Film forming method and film forming apparatus

Abstract

The present invention is a film-forming method for forming a crystalline oxide film composed mainly of gallium oxide on a substrate by mist CVD. The film-forming method includes a step for heating the substrate, a step for heating a nozzle for supplying a mist containing a raw material solution, and a step for supplying the mist over the heated substrate so that the direction of discharge of the heated nozzle will be the perpendicular direction to the surface of the substrate to form a crystalline oxide film. The step for heating the nozzle involves heating the nozzle in a state where the substrate is not present in the direction of discharge of the nozzle. The step for forming the crystalline oxide film involves forming the film in a state where the substrate is present in the direction of discharge of the nozzle. Provided thereby are: a crystalline oxide film composed mainly of gallium oxide that has excellent crystallinity and a favorable in-plane film thickness distribution even with large surface areas and thin film thicknesses; a film-forming method for forming this crystalline oxide film; and a film-forming device for performing this film-forming method.

Description

[Technical Field]

[0001] The present invention relates to a film forming method, a film forming apparatus, and a crystalline oxide film. [Background technology]

[0002] Semiconductor devices using gallium oxide (Ga2O3), which has a large band gap, are attracting attention as next-generation switching elements that can achieve high voltage resistance, low loss, and high heat resistance, and are expected to be applied to power semiconductor devices such as inverters. Furthermore, due to its wide band gap, gallium oxide is also expected to be used in a wide range of light-emitting and receiving devices such as LEDs and sensors. In particular, among gallium oxides, α-Ga2O3 and the like, which have a corundum structure, can control the band gap by forming mixed crystals with indium and aluminum, individually or in combination, and constitute an extremely attractive material family as InAlGaO-based semiconductors. Here, InAlGaO-based semiconductors are defined as those containing In X Al Y Ga Z O3 (0≦X≦2, 0≦Y≦2, 0≦Z≦2, X+Y+Z=1.5~2.5), and can be viewed as the same material family containing gallium oxide.

[0003] However, since the most stable phase of gallium oxide is the β-gallium structure, it is difficult to form a crystalline film with a corundum structure, which is a metastable phase, unless a special film formation method is used. For example, the crystal growth conditions are often restricted in heteroepitaxial growth, etc., which tends to result in a high dislocation density. In addition, there are still many challenges not only in the formation of corundum structure crystalline films, but also in improving the film formation rate and crystal quality, suppressing cracks and abnormal growth, suppressing twins, and cracking of the substrate due to warping. Under these circumstances, several studies are currently being conducted on the formation of crystalline semiconductors with a corundum structure.

[0004] Patent Document 1 describes a method for producing an oxide crystal thin film by mist CVD using gallium or indium bromide or iodide. Patent Documents 2 to 4 describe a multilayer structure in which a semiconductor layer having a corundum crystal structure and an insulating film having a corundum crystal structure are stacked on a base substrate having a corundum crystal structure. Furthermore, as described in Patent Documents 5 to 7, film formation by mist CVD using an ELO substrate or void formation has also been investigated.

[0005] Patent Document 8 describes the formation of a gallium oxide film having a corundum structure by halide vapor phase epitaxy (HVPE) using at least a gallium source and an oxygen source. Patent Document 9 also describes the formation of a gallium oxide film having a corundum structure by ELO crystal growth using a patterned substrate, with a surface area of ​​9 μm 2 or more, and the transition density is 5×10 6 cm -2 It is described that the following crystalline films are obtained: [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Patent No. 5397794 [Patent Document 2] Patent No. 5343224 [Patent Document 3] Patent No. 5397795 [Patent Document 4] Japanese Patent Application Laid-Open No. 2014-072533 [Patent Document 5] Japanese Patent Application Laid-Open No. 2016-100592 [Patent Document 6] Japanese Patent Application Laid-Open No. 2016-098166 [Patent Document 7] Japanese Patent Application Laid-Open No. 2016-100593 [Patent Document 8] Japanese Patent Application Laid-Open No. 2016-155714 [Patent Document 9] Japanese Patent Application Publication No. 2019-034883 [Patent Document 10] International Publication No. 2021 / 065940 Summary of the Invention [Problem to be solved by the invention]

[0007] However, gallium oxide has a problem with heat dissipation, and to solve the heat dissipation problem, it is necessary to thin the gallium oxide film to, for example, 30 μm or less. However, this requires a complicated polishing process, which increases costs. In addition, when thinning the film by polishing, it is difficult to obtain a large-area gallium oxide film while maintaining the film thickness distribution. Furthermore, the series resistance when applied to vertical devices is not fully satisfactory. Therefore, in order to fully utilize the performance of gallium oxide as a power semiconductor device, it is desirable to obtain a thin gallium oxide film with a large area and good film thickness distribution, for example, a film thickness of 30 μm or less. Such a crystalline film has been long awaited.

[0008] To address this issue, Patent Document 10 discloses a method for obtaining a gallium oxide film with good film thickness distribution using an ELO mask. However, this method requires peeling and polishing steps, making the process complicated, and the complicated process results in reduced yield.

[0009] The present invention aims to provide a crystalline oxide film containing gallium oxide as its main component, which has excellent crystallinity and a good in-plane film thickness distribution even when it has a thin film thickness over a large area, and which has excellent semiconductor properties when applied to a semiconductor device; a film formation method for forming such a crystalline oxide film; and a manufacturing apparatus for carrying out the film formation method. [Means for solving the problem]

[0010] The present invention has been made to achieve the above-mentioned object, and provides a film formation method for forming a crystalline oxide film containing gallium oxide as a main component on a substrate by a mist CVD method, the film formation method comprising the steps of: heating the substrate; heating a nozzle that supplies a mist containing a raw material solution; and supplying the mist onto the heated substrate so that the discharge direction of the heated nozzle is perpendicular to the surface of the substrate, thereby forming a crystalline oxide film; in the step of heating the nozzle, the nozzle is heated while the substrate is not present in the discharge direction of the nozzle; and in the step of forming the crystalline oxide film, the film formation method comprises the steps of: heating the nozzle while the substrate is present in the discharge direction of the nozzle;

[0011] According to this film formation method, it is possible to obtain a crystalline oxide film containing gallium oxide as its main component, which has excellent crystallinity and a good in-plane film thickness distribution even when the film thickness is thin, and which has excellent semiconductor properties when applied to a semiconductor device.

[0012] In this case, the substrate can be heated by using a substrate heating means having a substrate mounting portion and a substrate non-mounting portion, with the substrate being mounted on the substrate mounting portion, and in the step of heating the nozzle, the substrate non-mounting portion can be positioned in the discharge direction of the nozzle, and the nozzle can be heated by the substrate heating means, making this a film formation method.

[0013] This allows the use of a simplified film forming apparatus, which is advantageous in terms of cost.

[0014] In this case, the nozzle may be heated by a nozzle heating means provided in the nozzle.

[0015] This allows the nozzle to be heated efficiently.

[0016] The present invention also provides a film formation method for forming a crystalline oxide film containing gallium oxide as a main component on a substrate by a mist CVD method, the film formation method comprising the steps of heating the substrate, heating a film formation member, and supplying mist to form a crystalline oxide film in a state where the heated film formation member is present on the substrate in the normal direction to the surface of the substrate, wherein in the step of heating the film formation member, the film formation member is heated in a state where the film formation member is not present on the substrate in the normal direction to the surface of the substrate.

[0017] According to this film formation method, it is possible to obtain a crystalline oxide film containing gallium oxide as its main component, which has excellent crystallinity and a good in-plane film thickness distribution even when the film thickness is thin, and which has excellent semiconductor properties when applied to a semiconductor device.

