Composite substrate and method for manufacturing the composite substrate

Abstract

This composite substrate includes: a piezoelectric material substrate configured from LiNbO3 or LiTaO3; a support substrate supporting the piezoelectric material substrate; and an intermediate layer provided on the support substrate. The piezoelectric material substrate and the support substrate are joined to each other via the intermediate layer. The intermediate layer includes at least one of SiO2, MgF2, and CaF2. The piezoelectric material substrate includes: a first layer that does not contain inert gas atoms; a second layer that is disposed on a side closer to the intermediate layer than the first layer and that contains the inert gas; and a third layer that is in contact with the intermediate layer, and does not contain the inert gas or does contain same at a content lower than that of the second layer.

Description

[Technical Field]

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

[0002] Conventionally, composite substrates have been known for use in surface acoustic wave devices, formed by bonding a piezoelectric substrate made of a material such as LN (LiNbO3: lithium niobate) or LT (LiTaO3: lithium tantalate) to a support substrate made of a material such as Si. One known method for fabricating such composite substrates involves irradiating the bonding surfaces of the piezoelectric substrate and the support substrate with fast atom beams (FAB) to activate them, and then directly bonding these surfaces together. However, this method suffers from the problem of low bonding strength between the substrates, which can lead to separation during post-bonding processing.

[0003] To solve the above problem, the technology described in Patent Document 1 is known. Patent Document 1 describes a method in which a silicon oxide (SiO2) film is formed as an intermediate layer on a support substrate, and a bonding layer made of a material such as silicon nitride (Si3N4) is further formed on this film, and the piezoelectric substrate and the bonding layer are then directly bonded together. This method improves the bonding strength between the piezoelectric substrate and support substrate and prevents peeling after bonding. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] International Publication No. 2017 / 163722 Summary of the Invention [Problem to be solved by the invention]

[0005] In the composite substrate having the structure of Patent Document 1, a bonding layer made of Si3N4 is provided. However, when using a piezoelectric material substrate such as LN (LiNbO3) or LT (LiTaO3) as a functional layer, there is a demand for a composite substrate without a bonding layer from the viewpoint of confining energy (light, elastic waves, etc.). In order to obtain a composite substrate without a bonding layer, the manufacturing process for the composite substrate required bonding between a piezoelectric substrate and a support substrate with a silicon oxide intermediate layer, but the bonding strength was insufficient and needed to be improved. The same was true when directly bonding the piezoelectric substrate and the support substrate. Therefore, there was an issue with the bonding strength between the intermediate layer or support substrate and the piezoelectric material substrate made of LiNbO3 or LiTaO3.

[0006] The present invention has been made in view of the above, and its main object is to provide a composite substrate and a manufacturing method thereof that can improve the bonding strength between an intermediate layer provided on a support substrate or between the support substrate and a piezoelectric material substrate made of LiNbO3 or LiTaO3 material. [Means for solving the problem]

[0007] A composite substrate according to a first aspect of the present invention comprises a piezoelectric material substrate made of LiNbO3 or LiTaO3 material, a support substrate supporting the piezoelectric material substrate, and an intermediate layer provided on the support substrate, the piezoelectric material substrate and the support substrate being bonded to each other via the intermediate layer, the intermediate layer containing at least one of SiO2, MgF2, and CaF2, the piezoelectric material substrate comprising a first layer not containing inert gas atoms, and a second layer disposed closer to the intermediate layer than the first layer and containing the inert gas atoms. atom a second layer containing the inert gas, the second layer being in contact with the intermediate layer; atom and a third layer that does not contain or contains at a lower content than the second layer. A composite substrate according to a second aspect of the present invention includes a piezoelectric material substrate made of LiNbO3 or LiTaO3 material, and a support substrate that supports the piezoelectric material substrate and is bonded to the piezoelectric material substrate, the support substrate containing SiO2, MgF2, or CaF2, and the piezoelectric material substrate includes a first layer that does not contain inert gas atoms and a second layer that is disposed closer to the support substrate than the first layer and contains the inert gas atoms. atom a second layer contacting the support substrate and containing the inert gas; atom and a third layer that does not contain or contains at a lower content than the second layer. A method for manufacturing a composite substrate according to a third aspect of the present invention includes the steps of forming an intermediate layer containing at least one of SiO2, MgF2, and CaF2 on a support substrate, irradiating with a fast atomic beam the surface of a piezoelectric material substrate formed using LN or LT as a material and the surface of the intermediate layer formed on the support substrate, respectively, further irradiating with the fast atomic beam the surface of the piezoelectric material substrate to form a sputtered film made of the material of the piezoelectric material substrate on the surface of the intermediate layer, bonding the piezoelectric material substrate and the intermediate layer on which the sputtered film has been formed to obtain a bonded body, and heating the bonded body to a predetermined temperature. A method for manufacturing a composite substrate according to a fourth aspect of the present invention includes the steps of irradiating a surface of a piezoelectric material substrate formed using LN or LT as a material and a surface of a support substrate containing SiO2, MgF2, or CaF2 with a fast atomic beam, respectively; further irradiating the surface of the piezoelectric material substrate with the fast atomic beam to form a sputtered film made of the material of the piezoelectric material substrate on the surface of the support substrate; bonding the piezoelectric material substrate and the support substrate on which the sputtered film has been formed to obtain a bonded body; and heating the bonded body to a predetermined temperature. [Effects of the Invention]

[0008] According to the present invention, it is possible to realize a composite substrate and a manufacturing method thereof that can improve the bonding strength between an intermediate layer provided on a support substrate or between the support substrate and a piezoelectric material substrate made of LiNbO3 or LiTaO3 material. [Brief explanation of the drawings]

