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

Abstract

When a piezoelectric material substrate including lithium tantalate and the like is bonded to a support substrate including crystal, the bonding strength is increased so that the piezoelectric material substrate will not peel off even if it is thinned. The composite substrate 7, 7A comprises: a support substrate 4 including crystal; a piezoelectric material substrate 1, 1A including a material selected from the group consisting of lithium niobate, lithium tantalate, and lithium niobate-lithium tantalate; and an interface layer 5 located at the bonding interface between the support substrate 4 and the piezoelectric material substrate 1, 1A. The interface layer 5 is an amorphous structure composed of at least one of tantalum and niobium, silicon, and oxygen. The hydrogen atom concentration, nitrogen atom concentration, and fluorine atom concentration in the interface layer 5 are 1×10 18 atoms / cm 3 Above 5×10 21 atoms / cm 3 the following.

Description

Technical Field

[0001] The present invention relates to a composite substrate of a piezoelectric material substrate and a support substrate and a manufacturing method thereof. Background Art

[0002] To achieve high-performance semiconductor devices, SOI substrates composed of high-resistance Si / SiO2 thin film / Si thin film are widely used. Plasma activation is used to create SOI substrates because they can be bonded at relatively low temperatures (400°C). Similar composite substrates composed of Si / SiO2 thin film / piezoelectric thin film have been proposed to improve the characteristics of piezoelectric devices.

[0003] Furthermore, to improve the temperature characteristics of SAW filters and increase their Q value, SAW filters with a structure in which a piezoelectric material substrate is bonded to a supporting substrate have been reported. In particular, acoustic wave devices using a composite substrate formed by bonding a quartz crystal substrate to a lithium tantalate substrate have been reported to exhibit exceptionally excellent characteristics (Non-Patent Documents 1 and 2, Patent Documents 1 and 2).

[0004] Prior art literature

[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 2018 Proceedings

[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 2018 Proceedings

[0008] Patent Literature

[0009] Patent Document 1: US 10,084,427 B2

[0010] Patent Document 2: Japanese Patent Application Laid-Open No. 2018-026695 Summary of the Invention

[0011] In the aforementioned composite substrates, thinning the piezoelectric substrate is a design requirement. However, the thinner the piezoelectric substrate, the stronger the bonding strength required. For example, Patent Document 2 proposes a bonded structure of a quartz crystal and a piezoelectric layer. However, when the piezoelectric substrate is thinned, there is a problem of separation from the supporting substrate, requiring further improvement in bonding strength.

[0012] The present invention aims to improve the bonding strength when bonding a piezoelectric substrate made of a material selected from the group consisting of lithium niobate, lithium tantalate, and lithium niobate-lithium tantalate to a support substrate made of quartz crystal so that the piezoelectric substrate does not peel off even when the substrate is thinned.

[0013] The present invention is characterized in that:

[0014] a supporting substrate comprising a crystal;

[0015] a piezoelectric material substrate comprising a material selected from the group consisting of lithium niobate, lithium tantalate, and lithium niobate-lithium tantalate; and

[0016] an amorphous interface layer located at the bonding interface between the support substrate and the piezoelectric material substrate, and comprising silicon and oxygen, at least one of tantalum and niobium,

[0017] The hydrogen atom concentration, nitrogen atom concentration and fluorine atom concentration in the interface layer are 1×10 18 atoms / cm 3 Above 5×10 21 atoms / cm 3 the following.

[0018] The present invention also relates to an elastic wave device characterized by comprising: the composite substrate and electrodes on the piezoelectric single crystal substrate.

[0019] The present invention also relates to a method for manufacturing a composite substrate comprising: a support substrate made of quartz crystal; and a piezoelectric material substrate made of a material selected from the group consisting of lithium niobate, lithium tantalate, and lithium niobate-lithium tantalate.

