Hybrid structure for surface acoustic wave devices

Abstract

The invention relates to a hybrid structure for a surface acoustic wave device, the hybrid structure comprising a useful layer of piezoelectric material, the useful layer having a first free face and a second face placed on a support substrate, the support substrate having a coefficient of thermal expansion lower than the coefficient of thermal expansion of the useful layer, wherein the hybrid structure comprises: a second intermediate layer arranged on the second face of the useful layer; a trapping layer on the support substrate; at least one functional interface having a determined roughness between the useful layer and the trapping layer, wherein the at least one functional interface comprises a second functional interface having a determined roughness with a peak-to-valley amplitude greater than 0.1 microns between the useful layer and the second intermediate layer, wherein the second intermediate layer has a flat surface remote from the second functional interface, wherein the entire surface of the flat surface of the second intermediate layer is bonded to the trapping layer on the support substrate.

Description

[0001] This application is a divisional application of the patent application filed on June 26, 2017, with application number 201780040275.X (international application number PCT / FR2017 / 051701) and entitled "Hybrid Structure for Surface Acoustic Wave Devices". Technical Field

[0002] This invention relates to the field of surface acoustic wave (SAW) devices. More particularly, it relates to a hybrid structure suitable for manufacturing SAW devices and a method for manufacturing said hybrid structure. Background Technology

[0003] Surface acoustic wave (SAW) devices use one or more interdigital transducers developed on a piezoelectric substrate to convert electrical signals into sound waves and vice versa. Such SAW devices, or resonators, are often used in filtering applications. Radio frequency (RF) SAW technology on piezoelectric substrates offers excellent performance such as high insulation and low insertion loss. For this reason, it is used in RF duplexers for wireless communication applications. However, to be more competitive with RF duplexers based on bulk acoustic wave (BAW) technology, RF SAW devices require improved temperature stability of their frequency response.

[0004] The operating frequency dependence of SAW devices, based on the temperature or frequency thermal coefficient (TCF), depends on two factors: firstly, the variation in the spacing between the interdigitated electrodes of the transducer, which is typically due to the relatively high coefficient of thermal expansion (CTE) of the piezoelectric substrate used; and secondly, the TCF depends on the thermal velocity coefficient, as the expansion or contraction of the piezoelectric substrate is accompanied by an increase or decrease in the velocity of the surface acoustic waves. To minimize the frequency thermal coefficient (TCF), the goal is therefore to minimize the expansion / contraction of the piezoelectric substrate, especially in the surface region where the acoustic waves will propagate.

[0005] The article "Recent development of temperature-compensated SAW devices" by K. Hashimoto, M. Kadota, et al., IEEE Ultrasonic. Symp. 2011, pages 79-86, 2011, provides an overview of methods commonly used to overcome the temperature dependence of the frequency response of SAW devices.

[0006] One approach is to use a hybrid substrate, for example, consisting of a piezoelectric material layer disposed on a silicon substrate. The low CTE of silicon makes it possible to limit the expansion / contraction of the piezoelectric layer according to temperature. In the case of a lithium tantalate (LiTaO3) piezoelectric layer, the article shows that a LiTaO3 thickness to silicon substrate thickness ratio of 10 makes it possible to sufficiently improve the thermal coefficient of frequency (TCF).

[0007] Document DE102004045181 also discloses a structure suitable for SAW applications, including a piezoelectric layer disposed on a compensation layer (e.g., silicon).

[0008] One drawback of this hybrid substrate is the presence of interfering acoustic waves (referred to as "spurious acoustic modes" in the article "Characterization of bonded wafer for RF filters with reduced TCF", BPAbbott et al., Proc 2005 IEEE International Ultrasonics Symposium, Sept 19-21, 2005, pp. 926-929), which negatively affect the frequency characteristics of resonators arranged on the hybrid substrate. These interfering resonances are particularly related to unwanted reflections at the underlying interfaces, especially at the interface between LiTaO3 and silicon. One solution to reduce these interfering resonances is to increase the thickness of the LiTaO3 layer; this is assumed to also increase the thickness of the silicon substrate to maintain TCF improvement, and the total thickness of the hybrid substrate then becomes incompatible with the requirements for reducing the thickness of the final component, especially in the mobile phone market. Another solution proposed by K. Hashimoto is to roughen the lower surface of the LiTaO3 layer to limit acoustic wave reflections thereon. This roughening introduces operational difficulties when direct bonding processes requiring very smooth surfaces for assembly are used in the fabrication of hybrid substrates.