[0009] [Figure 1] 1 is a schematic cross-sectional view showing a schematic configuration of a composite substrate according to a first embodiment of the present invention. [Figure 2] 2A to 2C are diagrams illustrating an example of a manufacturing process for a composite substrate according to a first embodiment of the present invention. [Figure 3] 2A to 2C are diagrams illustrating an example of a manufacturing process for a composite substrate according to a first embodiment of the present invention. [Figure 4] FIG. 4 is a schematic cross-sectional view showing a schematic configuration of a composite substrate according to a second embodiment of the present invention. [Figure 5] 5A to 5C are diagrams illustrating an example of a manufacturing process for a composite substrate according to a second embodiment of the present invention. [Figure 6] 5A to 5C are diagrams illustrating an example of a manufacturing process for a composite substrate according to a second embodiment of the present invention. [Figure 7] FIG. 10 is a schematic cross-sectional view showing a schematic configuration of a composite substrate according to a third embodiment of the present invention. [Figure 8] FIG. 10 is a schematic cross-sectional view showing a schematic configuration of a composite substrate according to a fourth embodiment of the present invention. [Figure 9] FIG. 1 shows photographs and EDX analysis results of Example 1. [Figure 10] FIG. 1 shows observation photographs and EDX analysis results of Example 2. [Figure 11] 10 is a diagram showing an observation photograph and EDX analysis results of a modified example of Example 1. FIG. DETAILED DESCRIPTION OF THE INVENTION

[0010] Hereinafter, embodiments of the present invention will be described with reference to the drawings, but the present invention is not limited to these embodiments. In addition, in order to clarify the description, the drawings may show the width, thickness, shape, etc. of each part more schematically than in the embodiments, but these are merely examples and do not limit the interpretation of the present invention.

[0011] (First embodiment) 1 is a schematic cross-sectional view showing the general configuration of a composite substrate according to a first embodiment of the present invention. The composite substrate 100 in this embodiment is used as an optical element that constitutes, for example, an optical waveguide, and has a structure in which a piezoelectric material substrate is bonded to a support substrate 30 via an intermediate layer 20.

[0012] In the first embodiment, the piezoelectric material substrate is a waveguide substrate 10 including an optical waveguide, and is processed (ridge processing) to form a ridge portion 50 corresponding to the optical waveguide by providing a step in a portion of the substrate so that the ridge portion 50 is thicker than the other portions. The waveguide substrate 10 is made of a piezoelectric material such as LN (LiNbO3: lithium niobate) or LT (LiTaO3: lithium tantalate). The waveguide substrate 10 contains a bonding interface 40 formed in a bonding process described below.

[0013] The intermediate layer 20 is provided on the support substrate 30 and is disposed between the waveguide substrate 10 and the support substrate 30. The material of the intermediate layer 20 is a low refractive index material that serves to trap energy, and contains, for example, at least one of SiO2, MgF2, and CaF2, and is preferably SiO2. Note that if the support substrate 30 is made of SiO2, MgF2, or CaF2, and thus has an energy trapping function, the intermediate layer 20 may not be provided.

[0014] The intermediate layer 20 can be formed by any suitable method, such as physical vapor deposition (e.g., sputtering, vacuum deposition, or ion beam assisted deposition (IAD)), chemical vapor deposition, or atomic layer deposition (ALD). The intermediate layer 20 can be formed at a temperature between room temperature (25°C) and 300°C.

[0015] The support substrate 30 supports the waveguide substrate 10. Any appropriate substrate can be used as the support substrate 30. The support substrate 30 may be made of a single crystal or a polycrystalline material. It may also be made of a metal. The waveguide substrate 10 and the support substrate 30 are bonded to each other via an intermediate layer 20.

[0016] The material constituting the support substrate 30 is preferably selected from the group consisting of silicon, sialon, sapphire, cordierite, mullite, glass, quartz, crystal, alumina, SUS, iron-nickel alloy (42 alloy), MgF2, CaF2, and brass. The thickness of the support substrate 30 is, for example, 0.3 to 1 mm, but any other appropriate thickness can be adopted.

[0017] The silicon may be single crystal silicon, polycrystalline silicon, or high resistance silicon, and the support substrate 30 may be SOI (Silicon on Insulator).

[0018] Typically, the sialon is a ceramic obtained by sintering a mixture of silicon nitride and alumina, and has a composition represented by, for example, Si6-wAlwOwN8-w. Specifically, the sialon has a composition in which alumina is mixed into silicon nitride, where w represents the alumina mixing ratio. w is preferably 0.5 or more and 4.0 or less.

[0019] Typically, the sapphire is a single crystal having a composition of Al2O3, and the alumina is a polycrystalline material having a composition of Al2O3. The alumina is preferably translucent alumina.

[0020] Typically, the cordierite is a ceramic having a composition of 2MgO·2Al2O3·5SiO2, and the mullite is a ceramic having a composition in the range of 3Al2O3·2SiO2 to 2Al2O3·SiO2.

[0021] Although not shown, the composite substrate 100 may further include any layer. The type, function, number, combination, arrangement, etc. of such layers may be appropriately set depending on the purpose.

[0022] The composite substrate 100 can be manufactured in any appropriate shape. In one embodiment, the composite substrate 100 can be manufactured in the form of a so-called wafer. The size of the composite substrate 100 can be appropriately set depending on the purpose, for example, with the diameter of the wafer (substrate) being 50 mm to 150 mm.

[0023] 2 and 3 are diagrams showing an example of a manufacturing process for the composite substrate according to the first embodiment of the present invention.

[0024] 2(a) shows a preparation step in the manufacturing process of the composite substrate 100. In this step, a support substrate 30 is prepared.

[0025] 2(b) shows the film formation step of the intermediate layer 20 in the manufacturing process of the composite substrate 100. In this step, the intermediate layer 20 is formed by forming an amorphous SiO film, for example, to a predetermined thickness on the surface of the support substrate 30 prepared in the preparation step of FIG.

[0026] 2(c) shows the activation step in the manufacturing process of the composite substrate 100. In this step, for example, an LN substrate 10A of a predetermined thickness is prepared, and an activation process is performed by irradiating the surfaces of the intermediate layer 20 formed on the surface of the support substrate 30 in the film formation step of FIG. 2(b) and the LN substrate 10A with a fast atomic beam (hereinafter referred to as FAB) using an inert gas such as Ar as the atomic species for a predetermined time. The FAB irradiation time in this case is preferably, for example, about 15 seconds. As mentioned above, it is also possible to use an LT substrate instead of the LN substrate, but in the following explanation, the LT substrate will also be referred to as the "LN substrate 10A."