[0020] The method for manufacturing a composite substrate is characterized by comprising the following steps:

[0021] a step of generating an activated surface by irradiating the surface of the support substrate with plasma containing nitrogen gas,

[0022] a step of irradiating the surface of the piezoelectric material substrate with plasma containing nitrogen gas to generate an activated surface;

[0023] a step of obtaining a bonded body by bringing the active surface of the support substrate into contact with the active surface of the piezoelectric material substrate,

[0024] The step of thinning the piezoelectric material substrate to less than 20 μm by processing, and

[0025] The step of heat-treating the bonded body at a temperature of 250° C. to 350° C.

[0026] Effects of the Invention

[0027] The inventors of the present invention have developed a method for directly bonding a piezoelectric material substrate made of, for example, lithium tantalate to a supporting substrate made of quartz crystal. This involves activating the surfaces of the piezoelectric material substrate and the supporting substrate separately by plasma irradiation, bringing the activated surfaces into contact and bonding them, followed by heat treatment. They discovered that heat treatment at a temperature between 250°C and 350°C significantly improves bonding strength, making it less likely that the piezoelectric material substrate will peel off from the supporting substrate, even when the piezoelectric material substrate is thinned.

[0028] The inventors of the present invention have further studied the reasons for the improved bonding strength and have found the following: Specifically, they discovered that in a composite substrate with improved bonding strength, a fine interface layer is formed along the interface between a piezoelectric material substrate made of lithium tantalate or the like and a supporting substrate made of quartz crystal, and that the hydrogen, nitrogen, and fluorine atom concentrations in this interface layer are increased, specifically, increasing to 1×10 18 atoms / cm 3 The present invention was completed by forming a peak as described above.

[0029] The reason for this effect is unclear, but it is speculated that nitrogen, trace amounts of water, and fluorine in the atmosphere adhere to the bond interface during plasma irradiation. During heat treatment, these elements concentrate near the interface and become more distributed in the interface layer, resulting in improved bond strength. Lower heat treatment temperatures, however, reduce the concentration of nitrogen, hydrogen, and fluorine in the interface layer, and in this case, the bond strength is thought to be less likely to improve.

[0030] Furthermore, Patent Document 2 describes bonding a support substrate made of quartz crystal and a piezoelectric material substrate made of lithium tantalate. However, the disclosure states that, preferably, an amorphous silicon oxide layer or an amorphous aluminum oxide layer is formed on the surface of the support substrate or the surface of the piezoelectric material substrate prior to bonding, and then heat treated at 150-200°C. In contrast, the method of the present invention activates the surfaces of the support substrate made of quartz crystal and the piezoelectric material substrate made of lithium tantalate or the like using a plasma containing nitrogen gas, directly bonds them, and then heat treats them at 250°C or higher. This generates a fine interface layer along the bonding interface, containing relatively high atomic concentrations of hydrogen, nitrogen, and fluorine atoms. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] Figure 1 In FIG. 1 , (a) shows a piezoelectric material substrate 1 , and (b) shows a state in which a bonding surface 1 a of the piezoelectric material substrate 1 is activated to generate an activated surface 1 c .

[0032] Figure 2 In the figures, (a) shows the supporting substrate 4, and (b) shows a state in which the surface of the supporting substrate 4 is activated.

[0033] Figure 3 , (a) shows a bonded structure 7 obtained by directly bonding the piezoelectric material substrate 1 and the support substrate 4 , (b) shows a state where the piezoelectric material substrate 1A of the bonded structure is polished and thinned, and (c) shows the elastic wave element 10 .

[0034] Figure 4 This is a graph showing an example of the relationship between the heating temperature after direct bonding and the bonding strength.

[0035] Figure 5 This is a graph showing the hydrogen atom concentration near the interface of the composite substrate.

[0036] Figure 6 This is a graph showing the fluorine atom concentration near the interface of the composite substrate.

[0037] Figure 7 This is a graph showing the nitrogen atomic concentration near the interface of the composite substrate.