[0018] In this case, the film formation method can be such that, in the step of heating the substrate, a substrate heating means having a substrate placement portion and a substrate non-placement portion is used, the substrate is placed on the substrate placement portion and heated, and in the step of heating the film formation member, the film formation member is positioned on the substrate non-placement portion in the normal direction to the surface of the substrate non-placement portion and the film formation member is heated by the substrate heating means.

[0019] This allows the use of a simplified film forming apparatus, which is advantageous in terms of cost.

[0020] In this case, the film formation method may be such that in the step of heating the film formation member, the film formation member is heated by a film formation member heating means provided on the film formation member.

[0021] This allows the film formation member to be heated efficiently.

[0022] At this time, the film forming member is a nozzle for supplying the mist to the substrate, In the step of heating the film formation member, the film formation method may be such that the nozzle is heated in a state where the nozzle outlet is not present on the substrate in a normal direction to the surface of the substrate.

[0023] This makes it possible to more effectively obtain a crystalline oxide film containing gallium oxide as its main component and having a good film thickness distribution.

[0024] At this time, the substrate has a film-forming surface area of ​​100 mm 2 The film formation method may use a diameter of 2 inches (50 mm) or more, or a diameter of 4 inches (100 mm) to 8 inches (200 mm).

[0025] According to the film forming method of the present invention, a crystalline oxide film with good film thickness distribution can be obtained even on such a large-area substrate.

[0026] The present invention has also been made to achieve the above-mentioned object, and provides a film formation apparatus for performing a mist CVD method, comprising: a substrate heating means having a substrate mounting portion on which a substrate is mounted; a nozzle for supplying a mist containing a raw material solution, the mist being discharged in a direction perpendicular to the surface of the substrate; and a position adjustment means for the nozzle and / or the substrate heating means, which is capable of adjusting the position of the substrate mounting portion between the nozzle in the discharge direction and a position other than the discharge direction.

[0027] Such a film formation apparatus can carry out the above-mentioned film formation method, and can provide a crystalline oxide film containing gallium oxide as its main component, which has excellent crystallinity and a good in-plane film thickness distribution even when the film thickness is thin.

[0028] In this case, the substrate heating means may further include a non-substrate placement portion, and the position adjustment means for the nozzle and / or the substrate heating means may be capable of adjusting the position of the non-substrate placement portion to the position of the nozzle in the discharge direction, thereby forming a film formation apparatus.

[0029] This simplifies the structure of the device, and also reduces the size of the device itself and the footprint, which is advantageous in terms of cost.

[0030] In this case, the nozzle may be a film forming device equipped with a nozzle heating means for heating the nozzle.

[0031] This makes it possible to heat the nozzle efficiently and with a high degree of freedom.

[0032] The present invention also provides a film formation apparatus for performing a mist CVD method, comprising: a substrate heating means having a substrate mounting portion on which a substrate is placed; a film formation member; and a position adjustment means capable of adjusting the position of the film formation member to a position other than a position on the substrate mounting portion in the normal direction to the surface of the substrate mounting portion.

[0033] Such a film formation apparatus can carry out the above-mentioned film formation method, and can provide a crystalline oxide film containing gallium oxide as its main component, which has excellent crystallinity and a good in-plane film thickness distribution even when the film thickness is thin.

[0034] In this case, the substrate heating means may further include a non-substrate placement portion, and the position adjustment means for the film formation member and / or the substrate heating means may be a film formation apparatus that is capable of adjusting the position of the film formation member to a position on the non-substrate placement portion in the normal direction of the surface of the non-substrate placement portion.

[0035] This simplifies the structure of the device, and also reduces the size of the device itself and the footprint, which is advantageous in terms of cost.

[0036] In this case, the film-forming member may be a film-forming device provided with a film-forming member heating means for heating the film-forming member.

[0037] This makes it possible to heat the film-forming member efficiently and with a high degree of freedom.

[0038] In this case, the film forming member may be a film forming device that is a nozzle for supplying mist to the substrate or a top plate for rectifying the supplied mist on the substrate.

[0039] This provides a film forming apparatus that can more effectively obtain a crystalline oxide film containing gallium oxide as its main component and having a good in-plane film thickness distribution.

[0040] The present invention has been made to achieve the above-mentioned object, and provides a crystalline oxide film containing gallium oxide as a main component, in which the V value obtained by the following formula (1) for the film thickness at 25 points in the plane is 0.045 or less.

number

[0041] Such a crystalline oxide film has a good film thickness distribution, and when used in a power semiconductor device, the performance of the crystalline oxide film can be fully exhibited, and the variation in performance can be suppressed.

[0042] In this case, the crystalline oxide film can have a V value of 0.041 or less.

[0043] This results in a better film thickness distribution, and makes it possible to further reduce variations in performance when used in a power semiconductor device.

[0044] In this case, a laminated structure including a substrate having a diameter of 4 inches (100 mm) to 8 inches (200 mm) and the crystalline oxide film provided on the substrate can be formed.

[0045] Such a laminated structure having a large area of ​​crystalline oxide film with good film thickness distribution can fully utilize the performance of the crystalline oxide film when used in a power semiconductor device, and can also suppress performance variations.

[0046] In this case, the product lot can be a product lot of semiconductor devices that includes two or more semiconductor devices manufactured from the above-mentioned laminated structure and has a breakdown voltage yield of 75% or more.

[0047] Such a product lot has a high yield.

[0048] The present invention also provides a film formation method for forming a crystalline oxide film containing gallium oxide as a main component on a substrate by a mist CVD method, the film formation method comprising the steps of heating the substrate, heating a nozzle that supplies a mist containing a raw material solution to a predetermined temperature, guiding the mist to the substrate to form a crystalline oxide film, and exhausting the mist after film formation, wherein in the step of heating the nozzle to the predetermined temperature, the discharged material discharged from the nozzle is exhausted without passing through the substrate.

[0049] According to this film formation method, it is possible to obtain a crystalline oxide film containing gallium oxide as its main component, which has excellent crystallinity and a good in-plane film thickness distribution even when the film thickness is thin, and which has excellent semiconductor properties when applied to a semiconductor device.

[0050] The present invention also provides a film formation apparatus for performing a mist CVD method, comprising: a substrate heating means having a substrate mounting portion on which a substrate is mounted; a nozzle for supplying mist to the substrate; and an exhaust means for exhausting the mist after film formation, wherein the exhaust means has a mechanism for exhausting the exhaust from the nozzle without passing through the substrate mounting portion.

[0051] Such a film formation apparatus can carry out the above-mentioned film formation method, and can provide a crystalline oxide film containing gallium oxide as its main component, which has excellent crystallinity and a good in-plane film thickness distribution even when the film thickness is thin. [Effects of the Invention]

[0052] As described above, the film formation method of the present invention makes it possible to form a crystalline oxide film containing gallium oxide as its main component, which has excellent crystallinity and a good in-plane film thickness distribution even when thin, and which has excellent semiconductor properties when applied to a semiconductor device.The film formation apparatus of the present invention is capable of implementing the above-mentioned film formation method and is capable of obtaining a crystalline oxide film containing gallium oxide as its main component, which has excellent crystallinity and a good in-plane film thickness distribution even when thin.The crystalline oxide film of the present invention has a good film thickness distribution, and when used in a power semiconductor device, the performance of the crystalline oxide film can be fully exhibited and performance variation can be suppressed. [Brief explanation of the drawings]

[0053] [Figure 1] The first example shows the nozzle heating. [Figure 2] A second example of nozzle heating is shown. [Figure 3] A third example of nozzle heating is shown. [Figure 4] A fourth example of nozzle heating is shown. [Figure 5] The outline of the film formation device for forming films by the mist CVD method is shown. [Figure 6] 1A and 1B are diagrams illustrating an example of a mist generating unit in a film forming apparatus. [Figure 7] 1 is a schematic diagram showing an example of a semiconductor device according to the present invention; DETAILED DESCRIPTION OF THE INVENTION

[0054] The present invention will be described in detail below, but the present invention is not limited thereto.

