JP2018082144A - Crystal oxide semiconductor film and semiconductor device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a crystal oxide semiconductor film superior in electrical characteristic.SOLUTION: An oxide semiconductor film is formed on a crystal substrate 20 by: using a mist CVD apparatus 19 to make a raw material solution including a dopant into a mist or drops; transporting, by a carrier gas, the resultant mist or drops into a film-forming chamber; and subsequently causing a thermal reaction of the mist or drops in the film-forming chamber. The film includes, as a primary component, a crystal oxide semiconductor having a corundum structure. Further, the film is a crystal oxide semiconductor film including the dopant and having a mobility of 30 cm/Vs or more.SELECTED DRAWING: Figure 1

Description

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

A semiconductor device using gallium oxide (Ga ₂ O ₃ ) having a large band gap has been attracting attention as a next-generation switching element that can achieve high breakdown voltage, low loss, and high heat resistance. Application is expected. Moreover, application as a light emitting / receiving device such as an LED or a sensor is also expected from a wide band gap. According to Non-Patent Document 1, the gallium oxide can control the band gap by mixing crystals of indium and aluminum, respectively, or in combination, and constitutes an extremely attractive material system as an InAlGaO-based semiconductor. . Here, the InAlGaO-based semiconductor means In _X Al _Y Ga Ga _Z O ₃ (0 ≦ X ≦ 2, 0 ≦ Y ≦ 2, 0 ≦ Z ≦ 2, X + Y + Z = 1.5 to 2.5). It can be overlooked as the same material system to be 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 O ₃ thin film having a rocking curve half-width of about 60 arcsec and a high crystallinity of X-ray diffraction, it cannot maintain sufficient pressure resistance, Further, the mobility is 1 cm ² / Vs or less, the semiconductor characteristics are not satisfactory, and it is still difficult to use the semiconductor device.

In Patent Document 2, c plane α-Ga ₂ O ₃ film doped with Ge on the sapphire substrate have been described, Patent Document 1 α-Ga ₂ O ₃ with excellent electrical characteristics than thin film according to Although a thin film was obtained, the mobility was 3.26 cm ² / Vs, which was still not satisfactory for use in a semiconductor device.

In Non-Patent Document 2, an α-Ga ₂ O ₃ film doped with Sn is formed on a c-plane sapphire substrate, then annealed to form an anneal buffer layer, and then Sn is doped onto the anneal buffer layer. by depositing -ga ₂ O ₃ film, thereby improving the mobility. In addition, Sn has a surfactant effect by doping with Sn, thereby improving the surface roughness and crystallinity of the α-Ga ₂ O ₃ thin film and improving the mobility. However, there is a problem of increasing resistance or insulation by annealing, and there are still problems to be used for semiconductor devices. In addition, the obtained film still has many dislocations and is strongly affected by dislocation scattering, which has a problem of impeding electrical characteristics. Furthermore, there are problems with many cracks, and an industrially useful α-Ga ₂ O ₃ film has been awaited.

JP 2013-028480 A JP2015-228495A

Kentaro Kaneko, “Growth and Physical Properties of Corundum Structure Gallium Oxide Mixed Crystal Thin Films”, Kyoto University Doctoral Dissertation, March 2013 Kazuaki Akaiwa, “Control of Electrical Properties of Corundum Structure Gallium Oxide Semiconductors and Device Applications”, Kyoto University Doctoral Dissertation, 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 intensive studies to achieve the above object, the present inventors have surprisingly found that when a film is formed using a mist CVD method under specific conditions, neither high resistance treatment nor insulation treatment is performed. In addition, even when the half 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 all at once.
In addition, after obtaining the above knowledge, the present inventors have further studied and completed the present invention.