[0038] Figure 8 This is a graph showing the carbon atom concentration near the interface of the composite substrate.

[0039] Figure 9 This is a high-resolution transmission electron micrograph (2,000,000 times) showing the vicinity of the interface of the composite substrate.

[0040] Figure 10 This is a high-resolution transmission electron micrograph (8 million times magnification) showing the vicinity of the interface of the composite substrate. DETAILED DESCRIPTION

[0041] Hereinafter, the present invention will be described in detail with reference to the accompanying drawings as appropriate.

[0042] First, if 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 used as a bonding surface. Figure 1 As shown in (b), the bonding surface 1a of the piezoelectric material substrate 1 is irradiated with plasma as indicated by arrow A, thereby obtaining a bonding surface 1c after surface activation.

[0043] On the other hand, Figure 2 As shown in (a), a supporting substrate 4 is prepared. Figure 2 As shown in (b), the surface 4a of the support substrate 4 is irradiated with plasma as indicated by arrow B, thereby performing surface activation and forming an activated bonding surface 6.

[0044] Next, if Figure 3 As shown in Figure (a), the activated bonding surface 1c on the piezoelectric material substrate 1 and the activated bonding surface 6 of the support substrate 4 are brought into contact and directly bonded to form a bonded product. The resulting bonded product is heated to achieve a bond strength sufficient to withstand grinding. During this heating stage, the heating temperature is preferably 50-150°C, more preferably 80-120°C.

[0045] Next, the piezoelectric substrate of the bonded body is processed to be thinner using a grinder. By heat treating the bonded body at a temperature of 250°C or higher, a bonded body 7 can be obtained. Here, an interface layer 5 mainly composed of silicon, oxygen, and one or both of tantalum and niobium is generated. Electrodes can be set on the piezoelectric material substrate 1 in this state. However, it is preferred that Figure 3 As shown in (b), the main surface 1b of the piezoelectric material substrate 1 is processed to make the substrate 1 thinner, thereby obtaining a thinned piezoelectric material substrate 1A. 1d is the processed surface. Figure 3 As shown in (c), predetermined electrodes 8 are formed on the processed surface 1 d of the piezoelectric material substrate 1A of the bonded body 7A, thereby obtaining the elastic wave element 10 .

[0046] Hereinafter, each component of the present invention will be described in sequence.

[0047] The support substrate 4 is made of quartz crystal. Quartz crystal is anisotropic, and the properties of the piezoelectric element are affected by its crystal orientation. Non-Patent Document 1 demonstrates that spurious signals can be suppressed by focusing on the speed of sound. Therefore, the orientation can be appropriately selected to achieve the desired properties.

[0048] The piezoelectric material substrate 1 used in the present invention is made of lithium tantalate (LT), lithium niobate (LN), or a lithium niobate-lithium tantalate solid solution. These materials have high elastic wave propagation speeds and large electromechanical coupling coefficients, making them suitable for high-frequency and broadband surface acoustic wave devices.

[0049] In addition, the normal direction of the main surfaces 1a and 1b of the piezoelectric material substrate 1 is not particularly limited. For example, when the piezoelectric material substrate 1 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 of (180°, 58 to 35°, 180°) is used. This has a small propagation loss and is therefore preferred. When the piezoelectric material substrate 1 is formed of LN, (a) a piezoelectric material substrate with an orientation expressed as (0°, 37.8°, 0°) with the X-axis, the direction of propagation of surface acoustic waves, being the center, rotated 37.8° from the Z-axis to the -Y-axis is preferably used, as this provides a high electromechanical coupling coefficient. Alternatively, (i) a piezoelectric material substrate with an orientation expressed as (180°, 50° to 25°, 180°) with the X-axis, the direction of propagation of surface acoustic waves, being the center, rotated 40° to 65° from the Y-axis to the Z-axis is preferably used, as this provides a high acoustic velocity. The size of the piezoelectric material substrate is not particularly limited, but may be, for example, 100 to 200 mm in diameter and 0.15 to 1 μm in thickness.