[0027] FIG. 2(d) shows the sputtering step in the manufacturing process of the composite substrate 100. In this step, of the FAB irradiation performed on the intermediate layer 20 and the LN substrate 10A in the activation step of FIG. 2(c), the FAB irradiation on the intermediate layer 20 side is stopped, and the FAB irradiation on the LN substrate 10A side is continued for a predetermined time. The FAB irradiation time at this time, including the irradiation time in the activation step of FIG. 2(c), is, for example, about 3 to 10 minutes, preferably 4 to 7 minutes. As a result, the LN constituting the LN substrate 10A is sputtered and attached to the surface of the intermediate layer 20, and a sputtered film 21 made of the same material as the LN substrate 10A is formed on the intermediate layer 20 side.

[0028] FIG. 3(e) shows the bonding step in the manufacturing process of the composite substrate 100. In this step, the LN substrate 10A irradiated with FAB in the activation step of FIG. 2(c) is bonded to the intermediate layer 20 on which the sputtered film 21 is formed in the sputtering step of FIG. 2(d), forming a bonded assembly. As a result, the LN substrate 10A and the sputtered film 21 are bonded together, and a bonding interface 40 between them is formed inside the LN substrate 10A. At this time, three layers (a first layer 11, a second layer 12, and a third layer 13) are formed in the LN substrate 10A near the bonding interface 40 (see FIG. 3(f)). The first layer 11 is a layer that does not contain inert gas atoms such as Ar irradiated with FAB in the activation step of FIG. 2(c), and the second layer 12 is a layer that is located closer to the intermediate layer 20 than the first layer 11 and contains the inert gas atoms. The third layer 13 is in contact with the intermediate layer 20 and does not contain the inert gas atoms or contains them at a lower content than the second layer 12. The first layer 11 is made of a crystalline LN or LT, which is the material of the LN substrate 10A, and the third layer 13 is an amorphous film formed by amorphizing LN or LT. The second layer 12 is either a crystalline LN or LT like the first layer 11, or an amorphous film formed by amorphizing LN or LT like the third layer 13. These layers may contain other atomic species that were mixed into the second layer 12 or the third layer 13 during the sputtering step of FIG. 2(d), such as Fe atoms, Al atoms, or Cr atoms that constitute the jig or pedestal used to secure the LN substrate 10A. Details of these layers will be described later. 3(e) and subsequent figures, the positional relationship between the LN substrate 10A, the intermediate layer 20, and the support substrate 30 is shown upside down compared to FIGS. 2(a) to 2(d).

[0029] FIG. 3(f) shows a preheating step in the manufacturing process of the composite substrate 100. In this step, the bonded assembly of the LN substrate 10A and the intermediate layer 20 formed in the bonding step of FIG. 3(e) is heated to a predetermined temperature. The heating temperature is lower than the heating temperature in the annealing step of FIG. 3(h), which will be described later. For example, the heating temperature is preferably around 100°C, and more preferably 100°C or lower. This improves the bonding strength between the LN substrate 10A and the intermediate layer 20 while suppressing cracking of the bonded assembly during heating due to the difference in thermal expansion coefficients between the LN substrate 10A and the support substrate 30. The preheating step of FIG. 3(f) may be omitted.

[0030] Fig. 3(g) shows the thinning step in the manufacturing process of the composite substrate 100. In this step, the LN substrate 10A is polished to a predetermined thickness using the bonded body after the preheating step shown in Fig. 3(f). For example, the LN substrate 10A can be polished to a thin thickness using grinding, CMP (Chemical Mechanical Polishing), surface planarization using a gas cluster ion beam, or the like.

[0031] FIG. 3(h) shows the annealing step in the manufacturing process of the composite substrate 100. In this step, the bonded assembly of the LN substrate 10A thinned in the thinning step of FIG. 3(g) and the intermediate layer 20 is heated to a predetermined temperature. The heating temperature is higher than the heating temperature in the preheating step of FIG. 3(f), and is preferably about 300 to 450°C, and more preferably 400 to 450°C. This improves the optical propagation characteristics of the waveguide substrate 10 and reduces optical loss in the waveguide substrate 10. The reason why the optical propagation characteristics of the waveguide substrate 10 are improved by the annealing step will be described later. Furthermore, by controlling the heating temperature in the annealing step, it is possible to obtain a layer in which the second layer is composed of an LN or LT crystal.

[0032] Inert gas atoms and other atomic species introduced into the second layer 12 and the third layer 13 during the sputtering process may diffuse into other layers when the LN substrate 10A is heated during the annealing process shown in FIG. 3(h). The degree of diffusion varies depending on the heating temperature and heating time. In other words, the Fe, Al, and Cr atom contents in the first layer 11, the second layer 12, and the third layer 13 vary depending on the heating temperature and heating time during the annealing process. In the second and third layers, the Fe atom content is preferably 0.5 to 20 atomic %, the Al atom content is preferably 0.5 to 8.5 atomic %, and the Cr atom content is preferably 0.5 to 4.5 atomic %. The inert gas atom content in the second layer is preferably 2.5 to 3.5 atomic %, and the inert gas atom content in the third layer is preferably 0 to 1.1 atomic %.

[0033] As described above, by performing the annealing step shown in Fig. 3(h) after thinning the LN substrate 10A in the thinning step shown in Fig. 3(g), it is possible to improve both the bonding strength and the optical propagation characteristics. However, the annealing step shown in Fig. 3(h) may be omitted.

[0034] Fig. 3(i) shows the ridge processing step in the manufacturing process of the composite substrate 100. In this step, the bonded body heated in the annealing step of Fig. 3(h) is cooled to room temperature, and then the LN substrate 10A thinned in the thinning step of Fig. 3(g) is further subjected to the above-mentioned ridge processing to form a ridge portion 50 that functions as an optical waveguide, thereby forming a waveguide substrate 10 including an optical waveguide. For example, the ridge processing can be performed by processing using laser light or dry etching such as RIE (Reactive Ion Etching).

[0035] Through the above steps, composite substrate 100 having the structure shown in FIG. 1 is manufactured.

