Method for transferring a film

Abstract

The invention relates to a method for producing a device (10) comprising a piezoelectric membrane (14) suspended over at least one cavity (11), the method comprising: a) providing a support substrate (1) equipped with a cavity (11) open on a front face (12) of the support substrate, said cavity (11) having a transverse dimension greater than 30 pm; b) providing a donor substrate (2) equipped with a weakened plane (20) located under the surface defining a surface layer (22); c) depositing a reinforcement layer (13) on a front face (21) of the donor substrate (2), the reinforcement layer (13) being made of a piezoelectric material having a thickness (e) greater than 500 nm; d) assembling the support substrate (1) and the donor substrate (2); e) splitting the donor substrate (2) at the weakened plane (20) so as to transfer a membrane (14) comprising the surface layer (22) and the reinforcement layer (13) onto the support substrate (1).

Description

Technical Field

[0001] This invention relates to the field of microelectronics and microsystems. In particular, this invention relates to a method for producing a structure comprising a membrane having piezoelectric properties capable of deforming over at least one cavity. Background Technology

[0002] MEMS (Micro-Electro-Mechanical Systems) devices are widely used in the production of various sensors. Many of these MEMS devices operate by vibrating a flexible diaphragm above a cavity. For example, PMUT (Piezoelectric Micromechanical Ultrasonic Transducer) microsystems can be mentioned. In operation, the vibration of the diaphragm, caused by physical parameters (e.g., the propagation of sound waves), is converted into an electrical signal (or vice versa, depending on whether the device is in receiver or transmitter mode).

[0003] Several methods can be used to fabricate structures with films suspended above cavities. One method involves removing an SOI (silicon-on-insulator) substrate previously bonded to a substrate with cavities. Another method involves steps of deposition and film release via chemical etching.

[0004] Forming suspended films via sacrificial deposition has several drawbacks: the empty space within the cavity may be limited, there is a risk of bonding the film to the bottom of the cavity during release, the risk of partial release, and difficulties in managing mechanical stress on the film. Furthermore, forming suspended films by bonding an SOI substrate before removing it via grinding / chemical etching allows for better control of the atmosphere within the cavity (sealing upon bonding). However, this operation is relatively expensive because it consumes the SOI substrate.

[0005] Another simpler alternative includes using Smart-Cut. TM The technology transfers the layers directly over the cavity to form a suspended membrane.

[0006] Using this alternative, it is difficult to transfer the film over a cavity with a large size. However, what is really needed is a cavity with a large size, especially for PMUT devices, where the cavity is typically measured in hundreds of micrometers, allowing them to operate at relatively low frequencies between 0.1 and 10 MHz.

[0007] French patent FR2715502 describes how to use a Smart-Cut transfer to transfer a film suspended above a cavity. According to this teaching, when the substrate including the cavity is made of silicon, the cavity size (Lmax) should be less than 10 times the thickness (e0) of the transferred film. The "size" of the cavity should be understood as the lateral dimension in the main plane of the substrate's front side, such as width, length, diameter, etc.

[0008] Additionally, using Smart-Cut TMThe maximum thickness (e0) of the film transferred by this method is limited by the donor substrate implantation energy and therefore cannot exceed a few micrometers. Specifically, high-energy ion implanters (>250 keV) that allow for deeper implantation have low flux, and the ion implantation step will require a significant amount of time. Therefore, in order to implant the target dose (several 10... 16 cm -2 This method would be difficult to implement (slow) and expensive. Furthermore, such a device is not standard. Consequently, the maximum lateral dimension of the cavity in this type of structure obtained using Smart-Cut cannot exceed tens of micrometers. Summary of the Invention

[0009] The present invention aims to overcome all or some of the aforementioned disadvantages. The present invention relates to a method for transferring a piezoelectric film onto a substrate comprising at least one large-sized cavity using a Smart-Cut method.