[0050] Next, plasma is irradiated onto the surface of the piezoelectric material substrate and the surface of the support substrate to activate the respective surfaces.

[0051] The atmosphere used for surface activation is an atmosphere containing nitrogen. This atmosphere may be nitrogen or oxygen alone, or a mixed gas of nitrogen, oxygen, hydrogen, or argon.

[0052] The atmospheric pressure during surface activation is preferably 100 Pa or less, more preferably 80 Pa or less. The atmospheric pressure is preferably 30 Pa or more, more preferably 50 Pa or more.

[0053] The temperature during plasma irradiation is set to 150° C. or lower. This provides a bonded body 7 having high bonding strength and no degradation of the piezoelectric material. From this viewpoint, the temperature during plasma irradiation is set to 150° C. or lower, more preferably 100° C. or lower.

[0054] 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 0.1 to 3.0 Wh.

[0055] In a preferred embodiment, the surface 1a of the piezoelectric material substrate and the surface 4a of the support substrate are planarized before plasma treatment. Methods for planarizing surfaces 1a and 4a include lapping (lap) and chemical mechanical polishing (CMP). The arithmetic mean roughness Ra of the flat surfaces is preferably 1 nm or less, more preferably 0.3 nm or less.

[0056] Next, the active surface of the piezoelectric material substrate is brought into contact with the active surface of the support substrate and bonded. Then, the bond strength is improved by performing a heat treatment (annealing) on ​​the bonded body. From the viewpoint of the present invention, the temperature during the heat treatment is set to be above 250°C, preferably above 270°C. In addition, the temperature during the heat treatment is preferably below 350°C, more preferably below 300°C.

[0057] In the present invention, the hydrogen atom concentration, nitrogen atom concentration, and fluorine atom concentration in each part of the junction (particularly the interface layer) are 1×10 18 atoms / cm 3 More than 1×10 19 atoms / cm 3 More than 5×10 19 atoms / cm 3 More than 1×10 20 atoms / cm 3 In addition, from the perspective of actual production, the concentration of these atoms in the interface layer is preferably 5×10 21 atoms / cm 3 Below, more preferably 3×10 21 atoms / cm 3 the following.

[0058] The hydrogen, fluorine, nitrogen, and carbon concentrations were measured using SIMS (Secondary Ion Mass Spectrometry). A CAMECA IMS-7f instrument was used, with Cs+ as the primary ion species, a primary acceleration voltage of 15.0 kV, and a detection area of ​​30 μm in diameter.

[0059] From the perspective of the present invention, the thickness of the interface layer is preferably 3 to 20 nm, more preferably 5 to 15 nm. The presence and thickness of the interface layer can be confirmed by examining a cross section of the composite substrate using a high-resolution transmission electron microscope (8 million times magnification).

[0060] Comparison between the interface layer and the upper and lower single crystal substrates shows that it is in an amorphous state. The interface layer is obtained by diffusion (transfer) from the composition of the piezoelectric material substrate and the composition of the supporting substrate, so it is composed of silicon, oxygen, and one or both of tantalum and niobium constituting the piezoelectric material substrate. Preferably, the interface layer substantially contains silicon, oxygen, and one or both of tantalum and niobium constituting the piezoelectric material substrate. However, in this case, it may also contain hydrogen atoms, fluorine atoms, nitrogen atoms, and other trace impurities.

[0061] According to the present invention, even if the piezoelectric material substrate is processed to be thinner, the piezoelectric material substrate can be prevented from peeling off from the supporting substrate. Therefore, from the perspective of the performance of the composite substrate, especially the elastic wave element, the thickness of the piezoelectric material substrate is preferably less than 2.0 μm, and more preferably less than 1.0 μm. There is no particular restriction on the lower limit of the thickness of the piezoelectric material substrate. From the perspective of actual processing, it can be 0.05 μm or more. It should be noted that the thickness of the piezoelectric material substrate was measured using an optical measuring machine (F20 manufactured by Filmetrix) using light interference.

