Composite substrate, device, and method for manufacturing composite substrate

Abstract

A composite substrate 1 includes a functional layer 21a and a support substrate 23 supporting the functional layer 21a. The composite substrate 1 has a beveling region 12 in an outer peripheral portion. The beveling region 12 causes the outer periphery of an effective region 13 other than the beveling region 12 to have a shape that includes an arcuate part 131 having an arc shape, a linear part 132 having a straight line shape, and an intermediate part 133 connecting the arcuate part 131 and the linear part 132. The intermediate part 133 passes inside a curve obtained by extending the arcuate part 131 and a straight line obtained by extending the linear part 132. The present invention thus provides a composite substrate and the like that, even when beveling is performed, are less likely to surfer chipping during polishing of a functional layer and are less likely to suffer scratches or peeling.

Description

Composite substrate, device, and method for manufacturing a composite substrate

[0001] The present invention relates to composite substrates, devices, and methods for manufacturing composite substrates. In particular, the present invention relates to composite substrates having a beveled region on the outer periphery.

[0002] It is known that when fabricating composite substrates, beveling the outer edge of the composite substrate in a circular shape during the fabrication process can suppress sagging at the outer edge (where the film thickness decreases as you approach the outer edge) when thinning the functional layer of the composite substrate.

[0003] Patent Document 1 describes a method of bonding a piezoelectric substrate wafer and a non-piezoelectric substrate wafer to form a bonded wafer. The non-piezoelectric substrate wafer is thicker than the piezoelectric substrate wafer and has an orientation flat. The piezoelectric substrate wafer does not have an orientation flat on its outer periphery.

[0004] Japanese Patent Publication No. 2021-158455

[0005] However, with conventional beveling shapes, when the functional layer is thinned by polishing, the ends of the orientation flat portion chip, and the chipped portions get trapped between the polishing pad and the composite substrate, causing scratches and peeling on the composite substrate. The present invention aims to provide a composite substrate that is less prone to chipping and scratches or peeling when polishing the functional layer even when beveling is performed.

[0006] To solve the above problems, the present invention provides a composite substrate comprising a functional layer and a support substrate that supports the functional layer, wherein the composite substrate has a beveled region on its outer periphery, and the outer periphery of the effective region other than the beveled region has a shape that includes an arc-shaped arc portion, a straight portion, and a relay portion connecting the arc portion and the straight portion, and the relay portion passes inside the curve extended from the arc portion and the straight portion extended from the straight portion. The present invention also provides a device comprising the above composite substrate. Furthermore, the present invention provides a method for manufacturing a composite substrate having a beveled region, comprising: a bonding step of bonding a functional layer wafer which will be the basis of a functional layer and a support substrate which will support the functional layer; a beveling step of beveling the outer periphery of the bonded functional layer wafer and support substrate to form a beveled region; and a polishing step of polishing the functional layer wafer to form a functional layer, wherein the beveling step gives the outer periphery of the effective region other than the beveled region a shape that includes an arc-shaped arc portion, a straight-line portion, and a relay portion connecting the arc portion and the straight-line portion, and the relay portion passes inside the curve that is an extension of the arc portion and the straight-line portion that is an extension of the straight-line portion.

[0007] The objective is to provide composite substrates and the like that are less prone to chipping, scratches, and peeling when polishing the functional layer even after beveling.

[0008] (a) to (b) are diagrams showing the composite substrate of this embodiment. (a) is an enlarged view of Figure 1(a) and illustrates the beveling region of this embodiment. (b) is a diagram illustrating a conventional beveling region. This diagram shows another example of the relay section. (a) to (b) are diagrams showing other examples of the laminated structure of the composite substrate. This is a flowchart illustrating the manufacturing method of the composite substrate. (a) to (f) are diagrams showing the state of each step in Figure 5.

[0009] The embodiments of the present invention will be described in detail below with reference to the attached drawings.

