Method for forming a primary stack for the manufacture of an electronic device
A protective thin layer with high acoustic impedance addresses edge damage issues during resonant thin film manufacturing, ensuring device performance and yield by protecting the film during etching.
Patent Information
- Authority / Receiving Office
- FR · FR
- Patent Type
- Applications
- Current Assignee / Owner
- COMMISSARIAT A LENERGIE ATOMIQUE ET AUX ENERGIES ALTERNATIVES
- Filing Date
- 2024-12-06
- Publication Date
- 2026-06-12
AI Technical Summary
The formation of a peripheral ring during the manufacture of resonant thin films in electronic devices leads to edge seepage and damage, particularly during chemical etching, reducing production yields and degrading device performance.
A method involving a protective thin layer with high acoustic impedance is deposited on the resonant thin layer to prevent edge damage during subsequent processing steps, using materials like AIN, Al₂O₃, HfN, SixNy, Ta₂O₅, TiN, TiO₂, WO₃, ZnO, or ZrO₂, which are suitable for protecting the resonant thin film during etching.
The protective layer effectively prevents edge damage during etching while maintaining the resonant thin film's performance, reducing defects and enhancing production yields.
Smart Images
Figure 00000000_0000_ABST
Abstract
Description
Title of the invention: Method for forming a primary stack for manufacturing an electronic device. Technical field of the invention
[0001] The present invention relates to microelectronic devices comprising at least one resonant thin layer transferred onto a substrate.
[0002] More particularly, the invention relates to a method for forming a primary stack comprising a thin layer of ferroelectric, pyro-, or piezoelectric material and a method for manufacturing an electronic device from such a primary stack. State of the art
[0003] Various processes for forming a thin layer on a supporting substrate are known from the prior art.These can include, for example, physical deposition techniques such as molecular beam epitaxy (MBE), plasma sputtering, or laser pulsed deposition (PLD), or chemical deposition techniques such as the sol-gel process or metalorganic chemical vapor deposition (MOCVD), or layer transfer techniques such as Smart Cut™ crystal ion slicing, in which a thin layer is removed from a bulk substrate by fracturing it at a weak zone (or weakening plane) created in the bulk substrate by implanting light species (e.g., H, He).
[0004] This latter method is particularly suitable for forming a single-crystal thin layer of a piezoelectric material, which is used as a resonant system.
[0005] These resonant thin films can, for example, be used in the manufacture of resonators or passive filters for surface acoustic waves (SAW), bulk acoustic waves (BAW), or lamb waves (also called plate waves). These devices are particularly useful in wireless communication systems, where they allow for the segregation of the numerous signals received by the antennas of a communication terminal, and thus ensure the signal-to-noise ratio levels required by current telecommunication standards.
[0006] In these devices, the thickness of the resonant thin film is a critical parameter for the proper functioning of the resonator or filter. Indeed, the width of The filter's bandwidth depends on the relative spacing between the resonant and antiresonant frequencies of its constituent resonators. This spacing is quantified by a coefficient called the electromechanical coupling coefficient (k2), which also quantifies the fraction of energy that can be converted from the electrical to the mechanical domain, or vice versa, within a resonator during each oscillation period. This coefficient depends directly on the resonator's geometry, the type of wave being processed, and the piezoelectric properties of the material used. Smart Cut™ technology is therefore particularly well-suited for manufacturing these types of devices because it allows for precise control of the resonant thin film's thickness. This technology also makes it possible to obtain thin films with different orientations (for example, X-, Y-, Y+36°-, Y+163°-, or Z-cut) in various sizes (from 75 to 300 mm).The document US20220166398Al describes a manufacturing process for such devices.
[0007] During the formation of substrates comprising this resonant thin layer, a trimming step is implemented at the edge of the plate, forming (for disc-shaped substrates) a peripheral ring devoid of the resonant thin layer. This peripheral ring is particularly useful for substrate transfer operations, as it allows the substrates to be gripped at their periphery by manufacturing equipment.
