Composite substrate

Abstract

Provided is a composite substrate having excellent bonding strength and excellent uniformity of a diamond layer. A composite substrate according to an embodiment of the present invention has a support substrate and a single crystal diamond layer directly bonded to the support substrate. In one embodiment, the composite substrate also has a cladding layer between the support substrate and the single crystal diamond layer. The cladding layer is formed on the support substrate and / or the single crystal diamond layer, and the support substrate and the single crystal diamond layer are bonded via the cladding layer.

Description

Composite PCB

[0001] The present invention relates to a composite substrate.

[0002] Diamond is known as an excellent semiconductor, possessing the following properties: (i) it is a wide-bandgap semiconductor with a wide bandgap of 5.47 eV at room temperature; (ii) it has an extremely high breakdown field strength of 10 MV / cm, enabling high-voltage operation; (iii) it has the highest thermal conductivity of any known material, resulting in excellent heat dissipation; (iv) it has extremely high carrier mobility and saturated drift velocity, making it suitable for high-speed devices; and (v) as a result of the above, it has an extremely high Johnson figure of merit, which indicates its performance as a high-frequency, high-power device. In addition, diamond can contain color centers (defect structures formed in solid materials such as diamond that absorb light and / or emit light upon external excitation), such as nitrogen-vacancy centers (NV centers), which enable the manipulation and detection of single spins at room temperature, and their state can be imaged using optically detected magnetic resonance (ODMR). Taking advantage of these properties, diamond is expected to be used in a wide range of fields as a highly sensitive sensor for magnetic fields, electric fields, temperature, pressure, and other conditions.

[0003] As a substrate for devices using diamond, for example, a laminated substrate including a diamond layer formed by heteroepitaxial growth on an intermediate layer (seed substrate) of Ir (111) has been proposed (Patent Document 1). However, according to the technology of Patent Document 1, lattice defects due to dislocations occur near the interface between the intermediate layer and the formed diamond layer, and the characteristics of the finally obtained device (for example, quantum optical device) may be insufficient.

[0004] There is also a known technique for attaching a diamond layer to a substrate by van der Waals forces (Non-Patent Documents 1 to 3). However, such a technique often results in a very weak bond strength as a composite substrate, making it difficult to process the substrate into a thin film.

[0005] Japanese Patent Application Laid-Open No. 2020-090408

[0006] Faraon 2013 New J. Phys. 15 025010J. Phys.: Photonics 1 (2019) 015003JOURNAL OF LIGHTWAVE TECHNOLOGY, VOL. 34, NO. 23, DECEMBER 1, 2016

[0007] A primary object of the present invention is to provide a composite substrate having excellent bonding strength and excellent uniformity of the diamond layer.

[0008] [1] A composite substrate according to an embodiment of the present invention has a support substrate and a single-crystal diamond layer directly bonded to the support substrate. [2] In [1] above, the composite substrate further has a cladding layer between the support substrate and the single-crystal diamond layer, the cladding layer being formed on the support substrate and / or the single-crystal diamond layer, and the support substrate and the single-crystal diamond layer being bonded via the cladding layer. [3] In [2] above, a waveguide is formed in the cladding layer. [4] In [2] or [3] above, a patterned cavity is formed in the cladding layer. [5] In [2] or [3] above, a patterned sacrificial layer is formed in the cladding layer. [6] In any of [2] to [5] above, the composite substrate further has a bonding layer between the single crystal diamond layer and the cladding layer formed on the support substrate, between the support substrate and the cladding layer formed on the single crystal diamond layer, or between the cladding layer formed on the support substrate and the cladding layer formed on the single crystal diamond layer. [7] In [6] above, the bonding layer is made of amorphous carbon, silicon oxide, amorphous silicon, tantalum oxide, aluminum oxide, yttrium oxide, zirconium oxide, hafnia, aluminum nitride, Cr / Au, or Cr / Cu. [8] In [6] above, the bonding layer is a sputtered layer of a material that constitutes the cladding layer, a sputtered layer of a material that constitutes the single crystal diamond layer, or a sputtered layer of a material that constitutes the support substrate. [9] In any of [1] to [8] above, the composite substrate has a bonding strength at the directly bonded portion of 0.5 (J / m２

[10] In any of the above [1] to [9], the single crystal diamond layer has a color center.

[11] In any of the above [1] to

[10] , the in-plane density of lattice defects due to dislocations in the single crystal diamond layer is 1.0 × 10 ５ ( / cm ２) or less.

[12] In any of [1] to

[11] above, the single crystal diamond layer has a thickness of 50 nm to 1000 nm.

[13] In any of [1] to

[12] above, the range of thickness variation of the single crystal diamond layer is 5 μm or less.

[14] In any of [1] to

[13] above, the surface roughness Ra of the single crystal diamond layer on the support substrate side is 1.0 nm or less.

[15] In any of [2] to

[14] above, the composite substrate further has an optical loss suppression layer between the single crystal diamond layer and the cladding layer, and the optical loss suppression layer and the cladding layer are directly bonded.

[16] In

[15] above, the optical loss suppression layer is made of amorphous carbon, silicon oxide, amorphous silicon, polycrystalline silicon, molybdenum, aluminum oxide, a compound thereof, or a mixture thereof.

[17] In

[15] or

[16] above, a patterned sacrificial layer is formed on the optical loss suppression layer.

[18] In any of [5] to

[17] above, the sacrificial layer is made of amorphous silicon, silicon, molybdenum, silicon oxide, aluminum oxide, a compound thereof, or a mixture thereof.

[19] In any of [2] to

[18] above, the composite substrate further has an overcoat layer between the cladding layer and the support substrate and / or between the cladding layer and the single-crystal diamond layer.

[20] In any of

[15] to

[19] above, the composite substrate further has an overcoat layer between the cladding layer and the optical loss suppression layer.

[21] In

[19] or

[20] above, the overcoat layer is made of amorphous silicon, niobium oxide, tantalum oxide, silicon oxide, titanium oxide, aluminum oxide, or hafnium oxide.

[22] In any of [2] to

[21] above, the composite substrate further comprises a delamination prevention layer between the single crystal diamond layer and the cladding layer, or between the support substrate and the cladding layer.

[23] In

[22] above, the delamination prevention layer is composed of amorphous silicon, tantalum oxide, niobium oxide, titanium oxide, aluminum oxide or hafnium oxide.

[0009] According to the embodiments of the present invention, a composite substrate having excellent bonding strength and excellent uniformity of the diamond layer can be realized.

