Method for producing metal oxide film, method for producing metal nitride film, si substrate with metal oxide film, and si substrate with metal nitride film

Abstract

To provide a method of manufacturing a metal oxide film or a metal nitride film on an Si substrate which is not affected by an Si oxide layer or is affected by the Si oxide layer to an extremely small extent.SOLUTION: The method for producing a metallic oxide film comprises growing a metallic oxide film or a metallic nitride film on an Si substrate, wherein the Si substrate is cleaned with a soln. containing NH4F. Supplying the Si substrate after the cleaning to a reaction chamber and adsorbing a metal layer made of a metal constituting the metal oxide film or the metal nitride film on the Si substrate, wherein the adsorption of the metal layer is performed by applying a pressure P (Pa) within a pressure range (Pa) in which an adsorption rate and a desorption rate of the metal constituting the metal oxide film show an equilibrium state in a Langmuir adsorption isotherm at an arbitrary temperature T (°C), subsequently, epitaxially growing the metal oxide film or the metal nitride film.SELECTED DRAWING: Figure 4

Description

[Technical Field]

[0001] The present invention relates to a method for producing a metal oxide film, a method for producing a metal nitride film, a Si substrate with a metal oxide film, and a Si substrate with a metal nitride film. [Background technology]

[0002] Although silicon semiconductors using SiC have been put to practical use, gallium nitride (GaN) is mainly used in high electron mobility transistors (HEMTs). Gallium oxide is also attracting attention as a next-generation power semiconductor device. This is because the band gap of gallium oxide is larger than the band gap of 3.26 eV of 4H-SiC substrates.

[0003] Methods for forming a film of a metal nitride or metal oxide such as gallium nitride or gallium oxide on a silicon (Si) substrate include physical vapor deposition (PVD), chemical vapor deposition (CVD), atomic layer deposition (ALD), and molecular beam epitaxy (MBE).

[0004] For example, in Non-Patent Document 1, gallium oxide is formed on a Si substrate via a SiC buffer layer, and in Non-Patent Document 2, gallium oxide is formed on a Si substrate via an Al2O3 buffer layer. [Prior art documents] [Non-patent literature]

[0005] [Non-Patent Document 1] Study of the Anisotropic Elastoplastic Properties of β-Ga2O3 Films Synthesized on SiC / Si Substrates,ASGrashchenko et al.,Phys.Solid State,60,852-857(2018)) [Non-patent document 2] β-Ga2O3 on Si (001) grown by plasma-assisted MBE with γ-Al2O3 (111) buffer layer:Structural characterization,T.Hadamek et al.,AIP Advances,11,045209(2021)) Summary of the Invention [Problem to be solved by the invention]

[0006] In contrast, when a Si substrate is cleaned in order to form a metal oxide film or metal nitride film, such as gallium oxide or gallium nitride, directly on the Si substrate, the Si substrate is highly susceptible to oxidation, resulting in the formation of a silicon oxide layer (Si oxide layer) of a certain thickness or more on its surface. This Si oxide layer can affect the crystallinity, surface roughness, electrical properties, etc. of the metal oxide film or metal nitride film. This effect is more pronounced as the thickness of the metal oxide film or metal nitride film becomes thinner.

[0007] Therefore, an object of the present invention is to provide a method for producing a metal oxide film or metal nitride film on a Si substrate, which is not affected by or is only affected by a Si oxide layer, and to provide a Si substrate with the metal oxide film or metal nitride film. [Means for solving the problem]

[0008] As a result of extensive research into the above-mentioned problems, the inventors have found that the above-mentioned problems can be solved by cleaning a Si substrate with a specific solution and growing a metal layer made of a metal that constitutes a metal oxide film or a metal nitride film on the Si substrate under specific conditions, and have thus completed the present invention.

[0009] That is, the gist of the present invention is as follows. [1] A method for producing a metal oxide film by growing a metal oxide film on a Si substrate, The surface of the Si substrate is washed with a solution containing NH4F. a metal layer made of a metal constituting the metal oxide film is adsorbed onto the cleaned Si substrate; adsorption of the metal layer is carried out by applying a pressure P (Pa) within a pressure range (Pa) in which the adsorption rate and desorption rate of the metal constituting the metal oxide film are in equilibrium in a Langmuir adsorption isotherm at an arbitrary temperature T (°C); Next, the metal oxide film is epitaxially grown. [2] The adsorbed metal layer is a metal oxide layer, The method for producing a metal oxide film according to [1] above, further comprising epitaxially growing the metal oxide film. [3] A method for manufacturing a metal nitride film by growing a metal nitride film on a Si substrate, comprising: The surface of the Si substrate is washed with a solution containing NH4F. a metal layer made of a metal constituting the metal nitride film is adsorbed onto the cleaned Si substrate; adsorption of the metal layer is carried out by applying a pressure P (Pa) within a pressure range (Pa) in which an adsorption rate and a desorption rate of the metal constituting the metal nitride film are in equilibrium in a Langmuir adsorption isotherm at an arbitrary temperature T (°C); Next, the metal nitride film is epitaxially grown. [4] The adsorbed metal layer is a metal nitride layer, The method for producing a metal nitride film according to [3] above, further comprising epitaxially growing the metal nitride film. [5] The method according to any one of [1] to [4] above, wherein the metal is Ga, Al, Hf, Zr, Sc, Y, La, Ta, Ti, or an alloy thereof. [6] The method according to any one of [1] to [4] above, wherein the solution containing NH4F further contains HF.

[0010] [7] A Si substrate with a metal oxide film, having a metal oxide film on a Si substrate, a Si oxide layer between the Si substrate and the metal oxide film; A Si substrate with a metal oxide film, wherein the Si oxide layer has a thickness of 2 nm or less. [8] A Si substrate with a metal nitride film, having a metal nitride film on a Si substrate, a Si nitride layer between the Si substrate and the metal nitride film; There is no Si oxide layer between the Si substrate and the metal nitride film, The Si substrate with a metal nitride film, wherein the thickness of the Si nitride layer is 2 nm or less. [9] The Si substrate according to [7] or [8], wherein the metal constituting the metal oxide film or the metal nitride film is Ga, Al, Hf, Zr, Sc, Y, La, Ta, Ti, or an alloy thereof.