[0008] However, in the manufacture of certain devices, particularly resonators and filters, such a peripheral ring also serves as an entry point for plate edge seepage. This causes damage to the plate containing the devices at the edges. Such seepage generally occurs during the transfer and etching steps, and especially during chemical etching steps (e.g., hydrofluoric acid etching). This is particularly damaging in the manufacture of resonators and filters, as hydrofluoric acid etching is often used for its selectivity towards the piezoelectric material. This results in substantial degradation of the devices at the plate edge, which limits production yields and increases the amount of scrap.
[0009] Furthermore, since the piezoelectric resonant thin film is a sensitive layer in these devices, any layer coming into contact with it can negatively impact the performance of the devices. Therefore, there is a need to find a way to prevent degradation at the plate edge during the formation of a stack comprising a piezoelectric resonant thin film, without compromising the performance of said resonant thin film.
[0010] Object and invention
[0011] The present invention aims to provide a solution that addresses all or part of the aforementioned problems.
[0012] This goal can be achieved through the implementation of a method for forming a primary stack for the manufacture of an electronic device, the forming method comprising: - a supply step, in which an initial stack is supplied, said initial stack comprising: • an initial substrate having a front face, said front face comprising a central area and a peripheral trimming area, the peripheral trimming area being adjacent to a peripheral edge of the front face on one side, and surrounding the central area on the other; • a resonant thin layer of piezoelectric material having a top surface facing the initial substrate and a bottom surface opposite the top surface; and • a bonding layer, interposed between the central zone of the initial substrate, and the upper surface of the resonant thin layer; - a protection step, in which a thin protective layer is deposited on the initial stack on the lower surface side of the resonant thin layer, said thin protective layer covering the peripheral trimming area; the thin protective layer being made of a material having an acoustic impedance greater than 20 MRayl for longitudinal waves and / or greater than 12 MRayl for shear waves, the primary stack being formed at the end of the protection step.
[0013] The arrangements described above make it possible to propose a method for forming a primary stack comprising a thin protective layer intended to protect the resonant thin layer during subsequent steps of the process, particularly at the periphery of the thin protective layer.
[0014] Throughout the text and in general, 1 MRayl = 106 kg / (m2.s).
[0015] The formation process may also have one or more of the following characteristics, taken alone or in combination.
[0016] According to one embodiment, during the protection step, the protective thin layer is deposited so as to partially or totally cover the upper surface of the resonant thin layer, as well as the peripheral contouring area.
[0017] Thus, it is possible to protect the resonant thin film in a single process step. Furthermore, depositing the protective thin film over the entire apparent surface of the initial stack simplifies the formation process, thereby reducing costs.
[0018] According to one embodiment, during the protection step, the material of the thin protective film is chosen from the group consisting of AIN, A12O3, HfN, HfO2, SixNy, Ta2O5, TiN, TaN, TiO2, WO3, ZnO, and ZrO2.
[0019] Thus, the material chosen for the protective thin layer is particularly suitable for protecting the resonant thin layer during a chemical etching step, particularly with hydrofluoric acid.
[0020] According to one embodiment, during the supply step, the resonant thin film has a thickness of less than 2 pm, and in particular less than 1 pm.
[0021] In this way, the primary stack is suitable for the manufacture of radio frequency filters.
[0022] According to one embodiment, the supply step comprises: - the provision of a donor substrate comprising a thick layer, the donor substrate having a main face on the side of the thick layer; - the implantation of light species in the thick layer to generate a weakening plane and thus define the thin resonant layer between the weakening plane and the main face of the donor substrate; - bringing the main face of the donor substrate into contact with the front face of the initial substrate; - the detachment of the resonant thin layer at the level of the embrittlement plane, by the application of a heat treatment.
