Process for depositing a thin layer of sulfide of a transition metal or one of its alloys

Abstract

Method for depositing a thin layer of sulfide of a transition metal or one of its alloys The present description relates to a method for vapor deposition of a sulfide layer of a transition metal by ALD according to the following cycle: - exposing a substrate to a precursor of the transition metal, whereby an intermediate layer is formed, - purging the reactor, - exposing the intermediate layer to a sulfur precursor, - purging the reactor, the substrate being at a temperature between 20°C and 250°C during the cycle, The cycle can be repeated several times with the same precursors or with different precursors, the precursor of the transition metal being chosen from molybdenum oxyhalides, tungsten oxyhalides, vanadium halides, niobium halides and tantalum halides. Figure for abstract: Fig. 2

Description

Title of the invention: Method for depositing a thin layer of sulfide of a transition metal or one of its alloys Technical field

[0001] The present description relates generally to the deposition of thin layers of transition metal sulfides, in particular thin layers of molybdenum, tungsten, vanadium, niobium or tantalum sulfide and / or one of their alloys. Such layers are particularly interesting in the microelectronics industry. Prior art

[0002] Transition metal dichalcogenides (TMDs) are currently attracting great interest due to their unique optoelectronic properties when isolated in the form of one or a few atomic monolayers, and their potential for the miniaturization and functional diversification of electronic components. In particular, the use of semiconductor TMDs such as MoS2 and WS2 would allow further miniaturization of transistors by offering better electrostatic control than silicon on channel dimensions below 10 nm.

[0003] The production of such components is currently limited by the difficulty of integrating the TMD material without degrading its structure or altering its properties. The lamellar structure of TMDs and the resulting low adhesion also generate numerous integration issues linked to the high complexity of the lithography steps. In this context, it appears important to develop TMD deposition methods allowing their deployment in 3D architectures (as opposed to the strategy which consists of growing the TMD on a dedicated substrate and then transferring it to a planarized structure), in order to be able to protect the TMD material throughout the integration steps and guarantee its integrity. Another critical point in the production of devices based on semiconductor TMDs is the difficulty of making efficient electrical contacts.

[0004] Semi-metallic TMDs such as VSX (notably VS2, V3S4 and V5S8 and all other VS2 self-intercalation compounds), NbS2 or TaS2 are among the most efficient metals for contacting MoS2 or WS2 with low contact resistance. They also have the advantage of being very similar to MoS2 and WS2 both chemically and crystallographically, and therefore of forming a clean, low-stress, thermally stable interface, free of other heteroelements such as oxygen or nitrogen that could alter the properties of the TMD. Finally, group 5 elements (V, Nb, Ta) make it possible to induce p-type doping in semi-metallic TMDs. group 6 conductors (MoS2 and WS2, naturally n-doped by the presence of sulfur vacancies) and thus control the polarity of the charge carriers.

[0005] Currently, two main routes for the production of thin layers of transition metal sulfide exist.

[0006] A first way consists of depositing the material by chemical vapor deposition (or CVD for 'Chemical Vapor Deposition').

[0007] For example, in application US 2019 / 0378898 A1, CVD is used to deposit layers of MoS2 and WS2. The precursors are, for example, Mo(CO)6 and W(C0)6 and diethyl sulfide.

[0008] However, with CVD deposition, it is difficult to obtain good control of the nucleation and therefore of the uniformity of the deposited layer. In addition, it is not possible to deposit TMD layers on substrates with high form factor architectures (in nano-cavities for example). The introduction of group 5 metals as dopant or the production of heterostructures of TMDs of groups 5 and 6 is also difficult to implement in CVD because the deposition conditions directly target the formation of crystals having the correct crystalline phase, and each material will require a very precise adjustment of the temperature and the partial pressures of reagents.

