Method for producing single crystal layer, in particular piezoelectric layer

Abstract

The invention relates to a method for producing a single crystal layer, in particular a piezoelectric layer. The method comprises the following consecutive steps: providing a donor substrate (100) comprising a piezoelectric material having a composition of A 'B' O3; growing a single crystal layer (103) consisting of A 'B' O3 on the piezoelectric material A 'B' O3 through epitaxy; providing a receptor substrate (110); transferring at least a portion of the epitaxial layer (103) having a composition of A "B" O3 onto the acceptor substrate (110) by bonding the donor substrate (100) to the acceptor substrate (110) via the epitaxial layer (103), followed by thinning the donor substrate (100) up to the epitaxial layer (103) having a composition of A "B" O3; after a layer (103) having a composition of A "B" O3 has been transferred onto the acceptor substrate, a single crystal layer (104) having a composition of A "B" O3 is grown by epitaxy on a material having a composition of A "B" O3, where A ', A "and A" are composed of one or more of the following elements Li, Na, K, H, and B', B "and B" are composed of one or more of the following elements Nb, Ta, Sb, V.

Description

[0001] This application is a divisional application. The international application number of the original application is PCT / EP2016 / 082245, the application date is December 21, 2016, the application number of the Chinese national phase is 201680080405.8, and the name of the invention is "Method for manufacturing a single crystal layer, especially a piezoelectric layer". Technical Field

[0002] The present invention relates to a method for manufacturing a single crystal layer, in particular a piezoelectric layer, in particular for applications employing microelectronic, photonic or optical devices. In particular, but not limiting, the device may be a surface acoustic wave device or a bulk acoustic wave device for radio frequency applications. Background Art

[0003] Among the acoustic components used for filtering in the RF field, two main types of filters can be distinguished:

[0004] - First, the surface acoustic wave filter, known by the abbreviation SAW (Surface Acoustic Wave);

[0005] - Secondly, bulk acoustic wave filters and resonators, known by the abbreviation BAW (Bulk Acoustic Wave).

[0006] For a review of these technologies, see W. Steichen and S. Ballandras, “Acoustic components used for filtering–Review of the different technologies”, Techniques de l'Ingénieur [Engineering Technology], E2000, 2008 [1].

[0007] Surface acoustic wave filters typically include a thick piezoelectric layer (usually hundreds of micrometers (μm) thick) and two electrodes in the form of interdigitated metal combs deposited on the surface of the piezoelectric layer. An electrical signal (usually a voltage change) applied to the electrodes is converted into an elastic wave, which propagates on the surface of the piezoelectric layer. If the frequency of the wave is equal to the frequency band of the filter, the propagation of the elastic wave is promoted. The wave is converted into an electrical signal again when it reaches the other electrode.

[0008] In the case of a bulk acoustic wave filter, it typically comprises a thin piezoelectric layer (i.e., typically less than approximately 1 μm thick) and two electrodes mounted on each major face of the thin layer. An electrical signal (usually a voltage change) applied to the electrodes is converted into an elastic wave, which propagates through the piezoelectric layer. If the frequency of this elastic wave is equal to the frequency band of the filter, the propagation of the elastic wave is facilitated. The wave is converted into an electrical signal again when it reaches the electrode on the opposite face.

[0009] In the case of surface acoustic wave filters, the piezoelectric layer must have excellent crystal quality in order not to cause any attenuation of the surface waves. In this case, monocrystalline layers are therefore preferred. Suitable materials that can be used industrially at present are quartz, LiNbO3 or LiTaO3. The piezoelectric layer is obtained by cutting an ingot of one of the materials mentioned, wherein the required accuracy of the thickness of the layer is not important if the waves will essentially propagate on its surface.

[0010] In the case of bulk acoustic wave filters, the piezoelectric layer must have a defined and uniform thickness throughout the layer in a precisely controlled manner. Conversely, since the crystal quality is secondary with regard to important criteria for filter performance, compromises have been made so far with regard to the crystal quality of the layer and polycrystalline layers have long been considered acceptable. The piezoelectric layer is therefore formed by deposition on a supporting substrate, for example a silicon substrate. Currently, the materials used industrially for such deposition are AlN, ZnO and Pb (Zr X ,Ti 1-X )O3(PZT).

[0011] Therefore, for both technologies, the material selection is extremely limited.

[0012] However, the material selection is the result of a compromise between different properties of the filter, depending on the filter manufacturer's specifications. In particular, the electromechanical coupling coefficient of the piezoelectric material is a criterion for the selection of the material that must be used for a given application and a given component architecture.

[0013] For example, LiNbO3 and LiTaO3 are highly anisotropic materials. Since the coupling coefficient depends on the crystal orientation, the choice of a specific orientation of the material provides the first degree of freedom for the choice of material. As a result, substrates with a multiplicity of crystal orientations can be seen, such as: X-cut, Y-cut, Z-cut, YZ-cut, 36° rotated Y axis, 42° rotated Y axis, etc.

[0014] However, aside from the ability of a person skilled in the art to select a specific crystal orientation, one has only quartz, LiNbO3 and LiTaO3 to design surface acoustic wave filters, thereby providing only a limited range of parameters to optimize the filter's characteristics, even though several other materials (e.g., lanthanum gallium silicate La3Ga5SiO3) may be available in the future. 14 ) to join the list.

