Composite substrate

Abstract

The composite substrate is provided with: a functional substrate having a predetermined function; a support substrate that supports the functional substrate; and an intermediate layer that is formed of SiO2 and is provided between the support substrate and the functional substrate, the functional substrate and the support substrate being bonded to each other via the intermediate layer. The intermediate layer has SiO2 regions that are respectively provided on the functional substrate side and the support substrate side and are composed of SiO2, and a Si high-concentration region that is provided so as to be sandwiched between the SiO2 regions and that has a higher Si content than the SiO2 regions.

Description

Technical Field

[0001] This invention relates to composite substrates. Background Technology

[0002] Previously, composite substrates, which are formed by bonding multiple substrates, have been widely used as materials for various devices such as semiconductor elements. For example, SOI (Silicon On Insulator) substrates, which are composite substrates for achieving high-performance semiconductor elements with excellent response speed and power consumption, are known to be formed by bonding a support substrate and a Si substrate using a SiO2 layer. In addition, composite substrates using piezoelectric material substrates such as LN (LiNbO3) and LT (LiTaO3) to replace Si substrates are also known to be used to realize piezoelectric devices such as SAW (Surface Acoustic Wave) filters.

[0003] For example, Patent Document 1 discloses a method for manufacturing a composite substrate, in which a single crystal wafer of LN or LT and a silicon wafer with an oxide film are bonded together after the bonding surfaces of the two wafers are activated.

[0004] Existing technical documents

[0005] Patent documents

[0006] Patent Document 1: Japanese Patent Application Publication No. 2016-225537 Summary of the Invention

[0007] One method for fabricating a composite substrate as described above involves directly bonding a functional substrate (such as a Si substrate or a piezoelectric material substrate) and a support substrate, which function as an interlayer, together. In this case, the SiO2 layer forming the interlayer is deposited on both the functional substrate and the support substrate. After surface activation treatment of the bonding surfaces on both the functional substrate and the support substrate sides, direct bonding is performed, thereby forming a composite substrate. This improves the bonding strength compared to bonding the functional substrate and the support substrate without an interlayer.

[0008] However, even with the methods described above, the bonding strength between the SiO2 layers is sometimes insufficient, leaving room for improvement in subsequent processes such as functional substrate peeling.

[0009] The present invention was carried out in view of the above circumstances, and its main objective is to improve the bonding strength in a composite substrate obtained by bonding a functional substrate and a support substrate by means of an intermediate layer.

[0010] The composite substrate of the present invention comprises: a functional substrate having a defined function; a support substrate supporting the functional substrate; and an intermediate layer composed of SiO2 disposed between the support substrate and the functional substrate, wherein the functional substrate and the support substrate are bonded to each other by means of the intermediate layer, the intermediate layer having: SiO2 regions disposed on the side of the functional substrate and the side of the support substrate and composed of SiO2, and a high-concentration Si region sandwiched between the SiO2 regions and having a higher Si content than the SiO2 regions.

[0011] Invention Effects

[0012] According to the present invention, in a composite substrate obtained by bonding a functional substrate and a support substrate by means of an intermediate layer, the bonding strength can be improved. Attached Figure Description

[0013] Figure 1 This is a simplified cross-sectional view illustrating the general structure of a composite substrate according to one embodiment of the present invention.

[0014] Figure 2 This is a diagram illustrating an example of the manufacturing process of a composite substrate according to an embodiment of the present invention.

[0015] Figure 3 This is a diagram illustrating an example of the manufacturing process of a composite substrate according to an embodiment of the present invention.

[0016] Figure 4 This is a diagram illustrating an example of the manufacturing process of a composite substrate according to an embodiment of the present invention.

[0017] Figure 5 This is a simplified cross-sectional view showing the general structure of the composite of the comparative example.

[0018] Figure 6 It is a chart summarizing the relationship between Si content and bonding strength.

