Process for fabricating a piezoelectric layer on a substrate - Patent Application 20070122997

Abstract

The present invention relates to a process for manufacturing a piezoelectric layer (10) on a substrate (11), characterized in that the process comprises the steps of: forming a pseudomorphic seed layer (102) of a first piezoelectric material on a donor substrate (100) by a first epitaxy; transferring the seed layer (102) and a portion (103) of the donor substrate (100) onto a receiver substrate (110) via at least one electrically insulating layer and / or at least one conductive layer (105) adapted to allow relaxation of the seed layer; removing the transferred portion (103) of the donor substrate (100) to expose the surface of the seed layer (102); and forming a monocrystalline layer (104) of a second piezoelectric material on the seed layer (102).

Description

[Technical Field]

[0001] The present invention relates to a process for fabricating a piezoelectric layer on a substrate. [Background technology]

[0002] Various acoustic components are used for filtering in the radio frequency range, including surface acoustic wave (SAW) filters, which typically comprise a thick piezoelectric layer (i.e., generally tens of nanometers to tens of micrometers thick) and two electrodes in the form of two interdigitated metal combs deposited on the surface of the piezoelectric layer. An electrical signal, typically a voltage change, applied to the electrodes is converted into an acoustic wave that propagates on the surface of the piezoelectric layer. This acoustic wave propagation is favorable if the acoustic wave frequency corresponds to the frequency band of the filter. Upon reaching the other electrode, this wave is converted back into an electrical signal. The piezoelectric layer must have excellent crystalline quality to avoid attenuation of the surface wave. Therefore, it is preferable to use a monocrystalline layer here. Currently, the materials preferred for industrial applications are quartz, LiNbO3, or LiTaO3.

[0003] Currently, the piezoelectric layer is obtained by cutting an ingot of one of the materials, which results in a less accurate thickness of the layer and a non-uniform thickness across the layer.

[0004] Furthermore, the diameter of an ingot of piezoelectric material is smaller than the diameter of an ingot of material used for the substrate, such as silicon. However, to achieve direct transfer, especially Smart Cut™ type layer transfer, the donor and receiver substrates need to be of the same diameter.

[0005] There remains a need for a process that can form uniform, high quality, thick piezoelectric layers on large diameter substrates. Summary of the Invention

[0006] One object of the present invention is to design a process for manufacturing substrates for microelectronic, photonic or optical devices, including but not limited to surface acoustic wave devices, by making it possible to obtain thick (i.e., thicknesses greater than 5 μm, or even greater than 15 μm), uniform, high-quality layers, in particular of large diameter (i.e., diameters greater than 15 or 20 cm).

[0007] According to the present invention, there is provided a process for fabricating a piezoelectric layer on a substrate, comprising the steps of: - forming a seed layer of a first piezoelectric material on a donor substrate by a first epitaxy; - transferring the seed layer and a portion of the donor substrate to a receiver substrate via at least one electrically insulating layer and / or at least one electrically conductive layer adapted to allow relaxation of the seed layer; removing the transferred portion of the donor substrate to expose a surface of the seed layer; forming a second monocrystalline layer of piezoelectric material on the seed layer.

[0008] According to a first embodiment, transferring the seed layer and the portion of the donor substrate comprises: - forming an embrittlement area in the donor substrate to define the portion to be transferred; - bonding the donor substrate to the receiver substrate with the seed layer at the bonding interface; - separating the donor substrate along the embrittlement zone, wherein the formation of the seed layer on the donor substrate is performed before the formation of the embrittlement zone.

[0009] According to a second embodiment, transferring the seed layer and the portion of the donor substrate comprises: - forming an embrittlement area in the donor substrate to define the portion to be transferred; - bonding the donor substrate to the receiver substrate with the seed layer at the bonding interface; - separating the donor substrate along the embrittlement zone, wherein the formation of the seed layer on the donor substrate is performed after the formation of the embrittlement zone.

[0010] The embrittlement zone can be formed by ion implantation, particularly with hydrogen and / or helium, into the donor substrate.

