Method of manufacturing acoustic wave device

Abstract

To provide a method of manufacturing an acoustic wave device capable of improving crystallinity of a piezoelectric film and improving productivity.SOLUTION: A method of manufacturing an acoustic wave device includes the steps of: preparing a substrate 22 and a support member 33; providing a buffer layer 23 on the substrate 22; providing a piezoelectric film 28 on the buffer layer 23; joining the piezoelectric film 28 in a laminate of the substrate 22, the buffer layer 23 and the piezoelectric film 28 to the support member 33; and removing the buffer layer 23 and the substrate 22 from the piezoelectric film 28. When a lattice constant of the substrate 22 is defined as LS, a lattice constant of the buffer layer 23 is defined as LB and a lattice constant of the piezoelectric film 28 is defined as LP, (|LS-LB| / LS)×100[%]≤20[%] is satisfied and (|LP-LB| / LP)×100[%]≤10[%] is satisfied.SELECTED DRAWING: Figure 3

Description

Technical Field

[0001] The present invention relates to a method for manufacturing an elastic wave device.

[0002] Conventionally, elastic wave devices have been widely used in filters for mobile phones and the like. Patent Document 1 below describes an example of an elastic wave device and a manufacturing method thereof. In the manufacturing method described in Patent Document 1, a piezoelectric substrate is prepared as a piezoelectric layer. However, at the stage of preparing the piezoelectric layer, the thickness of the piezoelectric layer is not the desired thickness. Therefore, in this manufacturing method, the piezoelectric layer is thinned by grinding to adjust the thickness of the piezoelectric layer to the desired thickness.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] However, in the conventional manufacturing method as described in Patent Document 1, most of the prepared piezoelectric layer may be removed by grinding and discarded. Therefore, it is difficult to sufficiently increase productivity. Conventionally, in order to sufficiently increase the crystallinity of the thin-film piezoelectric layer used in the elastic wave device, it has been necessary to thin the piezoelectric substrate after preparing a piezoelectric substrate with high crystallinity.

[0005] An object of the present invention is to provide a method for manufacturing an elastic wave device that can increase the crystallinity of a piezoelectric film and can increase productivity.

Means for Solving the Problems

[0006] The manufacturing method of the elastic wave device according to the present invention includes a step of preparing a substrate and a support member, a step of providing a buffer layer on the substrate, a step of providing a piezoelectric film on the buffer layer, a step of bonding the piezoelectric film in the laminate of the substrate, the buffer layer, and the piezoelectric film to the support member, and a step of removing the buffer layer and the substrate from the piezoelectric film. When the lattice constant of the substrate is LS, the lattice constant of the buffer layer is LB, and the lattice constant of the piezoelectric film is LP, (|LS - LB| / LS) × 100 [%] ≤ 20 [%] and (|LP - LB| / LP) × 100 [%] ≤ 10 [%].

Effect of the Invention

[0007] According to the manufacturing method of the elastic wave device according to the present invention, the crystallinity of the piezoelectric film can be increased, and the productivity can be increased.

Brief Description of the Drawings

[0008]

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Embodiments for Carrying Out the Invention

[0009] Hereinafter, the present invention will be clarified by explaining specific embodiments of the present invention with reference to the drawings.

[0010] Note that each embodiment described in this specification is exemplary, and it is pointed out that partial substitution or combination of configurations is possible between different embodiments.

[0011] FIG. 1 is a schematic front cross-sectional view of an elastic wave device according to a first embodiment of the present invention.

[0012] The elastic wave device 1 includes a piezoelectric substrate 2 and a functional electrode 14. The piezoelectric substrate 2 is a substrate having piezoelectricity. Specifically, the piezoelectric substrate 2 includes a support member 3 and a piezoelectric film 8. In the present embodiment, the support member 3 includes a support substrate 4 and an intermediate layer 5. The intermediate layer 5 is a laminate of two dielectric layers. More specifically, the intermediate layer 5 includes a first layer 6 and a second layer 7. The first layer 6 is provided on the support substrate 4. The second layer 7 is provided on the first layer 6. The piezoelectric film 8 is provided on the second layer 7. Note that the intermediate layer 5 may be, for example, a single dielectric layer.

[0013] The piezoelectric film 8 has a first main surface 8a and a second main surface 8b. The first main surface 8a and the second main surface 8b face each other. Of the first main surface 8a and the second main surface 8b, the second main surface 8b is located on the support member 3 side.

[0014] FIG. 2 is a schematic plan view of the elastic wave device according to the first embodiment.

[0015] A functional electrode 14 is provided on the first main surface 8a of the piezoelectric film 8. In the present embodiment, the functional electrode 14 is an IDT (Interdigital Transducer) electrode. The functional electrode 14 has a pair of bus bars and a plurality of electrode fingers. Specifically, the pair of bus bars are the first bus bar 16 and the second bus bar 17. The first bus bar 16 and the second bus bar 17 face each other. The plurality of electrode fingers are specifically a plurality of first electrode fingers 18 and a plurality of second electrode fingers 19. One ends of the plurality of first electrode fingers 18 are each connected to the first bus bar 16. One ends of the plurality of second electrode fingers 19 are each connected to the second bus bar 17. The plurality of first electrode fingers 18 and the plurality of second electrode fingers 19 are interposed with each other.

[0016] Hereinafter, the first electrode finger 18 and the second electrode finger 19 may be collectively referred to simply as electrode fingers. The direction in which the plurality of electrode fingers extend is defined as the electrode finger extension direction, and the direction orthogonal to the electrode finger extension direction is defined as the electrode finger orthogonal direction.

[0017] A pair of reflectors 15A and 15B are provided on the first main surface 8a of the piezoelectric film 8. The reflectors 15A and 15B sandwich the functional electrode 14 in the electrode finger orthogonal direction and face each other. The reflector 15A has a plurality of electrode fingers 15c. In the reflector 15A, both ends of the plurality of electrode fingers 15c are electrically short-circuited. The reflector 15B is also configured in the same manner as the reflector 15A. The functional electrode 14, the reflector 15A, and the reflector 15B may be made of a single-layer metal film or a laminated metal film. Note that the reflectors 15A and 15B do not necessarily have to be provided.

[0018] By applying an alternating voltage to the functional electrode 14, an elastic wave is excited. The elastic wave device 1 is a surface acoustic wave resonator. However, the elastic wave utilized by the elastic wave device 1 as the main mode is not limited to the surface acoustic wave. For example, the elastic wave device 1 may be configured to utilize the bulk wave of the thickness shear mode as the main mode. In this case, when the thickness of the piezoelectric film 8 is d and the center-to-center distance between the adjacent first electrode fingers 18 and second electrode fingers 19 is p, it is preferable that d / p is 0.5 or less. Thereby, the thickness shear mode is preferably excited.

[0019] The elastic wave device 1 can be obtained, for example, by singulating a wafer provided with a plurality of functional electrodes 14. The substrate on which the wafer is singulated is the piezoelectric substrate 2.

[0020] Hereinafter, an example of the manufacturing method of the elastic wave device 1 will be described. Note that the manufacturing method is the first embodiment of the manufacturing method of the elastic wave device in the present invention.

[0021] FIGS. 3(a) to 3(d) are schematic front cross-sectional views for explaining the first embodiment of the manufacturing method of the elastic wave device in the present invention. FIGS. 4(a) and 4(b) are schematic front cross-sectional views for explaining the first embodiment of the manufacturing method of the elastic wave device. In FIGS. 4(a) and 4(b), the functional electrode 14, the reflector 15A, and the reflector 15B are shown by a schematic diagram with two diagonals added to a rectangle. The same applies to other schematic front cross-sectional views.

[0022] As shown in FIG. 3(a), a substrate 22 is prepared. Next, a buffer layer 23 is provided on the substrate 22. At this time, the buffer layer 23 is formed, for example, by epitaxially growing it on the substrate 22. In this case, for example, the buffer layer 23 may be formed using the HVPE (Hydride Vapor Phase Epitaxy) method, the MOCVD (Metal Organic Chemical Vapor Deposition) method, or the like. In the present embodiment, the buffer layer 23 is an epitaxial layer.

