Amorphous metal oxide film, method for forming the same, and laminate

Abstract

To provide an amorphous metal oxide film, a method for forming the same, and a laminate, ensuring industrial usefulness and superior quality.SOLUTION: An amorphous metal oxide film contains gallium as a main metal component and an absorption edge derived from a transmittance spectrum is 280 nm or less. A method for forming an amorphous metal oxide film comprises forming an amorphous metal oxide film containing gallium as a main metal component on a quartz substrate by a mist CVD method. A laminate includes at least a quartz substrate and an amorphous metal oxide film containing gallium as a main metal component.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to an amorphous metal oxide film, a method for forming the same, and a laminate thereof. [Background technology]

[0002] As examples of conventional amorphous metal oxide films, methods for forming the films, and laminates thereof, for example, Patent Document 1 discloses a photodiode using amorphous gallium oxide formed by sputtering, and Patent Document 2 discloses an ultraviolet sensor using a gallium oxide layer obtained by a sol-gel method. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2017-28103 [Patent Document 2] Japanese Patent Application Laid-Open No. 2008-282881 Summary of the Invention [Problem to be solved by the invention]

[0004] Although the sputtering method is simple, there are problems with the quality of the films obtained. For example, UV sensors using this method have problems such as poor sensitivity to UV rays, large leakage current when not irradiated, and high resistance. Furthermore, the sol-gel method has a problem in that the film formation speed is very slow and it is not suitable for industrial use.

[0005] The present invention has been made to solve the above problems, and an object of the present invention is to provide an industrially useful and high-quality amorphous metal oxide film, a method for forming the film, and a laminate thereof. [Means for solving the problem]

[0006] The present invention has been made to achieve the above-mentioned object, and provides an amorphous metal oxide film containing gallium as a main metal component, characterized in that the absorption edge obtained from the transmittance spectrum is 280 nm or less.

[0007] Such amorphous metal oxide films have good film quality and are industrially useful. Therefore, when applied to semiconductor devices, they have excellent semiconductor properties. They also have excellent surface smoothness. In particular, when applied to optical systems, they have excellent optical properties. For example, when used in optical sensors such as ultraviolet sensors or optical devices such as photodiodes, improved sensitivity and reduced loss can be expected.

[0008] Furthermore, the amorphous metal oxide film preferably has an absorption coefficient of 40000 / cm or less when the incident light wavelength is 280 nm.

[0009] Such an amorphous metal oxide film improves the sensitivity, particularly when used in an optical device.

[0010] Furthermore, the amorphous metal oxide film preferably has a surface root mean square roughness (RMS) of 5 nm or less.

[0011] Such an amorphous metal oxide film has excellent surface smoothness, and improves stability when an electrode is formed, for example.

[0012] The present invention also provides a method for forming an amorphous metal oxide film, which comprises forming an amorphous metal oxide film containing gallium as a main metal component on a quartz substrate by a mist CVD method.

[0013] The amorphous metal oxide films obtained by this film formation method have good film quality and are industrially useful. Therefore, when applied to semiconductor devices, they have excellent semiconductor properties. They also have excellent surface smoothness. In particular, when applied to optical systems, they have excellent optical properties. For example, when used in optical sensors such as ultraviolet sensors or optical devices such as photodiodes, improved sensitivity and reduced loss can be expected.

[0014] Furthermore, with this type of film formation method, the mist CVD method has a high film formation speed, and is expected to improve productivity.

[0015] In addition, in the mist CVD method, it is preferable that a raw material solution containing at least gallium and acetylacetone is misted to generate mist, and the mist is heated on the quartz substrate to form an amorphous metal oxide film containing gallium as a main metal component.

[0016] By using such a film formation method, an oxide film having excellent semiconductor properties and excellent surface smoothness can be obtained more reliably.

[0017] It is also preferable that the quartz crystal substrate is immersed in an aqueous solution containing at least hydrogen fluoride, and then the film is formed by the mist CVD method.

[0018] By using such a film forming method, it is possible to more reliably obtain an oxide film having excellent semiconductor properties and excellent surface smoothness.

[0019] The present invention also provides a laminate comprising at least a quartz substrate and an amorphous metal oxide film containing gallium as a main metal component.

[0020] Such a laminate is of good quality and industrially useful. Therefore, when applied to a semiconductor device, it will have excellent semiconductor properties. It will also have excellent surface smoothness. In particular, when applied to an optical system, it will have excellent optical properties. For example, when used in optical devices such as optical sensors (e.g., ultraviolet sensors) or photodiodes, it is expected to improve sensitivity and reduce loss.

