METHOD OF MANUFACTURE OF A FILM MADE OF VANADIUM DISULFIDE FILM AND FILM WHICH CAN BE OBTAINED BY THIS METHOD

Abstract

A method to manufacture a film made of vanadium disulphide by chemical vapor deposition on a previously heated substrate, includes successive procedures implemented in a vacuum reactor: injection of at least one organometallic molecule of vanadium, where the vanadium has a valence of less than or equal to 4; drainage of the reactor; injection of at least one sulphur molecule including at least one free thiol group, or forming a reaction intermediate comprising at least one free thiol group; injection of a reducing gas.

Claims

1. A film made of vanadium disulphide intended to be deposited on a substrate with a transmittance of over 50% for a wavelength of between 450 and 2750 nm, having a transmittance of over 50% for a wavelength of between 450 and 2750 nm, wherein the film has a surface roughness of less than 0.3 nm, where the surface roughness is measured by X-ray reflectometry.

2. The film according to claim 1, wherein the film is intended to be deposited conformally on the substrate.

3. The film according to claim 1, wherein the film is between 6 and 10 nm thick.

4. The film according to claim 1, wherein the film has a transmittance of over 60% for a wavelength of between 450 and 2750 nm.

5. A method of manufacture of a film made of vanadium disulphide according to claim 1, by chemical vapor deposition on a substrate, comprising a step of heating of the substrate and successive steps implemented in a vacuum reactor: i. injecting at least one organometallic molecule of vanadium, where the vanadium has a valence of less than or equal to 4; ii. draining the reactor; iii. injecting at least one sulphur molecule comprising at least one free thiol group, or forming a reaction intermediate comprising at least one free thiol group; iv. injecting a reducing gas.

6. The method of manufacture according to claim 5, wherein the steps i. to iv. are repeated multiple times.

7. The method of manufacture according to claim 5, wherein the steps i. to iv. are undertaken at a temperature of lower than 250 C.

8. The method of manufacture according to claim 5, wherein the substrate is heated to a temperature of between 100 C. and 250 C.

9. The method of manufacture according to claim 5, wherein the organometallic molecule of vanadium is chosen from among the following molecules: tetrakis(ethylmethylamino)vanadium TEMAV, tetrakis(dimethylamido)vanadium TDMAV, tetrakis(diethylamino)vanadium TDEAV, vanadium bromide VBr3, the molecules bearing a cyclopentadienyl functional group and/or bearing a carbonyl functional group, or the halogenated molecules of valence of less than or equal to 4.

10. The method of manufacture according to claim 5, wherein the organometallic molecule of vanadium is vanadium tetrachloride VCl.sub.4 or vanadium chloride VCl.sub.3.

11. The method of manufacture according to claim 5, wherein the sulphur molecule is chosen from among the following molecules: ethanedithiol EDT, hydrogen sulphide H.sub.2S, dimethyl disulphide DMDS, diethyl disulphide DEDS, dipropyl disulphide DPDS, dibenzyl disulphide DBDS, di-tert-butyl disulphide DTBDS.

12. The method of manufacture according to claim 5, wherein the sulphur molecule is blended with dihydrogen.

13. The method of manufacture according to claim 5, wherein the injected reducing gas is dihydrogen.

14. The method of manufacture according to claim 5, wherein the step of injection of a reducing gas comprises a sub-step of hydrogen-based reducing plasma treatment.

15. The method of manufacture according to claim 5, wherein a surface of the substrate is prepared by a flow of reducing gas.

16. The method of manufacture according to claim 15, wherein the surface preparation of the substrate comprises a sub-step of plasma treatment.

17. The method of manufacture according to claim 15, wherein the surface preparation of the substrate comprises a sub-step of exposure to a sulphur molecule.

18. The method of manufacture according to claim 5, further comprising draining the reactor between the step of injection of the molecule including at least one free thiol and the step of injection of a reducing gas, where the reducing gas is dihydrogen.

19. The method of manufacture according to claim 5, wherein the step of injection of the organometallic molecule of vanadium comprises a step of injection of a component including the organometallic molecule of vanadium.