[0009] A second route consists of depositing the material by atomic layer deposition (ALD). For this type of deposition, the precursors are used sequentially and not in a mixture as in the case of CVD deposition. ALD deposition allows for good control of uniformity even in architectures with a large form factor, and allows more easily than CVD the formation of heterostructures or the mixing of several metals to form alloys of well-defined composition. However, in order to ensure uniform growth of ultra-thin (typically less than 5 nm) and continuous TMD layers by ALD, the material must be deposited amorphously (therefore at low temperature), which implies the need for a post-deposition crystallization annealing step. The material obtained by this 2-step process typically has a smaller grain size than materials obtained by CVD growth.Optionally, a thermal sulfurization step before or during annealing allows the stoichiometry of the TMD to be corrected if necessary.

[0010] For example, document US 2015 / 0211112 Al describes the deposition of MoS2 by ALD. The Mo precursors are non-halogenated mono-metallic or bi-metallic compounds. These compounds are non-halogenated. The sulfur co-reactant is H2S or 1,2-ethanedithiol. An optional crystallization annealing can be implemented after deposition.

[0011] According to another example, document US 11,142,824 B2 describes the deposition of a layer of molybdenum metal by low-temperature ALD (below 300°C) using the precursor pair MoF6 / Si2H6. The molybdenum layer is then converted into MoS2 by a sulfurization heat treatment under H2S at a temperature between 300 and 600°C.

[0012] In document US 9,863,039 B2 a layer of MoS2 is formed by sequentially depositing the precursors Mo(CO)6 and dimethyl sulfide at a temperature of 100-120°C. The heat treatment to crystallize the MoS2 layer is carried out at a temperature between 400 and 1000°C.

[0013] Document WO 2016 / 191432 A1 describes a method for the ALD deposition of TMD layers, in particular Mo and W sulfides, selenides and tellurides. The Mo and W precursors are beta-diketonates, and the chalcogen precursors are, for example, H2S, H2Se or H2Te, Me2S, Me2Se and Me2Te. The deposition temperature is preferably between 250 °C and 600 °C. Several ALD depositions have been carried out using the Mo(thd)3 and H2S precursors with deposition temperatures ranging from 175 °C to 500 °C. No MoS2 deposition was observed at deposition temperatures between 175 °C and 350 °C. The amount of film deposited on the substrates seems to increase from 375 °C. The highest growth rates were obtained at a deposition temperature of about 500°C.

[0014] It may however be noted that the deposition temperatures used in some of these processes can lead to the growth of a directly crystalline material (typically when the deposition temperature is higher than 150-200°C), which is not optimal for obtaining ultra-thin layers (having a thickness of less than 5 nm), smooth (not very rough) and continuous.

[0015] Furthermore, the majority of these methods do not allow the deposition of heterostructures or alloys associating transition metals from groups 5 and 6. Summary of the invention

[0016] There is a need for a deposition method for forming a layer of transition metal sulfide or one of its alloys having low roughness and good crystalline quality.

[0017] This aim is achieved by a process for vapor deposition of a sulfide layer of a transition metal or one of its alloys, the process comprising a step of deposition of atomic layers according to the following cycle: - exposing a substrate to a precursor of a transition metal, whereby an intermediate layer is formed on the substrate, - purge the reactor, - expose the intermediate layer to a sulfur precursor, - purge the reactor, the substrate being at a temperature between 20°C and 250°C during the cycle, the cycle being able to be repeated several times, the transition metal precursor and / or the sulfur precursor being able to be identical or different during the repetitions of the cycle, the transition metal precursor being chosen from molybdenum oxyhalides, tungsten oxyhalides, vanadium halides, niobium halides and tantalum halides.

[0018] According to a particular embodiment, the precursor of the transition metal is chosen from MoO2C12, MoOC14, WOCI4, VC14, NbCl5 and TaCl5.

[0019] According to a particular embodiment, the sulfur precursor is chosen from hydrogen sulfide, hydrogen polysulfides and thiols, preferably dithiols.

[0020] According to a particular embodiment, the sulfur precursor is chosen from 1,2-ethanedithiol, 1,2-propanedithiol and 1,3-propanedithiol.

