Process for manufacturing a donor substrate for the transfer of a piezoelectric layer and process for the transfer of a piezoelectric layer to a support substrate - Patents.com

Abstract

The invention relates to a process for the manufacture of a donor substrate for the transfer of a piezoelectric layer onto a support substrate, the process comprising the steps of preparing a handling substrate, in particular a silicon-based substrate, preparing a piezoelectric substrate, depositing a polymer layer onto the free surface of the piezoelectric substrate or of the handling substrate, and assembling the piezoelectric substrate onto the handling substrate in such a way that the polymer layer is arranged sandwiched between the piezoelectric substrate and the handling substrate, characterized in that a step of surface activation treatment of the surface of the piezoelectric substrate that will come into contact with the polymer layer is carried out before the step of assembling the piezoelectric substrate onto the handling substrate. The invention also relates to a process for the transfer of a piezoelectric layer onto a support substrate.

Description

[Technical field]

[0001] The present invention relates to a process for the manufacture of a donor substrate for the transfer of a piezoelectric layer, and to a process for the transfer of such a piezoelectric layer to a support substrate. [Background technology]

[0002] Piezoelectric-on-insulator (POI) substrates comprise a thin layer of piezoelectric material on a substrate. To manufacture such POI substrates, the process used starts with a thick substrate of piezoelectric material and involves the transfer of a thin piezoelectric layer to a supporting substrate.

[0003] For this, a donor substrate is first used, in which a bulk substrate of piezoelectric material is assembled with a handling substrate by bonding with a polymer layer. The donor substrate then undergoes a stage of thinning of the bulk piezoelectric substrate so as to form a thinner piezoelectric layer before being assembled with a support substrate. Finally, the transfer of the piezoelectric layer to the support substrate is carried out mechanically or thermally at the level of the fracture zone previously created in the thinned piezoelectric layer. The donor substrate is introduced into the process in order to limit the adverse effects of differences in the thermal expansion coefficients between the piezoelectric material of the POI and the support substrate. This is because a heat treatment is carried out to strengthen the bonding interface between the different substrates and for the transfer of the thin layer. An example of this type of process is described in WO 2019 / 186032 A1.

[0004] Therefore, during the process for the manufacture of a POI substrate, the donor substrate must undergo several stages of thermal and / or mechanical treatment and must exhibit good mechanical strength against the different treatments.

[0005] However, delamination at the level of the bonding interface between the piezoelectric material substrate and the polymer layer of the donor substrate can occur during successive thermal and / or mechanical steps of the piezoelectric layer transfer process.

[0006] One object of the present invention is to overcome the aforementioned disadvantages and in particular to design a donor substrate for the transfer of a piezoelectric layer of a piezoelectric material substrate to a support substrate that exhibits better mechanical strength for the piezoelectric layer transfer process. Summary of the Invention

[0007] The object of the present invention is achieved by a process for the manufacture of a donor substrate for the transfer of a piezoelectric layer to a support substrate, the process comprising the steps of preparing a handling substrate, in particular a silicon-based substrate, preparing a piezoelectric substrate, depositing a polymer layer on the free face of the piezoelectric substrate and assembling the piezoelectric substrate to the handling substrate in such a way that the polymer layer is arranged sandwiched between the piezoelectric substrate and the handling substrate, characterized in that a step of surface activation treatment of the surface of the piezoelectric substrate that will come into contact with the polymer layer is carried out before the step of assembling the piezoelectric substrate to the handling substrate.

[0008] A surface treatment is a mechanical, chemical, electrochemical or physical treatment, the purpose of which is to modify the appearance or function of the surface of a material to make it suitable for a given use. The surface treatment allows for the functionalization, activation or cleaning of the surface or a combination of these effects. The stage of surface treatment of the piezoelectric substrate in the process according to the invention thus makes it possible to modify the appearance or function of the surface of the piezoelectric substrate to make it suitable for contact with a polymer layer in order to obtain a better interface between the piezoelectric material and the polymer layer. The process according to the invention therefore makes it possible to obtain a donor substrate with improved mechanical stability compared to the prior art.

[0009] According to one embodiment, during the stage of deposition of the polymer layer on the piezoelectric substrate, the polymer layer can be deposited directly on the treated surface of the piezoelectric substrate. The treated surface of the piezoelectric substrate makes it possible to provide improved adhesion to the polymer layer that will be deposited thereon. The polymer layer alone therefore makes it possible to generate good adhesion of the piezoelectric substrate to another layer or to another substrate. The polymer layer can for example be deposited by a centrifugal deposition process directly on the piezoelectric substrate.