[10] An electronic device having the Si substrate according to [7] or [8] above.

[11] An optical device having the Si substrate according to [7] or [8] above. [Effects of the Invention]

[0011] According to the present invention, it is possible to produce a metal oxide film or metal nitride film on a Si substrate, which has little or no influence of a Si oxide layer on crystallinity, surface roughness, electrical characteristics, etc. In other words, it is possible to obtain a Si substrate having a metal oxide film or metal nitride film that has little or no influence of the Si oxide layer. Therefore, even when the metal oxide film or metal nitride film is thinned, the occurrence of unexpected characteristics such as leakage current caused by the Si oxide layer can be suppressed, and a highly reliable Si substrate with a metal oxide film or metal nitride film can be obtained. [Brief explanation of the drawings]

[0012] [Figure 1]FIG. 1 is an XPS spectrum in the O1s region of the Si substrate after cleaning in Example 1. [Figure 2] FIG. 2 shows RHEED patterns of the gallium layer in Example 1 at different growth stages. [Figure 3] 3A and 3B are SEM images of the surface of the Si substrate with the gallium oxide film obtained in Example 1, where FIG. 3A is an image at a magnification of 5000 times, and FIG. 3B is an image at a magnification of 100,000 times. [Figure 4] FIG. 4 is an SEM image of the cross section of the Si substrate with the gallium oxide film obtained in Example 1, at a magnification of 20,000 times. [Figure 5] FIG. 5 shows an XRD pattern of the surface of the Si substrate with the gallium oxide film obtained in Example 1. [Figure 6] 6A and 6B are TEM images of the cross section of the Si substrate with the gallium oxide film obtained in Example 1, where FIG. 6A is an image at a magnification of 500 times, and FIG. 6B is an enlarged view of the interface in FIG. 6A. [Figure 7] FIG. 7 is an XPS spectrum in the O1s region of the Si substrate after cleaning in Example 2. [Figure 8] FIG. 8 shows the RHEED pattern at the stage when the Si substrate was heated during the growth of the gallium oxide film in Example 2. [Figure 9] 9A and 9B are SEM images of the surface of the Si substrate with the gallium oxide film obtained in Example 2, where FIG. 9A is an image at a magnification of 5000 times, and FIG. 9B is an image at a magnification of 100000 times. [Figure 10] FIG. 10 is an SEM image of a cross section of the Si substrate with the gallium oxide film obtained in Example 2, at a magnification of 20,000 times. [Figure 11] FIG. 11 shows an XRD pattern of the surface of the Si substrate with the gallium oxide film obtained in Example 2. [Figure 12] 12A and 12B are TEM images of the cross section of the Si substrate with the gallium oxide film obtained in Example 2, where FIG. 12A is an image at a magnification of 500 times, and FIG. 12B is an enlarged view of the interface in FIG. 12A. DETAILED DESCRIPTION OF THE INVENTION

[0013] The present invention will be described in detail below, but the present invention is not limited to the following embodiments and can be implemented in any modified form without departing from the gist of the present invention. In this specification, a single crystal substrate means a substrate in which the entire substrate is single crystal. In this specification, uniaxial orientation means that there are many crystal grains in which at least one of the crystal axes is aligned, and there are many crystal grains rotated around this one axis. The uniaxial orientation of the gallium oxide film can be confirmed, for example, by symmetric X-ray diffraction (symmetric XRD). In this specification, oxygen-composed particles are particles containing oxygen atoms including singlet oxygen atoms and triplet oxygen atoms, oxygen molecules, ozone, or excited states of these. In this specification, the use of "to" to indicate a range of values ​​means that the values ​​before and after it are included as the lower and upper limits.

[0014] <Method for manufacturing metal oxide film or metal nitride film> The method for manufacturing a metal oxide film or a metal nitride film according to this embodiment includes the following steps 1 to 3 in this order. Step 1: Cleaning the surface of the Si substrate with a solution containing NH4F Step 2: A step of adsorbing a metal layer made of a metal that constitutes a metal oxide film or a metal nitride film onto the cleaned Si substrate. Step 3: Next, a step of epitaxially growing a metal oxide film or a metal nitride film. The adsorption of the metal layer in the above step 2 is carried out by applying a pressure P (Pa) within the pressure range (Pa) where the adsorption rate and desorption rate of the metal constituting the metal oxide film or metal nitride film are in equilibrium in the Langmuir adsorption isotherm at an arbitrary temperature T (°C).

[0015] <Process 1> In this embodiment, step 1 is a step of cleaning the surface of a Si substrate with a solution containing NH4F (ammonium fluoride). Here, the Si substrate is a Si single crystal substrate. Conventionally, organic solvents such as water, acetone, isopropyl alcohol, ethanol, and methanol have been used to clean Si substrates. However, it has been found that a Si oxide layer remains on the surface of the Si substrate after cleaning. Furthermore, even if the Si oxide layer is removed using hydrofluoric acid for cleaning, the surface is highly susceptible to oxidation, and simply exposing the cleaned Si substrate to the atmosphere during transportation will result in the formation of a Si oxide layer on the surface.

[0016] Therefore, the inventors also investigated the use of the RCA cleaning method for cleaning Si substrates. As a result, they found that although RCA cleaning can suppress oxidation when the cleaned Si substrates are exposed to the atmosphere for transportation, when the cleaned Si substrates are supplied to the equipment for the subsequent steps 2 and 3, the Si substrates are oxidized by trace amounts of oxygen remaining in the equipment.

[0017] In contrast, in step 1 of this embodiment, a solution containing NHF is used for cleaning. As a result, even when the cleaned Si substrate is exposed to the atmosphere for transportation, no oxygen is present on the surface, and furthermore, even a trace amount of oxygen remaining in the equipment does not form a Si oxide layer.

[0018] The solution containing NHF may further contain HF. The solution is preferably an ammonium fluoride solution consisting of only NHF or a buffered hydrogen fluoride (BHF) solution, which is a mixture of NHF and HF, and more preferably an ammonium fluoride solution.

