Composite substrate and method of producing same

Abstract

Provided is a composite substrate which maintains an effective region of a functional layer and can be obtained with high productivity. A composite substrate according to an embodiment of the present invention has a functional layer and a support substrate. In the radial direction of the support substrate, an outer peripheral end of the functional layer is located inward of an outer peripheral end of the support substrate. The difference between the maximum value and the minimum value of the distance between the outer peripheral end of the functional layer and the outer peripheral end of the support substrate in the radial direction of the support substrate is 1-1000 μm.

Description

Composite substrate and method for manufacturing the same

[0001] The present invention relates to a composite substrate and a method for manufacturing the same.

[0002] Composite substrates are used in a variety of applications, including personal computers, smartphones, and automobiles. In the manufacturing process of composite substrates, beveling is sometimes performed to pre-cut the area around the outer edge of the functional layer, including the non-adhered area, in order to suppress yield deterioration due to chipping and peeling of the functional layer during the thinning process of the functional layer (see Patent Document 1). When beveling is performed, in order to reliably remove the non-adhered area of ​​the functional layer, the functional layer may be removed from inside the non-adhered area, which reduces the effective area of ​​the functional layer and, as a result, leads to a problem of reduced productivity of composite substrates.

[0003] Japanese Patent Publication No. 2015-126052

[0004] The present invention was made to solve the above-mentioned conventional problems, and its main objective is to provide a composite substrate that can be obtained with high productivity while maintaining the effective area of ​​the functional layer.

[0005] [1] The composite substrate according to an embodiment of the present invention comprises a support substrate and a functional layer, wherein in the radial direction of the support substrate, the outer peripheral edge of the functional layer is located inward from the outer peripheral edge of the support substrate, and the difference between the maximum and minimum distances between the outer peripheral edge of the functional layer and the outer peripheral edge of the support substrate in the radial direction is 1 μm to 1000 μm. [2] In the composite substrate described in item [1] above, the number of locations where the sign of the rate of change (C) expressed by the following formula (I) reverses between the distance (A) at any one location measured multiple times clockwise from any one point along the outermost circumference of the support substrate at intervals of 1.0 μm, and the distance (B) measured at a location 1.0 μm away clockwise from the arbitrary one point along the outermost circumference of the support substrate, is 10 or more and 300 or less: Formula (I): C = (A - B) / A Here, A is the distance between the outer edge of the functional layer and the outer edge of the support substrate at any one location measured multiple times clockwise from any one point along the outermost circumference of the support substrate at intervals of 1.0 μm, and B is the distance between the outer edge of the functional layer and the outer edge of the support substrate measured at a location 1.0 μm away clockwise from the arbitrary one point along the outermost circumference of the support substrate. [3] In the composite substrate described in item [1] or [2] above, the average of the distances is 1 μm to 4000 μm. [4] In the composite substrate described in any of items [1] to [3] above, an intermediate layer is provided between the support substrate and the functional layer. [5] In the composite substrate described in any of items [1] to [4] above, at least a portion of the support substrate is beveled radially outward from the outer peripheral edge of the functional layer. [6] In the composite substrate described in any of items [1] to [5] above, the outer peripheral edge of the functional layer has irregularities radially outward from the functional layer. [7] A method for manufacturing a composite substrate according to an embodiment of the present invention is a method for manufacturing a composite substrate having a support substrate and a functional layer, wherein the outer peripheral edge of the functional layer is located inside the outer peripheral edge of the support substrate in the radial direction of the support substrate, and includes a bonding step of bonding the support substrate and the functional substrate, a thinning step of thinning the functional substrate to form the functional layer, and a removal step of directly applying external force to the non-bonded area of ​​the functional layer to remove the non-bonded area.[8] A method for manufacturing a composite substrate according to another embodiment of the present invention is a method for manufacturing a composite substrate having a support substrate and a functional layer, wherein the outer peripheral edge of the functional layer is located inside the outer peripheral edge of the support substrate in the radial direction of the support substrate, comprising: a bonding step of bonding the support substrate and the functional substrate; a first thinning step of thinning the functional substrate to form a functional layer precursor; a removal step of applying an external force directly to a non-bonded region of the functional layer precursor to remove the non-bonded region; and a second thinning step of thinning the functional layer precursor to form the functional layer. [9] A method for manufacturing a composite substrate according to item [7] or [8] above, wherein the removal step includes applying an external force directly to the non-bonded region using one of the following methods: using an adhesive, using a pressurizing method, or using a vibration method.

[10] A method for manufacturing a composite substrate according to any one of the items [7] to [9] above, wherein in the bonding step, an intermediate layer is formed on at least one of the support substrate and the functional substrate, and the support substrate and the functional substrate are bonded together via the intermediate layer.

[11] In the method for manufacturing a composite substrate according to any of the above items [7] to

[10] , the removal step is performed after the thickness of the functional substrate has been reduced to 0.5 μm to 30 μm.

[12] In the method for manufacturing a composite substrate according to any of the above items [7] to

[11] , the removal step is further followed by an adhesive removal step of removing the adhesive.

[13] In the method for manufacturing a composite substrate according to any of the above items [7] to

[12] , the heating step is further included.

