Connected body and acoustic wave element

Abstract

Connected body (15A), comprising: a support substrate (1) comprising a metal oxide; a substrate made of a piezoelectric material (4A); a connecting layer (2B) provided between the support substrate (1) and the substrate made of a piezoelectric material (4A), wherein the connecting layer (2B) has a composition of Si (1-x) O x [0.008 ≤ x ≤ 0.408] exhibits; and an amorphous layer (10) provided between the connecting layer (2B) and the support substrate (1), where the oxygen content of the amorphous layer (10) is higher than the oxygen content of the support substrate (1), wherein the metal oxide is selected from the group consisting of sialon, sapphire, cordierite, mullite and aluminum oxide, and wherein the substrate is selected from a piezoelectric material (4A) from the group consisting of lithium niobate, lithium tantalate and a solid solution of lithium niobate-lithium tantalate.

Description

Technical field

[0001] The present invention relates to a connected body comprising a substrate made of a piezoelectric material and a support substrate comprising a metal oxide; as well as an acoustic wave device comprising this connected body. STATE OF THE ART

[0002] A surface acoustic wave device acting as a filter or oscillator, used in mobile phones or the like, and an acoustic wave device, such as a Lamb wave device or a film mass acoustic resonator (FBAR), employing a piezoelectric thin film, are known. Such an acoustic wave device is known to be constructed by attaching a carrier body and a piezoelectric substrate that propagates a surface acoustic wave, and by providing interlocking electrodes that can cause the surface acoustic wave to oscillate on a surface of the piezoelectric substrate.By attaching the carrier body, whose coefficient of thermal expansion is lower than that of the piezoelectric substrate, to the piezoelectric substrate, the change in the size of the piezoelectric substrate in response to a temperature change is reduced, thus reducing the change in the frequency characteristics as a surface acoustic wave device.

[0003] When a piezoelectric substrate and a silicon substrate are connected, it is known that a silicon oxide film is formed on the piezoelectric substrate and that the piezoelectric substrate and the silicon substrate are directly connected to each other by means of the silicon oxide film (Patent Document 1). During the connection process, a plasma beam is directed onto the surfaces of the silicon oxide film and the silicon substrate to activate the surfaces, and the direct connection is then carried out (plasma activation method).

[0004] Furthermore, it is known that the surface of the piezoelectric substrate is formed into a rough surface, that a filler layer is provided on the rough surface to make it flat, and that the filler layer is bonded to the silicon substrate by an adhesive layer (Patent Document 2). According to the method, an epoxy or acrylic resin is used for the filler and adhesive layers, and the interface of the piezoelectric substrate is provided as the rough surface, so that the reflection of a volume wave is suppressed and interference waves are reduced.

[0005] Furthermore, a method of direct joining according to a so-called FAB (“Fast Atom Beam”) system is known (Patent Document 3). According to this method, a neutralized atom beam is directed onto the respective joining surfaces to activate them at ambient temperature, and these are then directly joined together.

[0006] On the other hand, patent document 4 describes how a substrate made of a piezoelectric material is directly connected to a support substrate composed of a ceramic material (aluminum oxide, aluminum nitride, silicon nitride) by means of an intermediate layer instead of a silicon substrate. The intermediate layer material is made of silicon, silicon oxide, or aluminum nitride. Patent document 5 describes connected bodies and acoustic wave devices. (Documents of the state of the art) (Patent documents) (Patent document 1] US 7 213 314 B2 (Patent document 2] JP 5 814 727 B2 (Patent document 3] JP 2014 - 086 400 A (Patent document 4] JP 3 774 782 B2 (Patent document 5] WO 2018 / 180 827 A1 SUMMARY OF THE INVENTION (Problem to be solved by the invention)

[0007] Depending on the applications of a connected body, it is preferable to improve the electrical resistance of a compound layer, thereby enhancing its insulating properties. For example, in the case of acoustic wave elements, noise or loss can be reduced by improving the insulating properties of the compound layer. Consequently, the applicant has disclosed that the composition of the compound layer is silicon oxide with a lower oxygen content to form the compound layer with the improved insulating properties (Patent Document 5).

[0008] However, it can be difficult to firmly and stably bond a piezoelectric material substrate to a metal oxide support substrate via the bonding layer, which is composed of silicon oxide with a lower oxygen content. Separation can occur if the piezoelectric material substrate undergoes processing, such as polishing.

