Bonded body and elastic wave element

Abstract

The present application provides a bonded body capable of improving the Q value of an elastic wave element. The bonded body 9A includes a support substrate 6, a piezoelectric material substrate 1A, and a multilayer film 22 between the support substrate and the piezoelectric material substrate. The multilayer film 22 includes a laminated structure 2 having a first layer 3A, a second layer 7A, a third layer 3B, and a fourth layer 7B in the following order. The first layer 3A and the third layer 3B include silicon oxide, and the second layer 7A and the fourth layer 7B include metal oxide. The refractive index of the second layer 7A is higher than the refractive index of the first layer 3A and the refractive index of the third layer 3B. The refractive index of the second layer 7A is different from the refractive index of the fourth layer 7B.

Description

Technical Field

[0001] This invention relates to a joint between a piezoelectric material substrate and a support substrate, and an elastic wave element. Background Technology

[0002] Surface wave devices used in mobile phones and other applications, such as elastic surface wave devices (SSWs) that function as filters and oscillators, Lamb wave devices using piezoelectric thin films, and thin-film acoustic resonators (FBARs), are known. Among these SSWs, a known SSW device involves bonding a support substrate to a piezoelectric substrate that propagates the elastic surface wave, and providing comb-shaped electrodes on the surface of the piezoelectric substrate to excite the elastic surface wave. By bonding a support substrate with a smaller coefficient of thermal expansion than the piezoelectric substrate to the piezoelectric substrate in this way, changes in the size of the piezoelectric substrate due to temperature variations are suppressed, thereby suppressing changes in the frequency characteristics of the SSW device.

[0003] When bonding a piezoelectric substrate to a silicon substrate, it is known to form a silicon oxide film on the surface of the piezoelectric substrate and directly bond the piezoelectric substrate to the silicon substrate via the silicon oxide film (Patent Document 1). In this bonding process, a plasma beam is irradiated onto the surface of the silicon oxide film and the surface of the silicon substrate to activate the surfaces and perform direct bonding (plasma activation method).

[0004] In addition, a direct bonding method known as the so-called FAB (Fast Atom Beam) method is known (Patent Document 2). In this method, each bonding surface is activated by irradiating a neutralized atomic beam at room temperature to perform direct bonding.

[0005] In addition, the following scheme is proposed: an intermediate layer containing Ta2O5 or the like is provided between the piezoelectric single crystal substrate and the support substrate, and the intermediate layer and the support substrate are irradiated with a neutral beam to activate the surface and perform direct bonding (Patent Document 3).

[0006] Patent document 4 proposes a structure in which a multilayer film obtained by stacking multiple SiO2 layers or Ta2O5 layers is disposed between a support substrate and a piezoelectric material substrate.

[0007] Existing technical documents

[0008] Patent documents

[0009] Patent Document 1: U.S. Patent No. 7,213,314,B2

[0010] Patent Document 2: Japanese Patent Application Publication No. 2014-086400

[0011] Patent Document 3: WO2017 / 163722 A1

[0012] Patent Document 4: WO2018 / 154950 A1 Summary of the Invention

[0013] Regarding the elastic wave element in Patent Document 3, improvements in characteristics such as Q value were observed when targeting mid-frequency applications (e.g., 4G at 0.7–3.5 GHz). However, when targeting high-frequency applications (e.g., 5G at 3.5–6 GHz), the improvement in Q value was less pronounced.

[0014] Furthermore, as described in Patent Document 4, in an elastic wave element in which a multilayer film of SiO2 / Ta2O5 is inserted between a support substrate and a piezoelectric material substrate, the elastic wave leaking from the piezoelectric material substrate toward the support substrate is reflected by the multilayer film, thereby reducing losses. However, it has been found that even with this type of elastic wave element, the improvement in Q value may not be sufficient for high-frequency applications (such as 5G at 3.5–6 GHz).

[0015] The objective of this invention is to provide a bonding assembly capable of improving the Q value of an elastic wave element.

[0016] The present invention is characterized by having:

[0017] Support substrate,

[0018] piezoelectric material substrates, and

[0019] The multilayer film between the supporting substrate and the piezoelectric material substrate

[0020] The multilayer film has a stacked structure having a first layer, a second layer, a third layer, and a fourth layer in the following order.

[0021] The first and third layers comprise silicon oxide, and the second and fourth layers comprise metal oxide. The refractive index of the second layer is higher than that of the first and third layers, and the refractive index of the second layer is different from that of the fourth layer.