[0055] As described above, there has been a need to provide a crystalline oxide film containing gallium oxide as its main component, which has excellent crystallinity and a good in-plane film thickness distribution even when it has a large area and a thin film thickness, and which has excellent semiconductor properties when applied to a semiconductor device, as well as a film formation method for forming such a crystalline oxide film, and a manufacturing apparatus for carrying out the film formation method.

[0056] As a result of intensive research into the above-mentioned problems, the present inventors have found a film formation method for forming a crystalline oxide film mainly composed of gallium oxide on a substrate by a mist CVD method, the film formation method comprising the steps of: heating the substrate; heating a nozzle that supplies a mist containing a raw material solution; and supplying the mist onto the heated substrate so that the discharge direction of the heated nozzle is perpendicular to the surface of the substrate to form a crystalline oxide film, wherein in the step of heating the nozzle, the nozzle is heated while the substrate is not present in the discharge direction of the nozzle; and in the step of forming the crystalline oxide film, the film formation is performed while the substrate is present in the discharge direction of the nozzle. This film formation method produces a crystalline oxide film mainly composed of gallium oxide that has excellent crystallinity and a good in-plane film thickness distribution even when the film is thin, and has excellent semiconductor properties when applied to a semiconductor device.The present invention has been completed.

[0057] The present inventors have also discovered that a film formation method for forming a crystalline oxide film mainly composed of gallium oxide on a substrate by a mist CVD method includes the steps of heating the substrate, heating a film formation member, and supplying mist to form a crystalline oxide film in a state where the heated film formation member is present on the substrate in the normal direction to the surface of the substrate, wherein in the step of heating the film formation member, the film formation member is heated in a state where the film formation member is not present on the substrate in the normal direction to the surface of the substrate, and this film formation method makes it possible to obtain a crystalline oxide film mainly composed of gallium oxide that has excellent crystallinity and a good in-plane film thickness distribution even when it is thin, and that has excellent semiconductor properties when applied to a semiconductor device, and have completed the present invention.

[0058] The present inventors have also discovered that a film formation apparatus for performing a mist CVD method, which comprises substrate heating means having a substrate mounting portion on which a substrate is placed, a nozzle for supplying a mist containing a raw material solution, the mist being discharged in a direction perpendicular to the surface of the substrate, and position adjustment means for the nozzle and / or the substrate heating means, which can adjust the position of the substrate mounting portion between the nozzle in the discharge direction and a position other than the discharge direction, can provide a film formation apparatus that can obtain a crystalline oxide film containing gallium oxide as its main component, which has excellent crystallinity and a good in-plane film thickness distribution even when the film thickness is thin, and have completed the present invention.

[0059] The present inventors have also discovered that the above-mentioned film formation method can be carried out by a film formation apparatus that performs a mist CVD method and that includes a substrate heating means having a substrate mounting portion on which a substrate is placed, a film formation member, and a position adjustment means that can adjust the position of the film formation member to a position other than its position on the substrate mounting portion in the normal direction to the surface of the substrate mounting portion, and that this film formation apparatus can provide a crystalline oxide film that has excellent crystallinity and is primarily composed of gallium oxide, and that has a good in-plane film thickness distribution even when the film thickness is thin, and have thereby completed the present invention.

[0060] The present inventors have also discovered that a crystalline oxide film containing gallium oxide as its main component, in which the V value obtained by the following formula (1) for the film thickness at 25 points on the surface is 0.045 or less, has a good film thickness distribution, and when made into a power semiconductor device, the performance of the crystalline oxide film can be fully exhibited and performance variation can be suppressed, thereby completing the present invention.

number

[0061] The present inventors have also discovered that a film formation method for forming a crystalline oxide film mainly composed of gallium oxide on a substrate by a mist CVD method includes the steps of heating the substrate, heating a nozzle that supplies a mist containing a raw material solution to a predetermined temperature, directing the mist to the substrate to form a crystalline oxide film, and exhausting the mist after film formation, in which in the step of heating the nozzle to a predetermined temperature, the discharged material discharged from the nozzle is exhausted without passing through the substrate, thereby making it possible to obtain a crystalline oxide film mainly composed of gallium oxide that has excellent crystallinity and a good in-plane film thickness distribution even when it is thin, and that has excellent semiconductor properties when applied to a semiconductor device, and have completed the present invention.

[0062] The present inventors have also discovered that the above-mentioned film formation method can be carried out by a film formation apparatus that performs a mist CVD method, the film formation apparatus comprising: a substrate heating means having a substrate mounting portion on which a substrate is mounted; a nozzle for supplying mist to the substrate; and exhaust means for exhausting the mist after film formation, the exhaust means having a mechanism for exhausting the exhaust from the nozzle without passing through the substrate mounting portion; and that this film formation apparatus is capable of obtaining a crystalline oxide film containing gallium oxide as its main component, which has excellent crystallinity and a good in-plane film thickness distribution even when the film is thin, and thus completed the present invention.

[0063] The following description will be made with reference to the drawings.

[0064] (crystalline oxide film) First, the crystalline oxide film according to the present invention will be described. The crystalline oxide film according to the present invention is a crystalline oxide film containing gallium oxide as a main component, and has a V value of 0.045 or less, as calculated by the following formula (1), for the film thickness at 25 points in the plane:

number

[0065] The crystalline oxide film according to the present invention has a good film thickness distribution, and when used in a power semiconductor device, the performance of the crystalline oxide film can be fully exhibited, and the performance variation can be suppressed. In the following description, the "crystalline oxide film mainly composed of gallium oxide" may also be simply referred to as the "crystalline oxide film."

[0066] Generally, crystalline oxide films are composed of metal and oxygen, but the crystalline oxide film of the present invention may contain gallium as the main metal component. In the present invention, "containing gallium as the main component" means that 50 to 100% of the metal components are 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.

[0067] The crystalline 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, tin, iridium, rhodium, and magnesium. The dopant concentration is, for example, about 1×10 16 / cm 3 ~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.

[0068] The crystal structure of the crystalline oxide film is not particularly limited, and may be a β-gallium structure, a corundum structure, or an orthorhombic crystal. It may be a mixture of multiple crystal structures or 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 diffraction device or an electron beam diffraction device. When a film is irradiated with X-rays or an electron beam, a diffraction pattern corresponding to the crystal structure is obtained, and if the film is uniaxially oriented, only a specific peak appears. This indicates that the film is uniaxially oriented.

[0069] 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 a stylus-type step gauge, a spectroscopic reflection film thickness gauge, an ellipsometer, or by observing the cross section with an SEM or TEM, and any method is acceptable. In the crystalline oxide film according to the present invention, the V value is 0.045 or less when the film thickness is measured at 25 points within the surface of the crystalline oxide film. Here, the V value is a dimensionless quantity defined by the following formula (1):

number

[0070] The smaller the V value, the smaller the film thickness variation. Therefore, a V value of 0.041 or less is preferable. A crystalline oxide film with a V value of 0.041 or less is preferable because it has a better film thickness distribution and can more effectively suppress the performance variation when made into a power semiconductor device. Such a crystalline oxide film can be obtained by film formation by a mist CVD method using a mist CVD apparatus (film formation apparatus) described below. The lower limit of the V value is 0 or more.

