CHEMICAL VACUUM DEPOSITION OF A THIN TUNGSTEN AND/OR MOLYBDENUM SULFIDE FILM METHOD

Abstract

A method is for depositing a thin tungsten and/or molybdenum sulfide film on a substrate chemically, under vacuum.

Claims

1. A method for forming, on a surface of a substrate, chemically under vacuum, of a thin film comprising a compound of formula WS.sub.x, MoS.sub.x or Mo.sub.y W.sub.1-yS.sub.x, with y being between 0 and 1, and x being from 1.5 to 2, comprising the following steps: a) A step of introducing the substrate in a reactional chamber under vacuum, at a substrate temperature of between 200 and 500° C.; b) A step of preparing the substrate comprising the injection of a dihydrogen-, helium-, argon-, dinitrogen- or NH.sub.3-based gas, taken individually or in a mixture; c) A step of injecting, into the reactional chamber, a gaseous mixture comprising a tungsten hexacarbonyl and/or an Mo hexacarbonyl, and at least one nitrogen element d) A step of draining said gaseous mixture; e) A step of contacting the treated substrate such as obtained from step c) with a sulphurous gas comprising at least one free thiol group or forming a reactional intermediary comprising at least one free thiol group, to form on the substrate, a layer comprising the compound of formula WS.sub.x, MoS.sub.x or Mo.sub.y W.sub.1-yS.sub.x l .

2. The method according to claim 1, wherein step c) leads to the formation on the substrate of tungsten and/or molybdenum nitride, step e) being carried out under sulphurous gas saturation to totally or substantially convert the tungsten and/or molybdenum nitride formed from step c) into the compound of formula WS.sub.x, MoS.sub.x or Mo.sub.y W.sub.1-yS.sub.x such.

3. The method according to claim 1, wherein the substrate is chosen from among silicon, silica, silicon nitride, metal oxides, and metal nitrides, the substrate being: silicon or silica; chosen from among silicon nitride SiN and metal nitrides, the substrate being more specifically SiN, TiN, WN ou AlN; or chosen from among metal oxides.

4. Method according to claim 1, wherein at least one of the steps or all of the steps is/are carried out at a temperature of between 360 and 450° C.

5. The method according to claim 1, wherein: the gas of step b) is dihydrogen, argon, a dihydrogen-argon mixture, dinitrogen, ammoniac, a dinitrogen-dihydrogen mixture, a dinitrogen-ammoniac mixture, a dihydrogen-ammoniac mixture, helium, a dihydrogen-helium mixture, or an argon-helium mixture; and/or step b) is carried out under plasma enhancement; and/or step b) is carried out for a duration of 2 to 900 seconds.

6. The method according to claim 1, wherein the substrate is: a silicon nitride or a metal nitride, and step b) is carried out without plasma enhancement, the gas of step b) being, dihydrogen, a dihydrogen-argon mixture, ammoniac, a dinitrogen-dihydrogen mixture, a dinitrogen-ammoniac mixture, a dihydrogen-ammoniac mixture, helium, a dihydrogen-helium mixture, or an argon-helium mixture; or silicon, or silica or a metal oxide, and step b) is carried out under plasma enhancement, with a gas chosen from among dihydrogen, argon, helium, and their mixtures; or from among dinitrogen, ammoniac and their mixtures.

7. The method according to claim 1, wherein the vacuum is a primary or secondary vacuum.

8. The method according to claim 1, wherein step c) is carried out: by injecting a gaseous mixture comprising a tungsten hexacarbonyl and/or an Mo hexacarbonyl and NH.sub.3, or simultaneously injecting tungsten hexacarbonyl and/or an Mo hexacarbonyl, and NH.sub.3; or by injecting a gaseous mixture comprising a tungsten hexacarbonyl and/or an Mo hexacarbonyl, and at least one nitrogen element and at least one hydrogen element, or simultaneously injecting tungsten hexacarbonyl and/or an Mo hexacarbonyl, and at least one nitrogen element and at least one hydrogen element; and/or for a duration of 2 to 20 seconds.

9. The method according to claim 1, wherein the draining step d) is carried out: by passage of an inert gas; and/or for a duration less than or equal to 2 seconds.

10. The method according to claim 1, wherein the sulphurous gas is chosen from among ethane-1,2-dithiol (EDT), dimethyl disulfide (DMDS), diethyl disulfide (DEDS), dipropyl disulfide (DPDS), dibenzyl disulfide (DBDS), di-tert-butyl disulfide (DTBDS), tert-butylthiol (t-BuSH), thiophenol and mixtures thereof.

11. The method according to claim 1, wherein step e) is carried out: in the presence of dihydrogen, and/or an inert carrier gas; and/or under plasma activation.

12. The method according to claim 1, wherein step e) is: carried out for a duration of 1 to 20 seconds; and/or followed by a step f) of draining said sulphurous gas, which is carried out: by passage of an inert gas; and/or for a duration less than or equal to 2 seconds.

