Composite substrate, elastic wave element, and method for manufacturing composite substrate

Abstract

When a piezoelectric material substrate and a support substrate containing quartz are joined, the joining strength is improved so that peeling does not occur even if the piezoelectric material substrate is thinned. The composite substrate 7, 7A has a support substrate 4 containing quartz, a piezoelectric material substrate 1, 1A, a first amorphous layer 5 present between the support substrate 4 and the piezoelectric material substrate 1, 1A, and a second amorphous layer 11 present between the support substrate 4 and the first amorphous layer 5. The first amorphous layer 5 contains 10 to 30 atom% of silicon atoms, and the second amorphous layer 11 contains 1 to 10 atom% of fluorine atoms.

Description

Technical Field

[0001] This invention relates to a composite substrate of a piezoelectric material substrate and a support substrate, and a method for manufacturing the same. Background Technology

[0002] SOI substrates composed of high-resistivity Si / SiO2 thin films / Si thin films are widely used for realizing high-performance semiconductor devices. Plasma activation is used in the fabrication of SOI substrates because bonding can be performed at relatively low temperatures (400°C). To improve the characteristics of piezoelectric devices, similar composite substrates composed of Si / SiO2 thin films / piezoelectric thin films have been proposed.

[0003] Furthermore, SAW filters with a structure in which a piezoelectric material substrate is bonded to a support substrate have been reported for the purpose of improving the temperature characteristics and increasing the Q value of SAW filters. In particular, elastic wave elements using a composite substrate obtained by bonding a crystal substrate and a lithium tantalate substrate have been reported to exhibit very superior characteristics (Non-Patent Literature 1, 2, Patent Literature 1, 2).

[0004] Existing technical documents

[0005] Non-patent literature

[0006] Non-patent document 1: Shogo Inoue et.al.''Spurious Free SAW Resonators onLayered Substrate with Ultra-High Q, High Coupling and Small TCF'' IEEEInternational Ultrasonic Symposium 2018Proceedings

[0007] Non-patent document 2: Michio Kadota et.al.''Suprious-Free, Near-Zero-TCF HeteroAcoustic Layer(HAL)SAW Resonators Using LiTaO3 Thin Plate on Quartz'' IEEEInternational Ultrasonic Symposium 2018Proceedings

[0008] Non-Patent Literature 3: Semiconductor Wafer Bonding, Q.-Y. Tong, U. Gosele, Wiley-Inter Science. p. 27

[0009] Patent documents

[0010] Patent Document 1: US 10,084,427B2

[0011] Patent Document 2: Japanese Patent Application Publication No. 2018-026695 Summary of the Invention

[0012] In the aforementioned composite substrates, thinning the piezoelectric material substrate is a design requirement. However, generally, the thinner the piezoelectric material substrate, the stronger the bonding strength required. For example, Patent Document 2 proposes a bonding body between a crystal and a piezoelectric layer; however, when the piezoelectric material substrate is thinned, there is a problem of self-supporting substrate peeling, requiring further improvement in bonding strength.

[0013] The objective of this invention is to improve the bonding strength when bonding a piezoelectric material substrate to a support substrate containing crystal, so that the piezoelectric material substrate will not peel off even when it is thinned.

[0014] The present invention is characterized by having:

[0015] Support substrate containing crystal,

[0016] piezoelectric material substrate,

[0017] The first amorphous layer existing between the supporting substrate and the piezoelectric material substrate, and

[0018] The second amorphous layer exists between the supporting substrate and the first amorphous layer.

[0019] The first amorphous layer contains 10-30 atom% silicon atoms, and the second amorphous layer contains 1-10 atom% fluorine atoms.

[0020] In addition, the present invention relates to an elastic wave element, characterized in that it comprises: the composite substrate and electrodes on the piezoelectric single crystal substrate.

[0021] Furthermore, the present invention relates to a method for manufacturing a composite substrate, the composite substrate comprising: a support substrate containing crystal and a piezoelectric material substrate.

[0022] The method for manufacturing the composite substrate is characterized by including the following steps:

[0023] The process of generating an activated surface by irradiating the surface of the support substrate with a plasma containing at least one of oxygen and nitrogen.

[0024] The process of generating an activated surface by irradiating the surface of the piezoelectric material substrate with a plasma containing at least one of oxygen and nitrogen.

[0025] The process of obtaining a bond by contacting the activated surface of the support substrate and the activated surface of the piezoelectric material substrate, and

[0026] The process of heat-treating the joint at a temperature of 250°C to 350°C.