[0022] This invention relates to an elastic wave element, characterized in that it comprises:

[0023] The aforementioned joint, and

[0024] Electrodes disposed on the aforementioned piezoelectric material substrate.

[0025] Invention Effects

[0026] The inventors of this invention investigated the reasons why the improvement in Q value is not sufficient in the case of elastic wave elements with a multilayer film of SiO2 / Ta2O5 inserted between a support substrate and a piezoelectric material substrate, as described in Patent Document 4. As a result, it is speculated that because the quality of multilayer films suitable for mid-frequency (4G, etc.) differs from that suitable for higher frequency (5G, etc.) multilayer films, it is difficult to obtain the desired Q value in the high-frequency region.

[0027] Based on the above-mentioned speculation, the inventors of this invention have constructed a multilayer film comprising a first layer, a second layer, a third layer, and a fourth layer in the following order: the first and third layers are made of silicon oxide, and the second and fourth layers are made of metal oxides with a refractive index higher than that of silicon oxide. Furthermore, by making the refractive indices of the second and fourth layers, which contain metal oxides, different, it was found that the Q value was further improved. In particular, a high Q value was found even in the high-frequency band (5G band), thus realizing this invention. Attached Figure Description

[0028] Figure 1 In the diagram, (a) indicates a state in which a multilayer film 22 is provided on the piezoelectric material substrate 1, (b) indicates a state in which a bonding layer 4 is provided on the multilayer film 22, and (c) indicates a state in which the surface of the bonding layer 4 is activated.

[0029] Figure 2 In the diagram, (a) represents the state in which the surface of the support substrate 6 is activated, and (b) represents the joint 9 between the support substrate and the piezoelectric material substrate.

[0030] Figure 3 In the diagram, (a) represents the state in which the piezoelectric material substrate 1A of the bonding body 9A is thinned through processing, and (b) represents the state in which electrodes are provided on the bonding body 9A.

[0031] Figure 4 In the diagram, (a) represents a bond 9B obtained by directly bonding a bonding layer 4 disposed on a multilayer film and a bonding layer 14 disposed on a support substrate 6, and (b) represents an elastic wave element 10B obtained by disposing an electrode 11 on a piezoelectric material substrate 1A of the bond 9B.

[0032] Figure 5 In the diagram, (a) represents the bonding body 9C obtained by directly bonding the multilayer film 22 and the support substrate 6, and (b) represents the state in which an electrode is provided on the piezoelectric material substrate 1A of the bonding body 9C.

[0033] Figure 6 This is a graph showing the refractive index distribution obtained using the optical ellipsometric method when the refractive indices of the fourth layer and the second layer are different.

[0034] Figure 7 This is a graph showing the refractive index distribution obtained using the optical ellipsometric method when the refractive indices of the second and fourth layers are the same and relatively low.

[0035] Figure 8 This is a graph showing the refractive index distribution obtained using the optical ellipsometric method when the refractive indices of the second and fourth layers are the same and relatively high. Detailed Implementation

[0036] The present invention will now be described in detail with appropriate reference to the accompanying drawings.

[0037] like Figure 1 As shown in (a), the piezoelectric material substrate 1 has a pair of surfaces 1a and 1b. A multilayer film 22 is formed on one of the surfaces 1a. In this example, the multilayer film 22 is obtained by providing, for example, two stacked structures 2 on the piezoelectric material substrate 1. Each stacked structure 2 is such that, viewed from the piezoelectric material substrate 1 side, a first layer 3A, a second layer 7A, a third layer 3B, and a fourth layer 7B are alternately disposed. It should be noted that, in this example, the first layer, the second layer, the third layer, and the fourth layer are stacked sequentially from the piezoelectric material substrate side; however, it is also possible that, viewed from the piezoelectric material substrate 1 side, the fourth layer, the third layer, the second layer, and the first layer are stacked sequentially.

[0038] like Figure 1 As shown in (b), a bonding layer 4 can be further disposed on the surface 22a of the multilayer film 22. In this case, as Figure 1 As shown in (c), a neutral beam can be irradiated onto the surface of the bonding layer 4 as shown by arrow A to activate the surface of the bonding layer 4 and create the activated surface 5.

