Bonded body of piezoelectric material substrate and supporting substrate

Abstract

The present invention provides a structure capable of suppressing parasitic waves that cannot be suppressed by controlling the surface shape of the bonding surface of the piezoelectric material substrate or the supporting substrate of the bonded body. The bonded body comprises: a supporting substrate; a piezoelectric material substrate formed of a material selected from the group consisting of lithium niobate, lithium tantalate, and lithium niobate-lithium tantalate; and a bonding layer that bonds the supporting substrate and the piezoelectric material substrate and contacts the main surface of the piezoelectric material substrate. At least one of the bonding surface of the supporting substrate and the bonding surface of the piezoelectric material substrate is measured using an X-ray reflectivity method. In this case, when the signal intensity during total reflection is set to 1, the relative intensity I of the reflected light from the bonding surface is 1.0×10 －4 Above 1.0×10 －1 In the following range, the approximation is performed by the following formula (1). [Formula 1] I = a(2θ) ‑b ·····(1)(θ is the incident angle to the bonding surface, a is 1.0×10 －5 Above 2.0×10 －3 Below, b is 5.0 or more and 9.0 or less).

Description

Technical Field

[0001] The present invention relates to a bonded structure of a piezoelectric material substrate and a supporting substrate, and an elastic wave element. Background Art

[0002] Surface acoustic wave filters, made by bonding lithium tantalate and sapphire via a silicon oxide layer, are known to generate bulk waves at the bonding interface, leading to unwanted responses in the passband and high-frequency range. To prevent these responses, a method has been proposed that introduces roughness at the bonding interface to scatter the bulk waves and suppress the unwanted responses (Patent Documents 1 and 2).

[0003] Patent Document 1 stipulates that when roughening a bonding surface, the geometric specifications for the roughened surface are to set the ratio of the average length RSm of the elements at the cross-sectional curve of the uneven structure of the roughened surface to the wavelength λ of the surface acoustic wave to be 0.2 or more and 7.0 or less. Furthermore, the arithmetic mean roughness Ra at the cross-sectional curve of the uneven structure is to be 100 nm or more. Meanwhile, Patent Document 2 specifies the height difference of the roughened surface.

[0004] Prior art literature

[0005] Patent Literature

[0006] Patent Document 1: Japanese Patent No. 6250856

[0007] Patent Document 2: U.S. Patent Application Publication No. 2017-063333 Summary of the Invention

[0008] Conventionally, parasitic waves have been suppressed by measuring the surface roughness (e.g., RSm, Ra) of the bonding surface between the support substrate and the piezoelectric material substrate and controlling them to a significant level. However, even with the same RSm on the bonding surface, parasitic waves may not be suppressed. This indicates that simply controlling the surface roughness of the bonding surface is not enough to suppress parasitic waves.

[0009] An object of the present invention is to provide a new structure capable of suppressing spurious waves that cannot be suppressed by controlling the surface shape of the bonding surface of a piezoelectric material substrate or a support substrate of a bonded structure.

[0010] The present invention is a conjugate comprising:

[0011] a supporting substrate;

[0012] a piezoelectric material substrate formed of a material selected from the group consisting of lithium niobate, lithium tantalate, and lithium niobate-lithium tantalate; and

[0013] a bonding layer that bonds the support substrate and the piezoelectric material substrate and is in contact with the main surface of the piezoelectric material substrate;

[0014] The conjugate is characterized in that

[0015] At least one of the bonding surface of the support substrate and the bonding surface of the piezoelectric material substrate is measured by X-ray reflectivity method. When the signal intensity during total reflection is set to 1, the relative intensity I of the reflected light from the bonding surface is 1.0×10 －4 Above 1.0×10 －1 In the following range, approximation is performed by the following formula (1).

[0016]

Mathematical formula 1

[0017] I=a(2θ) -b ·····(1)

[0018] (In formula (1),

[0019] θ is the incident angle of X-ray relative to the bonding surface,

[0020] a is 1.0×10 －5 Above 2.0×10 －3 the following,

[0021] b is 5.0 or more and 9.0 or less.

[0022] Effects of the Invention

[0023] The inventors of the present invention attempted to mirror-polish the bonding surfaces of a supporting substrate or a piezoelectric material substrate, then roughen them through mechanical processing. The resulting microstructures were then carefully observed and analyzed. The results revealed that the mechanically processed bonding surfaces exhibited minute defects and film degradation that could not be measured based on surface irregularities. These measurement results indicate that the parasitic wave suppression effect should be controlled not by surface irregularities but by the effective crystallographic and geometric properties of the surface regions of the piezoelectric material substrate and the bonding layer.

