Film deposition method, film deposition apparatus, and α-Ga2O3 film

Abstract

This film deposition method is a method for depositing a film of a crystalline oxide by a mist CVD method, in which a mist is fed together with a carrier gas to a heated substrate inside a film deposition zone surrounded by partitions. The film deposition method is characterized in that at least when the substrate is being heated, a gas other than the carrier gas is sent into the film deposition zone. Due to the configuration, a high-quality crystalline-oxide film is formed in which the film surface has a significantly reduced particle density.

Description

[Technical Field]

[0001] The present invention relates to a film deposition method, a film deposition apparatus, and an α-Ga2O3 film. [Background technology]

[0002] Mist chemical vapor deposition (Mist CVD), a method that uses atomized mist-like raw materials to form thin films on substrates, has been developed and is used for fabricating oxide semiconductor films and the like (Patent Documents 1 and 2). [Prior art documents] [Patent Documents]

[0003] [Patent Document 1] Japanese Patent Publication No. 2013-028480 [Patent Document 2] Japanese Patent Publication No. 2014-063973 [Patent Document 3] Japanese Patent Publication No. 2021-136445 [Overview of the project] [Problems that the invention aims to solve]

[0004] However, in the mist CVD method, mist aggregates within the deposition chamber, and products adhering to the walls detach and become airborne, creating particle sources. Furthermore, since this method inherently supplies mist (particles), no particular attention was paid to particles. In addition, a method for atomizing raw materials to form high-quality films had not been established until now. This resulted in a problem where numerous particles, stemming from the quality of the raw material mist, adhered to the fabricated films. Moreover, it is known that increasing the mist supply rate, for example, makes such particle adhesion more pronounced, making it a challenge to balance film quality and productivity.

[0005] To address these challenges, for example, Patent Document 3 discloses a method for suppressing particle generation by controlling the atomization method. However, as the film thickness increases and the film deposition time is extended, the mist aggregates in the deposition chamber, and products adhering to the walls of the deposition chamber detach and become suspended, creating new sources of particle generation. Furthermore, in order to disperse the mist within the deposition chamber, it was common practice to maintain negative pressure inside the chamber. As a result, a considerable amount of outside air flowed in from outside the deposition chamber, leading to problems such as contamination of the film by particles in the outside air.

[0006] The present invention was made to solve the above problems and aims to provide a film deposition method and apparatus for forming a high-quality crystalline oxide film with significantly reduced particle density on the film surface. Furthermore, the present invention aims to provide a high-quality α-Ga2O3 film in which the particle density on the film surface is significantly reduced. [Means for solving the problem]

[0007] The present invention has been made to achieve the above objective, and provides a method for forming a crystalline oxide film by mist CVD in which mist is supplied to a heated substrate along with a carrier gas within a film formation section covered by a partition wall, characterized in that a gas other than the carrier gas is supplied to the film formation section at least while the substrate is being heated.

[0008] This film deposition method makes it possible to obtain high-quality semiconductor films with significantly reduced particle density on the film surface.

[0009] At this time, when mist is not supplied, the particle density of 0.3 μm particles in the film-forming section is 100,000 / m². 3 The following is preferable.

[0010] This film deposition method makes it possible to obtain high-quality semiconductor films with significantly reduced particle density on the film surface.

[0011] At this time, it is preferable to use air as the gas other than the carrier gas.

[0012] According to such a film-forming method, a crystalline oxide film can be manufactured at low cost, and the safety during the production of the crystalline oxide film is also excellent.

[0013] The present invention has been made to achieve the above object, and is a method for forming a crystalline oxide film by supplying a mist together with a carrier gas to a heated substrate in a film-forming portion covered with a partition wall and forming a film by mist CVD method. At least when the mist is not supplied, the particle density of particles having a particle size of 0.3 μm or more in the film-forming portion is 100000 / m 3 A film-forming method is provided, which is characterized by the following.

[0014] At this time, it is preferable to provide an exhaust portion so as to surround the film-forming portion, and to exhaust from the film-forming portion through the exhaust portion.

[0015] According to such a film-forming method, the manufacturing apparatus can be simplified and the safety is also excellent.

[0016] At this time, it is preferable that the exhaust flow rate exhausted from the exhaust portion is larger than the flow rate of the carrier gas.

[0017] According to such a film-forming method, the safety is more excellent, and a high-quality semiconductor film with a significantly reduced surface defect density as well as particles can be obtained.

[0018] At this time, it is preferable to use a substrate having a diameter of 4 inches (100 mm) to 8 inches (200 mm).

[0019] According to such a film-forming method, a high-quality semiconductor film with a significantly reduced particle density on the film surface can be obtained even for a large-area substrate.

[0020] The present invention has been made to achieve the above objective, and provides a film deposition apparatus having a film deposition section covered by a partition wall, a carrier gas supply section, and a misting section that generates mist, wherein a film deposition is performed by supplying mist together with a carrier gas to the film deposition section, and the film deposition section is provided with an air supply section for supplying gases other than the carrier gas.

[0021] Such a film deposition apparatus enables the implementation of the aforementioned film deposition method, resulting in a high-quality semiconductor film with significantly reduced particle density on the film surface. Furthermore, it allows for the inexpensive manufacture of the crystalline oxide film and offers excellent safety during the manufacturing process.

[0022] In this case, it is preferable that a filter is provided in the air supply section.

[0023] Such a film deposition apparatus makes it possible to obtain high-quality semiconductor films with a significantly reduced particle density on the film surface.

[0024] In this case, it is preferable that an exhaust section is provided so as to surround the film-forming section, and that exhaust is discharged from the film-forming section through the exhaust section.

[0025] Such a film deposition apparatus allows for simplification and offers superior safety.

[0026] In this case, it is preferable that the air supply unit supplies air as a gas other than the carrier gas.

[0027] Such a film deposition apparatus makes it possible to manufacture crystalline oxide films at low cost, and also offers superior safety during the manufacturing process.

