Patent Grant
11967618
The present inventive subject matter relates to a crystalline oxide semiconductor film, which is useful for a semiconductor device. Also, the present inventive subject matter relates to a semiconductor device including the crystalline oxide semiconductor film, and also relates to a semiconductor system including the crystalline oxide semiconductor film.
As a switching device of the next generation achieving a high withstand voltage, a low loss, and high temperature resistance, a semiconductor device using gallium oxide (Ga2O3) with a large band gap attracts attention and is expected to be applied to power semiconductor devices including an inverter. Also, gallium oxide is expected to be applied to a light emitting and/or receiving element such as a light emitting diode (LED) and a sensor, due to a wide band gap of gallium oxide. According to NPL 1, such gallium oxide has a band gap that may be controlled by forming mixed crystal with indium or aluminum singly or in combination and such a mixed crystal is an extremely attractive material as an InAlGaO-based semiconductor. Here, InAlGaO-based semiconductors refer to InXAlYGaZO3 (0≤X≤2, 0≤Y≤2, 0≤Z≤2, X+Y+Z=1.5˜2.5) and can be viewed as the same material system containing gallium oxide.
Patent Document 1 describes a highly crystalline and electrically-conductive α-Ga2O3 film that is doped with Sn and formed on a c-plane sapphire substrate. The film described in Patent Document 1 had a high crystallinity with a full width at half maximum of rocking curve by X-ray diffraction measurement that is approximately 60 arcsec, however, was still difficult to maintain breakdown voltage performance, and insufficient in semiconductor properties such as mobility that was 1 cm2/Vs or less.
Also, Patent Document 2 describes an α-Ga2O3 film doped with Ge and formed on a c-plane sapphire substrate, and the α-Ga2O3 film was superior in electric properties to the α-Ga2O3 film described in Patent Document 1. However, the mobility of the α-Ga2O3 film was 3.26 cm2/Vs, which was still insufficient for a semiconductor device.
In Non-Patent Document 2, an α-Ga2O3 film doped with Sn was formed on a c-plane sapphire substrate, and then, the α-Ga2O3 film was annealed to become an annealed buffer layer. By forming an α-Ga2O3 film doped with Sn on the annealed buffer layer, mobility was enhanced. In addition, Sn doped into the α-Ga2O3 film acts as a kind-of surfactant, the surface roughness and the crystallinity of the α-Ga2O3 film were improved and the mobility was enhanced as a result. However, there were still problems that the annealing treatment increases the resistance of the film or makes the film electrically-insulated, and thus, the film had problems to be used for the semiconductor device. Also, since the obtained film still has a number of dislocations, and the influence of scattering dislocations was great, and that tends to affect the electrical characteristics negatively. Furthermore, there is also a problem of many cracks, and thus, an industrially useful α-Ga2O3 film has been desired.
NPL 1: Kaneko, Kentaro, “Fabrication and physical properties of corundum structured alloys based on gallium oxide”, Dissertation, Kyoto Univ., March 2013.
NPL2: Akaiwa, Kazuaki, “Conductivity control and device applications of corundum-structured gallium oxide-based semiconductor”, Dissertation, Kyoto Univ., March 2016.
An object of the present inventive subject matter is to provide a crystalline oxide semiconductor film with enhanced electrical characteristics, particularly mobility.
As a result of intensive investigations to achieve the above object, the present inventors found that a crystalline oxide semiconductor film formed under specified conditions by use of a mist CVD method surprisingly obtained enhanced mobility even without performing a treatment that gives high resistance and makes the crystalline oxide semiconductor film insulative, and also, even if the crystalline oxide semiconductor film has a full width at half maximum of 100 arcsec or more, for example. Furthermore, the crystalline oxide semiconductor film that was obtained was found to have decreased number of cracks and to solve the above-mentioned problem(s). Also, the inventors obtained the knowledge above, further investigated and completed the present inventive subject matter.
That is, the present inventive subject matter relates to followings.
[1] A crystalline oxide semiconductor film includes a corundum-structured crystalline oxide semiconductor as a major component; a dopant that is an n-type dopant; and a principal plane that is an a-plane or an m-plane.
[2] The crystalline oxide semiconductor film of [1], wherein the crystalline oxide semiconductor film includes carrier concentration that is 1.0×1018/cm3 or more.
[3] The crystalline oxide semiconductor film of [1] or [2], wherein the crystalline oxide semiconductor film comprises mobility that is 30 cm2/Vs or more.
[4] The crystalline oxide semiconductor film of [1] to [3], wherein the crystalline oxide semiconductor film comprises a full width at half maximum of 300 arcsec or more.
[5] wherein the crystalline oxide semiconductor film of [1] to [4] has electrical resistivity that is 50 mΩcm or less.
[6] The crystalline oxide semiconductor film of any of [1] to [5], wherein the crystalline oxide semiconductor film includes an off-angle.
[7] The crystalline oxide semiconductor film of any of [1] to [6], wherein the dopant contains tin, germanium, or silicon.
[8] The crystalline oxide semiconductor film of any of [1] to [7], wherein the dopant comprises tin.
[9] The crystalline oxide semiconductor film of any of [1] to [8], wherein the crystalline oxide semiconductor comprises gallium, indium, or aluminum.
[10] The crystalline oxide semiconductor film of any of [1] to [9], wherein the crystalline oxide semiconductor contains at least gallium.
[11] A semiconductor device includes at least an electrode and the crystalline oxide semiconductor film of any of [1] to [10] as a semiconductor layer; and an electrode.
[12] A semiconductor system includes the semiconductor device of [11].
Crystalline oxide semiconductor films according to a present inventive subject matter include enhanced electrical properties, and are particularly enhanced in mobility.
