JP7078581B2 - Laminated structure, semiconductor device, and method for manufacturing the laminated structure - Google Patents

Description

The present invention relates to a laminated structure, a semiconductor device, and a method for manufacturing the laminated structure.

Oxide semiconductors typified by gallium oxide (Ga ₂ O ₃ ) are expected to be applied to next-generation switching devices capable of achieving high withstand voltage, low loss, and high heat resistance as semiconductors with a large bandgap.

Japanese Unexamined Patent Publication No. 2014-072463 Japanese Unexamined Patent Publication No. 2014-015366 JP-A-2015-091740

Patent Document 1 describes a method for producing gallium oxide (α-Ga ₂ O ₃ ) having a corundum structure at a relatively low temperature, but since α-Ga ₂ O ₃ is a metastable phase, There is the problem of thermal instability.

On the other hand, β-Ga ₂ O ₃ is the most stable phase, and the above-mentioned phase transition does not occur. However, as described in Patent Documents 2 and 3, it is necessary to heat the film to an extremely high temperature in order to form a film, and there is a demand for a simple and inexpensive film forming method at a lower temperature. rice field.

When a crystalline oxide film having a beta-gallian structure is used in a semiconductor device, the thermal stability of the film is high as described above, and the smoothness of the film surface affects the conductivity of the film, so that the film surface is smooth. Is preferable.
As a method for smoothing the film surface, there is a surface treatment method such as etching, but if the surface treatment is performed after the thin film is formed, there is a concern that the thin film is scraped and the semiconductor characteristics are deteriorated.

The present invention has been made to solve the above problems, to provide an inexpensive laminated structure having a crystalline oxide film which is thermally stable and has excellent surface smoothness, and heat. It is an object of the present invention to provide a film forming method capable of forming a laminated structure having a crystalline oxide film which is stable and has excellent surface smoothness easily and inexpensively by a low temperature process.

The present invention has been made to achieve the above object, and is a laminated structure having a crystalline substrate and a crystalline oxide film containing gallium as a main component and having a betagallian structure, and the crystalline substrate. Is a crystalline substrate containing lithium tantalum as a main component, and provides a laminated structure in which the surface roughness Ra of the crystalline oxide film is 0.1 μm or less.

Such a laminated structure can be obtained easily and inexpensively, is thermally stable, has excellent surface smoothness, and can be suitably used for a semiconductor device.
The surface roughness Ra represents an arithmetic mean roughness calculated based on JIS B0601.

At this time, the crystalline oxide film can be a laminated structure containing an abnormal grain inhibitor composed of at least one selected from Br and I.

As a result, a laminated structure having a crystalline oxide film having excellent surface smoothness is more reliably obtained.

At this time, the crystalline substrate can be a laminated structure which is a lithium tantalate single crystal substrate.

This results in a laminated structure having a crystalline oxide film having a beta-galia structure with higher crystallinity.

At this time, the crystalline oxide film can be a laminated structure containing β-Ga ₂ O ₃ as a main component.

This results in a laminated structure with a thermally more stable crystalline oxide film.

At this time, it is possible to form a laminated structure in which the film thickness of the crystalline oxide film is 1 μm or more.

This makes it more useful for semiconductor devices.

At this time, it is possible to form a laminated structure in which the area of the crystalline oxide film is 100 mm ² or more.

This makes the area more useful for semiconductor devices.

At this time, the semiconductor device including the above-mentioned laminated structure can be obtained.

As a result, the semiconductor device has excellent characteristics.

Further, the mist generated by atomizing or dropletizing an aqueous solution containing at least gallium is conveyed to a substrate using a carrier gas, and the mist is thermally reacted on the substrate to have gallium as a main component in beta gallia. A method for forming a crystalline oxide film having a structure, in which a crystalline substrate containing lithium tantalate as a main component is used as the substrate, and the aqueous solution contains at least one abnormality selected from Br and I. A laminate in which a grain inhibitor is contained and the abnormal grain inhibitor is doped during the formation of the crystalline oxide film to form the crystalline oxide film having a surface roughness Ra of 0.1 μm or less. A method for manufacturing a structure is provided.

According to the method for producing such a laminated structure, a laminated structure containing a crystalline oxide film having a beta-galia structure, being thermally stable, and having excellent surface smoothness can be produced with high productivity by a low temperature process. , Can be manufactured easily and inexpensively.

At this time, a method for manufacturing a laminated structure using a lithium tantalate single crystal substrate as the crystalline substrate can be used.

This makes it possible to produce a laminated structure having a crystalline oxide film having a beta-galia structure having higher crystallinity.

At this time, it is possible to use a method for manufacturing a laminated structure in which the temperature of the thermal reaction is 250 to 900 ° C.

As a result, the laminated structure having a beta-galia structure can be manufactured at a lower temperature, so that not only the running cost can be reduced, but also the time required for manufacturing can be shortened.

At this time, a method for producing a laminated structure in which the crystalline oxide film contains β-Ga ₂ O ₃ as a main component can be used.