[0019] The cleaning with the solution containing NH4F (ammonium fluoride) is carried out by, for example, immersing the Si substrate in the solution. When washing is performed by immersion, the washing time is preferably, for example, 5 to 60 seconds, and the washing temperature is preferably 15 to 50°C.

[0020] Before cleaning with a solution containing NH4F (ammonium fluoride), the Si substrate may be pre-cleaned, preferably by RCA cleaning.

[0021] After cleaning with a solution containing NH4F (ammonium fluoride), it is preferable to dry the Si substrate, and the drying method is not particularly limited. For example, a spin dryer is preferable from the viewpoint of productivity.

[0022] <Process 2> Step 2 in this embodiment is a step of adsorbing a metal layer made of the metal that constitutes the metal oxide film or metal nitride film onto the Si substrate that has been cleaned in step 1. The adsorption of the metal layer is carried out by applying a pressure P (Pa) within the pressure range (Pa) where the adsorption rate and desorption rate of the metal constituting the metal oxide film or metal nitride film are in equilibrium in the Langmuir adsorption isotherm at an arbitrary temperature T (°C). This pressure range can be said to be the pressure range where the metal constituting the metal oxide film or metal nitride film is in the Langmuir adsorption state.

[0023] When a metal layer is adsorbed under the above conditions, the metal accumulates on the Si substrate surface until a certain temperature T (°C) is reached, at which point the amount of metal deposition stops. In other words, a state of thermodynamic equilibrium based on the Langmuir adsorption isotherm is reached, with a monoatomic layer of metal adsorbed on the Si substrate surface. It was found that by going through step 2, a metal oxide film or metal nitride film can be obtained on the Si substrate in the subsequent step 3, with little or no influence from the Si oxide layer.

[0024] The temperature T (°C) is arbitrary, but is preferably set to the temperature at which a metal oxide film or a metal nitride film is grown in step 3. It is preferable to raise the temperature of the cleaned Si substrate from room temperature to temperature T (°C) while supplying metal, rather than raising the temperature from room temperature to temperature T (°C) and then supplying metal to adsorb a metal layer.

[0025] The temperature rise rate is not particularly limited, but is preferably 1 to 50°C / min, and more preferably 5 to 20°C / min. From the viewpoint of process throughput, the temperature rise rate is preferably 1°C / min or more, more preferably 5°C / min or more, even more preferably 7°C / min or more, and even more preferably 8°C / min or more. From the viewpoint of uniform heating, the temperature rise rate is preferably 50°C / min or less, more preferably 25°C / min or less, even more preferably 20°C / min or less, even more preferably 18°C / min or less, especially preferably 15°C / min or less, and particularly preferably 12°C / min or less.

[0026] The applied pressure P (Pa) is not particularly limited as long as it is within the pressure range (Pa) that indicates the equilibrium state, but if the pressure is lower than the pressure range (Pa) that indicates the equilibrium state, the metal will not be adsorbed to the Si substrate surface in the first place. Therefore, the applied pressure P (Pa) is a pressure that is equal to or higher than the pressure at which the metal is adsorbed to the Si substrate surface and lower than the pressure at which the metal is deposited on the Si substrate surface.

[0027] The difference between the above pressure range and the applied pressure P (Pa) is not particularly limited, but the pressure P (Pa) must be within the above pressure range.

[0028] More specifically, when a gallium oxide film is grown as the metal oxide film in step 3, if the temperature T is, for example, 300°C, the pressure range (Pa) in which the adsorption rate and desorption rate of metal gallium (Ga) are in equilibrium in the Langmuir adsorption isotherm is 1.0 × 10 -8 (Pa) or more 1.0×10 -6 (Pa). Therefore, the pressure P applied when adsorbing the Ga metal layer in step 2 is not particularly limited as long as it is within the above pressure range, but it takes time to identify the lower limit of the pressure range (Pa) that indicates the equilibrium state. On the other hand, the upper limit of the pressure range (Pa) that indicates the equilibrium state is easy to identify because Ga deposition begins when the pressure range (Pa) that indicates the equilibrium state is exceeded. Therefore, Ga will certainly be adsorbed if the pressure is set to a value slightly below the above upper limit, so it is desirable that the applied pressure P (Pa) be as close as possible to the pressure at which Ga deposition begins but below that pressure.

[0029] The adsorption of the metal layer is preferably carried out for 20 to 1000 seconds after the temperature is raised to T (°C). From the viewpoint of removing the deposited metal, the adsorption time is preferably 20 seconds or more, more preferably 30 seconds or more. From the viewpoint of Langmuir adsorption, the adsorption time is preferably 1000 seconds or less, more preferably 600 seconds or less, even more preferably 100 seconds or less, and particularly preferably 60 seconds or less.

[0030] The metal layer can be adsorbed by the MBE method. For example, a cleaned Si substrate is placed in the reaction chamber of an MBE device, and while the Si substrate is heated to a desired temperature by a heating device, a desired metal element is supplied into the reaction chamber from a metal supply device, resulting in the adsorption of a monoatomic metal layer.

[0031] <Process 3> Step 3 in this embodiment is a step of epitaxially growing a metal oxide film or a metal nitride film on the Si substrate on which the metal layer has been formed in step 2.

[0032] In step 3, the metal layer formed in step 2 reacts with oxygen radicals for forming a metal oxide film or nitrogen for forming a metal nitride film to form a metal oxide layer or a metal nitride layer. This metal oxide layer or metal nitride layer cannot be distinguished from the epitaxially grown metal oxide layer or metal nitride layer. Therefore, in the obtained Si substrate with a metal oxide film or metal nitride film, it is included in the metal oxide film or metal nitride film.

[0033] The metal oxide layer or metal nitride layer can be formed under the epitaxial growth conditions of the metal oxide film or metal nitride film in step 3, but it is also possible to first convert the metal layer into a metal oxide layer or metal nitride layer, and then perform epitaxial growth of the metal oxide film or metal nitride film separately in step 3.