[0028] This invention was made to achieve the above objectives, and the film thickness variation is 3.3% or less, and the number of particles on the film that can be confirmed by optical microscope is 29 / cm². 2The present invention provides an α-Ga2O3 film characterized by the following:

[0029] Such an α-Ga2O3 film exhibits excellent film thickness distribution and suppresses the incorporation of foreign matter into the film, resulting in a high-quality film with significantly reduced particle density on the film surface, making it suitable for semiconductor device manufacturing.

[0030] In this case, it is preferable that the full width at half maximum of the rocking curve of the (006) plane obtained by X-ray diffraction is 8 seconds or less.

[0031] Such an α-Ga2O3 film exhibits good crystallinity.

[0032] In this case, the diameter is preferably 4 inches (100 mm) to 8 inches (200 mm).

[0033] Such an α-Ga2O3 film results in a significantly lower particle density on the film surface, even on large-area substrates, and thus produces a high-quality product. [Effects of the Invention]

[0034] As described above, the film formation method of the present invention makes it possible to obtain a high-quality crystalline oxide film with a significantly reduced particle density on the film surface. According to the film deposition apparatus of the present invention, it is possible to obtain a high-quality crystalline oxide film in which the particle density on the film surface is significantly reduced. The α-Ga2O3 film of the present invention results in a high-quality film with significantly reduced particle density on the film surface. [Brief explanation of the drawing]

[0035] [Figure 1] This is a schematic diagram showing an example of the film deposition apparatus of the present invention. [Figure 2] This is a schematic diagram showing an example of a semiconductor device using a multilayer structure fabricated by the film deposition method and apparatus of the present invention. [Figure 3]This is a schematic diagram showing another example of the film deposition section of the film deposition apparatus of the present invention. [Figure 4] This is a schematic diagram showing yet another example of the film deposition section of the film deposition apparatus of the present invention. [Figure 5] This is a schematic diagram showing yet another example of the film deposition section of the film deposition apparatus of the present invention. [Figure 6] This is a schematic diagram showing yet another example of the film deposition section of the film deposition apparatus of the present invention. [Modes for carrying out the invention]

[0036] The present invention will be described in detail below, but the present invention is not limited to these descriptions. As described above, there has been a need for a film deposition method and apparatus capable of obtaining high-quality crystalline oxide films with significantly reduced particle density on the film surface. As a result of diligent study on the above problems, the present inventors have provided a method for forming a crystalline oxide film by mist CVD in which mist is supplied to a heated substrate along with a carrier gas within a film-forming section covered by a partition wall, characterized in that a gas other than the carrier gas is supplied to the film-forming section at least while the substrate is being heated, or a method for forming a crystalline oxide film by mist CVD in which mist is supplied to a heated substrate along with a carrier gas within a film-forming section covered by a partition wall, characterized in that at least when mist is not supplied, the particle density in the film-forming section with a particle size of 0.3 μm or larger is 100,000 / m 3 The present invention was completed by discovering that a film deposition method characterized as described below makes it possible to obtain a high-quality crystalline oxide film with a significantly reduced particle density on the film surface, and a film deposition apparatus having a film deposition section covered by a partition wall, a carrier gas supply section, and a misting section that generates mist, wherein the film deposition apparatus performs film deposition by supplying mist together with the carrier gas to the film deposition section, and the film deposition section is provided with an air supply section for supplying gases other than the carrier gas, thereby making it possible to obtain a high-quality crystalline oxide film with a significantly reduced particle density on the film surface.

[0037] Furthermore, as mentioned above, there was a demand for high-quality α-Ga2O3 films with significantly reduced particle density on the film surface. The inventors have diligently investigated the above problems and have found that the film thickness variation is 3.3% or less, and the number of particles on the film that can be confirmed by optical microscope is 29 / cm². 2 We have discovered that an α-Ga2O3 film with the following characteristics results in a high-quality α-Ga2O3 film with significantly reduced particle density on the film surface, thus completing the present invention.

[0038] (First Embodiment of the Invention) (Film forming equipment) The following describes a film deposition method and apparatus according to the first embodiment of the present invention. Figure 1 is a schematic diagram showing an example of the film deposition apparatus of the present invention. As shown in Figure 1, the film deposition apparatus 201 of the present invention has a film deposition section 215 covered by a partition wall (film deposition chamber) 207, a carrier gas supply section 230, and a misting section 220 that generates mist.

[0039] (Misting section) The misting unit 220 atomizes the raw material solution 204a to generate mist. In this invention, "mist" refers to a general term for fine liquid particles dispersed in a gas, and includes what are called fog, droplets, etc. The atomizing means is not particularly limited as long as it can atomize the raw material solution 204a, and any known atomizing means may be used, however, it is preferable to use an atomizing means using ultrasonic vibration, because it can atomize more stably.

[0040] As shown in Figure 1, the misting unit 220 includes a mist source 204 containing a raw material solution 204a, a container 205 containing a medium capable of transmitting ultrasonic vibrations, such as water 205a, and an ultrasonic transducer 206 attached to the bottom of the container 205. Specifically, the mist source 204, consisting of the container containing the raw material solution 204a, is housed in the container 205 containing the water 205a using a support (not shown). The ultrasonic transducer 206 is mounted on the bottom of the container 205, and the ultrasonic transducer 206 is connected to an oscillator 216. When the oscillator 216 is activated, the ultrasonic transducer 206 vibrates, and ultrasonic waves are transmitted into the mist source 204 via the water 205a, causing the raw material solution 204a to be atomized.

[0041] (Raw material solution) The raw material solution 204a is not particularly limited in terms of the materials contained in the solution, as long as it can be atomized, and may be inorganic or organic materials. Preferably, metals or metal compounds are used as materials, and for example, a solution containing one or more metals selected from gallium, iron, indium, aluminum, vanadium, titanium, chromium, rhodium, nickel, and cobalt may be used. As such a raw material solution, a solution in which the metal is dissolved or dispersed in an organic solvent or water in the form of a complex or salt can be preferably used. Examples of salt forms include metal chloride salts, metal bromide salts, metal iodide salts, and other halide salts. Furthermore, a solution of the above metal dissolved in a hydrogen halide such as hydrobromic acid, hydrochloric acid, or hydroiodic acid can also be used as a salt solution. Examples of complex forms include acetylacetonate complexes, carbonyl complexes, ammine complexes, and hydride complexes. An acetylacetonate complex can also be formed by mixing acetylacetone with the aforementioned salt solution. The metal concentration in the raw material solution 204a is not particularly limited and can be 0.005 to 1 mol / L. A temperature of 20°C or higher is preferred during mixing and dissolution.

