Process for manufacturing a crystalline layer

Abstract

This process comprises the steps: a) using a substrate (1) comprising a surface film (2) made of a dichalcogenide of a transition metal, denoted MX2, where "M" denotes a transition metal and "X" denotes a chalcogen; the surface film (2) comprising a set of monolayers linked together by van der Waals bonds; b) forming a film (3) of polycrystalline aluminum nitride AlN, having grain boundaries, on the surface film (2); c) diffusing metallic elements (E) into the surface film (2), through the grain boundaries of the polycrystalline aluminum nitride AlN film (3), the metallic elements (E) being chosen to react chemically with MX2 by a redox reaction so as to transform the van der Waals bonds into covalent bonds; d) form a crystalline layer on the polycrystalline AlN aluminum nitride film (3) after step c). Figure 7

Description

Title of the invention: Method for manufacturing a crystalline layer technical field

[0001] The invention relates to the technical field of manufacturing a thick (i.e. greater than 200 nm) crystalline layer, in particular of high crystalline quality aluminum nitride AIN.

[0002] The invention finds its application in particular in obtaining power electronic devices, or in obtaining acoustic filters for RF (radio frequency) signals. State of the art

[0003] A process for manufacturing a crystalline layer known from the prior art, in particular from document FR3105591 Al, comprises the following steps: A) use a substrate, for example silicon, coated with a dielectric layer (e.g. oxide, §0037); B) form a surface film on the substrate coated with the dielectric layer, the surface film being made in a dichalcogenide of a transition metal, denoted MX2, where "M" designates a transition metal and "X" designates a chalcogen; C) form a crystalline layer of aluminium nitride AIN on the surface film.

[0004] The direct formation of a crystalline layer of aluminium nitride AIN on the dielectric layer (quasi-amorphous surface) leads to a layer of low crystalline quality.

[0005] Intercalating such a surface film, acting as a nucleation layer, between the dielectric layer and the crystalline layer of aluminum nitride AIN makes it possible to improve the crystalline quality of the aluminum nitride AIN layer formed, because the crystalline lattice mismatch between the surface film and the aluminum nitride AIN layer is typically less than or equal to 1.5%.

[0006] However, such a prior art process is not entirely satisfactory insofar as the formation of a thick (greater than 200 nm) aluminum nitride crystalline layer, necessary for the manufacture of components such as acoustic filters, is likely to lead to delamination of the crystalline layer. Description of the invention

[0007] The invention aims to remedy, in whole or in part, the aforementioned drawbacks. To this end, the invention relates to a method for manufacturing a crystalline layer, comprising the following steps: a) use a substrate comprising a surface film made of a dichalcogenide of a transition metal, denoted MX2, where "M" designates a transition metal and "X" designates a chalcogen; the surface film comprising a set of monolayers linked together by van der Waals bonds; b) form a polycrystalline aluminum nitride AIN film, possessing grain boundaries, on the surface film; c) diffuse metallic elements into the surface film, through the grain boundaries of the polycrystalline aluminum nitride film AIN, the metallic elements being chosen to react chemically with MX2 by a redox reaction so as to transform van der Waals bonds into covalent bonds; d) form a crystalline layer on the polycrystalline AIN aluminium nitride film after step c).

[0008] Thus, such a process according to the invention allows the formation of a thick crystalline layer (greater than 200 nm) while greatly reducing the risks of delamination of the crystalline layer thanks to steps b) and c). In other words, the chemical transformation of the surface film obtained by reducing MX2 makes it possible to avoid the risks of delamination of the crystalline layer formed during step d).

[0009] The method according to the invention may include one or more of the following features.

[0010] According to one feature of the invention, step c) is preceded by an exposure of the metallic elements on the polycrystalline AIN aluminum nitride film.

[0011] Thus, one advantage provided is to reduce the operating time (process time) by eliminating the need to deposit a material containing the metallic elements.

[0012] According to a feature of the invention, step c) is preceded by the formation of a material, comprising the metallic elements, on the polycrystalline aluminum nitride film AIN.

[0013] Thus, one advantage provided is the ease of execution compared to a direct exposure of the metallic elements, which may require more advanced techniques.

[0014] According to a feature of the invention, step d) is preceded by a removal of the residues of the material formed on the polycrystalline aluminum nitride AIN film, after the diffusion of the metallic elements in the surface film at the end of step c).

[0015] Thus, one advantage provided is to facilitate the formation of the crystalline layer by epitaxial growth on the polycrystalline AIN aluminum nitride film and to increase the crystalline quality.