[0009] One object of the present invention is the firm and stable joining of a substrate made of a piezoelectric material with a support substrate composed of a metal oxide by means of a bonding layer composed of silicon oxide with a low oxygen content. (Solution to the problem)

[0010] The present invention provides a connected body comprising: a support substrate comprising a metal oxide; a substrate made of a piezoelectric material; a connecting layer provided between the support substrate and the substrate made of a piezoelectric material, wherein the connecting layer has a composition of Si (1-x) O x [0.008 ≤ x ≤ 0.408] exhibits; and an amorphous layer provided between the compound layer and the support substrate, where the oxygen content of the amorphous layer is higher than the oxygen content of the support substrate, wherein the metal oxide is selected from the group consisting of sialon, sapphire, cordierite, mullite and aluminum oxide, and wherein the substrate is selected from a piezoelectric material (4A) from the group consisting of lithium niobate, lithium tantalate and a solid solution of lithium niobate-lithium tantalate.

[0011] The present invention further provides an acoustic wave device comprising: the connected body; and an electrode that is provided on the substrate made of a piezoelectric material. (Effects of the invention)

[0012] According to the present invention, the substrate made of a piezoelectric material can be firmly and stably connected to a support substrate composed of the metal oxide by means of the connecting layer composed of silicon oxide with a low oxygen content. BRIEF DESCRIPTION OF THE DRAWINGS Fig. Figure 1(a) shows the state in which a compound layer 2 is provided on a substrate made of a piezoelectric material 4, Fig. Figure 1(b) shows the state in which a surface 2b of a compound layer 2A is activated by a neutralized beam A, and Fig.Figure 1(c) shows the state in which a surface 1a of a support substrate 1 is activated by a neutralized beam A. Fig. 2(a) shows the state in which the substrate made of a piezoelectric material 4 and the support substrate 1 are connected to each other, Fig. Figure 2(b) shows the state in which a substrate made of a piezoelectric material 4A has been made thinner by machining, and Fig. Figure 2(c) shows the state in which an electrode 6 is provided on the substrate made of a piezoelectric material 4A. Fig. Figure 3(a) shows the state in which an intermediate layer 11 and a connecting layer 2 are provided on the substrate made of a piezoelectric material 4, Fig. Figure 3(b) shows the state in which a surface 2b of a compound layer 2A is activated by a neutralized beam A, and Fig.Figure 3(c) shows the state in which the surface 1a of the support substrate 1 is activated by a neutralized beam A. Fig. Figure 4(a) shows the state in which the substrate made of a piezoelectric material 4 and the support substrate 1 are connected, Fig. Figure 4(b) shows the state in which a substrate made of a piezoelectric material 4A has been made thinner by machining, and Fig. Figure 4(c) shows the state in which an electrode 6 is provided on the substrate made of a piezoelectric material 4A. MODES FOR EXECUTING THE INVENTION

[0013] The present invention is described in detail below, with reference to the drawings.

[0014] The Fig. 1 and Fig. Figure 2 shows schematic diagrams illustrating manufacturing examples of directly connecting a support substrate to a substrate made of a piezoelectric material.

[0015] As it is in the Fig. As shown in Figure 1(a), the interconnect layer 2 is a film formed on a principal surface 4a of a substrate made of a piezoelectric material 4. Figure 4b represents a principal surface on the opposite side of the substrate made of a piezoelectric material 4. Then, as shown in the Fig. As shown in Figure 1(b), a neutralized beam is directed onto a surface 2a of the bonding layer 2 according to arrow A, so that the surface of the bonding layer 2 is activated to provide an activated surface 2b. On the other hand, as shown in the Fig. Figure 1(c) shows a neutralized beam A being directed onto a principal surface 1a of a support substrate 1 to activate it, so that the support substrate 1 is obtained with an activated surface on it. Figure 1b represents a principal surface on the opposite side of the activated surface.

[0016] Then, as it says in the Fig. As shown in Figure 2(a), the activated surface of the compound layer and the activated surface 1a of the support substrate 1 are directly connected to each other, so that a connected body 5 is obtained. The output power, irradiation time, or the like of the neutralized beam A can be adjusted such that an amorphous layer 10 is produced along an interface between the activated surface 1a of the support substrate 1 and the compound layer 2B.

[0017] According to a preferred embodiment, a surface 4b of the substrate made of a piezoelectric material 4 of the connected body 5 is further subjected to a polishing treatment to thin the substrate made of a piezoelectric material 4A, as described in the Fig. 2(b) is shown, so that a connected body 5A is provided. 4c represents a polished surface.

[0018] As it is in the Fig.As shown in Figure 2(c), predefined electrodes 6 are formed on the polished surface 4c of the substrate made of a piezoelectric material 4A, so that an acoustic wave element 7 is generated.

[0019] According to one embodiment, which is described in the Fig. 3 and Fig. As shown in Figure 4, an intermediate layer 11 is provided between the substrate made of a piezoelectric material 4 and the connecting layer 2, 2A or 2B.