[0027] Invention Effects

[0028] The inventors of this invention investigated a method in which, when directly bonding a piezoelectric material substrate and a support substrate containing crystal, the surfaces of the piezoelectric material substrate and the support substrate are respectively activated by plasma irradiation, so that the activated surfaces come into contact and bond. Next, heat treatment is performed. It was found that, in this process, heat treatment at a temperature above 250°C significantly improves the bonding strength, and even when the piezoelectric material substrate is processed to be relatively thin, the piezoelectric material substrate is not easily peeled off from the support substrate.

[0029] The inventors of this invention further investigated the reasons for the improved bonding strength and obtained the following insights. Specifically, in the composite substrate with improved bonding strength, multiple amorphous layers exist between the support substrate and the piezoelectric material substrate. Analysis of these amorphous layers revealed that the bonding strength is particularly high when an amorphous layer containing 10–30 atom% silicon atoms and an amorphous layer containing 1–10 atom% fluorine atoms are present. Even when the piezoelectric material substrate is processed to be relatively thin, it is not easily peeled off from the support substrate, thus achieving the present invention.

[0030] The reason for the aforementioned effect is not yet clear, but it is speculated that silicon atoms from the support substrate containing crystal diffuse towards the piezoelectric material substrate, thereby generating an amorphous layer containing 10-30 atom% silicon atoms. Furthermore, fluorine atoms generated by plasma activation adsorb onto the piezoelectric material substrate, generating an amorphous layer containing 1-10 atom% fluorine atoms, resulting in particularly high bonding strength. It is believed that if the heat treatment temperature is low, the diffusion of silicon atoms and fluorine in the atmosphere is less likely to occur, making it difficult to improve the bonding strength.

[0031] Furthermore, it is believed that the fluorine atoms in the composition of the amorphous layer originate from the fluorinated rubber (perfluorocarbon polymer) of the O-ring that constitutes the plasma processing chamber.

[0032] Furthermore, while Patent Document 2 describes bonding a support substrate containing crystal and a piezoelectric material substrate containing lithium tantalate, it specifies that, preferably, an amorphous silicon oxide layer or an amorphous aluminum oxide layer is formed on the surface of the support substrate or the piezoelectric material substrate before bonding, followed by heat treatment at 150–200°C. In contrast, the method of this invention involves surface activation of each surface of the support substrate containing crystal and the piezoelectric material substrate containing lithium tantalate, etc., using a plasma containing at least one of oxygen and nitrogen, followed by direct bonding and heat treatment at 250°C or higher, during which multiple amorphous layers of a specific composition are formed along the bonding interface. Attached Figure Description

[0033] Figure 1 In the diagram, (a) represents the piezoelectric material substrate 1, and (b) represents the state in which the bonding surface 1a of the piezoelectric material substrate 1 is activated to produce the activated surface 1c.

[0034] Figure 2 In the diagram, (a) represents the support substrate 4, and (b) represents the state in which the surface of the support substrate 4 has been activated.

[0035] Figure 3 In the diagram, (a) represents the joint 7 obtained by directly bonding the piezoelectric material substrate 1 and the support substrate 4, (b) represents the state in which the piezoelectric material substrate 1A of the joint is thinned by grinding, and (c) represents the elastic wave element 10.

[0036] Figure 4 This is a graph showing the relationship between heating temperature and bond strength after direct bonding.

[0037] Figure 5 This is a high-resolution transmission electron microscope image (8 millionx) showing the area near the interface of the composite substrate. Detailed Implementation

[0038] The present invention will now be described in detail with appropriate reference to the accompanying drawings.

[0039] First, such as Figure 1 As shown in (a), a piezoelectric material substrate 1 having a pair of main surfaces 1a and 1b is prepared. In this example, 1a is designated as the bonding surface. Next, as... Figure 1 As shown in (b), plasma is irradiated onto the bonding surface 1a of the piezoelectric material substrate 1 as shown by arrow A to obtain the surface-activated bonding surface 1c.

[0040] On the other hand, such as Figure 2 As shown in (a), prepare the support substrate 4. Next, as... Figure 2 As shown in (b), plasma is irradiated onto the surface 4a of the support substrate 4 as indicated by arrow B, thereby activating the surface and forming the activated bonding surface 6.