[0062] Composite substrates 7 and 7A of the present invention can be preferably used in acoustic wave device 10 .

[0063] Known examples of acoustic wave elements 10 include surface acoustic wave devices, Lamb wave elements, and thin film resonators (FBARs). 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 substrate. This electrode excites surface acoustic waves on the input side, and receives them on the output side. Applying a high-frequency signal to the input-side IDT electrode generates an electric field between the electrodes, exciting surface acoustic waves that propagate across the piezoelectric substrate. The propagated surface acoustic waves can then be output as electrical signals from the output-side IDT electrode, located in the direction of propagation.

[0064] The material constituting the electrodes (electrode pattern) 8 on the piezoelectric material substrate 1A is preferably aluminum, an aluminum alloy, copper, or gold, 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.

[0065] Example

[0066] (Example 1)

[0067] As reference Figures 1 to 3 A surface acoustic wave element is produced as described above.

[0068] Specifically, a 250 μm thick, mirror-polished 42Y-cut X-propagation LiTaO substrate (piezoelectric substrate) 1 and a 350 μm thick AT-cut quartz crystal substrate (support substrate) 4 were prepared. Both substrates were 100 mm in size. Next, the surface 1a of the piezoelectric substrate 1 and the surface 4a of the support substrate 4 were cleaned and activated.

[0069] Specifically, ultrasonic cleaning with pure water was performed, and the substrate surface was dried by spin drying. Next, the cleaned support substrate was introduced into a plasma activation chamber, and the substrate surface was activated by nitrogen plasma at 30°C. In addition, the piezoelectric material substrate was similarly introduced into the plasma activation chamber, and the substrate surface was surface activated by nitrogen plasma at 30°C. The surface activation time was 40 seconds and the energy was 100W. In order to remove the particles attached during the surface activation, the same ultrasonic cleaning and spin drying as above were performed again.

[0070] Next, the support substrate and the piezoelectric material substrate were aligned, and the activated surfaces of the two substrates were brought into contact with each other at room temperature. The center of the overlapping substrates was pressurized, and the close contact and expansion between the support substrate and the piezoelectric material substrate (the so-called bonding wave) were 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 for 10 hours. The relationship between the heat treatment temperature and the bonding strength was investigated, and the results were obtained. Figure 4 The data shown. Non-patent literature 1, 2, and patent literature 1 state that in order to realize a high-performance SAW filter by pasting a piezoelectric material and a crystal together, the thickness of the piezoelectric material must be made very thin. If such a structure is to be realized by CMP, a very strong bond is required. Specifically, 3 J / m 2 The bonding strength is above 250° C. It is known that the heat treatment temperature of the present invention is required to be 250° C. or higher. The bonding strength was evaluated by the scraper method described in the following literature.

[0071] “SEMICONDUCTOR WAFER BONDING” Q.-Y.Tong,U.Gosele,Wiley-InterScience.P.27

[0072] The piezoelectric material substrate of the composite substrate after heat treatment at 100°C was processed by a grinder until the thickness reached 10μm. The processed substrate was further heated at 250°C for 10 hours. Next, the composite substrate was mounted on a grinding machine, and while supplying diamond slurry, the piezoelectric material substrate was processed until the thickness reached 5μm. Finally, it was polished using a CMP processor to remove the modified layer and make the final adjustment to the thickness. Colloidal silica was used as the slurry during polishing. After polishing, the composite substrate was taken out. As a result, no peeling of the piezoelectric material substrate from the supporting substrate was observed at all, and it was confirmed that a very strong bond could be achieved. The thickness of the piezoelectric material substrate was measured using an optical measuring machine (F20 manufactured by Filmetrix) using light interference, and a very thin layer of 2.0μm was obtained.

