Bonded substrate, bonded substrate with device, and method for manufacturing bonded substrate with device

Abstract

Provided is a bonded substrate having a wide region that is suitable for device processing. A bonded substrate (10) according to the present invention comprises a quartz substrate (11) and a functional substrate (12) bonded to the quartz substrate (11) via a bonding surface, wherein the quartz substrate (11) does not include a seed portion.

Description

Bonded substrate, bonded substrate with device, and method for manufacturing bonded substrate with device

[0001] The present invention relates to a bonded substrate, a bonded substrate with a device, and a method for manufacturing a bonded substrate with a device.

[0002] In the manufacture of optical waveguides, surface acoustic wave (SAW) devices, optical modulators, etc., a bonded substrate in which a functional substrate such as lithium tantalate and a quartz substrate are bonded may be used. For example, when manufacturing an optical waveguide, a plurality of optical waveguides can be manufactured simultaneously by forming a pattern on a wafer-type bonded substrate and cutting it out. Patent Document 1 discloses an example of a bonded substrate in which a functional substrate and a quartz substrate are bonded.

[0003] Japanese Patent Application Laid-Open No. 2021-158666

[0004] For the above-mentioned quartz substrate, synthetic quartz produced by growing a seed crystal is generally used. Since synthetic quartz grows around the seed crystal, the vicinity of the center of the synthetic quartz cut into a wafer type usually corresponds to the seed part. For example, when the wafer of synthetic quartz has an orifla (orientation flat), the straight line connecting the midpoint of the orifla and the center of the wafer (the perpendicular bisector of the orifla) is included in the region of the seed part. Also, when the wafer of synthetic quartz has a notch, the straight line connecting the center of the notch and the center of the quartz wafer is included in the region of the seed part. FIG. 1 is a plan view of a bonded substrate 90 in which a quartz substrate 91 including such a seed part S and a functional substrate 92 are bonded. FIG. 2 is a cross-sectional view of the bonded substrate 90 taken along the cutting line II-II in FIG. 1.

[0005] When manufacturing a plurality of optical waveguides from the bonded substrate 90, it is preferable to use a region that does not include the seed part S (for example, the region A' shown in FIGS. 1 and 2) for processing. This is because, during the growth process of synthetic quartz, a thin film (seed veil) derived from impurities is likely to be formed at the boundary between the seed part S and the surrounding growth region, and the seed veil deteriorates the quality of the optical waveguide.

[0006] The above example described the manufacturing of optical waveguides, but it is known that the area near the seed portion is unsuitable for processing in the manufacturing of devices such as SAW devices and optical modulators for similar reasons. In other words, bonded substrates containing artificial quartz have the problem that the area suitable for device manufacturing is limited.

[0007] In view of the above issues, the object of this disclosure is to provide a bonded substrate having a wide area suitable for device processing, a bonded substrate with a device attached, and a method for manufacturing a bonded substrate with a device attached.

[0008] A bonded substrate according to one aspect of the present disclosure comprises a quartz substrate and a functional substrate bonded to the quartz substrate via a bonding surface, wherein the quartz substrate does not include a seed portion.

[0009] The present invention provides a bonded substrate having a wide area suitable for device processing, a bonded substrate with a device attached, and a method for manufacturing a bonded substrate with a device attached.

[0010] This is a plan view showing a conventional bonded substrate. This is a cross-sectional view of the bonded substrate in Figure 1 along the cutting line II-II. This is a plan view showing the bonded substrate according to this embodiment. This is a cross-sectional view of the bonded substrate in Figure 3 along the cutting line IV-IV. This is a flowchart for explaining the manufacturing method of the bonded substrate according to this embodiment. This is a schematic diagram of the artificial quartz from which the quartz substrate according to this embodiment is cut.

[0011] (Bonding Substrate) Hereinafter, specific embodiments to which the present invention is applied will be described in detail with reference to the drawings. However, the present invention is not limited to the following embodiments. Also, in order to clarify the explanation, the following description and drawings have been simplified as appropriate. Note that the right-handed xyz coordinates shown in Figures 1 to 4 are for explaining the positional relationship of the components, and the positive z-axis direction indicates vertically upward. The right-handed XYZ coordinates shown in Figure 6 represent the crystal axis of the quartz.

[0012] Figure 3 is a plan view of the bonded substrate 10 according to this embodiment. Figure 4 is a cross-sectional view of the bonded substrate 90 along the cutting line IV-IV in Figure 3. As shown in Figures 3 and 4, the bonded substrate 10 comprises a quartz substrate 11 and a functional substrate 12 bonded to the quartz substrate 11 via a bonding surface.

