Method for producing chalcogenide-based layered material and method for producing semiconductor device

Abstract

To provide chalcogenide layered materials with few atomic defects.SOLUTION: A manufacturing method has a first step of forming a metal chalcogenide film with a compound of metal and chalcogen on a substrate, a second step of forming a chalcogen film with chalcogen on the metal chalcogenide film, a third step of placing graphene or hexagonal boron nitride on the chalcogen film, and a fourth step of heating the chalcogen film and the metal chalcogenide film after the third step.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a method for manufacturing a chalcogenide-based layered material and a method for manufacturing a semiconductor device.

Background Art

[0002] A layered material is a material in which atomic layers having a plurality of atoms strongly bonded to each other by covalent bonds or the like are weakly bonded to each other by van der Waals forces or the like. The atomic layer itself is also called a layered material. For example, graphite is a layered material in which atomic layers of carbon (that is, graphene) are weakly bonded to each other. Graphene itself is also a layered material.

[0003] Chalcogenide-based layered materials are layered materials that have attracted attention in recent years (see, for example, Patent Documents 1 to 4). A chalcogenide-based layered material is a compound of a metal and a chalcogen. Therefore, a chalcogenide-based layered material is also called a metal chalcogenide (see, for example, Patent Document 2).

[0004] Particularly notable substances among the many metal chalcogenides are MoS2 and WSe2. MoS2 and WSe2 with a number of layers of several layers or less are flexible semiconductors. Therefore, MoS2 and WSe2 are expected to be applied to flexible devices and semiconductor devices (see, for example, Patent Documents 1 to 4).

[0005] Metal chalcogenides other than MoS2 and WSe2 (for example, WTe2) also exhibit physical properties different from those of bulk crystals when the number of their layers is several layers or less. Therefore, metal chalcogenides other than MoS2 and WSe2 (particularly, WTe2) are also attracting attention.

Prior Art Documents

Patent Documents

[0006]

Patent Document 1

Patent Document 2

[0007] The main methods for synthesizing metal chalcogenides are chemical vapor deposition (CVD) and thermal sulfidation. Metal chalcogenides synthesized by these methods are exposed to high temperatures during synthesis. Therefore, metal chalcogenides synthesized by these methods have a large deficiency (i.e., lack) of chalcogen atoms. This is because the vapor pressure of chalcogen is higher than that of the metal. Such deficiencies in chalcogen atoms lead to unintended carrier generation and low mobility in the metal chalcogenides.

[0008] When chalcogen atoms are deficient, vacancies are created. These vacancies combine with moisture or oxygen in the atmosphere, leading to undesirable chemical changes in the metal chalcogenide (e.g., the formation of an oxide film). Therefore, the absence of chalcogen atoms (hereinafter referred to as atomic deficiencies) makes the metal chalcogenide chemically unstable.

[0009] Therefore, the object of the present invention is to solve these problems. [Means for solving the problem]

[0010] To solve the above problems, in one embodiment, the manufacturing method comprises: a first step of forming a metal chalcogenide film having a compound of a metal and a chalcogen on a substrate; a second step of forming a chalcogen film having at least one of another chalcogen different from the chalcogen and the chalcogen on the metal chalcogenide film; a third step of placing graphene or hexagonal boron nitride on the chalcogen film; and a fourth step of heating the chalcogen film and the metal chalcogenide film after the third step. [Effects of the Invention]

[0011] In one respect, the present invention provides a chalcogenide-based layered material with fewer atomic defects. [Brief explanation of the drawing]

[0012] [Figure 1] Figure 1 shows an example of the manufacturing method according to Embodiment 1. [Figure 2] Figure 2 is a cross-sectional view of the manufacturing method shown in Figure 1. [Figure 3] Figure 3 is a cross-sectional view of the manufacturing method shown in Figure 1. [Figure 4] Figure 4 is a cross-sectional view of the manufacturing method shown in Figure 1. [Figure 5] Figure 5 shows an example of a side view of a single layer of MoS2 deposited by the CVD method. [Figure 6] Figure 6 is a plan view of a single layer of MoS2 deposited by the CVD method. [Figure 7] Figure 7 shows another method for filling in the missing S atoms. [Figure 8] Figure 8 is a diagram illustrating why the S atom 112 cannot pass through graphene 122. [Figure 9] Figure 9 is a cross-sectional view of the copper foil after heating. [Figure 10] Figure 10 shows an example of metal chalcogenide film formation by CVD. [Figure 11]FIG. 11 is a diagram showing an example of forming a metal chalcogenide film by a hot vulcanization method. [Figure 12] FIG. 12 is a process cross-sectional view showing an example of a process of transferring graphene 22 onto an S film 20. [Figure 13] FIG. 13 is a process cross-sectional view showing an example of a process of transferring graphene 22 onto an S film 20. [Figure 14] FIG. 14 is a diagram showing an example of a manufacturing method according to Embodiment 2. [Figure 15] FIG. 15 is a process cross-sectional view of the manufacturing method shown in FIG. 14. [Figure 16] FIG. 16 is a process cross-sectional view of the manufacturing method shown in FIG. 14.

MODE FOR CARRYING OUT THE INVENTION

[0013] Hereinafter, embodiments of the present invention will be described with reference to the drawings. However, the technical scope of the present invention is not limited to these embodiments, and extends to the matters described in the claims and their equivalents. Even if the drawings are different, the same reference numerals are given to parts having the same structure, and the description thereof is omitted.

[0014] (Embodiment 1) Embodiment 1 relates to a method for manufacturing a chalcogenide-based layer material (that is, a metal chalcogenide). FIG. 1 is a diagram showing an example of a manufacturing method according to Embodiment 1. FIGS. 2 to 4 are process cross-sectional views of the manufacturing method shown in FIG. 1.

[0015] The manufacturing method illustrated in FIGS. 1 to 4 is a method for manufacturing molybdenum disulfide (that is, MoS2). However, the manufacturing method illustrated in FIGS. 1 to 4 can also be applied to the manufacture of other chalcogenide-based layer materials (for example, WSe2 and WTe2) by appropriately changing the precursor and the like.