[0011] Preferably, the seed layer is formed on the donor substrate by atomic layer deposition. Alternatively, the seed layer is formed on the donor substrate by molecular beam epitaxy.

[0012] Preferably, the monocrystalline layer of second piezoelectric material is formed by second epitaxy.

[0013] Preferably, the second epitaxy of the second piezoelectric material on the seed layer is metal organic chemical vapor deposition.

[0014] Alternatively, the formation of a monocrystalline layer on a seed layer is achieved by depositing a second piezoelectric material in amorphous form, followed by recrystallization of the second material.

[0015] Advantageously, the seed layer has a thickness of between 2 nm and 20 nm.

[0016] Advantageously, the portion of the donor substrate that is transferred to the receiver substrate has a thickness of less than 2 μm, preferably less than 1 μm.

[0017] Advantageously, the thickness of the layer of second piezoelectric material after the second epitaxy is between 20 nm and 15 μm.

[0018] In certain embodiments, the process includes forming a single crystalline layer of the second piezoelectric material, followed by transferring at least a portion of the layer of the second piezoelectric material to a final substrate.

[0019] Advantageously, the portion of the layer of second piezoelectric material transferred to the final substrate has a thickness of less than 2 μm, preferably less than 1 μm.

[0020] The receiver substrate or final substrate may comprise at least one electronic device or interconnect.

[0021] The receiver substrate or the final substrate may comprise a trap rich layer.

[0022] The first piezoelectric material and the second piezoelectric material can be the same. Alternatively, the first piezoelectric material and the second piezoelectric material can be different.

[0023] In one embodiment, prior to the formation of the seed layer, an intermediate layer suitable for epitaxially growing the seed layer on the donor substrate may be formed on the donor substrate.

[0024] Another object relates to a process for manufacturing a surface acoustic wave device comprising the formation of two interdigitated electrodes on the surface of a piezoelectric layer, characterized in that it comprises manufacturing the piezoelectric layer by the process described above.

[0025] A further object relates to a process for manufacturing a photonic device, comprising forming at least one photonic component, such as a laser or a light emitting diode, at least partially in a piezoelectric layer, characterized in that it comprises manufacturing the piezoelectric layer by the process described above.

[0026] A further object relates to a surface acoustic wave device, characterized in that it comprises a piezoelectric layer obtainable by the process described above and two interdigitated electrodes on one face of the piezoelectric layer.

[0027] Another object relates to a photonic device, characterized in that it comprises a piezoelectric layer obtainable by the process described above and at least one photonic component, such as a laser, a modulator, a waveguide or a multiplexer, at least partially formed in said piezoelectric layer.

[0028] The invention further relates to a structure comprising at least one such surface acoustic wave device and one such photonic device, the structure comprising a single piezoelectric layer on which the surface acoustic wave device and the photonic device are arranged. [Brief explanation of the drawings]

[0029] Other features and advantages of the present invention will become apparent from the following detailed description which refers to the accompanying drawings. [Figure 1] 1 is a schematic cross-sectional view of a surface acoustic wave filter. [Figure 2A] 1 illustrates two successive first steps in a process for manufacturing a single crystal piezoelectric layer according to a first embodiment of the present invention. [Figure 2B] 1 illustrates two successive first steps in a process for manufacturing a single crystal piezoelectric layer according to a first embodiment of the present invention. [Figure 3A] 1 illustrates two successive first steps of the process according to a second embodiment of the invention. [Figure 3B] 1 illustrates two successive first steps of the process according to a second embodiment of the invention. [Figure 4] 1 illustrates the successive steps of the process according to the first or second embodiment of the present invention. [Figure 5] 1 illustrates the successive steps of the process according to the first or second embodiment of the present invention. [Figure 6] 1 illustrates the successive steps of the process according to the first or second embodiment of the present invention. [Figure 7] 1 illustrates the successive steps of the process according to the first or second embodiment of the present invention. [Figure 8] 1 illustrates the successive steps of the process according to the first or second embodiment of the present invention. [Figure 9] Illustrates an optional further step in the process. [Figure 10]Illustrates an optional further step in the process. [Figure 11] Illustrates an optional further step in the process.

