Film forming device, film forming method, crystalline metal oxide film, and laminated structure and semiconductor device using same

Abstract

The present invention is a film forming device comprising: an atomization unit that generates mist by atomizing a raw material solution; a carrier gas supply unit that supplies a carrier gas for conveying the mist; a film formation unit that subjects the mist to a heat treatment to form a film on a base body; a conveyance unit which has a supply pipe through which the mist is conveyed by the carrier gas and which connects the atomization unit and the inside of the film formation unit; and a microwave heating device that irradiates the mist with microwaves to heat the mist between the atomization unit and the base body. Consequently, a film forming device capable of forming a film having high crystallinity at a high film formation rate on a large-diameter substrate while suppressing foreign matter and abnormal growth is provided.

Description

Film forming apparatus, film forming method, crystalline metal oxide film, stacked structure using the same, and semiconductor device

[0001] The present invention relates to a film forming apparatus, a film forming method, a crystalline metal oxide film, and a stacked structure and a semiconductor device using the same.

[0002] High-vacuum film-forming apparatuses capable of realizing a non-equilibrium state, such as pulsed laser deposition (PLD), molecular beam epitaxy (MBE), and sputtering, have been developed to date, and it has become possible to produce oxide semiconductors that could not be produced by conventional melt methods or the like.

[0003] Furthermore, a mist chemical vapor deposition (Mist CVD) method has been developed, which uses atomized mist-like raw materials to grow crystals on a substrate, and has been used to produce gallium oxide (α-Ga) having a corundum structure. ２ O ３ ) has become possible to produce. ２ O ３ As a semiconductor with a large band gap, it is expected to be applied to next-generation switching elements that can achieve high voltage resistance, low loss, and high heat resistance.

[0004] Regarding mist CVD methods, Patent Document 1 describes a tubular furnace-type mist CVD apparatus. Patent Document 2 describes a fine channel-type mist CVD apparatus. Patent Document 3 describes a linear source-type mist CVD apparatus. Patent Document 4 describes a tubular furnace-type mist CVD apparatus, which differs from the mist CVD apparatus described in Patent Document 1 in that a carrier gas is introduced into the mist generator. Patent Document 5 describes a mist CVD apparatus in which a substrate is placed above a mist generator and a susceptor is a rotating stage mounted on a hot plate.

[0005] Japanese Patent Application Laid-Open No. 01-257337 Japanese Patent Application Laid-Open No. 2005-307238 Japanese Patent Application Laid-Open No. 2012-046772 Japanese Patent No. 5397794 Japanese Patent Application Laid-Open No. 2014-063973 Japanese Patent No. 7080115 Japanese Patent No. 6875336 Japanese Patent No. 7239919

[0006] Unlike other CVD methods, the mist CVD method can form films at relatively low temperatures. ２ O ３ However, the inventors have found that in conventional mist CVD methods, the generated mist condenses and aggregates in the supply pipe before being transported to the substrate, resulting in a decrease in the film formation rate, and the condensed mist is not sent to the film formation section.

[0007] Furthermore, when forming a film on a large diameter substrate in order to improve productivity, if a large amount of mist is supplied to the substrate, the mist is at a low temperature, which causes a rapid drop in temperature on the film-forming surface of the substrate, resulting in problems such as a decrease in the crystallinity of the film and damage to the substrate.

[0008] α-Ga by mist CVD method ２ O ３ Regarding the fabrication, Patent Document 6 reports an example in which the life of the mist is extended and the film formation rate is improved by heating the pipe that transports the mist with a heater. Also, as a similar attempt, Patent Document 7 reports an example in which the life of the mist is extended and the film formation rate is improved by heating the carrier gas that transports the mist.

[0009] However, in the methods described in Patent Documents 6 and 7, as the gas temperature increases, the saturated water vapor pressure increases, accelerating the evaporation of the mist, which not only reduces the amount of mist supplied to the substrate, but also causes the raw material in the mist to precipitate and adhere to the film as foreign matter, resulting in abnormal growth.

[0010] Furthermore, when a semiconductor device is fabricated using a film containing a large number of such foreign particles, the foreign particles become killer defects, resulting in problems such as a decrease in breakdown voltage. Large foreign particles are particularly likely to become killer defects. These foreign particles, which are generated during film formation, can cause abnormal growth if they are embedded in or adhere to the film during film formation, so it is desirable to suppress their generation during the film formation process.

[0011] Furthermore, Patent Document 8 reports an example in which the deposition rate was improved by adding moisture to the carrier gas that transports the mist and increasing the relative humidity as a method for suppressing the evaporation of the mist. However, this method could not be used to deposit films at high deposition rates on large diameter substrates because the moisture in the carrier gas lowers the temperature of the deposition surface of the substrate, which reduces the crystallinity of the film or damages the substrate.

[0012] The present invention has been made to solve the above problems, and aims to provide a film formation apparatus and film formation method that are capable of forming a highly crystalline film on a large diameter substrate at a high film formation rate while suppressing foreign matter and abnormal growth, as well as a crystalline metal oxide film with suppressed foreign matter.

[0013] The present invention has been made to achieve the above-mentioned object, and provides a film formation apparatus comprising: a mist-forming section that generates mist by turning a raw material solution into mist; a carrier gas supply section that supplies a carrier gas that transports the mist; a film formation section that heat-treats the mist to form a film on a substrate; a transport section that connects the mist-forming section to the inside of the film formation section and has a supply pipe through which the mist is transported by the carrier gas; and a microwave heating device that irradiates microwaves onto the mist between the mist-forming section and the substrate to heat the mist.

[0014] With this type of film formation apparatus, the mist and carrier gas supplied to the substrate can be selectively and rapidly heated, preventing the saturated water vapor pressure of the carrier gas from increasing and suppressing the evaporation of the mist. This allows for a high film formation rate while suppressing the formation of foreign matter and abnormal growth. Furthermore, because high-temperature mist can be supplied to the substrate, a decrease in the temperature of the substrate is suppressed even when the amount of mist supplied is increased, making it possible to form films at a high film formation rate even on large-diameter substrates without impairing crystallinity.

[0015] In this case, the microwave heating device may include a microwave generating unit, a microwave irradiating unit that irradiates the mist with microwaves generated by the microwave generating unit, and a microwave guiding unit that propagates the microwaves from the microwave generating unit to the microwave irradiating unit.

[0016] This allows the microwaves to be irradiated onto the mist in a stable manner.

[0017] In this case, the portion of the supply pipe that is disposed inside the microwave irradiation unit may be formed of a microwave-transparent material.

[0018] This allows microwaves to directly reach the mist inside, enabling direct microwave heating of the mist.

[0019] In this case, the portion of the supply pipe that is placed within the microwave irradiation section can be made of any of quartz, ceramic, alumina, polytetrafluoroethylene resin, tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer resin, tetrafluoroethylene-hexafluoropropylene copolymer resin, and polyether ether ketone resin.

[0020] This effectively prevents unintentional contamination from the microwave irradiated portion of the supply pipe.

[0021] In order to achieve the above-mentioned object, the present invention also provides a film formation method comprising the steps of: atomizing or dropletizing a raw material solution to generate a mist; transporting the mist to a film formation unit using a carrier gas; heating the mist with microwaves before the mist reaches a substrate placed in the film formation unit; and supplying the mist to the substrate in the film formation unit and performing a heat treatment on the substrate to form a film on the substrate.

[0022] According to this film formation method, only the mist can be selectively and rapidly heated out of the mist and carrier gas supplied to the substrate, so the saturated water vapor pressure of the carrier gas does not increase, and evaporation of the mist can be suppressed. This makes it possible to increase the film formation rate while suppressing foreign matter and abnormal growth. Furthermore, because high-temperature mist can be supplied to the substrate, a decrease in the temperature of the substrate is suppressed even when the amount of mist supplied is increased, making it possible to form films at a high film formation rate without impairing crystallinity, even on substrates with large diameters.

[0023] In this case, the raw material solution may contain a metal raw material and at least one solvent selected from water, methanol, ethanol, ethylene glycol, diethylene glycol, propylene glycol, tetraethylene glycol, glycerol, benzyl alcohol, and dipropylene glycol.

[0024] This allows the mist to be selectively and rapidly heated by microwave heating.

[0025] In this case, the solvent of the raw material solution may be one containing water as a main component.

[0026] This makes it difficult for impurities derived from the solvent to remain in the film, resulting in excellent atomization efficiency and an advantage in terms of cost.

[0027] In this case, the metal raw material may contain Ga.

[0028] This allows stable α-Ga ２ O ３ A membrane can be prepared.

[0029] In this case, the substrate to be used may have a film-forming surface with a diameter of 10 cm (4 inches) or more.

[0030] By using a substrate with such a large diameter, the crystalline metal oxide film formed on the substrate can be of higher quality and with higher productivity.

[0031] In this case, the frequency of the microwaves can be set to 0.9 GHz or more and 300 GHz or less.

[0032] This allows the mist to be heated stably, and the penetration depth of the microwaves to be maintained at an appropriate length, allowing the mist to be heated uniformly all the way to its interior.

[0033] In this case, the frequency of the microwaves can be set to 2.45 GHz or more and 25 GHz or less.

[0034] This allows the mist to be heated more stably, and the penetration depth of the microwaves can be maintained at an appropriate length, allowing more uniform heating to be achieved even inside the mist.

[0035] The present invention has also been made to achieve the above object, and provides a crystalline metal oxide film containing at least one of gallium and aluminum as a main component, wherein the number density of foreign particles observed from the surface direction of the crystalline metal oxide film is 48 particles / cm ２ and the standard deviation in particle size distribution of the foreign matter is less than 1.25 μm.

[0036] Such a crystalline metal oxide film has good film smoothness due to the small amount of foreign matter, and the foreign matter size is small and uniform. Therefore, when a semiconductor device is fabricated using the crystalline metal oxide film, the influence of the foreign matter on the device characteristics is minor, making the film suitable for use in semiconductor devices.

[0037] In this case, the particle size distribution of the foreign matter can be such that the particle size distribution index (particle size D90 / particle size D10) is 4.0 or less.

[0038] Such a crystalline metal oxide film is suitable for use in semiconductor devices because the size of the foreign particles is more uniform, making it easier to design the semiconductor device.

[0039] In this case, the proportion of particles having a particle diameter equal to or greater than the particle diameter D50 minus the standard deviation and equal to or less than the particle diameter D50 plus the standard deviation relative to the total number of the foreign matter can be 60% or more.

[0040] Such a crystalline metal oxide film is suitable for use in semiconductor devices because the size of the foreign particles is more uniform, making it easier to design the semiconductor device.

[0041] In this case, the particle diameter D50 of the foreign matter can be made smaller than 2.75 μm.

[0042] In such a crystalline metal oxide film, the foreign matter is small, so when a semiconductor device is fabricated using the crystalline metal oxide film, the influence of the foreign matter on the device characteristics is less, making the film suitable for use in semiconductor devices.

[0043] At this time, the particle diameter D90 of the foreign matter can be made to be less than 4.25 μm.

[0044] In such a crystalline metal oxide film, the foreign matter is small, so when a semiconductor device is fabricated using the crystalline metal oxide film, the influence of the foreign matter on the device characteristics is less, making the film suitable for use in semiconductor devices.

[0045] In this case, the crystalline metal oxide film may have a corundum structure.

[0046] Such a crystalline metal oxide film has a corundum structure with better smoothness.