[0010] FIG. 1 is a schematic cross-sectional view of a composite substrate according to one embodiment of the present invention. FIG. 2 is a schematic cross-sectional view of a composite substrate according to another embodiment of the present invention. FIG. 3 is a schematic cross-sectional view of a composite substrate according to yet another embodiment of the present invention. FIG. 4 is a schematic cross-sectional view of a composite substrate according to yet another embodiment of the present invention. FIG. 5 is a schematic cross-sectional view of a composite substrate according to yet another embodiment of the present invention. FIG. 6 is a schematic cross-sectional view of a composite substrate according to yet another embodiment of the present invention. FIG. 7 is a schematic cross-sectional view of a composite substrate according to yet another embodiment of the present invention. FIG. 8 is a schematic cross-sectional view illustrating a step in a representative method for manufacturing a composite substrate according to an embodiment of the present invention. FIG. 9 is a schematic cross-sectional view illustrating a step in a representative method for manufacturing a composite substrate according to an embodiment of the present invention. FIG. 10 is a schematic cross-sectional view illustrating a step in a representative method for manufacturing a composite substrate according to an embodiment of the present invention.

[0011] Hereinafter, embodiments of the present invention will be described, but the present invention is not limited to these embodiments.

[0012] A. Composite Substrate A-1. Overall Configuration and Modifications Figure 1 is a schematic cross-sectional view of a composite substrate according to one embodiment of the present invention. The composite substrate 100 in the illustrated example has a support substrate 10 and a single-crystal diamond layer 20 directly bonded to the support substrate 10. That is, the composite substrate 100 is integrated by directly bonding the support substrate 10 and the single-crystal diamond layer 20. The composite substrate according to the embodiment of the present invention has excellent bonding strength because the support substrate and the single-crystal diamond layer are directly bonded. As a result, very good processability (e.g., thin film) can be achieved. Furthermore, the single-crystal diamond layer in the composite substrate according to the embodiment of the present invention has significantly better uniformity than a polycrystalline diamond layer, and has significantly fewer lattice defects due to dislocations than a diamond layer epitaxially grown on a seed substrate. That is, the single-crystal diamond layer in the composite substrate according to the embodiment of the present invention has very good uniformity. Due to the synergistic effect of this effect and the effect of the excellent bonding strength, the composite substrate according to the embodiment of the present invention can realize a device (for example, a quantum optical device) with very excellent properties.

[0013] The reason why a single-crystal diamond layer with excellent uniformity can be obtained by direct bonding is as follows. As will be described later in Section B, in one embodiment, a composite substrate according to an embodiment of the present invention can be produced by a method including: directly bonding a single-crystal diamond substrate (or a clad layer formed on the single-crystal diamond substrate) on a seed substrate to a support substrate (or a clad layer formed on the support substrate); peeling off the seed substrate after direct bonding; and thinning the single-crystal diamond substrate to form a single-crystal diamond layer after peeling off the seed substrate. Thinning of the single-crystal diamond substrate is typically carried out by polishing. According to this method, polishing removes lattice defects caused by dislocations near the interface between the seed substrate and the single-crystal diamond substrate, and the portion with excellent crystal quality separated from the interface becomes the single-crystal diamond layer. Therefore, the single-crystal diamond layer of the composite substrate according to an embodiment of the present invention has few lattice defects caused by dislocations (they are substantially removed) and has very good crystal quality overall. In another embodiment, the composite substrate may be produced using a free-standing single-crystal diamond substrate. In this case, the single-crystal diamond freestanding substrate may be one produced by a high-temperature, high-pressure method, one produced by homoepitaxial growth, or one produced by heteroepitaxial growth. If the single-crystal diamond freestanding substrate is one produced by epitaxial growth, for example, the vicinity of the interface between the epitaxial crystal and the substrate may be removed by slicing, and a portion with excellent crystal quality away from the interface may be used.

[0014] Furthermore, direct bonding enables the single-crystal diamond layer to be thinned. Diamond is extremely hard and difficult to process, but by firmly adhering to the support substrate through direct bonding, thinning under realistic processing conditions and processing times becomes possible. As will be described in detail in Section B, for example, by polishing using plasma-assisted etching, it is possible to thin the single-crystal diamond layer to a thickness of approximately 300 nm in approximately 20 hours (note that, as will be described later, according to embodiments of the present invention, thinning to approximately 50 nm may be possible). Achieving such thinning can provide the following advantages. By enabling thinning, a single-crystal diamond layer can be obtained that is not only very thin but also has excellent flatness and little thickness variation. As a result, color center formation can be easily controlled. Specifically, color center alignment can be easily controlled by electron beam irradiation and / or ion implantation, and the energy applied to form the color center can be reduced. In addition, because direct bonding does not use an adhesive (resin), by appropriately selecting the material and / or thickness of the support substrate, adverse effects of high-temperature processes (e.g., 600°C or higher) in post-processing after color center formation can be suppressed.

[0015] In one embodiment, the single crystal diamond layer 20 may be patterned. The single crystal diamond layer may be patterned, for example, by dry etching. The pattern of the single crystal diamond layer may be appropriately set depending on the purpose. For example, a waveguide or a resonator may be formed by forming a photonic crystal, a phononic crystal, or a nanowire structure. By appropriately designing the pattern of the diamond layer, it is possible to control the light-matter interaction, and a device (e.g., a quantum optical device) having desired properties depending on the purpose may be realized.

[0016] In one embodiment, an amorphous layer (not shown) may be formed at the bonding interface of the direct bond. In the illustrated embodiment, the amorphous layer is a layer formed at the bonding interface by direct bonding of the support substrate 10 and the single crystal diamond layer 20. The amorphous layer is typically composed of elements that make up the support substrate 10 and elements that make up the single crystal diamond layer 20. The thickness of the amorphous layer may be, for example, 0.1 nm to 100 nm, or may be, for example, 2 nm to 15 nm. It should be noted that embodiments of the present invention are not limited to the embodiment shown in Figure 1, and an amorphous layer may typically be formed at the bonding interface of the direct bond.

[0017] In another embodiment, a bonding layer (not shown) may be separately provided on at least one of the layers or substrates to be directly bonded. For example, in the embodiment shown in Fig. 1 , the bonding layer may be provided on the support substrate 10, on the single crystal diamond layer 20, or on both the support substrate 10 and the single crystal diamond layer 20. When the bonding layer is provided on the support substrate 10, the bonding layer and the single crystal diamond layer 20 may be directly bonded; when the bonding layer is provided on the single crystal diamond layer 20, the bonding layer and the support substrate 10 may be directly bonded; when the bonding layer is provided on both the support substrate 10 and the single crystal diamond layer 20, the respective bonding layers may be directly bonded. That is, direct bonding may be performed via a bonding layer. As described above, an amorphous layer may be formed at the bonding interface of direct bonding. Alternatively, the bonding layer may be a sputtered layer of the material constituting the single crystal diamond layer, or a sputtered layer of the material constituting the support substrate. It should be noted that the embodiment of the present invention is not limited to the embodiment shown in Fig. 1 , and direct bonding may be performed via a bonding layer.