[0006] According to embodiments of the present invention, it is possible to provide a composite substrate that maintains the effective area of ​​the functional layer and can be obtained with high productivity.

[0007] 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. 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 schematic plan view and an enlarged plan view of a key part of a composite substrate according to one embodiment of the present invention, viewed from the direction of its main surface. Figure 4 is a schematic enlarged plan view of a key part of a composite substrate according to one embodiment of the present invention, viewed from the direction of its main surface.

[0008] The embodiments of the present invention will be described below, but the present invention is not limited to these embodiments. While the drawings may schematically represent the width, thickness, shape, etc., of each part compared to the embodiments in order to clarify the explanation, 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 composite substrate 100 in the illustrated example 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 composite substrate 110 may have 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] In the illustrated example of the composite substrate 100, typically, the outer peripheral edge 21 of the functional layer 20 may be located inside the outer peripheral edge 11 of the support substrate 10 in the radial direction.

[0012] Figure 3 is a schematic enlarged plan view of a main part of a composite substrate according to one embodiment of the present invention, viewed from the direction of its main surface. In the embodiment of the present invention, the composite substrate 100, as typically shown in Figure 3, has irregularities on the outer peripheral edge 21, which is the side surface of the functional layer 20, toward the radially outward direction of the functional layer. Furthermore, the difference between the maximum and minimum values ​​of the distance (hereinafter sometimes referred to as distance or distance D) between the outer peripheral edge of the functional layer and the outer peripheral edge of the support substrate in the radial direction of the support substrate is 1 μm to 1000 μm. In the illustrated example, the difference between the maximum value D1 and the minimum value D2 of the distance is 1 μm to 1000 μm. The inventors have diligently studied how to maximize the effective area of ​​the functional layer in a composite substrate and have found that by directly applying an external force to the non-adhered area of ​​the functional layer (functional layer precursor) and removing that non-adhered area, the adhesive area of ​​the functional layer can be maximized. Furthermore, by removing the non-adhered region of the functional layer (functional layer precursor) in this manner, it was found that irregularities are formed such that the difference between the maximum and minimum distances between the outer peripheral edge of the functional layer and the outer peripheral edge of the support substrate in the radial direction is 1 μm to 1000 μm. In other words, the inventors have found that the effective area of ​​the functional layer can be maximized by having such irregularities on the outer peripheral edge of the functional layer, and have completed the present invention.

[0013] In the composite substrate 100 according to an embodiment of the present invention, the maximum value D1 of distance D is, for example, 1000 μm to 5000 μm, preferably 1000 μm to 4000 μm, and more preferably 1000 μm to 3000 μm. Also, in the composite substrate 100, the minimum value D2 of distance D is, for example, 500 μm to 4000 μm, preferably 500 μm to 3000 μm, and more preferably 500 μm to 2000 μm. The maximum value D1 and minimum value D2 of distance D are determined by identifying measurement points at the outer peripheral edge of the functional layer and the outer peripheral edge of the support substrate at intervals of 1.0 μm clockwise from an arbitrary point along the outermost circumference of the support substrate, measuring the distance between the outer peripheral edge of the functional layer and the outer peripheral edge of the support substrate in the radial direction of the support substrate, and extracting the maximum and minimum values ​​of distance from the obtained distances between the outer peripheral edge of the functional layer and the outer peripheral edge of the support substrate in the radial direction of the support substrate. As shown in Figure 3, the difference between the maximum distance D1 and the minimum distance D2 (the difference between the maximum and minimum distances between the outer peripheral edge of the functional layer and the outer peripheral edge of the support substrate in the radial direction of the support substrate) is typically 1 μm to 1000 μm, preferably 5 μm to 500 μm, more preferably 5 μm to 300 μm, even more preferably 10 μm to 200 μm, and particularly preferably 10 μm to 100 μm. If the difference between the maximum distance D1 and the minimum distance D2 is within this range, the area for attaching the functional layer can be maximized, and as a result, the effective area of ​​the functional layer can be maximized, and high productivity of the composite substrate can be obtained. The outer peripheral edge 11 of the support substrate 10 is the outermost region when viewing the composite substrate 100 from the main surface direction of the support substrate 10.

[0014] The average (arithmetic mean) of distance D is, for example, 1 μm to 4000 μm, preferably 500 μm to 2000 μm, more preferably 500 μm to 1300 μm, even more preferably 500 μm to 1000 μm, and particularly preferably 500 μm to 850 μm. If the average distance is within this range, it is possible to suitably provide the effective area necessary for manufacturing the device. The average distance D is calculated by identifying measurement points at the outer peripheral edge of the functional layer and the outer peripheral edge of the support substrate at intervals of 1.0 μm clockwise from an arbitrary point along the outermost circumference of the support substrate, measuring the distance between the outer peripheral edge of the functional layer and the outer peripheral edge of the support substrate in the radial direction of the support substrate, and taking the arithmetic mean of the obtained distances between the outer peripheral edge of the functional layer and the outer peripheral edge of the support substrate in the radial direction of the support substrate.