[0023] The steps described above allow for the extraction of a thin layer from a bulk substrate by fracture, using Smart Cut™ technology, thereby forming the resonant thin layer. An embodiment of implementing such steps is described in document US20230353115A1.
[0024] According to one embodiment, during the protection step, the thin protective layer is made of silicon nitride, and has a thickness less than or equal to 100 nm.
[0025] In this way, it is possible to benefit from protection against etching by the material with high acoustic impedance, and to have a thin protective film thickness sufficiently low so as not to degrade the performance of the resonator, in particular in terms of resonance frequency, coupling coefficient and quality factor.
[0026] According to one embodiment, during the protection step, the thin protective layer is made of aluminum nitride, and has a thickness less than or equal to 50 nm.
[0027] In this way, it is possible to benefit from protection against etching by the material with high acoustic impedance, and to have a thin film thickness of protection low enough not to degrade the performance of the resonator, particularly in terms of resonance frequency, coupling coefficient and quality factor.
[0028] According to one embodiment, during the supply step, the initial stack includes lower electrodes in electrical contact with the lower surface of the resonant thin film.
[0029] Thus, it is possible to re-establish electrical contact at the level of the resonant thin layer.
[0030] Generally, the lower electrodes are in direct contact with the resonant thin layer.
[0031] The object of the invention can also be achieved through the implementation of a method for manufacturing a resonant electronic device, the manufacturing method comprising: - a provisioning step, in which a primary stack obtained by a formation process as described above, and a receiving stack are made available, the receiving stack having a receiving face; - a bonding layer deposition step, in which a bonding layer is deposited on the lower surface side of the resonant thin layer; - a bonding step, in which the receiving face of the receiving stack and the bonding layer are brought into intimate contact, so as to bond the primary stack with the receiving stack; - a removal phase, in which the initial substrate and the bonding layer are removed mechanically and chemically; and - an electrode definition step, in which upper electrodes are deposited on the upper surface of the resonant thin film, then defined by photolithography, etching and resin removal, so that the upper electrodes are in electrical contact with the resonant thin film.
[0032] The above-described arrangements make it possible to manufacture a resonant electronic device in which the protective thin film provides protection against wet etching, particularly hydrofluoric acid. This makes it possible to limit damage to the resonant thin film near the peripheral edge, especially by seepage.
[0033] Surprisingly, it was found that the presence of a thin protective layer with high acoustic impedance made it possible to protect the resonant thin layer without compromising the resonance performance of that layer. This is particularly counterintuitive in the fabrication of a resonant electronic device, where the presence of a layer of high acoustic impedance near the resonant thin layer should a priori alter its performance.
[0034] The manufacturing process may also have one or more of the following characteristics, taken alone or in combination.
[0035] According to one embodiment, the step of depositing the adhesive layer includes the deposition and realization of the adhesive layer, by deposition and then planarization of this adhesive layer on the side of the lower surface of the resonant thin layer.
[0036] According to one embodiment, the bonding layer comprises a metal oxide such as silicon dioxide SiO2, or a polymer.
[0037] According to one embodiment, during the provisioning step, the receiving stack includes a layer of acoustic insulation, said layer of acoustic insulation bearing the receiving face of the receiving stack.
[0038] The manufacturing process is thus adapted for the manufacture of a volume acoustic wave resonator.
[0039] According to one embodiment, the acoustic insulation layer is a Bragg mirror.
[0040] The manufacturing process is thus adapted for the manufacture of a wave resonator volume acoustics on reflector.
[0041] According to one embodiment, the engraving phase comprises: - a first etching stage, in which the initial substrate is removed by grinding and then by anisotropic chemical etching; and - a second etching stage, in which the bonding layer is removed by chemical etching with hydrofluoric acid.
[0042] Advantageously, the initial substrate is removed first by grinding to remove a greater quantity of material, and then by selective chemical etching with the initial substrate material. Furthermore, the second etching step allows for the selective removal of the bonding layer, generally formed of silicon dioxide, without damaging the resonant thin film.
