Bonded substrate, and method for manufacturing a bonded substrate

Abstract

To provide a bonding substrate that has sufficient bonding strength even when the functional substrate has irregularities on the bonding surface, and a method for manufacturing the same. [Solution] The bonded substrate 100 according to the present invention comprises a support substrate 11, a buffer film 13 formed on the upper surface of the support substrate 11, and a functional substrate 12 bonded to the upper surface of the buffer film 13. The buffer film 13 has a Young's modulus smaller than that of the support substrate 11, and the functional substrate 12 has irregularities at the bonding surface with the buffer film 13.

Description

[Technical Field]

[0001] This invention relates to a bonded substrate and a method for manufacturing a bonded substrate. [Background technology]

[0002] In the manufacture of devices such as optical waveguides, surface acoustic wave (SAW) devices, and optical modulators, bonded substrates are sometimes used, which consist of a functional substrate and a support substrate joined together. Patent Document 1 discloses a bonded substrate suitable for the fabrication of SAW devices. In the bonded substrate disclosed in Patent Document 1, the functional substrate (piezoelectric substrate) and the support substrate (quartz substrate) are joined by covalent bonding. [Prior art documents] [Patent Documents]

[0003] [Patent Document 1] Japanese Patent Publication No. 2021-158666 [Overview of the project] [Problems that the invention aims to solve]

[0004] To assist with alignment during device manufacturing, a fine pattern of bumps and dips is sometimes pre-applied to the surface of the functional substrate that joins with the support substrate. However, this pattern of bumps and dips reduces the contact area between the functional substrate and the support substrate, leading to a problem of reduced bonding strength between the two substrates.

[0005] In view of the above issues, the object of this disclosure is to provide a bonding substrate that has sufficient bonding strength even when the functional substrate has irregularities on the bonding surface, and a method for manufacturing the same. [Means for solving the problem]

[0006] A bonded substrate according to one aspect of the present disclosure comprises a support substrate, a buffer film formed on the upper surface of the support substrate, and a functional substrate bonded to the upper surface of the buffer film, wherein the Young's modulus of the buffer film is smaller than that of the support substrate, and the functional substrate has irregularities at the bonding surface with the buffer film.

[0007] A method for manufacturing a bonded substrate according to one aspect of the present disclosure involves preparing a support substrate and a functional substrate having irregularities, forming a buffer film on the upper surface of the support substrate made of a material with a lower Young's modulus than the support substrate, and bonding the upper surface of the buffer film to the surface of the functional substrate having irregularities. [Effects of the Invention]

[0008] The present invention provides a bonded substrate that has sufficient bonding strength even when the functional substrate has irregularities on the bonding surface, and a method for manufacturing the same. [Brief explanation of the drawing]

[0009] [Figure 1] This is a cross-sectional view of the bonded substrate of this embodiment. [Figure 2] This is a flowchart illustrating the manufacturing method of the bonded substrate according to this embodiment. [Figure 3] This is a schematic diagram illustrating the manufacturing method of the bonded substrate according to this embodiment. [Figure 4] This is a schematic diagram illustrating the manufacturing method of the bonded substrate according to this embodiment. [Modes for carrying out the invention]

[0010] The following describes specific embodiments to which the present invention is applied, with reference to the drawings. However, the present invention is not limited to the following embodiments. For clarity, the following descriptions and diagrams have been simplified as appropriate. In each diagram, identical or corresponding elements are denoted by the same reference numeral, and redundant explanations are omitted where necessary for clarity. Furthermore, the right-handed xyz coordinate system shown in Figure 1 and other diagrams is for explaining the positional relationships of the components, with the positive z-axis pointing vertically upward.

[0011] (Bonded substrate) First, the bonding substrate according to this embodiment will be described using Figure 1. Figure 1 is a schematic cross-sectional view of the bonding substrate 100 according to this embodiment. As shown in Figure 1, the bonding substrate 100 comprises a support substrate 11, a functional substrate 12, and a buffer film 13.