This makes it possible to provide a laminated structure having a thermally more stable crystalline oxide film.

At this time, it is possible to use a method for manufacturing a laminated structure in which the film thickness of the crystalline oxide film is 1 μm or more.

Thereby, a useful laminated structure can be obtained by the semiconductor device.

At this time, it is possible to use a method for manufacturing a laminated structure using a substrate having a film-forming surface area of 100 mm ² or more.

This makes it possible to easily and inexpensively obtain a large-area laminated structure.

As described above, according to the laminated structure of the present invention, the laminated structure is thermally stable, has excellent surface smoothness, and can be suitably used for a semiconductor device. In addition, the semiconductor device has excellent characteristics. Further, according to the method for producing a laminated structure of the present invention, a laminated structure containing a crystalline oxide film having a beta-galia structure, being thermally stable, and having excellent surface smoothness can be easily and inexpensively produced. Can be manufactured.

It is a schematic sectional drawing which shows an example of the laminated structure which concerns on this invention. It is a schematic block diagram which shows an example of the film-forming apparatus used in the manufacturing method of the laminated structure which concerns on this invention. It is a figure explaining an example of the mist formation part in the film forming apparatus. 3 is a graph showing the relationship between the surface roughness Ra of the crystalline oxide film and the concentration of the abnormal grain inhibitor in Example 1 and Comparative Example 2.

Hereinafter, the present invention will be described in detail, but the present invention is not limited thereto.

As described above, it is possible to provide an inexpensive laminated structure having a crystalline oxide film which is thermally stable and has excellent surface smoothness, and is thermally stable and has excellent surface smoothness. It has been required to provide a method for producing a laminated structure in which a crystalline oxide film is formed by a low-temperature process easily and inexpensively.

As a result of diligent studies on the above problems, the present inventors have found that the crystalline substrate is a laminated structure having a crystalline substrate and a crystalline oxide film containing gallium as a main component and having a betagallian structure. , A crystalline substrate containing lithium tantalum as a main component, which can be easily and inexpensively obtained by a laminated structure having a surface roughness Ra of 0.1 μm or less of the crystalline oxide film, and is thermally obtained. The present invention has been completed by finding that it is stable and has excellent surface smoothness and can be suitably used for semiconductor devices.

Further, the present inventors transport the mist generated by atomizing or dropletizing an aqueous solution containing at least gallium to a substrate using a carrier gas, and thermally react the mist on the substrate. A method for forming a crystalline oxide film having a beta-gallian structure containing gallium as a main component, wherein a crystalline substrate containing lithium tantalate as a main component is used as the substrate, and the aqueous solution is selected from Br and I. The crystalline oxide having a surface roughness Ra of 0.1 μm or less is contained by containing an abnormal grain inhibitor composed of at least one kind and doping the abnormal grain inhibitor at the time of forming the crystalline oxide film. By the method for producing a laminated structure for forming a film, a laminated structure containing a crystalline oxide film having a beta-gallium structure, being thermally stable, and having excellent surface smoothness can be produced at a low temperature with high productivity. The present invention has been completed by finding that it can be manufactured easily and inexpensively.

Hereinafter, description will be given with reference to the drawings.

(Laminated structure)
As shown in FIG. 1, one embodiment of the laminated structure 1 according to the present invention is a crystalline oxide film having a beta-galia structure containing gallium as a main component on a crystalline substrate 10 containing lithium tantalate as a main component. It is a laminated structure 1 in which 20 is laminated. A buffer layer or the like may be interposed between the crystalline substrate 10 and the crystalline oxide film 20.
Further, the surface roughness Ra of the crystalline oxide film 20 is 0.1 μm or less, has excellent surface smoothness, and has excellent semiconductor characteristics.

Here, the term "crystallinity" means that the crystalline state includes a polycrystalline state or a single crystal state. Amorphous may be mixed in polycrystal or single crystal.

(Crystalline substrate containing lithium tantalate as the main component)
First, a crystalline substrate containing lithium tantalate as a main component of the laminated structure according to the present invention will be described.

When manufacturing the laminated structure according to the present invention, first, a crystalline substrate containing lithium tantalate as a main component is prepared. Here, the "crystalline substrate containing lithium tantalate as a main component" includes a substrate containing 50 to 100% lithium tantalate, which contains lithium tantalate as a single crystal or a polycrystalline substrate.

Lithium tantalate has an ilmenite structure and its lattice constant is relatively close to α-Ga ₂ O ₃ . The magnitude relationship between oxygen atoms on the α-Ga ₂ O ₃ (001) plane, β-Ga ₂ O ₃ (-201) plane, and lithium tantalate (001) plane is generally α-Ga ₂ O ₃ <Lithium tantalate <β-Ga ₂ O ₃ . Since β-Ga ₂ O ₃ is energetically more stable than α-Ga ₂ O ₃ , α-Ga ₂ O ₃ is not formed on the lithium tantalate substrate even at low temperatures, and β-Ga ₂ O ₃ is formed. It is presumed that they are formed preferentially.