[0039] On the other hand, such as Figure 2 As shown in (a), a neutral beam is irradiated onto the surface of the support substrate 6 as indicated by arrow B, thereby activating the surface of the support substrate 6 and creating an activated surface 6a. Next, as... Figure 2 As shown in (b), the activated surface 5 of the bonding layer 4 and the activated surface 6a of the support substrate 6 are brought into direct contact, and pressure is applied, thereby achieving the desired effect. Figure 2 (b) shows the resulting joint 9. Arrow C indicates the joint boundary.

[0040] In a preferred embodiment, the surface 1b of the piezoelectric material substrate 1 of the bonding body 9 is further ground, such as... Figure 3 As shown in (a), the thickness of the piezoelectric material substrate 1A is reduced to obtain the bonding body 9A. 1c is the polished surface. Figure 3 In (b), a predetermined electrode 11 is formed on the polished surface 1c of the piezoelectric material substrate 1A, thereby fabricating an elastic wave element 10A.

[0041] In a preferred embodiment, a bonding layer 14 is also provided on the support substrate and directly bonded to the bonding layer on the multilayer film. Thus, a... Figure 4 (a) shows the joint 9B. The joint boundary is indicated by arrow C. Figure 4 As shown in (b), by providing an electrode 11 on the piezoelectric material substrate 1A of the bonding body, an elastic wave element 10B can be obtained.

[0042] In a preferred embodiment, the support substrate and the multilayer film are directly bonded. This results in... Figure 5 (a) shows the joint 9C. The joint boundary is indicated by arrow C. Figure 5 As shown in (b), by providing an electrode 11 on the piezoelectric material substrate 1A of the bonding body, an elastic wave element 10C can be obtained.

[0043] In this invention, the multilayer film disposed between the support substrate and the piezoelectric material substrate has a stacked structure having a first layer, a second layer, a third layer, and a fourth layer in the following order: the first and third layers comprise silicon oxide, and the second and fourth layers comprise metal oxide; the refractive index of the second layer is higher than that of the first and third layers, and the refractive indices of the second and fourth layers are different. The first, second, third, and fourth layers can be arranged sequentially from the support substrate side toward the piezoelectric material substrate side, or sequentially from the piezoelectric material substrate side toward the support substrate side.

[0044] The silicon oxide constituting the first and third layers is preferably composed of SiO2. x (1.80≤x≤2.50).

[0045] Furthermore, the metal oxides constituting the second and fourth layers are not particularly limited, but from the viewpoint of improving the Q value, hafnium oxide, tantalum oxide, or zirconium oxide are particularly preferred.

[0046] Here, the preferred composition of hafnium oxide is HfO. z (1.80≤z≤2.50). The preferred composition of tantalum oxide is Ta₂O. y (4.60≤y≤5.50). Furthermore, the preferred composition of the zirconium oxide is ZrO. z (1.80≤z≤2.50).

[0047] In a preferred embodiment, the multilayer film has multiple of the aforementioned stacked structures. This makes refractive index modulation more effective and the Q value more effectively improved. The number of stacked structures in the multilayer film is preferably two or more. However, if the number of stacked structures is too large, the constraint effect of the supporting substrate on the piezoelectric material substrate decreases; therefore, the number of stacked structures is preferably five or less, more preferably three or less.

[0048] From the perspective of this invention, the difference between the refractive index of the second layer and the refractive index of the first layer, and the difference between the refractive index of the second layer and the refractive index of the third layer, is preferably 0.2 or more, and more preferably 0.3 or more. On the other hand, the difference between the refractive index of the second layer and the refractive index of the first layer, and the difference between the refractive index of the second layer and the refractive index of the third layer, is preferably 0.8 or less, and more preferably 0.6 or less.

[0049] From the perspective of this invention, the difference between the refractive index of the fourth layer and the refractive index of the second layer is preferably 0.02 or more, more preferably 0.03 or more. On the other hand, this difference is preferably 0.10 or less.

[0050] The first and third layers comprise silicon oxide, and their refractive indices are typically between 1.40 and 1.58. Preferably, the refractive indices of the first and third layers are substantially the same; from this viewpoint, the difference between the refractive indices of the first and third layers is preferably 0.01 or less. However, by making the refractive indices of the first and third layers different, the Q value can be further improved. Therefore, from this viewpoint, it is preferable that the difference between the refractive indices of the first and third layers is 0.02 or more, more preferably 0.03 or more. However, this difference is preferably 0.10 or less.

[0051] The refractive index of each layer was measured under the following conditions.