[0010] Therefore, the present invention relates to a method for producing a device comprising a piezoelectric membrane above at least one cavity, the method comprising the following steps: a) Provide a carrier substrate having a first surface extending over a plane (x, y) and having a cavity opening onto the first surface, the cavity having a lateral dimension greater than 30 μm in the plane (x, y). b) Provide a donor substrate having a buried weakening plane formed by implanting a light material through the front side of the donor substrate, the weakening plane defining a surface layer. c) Deposit a reinforcement layer on the front side of the donor substrate, the reinforcement layer being made of a piezoelectric material with a thickness greater than 500 nm. d) Joining the carrier substrate and the donor substrate at the bonding interface between the first surface of the carrier substrate and the reinforcing layer. e) After step d), the donor substrate is separated at the buried weakened plane to transfer a film including the surface layer and the reinforcing layer to the carrier substrate, the film being located above the cavity.

[0011] Depending on other advantageous and non-limiting features of the production method, the method can be implemented alone or in any technically feasible combination: The donor substrate is made of silicon or silicon carbide.

[0012] The carrier substrate is made of silicon. The donor substrate is made of silicon, and the reinforcing layer is deposited at a temperature below 450°C.

[0013] The donor substrate is made of silicon carbide, and the reinforcing layer is deposited at a temperature below 850 °C.

[0014] The implanted light material consists of hydrogen ions and / or helium ions.

[0015] A first conductive layer is inserted between the reinforcing layer and the carrier substrate. The first layer is in direct contact with the reinforcing layer and is configured to form the lower electrode of the device. A bonding layer is inserted between the reinforcing layer and the carrier substrate, the bonding layer being in direct contact with the carrier substrate, and the bonding layer is preferably made of silicon oxide. A second conductive layer is formed on the reinforcing layer, and the second layer is configured to form the upper electrode of the device. The method includes performing at least one mechanical polishing operation and / or at least one chemical mechanical polishing operation and / or at least one chemical etching operation on the surface layer after separation step e). Step d) of bonding includes bonding the donor substrate (2) on one side, where the reinforcing layer (3) is disposed, to the first surface (12) of the carrier substrate (1) on the other side by molecular adhesion. After step e), a deposition step is performed on the free surface of the surface layer to increase the thickness of the surface layer.

[0016] According to another aspect of the invention, the invention also relates to a donor substrate configured to transfer a piezoelectric film to a carrier substrate, the carrier substrate having at least one cavity having a lateral dimension greater than 30 μm, the donor substrate comprising: A weakening plane, which is arranged in the donor substrate (2) and defines a surface layer, and A reinforcing layer is disposed on the surface layer (22), the reinforcing layer being made of a piezoelectric material with a thickness (e) greater than 500 nm. Attached Figure Description

[0017] Other features and advantages of the invention will become apparent from the following detailed description of the invention, taken with reference to the accompanying drawings, in which: Figures 1 to 5 The steps of a method according to the invention for transferring a membrane disposed above a buried cavity are shown; Figures 6A to 6DVariations and other steps in the transfer method according to the present invention are shown. Detailed Implementation

[0018] In this specification, the same reference numerals in the accompanying drawings may be used for the same type of elements. The drawings are schematic representations and are not drawn to scale for clarity. In particular, the thickness of layers along the z-axis is not proportional to the lateral dimensions along the x- and y-axis; the relative thicknesses of these layers relative to each other are not necessarily taken into account in the drawings.

[0019] This invention relates to a method for transferring a piezoelectric membrane 14 to a cavity 11 ( Figures 1 to 5 A method for transferring a carrier substrate 1, the transfer method being designed to produce a structure 10 including a large-sized buried cavity 11.

[0020] The method according to the invention includes the step of providing a carrier substrate 1 (see...) Figure 1 The latter has a first surface 12 for bonding to the donor substrate 2 and a second surface 12' opposite to the first surface 12, referred to as the back surface. As a non-limiting example, the carrier substrate 1 may include silicon, glass, sapphire, etc. The thickness of the carrier substrate 1 can be on the order of several hundred μm, typically 775 μm for a substrate with a diameter of approximately 300 mm.

