Method and apparatus for forming transition metal chalcogenide layered films

Abstract

To provide a method for forming a transition metal chalcogenide layered film high in the controllability and stability of film deposition, capable of increasing an area and low in cost.SOLUTION: A method for forming a film comprises: oxidizing a transition metal block 32 to form a transition metal oxide layer on the surface; sublimating an oxide from the oxide layer to supply oxide gas and first inactive carrier gas to a substrate 38 through an exclusive pipe line 23; supplying chalcogen atom containing reactive gas and second inactive carrier gas to the substrate 38; heating the substrate 38 when supplying the oxide gas and the reactive gas to the substrate 38; and exhausting the oxide gas, the reactive gas, the first inactive carrier gas and the second inactive carrier gas.SELECTED DRAWING: Figure 2

Description

[Technical field]

[0001] The present invention relates to a method for forming a layered film of a transition metal chalcogenide and an apparatus therefor. [Background technology]

[0002] In recent years, attention has been focused on semiconductor materials with molecular layer-level thicknesses called transition metal dichalcogenide layered films (hereinafter, also referred to as TMDCs), such as MoS2 and WSe2.

[0003] This material is a two-dimensional layered semiconductor with a finite band gap. TMDCs are crystals with a unit cell thickness of just three atomic layers, which makes them inherently extremely thin and flat. In addition, because it has a unique crystal structure that has no unsaturated bonds (dangling bonds) in the direction perpendicular to the plane of the two-dimensional crystal (c-axis), it is expected that the problems associated with conventional semiconductor materials, such as lattice mismatch and surface recombination, will be significantly alleviated. In addition to the formation of monolayer films, heterostructures between TMDCs mediated by van der Waals (vdW) forces are also of interest. Applications of these materials to electronic devices that are lightweight, consume very little power, and have excellent mechanical flexibility, including MOSFET channels and tunnel transistors, are also being considered. Furthermore, it has been shown that monolayer TMDCs have a direct transition band structure and exhibit unique physical properties, such as extremely large exciton effects, making them highly promising materials for use in ultrathin and flexible light-emitting and light-receiving elements, as well as optical functional device materials.

[0004] As described above, TMDCs have many characteristics and possibilities not found in conventional semiconductors; however, there are many issues to be resolved in their film formation technology, and there are problems in that no formation method has been established that is excellent in terms of controllability, stability, large area, and mass productivity.

[0005] Research into the properties and device applications of TMDCs has become more active since around 2010, but in the early days, many studies used MoS2, which is a natural mineral, after peeling off the crystal surface with Scotch tape. In 2012, as disclosed in Non-Patent Document 1, a method was reported for the first time to synthesize a single layer of MoS2 using gas components sublimated from powders of molybdenum trioxide (MoO3) and sulfur (S). This method is also known as the powder sublimation method, and even now, many reports on the formation of MoS2 films use the same method or an improved version of it.

[0006] For example, in the technology disclosed in Non-Patent Document 2, powdered MoO3 and S are used as the Mo and S raw materials, and each is placed in the optimal temperature range inside a hot-wall type quartz tube, where the volatile gas components are sublimated and transported, causing a reaction on the substrate. This method has problems such as the initiation and termination of sublimation, as well as the difficulty of controlling the amount of raw material transport. In addition, there are also issues such as a decrease in the amount of sublimation due to a decrease or depletion of the powder raw material, and the MoO3 powder reacting with S in the boat and changing, which prevents sublimation. For this reason, it is necessary to replace the MoO3 powder every time during the film formation process, but even with this, it is difficult to obtain reproducibility. In addition, the geometric arrangement relationship between the MoO3 powder and the substrate placed in the small boat is also called the point-to-face supply method, but this method has problems such as the difficulty of achieving uniform spatial concentration of gas components in the film formation area, and in principle, it is not easy to achieve uniform film formation or large area formation.

[0007] Non-Patent Document 3 discloses a Mo foil method (Mo foil method), which is a type of face-to-face technique in which a Mo metal foil is placed over the substrate area for film formation as a cover, and Mo oxide is sublimated from the surface of the Mo foil and supplied onto the substrate. This method is reported to have the advantage of being easier to achieve uniform deposition of films compared to methods using MoO3 powder, because the Mo raw material is uniformly supplied onto the substrate placed in the space below the Mo foil. However, this method supplies elemental sulfur (S) not only onto the substrate but also onto the Mo foil surface, which can lead to various problems, such as the unintended formation of MoS2 on the Mo foil surface, or the conversion of highly volatile components such as MoO3 into substances with low oxidation numbers such as less volatile MoO2, reducing the efficiency of Mo oxide gas generation and making its generation unstable.

[0008] As mentioned above, it is difficult to stably supply the source gas and therefore to form a uniform MoS2 film when using the powdered MoO3 source material. One of the reasons for this is the non-uniformity of the particle size distribution of the powdered source material, and Non-Patent Document 4 discloses a method in which a small amount of MoO3 is deposited on a substrate in advance to homogenize the particle size, and this is then placed opposite the substrate to be used as the Mo source material. Furthermore, in order to increase the single crystal domain size of single-layer MoS2, it is considered extremely important to significantly reduce the degree of supersaturation of MoO3 in the gas phase by using a very small volume of MoO3. Based on this idea, Non-Patent Document 5 discloses a method in which a solution of MoO3 is dispersed and dried in advance on a substrate by a spin coating method, and this is used as a sublimation source of MoO3. The methods disclosed in Non-Patent Documents 4 and 5 are techniques positioned as a composite method intermediate between the powder method and the Mo foil method described above.

[0009] However, even with these composite methods, it has not been possible to form a completely coated continuous MoS2 film on the substrate. This is thought to be because the amount of MoO3 previously deposited on the substrate is so small that it all sublimes within the film formation time, resulting in a complete depletion of the raw material. In addition, the method of Non-Patent Document 4 involves a direct reaction between MoO3 for sublimation and the raw material S, and it has been pointed out that there is a problem with the stable supply of the raw material gas. Patent documents relating to the TMDC film formation method include Patent Documents 1 and 2. As described above, conventional methods have had quality and practical problems, such as film formation stability, controllability, large film formation area, and cost. Note that, although the conventional technology for MoS2 films has been mainly described here, the above problems are not limited to MoS2 films, but are thought to be similar for MoSe2, WS2, and WSe2 films, and are common to all TMDCs. [Prior art documents] [Patent documents]

[0010] [Patent Document 1] Japanese Patent Application Publication No. 7-069782 [Patent Document 2] Special Publication No. 2019-522106 [Non-patent literature]

[0011] [Non-Patent Document 1] YHLee et al.,Adv.Mater.,24,2320(2012) [Non-Patent Document 2] H.Nguyen et al.,Mater.Lett.,168,1(2016) [Non-Patent Document 3] J. Zheng et al.,Adv. Mater.,29,1604540(2017) [Non-Patent Document 4] SSWithanage.,ACS Omega,3,18943(2018) [Non-Patent Document 5] J.Lee et al.,Adv.Mater.,29,1702206(2017) Summary of the Invention [Problem to be solved by the invention]

[0012] The present invention aims to provide a film formation method and a manufacturing apparatus therefor that solve the problems of the prior art described in the Background Art section. That is, the present invention aims to provide a film formation method and a manufacturing apparatus therefor that have high stability and controllability in the formation of a layered film of a transition metal dichalcogenide such as MoS2, can increase the area of ​​the film formation, and are also excellent in terms of cost. [Means for solving the problem]