[0052] The measurements were performed using a high-speed spectrophotometer and the following apparatus and measurement conditions.

[0053] “device”

[0054] M-2000 (manufactured by JAWoollam), rotary compensator type

[0055] "Measurement conditions"

[0056] Angle of incidence: 65, 70, 75 degrees

[0057] Measurement wavelength: 195–1680 nm

[0058] Beam diameter: 2mm×8mm

[0059] Then, perform the following analysis.

[0060] "Analytical Model"

[0061] Metal oxide / silicon oxide / metal oxide / silicon oxide / metal oxide / silicon oxide / metal oxide / silicon oxide / substrate

[0062] "Analysis Method"

[0063] The measured spectra of Δ (phase difference) and ψ (amplitude reflectivity) are compared with those calculated based on the analytical model described above. The dielectric function or film thickness is then varied to approximate the measured values ​​(Δ, ψ), and a fitting is performed. For the optical constants of each film, the values ​​obtained from the reference during monolayer film formation are set as initial values. Based on the best fit between the measured and theoretical values ​​(mean square error converges to a minimum), the wavelength dispersion of the refractive index is obtained.

[0064] The thicknesses of the first layer, the second layer, the third layer, and the fourth layer are preferably 20 nm or more, and more preferably 100 nm or more. On the other hand, if the thickness of each layer is too thick, the constraint of the supporting substrate on the piezoelectric material substrate will be weakened. Therefore, from this point of view, the thickness of each layer is preferably 300 nm or less.

[0065] The methods for forming the first, second, third, and fourth layers of a multilayer film are not limited, and examples include sputtering, chemical vapor deposition (CVD), and evaporation. For instance, in sputtering, the refractive indices of the second and fourth layers can be changed depending on the presence or absence of a bias voltage. That is, by applying an external bias voltage, the refractive index of the metal oxide layer can be relatively increased, and by not applying an external bias voltage, the refractive index of the same metal oxide layer can be decreased. Furthermore, in ion-assisted evaporation, the refractive index of each layer can be adjusted by the auxiliary energy. That is, by increasing the auxiliary energy, the refractive index of the metal oxide layer can be relatively increased, and by decreasing the auxiliary energy, the refractive index of the same metal oxide layer can be decreased.

[0066] The specific manufacturing conditions for each layer constituting the multilayer membrane depend on the cavity specifications; therefore, appropriate selection is necessary. However, in a preferred embodiment, the total pressure is set to 0.28–0.34 Pa, and the oxygen partial pressure is set to 1.2 × 10⁻⁶ Pa. -3 ~5.7×10 －2 Pa, so that the film-forming temperature is room temperature.

[0067] In a preferred embodiment, one or more bonding layers may be provided between the piezoelectric material substrate and the support substrate. Examples of materials that can be used as the bonding layer include the following.

[0068] Si (1－v) O v , Ta2O5, Al2O3, Nb2O5, TiO2.

[0069] In a more preferred embodiment, the bonding layer disposed between the support substrate and the piezoelectric material substrate is composed of Si. (1－v) O v (0.008≤v≤0.408).

[0070] This composition has a relatively low oxygen ratio compared to SiO2 (corresponding to v = 0.667). This is achieved by further sandwiching silicon oxide Si containing this composition. (1－v) O v The bonding layer can further improve the insulation of the bonding layer.

[0071] Si constituting each bonding layer (1－v) O v In the composition, if v is less than 0.008, the resistance of the bonding layer decreases. Therefore, it is preferable that v is 0.008 or more, more preferably 0.010 or more, particularly preferably 0.020 or more, and especially preferably 0.024 or more. Furthermore, by making v 0.408 or less, the bonding strength is further improved; therefore, it is preferable that v is 0.408 or less, more preferably 0.225 or less.

[0072] The thickness of each bonding layer is not particularly limited, but from the point of view of manufacturing cost, it is preferably 0.01 to 10 μm, and more preferably 0.01 to 0.5 μm.

[0073] The film formation method for each bonding layer is not limited, but examples include sputtering, chemical vapor deposition (CVD), and evaporation. Here, it is particularly preferred that when the sputtering target is set to reactive sputtering of Si, the amount of oxygen flowing into the cavity is adjusted, thereby controlling the oxygen ratio (v) of each bonding layer.