[0012] The support substrate 11 is a substrate that supports the functional substrate 12. The material of the support substrate 11 is not particularly limited, but it is preferably made of quartz, single-crystal silicon, glass, sapphire, or lithium niobate, as these materials offer excellent frequency-temperature characteristics and optical properties. Furthermore, the statement that the support substrate 11 is made of quartz, single-crystal silicon, glass, sapphire, or lithium niobate means that the support substrate 11 contains quartz, single-crystal silicon, glass, sapphire, or lithium niobate, and may also contain other unavoidable components to the extent that they do not impair the effects of the present invention.

[0013] The functional substrate 12 is a substrate made of an electro-optic material. The material of the functional substrate 12 is not particularly limited as long as it is an electro-optic material, but it is preferably made of lithium tantalate or lithium niobate because of its excellent piezoelectric properties and electro-optic properties. The functional substrate 12 is bonded to the upper surface of the buffer film 13, which will be described later, and has irregularities at the bonding surface with the buffer film 13. In the example in Figure 1, the irregularities of the functional substrate 12 are formed by having a plurality of protrusions 121 that extend in one direction (y-axis direction). The protrusions 121 are patterns provided to assist in alignment during device manufacturing, and their maximum height h is, for example, 20 nm. In the example in Figure 1, the maximum depth of the irregularities of the functional substrate 12 coincides with the maximum height h of the protrusions 121. Note that the functional substrate 12 being made of lithium tantalate or lithium niobate means that the functional substrate 12 contains lithium tantalate or lithium niobate and may contain other inevitable components as long as the effects of the present invention are not impaired.

[0014] The buffer film 13 is formed on the upper surface of the support substrate 11 and has a Young's modulus smaller than that of the support substrate 11. Therefore, it has elasticity compared to the support substrate 11 and is likely to deform according to the unevenness of the functional substrate 12. Thus, it can be bonded with a larger bonding area than when the support substrate 11 and the functional substrate 12 are directly bonded, and high bonding strength can be achieved. The bonding strength between the functional substrate 12 and the buffer film 13 is preferably 0.8 J / m 2 or more, more preferably 1.0 J / m 2 or more, and even more preferably 1.5 J / m 2 or more.

[0015] The thickness of the buffer film 13 is preferably 10 times or more the maximum depth of the unevenness of the functional substrate 12, and even more preferably 20 times or more the maximum depth of the unevenness of the functional substrate 12. If the thickness of the buffer film 13 is less than 10 times the maximum depth of the unevenness of the functional substrate 12, it is difficult for the buffer film 13 to sufficiently deform with respect to the shape of the unevenness of the functional substrate 12, and there is a risk that sufficient bonding strength cannot be achieved.

[0016] Also, the Young's modulus of the buffer film 13 is preferably 10 GPa or more. If the Young's modulus of the buffer film 13 is less than 10 GPa, the film rigidity of the buffer film 13 becomes small, and there is a risk that the support substrate 11 and the functional substrate 12 cannot be sufficiently bonded.

[0017] Furthermore, the relationship between the maximum height h of the convex portion 121, the minimum distance R between the convex portions 121, the Young's modulus E sub of the functional substrate 12, and the Young's modulus E buf of the buffer film 13 preferably satisfies the following formula (1). For example, when the maximum height h of the convex portion 121 is 20 nm, the minimum distance R between the convex portions 121 is 5 μm, and the material of the functional substrate 12 is lithium niobate (E subWhen (≒150 GPa), the Young's modulus E of the buffer film 13 buf is preferably 20 GPa or less.

Number

[0018] Note that Equation (1) is a relational expression for satisfying the bonding strength between the functional substrate 12 and the buffer film 13 of 1.0 J / m 2 or more. In other words, the maximum height h of the convex portions 121, the minimum distance R between the convex portions 121, the Young's modulus E of the functional substrate 12 sub , and the Young's modulus E of the buffer film 13 buf If the relationship of Equation (1) is satisfied, the functional substrate 12 and the buffer film 13 can be bonded with a bonding strength of 1.0 J / m 2 or more. As the basis of Equation (1), the following literature can be cited. Q.-Y. Tong, U. Goesele, “Semiconductor wafer bonding: recent developments”, Materials Chemistry and Physics, Volume 37, Issue 2, March 1994, p.101-127.