[0013] The configuration of the present invention for solving the problems is shown below. (Configuration 1) oxidizing a transition metal block to form an oxide layer of the transition metal on a surface of the transition metal; sublimating the oxide from the oxide layer and supplying the oxide gas together with a first inert carrier gas to a substrate via a dedicated pipe; supplying a reactive gas containing chalcogen atoms to the substrate together with a second inert carrier gas; heating the substrate while delivering the oxidizing gas and the reactive gas to the substrate; evacuating the oxide gas, the reactive gas, the first inert carrier gas, and the second inert carrier gas. (Configuration 2) 2. The method for forming a transition metal chalcogenide layered film according to claim 1, wherein the transition metal is selected from the group consisting of titanium (Ti), zirconium (Zr), hafnium (Hf), vanadium (V), niobium (Nb), tantalum (Ta), molybdenum (Mo), chromium (Cr), tungsten (W) and rhenium (Re). (Configuration 3) 3. The method for forming a transition metal chalcogenide layered film according to claim 1, further comprising converting the oxide layer into a hydrogenated oxide layer. (Configuration 4) 4. The method for forming a transition metal chalcogenide layered film according to claim 3, wherein the hydrogenation is performed by adding hydrogen gas when the oxidation is performed. (Configuration 5) heating a block made of molybdenum at a first temperature T1 while supplying a gas containing oxygen to form a molybdenum oxide layer on a surface of the block; sublimating molybdenum trioxide (MoO3) from the molybdenum oxide layer and supplying the MoO3 gas together with a first inert carrier gas to a substrate via a dedicated pipe; supplying a reactive gas containing chalcogen atoms to the substrate together with a second inert carrier gas; heating the substrate at a second temperature T2 while supplying the MoO3 gas and the reactive gas to the substrate; evacuating the MoO3 gas, the reactive gas, the first inert carrier gas, and the second inert carrier gas. (Configuration 6) 6. The method for forming a chalcogenide layered film according to claim 5, wherein the first temperature T1 is 500° C. or more and 1200° C. or less. (Configuration 7) 7. The method for forming a transition metal chalcogenide layered film according to aspect 5 or 6, wherein the second temperature T2 is 300° C. or higher and 1200° C. or lower. (Configuration 8) A method for forming a transition metal chalcogenide layered film according to any one of configurations 5 to 7, wherein the dedicated pipe is heated at a temperature that prevents the generated MoO3 raw material gas components from being redeposited midway through the pipe, at least from the location where the block is located to the region immediately in front of the substrate. (Configuration 9) 9. The method for forming a transition metal chalcogenide layered film according to any one of claims 1 to 8, wherein the chalcogen atom is one selected from the group consisting of sulfur (S), selenium (Se) and tellurium (Te). (Configuration 10) 10. The method for forming a transition metal chalcogenide layered film according to any one of claims 1 to 9, wherein the first inert gas and the second inert gas are one or more selected from the group consisting of nitrogen gas, argon gas, krypton gas, neon gas, helium gas, and xenon gas. (Configuration 11) 10. The method for forming a transition metal chalcogenide layered film according to any one of claims 1 to 9, wherein the first inert gas and the second inert gas are nitrogen gas. (Configuration 12) 12. The method for forming a transition metal chalcogenide layered film according to any one of claims 1 to 11, wherein the substrate contains an alkali metal element as a composition. (Configuration 13) 13. The method for forming a transition metal chalcogenide layered film according to claim 12, wherein the alkali metal element is at least one selected from the group consisting of sodium (Na), lithium (Li) and potassium (K). (Configuration 14) 13. The method for forming a transition metal chalcogenide layered film according to any one of claims 1 to 12, wherein the substrate is an alkali aluminosilicate glass. (Configuration 15) The method includes: an oxide gas supplying means for supplying an oxide gas to a substrate; a reactive gas supplying means for supplying a reactive gas to the substrate; a reaction chamber for forming a transition metal chalcogenide as a layered film on the substrate; and an exhausting means; the oxide gas supplying means comprises: a means for supplying an oxygen-containing gas at a controlled flow rate; a means for supplying a first inert gas at a controlled flow rate; a block-shaped transition metal; a first heating means for heating the transition metal; and a dedicated pipe for supplying an oxide gas generated by sublimation from the transition metal onto the substrate; the reactive gas supply means includes a means for supplying a reactive gas containing chalcogen atoms while controlling a flow rate thereof, and a means for supplying a second inert gas while controlling a flow rate thereof; the reaction chamber includes a sample stage and a second heating means for heating the substrate placed on the sample stage, and is a separate chamber from a location where the transition metal is placed; The apparatus for forming a transition metal chalcogenide layered film, wherein a heat treatment means is provided on a wall of the dedicated piping for maintaining a temperature at or above the sublimation temperature of the transition metal oxide. (Configuration 16) 16. The apparatus for forming a transition metal chalcogenide layered film according to claim 15, wherein the oxide gas supplying means further comprises a means for supplying a gas containing hydrogen at a controlled flow rate. (Configuration 17) The apparatus includes: an MoO3 gas supply means for supplying MoO3 gas to a substrate; a reactive gas supply means for supplying a sulfur-containing reactive gas to the substrate; a reaction chamber for forming MoS2 as a layered film on the substrate; and an exhaust means; The MoO3 gas supply means includes a means for supplying a gas containing oxygen at a controlled flow rate, a means for supplying a first inert gas at a controlled flow rate, a block made of molybdenum, a first heating means for heating the block, and a dedicated pipe for supplying the MoO3 gas generated by sublimation from the block onto the substrate; The reactive gas supply means includes a means for supplying the reactive gas at a controlled flow rate, and a means for supplying a second inert gas at a controlled flow rate; the reaction chamber includes a sample stage and a second heating means for heating the substrate placed on the sample stage, and is a separate chamber from a place where the block is placed; An apparatus for forming a MoS2 layered film, wherein the wall of the dedicated piping is provided with a heat treatment means for maintaining a temperature equal to or higher than the sublimation temperature of MoO3. (Configuration 18) 18. The apparatus of claim 17, wherein the reactive gas is one or more selected from the group consisting of sulfur (S), hydrogen sulfide (HS), dimethyl sulfur ((CH)S), diethyl sulfur ((CH)S), ditertiary butyl sulfur ([(CH)C]S), and diisopropyl sulfur ((i-CH)S). (Configuration 19) 19. The apparatus according to any one of claims 15 to 18, wherein the first heating means and the second heating means are heated by one or more methods selected from the group consisting of resistance heating, induction heating, and lamp heating. (Configuration 20) 20. The apparatus of any one of configurations 15 to 19, wherein the first inert gas and the second inert gas are one or more selected from the group consisting of nitrogen gas, argon gas, krypton gas, neon gas, helium gas, and xenon gas. (Configuration 21) 20. The apparatus of any one of aspects 15 to 19, wherein the first inert gas and the second inert gas are nitrogen gas. (Configuration 22) 22. The apparatus according to any one of claims 15 to 21, wherein the dedicated piping is made of one selected from the group consisting of quartz glass, glass, stainless steel, and ceramics. (Configuration 23) 23. The apparatus of claim 22, wherein the ceramic is selected from the group consisting of alumina and SiC. (Configuration 24) 24. The apparatus of any one of configurations 15 to 23, wherein the dedicated piping is provided with a shower head in a portion adjacent to the substrate. (Configuration 25) 25. The apparatus of any one of configurations 15 to 24, wherein the sample stage is equipped with a rotation mechanism.

[0014] According to the present invention, there is provided a film formation method and a manufacturing apparatus therefor that have high stability and controllability in film formation of transition metal dichalcogenides, particularly MoS2, enable a large film formation area, and are also excellent in terms of cost. [Brief description of the drawings]

[0015] [Figure 1] FIG. 2 is an explanatory diagram showing a schematic configuration of the device. [Diagram 2] FIG. 2 is an explanatory diagram showing a schematic configuration of the device. [Diagram 3] FIG. 2 is an explanatory diagram showing a schematic configuration of the device. [Figure 4] FIG. 2 is an explanatory diagram showing a configuration of a gas supply system. [Diagram 5] FIG. 2 is a flow chart showing a film forming method of the present invention. [Figure 6] FIG. 2 is a flow chart showing a film forming method of the present invention. [Figure 7] FIG. 2 is an explanatory diagram showing the mechanism of MoO3 gas generation. [Figure 8] FIG. 2 is a cross-sectional view of a prototype device. [Figure 9]FIG. 1 is a configuration diagram focusing on the gas piping system of a prototype device. [Figure 10] 1 is an optical microscope photograph of the MoS2 film prepared. [Figure 11] 1 is an optical microscope photograph of the MoS2 film prepared. [Figure 12] 1 is an optical microscope photograph of the MoS2 film prepared. [Figure 13] 1 is an optical microscope photograph of the MoS2 film prepared. [Figure 14] 1 is an optical microscope photograph of the MoS2 film prepared. [Figure 15] 1 is an optical microscope photograph of the MoS2 film prepared. [Figure 16] The results of film evaluation of the fabricated MoS2 film are shown in Fig. 1(a) by Raman spectroscopy and in Fig. 1(b) by emission spectroscopy. [Figure 17] 1 is an optical microscope photograph of the MoS2 film prepared. [Figure 18] The results of film evaluation of the fabricated MoS2 film are shown in Fig. 1(a) by Raman spectroscopy and in Fig. 1(b) by emission spectroscopy. [Figure 19] 1 is a SEM photograph of the MoS2 film that was prepared. [Figure 20] 1 shows an SEM photograph of the prepared WS2 film and the film properties evaluated by Raman and PL spectroscopy. [Figure 21] 1 is a SEM photograph of the MoS2 film that was prepared. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0016] Hereinafter, an embodiment of the present invention will be described with reference to the drawings.