[0021] Furthermore, the amorphous metal oxide film preferably has an absorption edge of 280 nm or less as determined from a transmittance spectrum.

[0022] Such a laminated body will have better semiconductor properties when applied to a semiconductor device.

[0023] The amorphous metal oxide film of the laminate preferably has an absorption coefficient of 40000 / cm or less when incident light has a wavelength of 280 nm.

[0024] Such a laminate improves the sensitivity when used in an optical device.

[0025] The amorphous metal oxide film of the laminate preferably has a surface root mean square roughness (RMS) of 5 nm or less.

[0026] Such a laminate will have improved stability when an electrode is formed, and will also have excellent surface smoothness. [Effects of the Invention]

[0027] As described above, the amorphous metal oxide film of the present invention has good film quality and is industrially useful. Therefore, when applied to semiconductor devices, it exhibits excellent semiconductor properties. It also exhibits excellent surface smoothness. In particular, when applied to optical systems, it exhibits excellent optical properties. For example, when used in optical sensors such as ultraviolet sensors or optical devices such as photodiodes, it is expected to improve sensitivity and reduce loss.

[0028] Furthermore, the amorphous metal oxide film deposition method of the present invention can easily deposit the above-described amorphous metal oxide film. Furthermore, with such a film deposition method, the mist CVD method has a high film deposition rate, and is expected to improve productivity.

[0029] Furthermore, the laminate of the present invention is of good quality and industrially useful. Therefore, when applied as a laminate to a semiconductor device, the laminate exhibits excellent semiconductor properties. Furthermore, the laminate also exhibits excellent surface smoothness. In particular, when applied as a laminate to an optical system, the laminate exhibits excellent optical properties. For example, when used in optical devices such as optical sensors (e.g., ultraviolet sensors) or photodiodes, improved sensitivity and reduced loss can be expected. [Brief explanation of the drawings]

[0030] [Figure 1] 1 is a schematic diagram showing an example of a semiconductor device using a laminate including an amorphous metal oxide film according to the present invention. [Figure 2] FIG. 1 is a schematic diagram showing an example of a film-forming apparatus (mist CVD apparatus) that can be suitably used to form a laminate including an amorphous metal oxide film according to the present invention. [Figure 3] FIG. 2 is a diagram illustrating an example of a mist-generating unit used in the present invention. [Figure 4] 1 is a schematic diagram showing an example of a semiconductor device using a laminate including an amorphous metal oxide film according to the present invention. [Figure 5] FIG. 1 is a schematic diagram showing another example of a film formation apparatus (mist CVD apparatus) that can be suitably used to form a laminate including an amorphous metal oxide film according to the present invention. [Figure 6] FIG. 1 is a diagram showing an example of the results of XRD analysis of a laminate including an amorphous metal oxide film according to the present invention. [Figure 7] FIG. 1 is a diagram showing an example of the transmittance spectrum of a laminate including an amorphous metal oxide film according to the present invention. [Figure 8] FIG. 1 is a diagram analyzing the absorption edge of a stack including an amorphous metal oxide film according to the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0031] The present invention will be described in detail below, but the present invention is not limited thereto.

[0032] As described above, there has been a demand for industrially useful, high-quality amorphous metal oxide films.

[0033] As a result of extensive research into the above-mentioned problems, the present inventors have found that when an amorphous metal oxide film containing gallium as a main metal component and characterized in that the absorption edge obtained from the transmittance spectrum is 280 nm or less, is applied to a semiconductor device, the film exhibits excellent semiconductor properties, and have completed the present invention.

[0034] Hereinafter, a detailed description will be given with reference to the drawings.

[0035] (oxide film) The oxide film according to the present invention is composed primarily of gallium. Generally, metal oxide films are composed of metal and oxygen, but the amorphous metal oxide film according to the present invention only needs to contain gallium as the metal. In the present invention, "containing gallium as the metal main component" means that 50 to 100% of the metal components is gallium. Metal components other than gallium may include, for example, one or more metals selected from iron, indium, aluminum, vanadium, titanium, chromium, rhodium, iridium, nickel, and cobalt. The film composition can be analyzed by known methods such as EDX and SIMS.

[0036] The amorphous metal oxide film may contain a dopant element. Examples of the dopant include, but are not limited to, n-type dopants such as tin, germanium, silicon, titanium, zirconium, vanadium, and niobium, and p-type dopants such as copper, silver, iridium, rhodium, magnesium, cobalt, and nickel. The dopant concentration is, for example, about 1×10 16 / cm3 ~1×10 22 / cm 3 may be about 1 x 10 17 / cm 3 Even at a low concentration of less than 1 × 10 20 / cm 3 A concentration higher than this may be used.

