JP7313530B2 - Deposition method - Google Patents

Description

The present invention relates to a film forming method for forming a film on a substrate using mist-like raw materials.

Conventionally, pulsed laser deposition (PLD), molecular beam epitaxy (MBE), sputtering, and other high-vacuum film deposition apparatuses capable of achieving a non-equilibrium state have been developed. In addition, a mist chemical vapor deposition (Mist CVD) method for growing crystals on a substrate using an atomized mist-like raw material (hereinafter also referred to as "mist CVD method") has been developed, making it possible to produce gallium oxide (α-Ga ₂ O ₃ ) having a corundum structure. As a semiconductor with a large bandgap, α-Ga ₂ O ₃ is expected to be applied to next-generation switching elements capable of achieving high withstand voltage, low loss and high heat resistance.

As a method for forming a film of α-Ga ₂ O ₃ using water fine particles such as the mist CVD method, Patent Document 1 discloses that a gallium compound such as gallium acetylacetonate or gallium chloride and a tin (II) compound such as tin (II) chloride are dissolved in a solution containing water, hydrochloric acid, and hydrogen peroxide to prepare a raw material solution, and the raw material solution is atomized to generate raw fine particles. discloses a method of forming a highly crystalline gallium oxide-based thin film on a sample to be deposited by forming a thin film on a sample.

JP 2013-028480 A JP 2015-199649 A

According to the method of Patent Document 1, an α-Ga ₂ O ₃ thin film with excellent conductivity can be formed, but there is a unique problem that the film surface is not smooth, and it is still unsatisfactory for use in semiconductor devices. In order to smoothen the surface of the film, it may be possible to perform a surface treatment such as etching.

On the other hand, Patent Document 2 discloses that a film having excellent surface smoothness can be obtained by mixing hydrobromic acid or hydroiodic acid in the raw material solution. However, according to this method, substances other than gallium and oxygen are included in the film, which causes a problem that the crystallinity and electrical characteristics of the film are impaired. In addition, since the solution becomes a strong acid, there is also a problem that corrosion of the film forming apparatus is accelerated.

SUMMARY OF THE INVENTION It is an object of the present invention to solve the above-mentioned problems, and to provide a film forming method capable of forming a film with less impurities and excellent crystallinity and surface flatness.

In order to solve the above problems, in the present invention,
a step of preparing a raw material solution;
a mist generation step of misting the raw material solution in a misting unit to generate mist;
a carrier gas supplying step of supplying a carrier gas for transporting the mist to the misting section;
a conveying step of conveying the mist from the mist generating unit to the film forming chamber using the carrier gas through a supply pipe connecting the mist generating unit and the film forming chamber;
and a film forming step of heat-treating the conveyed mist to form a film on a substrate,
In the step of preparing the raw material solution,
A method for forming a film is provided, wherein the raw material solution is prepared by mixing a metal chloride salt or an aqueous solution thereof with hydrogen peroxide, or the raw material solution is prepared by dissolving a metal in a mixed solution of hydrochloric acid and hydrogen peroxide.

According to such a film forming method, it is possible to form a film having excellent surface flatness, few impurities in the film, and excellent crystallinity.

It is preferable that the amount of the hydrogen peroxide used in the step of preparing the raw material solution is 0.2 times or more in molar ratio with respect to the amount of chlorine atoms contained in the chloride salt or the amount of chlorine atoms contained in the hydrochloric acid.

As a result, the reaction efficiency of the raw material solution can be increased, and as a result, impurities in the film can be reduced, and a film with excellent crystallinity and surface flatness can be obtained.

In the step of preparing the raw material solution, it is preferable to prepare the raw material solution at a liquid temperature of 15 to 90°C.

As a result, the reaction efficiency of the raw material solution can be increased, and as a result, impurities in the film can be reduced, and a film with excellent crystallinity and surface flatness can be obtained.

As the metal, one containing gallium as a main component may be used.

This makes it possible to obtain a gallium oxide film with less impurities in the film and excellent crystallinity and surface flatness.

As described above, according to the film forming method of the present invention, it is possible to form a film containing few impurities and excellent in crystallinity and surface flatness. When a semiconductor film is formed by the film forming method of the present invention, the formed film has few impurities in the film and is excellent in crystallinity and surface flatness, and thus can exhibit excellent semiconductor characteristics.

