JP7656914B2 - Method and apparatus for forming transition metal chalcogenide layered films - Google Patents

Description

The present invention relates to a method for forming a transition metal chalcogenide layered film and an apparatus for doing so.

In recent years, attention has been focused on semiconductor materials with a thickness on the order of a molecular layer, called transition metal dichalcogenide layered films (hereinafter also referred to as TMDC), such as _MoS2 and _WSe2 .

This material is a two-dimensional layered semiconductor with a finite band gap. TMDC is a crystal with a unit cell thickness of just three atomic layers, and is inherently extremely thin and flat.
In addition, because it has a unique crystal structure with no unsaturated bonds (dangling bonds) in the direction perpendicular to the two-dimensional crystal plane (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, and applications 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 TMDC has a direct transition band structure and exhibits unique physical properties, such as an extremely large exciton effect, and is therefore considered to be extremely promising not only for use in extremely thin and flexible light-emitting and light-receiving elements, but also as a material for optical functional devices.

As described above, TMDC has many features and possibilities not found in conventional semiconductors, but there are many issues to be resolved in its film formation technology, and there are problems in that no formation method has been established that is excellent in controllability, stability, large area, and mass productivity.

Research into the properties and device applications of TMDC has been active since around 2010, but in many early studies, the crystal surface of _MoS2 , which is produced as a natural mineral, was peeled off with Scotch tape and used. In 2012, as disclosed in Non-Patent Document 1, a method for synthesizing a single layer of _MoS2 was reported for the first time using gas components sublimated from powders of molybdenum trioxide ( _MoO3 ) and sulfur (S). This method is also called the powder sublimation method (powder method), and even now, many reports on the formation of _MoS2 films use the same method or an improved version of it.

For example, in the technology disclosed in Non-Patent Document 2, powdered _MoO3 and S are used as the raw materials for Mo and S, and each is placed in an optimal temperature region in a hot-wall type quartz tube, whereby volatile gas components are sublimated and transported, and reacted on the substrate.
In this method, there are problems such as the initiation and termination of sublimation, as well as the difficulty of controlling the amount of raw material transport, the decrease in the amount of sublimation due to the reduction or depletion of the powder raw material, and the MoO ₃ powder reacting with S in the boat and changing, which hinders sublimation. For this reason, it is necessary to replace the MoO ₃ powder every time in the film formation process, but even so, it is difficult to obtain reproducibility. In addition, the geometric arrangement relationship between the MoO ₃ powder and the substrate placed in the small boat is also called the point-to-face supply method, but this method has the problem that it is difficult to achieve uniform spatial concentration of gas components in the film formation region, and in principle, it is not easy to uniformize the film formation or to increase the area.

Non-Patent Document 3 discloses a foil method using Mo (Mo foil method), which is a type of face-to-face method in which a Mo metal foil is placed as a cover over a substrate area for film formation, and Mo oxide is sublimated from the surface of the Mo foil and supplied onto the substrate.
In this method, the Mo raw material is uniformly supplied onto the substrate placed in the space below the Mo foil, and it has been reported that this method has the advantage of making it easier to obtain uniform film formation compared to the method using _MoO3 powder. However, in this method, sulfur element S is supplied not only onto the substrate but also onto the Mo foil surface, which causes various problems such as the unintended formation of _MoS2 on the Mo foil surface, the conversion of highly volatile components such as _MoO3 into substances with low oxidation numbers such as less volatile _MoO2 , and the reduction in the efficiency of Mo oxide gas generation and the instability of its generation.

As described above, in the method using the powdered _MoO3 raw material, it is difficult to stably supply the raw material gas and, in turn, to form a uniform _MoS2 film. One of the reasons for this is the non-uniformity of the particle size distribution of the powdered raw material, and Non-Patent Document 4 discloses a method in which a small amount of _MoO3 is deposited on a substrate in advance to uniformize the particle size, and this is then placed opposite the substrate to be used as the Mo raw material.
In addition, 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 in which _MoO3 is dissolved 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.

However, even with these composite methods, it has not been possible to form a completely coated _MoS2 continuous film on the substrate. This is thought to be because the amount of _MoO3 previously deposited on the substrate is so small that it is completely sublimated within the film formation time, resulting in complete depletion of the raw material.
In addition, with regard to the method of Non-Patent Document 4, a problem has been raised that there is a direct reaction between _MoO3 for sublimation and the raw material S, and 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, the conventional methods had quality and practical problems such as film formation stability, controllability, enlarging the 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 also considered to be the same for MoSe2 _{, WS2} , and _WSe2 films, and are common problems for TMDC.