[0071] (Laminated structure) As shown in FIG. 7, the laminated structure 210 according to the present invention can be one in which a crystalline oxide film 203 is provided at least on a substrate 110. The crystalline oxide film 203 may be a single layer or multiple layers as shown in FIG. 7. The substrate in this case can have a diameter of 4 inches (100 mm) to 8 inches (200 mm). This provides excellent film thickness distribution over a large area, and when applied to a semiconductor device, the semiconductor properties are excellent. That is, when a semiconductor device such as a power semiconductor device is manufactured from such a laminated structure, a product lot containing two or more of the semiconductor devices can have a breakdown voltage yield of 75% or more.

[0072] Another layer may be interposed between the substrate 110 and the crystalline oxide film 203. This other layer is a layer having a different composition from the substrate and the outermost crystalline oxide film, and is also called a buffer layer. The buffer layer may be an oxide semiconductor film, an insulating film, a metal film, or the like, and suitable materials include Al2O3, Ga2O3, Cr2O3, Fe2O3, In2O3, Rh2O3, V2O3, Ti2O3, and Ir2O3. The thickness of the buffer layer is preferably 0.1 μm to 2 μm.

[0073] (substrate) The substrate used in the layered structure containing the crystalline oxide according to the present invention and the film-forming method according to the present invention is not particularly limited as long as it can serve as a support for the crystalline oxide film. The material is not particularly limited, and known substrates can be used, and they may be organic 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, single-crystal substrates such as silicon, sapphire, lithium tantalate, lithium niobate, SiC, GaN, iron oxide, and chromium oxide are also suitable. These single-crystal substrates are desirable for the layered structure according to the present invention. These substrates enable the production of higher-quality crystalline oxide films. In particular, sapphire substrates, lithium tantalate substrates, and lithium niobate substrates are relatively inexpensive and industrially advantageous.

[0074] The thickness of the substrate is preferably 100 to 5000 μm, as this range makes it easy to handle and reduces thermal resistance during film formation, making it easier to obtain a high-quality film.

[0075] There is no particular limit to the size of the board, but the board area must be 100mm 2 A substrate having a diameter of 2 inches (50 mm) or more is preferred because it allows for the production of a large-area film with good crystallinity. The upper limit of the substrate area is not particularly limited, but it is preferred that it be 100,000 mm 2 Furthermore, if the diameter of the substrate is 4 inches (100 mm) to 8 inches (200 mm), the obtained laminated structure can be easily processed using existing processing equipment, which is industrially advantageous when manufacturing semiconductor devices.

[0076] (Configuration example of semiconductor device) FIG. 7 shows a preferred example of a semiconductor device 200 using a stacked structure 210 according to the present invention. In the example of FIG. 7, a crystalline oxide film 203 is formed on a substrate 110. The crystalline oxide film 203 is configured by stacking an insulating thin film 203a and a conductive thin film 203b in this order from the substrate 110 side. A gate insulating film 205 is formed on the conductive thin film 203b. A gate electrode 207 is formed on the gate insulating film 205. Furthermore, source-drain electrodes 209 are formed on the conductive thin film 203b so as to sandwich the gate electrode 207. With this configuration, it is possible to control the depletion layer formed in the conductive thin film 203b by applying a gate voltage to the gate electrode 207, enabling transistor operation (FET device).

[0077] Examples of semiconductor devices formed using the stacked structure according to the present invention include transistors such as MIS, HEMT, and IGBT, TFTs, Schottky barrier diodes (SBDs) using semiconductor-metal junctions, PN or PIN diodes combined with other P layers, and light-emitting / receiving elements. The stacked structure according to the present invention is useful for improving the characteristics of these devices.

[0078] The crystalline oxide film and laminated structure according to the present invention as described above can be produced by a mist CVD method. A film-forming apparatus and a film-forming method suitable for producing the crystalline oxide film and laminated structure according to the present invention will be described below. 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 are called fog, droplets, etc. The following description will be made with reference to the drawings.

[0079] [Film forming equipment] (First film forming device) First, a first example of a film formation apparatus according to the present invention will be described. Fig. 5 shows an outline of a film formation apparatus 101 that forms a film by mist CVD. The film formation apparatus 101 includes at least a mist-forming unit 120 that generates mist by misting a raw material solution 104a, a carrier gas supply unit 130 that supplies a carrier gas that transports the mist, a supply pipe 109 that connects the mist-forming unit 120 to a film formation chamber 107 and transports the mist by the carrier gas, the film formation chamber 107 that heat-treats the mist to form a film on a substrate 110, and a nozzle 150 that sprays the mist, supplied from the supply pipe 109 together with the carrier gas, onto the substrate.

[0080] (Mist generating section) In the mist generating section 120, the raw material solution 104a is turned into mist to generate mist. The mist generating means is not particularly limited as long as it can turn the raw material solution 104a into mist, and any known mist generating means may be used, but it is preferable to use a mist generating means that uses ultrasonic vibrations, as this allows for more stable mist generation.

[0081] An example of such a mist-generating unit 120 is shown in FIG. 6. The mist-generating unit 120 may include a mist source 104 containing a raw solution 104a, a container 105 containing a medium capable of transmitting ultrasonic vibrations, such as water 105a, and an ultrasonic vibrator 106 attached to the bottom of the container 105. Specifically, the mist source 104, which is a container containing the raw solution 104a, may be housed in the container 105 containing the water 105a using a support (not shown). The bottom of the container 105 may be equipped with an ultrasonic vibrator 106, or the ultrasonic vibrator 106 may be connected to an oscillator 116. When the oscillator 116 is activated, the ultrasonic vibrator 106 vibrates, and ultrasonic waves propagate through the water 105a into the mist source 104, turning the raw solution 104a into mist.

[0082] (Raw material solution) The raw material solution 104a may contain any material, inorganic or organic, as long as it can be misted. Metals or metal compounds are preferably used, including, for example, one or more metals selected from gallium, iron, indium, aluminum, vanadium, titanium, chromium, rhodium, nickel, and cobalt. Such raw material solutions may be prepared by dissolving or dispersing metals in the form of complexes or salts in an organic solvent or water. Examples of salts include halide salts such as metal chlorides, metal bromides, and metal iodides. Furthermore, solutions of the above metals 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. The metal concentration in the raw material solution 104a is not particularly limited, and can be set to, for example, 0.005 to 1 mol / L.

[0083] 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.

[0084] The raw material solution may contain a dopant. The dopant is not particularly limited. Examples of the dopant include n-type dopants such as tin, germanium, silicon, titanium, zirconium, vanadium, and niobium, and p-type dopants such as copper, silver, iridium, rhodium, and magnesium.

[0085] (Carrier gas supply unit) 5, the carrier gas supply unit 130 has a carrier gas source 102a that supplies a carrier gas. In this case, a flow rate control valve 103a for adjusting the flow rate of the carrier gas delivered from the carrier gas source 102a may be provided. In addition, if necessary, a dilution carrier gas source 102b for supplying a dilution carrier gas and a flow rate control valve 103b for adjusting the flow rate of the dilution carrier gas delivered from the dilution carrier gas source 102b may also be provided.

[0086] 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., diluted 10 times) may be used as the second carrier gas, or air may be used.