[0016] (1) Manufacturing method (1-1) Formation of a metal chalcogenide film (the first step S1 shown in FIG. 1) First, a MoS2 film 18 is deposited on the substrate 16 (see Figure 2(a)) by CVD.

[0017] The substrate 16 is, for example, a silicon substrate with a thermal oxide film. The number of layers of the deposited MoS2 film 18 is, for example, one to several layers. The number of layers of the MoS2 film 18 may be more than one to several layers.

[0018] Details of the CVD method are described below in "(5) Method for Forming Metal Chalcogenide Films". In the following explanation, the process of forming a film by the CVD method will be referred to as CVD.

[0019] A compound word containing the word representing substance X and the word "film" in this order (for example, MoS2 film) means a film containing substance X. "Film" means a thin material that covers the surface of something. Therefore, the above compound word means a thin material that contains substance X and covers the surface of something. Hence, the MoS2 film 18 (see Figure 2(a)) is a thin material (in this case, an atomic layer) that contains MoS2 and covers the surface of the substrate 16.

[0020] Figure 5 is an example of a side view of a single layer of MoS2 (i.e., MoS2 with only one layer) deposited by the CVD method. Figure 6 is a plan view of this single layer of MoS2.

[0021] As shown in Figure 5, monolayer MoS2 has a plurality of S atoms 12 (i.e., sulfur atoms) arranged on the first surface 2 and a plurality of Mo atoms 8 arranged on the second surface 6 located above the first surface 2. Monolayer MoS2 further has a plurality of S atoms 12 arranged on the third surface 10 located above the second surface 6.

[0022] When viewed from directly above, monolayer MoS2 has two types of atoms arranged alternately at the vertices of a tightly packed regular hexagon (not shown), as shown in Figure 6. These two types of atoms are 8 Mo atoms and 12 S atoms. Mo is a metallic element, and S is a chalcogen element.

[0023] Chalcogens (e.g., sulfur, S) are elements with a higher vapor pressure than metals (e.g., Mo). During CVD, the deposited film is exposed to high temperatures. As a result, MoS2 films synthesized by CVD have large vacancies (i.e., deficiencies) of S atoms. Such MoS2 films contain numerous S atom vacancies.

[0024] Even when MoS2 films are formed by methods other than CVD, S atom vacancies occur. The same is true for metal chalcogenide films other than MoS2 films. Furthermore, naturally occurring metal chalcogenide crystals also contain chalcogen atom vacancies.

[0025] Furthermore, the chalcogens that can be constituent elements of metallic chalcogenides are sulfur (S), selenium (Se), and tellurium (Te). Therefore, unless otherwise specified, "chalcogen" refers to one of sulfur (S), selenium (Se), or tellurium (Te).

[0026] (1-2) Formation of chalcogen membrane (second step S2 shown in Figure 1) Next, a sulfur film 20 (hereinafter referred to as the S film) is formed on the MoS2 film 18 (see Figure 2(b)) formed in the first step S1. The S film 20 is formed, for example, by vacuum deposition. The thickness of the S film 20 to be formed is, for example, 1 nm to 1000 nm. The S film 20 is preferably elemental sulfur.

[0027] (1-3) Coating of the chalcogen film with graphene (third step S3 shown in Figure 1) Graphene 22 is placed on top of the S film 20 (see Figure 2(c)) formed in the second step S2. As a result, the S film 20 is coated with graphene 22. The graphene 22 may be a single layer or a multilayer.

[0028] Specifically, first, graphene 22 is formed on a substrate separate from substrate 16. Then, this graphene 22 is transferred to the S film 20. The method for transferring graphene is shown in "(6) Method for transferring graphene".

[0029] (1-4) Heating of the metal chalcogenide film and the chalcogen film (Step 4 S4 shown in Figure 1) After the third step S3, the S film 20 coated with graphene 22 and the MoS2 film 18 are heated (see Figure 3(a)).

[0030] The S atoms in the S film, having gained thermal energy from this heating, migrate to the MoS2 film 18 and bond with the Mo atoms 108 surrounding the S atom vacancies 14 (see Figure 6). In other words, the atomic vacancies in the MoS2 film 18 are filled by the S atoms in the S film 20.

[0031] In this process, the graphene 22 formed in the third step S3 suppresses the diffusion of S atoms into the atmosphere, so that the atomic vacancies present in the MoS2 film 18 formed in the first step S1 are effectively filled by the S atoms of the S film 20 (see "(2) Comparative Example"). The above-mentioned "atmosphere" refers to the gas surrounding the substrate 16.

[0032] The fourth step is specifically the step of heating the substrate 16, on which the MoS2 film 18, S film 20, and graphene 22 are stacked in this order, in an inert atmosphere maintained at atmospheric pressure, for example (see Figure 3(a)). The substrate 16 is heated, for example, by an electric furnace (not shown) having a heater 24. The heating temperature is, for example, 200°C to 1000°C. The heating time is, for example, 1 minute to 24 hours.

[0033] (1-5) Removal of graphene (Step 5 S5 shown in Figure 1) After step S4, the graphene 22 is removed, for example, by oxygen plasma treatment (see Figure 3(b)). The duration of this plasma treatment is the time required to completely remove the graphene 22. The plasma treatment time is, for example, 10 seconds to 60 minutes.

[0034] (1-6) Removal of chalcogen film (Step 6, S6, shown in Figure 1) After step S5, the S film 20 (see Figure 3(b)) is removed in the exhausted space 26 (see Figure 4(a)).

[0035] Specifically, the substrate 16 with the S film 20 (see Figure 3(b)) exposed is heated inside the vacuum apparatus (i.e., in the evacuated space 26). The substrate 16 is heated, for example, by a heater 124 provided inside the vacuum apparatus.

[0036] Then, S (i.e., sulfur), which has a high vapor pressure, evaporates, exposing the MoS2 film 18 (see Figure 4(a)). The heating temperature is, for example, 100°C to 600°C. The heating time is, for example, 10 seconds to 60 minutes.

[0037] As will be described later, it is possible to compensate for the chalcogen atom deficiencies in the MoS2 film 18 by using a different chalcogen film than the S film (see "(4) Variations of Chalcogen Films"). When using a different chalcogen film, the substrate 16 is heated to a temperature suitable for the evaporation of this different chalcogen film.

