Composite substrate and method for manufacturing the same

Abstract

Provided is a composite substrate which does not develop cracks even when exposed to high or low temperatures, and thus does not develop performance degradation. A composite substrate (10) of the present invention has, in the listed order, a support substrate (2), a stress relaxation interlayer (3), and an oxide single-crystal thin film (1). The stress relaxation interlayer (3) has a coefficient of thermal expansion which is between the coefficient of thermal expansion of the support substrate (2) and the coefficient of thermal expansion of the oxide single-crystal thin film (1).

Description

Technical Field

[0001] This invention relates to composite substrates and their manufacturing methods. Background Technology

[0002] To expand the application range of traditional functional materials (such as semiconductors and oxide single crystals), extensive research has been conducted in recent years on bonding different types of substrates to achieve higher performance. In the semiconductor field, silicon-on-insulator (SOI) is known, while in the oxide single crystal field, reports have been made of improving the temperature characteristics of composite substrates by bonding oxide single crystal substrates such as lithium tantalate (LiTaO3, abbreviated as LT) or lithium niobate (LiNbO3, abbreviated as LN) to sapphire and thinning the oxide single crystal substrate.

[0003] Some researchers have attempted to create a sandwich layer (also known as an "interlayer" or "intermediate layer") between the functional thin film and the supporting substrate for separation. Specifically, materials with high insulation, low high-frequency loss (low dielectric loss), and easy processing (planarization), such as SiO2, are often used as sandwich materials. To meet these properties, metal oxides (such as TiO2, Ta2O5, Nb2O5, ZrO2, etc., other than SiO2) are often chosen for the sandwich layer. Composite substrates with sandwich layers as described above (e.g., LT on SiO2 on Si substrate) generally exhibit excellent high-frequency performance (low high-frequency loss, improved linearity, and reduced crosstalk) due to their thinner active layer. Summary of the Invention

[0004] The technical problem to be solved by the present invention

[0005] However, the aforementioned composite substrates obtained by bonding different types of substrates also have drawbacks. Compared to silicon, glass, and sapphire, which are commonly used as support substrate materials, oxide single crystals have a considerably larger coefficient of thermal expansion (e.g., the coefficient of thermal expansion of LT or LN is approximately 15 to 16 ppm). On the other hand, the coefficients of thermal expansion of silicon, glass, and sapphire are approximately 2.5 ppm, 0.5 ppm, and 7.5 ppm, respectively. In practice, when devices using oxide single crystal layers on support substrates are exposed to high or low temperatures in real-world environments, the large stress applied to the oxide single crystal layer and the propagation of microcracks from the interface gradually damage the oxide single crystal layer inevitably lead to performance degradation. This problem stems from the structure itself, which is formed by stacking oxide single crystal thin films on a support substrate with a low coefficient of thermal expansion to improve temperature characteristics.

[0006] In view of the above problems, the object of the present invention is to provide a composite substrate and a method for manufacturing the composite substrate, wherein the composite substrate will not crack even when exposed to high or low temperatures, thereby not causing property degradation.

[0007] Problem Solving Methods

[0008] To achieve the above objectives, the present invention provides a method for manufacturing a composite substrate having a support substrate, a stress relaxation interlayer (also referred to herein as a "stress relaxation sandwich layer"), and an oxide single-crystal thin film stacked in a listed order. The method includes the following steps: forming a stress relaxation interlayer between the support substrate and the oxide single-crystal substrate, the stress relaxation interlayer having a coefficient of thermal expansion between the coefficient of thermal expansion of the support substrate and the coefficient of thermal expansion of the oxide single-crystal substrate; bonding the support substrate and the oxide single-crystal substrate together via the stress relaxation interlayer to obtain a bond; and thinning the oxide single-crystal substrate of the bond to form an oxide single-crystal thin film.

[0009] On the other hand, the method for manufacturing a composite substrate according to the present invention is a method for manufacturing a composite substrate having a support substrate, a sandwich layer, a stress relaxation interlayer and an oxide single crystal thin film stacked in a listed order, and is manufactured by using an adhesive method in such a way that the following inequality "the sandwich layer < the stress relaxation interlayer < the oxide single crystal thin film" is satisfied in the comparison of the coefficients of thermal expansion.

[0010] The interlayer preferably contains SiO2, SiON or SiN.

[0011] The interlayer is preferably formed by chemical vapor deposition (CVD) or physical vapor deposition (PVD).