[0021] The carrier substrate 1 includes a plurality of cavities 11 opening into its first surface 12. Each cavity 11 has a bottom and a peripheral wall. Preferably, the carrier substrate 1 is a silicon substrate.

[0022] The geometry of each cavity 11, depending on the target device (especially the target MEMS device), is defined by the following: The shape of the cavity 11 in the plane (referred to as the principal plane (x, y)) of the first surface 12 of the carrier substrate 1: the shape may be circular, square, rectangular or polygonal; The lateral dimensions L of cavity 11 in the principal plane (x, y): they may range from tens of micrometers to several millimeters; The depth of cavity 11 along the z-axis perpendicular to the principal plane (x, y): This depth may vary from hundreds of nanometers to tens of micrometers, or even hundreds of micrometers.

[0023] According to the present invention, the transfer method includes transferring a piezoelectric film 14 to a carrier substrate 1 comprising a large-sized buried cavity 11. "Large-sized" means that the lateral dimension L of the cavity 11 in the plane (x, y) is greater than 30 μm.

[0024] The planar distribution of cavities 11 (i.e., their distribution in the principal plane (x, y)) also depends on the target device and will define the inter-cavity spacing 11: this spacing may vary from a few micrometers to hundreds of micrometers, or even a few millimeters. The inter-cavity spacing may be uniform and the same across the entire surface of the carrier substrate 1, or it may vary between regions on the surface of the carrier substrate 1.

[0025] It should be noted that the carrier substrate 1 may contain cavities 11 with different shapes, lateral dimensions, depths and / or planar distributions, especially if a structure 10 is provided that integrates various types of devices into the buried cavities.

[0026] Depending on the type of device to be manufactured using the structure 10, which includes the buried cavity 11, various layers may be deposited on the bottom and / or walls of the cavity 11 (e.g., silicon nitride, silicon oxide, etc.).

[0027] The method according to the invention also includes providing a front side 21 and a back side 21' (see...) Figure 2 The step of the donor substrate 2, wherein the front side 21 is used for bonding to the carrier substrate 1.

[0028] As an example, and in a non-limiting manner, the donor substrate 2 may include at least one semiconductor material (e.g., silicon, silicon carbide, gallium nitride, etc.) or a piezoelectric material (e.g., lithium tantalate, lithium niobate, aluminum nitride, zinc oxide, PZT, etc.). Preferably, the donor substrate 2 is a silicon substrate or a silicon carbide (SiC) substrate.

[0029] The step of providing the donor substrate 2 further includes implanting a light material into the donor substrate 2 via the front side 21 to form a weakening plane 20 located between a first portion and a second portion 23 of the donor substrate 2, the first portion forming a surface layer 22 and the second portion constituting the remainder of the donor substrate 2. Preferably, the implanted light material is hydrogen ions and / or helium ions.

[0030] The thickness of the first portion, and therefore the thickness of the future surface layer 22, depends on the implantation energy of the light material (e.g., hydrogen and / or helium). Advantageously, the implantation energy is selected such that the first portion of the donor substrate 2 has a thickness of about 0.2 micrometers to 2 micrometers.

[0031] Additionally, the method according to the invention further includes the step of depositing a reinforcing layer 13 made of a material having piezoelectric properties on the front side 21 of the donor substrate 2 (see...). Figure 3 The deposition step is performed after the step of implanting light material ions into the donor substrate 2. The thickness e of layer 13 is greater than 500 nm. Even more preferably, the thickness e of layer 13 is greater than 1 μm or even greater than 4 μm.

[0032] The reinforcing layer 13 may include materials selected from: lithium niobate (LiNbO3), lithium tantalate (LiTaO3), potassium sodium niobate (K... x Na 1－x NbO3 or KNN), barium titanate (BaTiO3), quartz, lead zirconate titanate or PZT (Pb(Zr,Ti)O3), magnesium lead niobate and lead titanate compounds in variable proportions (e.g., 70 / 30 or 90 / 10) according to the required properties (PMN-PT), zinc oxide (ZnO), aluminum nitride (AlN) or scandium aluminum nitride (AlScN), etc.