[0016] According to a feature of the invention, the metallic elements diffused during step c) are atoms chosen as reducing agent of MX2.

[0017] Thus, one advantage provided is to obtain a chemical reaction with MX2 (redox reaction) so as to transform the van der Waals bonds into bonds covalent.

[0018] According to one feature of the invention, step a) is carried out so that MX2 is chosen to have a crystal lattice mismatch with polycrystalline aluminum nitride AIN of less than or equal to 1.5%.

[0019] Thus, one advantage provided is to obtain a satisfactory crystalline quality for polycrystalline aluminum nitride AIN.

[0020] According to one feature of the invention, step a) is carried out so that MX2 is chosen from molybdenum disulfide MoS2, tungsten disulfide WS2, vanadium disulfide VS2.

[0021] Thus, an advantage provided by such materials is their crystalline symmetry (i.e. hexagonal) compatible with aluminum nitride AIN, as well as a low crystal lattice mismatch with aluminum nitride AIN.

[0022] According to a feature of the invention: - step a) is executed so that MX2 is molybdenum disulfide MoS2; - the atoms chosen as reducing agent of molybdenum disulfide MoS2 are chosen from gallium Ga, aluminium Al, manganese Mn.

[0023] According to one feature of the invention, step d) is carried out so that the crystalline layer is made of a crystalline material having a crystalline lattice mismatch with polycrystalline aluminum nitride AIN less than or equal to 1.5%.

[0024] Thus, one advantage provided is to obtain a satisfactory crystalline quality for the crystalline layer.

[0025] According to one feature of the invention, step d) is carried out so that the crystalline layer is made of a crystalline material selected from silicon carbide SiC and a type III-N alloy.

[0026] Thus, one advantage provided by these materials is their weak lattice disagreement with polycrystalline aluminum nitride AIN.

[0027] According to one feature of the invention, the type III-N alloy is selected from aluminium nitride AIN, gallium nitride GaN, aluminium-gallium nitride AlGaN.

[0028] Thus, an advantage provided by these materials is their weak lattice mismatch (or even zero for aluminum nitride AIN) with polycrystalline aluminum nitride AIN.

[0029] According to one feature of the invention, step b) is carried out so that the polycrystalline AIN aluminum nitride film has a thickness less than or equal to 5 nm.

[0030] Thus, one advantage provided is to facilitate the diffusion of metallic elements within it in order to reach the underlying MX2 film.

[0031] According to one feature of the invention, step b) is carried out by a physical vapor phase deposition.

[0032] According to one feature of the invention, step d) is carried out by physical vapor deposition or by vapor-phase epitaxy with organometallics.

[0033] Organometallic vapor phase epitaxy, carried out at high temperature (above 950°C), allows for better crystalline quality (increased grain size) compared to physical vapor phase deposition.

[0034] According to one feature of the invention, step d) is carried out so that the crystalline layer has a thickness greater than or equal to 200 nm.

[0035] Thus, one advantage provided is to allow the manufacture of components such as acoustic filters.

[0036] Definitions

[0037] - By "crystalline" is meant a solid whose constituents are assembled in a regular manner. In other words, the diffraction pattern is essentially discrete, in accordance with the official definition given by the International Union of Crystallography (IUCR). The solid can be single-crystal or polycrystalline, but not amorphous.

[0038] - By "substrate", we mean a self-supporting physical support. A substrate can be a A wafer (also called a "plate" or "wafer") is generally a disc cut from an ingot of crystalline material. The substrate may be coated with a dielectric layer, for example, by deposition of a dedicated dielectric layer, or by oxidation of the substrate.

[0039] - By "lattice mismatch", one refers to the quantitative difference between the mesh parameters of the materials concerned.

[0040] - By "type IIIN alloy", we mean an alloy between at least one element located in column III of the periodic table of elements (PTE) and the element nitrogen N. As a non-limiting example, the alloy can be binary in the presence of a single element from column III of the PTE and nitrogen N. The alloy can be ternary in the presence of two elements from column III of the PTE and nitrogen N etc.

[0041] - By "thickness", we mean the dimension along the normal to the surface of the substrate on which the surface film is formed. Brief description of the drawings

[0042] Other features and advantages will become apparent in the detailed description of different embodiments of the invention, the description being accompanied by examples and references to the accompanying drawings.

[0043] [Fig.1] is a schematic cross-sectional view illustrating a step a) of a process according to the invention.

[0044] [Fig.2] is a schematic cross-sectional view, illustrating step b) of a process according to the invention.