[0037] The thickness of the amorphous metal oxide film is not particularly limited, but is preferably 150 nm or more. There is no particular upper limit. For example, it may be 100 μm or less, preferably 50 μm or less, and more preferably 20 μm or less.

[0038] There is no particular limit to the size of the amorphous metal oxide film, but the surface area must be less than 100 mm 2 If the diameter is 2 inches (50 mm) or more, a large-area film with good crystallinity can be obtained, which is preferable.

[0039] The crystal structure of an amorphous metal oxide film is amorphous, which can be determined by the absence of peaks derived from crystals in X-ray diffraction.

[0040] The amorphous metal oxide film according to the present invention further has an absorption edge of 280 nm or less obtained from the transmittance spectrum. The absorption edge is calculated as follows: The transmittance spectrum is measured using a spectrophotometer, and the transmittance is converted to an absorption coefficient α from the film thickness. The vertical axis is (αhν), where h is the Planck constant and ν is the frequency of incident light. 2 After converting the horizontal axis to hν, a straight line is fitted to the portion where absorption begins, and the value where this line intersects with the horizontal axis is obtained. Although not particularly limited, the lower limit of the absorption edge can be set to 230 nm. If the lower limit of the absorption edge is 230 nm or more, crystallization of the metal oxide film can be effectively suppressed, and the desired characteristics can be reliably obtained. It is also possible to modulate the absorption edge by forming a solid solution of gallium oxide and an oxide of a metal other than gallium.

[0041] The amorphous metal oxide film according to the present invention preferably has an absorption coefficient of 40,000 / cm or less at an incident light wavelength of 280 nm. This corresponds to a sharp increase in transmittance at wavelengths longer than the absorption edge. This increases the light absorption sensitivity at specific wavelengths, making it suitable for use in optical sensors and the like. Although not particularly limited, the lower limit of the absorption coefficient can be set to 0.04 / cm. If the lower limit of the absorption coefficient is 0.04 / cm or more, it can be made to be approximately the same as the light absorption that occurs to a certain extent due to the absorption of free carriers.

[0042] The amorphous metal oxide film of the present invention preferably has a surface root mean square roughness (RMS) of 5 nm or less. This contributes to uniform current when an electrode is formed on the film surface and to improved sensitivity when used as an optical sensor. Although not particularly limited, the lower limit of the RMS can be 0.1 nm. If the lower limit of the RMS is 0.1 nm or more, it can be made approximately the same as the RMS of the substrate.

[0043] (Laminate) The amorphous metal oxide film may form a laminate with the base substrate directly or via another layer.

[0044] The base substrate in the laminate according to the present invention is a quartz substrate. Quartz is crystalline silicon oxide, and in the present invention, it may be either single crystal or polycrystalline.

[0045] Although not particularly limited, the thickness of the base substrate (quartz crystal substrate) 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.

[0046] The substrate may be pretreated before film formation. For example, the substrate may be heat-treated at a high temperature of 600 to 1200°C in an air or nitrogen atmosphere. While not particularly limited, the heat treatment time is preferably 5 minutes to 3 hours. This modifies the substrate surface, facilitating film growth and improving surface roughness. Another pretreatment method is a chemical method. For example, the substrate is immersed in an aqueous solution containing at least sulfuric acid, hydrochloric acid, hydrogen fluoride, aqueous ammonia, or the like. The concentration is determined appropriately, but may be 1 to 50% or the like. Furthermore, hydrogen peroxide solution may be mixed with these solutions to promote surface modification. Although not particularly limited, the immersion time may be 1 to 60 minutes or the like. Alternatively, the surface may be modified by irradiation with ultraviolet light, for example, light having a wavelength of 254 nm or 220 nm.

[0047] Another layer may be interposed between the substrate and the oxide film. The other layer, which has a different composition from the substrate and the outermost oxide film, is also called a buffer layer. The buffer layer may be any of a crystalline oxide film, an amorphous oxide film, a semiconductor film, an insulating film, a metal film, etc., and examples of suitable materials include Al2O3, Ga2O3, Cr2O3, Fe2O3, In2O3, Rh2O3, V2O3, Ti2O3, and Ir2O3, or solid solutions thereof may also be used. The thickness of the buffer layer is not particularly limited, but is preferably 0.1 μm to 2 μm.