[0012] The stress relaxation interlayer preferably contains SiN, SiC, AlN, Al2O3, Y2O3, TiO2, or ZrO2.

[0013] The oxide single crystal substrate preferably contains lithium tantalate (LT) or lithium niobate (LN).

[0014] The stress relaxation interlayer is preferably formed by chemical vapor deposition (CVD) or physical vapor deposition (PVD).

[0015] The oxide single-crystal substrate of the bond can be thinned by grinding or polishing, or a combination thereof.

[0016] The manufacturing method may also include: subjecting the bonding surface (hereinafter referred to as the "bonding surface") of the oxide single crystal substrate to ion implantation treatment to form an ion implantation layer inside the oxide single crystal substrate; and thinning the oxide single crystal substrate of the bonding body by leaving the ion implantation layer as an oxide single crystal film and peeling the remaining portion of the oxide single crystal substrate from the bonding body.

[0017] Another aspect of the present invention is a composite substrate having a support substrate, a stress relaxation interlayer and an oxide single crystal thin film stacked in a listed order, wherein the stress relaxation interlayer has a coefficient of thermal expansion between that of the support substrate and that of the oxide single crystal thin film.

[0018] Another aspect of the present invention is a composite substrate having a support substrate, an interlayer, a stress relaxation interlayer and an oxide single crystal thin film stacked in a listed order, wherein the stress relaxation interlayer has a thermal expansion coefficient between that of the interlayer and that of the oxide single crystal thin film.

[0019] The interlayer preferably contains SiO2, SiON or SiN.

[0020] The stress relaxation interlayer preferably contains SiN, SiC, AlN, Al2O3, Y2O3, TiO2, or ZrO2.

[0021] The oxide single crystal substrate preferably contains lithium tantalate (LT) or lithium niobate (LN).

[0022] Technical effect

[0023] Thus, based on the present invention, by inserting a stress relaxation interlayer made of a material with a thermal expansion coefficient less than that of the oxide single crystal film and greater than that of the support substrate between the oxide single crystal film and the support substrate, the stress applied to the interface of the oxide single crystal film when the temperature changes can be reduced, thereby preventing cracks and performance degradation. Attached Figure Description

[0024] Figure 1 This is a schematic cross-sectional view illustrating one embodiment of the composite substrate of the present invention.

[0025] Figure 2 This is a graph showing the coefficients of thermal expansion of typical materials used in the composite substrate of the present invention.

[0026] Figure 3 This is a schematic cross-sectional view illustrating another embodiment of the composite substrate of the present invention.

[0027] Figure 4This is a schematic flowchart illustrating one embodiment of the method for manufacturing a composite substrate according to the present invention.

[0028] Figure 5 This is a schematic flowchart illustrating another embodiment of the method for manufacturing a composite substrate according to the present invention.

[0029] Figure 6 This is a schematic flowchart illustrating another embodiment of the method for manufacturing a composite substrate according to the present invention. Detailed Implementation

[0030] Hereinafter, embodiments of the composite substrate of the present invention and its manufacturing method will be described with reference to the accompanying drawings, but the scope of the present invention is not limited thereto.

[0031] like Figure 1 As shown, the composite substrate 10 of this embodiment has a support substrate 2, a stress relaxation interlayer 3 and an oxide single crystal thin film stacked in the order listed.

[0032] As the oxide single-crystal thin film 1, a piezoelectric single crystal (piezoelectric body single crystal) is preferred, for example, a compound composed of various metal elements such as lithium, tantalum, or niobium and oxygen. Examples of such compounds include lithium tantalate (LiTaO3, abbreviated as "LT") and lithium niobate (LiNbO3, abbreviated as "LN"). The thickness of the oxide single-crystal thin film 1 is preferably, for example, 0.1 to 30 mm. μ m.

[0033] The support substrate 2 is not particularly limited as long as it is an insulating substrate commonly used in composite substrates. Examples include silicon substrates, glass substrates, and sapphire substrates. The support substrate 2 can be used in the form of a wafer. The wafer size is preferably, for example, 2 to 12 inches in diameter and 100 to 2000 micrometers in thickness (plate thickness).

[0034] For the stress relaxation interlayer 3, a material with a coefficient of thermal expansion that is less than that of the oxide single-crystal thin film 1 and greater than that of the support substrate 2 is used. In this invention, this layer is called a "stress relaxation interlayer" because a material layer with this coefficient of thermal expansion between the oxide single-crystal thin film 1 and the support substrate 2 can reduce the stress applied to the interface of the oxide single-crystal thin film 1 and prevent its deterioration when the temperature changes.