[0009] Another drawback of hybrid substrates according to the prior art stems from the presence of a supporting semiconductor silicon material, which, even if it is high-resistivity, can contain free charge carriers and affect device performance, particularly by increasing the insertion loss and distortion (linearity) of the RF signal relative to the solid piezoelectric substrate.

[0010] To improve the performance of radio frequency devices, document WO2016 / 087728 proposes a structure including a trapping layer arranged on a support substrate, wherein the trapping layer is characterized by a density of specific defects. Summary of the Invention

[0011] The purpose of this invention is to overcome some or all of the shortcomings of the prior art. Specifically, it is to provide a hybrid structure capable of reducing and / or eliminating the interfering acoustic waves and ensuring the stable performance of a device operating at high frequencies.

[0012] This invention relates to a hybrid structure for a surface acoustic wave (SAW) device, the hybrid structure comprising a useful layer of piezoelectric material having a free first surface and a second surface placed on a supporting substrate, the supporting substrate having a lower coefficient of thermal expansion than the useful layer, the hybrid structure being characterized in that it comprises: a second intermediate layer disposed on the second surface of the useful layer; a trapping layer located on the supporting substrate; and at least one functional interface having a defined roughness located between the useful layer and the trapping layer, wherein the at least one functional interface includes a second functional interface having a defined roughness with a peak-valley amplitude greater than 0.1 micrometers located between the useful layer and the second intermediate layer, wherein the second intermediate layer has a flat surface remote from the second functional interface, and wherein the entire surface of the flat surface of the second intermediate layer is bonded to the trapping layer on the supporting substrate.

[0013] The present invention also relates to a hybrid structure for a surface acoustic wave device, the hybrid structure comprising a useful layer of piezoelectric material having a free first side and a second side placed on a supporting substrate, the supporting substrate having a lower coefficient of thermal expansion than the useful layer. The hybrid structure includes:

[0014] • A trapping layer sandwiched between the useful layer and the supporting substrate;

[0015] • At least one functional interface with a defined roughness located between the useful layer and the capturing layer.

[0016] The trapping layer of the hybrid structure according to the invention effectively traps potentially generated free charge carriers in the supporting substrate while operating a carefully fabricated SAW RF device on the hybrid structure. RF performance (linearity, insertion loss) is thus achieved at a good level, comparable to or even better than that of technology on large-scale piezoelectric substrates.

[0017] The defined roughness of the functional interface allows for the efficient diffusion of acoustic waves that can diffuse in depth within the useful layer, thereby avoiding interference reflections, which are known to negatively impact the signal quality of SAW devices. This diffusion is further enhanced by the fact that the functional interface lies between the useful layer and the trapping layer: in fact, in addition to its ability to trap free carriers, the trapping layer also makes it possible to efficiently shield the interface with the supporting substrate below, which contributes to the reflection of acoustic waves by the hybrid structure.

[0018] According to the advantageous features of the invention, they can be carried out individually or in combination:

[0019] • The trapping layer is in direct contact with the supporting substrate;

[0020] • The trapping layer is formed of a material selected from amorphous silicon, polycrystalline silicon, amorphous germanium, or polycrystalline germanium;

[0021] • The trapping layer is formed by implantation into the surface layer of the supporting substrate or by etching and structuring the surface layer of the supporting substrate;

[0022] • The roughness of the defined surface of the functional interface has a peak-to-valley amplitude greater than 0.3 micrometers, advantageously greater than or equal to 0.5 micrometers, or even 1 micrometer.

[0023] • The functional interface is formed by the interface between the useful layer and the capture layer, and the second surface of the useful layer has the determined roughness;

[0024] • The functional interface is formed by the interface between the first intermediate layer disposed on the second surface of the useful layer and the trapping layer; the trapping layer has the defined roughness;

[0025] • The first intermediate layer includes a material selected from silicon oxide, silicon nitride, silicon oxynitride, or a material of the same type as the material forming the useful layer;

[0026] • The hybrid architecture includes a second functional interface;

[0027] • The second functional interface is formed by the interface between the useful layer and the second intermediate layer disposed on the first intermediate layer, and the second functional interface has a second defined roughness with a peak-valley amplitude greater than 0.1 micrometers;

[0028] • The second intermediate layer includes a material selected from silicon oxide, silicon nitride, silicon oxynitride, or a material of the same type as the material forming the useful layer;

[0029] The first and second intermediate layers are formed of the same material;

[0030] Useful layers include lithium tantalate (LiTaO3), lithium niobate (LiNbO3), quartz, and zinc oxide (ZnO).