[0041] Next, as Figure 3 As shown in (a), the activated bonding surface 1c on the piezoelectric material substrate 1 and the activated bonding surface 6 on the support substrate 4 are brought into contact and directly bonded to obtain a bond. The resulting bond is heated to, for example, 1000°C to obtain a bonding strength capable of withstanding grinding. Next, the piezoelectric substrate of the bond is machined to a thinner thickness using a grinding machine. By heat-treating the bond at a temperature between 250°C and 350°C, a bond 7 can be obtained. Here, a second amorphous layer 11 and a first amorphous layer 5 are formed between the support substrate 4 and the piezoelectric material substrate 1. Electrodes can be provided on the piezoelectric material substrate 1 in this state. However, it is preferable that, as shown in the diagram... Figure 3 As shown in (b), the main surface 1b of the piezoelectric material substrate 1 is processed to thin the substrate 1, resulting in a thinned piezoelectric material substrate 1A. 1d is the processed surface. Next, as... Figure 3 As shown in (c), a predetermined electrode 8 is formed on the processing surface 1d of the piezoelectric material substrate 1A of the bonding body 7A, and an elastic wave element 10 can be obtained.

[0042] The constituent elements of the present invention will be described in turn below.

[0043] The support substrate 4 is made of crystal. Crystal is anisotropic, and the characteristics of piezoelectric elements are affected by their crystal orientation. According to Non-Patent Document 1, parasitic signals are suppressed by focusing on the speed of sound. Therefore, the orientation can be appropriately selected to obtain the desired characteristics.

[0044] The piezoelectric material substrate 1 used in this invention is preferably lithium tantalate (LT), lithium niobate (LN), or a lithium niobate-lithium tantalate solid solution. These materials have relatively fast elastic wave propagation speeds and large electromechanical coupling coefficients, making them suitable as elastic surface wave devices for high-frequency and broadband applications.

[0045] Furthermore, the normal directions of the main surfaces 1a and 1b of the piezoelectric material substrate 1 are not particularly limited. For example, when the piezoelectric material substrate 1 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 1 is formed from LN, it is preferable to use a piezoelectric material substrate with a direction centered on the propagation direction of the elastic surface wave, i.e., the X-axis, and rotated 37.8° from the Z-axis to the Y-axis, with Euler angles of (0°, 37.8°, 0°), as this results in a larger electromechanical coupling coefficient. Alternatively, it is preferable to use a piezoelectric material substrate with a direction centered on the propagation direction of the elastic surface wave, i.e., the X-axis, and rotated 40 to 65° from the Y-axis to the Z-axis, with Euler angles of (180°, 50 to 25°, 180°), as this results in high-speed sound. Furthermore, the size of the piezoelectric material substrate is not particularly limited, for example, it can be 100 to 200 mm in diameter and 0.15 to 1 μm in thickness.

[0046] Next, plasma is irradiated onto the surface of the piezoelectric material substrate and the surface of the supporting substrate to activate each surface.

[0047] The atmosphere used for surface activation is an oxygen-containing atmosphere. This atmosphere can be oxygen only, nitrogen only, or a mixture of oxygen, nitrogen, hydrogen, and argon. In the case of a mixed gas, there are no particular limitations, and the ratio can be appropriately adjusted according to its relationship with the bonding strength.

[0048] The atmospheric pressure during surface activation is preferably 100 Pa or less, more preferably 80 Pa or less. Furthermore, the atmospheric pressure is preferably 30 Pa or more, more preferably 50 Pa or more.

[0049] The temperature during plasma irradiation is set to 150°C or below. Accordingly, a joint 7 with high bonding strength and no degradation of the piezoelectric material is obtained. From this viewpoint, the temperature during plasma irradiation is set to 150°C or below, more preferably 100°C or below.

[0050] 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 0.1–1.0 Wh.

[0051] In a preferred embodiment, the surface 1a of the piezoelectric material substrate and the surface 4a of the supporting substrate are planarized before plasma treatment. Methods for planarizing surfaces 1a and 4a include lapping and chemical mechanical polishing (CMP). Furthermore, the arithmetic mean roughness Ra of the planarized surfaces is preferably 1 nm or less, more preferably 0.3 nm or less.

[0052] Next, the activated surface of the piezoelectric material substrate and the activated surface of the support substrate are brought into contact and bonded. Then, preferably, the bond is heat-treated, thereby providing strength that can withstand the grinding of the piezoelectric material substrate. The heat treatment temperature is preferably 100 to 150°C. In this embodiment, the thickness can be reduced by grinding the piezoelectric material substrate after the heat treatment.