[0010] <Description of the Composite Substrate Configuration> Figures 1(a) and 1(b) show the composite substrate 1 of this embodiment. Of these, Figure 1(a) is a top view of the composite substrate 1, and Figure 1(b) is a cross-sectional view taken along line Ib-Ib in Figure 1(a). As shown in Figure 1(a), the composite substrate 1 has a substantially circular shape with an orientation flat (orifura) portion 11. The orientation flat portion 11 is a planar portion formed on the side surface of the composite substrate 1 to indicate the crystal orientation of the composite substrate 1. The composite substrate 1 has an outer diameter of, for example, φ100 mm or more and φ200 mm or less, and a thickness of, for example, 200 μm or more and 1000 μm or less. The composite substrate 1 also has a beveling region 12 on its outer periphery. The beveling region 12 is formed by chamfering the outer periphery of the composite substrate 1. Here, chamfering refers to the process of cutting the corners of the outer periphery of the functional layer 21a and a part of the support substrate 23. In this embodiment, as shown in Figure 1(b), the corners are chamfered by cutting them into a rectangular shape. However, this is not the only method; R-chamfering and C-chamfering can also be used. This suppresses sagging of the outer edge when forming the functional layer 21a of the composite substrate 1. Furthermore, the area other than the beveling region 12, which is inside the beveling region 12, is the effective region 13 used when actually creating the device. In this embodiment, "inside" refers to the central side of the composite substrate 1.

[0011] Furthermore, as shown in Figure 1(b), the composite substrate 1 has a structure in which a functional layer 21a, an intermediate layer 22, and a support substrate 23 are stacked from top to bottom in the figure.

[0012] The functional layer 21a is selected for the application in which the composite substrate 1 is used. The functional layer 21a is made of, for example, a piezoelectric material. The piezoelectric material is, for example, LiNbO ３ (LN), LiTaO ３ (LT) is a solid solution of lithium niobate and lithium tantalate. In this case, the direction normal to the main surface of the functional layer 21a is such that the functional layer 21a is LiNbO ３When the functional layer 21a is made of LN, it is preferable to use one having a direction rotated 37.8° from the Z axis to the -Y axis about the X axis, which is the propagation direction of the surface acoustic wave, that is, one having Euler angles (0°, 37.8°, 0°), because the electromechanical coupling coefficient is large. Further, when the functional layer 21a is made of LiTaO ３ (LT), it is preferable to use one having a direction rotated 32° to 50° from the Y axis to the Z axis about the X axis, which is the propagation direction of the surface acoustic wave, that is, one having Euler angles (180°, 58° to 40°, 180°), because the propagation loss is small. Note that the materials used for the functional layer 21a are not limited to these, and silicon (Si), gallium arsenide (GaAs), silicon carbide (SiC), gallium nitride (GaN), zinc oxide (ZnO), solid solution ceramics (PZT) and the like are appropriately selected.

[0013] The thickness of the functional layer 21a can be, for example, 100 nm or more and 10 μm or less. The thickness of the functional layer 21a is appropriately set according to the function exhibited by the functional layer 21a.

[0014] The intermediate layer 22 functions as a bonding layer that bonds the functional layer 21a and the support substrate 23. By providing the intermediate layer 22, the bonding strength between the functional layer 21a and the support substrate 23 is improved, and peeling between the functional layer 21a and the support substrate 23 can be suppressed when beveling is performed. The intermediate layer 22 is determined by the combination of the functional layer 21a and the support substrate 23. According to the combination of the functional layer 21a and the support substrate 23, silicon oxide (SiO ２ ), tantalum pentoxide (Ta ２ O ５ ), amorphous silicon, or SiCN can be used. Further, depending on the combination of the functional layer 21a and the support substrate 23, niobium oxide (Nb ２ O ５ ), aluminum oxide (Al ２ O ３ ), aluminum nitride (AlN), silicon nitride (Si ３ N ４ ), hafnium oxide (HfO ２) and the like can also be used. The thickness of the intermediate layer 22 can be, for example, 0.01 μm or more and 10 μm or less. If the thickness of the intermediate layer 22 is less than 0.01 μm, it is difficult to improve the bonding strength. Also, if the thickness of the functional layer 21a exceeds 10 μm, the degree of adhesion at the film formation interface of the intermediate layer 22 decreases, and peeling or chipping between the functional layer 21a and the support substrate 23 is more likely to occur when beveling is performed.