[0036] (Second embodiment) 4 is a schematic cross-sectional view showing a schematic configuration of a composite substrate according to a second embodiment of the present invention. A composite substrate 110 according to this embodiment has a structure in which a waveguide substrate 10 is bonded to a support substrate 30 without an intermediate layer 20 therebetween, as compared with the composite substrate 100 shown in FIG. 1 described in the first embodiment.

[0037] As described above, by using a substrate made of SiO2, MgF2, or CaF2 as the support substrate 30, if the support substrate 30 has an energy trapping function, it is possible to form a composite substrate 110 that can be used as an optical element that constitutes an optical waveguide, even without providing an intermediate layer 20 as in the structure shown in Figure 4.

[0038] In this embodiment, as in the first embodiment, the composite substrate 110 may further include any layer. The type, function, number, combination, arrangement, etc. of such layers may be appropriately set depending on the purpose. Furthermore, the composite substrate 110 may be manufactured in any appropriate shape depending on the purpose.

[0039] 5 and 6 are diagrams showing an example of a manufacturing process for a composite substrate according to the second embodiment of the present invention.

[0040] 5(a) shows a preparation step in the manufacturing process of the composite substrate 110. In this step, a support substrate 30 is prepared, similar to the step of FIG. 2(a) described in the first embodiment. Note that in this embodiment, unlike the first embodiment, the step of forming an intermediate layer 20 on the support substrate 30 is omitted.

[0041] 5(b) shows an activation step in the manufacturing process of the composite substrate 110. In this step, for example, an LN substrate 10A having a predetermined thickness is prepared, and an activation process is performed by irradiating the surfaces of the support substrate 30 prepared in the preparation step of FIG. 5(a) and the LN substrate 10A with FAB using an inert gas such as Ar as an atomic species for a predetermined time, similar to the step of FIG. 2(c) described in the first embodiment.

[0042] FIG. 5(c) shows a sputtering step in the manufacturing process of the composite substrate 110. In this step, similar to the step of FIG. 2(d) described in the first embodiment, the FAB irradiation on the support substrate 30 side, which was irradiated on both the support substrate 30 and the LN substrate 10A in the activation step of FIG. 5(b), is stopped, and the FAB irradiation on the LN substrate 10A side is continued for a predetermined time. The FAB irradiation time at this time, including the irradiation time in the activation step of FIG. 5(b), is, for example, about 3 to 10 minutes, preferably 4 to 7 minutes. As a result, the LN constituting the LN substrate 10A is sputtered and attached to the surface of the support substrate 30, forming a sputtered film 21 on the support substrate 30 side, made of the same material as the LN substrate 10A.

[0043] FIG. 6(d) shows the bonding step in the manufacturing process of the composite substrate 110. In this step, similar to the step of FIG. 3(e) described in the first embodiment, the LN substrate 10A irradiated with FAB in the activation step of FIG. 5(b) and the support substrate 30 on which the sputtered film 21 is formed in the sputtering step of FIG. 5(c) are bonded to form a bonded assembly. As a result, the LN substrate 10A and the sputtered film 21 are bonded and integrated, and a bonded interface 40 between them is formed inside the LN substrate 10A. Note that in FIG. 6(d) and subsequent figures, the positional relationship between the LN substrate 10A and the support substrate 30 is illustrated upside down compared to FIGS. 5(a) to 5(c).

[0044] FIG. 6(e) shows a preheating step in the manufacturing process of the composite substrate 100. In this step, similar to the step of FIG. 3(f) described in the first embodiment, the bonded assembly of the LN substrate 10A and the support substrate 30 formed in the bonding step of FIG. 6(d) is heated to a predetermined temperature. The heating temperature is lower than the heating temperature in the annealing step of FIG. 6(g) described below, and is preferably about 100°C, for example, and more preferably 100°C or lower. As a result, similar to the first embodiment, cracking of the bonded assembly during heating due to the difference in thermal expansion coefficients between the LN substrate 10A and the support substrate 30 can be suppressed, while the bonding strength can be improved. Note that the preheating step of FIG. 6(e) may be omitted.

[0045] Fig. 6(f) shows a thinning process in the manufacturing process of the composite substrate 110. In this process, similar to the process of Fig. 3(g) described in the first embodiment, the LN substrate 10A is thinned by polishing it to a predetermined thickness for the bonded body after the preheating process shown in Fig. 6(e).

[0046] FIG. 6(g) shows the annealing step in the manufacturing process of the composite substrate 110. In this step, similar to the step of FIG. 3(h) described in the first embodiment, the bonded assembly of the LN substrate 10A thinned in the thinning step of FIG. 6(f) and the support substrate 30 is heated to a predetermined temperature. The heating temperature here is higher than the heating temperature in the preheating step of FIG. 6(e), and is preferably about 300 to 450°C, for example, and more preferably 400 to 450°C. As a result, similar to the first embodiment, it is possible to achieve both improved bonding strength and improved optical propagation characteristics. However, the annealing step of FIG. 6(g) may be omitted.

[0047] Fig. 6(h) shows a ridge processing step in the manufacturing process of the composite substrate 110. In this step, similar to the step of Fig. 3(h) described in the first embodiment, the bonded body heated in the annealing step of Fig. 6(g) is cooled to room temperature, and then the LN substrate 10A thinned in the thinning step of Fig. 6(f) is subjected to the above-mentioned ridge processing to form a ridge portion 50 that functions as an optical waveguide, thereby forming a waveguide substrate 10 including an optical waveguide.

[0048] Through the above steps, composite substrate 110 having the structure shown in FIG. 4 is manufactured.

[0049] (Third embodiment) 7 is a schematic cross-sectional view showing the overall configuration of a composite substrate according to a third embodiment of the present invention. A composite substrate 120 according to this embodiment is used as a piezoelectric element constituting, for example, a surface acoustic wave (SAW) filter, and has a structure in which, compared to the composite substrate 100 shown in FIG. 1 described in the first embodiment, a piezoelectric substrate 15 is included instead of the waveguide substrate 10, and the piezoelectric substrate 15 is bonded to a support substrate 30 via an intermediate layer 20.