[0030] For ease of reading the drawings, some elements are not necessarily drawn to scale. Furthermore, elements designated by the same reference numerals in different drawings are identical. DETAILED DESCRIPTION OF THE INVENTION

[0031] FIG. 1 is a schematic diagram of a surface acoustic wave filter.

[0032] The filter comprises a piezoelectric layer 10 and two electrodes 12, 13 in the form of two interdigitated metal combs deposited on the surface of the piezoelectric layer. Opposite the electrodes 12, 13, the piezoelectric layer rests on a substrate 11. The piezoelectric layer 10 is single crystalline, preferably of good crystalline quality to avoid attenuation of surface waves.

[0033] Generally speaking, the present invention proposes the formation of a monocrystalline piezoelectric layer by the transfer of an epitaxially grown seed layer of a first piezoelectric material onto a donor substrate, the transfer being carried out from the donor substrate to a receiver substrate, followed by the formation of a layer of a second piezoelectric material on the seed layer to achieve a desired thickness of the monocrystalline layer of the second piezoelectric material.

[0034] The donor substrate can be a bulk single-crystal substrate of the first piezoelectric material or of another material. Alternatively, the donor substrate can be a composite substrate, i.e., formed from a stack of at least two layers of different materials, one surface layer of which consists of the first single-crystal piezoelectric material or another single-crystal material. The single-crystal material is suitable for epitaxial growth of the seed layer, in particular, has a lattice constant sufficiently close to that of the seed layer so as not to introduce crystalline defects during growth of the seed layer.

[0035] Particularly advantageously, the seed layer is pseudomorphic, i.e., the actual lattice constant of the seed layer material is forced, for example by atomic forces, to substantially match the lattice constant of the donor substrate on which the seed layer is formed. To this end, the seed layer thickness must not exceed a critical thickness, beyond which stress relaxation and defect generation occur in the seed layer. This critical thickness depends on the seed layer material. For example, the critical thickness is typically less than 5 nm for a germanium seed layer formed on a silicon substrate. Generally, the critical thickness is between 2 nm and 20 nm, depending on the materials selected for the seed layer and the substrate.

[0036] In some embodiments, an intermediate layer of a material suitable for growing a seed layer on the donor substrate (known as an “epitaxial intermediate layer”) can be formed on the donor substrate prior to the formation of the seed layer. The usefulness of such an intermediate layer depends, among other things, on the chemical stability between the seed layer and the donor substrate. Thus, if growing a seed layer directly on the donor substrate is not hindered by interactions or chemical reactions between the seed layer material and the donor substrate material, an intermediate layer is unnecessary. On the other hand, if chemical interactions or reactions between the seed layer material and the donor substrate material may hinder seed layer growth, it may be desirable to use an intermediate layer made of a material that is stable with respect to the donor substrate material and the seed layer material. For example, a single-crystal germanium layer can be formed on a silicon donor substrate to facilitate the growth of a seed layer of the first piezoelectric material. In other embodiments, the intermediate layer can be made of single-crystal strontium titanate (SrTiO), single-crystal aluminum oxide (AlO), single-crystal lanthanum aluminate (LaAlO), or a single-crystal metal such as aluminum.

[0037] The receiver substrate serves as a mechanical support for the seed layer. The receiver substrate can be of any type that is suitable for epitaxy (especially with regard to temperature resistance) and that is advantageously, but not necessarily, suitable for the intended application. The receiver substrate can be solid or composite. Advantageously, the receiver substrate can comprise at least one electronic device or interconnect.

