Method for manufacturing ε-type gallium oxide film, and ε-type gallium oxide film

Abstract

A method for manufacturing an ε-type gallium oxide film includes a film forming step for forming a gallium oxide film on a substrate by a plasma-assisted film forming method. At least in the initial stage of the film forming step, a film is formed in a film-forming atmosphere containing nitrogen activated by the plasma, and an ε-type gallium oxide film containing ε-type gallium oxide is formed as the gallium oxide film.

Description

Method for producing ε-type gallium oxide film and ε-type gallium oxide film

[0001] The present disclosure relates to a method for producing an ε-type gallium oxide film and an ε-type gallium oxide film.

[0002] Gallium oxide is expected to be a power semiconductor material with high breakdown voltage and low power consumption. Gallium oxide is known to have five crystal structures: α, β, γ, ε, and γ. β-type gallium oxide is the most stable, and so far, research has focused primarily on β-type gallium oxide. However, α-type and ε-type gallium oxide are also beginning to be investigated as effective materials.

[0003] Japanese Patent Application Laid-Open Publication No. 2021-170579 proposes a method for growing a single crystal film of β-type gallium oxide by halide vapor phase epitaxy (HVPE). Japanese Patent Application Laid-Open Publication No. 2016-100592 proposes a method for growing α-type gallium oxide by mist chemical vapor deposition (mist CVD). Japanese Patent Application Laid-Open Publication No. 2017-007871 proposes a method for growing a single crystal film of ε-type gallium oxide by HVPE.

[0004] Since β-type gallium oxide is a monoclinic crystal, killer defects are likely to occur. Furthermore, since α-type gallium oxide transitions to β-type at about 650°C, heat treatment at temperatures exceeding 600°C cannot be performed in the manufacturing process of semiconductor devices, etc., limiting the process. In contrast, ε-type gallium oxide, which is a hexagonal crystal, is less likely to cause killer defects than β-type gallium oxide and is stable up to about 870°C, so it has the advantage of having fewer restrictions on the implementation of manufacturing processes for semiconductor devices, etc., compared to α-type gallium oxide.

[0005] As mentioned above, Japanese Patent Application Laid-Open No. 2017-007871 proposes a method for forming ε-type gallium oxide by the HVPE method, but the HVPE method uses hydrogen chloride (HCl), which makes handling of the device cumbersome. Furthermore, the concentration of chlorine (Cl) contained in the film cannot be sufficiently suppressed. If chlorine is contained, it is thought that the electrical properties will be affected, so it is desirable to sufficiently suppress the chlorine concentration.

[0006] An object of the present disclosure is to provide an ε-type gallium oxide film and a method for producing the same that are easy to produce and have a reduced chlorine concentration.

[0007] The method for producing an epsilon-type gallium oxide film according to the present disclosure includes a film formation step of forming a gallium oxide film on a substrate by a plasma-based film formation method, wherein the film formation is performed in a film formation atmosphere containing nitrogen activated by the plasma at least in the initial stage of the film formation step, to form an epsilon-type gallium oxide film containing epsilon-type gallium oxide as the gallium oxide film.

[0008] It is preferable that the film formation method is a sputtering method, the film formation gas introduced into the film formation chamber contains a gas for generating plasma and a reactive gas, and the proportion of nitrogen gas in the reactive gas is 20% or more.

[0009] The film formation method is preferably a sputtering method, and liquid gallium is preferably used as the sputtering target.

[0010] A single crystal substrate may be used as the substrate, and an ε-type gallium oxide film may be epitaxially grown on the substrate.

[0011] A silicon substrate having an electrode layer on one surface may be used as the substrate, and an ε-type gallium oxide film may be formed on the electrode layer.

[0012] The ε-type gallium oxide film of the present disclosure does not contain chlorine.

[0013] The ε-type gallium oxide film of the present disclosure is a sputtered film. The sputtered ε-type gallium oxide film may be chlorine-free.

[0014] The ε-type gallium oxide film of the present disclosure preferably contains nitrogen on at least one surface.

[0015] The ε-type gallium oxide film of the present disclosure may contain, as a dopant, at least one element selected from nitrogen (N), magnesium (Mg), calcium (Ca), barium (Ba), strontium (Sr), silicon (Si), antimony (Sb), bismuth (Bi), tin (Sn), selenium (Se), tellurium (Te), zirconium (Zr), hafnium (Hf), Ge (germanium), nickel (Ni), titanium (Ti), lithium (Li), iron (Fe), cobalt (Co), manganese (Mn), zinc (Zn), indium (In), and copper (Cu).

[0016] In the ε-type gallium oxide film of the present disclosure, the length of the c-axis of the crystal lattice of the ε-type gallium oxide is preferably 0.930 nm or more and 0.955 nm or less.

[0017] According to the method for producing ε-type gallium oxide of the present disclosure, an ε-type gallium oxide film can be obtained that is easy to produce and has a more controlled chlorine concentration than conventional ε-type gallium oxide films.