[0087] (supply pipe) The film forming apparatus 101 has a supply pipe 109 that connects the mist generating unit 120 and the film forming chamber 107. In this case, mist is carried by a carrier gas from the mist generating source 104 of the mist generating unit 120 via the supply pipe 109 and supplied into the film forming chamber 107. The supply pipe 109 may be, for example, a quartz tube, a glass tube, or a resin tube.

[0088] (Film forming chamber) A substrate 110 is placed in the film formation chamber 107, and the chamber is equipped with a substrate heating means 108, such as a heater, for heating the substrate 110 placed on the substrate placement portion. Hereinafter, the area of ​​the substrate heating means 108 where the substrate is placed is referred to as the "substrate placement portion." Furthermore, the "non-substrate placement portion" described below refers to an area of ​​the substrate heating means where no substrate is placed. For example, if the substrate placement surface of the substrate heating means is larger than the substrate, the substrate heating means will have a "substrate placement portion" and a "non-substrate placement portion" (see Figures 1 and 2). The substrate heating means may not have a "non-substrate placement portion," such as when the size of the substrate placement surface of the substrate heating means is the same as (or smaller than) the substrate (see Figures 3 and 4).

[0089] 5, the substrate heating means 108 may be provided outside the film formation chamber 107, or may be provided inside the film formation chamber 107. The film formation chamber 107 also has a nozzle 150 for spraying a mist containing the raw material solution supplied from a supply pipe 109, together with a carrier gas, toward the substrate 110. The direction of spray from the nozzle 150 during film formation is perpendicular to the surface of the substrate 110.

[0090] The film formation apparatus according to the present invention is provided with a position adjustment means for the nozzle and / or substrate heating means that can adjust the position of the substrate mounting part to a position in the discharge direction of the nozzle 150 or to a position other than the discharge direction. In this way, if the position of the substrate mounting part can be adjusted relative to the position in the discharge direction of the nozzle 150, it is possible to suppress adverse effects on the substrate when the nozzle is heated as in the film formation method described below.

[0091] An example of nozzle heating is shown in Figures 1-4. The example shown in Figures 1 and 3 is equipped with a nozzle position adjustment means 170, and after heating the nozzle, the nozzle can be moved above the substrate 110 (substrate mounting part 111A) so that the substrate is present in the nozzle discharge direction. Note that the nozzle position adjustment means 170 is not limited to the one that moves parallel to the substrate as shown in Figures 1 and 3, but may also be a mechanism that tilts the angle of the nozzle.

[0092] The example shown in Figures 2 and 4 is equipped with a position adjustment means 180 for the substrate heating means 108, and after heating the nozzle, the substrate 110 (substrate placement portion 111A) can be moved below the nozzle (in the discharge direction) so that the substrate is present in the discharge direction of the nozzle.

[0093] 1 and 2, the substrate heating means 108 has a substrate placement portion 111A and a substrate non-placement portion 111B. In this case, it is preferable that the nozzle position adjustment means 170 and / or the substrate heating means position adjustment means 180 are capable of adjusting the position of the substrate non-placement portion 111B to a position in the nozzle discharge direction. Such an apparatus simplifies the structure of the apparatus, and the apparatus itself is made smaller and has a smaller footprint, which is advantageous in terms of cost and allows the nozzle to be heated efficiently by the substrate heating means.

[0094] 3 and 4, a nozzle heating means 151 for heating the nozzle is provided on the nozzle 150. This allows the nozzle to be heated and the temperature to be controlled independently of the substrate, increasing the degree of freedom and resulting in a film formation apparatus that can heat and control the temperature of the nozzle more efficiently.

[0095] 1 and 2, the nozzle 150 may be provided with a nozzle heating means 151. In the film formation apparatus shown in Figures 3 and 4, the substrate heating means 108 may have a substrate placement portion 111A and a non-substrate placement portion 111B. In this case, the nozzle can be heated more efficiently.

[0096] The film formation chamber 107 may be provided with an exhaust gas outlet 112 at a position that does not affect the supply of mist to the substrate 110. The substrate 110 may be placed face-down, for example, on the top surface of the film formation chamber 107, or may be placed face-up, for example, on the bottom surface of the film formation chamber 107. The angle of the surface of the substrate heating means at which the substrate 110 is placed relative to the horizontal plane is not particularly limited. The nozzle discharge direction may be adjusted depending on the installation angle of the substrate.

[0097] (Second film forming device) Next, a second example of a film formation apparatus according to the present invention will be described. The following explanation will focus on the differences from the first example. The second example of a film formation apparatus for performing the mist CVD method comprises a substrate heating means having a substrate mounting portion on which a substrate is mounted, a film formation member, and a position adjustment means capable of adjusting the position of the film formation member to a position other than the position on the substrate mounting portion in the normal direction of the surface of the substrate mounting portion. In this way, if the position of the substrate mounting portion can be adjusted relative to the positions of the film formation members, such as the nozzle 150 and the flow-regulating top plate, it is possible to suppress adverse effects on the substrate when the film formation member is heated, as in the film formation method described below.

[0098] The substrate heating means may further include a non-substrate placement portion. Preferably, the position adjusting means for the film deposition member and / or the substrate heating means is capable of adjusting the position of the film deposition member to a position on the non-substrate placement portion in the normal direction to the surface of the non-substrate placement portion.

[0099] The position of the film formation member on the non-substrate placement portion in the normal direction to the surface of the non-substrate placement portion means that the film formation member exists (is located) in the space that the non-substrate placement portion stretches in the normal direction. When the film formation member exists (is located) in the space that the substrate placement portion stretches in the normal direction, it can be said that the film formation member is located on the substrate placement portion in the normal direction to the surface of the substrate placement portion.

[0100] The film-forming member may be provided with a film-forming member heating means for heating the film-forming member. For example, a film-forming member such as a nozzle or a top plate for straightening may be provided with a heating means such as a heater, so that the temperature of the film-forming member such as the nozzle or the top plate for straightening can be controlled independently.

[0101] The film-forming member is not particularly limited as long as it is a member used in the film-forming apparatus during film formation, but examples thereof include a nozzle for supplying mist to the substrate and a top plate for rectifying the supplied mist on the substrate.

[0102] (Third film forming device) Next, a third example of a film formation apparatus according to the present invention will be described. The following explanation will focus on differences from the first example. The third example of a film formation apparatus for performing a mist CVD method includes a substrate heating means having a substrate mounting portion on which a substrate is mounted, a nozzle for supplying mist to the substrate, and an exhaust means for exhausting the mist after film formation. The exhaust means has a mechanism for exhausting the exhaust from the nozzle without passing through the substrate mounting portion. As described above, the film formation chamber 107 is provided with an exhaust gas outlet 112 at a position that does not affect the supply of mist to the substrate 110. The film formation apparatus of the third example includes a position adjustment means for the film formation member and / or the substrate heating means that can adjust the relative position of the film formation member, such as the nozzle 150 or the rectifying top plate, and the substrate mounting portion, as described above. This allows the exhaust means to exhaust the exhaust from the nozzle without passing through the substrate mounting portion, thereby suppressing adverse effects on the substrate when the film formation member is heated, as in the film formation method described below.

[0103] [Film forming method] (First film formation method) 1 to 6, a first example of a film formation method according to the present invention will be described. The film formation method according to the present invention includes a step of heating a substrate, a step of heating a nozzle that supplies a mist containing a raw material solution, and a step of supplying the mist onto the heated substrate so that the direction of the mist from the heated nozzle is perpendicular to the surface of the substrate to form a crystalline oxide film, wherein the nozzle heating step is performed without the substrate being present in the direction of the nozzle discharge, and the crystalline oxide film formation step is performed with the substrate being present in the direction of the nozzle discharge.