[0019] Figure 7 This is a graph showing the variation in Si content near the bonding interface. Detailed Implementation

[0020] Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings; however, the present invention is not limited to these embodiments. Furthermore, to make the description clearer, the drawings sometimes schematically represent the width, thickness, shape, etc., of various parts compared to the embodiments; however, this is merely an example and does not limit the interpretation of the present invention.

[0021] Figure 1This is a simplified cross-sectional view showing the general structure of a composite substrate according to one embodiment of the present invention. The composite substrate 100 in this embodiment has the following structure: a functional substrate 10 having a defined function is bonded to a support substrate 30 via an intermediate layer 20.

[0022] The functional substrate 10 has the function of realizing various devices and is constructed using materials corresponding to its function. For example, in the composite substrate 100 used for SAW filters or optical waveguides, piezoelectric materials such as LN (LiNbO3: lithium niobate) and LT (LiTaO3: lithium tantalate) can be used to construct the functional substrate 10. In addition, in the composite substrate 100 used as an SOI substrate, the functional substrate 10 is constructed using a Si substrate as a semiconductor. In addition, various materials corresponding to the application of the composite substrate 100 can be used as the functional substrate 10.

[0023] The following describes an example of using LT material to construct the functional substrate 10; the same applies to the use of other materials.

[0024] An intermediate layer 20 is disposed on a support substrate 30 and positioned between the functional substrate 10 and the support substrate 30. The intermediate layer 20 is made of SiO2. The intermediate layer 20 is configured such that a high-concentration Si region 22, with a higher Si content than the SiO2 regions 21A and 21B, is sandwiched between SiO2 regions 21A and 21B (first SiO2 region 21A and second SiO2 region 21B) respectively disposed on the functional substrate 10 side and the support substrate 30 side. It should be noted that, regarding the high-concentration Si region 22, if the Si content is higher than that of the SiO2 regions 21A and 21B, the bonding strength is improved. That is, by providing a region in the intermediate layer 20 with a higher Si content than other portions (e.g., 33 atomic% or more), the bonding strength between the functional substrate 10 and the support substrate 30 is improved by means of the intermediate layer 20 compared to the case where this region is not provided. Regarding the effect of this improved bonding strength, the inventors of the present invention speculate as follows.

[0025] When fabricating the composite substrate 100, the surface regions of SiO2 regions 21A and 21B respectively provided on the functional substrate 10 side and the support substrate 30 side are configured such that the Si content is higher than that of other regions, thereby forming Si high-concentration regions 22 in these surface regions. Furthermore, the functional substrate 10 and the support substrate 30 are bonded using the Si high-concentration regions 22 as bonding interfaces. It is believed that, in addition to the Si-O-Si covalent bonds formed by the following reaction formula (1) using conventional bonding methods, SiO2 covalent bonds obtained by the following reaction formula (2) can also be formed at the bonding interface. As a result, compared with conventional bonding methods that do not provide Si high-concentration regions 22, the number of final covalent bonds at the bonding interface can be increased, thus improving the bonding strength and suppressing the peeling of the functional substrate 10.

[0026] Si-OH (supporting substrate 30 side) + Si-OH (functional substrate 10 side)

[0027] →Si-O-Si+H2O···(1)

[0028] Si (supporting substrate 30 sides, functional substrate 10 sides) + 2H2O

[0029] →SiO2+2H2 ···(2)

[0030] It should be noted that the Si content in the high Si concentration region 22 before bonding is preferably 35 to 45 atomic%, more preferably 35 to 40 atomic%. If it is less than 40 atomic%, the Si-O-Si covalent bonds obtained by the above reaction formula (1) are sufficient, and the voids are suppressed, so it is more preferable.

[0031] The intermediate layer 20 can be formed using any suitable method. For example, it can be formed using physical vapor deposition (PVD), chemical vapor deposition (CVD), atomic layer deposition (ALD), or other methods such as sputtering, vacuum evaporation, ion beam assisted vapor deposition (IAD). The formation of the intermediate layer 20 can be carried out at temperatures ranging from, for example, room temperature (25°C) to 300°C.