[0073] CMP was further continued, and as a result, even when the thickness of the piezoelectric material substrate became 0.3 μm, no peeling was observed.

[0074] (Example 2)

[0075] In Example 1, a plasma composed of a mixture of 80% nitrogen and 20% oxygen was used instead of nitrogen plasma. When changing the gas composition, the matching was appropriately adjusted to minimize the reflected RF power. Otherwise, the composite substrate was processed in the same manner as in Example 1. In this case, as in Example 1, 3.2 J / m was measured after heating at 250°C. 2 The bonding strength was high. In addition, in the composite substrate obtained, even when the piezoelectric layer was reduced to a thickness of 1 μm by CMP processing, no separation of the self-supporting substrate occurred. The results are shown in Table 1.

[0076] (Comparative Example 1)

[0077] In Example 1, a high-speed neutral argon beam is used instead of nitrogen plasma to activate the surfaces of the piezoelectric material substrate and the supporting substrate. The acceleration voltage at this time is set to 1 kV, the Ar flow rate is set to 27 sccm, and the surface activation time is set to 120 seconds. The piezoelectric material substrate and the supporting substrate are brought into contact in the vacuum chamber of the above-mentioned bonding machine, and a pressure of 10 kN is applied for bonding. The taken-out bonded body is placed in an oven at 100°C in the same manner as in Example 1, and the composite substrate is taken out after 10 hours. The obtained composite substrate is ground using a grinder. Although it is intended to process the piezoelectric material substrate to a thickness of 10 μm, the grinder displays an error when about 20 μm is processed. The wafer is taken out, and as a result, the piezoelectric material is largely peeled off. It can be seen from this that only very weak bonding strength is obtained.

[0078] (Comparative Example 2)

[0079] A bonded body was prepared by plasma activation in the same manner as in Example 1 except that the maximum heating temperature was set to a low temperature of 150°C. CMP processing was performed, and peeling occurred when the piezoelectric material substrate was cut off by 5 μm. The results are shown in Table 2.

[0080] The hydrogen, fluorine, nitrogen, and carbon concentrations in various parts of the composite substrates of Example 1 and Comparative Example 2 were measured using SIMS (secondary ion mass spectrometry). A CAMECA IMS-7f SIMS instrument was used, with Cs+ as the primary ion species and a primary acceleration voltage of 15.0 kV. The detection area was 30 μm in diameter.

[0081] Results, such as Figure 5 As shown, in Example 1, hydrogen atoms were locally present along the bonding interface and also diffused into the interior of the piezoelectric material substrate. On the other hand, in Comparative Example 1, no hydrogen atoms were detected.

[0082] In addition, if Figure 6 As shown, in both Example 1 and Comparative Example 1, fluorine atoms are locally present near the bonding interface. However, in Example 1, the fluorine atom concentration is significantly increased.

[0083] The sources of these mixed atoms are believed to be as follows: heating the wafer at high temperatures causes the desorption of Li ions from the piezoelectric substrate, introducing hydrogen from the atmosphere. Fluorine atoms are also mixed in through outgassing from the O-ring within the plasma activation chamber.

[0084] In addition, if Figure 7 As shown, in both Example 1 and Comparative Example 1, nitrogen atoms are locally present near the bonding interface. However, in Example 1, the concentration of nitrogen atoms is significantly increased.

[0085] In addition, if Figure 8 As shown, carbon atoms are localized near the bonding interface in both Example 1 and Comparative Example 1. No significant difference in the carbon atom concentration in the interface layer is observed between the Example and the Comparative Example.