Japanese Unexamined Patent Publication No. 7-069782 Special table 2019-522106 publication

Y. H. Lee et al. , Adv. Mater. , 24, 2320 (2012) H. Nguyen et al. , Mater. Lett. , 168, 1 (2016) J. Zheng et al. , Adv. Mater. , 29, 1604540 (2017) S. S. Withanage. , ACS Omega, 3, 18943 (2018) J. Lee et al. , Adv. Mater. , 29, 1702206 (2017)

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.

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 said oxide gas, said reactive gas, said first inert carrier gas and said second inert carrier gas.
(Configuration 2)
2. The method of 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 the step of: forming 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 (MoO ₃ ) from the molybdenum oxide layer and supplying the MoO ₃ gas to the substrate together with a first inert carrier gas through 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 when the _MoO3 gas and the reactive gas are supplied to the substrate;
and exhausting the _MoO3 gas, the reactive gas, the first inert carrier gas, and the second inert carrier gas.
(Configuration 6)
6. The method of 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 claim 5, wherein the second temperature T2 is 300° C. or more and 1200° C. or less.
(Configuration 8)
The 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 component from being redeposited midway through the pipe, at least from the location where the block is placed to a 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 of claim 1, 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 equal to or higher than 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: a _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 supplying 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 device for forming a _MoS2 layered film, wherein the dedicated piping is provided on its wall with a heat treatment means that maintains 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 (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), and diisopropyl sulfur ((iC ₃ H ₇ ) 2 S).
(Configuration 19)
19. The apparatus of any one of configurations 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 configurations 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 embodiment 22, wherein the ceramic is selected from the group consisting of alumina, SiC.
(Configuration 24)
24. The apparatus of any one of configurations 15 to 23, wherein the dedicated piping is provided with a showerhead 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.

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.

FIG. 2 is an explanatory diagram showing a schematic configuration of the device. FIG. 2 is an explanatory diagram showing a schematic configuration of the device. FIG. 2 is an explanatory diagram showing a schematic configuration of the device. FIG. 2 is an explanatory diagram showing a configuration of a gas supply system. FIG. 2 is a flow chart showing a film forming method of the present invention. FIG. 2 is a flow chart showing a film forming method of the present invention. FIG. 2 is an explanatory diagram showing the mechanism of _MoO3 gas generation. FIG. 2 is a cross-sectional view of a prototype device. FIG. 1 is a configuration diagram focusing on the gas piping system of a prototype device. 1 is an optical microscope photograph of the fabricated _MoS2 film. 1 is an optical microscope photograph of the fabricated _MoS2 film. 13 is an optical microscope photograph of the fabricated _MoS2 film. 13 is an optical microscope photograph of the fabricated _MoS2 film. 1 is an optical microscope photograph of the fabricated _MoS2 film. 1 is an optical microscope photograph of the fabricated _MoS2 film. The results of film evaluation of the produced _MoS2 film are shown in Fig. 1A by Raman spectroscopy and in Fig. 1B by emission spectroscopy. 1 is an optical microscope photograph of the fabricated _MoS2 film. The results of film evaluation of the produced _MoS2 film are shown in Fig. 1A by Raman spectroscopy and in Fig. 1B by emission spectroscopy. 1 is a SEM photograph of the fabricated _MoS2 film. FIG. 1 shows an SEM photograph of the prepared _WS2 membrane and the membrane properties evaluated by Raman and PL spectra. 1 is a SEM photograph of the fabricated _MoS2 film.

The following describes the embodiment of the present invention with reference to the drawings.

(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.

<Apparatus>
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.

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 piping 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 generating 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 also be integrated into a single opening/closing/flow rate control device, as shown in an opening/closing/flow rate control device 40 described below.

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). When Mo is used, it is possible to form a MoS ₂ 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 in cost.

The form of the transition metal used is preferably single crystal. In polycrystals, many grain boundaries exist, and in this state, the generation, accumulation, and sublimation of oxides progress 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 progress differently between the single crystal portion and the grain boundary portion. Here, generally, the generation, accumulation, and sublimation of Mo oxides tend to proceed 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.

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.

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 low cost.