[0015] The support substrate 23 serves as the support for the entire composite substrate 1. The support substrate 23 is bonded to the intermediate layer 22 and supports the functional layer 21a and the intermediate layer 22. Any suitable substrate can be used as the support substrate 23. The support substrate 23 may be made of a single crystal, a polycrystalline material, or a composite in which a polycrystalline layer is provided on a single crystal. It may also be made of metal.

[0016] The materials constituting the support substrate 23 are preferably silicon (Si), glass, sapphire, quartz, crystal, or silicon carbide (SiC). However, it is not limited to these, and other materials such as sialon, cordierite, mullite, alumina, SUS, iron-nickel alloy (42 alloy), or brass may also be used. The outer diameter of the support substrate 23 is φ100 mm or more and φ200 mm or less, and the thickness is, for example, 200 μm or more and 1000 μm or less, but any other appropriate thickness can be adopted.

[0017] As shown in Figure 1(b), the beveling region 12 removes a portion of the functional layer 21a, the intermediate layer 22, and the support substrate 23. The beveling width, which is the width of the beveling region 12, is the width from the edge of the support substrate 23 to the outer surface of the functional layer 21a, as shown in the figure. The beveling width can be between 0.5 mm and 4 mm. Setting the beveling width to 0.5 mm or more makes chipping less likely to occur when beveling. On the other hand, if the beveling width exceeds 4 mm, the area of ​​the effective region 13 that can be used when creating the device becomes too small. Also, when the amount removed in the thickness direction of the support substrate 23 is defined as the beveling depth, the beveling depth is between 5 μm and 60 μm. If the beveling depth is less than 5 μm, the pad will come into contact with the support substrate 23 when polishing the functional layer 21a, causing the pad to dress and the polishing rate to become unstable. On the other hand, if the beveling width exceeds 60 μm, the amount of material to bevel becomes too large, and production efficiency decreases.

[0018] <Detailed Description of Beveling Region 12> Figure 2(a) is an enlarged view of Figure 1(a) and illustrates the beveling region 12 of this embodiment. Figure 2(b) illustrates a conventional beveling region 12. In Figure 2(a), the shape of the conventional beveling region 12 is shown with a dotted line. The beveling region 12 will be described in detail below using Figures 1(a) and 2(a) to (b).

[0019] As shown in Figure 2(a), the beveling region 12 of this embodiment gives the outer periphery of the effective region 13 a shape consisting of an arc-shaped arc portion 131, a straight portion 132, and a connecting portion 133 that connects the arc portion 131 and the straight portion. In this case, it can also be said that the arc portion 131 and the straight portion 132 are connected via the curved connecting portion 133.

[0020] On the other hand, as shown in Figure 2(b), in the conventional beveling region 12, the outer circumference of the effective region 13 has a shape consisting of an arc-shaped arc portion 131 and a straight portion 132. That is, there is no intermediate portion 133, and the arc portion 131 and the straight portion 132 are directly connected. As a result, protrusions 134 are created at both ends of the straight portion 132 where they connect to the arc portion 131. Therefore, when the functional layer 21a is formed by polishing, chipping is likely to occur at these protrusions 134. In contrast, in the case of the beveling region 12 in Figure 2(a), since no protrusions 134 are created by the intermediate portion 133, chipping is less likely to occur. Furthermore, compared to the conventional technology in which the support substrate 23 has an orientation flat portion 11 and the functional layer 21a does not have an orientation flat portion 11 on its outer circumference, the usable area of ​​the composite substrate 1 can be increased.

[0021] Furthermore, in order for the protrusion 134 to not occur, the intermediate section 133 must pass inside the curve extended from the arc section 131 and the straight line extended from the straight section 132. In other words, the intermediate section 133 passes inside the arc section 131 and the straight section 132, respectively, in Figure 2(b). To illustrate this with Figure 2(a), the curve extended from the arc section 131 is the dotted curve 131a, and the straight line extended from the straight section 132 is the dotted straight line 132a, and the intermediate section 133 passes inside the curve 131a and the straight line 132a.