[0035] The corresponding coefficients of thermal expansion for typical materials used in composite substrates are as follows: Figure 2 As shown. Among these materials, SiN, SiC, AlN, Al2O3, Y2O3, TiO2, and ZrO2 have thermal expansion coefficients between those of the oxide single-crystal thin film 1 (LT or LN) and the supporting substrate 2 (silicon or glass), and are therefore preferred as materials for the stress relaxation interlayer 3. The thickness of the stress relaxation interlayer 3 is preferably, for example, 0.1 to 5.0 mm. μ m.

[0036] This invention is not limited to, for example Figure 1 The structure of the composite substrate 10 shown can also be, for example, Figure 3 The structure shown. (As illustrated) Figure 3 As shown, another embodiment of the composite substrate 20 has a support substrate 2, a sandwich layer 4, a stress relaxation interlayer 3 and an oxide single crystal thin film 1 stacked in the order listed.

[0037] The material used for interlayer 4 can be a material commonly used for interlayers in composite substrates, and it is a material with a coefficient of thermal expansion that is less than that of the oxide single-crystal thin film 1 and greater than that of the stress relaxation interlayer 3. Examples of such materials include SiO2, SiON, and SiN. When interlayer 4 is made of such a material, as described above, the stress applied to the interface of the oxide single-crystal thin film 1 due to temperature changes can be reduced by the stress relaxation interlayer 3, and deterioration can be prevented. In other words, in another embodiment of the composite substrate 20, a material having a coefficient of thermal expansion that is less than that of the oxide single-crystal thin film 1 and greater than that of the interlayer 4 is used for the stress relaxation interlayer 3.

[0038] Next, the method for manufacturing a composite substrate according to this embodiment will be described. For example... Figure 4 As shown, it includes the step of preparing an oxide single-crystal substrate 1A. Figure 4 (a) of the above, the step of preparing the support substrate ( Figure 4 (b) In the step of forming a stress relaxation interlayer 3 on an oxide single crystal substrate and a support substrate, Figure 4 (c) The step of bonding the oxide single crystal substrate 1 and the support substrate 2 through the stress relaxation interlayer 3. Figure 4 (d) and the step of thinning the oxide single crystal substrate of the bond 4 obtained by bonding to obtain the composite substrate 10. Figure 4 (e)). These steps will be described in detail below. The methods shown below are for illustrative purposes only. The stress relaxation interlayer 3 can be formed on any substrate by any method and can be bonded on any surface.

[0039] The oxide single crystal substrate 1A prepared in step (a) is to become Figure 1 The composite substrate 10 shown is a substrate of the oxide single-crystal thin film 1. Since the oxide single crystal has already been described above, its description is omitted here. The oxide single-crystal substrate 1 can be used in wafer form. There are no particular limitations on the wafer size; for example, the wafer diameter can be 2 to 8 inches, and the wafer thickness (plate thickness) can be 100 to 1000 mm. μ m.

[0040] The support substrate 2 prepared in step (b) is Figure 1 The supporting substrate 2 of the composite substrate 10 shown. Since it has already been described above, the description is omitted here.

[0041] The bonding surface of the oxide single crystal substrate 1 or the bonding surface of the support substrate 2 is not necessarily a mirror surface, because the bonding surface of the oxide single crystal substrate 1 and the bonding surface of the support substrate 2 are bonded to each other through the stress relaxation interlayer 3.

[0042] Next, as Figure 4 As shown in step (c), stress relaxation interlayers 3a and 3b are formed on the bonding surfaces of the oxide single crystal substrate 1 and the support substrate 2. Since the material of the stress relaxation interlayer 3 has already been described above, its description is omitted here.

[0043] Examples of methods for forming the stress relaxation interlayer 3 include chemical vapor deposition (CVD) and physical vapor deposition (PVD). Examples of CVD methods include thermal CVD, plasma CVD, and photochemical CVD. Examples of PVD methods include vapor deposition, ion plating, and sputtering. By using these CVD or PVD methods under known film-forming conditions for forming films such as silicon nitride films, the stress relaxation interlayer 3 can be formed on the surface to be bonded of the oxide single-crystal substrate 1 or the support substrate 2.