[0038] (1-7) Coating of a metal chalcogenide film with an insulating film (Step 7 S7 shown in Figure 1) After the sixth step S6, an insulating film 28 (see Figure 4(b)) is formed on the MoS2 film 18 in the evacuated space 26. As a result, the MoS2 film 18 is covered with the insulating film 28. The space 26 is continuously evacuated from the beginning of the sixth step S6, which removes the S film 20, until the end of the seventh step S7, which covers the MoS2 film 18 with the insulating film 28.

[0039] Specifically, an insulating film 28 is deposited on the MoS2 film 18 inside the evacuated vacuum chamber (i.e., the evacuated space 26). Finally, air is introduced into the vacuum chamber, and then the substrate 16 on which the insulating film 28 has been deposited is removed from the vacuum chamber.

[0040] The insulating film 28 is, for example, an SiO2 film. The insulating film 28 may also be another insulator (for example, an Al2O3 film or an HfO2 film). The thickness of the insulating film 28 is, for example, 0.5 nm to 100 nm.

[0041] Since steps 6 and 7 are a continuous vacuum process, the MoS2 film 18, whose atomic deficiencies were filled in step 4 S4, can be coated with the insulating film 28 without being exposed to the atmosphere. Therefore, steps 6 and 7 can suppress the degradation of the MoS2 film 18 due to the atmosphere (e.g., oxidation).

[0042] Steps 5 through 7 may be omitted. Even if steps 5 through 7 are omitted, steps 1 through 4 are still performed, so the atomic deficiencies in the MoS2 film 18 formed in step 1 S1 are effectively filled by chalcogen atoms supplied from the chalcogen film.

[0043] (2) Comparative Example In the example described with reference to Figures 1-4, the substrate 16, on which the MoS2 film 18 (see Figure 3(a)), S film 20, and graphene 22 are stacked in this order, is heated to fill in the S atom deficiencies present in the MoS2 film 18.

[0044] However, it is also possible to compensate for the absence of S atoms by other methods. Figure 7 shows an example of another method for compensating for the absence of S atoms (hereinafter referred to as the comparative example). In this comparative example, the substrate 16 on which the MoS2 film 18 is formed is sealed together with solid sulfur 120 in a single container 30 (for example, a quartz ampoule). Next, the container 30, along with the MoS2 film 18 and sulfur 120, is heated, for example, by a heater 224.

[0045] When the sulfur 120 is heated, sulfur vapor (hereinafter referred to as S vapor) is generated. When this S vapor comes into contact with the MoS2 film 18, the S atoms in the S vapor bond with the Mo atoms surrounding the vacancies 14 (i.e., S atom vacancies) in the MoS2 film 18. In other words, the atomic vacancies in the MoS2 film 18 are filled by the S atoms from the S vapor.

[0046] On the other hand, some of the sulfur atoms in the MoS2 film escape from the MoS2 film 18 and diffuse into the atmosphere. As a result, new sulfur atom vacancies occur in the MoS2 film 18. For this reason, it is difficult to sufficiently reduce the overall sulfur atom vacancies using the comparative example shown in Figure 7. The same situation applies to metal chalcogenide films other than MoS2 films.

[0047] On the other hand, as shown in the example described with reference to Figures 1-4, the amount of S atoms diffusing from the heated MoS2 film 18 (see Figure 3(a)) into the atmosphere can be reduced compared to the comparative example. This is because S atoms can hardly pass through graphene 22, thus suppressing the diffusion of S atoms into the atmosphere surrounding the MoS2 film 18.

[0048] Figure 8 illustrates why S atom 112 can barely pass through graphene 122. Graphene is a monolayer with multiple carbon atoms arranged regularly on a single surface.

[0049] The interatomic distance d between carbon atoms in graphene is 0.142 nm. This distance is approximately the same as the radius R (=0.105 nm) of sulfur atom 112. Therefore, as shown in Figure 8, sulfur atoms 112 can hardly pass through graphene 122. This is even more true for sulfur molecules that are larger than sulfur atoms 112. The same applies to other chalcogens (i.e., Se and Te).

[0050] The inventor confirmed through the following experiment that even oxygen, which has an atomic radius smaller than chalcogen, can barely pass through graphene. First, graphene partially coating a copper foil was formed by the CVD method. Then, this copper foil was heated in air, and the surface was observed. The heating temperature was 200°C.

[0051] Figure 9 is a cross-sectional view of the copper foil 32 after heating. The portion of the copper foil 32 covered with graphene 122 retained its copper color, just as it was before heating. On the other hand, the portion 34 not covered with graphene 122 (hereinafter referred to as the exposed portion) was discolored.

[0052] These facts indicate that the exposed portion 34 was oxidized, but the portion covered with graphene 122 was not. This indicates that oxygen can hardly penetrate graphene 122.

[0053] Hexagonal boron nitride is a layered material with interatomic distances approximately the same as those of graphene. Therefore, instead of graphene 22 (see Figure 3(a)), the S film 20 may be coated with a single to several layers of hexagonal boron nitride.

[0054] Incidentally, in the example explained with reference to Figures 1-4, the sulfur atoms in the S film 20 (see Figure 3(a)) fill in the atomic vacancies in the MoS2 film 18. The amount of sulfur contained in the S film 20 is extremely small compared to the amount of sulfur 120 (see Figure 7) used in the comparative example. Therefore, according to the example explained with reference to Figures 1-4, the vacancies of sulfur atoms can be filled with an extremely small amount of sulfur compared to the comparative example.

[0055] Similarly, when chalcogen deficiencies are filled with chalcogen films other than the S film (see "(4) Variations of Chalcogen Films"), the atomic deficiencies can be filled with only a small amount of chalcogen.

[0056] (3) Variations of metal chalcogenide films In the manufacturing method illustrated in Figures 1-4, a MoS2 film 18 is formed in the first step S1 (see Figure 1). However, a metal chalcogenide film other than the MoS2 film 18 may also be formed in the first step S1. The metal chalcogenide film formed in the first step S1 may be single-layer or multi-layer.

