Hypotaxy method using two-dimensional material for forming crystalline thin film

Abstract

The present invention relates to a method for forming a crystalline thin film and, specifically, to a method capable of forming a single-crystal or polycrystalline thin film without defects regardless of the type of a lower substrate by using a two-dimensional material template.

Description

Hypotaxis method using two-dimensional materials for forming crystalline thin films

[0001] The present invention relates to a method for forming a crystalline thin film, and more particularly, to a hypotaxy method capable of forming a defect-free single-crystal or polycrystalline thin film regardless of the type of the lower substrate.

[0002] This invention claims the benefit of Korean Patent Application No. 10-2023-0187156 filed with the Korean Intellectual Property Office on December 20, 2023, the entire contents of which are incorporated herein by reference.

[0003] Materials are classified as amorphous, single crystal, and polycrystalline based on their crystal structure. Amorphous materials lack a crystalline structure and contain numerous defects, which hinder the movement and control of carriers such as electrons and holes, resulting in deterioration of material properties. Polycrystalline materials are composed of larger grains but have numerous grain boundaries, resulting in better device properties than amorphous materials, but still with limitations. On the other hand, single crystal materials have a single crystal structure throughout, do not contain grain boundaries, and have superior material properties, making them essential in various fields, including the semiconductor industry.

[0004] Meanwhile, epitaxial growth, a method of growing a single-crystal thin film on a substrate, has limitations in the type of substrate on which the crystal is grown, as the thin film to be grown and the substrate must have similar crystal structures and lattice constants. In addition, the method of epitaxially growing a single-crystal thin film on top of a single-crystal template has limitations, such as defect formation due to large strain and damage to the grown thin film during the process of removing the template after thin film synthesis. In addition, there is a limitation in that it is impossible to form a polycrystalline or single-crystal thin film on a substrate with a different crystal structure or that is amorphous, making it impossible to create a layered device.

[0005] The technical problem to be achieved by the present invention is to provide a method for forming a single crystal or polycrystalline thin film having excellent material properties even on an amorphous substrate rather than a single crystal substrate on which epitaxy is impossible.

[0006] However, the problems to be solved by the present invention are not limited to the problems mentioned above, and other problems not mentioned will be clearly understood by those skilled in the art from the description below.

[0007] One embodiment of the present invention provides a method for forming a crystalline thin film, comprising: forming a raw material thin film on a substrate; forming a template including a crystalline two-dimensional material on top of the raw material thin film; and heating the raw material thin film on which the template has been formed under an inert gas atmosphere to crystallize the raw material thin film, thereby forming a crystalline thin film, wherein the crystalline thin film is hypotaxially grown from below the template.

[0008] A method for forming a crystalline thin film according to one embodiment of the present invention can form a defect-free single-crystal thin film even on a substrate that is not a single crystal.

[0009] A method for forming a crystalline thin film according to one embodiment of the present invention can form a polycrystalline thin film having the same microstructure along the microstructure of a two-dimensional template, thereby enabling precise control of the crystal direction and microstructure of the thin film to be formed.

[0010] A method for forming a crystalline thin film according to one embodiment of the present invention may not require an additional process for template removal since the template can be naturally removed during the crystalline thin film formation process.

[0011] A method for forming a crystalline thin film according to one embodiment of the present invention can precisely control the number of layers of a crystalline thin film to be formed.

[0012] The effects of the present invention are not limited to the effects described above, and effects not mentioned will be clearly understood by those skilled in the art from the present specification and the attached drawings.

[0013] Figure 1 is a schematic drawing showing (a) the epitaxial growth of a transition metal dichalcogenide (TMD) on a crystalline substrate and (b) the hypotaxic growth of a crystalline thin film from below a template according to one embodiment of the present invention.

[0014] FIG. 2 is a drawing sequentially showing each step of a method for forming a crystalline thin film according to an embodiment of the present invention, which is performed while supplying a reaction gas.

[0015] Figure 3 is a schematic diagram showing a nucleus formed in a defective portion of a template.

[0016] Figure 4 is a TEM image of single crystal graphene synthesized in Manufacturing Example 1 (a), single crystal graphene of Manufacturing Example 1 supplied with hydrogen sulfide for 30 minutes (b), and single crystal graphene of Manufacturing Example 1 treated with O2 plasma (c).

[0017] Figure 5 is a drawing showing the SEM image (a), TEM image (b), diffraction pattern (c), and side TEM image (d) of the surface of the MoS2 thin film obtained in Experimental Example 1.

[0018] Figure 6 is a drawing showing optical microscope images of the number of MoS2 single crystal layers in the obtained thin film depending on the thickness of the deposited molybdenum metal thin film.

[0019] Figure 7a is a graph showing the relationship between the thickness of the deposited molybdenum metal thin film and the number of MoS2 single crystal layers in the obtained thin film.

[0020] Figure 7b is a Raman spectrum for a MoS2 single crystal thin film having 1 to 4 layers.

[0021] Figure 7c is a side TEM image of a MoS2 single crystal thin film formed with the number of layers being 1 to 4, 6, 8, 14, and 99.

[0022] Figure 8 is a diagram showing Raman spectra for WS2, MoSe2, and WSe2 thin films obtained in Examples 2 to 4.

[0023] Figure 9 shows TEM images and EDS analysis images of the surface (a) and side (b) of WS2, MoSe2, and WSe2 thin films obtained in Examples 2 to 4.

[0024] Figure 10 is a drawing showing TEM images and diffraction patterns of the side surfaces of Mo, W, and MoO2 thin films obtained in Examples 5 to 7.

[0025] Figure 11 is a diagram showing the Raman spectrum results (a), side TEM image (b), and diffraction pattern (c) for the MoS2 thin film obtained in Example 8.

[0026] Figure 12 is a diagram showing a side TEM image (a), a top view TEM image and diffraction pattern (c), and a Raman spectrum result (c) for the WS2 thin film obtained in Example 9.

