JP6994181B2 - Crystalline oxide semiconductor membranes and semiconductor devices - Google Patents

Description

The present invention relates to a crystalline oxide semiconductor film useful for a semiconductor device, and a semiconductor device and a system using the crystalline semiconductor oxide film.

As a next-generation switching element capable of achieving high withstand voltage, low loss, and high heat resistance, semiconductor devices using gallium oxide (Ga ₂ O ₃ ) with a large bandgap are attracting attention, and are used for power semiconductor devices such as inverters. Expected to be applied. Moreover, due to the wide bandgap, it is expected to be applied as a light receiving / receiving device such as an LED or a sensor. According to Non-Patent Document 1, the gallium oxide can control the bandgap by mixing indium and aluminum individually or in combination, and constitutes an extremely attractive material system as an InAlGaO-based semiconductor. .. Here, the _InAlGaO -based semiconductor is In _X Al _Y Ga ZO ₃ (0 ≦ X ≦ 2, 0 ≦ Y ≦ 2, 0 ≦ Z ≦ 2, X + Y + Z = 1.5 to 2.5), and gallium oxide is used. It can be overlooked as the same material system included.

Patent Document 1 describes a highly crystalline conductive α-Ga ₂ O ₃ thin film in which Sn is doped on a c-plane sapphire substrate. Although the thin film described in Patent Document 1 is an α _- Ga ₂ O3 thin film having a rocking curve half width of about 60 arcsec and high crystallinity in the X-ray diffraction method, it cannot maintain sufficient pressure resistance. In addition, the mobility is 1 cm ² / Vs or less, and the semiconductor characteristics are not satisfactory, and it is still difficult to use it in a semiconductor device.

Further, Patent Document 2 describes an α-Ga ₂ O ₃ film doped with Ge on a c-plane sapphire substrate, and α-Ga ₂ O ₃ which is superior in electrical characteristics to the thin film described in Patent Document 1. Although a thin film has been obtained, the mobility is 3.26 cm ² / Vs, which is still unsatisfactory for use in semiconductor devices.

In Non-Patent Document 2, a Sn-doped α _- Ga ₂ O3 film is prepared on a c-plane sapphire substrate, then annealed to form an annealing buffer layer, and then Sn-doped α is applied onto the annealing buffer layer. -The mobility is improved by forming a Ga ₂ O ₃ film. Further, it has been obtained that the surface roughness and crystallinity of the α-Ga ₂ O ₃ thin film are improved and the mobility is improved because Sn exerts a surfactant effect by doping with Sn. However, there is a problem that the resistance is increased or the insulation is increased by the annealing treatment, and there is still a problem in using it in a semiconductor device. In addition, the obtained film still has many dislocations and is strongly affected by dislocation scattering, which causes a problem of impairing electrical characteristics. Further, there is a problem that there are many cracks, and an industrially useful α-Ga ₂ O ₃ film has been long-awaited.

Japanese Unexamined Patent Publication No. 2013-028480 Japanese Unexamined Patent Publication No. 2015-228495

Kentaro Kaneko, "Growth and Physical Properties of Corundum Structure Gallium Oxide Mixed Crystal Thin Film", Doctoral Dissertation, Kyoto University, March 2013 Kazuaki Akaiwa, "Electrical Property Control and Device Application of Corundum Structure Gallium Oxide Semiconductor", Doctoral Dissertation, Kyoto University, March 2016

An object of the present invention is to provide a crystalline oxide semiconductor film having excellent electrical characteristics, particularly mobility.

As a result of diligent studies to achieve the above object, the present inventors surprisingly, when a film is formed by using the mist CVD method under specific conditions, without performing high resistance treatment or insulation treatment. Further, even if the half price width is, for example, 100 arcsec or more, a crystalline oxide semiconductor film having excellent mobility can be obtained, and the obtained crystalline oxide semiconductor film has reduced cracks. It was found that this crystalline oxide semiconductor film can solve the above-mentioned conventional problems at once.
In addition, after obtaining the above findings, the present inventors have further studied and completed the present invention.

That is, the present invention relates to the following invention.
[1] A crystalline oxide semiconductor film containing a crystalline oxide semiconductor having a corundum structure as a main component and further containing a dopant, characterized by having a mobility of 30 cm ² / Vs or more. Material semiconductor film.
[2] The crystalline oxide semiconductor film according to the above [1], which has a carrier density of 1.0 × 10 ¹⁸ / cm ³ or more.
[3] The crystalline oxide semiconductor film according to the above [1] or [2], which has a resistivity of 50 mΩcm or less.
[4] The crystalline oxide semiconductor film according to any one of the above [1] to [3], which has a resistivity of 5 mΩcm or less.
[5] The crystalline oxide semiconductor film according to any one of the above [1] to [4], wherein the main surface is the a-plane or the m-plane.
[6] The crystalline oxide semiconductor film according to any one of the above [1] to [5], wherein the dopant is tin, germanium or silicon.
[7] The crystalline oxide semiconductor film according to any one of the above [1] to [6], wherein the dopant is tin.
[8] The crystalline oxide semiconductor film according to any one of the above [1] to [7], wherein the crystalline oxide semiconductor contains gallium, indium or aluminum.
[9] The crystalline oxide semiconductor film according to any one of the above [1] to [9], wherein the crystalline oxide semiconductor contains at least gallium.
[10] A semiconductor device including at least a semiconductor layer and electrodes, wherein the crystalline oxide semiconductor film according to any one of claims 1 to 9 is used as the semiconductor layer.
[11] A semiconductor system including a semiconductor device, wherein the semiconductor device is the semiconductor device according to claim 10.

The crystalline oxide semiconductor film of the present invention is excellent in electrical characteristics, particularly mobility.