[0038] At least one intermediate layer (known as a "relaxed intermediate layer") is sandwiched between the receiver substrate and the seed layer. For example, such an intermediate layer can be electrically conductive or electrically insulating. Those skilled in the art will be able to select the material and thickness of this layer according to the desired properties of the radio-frequency device intended to include the piezoelectric layer. This intermediate layer allows the seed layer to relax freely. Thus, the transferred pseudomorphic seed layer can freely recover its lattice constant during transfer, or between transfer and the formation of the second layer of the second piezoelectric material, or during the formation of the second layer of the second piezoelectric material.

[0039] The material of the intermediate layer may advantageously be chosen from silicon oxide (SiO2), nitrides or metals.

[0040] The intermediate layer can be formed on the donor substrate (on the seed layer) or on the receiver substrate.

[0041] The intermediate layer made of silicon oxide can be deposited or obtained by thermal oxidation. The technique for forming the layer is selected depending in particular on the substrate on which it is formed and on any limitations (e.g., thermal) that must be met. For example, if the intermediate layer is formed on a receiver substrate and the receiver substrate contains electronic components, a technique will be selected that has a thermal budget that does not risk damaging the components.

[0042] Advantageously, the receiver substrate can be made of a semiconductor material: it can be, for example, a silicon substrate.

[0043] In some embodiments, particularly when the receiver substrate is the final support for the piezoelectric layer, the receiver substrate comprises a trap rich layer, which may be formed either on the receiver substrate or in a surface region of the receiver substrate. Thus, the trap rich layer is located between the seed layer and the receiver substrate and improves the electrical insulation performance of the receiver substrate. The trap rich layer may be formed by at least one polycrystalline, amorphous, or porous semiconductor material, in particular, but not limited to, polycrystalline silicon, amorphous silicon, or porous silicon. Furthermore, depending on the temperature tolerance of the trap rich layer for epitaxy, it may be advantageous to introduce an additional layer between the receiver substrate and the trap rich layer to avoid recrystallization of the trap rich layer during thermal treatment.

[0044] The seed layer has a thickness that is negligible compared to the thickness of the final single crystal piezoelectric layer, and as a result is not expected to significantly affect the operation of a radio frequency device incorporating the single crystal piezoelectric layer.

[0045] The seed layer typically has a thickness of 1 to 20 nm.

[0046] The thickness of the layer of second piezoelectric material formed on the seed layer depends on the specifications of the device in which the single crystal piezoelectric layer is intended to be incorporated. In this regard, the thickness of the layer formed on the seed layer is not limited in either minimum or maximum value. The thickness of the final piezoelectric layer is typically between 20 nm and 15 μm.

[0047] The first piezoelectric material is advantageously selected from compounds of formula ABO3, where A is selected from barium and lithium, and B is selected from titanium and niobium. However, interest in these materials is not limited to their piezoelectric properties. In particular, for other applications such as integrated optics, they may also be of interest for example due to their dielectric constant, refractive index, or pyroelectric, ferroelectric, or ferromagnetic properties.

[0048] The first epitaxy can be performed using any technique suitable for achieving high crystalline quality, such as atomic layer deposition (ALD) or molecular beam epitaxy (MBE). These techniques are characterized by very low growth rates. However, since the seed layer has a low thickness, using one of these techniques to grow the seed layer has a low economic impact on the process, but achieves a crystalline quality of the seed layer that will promote the crystalline quality of the monocrystalline layer of the second piezoelectric material.

[0049] According to a first alternative, a layer of a second piezoelectric material can be formed on the seed layer by a second epitaxy.

[0050] The second epitaxy can be carried out using any technique that offers a higher growth rate than the first epitaxy, in particular metal organic chemical vapor deposition (MOCVD), which offers lower crystalline quality than ALD or MBE techniques but is more economical for growing relatively thick monocrystalline layers.

[0051] According to a second alternative, the layer of second piezoelectric material can be formed by depositing the piezoelectric material in amorphous form and subsequently recrystallizing the material to give it a single-crystal structure. Alternatively, this process can be carried out in several successive cycles, each comprising depositing amorphous piezoelectric material over a particular thickness followed by recrystallizing the material over that thickness, until the desired total thickness of the layer of second piezoelectric material is obtained.

