The joint between the piezoelectric material substrate and the support substrate

Abstract

This 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 support substrate of the bonding body. The bonding body comprises: a support 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 support substrate and the piezoelectric material substrate and contacts the main surface of the piezoelectric material substrate. When measuring at least one of the bonding surfaces of the support substrate and the piezoelectric material substrate using elliptic polarization spectroscopy, and setting the phase difference between the p-polarized and s-polarized reflected light as Δ, the difference between the maximum and minimum values ​​of the phase difference Δ in the wavelength range of 400 nm to 760 nm is 70° or less.

Description

Technical Field

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

[0002] It is known that surface elastic wave filters made by bonding lithium tantalate and sapphire with a silicon oxide layer generate bulk waves at their bonding interface, resulting in unwanted responses in the passband and high-frequency domain. To prevent this response, a method has been proposed that introduce a rough surface at the bonding interface to scatter the bulk waves and suppress the unwanted response (Patent Document 1, Patent Document 2).

[0003] In Patent Document 1, when roughening the mating surface, the ratio of the average length RSm of the elements at the cross-sectional curve of the uneven structure constituting the rough surface to the wavelength λ of the surface elastic wave is set to 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 set to 100 nm or more. On the other hand, Patent Document 2 specifies the height difference of the rough surface.

[0004] Existing technical documents

[0005] Patent documents

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

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

[0008] Previously, the unevenness (e.g., RSm, Ra) of the bonding surface of a support substrate or piezoelectric material substrate was measured and controlled to a considerable level to suppress parasitic waves. However, even if the RSm of the bonding surface is the same, parasitic waves are sometimes not suppressed, indicating that controlling only the unevenness of the bonding surface is insufficient to suppress parasitic waves.

[0009] The objective of this invention is to provide a novel 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 support substrate of the bonding body.

[0010] This invention is a joint comprising:

[0011] Support substrate;

[0012] A piezoelectric material substrate, the piezoelectric material substrate being 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.

[0014] The characteristic of the joint is that...

[0015] When measuring at least one of the bonding surfaces of the support substrate and the piezoelectric material substrate using elliptic polarization spectroscopy, when the phase difference between the p-polarized and s-polarized reflected light is set as Δ, the difference between the maximum and minimum values ​​of the phase difference Δ in the region between wavelengths of 400 nm and 760 nm is less than 70°.

[0016] Invention Effects

[0017] The inventors of this invention attempted to roughen the bonding surface of a support substrate or piezoelectric material substrate by mechanical processing after mirror polishing, and then observed and analyzed its microstructure in detail. The results showed that the mechanically processed bonding surface produced micro-defects or film deterioration that could not be deduced from the surface irregularity. These results indicate that the suppression effect of parasitic waves should not be controlled by the surface irregularity, but rather by the effective crystallographic and geometric properties of the surface region of the piezoelectric material substrate and the bonding layer.

[0018] Based on the above insights, the inventors of this invention have studied various processing methods and methods for measuring the joint surface. In this process, they have focused on elliptic polarization spectroscopy.

[0019] In other words, elliptic polarization spectroscopy is an analytical method that measures the changes in the polarization state of incident light and reflected light relative to the surface of a sample (in this invention, a piezoelectric material substrate and a supporting substrate). Specifically, for example, as... Figure 1 As shown, the surface perpendicular to the substrate surface and containing both incident and reflected light is designated as the incident surface. The polarized light component whose electric field vibrates parallel to this incident surface is called p-polarized light, and the polarized light component whose electric field vibrates perpendicular to the incident surface is called s-polarized light. Here, the incident light is linearly polarized light with the same amplitude and phase as both the p-polarized and s-polarized components. If this incident light is irradiated onto the substrate, the light reflected from the substrate surface and the light reflected from layer boundaries, defects, etc., near the substrate surface interfere with each other. Furthermore, the speed of light propagating within the substrate slows down according to the refractive index of that portion, thus causing a phase shift. These changes differ between the component parallel to the incident surface (p-polarized light) and the component perpendicular to the incident surface (s-polarized light), therefore, as... Figure 1 As shown, the polarization state of the reflected light is different from that of the incident light, becoming elliptically polarized light.

[0020] Therefore, the measurement results obtained by elliptic polarization spectroscopy not only reflect the unevenness of the thin film on the substrate surface, but also reflect information in the depth direction of the thin film (information on film thickness and density).