[0019] Also, the chemical compositions of the support substrate 11 and the buffer film 13 are preferably the same. For example, when the support substrate 11 is quartz, the chemical composition of the buffer film 13 is preferably SiO2. When the chemical compositions of the support substrate 11 and the buffer film 13 are the same, since the support substrate 11 and the buffer film 13 have similar refractive indices, the design of optical waveguides, optical modulators, etc. becomes easy.

[0020] Note that in the above description, the case where the functional substrate has a plurality of convex portions extending in one direction and thus has unevenness has been taken as an example, but the shape of the unevenness of the functional substrate is not limited to the above example and may be appropriately changed. For example, the convex portions may be provided in a dot shape, or there may be one convex portion. Even in such a case, a suitable bonded substrate can be obtained by bonding the functional substrate and the support substrate through the buffer film.

[0021] (Method of manufacturing bonded substrates) Next, the method for manufacturing the bonded substrate of this embodiment will be described using Figures 2 to 4. Figure 2 is a flowchart illustrating the method for manufacturing the bonded substrate 100 of this embodiment. Figures 3 and 4 are schematic diagrams illustrating the method for manufacturing the bonded substrate 100 of this embodiment. Figure 3 is a diagram illustrating steps S1 to S9, which will be described later, and Figure 4 is a diagram illustrating steps S10 to S12, which will be described later.

[0022] When manufacturing the bonded substrate 100 of this embodiment, first in step S1, a functional substrate 12 is prepared. The functional substrate 12 is a substrate made of an electro-optic material and has irregularities. For example, the functional substrate 12 is a lithium niobate substrate, the thickness of the substrate is 10 μm or more and 1000 μm or less, and the maximum depth of the irregularities is about 20 nm. The functional substrate 12 may be provided with an orientation flat (orientation flat) or a V-shaped groove notch, which is a linear cut in a part of the functional substrate, to indicate the crystal orientation of the substrate.

[0023] Next, the functional substrate 12 is cleaned (step S2). For example, the functional substrate 12 can be cleaned using a chemical solution such as APM (Ammonia hydrogen Peroxide Mixture) or SPM (Sulfuric acid-hydrogen Peroxide Mixture). By using the above chemical solution, hydrophilic groups (OH groups) are added to the surface of the functional substrate 12, which then bond with the hydrogen on the surface of the buffer film 13, resulting in good bonding strength.

[0024] Next, the functional substrate 12 is subjected to plasma treatment (step S3). Plasma treatment of the functional substrate 12 allows for the formation of a modified layer on its surface. The modified layer formed on the surface of the functional substrate 12 is an amorphous layer mainly composed of the material of the functional substrate 12. The plasma treatment conditions are preferably as described in, for example, International Publication No. 2024 / 063072. This makes it possible to manufacture a bonded substrate with high bonding strength while suppressing the generation of voids.

[0025] Next, the support substrate 11 is prepared (step S4). For example, the support substrate 11 is a quartz substrate with a thickness of 100 μm or more and 1000 μm or less. If the support substrate 11 is a crystalline substrate, an orientation flat (orientation flat) or a V-shaped groove notch may be provided in a part of the support substrate that is cut in a straight line to indicate the crystal orientation of the substrate.

[0026] Next, a buffer film 13 made of a material with a lower Young's modulus than the support substrate 11 is formed on the upper surface of the support substrate 11 (step S5). The method for forming the buffer film 13 is not particularly limited, but it can be formed by depositing material onto the upper surface of the support substrate 11 using methods such as PVD (Physical Vapor Deposition) or plasma CVD (Chemical Vapor Deposition). The thickness of the buffer film 13 is preferably 10 times or more the maximum depth of the irregularities of the functional substrate 12, and preferably 10 μm or less. Furthermore, it is preferable that the buffer film 13 is made of a material with the same chemical composition as the support substrate 11. For example, if the support substrate 11 is a quartz substrate, it is preferable to form the buffer film 13 by depositing SiO2.

[0027] In step S5, it is preferable to deposit the buffer film 13 at a temperature of 100°C or lower. By depositing the film at a temperature of 100°C or lower, thermal stress on the buffer film 13 can be suppressed. In particular, if the buffer film 13 is an SiO2 film, depositing it at a temperature of 100°C or lower can keep the Young's modulus of the film low. One example of a method for depositing the buffer film 13 at a temperature of 100°C or lower is sputtering.