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, the controllability and stability of the supply of the transition metal oxide gas to the sample 38 decreases. By using the above configuration, this problem can be solved.

The material of the 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.

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 means for supplying a reactive gas containing chalcogen atoms at a controlled flow rate, an opening/closing flow rate control device 40 as a means for supplying a second inert gas at a controlled flow rate, and a pipe 43 for supplying the reactive gas from the opening/closing flow rate control device 40 to the vicinity of the sample 38. Here, the opening/closing 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. In Fig. 2, the opening/closing flow rate control device 40 is shown as one device, but it may be two opening/closing flow rate control devices, one for supplying a reactive gas and one for supplying a second inert gas.

The chalcogen atom may be one selected from the group consisting of sulfur (S), selenium (Se) and tellurium (Te).
Examples of reactive gases containing chalcogen atoms include one or more selected from the group consisting of 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), and diisopropyl sulfur ((i-C ₃ H ₇ ) ₂ S). Among these, S and H ₂ S are preferably used because they are easily available and low cost.

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 low cost.

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 pipe 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 setting range of the temperature T2 by the second heating means is preferably 300° C. or more and 1200° C. or less. This temperature range makes it possible to efficiently and stably form a transition metal chalcogenide layered film that is uniform and has few defects.
It is preferable that the sample stage 37 is provided with a rotation mechanism, so that when the transition metal chalcogenide layered film is formed on the sample 38, the sample 38 is rotated while the film is formed, thereby improving the in-plane uniformity of the film formation.

The temperature control of the first heating means and the second heating means may be separate, or may be combined into one to simplify the device. That is, there may be two or more zones, or there may be one zone. 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.

In addition, in the first embodiment of the present invention, an apparatus classified as a horizontal reactor was described as an example of the apparatus of the present invention. However, this is not essential, and a vertical reactor in which the gas flows vertically may also be used.

The gas supply system 12 in which the opening/closing and flow rate are controlled shown in FIG. 4 is an example of 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 the pipe 55. In addition, an exhaust pipe 57 is provided to ensure sufficient gas purity in the pipe, and 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.

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) of the transition metal block 32 are controlled to thereby control the flow rate of the oxide gas supplied to the sample 38.
If it is attempted 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 results in 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 on-off and flow rate control devices 40 and 44 are connected to the reaction chamber 22. When a plurality of on-off and flow rate control devices are connected to the reaction chamber 22 in this way, not only the introduction of the reactive gas and the second inert gas but also the supply of _O2 gas mixed with an inert carrier gas as environmental control can be performed, enabling more advanced control. Pipes 45, 46, and 47 are connected to the on-off and flow rate control device 44.

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 heat treatment is performed on the sample 38, whereby a _MoS2 layered film can be formed on the sample 38.

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 the formation of a layered film of a transition metal dichalcogenide such as _MoS2 , can increase the area of the film formation, and is also excellent in terms of cost.

(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 region 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 shaping the gas outlet, such as a shower head.
(6) A reactive gas such as an 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.

Methods
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.

Here, 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).

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 the substrate together with a first inert carrier gas through 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 when 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 including the time of step S14 (step S15), thereby forming a _MoS2 layered film. Here, steps S12 and S13 may be performed simultaneously, or step S13 may be performed prior to step S12.

Here, the first temperature T1 is preferably 500° C. or more and 1200° C. or less. 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.
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.

As described in the device description, the dedicated pipe is preferably heated at least from the location where the metal block is placed to the region immediately before the substrate in order to prevent the generated source gas components such as _MoO3 from being redeposited midway through the pipe.

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

The first inert gas and the second inert gas can 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 ease of availability.

The oxygen content of the oxygen-containing gas is preferably 0.01% by volume or more and 100% by volume or less.
The ratio S ₂ /S ₀₂ of the sccm flow rate S ₂ of H ₂ S to the sccm flow rate S ₀₂ of the second inert gas is preferably 0.01 vol % or more and 100 vol % or less.
Under the above conditions, a transition metal chalcogenide layered film can be stably formed.

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 may 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 is improved due to the catalytic effect of the alkali metal, increasing the production efficiency of the film formation, and the size of the single crystal domain is also increased, contributing to improving the quality of the film formation.
A specific example of this substrate is alkali aluminosilicate glass, which was developed to promote _ion exchange reactions on the surface of reinforced cover glass for smartphones and other devices, and contains _SiO2 , _Al2O3 , and about 20% _Na2O by weight.