[0031] Or a piezoelectric material selected from aluminum nitride (AlN);

[0032] • The supporting substrate is a solid substrate or a composite substrate that includes at least one blank layer or includes all or part of a microelectronic component.

[0033] The present invention also relates to a surface acoustic wave device comprising the hybrid structure described above.

[0034] The present invention further relates to a method for manufacturing a hybrid structure for a surface acoustic wave device, the method comprising:

[0035] • The step of providing a useful layer of piezoelectric material, said useful layer comprising a first surface and a second surface having a defined roughness;

[0036] • The step of providing a support substrate having a lower coefficient of thermal expansion than the useful layer;

[0037] • An assembly step for arranging the useful layer on the support substrate;

[0038] The method is characterized in that it includes, prior to the assembly step, a trapping layer formation step on the second surface of the useful layer, wherein the interface between the trapping layer and the useful layer forms a functional interface having the determined roughness; the assembly step is performed between the trapping layer and the supporting substrate.

[0039] The present invention also relates to another method for manufacturing a hybrid structure for a surface acoustic wave device, the other method comprising:

[0040] • The step of providing a useful layer of piezoelectric material, said useful layer comprising a first surface and a second surface;

[0041] • The step of providing a support substrate having a lower coefficient of thermal expansion than the useful layer;

[0042] • An assembly step for arranging the useful layer on the support substrate;

[0043] The method is characterized in that, prior to the assembly step:

[0044] • The step of forming a trapping layer with a defined roughness on the supporting substrate;

[0045] • In the step of forming a first intermediate layer on the capture layer, the interface between the capture layer and the first intermediate layer forms a functional interface with a defined roughness.

[0046] Based on the advantageous features of this manufacturing method, it can be carried out alone or in combination:

[0047] • The determined roughness of the functional interface has a peak-valley amplitude greater than 0.3 micrometers, advantageously greater than or equal to 0.5 micrometers, or even 1 micrometer.

[0048] • The assembly step occurs between the first intermediate layer and the second surface of the useful layer;

[0049] The method for manufacturing a hybrid structure includes, prior to an assembly step, a step of forming a second intermediate layer on a second surface of a useful layer having a second defined roughness, wherein the assembly step is performed between the first intermediate layer and the second intermediate layer; and the interface between the useful layer and the second intermediate layer forms a second functional interface. Attached Figure Description

[0050] Other features and advantages of the invention will become apparent from the following detailed description with reference to the accompanying drawings, in which:

[0051] · Figures 1 to 3 The hybrid structure according to the present invention is shown;

[0052] · Figure 4 A surface acoustic wave device according to the present invention is shown;

[0053] · Figures 5a to 5e , Figures 6a to 6e and Figures 7a to 7e A method for manufacturing the hybrid structure according to the present invention is shown. Detailed Implementation

[0054] In the description section, the same markings in the diagram can be used for the same type of element.

[0055] The diagram is for illustrative purposes and is not drawn to scale for clarity. Specifically, the thickness of each layer along the z-axis is not drawn to scale relative to the lateral dimensions along the x and y axes.

[0056] like Figure 1 As illustrated, the present invention relates to a hybrid structure 100 for a surface acoustic wave device, the hybrid structure 100 comprising a useful layer 10 of piezoelectric material having a free first surface 1 and a second surface 2. The useful layer 10 comprises a piezoelectric material selected from, for example, lithium tantalate (LiTaO3), lithium niobate (LiNbO3), quartz, zinc oxide (ZnO), or aluminum nitride (AlN).

[0057] A useful layer 10 is disposed on a support substrate 20, the coefficient of thermal expansion of which is lower than that of the useful layer 10. The support substrate 20 is formed, for example, from silicon or germanium.

[0058] The hybrid structure 100 according to the invention further includes a trapping layer 30 sandwiched between the useful layer 10 and the support substrate 20. The term "trapping layer" is understood to mean a layer capable of trapping free charge carriers likely present in the support substrate 20. As an example, the trapping layer 30 is formed of a material selected from amorphous silicon, polycrystalline silicon, amorphous germanium, or polycrystalline germanium. The trapping layer 30 can also be formed by techniques or combinations thereof including:

[0059] • Ion implantation into the surface layer of the support substrate 20; for silicon substrates, implantation of argon, silicon or nitrogen ions can be performed to create a perturbed surface layer capable of trapping charge carriers originating from the support substrate 20.

