EP3577257A1

EP3577257A1 - Process for manufacturing a two-dimensional film of hexagonal crystalline structure

Info

Publication number: EP3577257A1
Application number: EP18705964.7A
Authority: EP
Inventors: Bruno Ghyselen; Jean-Marc Bethoux
Original assignee: Soitec SA
Current assignee: Soitec SA
Priority date: 2017-02-02
Filing date: 2018-01-31
Publication date: 2019-12-11
Also published as: US11913134B2; US20190390366A1; FR3062398B1; US20230416940A1; JP7341059B2; CN110234800B; FR3062398A1; SG11201906821PA; WO2018142061A1; JP2020506150A; KR102523183B1; CN110234800A; KR20190110613A

Abstract

The invention relates to a process for manufacturing a two-dimensional film of a group IV material having a hexagonal crystalline structure, in particular graphene, comprising: - the formation of a growth substrate (100), comprising the transfer of a single-crystal metal film (1) suitable for the growth of said two-dimensional film on a support substrate (2), and - the epitaxial growth of the two-dimensional film (3) on the metal film of said substrate (100).

Description

METHOD FOR MANUFACTURING A TWO-DIMENSIONAL FILM

HEXAGONAL CRYSTALLINE STRUCTURE

FIELD OF THE INVENTION

The present invention relates to the growth of a two-dimensional film of a Group IV material of the periodic table of elements having a hexagonal crystalline structure, especially graphene, and a structure comprising such a film.

STATE OF THE ART

Graphene films have a growing interest in different technologies, including electronics, optoelectronics, energy, sensors, biotechnology, composite materials. A graphene film is composed of carbon atoms arranged in the form of a two-dimensional hexagonal crystalline structure. Among the particularly interesting properties of graphene, we can note the mobility of the charge carriers, the thermal conductivity in the plane of the film, the optical transparency, good mechanical properties such as strong cohesion or tensile strength, flexibility, or even biocompatibility.

There are already methods for growing a graphene film, in the form of a monoatomic layer, or even a few atomic layers, on a support substrate.

A first technique uses as support substrate a metal foil ("foil" in the English terminology), in particular copper or nickel, and implements a chemical vapor deposition process (CVD), which stands for Anglo-Saxon. "Chemical Vapor Deposition") for growing a graphene layer on said support substrate. Optionally, the graphene film thus formed can then be transferred to another medium.

A first disadvantage of this technique is that the coefficients of thermal expansion (CTE, acronym for the term "Coefficient of Thermal Expansion" of graphene and support substrate of copper or nickel are very different.

Since the growth of the graphene film is carried out at high temperature (typically of the order of 1000 to 1100 ° C.), this difference in the coefficient of thermal expansion generates high stresses in the graphene film during the return to ambient temperature. .

As the graphene film consists of at most a few atomic layers, these stresses cause deformation and damage to graphene during cooling. These effects are possibly exacerbated during subsequent process steps undergone by the graphene film. A second disadvantage of the aforementioned technique is that, in order to perfectly and reproducibly control the number of deposited atomic layers of graphene (in particular by avoiding forming areas where an additional layer begins to form), it must be possible to guarantee that the only source of carbon atoms comes from the deposition atmosphere and not from the growth substrate itself.

However, the metal sheets tend to absorb the carbon atoms, moreover voluntarily strongly present in the deposition atmosphere, and to release them unintentionally during growth or cooling. As regards copper, it is considered that this absorption is localized, essentially through the grain boundaries and other defects present in copper sheets, which are polycrystalline. With respect to nickel, it is considered that it tends to temporarily absorb carbon throughout its thickness, or at least several microns from the surface exposed to the carbon atmosphere. However, the limiting solubility of carbon in nickel decreases with temperature, leading to a release of carbon during cooling following growth of the graphene film.

Finally, to precisely and reproducibly control the growth of graphene, it is not enough that the copper sheet is well textured and / or oriented (for example by having only oriented grains (1 1 1), because the arrangement different grains (in the manner of a mosaic) can significantly affect the properties of the graphene film.

A second technique therefore aims to replace the aforementioned metal sheet with a composite substrate formed of a layer of copper deposited on a silicon or sapphire substrate [Miller 2012] [Miller 2013] [Ismach 2010] [Rahimi 2014] [Tao 2012 ].