[0034] In step 3, because the metal layer adsorbed in step 2 is an extremely thin layer of one atom, oxygen radicals and nitrogen generated during epitaxial growth of the metal oxide film or metal nitride film oxidize or nitride the Si on the underlying Si substrate surface, forming a Si oxide layer or Si nitride layer. Specifically, part of the oxygen or nitrogen constituting the metal oxide layer or metal oxide film, or the metal nitride layer or metal nitride film, diffuses to the interface with the Si substrate and reacts with Si, forming a Si oxide layer or Si nitride layer.

[0035] However, in the manufacturing method according to the present embodiment, instead of growing a metal oxide film or metal nitride film directly on a Si substrate, a metal layer is first adsorbed onto a Si substrate that has been cleaned with a solution containing NHF. This allows the Si oxide layer or Si nitride layer formed as described above to be an extremely thin layer with a thickness of 2 nm or less. This minimizes the effects on the crystallinity, surface roughness, electrical characteristics, etc. of the metal oxide film or metal nitride film.

[0036] Note that, due to the cleaning in step 1, impurity atoms such as oxygen are absent or the amount thereof can be extremely reduced on the Si substrate surface, so that no layers other than a Si oxide layer or a Si nitride layer are formed. That is, in the method for producing a metal oxide film according to this embodiment, the layers are formed in the order of Si substrate / Si oxide layer / metal oxide film, and the growth of layers other than the Si oxide layer, such as a Si nitride layer, between the Si substrate and the metal oxide film is prevented. Similarly, in the method for producing a metal nitride film according to this embodiment, the layers are formed in the order of Si substrate / Si nitride layer / metal nitride film, and the growth of layers other than the Si nitride layer, such as a Si oxide layer, between the Si substrate and the metal nitride film is prevented.

[0037] A conventionally known method can be used for epitaxial growth of a metal oxide film or a metal nitride film, or optionally, for converting a metal layer into a metal oxide layer or a metal nitride layer after step 2 and before step 3. For example, the MBE method is preferred because it is preferable to use the same apparatus as in step 2.

[0038] The epitaxial growth temperature in step 3 varies depending on the type of metal oxide film or metal nitride film to be formed, but may be, for example, 100 to 1000°C.

[0039] A preferred embodiment for epitaxially growing a gallium oxide film will be described below as step 3, but this can be modified as appropriate by adopting a conventionally known method in accordance with the metal oxide film or metal nitride film to be grown.

[0040] In the epitaxial growth of gallium oxide films, the gas pressure (Ga pressure) when supplying gallium into the device is, for example, 1.0 × 10 -5 ~5.0×10 -3 Pa is preferred, 5.0 x 10 -5 ~1.0×10 -3 Pa is more preferred, 9.0 × 10 -5 ~5.0×10 -4 From the viewpoint of supplying a sufficient amount of Ga element, the gas pressure is preferably 1.0×10 Pa. -5 Pa or more is preferable, 5.0 × 10 -5 Pa or more is more preferable, 9.0 × 10 -5 In order to prevent the Ga deposition rate from becoming too high and becoming uncontrollable, the gas pressure is preferably 5.0×10 -3 Pa or less is preferable, and 1.0 × 10 -3 Pa or less is more preferable, and 9.0 × 10 -4 Pa or less is more preferable, and 5.0 × 10 -4 Pa or less is even more preferable.

[0041] The temperature of the Si substrate when elemental gallium is supplied is preferably 600°C or lower, more preferably 0 to 600°C, even more preferably 10 to 500°C, even more preferably 20 to 400°C, and may be 200 to 350°C or 250 to 330°C. From the viewpoint of crystal growth, the film formation temperature is preferably 0°C or higher, and may be 10°C or higher, or about room temperature or higher, i.e., 20°C or higher, 200°C or higher, or 250°C or higher. From the viewpoint of growth rate, the film formation temperature is preferably 600°C or lower, more preferably 500°C or lower, even more preferably 400°C or lower, and may be 350°C or lower, or 330°C or lower. As mentioned above, it is preferable that steps 2 and 3 are carried out at the same temperature.

[0042] The time for supplying the gallium element varies depending on the growth temperature, but is preferably 10 to 500 minutes when the substrate temperature is 300° C. Here, the heat treatment time is preferably 10 minutes or more, more preferably 20 minutes or more, and even more preferably 30 minutes or more, and is preferably 500 minutes or less, more preferably 400 minutes or less, and even more preferably 300 minutes or less.

[0043] On the other hand, in the epitaxial growth of a gallium oxide film, oxygen radicals are supplied into the device as an oxygen source. Specifically, a mixed gas containing oxygen and ozone is converted into plasma, and the ozone is dissociated into oxygen-constituting particles, which are then supplied into the device under reduced pressure, thereby growing a gallium oxide layer.

[0044] The concentration of ozone relative to the total of oxygen and ozone is, for example, preferably 10% by volume or more, more preferably 20% by volume or more, and even more preferably 25% by volume or more. The upper limit of this volume is not particularly limited, but is usually 50% by volume or less.

[0045] The method for dissociating ozone into oxygen-constituting particles is not particularly limited. For example, ozone can be decomposed by plasma to produce oxygen molecules and singlet oxygen atoms O( 1 It is preferable to generate oxygen radicals with strong oxidizing power containing a large amount of singlet oxygen atoms O(1 D) and triplet oxygen atom O( 3 P) and singlet oxygen atoms O( 1 D) is a triplet oxygen atom O( 3 P).

[0046] In step 3, the gas pressure in the furnace containing the oxygen constituent particles is 1.0 × 10 -5 ~1.0×10 -1 Pa is preferred, 1.0 x 10 -4 ~1.0×10 -1 Pa is more preferable, and 1.0 × 10 -3 ~1.0×10 -2 From the viewpoint of supplying a sufficient amount of oxygen radicals, the gas pressure is preferably 1.0×10 Pa. -5 Pa or more is preferable, and 1.0×10 -4 Pa or more is more preferable, and 1.0×10 -3 From the viewpoint of the mean free path of molecules in the chamber, the gas pressure is preferably 1.0×10 Pa or more. -1 Pa or less is preferable, and 1.0 × 10 -2 Pa or less is more preferable.