[0048] (Configuration example of semiconductor device) 1, an oxide film (amorphous metal oxide film) 103 is formed on a base substrate (quartz substrate) 101. The oxide film 103 is configured by laminating an insulating thin film 103a and a conductive thin film 103b in this order from the base substrate 101 side. The base substrate 101 and the oxide film 103 together form a laminate 110.

[0049] 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. Furthermore, source-drain electrodes 109 are formed on the conductive thin film 103b so as to sandwich the gate electrode 107. With this configuration, it is possible to control the depletion layer formed in the conductive thin film 103b by applying a gate voltage to the gate electrode 107, thereby enabling transistor operation (FET device).

[0050] Other examples of semiconductor devices formed using the amorphous metal oxide film of the present invention include transistors and TFTs such as MIS, HEMT, and IGBT, Schottky barrier diodes using semiconductor-metal junctions, PN or PIN diodes combined with other P layers, and light-emitting and receiving elements. The amorphous metal oxide film of the present invention is useful for improving the characteristics of these devices.

[0051] FIG. 4 shows a photodetector 400 as an example of a semiconductor device. It is composed of an oxide film (amorphous metal oxide film) 403, which serves as an active layer, and an electrode 409 on a base substrate (quartz substrate) 401. The oxide film 403 can be the amorphous metal oxide film of the present invention. When a voltage of about 10 V is applied between the electrodes, the resistance of the oxide film 403 decreases when light with a wavelength shorter than the absorption edge is incident, and the presence or absence of light can be detected as a change in current.

[0052] The oxide film (amorphous metal oxide film) and laminated body described above can be formed by known methods such as vapor deposition, MBE, sputtering, CVD, mist CVD, and liquid phase epitaxy.

[0053] The following describes a method for producing an oxide film (amorphous metal oxide film) and a laminate according to the present invention using the mist CVD method. Here, the term "mist" as used in the present invention refers to a general term for fine particles of liquid dispersed in a gas, and includes what is called fog, droplets, etc.

[0054] (Film forming equipment) 2 shows an example of a film formation apparatus 201 used in the mist CVD method. The film formation apparatus 201 has at least a mist-forming unit 220 that generates mist by turning a raw material solution 204a into mist, a carrier gas supply unit 230 that supplies a carrier gas that transports the mist, a supply pipe 209 that connects the mist-forming unit 220 and a film formation chamber 207 and through which the mist is transported by the carrier gas, and the film formation chamber 207 that heat-treats the mist supplied from the supply pipe 209 together with the carrier gas to form a film on a base substrate (quartz substrate) 210.

[0055] (Mist generating section) The mist generating section 220 generates mist by turning the raw solution 204a into mist. The mist generating means is not particularly limited as long as it can turn the raw solution 204a into mist, and any known mist generating means may be used, but it is more preferable to use a mist generating means that uses ultrasonic vibrations, as this allows for more stable mist generation.

[0056] An example of such a mist-generating unit 220 is shown in FIG. 3. The mist-generating unit 220 may include a mist source 204 that contains raw solution 204a, a container 205 that contains a medium capable of transmitting ultrasonic vibrations, such as water 205a, and an ultrasonic vibrator 206 attached to the bottom of the container 205. Specifically, the mist source 204, which is a container that contains raw solution 204a, is housed in the container 205 that contains water 205a using a support (not shown). The bottom of the container 205 may be equipped with an ultrasonic vibrator 206, or the ultrasonic vibrator 206 may be connected to an oscillator 216. When the oscillator 216 is activated, the ultrasonic vibrator 206 vibrates, and ultrasonic waves propagate through the water 205a into the mist source 204, turning the raw solution 204a into mist.

[0057] (Raw material solution) The raw material solution 204a contains gallium and may contain any material, inorganic or organic, as long as it can be formed into a mist. Other than gallium, metals or metal compounds are preferably used, including, for example, one or more metals selected from iron, indium, aluminum, vanadium, titanium, chromium, rhodium, nickel, and cobalt. The raw material solution may be a solution in which a metal is dissolved or dispersed in an organic solvent or water in the form of a complex or salt. Examples of salts include halide salts such as metal chlorides, metal bromides, and metal iodides. Furthermore, solutions in which the above metals are dissolved in hydrogen halides such as hydrobromic acid, hydrochloric acid, and hydroiodic acid can also be used. Examples of complexes include acetylacetonate complexes, carbonyl complexes, ammine complexes, and hydride complexes. Acetylacetonate complexes can also be formed by mixing acetylacetone with the aforementioned salt solutions, which is also preferred. The metal concentration in the raw material solution 204a is not particularly limited, and can be set to 0.005 to 1 mol / L, etc. Although not particularly limited, the temperature during mixing and dissolution is preferably 20° C. or higher.