[0047] In this case, the half-width of the rocking curve of the (006) plane of the crystalline metal oxide film as determined by X-ray diffraction can be less than 19.1 seconds.

[0048] Such a crystalline metal oxide film has good crystallinity and can therefore be suitably used in semiconductor devices.

[0049] In this case, the surface of the crystalline metal oxide film can have a diameter of 10 cm (4 inches) or more.

[0050] Such a crystalline metal oxide film has better smoothness and a large area, and therefore can be more suitably used in semiconductor devices.

[0051] In this case, a laminated structure can be formed which has a substrate, a buffer layer on the substrate, and the above-mentioned crystalline metal oxide film on the buffer layer.

[0052] Such a laminated structure can be suitably used in semiconductor devices because the crystalline metal oxide film has good smoothness.

[0053] In this case, the semiconductor device can include at least one of the crystalline metal oxide film and the laminated structure.

[0054] Such a semiconductor device has excellent electrical characteristics due to the excellent smoothness of the crystalline metal oxide film.

[0055] In this case, the semiconductor device is any one of a semiconductor laser, a diode, and a transistor.

[0056] Such a semiconductor device can be a semiconductor laser, a diode, or a transistor with excellent electrical characteristics.

[0057] As described above, the film deposition apparatus of the present invention makes it possible to deposit a highly crystalline film on a large diameter substrate at a high deposition rate while suppressing foreign matter and abnormal growth in a mist CVD process. Also, the film deposition method of the present invention makes it possible to deposit a highly crystalline film on a large diameter substrate at a high deposition rate while suppressing foreign matter and abnormal growth in a mist CVD process.

[0058] Furthermore, the crystalline metal oxide film of the present invention has good film smoothness due to the small amount of foreign matter, and the foreign matter is small and uniform in size, so when a semiconductor device is fabricated using the crystalline metal oxide film, the effect of the foreign matter on the device characteristics is minimal, making it suitable for use in semiconductor devices. The present invention also provides a stacked structure and a semiconductor device having a crystalline metal oxide film having such characteristics.

[0059] 7 is a schematic diagram showing an example of a film forming apparatus according to the present invention. FIG. 7 is a schematic diagram showing an example of a mist generating unit according to the present invention. FIG. 7 is a schematic diagram showing an example of a microwave heating device according to the present invention. FIG. 7 is a schematic diagram showing an example of an applicator according to the present invention ((a) perspective view, (b) side cross-sectional view). FIG. 7 is a graph showing (a) the electric field intensity ratio distribution in the waveguide longitudinal axis direction and (b) the electric field intensity in the propagation direction of the applicator when a microwave of 2.45 GHz is used. FIG. 7 is a diagram showing an example of foreign matter observed in a film produced in a comparative example. FIG. 7 is a diagram showing an example of an abnormally grown portion observed in a film produced in a comparative example. FIG. 7 is an electron diffraction image of the outside of the abnormally grown portion in FIG. 7. FIG. 7 is an electron diffraction image of a crystalline portion observed in the center of the abnormally grown portion in FIG. 7. FIG. 7 is a diagram showing the particle size distribution of foreign matter observed in the films produced in Example 1 and Comparative Example 1. FIG. 7 is a diagram showing evaluation results regarding the yield of the films produced in Example 1 and Comparative Example 1. FIG. 7 is a schematic cross-sectional view showing one embodiment of the structure of a stacked structure according to the present invention. FIG. 7 is a schematic cross-sectional view showing an example of a Schottky barrier diode according to the present invention. FIG. 7 is a schematic cross-sectional view showing an example of a high electron mobility transistor according to the present invention. FIG. 7 is a schematic cross-sectional view showing an example of a semiconductor field effect transistor according to the present invention. 1 is a schematic cross-sectional view showing an example of an insulated gate bipolar transistor according to the present invention; 2 is a schematic cross-sectional view showing an example of a light-emitting diode according to the present invention;

[0060] The present invention will be described in detail below, but the present invention is not limited thereto.

[0061] As described above, there has been a demand for a film formation apparatus and a film formation method that are capable of forming a highly crystalline film on a large diameter substrate at a high film formation rate while suppressing foreign matter and abnormal growth, as well as a crystalline metal oxide film with suppressed foreign matter.

[0062] As a result of extensive research into the above-mentioned problems, the inventors have found a film formation apparatus comprising: a mist-forming unit that generates mist by misting a raw material solution; a carrier gas supply unit that supplies a carrier gas that transports the mist; a film formation unit that heat-treats the mist to form a film on a substrate; a transport unit that connects the mist-forming unit to the film formation unit and has a supply pipe through which the mist is transported by the carrier gas; and a microwave heating device that irradiates the mist with microwaves between the mist-forming unit and the substrate to heat the mist. This allows for selective and rapid heating of only the mist out of the mist and carrier gas supplied to the substrate, thereby preventing the saturated water vapor pressure of the carrier gas from increasing and suppressing evaporation of the mist. This allows for a high film formation rate while suppressing foreign matter and abnormal growth. Furthermore, since high-temperature mist can be supplied to the substrate, the temperature drop of the substrate is suppressed even if the amount of mist supplied is increased, and it has been discovered that it is possible to form a film at a high film formation rate even on a substrate with a large diameter without impairing crystallinity, thereby completing the present invention.

[0063] The inventors also discovered that a film formation method comprising the steps of: atomizing or dropletizing a raw material solution to generate a mist; transporting the mist to a film formation unit using a carrier gas; heating the mist with microwaves before the mist reaches a substrate installed in the film formation unit; and supplying the mist to the substrate in the film formation unit and heat-treating the mist on the substrate to form a film on the substrate. This method selectively and rapidly heats only the mist from the mist and carrier gas supplied to the substrate, thereby preventing the saturated vapor pressure of the carrier gas from increasing and suppressing mist evaporation. This allows for a high film formation rate while suppressing the formation of foreign matter and abnormal growth. Furthermore, the present inventors discovered that the ability to supply high-temperature mist to the substrate prevents a decrease in the temperature of the substrate even when the amount of mist supplied is increased, making it possible to form films at a high film formation rate without impairing crystallinity, even on large-diameter substrates, and thus completed the present invention.

[0064] The present inventors further discovered a crystalline metal oxide film containing at least one of gallium and aluminum as a main component, in which the number density of foreign particles observed from the surface direction of the crystalline metal oxide film is 48 particles / cm ２The present inventors have found that a crystalline metal oxide film having a particle size distribution of less than 1.25 μm has good film smoothness due to the small amount of foreign matter, and the foreign matter is small and uniform in size, so that when a semiconductor device is fabricated using the crystalline metal oxide film, the influence of the foreign matter on the device characteristics is negligible, making the film suitable for use in semiconductor devices, and have completed the present invention.

[0065] The film forming apparatus of the present invention will be described below with reference to FIGS.

[0066] (Film Forming Apparatus) Figure 1 shows an example of a film forming apparatus of the present invention. As shown in Figure 1, the film forming apparatus 100 includes a mist-forming unit 120 that generates mist by misting a raw material solution, a carrier gas supply unit 130 that supplies a carrier gas for transporting the mist, a film forming unit 140 that heat-treats the mist to form a film on a substrate, a transport unit 109 that connects the mist-forming unit 120 to the inside of the film forming unit 140 and has a supply pipe 109a through which the mist is transported by the carrier gas, and a microwave heating device 200 that irradiates the mist with microwaves to heat the mist between the mist-forming unit 120 and the substrate. The operation of the film forming apparatus 100 may also be controlled by including a control unit (not shown) that controls all or part of the film forming apparatus 100.

[0067] With this type of film formation apparatus, it is possible to selectively and rapidly heat only the mist out of the mist and carrier gas supplied to the substrate (crystalline substrate) 110, so the saturated water vapor pressure of the carrier gas does not increase, and evaporation of the mist can be suppressed. This makes it possible to increase the film formation rate while suppressing foreign matter and abnormal growth. Furthermore, because high-temperature mist can be supplied to the substrate 110, a decrease in the temperature of the substrate 110 is suppressed even if the amount of mist supplied is increased, making it possible to form films at a high film formation rate even on large-diameter substrates 110 without impairing crystallinity.

[0068] [Mist-forming section] The mist-forming section 120 forms mist by forming the raw material solution into mist. The mist-forming means is not particularly limited as long as it can form mist from the raw material solution, and any known mist-forming means may be used, but it is preferable to use a mist-forming means that uses ultrasonic vibrations, as this allows for more stable mist formation.

[0069] An example of such a mist generating unit 120 is shown in FIG. 2 . For example, the mist generating unit 120 may include a mist generating source 104 consisting of a container that contains raw solution 104a, a container 105 that contains a medium capable of transmitting ultrasonic vibrations, such as water 105a, and an ultrasonic vibrator 106 attached to the bottom of the container 105. Specifically, the mist generating source 104 consisting of a container that contains raw solution 104a is housed in the container 105 that contains water 105a using a support (not shown). An ultrasonic vibrator 106 is attached to the bottom of the container 105, and the ultrasonic vibrator 106 is connected to an oscillator 116. When the oscillator 116 is activated, the ultrasonic vibrator 106 vibrates, and ultrasonic waves propagate through the water 105a into the mist generating source 104, turning the raw solution 104a into mist.

[0070] The carrier gas supply unit 130 has a carrier gas source 102a that supplies a carrier gas, and may also include a flow rate control valve 103a that controls the flow rate of the carrier gas delivered from the carrier gas source 102a. The carrier gas supply unit 130 may also include a dilution carrier gas source 102b that supplies a dilution carrier gas as needed, and a flow rate control valve 103b that controls the flow rate of the dilution carrier gas delivered from the dilution carrier gas source 102b.

[0071] The type of carrier gas is not particularly limited and can be appropriately selected depending on the film to be formed. Examples include inert gases such as oxygen, ozone, nitrogen, and argon, and reducing gases such as hydrogen gas and forming gas. The type of carrier gas may be one or more. For example, a dilution gas obtained by diluting the same gas as the first carrier gas with another gas (e.g., diluted 10 times) may be used as the second carrier gas, or air may be used.

[0072] Furthermore, the number of supply points for the carrier gas may not be one, but may be two or more.

[0073] The flow rate of the carrier gas is not particularly limited. For example, when forming a film on a substrate with a diameter of 10 cm (4 inches), the flow rate is preferably 1 to 80 L / min, and more preferably 4 to 40 L / min. The flow rate of the carrier gas in the present invention is a value measured at 20°C and atmospheric pressure. When measured at other temperatures and pressures or when a different type of flow rate (mass flow rate, etc.) is measured, the flow rate can be converted to a volumetric flow rate at 20°C and atmospheric pressure using the gas state equation.

[0074] [Film Forming Section] In the film forming section 140, the mist is heated to cause a thermal reaction, thereby forming a film on a part or all of the surface of the substrate 110. The film forming section 140 may include, for example, a film forming chamber 107 in which the substrate 110 is placed and a hot plate 108 for heating the substrate 110.

[0075] 1 , the hot plate 108 may be provided outside the film formation chamber 107, or may be provided inside the film formation chamber 107. In addition, the film formation chamber 107 may be provided with an exhaust gas outlet 112 at a position that does not affect the supply of mist to the substrate 110.