[0020] That is, as it is in the Fig. As shown in Figure 3(a), the intermediate layer 11 and the connecting layer 2 are formed in this order as a film on the main surface 4a of the substrate from a piezoelectric material 4. Then, as shown in the Fig.As shown in Figure 3(b), the neutralized beam is directed onto a surface 2a of the compound layer 2 according to arrow A, so that the surface of the compound layer 2A is activated to provide an activated surface 2b. Furthermore, as shown in the Fig. Figure 3(c) shows a neutralized beam A being directed onto the main surface 1a of the support substrate 1, thus activating it and providing the support substrate 1 with the activated surface formed thereon. Figure 1b represents a main surface on the opposite side of the activated surface.

[0021] Then, as it says in the Fig.As shown in Figure 4(a), the activated surface of the compound layer and the activated surface 1a of the support substrate 1 are directly connected to each other, so that a connected body 15 is obtained. The output power and the irradiation time of the neutralized beam A are adjusted such that an amorphous layer 10 can be generated along the interface between the activated surface 1a of the support substrate 1 and the compound layer 2B.

[0022] According to a preferred embodiment, the surface 4b of the substrate made of a piezoelectric material 4 of the substrate made of a piezoelectric material 15 is further subjected to polishing, so that the thickness of the substrate made of a piezoelectric material 4A is reduced, as described in the Fig. Figure 4(b) shows a connected body 15A. Figure 4c represents a polished surface.

[0023] According to the Fig.4(c) Predefined electrodes 6 are formed on the polished surface 4c of the substrate made of a piezoelectric material 4A, so that an acoustic wave device 17 is generated.

[0024] According to the present invention, the support substrate comprises a metal oxide. The metal oxide is selected according to the invention from the group consisting of sialon, sapphire, cordierite, mullite, and aluminum oxide. The aluminum oxide is preferably transparent.

[0025] The relative density of the support substrate can preferably be 95.5 percent or higher with regard to the bond strength, and can be 100 percent. The relative density is measured using the Archimedes method. Furthermore, although the method for producing the support substrate is not specifically restricted, the method can preferably be a sintering process.

[0026] Sialon is a ceramic material obtained by sintering a mixture of silicon nitride and aluminum oxide, and has the following composition. Si 6-z Al z O z N 8-z Dh, Sialon has the composition of a mixture of aluminum oxide with silicon nitride, and z indicates the proportion of added aluminum oxide. z may more preferably be 0.5 or more. Furthermore, z may more preferably be 4.0 or less.

[0027] Sapphire is a single crystal with the composition Al₂O₃, and aluminum oxide is a polycrystal with the composition Al₂O₃. Cordierite is a ceramic with the composition 2MgO · 2Al₂O₃ · 5SiO₂. Mullite is a ceramic with a composition ranging from 3Al₂O₃ · 2SiO₂ to 2Al₂O₃ · SiO₂.

[0028] According to the invention, the substrate material is selected from a piezoelectric material from the group consisting of lithium niobate, lithium tantalate or a solid solution of lithium niobate-lithium tantalate.

[0029] According to the present invention, a connecting layer between the support substrate and the substrate is provided made of a piezoelectric material and the connecting layer has a composition of Si (1-x) O x [0.008 ≤ x ≤ 0.408] on.

[0030] The composition is one whose oxygen concentration is considerably lower than that of SiO2 (corresponding to x = 0.667). The insulating properties of the compound layer can be improved by connecting the substrate made of a piezoelectric material to the support substrate by means of the compound layer, which is silicon oxide with the composition Si (1-x) O x It shows that it is very well done.

[0031] In the case where x is in the composition of Si (1-x) O x If the resistance of the junction forming the junction layer is lower than 0.008, the electrical resistance of the junction layer is low and the desired insulating properties cannot be achieved. Consequently, x is set to 0.008 or higher, and can preferably be 0.010 or higher, more preferably 0.020 or higher, and particularly 0.024 or higher. Furthermore, if x is higher than 0.408, the junction strength is reduced, leading to a tendency for the substrate to separate from the piezoelectric material. Therefore, x is set to 0.408 or lower, and can preferably be set to 0.225 or lower.

[0032] The electrical resistance of the compound layer can preferably be 4.8 × 10 3 Ω · cm or higher, preferably 5.8 × 10 3 Ω · cm or higher and in particular 6.2 × 10 3Ω · cm or higher. Furthermore, the electrical resistance of the compound layer is generally 1.0 × 10 8 Ω · cm or lower.

[0033] Although the thickness of the compound layer is not specifically limited, it can preferably be 0.01 to 10 µm and more preferably 0.01 to 0.5 µm with regard to manufacturing costs.