[0017] (First embodiment) In the first embodiment, a film forming apparatus for a transition metal chalcogenide layered film and a film forming method using the apparatus will be described, taking MoS2 as an example.

[0018] <Device> As shown in FIG. 1, the transition metal chalcogenide layered film forming apparatus of the present invention comprises an oxide gas supply means 6 for supplying an oxide gas onto a substrate, a reactive gas supply means 7 for supplying a reactive gas onto the substrate, a reaction chamber 8 for forming a transition metal chalcogenide as a layered film on the substrate (sample), and an exhaust means 9.

[0019] The oxide gas supplying means 6 includes a means for supplying an oxygen-containing gas at a controlled flow rate, a means for supplying a first inert gas at a controlled flow rate, a block-shaped transition metal, a first heating means for heating the transition metal, and a dedicated pipe for supplying the oxide gas generated by sublimation from the transition metal onto the substrate. Specifically, the oxide gas supply means of the transition metal chalcogenide layered film forming apparatus 10 of the present invention includes an opening / closing flow rate control device 33 as a means for controlling the flow rate of an oxygen-containing gas and supplying it, an opening / closing flow rate control device 34 as a means for controlling the flow rate of a first inert gas, an oxide gas generation chamber 21 including a block-shaped transition metal 32 and a stage 31 for placing it thereon, and a dedicated pipe 23 for supplying the oxide gas generated by sublimation from the transition metal onto the substrate, as shown in FIG. 2. Note that the opening / closing flow rate control device 33 and the opening / closing flow rate control device 34 can be integrated into a single opening / closing flow rate control device, as shown in an opening / closing flow rate control device 40 described below.

[0020] Here, the transition metal may be one selected from the group consisting of titanium (Ti), zirconium (Zr), hafnium (Hf), vanadium (V), niobium (Nb), tantalum (Ta), molybdenum (Mo), chromium (Cr), tungsten (W) and rhenium (Re). The use of Mo makes it possible to form a MoS2 layered film, which is particularly expected to be useful in applications. In addition, Mo metal has the advantage that high-purity polycrystalline Mo metal is easily available and is low cost.

[0021] The transition metal to be used is preferably in the form of a single crystal. In polycrystals, many grain boundaries exist, and in this state, the generation, accumulation, and sublimation of oxides proceed differently between the single crystal portion and the grain boundary portion, and the reproducibility and stability of the generation and sublimation of oxides tend to decrease. For example, polycrystalline Mo has high density grain boundaries, and the generation, accumulation, and sublimation of Mo oxides proceed differently between the single crystal portion and the grain boundary portion. Here, generally, the generation, accumulation, and sublimation of Mo oxides tend to proceed more predominantly in the grain boundary portion. Therefore, from the viewpoint of improving the reproducibility and stability of the generation and sublimation of MoO3 and controlling it more strictly, it is preferable to use single crystal Mo produced by, for example, an electron beam melting method.

[0022] Examples of the first heating means for heating the transition metal include resistance heating, induction heating, and lamp heating, and for example, the stage 31 may be equipped with a heater. Note that resistance heating is characterized by low cost and ease of handling, while lamp heating and induction heating are characterized by excellent responsiveness. The temperature T1 set by the first heating means is preferably in the range of 500° C. to 1200° C. This temperature range allows the transition metal oxide gas to be generated efficiently and with high stability, and as a result, it becomes possible to stably form a uniform transition metal chalcogenide layered film with few defects.

[0023] The first inert gas may be one or more selected from the group consisting of nitrogen gas, argon gas, krypton gas, neon gas, helium gas, and xenon gas. Nitrogen gas functions as a sufficient inert gas in terms of the temperature when a layer of transition metal oxide is formed on the block-shaped transition metal 32 and the transition metal oxide gas is sublimated from the layer. Nitrogen gas is particularly suitable as the first inert gas because it is easily available and has a low cost.

[0024] The dedicated pipe 23 must be constructed so that its tube wall can be kept at or above the sublimation temperature of the oxide of the transition metal used, and for example, a heater 25 is provided on the tube wall or in its vicinity, as shown in Fig. 3. The heater 25 may be a resistance heater, an induction heater, or a lamp heater. Also, as described in the examples, the dedicated pipe 23 may not be provided with a dedicated heater for the dedicated pipe 23, but may be installed in a furnace that is part of the heat treatment of the sample 38 and kept at or above the sublimation temperature of the oxide of the transition metal. If transition metal oxide adheres to the wall of the dedicated piping, it reduces the controllability and stability of the supply of the transition metal oxide gas to the sample 38. By using the above configuration, this problem can be solved.

[0025] The material of the pipe wall of the dedicated pipe 23 may be one selected from the group consisting of quartz glass, glass, stainless steel, and ceramics. The ceramic may be, for example, one selected from the group consisting of alumina and SiC. It is preferable that a shower head 36 be provided at the tip of the dedicated pipe 23 or near the location where the sample 38 is placed so that the transition metal oxide gas is supplied uniformly over the surface of the sample 38.

[0026] The reactive gas supplying means includes a means for supplying a reactive gas containing chalcogen atoms at a controlled flow rate, and a means for supplying a second inert gas at a controlled flow rate, and a means for supplying the reactive gas onto the substrate. Specifically, the reactive gas supply means of the transition metal chalcogenide layered film forming apparatus 10 of the present invention includes, as shown in Fig. 2, a switching / flow rate control device 40 as a means for controlling the flow rate of a reactive gas containing chalcogen atoms and a means for controlling the flow rate of a second inert gas, and a pipe 43 for supplying the reactive gas from the switching / flow rate control device 40 to the vicinity of the sample 38. Here, the switching / flow rate control device 40 is provided with a port (piping) 41 for supplying a reactive gas and a port (piping) 42 for supplying a second inert gas. Although the switching / flow rate control device 40 is shown as one device in Fig. 2, it may be two switching / flow rate control devices, one for supplying a reactive gas and one for supplying a second inert gas.

[0027] The chalcogen atom may be one selected from the group consisting of sulfur (S), selenium (Se) and tellurium (Te). In addition, examples of reactive gases containing chalcogen atoms include one or more selected from the group consisting of sulfur (S), hydrogen sulfide (H2S), dimethyl sulfur ((CH3)2S), diethyl sulfur ((C2H5)2S), ditertiary butyl sulfur ([(CH3)3C]2S), and diisopropyl sulfur ((i-C3H7)2S). Among these, S and H2S are preferably used because they are easily available and low cost.

[0028] The second inert gas may be one or more selected from the group consisting of nitrogen gas, argon gas, krypton gas, neon gas, helium gas, and xenon gas. Nitrogen gas is particularly suitable as the second inert gas because it is easily available and has a low cost.

[0029] The reaction chamber (reaction chamber section) 22 is a room equipped with a sample 38 and a sample stage 37 on which the sample 38 is placed, and is a separate room isolated from the oxide gas generation chamber 21 on which the transition metal is placed and the dedicated piping 23 in terms of gas flow. The reaction chamber (reaction chamber section) 22 is equipped with a second heating means for heating the sample 38. The second heating means may be resistance heating, induction heating, or lamp heating, and may be a single or combination of these. The sample stage 37 equipped with a heater may be used as the second heating means. The temperature T2 set by the second heating means is preferably in the range of 300°C or more and 1200°C or less. This temperature range makes it possible to efficiently and stably form a uniform transition metal chalcogenide layered film with few defects. It is preferable that the sample stage 37 is provided with a rotation mechanism. In this way, when the transition metal chalcogenide layered film is formed on the sample 38, the sample 38 is rotated while the film is formed, so that the in-plane uniformity of the film formation can be improved.

[0030] The temperature control of the first heating means and the second heating means may be separate, or may be integrated into one to simplify the device. That is, two or more zones may be used, or one zone may be used. In the case of multi-zone control, for example, the temperature of the sample 32 and the temperature in the oxide gas generation chamber 21 can be controlled independently, and interference between the parameters of each can be suppressed, improving controllability.

[0031] In addition, in the first embodiment, the apparatus of the present invention has been described by taking as an example an apparatus classified into a shape called a horizontal reactor. However, this is not essential, and the apparatus may be a vertical reactor in which the gas flows vertically.