1 is a schematic configuration diagram showing an example of a film forming apparatus that can be used in the film forming method of the present invention; FIG. It is a figure explaining an example of the misting part which can be used with the film-forming method of this invention.

As described above, in the mist CVD method, there has been a demand for the development of a film formation method capable of forming a film with less impurities in the film and with excellent crystallinity and surface flatness.

As a result of intensive studies on the above problems, the inventors of the present invention prepared a raw material solution by mixing a metal chloride salt or its aqueous solution with hydrogen peroxide, or dissolving a metal in a mixed solution of hydrochloric acid and hydrogen peroxide to prepare a raw material solution. The present invention was completed by finding that

That is, the present invention comprises a step of preparing a raw material solution;
a mist generation step of misting the raw material solution in a misting unit to generate mist;
a carrier gas supplying step of supplying a carrier gas for transporting the mist to the misting section;
a conveying step of conveying the mist from the mist generating unit to the film forming chamber using the carrier gas through a supply pipe connecting the mist generating unit and the film forming chamber;
and a film forming step of heat-treating the conveyed mist to form a film on a substrate,
In the step of preparing the raw material solution,
The method for forming a film is characterized in that the raw material solution is prepared by mixing a metal chloride salt or an aqueous solution thereof with hydrogen peroxide, or the raw material solution is prepared by dissolving a metal in a mixed solution of hydrochloric acid and hydrogen peroxide.

Although the present invention will be described in detail below, the present invention is not limited thereto.

The term "mist" as used in the present invention is a general term for fine particles of liquid dispersed in gas, and includes what is called fog, liquid droplets, and the like.

(Deposition device)
First, an example of a film forming apparatus capable of carrying out the film forming method according to the present invention will be described with reference to FIGS. 1 and 2. FIG. However, the film forming method according to the present invention can also be carried out in a film forming apparatus other than the film forming apparatus shown in FIGS.

The film forming apparatus 101 shown in FIG. 1 has at least a misting unit 120 that mists a raw material solution 104a to generate mist, a carrier gas supply unit 130 that supplies a carrier gas for transporting the mist, a supply pipe 109 that connects the misting unit 120 and the film formation chamber 107 and conveys the mist by the carrier gas, and a film formation chamber 107 that heats the mist supplied together with the carrier gas from the supply pipe 109 and forms a film on the substrate 110.

Each component of the film forming apparatus 101 will be described below.

(Misting part)
The mist generating unit 120 mists the raw material solution 104a to generate mist. The misting means is not particularly limited as long as it can mist the raw material solution 104a, and may be a known misting means, but it is preferable to use a misting means using ultrasonic vibration. This is because mist can be made more stably.

An example of such a mist generating unit 120 will be described with reference to FIG. 2 as well. For example, the mist generation unit 120 may include a mist generation source 104 containing a raw material solution 104a, a container 105 containing a medium capable of transmitting ultrasonic vibrations, such as water 105a, and an ultrasonic transducer 106 attached to the bottom surface of the container 105. Specifically, the mist generation source 104, which is a container containing the raw material solution 104a, can be accommodated in the container 105 containing the water 105a using a support (not shown). An ultrasonic transducer 106 may be provided at the bottom of the container 105, and the ultrasonic transducer 106 and the oscillator 116 may be connected. When the oscillator 116 is operated, the ultrasonic vibrator 106 vibrates, ultrasonic waves propagate into the mist generation source 104 through the water 105a, and the raw material solution 104a becomes mist.

Details of the raw material solution 104a will be described later.

(Carrier gas supply unit)
The carrier gas supply unit 130 shown in FIG. 1 has a carrier gas source 102 a that supplies carrier gas to the mist generation source 104 and a supply pipe 111 a that fluidly connects the carrier gas source 102 a and the mist generation source 104 . The supply pipe 111a may include a flow control valve 103a for adjusting the flow rate of the carrier gas delivered from the carrier gas source 102a to the mist generation source 104. In addition, the carrier gas supply unit 130 can also include a carrier gas source 102b for dilution that supplies the carrier gas for dilution to the supply pipe 9, a supply pipe 111b that fluidly connects the carrier gas source 102b for dilution and the supply pipe 9, and a flow control valve 103b for adjusting the flow rate of the carrier gas for dilution sent from the carrier gas source 102b for dilution, as shown in FIG.

