Composite substrate

Abstract

Provided is a composite substrate in which a large amount of chipping and a large amount of peeling are suppressed. A composite substrate according to an embodiment of the present invention has a support substrate and a functional layer, wherein: an edge of the functional layer in the radial direction of the support substrate is further inward than an outer peripheral end of the support substrate; and the functional layer in an outer peripheral region positioned within 5.0 mm inward in the radial direction from the outer peripheral end of the support substrate has a gentle gradient region in which the thickness decreases toward the radial outside by a reduction amount of 1.0-10.0 nm per 10 μm.

Description

Composite substrate

[0001] This invention relates to a composite substrate.

[0002] Composite substrates are used in a variety of applications, including personal computers, smartphones, and automobiles. In the manufacturing process of composite substrates, a functional substrate is sometimes bonded directly to another substrate or layer, and then the functional layer is formed by thinning it using an ion implantation delamination method (see Patent Document 1). However, in the polishing process after the formation of the functional layer, there is a problem in that the bonded functional layer may peel off from its outer edge, resulting in large chipping and peeling that extends to the area used in the device.

[0003] Special Publication No. 2022-528388

[0004] The present invention was made to solve the above-mentioned conventional problems, and its main objective is to provide a composite substrate in which large chipping and large peeling are suppressed.

[0005] [1] A composite substrate according to an embodiment of the present invention comprises a support substrate and a functional layer, wherein the edge of the functional layer is located inward from the outer peripheral edge of the support substrate in the radial direction, and the functional layer has a gently sloping region in the outer peripheral region within 5.0 mm radially inward from the outer peripheral edge of the support substrate, where the thickness of the functional layer decreases radially outward at a rate of 1.0 nm to 10.0 nm per 10 μm. [2] In the composite substrate according to item [1], at least a portion of the edge of the functional layer is located within the outer peripheral region. [3] In the composite substrate according to item [1] or [2], an intermediate layer is provided between the support substrate and the functional layer. [4] In the composite substrate according to any one of items [1] to [3], the support substrate is beveled radially outward from the edge of the functional layer.

[0006] According to embodiments of the present invention, it is possible to provide a composite substrate in which large chipping and large peeling are suppressed.

[0007] Figure 1 is a schematic cross-sectional view of a composite substrate according to an embodiment of the present invention, cut in the stacking direction. Figure 2 is a schematic cross-sectional view of a composite substrate according to another embodiment of the present invention, cut in the stacking direction. Figure 3 is a magnified schematic cross-sectional view of the main part of the composite substrate of Example 1, cut in the stacking direction. Figure 4 is a magnified schematic cross-sectional view of the main part of the composite substrate of Example 2, cut in the stacking direction. Figure 5 is a magnified schematic cross-sectional view of the main part of the composite substrate of Example 3, cut in the stacking direction. Figure 6 is a magnified schematic cross-sectional view of the main part of the composite substrate of Example 4, cut in the stacking direction. Figure 7 is a magnified schematic cross-sectional view of the main part of the composite substrate of Example 5, cut in the stacking direction. Figure 8 is a magnified schematic cross-sectional view of the main part of the composite substrate of Comparative Example 1, cut in the stacking direction.

[0008] The embodiments of the present invention will be described below, but the present invention is not limited to these embodiments. In order to make the explanation clearer, the drawings may schematically represent the width, thickness, shape, etc. of each part compared to the embodiments, but these are merely examples and do not limit the interpretation of the present invention.

[0009] A. Overall Structure of the Composite Substrate The composite substrate according to the embodiment of the present invention can typically be manufactured in the form of a so-called wafer, that is, in the form of a disc. The case where the composite substrate is in the form of a wafer will be described below. The size of the composite substrate can be appropriately set according to the purpose. For example, the diameter when it is in the form of a wafer may be, for example, 50 mm to 300 mm. Usually, multiple electro-optic elements can be manufactured from a single composite substrate. Note that the composite substrate is not limited to the form of a wafer and may be manufactured and provided in various forms, and may have an orientation flat portion or a notched portion.

[0010] Figure 1 is a schematic cross-sectional view of a composite substrate according to one embodiment of the present invention, cut in the stacking direction. The illustrated composite substrate 100 has a support substrate 10 and a functional layer 20. Figure 2 is a schematic cross-sectional view of a composite substrate according to another embodiment of the present invention, cut in the stacking direction. The illustrated composite substrate 110 has an intermediate layer 30 between the support substrate 10 and the functional layer 20. The intermediate layer is an arbitrary layer provided according to the purpose, and multiple intermediate layers may be provided, or the intermediate layer may be omitted. The type, function, number, combination, and position of the intermediate layer can be appropriately set according to the purpose. In the embodiment of the present invention, the composite substrate 100 is formed by bonding the support substrate 10 and the functional layer 20 via an adhesive layer or by direct bonding. In this specification, "direct bonding" means that the components of the composite substrate are bonded together without the interposition of an adhesive. The form of direct bonding can be appropriately set according to the configuration of the layers or substrates to be bonded together.

[0011] The composite substrate 100 in the illustrated example has a central portion and an outer peripheral region 25. The outer peripheral region 25 is the region radially inward from the outer peripheral end 11 of the support substrate 10, and is typically within 5.0 mm radially inward from the outer peripheral end 11 of the support substrate 10. The central portion of the composite substrate 100 is the region of the composite substrate 100 other than the outer peripheral region 25, and is typically located inside the outer peripheral region 25. When the outer peripheral region of the composite substrate is defined in this way, a sufficient number of device elements can be cut out with good yield when the composite substrate is cut out to form devices. Note that the outer peripheral end 11 of the support substrate 10 is the outermost region when the composite substrate 100 is viewed from the main surface direction of the support substrate 10.