It is a schematic block diagram of the film forming apparatus (mist CVD apparatus) used in an Example. It is a figure which shows typically a suitable example of a Schottky barrier diode (SBD). It is a figure which shows typically a suitable example of a high electron mobility transistor (HEMT). It is a figure which shows typically a suitable example of a metal oxide film semiconductor field effect transistor (PWM). It is a figure which shows typically a suitable example of a junction field effect transistor (JFET). It is a figure which shows typically a suitable example of an insulated gate type bipolar transistor (IGBT). It is a figure which shows typically a suitable example of a light emitting element (LED). It is a figure which shows typically a suitable example of a light emitting element (LED). It is a figure which shows typically a suitable example of a power-source system. It is a figure which shows typically a suitable example of a system apparatus. It is a figure which shows typically a preferable example of the power supply circuit diagram of a power supply device. It is a figure which shows the XRD measurement result in an Example. It is a figure which shows the Hall effect measurement result in a test example. The vertical axis is mobility (cm ² / Vs), and the horizontal axis is carrier density (/ cm ³ ). It is a figure which shows the temperature variable Hall effect measurement result in a test example. The vertical axis is mobility (cm ² / Vs), and the horizontal axis is temperature (K).

The crystalline oxide semiconductor film of the present invention is a crystalline oxide semiconductor film containing a crystalline oxide semiconductor having a corundum structure as a main component and further containing a dopant, and has a mobility of 30 cm ² / Vs or more. It is characterized by that. The mobility refers to the mobility obtained by measuring the Hall effect, and in the present invention, the mobility is preferably 40 cm ² / Vs or more, more preferably 50 cm ² / Vs or more, and 100 cm. Most preferably, it is ² / Vs or more. Further, in the present invention, it is also preferable that the carrier density of the crystalline oxide semiconductor film is 1.0 × 10 ¹⁸ / cm ³ or more. Here, the carrier density refers to the carrier density in the semiconductor film obtained by the Hall effect measurement. The upper limit of the carrier density is not particularly limited, but is preferably about 1.0 × 10 ²³ / cm ³ or less, and more preferably about 1.0 × 10 ²² / cm ³ or less. The resistivity of the crystalline oxide semiconductor film is preferably 50 mΩcm or less, more preferably 10 mΩcm or less, and most preferably 5 mΩcm or less. In the present invention, it is preferable that the main surface of the crystalline oxide semiconductor film is the a-plane or the m-plane because the electrical characteristics can be further improved, and the m-plane is more preferable. Further, the crystalline oxide semiconductor film preferably has an off-angle. The "off angle" means an inclination angle formed with a predetermined crystal plane (main plane) as a reference plane, and usually means an angle formed by a predetermined crystal plane (main plane) and a crystal growth plane. The inclination direction of the off angle is not particularly limited, but in the present invention, when the main surface is the m surface, it is preferable that the inclination angle is formed from the reference surface toward the a-axis direction. The size of the off angle is not particularly limited, but is preferably 0.2 ° to 12.0 °, more preferably 0.5 ° to 4.0 °, and 0.5 ° to 3.0 °. Most preferably. By having a preferable off-angle, the semiconductor characteristics of the crystalline semiconductor film, particularly the mobility, are further improved. Further, in the present invention, the crystalline oxide semiconductor preferably contains indium, gallium or aluminum, more preferably contains an InAlGaO-based semiconductor, and most preferably contains at least gallium. The "main component" is, for example, when the crystalline oxide semiconductor is α _- Ga ₂ O ₃ , the atomic ratio of gallium in the metal element in the film is 0.5 or more. If ₃ is included, that is fine. In the present invention, the atomic ratio of gallium in the metal element in the film is preferably 0.7 or more, more preferably 0.8 or more. The thickness of the crystalline oxide semiconductor film is not particularly limited, and may be 1 μm or less, or may be 1 μm or more. Further, the shape of the crystalline oxide semiconductor film is not particularly limited, and whether it is a square shape (including a square shape or a rectangular shape) or a circular shape (including a semicircular shape), it has a polygonal shape. It may be. The surface area of the crystalline oxide semiconductor film is not particularly limited, and is preferably 3 mm square or more, more preferably 5 mm square or more, and most preferably 50 mm or more in diameter. In the present invention, the crystalline oxide semiconductor film preferably has no cracks in the central 3 mm square region, and more preferably has no cracks in the central 5 mm square region when observed with an optical microscope on the film surface. Most preferably, there are no cracks in the central 9.5 mm square region. Further, the crystalline oxide semiconductor film may be a single crystal film or a polycrystalline film, but a single crystal film is preferable.

The crystalline oxide semiconductor film contains a dopant, but the dopant is not particularly limited and may be known. Examples of the dopant include n-type dopants such as tin, germanium, silicon, titanium, zirconium, vanadium, niobium, and lead, p-type dopants, and the like. In the present invention, the dopant is preferably tin, germanium, or silicon, more preferably tin or germanium, and most preferably tin. The content of the dopant is preferably 0.00001 atomic% or more, more preferably 0.00001 atomic% to 20 atomic%, and 0.00001 atomic% in the composition of the crystalline oxide semiconductor film. Most preferably, it is ~ 10 atomic%. By setting the range to such a preferable range, the electrical characteristics of the crystalline oxide semiconductor film can be further improved.

Further, the crystalline oxide semiconductor film preferably has a half-value width of the locking curve of the X-ray diffraction method of 100 arcsec or more, and more preferably 300 arcsec or more. The upper limit of the half width is not particularly limited, but is preferably 1300 arcsec, and more preferably 1100 arcsec. By setting such a preferable half-value width, the mobility of the obtained crystalline oxide semiconductor film can be made more excellent.
The above-mentioned "half-value width" means a value obtained by measuring the half-value width of the locking curve by XRD (X-ray diffraction: X-ray diffraction method). The measurement plane orientation is not particularly limited, and examples thereof include [11-20] and [30-30].