[0045] [Fig.3] is a schematic cross-sectional view, illustrating a first method of putting into work of a step c) of a process according to the invention, that is to say a (direct) exposure of the metallic elements on the polycrystalline AIN aluminum nitride film, which diffuse into the surface film.

[0046] [Fig.4] is a schematic cross-sectional view, illustrating the outcome of step c) of [Fig.3] with the transformation of van der Waals bonds into covalent bonds in the surface film.

[0047] [Fig. 5] is a schematic cross-sectional view, illustrating a step d) of a process according to the invention executed at the end of step c) illustrated in [Fig.4].

[0048] [Fig.6] is a schematic cross-sectional view, illustrating a second method of putting into work of a step c) of a process according to the invention, that is to say the formation of a material, comprising the metallic elements, on the polycrystalline aluminum nitride film AIN.

[0049] [Fig.7] is a schematic cross-sectional view, illustrating the diffusion of the elements tallics from the material illustrated in [Fig.6] to the surface film, via the polycrystalline aluminum nitride film AIN.

[0050] [Fig.8] is a schematic cross-sectional view, illustrating the outcome of step c) of [Fig.7] with the transformation of van der Waals bonds into covalent bonds in the surface film.

[0051] [Fig.9] is a schematic cross-sectional view, illustrating a removal of the residues of the material formed on the polycrystalline AIN aluminium nitride film, at the end of step c) illustrated in [Fig.8].

[0052] [Fig. 10] is a schematic cross-sectional view, illustrating a step d) of a process according to the invention carried out after the removal of residues illustrated in [Fig.9].

[0053] It should be noted that the drawings described above are schematic and are not necessarily to scale for the sake of legibility and to simplify their understanding. The sections are made along the normal to the surface of the substrate on which the surface film is formed. Detailed description of the implementation methods

[0054] Identical elements or elements performing the same function shall bear the same references for the different embodiments, for the sake of simplification.

[0055] An object of the invention is a method for manufacturing a crystalline layer C, comprising the steps: a) use a substrate 1 comprising a surface film 2 made in a dichal- cogenide of a transition metal, denoted MX2, where "M" designates a transition metal and "X" designates a chalcogen; the surface film 2 comprising a set of monolayers linked together by van der Waals bonds; b) form a polycrystalline aluminium nitride AIN film 3, having grain boundaries, on the surface film 2; c) diffuse metallic E elements into the surface film 2, through the grain boundaries of the polycrystalline aluminum nitride AIN film 3, the metallic E elements being chosen to react chemically with MX2 by a redox reaction so as to transform the van der Waals bonds into covalent bonds; d) form a crystalline layer C on the polycrystalline aluminium nitride film 3 after step c).

[0056] Step a)

[0057] Step a) consists of using a substrate 1 comprising a surface film 2 made of a dichalcogenide of a transition metal, denoted MX2, where "M" designates a transition metal and "X" designates a chalcogen. The transition metal "M" can be chosen from titanium Ti, zirconium Zr, hafnium Hf, vanadium V, niobium Nb, tantalum Ta, chromium Cr, molybdenum Mo, tungsten W, rhenium Re. The chalcogen "X" can be chosen from sulfur S, selenium Se, tellurium Te.

[0058] The substrate 1 can be coated with a dielectric layer 10. By way of non-limiting example, the substrate 1 can be made of silicon, and the dielectric layer 10 can be made of silicon dioxide SiO2. Such a dielectric layer 10 is particularly suitable for the formation of the surface film 2 in MX2, for example by atomic layer deposition or by metal-organic vapor deposition. Atomic layer deposition, which can be carried out at low temperatures (below 300°C), is advantageous compared to other techniques such as metal-organic vapor deposition or chemical vapor deposition.

[0059] The surface film 2 comprises a set of monolayers linked together by van der Waals bonds. By way of non-limiting example, the surface film 2 may have a thickness of 2 nm. The number of monolayers is advantageously less than or equal to 50.

[0060] Step a) is advantageously carried out such that MX2 is chosen to have a lattice mismatch with polycrystalline aluminum nitride AIN of less than or equal to 1.5%. Step a) is advantageously carried out such that MX2 is chosen from molybdenum disulfide MoS2, tungsten disulfide WS2, and vanadium disulfide VS2.

[0061] The surface film 2 of MX2 allows the crystal growth of the polycrystalline aluminum nitride film 3 to be directed during step b), more precisely in the direction “c” (vertical axis) of the hexagonal crystal system.

