Composite substrate and method for manufacturing composite substrate

Abstract

The invention provides a composite substrate which can contribute to high performance of a SAW filter. A composite substrate according to an embodiment of the present invention is provided with: a support substrate having an upper surface and a lower surface facing each other; a piezoelectric layer disposed on the upper surface side of the support substrate; and an intermediate layer disposed between the support substrate and the piezoelectric layer, in which a low-crystallinity region having lower crystallinity than a region located on the lower surface side is formed at an end of the support substrate on the upper surface side.

Description

Technical Field

[0001] The invention relates to a composite substrate and a method for manufacturing the composite substrate. Background Art

[0002] In information communication equipment, in order to extract an electrical signal of any frequency, a filter using a surface elastic wave (SAW filter) is used. In recent years, the amount of communication in the field of information communication equipment has increased dramatically, and the performance of SAW filters has been required to be improved. For example, non-patent document 1 discloses a SAW filter that uses a substrate including a piezoelectric body, a silicon oxide film, and a silicon substrate.

[0003] Prior art literature

[0004] Patent Literature

[0005] Non-patent document 1: Tsutomu Takai et al., "IHPSAW Technology and its Application to Microacoustic Components (Invited)", Proceedings of International Ultrasonics Symposium, 2017 Summary of the invention

[0006] However, there is a demand for further improvement in the performance of the SAW filter.

[0007] In view of the above circumstances, a main object of the present invention is to provide a composite substrate that can contribute to improvement in the performance of a SAW filter.

[0008] 1. The composite substrate involved in an embodiment of the present invention comprises: a supporting substrate having an upper surface and a lower surface opposite to each other; a piezoelectric layer, which is arranged on the upper surface side of the supporting substrate; and an intermediate layer, which is arranged between the supporting substrate and the piezoelectric layer, and a low-crystalline region with lower crystallinity than the region located on the lower surface side is formed at the end of the upper surface side of the supporting substrate.

[0009] 2. In the composite substrate described in 1 above, the thickness of the low crystallinity region may be 30 nm or more.

[0010] 3. In the composite substrate described in 1 or 2 above, the intermediate layer may include a silicon film.

[0011] 4. In the composite substrate described in any one of 1 to 3 above, the intermediate layer may include a first oxide layer, a silicon film, and a second oxide layer in order from the support substrate side.

[0012] 5. The manufacturing method of the composite substrate involved in the embodiment of the present invention includes: forming a damaged area at the end of the upper surface side of a supporting substrate having an upper surface and a lower surface facing each other; and bonding a piezoelectric substrate to the upper surface side of the above-mentioned supporting substrate with the aid of an intermediate layer.

[0013] 6. In the method for manufacturing a composite substrate according to 5 above, the damaged region may be formed by spraying abrasive grains onto the upper surface of the support substrate.

[0014] 7. In the method for manufacturing a composite substrate described in 5 or 6 above, the intermediate layer may include a silicon film formed by physical vapor deposition.

[0015] Effects of the Invention

[0016] According to the embodiment of the present invention, for example, it is possible to contribute to improving the performance of a SAW filter. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 This is a schematic cross-sectional view showing a schematic structure of a composite substrate according to one embodiment of the present invention.

[0018] Figure 2A It is a diagram showing an example of a manufacturing process of a composite substrate according to one embodiment.

[0019] Figure 2B It is immediately followed Figure 2A .

[0020] Figure 2C It is immediately followed Figure 2B .

[0021] Figure 2D It is immediately followed Figure 2C .

[0022] Figure 2E It is immediately followed Figure 2D .

[0023] Figure 3 This is a cross-sectional observation photograph of the composite substrate of Example 1.

[0024] Figure 4A It is an explanatory diagram of a pattern of a coplanar waveguide used for evaluation of high-frequency characteristics.

[0025] Figure 4B Yes Figure 4A The portion surrounded by the dotted line in FIG.