[0057] For example, the metal chalcogenide film formed in the first step S1 may be a metal chalcogenide film having any of the following: a transition metal dichalcogenide, a group 13 chalcogenide, a group 14 chalcogenide, or a bismuth chalcogenide.

[0058] Transition metal dichalcogenides are compounds of transition metals (i.e., Mo, Nb, W, Ta, Ti, Zr, Hf, V, etc.) and chalcogens (i.e., S, Se, Te). Group 13 chalcogenides are compounds of Group 13 elements (i.e., Ga, In, Tl) and chalcogens. Group 14 chalcogenides are compounds of Group 14 elements (i.e., Ge, Sn, Pb) and chalcogens. Bismuth chalcogenides are compounds of bismuth and chalcogens.

[0059] (4) Variations of chalcogen membrane In the manufacturing method illustrated in Figures 1-4, the S film 20 (see Figure 2(b)) is formed in the second step S2 (see Figure 1). However, a chalcogen film other than the S film may also be formed in the second step S2. The main chalcogen films that can be formed in the second step S2 can be classified into the first to third types described below.

[0060] -Type 1 chalcogen membrane- By the way, a metallic chalcogenide film is an object that contains metallic chalcogenides and covers the surface of a certain object (for example, a substrate). In the following explanation, the chalcogen (for example, S) among the constituent elements (for example, Mo and S) of the above-mentioned "metallic chalcogenide" (for example, MoS2) will be referred to as the chalcogen constituent element.

[0061] The first type of chalcogen film is the elemental chalcogen component of the metal chalcogenide film formed in the first step S1. In the manufacturing method illustrated in Figures 1-4, a MoS2 film is formed in the first step S1. Therefore, the first type of chalcogen film in the manufacturing method illustrated in Figures 1-4 is elemental S.

[0062] When WSe2 is formed in the first step S1, the first type of chalcogen film is elemental Se. When WTe2 is formed in the first step S1, the first type of chalcogen film is elemental Te.

[0063] The first type of chalcogen film fills in the atomic deficiencies of the metal chalcogenide film with the chalcogen constituent elements of the metal chalcogenide film. Therefore, the first type of chalcogen film can fill in the atomic deficiencies of the metal chalcogenide film without increasing the impurity concentration.

[0064] -Type 2 chalcogen membrane- The second type of chalcogen film is an element of a different chalcogen (e.g., Se) than the chalcogen constituent element (e.g., S) present in the metal chalcogenide film (e.g., MoS2 film 18) formed in the first step S1.

[0065] In the manufacturing method illustrated in Figures 1-4, a MoS2 film is formed in the first step S1. Therefore, the second type of chalcogen film is either elemental Se or elemental Te.

[0066] The second type of chalcogen film not only allows for the filling of atomic deficiencies in a metal chalcogenide film (e.g., a MoS2 film), but also enables doping of this metal chalcogenide film. In this case, the dopant is a "different chalcogen" (e.g., Se) that is different from the chalcogen constituent elements (e.g., S) of the metal chalcogenide film.

[0067] -Third type of chalcogen membrane- The third type of chalcogen film is a mixture containing both the individual chalcogen constituent elements of the metal chalcogenide film formed in the first step S1, and individual "other chalcogens" that are different from these chalcogen constituent elements.

[0068] In the manufacturing method illustrated in Figures 1-4, a MoS2 film is formed in the first step S1. Therefore, the third type of chalcogen film is, for example, a mixture of elemental S and elemental Se.

[0069] The third type of chalcogen film can not only fill in atomic deficiencies in a metal chalcogenide film (e.g., a MoS2 film), but it can also be used to dope this metal chalcogenide film (e.g., a MoS2 film). In this case as well, the dopant is the "other chalcogen" (e.g., Se) mentioned above.

[0070] Furthermore, by controlling the proportion of "other chalcogens" mixed in the third type of chalcogen membrane, the density of dopants introduced into the metal chalcogenide can be controlled.

[0071] While the chalcogen membranes of types 1 to 3 contain up to two types of chalcogen, the chalcogen membrane formed in the second step may contain all three types of chalcogen (i.e., S, Se, Te).

[0072] (5) Method for forming a metal chalcogenide film In the first step S1 (see Figure 1) of the manufacturing method illustrated in Figures 1-4, a metal chalcogenide film is formed using the CVD method. However, in the first step S1, the metal chalcogenide film may also be formed by a method other than the CVD method (for example, the thermal sulfidation method). Here, the CVD method and the thermal sulfidation method will be explained.

[0073] (5-1)CVD method Figure 10 shows an example of metal chalcogenide film formation by CVD. In the example shown in Figure 10, a MoS2 film is formed. The CVD method shown in Figure 10 is performed under atmospheric pressure.

[0074] First, the substrate 16, MoO340 (molybdenum trioxide), and S42 (e.g., sulfur powder) are placed in this order inside the reaction tube 38, which has three zones surrounded by separate heaters 36a, 36b, and 36c. The substrate 16 is placed in the first zone surrounded by the first heater 36a. The MoO340 is placed in the second zone surrounded by the second heater 36b. The S42 is placed in the third zone surrounded by the third heater 36c. Figure 10 shows the MoS2 film 18 being formed.

[0075] The weight of MoO340 placed in the second zone is, for example, 1 mg to 100 mg. The weight of S42 placed in the third zone is, for example, 10 mg to 1000 mg.

[0076] In this state, Ar gas 44 is introduced into the reaction tube 38 from the end closest to S42. The flow rate of the Ar gas is, for example, 100 sccm to 1000 sccm. Ar gas 44 is the carrier gas.

[0077] Next, the substrate 16 is heated to 500°C to 1000°C by the first heater 36a. Furthermore, the MoO340 is heated to 300°C to 600°C by the second heater 36b. Furthermore, the S42 is heated to 100°C to 200°C by the third heater 36c. As a result, vapor of MoO3 is generated from MoO340, and vapor of S is generated from S42.

[0078] The vapor of MoO3 and the vapor of S react in the gas phase, causing a MoS2 film 18 to precipitate on the substrate 16. In other words, a MoS2 film 18 is formed on the substrate 16.