[0033] Preferably, the reinforcing layer 13 is made of AlN or PZT. Specifically, these two materials are considered to be the most commonly used piezoelectric materials in the field of MEMS. In addition, the elastic modulus of AlN is on the order of 300 GPa, which is significantly higher than that of PZT. Therefore, even more preferably, AlN is chosen as the piezoelectric material for the reinforcing layer 13.

[0034] As an exemplary implementation, when the reinforcing layer 13 is made of AlN and the donor substrate 2 is made of silicon with a cavity having a lateral dimension of approximately 50 μm, the thickness of the reinforcing layer is preferably greater than or equal to 1.5 μm. According to another similar exemplary implementation where the reinforcing layer 13 is made of PZT, the thickness of the reinforcing layer 13 is preferably selected to be greater than 7.5 μm.

[0035] Furthermore, those skilled in the art will be able to select the thickness of the reinforcing layer 13 based on the lateral dimension L of the cavity 11 and the mechanical properties of the reinforcing layer 13 (e.g., Young's modulus) in order to successfully transfer the membrane 14.

[0036] Those skilled in the art can also adjust the temperature used to deposit the reinforcing layer 13 according to the properties of the donor substrate 2 to prevent blistering.

[0037] In other words, the reinforcing layer 13 is advantageously deposited at a temperature that is adjusted and configured to prevent blistering of the weakened plane 20 under the action of heat treatment with a high thermal budget.

[0038] Specifically, the effect of implanting light ions is to create defects (vacancies or interstitial defects) at the weakened plane 20. These defects are commonly referred to as platelets and have a size on the order of approximately 10 nanometers. The effect of temperature causes a change in the number of these defects through Ostwald ripening, resulting in the appearance of microcracks or microcavities. When supersaturated, the light ions implanted in the donor substrate 2 precipitate into these microcavities in gaseous form under the influence of temperature. When a high thermal budget is applied, the cavities then grow and coalesce in the form of bubbles, both vertically and laterally, resulting in bubbling on the front side 21.

[0039] According to a variant embodiment, when the donor substrate 2 is made of silicon (or includes a silicon layer in which light ions have been implanted), the deposition temperature is preferably below 450 °C, and even more preferably below 400 °C.

[0040] According to another variant, when the donor substrate 2 is made of silicon carbide (or includes a silicon carbide layer in which light ions have been implanted), the deposition temperature is preferably below 850°C.

[0041] Layer 13 can be deposited using any technique known to those skilled in the art that is compatible with conventional methods in the field of microelectronics. Preferably, the reinforcing layer 13 is deposited using cathode sputtering or sol-gel technology (chemical deposition technology).

[0042] As an example, deposition via cathode sputtering advantageously makes it possible to obtain crystalline piezoelectric layers for certain materials (such as aluminum nitride (AlN)) at low deposition temperatures on the order of 300 °C or 400 °C.

[0043] Advantageously, the piezoelectric reinforcement layer 13 made of AlN is deposited using cathode sputtering according to the invention.

[0044] In addition, PZT is deposited using cathode sputtering at a relatively higher temperature than that used for AlN deposition to facilitate crystallization. The deposition temperature of PZT can reach 700 °C.

[0045] According to one embodiment of the invention, a reinforcing layer 13 made of PZT can be deposited using a sol-gel method. This is a chemical deposition technique: the precursor to be deposited is added to a solvent in solid form. The resulting solution is then spread onto the front side 21 of the donor substrate 2. Spreading can be achieved by spin coating. The substrate is then dried to evaporate the solvent before undergoing a calcination step to break the carbon chains. The sequence of spreading, drying, and calcination steps can be repeated multiple times to increase the thickness of the obtained layer. Furthermore, the obtained layer is typically amorphous in nature and requires a final crystallization / densification heat treatment step.