[0104] (Substrate heating process) The above-mentioned raw material solution 104a is contained in the mist generating source 104, the substrate 110 is placed in the film forming chamber 107, the heater 108 is operated, and the substrate is heated and raised to a predetermined temperature.

[0105] (Nozzle heating process) In addition, the nozzle 150 is heated. This is because abnormal growth may occur if the nozzle temperature changes during film formation. The method for heating the nozzle is not particularly limited, and as explained in the film formation apparatus above, the nozzle may be equipped with a nozzle heating means 151 such as a heater to adjust the temperature of the nozzle alone, or the nozzle may be heated by a substrate heating means 108 until the nozzle temperature stabilizes. When the nozzle is heated by a nozzle heating means provided in the nozzle, the nozzle can be heated efficiently.

[0106] Here, the positional relationship between the nozzle 150 and the substrate when the nozzle is heated is such that the substrate is not present in the nozzle's discharge direction. This is because if the substrate is present in the nozzle's discharge direction when the nozzle is heated, an unintended film will grow on the substrate, significantly worsening the film thickness distribution and crystallinity. Although the cause is unclear, it is thought that mist and droplets remaining in the nozzle and piping evaporate due to heating and adhere to the substrate.

[0107] Although it is conceivable to place the substrate after the nozzle heating has finished, this is not preferable due to concerns about the influence of temperature changes caused by opening and closing the film formation chamber, etc. Therefore, in the film formation method according to the present invention, the above problem can be solved by providing a substrate heating means or a position adjustment means for the nozzle.

[0108] Examples of methods for heating the nozzle before film formation will be described with reference to Figures 1 to 4. In all of these methods, the substrate is not present in the discharge direction of the nozzle 150.

[0109] As described above, the nozzle can be heated using a substrate heating means. Heating the nozzle until the temperature is stabilized using the substrate heating means 108 simplifies the structure of the film formation apparatus, and the apparatus itself is made smaller, resulting in a smaller footprint, which is cost-effective. In this case, as shown in FIGS. 1 and 2 , it is preferable to use a substrate heating means 108 having a substrate placement portion 111A and a non-substrate placement portion 111B, place a substrate on the substrate placement portion 111A, and position the non-substrate placement portion 111B in the nozzle discharge direction, and then heat the nozzle 150 using the substrate heating means 108. This is cost-effective and allows for more efficient nozzle heating.

[0110] 3 and 4, the nozzle can also be heated by a nozzle heating means 151 provided on the nozzle 150. In this case, the nozzle can be heated and the temperature can be controlled more efficiently. Note that even when the nozzle is heated by the nozzle heating means 151, it is also possible to use a substrate heating means 108 having a substrate placement portion 111A and a substrate non-placement portion 111B.

[0111] 1 and 3, after the nozzle is heated, the nozzle is moved above the substrate by the nozzle position adjustment means 170 so that the substrate is positioned in the direction of nozzle discharge. In Figures 2 and 4, after the nozzle is heated, the substrate is moved below the nozzle by the substrate heating means position adjustment means 180 so that the substrate is positioned in the direction of nozzle discharge.

[0112] The nozzle temperature can be, for example, 50 to 250° C. The film formation reaction also depends on the temperature of the environment around the substrate. Therefore, it is desirable to set the temperature of not only the nozzle but also the inner wall of the film formation chamber higher than room temperature.

[0113] (Film forming process, etc.) Once the nozzle temperature has stabilized, the nozzle or substrate (substrate heating means) is moved so that the substrate is positioned in the nozzle discharge direction, and then the film formation process is carried out.

[0114] Film formation by the mist CVD method generally includes the following steps: a mist generation step in which a raw material solution containing gallium is converted into mist in a mist-forming section to generate mist, a carrier gas supply step in which a carrier gas for transporting the mist is supplied to the mist-forming section, a transport step in which the mist is transported from the mist-forming section to the film-forming chamber by the carrier gas via a supply pipe connecting the mist-forming section to the film-forming chamber, and a film-forming step in which the transported mist is heat-treated to form a film on a substrate. These steps are explained below.

[0115] First, the flow rate control valves 103a and 103b are opened to supply carrier gas from the carrier gas sources 102a and 102b into the film formation chamber 107. After the atmosphere in the film formation chamber 107 is sufficiently replaced with the carrier gas, the flow rates of the carrier gas and the dilution carrier gas are adjusted. The flow rate of the carrier gas is not particularly limited. For example, when forming a film on a 2-inch substrate, the flow rate of the carrier gas is preferably 0.05 to 50 L / min, and more preferably 5 to 20 L / min.

[0116] Next, in the mist generating step, the ultrasonic vibrator 106 is vibrated, and the vibration is propagated to the raw material solution 104a through the water 105a, thereby turning the raw material solution 104a into mist and generating the mist.

[0117] Next, in the carrier gas supply step, a carrier gas for transporting the mist is supplied to the mist generating section 120.

[0118] Next, in the transport step, the mist is transported by a carrier gas from the mist-producing section 120 to the film-forming chamber 107 via the supply pipe 109 connecting the mist-producing section 120 and the film-forming chamber 107.

[0119] Next, in the film formation process, the mist supplied from the supply pipe 109 passes through piping in the film formation chamber 107, and is ejected and supplied from the nozzle 150 toward the substrate 110 together with a carrier gas. The mist transported to the film formation chamber 107 is heated to cause a thermal reaction, thereby forming a film on part or all of the surface of the substrate 110.

[0120] As shown in FIG. 5, mist is supplied onto a heated substrate so that the direction of the mist discharge from the heated nozzle is perpendicular to the surface of the substrate, forming a crystalline oxide film. The substrate is positioned in the direction of the nozzle discharge. By adjusting the relative positions of the nozzle and the substrate during heating and film formation, a crystalline oxide film containing gallium oxide as its main component can be obtained, which has excellent crystallinity and a good in-plane film thickness distribution even at thin thicknesses, and which exhibits excellent semiconductor properties when applied to semiconductor devices. In particular, a crystalline oxide film containing gallium oxide as its main component can be produced, in which the V value obtained from the above formula (1) for the film thickness at 25 points within the plane is 0.045 or less.

[0121] Thermal reactions require heating to promote the reaction of gallium and other substances contained in the mist. Therefore, the temperature of the substrate surface during the reaction must be at least 400°C. Unlike other CVD methods, mist CVD requires the raw materials to reach the substrate surface in liquid form. This significantly reduces the temperature of the substrate surface. Therefore, the temperature of the substrate surface during the reaction differs from the temperature set in the equipment. It is preferable to be able to measure the temperature of the substrate surface during the reaction. However, if this is difficult, the reaction can be simulated by introducing only carrier gas or water mist without solute, and the temperature can be measured instead.

[0122] 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.

[0123] (Buffer layer formation) As described above, a buffer layer may be appropriately provided between the substrate and the crystalline 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, 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. After the buffer layer is formed to a predetermined thickness, a crystalline oxide film is formed by the film forming method according to the present invention.

[0124] (Heat treatment) Furthermore, the film obtained by the film forming method according to the present invention may be heat-treated at 200 to 600°C. This removes unreacted species in the film, resulting in a crystalline oxide film of higher quality. The heat treatment may be carried out in air or an oxygen atmosphere, or in an inert gas atmosphere such as nitrogen or argon. The heat treatment time is determined appropriately, but may be, for example, 5 to 240 minutes.

[0125] (peeling) After obtaining a laminated structure including a substrate and a crystalline oxide film, the crystalline oxide film can 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 a mechanical impact, peeling by applying heat and using thermal stress, peeling by applying vibration such as ultrasonic waves, and peeling by etching. By peeling, the crystalline oxide film can be obtained as a free-standing film.