[0052] The amorphous material can be deposited by any technique known to those skilled in the art, advantageously by MOCVD, Low-Pressure Chemical Vapor Deposition (LPCVD), Plasma-Enhanced Chemical Vapor Deposition (PECVD), or sputtering.

[0053] Those skilled in the art will be able to determine the reagents and operating conditions depending on the piezoelectric material being grown and the technique chosen.

[0054] Transferring the seed layer typically involves bonding a donor substrate to a receiver substrate with the seed layer and intermediate relaxed layer at the bonding interface, followed by thinning the receiver substrate to expose the seed layer for subsequent epitaxy.

[0055] The bonding step can be performed, for example, by direct molecular bonding, also known as wafer bonding, with or without an additional intermediate layer.

[0056] Particularly advantageously, the transfer is carried out using the Smart Cut™ process, which is well known for transferring semiconductor thin films, in particular silicon.

[0057] To this end, referring to FIG. 2A, according to a first embodiment, a donor substrate 100 is provided and a layer of a first monocrystalline piezoelectric material, called a seed layer 102, is grown by first epitaxy. The first piezoelectric material has a lattice constant close to that of the donor substrate. In this way, the donor substrate 100 imposes its lattice constant, enabling the growth of a good quality monocrystalline material. Growth is stopped when the seed layer reaches the desired thickness. In this illustration, the donor substrate 100 is shown as a solid, but as noted above, it can also be a composite material.

[0058] Advantageously but optionally, an intermediate epitaxy layer 106 can be formed on the donor substrate 100 prior to the epitaxy of the seed layer 102. For simplicity, this layer 106 is not shown in the following figures.

[0059] Referring to FIG. 2B, an embrittlement zone 101 is formed by ion implantation (indicated by the arrow) into the donor substrate through the seed layer, defining the transferred monocrystalline layer 103, including the seed layer and part of the donor substrate. Advantageously, depending on the piezoelectric material in question, the implanted species are hydrogen or helium, alone or in combination. A person skilled in the art will be able to determine the dose and implantation energy of these species to form the embrittlement zone to a given depth, preferably between 0.2 μm and 0.6 μm. Typically, and depending on the piezoelectric material considered and the species implanted, the dose will be between 2 E+16 and 2 E+17 ion species / cm. 2 and the implantation energy is in the range of 30 keV to 500 keV. The buried embrittlement layer can also be obtained by any other means known to those skilled in the art, for example by porosifying the material or by laser irradiation. However, as explained below, there are transfer processes that do not require ion implantation, and the present invention can be implemented with these processes.

[0060] 3A and 3B illustrate a second embodiment of a process for manufacturing a single-crystal piezoelectric layer, which is an alternative to the first embodiment shown in FIGS. 2A and 2B, in which implantation into the donor substrate is performed before the seed layer is first formed by epitaxy.

[0061] Referring to FIG. 3A, a donor substrate 100 is provided and an embrittlement region 101 is formed by ion implantation (indicated by the arrow) into the donor substrate 100, defining the monocrystalline layer 103 to be transferred.

[0062] Referring to FIG. 3B, a layer of a first single-crystal piezoelectric material, called the seed layer 102, is grown by first epitaxy on the transferred layer 103. As mentioned earlier, the donor substrate 100 imposes its lattice constant, enabling the growth of a good quality single-crystal material. The first piezoelectric material has a lattice constant close to that of the donor substrate. Growth is stopped when the seed layer reaches a desired thickness. In this illustration, the donor substrate 100 is shown as a solid, but as noted above, it can be a composite material.

[0063] Advantageously, the thermal budget of the first epitaxy is lower than the thermal budget that would cause the donor substrate to fracture along the embrittlement zone, thus allowing the donor substrate to maintain its mechanical integrity until the seed layer growth is complete.

[0064] After the steps shown in Figures 2A and 2B or Figures 3A and 3B, a seed layer 102 is obtained on the donor substrate 100 and an embrittlement region is formed by implantation to define a transferred layer 103 comprising the seed layer 102.