[0018] 1 is a diagram showing a schematic configuration of a film forming apparatus; FIG. 2 is a diagram showing an XRD pattern of the gallium oxide film of Example 1; ２ O ３ 1 shows the symmetry of the (11-24) plane of the gallium oxide film (top) and the symmetry of the sapphire substrate (bottom). ２ O ３ 1 is a diagram showing the symmetry of the (10-15) plane (upper diagram) and the symmetry of the sapphire substrate (lower diagram). FIG. 2 is a diagram showing the XRD pattern of Example 3. FIG. 3 is a diagram showing the XRD pattern of Comparative Example 1.

[0019] Hereinafter, embodiments of the method for producing an ε-type gallium oxide film and the ε-type gallium oxide film according to the present disclosure will be described.

[0020] The method for producing an ε-type gallium oxide film of the present disclosure includes a film formation step of forming a gallium oxide film on a substrate by a film formation method using plasma. In the method for producing an ε-type gallium oxide film of the present disclosure, at least in the early stage of the film formation step, the gallium oxide film is formed in a film formation atmosphere containing nitrogen activated by plasma. This results in the formation of an ε-type gallium oxide film containing ε-type gallium oxide as the gallium oxide film. The ε-type gallium oxide film of one embodiment of the present disclosure does not contain chlorine. The ε-type gallium oxide of another embodiment of the present disclosure is a sputtered film. Note that the ε-type gallium oxide of yet another embodiment is a sputtered film and does not contain chlorine. Note that the ε-type gallium oxide film of the present disclosure may contain nitrogen on at least one surface. Here, "not containing chlorine" means that the chlorine concentration (Cl concentration) in the film is 1×10 or less when measured by secondary ion mass spectrometry (SIMS), a common analytical method. １５ atoms / cm ３ This means that:

[0021] Here, "ε-type gallium oxide film containing ε-type gallium oxide" does not mean a gallium oxide film entirely composed of ε-type gallium oxide, but means a gallium oxide film containing ε-type gallium oxide. In the "ε-type gallium oxide film containing ε-type gallium oxide," the volume ratio of ε-type gallium oxide in the film is preferably 50% or more, more preferably 70% or more, and even more preferably 90% or more. Furthermore, the ε-type gallium oxide film produced by the method for producing an ε-type gallium oxide film of the present disclosure may be a single-crystal ε-type gallium oxide film containing 100% ε-type gallium oxide. Whether or not ε-type gallium oxide is contained can be confirmed by analysis using X-ray diffraction (XRD). For example, an XRD pattern obtained by the θ-2θ method can confirm the presence or absence of a peak of ε-type gallium oxide. If an XRD pattern contains a peak of ε-type gallium oxide, it is considered to "contain ε-type gallium oxide." In addition, in recent years, ε-type gallium oxide (ε-Ga ２ O ３ ) with respect to κ(ε)-Ga ２ O ３ Or ε(κ)-Ga ２ O ３At present, the ε-type and κ-type are not strictly distinguished from each other. The ε-type and κ-type are considered to have very similar structures or to be substantially equivalent phases. Therefore, although the term "ε-type gallium oxide" is used in this specification, this also includes indistinguishable κ-type gallium oxide, or is substantially equivalent to κ-type gallium oxide.

[0022] The film formation method using plasma refers to a film formation method including a step in which reactive gases or film formation particles are excited into active radicals or ions by plasma. Specific examples of the film formation method using plasma include plasma CVD, sputtering, and ion plating. In this embodiment, the film formation method using plasma is performed in a reduced pressure film formation atmosphere.

[0023] The "initial stage of the film formation process" refers to the period from the start of film formation until a film of at least 1 nm is formed on the substrate. However, it is preferable that activated nitrogen is contained in the film formation atmosphere from the start of film formation until a film of 2 to 3 nm is formed. Furthermore, activated nitrogen may be contained in the film formation atmosphere from the start of film formation until a film of about 10 nm is formed. Furthermore, activated nitrogen may be contained in the film formation atmosphere throughout the entire film formation period or intermittently during the film formation period.

[0024] A method for producing an ε-type gallium oxide film using a sputtering method will be described below as an example of a plasma-based film formation method. In this embodiment, liquid gallium is used as a sputtering target 20 (hereinafter referred to as target 20) during film formation.

[0025] First, a description will be given of a film forming apparatus 1 used in the manufacturing method of this embodiment. Fig. 1 is a schematic configuration diagram of the film forming apparatus 1. The film forming apparatus 1 is an example for realizing the manufacturing method of this embodiment, and is a magnetron sputtering apparatus.

[0026] The film formation apparatus 1 includes a film formation chamber 10 consisting of a vacuum vessel, and a substrate holder 12, a target setting unit 14, a magnetic field generator 16, a temperature holding mechanism 18, and a power supply 19 that supplies power to a target 20, all of which are provided within the film formation chamber 10. The film formation apparatus 1 is configured so that liquid gallium can be placed as the target 20.