[0015] Figure 4 is a schematic enlarged plan view of a main part of a composite substrate 100 according to one embodiment of the present invention, viewed from the direction of its main surface. In the illustrated example of the composite substrate 100, the number of locations where the sign of the rate of change C, expressed by the following formula (I), is reversed between a distance A at any one point measured multiple times at 1.0 μm intervals clockwise from any one point along the outermost circumference of the support substrate 10, and a distance B measured at a point 1.0 μm away from that point along the outermost circumference of the support substrate 10, is, for example, 10 to 300 locations, preferably 20 to 200 locations, more preferably 30 to 100 locations, and even more preferably 50 to 80 locations. If the number of locations where the sign of the rate of change C is reversed is within this range, peeling of the functional layer during the manufacturing process can be suppressed. Equation (I): C = (A - B) / A Here, distance A is the distance between the outer edge of the functional layer and the outer edge of the support substrate at any one of several measurements taken along the outermost circumference of the support substrate at intervals of 1.0 μm clockwise from any one point, and distance B is the distance between the outer edge of the functional layer and the outer edge of the support substrate measured at a point 1.0 μm apart clockwise along the outermost circumference of the support substrate from the aforementioned arbitrary point.

[0016] In the composite substrate 100, for example, at least a portion of the support substrate 10 is beveled radially outward from the outer peripheral edge 21 of the functional layer 20, and preferably, the entire outer circumference of the support substrate 10 is beveled radially outward from the outer peripheral edge 21 of the functional layer 20. With such a configuration, the visibility of the front and back sides of the composite substrate can be improved, and furthermore, if the composite substrate has an intermediate layer, delamination of the intermediate layer can be suppressed. Note that the position of the radial beveling of the support substrate can be any appropriate position as long as it is outside the outer peripheral edge of the functional layer.

[0017] The thickness of the composite substrate 100 is, for example, 200 μm to 2000 μm, preferably 300 μm to 1000 μm. If the composite substrate 100 has an intermediate layer 30, the thickness of the composite substrate 100 includes the thickness of the intermediate layer 30. The diameter of the composite substrate 100 is substantially the diameter of the support substrate 10, preferably 80 mm to 200 mm, more preferably 100 mm to 200 mm.

[0018] The following describes each component of the composite substrate in detail. B. Support Substrate Any suitable substrate can be used as the support substrate 10. The support substrate may be composed of a single crystal, a polycrystalline material, or a combination thereof. Examples of materials that make up the support substrate include silicon, sapphire, sialon, cordierite, mullite, glass, quartz glass, crystal, alumina, germanium, silicon carbide, gallium nitride, indium phosphide, and aluminum nitride. Preferably, the support substrate contains at least one material from silicon, silicon carbide, gallium nitride, and glass, more preferably contains silicon, and even more preferably consists of silicon.

[0019] The silicon mentioned above may be single-crystal silicon, polycrystalline silicon (polysilicon), high-resistance silicon, or a combination thereof. Furthermore, a thermal oxide film (silicon oxide (SiO₂)) may be formed by heating the silicon. ２ )) may be formed.

[0020] Any appropriate thickness can be used for the support substrate 10. The thickness of the support substrate is, for example, 200 μm to 2000 μm, and preferably 300 μm to 1000 μm.

[0021] The surface roughness Sa of 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 of the functional layer side of the support substrate, for example, a high-performance (e.g., one with a high Q value) surface acoustic wave element can be obtained. Note that the surface roughness Sa is a value measured by the stylus scanning method of JIS B 0681-6:2014.

[0022] C. Functional Layer The outer peripheral end 21, which is the side surface of the functional layer 20, has irregularities toward the radially outward direction of the functional layer, as described above. The outer peripheral end 21 of the functional layer 20 may be a curved surface if it is the side surface of the functional layer 20, and may include a chamfered portion. The difference between the maximum and minimum length of the functional layer 20 from the center of the functional layer 20 to the outer peripheral end 21 of the functional layer 20 in the radial direction is, for example, 1 μm to 1000 μm, preferably 5 μm to 500 μm, and more preferably 10 μm to 200 μm. If the difference between the maximum and minimum length of the functional layer from the center of the functional layer to the outer peripheral end of the functional layer in the radial direction is within this range, the irregularities on the outer peripheral end of the functional layer can suppress peeling of the functional layer from the support substrate. The difference between the maximum and minimum values ​​of the length from the center of the functional layer to its outer edge in the radial direction is calculated by identifying measurement points at the outer edge of the functional layer at 1.0 μm intervals clockwise from an arbitrary point along the outermost edge of the support substrate, measuring the length from the center of the functional layer (composite substrate) to its outer edge in the radial direction, and extracting the maximum and minimum values ​​of the obtained length from the center of the functional layer (composite substrate) to its outer edge in the radial direction.

[0023] 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 may 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. Specific materials constituting the functional substrate include, for example, lithium niobate (LiNbO ３ : LN), lithium tantalate (LiTaO ３ : LT), lithium niobate-lithium tantalate solid solution, potassium titanyl phosphate (KTiOPO ４ : KTP), potassium lithium niobate (K ｘ Li （１－ｘ） NbO ２ , 0≦x≦1: KLN), potassium niobate (KNbO ３ : KN), potassium tantalate niobate (KNb ｘ Ta （１－ｘ） O ３ , 0≦x≦1: KTN), silicon carbide, quartz, quartz glass, silicon carbide, aluminum oxide, gallium nitride, indium phosphide, silicon, lead zirconate titanate (PZT).