Hereinafter, preferred methods for producing the crystalline oxide semiconductor film will be described, but the present invention is not limited to these preferred methods.

As a preferable method for producing the crystalline oxide semiconductor film, for example, a mist CVD apparatus as shown in FIG. 1 is used to atomize or atomize a raw material solution containing a dopant (atomization / droplet atomization step). The crystallized oxide semiconductor film is formed on the crystalline substrate by transporting the mist or droplets with a carrier gas into the film forming chamber (transport step) and then thermally reacting the mist or droplets in the film forming chamber. In the method of forming a film (deposition step), a crystal substrate having a corundum structure whose main surface is the a-plane or the m-plane is used, or a crystal substrate having a buffer layer formed and having an off-angle is formed. However, in the present invention, a crystal substrate having a corundate structure in which the main surface is the a-plane or the m-plane and in which a buffer layer may be formed is used. It is preferable to use a crystal substrate having a colland structure in which the main surface is the a-plane or the m-plane and in which a buffer layer containing no dopant may be formed, the mobility is high. It is more preferable because it improves more.

(Crystal substrate)
The crystal substrate is not particularly limited as long as it is a substrate having a corundum structure on all or part of the main surface, but is a substrate having a corundum structure on all or part of the main surface on the crystal growth surface side. It is preferable that the substrate has a corundum structure on the entire main surface on the crystal growth surface side. Further, in the present invention, it is preferable that the main surface is the a-plane or the m-plane because the electrical characteristics can be further improved. Further, the crystal substrate may have an off angle, and examples of the off angle include an off angle of 0.2 ° to 12.0 °, but in the present invention, the off angle is described. The angle is preferably 0.5 ° to 4.0 °, more preferably 0.5 ° to 3.0 °. Here, the "off angle" means the angle formed by the surface of the substrate and the crystal growth surface. The substrate shape is not particularly limited as long as it is plate-shaped and serves as a support for the crystalline oxide semiconductor film. It may be an insulator substrate, a semiconductor substrate, or a conductive substrate, but the substrate is preferably an insulator substrate and has a metal film on the surface. It is also preferable that it is a substrate. The shape of the substrate is not particularly limited, and may be a substantially circular shape (for example, a circle, an ellipse, etc.) or a polygonal shape (for example, a triangle, a square, a rectangle, a pentagon, a hexagon, or a heptagon). , Heptagon, nonagon, etc.), and various shapes can be preferably used. In the present invention, the shape of the film formed on the substrate can be set by making the shape of the substrate a preferable shape. Further, in the present invention, a large-area substrate can be used, and by using such a large-area substrate, the area of the crystalline oxide semiconductor film can be increased. The substrate material of the crystal substrate is not particularly limited and may be a known one as long as the object of the present invention is not impaired. As the substrate material having the corundum structure, for example, α-Al ₂ O ₃ (sapphire substrate) or α-Ga ₂ O ₃ is preferably mentioned, and a-plane sapphire substrate, m-plane sapphire substrate or α-gallium oxide substrate (sapphire substrate). A-plane or m-plane) is a more preferable example.

Examples of the buffer layer containing no dopant include α-Fe ₂ O ₃ , α-Ga ₂ O ₃ , α-Al ₂ O ₃ , and mixed crystals thereof. In the present invention, the buffer layer is preferably α-Ga ₂ O ₃ . The means for laminating the buffer layer is not particularly limited, and may be a known laminating means, and may be the same as the means for forming the crystalline oxide semiconductor film.

(Atomization / droplet formation process)
The atomization / droplet atomization step atomizes or atomizes the raw material solution. The means for atomizing or dropletizing the raw material solution is not particularly limited as long as the raw material solution can be atomized or atomized, and may be known means, but in the present invention, ultrasonic waves are used. The atomizing means or droplet forming means used is preferable. Mists or droplets obtained using ultrasonic waves are preferable because they have a zero initial velocity and float in the air. For example, they may float in space and be transported as gas instead of being sprayed like a spray. Since it is a possible mist, it is not damaged by collision energy, so it is very suitable. The droplet size is not particularly limited and may be a droplet of about several mm, but is preferably 50 μm or less, and more preferably 0.1 to 10 μm.

(Raw material solution)
The raw material solution is a solution from which the crystalline oxide semiconductor is obtained by mist CVD, and is not particularly limited as long as it contains the dopant. Examples of the raw material solution include an aqueous solution of a metal organic metal complex (for example, an acetylacetonate complex) and a halide (for example, fluoride, chloride, bromide, iodide, etc.). The metal may be any metal that can form a semiconductor, and examples of such a metal include gallium, indium, aluminum, and iron. In the present invention, the metal preferably contains at least gallium, indium or aluminum, more preferably at least gallium. The content of the metal in the raw material solution is not particularly limited as long as the object of the present invention is not impaired, but is preferably 0.001 mol% to 50 mol%, and more preferably 0.01 mol% to 50 mol%. Is.

In addition, the raw material solution usually contains a dopant. By including the dopant in the raw material solution, the conductivity of the crystalline oxide semiconductor film can be easily controlled without damaging the crystal structure without performing ion implantation or the like. Examples of the dopant include n-type dopants such as tin, germanium, silicon and lead when the metal contains at least gallium. In the present invention, the dopant is preferably tin, germanium, or silicon, more preferably tin or germanium, and most preferably tin. The concentration of the dopant may be usually about 1 × 10 ¹⁶ / cm ³ to 1 × 10 ²² / cm ³ , and the concentration of the dopant may be as low as about 1 × 10 ¹⁷ / cm ³ or less, for example. Alternatively, the dopant may be contained in a high concentration of about 1 × 10 ²⁰ / cm ³ or more. In the present invention, the concentration of the dopant is preferably 1 × 10 ²⁰ / cm ³ or less, and more preferably 5 × 10 ¹⁹ / cm ³ or less.