[0042] Additives such as hydrohalic acid and oxidizing agents may be mixed into the raw material solution 204a. Examples of hydrohalic acid include hydrobromic acid, hydrochloric acid, and hydroiodic acid, but hydrobromic acid or hydroiodic acid are preferred because they provide a high film formation rate. Examples of oxidizing agents include peroxides such as hydrogen peroxide (H2O2), sodium peroxide (Na2O2), barium peroxide (BaO2), and benzoyl peroxide (C6H5CO)2O2, as well as organic peroxides such as hypochlorous acid (HClO), perchloric acid, nitric acid, ozonated water, peracetic acid, and nitrobenzene.

[0043] The raw material solution 204a may contain a dopant source. The dopant source is not particularly limited. Examples include n-type dopant sources such as tin, germanium, silicon, titanium, zirconium, vanadium, or niobium, or p-type dopant sources such as copper, silver, iridium, rhodium, or magnesium.

[0044] (Carrier gas supply department) The carrier gas supply unit 230 supplies carrier gas for transporting the mist. As shown in Figure 1, the carrier gas supply unit 230 has a carrier gas source 202a for supplying carrier gas and a flow control valve 203a for adjusting the flow rate of carrier gas discharged from the carrier gas source 202a. It also has a dilution carrier gas source 202b and a flow control valve 203b for adjusting the flow rate of dilution carrier gas discharged from the dilution carrier gas source 202b. This allows for the supply of dilution carrier gas in addition to carrier gas as needed. In this invention, the sum of the carrier gas flow rate and the dilution carrier gas flow rate is referred to as the total carrier gas flow rate.

[0045] The type of carrier gas is not particularly limited and can be appropriately selected depending on the film to be deposited. Examples include inert gases such as oxygen, ozone, nitrogen, and argon, or reducing gases such as hydrogen gas and foaming gas. Furthermore, there may be one type of carrier gas or two or more types. For example, as a second carrier gas, a dilution gas obtained by diluting the same gas as the first carrier gas with another gas (for example, diluted 10 times) may be used, or air may be used. The total flow rate of the carrier gas is not particularly limited. For example, when depositing a film on a substrate with a diameter of 2 inches (approximately 50 mm), the total flow rate of the carrier gas is preferably 0.05 to 50 NL / min, and more preferably 5 to 20 NL / min. Hereinafter, NL is the value obtained by converting the volume of the gas to standard conditions (0°C, 1 atm).

[0046] (supply pipe) The supply pipe 209 connects the atomizing section 220 and the film deposition section 215, and transports the mist by carrier gas. The mist is transported from the mist generation source 204 of the atomizing section 220 via the supply pipe 209 by carrier gas and supplied into the film deposition section 215. The supply tube 209 can be made of, for example, a quartz tube, a glass tube, or a resin tube. The tip of the supply tube 209 is a nozzle.

[0047] (Film forming section) Figure 1 shows an example of the film deposition section of the film deposition apparatus of the present invention. As shown in Figure 1, the film deposition section 215 is a portion that is almost entirely covered by a partition wall (film deposition chamber) 207. A configuration where "almost the entire area is covered" may be one in which the area including the substrate is completely covered by a partition wall, as shown in Figures 1, 3, and 4, or it may be one in which a part of the surface is open, as shown in Figures 5 and 6. The material of the partition wall (deposition chamber) 207 can be metal such as iron, aluminum, or stainless steel, but it can also be made of resin such as acrylic or polyvinyl chloride. Using resin will make the device lighter and reduce its cost. Using a transparent material will allow for visual observation of the film deposition process, making it easier to prevent equipment malfunctions.

[0048] A substrate 210 is installed inside the partition wall (film deposition chamber) 207, and a heater 208 is provided for heating the substrate 210. The heater 208 may be provided outside the partition wall (film deposition chamber) 207, for example, as shown in Figure 1, or it may be provided inside the partition wall (film deposition chamber) 207, for example, as shown in Figures 5 and 6.

[0049] The film deposition section 207 is designed to allow the introduction of mist along with the film deposition gas (carrier gas) supplied from the supply pipe 209. The mist, along with the carrier gas, is ejected from the nozzle toward the substrate 210, where it is heat-treated to deposit the film.

[0050] Furthermore, a top plate may be provided to rectify the supplied mist on the circuit board. Furthermore, the partition wall (film deposition chamber) 207 is provided with an air supply section 501 for supplying gases other than the carrier gas.

[0051] (Air supply unit) In this invention, in addition to the carrier gas for film formation, an air supply unit 501 is connected to the partition wall (film formation chamber) 207 for supplying a gas other than the carrier gas, such as air. The gas supplied is not particularly limited and can be an inert gas in addition to air, but air is particularly preferred. The air supply unit 501 may be located vertically above the substrate 210 as shown in Figure 1, or to the side of the substrate 210 as shown in Figure 3. A filter may be installed inside the air supply unit 501. By using a high-performance filter such as a HEPA filter, the cleanliness of the film formation area can be increased. By supplying air from the air supply unit 501, the density of airborne particles with a particle size of 0.3 μm or larger inside the film formation area can be reduced to 100,000 / m³. 3 The following is possible. Since a lower particle density is better, the lower limit is 0 / m 3In this case, airborne particles can be measured using a commercially available particle counter employing a light scattering method. A light-blocking method may also be used, but the light scattering method is more common and preferable. The particle counter may be permanently installed in the film deposition apparatus, and a mechanism may be provided to continuously monitor the particle density within the deposition section and, furthermore, to determine whether or not film deposition is possible based on the measured particle density. There is no particular upper limit to the diameter of the particles, but for example, it is 1000 μm.

[0052] (Exhaust vent) An exhaust port 212 for exhaust gas may be provided in the partition wall (film deposition chamber) 207. In Figures 5 and 6, the open surface of the partition wall can be considered as a large exhaust port.