[0024] The thickness of the functional layer 20 is, for example, 30 µm or less, preferably 10 µm or less, more preferably 5 µm or less, still more preferably 1 µm or less, particularly preferably 0.5 µm or less, and most preferably 0.4 µm or less. The thickness of the functional layer 20 may be, for example, 0.1 µm or more, and may also be, for example, 0.2 µm or more. When the thickness of the functional layer is within this range, the non-adhesion region can be suitably removed during the removal step. Hereinafter, a piezoelectric layer and an electro-optical layer will be described as representative examples of the functional layer. However, it is obvious to those skilled in the art that the effect according to the embodiment of the present invention does not depend on the type of the functional layer.

[0025] 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, 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.

[0026] 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.

[0027] 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°).

[0028] The thickness of the piezoelectric layer is, for example, 30 µm or less, preferably 10 µm or less, more preferably 5 µm or less, still more preferably 1 µm or less, and particularly preferably 0.5 µm or less. With such a thickness of the piezoelectric layer, for example, a high-performance surface acoustic wave element (for example, having favorable temperature characteristics and / or a high Q value) can be obtained. On the other hand, the thickness of the piezoelectric layer may be, for example, 0.1 µm or more, or may be, for example, 0.2 µm or more.

[0029] The electro-optical layer may be produced from any appropriate electro-optic crystal substrate. Any appropriate electro-optic crystal material may be used as a material constituting the electro-optic crystal substrate (a material having an electro-optic effect). Examples of such materials include those similar to piezoelectric materials. Note that the electro-optical layer may be the electro-optic crystal substrate itself.

[0030] Part or all of the electro-optical layer can serve as an optical waveguide that transmits light in an electro-optical element. That is, the electro-optical layer has a photonic band structure similar to the electron band structure, and can develop a photonic band gap for light. When a line defect that disturbs periodicity is introduced into an electro-optical layer having a photonic band gap, a guided mode is formed within the frequency region of the band gap, and an optical waveguide that propagates light with low loss can be realized. The optical constant (for example, refractive index) of the electro-optical layer can change when an electric field is applied thereto.

[0031] The thickness of the electro-optical layer may be set to any appropriate thickness depending on the purpose. The thickness of the electro-optical layer may be, for example, 0.1 µm to 10 µm, and preferably 0.2 µm to 10 µm. When the lower limit of the thickness of the electro-optical layer falls within such a range, light propagation loss in the electro-optical element can be reduced. On the other hand, the thickness of the electro-optical layer is preferably 5.0 µm or less, more preferably 2.5 µm or less, still more preferably 1.0 µm or less, and particularly preferably 0.5 µm or less. When the upper limit of the thickness of the electro-optical layer falls within such a range, the high-speed and low-voltage driving performance of the electro-optical element can be improved. Therefore, driving at higher speed and lower voltage can be realized while suppressing an increase in light propagation loss.

[0032] The surface roughness Sa of the functional layer 20 may be, for example, 1.0 nm or less, may be for example 0.8 nm or less, may be for example 0.6 nm or less, and may be for example 0.4 nm or less. With such a surface roughness of the functional layer, for example, a high-performance surface acoustic wave element (for example, having a high Q value) can be obtained. The surface roughness Sa of the functional layer 20 can be, for example, 0.05 nm or more, and can be, for example, 0.1 nm or more.

[0033] D. Intermediate Layer As described above, the composite substrate may have an intermediate layer. Examples of the intermediate layer include a dielectric layer, an ionized layer, 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 can be, for example, the same as that of the support substrate described above.

[0034] The above intermediate layer can be formed by any appropriate method. For example, it can be formed by physical vapor deposition such as sputtering and ion beam assisted deposition (IAD), chemical vapor deposition, or atomic layer deposition (ALD).

[0035] E. Method for Producing Composite substrate A method for producing a composite substrate 100 according to one embodiment of the present invention typically includes a bonding step of bonding a support substrate 10 and a functional substrate, a thinning step of thinning the bonded functional substrate to form a functional layer 20, and a removing step of removing a non-bonded region of the functional layer 20 with an adhesive. In this embodiment, after the thickness of the functional substrate is thinned to, for example, 0.1 μm to 30 μm, preferably 0.5 μm to 30 μm to form the functional layer in the thinning step, the removing step is performed, whereby the functional layer 20 can be formed.

[0036] In the above-described embodiment, the removal step was performed after the functional layer was formed in the thin-filming step, but in another embodiment, the removal step is performed during the thin-filming step. Specifically, the method for manufacturing the composite substrate 100 according to another embodiment includes a bonding step of bonding the support substrate 10 and the functional substrate, a first thin-filming step of forming a functional layer precursor by thinning the bonded functional substrate, a removal step of removing the non-bonded area of ​​the functional layer precursor with an adhesive, and a step of forming a functional layer 20 by thinning the functional layer precursor. In this embodiment, after forming a functional layer precursor with a thickness of, for example, 0.5 μm to 30 μm in the first thin-filming step, a removal step is performed, and then a second thin-filming step is performed, thereby forming a functional layer with a thickness of, for example, 0.1 μm or more and less than 0.5 μm. The following describes each step of the method for manufacturing the composite substrate in detail. The thin-filming step will be described in the case where the first thin-filming step and the second thin-filming step are performed.