[0022] Furthermore, the relay portion 133 in Figure 2(a) can also be described as having an R shape. When the relay portion 133 has an R shape, it is preferable that the radius of curvature when viewed from above is 0.1 mm or more and 5 mm or less. If the radius of curvature is less than 0.1 mm, the shape of the beveling region 12 will become close to the shape in Figure 2(b), making chipping more likely. On the other hand, if the radius of curvature exceeds 5 mm, the area of ​​the effective region 13 that can be used when creating the device becomes too small.

[0023] Note that the shape of the relay section 133 is not limited to the shape shown in Figure 2(a). Figure 3 shows another example of the relay section 133. The relay section 133 in Figure 3 has a straight shape. In this case, it can also be said that the arc section 131 and the straight section 132 are connected via the straight relay section 133. Note that, as in the case of Figure 2(a), the relay section 133 passes inside the curve 131a, which is an extension of the arc section 131, and the straight line 132a, which is an extension of the straight section 132.

[0024] When the relay portion 133 is linear in shape, it is preferable that its length when viewed from above be between 0.05 mm and 1 mm. If the length of the relay portion 133 is less than 0.05 mm, the shape of the beveling region 12 will become similar to the shape in Figure 2(b), making chipping more likely. On the other hand, if the length of the relay portion 133 exceeds 1 mm, the area of ​​the effective region 13 that can be used when creating the device becomes too small.

[0025] In the case of the shape of the intermediate section 133 in Figure 3, compared to the case in Figure 2(a), the protrusion 134 in Figure 2(b) does not completely disappear, and small protrusions remain at both ends of the intermediate section 133, that is, at the connection points between the intermediate section 133 and the arc section 131 and the straight section 132. However, because the size of these protrusions is reduced, chipping is less likely to occur.

[0026] Furthermore, the laminated structure of the composite substrate 1 is not limited to the form shown in Figure 1(b). Figures 4(a) and 4(b) show other examples of the laminated structure of the composite substrate 1. Of these, Figure 4(a) has a structure in which the functional layer 21a and the support substrate 23 are laminated. That is, compared to the composite substrate 1 in Figure 1(b), the composite substrate 1 in Figure 4(a) has a laminated structure without the intermediate layer 22. If the functional layer 21a and the support substrate 23 can be bonded with sufficient strength even without the intermediate layer 22, then it is not necessary to provide the intermediate layer 22.

[0027] Figure 4(b) shows a structure in which a functional layer 21a and a support substrate 23 are laminated, similar to the composite substrate 1 in Figure 4(a), but with a modified beveling shape. In this case, the cutting angle is changed. As shown in the figure, the cutting angle is the angle formed by the portion remaining after beveling with respect to the main surface of the support substrate 23 in the cross-section of the composite substrate 1. The cutting angle is preferably 30° or more and 90° or less. If the cutting angle is less than 30°, the rotation axis of the grinding wheel used for beveling may tilt inward, which can cause peeling or scratching of the functional layer 21a. On the other hand, if the cutting angle exceeds 90°, this does not occur during the process. In the cases of Figure 1(b) and Figure 4(a), the cutting angle is 90°. The beveling width is the same as described above, and is the width between the edge of the support substrate 23 and the outer surface of the functional layer 21a. Therefore, the beveling width in this case is the width shown in Figure 4(b).

[0028] <Device> The structure of the composite substrate 1 shown in the figure can be used as the structure of various devices. Examples of devices include high-frequency devices, power semiconductors, semiconductor lasers, surface acoustic wave filters (SAW filters), thin-film piezoelectric MEMS (Micro Electro Mechanical Systems), etc.

[0029] <Explanation of the manufacturing method of the composite substrate 1> Next, the manufacturing method of the composite substrate 1 will be explained. Figure 5 is a flowchart illustrating the manufacturing method of the composite substrate 1. Figures 6(a) to 6(f) show the state of each step in Figure 5. First, a functional layer wafer 21, which will be the basis of the functional layer 21a, is prepared (Step 101: Functional layer wafer preparation step, Figure 6(a)). It is also preferable that the surface of the support substrate 23 be mirror polished. Next, a support substrate 23 to support the functional layer 21a is prepared (Step 102: Support substrate preparation step, Figure 6(b)). It is also preferable that the surface of the functional layer wafer 21 be mirror polished.