That is, the present invention relates to the following inventions.
[1] A crystalline oxide semiconductor film containing a crystalline oxide semiconductor having a corundum structure as a main component and further containing a dopant, and having a mobility of 30 cm ² / Vs or more Semiconductor film.
[2] The crystalline oxide semiconductor film according to [1], wherein the carrier density is 1.0 × 10 ¹⁸ / cm ³ or more.
[3] The crystalline oxide semiconductor film according to [1] or [2], wherein the resistivity is 50 mΩcm or less.
[4] The crystalline oxide semiconductor film according to any one of [1] to [3], which has a resistivity of 5 mΩcm or less.
[5] The crystalline oxide semiconductor film according to any one of [1] to [4], wherein the main surface is an a-plane or an m-plane.
[6] The crystalline oxide semiconductor film according to any one of [1] to [5], wherein the dopant is tin, germanium, or silicon.
[7] The crystalline oxide semiconductor film according to any one of [1] to [6], wherein the dopant is tin.
[8] The crystalline oxide semiconductor film according to any one of [1] to [7], wherein the crystalline oxide semiconductor contains gallium, indium, or aluminum.
[9] The crystalline oxide semiconductor film according to any one of [1] to [9], wherein the crystalline oxide semiconductor includes at least gallium.
[10] A semiconductor device including at least a semiconductor layer and an electrode, 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 comprising a semiconductor device, wherein the semiconductor device is the semiconductor device according to [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 (MOSFET). 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 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 supply system. It is a figure which shows a suitable example of a system apparatus typically. It is a figure which shows typically a suitable 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 represents mobility (cm ² / Vs), and the horizontal axis represents carrier density (/ cm ³ ). It is a figure which shows the temperature variable Hall effect measurement result in a test example. In addition, a vertical axis | shaft is a mobility (cm < ² > / Vs) and a horizontal axis is temperature (K).

The crystalline oxide semiconductor film of the present invention is a crystalline oxide semiconductor film including a crystalline oxide semiconductor having a corundum structure as a main component and further including 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 Hall effect measurement. 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. In the present invention, it is also preferable that a 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 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, the main surface of the crystalline oxide semiconductor film is preferably an a-plane or m-plane because electrical characteristics can be further improved, and more preferably an m-plane. The crystalline oxide semiconductor film preferably has an off angle. The “off angle” refers to an inclination angle formed with a predetermined crystal plane (main surface) as a reference plane, and usually refers to an angle formed between the predetermined crystal surface (main surface) and the crystal growth surface. The inclination direction of the off-angle is not particularly limited. In the present invention, when the main surface is an m-plane, it is preferable that the inclination angle is formed from the reference plane 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. 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. Incidentally, the "main component" such as crystalline If oxide semiconductor is α-Ga ₂ O _3, the atomic ratio of gallium in a proportion of more than 0.5 α-Ga ₂ O of metal elements in the film _{If 3} is included, that's fine. In the present invention, the atomic ratio of gallium in the metal element in the film is preferably 0.7 or more, and 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 1 μm or more. The shape or the like of the crystalline oxide semiconductor film is not particularly limited, and may be a quadrangular shape (including a square shape or a rectangular shape), a circular shape (including a semicircular shape), or a polygonal shape. It may be. The surface area of the crystalline oxide semiconductor film is not particularly limited, is preferably 3 mm square or more, more preferably 5 mm square or more, and most preferably 50 mm square or more. In the present invention, the crystalline oxide semiconductor film preferably has no crack in the central 3 mm square region and more preferably has no crack in the central 5 mm square region in the observation of the film surface with an optical microscope. Most preferably, there is no crack in the central 9.5 mm square region. The crystalline oxide semiconductor film may be a single crystal film or a polycrystalline film, but is preferably a single crystal film.

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

The crystalline oxide semiconductor film preferably has a rocking curve half-width of 100 arcsec or more, more preferably 300 arcsec or more in the X-ray diffraction method. The upper limit of the half width is not particularly limited, but is preferably 1300 arcsec, and more preferably 1100 arcsec. By setting it as such a preferable half value width, the mobility of the crystalline oxide semiconductor film obtained can be made more excellent.
The above-mentioned “half-value width” means a value obtained by measuring the half-value width of a rocking curve by XRD (X-ray diffraction: X-ray diffraction method). Although it does not specifically limit as a measurement surface orientation, For example, [11-20] or [30-30] etc. are mentioned.

  Hereinafter, although the preferable manufacturing method of the said crystalline oxide semiconductor film is demonstrated, this invention is not limited to these preferable manufacturing methods.