[0046] According to another embodiment, a reinforcing layer 13 made of PZT can be produced using low-temperature MOCVD (metal-organic chemical vapor deposition). Specifically, this technique is known to enable the deposition of PZT in a crystalline state at temperatures potentially below 400 °C or even lower.

[0047] According to one embodiment of the invention, the method may optionally include a heat treatment for repairing the deposited reinforcing layer 13. The repair heat treatment can advantageously be used to partially or completely recrystallize the reinforcing layer 13. The treatment can also be used to degas the deposited piezoelectric layer and / or remove impurities that may have been introduced into the layer during, before, or after its deposition. According to an alternative, the heat treatment may include thermal annealing to improve the crystal quality of the deposited layer 13.

[0048] like Figure 4 As shown, the method according to the present invention further includes the step of bonding the carrier substrate 1 and the donor substrate 2. The carrier substrate 1 and the donor substrate 2 are bonded at a bonding interface 30 between a first surface 12 of the carrier substrate 1 and a reinforcing layer 13 disposed on the front surface 21 of the donor substrate 2.

[0049] Advantageously, this step involves direct bonding via molecular adhesion between the first surface 12 of the donor substrate 1 and the reinforcing layer 13 of the carrier substrate 1. The principles of molecular adhesion, well-known in the prior art, will not be described in further detail here. It should be noted that the surfaces to be bonded must have very good surface finish (cleanliness, low roughness, etc.) to achieve a good quality bond.

[0050] Advantageously, to ensure good quality bonding, the bonding step includes cleaning the surfaces to be bonded on the donor substrate 2 (in this embodiment, the surface of the reinforcing layer 13) and the carrier substrate 1 before the surfaces come into contact. As an example, a conventional sequence used in microelectronics (particularly for silicon-based substrates) includes ozone cleaning, SC1 cleaning (SC1 being an abbreviation for Standard Clean 1) with an intermediate rinse, and SC2 cleaning (SC2 being an abbreviation for Standard Clean 2). To promote high bonding energy between the surfaces, the surfaces to be bonded may also be activated, for example, using plasma before contact.

[0051] The method according to the invention also provides a step of separating the donor substrate 2 at a buried weakening plane 20 in order to transfer the film 14, including the surface layer 22 and the reinforcing layer 13, to the carrier substrate 1. Separation occurs at the buried weakening plane 20 between the surface layer 22 and the remainder 23 of the donor substrate 2 (see...). Figure 2 , 4 and 5).

[0052] Furthermore, the separation step is performed after the step of bonding the carrier substrate 1 and the donor substrate 2 with the reinforcing layer 13. It is a conventional separation step according to the Smart Cut method.

[0053] like Figure 5 As shown, after the separation step is completed, a film 14 is obtained transferred onto the carrier substrate 1. It is worth recalling that the SmartCut method advantageously allows for the acquisition of thin layers with excellent thickness uniformity. This standard is highly advantageous for certain MEMS devices that require flexible films with controlled thickness.

[0054] This separation is preferably performed during heat treatment at a temperature between several hundred degrees and 950 °C. Preferably, when the weakening plane is disposed in the silicon layer of the donor substrate 2, separation is performed during heat treatment at a temperature below 700 °C. According to another embodiment, when the weakening plane is disposed in the silicon carbide layer of the donor substrate 2, separation is performed during heat treatment at a temperature below 950 °C.

[0055] According to one embodiment, the separation step may alternatively be mechanically assisted or performed by means of mechanical stress after heat treatment.

[0056] According to an embodiment where the reinforcing layer 13 is made of PZT using sol-gel deposition, a separation heat treatment performed at a temperature between 500 °C and 750 °C will advantageously allow for the separation of the donor substrate and the recrystallization of the deposited PZT. In other words, the separation heat treatment also includes heat treatment for repairing the PZT layer.

[0057] After the film 14 has been transferred to the carrier substrate 1, the separation step may include finishing processes aimed at improving crystal quality (removing defects from the layer), surface quality (removing residual roughness from the free surface of layer 22), and / or modifying the thickness of the surface layer 22. This process may include one or more thermal treatments, chemical mechanical polishing, chemical etching, epitaxial growth, and / or deposition of additional layers.