[0044] exist Figure 4 Step (c) describes forming stress relaxation interlayers 3a and 3b on the respective surfaces to be bonded of the oxide single-crystal substrate 1 and the support substrate 2, but the present invention is not limited thereto. For example, similar effects can be obtained by forming stress relaxation interlayer 3a only on the surface to be bonded of the oxide single-crystal substrate 1 or only on the surface to be bonded of the support substrate 2. As described above, the stress relaxation interlayer 3 can be formed on any substrate, and how it is formed and on which surface bonding is performed are completely arbitrary. This has no effect on the effects of the present invention.

[0045] Then, as Figure 4 As shown in step (d), the oxide single crystal substrate 1 and the support substrate 2 are bonded together by stress-relaxed interlayer 3 to obtain the bond 4. It should be noted that before bonding, both surfaces of the oxide single crystal substrate 1 and the support substrate 2 to be bonded are subjected to surface activation treatment. As a surface activation treatment, any treatment capable of activating the surfaces to be bonded is acceptable and is not particularly limited. Examples of surface activation treatments include plasma activation treatment, vacuum ion beam method, ozone water treatment method, and UV ozone treatment method. As an atmosphere for surface activation treatment, an inert gas (e.g., nitrogen or argon) and oxygen can be used alone or in combination.

[0046] The bond 4, obtained by bonding the oxide single crystal substrate 1 and the support substrate 2 together via the stress relaxation interlayer 3, can be subjected to heat treatment. This treatment can improve the bonding strength between them.

[0047] Then, as Figure 4 As shown in step (e), the oxide single-crystal substrate 1A of the bonding body 4 is thinned. As a result, a composite substrate 10 having an oxide single-crystal thin film 1 formed on the support substrate 2 via a stress relaxation interlayer 3 is obtained.

[0048] Reference Figure 4 The method for preparing the composite substrate 10 will be described. The invention is not limited thereto, and various modifications can be made, such as changing the order of the above steps and rearranging other steps. For example, the composite substrate 10 can be prepared by... Figure 5 It is manufactured using the method shown.

[0049] like Figure 5 As shown, the method for manufacturing a composite substrate based on this other embodiment includes the step of preparing an oxide single-crystal substrate 1A. Figure 5 (a) in the text refers to the step of ion implantation X on the oxide single crystal substrate 1A. Figure 5 (a1) in the step of forming an ion implantation layer 1X on an oxide single crystal substrate 1. Figure 5 (a2) in the middle, the step of preparing the support substrate 2 ( Figure 5 (b) of the above, the step of forming a stress relaxation interlayer 3 on the oxide single crystal substrate 1A and the support substrate 2. Figure 5 (c) In the step of bonding the oxide single crystal substrate 1A and the support substrate 2 together through the stress relaxation interlayer 3, Figure 5 (d) in the example, and the step of peeling a portion 1b of the oxide single crystal substrate from the bond 4 thus obtained by bonding to obtain the composite substrate 10. Figure 5 (e)). The following will explain each of the newly added steps in detail. The method shown below is for illustrative purposes only. The substrate on which the stress relaxation interlayer 3 is formed, how it is formed, and on which surface the bonding is performed can be chosen arbitrarily.

[0050] In step (a1), an ion implantation treatment A is performed on the surface of the oxide single-crystal substrate 1A to be bonded. Through this treatment, as shown in step (a2), an ion-implanted layer 1X is formed on the surface of the oxide single-crystal substrate 1A to be bonded. The conditions for the ion implantation treatment are as follows. For example, when hydrogen ions (H+) are used... + When the injection volume is 5.0 × 10⁻⁶, the preferred injection volume is 5.0 × 10⁻⁶. 16 atom / cm 2 Up to 2.75×10 17 atom / cm2 When the injection volume is less than 5.0 × 10 16 atom / cm 2 When the ion implantation layer is sufficiently dense, it is less prone to embrittlement in subsequent steps. When the implantation depth exceeds 2.75 × 10⁻⁶, the ion implantation layer is less likely to become embrittled. 17 atom / cm 2 During ion implantation, microcavities may appear on the implanted surface, making the wafer surface uneven and difficult to achieve the desired surface roughness. When using hydrogen molecular ions (H2O), + When ), the injection volume is preferably 2.5 × 10⁻⁶. 16 atom / cm 2 Up to 1.37×10 17 atom / cm 2 .