[0018] In this specification, "direct bonding" means that the components of the composite substrate (the support substrate 10 and the single-crystal diamond layer 20 in the embodiment of FIG. 1) are bonded together without the use of an adhesive. The form of direct bonding can be appropriately set depending on the configuration of the layers or substrates to be bonded together. For example, direct bonding can be achieved by the following procedure. In a high-vacuum chamber (for example, 1×10－６ A neutralization beam is irradiated onto the bonding surfaces of the components (layers or substrates) to be bonded at a pressure of approximately 100 Pa. This activates each bonding surface. Next, the activated bonding surfaces are brought into contact with each other in a vacuum atmosphere and bonded at room temperature. The load during bonding can be, for example, 100 N to 20,000 N. In one embodiment, when performing surface activation using the neutralization beam, an inert gas is introduced into the chamber, and a high voltage is applied from a DC power supply to an electrode placed in the chamber. With this configuration, an electric field generated between the electrode (positive electrode) and the chamber (negative electrode) causes electrons to move, generating a beam of atoms and ions from the inert gas. Of the beams that reach the grid, the ion beam is neutralized by the grid, and a beam of neutral atoms is emitted from the fast atom beam source. The atomic species constituting the beam are preferably inert gas elements (e.g., argon (Ar) or nitrogen (N)). The voltage during activation by beam irradiation is, for example, 0.5 kV to 2.0 kV, and the current is, for example, 50 mA to 200 mA. The direct bonding method is not limited to this, and other methods such as surface activation using an ion gun, atomic diffusion, and plasma bonding can also be applied. Alternatively, particles of the constituent material of one of the layers or substrates to be directly bonded can be sputtered out, forming a sputtered layer on the surface of the other layer or substrate, and this sputtered layer can be used as the bonding layer.

[0019] The composite substrate preferably has a bonding strength of 0.5 (J / m ２ ) or more, and more preferably 0.75 (J / m ２ ) or more, and more preferably 1.0 (J / m ２ ) or more, and particularly preferably 1.2 (J / m ２ On the other hand, the bonding strength at the direct bonding portion is, for example, 12.0 (J / m ２ ) or less, and may be, for example, 8.0 (J / m ２ ) or less, and may be, for example, 4.0 (J / m ２ ) or less, and may be, for example, 2.0 (J / m ２) or less. If the bonding strength at the directly bonded portion is within this range, it may be easy to thin the composite substrate. For example, it may be possible to further thin the single-crystal diamond layer. The bonding strength at the directly bonded portion may be, for example, the bonding strength of the bonding layer, or may be, for example, the bonding strength of the amorphous layer. The bonding strength may be measured, for example, by the crack opening method. The crack opening method is a technique in which a razor-like blade is inserted into the bonding interface of the bonded substrates and the bonding strength is determined from the peel length of the substrates from the tip of the blade. The shorter the peel length, the higher the bond energy and the higher the bonding strength.

[0020] Preferably, the composite substrate is such that peeling between the support substrate and the single-crystal diamond layer is substantially absent at a position at least a predetermined distance inward in the plane direction from the outer periphery. The predetermined distance may be, for example, 200 μm or 250 μm. Furthermore, the composite substrate has a number of voids between the support substrate and the single-crystal diamond layer of 50 μm or more in diameter that is preferably 10 / mm ２ More preferably, 7 particles / mm ２ More preferably, 5 pieces / mm ２ With this configuration, an excellent yield can be achieved when fabricating devices on the composite substrate.

[0021] Figure 2 is a schematic cross-sectional view of a composite substrate according to another embodiment of the present invention. In the composite substrate 101 of the illustrated example, a cladding layer 30 is provided between a support substrate 10 and a single crystal diamond layer 20. The cladding layer 30 may be provided on the support substrate 10, on the single crystal diamond layer 20, or on both the support substrate 10 and the single crystal diamond layer 20. In this case, the support substrate 10 and the single crystal diamond layer 20 may be bonded via the cladding layer 30. Specifically, when the cladding layer 30 is provided on the support substrate 10, the cladding layer and the single crystal diamond layer 20 may be directly bonded; when the cladding layer 30 is provided on the single crystal diamond layer 20, the cladding layer and the support substrate 10 may be directly bonded; and when the cladding layer 30 is provided on both the support substrate 10 and the single crystal diamond layer 20, the respective cladding layers may be directly bonded. The cladding layer 30 may be formed on the support substrate 10 and / or single crystal diamond layer 20 by any suitable method (eg, sputtering).

[0022] As mentioned above, direct bonding may be performed via a bonding layer. Thus, in the embodiment of Figure 2, a bonding layer may be provided on at least one of the directly bonded layers or substrates among the support substrate 10, cladding layer 30 and single-crystal diamond layer 20. In this case, the bonding layer may be, for example, a sputtered layer of the material that constitutes the cladding layer, a sputtered layer of the material that constitutes the single-crystal diamond layer, or a sputtered layer of the material that constitutes the support substrate. When direct bonding is performed without a bonding layer, an amorphous layer may be formed between the cladding layer 30 formed on the support substrate 10 and the single-crystal diamond layer 20, between the cladding layer 30 formed on the single-crystal diamond layer 20 and the support substrate 10, or between the cladding layer formed on the support substrate and the cladding layer formed on the single-crystal diamond layer.

[0023] Further modifications of the composite substrate are described below. The configurations of these modifications can be appropriately combined depending on the purpose. Specific configurations of the components (layers or substrates) of the composite substrate will be described later in sections A-2 to A-10.

[0024] Figure 3A is a schematic cross-sectional view of a composite substrate according to yet another embodiment of the present invention. In the illustrated composite substrate 102, a patterned sacrificial layer 40 is formed on the cladding layer 30. The sacrificial layer 40 can be removed by etching to form cavities 50 as shown in Figure 3B. The pattern of the sacrificial layer 40 can therefore correspond to the pattern of the cavities 50. The patterns of the sacrificial layer and the cavities can be appropriately set depending on the purpose. In one embodiment, the cavities 50 can function as cladding that is particularly excellent in confining light or electromagnetic waves. In this case, the single-crystal diamond layer 20 can function as a waveguide with excellent propagation performance. When the single-crystal diamond layer is patterned as described above, light or electromagnetic waves of a desired wavelength can be propagated extremely well by designing the pattern of the single-crystal diamond layer in combination with the pattern of the cavities. As a result, devices with excellent properties (e.g., quantum optical devices) can be realized.

[0025] Figure 4 is a schematic cross-sectional view of a composite substrate according to yet another embodiment of the present invention. In the composite substrate 103 shown in the figure, a waveguide 60 is formed in the cladding layer 30. The waveguide 60 is typically constructed by patterning a material different from the material constituting the cladding layer. By appropriately designing the waveguide pattern, a waveguide that propagates light or electromagnetic waves of a desired wavelength can be obtained. The waveguide 60 shown in Figure 4 may be combined with a patterned cavity (e.g., Figure 3) and / or a patterned single-crystal diamond layer. By combining a waveguide with a patterned cavity and / or a patterned single-crystal diamond layer, propagating light can be coupled between the waveguide 60 and the single-crystal diamond layer 20, and a device (e.g., a quantum optical device) with excellent properties can be realized.