[0021] According to a particular embodiment, after the atomic layer deposition step, the method comprises a sulfurization step during which the substrate is exposed to a sulfur molecule having at least one sulfur-hydrogen or sulfur-carbon bond, at a temperature between 250°C and 1150°C, preferably between 300°C and 400°C.

[0022] Advantageously, the sulfur molecule is a dithiol, preferably 1,2-ethanedithiol.

[0023] According to a particular embodiment, after the atomic layer deposition step, or after the sulfurization step, an annealing step is implemented.

[0024] Advantageously, the annealing step is carried out under an inert atmosphere at a temperature between 400°C and 1150°C, preferably between 650°C and 950°C.

[0025] According to a particular embodiment, the substrate is at a temperature between 50°C and 150°C, preferably between 80°C and 120°C, during the cycle.

[0026] According to a particular embodiment, the precursor of the transition metal is chosen from MoO2C12, MoOC14, WOCI4 and VC14 and in that the precursor of the sulfur is 1,2-ethanedithiol.

[0027] This aim is also achieved by a device comprising a substrate covered by a thin crystalline layer of molybdenum, tungsten, vanadium, niobium, tantalum sulfide or one of their alloys such as Mo(V)S2 or W(V)S2, the thin layer having a thickness of less than 100 nm, preferably less than 20 nm, even more preferably less than 10 nm, the crystals of the thin layer being oriented, their crystallographic plane (001) being parallel to the plane of the substrate. Brief description of the drawings

[0028] These and other features and advantages will be set forth in detail in the following description of particular embodiments made without limitation in relation to the attached figures among which:

[0029] - [Fig.l] is a functional diagram of an ALD cycle according to one embodiment particular of the invention,

[0030] - [Fig.2] is a STEM (HAADF) image of a MoS2 (1 nm) / VSX heterostructure (5 nm) obtained according to a particular embodiment of the process. Description of the embodiments

[0031] Unless otherwise specified, the expression "approximately" means to within 10%, of preferably to within 5%, and the expression "between ... and " means that the limits are included.

[0032] We will now describe in more detail the process of atomic layer deposition (ALD) of a thin layer of transition metal sulfide or transition metal alloy sulfide. The process comprises the following steps: a) carry out the ALD deposition cycle according to the following sub-steps ([Fig.l]): - exposing a substrate to a precursor of the transition metal, whereby an intermediate layer is formed on the substrate (substep i)), - purge the reactor (sub-step ii)), - exposing the substrate and the intermediate layer to a sulfur precursor (substep iii)), whereby a transition metal sulfide layer is formed, - purge the reactor (sub-step iv)), b) preferably, carrying out a sulfurization step, for example at a temperature above 250°C, c) preferably, carrying out annealing, advantageously, under an inert atmosphere, and preferably at a temperature above 400°C.

[0033] Step b) of sulfurization and step c) of annealing can be one and the same step.

[0034] The deposition cycle can be repeated N times, with N an integer ([Fig.l]). In other words, the sequence formed by sub-steps i), ii), iii) and iv) can be repeated N times.

[0035] The entire ALD sequence is carried out at low temperature, i.e. at a deposition temperature below 250°C, and preferably at a deposition temperature of between 20 and 250°C, even more preferably between 50 and 250°C, even more preferably between 50 and 200°C, and even more preferably between 80 and 150°C. The deposition temperature corresponds to the temperature of the substrate.

[0036] Such temperatures ensure the growth of an amorphous layer in the ALD regime. The deposited layer is thus perfectly uniform and not very rough. The thickness and morphology of the layer are, advantageously, identical at every point of the substrate. The low roughness guarantees that each crystal which will be formed in the layer at the end of the process will have the same thickness and that there will be no fracture or discontinuity in the deposit.

[0037] The low growth rates during ALD deposition allow better control of the composition of the layer in the case of the formation of alloys with group 5 transition metals (V, Nb, Ta).

[0038] Thus, the ALD deposition process makes it possible, not only, to grow a TMD in cavities with a high form factor, but also to control the formation of an alloy or a heterostructure. Indeed, with such a process, it is possible, in a first step, to deposit the different materials in successive layers or in alloy, then to carry out the simultaneous crystallization of the different materials in a second step.