[0060] Alternatively, the surface layer of the support substrate 20 may be etched and structured; for example, by mechanical, wet or dry chemical etching, induced surface structuring, for preferred trapping sites for charge carriers originating from the support substrate 20.

[0061] The thickness of the trapping layer 30 can range from tens of nanometers to a few micrometers or even tens of micrometers.

[0062] Advantageously, the trapping layer 30 is in direct contact with the support substrate 20, which allows for the effective trapping of charge carriers generated in the support substrate 20.

[0063] The hybrid structure 100 according to the invention further includes at least one functional interface 31 with a roughness defined between the useful layer 10 and the trapping layer 30. The roughness of the functional interface 31 is defined by the maximum peak-valley amplitude, for example, by mechanical or optical profilometry on a measurement profile of approximately 50 to 500 micrometers or on a measurement surface of approximately 50 × 50 to 500 × 500 μm². Advantageously, the roughness defined by the peak-valley is greater than 0.3 micrometers. Advantageously, it is even greater than or equal to 0.5 micrometers, or even 1 micrometer. Preferably, it is between 0.3 micrometers and 5 micrometers.

[0064] Advantageously, the spectral density (PSD) of the roughness of the functional interface 31 covers all or a portion of the spectral band of the wavelength of the interfering wave to be eliminated. Preferably, the determined roughness has a spatial wavelength and amplitude at least one-quarter of the interfering wavelength.

[0065] Because of its ability to effectively diffuse acoustic waves that are readily diffused in the useful layer 10, the roughness of the functional interface 31 can be adapted in terms of amplitude and potentially in terms of spectral density according to the frequency of the acoustic waves of the SAW device to be fabricated on the hybrid structure 100.

[0066] The trapping layer 30 of the hybrid structure 100 according to the invention, developed on the first surface 1 of the hybrid structure 100, effectively traps free charge carriers potentially generated in the supporting substrate 20 during operation of the RFSAW device. RF performance (linearity, insertion loss) thus reaches a very good level, comparable to or even better than that of technology on large-scale piezoelectric substrates.

[0067] The defined roughness of the functional interface 31 enables effective diffusion of acoustic waves that can diffuse in depth within the useful layer 10, thereby avoiding interference reflections, which are known to negatively impact the signal quality of SAW devices.

[0068] according to Figure 1 In the first embodiment illustrated, the functional interface 31 is formed by the interface between the useful layer 10 and the capture layer 30.

[0069] according to Figure 2 In the illustrated second embodiment, the functional interface 31 is formed by the interface between the first intermediate layer 40 disposed on the second surface 2 of the useful layer 10 and the trapping layer 30. As an example, the first intermediate layer 40 may comprise a material selected from silicon oxide, silicon nitride, silicon oxynitride, or a material of the same type as the useful layer.

[0070] The advantage of these two implementations is that the trapping layer 30 allows the interface with the underlying support substrate 20 to be moved away from and shielded. The support substrate 20 is a strong contributor to the reflection of sound waves diffused in the volume of the useful layer 10 in a typical hybrid structure. The interface with the support substrate 20 is shielded in such a sense that most (if not all) of the sound waves reaching the functional interface 31 will be effectively diffused by the functional interface 31 and therefore will never reach the interface.

[0071] according to Figure 3 In the illustrated third embodiment, the hybrid structure 100 includes a second functional interface 32 having a second defined roughness, with peak-valley amplitudes greater than 0.1 micrometers. It is preferably between 0.1 micrometers and 5 micrometers. It should be noted that the second functional interface 32 may have a second defined roughness different from that of the first functional interface 31 in both amplitude and spectral density. Advantageously, the spectral density can be selected to complementaryly cover the spectral band of the wavelength of the interference wave to be eliminated.

[0072] The second functional interface 32 is formed by the interface between the useful layer 10 and the second intermediate layer 50 disposed on the first intermediate layer 40. As an example, the second intermediate layer 50 includes a material selected from silicon oxide, silicon nitride, and silicon oxynitride; it may also include a material of the same type as the material constituting the useful layer 10: for the useful layer 10 made of LiTaO3, the second intermediate layer 50 may be formed, for example, by depositing an amorphous LiTaO3 layer.

[0073] According to an advantageous variation of this third embodiment, the first intermediate layer 40 and the second intermediate layer 50 are formed of the same material; therefore, since there is no difference in acoustic impedance between the two layers, the interface between the two layers contributes little or no to interference reflection.