[0030] Next, the intermediate layer 22 is formed (Step 103: Intermediate layer formation process, Figure 6(c)). The intermediate layer 22 can be formed by sputtering the material that will form the intermediate layer 22. When forming the intermediate layer 22 by sputtering, the intermediate layer 22 may be formed on the functional layer wafer 21 side or on the support substrate 23 side. Alternatively, it may be formed on both. Note that the support substrate 23 is Si and the intermediate layer 22 is SiO ２ In this case, the intermediate layer 22 can also be formed by a thermal oxide film formation method that thermally oxidizes the Si of the support substrate 23. Figure 6(c) shows the case in which the intermediate layer 22 is formed on both the functional layer wafer 21 side and the support substrate 23 side, and these are referred to as intermediate layer 22a and intermediate layer 22b, respectively.

[0031] Next, the functional layer wafer 21 and the support substrate 23 are joined (Step 104: Joining process, Figure 6(d)). In this case, a plasma activation treatment is performed to activate the surface of at least one of the joining surfaces, the functional layer wafer 21 side and the support substrate 23 side, with plasma. As the plasma, for example, Ar, O ２ , N ２ H ２ Plasma such as O can be used. Furthermore, the method is not limited to using plasma; for example, an ion beam can also be used. The surfaces are then brought into contact with each other and pressed together at a predetermined pressure under room temperature. This joins the functional layer wafer 21 and the support substrate 23 via the intermediate layer 22. At this time, an annealing process may be performed to heat the joined functional layer wafer 21 and support substrate 23.

[0032] Next, beveling is performed on the outer periphery of the bonded functional layer wafer 21, intermediate layer 22 and support substrate 23 to form the beveling region 12 (step 105: beveling step, Fig. 6(e)). Beveling can be performed, for example, by a grinding device that grinds the outer periphery by rotating a disc-shaped grindstone at high speed and rotating the bonded functional layer wafer 21 and support substrate 23 slowly while bringing their side surfaces into contact with the grindstone via the intermediate layer 22. At this time, beveling is performed such that the outer periphery of the effective region 13 has the shape shown in Fig. 1(a), Fig. 2(a), and Fig. 3. When the relay part 133 is formed into an R shape, R chamfering is performed so as to obtain the shape shown in Fig. 1(a) and Fig. 2(a). Further, when the relay part 133 is linear, C chamfering is performed so as to obtain the shape shown in Fig. 3.

[0033] Then, the main surface of the functional layer wafer 21 is polished to a desired film thickness to obtain the functional layer 21a (step 106: polishing step, Fig. 6(f)). Thereby, the composite substrate 1 can be manufactured. Polishing can be performed by a known method using a polishing machine.

[0034] (Example 1) As the functional layer wafer 21 that becomes the base of the functional layer 21a, a lithium niobate substrate (LT substrate) having an orientation flat part 11, a diameter of 4 inches, and a thickness of 250 µm was prepared. For the LT substrate, a 46° Y-cut X-propagation LT substrate which is a rotated Y-cut plate with the cutting angle set such that the propagation direction of the surface acoustic wave (SAW) is X was used. The surface of the LT substrate was mirror-polished so that the arithmetic average roughness Ra was 0.3 nm.

[0035] As the support substrate 23, a Si substrate having an orientation flat part 11, a diameter of 4 inches, and a thickness of 230 µm was prepared. The surface of the Si substrate was mirror-polished so that the arithmetic average roughness Ra was 0.3 nm (functional layer wafer preparation step).

[0036] SiO by sputtering ２ was formed into a film on the respective bonding surfaces of the functional layer wafer 21 and the support substrate 23, to form intermediate layers 22a and 22b (intermediate layer film-forming step).

[0037] Plasma activation treatment was performed on the intermediate layers 22a and 22b of the functional layer wafer 21 and the support substrate 23, followed by bonding (bonding step).

[0038] The outer peripheral portions of the bonded functional layer wafer 21, intermediate layer 22 and support substrate 23 are ground with a grindstone, and the functional layer wafer 21, intermediate layer 22 and part of the support substrate 23 are removed (beveling step). At this time, beveling is performed so that the outer periphery of the effective region 13 has the shape shown in FIG. 1(a) or FIG. 2(a), and the relay portion 133 is formed into an R shape. Specifically, the grindstone is continuously moved from the arc portion 131 to the straight portion 132 at the relay portion 133, and R chamfering is performed so that the radius of curvature is 2 mm. At this time, the beveling width was set to 2 mm, the beveling depth was set to 15 mm, and the cutting angle was set to 60°.