  As a preferred method for producing the crystalline oxide semiconductor film, for example, a mist CVD apparatus as shown in FIG. 1 is used to atomize or drop the raw material solution containing the dopant (atomization / droplet forming step). The produced mist or droplet is transported into the deposition chamber with a carrier gas (conveying step), and then the mist or droplet is thermally reacted in the deposition chamber to thereby form a crystalline oxide semiconductor film on the crystal substrate. In a method of forming a film (film forming step), a crystal substrate having a corundum structure whose main surface is a-plane or m-plane is used, or a crystal substrate having a buffer layer and having an off-angle In the present invention, a crystal substrate having a corundum structure whose main surface is an a-plane or an m-plane and having a buffer layer formed thereon is used. This It is preferable to use a crystal substrate having a corundum structure in which the main surface is an a-plane or m-plane and in which a buffer layer not containing a dopant may be formed has a higher mobility. Since it improves, it is more preferable.

(Crystal substrate)
The crystal substrate is not particularly limited as long as it has a corundum structure on all or part of the main surface, but the substrate has 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. In the present invention, it is preferable that the main surface is an a-plane or an m-plane because 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 °. The angle is preferably from 0.5 ° to 4.0 °, and more preferably from 0.5 ° to 3.0 °. Here, the “off angle” refers to an angle formed by the substrate surface and the crystal growth surface. The substrate shape is not particularly limited as long as it is a plate shape and serves as a support for the crystalline oxide semiconductor film. The substrate 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. A substrate is also preferred. The shape of the substrate is not particularly limited, and may be a substantially circular shape (for example, a circle or an ellipse), or a polygonal shape (for example, a triangle, a square, a rectangle, a pentagon, a hexagon, a heptagon). , Octagons, 9-gons, etc.), and various shapes can be suitably used. In the present invention, the shape of the film formed on the substrate can be set by setting the shape of the substrate to a preferable shape. In the present invention, a large-area substrate can also be used. 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 as long as the object of the present invention is not impaired, and may be a known material. 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 used, and an a-plane sapphire substrate, m-plane sapphire substrate, or α-gallium oxide substrate ( (a-plane or m-plane) is a more preferable example.

Examples of the buffer layer not containing the 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 buffer layer stacking means is not particularly limited, and may be a known stacking means, which may be the same as the film forming means for the crystalline oxide semiconductor film.

(Atomization / droplet forming process)
In the atomization / droplet forming step, the raw material solution is atomized or dropletized. The atomizing means or droplet forming means of the raw material solution is not particularly limited as long as the raw material solution can be atomized or formed into droplets, and may be a known means. The atomizing means or droplet forming means used is preferred. Mist or droplets obtained using ultrasonic waves have a zero initial velocity and are preferable because they float in the air.For example, instead of spraying like a spray, they can be suspended in a space and transported as a gas. Since it is a possible mist, there is no damage due to collision energy, which 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, 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 a metal organometallic complex (for example, acetylacetonate complex) and an aqueous solution of a halide (for example, fluoride, chloride, bromide, or iodide). The metal may be any metal that can form a semiconductor. 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, and more preferably contains 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%, more preferably 0.01 mol% to 50 mol%. It is.

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

(Conveying process)
In the transfer step, the mist or the droplets are transferred into the film forming chamber with a carrier gas. The carrier gas is not particularly limited as long as it does not hinder the object of the present invention. For example, oxygen, ozone, an inert gas such as nitrogen or argon, or a reducing gas such as hydrogen gas or forming gas can be mentioned as a suitable example. . Further, the type of carrier gas may be one, but it may be two or more, and a diluent gas with a reduced flow rate (for example, 10-fold diluted gas) is further used as the second carrier gas. Also good. Further, the supply location of the carrier gas is not limited to one location but may be two or more locations. The flow rate of the carrier gas is not particularly limited, but is preferably 0.01 to 20 L / min, and more preferably 1 to 10 L / min. In the case of a dilution gas, the flow rate of the dilution gas is preferably 0.001 to 2 L / min, and more preferably 0.1 to 1 L / min.