[0058] The raw material solution may contain additives such as hydrohalic acid and oxidizing agents. Examples of hydrohalic acids include hydrobromic acid, hydrochloric acid, and hydroiodic acid, with hydrobromic acid and hydroiodic acid being preferred. Examples of oxidizing agents include peroxides such as hydrogen peroxide (HO), sodium peroxide (NaO), barium peroxide (BaO), and benzoyl peroxide (CHCO)O, as well as hypochlorous acid (HClO), perchloric acid, nitric acid, ozone water, and organic peroxides such as peracetic acid and nitrobenzene.

[0059] The raw material solution may contain a dopant. The dopant is not particularly limited. Examples include n-type dopants such as tin, germanium, silicon, titanium, zirconium, vanadium, and niobium, and p-type dopants such as copper, silver, iridium, rhodium, magnesium, cobalt, and nickel. As the dopant, a metal such as the above in the form of a complex or salt dissolved or dispersed in an organic solvent or water can be suitably used.

[0060] (Carrier gas supply unit) 2, the carrier gas supply unit 230 has a carrier gas source 202a that supplies a carrier gas. In this case, a flow rate control valve 203a for adjusting the flow rate of the carrier gas sent out from the carrier gas source 202a may be provided. In addition, if necessary, a dilution carrier gas source 202b for supplying a dilution carrier gas and a flow rate control valve 203b for adjusting the flow rate of the dilution carrier gas sent out from the dilution carrier gas source 202b may also be provided.

[0061] The type of carrier gas is not particularly limited and can be selected appropriately depending on the film to be formed. Examples include inert gases such as oxygen, ozone, nitrogen, and argon, and reducing gases such as hydrogen gas and forming gas. The type of carrier gas may be one or more. For example, a dilution gas obtained by diluting the same gas as the first carrier gas with another gas (e.g., 10 times dilution) may be used as the second carrier gas, or air may be used. The flow rate of the carrier gas is not particularly limited. For example, when forming a film on a substrate with a diameter of 2 inches (approximately 50 mm), the flow rate of the carrier gas is preferably 0.05 to 50 NL / min, and more preferably 5 to 20 NL / min. NL represents the volume converted to standard conditions (0°C, 1 atmosphere).

[0062] (supply pipe) The film forming apparatus 201 has a supply pipe 209 that connects the mist generating unit 220 and the film forming chamber 207. In this case, mist is carried by a carrier gas from the mist generating source 204 of the mist generating unit 220 through the supply pipe 209 and supplied into the film forming chamber 207. The supply pipe 209 is not particularly limited, and may be, for example, a quartz tube, a glass tube, or a resin tube.

[0063] (Film forming chamber) A base substrate 210 is placed in the film formation chamber 207, and a heater 208 for heating the base substrate 210 may be provided. The heater 208 may be provided outside the film formation chamber 207 as shown in FIG. 2, or may be provided inside the film formation chamber 207. The mist supplied from the supply pipe 209 passes through piping inside the film formation chamber 207 and is ejected from a nozzle toward the base substrate 210 together with the carrier gas. The film formation chamber 207 may also be provided with an exhaust gas outlet 212 at a position that does not affect the supply of mist to the base substrate 210. The base substrate 210 may be placed face-down, for example, on the top surface of the film formation chamber 207, or may be placed face-up, for example, on the bottom surface of the film formation chamber 207.

[0064] Another example of a film formation apparatus used in the mist CVD method is shown in Figure 5. Film formation apparatus 501 has at least mist-forming section 520 that generates mist by turning raw material solution 504a into mist, supply pipe 509 that connects mist-forming section 520 to film formation chamber 507 and through which the mist is transported by a carrier gas, and film formation chamber 507 that heat-treats the mist supplied from supply pipe 509 together with the carrier gas to form a film on base substrate (quartz substrate) 510.

[0065] (Film forming method) The mist CVD method roughly comprises a mist generation process in which a raw material solution containing gallium is turned into mist in a mist generation section to generate mist; a carrier gas supply process in which a carrier gas for transporting the mist is supplied to the mist generation section; a transport process in which the mist is transported from the mist generation section to the film formation chamber by the carrier gas via a supply pipe connecting the mist generation section to the film formation chamber; and a film formation process in which the transported mist is heat-treated to form a film on a base substrate (quartz substrate).