[0043] The object of the invention can also be achieved through the implementation of a resonant electronic device obtained by a manufacturing process as described above, the resonant electronic device comprising the successive stacking of at least: - a receiving stack; - a layer of adhesive; - a thin protective layer comprising an electrically insulating material; - lower electrodes in direct contact with the thin layer of protection; - a resonant thin layer of piezoelectric material having an opposing upper and lower surface, the lower surface being in electrical contact with the lower electrodes; - upper electrodes in electrical contact with the upper surface of the resonant thin layer;
[0044] In this resonant electronic device, the thin protective layer has an acoustic impedance greater than 20 MRayl for longitudinal waves and / or greater than 12 MRayl for shear waves.
[0045] The arrangements described above make it possible to propose a resonant electronic device exhibiting few defects near the peripheral edge.
[0046] Brief description of the drawings
[0047] Other aspects, objectives, advantages and features of the invention will become more apparent upon reading the following detailed description of preferred embodiments thereof, given by way of non-limiting example, and made with reference to the accompanying drawings in which:
[0048] [Fig-1] Fig. 1 is a schematic representation of a supply step according to a particular embodiment of the invention.
[0049] [Fig.2] Fig.2 is a schematic representation of the formation process and of a step of depositing a bonding layer according to a particular embodiment of the invention.
[0050] [Fig.3] Fig.3 is a schematic representation of the formation process and of a withdrawal phase according to a particular embodiment of the invention.
[0051] [Fig.4] Fig.4 is a schematic representation of certain steps in the process manufacturing.
[0052] [Fig. 5] Fig. 5 is a schematic representation of the formation process and the manufacturing process according to a particular embodiment of the invention. Detailed description
[0053] In the figures and throughout the description, the same reference numerals represent identical or similar elements. Furthermore, the various elements are not drawn to scale in order to enhance the clarity of the figures. Moreover, the different embodiments and variants are not mutually exclusive and may be combined.
[0054] As can be seen in Figures 1 to 5, the invention relates to a method of forming PI of a primary stack 30 for the manufacture of an electronic device 100, as well as a method of manufacturing P2 of a resonant electronic device 100 which will be described later.
[0055] The PI formation process includes firstly a supply step El, in which an initial stack 10 is supplied. This initial stack 10 includes in particular: an initial substrate 11 having a front face denoted "Fav", a resonant thin film 13 of piezoelectric material, and a bonding layer 15, interposed between the initial substrate 11 and the resonant thin film 13.
[0056] Figure 1 illustrates an embodiment of this supply step E1, comprising a succession of substeps leading to the supply of the initial stack 10, known as SmartCut™. In summary, this embodiment may first include the supply E01 of a donor substrate 1. This donor substrate 1 comprises a thick layer 3 (generally having a thickness greater than 10 pm), and optionally a primary bonding layer 2 disposed on the thick layer 3. The donor substrate 1 thus presents a main face fp3 on the side of the thick layer 3, and in particular on the side of the primary bonding layer 2.
[0057] An implantation step E02 can then be implemented, in which light chemical species are implanted in the thick layer 3 to generate a Pf3 embrittlement plane, and thus to define the resonant thin layer 13 between the Pf3 embrittlement plane and the main face fp3 of the donor substrate 1. It is therefore well understood that this Pf3 embrittlement plane will subsequently delimit the resonant thin layer 13 with the main face fp3.
[0058] A contacting step E03 is then implemented by bringing the main face fp3 of the donor substrate 1 into contact with the front face Fav of the initial substrate 11. As before, it may be advantageous for the front face Fav of the initial substrate 11 to be formed on a secondary bonding layer 4. Bonding is thus achieved between the main face fp3 and the front face Fav via the primary and secondary bonding layers 2, 4. These primary and secondary bonding layers 2, 4 thus form a single bonding layer 15.