[0058] Specifically, in some cases where the thickness of the surface layer 22 transferred using the Smart Cut method is insufficient, this thickness can be increased during the aforementioned finishing process by depositing an additional layer on the free surface of the surface layer 22 (e.g., by epitaxial growth or other known deposition methods) (see [link to documentation]). Figure 6D The additional layer preferably has the same properties as the surface layer 22.

[0059] When the method according to the invention is completed, the obtained structure 10 is provided with a large-sized buried cavity 11 and a piezoelectric membrane 14 (including a surface layer 22 and a reinforcing layer 13) above one or more cavities 11.

[0060] The method according to the invention is easy to implement and advantageously allows for the efficient transfer of the membrane to a carrier substrate with a large-sized cavity having a lateral dimension greater than 30 μm. The membrane is transferred as a whole and benefits from the advantages of the SmartCut method. Specifically, the applicant has observed that a reinforcing layer with a thickness greater than 500 nm can increase the reinforcing effect on the donor substrate, even if its properties are piezoelectric and different from those of the donor substrate. This advantageously avoids the problems of membrane bubbling and / or partial transfer that can occur when the Smart Cut method involves a carrier substrate covered with a large-sized cavity. "Partial transfer" refers to a portion of the membrane not being transferred to the carrier substrate after the separation step.

[0061] Furthermore, the reinforcing layer according to the invention possesses piezoelectric properties. Therefore, the method according to the invention provides a solution for fabricating piezoelectric films on substrates with large-size cavities, a solution that is simple, easily implemented, and effective, while benefiting from the advantages of the Smart Cut method. In other words, the transferred film exhibits excellent thickness uniformity, which can be highly advantageous for certain MEMS devices requiring flexible films with controlled thickness above cavities. In particular, the resulting structure can be used to produce PMUT devices, in which cavities are typically measured in the hundreds of micrometers. With the advantages of the Smart Cut method, the piezoelectric properties of the transferred film, and the large size of the cavity in the carrier substrate, the method according to the invention makes it possible to obtain structures configured for the production of PMUT devices, especially those with precise and uniform operating frequencies.

[0062] according to Figure 6A In one embodiment shown, the carrier substrate 1 and / or donor substrate 2 may each include a bonding layer 32 at the first surface 12 and / or above the reinforcing layer 13, respectively, to improve the bonding amount and bonding energy at their interfaces. The bonding layer 32 is preferably disposed on the reinforcing layer 13 such that the bonding interface 30 is between the first surface 12 of the carrier substrate 1 and the bonding layer 32 (see [reference]). Figure 6A and Figure 6C Advantageously, the bonding layer 32 is made of silicon oxide. Specifically, silicon oxide is an easily deposited material and allows for a roughness compatible with direct bonding.

[0063] Preferably, the bonding layer 32 is made of silicon oxide and formed using TEOS (tetraethyl orthosilicate) PECVD. After its deposition, the oxide layer can be planarized and then cleaned in preparation for the direct bonding step, as described above.

[0064] In addition to layer 32, which is configured to improve the bonding, additional layers may be provided, particularly at reinforcing layer 13. The arrangement, properties, and functions of these layers will be described in detail below.

[0065] according to Figure 6B In one embodiment shown, a first conductive layer 31 is inserted between the reinforcing layer 13 and the carrier substrate 1. The first layer 31 is in direct contact with the reinforcing layer 13 and is configured to form the lower electrode 31 of the device 10 produced after the method according to the invention is completed.

[0066] The first layer 31 can be deposited after the step of depositing the reinforcing layer 13. This layer 31 can be made of platinum (Pt), gold (Au), copper (Cu), molybdenum, or aluminum (Al). Furthermore, the first layer 31 can be produced using any technique known to those skilled in the art that is compatible with conventional methods in the field of microelectronics. The lower electrode 31 can advantageously take the form of a cross-comb.