[0051] The ion acceleration voltage is preferably between 50 keV and 200 keV. The ion implantation depth can be changed by adjusting the acceleration voltage. The thickness of the ion implantation layer 1X is preferably adjusted to between 100 nm and 2000 nm. The thickness of this ion implantation layer 1X is approximately equivalent to the thickness of the oxide single-crystal thin film 1 of the composite substrate 10 to be obtained.

[0052] Then, in Figure 5 In step (e), a portion 1a of the oxide single-crystal substrate is peeled off from the bonding body 4, while leaving an ion-implanted layer 1X on the stress relaxation interlayer 3 side. Thus, a composite substrate 10 having an ion-implanted layer (oxide single-crystal thin film) 1 formed on the support substrate 2 via the stress relaxation interlayer 3 is obtained. The peeling can be performed by applying mechanical impact using a wedge-shaped blade (not shown).

[0053] in addition, Figure 6 The manufacturing process is shown in the diagram. Figure 3 One embodiment of the method for the composite substrate 20 shown. Figure 6 The method for manufacturing the composite substrate shown includes the step of preparing an oxide single-crystal substrate 1A. Figure 6 (a) in the text, the step of preparing the support substrate 2 ( Figure 6 In step (b), the process of forming the interlayer 4 on the support substrate 2. Figure 6 (b1)) The step of forming a stress relaxation interlayer 3 on the oxide single crystal substrate 1A and the interlayer 4. Figure 6 (c) In the step of bonding the oxide single crystal substrate 1A to the support substrate 2 having the interlayer 4 via the stress relaxation interlayer 3. Figure 6 (d) in the text, and the step of thinning the oxide single crystal substrate 1A of the bonded assembly by grinding, polishing, etc., to obtain the composite substrate 20. Figure 6(e)). The newly added steps are described in detail below. However, the method shown below is only an example and can be arbitrarily chosen on which substrate the sandwich 4 or stress relaxation interlayer 3 is formed on, how it is formed, and on which surface the bonding is performed.

[0054] like Figure 6 As shown in step (b1), a sandwich layer 4 is formed on the surface of the support substrate 2 to be bonded. Since the material of the sandwich layer 4 has already been described above, its description is omitted here. Examples of methods for forming the sandwich layer 4 include chemical vapor deposition (CVD) and physical vapor deposition (PVD). Examples of CVD methods include thermal CVD, plasma CVD, and photochemical CVD. Examples of PVD methods include vapor deposition, ion plating, and sputtering. By using these CVD or PVD methods under known film-forming conditions for forming films such as silicon oxide films, the sandwich layer 4 can be formed on the surface of the support substrate 2 to be bonded.

[0055] Example

[0056] The following description focuses on embodiments and comparative examples, but the present invention is not limited to these examples.

[0057] Example 1

[0058] When bonding a 150 mm diameter silicon substrate to a lithium tantalate (LT) substrate, a stress relaxation interlayer made of a material composed of SiN, SiC, AlN, Al2O3, Y2O3, TiO2, and ZrO2 is inserted between the silicon and LT substrates to obtain a bond. The stress relaxation interlayer is formed on the silicon substrate using CVD. The corresponding bonding surfaces of the silicon and LT substrates are pre-treated with plasma activation. The resulting LT substrate of the bond is then thinned to 6 mm by grinding or polishing. μ m is used to obtain a composite substrate.

[0059] The composite substrate thus obtained was subjected to thermal shock testing under the following conditions. The substrate was moved between a low-temperature chamber (-60°C) and a high-temperature chamber (170°C), with a dwell time of 10 minutes at each temperature. A thermal shock test chamber (“TSE-12-A”, manufactured by ESPEC) was used in the test. After 10 cycles of movement between the two chambers, the resulting composite substrate was removed from the chamber and inspected for cracks using an external inspection system (“BB-Master”, manufactured by Kurabo Industry Ltd.). The test was stopped when a crack was found at any of the five locations on the composite substrate. Thermal shock testing continued when no cracks were found. The number of cycles (LT on Si) at which cracks were found is shown in Table 1 as the test results. In Table 1, the numbers in parentheses for each material in the stress relaxation interlayer item represent the coefficient of thermal expansion (ppm) of the material.

[0060] Table 1

[0061]

[0062] The results above show that composite substrates with stress relaxation interlayers inserted in between have improved reliability compared to any composite substrate without stress relaxation interlayers. This improvement is attributed to the effect of stress relaxation, as the coefficient of thermal expansion of any material used for the stress relaxation interlayer is greater than that of silicon, the supporting substrate (2.5 ppm), and less than that of LT (15 ppm).