[0027] Figure 13 is a schematic diagram showing an intermediate process of forming a thin film in Example 10 using polycrystalline graphene as a template (a), a TEM image and diffraction pattern of the obtained MoS2 thin film (b), a DF-TEM image of the obtained MoS2 thin film (d), and a DF-TEM image of the polycrystalline graphene template (c).

[0028] FIG. 14 is a diagram showing an optical microscope image (a) of a WSe2 thin film obtained in Example 12 and polycrystalline graphene grown directly on a tungsten substrate, and a Raman spectrum (b) of MoS2 and WSe2 thin films obtained in Examples 11 and 12.

[0029] Figure 15 is a drawing showing a TEM image (a) of a template in which a defective portion was formed in advance in Example 13, a TEM image (b) of the obtained MoS2 single crystal thin film, a diffraction pattern (c), and a Raman spectrum (d).

[0030] Figure 16 is a drawing showing a TEM image and a diffraction pattern for each of the MoS2 thin films obtained in Examples 14 to 16.

[0031] Figure 17 is a diagram showing the horizontal and vertical thermal characteristics of the MoS2 thin film obtained in Example 1.

[0032] Figure 18 is a diagram showing an optical microscope and SEM image (a), a characteristic curve (transfer curve, output curve) (b), and a characteristic curve according to drain voltage (c) of a field effect transistor (FET) device array manufactured using the MoS2 thin film obtained in Example 1 as a channel.

[0033] Throughout this specification, whenever a part is said to "include" a component, this does not mean that it excludes other components, but rather that it may include other components, unless otherwise specifically stated.

[0034] Throughout this specification, when it is said that an element is "on" another element, this includes not only cases where the element is in contact with the other element, but also cases where another element exists between the two elements.

[0035] Throughout this specification, the unit “parts by weight” may mean the weight ratio between each component.

[0036] Throughout this specification, “A and / or B” means “A and B, or A or B.”

[0037] Throughout this specification, the word "hypotaxy" is a compound word of hypo, meaning below, and taxy, meaning aligned, and refers to a state in which the template is aligned in accordance with the crystal structure of the template in the direction below the template.

[0038] Hereinafter, the present invention will be described in more detail.

[0039] One embodiment of the present invention provides a method for forming a crystalline thin film, comprising: forming a raw material thin film on a substrate; forming a template including a crystalline two-dimensional material on top of the raw material thin film; and heating the raw material thin film on which the template has been formed under an inert gas atmosphere to crystallize the raw material thin film, thereby forming a crystalline thin film, wherein the crystalline thin film is hypotaxially grown from below the template.

[0040] A method for forming a crystalline thin film according to one embodiment of the present invention does not require an additional process for template removal since the template can be naturally removed during the crystalline thin film forming process, and the number of layers of the crystalline thin film to be formed can be precisely controlled.

[0041] A method for forming a crystalline thin film according to one embodiment of the present invention can form a defect-free single-crystal thin film even on a substrate other than a single crystal, and is not limited to the type of substrate and can be applied to various processes and substrates.

[0042] Figure 1 is a schematic drawing showing (a) the epitaxial growth of a transition metal dichalcogenide (TMD) on a crystalline substrate and (b) the hypotaxic growth of a crystalline thin film from below a template according to one embodiment of the present invention.

[0043] Referring to Fig. 1, unlike the conventional epitaxial growth method that requires the substrate under the thin film to be formed to be crystalline, particularly a single crystal, the method for forming a crystalline thin film according to an embodiment of the present invention can form a defect-free single crystal or polycrystalline thin film regardless of the type of substrate by hypotaxially growing from under the template.

[0044] According to one embodiment of the present invention, any material included in the crystalline thin film to be formed may be applied without particular limitation as long as it is a material capable of being crystalline. Specifically, the crystalline thin film may include a polymer, a metal, a ceramic, or a combination thereof, and more specifically, may include a transition metal, a transition metal chalcogenide, or a transition metal oxide.

[0045] According to one embodiment of the present invention, the transition metal may include Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Y, Zr, Nb, Mo, Tc, Ru, Rh, Pd, Ag, Cd, Hf, Ta, W, Re, Os, Ir, Pt, Au, Hg, Rf, Db, Sg, Bh, Hs, Mt, Ds, Rg, Cn and alloys thereof.

[0046] According to one embodiment of the present invention, the transition metal chalcogenide may be a transition metal dichalcogenide represented by the chemical formula MX2 (M: transition metal, X: chalcogen element). For example, the transition metal dichalcogenide may be MoS2, MoSe2, MoTe2, WS2, WSe2, or WTe2, but is not necessarily limited thereto.

[0047] According to one embodiment of the present invention, the transition metal oxide may be MoO2, WO3, Sc2O3, TiO2, V2O5, Cr2O3, Mn3O4, Fe3O4, Co3O4, NiO, or CuO, but is not necessarily limited thereto.

[0048] According to one embodiment of the present invention, the substrate may be monocrystalline, polycrystalline or amorphous, and the material or crystal structure of the substrate may be used without any particular limitation.

[0049] According to one embodiment of the present invention, the raw material thin film may include a material to be formed as the crystalline thin film or may include a reactant material of the crystalline thin film.

[0050] For example, when forming a crystalline thin film containing a transition metal, the raw material thin film may contain the transition metal, and when forming a crystalline thin film containing a transition metal chalcogenide, the raw material thin film may contain a transition metal that is a reactant of the transition metal chalcogenide.

[0051] According to one embodiment of the present invention, the step of forming the raw material thin film may be performed by physical vapor deposition (PVD), thermal vapor deposition, electron beam vacuum deposition, sputtering, chemical vapor deposition (CVD), or atomic layer deposition (ALD), but is not necessarily limited thereto.

[0052] The thickness of the formed raw material thin film can be adjusted according to the desired thickness of the crystalline thin film to be formed.