[0053] Next, the bond strength is improved by performing heat treatment (annealing) on ​​the bonded body. From the viewpoint of the present invention, the temperature during heat treatment is set to 250°C or higher, preferably 270°C or higher. In addition, in order to prevent breakage of the bonded body, the temperature during heat treatment is set to 350°C or lower, preferably 300°C or lower.

[0054] In this invention, the first amorphous layer contains 10 to 30 atom% silicon atoms. More preferably, the silicon atom content of the first amorphous layer is 15 atom% or more, and more preferably 25 atom% or less.

[0055] Furthermore, the second amorphous layer contains 1 to 10 atom% of fluorine atoms. The fluorine atom content of the second amorphous layer is preferably 3 atom% or more, and preferably 8 atom% or less.

[0056] In a preferred embodiment, the piezoelectric material substrate comprises a material selected from the group consisting of lithium niobate, lithium tantalate, and lithium niobate-lithium tantalate, and the first amorphous layer comprises silicon atoms and atoms constituting the material as main components. In this case, the atoms constituting the piezoelectric material substrate are one or two atoms selected from the group consisting of niobium and tantalum, lithium, and oxygen. However, in the method described in this application, since the ratio of lithium atoms cannot be directly measured, the lithium ratio is excluded from the ratios of the atoms constituting the material.

[0057] In this embodiment, the total ratio of one or two atoms selected from the group consisting of niobium and tantalum, and oxygen atoms in the first amorphous layer is preferably 70 atom% or more, and more preferably 90 atom% or less. Furthermore, the total ratio of one or two atoms selected from the group consisting of niobium and tantalum in the first amorphous layer is more preferably 75 atom% or more, and more preferably 85 atom% or less. Furthermore, the ratio of oxygen atoms in the second amorphous layer is more preferably 60 atom% or more, and more preferably 50 atom% or less.

[0058] In a preferred embodiment, the second amorphous layer comprises fluorine atoms, silicon atoms, and oxygen atoms as main components. In this embodiment, the proportion of silicon atoms in the second amorphous layer is preferably 35 atom% or more, and more preferably 50 atom% or less. Furthermore, the proportion of oxygen atoms in the second amorphous layer is preferably 45 atom% or more, and more preferably 60 atom% or less.

[0059] The concentration of each atom was determined using EDX (energy-dispersive X-ray diffraction). The EDX measuring device used was a JEM-ARM200F manufactured by Nippon Electronics.

[0060] Accelerating voltage: 200kV, beam diameter: approximately φ0.1nm.

[0061] From the viewpoint of this invention, the thickness of the first amorphous layer is preferably 1.0 nm to 3.0 nm. Furthermore, from the viewpoint of this invention, the thickness of the second amorphous layer is preferably 4 to 10 nm, more preferably 6 to 8 nm. It should be noted that the presence and thickness of the first and second amorphous layers can be confirmed by examining the cross-section of the composite substrate using a high-resolution transmission electron microscope image (8 millionx magnification).

[0062] According to the present invention, even when the piezoelectric material substrate is processed to be relatively thin, the peeling of the piezoelectric material substrate from the supporting substrate can be suppressed. Therefore, from the viewpoint of the performance of composite substrates, particularly elastic wave elements, the thickness of the piezoelectric material substrate is preferably 2.0 μm or less, more preferably 1.0 μm or less. There is no particular limitation on the lower limit of the thickness of the piezoelectric material substrate; from a practical processing viewpoint, it can be 0.05 μm or more. It should be noted that the thickness of the piezoelectric material substrate is measured using an optical measuring machine (Filmetrix F20) employing light interference.

[0063] The composite substrates 7 and 7A of the present invention are preferably used in the elastic wave element 10.

[0064] As the elastic wave element 10, known examples include surface wave devices, Lamb wave elements, and thin-film resonators (FBARs). For instance, an elastic surface wave device is a device in which an IDT (Interdigital Transducer) electrode (also called a comb electrode or curtain electrode) for exciting an elastic surface wave and an IDT electrode for receiving the elastic surface wave are 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 an elastic surface wave that propagates on the piezoelectric material substrate. Then, the propagated 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.

[0065] The electrode (electrode pattern) 8 constituting the piezoelectric material substrate 1A is preferably made of aluminum, aluminum alloy, copper, or gold, and more preferably aluminum or 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.

[0066] Example

[0067] (Example 1)

[0068] For reference Figures 1-3 The surface elastic wave element was fabricated as described.