Description

BRIEF DESCRIPTION OF THE FIGURES

[0052] The figures are given for information only, and are not restrictive of the invention in any manner.

[0053] FIG. 1 shows a block diagram representing the sequencing of the steps of a manufacturing method according to a first aspect of the invention.

[0054] FIG. 2 shows a diagrammatic representation of a film according to a second aspect of the invention, obtained by the method according to a first aspect of the invention.

[0055] FIG. 3 is a graph illustrating the transmittance percentage as a function of the wavelength in nanometres for a substrate and for a film according to a second aspect of the invention, which is 6 nm thick, deposited on the substrate.

[0056] FIG. 4 is a graph illustrating the current in unified atomic mass units as a function of the energy in electronvolts for the atomic orbital of nitrogen, obtained by X-ray photoelectron spectrometry on the film according to a second aspect of the invention, with or without a step of thermal crystallisation.

DETAILED DESCRIPTION

[0057] Unless otherwise stipulated, a given element shown in different figures has a single reference.

[0058] A first aspect of the invention concerns a method of manufacture of a film made of vanadium disulphide of chemical formula VS.sub.2, and a second aspect of the invention concerns a film made of vanadium disulphide obtained by the method according to a first aspect of the invention.

[0059] The term film is understood to mean a thin layer of material covering a surface, for example of the order of several nanometres thick.

[0060] FIG. 2 shows a diagrammatic representation of film 200 according to a second aspect of the invention, obtained by the method according to a first aspect of the invention.

[0061] The method according to a first aspect of the invention is implemented in a vacuum reactor 202. The volume of reactor 202 is generally less than 5 litres. The pressure in reactor 202 is, for example, 2 Torr. According to one implementation, all steps of the method are implemented in this vacuum reactor 202.

[0062] The method according to a first aspect of the invention is chemical vapor deposition, or CVD, on a substrate 201.

[0063] Substrate 201 is, for example, silicon Si, silicon dioxide SiO.sub.2, silicon carbide SiC, sapphire Al.sub.2O.sub.3, an oxide of the transition metals, such as TiO.sub.2, ZrO.sub.2, HfO.sub.2, VO.sub.2, V.sub.2O.sub.5, NbO.sub.2, Nb.sub.2O.sub.5, Ta.sub.2O.sub.5, MoO.sub.x, WO.sub.x, SnO.sub.2, In.sub.xSn.sub.yO.sub.z, ZnO, CuO.sub.x, NiO.sub.x, ZnO Al.sub.xZn.sub.yO.sub.z, Ga.sub.xZn.sub.yO.sub.z or Al.sub.xGa.sub.yZn.sub.zO.sub.w, aluminium nitride AlN, gallium nitride GaN, titanium nitride TiN, tungsten W, a sulphide or selenide or tellurium of the transition metals, TiS.sub.2, ZrS.sub.2, HfS.sub.2, NbS.sub.2, TaS.sub.2, MoS.sub.2, WS.sub.2, ZnS, SnS.sub.2, NiS.sub.x, InS.sub.x, GaS.sub.x, In.sub.xGa.sub.yS.sub.z, TiSe.sub.2, ZrSe.sub.2, HfSe.sub.2, NbSe.sub.2, TaSe.sub.2, MoSe.sub.2, WSe.sub.2, ZnSe, InSe.sub.x, GaSe.sub.x, NiSe.sub.x, In.sub.xNi.sub.ySe.sub.zIn.sub.xGa.sub.ySe.sub.z, TiTe.sub.2, ZrTe.sub.2, HfTe.sub.2, NbTe.sub.2, TaTe.sub.2, MoTe.sub.2, WTe.sub.2, ZnTe, or a chalcogenide, CdTe, Cd.sub.xZn.sub.yTe.sub.z, GeTe, Ge.sub.xSb.sub.yTe.sub.z, Ge.sub.xN.sub.yTe.sub.z, where x, y and z are natural integers.

[0064] Substrate 201 is transparent, i.e. it has a transmittance greater than or equal to 50% for a given wavelength.