[0067] As an example, PVD (Physical Vapor Deposition) can be used to deposit the first layer 31. Deposition is preferably performed at a low temperature (below 450 °C). For the deposition of layer 31, a tie layer and / or a diffusion barrier layer may also be provided. The tie layer is used to improve the deposition quality of layer 31 on the donor substrate 2, especially if layer 31 has metallic properties. Additionally, the diffusion barrier layer advantageously prevents the diffusion of metal into the final structure during possible subsequent process steps.

[0068] According to one embodiment, when layer 31 is compatible with direct bonding (sufficient roughness level), it can be directly bonded to the carrier substrate 1 (e.g., Au / Au direct bonding). In this case, thermocompression bonding is also conceivable.

[0069] According to one embodiment of the present invention using bonding layer 32 as described above, bonding layer 32 may be deposited on first layer 31.

[0070] according to Figure 6B In another embodiment shown, a second conductive layer 33 is formed on the surface layer 22. The second layer 32 is in direct contact with the surface layer 22 and is configured to form the upper electrode 32 of the device 10 produced after the method according to the invention is completed.

[0071] The second layer 33 can be added after the separation step (see...). Figure 6B ) or before the deposition of reinforcing layer 13 (see Figure 6C The layer 33 can be deposited from platinum (Pt), gold (Au), copper (Cu), molybdenum, or aluminum (Al).

[0072] Preferably and as Figure 6CAs shown, layer 33 is deposited prior to the deposition of reinforcing layer 13, such that it is inserted between surface layer 22 and reinforcing layer 13 after the separation step. According to this embodiment, electrodes 31 and 33 are advantageously buried and thus passivated, so that they are less exposed to undesirable oxidation or degradation.

[0073] Furthermore, the second layer 33 can be manufactured in the same manner as layer 31; in other words, using any technique known to those skilled in the art that is compatible with conventional methods in the field of microelectronics. Additionally, layers 31 and 33 can have thicknesses ranging from a few nanometers to tens of nanometers.

[0074] The present invention also relates to a donor substrate 2 configured to transfer a piezoelectric film 14 to a carrier substrate 1 including a large-sized cavity 11. Figures 1 to 5 ).

[0075] like Figure 3 As shown, the donor substrate 2 includes a bulk substrate comprising at least one semiconductor material (e.g., silicon, silicon carbide, gallium nitride, etc.) or a piezoelectric material (e.g., lithium tantalate, lithium niobate, aluminum nitride, zinc oxide, PZT, etc.). Preferably, the donor substrate 2 is a silicon substrate or a silicon carbide (SiC) substrate.

[0076] The donor substrate according to the present invention has a weakening plane 20 located between a first portion and a second portion 23 of the donor substrate 1. The first portion is used to form a surface layer 22, and the second portion is used to constitute the remainder of the donor substrate 2. The weakening plane is formed by implanting a light material into the donor substrate 2. Preferably, the implanted light material is hydrogen ions and / or helium ions.

[0077] Furthermore, the donor substrate 2 is provided with a piezoelectric reinforcing layer 13, which is disposed on the front side 21 of the donor substrate 2. The thickness e of layer 13 is greater than 500 nm. Even more preferably, the thickness e of layer 13 is greater than 1 μm or even greater than 4 μm.

[0078] The reinforcing layer 13 may include materials selected from: lithium niobate (LiNbO3), lithium tantalate (LiTaO3), potassium sodium niobate (K... x Na 1－x NbO3 or KNN), barium titanate (BaTiO3), quartz, lead zirconate titanate or PZT (Pb(Zr,Ti)O3), magnesium lead niobate and lead titanate compounds in variable proportions (e.g., 70 / 30 or 90 / 10) according to the required properties (PMN-PT), zinc oxide (ZnO), aluminum nitride (AlN) or scandium aluminum nitride (AlScN), etc.

[0079] Preferably, the reinforcing layer 13 is made of AlN or PZT.

[0080] Layer 13 can be deposited using any technique known to those skilled in the art that is compatible with conventional methods in the field of microelectronics. Preferably, the reinforcing layer 13 is deposited using cathode sputtering or a sol-gel technique (which is a chemical deposition technique).