[0015] In order to allow greater freedom in designing a bulk acoustic wave filter or a surface acoustic wave filter, it would be desirable to be able to use more materials than those listed above, provided that the quality of the material is not compromised. Summary of the invention

[0016] One object of the present invention is to remedy the above-mentioned drawbacks and in particular to devise a method for manufacturing single-crystalline layers, in particular piezoelectric layers, made of materials other than those used for this application, in particular for surface acoustic wave devices, in particular by making it possible to obtain thin (i.e. less than 20 μm thick, or less than 1 μm thick) and uniform layers. The method must also make it possible to use a wider variety of support substrates than the existing bulk acoustic wave devices.

[0017] According to the invention, a method for manufacturing a single crystal layer is proposed, characterized in that the method comprises the following consecutive steps:

[0018] - providing a donor substrate comprising a piezoelectric material having an ABO3 composition, wherein

[0019] A is composed of at least one element selected from Li, Na, K, and H;

[0020] B is composed of at least one element selected from Nb, Ta, Sb, and V;

[0021] - providing a receptor substrate,

[0022] - transferring a layer called "seed layer" from a donor substrate to an acceptor substrate by bonding the donor substrate to the acceptor substrate so that the seed layer is at the bonding interface and subsequently thinning the donor substrate down to the seed layer;

[0023] - growing a single crystal layer having a composition of A'B'O3 by epitaxy on the piezoelectric material ABO3 of the seed layer, wherein:

[0024] A' is composed of at least one of the following elements: Li, Na, K, H;

[0025] B' is composed of at least one of the following elements: Nb, Ta, Sb, V;

[0026] A' is different from A, or B' is different from B.

[0027] The expression "a layer is at a bonding interface" should be understood as meaning that the layer is on the side of the face of the first substrate bonded to the second substrate, but this does not necessarily mean that there is direct contact between the layer and the second substrate. The layer can thus be directly bonded to the second substrate, or covered by a bonding layer (e.g. a dielectric layer) or any other type of layer by which bonding is achieved.

[0028] The expression “A is different from A′” is understood to mean that A and A′ consist of different elements, and / or consist of the same elements but in different stoichiometric ratios.

[0029] According to one embodiment, A′ includes at least one element in common with A, and / or B′ includes at least one element in common with B.

[0030] The expression "A' comprises at least one element in common with A" is understood to mean that the given element (or elements) are present both in A and in A' in the same or different stoichiometric ratios.

[0031] According to one embodiment, A' is identical to A when B' is different from B, and B' is identical to B when A' is different from A.

[0032] The expression “A′ is identical to A” is understood to mean that A′ and A consist of the same elements in the same stoichiometric ratio.

[0033] According to one embodiment, A consists of a single element and B consists of a single element.

[0034] According to one embodiment of the present invention, the transfer of the seed layer comprises the following steps:

[0035] - forming an embrittled zone in the donor substrate so as to define a layer, called seed layer, containing said piezoelectric material having the composition ABO3,

[0036] - bonding the donor substrate to the acceptor substrate, wherein the seed layer is at the bonding interface,

[0037] - Peeling off the donor substrate along the embrittled zone, thereby transferring the seed layer to the acceptor substrate.

[0038] Prior to the epitaxial step, part of the thickness of the seed layer transferred to the acceptor substrate may be removed.

[0039] Advantageously, the seed layer has a thickness of less than 2 μm, and preferably less than 1 μm.

[0040] The acceptor substrate is advantageously made of a semiconductor material and comprises an intermediate charge-trapping layer between said seed layer and said acceptor substrate.

[0041] Another object of the invention relates to a method for producing a single-crystal layer, characterized in that the method comprises the following consecutive steps:

[0042] - providing a donor substrate comprising a piezoelectric material having a composition of A'B'O3, wherein

[0043] A' is composed of one or more of the following elements: Li, Na, K, H;

[0044] B' is composed of one or more of the following elements: Nb, Ta, Sb, V;

[0045] - epitaxially growing a single-crystalline layer having a composition of A"B"O3 on said piezoelectric material A'B'O3, wherein

[0046] A” is composed of one or more of the following elements: Li, Na, K, H;

[0047] B" is composed of one or more of the following elements: Nb, Ta, Sb, V;

[0048] - providing a receptor substrate,

[0049] - transferring at least a portion of the epitaxial layer (103) having a composition of A"B"O3 onto the acceptor substrate by bonding the donor substrate to the acceptor substrate via the epitaxial layer and subsequently thinning the donor substrate until the epitaxial layer having a composition of A"B"O3 is obtained.

[0050] According to one embodiment, after the layer (103) having the composition A"B"O3 has been transferred to the acceptor substrate, a single-crystalline layer having the composition A"'B"'O3 is grown by epitaxial growth on the material having the composition A"B"O3, wherein in the composition A"'B"'O3

[0051] A'' is composed of one or more of the following elements: Li, Na, K, H;

[0052] B'' is composed of one or more of the following elements: Nb, Ta, Sb, and V.

[0053] According to one embodiment, A'' is different from A'', or B'' is different from B''.

[0054] According to one mode of implementing the present invention, transferring at least a portion of the epitaxial layer having the composition of A"B"O3 to an acceptor substrate comprises the following steps:

[0055] - forming an embrittled zone in the donor substrate or in the epitaxial layer with the composition A"B"O3, thereby defining the layer to be transferred,

[0056] -bonding the donor substrate to the acceptor substrate, wherein the epitaxial layer having the composition of A"B"O3 is at the bonding interface;

[0057] - Peeling off the donor substrate or epitaxial layer along the embrittled zone.

[0058] According to one embodiment, an embrittled zone is formed in the donor substrate and after said transfer step the transferred layer is thinned to reveal a material having the composition A"B"O3.

[0059] According to one embodiment, A" is different from A', or B" is different from B'.

[0060] According to one embodiment, A" comprises at least one element in common with A' and / or B" comprises at least one element in common with B'.