[0053] According to one embodiment of the present invention, the crystalline two-dimensional material may include graphene, hexagonal boron nitride (hBN), a transition metal chalcogenide, graphene oxide, a two-dimensional oxide, black phosphorus, phosphorene, or a combination thereof.

[0054] According to one embodiment of the present invention, the template may be grown directly on the raw material thin film or may be transferred onto the raw material thin film.

[0055] According to one embodiment of the present invention, the template may be grown directly on the raw material thin film by physical vapor deposition (PVD), thermal vapor deposition, electron beam vacuum deposition, sputtering, chemical vapor deposition (CVD), atomic layer deposition (ALD), or the like, or may be grown on another substrate and then transferred to the raw material thin film.

[0056] According to one embodiment of the present invention, the crystalline two-dimensional material may be a polycrystalline or single crystal.

[0057] Specifically, when the template includes a single-crystal two-dimensional material, the formed crystalline thin film may be a single-crystal thin film aligned along the crystal direction of the single-crystal two-dimensional material. Alternatively, when the template includes a polycrystalline two-dimensional material, the formed crystalline thin film may be a polycrystalline thin film having the same microstructure along the microstructure of the polycrystalline two-dimensional material.

[0058] A method for forming a crystalline thin film according to one embodiment of the present invention can form a polycrystalline thin film having the same microstructure along the microstructure of a two-dimensional template, thereby enabling precise control of the crystal direction and microstructure of the thin film to be formed.

[0059] Hereinafter, the step of crystallizing the raw material thin film on which the template is formed by heating the raw material thin film under an inert gas atmosphere to form a crystalline thin film will be described in more detail.

[0060] According to one embodiment of the present invention, the raw material thin film can be converted into a crystalline thin film by hypotaxis growth in the step of forming the crystalline thin film.

[0061] In the step of crystallizing the above raw material thin film to form a crystalline thin film, the raw material thin film may be converted into a crystalline thin film by being heated under an inert gas atmosphere and recrystallized along the crystal structure under the template without a chemical reaction, or may be converted into a crystalline thin film having the same crystal structure as the crystal structure under the template by being heated while a reaction gas is supplied under an inert gas atmosphere and a chemical reaction between the raw material thin film and the reaction gas occurs.

[0062] According to one embodiment of the present invention, when forming a crystalline thin film including a transition metal, the raw material thin film may include the transition metal, and by heating the raw material thin film on which the template is formed under an inert gas atmosphere, the raw material thin film can be converted into a crystalline thin film having the same crystal structure as the crystal structure of the template without undergoing a chemical reaction.

[0063] According to one embodiment of the present invention, the step of forming the crystalline thin film can be performed while supplying a reaction gas.

[0064] According to one embodiment of the present invention, when forming a crystalline thin film including a transition metal chalcogen compound, the raw material thin film may include a transition metal, and the reaction gas may be a gas including a chalcogen element.

[0065] According to one embodiment of the present invention, when forming a crystalline thin film including a transition metal oxide, the raw material thin film may include a transition metal, and the reaction gas may be a gas including an oxygen element.

[0066] According to one embodiment of the present invention, the template may have a defect formed therein. The defect may be a hole or a nanohole, and preferably has a size of 10 nm or less.

[0067] According to one embodiment of the present invention, the defective portion may be formed during or before the step of forming the crystalline thin film.

[0068] According to one embodiment of the present invention, by heating the raw material thin film on which the template is formed at a high temperature under an inert gas atmosphere, a defect may be formed in the template during the step of forming the crystalline thin film. The heating temperature for forming the defect may vary depending on the type of two-dimensional material included in the template, and for example, when the template includes graphene, a temperature of 800°C or higher may be preferable.

[0069] According to one embodiment of the present invention, a method of forming a defective portion prior to the step of forming the crystalline thin film may be by plasma treatment or high-temperature gas supply, but is not necessarily limited thereto.

[0070] FIG. 2 is a drawing sequentially showing each step of a method for forming a crystalline thin film according to an embodiment of the present invention, which is performed while supplying a reaction gas.

[0071] Referring to FIG. 2, the mechanism of a method for forming a crystalline thin film according to an embodiment of the present invention performed while supplying a reaction gas is described in detail.

[0072] When a raw material thin film having a template including a defective portion is heated under an inert gas atmosphere while supplying a reaction gas, the reaction gas can pass through the defective portion and react with the raw material thin film to form nuclei of several nanometers in size. Fig. 3 is a diagram schematically showing nuclei formed in the defective portion of the template. The nuclei are first formed in the overlapped area under the template at the edge of the defective portion and can be aligned in the same direction as the crystal direction of the template. As the reaction gas continues to be supplied, the nuclei can grow while maintaining the crystal structure in the horizontal direction to the center of the defective portion (the basal plane). As the reaction gas continues to be supplied, the defective portion expands, and the nuclei formation and growth process can occur at a new edge. At this time, each of the nuclei formed in the multiple defective portions can all be aligned in the same crystal direction as the template, and thus the obtained crystalline layer can be aligned in the same crystal direction as the template. In addition, as the reaction gas is continuously supplied, the crystalline layer in contact with the lower part of the template is formed as described above, and growth of the formed crystalline layer in the downward direction also occurs, and ultimately, a multilayer crystalline thin film aligned in the same crystal direction as the template can be formed.

[0073] According to one embodiment of the present invention, when the template is a single-crystal two-dimensional material, a single-crystal thin film without grain boundaries can be formed, and when the template is a polycrystalline two-dimensional material, a polycrystalline thin film having the same microstructure as the microstructure of the polycrystalline two-dimensional material can be formed.

[0074] According to one embodiment of the present invention, the template can be naturally removed by a step of crystallizing the raw material thin film on which the template is formed by heating the raw material thin film under an inert gas atmosphere to form a crystalline thin film.

[0075] A method for forming a crystalline thin film according to one embodiment of the present invention can enable precise control of the number of layers of a single crystal thin film to be formed.