[0023] In this specification, an epitaxial layer refers to a layer composed of an epitaxially grown oriented film. Further, in this specification, an epitaxially grown oriented film refers to a single crystal film or a polycrystalline film having a twin structure. Whether a certain layer is an epitaxial layer can be confirmed by performing pole measurement by X-ray diffraction method. When the layer has a twin structure, the diffraction pattern has a plurality of centers of symmetry. In this case, the layer is an epitaxial layer.

[0024] Next, a piezoelectric film 28 is provided on the buffer layer 23. At this time, the piezoelectric film 28 is formed, for example, by epitaxially growing on the buffer layer 23. In this case, for example, the piezoelectric film 28 may be formed using the HVPE method, the MOCVD method, or the like. In the present embodiment, the piezoelectric film 28 is an epitaxial layer. Note that the piezoelectric film 28 is diced in a later process to become the piezoelectric film 8 shown in FIG. 1.

[0025] The piezoelectric film 28 has a first main surface 28a and a second main surface 28b. The first main surface 28a and the second main surface 28b face each other. Of the first main surface 28a and the second main surface 28b, the first main surface 28a is located on the buffer layer 23 side.

[0026] On the other hand, as shown in FIG. 3(b), a support member 33 is prepared. The support member 33 is diced in a later process to become the support member 3 shown in FIG. 1. In the process of preparing the support member 33 shown in FIG. 3(b), first, a support substrate 34 is prepared. Next, an intermediate layer 35 is provided on the support substrate 34. More specifically, a first layer 36 is provided on the support substrate 34. Next, a second layer 37 is provided on the first layer 36. The first layer 36 is a silicon nitride layer in the present embodiment. The second layer 37 is a silicon oxide layer in the present embodiment. The first layer 36 and the second layer 37 can be formed, for example, by sputtering or vacuum evaporation.

[0027] Next, as shown in FIG. 3(c), the piezoelectric film 28 in the laminate of the substrate 22, the buffer layer 23, and the piezoelectric film 28 is bonded to the support member 33. Specifically, in the present embodiment, the second main surface 28b of the piezoelectric film 28 is bonded to the intermediate layer 35 of the support member 33.

[0028] Next, the buffer layer 23 and the substrate 22 are removed from the piezoelectric film 28 by wet etching. Specifically, the buffer layer 23 is removed by wet etching, and as shown in FIG. 3(d), the substrate 22 is peeled off from the piezoelectric film 28. Thereby, the wafer 32 is obtained. More specifically, the wafer 32 is a laminate of the support member 33 and the piezoelectric film 28. When removing the buffer layer 23 and the substrate 22 from the piezoelectric film 28, for example, a laser lift-off method or the like may be used.

[0029] Next, the first main surface 28a of the piezoelectric film 28 is cleaned. The first main surface 28a is the main surface of the piezoelectric film 28 on the side where the buffer layer 23 shown in FIG. 3(c) was laminated. The buffer layer 23 may not be completely removed from the first main surface 28a. By this cleaning, the buffer layer 23 can be more surely removed from the first main surface 28a. Thereby, defects caused by residues of the buffer layer 23 can be suppressed, and productivity can be increased. However, the cleaning of the first main surface 28a is not necessarily performed.

[0030] Next, the piezoelectric film 28 is subjected to a high-temperature heat treatment or a discharge treatment. Thereby, the polarization state in the piezoelectric film 28 can be more surely aligned. However, the high-temperature heat treatment or the discharge treatment of the piezoelectric film 28 is not necessarily performed.

[0031] Next, the arithmetic mean roughness Ra of the first main surface 28a of the piezoelectric film 28 is adjusted. The adjustment of the arithmetic mean roughness Ra of the first main surface 28a may be performed, for example, by polishing or the like. In this case, for example, a CMP (Chemical Mechanical Polishing) method or the like may be used. It is preferable that the arithmetic mean roughness Ra of the first main surface 28a be 1 nm or less. Thereby, the electrical characteristics of the obtained elastic wave device 1 can be improved. Note that the arithmetic mean roughness in this specification conforms to the arithmetic mean roughness Ra in JIS B 0601:2001. However, the step of adjusting the arithmetic mean roughness Ra of the first main surface 28a of the piezoelectric film 28 does not necessarily have to be performed.

[0032] Next, as shown in FIG. 4(a), a plurality of functional electrodes 14, a plurality of reflectors 15A, and a plurality of reflectors 15B are provided on the first main surface 28a of the piezoelectric film 28. Note that wirings other than the functional electrodes 14 and each reflector may be provided on the first main surface 28a simultaneously with the functional electrodes 14 and each reflector. The functional electrodes 14, each reflector, and the wiring can be formed, for example, by a photolithography method using a sputtering method or a vacuum evaporation method.

[0033] Next, the wafer 32 is diced. The dicing of the wafer 32 may be performed, for example, by dicing or the like. Thereby, as shown in FIG. 4(b), a plurality of elastic wave devices 1 can be obtained.

[0034] Hereinafter, the lattice constant of the substrate 22 shown in FIG. 3(a) is defined as LS, the lattice constant of the buffer layer 23 is defined as LB, and the lattice constant of the piezoelectric film 28 is defined as LP. The misfit between the lattice constant LS of the substrate 22 and the lattice constant LB of the buffer layer 23 is defined as (|LS - LB| / LS)×100 [%], and the misfit between the lattice constant LB of the buffer layer 23 and the lattice constant LP of the piezoelectric film 28 is defined as (|LP - LB| / LP)×100 [%].

[0035] The features of this embodiment are as follows. 1) It includes a step of providing a buffer layer 23 on a substrate 22 and a step of providing a piezoelectric film 28 on the buffer layer 23. 2) It includes a step of bonding the piezoelectric film 28 in the laminate of the substrate 22, the buffer layer 23, and the piezoelectric film 28 to a support member 33, and a step of removing the buffer layer 23 and the substrate 22 from the piezoelectric film 28. 3) The misfit between the lattice constant LS of the substrate 22 and the lattice constant LB of the buffer layer 23 satisfies (|LS - LB| / LS)×100[%]≦20[%]. 4) The misfit between the lattice constant LB of the buffer layer 23 and the lattice constant LP of the piezoelectric film 28 satisfies (|LP - LB| / LP)×100[%]≦10[%]. Thereby, the crystallinity of the piezoelectric film 8 in the obtained elastic wave device 1 can be more reliably increased. In addition, the productivity of the elastic wave device 1 can be increased. This will be described below.

[0036] In this embodiment, as shown in Fig. 3(a), a buffer layer 23 is formed on a substrate 22. And the misfit between the lattice constant LS of the substrate 22 and the lattice constant LB of the buffer layer 23 is 20% or less. Thereby, the crystallinity of the buffer layer 23 can be more reliably increased. Next, a piezoelectric film 28 is formed on the buffer layer 23. And the misfit between the lattice constant LB of the buffer layer 23 and the lattice constant LP of the piezoelectric film 28 is 10% or less. Thereby, the crystallinity of the piezoelectric film 28 can be more reliably increased. By bonding this piezoelectric film 28 to a support member 33 as shown in Fig. 3(d), a wafer 32 is obtained. Next, as shown in Fig. 4(b), by singulating the wafer 32, a plurality of piezoelectric substrates 2 are obtained. Thereby, the crystallinity of the piezoelectric film 8 in each piezoelectric substrate 2 can be more reliably increased.

[0037] Note that, as described above, in the step of removing the buffer layer 23 and the substrate 22 from the piezoelectric film 28, which is shown in Figs. 3(c) and 3(d), the laser lift-off method may be used. This will be described as the first modification of the first embodiment.

[0038] Figs. 5(a) and 5(b) are schematic front cross-sectional views for explaining a process of irradiating a buffer layer with laser light in a first modification of the first embodiment of a method for manufacturing an elastic wave device. Figs. 6(a) and 6(b) are schematic front cross-sectional views for explaining a process of removing a buffer layer and a substrate from a piezoelectric film in a first modification of the first embodiment of a method for manufacturing an elastic wave device.