[0032] 4 shows an example of a gas supply system 12 in which the opening / closing and flow rate are controlled, which includes a first gas system consisting of a pipe 51, a manual valve 52, a mass flow controller 53, and air valves 54 and 56, and a second gas system consisting of a pipe 61, a manual valve 62, a mass flow controller 63, and air valves 64 and 66. The gas from the first gas system and the gas from the second gas system are mixed, turned on / off, and flow rate controlled, and supplied through a pipe 55. Also, an exhaust pipe 57 is provided to ensure sufficient gas purity in the pipe, and the inside of the pipe can be exhausted by opening and closing the air valves 56 and 66. The gas supply system 12 shown here can be applied to the opening / closing and flow rate control devices 33, 34, 40, and 44.

[0033] In the gas supply system 12, the gas flow rate on the supply side is controlled by mass flow controllers 53 and 63. One of the features of the present invention is that, as shown in Fig. 2, the flow rates of the O2-containing gas and the first inert gas supplied to the oxide gas generation chamber 21 and the heat treatment temperature (T1) for the transition metal block 32 are controlled to thereby control the flow rate of the oxide gas supplied to the sample 38. If one attempts to control the flow rate and On / Off of the oxide gas generated in the oxide gas generation chamber 21 downstream of the oxide gas generation chamber 21, it becomes necessary to control the On / Off and flow rate at high temperatures, which leads to problems such as increased equipment costs, reduced control accuracy and instability, frequent breakdowns, and difficult maintenance. The configuration of the present invention makes it possible to avoid such problems. 3 shows an example in which two opening / closing and flow rate control devices 40, 44 are connected to the reaction chamber 22. When multiple opening / closing and flow rate control devices are connected to the reaction chamber 22 in this way, not only can the reactive gas and the second inert gas be introduced, but also O2 gas mixed with an inert carrier gas can be supplied as environmental control, making it possible to achieve more advanced control. Pipes 45, 46, and 47 are connected to the opening / closing and flow rate control device 44.

[0034] In the above, the case where the source of the oxide gas is a block-shaped transition metal has been shown, but if the transition metal block 32 is a block-shaped metallic molybdenum (Mo), the oxide gas generated by sublimation will be MoO3. This gas is introduced into the reaction chamber 22 via a dedicated pipe 23, and a reactive gas containing sulfur is also introduced into the reaction chamber 22 with flow rate control from a separate system, and a MoS2 layered film can be formed on the sample 38 by subjecting the sample 38 to a heat treatment.

[0035] The features of the device of the present invention are as follows. These features make it possible to provide a manufacturing device that has high stability and controllability in forming layered films of transition metal dichalcogenides such as MoS2, can increase the film forming area, and is also cost-effective.

[0036] (1) The oxide gas generation chamber 21 in which the transition metal block 32 such as Mo is placed is separated from other reactive gases such as S raw material gas so that they do not unintentionally enter and react with each other. (2) The oxide gas generation chamber 21 in which the transition metal block is placed is configured to be capable of supplying both an inert gas such as N2 and reactive O2, and the gas that comes into contact with the transition metal block 32 can be switched by operating the valve. (3) In the configuration of (2) above, flow control devices such as mass flow controllers are installed on each gas line, which allows control of the flow rate and concentration of N2 and O2 gases. Moreover, this flow control can be performed at room temperature, so it is highly stable, controllable, and easy to maintain, and costs are kept low and the frequency of breakdowns is low. (4) The oxide gas generation chamber 21 in which the transition metal block is placed is independent of the area in which the sample 38 is placed, and is configured so that the generated oxide gas can be guided to the area in which the sample 38 is placed. (5) The oxide gas introduced into the area where the sample 38 is placed is structured so that the gas concentration at the location where the sample 38 is placed can be made uniform by processing the shape of the gas outlet, such as a shower head system. (6) A reactive gas such as a S raw material is mixed with the oxide gas introduced to the location where the sample 38 is placed as in (5) near the sample 38 and reacts with it.

[0037] <Method> The method of the present invention will now be described with reference to flow chart diagrams FIGS. In the method of the present invention, the following steps are performed: oxidizing a transition metal block to form an oxide layer of the transition metal on the surface of the transition metal (FIG. 5, step S1); sublimating the oxide from the oxide layer, and supplying the oxide gas together with a first inert carrier gas to a substrate (sample) through a dedicated pipe (step S2); supplying a reactive gas containing chalcogen atoms together with a second inert carrier gas to the substrate (step S3); heating the substrate while supplying the oxide gas and the reactive gas to the substrate to form a transition metal chalcogen layered film on the substrate (step S4); and exhausting the oxide gas, reactive gas, first inert carrier gas, and second inert carrier gas (step S5) including during step S4. Here, steps S2 and S3 may be performed simultaneously, or step S3 may be performed prior to step S2.

[0038] Here, the transition metal is selected from the group consisting of titanium (Ti), zirconium (Zr), hafnium (Hf), vanadium (V), niobium (Nb), tantalum (Ta), molybdenum (Mo), chromium (Cr), tungsten (W) and rhenium (Re).

[0039] In the case of forming a MoS2 layered film, which is highly desired as a transition metal chalcogenide layered film, a block made of molybdenum is heated at a first temperature T1 while supplying a gas containing oxygen to form a molybdenum oxide layer on the surface of the block (FIG. 6, step S11), molybdenum trioxide (MoO3) is sublimated from the molybdenum oxide layer, and the MoO3 gas is supplied to a substrate together with a first inert carrier gas via a dedicated pipe (step S12), a reactive gas containing chalcogen atoms is supplied to the substrate together with a second inert carrier gas (step S13), the substrate is heated at a second temperature T2 while the MoO3 gas and the reactive gas are supplied to the substrate (step S14), and the MoO3 gas, the reactive gas, the first inert carrier gas, and the second inert carrier gas are exhausted (step S15), including during step S14, to form a MoS2 layered film. Here, steps S12 and S13 may be performed simultaneously, or step S13 may be performed prior to step S12.

[0040] Here, the first temperature T1 is preferably not less than 500° C. and not more than 1200° C. This temperature range allows the transition metal oxide gas to be generated efficiently and with high stability, and as a result, it becomes possible to stably form a uniform transition metal chalcogenide layered film with few defects. Moreover, the second temperature T2 is preferably not less than 300° C. and not more than 1200° C. This temperature range makes it possible to efficiently and stably form a uniform transition metal chalcogenide layered film with few defects.

[0041] As described in the apparatus section, it is preferable that the dedicated piping is heated at least from where the metal block is located to the region immediately in front of the substrate in order to prevent the generated source gas components such as MoO3 from being redeposited midway through the piping.

[0042] The chalcogen atom may be one selected from the group consisting of sulfur (S), selenium (Se) and tellurium (Te).

[0043] The first inert gas and the second inert gas may be one or more selected from the group consisting of nitrogen gas, argon gas, krypton gas, neon gas, helium gas, and xenon gas. Among these, nitrogen gas is particularly preferred because of its low cost and easy availability.

[0044] The oxygen content of the oxygen-containing gas is preferably 0.01% by volume or more and 100% by volume or less. sccm flow rate of second inert gas S 02 The ratio of the sccm flow rate S2 of H2S to the sccm flow rate S2 / S 02 is preferably 0.01% by volume or more and 100% by volume or less. Under the above conditions, a transition metal chalcogenide layered film can be stably formed.

[0045] The substrate (sample substrate) on which the transition metal chalcogenide layered film is formed preferably contains an alkali metal element as a composition. Here, the alkali metal element can be one or more selected from the group consisting of sodium (Na), lithium (Li) and potassium (K). When CVD of TMDC such as MoS2 is performed on a substrate containing an alkali metal, the deposition rate increases due to the catalytic effect of the alkali metal, improving the production efficiency of the film formation, and the size of the single crystal domain also increases, contributing to improving the quality of the film formation. A specific example of this substrate is alkali aluminosilicate glass, a material developed to promote ion exchange reactions on the surface for use in reinforced cover glass for smartphones and other devices, and which contains SiO2, Al2O3, and about 20% Na2O by weight.

[0046] Next, the mechanism of TMDC formation will be explained using MoS2 as an example of TMDC. The important point of the present invention is to place metallic molybdenum (Mo) in an independently provided oxide gas generation chamber 21 and supply a gas containing oxygen (O2) thereto, thereby generating molybdenum oxide (mainly molybdenum trioxide (MoO3)) which serves as a source gas for Mo, and guiding this Mo source gas to a film formation region where a sample (substrate) 38 is placed for utilization. Generally, Mo, which is a transition metal element, is classified as a high melting point metal, and its melting point is extremely high at about 2600 °C or higher. An extremely high temperature is required to evaporate the metal raw material itself. On the other hand, MoO3, a hexavalent oxide obtained by oxidizing Mo, has a relatively high vapor pressure and rapidly sublimes at 500 °C or higher. In the present invention, the formation reaction and sublimation of MoO3 that occur simultaneously when a dilute O2 gas is supplied to the surface of metallic Mo are actively utilized.