[0021] The inventors of this invention applied elliptic polarization spectroscopy to the bonding surfaces of piezoelectric material substrates or support substrates after roughening the surfaces, thereby obtaining information on the degradation and density changes in the regions near the surface of these bonding surfaces, and studied the relationship between this information and the suppression effect of parasitic waves.

[0022] That is, the bonding surfaces of the piezoelectric material substrate or the support substrate are roughened. Then, the inventors of this invention used elliptic polarization spectroscopy to measure the bonding surfaces of the support substrates or the piezoelectric material substrates that had undergone various roughening treatments, and measured the polarization state of the reflected light in various ways. The results showed that, especially in the visible light region (wavelength between 400 nm and 760 nm), when the phase difference between the p-polarized and s-polarized light of the reflected light was set to Δ, the suppression effect of parasitic waves was significantly improved by making the difference between the maximum and minimum values ​​of the wavelength phase difference Δ less than 70°, thus realizing the present invention. Attached Figure Description

[0023] Figure 1 This is a schematic diagram used to illustrate the principle of elliptic polarization spectroscopy.

[0024] Figure 2 In the diagram, (a) indicates the state in which the bonding surface 1a of the support substrate 1 is processed, (b) indicates the state in which the bonding layer 2 is provided on the bonding surface 1a of the support substrate 1, and (c) indicates the state in which the bonding surface of the bonding layer 2 is activated by irradiating the bonding surface with plasma B.

[0025] Figure 3 In the diagram, (a) represents the piezoelectric material substrate 3, and (b) represents the state in which the bonding surface 3b of the piezoelectric material substrate 3 has been activated.

[0026] Figure 4 In the diagram, (a) represents the joint 5 of the support substrate 1 and the piezoelectric material substrate 3, (b) represents the state in which the piezoelectric material substrate 3A of the joint 5A is thinned by processing, and (c) represents the elastic wave element 6.

[0027] Figure 5 In the diagram, (a) represents the piezoelectric material substrate 3, and (b) represents the state in which the bonding surface 12a of the intermediate layer 12 on the piezoelectric material substrate 3 has been activated.

[0028] Figure 6 In the diagram, (a) represents the joint 15 of the support substrate 1 and the piezoelectric material substrate 3, (b) represents the state in which the piezoelectric material substrate 3A of the joint 15A is thinned by processing, and (c) represents the elastic wave element 16.

[0029] Figure 7The curve represents the result of elliptic polarization spectroscopy of the surface elastic wave elements of the embodiments and comparative examples.

[0030] Figure 8 This is a curve representing the reflection characteristics of the surface elastic wave element in an embodiment of the present invention.

[0031] Figure 9 The curve represents the reflection characteristics of the surface elastic wave element in the comparative example. Detailed Implementation

[0032] Hereinafter, embodiments of the present invention will be described in detail with appropriate reference to the accompanying drawings.

[0033] Initially, the joint and the elastic wave element utilizing the joint will be described.

[0034] First, such as Figure 2 As shown in (a), a support substrate 1 having a pair of main surfaces 1a and 1b is prepared. Next, the main surface (joint surface) 1a is roughened by processing A. Then, as... Figure 2 As shown in (b), a bonding layer 2 is formed on the main surface 1a of the support substrate 1. To achieve a mirror finish, the surface 2a of the bonding layer 2 is CMP polished. Next, as... Figure 2 As shown in (c), plasma is irradiated onto the surface 2a of the bonding layer 2 as indicated by arrow B, resulting in a surface-activated bonding surface 2b.

[0035] On the other hand, such as Figure 3 As shown in (a), a piezoelectric material substrate 3 having a main surface 3a is prepared. Next, the main surface of the piezoelectric material substrate 3 is irradiated with plasma as shown by arrow C to activate its surface and form an activated bonding surface 3b.

[0036] 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 for direct bonding, thereby obtaining... Figure 4 (a) shows the joint 5.

[0037] In this state, electrodes can be disposed on the piezoelectric material substrate 3. However, preferably, as shown below, Figure 4 As shown in (b), the main surface 3c of the piezoelectric material substrate 3 is processed to thin the substrate 3, forming a thinned piezoelectric material substrate 3A, and a bonding body 5A is then formed. 9 is the processed surface. Next, as... Figure 4 As shown in (c), a predetermined electrode 10 is formed on the processing surface 9 of the piezoelectric material substrate 3A of the bonding body 5A, and an elastic wave element 6 can be obtained.