[0126] (Second film forming method) Next, a second example of the film formation method according to the present invention will be described. The second example includes a step of heating a substrate, a step of heating a film formation member, and a step of supplying mist to form a crystalline oxide film on the substrate in a state where the heated film formation member is present on the substrate in the normal direction of the surface of the substrate, and in the step of heating the film formation member, the film formation member is heated in a state where the film formation member is not present on the substrate in the normal direction of the surface of the substrate, and is a film formation method for forming a crystalline oxide film mainly composed of gallium oxide on a substrate by a mist CVD method. The following explanation will focus on the differences from the first example of the film formation method.

[0127] (Step of heating the film-forming member) In the process of heating the film formation members, the film formation members, such as the nozzle 150 and the rectifying top plate, are heated. This is because abnormal growth can occur if the temperature of the film formation members, such as the nozzle and the rectifying top plate, changes during film formation. The method for heating the film formation members, such as the nozzle and the rectifying top plate, is not particularly limited. As described in the film formation apparatus above, the temperature of the film formation members, such as the nozzle and the rectifying top plate, can be controlled independently by installing a heating means such as a heater on the film formation members, or the film formation members, such as the nozzle and the rectifying top plate, can be heated by the substrate heating means 108 until their temperatures stabilize. When the film formation members, such as the nozzle and the rectifying top plate, are heated by a heating means provided on the film formation members, such as the nozzle and the rectifying top plate, the film formation members, such as the nozzle and the rectifying top plate, can be heated efficiently.

[0128] Here, when heating the nozzle 150, the flow straightening top plate, and other film formation members, the positional relationship between the nozzle 150, the flow straightening top plate, and the substrate is such that no film formation members are present on the substrate in the normal direction to the surface of the substrate. In other words, no film formation members are present in the space stretched by the substrate in the normal direction. By using this method, when the nozzle is heated to a predetermined temperature, gases and the like discharged from the nozzle can be exhausted without passing through the substrate.

[0129] If a film-forming component such as a nozzle or a straightening top plate is positioned on the substrate in the normal direction to the surface of the substrate when the component is heated, an unintended film will grow on the substrate, resulting in a significant deterioration in film thickness distribution and crystallinity. The cause is unclear, but it is thought that mist and droplets remaining in the film-forming component such as the nozzle or straightening top plate or in the piping evaporate due to heating and adhere to the substrate.

[0130] Although it is conceivable to place the substrate after heating of the film formation members such as the nozzle and the rectifying top plate has finished, this is not preferable due to concerns about the influence of temperature changes caused by opening and closing the film formation chamber, etc. Therefore, in the second example of the film formation method according to the present invention, the above problem can be solved by providing a position adjustment means for the substrate heating means and the film formation members such as the nozzle and the rectifying top plate.

[0131] In the step of heating the substrate, it is preferable to use a substrate heating means having a substrate placement portion and a substrate non-placement portion, place the substrate on the substrate placement portion and heat the substrate, and in the step of heating the film-forming member, position the film-forming member on the substrate non-placement portion in the normal direction to the surface of the substrate non-placement portion and heat the film-forming member by the substrate heating means.

[0132] In the step of heating the film-forming member, the film-forming member is preferably heated by a film-forming member heating means provided on the film-forming member.

[0133] The film-forming member is a nozzle for supplying mist to the substrate, and in the process of heating the film-forming member, it is preferable to heat the nozzle in a state where the nozzle outlet is not present on the substrate in the normal direction to the surface of the substrate.

[0134] (Third film formation method) Next, a third example of the film formation method according to the present invention will be described. This third example includes the steps of heating a substrate, heating a nozzle that supplies a mist containing a raw material solution to a predetermined temperature, and directing the mist toward the substrate to form a crystalline oxide film, followed by exhausting the mist after film formation. This film formation method forms a crystalline oxide film primarily composed of gallium oxide on a substrate by mist CVD, in which the discharged material from the nozzle during the step of heating the nozzle to a predetermined temperature is exhausted without passing through the substrate. This film formation method can produce a crystalline oxide film primarily composed of gallium oxide that has excellent crystallinity and a good in-plane film thickness distribution even when thin, and that exhibits excellent semiconductor properties when applied to a semiconductor device. This film formation method can be performed using an apparatus such as the third example of the film formation apparatus described above. [Example]

[0135] The present invention will be specifically explained below with reference to examples, but the present invention is not limited to these examples.

[0136] [Example 1] 5, the film formation apparatus 101 used in this example will be described. The film formation 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 delivered from the carrier gas source 102a, a dilution carrier gas source 102b for supplying a dilution carrier gas, a flow rate control valve 103b for adjusting the flow rate of the dilution carrier gas delivered from the dilution carrier gas source 102b, a mist generation source 104 containing a raw material solution 104a, a container 105 containing water 105a, an ultrasonic vibrator 106 attached to the bottom of the container 105, a film formation chamber 107 equipped with a substrate heating means 108, a quartz supply pipe 109 connecting the mist generation source 104 to the film formation chamber 107, and a nozzle 150. Furthermore, as shown in FIG. 2, the substrate heating means 108 is provided with a transport mechanism so that the substrate can be placed in a state where it is not present in the vertical direction, which is the ejection direction of the nozzle, before film formation.

[0137] A 4-inch (100 mm) c-plane sapphire substrate was prepared as the substrate 110, and the substrate was placed in the film formation chamber 107. Before film formation began, the substrate heating means 108 was moved as shown in FIG. 2 so that the nozzle was not in the vertical direction of the substrate, and then the substrate heating means 108 was set to 450°C, heated, and left for 30 minutes to stabilize the temperature inside the film formation chamber, including the nozzle. The temperature at the tip of the nozzle 150 at this time was measured using a thermocouple and was found to be 146°C. After confirming that the nozzle temperature had stabilized, the substrate heating means 108 was moved together with the substrate to a position below the nozzle in the discharge direction (the position shown in FIGS. 2 to 5).

[0138] The raw material solution 104a had ultrapure water as the solvent and gallium bromide as the solute. The gallium concentration was 0.1 mol / L. The obtained raw material solution 104a was placed in the mist generation source 104. Next, the flow control valves 103a and 103b were opened to supply carrier gas from the carrier gas sources 102a and 102b into the film formation chamber 107. After the atmosphere in the film formation chamber 107 was sufficiently replaced with the carrier gas, the flow rate of the carrier gas was adjusted to 2 L / min and the flow rate of the dilution carrier gas was adjusted to 6 L / min. Nitrogen was used as the carrier gas.

[0139] Next, ultrasonic vibrator 106 was vibrated at 2.4 MHz, and the vibrations were propagated through water 105a to raw material solution 104a, thereby misting raw material solution 104a to generate mist. This mist was introduced into film formation chamber 107 via supply pipe 109 by a carrier gas, and the mist was thermally reacted on substrate 110 to form a thin film of gallium oxide on substrate 110. The film formation time was 30 minutes.

[0140] (evaluation) X-ray diffraction confirmed the formation of α-Ga2O3 in the thin film formed on the substrate 110. Measurement of the rocking curve of the (006) plane of α-Ga2O3 revealed a half-width of 9.2 seconds, indicating excellent crystallinity. Film thickness was measured at 25 points on the surface using a Filmetrics F50 spectroscopic reflectance film thickness meter. The average film thickness was 824 nm, and the V value calculated from the above formula (1) was 0.040. The film also exhibited a uniform color across the surface, indicating excellent film thickness distribution. Furthermore, when SBDs, which are semiconductor devices, were manufactured from this stacked structure, the breakdown voltage yield of a production lot consisting of 66 SBDs was 82%.