Next, the mechanism of TMDC formation will be explained using _MoS2 as an example of TMDC.
The important point of the present invention is that metallic molybdenum (Mo) is placed in an independently provided oxide gas generation chamber 21, and a gas containing oxygen ( _O2 ) is supplied thereto to generate molybdenum oxide (mainly molybdenum trioxide ( _MoO3 )) which serves as the Mo raw material gas, and this Mo raw material gas is introduced into a film formation area in which a sample (substrate) 38 is placed for use.
Generally, Mo, which is a transition metal element, is classified as a high melting point metal, and has a very high melting point of about 2600° C. or higher, so that 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 temperatures above 500° C. In the present invention, the formation reaction and sublimation of _MoO3 , which proceed simultaneously when dilute _O2 gas is supplied to the surface of metallic Mo, are actively utilized.

Next, the present invention will be described with respect to the formation of an oxide film (also called oxide scale) and its sublimation reaction which proceeds when _O2 gas is supplied to a Mo metal surface.
Figure 7 shows the possible oxide scale formation and sublimation when _O2 gas is supplied to Mo metal 1 in a heated environment. The supplied _O2 (4) is adsorbed on the Mo surface and reacts with Mo to form oxide scale (2 or 3). After an oxide scale of a finite thickness is formed, _O2 diffuses to the interface between the Mo metal and the oxide scale, where new oxide scale is formed. Then, _MoO3 becomes gas and sublimes. Here, Figure 7(a) shows the case where dilute _O2 gas is supplied, as will be explained later, and Figure 7(b) shows the case where sufficient _O2 gas is supplied.
Regarding the chemical composition of the oxide scale formed, under sufficient _O2 partial pressure, most of the surface layer is _MoO3 (3), which has a high vapor pressure (sublimability), but near the interface with the Mo metal, there is _MoO2 , which has a low sublimability and is very thin. In addition, suboxides such as _MoOx (2<x<3) also exist in the transition region from _MoO3 to _MoO2 . In Figure 7, _MoO2 and suboxides are displayed as 2.

On the other hand, it has been reported that the thickness of the oxide scale increases linearly with time (t) in the early stage of oxidation, and gradually changes to t1 ^/2 (parabolic law), but it also depends on the temperature and O2 _partial pressure. Thus, the formation process and structure of Mo oxide scale are complex.

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 (2, 3) is determined by the magnitude of the rate of oxide scale formation and the rate of sublimation. This competitive relationship is influenced by temperature and the amount of _O2 supply (partial pressure).

FIG. 7 shows two possible extremes of the competition between oxide scale formation and sublimation.
FIG. 7(a) shows the case where the sublimation rate is overwhelmingly larger than the formation rate of the oxide scale, i.e., "oxide scale formation rate << sublimation rate". This situation is realized when the _O2 supply amount is small or the temperature is high and sublimation occurs extremely actively. Under ideal extreme conditions, the _MoO3 component of the formed oxide scale immediately becomes _MoO3 (5) and sublimes, and does not remain on the surface, resulting in a depiction of a steadily low-volatility thin film of _MoOx or _MoO2 being exposed. In this case, the amount of _MoO3 sublimation per unit time, which is important for CVD of _MoS2 , is considered to be rate-limited by the supply flow rate of _O2 . Therefore, if the supply amount of _O2 is kept constant, the growth rate of _MoS2 becomes constant, and the amount of _MoS2 deposition (integral amount within the growth time) is proportional to time.

On the other hand, Fig. 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 of "oxide scale formation rate > sublimation rate". This is realized when the _O2 supply is sufficient and the temperature is relatively low, suppressing the sublimation rate.
In such a situation, the surface of Mo metal is always covered with MoO ₃ (3), and the thickness (i.e., volume) of MoO ₃ (3) increases with time. When CVD of MoS ₂ is performed in such a situation, even if the supply amount of O ₂ gas is constant, the sublimation amount of MoO ₃ does not become constant with time, and it is thought that it increases in proportion to the time along with the thickness of MoO _3. Therefore, it is expected that the growth rate of MoS ₂ 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 a situation, even if the O ₂ supply is stopped by valve operation, the generation will continue until the MoO ₃ (3) accumulated on the Mo (1) surface is sublimated and disappears, so the response will be poor when the growth of MoS ₂ is stopped.
As described above, two states can occur in the CVD of _MoS2 using the oxide scale formation on the metal Mo surface and the sublimation of _MoO3 . Although the deposition of _MoS2 can be realized under either state, from the viewpoint of controllability and responsiveness, it is preferable to achieve the state shown in Fig. 7(a).
From the above, according to the first embodiment, it is possible to provide a film formation method that has high stability and controllability in the formation of a transition metal dichalcogenide layered film such as _MoS2 , can increase the film formation area, and is also excellent in terms of cost.