[0012] In the illustrated example, the composite substrate 100 typically has a functional layer 20 edge 21 located inside the outer peripheral edge 11 of the support substrate 10 in the radial direction. The functional layer 20 usually has a flat region 23 with substantially constant thickness in its central part (the region overlapping with the central part of the composite substrate 100). A flat region with substantially constant thickness is a region where the thickness changes by an amount of change (decrease or increase) of less than 1.0 nm per 10 μm toward the radially outward direction of the support substrate 10, or a region where the thickness does not change (the amount of change in thickness is 0). The functional layer 20 can be divided in its planar direction into a flat region 23, a gently sloping region 22 (described later), and a steep region 24 (described later). One method for dividing the functional layer into separate regions is to measure the thickness of the functional layer at every 10 μm along any one of several lines that radiate from the center of the composite substrate (functional layer) to the edge of the functional layer using an optical thickness gauge, and then calculate the change in the thickness of the functional layer per 10 μm line using the following formula (I), and use that value to determine x ｎ From the measurement point x ｎ＋１ Determine which of the three regions above the area up to the measurement point is. Equation (I): Change in thickness of the functional layer per 10 μm line ([nm]) = (x ｎ [μm] - x ｎ＋１ [μm]) × 1000 where x ｎ x is the thickness of the functional layer at any given measurement point, ｎ＋１ is x ｎ Further outward in the radial direction of the support substrate x ｎ This is the thickness of the functional layer at the measurement point adjacent to it.

[0013] The flat region 23 in the functional layer 20 is, for example, 85% to 97%, preferably 90% to 95%, of the entire line extending radially from the center of the functional layer 20 to the edge 21 of the functional layer 20 in the planar direction of the functional layer 20. If the flat region in the functional layer is within this range, devices can be produced with a sufficiently high yield even if areas other than the flat region in the functional layer cannot be used as devices. The flat region 23 in the functional layer 20 extends, for example, from the center of the functional layer 20 to the boundary with the outer peripheral region 25 in the radial direction of the support substrate 10, and also extends, for example, from the center of the functional layer 20 to within 5.0 mm inside the edge 21 of the functional layer. If the flat region in the functional layer is configured in this way, devices can be created by simply removing the area outside the flat region in the functional layer in the radial direction of the support substrate, thus enabling the production of devices with a high yield.

[0014] In an embodiment of the present invention, the composite substrate 100 typically has a gently sloping region 22 in the outer peripheral region 25 within 5.0 mm radially inward from the outer peripheral edge 11 of the support substrate 10, as shown in Figure 1, where the thickness of the functional layer 20 decreases by 1.0 nm to 10.0 nm per 10 μm toward the radially outward direction of the support substrate 10. The inventors diligently studied how to suppress the peeling of the functional layer and found that, while normally a flat region extends to the outer peripheral edge of the functional layer, forming a gently sloping region in the functional layer within a certain range from the outer peripheral edge of the support substrate, where the thickness of the functional layer gradually decreases, can suppress the peeling of the functional layer, thus completing the present invention. According to one embodiment of the present invention, in the outer peripheral region within 5.0 mm radially inward from the outer peripheral edge of the support substrate, the functional layer has a gently sloping region in which its thickness decreases by 1.0 nm to 10.0 nm per 10 μm toward the radially outward direction of the support substrate. Although the effective area of ​​the functional layer is reduced, large chipping and peeling of the composite substrate can be suppressed, thereby enabling the production of a highly productive composite substrate.

[0015] In the illustrated example, the composite substrate 100 preferably has at least a portion of the edge 21 of the functional layer 20 located within the outer peripheral region 25 of the composite substrate 100, and more preferably, the entire edge 21 of the functional layer 20 located within the outer peripheral region 25 of the composite substrate 100. With such a configuration, large chipping and peeling of the composite substrate can be suppressed, thus enabling the production of a highly productive composite substrate. The position of the edge of the functional layer in the radial direction of the support substrate can be any appropriate position within the outer peripheral region of the composite substrate.

[0016] Figure 3 is a schematic cross-sectional view of the main part of the composite substrate shown in Figure 1, cut in the stacking direction. Within the outer peripheral region 25 of the illustrated example composite substrate 100, the functional layer 20 has only a gently sloping region 22. That is, the end of the flat region 23 coincides with the radially inward end of the support substrate 10 in the outer peripheral region 25. The gently sloping region 22 is a region in which the thickness of the functional layer 20 decreases towards the radially outward direction of the support substrate 10, typically at a decrease of 1.0 nm to 10.0 nm per 10 μm, as described above. With such a configuration of the functional layer, although the effective area of ​​the functional layer is reduced, large chipping and peeling of the composite substrate can be suppressed, thus enabling the production of a highly productive composite substrate.

[0017] Figure 4 is a schematic cross-sectional view of a key part of a composite substrate according to another embodiment of the present invention, cut in the stacking direction. As shown in the illustrated example, the functional layer 20 has a flat region 23 extending from the central part into the outer peripheral region 25 of the composite substrate 100, and a gently sloping region 22 on the radially outer side of the support substrate 10 of the flat region 23. With such a configuration of the functional layer, large chipping and peeling of the composite substrate can be suppressed, and the flat region that is an effective area in the functional layer can be expanded, thereby increasing the area that can be used for devices and enabling the production of a highly productive composite substrate. Although not shown, within the outer peripheral region 25 of the composite substrate 100, the flat region 23 may be arranged between and / or outside the gently sloping regions 22 in the radial direction of the support substrate 10.

[0018] Figure 5 is a schematic cross-sectional view of a key part of a composite substrate according to yet another embodiment of the present invention, cut in the stacking direction. As shown in the illustrated example, the functional layer 20 has a gently sloping region 22 within the outer peripheral region 25 of the composite substrate 100, and a steep region 24 radially outward of the gently sloping region 22 from the support substrate 10. That is, the end of the flat region 23 coincides with the radially inward end of the outer peripheral region 25 from the support substrate 10. The steep region 24 is a region in which the thickness decreases by more than 10.0 nm per 10 μm toward the radially outward direction from the support substrate 10. With such a configuration of the functional layer, large chipping and peeling of the composite substrate can be suppressed, and a composite substrate with high productivity can be obtained. Although not shown, within the outer peripheral region 25 of the composite substrate 100, the steep region 24 may be located between and / or inside the gently sloping regions 22 in the radial direction of the support substrate 10.