[0062] Step b)

[0063] Step b) consists of forming a polycrystalline aluminum nitride AIN film 3, having grain boundaries, on the surface film 2.

[0064] Step b) is advantageously carried out so that the polycrystalline aluminum nitride AIN film 3 has a thickness less than or equal to 5 nm. The thickness is advantageously between 3 nm and 4 nm.

[0065] Step b) is advantageously carried out by physical vapor phase deposition.

[0066] Step c)

[0067] Step c) consists of diffusing metallic elements E into the surface film 2, through the grain boundaries of the polycrystalline aluminum nitride AIN film 3. The diffusion is chemical in nature due to a chemical concentration gradient.

[0068] Metallic elements E are chosen to react chemically with MX2 via a redox reaction in such a way as to transform the van der Waals bonds into covalent bonds. For example, when the chalcogen "X" is sulfur S, the metallic elements E allow the formation of ExSy metallic sulfides at the expense of the initial MS2, "E" denoting the metal composing the metallic elements E. The van der Waals bonds of the initial MS2 are transformed into covalent bonds of the transition metal "M" and into covalent bonds of ExSy.

[0069] The metallic elements E diffused during step c) are advantageously atoms chosen as reducing agents for MX2. When step a) is carried out such that MX2 is molybdenum disulfide MoS2, then the atoms chosen as reducing agents for molybdenum disulfide MoS2 are advantageously chosen from gallium Ga, aluminum Al, and manganese Mn. For example, gallium atoms Ga reduce molybdenum disulfide MoS2 to form gallium sulfides GaxSy at the expense of the initial molybdenum disulfide MoS2. The van der Waals bonds of the initial molybdenum disulfide MoS2 are transformed into covalent bonds of molybdenum Mo and into covalent bonds of GaxSy, with the release of gallium sulfide GaS in gaseous form.

[0070] According to a first embodiment, step c) is preceded by exposing the metallic E elements to the polycrystalline aluminum nitride AIN film 3. The exposure of the metallic E elements to the polycrystalline aluminum nitride AIN film 3 may consist of depositing atoms, chosen as the reducing agent for MX 2, onto the polycrystalline aluminum nitride AIN film 3. By way of non-limiting example, the deposition of the atoms onto the polycrystalline aluminum nitride AIN film 3 may be carried out by metal-organic vapor deposition or by molecular beam epitaxy.

[0071] According to a second embodiment, step c) is preceded by training of a material 4, comprising the metallic elements E, on the polycrystalline aluminum nitride (AIN) film 3. Material 4 is a solid material. The material 4 formed advantageously has a thickness strictly less than 3 nm. Material 4 can be formed by metal-organic vapor epitaxy or by molecular beam epitaxy. When step a) is carried out such that MX2 is molybdenum disulfide (MoS2) and the atoms chosen as the reducing agent for molybdenum disulfide (MoS2) are gallium atoms (Ga), the material 4 formed can be a thin layer of gallium nitride (GaN). By way of non-limiting example, the thin layer of gallium nitride (GaN) forming material 4, with a thickness strictly less than 3 nm, can be obtained by metal-organic vapor epitaxy with the following experimental parameters: - temperature between 800°C and 1040°C, - NH3 / N2 or NH3 / H2 type atmosphere, - precursor gases selected from trimethylgallium (TMGa) and triethylgallium (TEGa), - pressure between 150 mbar and 400 mbar.

[0072] The diffusion of metallic E elements through the grain boundaries of the polycrystalline aluminum nitride AIN film 3 can occur concomitantly with the formation of the material 4, for example by metal-organic vapor epitaxy. For example, atoms (forming the metallic E elements) that reach the surface of the polycrystalline aluminum nitride AIN film 3 are available to diffuse through the polycrystalline aluminum nitride AIN film 3.

[0073] Step d)

[0074] Step d) consists of forming a crystalline layer C on the polycrystalline aluminium nitride film 3 after step c).

[0075] When step c) is preceded by the formation of a material 4, comprising the metallic elements E, on the polycrystalline aluminum nitride AIN film 3, then step d) is advantageously preceded by the removal of residues of the material 4 formed on the polycrystalline aluminum nitride AIN film 3, after the diffusion of the metallic elements E into the surface film 2 at the end of step c). By way of non-limiting example, when the material 4 is a thin layer of gallium nitride GaN, the removal of residues can be carried out by surface cleaning with dihydrogen H2 at a pressure of 150 mbar.