[0076] [Transportation Unit] The transport unit 109 has a supply pipe 109a and connects the mist-generating unit 120 with the inside of the film-forming unit 140. Mist is transported by a carrier gas from the mist generation source 104 of the mist-generating unit 120 to the film-forming chamber 107 of the film-forming unit 140 via the transport unit 109. A quartz tube or a resin tube, for example, can be used as the supply pipe 109a.

[0077] [Microwave Heating Device] The microwave heating device is not particularly limited as long as it can irradiate microwaves, and is composed of a known microwave generating unit, a microwave irradiating unit and a microwave guide unit formed of a conductive material such as aluminum, copper, brass, etc., and within the microwave irradiating unit, a supply pipe through which the mist to be heated passes is arranged so that a part of the supply pipe passes through the microwave irradiation space of the microwave irradiating unit.

[0078] An example of a single-mode microwave heating device according to the present invention is shown in Fig. 3. As shown in Fig. 3, the microwave heating device 200 has a microwave generating unit 201, a microwave irradiating unit 204 that irradiates the mist with microwaves generated in the microwave generating unit, and a microwave guide unit 205 that propagates the microwaves from the microwave generating unit to the microwave irradiating unit.

[0079] Such a microwave heating device can stably irradiate the mist with microwaves.

[0080] The microwave heating device 200 may be disposed anywhere between the mist generation section 120 and the substrate 110 of the film formation section 140, but it is preferable that at least a portion of the microwave heating device 200 is disposed within the film formation section 140. With the microwave heating device 200 disposed in this manner, the temperature of the mist decreases due to heat dissipation from the mist heated by microwaves, and the temperature of the surrounding carrier gas increases, increasing the saturated vapor pressure and accelerating the evaporation of the mist, effectively preventing a decrease in the film formation rate.

[0081] The microwave heating device 200 includes a microwave oscillator as a microwave generating unit 201, a waveguide as a microwave guide unit 205 through which microwaves propagate, a power monitor 202 that controls incident and reflected microwave waves, a stub tuner 203 that adjusts impedance within the device, and an applicator having a microwave irradiation space therein as a microwave irradiation unit 204, the applicator 204 having a short-circuit surface 206, and being arranged so that a portion of a supply pipe 109a through which a mist 220 and a carrier gas pass passes through the microwave irradiation space within the applicator 204. The microwave heating device 200 may also include a thermometer 207 that measures the temperature of the supply pipe 109a.

[0082] The microwave oscillator 201 may be of a magnetron type or a semiconductor (solid state) type, but the semiconductor type is preferable because there is less fluctuation in frequency.

[0083] The material of the waveguide 205 is not particularly limited, and it may be formed of a conductive material such as aluminum, copper, brass, etc. The outer surface of the waveguide 205 may be coated with an acid-resistant material to prevent corrosion even in an acidic raw material solution. The acid-resistant coating material is not particularly limited, and known coating materials such as Teflon (registered trademark) can be used.

[0084] It is preferable that the portion of supply pipe 109a that is disposed within the microwave irradiation portion (hereinafter simply referred to as the "microwave irradiation portion of supply pipe") is formed from a microwave-transparent material.

[0085] The microwave irradiation portion of the supply pipe is made of a material that easily transmits microwaves, so that the microwaves can directly reach the mist inside, enabling direct microwave heating of the mist.

[0086] Microwave heating can generate heat in a much shorter time than conventional heating by heat transfer, so the mist can be heated to a predetermined temperature quickly.

[0087] The material for forming the microwave irradiation portion of the supply pipe is not particularly limited as long as it is microwave transparent, and can be appropriately selected depending on the purpose. Examples include quartz, ceramic, alumina, polytetrafluoroethylene resin, tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer resin, tetrafluoroethylene-hexafluoropropylene copolymer resin, polyether ether ketone resin, glass, sapphire, polyethylene resin, etc., but among these, any of quartz, ceramic, alumina, polytetrafluoroethylene resin, tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer resin, tetrafluoroethylene-hexafluoropropylene copolymer resin, and polyether ether ketone resin is more preferred.

[0088] Such a material can effectively prevent unintentional contamination from the microwave irradiated portion of the supply pipe.

[0089] In order to prevent contact between the microwave irradiated portion of the supply pipe and the reaction solution, the inner wall surface of the microwave irradiated portion of the supply pipe may be surface-treated depending on the type of solvent contained in the reaction solution. For example, when the solvent is water, the surface of the inner wall surface may be hydrophobized by irradiating it with ultraviolet light, ultrasonic waves, or radiation, or may be hydrophobized using a hydrophobic material such as a silane coupling agent or the polytetrafluoroethylene resin.

[0090] The shape of the microwave irradiation portion of the supply pipe is not particularly limited, but a tubular shape is preferable. This is because microwaves can be uniformly irradiated onto the mist. The shape of the pipe length is not particularly limited and can be selected appropriately depending on the purpose, and may be linear (straight pipe) or a pipe that bends in a gentle curve such as a spiral (curved pipe). The pipe length is determined by taking into account the size of the microwave irradiation portion of the supply pipe, the size of the applicator 204, the microwave output, the heating time, the flow rate of the carrier gas, etc. A straight pipe is sufficient if the heating time is to be shortened, and a curved pipe such as a spiral pipe is sufficient if the heating time is to be lengthened.

[0091] The cross-sectional shape of the microwave irradiating portion of the supply pipe may be circular, elliptical or rectangular, but a circular shape with good symmetry is preferred.

[0092] The wall thickness of the microwave irradiating portion of the supply pipe is not particularly limited and can be appropriately selected depending on the purpose, but is preferably 0.05 mm to 10 mm, more preferably 0.1 mm to 2 mm. A thickness in the range of 0.05 mm to 10 mm can maintain appropriate strength, effectively prevent damage due to pressure fluctuations within the pipe, and effectively prevent a decrease in heating efficiency due to microwave transmission loss.

[0093] The specifications for the microwave irradiated portion of the supply pipe can also be applied to the entire supply pipe 109a. In any case, the material of the portion of the supply pipe 109a that is not irradiated with microwaves is not particularly limited.

[0094] An example of an applicator according to the present invention is shown in Figure 4 ((a) perspective view, (b) side cross-sectional view). The material of the applicator 204 is not particularly limited, and it may be made of a conductive material such as aluminum, copper, brass, etc.

[0095] The outer surface of the applicator 204 may be coated with an acid-resistant material to prevent corrosion even in the acidic raw material solution. The acid-resistant coating material is not particularly limited, and known coating materials such as Teflon (registered trademark) can be used.

[0096] The shape of the applicator 204 is not particularly limited, and may be circular, elliptical, rectangular, etc. Specifically, a rectangular waveguide or a circular cavity resonator may be used.

[0097] The shape of the standing wave formed in the microwave irradiation space of the applicator 204 depends on the microwave frequency and the shape of the microwave irradiation space. Here, a standing wave refers to a wave motion that appears to be stationary and vibrating without progressing, creating a state in which the positions of areas with zero electric field strength and areas with strong electric field strength do not change over time. The microwave irradiation portion of the applicator 204 and the supply pipe form standing waves of TEn0 and TM0m0 modes (n and m are integers of 1 or greater) in the microwave irradiation space, and within the microwave irradiation portion of the supply pipe, the difference between the maximum and minimum values ​​of either the electric field strength or the magnetic field strength of the standing wave is preferably 50% or more, and particularly preferably within 20% of the maximum value. This is because uneven heating is reduced.

[0098] When using microwaves of 2.45 GHz, a standing wave in TE10 mode is formed in a waveguide (waveguide standard: WRI-22) with an internal space of 109 mm long and 55 mm short. In this mode, there is no change in the electric field strength in the short axis direction of the waveguide. The electric field strength ratio distribution in the long axis direction of the waveguide is as shown in the graph of FIG. 5(a), and the electric field strength in the propagation direction is as shown in the graph of FIG. 5(b). In the case of such an applicator, by placing a supply pipe with an inner diameter of 30 mm or less at a position 37 mm from the short-circuit surface, the difference between the maximum and minimum electric field strength values ​​of the standing wave in the supply pipe is within 20%.

[0099] As a circular cavity resonator, a microwave heating device (manufactured by Ryowa Electronics Co., Ltd.) can be used, where the inner diameter of the irradiation space within the cavity resonator is set to 91 mm, and a standing wave in TM010 mode can be formed when using microwaves of 2.45 GHz.

[0100] Furthermore, the number of microwave irradiation portions of the applicator 204 or the supply pipe is not particularly limited. By changing the shape of the applicator, microwave irradiation portions of a plurality of supply pipes may be arranged in a plurality of locations where the electric field strength is high.

[0101] With this configuration, it is possible to increase the volume irradiated with microwaves without reducing the heating efficiency. When multiple microwave irradiating portions of the supply pipe are provided, heated mist may be supplied to one substrate from the microwave irradiating portions of the multiple supply pipes.

[0102] Furthermore, since microwaves also have a heating effect due to the magnetic field, the same effect can be obtained by utilizing areas where the magnetic field is stronger.

[0103] (Crystalline Metal Oxide Film) Next, the crystalline metal oxide film of the present invention will be described. The crystalline metal oxide film of the present invention is a crystalline metal oxide film containing at least one of gallium and aluminum as a main component, and the number density of foreign particles observed from the surface direction of the crystalline metal oxide film is 48 particles / cm. ２ The standard deviation of the particle diameter of the foreign matter is less than 1.25 μm.

[0104] Such a crystalline metal oxide film has good film smoothness due to the small amount of foreign matter, and the foreign matter size is small and uniform. Therefore, when a semiconductor device is fabricated using the crystalline metal oxide film, the influence of the foreign matter on the device characteristics is minor, making the film suitable for use in semiconductor devices.

[0105] The surface of the crystalline metal oxide film in the present invention refers to one of the surfaces of the crystalline metal oxide film, which has a front surface and a back surface.

[0106] In the present invention, the surface direction refers to the direction from the side with a larger z coordinate than the surface of the crystalline metal oxide film to the side with a smaller z coordinate, when the direction from the back side to the front side of the crystalline metal oxide film is defined as the positive z-axis direction.

[0107] In the present invention, the location of the foreign matter is not particularly limited as long as it can be observed from the surface direction. It may be attached to the surface, or may be partially or completely embedded in the film. The observation method will be described later, but is not particularly limited. The height in the observation direction can also be distinguished by using a confocal microscope or the like.

[0108] Generally, crystalline metal oxide films are composed of metal and oxygen, but in the crystalline metal oxide film according to the present invention, the metal is primarily composed of at least one of gallium and aluminum. The term "primary component" as used herein means that 50 to 100 atomic % of the metal component is gallium or aluminum. It also means that the combined total of gallium and aluminum is 50 to 100 atomic %.

[0109] The metal component other than gallium or aluminum may include, for example, one or more metals selected from iron, indium, vanadium, titanium, chromium, rhodium, iridium, nickel, and cobalt.

[0110] The crystalline metal oxide film has a density of 48 particles / cm2 when observed from the surface of the film. ２ less than 10 particles / cm ２ Preferably, the density is 1 particle / cm or less. ２ It is more preferable that the number of foreign particles is less than 0.01 particles / cm. ２ Such a crystalline metal oxide film has good film smoothness due to the small amount of foreign matter, and can be more suitably used in semiconductor devices.