[0019] Figure 6 is a schematic cross-sectional view of a key part of a composite substrate according to yet another embodiment of the present invention, cut in the stacking direction. As shown in the illustrated example, the functional layer 20 has a flat region 23 extending from the central part into the outer peripheral region 25 of the composite substrate 100, a gently sloping region 22 radially outside the support substrate 10 of the flat region 23, and a steep region 24 radially outside the support substrate 10 of the gently sloping region 22. With such a configuration for the functional layer, the flat region that is an effective area in the functional layer can be expanded, thereby increasing the area that can be used for devices and enabling the production of a highly productive composite substrate.

[0020] FIG. 7 is a schematic cross-sectional view of a composite substrate according to still another embodiment of the present invention, cut along the lamination direction. In the illustrated composite substrate 100, for example, at least a part of the support substrate 10 is beveled radially outward of the support substrate beyond an edge 21 of the functional layer 20, and preferably, the entire outer circumference of the support substrate 10 in the circumferential direction is beveled radially outward of the support substrate 10 beyond the edge 21 of the functional layer 20. When the composite substrate has such a configuration, large chipping and large peeling of the composite substrate can be suppressed, so that a composite substrate with high productivity can be obtained. It should be noted that any appropriate position can be adopted for the position of the beveling in the radial direction of the support substrate as long as the position is outside the edge of the functional layer. The beveling in the radial direction of the support substrate 10 is started from a position radially inward from an outer peripheral end 11 of the support substrate 10, for example, 2.5 mm or less, preferably 1.0 mm to 2.0 mm from the outer peripheral end 11.

[0021] In the plane direction of the functional layer 20, a region overlapping with the outer peripheral region 25 is referred to as a functional layer outer peripheral region. When the range in which any one radially extending line from the center of the functional layer 20 to the edge 21 of the functional layer 20 is included in the functional layer outer peripheral region is defined as 100%, the proportion of the gentle slope region 22 in the functional layer outer peripheral region is, for example, 40% or more, preferably 50% or more, more preferably 60% or more, still more preferably 70% or more, and particularly preferably 90% or more. When the proportion of the gentle slope region in the functional layer outer peripheral region falls within such a range, large chipping and large peeling of the composite substrate can be suppressed, so that a composite substrate with high productivity can be obtained.

[0022] When the range in which any one radially extending line from the center of the functional layer 20 to the edge 21 of the functional layer 20 is included in the functional layer outer peripheral region is defined as 100%, the proportion of the flat region 23 in the functional layer outer peripheral region is, for example, 50% or less, preferably 45% or less, more preferably 39% or less, still more preferably 30% or less, and particularly preferably 10% or less. When the proportion of the flat region in the functional layer outer peripheral region falls within such a range, a sufficient number of device elements can be cut out with good yield when the composite substrate is cut to obtain devices.

[0023] When the range in which any one radially extending line from the center of the functional layer 20 to the edge 21 of the functional layer 20 is included in the outer peripheral region of the functional layer is defined as 100%, the proportion of the steep region 24 in the outer peripheral region of the functional layer is, for example, 10% or less, preferably 5% or less, more preferably 1% or less, and still more preferably 0%. When the proportion of the steep region in the outer peripheral region of the functional layer falls within this range, large chipping and large peeling of the composite substrate can be suppressed, so that a composite substrate with high productivity can be obtained. Note that the sum of the proportion of the gentle slope region 22, the proportion of the flat region 23, and the proportion of the steep region 24 in the outer peripheral region of the functional layer is 100%.

[0024] Regarding the gentle slope region 22, flat region 23, steep region 24 and beveling described in FIGS. 3 to 7 above, their respective arrangements may be arbitrarily and appropriately combined. For example, in each of the composite substrates shown in FIGS. 3 to 6, the supporting substrate may be beveled as shown in FIG. 7.

[0025] Note that, in the present invention, the functional layer 20 does not have a gentle slope region in the central portion inside the outer peripheral region 25 of the composite substrate 100 in the radial direction of the supporting substrate 10. If the functional layer is configured to have a gentle slope region in the central portion inside the outer peripheral region 25 of the composite substrate, it may become impossible to maintain the effective region of the functional layer.

[0026] The thickness of the composite substrate 100 is, for example, 200 μm to 2000 μm, and preferably 300 μm to 1000 μm. When the composite substrate 100 includes an intermediate layer, the thickness of the composite substrate 100 is a thickness including the thickness of the intermediate layer. The diameter of the composite substrate 100 is substantially the same as the diameter of the supporting substrate 10, and is preferably 80 mm to 200 mm, more preferably 100 mm to 200 mm.

[0027] Hereinafter, each component of the composite substrate will be specifically described. B. Support Substrate Any appropriate substrate can be used as the support substrate 10. The support substrate may be composed of a single crystal, a polycrystal, or a combination thereof. Examples of materials constituting the support substrate include silicon, sapphire, sialon, cordierite, mullite, glass, quartz glass, quartz, alumina, germanium, silicon carbide, gallium nitride, indium phosphide, and aluminum nitride. The support substrate preferably contains at least one material selected from the group consisting of silicon, silicon carbide, gallium nitride, and glass, more preferably contains silicon, and even more preferably is made of silicon.

[0028] The above silicon may be single crystal silicon, polycrystalline silicon, high-resistance silicon, or a combination thereof. In addition, silicon may be heated to form a thermal oxide film (silicon oxide (SiO ２ )).

[0029] Any appropriate thickness can be adopted as the thickness of the support substrate 10. The thickness of the support substrate is, for example, 100 μm to 1000 μm, preferably 200 μm to 725 μm.

[0030] The surface roughness Sa on the functional layer side of the support substrate 10 is, for example, 0.1 nm to 1.0 nm, preferably 0.2 nm to 0.8 nm. With such a surface roughness Sa on the functional layer side of the support substrate, for example, a high-performance surface acoustic wave element (for example, having a high Q value) can be obtained. The surface roughness Sa is a value measured by the stylus scanning method in accordance with JIS B 0681-6:2014.