[0034] Although the film formation process for the compound layer is not specifically limited, sputtering, chemical vapor deposition (CVD), and vapor deposition processes can be mentioned. During reactive sputtering using a Si sputtering target, it is particularly preferred that the amount of oxygen gas flowing into a chamber is adjusted so that the oxygen fractions (x) in the compound layer can be controlled.

[0035] Although specific conditions for the production of the compound layer are selected in a suitable manner depending on the chamber specification, according to a preferred example the total pressure is set to 0.28 to 0.34 Pa and the partial pressure of oxygen to 1.2 × 10 -3 up to 5.7 × 10 -2 Pa was set and the film formation temperature was adjusted to ambient temperature. Furthermore, silicon doped with boron is mentioned as an example of the silicon target. As described later, the amount of boron as a foreign atom at an interface between the compound layer and the support substrate 1 is reduced to approximately 5 × 10⁻⁶. 18 atoms / cm² 3 up to 5 × 10 19 atoms / cm² 3 This adjusts the insulation properties of the bonding layer with greater reliability.

[0036] According to a preferred embodiment, the activated surface of the compound layer and the activated surface of the support substrate are directly bonded together. In other words, a bonding interface exists along an interface between the compound layer and the support substrate. In this case, the arithmetic mean roughness Ra of the activated surface of the compound layer can preferably be 1 nm or lower, and more preferably 0.3 nm or lower. Furthermore, the arithmetic mean roughness Ra of the activated surface of the support substrate can preferably be 1 nm or lower, and more preferably 0.3 nm or lower. This further improves the bond strength between the support substrate and the compound layer.

[0037] The composite body of the present invention further comprises an amorphous layer that is formed between the compound layer and the support substrate. The oxygen content of the amorphous layer is higher than the oxygen content of the support substrate. That is, the amorphous layer is formed along the activated surface of the support substrate, and as the diffusion of oxygen in the amorphous layer progresses, it is found that the oxygen content of the metal oxide forming the amorphous layer can become higher than the oxygen content of the metal oxide forming the support substrate.In addition, in the case where the diffusion of oxygen as such progresses, it is found that the bond strength of the substrate made of a piezoelectric material with the support substrate can become high, and, for example, even if the substrate made of a piezoelectric material is made thinner by processing, the separation of the substrate made of a piezoelectric material is suppressed.

[0038] According to a preferred embodiment, the composition of the amorphous layer comprises a metal forming the support substrate, oxygen (O), and argon (Ar) as its main components. However, in cases where the support substrate is composed of Sialon, the composition of the amorphous layer comprises silicon (Si), forming the support substrate, aluminum (Al), nitrogen (N), oxygen (O), and argon (Ar) as its main components. "Main components" means that the sum of the atomic fractions of the atoms is 95 atomic percent or higher, and preferably 97 atomic percent or higher, with 100 atomic percent being allocated to a total atomic fraction. More preferably, the composition of the amorphous layer is of the same type as the material of the support substrate, and the oxygen fraction is higher than that of the material of the support substrate, and the composition includes argon.

[0039] According to the present invention, the oxygen content of the amorphous layer is higher than the oxygen content of the support substrate. For the purpose of improving the bond strength, the difference in oxygen content can preferably be 0.5 atomic percent or higher, and more preferably 1.0 atomic percent or higher. Furthermore, for practical reasons, the difference in oxygen content can preferably be 7.0 atomic percent or lower.

[0040] Furthermore, with a view to improving the bond strength, the atomic fraction of argon (Ar) in the amorphous layer can preferably be 1.0 atomic percent or higher, and more preferably 1.5 atomic percent or higher. Furthermore, the atomic fraction of argon (Ar) in the amorphous layer can preferably be 5.0 atomic percent or lower, and more preferably 4.8 atomic percent or lower.

[0041] Although the material of the interlayer is not specifically limited, as long as it can connect the interlayer and the substrate made of a piezoelectric material, the material can preferably be SiO2, Ta2O5, TiO2, ZrO2, HfO2, Nb2O3, Bi2O3, Al2O3, MgO, AIN or Si3N4.

[0042] In particular, for a high-frequency application (frequency band for 5G communication at 3.5 to 6 GHz or the like), it is necessary to improve the frequency of an acoustic wave, and in this case, the interlayer material can preferably be a high-speed sound material. The speed of sound of such a high-speed sound material can preferably be 6000 m / s or higher, and more preferably 10000 m / s or higher. Although the speed of sound of the interlayer material is not specifically limited, it is practically difficult to exceed 30000 m / s, and it can in many cases be 30000 m / s or lower, and preferably 25000 m / s or lower. Such a high-speed sound material includes AIN and Si3N4.Furthermore, the speed of sound of the material is calculated on the basis of the density measured by the JIS method (JIS C2141), the Young's modulus (JIS R1602) and the Poisson ratio (JIS R1602).