[0026] FIG. 5 is a schematic cross-sectional view of a composite substrate according to yet another embodiment of the present invention. In the composite substrate 104 of the illustrated example, an optical loss suppression layer 70 is provided between the single crystal diamond layer 20 and the cladding layer 30, and the optical loss suppression layer 70 and the cladding layer 30 are directly bonded together. By providing the optical loss suppression layer, it is possible to prevent an amorphous layer from being formed in the single crystal diamond layer during direct bonding, thereby suppressing the optical loss of the single crystal diamond layer. In this embodiment, a patterned sacrificial layer (not shown) may be formed in the optical loss suppression layer 70. As described with respect to the embodiment of FIGS. 3A and 3B , the sacrificial layer may be removed by etching to form a cavity (not shown). Therefore, the pattern of the sacrificial layer may correspond to the pattern of the cavity. The patterns of the sacrificial layer and the cavity may be appropriately set depending on the purpose. The sacrificial layer (and consequently the cavity) may be formed only in the optical loss suppression layer, or in both the optical loss suppression layer and the cladding layer. When the sacrificial layer is formed only on the cladding layer as in the embodiment of Figure 3A, the optical loss suppression layer can function as a protective film when the sacrificial layer is etched, and therefore damage to the single-crystal diamond layer due to etching (and consequently optical loss in the single-crystal diamond layer) can also be suppressed.

[0027] Figure 6 is a schematic cross-sectional view of a composite substrate according to yet another embodiment of the present invention. In the composite substrate 105 shown in the figure, an overcoat layer 80 is provided between the cladding layer 30 and the single-crystal diamond layer 20. The overcoat layer 80 can typically be provided as a layer for planarizing the cladding layer 30 when it has irregularities. Specifically, when a sacrificial layer 40 is formed on the cladding layer 30 as in the embodiment of Figure 3A, the sacrificial layer 40 and the cladding layer 30 are formed in separate processes, which can result in irregularities on the surface of the cladding layer 30. In this case, by forming the overcoat layer 80, it is possible to form a surface as a single layer, which can facilitate the planarization process. The overcoat layer may be provided between the cladding layer 30 and the support substrate 10, or may be provided both between the cladding layer 30 and the single-crystal diamond layer 20 and between the cladding layer 30 and the support substrate 10. In embodiments of the present invention, particularly significant effects can be obtained when an overcoat layer is provided between the cladding layer 30 and the single-crystal diamond layer 20 (typically on the surface of the single-crystal diamond layer 20). Specifically, the reasons are as follows: Diamond is very hard and difficult to process, and it may be difficult to smooth the surface of the single-crystal diamond layer (i.e., even after smoothing treatment, unevenness may remain on the surface of the single-crystal diamond layer). As a result, direct bonding of the single-crystal diamond layer may be difficult. In response to this, by providing an overcoat layer on the single-crystal diamond layer, surface smoothing suitable for direct bonding can be achieved.

[0028] FIG. 7 is a schematic cross-sectional view of a composite substrate according to yet another embodiment of the present invention. In the illustrated composite substrate 106, an overcoat layer 80 is provided between the cladding layer 30 and the optical loss suppression layer 70. As described with respect to the embodiment of FIG. 6, by forming the overcoat layer 80, even if the surface of the cladding layer is uneven (e.g., by forming a sacrificial layer), the overcoat layer 80 can be formed to perform an appropriate planarization process on the surface. As in the embodiment of FIG. 6, an overcoat layer may be provided between the cladding layer 30 and the supporting substrate 10, or may be provided both between the cladding layer 30 and the optical loss suppression layer 70 and between the cladding layer 30 and the supporting substrate 10.

[0029] Figure 8 is a schematic cross-sectional view of a composite substrate according to yet another embodiment of the present invention. In the composite substrate 107 of the illustrated example, a delamination prevention layer 90 is provided between the single crystal diamond layer 20 and the cladding layer 30. Although not shown, the delamination prevention layer 90 may be provided between the support substrate 10 and the cladding layer 30, or may be provided both between the single crystal diamond layer 20 and the cladding layer 30 and between the support substrate 10 and the cladding layer 30. By providing a delamination prevention layer, it is possible to suppress delamination of adjacent layers (substantially, between the single crystal diamond layer and the cladding layer, and / or between the support substrate and the cladding layer).

[0030] The above-described embodiments may be appropriately combined depending on the purpose, and / or modifications well known in the art may be made to the above-described embodiments.

[0031] A-2. Single Crystal Diamond Layer The single crystal diamond layer 20 typically has a main surface with a crystal plane orientation of (111) or (100). Alternatively, the crystal axes may have an off-angle of several degrees.

[0032] The single crystal diamond layer typically has a color center. A color center is a defect structure formed in diamond, and can absorb light and / or emit light upon external excitation. Any appropriate structure may be employed as the color center. Specific examples of color centers include the NV center, SiV center, GeV center, SnV center, and PbV center. The NV center is a complex defect in which a carbon atom in a diamond crystal is replaced with a nitrogen atom, with a vacancy located adjacent to it. In this case, the single crystal diamond layer may typically be composed of Type I, which contains a single nitrogen atom. The SiV center is a complex defect in which a Si atom is located between two adjacent vacancies. In this case, the single crystal diamond layer may typically be composed of Type IIa, which has an ultra-low nitrogen concentration and no boron impurities. The GeV center, SnV center, and PbV center are SiV centers in which Ge, Sn, and Pb are substituted for Si, respectively.

[0033] The color center concentration in the single crystal diamond layer is preferably 0.01 ppb to 20 ppm, more preferably 10 ppb to 10 ppm, and even more preferably 200 ppb to 5 ppm. With such a configuration, the layer can be used as a single photon source with only one color center in the photoexcitation region, or as an ensemble that simultaneously handles multiple color centers, and it is possible to avoid a situation in which the color center density is too high and the spin coherence time becomes short.

[0034] The in-plane density of lattice defects due to dislocations in the single crystal diamond layer (sometimes referred to as lattice defect concentration) is preferably 1.0×10 ５ ( / cm ２ ) or less, more preferably 1.0 × 10 ４ ( / cm ２ ) or less, and more preferably 1.0 × 10 ３ ( / cm ２ The lower the concentration of lattice defects due to dislocations, the more preferable it is. The lower limit of the concentration of lattice defects due to dislocations can be, for example, zero, or, for example, 10 ( / cm ２) As described above, according to the embodiments of the present invention, direct bonding enables thinning (polishing) of the single crystal diamond, and lattice defects due to dislocations near the interface between the seed substrate and the single crystal diamond can be effectively removed. Therefore, the concentration of lattice defects due to dislocations can be made very small in the single crystal diamond layer. As a result, the composite substrate according to the embodiments of the present invention can realize devices (e.g., quantum optical devices) with very excellent properties.