13. The method according to claim 1, which comprises the following steps: a) A step of introducing the substrate into a primary reactional chamber under vacuum, at a substrate temperature of between 200 and 500° C.; b) A step of preparing the substrate comprising the injection of a dihydrogen-, helium-, argon-, dinitrogen- or NH.sub.3-based gas, taken individually or in a mixture, for a duration of 2 to 900 seconds; c) A step of injecting, into the reactional chamber, a gaseous mixture comprising a tungsten hexacarbonyl and/or an Mo hexacarbonyl, and NH.sub.3, or simultaneously injecting tungsten hexacarbonyl and/or an Mo hexacarbonyl, and NH.sub.3, for a duration of 2 to 20 seconds; d) A step of draining said gaseous mixture by passage of an inert gas, for a duration less than or equal to 2 seconds; e) A step of contacting the treated substrate obtained from step c) with a with a sulphurous gas comprising at least one free thiol group or forming a reactional intermediary comprising at least one free thiol group, chosen from among ethane-1,2-dithiol (EDT), dimethyl disulfide (DMDS), diethyl disulfide (DEDS), dipropyl disulfide (DPDS), dibenzyl disulfide (DBDS), di-tert-butyl disulfide (DTBDS), tert-butylthiol (t-BuSH), thiophenol and mixtures thereof to form on the substrate, a layer comprising the compound of formula WS.sub.x, MoS.sub.x or Mo.sub.y W.sub.1-yS.sub.x, in the presence of dihydrogen, and/or an inert carrier gas, and/or under plasma activation, for a duration of 1 to 20 seconds.

14. The method according to claim 1, wherein: a residual nitrogen rate of the layer obtained from step e) is less than 5 atomic %; a thickness of the layer obtained from step e) is about 0.7 Å per cycle of steps b) to e); steps b) to e) are renewed, until obtaining the desired number of sheets; and/or step e) is followed by an annealing step.

15. The method for preparing a stack of layers, comprising steps a) to e) even f) such as defined in claim 1, step e) being followed by an annealing step, then a step of depositing a layer of a nitride of element(s) III or of a compound III-V.

16. The method according to claim 1, wherein x is greater than or equal to 1.7.

17. The method according to claim 1, wherein the gaseous mixture comprises at least one hydrogen element, or simultaneously injecting tungsten hexacarbonyl and/or an Mo hexacarbonyl, and at least one nitrogen element, and at least one hydrogen element.

18. The method according to claim 6, wherein step b) is carried out under plasma enhancement, in the presence of dihydrogen, argon and/or helium.

19. The method according to claim 13, further comprising a step of draining said sulphurous gas by passage of an inert gas for a duration less than or equal to 2 seconds

20. The method according to claim 13, wherein steps b) to f) are renewed, until obtaining the desired number of sheets.

Description

FIGURES

[0118] FIG. 1 illustrates the steps of an example of a method for forming a WS.sub.x, MoS.sub.x or Mo.sub.y W.sub.1-yS.sub.x layer, with y being between 0 and 1, and x being from 1.5 to 2 by CVD, according to the invention.

[0119] FIG. 2 presents the growth speed of the thin film according to example 1, according to the temperature of the substrate.

[0120] FIG. 3 shows the study of the stoichiometry of the WS.sub.x tungsten sulfide obtained according to example 1 according to the temperature by wavelength dispersive X-ray fluorescence spectroscopy (WDXRF).

[0121] FIG. 4 relates to the topology of a square of 1×1 μm of the surface of a thin film after deposition according to example 1. Roughness RMS=0.4 nm.

[0122] FIGS. 5A, 5B, and 5C correspond to an analysis of the surface of a thin film after deposition according to example 1 by X photoelectronic spectrometry (XPS) relative to W4f (A), S2p (B), N/s (C).

EXAMPLES

Example 1: Obtaining of a Tungsten Sulfide

[0123] In a standard CVD deposition reactor, under primary vacuum (2 Torr), wherein a silicon trench-type substrate (bulk or SOI (silicon on insulator)) has been placed beforehand, at 410° C., said substrate has been prepared by injection of a dihydrogen-, helium-, argon-, dinitrogen- or NH.sub.3 (ammoniac)-based gas, taken individually or in a mixture, with or without plasma enhancement, generally in situ or remote, in particular in order to reduce, if necessary, the duration of this step and therefore of the method. This preparation makes it possible to remove the residual oxygen in the reactor, as well as the wet condensates on the surface. If necessary, it also has the role of reducing the number of hydroxyl bonds on the oxidized surfaces.

[0124] The duration of this step is typically in the range 2-900 s, depending on the presence or not of plasma enhancement, and if so, of the plasma enhancement chosen.