[0053] (Exhaust section) An exhaust section may be provided so as to surround the partition wall (film deposition chamber) 207. In the examples shown in Figures 4 to 6, the exhaust section 511 surrounds the partition wall (film deposition chamber) 207. As shown in Figure 6, a part of the partition wall (film deposition chamber) 207 and a part of the outer wall of the exhaust section 511 may be common. The exhaust section 511 has one or more exhaust ports 512, which are connected to a fan or the like to forcibly exhaust the air from inside. For its purpose, it is sufficient for the exhaust section 511 to be able to exhaust air, and it does not need to be completely sealed.

[0054] (substrate) The substrate 210 is a base substrate for forming a crystalline oxide film. It is not particularly limited as long as it serves as a support for the crystalline oxide film. The material is not particularly limited, and known substrates can be used, and may be organic compounds or inorganic compounds. Examples include polysulfone, polyethersulfone, polyphenylene sulfide, polyetheretherketone, polyimide, polyetherimide, fluororesin, metals such as iron, aluminum, stainless steel, and gold, quartz, glass, calcium carbonate, gallium oxide, and ZnO. In addition to these, single-crystal substrates such as silicon, sapphire, lithium tantalate, lithium niobate, SiC, GaN, iron oxide, and chromium oxide can be used, and in the present invention, such single-crystal substrates are desirable. These allow for the acquisition of higher quality crystalline oxide films. In particular, sapphire substrates, lithium tantalate substrates, and lithium niobate substrates are relatively inexpensive and industrially advantageous.

[0055] The thickness of the substrate 210 is preferably 100 to 5000 μm. Within this range, handling is easy, and thermal resistance during film formation can be suppressed, making it easier to obtain a high-quality film.

[0056] There are no particular restrictions on the size of the circuit board 210, but the area of ​​the circuit board must be 100mm². 2 If the film diameter is 2 inches (50 mm) or larger, it is preferable to obtain a large-area film with good crystallinity. Furthermore, if the substrate diameter is 4 inches (100 mm) to 8 inches (200 mm), the obtained crystalline oxide film can be easily processed using existing processing equipment, which is industrially advantageous in semiconductor device manufacturing. In addition, it has a large area and excellent film thickness distribution, resulting in superior semiconductor properties when applied to semiconductor devices. For example, when semiconductor devices such as power semiconductor devices are manufactured from such a crystalline oxide film, a product lot containing two or more of these semiconductor devices can achieve a breakdown yield of 75% or more.

[0057] Another layer may be interposed between the substrate 210 and the crystalline oxide film. This other layer is a layer with a different composition from the substrate and the outermost crystalline oxide film, and is also called a buffer layer. The buffer layer can be an oxide semiconductor film, an insulating film, a metal film, etc., and suitable materials include, for example, Al2O3, Ga2O3, Cr2O3, Fe2O3, In2O3, Rh2O3, V2O3, Ti2O3, Ir2O3, etc. The thickness of the buffer layer is preferably 0.1 μm to 2 μm.

[0058] In Figure 1, the substrate 210 is placed on the bottom surface of the partition wall (deposition chamber) 207 and positioned face up. However, the substrate 210 may also be placed on the top surface of the partition wall (deposition chamber) 207 and positioned face down.

[0059] Furthermore, the heater 208 or nozzle may be connected to a transport mechanism and configured to allow movement such as reciprocating motion or rotational motion. Performing these movement operations during film formation improves the uniformity of the resulting film.

[0060] (Film forming method) The film formation method of the present invention will be described below. The present invention relates to a film deposition method for a crystalline oxide film, in which mist is supplied to a heated substrate 210 along with a carrier gas within a film deposition section 215 covered by a partition wall (film deposition chamber) 207, and the film is deposited by mist CVD, wherein at least while the substrate 210 is being heated, a gas other than the carrier gas is supplied into the film deposition section 215.

[0061] More specifically, the system includes a misting step in which a raw material solution is atomized in a misting unit 220 to generate mist; a carrier gas supply step in which a carrier gas for transporting the mist is supplied to the misting unit 220; a transport step in which the mist is transported from the misting unit 220 to the film-forming unit 215 by the carrier gas via a supply pipe 209 connecting the misting unit 220 and the film-forming unit 215; and a film-forming step in which the transported mist is heat-treated to form a film on a base substrate (substrate) 210.

[0062] First, place the substrate 210 in the film formation part 215 that is substantially entirely covered by the partition wall (film formation chamber) 207, and operate the heater 208. During at least substrate heating, a gas other than the carrier gas is supplied. The supply flow rate can be 20 to 10,000 NL / min. For example, air can be supplied from the supply part 501. At least when the mist is not supplied, the particle density with a particle size of 0.3 μm or more in the film formation part 215 is 100,000 / m 3 It is preferably the following. Also, for example, nitrogen may be supplied from the supply part 501. In this case, a diffuser (diffusion plate) or the like may be provided so that the gas is dispersed over a wide area in the film formation chamber. Note that although it is possible to improve the cleanliness in the film formation part 215 by supplying a large amount of carrier gas, at a general carrier gas flow rate, the flow rate is small and the effect is limited. Also, it is common for the carrier gas to be pressurized or highly purified more than necessary, and flowing a large amount of this will increase the cost.

[0063] Forced exhaust may be performed from the exhaust port 212. At this time, it is desirable that the flow rate exhausted from the exhaust port 212 is the same as or smaller than the flow rate supplied from the supply part 501. This is because if the exhaust flow rate is large, outside air will flow into the film formation part 207, resulting in a decrease in cleanliness.

[0064] Furthermore, when there is an exhaust part 511 as shown in FIGS. 4 to 6, an exhaust fan or the like can be operated to exhaust the exhaust part 511. The inside of the exhaust part 511 (the region excluding the partition wall (film formation chamber) 207) has a lower pressure than the outside of the exhaust part 511, and the differential pressure is preferably about 0.1 to 100 Pa.

[0065] Also, it is preferable that the exhaust flow rate exhausted from the exhaust part 511 is more than the flow rate of the carrier gas. Thereby, a high-quality semiconductor film with better safety and a significantly reduced surface defect density as well as particle density can be obtained.

