Method of making a transition metal dichalcogenide film

Abstract

The present disclosure relates to a fabrication method for a crystalline 2D transition metal dichalcogenide (TMD) thin film. In one aspect, a co-deposition process is provided to form a first super-stoichiometric preliminary film through a sputtering-based process, followed by a flash-heat treatment in vacuum or in an inert gas environment, to form a clean and highly crystallized 2D TMD thin film. The process may be integrated for making functional devices continuously without interface contamination concern.

Description

[0001] PCT Application N3253.10202W001 (G4655)

[0002] METHOD OF MAKING A TRANSITION METAL DICHALCOGENIDE FILM

[0003] Inventor: Liping Ma

[0004] FIELD

[0005] The present disclosure generally relates to a method of making a transition metal dichalcogenide film, and more particularly but not exclusively relates to a method of making a sputtering-based transition metal dichalcogenide crystalline film.

[0006] BACKGROUND

[0007] Silicone based semiconductors find many uses across money different industries and technologies. Other new materials are emerging, including two- dimensional (2D) materials which include the combination of a transition metal and a chalcogen element (known as a transition metal dichalcogenide (2D TMD)). There are many combinations of transition metals and chalcogen elements, including for example M0S2 and WS2. TMDs may form polymorphic phases including insulating and semiconducting metallic and superconducting, and the phase transition among them makes it potential for many applications such as stress sensors, pressure sensors, and irradiation sensors, amongst others. 2D TMD materials have no surface dangling bonds, and no passivation is required. Further, 2D TMD materials may be stable in or as ultrathin and flexible devices, which makes it possible for 1 -2 nm thick CVMS technology other than Si-based semiconductors. Semiconducting TMD materials have a high charge carrier mobility, a tunable band gap and a high-light absorption coefficient, which may make them desirable for many optoelectronic devices such as photovoltaic devices, photo sensors, position sensors, and catalysts for water electrolysis hydrogen evolution, amongst others. The larger interlayer distance (about 6-7 A) in some 2D TMD materials may be suitable for intercalation, which can be used for gas sensors, bio sensors, metal-ion batteries, supercapacitors, molecules separation and water desalination. In addition, the weak interlayer force of some 2D TMD materials make them suitable for use as a solid-state lubricant. PCT Application

[0008] N3253.10202W001 (G4655)

[0009] While 2D TMD materials may have many promising qualities, widespread use thereof faces several challenges. For example, one or more of scalable production, a lack of production standards, production costs, material uniformity, purity, consistency, durability, and stability, integration with existing technologies, regulatory compliance, and environmental impact may all be factors in more widespread use of 2D TMD materials.

[0010] Regarding the fabrication of 2D TMD materials, MOCVD may be used (as disclosed in U.S. Patent No. 10,309,011 B2 for example) but suffers from the use of high substrate temperatures (up to 1000 °C) which limits substrate selection, and a transfer process is required for use of the TMD thin film to make functional devices. In addition, toxic gases such as H2S that are used as precursors in this process may cause environmental and safety concerns, and fabrication with many continuous layers with various materials for functional thin films and devices is another challenge for MOCVD.

[0011] A TMD thin film may also be fabricated using tube CVD (as disclosed in U.S. Patent No. 11 ,339,501 B2). In this process, a metal oxide or metal- chalcogen-oxide thin film on a substrate like sapphire that can withstand high temperatures is made, and then under a sulfurization or selenization process under high substate temperature (about 800 °C) the top layer of oxides may be converted into a TMD. However, the chalcogen vapor penetration depth into the metal oxide thin film is limited, so it can only convert a limited thickness of oxide into a TMD material, such as 10 nm. Further, after the sulfurization or selenization process, additional processing (such as laser ablation) is required to remove any extra sulphur coating on top of the converted TMD layer, and a transfer process may be needed to make functional devices. Due to the poor reproducibility of a transfer process for larger area TMD thin films, the tube CVD method may generally be considered to be limited to academic study, and as such may not be promising for widescale production of TMD materials for functional thin films and device applications.

[0012] ALD (atomic layer deposition) (as disclosed in U.S. Patent Nos. 10,916,426, 2021 and 11 ,649,545 B2 for example) has also been used in attempts to fabricate TMD thin films. However, the ALD process in the context of TMD thin film fabrication suffers due to poor chalcogen concentration, and a post PCT Application N3253.10202W001 (G4655) sulfurization or selenization process is required under toxic gas of H2S or H2Se environment.

[0013] Sputtering may be an approach for the commercialization of functional thin films and devices. Under sputtering-based TMD thin film fabrication involving the so-called preferential sputtering property, chalcogen deficiency may be present and the chalcogen over transition metal atomic ratio may be as low as 0.3 for sputtered sub-stoichiometric TMD thin film under pure Ar processing gas (Surface & Coatings Technology 252 (2014)186. Phys. Stat. Sol. (b) 245, No. 9, (2008)1745. Thin Solid Films 280, 67 (1996). Nature-Scientific Reports 2020. J. Appl. Phys. 101 , 103502 (2007)). This process also involves performing the addition of H2S with Ar as the processing gases during sputtering TMD and (b) a post tube-CVD treatment involving a sulfurization or selenization process under high substrate temperature (Superlattices and Microstructures 143 (2020)106555. J. Mater. Chem. C, 2016, 4, 7846), such as at 800 °C in an H2S environment or a sulphur gas environment (Nature-Scientific Reports 2020 10:771 ).