[0032] The support substrate 30 supports the functional substrate 10. Any suitable substrate can be used as the support substrate 30. The support substrate 30 can be made of a single crystal or a polycrystalline material. Alternatively, it can be made of metal. The functional substrate 10 and the support substrate 30 are bonded to each other via an intermediate layer 20.

[0033] The material constituting the support substrate 30 is preferably selected from the group consisting of silicon, silicon aluminum oxynitride ceramic, sapphire, cordierite, andalusite, glass, quartz, crystal, alumina, SUS, iron-nickel alloy (42 alloy), MgF2, CaF2, and brass. The support substrate 30 can have any suitable thickness.

[0034] The silicon mentioned above can be monocrystalline silicon, polycrystalline silicon, or high-resistivity silicon.

[0035] Typically, the aforementioned silicon-aluminum-oxygen-nitrogen ceramics are ceramics obtained by sintering a mixture of silicon nitride and aluminum oxide, for example, having a silicon content of 0.5%. 6－w Al w O w N 8－w The composition is indicated by w. Specifically, the silicon-aluminum-oxygen-nitrogen ceramic has a composition in which alumina is mixed in silicon nitride, where w represents the mixing ratio of alumina. w is preferably 0.5 or more and 4.0 or less.

[0036] Typically, the sapphire described above is a single crystal with an Al2O3 composition, and the alumina described above is a polycrystalline material with an Al2O3 composition. The alumina is preferably a transparent alumina.

[0037] Representatively, the cordierite mentioned above is a ceramic having a composition of 2MgO·2Al2O3·5SiO2, and the andalusite mentioned above is a ceramic having a composition in the range of 3Al2O3·2SiO2 to 2Al2O3·SiO2.

[0038] It should be noted that, although not illustrated, the composite substrate 100 may further have any layers. The type, function, number, combination, and configuration of such layers can be appropriately set according to the purpose.

[0039] The composite substrate 100 can be manufactured in any suitable shape. In one embodiment, the composite substrate 100 can be manufactured in the form of a so-called wafer. In addition, the size of the composite substrate 100, for example, the diameter of the wafer (substrate) is 50 mm to 200 mm, can be appropriately set according to the purpose.

[0040] Figures 2-4 This is a diagram illustrating an example of the manufacturing process of a composite substrate according to an embodiment of the present invention.

[0041] Figure 2 (a) shows a preparation step in the manufacturing process of the composite substrate 100. In this step, a support substrate 30 is prepared. For example, a high-resistivity Si substrate (resistivity of 2kΩ·cm or more) with a thickness of 0.23 mm is used as the support substrate 30.

[0042] Figure 2(b) shows a first film deposition step for the support substrate 30 in the manufacturing process of the composite substrate 100. In this step, in Figure 2 In the preparation process of (a), an amorphous SiO2 film is formed on the surface of the support substrate 30, for example, with a specified thickness, thereby forming the second SiO2 region 21B in the intermediate layer 20.

[0043] Figure 2 (c) shows a second film deposition step for the support substrate 30 in the manufacturing process of the composite substrate 100. In this step, in Figure 2 In step (b), an amorphous SiO2 with a higher Si content than the second SiO2 region 21B is formed on the second SiO2 region 21B formed on the support substrate 30, thereby forming a second high Si concentration region 22B that constitutes a high Si concentration region 22 in the intermediate layer 20.

[0044] Figure 2 (d) shows the planarization process of the bonding surface in the manufacturing process of the composite substrate 100. In this process, the bonding surface is planarized by... Figure 2 In step (c), the surface of the second high-Si concentration region 22B formed on the support substrate 30 is ground, thereby planarizing the bonding surface of the support substrate 30 (second high-Si concentration region 22B).

[0045] Figure 3 (e) shows the activation process in the manufacturing process of the composite substrate 100. In this process, firstly, an LT substrate 10A containing LT material of a predetermined thickness with a surface polished to a mirror finish is prepared, and then activated with... Figure 2 The same film-forming and planarization processes as in (b), (c), and (d) are used to form a first SiO2 region 21A and a first Si high-concentration region 22A on the LT substrate 10A, thereby planarizing its surface. Next, regarding the process... Figure 2 In the planarization process (d), the surfaces of the second high-Si concentration region 22B on the support substrate 30 and the first high-Si concentration region 22A on the LT substrate 10A are respectively irradiated with N2 plasma to activate their respective surfaces.