[0076] More specifically, precise control of the number of layers of the single crystal thin film formed can be achieved by adjusting the thickness of the raw material thin film in consideration of the interlayer distance and number of layers of the single crystal material to be formed.

[0077] According to one embodiment of the present invention, the step of forming the crystalline thin film can be performed at a temperature of 150°C to 1,000°C. For example, the step of forming the crystalline thin film can be performed at a temperature of 150°C to 1,000°C, 300°C to 1,000°C, 500°C to 1,000°C, 700°C to 1,000°C, 800°C to 1,000°C, 900°C to 1,000°C, 150°C to 800°C, 300°C to 800°C, 500°C to 800°C, 150°C to 500°C, or 300°C to 500°C. The temperature of the step of forming the above crystalline thin film can be appropriately controlled depending on the type of the reaction gas and whether or not the defective portion is formed preemptively.

[0078] Since the step of forming the crystalline thin film is performed at a temperature of 800°C to 1,000°C or 900°C to 1,000°C, a defect may be formed during the step of forming the crystalline thin film.

[0079] If a defective portion is preemptively formed prior to the step of forming the crystalline thin film, the step of forming the crystalline thin film may be performed at a temperature of 150°C to 800°C, 300°C to 800°C, 500°C to 800°C, 150°C to 500°C, or 300°C to 500°C.

[0080] Hereinafter, the present invention will be described in detail using examples. However, the examples according to the present invention may be modified in various ways, and the scope of the present invention is not limited to the examples described below. The examples in this specification are provided to more fully explain the present invention to those of ordinary skill in the art.

[0081] Manufacturing Example 1. Synthesis of single-crystal graphene template

[0082] Single-crystal graphene was synthesized using chemical vapor deposition (CVD). Specifically, single-crystal graphene was synthesized by supplying methane (CH4) and hydrogen (H2) gases onto a single-crystal copper foil, heating, and reacting for approximately 30 minutes.

[0083] Manufacturing Example 2. Synthesis of polycrystalline graphene templates

[0084] Single-crystal graphene was synthesized using chemical vapor deposition (CVD). Specifically, methane (CH4) and hydrogen (H2) gases were supplied onto polycrystalline copper foil, heated, and reacted for approximately 30 minutes to synthesize polycrystalline single-crystal graphene.

[0085] <Experimental Example 1. Confirmation of Defect Formation in Single-Crystal Graphene Template>

[0086] After the single crystal graphene synthesized in Manufacturing Example 1 was positioned on a substrate using a wet transfer method or a dry transfer method, hydrogen sulfide (H2S) gas was supplied onto the single crystal graphene at a temperature of 1,000°C at a flow rate of 20 sccm for 30 minutes. Thereafter, a TEM image was obtained for the single crystal graphene treated with the hydrogen sulfide gas using a transmission electron microscope.

[0087] For the single crystal graphene synthesized in Manufacturing Example 1, O2 plasma treatment was performed at a power of 60 W in an O220 sccm atmosphere using an O2 plasma treatment device (Femto CUTE), and a TEM image was obtained for the single crystal graphene of Manufacturing Example 1 treated with oxygen plasma.

[0088] Figure 4 is a TEM image of single crystal graphene synthesized in Manufacturing Example 1 (a), single crystal graphene of Manufacturing Example 1 supplied with hydrogen sulfide for 30 minutes (b), and single crystal graphene of Manufacturing Example 1 treated with O2 plasma (c).

[0089] Referring to FIG. 4, it can be confirmed that the single crystal graphene synthesized in Manufacturing Example 1 does not contain a defect, but the single crystal graphene supplied with hydrogen sulfide at about 1,000°C for 30 minutes and the single crystal graphene treated with O2 plasma contain a vacancy defect.

[0090] Example 1. Formation of molybdenum disulfide (MoS2) single crystal thin film

[0091] As a substrate, a silicon substrate having an oxide film (thickness: 285 nm) formed thereon was used. As a template containing a crystalline two-dimensional material, single-crystal graphene synthesized in Manufacturing Example 1 was prepared. Hydrogen sulfide (H2S) gas was used as a reaction gas for supplying sulfur.

[0092] First, a molybdenum (Mo) metal thin film was deposited as a raw material thin film on the substrate using electron beam vacuum deposition. At this time, the thickness of the deposited molybdenum metal thin film was controlled from 0.3 nm to 40 nm depending on the desired thickness of the MoS2 thin film.

[0093] Then, the single crystal graphene was transferred onto the molybdenum metal thin film using a dry transfer method.

[0094] After the substrate on which the template and raw material thin film are formed is placed in the reaction chamber, the pressure of the reaction chamber is 10 -3The pressure was adjusted to 760 Torr (atmospheric pressure). In order to form a thin film, the reaction chamber temperature was increased to 1,000°C at a rate of 15°C / min, and then argon (Ar) gas and hydrogen sulfide (H2S) gas were supplied at flow rates of 130 and 20 sccm, respectively, to proceed with the reaction.

[0095] After the reaction was completed after about 120 minutes, a MoS2 single crystal thin film formed on the substrate was obtained.

[0096] <Experimental Example 2. Observation of MoS2 growth time and confirmation of single crystallinity of the thin film>

[0097] In order to observe the MoS2 formation process of Example 1 according to the growth time and to confirm whether the formed thin film has single crystallinity, SEM images, TEM images, and diffraction patterns were taken for each MoS2 formed when the reaction was conducted for 30 minutes, 60 minutes, 90 minutes, and 120 minutes while supplying the reaction gas using a scanning electron microscope and a transmission electron microscope.

[0098] Figure 5 is a drawing showing the SEM image (a), TEM image (b), diffraction pattern (c), and side TEM image (d) of the surface of the MoS2 thin film obtained in Experimental Example 1.