The type of carrier gas is not particularly limited, and can be appropriately selected according to the film to be deposited. Examples thereof include oxygen, ozone, inert gases such as nitrogen and argon, and reducing gases such as hydrogen gas and forming gas. Also, the number of carrier gases may be one, or two or more. For example, as the second carrier gas, a diluent 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 flow rate of carrier gas is not particularly limited. For example, when forming a film on a 30 mm square substrate, the flow rate of the carrier gas (when using a carrier gas for dilution, the sum of the flow rate of the carrier gas and the flow rate of the carrier gas for dilution) is preferably 0.01 to 20 L / min, more preferably 1 to 10 L / min.

(supply pipe)
The film forming apparatus 101 has a supply pipe 109 that connects the misting section 120 and the film forming chamber 107 . In this case, the mist is transported by the carrier gas from the mist generation source 104 of the mist generator 120 through the supply pipe 109 and supplied into the film forming chamber 107 . A quartz tube, a glass tube, a resin tube, or the like can be used as the supply tube 109, for example.

(Deposition chamber)
The film formation chamber 107 is configured such that the substrate 110 can be placed therein. In the film formation chamber 107, the substrate 110 may be placed face down, for example, on the upper surface of the film formation chamber 107, or, as shown in FIG.

The deposition chamber 107 can be equipped with a heater 108 for heating the substrate 110 . The heater 108 may be provided outside the film forming chamber 107 as shown in FIG. 1 or may be provided inside the film forming chamber 107 . Further, the deposition chamber 107 may be provided with an exhaust port 112 for exhaust gas at a position that does not affect the supply of mist to the substrate 110 .

(Film formation method)
Next, the film-forming method of this invention is demonstrated.

The film forming method of the present invention is
a step of preparing a raw material solution;
a mist generation step of misting the raw material solution in a misting unit to generate mist;
a carrier gas supplying step of supplying a carrier gas for transporting the mist to the misting section;
a conveying step of conveying the mist from the mist generating unit to the film forming chamber using the carrier gas through a supply pipe connecting the mist generating unit and the film forming chamber;
and a film forming step of heat-treating the transported mist to form a film on the substrate.

Further, in the film forming method of the present invention, in the step of preparing the raw material solution,
(1) The raw material solution is prepared by mixing a metal chloride salt or an aqueous solution thereof with hydrogen peroxide, or (2) The raw material solution is prepared by dissolving a metal in a mixed solution of hydrochloric acid and hydrogen peroxide.

By performing film formation by the mist CVD method as described above using the raw material solution prepared in this manner, impurities in the film are reduced, and a film exhibiting excellent crystallinity and excellent surface flatness can be formed. While not wishing to be bound by theory, we believe the reasons are as follows.

Hydrogen peroxide oxidizes chloride ions in the source solution to chlorine gas. The generated chlorine gas scatters as gas during solution preparation or film formation, and does not remain in the film. By reducing the chlorine concentration in the film in this way, the surface flatness of the resulting film is improved. In addition, since hydrogen peroxide is composed of hydrogen and oxygen, and only becomes water after the reaction, even if hydrogen peroxide exists excessively and remains unreacted, there is no particular problem with the properties of the film produced, particularly with regard to crystallinity. Therefore, by forming a film by the mist CVD method using the raw material solution prepared as described above, impurities in the film are reduced, and a film exhibiting excellent crystallinity and excellent surface flatness can be obtained. In particular, when a semiconductor film is formed, the obtained film can exhibit excellent crystallinity, and thus can exhibit excellent semiconductor characteristics.

On the other hand, in the above-mentioned Patent Document 2, since the raw material solution contains components other than the components of the target film, impurities are introduced into the film, and a film showing sufficiently excellent crystallinity cannot be obtained.

In addition, although the detailed reason is unknown, as in Patent Document 1, when a raw material solution prepared by dissolving a gallium compound such as gallium chloride in a solution containing water, hydrochloric acid, and hydrogen peroxide is used, as described above, there is a unique problem that the film surface is not smooth. This point will be described later as a comparative example.

The process of preparing the raw material solution will be described in more detail below.

(1) Mixing a metal chloride salt or an aqueous solution thereof with hydrogen peroxide When using a metal chloride salt, the solvent for the raw material solution is not particularly limited, but water is preferred.