[0065] 4, at least one electrically insulating or conductive intermediate relaxed layer 105 is formed on the surface of a receiver substrate 110. The receiver substrate 110 may further comprise a trap rich layer 107. For simplicity, layer 107 is not shown in the following figures.

[0066] Referring to FIG. 5, the thus-embrittled donor substrate 100 is bonded to a receiver substrate 110 with the seed layer 102 and intermediate relaxed layer 105 at the bonding interface.

[0067] 6, donor substrate 100 is separated along embrittled region 101. Such separation can be achieved by any means known to those skilled in the art, for example, thermal, mechanical, chemical, etc. Layer 103 is then transferred to receiver substrate 110. Advantageously, the remainder of the donor substrate can be recovered for recycling.

[0068] 7, a surface portion of the transferred layer is removed, for example, by mechanical polishing and / or chemical etching. The purpose of this material removal is to expose the seed layer 102. The result of the removal is a thinned layer 102 on the receiver substrate 110, which will serve as a seed layer for the next step.

[0069] Referring to FIG. 8 , a layer 104 of a second piezoelectric material is formed on the seed layer 102. The material of layer 104 has a lattice constant close to or identical to that of the seed layer 102. In this way, the seed layer 102 imposes its lattice constant, enabling the growth of a high-quality single-crystalline material. Layer 104 may differ slightly in properties from the seed layer 102, particularly due to the controlled introduction of small levels of impurities for various purposes (doping, tuning of piezoelectric properties, optimization of crystal defect / dislocation density, surfactants, etc.). Growth is stopped when the single-crystalline piezoelectric layer reaches the desired thickness. The final piezoelectric layer 10 is formed by stacking the seed layer 102 and layer 104.

[0070] The first piezoelectric material and the second piezoelectric material may be the same.

[0071] Alternatively, the first piezoelectric material and the second piezoelectric material may be different.

[0072] As noted above, the seed layer is believed to have no effect, or a secondary effect, on the operation of a radio frequency device incorporating a piezoelectric layer formed thereon. As a result, even if the implants performed to implement the Smart Cut™ process damage the seed layer and interfere with its piezoelectric properties, these defects pose little or no disadvantage.

[0073] In a non-illustrated embodiment, the embrittlement zone is not formed in the donor substrate. In this case, the transfer of the seed layer to the receiver substrate is achieved by bonding the donor substrate to the receiver substrate and then etching the donor substrate until the seed layer is exposed. However, this process results in greater material loss and is therefore less preferred than processes that include the formation of an embrittlement zone in the donor substrate.

[0074] In a further embodiment not shown, no embrittlement zone is formed in the donor substrate, but a separable interface is formed by a chemical or thermal reaction, in which case the transfer of the seed layer to the receiver substrate is achieved by bonding the donor substrate to the receiver substrate and then separating the interface after a chemical or thermal reaction to expose the seed layer.

[0075] 8, this process results in a substrate for a surface acoustic wave device comprising a receiver substrate 110 and a single crystal piezoelectric layer 10 on the substrate 110. Such a substrate may also prove useful in other applications such as photonics and integrated optics.

[0076] The layer 10 is made up of two parts with different properties: a first portion 102 located at the interface with the receiver substrate 110, corresponding to the seed layer; - characterized by the presence of a second portion 104 extending from the first portion 102, corresponding to a layer formed on the portion 102, which second portion 104 may have a crystalline quality different from that of the first portion (which quality may, for example, be adjusted and optimized during the second epitaxy step) and / or a different composition (especially if impurities such as dopants have been introduced during epitaxy), possibly imparting special properties to the layer formed on the portion 102.

[0077] This substrate is advantageously used to manufacture a surface acoustic wave device such as that shown in FIG. 1 and / or any other microelectronic, photonic or optical device comprising a piezoelectric layer.