[0111] Furthermore, the foreign matter according to the present invention is a particle as shown in FIG. 6, which originates from the metal raw material in the mist. The mechanism by which the foreign matter is formed is unclear, but possible causes include deposition of the metal raw material due to evaporation of water in the mist during film formation, and formation of metal oxide due to a side reaction of the metal raw material in the gas phase. The majority of these particles are amorphous. There are no particular limitations on the method for analyzing the particle composition. They can be examined using EDX, Auger electron spectroscopy, SIMS, or the like. There are also no particular limitations on the method for analyzing the crystal structure. They can be examined using common methods such as electron beam diffraction.

[0112] When these particles adhere to or are embedded in the film surface, they are partially or completely crystallized by heat. However, in this case, aluminum oxide crystals or gallium oxide crystals of the γ phase, or mixed crystals thereof, grow, rather than the α phase. Therefore, when a voltage is applied to a film containing foreign matter, the electric field concentrates at the grain boundary between the α phase and the γ phase, easily causing dielectric breakdown. When the number density of foreign matter is 48 particles / cm ２ If the thickness is less than 1000 nm, dielectric breakdown due to the formation of grain boundaries can be sufficiently suppressed, and therefore, semiconductor devices can be manufactured with a high yield using the crystalline metal oxide film.

[0113] In addition to the SEM used to observe the foreign matter shown in Figure 6, foreign matter shapes can be observed and the number of occurrences can be evaluated using electron microscopes such as TEM, optical microscopes, surface inspection devices that detect defects from the difference in brightness, and surface inspection devices that use image recognition AI to learn and detect defects, but there are no particular limitations on the observation method and the method for evaluating the number of occurrences.

[0114] The foreign matter in the present invention has a particle diameter of 10 nm to 10 μm. The particle diameter here refers to the circle-equivalent diameter in a two-dimensional image observed from the surface direction of the crystalline metal oxide film. The circle-equivalent diameter is the diameter of a circle having an area equivalent to the area of ​​the particle captured in the two-dimensional image, and the particle area can be calculated by image analysis or the like.

[0115] A particle size distribution can be created by calculating the particle size of the foreign particles using the method described above. For the crystalline metal oxide film according to the present invention, the standard deviation (σ) of the particle size is less than 1.25 μm, preferably less than 0.50 μm, and more preferably 0.30 μm or less. The smaller σ is, the better, so the lower limit is, for example, greater than 0 μm. Because such a crystalline metal oxide film has small and uniform foreign particle sizes, when a semiconductor device is fabricated using the crystalline metal oxide film, the impact of the foreign particles on the device characteristics is minimal, making the film suitable for use in semiconductor devices. σ can be calculated using the following formula:

[0116]

[0117] Furthermore, the crystalline metal oxide film according to the present invention preferably has a particle size distribution index D90 / D10 of less than 5.7, preferably 4.0 or less, and more preferably 3.0 or less. Since such a crystalline metal oxide film has more uniformly sized foreign particles, it facilitates the design of semiconductor devices and is suitable for use in semiconductor devices. The lower limit is not particularly limited, but is typically around 1.5.

[0118] In the present invention, the particle diameter D90 refers to the particle diameter corresponding to a cumulative ratio of 90% in the particle diameter distribution, the particle diameter D10 refers to the particle diameter corresponding to a cumulative ratio of 10%, and the particle diameter D50 refers to the particle diameter corresponding to a cumulative ratio of 50%.

[0119] The particle diameter D90 value is not particularly limited, but is preferably less than 4.25 μm, and more preferably 1.0 μm or less. The lower limit is also not particularly limited. The smaller the value, the better, and it can be, for example, greater than 1 nm. Because the size of foreign particles in such a crystalline metal oxide film is small, when a semiconductor device is fabricated using the crystalline metal oxide film, the impact of foreign particles on the device characteristics is less severe, making the crystalline metal oxide film suitable for use in semiconductor devices.

[0120] The value of the particle diameter D10 is not particularly limited. The smaller the particle diameter D10, the less the influence of the foreign matter on the device characteristics when a semiconductor device is manufactured, and the more suitable the particle diameter D10 is for use in a semiconductor device.

[0121] Furthermore, for the crystalline metal oxide film according to the present invention, the particle diameter D50, which is the cumulative ratio of 50% in the particle diameter distribution, is preferably less than 2.75 μm, preferably 2.0 μm or less, and more preferably 0.5 μm or less. The lower limit is not particularly limited. The smaller the D50, the better, and it can be, for example, greater than 1 nm. Since such a crystalline metal oxide film contains small foreign particles, the impact of the foreign particles on the device characteristics during the fabrication of a semiconductor device is less severe, making it suitable for use in semiconductor devices.

[0122] Furthermore, in the crystalline metal oxide film according to the present invention, the proportion of particles having a particle size of at least D50 minus the standard deviation σ and at most D50 plus the standard deviation σ, relative to the total number of foreign particles, is preferably at least 60%, and more preferably at least 75%. Such a crystalline metal oxide film has more uniform foreign particle sizes, which makes it easier to design semiconductor devices and makes it suitable for use in semiconductor devices.

[0123] The crystalline metal oxide film may have a corundum structure, and such a crystalline metal oxide film has a corundum structure with better smoothness.

[0124] Furthermore, in the crystalline metal oxide film according to the present invention, the half-width of the rocking curve of the (006) plane X-ray diffraction peak is preferably less than 19.1 seconds, more preferably 9.4 seconds or less.

[0125] The measurement device and method for the (006) plane X-ray diffraction peak half-width are not particularly limited. For example, an X-ray diffractometer (SmartLab manufactured by Rigaku Corporation) is used to perform out-of-plane XRD 2θ / ω scan measurement of an oxide semiconductor film formed on a substrate, and the 2θ and ω at which the (006) plane peak is obtained are examined. Thereafter, the diffraction angle is fixed at 2θ at which the (006) plane peak is obtained, and ω scan is performed to measure the rocking curve half-width. The measurement conditions are not particularly limited, and can be, for example, as follows: Measurement equipment: SmartLab (product name) manufactured by Rigaku Analysis conditions Measurement method: Out-of-plane XRD method (2θ / ω scan) X-ray generator: Cu anticathode: Output 45 kV 200 mA Detector: Semiconductor detector Incident optical system: Ge (220) channel cut monochromator Soller slit: Incident side -: Receiving side 5.0° Slit: Incident side IS = 1 (mm): Length limit 0.5 (mm): Receiving side RS1 = 1 RS2 = 1.1 (mm) Scanning conditions: Scan axis 2θ / ω: Scanning mode Step measurement: Scan range 35 to 45°: Step width 0.005°: Integration time 0.5 sec. / step Measurement device: SmartLab (product name) manufactured by Rigaku Analysis conditions Measurement method: Rocking curve measurement (ω scan) X-ray generator: Cu anticathode: Output 45 kV 200 mA Detector: Semiconductor detector Incident optical system: Ge (220) channel cut monochromator Soller slit: Incident side -: Receiving side 5.0° Slit: Incident side IS = 1 (mm): Length limit 0.5 (mm): Receiving side RS1 = 1 RS2 = 1.1 (mm) Scanning conditions: Evaluation diffraction surface Ga ２ O ３ (006): Scan axis ω: Scan mode step measurement: Scan range 19-22°: Step width 0.005°: Integration time 0.5 sec. / step

[0126] Such a crystalline metal oxide film has better crystal orientation and can be suitably used in semiconductor devices. Note that the smaller the half-width of the rocking curve, the more preferable it is, so the lower limit is, for example, more than 0 seconds.

[0127] The crystalline metal oxide film can contain a dopant depending on the application. The dopant is not particularly limited. Examples include n-type dopants such as tin, germanium, silicon, titanium, zirconium, vanadium, or niobium, and p-type dopants such as copper, silver, tin, iridium, or rhodium. The dopant concentration is, for example, about 1.0×10 １６ ~1.0 x 10 ２２ / cm ３ may be about 1.0×10 １７ / cm ３ Even at a low concentration of about 1.0 × 10 ２０ / cm ３ A concentration higher than this may be used.

[0128] The thickness of the crystalline metal oxide film according to the present invention is not particularly limited, and may be, for example, 0.05 to 100 μm, preferably 0.1 to 50 μm, and more preferably 0.5 to 20 μm.

[0129] The crystalline metal oxide film may be formed directly on a substrate, or may be laminated on an intermediate layer 252 (a buffer film or a release film) formed on a substrate 253 as shown in Fig. 12. The intermediate layer is not particularly limited as long as it is a metal oxide that can have a corundum structure, and may be primarily composed of an oxide containing any of aluminum, titanium, vanadium, chromium, iron, gallium, rhodium, indium, and iridium, for example.

[0130] More specifically, the intermediate layer is Al ２ O ３ , Ti ２ O ３ , V ２ O ３ , Cr ２ O ３ , Fe ２ O ３ , Ga ２ O ３ , Rh２ O ３ , In ２ O ３ , Ir ２ O ３ Furthermore, when two elements selected from the above metal elements are designated as A and B, (A ｘ B １－ｘ ) ２ O ３ Binary metal oxides represented by (0<x<1), or when three elements selected from the above metal elements are A, B, and C, (A ｘ B ｙ C １－ｘ－ｙ ) ２ O ３ The oxide may be a ternary metal oxide represented by (0<x<1, 0<y<1).

[0131] The crystalline metal oxide film preferably has a diameter of 10 cm (4 inches) or more. The upper limit of the area is not particularly limited, but it is preferably 750 cm. ２ The crystalline metal oxide film is preferably one having an area equivalent to a diameter of 12 inches (300 mm) or less, and in the case of a circle, it is preferable that the area is equivalent to a diameter of 12 inches (300 mm) or less. Such a crystalline metal oxide film has better smoothness and a large area, and therefore can be more suitably used in semiconductor devices.

[0132] The crystalline metal oxide film according to the present invention can be used in semiconductor devices by appropriately designing the structure, examples of which will be described in detail later.

[0133] (Method for Producing Crystalline Metal Oxide Film) The method for producing a crystalline metal oxide film according to the present invention can be carried out by a mist CVD method including a microwave heating step, as will be described later.

[0134] 12 is a diagram showing one embodiment of the structure of a laminated structure according to the present invention. A laminated structure 250 having a crystalline metal oxide film according to the present invention basically includes a substrate 253 and a crystalline metal oxide film 251. In this case, the aforementioned intermediate layer 252 may be included between the substrate 253 and the crystalline metal oxide film 251.

[0135] The crystalline metal oxide film and stacked structure according to the present invention can be used in semiconductor devices by appropriately designing the structure, such as to form semiconductor layers in Schottky barrier diodes (SBDs), metal semiconductor field effect transistors (MESFETs), high electron mobility transistors (HEMTs), metal oxide semiconductor field effect transistors (MOSFETs), static induction transistors (SITs), junction field effect transistors (JFETs), insulated gate bipolar transistors (IGBTs), and light emitting diodes (LEDs).

[0136] (Semiconductor Device) The semiconductor device according to the present invention includes at least one of the above-described crystalline metal oxide film and the above-described stacked structure. For example, a semiconductor device (semiconductor element) such as a semiconductor laser, a diode, or a transistor can be provided. Such a semiconductor device may include a substrate or may have the substrate removed. The semiconductor device according to the present invention uses a high-quality crystalline metal oxide film with good flatness, and is a high-quality semiconductor device. Application examples (specific examples) of the semiconductor device are as follows.