[0065] FIG. 3 For example, in FIG. 3, substrate 201 is made of borosilicate and has a transmittance of greater than 80% for a wavelength of between 300 and 2700 nm.

[0066] Substrate 201 is previously heated, for example to a temperature of between 100 C. and 250 C.

[0067] The surface of substrate 201 can be previously prepared to facilitate the reactions, and in particular to remove the moist condensates, for example by gas flow. The gas used is a reducing gas, for example dihydrogen H.sub.2, dinitrogen N.sub.2 or argon Ar. Substrate 201 is prepared, for example, after substrate 201 is heated.

[0068] Substrate 201 can also be prepared with using a plasma treatment to reduce the overall time to implement the method. Substrate 201 is prepared using a plasma treatment, for example, after substrate 201 is prepared by gas flow.

[0069] The preparation of substrate 201 can also comprise a sub-step of exposure of the surface of substrate 201 to a sulphur molecule. This sulphur molecule is, for example, identical to the one which will be injected in reactor 202 in a step described below, called the third step, of the method according to a first aspect of the invention.

[0070] FIG. 1 shows a block diagram representing the sequencing of the steps of method 100 according to a first aspect of the invention.

[0071] Steps 101 to 104 of method 100 according to a first aspect of the invention are implemented at least once, i.e. method 100 according to a first aspect of the invention comprises at least one cycle.

[0072] A first step 101 of method 100 according to a first aspect of the invention consists in injecting at least one organometallic molecule of vanadium in reactor 202. In other words, first step 101 consists in injecting a component comprising at least one organometallic molecule of vanadium in reactor 202, where the component is, for example, a gas.

[0073] The term organometallic molecule is understood to mean a molecule comprising at least one carbon atom and a core metal. An organometallic molecule can, for example, also include at least one nitrogen atom linked directly with the core metal; this is the case in particular with metal amides.

[0074] In the remainder of the description the term organometallic molecule of vanadium refers to a molecule comprising carbon atoms and a vanadium atom as the core metal.

[0075] In the organometallic molecule of vanadium the vanadium has a valence of between 1 and 4. The term valence is understood to mean the number of covalent links which an atom has formed in a molecule.

[0076] The organometallic molecule of vanadium is, for example, tetrakis(ethylmethylamino)vanadium(IV) TEMAV, tetrakis(dimethylamido)vanadium(IV) TDMAV, tetrakis(diethylamino)vanadium(IV) TDEAV, vanadium bromide VBr.sub.3, the molecules comprising vanadium and bearing a cyclopentadienyl functional group and/or bearing a carbonyl functional group, for example bis(cyclopentadienyl)vanadium, vanadium hexacarbonyl V(CO).sub.6 or, alternatively, vanadium tetracarbonyl cyclopentadienide. The halogenated organometallics can also be used with a valence of less than or equal to 4 with vanadium, for example Bis(cyclopentadienyl)vanadium dichloride.

[0077] The organometallic molecule of vanadium can also be vanadium tetrachloride VCl.sub.4 or vanadium(III) chloride VCl.sub.3.

[0078] Method 100 according to a first aspect of the invention can also function for an organometallic molecule of vanadium in which the vanadium has a valence which is strictly higher than 4 if a step of reduction is implemented on film 200 finally obtained by method 100 to lower the stoichiometry of film 200 and obtain a disulphide. This step of reduction is, for example, implemented using a dihydrogen-based reducing plasma.

[0079] The organometallic molecule of vanadium can be injected pure or diluted in an organic solvent. For example, the organic solvent may have a saturating vapour pressure higher than the organometallic molecule, such that the organic solvent evaporates without interacting on film 200. The organic solvent is, for example, octane or cyclohexane. The organometallic molecule is, for example, diluted to 0.1 mole/litre in the organic solvent.

[0080] The duration of the injection of the organometallic molecule of vanadium 101 depends on the speed at which the organometallic molecule of vanadium is grafted on substrate 201 in a first cycle, or on the surface of the film generated in the previous cycle for following cycles. In general, the duration of first step 101 is less than 2 seconds.