[0076] Step d) is advantageously carried out such that the crystalline layer C is made of a crystalline material having a lattice mismatch with polycrystalline aluminum nitride AIN of less than or equal to 1.5%. Step d) is advantageously carried out such that the crystalline layer C is made of a crystalline material selected from silicon carbide SiC and a type IIIN alloy. The alloy of type III-N is advantageously chosen from aluminium nitride AIN, gallium nitride GaN, aluminium-gallium nitride AlGaN.

[0077] Step d) is advantageously carried out by physical vapor deposition or by metal-organic vapor epitaxy. In particular, metal-organic vapor epitaxy is possible, despite a high temperature that can exceed, for example, 950°C, thanks to the presence of the polycrystalline aluminum nitride (AIN) film 3, which allows for resumption of epitaxy. In the absence of the polycrystalline aluminum nitride (AIN) film 3, the surface film 2 of MX2 would undergo thermal decomposition.

[0078] Step d) is advantageously carried out so that the crystalline layer C has a thickness greater than or equal to 200 nm. By way of non-limiting example, the thickness of the crystalline layer C can be on the order of a micron.

[0079] The invention is not limited to the embodiments described. A person skilled in the art is able to consider their technically operative combinations and to substitute equivalents for them.

Claims

Demands

1. A method for manufacturing a crystalline layer (C), comprising the steps: a) using a substrate (1) comprising a surface film (2) made of a dichalcogenide of a transition metal, denoted MX2, where "M" denotes a transition metal and "X" denotes a chalcogen; the surface film (2) comprising a set of monolayers linked together by van der Waals bonds; b) forming a film (3) of polycrystalline aluminum nitride AIN, having grain boundaries, on the surface film (2); c) diffusing metallic elements (E) into the surface film (2), through the grain boundaries of the polycrystalline aluminum nitride AIN film (3), the metallic elements (E) being chosen to react chemically with MX2 by a redox reaction so as to transform the van der Waals bonds into covalent bonds; d) form a crystalline layer (C) on the polycrystalline aluminum nitride AIN film (3) after step c).

2. A method according to claim 1, wherein step c) is preceded by an exposure of the metallic elements (E) on the polycrystalline aluminum nitride AIN film (3).

3. A method according to claim 1, wherein step c) is preceded by the formation of a material (4), comprising the metallic elements (E), on the polycrystalline aluminum nitride AIN film (3).

4. A method according to claim 3, wherein step d) is preceded by the removal of residues of the material (4) formed on the polycrystalline aluminum nitride AIN film (3), after the diffusion of the metallic elements (E) in the surface film (2) at the end of step c).

5. A method according to any one of claims 1 to 4, wherein the metallic elements (E) diffused during step c) are atoms selected as reducing agent of MX2.

6. A method according to any one of claims 1 to 5, wherein step a) is carried out such that MX2 is chosen to have a crystal lattice mismatch with polycrystalline aluminum nitride AIN of less than or equal to 1.5%.

7. A method according to claim 6, wherein step a) is carried out so that MX2 is selected from molybdenum disulfide MoS2, tungsten disulfide WS2, vanadium disulfide VS2.

8. A process according to claim 7 in combination with claim 5, wherein: - step a) is carried out so that MX2 is molybdenum disulfide MoS2; - the atoms chosen as reducing agent of molybdenum disulfide MoS2 are chosen from gallium Ga, aluminium Al, manganese Mn.

9. A method according to any one of claims 1 to 8, wherein step d) is carried out so that the crystalline layer (C) is made of a crystalline material having a crystalline lattice mismatch with polycrystalline aluminum nitride AIN less than or equal to 1.5%.

10. A method according to any one of claims 1 to 9, wherein step d) is carried out so that the crystalline layer (C) is made of a crystalline material selected from silicon carbide SiC and a type III-N alloy.

11. A process according to claim 10 in combination with claim 9, wherein the type III-N alloy is selected from aluminium nitride AIN, gallium nitride GaN, aluminium-gallium nitride AlGaN.

12. A method according to any one of claims 1 to 11, wherein step b) is carried out so that the polycrystalline AIN aluminium nitride film (3) has a thickness less than or equal to 5 nm.

13. A method according to any one of claims 1 to 12, wherein step b) is carried out by physical vapor phase deposition.

14. A method according to any one of claims 1 to 13, wherein step d) is carried out by physical vapor deposition or by metal-organic vapor epitaxy.

15. A method according to any one of claims 1 to 14, wherein step d) is carried out so that the crystalline layer (C) has a thickness greater than or equal to 200 nm.

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