[0099] Referring to Fig. 5, since the graphene template was not completely removed during the intermediate process of MoS2 formation, a portion of the graphene template could be observed on the sample surface, and it was confirmed that all formed MoS2 nuclei had a crystal direction that matched that of the graphene template and had a defect-free single crystal structure. In addition, the side-view TEM image confirmed that the formed MoS2 thin film had an intact layered structure and that the growth of the MoS2 layer occurred horizontally from the formed nuclei.

[0100] Furthermore, referring to Fig. 5, a TEM image of the side of the sample during the intermediate stage of MoS2 formation confirmed that a portion of the molybdenum metal thin film was converted into a MoS2 single crystal layer, and that an unconverted molybdenum metal layer existed beneath the formed MoS2 single crystal layer. This suggests that the method for forming a single crystal thin film according to the present invention can be applied regardless of the substrate, since hypotaxis growth begins from the bottom of the template, and a single crystal layer is sequentially formed in the direction of the substrate by the hypotaxis growth.

[0101] In addition, referring to Fig. 5, it was confirmed that the template was naturally removed during the reaction process, as no graphene template was present on the MoS2 thin film obtained by proceeding the reaction for 120 minutes even though there was no additional process for removing the graphene template in Example 1.

[0102] <Experimental Example 3. Confirmation of single crystal layer growth according to raw material thin film thickness>

[0103] In Example 1, the thickness of the molybdenum metal thin film deposited as a raw material thin film was controlled to 0.3 nm to 40 nm, and the number of MoS2 single crystal layers in the obtained thin film was investigated.

[0104] Specifically, TEM images were taken using a transmission electron microscope for each MoS2 single crystal thin film formed by controlling the thickness of the molybdenum metal thin film to 0.3 nm, 0.5 nm, 0.8 nm, 1.2 nm, 1.5 nm, 2 nm, 2.5 nm, 3 nm, 4.5 nm, 6 nm, 7.5 nm, 15 nm, 25 nm, and 40 nm, and the number of layers was calculated, and Raman spectrum analysis was performed.

[0105] The number of layers of each MoS2 single crystal thin film formed by controlling the thickness of the molybdenum metal thin film to 0.3 nm, 0.5 nm, 0.8 nm, 1.2 nm, 1.5 nm, 2 nm, 2.5 nm, 3 nm, 4.5 nm, 6 nm, 7.5 nm, 15 nm, 25 nm and 40 nm was 1, 2, 3, 4, 5, 6, 8, 10, 12, 14, 19, 23, 69, 80 and 99, respectively.

[0106] Figure 6 is a drawing showing optical microscope images of the number of MoS2 single crystal layers in the obtained thin film depending on the thickness of the deposited molybdenum metal thin film.

[0107] Referring to Fig. 6, it was confirmed that the formed MoS2 single crystal thin film had a very uniform thin film surface regardless of the number of layers.

[0108] Figure 7a is a graph showing the relationship between the thickness of a deposited molybdenum metal thin film and the number of MoS2 single crystal layers in the obtained thin film. Figure 7b is a Raman spectrum for MoS2 single crystal thin films having 1 to 4 layers. Figure 7c is a side TEM image showing the appearance of MoS2 single crystal thin films having 1 to 4, 6, 8, 14, and 99 layers.

[0109] Referring to Figures 7a to 7c, it was confirmed that the number of layers of the crystalline thin film manufactured can be precisely controlled by adjusting the thickness of the raw thin film, and when the number of layers increases from 1 to 4, two peaks (E) appear in the Raman spectrum of the manufactured MoS2 single crystal thin film. 1 2g , A 1g ) was confirmed to increase the distance between them.

[0110] Raman spectrum analysis results confirmed that the peak position no longer changes when the number of layers is 5 or more.

[0111] Example 2. Formation of a tungsten disulfide (WS2) single crystal thin film

[0112] A tungsten disulfide single crystal thin film was formed in the same manner as Example 1, except that a tungsten (W) metal thin film was deposited with a thickness of 40 nm as a raw material thin film.

[0113] Example 3. Formation of molybdenum diselenide (MoSe2) single crystal thin film

[0114] A molybdenum (Mo) metal thin film was deposited as a raw material thin film to a thickness of 10 nm, and a molybdenum diselenide single crystal thin film was formed in the same manner as in Example 1, except that instead of supplying hydrogen sulfide (H2S) gas, selenium gas and hydrogen (H2) gas obtained by vaporizing selenium (Se) powder (purchased from Alfa Aesar, 100 mg) were supplied at a flow rate of 5 sccm for 6 hours.

[0115] Example 4. Formation of a tungsten diselenide (WSe2) single crystal thin film

[0116] A tungsten (W) metal thin film was deposited as a raw material thin film to a thickness of 30 nm, and a tungsten diselenide single crystal thin film was formed in the same manner as in Example 1, except that instead of supplying hydrogen sulfide (H2S) gas, selenium gas and hydrogen (H2) gas obtained by vaporizing selenium (Se) powder (purchased from Alfa Aesar, 100 mg) were supplied at a flow rate of 5 sccm for 9 hours.

[0117] Example 5. Formation of a molybdenum (Mo) single crystal thin film

[0118] A molybdenum (Mo) metal thin film was deposited as a raw material thin film with a thickness of 5 nm, and a molybdenum single crystal thin film was formed in the same manner as in Example 1, except that hydrogen sulfide (H2S) gas was not supplied.

[0119] Example 6. Formation of a tungsten (W) single crystal thin film

[0120] A tungsten (W) metal thin film was deposited as a raw material thin film with a thickness of 10 nm, and a tungsten single crystal thin film was formed in the same manner as in Example 1, except that hydrogen sulfide (H2S) gas was not supplied.

[0121] Example 7. Formation of a molybdenum dioxide (MoO2) single crystal thin film

[0122] A molybdenum (Mo) thin film was deposited as a raw material thin film with a thickness of 10 nm, and a molybdenum dioxide single crystal thin film was formed in the same manner as in Example 1, except that instead of supplying hydrogen sulfide (H2S) gas, oxygen (O2) gas was supplied at a flow rate of 10 sccm for 4 hours.

