Process for manufacturing a crystalline layer

Abstract

This method 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 film (3) of polycrystalline aluminum nitride AlN, the metallic elements (E) being chosen to react chemically with MX2 by an oxidation-reduction reaction so as to transform the van der Waals bonds into covalent bonds; d) forming a crystalline layer on the polycrystalline aluminum nitride AlN 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 the manufacture of a thick crystalline layer (i.e. greater than 200 nm), in particular of aluminum nitride AIN, of high crystalline quality.

[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 method for manufacturing a crystalline layer known from the state of the art, in particular from document FR3105591 A1, comprises the steps: A) use a substrate, for example silicon, coated with a dielectric layer (eg oxide, §0037); B) forming a surface film on the substrate coated with the dielectric layer, the surface film being made of a dichalcogenide of a transition metal, denoted MX2, where “M” denotes a transition metal and “X” denotes a chalcogen; C) form a crystalline layer of aluminum nitride AIN on the surface film.

[0004] The direct formation of a crystalline layer of aluminum 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 layer of aluminum nitride AIN formed, since the crystal lattice mismatch between the surface film and the layer of aluminum nitride AIN is typically less than or equal to 1.5%.

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

[0007] The invention aims to remedy all or part of the aforementioned drawbacks. To this end, the invention relates to a method for manufacturing a crystalline layer, comprising the steps: a) use a substrate comprising a surface film made from a dichalcogenide of a transition metal, denoted MX2, where “M” denotes a transition metal and “X” denotes a chalcogen; the surface film comprising a set of monolayers linked together by van der Waals bonds; b) forming a polycrystalline aluminum nitride AIN film, having grain boundaries, on the surface film; c) diffusing metallic elements into the surface film, through the grain boundaries of the polycrystalline AIN aluminum nitride film, the metallic elements being chosen to react chemically with MX2 by an oxidation-reduction reaction so as to transform the van der Waals bonds into covalent bonds; d) forming a crystalline layer on the polycrystalline aluminum nitride AIN film after step c).

[0008] Thus, such a method according to the invention allows the formation of a thick crystalline layer (greater than 200 nm) by 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 the 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 comprise one or more of the following characteristics.

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

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

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

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

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

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

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

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

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

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

[0020] According to a characteristic 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 characteristic of the invention: - step a) is performed so that MX2 is molybdenum disulfide MoS2; - the atoms chosen as reducing agent of molybdenum disulfide MoS2 are chosen from gallium Ga, aluminum Al, manganese Mn.

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

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

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

[0026] Thus, an advantage provided by these materials is their low mesh mismatch with polycrystalline aluminum nitride AIN.

[0027] According to a characteristic of the invention, the III-N type alloy is chosen from aluminum nitride AIN, gallium nitride GaN, aluminum-gallium nitride AlGaN.

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

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

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

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

[0032] According to a characteristic of the invention, step d) is carried out by physical vapor deposition or by organometallic vapor phase epitaxy.

[0033] Organometallic vapor phase epitaxy, performed at high temperature (above 950°C), makes it possible to obtain better crystalline quality (increase in grain size) compared to physical vapor phase deposition.

[0034] According to a characteristic 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, an 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 definition officially given by the International Union of Crystallography (IUCR). The solid can be monocrystalline or polycrystalline, but not amorphous.

[0038] - By "substrate" is meant a self-supporting physical medium. A substrate may be a wafer (also called a "platelet") which generally takes the form of a disc cut from an ingot of a crystalline material. The substrate can be coated with a dielectric layer, for example by depositing a dedicated dielectric layer, or by oxidizing the substrate.

[0039] - By "lattice mismatch" we mean means the quantitative difference between the mesh parameters of the materials concerned.

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

[0041] - By "thickness" is meant 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 attached drawings.

[0043] [Fig.l] is a schematic sectional view illustrating a step a) of a method according to the invention.

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

[0045] [Fig.3] is a schematic sectional view, illustrating a first mode of implementation implementation of a step c) of a method according to the invention, i.e. (direct) exposure of the metallic elements on the polycrystalline aluminum nitride AIN film, which diffuse into the surface film.

[0046] [Fig.4] is a schematic 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 sectional view, illustrating a step d) of a method according to the invention carried out at the end of step c) illustrated in [Fig.4].

[0048] [Fig.6] is a schematic sectional view, illustrating a second mode of implementation implementation of a step c) of a method according to the invention, i.e. the formation of a material, comprising the metallic elements, on the polycrystalline aluminum nitride AIN film.

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

[0050] [Fig.8] is a schematic 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 sectional view, illustrating a removal of the residues of the material formed on the polycrystalline aluminum nitride AIN film, at the end of step c) illustrated in [Fig.8].