[0039] As shown in Fig. 5(a), the buffer layer 23 is irradiated with laser light L from the substrate 22 side. By irradiating the buffer layer 23 with the laser light L, a part of the buffer layer 23 is decomposed. Next, the substrate 22 is peeled off from the buffer layer 23. In other words, the substrate 22 is removed from the piezoelectric film 28 side. It is preferable that the bandgap of the substrate 22 is smaller than the bandgap of the buffer layer 23. Thereby, the transmittance of the laser light L transmitted through the substrate 22 can be increased. As a result, the buffer layer 23 can be suitably irradiated with the laser light L.

[0040] Note that a modified layer 23A may be formed as a part of the buffer layer 23 is decomposed by the irradiation of the laser light L. In the present embodiment, an example in which the modified layer 23A is formed is shown. However, the modified layer 23A does not have to be formed.

[0041] Next, the buffer layer 23 and the modified layer 23A are removed from the piezoelectric film 28 as shown in Fig. 6(b). When removing the buffer layer 23 and the modified layer 23A from the piezoelectric film 28, for example, wet etching may be used. In a state where the substrate 22 is removed, since processes such as wet etching are performed, the buffer layer 23 and the modified layer 23A can be easily removed. Thus, a wafer 32 is obtained.

[0042] In the process shown in Fig. 5(a), it is preferable that the wavelength of the laser beam L is 150 nm or more and 450 nm or less. Thereby, the portion near the surface on the substrate 22 side in the buffer layer 23 can be more surely decomposed. As a result, the substrate 22 can be more surely and easily removed from the piezoelectric film 28 side.

[0043] Also in this modified example, after removing the buffer layer 23 from the piezoelectric film 28, the first main surface 28a of the piezoelectric film 28 is cleaned. Thereby, defects caused by residues of the buffer layer 23 can be suppressed, and productivity can be increased. Next, a high-temperature heat treatment, a discharge treatment, or the like is performed on the piezoelectric film 28. Thereby, the polarization state in the piezoelectric film 28 can be more surely made uniform.

[0044] In this modified example, the steps other than the step of removing the buffer layer 23 and the substrate 22 from the piezoelectric film 28 can be performed in the same manner as in the first embodiment. Therefore, also in this modified example, the crystallinity of the piezoelectric film in the obtained elastic wave device can be more surely increased.

[0045] After the steps shown in Figs. 6(a) and 6(b), a part of the buffer layer 23 or the altered layer 23A may remain on the substrate 22. Therefore, after removing the buffer layer 23, the altered layer 23A, and the substrate 22 from the piezoelectric film 28, the surface of the substrate 22 on which the buffer layer 23 was laminated may be cleaned. This will be described as a second modified example of the first embodiment.

[0046] Figs. 7(a) and 7(b) are schematic front cross-sectional views for explaining a second modified example of the first embodiment of a method for manufacturing an elastic wave device.

[0047] As shown in FIG. 7(a), a modified layer 23A remains on one surface of the substrate 22. In this modification, the surface of the substrate 22 on which the modified layer 23A remains is cleaned. In other words, the surface of the substrate 22 on which the buffer layer 23 shown in FIG. 5(a) etc. was provided is cleaned. Thereby, the modified layer 23A is removed. Alternatively, even when the buffer layer 23 remains on one surface of the substrate 22, the buffer layer 23 can be removed by the cleaning.

[0048] By the cleaning, the substrate 22 shown in FIG. 7(b) in which neither the modified layer 23A nor the buffer layer 23 remains can be obtained more reliably. Thereby, the substrate 22 can be suitably reused for manufacturing the surface acoustic wave device. Therefore, the productivity can be effectively increased.

[0049] In this modification, steps other than the step of cleaning the surface of the substrate 22 on which the buffer layer 23 was provided can be performed in the same manner as in the first modification. Therefore, also in this modification, the crystallinity of the piezoelectric film in the obtained surface acoustic wave device can be made more reliably high.

[0050] Note that, also in the method for manufacturing a surface acoustic wave device according to the present invention other than this modification, the cleaning step of the substrate 22 can be adopted. For example, as shown in FIGS. 3(c) and 3(d), in the first embodiment, in the step of removing the buffer layer 23 and the substrate 22 from the piezoelectric film 28, the buffer layer 23 is removed by wet etching. At this time, a part of the buffer layer 23 may remain on the substrate 22. By cleaning the surface of the substrate 22 on which the buffer layer 23 was provided, the substrate 22 can be suitably reused.

[0051] In the present invention, it is preferable that the piezoelectric film 28 shown in FIG. 3(a) etc. is formed by film formation. Forming by film formation means forming as a thin film. When the piezoelectric film 28 is formed by film formation, the piezoelectric film 28 is a thin film before adjusting the thickness or the arithmetic mean roughness Ra of the piezoelectric film 28.

[0052] More specifically, in the step of forming the piezoelectric film 28, it is preferable that the thickness of the piezoelectric film 28 be 1500 nm or less, and more preferably 400 nm or less. In this case, even when the thickness of the piezoelectric film 28 is adjusted by polishing or the like after the piezoelectric film 28 is formed, the amount of polishing or the like can be reduced. Alternatively, by setting the conditions for forming the piezoelectric film 28 and adjusting the thickness of the piezoelectric film 28, the piezoelectric film 28 can be made into a thin film with a desired thickness. In this case, after the piezoelectric film 28 is formed, it is not necessary to adjust the thickness of the piezoelectric film 28 by polishing or the like. Therefore, productivity can be further increased.

[0053] In addition, in the present invention, the piezoelectric film 28 is provided on the laminate of the substrate 22 and the buffer layer 23. Therefore, even when the piezoelectric film 28 is formed by film formation, the crystallinity of the piezoelectric film 28 can be more surely increased. Therefore, for example, the crystallinity of the piezoelectric film 8 in the surface acoustic wave device 1 shown in FIG. 1 can be more surely increased.

[0054] Examples of the materials of the respective members are shown below. When showing examples of the materials of the respective members in the piezoelectric substrate 2 or the wafer 32, the reference numerals indicating the respective members are the reference numerals before singulation.

[0055] As the material of the piezoelectric film 28, for example, one of lithium niobate and lithium tantalate can be used. When lithium niobate or lithium tantalate is used as the material of the piezoelectric film 28, the Euler angles (φ, θ, ψ) of lithium niobate or lithium tantalate are within the range of (0° ± 10°), (120° ± 30°), (0° ± 10°) or an equivalent (φ, θ, ψ), and the Euler angles (φ, θ, ψ) are within the range of (30° ± 30°), (90° ± 10°), (90° ± 10°) or an equivalent (φ, θ, ψ). More preferably, it is any one of them. In these cases, the electrical characteristics of the surface acoustic wave device 1 can be made more surely good.

[0056] As the material of the substrate 22, it is preferable to use any one of lithium niobate, lithium tantalate, and sapphire. On the substrate 22, a piezoelectric film 28 is provided indirectly via a buffer layer 23. By using any one of the above materials for the substrate 22, when forming the piezoelectric film 28, it is easy to epitaxially grow the piezoelectric film 28. Thereby, the crystallinity of the piezoelectric film 28 can be more surely increased.

[0057] When using lithium niobate or lithium tantalate as the material of the substrate 22, it is more preferable that the Euler angles (φ, θ, ψ) of lithium niobate or lithium tantalate are within the range of (0° ± 10°, 120° ± 30°, 0° ± 10°) or (φ, θ, ψ) equivalent thereto. It is even more preferable to use either rotated Y-cut lithium niobate with a cut angle of 30° ± 30° or rotated Y-cut lithium tantalate with a cut angle of 30° ± 30° as the material of the substrate 22. Thereby, when using lithium niobate or lithium tantalate as the material of the piezoelectric film 28, it is easy to make the Euler angles (φ, θ, ψ) of lithium niobate or lithium tantalate within the range of (0° ± 10°, 120° ± 30°, 0° ± 10°) or (φ, θ, ψ) equivalent thereto.