The solvent of the raw material solution is not particularly limited, and may be an inorganic solvent such as water, an organic solvent such as alcohol, or a mixed solvent of an inorganic solvent and an organic solvent. In the present invention, the solvent preferably contains water, more preferably water or a mixed solvent of water and alcohol, and most preferably water. More specific examples of the water include pure water, ultrapure water, tap water, well water, mineral spring water, mineral water, hot spring water, spring water, fresh water, seawater, and the like. Ultrapure water is preferred.

(Transport process)
In the transport step, the mist or the droplets are transported to the film forming chamber by the carrier gas. The carrier gas is not particularly limited as long as the object of the present invention is not impaired, and examples thereof include an inert gas such as oxygen, ozone, nitrogen and argon, and a reducing gas such as hydrogen gas and forming gas as suitable examples. .. Further, the type of the carrier gas may be one type, but may be two or more types, and a diluted gas having a reduced flow rate (for example, a 10-fold diluted gas) or the like is further used as the second carrier gas. May be good. Further, the carrier gas may be supplied not only at one place but also at two or more places. The flow rate of the carrier gas is not particularly limited, but is preferably 0.01 to 20 L / min, and more preferably 1 to 10 L / min. In the case of the diluted gas, the flow rate of the diluted gas is preferably 0.001 to 2 L / min, more preferably 0.1 to 1 L / min.

(Film formation process)
In the film forming step, a crystalline oxide semiconductor film is formed on the substrate by thermally reacting the mist or droplets in the film forming chamber. The thermal reaction may be any effect as long as the mist or droplet reacts with heat, and the reaction conditions and the like are not particularly limited as long as the object of the present invention is not impaired. In this step, the thermal reaction is usually carried out at a temperature equal to or higher than the evaporation temperature of the solvent, but is preferably not too high (for example, 1000 ° C.) or lower, more preferably 650 ° C. or lower, and most preferably 400 ° C. to 650 ° C. preferable. Further, the thermal reaction may be carried out under any atmosphere of vacuum, non-oxygen atmosphere, reducing gas atmosphere and oxygen atmosphere as long as the object of the present invention is not impaired, and the thermal reaction may be carried out under atmospheric pressure or pressure. It may be carried out under either reduced pressure or reduced pressure, but in the present invention, it is preferably carried out under atmospheric pressure. The film thickness can be set by adjusting the film formation time.

The crystalline oxide semiconductor film obtained as described above is not only excellent in electrical properties, particularly mobility, but also has reduced cracks, and is industrially useful. Such a crystalline oxide semiconductor film can be suitably used for semiconductor devices and the like, and is particularly useful for power devices. For example, the crystalline oxide semiconductor film is used for an n-type semiconductor layer (including an n + type semiconductor layer and an n− type semiconductor layer) of the semiconductor device. Further, in the present invention, the crystalline oxide semiconductor film may be used as it is, or may be applied to a semiconductor device or the like after using a known means such as peeling from the substrate or the like.

Further, the semiconductor device is classified into a horizontal element (horizontal device) in which electrodes are formed on one side of the semiconductor layer and a vertical element (vertical device) in which electrodes are provided on both front and back sides of the semiconductor layer. Therefore, in the present invention, it can be suitably used for both horizontal and vertical devices, but it is particularly preferable to use it for vertical devices. Examples of the semiconductor device include a Schottky barrier diode (SBD), a metal semiconductor field effect transistor (MESFET), a high electron mobility transistor (HEMT), a metal oxide film semiconductor field effect transistor (PWM), and an electrostatic induction transistor (MSFET). SIT), junction field effect transistor (JFET), isolated gate type bipolar transistor (IGBT), light emitting diode (LED) and the like.

Hereinafter, suitable examples when the crystalline oxide semiconductor film of the present invention is applied to an n-type semiconductor layer (n + type semiconductor, n-semiconductor layer, etc.) will be described with reference to the drawings. It is not limited to the example of. In the semiconductor device exemplified below, other layers (for example, an insulator layer, a semi-insulator layer, a conductor layer, a semiconductor layer, a buffer layer, another intermediate layer, etc.) may be used as long as the object of the present invention is not impaired. It may be contained, or a buffer layer (buffer layer) or the like may be omitted as appropriate.

FIG. 2 shows an example of a Schottky barrier diode (SBD) according to the present invention. The SBD of FIG. 2 includes an n-type semiconductor layer 101a, an n + type semiconductor layer 101b, a Schottky electrode 105a, and an ohmic electrode 105b.

The material of the Schottky electrode and the ohmic electrode may be a known electrode material, and the electrode material may be, for example, Al, Mo, Co, Zr, Sn, Nb, Fe, Cr, Ta, Ti, Au, etc. Metals such as Pt, V, Mn, Ni, Cu, Hf, W, Ir, Zn, In, Pd, Nd or Ag or alloys thereof, tin oxide, zinc oxide, renium oxide, indium oxide, indium tin oxide (ITO). ), Metal oxide conductive films such as indium zinc oxide (IZO), organic conductive compounds such as polyaniline, polythiophene or polypyrrol, or mixtures and laminates thereof.

The Schottky electrode and the ohmic electrode can be formed by a known means such as a vacuum vapor deposition method or a sputtering method. More specifically, for example, when a shotkey electrode is formed by using two kinds of the first metal and the second metal among the metals, the layer made of the first metal and the layer made of the second metal are formed. It can be performed by laminating and patterning the layer made of the first metal and the layer made of the second metal by using a photolithography technique.

When a reverse bias is applied to the SBD of FIG. 2, the depletion layer (not shown) spreads in the n-type semiconductor layer 101a, resulting in a high withstand voltage SBD. Further, when a forward bias is applied, electrons flow from the ohmic electrode 105b to the Schottky electrode 105a. The SBD using the semiconductor structure in this way is excellent for high withstand voltage and large current, has a high switching speed, and is also excellent in withstand voltage and reliability.