[0047] The lattice constant mismatch rate between the obtained gallium oxide film and the Si substrate is preferably 15% or less, more preferably 12% or less, even more preferably 8% or less, and particularly preferably 5% or less. The lower the rate, the better, but it may be, for example, 3% or more, or 4% or more. The rate of lattice constant mismatch is uniquely determined from the epitaxial relationship that is physically optimal due to the bond energy between the single crystal constituent elements and the constituent elements of gallium oxide with respect to the Si substrate.

[0048] When a separate step of converting the metal layer adsorbed in step 2 into a metal oxide layer or a metal nitride layer is included after step 2 and before step 3, it is preferable to supply (preflow) elemental gallium into the apparatus, stop the supply, and then supply oxygen radicals.

[0049] The gallium element and oxygen radicals supplied above can be obtained using the same equipment as that used to supply the gallium element and oxygen radicals in step 3 above, and the supply conditions, such as the pressure, may be changed as appropriate.

[0050] The gas pressure of Ga (Ga pressure) when supplying gallium element is, for example, 5.0 × 10 -7 ~1.0×10 -4 Pa is preferred, 1.0 x 10 -6 ~5.0×10 -5 Pa is more preferred, 5.0 × 10 -6 ~1.0×10 -5 From the viewpoint of supplying a sufficient amount of Ga element, the gas pressure is preferably 5.0×10 Pa. -7 Pa or more is preferable, and 1.0×10 -6 Pa or more is more preferable, 5.0 × 10 -6 The gas pressure is more preferably 1.0×10 Pa or more. -4 Pa or less is preferable, and 5.0 × 10 -5 Pa or less is preferable, and 1.0 × 10 -5 Pa or less is more preferable.

[0051] The time for supplying (preflowing) elemental gallium varies depending on the growth temperature, but is preferably 10 to 60 seconds when the Si substrate temperature is 300°C. Here, the time is preferably 10 seconds or more, more preferably 15 seconds or more, even more preferably 20 seconds or more, and even more preferably 25 seconds or more. The time is preferably 60 seconds or less, more preferably 50 seconds or less, even more preferably 40 seconds or less, and even more preferably 35 seconds or less.

[0052] Next, the supply of Ga is stopped, and oxygen radicals are supplied into the device. Note that the supply of oxygen radicals does not exclude the supply of not only oxygen constituent particles, but also a mixed gas containing non-plasma oxygen and ozone.

[0053] The supply of oxygen radicals transforms the metal Ga layer into a metal oxide layer, a gallium oxide layer, and at the same time, some of the oxygen that makes up the gallium oxide diffuses to the interface with the Si substrate, forming a very thin Si oxide layer.

[0054] In forming the metal oxide layer, an inert gas such as Ar gas may be further mixed with the mixed gas containing oxygen and ozone to prepare a mixed gas containing oxygen, ozone, and an inert gas.

[0055] The mixing ratio of the mixed gas containing oxygen and ozone to the inert gas is preferably 230 to 1900 parts by volume, more preferably 230 to 1500 parts by volume, even more preferably 350 to 1000 parts by volume, and even more preferably 350 to 460 parts by volume, when the mixed gas containing oxygen and ozone is taken as 100 parts by volume. From the viewpoint of plasma ignition, the ratio of the inert gas is preferably 230 parts by volume or more, and more preferably 350 parts by volume or more. From the viewpoint of oxygen radical density, the ratio of the inert gas is preferably 1900 parts by volume or less, more preferably 1500 parts by volume or less, even more preferably 1000 parts by volume or less, and even more preferably 460 parts by volume or less.

[0056] The time for supplying the oxygen radicals, i.e., the time for converting the Ga layer into a gallium oxide layer, is preferably 10 to 60 seconds. From the viewpoint of converting all Ga into gallium oxide, the growth time is preferably 10 seconds or longer, more preferably 15 seconds or longer, even more preferably 20 seconds or longer, and even more preferably 30 seconds or longer. Furthermore, from the viewpoint of preventing the generated gallium oxide from becoming oxygen-rich, the growth time is preferably 60 seconds or shorter, more preferably 55 seconds or shorter, even more preferably 50 seconds or shorter, and even more preferably 45 seconds or shorter.

[0057] The metal of the metal oxide film or metal nitride film obtained by the manufacturing method according to this embodiment can be appropriately selected depending on the purpose, and is not particularly limited. For example, Ga, Al, Hf, Zr, Sc, Y, La, Ta, Ti, or alloys thereof may be mentioned.

[0058] <Si substrate> One aspect of the Si substrate according to this embodiment is a Si substrate with a metal oxide film, which has a metal oxide film on the Si substrate and a Si oxide layer between the Si substrate and the metal oxide film, and the thickness of the Si oxide layer is 2 nm or less. Another aspect of the Si substrate according to this embodiment is a metal nitride film-attached Si substrate having a metal nitride film on the Si substrate and a Si nitride layer between the Si substrate and the metal nitride film, the thickness of which is 2 nm or less.

[0059] In the Si substrate with a metal oxide film according to this embodiment, a Si oxide layer is present between the Si substrate and the metal oxide film, but because the Si substrate is highly cleanable and a metal layer is adsorbed onto the Si substrate before the metal oxide film is grown, it is difficult for layers other than the Si oxide layer to form. Therefore, it is preferable that no layers other than the Si oxide layer, such as a Si nitride layer, exist between the Si substrate and the metal oxide film.

[0060] Similarly, the Si substrate with a metal nitride film according to this embodiment has a Si nitride layer between the Si substrate and the metal nitride film, but because the Si substrate is highly cleanable and a metal layer is adsorbed onto the Si substrate before the metal nitride film is grown, it is difficult for layers other than the Si nitride layer to be formed. Therefore, it is preferable that no layers other than the Si nitride layer, such as a Si oxide layer, exist between the Si substrate and the metal nitride film.

[0061] In the Si substrate with a metal oxide film according to this embodiment, the thickness of the Si oxide layer is 2 nm or less. This can be achieved by adsorbing a monoatomic metal layer onto the Si substrate and then growing the metal oxide film. With this thickness, the Si oxide layer has very little effect on the crystallinity, surface roughness, electrical properties, etc. of the metal oxide film.