[0081] The donor substrate according to the invention is advantageously configured to transfer the film 14 formed by the reinforcing layer 13 and the surface layer 22 to a carrier substrate 1 provided with a large-sized cavity 11 (see...). Figure 5 The donor substrate 2 according to the invention advantageously allows for the transfer of the film, which provides enhanced properties that promote successful and efficient film transfer and piezoelectric properties that are necessary for the production of devices (especially PMUT devices) requiring this material.

Claims

1. A method for manufacturing a device (10) comprising a piezoelectric membrane (14) above at least one cavity (11), the method comprising the steps of: a) A carrier substrate (1) is provided, the carrier substrate (1) having a first surface (12) extending above a plane (x, y) and having a cavity (11) opening into the first surface (12), the cavity (11) having a lateral dimension greater than 30 μm in the plane (x, y). b) Provide a donor substrate (2) having a buried weakened plane (20) formed by implanting a light material through the front side (21) of the donor substrate (2) and the weakened plane (20) defining a surface layer (22). c) Deposit a reinforcing layer (13) on the front side (21) of the donor substrate (2), the reinforcing layer (13) being made of a piezoelectric material with a thickness (e) greater than 500 nm. d) Join the carrier substrate (1) and the donor substrate (2) at the bonding interface (30) between the first surface (12) of the carrier substrate (1) and the reinforcing layer (13). e) After step d), the donor substrate (2) is separated at the buried weakened plane (20) so as to transfer the film (14) including the surface layer (22) and the reinforcing layer (13) to the carrier substrate (1), the film (14) being located above the cavity (11).

2. The method according to claim 1, wherein, The donor substrate (2) is made of silicon or silicon carbide.

3. The method according to claim 1, wherein, The carrier substrate (1) is made of silicon.

4. The method according to claim 1, wherein, The donor substrate (2) is made of silicon, and the reinforcing layer (13) is deposited at a temperature below 450°C.

5. The method according to claim 1, wherein, The donor substrate is made of silicon carbide, and the reinforcing layer (13) is deposited at a temperature below 850°C.

6. The method according to claim 1, wherein, The implanted light material consists of hydrogen ions and / or helium ions.

7. The method according to claim 1, wherein, A first conductive layer (31) is inserted between the reinforcing layer (13) and the carrier substrate (1), the first conductive layer (31) being in direct contact with the reinforcing layer (13) and configured to form the lower electrode (31) of the device (10).

8. The method according to claim 1, wherein, A bonding layer (32) is inserted between the reinforcing layer (13) and the carrier substrate (1), and the bonding layer (32) is in direct contact with the carrier substrate (1).

9. The method according to claim 8, wherein, The bonding layer (32) is made of silicon oxide.

10. The method according to claim 1, wherein, A second conductive layer (33) is formed on the reinforcing layer (13), and the second conductive layer (33) is configured to form the upper electrode (33) of the device (10).

11. The method according to claim 1, wherein the method comprises performing at least one mechanical polishing operation and / or at least one chemical mechanical polishing operation and / or at least one chemical etching operation on the surface layer (22) after separation step e).

12. The method according to claim 1, wherein, Step d) of bonding includes bonding between the donor substrate (2) on one side where the reinforcing layer (13) is disposed and the first surface (12) of the carrier substrate (1) on the other side by molecular adhesion.

13. The method according to claim 1, wherein, After step e), a deposition step is performed on the free surface of the surface layer (22) to increase the thickness of the surface layer (22).

14. A donor substrate (2) configured to transfer a piezoelectric film (14) to a carrier substrate, the carrier substrate having at least one cavity having a lateral dimension greater than 30 μm, the donor substrate (2) comprising: A weakening plane (20) is disposed in the donor substrate (2) and defines a surface layer (22), and A reinforcing layer (13) is disposed on the surface layer (22) and the reinforcing layer (13) is made of a piezoelectric material with a thickness (e) greater than 500 nm.

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