[0050] Unlike the waveguide substrate 10, the piezoelectric substrate 15 is not subjected to ridge processing, and therefore does not have a ridge portion 50. As with the waveguide substrate 10, the piezoelectric substrate 15 is made of a piezoelectric material such as LN (LiNbO3: lithium niobate) or LT (LiTaO3: lithium tantalate). In other words, the waveguide substrate 10 and the piezoelectric substrate 15 can also be referred to as piezoelectric material substrates made of piezoelectric material.

[0051] Although not shown, the composite substrate 120 of this embodiment can be fabricated by performing the steps shown in FIGS. 2(a) to 3(h) described in the first embodiment. That is, by omitting the ridge processing step shown in FIG. 3(i), the LN substrate 10A that has been thinned by polishing to a predetermined thickness is used as the piezoelectric substrate 15 as is, without forming the ridge portion 50. Note that other steps may be performed thereafter. As a result, the interior of the piezoelectric substrate 15 includes a bonding interface 40, similar to the waveguide substrate 10. An IDT electrode is provided on the surface of the piezoelectric substrate 15 as needed.

[0052] (Fourth embodiment) Fig. 8 is a schematic cross-sectional view showing the overall configuration of a composite substrate according to a fourth embodiment of the present invention. Similar to the composite substrate 120 of Fig. 7 described in the third embodiment, a composite substrate 130 of this embodiment is used as a piezoelectric element constituting, for example, a surface acoustic wave (SAW) filter. Compared to the composite substrate 110 of Fig. 4 described in the second embodiment, this composite substrate 130 has a piezoelectric substrate 15 instead of the waveguide substrate 10, and has a structure in which the piezoelectric substrate 15 is bonded to the support substrate 30 without an intermediate layer 20. The material and shape of the piezoelectric substrate 15 are the same as those described in the third embodiment.

[0053] Although not shown, the composite substrate 130 of this embodiment can be fabricated by performing the steps shown in FIGS. 5(a) to 6(g) described in the second embodiment. That is, by omitting the ridge processing step shown in FIG. 6(h), the LN substrate 10A that has been thinned by polishing to a predetermined thickness is used as the piezoelectric substrate 15 as is, without forming the ridge portion 50. Note that other steps may be performed thereafter. As a result, the interior of the piezoelectric substrate 15 includes a bonding interface 40, similar to the waveguide substrate 10. An IDT electrode is provided on the surface of the piezoelectric substrate 15 as needed. [Example]

[0054] Examples for verifying the structure of the composite substrate according to the present invention will be specifically described below. Unless otherwise specified, the following procedures were carried out at room temperature.

[0055] Example 1 A bonded body was fabricated according to the manufacturing process described with reference to Figures 2 and 3. Specifically, an LN substrate 10A having a diameter of 4 inches and a thickness of 500 µm and a silicon substrate were prepared, and the silicon substrate was used as the support substrate 30. An amorphous SiO2 film was then formed on the surface of the support substrate 30 to a thickness of 1.0 µm, thereby forming the intermediate layer 20.

[0056] Next, the surface of the LN substrate 10A and the surface of the support substrate 30 (on the intermediate layer 20 side) are cleaned, and then both substrates are placed in a vacuum chamber. -6 The vacuum was drawn to the Pa range, and the surfaces of both substrates were simultaneously irradiated with FAB using Ar gas (accelerating voltage 1 kV, Ar flow rate 27 sccm) for 15 seconds. Thereafter, the FAB irradiation on the support substrate 30 side was stopped, and the FAB irradiation on the LN substrate 10A side was continued for an additional 285 seconds (5 minutes in total). As a result, a sputtered film 21 with a thickness of 1.1 nm was formed on the surface of the support substrate 30 on the intermediate layer 20 side.

[0057] Next, the LN substrate 10A was directly bonded to the support substrate 30. Specifically, the beam-irradiated surfaces of both substrates were placed one on top of the other, and the two substrates were bonded together by applying a pressure of 10,000 N at room temperature for 2 minutes, thereby obtaining a bonded assembly.

[0058] Next, the resulting bonded body was placed in a high-temperature furnace, heated from room temperature to 100° C., held there for a certain period of time, and then returned to room temperature, thereby carrying out preheating.

[0059] Next, the LN substrate 10A of the preheated bonded body was ground and polished, and then ridge processing was performed without annealing to form a ridge portion 50, thereby forming a waveguide substrate 10 including an optical waveguide, and a composite substrate 100 with the structure shown in Figure 1 was obtained. At this time, no peeling of the bonded portion was observed during the grinding and polishing process. In addition, when the bond strength was evaluated using the crack opening method, it was found to be 2.5 J / m 2 As a result, sufficient bonding strength was obtained.

[0060] The loss of the optical waveguide in composite substrate 100 of Example 1 was measured and found to be approximately 13 to 15 dB / cm.

[0061] Example 2 As in Example 1, the bonded body obtained by the above-mentioned method was placed in a high-temperature furnace, heated from room temperature to 100°C, held for a certain period of time, and then returned to room temperature for preheating. The LN substrate 10A of the preheated bonded body was then ground and polished, and then placed in a high-temperature furnace, heated from room temperature to a temperature higher than 100°C, held for a certain period of time, and then returned to room temperature for annealing. Ridge processing was then performed to form a ridge portion 50, thereby forming a waveguide substrate 10 including an optical waveguide, and a composite substrate 100 with the structure shown in Figure 1 was obtained. No peeling of the bonded portion was observed during the grinding and polishing processes. Furthermore, the bond strength was evaluated using a crack opening method, and was found to be 2.5 J / m 2 As a result, sufficient bonding strength was obtained.

[0062] When the loss of the optical waveguide in composite substrate 100 of Example 2 was measured, it was found to be about 1.5 to 2 dB / cm, and the optical propagation characteristics were improved compared to Example 1.