[0010] The subject of the present invention is also achieved by a process for the manufacture of a donor substrate for the transfer of a piezoelectric layer to a support substrate, the process comprising the steps of preparing a handling substrate, in particular a silicon-based substrate, preparing a piezoelectric substrate, depositing a polymer layer on a free side of the handling substrate and assembling the piezoelectric substrate to the handling substrate in such a way that the polymer layer is arranged sandwiched between the piezoelectric substrate and the handling substrate, characterized in that a step of activation treatment of the surface of the piezoelectric substrate that will come into contact with the polymer layer of the handling substrate during the assembling step is carried out before the step of assembling the piezoelectric substrate to the handling substrate.

[0011] Likewise, the stage of surface treatment of the piezoelectric substrate in the process according to the invention makes it possible to modify the appearance or functionality of the surface of the piezoelectric substrate in order to adapt it to contact with the polymer layer of the handling substrate in order to obtain a better interface between the piezoelectric material and the polymer layer.The process according to the invention thus makes it possible to obtain a donor substrate with improved mechanical stability compared to the prior art.

[0012] According to one embodiment, during the step of deposition of the polymer layer on the handling substrate, the polymer layer can be placed directly on the handling substrate. The polymer layer alone makes it possible to generate good adhesion to another layer or to another substrate. The polymer layer can for example be deposited by a centrifugal deposition process directly on the handling substrate.

[0013] According to an embodiment, the assembly stage of the process for the manufacture of the donor substrate may include a stage of polymer layer treatment to obtain a cross-linked polymer layer for bonding the handling substrate to the piezoelectric substrate. The formation of the cross-linked polymer layer by the stage of polymer layer treatment is simple to perform and not very costly.

[0014] According to one embodiment, the surface activation step can be an oxygen-based surface activation treatment that creates pendant bonds on the surface of the piezoelectric substrate that comes into contact with the polymer layer. The oxygen-based surface activation treatment consists of the oxidation of the surface of the material. The oxidation of the surface molecules makes it possible to increase the surface tension of the support. The oxygen-based surface activation treatment makes it possible to create free radicals at the surface, which promotes the adhesion of thin layers that come into contact with these free radicals.

[0015] According to one embodiment, the surface activation treatment step of the piezoelectric substrate can be a treatment with ozone, in particular wet or UV-assisted, which is a treatment making it possible to modify the surface of the piezoelectric substrate in order to improve the interface between the polymer layer and the surface of the piezoelectric substrate.

[0016] According to one embodiment, the stage of surface activation treatment of the piezoelectric substrate may consist in a treatment with a hydrogen peroxide-based solution, which makes it possible to modify the surface of the piezoelectric substrate in order to improve the interface between the polymer layer and the surface of the piezoelectric substrate.

[0017] According to one embodiment, the stage of surface activation treatment of the piezoelectric substrate can be a plasma treatment, in particular an oxygen-based plasma treatment. Plasma surface treatment is a dry treatment that makes it possible to improve the chemical properties of the material for better adhesion to the coating layer. The plasma treatment stage of the process according to the invention thus makes it possible to improve the adhesion between the polymer layer and the surface of the piezoelectric substrate of the donor substrate, resulting in an improved mechanical stability of the donor substrate compared to the prior art.

[0018] According to one embodiment, the piezoelectric substrate can be a Lithium Tantalate Oxide (LTO), Lithium Niobate (LNO), Aluminum Nitride (AlN), Lead Zirconate Titanate (PZT), Langasite or Langatate substrate. The process according to the invention can be used for these materials, which play a key role in devices utilizing the piezoelectric effect.

[0019] According to one embodiment, a step of thinning of the piezoelectric substrate of the donor substrate can be carried out after the assembly step, in particular after the step of processing the polymer layer of the assembly step, so as to obtain either a thinned piezoelectric substrate having a thickness t less than the thickness t1 of the piezoelectric substrate, or a piezoelectric layer having a thickness t2 less than the thickness t1 of the piezoelectric substrate. Thus, starting from a thick piezoelectric substrate, a thinner piezoelectric substrate or a piezoelectric layer of the desired thickness is obtained, and the donor substrate manufactured according to the process of the invention can be used as a donor substrate for the transfer of a thin piezoelectric layer to a support substrate, in order to obtain a Piezoelectric-on-Insulator (POI) substrate.