[0137] (Examples of Applicable Semiconductor Devices) The above-described crystalline metal oxide film and stacked structure having the crystalline metal oxide film have good flatness and excellent electrical properties, and are industrially useful. Such crystalline metal oxide film and stacked structure having the crystalline metal oxide film can be suitably used in various semiconductor devices, and are particularly useful in power devices.

[0138] Semiconductor devices can be classified into horizontal elements (horizontal devices) in which an electrode is formed on one side of a crystalline metal oxide film, and vertical elements (vertical devices) in which an electrode is formed on both the front and back sides of a crystalline metal oxide film. The semiconductor device of the present invention can be suitably used in both horizontal and vertical devices, but is preferably used in vertical devices. Examples of semiconductor devices include Schottky barrier diodes (SBDs), metal-semiconductor field-effect transistors (MESFETs), high-electron-mobility transistors (HEMTs), semiconductor field-effect transistors (MOSFETs), junction field-effect transistors (JFETs), insulated-gate bipolar transistors (IGBTs), and light-emitting diodes (LEDs).

[0139] (Method for manufacturing a semiconductor device) First, a crystalline metal oxide film is formed on the main surface of a substrate, either directly or via another layer, to obtain a stacked structure according to the present invention. Then, electrodes and the like are formed on the crystalline metal oxide film to manufacture a semiconductor device. At this time, the stacked structure including the substrate and the crystalline metal oxide film can be used as is, or the substrate can be removed to leave the intermediate layer and the crystalline oxide semiconductor film, or the substrate and the intermediate layer can be removed to leave only the crystalline oxide semiconductor film. In this way, a high-performance semiconductor device can be manufactured using a high-quality crystalline metal oxide film with excellent flatness.

[0140] Below, preferred examples of the application of the crystalline metal oxide film of the present invention to an n-type semiconductor layer (such as an n+ type semiconductor or an n- type semiconductor layer) will be described with reference to the drawings, but the present invention is not limited to these examples. Note that the semiconductor elements exemplified below may further include other layers (such as an insulator layer or a conductor layer), and intermediate layers and buffer layers may be omitted as appropriate.

[0141] 13 shows an example of an SBD (Schottky barrier diode) according to the present invention. The SBD 300 includes a relatively lightly doped n-type semiconductor layer 301a, a relatively heavily doped n+ type semiconductor layer 301b, a Schottky electrode 302, and an ohmic electrode 303.

[0142] The material of the Schottky electrode 302 and the ohmic electrode 303 may be a known electrode material, and examples of this electrode material include metals such as aluminum, molybdenum, cobalt, zirconium, tin, niobium, iron, chromium, tantalum, titanium, gold, platinum, vanadium, manganese, nickel, copper, hafnium, tungsten, iridium, zinc, indium, palladium, neodymium, and silver, and alloys thereof; conductive metal oxide films such as tin oxide, zinc oxide, rhenium oxide, indium oxide, indium tin oxide (ITO), and indium zinc oxide (IZO); organic conductive compounds such as polyaniline, polythiophene, and polypyrrole; and mixtures and laminates thereof.

[0143] The Schottky electrode 302 and the ohmic electrode 303 can be formed by known means such as vacuum deposition or sputtering. More specifically, when forming a Schottky electrode using two types of metals, a first metal and a second metal, among the above-mentioned metals, the Schottky electrode can be formed by stacking a layer made of the first metal and a layer made of the second metal, and then patterning the layer made of the first metal and the layer made of the second metal using a photolithography technique.

[0144] When a reverse bias is applied to the SBD 300, a depletion layer (not shown) expands into the n-type semiconductor layer 301a, resulting in a high breakdown voltage SBD 300. When a forward bias is applied, electrons flow from the ohmic electrode 303 to the Schottky electrode 302. Therefore, the SBD according to the present invention is excellent for high breakdown voltage and large current applications, has a fast switching speed, and is excellent in breakdown voltage and reliability.

[0145] 14 shows an example of a HEMT (High Electron Mobility Transistor) according to the present invention. HEMT 400 includes a wide bandgap n-type semiconductor layer 401, a narrow bandgap n-type semiconductor layer 402, an n+ type semiconductor layer 403, a semi-insulating layer 404, a buffer layer 405, a gate electrode 406, a source electrode 407, and a drain electrode 408.

[0146] 15 shows an example of a MOSFET (semiconductor field effect transistor) according to the present invention. The MOSFET 500 includes an n-type semiconductor layer 501, n+ type semiconductor layers 502 and 503, a gate insulating film 504, a gate electrode 505, a source electrode 506, and a drain electrode 507.

[0147] 16 shows an example of an IGBT (insulated gate bipolar transistor) according to the present invention. The IGBT 600 includes an n-type semiconductor layer 601, an n-type semiconductor layer 602, an n+ type semiconductor layer 603, a p-type semiconductor layer 604, a gate insulating film 605, a gate electrode 606, an emitter electrode 607, and a collector electrode 608.

[0148] 17 shows an example of an LED (light emitting diode) according to the present invention. The LED 700 includes a first electrode 701, an n-type semiconductor layer 702, a light emitting layer 703, a p-type semiconductor layer 704, a light-transmitting electrode 705, and a second electrode 706.

[0149] Examples of materials for the transparent electrode include conductive oxide materials containing indium or titanium. ２ O ３ , ZnO, SnO ２ , Ga ２ O ３ , TiO ２ , CeO ２ Alternatively, a mixed crystal of two or more of these or a doped crystal thereof may be used.

[0150] The transparent electrode can be formed by providing these materials by a known method such as sputtering. After the transparent electrode is formed, it may be subjected to thermal annealing in order to make the transparent electrode transparent.

[0151] Examples of materials for the first electrode 701 and the second electrode 706 include metals such as aluminum, molybdenum, cobalt, zirconium, tin, niobium, iron, chromium, tantalum, titanium, gold, platinum, vanadium, manganese, nickel, copper, hafnium, tungsten, iridium, zinc, indium, palladium, neodymium, and silver, and alloys thereof; conductive metal oxide films such as tin oxide, zinc oxide, rhenium oxide, indium oxide, indium tin oxide (ITO), and indium zinc oxide (IZO); organic conductive compounds such as polyaniline, polythiophene, and polypyrrole; and mixtures thereof.

[0152] The method for forming the electrode film is not particularly limited, and the electrode can be formed on the substrate by a method appropriately selected from wet methods such as printing, spraying, and coating; physical methods such as vacuum deposition, sputtering, and ion plating; and chemical methods such as CVD and plasma CVD, taking into consideration the suitability for the material.

[0153] (Film Forming Method) Next, the film forming method of the present invention will be described. The film forming method of the present invention includes the steps of atomizing or dropletizing a raw material solution to generate a mist, transporting the mist to a film forming unit using a carrier gas, heating the mist with microwaves before the mist reaches a substrate placed in the film forming unit, and supplying the mist to the substrate in the film forming unit and performing a heat treatment on the substrate to form a film on the substrate.

[0154] According to this film formation method, only the mist can be selectively and rapidly heated out of the mist and carrier gas supplied to the substrate, so the saturated water vapor pressure of the carrier gas does not increase, and evaporation of the mist can be suppressed. This makes it possible to increase the film formation rate while suppressing foreign matter and abnormal growth. Furthermore, because high-temperature mist can be supplied to the substrate, a decrease in the temperature of the substrate is suppressed even when the amount of mist supplied is increased, making it possible to form films at a high film formation rate without impairing crystallinity, even on substrates with large diameters.

[0155] Hereinafter, an embodiment of the film forming method of the present invention will be described with reference to an example of the film forming method using the film forming apparatus 200 of the present invention shown in FIG.

[0156] First, the substrate 110 is placed on the hot plate 108, and the hot plate 108 is operated. Flow rate control valves 103 a and 103 b are opened to supply carrier gas from the carrier gas source 102 a (main carrier gas) and the dilution carrier gas source 102 b (dilution carrier gas) into the film formation chamber 107 through the transfer unit 109, so that the atmosphere in the film formation chamber 107 is sufficiently replaced with the carrier gas, and the flow rates of the main carrier gas and the dilution carrier gas are adjusted and controlled, respectively.

[0157] [Step of atomizing or turning the raw solution into droplets to generate mist] The raw solution 104a is contained in the mist generating source 104 of the mist generating section 120, and the ultrasonic vibrator 106 is vibrated. The vibrations are propagated to the raw solution 104a through the water 105a, thereby atomizing or turning the raw solution 104a into droplets to generate mist.

[0158] The raw material solution 104a preferably contains a metal raw material and at least one solvent selected from water, methanol, ethanol, ethylene glycol, diethylene glycol, propylene glycol, tetraethylene glycol, glycerol, benzyl alcohol, and dipropylene glycol.

[0159] By using such a solvent, it becomes possible to selectively and rapidly heat the mist by microwave heating.

[0160] The raw material solution (aqueous solution) 104a is not particularly limited as long as it contains a material that can be turned into a mist, and may be an inorganic material or an organic material. A solution of a metal or a metal compound is preferably used as the raw material solution 104a, and a solution containing one or more metals selected from gallium, iron, indium, aluminum, vanadium, titanium, chromium, rhodium, nickel, and cobalt can be used, but a solution containing Ga is particularly preferred.

[0161] This allows stable α-Ga ２ O ３ A membrane can be prepared.

[0162] The raw material solution 104a is not particularly limited as long as it can turn the metal solution into mist, but a solution in which a metal is dissolved or dispersed in an organic solvent or water in the form of a complex or salt can be suitably used as the raw material solution 104a. Examples of the complex include an acetylacetonate complex, a carbonyl complex, an ammine complex, and a hydride complex. Examples of the salt include a metal chloride salt, a metal bromide salt, and a metal iodide salt.

[0163] Alternatively, the above metals may be dissolved in hydrobromic acid, hydrochloric acid, hydroiodic acid, or the like to form aqueous salt solutions. The solute concentration is preferably 0.01 to 1 mol / L, more preferably 0.05 to 0.5 mol / L, and even more preferably 0.08 to 0.30 mol / L. Within these concentration ranges, a decrease in the film formation rate and the introduction of foreign matter and abnormal growth due to side reactions and precipitation of excess raw materials can be efficiently prevented.

[0164] The solvent for dissolving the metal raw material in the present invention is one that has microwave absorption properties, and in addition to the above-mentioned alcohols such as water, methanol, ethanol, ethylene glycol, diethylene glycol, propylene glycol, tetraethylene glycol, glycerol, benzyl alcohol, and dipropylene glycol, acidic solvents such as acetic acid, nitric acid, and formic acid, and basic solvents such as aqueous sodium hydroxide solution, aqueous potassium hydroxide solution, and aqueous ammonia can also be used. Among these, it is particularly preferable to use a solvent that contains water as the main component. A solvent that contains water as the main component is less likely to leave impurities derived from the solvent in the film, has excellent atomization efficiency, and is advantageous in terms of cost.

[0165] In the present invention, the term "main component" refers to the component that is contained in the largest amount relative to all components, and means that it is contained in an amount of preferably 50% by mass or more, more preferably 70% by mass or more, and even more preferably 90% by mass or more, and may be contained in an amount of 100% by mass.