[0039] In CVD, it is more difficult to obtain alloys of controlled composition because the precursors are introduced in a mixture and only the thermodynamically most stable composition under the temperature and partial pressure conditions used for deposition is obtained.

[0040] During step a), and more particularly during sub-step i), the precursor of the transition metal is chosen from the family of oxyhalides for the transition metals of group 6 typically having the formula MO2X2 or MOX4 (X = F, Cl, Br, I) or from the family of halides for the transition metals of group 5 typically having the formula MXn (with n between 3 and 5 and X = F, Cl, Br, I).

[0041] Preferably, it is chosen from molybdenum oxychlorides, tungsten oxychlorides, vanadium chlorides, niobium chlorides and tantalum chlorides.

[0042] Such precursors are less expensive than other precursors of the prior art (for example amides or organometallics). In addition, their greater thermal stability allows the implementation of the process in “batch” type reactors, more suited to large-scale production.

[0043] The saturated vapor pressure (Vp) of the precursor of the metal M will advantageously be greater than 0.1 torr, and even more preferably greater than 1 Torr, at the temperature used for the deposition process in order to ensure sufficient mass transport to the reactor.

[0044] Preferably, the precursor is chosen from MoO2C12, MoOC14, WOC14, VCC, NbCl 5 and TaCl5. These precursors meet the volatility criterion previously mentioned (Vp >0.1 torr at the deposition temperature).

[0045] At the end of sub-step i), an intermediate layer comprising the transition metal or an intermediate molecule comprising the transition metal is formed on the substrate. This intermediate layer will react with the sulfur molecule during sub-step iii).

[0046] In sub-step iii), the sulfur precursor is chosen from sulfide hydrogen, a hydrogen polysulfide, an organosulfur compound containing, preferably, at least 2 sulfur-hydrogen bonds or any other system allowing the in situ formation of the precursors mentioned (plasma generator or so-called thermal pre-cracking unit ('pre-cracking') for example).

[0047] Preferably, the sulfur precursor is chosen from hydrogen sulfide, a polyhydrogen sulfide and thiols, preferably dithiols.

[0048] Even more preferably, the dithiol is chosen from 1,2-ethanedithiol, 1,2-propanedithiol and 1,3-propanedithiol.

[0049] The precursors of the transition metal or sulfur can be in solid, liquid or gaseous form. The precursors in solid or liquid form are stored in a stainless steel saturator.

[0050] Preferably, the precursors are introduced into the reactor in the form of vapor (gas). The temperature to which the precursors are heated in the saturator depends on their volatility. The temperature will be chosen so as to achieve a vapor pressure sufficient to feed the reactor (typically about 0.1 to 5 torr, i.e. between about 13.3 and 666.6 Pa).

[0051] It is possible to carry out the ALD cycle with the same precursors or with different precursors during the different repetitions of the cycle.

[0052] For example, to form Mo(V)S2 alloys or MoS2 / VS2 heterostructures, during the ALD cycle, the precursor pairs MoO2C12 / EDT and / or VCVEDT can be used.

[0053] The VS2 deposition temperature is preferably identical to the MoS2 deposition temperature (less than 150°C) and the same sulfur precursor (EDT) is used, which allows the realization of Mo(V)S2 deposition sequences where the proportion of vanadium can be perfectly controlled.

[0054] Preferably, the sulfur precursor is identical throughout the process. Preferably, it is 1,2-ethanedithiol (EDT).

[0055] The ALD cycle is implemented in a reactor allowing the sequential delivery of the precursors. The precursors are not introduced concomitantly. A purge (sub-steps ii) and iv)) is carried out between each introduction of precursors to evacuate the precursors which have not reacted during the previous sub-step as well as the volatile reaction by-products. The purge is carried out with a neutral gas, such as argon or nitrogen.

[0056] The working pressure is preferably between 1 mtorr and 50 torr (i.e. between approximately 0.1 Pa and 6666.1 Pa), and even more preferably between 0.1 and 10 torr. The working pressure may vary depending on the volume and the size of the reactor.