[0078] In some cases, the receiver substrate onto which the seed coat is transferred may not be optimal for the intended application. In some embodiments, the receiver substrate must be subjected to epitaxy operating conditions, limiting the selection of suitable materials. In particular, the receiver substrate cannot contain layers or elements that may be damaged by epitaxy temperatures. It may then be advantageous to transfer the piezoelectric layer 10 onto a final substrate 120, the properties of which are selected according to the intended application, by bonding the piezoelectric layer 10 to the final substrate 120 via the surface of the layer 104 formed on the seed layer 102 (see FIG. 9 ) and removing the receiver substrate (see FIG. 10 ). This transfer can be performed using any of the transfer techniques mentioned above. A further advantage of this transfer to the final substrate is that the seed layer 102, which was embedded in the structure created by the formation of the layer of the second piezoelectric material, is now exposed and can be removed, if necessary, especially if the seed layer has defects (see FIG. 11 ). Only the layer 104 of the second piezoelectric material then remains on the final substrate 120.

[0079] The final substrate can be a solid or composite material.

[0080] Advantageously, the final substrate may comprise at least one electronic device or interconnect.

[0081] In some embodiments, the final substrate comprises a trap rich layer (designated 121 in FIG. 9) which may be either formed on the final substrate or formed within a surface region of the final substrate. The trap rich layer is therefore located between the piezoelectric layer and the final substrate and improves the electrical insulation performance of the final substrate. The trap rich layer may be formed by at least one polycrystalline, amorphous, or porous semiconductor material, in particular, but not limited to, polycrystalline silicon, amorphous silicon, or porous silicon.

[0082] In the case of a surface acoustic wave device, two interdigitated comb-shaped metal electrodes 12, 13 are deposited on the surface of the piezoelectric layer 10 opposite the receiver substrate, or possibly the final substrate (whether it is the receiver substrate 110 or the final substrate 120, which forms the support substrate shown at 11 in Figure 1).

[0083] In other applications, at least one photonic component, such as a laser, a modulator, a waveguide, or a multiplexer, can be formed in the piezoelectric layer or in a stack of layers that includes the piezoelectric layer.

[0084] It is particularly advantageous to integrate surface acoustic wave devices and photonic devices in the same substrate. For this purpose, at least one surface acoustic wave device and one photonic device, such as a laser, a modulator, a waveguide, or a multiplexer, are formed in the same piezoelectric layer. It is also possible to combine these devices as described with other devices present in a receiver substrate or a final substrate, thereby aiming at the known approach of co-integration of 2D, 2.5D, and 3D devices.

Claims

1. A process for producing a piezoelectric layer (10) on a substrate (11), comprising: - forming, by a first epitaxy, a seed layer (102) of a first piezoelectric material on a donor substrate (100); - transferring said seed layer (102) and a portion (103) of said donor substrate (100) to a receiver substrate (110) via at least one electrically insulating layer and / or at least one conductive layer (105) adapted to allow relaxation of said seed layer; - removing the transferred portion (103) of the donor substrate (100) so as to expose the surface of the seed layer (102); - forming a second monocrystalline layer (104) of piezoelectric material on said seed layer (102); A process comprising:

2. The step of transferring the seed layer (102) and the portion (103) of the donor substrate (100) comprises the steps of: - forming an embrittlement area (101) in said donor substrate (100) so as to define said portion (103) to be transferred; - bonding the donor substrate (100) to the receiver substrate (110) with the seed layer (102) at the bonding interface; - separating the donor substrate (100) along the embrittlement zone (101), The process of claim 1 , wherein the formation of the seed layer (102) on the donor substrate (100) occurs after the formation of the embrittlement region (101).

3. The transfer of the seed layer (102) and the portion (103) of the donor substrate (100) comprises the following steps: - forming an embrittlement area (101) in said donor substrate (100) so as to define said portion (103) to be transferred, - bonding the donor substrate (100) to the receiver substrate (110) with the seed layer (102) at the bonding interface; - separating the donor substrate (100) along the embrittlement zone (101), The process of claim 1 , wherein the formation of the seed layer (102) on the donor substrate (100) occurs before the formation of the embrittlement region (101).