[0166] The raw material solution 104a may be mixed with additives such as halogen-containing substances (e.g., hydrohalic acid) or oxidizing agents. Examples of hydrohalic acids include hydrobromic acid, hydrochloric acid, and hydroiodic acid, with hydrobromic acid and hydroiodic acid being preferred. Examples of oxidizing agents include hydrogen peroxide (H ２ O ２ ), sodium peroxide (Na ２ O ２ ), barium peroxide (BaO ２ ), benzoyl peroxide (C ６ H ５ CO) ２ O ２ hypochlorous acid (HClO), perchloric acid, nitric acid, ozone water, peracetic acid, nitrobenzene, and other organic peroxides.

[0167] Furthermore, the raw material solution 104a may contain a dopant. The dopant is not particularly limited. For example, n-type dopants such as tin, germanium, silicon, titanium, zirconium, vanadium, or niobium, or p-type dopants such as copper, silver, tin, iridium, or rhodium, can be used. The concentration of the dopant is, for example, about 1.0×10 －９ It may be up to 1.0 mol / L, and may be about 1.0×10 －７ The concentration may be as low as 0.01 mol / L or less, or as high as about 0.01 mol / L or more.

[0168] In addition, a crystalline metal oxide film consisting of two or more metals (for example, α-(Al ｘ Ga １－ｘ ) ２ O ３ When forming a film (0≦X<1), the raw material solution 104a, which is a mixture of the metal raw material solutions, may be contained in the mist generating source 104 of a single mist-forming unit 120 and turned into mist, or multiple mist-forming units may be provided and each metal raw material solution may be turned into mist in a different mist-forming unit. When multiple mist-forming units are provided, a mist mixer (not shown) may be provided to mix the mist-formed raw material solutions, or the raw material solutions may be supplied separately to the film formation chamber without providing a mist mixer.

[0169] [Step of transporting mist to film formation unit by carrier gas] In the step of transporting mist to film formation unit 140 by carrier gas, the mist is transported by the carrier gas from mist-forming unit 120 to film formation unit 140 via transport unit 109 and introduced into film formation chamber 107. The mist transported by the carrier gas simultaneously passes through microwave heating device 200 arranged between mist-forming unit 120 and substrate 110 arranged in film formation chamber 107.

[0170] [Step of Heating Mist with Microwaves Before the Mist Reaches a Substrate Installed in a Film Forming Unit] In microwave heating device 200, microwaves (2.45 GHz) generated by microwave oscillator 201 propagate through waveguide 205 and are irradiated onto a microwave irradiation portion of a supply pipe disposed within applicator 204, through which mist 220 and carrier gas pass. At this time, the positions of stub tuner 203 and short-circuit surface 206 are adjusted so that a standing wave in TE10 mode is formed. Microwave heating can be performed in this manner.

[0171] The microwave heating is performed after the mist 220 leaves the mist-forming section 120 and before it reaches the substrate 110 placed in the film-forming section 140 .

[0172] Generally, to improve the film formation rate in the mist CVD method, it is necessary to increase the amount of mist supplied. However, supplying a large amount of mist lowers the temperature of the substrate 110 and reduces the crystallinity of the film. On the other hand, by performing microwave heating according to the present invention, high-temperature mist can be supplied onto the substrate 110, which prevents heat from being removed from the substrate 110 and improves the film formation rate while also preventing a decrease in crystallinity.

[0173] Furthermore, when using heat transfer heating such as a heater, the temperature of not only the mist but also the carrier gas rises, increasing the saturated vapor pressure and promoting the evaporation of the mist. This makes it easier for the raw materials in the mist to precipitate, causing them to adhere to or become embedded in the film as foreign matter, thereby reducing film quality. On the other hand, microwave heating according to the present invention can directly heat the mist 220 without heating the carrier gas. As a result, the saturated vapor pressure does not increase, so the mist temperature can be increased without promoting the evaporation of the mist, improving the film formation rate without reducing film quality.

[0174] The microwave irradiation method is not particularly limited. It may be a multimode method as typified by a microwave oven, or a single-mode method in which one standing wave is formed in a waveguide. The single-mode method is preferred as the microwave irradiation means used in the present invention. This is because by arranging the microwave irradiation portion of the supply pipe in an area with strong electric field strength, microwaves can be efficiently irradiated onto the mist, resulting in good heating efficiency.

[0175] Microwaves are output from microwave oscillator 201 and reflected by short-circuit surface 206. At this time, by adjusting the positions of stub tuner 203 and short-circuit surface 206, standing waves can be formed in waveguide 205 and applicator 204. In microwave heating, part of the energy of the output microwaves is absorbed by the mist in the microwave irradiation part of the supply pipe, and the remainder is returned to microwave oscillator 201 and absorbed.

[0176] The microwave output control method is not particularly limited. The output may be kept constant, or the power consumption (incident wave power - reflected wave power) may be controlled to be constant. Alternatively, the temperature of the microwave irradiated portion of the supply pipe may be measured and fed back to automatically adjust the output so that the temperature is constant. Controlling the power consumption or temperature is preferred, and controlling the temperature is more preferred, as this is because the temperature of the heated portion is less likely to fluctuate over time.

[0177] Although the temperature measurement method is not particularly limited, when measuring the temperature of the microwave irradiated portion, it is advisable to use an infrared radiation thermometer or an optical fiber thermometer depending on the object to be measured in order to prevent the thermometer from absorbing microwaves. In this case, it is preferable that the temperature measurement portion of the optical fiber thermometer is made of a microwave-transparent material such as a nonmetal.

[0178] The microwave irradiation intensity is not particularly limited and can be appropriately selected depending on the raw material solution, but when heating the mist, it is preferably 0.1 mW to 20 kW, and more preferably 1 mW to 500 W. If the irradiation intensity is in the range of 0.1 mW to 20 kW, the mist can be effectively heated and discharge within the applicator 204 can be effectively suppressed.

[0179] The microwave frequency is not particularly limited and can be appropriately selected depending on the physical properties of the raw material solution. For example, when water is used as the solvent, the microwave frequency is preferably 0.9 GHz or more and 300 GHz or less, at which point water can absorb the microwave.

[0180] If the frequency is within this range, the mist can be stably heated, and the penetration depth of the microwaves can be maintained at an appropriate length, allowing uniform heating to be achieved even inside the mist.

[0181] It is particularly preferable that the frequency of the microwaves be 2.45 GHz or more and 25 GHz or less.

[0182] A frequency within this range allows the mist to be heated more stably, and the penetration depth of the microwaves can be maintained at an appropriate length, allowing for more uniform heating to be achieved even inside the mist.

[0183] When microwaves are irradiated to the applicator 204, if the mist 220 is supplied in excess of the volume of the microwave irradiation area of ​​the microwave irradiation portion of the supply pipe, the microwaves are absorbed more by the mist 220, and the microwaves may not resonate. For this reason, the flow rate of the mist is set to m [cm ３ / s], and the flow rate of the carrier gas is q [cm ３ / s], when the reaction solution is an aqueous solvent, it is preferable that m / q≦1 / 450, and when the reaction solution is an alcohol, it is preferable that m / q≦1 / 200. If m / q is in the above range, the microwaves resonate stably and a decrease in the heating efficiency of the mist can be effectively prevented. The lower limit of m / q is not particularly limited, but it is preferably 1 / 45,000 or more. If it is less than 1 / 45,000, the amount of mist supplied is small, resulting in poor productivity.

[0184] The mist flow rate can be calculated from the consumption amount of the raw material solution per hour and the density of the raw material solution. The flow rate of the carrier gas is a value converted to 20°C, and if the temperature is different, it can be converted to the flow rate at 20°C using the gas state equation.

[0185] [Process of supplying mist to a substrate in a film-forming section and forming a film on the substrate by heat treatment on the substrate] In the film-forming process, mist is supplied onto the substrate 110 placed on the hot plate 108, and is subjected to heat treatment (thermal reaction) on the substrate 110 in the film-forming chamber 107 by the heat of the hot plate 108, thereby forming a film on the substrate 110.

[0186] The substrate 110 is not particularly limited as long as it can be formed on and support a film. It may be a known substrate. It may be an insulator, a conductor, a semiconductor, a single crystal, or a polycrystalline. Examples of the substrate include, but are not limited to, polysulfone, polyethersulfone, polyphenylene sulfide, polyetheretherketone, polyimide, polyetherimide, fluororesin, metals such as iron, aluminum, stainless steel, and gold, silicon, sapphire, quartz, glass, gallium oxide, lithium niobate, and lithium tantalate.

[0187] It is also preferable to use a substrate in which aluminum is the main component metal element contained in the greatest amount among the metal elements contained in the substrate 110. Among these, it is preferable to use a sapphire wafer from the viewpoints of quality and cost.

[0188] The plane orientation of the main surface of the substrate 110 is not particularly limited, and in the case of a sapphire wafer, a main plane such as the c-plane, m-plane, or a-plane can be used. The main surface may also have an off-angle with respect to the just plane. The off-angle is not particularly limited, but is preferably 0° to 15°.

[0189] The thickness of the substrate 110 is not particularly limited, but is preferably about 200 to 800 μm from the viewpoint of cost.

[0190] The main surface of the substrate 110 preferably has a diameter of about 10 cm (4 inches) or more, and more preferably a diameter of about 15 cm (6 inches) or more. The upper limit of the size of the main surface of the substrate 110 is not particularly limited, but is preferably 750 cm ２ If it is circular, it should have an area equivalent to a diameter of 12 inches (300 mm) or less.

[0191] By using a substrate 110 with a large diameter in this way, the crystalline metal oxide film formed on the substrate 110 can be of higher quality and with higher productivity.

[0192] The shape of the substrate 110 is not particularly limited in the present invention.

[0193] The substrate 110 may be placed face down on the top surface of the film formation chamber 107, or may be placed face up on the bottom surface of the film formation chamber 107.

[0194] The heat treatment (thermal reaction) of the mist supplied onto the substrate 110 is not particularly limited as long as the mist reacts when heated. The reaction conditions can be set appropriately depending on the raw material and the film to be formed. For example, the heating temperature is preferably in the range of 120 to 600°C, more preferably in the range of 200 to 600°C, and even more preferably in the range of 400 to 550°C.

[0195] The heat treatment (thermal reaction) may be carried out under any of a vacuum, a non-oxygen atmosphere, a reducing gas atmosphere, an air atmosphere, and an oxygen atmosphere, and may be appropriately set depending on the film to be formed. The reaction pressure may be any of atmospheric pressure, increased pressure, and reduced pressure, but film formation under atmospheric pressure is preferred because it simplifies the device configuration.

[0196] The film may be formed directly on the substrate 110, or may be laminated on an intermediate layer (a buffer film or a release film) formed on the substrate 110. The intermediate layer is not particularly limited as long as it is a metal oxide that can have a corundum structure, and may be primarily composed of, for example, an oxide containing any of aluminum, titanium, vanadium, chromium, iron, gallium, rhodium, indium, and iridium.

[0197] More specifically, Al ２ O ３ , Ti ２ O ３ , V ２ O ３ , Cr ２ O ３ , Fe ２ O ３ , Ga ２ O ３ , Rh ２ O ３ , In ２ O ３ , Ir ２ O ３ Furthermore, when two elements selected from the above metal elements are designated as A and B, (A ｘ B １－ｘ ) ２ O ３ Binary metal oxides represented by (0<x<1), or when three elements selected from the above metal elements are A, B, and C, (A ｘ B ｙ C １－ｘ－ｙ ) ２ O ３ The oxide may be a ternary metal oxide represented by (0<x<1, 0<y<1).