[0061] According to one embodiment, A" is identical to A' when B" is different from B', and B" is identical to B' when A" is different from A'.

[0062] According to one embodiment, A' consists of a single element and B' consists of a single element.

[0063] According to a particular way of implementing the invention, the embrittled zone is formed by ion implantation in the donor substrate.

[0064] In a particularly advantageous manner, after the epitaxy step, the thickness of the monocrystalline layer having the composition A"B"O3 is between 0.2 μm and 20 μm.

[0065] In addition, at least one electrically insulating layer and / or at least one electrically conductive layer may be formed at the interface between the acceptor substrate and the donor substrate.

[0066] According to one mode of carrying out the invention, the method comprises transferring at least a portion of the single crystal layer on the acceptor substrate to a final substrate.

[0067] Another object relates to a substrate for microelectronic, photonic or optical devices, characterized in that the substrate comprises a support substrate and a single-crystalline layer with a composition of A"B"O3 on the support substrate and a layer with a composition of A'B'O3 between the support substrate and the layer with a composition of A"B"O3, wherein

[0068] A” is composed of one or more of the following elements: Li, Na, K, H;

[0069] B" is composed of one or more of the following elements: Nb, Ta, Sb, V;

[0070] At least one of A" and B" consists of at least two elements,

[0071] in

[0072] A' is composed of at least one element from Li, Na, K, H, and

[0073] B' is composed of at least one element selected from Nb, Ta, Sb, and V.

[0074] According to one embodiment, the substrate further comprises a single crystalline layer having a composition of A"'B"'O3 on the layer having a composition of A"B"O3, wherein

[0075] A'' is composed of one or more of the following elements: Li, Na, K, H;

[0076] B'' is composed of one or more of the following elements: Nb, Ta, Sb, and V.

[0077] Another object relates to a method for manufacturing a surface acoustic wave device, characterized in that the method comprises manufacturing the piezoelectric layer by the method described above.

[0078] Another object relates to a surface acoustic wave device, characterized in that the device comprises a single-crystal piezoelectric layer obtainable by the above method and two electrodes mounted on the surface of the single-crystal piezoelectric layer.

[0079] Another object relates to a method for manufacturing a bulk acoustic wave device, comprising depositing electrodes on two opposite faces of a single-crystal piezoelectric layer, characterized in that the method comprises manufacturing the piezoelectric layer by the method described above.

[0080] Another object relates to a bulk acoustic wave device, characterized in that the device comprises a single-crystal piezoelectric layer obtainable by the method described above and two electrodes mounted on two opposite faces of the single-crystal piezoelectric layer.

[0081] Another object of the invention relates to a microsensor designed to measure deformations caused by external stresses, characterized in that it comprises a single-crystal piezoelectric layer obtainable by the method described above.

[0082] Another object of the present invention relates to a microactuator designed to cause deformation of an element or movement of a moving part by applying a continuous or variable electric field, characterized in that the microactuator comprises a single-crystal piezoelectric layer obtainable by the method described above. BRIEF DESCRIPTION OF THE DRAWINGS

[0083] Other features and advantages of the present invention will become apparent from the detailed description given below with reference to the accompanying drawings, in which:

[0084] - Figure 1 is a functional cross-sectional diagram of a surface acoustic wave filter,

[0085] - Figure 2 is a functional cross-sectional diagram of a bulk acoustic wave filter,

[0086] - Figures 3A to 3E shows the successive steps of a method for manufacturing a single crystal layer according to a first embodiment of the present invention;

[0087] - Figures 4A to 4E shows the successive steps of a method for manufacturing a single crystal layer according to a second embodiment of the present invention;

[0088] - Figure 4F Shown in Figures 4A to 4E Additional steps implemented in variations of the illustrated embodiment;

[0089] - Figures 5A to 5C Optional subsequent steps of the method are shown.

[0090] For reasons of legibility in the drawings, the elements shown are not necessarily presented to scale. Elements designated by the same reference numerals in different figures are identical. DETAILED DESCRIPTION

[0091] Figure 1 is a functional diagram of a surface acoustic wave filter.

[0092] The filter shown comprises a piezoelectric layer 10 and two electrodes 12, 13 in the form of two interdigitated metal combs deposited on the surface of said piezoelectric layer. On the side opposite to the electrodes 12, 13, the piezoelectric layer resides on a supporting substrate 11. The piezoelectric layer 10 is single crystalline; in fact, excellent crystal quality is required in order not to attenuate surface waves.

[0093] Figure 2 is a functional diagram of a bulk acoustic wave resonator.

[0094] The resonator comprises a thin piezoelectric layer (i.e. typically less than 1 μm thick, preferably less than 0.2 μm thick) and two electrodes 12, 13 mounted on either side of the piezoelectric layer 10, which is single crystalline due to the manufacturing method of the invention. The piezoelectric layer 10 resides on a supporting substrate 11. In order to isolate the resonator from the substrate and thereby prevent waves from propagating in the substrate, a Bragg mirror 14 is inserted between the electrode 13 and the substrate 11. In an alternative (not shown), this isolation can be achieved by creating a cavity between the substrate and the piezoelectric layer. These various arrangements are known to those skilled in the art and will not be described in detail herein.

[0095] In a general manner, the present invention proposes the formation of a single crystal layer, in particular a piezoelectric layer, by means of the following steps: epitaxy is carried out on a material of a donor substrate serving as a seed for the epitaxy until the desired thickness for the single crystal layer is obtained and transfer to an acceptor substrate, wherein the transfer can be effected before the epitaxy (in which case a surface layer of the donor substrate, called the seed layer, is transferred to the acceptor substrate) or after the epitaxy (in which case at least a portion of the epitaxial layer is transferred to the acceptor substrate).