[0074] The specific manufacturing conditions for each bonding layer depend on the cavity specifications; therefore, appropriate selection is necessary. However, in a preferred embodiment, the total pressure is set to 0.28–0.34 Pa, and the oxygen partial pressure is set to 1.2 × 10⁻⁶ Pa. -3 ~5.7×10 -2 Pa keeps the film formation temperature at room temperature. Additionally, Si doped with B can be used as a Si target.

[0075] The oxygen concentration of the bonding layer was determined by EDS under the following conditions.

[0076] Measuring apparatus:

[0077] Elemental analysis was performed using an elemental analysis apparatus (JEM-ARM200F, Japan Electronics).

[0078] Measurement conditions:

[0079] For samples that have been thinned using the FIB (Focused Ion Beam) method, observations were conducted at an accelerating voltage of 200 kV.

[0080] In this invention, the support substrate can be made of single crystal or polycrystalline material. The preferred material for the support substrate is a combination of free silicon, silicon-aluminum-oxygen-nitrogen ceramic, sapphire, cordierite, andalusite, and alumina. The alumina is preferably transparent alumina.

[0081] Silicon can be monocrystalline silicon, polycrystalline silicon, or high-resistivity silicon.

[0082] Silicon-aluminum-oxygen-nitrogen ceramics are ceramics obtained by sintering a mixture of silicon nitride and aluminum oxide, and have the following composition.

[0083] Si 6－w Al w O w N 8－w

[0084] That is, the silicon-aluminum-oxygen-nitrogen ceramic has a composition in which alumina is mixed in silicon nitride, where w represents the mixing ratio of alumina. More preferably, w is 0.5 or more. Furthermore, w is more preferably 4.0 or less.

[0085] Sapphire is a single crystal with an Al₂O₃ composition, while alumina is a polycrystalline material with an Al₂O₃ composition. Cordierite is a ceramic with a composition of 2MgO·2Al₂O₃·5SiO₂. Andalusite is a ceramic with a composition ranging from 3Al₂O₃·2SiO₂ to 2Al₂O₃·SiO₂.

[0086] The substrate material of the piezoelectric material can be any material that has the required piezoelectricity, and is not limited thereto, but is preferably a single crystal with the composition of LiAO3. Here, A is one or more elements selected from the group consisting of niobium and tantalum. Therefore, LiAO3 can be lithium niobate, lithium tantalate, or a lithium niobate-lithium tantalate solid solution.

[0087] The constituent elements of the present invention will be further described below.

[0088] The application of the connector of the present invention is not particularly limited, but it can be preferably used for elastic wave elements and optical elements.

[0089] As elastic wave elements, surface wave devices, Lamb wave elements, and thin-film resonators (FBARs) are known. For example, an elastic surface wave device has an IDT (Interdigital Transducer) electrode (also called a comb electrode or curtain electrode) on the input side to excite the elastic surface wave and an IDT electrode on the output side to receive the elastic surface wave, disposed on the surface of a piezoelectric material substrate. If a high-frequency signal is applied to the IDT electrode on the input side, an electric field is generated between the electrodes, exciting the elastic surface wave, which then propagates on the piezoelectric material substrate. Furthermore, the propagating elastic surface wave can be output as an electrical signal from the IDT electrode on the output side, which is positioned in the propagation direction.

[0090] A metal film can be present on the bottom surface of the piezoelectric material substrate. When manufacturing a Lamb wave element as an elastic wave device, the metal film increases the electromechanical coupling coefficient near the back surface of the piezoelectric material substrate. In this case, the Lamb wave element has the following structure: a comb-tooth electrode is formed on the surface of the piezoelectric material substrate, and the metal film of the piezoelectric material substrate is exposed by a cavity provided in the support substrate. Examples of materials for such a metal film include aluminum, aluminum alloy, copper, and gold. It should be noted that when manufacturing a Lamb wave element, a composite substrate having a piezoelectric material layer without a metal film on the bottom surface can be used.

[0091] Furthermore, a metal film and an insulating film can be formed on the bottom surface of the piezoelectric material substrate. When manufacturing a thin-film resonator as an elastic wave device, the metal film functions as an electrode. In this case, the thin-film resonator has the following structure: electrodes are formed on the surface and back of the piezoelectric material substrate, and the metal film of the piezoelectric material substrate is exposed by making the insulating film a cavity. Examples of materials for such metal films include molybdenum, ruthenium, tungsten, chromium, and aluminum. Examples of materials for the insulating film include silicon dioxide, phosphosilicate glass, and borosilicate glass.