[0063] Example 2

[0064] Except that a sapphire substrate was used instead of a silicon substrate, a composite substrate was prepared in the same manner as in Example 1, and thermal shock tests were conducted under the same conditions as in Example 1. The results are shown in Table 1 (LT on sapphire). These results indicate that the composite substrate with an intercalated stress relaxation intercalator has improved reliability only when the coefficient of thermal expansion of the stress relaxation intercalator material is greater than that of sapphire (7.5 ppm).

[0065] Example 3

[0066] Except that a glass substrate was used instead of a silicon substrate, a composite substrate was prepared in the same manner as in Example 1, and thermal shock tests were conducted under the same conditions as in Example 1. The results are shown in Table 1 (LT on glass). These results indicate that any composite substrate with an intercalated stress relaxation intercalator has improved reliability, which is attributed to the effect of stress relaxation. This is believed to be due to the fact that the coefficient of thermal expansion of the various materials used for the stress relaxation intercalator is greater than that of glass (0.5 ppm) and less than that of LT.

[0067] Example 4

[0068] In addition to inserting a layer of approximately 1.0 mm thickness between the silicon substrate and the stress relaxation interlayer. μ Except for the inclusion of a SiO2 interlayer, a composite substrate was prepared in the same manner as in Example 1, and thermal shock tests were performed under the same conditions as in Example 1. An interlayer was formed on a silicon substrate using CVD, and a stress relaxation interlayer was formed on the interlayer. The results are shown in Table 2 (LT on silicon dioxide).

[0069] Table 2

[0070]

[0071] The results show that any composite substrate with a stress relaxation interlayer inserted between the sandwich layer and the LT film has higher reliability compared to composite substrates without a stress relaxation interlayer.

[0072] These results are attributed to the effect of stress relaxation, because the coefficient of thermal expansion of the various materials used in the stress relaxation interlayer is greater than that of SiO2 (0.6 ppm) as the interlayer and less than that of LT.

[0073] Example 5

[0074] Except that a sapphire substrate was used instead of a silicon substrate, a composite substrate was prepared in the same manner as in Example 4, and thermal shock tests were conducted under the same conditions as in Example 1. The results are shown in Table 2 (LT on sapphire and silicon dioxide). These results indicate that the composite substrate with a stress relaxation interlayer inserted between the interlayer and the LT film only has improved reliability when the coefficient of thermal expansion of the stress relaxation interlayer material is greater than that of the sapphire material.

[0075] Example 6

[0076] Except that a lithium niobate (LN) substrate was used instead of an LT substrate as the oxide single-crystal substrate, composite substrates were prepared in the same manner as in Examples 1-5, and thermal shock tests were conducted under the same conditions as in Example 1. The coefficient of thermal expansion of LN was 16 ppm, and that of LT was 15 ppm. As a result, the composite substrates with LN thin films and the composite substrates with LT thin films showed the same trend.

[0077] Example 7

[0078] Except that SiON and SiN were used instead of SiO2 as the interlayer material, composite substrates were prepared in the same manner as in Examples 4 and 5, and thermal shock tests were conducted under the same conditions as in Example 1. The coefficient of thermal expansion of SiON was approximately 2.0 ppm, and that of SiN was approximately 2.8 ppm. The results confirm that as long as the stress relaxation interlayer is composed of a material with a coefficient of thermal expansion greater than that of the interlayer, it has the effect of improving the reliability of the composite substrate, although the degree of improvement varies.

[0079] Example 8

[0080] In addition to using various treatment methods such as vacuum ion beam method, ozone water treatment method, and UV ozone treatment method to replace plasma activation treatment, composite substrates were prepared in the same manner as in Examples 1 to 5, and thermal shock tests were conducted under the same conditions as in Example 1. The results showed that they were substantially the same as those in Examples 1 to 5, and the stress relaxation effect did not depend on the treatment method applied to the surfaces to be bonded.

[0081] Example 9

[0082] Except that the thinning of the LT substrate by grinding and polishing the bonded body was replaced by pre-implanting hydrogen ions into the surfaces of the LT substrate to be bonded and then peeling along the implantation interface in the bonded assembly, composite substrates were prepared in the same manner as in Examples 1 and 2, and thermal shock tests were performed under the same conditions as in Example 1. The thickness of the LT film was 0.8 mm. μ The results showed the same trend as in Examples 1 and 2, and the effect of stress relaxation was independent of the thinning method of the LT substrate.