As the metal chloride salt, one containing a metal required for the film to be formed can be used. For example, one or more salts selected from gallium chloride, iron chloride, indium chloride, aluminum chloride, vanadium chloride, titanium chloride, chromium chloride, rhodium chloride, nickel chloride, and cobalt chloride can be used.

For example, by using a metal containing gallium as a main component in the chloride salt, it is possible to obtain a gallium oxide film with few impurities in the film and excellent crystallinity and surface flatness.

The amount of hydrogen peroxide to be mixed with the metal chloride salt or its aqueous solution is not particularly limited, but since the stoichiometric ratio of hydrogen peroxide and chloride ions in the reaction between hydrogen peroxide and chloride ions in the raw material solution is 1:2, the molar ratio is preferably at least 0.5 times the amount of chlorine atoms contained in the chloride salt. As a result, the chloride ions in the raw material solution can be sufficiently oxidized, and the reaction efficiency of the raw material solution can be enhanced. As a result, impurities in the film are reduced, and a film having excellent crystallinity and surface flatness can be obtained.

(2) In the case of dissolving a metal in a mixed solution of hydrochloric acid and hydrogen peroxide As the metal, one containing the metal required for the film to be formed can be used. For example, one containing one or more metals selected from gallium, iron, indium, aluminum, vanadium, titanium, chromium, rhodium, nickel and cobalt can be used.

For example, by using a metal containing gallium as a main component, it is possible to obtain a gallium oxide film with few impurities in the film and excellent crystallinity and surface flatness.

The concentration of hydrochloric acid is not particularly limited as long as the metal can be dissolved, but it is preferably 2 to 4 times the metal concentration in terms of molar ratio.

By setting the hydrochloric acid concentration to such a value, the metal can be sufficiently dissolved, the acid concentration of the raw material solution to be prepared can be suppressed, and corrosion of the film forming apparatus can be suppressed.

The amount of hydrogen peroxide to be mixed with hydrochloric acid is not particularly limited, but since the stoichiometric ratio of hydrogen peroxide and chloride ions in the reaction between hydrogen peroxide and chloride ions in the raw material solution is 1:2, the molar ratio is preferably at least 0.5 times the amount of chlorine atoms contained in hydrochloric acid. As a result, the chloride ions in the raw material solution can be sufficiently oxidized, and the reaction efficiency of the raw material solution can be enhanced. As a result, impurities in the film are reduced, and a film having excellent crystallinity and surface flatness can be obtained.

In the preparation of any of the raw material solutions of (1) and (2) above, the metal concentration in the raw material solution is not particularly limited, and may be 0.005 to 1 mol/L.

Moreover, in the preparation of the raw material solution of (1) or (2) above, it is preferable to prepare the raw material solution at a liquid temperature of 15 to 90°C.

As a result, the reaction efficiency of the raw material solution can be increased, and as a result, impurities in the film can be reduced, and a film with excellent crystallinity and surface flatness can be obtained.

Furthermore, the raw material solution may contain a dopant. A means for adding the dopant is not particularly limited. Further, the dopant is not particularly limited, and examples thereof include n-type dopants such as tin, germanium, silicon, titanium, zirconium, vanadium, and niobium, and p-type dopants such as copper, silver, iridium, and rhodium.

In the film forming method of the present invention, even if the raw material solution contains a dopant, a film having excellent surface flatness can be formed.

The substrate that can be used in the film forming method of the present invention is not particularly limited as long as it can form a film and can support a film, and a known substrate can be used, and it may be an organic compound or an inorganic compound. Examples 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, lithium tantalate, potassium tantalate, and gallium oxide. Although the thickness of the substrate is not particularly limited, it is preferably 10 to 2000 μm, more preferably 50 to 800 μm.

The size of the substrate is not particularly limited. Substrate areas of 100 mm ² or more can be used, and substrates with diameters of 2-8 inches (50-200 mm) or more can be used.

Next, an example of the film forming method according to the present invention will be described below with reference to FIGS. 1 and 2. FIG.