[0013] The quartz substrate 11 functions as a support substrate for the functional substrate 12. The quartz substrate 11 is not particularly limited as long as it does not contain seed portions; for example, artificial quartz without seed portions can be used.

[0014] The functional substrate 12 can be appropriately selected depending on the device to be manufactured. For example, when manufacturing optical waveguides or SAW devices, a ferroelectric substrate can be selected for the functional substrate 12, and among these, lithium tantalate substrates or lithium niobate substrates can be preferably selected because they have excellent piezoelectric properties.

[0015] In this embodiment, since the quartz substrate 11 does not contain seed portions, there is no seed veil that affects the performance of the device. Therefore, the entire surface of the bonded substrate 10 can be used for device processing. For example, when forming an optical waveguide, the portion of region A shown in the examples of Figures 3 and 4 can be used. Therefore, many more optical waveguides can be formed compared to a conventional bonded substrate 90 (see Figure 1).

[0016] In this embodiment, the Q value (material Q value) of the quartz substrate 11 is preferably 1.8 M or higher, and more preferably 2.4 M or higher. When the Q value of the quartz substrate 11 is 1.8 M or higher, a SAW device with better frequency-temperature characteristics can be manufactured. Furthermore, when the Q value of the quartz substrate 11 is 2.4 M or higher, the Q value (device Q value) and coupling coefficient of the SAW device fabricated from the bonded substrate will be of better value.

[0017] In this embodiment, it is preferable that the grade of the quartz substrate 11 according to JIS C6704:2017 by the Schlieren method is OPT C or higher. When the above grade of the quartz substrate 11 is OPT C or higher, the distortion of the refractive index within the quartz substrate 11 is small, so an optical waveguide with higher light transmittance can be manufactured.

[0018] In this embodiment, the diameter of the quartz substrate 11 is preferably 100 mm or more, and more preferably 150 mm or more. By making the diameter of the quartz substrate 11 100 mm or more, the area suitable for device processing is widened, which enables the manufacture of larger devices and allows for more flexible device design.

[0019] In this embodiment, the thickness of the functional substrate 12 is preferably 0.1 to 10 μm. By setting the thickness of the functional substrate 12 to 0.1 to 10 μm, surface acoustic waves and electromagnetic waves are efficiently guided within the functional substrate 12, resulting in a good SAW device or optical waveguide.

[0020] In this embodiment, it is preferable that the crystal axes of the quartz substrate 11 and the functional substrate 12 are substantially parallel. Specifically, it is preferable that the crystal axes of the quartz substrate 11 and the functional substrate 12 are within ±5°. By making the crystal axes of the quartz substrate 11 and the functional substrate 12 substantially parallel, the bonding strength is increased and crack formation during heating such as annealing can be suppressed.

[0021] (Bonded Substrate with Devices) The bonded substrate with devices according to this embodiment is a substrate on which devices such as SAW devices, optical waveguides, and optical modulators are provided on the bonded substrate according to this disclosure. In the bonded substrate with devices according to this embodiment, devices are provided in the region corresponding to the seed portion in a normal quartz substrate. In other words, if the quartz substrate has an orientation flat, at least one device is provided on the perpendicular bisector of the orientation flat of the quartz substrate, and if the quartz substrate has a notch, at least one device is provided on the straight line connecting the center of the notch of the quartz substrate and the center of the quartz substrate. Because the bonded substrate with devices having such a configuration has device processing performed over a wide area, more devices can be extracted from a single bonded substrate.

[0022] (Method for Manufacturing a Bonded Substrate) Next, the method for manufacturing a bonded substrate according to this embodiment will be explained with reference to Figures 5 and 6. Figure 5 is a flowchart for explaining the method for manufacturing a bonded substrate according to this embodiment.

[0023] When manufacturing the bonded substrate according to this embodiment, as shown in Figure 5, first, a quartz substrate 11 that does not include the seed portion is prepared (step S1). Specifically, for example, the quartz substrate 11 can be prepared by cutting out a sufficiently grown artificial quartz crystal without including the seed portion.

[0024] Figure 6 shows a schematic diagram of the artificial quartz 110 from which the quartz substrate 11 is cut. The artificial quartz 110 shown in the example in Figure 6 is a right-handed quartz crystal with a thickness T, grown around a seed portion that extends in the XY plane. In the figure, m, r, and R represent the types of crystal planes, respectively.