The crystalline oxide semiconductor film of a present inventive subject matter is a crystalline oxide semiconductor film containing as a major component a crystalline oxide semiconductor with a corundum structure, further containing a dopant that is an n-type dopant, and a principal plane that is an a-plane or an m-plane. Also, the crystalline oxide semiconductor film of the present inventive subject matter preferably has a carrier concentration that is 1.0×1018/cm3 or more. The principal plane is not particularly limited as long as the principal plane is an a-plane or an m-plane, however, according to the present inventive subject matter, the principal plane is preferably an m-plane. Also, the carrier concentration herein means a carrier concentration obtained by a Hall effect measurement in the crystalline oxide semiconductor film. The upper limit of the carrier concentration is not particularly limited, however, the carrier concentration is preferably 1.0×1023/cm3 or less, and further preferably 1.0×1022/cm3 or less. The crystalline oxide semiconductor film has mobility that is 30 cm3/Vs or more, further preferably 50 cm3/Vs or more, and most preferably 100 cm3/Vs or more. The mobility herein means a mobility obtained by a Hall effect measurement. Also, according to a present inventive subject matter, the crystalline oxide semiconductor film has a resistivity that is 50 mΩcm or less, further preferably 10 mΩcm or less, or further preferably 5 mΩcm or less.
The crystalline oxide semiconductor film preferably includes an off-angle. The term “off-angle” herein means an angle of inclination to a crystalline plane (principal plane) that is a reference plane, and usually the term “off-angle” is used as an inclination angle formed by the crystalline plane (principal plane) and a crystalline growth surface. The direction of inclination of “off-angle” is not particularly limited, however, according to the present inventive subject matter, if the crystalline plane (principal plane) is an m-plane with an off-angle, the off-angle is preferably inclined to the direction of an a-axis from the reference plane. The “off-angle” is not particularly limited, however, preferably in a range of 0.2° to 12.0°, further preferably 0.5° to 4.0°, and most preferably 0.5° to 3.0°. If the crystalline oxide semiconductor film includes an off-angle that is in a preferable range, semiconductor properties, especially in mobility, are enhanced.
Also, according to a present inventive subject matter, the crystalline oxide semiconductor may preferably contain indium, gallium or aluminum, and further preferably contains InAlGaO-based semiconductor. The crystalline oxide semiconductor most preferably contains at least gallium. The term “major component” herein means, for example, if a crystalline oxide semiconductor of a crystalline oxide semiconductor film is α-Ga2O3, α-Ga2O3 is contained in the crystalline oxide semiconductor film under the condition that the atomic ratio of gallium in all metal elements contained in the crystalline oxide semiconductor film is 0.5 or more. According to a present inventive subject matter, the atomic ratio of gallium in all metal elements contained in a crystalline oxide semiconductor film is preferably 0.7 or more, and further preferably 0.8 or more. The thickness of the crystalline oxide semiconductor film is not particularly limited, and may be 1 μm or less, and also may be 1 μm or more. The shape of the crystalline oxide semiconductor film is not particularly limited, and the crystalline oxide semiconductor film may be a quadrangle including a rectangular shape and a square shape. Also, the shape of the crystalline oxide semiconductor film may be a circular shape including a semicircle, for example. Furthermore, the shape of the first semiconductor film may be a polygonal shape. The surface area of the crystalline oxide semiconductor film may not be particularly limited, however, the surface area of the first semiconductor layer may be 3 mm square or more, and preferably 5 mm square or more. The crystalline oxide semiconductor film is most preferably 50 mm or more in diameter. According to a present inventive subject matter, the crystalline oxide semiconductor film is preferably free from crack(s) in a center area that is 3 mm square by an optical-microscopic surface observation. Also, the crystalline oxide semiconductor film is further preferably free from crack(s) in a center area that is 5 mm square by an optical-microscopic surface observation. Furthermore, the crystalline oxide semiconductor film is most preferably free from crack(s) in a center area that is 9.5 mm square or more by an optical-microscopic surface observation. The crystalline oxide semiconductor film may be a single crystal film or a polycrystalline film, and the crystalline oxide semiconductor film is preferably a single crystal film.
The crystalline oxide semiconductor film contains a dopant. The dopant is not particularly limited and may be a known dopant, as long as the dopant is an n-type dopant. Examples of the n-type dopant include tin (Sn), germanium (Ge), silicon (Si), titanium (Ti), zirconium (Zr), vanadium (V), niobium (Nb), and lead (Pb). According to a present inventive subject matter, the dopant is preferably tin (Sn), germanium (Ge), or silicon (Si), and the dopant is further preferably tin (Sn) or germanium (Ge). The dopant is most preferably tin (Sn). The contained amount of the dopant in a crystalline oxide semiconductor film is preferably 0.00001 atomic percent (at. %) or more in the composition of the crystalline oxide semiconductor film. The contained amount of the dopant in a crystalline oxide semiconductor film is further preferably in a range of 0.00001 at. % to 20 at. %. The range of the amount of the dopant contained in the crystalline oxide film is most preferably in a range of 0.00001 at. % to 10 at. % to enhance electrical properties of the crystalline oxide semiconductor film.
The crystalline oxide semiconductor film preferably has a rocking curve half width of 100 arcsec or more, and further preferably 300 arcsec or more as measured by X-ray diffraction. The upper limit of the half width is not particularly limited, however, is preferably 1300 arcsec, and further preferably 1100 arcsec. By setting such a preferable half width, the mobility of the obtained crystalline oxide semiconductor film can be further improved. The above-mentioned “half width” means a value obtained by measuring the rocking curve half width by XRD (X-ray diffraction: X-ray diffraction method). The measurement plane orientation is not particularly limited, however, examples of the measurement plane orientation include [11-20] and [30-30].
Hereinafter, although a preferable method of manufacturing the crystalline oxide semiconductor film is demonstrated, the present inventive subject matter is not limited to these embodiments of the method.