[0026] Figure 5 is a graph showing the evaluation results. DETAILED DESCRIPTION

[0027] Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings, but the present invention is not limited to these embodiments. In addition, with respect to the accompanying drawings, in order to make the description clearer, the width, thickness, shape, etc. of each part are sometimes schematically shown compared with the embodiments, but this is only an example and does not limit the interpretation of the present invention.

[0028] A. Composite substrate

[0029] Figure 1 1 is a schematic cross-sectional view showing the general structure of a composite substrate according to one embodiment of the present invention. The composite substrate 100 includes a support substrate 10, an intermediate layer 20, and a piezoelectric layer 30 in this order. Specifically, the piezoelectric layer 30 is arranged on the upper surface 10a side of the support substrate 10 having an upper surface 10a and a lower surface 10b facing each other, and the intermediate layer 20 is arranged between the piezoelectric layer 30 and the support substrate 10.

[0030] A low-crystalline region 12 is formed at the end portion on the upper surface 10a side of the support substrate 10. The low-crystalline region 12 is in a state where the crystallinity is lower than that of the region on the lower surface 10b side of the support substrate 10. For example, the crystallinity of the support substrate 10 can be confirmed by observation using a transmission electron microscope (TEM). By using this support substrate, a high-performance surface acoustic wave element can be obtained. The low-crystalline region 12 can be formed locally in the top view of the support substrate 10, but is preferably formed as a whole in the top view of the support substrate 10.

[0031] For example, from the viewpoint of obtaining a high-performance acoustic surface wave element, the intermediate layer 20 preferably includes a silicon film. In the example shown in the figure, the intermediate layer 20 has a multilayer structure including a first oxide layer 22, a silicon film 24, and a second oxide layer 26 from the side of the supporting substrate 10. Although not shown in the figure, the composite substrate 100 may further include any layer. The type, function, number, combination, and configuration of such layers may be appropriately set according to the purpose.

[0032] The composite substrate 100 can be manufactured in any appropriate shape. In one embodiment, it can be manufactured in the form of a so-called wafer. The size of the composite substrate 100 can be appropriately set according to the purpose. The diameter of the wafer is, for example, 100 mm to 200 mm.

[0033] A-1. Support substrate

[0034] Typically, the support substrate is made of silicon. The type of silicon constituting the support substrate is not particularly limited, but is preferably single crystal silicon. In addition, the silicon constituting the support substrate is preferably high-resistance silicon (for example, a volume resistivity of 1000 Ω·cm or more). The silicon constituting the support substrate may be doped with dopants such as phosphorus and boron.

[0035] The thermal expansion coefficient of the material constituting the support substrate is preferably smaller than the thermal expansion coefficient of the material constituting the piezoelectric layer. With such a support substrate, it is possible to suppress changes in the shape and size of the piezoelectric layer when the temperature changes, for example, it is possible to suppress changes in the frequency characteristics of the obtained surface acoustic wave device. For example, if the material constituting the support substrate is silicon, the relationship of the thermal expansion coefficient can be satisfied.

[0036] Any appropriate thickness may be adopted as the thickness of the support substrate. The thickness of the support substrate is, for example, 100 μm to 1000 μm.

[0037] The thickness of the low crystalline region of the support substrate is preferably 30 nm or more, more preferably 100 nm or more, and further preferably 300 nm or more. On the other hand, the thickness of the low crystalline region is preferably 3 μm or less, 2 μm or less, or 1 μm or less. It should be noted that the thickness of the low crystalline region can be equivalent to the depth (distance) from the upper surface of the support substrate to the site where the crystallinity changes. For example, the thickness of the low crystalline region can be the average value of the distance from the upper surface 10a of the support substrate to the interface of the low crystallinity at any cross section.