The differences between the three methods described in the Background Art section, 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, and the method of the present invention are summarized below.

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 that no powder raw material is required, and there is no direct reaction with chalcogen elements such as S in the raw material of the metal oxide, improving controllability.
The differences with the foil method are that it does not have to be a metal foil and is made in a block shape, 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; it is not necessary to face the metal foil to the substrate, so there is a high degree of freedom to direct the metal oxide gas generated in the oxide gas generation chamber to the reaction chamber in which the sample is placed via piping, nozzles, shower heads, 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 difference with the composite method is that metal oxides such as _MoO3 are generated on the spot by the reaction of metal with _O2 , so that depletion of metal oxides can be avoided, the amount of sublimation of metal oxides (particularly, realization of 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 no direct reaction with chalcogen elements such as S occurs in the raw material of metal oxide, so that controllability is improved.

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

The apparatus basically conforms to the first embodiment, but differs from the first embodiment in that it further includes 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 and flow rate control devices 33 and 34, it includes equipment similar to the opening/closing and flow rate control devices 33 and 34 that supply hydrogen gas to the oxide gas generation chamber 21.

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 _WO3 gas to the reaction chamber 22, _WO3 is significantly less likely to sublimate than _MoO3 , so a high-temperature treatment of 800°C or higher is required for the sublimation.

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 (H ₂ O) 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 a first heat treatment, generating _H2WO4 on the surface of the W metal block, and the _substance is sublimated. In this case, the sublimation temperature is lowered (the vapor pressure becomes relatively higher compared to _WO3 ), making it possible to form a WS _two- layer film at a temperature of 700°C.

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

Example 1
In Example 1, a film formation apparatus for _MoS2 was produced, and the _film was formed on a substrate using the apparatus and evaluated.

<Apparatus>
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 with their dimensions.
The apparatus 13 is configured such that a quartz tube 71 is placed on a base 72 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 in the quartz tube 71. In addition, piping tubes for an A line 76 and a B line 77 made of quartz are installed in the quartz tube 71, and a tube for a C line 78 is attached to the quartz tube 71, so that gas for the C line is supplied into the quartz tube 71.

Here, in the _MoS2 layered film formation chamber 79, a susceptor 75 on which a sample on which a _MoS2 layered film is to be formed is placed is arranged, and _MoO3 gas is supplied from a 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 a B line 77. The atmospheric gas, gas flow, and exhaust promotion can be controlled by gas from a C line 78 connected to the quartz tube 71.

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, and exhaust 80 was performed. 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.

FIG. 9 shows a configuration diagram of the device 13, focusing on the gas supply system.
In the device 13, the MoO ₃ gas can be generated and 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 O ₂ gas. In addition, mass flow controllers (MFCs) 53a and 63a are installed in the A-1 line and the diluted O ₂ line (A-2) dedicated to N ₂ , respectively, and the effective O ₂ concentration in the Mo reaction chamber can be precisely changed by the flow rate ratio of these two MFCs. In addition, air valves 56a and 66a connected to the exhaust 57a are arranged in the A-1 line and the A-2 line, respectively, so that the cleanliness of the inside of the piping is sufficiently maintained by the exhaust operation. In addition, N ₂ line gas is connected to the A-1 line, and a cylinder of O ₂ gas diluted to 1% with N ₂ is connected to the A-2 line. The apparatus 13 is provided with a manual valve 85, and the quartz tube 71 can be evacuated 80 by opening the manual valve 85. The apparatus 13 is also provided with a pressure indicator 84, and the pressure inside the quartz tube 71 can be monitored.

As the sulfur (S) raw material, H ₂ S gas was 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 H ₂ S gas diluted to 1% was supplied to the B-1 line via a manual valve 52b, an MFC 53b, and an air valve 54b, and N ₂ gas in the line was supplied to the B-2 line via a manual valve 62b, an MFC 63b, and an 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.