As a method of preferably forming the crystalline oxide semiconductor film, for example, using a mist CVD apparatus, for example, as shown in
(Crystalline Substrate)
The crystalline substrate is not particularly limited, however, a crystalline substrate having a corundum structure partly or entirely at a principal plane that is an a-plane or an m-plane is named as a preferable example of the crystalline substrate. The crystalline substrate preferably has the corundum structure at the principal plane that is positioned at the side of crystal growth, and further preferably the crystalline substrate has the corundum structure entirely at the principal plane. Also, according to a present inventive subject matter, the crystalline substrate may include an off-angle, that is preferable to enhance electrical properties. If the principal plane of the crystalline substrate is an m-plane, the angle inclined toward an a-axis from the m-plane that is a reference plane is preferably formed. Also, the off-angle of the crystalline substrate is not particularly limited, however, is preferable 0.2° to 12.0°, further preferably 0.5° to 4.0°, and most preferably 0.5° to 3.0°. The shape of the crystalline substrate is not particularly limited, as long as the crystalline substrate has a plate-like shape and is able to support the crystalline oxide semiconductor film. The crystalline substrate may be an electrically-insulating substrate, a semi-conductor substrate, and may be an electrically conductive substrate, however, the crystalline substrate is preferably an electrically-insulating substrate. Also, the crystalline substrate including a metal film arranged on a surface of the crystalline substrate is also preferable. The shape of the crystalline substrate is not particularly limited and may be a circular shape. Examples of the circular shape may include shapes of a circle, and an ellipse. The shape of the crystalline substrate may be, for example, a polygonal shape. Examples of the polygonal shape include a triangle, a square, a rectangle, a pentagon, a hexagon, a heptagon, an octagon and a nonagon. Various shapes of crystalline substrates may be available. According to a present inventive subject matter, the shape of the crystalline substrate would be selectable to form a semiconductor film in a desired shape on the crystalline substrate with the shape. Also, according to a present inventive subject matter, the crystalline substrate may have a larger area to form a crystalline oxide film that has a larger area on the crystalline substrate. The substrate material of the crystalline substrate is not particularly limited, as long as an object of the present inventive subject matter is not interfered with, and a known substrate material may be used. Examples of the substrate material with a corundum structure include α-Al2O3 (sapphire substrate) and α-Ga2O3. Preferable examples of the substrate material include a sapphire substrate with a principal plane that is an a-plane, a sapphire substrate with a principal plane that is an m-plane, a sapphire substrate with a principal plane that is an a-plane, an α-Ga2O3 (with a principal plane that is an a-plane or an m-plane).
Examples of the buffer layer without containing a dopant include α-Fe2O3, α-Ga2O3, α-Al2O3, and a mixed crystal thereof. According to a present inventive subject matter, the buffer layer is preferably α-Ga2O3. A method of forming the buffer layer on the crystalline substrate is not particularly limited, and may be a known method, and also, a similar method of forming a film as the method of forming the crystalline oxide semiconductor film may be used.
(Forming Atomized Droplets)
Forming atomized droplets, the raw material solution is turned into atomized droplets. A method of forming atomized droplets from the raw material solution is not particularly limited, as long as the raw material solution is able to be turned into atomized droplets, and a known method may be used, however, according to a present inventive subject matter, a method of forming atomized droplets using ultrasonic vibration is preferable. Atomized droplets including mist particles and obtained by using ultrasonic vibration and floating in the space have the initial velocity that is zero. Since atomized droplets floating in the space is carriable as a gas, the atomized droplets floating in the space are preferable to avoid damage caused by the collision energy without being blown like a spray. The size of droplets is not limited to a particular size, and may be a few mm, however, the size of atomized droplets is preferably 50 μm or less. The size of droplets is further preferably in a range of 0.1 to 10 μm.
(Raw-Material Solution)
The raw-material solution is not particularly limited as long as a semiconductor film is formed from the raw-material solution by a mist CVD method and contains the dopant. Examples of the raw-material solution include a solution of organometallic complex of a metal, and a solution of halide. Example of organometallic complex for the solution includes a solution of acetylacetonate complex. Examples of halide for the solution includes a solution of fluoride, a solution of chloride, a solution of bromide and a solution of iodide. Examples of the metal of organometallic complex include gallium, indium, and/or aluminum. According to an embodiment of a present inventive subject matter, the metal of organometallic complex preferably contains at least gallium. The amount of metal contained in the raw material solution is not particularly limited as long as an object of the present inventive subject matter is not interfered with, however, the amount of metal(s) contained in the raw material solution is preferably 0.001 mol % to 50 mol %. The amount of metal contained in the raw material solution is further preferably 0.01 mol % to 50 mol %.
Also, according to a present inventive subject matter, the raw material solution contains a dopant. By introducing a dopant into a raw material solution, it is possible to control electrical conductivity of a crystalline oxide semiconductor film while being formed, without ion implantation, for example, and thus, without breaking the crystalline structure of the crystalline oxide semiconductor film. The dopant may be an n-type dopant such as tin, germanium, silicon and lead, if the metal(s) contain at least gallium. The n-type dopant is preferably tin or germanium, and most preferably tin. The dopant concentration in general may be in a range of 1×1016/cm3 to 1×1022/cm3. The dopant concentration may be at a lower concentration of, for example, approximately 1×1017/cm3 or less, and also the dopant concentration may be at a high concentration of, for example, 1×1020/cm3 or more. According to embodiments of a present inventive subject matter, the dopant concentration is preferably 1×1020/cm3 or less, and further preferably 5×1019/cm3 or less.
A solvent of the raw material solution is not particularly limited and may be an inorganic solvent such as water or an organic solvent such as alcohol. Furthermore, according to an embodiment of a present inventive subject matter, a mixed solvent of water and alcohol may be used. According to embodiments of a present inventive subject matter, a solvent of the raw material solution preferably contains water, and a mixed solvent of water and alcohol is further preferably used, and most preferably, a solvent of the raw material solution is water, which may include, for example, pure water, ultrapure water, tap water, well water, mineral water, hot spring water, spring water, fresh water and ocean water. According to embodiments of a present inventive subject matter, ultrapure water is preferable as a solvent of a raw material solution.