[0059] Finally, a detachment step E04 can be implemented. During this step, the resonant thin film 13 is formed by detaching a portion 6 of the thick film 3 at the level of the embrittlement plane Pf3, for example by applying a heat treatment. It is therefore clearly understood that the resonant thin film 13 is the portion of the thick film 3 that remains attached to the secondary bonding layer 4 following the detachment of the portion 6 of the thick film 3.
[0060] Such a variant of the supply step El is advantageously implemented to form a resonant, single-crystal thin film 13 with a thickness typically less than 1 µm. Thus, the PI formation process is suitable for the manufacture of optical or acoustic devices. In particular, the PI formation process is suitable for the manufacture of acoustic resonators or filters, such as surface acoustic wave (SAW) resonators. Acoustic Wave according to the established Anglo-Saxon terminology), volume wave resonators (or BAW, for Bulk Acoustic Wave according to the established Anglo-Saxon terminology), or even Lamb wave resonators.
[0061] Regardless of the chosen implementation variant, the result is the formation of the initial stack 10 which comprises - the initial substrate 11, in which the front face Fav comprises a central zone Zc and a peripheral trimming zone Zdp, the peripheral trimming zone Zdp being adjacent to a peripheral edge Bp of the front face Fav on one side, and surrounding the central zone Zc on the other; - the resonant thin layer 13 having an upper surface sl3sup facing the initial substrate 11 and a lower surface sl3inf opposite to the upper surface sl3sup; and - the bonding layer 15, interposed between the central zone Zc of the initial substrate 11, and the upper surface sl3sup of the resonant thin film 13.
[0062] As illustrated in [Fig. 2], in order to provide an initial stack 10 suitable for the fabrication of resonant electronic devices 100, the initial stack 10 may include lower electrodes 12 in electrical contact with the lower surface sl3inf of the resonant thin film 13. Generally, the lower electrodes 12 are in direct contact with the resonant thin film 13. Thus, it is possible to re-establish electrical contact at the level of the resonant thin film 13. Furthermore, it is generally provided that the resonant thin film 13 has a thickness of less than 2 pm, and in particular less than 1 pm. In this way, the primary stack 30 is suitable for the fabrication of radio frequency (RF) filters.
[0063] The formation process then includes a protection step E2, in which a thin protective layer 17 is deposited on the initial stack 10 on the side of the lower surface sl3inf of the resonant thin layer 13. This thin protective layer 17 covers the peripheral trimming area Zdp and at least part of the upper surface.
[0064] As illustrated in [Fig. 2], during the protection step E2, the protective thin film 17 is deposited so as to partially or totally cover the upper surface sl3sup of the resonant thin film 13, as well as the peripheral contouring zone Zdp. Thus, it is possible to protect the resonant thin film 13 in a single process step. Furthermore, depositing the protective thin film 17 over the entire apparent surface of the initial stack 10 simplifies the forming process, thereby reducing costs.
[0065] In the embodiment of [Fig. 3], the thin protective layer 17 is deposited on the front face side Fav, and covers the peripheral contouring area Zdp. It covers the temporary support 45 located on the front face Fav, as well as the lower surface sl3inf and an adhesive layer 20 interposed between the temporary support 45 and the lower surface sl3inf. It is then possible to implement an etching phase P40 (which will be described later), to remove the temporary support 45 and the adhesive layer 20, thus forming the primary stack 30.
[0066] The protective thin film 17 is made of a material having an acoustic impedance greater than 20 MRayl for longitudinal waves and / or greater than 12 MRayl for shear waves. Throughout the text and generally, 1 MRayl = 106 kg / m².s. For example, the material of the protective thin film 17 is chosen from the group consisting of aluminum nitride AIN, aluminum oxide Al₂O₃, hafnium nitride HfN, hafnium dioxide HfO₂, silicon nitride SixNy, tantalum pentoxide Ta₂O₅, titanium nitride TiN, tantalum nitride TaN, titanium dioxide TiO₂, tungsten trioxide WO₃, zinc oxide ZnO, and zirconium dioxide ZrO₂. Thus, the material chosen for the protective thin layer 17 is particularly suitable for protecting the resonant thin layer 13 during a hydrofluoric acid etching step.