[0038] A-2. Middle layer

[0039] The silicon film that may be included in the intermediate layer may include at least one selected from amorphous silicon and polycrystalline silicon. The thickness of the silicon film is preferably 5 nm to 2 μm, and more preferably 50 nm to 1 μm.

[0040] Typically, the silicon film can be formed by physical vapor deposition such as sputtering.

[0041] Examples of materials constituting the oxide layer that may be contained in the intermediate layer include silicon oxide, tantalum oxide (Ta2O5), and niobium oxide (Nb2O5). The thickness of the oxide layer (the first oxide layer and the second oxide layer) is preferably 50 nm or more and 3 μm or less, more preferably 100 nm or more and 2.5 μm or less, and even more preferably 200 nm or more and 2 μm or less. Figure 1 As shown, when the intermediate layer includes a plurality of oxide layers, the plurality of oxide layers may have the same structure (eg, material, thickness) or different structures.

[0042] The oxide layer can be formed by any appropriate method, for example, by sputtering, physical vapor deposition such as ion beam assisted deposition (IAD), chemical vapor deposition, or atomic layer deposition (ALD).

[0043] A-3. Piezoelectric layer

[0044] As the material constituting the above-mentioned piezoelectric layer, any appropriate piezoelectric material can be used. As the piezoelectric material, a single crystal composed of LiAO3 is preferably used. Here, A is one or more elements selected from niobium and tantalum. Specifically, LiAO3 can be lithium niobate (LiNbO3), lithium tantalate (LiTaO3), or a lithium niobate-lithium tantalate solid solution.

[0045] When the piezoelectric material is lithium tantalate, the piezoelectric layer is preferably: for example, when the X-axis (crystal axis) of the piezoelectric material is set to the propagation direction (X1) of the elastic surface wave, the direction obtained by rotating 32° to 55° (for example, 42°) from its Y-axis toward the Z-axis corresponds to the direction (X3) perpendicular to the main surface of the piezoelectric layer, specifically, it is expressed as (180°, 58° to 35°, 180°) in Euler angles.

[0046] When the piezoelectric material is lithium niobate, the piezoelectric layer is preferably: for example, when the X-axis (crystal axis) of the piezoelectric material is set as the propagation direction (X1) of the elastic surface wave, the direction obtained by rotating 0° to 40° (for example, 37.8°) from the Z-axis toward the -Y-axis corresponds to the direction (X3) perpendicular to the main surface of the piezoelectric layer, specifically, it is expressed as (0°, 0° to 40°, 0°) in Euler angles. When the piezoelectric material is lithium niobate, the piezoelectric layer is also preferably: for example, when the X-axis (crystal axis) of the piezoelectric material is set as the propagation direction (X1) of the elastic surface wave, the direction obtained by rotating 40° to 65° from the Y-axis toward the Z-axis corresponds to the direction (X3) perpendicular to the main surface of the piezoelectric layer, specifically, it is expressed as (180°, 50° to 25°, 180°) in Euler angles.

[0047] The thickness of the piezoelectric layer can be set to any appropriate thickness according to the method of use and application of the composite substrate. The thickness of the piezoelectric layer is, for example, 0.2 μm to 30 μm, preferably 0.2 μm to 5 μm.

[0048] A-4. Manufacturing method

[0049] A method for manufacturing a composite substrate according to one embodiment of the present invention includes: forming a damaged area at the end of the upper surface side of a supporting substrate having an upper surface and a lower surface facing each other; and joining a piezoelectric substrate to the upper surface side of the supporting substrate having the damaged area formed thereon via an intermediate layer.

[0050] FIG. 2A to FIG. 2E It is a diagram showing an example of a manufacturing process of a composite substrate according to one embodiment.