[0028] Next, the buffer film 13 is annealed (step S6). The annealing temperature is, for example, between 300°C and 500°C. By annealing the buffer film 13 at 300°C or higher, water and organic impurities mixed in the buffer film 13 can be efficiently released. Furthermore, by setting the annealing temperature to 500°C or lower, cracking and crystal defects in the support substrate 11 and buffer film 13 due to thermal stress can be suppressed. The annealing treatment is preferably carried out by raising the temperature from room temperature (30°C or lower) to a predetermined treatment temperature in the range of 0.1 to 5°C / min. By setting the heating rate to 5°C / min or lower, damage to the substrate due to pyroelectricity can be suppressed. The annealing treatment can be carried out, for example, by heating the support substrate 11 on which the buffer film 13 has been deposited in an electric furnace.

[0029] Next, the upper surface of the buffer film 13 is processed to have a shape corresponding to the irregularities of the functional substrate 12 (step S7). That is, the buffer film 13 is processed to create recesses in the areas where it will be joined to the protrusions of the functional substrate 12. At this time, it is preferable that the height of the protrusions of the functional substrate 12 and the depth of the recesses of the buffer film 13 are approximately the same. By processing the upper surface of the buffer film 13 in this way, the functional substrate 12 can be joined more closely together. The processing method is not particularly limited and can be appropriately selected from known methods such as etching, cutting, and laser processing.

[0030] Next, the support substrate 11 is cleaned (step S8). For example, it is preferable to clean the support substrate 11 using a chemical solution such as APM (Ammonia hydrogen Peroxide Mixture) or SPM (Sulfuric acid-hydrogen Peroxide Mixture). By using the above chemical solution, hydrophilic groups (OH groups) are attached to the surface of the buffer film 13, so that hydrogen on the surface of the functional substrate 12 can be adsorbed during temporary bonding, and good bonding strength can be obtained.

[0031] Next, the support substrate 11 is subjected to plasma treatment (step S9). Plasma treatment of the support substrate 11 forms a modified layer on its surface. The modified layer formed on the surface of the support substrate 11 is an amorphous layer mainly composed of the material of the support substrate 11. The plasma treatment conditions are preferably as described in, for example, International Publication No. 2024 / 063072. This makes it possible to manufacture a bonded substrate with high bonding strength while suppressing the generation of voids.

[0032] Note that the order of processing in steps S1-S3 and steps S4-S9 may be reversed. In other words, processing in steps S4-S9 may be performed first, followed by processing in steps S1-S3. Also, processing in steps S1-S3 and steps S4-S9 may be performed in parallel (simultaneously).

[0033] Next, the upper surface of the buffer film 13 and the surface of the functional substrate 12 that has irregularities are temporarily joined (step S10). For example, after adjusting the in-plane position (horizontal position) of the support substrate 11 equipped with the buffer film 13 and the functional substrate 12, the support substrate 11 and the functional substrate 12 are moved vertically and temporarily joined in a vacuum atmosphere. By temporarily joining in a vacuum atmosphere, it is possible to suppress the incorporation of gas molecules into the joining interface during temporary joining, thereby suppressing the generation of voids. In addition, if the support substrate 11 and the functional substrate 12 have orientation flats or notches, the in-plane positions of the support substrate 11 and the functional substrate 12 can be aligned by aligning the direction of their orientation flats or notches.

[0034] Subsequently, the substrate after temporary bonding is annealed to bond the functional substrate 12 and the buffer film 13 (step S11). Annealing strengthens the bond between the modified layer of the functional substrate 12 and the modified layer of the buffer film 13, thereby creating a strong bond between the functional substrate 12 and the buffer film 13. The annealing temperature is preferably between 50°C and 300°C. By annealing at 50°C or higher, the modified layers of the functional substrate 12 and the buffer film 13 react with each other, resulting in high bonding strength. Furthermore, by keeping the annealing temperature below 300°C, cracks and crystal defects due to thermal stress can be suppressed. In addition, it is preferable to perform the annealing by raising the temperature from room temperature (below 30°C) to a predetermined processing temperature in the range of 0.1 to 5°C / min. By keeping the heating rate below 5°C / min, damage to the substrate due to pyroelectricity can be suppressed. The annealing can be performed, for example, by heating the substrate after temporary bonding in an electric furnace.