[0086] Figure 9 This is a high-resolution transmission electron micrograph (magnification 2,000,000) showing the vicinity of the interface of the composite substrate of Example 1. Figure 10 This is a high-resolution transmission electron microscope photograph (8 million times) showing the vicinity of the interface of the composite substrate of Example 1. The lower side of the photograph represents the crystal (support substrate), the darker contrast area on the upper side represents lithium tantalate (piezoelectric material substrate), and the brighter contrast portion in the center of the photograph represents the interface layer. Figures 4 to 7Since the horizontal axis (depth) of the data in each graph corresponds to the vertical position of these cross-sectional views, it is possible to associate the interface layer with each atomic concentration.

[0087] (Examples 3 to 4 and Comparative Example 3)

[0088] A surface acoustic wave device of each example was produced in the same manner as in Example 1.

[0089] By varying the plasma atmosphere, the energy during surface activation, and the heat treatment temperature of the bonded structure, the atomic concentrations and interface layer thicknesses of the resulting composite substrates were varied as shown in Table 1. The bonding strength of each composite substrate was measured. Furthermore, the piezoelectric material substrates of each composite substrate were processed in the same manner as in Example 1, and the minimum thickness at which no delamination occurred was measured. These results are shown in Tables 1 and 2.

[0090] At the same time, the hydrogen atom concentration, nitrogen atom concentration, and fluorine atom concentration in each of the Examples and Comparative Examples were measured as described above. The results are shown in Tables 1 and 2.

[0091] [Table 1]

[0092]

[0093] [Table 2]

[0094]

[0095] < indicates below the detection limit

[0096] These results show that according to the present invention, the piezoelectric material substrate and the supporting substrate are directly bonded by a surface activation method using plasma containing nitrogen. After the piezoelectric material substrate is processed, the bonded body is heat treated at a temperature of not less than 250°C and not more than 350°C, thereby obtaining a higher bonding strength.

[0097] At the same time, it was confirmed that high bonding strength can be reliably obtained by setting the hydrogen atom concentration, nitrogen atom concentration, and fluorine atom concentration in the interface layer to within the ranges of the present invention.

Claims

1. A composite substrate, characterized in that: have: a supporting substrate comprising a crystal; a piezoelectric material substrate comprising a material selected from the group consisting of lithium niobate, lithium tantalate, and lithium niobate-lithium tantalate; as well as an amorphous interface layer located at the bonding interface between the support substrate and the piezoelectric material substrate, and comprising silicon and oxygen, at least one of tantalum and niobium, The hydrogen atom concentration, nitrogen atom concentration and fluorine atom concentration in the interface layer are 1×10 18 atoms / cm 3 Above 5×10 21 atoms / cm 3 the following.

2. The composite substrate according to claim 1, wherein The hydrogen atom concentration, the nitrogen atom concentration, and the fluorine atom concentration in the interface layer are 1×10 19 atoms / cm 3 Above 5×10 21 atoms / cm 3 the following.

3. An elastic wave element, characterized in that: The invention comprises: the composite substrate according to claim 1 or 2, and electrodes on the piezoelectric material substrate.

4. A method for manufacturing a composite substrate, the method comprising manufacturing the composite substrate according to claim 1 or 2, the composite substrate comprising: a support substrate comprising crystal, and a piezoelectric material substrate comprising a material selected from the group consisting of lithium niobate, lithium tantalate, and lithium niobate-lithium tantalate; The method for manufacturing the composite substrate is characterized by comprising the following steps: a step of generating an activated surface by irradiating the surface of the support substrate with plasma containing nitrogen gas, a step of irradiating the surface of the piezoelectric material substrate with plasma containing nitrogen gas to generate an activated surface; a step of obtaining a bonded body by bringing the active surface of the support substrate into contact with the active surface of the piezoelectric material substrate, The step of thinning the piezoelectric material substrate to less than 20 μm by processing, and A step of heat-treating the bonded structure at a temperature of 250° C. to 350° C. after processing the piezoelectric material substrate.

5. The manufacturing method according to claim 4, characterized in that After the heat treatment, the thickness of the piezoelectric material substrate is reduced by grinding.

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