[0198] During film formation, the temperature at the outlet of the applicator 204, which is the microwave irradiating part of the supply pipe, may be measured by an optical fiber thermometer 207, and the output of the microwave oscillator 201 may be automatically adjusted as appropriate so that the measured temperature remains constant. In this way, the mist can be heated uniformly with little temperature unevenness.

[0199] In the present invention, an annealing treatment may be performed after the film formation. The temperature of the annealing treatment is not particularly limited, but is preferably 600°C or less, more preferably 550°C or less, so as not to impair the crystallinity of the film. The treatment time of the annealing treatment is not particularly limited, but is preferably 10 seconds to 10 hours, more preferably 10 seconds to 1 hour.

[0200] The crystalline metal oxide film formed by the above method may be peeled off from the substrate 110. The peeling means is not particularly limited and may be any known means. Examples include peeling by applying mechanical impact, peeling by applying heat and utilizing thermal stress, peeling by applying vibration such as ultrasonic waves, peeling by etching, and laser lift-off. The crystalline metal oxide film can be obtained as a free-standing film by peeling.

[0201] Conventional methods can be used to form the electrodes required for constructing a semiconductor device. These methods include vapor deposition, sputtering, CVD, plating, and printing, which involves bonding with resins. Electrode materials include metals such as Al, Ag, Ti, Pd, Au, Cu, Cr, Fe, W, Ta, Nb, Mn, Mo, Hf, Co, Zr, Sn, Pt, V, Ni, Ir, Zn, In, and Nd; conductive metal oxide films such as tin oxide, zinc oxide, indium oxide, indium tin oxide (ITO), and indium zinc oxide (IZO); and organic conductive compounds such as polyaniline, polythiophene, and polypyrrole. These materials may also be alloys or mixtures of two or more of these. The thickness of the electrode is preferably 1 to 1,000 nm, more preferably 10 to 500 nm.

[0202] The present invention will be specifically explained below with reference to examples, but the present invention is not limited to these examples.

[0203] Example 1 Gallium iodide was added to water to prepare a 0.1 mol / L aqueous solution, which was used as raw material solution 104a. The raw material solution 104a obtained as described above was placed in mist generating source 104. The temperature of the solution at this time was 25°C.

[0204] A 4-inch c-plane sapphire substrate was placed on the hot plate 108 in the film-forming chamber 107 as the substrate 110, and the hot plate 108 was operated to raise the temperature of the substrate 110 to 500°C.

[0205] Flow control valves 103a and 103b were opened to supply nitrogen gas as a carrier gas from carrier gas source 102a (main carrier gas) and dilution carrier gas supply source 102b (dilution carrier gas) into film formation chamber 107, and the atmosphere in film formation chamber 107 was thoroughly replaced with these carrier gases, while the flow rates of the main carrier gas and the dilution carrier gas were adjusted to 12 L / min and 12 L / min, respectively.

[0206] Next, the ultrasonic vibrator 106 was vibrated at 2.4 MHz, and the vibration was propagated to the raw material solution 104a through the water 105a, thereby turning the raw material solution 104a into mist and generating mist.

[0207] This mist was transported by a carrier gas through supply pipe 109a to microwave heating device 200, where microwaves (2.45 GHz) were irradiated, and the heated mist was supplied onto substrate 110. In this case, the microwave irradiating portion of the supply pipe was a straight quartz tube with an inner diameter of 30 mm and a wall thickness of 2 mm, and the microwave output was controlled so that the temperature measured by an optical fiber thermometer was constant at 40°C.

[0208] Then, under atmospheric pressure and at 500° C., the mist is thermally reacted in the film-forming chamber 107 while gas is being exhausted from the exhaust port 112, and α-Ga having a corundum structure is formed on the substrate 110. ２ O ３ The film formation time was 1 hour. At this time, the raw solution 104a was appropriately replenished into the mist generating source 104 using a liquid replenishment mechanism (not shown) so that the water level of the raw solution 104a in the mist generating source 104 during film formation was constant. The flow rate of the mist was set to m [cm ３ / s], and the flow rate of the carrier gas is q [cm ３ / s], m / q was 1 / 8000. The flow rate m of the mist was calculated by dividing the consumption amount of the raw material solution 104a by the film formation time.

[0209] (Comparative Example 1) In Example 1, a film formation apparatus without the microwave irradiation device 200 was used, and film formation was carried out under the same conditions as in Example 1, except that microwave irradiation was not performed on the mist and the film formation time was 2 hours.

[0210] (Comparative Example 2) In Example 1, a film formation apparatus without a microwave irradiation device 200 was used, and film formation was carried out under the same conditions as in Example 1, except that microwave irradiation was not performed on the mist, and the entire supply pipe 109a was heated at a set temperature of 40°C using a ribbon heater.

[0211] (Comparative Example 3) In Example 1, a film formation apparatus without a microwave irradiation device 200 was used, and film formation was performed under the same conditions as in Example 1, except that microwave irradiation was not performed on the mist, and the raw material solution was heated to 40°C by heating the water 105a.

[0212] (Example 2) As a raw material, gallium acetylacetonate was dissolved in a hydrochloric acid aqueous solution (1.0 vol%) to prepare a 0.1 mol / L aqueous solution, which was used as the raw material solution 104a, the flow rates of the main carrier gas and the dilution carrier gas were adjusted to 18 L / min and 6 L / min, respectively, a 6-inch sapphire substrate was used as the substrate, and the microwave output was controlled so that the temperature measured by the optical fiber thermometer was 50°C. Film formation was performed under the same conditions as in Example 1, except that the flow rate of the mist was set to m [cm ３ / s], and the flow rate of the carrier gas is q [cm ３ / s], m / q = 1 / 5000.

[0213] Comparative Example 4 A film was formed under the same conditions as in Example 2, except that a film forming apparatus not including the microwave irradiation device 200 was used and microwave irradiation was not performed on the mist.

[0214] (Example 3) As a raw material, gallium acetylacetonate was dissolved in a hydrochloric acid aqueous solution (1.0 vol%) to prepare a 0.1 mol / L aqueous solution, to which 10 vol% formic acid was added, and the solution was used as a raw material solution 104a. The flow rate of the main carrier gas was adjusted to 24 L / min, the flow rate of the dilution carrier gas was adjusted to 0 L / min, an 8-inch sapphire substrate was used as the substrate, and the microwave output was controlled so that the temperature measured by an optical fiber thermometer was 75°C. Film formation was performed under the same conditions as in Example 1. In addition, the flow rate of the mist was adjusted to m [cm ３ / s], and the flow rate of the carrier gas is q [cm ３ / s], m / q = 1 / 3200.

[0215] [Evaluation 1: Film Thickness Measurement] The film thickness of the crystalline metal oxide films formed in Examples 1-3 and Comparative Examples 1-4 was measured using an optical interference film thickness meter F50. The film formation rate was calculated from the film thickness. The calculation was made as follows: Film thickness (μm) ÷ Film formation time (hours) = Film formation rate (μm / hour).

[0216] [Evaluation 2: Crystal structure and crystallinity evaluation] The crystal structure of the prepared film was evaluated by XRD 2θ-ω scanning. ２ O ３ Thereafter, the (006) plane rocking curve was measured, and the half-value width of the (006) plane was measured.

[0217] [Evaluation 3: Measurement of the number of foreign particles and the number of abnormally grown areas] For the crystalline metal oxide films formed in Examples 1-3 and Comparative Examples 1-4, the number of foreign particles was counted in a dark field image at 20x magnification using an optical microscope. ２ Observe and 1 cm ２ The number of foreign particles (= foreign particle density) was calculated. Examples of observed foreign particles are shown in Figure 6, and examples of abnormal growth locations are shown in Figure 7.

[0218] The foreign particles in Figure 6 appear to be raw material deposits formed when the mist evaporates before reaching the substrate. The foreign particles can be observed as bright spots in a dark field microscope, as described above. They can also be counted using an electron microscope such as an SEM, a surface inspection machine that detects defects using differences in scattered light intensity, or a surface inspection device that takes images using a microscope and classifies them using machine learning. In this evaluation, foreign particles ranging from 0.01 μm to 10 μm in size were counted.

[0219] As shown in Figure 7, the abnormal growth area was circular with a diameter of 10 to 100 μm, and crystals other than the α phase were observed near the center. Cross-sectional analysis of the abnormal growth area revealed foreign matter measuring up to several μm in size at the bottom of the abnormal growth area, and a region that appeared to be a crystalline phase was present above the foreign matter. Analysis by electron diffraction revealed that the electron diffraction pattern in the flat area outside the abnormal growth area in Figure 7 was α-Ga as shown in Figure 8. ２ O ３ 7, the electron diffraction image of the region that appears to be a crystalline phase above the foreign matter in FIG. 7 is that of α-Ga, as shown in FIG. ２ O ３ This is because the Ga ２ O ３ It is believed that another crystalline phase (likely γ) was formed. The electron beam diffraction was performed under the following conditions.

[0220] Selected area electron diffraction method Transmission electron microscope: Hitachi High-Technologies H-9500 Acceleration voltage: 300 kV Camera length: 1.0 m Selected area: approx. 140 nmφ

[0221] The abnormal growth areas can be observed as bright spots in a dark-field image of a microscope, and the number of defects can be measured using an electron microscope such as an SEM, a surface inspection machine that detects defects using differences in scattered light intensity, or a surface inspection device that takes images with a microscope and classifies them using machine learning. Whether the defect is a γ phase or not can be determined by crystal orientation analysis such as the EBSD method. The results of evaluations 1 to 3 above are summarized in Table 1.

[0222]

[0223] [Evaluation 3-2: Measurement of particle size distribution of foreign matter] For the crystalline metal oxide films produced in Example 1 and Comparative Example 1, a machine learning type surface inspection device equipped with a confocal microscope was used to detect foreign matter observed from the surface direction of the film, and the particle size of the detected foreign matter was measured using a review function, and a particle size distribution of the foreign matter was created.

[0224] The particle diameter here is the equivalent circle diameter in a two-dimensional image observed from the surface direction of the crystalline metal oxide film. The equivalent circle diameter is the diameter of a circle having an area equivalent to the area of ​​the particle captured in the two-dimensional image, and the particle area can be calculated by image analysis. For example, an optical microscope using Optelics AI manufactured by Lasertec Corporation can be used. ２ The results are shown in Figure 10 and Table 2.

[0225] As shown in Table 2, the mode of particle diameter of the foreign matter in Example 1 was 0.225 μm. The particle diameter (D50) at which the cumulative frequency was 50% was 0.225 μm. The standard deviation σ was 0.07 μm. The ratio (D90 / D10) of the particle diameter (D90) at which the cumulative frequency was 90% to the particle diameter (D10) at which the cumulative frequency was 10% was 2.6.

[0226] The density of foreign matter obtained by dividing the number of foreign matter by the observation area was 0.4 pieces / cm ２ The ratio of foreign matter having a particle size of not less than particle size D50 - standard deviation σ and not more than particle size D50 + standard deviation σ to the total number of foreign matter was 75%.

[0227] In Comparative Example 1, larger particles were observed than in Example 1. The mode of particle size of the foreign matter was 3.25 μm. The particle size (D50) at which the cumulative frequency was 50% was 2.75 μm. The standard deviation was 1.25 μm. The ratio (D90 / D10) of the particle size (D90) at which the cumulative frequency was 90% to the particle size (D10) at which the cumulative frequency was 10% was 5.7.