(Carrying Atomized Droplets)
The atomized droplets are carried into a film-formation chamber by carrier gas. The carrier gas is not limited as long as an object of the present inventive subject matter is not interfered with, and thus, examples of the carrier gas may be oxygen, ozone, an inert gas such as nitrogen and argon, or a reducing gas such as a hydrogen gas and a forming gas. The type of carrier gas may be one or more, and a dilution gas at a reduced flow rate (e.g., 10-fold dilution gas) and the like may be used further as a second carrier gas. The carrier gas may be supplied from one or more locations. While the flow rate of the carrier gas is not particularly limited, the flow rate of the carrier gas may be in a range of 0.01 to 20 L/min. According to an embodiment of a present inventive subject matter, the flow rate of the carrier gas may be preferably in a range of 0.5 to 10 L/min. When a dilution gas is used, the flow rate of the dilution gas is preferably in a range of 0.001 to 2 L/min, and further preferably in a range of 0.1 to 1 L/min.
(Film Formation)
In the film-formation, an oxide semiconductor film is formed on the base by thermal reaction of the atomized droplets in the film-formation. Thermal reaction is not particularly limited if the atomized droplets react on heating, and reaction conditions are not particularly limited if an object of the present invention is not interfered with. In the film-formation, the thermal reaction is conducted at an evaporation temperature or higher temperature of the evaporation temperature of the solvent of the raw material solution. During the thermal reaction, the temperature should not too high (for example not higher than 1000° C.). For example, the temperature during the thermal reaction is preferably 650° C. or less. The temperature during the thermal reaction is most preferably in a range of 400° C. to 650° C. The thermal reaction may be conducted in any atmosphere of a vacuum, a non-oxygen atmosphere, a reducing-gas atmosphere, and an atmosphere of oxygen. Also, the thermal reaction may be conducted in any condition of under an atmospheric pressure, under an increased pressure, and under a reduced pressure. According to a present inventive subject matter, the thermal reaction is preferably conducted under an atmospheric pressure. Also, a film thickness of the oxide semiconductor film is able to be set by adjusting a film formation time.
The crystalline oxide semiconductor film obtained as mentioned above not only having enhanced electrical properties especially in mobility but also with reduction of crack is industrially useful. Such crystalline oxide semiconductor films are able to be preferably used for semiconductor devices, especially for power devices, and the crystalline oxide semiconductor film is, for example, used for an n-type semiconductor layer (which may include an n+-type semiconductor layer and an n−-type semiconductor layer) of the semiconductor device. Also, in a present inventive subject matter, the crystalline oxide semiconductor film may be used as it is, and also, the crystalline oxide separated from the substrate etc. by a known method may be used in semiconductor devices.
Semiconductor devices may be categorized as planar semiconductor devices and also as vertical semiconductor devices. According to a present inventive subject matter, embodiments are suitably used for both planar semiconductor devices and vertical semiconductor devices, and preferably used for vertical semiconductor devices. Examples of the semiconductor device include a Schottky barrier diode (SBD), a metal semiconductor field-effect transistor (MESFET), a high-electron-mobility transistors (HEMT), a metal-oxide-semiconductor field-effect transistor (MOSFET), a static induction transistor (SIT), a junction field-effect transistor (JFET), an insulated gate bipolar transistor (IGBT), and a light emitting diode (LED).
Hereinafter, examples in which a crystalline oxide semiconductor film is used as an n-type semiconductor layer (that may be an n+-type semiconductor layer or an type semiconductor layer) are explained with figures, however, the present inventive subject matter is not limited thereto. Also, the following semiconductor devices shown as examples may include other layer(s) such as an electrically-insulating layer, a semi-insulating layer, an electrically-conductive layer, a semiconductor layer, a buffer layer or another medium layer. Also, it is possible to omit a buffer layer suitably.
The material of the Schottky electrode and the ohmic electrode may be a known material. Examples of the electrode material include Al, Mo, Co, Zr, Sn, Nb, Fe, Cr, Ta, Ti, Au, Pt, V, Mn, Ni, Cu, Hf, W, Ir, Zn, Pd, Nd, Ag and/or alloys thereof, metal oxide conductive films such as tin oxide, zinc oxide, indium oxide, indium tin oxide (ITO), and indium zinc oxide (IZO), organic conductive compounds such as polyaniline, polythiophene, and polypyrrole, and mixtures of these materials.
The formation of the Schottky electrode and the ohmic electrode can be performed by, for example, a known method such as a vacuum evaporation method or a sputtering method. For more details, if a Schottky electrode is formed by using two metals including a first metal and a second metal, a layer of the first metal may be arranged on a layer of the second metal and a patterning may be made on the layers of the first metal and the second metal by use of a photolithography method.
When a reverse bias is applied to the SBD shown in
(HEMT)
(MOSFET)
(JFET)
(IGBT)
(LED)
Examples of the material of the light-transmitting electrode may include oxide conductive material containing indium or titanium. Regarding the material of the light-transmitting electrode, in detail, the material may be In2O3, ZnO, SnO2, Ga2O3, TiO2, a mixed crystal thereof. The material may contain a dopant. By providing those materials using known method such as sputtering, the translucent electrode would be formed. Also, annealing may be carried out after forming the light-transmitting electrode, in order to make the electrode more transparent.
According to the light emitting diode of
Examples of the material of the first electrode 165a and the second electrode 165b may include Al, Mo, Co, Zr, Sn, Nb, Fe, Cr, Ta, Ti, Au, Pt, V, Mn, Ni, Cu, Hf, W, Ir, Zn, Pd, Nd, Ag and/or alloys thereof, metal oxide conductive films such as tin oxide, zinc oxide, indium oxide, indium tin oxide (ITO), and indium zinc oxide (IZO), organic conductive compounds such as polyaniline, polythiophene, and polypyrrole, and mixtures of these materials. A forming method of the first and the second electrode is not particularly limited. Examples of the forming method of the first and the second electrode may include wet methods such as printing method, spray method, coating method, physical methods such as vacuum deposition method, sputtering method, ion plating method, chemical methods such as CVD method, plasma CVD method. The forming method may be selected from above mentioned methods in consideration of a suitability for the material of the first electrode and the second electrode.