Although powdered S can be used as the S raw material, the present configuration allows for more precise control of the supply amount using an On/Off valve and a mass flow controller (MFC). In order to avoid the problem of exhaustion of powdered S, it is preferable to use a configuration that allows for supplying organometallic compounds such as _H2S , ( _CH3 ) _2S , and ( _C2H5 ) _2S , which have a proven track record in _the MOCVD method, as gas raw materials.

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 , which is 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.

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 must be separated so that other reactive gases, such as S source gas, do not inadvertently enter and react with the Mo.
(2) The reaction chamber in which the metal 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 of (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 into the substrate region is structured so that the gas concentration in the substrate region can be made uniform by processing the shape of the gas outlet, such as a shower head.
(6) The raw material gas of the S raw material is mixed with the MoO3 introduced to the substrate portion as in (5) and reacts with the _MoO3 in the substrate portion region.

<Process>
A high-purity block (manufactured by Pansee) with a purity of 99.97% was prepared as metal Mo to be placed in the oxide gas ( _MoO3 gas) generation chamber (Mo reaction chamber) 81, and it was cut into a strip of 20 mm x 6 mm x 2 mm. Then, after cleaning with an organic solvent and pure water, it was 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
Film formation temperature: 700°C or 750°C
A-line flow rate: 100 sccm (1% _O2 / _N2 20 sccm + _N2 80 sccm, or _N2 100 sccm)
B line flow rate: 50 sccm (1% _H2S /N2 ₁₀ sccm + _N2 40 sccm, or N2 ₅₀ sccm)
C line flow rate: 250 sccm ( _N2 )
・Deposition time: 3 minutes to 15 minutes ・Substrate: Alkaline aluminosilicate glass (20 mm x 20 mm x 0.55 mm)

The substrate was ultrasonically cleaned with an organic solvent (acetone, IPS) and pure water, dried with N ₂ blowing, 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 predetermined 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 H ₂ S mixed gas was allowed to flow into line B 77 using the switching valve, and after waiting 30 seconds, the O ₂ mixed gas was allowed to flow 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 O ₂ started to flow into the A line 76 was defined as the film formation start time, and after a predetermined film formation time had elapsed, the generation of MoO ₃ was stopped by switching O ₂ to N ₂ using a switching valve, thereby terminating the film formation.
Thereafter, the electric furnace 74 was naturally cooled while the H ₂ S in the B line 77 was still flowing, and after the temperature had reached approximately room temperature, the sample was taken out.

<Materials evaluation>
10 to 13 show optical microscope photographs 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 (the left, center, and right locations of the area indicated by 79 in FIG. 8(b)), respectively.
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 obtained by conventional methods.
In addition, as the deposition time increased, the size of the triangular domains increased from several μm (deposition time 3 minutes) to several tens of μm (deposition time 10 minutes, 15 minutes), and finally 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, and with a deposition time of 15 minutes, taken further downstream than (c) in the above figure, is shown in FIG. 14.
It has also been confirmed that this can be achieved with good reproducibility without replacing the Mo metal raw material.

Although the time dependency was shown here, it was confirmed that it can also be controlled by the O ₂ flow rate. In this case, when the linearity (proportionality) and response speed of the time response of the film formation process to O ₂ are important, as explained using Figure 7, it was important to suppress the O ₂ flow rate to a range where the formation rate of the oxide scale is small and does not exceed the sublimation rate.

Figure 16(a) shows an example of the Raman spectrum of _MoS2 measured in the triangular domain part (see Figure 15) downstream of 10 minutes of deposition. _{The A1g} and ^E12g modes are clearly observed, and the wave number interval is 20 cm ^-1 , indicating that it is a single layer.
Fig. 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 Raman and PL spectra, respectively, measured on the continuous film portion of the sample grown for 15 min (see Figure 17), which again shows that the resulting film is a _MoS2 monolayer with excellent 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.

Example 2
In Example 2, the substrate dependency of _MoS2 film formation was examined using a film formation apparatus using the MOCVD (Metal-Organic Chemical Vapor Deposition) method.

The equipment used is a MOCVD device that uses a low-pressure horizontal reactor with a susceptor made of high-purity graphite. The wafer (sample) placed on the susceptor is heated from the backside of the susceptor by a halogen lamp, allowing it to be heat-treated at the desired temperature.