[0047] Next, the formation of an oxide film (also called an oxide scale) and its sublimation reaction that occur when O2 gas is supplied to the surface of Mo metal in the present invention will be described. Fig. 7 shows an image of oxide scale formation and sublimation that may occur when O2 gas is supplied to Mo metal 1 in a heated environment. The supplied O2 (4) adsorbs on the Mo surface and then reacts with Mo to form an oxide scale (2 or 3). After a finite thickness of the oxide scale is formed, O2 diffuses to the interface between the Mo metal and the oxide scale, and a new oxide scale is formed there. Then, MoO3 sublimes as a gas. Here, Fig. 7(a) shows the case where a dilute O2 gas is supplied, and Fig. 7(b) shows the case where a sufficient amount of O2 gas is supplied, as will be described later. Regarding the chemical composition of the formed oxide scale, if under a sufficient O2 partial pressure, most of the surface layer is MoO3 (3) with a high vapor pressure (sublimability), but MoO2 with a low sublimability and a very thin thickness exists near the interface with the Mo metal. Also, in the transition region from MoO3 to MoO2, suboxides such as MoO x (2 < x < 3) also exist. In Fig. 7, MoO2 and the suboxide are shown as 2.

[0048] On the other hand, the time evolution of the oxide scale thickness is as follows: in the early stage of oxidation, the thickness increases linearly with time (t), and then gradually decreases with time (t 1 / 2 It has been reported that the change follows a parabolic law, but it also depends on temperature and O2 partial pressure. Thus, the formation process and structure of Mo oxide scale are complex.

[0049] What is particularly important in the present invention is the competitive relationship between the rate of oxide scale formation and the rate of sublimation. The net growth rate or thickness of oxide scale is determined by the rate of oxide scale (2, 3) formation and the rate of sublimation. This competitive relationship is influenced by temperature and the amount of O2 supplied (partial pressure).

[0050] Figure 7 shows two possible extremes of the competition between oxide scale formation and sublimation. Figure 7(a) shows the case where the sublimation rate is overwhelmingly greater than the oxide scale formation rate, i.e., "oxide scale formation rate << sublimation rate." This situation occurs when the O2 supply is low or the temperature is high and sublimation occurs extremely actively. Under ideal extreme conditions, the MoO3 component of the formed oxide scale immediately sublimes to MoO3(5), does not remain on the surface, and steadily remains as the low-volatility MoO x The image is that a thin film of MoO2 is exposed. In this case, the amount of MoO3 sublimated per unit time, which is important for the CVD of MoS2, is considered to be rate-limited by the O2 supply flow rate. Therefore, if the O2 supply rate is kept constant, the MoS2 growth rate will be constant, and the amount of MoS2 deposition (integral amount within the growth time) will be proportional to the time.

[0051] On the other hand, Figure 7(b) shows a situation where the oxide scale formation exceeds the scale loss due to sublimation, resulting in an increase in the thickness of the MoO3 oxide scale. In other words, this is the case where the oxide scale formation rate is greater than the sublimation rate. This is achieved when the O2 supply is sufficient and the temperature is relatively low, suppressing the sublimation rate. In this situation, the surface of the Mo metal is always covered with MoO3(3), and the thickness (i.e., volume) of MoO3(3) increases with time. When CVD of MoS2 is performed under such conditions, even if the supply of O2 gas is constant, the amount of sublimation of MoO3 is not constant with time, but is thought to increase in proportion to the thickness of MoO3 with time. Therefore, it is expected that the growth rate of MoS2 in CVD also increases linearly with time, and the total deposition amount, which is the integral amount, increases quadratically with time. In addition, under such conditions, even if the O2 supply is stopped by operating the valve, generation will continue until the MoO3(3) accumulated on the Mo(1) surface sublimes and disappears, so the response will be poor when stopping the growth of MoS2. As described above, two states can occur in the CVD of MoS2 using the formation of an oxide scale on the surface of metal Mo and the sublimation of MoO3. Although MoS2 film formation can be achieved under either state, from the viewpoint of controllability and responsiveness, it is preferable to achieve the state shown in Figure 7(a). From the above, embodiment 1 makes it possible to provide a film formation method that has high stability and controllability in the formation of a layered film of a transition metal dichalcogenide such as MoS2, enables a large film formation area, and is also excellent in terms of cost.

[0052] The differences between the method of the present invention and the three methods mentioned in the background art, namely (i) a method using a powder raw material as a metal oxide such as MoO3 (powder method), (ii) a method using a metal foil such as Mo facing the sample (foil method), and (iii) a composite method combining the above two methods, are summarized below.

[0053] The difference from the powder method is that in the method of the present invention, metal oxides such as MoO3 are generated on the spot by supplying O2 gas to the surface of a block-shaped metal, so no powder raw material is required, and there is no direct reaction with chalcogen elements such as S in the metal oxide raw material, improving controllability. The differences with the foil method are that the metal raw material such as Mo does not need to be in the form of a metal foil but is in the form of a block, which gives the freedom to select the shape and size of the metal raw material, such as Mo, regardless of the size or number of samples; there is no need to face the metal foil to the substrate, so there is a high degree of freedom in directing the metal oxide gas generated in the oxide gas generation chamber to the reaction chamber in which the sample is placed via piping, nozzles, showerheads, etc., resulting in a structure that makes it easy to improve the uniformity of the film formation; and the metal used does not deteriorate and can be used repeatedly. The differences with the composite method are that metal oxides such as MoO3 are generated on the spot by the reaction of metals with O2, so depletion of metal oxides can be avoided, the amount of metal oxide sublimation (particularly to achieve a low degree of supersaturation) can be controlled over a wide range by the O2 flow rate and can be freely changed during film formation, and there is no direct reaction with chalcogen elements such as S in the metal oxide raw material, improving controllability.

[0054] (Second embodiment) In the second embodiment, a deposition apparatus for forming a layered film of a transition metal chalcogenide in which the deposition efficiency is improved by adding hydrogen gas and a deposition method using the apparatus will be described.

[0055] The apparatus basically conforms to the first embodiment, but differs from the first embodiment in that it further comprises a hydrogen gas (H2 gas) supply system capable of accurately controlling the flow rate to the oxide gas generation chamber. That is, in terms of Fig. 2 or Fig. 3, in addition to the opening / closing / flow rate control devices 33 and 34, it comprises equipment similar to the opening / closing / flow rate control devices 33 and 34 that supply hydrogen gas to the oxide gas generation chamber 21.

[0056] When a transition metal chalcogenide layered film is produced from a metal oxide having a high sublimation temperature, the temperature T1 of the first heat treatment for generating the oxide gas becomes high in the method of embodiment 1, and it is not easy to increase the efficiency of generating the oxide gas. For example, when a WS2 layered film is produced by oxidizing and sublimating a W metal block and introducing the WO3 gas to the reaction chamber 22, WO3 is much less likely to sublimate than MoO3, so a high-temperature treatment of 800°C or higher is required for the sublimation.

[0057] In the second embodiment, hydrogen gas is added to the metal oxide formed on the transition metal block or to the environment during its generation. In this way, water (H2O) is added to the metal oxide molecules. That is, a hydrogenated oxide layer is formed. In this way, the sublimation temperature is lowered, the equipment for applying the heat treatment temperature T1 can be simplified, and the equipment becomes easier to handle and control, which makes it easier to increase the efficiency of oxide gas generation. For example, oxygen gas and hydrogen gas are supplied to a W metal block to perform the first heat treatment, generating H2WO4 on the surface of the W metal block, and then the substance is sublimated. In this case, the sublimation temperature is lowered (the vapor pressure is relatively higher than that of WO3), making it possible to form a WS2 layered film at a temperature of 700°C. EXAMPLES

[0058] The present invention will be described in more detail below with reference to examples. However, these examples are provided merely to aid in the understanding of the present invention and are not intended to limit the present invention thereto.

[0059] Example 1 In Example 1, a film-forming apparatus for MoS2 was produced, and the apparatus was used to form MoS2 on a substrate, and the resulting film was evaluated.