[0046] Figure 3 (f) shows a bonding process in the manufacturing process of the composite substrate 100. In this process, the bonding process is performed on the composite substrate 100. Figure 3 In the activation process of (e), the surfaces of the second high Si concentration region 22B on the side of the support substrate 30 and the first high Si concentration region 22A on the side of the LT substrate 10A are directly bonded together, thereby forming a bond between the support substrate 30 and the LT substrate 10A with their surfaces as the bonding surfaces.

[0047] Figure 4 (g) shows the bonding between the support substrate 30 and the LT substrate 10A. Utilizing... Figure 4 In the bonding process (g), the first high-concentration Si region 22A and the second high-concentration Si region 22B are bonded together to achieve integration, thereby forming an intermediate layer 20 with the high-concentration Si region 22 sandwiched between the first SiO2 region 21A and the second SiO2 region 21B. As a result, the support substrate 30 and the LT substrate 10A are bonded together by means of the intermediate layer 20 to form Figure 4 The joint between the support substrate 30 and the LT substrate 10A shown in (g) is shown in the figure.

[0048] Figure 4 (h) shows the annealing process in the manufacturing process of the composite substrate 100. In this process, the substrate is subjected to annealing treatment. Figure 4 The bonding body formed by the bonding process (g) of the support substrate 30 and the LT substrate 10A is heated to a specified temperature. As a result, covalent bonds are formed inside the intermediate layer 20 by means of OH groups, thereby increasing the bonding strength of the bonding body.

[0049] Figure 4 (i) shows a thin-plate processing step in the manufacturing process of the composite substrate 100. In this step, for Figure 4 The bonded body after the annealing process shown in (h) is further thinned by grinding the LT substrate 10A to a specified thickness, thereby forming a functional substrate 10 containing LT material. For example, grinding, CMP (Chemical Mechanical Polishing), or surface planarization using a gas cluster ion beam can be used to grind the LT substrate 10A to achieve thinning.

[0050] Through the above processes, manufacturing Figure 1 The composite substrate 100 with the structure shown.

[0051] Example

[0052] The following describes in detail embodiments used to verify the structure of the composite substrate involved in the present invention. It should be noted that, unless otherwise explicitly stated, the following processes are performed at room temperature.

[0053] (Example 1)

[0054] According to reference Figures 2-4The manufacturing process described herein involves fabricating a bond. Specifically, an LT substrate 10A with a thickness of 0.25 mm and a support substrate 30 made of a high-resistivity Si substrate with a thickness of 0.23 mm are used. Furthermore, an amorphous SiO2 film is formed on the surfaces of the LT substrate 10A and the support substrate 30 with a thickness of 0.5 μm, thereby forming a first SiO2 region 21A and a second SiO2 region 21B. Then, an amorphous SiO2 film with increased Si content is formed on these regions with a thickness of 0.11 μm, thereby forming a first high-Si concentration region 22A and a second high-Si concentration region 22B. These film formation processes are performed using a reactive sputtering apparatus. During the film formation of SiO2 regions 21A and 21B, the oxygen free radical discharge output power is set to 3 kW, and the oxygen flow rate is set to 120 sccm. On the other hand, during film formation in the first high-Si concentration region 22A and the second high-Si concentration region 22B, the oxygen free radical discharge output power was still set to 3kW, but the oxygen flow rate was changed from 120 sccm to 60 sccm, thereby changing (increasing) the Si content. It should be noted that the target output power and Ar gas flow rate remained constant in both film formation processes. Afterwards, each surface was planarized by CMP polishing to approximately 0.1 μm.