[0058] Incidentally, for example, the Euler angles (φ, θ, ψ) in rotated Y-cut lithium niobate with a cut angle of 30° are (0°, 120°, 0°) or (φ, θ, ψ) equivalent thereto.

[0059] Alternatively, when using lithium niobate or lithium tantalate as the material of the substrate 22, it is more preferable that the Euler angles (φ, θ, ψ) of the lithium niobate or lithium tantalate are within the ranges of (90° ± 10°, 90° ± 10°, 30° ± 30°) or (φ, θ, ψ) equivalent thereto. It is even more preferable to use either lithium niobate with a rotational X-cut and a cut angle of 30° ± 30° or lithium tantalate with a rotational X-cut and a cut angle of 30° ± 30° as the material of the substrate 22. Thereby, when using lithium niobate or lithium tantalate as the material of the piezoelectric film 28, it is easy to set the Euler angles (φ, θ, ψ) of the lithium niobate or lithium tantalate within the ranges of (90° ± 10°, 90° ± 10°, 30° ± 30°) or (φ, θ, ψ) equivalent thereto.

[0060] For example, the Euler angles (φ, θ, ψ) in lithium niobate with a rotational X-cut and a cut angle of 30° are (90°, 90°, 30°) or (φ, θ, ψ) equivalent thereto.

[0061] When using sapphire as the material of the substrate 22, it is more preferable that the surface on which the buffer layer 23 is formed on the substrate 22 is the r-plane shown in FIG. 8 or a plane close thereto. When expressing the r-plane as the Euler angles (φ, θ, ψ) to the second decimal place, it is (0°, 122.23°, ψ).

[0062] When sapphire is used as the material of the substrate 22, specifically, it is more preferable that the Euler angles (φ, θ, ψ) of the sapphire are within the range of (0° ± 10°), within the range of (122.23° ± 30°), and any ψ, or (φ, θ, ψ) equivalent thereto. It is even more preferable that the Euler angles (φ, θ, ψ) of the sapphire are within the range of (0° ± 10°), within the range of (122.23° ± 30°), and within the range of (0° ± 10°), or (φ, θ, ψ) equivalent thereto. It is still more preferable that the Euler angles (φ, θ, ψ) of the sapphire are (0°), within the range of (122.23° ± 30°), and (0°), or (φ, θ, ψ) equivalent thereto. Thereby, when lithium niobate or lithium tantalate is used as the material of the piezoelectric film 28, it is easy to set the Euler angles (φ, θ, ψ) of the lithium niobate or lithium tantalate to be within the range of (0° ± 10°), within the range of (120° ± 30°), and within the range of (0° ± 10°), or (φ, θ, ψ) equivalent thereto.

[0063] As the material of the buffer layer 23, it is preferable to use any one of metals, nitrides, carbides, and oxides. In this case, when forming the buffer layer 23, it is easy to epitaxially grow the buffer layer 23. As the material of the buffer layer, it is more preferable to use any one of aluminum, titanium, gallium nitride such as GaN, titanium oxide such as TiO2, and aluminum nitride such as AlN. In this case, when forming the piezoelectric film 28 on the buffer layer 23, it is easy to epitaxially grow the piezoelectric film 28. Thereby, the crystallinity of the piezoelectric film 28 can be more reliably increased.

[0064] In the present invention, the combination of materials of the piezoelectric film 28, the buffer layer 23, and the substrate 22 is important. For example, when the combination of materials is represented as lithium niobate / zinc oxide / sapphire in the notation of piezoelectric film 28 / buffer layer 23 / substrate 22, the misfit between the lattice constant LS of the substrate 22 and the lattice constant LB of the buffer layer 23 is 31.8%. The misfit between the lattice constant LB of the buffer layer 23 and the lattice constant LP of the piezoelectric film 28 is 17.6%. In this case, the crystallinity of the piezoelectric film 28 cannot be made sufficiently high. Preferred examples of the combination of materials of the piezoelectric film 28, the buffer layer 23, and the substrate 22 are shown below.

[0065] When lithium niobate or lithium tantalate is used as the material of the piezoelectric film 28, the combination of materials of the buffer layer 23 and the substrate 22 is preferably any of the following. That is, in the notation of buffer layer 23 / substrate 22, the combination of materials is preferably any of gallium nitride / sapphire, gallium nitride / lithium niobate, titanium oxide / lithium niobate, and titanium oxide / lithium tantalate. Thereby, the misfit between the lattice constant LS of the substrate 22 and the lattice constant LB of the buffer layer 23, and the misfit between the lattice constant LB of the buffer layer 23 and the lattice constant LP of the piezoelectric film 28 can be effectively reduced. Thereby, the crystallinity of the piezoelectric film 28 can be more surely and effectively increased.

[0066] However, the buffer layer 23 may be a laminate including a plurality of layers. For example, the buffer layer 23 may include a first buffer layer and a second buffer layer. In this case, the first buffer layer is provided on the substrate 22. The second buffer layer is provided on the first buffer layer. The piezoelectric film 28 is provided on the second buffer layer.

[0067] When lithium niobate or lithium tantalate is used as the material of the piezoelectric film 28, it is preferable that the combination of the materials of the first buffer layer and the second buffer layer is any of the following. That is, in the notation of the second buffer layer / the first buffer layer, it is preferable that the combination of materials is any of gallium nitride / aluminum nitride, titanium oxide / gallium nitride, and titanium oxide / titanium. Thereby, the misfit between the lattice constant LB of the buffer layer 23 and the lattice constant LP of the piezoelectric film 28 can be made even smaller. As a result, the crystallinity of the piezoelectric film 28 can be made more surely and even higher.

[0068] When the buffer layer 23 is a laminate, when calculating the misfit between the lattice constant LB of the buffer layer 23 and the lattice constant LP of the piezoelectric film 28, the lattice constant LB of the layer closest to the piezoelectric film 28 in the buffer layer 23 may be used.

[0069] When lithium niobate or lithium tantalate is used as the material of the piezoelectric film 28 and the buffer layer 23 includes the first buffer layer and the second buffer layer, it is preferable that the combination of the materials of the buffer layer 23 and the substrate 22 is any of the following. That is, in the notation of the second buffer layer / the first buffer layer / the substrate 22, it is preferable that the combination of materials is any of gallium nitride / aluminum nitride / sapphire, titanium oxide / gallium nitride / sapphire, titanium oxide / titanium / lithium niobate, and titanium oxide / titanium / lithium tantalate. Thereby, the misfit between the lattice constant LS of the substrate 22 and the lattice constant LB of the buffer layer 23, and the misfit between the lattice constant LB of the buffer layer 23 and the lattice constant LP of the piezoelectric film 28 can be made even smaller. As a result, the crystallinity of the piezoelectric film 28 can be made more surely and even higher.

[0070] As the material of the support substrate 34, it is preferable to use any one of glass, quartz, sapphire, lithium tantalate, lithium niobate, silicon, silicon carbide such as SiC, gallium nitride such as GaN, gallium arsenide such as GaAs, DLC (diamond-like carbon), and aluminum oxide such as Al2O3.

[0071] The first layer 36 in the intermediate layer 35 is a silicon nitride layer. However, for example, the material of the first layer 36 is not limited to silicon nitride. For example, materials mainly composed of silicon, aluminum oxide, silicon carbide, silicon nitride, silicon oxynitride, sapphire, lithium tantalate, lithium niobate, quartz, alumina, zirconia, cordierite, mullite, steatite, forsterite, magnesia, DLC (diamond-like carbon), diamond, spinel, or sialon can be used. The above spinel contains an aluminum compound containing one or more elements selected from Mg, Fe, Zn, Mn, etc. and oxygen. Examples of the above spinel include MgAl2O4, FeAl2O4, ZnAl2O4, and MnAl2O4.