[0067] According to a first embodiment, the protective thin film 17 can be made of SixNy silicon nitride and can have a thickness of 100 nm or less. In this way, it is possible to benefit from the protection against etching by the high acoustic impedance material, and to have a protective thin film thickness 17 that is sufficiently small so as not to degrade the performance of the resonator, in particular in terms of resonant frequency, coupling coefficient and quality factor.
[0068] According to a second embodiment, the protective thin film 17 can be made of aluminum nitride AIN, and can have a thickness less than or equal to 50 nm. In this way, it is possible to benefit from the protection against etching by the material with high acoustic impedance, and to have a protective thin film thickness 17 low enough not to degrade the performance of the resonator, in particular in terms of resonant frequency, coupling coefficient and quality factor.
[0069] This PI formation process results in the formation of a primary stack 30, obtained at the end of the protection step E2.
[0070] All the arrangements described above make it possible to propose a process allowing the formation of a primary stack 30 comprising a thin protective layer 17 intended to protect the resonant thin layer 13 during subsequent steps of the process, in particular at the periphery of the thin protective layer 17.
[0071] The invention also relates to a manufacturing method P2 of a resonant electronic device 100, illustrated in [Fig.5].
[0072] The manufacturing process P2 first comprises a provisioning step E10, in which a primary stack 30 obtained by the formation process PI and a receiving stack 40 are provided. It is therefore possible that the steps of the formation process PI as described above may be included in the manufacturing process P2. The receiving stack 40 has a receiving face fr40.
[0073] During the provisioning step E10, the receiving stack 40 generally includes a layer of acoustic insulation 43, said acoustic insulation layer 43 bearing the receiving face fr40 of the receiving stack 40. The manufacturing process P2 is thus adapted for the fabrication of a volume acoustic wave resonator. More specifically, this layer of acoustic insulation 43 can be a Bragg mirror. The manufacturing process P2 is thus adapted for the fabrication of a volume acoustic wave resonator on a reflector.
[0074] As illustrated in [Fig.3], a bonding layer deposition step E20 is implemented, in which a bonding layer 20 is deposited on the lower surface side sl3inf of the resonant thin film 13. For example, this bonding layer 20 may comprise a metal oxide such as silicon oxide SiO2, or a polymer.
[0075] Next, and as illustrated in [Fig. 3], a bonding step E30 is implemented, in which the receiving face fr40 of the receiving stack 40 and the bonding layer 20 are brought into intimate contact, so as to bond the primary stack 30 with the receiving stack 40. As can be seen in the figure, during this bonding step E30, the primary stack 30 is reversed towards the receiving stack 40, with the bonding layer 20 positioned between the two stacks 30, 40. This results in particular in a reversal of the position of the lower surfaces sl3inf and upper surfaces sl3sup of the resonant thin layer 13 in the figures.
[0076] The manufacturing process P2 then includes a removal phase P40, one embodiment of which is illustrated in [Fig.4]. During this removal phase P40, the initial substrate 11 and the bonding layer 15 are removed by mechanical and chemical means.
[0077] For example, the P40 etching phase may include: - a first etching step E41, in which the initial substrate 11 is removed by grinding and then by anisotropic chemical etching; and - a second etching stage E42, in which the bonding layer 15 is removed by chemical etching with hydrofluoric acid.
[0078] Advantageously, the initial substrate 11 is removed first by grinding to remove a greater quantity of material, then by selective chemical etching with the material of the initial substrate 11. Furthermore, the second etching step E42 allows the bonding layer 15, generally formed of silicon dioxide, to be selectively removed without damaging the resonant thin layer 13.