[0037] E-1. Bonding Process In the bonding process, the support substrate and the functional substrate are bonded together. The support substrate and the functional substrate are bonded together via an adhesive layer or by direct bonding. If the composite substrate has an intermediate layer, an intermediate layer is formed on at least one of the support substrate and the functional substrate, and the support substrate and the functional substrate are bonded together via the intermediate layer. Specifically, an intermediate layer is formed on the bonding surface of either the support substrate or the functional substrate, and the bonding surface of the support substrate or functional substrate that does not have an intermediate layer is bonded to the intermediate layer via an adhesive layer or by direct bonding. Alternatively, for example, an intermediate layer may be formed on each of the bonding surfaces of both the support substrate and the functional substrate, and the intermediate layers may be bonded together via an adhesive layer or by direct bonding.

[0038] In the bonding process, for example, the support substrate 10 and the functional substrate are each subjected to plasma hydrophilic treatment, and then the support substrate 10 and the functional substrate are bonded together directly. 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 hydrophilic treatment.

[0039] 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.

[0040] 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 ６ In Pa), the plasma-hydrophilized surfaces of the support substrate and the functional substrate are directly bonded together. This directly bonds the support substrate and the functional substrate, resulting in a bonded body in which the functional substrate has bonded and non-bonded regions.

[0041] E-2. 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. Performing the first heating step can improve the bonding strength of each layer.

[0042] 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.

[0043] E-3. First Thinning Process In the first thinning process, the surface of the obtained bonded body opposite to the bonding surface of the functional substrate is thinned by, for example, grinding and then polishing to form a functional layer precursor. Grinding methods include, for example, grinding with a grinder. Polishing methods include, for example, mirror polishing by chemical mechanical polishing (CMP) or lapping. Chemical mechanical polishing is preferably employed. Specifically, chemical mechanical polishing using a polishing pad with a polishing slurry (for example, colloidal silica) is employed.

[0044] Instead of thinning by grinding and polishing as described above, thinning by ion implantation may be used. In the ion implantation method, before the bonding process, ions are implanted into the functional substrate from the bonding surface side of the prepared functional substrate. In the first thinning process, heating causes the functional substrate to peel off at the surface where the ions have been implanted to the maximum depth, resulting in thinning of the functional substrate and the formation of a functional layer precursor. Examples of ions include hydrogen ions and helium ions. The energy amount when implanting ions is, for example, 30 keV to 300 keV, preferably 50 keV to 100 keV. The dose amount when implanting ions is, for example, 1.0 × 10⁻⁶ １６ atoms / cm ２ ~5.0 x 10 １７ atoms / cm ２ Preferably 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 0.4 μm to 1.5 μm, and more preferably 0.5 μm to 1.0 μm. The heating temperature for peeling is, for example, greater than 250°C and 600°C or less, preferably 300°C or more and 500°C or less.

[0045] The thickness of the functional layer precursor after the first thin-film formation step is, for example, 0.5 μm to 30 μm, preferably 0.5 μm to 10 μm, and more preferably 0.5 μm to 5 μm. If the thickness of the functional layer precursor after the first thin-film formation step is within this range, the non-attached region of the functional layer precursor can be suitably removed in the removal step.

[0046] E-4. Removal Step Next, in the removal step, an external force is applied directly to the non-adhered region of the functional layer precursor in the bonded body to remove the non-adhered region. Specifically, the removal step includes applying an external force directly to the non-adhered region of the functional layer precursor using one of the following methods: using an adhesive, using a pressurizing method, or using a vibration method. The preferred method for applying an external force directly to the non-adhered region of the functional layer precursor is the method using an adhesive. Using an adhesive allows for the efficient production of composite substrates.

[0047] As a method using adhesive, specifically, adhesive is applied from above to the non-adhered area of ​​the functional layer precursor, and the adhesive is peeled off upwards. This tears the non-adhered area of ​​the functional layer precursor away from the adhered area and removes it along with the adhesive. Preferably, as a method using adhesive, the adhesive is applied to the non-adhered area near the boundary between the adhered and non-adhered areas of the functional layer precursor. By peeling off the adhesive at this application point, the non-adhered area of ​​the functional layer precursor can be removed near the boundary on the non-adhered side of the functional layer precursor, further favorably maintaining the effective area of ​​the functional layer. As a method using pressure, for example, water pressure is applied to the non-adhered area of ​​the functional layer precursor, or the non-adhered area of ​​the functional layer precursor is wiped. As a method using vibration, for example, ultrasound (e.g., ultrasound in the range of 1 kHz to 1 MHz) is applied to the non-adhered area of ​​the functional layer precursor. Furthermore, methods using pressurization and vibration can also serve to clean the functional layer precursor.