[0038] Alternatively, an intermediate layer can be provided between the bonding layer 2 and the piezoelectric material substrate 3. Figure 5 , Figure 6 This implementation method is relevant.

[0039] In this example, as Figure 2 As shown in (a), a support substrate 1 having a pair of main surfaces 1a and 1b is prepared. Next, the main surface (joint surface) 1a is roughened by processing A. Then, as... Figure 2 As shown in (b), a bonding layer 2 is formed on the main surface 1a of the support substrate 1. To achieve a mirror finish, the surface of the bonding layer 2 is CMP polished. Next, as... Figure 2 As shown in (c), plasma is irradiated onto the bonding surface of bonding layer 2 as indicated by arrow B to obtain a surface-activated bonding surface 2b.

[0040] On the other hand, such as Figure 5 As shown in (a), a piezoelectric material substrate 3 having a main surface 3a is prepared. Next, as... 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. Plasma is irradiated onto the surface of the intermediate layer 12 as shown by arrow C to activate the surface and form the activated bonding surface 12a.

[0041] 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, thereby obtaining... Figure 6 (a) shows the joint 15.

[0042] In this state, electrodes can be disposed on the piezoelectric material substrate 3. However, preferably, as shown below, Figure 6 As shown in (b), the main surface 3c of the piezoelectric material substrate 3 is processed to thin the substrate 3, forming a thinned piezoelectric material substrate 3A, and a bonding body 15A is manufactured. 9 is the processed surface. Next, as... Figure 6 As shown in (c), a predetermined electrode 10 is formed on the processing surface 9 of the piezoelectric material substrate 3A of the bonding body 15A, and an elastic wave element 16 can be obtained.

[0043] Alternatively, an intermediate layer 12 can be formed on top of the bonding layer 2 after the bonding layer 2 is formed. In this case, the surface of the intermediate layer 12 is CMP processed to obtain a bonding surface (mirror finish). The obtained bonding surface is then activated by plasma irradiation. Next, the surface of the support substrate is plasma activated and then directly bonded to the bonding surface of the intermediate layer.

[0044] In this invention, within the visible light region (the region between wavelengths of 400 nm and 760 nm), when the phase difference between the p-polarized and s-polarized reflected light is set to Δ, the difference between the maximum and minimum values ​​of the wavelength phase difference Δ is less than 70°. This will be further explained in more detail.

[0045] In other words, elliptic polarization spectroscopy is an analytical method that measures the changes in the polarization state of incident light and reflected light relative to the surface of a sample. For example... Figure 1 As shown, the surface perpendicular to the surface of the supporting substrate or piezoelectric material substrate and containing both incident and reflected light is designated as the incident surface. The polarized light component whose electric field vibrates parallel to this incident surface is called p-polarized light, and the polarized light component whose electric field vibrates perpendicular to the incident surface is called s-polarized light. Here, the incident light is linearly polarized light (circularly polarized light) with the same amplitude and phase as the p-polarized and s-polarized light components. If this incident light is irradiated onto the substrate surface, the light reflected from the substrate surface and the light reflected from layer boundaries, defects, etc., present inside the substrate interfere with each other. Furthermore, the speed of light propagating within the substrate slows down according to the refractive index of that portion, thus causing a phase shift. These changes are not the same for the component parallel to the incident surface (p-polarized light) and the component perpendicular to the incident surface (s-polarized light), therefore, as... Figure 1 As shown, the polarization state of the reflected light becomes elliptically polarized light, which is different from that of the incident light.

[0046] Here, the change in polarization state is represented by the Fresnel amplitude reflection coefficient ratio ρ.

[0047] ρ=r p / r s …(1)

[0048] Here, r p Let r be the Fresnel amplitude reflection coefficient (the ratio of the electric field vectors of the incident and reflected light) for p-polarized light. s Let be the Fresnel amplitude reflection coefficient for s-polarized light.

[0049] r p =E rp / E ip …(2)

[0050] r s =E rs / E is …(3)

[0051] like Figure 1 As shown, E ip E represents the p-polarized component of the incident light. is This represents the s-polarized component of the incident light. Additionally, E... rp E represents the p-polarized component of the emitted light. rsN represents the s-polarized component of the emitted light. N0 and N1 represent the refractive indices of the atmosphere and the substrate, respectively.