However, even when the deposition of the copper layer is optimized to promote the orientation (1 1 1) along the axis normal to the substrate, said layer remains textured (polycrystalline) with the presence of orientation variants in the plan ("twins" according to the English terminology). Similarly, the annealing of a copper layer at high temperature (around 950 ° C) makes it possible to grow certain grains but their dimension remains well below one millimeter.

The graphene films deposited on these composite substrates are of comparable quality to those obtained on copper foils.

To overcome the disadvantages of the polycrystallinity of copper, tests were carried out by depositing graphene on small monocrystalline copper crystals, which are naturally free from grain boundaries [Gao 2010].

However, this third technique does not solve the problem of the difference in coefficient of thermal expansion. Moreover, the use of copper monocrystals, which are very expensive and too small, does not lend itself to industrial application. Finally, this technique does not solve the problem of the volume absorption by nickel.

The document US Pat. No. 8,501,531 proposes to overcome the deposit of graphene by CVD and describes a method in which a metal layer having a determined carbon concentration is deposited on a substrate, a heat treatment comprising a heat treatment is carried out. a heating step for diffusing the carbon inside the metal layer and then a cooling step sufficiently fast to migrate the carbon out of the metal layer and organize in the form of graphene on the surface of said metal layer . However, this technique has certain disadvantages. First, it should be noted that the formation temperature of graphene is poorly defined. Indeed, this technique requires exposing the structure at high temperatures to incorporate carbon in the metal layer, and graphene is formed during cooling due to carbon supersaturation. Wrinkles ("wrinkles" according to the English terminology) of the graphene film are therefore generally observed. Moreover, the metal layer obtained by deposit is polycrystalline. The roughness of the deposited films is generally high, which may be greater than ten nanometers. The thickness control for deposited films is therefore delicate for low thicknesses, that is to say less than 10 nm.

SUMMARY OF THE INVENTION

An object of the invention is to overcome the aforementioned drawbacks and to design a method for manufacturing a two-dimensional film of a Group IV material having a hexagonal crystalline structure, in particular graphene, which makes it possible to precisely control the growth of one or more atomic layers and which provides a film of better quality than currently available films.

For this purpose, the invention provides a method for producing a two-dimensional film of a Group IV material having a hexagonal crystalline structure, said method comprising:

the formation of a growth substrate, comprising the transfer of a monocrystalline metal film adapted for the growth of said two-dimensional film on a support substrate, and

the epitaxial growth of the two-dimensional film on the metal film of said substrate.

Advantageously, the metal film comprises at least one of the following metals: nickel, copper, platinum, cobalt, chromium, iron, zinc, aluminum, iridium, ruthenium, silver. Preferably, the metal film has a thickness less than or equal to 1 μηη, preferably less than or equal to 0.1 μηη.

The support substrate may be a substrate of quartz, graphite, silicon, sapphire, ceramic, nitride, carbide, alumina or metal.

According to one embodiment, the support substrate has, vis-à-vis the material of the two-dimensional film, a difference in thermal expansion coefficient lower than between the metal film and said two-dimensional film.

According to one embodiment of the invention, the transfer of the metal film comprises:

the provision of a monocrystalline metal donor substrate,

the assembly of the donor substrate and the support substrate,

thinning the donor substrate so as to transfer the metal film onto the support substrate.

Said monocrystalline metal donor substrate is advantageously obtained by drawing an ingot.

According to one embodiment, the method further comprises a step of forming an embrittlement zone in the donor substrate, so as to delimit the monocrystalline metal film to be transferred, and the thinning of the donor substrate comprises a detachment of the donor substrate along the weakened zone.

According to one embodiment, the weakening zone is formed by implantation of atomic species in the donor substrate.

According to one embodiment, the assembly of the donor substrate and the support substrate is implemented by gluing.

Alternatively, which assembly of the donor substrate and the support substrate is implemented by depositing the support substrate on the donor substrate.

According to a particular embodiment, the monocrystalline metal film is in the form of a plurality of blocks each transferred to the support substrate.

Each block advantageously has the same area as the donor substrate, said area being less than the area of the support substrate.

According to one embodiment, the growth substrate comprises a removable interface.

Said interface can be configured to be disassembled by a laser lift-off technique, a chemical attack, or a mechanical stress.

Moreover, the method may comprise, after the growth of the two-dimensional film, a step of separating said two-dimensional film from the growth substrate. According to one embodiment, said separation may comprise a delamination of the interface between the monocrystalline metal film and the support substrate.

Alternatively, said separation may comprise implantation of atomic species into the support substrate so as to form an embrittlement zone, and then detachment of the growth substrate along said embrittlement zone.

