carrier gas was regulated at 1.0 L/min and the flow rate of the diluted carrier gas was regulated at 1.0 L/min. In this embodiment, nitrogen was used as the carrier gas.
The ultrasonic transducer 26 was then vibrated at 2.4 MHz, and the vibration propagated through the water 25a to the raw material solution 24a to atomize the raw material solution 24a to form a mist (atomized droplets) 24b. The mist 24b was introduced in the film deposition chamber 30 by the carrier gas through the supply pipe 27. The mist was thermally reacted at 600° C. under atmospheric pressure to deposit a film on the substrate 20. A deposition time was one hour. The obtained film was identified by X-ray diffraction device, and revealed to be α-Ga2O3 single-crystal film.
2. Formation of an n-Type Semiconductor Layer
An n−-type semiconductor layer was formed on the n+-type semiconductor layer obtained at 1. by a method similarly to the method of 1. except the following conditions: gallium bromide was mixed to a ultra pure water to make a 0.1 M aqueous gallium bromide solution, and at this point, hydrobromic acid was contained in the aqueous gallium bromide solution to have a volume ratio of 10% of the aqueous solution that would be a raw-material solution; the film formation time was set to be 50 minutes. The obtained film was identified by X-ray diffraction device, and revealed to be α-Ga2O3 single-crystal film. Here, the n−-type semiconductor layer was formed to be patterned by using a mask, so that a part of the n+-type semiconductor layer is exposed.
A mask pattern for embedded p-type semiconductor layer was formed by following steps: SiOe2 film was deposited on the n−-type semiconductor layer obtained at above 2.; then, conducting photolithography and wet etching.
4. Formation of Embedded p-Type Semiconductors
A p-type semiconductor was formed on the mask pattern obtained at above 3. by a method similarly to the method of above 1. except the following conditions: magnesium bromide was mixed to a 0.1 M aqueous gallium bromide solution, and the aqueous gallium bromide solution containing tin bromide was prepared to have an atomic ratio of magnesium to gallium that is 1:0.1, and at this point, hydrobromic acid was contained in the aqueous gallium bromide solution containing magnesium bromide to have a volume ratio of 20% of the aqueous solution that would be a raw-material solution; the temperature of film formation was set to be 540° C.; the film formation time was set to be 50 minutes. Here, a p-type semiconductor located between both ends of the Schottky electrode and the n−-type semiconductor layer was formed as a guard ring. The obtained p-type semiconductor was identified by X-ray diffraction device, and revealed to be α-Ga2O3 single-crystal film.
5. Regrowth of the n-Type Semiconductor Layer
After removing SiO2 mask pattern formed at the above 3. by etching, an n−-type semiconductor layer was regrown so that a part of the p-type semiconductor obtained at the above 4. is embedded in the n−-type semiconductor layer. The regrowth of the n−-type semiconductor layer was conducted by a method similarly to the method of the above 2. except that the film formation time was set to be 25 minutes. A number of embedded p-type semiconductors was forty.
Co was formed as a Schottky electrode on the n−-type semiconductor layer in which the p-type semiconductors were embedded. Here, the formation of Co was carried out by using EB evaporation. A film thickness of Co was 200 nm.
Ti was formed as an Ohmic electrode on the n+-type semiconductor layer that was exposed at the above 2. Here, the formation of Ti was carried out by using EB deposition. A film thickness of Ti was 200 nm.
A part of a cross section of the obtained JBS diode was observed by using TEM. As apparent from
1. Formation of an n+-Type Semiconductor Layer
An n+-type semiconductor layer was formed by a method similarly to the method of above 1. in the example 1, except the following conditions: tin bromide was mixed to a 0.1 M aqueous gallium bromide solution, and the aqueous gallium bromide solution containing tin bromide was prepared to have an atomic ratio of tin to gallium that is 1:0.04, and at this point, hydrobromic acid was contained in the aqueous gallium bromide solution containing tin bromide to have a volume ratio of 15% of the aqueous solution that would be a raw-material solution; the film formation time was set to be 10 minutes. The obtained film was identified by X-ray diffraction device, and revealed to be α-Ga2O3 single-crystal film.
2. Formation of an n−-Type Semiconductor Layer
An n−-type semiconductor layer was formed by a method similar to the method of above 2. in the example 1, except that the film formation time was set to be 20 minutes. The obtained film was identified by X-ray diffraction device, and revealed to be α-Ga2O3 single-crystal film.
3. Formation of Grooves for Embedding p-Type Semiconductors
Using photolithography and dry etching, grooves for embedding p-type semiconductors were formed in the n−-type semiconductor layer obtained in the above 2.
4. Formation of Embedded p-Type Semiconductors
P-type semiconductors were deposited by a method similar to the method of above 4. in the example 1, except that the deposition time was set to be 14 minutes. A number of p-type semiconductors embedded in the n−-type semiconductor was 75.
A Schottky electrode was formed on the n−-type semiconductor in which the p-type semiconductors were embedded by a method similar to the method of above 6. in the example 1.
An ohmic electrode was formed on an exposed surface of the n+-type semiconductor layer by a method similar to the method of above 7. in the example 1. Here, the exposed surface was provided by etching.
A part of a cross section of the obtained JBS diode was observed in the same manner as in Example 1. The observation revealed that the p-type semiconductors were embedded in the n-type semiconductor layer, and the p-type semiconductors were protruded into the Schottky electrode. In addition, the p-type semiconductors included an excellent lateral-growth region.
A SBD was fabricated by a method similar to the method of example 1, except that the formation of p-type semiconductors were not performed.
A JBS was fabricated by a method similar to the method of example 1 except the following conditions: p-type semiconductors were formed not to protruded into the electrode; the two p-type semiconductors were formed.
I-V measurement was performed regarding a JBS obtained in Example 2 and Comparative Example 1. The results are illustrated in
The semiconductor device according to one or more embodiments of the disclosure can be used in various fields such as semiconductors (e.g., compound semiconductor electronic devices), electronic parts, electric equipment parts, optical electrophotographic related apparatus, industrial members, and especially useful for power devices.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2018-132763 | Jul 2018 | JP | national |
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/JP2019/027378 | 7/10/2019 | WO | 00 |