[0057] The substrate is, for example, a silicon substrate (in particular a silicon wafer) covered with a thin layer of silica or any other material oxide, nitride or metal having a low surface roughness and not reacting with the deposited TMD layer or the reagents used during the deposition, sulfurization or annealing steps. Alternatively, growth can be carried out on another TMD (sulfide, selenide or tellurium). The exposed surface of the substrate can have different areas composed of the different materials mentioned above for the integration of the TMD layer into a microelectronic device.

[0058] As mentioned above, the deposit obtained at the end of step a) is amorphous. It is a coordination polymer containing metal-sulfur bonds as well as 1,2-ethanedithiolato ligands. Such a polymer is converted into a very uniform sulfide layer during the annealing step (step c).

[0059] At the end of step a), depending on the temperature and the reagents used during the ALD cycle, the thin layer obtained may still contain unsubstituted ligands or carbon present in the sulfur precursor. The optional sulfurization step (step b) which can be implemented before or during step c)) makes it possible to guarantee the elimination of residual ligands, in other words that the thin layer is exclusively made up of metal-sulfur bonds, and to obtain a sulfide having the correct stoichiometry. Another advantage of the sulfurization step is to pre-crystallize the TMD thin layer and thus give it better stability in air which makes it possible to limit the formation of metal-oxygen bonds during transfer to the thermal annealing equipment, and / or where appropriate during the steps of cleaning the rear face of the substrate.

[0060] The temperature of step b) is preferably at a temperature above 250°C, preferably at a temperature between 250 and 1150°C, even more preferably between 300 and 400°C.

[0061] The sulfurization step is carried out in the presence of a sulfur compound. The precursors used for this step can be sulfur in its native form or any volatile molecule containing SH or SC bonds, used in the form of vapor diluted in an inert gas, or in a mixture with hydrogen.

[0062] Preferably, it may be the same sulfur molecule as that used during the deposition step, which then makes it possible to carry out the sulfurization step directly in the equipment used for the deposition, without re-exposure to air. For example, the sulfurization of the thin layer obtained with the MoO2C12 / EDT precursor pair to form MoS2 can be carried out optimally at 360°C under EDT vapor for a period of 30 min.

[0063] Step b) of sulfurization can be directly applied to the final alloy or heterostructure. There is no need to repeat a separate sulfurization step between each layer of a different metal. Indeed, the diffusion of sulfur in an amorphous layer of TMD is largely sufficient to ensure the sulfurization of thin layers about ten nanometers thick in a few minutes.

[0064] The implementation of step c) depends on the temperatures used during steps a) and / or b).

[0065] Step c) of thermal annealing makes it possible to crystallize the thin layer of TMDs and / or to improve its crystalline quality. It ensures the formation of TMD crystals oriented in the plane of the substrate and of optimal size.

[0066] This step is preferably carried out under an inert atmosphere (N2, He or Ar, in particular)

[0067] This annealing is carried out at a temperature higher than the temperature used during sulfurization step b). The annealing is typically carried out at a temperature between 400 and 1150°C, ideally between 650°C and 950°C.

[0068] For example, the temperature of step c) is advantageously 900°C for MoS2 or WS2, as for example in the case where the intended application requires optimal crystallinity of the TMD.

[0069] The heat source may be a resistor or any other emissive source (halogen lamp or laser) that can be absorbed by the thin layer of TMD or any other constituent of the growth substrate.

[0070] With such a method, it is possible to manufacture thin layers of MS2 or M'Sx with M a group 6 transition metal and M' a group 5 transition metal, alloys of type M(M')S2, or even heterostructures consisting of a stack of different TMD materials (MS2 / M'SX for example).

[0071] More particularly, the device obtained comprises a substrate covered by a thin layer or a stack of thin crystalline layers of molybdenum sulfide, tungsten, vanadium (VS2 or VSX with x strictly greater than 1 and strictly less than 3), niobium, tantalum or one of their alloys such as Mo(V)S2 or W(Nb)S2.