[0027] The film formation chamber 10 is a container that maintains a predetermined vacuum level for sputtering, and is composed of a highly airtight container made of iron, stainless steel, aluminum, or the like. The film formation chamber 10 is equipped with a gas inlet pipe 10a for introducing a film formation gas G required for film formation and a gas outlet pipe 10b for exhausting gas VG from the film formation chamber 10. The gas inlet pipe 10a is connected to a supply source (not shown) of the film formation gas G. The gas outlet pipe 10b is connected to an exhaust means such as a vacuum pump to exhaust the film formation chamber 10 to a predetermined vacuum level and to maintain the film formation chamber 10 at the predetermined vacuum level.

[0028] The power supply 19 is a power supply that supplies sputtering power to the target 20, and more specifically, it supplies power to the mounting surface 14a of the target mounting portion 14 that constitutes the plasma electrode, for converting a gas such as Ar introduced into the film formation chamber 10 into plasma. The power supply 19 may be an RF (radio-frequency) power supply or a DC (direct current) power supply.

[0029] The substrate holder 12 holds a substrate S on which a gallium oxide film is to be formed. The substrate holder 12 is provided with a temperature control mechanism including a heater that heats the substrate S during film formation.

[0030] A target tray 22 (hereinafter simply referred to as tray 22) containing targets 20 is placed in the target placement unit 14. In this embodiment, the target placement unit 14 has a placement surface 14a, and the tray 22 is placed on the placement surface 14a. The substrate holding unit 12 and the target placement unit 14 are arranged opposite to each other. Therefore, the substrate S held by the substrate holding unit 12 and the target 20 are placed opposite to each other.

[0031] The target installation section 14 is a frame body including a storage section 15 that stores a heat medium HM circulated by a temperature maintenance mechanism 18, which will be described later. The storage section 15 also stores a magnetic field generating magnet 24 on the back side of the installation surface 14a on which the tray 22 is placed.

[0032] The magnetic field generating unit 16 is composed of a plurality of magnetic field generating magnets 24 provided in the housing unit 15 within the frame that constitutes the target setting unit 14. The magnetic field generating unit 16 generates a magnetic field on the target 20. By performing sputtering with a magnetic field generated, it is possible to increase the sputtering efficiency.

[0033] The temperature maintenance mechanism 18 is a mechanism for maintaining a constant temperature of the target 20, and is, for example, a heat medium circulation mechanism that circulates a heat medium HM at 30°C or higher behind the installation surface 14a. The heat medium HM is preferably a liquid, such as water or oil. The temperature maintenance mechanism 18 includes a supply pipe 18a that supplies the heat medium HM into the accommodation unit 15 behind the installation surface 14a of the target installation unit 14, and an exhaust pipe 18b that discharges the heat medium HM from the accommodation unit 15. The temperature maintenance mechanism 18 supplies temperature-adjusted heat medium HM, such as water at 30°C, into the accommodation unit 15 via the supply pipe 18a and discharges the heat medium HM from the accommodation unit 15 via the exhaust pipe 18b. The heat medium circulation mechanism readjusts the heat medium HM discharged from the exhaust pipe 18b to 30°C and then supplies it again via the supply pipe 18a.

[0034] The temperature of the supplied heat medium HM is set to 30°C or higher in order to keep the gallium in a liquid state at all times. The temperature of the heat medium HM is preferably set to 30°C to 100°C.

[0035] A method for producing an ε-type gallium oxide film using the above-described film-forming apparatus 1 will now be described.

[0036] First, a tray 22 containing a target 20 is placed on the placement surface 14a of the target placement unit 14 of the film formation apparatus 1 shown in Figure 1. Here, the target 20 is gallium. The target 20 may be solid or liquid at the time of placement. In addition, a substrate S is attached to and held by the substrate holder 12.

[0037] Next, the film formation chamber 10 is evacuated through the gas exhaust pipe 10b until the interior thereof reaches a predetermined vacuum level, and further, while continuing to evacuate the chamber 10 so as to maintain the predetermined vacuum level, a film formation gas G is supplied from the gas inlet pipe 10a in a predetermined amount at a time. Here, the film formation gas G supplied to the film formation chamber 10 is argon (Ar), oxygen gas (O), or the like, at least at the initial stage of film formation. ２ ) and nitrogen gas (N ２ ) is used. By adding nitrogen gas to the deposition gas G, a deposition atmosphere containing nitrogen activated by plasma can be realized. Argon is introduced as a plasma generating gas that is converted into plasma by applying power to the plasma electrode to form a plasma space, and oxygen gas and nitrogen gas are introduced as reactive gases.