[0072] The second layer 37 in the intermediate layer 35 is a silicon oxide layer. However, the material of the second layer 37 is not limited to silicon oxide. For example, materials mainly composed of glass, silicon oxide, silicon oxynitride, lithium oxide, tantalum pentoxide, or a compound obtained by adding fluorine, carbon, or boron to silicon oxide can be used.

[0073] Note that the intermediate layer 35 may include only the first layer 36 or may include only the second layer 37. Alternatively, the intermediate layer 35 may be a laminate of three or more layers.

[0074] It is preferable that the intermediate layer 35 includes at least one of a silicon nitride layer and a silicon oxide layer. Thereby, in the surface acoustic wave device 1 shown in FIG. 4(b), the energy of the surface acoustic wave can be effectively confined to the piezoelectric film 8 side.

[0075] More specifically, the silicon oxide layer is a low acoustic velocity layer. Specifically, the acoustic velocity of the bulk wave propagating in the low acoustic velocity layer is lower than the acoustic velocity of the bulk wave propagating in the piezoelectric film 28 shown in FIG. 4(a). The silicon nitride layer is a high acoustic velocity layer. Specifically, the acoustic velocity of the bulk wave propagating in the high acoustic velocity layer is higher than the acoustic velocity of the elastic wave propagating in the piezoelectric film 28. Similarly, when the above preferred material is used as the material of the support substrate 34, the support substrate 34 is a high acoustic velocity layer.

[0076] Therefore, when the intermediate layer 35 includes at least one of the silicon nitride layer and the silicon oxide layer, the elastic wave device 1 shown in FIG. 4(b) includes a stacked structure of a high acoustic velocity layer, a low acoustic velocity layer, and the piezoelectric film 8, or a stacked structure of a high acoustic velocity layer and the piezoelectric film 8. With these stacked structures, the energy of the elastic wave can be effectively confined to the piezoelectric film 8 side.

[0077] Hereinafter, an elastic wave device according to an embodiment other than the first embodiment of the present invention, and a method for manufacturing the same will be shown.

[0078] FIG. 9 is a schematic front cross-sectional view of an elastic wave device according to a second embodiment.

[0079] This embodiment is different from the first embodiment in that the intermediate layer 45 is a single-layer dielectric layer. This embodiment is also different from the first embodiment in that a plurality of through holes 8c are provided in the piezoelectric film 8, and a cavity 41a is provided between the piezoelectric film 8 and the support substrate 4. The plurality of through holes 8c reach the cavity 41a. Except for the above points, the elastic wave device 41 of this embodiment has the same configuration as the elastic wave device 1 of the first embodiment.

[0080] A recess is provided in the intermediate layer 45. A piezoelectric film 8 is provided on the intermediate layer 45 so as to close the recess. Thereby, a hollow portion is formed. This hollow portion is the cavity 41a. In this embodiment, the support member 43 and the piezoelectric film 8 are arranged such that a part of the support member 43 and a part of the piezoelectric film 8 face each other with the cavity 41a therebetween.

[0081] In a plan view, at least a part of the functional electrode 14 overlaps with the cavity portion 41a of the support member 43. In this specification, the plan view means looking along the stacking direction of the support member 43 and the piezoelectric film 8 from the direction corresponding to above in FIG. 9. In FIG. 9, for example, among the support substrate 4 side and the piezoelectric film 8 side, the piezoelectric film 8 side is above. Further, in this specification, it is assumed that the plan view is synonymous with looking from the main surface facing direction. The main surface facing direction is the direction in which the first main surface 8a and the second main surface 8b of the piezoelectric film 8 face each other. More specifically, the main surface facing direction is, for example, the normal direction of the first main surface 8a.

[0082] In this embodiment, by providing the cavity portion 41a, the energy of the elastic wave can be effectively confined to the piezoelectric film 8 side.

[0083] Hereinafter, an example of the manufacturing method of the elastic wave device 41 will be described. Note that the manufacturing method is the second embodiment of the manufacturing method of the elastic wave device in the present invention.

[0084] FIGS. 10(a) to 10(c) are schematic front cross-sectional views for explaining the second embodiment of the manufacturing method of the elastic wave device. FIGS. 11(a) to 11(d) are schematic front cross-sectional views for explaining the second embodiment of the manufacturing method of the elastic wave device.

[0085] As shown in FIG. 10(a), in this embodiment, in the step of preparing the support member 53, a plurality of sacrificial layers 59 are provided so as to be embedded in the intermediate layer 55. As the material of the sacrificial layer 59, for example, ZnO, SiO2, Cu, or resin can be used.

[0086] Specifically, for example, a plurality of sacrificial layers 59 may be formed on a substrate different from the support substrate 34. The sacrificial layer can be formed, for example, by a photolithography method using a sputtering method or a vacuum evaporation method. Next, an intermediate layer 55 is provided on the different substrate so as to cover the sacrificial layer 59. Next, the intermediate layer 55 is planarized. When planarizing the intermediate layer 55, for example, grinding or a CMP method may be used. Next, after laminating the support substrate 34 on the intermediate layer 55, the different substrate is peeled off from the intermediate layer 55. Note that the different substrate may be removed by polishing or the like.

[0087] Alternatively, for example, after laminating a layer that becomes a part of the intermediate layer 55 on the support substrate 34, a plurality of sacrificial layers 59 may be formed on the layer. Next, a layer that becomes the other part of the intermediate layer 55 is provided so as to cover the plurality of sacrificial layers 59. Thereafter, the plurality of sacrificial layers 59 are exposed from the intermediate layer 55 by polishing or the like.

[0088] On the other hand, similar to the first embodiment, a laminate of the substrate 22, the buffer layer 23, and the piezoelectric film 28 shown in FIG. 3(a) is prepared. Next, as shown in FIG. 10(b), the piezoelectric film 28 in the laminate of the substrate 22, the buffer layer 23, and the piezoelectric film 28 is bonded to the support member 53. Specifically, the second main surface 28b of the piezoelectric film 28 is bonded to the intermediate layer 55 of the support member 53.

[0089] Next, the buffer layer 23 and the substrate 22 are removed from the piezoelectric film 28 by wet etching. Specifically, the buffer layer 23 is removed by wet etching, and the substrate 22 is peeled off from the piezoelectric film 28 as shown in FIG. 10(c). Note that when removing the buffer layer 23 and the substrate 22 from the piezoelectric film 28, for example, a laser lift-off method or the like may be used.

[0090] Next, the first main surface 28a of the piezoelectric film 28 is cleaned. Next, a high-temperature heat treatment or a discharge treatment of the piezoelectric film 28 is performed. However, the cleaning of the first main surface 28a of the piezoelectric film 28 and the high-temperature heat treatment or the discharge treatment of the piezoelectric film 28 are not necessarily performed.

[0091] Next, the arithmetic mean roughness Ra of the first main surface 28a of the piezoelectric film 28 is adjusted by polishing or the like. However, the step of adjusting the arithmetic mean roughness Ra of the first main surface 28a of the piezoelectric film 28 is not necessarily performed.

[0092] Next, as shown in Fig. 11(a), a plurality of through holes 28c are provided in the piezoelectric film 28 so as to reach a plurality of sacrificial layers 59. The through holes 28c can be formed by, for example, a RIE (Reactive Ion Etching) method or the like. Next, the sacrificial layer 59 is removed through the through holes 28c. More specifically, the sacrificial layer 59 in the recess of the intermediate layer 55 is removed by flowing an etching solution from the through holes 28c. Thereby, as shown in Fig. 11(b), a plurality of cavity portions 41a are formed. Thus, the wafer 52 is obtained.

[0093] Next, as shown in Fig. 11(c), a plurality of functional electrodes 14, a plurality of reflectors 15A, and a plurality of reflectors 15B are provided on the first main surface 28a of the piezoelectric film 28. Note that wirings other than the functional electrodes 14 and each reflector may be provided on the first main surface 28a simultaneously with the functional electrodes 14 and each reflector. The functional electrodes 14, each reflector, and the wiring can be formed by, for example, a photolithography method using a sputtering method or a vacuum evaporation method.