[0069] Specifically, a 42Y-cut X-propagation LiTaO3 substrate (piezoelectric material substrate) 1 with a thickness of 250 μm and both sides polished to a mirror finish was prepared, and an AT-cut crystal substrate (support substrate) 4 with a thickness of 350 μm was prepared. The substrate size was 100 mm. Next, the surface 1a of the piezoelectric material substrate 1 and the surface 4a of the support substrate 4 were cleaned and surface activated, respectively.

[0070] Specifically, ultrasonic cleaning with pure water was performed, followed by spin drying to dry the substrate surface. Next, the cleaned support substrate was placed in a plasma activation chamber, where the bonding surfaces were activated using oxygen plasma at 30°C. Similarly, a piezoelectric material substrate was placed in the plasma activation chamber, and the bonding surfaces were activated using oxygen plasma at 30°C. The surface activation time was 40 seconds, and the energy was 100W. To remove particles adhering to the surface during activation, the same ultrasonic cleaning and spin drying process was repeated.

[0071] Next, the substrates were aligned, and the activated bonding surfaces of the two substrates were brought into contact at room temperature. Pressure was applied to the center of the overlapping substrates, and the resulting close-bonding expansion of the substrates (the so-called bonding wave) confirmed good pre-bonding. The bond was then placed in a nitrogen atmosphere oven for 10 hours. The relationship between heating temperature and bonding strength was investigated, and the results were... Figure 4 The data shown illustrates that to achieve a high-performance SAW filter with a structure that bonds piezoelectric material and crystal together, the piezoelectric material needs to be extremely thin. To achieve such a structure using CMP, a very strong bond is required. Specifically, a bond strength of 3 J / m is needed. 2 The above-mentioned bond strength. In this example, a heating temperature of 250°C or higher is known to be required. The bond strength was evaluated using the scraper method shown in Non-Patent Document 3.

[0072] The piezoelectric material substrate of the bond, heated at 100°C for 10 hours, was machined to a thickness of 10 μm using a grinding machine. The machined substrate was then further heated at 250°C for 10 hours. Next, the substrate was mounted in a grinding machine, and the thickness was further reduced to 5 μm while diamond slurry was supplied. Finally, CMP (Chemical Molecular Processing) was used for grinding to remove the processed altered layer and finalize the thickness. Colloidal silica was used as the slurry during grinding. After grinding, the substrate was removed, and no piezoelectric material substrate peeling was observed, confirming a very strong bond.

[0073] The thickness of the piezoelectric material substrate was measured using an optical measuring machine (Filmetrix F20) with light interference, and a very thin layer of 2 μm was obtained.

[0074] To determine the thickness limit of the piezoelectric material substrate, CMP was further performed, and no peeling was found even when the thickness became 0.3 μm.

[0075] The cross-section of the bonding interface in Example 1 was analyzed using high-resolution TEM (JEM-ARM200F, accelerating voltage 200kV, magnification 8 million times). The results showed an amorphous layer at the bonding interface. Figure 5 Upon closer inspection, the amorphous layer was found to consist of two layers.

[0076] Right now, Figure 5 In the diagram, region 1 is the end of a piezoelectric material substrate containing lithium tantalate single crystals, and region 4 is a supporting substrate containing silicon oxide. Region 1 is darker than region 4 because a large number of tantalum atoms with higher atomic weights are present. Furthermore, region 2 is the first amorphous layer, and region 3 is the second amorphous layer.

[0077] For the purpose of investigating the composition of the aforementioned amorphous layers, EDX analysis was performed under the following conditions. The results are shown in Table 1.

[0078] Transmission electron microscope: Hitachi HD-2700

[0079] Accelerating voltage: 200kV

[0080] Beam diameter: approximately φ0.2nm

[0081] Elemental analysis apparatus: EDAX Genesis

[0082] X-ray detector: Si / Li semiconductor detector

[0083] Energy resolution: approximately 140 eV

[0084] X-ray emission angle: 25.7°

[0085] Solid angle: 0.31sr

[0086] Capture time: 30 seconds

[0087] [Table 1]

[0088] Example 1

[0089]

[0090] (Example 2)

[0091] In Example 1, a plasma composed of 80% nitrogen and 20% oxygen was used instead of oxygen plasma. When changing the gas composition, the matching was appropriately modified to minimize the reflected power of the RF.

[0092] In addition, the joint was processed in the same manner as in Example 1. As a result, similar to Example 1, a strength of 3.2 J / m was measured after heating to 250°C. 2 High bonding strength. Even when the piezoelectric layer thickness is 1 μm using CMP processing, no peeling occurs on this substrate.