[0031] C. Functional Layer The functional layer 20 may be, for example, a piezoelectric layer, a nonlinear optical layer, or an electro-optical layer having an electro-optical effect. The functional layer 20 can be formed from any appropriate functional substrate. Examples of the functional substrate include a piezoelectric substrate, a nonlinear optical crystal substrate, an electro-optical crystal substrate, and a semiconductor substrate. As specific materials constituting the functional substrate, for example, lithium niobate (LiNbO３ :LN), Lithium tantalate (LiTaO) ３ :LT), lithium niobate-lithium tantalate solid solution, potassium titanate phosphate (KTiOPO ４ :KTP), potassium niobate lithium (K ｘ Li （１－ｘ） NboO ２ , 0 ≤ x ≤ 1: KLN), potassium niobate (KNbO ３ :KN), potassium tantalate / niobate (KNb ｘ Ta （１－ｘ） O ３ Examples include 0≦x≦1: KTN), silicon carbide, quartz, quartz glass, silicon carbide, aluminum oxide, gallium nitride, indium phosphide, silicon, and lead zirconate titanate (PZT).

[0032] The thickness of the functional layer 20 (substantially the thickness of the flat region 23) is, for example, 30 μm or less, preferably 10 μm or less, more preferably 5 μm or less, even more preferably 1 μm or less, particularly preferably 0.8 μm or less, and especially preferably 0.6 μm or less. The thickness of the functional layer 20 may be, for example, 0.1 μm or more, or for example, 0.2 μm or more. If the thickness of the functional layer is within this range, high-performance (e.g., having good temperature characteristics and / or a high Q value) surface acoustic wave elements and / or optical elements can be manufactured. Hereinafter, piezoelectric layers and electro-optical layers will be described as representative examples of functional layers. However, it will be apparent to those skilled in the art that the effects of the embodiments of the present invention do not depend on the type of functional layer.

[0033] Any suitable piezoelectric material can be used as the material constituting the piezoelectric layer. Examples of piezoelectric materials include lithium niobate, lithium tantalate, lithium niobate-lithium tantalate solid solution, potassium titanate phosphate, potassium niobate / lithium niobate, potassium niobate, potassium tantalate / potassium niobate, silicon, quartz, quartz glass, silicon carbide, gallium nitride, indium phosphide, and lead zirconate titanate. Preferably, the piezoelectric material is lithium niobate, lithium tantalate, or lithium niobate-lithium tantalate solid solution.

[0034] When the piezoelectric material is lithium tantalate, the cut angle can be appropriately set depending on the purpose. For example, when the X-axis (crystal axis) of the piezoelectric material is taken as the propagation direction of the surface acoustic wave (X1), the direction rotated 32° to 55° (e.g., 46.5°) from the Y-axis to the Z-axis corresponds to the direction perpendicular to the main surface of the piezoelectric layer (X3), specifically, (180°, 58° to 35°, 180°) in Euler angle notation.

[0035] When the piezoelectric material is lithium niobate, the cut angle can be appropriately set depending on the purpose. For example, it is preferable that the piezoelectric layer is positioned such that the direction rotated from the Z-axis to the -Y-axis by 0° to 40° (e.g., 37.8°) when the X-axis (crystal axis) of the piezoelectric material is the propagation direction of surface acoustic waves (X1) corresponds to the direction perpendicular to the main surface of the piezoelectric layer (X3), specifically in Euler angle notation (0°, 0° to 40°, 0°). When the piezoelectric material is lithium niobate, it is also preferable that the piezoelectric layer is positioned such that the direction rotated from the Y-axis to the Z-axis by 40° to 65° when the X-axis (crystal axis) of the piezoelectric material is the propagation direction of surface acoustic waves (X1) corresponds to the direction perpendicular to the main surface of the piezoelectric layer (X3), specifically in Euler angle notation (180°, 50° to 25°, 180°).

[0036] The thickness of the piezoelectric layer (the thickness of the substantially flat region 23) is, for example, 30 μm or less, preferably 10 μm or less, more preferably 5 μm or less, even more preferably 1 μm or less, and particularly preferably 0.5 μm or less. With such a piezoelectric layer thickness, for example, a high-performance (for example, having good temperature characteristics and / or a high Q value) surface acoustic wave element can be obtained. On the other hand, the thickness of the piezoelectric layer may be, for example, 0.1 μm or more, or for example, 0.2 μm or more.

[0037] The electro-optic layer can be fabricated from any suitable electro-optic crystal substrate. Any suitable electro-optic crystal material can be used as the material constituting the electro-optic crystal substrate (the material exhibiting the electro-optic effect). Examples of such materials include those similar to piezoelectric materials. The electro-optic layer may also be the electro-optic crystal substrate itself.

[0038] Part or all of an electro-optic layer can act as an optical waveguide for transmitting light in an electro-optic element. That is, the electro-optic layer has an optical band structure similar to the band structure of electrons, and can exhibit a photonic band gap. Introducing line defects that disrupt the periodicity of an electro-optic layer with a photonic band gap can form waveguide modes within the frequency domain of the band gap, realizing an optical waveguide that propagates light with low loss. The optical constants (e.g., refractive index) of the electro-optic layer can change when an electric field is applied.

[0039] The thickness of the electro-optic layer (essentially the thickness of the flat region 23) can be set to any appropriate thickness depending on the purpose. The thickness of the electro-optic layer may be, for example, 0.1 μm to 10 μm, preferably 0.2 μm to 10 μm. If the lower limit of the thickness of the electro-optic layer is within this range, the light propagation loss in the electro-optic element can be reduced. On the other hand, the thickness of the electro-optic layer may be preferably 5.0 μm or less, more preferably 2.5 μm or less, even more preferably 1.0 μm or less, and particularly preferably 0.5 μm or less. If the upper limit of the thickness of the electro-optic layer is within this range, the high-speed and low-voltage driving performance of the electro-optic element can be improved. Therefore, it is possible to achieve higher speed and lower voltage driving while suppressing a decrease in light propagation loss.

[0040] The surface roughness Sa of the functional layer 20 may be, for example, 1.0 nm or less, 0.8 nm or less, 0.6 nm or less, or 0.4 nm or less. With such a surface roughness of the functional layer, for example, a high-performance (for example, having a high Q value) surface acoustic wave element can be obtained. The surface roughness Sa of the functional layer 20 may be, for example, 0.05 nm or more, or for example, 0.1 nm or more.