[0055] Next, the surfaces of the first high-Si concentration region 22A on the LT substrate 10A and the second high-Si concentration region 22B on the support substrate 30 are respectively irradiated with N2 plasma for activation. After activation, their surfaces are overlapped and pressurized at room temperature to directly bond them together. Accordingly, the first high-Si concentration region 22A and the second high-Si concentration region 22B are integrated to form a high-Si concentration region 22. An intermediate layer 20 is formed between the first SiO2 region 21A and the second SiO2 region 21B, sandwiching the high-Si concentration region 22, resulting in a bonded body in which the support substrate 30 and the LT substrate 10A are bonded together by means of the intermediate layer 20.

[0056] Next, the resulting bond is placed in a high-temperature furnace and heated from room temperature to 130°C, held for about 4 hours, and then returned to room temperature for annealing.

[0057] Next, the LT substrate 10A of the annealed assembly is ground and polished to thin the LT substrate 10A to 1 μm, forming a functional substrate 10, thus obtaining... Figure 1 The composite substrate 100 with the structure shown. Regarding the composite substrate 100 of this embodiment 1, no peeling of the LT substrate 10A occurred during the thin-plate processing. Furthermore, the bond strength was evaluated using the crack opening method, and the result was 2.5 J / m. 2 It has sufficient bonding strength.

[0058] Furthermore, the composite substrate 100 of Example 1 was cut, and compositional analysis was performed using EDX on the cross-section including the interface between the first high-Si concentration region 22A and the second high-Si concentration region 22B formed in the intermediate layer 20, thereby determining the Si content in the high-Si concentration region 22. The result showed that the Si content in the high-Si concentration region 22 was 37 atomic%.

[0059] (Example 2)

[0060] In Example 2, the oxygen free radical discharge output power in the film formation process of the first high-Si concentration region 22A and the second high-Si concentration region 22B was changed compared to the film formation process of SiO2 regions 21A and 21B. Specifically, in the film formation process of the first high-Si concentration region 22A and the second high-Si concentration region 22B, the oxygen flow rate was still set to 120 sccm, but the oxygen free radical discharge output power was changed from 3 kW to 1.5 kW, thereby changing (increasing) the Si content. Moreover, all other conditions were the same as in Example 1, and even the other processes were performed using the same conditions as in Example 1 to obtain the desired result. Figure 1 The composite substrate 100 with the structure shown.

[0061] Regarding the composite substrate 100 of Example 2, similarly to Example 1, no peeling of the LT substrate 10A occurred during the thin-plate processing. Furthermore, the bond strength was evaluated using the crack opening method, and the result was 2.7 J / m. 2 It has sufficient bonding strength.

[0062] Furthermore, the composite substrate 100 of Example 2 was cut, and compositional analysis was performed using EDX on the cross-section including the interface between the first high-Si concentration region 22A and the second high-Si concentration region 22B formed in the intermediate layer 20, thereby determining the Si content in the high-Si concentration region 22. The result showed that the Si content in the high-Si concentration region 22 was 40 atomic%.

[0063] (Example 3)

[0064] In Example 3, the oxygen free radical discharge output power and oxygen flow rate in the film formation process of the first high-Si concentration region 22A and the second high-Si concentration region 22B were changed compared to the film formation process of SiO2 regions 21A and 21B. Specifically, in the film formation process of the first high-Si concentration region 22A and the second high-Si concentration region 22B, the oxygen flow rate was changed from 120 sccm to 60 sccm, and the oxygen free radical discharge output power was changed from 3 kW to 1.5 kW, thereby changing (increasing) the Si content. Moreover, all other conditions were the same as in Example 1, and even the other processes were performed using the same conditions as in Example 1 to obtain the desired result. Figure 1 The composite substrate 100 with the structure shown.

[0065] Regarding the composite substrate 100 of Example 3, similarly to Example 1, no peeling of the LT substrate 10A occurred during the thin-plate processing. Furthermore, the bond strength was evaluated using the crack opening method, and the result was 2.8 J / m. 2 It has sufficient bonding strength.