[0060] <Device> The configuration of the main part of the device 13 prototyped in Example 1 is shown in Fig. 8. Here, Fig. 8(a) is an overall overview, and Fig. 8(b) shows the configuration of the main parts inside the quartz tube 71 of the quartz tube part 14 with the dimensions also shown. The apparatus 13 is configured such that a quartz tube 71 is placed on a base 72 serving as a foundation via a support 73, and further, an electric furnace 74 is placed so as to cover an area including a MoS2 layered film formation chamber (reaction chamber) 79 and a Mo reaction chamber (MoO3 gas generation chamber) 81 placed inside the quartz tube 71. Furthermore, piping tubes for A line 76 and B line 77 made of quartz are installed inside the quartz tube 71, and a tube for C line 78 is attached to the quartz tube 71, so that gas for the C line is supplied into the quartz tube 71.

[0061] Here, a susceptor 75 on which a sample on which a MoS2 layered film is to be formed is placed is disposed in the MoS2 layered film formation chamber 79, and MoO3 gas is supplied from the Mo reaction chamber 81 through an upper nozzle 82 having a shower head, and H2S reactive gas is supplied from a lower nozzle 83 connected to the B line 77. The atmospheric gas, gas flow, and exhaust promotion can be controlled by gas from the C line 78 connected to the quartz tube 71.

[0062] The Mo reaction chamber 81 has a tube wall made of quartz, and a metal molybdenum block is disposed inside the Mo reaction chamber 81. Oxygen gas (O2 gas) and nitrogen gas (N2 gas) as an inert carrier gas are supplied from the A line 76 connected to the upstream side, and MoO3 gas is supplied to the MoS2 layered film formation chamber 79 from the upper nozzle 82 connected to the downstream side. Here, the tube from the Mo reaction chamber 81 to the upper nozzle 82 is in a dedicated piping state, but the dedicated piping is disposed inside the electric furnace 74, and when the electric furnace 74 is turned on, the tube wall is heated, so that Mo and MoOx are unlikely to adhere to the tube wall. An exhaust system was connected to the end of the quartz tube 71, allowing exhaust 80. An air-cooled small dry pump was used as the exhaust system. A detoxification device for dry adsorption of H2S was installed downstream of the pump.

[0063] FIG. 9 shows a configuration diagram of the device 13, focusing on the gas supply system. In the device 13, the MoO3 gas can be generated or stopped in the Mo reaction chamber 81 connected to the A line 76 by opening and closing the manual valve 62a and the air valve 64a installed in the supply line (A-2 line) of the diluted O2 gas. In addition, the A-1 line dedicated to N2 and the diluted O2 line (A-2) are respectively equipped with mass flow controllers (MFCs) 53a and 63a, and the effective O2 concentration in the Mo reaction chamber can be precisely changed by the flow rate ratio of these two MFCs. In addition, the A-1 line and the A-2 line are respectively equipped with air valves 56a and 66a connected to the exhaust 57a, so that the cleanliness of the inside of the piping is sufficiently maintained by the exhaust operation. In addition, the A-1 line is connected to the N2 line gas, and the A-2 line is connected to a cylinder of O2 gas diluted to 1% with N2. In addition, the device 13 is equipped with a manual valve 85, and the exhaust 80 of the quartz tube 71 can be performed by opening the manual valve 85. The apparatus 13 is also provided with a pressure indicator 84 so that the pressure within the quartz tube 71 can be monitored.

[0064] The sulfur (S) raw material was H2S gas supplied from a separate gas line (B-1). The gas supply system of the B line was configured similarly to the gas supply system of the A line. In this system, reactive gas supplied from a cylinder of H2S gas diluted to 1% was supplied to the B-1 line via a manual valve 52b, MFC 53b, and air valve 54b, and N2 gas in the line was supplied to the B-2 line via a manual valve 62b, MFC 63b, and air valve 64b. In order to increase the gas purity in the piping, an air valve 56b was placed on the B-1 line side and an air valve 64b was placed on the B-2 line side, so that exhaust could be taken from the ends of both air valves.

[0065] Although powdered S can be used as the S raw material, this configuration allows for On / Off operation with a valve and more precise control of the supply amount using a mass flow controller (MFC). In order to avoid the problem of powdered S depletion, a configuration that allows for the supply of organometallic compounds such as H2S, (CH3)2S, and (C2H5)2S, which have a proven track record in the MOCVD method, as gas raw materials is preferable.

[0066] Regarding the C line, N2 gas is supplied to the C-1 line via a manual valve 62c, an MFC 63c, and an air valve 64c, and diluted O2 gas supplied from an O2 gas cylinder diluted to 1% with N2 gas is supplied to the C-2 line via a manual valve 52c, an MFC 53c, and an air valve 54c.

[0067] The apparatus 13 has a configuration that satisfies the following technical requirements for forming the transition metal chalcogenide layered film described in the first embodiment. (1) The reaction chamber in which the metallic Mo is placed is separated so that other reactive gases, such as the S source gas, do not inadvertently enter and react with the Mo. (2) The reaction chamber in which the metallic Mo is placed is configured to be capable of supplying both an inert gas such as N2 and reactive O2, and the gas that comes into contact with the Mo metal can be switched by operating a valve. (3) In the configuration described in (2) above, a flow control device such as a mass flow controller is installed on each gas line, which makes it possible to control the flow rate and concentration of N2 and O2 gas. (4) The reaction chamber in which the metallic Mo is placed is independent of the substrate region, and is configured so that the generated MoO3 gas can be guided to the substrate region. (5) The MoO3 gas introduced to the substrate area is structured in such a way that the gas concentration in the substrate area can be made uniform by processing the shape of the gas outlet, such as by using a shower head. (6) The raw material gas of the S raw material is mixed with MoO3 introduced to the substrate portion as in (5) and reacts with it in the substrate portion region.

[0068] <Process> A high-purity block of Mo (manufactured by Pansee) with a purity of 99.97% was prepared as metallic Mo to be placed in the oxide gas (MoO3 gas) generation chamber (Mo reaction chamber) 81, and cut into strips of 20 mm x 6 mm x 2 mm. After cleaning with an organic solvent and pure water, the strips were charged into the oxide gas generation chamber 81. Both O2 gas and H2S were prepared in cylinders diluted to 1% with high-purity N2. The typical film formation conditions are as follows. Quartz reaction chamber 71 internal pressure: 20 Torr Deposition temperature: 700℃ or 750℃ A-line flow rate: 100sccm (1%O2 / N220sccm+N280sccm, or N2100sccm) B line flow rate: 50sccm (1%H2S / N210sccm+N240sccm, or N250sccm) C line flow rate: 250sccm(N2) ·Film formation time: 3 minutes or more and 15 minutes or less Substrate: Alkaline alumino-silicate glass (20mm x 20mm x 0.55mm)

[0069] The substrate was ultrasonically cleaned with an organic solvent (acetone, IPS) and pure water, dried with N2 blow, and then placed on an alumina susceptor 75 and introduced into a predetermined position in an electric furnace 74. After that, the inside of the quartz tube was sufficiently evacuated to a vacuum degree of about 2 Pa, and then the exhaust needle valve was adjusted so that the pressure inside the reactor was 20 Torr while flowing only N2 gas at a specified flow rate into each line from A line 76 to C line 78. From this N2 flow state, the temperature was raised to a film formation temperature of 700°C at a heating rate of 25°C / min, and after reaching 700°C, it was stabilized for 5 minutes. Thereafter, the H2S mixed gas was flowed into line B 77 using the switching valve, and after waiting 30 seconds, the O2 mixed gas was flowed into line A 76 using the switching valve, thereby starting the generation and sublimation of molybdenum oxide scale in the oxide gas generation chamber. The time when O2 started to flow into the A line 76 was defined as the start time of film formation, and after a predetermined film formation time had elapsed, the generation of MoO3 was stopped by switching O2 to N2 using a switching valve, thereby terminating the film formation. Thereafter, the electric furnace 74 was naturally cooled while the H2S in the B line 77 was still flowing, and after the temperature reached near room temperature, the sample was removed.

[0070] <Materials evaluation> Figures 10 to 13 show optical microscope images of MoS2 films formed at 700°C and 20 Torr for deposition times of 3, 5, 10, and 15 minutes, where (a), (b), and (c) in each figure show the upstream, center, and downstream locations, respectively (the left, center, and right locations of the area indicated by 79 in Figure 8(b)). It can be seen that the method of the present invention enables the formation of triangular domains of MoS2 with a size that can be recognized by an optical microscope. This fact is a breakthrough in this field, and results in TMDCs of higher quality than those produced by conventional methods. In addition, as the deposition time increased, the size of the triangular domains increased from several μm (deposition time 3 min) to several tens of μm (deposition time 10 min, 15 min), and finally they merged to form a continuous film. As an example of a continuous film, an optical microscope photograph of a film formed at 700°C, 20 Torr, with a deposition time of 15 min, taken further downstream than (c) in the above figure, is shown in Figure 14. Furthermore, it has been confirmed that this can be achieved with good reproducibility without replacing the Mo metal raw material.