[0079] The CVD method described with reference to Figure 10 is just one example, and various modifications are possible. For example, in the example shown in Figure 10, the carrier gas is Ar gas 44. However, the carrier gas may be an inert gas other than Ar gas 44. These carrier gases may also contain hydrogen.

[0080] In the example shown in Figure 10, the metal chalcogenide film (e.g., MoS2 film 18) is formed under atmospheric pressure. However, the metal chalcogenide film may also be formed under reduced pressure (e.g., in a vacuum).

[0081] The precursor of the metal chalcogenide film (e.g., MoS2 film) may be either an element or a compound. The "compound" may be an oxide, chloride, fluoride, hydride, or organic compound. However, both the "element" and the "compound" must be substances containing the constituent elements of the metal chalcogenide film.

[0082] In the example shown in Figure 10, the precursor consists of multiple substances. However, the precursor of the metal chalcogenide film may be a single substance containing all the constituent elements of the metal chalcogenide film.

[0083] MoS3 is one such precursor. When MoS3 is heated in an inert gas containing H2S, it changes to MoS2 and precipitates on the substrate. MoS4, Mo2S3, Mo2S5, and Mo3S4 also change to MoS2 and precipitate on the substrate when heated in an inert gas containing H2S. These compounds are also single precursors that contain all the constituent elements of the metal chalcogenide film.

[0084] The precursor may be in solid, liquid, or gaseous form. Solid precursors may be crystalline or amorphous. If the precursor is solid or liquid, it is vaporized by heat treatment or other means. The vaporized precursor transports the constituent elements of the metal chalcogenide film to the substrate. The amount of evaporation of the precursor depends on the heating temperature of the precursor, the atmospheric pressure, the amount of precursor loaded into the reaction tube, and the vapor pressure of the precursor.

[0085] These parameters related to the precursor (i.e., heating temperature, etc.) are set so that the thickness and area of ​​the metal chalcogenide film formed on the substrate (for example, the substrate 16 shown in Figure 10) reach their respective target values. Furthermore, the heating temperature of the substrate on which the metal chalcogenide film is formed is also set so that the thickness, area, and quality of the metal chalcogenide film formed on the substrate reach their respective target values.

[0086] Various substrates can be used as the substrate 16 for forming the metal chalcogenide film. For example, silicon substrates with a thermal oxide film, sapphire substrates, and magnesium oxide substrates can be used.

[0087] The arrangement of the substrate and precursor within the vessel used to synthesize the metal chalcogenide film (for example, the reaction tube 38 shown in Figure 10) is not limited to the example shown in Figure 10. The appropriate arrangement of the substrate and other components will vary depending on the synthesis conditions of the metal chalcogenide film and the structure of the reactor.

[0088] In a reactor in which the temperatures of multiple zones are controlled separately (hereinafter referred to as a multi-temperature reactor), two precursors can be heated to different temperatures. The apparatus shown in Figure 10 (i.e., an apparatus having a reaction tube 38 and three heaters 36a, 36b, and 36c) is an example of such a reactor.

[0089] With a multi-temperature reactor, the heating temperature of each of the multiple precursors can be controlled separately, allowing for independent control of the evaporation rate of each precursor. Therefore, a multi-temperature reactor allows for control of the stoichiometric composition ratio of the metal chalcogenide film formed on the substrate.

[0090] (5-2) Hot sulfurization method Figure 11 shows an example of the formation of a metal chalcogenide film by the thermal sulfidation method. In the example shown in Figure 11, a MoS2 film is formed. The thermal sulfidation method shown in Figure 11 is performed under atmospheric pressure.

[0091] First, a substrate 116, whose surface is covered with a Mo film 46 (preferably a pure molybdenum film), and S142 (for example, sulfur powder) are placed in this order inside a reaction tube 38 having three zones surrounded by separate heaters 36a, 36b, and 36c. The substrate 116 is placed in the first zone surrounded by the first heater 36a. The S142 is placed in the third zone surrounded by the third heater 36c. Figure 11 shows the MoS2 film 118 being formed.

[0092] The thickness of the Mo film 46 covering the surface of the substrate 116 is, for example, 0.5 nm to 1000 nm. The weight of S142 placed in the third zone is, for example, 1 mg to 1000 mg.

[0093] In this state, Ar gas 44 is introduced into the reaction tube 38 from the end closest to S142. The flow rate of the Ar gas is, for example, 10 sccm to 1000 sccm.

[0094] Next, the substrate 116 is heated to 500°C to 1000°C by the first heater 36a. Furthermore, the S142 is heated to 100°C to 300°C by the third heater 36c. As a result, sulfurous vapor is generated from the S142. This sulfurous vapor reacts with the Mo film 46 covering the substrate 116, causing a MoS2 film 118 to deposit on the substrate 116. In other words, a MoS2 film 118 is formed on the substrate 116. The heating time for the substrate 116 and S142 is, for example, 1 second to 10 hours. This time is set so that the thickness and area of ​​the MoS2 film 118 formed on the substrate 116 reach their respective target values.

[0095] The Mo film 46 covering the surface of the substrate 116 may be a compound of Mo (e.g., MoO3, MoCl5, etc.) rather than pure Mo. The Mo film 46 is deposited on the substrate 116 by, for example, vacuum deposition or sputtering. The substrate temperature when depositing the Mo film 46 is, for example, room temperature to 500°C. The target thickness of the Mo film 46 is the thickness at which a metal chalcogenide film of the desired thickness is formed on the substrate 116.

[0096] The thermal sulfidation method described with reference to Figure 11 is just one example, and various modifications are possible. For example, in the example shown in Figure 11, the formation of the metal chalcogenide film (e.g., MoS2 film 118) is carried out under atmospheric pressure. However, the formation of the metal chalcogenide may be carried out under reduced pressure or increased pressure.

[0097] In the example described with reference to Figure 11, the source of chalcogen is a solid (e.g., sulfur powder). However, the source of chalcogen does not have to be a solid. For example, the source of chalcogen may be a gas (e.g., hydrogen sulfide).

[0098] If the chalcogen source is solid, the chalcogen is transported to the substrate 116 by evaporating this solid. The amount of chalcogen evaporated from the source depends on the heating temperature of the source, the atmospheric pressure, the amount of source loaded into the reactor, and the vapor pressure of the source.