[0063] Example 3 As in Examples 1 and 2, the bonded body obtained by the above-described method was placed in a high-temperature furnace, heated from room temperature to 100°C, held for a certain period of time, and then returned to room temperature for preheating. The LN substrate 10A of the preheated bonded body was then ground and polished, and then placed in a high-temperature furnace. Annealing was then performed by raising the temperature from room temperature to a temperature higher than 100°C (a lower temperature than in Example 2), holding the temperature for a certain period of time, and then returning the temperature to room temperature. Ridge processing was then performed to form a ridge portion 50, thereby forming a waveguide substrate 10 including an optical waveguide, and a composite substrate 100 having the structure shown in FIG. 1 was obtained. No peeling of the bonded portion was observed during the grinding and polishing processes. Furthermore, the bond strength was evaluated using a crack opening method, and found to be 2.5 J / m 2 As a result, sufficient bonding strength was obtained.

[0064] When the loss of the optical waveguide in composite substrate 100 of Example 3 was measured, it was found to be about 4 to 5 dB / cm, which is a value between that of Examples 1 and 2.

[0065] (Structural analysis) A structural analysis of composite substrate 100 was performed by performing transmission electron microscope (TEM) observation and EDX analysis on a cross section including bonding interface 40 of composite substrate 100 produced in each of Examples 1 and 2. Fig. 9 shows an observation photograph and EDX analysis results for Example 1, and Fig. 10 shows an observation photograph and EDX analysis results for Example 2. Fig. 11 shows an observation photograph and EDX analysis results for a modified example of Example 1, in which the material of the fixing structure of LN substrate 10A was changed using the same process as in Example 1.

[0066] 9(a), it can be seen that three layers are formed inside the waveguide substrate 10. If these layers are designated as the first layer 11, the second layer 12, and the third layer 13 in order from the side furthest from the intermediate layer 20, then a bonding interface 40 formed in the above-mentioned bonding process exists between the second layer 12 and the third layer 13. The thickness of the second layer 12 was 1.8 nm, and the thickness of the third layer 13 was 1.1 nm.

[0067] 9(a) shows that, while the first layer 11 is made of crystalline LN, the second layer 12 and the third layer 13 do not have a crystalline structure and are made of amorphous LN. That is, in Example 1, it can be seen that the second layer 12 and the third layer 13 in the waveguide substrate 10 are formed as amorphous films in which the LN material of the waveguide substrate 10 has been made amorphous.

[0068] 9(b) shows the proportions of elemental components obtained from the EDX analysis results for each of the first layer 11, the second layer 12, the bonding interface 40, the third layer 13, and the intermediate layer 20 in Example 1. However, the analysis results for the bonding interface 40 correspond to the combined analysis results for the portions of the second layer 12 and the third layer 13 that contact the bonding interface 40.

[0069] 9(b), Ar, the inert gas used in the FAB irradiation, is not contained in the first layer 11, but is contained in the second layer 12 and the third layer 13. Furthermore, the Ar content is higher in the second layer 12 than in the third layer 13. From these results, it can be seen that the second layer 12 corresponds to the portion of the LN substrate 10A that was subjected to FAB irradiation in the sputtering process, and the third layer 13 corresponds to the sputtered film 21 formed on the surface of the intermediate layer 20 in the sputtering process.

[0070] 9(b) shows that Fe and Cr are contained in the second layer 12 and the third layer 13. This is thought to be because, during the sputtering process, the FAB is irradiated not only onto the LN substrate 10A but also onto the jig and base that hold the LN substrate 10A, causing these constituent elements to become mixed into the second layer 12 and the third layer 13.

[0071] In the observation photograph of Example 2 shown in Figure 10(a), of the first layer 11, second layer 12, and third layer 13 described in Figure 9(a), the second layer 12 has been recrystallized and has merged with the first layer 11. That is, it can be seen that while the first layer 11 and the second layer 12 are made of crystalline LN, the third layer 13 does not have a crystalline structure and is made of amorphous LN. As described above, in Example 2, the third layer 13 in the waveguide substrate 10 is formed as an amorphous film of amorphized LN, which is the material of the waveguide substrate 10, as in Example 1, but the second layer 12 is formed as a crystalline LN, which is the material of the waveguide substrate 10, unlike in Example 1.

[0072] 10(b) shows the proportions of elemental components obtained from the EDX analysis results for each of the first layer 11, the second layer 12, the bonding interface 40, the third layer 13, and the intermediate layer 20 in Example 2. However, as with the table of Example 1 shown in FIG. 9(b), the analysis results for the bonding interface 40 correspond to the combined analysis results for the portions of the second layer 12 and the third layer 13 that contact the bonding interface 40.

[0073] 10(b), Ar, which is an inert gas used in the FAB irradiation, is not contained in the first layer 11 or the third layer 13, but is contained in the second layer 12. The Ar content in the second layer 12 is also lower than that in Example 1. These results show that in Example 2, the high heating temperature causes some of the Ar accumulated in the second layer 12 and the third layer 13 by the FAB irradiation to volatilize.

[0074] 10(b) also shows that Cr, which was present in the third layer 13 in Example 1, is also contained in the second layer 12 in Example 2, and that Fe, which was present in the second layer 12 and the third layer 13 in Example 1, is also contained in the first layer 11 in Example 2. This is thought to be because the high heating temperature in Example 2 caused the Fe and Cr that had been mixed into the second layer 12 and the third layer 13 to diffuse.

[0075] 11(a), it can be seen that, like FIG. 9(a), the first layer 11 is made of crystalline LN, whereas the second layer 12 and the third layer 13 do not have a crystalline structure and are made of amorphous LN. In addition, a bonding interface 40 formed in the bonding process described above exists between the second layer 12 and the third layer 13. In this case, the thickness of the second layer 12 was 2.0 nm, and the thickness of the third layer 13 was 0.9 nm.

[0076] The table in FIG. 11(b) shows the proportions of elemental components obtained from the EDX analysis results for each of the first layer 11, the second layer 12, the bonding interface 40, the third layer 13 and the intermediate layer 20 in the modified example.

[0077] The table in Fig. 11(b) shows that the second layer 12 and the third layer 13 contain Fe and Al. In this modified example, the LN substrate 10A was placed on a stage made of AlN, and the support substrate 30 was supported by a jig made of stainless steel, and the activation step in Fig. 2(c) and the sputtering step in Fig. 2(d) were performed. That is, the table in Fig. 11(b) shows that these constituent elements were mixed into the second layer 12 and the third layer 13 as a result of part of the FAB being irradiated onto the stage and the jig during these steps.