[0024] Based on the above findings, the inventors of the present invention have studied various processing methods and methods for measuring joining surfaces, and during this process, they have focused on the X-ray reflectivity method (XRR method, X-ray Reflection).

[0025] The X-ray reflectivity method involves directing X-rays at a very shallow angle onto the sample surface and measuring the X-ray intensity curve of the incident angle and the reflected light in the specular direction. This measured curve is compared with simulation results, and the simulation parameters are optimized to determine the sample's film thickness and density. In other words, the X-ray reflectivity method originally measured the film thickness and density of thin films by reflecting X-rays from thin films. This means that the light reflected from a thin film not only reveals the surface irregularities of the film, but also provides information about the film's depth (thickness and density).

[0026] The inventors of the present invention applied the X-ray reflectivity method to the bonding surfaces of piezoelectric material substrates or supporting substrates after roughening, thereby obtaining information on the deterioration and density changes in the areas near the surface of these bonding surfaces, and studied the relationship between this information and the effect of suppressing parasitic waves.

[0027] That is, the bonding surface of the piezoelectric material substrate or the supporting substrate is roughened. Then, the X-ray reflectivity method is used to obtain information on the crystal state of the surface area of ​​the bonding surface. Specifically, the X-ray is incident on the bonding surface at a very low angle, and the reflected light is measured. Here, the incident angle of the X-ray is set to θ, and the relative intensity I of the reflected light when θ is gradually changed from 0° is recorded. At this time, the relative intensity I is the relative intensity when the signal intensity at the time of total reflection is set to 1. It is known that the relative intensity I is equal to 1×10 －4 However, it was found that when the bonding surface is a flat mirror surface, parasitic waves are generated, and even when the surface is roughened, the relative intensity is close to 1×10 －4 When the proportional coefficient is , the parasitic waves cannot be suppressed.

[0028] Therefore, the inventors of the present invention used X-ray reflectivity to measure the degree of parasitic wave suppression on the bonding surfaces subjected to various roughening treatments. The results showed that when the relative intensity I of the reflected light from the bonding surface was 1.0×10 －4 Above 1.0×10 －1 Within the following range, it can be approximated by formula (1).

[0029] That is, for example, Figure 1 As shown schematically, it can be seen that when the incident angle θ is between 0.0 and 0.5°, the relative intensity I stays at about 1, then decreases sharply, and then in the area surrounded by the quadrilateral (relative intensity I is 1.0×10 －4 Above 1.0×10 －1If the relative intensity is lower than this range, it forms a roughly straight line when viewed on a logarithmic scale.

[0030]

Mathematical formula 1

[0031] I=a(2θ) -b ·····(1)

[0032] Here, the index b can be 5.0 or more, the coefficient a = 1.0 × 10 －5 ~2.0×10 －3 This means that the relative intensity I decreases more dramatically with increasing angle of incidence θ than when the bonding surface is a mirror surface. This also means that the surface region of the bonding surface is undergoing crystallization degradation or that defects other than fine surface irregularities have occurred. In this case, it was found that parasitic waves are suppressed.

[0033] If the index b exceeds 9.0, spurious waves will increase instead, so b must be set to 9.0 or less. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] Figure 1 It is a model curve showing the relationship between the incident angle θ and the relative density I of the reflected light.

[0035] Figure 2 In the figure, (a) shows a state where the bonding surface 1a of the support substrate 1 is processed, (b) shows a state where a bonding layer 2 is provided on the bonding surface 1a of the support substrate 1, and (c) shows a state where the bonding surface of the bonding layer 2 is activated by irradiating the bonding surface with plasma B.

[0036] Figure 3 In FIG. 1 , (a) shows the piezoelectric material substrate 3 , and (b) shows a state in which the bonding surface 3 b of the piezoelectric material substrate 3 is activated.

[0037] Figure 4 In the drawings, (a) shows a bonded structure 5 of a support substrate 1 and a piezoelectric substrate 3 , (b) shows a state where the piezoelectric substrate 3A of the bonded structure 5A is thinned by processing, and (c) shows an elastic wave element 6 .

[0038] Figure 5 In FIG. 1 , (a) shows the piezoelectric material substrate 3 , and (b) shows a state in which the bonding surface 12 a of the intermediate layer 12 on the piezoelectric material substrate 3 is activated.