[0041] D. Intermediate Layer As described above, the composite substrate may have an intermediate layer. Examples of intermediate layers include a dielectric layer, an ionosphere, and a bonding layer. Examples of materials constituting the intermediate layer include silicon oxide, hafnium oxide, tantalum oxide, zirconium oxide, and aluminum oxide. The thickness of the intermediate layer is, for example, 0.1 μm to 20 μm. The size of the intermediate layer may be, for example, the same size as the composite substrate (support substrate) described above.

[0042] The above-mentioned intermediate layer can be deposited by any suitable method. For example, it can be deposited by physical vapor deposition such as sputtering and ion beam-assisted deposition (IAD), chemical vapor deposition, or atomic layer deposition (ALD).

[0043] E. Method for Manufacturing a Composite Substrate The method for manufacturing a composite substrate 100 according to an embodiment of the present invention includes, for example, a bonding step of bonding a support substrate 10 and a functional substrate, and a thinning step of thinning the functional substrate to form a functional layer 20. Examples of the thinning step include a thinning step by grinding and polishing, and a thinning step by ion implantation and peeling. Preferably, the thinning step is a thinning step by ion implantation and peeling. If the thinning step is by ion implantation and peeling, a composite substrate with a uniform thickness in the effective area of ​​the functional layer can be suitably manufactured. The thinning step by ion implantation and peeling includes an ion implantation step, a peeling step, and a finishing polishing step. Preferably, in the thinning step by ion implantation and peeling, the ion implantation step is performed before the bonding step, the peeling step is performed after the bonding step, and then the finishing polishing step is performed. Hereinafter, each step of the method for manufacturing a composite substrate will be specifically described when the thinning step is performed by ion implantation and peeling.

[0044] E-1. Ion Implantation Process In the ion implantation process, ions are implanted into the functional substrate from the bonding surface side of the functional substrate. When implanting ions, a jig is set up on the bonding surface side of the functional substrate so as to cover the area corresponding to the outer peripheral region 25 of the composite substrate 100, and the functional substrate is held down by the jig while the ions are guided to the jig to adjust the implantation depth, thereby forming a region with a gradient in the outer peripheral region of the functional layer 20 obtained by thinning the functional substrate.

[0045] The shape of the jig can be, for example, any shape that can cover the area of ​​the functional substrate corresponding to the outer peripheral region 25 of the composite substrate 100. For example, the cross-sectional shape of the jig along the stacking direction of the composite substrate when the jig is placed on the functional substrate may be semicircular or polygonal. Preferably, the cross-sectional shape of the jig along the stacking direction of the composite substrate is polygonal, and more preferably quadrilateral. The jig is installed so as to be in contact with the area of ​​the composite substrate 100 corresponding to the outer peripheral region 25 of the bonding surface of the functional substrate, and the contact surface is connected to the inner end surface of the jig.

[0046] Furthermore, by changing the shape of the jig, the path through which the induced ions move within the functional substrate can be altered, and the implantation depth of the implanted ions can be adjusted. As a result, the shape of the gradient of the functional layer 20 formed by heating in the peeling process can be altered, allowing for the formation of gently sloping regions 22 at desired positions and in desired proportions within the flat region 23 in the outer peripheral region of the functional layer, and, if necessary, steep regions 24 at desired positions and in desired proportions. One method for altering the shape of the jig is to adjust the angle between the inward direction of the contact surface of the jig and the inner end face of the jig. The angle between the inward direction of the contact surface of the jig and the inner end face of the jig is, for example, 30° to 95°, preferably 45° to 90°, more preferably 60° to 90°, and even more preferably 75° to 85°. If the angle between the inward direction of the contact surface of the jig and the inner end face of the jig is within this range, gently sloping regions and / or steeply sloping regions can be suitably formed in the functional layer in the outer peripheral region of the resulting composite substrate. As a result, large chipping and peeling of the composite substrate can be suppressed, and a composite substrate with high productivity can be obtained.

[0047] Examples of ions include hydrogen ions and helium ions. The energy level when implanting ions is, for example, 30 keV to 300 keV, preferably 50 keV to 100 keV. The dose when implanting ions is, for example, 1.0 × 10⁻⁶. １６ atoms / cm ２ ~5.0 x 10 １７ atoms / cm ２Preferably 5.0 × 10 １６ atoms / cm ２ ~1.0 x 10 １７ atoms / cm ２ The maximum depth to which ions are implanted is, for example, 0.2 μm to 2.0 μm from the bonding surface of the functional substrate, preferably 0.2 μm to 1.5 μm, and 0.2 μm to 1.0 μm.

[0048] Examples of jig materials include stainless steel (e.g., SUS), iron, aluminum, and brass. The jig material is preferably stainless steel, and more preferably SUS. With such a configuration for the jig material, ions can be suitably guided, and the ion implantation depth can be suitably adjusted.

[0049] E-2. Bonding Process In the bonding process, the support substrate 10 and the ion-implanted functional substrate are bonded together. The support substrate 10 and the functional substrate are bonded together via an adhesive layer or by direct bonding. In the bonding process, for example, the support substrate 10 and the functional substrate are each subjected to plasma hydrophilization treatment, and then the support substrate 10 and the functional substrate are bonded together by direct bonding. The functional substrate may have a handling substrate on one side (the side opposite to the bonding surface). In this case, the bonding surface of the functional substrate is subjected to plasma hydrophilization treatment.

[0050] One method for plasma hydrophilization treatment of the support substrate and the functional substrate is to irradiate them with plasma. Examples of plasma include oxygen plasma and nitrogen plasma. The system pressure when irradiating with plasma is, for example, 1.0 Pa to 100 Pa, preferably 5.0 Pa to 50 Pa. The system temperature when irradiating with plasma is, for example, 20°C to 100°C, preferably 23°C to 50°C.

[0051] Methods for bonding the support substrate and the functional substrate include applying pressure from a vacuum to an atmospheric environment (for example, 1.0 × 10⁻⁶). －６ Pa ~ 1.0 × 10 ６The plasma-hydrophilized surfaces of the support substrate and the functional substrate are directly bonded together using Pa. This directly bonds the support substrate and the functional substrate, resulting in a bonded body having the support substrate and the functional substrate.