[0066] (Mist generation process) In the mist generation process, the raw material solution 204a is placed inside the mist generation source 204, and the ultrasonic transducer 206 is vibrated. This vibration is then transmitted to the raw material solution 204a through the water 205a, thereby atomizing the raw material solution 204a and generating mist.

[0067] (Carrier gas supply process) In the carrier gas supply process, a carrier gas for transporting the mist and a carrier gas for dilution are supplied to the misting unit 220. Furthermore, by opening the flow control valves 203a and 203b, carrier gas and dilution carrier gas are supplied into the film deposition section 215 from the carrier gas source 202a and dilution carrier gas source 202b, respectively. After the atmosphere in the film deposition section 215 has been sufficiently replaced with the carrier gas and dilution carrier gas, the flow rates of the carrier gas and dilution carrier gas are adjusted.

[0068] (Conveying process) As part of the transport process, mist is transported from the misting unit 220 to the nozzle in the film-forming unit 215 via a supply pipe 209 connecting the misting unit 220 and the film-forming unit 215, using a carrier gas and a dilution carrier gas.

[0069] (Film forming process) In the film deposition process, mist and carrier gas transported to the nozzle are sprayed onto the substrate 210, heating the substrate 210 and causing a thermal reaction to deposit a film on the surface of the substrate 210. In the film deposition process, it is not always necessary to supply gases other than the carrier gas mentioned above. However, supplying gases other than the carrier gas during film deposition can reduce the particle density on the resulting film. Furthermore, the inclusion of foreign matter into the film is suppressed, thus improving crystallinity. In addition, the mist is appropriately dispersed on the substrate, improving the film thickness distribution.

[0070] Furthermore, the substrate 210 or nozzle may be connected to a transport mechanism to perform reciprocating or rotational movements during film formation. Performing these movement operations can further improve the uniformity of the resulting film.

[0071] The thermal reaction of the mist also depends on the ambient temperature around the substrate. Therefore, it is desirable that the temperature of the nozzle and the inner wall of the film deposition section 215 be higher than room temperature. This allows for a more stable thermal reaction. For example, the nozzle temperature can be set to 50-250°C.

[0072] The thermal reaction may be carried out under any of the following conditions: a non-oxygen atmosphere, a reducing gas atmosphere, an air atmosphere, or an oxygen atmosphere, and should be set appropriately depending on the film to be deposited. The reaction pressure may also be under atmospheric pressure, a pressurized atmosphere, or a reduced pressure, but deposition under atmospheric pressure is preferable because it simplifies the apparatus configuration.

[0073] (Heat treatment) Furthermore, the laminated structure produced by the film deposition method and apparatus of the present invention may be heat-treated at 200 to 600°C. This further removes unreacted species and other contaminants from the film, resulting in a higher quality laminated structure. The heat treatment may be carried out in air, an oxygen atmosphere, or under an inert gas atmosphere such as nitrogen or argon. The heat treatment time can be determined as appropriate, but for example, it can be 5 to 240 minutes.

[0074] (Peeling) In the laminated structure produced by the film deposition method and apparatus of the present invention, the crystalline oxide film may be peeled off from the substrate. The peeling means is not particularly limited and may be a known means. Examples of peeling methods include peeling by applying mechanical impact, peeling by applying heat and utilizing thermal stress, peeling by applying vibration such as ultrasound, and peeling by etching. By such peeling, the crystalline oxide film can be obtained as a self-supporting film.

[0075] (Crystalline oxide film) The crystalline oxide film produced by the film deposition method and apparatus of the present invention has a particle density of 50 / cm³ of particles with a diameter of 0.3 μm or more on the surface of the crystalline oxide film. 2The following applies: Particles with a diameter of 0.3 μm or larger significantly affect the properties when a semiconductor device is constructed using a crystalline oxide film. Crystalline oxide films with a particle density of 0.3 μm or larger are of high quality and suitable for semiconductor device manufacturing.

[0076] In this invention, "substrate particles" include particles incorporated into the crystalline oxide film and integrated with the film, as well as particles adhering to the surface of the crystalline oxide film as foreign matter, and refer to particles that are observed when the surface of the film is observed.

[0077] Furthermore, the diameter of particles on the substrate is a value based on the size of the particles measured by a light scattering particle counter. The size of the particles is determined by calibrating the counter with standard particles of multiple sizes. That is, it is a value classified by comparing the measured value when measuring particles with the measured value when measuring standard particles. Particles on the surface of a crystalline oxide film can be measured, for example, using a laser scattering particle counter. It is also possible to observe the film surface using an optical microscope and count them by size. For example, by using a dark-field microscope and a magnification of 50x, particles on the substrate of about 0.3 to 100 μm can be observed.

[0078] Generally, crystalline oxide films are composed of metal and oxygen, but in the crystalline oxide film according to the present invention, it is preferable that gallium is the main component as the metal. In this invention, "mainly composed of gallium oxide" means that 50 to 100% of the metal component is gallium. Other metal components may include, for example, one or more metals selected from iron, indium, aluminum, vanadium, titanium, chromium, rhodium, iridium, nickel, and cobalt.

[0079] The crystalline oxide film may contain dopant elements. Examples include, but are not limited to, n-type dopants such as tin, germanium, silicon, titanium, zirconium, vanadium, or niobium, or p-type dopants such as copper, silver, tin, iridium, rhodium, or magnesium. The concentration of the dopant is, for example, about 1 × 10⁻⁶. 16 / cm 3 ~1 × 10 22 / cm 3 It may be approximately 1 × 10 17 / cm 3 Even at the following low concentrations, approximately 1 × 10⁻⁶ 20 / cm 3 Higher concentrations than those mentioned above are also acceptable.

[0080] The crystal structure of the crystalline oxide film is not particularly limited; it may be a β-gallia structure, a corundum structure, or an orthorhombic structure. Multiple crystal structures may be mixed, or the film may be polycrystalline, but a single crystal or uniaxially oriented film is preferred. Whether a film is single crystal or uniaxially oriented can be confirmed using an X-ray diffractometer or an electron diffractometer. When the film is irradiated with X-rays or electron beams, a diffraction pattern corresponding to the crystal structure is obtained; however, if the film is uniaxially oriented, only specific peaks will appear. This allows for the determination that the film is uniaxially oriented.