As the crystalline substrate containing lithium tantalate as a main component, it is most preferable to use a lithium tantalate single crystal substrate. This is because the quality of the crystalline oxide film is the highest quality.

Hereinafter, a lithium tantalate single crystal substrate will be described as an example. The lithium tantalate single crystal substrate can be obtained, for example, by growing a lithium tantalate single crystal by the Czochralski method to form a lithium tantalate single crystal ingot, and slicing this ingot to process it into a substrate shape.

The lithium tantalate single crystal substrate that can be used in the present invention is preferably cut so that the lattice constant on its surface is close to the lattice constant of the crystalline oxide film to be deposited later. For example, when depositing a crystalline oxide film containing β-Ga ₂ O ₃ as a main component, it is preferable that the crystal orientation is cut so as to be within Z ± 10 °, and more preferably, the crystal orientation is It should be cut so that it is within Z ± 5 °.

Further, in the lithium tantalate single crystal substrate that can be used in the present invention, it is preferable that the uniform polarization state of the substrate promotes uniform growth of the oxide single crystal film. That is, it is preferable that the lithium tantalate substrate is subjected to a single polarization treatment or a multi-polarization treatment.

To obtain a monopolarized substrate, for example, a lithium tantalate single crystal ingot prepared by the Czochralski method is heated to 700 ° C., and a voltage of 200 V is applied in the Z direction of the crystal orientation for 10 hours. After performing the polling process, it is advisable to slice the ingot and process it into a substrate shape. Further, the substrate itself processed into the substrate shape may be heated to 700 ° C., and a voltage of 200 V may be applied in the crystal direction Z direction to perform polling processing for 10 hours.

When a substrate subjected to a single polarization treatment is used, further pyroelectricity suppressing treatment is performed on the substrate surface to prevent the substrate from being charged when the crystalline oxide film is deposited on the heated substrate. Is preferable. In the pyroelectric suppression treatment, for example, a lithium tantalate single crystal substrate subjected to a single polarization treatment is embedded in lithium carbonate powder, and the temperature is 350 ° C. or higher and the Curie temperature (about 610 ° C.) in a reducing gas atmosphere. Heat treatment is performed at the following temperature. At this time, the volume resistivity in the thickness direction of the substrate is 1.0 × 10 ¹¹ Ω · cm or more, 2.0 × 10 ¹³ Ω · cm or less, and the maximum and minimum values of the volume resistivity in the substrate. When the treatment is performed so that the ratio is 4.0 or less, the electrical resistivity of the substrate when the crystalline oxide film is deposited on the substrate can be effectively suppressed.

On the other hand, in order to obtain a multipolarized substrate, for example, a single crystal (ingot or substrate) once monopolarized or a single crystal (ingot or substrate) not subjected to the single polarization treatment is subjected to. It is heated to 700 ° C. or higher, annealed for several hours (preferably 1000 ° C. or higher, preferably 5 hours or longer, more preferably 10 hours or longer), subjected to strain relaxation treatment, and in the case of an ingot, it is sliced to form a substrate. It is good to process it into. It is preferable to use a multipolarized substrate because it is possible to suppress the charge of the substrate when the crystalline oxide film is deposited on the heated substrate. In particular, if the average polarization size of the surface of the substrate is set to 5 μm or less, charging can be effectively suppressed. When the charging effect of the lithium tantalate substrate is suppressed, it is preferable that the crystalline oxide film is stably deposited. It is preferable that the composition of the lithium tantalate single crystal (at least on the surface of the substrate) is a congluent composition, because the average domain size of the polarization on the surface of the substrate tends to be small. Here, in the case of lithium tantalate, the congluent composition means that the ratio of Li to Ta is Li: Ta = 48.5-α: 51.5 + α, and α is −0.5 ≦ α ≦ 0.5. It means that it is a range.

When the surface of the crystalline substrate containing lithium tantalate as a main component is polished smoothly so that the unevenness becomes small, a flat laminated film of the crystalline oxide film can be obtained. Ra is preferably 10 nm or less. It is more preferable that Ra is 5 nm or less.

In addition, ions selected from hydrogen, helium, argon, and other rare gases are injected in advance into the surface of the crystalline substrate containing lithium tantalate as the main component to deposit the crystalline oxide film, and the ion is injected from 50 nm of the deposited surface. It is also possible to form a fragile layer directly below 3 μm. By doing so, after the crystalline oxide film is deposited, the deposited crystalline oxide film can be easily peeled off from the lithium tantalate single crystal substrate by giving an impact to the fragile layer.

The thickness of the crystalline substrate is not particularly limited, but is preferably 10 to 2000 μm, and more preferably 50 to 800 μm. The area of the substrate is preferably 100 mm ² or more, and more preferably the diameter is 2 inches (50 mm) or more.