[0071] Although we showed the time dependency here, we confirmed that it can also be controlled by the O2 flow rate. When prioritizing the linearity (proportionality) and response speed of the time response of the film formation process to O2, as explained using Figure 7, it was important to suppress the O2 flow rate to a range where the rate of oxide scale formation was small and did not exceed the sublimation rate.

[0072] FIG. 16(a) shows an example of the Raman spectrum of MoS2 measured in the triangular domain portion (see FIG. 15) at a downstream location 10 minutes after deposition. 1g and E 12g The modes were clearly observed, with wavenumber intervals of 20 cm. -1 This indicates that it is a single layer. Figure 16(b) shows the photoluminescence (PL) spectrum at room temperature obtained from the same measurement section. From this figure, very strong emission was observed around 666 nm, suggesting that this MoS2 is a single-layer film with a direct transition band structure. Figures 18(a) and (b) show the Raman and PL spectra, respectively, measured on the continuous film portion of the sample grown for 15 min (see Figure 17). In this case too, it is shown that the obtained film is a MoS2 monolayer film with extremely good crystallinity. As described above, it has been experimentally demonstrated that the present invention is useful as a method for forming a single layer film of MoS2 with good crystallinity.

[0073] Example 2 In Example 2, the substrate dependency of MoS2 film formation was investigated using a film formation apparatus of the MOCVD (Metal-Organic Chemical Vapor Deposition) type.

[0074] The equipment used is a MOCVD equipment using a low-pressure horizontal reactor with a susceptor made of high-purity graphite. The wafer (sample) placed on the susceptor can be heat-treated at the desired temperature by heating it from the backside of the susceptor with a halogen lamp.

[0075] The precursor of molybdenum element was oxychloride, specifically molybdenum dioxide dichloride (MoO2Cl2), while hydrogen sulfide (H2S) gas diluted to 10% by volume with N2 gas was used as the source of sulfur (S) of chalcogen element. Here, MoO2Cl2 is a solid at room temperature, but can generate gas by sublimation when heated. In Example 2, the sealed container was kept warm in a thermostatic chamber at about 20°C to generate steam, and the raw material gas was transported using N2 gas as a carrier.

[0076] Example 2 is a carbonless film formation using the oxychloride and H2S. Therefore, although an MOCVD apparatus is used in Example 2, strictly speaking, this is not MOCVD film formation. To repeat, this is carbonless (organic-less) film formation similar to Example 1.

[0077] Typical deposition conditions for the MoS2 film in Example 2 are shown below. ·Growth temperature: 700℃ Pressure: 50 Torr Growth time: 1 hour Total flow rate in reactor: N2 gas 2.5slm MoO2Cl2 supply conditions: N2 gas 75sccm, filled container 18.0℃, internal pressure controlled at 760Torr ·10%H2S flow rate: 10sccm

[0078] As the substrate, alumino-silicate glass with a high softening point and containing alumina (Al2O3) in the glass was selected from the viewpoint of avoiding deformation or melting of the substrate due to heat applied during film formation, and alkali alumino-silicate glass, which is also expected to have the catalytic effect of alkali elements such as Na and K, and film formation properties were evaluated. The list of glasses is shown in Tables 1 and 2 below. The composition was measured by fluorescent X-ray. Here, A is Dragontrail TM (DT) (AGC), B is Dragontrail Pro TM (AGC), C is Dinorex TM (NEG), D is Gorilla-3 TM (made by Corning), and E is Eagle-XG TM (manufactured by Corning). A to D are alkali alumino-silicate glasses, and E is a non-alkali alumino-silicate glass.

[0079] [Table 1]

[0080] [Table 2]

[0081] Under the above film formation conditions, MoS2 films were formed on different types of glass substrates. Figure 19 shows the results of SEM observation of the sample surface. It can be seen from Figure 19 that the domain size and density of MoS2 vary greatly depending on the type of glass. In particular, since no MoS2 film was observed in the alkali-free glass E, it is presumed that the catalytic effect of alkali metal elements such as Na and K in the glass is at work. The largest single crystal domains were obtained when glasses A and B were used, and this was highly reproducible.

[0082] Here, we have shown the formation of a MoS2 film using molybdenum dioxide dichloride (MoO2Cl2) as a precursor, but similar results were obtained when forming a WS2 film using tungsten tetrachloride oxide (WOCl4) instead of MoO2Cl2. One example is A's Dragontrail. TM (DT) (AGC) The results of forming a WS2 film on glass using an MOCVD device (electron microscope photograph, Raman spectrum, and PL spectrum) are shown in Figure 20. In the case of WS2, the Dragontrail of A TM (DT) (AGC) Large single crystal domains were formed on the glass, and the Raman and PL spectra showed good crystallinity. When WOCl4 was used, the container was kept warm in a thermostatic chamber at 40-45°C to generate steam, and the source gas was transported using N2 gas as a carrier.

[0083] Typical deposition conditions for the WS2 film are shown below. ·Growth temperature: 700℃ Pressure: 50 Torr Growth time: 1 hour Total flow rate in reactor: N2 gas 2.5slm WOCl4 supply conditions: N2 gas 250sccm, filled container 45.0℃, internal pressure controlled at 760Torr ·10%H2S flow rate: 5sccm

[0084] As described above, in Example 2, a case where a MoS2 film was formed using an MOCVD apparatus was shown. However, the first embodiment and Examples 1 and 2 all used inorganic film formation methods that used carbonless source gases, and the film formation characteristics on the glass substrate were also common to the first embodiment and Examples 1 and 2.

[0085] Example 3 In Example 3, the effect of adding a small amount of oxygen gas (O2 gas) in Example 2 was examined using the device described in Example 2.

[0086] Typical deposition conditions for the MoS2 film in Example 3 are shown below. ·Growth temperature: 700℃ Pressure: 50 Torr Growth time: 1 hour Total flow rate in reactor: N2 gas 2.5slm MoO2Cl2 supply conditions: N2 gas 75sccm, filled container 18.0℃, internal pressure controlled at 760Torr ·10%H2S flow rate: 10sccm ·0.1%O2 flow rate: 100sccm Therefore, other than the addition of 0.1% O2, the conditions are the same as in Example 2. Here, 0.1% O2 refers to 0.1% O2 gas by volume relative to N2 gas. As the substrate, four types of alkali alumino-silicate glass, A to D, shown in Example 2 were used for evaluation.

[0087] FIG. 21 shows the results of SEM observation of the MoS2 film sample surface. When glass A was used as the substrate, the single crystal domain was approximately 10 μm, which was overwhelmingly larger than when the other glass substrates were used. It was several times larger than glass substrate B and an order of magnitude larger than glass substrates C and D. The effect of adding O2 can be seen in comparison with Example 2, but a significant difference in the single crystal domain was only observed when glass substrate A was used, and no significant difference was observed when other glass substrates were used in response to the addition of O2. The glass substrate A was uniquely effective for forming a single crystal MoS2 film. In the first embodiment and Example 1, O2 is automatically added during film formation. Also in Example 1, when glass substrate A was used, an effect was observed in the formation of a MoS2 film with a large single crystal domain. [Industrial Applicability]

[0088] As described above, transition metal chalcogenide layered films (TMDCs) are highly anticipated as the main functional materials for extremely thin and highly flexible light emitting and receiving elements, optical functional devices, and ultra-low power consumption electronic devices. According to the present invention, there is provided a film formation method and manufacturing apparatus therefor which has high stability and controllability in the formation of transition metal chalcogenide layered films, particularly MoS2, enables the formation of large film areas, and is also cost-effective. Therefore, the present invention is believed to make an innovative contribution to industry, focusing on the above elements and devices. [Explanation of symbols]