[0093] For the purpose of investigating the composition of the amorphous layer of the obtained conjugate, EDX analysis was performed in the same manner as in Example 1. The results are shown in Table 2.

[0094] [Table 2]

[0095] Example 2

[0096]

[0097] (Example 3)

[0098] In Example 1, the heating temperature of the bond was changed from 250°C to 270°C. Similar to Example 1, the resulting bond was ground, and even after CMP processing to a thickness of 0.3 μm, no peeling was observed.

[0099] Similar to Example 1, the cross-section of the bonding interface in Example 3 was analyzed using high-resolution TEM. As a result, a first amorphous layer and a second amorphous layer were observed at the bonding interface. For the purpose of investigating the composition of each of the aforementioned amorphous layers, EDX analysis was performed under the same conditions as in Example 1. The measurement results are shown in Table 3.

[0100] [Table 3]

[0101] Example 3

[0102]

[0103] As can be seen in this way, in the embodiments of the present invention, a first amorphous layer and a second amorphous layer with specific compositions are generated. It should be noted that the fluorine atoms in the composition are considered to originate from the fluorinated rubber (perfluorocarbon polymer) of the O-ring constituting the plasma processing chamber.

[0104] (Comparative Example 1)

[0105] In Example 1, a neutral argon beam was used instead of oxygen plasma for surface activation. The activation time was set to 60 seconds for both the crystal and piezoelectric substrates. The wafers were brought into contact with each other in the vacuum chamber of a bonding machine, and pressure was applied to bond them, resulting in a bond. The removed wafers were placed in an oven at 100°C in the same manner as in Example 1, and removed after 10 hours. Although the goal was to process the piezoelectric substrate to a thickness of 10 μm using a grinding machine, the grinding machine displayed an error after processing approximately 20 μm. The wafers were removed, and as a result, the piezoelectric material peeled off significantly. This indicates that only a very weak bond strength was obtained.

[0106] (Comparative Example 2)

[0107] The maximum heating temperature was kept at a low temperature of 150°C. Otherwise, plasma activation was performed in the same manner as in Example 1 to form a bond. CMP processing was then carried out, and as a result, peeling occurred when 5 μm of the thickness of the piezoelectric material substrate was removed.

[0108] For the purpose of investigating the composition of the amorphous layer of the obtained conjugate, TEM and EDX analyses were performed in the same manner as in Example 1. The results are shown in Table 4. Perhaps due to the lower heating temperature, the composition differs significantly from that of the example.

[0109] In addition, it was found that the thickness of the amorphous layer became extremely thin.

[0110] [Table 4]

[0111] Comparative Example 2

[0112]

Claims

1. A composite substrate, characterized by, have: Support substrate containing crystal, piezoelectric material substrate, The first amorphous layer existing between the supporting substrate and the piezoelectric material substrate, and The second amorphous layer exists between the supporting substrate and the first amorphous layer. The first amorphous layer contains 10-30 atom% silicon atoms, and the second amorphous layer contains 1-10 atom% fluorine atoms.

2. The composite substrate according to claim 1, characterized in that, The piezoelectric material substrate comprises a material selected from the group consisting of lithium niobate, lithium tantalate, and lithium niobate-lithium tantalate. The first amorphous layer comprises silicon atoms and one or two atoms selected from the group consisting of niobium and tantalum, and oxygen atoms as the main components. The total ratio of one or two atoms selected from the group consisting of niobium and tantalum and oxygen atoms in the first amorphous layer is more than 70 atom% and less than 90 atom%.

3. The composite substrate according to claim 1, characterized in that, The second amorphous layer contains fluorine atoms, silicon atoms and oxygen atoms as main components. The proportion of silicon atoms in the second amorphous layer is more than 35 atom% and less than 50 atom%, and the proportion of oxygen atoms in the second amorphous layer is more than 45 atom% and less than 60 atom%.

4. The composite substrate according to claim 2, characterized in that, The second amorphous layer contains fluorine atoms, silicon atoms and oxygen atoms as main components. The proportion of silicon atoms in the second amorphous layer is more than 35 atom% and less than 50 atom%, and the proportion of oxygen atoms in the second amorphous layer is more than 45 atom% and less than 60 atom%.

5. The composite substrate according to any one of claims 1 to 4, characterized in that, The thickness of the first amorphous layer is 1 nm to 3 nm, and the thickness of the second amorphous layer is 4 nm to 10 nm.

6. An elastic wave element, characterized in that, It comprises: the composite substrate as described in any one of claims 1 to 5, and the electrodes on the piezoelectric material substrate.

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