[0074] In the various embodiments described, the support substrate is a bulk substrate. Alternatively, it may be composed of a composite substrate comprising at least one blank layer or structured layer, including all or part of a microelectronic component; these configurations are particularly advantageous for producing co-integrated systems, including surface acoustic wave devices located in and on the useful layer 10, as well as components (switches, amplifiers, other filters, etc.) in the support substrate.

[0075] This invention also relates to, for example Figure 4 The illustrated surface acoustic wave device 200 includes a hybrid structure 100. The device 200 includes, for example, interdigitated metal electrodes 201 located on a first surface 1 of the useful layer 10, between which acoustic waves diffuse.

[0076] The hybrid structure 100 is particularly suitable for manufacturing surface acoustic wave devices 200 using acoustic wave frequencies ranging from 700MHz to 3GHz.

[0077] The present invention also relates to a method for manufacturing a hybrid structure 100 for a surface acoustic wave device 200, which will be referred to in the following text. Figures 5a to 7e Describe it.

[0078] The manufacturing method first includes the step of providing a useful layer 10 of piezoelectric material, the useful layer 1 comprising a first surface 1 and a second surface 2 having a defined roughness. The roughness is defined by the maximum amplitude of peaks and valleys, for example, measured by mechanical or optical profilometry on a measurement profile of approximately 50 to 500 micrometers or on a measurement surface of approximately 50 × 50 to 500 × 500 μm². Advantageously, the defined roughness is greater than 0.3 micrometers, even greater than or equal to 0.5 micrometers, or even greater than 1 micrometer. Preferably, it is even between 0.3 micrometers and 5 micrometers.

[0079] Advantageously, the spectral density of the roughness of the functional interface 31 covers all or a portion of the spectral band of the wavelength of the interfering wave to be eliminated. Preferably, the determined roughness has a spatial wavelength and amplitude that is at least one-quarter of the interfering wavelength.

[0080] Because of its ability to effectively diffuse acoustic waves that are readily diffused in the useful layer 10, the roughness of the functional interface 31 can be adapted in terms of amplitude and potentially in terms of spectral density according to the frequency of the acoustic waves of the SAW device to be fabricated on the hybrid structure 100.

[0081] The defined roughness on the second surface 2 can be achieved through mechanical polishing, chemical mechanical polishing, wet or dry chemical etching, or a combination of these techniques. The aim is to create a uniform roughness of defined amplitude across the entire surface of the second surface 2 of the useful layer 10. As an example, this roughness can be obtained through typical post-roughening surface treatments of wafers (lithium tantalate, lithium niobate, etc.) used in the semiconductor industry.

[0082] As previously stated and without limitation, the useful layer 10 includes a piezoelectric material selected from lithium tantalate (LiTaO3), lithium niobate (LiNbO3), quartz, zinc oxide (ZnO) or aluminum nitride (AlN).

[0083] According to an advantageous embodiment, a useful layer 10 is included in a donor substrate 11, the donor substrate 11 having a first surface 1' and a second surface 2 with a defined roughness. Figure 5a ).

[0084] The manufacturing method according to the invention further includes the step of forming a trapping layer 30 on the second surface 2 of the useful layer 10 or the donor substrate 11. Figure 5b The interface between the trapping layer 30 and the useful layer 10 (or donor substrate 11) forms a functional interface 31 with a defined roughness. Advantageously, the trapping layer 30 is formed from a material selected from amorphous silicon, polycrystalline silicon, amorphous germanium, or polycrystalline germanium. The trapping layer 30 can be prepared by known chemical deposition techniques (PECVD, LPCVD, etc.).

[0085] The trapping layer 30 typically has a thickness between tens of nanometers and a few micrometers or even tens of micrometers.

[0086] Advantageously, the formation steps of the trapping layer 30 include smoothing the free surface of the trapping layer 30, including, for example, chemical mechanical polishing, smoothing plasma etching, or wet chemical etching. Preferably, for subsequent assembly steps, the free surface of the trapping layer 30 will have low roughness (typically <0.5 nm RMS, measured by atomic force microscopy) and good flatness.

[0087] The manufacturing method further includes providing a support substrate 20 having a lower coefficient of thermal expansion than the useful layer 10. Figure 5c The steps of the process are as follows. Advantageously, the support substrate 20 is made of silicon, a widely available material compatible with the semiconductor industry. Alternatively, it may be made of germanium or other materials compatible with the methods and subsequent steps of the fabrication of surface acoustic wave devices.