[0014] TMD thin films resulting from sputtering and post CVD treatment may need additional processing to remove any additional sulphur coating deposited on the TMD film. A transfer process is also generally required to make a functional device (Nature-Scientific Reports (2022) 12:11315). In addition, H2S is an extremely toxic gas where even 20 ppm concentration can kill people if inhaled, so the post tube- CVD sulfurization requires a special in-let gas line, processing chamber and exhaust gas treatment.

[0015] In view of the above, the use of conventional sputtering-based TMD thin- film fabrication technologies and other TMD thin film fabrication technologies suffer from a number of drawbacks, including for example: (1 ) a high substrate temperature; (2) a transfer process required for making functional devices; (3) use of extremely toxic processes involving H2S; (4) the ability to only make a single coating of TMD material so that many functional layers with different coating materials cannot be made; (5) and difficulties in making reproducible, high-yield and high-quality TMD thin films with controlled layer thickness. PCT Application

[0016] N3253.10202W001 (G4655)

[0017] SUMMARY

[0018] The current disclosure relates to a method for fabricating a two-dimensional (2D) transition metal dichalcogenide (TMD) thin film. In one form, the fabrication method may be based on a sputtering process. Amongst other things, the methods described herein may facilitate (1 ) use of a low substrate temperature (room temperature during sputtering may achieved), (2) use of non-toxic gasses during processing, (3) elimination of post-CVD treatment, (4) controlled layer thickness of the deposited 2D-TMD thin film from nano-to-micro meter scale, (5) production of a stoichiometric composition TMD (chalcogen element over transition metal element atomic ratio (C / M = 2.0 or about 2)), (6) production of highly crystallized 2D TMD films with horizontal orientation, and (7) elimination of transfer processes required for making functional devices.

[0019] In one embodiment, a method of making a transition metal dichalcogenide film, which may be a thin film, includes providing a target substrate in a vacuum chamber; co-depositing a first material and a second material onto a first surface of the target substrate to form a preliminary film; and applying a flash-heat treatment to the preliminary film in the vacuum chamber to form a crystalline transition metal dichalcogenide film. In one aspect, the preliminary film includes a super-stoichiometric composition and the crystalline transition metal dichalcogenide film includes a stoichiometric, or near stoichiometric, composition.

[0020] In one form, the vacuum chamber includes a first deposition source and a second deposition source. Further, co-depositing the first material and the second material may include sputtering the first material as a sputtering target material from the first deposition source onto the first surface of the target substrate and chemically depositing the second material from the second deposition source onto the first surface of the target substrate.

[0021] In some forms, the method may further include depositing a buffer layer onto the target substrate prior to depositing the first material and the second material onto the target substrate. In some forms, the buffer layer may include an adhesive layer in the form of an oxide layer, a nitride layer, a transition metal layer, or a combination thereof. In some forms, the buffer layer may have a thickness of less than about 10 nm. PCT Application

[0022] N3253.10202W001 (G4655)

[0023] In some embodiments, the first material or sputtering target material may include a first composition of the formula MCx, where M is a transition metal element, C is a chalcogen element, and 1 < x <3 is satisfied. In some embodiments, the sputtering target material may include one or more of M0S2, WS2, MoSe2, and WSe2.

[0024] In some forms, the first material or sputtering target material may include a second composition of the formula MCy, where M is a transition metal element, C is a chalcogen element, and y < x is satisfied.

[0025] In some embodiments, the second material may include a chalcogen material including a chalcogen solid-state material. The chalcogen solid-state material may include at least one of oxygen, sulfur, selenium, tellurium, and polonium.

[0026] In some forms, the temperature of the target substrate during co-depositing the first material and the second material may be less than about 300 °C. In some forms, application of the flash-heat treatment to the preliminary film may include emitting electromagnetic waves to be absorbed by the preliminary film in order to increase the temperature of the preliminary film. In some forms, the temperature of the preliminary film during application of the flash-heat treatment to the preliminary film is about 800 °C to about 1200 °C for less than about 100 seconds. In some forms, the flash-heat treatment may include a resistive heating source, an IR lamp heating source, a microwave heating source, a form of electromagnetic wave heating, or a combination thereof.

[0027] In some forms, the target substrate may include a glass, a polymer, a silicon wafer, a sapphire, or any other substrates that may be used in semiconductors. In some forms, the target substrate may include a target substrate material having a low melting point.

[0028] In some forms, the first deposition source may include a magnetron sputtering source, a pulsed laser deposition source, or an e-beam evaporation source. In some forms, the second deposition source may include a thermal evaporation source, an e-beam evaporation, a magnetro sputtering, or a pulsed laser deposition.

[0029] In one embodiment, a crystallized 2-dimensional transition metal dichalcogenide thin film is made according to a method described herein. In some PCT Application N3253.10202W001 (G4655) forms, the crystallized 2-dimensional transition metal dichalcogenide thin film may include an atomic ratio of chalcogen element over transition metal element of 2 or about 2. In some forms, the crystallized 2-dimensional transition metal dichalcogenide thin film may have a thickness from about 1 nm to about 1000nm.