[0099] Therefore, these parameters relating to the supply source are set so that the thickness and area of ​​the metal chalcogenide film (e.g., MoS2 film 118) formed on the substrate (e.g., substrate 116 shown in Figure 11) reach their respective target values. Similarly, the heating temperature of the substrate is also set so that the thickness, area, and quality of the metal chalcogenide film formed on the substrate reach their respective target values.

[0100] Various substrates can be used as the substrate 116 on which the metal chalcogenide film is formed. For example, silicon substrates with a thermal oxide film, sapphire substrates, and magnesium oxide substrates can be used.

[0101] The arrangement of the substrate 116 and the chalcogen supply source (e.g., S142) within the vessel for synthesizing the metal chalcogenide film (e.g., reaction tube 38) is not limited to the example shown in Figure 11. The optimal arrangement of the substrate and other components depends on the synthesis conditions of the metal chalcogenide film (e.g., MoS2 film 118) and the structure of the reactor.

[0102] (6) Method for transferring graphene Graphene transfer refers to the process of transferring graphene, formed on a catalyst by, for example, CVD, to a substrate separate from the catalyst. Figures 12-13 are cross-sectional views showing an example of the process of transferring graphene 22 to an S film 20 (see Figure 2(c)). By transferring graphene 22 to the S film 20 using the method shown in Figures 12-13, a high coverage rate (e.g., 99%) can be achieved.

[0103] First, a substrate 48 is prepared in which the catalyst 50 (see Figure 12(a)) and graphene 22 are stacked in that order. Instead of such a substrate 48, a self-supporting catalyst foil on which graphene is formed may be prepared. The catalyst 50 is, for example, one of the elements Fe, Ni, and Cu. The graphene 22 is, for example, an atomic film formed on the catalyst 50 by CVD.

[0104] Next, a support film 52 (see Figure 12(b)) with a thickness of, for example, 0.1 μm to 100 μm is formed on the graphene 22. Specifically, first, a resist is applied to the graphene 22 by spin coating or the like. A polymer may be applied instead of the resist. After that, the applied resist (or polymer) is heated. The heating temperature is, for example, room temperature to 200°C.

[0105] The applied resist (or polymer) then solidifies to form a support film 52. The support film 52 may also be formed by methods other than those described above (for example, vacuum deposition).

[0106] Next, the graphene 22 supported by the support film 52 is peeled off from the catalyst 50 (see Figure 12(c)). Specifically, the substrate 48, on which the catalyst 50, graphene 22, and support film 52 are stacked in this order, is immersed in an etching solution for the catalyst 50. As a result, the catalyst 50 is removed by side etching. The etching solution is, for example, an aqueous solution of iron(III) chloride (i.e., FeCl3).

[0107] Through the processes described so far, graphene 22 supported by the support film 52 (hereinafter referred to as graphene 222 with support film) is formed. Subsequently, the etching solution adhering to the graphene 222 with support film is removed by washing with water.

[0108] Next, the graphene 222 with the support film and the S film 20 are placed on top of each other so that they are in contact (see Figure 13(a)). In this state, the substrate 16 is heated to make the graphene 222 with the support film and the S film 20 adhere tightly to each other. The heating temperature is, for example, room temperature to 300°C.

[0109] Finally, the support film 52 is removed by dissolving it with an organic solvent (e.g., acetone) (see Figure 13(b)). This completes the transfer of graphene 22 to the S film 20.

[0110] The manufacturing method according to Embodiment 1 includes a first step S1 (see Figure 2(a)) of forming a metal chalcogenide film (e.g., MoS2 film 18) having a compound (e.g., Mo) of a metal (e.g., Mo) and a chalcogen (e.g., S) on a substrate.

[0111] The manufacturing method according to Embodiment 1 further comprises a second step S2 (see Figure 2(b)) of forming a chalcogen film (e.g., S film 20) on the metal chalcogenide film. Such a chalcogen film has at least one of another chalcogen (e.g., Se or Te) different from the chalcogen (e.g., S) and the chalcogen (e.g., S).

[0112] The manufacturing method according to Embodiment 1 further includes a third step S3 (see Figure 2(c)) in which graphene 22 or hexagonal boron nitride is placed on the chalcogen film (for example, S film 20).

[0113] The manufacturing method according to Embodiment 1 further includes a fourth step S4 (see Figure 3(a)) after the third step S3, in which the chalcogen film (e.g., S film 20) and the metal chalcogenide film (e.g., MoS2 film 18) are heated. The "chalcogen" is one of sulfur, selenium, and tellurium. Furthermore, the "other chalcogen" is also one of sulfur, selenium, and tellurium.

[0114] In the fourth step S4, the deficiencies in chalcogen atoms (e.g., S atoms) in the metal chalcogenide film (e.g., MoS2 film 18) are filled. Meanwhile, some of the chalcogen atoms in the metal chalcogenide film escape from the film and diffuse into the atmosphere.

[0115] When chalcogen atoms escape from a metal chalcogenide film, a chalcogen vacancy is left behind. In other words, a new atomic defect is created in the metal chalcogenide film.

[0116] However, since chalcogen atoms can hardly pass through graphene (or hexagonal boron nitride) on the chalcogen film, very few new atomic vacancies occur in the metal chalcogenide film. Therefore, according to Embodiment 1, a metal chalcogenide film with few atomic vacancies (i.e., a chalcogenide-based layered material) can be manufactured.

[0117] The manufacturing method of Embodiment 1 preferably further comprises steps 5 to 7. Step 5 S5 is a step of removing graphene 22 (or hexagonal boron nitride) after step 4 S4. Step 6 S6 is a step of removing the chalcogen film (e.g., S film 20) in an evacuated space 26 (e.g., inside a vacuum device) after step 5 S5. Step 7 S7 is a step of forming an insulating film 28 on the metal chalcogenide film (e.g., MoS2 film 18) in the evacuated space 26 after step 6 S6. However, the space 26 is continuously evacuated from the beginning of step 6 S6 to the end of step 7 S7.