As a precursor of the molybdenum element, oxychloride was used, specifically, molybdenum dioxide _dichloride ( _MoO2Cl2 ) was used as a precursor. On the other hand, as a source of sulfur (S) of the chalcogen element, hydrogen sulfide ( _H2S ) gas diluted with _N2 gas to a volume concentration of 10% was used.
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 source gas was transported using _N2 gas as a carrier.

Example 2 is a carbonless film formation using the oxychloride and _H2S .
Therefore, although the MOCVD apparatus is used in the second embodiment, strictly speaking, the deposition is not MOCVD. To repeat, the deposition is carbonless (organic-less) like the deposition in the first embodiment.

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 2.5 slm
_MoO2Cl2 supply conditions: _N2 gas 75 _sccm , filled container 18.0°C, internal pressure controlled at 760 Torr 10% _H2S flow rate: 10 sccm

As the substrate, aluminosilicate glass containing alumina ( _Al2O3 ) and having a high softening point in order to avoid deformation or _melting of the substrate due to heat applied during film formation, and alkali aluminosilicate glass, which is also expected to have a catalytic effect of alkali elements such as Na and K, were selected and film formability was 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 ^™ (DT) (manufactured by AGC), B is Dragontrail Pro ^™ (manufactured by AGC), C is Dinorex ^™ (manufactured by NEG), D is Gorilla-3 ^™ (manufactured by Corning), and E is Eagle-XG ^™ (manufactured by Corning). A to D are alkali alumino silicate glasses, and E is non-alkali alumino silicate glass.

Under the above film formation conditions, _MoS2 films were formed on different types of glass substrates. The results of SEM observation of the sample surfaces are shown in FIG.
It can be seen from Fig. 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 using glasses A and B. This was highly reproducible.

In this example, the formation of a _MoS2 film using molybdenum dioxide _dichloride ( _MoO2Cl2 ) as a precursor is shown, but similar results were obtained when _{a WS2} film was formed using tungsten tetrachloride oxide ( _WOCl4 ) instead of _MoO2Cl2 .
As an example, the results of forming a film of _WS2 on Dragontrail ^™ (DT) (AGC) glass A using an MOCVD device (electron microscope photograph, Raman spectrum, and PL spectrum) are shown in Figure 20. In the case of _WS2 , a large single crystal domain was also formed on Dragontrail ^™ (DT) (AGC) glass A, and the Raman and PL spectra show good crystallinity. Here, when _WOCl4 was used, the sealed container was kept warm in a thermostatic chamber at 40 to 45°C to generate steam, and the raw material gas was transported using _N2 gas as a carrier.

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 2.5 slm
_WOCl4 supply conditions: _N2 gas 250 sccm, filled container 45.0°C, internal pressure controlled at 760 Torr 10% _H2S flow rate: 5 sccm

As described above, in Example 2, a case where a _MoS2 film was formed using an MOCVD apparatus was shown, but the first embodiment and Examples 1 and 2 were all inorganic film formation methods using carbonless source gases, and the film formation characteristics for a glass substrate were also common to the first embodiment and Examples 1 and 2.

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.

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 2.5 slm
_MoO2Cl2 supply conditions: _N2 gas 75 _sccm , filled container 18.0°C, internal pressure controlled at 760 Torr 10% _H2S flow rate: 10 sccm
・0.1% _O2 flow rate: 100sccm
Therefore, the conditions are the same as those in Example 2 except for the addition of 0.1% _O2 . Here, 0.1% _O2 means 0.1% _O2 gas in terms of volume ratio to _N2 gas.
As the substrate, the four types of alkali alumino-silicate glass A to D shown in Example 2 were used for evaluation.

FIG. 21 shows the results of SEM observation of the surface of the _MoS2 film sample.
When glass A was used as the substrate, the single crystal domain was about 10 μm, which was overwhelmingly larger than when 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. A significant difference in the single crystal domain was only observed when glass substrate A was used, and no significant difference was observed with the addition of _O2 when other glass substrates were used.
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 the glass substrate A was used, an effect was observed in the formation of a _MoS2 film with a large single crystal domain.

As described above, transition metal chalcogenide layered films (TMDC) are highly anticipated as the main functional material 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 are provided a film formation method and a manufacturing apparatus therefor, which have high stability and controllability in the formation of transition metal chalcogenide layered films, particularly _MoS2 , enable the formation of a large film area, and are also excellent in terms of cost.
Therefore, the present invention is believed to make an innovative contribution to industry, focusing on the above elements and devices.