Also,
The semiconductor device is used for a system using a power source device. The power source device is able to be obtained by connecting the semiconductor device to a wiring pattern by use of a known method.
Some practical examples according to a present inventive subject matter are explained as follows, but the present inventive subject matter is not particularly limited thereto.
1. Film-Formation Apparatus
2. Preparation of a Raw-Material Solution
Gallium acetylacetonate and tin (II) chloride are mixed in ultrapure water to be a raw material solution 24a such that the atomic ratio of gallium to tin is 1:0.002 and gallium is 0.005 mol/L, and the raw material solution 24a contains hydrochloric acid to be 1.5% by volume ratio.
3. Preparation of Film-Formation
The raw-material solution 24a obtained at 2. the Preparation of the Raw-Material Solution above was set in the mist generator 24. Then, an m-plane sapphire substrate as a base 20 was placed on the susceptor 21, and the heater 28 was activated to raise the temperature in the film-formation chamber 27 up to 460° C. The first flow-control valve 23a and the second flow-control valve 23b were opened to supply a carrier gas from the carrier gas source 22a and the diluted carrier gas source 22b, which are the source of carrier gas, into the film-formation chamber 27 to replace the atmosphere in the film-formation chamber 27 with the carrier gas sufficiently. After the atmosphere in the film-formation chamber 27 was sufficiently replaced with the carrier gas, the flow rate of the carrier gas from the carrier gas source 22a was regulated at 1.0 L/min. and the diluted carrier gas from the diluted carrier gas source 22b was regulated at 0.5 L/min. Also, nitrogen was used as the carrier gas.
4. Formation of Semiconductor Film
Next, the ultrasonic transducer 26 was then vibrated at 2.4 MHz, and the vibrations were propagated through the water 25a to the raw material solution 24a to generate atomized droplets from the raw material solution 2. The atomized droplets were introduced in the film-formation chamber 27 with the carrier gas. In the film-formation chamber 27, the atomized droplets were reacted at 460° C. under atmospheric pressure in the supply pipe 27 to form a semiconductor film on the base 20. The film was 2.5 μm in film thickness. The film-formation time was 360 minutes.
Crystalline oxide semiconductor films were obtained by the same conditions as the conditions of the Example 1 except the following condition: using an m-plane sapphire substrate with an off-angle as the base. In the Example 2, the off-angle was 0.5°. In the Example 3, the off-angle was 2.0°. In the Example 3, the off-angle was 2.0°. In the Example 4, the off-angle was 3.0°. The crystalline oxide semiconductor film in the Example 2 was 3.0 μm in film thickness. The crystalline oxide semiconductor film in the Example 3 was 2.9 μm in film thickness. The crystalline oxide semiconductor film in the Example 4 was 3.3 μm in film thickness.
To confirm reproducibility, a crystalline oxide semiconductor film was obtained by the same conditions as the conditions of the Example 4, and the crystalline oxide semiconductor film obtained herein was 3.4 μm in film thickness. Also, to confirm reproductivity, following Test Examples were conducted, and as clearly shown in Table 1, reproducibility was confirmed to be favorable. Also, the film thickness of the obtained crystalline oxide semiconductor films indicates favorable reproductivity.
A crystalline oxide semiconductor film was obtained by the same conditions as the conditions of the Example 1 except the following conditions that gallium bromide and tin bromide are mixed in ultrapure water to be a raw material solution 24a such that the atomic ratio of gallium to tin is 1:0.08 and gallium is 0.1 mol/L in aqueous solution which contains hydrobromic acid that is to be 10% by volume ratio, an a-plane sapphire substrate without a buffer layer on a surface of the a-plane sapphire substrate was used as a base instead of using an m-plane sapphire substrate on that α-Ga2O3 film (non-doped) was arranged as a buffer layer, and the film-formation time was set to be ten minutes.
A crystalline oxide semiconductor film was obtained by the same conditions as the conditions of the Example 6 except the following condition that α-Ga2O3 film (non-doped) arranged as a buffer layer on an a-plane sapphire substrate was used as the substrate instead of an a-plane sapphire substrate being used. The crystalline oxide semiconductor film that was obtained was 0.3 μm in film thickness.
To confirm reproducibility, a crystalline oxide semiconductor film was obtained by the same conditions as the conditions of the Example 7, and the crystalline oxide semiconductor film obtained herein was 0.3 μm in film thickness. Also, to confirm reproductivity, following Test Examples were conducted, and as clearly shown in Table 1, reproducibility was confirmed to be favorable. Also, the film thickness of the obtained crystalline oxide semiconductor films indicates favorable reproductivity.
A crystalline oxide semiconductor film was obtained by the same conditions as the conditions of the Example 1 except the following conditions that α-Ga2O3 film (Sn-doped) arranged as a buffer layer on a surface of an a-plane sapphire substrate was used as the substrate instead of α-Ga2O3 film (non-doped) arranged as a buffer layer on a surface of an m-plane sapphire substrate being used, and the film-formation time was set to be 180 minutes.
A crystalline oxide semiconductor film was obtained by the same conditions as the conditions of the Example 9 except the following conditions that α-Ga2O3 film (non-doped) arranged as a buffer layer on an a-plane sapphire substrate was used as the substrate, and a raw material solution was prepared such that the atomic ratio of gallium to tin is to be 1:0.0002. The crystalline oxide semiconductor film was 1.0 μm in film thickness.