[0039] Figure 6 , (a) shows a bonded structure 15 of the support substrate 1 and the piezoelectric substrate 3 , (b) shows a state where the piezoelectric substrate 3A of the bonded structure 15A is thinned by processing, and (c) shows the elastic wave element 16 .

[0040] Figure 7 Graphs showing the reflection characteristics of the surface acoustic wave device according to the embodiment of the present invention.

[0041] Figure 8 is a graph showing the reflection characteristics of a surface acoustic wave device according to a comparative example. DETAILED DESCRIPTION

[0042] Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings as appropriate.

[0043] First, if Figure 2 As shown in (a), a supporting substrate 1 having a pair of main surfaces 1a and 1b is prepared. Next, the main surface (bonding surface) 1a is subjected to processing A to make it rough. Figure 2 As shown in (b), a bonding layer 2 is formed on the main surface 1a of the support substrate 1. In order to obtain a mirror surface, the surface 2a of the bonding layer 2 is subjected to CMP polishing. Figure 2 As shown in (c), plasma is irradiated onto the surface 2a of the bonding layer 2 as indicated by arrow B, thereby obtaining a bonding surface 2b after surface activation.

[0044] On the other hand, Figure 3 As shown in (a), a piezoelectric material substrate 3 having a principal surface 3a is prepared. Next, the principal surface of the piezoelectric material substrate 3 is irradiated with plasma as indicated by arrow C to activate the surface, thereby forming an activated bonding surface 3b.

[0045] Next, the activated bonding surface 2b of the bonding layer 2 on the support substrate and the activated bonding surface 3b of the piezoelectric material substrate 3 are brought into contact with each other and directly bonded to obtain a bonded structure. Figure 4 (a) shows a joined body 5.

[0046] In this state, electrodes can be provided on the piezoelectric material substrate 3. However, it is preferable that Figure 4 As shown in (b), the main surface 3c of the piezoelectric material substrate 3 is processed to make the substrate 3 thinner, forming a thinned piezoelectric material substrate 3A, and making a bonded body 5A. 9 is the processed surface. Figure 4 As shown in (c), predetermined electrodes 10 are formed on the processed surface 9 of the piezoelectric material substrate 3A of the bonded body 5A, thereby obtaining the elastic wave element 6.

[0047] In addition, an intermediate layer may be provided between the bonding layer 2 and the piezoelectric material substrate 3 . Figure 5 、 Figure 6 This relates to the embodiment.

[0048] In this example, if Figure 2As shown in (a), a supporting substrate 1 having a pair of main surfaces 1a and 1b is prepared. Next, the main surface (bonding surface) 1a is subjected to processing A to make it rough. Figure 2 As shown in (b), a bonding layer 2 is formed on the main surface 1a of the support substrate 1. In order to obtain a mirror surface, the surface of the bonding layer 2 is subjected to CMP polishing. Figure 2 As shown in (c), plasma is irradiated onto the bonding surface of the bonding layer 2 as indicated by arrow B, thereby obtaining a bonding surface 2b after surface activation.

[0049] On the other hand, Figure 5 As shown in (a), a piezoelectric material substrate 3 having a main surface 3a is prepared. Figure 5 As shown in (b), an intermediate layer 12 is formed on the main surface (bonding surface) 3a of the piezoelectric material substrate 3, and the surface of the intermediate layer 12 is activated by irradiating plasma as shown by arrow C, thereby forming an activated bonding surface 12a.

[0050] Next, the activated bonding surface 2b of the bonding layer 2 on the support substrate and the activated bonding surface 12a of the intermediate layer 12 on the piezoelectric material substrate 3 are brought into contact and directly bonded to obtain a Figure 6 (a) shows a joined body 15.

[0051] In this state, electrodes can be provided on the piezoelectric material substrate 3. However, it is preferable that Figure 6 As shown in (b), the main surface 3c of the piezoelectric material substrate 3 is processed to make the substrate 3 thinner, forming a thinned piezoelectric material substrate 3A, and making a bonded body 15A. 9 is the processed surface. Next, as Figure 6 As shown in (c), predetermined electrodes 10 are formed on the processed surface 9 of the piezoelectric material substrate 3A of the bonded body 15A, thereby obtaining an elastic wave element 16.