[0035] The single crystal diamond layer preferably does not substantially contain impurity elements resulting from ion implantation. More specifically, the hydrogen concentration in the single crystal diamond layer is preferably less than 1×10 ２０ atoms / cm ―３ or less, more preferably 1×10 １８ atoms / cm ―３ or less, and more preferably 1×10 １７ atoms / cm ―３ The lower the hydrogen concentration in the single crystal diamond layer, the better, and the lower limit is, for example, 1×10 １５ atoms / cm ―３ The helium concentration in the single crystal diamond layer may preferably be 1×10 ２０ atoms / cm ―３ or less, more preferably 1×10 １８ atoms / cm ―３ or less, and more preferably 1×10 １７ atoms / cm ―３ The lower the helium concentration in the single crystal diamond layer, the better, and the lower limit is, for example, 1×10 １５ atoms / cm ―３ If the hydrogen and helium concentrations in the single crystal diamond layer are within these ranges, the spin coherence time of the color centers can be lengthened, and the detection efficiency can be improved when the composite substrate is used as a sensing device. The hydrogen and helium concentrations in the single crystal diamond layer can be measured by, for example, secondary ion mass spectrometry (SIMS).

[0036] In a specific embodiment, a hydrogen concentration increased region may be formed in the single crystal diamond layer. Such a configuration can improve bonding strength. Here, the hydrogen concentration increased region is typically a region that can be formed when water vapor plasma is irradiated onto the bonding surface of the single crystal diamond as a pretreatment for direct bonding. The hydrogen concentration increased region can be formed in a region, for example, of 100 nm or less, preferably 80 nm or less, and more preferably 60 nm or less, from the surface of the single crystal diamond layer on the bonding interface side with the support substrate toward the opposite surface. In other words, the thickness of the hydrogen concentration increased region is, for example, 100 nm or less, preferably 80 nm or less, and more preferably 60 nm or less. On the other hand, the thickness of the hydrogen concentration increased region can be, for example, greater than 0 nm, or, for example, 20 nm or more. The hydrogen concentration in the hydrogen concentration increased region can be, for example, 1×10 １８ atoms / cm ―３ or more, preferably 5×10 １８ atoms / cm ―３ More preferably, 1×10 １９ atoms / cm ―３ or more, and more preferably 5×10 １９ atoms / cm ―３ The upper limit of the hydrogen concentration in the hydrogen concentration increasing region is, for example, 1×10 ２２ atoms / cm ―３ It could be.

[0037] Furthermore, in certain embodiments, an oxygen concentration increased region may be formed in the single crystal diamond layer. Such a configuration can improve bonding strength. Here, like the hydrogen concentration increased region described above, the oxygen concentration increased region is a region that can be formed when water vapor plasma is irradiated onto the bonding surface of the single crystal diamond as a pretreatment for direct bonding. The oxygen concentration increased region can be formed in a region, for example, of 80 nm or less, preferably 40 nm or less, and more preferably 20 nm or less, from the surface of the single crystal diamond layer on the bonding interface side with the support substrate toward the opposite surface. In other words, the thickness of the oxygen concentration increased region is, for example, 80 nm or less, preferably 40 nm or less, and more preferably 20 nm or less. On the other hand, the thickness of the oxygen concentration increased region can be, for example, 0.1 nm or more. The oxygen concentration in the oxygen concentration increased region can be, for example, 5 × 10 １７ atoms / cm ―３ or more, preferably 1×10 １８ atoms / cm ―３ More preferably, 2×10 １８ atoms / cm ―３ or more, and more preferably 1×10 １９ atoms / cm ―３ The upper limit of the oxygen concentration in the oxygen concentration increasing region is, for example, 1×10 ２２ atoms / cm ―３ The oxygen concentration in the region other than the oxygen concentration increased region in the single crystal diamond layer may be, for example, 1×10 １９ atoms / cm ―３ or less, preferably 5 × 10 １８ atoms / cm ―３ or less, more preferably 1×10 １８ atoms / cm ―３ With this configuration, it is possible to reduce the propagation loss of light in the single crystal diamond layer, and to facilitate the production of color centers. The lower limit of the oxygen concentration in the region other than the oxygen concentration increased region is, for example, 1×10 １７ atoms / cm ―３The oxygen concentration in the single crystal diamond layer may be measured, for example, by secondary ion mass spectrometry (SIMS).

[0038] The single crystal diamond layer is preferably substantially free of impurity elements resulting from reactive ion etching (RIE). More particularly, the argon concentration in the single crystal diamond layer is preferably less than 1×10 ２０ atoms / cm ３ or less, more preferably 1×10 １９ atoms / cm ３ or less, and more preferably 1×10 １８ atoms / cm ３ The lower the argon concentration in the single crystal diamond layer, the better, and the lower limit is, for example, 1×10 １７ atoms / cm ３ The chlorine concentration in the single crystal diamond layer is preferably 1×10 １９ atoms / cm ３ or less, more preferably 1×10 １８ atoms / cm ３ or less, and more preferably 1×10 １７ atoms / cm ３ The lower the chlorine concentration in the single crystal diamond layer, the better, and the lower limit is, for example, 1×10 １６ atoms / cm ３ The total concentration of argon and chlorine in the single crystal diamond layer may preferably be 5×10 １９ atoms / cm ３ or less, more preferably 1×10 １８ atoms / cm ３ or less, and more preferably 1×10 １７ atoms / cm ３ The lower the total concentration of argon and chlorine in the single crystal diamond layer, the better, and the lower limit is, for example, 1×10 １６ atoms / cm ３If the argon and chlorine concentrations in the single crystal diamond layer are in these ranges, the detection efficiency can be improved when the composite substrate is used as a sensing device. The argon and chlorine concentrations in the single crystal diamond layer can be measured by, for example, secondary ion mass spectrometry (SIMS) or Rutherford backscattering spectrometry (RBS).

[0039] The pit density of the single crystal diamond layer is preferably 1×10 ６ cm ―２ or less, more preferably 1×10 ４ cm ―２ or less, and more preferably 1×10 １ cm ―２ The smaller the pit density, the better, and the lower limit is, for example, 1×10 ０ cm ―２ The pits refer to depressions resulting from dislocations that can be formed on the surface due to etching damage during RIE. The pit density can be measured, for example, using an optical microscope or a scanning electron microscope (SEM).

[0040] The peak wave number when the Raman spectroscopy measurement value of the single crystal diamond layer is subjected to Lorentz fitting is preferably 1330 cm ―１ 1340cm or more ―１ More preferably, it is 1332 cm or less. ―１ 1338cm or more ―１ More preferably, it is 1333 cm or less. ―１ 1337cm or more ―１ The following is the result.

[0041] 1335 cm when the Raman spectroscopy measurement value of the single crystal diamond layer is fitted with Lorentzian fitting ―１ The half-width of the peak observed in the vicinity is preferably 10 cm ―１ More preferably, it is 5 cm or less. ―１ It is preferably 3 cm or less. ―１ The smaller the half-width, the higher the uniformity of the crystal lattice, which can improve device characteristics.