1: Metallic molybdenum (Mo)
2: Oxide scale (MoO _x layer (2≦x<3)
3: Oxide scale (MoO ₃ layers)
4: _O2
5: _MoO3
6: Oxide gas supply means 7: Reactive gas supply means 8: Reaction chamber 9: Exhaust means 10: Film forming apparatus 11: Film forming apparatus 12: Gas supply system 13: Apparatus 14: Quartz tube 21: Oxide gas generation chamber 22: Reaction chamber 23: Dedicated piping 25: Heater 31: Stage (stage with heater)
32: Transition metal block 33: Opening/closing and flow rate control device 34: Opening/closing and flow rate control device 35: Exhaust pipe 36: Nozzle 37: Sample stage (sample stage with heater)
38: Sample 40: Opening/closing/flow rate control device 41: Piping (port)
42: Piping (port)
43: Piping 44: Opening/closing/flow rate 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 controllers 54, 54a, 54b, 54c: Valves (air valves)
55: Pipe 56, 56a, 56b: Valve (air valve)
57: Exhaust pipe 61: Pipe 62, 62a, 62b, 62c: Valves (manual valves)
63, 63a, 63b, 63c: Mass flow controllers 64, 64a, 64b, 64c: Valves (air valves)
66, 66a, 66b: Valve (air valve)
71: Quartz tube 72: Base (base)
73: Support 74: Electric furnace 75: Sample stage (susceptor for substrate)
76: Line A 77: Line B 78: Line C 79: MoS _2- layer 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 (25)

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. 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). The method for forming a transition metal chalcogenide layered film according to claim 1 or 2, further comprising converting the oxide layer into a hydrogenated oxide layer. 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. 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;
simultaneously with the formation of the molybdenum oxide layer, sublimating molybdenum trioxide (MoO ₃ ) from the molybdenum oxide layer, and supplying the MoO ₃ gas to the substrate together with a first inert carrier gas through 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 when the _MoO3 gas and the reactive gas are supplied to the substrate;
and exhausting the _MoO3 gas, the reactive gas, the first inert carrier gas, and the second inert carrier gas. 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. The method for forming a transition metal chalcogenide layered film according to claim 5 or 6, wherein the second temperature T2 is 300°C or higher and 1200°C or lower. 8. The method for forming a transition metal chalcogenide layered film according to claim 5, wherein the dedicated pipe is heated at a temperature that prevents the generated _MoO3 raw material gas component from being redeposited midway through the pipe, at least from the location where the block is placed to a region immediately in front of the substrate. 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). 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. 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. The method for forming a transition metal chalcogenide layered film according to any one of claims 1 to 11, characterized in that the substrate contains an alkali metal element as a composition. The method for forming a transition metal chalcogenide layered film according to claim 12, wherein the alkali metal element is one or more selected from the group consisting of sodium (Na), lithium (Li) and potassium (K). The method for forming a transition metal chalcogenide layered film according to any one of claims 1 to 12, wherein the substrate is alkali aluminosilicate glass. 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. The apparatus for forming a transition metal chalcogenide layered film according to claim 15, wherein the oxide gas supply means further includes a means for supplying a gas containing hydrogen at a controlled flow rate. The apparatus includes: a _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 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 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;
The device for forming a _MoS2 layered film, wherein the dedicated piping is provided on its wall with a heat treatment means that maintains a temperature equal to or higher than the sublimation temperature of _MoO3 . _18. The apparatus of claim 17, wherein the reactive gas is one or more selected from the group consisting of 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), and diisopropyl sulfur ((i-C ₃ H ₇ ) 2 S). The device 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. The apparatus according to any one of claims 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. The apparatus according to any one of claims 15 to 19, wherein the first inert gas and the second inert gas are nitrogen gas. The device according to any one of claims 15 to 21, wherein the dedicated piping is made of a material selected from the group consisting of quartz glass, glass, stainless steel, and ceramics. The device according to claim 22, wherein the ceramic is selected from the group consisting of alumina and SiC. The apparatus according to any one of claims 15 to 23, wherein a shower head is provided in the portion of the dedicated pipe adjacent to the substrate. The apparatus according to any one of claims 15 to 24, wherein the sample stage is provided with a rotation mechanism.