[0228] The density of foreign matter obtained by dividing the number of foreign matter by the observation area is 47.8 pieces / cm ２ The ratio of foreign matter having a particle size of not less than particle size D50 - standard deviation σ and not more than particle size D50 + standard deviation σ to the total number of foreign matter was 59%.

[0229] A comparison between Example 1 and Comparative Example 1 reveals that there was less foreign matter and less variation in particle size in Example 1, in which microwaves were irradiated onto the mist. When a semiconductor device is fabricated using a crystalline metal oxide film with less foreign matter and less variation in particle size, as in Example 1, the impact of the foreign matter on the device characteristics is negligible.

[0230]

[0231] [Evaluation 4: Evaluation of Electrical Characteristics] Using the crystalline metal oxide films prepared in Example 1 and Comparative Example 1, SBDs, which are semiconductor devices, were fabricated.

[0232] The current-voltage characteristics of the obtained semiconductor devices were evaluated. The voltage at which breakdown occurred was determined by measuring the reverse current-voltage characteristics. Semiconductor devices with a breakdown voltage of 600 V or more were considered to be acceptable products, and the yield was calculated by dividing the number of acceptable products by the total number of semiconductor devices produced = yield [%]. The yield of Example 1 was 97.8%, and the yield of the film of Comparative Example 1 was 42.4%.

[0233] Next, for the devices fabricated in Example 1 and Comparative Example 1 that contained one foreign particle, the yield was calculated for each particle size of the foreign particle. The results are shown in Figure 11. It can be seen that the yield drops sharply as the foreign particle size increases.

[0234] The film produced in Comparative Example 1 had many large foreign particles and associated abnormal growth sites, which significantly affected the device characteristics, resulting in a low yield of less than 50%. On the other hand, the film produced in Example 1 had fewer foreign particles and, in addition, the foreign particles were small and uniform in size, which reduced the impact of the foreign particles on the device characteristics, resulting in a high yield of over 95%.

[0235] A comparison between Example 1-3 and Comparative Example 1-4 confirmed that Example 1-3 of the present invention is a film formation method in which a mist-formed raw material solution is heat-treated on a substrate to form a crystalline metal oxide film, and that by irradiating microwaves on the mist between the mist-forming section and the substrate to heat it, it is possible to suppress the formation of foreign matter and abnormal areas and to rapidly form a film with good crystallinity.

[0236] This specification includes the following aspects. [1]: A film formation apparatus comprising: a mist-forming unit that generates mist by misting a raw material solution; a carrier gas supply unit that supplies a carrier gas that transports the mist; a film formation unit that heat-treats the mist to form a film on a substrate; a transport unit that connects the mist-forming unit to the film formation unit and has a supply pipe through which the mist is transported by the carrier gas; and a microwave heating device that irradiates the mist with microwaves between the mist-forming unit and the substrate to heat the mist. [2]: The film formation apparatus of [1] above, wherein the microwave heating device comprises a microwave generation unit, a microwave irradiation unit that irradiates the mist with microwaves generated by the microwave generation unit, and a microwave guide unit through which the microwaves propagate from the microwave generation unit to the microwave irradiation unit. [3]: The film formation apparatus of [2] above, wherein a portion of the supply pipe located within the microwave irradiation unit is formed of a microwave-transparent material. [4]: The film formation device of [2] or [3] above, wherein the portion of the supply pipe disposed within the microwave irradiation unit is formed from any one of quartz, ceramic, alumina, polytetrafluoroethylene resin, tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer resin, tetrafluoroethylene-hexafluoropropylene copolymer resin, and polyether ether ketone resin. [5]: A film formation method including the steps of: atomizing or dropletizing a raw material solution to generate a mist; transporting the mist to a film formation unit using a carrier gas; heating the mist with microwaves before the mist reaches a substrate placed in the film formation unit; and supplying the mist to the substrate in the film formation unit and performing heat treatment on the substrate to form a film on the substrate. [6]: The film-forming method according to [5] above, which includes using, as the raw material solution, one containing a metal raw material and at least one solvent selected from water, methanol, ethanol, ethylene glycol, diethylene glycol, propylene glycol, tetraethylene glycol, glycerol, benzyl alcohol, and dipropylene glycol. [7]: The film-forming method according to [5] above or [6] above, which includes using, as the solvent for the raw material solution, one containing water as a main component.[8]: The film formation method of [6] or [7] above, which includes using a metal raw material containing Ga. [9]: The film formation method of [5], [6], [7] or [8] above, which includes using a substrate having a film formation surface with a diameter of 10 cm (4 inches) or more as the substrate.

[10] : The film formation method of [5], [6], [7], [8] or [9] above, which includes setting the microwave frequency to 0.9 GHz or more and 300 GHz or less.

[11] : The film formation method of [5], [6], [7], [8], [9] or

[10] above, which includes setting the microwave frequency to 2.45 GHz or more and 25 GHz or less.

[12] : A crystalline metal oxide film containing at least one of gallium and aluminum as a main component, wherein the number density of foreign particles observed from the surface direction of the crystalline metal oxide film is 48 particles / cm. ２

[13] : A crystalline metal oxide film according to

[12] above, wherein the particle size distribution of the foreign matter has a particle size distribution index (particle size D90 / particle size D10) of 4.0 or less.

[14] : A crystalline metal oxide film according to

[12] above, wherein the proportion of particles having a particle size equal to or greater than (particle size D50 - said standard deviation) and equal to or less than (particle size D50 + said standard deviation) relative to the total number of the foreign matter is 60% or more.

[15] : A crystalline metal oxide film according to

[12] ,

[13] or

[14] above, wherein the particle size D50 of the foreign matter is less than 2.75 μm.

[16] : The crystalline metal oxide film of

[12] ,

[13] ,

[14] or

[15] above, wherein the particle diameter D90 of the foreign matter is less than 4.25 μm.

[17] : The crystalline metal oxide film of

[12] ,

[13] ,

[14] ,

[15] or

[16] above, wherein the foreign matter has a corundum structure.

[18] : The crystalline metal oxide film of

[12] ,

[13] ,

[14] ,

[15] ,

[16] or

[17] above, wherein the half-width of the rocking curve of the (006) plane measured by X-ray diffraction of the crystalline metal oxide film is less than 19.1 s.

[19] : The crystalline metal oxide film of

[12] ,

[13] ,

[14] ,

[15] ,

[16] ,

[17] or

[18] above, wherein the surface of the crystalline metal oxide film has a diameter of 10 cm (4 inches) or more.

[20] : A stacked structure having a substrate, a buffer layer on the substrate, and a crystalline metal oxide film of

[12] ,

[13] ,

[14] ,

[15] ,

[16] ,

[17] ,

[18] or

[19] above on the buffer layer.

[21] : A semiconductor device comprising at least one of the crystalline metal oxide film of

[12] ,

[13] ,

[14] ,

[15] ,

[16] ,

[17] ,

[18] or

[19] above or the stacked structure of

[20] above.

[22] : The semiconductor device according to

[21] , wherein the semiconductor device is any one of a semiconductor laser, a diode, and a transistor.

[0237] The present invention is not limited to the above-described embodiments. The above-described embodiments are merely examples, and anything that has substantially the same configuration as the technical idea described in the claims of the present invention and that exhibits similar effects is included within the technical scope of the present invention.

Claims

1. A film formation apparatus comprising: a mist-forming section that generates mist by turning a raw material solution into a mist; a carrier gas supply section that supplies a carrier gas for transporting the mist; a film formation section that heat-treats the mist to form a film on a substrate; a transport section that connects the mist-forming section with the inside of the film formation section and has a supply pipe through which the mist is transported by the carrier gas; and a microwave heating device that irradiates the mist with microwaves to heat the mist between the mist-forming section and the substrate.

2. The film forming apparatus as described in claim 1, characterized in that the microwave heating device comprises: a microwave generating unit; a microwave irradiation unit that irradiates the mist with microwaves generated in the microwave generating unit; and a microwave guide unit through which the microwaves propagate from the microwave generating unit to the microwave irradiation unit.

3. The film forming apparatus according to claim 2, wherein the portion of the supply pipe disposed within the microwave irradiation section is formed from a microwave-transparent material.

4. A film forming apparatus as described in claim 3, wherein the portion of the supply pipe arranged within the microwave irradiation section is formed from any one of quartz, ceramic, alumina, polytetrafluoroethylene resin, tetrafluoroethylene-perfluoroalkylvinyl ether copolymer resin, tetrafluoroethylene-hexafluoropropylene copolymer resin, and polyether ether ketone resin.

5. A film formation method comprising the steps of: atomizing or converting a raw material solution into droplets to generate a mist; transporting the mist to a film formation section using a carrier gas; heating the mist with microwaves before the mist reaches a substrate placed in the film formation section; and supplying the mist to the substrate in the film formation section and subjecting the substrate to a heat treatment to form a film on the substrate.

6. The film forming method according to claim 5, characterized in that the raw material solution contains a metal raw material and at least one solvent selected from the group consisting of water, methanol, ethanol, ethylene glycol, diethylene glycol, propylene glycol, tetraethylene glycol, glycerol, benzyl alcohol, and dipropylene glycol.

7. The film forming method according to claim 6, wherein the solvent of the raw material solution is mainly composed of water.

8. The film forming method according to claim 6, wherein the metal source contains Ga.

9. The method according to claim 5, wherein the substrate has a film-forming surface having a diameter of 10 cm (4 inches) or more.

10. A film forming method according to any one of claims 5 to 9, characterized in that the frequency of the microwaves is 0.9 GHz or more and 300 GHz or less.

11. The film forming method according to claim 10, wherein the frequency of the microwaves is set to be not less than 2.45 GHz and not more than 25 GHz.

12. A crystalline metal oxide film containing at least one of gallium and aluminum as a main component, wherein the density of foreign matter observed from the surface direction of the crystalline metal oxide film is 48 / cm ２ and a standard deviation in particle size distribution of the foreign matter is less than 1.25 μm.

13. The crystalline metal oxide film according to claim 12, characterized in that in the particle size distribution of the foreign matter, the particle size distribution index (particle size D90 / particle size D10) is 4.0 or less.

14. A crystalline metal oxide film as described in claim 12, characterized in that the proportion of particles having a particle diameter of at least D50 minus the standard deviation and at most D50 plus the standard deviation relative to the total number of said foreign matter is 60% or more.

15. The crystalline metal oxide film according to claim 12, characterized in that the particle diameter D50 of the foreign matter is less than 2.75 μm.

16. The crystalline metal oxide film according to claim 12, characterized in that the particle diameter D90 of the foreign matter is less than 4.25 μm.

17. The crystalline metal oxide film according to claim 12, which has a corundum structure.

18. The crystalline metal oxide film according to claim 12, characterized in that the half-width of the rocking curve of the (006) plane of said crystalline metal oxide film by X-ray diffraction is less than 19.1 s.

19. The crystalline metal oxide film of claim 12, wherein the surface of said crystalline metal oxide film is 10 cm (4 inches) or greater in diameter.

20. A laminated structure comprising a substrate, a buffer layer on the substrate, and the crystalline metal oxide film according to claim 12 on the buffer layer.

21. A semiconductor device comprising at least one of the crystalline metal oxide film according to any one of claims 12 to 19 and the laminated structure according to claim 20.

22. The semiconductor device according to claim 21, wherein the semiconductor device is any one of a semiconductor laser, a diode, and a transistor.

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