[0123] <Experimental Example 4. Confirmation of single crystallinity of WS2, MoSe2, WSe2, Mo, W, MoO2 thin films>

[0124] To confirm the single crystallinity of the WS2, MoSe2, and WSe2 thin films obtained in Examples 2 to 4, respectively, Raman spectrum analysis, energy dispersive spectroscopy (EDS), and TEM image analysis were performed on the obtained thin films.

[0125] Figure 8 is a diagram showing Raman spectra for WS2, MoSe2, and WSe2 thin films obtained in Examples 2 to 4.

[0126] Figure 9 shows TEM images and EDS analysis images of the surfaces of WS2, MoSe2, and WSe2 thin films obtained in Examples 2 to 4.

[0127] Referring to FIGS. 8 and 9, it was confirmed that the crystals of WS2, MoSe2, and WSe2 formed through the method according to the present invention have high crystallinity, and that each component element is uniformly distributed.

[0128] Figure 10 is a drawing showing TEM images and diffraction patterns of the side surfaces of Mo, W, and MoO2 thin films obtained in Examples 5 to 7.

[0129] Referring to FIG. 10, it was confirmed that the Mo, W, and MoO2 thin films formed through the method according to the present invention were well formed as single crystals, and it was confirmed that the method for forming a single crystal thin film according to the present invention can be universally applied to form a single crystal thin film not only with a transition metal chalcogenide compound but also with various other materials.

[0130] Example 8. Formation of MoS2 single crystal thin film using hexagonal boron nitride

[0131] A MoS2 single crystal thin film was formed in the same manner as in Example 1, except that a single layer of hexagonal boron nitride (1L-hBN) was used as a template. The single layer of hexagonal boron nitride was obtained by exfoliation from a boron nitride crystal (Kenji Watanabe Co., Ltd., Takashi Taniguchi).

[0132] Example 9. Formation of WS2 single crystal thin film using single crystal tungsten disulfide

[0133] A two-layer single-crystal tungsten disulfide (2L-WS2) was used as a template, and a WS2 single-crystal thin film was formed in the same manner as in Example 1, except that a 40 nm thick tungsten (W) metal thin film was deposited. The two-layer single-crystal tungsten disulfide (2L-WS2) used as a template was grown as a single crystal on a silicon substrate on which the oxide film (thickness: 285 nm) was formed by physical vapor deposition (PVD) using WS2 powder (Alfa Aesar, LOT: M11F022) in an argon gas (300 sccm) atmosphere at about 1000°C for 1 hour.

[0134] Example 10. Formation of MoS2 polycrystalline thin films using polycrystalline graphene.

[0135] A MoS2 single crystal thin film was formed in the same manner as in Example 1, except that the polycrystalline graphene synthesized in Manufacturing Example 2 was used as a template.

[0136] Example 11. Formation of MoS2 polycrystalline thin films using polycrystalline graphene grown directly on a substrate.

[0137] A MoS2 polycrystalline thin film was formed using the same method as Example 1, except that methane (CH4) and hydrogen (H2) gases were supplied onto the deposited molybdenum raw material thin film using chemical vapor deposition, heated, and reacted for about 30 minutes to directly grow polycrystalline graphene as a template.

[0138] Example 12. Formation of WSe2 polycrystalline thin films using polycrystalline graphene grown directly on a substrate.

[0139] A WSe2 polycrystalline thin film was formed using the same method as Example 4, except that methane (CH4) and hydrogen (H2) gases were supplied onto the deposited tungsten raw material thin film using chemical vapor deposition, heated, and reacted for about 30 minutes to directly grow polycrystalline graphene as a template.

[0140] <Experimental Example 7. Observation by Type of 2D Material Template>

[0141] Raman spectra, TEM images, and diffraction pattern analyses were performed on the thin films obtained in Examples 8 to 12.

[0142] In addition, in order to confirm whether the polycrystalline microstructure is identically implemented in the thin film formed when a polycrystalline two-dimensional material is used as a template, DF-TEM (Dark-field TEM) images were taken of the MoS2 polycrystalline thin film obtained in Example 10 and the polycrystalline graphene template used.

[0143] Figure 11 is a diagram showing the Raman spectrum results (a), side TEM image (b), and diffraction pattern (c) for the MoS2 thin film obtained in Example 8.

[0144] Figure 12 is a diagram showing the Raman spectrum results, side TEM image, top TEM image, and diffraction pattern for the WS2 thin film obtained in Example 9.

[0145] Referring to FIGS. 11 and 12, it was confirmed that the MoS2 thin film and the WS2 thin film obtained using a single layer of hexagonal boron nitride (1L-hBN) or a two-layer single crystal tungsten disulfide (2L-WS2) as a template had a defect-free single crystal structure and formed a complete layered structure without vertical growth.

[0146] Figure 13 is a schematic diagram showing an intermediate process of forming a thin film in Example 10 using polycrystalline graphene as a template (a), a TEM image and diffraction pattern of the obtained MoS2 thin film (b), a DF-TEM image of the obtained MoS2 thin film (d), and a DF-TEM image of the polycrystalline graphene template (c).

[0147] Referring to Fig. 13, it was confirmed through the diffraction pattern that the M1 and M2 patterns of MoS2 were aligned with the G1 and G2 patterns of graphene, and by comparing the DF-TEM image of polycrystalline graphene (Poly-Gr) and the obtained DF-TEM image of MoS2, it was confirmed that the crystal grains corresponding to the G1 spot and the G2 spot in the DF-TEM image of polycrystalline graphene matched the structure of the grains distinguished for the M1 and M2 spots in the DF-TEM image of MoS2. In other words, the results clearly confirmed that the lower thin film could be grown by following the microstructure of the upper two-dimensional template as it is.

[0148] FIG. 14 is a diagram showing an optical microscope image (a) of a WSe2 thin film obtained in Example 12 and polycrystalline graphene grown directly on a tungsten substrate, and a Raman spectrum (b) of MoS2 and WSe2 thin films obtained in Examples 11 and 12.