(Film formation process)
In the film formation step, the crystalline mist semiconductor film is formed on the substrate by thermally reacting the mist or droplets in the film formation chamber. The thermal reaction may be performed as long as the mist or droplet reacts with heat, and the reaction conditions are not particularly limited as long as the object of the present invention is not impaired. In this step, the thermal reaction is usually performed at a temperature equal to or higher than the evaporation temperature of the solvent, but is preferably not too high (for example, 1000 ° C.) or less, more preferably 650 ° C. or less, and most preferably 400 ° C. to 650 ° C. preferable. Further, the thermal reaction may be performed in any atmosphere of a vacuum, a non-oxygen atmosphere, a reducing gas atmosphere, and an oxygen atmosphere as long as the object of the present invention is not impaired. Although it may be carried out under any conditions of reduced pressure and reduced pressure, it is preferably carried out under atmospheric pressure in the present invention. 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 characteristics, particularly in mobility, but also has reduced cracks and is industrially useful. Such a crystalline oxide semiconductor film can be suitably used for a semiconductor device or the like, and is particularly useful for a power device. 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. 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.

  The semiconductor device is classified into a horizontal element (a horizontal device) in which an electrode is formed on one side of a semiconductor layer, and a vertical element (a vertical device) having electrodes on both sides of the semiconductor layer. In the present invention, it can be suitably used for a horizontal device and a vertical device, but among them, it is preferably used for a vertical device. 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 semiconductor field effect transistor (MOSFET), and an electrostatic induction transistor ( SIT), junction field effect transistor (JFET), insulated gate bipolar transistor (IGBT) or light emitting diode (LED).

  Hereinafter, preferred examples when the crystalline oxide semiconductor film of the present invention is applied to an n-type semiconductor layer (such as an n + -type semiconductor or an n − semiconductor layer) will be described with reference to the drawings. It is not limited to the example. Note that 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, or other intermediate layers) are provided as long as the object of the present invention is not impaired. It may be included, and a buffer layer (buffer layer) and 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. Examples of the electrode material include Al, Mo, Co, Zr, Sn, Nb, Fe, Cr, Ta, Ti, Au, Metals such as Pt, V, Mn, Ni, Cu, Hf, W, Ir, Zn, In, Pd, Nd, or Ag or alloys thereof, tin oxide, zinc oxide, rhenium oxide, indium oxide, indium tin oxide (ITO ), Metal oxide conductive films such as zinc indium oxide (IZO), organic conductive compounds such as polyaniline, polythiophene or polypyrrole, or mixtures and laminates thereof.

  Formation of a Schottky electrode and an ohmic electrode can be performed by well-known means, such as a vacuum evaporation method or sputtering method, for example. More specifically, for example, when a Schottky electrode is formed using two kinds of the first metal and the second metal among the metals, a layer made of the first metal and a 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 using a photolithography technique.

  When a reverse bias is applied to the SBD of FIG. 2, a depletion layer (not shown) spreads in the n-type semiconductor layer 101a, so that a high breakdown voltage SBD is obtained. In addition, when a forward bias is applied, electrons flow from the ohmic electrode 105b to the Schottky electrode 105a. Thus, the SBD using the semiconductor structure is excellent for high withstand voltage and large current, has a high switching speed, and is 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 in FIG. 3 includes an n-type semiconductor layer 121a having a wide band gap, an n-type semiconductor layer 121b having a narrow band gap, an n + type semiconductor layer 121c, a semi-insulator layer 124, a buffer layer 128, a gate electrode 125a, a source electrode 125b, A drain electrode 125c is provided.

(MOSFET)
An example in which the semiconductor device of the present invention is a MOSFET is shown in FIG. The MOSFET in FIG. 4 is a trench type MOSFET, and includes an n− type semiconductor layer 131a, 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)
6 shows 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)
An example in which the semiconductor device of the present invention is a light emitting diode (LED) is shown in FIG. The semiconductor light emitting element of FIG. 7 includes an n-type semiconductor layer 161 on the second electrode 165b, and a light-emitting layer 163 is stacked on the n-type semiconductor layer 161. A p-type semiconductor layer 162 is stacked on the light emitting layer 163. A light-transmitting electrode 167 that transmits light generated by the light-emitting layer 163 is provided over the p-type semiconductor layer 162, and a first electrode 165 a is stacked over the light-transmitting electrode 167. 7 may be covered with a protective layer except for the electrode portion.