[0038] A temperature holding mechanism 18 circulates a heat medium HM at 30°C or higher in the housing 15 on the back surface of the installation surface 14a, maintaining the gallium target 20 in a liquid state. The substrate temperature is set to a range below 870°C, for example, between 250°C and 850°C, based on the thermal stability of ε-type gallium oxide. It is preferably 400°C or higher, and more preferably 550°C or higher. Then, power is applied from a power source 19 to the plasma electrode to form a plasma space and start the film formation process.

[0039] The time when power is turned on is the start of film formation, and film formation on the substrate S begins, and the film formation process is continued until the desired thickness is reached. The thickness of the gallium oxide film can be determined appropriately depending on the application. For example, a gallium oxide film having a thickness of several nm to several mm can be obtained. Gallium oxide films with thicknesses ranging from 50 nm to several hundred nm, those with a thickness of about several μm, such as 2 to 3 μm, those with a thickness of 10 μm or more, and even those with a thickness of 50 μm or more can be produced depending on the application.

[0040] As described above, the method includes a film formation step of forming a gallium oxide film on a substrate by a film formation method using plasma, and by performing film formation in a film formation atmosphere containing nitrogen activated by plasma at least in the early stage of the film formation step, it is possible to form a gallium oxide film containing ε-type gallium oxide on a substrate.

[0041] As described above, the film formation gas G contains a gas for generating plasma and a reactive gas. The gas for generating plasma is a rare gas, which is Ar in this embodiment. The gas other than the rare gas in the film formation gas G is a reactive gas. When forming a gallium oxide film, oxygen alone is generally used as the reactive gas. In contrast, in this embodiment, nitrogen gas is included in the film formation gas G at least at the beginning of the film formation process. The inventors have found that ε-type gallium oxide can be produced by including nitrogen as a reactive gas in addition to oxygen at least at the beginning of the film formation process of a gallium oxide film. In the film formation chamber 10, the nitrogen in the film formation gas G is activated by plasma to become radical nitrogen or nitride ions. Activated nitrogen refers to nitrogen in a highly reactive state containing this radical nitrogen or nitride ions.

[0042] Here, the proportion of nitrogen gas in the reactive gas is the proportion at the time when the film formation gas G is supplied to the film formation chamber 10. The proportion of nitrogen gas in the reactive gas is preferably 20% or more. The proportion of nitrogen gas in the reactive gas is preferably 90% or less, and more preferably 50% or more and 80% or less. Even if the reactive gas contains nitrogen gas, gallium oxide is likely to grow because the reactivity of gallium is sufficiently greater with oxygen than with nitrogen, and gallium oxide can be grown if the proportion of nitrogen gas in the reactive gas is 90% or less.

[0043] Since nitrogen is contained in the film formation gas at least at the beginning of the film formation process, it is presumed that a nitrogen-containing film is formed on one surface of the substrate side. The relationship between the time from the start of film formation and the film thickness can be investigated in advance, and the period until the film reaches the desired film thickness can be controlled by time. Nitrogen gas may be introduced at the beginning of the growth process, and after ε-type gallium oxide has grown to the desired film thickness, the nitrogen gas may be reduced for growth. After ε-type gallium oxide has grown to the desired film thickness at the beginning of film formation, ε-type gallium oxide can be grown by homoepitaxial growth on ε-type gallium oxide even without including nitrogen gas in the film formation gas. However, nitrogen gas may be included in the film formation gas G throughout the entire film formation period or intermittently during the film formation period. When nitrogen gas is introduced throughout the growth process or intermittently, N may be included as a dopant in ε-type gallium oxide. In this regard, when forming an ε-type gallium oxide film that does not contain N as a dopant, after growing the ε-type gallium oxide at the beginning of the growth process, it is preferable not to include nitrogen gas in the film formation gas G. Note that the scope of the present disclosure does not include an embodiment in which nitrogen gas is included in the film formation gas G to such an extent that a film containing gallium nitride crystals in the gallium oxide film or an amorphous gallium oxynitride film is formed.

[0044] In this embodiment, liquid gallium is used as the target 20, but the target 20 is not limited to this, and a sintered body of gallium oxide or a sintered body of gallium oxide doped with nitrogen may also be used. However, using gallium and adjusting the reactive gas rather than using a sintered body of gallium oxide provides higher controllability of the mixture ratio of nitrogen and oxygen in the film formation atmosphere. Furthermore, using liquid gallium as the target 20 also has the effect of enabling an improvement in the film formation rate.

[0045] The substrate S is not particularly limited and can be appropriately selected depending on the application from a silicon substrate, an oxide substrate, a nitride substrate, a glass substrate, various flexible substrates, etc. A single crystal substrate may also be used as the substrate S.

[0046] That is, a single crystal substrate may be used as the substrate S, and an ε-type gallium oxide film may be epitaxially grown on it. In this case, an epitaxial film that is a single crystal film of ε-type gallium oxide is obtained. As the single crystal substrate, a sapphire substrate, a silicon carbide (SiC) substrate, a β-type gallium oxide substrate, or the like is suitable. Note that a single crystal substrate on which a thin film of aluminum (Al), gallium nitride (GaN), silicon carbide (SiC), or the like is formed may also be used as the substrate S.