(HEMT)
FIG. 3 shows an example of a high electron mobility transistor (HEMT) according to the present invention. The HEMT of FIG. 3 includes an n-type semiconductor layer 121a with a wide bandgap, an n-type semiconductor layer 121b with a narrow bandgap, an n + type semiconductor layer 121c, a semi-insulator layer 124, a buffer layer 128, a gate electrode 125a, a source electrode 125b, and the like. A drain electrode 125c is provided.

(MOSFET)
FIG. 4 shows an example of the case where the semiconductor device of the present invention is a MOSFET. The MOSFET in FIG. 4 is a trench-type MOSFET, and includes an n-type semiconductor layer 131a, an n + type semiconductor layers 131b and 131c, a gate insulating film 134, a gate electrode 135a, a source electrode 135b, and a drain electrode 135c.

(JFET)
FIG. 5 includes an n-type semiconductor layer 141a, a first n + type semiconductor layer 141b, a second n + type semiconductor layer 141c, a p-type semiconductor layer 142, a gate electrode 145a, a source electrode 145b, and a drain electrode 145c. A suitable example of a junction field effect transistor (JFET) is shown.

(IGBT)
FIG. 6 shows insulation including an n-type semiconductor layer 151, an n-type semiconductor layer 151a, an n + type semiconductor layer 151b, a p-type semiconductor layer 152, a gate insulating film 154, a gate electrode 155a, an emitter electrode 155b, and a collector electrode 155c. A suitable example of a gate type bipolar transistor (IGBT) is shown.

(LED)
FIG. 7 shows an example of the case where the semiconductor device of the present invention is a light emitting diode (LED). The semiconductor light emitting device of FIG. 7 includes an n-type semiconductor layer 161 on the second electrode 165b, and a light emitting layer 163 is laminated on the n-type semiconductor layer 161. A p-type semiconductor layer 162 is laminated on the light emitting layer 163. A translucent electrode 167 that transmits light generated by the light emitting layer 163 is provided on the p-type semiconductor layer 162, and a first electrode 165a is laminated on the translucent electrode 167. The semiconductor light emitting device of FIG. 7 may be covered with a protective layer except for the electrode portion.

Examples of the material of the translucent electrode include a conductive material of an oxide containing indium (In) or titanium (Ti). More specifically, for example, In ₂ O ₃ , ZnO, SnO ₂ , Ga ₂ O ₃ , TIO ₂ , CeO ₂ or a mixed crystal of two or more of these, or those doped with these can be mentioned. A translucent electrode can be formed by providing these materials by a known means such as sputtering. Further, after forming the translucent electrode, thermal annealing may be performed for the purpose of making the translucent electrode transparent.

According to the semiconductor light emitting element of FIG. 7, the first electrode 165a is used as a positive electrode and the second electrode 165b is used as a negative electrode, and a current is passed through both of them to the p-type semiconductor layer 162, the light emitting layer 163, and the n-type semiconductor layer 161. As a result, the light emitting layer 163 emits light.

The materials of the first electrode 165a and the second electrode 165b include, for example, Al, Mo, Co, Zr, Sn, Nb, Fe, Cr, Ta, Ti, Au, Pt, V, Mn, Ni, Cu, and the like. Metals such as Hf, W, Ir, Zn, In, Pd, Nd or Ag or alloys thereof, tin oxide, zinc oxide, renium oxide, indium oxide, indium tin oxide (ITO), indium zinc oxide (IZO) and the like. Examples thereof include metal oxide conductive films, organic conductive compounds such as polyaniline, polythiophene or polypyrrole, or mixtures thereof. The film forming method of the electrode is not particularly limited, and is a wet method such as a printing method, a spray method, and a coating method, a physical method such as a vacuum vapor deposition method, a sputtering method, and an ion plating method, CVD, and plasma CVD. It can be formed on the substrate according to a method appropriately selected in consideration of suitability with the material from chemical methods such as a method.

In addition, another aspect of the light emitting element is shown in FIG. In the light emitting device of FIG. 8, the n-type semiconductor layer 161 is laminated on the substrate 169, and the n-type semiconductor exposed by cutting out a part of the p-type semiconductor layer 162, the light emitting layer 163, and the n-type semiconductor layer 161. The second electrode 165b is laminated on a part of the exposed surface of the semiconductor layer of the layer 161.

The semiconductor device is used, for example, in a system using a power supply device. The power supply device can be manufactured by connecting the semiconductor device to a wiring pattern or the like by using a known means. FIG. 9 shows an example of a power supply system. In FIG. 9, a power supply system is configured by using the plurality of power supply devices and control circuits. As shown in FIG. 10, the power supply system can be used in a system device in combination with an electronic circuit. An example of the power supply circuit diagram of the power supply device is shown in FIG. FIG. 11 shows a power supply circuit of a power supply device including a power circuit and a control circuit. A DC voltage is switched at a high frequency by an inverter (composed of MOSFETs A to D), converted to AC, and then isolated and transformed by a transformer. After being rectified by a rectifying MOSFET, it is smoothed by a DCL (smoothing coils L1 and L2) and a capacitor, and a DC voltage is output. At this time, the output voltage is compared with the reference voltage by the voltage comparator, and the inverter and the rectifier MOSFET are controlled by the PWM control circuit so as to obtain the desired output voltage.

Hereinafter, examples of the present invention will be described, but the present invention is not limited thereto.