[0062] In the Si substrate with a metal nitride film according to this embodiment, the thickness of the Si nitride layer is 2 nm or less. This can be achieved by adsorbing a monoatomic metal layer onto the Si substrate and then growing the metal nitride film. With this thickness, the Si nitride layer has very little effect on the properties of the metal nitride film. Furthermore, there is no Si oxide layer. Therefore, the Si oxide layer does not affect the crystallinity, surface roughness, electrical properties, etc., of the metal nitride film.

[0063] The metal constituting the metal oxide film or metal nitride film of the Si substrate in this embodiment can be appropriately selected depending on the purpose, and is not particularly limited. For example, Ga, Al, Hf, Zr, Sc, Y, La, Ta, Ti, or alloys thereof may be mentioned. The metal oxide film or metal nitride film functions as a gate insulating film, a passivation film, an interlayer insulating film, or a high dielectric film in an electronic device. The metal oxide film or metal nitride film functions as a light-emitting active layer, a light-receiving active layer, or a cladding layer in an optical device.

[0064] The crystallinity and surface flatness of metal oxide or metal nitride films on Si substrates can be investigated by reflection high energy electron diffraction (RHEED) techniques. Specifically, this technique involves in-situ observation of the surface structure during growth of metal oxide or metal nitride films using molecular beam epitaxy (MBE).

[0065] In this embodiment, the metal oxide film or metal nitride film is more preferable if the rate of lattice constant mismatch with the Si substrate is as small as possible. For example, when the metal oxide film is a gallium oxide film, the lattice constant mismatch rate with the Si substrate is preferably 15% or less, more preferably 12% or less, even more preferably 8% or less, and particularly preferably 5% or less. The lower the rate, the better, but it is greater than the lattice constant mismatch rate between the Si substrate and the Si oxide layer. The lattice constant mismatch rate between the gallium oxide film and the Si substrate may be, for example, 3% or more, or 4% or more.

[0066] Here, the lattice constant mismatch is the ratio of the difference in lattice constant of the gallium oxide layer in the same direction to the lattice constant of the Si single crystal substrate. The lattice mismatch ratio can be determined by analyzing the epitaxial relationship between the Si single crystal substrate and the gallium oxide layer from the results of symmetric and in-plane X-ray diffraction measurements. For example, it can be calculated from the ratio between the lattice constant of the Si single crystal substrate and the lattice constant of the gallium oxide layer projected in a certain direction onto the Si single crystal substrate.

[0067] In this embodiment, the thickness of the metal oxide film or metal nitride film is preferably 0.5 to 50 μm, more preferably 0.8 to 30 μm, and even more preferably 1 to 20 μm. From the viewpoint of the withstand voltage for applications such as power devices, the thickness is preferably 0.5 μm or more, more preferably 0.8 μm or more, and even more preferably 1 μm or more. While there is no particular upper limit, from the viewpoint of film formation rate and film quality, the thickness is preferably 50 μm or less, more preferably 30 μm or less, and even more preferably 20 μm or less. In this embodiment, the thickness of the Si oxide layer or Si nitride layer can be made extremely thin, at 2 nm or less, so that even if the metal oxide film or metal nitride film is thin, the influence of the Si oxide layer on crystallinity, surface roughness, electrical properties, and the like can be prevented. To more effectively obtain this effect, the thickness of the metal oxide film or metal nitride film may be 50 μm or less, or may be 10 μm or less.

[0068] The arithmetic mean surface roughness Ra of the metal oxide film or metal nitride film in this embodiment is preferably 4.5 nm or less. From the viewpoint of improving the flatness of the metal oxide film or metal nitride film in this embodiment and realizing higher withstand voltage, the arithmetic mean surface roughness Ra is preferably 4.5 nm or less, more preferably 4.0 nm or less, and even more preferably 3.0 nm or less. The smaller the better, but it is usually 0.1 nm or more.

[0069] When the metal oxide film in this embodiment is a gallium oxide film, gallium oxide is a crystalline polymorph, and has at least five crystalline structures called α-type, β-type, γ-type, δ-type, and ε-type. Among these, a β-type gallium oxide film is preferred from the viewpoint that it is the most stable phase and is therefore expected to be useful in industrial applications, although the gallium oxide film in this embodiment is not limited to a β-type gallium oxide film.

[0070] For example, an α-type gallium oxide film, which is a metastable phase and has a corundum crystal structure, is preferred because it has the largest band gap. In addition, a γ-type gallium oxide film, which is a metastable phase and has a cubic defect spinel structure, a δ-type gallium oxide film, which has a cubic bixbyite structure, and an ε-type gallium oxide film, which is an orthorhombic polar crystal, each have their own reasons for being suitable according to their respective characteristics.

[0071] From the viewpoint of crystallinity, the gallium oxide film is preferably uniaxially oriented.

[0072] The gallium oxide film may be either single crystal or polycrystalline, but from the viewpoint of the yield and characteristics of semiconductor devices, a single crystal or a crystal close to a single crystal is preferred, and a single crystal is more preferred. Furthermore, when a small amount of impurities is mixed in to grow an n-type or p-type gallium oxide semiconductor, the gallium oxide film may contain the impurities. In this specification, the crystal structure of a gallium oxide film and whether it is a single crystal film or not can be measured, for example, by a crystal X-ray diffraction (XRD) device using CuKα radiation as a radiation source. The crystal structures of α-type to ε-type each have their own unique XRD patterns. Furthermore, if they are single crystals, an XRD pattern specific to single crystals can be obtained.

[0073] When the gallium oxide film is single crystal, the plane orientation of the gallium oxide film is preferably (100), and it is more preferable that the gallium oxide film has a (100) plane orientation provided on a Si substrate with a (100) plane orientation, and it is even more preferable that the gallium oxide film here is a β-type gallium oxide film.

[0074] The Si substrate according to this embodiment is effective for electronic devices and optical devices, that is, the present invention also relates to electronic devices and optical devices having the above-mentioned Si substrate. [Example]

[0075] The present invention will be described in detail below with reference to examples, but the present invention is not limited to these. Here, Example 1 is an example, and Example 2 is a comparative example.