[0081] The thickness of the crystalline oxide film is not particularly limited, but is preferably 0.1 μm or more. The upper limit is not particularly limited. For example, it may be 100 μm or less, preferably 50 μm or less, and more preferably 30 μm or less. The film thickness can be measured by methods such as a stylus-type step meter, a reflection spectrometer, an ellipsometer, or by observing the cross-section with an SEM or TEM, and any of these methods is acceptable. Such crystalline oxide films can be obtained by forming them using a mist CVD method with a mist CVD apparatus (film deposition apparatus).

[0082] (α-Ga2O3 membrane) A specific example of a crystalline oxide film is the α-Ga2O3 film. For example, the α-Ga2O3 film has a film thickness variation of 3.3% or less, and the number of particles on the film that can be observed with an optical microscope is 29 / cm². 2 The following applies:

[0083] Such an α-Ga2O3 film exhibits excellent film thickness distribution and suppresses the incorporation of foreign matter into the film, resulting in a high-quality film with significantly reduced particle density on the film surface, making it suitable for semiconductor device manufacturing. Since a small variation in film thickness is desirable, a lower limit of 0% is preferred. Also, since fewer particles on the film are desirable, a lower limit of 0 / cm² is preferred. 2 It is preferable.

[0084] For α-Ga2O3 films, it is preferable that the full width at half maximum of the (006) plane rocking curve obtained by X-ray diffraction is 8 seconds or less. Such an α-Ga2O3 film exhibits good crystallinity. Since a smaller full width at half maximum (FMAX) is desirable, the lower limit is greater than 0 seconds.

[0085] Furthermore, the α-Ga2O3 film is preferably 4 inches (100 mm) to 8 inches (200 mm) in diameter. Such an α-Ga2O3 film results in a significantly lower particle density on the film surface, even on large-area substrates, and thus produces a high-quality product.

[0086] (Formation of a buffer layer) A buffer layer may be provided between the substrate and the crystalline oxide film as appropriate. The method for forming the buffer layer is not particularly limited, and it can be formed by known methods such as sputtering and vapor deposition. However, when using the mist CVD method, it is convenient as it can be formed simply by appropriately changing the raw material solution. Specifically, one or more metals selected from aluminum, gallium, chromium, iron, indium, rhodium, vanadium, titanium, and iridium can be suitably used as the raw material aqueous solution by dissolving or dispersing them in water in the form of a complex or salt. Examples of complex forms include acetylacetonate complexes, carbonyl complexes, ammine complexes, and hydride complexes. Examples of salt forms include metal chloride salts, metal bromide salts, and metal iodide salts. Furthermore, solutions of the above metals dissolved in hydrobromic acid, hydrochloric acid, hydroiodic acid, etc., can also be used as the aqueous salt solution. In this case as well, the solute concentration is preferably 0.005 to 1 mol / L, and the dissolution temperature is preferably 20°C or higher. The buffer layer can be formed under other conditions in the same manner as described above. After depositing a buffer layer to a predetermined thickness, the film is deposited using the method described above.

[0087] In a special case of buffer layer formation, the same material as the crystalline oxide film may be used. In this case, the deposition temperature of the buffer layer may be higher than that of the crystalline oxide film. For example, the deposition temperature of the buffer layer may be 450°C and the deposition temperature of the crystalline oxide film may be 400°C, or the buffer layer may be 500°C and the crystalline oxide film 450°C. Doing so will further improve the crystallinity of the crystalline oxide film.

[0088] (Semiconductor device) Figure 2 is a schematic diagram showing an example of a semiconductor device using a multilayer structure containing a crystalline oxide film fabricated by the film deposition method and apparatus of the present invention. As shown in Figure 2, the semiconductor device 100 using a laminated structure containing a crystalline oxide film fabricated by the film deposition method and apparatus of the present invention has a laminated structure 110 in which a crystalline oxide film 103 is laminated on a substrate 101, and the crystalline oxide film 103 has a conductive thin film 103b laminated on an insulating thin film 103a. Furthermore, a gate insulating film 105 is formed on the conductive thin film 103b. A gate electrode 107 is formed on the gate insulating film 105. Moreover, source and drain electrodes 109 are formed on the conductive thin film 103b so as to sandwich the gate electrode 107. With this configuration, the depletion layer formed on the conductive thin film 103b can be controlled by the gate voltage applied to the gate electrode 107, enabling transistor operation (FET device).

[0089] This semiconductor device 100 can be used as a transistor such as MIS, HEMT, or IGBT, as well as a TFT, a Schottky barrier diode utilizing a semiconductor-metal junction, a PN or PIN diode combined with other P layers, and a light-emitting / receiving device. The crystalline oxide film deposited using the film deposition method and apparatus of the present invention can be a high-quality crystalline film, which can be useful in improving the characteristics of these devices.

[0090] (Second Embodiment of the Invention) The following describes a film deposition apparatus according to a second embodiment of the present invention. Figure 3 is a schematic diagram showing another example of the film deposition section of the film deposition apparatus of the present invention. As shown in Figure 3, the film deposition apparatus according to the second embodiment of the present invention has the same configuration as the film deposition apparatus according to the first embodiment of the present invention, except that the position of the air supply unit 501 has been changed from the ceiling to the side. This configuration also allows the gas from the air supply unit 501 to reduce the number of particles in the air within the film deposition unit, enabling the production of high-quality crystalline films.

[0091] (Third embodiment of the present invention) The following describes a film deposition apparatus according to a third embodiment of the present invention. Figure 4 is a schematic diagram showing yet another example of the film deposition section of the film deposition apparatus of the present invention. As shown in Figure 4, the film deposition apparatus according to the third embodiment of the present invention has the same configuration as the film deposition apparatus according to the first embodiment of the present invention, except that an exhaust section 511 is provided so as to surround the partition wall (film deposition chamber) 207, and exhaust is discharged from the partition wall (film deposition chamber) 207 through the exhaust section 511. This configuration also allows the gas from the air supply unit 501 to reduce the number of particles in the air within the film deposition unit, enabling the production of high-quality crystalline films. In particular, by creating positive pressure in the film deposition unit and negative pressure in the exhaust unit, the number of particles in the air within the film deposition unit can be further reduced.