According to one particular embodiment, the method comprises, after said separation, the transfer of a new monocrystalline metal film onto the support substrate, so as to form a new growth substrate, then the growth of a new two-dimensional film of a Group IV material having a hexagonal crystal structure on said novel growth substrate.

According to another embodiment, said separation comprises a delamination of the interface between the two-dimensional film and the monocrystalline metal film of the growth substrate.

According to a particular embodiment, the method comprises, after said separation, the reuse of the growth substrate to grow a new two-dimensional film of a group IV material having a hexagonal crystal structure on said substrate.

Optionally, the method may comprise, after the growth of the two-dimensional film, an etching of the metal film so as to transfer the two-dimensional film on the support substrate.

According to an advantageous application of the invention, the two-dimensional film is a graphene film.

Another object of the invention relates to a structure obtained by the method which has just been described. Said structure successively comprises a support substrate, a monocrystalline metal film and a two-dimensional film of a Group IV material having a hexagonal crystalline structure on the metal film.

According to one embodiment, the metal film is in the form of a plurality of blocks distributed on the surface of the support substrate.

Advantageously, said two-dimensional film consists of one or more monatomic layers.

According to one embodiment, the two-dimensional film is a graphene film.

DESCRIPTION OF THE FIGURES

Other features and advantages of the invention will be better understood on reading the detailed description which follows, with reference to the appended drawings in which:

FIG. 1 illustrates a substrate for the growth of a graphene film according to one embodiment of the invention; FIG. 2 illustrates a substrate for the growth of a graphene film according to an alternative embodiment of the invention;

FIGS. 3A to 3B illustrate the principal of a method of manufacturing the substrate of FIG. 1 according to one embodiment of the invention;

FIGS. 4A to 4B illustrate the main steps of a method of manufacturing the substrate of FIG. 2 according to one embodiment of the invention;

FIGS. 5A to 5B illustrate the main steps of a method of manufacturing the substrate of FIG. 2 according to an alternative embodiment of the invention;

FIG. 6 illustrates a structure comprising a graphene film formed by epitaxial growth on the substrate of FIG. 1;

FIG. 7 illustrates a structure comprising a graphene film on a growth substrate comprising a removable interface;

FIG. 8 illustrates a structure in which the metal film of the growth substrate has been etched after growth of the graphene film.

To promote the readability of the figures, the different layers are not necessarily represented on the scale.

DETAILED DESCRIPTION OF EMBODIMENTS OF THE INVENTION

For the sake of brevity, the following description relates to the growth of a graphene film, but the invention also applies to the other elements of group IV of the periodic table of elements which make it possible to form a two-dimensional film of crystalline structure. hexagonal, namely silicon (the film material is called "silicene"), germanium (the film material is called "Germanian") and tin (the film material is called "stanene").

FIG. 1 illustrates a substrate 100 for the growth of a graphene film according to one embodiment of the invention.

Said substrate comprises a monocrystalline metal film 1 adapted for the growth of graphene, on a support substrate 2.

Said substrate is obtained by transfer of the metal film onto the support substrate from a donor substrate. This transfer can be carried out by the Smart Cut ™ process as described below, but other transfer processes involving an assembly of the donor substrate on the support substrate and then a thinning of the donor substrate until the thickness is obtained. desired for the metal film can be implemented.

The metal film 1 comprises at least one of the following metals: nickel, copper, platinum, cobalt, chromium, iron, zinc, aluminum, iridium, ruthenium, silver. Optionally, the film may consist of an alloy of said metals, or even an alloy comprising at least one of said metals and at least one other metal. The thickness of the monocrystalline film is advantageously less than or equal to 1 μηη, preferably less than or equal to 0.1 μηη.

This thickness is typically at least 10 times lower than the thickness of metal foils conventionally used for the growth of graphene. Thus, the absorption effect of the atoms mentioned above is therefore considerably reduced, especially in the case of nickel for which the absorption phenomenon occurs throughout the thickness of the film.

However, such a thickness is sufficient to fulfill the main function of the metal film, which is to constitute a seed layer for the growth of graphene. Indeed, the monocrystalline nature of the metal film makes it possible to form a graphene film having excellent crystalline quality.

Finally, because of its small thickness, the metal film has little influence on the thermal expansion of the substrate during the growth of the graphene film, said thermal expansion being essentially due to the thermal expansion of the support substrate.

The support substrate 2 has the main function of mechanically supporting the metal film during the growth of the graphene film.