[0051] Figure 2A 10 shows a state where surface processing is applied from the upper surface 10a side of a support substrate 10 having an upper surface 10a and a lower surface 10b facing each other. Figure 2BThe state in which a damaged region (low crystallinity region) 12 is formed at the end of the upper surface 10a side of the supporting substrate 10 is shown. For example, by applying sandblasting using abrasive grains, the low crystallinity region 12 can be well formed. Specifically, by applying sandblasting to the supporting substrate 10, the crystallinity is reduced, and a region with low crystallinity can be formed. As materials constituting the abrasive grains to be sprayed, for example, aluminum oxide and silicon carbide (SiC) can be cited. The average particle size of the abrasive grains to be sprayed is preferably 1 μm to 7 μm. The low crystallinity region 12 can be formed locally on the upper surface 10a of the supporting substrate 10, but is preferably formed on the entire upper surface 10a.

[0052] By forming the low crystalline region 12, the upper surface 10a of the support substrate 10 can have a concavo-convex shape (not shown). The arithmetic mean roughness Sa of the upper surface 10a of the processed support substrate 10 can be, for example, 1 nm or more, 1 nm or more and 50 nm or less, or 1 nm or more and 30 nm or less. The arithmetic mean roughness Sa is the average value of the absolute value of the height of each point in the defined area, and is calculated using the following formula. The arithmetic mean roughness Sa is equivalent to the parameter of extending the arithmetic mean roughness Ra on the roughness curve specified in JIS B 0601 to the surface, and is a parameter specified in ISO 25178.

[0053] [Mathematical formula 1]

[0054]

[0055] Figure 2C FIG. 2 shows a state where a first oxide layer 22 and a silicon film 24 are formed in a film-like state on the upper surface 10 a of the support substrate 10 after processing. Figure 2D The state in which the first layer 61 is formed in a film shape on the silicon film 24 of the support substrate 10 and the second layer 62 is formed in a film shape on one side of the piezoelectric substrate 32 is shown. The formation of the first layer 61 and the second layer 62 can be performed using the above-mentioned film forming method of the oxide layer. In one embodiment, the material constituting the first layer 61 and the material constituting the second layer 62 are substantially the same. For example, by using the same target and sputtering under the same conditions, the first layer 61 and the second layer 62 are formed in a film shape. It should be noted that any appropriate material can be selected as the material constituting the first layer 61 and the material constituting the second layer 62, respectively, as long as the bonding described later can be performed. In addition, the thickness of the first layer 61 and the thickness of the second layer 62 can be set to any appropriate thickness, respectively.

[0056] Figure 2EThe figure shows a state in which a bonding surface of a support substrate 10 having a first oxide layer 22, a silicon film 24, and a first layer 61 formed in a film state and a bonding surface of a piezoelectric substrate 32 having a second layer 62 formed in a film state are brought into contact and bonded (directly bonded) to form a bonded body 90. The first layer 61 and the second layer 62 are bonded to form a second oxide layer 26, and a bonded body 90 is obtained in which the support substrate 10 and the piezoelectric substrate 32 are bonded via an intermediate layer 20. Typically, grinding, polishing, and other processing are applied to the surface 32a of the piezoelectric substrate 32 of the obtained bonded body 90 so as to form a piezoelectric layer of the desired thickness described above. It can be obtained Figure 1 The composite substrate 100 is shown.

[0057] In the above-mentioned bonding, it is preferred that the bonding surfaces be flattened in advance. Figure 2D In the example shown, the bonding surface is the surface 61a of the first layer 61 and the surface 62a of the second layer 62. In particular, since the surface 61a of the first layer 61 can have a concave-convex shape that imitates the concave-convex shape of the upper surface 10a of the supporting substrate 10, it is preferably smoothed by flattening. The arithmetic mean roughness Ra of the bonding surface is preferably less than 1 nm, and more preferably less than 0.3 nm. Such a Ra can be achieved by, for example, mirror polishing based on chemical mechanical polishing (CMP). It should be noted that the arithmetic mean roughness Ra is a value measured using an atomic force microscope (AFM) in a field of view of 10 μm×10 μm.