[0043] Furthermore, in a high-frequency application (application for a frequency band for 5G communication at 3.5 to 6 GHz or the like), it is necessary to improve the heat dissipation properties because a high-power signal is injected. In this case, it is preferred that the interlayer material be a material with high thermal conductivity. The thermal conductivity of such a material with high thermal conductivity may preferably be 100 W / (m·K) or higher, more preferably 900 W / (m·K) or higher, and particularly 1000 W / (m·K) or higher. Although the upper limit of the thermal conductivity of the interlayer material is not specifically defined, in many cases it may be 5000 W / (m·K) or lower, and furthermore 3000 W / (m·K) or lower, since in practical terms it is difficult to exceed 5000 W / (m·K). Such a material with high thermal conductivity includes AIN and Si3N4.Furthermore, the thermal conductivity of the material is measured according to JIS R1611.

[0044] The individual components of the present invention are described in more detail below.

[0045] The application of the connected body of the present invention is not specifically limited and it can preferably be used as an acoustic wave device or an optical device.

[0046] Acoustic wave devices include surface acoustic wave devices, Lamb wave-type devices, thin-film resonators (FBARs), and the like. For example, a surface acoustic wave device is constructed by providing input-side IDT (interdigital transducer) electrodes (also called comb electrodes or interlocking electrodes) for oscillating a surface acoustic wave and output-side IDT electrodes for receiving the surface acoustic wave on the surface of a piezoelectric substrate. Applying a high-frequency signal to the input-side IDT electrodes generates an electric field between the electrodes, causing the surface acoustic wave to oscillate and propagate on the piezoelectric substrate.The propagated surface acoustic wave is then extracted as an electrical signal by the IDT electrodes on the output side, which is positioned in the direction of propagation.

[0047] A metal film can be applied to the lower surface of a piezoelectric substrate. Once the Lamb-type device has been constructed as an acoustic wave device, the metal film serves to improve the electromechanical coupling near the lower surface of the piezoelectric substrate. In this case, the Lamb-type device has a structure in which interlocking electrodes are formed on the surface of the piezoelectric substrate, and the metal film is exposed through a cavity provided in the substrate. Materials for such metal films include, for example, aluminum, an aluminum alloy, copper, gold, or similar materials.Furthermore, in the case where the Lamb wave device is manufactured, a composite substrate can be used which has the piezoelectric single crystal substrate without the metal film on the lower surface.

[0048] Furthermore, a metal film and an insulating film can be provided on the lower surface of the piezoelectric single-crystal substrate. The metal film acts as electrodes when the thin-film resonator is used as the acoustic wave device. In this case, the thin-film resonator has a structure in which electrodes are formed on the upper and lower surfaces of the piezoelectric single-crystal substrate, and the insulating film forms a cavity, leaving the metal film exposed on the piezoelectric single-crystal substrate. Materials for such metal films include, for example, molybdenum, ruthenium, tungsten, chromium, aluminum, or similar materials. Materials for the insulating films include silicon dioxide, phosphosilicate glass, boron phosphosilicate glass, or similar materials.

[0049] Furthermore, the optical device can be an optical switching device, a wavelength conversion device, and an optical modulating device. Additionally, a periodic domain inversion structure can be formed in the substrate made of a piezoelectric material.

[0050] If the subject matter of the present invention is an acoustic wave device and the substrate is made of a piezoelectric material made of lithium tantalate, it is preferred to use the substrate such that it is rotated from the Y-axis to the Z-axis by 36 to 47° (for example 42°) about the X-axis, which is the direction of propagation of a surface acoustic wave, due to low propagation loss.

[0051] Furthermore, in the case where the substrate is made of a lithium niobate piezoelectric material, it is preferred to use the substrate such that it is rotated 60 to 68° (for example, 64°) around the X-axis from the Y-axis to the Z-axis, where this is the direction of propagation of the surface acoustic wave, due to lower propagation loss. Furthermore, although the size of the piezoelectric substrate is not specifically limited, for example, the diameter can be 50 to 150 mm and the thickness can be 0.2 to 60 µm.

[0052] The following method is preferred for obtaining the connected body according to the invention.

[0053] First, the surface of the compound layer and the surface (bonding area) of the support substrate are leveled to obtain flat surfaces. The leveling process includes lapping, chemical-mechanical polishing (CMP), and the like. Furthermore, the flat surfaces preferably have a surface roughness (Ra) of 1 nm or lower, and more preferably of 0.3 nm or lower.