[0081] The optimal duration of first step 101 is, for example, obtained after a finite number of cycles, after a saturation curve representing the speed of growth of the cycle as a function of grafting time of the organometallic molecule reaches a threshold.

[0082] A second step 102 of method 100 according to a first aspect of the invention consists in draining reactor 202.

[0083] Second step 102 of method 100 according to a first aspect of the invention is, for example, implemented by a flow of inert gas.

[0084] Second step 102 of method 100 according to a first aspect of the invention is, for example, implemented by successive steps of vacuum suction and of refilling reactor 202 with inert gas. The number of steps of vacuum suction and refilling with inert gas is, for example, chosen to ensure that the organometallic molecule is eliminated from reactor 202.

[0085] The inert gas used is, for example, dinitrogen N.sub.2, argon Ar, or helium He.

[0086] The duration of second step 102 depends on the geometry of reactor 202 and on its pumping capacity. For a reactor 202 with a volume of less than 5 litres and a primary pump, the duration of second step 102 is less than 2 seconds.

[0087] The optimal duration of second step 102 is, for example, obtained after a finite number of cycles, after a saturation curve representing the speed of growth of the cycle as a function of drainage time reaches a threshold.

[0088] A third step 103 of method 100 according to a first aspect of the invention consists in injecting at least one sulphur molecule.

[0089] The term sulphur molecule is understood to mean a molecule comprising at least one sulphur atom. According to a first implementation, the sulphur molecule comprises at least one free thiol group. A thiol is a group of generic formula RSH where R is an organic residue and SH the sulfhydryl group.

[0090] According to a second implementation, the sulphur molecule forms a reaction intermediate comprising at least one free thiol group. The term reaction intermediate is understood to mean a species participating in a reaction mechanism which is neither a reagent nor a product of the reaction.

[0091] The sulphur molecule is, for example, ethanedithiol EDT, hydrogen sulphide H.sub.2S, dimethyl disulphide DMDS, diethyl disulphide DEDS, dipropyl disulphide DPDS, dibenzyl disulphide DBDS or di-tert-butyl disulphide DTBDS. The sulphur molecule can be blended with dihydrogen H.sub.2.

[0092] Third step 103 of method 100 according to a first aspect of the invention can be implemented using a reducing plasma.

[0093] The sulphur molecule can be injected pure or blended with dihydrogen H.sub.2 and/or blended with an inert carrier gas. The inert carrier gas is, for example, dinitrogen N.sub.2 or argon Ar or helium He.

[0094] The duration of third step 103 depends on the grafting speed of the sulphur molecule. In general, the duration of third step 103 is less than 2 seconds.

[0095] Third step 103 of method 100 according to a first aspect of the invention can be followed by a step of drainage of reactor 202. This step of draining of reactor 202 can be identical to second step 102 of draining of reactor 202, and enables the reaction to be accelerated whilst ensuring separation of the chemical processes.

[0096] A fourth step 104 of method 100 according to a first aspect of the invention consists in injecting a reducing gas in reactor 202. The reducing gas is, for example, dihydrogen H.sub.2.

[0097] The reducing gas can be injected pure or blended with an inert carrier gas. The inert carrier gas is, for example, dinitrogen N.sub.2, argon Ar or helium He.

[0098] Fourth step 104 of method 100 according to a first aspect of the invention can comprise a sub-step of treatment of substrate 200 by a reducing plasma. The reducing plasma is, for example, based on dihydrogen H.sub.2. This sub-step of treatment of substrate 200 enables the overall time of method 100 to be reduced.

[0099] Steps 101 to 104 of method 100 are, for example, undertaken at a temperature of lower than 250 C.

[0100] As illustrated in FIG. 1, steps 101 to 104 of method 100 according to a first aspect of the invention are implemented N times in order to attain the desired thickness. N is, for example, between 1 and 10.sup.5 cycles. The number of cycles N is adjusted as a function of the growth speed per cycle to attain the desired thickness.

[0101] With each cycle the thickness of film 200 of vanadium disulphide increases. The growth speed is between 0.5 and 2 Angstm per cycle. Film 200 is then 10 nm thick after some one hundred cycles.