[0052] Alternatively, after forming the bonding layer 2, the intermediate layer 12 may be formed on the bonding layer 2. In this case, the surface of the intermediate layer 12 is subjected to CMP processing to obtain a bonding surface (mirror surface). The obtained bonding surface is irradiated with plasma for activation. Next, the surface of the supporting substrate is plasma activated and then directly bonded to the bonding surface of the intermediate layer.

[0053] In the present invention, b is set to be 5.0 or more. In addition, b is set to be 9.0 or less, but more preferably 7.0 or less. In addition, in the present invention, a is set to be 1.0×10 －5 However, it is preferably 1.0×10 －4 In addition, a is 2.0×10 －3 However, it is more preferably 1.0×10 －3 the following.

[0054] In a preferred embodiment, a and b satisfy the following relational expression (2).

[0055] -0.713ln(a)+0.5≤b≤-0.713ln(a)+0.7…(2)

[0056] In a more preferred embodiment, a and b satisfy the following relational expression (3).

[0057] b=-0.713ln(a)+0.6…(3)

[0058] The measurement conditions of the X-ray reflectivity method are as follows.

[0059] Measuring device: SmartLab manufactured by Rigaku

[0060] Measurement conditions

[0061] X-ray generating part: cathode Cu

[0062] : Output 45kV 200mA

[0063] Detection unit: semiconductor detector

[0064] Incident optical system: Ge(111) asymmetric beam compression crystal

[0065] Solar slit: incident side

[0066] :Light receiving side 5.0゜

[0067] Slit: incident side IS = 0.05 (mm)

[0068] :Length limit 5(mm)

[0069] :Light receiving side RS1=0.1RS2=0.1(mm)

[0070] Scanning conditions: Scanning axis 2θ / ω

[0071] Scan mode: continuous scan

[0072] Scanning speed: 0.2° / min

[0073] Stride: 0.002°

[0074] Resolution range: 0.3~3.0゜

[0075] In order to control the measurement results of the X-ray reflectivity method of the bonding surface of the piezoelectric material substrate and the bonding surface of the support substrate as described above, it is preferable to adopt the following processing method.

[0076] Examples of the surface roughening method include grinding using a grinding stone, machining such as sandblasting using a fine medium such as alumina or silicon nitride, and ion beam processing in which ions are collided at high speed.

[0077] Hereinafter, each component of the present invention will be described in sequence.

[0078] The material of support substrate 1 is not particularly limited, but is preferably formed of a material selected from the group consisting of silicon, quartz crystal, sialon, mullite, sapphire, and translucent alumina. This can further improve the frequency-temperature characteristics of acoustic wave elements 6 and 16.

[0079] The method for forming the bonding layer and the intermediate layer is not limited, and examples thereof include sputtering, chemical vapor deposition (CVD), and vapor deposition.

[0080] The material of the bonding layer 2 is not particularly limited as long as it can be surface activated. A metal oxide film is preferred, and a material selected from the group consisting of silicon oxide, silicon nitride, aluminum nitride, aluminum oxide, tantalum pentoxide, mullite, niobium pentoxide, and titanium oxide is particularly preferred. The surface activation method can be selected appropriately depending on the material of the bonding layer. Examples of surface activation methods include plasma activation and FAB (Ar atomic beam).

[0081] The material of the intermediate layer 12 is not particularly limited as long as it can undergo surface activation treatment. A metal oxide film is preferred, and a material selected from the group consisting of silicon oxide, silicon nitride, aluminum nitride, aluminum oxide, tantalum pentoxide, mullite, niobium pentoxide, and titanium oxide is particularly preferred. However, the intermediate layer is preferably made of a different material than the bonding layer.

[0082] From the perspective of the present invention, the thickness of the bonding layer 2 is preferably 0.05 μm or greater, more preferably 0.1 μm or greater, and particularly preferably 0.2 μm or greater. The thickness of the bonding layer 2 is preferably 3 μm or less, more preferably 2 μm or less, and even more preferably 1 μm or less.

[0083] The piezoelectric material substrate 3 used in the present invention is made of lithium tantalate (LT) single crystal, lithium niobate (LN) single crystal, or a lithium niobate-lithium tantalate solid solution. These materials exhibit high elastic wave propagation speeds and high electromechanical coupling coefficients, making them suitable for high-frequency and broadband surface acoustic wave devices.