[0079] Finally, an electrode definition step E50 is implemented, in which upper electrodes 14 are deposited on the upper surface sl3sup of the resonant thin film 13, and then defined by photolithography, etching and resin removal, so that the upper electrodes 14 are in electrical contact with the resonant thin film 13.
[0080] All the arrangements described above make it possible to manufacture a resonant electronic device 100 in which the protective thin film 17 provides protection against etching and in particular against hydrofluoric acid generally used during the etching phase P40. It is thus possible to limit damage to the resonant thin film 13 near the peripheral edge Bp, in particular by infiltration.
[0081] Surprisingly, it was found that the presence of a protective thin layer 17 with high acoustic impedance made it possible to protect the resonant thin layer 13 without impairing the resonance performance of that layer. This is particularly counterintuitive in the fabrication of a resonant electronic device 100, where the presence of a layer with high acoustic impedance near the resonant thin layer 13 should, a priori, alter its performance.
[0082] The invention also relates to a 100% resonant electronic device obtained by manufacturing process P2. This 100% resonant electronic device comprises the successive stacking of at least: - a receiver stack 40; - a 20 layer of adhesive; - a thin protective layer 17 comprising an electrically insulating material; - lower electrodes 12 in direct contact with the thin protective layer 17; - a resonant thin layer 13 of piezoelectric material having an opposing upper surface sl3sup and lower surface sl3inf, the lower surface sl3inf being in electrical contact with the lower electrodes 12; and - upper electrodes 14 in electrical contact with the upper surface sl3sup of the resonant thin layer 13;
[0083] In this resonant electronic device 100, the material of the protective thin film 17 exhibits an acoustic impedance greater than 20 MRayl for longitudinal waves and / or greater than 12 MRayl for shear waves. The arrangements described above make it possible to propose a resonant electronic device 100 with few defects near the peripheral edge Bp.
Claims
Demands
1. A method for forming (PI) a primary stack (30) for manufacturing an electronic device (100), the forming method (PI) comprising: • a supply step (El), in which an initial stack (10) is supplied, said initial stack (10) comprising: • an initial substrate (11) having a front face (Fav), said front face (Fav) comprising a central zone (Zc) and a peripheral trimming zone (Zdp), the peripheral trimming zone (Zdp) being adjacent to a peripheral edge (Bp) of the front face (Fav) on the one hand, and surrounding the central zone (Zc) on the other hand; • a resonant thin film (13) of piezoelectric material having an upper surface (sl3sup) facing the initial substrate (11) and a lower surface (sl3inf) opposite the upper surface (sl3sup); and • a bonding layer (15), interposed between the central zone (Zc) of the initial substrate (11), and the upper surface (sl3sup) of the resonant thin layer (13); • a protection step (E2), in which a thin protective layer (17) is deposited on the initial stack (10) on the lower surface side (sl3inf) of the resonant thin layer (13), said thin protective layer (17) covering the peripheral trimming zone (Zdp); the thin protective layer (17) being of a material having an acoustic impedance greater than 20 MRayl for longitudinal waves and / or greater than 12 MRayl for shear waves, the primary stack (30) being formed at the end of the protection step (E2).
2. A forming method (PI) according to claim 1, wherein during the protection step (E2), the protective thin layer (17) is deposited so as to partially or totally cover the upper surface (sl3sup) of the resonant thin layer (13), as well as the peripheral decoupling zone (Zdp).
3. A forming method (PI) according to any one of claims 1 or 2, wherein during the protection step (E2), the material of the protective thin film (17) is selected from the group consisting of AIN, A12O3, HfN, HfO2, SixNy, Ta2O5, TiN, TaN, TiO2, WO3, ZnO, and ZrO2.
4. A formation method (PI) according to any one of claims 1 to 3, wherein during the supply step (El), the resonant thin film (13) has a thickness of less than 2 pm, and in particular less than 1 pm.