[0094] Next, the wafer 52 is singulated. The singulation of the wafer 52 may be performed by, for example, dicing or the like. Thereby, as shown in Fig. 11(d), a plurality of surface acoustic wave devices 41 can be obtained.

[0095] Also in this embodiment, similar to the first embodiment, a piezoelectric film 28 is provided on the laminate of the substrate 22 and the buffer layer 23. And the misfit between the lattice constant LS of the substrate 22 and the lattice constant LB of the buffer layer 23 is (|LS - LB| / LS)×100[%]≦20[%]. The misfit between the lattice constant LB of the buffer layer 23 and the lattice constant LP of the piezoelectric film 28 is (|LP - LB| / LP)×100[%]≦10[%]. Thereby, the crystallinity of the piezoelectric film 28 can be made more surely high. Therefore, the crystallinity of the piezoelectric film 8 in the obtained elastic wave device 41 can be made more surely high.

[0096] FIG. 12 is a schematic front cross-sectional view of an elastic wave device according to the third embodiment.

[0097] This embodiment is different from the first embodiment in that the support member 63 is a laminate of the support substrate 4 and the acoustic reflection film 65. Except for the above points, the elastic wave device of this embodiment has the same configuration as the elastic wave device 1 of the first embodiment.

[0098] An acoustic reflection film 65 is provided on the support substrate 4. A piezoelectric film 8 is provided on the acoustic reflection film 65. In this embodiment, the whole of the support substrate 4 and the whole of the piezoelectric film 8 face each other with the acoustic reflection film 65 interposed therebetween. However, it is sufficient that the support substrate 4 and the piezoelectric film 8 are arranged so that at least a part of the support substrate 4 and at least a part of the piezoelectric film 8 face each other with the acoustic reflection film 65 interposed therebetween. And it is sufficient that the functional electrode 14 and the acoustic reflection film 65 overlap in plan view.

[0099] The acoustic reflection film 65 is a laminate of a plurality of acoustic impedance layers. Specifically, the acoustic reflection film 65 has a plurality of low acoustic impedance layers and a plurality of high acoustic impedance layers. The low acoustic impedance layer is a layer having a relatively low acoustic impedance. The plurality of low acoustic impedance layers of the acoustic reflection film 65 are, more specifically, the low acoustic impedance layer 66a, the low acoustic impedance layer 66b, and the low acoustic impedance layer 66c.

[0100] On the one hand, the high acoustic impedance layer is a layer with relatively high acoustic impedance. The plurality of high acoustic impedance layers of the acoustic reflection film 65 are, more specifically, the high acoustic impedance layer 67a and the high acoustic impedance layer 67b. The low acoustic impedance layer and the high acoustic impedance layer are alternately laminated. Note that the low acoustic impedance layer 66a is the layer located closest to the piezoelectric film 8 side in the acoustic reflection film 65.

[0101] The acoustic reflection film 65 has three low acoustic impedance layers and two high acoustic impedance layers. However, the acoustic reflection film 65 may have at least one layer each of the low acoustic impedance layer and the high acoustic impedance layer.

[0102] As the material of the low acoustic impedance layer, for example, silicon oxide or aluminum can be used. As the material of the high acoustic impedance layer, for example, metals such as platinum or tungsten, or dielectrics such as aluminum nitride, silicon nitride, or hafnium oxide can be used.

[0103] In this embodiment, by providing the acoustic reflection film 65, the energy of the elastic wave can be effectively confined to the piezoelectric film 8 side.

[0104] Hereinafter, an example of the manufacturing method of the elastic wave device according to the third embodiment will be described. Note that the manufacturing method is the third embodiment of the manufacturing method of the elastic wave device in the present invention.

[0105] Figs. 13(a) to 13(c) are schematic front cross-sectional views for explaining the step of preparing a support member in the third embodiment of the manufacturing method of the elastic wave device. Figs. 14(a) and 14(b) are schematic front cross-sectional views for explaining the step of bonding a piezoelectric film to a support member and the step of removing a buffer layer and a substrate from the piezoelectric film in the third embodiment of the manufacturing method of the elastic wave device.

[0106] As shown in FIG. 13(a), a low acoustic impedance layer 76c is provided on the support substrate 34. Next, as shown in FIG. 13(b), a high acoustic impedance layer 77b is provided on the low acoustic impedance layer 76c. In this way, the low acoustic impedance layer and the high acoustic impedance layer are alternately laminated. Specifically, as shown in FIG. 13(c), the low acoustic impedance layer 76b, the high acoustic impedance layer 77a, and the low acoustic impedance layer 76a are laminated in this order. Thereby, the acoustic reflection film 75 is provided. The low acoustic impedance layer and the high acoustic impedance layer can be formed, for example, by a sputtering method or a vacuum evaporation method. Thus, the support member 73 is obtained.

[0107] On the other hand, similar to the first embodiment, a laminate of the substrate 22, the buffer layer 23, and the piezoelectric film 28 shown in FIG. 3(a) is prepared. Next, as shown in FIG. 14(a), the piezoelectric film 28 in the laminate of the substrate 22, the buffer layer 23, and the piezoelectric film 28 is bonded to the support member 73. Specifically, the second main surface 28b of the piezoelectric film 28 is bonded to the acoustic reflection film 75 of the support member 73.

[0108] Next, the buffer layer 23 and the substrate 22 are removed from the piezoelectric film 28 by wet etching. Specifically, the buffer layer 23 is removed by wet etching, and the substrate 22 is peeled off from the piezoelectric film 28 as shown in FIG. 14(b). When removing the buffer layer 23 and the substrate 22 from the piezoelectric film 28, for example, a laser lift-off method or the like may be used. The subsequent steps can be performed in the same manner as in the first embodiment.

[0109] Also in this embodiment, similar to the first embodiment, a piezoelectric film 28 is provided on the laminate of the substrate 22 and the buffer layer 23. And the misfit between the lattice constant LS of the substrate 22 and the lattice constant LB of the buffer layer 23 is (|LS - LB| / LS)×100[%]≦20[%]. The misfit between the lattice constant LB of the buffer layer 23 and the lattice constant LP of the piezoelectric film 28 is (|LP - LB| / LP)×100[%]≦10[%]. Thereby, the crystallinity of the piezoelectric film 28 can be made higher more reliably. Therefore, the crystallinity of the piezoelectric film 8 in the obtained elastic wave device can be made higher more reliably.

[0110] FIG. 15 is a schematic front cross-sectional view of an elastic wave device according to the fourth embodiment.

[0111] This embodiment is different from the first embodiment in that the support member 83 consists only of the support substrate. The piezoelectric film 8 is directly provided on the support substrate as the support member 83. Except for the above points, the elastic wave device of this embodiment has the same configuration as the elastic wave device 1 of the first embodiment.

[0112] Hereinafter, an example of a manufacturing method of an elastic wave device according to the fourth embodiment will be described. Note that the manufacturing method is the fourth embodiment of the manufacturing method of the elastic wave device in the present invention.

[0113] FIGS. 16(a) to 16(d) are schematic front cross-sectional views for explaining the fourth embodiment of the manufacturing method of the elastic wave device in the present invention.

[0114] As shown in FIG. 16(a), a support member 93 is prepared. On the other hand, similar to the first embodiment, as shown in FIG. 16(b), a laminate of the substrate 22, the buffer layer 23, and the piezoelectric film 28 is prepared. Next, the arithmetic mean roughness Ra of the second main surface 28b of the piezoelectric film 28 is made 1 nm or less by, for example, the CMP method or the like. Note that the second main surface 28b is the main surface that is joined to the support substrate as the support member 93 shown in FIG. 16(a).

[0115] On the one hand, the arithmetic mean roughness Ra of the main surface of the support substrate as the support member 93 that is joined to the piezoelectric film 28 is made 1 nm or less by, for example, the CMP method or the like. Next, as shown in FIG. 16(c), the second main surface 28b of the piezoelectric film 28 having an arithmetic mean roughness Ra of 1 nm or less and the main surface of the support substrate as the support member 93 having an arithmetic mean roughness Ra of 1 nm or less are joined by optical contact.