[0048] Examples of adhesives include adhesive tapes and rollers with adhesive tapes. The adhesive force of the adhesive to the functional layer (functional layer precursor) is, for example, 0.10 N / 10 mm to 10 N / 10 mm, and more preferably 1.0 N / 10 mm to 5.0 N / 10 mm. If the adhesive force of the adhesive is within this range, the non-adhered area of ​​the functional layer precursor can be suitably removed. The adhesive force of the adhesive is measured by a 90° peel test in accordance with JIS Z 0237:2009. The force applied to the adhesive to peel it upward (initial peel force) is, for example, 0.10 N to 5.0 N, and preferably 1.0 N to 3.0 N. If the force applied to the adhesive is within this range, the non-adhered area of ​​the functional layer precursor can be suitably removed. The force applied to the adhesive is a value measured by a force gauge in accordance with JIS B 7721:2018.

[0049] E-5. 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 removal step described above. In the second heating step, the functional layer (functional layer precursor) is heated while it is still in a thin film state, so the second heating step can be performed at a higher temperature than the first heating step, and even in a bond with a large difference in thermal expansion coefficients, cracking can be suppressed during heating, and a bond with stronger bonding strength than when the first heating step is performed can be obtained. Furthermore, the heating step preferably includes both the first heating step and the second heating step described above. By performing both the first heating step and the second heating step, even stronger bonding strength can be obtained, thus suppressing peeling in subsequent steps.

[0050] 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 This is carried out in Pa, preferably in a vacuum (for example, 1.0 × 10⁻⁶). －６ The heating 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 10 hours, preferably 1 hour to 5 hours.

[0051] E-6. Adhesive Removal Process The manufacturing method of the composite substrate 100 preferably includes an adhesive removal process for removing the adhesive. In the manufacturing method of the composite substrate 100, the adhesive removal process is preferably performed after the second heating process, and more specifically, the adhesive removal process is performed before or simultaneously with the second thin-film formation process described later. Examples of adhesive removal methods include polishing of the functional layer precursor and cleaning with a chemical solution. These adhesive removal methods may be used individually or in combination of two or more. Examples of chemical solutions include acidic cleaning agents and alkaline cleaning agents.

[0052] E-7. Second Thin-Film Forming Step The manufacturing method of the composite substrate 100 preferably includes a second thin-film forming step. For example, the polishing method described above is used as the second thin-film forming step, and the functional layer precursor is thinned to form the functional layer 20. The second thin-film forming step may also serve as an adhesive removal step. The thickness of the functional layer 20 after the second thin-film forming step is, for example, 0.1 μm or more and less than 0.5 μm, preferably 0.2 μm or more and 0.4 μm or less. If the thickness of the functional layer after the second thin-film forming step is within this range, high frequencies of a specific wavelength can be excited, and the light confinement effect can be enhanced.

[0053] A composite substrate 100 is obtained from the above process. The composite substrate may be 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.

[0054] 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.

[0055] (1) Thickness measurement method: Thickness was measured using an optical interference film thickness measuring device. (2) Method of measuring the distance between the outer edge of the functional layer and the outer edge of the support substrate in the radial direction of the support substrate: The distance between the outer edge of the functional layer and the outer edge of the support substrate in the radial direction of the support substrate was measured using a microscope (product name "ECLIPSE L200N", manufactured by Nikon Solutions Inc.). Specifically, first, the coordinates of the outer edge of the support substrate were measured at multiple points in the planar direction of the composite substrate, and the center coordinates of the composite substrate were calculated from these coordinates. The center coordinates of the composite substrate were then matched with the center coordinates of the rotation axis of the microscope stage. Next, while visually observing the composite substrate using a microscope, the microscope stage was rotated clockwise around its axis of rotation, ensuring that the center of the composite substrate did not shift. Along the entire circumference of the support substrate, the coordinates of measurement points at the outer edges of the functional layer and the support substrate were identified at intervals of 1.0 μm clockwise from an arbitrary point along the outermost edge of the support substrate. The distance between the outer edges of the functional layer and the support substrate in the radial direction was measured using image processing within the software (NIS-Elements D). For visual observation, a sample stage was used that allowed rotation of the composite substrate in the radial direction in addition to movement along the x and y axes. The difference between the maximum and minimum distances between the outer edges of the functional layer and the support substrate in the radial direction was calculated by extracting the maximum and minimum distances from the distances obtained above. The average distance was calculated by taking the arithmetic mean of the distances obtained above between the outer edges of the functional layer and the support substrate in the radial direction. (3) Method for measuring the length of the functional layer from its center to its outer edge in the radial direction The length of the functional layer from its center to its outer edge in the radial direction was measured using a microscope (product name "ECLIPSE L200N", manufactured by Nikon Solutions Inc.). Specifically, first, the coordinates of multiple points on the outer edge of the support substrate were measured in the planar direction of the composite substrate, and the center coordinates of the composite substrate were calculated from these coordinates. The center coordinates of the composite substrate were then matched with the center coordinates of the rotation axis of the microscope stage.Next, while visually observing the outer edge of the functional layer using a microscope, the microscope stage was rotated clockwise around its axis of rotation, ensuring that the center of the composite substrate did not shift. Along the entire circumference of the support substrate, the coordinates of measurement points on the outer edge of the functional layer were identified at intervals of 1.0 μm clockwise from an arbitrary point along the outermost edge of the support substrate, and the length from the center of the functional layer to the outer edge of the functional layer in the radial direction was measured using image processing in the software (NIS-Elements D). For visual observation, a sample stage was used that allowed rotation of the composite substrate in the radial direction in addition to movement along the x and y axes. The difference between the maximum and minimum values ​​of the length from the center of the functional layer to the outer edge of the functional layer in the radial direction was calculated by extracting the maximum and minimum values ​​from the lengths obtained above. (4) Measurement method of surface roughness Sa The surface roughness Sa was measured using an atomic force microscope in accordance with the stylus scanning method of JIS B 0681-6:2014. (5) Method for measuring the adhesive strength of the adhesive The adhesive strength of the adhesive was measured by performing a 90° peel test in accordance with JIS Z 0237:2009 at a measurement temperature of 23°C and a peeling speed of 300 mm / min. (6) Evaluation of chipping and peeling at a point 0.3 μm inward from the outer edge of the functional layer The presence or absence of chipping and peeling of the functional layer at a point 0.3 μm radially inward from the outer edge of the functional layer to the support substrate, obtained in the examples and comparative examples, was observed using a microscope (product name "ECLIPSE L200N", manufactured by Nikon Solutions Co., Ltd.) and evaluated as follows: "○": There were 3 or fewer chipping / peeling locations. "△": There were 4 to 10 chipping / peeling locations. "×": There were 11 or more chipping / peeling locations. (7) Evaluation of the effective area of ​​the functional layer In the composite substrates obtained in the examples and comparative examples, imaging was performed on the entire surface of the composite substrate using a microscope, and image processing was performed to express the area of ​​the remaining functional layer as a percentage, with the area of ​​the support substrate set to 100%, and the effective area of ​​the functional layer was evaluated as follows: "○": 96% or more. "△": 92% or more and less than 96%. "×": Less than 92%.