[0083] Example 10

[0084] Except for using PVD instead of CVD as the method for forming sandwich and stress relaxation interlayer, composite substrates were prepared in the same manner as in Examples 1 and 4, and thermal shock tests were conducted under the same conditions as in Example 1.

[0085] The results showed the same trend as in Examples 1 and 4, and the effect of stress relaxation was independent of the method of forming the interlayer and stress relaxation layer (film formation method).

[0086] Explanation of reference numerals in the attached figures

[0087] 1: Oxide single-crystal thin films

[0088] 1A: Oxide single crystal substrate

[0089] 1X: Ion implantation layer

[0090] 2: Support base plate

[0091] 3: Stress relaxation interlayer

[0092] 4: Mezzanine

[0093] 10, 20: Composite substrate

Claims

1. A method for manufacturing a composite substrate, the composite substrate having a support substrate, a stress relaxation interlayer, and an oxide single-crystal thin film stacked in a listed order, the method comprising the following steps: A stress relaxation interlayer is formed between a support substrate and an oxide single crystal substrate. The stress relaxation interlayer has a thermal expansion coefficient between that of the support substrate and the oxide single crystal substrate. The stress relaxation interlayer contains Y2O3, TiO2, or ZrO2. A joint is formed by bonding the support substrate and the oxide single crystal substrate together via the stress relaxation interlayer; and The oxide single-crystal substrate of the bonding body is thinned to become an oxide single-crystal thin film.

2. The method of manufacturing a composite substrate as claimed in claim 1, wherein the oxide single-crystal substrate of the bonding body is thinned by grinding or polishing or a combination thereof.

3. The method for manufacturing a composite substrate as described in claim 1, further comprising the step of: performing ion implantation treatment on the surface of the oxide single crystal substrate to be bonded to form an ion implantation layer inside the oxide single crystal substrate; in, The oxide single-crystal substrate of the bonding assembly is thinned by leaving the ion-implanted layer as an oxide single-crystal thin film on the bonding assembly and peeling off the remaining portion of the oxide single-crystal substrate from the bonding assembly.

4. A method for manufacturing a composite substrate, the composite substrate having a support substrate, a sandwich layer, a stress relaxation interlayer and an oxide single crystal thin film stacked in a listed order, the stress relaxation interlayer comprising SiC, Y2O3, TiO2 or ZrO2; The method includes manufacturing in a manner that satisfies the following inequality in a comparison of the coefficients of thermal expansion: The interlayer < the stress relaxation interlayer < the oxide single crystal thin film.

5. The method of manufacturing a composite substrate as claimed in claim 4, wherein the interlayer comprises SiO2, SiON, or SiN.

6. The method for manufacturing a composite substrate as described in claim 4 or 5, wherein, The interlayer is formed by chemical vapor deposition (CVD) or physical vapor deposition (PVD).

7. The method of manufacturing a composite substrate according to any one of claims 1 to 5, wherein the oxide single crystal substrate comprises lithium tantalate LT or lithium niobate LN.

8. The method for manufacturing a composite substrate according to any one of claims 1 to 5, wherein, The stress relaxation interlayer is formed by chemical vapor deposition (CVD) or physical vapor deposition (PVD).

9. A composite substrate having a support substrate, a stress relaxation interlayer, and an oxide single-crystal thin film stacked in a listed order, wherein the stress relaxation interlayer has a coefficient of thermal expansion between the coefficient of thermal expansion of the support substrate and the coefficient of thermal expansion of the oxide single-crystal thin film, and the stress relaxation interlayer comprises Y2O3, TiO2, or ZrO2.

10. A composite substrate having a support substrate, a sandwich layer, a stress relaxation interlayer and an oxide single-crystal thin film stacked in a listed order, wherein the stress relaxation interlayer has a coefficient of thermal expansion between the coefficient of thermal expansion of the sandwich layer and the coefficient of thermal expansion of the oxide single-crystal thin film, and the stress relaxation interlayer comprises SiC, Y2O3, TiO2 or ZrO2.

11. The composite substrate of claim 10, wherein the interlayer comprises SiO2, SiON or SiN.

12. The composite substrate according to any one of claims 9 to 11, wherein the oxide single crystal thin film comprises lithium tantalate LT or lithium niobate LN.

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