[0020] In the process for the manufacture of the POI substrate, the piezoelectric material and the material of the support substrate exhibit very different thermal expansion coefficients, which leads to significant deformations of the assembly. In such a process, thanks to the use of a donor substrate, the thick piezoelectric substrate is held between a handling substrate and a support substrate. The selection of the material and thickness of the handling substrate and the support substrate ensures a certain symmetry of the thermal expansion coefficients and thus makes it possible to minimize deformations of the assembly during the application of heat treatments during the process for the manufacture of the piezoelectric-on-insulator (POI) substrate.

[0021] The subject of the present invention can also be achieved by a process for the transfer of a piezoelectric layer to a support substrate, comprising the steps of preparing a donor substrate obtained by the above-mentioned manufacturing process, forming a weakened zone inside the piezoelectric substrate, preparing a support substrate, in particular a silicon-based substrate, attaching the donor substrate to the support substrate to obtain a support substrate-donor substrate assembly, and performing a break along the weakened zone to separate the piezoelectric layer from the rest of the donor substrate. In the process for the manufacture of a POI substrate, the piezoelectric material and the material of the support substrate exhibit very different thermal expansion coefficients, resulting in significant deformations of the assembly. In such a process, thanks to the use of a donor substrate, the thick piezoelectric substrate is held between a handling substrate and a support substrate. The selection of the materials and thicknesses of the handling substrate and the support substrate ensures a certain symmetry of the thermal expansion coefficients and thus makes it possible to minimize deformations of the assembly during the application of heat treatments during the process for the manufacture of a piezoelectric-on-insulator (POI) substrate.

[0022] The invention and its advantages will be explained in more detail hereinafter using preferred embodiments and in particular with the support of the following attached drawings in which reference numbers identify the features of the invention. [Brief description of the drawings]

[0023] [Figure 1] 1A-1D diagrammatically represent a process for the manufacture of a donor substrate according to a first embodiment of the invention; [Diagram 2] 3A-3D diagrammatically represent a process for the manufacture of a donor substrate according to an alternative of the first embodiment of the present invention. [Diagram 3] 5A-5D diagrammatically represent a process for the manufacture of a donor substrate according to a second embodiment of the invention. [Figure 4] 5A-5D diagrammatically represent a process for the transfer of a piezoelectric layer according to a third embodiment of the invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0024] The present invention will now be described in more detail using advantageous embodiments in an exemplary manner and with reference to the drawings. It should be noted that the described embodiments are merely possible configurations, and that the individual features as described above can be provided independently of one another or can be omitted altogether during the implementation of the present invention.

[0025] FIG. 1 shows diagrammatically a process for the manufacture of a donor substrate, used for the transfer of a piezoelectric layer of the donor substrate to a support substrate according to a first embodiment of the invention.

[0026] The process for the manufacture of a donor substrate starts with a step I) of preparing a handling substrate 100, in particular a bulk substrate. A bulk substrate is a substrate based only on one material, usually with a thickness between 300 μm and 800 μm. The handling substrate 100 is made of a material whose thermal expansion coefficient is close to that of the material of the support substrate onto which the piezoelectric layer is intended to be transferred. The term "close" is understood to mean that the difference in thermal expansion coefficient between the material of the handling substrate 100 and the material of the support substrate is less than or equal to 5%, and preferably equal to or close to 0%. The handling substrate 100 can be a substrate based on silicon, sapphire, aluminum nitride (AlN), silicon carbide (SiC) or also gallium arsenide (GaAs). The handling substrate 100 can be a crystalline or polycrystalline substrate.

[0027] During stage II) of the process according to the first embodiment, a piezoelectric substrate 106 is prepared. This is preferably a bulk substrate of piezoelectric material, typically having a thickness of at least about 300 μm, preferably at least 350 μm. According to an alternative, the substrate 106 of piezoelectric material can also be a thick layer of piezoelectric material, with a thickness between 25 μm and 50 μm, deposited on another substrate.

[0028] The piezoelectric material may be, for example, lithium tantalate (LTO), lithium niobate (LNO), aluminum nitride (AlN), lead zirconate titanate (PZT), langasite or langatate.