[0052] E-3. The manufacturing method of the composite substrate 100 preferably includes a heating step. In the manufacturing method of the composite substrate 100, the first heating step is preferably performed after the bonding step and before the peeling step. By performing the first heating step, the bonding strength between the support substrate and the functional substrate can be made strong enough to prevent peeling in subsequent steps.

[0053] The first heating step is performed, for example, under pressure from a vacuum to an atmospheric pressure (e.g., 1.0 × 10⁻⁶). －６ Pa ~ 1.0 × 10 ６ The heating is carried out in Pa). The heating temperature in the first heating step is, for example, 100°C to 250°C, preferably 120°C to 200°C. The heating time in the first heating step is, for example, 1 hour to 12 hours, preferably 2 hours to 10 hours.

[0054] E-4. Peeling Process In the peeling process, the functional substrate is peeled off at the plane where the ions are implanted to the maximum depth by heating at a higher temperature than the heating temperature in the first heating process described above. As a result, the functional substrate is thinned and the functional layer 20 is formed. The heating temperature for peeling is, for example, greater than 250°C and 700°C or less, and preferably 300°C or more and 600°C or less.

[0055] Instead of the process of thinning by ion implantation exfoliation, a process of thinning by grinding and polishing may be used. In the process of thinning by grinding and polishing, the functional substrate is thinned to form a functional layer 20 by grinding and polishing the surface of the functional substrate on the opposite side of the bonding surface of the functional substrate in the resulting bonded body, for example, forming a gently sloping region 22 in the flat region 23 of the functional layer 20 in the outer peripheral region 25 of the bonded body (later composite substrate 100), and a steep region 24 can be formed as needed. Examples of grinding methods include grinding with a grinder. Examples of polishing methods include mirror polishing by chemical mechanical polishing (CMP) and lapping. Preferably, chemical mechanical polishing is used. Specifically, chemical mechanical polishing using a polishing pad with polishing slurry (for example, colloidal silica) is used.

[0056] The thickness of the functional layer 20 after the peeling process (substantially the thickness of the flat region 23) is, for example, 0.15 μm to 1.95 μm, preferably 0.15 μm to 1.35 μm, and more preferably 0.15 μm to 0.95 μm. If the thickness of the functional layer after the peeling process is within this range, sufficient thickness can be secured to remove the altered surface layer in the subsequent polishing process.

[0057] E-5. Beveling Process The manufacturing method of the composite substrate 100 preferably includes a beveling step. In the manufacturing method of the composite substrate 100, the beveling step is preferably performed after the peeling step. In the beveling step, any suitable position can be adopted as long as it is outside the edge of the functional layer. As for the position of beveling in the radial direction of the support substrate 10, beveling is performed from a position radially inward from the outer peripheral end 11 of the support substrate 10, for example, 2.5 mm or less, preferably 1.0 mm to 2.0 mm. A beveling method can be, for example, grinding. This results in a bonded body in which the support substrate 10 has been beveled.

[0058] E-6. Second Heating Step The manufacturing method of the composite substrate 100 preferably includes a second heating step. In the manufacturing method of the composite substrate 100, the second heating step is preferably performed after the peeling step (or after the beveling step). Since the heating in the second heating step is performed after the functional layer has been formed, it may be heated at a higher temperature than in the first heating step, and even if the bonded body has a large difference in thermal expansion coefficients, it is possible to heat it at a high temperature while suppressing cracking. By performing the second heating step, the bonding strength between the support substrate and the functional layer can be made stronger than by performing the first heating step, and peeling in subsequent steps can be suppressed. Furthermore, the heating step preferably includes both the first heating step and the second heating step. Performing both the first heating step and the second heating step can further strengthen the bonding strength between the support substrate and the functional layer, and peeling in subsequent steps can be suppressed.

[0059] The second heating step is performed, for example, under pressure from a vacuum to a nitrogen atmosphere (e.g., 1.0 × 10⁻⁶). －６ Pa ~ 1.0 × 10 ６ Pa), preferably in a vacuum (for example, 1.0 × 10⁻⁶). －６ The process is carried out under a Pa (approximately) or nitrogen atmosphere. The heating temperature in the second heating step is, for example, 300°C to 800°C, preferably 400°C to 600°C. The heating time in the second heating step is, for example, 0.5 hours to 12 hours, preferably 1 hour to 10 hours.

[0060] E-7. Finishing Polishing Process In the process of thinning by ion implantation delamination, a finishing polishing process is performed to remove the altered layer formed on the delamination surface of the functional layer 20 formed by delamination of the functional substrate in the delamination process, and to improve the surface roughness of the delamination surface. As a method of finishing polishing, for example, a method of setting the composite substrate in a polishing machine and polishing it can be mentioned. The amount of polishing in the finishing polishing is, for example, 100 nm to 500 nm, preferably 150 nm to 400 nm. The thickness of the functional layer 20 after finishing polishing (substantially the thickness of the flat region 23) is, for example, 0.1 μm or more, preferably 0.5 μm to 3.5 μm, and more preferably 0.6 μm to 1.5 μm. If the thickness of the functional layer after finishing polishing is within this range, peeling due to finishing polishing can be suppressed. The surface roughness Sa of the delamination surface of the functional layer 20 after finishing polishing may be, for example, 1.0 nm or less, or for example 0.8 nm or less, or for example 0.6 nm or less, or for example 0.4 nm or less. With such a surface roughness on the peeled surface of the functional layer, for example, a high-performance (e.g., high Q-factor) surface acoustic wave element can be obtained. The surface roughness Sa of the peeled surface of the functional layer 20 may be, for example, 0.05 nm or more, or for example, 0.1 nm or more.

[0061] A composite substrate 100 is obtained through the above process. The composite substrate 100 may be further cleaned and dried. Examples of methods for cleaning the composite substrate include two-fluid cleaning, ultrasonic cleaning, and scrubbing. These cleaning methods may be used individually or in combination of two or more. Examples of methods for drying the composite substrate include IPA drying, spin drying (e.g., spin coating method), Marangoni drying, and Rotagoni drying.