[0030] In another embodiment, a semiconductor device may include a crystallized 2-dimensional transition metal dichalcogenide thin film described herein.

[0031] These and other embodiments are described in greater detail below.

[0032] BRIEF DESCRIPTION OF THE DRAWINGS

[0033] FIG. 1 is a schematic illustration of a process for co-deposition of materials.

[0034] FIG. 2 is a schematic illustration of a flash-heat treatment to the surface of a preliminary film in a vacuum chamber or in an inert gas environment.

[0035] FIG. 3 is a graphical illustration showing the Sulfur 2P peaks of X-ray photoelectron spectroscopy (XPS) measurements of an embodiment described herein for a deposited film before and after flash-heat treatment in vacuum

[0036] FIG. 4 is a graphical illustration showing the Sulfur 2S and Mo 3d peaks of X-ray photoelectron spectroscopy (XPS) measurements of an embodiment described herein.

[0037] FIG. 5 is a graphical illustration showing the XRD spectrum measurements of an embodiment described herein on a glass substrate.

[0038] FIG. 6 is a graphical illustration showing the light absorbance performance of an embodiment described herein on a glass substrate.

[0039] FIG. 7 is a graphical illustration showing the XRD spectrum measurements of an embodiment described herein on a Si wafer substrate.

[0040] DETAILED DESCRIPTION

[0041] The present disclosure generally relates to a method of making a transition metal dichalcogenide film, and more particularly but not exclusively relates to a method of making a sputtering-based transition metal dichalcogenide crystalline film.

[0042] It is to be understood that the embodiments disclosed herein do not thereby limit the scope of the disclosure; modifications and further applications of the disclosed principles as described herein are contemplated. PCT Application

[0043] N3253.10202W001 (G4655)

[0044] In one aspect, the present disclosure relates to a method for 2D TMD thin film fabrication based on a sputtering process. In one embodiment, a method of making a transition metal dichalcogenide film, which may be a thin film, is described. In some forms, the method of making a transition metal dichalcogenide thin film may be performed in a vacuum chamber where two deposition sources are positioned or provided. The first deposition source may be for sputtering deposition of a first material such as a sputtering target material of a transition metal dichalcogenide (such as one represented by MC2 where M represents a transition metal element and C represents a chalcogen element). The second deposition source may be for chemical deposition of a second material such as a chalcogen (C) material from a chalcogen source that contains a chalcogen solid- state material.

[0045] In one embodiment, a method of making a transition metal dichalcogenide thin film may include: providing a target substrate; co-depositing a first material and a second material onto the target substrate in an environment including the second material, wherein the co-depositing includes sputtering the first material at the target substrate and chemically depositing the second material onto the target substrate to form a preliminary film having a super-stoichiometric composition. In some forms, co-depositing the first material and the second material onto the target substrate may be done in an environment including the second material. In some forms, the first material may include a transition metal dichalcogenide material. In some forms, the second material may include a chalcogen material. In some forms, the method may also include applying a flash-heat treatment to the preliminary film under a vacuum and / or inert gas to form a crystalline transition metal dichalcogenide film having a stoichiometric composition where, by way of example, the stoichiometric composition of the crystalline transition metal dichalcogenide film includes an atomic ratio of the chalcogen element over the transition metal element which is less than the atomic ratio of the chalcogen element over the transition metal element in the super-stoichiometric composition of the preliminary film.

[0046] In one embodiment, a method of making a transition metal dichalcogenide thin film may include: providing a target substrate in a vacuum chamber; codepositing a first material and a second material onto a first surface of the target PCT Application N3253.10202W001 (G4655) substrate to form a preliminary film; and applying a flash-heat treatment to the preliminary film in the vacuum chamber to form a crystalline transition metal dichalcogenide film.

[0047] In some forms, the target substrate may be formed of any inorganic and / or organic material, and / or may be a material selected for having a low melting point such as glass and polymer substrates. In some forms, the target substrate may include a glass, a polymer, a silicon wafer, sapphire, or any suitable substrate that is commonly used in semiconductors.

[0048] In some forms, the vacuum chamber may include the first deposition source and the second deposition source. In some forms, co-depositing the first material and the second material may include sputtering the first material as a sputtering target material from the first deposition source onto a first surface of the target substrate and chemically depositing the second material from the second deposition source onto the first surface of the target substrate.

[0049] In some forms, the first deposition source may include a sputtering source. In some forms, the sputtering source may include a sputtering target material which may include a first composition of the formula MCx, where “M” is a transition metal element, “C” is a chalcogen element, and 1 < x <3 is satisfied. The transition metal element (M) may be any transition metal such as Mo, W, Zn, Ti, Pt, Ta, Or, V, Zr, Hf, Ni, Cu, Y, or a combination thereof. The chalcogen element (C) may be oxygen, sulfur, selenium, tellurium, polonium, or a combination thereof. In MCx, (x) may be the chalcogen concentration (the atomic ratio of the chalcogen element over the transition metal element) in the sputtering target material. In some forms, the first deposition source may include a magnetron sputtering source, a pulsed laser deposition source, or an e-beam evaporation source, just to provide a few non-limiting examples.