[0078] According to the embodiment of the present invention described above, the following advantageous effects are achieved.

[0079] (1) Composite substrates 100, 120 include a piezoelectric material substrate (waveguide substrate 10, piezoelectric substrate 15) made of LN (LiNbO3) or LT (LiTaO3), a support substrate 30 that supports the piezoelectric material substrate, and an intermediate layer 20 provided on the support substrate 30. The piezoelectric material substrate and support substrate 30 are bonded to each other via the intermediate layer 20, which contains at least one of SiO2, MgF2, and CaF2. The piezoelectric material substrate includes a first layer 11 that does not contain inert gas atoms, a second layer 12 that is located closer to the intermediate layer 20 than the first layer 11 and contains an inert gas, and a third layer 13 that is in contact with the intermediate layer 20 and does not contain the inert gas or contains the inert gas at a lower content than the second layer 12. By doing this, even when the piezoelectric material substrate is directly bonded to the intermediate layer 20 without providing any other layers, the bonding strength between the intermediate layer 20 provided on the support substrate 30 and the piezoelectric material substrate made of LiNbO3 or LiTaO3 material can be improved.

[0080] (2) The composite substrates 110 and 130 each include a piezoelectric material substrate (waveguide substrate 10, piezoelectric substrate 15) made of LN (LiNbO) or LT (LiTaO) material and a support substrate 30 that supports the piezoelectric material substrate and is bonded to the piezoelectric material substrate. The support substrate 30 includes SiO, MgF, or CaF. The piezoelectric material substrate includes a first layer 11 that does not contain inert gas atoms, a second layer 12 that is located closer to the intermediate layer 20 than the first layer 11 and contains an inert gas, and a third layer 13 that is in contact with the intermediate layer 20 and does not contain the inert gas or contains the inert gas at a lower content than the second layer 12. This configuration improves the bonding strength between the support substrate 30 and the piezoelectric material substrate made of LiNbO or LiTaO even when the piezoelectric material substrate is directly bonded to the support substrate 30 without the need for any additional layers.

[0081] (3) In the composite substrates 100 and 110, the piezoelectric material substrate is the waveguide substrate 10 including an optical waveguide. In this way, the composite substrates 100 and 110 can be formed that can be used as optical elements that constitute an optical waveguide.

[0082] (4) As shown in Figures 9(a), 10(a), and 11(a), the first layer 11 is made of a crystalline material of the piezoelectric material substrate, and the third layer 13 is an amorphous film made by amorphizing the material of the piezoelectric material substrate. As shown in Figure 10(a), the second layer 12 is a crystalline material of the piezoelectric material substrate, or as shown in Figures 9(a) and 11(a), the second layer 12 is an amorphous film made by amorphizing the material of the piezoelectric material substrate. This configuration makes it possible to realize composite substrates 100, 110 that have excellent light propagation characteristics while firmly bonding the piezoelectric material substrate and intermediate layer 20 or support substrate 30 by direct bonding.

[0083] (5) A bonding interface 40 that bonds the piezoelectric material substrate to the intermediate layer 20 or the support substrate 30 is formed between the second layer 12 and the third layer 13. In this way, by directly bonding the second layer 12 and the third layer 13, bonding between the piezoelectric material substrate and the intermediate layer 20 or the support substrate 30 can be achieved.

[0084] (6) The second layer 12 and the third layer 13 may each contain Fe atoms or Al atoms. The inert gas atoms contained in the second layer 12 or the third layer 13 may be Ar atoms. In this manner, the second layer 12 or the third layer 13 can be formed by FAB irradiation, and the composite substrates 100 to 130 can be produced.

[0085] (7) It is preferable that the intermediate layer 20 is made of SiO 2 . This makes it possible to firmly bond the waveguide substrate 10 and the support substrate 30 via the intermediate layer 20.

[0086] (8) The method for manufacturing the composite substrates 100 and 120 includes a film-forming process (FIG. 2(b)) of forming an intermediate layer 20 containing at least one of SiO2, MgF2, and CaF2 on a support substrate 30, an activation process (FIG. 2(c)) of irradiating the surface of an LN substrate 10A formed using LN (or LT) as a material and the surface of the intermediate layer 20 formed on the support substrate 30 with FAB, and a sputtering process (FIG. 2(c)) of further irradiating the surface of the LN substrate 10A with FAB to form a sputtered film 21 made of the material of the LN substrate 10A on the surface of the intermediate layer 20. 2(d)), a bonding step (FIG. 3(e)) of bonding the LN substrate 10A to the intermediate layer 20 on which the sputtered film 21 is formed to obtain a bonded body, and a preheating step (FIG. 3(f) and / or annealing step (FIG. 3(h)) of heating the bonded body to a predetermined temperature. The total time for irradiating the surface of the LN substrate 10A with the FAB is 3 to 10 minutes, and the predetermined temperature during heating in the annealing step is preferably 300 to 450°C. In this manner, the composite substrates 100, 120 can be produced.

[0087] (9) The method for manufacturing the composite substrates 110 and 130 includes an activation step (FIG. 5(b)) of irradiating the surface of the LN substrate 10A formed using LN (or LT) as a material and the surface of the support substrate 30 containing SiO2, MgF2, or CaF2 with FAB, respectively; a sputtering step (FIG. 5(c)) of further irradiating the surface of the LN substrate 10A with FAB to form a sputtered film 21 made of the material of the LN substrate 10A on the surface of the support substrate 30; and a sputtering step (FIG. 5(d)) of forming a sputtered film 21 on the surface of the LN substrate 10A and the sputtered film 21. The method includes a bonding step (FIG. 6(d)) of bonding the LN substrate 10A to a supporting substrate 30 to obtain a bonded body, and a preheating step (FIG. 6(e)) and / or an annealing step (FIG. 6(g)) of heating the bonded body to a predetermined temperature. The total time for irradiating the surface of the LN substrate 10A with the FAB is preferably 3 to 10 minutes, and the predetermined temperature during heating in the annealing step is preferably 300 to 450°C. In this manner, the composite substrates 110, 130 can be produced.