[0089] 1: Metallic molybdenum (Mo) 2: Oxide scale (MoO x Layer (2≦x<3) 3: Oxide scale (MoO3 layer) 4:O2 5: MoO3 6: Oxide gas supply means 7: Reactive gas supply means 8: Reaction chamber 9: Exhaust means 10: Film deposition equipment 11: Film deposition equipment 12: Gas supply system 13: Equipment 14:Quartz tube part 21: Oxide gas generation chamber 22: Reaction chamber 23: Dedicated piping 25: Heater 31: Stage (Heated stage) 32: Transition metal block 33: Opening / closing and flow control device 34: Opening / closing and flow control device 35: Exhaust piping 36: Nozzle 37: Sample stage (sample stage with heater) 38: Sample 40: Opening / Closing / Flow Control Device 41: Piping (port) 42: Piping (port) 43: Piping 44: Opening / Closing / Flow Control Device 45: Piping (port) 46: Piping (port) 47: Piping 51: Piping 52, 52a, 52b, 52c: Valves (manual valves) 53, 53a, 53b, 53c: Mass flow controller 54, 54a, 54b, 54c: Valve (air valve) 55: Piping 56, 56a, 56b: Valve (air valve) 57: Exhaust pipe 61: Piping 62, 62a, 62b, 62c: Valves (manual valves) 63, 63a, 63b, 63c: Mass flow controller 64, 64a, 64b, 64c: Valve (air valve) 66, 66a, 66b: Valve (air valve) 71:Quartz tube 72: Base (foundation) 73: Support 74: Electric furnace 75: Sample stage (susceptor for substrate) 76: A-line 77: B-Line 78: C-Line 79: MoS2 layered film formation chamber (reaction chamber) 80: Exhaust 81: Mo reaction chamber (MoO3 gas generation chamber) 82: Upper nozzle 83: Lower nozzle 84: Pressure indicator 85: Manual valve

Claims

1. oxidizing a transition metal block to form an oxide layer of the transition metal on a surface of the transition metal; simultaneously with the formation of an oxide layer of the transition metal, sublimating the oxide from the oxide layer, and supplying the oxide gas together with a first inert carrier gas to the substrate via a dedicated pipe; supplying a reactive gas containing chalcogen atoms to the substrate together with a second inert carrier gas; heating the substrate while delivering the oxidizing gas and the reactive gas to the substrate; evacuating said oxide gas, said reactive gas, said first inert carrier gas and said second inert carrier gas.

2. 2. The method for forming a transition metal chalcogenide layered film according to claim 1, wherein the transition metal is one selected from the group consisting of titanium (Ti), zirconium (Zr), hafnium (Hf), vanadium (V), niobium (Nb), tantalum (Ta), molybdenum (Mo), chromium (Cr), tungsten (W) and rhenium (Re).

3. 3. The method for forming a transition metal chalcogenide layered film according to claim 1, further comprising the step of: forming said oxide layer into a hydrogenated oxide layer.

4. 4. The method for forming a transition metal chalcogenide layered film according to claim 3, wherein said hydrogenation is performed by adding hydrogen gas when said oxidation is performed.

5. heating a block made of molybdenum at a first temperature T1 while supplying a gas containing oxygen to form a molybdenum oxide layer on a surface of the block; At the same time as the formation of the molybdenum oxide layer, molybdenum trioxide (MoO ３ ) is sublimated and the MoO is then introduced into the reactor together with a first inert carrier gas via a dedicated pipe. ３ supplying the gas to the substrate; supplying a reactive gas containing chalcogen atoms to the substrate together with a second inert carrier gas; The MoO ３ heating the substrate at a second temperature T2 while supplying the gas and the reactive gas to the substrate; The MoO ３ and evacuating the first gas, the reactive gas, the first inert carrier gas, and the second inert carrier gas.

6. 6. The method of claim 5, wherein said first temperature T1 is 500[deg.] C. or more and 1200[deg.] C. or less.

7. 7. The method for forming a transition metal chalcogenide layered film according to claim 5, wherein the second temperature T2 is 300[deg.] C. or more and 1200[deg.] C. or less.

8. The dedicated pipe is ３ 8. A method for forming a transition metal chalcogenide layered film according to claim 5, wherein the source gas components are heated at a temperature that prevents redeposition of the source gas components midway through the tube, from at least the area where the block is located to the area immediately in front of the substrate.

9. 9. The method for forming a transition metal chalcogenide layered film according to claim 1, wherein the chalcogen atom is one selected from the group consisting of sulfur (S), selenium (Se) and tellurium (Te).

10. 10. The method for forming a transition metal chalcogenide layered film according to claim 1, wherein the first inert gas and the second inert gas are one or more selected from the group consisting of nitrogen gas, argon gas, krypton gas, neon gas, helium gas and xenon gas.

11. 10. The method for forming a transition metal chalcogenide layered film according to claim 1, wherein the first inert gas and the second inert gas are nitrogen gas.

12. 12. The method for forming a transition metal chalcogenide layered film according to claim 1, wherein the substrate contains an alkali metal element as a composition.

13. 13. The method for forming a transition metal chalcogenide layered film according to claim 12, wherein the alkali metal element is at least one selected from the group consisting of sodium (Na), lithium (Li) and potassium (K).

14. 13. The method for forming a transition metal chalcogenide layered film according to claim 1, wherein the substrate is an alkali aluminosilicate glass.

15. The method includes: an oxide gas supplying means for supplying an oxide gas to a substrate; a reactive gas supplying means for supplying a reactive gas to the substrate; a reaction chamber for forming a transition metal chalcogenide as a layered film on the substrate; and an exhausting means; the oxide gas supplying means comprises a block-shaped transition metal, a first heating means for heating the transition metal, a means for supplying an oxygen-containing gas to the heated block-shaped transition metal at a controlled flow rate, a means for supplying a first inert gas at a controlled flow rate, and a dedicated pipe for supplying an oxide gas generated by sublimation of the transition metal onto the substrate; the reactive gas supply means includes a means for supplying a reactive gas containing chalcogen atoms while controlling a flow rate thereof, and a means for supplying a second inert gas while controlling a flow rate thereof; the reaction chamber includes a sample stage and a second heating means for heating the substrate placed on the sample stage, and is a separate chamber from a location where the transition metal is placed; The apparatus for forming a transition metal chalcogenide layered film, wherein a heat treatment means is provided on a wall of the dedicated piping for maintaining a temperature equal to or higher than the sublimation temperature of the transition metal oxide.

16. 16. The apparatus for forming a transition metal chalcogenide layered film according to claim 15, wherein said oxide gas supply means further comprises means for supplying a gas containing hydrogen at a controlled flow rate.

17. MoO ３ The gas is supplied to the substrate. ３ A gas supplying means, a reactive gas supplying means for supplying a reactive gas containing sulfur to the substrate, and a MoS ２ The method includes the steps of: forming a layered film by a reaction chamber; and exhaust means; The MoO ３ The gas supplying means includes a block made of molybdenum, a first heating means for heating the block, a means for supplying a gas containing oxygen to the heated block made of molybdenum while controlling the flow rate, a means for supplying a first inert gas while controlling the flow rate, and a supplying means for supplying MoO generated by sublimation from the block. ３ and a dedicated pipe for supplying the gas onto the substrate, The reactive gas supply means includes a means for supplying the reactive gas at a controlled flow rate, and a means for supplying a second inert gas at a controlled flow rate; the reaction chamber includes a sample stage and a second heating means for heating the substrate placed on the sample stage, and is a separate chamber from a place where the block is placed; The walls of the dedicated piping are made of MoO ３ The heat treatment means is provided to keep the temperature of the MoS at or above the sublimation temperature. ２ An apparatus for forming layered films.

18. The reactive gases include sulfur (S), hydrogen sulfide (H ２ S), dimethyl sulfur ((CH ３ ) ２ S), diethyl sulfur ((C ２ H ５ ) ２ S), ditertiary butyl sulfur ([(CH ３ ) ３ C] ２ S), diisopropyl sulfur ((i-C ３ H ７ ) ２ S).

19. 19. The apparatus according to claim 15, wherein the first heating means and the second heating means are heated by one or more methods selected from the group consisting of resistance heating, induction heating, and lamp heating.

20. 20. The apparatus according to claim 15, wherein the first inert gas and the second inert gas are one or more selected from the group consisting of nitrogen gas, argon gas, krypton gas, neon gas, helium gas, and xenon gas.

21. 20. The apparatus of claim 15, wherein the first inert gas and the second inert gas are nitrogen gas.

22. 22. The apparatus according to claim 15, wherein the dedicated piping is made of one selected from the group consisting of quartz glass, glass, stainless steel, and ceramics.

23. 23. The apparatus of claim 22, wherein the ceramic is selected from the group consisting of alumina and SiC.

24. 24. The apparatus according to claim 15, wherein a showerhead is provided in the portion of the dedicated piping adjacent to the substrate.

25. 25. The apparatus according to claim 15, wherein the sample stage is provided with a rotation mechanism.

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