[0076] Example 1: Manufacturing of Si substrates with gallium oxide films <Si substrate cleaning> A 10 × 10 mm, 650 μm-thick (100) Si substrate was pre-cleaned using the RCA cleaning method. Specifically, the Si substrate was immersed in an RCA-1 aqueous solution (NH4OH:HO2:HO = 1:1:5 (volume ratio)) at 70 °C for 15 minutes and then rinsed with ion-exchanged water. Next, it was etched with a 4% HF aqueous solution for 10 seconds and then rinsed with ion-exchanged water. It was then immersed in an RCA-2 aqueous solution (HCl:HO2:HO = 1:1:6 (volume ratio)) at 70 °C for 10 minutes and then rinsed with ion-exchanged water. It was then immersed again in an RCA-1 aqueous solution (NH4OH:HO2:HO = 1:1:5 (volume ratio)) at 70 °C for 15 minutes and then rinsed with ion-exchanged water. Next, the pre-cleaned Si substrate was immersed in an NH4F solution at room temperature for 20 seconds, then washed with ion-exchanged water, and dried with a spin dryer.

[0077] The cleaned Si substrate was transferred in air, i.e., exposed to the atmosphere, and the impurity atoms remaining on the surface were measured using X-ray photoelectron spectroscopy (XPS). The results are shown in Figure 1, and it was confirmed that no oxygen remained on the Si substrate surface.

[0078] <Adsorption of Gallium Layer> The Si substrate after the cleaning was fed into the reaction chamber of the MBE apparatus and placed on a sample susceptor. The degree of vacuum in the reaction chamber was 5.33×10 -7 The pressure was evacuated until the pressure reached 100 Pa. Next, the Ga vapor pressure P in the reaction chamber was 1.33 × 10 -7 The Ga flux was adjusted to Pa, the temperature was raised to 300°C at a rate of 10°C / min, and the temperature was maintained at 300°C for 5 seconds or more to allow the adsorption of a gallium layer. In addition, in the Langmuir adsorption isotherm of gallium oxide (Ga2O3) at 300°C, the above Ga vapor pressure P is 1.33 × 10 -7 Pa is within the pressure range where the adsorption and desorption rates of gallium are in equilibrium, and can be said to be in the Langmuir adsorption state.

[0079] The intensity change of the reflection high-energy electron diffraction (RHEED) pattern during the growth stage of the gallium layer is shown in Figure 2. The time on the horizontal axis is 1800 seconds, when the temperature of the Si substrate reaches 300°C. Although Ga continues to deposit until the temperature of the Si substrate reaches 300°C, the intensity becomes constant at 300°C, and it was confirmed that a monoatomic layer of gallium is adsorbed in a state of thermodynamic equilibrium based on the Langmuir adsorption isotherm.

[0080] <Formation of Gallium Oxide Layer> Next, the Ga vapor pressure in the reaction chamber was 6.13 × 10 -6The Ga flux was adjusted to 0.1 Pa, and Ga preflow was performed at 300°C for 30 seconds. Then, oxygen radicals were irradiated at 600 W for 40 seconds. At this time, Ar was introduced at 8.5 sccm and O3 + O2 at 1.5 sccm as oxygen radical sources. This converted the gallium layer adsorbed above into a gallium oxide layer.

[0081] <Growth of Gallium Oxide Film> Next, the Ga vapor pressure in the reaction chamber was 1.067 × 10 -4 The Ga flux was adjusted to 0.05 Pa, and oxygen radicals were irradiated at 1000 W for 60 minutes. At this time, 0 sccm of Ar and 8 sccm of O3 + O2 were introduced as oxygen radical sources. The sample was then cooled to room temperature at 10 °C / min.

[0082] Scanning electron microscope (SEM) images of the surface of the Si substrate with the gallium oxide film obtained above are shown in Figures 3(a) and 3(b), an SEM image of the cross section is shown in Figure 4, an X-ray diffraction (XRD) pattern of the surface is shown in Figure 5, and transmission electron microscope (TEM) images of the cross section are shown in Figures 6(a) and 6(b).

[0083] The results in Figures 3(a), 3(b), and 4 confirm that the surface of the gallium oxide film is very flat. Furthermore, the results in Figure 4 indicate that the thickness of the gallium oxide film is 425 nm (0.425 μm). From the results in Figure 5, the obtained gallium oxide film exhibited a diffraction peak for the (400) plane, which has a different orientation from the Si substrate, near 2θ-θ=30°, and a diffraction peak for the (60-1) plane, which has a different orientation from the Si substrate, near 2θ-θ=44°. This indicates that gallium oxide single crystals had been successfully grown. Furthermore, the results in Figure 6(a) confirmed the presence of a thin atomic layer at the interface between the Si substrate and the gallium oxide film. Figure 6(b) is an enlarged view of the interface in Figure 6(a), revealing that the atomic layer is approximately 1 nm thick and revealing an atomic arrangement. This is presumed to be a Si oxide layer, but it is not formed by the oxidation of Si prior to the epitaxial growth of the gallium oxide film. Rather, it is thought to be a Si oxide layer formed when the gallium layer adsorbed on the Si substrate was converted into a gallium oxide layer, and some of the oxygen from the gallium oxide diffused to the interface and reacted with Si.

[0084] Thus, in Example 1, no signs of direct oxidation of the Si substrate were observed between the Si substrate and the gallium oxide film grown thereon, and it can be said that the oxidation was suppressed, which prevents the effects of the oxidation on the crystallinity, surface roughness, electrical properties, etc. of the gallium oxide film.

[0085] Example 2: Manufacturing of Si substrates with gallium oxide films <Si substrate cleaning> A 10 × 10 mm, 650 μm-thick (100) Si substrate was cleaned using the RCA cleaning method. Specifically, the Si substrate was immersed in an RCA-1 aqueous solution (NH4OH:HO2:HO = 1:1:5 (volume ratio)) at 70 °C for 15 minutes and then rinsed with ion-exchanged water. Next, it was etched with a 4% HF aqueous solution for 10 seconds and then rinsed with ion-exchanged water. It was then immersed in an RCA-2 aqueous solution (HCl:HO2:HO = 1:1:6 (volume ratio)) at 70 °C for 10 minutes and then rinsed with ion-exchanged water. It was then immersed again in an RCA-1 aqueous solution (NH4OH:HO2:HO = 1:1:5 (volume ratio)) at 70 °C for 15 minutes, rinsed with ion-exchanged water, and dried using a spin dryer.