[0088] (10) The method for manufacturing the composite substrates 100-130 may further include a thinning step (FIGS. 3(g) and 6(f)) in which the bonded body is heated to a first predetermined temperature in a preheating step, and then polishing and thinning the LN substrates 10A, and an annealing step in which the bonded body, in which the LN substrates 10A have been thinned in the thinning step, is heated to a second predetermined temperature higher than the first predetermined temperature. In this case, it is preferable that the first predetermined temperature to which the bonded body is heated in the preheating step is 100°C or lower, and the second predetermined temperature to which the bonded body is heated in the annealing step is 300-450°C. In this way, composite substrates 100-130 can be manufactured that achieve both improved bonding strength and improved optical propagation characteristics.

[0089] The present invention is not limited to the above-described embodiment, and can be implemented using any components without departing from the spirit of the present invention.

[0090] The above-described embodiments and modifications are merely examples, and the present invention is not limited to these details as long as the features of the invention are not impaired. Furthermore, although various embodiments and modifications have been described above, the present invention is not limited to these details. Other aspects that can be considered within the scope of the technical idea of ​​the present invention are also included within the scope of the present invention. [Explanation of symbols]

[0091] 10: Waveguide substrate 10A: LN substrate 11: 1st layer 12:Second layer 13:Third layer 15: Piezoelectric substrate 20: Middle class 21: Sputtered film 30: Support substrate 40: Bonding interface 50: Ridge 100, 110, 120, 130: Composite board

Claims

1. LiNbO ３ or LiTaO ３ a piezoelectric material substrate made of a material; a support substrate that supports the piezoelectric material substrate; an intermediate layer provided on the support substrate, the piezoelectric material substrate and the support substrate are bonded to each other via the intermediate layer, The intermediate layer is made of SiO ２ , MgF ２ , CaF ２ and The piezoelectric material substrate is a composite substrate having a first layer that does not contain inert gas atoms, a second layer that is positioned closer to the intermediate layer than the first layer and contains the inert gas atoms, and a third layer that is in contact with the intermediate layer and does not contain the inert gas atoms or contains them at a lower content than the second layer.

2. LiNbO ３ or LiTaO ３ a piezoelectric material substrate made of a material; a support substrate that supports the piezoelectric material substrate and is bonded to the piezoelectric material substrate, The support substrate is made of SiO ２ , MgF ２ , or CaF ２ Including, The piezoelectric material substrate is a composite substrate having a first layer that does not contain inert gas atoms, a second layer that is arranged closer to the support substrate than the first layer and contains the inert gas atoms, and a third layer that is in contact with the support substrate and does not contain the inert gas atoms or contains them at a lower content than the second layer.

3. The composite substrate according to claim 1 or 2, A composite substrate, wherein the piezoelectric material substrate is a waveguide substrate including an optical waveguide.

4. The composite substrate according to claim 1 or 2, the first layer is made of a crystal of the material of the piezoelectric material substrate; A composite substrate, wherein the third layer is an amorphous film obtained by amorphizing the material of the piezoelectric material substrate.

5. The composite substrate according to claim 4, A composite substrate, wherein the second layer is a crystal of the material of the piezoelectric substrate.

6. The composite substrate according to claim 4, A composite substrate, wherein the second layer is an amorphous film obtained by amorphizing the material of the piezoelectric material substrate.

7. The composite substrate according to claim 1 , A composite substrate, wherein a bonding interface bonding the piezoelectric material substrate and the intermediate layer is formed between the second layer and the third layer.

8. The composite substrate according to claim 2, A composite substrate, wherein a bonding interface that bonds the piezoelectric material substrate and the support substrate is formed between the second layer and the third layer.

9. The composite substrate according to claim 1 or 2, The composite substrate, wherein the second layer and the third layer each contain Fe atoms.

10. The composite substrate according to claim 1 or 2, The composite substrate, wherein the second layer and the third layer each contain Al atoms.

11. The composite substrate according to claim 1 or 2, A composite substrate, wherein the inert gas atoms are Ar atoms.

12. The composite substrate according to claim 1 , The intermediate layer is SiO ２ This is a composite substrate.

13. A method for manufacturing a composite substrate, comprising: SiO ２ , MgF ２ , CaF ２ forming an intermediate layer containing at least one of the following on a support substrate; a step of irradiating a surface of a piezoelectric material substrate formed using LN or LT as a material and a surface of the intermediate layer formed on the support substrate with a fast atomic beam; a step of further irradiating the surface of the piezoelectric material substrate with the fast atomic beam to form a sputtered film made of the material of the piezoelectric material substrate on the surface of the intermediate layer; a step of bonding the piezoelectric material substrate and the intermediate layer on which the sputtered film is formed to obtain a bonded body; and heating the bonded body to a predetermined temperature.

14. A method for manufacturing a composite substrate, comprising: The surface of a piezoelectric material substrate formed using LN or LT as a material, and SiO ２ , MgF ２ , or CaF ２ and a surface of a support substrate including the above-mentioned compound, each of which is irradiated with a fast atomic beam. a step of further irradiating the surface of the piezoelectric material substrate with the fast atomic beam to form a sputtered film made of the material of the piezoelectric material substrate on the surface of the support substrate; a step of bonding the piezoelectric material substrate and the support substrate on which the sputtered film is formed to obtain a bonded body; and heating the bonded body to a predetermined temperature.

15. 15. The method for producing a composite substrate according to claim 13 or 14, The method for producing a composite substrate, wherein the surface of the piezoelectric material substrate is irradiated with the fast atomic beam for a total time of 3 to 10 minutes.

16. 15. The method for producing a composite substrate according to claim 13 or 14, The method for manufacturing a composite substrate, wherein the predetermined temperature is 300 to 450°C.

17. 15. The method for producing a composite substrate according to claim 13 or 14, a step of heating the bonded body to a first predetermined temperature and then polishing the piezoelectric material substrate to make it a thin plate; a step of heating the bonded body in which the piezoelectric material substrates have been thinned to a second predetermined temperature that is higher than the first predetermined temperature.

18. The method for manufacturing a composite substrate according to claim 17, the first predetermined temperature is 100°C or less; The method for manufacturing a composite substrate, wherein the second predetermined temperature is 300 to 450°C.

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