The material of the support substrate 2 must therefore withstand the conditions (in particular temperature and chemical environment) of the growth of the graphene film, which may vary according to the deposition technique chosen. Thus, chemical vapor deposition (CVD) is carried out at a higher temperature than molecular beam epitaxy (MBE), the acronym for the term "Molecular Beam Epitaxy".

According to an advantageous but not imperative embodiment, the material of the support substrate 2 is chosen to have, vis-à-vis the graphene, a difference in coefficient of thermal expansion lower than between the metal film and graphene. Preferably, the difference in coefficient of thermal expansion between graphene and the material of the support substrate is minimized, it being recalled, however, that the difference in the coefficient of thermal expansion between the graphene and the substrate substrate material is all the more acceptable if the graphene growth temperature is low.

The support substrate 2 is advantageously monocrystalline because this configuration is more favorable for polishing the surface of said substrate before the transfer of the metal film (when this transfer involves bonding), but this property is not imperative. As indicated below, the support substrate may optionally be formed by deposition.

Advantageously, the preferred materials for the support substrate include quartz, graphite, silicon, sapphire, ceramics, nitrides, carbides, alumina, and metals.

Optionally, the support substrate may have, at the interface with the metal film, an encapsulation layer (not shown) intended to promote adhesion between the metal film and the support substrate, and / or to form a diffusion barrier to prevent pollution of graphene by elements of the support substrate. Conversely, the material of the support substrate may in some cases show signs of decomposition or deterioration when it is directly exposed to the growth atmosphere of the graphene film, or when exposed to the conditions of assembly of the film. metallic. In this case, a diffusion barrier also makes it possible to eliminate or limit these effects. Said encapsulation layer may for example be formed of one of the following materials among oxides, nitrides and carbides.

After obtaining the graphene film, it is possible to detach it from the substrate used for its growth.

It should be noted that the metal film is not necessarily continuous on the surface of the support substrate. On the contrary, the metal film 1 may be formed of a set of monocrystalline metal blocks 10 distributed on the surface of the support substrate 2, said blocks 10 being contiguous or distant from each other, as shown in FIG. As will be seen below, these blocks make it possible to exploit small metal monocrystals with respect to the dimension of the support substrate. By dimension, here means the area of the surfaces in contact with the blocks and the support substrate. The pavers are advantageously rectangular, but this form is not limiting. As another example, these blocks can also be in the form of bands, disks, hexagons, etc. Those skilled in the art are able to determine the shape of the blocks and their distribution on the surface of the support substrate depending on the geometry of the donor substrates at its disposal and the area of the graphene film to be formed.

Examples of Growth Substrates According to Embodiments of the Invention

Example 1

In this example, the monocrystalline metal film 1 is copper and the support substrate 2 is a silicon substrate successively covered with a film of 0.4 μηη of Si0 ₂ and a film of 0.1 μηη of copper intended for ensure a direct Cu / Cu metal bonding between the support substrate 2 and the metal film 1. Example 2

In this example, the monocrystalline metal film 1 is nickel and the support substrate 2 is a molybdenum substrate, each being covered with a film of 0.2 μηη of copper intended to ensure a direct Cu / Cu metal bonding between the substrate support 2 and the metal film 1.

Example 3

In this example, the monocrystalline metal film 1 is nickel and the support substrate 2 is a polycrystalline AlN ceramic coated successively with a film of 0.3 μηη of Si ₃ N ₄ and a film of 0.5 μηη of Si0 ₂ .

Example 4

In this example, the monocrystalline metal film 1 is copper and the support substrate 2 is sapphire coated with a film of 0.3 μηη of Si0 ₂ .

Example 5

In this example, the monocrystalline metal film 1 is copper and the support substrate 2 is a 20 μηη thick polycrystalline copper film assembled by direct Cu / Cu metal bonding on a donor substrate after formation of an embrittlement zone. implantation in this one.

Example 5

In this example, the monocrystalline metal film 1 is copper and the support substrate 2 is a nickel film deposited by electrolytic deposition up to a thickness of 15 μηη directly on a donor substrate after formation of an embrittlement zone by implantation in this one.

Example 6

In this example, the monocrystalline metal film 1 is copper and the support substrate 2 is a nickel-copper alloy film electroplated to a thickness of 15μηι directly on a donor substrate after formation of an embrittlement zone. by implantation in it.