(Crystalline oxide film)
The crystalline oxide film in the laminated structure according to the present invention is a crystalline oxide film containing gallium as a main component and having a beta-gallian structure. The crystalline oxide film is usually composed of metal and oxygen, but in the present invention, there is no problem as long as gallium is the main component as the metal. Here, when the term "gallium is the main component" in the present invention, it means that 50 to 100% of the metal components are gallium. The metal component 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 crystalline oxide film may be single crystal or polycrystal as long as it has a beta-gallian structure.

Among the crystalline oxide films having gallium as a main component and having a beta-gallian structure, those having β-Ga ₂ O ₃ as a main component are particularly preferable. β-Ga ₂ O ₃ is a thermally more stable crystalline oxide film.

The crystalline oxide film may contain a dopant. For example, n-type dopants such as tin, germanium, silicon, titanium, zirconium, vanadium or niobium, or p-type dopants such as copper, silver, tin, iridium and rhodium can be mentioned. The dopant is not particularly limited, but is preferably tin. The concentration of the dopant may be, for example, about 1 × 10 ¹⁶ / cm ³ to 1 × 10 ²² / cm ³ , or even at a low concentration of about 1 × 10 ¹⁷ / cm ³ or less, about 1 × 10 ²⁰ . A high concentration of / ^cm3 or more may be used.

In the present invention, the film thickness of the crystalline oxide film is not particularly limited, but can be 1 μm or more. For example, it may be 1 to 100 μm, preferably 5 to 50 μm, and more preferably 10 to 20 μm. Further, another layer may be interposed between the substrate and the crystalline oxide film. The other layer is a layer having a composition different from that of the substrate and the crystalline oxide film of the outermost layer, and may be, for example, a crystalline oxide film, an insulating film, a metal film, or the like.

Further, it is preferable that the crystal oxide film contains an abnormal grain inhibitor. The abnormal grain inhibitor has an effect of suppressing the generation of by-produced particles at the time of film formation, and particularly preferably one composed of at least one selected from Br and I. By including these, it is possible to prevent the surface roughness from becoming rough due to the growth of abnormal grains, and more reliably obtain a crystalline oxide film having excellent surface smoothness of 0.1 μm or less as described above. ..

The laminated structure according to the present invention or the crystalline oxide film obtained from the laminated structure can be used in a semiconductor device by appropriately designing the structure. For example, Schottky barrier diode (SBD), metal semiconductor field effect transistor (MESFET), high electron mobility transistor (HEMT), metal oxide film semiconductor field effect transistor (PWM), electrostatic induction transistor (SIT), junction electric field effect. Each semiconductor layer such as a transistor (JFET), an insulated gate type bipolar transistor (IGBT), and a light emitting diode (LED) can be configured.

(Film formation device)
In one embodiment of the laminated structure according to the present invention, a mist generated by atomizing or dropletizing an aqueous solution containing at least gallium is conveyed to a substrate by a carrier gas, and then the mist is heated on the substrate. A method of reacting to form a crystalline oxide film, wherein the substrate is a crystalline substrate containing lithium tantalum as a main component, and the crystalline oxide film contains gallium as a main component and has a beta-gallian structure. It is characterized by being a thing. Further, the aqueous solution contains an abnormal grain inhibitor consisting of at least one selected from Br and I, and the abnormal grain inhibitor is doped during the formation of the crystalline oxide film to form a surface roughness Ra. It is characterized in that a crystalline oxide film having a thickness of 0.1 μm or less is formed.

FIG. 2 shows an example of a film forming apparatus 101 that can be used in the method for manufacturing a laminated structure according to the present invention. The film forming apparatus 101 has a mist-forming unit 120 that converts a raw material solution into a mist to generate mist, a carrier gas supply unit 130 that supplies a carrier gas that conveys the mist, and a heat-treated mist to form a film on a substrate. It has a film forming section 140, a mist forming section 120, and a transport section 109 that connects the film forming section 140 and conveys mist by a carrier gas. Further, the film forming apparatus 101 may be controlled in its operation by providing a control unit (not shown) for controlling the whole or a part of the film forming apparatus 101.

Here, the mist in the present invention refers to a general term for fine particles of liquid dispersed in a gas, and includes those called mist, droplets, and the like.

(Raw material solution)
The raw material solution (aqueous solution) 104a is not particularly limited as long as it contains at least gallium and an abnormal grain inhibitor (at least one selected from Br and I). That is, in addition to gallium, it may contain one or more metals selected from, for example, iron, indium, aluminum, vanadium, titanium, chromium, rhodium, iridium, nickel and cobalt. A complex or salt obtained by dissolving or dispersing the metal in water can be preferably used. Examples of the form of the complex include an acetylacetonate complex, a carbonyl complex, an ammine complex, and a hydride complex. Examples of the salt form include metal chloride salt, metal bromide salt, metal iodide salt and the like. Further, a metal obtained by dissolving the above metal in hydrobromic acid, hydrochloric acid, hydroiodic acid or the like can also be used as an aqueous salt solution. The solute concentration is preferably 0.01 to 1 mol / L.