[0096] The donor substrate may be a homogeneous single-crystalline substrate of the material under consideration. Alternatively, the donor substrate may be a composite substrate, ie in the form of a stack of at least two layers of different materials, the surface layer of which consists of the single-crystalline material under consideration.

[0097] Of particular interest among piezoelectric materials are perovskites of the ABO3 structure and similar materials. However, the interest these materials bring is not limited to their piezoelectric properties. In particular for other applications, such as those involving integrated optics, they may also be of interest for their dielectric constant, their refractive index, or their thermoelectric properties, ferroelectric properties or ferromagnetism (for example, where applicable).

[0098] A large family emerges. They are derived in particular from binary materials such as LiNbO3, LiTaO3, KNbO3, KTaO3, resulting in a general formula of the ABO3 type, wherein A is composed of one or more of the following elements Li, Na, K, H, and wherein B is composed of one or more of the following elements Nb, Ta, Sb, V.

[0099] In summary, it will be considered that A is composed of one or more of the following elements Li, Na, K, and H, and B is composed of one or more of the following elements Nb, Ta, Sb, and V.

[0100] The acceptor substrate acts as mechanical support for the seed layer. It may be of any type suitable for carrying out epitaxy, in particular in terms of performance stability at high temperatures, and advantageously, but not mandatory, for the application under consideration. It may be homogeneous or composite.

[0101] At least one intermediate layer may be inserted between the receptor substrate and the seed layer. For example, such an intermediate layer may be electrically conductive or electrically insulating. A person skilled in the art will be able to select the material and thickness of this layer according to the properties that the radio frequency device that the piezoelectric layer is intended to have.

[0102] Advantageously, the acceptor substrate can be made of a semiconductor material. This can be, for example, a silicon substrate. The conductive material comprises a "well-rich" type intermediate layer, which can be formed on the acceptor substrate or on the surface of the acceptor substrate. The well-rich intermediate layer is therefore located between the seed layer and the acceptor substrate and enables the electrical insulation of the acceptor substrate to be improved. The well-rich intermediate layer can be formed of at least one of a polycrystalline, amorphous or porous material, in particular polycrystalline silicon, amorphous silicon or porous silicon, but is not limited to these materials. In addition, depending on the performance stability of the well-rich intermediate layer used to complete the epitaxy at high temperatures, it may be advantageous to introduce an additional layer between the acceptor substrate and the well-rich intermediate layer to avoid its recrystallization during thermal treatment.

[0103] According to a first embodiment, the method comprises transferring the seed layer of the donor substrate onto the support substrate, followed by the above-mentioned epitaxial step. In this case, the material of the seed layer is advantageously a material having a composition of ABO3, wherein A is composed of at least one element from Li, Na, K, H, and B is composed of at least one element from Nb, Ta, Sb, V. According to one embodiment, both A and B are composed of a single element. For example, the formula ABO3 can be Li x1 K 1-x1 Nb y1 Ta 1-y1 O3, where x1=0 or 1 and y1=0 or 1. Two very widely used representatives of this family of materials are LiNbO3 and LiTaO3. To a lesser extent, KNbO3 and KTaO3 substrates are also available. In this article, such compositions are called binary compositions. Such binary materials are usually formed by drawing in the form of ingots. In this case, it is advantageous that the composition of the epitaxial layer is different from the composition of the seed layer of the A'B'O3 type, where A' is composed of one or more of the following elements Li, Na, K, H; B' is composed of one or more of the following elements Nb, Ta, Sb, V; A' is different from A, or B' is different from B. Continuing with the previous example, the formula A'B'O3 can be Li x2 K 1- x2 Nb y2 Ta 1-y2 O3, where 0≤x2≤1 and 0≤y2≤1, and where x2 is different from x1, or y2 is different from y1.

[0104] In this document, if the total number of elements including A and B is equal to 3, then the composition is called ternary; if the total number of elements including A' and B' is equal to 4, then the composition is called quaternary. Unlike binary materials, such ternary or quaternary materials are not obtained by drawing an ingot in most cases, but must be obtained by epitaxy on a suitable support in order to have sufficient quality for the required size.

[0105] In the first embodiment of the material of the ABO3 binary composition, the material of the A'B'O3 ternary (or higher) composition will be preferred. More specifically, the aforementioned ABO3 and A'B'O3 compositions are preferred, wherein A' includes at least one element in common with A and / or B' includes at least one element in common with B, wherein the common element is advantageously the main element in the composition of A or B. In a further more preferred manner, the aforementioned ABO3 and A'B'O3 compositions will be selected in which A' is the same as A when B' is different from B and B' is the same as B when A' is different from A. When the content of the main element of A or B changes slightly (for example, when A is Li and A' is Li 0,9 Na 0,1When, or as an alternative, when B is Ta 0,5 Nb 0,5 And B' is Ta 0,6 Nb 0,4 ), A' may be approximately the same as A, or B' may be approximately the same as B.