[0072] With such a method, it is possible to obtain layers of different thicknesses depending on the intended application.

[0073] The thin layer can have a thickness of up to 50 nm or even up to 100 nm, in particular to form contacts in metallic TMDs (group 5).

[0074] The thin layer may have a smaller thickness. For example, it may be less than 20 nm, preferably less than 10 nm.

[0075] The minimum thickness of the thin layer can correspond to the thickness of an atomic monolayer according to the 001 plane, i.e. for example 0.65nm for a monolayer of MoS2.

[0076] The thin layers obtained can have very low roughness. The RMS roughness (determined by AFM) can typically be less than 0.3nm.

[0077] The process is particularly interesting because it makes it possible to obtain ultra- thin (typically having a thickness less than 5nm), smooth (low roughness; typically having a roughness less than 0.3nm) and continuous.

[0078] The (001) planes of the TMD crystals are oriented parallel to the plane of the substrate.

[0079] The process is easily industrializable due to its low cost and the thermal stability of the precursors used.

[0080] The method is particularly interesting for manufacturing (micro)electronic devices such as field effect transistors, memristors, radio frequency switches ('RF switches'), and devices for spintronics or quantum computing.

[0081] Vanadium, niobium and tantalum allow to induce robust p-type doping in MoS2 and WS2 materials. In addition, VS2 exhibits near-ideal lattice agreement with MoS2 and WS2.

[0082] It is thus possible to form very lightly constrained VS2 / MoS2 or VS2 / WS2 heterostructures or Mo(V)S2 or W(V)S2 semiconductor alloys which can have more interesting conduction properties than pure MoS2 and WS2.

[0083] Vanadium lamellar sulfides (VS2 and V5S8) are good conductors (resistivities lower than mOhm.cm). In particular, VS2 has a lower contact resistance on MoS2. The implementation of a sulfide-based contact is also particularly interesting to avoid damaging a TMD semiconductor based on MoS2 or WS2.

[0084] Various embodiments and variations have been described. Those skilled in the art will understand that certain features of these various embodiments and variations could be combined, and other variations will occur to those skilled in the art.

[0085] Finally, the practical implementation of the embodiments and variants described is within the reach of those skilled in the art from the functional indications given above.

[0086] Illustrative and non-limiting examples of different embodiments

[0087] Example 1: Deposition of a layer of MoS2

[0088] The ALD cycle is carried out by successively alternating pulses of the precursors MoO2C12 and EDT (1,2-ethanedithiol) at 100°C.

[0089] The temperature of the MoO2C12 source is 68°C. The temperature of the EDT source is 40°C.

[0090] After the formation of the thin layer, a sulfurization step is carried out in the presence of EDT for 30 min at 360°C. Rapid thermal annealing (RTP) under N2 for 30 seconds at 900°C leads to the crystallization of the MoS2 thin layer.

[0091] Example 2: Deposition of a layer of vanadium sulfide

[0092] The ALD cycle is carried out by successively alternating pulses of VC1 precursors 4 and EDT (1,2-ethanedithiol) at 100°C.

[0093] The temperature of the VC14 source is 30°C. The temperature of the EDT source is 40°C.

[0094] After the formation of the thin layer, a sulfurization step is carried out in the presence of EDT for 30 min at 360°C, without re-exposure to air between the deposition and sulfurization steps.

[0095] The resistivity of the vanadium sulfide layer obtained after sulfurization is approximately 1000 pOhm.cm for 10 nm of thickness.

[0096] Thermal annealing after the sulfurization step allows the material to crystallize and give it better resistance to oxidation. The material retains metallic properties for annealing temperatures up to 950°C with a non-linear variation in resistivity.

[0097] Example 3: Deposition of a layer of Mo(V)S2 (vanadium-doped molybdenum sulfide)

[0098] The layer is obtained by ALD using the precursors MoO2C12, VC14 and EDT (1,2-ethanedithiol) at a temperature of 100 °C. The precursors are introduced according to the sequence [(MoO2C12 / EDT)x / (VC14 / EDT)]y with x and y being positive integers.