[0050] In some forms, the second deposition source may include a second material such as a solid-state chalcogen material. In some forms, the solid-state chalcogen material may include at least one of oxygen, sulfur, selenium, tellurium, and polonium.

[0051] In some forms, the first material may include M0S2, WS2, M0S2, WSe2, or a combination thereof. In some forms, the first material deposited on the first surface of the substrate may also include a second composition of the formula PCT Application

[0052] N3253.10202W001 (G4655)

[0053] MCy, where “M” is a transition metal element, “C” is a chalcogen element, and y < x, where “x” refers to the “x” in formula MCx. In some forms, the transition metal element (M) in MCy may be any transition metal element such as Mo, W, Zn, Ti, Pt, Ta, Cr, V, Zr, Hf, Ni, Cu, Y, or a combination thereof. In some forms, the chalcogen element (C) in MCy may include oxygen, sulfur, selenium, tellurium, polonium, or a combination thereof.

[0054] In some forms, the co-deposition of the first material and the second material onto the first surface of the target substrate forms a preliminary film. In some forms, the preliminary film may be formed on the first surface of the target substrate by co-deposition from sputtering the first material as a sputtering target material and thermal evaporation of the second material. In some forms, the preliminary film may include a super-stoichiometric composition (MCz) where M is a transition metal and C is a chalcogen element. In some forms, (z) in the super- stoichiometric composition MCz may be greater than about 2, greater than about 2.2, greater than about 2.5, greater than about 3, greater than about 3.5, greater than about 4.0, greater than about 4.5, greater than about 5.0, greater than about 5.5, or any super-stoichiometric composition bounded by these ranges.

[0055] In some forms, co-depositing the first material and the second material onto the target substrate may include chemically depositing the second material onto the target substrate in an environment including the second material. For example, an environment including the second material may be contained within a vacuum chamber and may be filled by the second deposition source with the second material. During sputtering the first material at the target substrate, the second material may be deposited onto the first surface of the target substrate via the second deposition source, and the second material may be evaporated under heating. The second deposition source may include e-beam evaporation, magnetro sputtering, or pulsed laser deposition, just to provide a few non-limiting examples.

[0056] In some forms, the method may further include depositing a buffer layer onto the target substrate prior to depositing the first material and the second material onto the target substrate. As such, in some forms a buffer layer may be deposited between the first surface of the substrate and the preliminary film. In some forms, the buffer layer may include an adhesive layer. In some forms, the PCT Application N3253.10202W001 (G4655) buffer layer may include an oxide layer, a nitride layer, a transition metal layer, or a combination thereof. In some forms where the buffer layer includes a transition metal layer, it may include molybdenum.

[0057] Without being bound to any particular dimension, the buffer layer may have a thickness of less than about 10 nm, less than about 5 nm, less than about 4 nm, less than about 2 nm, or any thickness bounded by these ranges.

[0058] Further, the buffer layer may provide an adhesive function. In some forms, the adhesion between the target substrate and the primary film may be sufficient under the flash-heat treatment so the buffer layer may function as an adhesive layer to keep the crystalline transition metal dichalcogenide film uniform on the target substrate after the flash-heat treatment.

[0059] Application of the flash-heat treatment to the preliminary film in the vacuum chamber may form a crystalline transition metal dichalcogenide film. In some forms, application of the flash-heat treatment to the preliminary film may be performed with a heating source facing the first surface of the target substrate. In some forms, the flash-heat treatment may include application of an electromagnetic wave onto a surface of the preliminary film during a short period of time. During this period of time, the preliminary film may absorb the electromagnetic waves and the electromagnetic waves may be transferred into heat, resulting in locally heating the preliminary film. Stated alternatively, the heating may be focused on or limited to the preliminary film itself, and not to the underlying substrate. The temperature of the preliminary film during application of the flash-heat treatment to the surface of the preliminary film may be less than one second at a higher intensity of incident electromagnetic waves. In some forms, the temperature of the preliminary film during application of the flash-heat treatment may be about 600 °C, about 700 °C, about 800 °C, about 900 °C, about 1000 °C, about 1200 °C, about 1300 °C, and / or any permutation of the aforementioned values, e.g., 800 °C to 1200 °C, for less than about 100 seconds, less than about 30 seconds, or less than about 1 second. In some forms, the period of time for during which the flash-heat treatment is applied may be in the sub-second range; e.g., from about 0.1 seconds to about 1 second. In some other forms, the period of time during which the flash-heat treatment is applied may be in the microsecond range; e.g., from about 1 microsecond to about 100 microseconds. In some forms, PCT Application N3253.10202W001 (G4655) the period of time during which the flash-heat treatment is applied to the surface of the preliminary film may be less than one second at a higher intensity of incident electromagnetic waves.