4. The process of claim 2 or 3, wherein the embrittlement zone (101) is formed by ion implantation of hydrogen and / or helium into the donor substrate (100).

5. The process of any one of claims 1 to 4, wherein the formation of the seed layer (102) on the donor substrate (100) is performed by atomic layer deposition.

6. The process according to one of claims 1 to 4, wherein the formation of the seed layer (102) on the donor substrate (100) is performed by molecular beam epitaxy.

7. The process according to one of claims 1 to 6, wherein the formation of the monocrystalline layer (104) on the seed layer (102) is performed by second epitaxy.

8. 8. The process of claim 7, wherein the second epitaxy of the second piezoelectric material on the seed layer (102) is metalorganic chemical vapor deposition.

9. 7. The process of claim 1, wherein the formation of the monocrystalline layer (104) on the seed layer (102) is achieved by depositing the second piezoelectric material in amorphous form, followed by recrystallizing the second material.

10. The process of any one of claims 1 to 9, wherein the seed layer (102) is between 2 nm and 20 nm.

11. The process according to one of the preceding claims, wherein the portion (103) of the donor substrate (100) transferred to the receiver substrate (110) has a thickness of less than 2 μm, preferably less than 1 μm.

12. The process according to one of the preceding claims, wherein the thickness of the layer (104) of second piezoelectric material at the end of the second epitaxy is between 20 nm and 15 μm.

13. The process of any one of claims 1 to 12, wherein the receiver substrate (110) comprises at least one electronic device or interconnect.

14. The process of any one of claims 1 to 13, wherein the receiver substrate (110) comprises a trap rich layer (107).

15. The process of any one of claims 1 to 12, comprising, after forming the single crystalline layer of the second piezoelectric material, transferring at least a portion of the layer (104) of the second piezoelectric material onto a final substrate (120).

16. 16. The process of claim 15, wherein the portion of the layer (104) of the second piezoelectric material transferred onto the final substrate (120) has a thickness of less than 2 μm, preferably less than 1 μm.

17. The process of claim 15 or 16, wherein the final substrate (120) comprises at least one electronic device or interconnect.

18. The process of one of claims 15 to 17, wherein the final substrate (120) comprises a trap rich layer (121).

19. The process of any one of claims 1 to 18, wherein the first piezoelectric material and the second piezoelectric material are identical.

20. The process of any one of claims 1 to 18, wherein the first piezoelectric material and the second piezoelectric material are different.

21. The process of any one of claims 1 to 20, comprising, prior to the formation of the seed layer (102), the formation of an intermediate layer (106) on the donor substrate (100), the intermediate layer being adapted to epitaxially grow the seed layer (102) on the donor substrate (100).

22. A process for manufacturing a surface acoustic wave device, comprising the step of forming two interdigitated electrodes (12, 13) on the surface of a piezoelectric layer (10), characterized in that the process comprises manufacturing the piezoelectric layer (10) by a process according to one of claims 1 to 21.

23. A process for manufacturing a photonic device, comprising a step of forming at least one photonic component, such as a laser, a modulator, a waveguide or a multiplexer, at least partially in a piezoelectric layer, characterized in that it comprises manufacturing the piezoelectric layer (10) by a process according to one of claims 1 to 21.

24. A surface acoustic wave device, characterized in that it comprises a piezoelectric layer (10) obtainable by a process according to one of claims 1 to 21, and two interdigitated electrodes (12, 13) on one side of said piezoelectric layer (10).

25. Photonic device, characterized in that it comprises a piezoelectric layer obtainable by a process according to one of claims 1 to 21 and at least one photonic component, such as a laser, a modulator, a waveguide or a multiplexer, at least partially formed in said piezoelectric layer.

26. 26. A structure comprising a surface acoustic wave device according to claim 24 and a photonic device according to claim 25, wherein the surface acoustic wave device and the photonic device are at least partially disposed within the same piezoelectric layer.

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