[0066] Furthermore, the composite substrate 100 of Example 3 was cut, and compositional analysis was performed using EDX on the cross-section including the interface between the first high-Si concentration region 22A and the second high-Si concentration region 22B formed in the intermediate layer 20, thereby determining the Si content in the high-Si concentration region 22. The result showed that the Si content in the high-Si concentration region 22 was 45 atomic%.

[0067] (Comparative Example 1)

[0068] In Comparative Example 1, the film formation process for the first high-Si concentration region 22A and the second high-Si concentration region 22B, and the thinning process for the LT substrate 10A, were omitted. All other processes were performed under the same conditions as in Example 1, thereby obtaining… Figure 5 Composite 100A with the structure shown in (a) is a composite material. In this composite 100A, the support substrate 30 and the LT substrate 10A are bonded to each other by means of an intermediate layer 20A, and no image is formed inside the intermediate layer 20A. Figure 1 Such a high Si concentration region 22.

[0069] Regarding composite 100A of Comparative Example 1, the bond strength was evaluated using the crack opening method, and the result was 1.8 J / m. 2 Left and right, insufficient.

[0070] (Comparative Example 2)

[0071] In Comparative Example 2, a low-concentration Si region with a lower Si content than SiO2 regions 21A and 21B was used to replace the first high-concentration Si region 22A and the second high-concentration Si region 22B, respectively, and was deposited on the first SiO2 region 21A (deposited on the LT substrate 10A side) and the second SiO2 region 21B (deposited on the support substrate 30 side). Specifically, when depositing SiO2 regions 21A and 21B, as in Example 1, the oxygen free radical discharge output power was set to 3kW and the oxygen flow rate was set to 120sccm. On the other hand, when depositing Si low-concentration regions, the oxygen free radical discharge output power was still set to 3kW, but the oxygen flow rate was changed from 120sccm to 200sccm, thereby changing (reducing) the Si content. In addition, the thinning process of the LT substrate 10A was omitted, and all other processes were performed under the same conditions as in Example 1, thereby obtaining... Figure 5 Composite 100B with the structure shown in (b) is an example. In this composite 100B, the support substrate 30 and the LT substrate 10A are bonded together by means of an intermediate layer 20B. The intermediate layer 20B is configured such that a low-concentration Si region 23, with a lower Si content than these SiO2 regions 21A and 21B, is sandwiched between the first SiO2 region 21A and the second SiO2 region 21B. The low-concentration Si region 23 is formed by bonding the aforementioned low-concentration Si regions together.

[0072] Regarding composite 100B of Comparative Example 2, the bond strength was evaluated using the crack opening method, and the result was 1.5 J / m. 2 Left and right, insufficient.

[0073] Furthermore, the composite 100B of Comparative Example 2 was cut, and compositional analysis was performed using EDX on the cross-section including the interface between the low-concentration Si regions formed within the intermediate layer 20B, thereby determining the Si content in the low-concentration Si region 23. The results showed that the Si content in the low-concentration Si region 23 was 30 atomic%.

[0074] Figure 6 This is a chart summarizing the relationship between the Si content and bonding strength in the high Si concentration region 22 or low Si concentration region 23 of each composite substrate 100 of Examples 1 to 3 and composites 100A and 100B of Comparative Examples 1 and 2. Figure 6 In the diagram, point 101 represents Example 1, point 102 represents Example 2, point 103 represents Example 3, point 104 represents Comparative Example 1, and point 105 represents Comparative Example 2. It should be noted that in Comparative Example 1, as described above, no high-concentration Si region 22 and low-concentration Si region 23 were formed within the intermediate layer 20; therefore, the Si content was set to 33 atomic%, equivalent to the value of SiO2.

[0075] Depend on Figure 6 As shown in the diagram, if a high-concentration Si region 22 is formed within the intermediate layer 20, with a Si content greater than that of the SiO2 regions 21A and 21B composed of amorphous SiO2 (a Si content greater than 33 atomic%), the bonding strength is improved compared to the case without the high-concentration Si region 22 or with the low-concentration Si region 23. However, if the Si content is increased to approximately 45 atomic%, as in Example 3, the Si-O-Si covalent bonds at the bonding interface may decrease due to insufficient O atoms, potentially creating voids. Therefore, a Si content more preferably in the range of 35 to 40 atomic%. Figures 2-4 In the composite substrate 100 manufactured in each process, by setting the conditions of the aforementioned second film formation process in such a way that a high Si concentration region 22 with a higher Si content than other parts is formed inside the intermediate layer 20, it is possible to achieve a composite substrate 100 with improved bonding strength.