[0060] Application of the flash-heat treatment to the preliminary film may include emitting electromagnetic waves to be absorbed by the preliminary film, where the electromagnetic waves cause the temperature of the preliminary film to increase and form a crystalline transition metal dichalcogenide film. The electromagnetic waves may be provided by an IR lamp heating source, a microwave heating source, or laser, just to provide a few non-limiting examples. In some embodiments, the crystalline transition metal dichalcogenide film may include a stoichiometric composition (MC2), although other variations in the quantity of C are possible and contemplated. For example, C may be present at about 2, for example in a range of about 1.9 to about 2.1 , although other variations are contemplated and possible. Further, by way of example, the stoichiometric composition of the crystalline transition metal dichalcogenide film may include an atomic ratio of the chalcogen element over the transition metal element which is less than the atomic ratio of the chalcogen element over the transition metal element in the super-stoichiometric composition of the preliminary film. Similarly, if the stoichiometric composition of the crystalline transition metal dichalcogenide film includes an atomic ratio of the chalcogen element over the transition metal element which is 2, or about 2, then the atomic ratio of the chalcogen element over the transition metal element in the super-stoichiometric composition of the preliminary film is greater than 2, or greater than about 2.

[0061] It is contemplated that in some forms the flash-heat treatment may be so quick that the temperature of the target substrate may be much lower than the surface temperature of the preliminary film. By way of non-limiting example, the temperature of the target substrate during the flash-heat treatment may be less than about 200 °C, less than about 300 °C, less than about 400 °C, or less than about 800 °C. During co-deposition of the first material and the second material, the temperature of the target substrate may increase to a temperature less than the condensation temperature of the chalcogen element and / or to a temperature higher than its condensation temperature. PCT Application

[0062] N3253.10202W001 (G4655)

[0063] The flash-heat treatment may be performed by a variety of sources, nonlimiting examples of which include a resistive heating source, an IR lamp heating source, a laser, a form of electromagnetic wave heating such as microwave heating, or a combination thereof. In some forms, the flash-heat treatment may be any kind of heating source that may emit an electromagnetic wave that can be transferred into heat when it is absorbed by the preliminary film.

[0064] Application of the flash-heat treatment may be done under vacuum without inlet of any chalcogen gases in some forms. The pressure in the vacuum chamber may be about 10’1torr, about 10’2torr, about 10’3torr, about 10’4torr, about 10’5torr, or about 10’6torr. Application of the flash-heat treatment may done under inert gas such as Ar. In some forms, the flash-heat treatment may be applied in the same vacuum chamber as the vacuum chamber used for co-depositing the first material and the second material. In some forms, the flash-heat treatment may be applied in a connecting processing chamber.

[0065] In some forms, due to the lower temperature of the target substrate during fabrication of the crystalline transition metal dichalcogenide film, high- temperature-tolerance substrates (higher than 800 °C) such as sapphire may not be necessary. For example, in some forms target substrates such as glass and polymer substrates may be used for fabrication of flexible electronic and optoelectronic device applications. In some forms, fabrication of the crystalline transition metal dichalcogenide film may be done on Si-wafer based electronics without damaging other integrated circuits.

[0066] While not previously discussed, it should be appreciated that the whole process of the deposition of the preliminary film and the flash-heat-treatment may be done continuously in a fabrication system. In some forms, the preliminary film may include both a transition metal element, e.g., Mo, W, Zn, Ti, Pt, Ta, Cr, V, Zr, Hf, Ni, Cu, and / or Y, and a chalcogen element, e.g., oxygen, sulfur, selenium, tellurium, and / or polonium, with an atomic ratio of the chalcogen element over the transition metal element greater than 2, or great than about 2, forming a super- stoichiometric composition preliminary film layer. In some forms, the preliminary film may undergo a composite change, phase change and crystallization process during the flash-heat treatment. In some forms, the preliminary film after the flashheat treatment may have an atomic ratio of the chalcogen element over the PCT Application

[0067] N3253.10202W001 (G4655) transition metal element of 2, or of about 2.0, forming a stoichiometric composition. By way of example, the preliminary film after the flash-heat treatment may have an atomic ratio of the chalcogen element over the transition metal element which is less than the atomic ratio of the chalcogen element over the transition metal element in the preliminary film before the flash-heat treatment. In some forms, after the flash-heat treatment the preliminary film may be highly crystallized; e.g., it may become a crystalline transition metal dichalcogenide film. By way of example, the crystalline transition metal dichalcogenide film may be a highly horizontal crystalline transition metal dichalcogenide film. In some forms, the thickness of the preliminary film may be well controlled from less than about 5 nm to about 1 micrometer. In some forms, the crystalline transition metal dichalcogenide film can be as thin as a monolayer for nanoelectronic devices. In some forms however, the crystalline transition metal dichalcogenide film can be thicker, e.g. about 100 nm to about 1 micrometer, to have more light absorption for photonic device applications. In various forms, the concentration of the chalcogen element can be controlled to form a sub-stoichiometric composition, a stoichiometric composition, or a super-stoichiometric composition to tune the electronic properties of the crystalline transition metal dichalcogenide film for various different applications.

[0068] In some forms, a semiconductor device may be fabricated continuously with formation of the crystalline transition metal dichalcogenide film. In some forms, a fabrication system can be made to fabricate various functional layers with different materials including the transition metal dichalcogenide continuously for the fabrication of a functional device. Non-limiting examples of the functional device may include a solar cell, photo sensor, and semiconductor building block (such as a transistor or diode capacitor). In some forms, fabrication methods described herein do not involve toxic gases that cause safety and environmental concerns.