[0029] First, the piezoelectric substrate 106 may undergo one or more steps of cleaning, brushing or polishing its free surface 110 to remove any particles or dust and thus obtain a clean and good quality free surface 110 for subsequently performing successive layer depositions.

[0030] According to the invention, the piezoelectric substrate 106 then undergoes a surface treatment 108 stage III) on one of its free faces 110 in order to obtain an active surface 112 .

[0031] The surface treatment 108 of the surface 110 of the piezoelectric substrate 106 is a treatment that allows the activation of the surface to be treated. Such a surface activation treatment 108 makes it possible to prepare the surface of the material for contact with a successive layer, either during a successive deposition or during a step of contacting with another substrate. For this purpose, the surface activation treatment 108 modifies the properties of the surface. The surface activation treatment can be mechanical, chemical, electrochemical or physical.

[0032] The surface activation treatment 108 can be an oxygen-based surface activation treatment. The oxidation of the surface molecules makes it possible to increase the surface tension of the support, which creates pendant bonds on the surface. The oxygen-based surface activation treatment 108 makes it possible to create free radicals on the surface, which promote the adhesion of thin layers in contact with these free radicals. The active surface 112 of the piezoelectric substrate 106 thus comprises pendant bonds. These pendant bonds represent bonding sites that allow a better bonding of the pendant bonds with the surface of the material with which it is in contact. This is because the pendant bonds of the active surface 112 of the piezoelectric substrate 106 create covalent bonds with the pendant bonds of the surface of the material with which it is in contact.

[0033] According to one embodiment, stage III) of the surface activation treatment 108 of the piezoelectric substrate 106 can be a treatment with ozone, in particular wet or UV-assisted. The presence of ozone makes it possible to oxidize the surface molecules. The use of UV irradiation makes it possible to create free radicals.

[0034] According to another embodiment, stage III) of the surface activation treatment 108 of the piezoelectric substrate 106 can be a treatment with a solution based on hydrogen peroxide, also known as active oxygen treatment, which allows the formation of free radicals by oxidation.

[0035] According to another embodiment, the surface activation treatment 108 of the piezoelectric substrate 106, step III) can be a plasma treatment, in particular an oxygen-based plasma treatment. The plasma treatment is a dry treatment that allows activation of the surface. The plasma surface treatment consists of a very strong oxidation of the surface of the material.

[0036] Thus, the surface treatment 108 of the process according to the invention makes it possible to improve the chemical properties of the surface 112 of the piezoelectric substrate 106 by creating bonding sites for better adhesion with layers that are deposited on or in contact with the active surface 112 of the piezoelectric substrate 106 later in the process.

[0037] Stage IV) of deposition of a polymer layer 104 on the active surface 112 of the piezoelectric substrate 106 is then carried out.

[0038] The deposition of the polymer layer 104 is advantageously carried out by spin-coating. This technique consists in rotating at a given speed the substrate on which the deposition of the polymer layer is intended to occur, so as to spread said polymer layer 104 evenly over the entire free surface 112 of the piezoelectric substrate 106 by centrifugal forces. To this end, the piezoelectric substrate 106 is usually positioned and held by applying a vacuum to a rotating plate. The thickness of the polymer layer 104 obtained depends on the parameters used during the deposition of the layer, i.e. for example on the speed and duration of the rotation of the substrate and on the volume of the polymer solution deposited on the surface 112 of the substrate 106. The thickness of the polymer layer 104 is usually between 1 μm and 6 μm, preferably around 3.5 μm.

[0039] The polymer layer 104 can be a photopolymerizable layer based on a thiol-ene resin. For example, the layer sold by Norland Products as "NOA61" can be used as the polymer layer 104 in the present invention.

[0040] During the step of depositing the polymer layer 104 , the polymer layer 104 is deposited in direct contact with the active surface 112 of the piezoelectric substrate 106 .

[0041] The free surface 110 of the piezoelectric substrate 106 has previously undergone a step of surface treatment 108 for activation of the free surface 110 and therefore for obtaining good adhesion of the polymer layer 104 to the free surface 110 of the piezoelectric substrate 106 .

[0042] Thus, the pendant bonds present on the active surface 112 of the piezoelectric substrate 106 create bonding sites that promote the attachment of the polymer layer 104 formed on the active surface 112 of the piezoelectric substrate 106. The pendant bonds present on the active surface 112 of the piezoelectric substrate 106 become covalently bonded with the pendant bonds of the polymer layer 104. Thus, the contact interface 116 between the piezoelectric substrate 106 and the polymer layer 104 is strengthened / reinforced.