A crystalline oxide semiconductor film was obtained by the same conditions as the conditions of the Example 9 except the following conditions that an a-plane sapphire substrate without a buffer layer arranged on the a-plane sapphire substrate was used instead of an α-Ga2O3 film (Sn-doped) arranged as a buffer layer on an a-plane sapphire substrate being used. The crystalline oxide semiconductor film obtained herein was 0.9 μm in film thickness.
A crystalline oxide semiconductor film was obtained by the same conditions as the conditions of the Example 6 except the following conditions that a raw material solution was prepared such that the atomic ratio of germanium to gallium is to be 1:0.01, gallium is to be 0.1 mol/L in aqueous solution which contains hydrobromic acid that is to be 20% by volume ratio, and the film-formation time was set to be 30 minutes.
A crystalline oxide semiconductor film was obtained by the same conditions as the conditions of the Example 3 except the following condition that the film-formation time was set to be 720 minutes. The crystalline oxide semiconductor film was 3.8 μm in film thickness.
A crystalline oxide semiconductor film was obtained by the same conditions as the conditions of the Example 1 except the following condition that a c-plane sapphire substrate without a buffer layer arranged on the c-plane sapphire substrate was used instead of an α-Ga2O3 film (non-doped) arranged as a buffer layer on an m-plane sapphire substrate being used.
A crystalline oxide semiconductor film was obtained by the same conditions as the conditions of the Example 6 except the following conditions that gallium bromide and germanium oxide are mixed in ultrapure water to be a raw material solution such that the atomic ratio of gallium to germanium is to be 1:0.005, and a c-plane sapphire substrate without a buffer layer on a surface of the c-plane sapphire substrate was used as a base instead of an a-plane sapphire substrate without a buffer layer on a surface of the a-plane sapphire substrate being used.
A crystalline oxide semiconductor film was obtained by the same conditions as the conditions of the Example 6 except the following conditions that a raw material solution is adjusted such that the atomic ratio of gallium to tin is to be 1:0.005, and a c-plane sapphire substrate without a buffer layer on a surface of the c-plane sapphire substrate was used as a base instead of an a-plane sapphire substrate without a buffer layer on a surface of the a-plane sapphire substrate being used.
Using an X-ray diffraction (XRD) device, phases of the crystalline oxide semiconductor films obtained in Examples 1 to 13 and in Comparative Examples 1 to 3 were identified by conducting 2Θ/ω-scan at angles from 15° to 95°. The measurement was conducted by use of CuKα radiation. As the result, all of the crystalline oxide semiconductor films obtained in Examples 1 to 5 and in Example 13 were m-plane α-Ga2O3 films. Also, all of the crystalline oxide semiconductor films obtained in Examples 6 to 12 were a-plane α-Ga2O3 films, and all of the crystalline oxide semiconductor films obtained in Comparative Examples 1 to 3 were c-plane α-Ga2O3 films. Also, a full width of half maximum (FWHM) of rocking curve of each of crystalline oxide semiconductor films obtained in Examples 1, 2, 4, 7 to 12 and in Comparative Example 1 was measured, and the measurement results were shown in Tables 1 to 3.
Hall effect measurement was conducted by van der pauw method on the crystalline oxide films obtained in Examples 1 to 13 and in Comparative Examples 1 to 3. Carrier concentration, mobility and resistivity of the crystalline oxide semiconductor films are indicated I Tables 1 to 3. As shown in the Tables 1 to 3, the crystalline oxide semiconductor films of the present inventive subject matter are enhanced in electric properties, especially in mobility.
Film surfaces of the crystalline oxide semiconductor films obtained in Examples 1 to 13 and in Comparative Examples 1 to 3 were observed by use of an optical microscope. Observation results are shown in Tables 1 to 3, and in the observation, a crystalline oxide semiconductor film without crack(s) in 3 mm square at the center of the crystalline oxide semiconductor film is indicated as ∘, and a crystalline oxide semiconductor film with crack(s) in 3 mm square at the center of the crystalline oxide semiconductor film is indicated as x. As shown in Tables 1 to 3, the crystalline oxide semiconductor films of the present inventive subject matter, it is clear that cracks were decreased.
A crystalline oxide semiconductor film was obtained by the same conditions as the conditions of the Example 6 except the following condition that silicon bromide was used as a dopant material. As the result, the crystalline oxide semiconductor film was found to have performance equivalent to that of the crystalline oxide semiconductor film in the Example 1 exhibited.
A crystalline oxide semiconductor film was obtained by the same conditions as the conditions of the Example 1. The crystalline oxide semiconductor film obtained herein was 2.3 μm in film thickness.
A crystalline oxide semiconductor film was obtained by the same conditions as the conditions of the Example 1 except the following condition that an m-plane sapphire substrate with an off-angle of 2° to an a-axis. The crystalline oxide semiconductor film obtained herein was 3.2 μm in film thickness.
A crystalline oxide semiconductor film was obtained by the same conditions as the conditions of the Example 16. The crystalline oxide semiconductor film obtained herein was 2.2 μm in film thickness.
A crystalline oxide semiconductor film was obtained by the same conditions as the conditions of the Example 1 except the following condition that an m-plane sapphire substrate with an off-angle of 2° to an a-axis and without an α-Ga2O3 film (non-doped) as a buffer layer layered on a surface of the m-plane sapphire substrate was used as a base. The crystalline oxide semiconductor film obtained herein was 2 μm in film thickness.
A crystalline oxide semiconductor film was obtained by the same conditions as the conditions of the Example 1 except the following condition that an m-plane sapphire substrate with an off-angle of 4° to an a-axis was used as a base. The crystalline oxide semiconductor film obtained herein was 2.6 μm in film thickness.
A crystalline oxide semiconductor film was obtained by the same conditions as the conditions of the Example 18 except the following condition that Gallium acetylacetonate and tin (II) chloride are mixed in ultrapure water to be a raw material solution such that the atomic ratio of gallium to tin is 1:0.0002 and gallium is 0.05 mol/L. The crystalline oxide semiconductor film obtained herein was 1.8 μm in film thickness.