[0062] The present invention will be specifically described below with reference to examples, but the present invention is not limited to these examples. Unless otherwise specified, "parts" and "%" in the examples are based on weight. The measurement and evaluation methods for each characteristic are as follows.

[0063] (1) Method for Calculating the Change in Functional Layer Thickness The thickness of the functional layer of the composite substrates obtained in the examples and comparative examples was measured using an optical film thickness gauge. The thickness of the functional layer in the peripheral region of the functional layer was measured every 10 μm along a line parallel to the orientation flat portion passing through the center of the composite substrate, and the change in the thickness of the functional layer along the line was calculated using the following formula (I). The measurement spot diameter was 5 μm. Formula (I): Change in the thickness of the functional layer per 10 μm of line ([nm]) = (x ｎ [μm] - x ｎ＋１ [μm]) × 1000 where x ｎ x is the thickness of the functional layer at any given measurement point, ｎ＋１ is x ｎ Further outward in the radial direction of the support substrate x ｎ This is the thickness of the functional layer at the measurement point adjacent to the previous one. Based on the numerical value of the change in the thickness of the functional layer per 10 μm line obtained, x is calculated as follows: ｎ From the measurement point x ｎ＋１The region up to the measurement point was determined to fall into one of the following three regions: "Flat region": The change was less than 1.0 nm per 10 μm, or the change was 0. "Gentle slope region": The change was between 1.0 nm and 10.0 nm per 10 μm. "Steep region": The change was greater than 10.0 nm per 10 μm. (2) Evaluation of chipping and peeling of the functional layer The presence or absence of chipping and peeling of the functional layer of the composite substrate obtained in the examples and comparative examples was observed around the entire circumference of the composite substrate using a microscope (product name "ECLIPSE L200N", manufactured by Nikon Solutions Inc.), and the number of chips and peeling of the functional layer was counted and evaluated as follows. Here, chipping and peeling of the functional layer refers to chipping and peeling that originates from the edge of the functional layer on the composite substrate and continues radially inward from the outer peripheral region of the composite substrate to the support substrate (continuing in a region of 5.0 mm or more from the outer peripheral edge of the support substrate). "○": The number of chipped or peeled areas in the functional layer is 3 or less. "△": The number of chipped or peeled areas in the functional layer is 4 or more and 10 or less. "×": The number of chipped or peeled areas in the functional layer is 11 or more. (3) Evaluation of the ratio of the effective area of ​​the functional layer In the functional layer of the composite substrate obtained in the examples and comparative examples, the ratio of the flat area to the area more than 5.0 mm inward from the outer edge of the support substrate in the radial direction of the support substrate was calculated using the method for calculating the change in thickness described in (1) above, and the result was evaluated as the ratio of the effective area as follows: "○": The ratio of the effective area is 95% or more. "△": The ratio of the effective area is 85% or more and less than 95%. "×": The ratio of the effective area is less than 85%.

[0064] <Manufacturing Example 1: Fabrication of Functional Substrates> A roughly disc-shaped lithium tantalate substrate (LiTaO) with a diameter of 100 mm. ３ An orientation flat section and a sub-orientation section were formed on an (LT) substrate (thickness: 500 μm, cutting angle: 46.3°Y). Both sides of the LT substrate were polished to a mirror finish using a double-sided polishing machine. The surface roughness (Sa) of both sides of the LT substrate at this time was 0.2 nm. A handling substrate of the same size as the LT substrate (thickness: 1 mm, material: Al) was also prepared. ２ O ３A handling substrate was prepared, and the handling substrate and the LT substrate were directly bonded by plasma activated bonding to obtain an LT composite substrate. Subsequently, the surface of the LT substrate was cleaned using two-fluid cleaning, ultrasonic cleaning, and scrubbing, and then dried using a spin coater to obtain a functional substrate with a thickness of 1500 μm.

[0065] <Manufacturing Example 2: Fabrication of Support Substrate> A silicon substrate of the same size as the LT substrate in Manufacturing Example 1 (thickness: 525 μm, crystal orientation

[100] , volume resistivity: 10000 Ω・cm) was mirror-finished on both sides using a double-sided polishing machine. At this time, the surface roughness (Sa) of both sides of the silicon substrate was 0.2 nm. Next, the silicon substrate was set in an LP-CVD apparatus and polysilicon layers were formed on both sides of the silicon substrate. The thickness of the formed polysilicon layer was 1.8 μm. After that, this silicon substrate was heated in an oxygen atmosphere at 500°C for 10 hours to form a thermal oxide film (SiO₂) covering the entire circumference of the silicon substrate. ２ A thermal oxide film was formed. The thickness of this thermal oxide film was 0.75 μm. The thermal oxide film on the bonding surface of the silicon substrate was polished to a mirror finish until it was 0.7 μm thick, and its surface roughness (Sa) was set to 0.3 nm. After that, the polished surface was cleaned using two-fluid cleaning, ultrasonic cleaning, and scrubbing, and then dried using a spin coater to obtain a support substrate with a thickness of 525 μm.

[0066] <Example 1> [Ion Implantation Process] A jig (made of SUS) with a rectangular cross-sectional shape along the stacking direction of the composite substrate was installed so as to cover the area corresponding to the outer peripheral region of the composite substrate of the functional substrate obtained in Manufacturing Example 1. The angle between the inner direction of the contact surface of the installed jig and the inner end face was 80°. Next, hydrogen ions were implanted from the bonding surface side of the functional substrate at an energy of 100 keV, at a rate of 1.0 × 10⁻¹⁶ １７ atoms / cm ２Hydrogen ions were injected at a dose of 1.0 μm to a maximum depth. [Bonding process] The functional substrate with the above ion implantation and the support substrate obtained in Manufacturing Example 2 were set in a plasma chamber and treated with plasma hydrophilization by irradiating with nitrogen plasma. The pressure in the plasma chamber during the treatment was 10 Pa and the temperature was 30°C. The functional substrate and support substrate that had undergone plasma hydrophilization were set in a bonding machine and bonded together in an atmospheric environment, with the LT substrate side of the functional substrate and the polished side of the support substrate being bonded together to obtain a bonded body. [First heating process] The bonded body was then heated in an atmospheric environment at 150°C for 10 hours. [Delamination process] Next, the bonded body was heated to 600°C to induce delamination within the functional substrate, forming a functional layer having only a gentle slope region within the outer peripheral region of the composite substrate (within 5.0 mm from the outer peripheral edge of the support substrate), as shown in Figure 3. [Second heating process] The bonded body was then heated in a nitrogen atmosphere at 500°C for 10 hours. [Finishing Polishing Process] Next, the bonded assembly was set in a polishing machine and the peeled surface of the functional layer was polished to 400 nm. The surface roughness (Sa) of the peeled surface of the functional layer was 0.2 nm. Composite substrate A was obtained through the above process. Composite substrate A was cleaned using two-fluid cleaning, ultrasonic cleaning, and scrubbing, and then dried with a spin coater. The thickness of the functional layer was 0.6 μm.