[0069] One non-limiting example of a set-up for a method of fabrication of a transition metal dichalcogenide thin film is shown in FIG. 1 and FIG. 2. Generally speaking, FIG.1 relates to the formation of a preliminary film 102 through a codeposition process where the target substrate 101 is loaded in a vacuum chamber which includes a first deposition source and a second deposition source. The PCT Application N3253.10202W001 (G4655) preliminary film 102 may have a super-stoichiometric composition where the atomic ratio of a chalcogen element over a transition metal element is greater than 2.0, or about 2, for example. A first deposition source 104 which may be a transition metal dichalcogenide deposition source and a second deposition source 103 which may be a chalcogen deposition source may be used for co-depositing a first material from the first deposition source 104 and a second material from the second deposition source 103 onto a surface of the target substrate 101 to form the preliminary film 102. The preliminary film 102 may have a chemical composition of MCy, where M represents the transition metal, C represents the chalcogen element, and “y” represents the atomic ratio of chalcogen over transition metal. In the preliminary film 102, ”y” is larger than 2 or about 2 for example.

[0070] FIG. 2 relates to flash-heat treatment of the preliminary film 102. For example, the preliminary film 102 may face a heating source 105, and the heating source 105 may produce electromagnetic waves that can be absorbed by the preliminary film 102 where the electromagnetic waves transfer into heat and locally heat up the preliminary film 102. The heating power and the heating period may be tuned in such a way that the preliminary film 102 will undergo a phase forming and crystallization process to form a crystalline 2-dimensional TMD thin film. Excessive chalcogen element may be evaporated from the preliminary film resulting in a pure, uniform, crystalline 2D TMD thin film with a desired stoichiometric composition of 2, or about 2, where, by way of example, the atomic ratio of the chalcogen element over the transition metal element in the crystalline 2D TMD thin film is less than the atomic ratio of the chalcogen element over the transition metal element in the preliminary film 102.

[0071] In one embodiment, a crystallized 2-dimensional transition metal dichalcogenide thin film made according to a method described herein is provided. In some forms, the crystallized 2-dimensional transition metal dichalcogenide thin film may include an atomic ratio of chalcogen over transition metal of 2, or about 2. In some forms, the crystallized 2-dimensional transition metal dichalcogenide thin film may have a thickness from about 1 nm to about 1000 nm.

[0072] In another embodiment, a semiconductor may include a stoichiometric composition film described herein. PCT Application

[0073] N3253.10202W001 (G4655)

[0074] EXAMPLES

[0075] It has been discovered that the subject matter described herein may provide 2D TMD thin films having desired properties and characteristics. The following Examples illustrate the formation of a highly crystallized stoichiometric composition 2D TMD thin film. Further, the Examples do not require post CVD treatment and hence avoid the drawbacks thereof including excess chalcogen material, high substrate temperatures and the use of toxic gases during the post CVD treatment. The process described involves a low substrate temperature which allows the preliminary film deposition to be performed at room temperature, while the flash-heat treatment in vacuum mainly locally heats up the preliminary film and not the substrate itself due to a very short heating period from the film side which increases the number of possible material candidates for the substrate. The foregoing is further demonstrated by the following Examples. It should be appreciated that the following Examples are for illustration purposes and are not intended to be construed as limiting the subject matter disclosed in this document to only the embodiments disclosed in these examples.

[0076] Preparation of Glass / Mo(1nm) / MoSx (100nm) by co-deposition of sputtering M0S2 and thermal evaporation of Sulphur

[0077] Example 1

[0078] A preclean glass substrate was loaded into a deposition chamber with a base vacuum of about 1 x 10’6torr. The substrate was kept at environmental or room temperature without heating or cooling. A buffer layer or adhesive layer for TMD to the glass substrate was first added by sputtering Mo from an Mo sputtering target at 0.2A / s, for 1 nm thickness. This was followed by co-depositing Sulphur and M0S2-X at a vacuum level of about 5 mtorr. The Sulphur deposition was through a thermal source containing a heating crucible and Sulphur pellets, with the crucible heating up to about 70 °C where the sulphur starts to sublimit and the rate is a nominal rate controlled to about 0.5 A / s reading from a thickness monitor. The M0S2-X was deposited through sputtering from an M0S2 target with a deposition rate of about 1 A / s reading from a thickness monitor. The real thickness of the deposited TMD film was calibrated to be about 100 nm. The deposited TMD film is named AS-deposited. After that in the same deposition chamber a flash heat treatment was done in a vacuum of about 1 x 10’6torr by putting the deposited PCT Application

[0079] N3253.10202W001 (G4655)

[0080] TMD sample near a W-heating filament with the surface of the deposited film facing the heating filament. The distance between the TMD surface and the W- heating filament was about 1 cm. By applying 45% heating power from a transformer, the surface peak temperature of the TMD film may reach about 800 °C, and the total heating duration from beginning to end was about 30 seconds. The TMD sample after such Flash-heat treatment is named Flash-heat treated.