[0052] The amplitude reflection coefficient is a complex number, representing the change in amplitude and phase. Therefore, the Fresnel amplitude reflection coefficient ratio ρ is defined by the following equation (4).

[0053] ρ=tanΨ×eiΔ…(4)

[0054] Here, tanΨ is the amplitude ratio of the p-polarized light to the s-polarized light of the reflected light (refer to Equation (5)), and Δ is the phase difference between the p-polarized light and the s-polarized light of the reflected light (refer to Equation (6)).

[0055] tanΨ=|r p | / |r s |…(5)

[0056] Δ=δr p -δr s …(6)

[0057] Furthermore, the inventors of this invention, particularly in the visible light region (wavelength between 400 nm and 760 nm), focused on the phase difference Δ between the p-polarized and s-polarized light of the reflected light (refer to Equation (6)), and performed various processing on the bonding surface of the piezoelectric material substrate or support substrate, measured Δ, and observed the relationship between Δ and parasitic waves. The results showed that in the visible light region (wavelength between 400 nm and 760 nm), when the relative change (difference between the maximum and minimum values) of the phase difference Δ between the p-polarized and s-polarized light of the reflected light was small, parasitic waves were significantly suppressed. Specifically, when the difference between the maximum and minimum values ​​of the phase difference Δ was less than 70°, the suppression effect on parasitic waves was observed.

[0058] The reason for the aforementioned effect is not yet clear; however, it is known that the vicinity of the processing surface of the piezoelectric material substrate or supporting substrate exhibits visible light rotation, causing a change in polarization state. Here, for example, as... Figure 7 As shown, there is generally a trend where the phase difference Δ increases on the short wavelength side and decreases on the long wavelength side. This means that short-wavelength light has a greater optical rotation effect. Here, in the examples of the present invention (Examples 1 and 3), the difference between the phase difference Δ on the short wavelength side and the phase difference Δ on the long wavelength side is relatively small, and the curve is gentle. In contrast, in the comparative examples, although the substrate surface is mirrored, the difference between the phase difference Δ on the short wavelength side and the phase difference Δ on the long wavelength side is large, and the curve is steep. These results are considered to reflect the microstructural changes of the surface alteration layer near the processed surface.

[0059] From the perspective of the present invention, in the region of wavelength between 400 nm and 760 nm, the phase difference Δ between the p-polarized light and the s-polarized light of the reflected light is 70° or less, preferably 65° or less, and more preferably 60° or less. Furthermore, in the region of wavelength between 400 nm and 760 nm, the phase difference Δ between the p-polarized light and the s-polarized light of the reflected light is preferably 20° or more, and more preferably 25° or more.

[0060] In order to control the elliptic polarization spectroscopy measurement results of the bonding surface of the piezoelectric material substrate and the bonding surface of the support substrate as described above, the following processing method is preferred.

[0061] Methods for roughening surfaces include: grinding with grinding stones, sandblasting with small media such as alumina and silicon nitride, and ion beam processing that uses high-speed ion collisions.

[0062] The constituent elements of the present invention will be described in turn below.

[0063] The material of the support substrate 1 is not particularly limited, but it is preferably formed from a material selected from the group consisting of silicon, crystal, silicon aluminum oxynitride ceramic, polyaluminum andalusite, sapphire, and transparent alumina. This allows for further improvement in the temperature characteristics of the elastic wave elements 6 and 16 at their frequencies.

[0064] There are no limitations on the film formation methods for the bonding layer and intermediate layer. Examples include sputtering, chemical vapor deposition (CVD), and evaporation.

[0065] The material of the bonding layer 2 can be surface activated without particular limitation, but is preferably a metal oxide film, and particularly preferably a material selected from the group consisting of silicon oxide, silicon nitride, aluminum nitride, aluminum oxide, tantalum pentoxide, andalusite, niobium pentoxide, and titanium oxide. Furthermore, the surface activation method can be selected appropriately depending on the material of the bonding layer. Examples of such surface activation methods include plasma activation and FAB (Ar atom beam).

[0066] The material of the intermediate layer 12 can be surface activated and is not particularly limited. It is preferably a metal oxide film, and more preferably a material selected from the group consisting of silicon oxide, silicon nitride, aluminum nitride, aluminum oxide, tantalum pentoxide, andalusite, niobium pentoxide, and titanium oxide. However, the material of the intermediate layer is preferably different from that of the bonding layer.