[0042] The thickness of the single crystal diamond layer may be, for example, 50 nm to 90 μm. According to an embodiment of the present invention, a thin film of approximately 50 nm is possible. The thickness of the single crystal diamond layer can be appropriately set within this range depending on the purpose. In one embodiment, the thickness of the single crystal diamond layer is preferably 50 nm to 5,000 nm, more preferably 50 nm to 1,000 nm, even more preferably 100 nm to 1,000 nm, and particularly preferably 200 nm to 600 nm. Such a very thin single crystal diamond layer facilitates control of the color center arrangement and reduces the energy applied to form the color centers. In another embodiment, the thickness of the single crystal diamond layer is preferably 5 μm to 90 μm, more preferably 10 μm to 50 μm, and even more preferably 20 μm to 40 μm. If the thickness of the single crystal diamond layer is within this range, when used as a sensing device, light emission from the single crystal diamond layer can be detected without being affected by the underlying substrate, enabling highly sensitive sensing.

[0043] The range of thickness variation of the single crystal diamond layer is, for example, 5 μm or less, preferably 1 μm or less, more preferably 100 nm or less, even more preferably 50 nm or less, and particularly preferably 10 nm or less. The lower limit of the range of thickness variation of the single crystal diamond layer may be, for example, 1 nm. If the range of thickness variation of the single crystal diamond layer is within this range, variations in optical properties and propagation loss can be reduced. On the other hand, from the perspective of facilitating fabrication, the range of thickness variation of the single crystal diamond layer may be, for example, 100 nm or more, or may be, for example, 200 nm or more. In this case, by forming an overcoat layer on the surface of the single crystal diamond layer, it is possible to compensate for thickness variation and / or surface roughness of the single crystal diamond layer during direct bonding.

[0044] The surface roughness (arithmetic mean height) Sa of the single crystal diamond layer on the support substrate 10 side is preferably 1.0 nm or less, more preferably 0.6 nm or less, and even more preferably 0.3 nm or less. The smaller the surface roughness Sa, the more preferable, and its lower limit may be, for example, 0.05 nm, or may be, for example, 0.1 nm. If the surface roughness Sa is within this range, a composite substrate with very excellent bonding strength can be obtained. Note that the surface roughness Sa is a value measured in a field of view of 10 μm × 10 μm using an atomic force microscope (AFM).

[0045] A-3. Support Substrate The support substrate 10 has an upper surface located within the composite substrate and a lower surface exposed to the outside. The support substrate 10 is provided to increase the strength of the composite substrate, thereby making it possible to reduce the thickness of the single-crystal diamond layer. Any appropriate configuration may be adopted for the support substrate 10. Specific examples of materials that may be used to form the support substrate 10 include silicon (Si), glass, sialon (Si ３ N ４ -Al ２ O ３ ), mullite (3Al ２ O ３ 2SiO ２ , 2Al ２ O ３ 3SiO ２ ), aluminum nitride (AlN), silicon nitride (Si ３ N ４ ), magnesium oxide (MgO), sapphire, quartz, crystal, gallium nitride (GaN), silicon carbide (SiC), gallium oxide (Ga ２ O ３ ), and diamond. The linear expansion coefficient of the material constituting the support substrate 10 is preferably as close to that of single crystal diamond. With such a configuration, thermal deformation (typically warpage) of the composite substrate can be suppressed. Preferably, the linear expansion coefficient of the material constituting the support substrate 10 is within the range of 50% to 150% of that of single crystal diamond.

[0046] The thickness of the support substrate may be any appropriate thickness as long as it has the effect of reinforcing the composite substrate. The thickness of the support substrate may be, for example, 100 μm to 1000 μm. If the support substrate is too thin, the reinforcing effect and handling may be insufficient. If the support substrate is too thick, the package size of the resulting device may be large and / or the heat dissipation properties of the support substrate may be insufficient.

[0047] A-4. Cladding Layer The cladding layer 30 may be provided to confine light, electromagnetic waves, mechanical vibrations, etc. propagating through the single-crystal diamond layer within the single-crystal diamond layer and to suppress absorption of these by electrodes, etc. The cladding layer may be made of any appropriate material as long as it has the above-mentioned functions. Specific examples include silicon oxide, tantalum oxide, aluminum oxide, titanium oxide, niobium oxide, magnesium oxide, tungsten oxide, and hafnium oxide. The thickness of the cladding layer may be, for example, 0.1 μm to 1 μm.

[0048] As explained in Section A above, the cladding layer 30 may be provided on both the support substrate and the single-crystal diamond layer. In this case, each cladding layer may be made of the same material or different materials. When the cladding layers are directly bonded to each other, a modified layer may be formed at the bonding interface. The thickness of the modified layer may be, for example, 20 nm or less. On the other hand, the thickness of the modified layer may be, for example, 5 nm or more. With this configuration, the degree of freedom in selecting the bonding method may be increased compared to, for example, directly bonding diamond to a thermally oxidized Si substrate, and as a result, the bonding strength may be increased by selecting an appropriate bonding method. The modified layer may be confirmed using a transmission electron microscope (TEM).

[0049] A-5. Bonding Layer As described above, the bonding layer is separately provided on at least one of the layers or substrates to be directly bonded, and can increase the bonding strength of the direct bond to achieve strong integration. Any appropriate configuration can be adopted as the bonding layer depending on the configuration of the substrate or layer to be bonded. Examples of materials that constitute the bonding layer include amorphous carbon, silicon oxide, amorphous silicon, tantalum oxide, and aluminum oxide (alumina: Al ２ O ３ ), yttrium oxide, zirconium oxide, aluminum nitride, hafnia (HfO ２ ), Cr / Au, Cr / Cu. In this embodiment, the thickness of the bonding layer may be, for example, 0.01 μm to 0.1 μm, or may be, for example, 0.01 μm to 0.05 μm.

[0050] Alternatively, the bonding layer may be a sputtered layer of material that constitutes one of the layers or substrates that are to be directly bonded together, as also described above. In this embodiment, the thickness of the bonding layer may be, for example, 0.1 nm to 100 nm, and may be, for example, 2 nm to 15 nm.

[0051] A-6. Sacrificial Layer The sacrificial layer 40 is provided to form the cavity 50 at the designed position and in the designed shape. The sacrificial layer may typically have a cavity processing function and an etching stop function. Any appropriate configuration may be adopted for the sacrificial layer depending on the purpose. Examples of materials that may be used to form the sacrificial layer include amorphous silicon, polycrystalline silicon, single crystal silicon, molybdenum, silicon oxide, aluminum oxide, compounds of these materials, and mixtures of these materials. The thickness of the sacrificial layer is, for example, 0.1 μm to 1.0 μm, or, for example, 0.2 μm to 0.7 μm.