[0088] The manufacturing method then includes an assembly step for arranging the donor substrate 11 (or useful layer 10) on the support substrate 20. Figure 5dThe assembly step occurs between the trapping layer 30 and the supporting substrate 20, so the surface properties of the trapping layer 30 and the supporting substrate 20 must be properly controlled. Advantageously, the assembly step includes direct bonding via molecular adhesion: this bonding technique is preferred because it does not require the use of additional material layers.

[0089] Alternatively, the assembly steps may include adhesive bonding, metal bonding, anodic bonding, or any other type of bonding known to the art and compatible with the intended use.

[0090] Advantageously, the assembly steps include a cleaning sequence prior to bonding to ensure good cleanliness of the surfaces (removal of particles, hydrocarbons, and metallic contaminants, etc.) prior to bonding.

[0091] According to a variation of the method, a layer of the same type as the trapping layer 30 can be arranged on the support substrate 20 prior to the assembly step and prepared for bonding to the trapping layer 30. In practice, depending on the type of trapping layer 30 and the type of support substrate 20, especially in the case of direct bonding via molecular adhesion, forming a bonding interface between two materials of the same type can be advantageous.

[0092] To strengthen the bonding interface, the bonded hybrid structure 101 can be subjected to heat treatment. It should be noted that the materials of the donor substrate 11 (or the useful layer 10) and the support substrate 20 exhibit very different coefficients of thermal expansion, therefore the applied heat treatment must be maintained below the temperature at which damage or breakage of the bonded structure 101 would occur. The temperature range is typically between tens of degrees and 500°C.

[0093] exist Figures 5a to 5e In the illustrated case, the useful layer 10 is included in the donor substrate 11, and the manufacturing process further includes a step of thinning the donor substrate 11. Figure 5e To form a useful layer 10 and a first surface 1 on which a surface acoustic wave device will be fabricated.

[0094] This thinning step can be performed using various known techniques from the existing technology, in particular:

[0095] · The process, which is particularly suitable for forming very thin useful layers (typically less than or equal to 1 micrometer thick): it is based on injecting gas species into the donor substrate 11 at the level of its second side 2 prior to the assembly step to form a weakened buried plane; after assembly, the donor substrate 11 is separated along the weakened plane so that only the useful layer 10 and the support substrate 20 are integrated.

[0096] Chemical mechanical thinning processes, including mechanical grinding or polishing, chemical mechanical polishing, and chemical etching, are suitable for forming useful layers with thicknesses ranging from a few micrometers to tens or even hundreds of micrometers.

[0097] At the end of this manufacturing process, the hybrid structure 100 according to the present invention is obtained. Figure 5e ).

[0098] The present invention relates to another method of manufacturing a hybrid structure 100 for a surface acoustic wave device, the other method comprising firstly providing a useful layer 10 of piezoelectric material, the useful layer 10 comprising a first surface 1 and a second surface 2.

[0099] As stated above and not limited thereto, the useful layer 10 includes a piezoelectric material selected from lithium tantalate (LiTaO3), lithium niobate (LiNbO3), quartz, zinc oxide (ZnO) or aluminum nitride (AlN).

[0100] According to an advantageous embodiment, the useful layer 10 is included in a donor substrate 11 having a second surface 2 and a first surface 1'. Figure 6a ).

[0101] The manufacturing method further includes the step of providing a support substrate 20 having a lower coefficient of thermal expansion than the useful layer 10. Advantageously, the support substrate 20 is made of silicon, a widely available material compatible with the semiconductor industry. As mentioned above, it may alternatively be formed of or include germanium or other materials compatible with subsequent manufacturing steps.

[0102] The manufacturing method further includes the step of forming a trapping layer 30 on the support substrate 20. Figure 6b The captured layer 30 has a predetermined roughness.

[0103] Advantageously, the trapping layer 30 is formed of a material selected from amorphous silicon, polycrystalline silicon, amorphous germanium, or polycrystalline germanium. It can be prepared by known techniques of chemical deposition (CVD).

[0104] The capture layer 30 can also be formed by techniques or combinations thereof including:

[0105] • Ion implantation in the surface layer of the support substrate 20; for silicon substrates, implantation of argon ions, silicon, nitrogen, etc., can be performed to generate an interfering surface layer capable of trapping charge carriers from the support substrate 20.