As a material for the light-transmitting electrode, an oxide conductive material containing indium (In) or titanium (Ti) can be given. More specifically, for example, In ₂ O ₃ , ZnO, SnO ₂ , Ga ₂ O ₃ , TiO ₂ , CeO _2, a mixed crystal of two or more thereof, or a material doped with these may be used. A translucent electrode can be formed by providing these materials by known means such as sputtering. Moreover, after forming the translucent electrode, thermal annealing for the purpose of making the translucent electrode transparent may be performed.

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

  Examples of the material of the first electrode 165a and the second electrode 165b include Al, Mo, Co, Zr, Sn, Nb, Fe, Cr, Ta, Ti, Au, Pt, V, Mn, Ni, Cu, Metals such as Hf, W, Ir, Zn, In, Pd, Nd, or Ag or alloys thereof, tin oxide, zinc oxide, rhenium oxide, indium oxide, indium tin oxide (ITO), indium zinc oxide (IZO), etc. Examples thereof include metal oxide conductive films, organic conductive compounds such as polyaniline, polythiophene, and polypyrrole, or mixtures thereof. The electrode film forming method 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 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 among chemical methods such as methods.

  Note that another mode of the light-emitting element is illustrated in FIGS. In the light-emitting element of FIG. 8, an n-type semiconductor layer 161 is stacked on a substrate 169, and the n-type semiconductor exposed by cutting out part of the p-type semiconductor layer 162, the light-emitting layer 163, and the n-type semiconductor layer 161. A second electrode 165b is stacked on a portion of the layer 161 on the exposed surface of the semiconductor layer.

  The semiconductor device is used in, for example, 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 using known means. FIG. 9 shows an example of a power supply system. In FIG. 9, a power supply system is configured by using a plurality of the power supply devices and control circuits. As shown in FIG. 10, the power supply system can be used in a system apparatus in combination with an electronic circuit. An example of a 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 composed of a power circuit and a control circuit. After the DC voltage is switched at a high frequency by an inverter (configured by MOSFETs A to D) and converted to AC, insulation and transformation are performed with a transformer. After rectification by the rectification MOSFET, the DC voltage is smoothed by DCL (smoothing coils L1, 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 rectifier MOSFET are controlled by the PWM control circuit so as to obtain the desired output voltage.

  Examples of the present invention will be described below, but the present invention is not limited thereto.

Example 1
1. Film Forming Apparatus The mist CVD apparatus used in this example will be described with reference to FIG. The mist CVD apparatus 19 includes a susceptor 21 on which the substrate 20 is placed, a carrier gas supply means 22a for supplying a carrier gas, and a flow rate adjusting valve 23a for adjusting the flow rate of the carrier gas sent from the carrier gas supply means 22a. The carrier gas (dilution) supply means 22b for supplying the carrier gas (dilution), the flow rate adjusting valve 23b for adjusting the flow rate of the carrier gas sent from the carrier gas (dilution) supply means 22b, and the raw material solution 24a are accommodated. Mist generating source 24, a container 25 in which water 25a is placed, an ultrasonic vibrator 26 attached to the bottom surface of the container 25, a supply pipe 27 made of a quartz tube having an inner diameter of 40 mm, and a peripheral portion of the supply pipe 27 And a heater 28 installed in the vehicle. The susceptor 21 is made of quartz, and the surface on which the substrate 20 is placed is inclined from the horizontal plane. Both the supply pipe 27 and the susceptor 21 serving as a film formation chamber are made of quartz, so that impurities derived from the apparatus are prevented from being mixed into the film formed on the substrate 20.

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

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

4). Formation of Semiconductor Film Next, the ultrasonic vibrator 26 was vibrated at 2.4 MHz, and the vibration was propagated to the raw material solution 24a through the water 25a, whereby the raw material solution 24a was atomized 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.

(Example 2 to Example 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 thicknesses of the obtained crystalline oxide semiconductor films were 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 reproducibility, a crystalline oxide semiconductor film was obtained in the same manner as in Example 4. The thickness of the obtained crystalline oxide semiconductor film was 3.4 μm. The reproducibility was confirmed in the following test example. And as clear from Table 1, it confirmed that reproducibility was favorable. 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 in 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, Instead of an m-plane sapphire substrate having an α-Ga ₂ O ₃ film (non-doped) laminated as a buffer layer on the surface, an aqueous solution containing 10% by volume of hydrobromic acid was used as the substrate. A crystalline oxide semiconductor film was obtained in the same manner as in Example 1 except that an a-plane sapphire substrate on which no buffer layer was laminated was used and the film formation time was 10 minutes.