[0125] Then, at the same time, ammoniac NH.sub.3 and W(CO).sub.6 tungsten hexacarbonyl (commercially available) have been injected.

[0126] The duration of this step must not exceed a value which would not enable sulfidation at the core of the W.sub.zN.sub.z′ phase at the time of exposure of the sulphurous gas such as described below. The duration of this step is generally in the range 2-20 s, preferably 10 s.

[0127] From this step, an extremely thin tungsten nitride film (of W.sub.zN.sub.z-type) is formed.

[0128] A draining step, carried out by flow rate of a neutral gas, has then been carried out, such that the injected sulphurous gas as described below is not mixed with ammoniac NH.sub.3 and with W(CO).sub.6 tungsten hexacarbonyl (which would lead to a W.sub.zN.sub.z′S.sub.z″ mixture that is not sought to achieve, as well as the uncontrolled formation of powders).

[0129] The draining time, and in particular the maximum draining time, depends in particular on the geometry of the reactor, and is typically less than 2 seconds. This draining time is suitable for the device used to achieve the aim described above.

[0130] A sulphurous gas of the 1,2 ethane di-thiol (EDT) type is then injected. The latter can be used pure or in a mixture with a neutral carrier gas. Other molecules of the same family can be successfully used (pure or in a mixture), in particular, ethane thiol, DMDS, DEDS, DPDS, DBDS, DTBDS, t-BuSH, di-tertbuthyl disulfide, thiophenol, in a mixture or not with H.sub.2, and optionally with a reducing plasma activation.

[0131] More specifically, it can be 1,2-ethane di-thiol, ethane thiol, t-BuSH or thiophenol, in particular in the absence of H.sub.2, optionally with a reducing plasma activation.

[0132] It can also be DMDS, DEDS, DPDS, DBDS, DTBDS, or di-tertbuthyl disulfide, in a mixture with H.sub.2, and optionally with a reducing plasma activation. This step makes it possible to convert the tungsten nitride formed beforehand into WS.sub.x-type tungsten sulfide, x being from 1.5 to 2.

[0133] The duration of this step depends on the conversion time of W.sub.zN.sub.z′-type tungsten nitride into WS.sub.x-type tungsten sulfide, and therefore on the thickness of W.sub.zN.sub.z′, and is generally in the range 1-20 seconds, preferably 10 seconds.

[0134] A new draining step, this time optional, can be carried out here.

[0135] A growth cycle corresponds to the sequential exposure of the substrate to the W(CO).sub.6+NH.sub.3 mixture, then the EDT, it all separated by a draining step. The final thickness of the deposition is obtained by multiplying the cycles.

[0136] The growth speed depends on the deposition temperature, in the range 200-500° C., preferably 360-450° C., for example 410° C. This is a so-called pulsed chemical deposition regime. The term “pulsed” describes a technical solution where the substrate is sequentially exposed to gases, in order to limit the chemical interactions by direct mixture, and wherein neutral gas draining sequences are associated to guarantee the separation of the chemistries.

[0137] The deposition speed is around 0.7 Ang. per cycle. An Arrhenius-type analysis of FIG. 2 makes it possible to extract an activation energy of around 1 eV.

[0138] The film obtained is closed, uniform, slightly rough, in particular having a roughness Ra less than 0.6 or 0.5 nm, and conform (FIG. 4).

[0139] It must be noted that a very low residual atomic percentage of N (<5%) can optionally be detected by XPS in the film after deposition (FIG. 5).

[0140] It must be noted also that the value x can, for example, and if necessary, be modified by way of the temperature at which the substrate is carried. For example, a temperature of 360° C., 410° C. and 450° C. can make it possible to obtain a value x of about 2, about 1.7 and 1.6, respectively (FIG. 3).

Example 2: Obtaining a Molybdenum Sulfide or an Mo-W Sulfide.

[0141] A compound of formula Mos such as defined above is successfully obtained according to a protocol similar to that described in example 1, by using a molybdenum hexacarbonyl instead of tungsten hexacarbonyl.

[0142] In addition, a compound of formula Mo.sub.y W.sub.1-yS.sub.x such as defined above is successfully obtained according to a protocol similar to that described in example 1, by using a tungsten hexacarbonyl/molybdenum hexacarbonyl mixture instead of tungsten hexacarbonyl.

Example 3: Implementation of a crystallization annealing

[0143] The thin film obtained from examples 1 and 2 can be used with or without annealing, in particular to produce an active layer of a memory in Metal/Insulator/Metal (MIM) integration.

[0144] This annealing can be necessary for other applications, where the presence of a thin crystallized film is desirable, even necessary.

[0145] Thus, the thin film obtained from example 1 or 2 has been annealed at a temperature of 700° C. or more, successfully, to obtain a thin, crystallized WS.sub.x, MoS.sub.x or Mo.sub.y W.sub.1-yS.sub.x film.