[0056] <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 mirror-polished using a double-sided polishing machine to achieve a surface roughness (Sa) of 0.2 nm on both sides of the LT substrate. A handling substrate of the same size as the LT substrate (thickness: 1 mm, material: Al ２ O ３ A handling substrate was prepared, and a thermosetting resin was spin-coated onto it to bond the handling substrate and the LT substrate by heating. After that, the surface of the LT substrate was cleaned using two-fluid cleaning, ultrasonic cleaning, and scrubbing, and then dried with a spin coater to obtain a functional substrate with a thickness of 1500 μm.

[0057] <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-polished on both sides using a double-sided polishing machine to achieve a surface roughness (Sa) of 0.2 nm on both sides of the silicon substrate. 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. Subsequently, 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 side of the silicon substrate that would be joined to the functional substrate was polished to a mirror finish until it was 0.70 μm thick, and its surface roughness (Sa) was reduced 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.

[0058] <Example 1> [Bonding Process] The functional substrate obtained in Manufacturing Example 1 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 inside the plasma chamber during the treatment was 10 Pa and the temperature was 30°C. The plasma hydrophilized functional substrate and support substrate were each 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 to obtain a bonded body. The peel force of the functional substrate (functional layer) from the support substrate was 3.0 N / 10 mm or more. [First Heating Process] The obtained bonded body was then heated in an atmospheric environment at 150°C for 10 hours. [First Thinning Process] Furthermore, the bonded body was set in a grinder and ground to reduce the thickness of the functional substrate to 30 μm. Next, the bonded body was set in a polishing machine and polished to reduce the thickness of the functional substrate to 28 μm, forming a functional layer precursor. [Removal Process] Next, an adhesive tape (width 15,000 μm, adhesive strength: 1.5 N / 10 mm) was applied to the edge of the non-adhesive region of the functional layer precursor of the bonded body on the adhesive region side (the circumference 5,000 μm from the outer edge of the functional layer precursor). Then, it was peeled off upward with a force of 3.0 N to remove the adhesive tape along with the non-adhesive region of the functional layer precursor. The force applied when peeling upward was measured using a force gauge (product name "ZTS-200N", manufactured by IMADA Corporation). [Second Heating Process] After that, the bonded body was heated at 500°C for 5 hours in an atmospheric environment. [Second Thinning Process and Adhesive Removal Process] Next, the bonded body was set in a polishing machine again to thin the functional layer precursor by polishing, and residual adhesive on the surface of the functional layer precursor was removed using a chemical solution. This formed a functional layer with a thickness of 0.3 μm. This obtained composite substrate A, which was then subjected to two-fluid cleaning, ultrasonic cleaning and scrubbing, and dried with a spin coater.

[0059] <Example 2> In the first thin-film formation step, the thickness of the functional layer precursor was reduced to 10 μm instead of 28 μm by polishing, except that the procedure was the same as in Example 1 to obtain composite substrate B.

[0060] <Example 3> A composite substrate C was obtained in the same manner as in Example 1, except that in the first thin-film formation step, the thickness of the functional layer precursor was reduced to 1.5 μm by polishing instead of 28 μm, and the first and second heating steps were not performed.