[0141] [Comparative Example] In Example 1, before film formation, the substrate and nozzle were heated with the nozzle positioned vertically above the substrate. Except for this, film formation and evaluation were performed in the same manner as in Example 1. As a result, the average film thickness was 932 nm, and the V value obtained from equation (1) was 0.046. Furthermore, the reflected light from the substrate showed a distribution of various colors within the surface, which was visible to the naked eye, and the appearance was also unsatisfactory. Furthermore, when SBDs, which are semiconductor devices, were manufactured from this stacked structure, the breakdown voltage yield of a product lot consisting of 66 SBDs was 30%.

[0142] [Examples 2 to 7] The experiment and evaluation were carried out in the same manner as in Example 1, except for the conditions described in the table below.

[0143] [Table 1]

[0144] From the above results, it can be seen that the film thickness distribution can be significantly improved by the simple method of heating the nozzle before film formation without the substrate being present in the nozzle discharge direction. The crystalline gallium oxide film obtained by the film formation method of the present invention has a large area and is very good in film thickness distribution and crystallinity, and is useful for semiconductor devices, etc.

[0145] The present invention is not limited to the above-described embodiments. The above-described embodiments are merely examples, and anything that has substantially the same configuration as the technical idea described in the claims of the present invention and that exhibits similar effects is included within the technical scope of the present invention.

Claims

1. A film formation method for forming a crystalline oxide film containing gallium oxide as a main component on a substrate by a mist CVD method, comprising: a step of heating a substrate; a step of heating a nozzle for supplying a mist containing a raw material solution; and a step of supplying the mist onto the heated substrate so that the discharge direction of the heated nozzle is perpendicular to the surface of the substrate, thereby forming a crystalline oxide film, In the step of heating the nozzle, the nozzle is heated in a state where the substrate is not present in a discharge direction of the nozzle; The film forming method, wherein in the step of forming the crystalline oxide film, the film is formed in a state where the substrate is present in the ejection direction of the nozzle.

2. heating the substrate by using a substrate heating means having a substrate placement portion and a substrate non-placement portion, and placing the substrate on the substrate placement portion; 2. The film forming method according to claim 1, wherein in the step of heating the nozzle, the non-substrate placement portion is positioned in a discharge direction of the nozzle, and the nozzle is heated by the substrate heating means.

3. 2. The film forming method according to claim 1, wherein the nozzle is heated by a nozzle heating means provided in the nozzle.

4. A film formation method for forming a crystalline oxide film containing gallium oxide as a main component on a substrate by a mist CVD method, comprising: heating the substrate; a step of heating the film-forming member; and supplying mist onto the substrate in a direction normal to the surface of the substrate in a state where the heated film-forming member is present, thereby forming a crystalline oxide film, A film formation method, characterized in that in the step of heating the film formation member, the film formation member is heated in a state where the film formation member is not present on the substrate in a normal direction to the surface of the substrate.

5. In the step of heating the substrate, a substrate heating means having a substrate placement portion and a substrate non-placement portion is used, and the substrate is placed on the substrate placement portion and heated; The film formation method according to claim 4, characterized in that in the process of heating the film formation member, the film formation member is positioned on the non-substrate placement portion in a direction normal to the surface of the non-substrate placement portion, and the film formation member is heated by the substrate heating means.

6. 5. The film formation method according to claim 4, wherein in the step of heating the film formation member, the film formation member is heated by a film formation member heating means provided on the film formation member.

7. the film forming member is a nozzle for supplying the mist to the substrate, 5. The film deposition method according to claim 4, wherein in the step of heating the film deposition member, the nozzle is heated in a state where the nozzle outlet is not present on the substrate in a normal direction to the surface of the substrate.

8. The substrate has a film-forming surface area of ​​100 mm ２ 2. The film forming method according to claim 1, wherein a diameter of 2 inches (50 mm) or more is used.

9. The substrate has a film-forming surface area of ​​100 mm ２ 5. The film forming method according to claim 4, wherein a diameter of 2 inches (50 mm) or more is used.

10. 10. The film forming method according to claim 1, wherein the substrate has a diameter of 4 inches (100 mm) to 8 inches (200 mm).

11. A film forming apparatus for performing a mist CVD method, a substrate heating means having a substrate placement portion on which a substrate is placed; a nozzle for supplying a mist containing the raw material solution, the mist being discharged in a direction perpendicular to the surface of the substrate; a position adjusting means for adjusting the position of the nozzle and / or the substrate heating means, which is capable of adjusting the position of the substrate mounting part between a position of the nozzle in the discharge direction and a position other than the discharge direction, the substrate heating means further comprises a substrate non-mounting portion, The film forming apparatus is characterized in that the position adjusting means for the nozzle and / or the substrate heating means is capable of adjusting the position of the substrate non-placing portion to the position of the nozzle in the discharge direction.

12. 12. The film forming apparatus according to claim 11, wherein the nozzle is provided with a nozzle heating means for heating the nozzle.

13. A film forming apparatus for performing a mist CVD method, a substrate heating means having a substrate placement portion on which a substrate is placed; a nozzle for supplying a mist containing the raw material solution, the mist being discharged in a direction perpendicular to the surface of the substrate; a position adjusting means for adjusting the position of the nozzle and / or the substrate heating means, which is capable of adjusting the position of the substrate mounting part between a position of the nozzle in the discharge direction and a position other than the discharge direction, The film forming apparatus is characterized in that the nozzle is provided with a nozzle heating means for heating the nozzle.

14. A film forming apparatus for performing a mist CVD method, a substrate heating means having a substrate placement portion on which a substrate is placed; a film-forming member; a position adjusting means for adjusting the position of the film formation member to a position other than a position on the substrate placement part in a normal direction to the surface of the substrate placement part, the substrate heating means further comprises a substrate non-mounting portion, A film forming apparatus characterized in that the position adjustment means for the film forming member and / or the substrate heating means is capable of adjusting the position of the film forming member to a position on the non-substrate placing portion in the normal direction of the surface of the non-substrate placing portion.

15. A film forming apparatus for performing a mist CVD method, a substrate heating means having a substrate placement portion on which a substrate is placed; a film-forming member; a position adjusting means for adjusting the position of the film formation member to a position other than a position on the substrate placement part in a normal direction to the surface of the substrate placement part, The film-forming apparatus is characterized in that the film-forming member is provided with a film-forming member heating means for heating the film-forming member.

16. 16. The film forming apparatus according to claim 14, wherein the film forming member is a nozzle for supplying mist to the substrate or a top plate for rectifying the supplied mist on the substrate.

17. A film formation method for forming a crystalline oxide film containing gallium oxide as a main component on a substrate by a mist CVD method, comprising: heating the substrate; a step of heating a nozzle for supplying a mist containing the raw material solution to a predetermined temperature; and guiding the mist to the substrate to form a crystalline oxide film, and exhausting the mist after the film formation. A film forming method, characterized in that in the step of heating the nozzle to a predetermined temperature, a substance discharged from the nozzle is exhausted without passing through the substrate.

18. A film forming apparatus for performing a mist CVD method, a substrate heating means having a substrate placement portion on which a substrate is placed; a nozzle for supplying mist to the substrate; and an exhaust means for exhausting the mist after film formation, The film forming apparatus is characterized in that the exhaust means has a mechanism for exhausting the effluent discharged from the nozzle without passing through the substrate placement part.

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