[0047] Alternatively, a silicon substrate having an electrode layer on one surface may be used as the substrate S, and an ε-type gallium oxide film may be formed on the electrode layer. It is preferable to form a c-axis oriented ε-type gallium oxide film on the electrode layer. Forming an ε-type gallium oxide film on the electrode layer in this manner allows application to semiconductor devices, piezoelectric devices, and the like. The electrode layer provided on the silicon substrate may be made of a material that can withstand the substrate temperature during the formation of the ε-type gallium oxide film. Specific examples of such electrode layers include precious metal layers such as platinum (Pt), palladium (Pd), and Ir (iridium), as well as strontium ruthenate (SrRuO ３ ) and lanthanum nickelate (LaNiO ３ ) and other conductive oxide layers. As the electrode layer, a noble metal layer is preferred, and among them, Pt is particularly preferred. In order to obtain a c-axis oriented ε-type gallium oxide film, the film formation gas pressure is preferably a higher vacuum, for example, preferably 1 Pa or less, more preferably 0.5 Pa or less, and even more preferably 0.2 Pa or less, but 0.1 Pa or more is preferred from the viewpoint of discharge stability. In addition, from the viewpoint of improving crystallinity, the substrate temperature is preferably 400°C or higher.

[0048] As described above, according to the method for producing an ε-type gallium oxide film of the present embodiment, an ε-type gallium oxide film containing ε-type gallium oxide can be obtained. There have been no reports of an ε-type gallium oxide film being produced by a sputtering method. That is, the ε-type gallium oxide film itself, which is a sputtered film, has a novel structure.

[0049] In addition, since the method for producing an ε-type gallium oxide film of this embodiment is a sputtering method, the obtained ε-type gallium oxide film essentially contains almost no unintended impurities other than the target material and the film-forming gas. １８ atoms / cm ３ However, as long as the HVPE method is used, there is a limit to the suppression of the Cl concentration. For example, in the example shown in JP 2017-007871 A, the Cl concentration as an impurity is controlled to 2 × 10 １８ atoms / cm ３ The Cl concentration in the above-mentioned ε-type gallium oxide film obtained by sputtering is 1×10 １５ atoms / cm ３ or less and does not substantially contain Cl. If Cl is contained, the electrical properties may change, but the ε-type gallium oxide film of the present disclosure does not substantially contain Cl, and therefore can exhibit the inherent electrical properties of ε-type gallium oxide.

[0050] On the other hand, the ε-type gallium oxide film obtained by the method for producing an ε-type gallium oxide film of this embodiment contains nitrogen. The inventors confirmed a nitrogen peak in the ε-type gallium oxide film produced by the method of this embodiment using XPS (X-ray Photoelectron Spectroscopy). Although they attempted to quantify nitrogen from the peak, the nitrogen content relative to the entire film was very small, and quantification was not possible. The nitrogen content relative to the entire film is estimated to be 1 at% or less, and may even be 0.1 at% or less. The inventors presume that the ε-type gallium oxide film obtained by the method for producing an ε-type gallium oxide film of this embodiment contains nitrogen at least at the interface (here, the surface facing the substrate) at the initial stage of growth, due to its characteristics of being formed in an activated nitrogen atmosphere at least in the initial stage of film formation. In this specification, "containing nitrogen" refers to a state in which it is technically estimated that at least a trace amount of nitrogen has been introduced into the film based on the film formation conditions. For example, this includes cases where a nitrogen peak is observed even though quantitative determination is difficult using XPS or SIMS, cases where activated nitrogen gas is introduced during film formation, or cases where the influence of nitrogen is confirmed in XRD or electrical properties, etc.

[0051] Furthermore, it is clear in principle that the concentration of impurities other than nitrogen can be suppressed in the sputtered ε-type gallium oxide film more effectively than in the gallium oxide film fabricated using the HVPE method. As such, the concentration of unintended impurities is extremely low, allowing the inherent properties of ε-type gallium oxide to be exhibited.

[0052] The c-axis length of the crystal lattice of ε-type gallium oxide in the ε-type gallium oxide film of the present disclosure is preferably 0.930 nm or more and 0.955 nm or less, and more preferably 0.948 nm or more. Here, the c-axis length is the length estimated from the peak of the (008) plane of ε-type gallium oxide in the XRD pattern. Note that, according to the studies of the present inventors, increasing the nitrogen gas in the film formation gas G tends to increase the c-axis length.