(Example 7)
Other than using an a-plane sapphire substrate in which an α-Ga ₂ O ₃ film (non-doped) is laminated on the surface as a buffer layer instead of an a-plane sapphire substrate on which the buffer layer is not laminated on the surface. In the same manner as in Example 6, a crystalline oxide semiconductor film was obtained. The film thickness of the obtained crystalline oxide semiconductor film was 0.3 μm.

(Example 8)
In order to confirm 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. And as clear from Table 1, it confirmed that reproducibility was favorable. It can also be seen from the film thickness that the reproducibility is good.

Example 9
Instead of an m-plane sapphire substrate having an α-Ga ₂ O ₃ film (non-doped) laminated on the surface as a buffer layer, an α-Ga ₂ O ₃ film (Sn doped) is laminated on the surface as a 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 having an α-Ga ₂ O ₃ film (non-doped) laminated on the surface as a buffer layer 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)
Other than using an a-plane sapphire substrate with no buffer layer laminated on the surface, instead of an a-plane sapphire substrate with an α-Ga ₂ O ₃ film (Sn doped) laminated on the surface as a buffer layer Obtained a crystalline oxide semiconductor film in the same manner as in Example 9. The thickness of the obtained crystalline oxide semiconductor film was 0.9 μm.

(Example 12)
As the raw material solution, gallium bromide and germanium oxide were mixed in ultrapure water, and the raw material solution was adjusted so that the atomic ratio of germanium to gallium was 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 formation time was 720 minutes. The thickness of the obtained crystalline oxide semiconductor film was 3.8 μm.

(Comparative Example 1)
Other than using a c-plane sapphire substrate with no buffer layer laminated on the surface instead of an m-plane sapphire substrate with an α-Ga ₂ O ₃ film (non-doped) laminated on the surface as a buffer layer as the substrate. In the same manner as in Example 1, a crystalline oxide semiconductor film was obtained.
(Comparative Example 2)
Gallium bromide and germanium oxide are mixed in ultrapure water, and the raw material solution is adjusted so that the atomic ratio of germanium to gallium is 1: 005, and the a-plane in which no buffer layer is laminated on the surface as a substrate 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 thereof 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 a buffer layer was laminated on the surface instead of an a-plane sapphire substrate on which the buffer layer was not laminated. A crystalline oxide semiconductor film was obtained in the same manner as in Example 6 except that an unprocessed c-plane sapphire substrate was used.

(Test Example 1)
The phase was identified about the crystalline oxide semiconductor film obtained in Examples 1-13 and Comparative Examples 1-3 using the X-ray diffraction apparatus. 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 rays. 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 ₂ O ₃ , and the films obtained in Comparative Examples 1 to 3 were all c-plane α-Ga ₂ O ₃ . . Moreover, the result of having measured the rocking curve half value width of the crystalline oxide semiconductor film obtained in Example 1, 2, 4, 7-12 and the comparative example 1 is shown to Tables 1-3.

(Test Example 2)
With respect to the crystalline oxide semiconductor films obtained in Examples 1 to 13 and Comparative Examples 1 to 3, Hall effect measurement was performed 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, it can be seen that the crystalline oxide semiconductor film of the present invention is excellent in electrical characteristics, particularly mobility.

(Test Example 3)
About the crystalline oxide semiconductor film obtained in Examples 1-13 and Comparative Examples 1-3, the film | membrane surface was observed using the optical microscope. In observation, Tables 1 to 3 show the observation results, where ◯ indicates that no crack was observed in the central 3 mm square region of the film surface, and x indicates that cracks were observed in the central 3 mm square region. 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 material. As a result, it was found that the same performance as that of the crystalline oxide semiconductor film obtained in Example 1 was exhibited.

(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 film thickness obtained was 3.2 μm.

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

(Example 18)
Example 1 except that an m-plane sapphire substrate having an α-Ga ₂ O ₃ film (non-doped) laminated as a buffer layer on the surface and having an off angle of 2 ° toward the a-axis is used as the substrate. In the same manner as described above, a crystalline oxide semiconductor film was obtained. The film thickness obtained 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)
Other than adjusting the aqueous solution so that the atomic ratio of tin to gallium is 1: 0.0002 and gallium 0.05 mol / L when gallium acetylacetonate and tin (II) chloride are mixed in ultrapure water In the same manner as in Example 18, a crystalline oxide semiconductor film was obtained. The film thickness obtained was 1.8 μm.