[0149] Referring to Figure 14, it was confirmed that a thin film matching the microstructure of the template was well formed even when a template grown directly on the substrate was used.

[0150] As a result of the above experimental example 7, it was confirmed that the single crystal formation method according to the present invention can be applied universally regardless of the type of single crystal or polycrystalline two-dimensional material used as a template.

[0151] Example 13. Formation of MoS2 single crystal thin film under low temperature conditions using a template with pre-formed defects.

[0152] Before transferring the single crystal graphene template obtained in the above Manufacturing Example 1 onto the raw material thin film, a defect was formed in advance by supplying hydrogen sulfide (H2S) gas at a temperature of 1,000°C and a flow rate of 20 sccm for 90 minutes, and a MoS2 single crystal thin film was formed in the same manner as in Example 1, except that the reaction chamber temperature was increased to 300°C at a rate of 15°C / min.

[0153] <Experimental Example 8. Synthesis Verification Using a Template Including Preformed Defects>

[0154] To confirm that formation of a crystalline thin film is possible even at low temperatures when a template in which a defect is preemptively formed is used, TEM images and diffraction pattern analyses were performed on the MoS2 thin film obtained in Example 13.

[0155] Figure 15 is a drawing showing a TEM image (a) of a template in which a defective portion was formed in advance in Example 13, a TEM image (b) of the obtained MoS2 single crystal thin film, a diffraction pattern (c), and a Raman spectrum (d).

[0156] Referring to Figure 15, it was confirmed that a single crystal thin film was well formed even at a reaction temperature of 300°C when a template in which a defective portion was preemptively formed was used.

[0157] Example 14. Formation of a MoS2 single crystal thin film on a single crystal graphene substrate.

[0158] Instead of a silicon substrate on which an oxide film (thickness: 285 nm) was formed, single-crystal graphene was used as a substrate, and before transferring the single-crystal graphene template obtained in Manufacturing Example 1 onto a raw material thin film, a defect portion was formed in advance by performing O2 plasma treatment at a power of 60 W in an O220 sccm atmosphere using an O2 plasma treatment device (Femto CUTE), and a MoS2 single-crystal thin film was formed in the same manner as in Example 1, except that the reaction chamber temperature was increased to 400°C at a rate of 15°C / min.

[0159] Example 15. Formation of a MoS2 single crystal thin film on a hafnium oxide (HfO2) substrate.

[0160] Instead of a silicon substrate on which an oxide film (thickness: 285 nm) was formed, hafnium oxide (HfO2), which is an insulating material and has a mixed amorphous and polycrystalline phase, was used as a substrate, and before transferring the single-crystal graphene template onto the raw material thin film, an O2 plasma treatment device (Femto CUTE) was used to perform an O2 plasma treatment at a power of 60 W in an O220 sccm atmosphere to form a defect in advance, and a MoS2 single-crystal thin film was formed in the same manner as in Example 1, except that the reaction chamber temperature was increased to 400°C at a rate of 15°C / min.

[0161] Example 16. Formation of a MoS2 single crystal thin film on a gold (Au) substrate

[0162] Instead of a silicon substrate on which an oxide film (thickness: 285 nm) was formed, polycrystalline metal gold (Au) was used as a substrate, and before transferring the single-crystal graphene template onto the raw material thin film, an O2 plasma treatment device (Femto CUTE) was used to perform O2 plasma treatment at a power of 60 W in an O220 sccm atmosphere to form a defect in advance, and a MoS2 single-crystal thin film was formed in the same manner as in Example 1, except that the reaction chamber temperature was increased to 400°C at a rate of 15°C / min.

[0163] <Experimental Example 9. Confirmation of thin films according to the type of lower substrate>

[0164] In order to confirm that formation of the desired crystalline thin film is possible regardless of the type and crystal structure of the lower substrate material, TEM images and diffraction pattern analyses were performed on each of the MoS2 thin films obtained in Examples 14 to 16.

[0165] Figure 16 is a drawing showing a TEM image and a diffraction pattern for each of the MoS2 thin films obtained in Examples 14 to 16.

[0166] Referring to Fig. 16, the MoS2 thin film obtained in Example 14 has a single crystallinity that does not match the crystal direction of the substrate graphene, suggesting that the crystal structure of the formed thin film follows the template. In addition, it was confirmed that the MoS2 thin films obtained in Examples 15 and 16, which used hafnium oxide (HfO2), which is an insulating material and has a mixture of amorphous and polycrystalline phases, as a substrate or polycrystalline metal gold (Au), as a substrate, also had a single crystal structure derived from the single crystal graphene template, regardless of the substrate.

[0167] <Experimental Example 10. Analysis of Thermal Properties of Thin Films>

[0168] To analyze the thermal properties of the single-crystal MoS2 layer obtained in Example 1, the vertical / horizontal thermal conductivity was measured using time-domain thermoreflectance (TDTR).

[0169] Specifically, an aluminum (Al) thin film, which acts as a thermometer, was deposited on the material to be measured, and the reflectivity change was measured. Then, the surface temperature could be observed in the time domain using the linear relationship between the temperature change and the aluminum reflectivity. Therefore, for this measurement, a DC sputter was used to deposit aluminum with a thickness of approximately 80 nm on a single layer of single-crystal MoS2 obtained in Example 1.

[0170] Figure 17 is a diagram showing the horizontal and vertical thermal characteristics of the MoS2 thin film obtained in Example 1.

[0171] In the case of vertical thermal conductivity, the change in thermal reflectance (ΔR(t) = Ratio) according to the difference in the arrival times of the two beams at the specimen was measured on a time scale of ~4 ns under the condition that the pump and probe were completely overlapped, and the vertical thermal conductivity was derived by comparing it with the change in thermal reflectance calculated through heat transfer modeling based on the measurement conditions and the properties of the materials constituting the specimen structure. The modulation frequency (f) of the pump was measured at two conditions of 10.9 MHz and 1.8 MHz, and the heat penetration depth (dp = √(Λ / πCf), Λ: vertical thermal conductivity, C: volumetric heat capacity, f: modulation frequency) was adjusted to independently separate and derive the vertical thermal conductivity.