[0052] A-7. Waveguide The waveguide 60 can typically be composed of a material different from that of the cladding layer 30. Examples of materials that can be used to compose a waveguide include lithium niobate, silicon, silicon nitride, silicon carbide, compounds of these materials, and mixtures of these materials. Waveguides can be formed by using such materials to construct, for example, photonic crystals, phononic crystals, or nanowire structures. For example, photonic crystals are multidimensional periodic structures composed of high-refractive-index and low-refractive-index media with a period comparable to the wavelength of light, and have a band structure for light or electromagnetic waves similar to the band structure of electrons. Therefore, by appropriately designing the periodic structure, it is possible to create a forbidden band (photonic band gap) for a specific light or electromagnetic wave. A photonic crystal with a forbidden band functions as an object that neither reflects nor transmits light or electromagnetic waves of a specific wavelength. Introducing a line defect that disrupts the periodicity into a photonic crystal with a photonic band gap creates a guided mode within the frequency range of the band gap, enabling the realization of a waveguide that propagates light or electromagnetic waves with low loss. In any of the photonic crystal, phononic crystal, and nanowire structure, a predetermined photonic band gap can be realized by appropriately designing the periodic structure. Alternatively, the waveguide may be a ridge-type waveguide (not shown). The ridge-type waveguide is typically provided on the upper part (surface) of the cladding layer so as to extend in a predetermined direction. The ridge-type waveguide is typically made of a material having a higher refractive index than the material constituting the cladding layer.

[0053] A-8. Optical Loss Suppression Layer As described above, the optical loss suppression layer 70 has the function of suppressing the optical loss of the single crystal diamond layer. By providing the optical loss suppression layer, it is possible to prevent the formation of an amorphous layer in the single crystal diamond layer during direct bonding, and therefore the optical loss of the single crystal diamond layer can be suppressed. Furthermore, for example, when a sacrificial layer formed on a cladding layer is etched to form a cavity, the optical loss suppression layer can function as a protective film when the sacrificial layer is etched, and therefore damage to the single crystal diamond layer due to etching (and consequently the optical loss of the single crystal diamond layer) can also be suppressed. Any appropriate configuration can be adopted as the optical loss suppression layer as long as it has such a function. Examples of materials that constitute the optical loss suppression layer include silicon oxide (SiO ２ ), amorphous silicon (a-Si), polycrystalline silicon (i.e., excluding single crystal silicon), molybdenum, aluminum oxide (Al ２ O ３ ), compounds of these materials, or mixtures of these materials. The thickness of the optical loss suppression layer can be, for example, 0.01 μm (10 nm) to 0.1 μm (100 nm), and can be, for example, 0.01 μm (10 nm) to 0.05 μm (50 nm).

[0054] A-9. Overcoat Layer As described above, the overcoat layer 80 is provided to smooth out any irregularities present in the single crystal diamond layer 20, cladding layer 30, and / or optical loss suppression layer 70. In particular, as described above, in embodiments of the present invention, particularly significant effects can be obtained when the overcoat layer is provided between the cladding layer 30 and the single crystal diamond layer 20 (typically, on the surface of the single crystal diamond layer 20). Specifically, this is as follows: Diamond is very hard and difficult to process, making it difficult to smooth the surface of the single crystal diamond layer (i.e., even after smoothing treatment, irregularities may remain on the surface of the single crystal diamond layer). As a result, direct bonding of the single crystal diamond layer may be difficult. In contrast, providing an overcoat layer on the single crystal diamond layer can achieve surface smoothing suitable for direct bonding. Any appropriate configuration can be adopted for the overcoat layer depending on the purpose and the configuration of the adjacent layer. Examples of materials that can be used for the overcoat layer include amorphous silicon, niobium oxide, tantalum oxide, silicon oxide, titanium oxide, aluminum oxide, and hafnium oxide. The thickness of the overcoat layer is, for example, 0.01 μm to 1 μm.

[0055] A-10. Anti-Peeling Layer The anti-peeling layer 90 is provided to suppress or prevent peeling between the single crystal diamond layer 20 and the cladding layer 30, and / or between the support substrate 10 and the cladding layer 20, as described above. Any appropriate configuration may be adopted as the anti-peeling layer depending on the configuration of the adjacent layer. Examples of materials that constitute the anti-peeling layer include amorphous silicon, tantalum oxide (Ta ２ O ５ ), niobium oxide (Nb ２ O ５ ), titanium oxide (TiO ２ ), aluminum oxide, hafnium oxide (HfO ２ The thickness of the anti-peeling layer is, for example, 0.01 μm to 0.1 μm.

[0056] B. Manufacturing method of composite substrate One example of a manufacturing method of a composite substrate will be described with reference to Figures 9A to 9E. The manufacturing method of a composite substrate includes directly bonding a single crystal diamond substrate (or a clad layer formed on the single crystal diamond substrate) on a seed substrate to a support substrate (or a clad layer formed on the support substrate); peeling off the seed substrate after the direct bonding; and thinning the single crystal diamond substrate to form a single crystal diamond layer after peeling off the seed substrate. This will be described in detail below.

[0057] First, as shown in Figure 9A, the seed substrate 25 of a stack of a single-crystal diamond substrate 20' and a seed substrate 25 is temporarily and releasably attached to a handling wafer 200. This stack can be typically fabricated by forming nuclei on the seed substrate 25 and then heteroepitaxially growing the diamond substrate. Temporary attachment can typically be performed via UV release tape. UV release tape has strong adhesive strength before UV curing, but its adhesive strength drops sharply after UV curing.

[0058] Next, as shown in Figure 9B, a support substrate 10 is separately prepared. In the illustrated example, a cladding layer 30 is formed on the support substrate 10 and the single-crystal diamond substrate 20'. The cladding layer 30 can be formed by, for example, sputtering. The formed cladding layer 30 can be flattened and smoothed by polishing.

[0059] Next, as shown in Figure 9C, the cladding layer 30 formed on the support substrate 10 and the cladding layer 30 formed on the single crystal diamond substrate 20' are directly bonded together. Direct bonding is as explained in section A-1 above.

[0060] 9D, the handling wafer 200 is peeled off and then the seed substrate 25 is removed. More specifically, after the direct bonding is completed, the UV peeling tape is irradiated with ultraviolet light to reduce the adhesive strength of the tape, so that the handling wafer can be easily peeled off and removed. The seed substrate can be removed by, for example, polishing.

[0061] Finally, as shown in Figure 9E, the single crystal diamond substrate 20' may be thinned to form a single crystal diamond layer 20, resulting in a composite substrate. Thinning of the single crystal diamond substrate may be performed, for example, by polishing using plasma-assisted etching. By this method, the single crystal diamond substrate may be thinned to a thickness of about 300 nm in about 20 hours (although, as noted above, thinning to a thickness of around 50 nm may be possible according to embodiments of the present invention).

[0062] If desired, the composite substrate may be chipped and if desired, the single crystal diamond layer may be patterned.