[0066] 2, first, the raw material solution 204a mixed as described above is placed in the mist generating source 204, a base substrate 210 is placed in the film formation chamber 207, and a heater 208 is activated. Next, flow rate control valves 203a and 203b are opened to supply carrier gas from carrier gas sources 202a and 202b into the film formation chamber 207, and after the atmosphere in the film formation chamber 207 is sufficiently replaced with the carrier gas, the flow rates of the carrier gas and the dilution carrier gas are each adjusted.

[0067] Next, in the mist generating step, the ultrasonic vibrator 206 is vibrated, and the vibration is propagated to the raw material solution 204a through the water 205a, thereby turning the raw material solution 204a into mist and generating the mist.

[0068] Next, in the carrier gas supply step, a carrier gas for transporting the mist is supplied to the mist-forming section 220.

[0069] Next, in the transport step, the mist is transported by a carrier gas from the mist-generating section 220 to the film-forming chamber 207 via the supply pipe 209 connecting the mist-generating section 220 and the film-forming chamber 207.

[0070] Next, in the film-forming step, the mist transported to the film-forming chamber 207 is heated on the base substrate 210 to cause a thermal reaction, thereby forming a film on a part or the entire surface of the base substrate 210 .

[0071] The thermal reaction may be carried out under any of the following atmospheres: vacuum, non-oxygen atmosphere, reducing gas atmosphere, air atmosphere, and oxygen atmosphere, and may be appropriately set depending on the film to be formed. The reaction pressure may be atmospheric pressure, elevated pressure, or reduced pressure, but film formation under atmospheric pressure is preferred because it simplifies the device configuration.

[0072] (Buffer layer formation) As described above, a buffer layer may be appropriately provided between the substrate and the amorphous metal oxide film. The buffer layer can be formed by any known method, such as sputtering or vapor deposition. However, the mist CVD method described above allows for easy formation by simply changing the source solution. Specifically, a source aqueous solution can be suitably used in which one 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 a complex or salt. Examples of complexes include acetylacetonate complexes, carbonyl complexes, ammine complexes, and hydride complexes. Examples of salts include metal chlorides, metal bromides, and metal iodides. Furthermore, solutions of the above metals in hydrobromic acid, hydrochloric acid, hydroiodic acid, etc. can also be used as salt aqueous solutions. In this case, although not particularly limited, 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 the same conditions as above, although other conditions are not particularly limited. After the buffer layer is formed to a predetermined thickness, film formation is performed by the method described above.

[0073] (Heat treatment) The amorphous metal oxide film or laminate according to the present invention may be heat-treated at, but is not limited to, 200 to 600°C. This further removes unreacted species in the film, resulting in a higher quality amorphous metal oxide film or laminate. The heat treatment may be performed in air, an oxygen atmosphere, or an inert gas atmosphere such as nitrogen or argon, but is not limited to this. The heat treatment time can be determined appropriately, but may be, for example, 5 to 240 minutes.

[0074] (peeling) In the laminate according to the present invention, the amorphous metal oxide film may be peeled off from the base substrate (quartz crystal substrate). The peeling means is not particularly limited and may be any 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 ultrasonic waves, and peeling by etching. By such peeling, the amorphous metal oxide film can be obtained as a free-standing film. [Example]

[0075] The present invention will be specifically explained below with reference to examples, but the present invention is not limited to these examples.

[0076] [Example 1] A film forming apparatus 501 used in this example will be described with reference to Fig. 5. The film forming apparatus 501 includes a mist generating source 504 containing a raw material solution 504a, a container 505 containing water 505a, an ultrasonic vibrator 506 attached to the bottom of the container 505, a film forming chamber 507 equipped with a heater 508, and a quartz supply pipe 509 connecting the mist generating source 504 to the film forming chamber 507.

[0077] (Gallium oxide film formation) A 10 mm square c-plane quartz crystal substrate was prepared as the base substrate (quartz crystal substrate) 510. This quartz crystal substrate 510 was immersed in a 15% hydrogen fluoride aqueous solution for 1 minute, then rinsed with pure water and dried. This substrate was placed in the film formation chamber 507, and the heater 508 was heated to 450°C and left for 30 minutes to stabilize the temperature inside the film formation chamber, including the nozzle.

[0078] The raw material solution 504a had ultrapure water as the solvent and gallium chloride and acetylacetone as the solutes. Gallium chloride was prepared by dissolving metallic gallium in hydrochloric acid. An equimolar mixture of acetylacetone and ammonia was mixed with this aqueous gallium chloride solution. The gallium concentration in the raw material solution was 0.02 mol / L, and the acetylacetone concentration was 0.06 mol / L. This raw material solution 504a was placed in the mist generation source 504. Next, the flow rate of the carrier gas was adjusted to 0.4 NL / min, and the flow rate of the dilution carrier gas was adjusted to 0.8 NL / min. Nitrogen was used as the carrier gas, and oxygen was used as the dilution carrier gas.