[0035] Subsequently, the surface of the functional substrate 12 is polished (step S12). The polishing process can be carried out, for example, using chemical mechanical polishing (CMP). In the polishing process, the functional substrate 12 is polished to a thickness of, for example, 0.1 to 10 μm.

[0036] By using the manufacturing method described above, the bonded substrate of this embodiment can be manufactured. This bonded substrate has sufficient bonding strength despite the functional substrate having irregularities on the bonding surface.

[0037] In the above example, an example of a method for manufacturing a bonded substrate comprising all of steps S1 to S12 has been described, but these steps may be omitted as appropriate, as long as they do not impair the effects of the present invention. Specifically, the method for manufacturing a bonded substrate according to the present invention comprises the steps of preparing a functional substrate 12 (step S1), preparing a support substrate 11 (step S4), forming a buffer film 13 (step S5), and joining the buffer film 13 and the functional substrate 12 (steps S10, S11), and other steps may be omitted as appropriate. A bonded substrate according to this embodiment can be manufactured by comprising the above steps.

[0038] Although the present invention has been specifically described above based on embodiments, it goes without saying that the present invention is not limited to the above embodiments and can be modified in various ways without departing from its essence. [Explanation of Symbols]

[0039] 100 bonded substrates 11 Support substrate 12 Functional boards 121 Convex part 13 Buffer membrane

Claims

1. Support substrate and A buffer film formed on the upper surface of the support substrate, The system comprises a functional substrate bonded to the upper surface of the buffer film, The buffer film has a Young's modulus smaller than that of the support substrate. The functional substrate has irregularities at the bonding surface with the buffer film. Bonded substrate.

2. The bonding strength between the functional substrate and the buffer film is 0.8 J / m ２ That's all. The bonded substrate according to claim 1.

3. The thickness of the buffer film is 10 times or more the maximum depth of the irregularities of the functional substrate. The bonded substrate according to claim 1.

4. The Young's modulus of the buffer film is 10 GPa or more. The bonded substrate according to claim 1.

5. The irregularities of the functional substrate are formed by having multiple protrusions extending in one direction. The maximum height h of the protrusions, the minimum distance R between the protrusions, and the Young's modulus E of the functional substrate. ｓｕｂ , and the Young's modulus E of the buffer film ｂｕｆ The relationship satisfies the following equation (1): The bonded substrate according to claim 1. [Math 1]

6. The chemical composition of the support substrate and the buffer film are the same. The bonded substrate according to claim 1.

7. The support substrate is made of quartz, silicon, glass, sapphire, or lithium niobate. The bonded substrate according to claim 1.

8. The functional substrate is made of lithium tantalate or lithium niobate. The buffer film is SiO ２ It consists of, The aforementioned support substrate is made of quartz. The bonded substrate according to claim 1.

9. Prepare a support substrate and a functional substrate having irregularities. A buffer film made of a material with a lower Young's modulus than the support substrate is formed on the upper surface of the support substrate. The upper surface of the buffer film and the surface of the functional substrate having the irregularities are joined together. A method for manufacturing bonded substrates.

10. The thickness of the buffer film is 10 times or more the maximum depth of the irregularities of the functional substrate. A method for manufacturing a bonded substrate according to claim 9.

11. When forming the buffer film, the film is formed at a temperature of 100°C or lower. A method for manufacturing a bonded substrate according to claim 9.

12. After forming the buffer film, the upper surface of the buffer film is processed to have a shape corresponding to the irregularities of the functional substrate. A method for manufacturing a bonded substrate according to claim 9.

13. After forming the buffer film, the buffer film is subjected to an annealing treatment. A method for manufacturing a bonded substrate according to claim 9.

14. When annealing the buffer film, the annealing is performed at a temperature of 300°C to 500°C. A method for manufacturing a bonded substrate according to claim 13.

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