The raw material solution 104a may contain a dopant element. For example, n-type dopants such as tin, germanium, silicon, titanium, zirconium, vanadium or niobium, or p-type dopants such as copper, silver, tin, iridium and rhodium can be mentioned. The dopant is not particularly limited, but is preferably tin. Further, it is preferable that the dopant element is ionized. Therefore, an acid may be mixed with the raw material solution 104a to promote the dissolution of the dopant element. Examples of the acid include hydrogen halides such as hydrobromic acid, hydrochloric acid, and hydroiodic acid, hypochlorous acid, hypochloric acid, hypobromic acid, bromine acid, hypoiodic acid, and iodic acid. Examples thereof include halogenoxo acids, carboxylic acids such as formic acid, nitric acid, and the like. It should be noted that heating or applying ultrasonic waves is also effective for promoting dissolution.

Further, when the abnormal grain inhibitor Br or I is contained in the raw material solution 104a, it can be added to the raw material solution 104a in the form of hydrogen bromide acid or hydrogen iodide acid, for example. The concentration of these abnormal grain inhibitors is not particularly limited. The concentration is most preferably 10-20 vol% in order to leave the abnormal grain inhibitor in the crystalline oxide film.
The concentration of the abnormal grain inhibitor represents the ratio of the volume of the abnormal grain inhibitor added to the volume of the raw material solution.
(Abnormal grain inhibitor concentration [vol%] = volume of abnormal grain inhibitor [mL] / volume of raw material solution [mL])
The volume of the abnormal grain inhibitor here means the volume of hydrogen bromide acid or hydrogen iodide acid as described above.
Further, when hydrogen bromide, hydrogen iodide, or the like is added to promote the dissolution of the dopant element as described above, it is advisable to adjust the concentration in consideration of the amount.

(Mist conversion department)
The mist-forming unit 120 adjusts the raw material solution 104a to mist the raw material solution 104a to generate mist. The mist-forming means is not particularly limited as long as the raw material solution 104a can be mist-ized, and may be a known mist-forming means, but it is preferable to use a mist-forming means by ultrasonic vibration. This is because it can be made into a mist more stably.

An example of such a mist-forming unit 120 is shown in FIG. For example, the mist generation source 104 in which the raw material solution 104a is housed, a container 105 in which a medium capable of transmitting ultrasonic vibration, for example, water 105a, and an ultrasonic oscillator 106 attached to the bottom surface of the container 105 may be included. good. Specifically, the mist generation source 104 consisting of a container containing the raw material solution 104a is stored in the container 105 containing the water 105a by using a support (not shown). An ultrasonic oscillator 106 is provided at the bottom of the container 105, and the ultrasonic oscillator 106 and the oscillator 116 are connected to each other. Then, when the oscillator 116 is operated, the ultrasonic oscillator 106 vibrates, the ultrasonic waves propagate into the mist generation source 104 via the water 105a, and the raw material solution 104a is configured to become mist.

(Transport section)
The transport unit 109 connects the mist-forming unit 120 and the film-forming unit 140. The mist is conveyed by the carrier gas from the mist generation source 104 of the mist-forming unit 120 to the film-forming chamber 107 of the film-forming unit 140 via the transport unit 109. The transport unit 109 may be, for example, a supply pipe 109a. As the supply tube 109a, for example, a quartz tube, a resin tube, or the like can be used.

(Film film part)
In the film forming section 140, the mist is heated to cause a thermal reaction to form a film on a part or all of the surface of the substrate (crystalline substrate) 110. The film forming section 140 is provided with, for example, a film forming chamber 107, and a substrate (crystalline substrate) 110 is installed in the film forming chamber 107, and a hot plate for heating the substrate (crystalline substrate) 110 is provided. 108 can be provided. The hot plate 108 may be provided outside the film forming chamber 107 as shown in FIG. 2, or may be provided inside the film forming chamber 107. Further, the film forming chamber 107 may be provided with an exhaust gas exhaust port 112 at a position that does not affect the supply of mist to the substrate (crystalline substrate) 110.

Further, in the present invention, the substrate (crystalline substrate) 110 may be placed on the upper surface of the film forming chamber 107 for face-down, or the substrate (crystalline substrate) 110 may be placed on the bottom surface of the film forming chamber 107. It may be installed and used as a face-up.

The thermal reaction may be such that the mist reacts by heating, and the reaction conditions and the like are not particularly limited. It can be appropriately set according to the raw material and the film film. For example, the heating temperature can be in the range of 250 to 900 ° C, preferably in the range of 300 ° C to 800 ° C, and more preferably in the range of 350 ° C to 700 ° C.

The thermal reaction may be carried out under any of a vacuum, a non-oxygen atmosphere, a reducing gas atmosphere, an air atmosphere and an oxygen atmosphere, and may be appropriately set according to the film film. Further, the reaction pressure may be carried out under any condition of atmospheric pressure, pressurization or reduced pressure, but the film formation under atmospheric pressure is preferable because the apparatus configuration can be simplified.