[0079] Next, ultrasonic vibrator 506 was vibrated at 2.4 MHz, and the vibrations were propagated through water 505a to raw material solution 504a, thereby misting raw material solution 504a to generate mist. This mist was introduced into film formation chamber 507 via supply pipe 509 using a carrier gas, and the mist was heated on quartz crystal substrate 510 to cause a thermal reaction, thereby forming a thin film of gallium oxide (amorphous metal oxide film) on quartz crystal substrate 510. The film formation time was 60 minutes.

[0080] (evaluation) The film thickness of the thin film formed on the quartz substrate 510 was measured using an optical interference film thickness meter, and was found to be 270 nm, with a refractive index of 1.84. X-ray diffraction was then performed. The results are shown in Figure 6. No peaks other than those of the substrate were observed, indicating that the thin film was amorphous gallium oxide (amorphous metal oxide film).

[0081] Next, the transmittance spectrum of the resulting laminated structure was measured using a JASCO V-770 spectrophotometer. The results are shown in Figure 7. When converted to an absorption coefficient using the film thickness, the absorption coefficient at an incident light wavelength of 280 nm was 11,000 / cm. The absorption edge was analyzed using the obtained results, and the results are shown in Figure 8. The absorption edge was 256 nm. In addition, the root-mean-square surface roughness (RMS) was evaluated using an AFM and was found to be 0.3 nm.

[0082] [Example 2] Film formation and evaluation were carried out under the same conditions as in Example 1, except that the solute in the raw material solution 504a was 0.02 mol / L gallium iodide. X-ray diffraction confirmed that an amorphous gallium oxide film (amorphous metal oxide film) was obtained. The film thickness was 277 nm, and the refractive index was 1.86. The absorption coefficient at an incident light wavelength of 280 nm was 31000 / cm. The absorption edge was 253 nm. The RMS was 3.3 nm.

[0083] [Example 3] Film formation and evaluation were carried out under the same conditions as in Example 1, except that the quartz crystal substrate 510 was not pretreated with hydrogen fluoride. X-ray diffraction confirmed that an amorphous gallium oxide film (amorphous metal oxide film) was obtained. The film thickness was 274 nm and the refractive index was 1.84. The absorption coefficient at an incident light wavelength of 280 nm was 32000 / cm. The absorption edge was 254 nm. The RMS was 1.8 nm.

[0084] [Example 4] The quartz crystal substrate 510 was irradiated with ultraviolet light containing light with a wavelength of 254 nm for 30 minutes to modify the surface. Other than this, film formation and evaluation were carried out under the same conditions as in Example 1. X-ray diffraction confirmed that an amorphous gallium oxide film (amorphous metal oxide film) was obtained. The film thickness was 271 nm and the refractive index was 1.85. The absorption coefficient at an incident light wavelength of 280 nm was 21,000 / cm. The absorption edge was 277 nm. The RMS was 3.3 nm.

[0085] [Comparative Example] Film formation was carried out under the same conditions as in Example 1, except that a glass substrate was used as the substrate, but no film grew on the substrate.

[0086] As described above, in all of Examples 1 to 4 of the present invention, the absorption edge obtained from the transmittance spectrum was 280 nm or less, the absorption coefficient at an incident light wavelength of 280 nm was 40,000 / cm or less, and the root mean square roughness (RMS) of the surface was 5 nm or less, so that an industrially useful film was formed that was of good quality, and the film could be formed in a short time of 60 minutes by using the mist CVD method.

[0087] Therefore, when the above-mentioned embodiment is applied to a semiconductor device, the semiconductor characteristics are excellent. The surface smoothness is also excellent. In particular, when applied to an optical system, the optical characteristics are excellent. For example, when used in optical sensors such as UV sensors or optical devices such as photodiodes, improved sensitivity and reduced loss can be expected. Furthermore, the mist CVD method has a fast film formation speed, and improved productivity can be expected.