[0039] The functional layer wafer 21 was ground and polished from an initial thickness of 250 μm to 1 μm to obtain composite substrate 1 (polishing step).

[0040] (Example 2) In the beveling step, composite substrate 1 was manufactured in the same manner as in Example 1, except that beveling was performed to obtain the shape shown in FIG. 3 and the relay portion 133 was formed into a linear shape. Specifically, the grindstone was continuously moved from the arc portion 131 to the straight portion 132 at the relay portion 133, and C chamfering was performed so that the length was 1 mm.

[0041] (Comparative Example 1) In Comparative Example 1, although beveling was performed, the relay portion 133 was not provided, and the shape was as shown in FIG. 2(b).

[0042] (Results) In the composite substrates 1 of Examples 1 and 2, no chipping occurred in the polishing step. In contrast, some of the composite substrates of Comparative Example 1 developed chipping during the polishing step, resulting in scratches and peeling on the composite substrates.

[0043] The present embodiment has been described above, but the technical scope of the present invention is not limited to the scope described in the above embodiment. It is clear from the description of the claims that various modifications or improvements added to the above embodiment are also included in the technical scope of the present invention.

[0044] 1...Composite substrate, 11...Orientation flat portion, 12...Beveling region, 13...Effective region, 21...Functional layer wafer, 21a...Functional layer, 22...Intermediate layer, 23...Support substrate, 131...Arc portion, 132...Straight portion, 133...Relay portion

Claims

1. A composite substrate comprising a functional layer and a support substrate for supporting the functional layer, wherein the composite substrate has a beveled region on its outer periphery, and the beveled region gives the outer periphery of the effective region other than the beveled region a shape including an arc-shaped arc portion, a straight portion, and a relay portion connecting the arc portion and the straight portion, and the relay portion passes inside the curve extended from the arc portion and the straight portion extended from the straight portion.

2. The composite substrate according to claim 1, wherein the relay portion has an R shape with a radius of curvature of 0.1 mm or more and 5 mm or less when viewed from above.

3. The composite substrate according to claim 1, wherein the relay portion has a straight shape with a length of 0.05 mm or more and 1 mm or less when viewed from above.

4. The composite substrate according to claim 1, wherein the beveling region has a beveling width of 0.5 mm or more and 4 mm or less.

5. The composite substrate according to claim 1, wherein the beveling region is defined as the beveling depth when the amount removed in the thickness direction of the support substrate is defined as the beveling depth, and the beveling depth is 5 μm or more and 60 μm or less.

6. The composite substrate according to claim 1, further comprising an intermediate layer having a thickness of 0.01 μm or more and 10 μm or less between the functional layer and the support substrate.

7. The composite substrate according to claim 1, wherein the functional layer has a thickness of 100 nm or more and 10 μm or less.

8. A device comprising a composite substrate according to any one of claims 1 to 7.

9. A method for manufacturing a composite substrate having a beveled region, comprising: a bonding step of bonding a functional layer wafer which will be the basis of a functional layer and a support substrate which will support the functional layer; a beveling step of beveling the outer periphery of the bonded functional layer wafer and the support substrate to form the beveled region; and a polishing step of polishing the functional layer wafer to form the functional layer, wherein the beveling step is such that the outer periphery of the effective region other than the beveled region has a shape including an arc-shaped arc portion, a straight-line portion, and a relay portion connecting the arc portion and the straight-line portion, and the relay portion passes inside the curve that is an extension of the arc portion and the straight-line portion that is an extension of the straight-line portion.

10. The method for manufacturing a composite substrate according to claim 9, wherein the beveling step is performed by chamfering the intermediate portion so that the radius of curvature when viewed from above is R-shaped, which is 0.1 mm or more and 5 mm or less.

11. The method for manufacturing a composite substrate according to claim 9, wherein the beveling step is performed by chamfering the intermediate portion so that it is a straight line with a length of 0.05 mm or more and 1 mm or less when viewed from above.

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