First, the raw material solution 104a prepared as described above is placed in the mist generation source 104, the substrate 110 is placed in the film forming chamber 107, and the heater 108 is activated. Next, the flow control valves 103a and 103b are opened to supply the carrier gas and the carrier gas for dilution from the carrier gas sources 102a and 102b into the deposition chamber 107 via the supply pipes 111a and 111b, the upper space of the mist generation source 104, and the supply pipe 109. After sufficiently replacing the atmosphere in the film forming chamber 107 with the carrier gas and the carrier gas for dilution, the flow rates of the carrier gas and the carrier gas for dilution are respectively adjusted.

Next, in the mist generating step, the ultrasonic vibrator 106 is vibrated in the mist generator 120, and the vibration is propagated to the raw material solution 104a through the water 105a, thereby misting the raw material solution 104a to generate mist.

Next, as a carrier gas supply step, a carrier gas for transporting mist is supplied to the mist generating section 120 .

Next, as a transport step, the mist is transported from the mist generating unit 120 to the film forming chamber 107 via the supply pipe 109 that connects the mist generating unit 120 and the film forming chamber 107 with a carrier gas.

Next, as a film forming process, the mist transported to the film forming chamber 107 is heated to cause a thermal reaction, thereby forming a film on part or all of the surface of the substrate 110 .

The thermal reaction is not particularly limited as long as the mist reacts by heating. It can be appropriately set according to the raw material and the target film-forming product. For example, the heating temperature can be in the range of 120-600°C, preferably in the range of 200-600°C, more preferably in the range of 300-550°C.

The thermal reaction may be carried out under vacuum, under a non-oxygen atmosphere, under a reducing gas atmosphere, under an air atmosphere, or under an oxygen atmosphere. In addition, the reaction pressure may be under atmospheric pressure, under increased pressure or under reduced pressure, but film formation under atmospheric pressure is preferable because the apparatus configuration can be simplified.

For the reason described in detail above, the film forming method described above makes it possible to release the chlorine in the raw material solution to the outside of the system as a gas, thereby reducing the chlorine concentration in the film. Thereby, the surface flatness is improved and the crystallinity is excellent. When a semiconductor film is formed, a film that can exhibit excellent semiconductor characteristics is obtained. Furthermore, corrosion of the device is suppressed because it is not necessary to use a strong acid.

The film forming method of the present invention can take various aspects. Examples thereof are shown below, but the present invention is not limited to these embodiments.

(Formation of buffer layer)
In the above film formation, a buffer layer may be appropriately provided between the substrate and the film. _As materials for the buffer layer _{, Al2O3 , Ga2O3} , _{Cr2O3 , Fe2O3 , In2O3} , _{Rh2O3 , V2O3 , Ti2O3 , Ir2O3} and the _like are preferably used. The method of forming the buffer layer is not particularly limited, and it can be formed by a known method such as a sputtering method or a vapor deposition method. Specifically, one or two or more metals selected from aluminum, gallium, chromium, iron, indium, rhodium, vanadium, titanium, and iridium are dissolved or dispersed in water in the form of complexes or salts. Examples of forms of the complex include acetylacetonate complexes, carbonyl complexes, ammine complexes, hydride complexes, and the like. Salt forms include, for example, metal chloride salts, metal bromide salts, and metal iodide salts. In addition, a solution obtained by dissolving the above metal in hydrobromic acid, hydrochloric acid, hydroiodic acid, or the like can also be used as an aqueous salt solution. The solute concentration is preferably 0.005 to 1 mol/L. Hydrogen peroxide may also be mixed. The buffer layer can also be formed under the same conditions as above. After forming the buffer layer to a predetermined thickness, film formation can be performed by the film forming method of the present invention. The thickness of the buffer layer is preferably 0.1 μm to 2 μm.

(Heat treatment)
Also, the film obtained by the film forming method according to the present invention may be heat-treated at 200 to 600.degree. As a result, unreacted species and the like in the film are removed, and a higher quality laminated structure can be obtained. The heat treatment may be performed in air, in an oxygen atmosphere, or in an inert gas atmosphere such as nitrogen or argon. The heat treatment time is appropriately determined, and can be, for example, 5 to 240 minutes.

EXAMPLES The present invention will be specifically described below using Examples and Comparative Examples, but the present invention is not limited to these.