[0102] On conclusion of method 100, film 200 is, for example, between 6 and 10 nm thick.

[0103] Film 200 obtained in this manner has a resistivity of less than 1500 .Math.cm, a roughness of less than 0.3 nm and output work of higher than 4.6 eV.

[0104] The term roughness of the film is understood to mean the absolute value of the maximum height difference between an irregularity of the surface of the film and a theoretical surface line. The roughness is therefore a surface roughness.

[0105] In addition, as illustrated in FIG. 3, film 200 deposited on substrate 201, and then annealed at 450 C., has a transmittance of greater than 60% for a wavelength of between 300 and 2700 nm and is 6 nm thick, which means that film 200 is transparent, although it can be observed that deposition of film 200 on transparent substrate 201 causes transmittance to be reduced.

[0106] As can be seen in FIG. 3, film 200 deposited on substrate 201 has a transmittance of greater than 50% for a wavelength of between 350 and 2700 nm, a transmittance greater than 60% for a wavelength of between 400 and 2700 nm, a transmittance greater than 70% for a wavelength of between 650 and 2700 nm and a transmittance of greater than 75% for a wavelength of between 1100 and 2700 nm.

[0107] It should be noted that the thickness of film 200 is constant across its entire surface; with this method 100 a film 200 is therefore obtained the deposit of which is conformal.

[0108] Resistivity is defined as the reverse of conductivity.

[0109] To improve the characteristics of film 200 of vanadium disulphide, i.e. to obtain a film with a lower resistivity, a lower roughness and a higher output work, a step of thermal crystallisation can be implemented after fourth step 104 of method 100 according to a first aspect of the invention.

[0110] The step of thermal crystallisation consists, for example, of annealing at 450 C. for 10 minutes in argon Ar. Another example is a thermal treatment at 950 C. under a flow of ethanedithiol EDT, leading to complete crystallisation of the film.

[0111] After this step of thermal crystallisation, film 200 obtained in this manner has a resistivity of less than 500 .Math.cm, a roughness of less than 0.2 nm and output work of higher than 5 eV.

[0112] It can be demonstrated that a film 200 according to a second aspect of the invention has been obtained by method 100 according to a first aspect of the invention, by undertaking X-ray photoelectron spectrometry of film 200.

[0113] FIG. 4 is a graph illustrating the current in unified atomic mass units a.u. as a function of the energy in electronvolts eV for the atomic orbital of nitrogen N1s, obtained by X-ray photoelectron spectrometry on film 200.

[0114] A peak representing the state of the links with nitrogen in film 200 is observed, showing that there are nitrogen residues in film 200. Thus, if film 200 has been obtained by using an organometallic molecule of vanadium amine such as TEMAV, for example, X-ray photoelectron spectrometry undertaken for the orbital of nitrogen will enable nitrogen residues to be identified.

[0115] Similarly, if film 200 has been obtained by using a chlorinated organometallic molecule of vanadium, X-ray photoelectron spectrometry undertaken for the orbital of chlorine will enable chlorine residues to be identified, and if film 200 has been obtained using a brominated organometallic molecule of vanadium, an X-ray photoelectron spectrometry undertaken for the orbital of bromine will enable bromine residues to be identified.

[0116] In FIG. 4, the dashed line curve concerns a film 200 obtained with a step of thermal crystallisation, and the continuous line curve concerns a film 200 obtained without a step of thermal crystallisation.

[0117] The step of thermal recrystallisation also therefore enables the quantity of residues in film 200 to be reduced.

[0118] Alternatively, or in combination, it can be demonstrated that a film 200 has been obtained by method 100 according to the invention, by observing by scanning electron microscopy that the deposit of the film is conformal, i.e. that it has the same thickness over its entire surface. When making this observation it is also possible to check that the film is indeed closed, i.e. not porous or only slightly porous.

[0119] Alternatively, or in combination, it is possible to demonstrate that a film 200 has been obtained by method 100 according to the invention by performing X-ray reflectometry (XRR), showing that the film has a roughness of less than 0.3 nm, regardless of the deposited thickness.