[0067] From the perspective of the present invention, the thickness of the bonding layer 2 is preferably 0.05 μm or more, more preferably 0.1 μm or more, and particularly preferably 0.2 μm or more. Furthermore, 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.

[0068] The piezoelectric material substrate 3 used in this invention is made of lithium tantalate (LT) single crystal, lithium niobate (LN) single crystal, or lithium niobate-lithium tantalate solid solution. These materials have fast propagation speed of elastic waves and large electromechanical coupling coefficient, therefore, they are suitable as elastic surface wave devices for high-frequency and wide-bandwidth applications.

[0069] Furthermore, 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 direction of propagation of the elastic surface wave, i.e., the X-axis, rotated from the Y-axis to the Z-axis by 32 to 55°, and expressed in Euler angles as (180°, 58 to 35°, 180°) is preferred because the propagation loss is small. When the piezoelectric material substrate 3 is formed from LN, it is preferable to use a piezoelectric material substrate with an Euler angle of (0°, 37.8°, 0°) centered on the X-axis (the direction of surface wave propagation) and rotated 37.8° from the Z-axis to the Y-axis. This results in a larger electromechanical coupling coefficient. Alternatively, it is preferable to use a piezoelectric material substrate with an Euler angle of (180°, 50-25°, 180°) centered on the X-axis (the direction of surface wave propagation) and rotated 40-65° from the Y-axis to the Z-axis. This results in high-speed sound. Furthermore, the size of the piezoelectric material substrate 3 is not particularly limited, but can be, for example, 100-200 mm in diameter and 0.15-1 μm in thickness.

[0070] Next, plasma is irradiated onto the bonding surfaces of the bonding layer 2 on the support substrate 1, the bonding surfaces of the piezoelectric material substrate 3, and the bonding surfaces of the intermediate layer 12 on the piezoelectric material substrate 3 at a temperature below 150°C to activate the bonding surfaces. From the viewpoint of the present invention, irradiation with nitrogen plasma is preferred; however, the bonding body of the present invention can also be obtained by irradiating with oxygen plasma.

[0071] The pressure during surface activation is preferably 100 Pa or less, more preferably 80 Pa or less. In addition, the atmosphere may be nitrogen only, oxygen only, or a mixture of nitrogen and oxygen.

[0072] The temperature during plasma irradiation is set to 150°C or below. This results in a bond with high bonding strength and no deterioration in crystallinity. From this perspective, the temperature during plasma irradiation is set to 150°C or below, more preferably 100°C or below.

[0073] Furthermore, the energy during plasma irradiation is preferably 30–150 W. Additionally, the product of the plasma irradiation energy and the irradiation time is preferably 0.12–1.0 Wh.

[0074] The bonding surfaces of the plasma-treated piezoelectric material substrate and the bonding layer are brought into contact with each other at room temperature. This process can be performed in a vacuum, but is more preferably carried out in the atmosphere.

[0075] When performing surface activation using an argon atom beam, it is preferable to use an apparatus as described in Japanese Patent Application Publication No. 2014-086400 to generate the argon atom 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 chamber, and a high voltage is applied to the electrodes from a DC power supply. This generates a saddle-type electric field between the electrode (positive electrode) and the shell (negative electrode), causing electrons (e) to move, thereby generating a beam of argon atoms and ions. The ion beam reaching the grid is neutralized at the grid, thus the argon atom beam is emitted from the high-speed atomic beam source. The voltage for activation using beam irradiation is preferably 0.5–2.0 kV, and the current is preferably 50–200 mA.

[0076] In a preferred embodiment, before surface activation treatment, the bonding surfaces of the bonding layers on the support substrate, the bonding surfaces of the piezoelectric material substrate, and the bonding surfaces of the intermediate layer on the piezoelectric material substrate are planarized. Methods for planarizing each bonding surface include lapping and chemical mechanical polishing (CMP). Furthermore, for planar surfaces, Ra ≤ 1 nm is preferred, and more preferably 0.3 nm or less.

[0077] 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 perform bonding. Then, annealing is preferably performed to improve the bonding strength. The annealing temperature is preferably 100°C or higher and 300°C or lower.

[0078] The connectors 5, 5A, 15, and 15A of the present invention can preferably be used in elastic wave elements 6 and 16. That is, an elastic wave element having the connectors of the present invention and electrodes disposed on a piezoelectric material substrate.