(Carrier gas supply section)
The carrier gas supply unit 130 has a carrier gas source 102a for supplying the carrier gas, and a flow rate control valve 103a for adjusting the flow rate of the carrier gas (hereinafter referred to as “main carrier gas”) sent out from the carrier gas source 102a. May be provided. Further, it is also possible to provide a dilution carrier gas source 102b for supplying a dilution carrier gas as needed, and a flow rate control valve 103b for adjusting the flow rate of the dilution carrier gas sent out from the dilution carrier gas source 102b. ..

The type of carrier gas is not particularly limited and can be appropriately selected depending on the film film. For example, an inert gas such as oxygen, ozone, nitrogen or argon, or a reducing gas such as hydrogen gas or forming gas can be mentioned. Further, the type of carrier gas may be one type or two or more types. For example, a diluted gas obtained by diluting the same gas as the first carrier gas with another gas (for example, diluted 10-fold) may be further used as the second carrier gas, or air may be used.

In the present invention, the flow rate Q of the carrier gas refers to the total flow rate of the carrier gas. In the above example, the total flow rate of the main carrier gas sent out from the carrier gas source 102a and the flow rate of the dilution carrier gas sent out from the dilution carrier gas source 102b is defined as the carrier gas flow rate Q.

The flow rate Q of the carrier gas is appropriately determined depending on the size of the film forming chamber and the substrate, but is usually 1 to 60 L / min, preferably 2 to 40 L / min.

(Film formation method)
Next, an example of the film forming method according to the present invention will be described with reference to FIG. 2. First, the raw material solution 104a is housed in the mist generation source 104 of the mist-forming unit 120, and the substrate (crystalline substrate) 110 is placed directly on the hot plate 108 or through the wall of the film forming chamber 107, and the hot plate 108 is placed. To operate. Since lithium tantalate has a large coefficient of thermal expansion, it is preferable to gradually raise the temperature from a low temperature.

Next, the flow control valves 103a and 103b are opened to supply the carrier gas from the carrier gas sources 102a and 102b into the film forming chamber 107, and the atmosphere of the film forming chamber 107 is sufficiently replaced with the carrier gas, and the main carrier gas is sufficiently replaced. The carrier gas flow rate Q is controlled by adjusting the flow rate of the carrier gas and the flow rate of the carrier gas for dilution, respectively.

In the step of generating mist, the ultrasonic vibrator 106 is vibrated and the vibration is propagated to the raw material solution 104a through water 105a to mist the raw material solution 104a and generate mist. Next, in the step of transporting the mist by the carrier gas, the mist is transported from the mist-forming section 120 to the film forming section 140 via the transport section 109 by the carrier gas, and is introduced into the film forming chamber 107. The mist introduced into the film forming chamber 107 in the process of forming a film is heat-treated by the heat of the hot plate 108 in the film forming chamber 107 and undergoes a thermal reaction to form a film on the substrate (crystalline substrate) 110. To.

(Peeling)
The crystalline substrate may be peeled off from the crystalline oxide film. The peeling means is not particularly limited and may be a known means. For example, a means for peeling by applying a mechanical impact, a means for peeling by applying heat and utilizing thermal stress, a means for peeling by applying vibration such as ultrasonic waves, a means for etching and peeling, laser lift-off, and the like can be mentioned. Be done. By the peeling, a crystalline oxide film can be obtained as a self-supporting film.

(electrode)
A general method can be used for forming the electrodes required for forming the semiconductor device. That is, in addition to vapor deposition, sputtering, CVD, plating, etc., any printing method such as bonding with a resin or the like may be used. The electrode materials include Al, Ag, Ti, Pd, Au, Cu, Cr, Fe, W, Ta, Nb, Mn, Mo, Hf, Co, Zr, Sn, Pt, V, Ni, Ir, Zn, In. , Nd and other metals, as well as metal oxide conductive films such as tin oxide, zinc oxide, indium oxide, indium tin oxide (ITO) and indium zinc oxide (IZO), and organic conductive compounds such as polyaniline, polythiophene or polypyrrole. Either of these may be used, and two or more of these alloys and mixtures may be used. The thickness of the electrode is preferably 1 to 1000 nm, more preferably 10 to 500 nm.

Hereinafter, the present invention will be described in detail with reference to examples, but this is not limited to the present invention.

(Example 1)
Based on the above-mentioned method for producing a laminated structure, a film of gallium oxide (β-Ga ₂ O ₃ ) having a β-galia structure was formed to obtain a laminated structure.

Specifically, first, a lithium tantalate single crystal substrate having a congluent composition (Li / (Li + Ta) value of 0.485) was prepared as a crystalline substrate. The lithium tantalate single crystal produced by the Czochralski method is Z-axis cut, processed into a C-plane substrate, heat-treated at 700 ° C. for 10 hours, subjected to multipolarization treatment, and the surface is polished. The surface roughness Ra was set to 0.5 nm. Next, as a raw material solution, an aqueous solution was prepared so that the concentration of gallium bromide was 1.0 × 10 ^-1 mol / L, and the atomic number ratio of gallium bromide and tin chloride was 1: 0.02. Prepared. In order to add Br as an abnormal grain inhibitor to the prepared solution, a 48% hydrobromic acid solution was contained so as to have a volume ratio of 20%, and this was used as a raw material solution 104a.