[0084] In addition, the normal direction of the main surface 3a of the piezoelectric material substrate 3 is not particularly limited. For example, when the piezoelectric material substrate 3 is formed by LT, a piezoelectric material substrate with the propagation direction of the elastic surface wave, that is, the X-axis as the center and rotated 32 to 55 degrees from the Y-axis to the Z-axis, and expressed as Euler angles (180°, 58 to 35°, 180°) is used. This has a smaller propagation loss and is therefore preferred. When the piezoelectric material substrate 3 is formed of LN, (a) a piezoelectric material substrate with an orientation expressed as (0°, 37.8°, 0°) rotated 37.8° from the Z axis to the -Y axis, centered on the surface acoustic wave propagation direction, is preferably used. This increases the electromechanical coupling coefficient and is therefore preferable. Alternatively, (i) a piezoelectric material substrate with an orientation expressed as (180°, 50° to 25°, 180°) rotated 40° to 65° from the Y axis to the Z axis, centered on the surface acoustic wave propagation direction, is preferably used. This achieves a high acoustic velocity and is therefore preferable. The size of the piezoelectric material substrate 3 is not particularly limited, but may be, for example, 100 to 200 mm in diameter and 0.15 to 1 μm in thickness.

[0085] Next, plasma is irradiated at 150° C. or less onto the bonding surfaces of the bonding layer 2 on the support substrate 1, the bonding surface of the piezoelectric material substrate 3, and the bonding surface of the intermediate layer 12 on the piezoelectric material substrate 3 to activate the bonding surfaces. From the perspective of the present invention, irradiation with nitrogen plasma is preferred, but the bonded product of the present invention can also be obtained by irradiation with oxygen plasma.

[0086] The pressure during surface activation is preferably 100 Pa or less, more preferably 80 Pa or less. The atmosphere may be nitrogen alone, oxygen alone, or a mixture of nitrogen and oxygen.

[0087] The temperature during plasma irradiation is set to 150°C or lower. This allows a bonded body with high bonding strength and no degradation of crystallinity to be obtained. From this viewpoint, the temperature during plasma irradiation is set to 150°C or lower, more preferably 100°C or lower.

[0088] The energy during plasma irradiation is preferably 30 to 150 W. The product of the energy during plasma irradiation and the irradiation time is preferably 0.12 to 1.0 Wh.

[0089] The bonding surface of the piezoelectric material substrate after the plasma treatment and the bonding surface of the bonding layer are brought into contact with each other at room temperature. In this case, the treatment may be performed in a vacuum, but more preferably, the contact is carried out in the atmosphere.

[0090] When surface activation is performed using an argon atom beam, it is preferred to use a device such as that described in Japanese Patent Application Laid-Open No. 2014-086400 to generate an argon atom beam for irradiation. That is, as a beam source, a saddle-type high-speed atom beam source is used. Then, an inert gas is introduced into the chamber, and a high voltage is applied to the electrode from a DC power supply. Thus, the saddle-type electric field generated between the electrode (positive electrode) and the shell (negative electrode) is used to move the electrons e, thereby generating a beam of argon atoms and ions. The ion beam in the beam reaching the grid is neutralized on the grid, and therefore, a beam of argon atoms is emitted from the high-speed atom beam source. The voltage for activation by beam irradiation is preferably 0.5 to 2.0 kV, and the current is preferably 50 to 200 mA.

[0091] In a preferred embodiment, the bonding surface of the bonding layer on the support substrate, the bonding surface of the piezoelectric material substrate, and the bonding surface of the intermediate layer on the piezoelectric material substrate are planarized before the surface activation treatment. Methods for planarizing each bonding surface include lapping (lap) and chemical mechanical polishing (CMP). Furthermore, for flat surfaces, Ra is preferably ≤ 1 nm, and more preferably 0.3 nm or less.

[0092] Next, the bonding surface of the bonding layer on the support substrate is brought into contact with the bonding surface of the piezoelectric material substrate 3 or the bonding surface of the intermediate layer to achieve bonding. Annealing is then preferably performed to enhance bonding strength. The annealing temperature is preferably between 100°C and 300°C.

[0093] The junction bodies 5, 5A, 15, and 15A of the present invention can be preferably used in the elastic wave devices 6 and 16. That is, the elastic wave device includes the junction body of the present invention and electrodes provided on a piezoelectric material substrate.