[0058] When the support substrate 10 and the piezoelectric substrate 32 are brought into contact, it is preferred to apply activation treatment to the bonding surface on the support substrate 10 side and the bonding surface on the piezoelectric substrate 32 side in advance. In one embodiment, the activation treatment is performed by plasma irradiation. As the gas contained in the atmosphere during the activation treatment, for example, oxygen, nitrogen, hydrogen, and argon can be cited. These gases can be used alone or in combination of two or more (in the form of a mixed gas). Nitrogen is preferably used.

[0059] The atmospheric pressure during activation treatment by plasma irradiation is preferably 10 Pa to 80 Pa, more preferably 30 Pa to 80 Pa. The energy during plasma irradiation is preferably 30 W to 150 W, more preferably 60 W to 120 W. The plasma irradiation time is preferably 5 seconds to 30 seconds.

[0060] Preferably, after the bonding surface on the support substrate 10 side and the bonding surface on the piezoelectric substrate 32 side are brought into contact, the bonded body is heated. By heating, the bonding strength between the support substrate 10 and the piezoelectric substrate 32 can be further improved. The heating temperature is, for example, 100° C. to 400° C. The heating time is, for example, 1 hour to 25 hours. The contact and heating can be performed in an inert gas atmosphere such as nitrogen or argon, or in the air.

[0061] In one embodiment, the heating includes a first heating step and a second heating (annealing) step in sequence. In the first heating step, the above-mentioned bonded body is heated from room temperature to a temperature T1 (e.g., 100°C to 150°C). In the second heating step, the bonded body is placed under the condition of temperature T2 for a specified time (e.g., 3 hours to 25 hours). The temperature T2 is, for example, above 180°C, above 200°C, above 230°C, above 250°C, or above 270°C. On the other hand, for example, from the viewpoint of suppressing damage to the bonded body, the temperature T2 is preferably below 350°C, more preferably below 300°C. After the second heating step, typically, the bonded body is cooled naturally.

[0062] During the above-mentioned film formation and bonding, for example, in order to remove the residue of the abrasive, the processing-deteriorated layer, etc., it is preferred to clean the surface of each layer. As the cleaning method, for example, wet cleaning, dry cleaning, and brushing can be cited. Among them, brushing is preferred in view of the fact that it can be cleaned simply and efficiently. As a specific example of brushing, the following method can be cited, that is, after using a cleaning agent (for example, the Sun wash series manufactured by LION), a solvent (for example, a mixed solution of acetone and isopropyl alcohol (IPA)) is used for cleaning in a brushing machine.

[0063] Each layer constituting the intermediate layer can be formed in a film-like manner on the supporting substrate side, or can be formed in a film-like manner on the piezoelectric substrate side. In the example shown in the figure, a part of the layer constituting the intermediate layer is formed in a film-like manner on the supporting substrate side, and a part of the layer constituting the intermediate layer is formed in a film-like manner on the piezoelectric substrate side, and they are joined to obtain a composite substrate. However, it can be different from the example shown in the figure, for example, the second layer 62 is not formed in a film-like manner on the piezoelectric substrate 32 side (the first layer 61 is directly used as the second oxide layer 26), and the supporting substrate 10 and the piezoelectric substrate 32 are joined to obtain a composite substrate. In addition, for example, all the layers constituting the intermediate layer can also be formed in a film-like manner on the piezoelectric substrate side, and the piezoelectric substrate formed with the intermediate layer and the supporting substrate are joined to obtain a composite substrate.

[0064] B. Surface elastic wave element

[0065] The composite substrate according to the embodiment of the present invention can be used for a surface acoustic wave element. Typically, the surface acoustic wave element comprises the composite substrate and an electrode (comb-shaped electrode) disposed on the piezoelectric layer side of the composite substrate. Such a surface acoustic wave element is suitable for use in communication equipment such as mobile phones, for example, as a SAW filter.