[0043] After deposition by spin coating of the polymer layer 104 onto the piezoelectric substrate 106 , a heat treatment may be performed to improve adhesion of the polymer layer 104 to the active surface 112 of the piezoelectric substrate 106 at the interface 116 .

[0044] The piezoelectric substrate 106 obtained after step IV) is then assembled with the handling substrate 100 prepared in step I) during an assembly step V) to obtain a donor substrate 114 .

[0045] Assembly of the piezoelectric substrate 106 to the handling substrate 100 is performed such that the polymer layer 104 is disposed sandwiched between the piezoelectric substrate 106 and the handling substrate 100 .

[0046] The contact interface 116 between the piezoelectric substrate 106 and the polymer layer 104 is strengthened / reinforced, resulting in improved mechanical stability of the donor substrate 114 compared to the prior art.

[0047] After the two substrates are assembled, a bonding step VI) is performed to bond the piezoelectric substrate 106 to the handling substrate 100 so as to form a stable donor substrate 122 .

[0048] The polymer layer 104 is subjected to a treatment 118 to cross-link the polymer layer 104 so as to modify the mechanical properties of the polymer layer 104. Cross-linking is a general term that describes the process of forming covalent bonds, or an array of relatively short chemical bonds to connect two polymer chains. When the polymer chains are cross-linked, the polymer layer 104 becomes stiffer. Covalent chemical cross-links are mechanically and thermally stable and therefore less likely to break once formed.

[0049] The cross-linking process 118 can be performed by using heat, pressure, by changing the pH or by irradiation. According to the present invention, the cross-linking process 118 can be performed by irradiation of the polymer layer 104 with a light beam 118. The irradiation 118 is performed through the piezoelectric substrate 106 or the substrate 100 in order to cross-link the polymer layer 104 and obtain a cross-linked polymer layer 120, also called polymerized layer 120.

[0050] Irradiation 118 of the donor substrate 114 is performed using a light source, preferably a laser. The optical radiation 118 or light beam is preferably ultraviolet radiation (UV) and preferably has a wavelength between 320 nm and 365 nm.

[0051] The thickness of the crosslinked polymer layer 120 is preferably between 1 μm and 6.5 μm, in particular about 3.5 μm, depending in particular on the material of the polymer layer 104 deposited before bonding, on the thickness of said polymer layer and on the irradiation conditions.

[0052] Cross-linking of the polymer layer 104 by UV irradiation 118 allows for the release of groups that result in polymerization of the polymer layer 104. The polymerization of the polymer layer 104 results in chemical bonds that are mechanically and thermally stable and therefore less likely to break once formed. Thus, the bond between the pendant bonds of the active surface 112 of the piezoelectric substrate 106 and the cross-linked polymer layer 120 results in a mechanically and thermally stable bond.

[0053] The polymeric layer 120 thus ensures mechanical intimacy of the donor substrate 122 by keeping the handling substrate 100 and the piezoelectric substrate 106 , which form the donor substrate 122 , bonded together.

[0054] Thanks to the surface activation treatment 108, the interface 116 between the cross-linked polymer layer 120 and the piezoelectric substrate 106 exhibits improved adhesion between the polymer layer 120 and the surface of the piezoelectric substrate 106, and the donor substrate 122 thus obtained by the manufacturing process according to the invention exhibits improved mechanical stability at the polymer-piezoelectric interface.

[0055] 2 diagrammatically represents a process for the manufacture of a donor substrate for the transfer of a piezoelectric layer to a support substrate according to an alternative form of the first embodiment of the invention. Those in common with the first embodiment and using the same reference numbers as above will not be mentioned again, but reference is made to the detailed description above.

[0056] The process according to the first embodiment comprises, after step VI) shown in FIG. 1, a step VII) of thinning the piezoelectric substrate 106 of the donor substrate 122 obtained by the process of the first embodiment.

[0057] This thinning step VII) can be performed by a process of grinding or by a process of chemical etching of the piezoelectric substrate 106 so as to reduce the thickness t1 of the layer 106 of piezoelectric material of the donor substrate 122 in order to obtain a thinned piezoelectric substrate 140 having a thickness t less than t1, or a piezoelectric layer 124 having a thickness t2 of the order of 20 μm, or between 5 μm and 25 μm.