[0081] X-ray photoelectron spectroscopy (XPS) measurements for Example 1 are shown in FIGs. 3-4. The AS-deposited film of Example 1 had a super stoichiometric composition where the Chalcogen over transition metal (C / M) atomic ratio is 5.68. After flash-heat treatment, the flash-heat treated TMD of Example 1 had a stoichiometric composition of C / M atomic ratio of 2.04. An XRD spectrum of the flash-heat treated TMD of Example 1 is shown in FIG. 5. The flash-heat treated TMD of Example 1 has an XRD peak at 14.33° which is exactly the same as the M0S2 2H phase (002) peak showing that after the flash-heat treatment the flash-heat treated TMD of Example 1 is a 2D M0S2 with horizontal orientation. The As-deposited film of Example 1 is amorphous. FIG. 6 is a graph depicting the light absorbance performance of the TMD of Example 1 before and after the flash-heat treatment, showing the semiconductor band gap-like phase forming after the flash-heat treatment.

[0082] Si-wafer / MoSx (100nm) by co-deposition of sputtering M0S2 and thermal evaporation of Sulphur.

[0083] Example 2

[0084] Device fabrication of Example 2 is similar as Example 1 except that the substrate was pre-cleaned Si-wafer substrate and the buffer layer of Mo(1 nm) was skipped for Example 2. On the Si wafer substrate, the TMD thin film exhibited better crystallinity. FIG. 7 provides a graph depicting the XRD spectrum of Example 2.

[0085] Use of the term “may” or “may be” or “can” should be construed as shorthand for “is” or “is not” or, alternatively, “does” or “does not” or “will” or “will not,” etc. For example, the statement “a thermally conductive composite may further comprise a backing layer” should be interpreted as, for example, “In some embodiments, a thermally conductive composite further comprises a backing PCT Application

[0086] N3253.10202W001 (G4655) layer,” or “In some embodiments, a thermally conductive composite does not further comprise a backing layer.”

[0087] Unless otherwise indicated, all numbers expressing quantities of ingredients, properties, such as, molecular weight, reaction conditions, and so forth used in the specification and embodiments are to be understood as being modified in all instances by the term “about.” The term “about” as used herein, can include any numerical value that can vary without changing the basic function of that value. When used with a range, “about” also discloses the range defined by the absolute values of the two endpoints. The term “about” may refer to plus or minus 10% of the indicated number.

[0088] Accordingly, unless indicated to the contrary, the numerical parameters set forth in the specification and attached embodiments are approximations that may vary depending upon the desired properties sought to be obtained. At the very least, and not as an attempt to limit the application of the doctrine of equivalents. To the scope of the embodiments, each numerical parameter should at least be construed in light of the number of reported significant digits and by applying ordinary rounding techniques.

[0089] For the processes and / or methods disclosed, the functions performed in the processes and methods may be implemented in differing order, as may be indicated by context. Furthermore, the outlined steps and operations are only provided as examples, and some of the steps and operations may be optional, combined into fewer steps and operations, or expanded into additional steps and operations.

[0090] This disclosure may sometimes illustrate different components contained within, or connected with, different other components. Such depicted architectures are merely examples, and many other architectures can be implemented which achieve the same or similar functionality.

[0091] The terms used in this disclosure, and in the appended embodiments, are generally intended as “open” terms (e.g., the term “including” should be interpreted as “including, but not limited to,” the term “having” should be interpreted as “having at least,” the term “includes” should be interpreted as “includes, but is not limited to,” etc.). In addition, if a specific number of elements is introduced, this may be interpreted to include at least the recited number, as may be indicated by context PCT Application

[0092] N3253.10202W001 (G4655)

[0093] (e.g., the bare recitation of "two recitations," without other modifiers, includes at least two recitations, or two or more recitations). As used in this disclosure, any disjunctive word and / or phrase presenting two or more alternative terms should be understood to contemplate the possibilities of including one of the terms, either of the terms, or both terms. For example, the phrase “A or B” will be understood to include the possibilities of “A” or “B” or “A and B.”

[0094] The terms and words used herein are not limited to the bibliographical meanings but are merely used to enable a clear and consistent understanding of the disclosure. The terms “a,” “an,” “the” and similar referents used in the context of describing the present disclosure (especially in the context of the following embodiments) are to be construed to cover both the singular and the plural, unless otherwise indicated herein or clearly contradicted by context. The use of any and all examples, or representative language (e.g., “such as”) provided herein is intended merely to better illuminate the present disclosure and does not pose a limitation on the scope of any embodiments. No language in the specification should be construed as indicating any non-embodied element essential to the practice of the present disclosure.

[0095] Groupings of alternative elements or embodiments disclosed herein are not to be construed as limitations. Each group member may be referred to and embodied individually or in any combination with other members of the group or other elements found herein. It is anticipated that one or more members of a group may be included in, or deleted from, a group for reasons of convenience and / or patentability. When any such inclusion or deletion occurs, the specification is deemed to contain the group as modified thus fulfilling the written description of all Markush groups used in the appended embodiments.