[0118] According to steps 5 to 7, the metal chalcogenide film (e.g., MoS2 film 18) whose atomic deficiencies have been filled in steps 1 to 4 can be coated with an insulating film 28 without being exposed to the atmosphere. Therefore, according to steps 5 to 7, it is possible to suppress the deterioration (e.g., oxidation) of the metal chalcogenide film (e.g., MoS2 film 18) whose atomic deficiencies have been filled in steps 1 to 4 by the atmosphere.

[0119] (Embodiment 2) Embodiment 2 relates to a method for manufacturing a semiconductor device having a metal chalcogenide film and a plurality of electrodes. Figure 14 is a diagram showing an example of the manufacturing method according to Embodiment 2. Figures 15-16 are cross-sectional views of the manufacturing method shown in Figure 14.

[0120] In one example shown in Figures 14-16, a semiconductor device having a MoS2 film and multiple electrodes is manufactured. However, the example shown in Figures 14-16 may also be applied to semiconductor devices having metal chalcogenide films other than MoS2 films.

[0121] (1) Formation of a metal chalcogenide film ~ Coating of the metal chalcogenide film with an insulating film (Steps 1 S1 to 7 S7 shown in Figure 1 or 14) First, following the steps 1 to 7 described in Embodiment 1 (see Figures 1 to 4), a MoS2 film 18 with filled atomic voids (see Figure 4(b)) and an insulating film 28 covering the MoS2 film 18 are formed on the substrate 16.

[0122] (2) Electrode formation process (Step 8 S8 shown in Figure 14) After step S7, the above-mentioned multiple electrodes are formed.

[0123] Specifically, first, air is introduced into the space 26 (see Figure 4(b)) where the substrate 16 is placed, and then the substrate 16 is removed from this space 26. After that, a strip-shaped photoresist film 54 is formed on the insulating film 28 (see Figure 15(a)) using lithography technology. Figure 15 is a cross-sectional view across this photoresist film 54.

[0124] The insulating film 28 and the MoS2 film 18 are etched through this photoresist film 54. This etching is performed, for example, by dry etching. This etching forms the insulating film 28 into a strip-shaped insulating film 128 (see Figure 15(b)) and further forms the MoS2 film 18 into a strip-shaped MoS2 film 218.

[0125] Next, a photoresist film 154 having a first opening 56a (see Figure 15(c)) that exposes the center of the strip-shaped insulating film 128, and second to third openings 56b and 56c that are in contact with the side surface of the insulating film 128, is formed by lithography.

[0126] A metal film 58 (see Figure 16(a)) is deposited onto the substrate 16 via this photoresist film 154. The deposition of the metal film 58 is controlled so that it does not become excessively thicker than the strip-shaped MoS2 film 218. The thickness of the metal film 58 is, for example, 10 nm to 100 nm. The metal film 58 is, for example, a Ti / Au film or a Pd film.

[0127] After the formation of the metal film 58, the photoresist film 154 is removed. This removes the portion of the metal film 58 that covers the photoresist film 154. As a result, the top gate electrode TG is formed on the strip-shaped insulating film 128 (see Figure 16(b)). Furthermore, a source electrode S is formed in contact with one side of the strip-shaped MoS2 film 218, and a drain electrode D is formed in contact with the other side of the strip-shaped MoS2 film 218. In other words, the top gate electrode TG, the source electrode S, and the drain electrode D are formed by lift-off.

[0128] Through the above process, a top-gate type transistor 62 is completed, which has an active layer 60 having a MoS2 film 218, a top gate electrode TG, a source electrode S, and a drain electrode D.

[0129] The manufacturing method illustrated in Figures 14-16 is a method for manufacturing top-gate transistors. However, the manufacturing method illustrated in Figures 14-16 can also be applied to the manufacture of semiconductor devices other than top-gate transistors (for example, thermoelectric conversion elements) by changing, for example, the electrodes formed in the eighth step S8.

[0130] As described above, the manufacturing method according to Embodiment 2 comprises the first to fourth steps described in Embodiment 1, and an electrode formation step after the fourth step in which a plurality of electrodes (for example, a top gate electrode TG, a source electrode S, and a drain electrode D) are formed.

[0131] The manufacturing method according to Embodiment 2 comprises the first to fourth steps described in Embodiment 1. Therefore, according to the manufacturing method of Embodiment 2, a semiconductor device having an active layer 60 with fewer chalcogen atom defects can be manufactured. The active layer 60 is a metal chalcogenide film in which atomic defects are filled.

[0132] The manufacturing method according to Embodiment 2 preferably includes steps 5 to 7, similar to the manufacturing method according to Embodiment 1. Furthermore, one of the multiple electrodes (for example, the top gate electrode TG) is formed on the insulating film 128.

[0133] Steps 5 to 7 can suppress the degradation of the active layer 60 due to the atmosphere (see Embodiment 1). However, steps 5 to 7 may be omitted, as in Embodiment 1.

[0134] Although embodiments of the present invention have been described above, embodiments 1 and 2 are illustrative and not limiting. For example, the third step S3 illustrated in embodiments 1 and 2 is a step of transferring graphene (or hexagonal boron nitride) onto a chalcogenide film. However, the third step may also be a step of growing graphene (or hexagonal boron nitride) directly onto the chalcogenide film.

[0135] Furthermore, the metal chalcogenide films (e.g., MoS2 films) exemplified in Embodiments 1 and 2 do not contain any substances other than metal chalcogenides. However, the metal chalcogenide films in Embodiments 1 and 2 may contain substances other than metal chalcogenides.

[0136] For example, the metal chalcogenide film in Embodiments 1 and 2 may be a composite film having a metal (e.g., Mo) and a metal chalcogenide (e.g., MoS2) in that order. Such a composite film may be formed, for example, when forming a metal chalcogenide film by a thermal sulfidation method.

[0137] When forming a metal chalcogenide film by thermal sulfidation, if the metal film (e.g., Mo film 46) formed on the substrate 116 (see Figure 11) is too thick, unreacted metal (e.g., Mo) is left between the metal chalcogenide and the substrate 116. As a result, a metal chalcogenide film having metal chalcogenide (e.g., MoS2) and metal in that order is formed on the substrate 116.

[0138] The following additional information is disclosed regarding the embodiments 1 and 2 described above.