Example 7

In this example, the monocrystalline metal film 1 is a nickel-copper alloy and the support substrate 2 is a nickel film electroplated to a thickness of 15μηι directly on a donor substrate after formation of an embrittlement zone. implantation in this one.

Example 8

In this example, the monocrystalline metal film 1 is in the form of a plurality of monocrystalline nickel blocks 10 positioned contiguously on a plane support and the support substrate 2 is a nickel film deposited directly on a weakened face by implantation. of the plurality of blocks, the deposition of said nickel film being performed by electrolytic deposition to a thickness of 10μηη. We will now describe a method of manufacturing a substrate as shown in Figure 1, according to one embodiment of the invention.

Referring to Figure 3A, there is provided a donor substrate 1 1 formed of a single crystal metal.

An embrittlement zone 12 in the donor substrate is formed by implantation of atomic species (schematized by the arrows), said weakening zone delimiting, on the surface of the donor substrate 11, the monocrystalline metal film to be transferred onto the support substrate. Said atomic species may in particular comprise hydrogen. Helium is another species particularly interesting from this point of view, replacing hydrogen or in combination with hydrogen.

With reference to FIG. 3B, the donor substrate 11 is assembled on a support substrate 2, the metal film to be transferred being at the bonding interface.

According to one embodiment, this assembly is made by bonding substrates 2 and 1 1.

According to another embodiment, this assembly is carried out by depositing the support substrate 2 on the donor substrate 1 1, by any suitable deposition technique depending on the nature of the support substrate.

Then, the donor substrate is detached along the embrittlement zone 12, said detachment being capable of being initiated, for example, by mechanical, chemical, and / or thermal stress. This detachment results in the transfer of the monocrystalline metal film 1 onto the support substrate 2. The structure shown in FIG. 1 is thus obtained.

Optionally, a finishing treatment of the surface of the monocrystalline metal film is carried out, in order to make it suitable for the subsequent deposition of the graphene film. This may be for example a polishing operation, annealing and / or etching.

Naturally, those skilled in the art are able to define the procedure according to the material of the donor substrate and the thickness of the film to be transferred.

This method of transferring the metal film comprises variants.

A first variant relates to the mode of assembly of the donor substrate and the support substrate. Thus, instead of a bonding assembly of the donor substrate on the support substrate, the assembly can consist of a deposition of the support substrate on the donor substrate, the film to be transferred lying on the side of the donor substrate on which the deposit is made. Optionally, a diffusion barrier layer is formed between the donor substrate and the support substrate to prevent diffusion of undesirable species from the support substrate to the graphene layer during growth thereof. A second variant - possibly combinable with the first - relates to the mode of thinning of the donor substrate to transfer the metal film on the support substrate. Thus, instead of thinning by detachment of the donor substrate along the embrittlement zone, it is possible to remove material (in particular by etching or by mechanical removal such as grinding or polishing) from the donor substrate by its face. opposite the interface with the support substrate, until the desired thickness for the metal film to be transferred is obtained.

A method of manufacturing a substrate as shown in FIG. 2 will now be described.

According to one embodiment, the blocks are assembled successively and then transferred collectively to the support substrate. For this purpose, there is provided a donor substrate 1 1 formed of a single metal crystal, whose area is smaller than that of the support substrate 2 intended to receive it.

As already explained with reference to FIG. 3A, a weakening zone 12 is formed in the donor substrate 11.

With reference to FIG. 4A, a first donor substrate 11 is then glued to the support substrate 2.

With reference to FIG. 4B, a second donor substrate 1 1 is bonded to the support substrate 2, and this assembly operation is continued until the bonding of all the donor substrates required to obtain all the pavers on the support substrate 2.

Then, all of the donor substrates 1 1 are detached according to the zone of weakness 12 to transfer all the monocrystalline metal blocks 10 to the support substrate 2.

The procedure described above for the transfer of a continuous metal film on the support substrate is applicable, with possible adaptations to the scope of those skilled in the art, the transfer of one or more metal blocks on the support substrate .

According to a variant (not shown) of this method, after the bonding of a first donor substrate on the support substrate, said donor substrate is detached along the zone of weakness to transfer a first monocrystalline metal pad on the support substrate, and this sequence is repeated with a subsequent donor substrate until the transfer of all the blocks 10 onto the support substrate 2.

The donor substrate may optionally be the same as that in which the pad 10 has been removed, and thus be used repeatedly to transfer a pad on the same support substrate 2.