[0054] Then, to remove residues of polishing compound and denatured machining layers, the surfaces of the compound layer and the substrate are cleaned. The surface cleaning method includes wet cleaning, dry cleaning, scrubbing, or the like, with scrubbing being preferred for its ease and effectiveness in achieving clean surfaces. It is particularly preferred to use "Sun Wash LH540" as the cleaning agent and then to carry out the cleaning using a scrubbing machine with a mixed solution of acetone and IPA.

[0055] Then, a neutralized beam is directed onto the surface of the bonding layer and the surface of the support substrate to activate the respective flat surfaces.

[0056] When surface activation is performed using the neutralized beam, the use of a system described in patent document 3 for generating the injected neutralized beam is preferred. That is, a high-speed saddle-field atomic beam source is used as the beam source. An inert gas is then introduced into the chamber, and a high voltage is applied to electrodes from a direct current source. This causes a saddle-field electric field, generated between the electrode (positive electrode) and a housing (negative electrode), to move electrons, generating atomic and ion beams originating from the inert gas. Of the beams reaching a grid, the ion beam is neutralized at the grid, and the beam of neutral atoms is emitted from the high-speed atomic beam source.

[0057] The atomic species forming the beam can preferably be an inert gas (argon, nitrogen or the like).

[0058] In the activation step by irradiation with the beam, the voltage can preferably be set to 0.5 to 2.0 kV and the current can preferably be set to 50 to 200 mA.

[0059] The activated surfaces are then brought into contact and joined together in a vacuum atmosphere. The temperature at this point can be ambient temperature, particularly 40 °C or lower, and more preferably 30 °C or lower. Furthermore, the temperature during joining can more preferably be 20 °C or higher and 25 °C or lower. The pressure during joining is preferably 100 to 20,000 N. EXAMPLES (Inventive examples 1, 2 and 3, Comparative examples 1 and 2)

[0060] The joined bodies 5 and 5A of the respective examples shown in Tables 1 and 2 were manufactured according to the procedure described with reference to the Fig. 1 and Fig. 2 has been described.

[0061] In particular, a lithium tantalate substrate (LT substrate) with an OF portion, a diameter of 4 inches (10.16 cm), and a thickness of 250 µm was used as the piezoelectric single-crystal substrate 4. A 46° Y-cut X-propagation LT substrate, in which the surface acoustic wave (SAW) propagation direction was set to X and the cut angle was a rotated Y-cut plate, was used as the LT substrate. The surface 4a of the piezoelectric substrate 4 was subjected to a mirror-polished surface such that the arithmetic mean roughness Ra reached 0.3 nm. Furthermore, Ra was measured by an atomic force microscope (AFM) in a field of view of 10 µm × 10 µm.

[0062] The compound layer 2 was then formed as a film on the surface 4a of the substrate using a piezoelectric material 4 via a direct current sputtering process. Boron-doped silicon was used as the target. Oxygen gas was introduced as the oxygen source. The amount of oxygen gas introduced was varied to change the total atmospheric pressure and the partial pressure of oxygen in a chamber, thereby altering the oxygen content in the compound layer 2. The thickness of the compound layer 2 was adjusted to 100 to 200 nm. The arithmetic mean roughness Ra of the surface 2a of the compound layer 2 was 0.2 to 0.6 nm. The compound layer 2 was then subjected to chemical-mechanical polishing (CMP) to adjust the film thickness to 80 to 190 nm and the Ra to 0.08 to 0.4 nm.

[0063] Furthermore, the support substrate 1 was produced, which was composed of Sialon (z = 2.5) and had a flat alignment part (OF part) with a diameter of 4 inches (10.16 cm) and a thickness of 500 µm. The surfaces 1a and 1b of the support substrate 1 were finished by chemical-mechanical polishing (CMP) so that the respective arithmetic mean roughness values ​​Ra reached 0.2 nm.

[0064] Then, the flat surface 2b of the compound layer 2A and the surface 1a of the support substrate 1 were cleaned to remove impurities, after which it was placed in a vacuum chamber. After evacuation to a volume of approximately 10 -6A high-speed atomic beam (acceleration voltage 1 kV and Ar flux rate 27 sccm) was directed onto the bonding surfaces 1a and 2b of the respective substrates for 120 s. Then, after the beam-irradiated surface (activated surface) 2b of the bonding layer 2A and the activated surface 1a of the support substrate 1 had been brought into contact, the substrates were bonded by applying a pressure of 10,000 N for 2 minutes (see the Fig. 2(a)). Then the combined bodies of the respective examples obtained in this way were heated for 20 hours at 100 °C.

[0065] The surface 4b of the substrate made of a piezoelectric material 4 was then ground and polished, so that the thickness was changed from the initial 250 µm to 1 µm (see the Fig. 2(b)).