[0106] Alternatively, the surface layer of the support substrate 20 may be etched and structured; for example, by mechanical etching, wet or dry chemistry, induced surface structuring, or specific sites for capturing charge carriers from the support substrate 20.

[0107] The trapping layer 30 can have a thickness ranging from tens of nanometers to a few micrometers or tens of micrometers.

[0108] After the trapping layer 30 is formed on the support substrate 20, the roughness of the free surface of the trapping layer 30 is defined by the maximum peak-valley amplitude, for example, by mechanical or optical profilometry on a measurement profile of approximately 50 to 500 micrometers or on a measurement surface of approximately 50 × 50 to 500 × 500 μm². Advantageously, the determined roughness is greater than 0.3 micrometers, or even greater than or equal to 0.5 micrometers, or even greater than or equal to 1 micrometer. It is preferably between 0.3 micrometers and 5 micrometers.

[0109] Advantageously, the spectral density of the roughness of the functional interface 31 covers all or a portion of the spectral band of the wavelength of the interfering wave to be eliminated. Preferably, the determined roughness has a spatial wavelength and amplitude that is at least one-quarter of the interfering wavelength.

[0110] The defined roughness can be obtained on the free surface of the trapping layer 30 directly after deposition or by mechanical polishing, chemical mechanical polishing, wet or dry chemical etching, or a combination of these techniques. The aim is to create a uniform roughness of defined amplitude on the free surface of the trapping layer 30. As an example, this roughness can be obtained by an "acid etching" type process or an "alkaline etching" process used to process the rough back side of silicon wafers used in the semiconductor industry. According to another example, the defined roughness of the free surface of the trapping layer 30 can be obtained by mechanical polishing (typically using a diamond wheel with a grit size of 2000) and wet chemical etching (typically by TMAH) of the surface of the support substrate 20 before depositing the trapping layer 30 in polysilicon; the free surface of the trapping layer 30 after deposition on the support substrate 20 then has a defined roughness (6b') with peaks and valleys of approximately 0.5 micrometers.

[0111] The manufacturing method then includes the step of forming a first intermediate layer 40 on the trapping layer 30. The interface between the trapping layer 30 and the first intermediate layer 40 forms a functional interface 31 with a defined roughness. The first intermediate layer 40 may comprise a material selected from silicon oxide, silicon nitride, silicon oxynitride, or a material of the same type as the useful layer 10. It can be prepared by chemical deposition. Advantageously, for subsequent assembly steps on the donor substrate 11 (or the useful layer 10), a smoothing step (e.g., chemical mechanical polishing) is performed on the free surface of the first intermediate layer 40. This option is particularly suitable when subsequent assembly steps involve bonding by molecular adhesion.

[0112] The first intermediate layer 40 may also include a polymeric material, which can be deposited, for example, by centrifugation. An advantage of this type of material is that smoothing can be performed directly during deposition. This option is particularly suitable when subsequent bonding steps involve adhesive bonding.

[0113] Finally, the manufacturing method includes an assembly step for arranging the donor substrate 11 (or useful layer 10) on the support substrate 20; specifically, assembly is performed between the first intermediate layer 40 and the second surface 2 of the donor substrate 11. Figure 6d ).

[0114] Advantageously, the assembly step includes direct bonding via molecular adhesion: this bonding technique has the advantage of not requiring the use of additional material layers. Alternatively, the bonding step may include adhesive bonding, metal bonding, anodic bonding, or any other type of bonding known in the art and compatible with the intended application. Advantageously, the assembly step includes a cleaning sequence prior to bonding to ensure good surface cleanliness (removal of particulate, hydrocarbon, and metallic contaminants) prior to bonding.

[0115] To strengthen the bonding interface, the bonded hybrid structure 101 can be heat-treated at low or medium temperatures to prevent damage to the heterostructure: typically between tens of degrees and 500 degrees Celsius.

[0116] exist Figures 6a to 6e In the illustrated example, the useful layer 10 is included in the donor substrate 11, and the manufacturing method further includes the donor substrate 11 ( Figure 6e The thinning step is used to form a useful layer 10 and a first surface 1 on which a surface acoustic wave device will be developed.

[0117] As previously discussed, this thinning step can be performed using various techniques known in the prior art.

[0118] At the end of this manufacturing method, the hybrid structure 100 according to the present invention is obtained. Figure 6e ).