Alternatively, the donor substrate may be different from that in which block 10 has been removed. At the end of the transfer operation of all the pavers 10 all donor substrates 1 1 can be reused to achieve a new cycle. Recycling operations may be desirable or even necessary. For example a polishing operation will start from a surface roughness adequate assembly of good quality.

Moreover, although the new donor substrate 1 1 is shown remote from the already transferred pad 10, it could be positioned contiguously to the pad 10 already transferred.

Thus, a plurality of blocks 10 are successively transferred onto the support substrate 2, making it possible to obtain the structure illustrated in FIG. 2.

According to another embodiment, the blocks 10 are assembled and transferred collectively on the support substrate 2.

For this purpose, as illustrated in FIG. 5A, a plurality of donor substrates 11 are assembled on an intermediate substrate 13, the said intermediate substrate serving essentially as mechanical support or as a handling tool for the donor substrates 1. The donor substrates 1 1 are shown distant from each other, but they could also be juxtaposed contiguously.

A weakening zone 12 is formed in each donor substrate, before or after their assembly on the intermediate substrate 13, so as to delimit a block 10 to transfer the support substrate.

With reference to FIG. 5B, the intermediate substrate 13 carrying the donor substrates 11 is bonded to the support substrate 2, the free surface of the donor substrates 11 being at the bonding interface.

Then, all of the donor substrates 11 are detached along their respective weakening zone 12, so as to transfer all the blocks 10 onto the support substrate 2. The structure illustrated in FIG. 2 is then obtained.

Preferably, the detachment step is performed collectively, for all the donor substrates.

According to one variant, the detachment step can be carried out successively for each donor substrate.

Optionally, the intermediate substrate 13 carrying the remainder of the donor substrates may be recycled for a new collective transfer of blocks. For this purpose, the free surface of the donor substrates is treated to remove defects related to detachment, a new weakening zone is formed in all the donor substrates, and the intermediate substrate carrying the weakened donor substrates is bonded to a new substrate support.

Advantageously, the preparation of the blocks is organized upstream of the process for manufacturing the growth substrate. For this purpose, for example, metal ingots are assembled together before being cut collectively to form the donor substrates, then are collectively implanted before being assembled to the support substrate.

The growth substrate having a continuous or discontinuous monocrystalline metal film (cobblestones) is then used for the growth of a graphene film.

Any known technique for growth of graphene can be employed.

By way of nonlimiting example, mention may be made of chemical vapor deposition (CVD) and molecular beam epitaxy (MBE). The parameters of these methods for the growth of a graphene layer are known or determinable by those skilled in the art, and therefore will not be described in detail in the present text.

Figure 6 shows a graphene film 3 formed on a growth substrate 100.

The graphene film advantageously consists of one or more monatomic layers of graphene, said layers being complete (i.e. continuous over the entire surface of the metal film) or not.

Depending on the applications targeted by the graphene film and the quality required for said film, it may be advantageous to form a single atomic layer of graphene, or a stack of two or more monoatomic layers of graphene, ensuring that each monoatomic layer be complete and avoid initiating the formation of a new (incomplete) layer on a complete monatomic layer.

This quality control of the graphene film is made possible not only by the parameters of the graphene deposition process but also by the excellent crystalline quality and / or the small thickness of the metal film which serves as a seed for the growth of graphene.

In fact, on the one hand, the precise control of the number of monoatomic layers formed is based on the fact that the carbon atoms constituting the graphene layer come solely from the deposition atmosphere and not from the growth substrate itself.

Thus, in the case of copper, the monocrystalline film used in the invention is of better quality than the copper foils used in the state of the art, which are polycrystalline. Insofar as the presence of grain boundaries or other crystalline defects is minimized in the copper film according to the invention, the absorption sites of the carbon atoms are thus minimized.

In the case of nickel, the superior quality of the monocrystalline film used in the invention has the same advantage as in the case of copper, to which is added a minimum volume for the absorption of carbon atoms, due to the thickness significantly reduced monocrystalline film compared to the usual sheets used.

Consequently, the absorption of carbon atoms in the monocrystalline metal film being minimized, the release of such atoms during the growth of the film of graphene or the subsequent cooling thereof is avoided or at least greatly reduced.

On the other hand, in the case where the support substrate 2 is chosen to have a small difference in coefficient of thermal expansion vis-à-vis the graphene film (the monocrystalline metal film being sufficiently thin to have a negligible influence), the Mechanical stresses applied to the graphene film during its cooling are minimized. This avoids or reduces the phenomena of relaxation or damage to the graphene film. This also contributes to a better quality of the graphene film.