[0092] Furthermore, examples of optical elements include optical switching elements, wavelength conversion elements, and optical modulation elements. Additionally, periodic polarization reversal structures can be formed in piezoelectric material substrates.

[0093] The present invention relates to an elastic wave element. When the piezoelectric material substrate is made of lithium tantalate, it is preferable to use a piezoelectric material substrate that is rotated 123 to 133° (e.g., 128°) from the Y-axis to the Z-axis with the X-axis as the center of the propagation direction of the elastic surface wave. This is because the propagation loss is small.

[0094] Furthermore, when the piezoelectric material substrate includes lithium niobate, a piezoelectric material substrate rotated 86 to 94° (e.g., 90°) from the Y-axis to the Z-axis with the X-axis as the center of the propagation direction of the elastic surface wave is used, is preferred because it has low propagation loss. Moreover, the size of the piezoelectric material substrate is not particularly limited, for example, a diameter of 50 to 150 mm and a thickness of 0.2 to 60 μm.

[0095] To obtain the assembly of the present invention, the following method is preferred.

[0096] First, the surfaces to be bonded (the surface of the multilayer film, the surface of the bonding layer, the surface of the piezoelectric material substrate, and the surface of the support substrate) are planarized to obtain a flat surface. Methods for planarizing each surface include lapping and chemical mechanical polishing (CMP). Furthermore, it is preferable that the flat surface has a Ra ≤ 1 nm, and more preferably, a Ra ≤ 0.3 nm.

[0097] Next, each surface of each bonding layer is cleaned to remove abrasive residue and process-degraded layers. Surface cleaning methods include wet cleaning, dry cleaning, and brushing; brushing is preferred for a simple and efficient way to obtain a clean surface. In this case, it is particularly preferred to use Sunwash LH540 as the cleaning solution, and then use a brushing machine to clean with a mixture of acetone and IPA.

[0098] Next, each bonding layer is activated by irradiating it with a neutral beam.

[0099] When performing surface activation using a neutral beam, it is preferable to use the apparatus described in Patent Document 2 to generate the neutral beam for irradiation. Specifically, a saddle-type high-speed atomic beam source is used as the beam source. Then, an inert gas is introduced into the cavity, and a high voltage is applied to the electrodes from a DC power supply. Thereby, utilizing the saddle-type electric field generated between the electrodes (positive electrode) and the casing (negative electrode), electrons (e) move and generate a beam of atoms and ions produced by the inert gas. In the beam reaching the grid, the ion beam is neutralized at the grid, thus a beam of neutral atoms is emitted from the high-speed atomic beam source. The atomic species constituting the beam are preferably inert gases (argon, nitrogen, etc.).

[0100] When activating by beam irradiation, the preferred voltage is 0.5–2.0 kV, and the preferred current is 50–200 mA.

[0101] Next, in a vacuum atmosphere, the activated mating surfaces are brought into contact with each other and joined. The temperature at this time is room temperature, specifically, preferably below 40°C, more preferably below 30°C. Furthermore, the joining temperature is particularly preferably between 20°C and 25°C. The joining pressure is preferably 100–20000 N.

[0102] Example

[0103] (Preliminary Experiment)

[0104] First, a silicon oxide layer and a hafnium oxide layer were formed on a piezoelectric material substrate, and the film formation conditions for each layer were recorded as follows. However, in order to adjust the refractive index of the hafnium oxide layer, the bias voltage was adjusted as follows.

[0105] Silicon oxide layer (SiO2): 150 nm thick, refractive index 1.52

[0106] Hafnium oxide layer (HfO2): Bias voltage 100V:

[0107] Thickness 150nm, refractive index 2.07

[0108] Hafnium oxide layer (HfO2): Bias voltage 200V:

[0109] Thickness 150nm, refractive index 2.12

[0110] Hafnium oxide layer (HfO2): Bias voltage 400V:

[0111] Thickness 150nm, refractive index 2.15

[0112] (Example A1)

[0113] Next, according to the reference Figures 1-3 The method described was used to trial-produce an elastic surface wave element.

[0114] Specifically, a lithium tantalate substrate (LT substrate) with an OF section, a diameter of 4 inches, and a thickness of 250 μm was used as the piezoelectric material substrate 1. The LT substrate used a 128° Y-cut X-propagation LT substrate with the surface wave (SAW) propagation direction as X and the cutting angle as the rotating Y-cutting plate. The surface 1a of the piezoelectric material substrate 1 was mirror-polished to achieve an arithmetic mean roughness Ra of 0.3 nm. Ra was measured using an atomic force microscope (AFM) within a 10 μm × 10 μm field of view.