A crystalline oxide semiconductor film was obtained by the same conditions as the conditions of the Example 18 except the following condition that Gallium acetylacetonate and tin (II) chloride are mixed in ultrapure water to be a raw material solution such that the atomic ratio of gallium to tin is 1:0.0002 and gallium is 0.05 mol/L. The crystalline oxide semiconductor film obtained herein was 1.8 μm in film thickness.
The crystalline oxide semiconductor films obtained in Examples 15 to 21 were identified under the same conditions as the conditions in the Test Example 1. As the result, all of the crystalline oxide semiconductor films obtained in Examples 15 to 21 were m-plane α-Ga2O3 films. Also, XRD measurement results of the crystalline oxide semiconductor film obtained in the Example 20 and the crystalline oxide semiconductor film obtained in the Example 21 were shown in
Hall effect measurement by van der Pauw method was performed on an Sn-doped α-Ga2O3 film formed on an m-plane substrate, and mobility and carrier concentration were valued. Also, an α-Ga2O3 film was obtained under the same conditions as the conditions in the Example 1 except the following conditions that a raw material solution in that gallium acetylacetonate and tin (II) chloride dihydrate were mixed to be dissolved in ultrapure water while a small amount of hydrochloric acid was added to the ultrapure water was prepared, an m-plane sapphire substrate was used, and the film-formation temperature was set to be 500° C. In this occasion, two or more raw material solutions were prepared to have carrier concentration adjusted to be around 1×1018/cm3 by changing the mixing ratio of tin (II) chloride dihydrate, and two or more α-Ga2O3 films were obtained from the raw material solutions and evaluated. The results of the Hall effect measurements are shown in
Also, temperature characteristics of mobility were examined on the α-Ga2O3 film having carrier concentration of 1.1×1018 cm−3 and obtained in the Test Example 5 by use of a variable temperature hall effect measurement system. The results are shown in
1. Film (Layer) Formation Apparatus
2. Preparation of a Raw-Material Solution
Gallium bromide and tin chloride are mixed in ultrapure water to be a raw material solution under the conditions in that the atomic ratio of gallium to tin is to be 1:0.08 and gallium is to be 0.1 mol/L in an aqueous solution which contains hydrobromic acid that is to be 20% by volume ratio.
3. Preparation of Film-Formation
The raw-material solution 4a obtained at 2. the Preparation of the Raw-Material Solution above was set in the mist generator 4. Then, α-Ga2O3 film (non-doped) arranged as a buffer layer on an m-plane sapphire substrate (with an off-angle of 2.0°) as a base 20 was placed on the hot plate 8, and the hot plate 28 was activated to raise the temperature of the base up to 410° C. The first flow-control valve 3a and the second flow-control valve 3b were opened to supply a carrier gas from the carrier gas source 2a and the diluted carrier gas source 2b, which are the source of carrier gas, into the film-formation chamber 7 to replace the atmosphere in the film-formation chamber 7 with the carrier gas sufficiently. After the atmosphere in the film-formation chamber 7 was sufficiently replaced with the carrier gas, the flow rate of the carrier gas from the carrier gas source was regulated at 0.6 L/min. and the diluted carrier gas from the diluted carrier gas source was regulated at 1.0 L/min. Also, nitrogen was used as the carrier gas.
4. Formation of a Semiconductor Film
Next, the ultrasonic transducer 6 was vibrated at 2.4 MHz, and the vibrations were propagated through the water 5a to the raw material solution 4a to atomize the raw material solution 4a to form atomized droplets. The atomized droplets that were introduced through the supply pipe 9 into the film-formation chamber 7 with the carrier gas were thermally reacted under atmospheric pressure to form a film on the base 20 at 410° C. The film that was obtained was 20 μm in film thickness. The film formation time was 150 minutes.
A crystalline oxide semiconductor film was obtained by the same conditions as the conditions of the Example 22 except the following condition that a c-plane sapphire substrate (with an off-angle of 0.2°) without a buffer layer on the c-plane sapphire substrate was used instead of an α-Ga2O3 (non-doped) as a buffer layer formed on an m-plane sapphire substrate. The crystalline oxide semiconductor film obtained herein was 2.0 μm in film thickness.
A crystalline oxide semiconductor film was obtained by the same conditions as the conditions of the Example 22 except the following condition that the flow rate of carrier gas was set to be 0.9 L/min.
A crystalline oxide semiconductor film was obtained by the same conditions as the conditions of the Example 23 except the following condition that a c-plane sapphire substrate (with an off-angle of 0.2°) without a buffer layer on a surface of the c-plane sapphire substrate was used instead of an α-Ga2O3 (non-doped) arranged on an m-plane sapphire substrate being used.
Phases of the crystalline oxide semiconductor films obtained in Examples 22 to 23 and Comparative Examples 4 to 5 were identified under the same conditions as the conditions in the Test Example 1. All of the crystalline oxide semiconductor films obtained in the Examples 22 to 23 were m-plane α-Ga2O3, and all of the crystalline oxide semiconductor films obtained in the Comparative Examples 4 to 5 were c-plane α-Ga2O3. Using a tester, resistivity of the crystalline oxide semiconductor films obtained in the Examples 22 to 23 and in Comparative Examples 4 to 5 were measured. The results are shown in
A crystalline oxide semiconductor film was obtained by the same conditions as the conditions of the Example 22 except the following conditions that gallium bromide and germanium oxide were mixed in ultrapure water to be a raw material solution such that the atomic ratio of gallium to germanium is to be 1:0.01, gallium is to be 0.1 mol/L in aqueous solution which contains hydrobromic acid that is to be 10% by volume ratio, and the flow rate of carrier gas was set to be 1.0 L/min. The crystalline oxide semiconductor film that was obtained herein was 2.0 μm in film thickness.