Finally, as opposed to the composite substrates of the state of the art in which a polycrystalline copper film is deposited on a support substrate, the fact that the metal film of the invention is monocrystalline makes it possible to control the orientation (for example 1 1 1) of the graphene film over the entire surface of the metal film.

After the formation of the graphene film, it can be separated from the growth substrate, to be transferred to another medium or not.

This separation can be done in different ways.

According to one embodiment, the growth substrate comprises a removable interface, that is to say an interface at which the application of a bias (or a treatment) allows detachment of two parts of the substrate. It is necessary here to hear the term interface in the broad sense, in particular in that it can contain one or more layers of non-zero thickness.

In this respect, any separation technique known in the field of microelectronics can be employed, the person skilled in the art being able to select the appropriate materials according to the chosen technique.

Among the conceivable techniques, mention may be made (possibly in combination):

- the application of a mechanical stress,

- a chemical attack,

- a decomposition,

- a merger,

laser detachment ("laser lift-off" according to the English terminology). Said removable interface may be located between the monocrystalline metal film and the support substrate, or located inside the support substrate.

FIG. 7 thus illustrates an embodiment in which the removable interface I is located within the support substrate 2.

For example, said interface I may consist of a bonding interface, a region of a material adapted to confine a mechanical fracture, such as a porous layer (for example made of silicon), a layer allowing selective etching with respect to on the other hand, an embrittlement zone formed by implantation in the support substrate, etc.

Alternatively, the separation of the graphene film from the growth substrate can be based on any disassembly technique known in the graphene field.

According to one embodiment, the disassembly of the graphene film comprises a delamination of the interface between the metal film and the support substrate, and optionally a chemical etching of the metal film. In this case, the support substrate can be reused for the transfer of a new metal film, to form a new substrate for the growth of graphene.

According to another embodiment, the disassembly of the graphene film comprises a delamination of the interface between the graphene film and the metal film. Such a delamination technique is described in [Wang 201 1], in the case of a growth substrate consisting of a copper sheet. At the end of such delamination, the growth substrate can be reused for the growth of a new graphene film.

It is also possible to transfer the graphene film directly to the support substrate, by etching the monocrystalline metal film located between the graphene film and the support substrate. The structure illustrated in FIG. 8 is thus obtained. Such a method is described in particular in [Levendorf 2009], in the case where the growth substrate comprises a copper film formed by evaporation on a silicon substrate covered with a thermal oxide. .

REFERENCES

[Miller 2012] David L. Miller et al., Epitaxial (1 1 1) films of Cu, Ni and CuxNiy have AI203 (0001) for graphene growth by chemical vapor deposition, J. Appl. Phys. 1 12, 064317 (2012)

[Miller 2013] David L. Miller et al., Giant Secondary Growth Growth in Cu films of sapphire, AIP Advances 3, 082105 (2013)

[Ismach 2010] Ariel Ismach et al., Direct chemical vapor deposition of graphene on dielectric surfaces, Nano Lett. 2010, 10, 1542-1548

[Rahimi 2014] Somayyeh Rahimi et al., Toward 300 mm wafer-scalable high-performance polycrystalline chemical vapor deposited graphene transistors, ACS Nano, Vol. 8, No. 10, 10471-10479 (2014)

[Tao 2012] Li Tao et al, Uniform wafer-scale chemical vapor deposition of graphene on evaporated Cu (1 1 1) film with comparable quality to exfoliated monolayer, J. Phys. Chem. C 2012, 1, 16, 24068-24074

[Gao 2010] Li Gao et al., Epitaxial graphene on Cu (11), Nano Lett. 2010, 10, 3512-

3516

US 8,501,531

[Wang 201 1] Yu Wang et al, Electrochemical delamination of CVD-grown graphene film: Towards the recyclable use of copper catalyst, ACS Nano, Vol. 5, No. 12, 9927-9933, 201

[Levendorf 2009] Mark P. Levendorf et al., Transfer-free batch manufacturing of single layer graphene transistors, Nano Lett., Vol. 9, No. 12, 2009

Claims

1. A method of making a two-dimensional film (3) of a Group IV material having a hexagonal crystalline structure, comprising:

- forming a growth substrate (100) comprising transferring a monocrystalline metal film (1) adapted for growth of said two-dimensional film on a support substrate (2), and

the epitaxial growth of the two-dimensional film (3) on the metal film of said substrate (100).