(Example 21)
Other than adjusting the aqueous solution so that the atomic ratio of tin to gallium is 1: 0.0002 and gallium 0.05 mol / L when gallium acetylacetonate and tin (II) chloride are mixed in ultrapure water In the same manner as in Example 18, a crystalline oxide semiconductor film was obtained. The film thickness obtained 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 It was m-plane α-Ga ₂ O ₃ . For reference, the XRD measurement results of the crystalline semiconductor films obtained in Example 20 and Example 21 are shown in FIG. The crystalline oxide semiconductor films obtained in Examples 15 to 21 were evaluated in the same manner as in Test Examples 1 to 3, for carrier density, mobility, half width, and presence / absence of cracks. The results are shown in Table 4.

(Test Example 5)
With respect to the Sn-doped α-Ga ₂ O ₃ film on the m-plane sapphire substrate, Hall effect measurement was performed by the van der Pauw method, and mobility and carrier density were evaluated. For the α-Ga ₂ O ₃ film, gallium acetylacetonate and tin (II) chloride dihydrate were mixed until dissolved while adding a small amount of hydrochloric acid, and the resulting solution was used as a raw material solution. In addition, 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 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 around 1 × 10 ¹⁸ / cm ^3, and a plurality of α-Ga ₂ are prepared. An O ₃ film was obtained and used for this evaluation.
The results of Hall effect measurement are shown in FIG. Further, for comparison testing, in place of the m-plane sapphire substrate, 13 together also measurement results of the α-Ga ₂ O ₃ film obtained in the same manner as described above using c-plane sapphire substrate. 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 as compared with the film formed using the c-plane sapphire substrate.

(Test Example 6)
Moreover, the temperature characteristic of the mobility was examined for the α-Ga ₂ O ₃ film having a carrier density of 1.1 × 10 ¹⁸ cm ⁻³ obtained in Test Example 1 using a temperature variable Hall effect measuring apparatus. The results are shown in FIG. As is apparent from FIG. 14, the mobility is 40 cm ² / Vs or higher even in the low temperature region, and the electrical characteristics are good even in the high temperature region.

  The crystalline oxide semiconductor film of the present invention can be used in various fields such as semiconductor devices (for example, compound semiconductor electronic devices), electronic components / electric equipment components, optical / electrophotographic related devices, industrial members, etc. Useful for semiconductor devices and the like.

19 Mist CVD apparatus 20 Substrate 21 Susceptor 22a Carrier gas supply means 22b Carrier gas (dilution) supply means 23a Flow control valve 23b Flow control valve 24 Mist generation source 24a Raw material solution 25 Container 25a Water 26 Ultrasonic vibrator 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 insulator layer 105a Schottky electrode 105b ohmic electrode 121a n-type semiconductor layer 121b with wide band gap n with narrow band gap 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 (11)

A crystalline oxide semiconductor film containing a crystalline oxide semiconductor having a corundum structure as a main component and further containing a dopant, wherein the mobility is 30 cm ² / Vs or more. . 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, wherein the resistivity is 50 mΩcm or less.   The crystalline oxide semiconductor film according to claim 1, which has a resistivity of 5 mΩcm or less.   The crystalline oxide semiconductor film according to claim 1, wherein the main surface is an a-plane or an m-plane.   The crystalline oxide semiconductor film according to claim 1, wherein the dopant is tin, germanium, or silicon.   The crystalline oxide semiconductor film according to claim 1, wherein the dopant is tin.   The crystalline oxide semiconductor film according to claim 1, wherein the crystalline oxide semiconductor contains gallium, indium, or aluminum.   The crystalline oxide semiconductor film according to claim 1, wherein the crystalline oxide semiconductor contains at least gallium.   A semiconductor device including at least a semiconductor layer and an electrode, wherein the crystalline oxide semiconductor film according to claim 1 is used as the semiconductor layer. A semiconductor system comprising a semiconductor device, wherein the semiconductor device is the semiconductor device according to claim 10.