[0094] Specifically, surface acoustic wave devices, Lamb wave devices, and thin film resonators (FBARs) are known as acoustic wave elements 6 and 16. For example, a surface acoustic wave device is a device in which an IDT (Interdigital Transducer) electrode (also known as a comb electrode or curtain electrode) is provided on the surface of a piezoelectric material substrate. It excites surface acoustic waves on the input side, and receives them on the output side. When a high-frequency signal is applied to the input-side IDT electrode, an electric field is generated between the electrodes, exciting surface acoustic waves that propagate along the piezoelectric material substrate. The propagated surface acoustic waves can then be output as electrical signals from the output-side IDT electrode, which is located in the direction of propagation.

[0095] The material constituting the electrode 10 on the piezoelectric material substrate 3A is preferably aluminum, an aluminum alloy, copper, or gold, and more preferably aluminum or an aluminum alloy. The aluminum alloy is preferably one in which 0.3 to 5% by weight of Cu is mixed with Al. In this case, Ti, Mg, Ni, Mo, or Ta can be used in place of Cu.

[0096] Example

[0097] (Example 1)

[0098] According to the reference Figures 2 to 4 Method of explanation, production Figure 4 (c) shows the elastic wave element 6.

[0099] Specifically, one principal surface 3c of a 250μm-thick 42Y-cut X-propagation LiTaO3 substrate (piezoelectric material substrate) 3 was polished to a mirror finish, and the other principal surface 3a was lapped using GC#1000. Separately, a 0.23mm-thick, high-resistance (>2kΩ·cm) Si(100) substrate (support substrate) 1 was prepared. Both substrates had a size of 150mm.

[0100] Next, the bonding surface of the support substrate is roughened. In this embodiment, a #6000 grinding stone is used for the grinding process. The grinding depth is approximately 3 μm.

[0101] The spectrum of the bonding surface of the support substrate was obtained by X-ray reflectivity method, and the relative signal intensity was approximated by formula (1). As a result, a=9.2×10 －4 , b=5.55.

[0102] Next, a 0.7 μm thick silicon oxide film 2 was formed on the bonding surface 1a of the support substrate 1, and its surface was polished away by approximately 0.2 μm using CMP (chemical mechanical polishing) to flatten it. Next, the bonding surface 3b of the piezoelectric material substrate 3 and the bonding surface of the silicon oxide film 2 were activated using N2 plasma, and then bonded in the atmosphere. Specifically, the surface roughness of the polished bonding layer was measured using AFM (atomic force microscopy), and the result was Ra of 0.4 nm, confirming that a mirror surface sufficient for bonding was obtained.

[0103] Next, the bonding surface 3b of the piezoelectric material substrate 3 and the bonding surface 2b of the bonding layer 2 are cleaned and surface activated respectively. Specifically, ultrasonic cleaning using pure water is implemented, and the substrate surface is dried by spin drying. Next, the cleaned supporting substrate is introduced into a plasma activation chamber, and the bonding surface of the bonding layer is activated at 30°C using nitrogen plasma. In addition, the piezoelectric material substrate 3 is similarly introduced into a plasma activation chamber, and surface activation is performed at 30°C using nitrogen plasma. The surface activation time is set to 40 seconds, and the energy is set to 100W. In order to remove the particles attached during the surface activation, the same ultrasonic cleaning and spin drying as above are implemented again.

[0104] Next, the substrates were aligned and the activated bonding surfaces of the two substrates were brought into contact at room temperature. The contact was made with the piezoelectric material substrate 3 facing upward. As a result, the expansion of the close contact between the substrates (the so-called bonding wave) was observed, and it was confirmed that the pre-bonding was performed well. Next, in order to increase the bonding strength, the bonded body was placed in a nitrogen atmosphere oven and kept at 130°C for 40 hours.

[0105] The surface 3 c of the piezoelectric material substrate 3 of the heated bonded body was subjected to grinding, lapping, and CMP processing, so that the thickness of the piezoelectric material substrate 3A was reduced to 7 μm.

[0106] Next, to confirm the effects of the present invention, comb-shaped electrodes made of aluminum were formed on the piezoelectric substrate of the bonded structure to produce a surface acoustic wave resonator. The product specifications are shown below.

[0107] IDT period 6μm

[0108] IDT opening length 300um

[0109] Number of IDT entries: 80

[0110] Number of reflectors: 40

[0111] The reflection characteristics of the resonator were measured using a network analyzer. The results were as follows: Figure 7 As shown in the figure, there is almost no spurious signal in the region above the anti-resonance frequency, and the spurious wave value is 2.7 dB.