The raw material solution 104a obtained as described above was housed in the mist generation source 104. Next, as the substrate (crystalline substrate) 110, a 2-inch (50 mm diameter) c-plane lithium tantalate substrate having a thickness of 200 μm was placed on the hot plate 108 in the film forming chamber 107, and the hot plate 108 was operated. The temperature was raised to 400 ° C.

Subsequently, the flow control valves 103a and 103b are opened to supply nitrogen gas as a carrier gas from the carrier gas sources 102a and 102b into the film forming chamber 107, and the atmosphere of the film forming chamber 107 is sufficiently replaced with the carrier gas. The flow rate of the main carrier gas was adjusted to 2 L / min, and the flow rate of the diluting carrier gas was adjusted to 4.5 L / min. That is, the carrier gas flow rate Q = 6.5 L / min.

Next, the ultrasonic vibrator 106 was vibrated at 2.4 MHz, and the vibration was propagated to the raw material solution 104a through water 105a to mist the raw material solution 104a to generate mist. This mist was introduced into the film forming chamber 107 through the supply pipe 109a by the carrier gas. Then, under the condition of atmospheric pressure and 400 ° C., the mist is thermally reacted in the film forming chamber 107 to form a thin film of gallium oxide (β-Ga ₂ O ₃ ) having a beta-gallium structure on the substrate (crystalline substrate) 110. Formed. The film formation time was 60 minutes.

In addition to the above, an aqueous solution was prepared in the same manner as above, except that gallium bromide and gallium iodide and hydrogen iodide solutions were used instead of hydrobromic acid, respectively, and another raw material solution 104a was prepared. As a result, a thin film was formed in the same manner.

The phase of the formed thin film was identified by performing a 2θ / ω scan from 10 degrees to 120 degrees using an XRD diffractometer. The measurement was performed using CuKα ray. As a result, the formed thin film was β-gallium oxide having a beta-gallium structure.
The film thickness of the thin film was measured using a reflectance spectroscopic film thickness meter. The film thickness was 1.0 μm.
For the surface roughness Ra, the result of surface shape measurement for a region of 10 μm square by an atomic force microscope (AFM) was used. The results of the surface roughness Ra are shown in Tables 1, 2 and 4 below in relation to the presence and concentration of the abnormal grain inhibitor. Note that FIG. 4 is a graph of Table 2. However, the item without the abnormal grain inhibitor is the result of Comparative Example 2 described later.
Further, after the film was formed, the film was allowed to stand in a horizontal furnace and annealed at 600 ° C. for 3 hours under a nitrogen stream of 10 L / m, and the crystallinity did not change.

Further, as shown in Tables 2 and 4, the concentration of the abnormal grain inhibitor in the raw material solution was set to various concentrations, and other than that, a thin film was formed in the same manner as described above.
As can be seen from Tables 1, 2 and 4, the surface roughness Ra (150 μm) is superior in the present invention in which the abnormal grain inhibitor is added to the raw material solution and the thin film is doped, as compared with the case where there is no abnormal grain inhibitor (150 μm). It can be seen that (100 μm or less) is obtained. In particular, it can be seen that a better surface roughness Ra is obtained in the case of 10-20 vol% (5-25 μm).

(Comparative Example 1)
The film formation and evaluation were carried out in the same manner as in Example 1 except that the c-plane sapphire substrate was used as the substrate.
When the phase of the crystalline oxide film of the obtained laminated structure was identified, it was α-gallium oxide. The film thickness was 1.2 μm. The surface roughness Ra was 85 nm.
After film formation, the film was allowed to stand in a horizontal furnace and annealed at 600 ° C. for 3 hours under a nitrogen flow of 10 L / m. As a result, the peak intensity of α-gallium oxide decreased and a new peak of β-gallium oxide appeared. did.

(Comparative Example 2)
The film formation and evaluation were carried out in the same manner as in Example 1 except that the abnormal grain inhibitor was not used in the raw material solution.
When the phase of the crystalline oxide film of the obtained laminated structure was identified, it was β-gallium oxide. The film thickness was 1.1 μm. The surface roughness Ra was 150 nm.
After the film formation, the film was allowed to stand in a horizontal furnace and annealed at 600 ° C. for 3 hours under a nitrogen stream of 10 L / m, and the crystallinity did not change.

(Example 2)
The film formation and evaluation were carried out in the same manner as in Example 1 except that the film formation time was set to 120 minutes.
When the phase of the crystalline oxide film of the obtained laminated structure was identified, it was β-gallium oxide. The film thickness was 2.4 μm. The surface roughness Ra was 17 nm.
After the film formation, the film was allowed to stand in a horizontal furnace and annealed at 600 ° C. for 3 hours under a nitrogen stream of 10 L / m, and the crystallinity did not change.