[0106] According to a second embodiment, the epitaxy step is completed before the transfer step. In this case, the donor substrate material that serves as the seed for epitaxy is a material having a composition of A'B'O3, wherein A' is composed of one or more of the following elements Li, Na, K, H; B' is composed of one or more of the following elements Nb, Ta, Sb, V. In this case, the composition of the epitaxial layer is of the A"B"O3 type, wherein A" is composed of one or more of the following elements Li, Na, K, H; B" is composed of one or more of the following elements Nb, Ta, Sb, V. For example, the composition of the seed layer is Li x1 K 1-x1 Nb y1 Ta 1-y1 O3, where 0≤x1≤1 and 0≤y1≤1, and the composition of the epitaxial layer is Li x2 K 1-x2 Nb y2 Ta 1-y2 O3, where 0≤x2≤1 and 0≤y2≤1. The material of the epitaxial layer may be the same as the material of the seed layer (in other words, A' is the same as A" and B' is the same as B", i.e., in the above example, x1=x2 and y1=y2). Alternatively, the material of the epitaxial layer is different from the material of the seed layer (in other words, A' is different from A" or B' is different from B", i.e., in the above example, x1 is different from x2 or y1 is different from y2).

[0107] In a second embodiment, materials of binary composition A'B'O3 and materials of ternary (or higher) composition A"B"O3 are preferred. More specifically, preferred are the aforementioned A'B'O3 and A"B"O3 compositions in which A" includes at least one element in common with A' and / or B" includes at least one element in common with B', wherein the common element is advantageously the main element in the composition of A or B. In an even more preferred manner, the aforementioned A'B'O3 and A"B"O3 compositions are selected in which A" is the same as A' when B" is different from B' and B" is the same as B' when A" is different from A'. When the content of the main element of A or B is slightly different (for example, when A is Li and A' is Li 0,9 Na 0,1 When, or as an alternative, when B is Ta 0,5 Nb 0,5 And B' is Ta 0,6 Nb 0,4), A' may be approximately the same as A, or B' may be approximately the same as B.

[0108] According to a variant of the second embodiment, the method further comprises, after the transfer step, resuming epitaxy on the transferred layer, thereby forming a single-crystalline layer having a composition of A''B''O3, wherein A'' is composed of one or more of the following elements Li, Na, K, H; B'' is composed of one or more of the following elements Nb, Ta, Sb, V. For example, the composition of the additional epitaxial layer may be Li x3 K 1-x3 Nb y3 Ta 1-y3 O3 type, where 0≤x3≤1 and 0≤y3≤1. Preferably x3 is different from x2 or y3 is different from y2 (in other words, more generally, A'' is different from A'' or B'' is different from B'').

[0109] The present invention therefore enables in particular the formation of thin layers of the compound A'B'O3, A"B"O3 or A"'B"'O3 with excellent crystal quality, at least comparable to that of a homogeneous substrate of this family of binary materials, with controlled thickness over a very wide thickness range, in particular thicknesses of less than 20 μm, and a wide variety of properties that can be adjusted by the material composition.

[0110] Epitaxy can be accomplished by any suitable technique, in particular by chemical vapor deposition (CVD), liquid phase epitaxy (LPE) or pulsed laser deposition (PLD), etc. For the materials considered herein, reference may be made, for example, to publications [2], [3], [4], [5], [6].

[0111] One skilled in the art will be able to determine the reagents and operating conditions depending on the material that must be grown and the technique chosen.

[0112] The composition of the materials of the different layers is adjusted by choosing the elements constituting A, A', A" and / or A'" and B, B', B" and / or B'" and their stoichiometric ratios according to the desired properties (e.g., depending on the application: piezoelectric coupling coefficient, refractive index, etc.), but also taking into account the need to achieve uniformity in the lattice constants of the materials of the epitaxial layers and their epitaxial support. The adaptation of the lattice constants in the field of epitaxy is known to those skilled in the art.

[0113] It should be understood that in addition to the various epitaxial layers described, additional epitaxial layers may be added, in particular buffer layers intended to control variations in lattice constant or variations in stored stress, or alternatively layers intended to provide a selective etch stop layer.

[0114] The transfer of the seed layer (or respectively, the transfer of the epitaxial layer) typically means a step of bonding a donor substrate and an acceptor substrate (because the seed layer (respectively, the epitaxial layer) is located at the bonding interface), and a subsequent step of thinning the acceptor substrate to expose the seed layer (respectively, the epitaxial layer).

[0115] In a particularly advantageous manner, the known Smart Cut method for transferring thin semiconductor layers, in particular when made of silicon, is used. TM Method to transfer.

[0116] To this end, according to the first embodiment, see Figure 3A , a donor substrate 100 of a material of binary composition ABO3 is provided and an embrittled zone 101 (illustrated by arrows) is formed by ion implantation, which delimits a single crystal layer 102 to be transferred (intended to form a seed layer). In this figure, the donor substrate 100 is presented as homogeneous, but it can alternatively be composite, as described above. Advantageously, and depending on the piezoelectric material considered, the implanted species is hydrogen and / or helium. A person skilled in the art is able to determine the dose and implantation energy of these species to form an embrittled zone at a determined depth (typically less than 2 μm): typically, and again depending on the material considered and the implanted species, the dose is 2E+16 ion species / cm 2 Up to 2E+17 ion species / cm 2 , and the implantation energy is 30 keV to 500 keV. The buried embrittled layer can be obtained by any other means known to those skilled in the art, for example by porosification of the material or by laser irradiation.

[0117] Reference Figure 3B The donor substrate 100 embrittled in this way is bonded to the acceptor substrate 110, wherein the implanted donor substrate surface is at the bonding interface. Before bonding, the donor substrate and / or the acceptor substrate may be covered by an electrically insulating layer or a conductive layer (not shown), which will be inserted between the acceptor substrate and the seed layer after transfer.

[0118] Reference Figure 3C , the donor substrate 100 is peeled off along the embrittled area 101. This peeling can be accomplished by any means known to those skilled in the art, such as thermal, mechanical or chemical means, etc. The remaining portion of the donor substrate is then recovered and can be recycled, thereby enabling the layer 102 to be transferred to the acceptor substrate 110.