[0053] The ε-type gallium oxide film may contain at least one element selected from nitrogen (N), magnesium (Mg), calcium (Ca), barium (Ba), strontium (Sr), silicon (Si), antimony (Sb), bismuth (Bi), tin (Sn), selenium (Se), tellurium (Te), zirconium (Zr), hafnium (Hf), Ge (germanium), nickel (Ni), titanium (Ti), lithium (Li), iron (Fe), cobalt (Co), manganese (Mn), zinc (Zn), indium (In), and copper (Cu) as a dopant. By adding any of elements selected from N, Mg, Ca, Ba, Sr, Si, Sb, Bi, Sn, Se, Te, Zr, Hf, Ge, Ni, Ti, Li, Fe, Co, Mn, and Zn to the ε-type gallium oxide, it can function as a p-type or n-type semiconductor. The content of these additive elements in the film is preferably 5 atom % or less, more preferably 1 atom % or less. Furthermore, when Cu, Ni, Zn, In, Sn, or the like is added to ε-type gallium oxide, it is expected to exhibit higher piezoelectricity. The amount of additive elements may be appropriately determined depending on the material, application, and film formation conditions.

[0054] The ε-type gallium oxide film obtained by the manufacturing method of the present disclosure is obtained by film formation on a substrate S, and may be applied to a device or the like in the form provided on the substrate S, or may be used after peeling or removing the substrate S from the substrate S. It is also possible to use the ε-type gallium oxide film itself as a substrate by setting the thickness to 200 μm or more.

[0055] The method for producing gallium oxide disclosed herein is a sputtering method, a film formation method with excellent suitability for semiconductor processes. Gallium nitride films can be obtained by using only nitrogen gas as the reactive gas, while β-type gallium oxide can be obtained by using only oxygen gas without nitrogen gas as the reactive gas. By adjusting the reactive gas, ε-type gallium oxide, β-type gallium oxide, and gallium nitride can be selectively produced, making it easy to fabricate laminates of different types of films. In particular, ε-type gallium oxide has a high affinity because it has the same hexagonal crystal structure as gallium nitride, and is therefore expected to be applied to semiconductor devices.

[0056] Although the principle by which ε-type gallium oxide is formed by including activated nitrogen in the film formation atmosphere is not clear, the present inventors speculate that in the early stages of formation of a gallium oxide film on the substrate S, activated nitrogen reacts with gallium to produce a small amount of gallium nitride, and this gallium nitride serves as a nucleus for the formation of ε-type gallium oxide. From this perspective, it is believed that an ε-type gallium oxide film can be formed by any film formation method that can activate nitrogen using plasma, not limited to the sputtering method described above. Furthermore, since it is sufficient that activated nitrogen is included in the film formation atmosphere, the method of introducing active nitrogen into the film formation atmosphere may be a method other than including nitrogen gas in the film formation gas.

[0057] Examples and comparative examples of the method for producing an ε-type gallium oxide film according to the present disclosure will be described below. The gallium oxide film was formed using the film formation apparatus 1 shown in FIG.

[0058] Example 1 The manufacturing method of a gallium oxide film in Example 1 was as follows. A sapphire substrate was used as the substrate S, and metallic gallium was used as the target 20. Gallium was placed in a tray 22 and placed in the film-forming apparatus 1, and a film was formed on the sapphire substrate by RF (radio frequency) sputtering. The substrate temperature during film formation was 800°C. In this specification, the substrate temperature is the set substrate temperature in the film-forming apparatus. The film-forming gas was a mixture of 50% Ar + 25% O with a flow rate ratio of 1000 saturates. ２ +25%N ２ That is, the ratio of nitrogen gas in the reaction gas was set to 50%. N was contained in the film formation atmosphere not only during the initial film formation but also throughout the entire film formation process. ２ It is assumed to include the following.

[0059] The XRD pattern of the film obtained by the manufacturing method of Example 1, measured by θ-2θ X-ray diffraction, is shown in FIG. 2. As shown in FIG. 2, ε-type gallium oxide (ε-Ga ２ O ３) was formed. Furthermore, Figure 3 shows XRD patterns by in-plane φ scanning measured for the (11-24) plane of ε-type gallium oxide (top diagram) and a specific plane of the sapphire substrate (bottom diagram) exhibiting hexagonal rotational symmetry. Figure 4 shows XRD patterns by in-plane φ scanning measured for the (10-15) plane of ε-type gallium oxide (top diagram) and a specific plane of the sapphire substrate (bottom diagram) exhibiting hexagonal rotational symmetry. From Figures 3 and 4, it can be seen that the peaks of the (11-24) plane and the (10-14) plane of ε-type gallium oxide appear at the same intervals as the peaks of the hexagonal rotational symmetry of the sapphire substrate. In other words, this confirms that the obtained film is ε-type gallium oxide, a hexagonal crystal exhibiting hexagonal rotational symmetry.

[0060] The c-axis length determined from the (008) plane of ε-type gallium oxide in the XRD pattern was 0.955 nm (=9.55 Å).