[0025] The cutting direction of the quartz substrate 11 from the artificial quartz 110 is not particularly limited. The cutting direction of the quartz substrate 11 can be appropriately selected depending on the application from, for example, a z-cut, which is cut perpendicular to the Z-axis; an x-cut, which is cut perpendicular to the X-axis; or an AT-cut, which is cut parallel to the X-axis and at an angle of 35°15' to the Z-axis. For example, when the purpose is to manufacture SAW devices, an AT-cut is preferred in terms of excellent temperature characteristics, and when the purpose is to manufacture optical waveguides, an x-cut is preferred in terms of excellent light wave propagation characteristics. Furthermore, when cutting the quartz substrate 11 with an AT-cut or x-cut, it is preferable to use artificial quartz 110 with a thickness T of 200 mm or more. By using artificial quartz 110 with a thickness T of 200 mm or more, a quartz substrate 11 with a diameter of 100 mm or more can be cut. The quartz substrate 11 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 substrate, to indicate the crystal orientation of the substrate.

[0026] Next, the quartz substrate 11 is cleaned (step S2). For example, it is preferable to clean the quartz 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 added to the surface of the quartz substrate 11, so that hydrogen on the surface of the functional substrate 12 can be adsorbed during temporary bonding, and good bonding strength can be obtained.

[0027] Next, the quartz substrate 11 is subjected to plasma treatment (step S3). Plasma treatment of the quartz substrate 11 forms a modified layer on the surface of the quartz substrate 11. The modified layer formed on the surface of the quartz substrate 11 is an amorphous layer mainly composed of the material of the quartz substrate 11, and the thickness of the modified layer is greater than 2.7 nm and less than or equal to 3.2 nm, preferably between 2.9 nm and 3.1 nm. The plasma treatment conditions are preferably as described in, for example, International Publication No. 2024 / 063072. By performing the above plasma treatment, a bonded substrate with high bonding strength can be manufactured while suppressing the generation of voids.

[0028] Next, the functional substrate 12 is prepared (step S4). The cutting direction of the functional substrate 12 is not particularly limited, but it is preferable that it be in the same direction as the quartz substrate 11. That is, it is preferable that the cutting direction of both the quartz substrate 11 and the functional substrate 12 be, for example, x-cut or z-cut. By joining the quartz substrate 11 and the functional substrate 12 having the same cutting direction so as to align the orientation of their respective crystal axes, a joined substrate 10 can be manufactured in which the crystal axes of the quartz substrate 11 and the functional substrate 12 are substantially parallel. 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 substrate, to indicate the crystal orientation of the substrate.

[0029] Next, the functional substrate 12 is cleaned (step S5). 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, so that hydrogen from the surface of the quartz substrate 11 can be adsorbed during the temporary bonding, and good bonding strength can be obtained.

[0030] Next, the functional substrate 12 is subjected to plasma treatment (step S6). By plasma treatment of the functional substrate 12, a modified layer can be formed on the surface of the functional substrate 12. 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, and the thickness of the modified layer is 2.2 nm or more and 2.7 nm or less, preferably 2.4 nm or more and 2.6 nm or less. The plasma treatment conditions are preferably as described in, for example, International Publication No. 2024 / 063072. By performing the above plasma treatment, a bonded substrate with high bonding strength can be manufactured while suppressing the generation of voids.

[0031] Note that the order of the processes in steps S1 to S3 and steps S4 to S6 may be reversed. In other words, steps S4 to S6 may be performed first, followed by steps S1 to S3. Also, steps S1 to S3 and steps S4 to S6 may be performed in parallel (simultaneously).

[0032] Next, with the modified layer of the quartz substrate 11 and the modified layer of the functional substrate 12 facing each other, the quartz substrate 11 and the functional substrate 12 are temporarily joined (step S7). For example, after adjusting the in-plane position (horizontal position) of the quartz substrate 11 and the functional substrate 12, the quartz substrate 11 and the functional substrate 12 are moved vertically and temporarily joined in a vacuum atmosphere. By using 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. Also, if the quartz substrate 11 and the functional substrate 12 have orientation flats or notches, the in-plane position of the quartz substrate 11 and the functional substrate 12 can be aligned by aligning the direction of their respective orientation flats or notches.