[0119] Reference Figure 3D, the surface of the transferred layer 102 may optionally be partially removed, for example by mechanical polishing and / or by chemical etching. The purpose of this removal of material is to eliminate any defects associated with the implantation and peeling near the embrittlement zone. After this removal, a thinned layer 102 is obtained on the acceptor substrate 110, which will serve as a seed layer for the subsequent epitaxial step. As an alternative, Figure 3C The transferred layer 102 can be directly used as a seed layer for epitaxy.

[0120] Reference Figure 3E , a single crystal layer 103 having a composition of A'B'O3 is grown by epitaxy on a seed layer 102, wherein the material of the epitaxial layer 104 is different from the material of the seed layer 102. Therefore, the seed layer 102 affects its lattice constant and enables the growth of high-quality single crystal material. The growth stops when the thickness required for the single crystal layer is reached. The final layer 10 is formed by a stack of the seed layer 102 and the epitaxial layer 103. The composition of the epitaxial layer 103 may change gradually or discontinuously at different depths therein.

[0121] like Figure 3E As can be seen in FIG. 1 , after the method just described, a substrate for a surface acoustic wave device or a bulk acoustic wave device is obtained, which comprises an acceptor substrate 110 and a single crystal layer 10 on the acceptor substrate 110 .

[0122] Layer 10 includes:

[0123] a first portion 102 at the interface with the acceptor substrate 110, corresponding to the seed layer,

[0124] A second portion 103 extending from the first portion 102 , corresponding to an epitaxial layer, made of a material having a composition of A′B′O 3 , wherein said material may be at least ternary.

[0125] The substrate is advantageously used to manufacture Figure 1 The surface acoustic wave device shown or Figure 2 The bulk acoustic wave device shown, or other devices used in microelectronics, photonics or integrated optics.

[0126] The seed layer is typically less than 2 μm thick, and preferably less than 1 μm thick.

[0127] The thickness of the epitaxial layer depends on the specifications of the device intended to include the single crystal layer. In this regard, the thickness of the epitaxial layer is not limited in terms of minimum or maximum values. For reference only, the following table gives the combination of the thickness of the seed layer and the epitaxial layer:

[0128] Seed layer 0.5μm 0.05μm 0.1μm 0.03μm Epitaxial layer 2.5μm 0.95μm 5μm 0.15μm

[0129] Figures 4A to 4EThe essential steps of a method according to a second embodiment are shown, in which epitaxy is carried out before transfer.

[0130] See also Figure 4A , a donor substrate 100 including a piezoelectric material having a composition of A'B'O3 is provided. The donor substrate may be homogeneous (e.g. Figure 4A ) or composite; in the latter case, it comprises a surface layer with a composition of A'B'O3. This is particularly true when the material is at least ternary, if there is no ingot composed of such a material. A single-crystal layer 103 with a composition of A"B"O3 is then grown on the material A'B'O3 by epitaxy, the material with a composition of A'B'O3 being used as a seed for epitaxy. The material of the epitaxial layer 103 may be the same as or different from the material of the donor substrate 100.

[0131] Then, an embrittled zone is formed in the embrittled zone of the donor substrate 100 or in the epitaxial layer 103 having the composition A"B"O3, thereby defining the layer to be transferred. The embrittled zone can be formed by implanting ion species (in Figure 4B (illustrated by arrows in the figure).

[0132] exist Figure 4B In the example shown, an embrittled zone 101 is formed in the donor substrate 100 below the epitaxial layer 103. In this case, the layer to be transferred consists of the entire epitaxial layer 103 and a portion 100' of the donor substrate 100.

[0133] According to another embodiment (not shown), the embrittled zone is formed in the layer 103. In this case, the layer to be transferred consists of the portion extending between the free surface of the layer 103 and the embrittled zone 101.

[0134] See also Figure 4C , the donor substrate is bonded to the acceptor substrate 110, and the epitaxial layer 103 having the composition of A"B"O3 is at the bonding interface.

[0135] See also Figure 4D , the donor substrate 100 is peeled off along the embrittled region 101 , thereby recovering the remaining portion of the donor substrate and transferring the layer consisting of the stack 103 , 100 ′ to the acceptor substrate 110 .

[0136] See also Figure 4E , at least a surface portion of the transferred layer is removed. The purpose of this removal is to eliminate at least the portion 100' and possibly a portion of the layer 103, in order to expose a material having the composition A"B"O3.

[0137] The layer 103 obtained in this way can then be used to produce a surface acoustic wave or bulk acoustic wave device.

[0138] According to a variation of the second embodiment, Figure 4F An additional step is shown which consists of resuming the epitaxy carried out on the layer 103 having the composition A"B"O3, so as to form an additional single-crystalline layer 104 having the composition A"'B"'O3. The material of said additional layer 104 can be identical to that of the layer 103, in which case the latter epitaxy step results in a thickening of the layer 103 (the layer 104 is shown separated from the layer 103 in the figure only to enable its display, but is not separated in the final layer, except possibly for a difference in quality). As an alternative, the additional layer 104 is made of a material different from that of the layer 103.

[0139] The thickness of layer 103 and layer 104 (where applicable) is chosen according to the specifications of the radio frequency device intended to include said layers. The thickness of layer 103 is typically 0.05 μm to 2 μm. The thickness of layer 104 is typically 0.05 μm to 20 μm.