[0061] According to the study by the inventors, this c-axis length is determined by the N in the film-forming gas. ２ The change is caused by changing the gas concentration. ２ It has been confirmed that the c-axis length increases slightly when the gas concentration is increased. From multiple experiments, the c-axis length was found to be between 0.930 nm and 0.955 nm.

[0062] Example 2 In the manufacturing method of Example 1, Ga metal to which 1 atm % of Sn metal was added was used as a target. Film formation was performed under the same conditions as Example 1 except for the above. The film obtained in this example is ε-type gallium oxide to which Sn was added. It was confirmed that the film obtained in Example 2 was ε-type gallium oxide, as in Example 1.

[0063] According to the study by the present inventors, when 5 atm % of Sn was added, a different phase other than ε-type gallium oxide appeared, and a good film could not be formed. When adding impurities such as Sn, it is considered preferable to add less than 5 atm % of Ga metal.

[0064] Example 3: A silicon substrate with an electrode was prepared by laminating a 5 nm thick tantalum (Ta) film on one side of a silicon substrate (silicon wafer) and a 100 nm thick platinum (Pt) film on the Ta film. This silicon substrate with an electrode was used as a substrate to be film-formed, and a gallium oxide film was formed on the Pt film under the same conditions as in Example 1.

[0065] The XRD pattern of the film obtained by the manufacturing method of Example 3, obtained in the same manner as in Example 1, is shown in Figure 5. The XRD pattern in Figure 5 shows ε, δ, γ-Ga ２ O ３ Peaks of β, ε, δ, γ-Ga ２ O ３ The peaks of ε, δ, γ-Ga were observed. ２ O ３ The peaks are presumed to be peaks containing at least one type of gallium oxide selected from the ε-type, δ-type, and γ-type. ２ O ３ is a peak that is presumed to contain at least one type of gallium oxide selected from the group consisting of β-, ε-, δ-, and γ-types. Thus, it is presumed that a mixed crystal gallium oxide film of ε-, β-, δ-, and γ-types was obtained in Example 3.

[0066] An upper electrode was formed on the surface of the gallium oxide film obtained in this Example 3, and the dielectric constant was measured to be about 16, indicating that the film contained ε-type gallium oxide with a high dielectric constant. The dielectric constant was measured using an impedance analyzer at an applied voltage of 1 kHz ± 1 V. In the XRD pattern shown in FIG. 5, the peak values ​​of the ε-type and δ-type gallium oxide films are very close, so it was difficult to prove the presence of the ε-type gallium oxide film in Example 3 from the XRD pattern alone. However, since a higher dielectric constant than the δ-type, γ-type, and β-type gallium oxide films was obtained, it is believed that the film contained ε-type gallium oxide. The relative dielectric constant of β-type gallium oxide is approximately 10-12, as described in A. Fiedler, R. Schewski, Z. Galazka, and K. Irmscher, "Static Dielectric Constant of β-Ga2O3 Perpendicular to the Principal Planes (100), (010), and (001)," ECS Journal of Solid State Science and Technology, Volume 8, Number 7, pp. 3083-3085. The relative dielectric constant of α-type gallium oxide is also said to be comparable to that of β-type gallium oxide. The relative dielectric constant of γ-type gallium oxide is approximately 10, as described in Kaizheng Gao, Feihua Liu, Fu Lv, Nuomei Li, Man Liu, Ziheng Ye, Minghan Yu, Rui Yin, Chen Zhang, Yuhui Huang, and Weiwei Zhao, "Enhanced Dielectric Energy Storage Performance of Polyimide / γ-Ga2O3 Nanocomposites under Dual Trap Mechanisms." It is clear that the value of the relative dielectric constant of 16 of the gallium oxide film obtained in Example 3 is a large relative dielectric constant compared to those disclosed in these documents.

[0067] This example reveals that an ε-type gallium oxide film containing ε-type gallium oxide at least in part can be formed on a silicon substrate via an electrode.

[0068] Comparative Example 1: In the manufacturing method of Example 1, the deposition gas was 50% Ar, 50% O ２ The mixed gas is used, and N is added to the film forming gas. ２ The gallium oxide film was formed under the same conditions as in Example 1 except for the deposition gas. FIG. 6 shows an XRD pattern obtained in the same manner as in Example 1 for the film obtained by the manufacturing method of Comparative Example 1. In the XRD pattern of FIG. 6, no peak (see FIG. 2) that would be observed at 2θ of approximately 80° in the case of ε-type gallium oxide was observed, and a β-type gallium oxide film was formed. In other words, the manufacturing method of Comparative Example 1 only yielded a gallium oxide film that did not contain ε-type gallium oxide.

[0069] In addition, O in the film forming gas ２ When the film was formed under conditions where the gas ratio was 10%, 20%, 50%, 80% or 100%, β-type gallium oxide containing no ε-type gallium oxide was formed.

[0070] The results of Examples 1 to 3 and Comparative Example 1 above indicate that the presence of activated nitrogen in the film-forming atmosphere contributes to the growth of ε-type gallium oxide.