[0033] Subsequently, the substrate after temporary bonding is annealed to bond the quartz substrate 11 and the functional substrate 12 (step S8). Annealing strengthens the bond between the modified layer of the quartz substrate 11 and the modified layer of the functional substrate 12, thereby creating a strong bond between the quartz substrate 11 and the functional substrate 12. For example, the annealing temperature is between 50°C and 300°C. By annealing at 50°C or higher, the modified layers of the quartz substrate 11 and the functional substrate 12 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.

[0034] In this embodiment, after joining the quartz substrate 11 and the functional substrate 12, the embodiment may further include a step (step S9) of polishing the surface of the functional substrate 12. The polishing step can be carried out, for example, using chemical mechanical polishing (CMP). For example, the functional substrate 12 may be polished to a thickness of 0.1 to 10 μm.

[0035] By using the manufacturing method (substrate bonding method) described above, the bonded substrate according to this embodiment can be manufactured. By forming patterns such as optical waveguides and electrodes on this bonded substrate, optical waveguides or SAW devices with high characteristics can be efficiently manufactured.

[0036] Furthermore, if hydrophilic groups are applied to the surface of the quartz substrate 11 or functional substrate 12 during the cleaning process (steps S2 and S5), it is preferable to perform the process from the cleaning process to the temporary bonding process (step S7) within 5 hours. By performing the process from the cleaning process to the temporary bonding process within 5 hours, bonding can be achieved before the hydrophilicity applied during the cleaning process returns to its original state, thereby achieving high bonding strength.

[0037] Furthermore, when manufacturing a bonded substrate with a device according to this embodiment, after step S9, a step (step S10) is provided in which a device is manufactured on the bonded substrate. Specifically, optical waveguides, SAW (surface acoustic wave) devices, optical modulators, etc., can be formed. For example, optical waveguide patterns can be formed by RIE, wet etching, grinding, etc. If the quartz substrate 11 has an orientation flat or a notch, at least one of the devices is formed on the perpendicular bisector of the orientation flat of the quartz substrate 11, or on a straight line connecting the center of the notch of the quartz substrate 11 and the center of the quartz substrate 11.

[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.

[0039] This application claims priority based on Japanese Patent Application No. 2025-026689, filed on 21 February 2025, and incorporates all of its disclosures herein.

[0040] 10, 90 Bonding substrate 11, 91 Crystal substrate 12, 92 Functional substrate 110 Artificial crystal A, A' region S Seed part

Claims

1. A bonded substrate comprising a quartz substrate and a functional substrate bonded to the quartz substrate via a bonding surface, wherein the quartz substrate does not contain a seed portion.

2. The bonding substrate according to claim 1, wherein the thickness of the functional substrate is 0.1 to 10 μm.

3. The bonded substrate according to claim 1, wherein the Q value of the quartz substrate is 1.8 M or higher.

4. The bonded substrate according to claim 1, wherein the grade of the quartz substrate by the Schlieren method in accordance with JIS C6704:2017 is OPTC C or higher.

5. The bonded substrate according to claim 1, wherein the crystal axis of the quartz substrate and the crystal axis of the functional substrate are substantially parallel.

6. The bonded substrate according to claim 1, wherein the diameter of the quartz substrate is 100 mm or more.

7. The bonding substrate according to claim 1, wherein the functional substrate is a lithium tantalate substrate or a lithium niobate substrate.

8. A bonded substrate with a device, comprising a quartz substrate, a functional substrate bonded to the quartz substrate via a bonding surface, and a device provided on the functional substrate, wherein the quartz substrate has an orientation flat or a notch, and at least one of the devices is provided on the perpendicular bisector of the orientation flat of the quartz substrate, or on a straight line connecting the center of the notch of the quartz substrate and the center of the quartz substrate.

9. The device-equipped bonded substrate according to claim 8, wherein the device is a surface acoustic wave device, an optical waveguide, or an optical modulator.

10. The bonded substrate with a device according to claim 8, wherein the crystal substrate is a bonded substrate according to any one of claims 1 to 7.

11. A method for manufacturing a bonded substrate with a device, comprising the steps of: preparing a quartz substrate having an orientation flat or notch and a functional substrate; cleaning the quartz substrate and the functional substrate by chemical treatment; plasma activating the quartz substrate and the functional substrate; temporarily bonding the quartz substrate and the functional substrate in a vacuum atmosphere; heat treating the temporarily bonded substrate at 50 to 300°C; processing the thickness of the functional substrate to 0.1 to 10 μm; and forming a device on the perpendicular bisector of the orientation flat of the quartz substrate, or on a straight line connecting the center of the notch of the quartz substrate and the center of the quartz substrate.

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