[0099] The temperature of the MoO2C12 source is 68°C. The temperature of the VC14 source is 30°C. The temperature of the EDT source is 40°C.

[0100] After the formation of the thin layer, a sulfurization step is carried out in the presence of EDT for 30 min at 360°C.

[0101] Rapid thermal annealing (RTP) under N2 for 30 seconds at 900°C leads to the crystallization of the thin layer of Mo(V)S2. The resistivity of the MoS2 layer is lower as the quantity of vanadium incorporated is high.

[0102] Example 4: formation of a MoS2 / VSx heterostructure

[0103] The layers of the heterostructure were deposited by ALD at 100°C by abutting the sequences described in Examples 1 and 2 and adjusting the number of ALD cycles to obtain 2 atomic monolayers of MoS2 covered with 5nm of vanadium sulfide. The heterostructure was then sulfided at 350°C and crystallized by rapid thermal annealing at 850°C.

[0104] The obtained heterostructure was characterized by transmission electron microscopy (STEM-HAADF), thus highlighting the formation of a MoS2 (1 nm) / VSX (5 nm) stack ([Fig.2]).

Claims

Claims

1. A method of vapor deposition of a sulfide layer of a transition metal or one of its alloys, the method comprising a step of depositing atomic layers according to the following cycle: - exposing a substrate to a precursor of a transition metal, whereby an intermediate layer is formed on the substrate, - purging the reactor, - exposing the intermediate layer to a sulfur precursor, - purging the reactor, the substrate being at a temperature between 20°C and 250°C during the cycle, the cycle being able to be repeated several times, the precursor of the transition metal and / or the precursor of the sulfur being able to be identical or different during the repetitions of the cycle, the precursor of the transition metal being chosen from molybdenum oxyhalides, tungsten oxyhalides, vanadium halides, niobium halides and tantalum halides.

2. Method according to claim 1, characterized in that the precursor of the transition metal is chosen from MoO2C12, MoOC14, WOC14, VC14, NbCl5 and TaCl5.

3. Method according to one of the preceding claims, characterized in that the sulfur precursor is chosen from hydrogen sulfide, hydrogen polysulfides and thiols, preferably dithiols.

4. Process according to any one of the preceding claims, characterized in that the sulfur precursor is chosen from 1,2-ethanedithiol, 1,2-propanedithiol and 1,3-propanedithiol.

5. Method according to any one of the preceding claims, characterized in that, after the atomic layer deposition step, the method comprises a sulfurization step during which the substrate is exposed to a sulfur molecule having at least one sulfur-hydrogen or sulfur-carbon bond, at a temperature between 250°C and 1150°C, preferably between 300°C and 400°C.

6. Method according to the preceding claim, characterized in that the sulfur molecule is a dithiol, preferably 1,2-ethanedithiol.

7. Method according to any one of the preceding claims, characterized in that, after the step of depositing atomic layers, or after the sulfurization step, an annealing step is implemented.

8. Method according to the preceding claim, characterized in that the annealing step is carried out under an inert atmosphere at a temperature between 400°C and 1150°C, preferably between 650°C and 950°C.

9. Method according to any one of the preceding claims, characterized in that the substrate is at a temperature between 50°C and 150°C, preferably between 80°C and 120°C, during the cycle.

10. Process according to any one of the preceding claims, characterized in that the precursor of the transition metal is chosen from MoO2C12, MoOCLi, WOCI4 and VC14 and in that the precursor of the sulfur is 1,2-ethanedithiol.

11. Device comprising a substrate covered by a thin crystalline layer of molybdenum, tungsten, vanadium, niobium, tantalum sulfide or one of their alloys such as Mo(V)S2 or W(V)S2, the thin layer having a thickness of less than 100 nm, preferably less than 20 nm, even more preferably less than 10 nm, the crystals of the thin layer being oriented, their crystallographic plane (001) being parallel to the plane of the substrate.

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