[0066] Example

[0067] Hereinafter, the present invention will be specifically described by way of examples, but the present invention is not limited to these examples. It should be noted that the arithmetic mean roughness Sa is a value measured by the following measuring method.

[0068] <Arithmetic mean roughness Sa>

[0069] The arithmetic mean roughness Sa was measured in accordance with ISO 25178 using an atomic force microscope (AFM) within a field of view of 10 μm×10 μm.

[0070] [Example 1]

[0071] A high-resistance (>2 kΩ·cm) silicon substrate having a diameter of 150 mm, a mirror-polished upper surface and a mirror-polished lower surface, and a thickness of 0.50 mm was prepared.

[0072] In addition, a 42° Y-cut black lithium tantalate (LT) substrate having a diameter of 150 mm, a mirror-polished surface and a back surface, and a thickness of 0.25 mm was prepared.

[0073] The upper surface of the silicon substrate was subjected to sandblasting using abrasive grains (alumina grains) having an average grain size of 2 μm. The Sa of the sandblasted surface was 1.8 nm to 27.5 nm.

[0074] After that, the silicon substrate subjected to sandblasting was introduced into the chamber of a sputtering device (manufactured by Shincron, "RAS-1100BII"), and a silicon oxide layer (first oxide layer) with a thickness of about 500 nm was formed on the sandblasted surface of the silicon substrate, and then a silicon film with a thickness of about 100 nm was formed on the silicon oxide layer. After the silicon film was formed on the silicon substrate, an LT substrate was introduced into the chamber of the sputtering device, and a silicon oxide layer with a thickness of about 500 nm was formed on the silicon film of the silicon substrate and on the surface of the LT substrate under the same conditions as the first oxide layer. It should be noted that a Si target was used for film formation, oxygen gas as an oxygen source was introduced into the chamber, and the amount of oxygen introduced was adjusted, thereby adjusting the total pressure and oxygen partial pressure of the atmosphere in the chamber, and each layer was formed under the following conditions.

[0075] Rate: 0.3nm / sec

[0076] ·Pressure in the chamber during film formation: 0.3Pa

[0077] After the film formation, the silicon oxide layers of the silicon substrate and the LT substrate were polished off by about 100 nm by CMP processing to make them smooth (Ra: about 0.2 nm).

[0078] The bonding surface of the silicon substrate (the surface on the silicon oxide layer side) and the bonding surface of the LT substrate (the surface on the silicon oxide layer side) were cleaned to remove particles, and then introduced into a plasma activation chamber to activate the bonding surfaces of each substrate. Specifically, the activation treatment was performed for 10 seconds at room temperature using nitrogen plasma (energy: 100 W).

[0079] Next, the activated surfaces of the two substrates were superposed on each other in the atmosphere at room temperature to obtain a bonded body.

[0080] Next, the obtained bonded body was placed in an oven (120° C.) in a nitrogen atmosphere and heated for 10 hours. After that, the LT substrate of the bonded body (composite substrate) taken out of the oven was ground and polished, and then processed by CMP to form an LT layer with a thickness of 1 μm, thereby obtaining a composite substrate.

[0081] The cross section of the composite substrate obtained in Example 1 was observed using a transmission electron microscope (manufactured by Hitachi High-Technologies Corporation, "H-9500") at an accelerating voltage of 200 kV and a comprehensive magnification of 25,000 times. Figure 3 As shown, it was confirmed that a region (damaged region) having lower crystallinity than the region on the lower surface side was formed at the end of the upper surface side of the silicon substrate. The depth of the damaged region from the upper surface of the silicon substrate was 50 nm or more.

[0082] [Example 2]

[0083] A composite substrate was obtained in the same manner as in Example 1 except that a tantalum oxide layer was formed in a film form on the silicon film of the silicon substrate and on the surface of the LT substrate instead of the silicon oxide layer. The tantalum oxide layer was formed in the same manner as the silicon oxide layer except that a Ta target was used instead of a Si target.