[0096] Certain embodiments are included herein, including the best mode known to the inventors for carrying out the present disclosure. Of course, variations on these described embodiments, will become apparent to those of ordinary skill in the art upon reading the foregoing description. The inventor expects skilled artisans to employ such variations as appropriate, and the inventors intend for the present disclosure to be practiced otherwise than specifically described herein. Accordingly, the embodiments include all modifications and equivalents of the subject matter recited in the embodiments as permitted by applicable law. PCT Application N3253.10202W001 (G4655)

[0097] Moreover, any combination of the above-described elements in all possible variations thereof is contemplated unless otherwise indicated herein or otherwise clearly contradicted by context. In closing, it is to be understood that the embodiments disclosed herein are illustrative of the principles of the embodiments. Other modifications that may be employed are within the scope of the embodiments. Thus, by way of example, but not of limitation, alternative embodiments may be utilized in accordance with the teachings herein. Accordingly, the embodiments are not limited to the embodiments precisely as shown and described.

[0098] By the term "substantially" it is meant that the recited characteristic, parameter, or value need not be achieved exactly, but that deviations or variations, including for example, tolerances, measurement error, measurement accuracy limitations and other suitable factors, may occur in amounts that do not preclude the effect the characteristic was intended to provide.

[0099] Aspects of the present disclosure may be embodied in other forms without departing from its spirit or essential characteristics. The described aspects are to be considered in all respects illustrative and not restrictive. The embodied subject matter is indicated by the appended embodiments rather than by the foregoing description. All changes, which come within the meaning and range of equivalency of the embodiments, are to be embraced within their scope.

Claims

PCT ApplicationN3253.10202W001 (G4655)CLAIMSWhat is claimed is:

1. A method of making a transition metal dichalcogenide thin film, comprising: providing a target substrate including a first surface in a vacuum chamber including a first deposition source and a second deposition source; co-depositing a first material and a second material onto the first surface of the target substrate to form a preliminary film comprising a super-stoichiometric composition, wherein co-depositing the first material and the second material comprises sputtering a sputtering target material from the first deposition source onto the first surface of the target substrate and chemically depositing the second material from the second deposition source onto the first surface of the target substrate; and applying a flash-heat treatment to the preliminary film in the vacuum chamber to form a crystalline transition metal dichalcogenide film comprising a stoichiometric composition.

2. The method of claim 1 , further comprising depositing a buffer layer onto the target substrate prior to depositing the first material and the second material onto the target substrate.

3. The method of claim 2, wherein the buffer layer comprises an adhesive layer.

4. The method of claim 2, wherein the buffer layer comprises at least one of an oxide layer, a nitride layer, and a transition metal layer.

5. The method of claim 2, wherein the buffer layer includes a thickness of less than about 10 nm.

6. The method of claim 1 , wherein the sputtering target material comprises a first composition of the following formula:MCxPCT Application N3253.10202W001 (G4655) wherein M is a transition metal element, C is a chalcogen element, and 1 < x < 3 is satisfied.

7. The method of claim 6, wherein the sputtering target material comprises at least one of M0S2, WS2, MoSe2, and WSe2.

8. The method of claim 6, wherein the first material further comprises a second composition of the following formula:MCy wherein M is a transition metal element, C is a chalcogen element, and y < x is satisfied.

9. The method of claim 1 , wherein the second material comprises a chalcogen material, and the chalcogen material comprises a chalcogen solid-state material comprising at least one of oxygen, sulfur, selenium, tellurium, and polonium.

10. The method of claim 1 , wherein the temperature of the target substrate during co-depositing of the first material and the second material is less than about 300 °C.11 . The method of claim 1 , wherein applying the flash-heat treatment to the preliminary film comprises emitting electromagnetic waves absorbable by the preliminary film and increasing the temperature of the preliminary film with the electromagnetic waves.

12. The method of claim 1 , wherein the temperature of the preliminary film during application of the flash-heat treatment to the preliminary film is about 800 °C to about 1200 °C for less than about 100 seconds.

13. The method of claim 1 , wherein the flash-heat treatment comprises heat from at least one of a resistive heating source, an IR lamp heating source, a microwave heating source, and an electromagnetic wave heating source.PCT ApplicationN3253.10202W001 (G4655)14. The method of claim 1 , wherein the target substrate comprises at least one of a glass, a polymer, a silicon wafer, and a sapphire.

15. The method of claim 1 , wherein the first deposition source comprises one of a magnetro sputtering source, a pulsed laser deposition source, and an e- beam evaporation source.

16. The method of claim 1 , wherein the second deposition source comprises one of a thermal evaporation source, an e-beam evaporation source, a magnetro sputtering source, and a pulsed laser deposition.

17. The method of claim 1 , wherein the crystalline transition metal dichalcogenide film includes an atomic ratio of a chalcogen element over a transition metal element which is less than an atomic ratio of the chalcogen element over the transition metal element in the preliminary film.

18. A crystallized 2-dimensional transition metal dichalcogenide thin film made according to the method of any one of claims 1 -17.

19. The crystallized 2-dimensional transition metal dichalcogenide thin film of claim 18, comprising an atomic ratio of a chalcogen element over a transition metal element of about 2.0.

20. The crystallized 2-dimensional transition metal dichalcogenide thin film of claim 18, comprising a thickness from about 1 nm to about 1000 nm.

21. A semiconductor device, comprising a crystallized 2-dimensional transition metal dichalcogenide thin film of any one of claims 18-20.

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