5. A formation method (PI) according to any one of claims 1 to 4, wherein the supply step (E1) comprises: • supplying (E01) a donor substrate (1) comprising a thick layer (3), the donor substrate (1) having a principal face (fp3) on the side of the thick layer (3); • implanting (E02) light species into the thick layer (3) to generate a weakening plane (Pf3) and thus to define the resonant thin layer (13) between the weakening plane (Pf3) and the principal face (fp3) of the donor substrate (1); • bringing into contact (E03) the principal face (fp3) of the donor substrate (1) with the front face (Fav) of the initial substrate (11); • the detachment (E04) of the resonant thin layer (13) at the level of the embrittlement plane (Pf3), by the application of a heat treatment.
6. Forming method (PI) according to any one of claims 1 to 5, wherein in the protection step (E2), the protective thin layer (17) is made of silicon nitride (SiN), and has a thickness less than or equal to 100 nm.
7. Forming process (PI) according to any one of claims 1 to 5, wherein in the protection step (E2), the protective thin layer (17) is made of aluminium nitride (AIN), and has a thickness less than or equal to 50 nm.
8. Formation method (PI) according to any one of claims 1 to 7, wherein during the supply step (E1), the initial stack (10) comprises lower electrodes (12) in electrical contact with the lower surface (s13inf) of the resonant thin film (13).
9. A manufacturing method (P2) for a resonant electronic device (100), the manufacturing method (P2) comprising: • a provisioning step (E10), in which a primary stack (30) obtained by a forming process (PI) according to claim 8, and a receiving stack (40) are provided, the receiving stack (40) having a receiving face (fr40); • a bonding layer deposition step (E20), in which a bonding layer (20) is deposited on the lower surface side (sl3inf) of the resonant thin layer (13); • a bonding step (E30), in which the receiving face (fr40) of the receiving stack (40), and the bonding layer (20) are brought into intimate contact, so as to bond the primary stack (30) with the receiving stack (40);• a removal phase (P40), in which the initial substrate (11) and the bonding layer (15) are removed by mechanical and chemical means; and • an electrode definition step (E50), in which upper electrodes (14) are deposited on the upper surface (sl3sup) of the resonant thin film (13), and then defined by photolithography, etching and resin removal, so that the upper electrodes (14) are in electrical contact with the resonant thin film (13).
10. Manufacturing method (P2) according to claim 9, wherein during the provisioning step (E10), the receiving stack (40) comprises a layer of acoustic insulation (43), said layer of acoustic insulation (43) bearing the receiving face (fr40) of the receiving stack (40).
11. Manufacturing method (P2) according to claim 10, wherein the acoustic insulation layer (43) is a Bragg mirror.
12. A manufacturing process (P2) according to any one of claims 9 to 11, wherein the etching stage (P40) comprises: • a first etching stage (E41), in which the initial substrate (11) is removed by grinding and then by anisotropic chemical etching; and • a second etching stage (E42), in which the bonding layer (15) is removed by chemical etching with hydrofluoric acid.
13. A resonant electronic device (100) obtained by a manufacturing process (P2) according to any one of claims 9 to 12, the resonant electronic device (100) comprising the successive stacking of at least: • a receiving stack (40); • an adhesive layer (20); • a protective thin layer (17) comprising an electrically insulating material; • lower electrodes (12) in direct contact with the protective thin layer (17); • a resonant thin layer (13) of piezoelectric material having an opposing upper surface (sl3sup) and lower surface (sl3inf), the lower surface (sl3inf) being in electrical contact with the lower electrodes (12); • upper electrodes (14) in electrical contact with the upper surface (sl3sup) of the resonant thin layer (13);resonant electronic device (100) wherein the material of the protective thin film (17) has an acoustic impedance greater than 20 MRayl for longitudinal waves and / or greater than 12 MRayl for shear waves.;