[0112] These results are shown in Table 1.

[0113] (Example 2)

[0114] A surface acoustic wave device resonator was fabricated in the same manner as in Example 1, and the reflection characteristics of the resonator were measured using a network analyzer. However, the bonding surface of the support substrate was ground using a #8000 grinding stone.

[0115] As a result, the spectrum of the bonding surface of the support substrate was obtained by X-ray reflectivity method, and the relative signal intensity was approximated by formula (1). As a result, a=7.1×10 －4 , b = 5.80. The magnitude of the spurious wave is 3.2 dB.

[0116] (Example 3)

[0117] A surface acoustic wave resonator was fabricated in the same manner as in Example 1, and its reflection characteristics were measured using a network analyzer. However, the bonding surface of the support substrate was processed by sandblasting the entire substrate using silicon nitride particles. The estimated processing depth was only 10 nm.

[0118] As a result, the spectrum of the bonding surface of the support substrate was obtained by X-ray reflectivity method, and the relative signal intensity was approximated by formula (1). As a result, a=2.2×10 －5 , b = 8.84. The magnitude of the parasitic wave is 4.8 dB.

[0119] (Example 4)

[0120] A surface acoustic wave resonator was fabricated in the same manner as in Example 1, and the reflection characteristics of the resonator were measured using a network analyzer. However, the bonding surface of the support substrate was processed by placing the support substrate in an ion processing device and impacting it with Ar ions accelerated at 0.5 keV.

[0121] As a result, the spectrum of the bonding surface of the support substrate was obtained by X-ray reflectivity method, and the relative signal intensity was approximated by formula (1). As a result, a=5.6×10 －5 , b = 7.63. The magnitude of the parasitic wave is 3.3 dB.

[0122] (Example 5)

[0123] A surface acoustic wave device resonator was fabricated in the same manner as in Example 1, and the reflection characteristics of the resonator were measured using a network analyzer. The supporting substrate was placed in an ion processing apparatus and subjected to collision with Ar ions accelerated at 1.0 keV to process the bonding surface.

[0124] As a result, the spectrum of the bonding surface of the support substrate was obtained by X-ray reflectivity method, and the relative signal intensity was approximated by formula (1). As a result, a=1.8×10 －3 , b = 5.12. The magnitude of the parasitic wave is 3.5 dB.

[0125] (Comparative Example 1)

[0126] A resonator of a surface acoustic wave element was fabricated in the same manner as in Example 1, and the reflection characteristics of the resonator were measured using a network analyzer. However, since the bonding surface of the support substrate was a mirror surface, Ra was 0.02 nm, and the above formula (1) could not be used for approximation. Regarding the reflection characteristics, Figure 8 As shown in the figure, a spurious signal is seen, and the magnitude of the spurious wave is 12dB.

[0127] Table 1

[0128] a b Parasitic signal (dB) Example 1 <![CDATA[9.2×10 -4 ]]> 5.55 2.7 Example 2 <![CDATA[7.1×10 -4 ]]> 5.80 3.2 Example 3 <![CDATA[2.2×10 -5 ]]> 8.84 4.8 Example 4 <![CDATA[5.6×10 -5 ]]> 7.63 3.3 Example 5 <![CDATA[1.8×10 -3 ]]> 5.12 3.5 Comparative Example 1 --- --- 12

Claims

1. A conjugate comprising: a supporting substrate; a piezoelectric material substrate formed of a material selected from the group consisting of lithium niobate, lithium tantalate, and lithium niobate-lithium tantalate; and a bonding layer bonding the support substrate and the piezoelectric material substrate together, The conjugate is characterized in that At least one of the bonding surface of the support substrate and the bonding surface of the piezoelectric material substrate is measured by X-ray reflectivity method. When the signal intensity during total reflection is set to 1, the relative intensity I of the reflected light from the bonding surface is 1.0×10 －4 Above 1.0×10 －1 Within the following range, the spurious waves are suppressed by approximating the following formula (1): 【Mathematical formula 1】 In formula (1), θ is the incident angle of X-ray relative to the bonding surface, a is 1.0×10 －5 Above 2.0×10 －3 the following, b is 5.0 or more and 9.0 or less.

2. The joint body according to claim 1, characterized in that The bonding layer is formed of a material selected from the group consisting of silicon oxide, silicon nitride, aluminum nitride, aluminum oxide, tantalum pentoxide, mullite, niobium pentoxide, and titanium oxide.

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