[0116] Next, the buffer layer 23 and the substrate 22 are removed from the piezoelectric film 28 by wet etching. Specifically, the buffer layer 23 is removed by wet etching, and as shown in FIG. 16(d), the substrate 22 is peeled off from the piezoelectric film 28. Thereby, a wafer 92 is obtained. Note that when removing the buffer layer 23 and the substrate 22 from the piezoelectric film 28, for example, a laser lift-off method or the like may be used. The subsequent steps can be performed in the same manner as in the first embodiment.

[0117] Also in this embodiment, similar to the first embodiment, a piezoelectric film 28 is provided on the laminate of the substrate 22 and the buffer layer 23. Then, the misfit between the lattice constant LS of the substrate 22 and the lattice constant LB of the buffer layer 23 is (|LS - LB| / LS)×100[%]≦20[%]. The misfit between the lattice constant LB of the buffer layer 23 and the lattice constant LP of the piezoelectric film 28 is (|LP - LB| / LP)×100[%]≦10[%]. Thereby, the crystallinity of the piezoelectric film 28 can be made more surely high. Therefore, the crystallinity of the piezoelectric film 8 in the obtained elastic wave device can be made more surely high.

[0118] Hereinafter, examples of forms of the method for manufacturing an elastic wave device according to the present invention will be collectively described.

[0119] <1> A step of preparing a substrate and a support member, a step of providing a buffer layer on the substrate, a step of providing a piezoelectric film on the buffer layer, a step of bonding the piezoelectric film in the laminate of the substrate, the buffer layer, and the piezoelectric film to the support member, and a step of removing the buffer layer and the substrate from the piezoelectric film, wherein when the lattice constant of the substrate is LS, the lattice constant of the buffer layer is LB, and the lattice constant of the piezoelectric film is LP, (|LS - LB| / LS)×100[%] ≦ 20[%] and (|LP - LB| / LP)×100[%] ≦ 10[%]. A method for manufacturing an elastic wave device.

[0120] <2> The method for manufacturing an elastic wave device according to <1>, wherein the buffer layer is formed by epitaxial growth on the substrate, and the piezoelectric film is formed by epitaxial growth on the buffer layer.

[0121] <3> The method for manufacturing an elastic wave device according to <1> or <2>, wherein the piezoelectric film is formed by film deposition on the buffer layer.

[0122] <4> The method for manufacturing an elastic wave device according to any one of <1> to <3>, wherein in the step of removing the buffer layer and the substrate from the piezoelectric film, the buffer layer is removed using wet etching.

[0123] <5> The method for manufacturing an elastic wave device according to any one of <1> to <4>, wherein the bandgap of the buffer layer is smaller than the bandgap of the substrate, and in the step of removing the buffer layer and the substrate from the piezoelectric film, the substrate is peeled off from the buffer layer by irradiating the buffer layer with laser light from the substrate side, and after the peeling, the buffer layer is removed from the piezoelectric film.

[0124] <6> The method for manufacturing an elastic wave device according to <5>, wherein the wavelength of the laser light is 150 nm or more and 450 nm or less.

[0125] <7>The method for manufacturing an elastic wave device according to any one of <1> to <6>, further comprising a step of performing high-temperature heat treatment or discharge treatment on the piezoelectric film after removing the buffer layer and the substrate from the piezoelectric film.

[0126] <8>The method for manufacturing an elastic wave device according to any one of <1> to <7>, further comprising a step of making the arithmetic mean roughness Ra of the main surface of the piezoelectric film on the side where the buffer layer was laminated 1 nm or less after removing the buffer layer and the substrate from the piezoelectric film.

[0127] <9>The method for manufacturing an elastic wave device according to any one of <1> to <8>, wherein the material of the substrate is any one of lithium niobate, lithium tantalate, and sapphire.

[0128] <10>The method for manufacturing an elastic wave device according to <9>, wherein the material of the substrate is lithium niobate with Euler angles (φ, θ, ψ) within the range of (0° ± 10°, 120° ± 30°, 0° ± 10°) or equivalent thereto, lithium niobate with Euler angles (φ, θ, ψ) within the range of (90° ± 10°, 90° ± 10°, 30° ± 30°) or equivalent thereto, lithium tantalate with Euler angles (φ, θ, ψ) within the range of (0° ± 10°, 120° ± 30°, 0° ± 10°) or equivalent thereto, lithium tantalate with Euler angles (φ, θ, ψ) within the range of (90° ± 10°, 90° ± 10°, 30° ± 30°) or equivalent thereto, or sapphire with Euler angles (φ, θ, ψ) within the range of (0° ± 10°, 122.23° ± 30°, any ψ) or equivalent thereto.

[0129] <11>The method for manufacturing an elastic wave device according to any one of <1> to <10>, wherein the material of the buffer layer is any one of aluminum, titanium, gallium nitride, titanium oxide, and aluminum nitride.

[0130] <12>The method for manufacturing an elastic wave device according to any one of <1> to <11>, wherein the material of the piezoelectric film is one of lithium niobate and lithium tantalate, and the combination of the materials of the buffer layer and the substrate is any one of gallium nitride / sapphire, gallium nitride / lithium niobate, titanium oxide / lithium niobate, and titanium oxide / lithium tantalate in the notation of the buffer layer / substrate.

[0131] <13>The method for manufacturing an elastic wave device according to any one of <1> to <11>, wherein the material of the piezoelectric film is one of lithium niobate and lithium tantalate, the buffer layer is a laminate including a first buffer layer and a second buffer layer, the first buffer layer is provided on the substrate, the second buffer layer is provided on the first buffer layer, the piezoelectric film is provided on the second buffer layer, and the combination of the materials of the buffer layer and the substrate is any one of gallium nitride / aluminum nitride / sapphire, titanium oxide / gallium nitride / sapphire, titanium oxide / titanium / lithium niobate, and titanium oxide / titanium / lithium tantalate in the notation of the second buffer layer / the first buffer layer / the substrate.

[0132] <14>The method for manufacturing an elastic wave device according to any one of <1> to <13>, wherein the support member includes at least a support substrate, and the material of the support substrate is any one of glass, quartz, sapphire, lithium tantalate, lithium niobate, silicon, silicon carbide, gallium nitride, gallium arsenide, diamond-like carbon, and aluminum oxide.

[0133] <15>The step of making the support member include only the support substrate and making the arithmetic mean roughness Ra of the main surface of the support substrate that joins to the piezoelectric film 1 nm or less, and the step of making the arithmetic mean roughness Ra of the main surface of the piezoelectric film that joins to the support substrate 1 nm or less, are further provided. In the step of joining the piezoelectric film in the laminate of the substrate, the buffer layer, and the piezoelectric film to the support substrate, the main surface of the support substrate with an arithmetic mean roughness Ra of 1 nm or less and the main surface of the piezoelectric film with an arithmetic mean roughness Ra of 1 nm or less are joined. The method for manufacturing an elastic wave device according to any one of <1> to <14>.

[0134] <16>The support member is a laminate of a support substrate and an intermediate layer. In the step of joining the piezoelectric film in the laminate of the substrate, the buffer layer, and the piezoelectric film to the support member, the piezoelectric film is joined to the intermediate layer. The method for manufacturing an elastic wave device according to any one of <1> to <14>.

[0135] <17>The method for manufacturing an elastic wave device according to <16>, wherein the intermediate layer includes at least one of a silicon oxide layer and a silicon nitride layer.

[0136] <18>In the step of preparing the support member, a sacrificial layer is provided so as to be embedded in the intermediate layer. After the step of removing the buffer layer and the substrate from the piezoelectric film, the method for manufacturing an elastic wave device according to <16> or <17> further includes a step of removing the sacrificial layer.