[0058] Also, in order to improve the quality of the free surface 126 of the piezoelectric layer 124, a treatment of the obtained free surface 126 of the piezoelectric layer 124 can be carried out after the thinning step VII) is completed.

[0059] Given the mechanical stability of the donor substrate 122 obtained by the process according to the first embodiment, the thinning and processing steps that the donor substrate 122 undergoes can be performed without the polymer-piezoelectric interface 116 being affected by these mechanical and / or thermal steps, and the risk of delamination at this interface 116 is reduced, and in particular eliminated. The donor substrate 128 thus exhibits a mechanical stability that allows it to be used upstream in a process for the transfer of the piezoelectric layer 124 to the support substrate 140.

[0060] A donor substrate 128 is thus obtained having a cross-linked polymer layer 120 disposed between the handling substrate 100 and the piezoelectric layer 124 , the handling substrate 100 being in contact with the cross-linked polymer layer 120 of the piezoelectric layer 124 .

[0061] According to the described embodiment, the assembly of the handling substrate 100 with the piezoelectric substrate 106, or with the piezoelectric layer 124 after thinning of the piezoelectric substrate 106 as described in the previous section, can be advantageous not only as a donor substrate 122, 128, but also constitute a substrate itself that can be used for the manufacture of acoustic components.

[0062] 3 shows a second embodiment of the invention, which differs in step IV) of the deposition of the polymer layer 152 compared to the first embodiment. The step of deposition of the polymer layer 152 is carried out on a handling substrate 100. All other steps I), II), III) and V) to VII) are the same as in the first embodiment and its alternatives. Those which are in common with the first embodiment and which use the same reference numbers as above will not be mentioned again, but reference is made to the detailed description above.

[0063] During stage IV) of the deposition of the polymer layer, the polymer layer 152 is deposited in direct contact with the free surface 102 of the handling substrate 100. First the handling substrate 100 may undergo one or more stages of cleaning, brushing or polishing its free surface 102 to remove particles or dust and thereby obtain a clean and good quality free surface 102 for subsequently performing the deposition of the polymer layer 152.

[0064] During the assembly stage V), the polymer layer 152 of the handling substrate 100 is brought into direct contact with the active surface 112 of the piezoelectric substrate 106. Thus, the contact interface 116 between the polymer layer 152 and the active surface 112 of the piezoelectric substrate 106 also exhibits better adhesion. This is because, similar to what has been described above, the pendant bonds present on the active surface 112 of the piezoelectric substrate 106 create bonding sites that promote the attachment of the polymer layer 152, formed on the handling substrate 100, by the active surface 112 of the piezoelectric substrate 106. Thus, the contact interface 116 between the piezoelectric substrate 106 and the polymer layer 152 is strengthened / reinforced, resulting in improved mechanical stability of the donor substrate 114 compared to the prior art.

[0065] FIG. 4 diagrammatically illustrates a process for the transfer of a piezoelectric layer according to a third embodiment of the invention.

[0066] The process for the transfer of a piezoelectric layer to a support substrate according to the present invention comprises a step of preparing a donor substrate obtained by carrying out the process for the manufacture of a donor substrate described with reference to Figures 1 to 3 according to the first embodiment of the present invention and its alternatives and according to the second embodiment of the present invention and its alternatives.

[0067] During step A), a donor substrate 128 and a support substrate 140 are prepared.

[0068] The support substrate 140 may be a bulk substrate based on silicon, sapphire, aluminum nitride (AlN), silicon carbide (SiC) or also gallium arsenide (GaAs). The support substrate 140 may be a crystalline or polycrystalline substrate.

[0069] 4, the support substrate 140 may comprise a dielectric layer 142 previously deposited on a free surface 144 of the support substrate 140 by deposition by spin coating or by a deposition technique such as plasma deposition or evaporation deposition. Also, a heat treatment may be performed after the deposition of the dielectric layer 142 in order to optimize the adhesion of this dielectric layer 142 to the support substrate 140, or alternatively a surface treatment may be performed to improve the quality of the surface of the deposited dielectric layer 142.

[0070] In the alternative, the support substrate 140 may include a layer of native oxide formed on the free surface 144 of the support substrate 140 .

[0071] The dielectric layer 142 is, for example, a layer of silicon dioxide. However, it can also be a layer of nitride, or a combination of nitride and oxide, or a layer comprising a superposition of a layer of oxide and a layer of nitride. For example, in the case of a support substrate made of silicon, a layer of oxide, or a layer of silicon nitride Si3N4, a combination of nitride and oxide SiO x N y , or a layer comprising a superposition of a layer of oxide and a layer of silicon nitride Si3N4.