[0140] Regardless of the implementation method involved, Smart Cut TM As an alternative to the Smart Cut method (not shown), after the donor substrate and the acceptor substrate are bonded, the transfer can be performed by removing material (e.g., by mechanical polishing and / or chemical etching of the donor substrate until the seed layer is exposed). This variant is less advantageous because it involves consuming the donor substrate, and Smart Cut TM This method allows the possibility of recycling the donor substrate. In contrast, this variant does not require implantation in the donor substrate.

[0141] like Figure 4E and 4F It can be seen that after the method according to the second embodiment, a substrate for a surface acoustic wave device or a bulk acoustic wave device is obtained, which includes an acceptor substrate 110 and a single crystal layer 103 with a composition of A"B"O3 on the acceptor substrate 110 and (if applicable) a layer 104 with a composition of A"'B"'O3 on the layer 103.

[0142] The substrate is advantageously used to manufacture Figure 1 The surface acoustic wave device shown or Figure 2 The BAW device shown, wherein layer 103 or (if applicable) layers 103 and 104 correspond to Figure 1 and 2 The present invention can be used as layer 10 in the process or for manufacturing all other microelectronic, photonic or optical devices including layers.

[0143] In some cases, the acceptor substrate on which the epitaxial growth is carried out may not be optimal for the final application. Since the acceptor substrate will be subjected to the operating conditions of the epitaxy, there is in fact a limited choice of suitable materials. In particular, the acceptor substrate must not contain layers or elements that could be damaged by the epitaxy temperatures. It may then be advantageous to transfer the layer 10 to a final substrate 111 whose properties are chosen according to the application sought, by bonding the layer 10 to said substrate 111 via the surface of the epitaxial layer 103 (or 104, if applicable) (see Figure 5A ) and remove the acceptor substrate (see Figure 5B ). This transfer can be performed by any of the transfer techniques described above. Another advantage of this transfer to the final substrate is that the seed layer 102 buried in the structure produced by epitaxy is then exposed and can be removed if necessary (see Figure 5C ), especially if it has defects. Then, only the epitaxial layer 103 (and layer 104, if applicable) (or a portion of said layer) having the desired properties remains on the final substrate 111.

[0144] If it is desired to manufacture a surface acoustic wave device, two metal electrodes 12, 13 in the form of interdigitated combs are deposited on the surface of the opposite layer 10 of the acceptor substrate 110 or, if applicable, the final substrate (regardless of whether it is the acceptor substrate 110 or the final substrate 111, the substrate forming the Figure 1 The supporting substrate is denoted by 11).

[0145] If you want to manufacture a bulk acoustic wave device, you must modify the method described above accordingly. First, Figure 3B Prior to the bonding step shown, a first electrode is deposited on the free surface of the layer 102 to be transferred from the donor substrate, and the first electrode ( Figure 2 The middle mark is 13) is embedded in the final stack. Figure 3E After the epitaxial growth step described in , a second electrode ( Figure 2 Another option is to transfer the layers onto the final substrate as described above and to form the electrodes before and after said transfer. Secondly, in order to avoid the propagation of acoustic waves in the receptor substrate 110, isolation means can be integrated into this substrate, which can be, for example, a Bragg mirror (e.g. Figure 2 ) or a pre-etched cavity in substrate 110 or final substrate 111 (if applicable).

[0146] Regardless of which embodiment is chosen, the method of the invention enables the formation of not only binary but also ternary or quaternary single-crystal layers and thus allows a greater choice of the properties of the layers than the materials conventionally used for surface acoustic wave or bulk acoustic wave devices. In this way, a satisfactory compromise between the coupling coefficient and the electromechanical efficiency of the piezoelectric material can be obtained more easily.

[0147] Another application field that is particularly concerned about the development of such piezoelectric materials is the field of microsensors and microactuators. In the case of microsensors, the purpose is usually to measure the deformation caused by external stress. On the contrary, in the case of microactuators, what is sought is to cause the deformation of the element or the movement of the moving part by applying an electric field (whether continuous or variable). The use of piezoelectric materials enables mechanical deformation and electrical signals to be associated. For example, in the field of acoustics, external stress is a pressure wave that deforms the membrane. It can be within the sound spectrum, and the objects typically concerned are microphones (sensor mode) and speakers (actuator mode). It can exceed audible frequencies, for example, for the production of piezoelectric micromechanical ultrasonic transducers (PMUT). It may also involve static pressure sensors or inertial sensors (accelerometers, gyroscopes, etc.), in which the motion of a moving object that moves under the influence of acceleration is measured by piezoelectric materials. The piezoelectric material comprises the entire deformable element (membrane, beam, cantilever, etc.) or advantageously only a part of it, for example by stacking it with other materials such as silicon, thereby ensuring improved mechanical properties of the deformable part. In the field of actuators, piezoelectric materials enable very precise movements to be controlled and can be used, for example, to drive ink out of printer cartridges or microfluidic systems, or to adjust the focus of optical microscopy systems.