(Example 3)
The film formation and evaluation were carried out in the same manner as in Example 1 except that the film formation temperature was set to 450 ° C.
When the phase of the crystalline oxide film of the obtained laminated structure was identified, it was β-gallium oxide. The film thickness was 1.6 μm. The surface roughness Ra was 12 nm.
After the film formation, the film was allowed to stand in a horizontal furnace and annealed at 600 ° C. for 3 hours under a nitrogen stream of 10 L / m, and the crystallinity did not change.

(Example 4)
The film formation and evaluation were carried out in the same manner as in Example 1 except that Sn was not used in the raw material solution.
When the phase of the crystalline oxide film of the obtained laminated structure was identified, it was β-gallium oxide. The film thickness was 1.3 μm. The surface roughness Ra was 10 nm.
After the film formation, the film was allowed to stand in a horizontal furnace and annealed at 600 ° C. for 3 hours under a nitrogen stream of 10 L / m, and the crystallinity did not change.

(Example 5)
The film formation and evaluation were carried out in the same manner as in Example 1 except that the concentration of gallium bromide was 0.05 mol / L and the film formation temperature was 450 ° C.
When the phase of the crystalline oxide film of the obtained laminated structure was identified, it was β-gallium oxide. The film thickness was 1.0 μm. The surface roughness Ra was 7 nm.
After the film formation, the film was allowed to stand in a horizontal furnace and annealed at 600 ° C. for 3 hours under a nitrogen stream of 10 L / m, and the crystallinity did not change.

By using the abnormal grain inhibitor as in Example 1-5, it was possible to obtain a crystalline oxide thin film having a beta-galia structure having an excellent surface smoothness of 0.1 μm or less in surface roughness Ra. Moreover, since both the β-gallium oxide and the lithium tantalate substrate are thermally stable, annealing at a high temperature is possible. It can be suitably used for semiconductor devices.

The present invention is not limited to the above embodiment. The above-described embodiment is an example, and any one having substantially the same structure as the technical idea described in the claims of the present invention and having the same effect and effect is the present invention. Is included in the technical scope of.

1 ... laminated structure, 10 ... crystalline substrate, 20 ... crystalline oxide film,
101 ... film forming apparatus, 102a ... carrier gas source,
102b ... Carrier gas source for dilution, 103a ... Flow control valve,
103b ... Flow control valve, 104 ... Mist source, 104a ... Raw material solution,
105 ... container, 105a ... water, 106 ... ultrasonic oscillator, 107 ... film formation chamber,
108 ... hot plate, 109 ... transport section, 109a ... supply pipe,
110 ... substrate (crystalline substrate), 112 ... exhaust port, 116 ... oscillator,
120 ... Mist conversion section, 130 ... Carrier gas supply section, 140 ... Film formation section.

Claims (13)

A laminated structure having a crystalline substrate and a crystalline oxide film containing gallium as a main component and having a beta-gallian structure.
The crystalline substrate is a crystalline substrate containing lithium tantalate as a main component.
A laminated structure characterized in that the surface roughness Ra of the crystalline oxide film is 0.1 μm or less. The laminated structure according to claim 1, wherein the crystalline oxide film contains an abnormal grain inhibitor consisting of at least one selected from Br and I. The laminated structure according to claim 1 or 2, wherein the crystalline substrate is a lithium tantalate single crystal substrate. The laminated structure according to any one of claims 1 to 3, wherein the crystalline oxide film contains β-Ga ₂ O ₃ as a main component. The laminated structure according to any one of claims 1 to 4, wherein the crystalline oxide film has a film thickness of 1 μm or more. The laminated structure according to any one of claims 1 to 5, wherein the crystalline oxide film has an area of 100 mm ² or more. A semiconductor device comprising the laminated structure according to any one of claims 1 to 6. The mist generated by atomizing or dropletizing an aqueous solution containing at least gallium is conveyed to a substrate using a carrier gas, and the mist is thermally reacted on the substrate to form a beta-gallium structure containing gallium as a main component. It is a method of forming a crystalline oxide film having a film.
A crystalline substrate containing lithium tantalate as a main component was used as the substrate.
The aqueous solution contains an abnormal grain inhibitor composed of at least one selected from Br and I, and the abnormal grain inhibitor is doped during the film formation of the crystalline oxide film to reduce the surface roughness Ra. A method for producing a laminated structure, which comprises forming the crystalline oxide film of 0.1 μm or less. The method for producing a laminated structure according to claim 8, wherein a lithium tantalate single crystal substrate is used as the crystalline substrate. The method for producing a laminated structure according to claim 8 or 9, wherein the temperature of the thermal reaction is 250 to 900 ° C. The method for producing a laminated structure according to any one of claims 8 to 10, wherein the crystalline oxide film contains β-Ga ₂ O ₃ as a main component. The method for producing a laminated structure according to any one of claims 8 to 11, wherein the crystalline oxide film has a film thickness of 1 μm or more. The method for manufacturing a laminated structure according to any one of claims 8 to 12, wherein a substrate having a film-forming surface area of 100 mm ² or more is used as the substrate.

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