[0084] [Example 3]

[0085] A composite substrate was obtained in the same manner as in Example 2 except that a tantalum oxide layer was formed as a first oxide layer on the silicon substrate in the form of a film instead of the silicon oxide layer. The tantalum oxide layer was formed in the same manner as the silicon oxide layer except that a Ta target was used instead of a Si target.

[0086] [Example 4]

[0087] A composite substrate was obtained in the same manner as in Example 1 except that a silicon film and a silicon oxide layer were not formed on the first oxide layer of the silicon substrate and a silicon oxide layer was not formed on the LT substrate.

[0088] [Comparative Example 1]

[0089] A composite substrate was obtained in the same manner as in Example 1 except that the silicon substrate was not subjected to sandblasting, a silicon film and a silicon oxide layer were not formed on the first oxide layer of the silicon substrate, and a silicon oxide layer was not formed on the LT substrate.

[0090] <Evaluation>

[0091] The high frequency characteristics of the composite substrates of the examples and comparative examples were evaluated.

[0092] On the LT layer of the obtained composite substrate, a 2 μm thick Au film was formed by sputtering, and then a coplanar waveguide (CPW) was formed on the obtained Au film by lithography and ion milling. The details of the formed coplanar waveguide are as follows Figure 4A and Figure 4B As shown in the figure, L1 is 2100μm, L2 is 2500μm, L3 is 3100μm, W1 is 60μm, W2 is 3000μm, and G1 is 340μm.

[0093] A high-frequency probe (TP40-GSG-250-N-L) manufactured by Technoprobe was brought into contact with both ends of the coplanar waveguide in the longitudinal direction, an RF power of 19 dBm was supplied using a signal generator, and the second harmonic was measured using a spectrum analyzer manufactured by Keysight Technologies.

[0094] The second harmonic was measured at 15 points in the surface of each substrate. The evaluation results are shown in Figure 5 .

[0095] It can be seen that in each embodiment, the second harmonic is suppressed.

[0096] Industrial Applicability

[0097] Typically, the composite substrate according to the embodiment of the present invention can be preferably used in an elastic wave device.

[0098] Explanation of symbols

[0099] 10 Support substrate

[0100] 12 Low crystallinity region (damaged region)

[0101] 20 Middle Layer

[0102] 22First oxide layer

[0103] 24 Silicon film

[0104] 26 Second oxide layer

[0105] 30 Piezoelectric layer

[0106] 32 Piezoelectric substrate

[0107] 100 composite substrate

Claims

1. A composite substrate, wherein: have: A supporting substrate having an upper surface and a lower surface facing each other; a piezoelectric layer disposed on the upper surface side of the support substrate; as well as an intermediate layer, the intermediate layer being arranged between the supporting substrate and the piezoelectric layer, A low-crystalline region having lower crystallinity than a region located on the lower surface side is formed at an end portion on the upper surface side of the support substrate.

2. The composite substrate according to claim 1, wherein: The low crystallinity region has a thickness of 30 nm or more.

3. The composite substrate according to claim 1, wherein: The intermediate layer includes a silicon film.

4. The composite substrate according to any one of claims 1 to 3, wherein: The intermediate layer includes a first oxide layer, a silicon film, and a second oxide layer in order from the support substrate side.

5. A method for manufacturing a composite substrate, wherein: Including in order: forming a damaged region at an end portion of an upper surface side of a support substrate having an upper surface and a lower surface facing each other; as well as A piezoelectric substrate is bonded to the upper surface side of the support substrate via an intermediate layer.

6. The method for manufacturing a composite substrate according to claim 5, wherein: The damaged region is formed by spraying abrasive grains onto the upper surface of the support substrate.

7. The method for manufacturing a composite substrate according to claim 5 or 6, wherein: The intermediate layer includes a silicon film formed by physical evaporation.

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