[0137] <19>The support member is a laminate of a support substrate and an acoustic reflection film. The acoustic reflection film includes a high acoustic impedance layer with a relatively high acoustic impedance and a low acoustic impedance layer with a relatively low acoustic impedance. In the step of joining the piezoelectric film in the laminate of the substrate, the buffer layer, and the piezoelectric film to the support member, the piezoelectric film is joined to the acoustic reflection film. The method for manufacturing an elastic wave device according to any one of <1> to <14>.

Explanation of reference numerals

[0138] 1…Elastic wave device 2…Piezoelectric substrate 3…Supporting member 4…Supporting substrate 5…Intermediate layer 6,7…First and second layers 8…Piezoelectric film 8a,8b…First and second main surfaces 8c…Through hole 14…Functional electrode 15A,15B…Reflector 15c…Electrode finger 16,17…First and second bus bars 18,19…First and second electrode fingers 22…Substrate 23…Buffer layer 23A…Modified layer 28…Piezoelectric film 28a,28b…First and second main surfaces 28c…Through hole 32…Wafer 33…Supporting member 34…Supporting substrate 35…Intermediate layer 36,37…First and second layers 41…Elastic wave device 41a…Hollow part 43…Supporting member 45…Intermediate layer 52…Wafer 53…Supporting member 55…Intermediate layer 59…Sacrificial layer 63…Supporting member 65…Acoustic reflection film 66a~66c…Low acoustic impedance layer 67a,67b…High acoustic impedance layer 73…Supporting member 75…Acoustic reflection film 76a~76c…Low acoustic impedance layer 77a,77b…High acoustic impedance layer 83…Supporting member 92…Wafer 93…Supporting member

Claims

1. A step of preparing a substrate and a support member; A step of providing a buffer layer on the substrate; A step of providing a piezoelectric film on the buffer layer; A step of bonding the piezoelectric film in the laminate of the substrate, the buffer layer, and the piezoelectric film to the support member; A step of removing the buffer layer and the substrate from the piezoelectric film; comprising; When the lattice constant of the substrate is LS, the lattice constant of the buffer layer is LB, and the lattice constant of the piezoelectric film is LP, (|LS - LB| / LS) × 100 [%] ≤ 20 [%], and (|LP - LB| / LP) × 100 [%] ≤ 10 [%], a method for manufacturing an elastic wave device.

2. The buffer layer is formed by epitaxial growth on the substrate, The piezoelectric film is formed by epitaxial growth on the buffer layer, The method for manufacturing an elastic wave device according to claim 1.

3. The piezoelectric film is formed by film formation on the buffer layer, The method for manufacturing an elastic wave device according to claim 1.

4. In the step of removing the buffer layer and the substrate from the piezoelectric film, the buffer layer is removed using wet etching, The method for manufacturing an elastic wave device according to claim 1.

5. The band gap of the buffer layer is smaller than the band gap of the substrate, In the step of removing the buffer layer and the substrate from the piezoelectric film, the substrate is peeled off from the buffer layer by irradiating the buffer layer with laser light from the substrate side, and after the peeling, the buffer layer is removed from the piezoelectric film, The method for manufacturing an elastic wave device according to claim 1.

6. The wavelength of the laser light is 150 nm or more and 450 nm or less, The method for manufacturing an elastic wave device according to claim 5.

7. After the step of removing the buffer layer and the substrate from the piezoelectric film, the method further comprises a step of performing a high-temperature heat treatment or a discharge treatment on the piezoelectric film, The method for manufacturing an elastic wave device according to claim 1.

8. After the step of removing the buffer layer and the substrate from the piezoelectric film, the method further comprises a step of making the arithmetic mean roughness Ra of the main surface of the piezoelectric film on the side where the buffer layer was laminated 1 nm or less, The method for manufacturing an elastic wave device according to claim 1.

9. The method for manufacturing an elastic wave device according to claim 1, wherein the material of the substrate is any one of lithium niobate, lithium tantalate, and sapphire.

10. The method for manufacturing an elastic wave device according to claim 9, wherein the material of the substrate is lithium niobate with Euler angles (φ, θ, ψ) within the range of (0° ± 10°, 120° ± 30°, 0° ± 10°) or equivalent thereto, lithium niobate with Euler angles (φ, θ, ψ) within the range of (90° ± 10°, 90° ± 10°, 30° ± 30°) or equivalent thereto, lithium tantalate with Euler angles (φ, θ, ψ) within the range of (0° ± 10°, 120° ± 30°, 0° ± 10°) or equivalent thereto, lithium tantalate with Euler angles (φ, θ, ψ) within the range of (90° ± 10°, 90° ± 10°, 30° ± 30°) or equivalent thereto, or sapphire with Euler angles (φ, θ, ψ) within the range of (0° ± 10°, 122.23° ± 30°, any ψ) or equivalent thereto.

11. The method for manufacturing an elastic wave device according to claim 1, wherein the material of the buffer layer is any one of aluminum, titanium, gallium nitride, titanium oxide, and aluminum nitride.

12. The material of the piezoelectric film is one of lithium niobate and lithium tantalate, The method for manufacturing an elastic wave device according to claim 1, wherein the combination of the materials of the buffer layer and the substrate is any one of gallium nitride / sapphire, gallium nitride / lithium niobate, titanium oxide / lithium niobate, and titanium oxide / lithium tantalate in the notation of the buffer layer / substrate.

13. The material of the piezoelectric film is one of lithium niobate and lithium tantalate, The buffer layer is a laminate including a first buffer layer and a second buffer layer. The first buffer layer is provided on the substrate, the second buffer layer is provided on the first buffer layer, and the piezoelectric film is provided on the second buffer layer. The method for manufacturing an elastic wave device according to claim 1, wherein the combination of the materials of the buffer layer and the substrate is any one of gallium nitride / aluminum nitride / sapphire, titanium oxide / gallium nitride / sapphire, titanium oxide / titanium / lithium niobate, and titanium oxide / titanium / lithium tantalate in the notation of the second buffer layer / the first buffer layer / the substrate.

14. The support member includes at least a support substrate, The method for manufacturing an elastic wave device according to claim 1, wherein the material of the support substrate is any one of glass, quartz, sapphire, lithium tantalate, lithium niobate, silicon, silicon carbide, gallium nitride, gallium arsenide, diamond-like carbon, and aluminum oxide.

15. The support member includes only the support substrate, A step of making the arithmetic mean roughness Ra of the main surface of the support substrate that is bonded to the piezoelectric film 1 nm or less, A step of making the arithmetic mean roughness Ra of the main surface of the piezoelectric film that is bonded to the support substrate 1 nm or less, further comprising, In the step of bonding the piezoelectric film in the laminate of the substrate, the buffer layer, and the piezoelectric film to the support substrate, the main surface of the support substrate having an arithmetic mean roughness Ra of 1 nm or less and the main surface of the piezoelectric film having an arithmetic mean roughness Ra of 1 nm or less are bonded. The method for manufacturing an elastic wave device according to claim 1.

16. The support member is a laminate of a support substrate and an intermediate layer, In the step of bonding the piezoelectric film in the laminate of the substrate, the buffer layer, and the piezoelectric film to the support member, the piezoelectric film is bonded to the intermediate layer. The method for manufacturing an elastic wave device according to claim 1.

17. The method for manufacturing an elastic wave device according to claim 16, wherein the intermediate layer includes at least one of a silicon oxide layer and a silicon nitride layer.

18. In the step of preparing the support member, a sacrificial layer is provided so as to be embedded in the intermediate layer, The method for manufacturing an elastic wave device according to claim 16, further comprising a step of removing the sacrificial layer after the step of removing the buffer layer and the substrate from the piezoelectric film.

19. The support member is a laminate of a support substrate and an acoustic reflection film, The acoustic reflection film includes a high acoustic impedance layer having a relatively high acoustic impedance and a low acoustic impedance layer having a relatively low acoustic impedance. The method for manufacturing an elastic wave device according to claim 1, wherein, in the step of bonding the piezoelectric film in the laminate of the substrate, the buffer layer, and the piezoelectric film to the support member, the piezoelectric film is bonded to the acoustic reflection film.

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