[0086] The cleaned Si substrate was transferred in air, i.e., exposed to the atmosphere, and the impurity atoms remaining on the surface were measured using XPS. The results are shown in Figure 7, and it was confirmed that no oxygen remained on the Si substrate surface.

[0087] <Growth of Gallium Oxide Film> The Si substrate after the cleaning was fed into the reaction chamber of the MBE apparatus and placed on a sample susceptor. The temperature of the Si substrate was raised to 300° C. at a rate of 10° C. / min and held at 300° C. for 120 seconds. The change in intensity of the RHEED pattern at this time is shown in Figure 8. The time on the horizontal axis is 1800 seconds, when the temperature of the Si substrate reaches 300°C, but the intensity decreases until the temperature of the Si substrate reaches 300°C, and the intensity continues to decrease even after it reaches 300°C. This is because the surface of the Si substrate is oxidized by trace amounts of oxygen remaining in the reaction chamber.

[0088] Next, the Ga vapor pressure in the reaction chamber was 1.067 × 10 -4 The Ga flux was adjusted to 0.05 Pa, and oxygen radicals were irradiated at 1000 W for 60 minutes. At this time, 0 sccm of Ar and 8 sccm of O3 + O2 were introduced as oxygen radical sources. The sample was then cooled to room temperature at 10 °C / min.

[0089] SEM images of the surface of the Si substrate with the gallium oxide film obtained above are shown in Figures 9(a) and 9(b), an SEM image of the cross section is shown in Figure 10, an XRD pattern of the surface is shown in Figure 11, and a TEM image of the cross section is shown in Figures 12(a) and 12(b).

[0090] 9(a), 9(b), and 10, it was confirmed that the surface of the gallium oxide film was rougher than that of Example 1. Furthermore, the result of FIG. 10 revealed that the thickness of the gallium oxide film was 450 nm (0.450 μm). From the results in Figure 11, the obtained gallium oxide film exhibited a diffraction peak for the (400) plane, which has a different orientation from the Si substrate, near 2θ-θ=30°, and a diffraction peak for the (60-1) plane, which has a different orientation from the Si substrate, near 2θ-θ=44°. This indicates that gallium oxide single crystals were successfully grown. Furthermore, the results in Figure 12(a) confirmed the presence of a thick interfacial layer at the interface between the Si substrate and the gallium oxide film. Figure 12(b) is an enlarged view of the interface in Figure 12(a), and shows that the thickness of the interfacial layer is approximately 3.5 nm. Since no atomic arrangement is visible, it is presumed to be an amorphous oxide film. This is thought to be a Si oxide film in which Si is oxidized before the gallium oxide film is epitaxially grown on the Si substrate.

[0091] Thus, a thick amorphous oxide film was formed between the Si substrate and the gallium oxide film grown thereon in Example 2. This amorphous oxide film is presumed to be a Si oxide film formed by direct oxidation of the Si substrate, and this oxide film may affect the crystallinity, surface roughness, electrical properties, etc. of the gallium oxide film.

Claims

1. A method for producing a metal oxide film, comprising growing a metal oxide film on a Si substrate, the method comprising: The surface of the Si substrate is treated with NH ４ Washing with a solution containing F, a metal layer made of a metal constituting the metal oxide film is adsorbed onto the cleaned Si substrate; adsorption of the metal layer is carried out by applying a pressure P (Pa) within a pressure range (Pa) in which an adsorption rate and a desorption rate of the metal constituting the metal oxide film are in equilibrium in a Langmuir adsorption isotherm at an arbitrary temperature T (°C); Next, the metal oxide film is epitaxially grown.

2. The adsorbed metal layer is made into a metal oxide layer, The method for producing a metal oxide film according to claim 1 , further comprising the step of epitaxially growing the metal oxide film.

3. A method for manufacturing a metal nitride film, comprising growing a metal nitride film on a Si substrate, the method comprising: The surface of the Si substrate is treated with NH ４ Washing with a solution containing F, a metal layer made of a metal constituting the metal nitride film is adsorbed onto the cleaned Si substrate; adsorption of the metal layer is carried out by applying a pressure P (Pa) within a pressure range (Pa) in which an adsorption rate and a desorption rate of the metal constituting the metal nitride film are in equilibrium in a Langmuir adsorption isotherm at an arbitrary temperature T (°C); Next, the metal nitride film is epitaxially grown.

4. The adsorbed metal layer is a metal nitride layer, 4. The method for producing a metal nitride film according to claim 3, further comprising the step of epitaxially growing said metal nitride film.

5. The method according to any one of claims 1 to 4, wherein the metal is Ga, Al, Hf, Zr, Sc, Y, La, Ta, Ti, or an alloy thereof.

6. Said NH ４ The method according to any one of claims 1 to 4, wherein the solution containing F further contains HF.

7. A metal oxide film-attached Si substrate having a metal oxide film on a Si substrate, a Si oxide layer between the Si substrate and the metal oxide film; A Si substrate with a metal oxide film, wherein the Si oxide layer has a thickness of 2 nm or less.

8. A Si substrate with a metal nitride film, comprising a Si substrate having a metal nitride film thereon, a Si nitride layer between the Si substrate and the metal nitride film; no Si oxide layer exists between the Si substrate and the metal nitride film; The Si substrate with a metal nitride film, wherein the Si nitride layer has a thickness of 2 nm or less.

9. 9. The Si substrate according to claim 7, wherein the metal constituting the metal oxide film or the metal nitride film is Ga, Al, Hf, Zr, Sc, Y, La, Ta, Ti, or an alloy thereof.

10. An electronic device comprising the Si substrate according to claim 7 or 8.

11. An optical device comprising the Si substrate according to claim 7 or 8.

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