[0061] <Example 4> In the first thin-film formation process, instead of polishing to make the thickness of the functional layer precursor 28 μm, hydrogen ions were introduced to a depth of 1.0 μm from the side of the functional substrate that is bonded to the support substrate in Manufacturing Example 1, at 60 keV, 6.0 × 10 １６ atoms / cm ２ A composite substrate D was obtained in the same manner as in Example 1, except that the material was injected, heated to 300°C in the first thin-film formation step of Example 1 to reduce the thickness of the functional layer precursor to 1.0 μm, and then polished to reduce the thickness of the functional layer precursor to 0.5 μm.

[0062] <Comparative Example 1> Only the bonding step and thinning step of Example 1 were performed, and when the thickness of the functional layer precursor was 30 μm, the bonded body was beveled in the conventional manner (from the bonding area of ​​the functional layer precursor) to obtain a composite substrate E.

[0063] <Comparative Example 2> Only the bonding step and thinning step of Example 1 were performed to obtain a composite substrate F, but chipping and peeling occurred during the thinning step to reduce the thickness of the functional layer precursor to 0.3 μm.

[0064] <Comparative Example 3> A composite substrate G was obtained in the same manner as in Example 1, except that the thickness of the functional layer precursor during the removal process was changed from 28 μm to 45 μm, and the heating process was not performed.

[0065] Table 1 shows the characteristics and evaluation of the composite substrates of Examples 1 to 4 and Comparative Examples 1 to 3.

[0066]

[0067] <Evaluation> As is clear from Table 1, the composite substrates of Examples 1 to 4 exhibit suppressed chipping and peeling compared to the composite substrates of Comparative Examples 2 and 3, and the effective area of ​​the functional layer is maintained compared to the composite substrates of Comparative Examples 1 to 3.

[0068] 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.

[0069] 10 Support substrate 11 Outer edge of support substrate 20 Functional layer 21 Outer edge of functional layer 30 Intermediate layer 100 Composite substrate 110 Composite substrate

Claims

1. A composite substrate comprising a support substrate and a functional layer, wherein, in the radial direction of the support substrate, the outer peripheral edge of the functional layer is located inward from the outer peripheral edge of the support substrate, and the difference between the maximum and minimum distances between the outer peripheral edge of the functional layer and the outer peripheral edge of the support substrate in the radial direction of the support substrate is 1 μm to 1000 μm.

2. In an arbitrary 1 mm range along the outermost circumference of the support substrate, the number of locations where the sign of the rate of change (C) expressed by the following formula (I) reverses between the distance (A) measured at an arbitrary point among multiple measurements taken at 1.0 μm intervals clockwise from an arbitrary point along the outermost circumference of the support substrate and the distance (B) measured at a location 1.0 μm away from the arbitrary point along the outermost circumference of the support substrate is 10 to 300: Formula (I): C = (A - B) / A where A is the distance between the outer edge of the functional layer and the outer edge of the support substrate at an arbitrary point among multiple measurements taken at 1.0 μm intervals clockwise from an arbitrary point along the outermost circumference of the support substrate, and B is the distance between the outer edge of the functional layer and the outer edge of the support substrate measured at a location 1.0 μm away from the arbitrary point along the outermost circumference of the support substrate.

3. The composite substrate according to claim 1 or 2, wherein the average of the distances is 1 μm to 4000 μm.

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

5. The composite substrate according to claim 1 or 2, wherein at least a portion of the support substrate is beveled radially outward from the outer peripheral edge of the functional layer.

6. The composite substrate according to claim 1 or 2, wherein the outer peripheral edge of the functional layer has irregularities on the radially outward side of the functional layer.

7. A method for manufacturing a composite substrate having a support substrate and a functional layer, wherein the outer peripheral edge of the functional layer is located inside the outer peripheral edge of the support substrate in the radial direction of the support substrate, the method comprising: a bonding step of bonding the support substrate and the functional substrate; a thinning step of thinning the functional substrate to form the functional layer; and a removal step of directly applying an external force to the non-bonded area of ​​the functional layer to remove the non-bonded area.

8. A method for manufacturing a composite substrate having a support substrate and a functional layer, wherein the outer peripheral edge of the functional layer is located inside the outer peripheral edge of the support substrate in the radial direction of the support substrate, the method comprising: a bonding step of bonding the support substrate and the functional substrate; a first thin-filming step of thinning the functional substrate to form a functional layer precursor; a removal step of directly applying external force to a non-bonded region of the functional layer precursor to remove the non-bonded region; and a second thin-filming step of thinning the functional layer precursor to form the functional layer.

9. The manufacturing method according to claim 7 or 8, wherein the removal step includes applying an external force directly to the non-adhered area using one of the following methods: using an adhesive, using a pressurizing method, or using a vibration method.

10. The manufacturing method according to claim 7 or 8, wherein in the bonding step, an intermediate layer is formed on at least one of the support substrate and the functional substrate, and the support substrate and the functional substrate are bonded together via the intermediate layer.

11. The manufacturing method according to claim 7 or 8, wherein the removal step is performed after the thickness of the functional substrate has been reduced to 0.5 μm to 30 μm.

12. The manufacturing method according to claim 7 or 8, further comprising an adhesive removal step of removing the adhesive after the removal step.

13. The manufacturing method according to claim 7 or 8, further comprising a heating step.

Images