(Example 1)
A film forming apparatus 101 used in this example will be described with reference to FIG. The film forming apparatus 101 includes a carrier gas source 102a for supplying a carrier gas, a flow rate control valve 103a for adjusting the flow rate of the carrier gas sent from the carrier gas source 102a, a dilution carrier gas source 102b for supplying a dilution carrier gas, a flow rate adjustment valve 103b for adjusting the flow rate of the dilution carrier gas sent from the dilution carrier gas source 102b, a mist generation source 104 containing a raw material solution 104a, and water 105a. an ultrasonic oscillator 106 attached to the bottom surface of the container 105; a film formation chamber 107 equipped with a heater 108; a quartz supply pipe 109 connecting the mist generation source 104 to the film formation chamber 107; a supply pipe 111a connecting the carrier gas source 102a and the mist generation source 104; . The flow control valve 103a is provided on the supply pipe 111a. The flow control valve 103b is provided on the supply pipe 111b.

(substrate)
As the substrate 110, a square c-plane sapphire substrate cut into 3 cm sides was placed in the film formation chamber 107, and the heater 108 was operated to raise the temperature to 500.degree.

(raw material solution)
A 0.1 mol/L aqueous solution of gallium chloride was prepared as a starting solution. Hydrogen peroxide water was mixed into this so that the molar ratio of the chlorine atom concentration and the hydrogen peroxide concentration was 2:1. This was used as the raw material solution 104a. The liquid temperature during mixing was room temperature (approximately 25° C.).

(deposition)
The raw material solution 104 a obtained as described above was accommodated in the mist generation source 104 . Subsequently, the flow control valves 103a and 103b were opened to supply the carrier gas and the carrier gas for dilution from the carrier gas sources 102a and 102b into the deposition chamber 107 via the supply pipes 111a and 111b, the upper space of the mist generation source 104, and the supply pipe 109. After sufficiently replacing the atmosphere in the film forming chamber 107 with the carrier gas and the carrier gas for dilution, the flow rate of the carrier gas and the carrier gas for dilution were adjusted to 1 L/min and 24 L/min, respectively. Nitrogen was used as the carrier gas. Nitrogen was used as the carrier gas for dilution.

Next, the ultrasonic vibrator 106 was oscillated at 2.4 MHz, and the vibration was propagated to the raw material solution 104a through the water 105a, thereby misting the raw material solution 104a to generate mist. This mist was introduced into the film formation chamber 107 through the supply pipe 109 by the carrier gas. Then, a thin film of gallium oxide (α-Ga ₂ O ₃ ) was formed on the substrate 110 by thermally reacting the mist in the film forming chamber 107 under the conditions of 500° C. under atmospheric pressure. The film formation time was 30 minutes.

(evaluation)
The thin film formed on the substrate 110 was measured using an interferometric film thickness meter F-50 manufactured by FILMETRICS. The average film thickness was calculated using 9 in-plane points on the substrate 110 as measurement points. Also, using an X-ray diffractometer, the rocking curve half width (FWHM) of the α-Ga ₂ O ₃ (006) peak was measured to evaluate the crystallinity. Surface roughness was measured using an atomic force microscope (AFM) and evaluated by arithmetic mean roughness Ra.

(Example 2)
In Example 2, films were formed in the same manner as in Example 1 except for the process of preparing the raw material solution, and the obtained films were evaluated.

In Example 2, a mixed solution of hydrochloric acid and hydrogen peroxide was mixed with metal gallium and dissolved therein, and this was used as the raw material solution. Metallic gallium was adjusted to a concentration of 0.1 mol/L, hydrochloric acid was adjusted to a molar ratio of 3 times that of gallium, and hydrogen peroxide was adjusted to a molar ratio of 1.5 times that of gallium. Other conditions were the same as in Example 1.

(Example 3)
In Example 3, the raw material solution was prepared while adjusting the temperature at which the raw material solution was mixed to 10°C. Other than this, film formation was performed in the same manner as in Example 1, and the resulting film was evaluated.

(Example 4)
In Example 4, a film was formed in the same manner as in Example 1 except for the process of preparing the raw material solution.

In Example 4, aluminum chloride was used instead of gallium chloride. Other conditions were the same as in Example 1.

In Example 4, a thin film of α-Al ₂ O ₃ was formed using the raw material solution thus prepared. Crystallinity was evaluated in the same manner as in Example 1, except that the rocking curve half width of the α-Al ₂ O ₃ (006) peak was evaluated.