[0076] Figure 7 This is a graph showing the variation of Si content near the bonding interface in the composite substrate 100 of Example 1. Figure 7 It can be seen that a high Si concentration region 22 is formed in the intermediate layer 20 with a thickness of about 20 nm, sandwiched between the bonding interface.

[0077] According to the embodiments of the present invention described above, the following effects are achieved.

[0078] (1) The composite substrate 100 comprises: a functional substrate 10 having a defined function; a support substrate 30 supporting the functional substrate 10; and an intermediate layer 20 made of SiO2 and disposed between the support substrate 30 and the functional substrate 10. The functional substrate 10 and the support substrate 30 are bonded to each other by means of the intermediate layer 20, which has: SiO2 regions 21A and 21B respectively disposed on the side of the functional substrate 10 and the side of the support substrate 30 and made of SiO2, and a high-concentration Si region 22 sandwiched between the SiO2 regions 21A and 21B and having a higher Si content than the SiO2 regions 21A and 21B. Thus, in the composite substrate 100 obtained by bonding the functional substrate 10 and the support substrate 30 by means of the intermediate layer 20, the bonding strength can be improved.

[0079] (2) In the high Si concentration region 22, the Si content is more preferably greater than 33 atomic%, and even more preferably in the range of 35 to 40 atomic%. Accordingly, the high Si concentration region 22 that helps to improve the bonding strength can be reliably formed.

[0080] (3) The functional substrate 10 can be a piezoelectric material substrate made of LN (LiNbO3) or LT (LiTaO3) material. Alternatively, the functional substrate 10 can be a semiconductor substrate made of Si material. Accordingly, substrates with various functions can be used as the functional substrate 10 depending on the application of the composite substrate 100.

[0081] It should be noted that the present invention is not limited to the above-described embodiments, and can be implemented using any constituent elements without departing from its spirit.

[0082] The above-described embodiments and modifications are merely examples, and the present invention is not limited to these descriptions as long as they do not impair the features of the invention. Furthermore, while various embodiments and modifications have been described above, the present invention is not limited to these descriptions. Other solutions conceived within the scope of the technical concept of the present invention are also included within the scope of the present invention.

[0083] Explanation of reference numerals in the attached figures

[0084] 10: Functional substrate

[0085] 10A: LT substrate

[0086] 20: Intermediate layer

[0087] 21A: First SiO2 region

[0088] 21B: Second SiO2 region

[0089] 22: High Si concentration region

[0090] 30: Support substrate

[0091] 100: Composite substrate

Claims

1. A composite substrate comprising: a functional substrate having a prescribed function; a support substrate supporting the functional substrate; and an intermediate layer composed of SiO2, provided between the support substrate and the functional substrate, the functional substrate and the support substrate being joined to each other by means of the intermediate layer, the intermediate layer having SiO2 regions composed of SiO2, respectively provided on the functional substrate side and the support substrate side, and a Si high concentration region provided so as to be interposed between the SiO2 regions and having a higher content of Si than the SiO2 regions.

2. The composite substrate according to claim 1, wherein the content of Si in the Si high concentration region is greater than 33 atomic %.

3. The composite substrate according to claim 2, wherein the content of Si in the Si high concentration region is in the range of 35 to 40 atomic %.

4. The composite substrate according to claim 1, wherein the functional substrate is a piezoelectric material substrate.

5. The composite substrate according to claim 4, wherein the piezoelectric material substrate is composed of LiNbO3 or LiTaO3 material.

6. The composite substrate according to claim 1, wherein the functional substrate is a semiconductor substrate composed of Si material. ​ ​ ​ ​ ​ ​ ​ ​ ​ ​

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