[0148] References

[0149] [1]W.Steichen and S.Ballandras, "Acoustic components used for filtering–Review of the different technologies", Techniques de l'Ingénieur, E2000, 2008

[0150] [2] Doctoral dissertation (Dipl. Phys. ETH Zurich), "K 1-y Na y Ta 1-x NbO3 thin film Electro-optics"(Diss.ETH No.17275)

[0151] [3]L.S. Hung, J.A. Agostinelli, J.M. Mir, and L.R. Zheng, "Epitaxial nonlinear optical films of LiTaO3 grown on GaAs in waveguide form", Appl. Phys. Lett. 62(24), June 14, 1993, p. 3071

[0152] [4]E. Dogheche and D. Remiens, S. Shikata, A. Hachigo, and H. Nakahata, "High-frequency surface acoustic wave devices based on LiNbO3 / diamond multilayered structure", APPLIED PHYSICS LETTERS 87, 213503, 2005

[0153] [5]A. Bartasyte, V. Plausinaitiene, A. Abrutis, T. Murauskas, P. Boulet, S. Margueron, J. Gleize, S. Robert, V. Kubilius, and Z. Saltyte, "Residual stresses and clamped thermal expansion in LiNbO3 and LiTaO3 thin films", APPLIED PHYSICS LETTERS 101, 122902(2012)

[0154] [6]Letters to Nature, Nature 432, 84 - 87 (4 November 2004) doi:10.1038 / nature03028; "Lead-free piezoceramics", Yasuyoshi Saito, Hisaaki Takao, Toshihiko Tani, Tatsuhiko Nonoyama, Kazumasa Takatori, Takahiko Homma, Toshiatsu Nagaya & Masaya Nakamura。

Claims

1. A method for manufacturing a single crystal layer, characterized in that: The method comprises the following consecutive steps: - providing a donor substrate (100) comprising a piezoelectric material having a composition of A'B'O3, wherein A' is composed of one or more of the following elements: Li, Na, K, H; B' is composed of one or more of the following elements: Nb, Ta, Sb, V; - growing a single crystal layer (103) having a composition of A"B"O3 on the piezoelectric material A'B'O3 by epitaxy, wherein A” is composed of one or more of the following elements: Li, Na, K, H; B" is composed of one or more of the following elements: Nb, Ta, Sb, V; - providing a receptor substrate (110), - transferring at least a portion of the epitaxial layer (103) having a composition of A"B"O3 onto the acceptor substrate (110), by bonding the donor substrate (100) to the acceptor substrate (110) via the epitaxial layer (103), and subsequently thinning the donor substrate (100) until the epitaxial layer (103) having a composition of A"B"O3 is obtained, - after the layer (103) with composition A"B"O3 has been transferred to the acceptor substrate, a single-crystalline layer (104) with composition A"'B"'O3 is grown by epitaxy on the material with composition A"B"O3, wherein A'' is composed of one or more of the following elements: Li, Na, K, H; B'' is composed of one or more of the following elements: Nb, Ta, Sb, and V.

2. The method of claim 1, wherein: A'' is different from A'', or B'' is different from B''.

3. The method of claim 1, wherein: Transferring the at least a portion of the epitaxial layer (103) having the composition of A"B"O3 onto the acceptor substrate (110) comprises the following steps: - forming an embrittled zone (101) in the donor substrate (100) or in the epitaxial layer (103) having the composition A"B"O3, thereby defining the layer to be transferred, - bonding the donor substrate (100) to the acceptor substrate (110), wherein the epitaxial layer (103) having the composition of A"B"O3 is located at the bonding interface; - Peeling off the donor substrate (100) or the epitaxial layer (103) along the embrittled zone (101).

4. The method of claim 3, wherein: The embrittled zone (101) is formed in the donor substrate (100) and after the transfer step, the transferred layer (100', 103) is thinned to expose a material having a composition of A"B"O3.

5. The method according to any one of claims 1 to 4, wherein: A" is different from A', or B" is different from B'.

6. The method according to any one of claims 1 to 4, characterized in that A" includes at least one element in common with A', and / or B" includes at least one element in common with B'.

7. The method according to any one of claims 1 to 4, characterized in that A" is identical to A' when B" is different from B', and B" is identical to B' when A" is different from A'.

8. The method according to any one of claims 1 to 4, characterized in that A' consists of a single element and B' consists of a single element.

9. The method of claim 3, wherein: The embrittled region (101) is formed by ion implantation in the donor substrate (100).

10. The method according to any one of claims 1 to 4, wherein: After the epitaxy step, the thickness of the single-crystalline layer (103) having the composition A"B"O3 is between 0.2 μm and 20 μm.

11. The method according to any one of claims 1 to 4, wherein: At least one electrically insulating layer and / or at least one electrically conductive layer is formed at an interface between the acceptor substrate and the donor substrate.

12. The method according to any one of claims 1 to 4, comprising transferring at least a portion of the single crystalline layer (104) on the acceptor substrate to a final substrate (111).

13. A method for manufacturing a surface acoustic wave device, comprising depositing electrodes (12, 13) on the surface of a single crystal piezoelectric layer (10), characterized in that: The method comprises manufacturing the piezoelectric layer by the method according to any one of claims 1 to 12.

14. A surface acoustic wave device, characterized in that: The device comprises a single-crystalline piezoelectric layer (10) obtainable by the method according to any one of claims 1 to 12 and two electrodes (12, 13) mounted on the surface of the single-crystalline piezoelectric layer.

15. A method for manufacturing a bulk acoustic wave device, comprising depositing electrodes (12, 13) on two opposite faces of a single crystal piezoelectric layer (10), characterized in that: The method comprises manufacturing the piezoelectric layer by the method according to any one of claims 1 to 12.

16. A bulk acoustic wave device, characterized in that: The device comprises a single-crystalline piezoelectric layer (10) obtainable by the method according to any one of claims 1 to 12 and two electrodes (12, 13) mounted on two opposite faces of the single-crystalline piezoelectric layer.

17. A microsensor designed to measure deformation caused by external stress, characterized in that The microsensor comprises a single-crystalline piezoelectric layer (10) obtainable by the method of any one of claims 1 to 12.

18. A microactuator designed to cause deformation of an element or movement of a moving part by applying a continuous electric field or a variable electric field, characterized in that: The microactuator comprises a single-crystalline piezoelectric layer (10) obtainable by the method according to any one of claims 1 to 12.

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