[0072] In an alternative embodiment, the support substrate 140 may also comprise other layers: for example, layers for producing Bragg mirrors or trapping layers may be present in the support substrate 140. Trapping layers of polycrystalline, amorphous or porous silicon type may be present, in particular with thicknesses varying between 500 nm and 5 μm.

[0073] In the alternative, the support substrate 140 is prepared without the dielectric layer 142 and / or without the native oxide layer.

[0074] In the alternative, the dielectric layer can be provided on the piezoelectric layer 132 of the donor substrate 138 instead of on the support substrate 140 .

[0075] In another alternative, a dielectric layer may be provided on both substrates, donor substrate 128 and support substrate 140 .

[0076] Step B) of forming a weakened zone 130 in the piezoelectric layer 124 of the donor substrate 128 is performed to define the extent of the piezoelectric layer 132 that is to be transferred to the support substrate 140 .

[0077] This step of forming the weakened zone 130 is carried out by implantation 134 of atomic or ionic elements in the piezoelectric layer 124 in the donor substrate 128. The atomic or ionic implantation 134 is carried out in such a way that the weakened zone 130 is located inside the piezoelectric layer 124 and separates the piezoelectric layer 136 from the remaining part 132 of the piezoelectric layer 124. The atomic or ionic elements are implanted at a predetermined depth in the piezoelectric layer 124, which determines the thickness t3 of the piezoelectric layer 136 to be transferred and the thickness t4 of the remaining part 132 of the piezoelectric layer 124. The thickness t3 is typically between 50 nm and 1 μm, in particular around 600 nm.

[0078] The resulting donor substrate 138 includes a weakened zone 130 that separates the piezoelectric layer 136 to be transferred from the remaining portion 132 of the piezoelectric layer 124 .

[0079] Stage C) of the transfer process according to the invention comprises assembling the donor substrate 138 with the support substrate 140 to obtain a support substrate-donor substrate assembly forming a heterostructure 148. The assembly of the donor substrate 138 and the support substrate 140 is performed at the level of the dielectric layer 142, such that the piezoelectric layer 136 of the donor substrate 138 is in contact with the dielectric layer 142 of the support substrate 140.

[0080] In the alternative, where the support substrate 140 does not include the dielectric layer 142, assembly occurs such that the piezoelectric layer 136 of the donor substrate 148 is in direct contact with the free surface 144 of the support substrate 140. Assembly occurs by molecular adhesion between the two substrates at the piezoelectric-support substrate interface.

[0081] Alternatively, as previously described, the assembly of the donor substrate 138 and the substrate 140 occurs between the dielectric layer 142 and a dielectric layer formed on the donor substrate 140. This dielectric layer can be, for example, a layer of silicon oxide, a layer of silicon nitride Si3N4 or a layer of silicon oxynitride, SiO x N y A layer comprising a combination of silicon nitride and oxide, also known as silicon nitride, or a superposition of a layer of oxide and a layer of nitride. According to an alternative, the formation of this dielectric layer may be followed by a heat treatment in order to improve the adhesion of the dielectric layer to the piezoelectric layer 124. A surface treatment in order to improve the quality of the surface of this dielectric layer may also be carried out, in particular after the step of implantation 134 and before the aforementioned step C).

[0082] Then, a step D) is carried out of creating a break along the weakened zone 130 of the donor substrate 148 in order to separate the piezoelectric layer 136 from the remaining part 146 of the donor substrate 148. This breaking step can be carried out thermally or mechanically. During the thermal separation, the temperatures used are up to 300° C.

[0083] The use of a donor substrate 128 manufactured according to the invention makes it possible to prevent delamination between the piezoelectric layer 124 and the polymer layer 120 of the donor substrate 128 during fracture of the donor substrate 128, thanks to the interface 116 between the polymer layer 120 and the piezoelectric layer 124 having a better mechanical stability. This makes it possible to obtain an actual fracture of the donor substrate 128 at the weakened zone 130 to obtain the POI substrate 150.

[0084] The POI substrate 150 shown in FIG. 4, stage D), is produced by the process of piezoelectric layer transfer according to the invention and comprises a support substrate 140 , a dielectric layer 142 and a piezoelectric layer 136 .