(Example 1)
1. 1. Film formation device The mist CVD device used in this embodiment will be described with reference to FIG. The mist CVD device 19 includes a susceptor 21 on which the substrate 20 is placed, a carrier gas supply means 22a for supplying the carrier gas, and a flow control valve 23a for adjusting the flow rate of the carrier gas sent out from the carrier gas supply means 22a. , A carrier gas (diluted) supply means 22b for supplying a carrier gas (diluted), a flow control valve 23b for adjusting the flow rate of the carrier gas sent out from the carrier gas (diluted) supply means 22b, and a raw material solution 24a are accommodated. A supply pipe 27 composed of a mist generation source 24, a container 25 in which water 25a is placed, an ultrasonic transducer 26 attached to the bottom surface of the container 25, and a quartz tube having an inner diameter of 40 mm, and a peripheral portion of the supply tube 27. It is equipped with a heater 28 installed in. The susceptor 21 is made of quartz, and the surface on which the substrate 20 is placed is inclined from the horizontal plane. By making both the supply tube 27 and the susceptor 21 serving as the film forming chamber from quartz, it is possible to prevent impurities derived from the apparatus from being mixed in the film formed on the substrate 20.

2. 2. Preparation of raw material solution Gallium acetylacetonate and tin (II) chloride are mixed with ultrapure water, and the aqueous solution is adjusted so that the atomic ratio of tin to gallium is 1: 0.002 and gallium 0.05 mol / L. At this time, 1.5% of hydrochloric acid was contained in a volume ratio, and this was used as a raw material solution 24a.

3. 3. Preparation for film formation 2. The raw material solution 24a obtained in 1) was housed in the mist generation source 24. Next, as the substrate 20, an m-plane sapphire substrate on which an α _- Ga ₂ O3 film (non-doped) is laminated as a buffer layer on the surface is installed on the susceptor 21, and the heater 28 is operated to operate the film forming chamber 27. The temperature inside was raised to 460 ° C. Next, the flow control valves 23a and 23b are opened, carrier gas is supplied into the film forming chamber 27 from the carrier gas supply means 22a and 22b which are carrier gas sources, and the atmosphere of the film forming chamber 27 is sufficiently filled with the carrier gas. After the substitution, the flow rate of the carrier gas was adjusted to 1.0 L / min, and the flow rate of the carrier gas (diluted) was adjusted to 0.5 L / min. Nitrogen was used as the carrier gas.

4. Semiconductor film formation Next, the ultrasonic transducer 26 was vibrated at 2.4 MHz, and the vibration was propagated to the raw material solution 24a through water 25a to atomize the raw material solution 24a to generate raw material fine particles. The raw material fine particles were introduced into the film forming chamber 27 by the carrier gas, and the mist reacted in the supply pipe 27 at 460 ° C. under atmospheric pressure to form a semiconductor film on the substrate 20. The film thickness was 2.5 μm, and the film formation time was 360 minutes.

(Examples 2 to 4)
A crystalline oxide semiconductor film was obtained in the same manner as in Example 1 except that an m-plane sapphire substrate having an off-angle was used as the substrate. The off-angle was 0.5 ° in Example 2, 2.0 ° in Example 3, and 3.0 ° in Example 4. The film thickness of the obtained crystalline oxide semiconductor film was 3.0 μm in Example 2, 2.9 μm in Example 3, and 3.3 μm in Example 4, respectively.

(Example 5)
In order to confirm the reproducibility, a crystalline oxide semiconductor film was obtained in the same manner as in Example 4. The film thickness of the obtained crystalline oxide semiconductor film was 3.4 μm. The reproducibility was confirmed in the following test example. Then, as is clear from Table 1, it was confirmed that the reproducibility was good. It can also be seen from the film thickness that the reproducibility is good.

(Example 6)
As a raw material solution, gallium bromide and tin bromide are mixed with ultrapure water, and the aqueous solution is adjusted so that the atomic ratio of tin to gallium is 1: 0.08 and gallium 0.1 mol / L. Using an aqueous solution containing 10% by volume of hydrobromic acid, the surface of the substrate was replaced with an m-plane sapphire substrate on which an α-Ga ₂ O3 film (non _- doped) was laminated as a buffer layer on the surface. A crystalline oxide semiconductor film was obtained in the same manner as in Example 1 except that the a-plane sapphire substrate on which the buffer layer was not laminated was used and the film formation time was set to 10 minutes.

(Example 7)
Except for the fact that instead of the a-side sapphire substrate on which the buffer layer is not laminated on the surface, the a-side sapphire substrate on which the α-Ga ₂ O3 film (non _- doped) is laminated as the buffer layer is used as the substrate. , A crystalline oxide semiconductor film was obtained in the same manner as in Example 6. The film thickness of the obtained crystalline oxide semiconductor film was 0.3 μm.

(Example 8)
In order to confirm the reproducibility, a crystalline oxide semiconductor film was obtained in the same manner as in Example 7. The film thickness of the obtained crystalline oxide semiconductor film was 0.3 μm. The reproducibility was confirmed in the following test example. Then, as is clear from Table 1, it was confirmed that the reproducibility was good. It can also be seen from the film thickness that the reproducibility is good.

(Example 9)
As a substrate, instead of the m-plane sapphire substrate on which the α-Ga ₂ O ₃ film (non-doped) is laminated as the buffer layer on the surface, the α-Ga ₂ O ₃ film (Sn-doped) is laminated on the surface as the buffer layer. A crystalline oxide semiconductor film was obtained in the same manner as in Example 1 except that the a-plane sapphire substrate was used and the film formation time was 180 minutes.

(Example 10)
As the substrate, an a-plane sapphire substrate in which an α _- Ga ₂ O3 film (non-doped) was laminated as a buffer layer on the surface was used, and the atomic ratio of gallium to tin in the raw material solution was 1: 0.0002. A crystalline oxide semiconductor film was obtained in the same manner as in Example 9 except that the raw material solution was adjusted so as to be. The film thickness of the obtained crystalline oxide semiconductor film was 1.0 μm.