[0079] Specifically, as elastic wave elements 6 and 16, surface wave devices, Lamb wave elements, and thin-film resonators (FBARs) are known. For example, an elastic surface wave device is a device in which an IDT (Interdigital Transducer) electrode (also called a comb electrode or curtain electrode) is disposed on the surface of a piezoelectric material substrate to excite elastic surface waves on the input side and an IDT electrode is disposed on the output side to receive the elastic surface waves. If a high-frequency signal is applied to the IDT electrode on the input side, an electric field is generated between the electrodes, which excites elastic surface waves that propagate on the piezoelectric material substrate. Then, the propagated elastic surface waves can be output as an electrical signal from the IDT electrode on the output side, which is disposed in the propagation direction.

[0080] The electrode 10 constituting the piezoelectric material substrate 3A is preferably made of aluminum, an aluminum alloy, copper, or gold, and more preferably aluminum or an aluminum alloy. The aluminum alloy is preferably an aluminum alloy in which 0.3 to 5% by weight of Cu is mixed into Al. In this case, Ti, Mg, Ni, Mo, or Ta can be used instead of Cu.

[0081] Example

[0082] (Example 1)

[0083] According to reference Figures 2-4 The method of explanation, production Figure 4 (c) shows the elastic wave element 6.

[0084] Specifically, one main surface 3c of a 250μm thick 42Y-cut X-propagation LiTaO3 substrate (piezoelectric material substrate) 3 is polished to a mirror finish, and the other main surface 3a is precision-machined using a GC#1000 milling machine. Additionally, a high-resistivity (>2kΩ·cm) Si(100) substrate (support substrate) 1 with a thickness of 0.23mm is prepared. All substrates have a size of 150mm.

[0085] Next, the bonding surface of the support substrate is roughened. In this embodiment, a grinding stone with a grit size of #6000 is used for grinding. The machining depth is approximately 3 μm.

[0086] When measuring the bonding surface of the support substrate using elliptic polarization spectroscopy, and setting the phase difference between the p-polarized and s-polarized reflected light as Δ, the difference between the maximum and minimum values ​​of the phase difference Δ in the wavelength range of 400 nm to 760 nm is 31.3°.

[0087] Next, a 0.7 μm silicon oxide film 2 is formed on the bonding surface 1a of the support substrate 1, and its surface is planarized by grinding away approximately 0.2 μm using CMP (chemical mechanical polishing). Then, the bonding surface 3b of the piezoelectric material substrate 3 and the bonding surface of the silicon oxide film 2 are activated using N2 plasma, and then bonded in atmosphere. Specifically, the surface roughness of the bonded layer after grinding is measured using AFM (atomic force microscopy), and the result shows Ra to be 0.4 nm, confirming that a mirror finish sufficient for bonding has been obtained.

[0088] Next, the bonding surface 3b of the piezoelectric material substrate 3 and the bonding surface 2b of the bonding layer 2 were cleaned and surface activated, respectively. Specifically, ultrasonic cleaning with pure water was performed, followed by rotary drying to dry the substrate surface. Next, the cleaned support substrate was introduced into a plasma activation chamber, where the bonding surface of the bonding layer was activated using nitrogen plasma at 30°C. Similarly, the piezoelectric material substrate 3 was introduced into the plasma activation chamber and surface activated using nitrogen plasma at 30°C. The surface activation time was set to 40 seconds, and the energy was set to 100W. To remove particles adhering to the surface during activation, the same ultrasonic cleaning and rotary drying process as described above was performed again.

[0089] Next, the substrates were aligned, and the activated bonding surfaces of the two substrates were brought into contact with each other at room temperature. Contact was made with the three sides of the piezoelectric material substrate facing upwards. The resulting adhesion and expansion of the substrates (the so-called bonding wave) was observed, confirming that good pre-bonding had been achieved. Next, to increase the bonding strength, the bond was placed in a nitrogen atmosphere oven and maintained at 130°C for 40 hours.

[0090] The surface 3c of the piezoelectric material substrate 3 of the heated joint is ground, precision ground and CMP processed to make the thickness of the piezoelectric material substrate 3A 7μm.

[0091] Next, to confirm the effectiveness of the invention, a comb-tooth electrode made of aluminum was formed on a piezoelectric material substrate of the bonding body to fabricate a resonator for a surface elastic wave element. Its product specifications are shown below.