[0088] The present specification includes the following aspects. [1]: An amorphous metal oxide film containing gallium as the main metal component, characterized in that the absorption edge obtained from the transmittance spectrum is 280 nm or less. [2]: The amorphous metal oxide film according to [1] above, characterized in that the absorption coefficient at an incident light wavelength of 280 nm is 40,000 / cm or less. [3]: The amorphous metal oxide film according to [1] or [2] above, characterized in that the root mean square roughness (RMS) of the surface is 5 nm or less. [4]: A method for forming an amorphous metal oxide film, characterized in that an amorphous metal oxide film containing gallium as a main metal component is formed on a quartz substrate by a mist CVD method. [5]: The method for forming an amorphous metal oxide film according to [4] above, wherein in the mist CVD method, a raw material solution containing at least gallium and acetylacetone is misted to generate mist, and the mist is heated on the quartz substrate to form an amorphous metal oxide film containing gallium as a main metal component. [6]: The method for forming an amorphous metal oxide film according to [4] or [5] above, characterized in that the quartz crystal substrate is immersed in an aqueous solution containing at least hydrogen fluoride, and then the film is formed by the mist CVD method. [7]: A laminate comprising at least a quartz substrate and an amorphous metal oxide film containing gallium as a main metal component. [8]: The laminate according to the above [7], wherein the amorphous metal oxide film has an absorption edge of 280 nm or less obtained from a transmittance spectrum. [9]: The laminate according to [7] or [8] above, wherein the amorphous metal oxide film has an absorption coefficient of 40,000 / cm or less at an incident light wavelength of 280 nm.

[10] : The laminate according to any one of [7] to [9] above, wherein the amorphous metal oxide film has a surface root mean square roughness (RMS) of 5 nm or less.

[0089] The present invention is not limited to the above-described embodiments. The above-described embodiments are merely examples, and anything that has substantially the same configuration as the technical idea described in the claims of the present invention and that exhibits similar effects is included within the technical scope of the present invention. [Explanation of symbols]

[0090] 100...semiconductor device, 101...underlying substrate (quartz crystal substrate), 103... oxide film (amorphous metal oxide film), 103a... insulating thin film, 103b...conductive thin film, 105...gate insulating film, 107...gate electrode, 109...source / drain electrode, 110...laminated body, 201...film forming apparatus, 202a...carrier gas source; 202b...dilution carrier gas source; 203a...flow rate control valve, 203b...flow rate control valve, 204...mist generation source, 204a...raw material solution, 205...container, 205a...water, 206...ultrasonic vibrator, 207...film formation chamber, 208...heater, 209...supply pipe, 210... base substrate (quartz crystal substrate), 212... exhaust port, 220... mist generating unit, 216...oscillator, 230...carrier gas supply unit, 400...light receiving element (semiconductor device), 401...underlying substrate (quartz crystal substrate), 403...Oxide film (amorphous metal oxide film), 409...Electrode, 501...film forming apparatus, 504...mist generating source, 504a...raw material solution, 505...container, 505a...water, 506...ultrasonic vibrator, 507...film forming chamber, 508... heater, 509... supply pipe, 510... base substrate (quartz substrate), 520...Mist generation section.

Claims

1. An amorphous metal oxide film containing gallium as a main metal component, characterized in that the absorption edge obtained from the transmittance spectrum is 280 nm or less.

2. 2. The amorphous metal oxide film according to claim 1, wherein the absorption coefficient at an incident light wavelength of 280 nm is 40,000 / cm or less.

3. 3. The amorphous metal oxide film according to claim 1, wherein the root mean square roughness (RMS) of the surface is 5 nm or less.

4. A method for forming an amorphous metal oxide film, comprising forming an amorphous metal oxide film containing gallium as a main metal component on a quartz substrate by a mist CVD method.

5. 5. The method for forming an amorphous metal oxide film according to claim 4, wherein in the mist CVD method, a raw material solution containing at least gallium and acetylacetone is misted to generate mist, and the mist is heated on the quartz substrate to form an amorphous metal oxide film containing gallium as a main metal component.

6. 6. The method for forming an amorphous metal oxide film according to claim 4, wherein the film is formed by the mist CVD method after the quartz substrate is immersed in an aqueous solution containing at least hydrogen fluoride.

7. A laminate comprising at least a quartz substrate and an amorphous metal oxide film containing gallium as a main metal component.

8. 8. The laminate according to claim 7, wherein the amorphous metal oxide film has an absorption edge obtained from a transmittance spectrum of 280 nm or less.

9. 9. The laminate according to claim 8, wherein the amorphous metal oxide film has an absorption coefficient of 40,000 / cm or less when incident light has a wavelength of 280 nm.

10. 10. The laminate according to claim 7, wherein the amorphous metal oxide film has a surface with a root mean square (RMS) roughness of 5 nm or less.

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