(Example 11)
As a substrate, an a-plane sapphire substrate in which an α _- Ga ₂ O3 film (Sn-doped) is laminated as a buffer layer on the surface is replaced with an a-plane sapphire substrate in which a buffer layer is not laminated on the surface. Obtained a crystalline oxide semiconductor film in the same manner as in Example 9. The film thickness of the obtained crystalline oxide semiconductor film was 0.9 μm.

(Example 12)
As a raw material solution, gallium bromide and germanium oxide are mixed with ultrapure water, and the raw material solution is adjusted so that the atomic ratio of gallium to gallium is 1: 0.01 and gallium 0.1 mol / L. A crystalline oxide semiconductor film was obtained in the same manner as in Example 6 except that an aqueous solution containing 20% by volume of hydrobromic acid was used and the film formation time was 30 minutes. ..

(Example 13)
A crystalline oxide semiconductor film was obtained in the same manner as in Example 3 except that the film forming time was set to 720 minutes. The film thickness of the obtained crystalline oxide semiconductor film was 3.8 μm.

(Comparative Example 1)
As a substrate, a c-plane sapphire substrate having no buffer layer laminated on the surface was used instead of the m-plane sapphire substrate on which the α-Ga ₂ O3 film (non _- doped) was laminated as the buffer layer on the surface. , A crystalline oxide semiconductor film was obtained in the same manner as in Example 1.
(Comparative Example 2)
Gallium bromide and germanium oxide were mixed with ultrapure water, and the raw material solution was adjusted so that the atomic ratio of germanium to gallium was 1: 005. A crystalline oxide semiconductor film was obtained in the same manner as in Example 6 except that a c-plane sapphire substrate having no buffer layer laminated on the surface was used instead of the sapphire substrate.
(Comparative Example 3)
The raw material solution was adjusted so that the atomic ratio of tin to gallium was 1: 0.005, and the buffer layer was laminated on the surface instead of the a-plane sapphire substrate on which the buffer layer was not laminated on the surface. A crystalline oxide semiconductor film was obtained in the same manner as in Example 6 except that a c-plane sapphire substrate was used.

(Test Example 1)
Using an X-ray diffractometer, the phases of the crystalline oxide semiconductor membranes obtained in Examples 1 to 13 and Comparative Examples 1 to 3 were identified. Identification was performed by performing a 2θ / ω scan at an angle of 15 to 95 degrees using an XRD diffractometer. The measurement was performed using CuKα ray. As a result, the crystalline oxide semiconductor films obtained in Examples 1 to 5 and Example 13 were all m-plane α-Ga ₂ O ₃ . The films obtained in Examples 6 to 12 were all a-plane α-Ga _{203, and the films obtained in Comparative Examples 1 to 3 were all c-plane α-Ga 2 O 3 .} .. The results of measuring the half-value width of the locking curve of the crystalline oxide semiconductor film obtained in Examples 1, 2, 4, 7 to 12 and Comparative Example 1 are shown in Tables 1 to 3.

(Test Example 2)
The Hall effect was measured for the crystalline oxide semiconductor films obtained in Examples 1 to 13 and Comparative Examples 1 to 3 by the van der pauw method. Tables 1 to 3 show the carrier density, mobility, and resistivity of the crystalline oxide semiconductor films obtained in Examples 1 to 13 and Comparative Examples 1 to 3. As can be seen from Tables 1 to 3, the crystalline oxide semiconductor film of the present invention is excellent in electrical characteristics, particularly mobility.

(Test Example 3)
The surface of the crystalline oxide semiconductor films obtained in Examples 1 to 13 and Comparative Examples 1 to 3 was observed using an optical microscope. Tables 1 to 3 show the observation results, where the case where no crack was found in the central 3 mm square region of the film surface was marked with ◯, and the case where the crack was found in the central 3 mm square region was marked with x. From Tables 1 to 3, it can be seen that the crystalline oxide semiconductor film of the present invention has reduced cracks.

(Example 14)
A crystalline oxide semiconductor film was obtained in the same manner as in Example 6 except that silicon bromide was used as the dopant raw material. As a result, it was found that the performance was equivalent to that of the crystalline oxide semiconductor film obtained in Example 1.

(Example 15)
A crystalline oxide semiconductor film was obtained in the same manner as in Example 1. The obtained film thickness was 2.3 μm.

(Example 16)
A crystalline oxide semiconductor film was obtained in the same manner as in Example 1 except that an m-plane sapphire substrate having an off angle of 2 ° toward the a-axis was used as the substrate. The obtained film thickness was 3.2 μm.

(Example 17)
A crystalline oxide semiconductor film was obtained in the same manner as in Example 16. The obtained film thickness was 2.2 μm.

(Example 18)
Example 1 except that an m-plane sapphire substrate having an off angle of 2 ° toward the a-axis, which is not laminated with an α-Ga ₂ O3 film (non _- doped) as a buffer layer on the surface, was used as the substrate. In the same manner as above, a crystalline oxide semiconductor film was obtained. The obtained film thickness was 2 μm.

(Example 19)
A crystalline oxide semiconductor film was obtained in the same manner as in Example 1 except that an m-plane sapphire substrate having an off angle of 4 ° toward the a-axis was used as the substrate. The obtained film thickness was 2.6 μm.

(Example 20)
Except for adjusting the aqueous solution so that the atomic ratio of tin to gallium is 1: 0.0002 and 0.05 mol / L of gallium when mixing gallium acetylacetonate and tin (II) chloride in ultrapure water. , A crystalline oxide semiconductor film was obtained in the same manner as in Example 18. The obtained film thickness was 1.8 μm.

(Example 21)
Except for adjusting the aqueous solution so that the atomic ratio of tin to gallium is 1: 0.0002 and 0.05 mol / L of gallium when mixing gallium acetylacetonate and tin (II) chloride in ultrapure water. , A crystalline oxide semiconductor film was obtained in the same manner as in Example 18. The obtained film thickness was 1.8 μm.