[0067] <Example 2> In the ion implantation process, the angle between the inner direction of the contact surface of the installed jig and the inner end face was changed to 65°, resulting in a functional layer having a flat region and a gently sloping region in the outer peripheral region of the composite substrate, as shown in Figure 4. Otherwise, a composite substrate B was obtained in the same manner as in Example 1. The thickness of the functional layer was 0.6 μm.

[0068] <Example 3> In the ion implantation process, the angle between the inner direction of the contact surface of the installed jig and the inner end face was changed to 50° to create a functional layer having a gently sloping region and a steeply sloping region in the outer peripheral region of the composite substrate, as shown in Figure 5. Otherwise, a composite substrate C was obtained in the same manner as in Example 1. The thickness of the functional layer was 0.6 μm. The surface roughness (Sa) of the peeled surface of the functional layer was 0.2 nm.

[0069] <Example 4> In the ion implantation process, the angle between the inner direction of the contact surface of the installed jig and the inner end face was changed to 35° to create a functional layer having a flat region, a gently sloping region and a steep region in the outer peripheral region of the composite substrate, as shown in Figure 6. Otherwise, a composite substrate D was obtained in the same manner as in Example 1. The thickness of the functional layer was 0.6 μm. The surface roughness (Sa) of the peeled surface of the functional layer was 0.2 nm.

[0070] <Example 5> A composite substrate E was obtained in the same manner as in Example 1, except that a beveling step was added after the peeling step, and the support substrate was beveled from a position 2 mm inward in the diameter direction from the outer edge of the support substrate as shown in Figure 7. The thickness of the functional layer was 0.6 μm. The surface roughness (Sa) of the peeled surface of the functional layer was 0.2 nm.

[0071] <Example 6> A composite substrate F was obtained in the same manner as in Example 2, except that a beveling step was added after the peeling step, and the support substrate was beveled from a position 2 mm inward in the diameter direction from the outer edge of the support substrate. The thickness of the functional layer was 0.6 μm. The surface roughness (Sa) of the peeled surface of the functional layer was 0.2 nm.

[0072] <Example 7> A composite substrate G was obtained in the same manner as in Example 3, except that a beveling step was added after the peeling step, and the support substrate was beveled from a position 2 mm inward in the diameter direction from the outer edge of the support substrate. The thickness of the functional layer was 0.6 μm. The surface roughness (Sa) of the peeled surface of the functional layer was 0.2 nm.

[0073] <Example 8> A composite substrate H was obtained in the same manner as in Example 4, except that a beveling step was added after the peeling step, and the support substrate was beveled from a position 2 mm inward in the diameter direction from the outer edge of the support substrate. The thickness of the functional layer was 0.6 μm. The surface roughness (Sa) of the peeled surface of the functional layer was 0.2 nm.

[0074] <Comparative Example 1> A composite substrate I was obtained in the same manner as in Example 1, except that the angle between the inner direction of the contact surface of the jig installed in the ion implantation process and the inner end face was changed to 20°, resulting in a functional layer without a gentle slope region in the outer peripheral region of the composite substrate, as shown in Figure 8. The thickness of the functional layer was 0.6 μm. The surface roughness (Sa) of the peeled surface of the functional layer was 0.2 nm.

[0075] <Comparative Example 2> A composite substrate J was obtained in the same manner as in Example 1, except that the angle between the inner direction of the contact surface of the jig installed in the ion implantation process and the inner end face was changed to 100°, so that the functional layer had a gently sloping region extending radially inward from the outer edge of the support substrate to 10 mm radially inward from the outer peripheral region of the composite substrate. The thickness of the functional layer was 0.6 μm. The surface roughness (Sa) of the peeled surface of the functional layer was 0.2 nm. The characteristics and evaluation of the composite substrates of Examples 1 to 8 and Comparative Examples 1 to 2 are shown in Table 1.

[0076]

[0077] <Evaluation> As is clear from Table 1, the composite substrates of Examples 1 to 8 exhibit suppressed chipping and peeling compared to the composite substrate of Comparative Example 1, and the effective area of ​​the functional layer is maintained compared to the composite substrates of Comparative Examples 1 and 2.

[0078] The composite substrate of the present invention can be suitably used to fabricate functional elements such as surface acoustic wave elements that can be used in high-frequency communication devices and electro-optic elements that can be used in optical communication devices.

[0079] 10 Support substrate 11 Outer edge of support substrate 20 Functional layer 21 Edge of functional layer 22 Gentle slope region 23 Flat region 24 Steep region 25 Outer edge region 30 Intermediate layer 100 Composite substrate 110 Composite substrate

Claims

1. A composite substrate comprising a functional layer and a support substrate, wherein, in the radial direction of the support substrate, the edge of the functional layer is located inward from the outer peripheral edge of the support substrate, and in the outer peripheral region within 5.0 mm radially inward from the outer peripheral edge of the support substrate, the functional layer has a gently sloping region in which its thickness decreases by an amount of 1.0 nm to 10.0 nm per 10 μm toward the radially outward direction.

2. The composite substrate according to claim 1, wherein at least a portion of the edge of the functional layer is located within the outer peripheral region.

3. The composite substrate according to claim 1 or 2, further comprising an intermediate layer between the support substrate and the functional layer.

4. The composite substrate according to claim 1 or 2, wherein the support substrate is beveled radially outward from the edge of the functional layer.

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