[0092] IDT period 6μm

[0093] IDT opening length 300um

[0094] Number of IDT entries: 80

[0095] 40 reflectors

[0096] The reflection characteristics of the resonator were measured using a network analyzer, and the results are as follows: Figure 8 As shown, almost no parasitic signal was observed in the region above the anti-resonance frequency. The value of the parasitic wave was 2.7 dB.

[0097] These results are shown in Table 1.

[0098] (Example 2)

[0099] The resonator of the surface elastic 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, the bonding surface of the support substrate was ground using a #8000 grinding stone.

[0100] Furthermore, when measuring the bonding surface of the support substrate using elliptic polarization spectroscopy, with the phase difference between the p-polarized and s-polarized reflected light set as Δ, the difference between the maximum and minimum values ​​of the phase difference Δ in the wavelength range of 400 nm to 760 nm was 37.4°. As a result, the magnitude of the parasitic wave was 3.2 dB.

[0101] (Example 3)

[0102] The resonator of the surface elastic 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, regarding the processing of the bonding surface of the supporting substrate, silicon nitride particles were used to sandblast the entire surface of the substrate. The estimated processing amount at this time was only 10 nm.

[0103] Furthermore, when measuring the bonding surface of the support substrate using elliptic polarization spectroscopy, with the phase difference between the p-polarized and s-polarized reflected light set as Δ, the difference between the maximum and minimum values ​​of the phase difference Δ in the wavelength range of 400 nm to 760 nm is 58.5°. The magnitude of the parasitic wave is 4.8 dB.

[0104] (Example 4)

[0105] The resonator of the surface elastic 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, regarding the processing of the bonding surface of the support substrate, the support substrate was placed in an ion processing machine and subjected to Ar ions accelerated at 0.5 keV to process its bonding surface.

[0106] In addition, when measuring the bonding surface of the support substrate using elliptic polarization spectroscopy, when the phase difference between the p-polarized light and the s-polarized light of the reflected light is set as Δ, the difference between the maximum and minimum values ​​of the phase difference Δ in the region between wavelengths of 400 nm and 760 nm is 42.8°.

[0107] As a result, the magnitude of the parasitic wave was 3.3 dB.

[0108] (Example 5)

[0109] The resonator of the surface elastic 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. The support substrate was placed in an ion processing machine and subjected to Ar ions accelerated at 1.0 keV to process its bonding surface.

[0110] In addition, when measuring the bonding surface of the support substrate using elliptic polarization spectroscopy, when the phase difference between the p-polarized light and the s-polarized light of the reflected light is set as Δ, the difference between the maximum and minimum values ​​of the phase difference Δ in the region between wavelengths of 400 nm and 760 nm is 50.9°.

[0111] The magnitude of the parasitic wave is 3.5 dB.

[0112] (Comparative Example)

[0113] A resonator for a surface elastic 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 supporting substrate was made mirror-like, Ra was 0.02 nm.

[0114] When measuring the bonding surface of the support substrate using elliptic polarization spectroscopy, if the phase difference between the p-polarized and s-polarized reflected light is set as Δ, the difference between the maximum and minimum values ​​of the phase difference Δ in the wavelength range of 400 nm to 760 nm is 85.0°.

[0115] Regarding reflection characteristics, such as Figure 9 As shown, a parasitic signal can be observed. The magnitude of the parasitic wave is 12 dB.

[0116] Table 1

[0117]

Claims

1. A joint comprising: Support substrate; A piezoelectric material substrate, the piezoelectric material substrate being 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 support substrate and the piezoelectric material substrate. The characteristic of the joint is that... When measuring at least one of the bonding surfaces of the supporting substrate and the piezoelectric material substrate using elliptic polarization spectroscopy, if the phase difference between the p-polarized and s-polarized reflected light is set as Δ, in the region between wavelengths of 400 nm and 760 nm, the difference between the maximum and minimum values ​​of the phase difference Δ is less than 70°, which significantly improves the suppression effect of parasitic waves. It also includes a surface-modified region adjacent to at least one of the bonding surface of the support substrate and the bonding surface of the piezoelectric material substrate, configured to be subjected to the elliptic polarization spectroscopy when measuring the phase difference Δ.

2. The joint 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, andalusite, niobium pentoxide, and titanium oxide.

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