[0092] (Fourth Embodiment of the Invention) The following describes a film deposition apparatus according to a fourth embodiment of the present invention. Figure 5 is a schematic diagram showing yet another example of the film deposition section of the film deposition apparatus of the present invention. As shown in Figure 5, the film deposition apparatus according to the fourth embodiment of the present invention has the same configuration as the film deposition apparatus according to the third embodiment of the present invention, except that the partition wall (film deposition chamber) 207 does not have a partition wall at the bottom and the bottom portion is a large exhaust port. This configuration also allows the gas from the air supply unit 501 to reduce the number of particles in the air within the film deposition unit, enabling the production of high-quality crystalline films. In particular, the large exhaust port further reduces the number of particles in the air within the film deposition unit.

[0093] (Fifth Embodiment of the Invention) The following describes a film deposition apparatus according to a fifth embodiment of the present invention. Figure 6 is a schematic diagram showing yet another example of the film deposition section of the film deposition apparatus of the present invention. As shown in Figure 6, the film deposition apparatus according to the fifth embodiment of the present invention has the same configuration as the film deposition apparatus according to the fourth embodiment of the present invention, except that the ceiling of the partition wall (film deposition chamber) 207 and the exhaust section 511 are shared. This configuration also allows the gas from the air supply unit 501 to reduce the number of particles in the air within the film deposition unit, enabling the production of high-quality crystalline films. [Examples]

[0094] The present invention will be described in detail below with reference to examples, but this is not intended to limit the present invention.

[0095] [Example 1] In the film deposition apparatus 201 shown in Figure 1, film deposition was performed within the partition wall (film deposition chamber) 207. The film deposition apparatus 201 includes a carrier gas source 202a for supplying carrier gas, a flow control valve 203a for adjusting the flow rate of carrier gas discharged from the carrier gas source 202a, a dilution carrier gas source 202b for supplying dilution carrier gas, a flow control valve 203b for adjusting the flow rate of dilution carrier gas discharged from the dilution carrier gas source 202b, a mist generator 204 containing the raw material solution 204a, a container 205 containing water 205a, and an ultrasonic transducer 206 attached to the bottom of the container 205.

[0096] The partition wall (film deposition chamber) 207 is equipped with a heater 208 and a quartz supply pipe 209 connecting the mist source 204 to the film deposition section 215. A fan (air supply section 501) is installed on the ceiling of the partition wall (film deposition chamber) 207, and clean air is supplied to the partition wall (film deposition chamber) 207 through a HEPA filter.

[0097] Using a Rion KC-31 particle counter, we measured the particles inside the partition (deposition chamber) 207 during air supply. The number of particles with a diameter of 0.3 μm was 12,830 / m². 3 That was the case.

[0098] (Deposition of gallium oxide film) A gallium oxide film was deposited using this apparatus. A 4-inch (100mm) chamfered sapphire substrate was prepared as substrate 210. The substrate was placed inside the partition wall (deposition chamber) 207, the heater 208 was set to 450°C, the temperature was raised, and it was left for 30 minutes to stabilize the temperature inside the partition wall (deposition chamber) 207, including the nozzle.

[0099] The raw material solution 204a used ultrapure water as the solvent and gallium bromide as the solute. The gallium concentration in the raw material solution was 0.1 mol / L. This raw material solution 204a was placed inside the mist generating source 204. Next, flow control valves 203a and 203b were opened to supply carrier gas from carrier gas sources 202a and 202b into the partition wall (deposition chamber) 207. After the atmosphere inside the partition wall (deposition chamber) 207 was sufficiently replaced with the carrier gas, the flow rate of the carrier gas was adjusted to 4 NL / min and the flow rate of the dilution carrier gas was adjusted to 6 NL / min. Nitrogen was used as the carrier gas.

[0100] Next, the ultrasonic transducer 206 was vibrated at 2.4 MHz, and the vibrations were propagated through water 205a to the raw material solution 204a, thereby atomizing the raw material solution 204a and generating a mist. This mist was introduced into the partition wall (deposition chamber) 207 via the supply pipe 209 using a carrier gas, and the mist was subjected to a thermal reaction on the substrate 210 to form a thin film of gallium oxide on the substrate 210. The deposition time was 30 minutes.

[0101] (evaluation) X-ray diffraction confirmed the formation of α-Ga2O3 in the thin film formed on substrate 210. When the rocking curve of the (006) plane of α-Ga2O3 was measured, the full width at half maximum was 8 seconds, indicating excellent crystallinity. For the rocking curve measurement, a four-crystal monochromator, consisting of two channel-cut crystals, was used to enhance the monochromaticity of the X-rays and achieve higher precision. Other measurement conditions are as follows: [Measurement conditions] Measurement device: Rigaku SmartLab Analysis conditions: Measurement method: Rocking curve measurement (ω scan) X-ray generation unit: Cathode Cu Output: 45kV 200mA Detection unit: Semiconductor detector Incident optical system: Ge(220) channel-cut monochromator Solar slit: Incident side — : Light receiving side 5.0° Slit: Incident side IS = 1 (mm) Length limit: 0.5 (mm) : Light receiving side RS1=1 RS2=1.1(mm) Scanning conditions: Evaluation diffraction surface Ga2O3(006) :scan axis ω Scanning mode, step measurement Scanning range: 18-22° Step width 0.005° Cumulative time: 0.5 sec. / step

[0102] Next, the film thickness was measured at 25 points using a Filmetrics F50 reflectance spectrometer, and the average film thickness was found to be 571 nm. Furthermore, the film thickness variation, calculated using the formula (maximum film thickness - minimum film thickness) / (maximum film thickness + minimum film thickness) × 100 (%), was a favorable 2.9%. Using an optical microscope, 69 points on the substrate surface were observed at 50x magnification to check for the presence or absence of particles on the film. No particles were found within the observed area. The particle density calculated from the observed area was 29 / cm³. 2 The results were as follows:

[0103] [Example 2] Except for using the partition wall (deposition chamber) 207 as shown in Figure 3, film deposition and evaluation were performed under the same conditions and methods as in Example 1.