A crystalline oxide semiconductor film was obtained by the same conditions as the conditions of the Example 24 except the following conditions that a c-plane sapphire substrate (with an off-angle of 0.2°) was used as the base instead of α-Ga2O3 (non-doped) as a buffer layer arranged on a surface of an m-plane sapphire substrate being used.
Phases of the crystalline oxide semiconductor films obtained in Example 24 and in Comparative Example 6 were identified under the same conditions as the conditions in the Test Example 1. The crystalline oxide semiconductor film obtained in the Example 24 was an m-plane α-Ga2O3 film and the crystalline oxide semiconductor film obtained in the Comparative Example 6 was a c-plane α-Ga2O3 film. Using the same conditions as the conditions in the Test Example 7, resistivity of the crystalline oxide semiconductor films obtained in the Example 24 and in the Comparative Example 6 were measured. As the result, the same tendency as the result of the Test Example 7 was shown, and the m-plane α-Ga2O3 film containing an n-type dopant (germanium) was superior in electrical properties to the c-plane α-Ga2O3 film containing an n-type dopant (germanium).
A crystalline oxide semiconductor film according to the present inventive subject matter can be used in various fields for semiconductor devices (for example, compound semiconductor electronic devices), electronic parts, electrical equipment parts, optical electrophotographic related apparatuses, industrial members, and especially useful for semiconductor devices.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2016-217661 | Nov 2016 | JP | national |
| 2017-137447 | Jul 2017 | JP | national |
| Number | Name | Date | Kind |
|---|---|---|---|
| 8310029 | Fujikura | Nov 2012 | B2 |
| 10439028 | Hitora et al. | Oct 2019 | B2 |
| 20100006836 | Koukitu | Jan 2010 | A1 |
| 20120045661 | Kumaran et al. | Feb 2012 | A1 |
| 20140217470 | Sasaki et al. | Aug 2014 | A1 |
| 20150279927 | Hitora | Oct 2015 | A1 |
| 20150325659 | Hitora | Nov 2015 | A1 |
| 20170200790 | Hitora | Jul 2017 | A1 |
| 20170278706 | Oda | Sep 2017 | A1 |
| 20180061952 | Tokuda | Mar 2018 | A1 |
| 20210272805 | Takahashi | Sep 2021 | A1 |
| 20210328026 | Sugimoto | Oct 2021 | A1 |
| Number | Date | Country |
|---|---|---|
| 2013-28480 | Feb 2013 | JP |
| 2015-228495 | Dec 2015 | JP |
| WO2016035696 | Mar 2016 | JP |
| 2016-201540 | Dec 2016 | JP |
| 2016013554 | Jan 2016 | WO |
| Entry |
|---|
| International Search Report issued Dec. 26, 2017 in International (PCT) Application No. PCT/JP2017/040039 with English translation. |
| Written Opinion of the International Searching Authority issued Dec. 26, 2017 in International (PCT) Application No. PCT/JP2017/040039 with English translation. |
| Kentaro Kaneko, “Growth and physical properties of corundum-structured gallium oxide alloy thin films”, Dissertation, Kyoto Univ., Mar. 2013, pp. 1-116, with English language abstract. |
| Kazuaki Akaiwa, “Conductivity control and device applications of corundum-structured gallium oxide-based Semiconductor”, Dissertation, Kyoto Univ., Mar. 2016, pp. 1-81, with English language abstract. |
| Raveen Kumaran, “New Solid State Laser Crystals Created By Epitaxial Growth”, B.A.Sc, The University of British Columbia, Sep. 2012, pp. 1-172. |
| Extended European Search Report issued Jun. 16, 2020 in European Application No. 17867324.0. |
| Hiroyuki Nishinaka et al., “Epitaxial growth of α-Ga2O3 thin films on a-, m-, and r-plane sapphire substrates by mist chemical vapor deposition using α-Fe2O3 buffer layers”, Materials Letters, vol. 205, Jun. 2, 2017, pp. 28-31. |
| Office Action issued Nov. 25, 2020 in corresponding Chinese Application No. 201780068749.1, with English Translation. |
| Office Action issued Dec. 7, 2020 in corresponding Indian Application No. 201917018252. |
| Communication pursuant to Article 94(3) EPC issued May 30, 2022, in corresponding European Patent Application No. 17867324.0. |
| Riena Jinno et al. “Reduction in edge dislocation density in corundum-structured α-Ga2O3 layers on sapphire substrates with quasi-graded a-(Al, Ga)2O3 buffer layers”, Applied Physics Express, vol. 9, No. 7, 2016, p. 071101-1 to 071101-4. |
| Zhao et al., (“growth and characterization of a-phase Ga2-xSnxO3 . . . ”) Semi. Sci. Technol. 31 (Year: 2016). |
| Kaneko et al. (“Kaneko ”) (“Growth and metal-oxide-semiconductor field-effect transistors of corundum-structured alpha indium oxide semiconductors,”) Applied Physics Express. (Year: 2015). |
| Rauf (Rauf) (“Low resistivity and high mobility tin-doped indium oxide films,”) Materials Letters 18 123-127 (Year: 1993). |
| Zhao et al., (“Impurity Compensation Effect Induced by Tin Valence Change in a-Ga1.4Sno.6O3 Thin Films,” ACS Applied Materials & Interfaces 983-988). (Year: 2016). |
| Riena Jinno et al., “Reduction in edge dislocation density in corundum-structured α-Ga2O3 layers on sapphire substrates with quasi-graded α-(Al,Ga)2O3 buffer layers”, Applied Physics Express, vol. 9, No. 7, 2016, pp. 071101-1 to 071101-4. |
| Number | Date | Country | |
|---|---|---|---|
| 20220302263 A1 | Sep 2022 | US |
| Number | Date | Country | |
|---|---|---|---|
| Parent | 16347360 | US | |
| Child | 17832984 | US |