[0119] according to Figures 7a to 7e In a variation of the above-described manufacturing method, the second surface 2 of the useful layer 10 (or, in the case where the useful layer 10 is included in the donor substrate, the donor substrate 11) has a second defined roughness. Figure 7a The peak-valley amplitude of the second determined roughness is advantageously greater than 0.1 micrometers.

[0120] This variation of the manufacturing method includes, for example: Figure 7bThe steps illustrate the formation of a second intermediate layer 50 on the second surface 2 of the useful layer 10 or the donor substrate 11. The second intermediate layer 50 may comprise a material selected from silicon oxide, silicon nitride, and silicon oxynitride, or a stack of materials. The second intermediate layer 50 may also comprise a material of the same type as that forming the useful layer 10 to limit problems associated with differences in thermal expansion.

[0121] The interface between the useful layer 10 and the second intermediate layer 50 forms a second functional interface 32. Advantageously, for the assembly step, the formation step of the second intermediate layer 50 includes a smoothing step of its free surface.

[0122] Prior to the assembly step, a trapping layer 30 with a first predetermined roughness is formed on the support substrate 20. Then, a first intermediate layer 40 is formed on the trapping layer 30. Figure 7c The interface between these two layers forms a functional interface with a defined roughness 31.

[0123] Optionally, the first intermediate layer 40 and the second intermediate layer 50 may be composed of the same material.

[0124] This variation of the manufacturing method also includes advantageously assembling the first intermediate layer 40 and the second intermediate layer 50 by direct bonding, but this will not be done in a restrictive manner.

[0125] Optionally, heat treatment may be performed to reinforce the bonding interface of the bonded structure 101.

[0126] When the useful layer 10 is included in the donor substrate 11, the thinning steps described above are performed, resulting in a hybrid structure 100. Figure 7e ).

[0127] Of course, the present invention is not limited to the described embodiments and can be applied to alternative embodiments as defined by the claims.

Claims

1. A hybrid structure (100) for a surface acoustic wave device, the hybrid structure (100) comprising a useful layer (10) of piezoelectric material, the useful layer (10) having a free first surface (1) and a second surface (2) disposed on a supporting substrate (20), the supporting substrate (20) having a lower coefficient of thermal expansion than the useful layer (10), the hybrid structure (100) being characterized in that the hybrid structure (100) comprises: A second intermediate layer (50) is disposed on the second surface (2) of the useful layer (10); The trapping layer (30) is located on the supporting substrate (20); The hybrid structure (100) comprises at least one functional interface (31, 32) with a defined roughness located between the useful layer (10) and the trapping layer (30), wherein the hybrid structure (100) further comprises a first intermediate layer (40) located on the trapping layer (30), the at least one functional interface (31, 32) comprising a first functional interface (31) formed by the interface between the first intermediate layer (40) and the trapping layer (30) and a second functional interface (32) with a defined roughness having a peak-valley amplitude greater than 0.1 micrometer located between the useful layer (10) and the second intermediate layer (50), wherein the second intermediate layer (50) has a flat surface away from the second functional interface (32), wherein the flat surface of the second intermediate layer (50) is bonded to the first intermediate layer (40) located on the trapping layer (30) on the support substrate (20).

2. The hybrid structure (100) for a surface acoustic wave device according to claim 1, wherein, The trapping layer (30) is formed by implantation into the surface layer of the support substrate (20) or by etching and structuring the surface layer of the support substrate (20).

3. The hybrid structure (100) for surface acoustic wave devices according to claim 1, wherein, The first functional interface (31) has a defined roughness with peak-valley amplitude greater than 0.3 micrometers.

4. The hybrid structure (100) for a surface acoustic wave device according to claim 3, wherein, The first intermediate layer (40) is formed on the captured layer (30) by chemical deposition.

5. The hybrid structure (100) for a surface acoustic wave device according to claim 1, wherein, The second intermediate layer (50) is formed on the useful layer (10) by depositing a material selected from silicon oxide, silicon nitride, silicon oxynitride, or a material of the same type as the material forming the useful layer (10).

6. The hybrid structure (100) for a surface acoustic wave device according to claim 1, wherein, The second intermediate layer (50) comprises a material selected from silicon oxide, silicon nitride, silicon oxynitride, or the same type of material as the material forming the useful layer (10); and / or, the trapping layer (30) is formed of a material selected from amorphous silicon, polycrystalline silicon, amorphous germanium, or polycrystalline germanium; and / or, the first intermediate layer (40) comprises a material selected from silicon oxide, silicon nitride, silicon oxynitride.

Images