(Example 5)
In Example 5, a film was formed in the same manner as in Example 1 except for the preparation of the raw material solution, and the obtained film was evaluated.

In Example 5, the raw material solution was prepared by mixing so that the molar ratio of the chlorine atom concentration and the hydrogen peroxide concentration was 10:1. Other conditions were the same as in Example 1.

(Comparative example 1)
In Comparative Example 1, a film was formed in the same manner as in Example 1 except for the process of preparing the raw material solution, and the obtained film was evaluated.

In Comparative Example 1, a raw material solution was prepared without mixing hydrogen peroxide. That is, a 0.1 mol/L aqueous solution of gallium chloride was used as the starting solution.

The conditions and results of Examples 1-5 and Comparative Example 1 are shown in Table 1 below.

As is clear from Table 1, the films obtained in Examples 1 to 5 of the present invention all have extremely small half widths and excellent crystallinity, compared to the films obtained in Comparative Example 1 in which an aqueous gallium chloride solution was used as a raw material solution without mixing hydrogen peroxide. Moreover, it can be seen that the films obtained in Examples 1 to 5 of the present invention had smaller surface roughness Ra and superior surface smoothness than the film obtained in Comparative Example 1.

In addition, the films obtained in Examples 1 to 5 of the present invention were subjected to composition analysis by secondary ion mass spectrometry (SIMS). The films obtained in Examples 1 to 3 and 5 had a chlorine content of 1×10 ¹⁶ /cm ³ or less. The film obtained in Example 4 had a chlorine content of 1×10 ¹⁶ /cm ³ . Thus, the films obtained in Examples 1 to 5 of the present invention had extremely low impurities in the film.

(Comparative example 2)
In Comparative Example 2, a film was formed in the same manner as in Example 1 except for the process of preparing the raw material solution, and the obtained film was evaluated.

In Comparative Example 2, a raw material solution was prepared by mixing a solution containing water, hydrochloric acid, and hydrogen peroxide with gallium chloride at room temperature (approximately 25° C.). At the time of preparation, hydrochloric acid was mixed in a molar ratio of 3 times that of gallium chloride, and hydrogen peroxide was mixed in a molar ratio of 1.5 times that of gallium chloride. Other conditions were the same as in Example 1.

The film obtained in Comparative Example 2 had a surface roughness Ra of 125 nm, which was larger than the films obtained in Examples 1-5.

In addition, this invention is not limited to the said embodiment. The above embodiment is an example, and any device having substantially the same configuration as the technical idea described in the claims of the present invention and having similar effects is included in the technical scope of the present invention.

DESCRIPTION OF SYMBOLS 101... Film-forming apparatus 102a... Carrier gas source 102b... Carrier gas source for dilution 103a... Flow control valve 103b... Flow control valve 104... Mist generation source 104a... Raw material solution 105... Container 105a... Water 106... Ultrasonic vibrator 107... Film-forming chamber 108... Heater 109, 111a and 111b ... supply pipe, 110 ... substrate, 116 ... oscillator, 112 ... exhaust port, 120 ... misting section, 130 ... carrier gas supply section.

Claims (3)

a step of preparing a raw material solution;
a mist generation step of misting the raw material solution in a misting unit to generate mist;
a carrier gas supplying step of supplying a carrier gas for transporting the mist to the misting section;
a conveying step of conveying the mist from the mist generating unit to the film forming chamber using the carrier gas through a supply pipe connecting the mist generating unit and the film forming chamber;
and a film forming step of heat-treating the conveyed mist to form a film on a substrate,
In the step of preparing the raw material solution,
A film forming method comprising: preparing the raw material solution by mixing an aqueous solution containing gallium chloride or aluminum chloride as a main component and hydrogen peroxide; or preparing the raw material solution by dissolving a metal containing gallium as a main component in a mixed solution of hydrochloric acid and hydrogen peroxide. 2. The film forming method according to claim 1, wherein the amount of hydrogen peroxide used in the step of preparing the raw material solution is 0.1 times or more in molar ratio with respect to the amount of chlorine atoms contained in the chloride salt or the amount of chlorine atoms contained in the hydrochloric acid. 3. The film forming method according to claim 1, wherein in the step of preparing the raw material solution, the raw material solution is prepared at a liquid temperature of 15 to 90.degree.

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