[0085] It should be noted that the described embodiments are merely possible configurations, and that individual features of the different embodiments can be combined with each other or can be brought about independently of each other.

Claims

1. A process for the manufacture of a donor substrate for the transfer of a piezoelectric layer to a support substrate (140), comprising the steps of: Providing a handling substrate (100), in particular a silicon-based substrate; Providing a piezoelectric substrate (106); depositing a polymer layer (104) on a free surface (110) of said piezoelectric substrate (106); assembling the piezoelectric substrate (106) to the handling substrate (100) such that the polymer layer (104) is disposed between the piezoelectric substrate (106) and the handling substrate (100); A process for the manufacture of a donor substrate, comprising:

13. A process for manufacturing a donor substrate, characterized in that a step of surface activation treatment (108) of the surface (110) of the piezoelectric substrate (106) that comes into contact with the polymer layer (104) is performed before the step of assembling the piezoelectric substrate (106) to the handling substrate (100).

2. The process for manufacturing a donor substrate according to claim 1 , wherein the polymer layer (104) is deposited directly on the active surface (112) of the piezoelectric substrate (106).

3. A process for the manufacture of a donor substrate for the transfer of a piezoelectric layer to a support substrate (140), comprising the steps of: Providing a handling substrate (100), in particular a silicon-based substrate; depositing a polymer layer (152) on a free surface (102) of said handling substrate (100); assembling a piezoelectric substrate (106) to the handling substrate (100) such that the polymer layer (152) is disposed between the piezoelectric substrate (106) and the handling substrate (100); A process for the manufacture of a donor substrate, comprising:

13. A process for manufacturing a donor substrate, characterized in that a step of surface activation treatment (108) of a surface (110) of the piezoelectric substrate (106), which surface (110) will come into contact with the polymer layer (152) of the handling substrate (100) during the assembly step, is performed prior to the step of assembling the piezoelectric substrate (106) to the handling substrate (100).

4. The process for manufacturing a donor substrate according to claim 3 , wherein during the step of deposition of the polymer layer (152), the polymer layer (152) is placed directly on the handle substrate (100).

5. 5. The process for manufacturing a donor substrate according to any one of claims 1 to 4, wherein the assembly step comprises a step of treating (108) the polymer layer (104, 152) to obtain a cross-linked polymer layer (120) for bonding the handling substrate (100) to the piezoelectric substrate (106).

6. 6. The process for manufacturing a donor substrate according to any one of claims 1 to 5, wherein the step of surface activation treatment (108) is an oxygen-based surface activation treatment (108) that creates pendant bonds on the surface (110) of the piezoelectric substrate (106) that comes into contact with the polymer layer (104, 152).

7. 7. Process for manufacturing a donor substrate according to any one of claims 1 to 6, wherein the step of surface activation treatment (108) of the piezoelectric substrate (106) is a treatment with ozone, in particular wet or UV-assisted.

8. The process for manufacturing a donor substrate according to any one of claims 1 to 6, wherein said step of surface activation treatment (108) of the piezoelectric substrate (106) is a treatment with a hydrogen peroxide-based solution.

9. Process for manufacturing a donor substrate according to any of the preceding claims, wherein said step of surface activation treatment (108) of the piezoelectric substrate (106) is a plasma treatment, in particular an oxygen-based plasma treatment.

10. The process for manufacturing a donor substrate according to any one of claims 1 to 9, wherein the piezoelectric substrate (106) is a Lithium Tantalate Oxide (LTO), Lithium Niobate (LNO), Aluminum Nitride (AIN), Lead Zirconate Titanate (PZT), Langasite or Langatate substrate.

11. Process for manufacturing a donor substrate according to any one of the preceding claims, wherein a step of thinning of the piezoelectric substrate (106) of the donor substrate (128) is carried out, in particular by grinding.

12. A process for the transfer of a piezoelectric layer to a supporting substrate, comprising the steps of: Providing a donor substrate (128, 138) obtained by carrying out a manufacturing process according to claim 11; forming a weakened zone (146) within the piezoelectric substrate (106) of the donor substrate (128, 138); Providing a support substrate (140), in particular a silicon-based substrate; attaching the donor substrate (128, 138) to the support substrate (140) to obtain a support substrate-donor substrate assembly (156); creating a break along the weakened zone (146) to separate the piezoelectric layer (148) from a remaining portion (158) of the donor substrate (156); The process includes:

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