[0139] (Note 1) A first step involves forming a metal chalcogenide film having a compound of a metal and chalcogen on a substrate, A second step of forming a chalcogen film on the metal chalcogenide film, the chalcogen film having at least one of another chalcogen different from the chalcogen and the chalcogen, A third step involves arranging graphene or hexagonal boron nitride on the chalcogen film, The process includes a fourth step, after the third step, in which the chalcogen film and the metal chalcogenide film are heated. A method for producing chalcogenide-based layered materials.

[0140] (Note 2) The chalcogen and the other chalcogen are, respectively, one of sulfur, selenium, and tellurium. A method for producing a chalcogenide-based layered substance as described in Appendix 1, characterized by its features.

[0141] (Note 3) The chalcogen membrane is made of chalcogen alone. A method for producing a chalcogenide-based layered substance as described in Appendix 1, characterized by its features.

[0142] (Note 4) The chalcogen membrane is made of the other chalcogen alone. A method for producing a chalcogenide-based layered substance as described in Appendix 1, characterized by its features.

[0143] (Note 5) The chalcogen membrane includes both the chalcogen itself and the other chalcogen itself. A method for producing a chalcogenide-based layered substance as described in Appendix 1, characterized by its features.

[0144] (Note 6) A fifth step is performed after the fourth step, to remove the graphene or the hexagonal boron nitride, After the fifth step, a sixth step is performed to remove the chalcogen film in the exhausted space, The process further includes a seventh step of forming an insulating film on the metal chalcogenide film in the space after the sixth step, The space is to be continuously exhausted from the beginning of the sixth step to the end of the seventh step. A method for producing a chalcogenide-based layered substance as described in any one of the appendices 1 to 5.

[0145] (Note 7) The sixth step is the step of heating the chalcogen film in the space. A method for producing a chalcogenide-based layered substance as described in Appendix 6, which is characterized by this method.

[0146] (Note 8) The third step is a step of transferring the graphene or the hexagonal boron nitride to the chalcogen film. A method for producing a chalcogenide-based layered substance as described in any one of the appendices 1 to 7.

[0147] (Note 9) A method for manufacturing a semiconductor device having a metal chalcogenide film having a compound of a metal and a chalcogen, and a plurality of electrodes, The first step is to form the aforementioned metal chalcogenide film on a substrate, A second step of forming a chalcogen film on the metal chalcogenide film, the chalcogen film having at least one of another chalcogen different from the chalcogen and the chalcogen, A third step involves arranging graphene or hexagonal boron nitride on the chalcogen film, A fourth step is performed after the third step, in which the chalcogen film and the metal chalcogenide film are heated. The process includes, after the fourth step, an electrode formation step in which the plurality of electrodes are formed. A method for manufacturing a semiconductor device.

[0148] (Note 10) The chalcogen and the other chalcogen are, respectively, one of sulfur, selenium, and tellurium. A method for manufacturing a semiconductor device as described in Appendix 9.

[0149] (Note 11) A fifth step is performed after the fourth step, to remove the graphene or the hexagonal boron nitride, After the fifth step, a sixth step is performed to remove the chalcogen film in the exhausted space, The process further includes a seventh step of forming an insulating film on the metal chalcogenide film in the space after the sixth step, The aforementioned space is continuously evacuated from the beginning of the sixth step to the end of the seventh step. One of the plurality of electrodes is formed on the insulating film. A method for manufacturing a semiconductor device as described in Appendix 9 or 10. [Explanation of symbols]

[0150] 16: Circuit board 18:MoS2 film 20 :S membrane 22: Graphene 26: Space 28: Insulating film

Claims

1. A first step involves forming a metal chalcogenide film having a compound of a metal and chalcogen on a substrate, A second step is to form a chalcogen film on the metal chalcogenide film, the chalcogen film having at least one of another chalcogen different from the chalcogen and the chalcogen, A third step involves arranging graphene or hexagonal boron nitride on the chalcogen film, The process includes a fourth step of heating the chalcogen film and the metal chalcogenide film after the third step described above. The chalcogen and the other chalcogen are, respectively, sulfur, selenium, and tellurium. A method for producing chalcogenide-based layered materials.

2. The chalcogen membrane is made of chalcogen alone. A method for producing a chalcogenide-based layered substance as described in claim 1.

3. The chalcogen membrane is made of the other chalcogen alone. A method for producing a chalcogenide-based layered substance as described in claim 1.

4. The chalcogen membrane includes both the chalcogen itself and the other chalcogen itself. A method for producing a chalcogenide-based layered substance as described in claim 1.

5. A fifth step is performed after the fourth step, to remove the graphene or the hexagonal boron nitride, After the fifth step, a sixth step is performed to remove the chalcogen film in the exhausted space, The process further includes a seventh step of forming an insulating film on the metal chalcogenide film in the space after the sixth step, The space is to be continuously exhausted from the beginning of the sixth step to the end of the seventh step. A method for producing a chalcogenide-based layered substance as described in any one of claims 1 to 4.

6. A method for manufacturing a semiconductor device having a metal chalcogenide film having a compound of a metal and a chalcogen, and a plurality of electrodes, The first step is to form the aforementioned metal chalcogenide film on a substrate, A second step is to form a chalcogen film on the metal chalcogenide film, the chalcogen film having at least one of another chalcogen different from the chalcogen and the chalcogen, A third step involves arranging graphene or hexagonal boron nitride on the chalcogen film, A fourth step is performed after the third step, in which the chalcogen film and the metal chalcogenide film are heated. The process includes, following the fourth step, an electrode formation step in which the plurality of electrodes are formed, The chalcogen and the other chalcogen are, respectively, sulfur, selenium, and tellurium. A method for manufacturing a semiconductor device.

7. A fifth step is performed after the fourth step, to remove the graphene or the hexagonal boron nitride, After the fifth step, a sixth step is performed to remove the chalcogen film in the exhausted space, The process further includes a seventh step of forming an insulating film on the metal chalcogenide film in the space after the sixth step, The space is continuously evacuated from the beginning of the sixth step to the end of the seventh step. One of the plurality of electrodes is formed on the insulating film. A method for manufacturing a semiconductor device as described in claim 6.

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