[0066] The following properties were evaluated for the connected bodies 5 and 5A of the respective examples obtained in this way. (Confirmation of the amorphous layer)

[0067] The presence of the amorphous layer was investigated as follows. Measurement system:

[0068] The microstructure was examined using an H-9500 transmission electron microscope supplied by Hitachi High-Tech Corporation. Measurement conditions:

[0069] A sample of a thinned piece was examined using FIB (focused ion beam method) at an accelerating voltage of 200 kV.

[0070] (Proportions of oxygen atoms and argon atoms in the compound layer, the support substrate and the amorphous layer)

[0071] Elemental analysis was performed using an EDS (energy-dispersive X-ray spectrometer) with the following system to measure the proportions of oxygen atoms and argon atoms in the compound layer, the support substrate and the amorphous layer. Measurement system:

[0072] The elemental analysis was carried out using an elemental analysis system “JEM-ARM200F” supplied by JEOL Ltd. Measurement conditions:

[0073] A sample of a thinned piece was examined using FIB (focused ion beam method) at an accelerating voltage of 200 kV. (Connection strength)

[0074] The bond strengths of the joined bodies in each example were measured using the crack opening method. Furthermore, in the case where the bond strength was 1.75 J / m², the following occurred: 2The threshold exceeded the limit, a separation near the bonding layer 2B did not occur, and the bonded body broke as a mass fracture. Table 1 Comparative example 1 Comparative example 2 Substrate made of a piezoelectric material Lithium tantalate Lithium tantalate carrier substrate Sialon (z = 2.5] Sialon (z = 2.5] FAB irradiation amount (kJ) 45 22,5 Bond strength (J / m) 2 ) 0,8 0,2 Atomic concentration (Atomic %) Compound layer Amorphous layer carrier substrate Compound layer Amorphous layer carrier substrate O 5,5 20,0 20,1 5,6 19,1 19,5 Ar 0,2 1,3 0,0 0,1 0,9 0,0 Table 2 Example according to the invention 1 Example 2 according to the invention Example according to the invention 3 Substrate made of a piezoelectric material Lithium tantalate Lithium tantalate Lithium tantalate carrier substrate Sialon Sialon Sialon FAB irradiation amount (kJ) 135 90 180 Bond strength (J / m) 2 ) 2,5 2,1 2,0 Atomic concentration (Atomic %) Compound layer Amorphous layer carrier substrate Compound layer Amorphous layer carrier substrate Compound layer Amorphous layer carrier substrate O 5,8 22,2 19,9 5,6 21,1 20,0 5,7 22,5 18,2 Ar 0,3 3,9 0,0 0,1 2,3 0,0 0,4 4,3 0,0

[0075] According to comparative examples 1 and 2, the oxygen content of the amorphous layer was slightly lower than the oxygen content of the support substrate, and the bond strength was low in each example.

[0076] According to examples 1, 2 and 3 of the invention, the oxygen content of the amorphous layer was higher than the oxygen content of the support substrate and the bond strength was considerably improved in the respective examples, so that separation did not occur during the polishing of the substrate made of a piezoelectric material. (Example according to the invention 4 and comparative example 3)

[0077] The material of the support substrate in Example 1 according to the invention was changed to sapphire, and the FAB irradiation quantity was modified. The joined bodies 5 and 5A were fabricated according to the same method as in Example 1 according to the invention, and the oxygen and argon content of the respective parts and the bond strength were measured. The results are shown in Table 3. Table 3 Example according to the invention 4 Comparative example 3 Substrate made of a piezoelectric material Lithium tantalate Lithium tantalate carrier substrate sapphire sapphire FAB irradiation amount (kJ) 135 45 Bond strength (J / m) 2 ) 2,2 0,7 Atomic concentration (Atomic %) Compound layer Amorphous layer carrier substrate Compound layer Amorphous layer carrier substrate O 5,5 32,2 30,3 5,5 30,2 30,3 Ar 0,3 3,5 0,0 0,1 1,3 0,0

[0078] According to comparative example 3, the oxygen content of the amorphous layer was slightly lower than the oxygen content of the support substrate, and it was found that the bond strength was low.