[0071] The disclosure of Japanese Patent Application No. 2024-105549, filed on June 28, 2024, is incorporated herein by reference in its entirety. All documents, patent applications, and technical standards mentioned herein are incorporated herein by reference to the same extent as if each individual document, patent application, and technical standard was specifically and individually indicated to be incorporated by reference.

[0072] The following supplementary notes are further disclosed regarding the above embodiments. <Supplementary Note 1> A method for producing an epsilon-type gallium oxide film, comprising: a film formation step of forming a gallium oxide film on a substrate by a film formation method using plasma; wherein, at least in an early stage of the film formation step, film formation is performed in a film formation atmosphere containing nitrogen activated by the plasma; and an epsilon-type gallium oxide film containing epsilon-type gallium oxide is formed as the gallium oxide film. <Supplementary Note 2> The method for producing an epsilon-type gallium oxide film according to claim 1, wherein the film formation method is a sputtering method, and a film formation gas introduced into the film formation chamber contains a gas for generating plasma and a reactive gas, and the proportion of nitrogen gas in the reactive gas is 20% or more. <Supplementary Note 3> The method for producing an epsilon-type gallium oxide film according to Supplementary Note 1 or 2, wherein the film formation method is a sputtering method, and liquid gallium is used as the sputtering target. <Supplementary Note 4> A method for producing an epsilon-type gallium oxide film according to any one of Supplementary Notes 1 to 3, wherein a single crystal substrate is used as the substrate, and the epsilon-type gallium oxide film is epitaxially grown. <Appendix 5> A method for producing an epsilon-type gallium oxide film according to any one of Appendices 1 to 3, wherein a silicon substrate having an electrode layer on one surface thereof is used as the substrate, and an epsilon-type gallium oxide film is formed on the electrode layer. <Appendix 6> An epsilon-type gallium oxide film not containing chlorine. <Appendix 7> An epsilon-type gallium oxide film that is a sputtered film. <Appendix 8> The epsilon-type gallium oxide film according to Appendices 7, not containing chlorine. <Appendix 9> The epsilon-type gallium oxide film according to any one of Appendices 6 to 8, which contains nitrogen on at least one surface thereof. <Appendix 10> The epsilon-type gallium oxide film according to any one of Appendices 6 to 9, which contains at least one element selected from nitrogen, magnesium, calcium, barium, strontium, silicon, antimony, bismuth, tin, selenium, tellurium, zirconium, hafnium, germanium, nickel, titanium, lithium, iron, cobalt, manganese, zinc, indium, and copper as a dopant. <Supplementary Note 11> The ε-type gallium oxide film according to any one of Supplementary Note 6 to Supplementary Note 10, wherein the length of the c-axis of the crystal lattice is 0.930 nm or more and 0.955 nm or less.

Claims

1. A method for producing an epsilon-type gallium oxide film, comprising: a film formation step of forming a gallium oxide film on a substrate by a film formation method using plasma; wherein, at least in an early stage of the film formation step, film formation is carried out in a film formation atmosphere containing nitrogen activated by the plasma; and an epsilon-type gallium oxide film containing epsilon-type gallium oxide is formed as the gallium oxide film.

2. The method for producing an epsilon-type gallium oxide film according to claim 1, wherein the film formation method is a sputtering method, the film formation gas introduced into the film formation chamber contains a gas for generating the plasma and a reactive gas, and the proportion of nitrogen gas in the reactive gas is 20% or more.

3. The method for producing an epsilon-type gallium oxide film according to claim 1, wherein the film formation method is a sputtering method, and liquid gallium is used as a sputtering target.

4. The method for producing an epsilon-type gallium oxide film according to claim 1, wherein the substrate is a single crystal substrate, and the epsilon-type gallium oxide film is epitaxially grown.

5. The method for producing an epsilon-type gallium oxide film according to claim 1, wherein the substrate is a silicon substrate having an electrode layer on one surface thereof, and the epsilon-type gallium oxide film is formed on the electrode layer.

6. Chlorine-free ε-type gallium oxide film.

7. ε-type gallium oxide film, a sputtered film.

8. The ε-type gallium oxide film according to claim 7, which does not contain chlorine.

9. The ε-type gallium oxide film according to any one of claims 6 to 8, which contains nitrogen on at least one surface.

10. The epsilon-type gallium oxide film according to any one of claims 6 to 8, containing as a dopant at least one element selected from nitrogen, magnesium, calcium, barium, strontium, silicon, antimony, bismuth, tin, selenium, tellurium, zirconium, hafnium, germanium, nickel, titanium, lithium, iron, cobalt, manganese, zinc, indium, and copper.

11. The ε-type gallium oxide film according to any one of claims 6 to 8, wherein the length of the c-axis of the crystal lattice is 0.930 nm or more and 0.955 nm or less.

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