(Test Example 4)
When the phases of the crystalline oxide semiconductor films obtained in Examples 15 to 21 were identified in the same manner as in Test Example 1, all the crystalline oxide semiconductor films obtained in Examples 15 to 21 were found. It was m-plane α-Ga ₂ O ₃ . For reference, the XRD measurement results of the crystalline semiconductor films obtained in Examples 20 and 21 are shown in FIG. Further, the crystalline oxide semiconductor films obtained in Examples 15 to 21 were evaluated in the same manner as in Test Examples 1 to 3 in terms of carrier density, mobility, half width and presence / absence of cracks. The results are shown in Table 4.

(Test Example 5)
The Hall effect of the Sn-doped α-Ga ₂ O ₃ film on the m-plane sapphire substrate was measured by the van der Pauw method, and the mobility and carrier density were evaluated. For the α _- Ga ₂ O3 membrane, gallium acetylacetonate and tin (II) chloride dihydrate are mixed while adding a small amount of hydrochloric acid until they are dissolved, and the obtained solution is used as a raw material solution. An α-Ga ₂ O ₃ film was obtained in the same manner as in Example 1 except that an m-plane sapphire substrate was used as the substrate and the film formation temperature was set to 500 ° C. At this time, a plurality of raw material solutions are prepared by appropriately changing the blending ratio of tin (II) chloride dihydrate so that the carrier density is about 1 × 10 ¹⁸ / cm ³ , and a plurality of α-Ga ₂ are prepared. An _O3 film was obtained and used for this evaluation.
The result of Hall effect measurement is shown in FIG. Further, for the comparative test, the measurement results for the α-Ga ₂ O ₃ film obtained in the same manner as above using the c-plane sapphire substrate instead of the m-plane sapphire substrate are also shown in FIG. As is clear from FIG. 13, it can be seen that the film formed using the m-plane sapphire substrate is superior in electrical characteristics to the film formed using the c-plane sapphire substrate.

(Test Example 6)
In addition, the temperature characteristics of the mobility of the α-Ga ₂ O ₃ film having a carrier density of 1.1 × 10 ¹⁸ cm ^-3 obtained in Test Example 1 were investigated using a temperature variable Hall effect measuring device. The results are shown in FIG. As is clear from FIG. 14, it can be seen that the mobility is 40 cm ² / Vs or more even in the low temperature range, and the electrical characteristics are good even in the high temperature range.

The crystalline oxide semiconductor film of the present invention can be used in all fields such as semiconductor devices (for example, compound semiconductor electronic devices, etc.), electronic parts / electrical equipment parts, optical / electrophotographic-related equipment, industrial parts, etc. It is useful for semiconductor devices and the like.

19 Mist CVD equipment 20 Substrate 21 Suceptor 22a Carrier gas supply means 22b Carrier gas (diluted) supply means 23a Flow control valve 23b Flow control valve 24 Mist generation source 24a Raw material solution 25 Container 25a Water 26 Ultrasonic transducer 27 Supply pipe 28 Heater 29 Exhaust port 101a n-type semiconductor layer 101b n + type semiconductor layer 102 p-type semiconductor layer 103 Semi-insulator layer 104 Insulation layer 105a Shotkey electrode 105b Ohmic electrode 121a Wide band gap n-type semiconductor layer 121b Narrow band gap n Type semiconductor layer 121c n + type semiconductor layer 123 p type semiconductor layer 124 Semi-insulator layer 125a Gate electrode 125b Source electrode 125c Drain electrode 128 Buffer layer 131a n-type semiconductor layer 131b First n + type semiconductor layer 131c Second n + type Semiconductor layer 132 p-type semiconductor layer 134 Gate insulating film 135a Gate electrode 135b Source electrode 135c Drain electrode 141a n-type semiconductor layer 141b First n + type semiconductor layer 141c Second n + type semiconductor layer 142 p-type semiconductor layer 145a Gate electrode 145b Source electrode 145c Drain electrode 151 n-type semiconductor layer 151a n-type semiconductor layer 151b n + type semiconductor layer 152 p-type semiconductor layer 154 Gate insulating film 155a Gate electrode 155b Emitter electrode 155c Collector electrode 161 n-type semiconductor layer 162 p-type semiconductor layer 163 Light emitting layer 165a First electrode 165b Second electrode 167 Translucent electrode 169 Substrate

Claims (10)

A crystalline oxide semiconductor film containing a crystalline oxide semiconductor having a corundum structure as a main component and further containing a dopant, having a mobility of 30 cm ² / Vs or more, and contained in the crystalline oxide semiconductor film. A crystalline oxide semiconductor film characterized in that the atomic ratio of gallium in the metal element is 0.5 or more . However, crystalline oxide semiconductor films having an atomic ratio of iron to gallium of 0.05 or more are excluded. The crystalline oxide semiconductor film according to claim 1, wherein the carrier density is 1.0 × 10 ¹⁸ / cm ³ or more. The crystalline oxide semiconductor film according to claim 1 or 2, wherein the resistivity is 50 mΩcm or less. The crystalline oxide semiconductor film according to any one of claims 1 to 3, wherein the resistivity is 5 mΩcm or less. The crystalline oxide semiconductor film according to any one of claims 1 to 4, wherein the main surface is an a-plane or an m-plane. The crystalline oxide semiconductor film according to any one of claims 1 to 5, wherein the dopant is tin, germanium or silicon. The crystalline oxide semiconductor film according to any one of claims 1 to 6, wherein the dopant is tin. The crystalline oxide semiconductor film according to any one of claims 1 to 7, wherein the crystalline oxide semiconductor contains indium or aluminum. A semiconductor device including at least a semiconductor layer and electrodes, wherein the crystalline oxide semiconductor film according to any one of claims 1 to 8 is used as the semiconductor layer. A semiconductor system including a semiconductor device, wherein the semiconductor device is the semiconductor device according to claim 9 .

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