[0079] According to example 4 of the invention, the oxygen content of the amorphous layer was higher than the oxygen content of the support substrate, so that the bond strength was considerably improved and separation did not occur during the polishing of the substrate made of a piezoelectric material. (Example according to the invention 5 and comparative example 4)

[0080] The material of the support substrate was changed to cordierite, and the FAB irradiation quantity was changed in Example 1 of the invention. The joined bodies 5 and 5A were otherwise prepared in the same manner as in Example 1 of the invention, and the oxygen and argon content of the respective parts and the bond strength were measured. The results are shown in Table 4. Table 4 Example according to the invention 5 Comparative example 4 Substrate made of a piezoelectric material Lithium tantalate Lithium tantalate carrier substrate Cordierite Cordierite FAB irradiation amount (kJ) 135 45 Bond strength (J / m) 2 ) 2,0 0,6 Atomic concentration (Atomic %) Compound layer Amorphous layer carrier substrate Compound layer Amorphous layer carrier substrate O 5,6 69,9 68,5 5,7 68,4 68,4 Ar 0,1 3,6 0,0 0,1 1,1 0,0

[0081] According to comparative example 4, the oxygen content of the amorphous layer was identical to the oxygen content of the support substrate and the bond strength was low.

[0082] According to example 5 of the invention, the oxygen content of the amorphous layer was higher than the oxygen content of the support substrate, the bond strength was considerably improved, and separation did not occur during the polishing of the substrate made of a piezoelectric material. (Example according to the invention 6 and comparative example 5)

[0083] The material of the support substrate was changed to mullite, and the FAB irradiation quantity was changed in Example 1 of the invention. The joined bodies 5 and 5A were otherwise prepared in the same manner as in Example 1 of the invention, and the oxygen and argon content of the respective parts and the bond strength were measured. The results are shown in Table 5. Table 5 Example according to the invention 6 Comparative example 5 Substrate made of a piezoelectric material Lithium tantalate Lithium tantalate carrier substrate Mullite Mullite FAB irradiation amount (kJ) 135 45 Bond strength (J / m) 2 ) 2,4 0,9 Atomic concentration (Atomic %) Compound layer Amorphous layer carrier substrate Compound layer Amorphous layer carrier substrate O 5,6 69,3 66,8 5,5 66,8 66,9 Ar 0,1 3,6 0,0 0,1 1,2 0,0

[0084] According to comparative example 5, the oxygen content of the amorphous layer was slightly lower than the oxygen content of the support substrate, and it was found that the bond strength was low.

[0085] According to example 6 of the invention, the oxygen content of the amorphous layer was higher than the oxygen content of the support substrate, the bond strength was considerably improved, and separation did not occur during the polishing of the substrate made of a piezoelectric material. (Example according to the invention 7 and comparative example 6)

[0086] The material of the support substrate was changed to translucent aluminum oxide, and the FAB irradiation quantity was changed in Example 1 of the invention. The joined bodies 5 and 5A were otherwise prepared in the same manner as in Example 1 of the invention, and the oxygen and argon content of the respective parts and the bond strength were measured. The results are shown in Table 6. Table 6 Example according to the invention 7 Comparative example 6 Substrate made of a piezoelectric material Lithium tantalate Lithium tantalate carrier substrate Translucent aluminum oxide Translucent aluminum oxide FAB irradiation amount (kJ) 135 45 Bond strength (J / m) 2 ) 2,0 0,7 Atomic concentration (Atomic %) Compound layer Amorphous layer carrier substrate Compound layer Amorphous layer carrier substrate O 5,5 30,7 28,6 5,5 28,5 28,7 Ar 0,3 3,5 0,0 0,1 1,2 0,0

[0087] According to comparative example 6, the oxygen content of the amorphous layer was slightly lower than the oxygen content of the support substrate, and it was found that the bond strength was low.

[0088] According to example 7 of the invention, the oxygen content of the amorphous layer was higher than the oxygen content of the support substrate, the bond strength was considerably improved, and separation did not occur during the polishing of the substrate made of a piezoelectric material.

Claims

[1] Connected body (15A), comprising: a support substrate (1) comprising a metal oxide; a substrate made of a piezoelectric material (4A); a connecting layer (2B) provided between the support substrate (1) and the substrate made of a piezoelectric material (4A), wherein the connecting layer (2B) has a composition of Si (1-x) O x [0.008 ≤ x ≤ 0.408] exhibits; and an amorphous layer (10) provided between the connecting layer (2B) and the support substrate (1), where the oxygen content of the amorphous layer (10) is higher than the oxygen content of the support substrate (1), wherein the metal oxide is selected from the group consisting of sialon, sapphire, cordierite, mullite and aluminum oxide, and wherein the substrate is selected from a piezoelectric material (4A) from the group consisting of lithium niobate, lithium tantalate and a solid solution of lithium niobate-lithium tantalate. [2] Composite body (15A) according to claim 1, further comprising an intermediate layer (11) provided between the interconnect layer (2B) and the substrate made of a piezoelectric material (4A). [3] Acoustic wave device (17) comprising: the connected body (15A) according to claim 1 or 2; and an electrode (6) which is provided on the substrate made of a piezoelectric material (4A).

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