[0115] Next, two stacked structures 2 are sequentially formed on the piezoelectric material substrate 1 by sputtering to obtain a multilayer film 22. However, on the piezoelectric material substrate, a first layer containing silicon oxide is formed first, followed by a second, third, and fourth layer formed sequentially. The thickness and refractive index of each layer are adjusted as follows based on preliminary experiments.

[0116] First layer (SiO2): 150nm thickness, refractive index 1.53

[0117] Second layer (HfO2): 150 nm thick, refractive index 2.12

[0118] Third layer (SiO2): 150nm thickness, refractive index 1.53

[0119] Fourth layer (HfO2): 150 nm thick, refractive index 2.07

[0120] Next, a bonding layer 4 is formed on the multilayer film 2. Specifically, a direct current sputtering method is used, and boron-doped Si is used as the target. Oxygen is introduced as an oxygen source. At this time, the total pressure and oxygen partial pressure of the atmosphere inside the chamber are adjusted by regulating the amount of oxygen introduced. The thickness of the bonding layer 4 is 50 nm. The arithmetic mean roughness Ra of the surface of the bonding layer 4 is 0.2–0.6 nm. Next, the bonding layer 4 is subjected to chemical mechanical polishing (CMP) to reduce the film thickness to 80–190 nm and the Ra value to 0.08–0.4 nm.

[0121] On the other hand, as the support substrate 6, a silicon-containing support substrate 6 with an orientation plane (OF) portion, a diameter of 4 inches, and a thickness of 500 μm is prepared. The surface of the support substrate 6 is finished by chemical mechanical polishing (CMP), and the arithmetic mean roughness Ra reaches 0.2 nm.

[0122] Next, a neutral beam is irradiated onto the surface of the bonding layer 4 and the surface of the supporting substrate 6, i.e., the Si substrate, to activate the surface and perform direct bonding.

[0123] Specifically, the surfaces of the bonding layer 4 and the supporting substrate 6 are cleaned to remove dirt, and then introduced into the vacuum chamber. A vacuum is then applied until 10... -6 After exposure to DAP, each surface was irradiated with a high-speed atomic beam for 120 seconds (accelerating voltage 1 kV, Ar flow rate 27 sccm). Next, the irradiated surface (activation surface) of the bonding layer 4 and the activation surface of the support substrate 6 were brought into contact, and bonding was performed by applying a pressure of 10000 N for 2 minutes. The resulting bonded bodies were then heated at 100°C for 20 hours. The bonded bodies were measured using optical ellipsometric analysis to obtain… Figure 6 The refractive index chart shown.

[0124] Next, the surface of the piezoelectric material substrate 1 was ground and polished to reduce its thickness from the original 250 μm to 1 μm. Then, an electrode pattern for measurement was formed to obtain an elastic surface wave element. The Q value at a frequency of 5.5 GHz was then measured, and the results are shown in Table 1.

[0125] The Q value was determined as follows.

[0126] A surface elastic wave resonator was fabricated on a wafer, and its frequency response was measured using a network analyzer. Based on the obtained frequency response, the resonant frequency f was calculated. r and its half-value width Δf r Find f r / Δf r Thus, the Q value is obtained.

[0127] (Example A2)

[0128] The same conjugate and elastic surface wave element were obtained as in Example A1. The layers constituting the multilayer film were adjusted as follows. The Q value of the obtained element was measured at a frequency of 5.5 GHz, and is shown in Table 1.

[0129] First layer (SiO2): 150nm thickness, refractive index 1.53

[0130] Second layer (HfO2): 150nm thickness, refractive index 2.15

[0131] Third layer (SiO2): 150nm thickness, refractive index 1.53

[0132] Fourth layer (HfO2): 150 nm thick, refractive index 2.05

[0133] (Comparative Example A1)

[0134] The same as in Example A1, a bond and an elastic surface wave element were obtained. The layers constituting the multilayer film were adjusted as follows. The obtained bond was measured using optical ellipsometrics, and the results were obtained. Figure 7 The refractive index chart is shown. Additionally, the Q value of the obtained component was measured at a frequency of 5.5 GHz, and is shown in Table 1.