[0172] For the horizontal thermal conductivity, the pump and probe were spatially separated while scanning, and the TDTR signal with a Gaussian distribution shape was measured according to the distance between the two beams. The full width at half maximum (FWHM) of the measured Gaussian distribution was derived and compared with the FWHM calculated through heat transfer modeling to derive the horizontal thermal conductivity. The spot size was measured in advance using the in-phase signal under the absolutely dominant conditions of f = 10.9 MHz, t = +100 ps for the spot size (w0) of the 1 / e2 radius used in the measurement (solid line in the graph in (a) of Fig. 17), and the FWHM for the out-of-phase signal was derived under the dominant conditions of f = 1.8 MHz, t = -100 ps for the measurement sensitivity to the horizontal radius.

[0173] As a result of the measurement, the vertical and horizontal thermal conductivities of the single-crystal MoS2 thin film obtained in Example 1 were each (1.8±0.2) Wm -1 K -1 , (130±30) Wm -1 K -1 was measured as

[0174] In the case of vertical thermal conductivity, it is consistent with the research results of MoS2 flakes exfoliated by considering the thickness dependence of MoS2 thin films (Fig. 17(d)), and in the case of horizontal thermal conductivity, the thermal conductivity range derived by error propagation according to measurement and specimen conditions is sufficiently consistent with the results of previous studies (Fig. 17(c)). Based on the thermal conductivity derived using TDTR, it was confirmed that the MoS2 thin film grown by the hypotaxis method according to the present invention in Example 1 exhibited excellent thermal properties equivalent to those of a single crystal.

[0175] Experimental Example 11. Electrical Performance Analysis of Thin Films

[0176] In order to analyze the electrical performance of the single-crystal MoS2 thin film obtained in Example 1, the thin film was used as a channel of a field effect transistor (FET) array to test the electrical performance.

[0177] Specifically, a single-crystal MoS2 thin film obtained in Example 1 was patterned through electron-beam lithography, and then a MoS2 channel region was formed through reactive ion etching (RIE). This was patterned again through electron-beam lithography, and then aluminum (Al) / chromium (Cr) / gold (Au) were deposited as source and drain electrodes, respectively, using an e-beam evaporator, to fabricate a total of 77 devices. A back-gate FET device was implemented by using the lower silicon as a gate and a silicon oxide layer as an insulating layer.

[0178] Figure 18 is a diagram showing an optical microscope and SEM image (a), a characteristic curve (transfer curve, output curve) (b), and a characteristic curve according to drain voltage (c) of a field effect transistor (FET) device array manufactured using the MoS2 thin film obtained in Example 1 as a channel.

[0179] Referring to Fig. 18, 77 out of 77 fabricated devices were operational, showing high yields, and exhibited similar performance, demonstrating uniform performance. In addition, compared to existing exfoliated MoS2 single crystal flakes or synthesized MoS2, the current on / off ratio was much better, specifically, 10 9 It showed an ideal current flickering ratio and the charge mobility was about 35-40 cm 2 / Vs and up to 79 cm 2 / Vs value was shown. Through this, it was confirmed that the quality of the MoS2 thin film manufactured by the method according to the present invention actually showed excellent electrical performance.

[0180] Although the present invention has been described above through limited embodiments, the present invention is not limited thereto, and it is obvious that various modifications and variations are possible within the scope of the technical idea of ​​the present invention and the equivalent scope of the patent claims to be described below by a person having ordinary skill in the art to which the present invention pertains.

Claims

1. A step of forming a raw material thin film on a substrate; A step of forming a template including a crystalline two-dimensional material on top of the raw material thin film; and It comprises a step of crystallizing the raw material thin film by heating the raw material thin film on which the template is formed under an inert gas atmosphere to form a crystalline thin film. A method for forming a crystalline thin film, wherein the crystalline thin film is hypotaxially grown from below the template.

2. In claim 1, A method for forming a crystalline thin film, wherein the crystalline two-dimensional material comprises graphene, hexagonal boron nitride (hBN), a transition metal chalcogenide, graphene oxide, a two-dimensional oxide, black phosphorus, phosphorene, or a combination thereof.

3. In claim 1, A method for forming a crystalline thin film, wherein the template comprises a single-crystal two-dimensional material, and the crystalline thin film is a single-crystal thin film aligned along the crystal direction of the single-crystal two-dimensional material.

4. In claim 1, A method for forming a crystalline thin film, wherein the template comprises a polycrystalline two-dimensional material, and the crystalline thin film is a polycrystalline thin film having the same microstructure along the microstructure of the polycrystalline two-dimensional material.

5. In claim 1, A method for forming a crystalline thin film, wherein the template is grown directly on the raw material thin film or transferred onto the raw material thin film.

6. In claim 1, A method for forming a crystalline thin film, wherein the step of forming the above crystalline thin film is performed at a temperature of 300° C. to 1,000° C.

7. In claim 1, A method for forming a crystalline thin film, wherein the step of forming the above crystalline thin film is performed while supplying a reaction gas.

8. In claim 7, The above template is a method for forming a crystalline thin film in which a defective portion is formed.

9. In claim 8, A method for forming a crystalline thin film, wherein the above-mentioned defective portion is formed during or before the step of forming the crystalline thin film.

10. In claim 7, The above raw material thin film contains a transition metal, The above reaction gas is a gas containing a chalcogen element, A method for forming a crystalline thin film, wherein the crystalline thin film comprises a transition metal chalcogenide compound.

11. In claim 7, The above raw material thin film contains a transition metal, The above reaction gas is a gas containing oxygen element, A method for forming a crystalline thin film, wherein the crystalline thin film comprises a transition metal oxide.

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