[0052] [Fig. 10] is a schematic sectional view, illustrating a step d) of a method according to the invention carried out after the removal of the 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 readability 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] Elements that are identical or provide the same function will bear the same references for the different embodiments, for the sake of simplification.

[0055] An object of the invention is a method of 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” 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 E elements into the surface film 2, through the grain boundaries of the polycrystalline AIN aluminum nitride film 3, the metallic E elements being chosen to react chemically with MX2 by an oxidation-reduction reaction so as to transform the van der Waals bonds into covalent bonds; d) forming a crystalline layer C on the polycrystalline aluminum nitride AIN 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” denotes a transition metal and “X” denotes 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 may be coated with a dielectric layer 10. By way of non-limiting example, the substrate 1 may be made of silicon, and the dielectric layer 10 may 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 organometallic vapor phase epitaxy. The atomic layer deposition, which can be carried out at low temperature (less than 300°C), is advantageous compared to other techniques such as organometallic vapor phase epitaxy 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 so that MX2 is chosen to have a crystal lattice mismatch with the polycrystalline aluminum nitride AIN of less than or equal to 1.5%. Step a) is advantageously carried out so that MX2 is chosen from molybdenum disulfide MoS2, tungsten disulfide WS2, vanadium disulfide VS2.

[0061] The surface film 2 of MX2 makes it possible to orient the crystalline growth of the film 3 of polycrystalline aluminum nitride AIN during step b), more precisely in the “c” direction (vertical axis) of the hexagonal crystal system.

[0062] Step b)

[0063] Step b) consists of forming a film 3 of polycrystalline aluminum nitride AIN, 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 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 of a chemical nature due to a chemical concentration gradient.

[0068] The metallic E elements are chosen to react chemically with MX2 by an oxidation-reduction reaction so as to transform the van der Waals bonds into covalent bonds. For example, when the chalcogen “X” is the sulfur S, the metallic E elements make it possible to form metallic sulfides ExSy at the expense of the initial MS2, “E” designating the metal composing the metallic E elements. The van der Waals bonds of the initial MS2 are transformed into covalent bonds of the transition metal “M” and into covalent bonds of the ExSy.

[0069] The metallic elements E diffused during step c) are advantageously atoms chosen as reducing agent of MX2. When step a) is carried out so that MX2 is molybdenum disulfide MoS2, then the atoms chosen as reducing agent of molybdenum disulfide MoS2 are advantageously chosen from gallium Ga, aluminum Al, manganese Mn. For example, the gallium Ga atoms make it possible to reduce molybdenum disulfide MoS2 in order 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 a release of a gallium sulfide GaS in gaseous form.

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

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

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

[0073] Step d)

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

[0075] When step c) is preceded by a formation of a material 4, comprising the metallic elements E, on the film 3 of polycrystalline aluminum nitride AIN, then step d) is advantageously preceded by a removal of the residues of the material 4 formed on the film 3 of polycrystalline aluminum nitride AIN, after the diffusion of the metallic elements E in 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 the residues can be carried out by surface cleaning with dihydrogen H2 at a pressure of 150 mbar.

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

[0077] Step d) is advantageously carried out by physical vapor deposition or by organometallic vapor phase epitaxy. In particular, organometallic vapor phase epitaxy is possible, despite a high temperature which may exceed, for example, 950°C, thanks to the presence of the polycrystalline aluminum nitride AIN film 3 which allows epitaxy to resume. 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 may be of the order of one micron.

[0079] The invention is not limited to the embodiments disclosed. Those skilled in the art are able to consider their technically operational combinations and to substitute equivalents for them.

Claims

Claims

1. 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 film (3) of polycrystalline aluminum nitride AIN, the metallic elements (E) being chosen to react chemically with MX2 by an oxidation-reduction reaction so as to transform the van der Waals bonds into covalent bonds; d) forming a crystalline layer (C) on the polycrystalline aluminum nitride AIN film (3) after step c).

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

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

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

5. Method according to one of claims 1 to 4, in which the metallic elements (E) diffused during step c) are atoms chosen as reducing agent of MX2.

6. Method according to one of claims 1 to 5, in which step a) is carried out so that MX2 is chosen to have a crystal lattice mismatch with the polycrystalline aluminum nitride AIN of less than or equal to 1.5%.

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

8. Method 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, aluminum Al, manganese Mn.

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

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

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

12. Method according to one of claims 1 to 11, in which step b) is carried out so that the film (3) of polycrystalline aluminum nitride AIN has a thickness less than or equal to 5 nm.

13. Method according to one of claims 1 to 12, in which step b) is carried out by physical vapor deposition.

14. Method according to one of claims 1 to 13, in which step d) is carried out by physical vapor deposition or by organometallic vapor epitaxy.

15. Method according to one of claims 1 to 14, in which 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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