[0135] First layer (SiO2): 150nm thickness, refractive index 1.53

[0136] Second layer (HfO2): 150nm thickness, refractive index 2.07

[0137] Third layer (SiO2): 150nm thickness, refractive index 1.53

[0138] Fourth layer (HfO2): 150 nm thick, refractive index 2.07

[0139] (Comparative Example A2)

[0140] The same as in Example A1, a bond and an elastic surface wave element were obtained. The layers constituting the multilayer film were adjusted as follows. The obtained bond was measured using optical ellipsometrics, and the results were obtained. Figure 8 The refractive index chart is shown. Additionally, the Q value of the obtained component was measured at a frequency of 5.5 GHz, and is shown in Table 1.

[0141] First layer (SiO2): 150nm thickness, refractive index 1.53

[0142] Second layer (HfO2): 150 nm thick, refractive index 2.12

[0143] Third layer (SiO2): 150nm thickness, refractive index 1.53

[0144] Fourth layer (HfO2): 150 nm thick, refractive index 2.12

[0145] [Table 1]

[0146]

[0147] As shown in Table 1, in Comparative Example A1, the refractive indices of the second and fourth layers were adjusted to be relatively low, such as... Figure 7 As shown, the refractive indices of the second and fourth layers are similar to those obtained in the preliminary experiment.

[0148] In Comparative Example A2, the refractive indices of the second and fourth layers were adjusted to be relatively high, such as... Figure 8 As shown, the refractive indices of the second and fourth layers are the same as those obtained in the preliminary experiment. Furthermore, the Q value is the same as that in Comparative Example A1, and no effect from increasing the refractive index was observed.

[0149] In Example A1, we obtained Figure 6 The refractive index distribution is shown.

[0150] Furthermore, as shown in Table 1, it was determined that the Q value was 20% higher than the baseline value.

[0151] In Example A2, although the refractive indices of the second and fourth layers were changed, it was observed that... Figure 6 Similar refractive index modulation is observed along the thickness direction.

[0152] Furthermore, as shown in Table 1, it is determined that the Q value has significantly improved compared to the baseline value.

[0153] (Examples B1, B2; Comparative Examples B1, B2)

[0154] In Examples A1, A2, and Comparative Examples A1, A2, the material of the second layer was changed from HfO2 to Ta2O5. Then, the Q value of the obtained element was measured, and the results were the same as those in Examples A1, A2, and Comparative Examples A1, A2.

[0155] (Examples C1, C2; Comparative Examples C1, C2)

[0156] In Examples A1, A2, and Comparative Examples A1, A2, the material of the second layer was changed from HfO2 to ZrO2. Then, the Q value of the obtained component was measured, and the results were the same as those in Examples A1, A2, and Comparative Examples A1, A2.

Claims

1. A joint, characterized in that, have: Support substrate, piezoelectric material substrates, and The multilayer film between the supporting substrate and the piezoelectric material substrate The multilayer film has a stacked structure having a first layer, a second layer, a third layer, and a fourth layer in the following order. The first and third layers comprise silicon oxide, and the second and fourth layers comprise metal oxide. The refractive index of the second layer is higher than that of the first and third layers, and the refractive index of the second layer is different from that of the fourth layer. The difference between the refractive index of the second layer and the refractive index of the fourth layer is greater than 0.02 and less than 0.

10.

2. The joint according to claim 1, characterized in that, The multilayer film has multiple of the aforementioned stacked structures.

3. The joint according to claim 1, characterized in that, The metal oxide is hafnium oxide, tantalum oxide, or zirconium oxide.

4. The joint according to any one of claims 1 to 3, characterized in that, The difference between the refractive index of the second layer and the refractive index of the first layer is 0.3 to 0.

8.

5. The joint according to any one of claims 1 to 3, characterized in that, The thicknesses of the first layer, the second layer, the third layer, and the fourth layer are respectively above 20 nm and below 300 nm.

6. The joint according to any one of claims 1 to 3, characterized in that, A silicon-based material is disposed between the piezoelectric material substrate and the supporting substrate. （1－v） O v The bonding layer, wherein 0.008≤v≤0.

408.

7. An elastic wave element, characterized in that, have: The joint as described in any one of claims 1 to 6, and Electrodes disposed on the piezoelectric material substrate.

8. The elastic wave element according to claim 7, characterized in that, The elastic wave element is used for elastic waves with a frequency of 3.5 to 6 GHz.

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