[0104] [Example 3] Except for using the partition wall (deposition chamber) 207 as shown in Figure 4 and performing forced exhaust from the exhaust port 512, film deposition and evaluation were carried out under the same conditions and methods as in Example 1.

[0105] [Example 4] Except for using the partition wall (deposition chamber) 207 as shown in Figure 5, film deposition and evaluation were performed under the same conditions and methods as in Example 3.

[0106] [Example 5] Except for using the partition wall (deposition chamber) 207 as shown in Figure 6, film deposition and evaluation were performed under the same conditions and methods as in Example 3.

[0107] [Comparative Example] Except for not installing an air supply unit (fan) on the ceiling of partition wall (deposition chamber) 207 and therefore not supplying air, film deposition and evaluation were performed under the same conditions and methods as in Example 1.

[0108] Table 1 shows the evaluation results for Examples 1-5 and the comparative examples.

[0109] [Table 1]

[0110] As described above, Examples 1-5 of the present invention were able to reduce the amount of airborne particles compared to the comparative example. Consequently, it was observed that the amount of particles adhering to the film was drastically reduced. Furthermore, Examples 1-5 showed a smaller rocking curve full width at half maximum compared to the comparative example. This also indicated an improvement in crystallinity. We surmised that this was due to the suppression of foreign matter contamination into the film. Furthermore, an improvement was observed in the film thickness distribution. This is thought to be because the mist was appropriately dispersed on the substrate due to the supply of air into the deposition chamber.

[0111] This specification includes the following embodiments: [1]: A method for forming a crystalline oxide film by mist CVD, wherein mist is supplied to a heated substrate along with a carrier gas within a film-forming section covered by a partition wall, characterized in that a gas other than the carrier gas is supplied to the film-forming section at least while the substrate is being heated. [2]: When mist is not supplied, the particle density of 0.3 μm particles in the film deposition area is 100,000 / m 3 The film formation method described in [1] above, characterized in that it is as follows: [3]: The method for forming a film according to [1] or [2] above, characterized in that air is used as a gas other than the carrier gas. [4]: A method for forming a crystalline oxide film by mist CVD, wherein mist is supplied to a heated substrate along with a carrier gas within a film formation section covered by a partition wall, At least when mist is not supplied, the particle density in the film-forming section with a particle size of 0.3 μm or larger is 100,000 / m³. 3 A film formation method characterized by the following: [5]: A film formation method according to any one of [1] to [4] above, characterized in that an exhaust section is provided so as to surround the film formation section, and exhaust is discharged from the film formation section through the exhaust section. [6]: The film formation method according to [5] above, characterized in that the exhaust flow rate discharged from the exhaust section is greater than the flow rate of the carrier gas. [7]: The film deposition method according to any one of [1] to [6] above, characterized in that the substrate has a diameter of 4 inches (100 mm) to 8 inches (200 mm). [8]: A film deposition apparatus comprising a film deposition section covered by a partition wall, a carrier gas supply section, and a misting section for generating mist, wherein mist is supplied to the film deposition section along with a carrier gas to perform film deposition, the film deposition section is provided with an air supply section for supplying gases other than the carrier gas. [9]: The film deposition apparatus according to [8] above, characterized in that a filter is provided in the air supply section.

[10] : The film deposition apparatus according to [8] or [9] above, characterized in that an exhaust section is provided so as to surround the film deposition section, and exhaust is discharged from the film deposition section via the exhaust section.

[11] : The film deposition apparatus according to any one of [8] to

[10] above, characterized in that the air supply unit supplies air as a gas other than the carrier gas.

[12] : Film thickness variation is 3.3% or less, and the number of particles on the film visible under an optical microscope is 29 / cm². 2 An α-Ga2O3 film characterized by the following:

[13] : The α-Ga2O3 film according to

[12] above, characterized in that the full width at half maximum of the rocking curve of the (006) plane obtained by X-ray diffraction is 8 arcseconds or less.

[14] : An α-Ga2O3 film according to either

[12] or

[13] above, characterized in that it has a diameter of 4 inches (100 mm) to 8 inches (200 mm).

[0112] It should be noted that the present invention is not limited to the embodiments described above. The embodiments described above are illustrative, and any configuration that is substantially identical to the technical idea described in the claims of the present invention and achieves similar effects is included within the technical scope of the present invention.

Claims

1. A method for forming a crystalline oxide film by mist CVD, wherein mist is supplied to a heated substrate along with a carrier gas within a film-forming section covered by a partition wall, A film deposition method characterized in that, at least while the substrate is being heated, a gas other than the carrier gas is supplied into the film deposition section from a separate air supply section from the supply pipe that supplies mist together with the carrier gas.

2. When mist is not supplied, the particle density in the film-forming section with a particle size of 0.3 μm or larger is 100,000 / m². ３ The film formation method according to claim 1, characterized in that it is as follows.

3. The method for forming a film according to claim 1, characterized in that air is used as a gas other than the carrier gas.

4. The film formation method according to claim 1, characterized in that an exhaust section is provided so as to surround the film formation section, and exhaust is discharged from the film formation section through the exhaust section.

5. The film formation method according to claim 4, characterized in that the exhaust flow rate discharged from the exhaust section is greater than the flow rate of the carrier gas.

6. The film deposition method according to any one of claims 1 to 5, characterized in that the substrate has a diameter of 4 inches (100 mm) to 8 inches (200 mm).

7. A film deposition apparatus comprising a film deposition section covered by a partition wall, a carrier gas supply section, and a misting section for generating mist, wherein mist is supplied to the film deposition section along with the carrier gas to perform film deposition, and the film deposition section is provided with an air supply section for supplying gases other than the carrier gas.

8. The film forming apparatus according to claim 7, characterized in that a filter is provided in the air supply section.

9. The film-forming apparatus according to claim 7, characterized in that an exhaust section is provided so as to surround the film-forming section, and exhaust is discharged from the film-forming section through the exhaust section.

10. The film deposition apparatus according to any one of claims 7 to 9, characterized in that the air supply unit supplies air as a gas other than the carrier gas.

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