2. Method according to claim 1, wherein the metal film (1) comprises at least one of the following metals: nickel, copper, platinum, cobalt, chromium, iron, zinc, aluminum, iridium, ruthenium, silver.

3. Method according to one of claims 1 or 2, wherein the metal film

(1) has a thickness less than or equal to 1 μηη, preferably less than or equal to 0.1 μηη.

4. Method according to one of claims 1 to 3, wherein the support substrate (2) is a substrate of quartz, graphite, silicon, sapphire, ceramic, nitride, carbide, alumina or aluminum. metal.

5. Method according to one of claims 1 to 4, wherein the support substrate

(2) has a smaller difference in thermal expansion coefficient vis-à-vis the two-dimensional film material than between the metal film and said two-dimensional film.

6. Method according to one of claims 1 to 5, wherein the transfer of the metal film (1) comprises:

the supply of a monocrystalline metal donor substrate (1 1),

the assembly of the donor substrate (1 1) and of the support substrate (2),

- Thinning the donor substrate (1 1) so as to transfer the metal film on the support substrate (2).

7. The method of claim 6, wherein the monocrystalline metal donor substrate (1 1) is obtained by drawing an ingot.

8. Method according to one of claims 6 or 7, further comprising a step of forming a weakening zone (12) in the donor substrate (1 1), so delimiting the monocrystalline metal film (1, 10) to be transferred, and wherein the thinning of the donor substrate comprises detachment of the donor substrate (1 1) along the embrittlement zone (12).

The method of claim 8, wherein the embrittlement zone (12) is formed by implanting atomic species into the donor substrate.

10. Method according to one of claims 6 to 9, wherein the assembly of the donor substrate (1 1) and the support substrate (2) is implemented by gluing.

1. Method according to one of claims 6 to 9, wherein the assembly of the donor substrate (1 1) and the support substrate (2) is implemented by depositing the support substrate (2) on the donor substrate ( 1 1).

12. Method according to one of claims 1 to 1 1, wherein the metal film

(1) monocrystalline is in the form of a plurality of blocks (10) each transferred to the support substrate (2).

13. The method of claim 12 in combination with claim 10, wherein each pad (10) has the same area as the donor substrate (1 1), said area being smaller than the area of the support substrate (2).

The method according to one of claims 1 to 13, wherein the growth substrate (100) comprises a removable interface.

The method of claim 14, wherein said interface (I) is configured to be disassembled by a laser lift-off technique.

The method of claim 14, wherein said interface (I) is configured to be disassembled by chemical etching.

17. The method of claim 14, wherein said interface (I) is configured to be disassembled by mechanical stress.

18. Method according to one of claims 1 to 17, comprising, after the growth of the two-dimensional film (3), a step of separating said two-dimensional film (3) vis-à-vis the growth substrate (100).

The method of claim 18, wherein said separating comprises delaminating the interface between the monocrystalline metal film (1) and the support substrate (2).

The method of claim 18, wherein said separating comprises implanting atomic species into the support substrate (2) so as to form an embrittlement zone, and then detaching the growth substrate along said embrittlement zone.

21. Method according to one of claims 18 to 20, comprising, after said separation, the transfer of a new monocrystalline metal film (1) on the support substrate (2), so as to form a new substrate (100) of growing, then growing a new two-dimensional film (3) of a Group IV material having a hexagonal crystal structure on said new growth substrate (100).

The method of claim 18, wherein said separating comprises delaminating the interface between the two-dimensional film (3) and the single-crystal metal film (1) of the growth substrate.

The method of claim 22 comprising, after said separation, reusing the growth substrate (100) to grow a new two-dimensional film of a Group IV material having a hexagonal crystal structure on said substrate.

The method of claim 23, further comprising, after growing the two-dimensional film, etching the metal film (1) so as to transfer the two-dimensional film to the support substrate.

25. The method according to one of claims 1 to 24, wherein the two-dimensional film (3) is a graphene film.

26. Structure successively comprising a support substrate (2), a single-crystal metal film (1) and a two-dimensional film (3) of a Group IV material having a hexagonal crystalline structure on the metal film (1).

27. Structure according to claim 26, wherein the metal film (1) is in the form of a plurality of blocks (10) distributed on the surface of the support substrate (2).

28. Structure according to one of claims 26 or 27, wherein the two-dimensional film (3) consists of one or more monatomic layers.

29. Structure according to one of claims 26 to 28, wherein the two-dimensional film (3) is a graphene film.