[0063] Preferably, color centers may be formed in the single-crystal diamond layer. The formation of color centers may be carried out at any appropriate time. Specifically, color centers may be formed before direct bonding (i.e., may be formed in the single-crystal diamond substrate 20' of the stack of the single-crystal diamond substrate 20' and the seed substrate 25); may be formed after direct bonding (substantially in the single-crystal diamond substrate 20' after the seed substrate 25 has been removed); or may be formed after thinning the single-crystal diamond substrate 20' (i.e., in the single-crystal diamond layer 10). Alternatively, a free-standing single-crystal diamond substrate on which color centers have been formed may be used. Color centers may be formed, for example, by chemical vapor deposition (CVD) with doping impurities to form a single-crystal diamond layer having color centers, or by subjecting the single-crystal diamond layer to ion implantation and / or electron beam irradiation, followed by annealing as necessary.

[0064] In the illustrated example, an embodiment has been described in which a cladding layer is formed on both the support substrate and the single-crystal diamond layer, but a cladding layer may be formed on only one of the support substrate or the single-crystal diamond layer, or no cladding layer may be formed as in Figure 1 (i.e., the support substrate and the single-crystal diamond layer may be directly bonded).

[0065] In direct bonding, the bonding surfaces of the single-crystal diamond layer, the support substrate, the cladding layer or the bonding layer may be irradiated with water vapor plasma as a pretreatment, which can increase the bonding strength.

[0066] In the illustrated example, a manufacturing method corresponding to the embodiment in Fig. 2 has been described, but it is also possible to form a sacrificial layer 40, a cavity 50, a waveguide 60, an optical loss suppression layer 70, an overcoat layer 80, and / or a peeling prevention layer 90 as shown in Fig. 3A and 3B and Fig. 4 to Fig. 8. It is obvious to those skilled in the art that these can be formed by any appropriate film formation method and etching, so specific descriptions of the formation methods and procedures thereof will be omitted.

[0067] In the illustrated example, an embodiment using a stack of a single crystal diamond substrate and a seed substrate has been described, but as mentioned above, a single crystal diamond freestanding substrate may also be used. In this case, the single crystal diamond freestanding substrate may be one produced by a high-temperature, high-pressure method, one produced by homoepitaxial growth, or one produced by heteroepitaxial growth. When the single crystal diamond freestanding substrate is one produced by epitaxial growth, the vicinity of the interface between the epitaxial crystal and the substrate may be removed by slicing, and the portion with excellent crystal quality away from the interface may be used.

[0068] The composite substrate according to the embodiment of the present invention can be suitably used in quantum optical devices, which can be suitably used in a wide range of fields such as quantum sensing, quantum computers, and quantum communications.

[0069] REFERENCE SIGNS LIST 10 Support substrate 20 Single crystal diamond layer 20' Single crystal diamond substrate 25 Seed substrate 30 Cladding layer 40 Sacrificial layer 50 Cavity 60 Waveguide 70 Optical loss suppression layer 80 Overcoat layer 90 Peel-off prevention layer 100 Composite substrate 101 Composite substrate 102 Composite substrate 103 Composite substrate 104 Composite substrate 105 Composite substrate 106 Composite substrate 107 Composite substrate

Claims

1. A composite substrate having a support substrate and a single crystal diamond layer bonded directly to the support substrate.

2. The composite substrate according to claim 1, further comprising a cladding layer between the support substrate and the single-crystal diamond layer, the cladding layer being formed on the support substrate and / or the single-crystal diamond layer, and the support substrate and the single-crystal diamond layer being bonded together via the cladding layer.

3. The composite substrate according to claim 2, wherein a waveguide is formed in said cladding layer.

4. The composite substrate of claim 2, wherein said cladding layer has patterned cavities formed therein.

5. The composite substrate of claim 2, wherein the cladding layer has a patterned sacrificial layer formed thereon.

6. A composite substrate according to claim 2, further comprising a bonding layer between the single crystal diamond layer and a cladding layer formed on the support substrate, between the support substrate and a cladding layer formed on the single crystal diamond layer, or between the cladding layer formed on the support substrate and a cladding layer formed on the single crystal diamond layer.

7. The composite substrate of claim 6, wherein the bonding layer is comprised of amorphous carbon, silicon oxide, amorphous silicon, tantalum oxide, aluminum oxide, yttrium oxide, zirconium oxide, hafnia, aluminum nitride, Cr / Au, or Cr / Cu.

8. A composite substrate according to claim 6, wherein the bonding layer is a sputtered layer of a material that constitutes the cladding layer, a sputtered layer of a material that constitutes the single-crystal diamond layer, or a sputtered layer of a material that constitutes the support substrate.

9. The bond strength at the direct bonded portion is 0.5 (J / m ２ 9. The composite substrate according to claim 1, wherein the thickness of the composite substrate is 100 nm or more.

10. The composite substrate of claim 1, wherein the single crystal diamond layer has color centers.

11. The in-plane density of lattice defects due to dislocations in the single crystal diamond layer is 1.0×10 ５ ( / cm ２ 11. The composite substrate according to claim 10, wherein the thickness of the composite substrate is 1 / 2 or less.

12. The composite substrate according to claim 1, wherein the single crystal diamond layer has a thickness of 50 nm to 1000 nm.

13. The composite substrate according to claim 1, wherein the thickness of the single crystal diamond layer varies within a range of 5 μm or less.

14. The composite substrate according to claim 1, wherein the surface roughness Ra of the single-crystal diamond layer on the support substrate side is 1.0 nm or less.

15. A composite substrate according to claim 2, further comprising an optical loss suppression layer between the single crystal diamond layer and the cladding layer, the optical loss suppression layer and the cladding layer being directly bonded to each other.

16. The composite substrate of claim 15, wherein the optical loss suppression layer is comprised of amorphous carbon, silicon oxide, amorphous silicon, polycrystalline silicon, molybdenum, aluminum oxide, compounds thereof, or mixtures thereof.

17. The composite substrate of claim 15, wherein the optical loss suppression layer is formed with a patterned sacrificial layer.

18. The composite substrate of claim 5 or 17, wherein the sacrificial layer is composed of amorphous silicon, silicon, molybdenum, silicon oxide, aluminum oxide, compounds thereof, or mixtures thereof.

19. A composite substrate according to claim 5, further comprising an overcoat layer between the cladding layer and the support substrate and / or between the cladding layer and the single crystal diamond layer.

20. The composite substrate of claim 17, further comprising an overcoat layer between the cladding layer and the optical loss suppression layer.

21. The composite substrate of claim 19 or 20, wherein the overcoat layer is composed of amorphous silicon, niobium oxide, tantalum oxide, silicon oxide, titanium oxide, aluminum oxide, or hafnium oxide.

22. A composite substrate according to claim 2, further comprising an anti-strip layer between the single crystal diamond layer and the cladding layer, or between the support substrate and the cladding layer.

23. The composite substrate according to claim 22, wherein the anti-exfoliation layer is composed of amorphous silicon, tantalum oxide, niobium oxide, titanium oxide, aluminum oxide, or hafnium oxide.

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